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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..04d5145 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #51897 (https://www.gutenberg.org/ebooks/51897) diff --git a/old/51897-0.txt b/old/51897-0.txt deleted file mode 100644 index b7f63ba..0000000 --- a/old/51897-0.txt +++ /dev/null @@ -1,17338 +0,0 @@ -The Project Gutenberg EBook of The Poetry of Science or, Studies of the -Physical Phenomena of Nature, by Robert Hunt - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The Poetry of Science or, Studies of the Physical Phenomena of Nature - -Author: Robert Hunt - -Release Date: April 30, 2016 [EBook #51897] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE POETRY OF SCIENCE *** - - - - -Produced by Emmanuel Ackerman and the Online Distributed -Proofreading Team at http://www.pgdp.net (This file was -produced from images generously made available by The -Internet Archive/Canadian Libraries) - - - - - - - - - -THE - -POETRY OF SCIENCE; - -OR, - -STUDIES - -OF THE - -PHYSICAL PHENOMENA OF NATURE. - -BY - -ROBERT HUNT, - -AUTHOR OF - -“RESEARCHES ON LIGHT;” “ELEMENTARY PHYSICS;” -“PANTHEA, OR THE SPIRIT OF NATURE,” ETC. - -PROFESSOR OF PHYSICS, METROPOLITAN SCHOOL OF SCIENCE, ETC., ETC. - -THIRD EDITION, REVISED AND ENLARGED. - -LONDON: - -HENRY G. BOHN, YORK STREET, COVENT GARDEN. - -MDCCCLIV. - - - From Shakespeare to Plato--from the philosophic poet to the poetic - philosopher--the transition is easy, and the road is crowded with - illustrations of our present subject. - - * * * * * - - Hast thou ever raised thy mind to the consideration of EXISTENCE, in - and by itself, as the mere act of existing? - - Hast thou ever said to thyself, thoughtfully, IT IS!--heedless, in - that moment, whether it were a man before thee, or a flower, or - a grain of sand,--without reference, in short, to this or that - particular mode or form of existence? If thou hast, indeed, - attained to this, thou wilt have felt the presence of a mystery, - which must have fixed thy spirit in awe and wonder. - - _Coleridge._ - - LONDON: - WILSON and OGILVY, - 57, Skinner Street. - - - - -PREFACE. - - -Since 1848, when the “Poetry of Science” was first submitted to the -public, two editions have been exhausted. This, were proofs required, -would of itself show that there is a large circle of readers to whom -the deductions of science have an unfailing interest. Beyond this, -it conveys an assurance that every truth, however abstract it may -appear, has a large popular value if studied in its relations to -those generalities which embrace great natural phenomena. With this -persuasion the third edition of the “Poetry of Science” has been -extended so as to include all the important discoveries which have -been made in Natural Philosophy to the end of the year 1853. It is now -presented to the world in a new and cheaper form, in the hope, that, -with the extension of its circulation, there may be awakened, in still -larger circles, a deep and healthful interest in the sciences of which -the volume treats. - - R. H. - -Edinburgh, March 7, 1854. - - - - -CONTENTS. - - Page - - - PREFACE. iii - - CONTENTS. v - - INTRODUCTION. ix - - - CHAPTER I. - - GENERAL CONDITIONS OF MATTER. - - Its varied Characters, and constant change of - external Form--The Grain of Dust, its Properties and - Powers--Combinations in inorganic Masses and in organized - Creations--Our knowledge of Matter--Theory of Ultimate - Atoms--The Physical Forces acting on the Composition - of Masses--The certainty of the exercise of subtile - principles, which are beyond the reach of experimental - Science 1 - - - CHAPTER II. - - MOTION. - - Are the Physical Forces modes of Motion?--Motion - defined--Philosophical Views of Motion, and the Principles - to which it has been referred--Motions of the Earth and - of the Solar System--Visible Proofs of the Earth’s Motion - on its Axis--Influence of the proper Motions of the Earth - on the Conditions of Matter--Theory of the Conversion of - Motion into Heat, &c.--The Physical Forces regarded as - principles independent of Motion, although the Cause and - often apparently the Effects of it 7 - - - CHAPTER III. - - GRAVITATION. - - The Forms of Matter--Shape of the Earth--Probability - of the Mass forming this Planet having existed in a - Nebulous State--Zodiacal Lights--Comets--Volatilization - of Solid Matter by Artificial means--The principle - of Gravitation--Its Influence through Space and - within the smallest Limits--Gravitating powers of the - Planets--Density of the Earth--Certainty of Newton’s Law - of the Inverse Square--Discovery of Neptune--State of a - Body relieved from Gravitation--Experiment explaining - Saturn’s Ring, &c.--General inference 21 - - - CHAPTER IV. - - MOLECULAR FORCES. - - Conditions of Matter--Variety of organized - Forms--Inorganic Forms--All matter reducible to the - most simple conditions--Transmutation, a natural - operation--Chemical Elementary Principles--Divisibility - of Matter--Atom--Molecules--Particles--Molecular - Force includes several Agencies--Instanced - in the Action of Heat on Bodies--All Bodies - porous--Solution--Mixture--Combination--Centres - of Force--Different States of Matter (Allotropic - Conditions)--Theories of Franklin, Æpinus, and - Coulomb--Electrical and Magnetic Agencies--Ancient - Notions--Cohesive Attraction, &c. 35 - - - CHAPTER V. - - CRYSTALLOGENIC FORCES. - - Crystallisation and Molecular Force - distinguished--Experimental Proof--Polarity of - Particles forming a Crystal--Difference between - Organic and Inorganic Forms--Decomposition of - Crystals in Nature--Substitution of Particles in - Crystals--Pseudomorphism--Crystalline Form not dependent - on Chemical Nature--Isomorphism--Dimorphism--Theories of - Crystallogenic Attraction--Influence of Electricity and - Magnetism--Phenomena during Crystallisation--Can a change - of Form take place in Primitive Atoms?--Illustrative - Example of Crystallisation 50 - - - CHAPTER VI. - - HEAT--SOLAR AND TERRESTRIAL. - - Solar and Terrestrial Heat--Position of the Earth - in the Solar System--Heat and Light associated in - the Sunbeam--Transparency of Bodies to Heat--Heating - Powers of the Coloured Rays of the Spectrum--Undulatory - Theory--Conducting Property of the Earth’s - Crust--Convection--Radiation--Action of the Atmosphere on - Heat Rays--Peculiar Heat Rays--Absorption and Radiation - of Heat by dissimilar Bodies--Changes in the Constitution - of Solar Beam--Differences between Transmitted and - Reflected Solar Heat--Phenomena of Dew--Action of - Solar Heat of the Ocean--Circulation of Heat by the - Atmosphere and the Ocean--Heat of the Earth--Mean - Temperature--Central Heat--Constant Radiation of Heat Rays - from all Bodies--Thermography--Action of Heat on Molecular - Arrangements--Sources of Terrestrial Heat--Latent Heat - of Bodies--Animal Heat--Eremacausis--Spheroidal State - Cold--Condensation--Freezing--Theories of Heat--Natural - Phenomena--and Philosophical Conclusion 62 - - - CHAPTER VII. - - LIGHT. - - Theories of the Nature of Light--Hypotheses - of Newton and Huygens--Sources of Light--The - Sun--Velocity of Light--Transparency--Dark - Lines of the Spectrum--Absorption of - Light--Colour--Prismatic Analysis--Rays of the - Spectrum--Rainbow--Diffraction--Interference--Goethe’s - Theory--Polarisation--Magnetisation of Light--Vision--The - Eye--Analogy--Sound and Light--Influence of Light on - Animals and Vegetables--Phosphorescence arising from - several Causes--Artificial Light--Its Colour dependent on - Matter 118 - - - CHAPTER VIII. - - ACTINISM--CHEMICAL RADIATIONS. - - The Sun-ray and its Powers--Darkening of - Horn Silver--Niepce’s Discovery--Prismatic - Spectrum--Refrangibility of Light, Heat, and - Actinism--Daguerre’s Discovery--Photography--Chemical - Effects produced by Solar Radiations--Absorption of - Actinism--Phenomena of the Daguerreotype--Chemical - Change produced upon all Bodies--Power of Matter to - restore its Condition--Light protects from Chemical - Change--Photographs taken in Darkness--Chemical Effects - of Light on organized Forms--Chemical Effects of Solar - Heat--Influence of Actinism on Electricity--Radiations in - Darkness--Moser’s Discoveries, &c. 166 - - - CHAPTER IX. - - ELECTRICITY. - - Discovery of Electrical Force--Diffused through all - Matter--What is Electricity?--Theories--Frictional - Electricity--Conducting Power of Bodies--Hypothesis - of two Fluids--Electrical Images--Galvanic - Electricity--Effects on Animals--Chemistry of Galvanic - Battery--Electricity of a Drop of Water--Electro-chemical - Action--Electrical Currents--Thermo-Electricity--Animal - Electricity--Gymnotus--Torpedo--Atmospheric - Electricity--Lightning Conductors--Earth’s Magnetism due - to Electrical Currents--Influence on Vitality--Animal and - Vegetable Development--Terrestrial Currents--Electricity - of Mineral Veins--Electrotype--Influence of Heat, Light, - and Actinism on Electrical Phenomena 193 - - - CHAPTER X. - - MAGNETISM. - - Magnetic Iron--Knowledge of, by the Ancients--Artificial - Magnets--Electro-Magnets--Electro-Magnetism--Magneto- - Electricity--Theories of Magnetism--The Magnetic - Power of soft Iron and Steel--Influence of Heat - on Magnetism--Terrestrial Magnetism--Declination - of the Compass-needle--Variation of the - Earth’s Magnetism--Magnetic Poles--Hansteen’s - Speculations--Monthly and Diurnal Variation--Dip and - Intensity--Thermo-Magnetism--Aurora Borealis--Magnetic - Storms--Magnetic conditions of Matter--Diamagnetism, &c. 235 - - - CHAPTER XI. - - CHEMICAL FORCES. - - Nature’s Chemistry--Changes produced by Chemical - Combination--Atomic Constitution of Bodies--Laws - of Combination--Combining Equivalents--Elective - Affinity--Chemical Decomposition--Compound Character - of Chemical Phenomena--Catalysis or action of - Presence--Transformation of Organic Bodies--Organic - Chemistry--Constancy of Combining Proportions--The Law of - Volumes, the Law of Substitutions, Isomeric States, &c. 270 - - - CHAPTER XII. - - CHEMICAL PHENOMENA. - - Water--Its Constituents--Oxygen--Hydrogen--Peroxide - of Hydrogen--Physical Property of - Water--Ice--Sea Water--Chlorine--Muriatic - Acid--Iodine--Bromine--Compounds of Hydrogen - with Carbon--Combustion--Flame--Safety - Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic - Acid--Influence of Plants on the Air--Chemical Phenomena - of Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c. - &c. 295 - - - CHAPTER XIII. - - TIME.--GEOLOGICAL PHENOMENA. - - Time, an element in Nature’s Operations--Geological - Science--Its Facts and Inferences--Nebular Hypothesis - applied--Primary Formations--Plutonic and Metamorphic - Rocks--Transition Series--Palæozoic Rocks--Commencement - of Organic Arrangements--Existence of Phosphoric - Acid in Plutonic Rocks--Fossil Remains--Coal - Formation--Sandstones--Tertiary Formations--Eocene, - Miocene, and Pliocene Formations--Progressive changes - now apparent--General Conclusions--Physics applied in - explanation 332 - - - CHAPTER XIV. - - PHENOMENA OF VEGETABLE LIFE. - - Psychology of Flowers--Progress of Matter - towards Organization--Vital Force--Spontaneous - Generation--The Vegetable Cell--Simplest Development - of Organization--The Crystal and the Cell--Primitive - Germ--Progress of Vegetation--Influence of - Light--Morphology--Germination--Production of Woody - Fibre--Leaves--Chlorophylle--Decomposition of - Carbonic Acid--Influence of Light, Heat, and Actinism - on the Phenomena of Vegetable Life--Flowers and - Fruits--Etiolation--Changes in the Sun’s Rays with the - Seasons--Distribution of Plants--Electrical and Combined - Physical Powers 357 - - - CHAPTER XV. - - PHENOMENA OF ANIMAL LIFE. - - Distinction between the Kingdoms - of Nature--Progress of Animal - Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent - Animals--Annelidans--Myriapoda--Animal - Metamorphoses--Fishes--Birds--Mammalia--Nervous - System--Animal Electricity--Chemical Influences--Influence - of Light on Animal Life--Animal Heat--Mechanical - Action--Nervous Excitement--Man and the Animal Races, &c. 383 - - - CHAPTER XVI. - - GENERAL CONCLUSIONS. - - The Changes produced on Physical Phenomena by the Movement - of the Solar System considered--Exertion of the Physical - Forces through the Celestial Spaces--The Balance of - Powers--Varieties of Matter--Extension of Matter--Theory - of Nonentity--A Material Creation an indisputable - fact--Advantages of the Study of Science--Conclusion 403 - - - INDEX. 413 - - BOHN’S BOOKS. - - TRANSCRIBER’S NOTE. - - - - -INTRODUCTION. - - -The True is the Beautiful. Whenever this becomes evident to our senses, -its influences are of a soul-elevating character. The beautiful, -whether it is perceived in the external forms of matter, associated in -the harmonies of light and colour, appreciated in the modulations of -sweet sounds, or mingled with those influences which are, as the inner -life of creation, ever appealing to the soul through the vesture which -covers all things, is the natural theme of the poet, and the chosen -study of the philosopher. - -But, it will be asked, where is the relation between the stern labours -of science and the ethereal system which constitutes poetry? The fumes -of the laboratory, its alkalies and acids, the mechanical appliances of -the observatory, its specula and its lenses, do not appear fitted for -a place in the painted bowers of the Muses. But, from the labours of -the chemist in his cell,--from the multitudinous observations of the -astronomer on his tower,--spring truths which the philosopher employs -to interpret nature’s mysteries, and which give to the soul of the poet -those realities to which he aspires in his high imaginings. - -Science solicits from the material world, by the persuasion of -inductive search, a development of its elementary principles, and of -the laws which these obey. Philosophy strives to apply the discovered -facts to the great phenomena of being,--to deduce large generalities -from the fragmentary discoveries of severe induction,--and thus to -ascend from matter and its properties up to those impulses which -stir the whole, floating, as it were, on the confines of sense, and -indicating, though dimly, those superior powers which, more nearly -related to infinity, mysteriously manifest themselves in the phenomena -of mind. Poetry seizes the facts of the one and the theories of the -other; unites them by a pleasing thought, which appeals for truth to -the most unthinking soul, and leads the reflective intellect to higher -and higher exercises; it connects common phenomena with exalted ideas; -and, applying its holiest powers, it invests the human mind with the -sovereign strength of the True. - -Truth is the soul of the poet’s thought;--truth is the reward of the -philosopher’s toil; and their works, bearing this stamp, live among -men through all time. Science at present rejoices in her ministry to -the requirements of advancing civilization, and is content to receive -the reward given to applications which increase the comforts of life, -or add to its luxuries. Every improvement in the arts or manufactures, -beyond encreasing utilities for society, has a tendency to elevate the -race. Science is ever useful in the working days of our week, but it is -not to be neglected on our Sabbath,--when, resting from our labours, -it becomes agreeable to contemplate the few truths permitted to our -knowledge, and thus enter into communion as closely as is allowed to -finite beings, with those influences which involve and interpenetrate -the earth, giving to all things Life, Beauty, and Divinity. - -The human mind naturally delights in the discovery of truth; and -even when perverted by the constant operations of prevailing errors, -a glimpse of the Real comes upon it like the smile of daylight to -the sorrowing captive of some dark prison. The Psychean labours to -try man’s soul, and exalt it, are the search for truth beneath the -mysteries which surround creation,--to gather amaranths, shining with -the hues of heaven, from plains upon which hang, dark and heavy, the -mists of earth. The poet may pay the debt of nature,--the philosopher -may return to the bosom of our common mother,--even their names fade -in the passage of time, like planets blotted out of heaven but the -truths they have revealed to man burn on for ever with unextinguishable -brightness. Truth cannot die; it passes from mind to mind, imparting -light in its progress, and constantly renewing its own brightness -during its diffusion. The True is the Beautiful; and the truths -revealed to the mind render us capable of perceiving new beauties on -the earth. The gladness of truth is like the ringing voice of a joyous -child, and the most remote recesses echo with the cheerful sound. To be -for ever true is the Science of Poetry,--the revelation of truth is the -Poetry of Science. - -Man, a creation endued with mighty faculties, but a mystery to himself, -stands in the midst of a wonderful world, and an infinite variety of -phenomena arise around him in strange form and magical disposition, -like the phantasma of a restless night. - -The solid rock obeys a power which brings its congeries of atoms into -a thousand shapes, each one geometrically perfect. Its vegetable -covering, in obedience to some external excitation, developes itself -in a curious diversity of forms, from the exquisitely graceful to the -singularly grotesque, and exhibits properties still more varied and -opposed. The animal organism quickened by higher impulses,--powers -working within, and modifying the influence of the external -forces,--presents, from the Monad to the Mammoth, and through every -phase of being up to Man, a yet more wonderful series of combinations, -and features still more strangely contrasted. - -Lifting our searching gaze into the measureless space beyond our earth, -we find planet bound to planet, and system chained to system, all -impelled by a universal force to roll in regularity and order around a -common centre. The pendulations of the remotest star are communicated -through the unseen bond; and our rocking world obeys the mysterious -impulse throughout all those forces which regulate the inorganic -combinations of this earth, and unto which its organic creation is -irresistibly compelled to bow. - -The glorious sun by day, and the moon and stars in the silence and the -mystery of night, are felt to influence all material nature, holding -the great Earth bound in a many-stranded cord which cannot be broken. -The tidal flow of the vast ocean, with its variety of animal and -vegetable life, the atmosphere, bright with light, obscured by the -storm-cloud, spanned by the rainbow, or rent with the explosions of -electric fire,--attest to the might of these elementary bonds. - -These are but a few of the great phenomena which play their part around -this globe of ours, exciting men to wonder, or shaking them with terror. - -The mind of man, in its progress towards its higher destiny, is tasked -with the physical earth as a problem, which, within the limits of a -life, it must struggle to solve. The intellectual spirit is capable of -embracing all finite things. Man is gifted with powers for studying -the entire circle of visible creation; and he is equal, under proper -training, to the task of examining much of the secret machinery which -stirs the whole. - -In dim outshadowing, earth’s first poets, from the loveliness of -external nature, evoked beautiful spiritualizations. To them the shady -forests teemed with aërial beings,--the gushing springs rejoiced in -fantastic sprites,--the leaping cataracts gleamed with translucent -shades,--the cavernous hills were the abodes of genii,--and the -earth-girdling ocean was guarded by mysterious forms. Such were the -creations of the far-searching mind in its early consciousness of the -existence of unseen powers. The philosopher picked out his way through -the dark and labyrinthine path, between effects and causes, and slowly -approaching towards the light, he gathered semblances of the great -Reality, like a mirage, beautiful and truthful, although still but a -cloud-reflection of the vast Unseen. - -It is thus that the human mind advances from the Ideal to the Real, -and that the poet becomes the philosopher, and the philosopher rises -into the poet; but at the same time as we progress from fable to -fact, much of the soul-sentiment which made the romantic holy, and -gave a noble tone to every aspiration, is too frequently merged in a -cheerless philosophy which clings to the earth, and reduces the mind -to a mechanical condition, delighting in the accumulation of facts, -regardless of the great laws by which these are regulated, and the -harmony of all Telluric combinations secured. In science we find the -elements of the most exalted poetry; and in the mysterious workings -of the physical forces we discover connections with the illimitable -world of thought,--in which mighty minds delight to try their -powers,--as strangely complicated, and as marvellously ordered, as in -the psychological phenomena which have, almost exclusively, been the -objects of their studies. - -In the aspect of visible nature, with its wonderful diversity of form -and its charm of colour, we find the Beautiful; and in the operations -of these principles, which are ever active in producing and maintaining -the existing conditions of matter, we discover the Sublime. - -The form and colour of a flower may excite our admiration; but when -we come to examine all the phenomena which combine to produce that -piece of symmetry and that lovely hue,--to learn the physiological -arrangement of its structural parts,--the chemical actions by which -its woody fibre and its juices are produced,--and to investigate those -laws by which is regulated the power to throw back the white sunbeam -from its surface in coloured rays,--our admiration passes to the higher -feeling of deep astonishment at the perfection of the processes, and -of reverence for their great Designer. There are, indeed, “tongues in -trees;” but science alone can interpret their mysterious whispers, and -in this consists its poetry. - -To rest content with the bare enunciation of a truth, is to perform -but one half of a task. As each atom of matter is involved in an -atmosphere of properties and powers, which unites it to every mass of -the universe, so each truth, however common it may be, is surrounded -by impulses which, being awakened, pass from soul to soul like musical -undulations, and which will be repeated through the echoes of space, -and prolonged for all eternity. - -The poetry which springs from the contemplation of the agencies which -are actively employed in producing the transformation of matter, and -which is founded upon the truths developed by the aids of science, -should be in no respect inferior to that which has been inspired by the -beauty of the individual forms of matter, and the pleasing character of -their combinations. - -The imaginative view of man and his world--the creations of the -romantic mind--have been, and ever will be, dwelt on with a -soul-absorbing passion. The mystery of our being, and the mystery -of our ceasing to be, acting upon intelligences which are for ever -striving to comprehend the enigma of themselves, leads by a natural -process to a love for the Ideal. The discovery of those truths which -advance the human mind towards that point of knowledge to which all -its secret longings tend, should excite a higher feeling than any mere -creation of the fancy, how beautiful soever it may be. The phenomena -of Reality are more startling than the phantoms of the Ideal. Truth -is stranger than fiction. Surely many of the discoveries of science -which relate to the combinations of matter, and exhibit results which -we could not by any previous efforts of reasoning dare to reckon on, -results which show the admirable balance of the forces of nature, and -the might of their uncontrolled power, exhibit to our senses subjects -for contemplation truly poetic in their character. - -We tremble when the thunder-cloud bursts in fury above our heads. The -poet seizes on the terrors of the storm to add to the interest of his -verse. Fancy paints a storm-king, and the genius of romance clothes -his demons in lightnings, and they are heralded by thunders. These -wild imaginings have been the delight of mankind; there is subject -for wonder in them: but is there anything less wonderful in the -well-authenticated fact, the dew-drop which glistens on the flower, -that the tear which trembles on the eye-lid, holds locked in its -transparent cells an amount of electric fire equal to that which is -discharged during a storm from a thunder-cloud? - -In these studies of the effects which are continually presenting -themselves to the observing eye, and of the phenomena of causes, as far -as they are revealed by Science in its search of the physical earth, -it will be shown that beneath the beautiful vesture of the external -world there exists, like its quickening soul, a pervading power, -assuming the most varied aspects, giving to the whole its life and -loveliness, and linking every portion of this material mass in a common -bond with some great universal principle beyond our knowledge. Whether -by the improvement of the powers of the human mind, man will ever be -enabled to embrace within his knowledge the laws which regulate these -remote principles, we are not sufficiently advanced in intelligence -to determine. But if admitted even to a clear perception of the -theoretical Power which we regard as regulating the known forces, we -must still see an unknown agency beyond us, which can only be referred -to the Creator’s will. - - - - -THE POETRY OF SCIENCE. - - - - -CHAPTER I. - -GENERAL CONDITIONS OF MATTER. - - Its varied Characters, and constant change of external Form--The - Grain of Dust, its Properties and Powers--Combinations in inorganic - Masses and in organized Creations--Our knowledge of Matter--Theory - of Ultimate Atoms--The Physical Forces acting on the Composition of - Masses--The certainty of the exercise of subtile principles, which - are beyond the reach of experimental Science. - - -The Physical Earth presents to us, in every form of organic and -inorganic matter, an infinite variety of phenomena. If we select -specimens of rocks, either crystalline or stratified,--of metals in -any of their various combinations with oxygen, sulphur, and other -bodies,--of gems glistening with light and glowing with colour,--if -we examine the varied forms and hues of the vegetable world, or the -more mysterious animal creations, we must inevitably come to the -conclusion, long since proclaimed, and admit that dust they are, and -to dust must they return. Whatever permanency may be given to matter, -it is certain that its form is ever in a state of change. The surface -of the “Eternal Hills” is worn away by the soft rains which fall to -fertilize, and from their wrecks, borne by the waters to the ocean, new -continents are forming. The mutations of the old earth may be read upon -her rocks and mountains, and these records of former changes tell us -the infallible truth, that as the present passes into the future, so -will the form of Earth undergo an important alteration. The same forces -which lifted the Andes and the Himalayas are still at work, and from -the particles of matter carried from the present lands by the rivers -into the sea, where they subside in stratified masses, there will, in -the great future, be raised new worlds, upon which the work of life -will go forward, and over which will be spread a vast Intelligence. - -If we regard the conditions of the beautiful and varied organic -covering of the Earth, the certainty, the constancy, of change is ever -before us. Vegetable life passes into the animal form, and both perish -to feed the future plant. Man, moving to-day the monarch of a mighty -people, in a few years passes back to his primitive clod, and that -combination of elementary atoms, which is dignified with the circle of -sovereignty and the robe of purple, after a period may be sought for in -the herbage of the fields, or in the humble flowers of the valley. - -We have, then, this certain truth,--all things visible around us are -but aggregations of atoms. From particles of dust, which under the -microscope could scarcely be distinguished one from the other, are all -the varied forms of nature created. This grain of dust, this particle -of sand, has strange properties and powers. Science has discovered -some truths, but still more are hidden within this irregular molecule -of matter which we now survey, than have yet been shadowed in the -dreams of our philosophy. How strangely it obeys the impulses of -heat--mysterious are the influences of light upon it--electricity -wonderfully excites it--and still more curious is the manner in which -it obeys the magic of chemical force. These are phenomena which we have -seen; we know them, and we can reproduce them at our pleasure. We have -advanced a little way into the secrets of nature, and from the spot we -have gained, we look forward with a vision somewhat brightened by our -task; but we discover so much to be yet unknown, that we learn another -truth,--our vast ignorance of many things relating to this grain of -dust. - -It gathers around it other particles; they cling together, and each -acting upon every other one, and all of them arranging themselves -around the little centre according to some law, a beautiful crystal -results, the geometric perfection of its form being a source of -admiration. - -It exerts some other powers, and atom cohering to atom, obeying the -influences of many external radiant forces, undergoes inexplicable -changes, and the same dust which we find forming the diamond, -aggregates into the lordly tree,--blends to produce the graceful, -scented, and richly painted flower,--and combines to yield the luxury -of fruit. - -It quickens with yet undiscovered energies; it moves with life: dust -is stirred by the mysterious excitement of vital force; and blood and -bone, nerve and muscle, are the results. Forces, which we cannot by -the utmost refinements of our philosophy detect, direct the whole, -and from the same dust which formed the rock and grew in the tree, is -produced a living and a breathing thing, capable of receiving a Divine -illumination, of bearing in its new state the gladness and the glory of -a Soul. - -These considerations lead us to reflect on the amount of our knowledge. -We are led to ask ourselves, what do we know? We know that the world -with all its variety is composed of certain material atoms, which, -although presented to us in a great variety of forms, do not in all -probability differ very essentially from each other. - -We know that those atoms obey certain conditions which appear to be -dependent upon the influences of motion, gravitation, heat, light, -electricity, and chemical force. These powers are only known to us -by their effects; we only detect their action by their operations -upon matter; and although we regard the several phenomena which we -have discovered, as the manifestations of different principles, it is -possible they may be but modifications of some one universal power, of -which these are but a few of its modes of action. - -In examining, therefore, the truths which science has revealed to us, -it is advantageous, for the purpose of fixing the mind to the subject, -that we assume certain conditions as true. These may be stated in a few -sentences, and then, without wasting a thought upon those metaphysical -subtleties which have from time to time perplexed science, and served -to impede the progress of truth, we shall proceed to examine our -knowledge of the phenomena which constantly occur around us. - -Every form, whether inorganic or organic, which we can discover within -the limits of human search, is composed of atoms, which are capable of -assuming, under the influence of certain physical forces, conditions -essential to the physical state of that body of which they constitute -a part.[1] The known forces, active in producing these conditions, -are modes of motion; gravitation and aggregation, heat, light; and -associated with these, actinism or chemical radiation; electricity, -under all its conditions, whether static or dynamic; and chemical -affinity, regarded as the result of a separate elementary principle. - -These forces must be considered as powers capable of acting in perfect -independence of each other. They are possibly modifications of one -principle; but this view being an hypothesis, which, as yet, is only -supported by loose analogies, cannot, without danger, be received in -any explanation which attempts to deal only with the truths of science. - -We cannot examine the varied phenomena of nature, without feeling that -there must be other and most active principles of a higher order than -any detected by science, to which belong the important operations of -vitality, whether manifested in the plant or the animal. In treating -of these, although speculation cannot be entirely avoided, it will be -employed only so far as it gives any assistance in linking phenomena -together. - -We have to deal with the active agencies which give form and feature to -nature--which regulate the harmony and beauty and vigour of life--and -upon which depend those grand changes in the conditions of matter, -which must convince us that death is but the commencement of a new -state of being. - - -FOOTNOTES: - -[1] Sir Isaac Newton supposed matter to consist of hard, impenetrable, -perfectly inelastic atoms. - -Boscovich regarded the constitution of matter differently. The ultimate -atom was with him a point surrounded by powers of infinite elasticity. -(See _Dr. Robisons Mechanical Philosophy_, for a full explanation of -the theory of Boscovich.) - -The view entertained by Dr. Faraday, which will be comprehended from -one or two short extracts from his valuable and suggestive paper, -claims attention:-- - -“If the view of the constitution of matter already referred to be -assumed to be correct--and I may be allowed to speak of the particles -of matter, and the space between them (in water, or in the vapour -of water, for instance), as two different things--the space must be -taken as the only continuous part, for the particles are considered -as separated by space from each other. Space will permeate all masses -of matter in every direction like a net, except that in the place of -meshes it will form cells, isolating each atom from its neighbours, and -itself only being continuous.” - -Examining the question of the conducting power of different bodies, -and observing that as space is the only continuous part, so space, -according to the received view of matter, must be at one time a -conductor, at others a non-conductor, it is remarked: - -“It would seem, therefore, that, in accepting the ordinary atomic -theory, space may be proved to be a non-conductor in non-conducting -bodies, and a conductor in conducting bodies; but the reasoning ends -in this--a subversion of that theory altogether; for, if space be -an insulator, it cannot exist in conducting bodies; and if it be a -conductor, it cannot exist in insulating bodies.”--_A Speculation -touching Electric Conduction, and the Nature of Matter_: by Michael -Faraday, D.C.L., F.R.S., &c.: Philosophical Magazine, vol. xxiv. Third -Series. - -See also Wollaston, _On the Finite Extent of the Atmosphere_.--Phil. -Trans. 1822. Young, _On the Essential Properties of Matter_.--Lectures -on Natural Philosophy. Mossotti, _On Molecular Action_.--Scientific -Memoirs, vol. i. p. 448. - - - - -CHAPTER II. - -MOTION. - - Are the Physical Forces modes of Motion?--Motion - defined--Philosophical Views of Motion, and the Principles to - which it has been referred--Motions of the Earth and of the Solar - System--Visible Proofs of the Earth’s Motion on its Axis--Influence - of the proper Motions of the Earth on the Conditions of - Matter--Theory of the Conversion of Motion into Heat, &c.--The - Physical Forces regarded as principles independent of Motion, - although the Cause and often apparently the Effects of it. - - -Many of the most eminent thinkers of the present time are disposed to -regard all the active principles of nature as “modes of motion,”--to -look upon light, heat, electricity, and even vital force, as phenomena -resulting from “change of place” among the particles of matter; this -change, disturbance, or motion, being dependent upon some undefined -mover.[2] - -The habit of leaving purely inductive examination for the delusive -charms of hypothesis--of viewing the material world as a metaphysical -bundle of essential properties, and nothing more--has led some eminent -philosophers to struggle with the task of proving that all the -wonderful manifestations of the great physical powers of the universe -are but modifications of motion, without the evidence of any antecedent -force.[3] - -The views of metaphysicians regarding motion involve many subtle -considerations which need not at present detain us. We can only -consider motion as a change of place in a given mass of matter. Now -matter cannot effect this of itself, no change of place being possible -without a mover; and, consequently, motion cannot be a _property_ of -matter, in the strict sense in which that term should be accepted.[4] - -Motion depends upon certain external disturbing and directing forces -acting upon all matter; and, consequently, as every mode of action -is determined by some excitement external to the body moved, motion -cannot, philosophically, be regarded otherwise than as a peculiar -affection of matter under determinable conditions. “We find,” says Sir -Isaac Newton, “but little motion in the world, except what plainly -flows from either the active principles of nature, or from the command -of the willer.”[5] - -Plato, Aristotle, and the Pythagoreans, supposed that throughout all -nature an active principle was diffused, upon which depended all the -properties exhibited by matter. This is the same as the “plastic -nature” of Cudworth,[6] the “intellectual and artificial fire” of -Bishop Berkeley;[7] and to these all modes of motion were referred. -Sir Isaac Newton also regards the material universe and its phenomena -as dependent upon “_active principles_”--for instance, the cause of -gravity--whereby the planets and comets preserve their motions in their -orbits, and all bodies acquire a degree of motion in falling; and the -cause of fomentation--whereby the heart and blood of animals preserve -a perpetual warmth and motion--the inner parts of the earth are kept -constantly warmed--many bodies burn and shine--and the sun himself -burns and shines, and with his light warms and cheers all things. - -The earth turns on its axis at the rate of more than 1,000 miles an -hour, and passes around the sun with the speed of upwards of 68,000 -miles in the same time.[8] The earth and the other planets of our -system move in ellipses around a common centre: therefore their motion -cannot have been originally communicated merely by the impressed force -of projection. Two forces, at least, must have operated, one making -the planets tend directly to the centre, and the other impelling them -to fly off at a tangent to the curve described. Here we have a system -of spheres, held by some power to a great central mass, around which -they revolve with a fearful velocity. Nor is this all; the Solar System -itself, bound by the same mystic chain to an undiscovered centre, moves -towards a point in space at the rate of 33,550,000 geographical miles, -whilst our earth performs one revolution around the sun.[9] - -The evidence of the motion of the Earth around its axis, as afforded -by the swinging of a pendulum or the rotation of a sphere, is too -interesting to be omitted. In mechanical philosophy, we have two -terms of the same general meaning--the conservation of the plane -of vibration--and the conservation of the axis of rotation. For -the non-scientific reader, these terms require explanation, and in -endeavouring to simplify this as much as possible, we must ask the -indulgence of the Mechanical Philosopher. Let us fix in the centre -of a small round table an upright rod, having an arm extending from -its top, to which we can suspend a tolerably heavy weight attached -to a string. This is our piece of apparatus: upon the table draw a -chalk line, along which line we intend our pendulum to swing, and -continuing this line upon the floor, or by a mark on the wall, our -arrangements are complete. Raise steadily the bob of our pendulum, -and set it free, so that its plane of vibration is along the line -which has been marked. As the pendulum is swinging firmly along this -line, slowly and steadily turn the table round. It will then be seen -that the pendulum will still vibrate in the direction of the line we -have continued onward to the wall, but that the line on the table is -gradually withdrawn from it. If we had no upright, we might turn the -table entirely round, without in the slightest degree altering the -line along which the pendulum performs its oscillations. Now, if from -some elevated spot, say, from the centre of the dome of St. Paul’s, -a long and heavy pendulum is suspended, and if on the floor we mark -the line along which we set the pendulum free to vibrate, it will be -seen, as in the experiment with the table, that the marked line moves -away from under the pendulum. It continues to vibrate in the plane it -first described, although the line on the earth’s surface continues -to move forward by the diurnal rotation around the axis. Similar to -this is the law of the conservation of the axis of rotation. If a -common humming-top, the spindle of which is its axis of rotation, is -set spinning obliquely, it will be seen that the axis will continue -to point along the line it took at the commencement of motion. By -placing a heavy sphere in a lathe, resting its projecting axial points -on some moveable bearings, and then getting the sphere into extremely -rapid motion, one of the bearings may be removed without the mass -falling to the ground. The rapidity of motion changes so constantly and -quickly the position of the particles which have a tendency to fall, -that we have motion balanced against the force of gravitation in a -striking manner; and we learn, from this experiment, the explanation -of the planetary and stellar masses revolving on their axis at a speed -sufficient to maintain them without support in space. A mass of matter, -a sphere or a disc, carefully balanced, is fixed in gymbals such as we -employ for fixing our compass needles, and it is set by some mechanical -contrivance in rapid rotation. The position of the axis of rotation -remains unaltered, although the earth is moving; and thus, by this -instrument,--called the gyroscope,--we can determine, as with the -pendulum, the motion of the earth around its axis; and we learn why, -during its movement around the sun, its axis is undeviatingly pointed -towards one point in space, marked in our Heavens as the Polar Star. - -In addition to these great rotations, the earth is subjected to other -motions, as the precession of the equinoxes and the nutation of its -axis. Rocking regularly upon a point round which it rapidly revolves, -whilst it progresses onward in its orbit, like some huge top in -tremulous gyration upon the deck of a vast aërial ship gliding rapidly -through space, is the earth performing its part in the great law of -motion. - -The rapidity of these impulses, supposing the powers of the physical -forces were for a moment suspended, would be sufficient to scatter the -mass of our planet over space as a mere star-dust. - -Limiting, as much as possible, the view which opens upon the mind as we -contemplate the adjustments by which this great machine, our system, is -preserved in all its order and beauty, let us forget the great movement -of the whole through space, and endeavour to consider the effect of -those motions which are directly related to the earth, as a member of -one small group of worlds. - -We cannot for a moment doubt, although we have not any experimental -proof of the fact, that the proper motions of the earth materially -influence the conditions of the matter of which it is formed. Every -pair of atoms is, like a balance, delicately suspended, under the -constant struggle which arises from the tendency to fly asunder, -induced by one order of forces--centrifugal force--and the efforts of -others, gravitation and cohesion, to chain them together. The spring is -brought to the highest state of tension--one tremor more, and it would -be destroyed. - -We cannot, by any comparison with the labours of the most skilful human -artisan, convey an idea of the exquisite perfection of planetary -mechanics, even so far as they have been discovered by the labours of -science; and we must admit that our insight into the vast machinery has -been very limited. - -All we know is the fact that this planet moves in a certain order, and -at a fixed rate, and that the speed is of itself sufficient to rend -the hardest rocks; yet the delicate down which rests so lightly upon -the flower is undisturbed. It is, therefore, evident that matter is -endued with powers, by which mass is bound to mass, and atom to atom; -these powers are not the results of any of the motions which we have -examined, but, acting in antagonism to them, they sustain our globe in -its present form. - -Are there other motions to which these powers can be referred? We -know of none. That absolute rest may not exist among the particles of -matter is probable. Electrical action, chemical power, crystalline -aggregation, the expansive force of heat, and many other known -agencies, are in constant operation to prevent it. It must, however, -be remembered, that each and every atom constituting a mass may be -so suspended between the balanced forces, that it may be regarded as -relatively at rest. - -Theory imagines Motion as producing Force--a body is moved, and its -mere mechanical change of place is regarded as generating heat; and -hence the refinements of modern science have advanced to the conclusion -that motion and heat are convertible. Admitting that the material atoms -of which this world is formed are never in a state of quiescence, yet -we cannot suppose any gross ponderable particle as capable of moving -itself; but once set in motion, it may become the secondary cause of -motion in other particles.[10] The difficulties of the case would -appear to have been as follows:--Are heat, light, electricity, &c., -material bodies? If they are material bodies--and heat, for example, is -the cause of motion--must not the calorific matter move itself--or if -it be not self-moving, by what is it moved? If heat is material, and -the primary cause of motion, then matter must have an innate power of -moving; it can convert itself into active force, or be at once a cause -and an effect, which can scarcely be regarded as a logical deduction. - -We move a particle of matter, and heat is manifested; the force being -continued, light, electricity, and chemical action result; all, -as appears from a limited view of the phenomena, arising out of -the mechanical force applied to the particle first moved.[11] This -mechanical force, it must be remembered, is external to the body moved, -and is, in all probability, set up by the movement of a muscle, acted -upon by nerves, under the influence of a will. - -The series of phenomena we have supposed to arise admit of an -explanation free of the hypothesis of motion, and we avoid the -dangerous ground of metaphysical speculation, and the subtleties of -that logic which rests upon the immateriality of all creation. This -explanation, it is freely admitted, is incomplete: we cannot distinctly -correlate each feature of the phenomena, combine link to link, and thus -form a perfect chain; but it is sufficiently clear to exhibit what we -do know, and leave the unknown free for unbiassed investigation. - -Each particle, each atom of that which conveys to our senses the only -ideas we have of natural objects--ponderable matter--is involved -in, or interpenetrated by, those principles which we call heat and -electricity, with probably many others which are unknown to us; and -although these principles or powers are, according to some law, bound -in statical equilibrium to inert matter, they are freely developed -by an external excitement, and the disturbance of any one of them, -upsetting the equilibrium, leaves the other power equally free to be -brought under the cognizance of human sense by their effects. - -When we come to an examination of the influences exerted by these -powers upon the physical earth, the position, that they must be -regarded as the causes of motion rather than the effects of it, will -be further considered. At present it is only necessary to state -thus generally the views we entertain of the conditions of matter -in connection with the imponderable forces and mechanical powers. -The conversion, as it has been called, of motion into heat, in the -experiments of Count Rumford and Mr. Joule,[12] are only evidences that -a certain uniformity exists between the mechanical force applied, and -the amount of heat liberated. It does not appear that we have any proof -of the conversion of motion into physical power. - -It is necessary, to a satisfactory contemplation of the wonderful -properties of matter, and of the forces regulating the forms of -the entire creation, that we should be content with regarding the -elementary bodies which chemistry instructs us form our globe, as -tangible, ponderable atoms, having specific and distinguishing -properties. That we should, as far as it is possible for finite minds -to do so, endeavour to conceive the powers or forces--gravitation, -molecular attraction, electricity, heat, light, and the principle which -determines all chemical phenomena--as manifestations of agencies which -hold a place between the most subtile form of matter and the hidden -principles of vitality, which is still vastly inferior to the spiritual -state, which reveals itself dimly in psychological phenomena, and -arrives at its sublimity in the God of the universe. - - -FOOTNOTES: - -[2] “Motion, therefore, is a change of rectilinear distance between -two points. Allowing the accuracy of this definition, it appears that -two points are necessary to constitute motion; that in all cases, when -we are inquiring whether or no any body or point is in motion, we must -recur to some other point which we can compare with it; and that if a -single atom existed alone in the universe, it could neither be said to -be in motion nor at rest. - -“The space which we call quiescent is in general the earth’s surface; -yet we well know, from astronomical considerations, that every point of -the earth’s surface is perpetually in motion, and that in very various -directions: nor are any material objects accessible to our senses which -we can consider as absolutely motionless, or even as motionless with -regard to each other; since the continual variation of temperature to -which all bodies are liable, and the minute agitations arising from the -motion of other bodies with which they are connected, will always tend -to produce some imperceptible changes in their distances.”--_Lectures -on Natural Philosophy, &c._, by Thomas Young, M.D. Edited by the Rev. -P. Kelland. 1845. - -[3] “The position which I seek to establish in this essay is, that -the various imponderable agencies, or the affections of matter which -constitute the main objects of experimental physics, viz., heat, -light, electricity, magnetism, chemical affinity, and motion, are all -correlative, or have a reciprocal dependence;--that neither, taken -abstractedly, can be said to be the essential or proximate cause of the -others; but that either may, as a force, produce, or be convertible -into, the other:--thus heat may mediately or immediately produce -electricity, electricity may produce heat, and so of the rest.... -Although strongly inclined to believe that the five other affections of -matter, which I have above named, are, and will ultimately be, resolved -into modes of motion, it would be going too far at present to assume -their identity with it: I, therefore, use the term force, in reference -to them, as meaning that active force inseparable from matter, which -induces its various changes.”--_On the Correlation of Physical Forces_, -by W. R. GROVE, Esq., M.A., F.R.S. - -[4] When discussing the hypothesis of Hobbes--_that no body can -possibly be moved but by a body contiguous and moved_--Boyle asks:-- - -“I demand how there comes to be local motion in the world? For either -all the portions of matter that compose the universe have motion -belonging to their natures, which the Epicureans affirmed for their -atoms, or some parts of matter have this motive power, and some have -not, or else none of them have it; but all of them are naturally -devoid of motion. If it be granted that motion does naturally belong -to all parts of matter, the dispute is at an end, the concession quite -overthrowing the hypothesis. - -“If Mr. Hobbes should reply that the motion is impressed upon any of -the parts of matter by God, he will say that which I most readily grant -to be true, but will not serve his turn, if he would speak congruously -with his own hypothesis. For I demand whether this Supreme Being -that the assertion has recourse to, be a corporeal or an incorporeal -substance? If it be the latter, and yet the efficient cause of motion -in bodies, then it will not be universally true that whatever body is -moved is so by a body contiguous and moved. For, in our supposition, -the bodies that God moves, either immediately or by the intervention -of any other immaterial being, are not moved by a body contiguous, -but by an incorporeal spirit.”--_Some Considerations about the -Reconcileableness of Reason and Religion_: Boyle, vol. iii. p. 520. - -[5] Boyle has some ingenious speculations on this point:-- - -“That there is local motion in many parts of matter is manifest to -sense, but how matter came by this motion was of old, and is still, -hotly disputed of: for the ancient Corpuscularian philosophers (whose -doctrine in most other points, though not in all, we are the most -inclinable to), not acknowledging an author of the universe, were -thereby reduced to make motion congenite to matter, and consequently -coeval with it. But since local motion, or an endeavour at it, is not -included in the nature of matter, which is as much matter when it rests -as when it moves; and since we see that the same portion of matter may -from motion be reduced to rest, and after it hath continued at rest, so -long as other bodies do not put it out of that state, may by external -agents be set a moving again; I, who am not wont to think a man the -worse naturalist for not being an atheist, shall not scruple to say -with an eminent philosopher of old, whom I find to have proposed among -the Greeks that opinion (for the main) that the excellent Des Cartes -has revived amongst us, that the origin of motion in matter is from -God; and not only so, but that thinking it very unfit to be believed, -that matter barely put into motion, and then left to itself, should -casually constitute this beautiful and orderly world; I think also -further, that the wise Author of things did, by establishing the laws -of motion among bodies, and by guiding the first motions of the small -parts of matter, bring them to convene after the manner requisite -to compose the world; and especially did contrive those curious and -elaborate engines, the bodies of living creatures, endowing most of -them with the power of propagating their species.”--_Considerations and -Experiments touching the Origin of Forms and Qualities_: Boyle’s Works, -vol. ii. p. 460. Edinburgh. 1744. - -[6] Cudworth’s _Intellectual System_. - -[7] “According to the Pythagoreans and Platonists, there is a life -infused throughout all things ... an intellectual and artificial -fire--an inward principle, animal spirit, or natural life, producing -or forming within, as art doth without--regulating, moderating, and -reconciling the various motions, qualities, and parts of the mundane -system. By virtue of this life, the great masses are held together in -their ordinary courses, as well as the minutest particles governed in -their natural motions, according to the several laws of attraction, -gravity, electricity, magnetism, and the rest. It is this gives -instincts, teaches the spider her web, and the bee her honey;--this -it is that directs the roots of plants to draw forth juice from the -earth, and the leaves and the cortical vessels to separate and attract -such particles of air and elementary fire as suit their respective -natures.”--Bishop Berkeley, _Siris_, No. 277. - -[8] “The revolution of the earth is performed in a natural day, -or, more strictly speaking, once in 23h. 56' 4", and as its mean -circumference is 24,871 miles, it follows that any point in its -equatorial surface has a rotatory motion of more than 1,000 miles per -hour. This velocity must gradually diminish to nothing at either pole. -Whilst the earth is thus revolving on its axis, it has a progressive -motion in its orbit. If we take the length of the earth’s orbit at -630,000,000, its motion through space must exceed 68,490 miles in the -hour.”--Enc. Brit. art. _Physical Geography_. - -[9] “Here then we have the splendid result of the united studies of -MM. Argelander, O. Struve, and Peters, grounded on observations made -at the three observatories of Dorpat, Abo, Pulkova, and which is -expressed in the following thesis:--The motion of the solar system in -space is directed to a point of the celestial vault situated on the -right line which joins the two stars π and μ _Herculis_, at a quarter -of the apparent distance of these stars, reckoning from π _Herculis_. -The velocity of this motion is such, that the sun, with all the bodies -which depend upon it, advances annually in the above direction 1·623 -times the radius of the earth’s orbit, or 33,550,000 geographical -miles. The possible error of this last number amounts to 1,733,000 -geographical miles, or to a _seventh_ of the whole value. We may then -wager 400,000 to 1 that the sun has a proper progressive motion, and -1 to 1 that it is comprised between the limits of thirty-eight and -twenty-nine millions of geographical miles.”--_Etudes d’Astronomie -Stellaire: Sur la Voie Lactée et sur les Distances des Etoiles Fixes_: -M. F. W. G. Struve. [A report addressed to his Excellency M. Le Comte -Ouvaroff; Minister of Public Instruction and President of the Imperial -Academy of Sciences at St. Petersburg.] - -[10] “The first great agent which the analysis of natural phenomena -offers to our consideration, more frequently and prominently than -any other, is force. Its effects are either, 1st, to counteract the -exertion of opposing force, and thereby to maintain _equilibrium_; or, -2ndly, to produce _motion_ in matter, - -“Matter, or that whatever it be of which all the objects in nature -which manifest themselves directly to our senses consist, presents us -with two general qualities, which at first sight appear to stand in -contradiction to each other--activity and inertness. Its activity is -proved by its power of spontaneously setting other matter in motion, -and of itself obeying their mutual impulse, and moving under the -influence of its own and other force; inertness, in refusing to move -unless obliged to do so by a force impressed externally, or mutually -exerted between itself and other matter, and by persisting in its state -of motion or rest unless disturbed by some external cause. Yet, in -reality, this contradiction is only apparent. Force being the cause, -and motion the effect produced by it on matter, to say that matter is -inert, or has _inertia_, as it is termed, is only to say that the cause -is expended in producing its effect, and that the same cause cannot -(without renewal) produce double or triple its own proper effect. -In this point of view, equilibrium may be conceived as a continual -production of two opposite effects, each, undoing at every instant what -the other has done,”?--See continuation of the argument in _Herschel’s -Discourse on the Study of Natural Philosophy_, page 223. - -In the Edinburgh New Philosophical Journal, vol. xlv., will be found a -paper by Dr Robert Brown--“_Of the sources of motions upon the Earth, -and of the means by which they are sustained_,” which will well repay -an attentive perusal, as pointing to a class of investigation of the -highest order, and containing deductions of the most philosophic -description. - -[11] Friction, it is well known, generates heat; by rapidly rubbing two -sticks together, the Indian produces their ignition; heat and light -being both manifested. Under every mechanical disturbance electrical -changes can be detected, and the action of heat in the combustion of -the wood is a chemical phenomenon. - -[12] Count Rumford’s experiment consisted in placing a mass of metal -in a box of water at a known temperature, and, by employing a boring -apparatus, ascertaining carefully the increase of heat after a given -number of revolutions. He thus describes his most satisfactory -experiment:-- - -“Everything being ready, I proceeded to make the experiment I had -projected, in the following manner. The hollow cylinder having been -previously cleaned out, and the inside of its bore wiped with a clean -towel till it was quite dry, the square iron bar, with the blunt steel -borer fixed to the end of it, was put into its place; the mouth of the -bore of the cylinder being closed at the same time by means of the -circular piston through the centre of which the iron bar passed. - -“This being done, the box was put in its place; and the joinings of -the iron rod, and of the neck of the cylinder with the two ends of -the box, having been made water-tight, by means of collars of oiled -leather, the box was filled with cold water (viz., at the temperature -of 60°) and the machine was put in motion. The result of this beautiful -experiment was very striking, and the pleasure it afforded me amply -repaid me for all the trouble I had had, in contriving and arranging -the complicated machinery used in making it. The cylinder, revolving -at the rate of about thirty-two times in a minute, had been in motion -but a short time, when I perceived, by putting my hand into the water -and touching the outside of the cylinder, that heat was generated, and -it was not long before the water which surrounded the cylinder began -to be sensibly warm. At the end of one hour, I found, by plunging a -thermometer into the water in the box (the quantity of which fluid -amounted to 18·77 lbs. avoirdupois, or 2-1/4 wine gallons), that -its temperature had been raised no less than 47°; being now 107° of -Fahrenheit’s scale. When thirty minutes more had elapsed, or one hour -and thirty minutes after the machinery had been put in motion, the heat -of the water in the box was 142°. At the end of two hours, reckoning -from the beginning of the experiment, the temperature of the water -was found to be raised to 178°. At two hours twenty minutes it was at -200°; and at two hours thirty minutes it _actually boiled_.”--_Inquiry -concerning the Source of the Heat excited by Friction_: Philosophical -Transactions, vol. lxxxviii. A.D. 1798. - -“Mr. Joule brought a communication on the same subject before the -British Association at Cambridge, which was afterwards published in the -Philosophical Magazine, and from that journal the following notices are -extracted:-- - -“The apparatus exhibited before the Association consisted of a brass -paddle-wheel, working horizontally in a can of water. Motion could -be communicated to this paddle by means of weights, pulleys, &c. The -paddle moved with great resistance in the can of water, so that the -weights (each of four pounds) descended at the slow rate of about one -foot per second. The height of the pulleys from the ground was twelve -yards, and consequently when the weights had descended through that -distance they had to be wound up again in order to renew the motion of -the paddle. After this operation had been repeated sixteen times, the -increase of the temperature of the water was ascertained by means of a -very sensible and accurate thermometer. - -“A series of nine experiments was performed in the above manner, and -nine experiments were made in order to eliminate the cooling or heating -effects of the atmosphere. After reducing the result to the capacity -for heat of a pound of water, it appeared that for each degree of heat -evolved by the friction of water, a mechanical power equal to that -which can raise a weight of 890 lbs. to the height of one foot, had -been expended. - -“Any of your readers who are so fortunate as to reside amid the -romantic scenery of Wales or Scotland could, I doubt not, confirm my -experiments by trying the temperature of the water at the top and at -the bottom of a cascade. If my views be correct, a fall of 817 feet -will of course generate one degree of heat, and the temperature of the -river Niagara will be raised about one fifth of a degree by its fall of -160 feet.”--_Relation between Heat and Mechanical Power_: Philosoph. -Mag. vol. xxvii. 1845. - - - - -CHAPTER III. - -GRAVITATION. - - The Forms of Matter--Shape of the Earth--Probability of the Mass - forming this Planet having existed in a Nebulous State--Zodiacal - Lights--Comets--Volatilization of Solid Matter by Artificial - means--The principle of Gravitation--Its Influence through - Space and within the smallest Limits--Gravitating powers of the - Planets--Density of the Earth--Certainty of Newton’s Law of the - Inverse Square--Discovery of Neptune--State of a Body relieved from - Gravitation--Experiment explaining Saturn’s Ring, &c.--General - inference. - - -Let us suppose the earth--consisting of three conditions of matter; -the solid, the fluid, and the aëriform--to be set free from that power -by which it is retained in its present form of a spheroid flattened -at the poles, but still subject to the influences of its diurnal and -annual rotations. Agreeably to the law which regulates the conditions -of all bodies moving at high velocities, the consequence of such a -state of things would be, that our planet would instantly spread itself -over an enormous area. The waters and even the solid masses of this -globe would, in all probability, present themselves amidst the other -phenomena of space in a highly attenuated state, revolving in an orbit -around the sun, as a band of nebulous matter, which might sometimes -be rendered sensible to sight by still reflecting solar light, or by -condensation in the form of flights of shooting stars.[13] - -This may be illustrated by experiment. If upon a rapidly revolving -disc we place a ball of dust, it will be almost immediately spread -out, and its particles will arrange themselves in a series of regular -curves, varying with the velocity of the motion. In addition to the -disintegration which would arise from the tendency of the atoms to fly -from the centre, the motion, in space, of the planetary mass would -naturally occasion a trailing out, and the only degree of uniformity -which this orb could, under these imaginary conditions, possibly -present, would be derived from the combined effects of motions in -different directions. - -Amid the remoter stars, some remarkable cloud-like appearances are -discovered. These nebulæ, presenting to the eye of the observer -only a gleaming light, as from some phosphorescent vapour, were -long regarded as indications of such a condition as that which we -have just been considering. Astronomers saw, in those mysterious -nebulæ, a confirmation of their views, which regarded all the orbs -of the firmament as having once been thin sheets of vapour, which -had gradually, from irregular bodies traversing space, been slowly -condensed about a centre, and brought within the limits of aggregating -agencies, until, after the lapse of ages, they become sphered stars, -moving in harmony amid the bright host of heaven.[14] Geologists seized -on those views with eagerness, as confirming theoretical conclusions -deduced from an examination of the structure of the earth itself, and -explained by them the gradual accretion of atoms into crystalline rocks -from a cooling mass. - -The researches of modern astronomers, aided by the magnificent -instruments of Lord Rosse,[15] have, however, shown that many of the -most remarkable nebulæ are only clusters of stars; so remote from -us, that the light from them appears blended into one diffused sheet -or luminous film. There are, however, the Magellanic clouds, and -other singular patches of light, exhibiting changes which can only -be explained on the theory of their slow condensation. There is no -evidence to disprove the position that world-formation may still be -going on; that a slow and gradual aggregation of particles, under the -influence of laws with which we are acquainted, may be constantly in -progress, to end, eventually, in the formation of a sphere. - -May we not regard the zodiacal light as the remains of a solar -luminiferous atmosphere, which once embraced the entire system of which -it is the centre?[16] Will not the strange changes which have been -_seen to take place_ in cometary bodies, even whilst they were passing -near the earth,--as the division of Biela’s comet and the ultimate -formation of a second nucleus from the detached portion,--strongly -tend to support the probability of the idea that attenuated matter -has, in the progress of time, been condensed into solid masses, and -that nebulous clouds must still exist in every state of tenuity in the -regions of infinite space,[17] which, in the mysterious processes of -world-formation, will, eventually, become stars, and reflect across -the blue immensity of heaven, in brightness, that light which is the -necessary agent of organisation and all manifestations of beauty? - -The inferences drawn from a careful study of the condition of our own -globe are in favour of the assumption of the existence of nebulous -matter. By the processes of art and manufacture, by the operation of -those powers on which organisation and life depend, solid matter is -constantly poured off in such a state that it cannot be detected, _as -matter_, by any of the human senses. Yet a thousand results, daily and -hourly accumulating as truths around us, prove that the solid metals, -the gross earths, and the constituents of animal and vegetable life, -all pass away invisible to us, and become “thin air.” We know that, -floating around us, these volatilized bodies exist in some material -form, and numerous experiments in chemistry are calculated to convince -us, that the most attenuated air is capable, with a slight change -of circumstances, of being converted into the condition of solid -masses. Hydrogen gas, the lightest, the most ethereal of the chemical -elements, dissolves iron and zinc, arsenic, sulphur, and carbon; and -from the transparent combinations thus formed, we can with facility -separate those ponderous bodies. Such substances must exist in our -own atmosphere; why not in the regions of space? Whether this planet -ever floated a mass of nebulous matter, only known by its dim and -filmy light, or comet-like rushed through space with widely eccentric -orbit, are questions which can only receive the reply of speculative -minds. Whether the earth and the other members of the Solar System were -ever parts of a Central Sun,[18] and thrown from it by some mighty -convulsion, though now revolving with all the other masses around that -orb, chained in their circuits by some infinite power, is beyond the -utmost refinements of science to discover. This hypothesis is, however, -in its sublime conception, worthy of the master-mind that gave it birth. - -All we know is, that our earth is an oblate sphere, which, by the -effects of its rotation around an axis, is somewhat enlarged at the -equator and flattened at the poles;--that it maintains its regular -course around the sun, in virtue of the operation of two forces, one -of which, acting constantly, would eventually draw it into the body -of the sun itself; but that it is opposed by the other, centrifugal -force, and the varying momentum of the revolving mass;--that the same -force acting from the centre of the earth itself, and from the centre -of every particle of its substance, resolves the whole into a globular -form. - -The principle of Gravitation[19] is that force which resides in every -form of matter, by which particle is attracted by particle, and mass -by mass, the less towards the greater. What this may be, we scarcely -dare to speculate. In the vast area of its action, which opens before -the eye of the mind, we see a power spanning all space, and linking -together every one of those myriads of worlds which spangle the robe -of the Infinite, and we are compelled to pause. Is this principle of -gravitation a property of matter, or is it a power higher than the -more tangible forces, is the question which presses on the mind. If -we regard it as a subtile principle pervading all space, we compel -ourselves to look beyond it for another power yet more refined; and we -cannot halt until, ascending from the limitable to the illimitable, we -resolve gravitation and its governing influences to the centre of all -power--the will of the eternal Creator. - -Science has developed the grand truth, that it is by the exercise -of this all-pervading influence that the earth is retained in its -orbit--that the pellucid globe of dew which glistens on the leaf is -bound together--that the débris which float upon the lake accumulate -into one mass--that the sea exhibits the phenomena of the tides--and -the aërial ocean its barometric changes. In all things this force is -active, and throughout nature it is ever present. Our knowledge of the -laws which it obeys, enables us to conclude that the sun and distant -planets are consolidated masses like this earth. We find that they have -gravitating power, and by comparing this influence with that exerted -by the earth, we are enabled to weigh the mass of one planet against -another. In the balance of the astronomer, it is as easy to poise the -remote star, as it is for the engineer to calculate the weight of the -iron tunnel of the Menai Straits, or any other mechanical structure. -Thus throughout the universe the balance of gravitating force is -unerringly sustained. If one of the most remote of those gems of light, -which flicker at midnight in the dark distance of the starry vault, -was, by any power, removed from its place, the disturbance of these -delicately balanced mysteries would be felt through all the created -systems of worlds. - -From the peculiarity of the laws which this power called gravity obeys, -it has been inferred that it acts from centres of force; it is proved -that its power diminishes in the inverse ratio of the square of the -distance, and that the gravitating power of every material body is in -the direct proportion of its mass. In astronomical calculations we have -first to learn the mass of our earth. Experiment informs us that the -density of our hardest rock is not above 2·8; but from the enormous -pressure to which matter must be subjected, at great depths from the -surface, the weight of the superincumbent mass constantly increasing, -it is quite certain that the earth’s density must be far more than -this. Maskelyne determined the attraction of large masses by a plummet -and line on the mountain Schehallion.[20] Cavendish, with exceedingly -delicate apparatus, observed the attraction of masses of known -weight and size upon each other. Applying the powers of arithmetical -calculation, and the data obtained from the small experiments to the -larger phenomena, Maskelyne determined the earth’s mean density to -be 4·71, whilst Cavendish made it 5·48, but the more recent refined -investigations of Baily have determined it to be 5·67.[21] - -From data thus obtained by severe inductive experiments and -mathematical analyses, the astronomer, by observing the deviations of -a distant star, is enabled to determine the influence of those stellar -bodies near which it passes, and, hence, to calculate the relative -magnitudes of each. The accuracy of the law is in this way put to the -severest test, and the precision of astronomical prediction is the -strongest proof of its universality and truth. - -Rolling onward its lonely way, in the far immensity of our system, -the planet Uranus was discovered by the elder Herschel,--so great -its distance that its diminished light could scarcely be detected -by the most powerful telescopes; but since its discovery its path -has been carefully watched, and some irregularities noticed. Most -of these disturbances were referable to known causes; but a little -alteration in its rate of motion observed when the planet was in one -portion of its vast orbit was unexplained. Convinced of the certainty -of Newton’s law, and having determined that the attraction of known -masses was insufficient to produce the disturbance observed, these -deviations were referred to the gravitating influence of a mass -beyond the known limits of our Solar System. By the investigations -of Adams in England,[22] and Le Verrier in France,[23] the place of -the hypothetical mass was determined, and its size computed. As a -grand confirmation of the great law, and to the glory of those two -far-searching minds, who do honour to their respective countries and -their age, the hypothesis became a fact, in the discovery of the planet -Neptune in the place determined by rigorous calculation. Astronomy -affords other examples of the sublime truth of the law of gravitation, -than which science can afford no more elevated poetry. - -So completely is all nature locked in the bonds of this infinite power, -that it is no poetic exaggeration to declare, that the blow which rends -any earthly mass is conveyed by successive impulses to every one of the -myriads of orbs, which are even too remote for the reach of telescopic -vision. - -An illustrative experiment must close our consideration of relative -operations of rotation and gravitation. We well know that a body in -a fluid state would, if suspended above the earth, it being at the -same time free to take any form, naturally assume that of a flattened -spheroid, from the action of the mass of the earth upon it: whereas the -force of cohesive attraction acting equally from all sides of a centre, -would, if uninfluenced, necessarily produce a perfect sphere. The best -method of showing that this would be the case, is as follows:-- - -Alcohol and water are to be mixed together until the fluid is of the -same specific gravity as olive oil. If, when this is effected, we -drop globules of the oil into the mixed fluid, it will be seen that -they take an orbicular form;--and, of course, in this experiment the -power of the earth’s gravitating influence is neutralized. The same -drops of oil under any other conditions would be flattened. Simple as -this illustration is, it tells much of the wondrous secret of those -beautifully balanced forces of cohesion and of gravitation; and from -the prosaic fact we rise to a great philosophical truth. Our experiment -may lead us yet farther in exemplification of known phenomena. If we -pass a steel wire through one of those floating spheres of oil, and -make it revolve rapidly and steadily, thus imitating the motion of a -planet on its axis, the oil spreads out, and we have the spheroidal -form of our earth. Increase the rapidity of this rotation, and when a -certain rate is obtained the oil widens into a disc, a ring separates -itself from a central globe, and at a distance from it still revolves -around it.[24] Here we have a miniature representation of the ring -of Saturn. This is a suggestive experiment, the repetition of which, -by reflective minds, cannot fail to lead to important deductions. The -phenomena of cohesion, of motion, and gravitation, are all involved; -and we produce results resembling, in a striking manner, the conditions -which prevail in the planetary spaces, under the influence of the same -powers. If we take a glass globe, and having filled it with a fluid of -the proper density, drop into it large and small globules of oil, we -may produce an instructive representation of the stellar vault, with -its beautiful spheres of light revolving in their respective orbits; -and though crossing each other’s paths, still moving in obedience to -attracting and repelling forces--onward in perfect harmony. - -From the centre of our earth to the utmost extremity of the -universe--from the infinitely small to the immensely vast--gravitation -exerts its force. It is met on all sides by physical powers acting in -antagonism to it, but, like a ruling spirit, it restrains them in their -wildest moods. - - The smallest dust which floats upon the wind - Bears this strong impress of the Eternal Mind. - In mystery round it, subtile forces roll; - And gravitation binds and guides the whole. - In every sand, before the tempest hurl’d, - Lie locked the powers which regulate a world, - And from each atom human thought may rise - With might to pierce the mysteries of the skies,-- - To try each force which rules the mighty plan, - Of moving planets, or of breathing man; - And from the secret wonders of each sod, - Evoke the truths, and learn the power of God. - - -FOOTNOTES: - -[13] Three hypotheses may be used to account for this most curious -phenomenon. - -1st. The body shines by its own light, and then explodes like a -sky-rocket, breaking into minute fragments too small to be any longer -visible to the naked eye. - -2nd. Such a body, having shone by its own light, suddenly ceases to -be luminous. “The falling stars and other fiery meteors which are -frequently seen at a considerable height in the atmosphere, and which -have received different names according to the variety of their figure -and size, arise from the fermentation of the effluvia of acid and -alkaline bodies which float in the atmosphere. When the more subtile -parts of the effluvia are burned away, the viscous and earthy parts -become too heavy for the air to support, and by their gravity fall to -the earth.”--Keith’s _Use of the Globes_. According to Sir Humphry -Davy, in the Philosophical Transactions for 1847, “the luminous -appearances of shooting stars and meteors cannot be owing to any -inflammation of elastic fluids, but must depend upon the ignition of -solid bodies.” - -3. The body shines by the reflected light of the sun, and ceases to be -visible by its passing into the earth’s shadow, or, in other words, -is eclipsed. Upon the two former suppositions the fact of the star’s -disappearance conveys to us no knowledge of its position, or of its -distance from the earth; and all that can be said is, that if it be -a satellite of the earth, the great rapidity of its motion involves -the necessity of its being at no great distance from the earth’s -surface--much nearer than the moon; while the resistance it would -encounter in traversing the air would be so great that it is probably -without the limits of our atmosphere. _Sir J. W. Lubbock leans to the -third hypothesis._--Sir J. W. Lubbock, _On Shooting Stars_: Phil. Mag. -No. 213, p. 81. - -Sir J. Lubbock also published a supplementary paper on the same -subject, in No. 214, p. 170. - -Mr. J. P. Joule entertains an hypothesis with respect to Shooting -Stars similar to that advocated by Chladni to account for meteoric -stones, and he reckons the ignition of these miniature planetary bodies -by their violent collision with our atmosphere, to be a remarkable -illustration of the doctrine of the equivalency of heat to mechanical -power, or _vis viva_. - -If we suppose a meteoric stone of the size of a six-inch cube to enter -our atmosphere at the rate of eighteen miles per second of time, the -atmosphere being 1/100 of its density at the earth’s surface, the -resistance offered to the motion of the stone will in this case be at -least 51,600 lbs.; and if the stone traverse twenty miles with this -amount of resistance, sufficient heat will thereby be developed to give -1° Fahrenheit to 6,967,980 lbs. of water. Of course by far the largest -portion of this heat will be given to the displaced air, every particle -of which will sustain the shock, whilst only the surface of the stone -will be in violent collision with the atmosphere. Hence the stone may -be considered as placed in a blast of intensely heated air, the heat -being communicated from the surface to the centre by conduction. Only -a small portion of the heat evolved will therefore be received by the -stone; but if we estimate it at only 1/100 it will still be equal -to 1° Fahrenheit per 69,679 lbs. of water, a quantity quite equal -to the melting and dissipation of any materials of which it may be -composed.--Mr. J. P. Joule, _On Shooting Stars_: Phil. Mag. No. 216, p. -348. - -[14] “Laplace conjectures that in the original condition of the solar -system, the sun revolved upon his axis, surrounded by an atmosphere -which, in virtue of an excessive heat, extended far beyond the orbits -of all the planets, the planets as yet having no existence. The heat -gradually diminished, and as the solar atmosphere contracted by -cooling, the rapidity of its rotation increased by the laws of rotatory -motion; and an exterior zone of vapour was detached from the rest, -the central attraction being no longer able to overcome the increased -centrifugal force. This zone of vapour might in some cases retain -its form, as we see it in Saturn’s ring; but more usually the ring -of vapour would break into several masses, and these would generally -coalesce into one mass, which would revolve about the sun,”--Whewell’s -_Bridgewater Treatise_. - -The following passage is translated by the same author from Laplace:-- - -“The anterior state (a state of cloudy brightness) was itself preceded -by other states, in which the nebulous matter was more and more -diffuse, the nucleus being less and less luminous. We arrive in this -manner at a nebulosity so diffuse, that its existence could scarce be -suspected. Such is in fact the first state of the nebula which Herschel -carefully observed by means of his telescope.” - -Sir William Herschel has the following observations on these remarkable -masses:-- - -“The nature of planetary nebulæ, which has hitherto been involved in -much darkness, may now be explained with some degree of satisfaction, -since the uniform and very considerable brightness of their apparent -disc accords remarkably well with a much condensed, luminous fluid; -whereas, to suppose them to consist of clustering stars will not so -completely account for the milkiness or soft tint of their light, to -produce which it would be required that the condensation of the stars -should be carried to an almost inconceivable degree of accumulation. - -“How far the light that is perpetually emitted from millions of suns -may be concerned in this shining fluid, it might be presumptuous to -attempt to determine; but notwithstanding the inconceivable subtilty -of the particles of light, when the number of the emitting bodies -is almost infinitely great, and the time of the continual emission -indefinitely long, the quantity of emitted particles may well become -adequate to the constitution of a shining fluid or luminous matter, -provided a cause can be found that may retain them from _flying off, -or reunite them_.”--_Observations on Nebulous Stars_: Philosophical -Transactions, vol. lxxxi. A.D. 1791. - -In addition, the following Memoirs on the same subject, by Sir -William Herschel, have been published in the Philosophical -Transactions:--_Catalogue of 1000 Nebulæ and Clusters of Stars_, vol. -lxxvi.; _Catalogue of another 1000, with remarks on the Heavens_, vol. -lxxix.; _Catalogue of 500 more, with remarks as above_, vol. xcii.; -_Of such as have a cometary appearance_, vol. ci.; _Of planetary -nebulæ_, ibid.; _Of stellar nebulæ_, ibid.; _On the sidereal part of -the heavens, and its connection with the nebulous_, vol. civ.; _On the -relative distances of clusters of nebulous stars_, vol. cviii. - -[15] Lord Rosse’s beautiful telescopes have been formed upon principles -which appear to embrace the best possible conditions for obtaining -a reflecting surface which should reflect the greatest quantity of -light, and retain that property little diminished for a length of -time. The alloy used for this purpose consists of tin and copper in -atomic proportions, namely, one atom of tin to four atoms of copper, -or by weight 58·9 to 126·4.--_On the Construction of large Reflecting -Telescopes_: by Lord Rosse. Report of the Fourteenth Meeting of the -British Association, 1844, p. 79. - -[16] The best description of the Zodiacal Light occurs in a letter -furnished by Sir John Herschel to the _Times_ newspaper in March, -1843:--“The zodiacal light, as its name imports, invariably appears -in the zodiac, or, to speak more precisely, in the plane of the sun’s -equator, which is 7° inclined to the zodiac, and which plane, seen from -the sun, intersects the ecliptic in longitude 78° and 258°, or so much -in advance of the equinoctial points: in consequence it is seen to the -best advantage at, or a little after, the equinoxes; after sunset, -at the spring, and before sunrise, at the autumnal equinox; not only -because the direction of its apparent axis lies at those times more -nearly perpendicular to the horizon, but also because at those epochs -we are approaching the situation when it is seen most completely in -section. - -“At the vernal equinox the appearance of the zodiacal light is that -of a pretty broad pyramidal, or rather lenticular, body of light, -which begins to be visible as soon as the twilight decays. It is very -bright at its lower or broader part near the horizon, and, if there -be broken clouds about, often appears like the glow of a distant -conflagration, or of the rising moon, only less red, giving rise, in -short, to amorphous masses of light such as have been noticed by one of -your correspondents as possibly appertaining to the comet. At higher -altitudes, its light fades gradually, and is seldom traceable much -beyond the Pleiades, which it usually, however, attains and involves, -and (what is most to my present purpose) its axis at the vernal equinox -is always inclined (to the northward of the equator) at an angle of -between 60° and 70° to the horizon, and it is most luminous at its -base, resting on the horizon, where also it is broadest, occupying, -in fact, an angular breadth of somewhere about 10° or 12° in ordinary -clear weather.” - -[17] “The assumption that the extent of the starry firmament is -literally infinite has been made by one of the greatest of astronomers, -the late Dr. Olbers, the basis of a conclusion that the celestial -spaces are, in some slight degree, deficient in _transparency_; so that -all beyond a certain distance is, and must remain for ever, unseen; the -geometrical progression of the extinction of light far outrunning the -effect of any conceivable increase in the power of our telescopes. Were -it not so, it is argued, every part of the celestial concave ought to -shine with the brightness of the solar disc, since no visual ray could -be so directed as not, in some point or other of its infinite length, -to encounter such a disc.”--_Edinburgh Review_, p. 185, for January, -1848; _Etudes d’Astronomie Stellaire_. - -[18] In the _Astronomische Nachrichten_ of July, 1846, appeared a -Memoir by M. Mädler, _Die Centralsonne_. The conclusions arrived at by -Mädler may be understood from the following quotation from a French -translation, made by M. A. Gautier, in the _Archives des Sciences -Physiques et Naturelles_, for October, 1846:--“Quoiqu’il résulte -de ce qui précède que la région du ciel que j’ai adoptée satisfait -à toutes les conditions posées plus haut, il n’en est pas moins -convenable de la soumettre à toutes les épreuves possibles. Plusieurs -essais de combinaisons différentes m’ont convaincu qu’on ne pourrait -trouver aucun autre point dans le ciel qui pût tenir lieu, même d’une -manière approchée, que celui que j’ai adopté. On pourrait maintenant -m’addresser l’objection que, si la région du ciel où se trouve le -centre de gravité de notre système d’étoiles fixes, est déterminée -par ce qui précède entre certaines limites, il n’en résulte pas la -nécessité de choisir Alcyone pour ce centre, attendu qu’il pourrait -bien tomber sur quelqu’autre étoile située dans le groupe ou dans son -voisinage. Mais outre que c’est tout près de là que se trouve le groupe -le plus brillant et le plus riche en étoiles de tout le ciel, et qu’il -ne s’agit point ici d’un point arbitraire situé dans le voisinage -peu apparent et qui n’ait rien qui le distingue, il ne se trouve nul -part, même dans la région voisine, une aussi exacte concordance des -mouvements propres qu’ici, et ces mouvements correspondent mieux que -tous les autres aux conditions établies plus haut. Or si l’on doit -considérer ce groupe central, entre les étoiles également éloignées, on -peut présumer que la plus brillante de beaucoup présente la plus grande -masse. Outre cela Alcyone, considérée optiquement, est au milieu du -groupe des Pleïades; et son mouvement propre, déterminé par Bessel, est -plus exactement en accord avec la moyenne de ceux des autres Pleïades; -ainsi que des étoiles de cette région jusqu’à 10° de distance. _Je puis -donc établir comme conséquence de tout ce qui précède, que le groupe -des Pleïades est le groupe central de l’ensemble du système des étoiles -fixes, jusqu’aux limites extérieures déterminées par la Voie Lactée; -et que Alcyone est l’étoile de ce groupe qui paraît être, le plus -vraisemblablement, le vrai Soleil central._” - -[19] See the article _On Gravitation_, Penny Cyclopædia, from the pen -of the Astronomer-Royal. - -[20] Delambre dates the commencement of modern astronomical observation -in its most perfect form from Maskelyne, who was the first who gave -what is now called a standard catalogue (A.D. 1790) of stars; that -is, a number of stars observed with such frequency and accuracy, that -their places serve as standard points of the heavens. His suggestion -of the _Nautical Almanack_, and his superintendence of it to the end -of his life, from its first publication in 1767, are mentioned in the -_Almanack_ (vol. i. p. 364); his _Schehallion Experiment on Attraction_ -in vol. iii. p. 69; and the character of his _Greenwich Observations in -Greenwich Observatory_ in vol. ii. p. 442. - -[21] _Experiments to determine the Density of the Earth._ By Henry -Cavendish, Esq., F.R.S. and F.A.S.--Philosophical Transactions, 1798. - -[22] Adams: _An Explanation of the observed irregularities in the -motion of Uranus, on the hypothesis of disturbance caused by a more -distant Planet_.--Appendix to Nautical Almanack for 1851. - -[23] Le Verrier: _Premier Mémoire sur la théorie d’Uranus_, Comptes -Rendus, vol. xxi.; _Sur la planête qui produit les anomalies observées -dans le mouvement d’Uranus_.--_Ib._ vol. xxiii. - -[24] The experiment alluded to is one of a series by M. Plateau, who -thus describes his arrangement of the fluid:--“We begin by making a -mixture of alcohol and distilled water, containing a certain excess -of alcohol, so that when submitted to the trial of the test tube -it lets the small sphere of oil fall to the bottom rather rapidly. -When this point is obtained, the whole is thrown upon filters, care -being taken to cover the funnels containing these last with plates -of glass; this precaution is taken in order to prevent, as much as -possible, the evaporation of the alcohol. The alcoholic liquor passes -the first through the filters, ordinarily carrying with it a certain -number of very minute spherules of oil When the greater part has thus -passed, the spherules become more numerous; what still remains in the -first filters, namely, the oil and a residue of alcoholic liquor, is -then thrown into a single filter placed on a new flask. This last -filtration takes place much more slowly than the first, on account of -the viscosity of the oil; it is considerably accelerated by renewing -the filter once or twice during the operation. If the funnel has been -covered with sufficient care, the oil will collect into a single mass -at the bottom of the flask under a layer of alcoholic liquor.”--_On the -Phenomena presented by a free Liquid Mass withdrawn from the action of -Gravity._ By Professor Plateau, of the University of Ghent. Translated -from the _Memoirs of the Royal Academy of Brussels_, vol. xvi.; in the -_Scientific Memoirs_, vol. iv. part 13. - - - - -CHAPTER IV. - -MOLECULAR FORCES. - - Conditions of Matter--Variety of organized - Forms--Inorganic Forms--All matter reducible to the - most simple conditions--Transmutation, a natural - operation--Chemical Elementary Principles--Divisibility of - Matter--Atoms--Molecules--Particles--Molecular Force includes - several Agencies--Instanced in the Action of Heat on Bodies--All - Bodies porous--Solution--Mixture--Combination--Centres of - Force--Different States of Matter (Allotropic Conditions)--Theories - of Franklin, Æpinus, and Coulomb--Electrical and Magnetic - Agencies--Ancient Notions--Cohesive Attraction, &c. - - -In contemplating the works of nature, we cannot but regard, with -feelings of religious admiration, the infinite variety of forms under -which matter is presented to our senses. On every hand the utmost -diversity is exhibited; through all things we trace the most perfect -order; and over all is diffused the charm of beauty. It is the -uneducated or depraved alone who find deformities in the creations by -which we are surrounded. - -The three conditions of matter are--the solid, the fluid, and the -aëriform; and these belong equally to the organic and the inorganic -world. - -In organic nature we have an almost infinite variety of animal form, -presenting developments widely different from each other, yet in every -case suited to the circumstances required by the position which the -creature, occupies in the scale of being. Through the entire series, -from the Polype to the higher order of animals, even to man, we find a -uniformity in the progress towards perfection, and a continuity in the -series, which betrays the great secret, that the mystery of life is -the same in all,--a pervading spiritual essence associated with matter, -and modifying it by the master-mechanism of an Infinite mind. - -In the vegetable clothing of the surface of the earth, which fits it -for the abode of man and animals--from the confervæ of a stagnant pool, -or the lichen of the wind-beaten rocks, to the lordly oak or towering -palm--a singularly beautiful chain of being presents itself to the -contemplative mind, and we cannot but trace the gradual elevation in -the scale of organization. - -In the inorganic world, where the great phenomena of life are wanting, -we have constantly exhibited the working of powers of a strangely -complicated kind. The symmetrical arrangement of crystals--the -diversified characters of mineral formations--the systematic -aggregations of particles to form masses possessing properties of a -peculiar and striking nature--all prove, that agencies, which science, -with all its refinements, has not yet detected, are unceasingly at -work. Heat, electricity, chemical power--whatever that may be--and -the forces of cohesion, are known to be involved in the production of -the forms we see; but contemplation soon leads to the conviction that -these powers are subordinate to others which we know not of. We know -only the things belonging to the surface of our planet, and these but -superficially. The geologist traces rock-formations succeeding each -other (from the primary strata holding no traces of organized forms, -through the Paleozoic series, in which, step by step, the history of -animal life is recorded,) to the more recent formations, teeming with -relics, which, though allied to some animal types still existing, are -generally such as have passed away. The naturalist searches the earth, -the waters, and the air, for their living things; and the diversity -of form, the variety of condition, and the perfection of organization -which he discovers as belonging to this our epoch--differing from, -indeed bearing but a slight relation to, those which mark the earth’s -mutations--exhibit, in a most striking view, the endless variety of -characters which matter can assume. - -We are so accustomed to all these phenomena of matter, that it is with -some difficulty we can bend ourselves to the study of the more simple -conditions in which it exists. - -The solid crusts of this telluric sphere--the waters and the -atmosphere--the diversified fabrics of the vegetable kingdom--and the -still more complicated structures of men and animals--are, altogether, -but the aggregation of minute particles in accordance with certain -fixed laws. By mechanical means all kinds of matter may be reduced to -powder, the fine particles of which would not appear very different -from each other, but each atom has been impressed with properties -peculiar to itself, which man has no power to change. - -To nature alone belongs the mysterious property of transmutation. The -enthusiastic alchemist, by the agency of physical forces, dissipates a -metal in vapour; but it remains a metal, and the same metal still. By -the Hermetic art he breaks up the combination of masses; but he cannot -alter the principles of any one of the elements which form the mass -upon which his skill is tried. - -Every atom is invested with properties peculiar to all of its class; -and each one possesses powers, to which in mute obedience it is -compelled, by which these properties are modified, and the character of -matter varied. What are those properties? Do we know anything of those -powers? - -The earth, so far as we are acquainted with it, is composed of about -sixty principles, which we call elementary. These are the most simple -states to which we can reduce matter, and from them all the forms of -creation yet examined by the chemist are produced. These elementary -principles are, some of them, permanently gaseous under the ordinary -temperature, and others exist as solid masses; the difference between -the two conditions being regulated, as it appears, by the opposing -forces of heat and cohesive attraction. - -Matter has been regarded by some as infinitely divisible; but the known -conditions of chemical combinations lead to the conclusion that there -are limits beyond which matter cannot be divided.[25] The theory of -atoms having determinate characters, and possessing symmetric forms, -certainly has the advantage of presenting to the human mind a starting -point--a sort of standing ground,--from which it can direct the survey -of cosmical phenomena. The metaphysical hypothesis, which resolves all -matter into properties, and refers all things to ideas, leaves the -mind in a state of uncertainty and bewilderment. - -Adapting the views of Dumas, with some modifications,[26] it will be -found more satisfactory to regard the _ultimate atoms_ of matter as -points beyond the reach of our examination; which, according to a law, -determined by the influences of the so-called imponderable forces, -unite to form _molecules_. Again, these molecules combine to form the -_particles_ of the mass which we may regard as the limit of mechanical -division. The particles of solid bodies are solid, those of fluids -fluid, and those of gaseous bodies are themselves aëriform; but it does -not follow that the molecules of any body should be necessarily solid, -fluid, or aëriform, from the circumstance of their having formed the -particles of a body in one of these states. - -As this planet--a molecule in space--is formed of aggregated atoms, and -enveloped by its own physical agencies--and as it is involved in the -infinitely extending influences of other planetary molecules, and thus -forms part of a system--so the molecules of any mass are grouped into a -system or particle, which possesses the great characteristic features -of the whole. - -In an aëriform body the particles are in a state of extreme tenuity, -the molecules being themselves, by the influence of some repulsive -force, just on the verge where cohesion exerts its decaying power. In -fluid bodies the attenuation of the particles is less--the particles -and also the molecules are nearer together,--whereas, in the solid -body, the forces of cohesion are most strongly exerted, and all the -molecular conditions brought more powerfully into action. - -Under the term molecular force, we include several agencies,--not -alike in the phenomena which they exhibit, but which are all-powerful -in producing the general characteristics of bodies. These require a -somewhat close examination. All the particles of even a solid mass may -be brought under conditions on which they are free to move. By heat we -can increase the length and thickness of a bar of iron, or any other -metal, and at length produce the fluid state,--a melted metal flows as -freely as water in a stream. Fluids, and gases in like manner obey the -dispersive influence of caloric. From these and other analogous results -we learn that all bodies have a greater or less degree of porosity. -The distance at which the particles of fluid bodies are maintained is -strikingly proved by the fact, that hydrated salts dissolved in water -occupy no more space than that which is equal to the water contained -in the crystalline body; while anhydrous salts dissolve without at -all increasing the bulk of the fluid. All the solid matter of the salt -must, in these cases, it would appear, go to fill up the interstitial -spaces which we suppose to exist in the liquid.[27] - -The conditions which regulate the solubility of bodies, and the power -of solution, regarded either as a mechanical or a chemical process, are -very obscure. We might be led to suppose, that those bodies possessing -the largest amount of unoccupied space were capable of holding the -greatest quantity of soluble matter dissolved. This, however, is far -from being the case, the denser fluids generally having the greatest -solvent power. - -The peculiar manner in which hydrogen gas appears to dissolve solid -substances,--as iron, potassium, sodium, sulphur, phosphorus, -selenium, and arsenic, may be explained by regarding the results as -a manifestation of the powers of chemical affinity over the forms of -bodies. In like manner, the solution of salt in water, or the mixture -of alcohol in that fluid, may be viewed as chemical phenomena, although -usually considered as simple cases of solution or mixture: alterations -of temperature and other physical changes taking place in either. If -two masses of metal,--either tin and copper, for example,--are melted -and combined, the united mass will not equal the bulk of the two -masses. If a pint measure of oil of vitriol and an equal quantity of -water are mixed together, the combined fluids will not fill a two pint -measure.[28] - -In these instances a large quantity of heat is rendered sensible, as -if it had been squeezed out by the force with which the particles -combined, from interstices, which were filled with, what we may be -allowed to call, an atmosphere of heat. Hence we conclude that, amongst -the influences determining the molecular constitution of a body, heat -performs an important part. All these facts go to prove that the atoms -which form the compound body, whatever may be its character, are -disposed of as so many centres of force, which act by influences of a -peculiar character upon each other. That these influences are dependent -upon known physical forces is certain; but the laws by which the powers -of the ultimate atom are altered remain still unknown. - -In the great operations of nature, changes are produced which we cannot -understand, and variations of condition do certainly occur, which may -be regarded as instances of transmutation. - -Amongst others, we may adduce the different states in which we -know carbon to exist. We have the diamond with its beautiful -light-refracting property, its hardness and high specific gravity, -capable of being converted into graphite and coke.[29] Charcoal, -graphite, and the diamond, are totally unlike each other, yet we know -they are each composed of the same atoms. Charcoal is a black irregular -substance, light, and readily inflammable; graphite is crystallizable; -but the forms of its crystals cannot be referred to those of the -diamond, and it burns with difficulty. The diamond occurs in the most -regular and beautifully transparent forms; and it can be burned only -at the highest artificial temperatures. We are, however, convinced by -experiment that the brilliant and transparent gem is made up of the -same atoms as those which go to form the dull black mass of charcoal. -From diamonds, as is above stated, coke has been formed by the heat -of the voltaic battery, and recent experiments have proved that the -volatilized carbon constantly passing off from one of the poles of a -sufficiently powerful battery, is deposited in a crystalline powder, -possessing most of the properties, as it regards hardness, &c. of true -diamond dust. What is the mystery of this? We know not. The peculiar -conditions have been the subjects of anxious study; but science has not -yet let in a ray of light upon the mystery. That a different state--it -has been called an _allotropic_ condition--is often induced in the -same class of atoms is certain; and hence the variety of the resulting -compounds. To continue our illustrations with carbon--may not its -combinations, in uniform proportions with oxygen and hydrogen,[30] owe -their differences to some allotropic change in the ultimate atoms of -this element. - -We know that silicon--the metallic base of flint--is capable of -assuming two or more different states; and that sulphur, selenium, -phosphorus, and arsenic, are susceptible of these remarkable changes -in which, without the slightest variation in the chemical character, a -complete change in the physical condition is produced. Copper, iron, -tin, and manganese, are known to exist in at least two states of -physical dissimilarity, and many of the rarer metals exhibit the same -peculiarity.[31] Hence, may we not infer that some of those substances, -which we now term elementary, are but altered conditions of the same -element? The resemblance between many of those bodies strengthens -the supposition. Iridium and platinum,--iron and nickel,--chlorine, -bromine, iodine, and probably fluorine,--are good examples of these -similarities, although these bodies are all distinguished by physical -and chemical differences. - -The light-refracting gem, which glistens on the neck of beauty, and is -valued for its transparency, differs only from the rude lump of coke in -its molecular arrangement. Chemistry teaches us that we may, without -producing any disarrangement of the affinities, but by merely setting -up molecular disturbance, effect decided changes, as is strikingly -shown in the colour of iodide of mercury changing from red to yellow -under slight influences of heat, and back again to red by a gentle -mechanical disturbance. By a slight change, merely molecular, iron may -be made to resemble platinum in its physical properties.[32] An iron -wire plunged into nitric acid is attacked by the acid with violence; -but if one extremity of the wire is heated in the flame of a spirit -lamp, such a change of state is produced throughout the entire length -of the wire, that if it be now plunged into nitric acid no effect is -produced upon it. On studying this question, we find good reason for -supposing that bodies which, though physically different, resemble -each other in some of their properties, iodine, bromine, &c., are the -results of different _allotropic_ conditions which have been impressed -upon the ultimate atoms, similar to those observed in the substances -named. This hypothesis appears to be more in accordance with the great -principles which we must conceive guided the labours of an Infinite -Mind, than that which supposes a vast number of individual creations. -It will be seen in the sequel that light, heat, electricity, and -chemical action, have the power of producing yet more striking changes -in the forms of bodies. Is it not probable that, according to the -operations of these agents, either combined or separate, acting over -different spaces of time, and under varying circumstances, in relation -to the molecular forces, all those _allotropic_ states may be produced? -Hence bodies may be discovered, which,--from the imperfections of -science,--resisting our means of analysis, must, for a time, be -regarded as new elements, whereas they are possibly only altered states -of the same substance. - -The experiments of Faraday and of Plücker prove that all matter exists -in certain polar conditions, having powers of mutual attraction -and repulsion.[33] Are the molecular forces, so called, to be -referred to any of those powers which are involved in the general -term magnetic-polarity? Are they not probably the result of some -ultimate principle of which these properties are but the modified -manifestations? These questions will now be generally answered in -favour of magnetism; but in our ignorance we should pause; the next -generation will without doubt find another solution for the problem. - -Franklin supposed the ultimate atoms of bodies to be surrounded by -a subtile fluid or ether, which they have the power of condensing -upon their surfaces with great force--and we have experiments showing -that this is probable[34]--whilst he regarded the atoms of the ether -itself as mutually repellent, thus establishing an equilibrium of -forces. Æpinus reduced the hypothesis of Franklin to a mathematical -theory; and Coulomb _proved_ that the force with which the repulsion -of the ethereal atoms and the attraction of the material molecules -are produced, is, like universal attraction,--to whatever power that -may be due,--regulated by the law of the inverse ratio of the square -of the distance. These views are found, upon minute examination, to -hold true to the phenomena with which inductive science has made us -acquainted; and the striking manner in which, when submitted to the -rigorous investigations of geometers, they agree with known conditions -of electricity, appears certainly to favour the opinion that this power -may be materially connected with these molecular arrangements. - -Many of the phenomena which are connected with the magnetic influences -also bear in a remarkable manner upon this inquiry. But, without -the necessary proof of direct experimental evidence, it were as -unphilosophical to refer the binding together of the molecules of -matter to the agency of electricity, as it would be to adopt the theory -of the hooked atoms of Epicurus, or the astrological dream of the -sympathies of matter.[35] - -Science, however, enables us to infer with safety that the mechanical -powers which regulate the constitution of a cube of marble, or a -granite mountain, are of a similar order to those which determine the -earth’s relation to the other planets in the solar system, and that -solar system itself a unit, in the immensity of space, to the myriads -of suns which spangle the stellar vault. - -In fine, cohesion, or the attraction of aggregation, is a power -employed in binding particle to particle. To cohesion, we find we have -heat opposed as a repellent force; and the mysterious operations of -those electrical phenomena, generally referred to as polar forces, are -constantly, it is certain, interfering with its powers. In addition, -we have seen that in nature there exists an agency which is capable -of changing the constitution of the ultimate atoms, and of thus -giving variety to each resulting mass. What this power may be, our -science cannot tell; but our reason leads us, with firm conviction, -to the belief that it is a principle which is, beyond all others in -its subtile influences which equally universal with, appears to rise -superior to gravitation; and which, like a spirituality, shadows forth -to our dwarf conceptions the immensity of the divine power of the -omniscient Creator. - -The molecular forces involve a consideration of all the known physical -powers, the study of which, in their operations on matter, will engage -our attention. But it is pleasant to learn, as we advance step by step -in our examination of the phenomena of creation, that we may study -the grand in what externally appears the simple, and learn, in the -mysteries of a particle, the high truths which science has to tell of a -planet. - -It may appear that the forces of gravitation and cohesion are regarded -as identical. Many phenomena, which we are enabled to reach by the -refinements of inductive inquiry, certainly present to us a striking -similarity in the laws which regulate the operations of these powers; -but it must be remembered that their identity is not established. So -far from this, we know the law of gravitating force. Newton determined -with surprising accuracy, that the action of this power diminishes with -the distance as the universe square, but cohesive force is exerted only -at such distances that it is impossible to determine whether or not it -is subjected to the same law. To quote the words of Young: “The whole -of our inquiries respecting the intimate nature of forces of any kind -must be considered merely as speculative amusements, which are of no -further utility than as they make our views more general, and assist -our experimental investigations.”[36] - - -FOOTNOTES: - -[25] “The divisibility of matter is great beyond the power of -imagination, but we have no reason for asserting that it is infinite; -for the demonstrations which have sometimes been adduced in favour -of this opinion are obviously applicable to space only. The infinite -divisibility of space seems to be essential to the conception that we -have of its nature, and it may be strictly demonstrated that it is -mathematically possible to draw an infinite number of circles between -any given circle and its tangent, none of which shall touch either of -them except at the general point of contact; and that a ship following -always the same oblique course with respect to the meridian,--for -example, sailing north-eastwards,--would continue perpetually to -approach the pole without ever completely reaching it. But when we -inquire into the truth of the old maxim of the schools, that all -matter is infinitely divisible, we are by no means able to decide so -positively. Newton observes that it is doubtful whether any human means -may be sufficient to separate the particles of matter beyond a certain -limit; and it is not impossible that there may be some constitution -of atoms, or single corpuscles, on which their properties, as matter, -depend, and which would be destroyed if the units were further divided; -but it appears to be more probable that there are no such atoms, and -even if there are, it is almost certain that matter is never thus -annihilated in the common course of matter.”--_The Essential Properties -of Matter_: Young’s _Natural Philosophy_; ed. by Rev. P. Kelland. - -[26] “Two very different hypotheses have been formed to explain the -nature of matter, or the mode of its formation; the one known as -the _atomic_ theory, the other, the _dynamic_. The founder of the -former and earlier was Leucippus: he considered the basis of all -bodies to be extremely fine particles, differing in form and nature, -which he supposed to be dispersed through space, and to which his -follower Epicurus first gave the name of atoms. To these atoms he -attributed a rectilinear motion, in consequence of which such as -are homogeneous united, whilst the lighter were dispersed through -space. The author of the second hypothesis was the famous Kant. He -imagined all matter existed, or was originated, by two antagonist and -mutually counteracting principles, which he called attraction and -repulsion, all the predicates of which he referred to motion. Most -modern philosophers, and foremost amongst them Ampère and Poisson, have -adopted an hypothesis combining the features of both the preceding. -They regarded the atoms as data, deriving their origin from the Deity -as the first cause, and consider their innate attractive and repulsive -force as a necessary condition to their combination in bodies. The -main features of this hypothesis are borrowed from Aristotle, inasmuch -as he supposed the basis of all bodies to be the four elements known -to the ancients, the particles of which, endued with certain powers, -constituted bodies. According to Ampère, all bodies consist of equal -particles, and they again of molecules that, up to a certain distance, -attract each other. Their distance from each other he supposed to be -regulated by the intensity of the attractive and repulsive forces, -the latter of which preponderates.”--Peschel’s _Elements of Physics_; -translated by E. West, 1845. - -[27] This was first proved by the researches of Dr. Dalton: the subject -will be again alluded to under the consideration of atomic volumes. - -[28] These peculiar phenomena may be studied advantageously in the -works of most of the eminent European chemists. In our own language the -reader is referred to Dr. Thompson’s _Outline of the Sciences of Heat -and Electricity_, 2nd edition; Brande’s _Manual of Chemistry_--Art. -_Specific Heat_; Graham’s _Elements of Chemistry_; and Daniell’s -_Introduction to the Study of Chemical Philosophy_. - -[29] The conversion of the diamond into graphite and coke was first -effected by the agency of the galvanic arc of flame, by M. Jaquelini, -and communicated to the Academy of Sciences in 1847, in a Memoir -entitled, _De l’action calorifique de la pile de Bunsen, du chalumeau à -gaz oxygène et hydrogène sur le carbon pur, artificiel et naturel_. See -_Comptes Rendus_, 1847, vol. xxiv. p. 1050; also _Report of the British -Association_, for 1847, (_Transactions of Sections_) p. 50. - -[30] “In the annual report on the progress of chemistry, presented -to the Royal Academy of Stockholm, in March 1840, I have proposed to -designate by the term _allotropic state_, that dissimilar condition -which is observed in certain elements, and long known examples of which -are found in the different forms of carbon, as graphite and diamond. - -“Although these dissimilar conditions, which I have here called -allotropic, have long since attracted attention in one or two elements, -still they have been regarded as exceptions to the general rule. It -is at present my object to show that they are not so rare; that it -is probably rather a general property of the elements to appear in -different allotropic conditions; and that although we have hitherto -been unable to obtain several of the elements when uncombined in -their allotropic states, still their compounds indicate the same with -tolerable distinctness.”--_Berzelius on the Allotropy of the Elementary -Bodies_, _&c._: Poggendorff’s Annalen, 1844. Scientific Memoirs, vol. -iv. p. 240. - -[31] “Copper, when reduced by hydrogen at a heat below that of -redness, on exposure to air soon becomes converted throughout its -mass into protoxide; and when it is triturated for some time with -an equivalent quantity of sulphur, it combines with it according to -Böttcher’s experiments, producing flame, and forming sulphuret of -copper. If, however, the copper be reduced by hydrogen at a red heat, -still considerably below the temperature at which it softens and -begins to melt, it remains for years unchanged by exposure to air, -and cannot be made to combine with sulphur without the application of -heat. Iron, cobalt, and nickel, when reduced by hydrogen below a red -heat, inflame after they have cooled, if exposed to the air; and if -they are immediately placed in water to avoid their taking fire, they -inflame when they are again removed, and have become nearly dry. If we -compare this behaviour with that of iron reduced by heat, and with iron -in that state in which it forms the conductor of a galvanic current -without becoming oxidized, it would appear that these peculiarities -depended upon something more than a difference of mechanical -condition.”--_Berzelius on the Allotropy of Elementary Bodies._ See -_On the Isomeric Conditions of the Peroxide of Tin_: by Prof. H. -Rose.--Chemical Gazette, Oct. 1848. - -[32] On this curious subject, and its history, see Bergman’s _Dissert. -de Phlog. quantitate in Metallis_, 1764. Kirwan, _On the Attractive -Powers of Mineral Acids_: Philosophical Transactions. Kier’s -_Experiments and Observations on the Dissolution of Metals in Acids_: -Phil. Trans. 1790. - -From these valuable papers it will be seen that the peculiar states -of iron had already attracted attention, particularly those “inactive -conditions” noticed in a “_Note sur la Manière d’agir de l’Acide -nitrique sur le Fer, par J. F. W. Herschel_,” Aug. 1833; and previously -indicated by M. H. Braconnot, _Sur quelques Propriétés de l’Acide -nitrique_, Annales de Chimie, vol. lii. p. 54. Reference should also be -made to the Memoirs of Sir John Herschel, _On the Action of the Rays -of the Solar Spectrum on Vegetable Colours_, _&c._: Phil. Trans. vol. -cxxxiii. p. 221; and _On the Separation of Iron from other Metals_: -Phil. Trans. vol. cxi. p. 293; and several papers by Schönbein, in the -Philosophical Magazine, from 1837. - -[33] Faraday, in his memoir _On new Magnetic Actions, and on the -Magnetic Conditions of all Matter_, says:--“By the exertion of this new -condition of force, the body moved may pass either along the magnetic -lines or across them, and it may move along or across them in either -or any direction, so that two portions of matter, simultaneously -subject to this power, may be made to approach each other as if they -were mutually attracted, or recede as if mutually repelled. All the -phenomena resolve themselves into this, that a portion of such matter, -when under magnetic action, tends to move from stronger to weaker -places or points of force. When the substance is surrounded by lines -of magnetic force of equal power on all sides, it does not tend to -move, and is then in marked contradistinction with a linear current of -electricity under the same circumstances.”--Phil. Trans. for 1846, vol. -cxxxvii. - -[34] _New Experiments and Observations on Electricity made at -Philadelphia, in America._--Addressed to Mr. Collinson, from 1747 -to 1754. By Benjamin Franklin. Of these Priestley remarks:--“It is -not easy to say whether we are most pleased with the simplicity and -perspicuity with which the author proposes every hypothesis of his own, -or the noble frankness with which he relates his mistakes, when they -were corrected by subsequent experiments.” - -[35] “The atomic philosophy of Epicurus, in its mere physical -contemplation, allows of nothing but matter and space, which are -equally infinite and unbounded, which have equally existed from all -eternity, and from different combinations of which every visible form -is created. These elementary principles have no common property with -each other; for whatever matter is, that space is the reverse of; and -whatever space is, matter is the contrary to. The actual solid part of -all bodies, therefore, are matter, their actual pores space, and the -parts which are not altogether solid, but an intermixture of solidity -and pore, are space and matter combined. - -“The infinite groups of atoms, flying through all time and space in -different directions and under different laws, have interchangeably -tried and exhibited every possible mode of rencounter: sometimes -repelled from each other by concussion, and sometimes adhering to each -other from their own jagged or pointed construction, or from the casual -interstices which two or more connected atoms must produce, and which -may be just adapted to those of other figures,--as globular, oval, or -square. Hence the origin of compound and visible bodies; hence the -origin of large masses of matter; hence, eventually, the origin of the -world itself.”--Dr. Good’s _Book of Nature_. - -[36] Young’s _Lectures on Natural Philosophy and the Mechanical Arts_. -Lecture 49, _On the Essential Properties of Matter_. - - - - -CHAPTER V. - -CRYSTALLOGENIC FORCES. - - Crystallisation and Molecular Force distinguished--Experimental - Proof--Polarity of Particles forming a Crystal--Difference - between Organic and Inorganic Forms--Decomposition - of Crystals in Nature--Substitution of Particles in - Crystals--Pseudomorphism--Crystalline Form not dependent - on Chemical Nature--Isomorphism--Dimorphism--Theories of - Crystallogenic Attraction--Influence of Electricity and - Magnetism--Phenomena during Crystallisation--Can a change of - Form take place in Primitive Atoms?--Illustrative Example of - Crystallisation. - - -“Crystallisation is a peculiar and most admirable work of nature’s -geometry, worthy of being studied by all the power of genius, and the -whole energy of the mind, not on account of the delight which always -attends the knowledge of wonders, but because of its vast importance -in revealing to us the secrets of nature; for here she does, as it -were, betray herself, and, laying aside all disguise, permits us -to behold, not merely the results of her operations, but the very -processes themselves.”--Such is the language of an Italian philosopher, -Gulielmini; and it is the striking peculiarity of beholding the process -of the formation of the regular geometric figures of crystals, the -gradual accretion of particle to particle, which induces us to separate -crystallization from mere molecular aggregation. Without doubt the -formation of a crystal and the production of an amorphous block are -due to powers which bear a close resemblance in many points; but they -present remarkable differences in others. - -Let us take some simple case in illustration. In quiet water we -have very finely divided matter suspended, and matter in a state of -solution. The first is slowly precipitated, and in process of time -consolidates into a hard mass at the bottom, presenting no particular -character, unless it has been placed in some peculiar physical -conditions; when, as in nature, we have a regular bedding which is -intersected by lines of lamination or of cleavage, which we are, from -experiment, enabled to refer to the influence of current electricity. -The second--the matter in solution--is also slowly deposited; but it is -accumulated upon nuclei which possess some peculiar disposing powers, -and every particle is united by some particular face, and an angular -figure of the most perfect character results. Many pleasing experiments -would appear to show that electricity has much to do in the process -of crystallization; but it is evident that it must be under some -peculiarly modified conditions that this power is exerted, if, indeed, -it has any direct action. - -The same substances always crystallize in the same forms, unless the -conditions of the crystallizing body are altered. It has been supposed -that each particle of a crystalline mass has certain points or poles -which possess definite properties, and that cohesion takes place only -along lines which have some relation to the attracting or repelling -powers of these poles. We shall have, eventually, to consider results -which appear to prove that magnetism is universal in its influence, and -that this polarity of the particles of matter may be referred to it. - -Be the cause of crystallisation what it may, it presents to us in -appearance a near approach in inorganic nature to some of the peculiar -conditions of growth in the organised creation. In one, we have the -gradual production of parts and the formation of members due to -peculiar powers of assimilation, each individual preserving all its -distinguishing features; and in the other, we have a regular order of -cohesion occurring under the influence of a power which draws like to -like, and arranges the whole into a form of beauty. - -This appears to be the proper place for correcting an error too -prevalent, relative to the formation of crystals, the development -of cells, and the yet more fatal falsehood of referring the great -phenomena of Life to any of the physical forces with which we are -acquainted. - -THE CRYSTAL _forms_, by the accretion of particle to particle, along -lines determined by some yet unknown power. There is no change in the -character of any particle--like coheres to like; the first atom and the -last of the series being identical in character. - -THE PLANT _grows_, not by the gathering together of similar particles -of matter, but by the absorption of a compound particle--by that one -which must be regarded as the primary nuclear atom or cell. After -this absorption--in virtue of a power which we call LIFE, excited -into action by LIGHT--the compound particle is decomposed, and one -constituent is retained to effect the formation of a new cell, whilst -the other is liberated as an invisible air. Here we have a change of -chemical constitution effected; and this takes place through the whole -period of vegetable growth, from the development of the plumule up to -the formation of the latest leaf upon the topmost branch of the most -lordly tree. - -Life has been referred to electricity and to chemical power--as the -effect of a known cause. Without doubt, during the operations of life -the whole of the physical powers are necessary to the production of -all the phenomena of growth in the vegetable and the animal world. But -these powers are ever subsidiary to vital force, and are like attendant -spirits chained to do an enchanter’s bidding. - -Life is a force beyond the reach of human search, and he who fancies he -has a hold upon the principle which produced biological phenomena, has -committed himself to as wild a pursuit as he who rashly endeavours to -catch a morass-meteor. - -Subtile as are the forces of light, heat, and electricity--that of -life, _vitality_, is infinitely more refined, and it must for ever -elude the search of the philosopher. - -Man is permitted to test and try all things which are created, and -to apply to useful ends the discoveries which he may make. But man -can never become a creator; and he who would attempt to give sense to -an inert mass of matter, by electricity, heat, or light, will prove -himself as ignorant of nature’s truth as is the senseless mass upon -which he works. - -“So far shalt thou go, and no further,” was said equally to the -great tide-wave of human intellect, as to the mighty surge of the -earth-girdling ocean. - -It must not be forgotten that a striking difference exists between -the productions of the mineral and the other kingdoms of nature. -Animals and vegetables arrive at maturity by successive developments, -and increase by the assimilation of substances, having the power of -producing the most important chemical changes upon such matter as comes -within the range of their influence; but minerals are equally perfect -in the earliest stages of their formation, and increase only, as -previously said, by the accretion of particles without their undergoing -any change. - -The animal and vegetable tribes cease to continue the functions of -life: death ensues, and a complete disorganisation takes place; but -this is not the case in the mineral world: the crystal being the result -of a constantly acting force is not necessarily liable to decomposition. - -Nevertheless, we sometimes find in nature that crystals, after arriving -at what may be regarded as, in some sort, their maturity, are, owing -to a change of the conditions under which they were formed, gradually -decomposed. In our mines we discover skeletons of crystals, and -within the hollow shell thus formed, other crystals of a different -constitution and figure find nuclei, and the conditions required for -their development. Again, to give a striking instance, the felspar -crystals of the granitic formations are liable to decomposition in a -somewhat peculiar manner. In decomposing, these crystals leave moulds -of their own peculiar forms, and it not unfrequently happens, in the -stanniferous districts of Cornwall, that oxide of tin gradually fills -these moulds, and we procure this metallic mineral in the form of the -earthy one. Then we have the curious instances of bodies crystallising -in a false form under change of circumstances. We find, for example, -Pseudomorphism, (or _false-form_), as this class of phenomena is named, -occurring by the removal of the constituent atoms of one crystal, while -another set--which naturally assumes a different form--takes their -place, yet still preserving the original shape. It often happens that -copper pyrites will, in this manner, exhibit the angles of an ordinary -variety of crystallised carbonate of iron. These curious changes may -be familiarised by supposing a beautiful statue of gold, from which -some skilful mechanic removes particle by particle, and so skilfully -substitutes a grain of brass for every one of gold removed, that the -loss of the precious metal cannot be detected by any mere examination -of its form. - -Crystalline form is not strictly dependent upon the chemical nature -of the parts forming the crystal. The same number of atoms, arranged -in the same way, produce the same form. Substances much unlike each -other will assume the same crystalline arrangement. Magnesia, lime, -oxide of cadmium, the protoxides of iron, nickel, and cobalt, combined -with the same acid, present similarly formed bodies. These Isomorphic -(_like-form_)[37] peculiarities are exceedingly common, and the -discoverer of the phenomena, Mitscherlich, announced the above law. -It cannot, however, be regarded as a philosophical expression of the -fact, and requires reconsideration--chemical elements of a dissimilar -character may have the same law of aggregation, and thus produce the -same form, without having any relation to the number of atoms. - -We also find compounds which have two distinct systems of -crystallisation. This property, Dimorphism, is very strikingly shown -in carbonate of lime, which occurs in rhombohedrons, in calc spar, and -in rhombic prisms in arragonite. The molecular arrangements here are -not, however, of equal stability, and one form is evidently forced upon -the other, and is abandoned by it on the slightest disturbance. When a -prism of arragonite is heated it breaks up into the rhombs of common -calc spar, at a temperature far below that at which the carbonate of -lime is decomposed; but no alteration of temperature can convert calc -spar into arragonite. - -Crystals are found in the most microscopic character, and of an -exceedingly large size. A crystal of quartz at Milan is three feet and -a quarter long, and five feet and a half in circumference, and its -weight is 870 pounds. Beryls have been found in New Hampshire measuring -four feet in length.[38] - -In the dark recesses of the earth, where the influences which produce -organisation and life cease to act, a creative spirit still pursues its -never-ending task of giving form to matter. - -The science of crystallogeny,[39] embracing the theoretical and -practical question of the causes producing these geometric forms, -has in various ways attempted to explain the laws according to which -molecules arrange themselves on molecules in perfect order, giving rise -to a rigidly correct system of architecture. But it cannot be said that -any theory yet propounded is sufficiently exact to embrace the whole -of the known phenomena, and the questions,--What is crystallogenic -attraction, and what is the physical nature of the ultimate particles -of matter,--are still open for the inquiries of that genius which -delights in wrestling with the secrets of nature. - -The great Epicurus speculated on the “plastic nature” of atoms, and -attributed to this _nature_ the power they possess of arranging -themselves into symmetric forms. Modern philosophers satisfy themselves -with attraction, and, reasoning from analogy, imagine that each atom -has a polar system. - -Electricity, and light, and heat, exert remarkable powers, and -accelerate or retard crystallisation according to the conditions under -which these forces are brought to bear on the crystallising mass. We -have recently obtained evidence which appears to prove that some form -of magnetism has an active influence in determining the natural forms -of crystals, and we discover that magnetism exerts a peculiar influence -in relation to the optic axes of crystals, which is not exerted in -lines at right angles to these. Electricity appears to quicken the -process of crystalline aggregation--to collect more readily together -those atoms which seek to combine--to bring them all within the limits -of that influence by which their symmetrical forms are determined; and -strong evidence is now afforded, in support of the theory of magnetic -polarity, by the refined investigations of Faraday and Plücker, which -prove that magnetism has a _directing_ influence upon crystalline -bodies.[40] - -It has been found that crystals of sulphate of iron, slowly forming -from a solution which has been placed within the range of sufficiently -powerful magnetic force, dispose themselves along certain magnetic -curves, such as are formed around a magnet by steel filings; whereas -the crystals of the Arbor Dianæ, or silver tree, forming under the -same circumstances, take a position nearly at right angles to these -curves. Certain groups of crystals have been found in nature, which -appear to show, by their positions, that terrestrial magnetism has been -active in producing the phenomena they exhibit; indeed, nearly all our -mineral formations indicate the influences of this, or some similarly -acting power.[41] - -During rapid crystallisation, some salts--as the sulphate of -soda, boracic acid, and arsenious acid crystallising in muriatic -acid--exhibit decided indications of electrical excitement; light is -given out in flashes. We have evidence that crystals exhibit a tendency -to move towards the light, and that crystallisation takes place more -readily, and progresses with greater activity in the sunshine than in -the shade. Professor Plücker has recently ascertained that certain -crystals--in particular the cyanite--“point very well to the north, -by the magnetic power of the earth only. It is a true compass needle; -and, more than that, you may obtain its declination.” We must remember -that this crystal, the cyanite, is a compound of silica and alumina -only. This is the amount of experimental evidence which science has -afforded in explanation of the conditions under which nature pursues -her wondrous work of crystal formation. We see just sufficient of -the operation to be convinced that the luminous star which shines in -the brightness of Heaven, and the cavern-secreted gem, are equally -the result of forces which are known to us in only a few of their -modifications. - -Every substance, when placed under circumstances which allow of the -free movement of its molecules, has a tendency to crystallise. All the -metals may, by slowly cooling from the melting state, be exhibited -with a crystalline structure. Of the metallic and earthy minerals, -nature furnishes us with an almost infinite variety of crystals, and, -by a reduction of temperature, yet more simple bodies assume the -most symmetric forms. Water, in the conditions of ice and snow, is a -familiar and beautiful example; and, by such extreme degrees of cold as -are artificially produced, many of the gases exhibit a tendency to a -crystalline condition. - -May not the solid elementary atoms be susceptible of change of form -under different influences? May not the different states under which -the same bodies are found--as, for example, silica, carbon, and -iron--be due entirely to a change in the form of the primitive atom? - -Admitting the probability of this, we then easily see that the central -molecule, formed of an aggregation of such atoms, uniting by particular -faces, would present a determinate form; and that the resulting -crystal, a mass of such molecules, cohering according to a given law, -at certain angles, would present such geometric figures as we find in -nature, or produce in our laboratories, when we avail ourselves of -processes which nature has taught us. - -If we take a particle of marble, and place it in a large quantity -of water acidulated with sulphuric acid, it dissolves, and a new -compound results. The marble disappears--the eye cannot detect it by -form or colour: the acid also has been disguised--the taste discovers -nothing sour in the fluid. We have, in combination with the water, -the lime and sulphuric acid; but that combination appears to the eye -in no respect different from the water itself. It is colourless and -perfectly transparent, although it holds a mass of solid matter which -previously would not allow of the permeation of a ray of light. Let -us expose this fluid to such circumstances that the water will slowly -evaporate, and we shall find forming in it, after a time, microscopic -particles of solid, light-refracting matter. These particles gradually -increase in size, and we may watch their growth until eventually we -have a symmetric figure, beautifully shaped, the primary form of -which is a right rhomboidal prism. Thus in nature, by the action, -in all probability, of vegetable matter on the sulphates held in -solution by the water of the great rivers and the ocean--aided by our -oxidizing atmosphere--sulphuric acid is produced to do its work upon -the limestone formations, and from this combination would result the -well-known gypsum, or plaster of Paris, which ordinarily exists as an -amorphous mass, but is often found in a crystalline form.[42] - -This is a very perfect illustration of the wonderful process we have -been considering, and in which, simple though it appears to be, we -have set to work a large proportion of the known physical elements -of the universe. By studying aright the result which we have it in -our power to obtain in a watch-glass, we may advance our knowledge of -gigantic phenomena, which are now progressing at the bottom of the -ocean, or of the wondrous agencies which are in operation, producing -light-refracting gems within the secret recesses of the rocky crust of -our globe. - -The force of crystallisation is a subject worthy of much consideration. -If we examine our slate rocks, through which little veins filled with -quartz crystals are spread, we shall see that the mechanical force -exerted during the production of these crystals has been capable of -rending those rocks in every direction. Those fissures formed by the -first system of crystalline veins, in order of time, are filled in by -another set of crystalline bodies, which equally exert their mechanical -power, and thus produce those curious intersections and dislocations -which were long a puzzle to the geologist. The simplest power, slowly -and constantly acting through a long period of time, may become -sufficient, eventually, to rend the Andes from base to summit, or to -lift a new continent above the waters of the ocean. - - -FOOTNOTES: - -[37] “Gay Lussac first made the remark, that a crystal of potash alum, -transferred to a solution of ammonia alum, continued to increase -without its form being modified, and might thus be covered with -alternate layers of the two alums, preserving its regularity and proper -crystalline figure. M. Beudant afterwards observed that other bodies, -such as the sulphates of iron and copper, might present themselves -in crystals of the same form and angles, although the form was not a -simple one, like that of alum. But M. Mitscherlich first recognised -this correspondence in a sufficient number of cases to prove that it -was a general consequence of similarity of composition in different -bodies.”--Graham’s _Elements of Chemistry_ (1842), p. 136. - -The following remarks are from a paper by Dr. Hermann Kopp, _On the -Atomic Volume and Crystalline Condition of Bodies, &c._, published in -the Philosophical Magazine for 1841:--“The doctrine of isomorphism -shows us that there are many bodies which possess an analogous -constitution, and the same crystalline form. Our idea of the volume -(or, in other words, of the crystalline form) of these bodies must -therefore be the same. From this it follows that their specific -weight is connected with mass contained in the same volume. From -these considerations the following law may be deduced: _The specific -weight of isomorphous bodies is proportional to their atomic weight, -or isomorphous bodies possess the same atomic volume_.”--page 255. -A translation appears in the Cavendish Society, from Dr. Otto’s -Chemistry, _On Isomorphism_, which may be advantageously consulted. See -also a paper by M. Rose, translated from the _Proceedings of the Royal -Berlin Academy_ for the _Chemical Gazette_, Oct. 1848, entitled, _On -the Isomeric Conditions of the Peroxide of Tin_. - -[38] _A System of Mineralogy, comprising the most recent discoveries_, -by James D. Dana, A.M., New York, 1844. - -[39] Crystallogeny, or the formation of crystals, is the term employed -by Dana, in his admirable work quoted above: whose remarks on -_Theoretical Crystallogeny_, p. 71, are well worthy of all attention. - -[40] _On the Magnetic Relations of the Positive and Negative Optic Axes -of Crystals_, by Professor Plücker, of Bonn.--Philosophical Magazine, -No. 231 (3rd Series), p. 450. _Experimental Researches on Electricity; -On the Crystalline Polarity of Bismuth and other bodies, and on its -Relation to the Magnetic form of Force_: by Michael Faraday, Esq., -F.R.S.--Transactions of the Royal Society for 1848. - -[41] In the _Memoirs of the Geological Survey of the United Kingdom, -and of the Museum of Economic Geology_, vol. i. 1846, will be found a -paper, by the author of this volume, _On the Influences of Magnetism on -Crystallisation, and other Conditions of Matter_, in which the subject -is examined with much care. See also _Magnétisme polaire d’une montagne -de Chlorite schisteuse et de Serpentine_: Annales de Chimie, vol. xxv. -p. 327; _Influence du Magnétisme sur les actions chimiques_, by l’Abbé -Rendus; and also a notice of the experiments of Ritter and Hansteen, -“Analysées par M. Œrsted;” also _Effets du Magnétisme terrestre sur -la précipitation de l’Argent, observés par M. Muschman_: Annales de -Chimie, vol. xxxviii. p. 196-201. - -[42] The transparent varieties of sulphate of lime are distinguished -by the name _Selenite_; and the fine massive varieties are called -_Alabaster_. Gypsum forms very extensive beds in secondary countries, -and is found in tertiary deposits; occasionally, in primitive rocks; it -is also a product of volcanoes. The finest foreign specimens are found -in the salt mines of Bex, in Switzerland; at Hall, in the Tyrol; in the -sulphur-mines of Sicily; and in the gypsum formation near Ocana, in -Spain. In England, the clay of Shotover Hill, near Oxford, yields the -largest crystals.--See Dana’s _Mineralogy_, second edition, p. 241. - - - - -CHAPTER VI. - -HEAT--SOLAR AND TERRESTRIAL. - - Solar and Terrestrial Heat--Position of the Earth in the Solar - System--Heat and Light associated in the Sunbeam--Transparency - of Bodies to Heat--Heating Powers of the Coloured Rays of - the Spectrum--Undulatory Theory--Conducting Property of the - Earth’s Crust--Convection--Radiation--Action of the Atmosphere - on Heat Rays--Peculiar Heat Rays--Absorption and Radiation - of Heat by dissimilar Bodies--Changes in the Constitution of - Solar Beam--Differences between Transmitted and Reflected - Solar Heat--Phenomena of Dew--Action of Solar Heat on the - Ocean--Circulation of Heat by the Atmosphere and the Ocean--Heat - of the Earth--Mean Temperature--Central Heat--Constant Radiation - of Heat Rays from all Bodies--Thermography--Action of Heat on - Molecular Arrangements--Sources of Terrestrial Heat--Latent - Heat of Bodies--Animal Heat--Eremacausis--Spheroidal State - Cold--Condensation--Freezing--Theories of Heat--Natural - Phenomena--and Philosophical Conclusion. - - -We receive heat from the sun, associated with light; and we have the -power of developing this important principle by physical, mechanical, -and chemical excitation, from every kind of matter. Our convictions -are, that the calorific element, whether derived from a solar or a -terrestrial source, presents no essential difference in its physical -characters; but as there are some remarkable peculiarities in the -phenomena, as they arise from either one or the other source, it will -assist our comprehension of this great principle, if we consider it -under the two heads. - -Untutored man finds health and gladness in the warmth and light of the -sun; he rears a rugged altar, and bows his soul in prayer, to the -principle of fire, which in his ignorance he regards as the giver and -the supporter of life. The philosopher finds life and organization -dependent upon the powers combined in the sunbeam; and, examining -the phenomena of this wonderful band of forces, he is compelled to -acknowledge that the flame upon the altar--on the Persian hills,--was -indeed a dim shadow of the infinite wisdom which abides behind the veil. - -The present condition of our earth is directly dependent upon the -amount of heat we receive from the sun. It has frequently been said, -that if it were possible to move this planet so much nearer that orb -that the quantity of heat would be increased, the circumstances of -life would necessarily be so far changed, that all the present races -of animals must perish; and that the same result would happen from -any alteration which threw us yet further from our central luminary, -when, owing to the extremity of cold and the wretchedness of gloom, all -living creatures would equally fail to support their organization. - -To move the earth nearer to, or more distant from the sun, is an -impossibility; but it has been argued that those planets which are near -to the sun must possess a temperature which would melt our solid rocks, -and vaporize the ocean,--while Uranus and Neptune must, from their -distance from the source of heat, have so small an amount, that water -must become solid as the rock, and such an atmosphere as that of the -earth exist as a dense liquid. - -It will be shown that according to the physical condition of the -material substances, so are their powers regulated of absorbing and -retaining the heat which falls as a radiant power upon their surfaces. -Heat rays, in passing through the attenuated medium of planetary space, -lose none of their power--this we know from the fact that even the less -dense upper region of the earth’s atmosphere takes from the solar rays -but an exceedingly small quantity of heat. Therefore, whether a solar -heat ray traverses through one million, or one hundred million miles of -space, it still retains its power equally of imparting warmth to the -solid matter by which it is intercepted. There is no law of variation -as the inverse square of the distance of those radiating powers. -Consequently, there is no reason why the physical conditions, alike -of the nearest and the most remote planetary bodies, should not be so -adjusted that they all enjoy that life promoting temperature which -belongs to the earth. - -All the objects around us are adapted to the circumstances of the -earth’s position in relation to the sun, to which we are bound by the -principle of gravitation; opposed to that centrifugal force which tends -constantly to drive the moving planetary mass off from the centre of -power. The balance maintains its perfect equilibrium, although we have -one power constantly drawing the earth towards the sun, and the other -as constantly exerting itself to move it off into space at a tangent -to the orbit in which the planet moves. In our examination it will be -found that one common system of harmony runs through all the cosmical -phenomena, by which everything is produced that is so beautiful and -joyous in this world. - -Heat, and the other elementary radiant principles, are often combined -as the common cause of effects evident to our senses. The warmth of the -solar rays, and their luminous influence, are not, however, commonly -associated in the mind as the results of a single cause. It is only -when we come to examine the physical phenomena connected with these -radiations that we discover the complexity of the inquiry. Yet it is -out of these very subtle researches that we draw the most refined -truths. The high inferences to which the analysis of the subtile -agencies of creation leads us, render science, pursued in the spirit of -truth, a great system of religious instruction. - -Although we do not fear that heat and light can be confounded in the -mind, so different are their phenomena,--we have heat rays, as from -dark hot iron, which give no light, while in the full flood of the -lunar rays the heat is scarcely appreciable by the most delicate -instruments;--yet it is important to show how far these two principles -have--been separated from each other. Transparent bodies have varied -powers of calorific transparency, or transcalescence: some obstructing -the heat radiated from bodies of the highest temperatures almost -entirely even in the thinnest layers; whilst others will allow the -warmth of the hand to pass through a thickness of several inches. -Liquid chloride of sulphur, which is of a deep red colour, will allow -63 out of 100 rays of heat to pass, and a solution of carmine in -ammonia, or glass stained with oxides of gold, or copper, rather a -greater number; yet these transparent media obstruct a large quantity -of light. Colourless media obstructing scarcely any light, will, on -the contrary, prevent the passage of calorific rays. Out of every -hundred rays, oil of turpentine will only transmit 31, sulphuric ether -21, sulphuric acid 17, and distilled water only 11. Pure flint glass, -however, is permeated by 67 per cent. of the thermic rays, and crown -glass by 49 per cent. The body possessing the most perfect transparency -to the rays of heat is diaphanous salt-rock, which transmits 92, while -alum, equally translucent, admits the passage of only 12 per cent.[43] - -Black mica, obsidian, and black glass, are nearly opaque to light, but -they allow 90 per cent. of radiant heat to pass through them; whereas -a pale green glass, coloured by oxide of copper,[44] covered with a -layer of water, or a very thin plate of alum, will, although perfectly -transparent to light, almost entirely obstruct the permeation of heat -rays. - -We thus arrive at the fact that heat and light may be separated from -each other; and if we examine the solar beam by that analysis which the -prism affords, we shall find that there is no correspondence between -intense light and ardent heat. By careful observation, it has been -proved, when we have a temperature of 62° F. in the yellow ray, which -ray has the greatest illuminating power; that below the red ray, out of -the point of visible light, the temperature is found to be 79°, while -at the other end of the spectrum, in the blue ray, it is 56°, and at -the end of the violet ray no thermic action can be detected.[45] - -From the circumstance, that as we, by artificial means, raise the -temperature of any body, and produce intense heat, so after a -certain point of thermic elevation has been obtained, we occasion a -manifestation of _light_.[46] It has been concluded, somewhat hastily, -that heat and light differ from each other only in the rapidity of the -undulations of an hypothetical ether. - -It must be admitted that the mathematical demonstrations of many of the -phenomena of calorific and luminous power are sufficiently striking to -convince us that a wave-movement is common to both heat and light. The -undulatory theory, however, requires the admission of so many premises -of which we have no proof; its postulates are, indeed, in many cases -so gratuitous, that notwithstanding the array of talent which stands -forward in its support, we must not allow ourselves to be deceived by -the deductions of its advocates, or dazzled by the brilliancy of their -displays of learning. - -Radiant heat appears to move in waves; but that calorific effects in -material bodies are established by any system of undulation, is a -deduction without a proof; and the thermic phenomena of matter are as -easily explained by the hypothesis of a diffusive subtile fluid. - -We have not, however, to prove the correctness of either of the -opposing views; indeed, it is acknowledged that many phenomena require -for their explanation conditions which are not indicated by either -theory. - -The earth receives its heat from the sun; a portion of it is -_conducted_ from particle to particle into the interior of the rocky -crust. Another portion produces warmth in the atmosphere around us, -by _convection_, or the circulation of particles; those warmed by -contact with the surface becoming lighter, and ascending to give place -to the colder and heavier ones. A third portion is radiated off into -space, according to laws which have not been sufficiently investigated, -but which are dependent upon the colour, chemical composition, and -mechanical structure of the surface. - -It cannot but be instructive to contemplate the indications which we -have of the dependence of all that is beautiful on earth, on the heat -and light radiations which we receive from the sun. Let us endeavour -to realise some of the effects which arise from even the temporary -deprivation of solar heat. - -It is winter, the vegetable world appears chilled to its centre. The -trees, except a few of the hardy evergreens, are bare of leaves, and -stretching forth their branches into the cold air, they realise the -condition of vegetable skeletons. The lowly plants of the hedge-row, -and the grasses of the field, show that their vital power is subdued -to that minimum degree of action which is but a few slight removes -from death. The life of the running stream is suspended, it is cased -in the “thick-ribbed ice,” and the waters beneath no longer send forth -their joyous music to the genial breeze. Even within the temperate -limits of our own land, the aspect of winter convinces the ordinary -observer, that the loss of heat has been followed by diminished -activity in the powers of life; and the philosopher discovers that the -lessened energies of solar light, and the weaker action of the radiant -heat, have aided in producing that repose which is a little more than -sleep--a little less than death. - -It is night, and winter: the earth is parting with its heat,--with -the absence of light, there is a still greater loss of vigour, a yet -further diminution of the powers of life. Even the animal races, -sustained by vital influences of a more exalted kind, sink under the -temporary deprivation of the solar rays to a monotonous, a melancholy -repose. All animals undergo different degrees of hybernation, and -each in his winter retreat supports vitality by preying upon himself. -The world is hung in mourning black; there is no play of colours to -harmonize the human spirit by sending their ethereal pulsations to the -human eye, and it is only the consciousness that when the night is at -the darkest, the day is nearest, that even man’s soul is sustained -against the depressing influences of the absence of the sun. - -The conditions which we must observe at our own doors cannot fail to -convey as a conviction to the least imaginative mind, that a slightly -prolonged continuance of darkness, with its consequent increase of -coldness, would be fatal to the existence of the organic world. - -The sun has entered Aries: it is spring. The length of the day and -night are equal, the powers of light and darkness are now exactly -balanced against each other, and light, like the Archangel, triumphs -over the sombre spirit. The organic world awakes. Chemical action -commences in the seed, the vital spark is kindled in the embryo, and -under the impulsive force of some solar radiations the plant struggles -into light and life. The same invigorating force impels the circulation -of the sap through the capillary tubes of the forest tree, until the -topmost branch trembles with the new flow of life. The buds burst forth -into leaf, and a fresh and lively covering spreads over those branches -which, in their nakedness, could scarcely be distinguished from the -dead. - -The animal races are no less sensible of the new influence which is -diffused around. The birds float joyously upon the breeze, and give -to heaven their trilling songs of praise. The beasts come forth from -the clefts of the rocks and the tangled shelters of the forests, and -gambol in the full luxury of their renewed vigour. Man, even man, the -inhabitant of cities, trained and tempered to an artificial state, -awakes of a spring morning with a fuller consciousness of mind, and a -deeper and more pleased sense of his intelligence, than when the fogs -and gloom of winter hung like the charmed robe upon the limbs of the -giant. Now, the dormant poetry of man seeks expression. As the morning -sun is said to have awakened the musical undulations of the Memnonian -statue, so the sun of the vernal morning produces in the mind of the -most earthly, faint pulsations of that heaven-born music, which neither -sin nor sorrow can entirely destroy. The psychologist, in studying the -peculiar phenomena of the human mind, must associate himself with the -natural philosopher, and learn to appreciate the influence of physical -causes in determining effects which our elder philosophers and the -poets of every age have attributed to spiritual agencies. - -Summer, with its increased heat and light, reigns over the land. The -work of life is now at its maximum, and every energy is quickened -throughout the organic creation. The laws of nature are arranged -on the principle of antagonistic forces, the constant struggle to -maintain them in equilibrium constituting the sensible phenomena of -existence. Heat and light, with chemical power and electricity, have -been quickening the unknown principle of life, until it has become -exhausted in the production of new parts--in the strange phenomenon of -growth--the formation of organized matter from the inorganic stores of -creation. - -The autumn, with its tempered sunlight, comes, but in the solar -radiance we discover new powers, and under the influence of these the -flower and the fruit have birth. The store of a new life is centered in -the seed, and though the leaf falls, and the flower fades, a new set -of organisms are produced, by which the continuance of the species is -secured. - -Let any man examine himself as the seasons change, and he will soon be -convinced that every alternation of light and darkness, of heat and -its absence, produces new sets of influences equally on the mind and -on the body, showing the entire dependence of the animal and vegetable -kingdoms upon those causes which appear to flow from the centre of our -planetary system. - -The phenomena which connect themselves with the changes of the seasons -cannot fail to convince the most superficial thinker that there is an -intimate connection between the sun and the earth which deserves our -close attention. - -Indeed, if we examine the most ancient of histories, we find one great -fact at the base of all their philosophies. Moses connects darkness -with a void and formless earth, and light with the creation of harmony -and life. Menis sings of a fearful world by “many formed darkness -encircled,” and links the idea of a “life-breathing divinity” with the -awakening of light upon created things. The Egyptian Isis, the Grecian -Apollo, who, - - The Lord of boundless light - Ascending calm o’er the empyrean sails, - And with ten-thousand beams his awful beauty veils, - -the fire-worshipper of the Persian hills and the sun-god of the -Peruvian mountains, exhibit, through time and space, the full -consciousness of man to the influences of solar light and heat upon the -organic creations of which he is himself the chief exemplar. - -The investigations of modern philosophers have extended these -influences to the inorganic masses which constitute the Planet -EARTH:--and we now know that the physical forces, ever active in -determining the chemical condition and the electrical relations of -matter, are directly influenced by the solar radiations. - -Few things within the range of our inquiry are more striking than -the phenomena of calorific radiation and absorption. They display so -perfectly the most refined system of order, and exhibit so strikingly -the admirable adaptation of every formation to its particular -conditions, and for its part in the great economy of being, that they -claim most strongly the study of all who would seek to discover a -poetry in the inferences of science. - -Owing to the nature of our atmosphere, we are protected from the -influence of the full flood of solar heat. The absorption of caloric by -the air has been calculated at about one-fifth of the whole in passing -through a column of 6,000 feet. This estimate is, of course, made near -the earth’s surface; but we are enabled, knowing the increasing rarity -of the upper regions of our gaseous envelope in which the absorption -is constantly diminishing, to prove, that about one-third of the solar -heat is lost by vertical transmission through the whole extent of our -atmosphere.[47] - -Experience has proved that the conditions of the sun’s rays are not -always the same; and there are few persons who have not observed that -a more than usual scorching influence prevails under some atmospheric -circumstances. This is also evidenced in the effects produced on the -foliage of trees, which, though often attributed to electricity, is -evidently due to heat. An examination of the solar radiations, as -exhibited in the prismatic spectrum, has proved the existence of a -class of heat rays, which manifest themselves by a very peculiar -deoxidizing power quite independent of their caloric properties, -to which the name of _parathermic rays_ has been given.[48] We are -protected from the severe effects of these rays by the ordinary state -of the medium through which the solar heat passes. Our atmosphere is a -mixture of gases and aqueous vapour; and it has been found, as already -stated, that even a thin film of water, however transparent, prevents -the passage of many calorific radiations, and the rays retarded are, -for the most part, of that class which have this peculiar scorching -power. The air is, in this way, the great equaliser of the solar -heat, rendering the earth agreeable to all animals, who, but for this -peculiar absorbent medium, would have to endure, even in our temperate -clime, the burning rays of a more than African sun. - -The surface of the earth during the sunshine--and, though in a less -degree, even when the sun is obscured by clouds--is constantly -receiving heat; but the rate of its absorption varies. Benjamin -Franklin showed, by a set of simple but most conclusive experiments, -that a piece of black cloth was warmed much sooner than cloth of a -lighter colour;[49] and we know, from observations of a similar class, -that the bare brown soil receives heat more readily than the bright -green grassy carpet of the earth. Consequently, during the winter -season, relatively to the quantity poured from its source, more heat -penetrates the uncovered soil, than during the spring or summer. - -There is a constant tendency to an equilibrium; and, during the night, -the surface is robbed of more heat, by the colder air, than by day; as, -when the earth is not receiving heat, it is constantly radiating it -back into space. Even in these processes of convection and radiation, a -similar law prevails to that which is discovered in examining into the -rate of calorific absorption. - -Every tree spreading its green leaves to the sunshine, or exposing -its brown branches to the air--every flower which lends its beauty to -the earth--possesses different absorbing and radiating powers. The -chalice-like cup of the pure white lily floating on the lake--the -variegated tulip--the brilliant anemony--the delicate rose--and the -intensely coloured peony or dahlia--have each powers peculiar to -themselves for drinking in the warming life-stream of the sun, and -for radiating it back again to the thirsting atmosphere. These are -no conceits of a scientific dreamer; they are the truths of direct -induction; and, by experiments of a simple character, they may be put -to a searching test.[50] - -A thermometric examination of the various coloured flowers, by -enclosing a delicate thermometer amongst their leaves, will readily -establish the correctness of the one; and by a discovery of recent -date, connected with calorific radiation, which must be particularly -described presently, we can, with equal ease and certainty, test the -truth of the other;[51] the absorption and radiation of heat being -directly regulated by the colours of the surfaces upon which the sun -rays fall. - -It follows, as a natural consequence of the position of the sun, as -it regards any particular spot on the earth at a given time, that the -amount of heat is constantly varying during the year. This variation -regulates the seasons. - -When it is remembered that the earth is, in the winter, nearly three -millions of miles nearer the sun than in the summer, some explanation -is required to account for our suffering more cold when nearer the -source of heat, than when at the remotest distance. - -The earth in her path around the sun describes an ellipse, the -sun’s place being one of its foci. In obedience to the law, already -described, of the conservation of the axis of rotation, the axis of -the earth constantly points towards the star in the constellation of -the Little Bear. Recollecting this, and also the two facts, that a -dense solid body absorbs heat more readily than a fluid one, and that -radiation from the surface is constantly going on when absorption is -not taking place, let us follow the earth in her orbit. - -It is the time of the vernal equinox--we have equal day and -night--therefore the periods of absorption and radiation of heat are -alike. But at this time of the year the southern hemisphere is opposite -to the sun, consequently the degree of absorption by the wide-spread -oceans small. - -It is the summer solstice--we have sixteen hours of daylight, when the -absorption of heat is going on--and but eight hours of night, during -which heat is passing off. The northern hemisphere is now presented -to the sun, and as here we have the largest portion of dry land, the -powers of absorption are at their maximum. - -The autumnal equinox has arrived, with its equal day and night, as in -the spring, but now the whole northern hemisphere is opposite the sun; -hence, according to the laws already explained, we see the causes of -the increased heat of the autumnal season. - -The winter solstice has come, with its long night and shortened day. -The time during which radiation is going on is nearly twice that in -which absorption takes place, and the earth is in her worst position -for receiving heat, as that half which has the largest surface of water -is towards the sun. - -These are the causes which lead to the variations of the seasons, and -through these we learn why we are colder when near the sun than when at -a considerably greater distance. - -An analysis of the spectrum shows us that there are some changes -regularly taking place in the state of the solar beam, which cannot -be referred to the mere alteration of position. It may be inferred, -from facts by long-continued observations, that the three classes of -phenomena--light, heat, and chemical power, distinguished by the term -Actinism--which we detect in the sun’s rays, are constantly changing -their relative proportions. In spring, the chemical agency prevails; in -summer, the luminous principle is the most powerful; and in the autumn, -the calorific forces are in a state of the greatest activity.[52] The -importance of these variations, to the great economy of vegetable life, -will be shown when we come to examine the phenomena connected with -organisation. - -A remarkable change takes place in the character of heat in being -reflected from material substances. In nature we often see this fact -curiously illustrated. Snow which lies near the trunks of trees or -wooden poles melts much quicker than that which is at a distance from -them, the sun shining equally on both--the liquefaction commencing on -the side facing the sun, and gradually extending. We see, therefore, -that the direct rays of solar heat produce less effect upon the snow -than those which are radiated from coloured surfaces. By numerous -experiments, it has been shown that these secondary radiations are -more abundantly absorbed by snow or white bodies than the direct solar -rays themselves. Here is one of the many very curious evidences, which -science lays open to us, of the intimate connection between the most -ethereal and the grosser forms of matter. Heat, by touching the earth, -becomes more earth-like. The subtile principle which, like the spirit -of superstition, has the power of passing, unfelt, through the crystal -mass, is robbed of its might by embracing the things of earth; and -although it still retains the evidences of its refined origin, its -movements are shackled as by a clog of clay, and its wings are heavy -with the dust of this rolling ball. It has, however, acquired new -properties, which fit it for the requirements of creation, and by which -its great tasks are facilitated. Matter and heat unite in a common -bond, and, harmoniously pursuing the necessities of some universal law, -the result is the extension of beautiful forms in every kingdom of -nature. - -An easy experiment pleasingly illustrates this remarkable change. If a -blackened card is placed upon snow or ice in the sunshine, the frozen -mass underneath it will be gradually thawed, and the card sink into -it, while that by which it is surrounded, although exposed to the full -power of solar heat, is but little disturbed. If, however, we reflect -the sun’s rays from a metal surface, an exactly contrary result takes -place; the uncovered parts are the first to melt, and the blackened -card stands high above the surrounding portion. - -The evidences of science all indicate the sun as the source, not only -of that heat which we receive directly through our atmosphere, but -even of that which has been stored by our planet, and which we can, -by several methods, develope. We have not to inquire if the earth was -ever an intensely heated sphere;--this concerns not our question; as -we should, even were this admitted, still have to speculate on the -origin--the primitive source of this caloric. - -Before, however, we proceed to the examination of the phenomena of -terrestrial heat, a few of the great results of the laws of radiation -and convection claim our attention. - -Nearly all the heat which the sun pours upon the ocean is employed in -converting its water into vapour at the very surface, or is radiated -back from it, to perform the important office of producing those -disturbing influences in the atmosphere, which are essential to the -preservation of the healthful condition of the great aërial envelope in -which we live. - -Currents of air are generally due to the unequal degrees in which the -atmosphere is warmed. Heat, by expanding, increases the elasticity, -and lessens the density, of a given mass. Consequently, the air heated -by the high temperature of the tropics, ascends charged with aqueous -vapours, whilst the colder air of the temperate and the frigid zones -flows towards the equator to supply its place. These great currents of -the atmosphere are, independent of the minor disturbances produced by -local causes, in constant flow, and by them a uniformity of temperature -is produced, which could not in any other way be accomplished. By these -currents, too, the equalisation of the constituents of the “breath -of life” is effected, and the purer oxygen of the “land of the sunny -south” is diffused in healthful gales over the colder climes of the -north. The waters, too, evaporated from the great central Atlantic -Ocean, or the far Pacific, are thus carried over the wide-spread -continents, and poured in fertilising showers upon distant lands. - -How magnificent are the operations of nature! The air is not much -warmed by the radiations of caloric passing from the sun to the earth; -but the surface soil is heated by its power of absorbing these rays. -The temperature of the air next the earth is raised, and we thus have -the circulation of those beneficial currents which are so remarkably -regular in the Trade Winds. The air heated within the tropics would -ascend directly to the poles, were the earth at rest, but being in -motion, those great aërial currents--the Trade Winds--are produced, -and the periodical monsoons are due to the same cause. A similar -circulation, quite independent of the ordinary tidal movement, -takes place also in the earth-girdling ocean. The water, warmed, by -convection, from the hot surface of the tropical lands, sets across -the Atlantic from the Gulf of Mexico; and being under the influence of -the two forces--gravity and motion--it illustrates the parallelogram -of forces, and flowing along the diagonal, reaches our own shores: the -genial influences of the gulf stream produce that tempered climate -which distinguishes our insular home. Here we have two immense -influences produced by one agency, rendering those parts of the earth -habitable and fertile, which but for these great results would sorrow -in the cheerless aspect of an eternal winter. - -The beautiful phenomenon of the formation of dew is also distinctly -connected with the peculiar properties which we have been studying. -When from the bright blue vault of heaven, the sparkling constellations -shower their mild light over the earth, the flowers of the garden -and the leaves of the forest become moist with a fluid of the most -translucid nature. Well might the ancients imagine that the dews were -actually shed from the stars; and the alchemists and physicians of the -middle ages conceive that this pure distillation of the night possessed -subtile and penetrating powers beyond most other things; and the -ladies of those olden times endeavour to preserve their charms in the -perfection of their youthful beauty through the influences of washes -procured from so pure a source.[53] - -Science has removed the veil of mystery with which superstition had -invested the formation of dew; and, in showing to us that it is -a condensation of vapour upon bodies according to a fixed law of -radiation, it has also developed so many remarkable facts connected -with the characters of material creations, that a much higher order of -poetry is opened to the mind than that which, though beautiful, sprang -merely from the imagination. - -Upon the radiation of heat depends the formation of dew, and bodies -must become colder than the atmosphere before it will be deposited -upon them. At whatever temperature the air may be, it is charged to -saturation with watery vapour, the quantity varying uniformly with -the temperature. Supposing the temperature of the air to be 70° F., -and that a bottle of water at 60° is placed in it, the air around -the bottle will be cooled, and will deposit on the glass exactly -that quantity of moisture which is due to the difference between the -temperature of the two bodies. Different substances, independent of -colour, have the property of parting with heat from their surfaces at -different rates. Rough and porous surfaces radiate heat more rapidly -than smooth ones, and are consequently reduced in temperature; and, if -exposed, are covered with dew sooner than such as are smooth and dense. -The grass parterre glistens with dew, whilst the hard and stony walk is -unmoistened.[54] - -Colourless glass is very readily suffused with dampness, but polished -metals are not so, even when dews are heavily condensed on other -bodies. To comprehend fully the phenomena of the formation of dew, -we must remember that the entire surface of the earth is constantly -radiating heat into space; and that, as by night no absorption is -taking place, it naturally cools.[55] As the substances spread over -the earth become colder than the air, they acquire the power of -condensing the vapour with which the atmosphere is always charged. The -bodies which cover this globe are very differently constituted; they -possess dissimilar radiating powers, and consequently present, when -examined by delicate thermometers, varying degrees of temperature. By -the researches of Dr. Wells,[56] which may be adduced as an example of -the best class of inductive experiments, we learn that the following -differences in sensible heat were observed at seven o’clock in the -evening:-- - - The air four feet above the grass 60-3/4 - Wool on a raised board 54-1/2 - Swandown on ditto 53 - The surface of the raised board 57 - Grass plat 51 - -Dew is most abundantly deposited on clear, calm nights, during which -the radiation from the surface of the earth is uninterrupted. The -increased cold of such nights over those obscured by clouds is well -known. The clouds, it has been proved, act in the same way as the -screens used by gardeners to protect their young plants from the -frosts of the early spring, which obstruct the radiation, and, in all -probability, reflect a small quantity of heat back to the earth. - -It is not improbable that the observed increase in grass crops, when -they have been strewn with branches of trees or any slight shades, may -be due to a similar cause.[57] - -There are many remarkable results dependent entirely on the colours -of bodies, which are not explicable upon the idea of difference in -mechanical arrangement. We know that different colours are regulated -by the powers which structures have of absorbing and reflecting light; -consequently a blue surface must have a different order of molecular -arrangement from a red one. But there are some physical peculiarities -which also influence heat radiation, quite independently of this -_surface_ condition. If we take pieces of red, black, green, and yellow -glass, and expose them when the dew is condensing, we shall find that -moisture will show itself first on the yellow, then on the green glass, -and last of all upon the black or red glasses. The same thing takes -place if we expose coloured fluids in white glass bottles or troughs, -in which case the surfaces are all alike. If against a sheet of -glass, upon which moisture has been slightly frozen, we place glasses -similarly coloured to those already described, it will be found that -the earliest heat-rays will so warm the red and the black glasses, that -the ice will be melted opposite to them, long before any change will be -seen upon the frozen film covered by the other colours. - -The order in which heat permeates coloured media, it has already been -shown, very nearly agrees with their powers of radiation. - -These most curious results have engaged the attention of Melloni, -to whose investigations we owe so much; and from the peculiar order -of radiations, which present phenomena of an analogous character to -those of the coloured rays of light, obtained by him from dissimilarly -coloured bodies, he has been led to imagine the existence of a -“heat-colouration.” That is, the heat-rays are supposed to possess -properties like luminous colour although invisible; and, consequently, -that a blue surface has a strong affinity for the blue heat-rays, -a red surface for the red ones, and so on through the scale. The -ingenuity of this hypothesis has procured it much attention; but now, -when the Newtonian hypothesis of the refrangibility of light is nearly -overturned, we must not, upon mere analogy, rush to the conclusion -that the rays of heat have different orders of refrangibility, which -Melloni’s hypothesis requires.[58] - -Can anything be more calculated to impress the mind with the -consciousness of the high perfection of natural phenomena, than the -fact, that the colour of a body should powerfully influence the -transmission of a principle which is diffused through all nature, -and also determine the rate with which it is to pass off from its -surface. Some recent experiments have brought us acquainted with other -facts connected with these heat-radiations, and the power of heat, -as influenced by the calorific rays, to produce molecular changes in -bodies, which bear most importantly on our subject. - -If we throw upon a plate of polished metal a prismatic spectrum -(deprived, as nearly as possible, of its chemical power, by being -passed through a deep yellow solution--which possesses this property -in a very remarkable manner, as will be explained when we come to the -examination of the chemical action of the sun’s rays)--it will be -found, if we afterwards expose the plate to the action of vapour, very -slowly raised from mercury, that the space occupied by the red rays, -and those which lie without the spectrum below it, will condense the -vapour thickly, while the portion corresponding with the other rays -will be left untouched. This affords us evidence of the power of solar -heat to produce, very readily, a change in the molecular structure of -solid bodies. If we allow the sun’s rays to permeate coloured glasses, -and then fall upon a polished metallic surface, the result, on exposing -the plate to vapourisation, will be similar to that just described. -Under yellow and green glasses no vapour will be condensed; but on the -space on which the rays permeating a red glass, or even a blackened -one, fall, a very copious deposit of vapour will mark with distinctness -the spaces these glasses covered. More remarkable still, if these or -any other coloured bodies are placed in a box, and a polished metal -plate is suspended a few lines above them, the whole being kept _in -perfect darkness_ for a few hours, precisely the same effect takes -place as when the arrangement is exposed to the full rays of the sun. -Here we have evidence of the radiating heat of bodies, producing even -in darkness the same phenomena as the transmitted heat-rays of the sun. -We must, however, return to the examination of some of these and other -analogous influences under the head of actino-chemistry. - -From these curious discoveries of inductive research we learn some high -truths. Associated with light--obeying many of the same laws--moving -in a similar manner--we receive a power which is essential to the -constitution of our planet. This power is often manifested in such -intimate combination with the luminous principle of the solar rays, -that it has been suspected to be but another form of the same agency. -While, however, we are enabled to show the phenomena of one without -producing those which distinguish the other, we are constrained to -regard heat as something dissimilar to light. It is true that we -appear to be tending towards some point of proof on this problem; but -we are not in a position to declare them to be forms of one common -power, or “particular solutions of one great physical equation.”[59] -In many instances it would certainly appear that one of these forces -was directly necessary to the production of the other; but we have also -numerous examples in which they do not stand in any such correlation. - -We learn, from the scientific facts which we have been discussing, a -few of the secrets of natural magic. In their relations to heat, every -flower, which adds to the adornment of the wilds of nature or the -carefully-tended garden of the florist, possesses a power peculiar to -itself; - - “Naiad-like lily of the vale,” - -and, - - “---- The pied wind-flowers, and the tulip tall, - And narcissi, the fairest among them all,” - -are, by their different colours, prevented from ever having the same -temperatures under the same sunshine. - -Every plant bears within itself the measure of the heat which is -necessary for its well-being, and is endued with functions which mutely -determine the relative amount of dew which shall wet its coloured -leaves. Some of the terrestrial phenomena of this remarkable principle -will still further illustrate the title of this volume. - -To commence with the most familiar illustrations, let us consider the -consequences of change of temperature. However slight the additional -heat may be to which a body is subjected, it expands under its -influence; consequently, every atom which goes to form the mass of -the earth moves under the excitation, and the first heat ray of the -morning which touches the earth’s surface, sets up a vibration which -is continued as a tremor to its very centre. The differences between -the temperature of day and night are considerable; therefore all bodies -expand under the influence of the higher, and contract under that of -the lower temperature. During the day, any cloud obscuring the sun -produces, in every solid, fluid, or aëriform body, within the range -of solar influence, a check: the particles which had been expanding -under the force of heat suddenly contract. Thus there must of necessity -be, during the hours of sunshine, a tendency in all bodies to dilate, -and during the hours of night they must be resuming their original -conditions. - -Not only do dissimilar bodies radiate heat in different degrees, but -they conduct it also with constantly varying rates. Heat passes along -silver or copper with readiness, compared to its progress through -platinum. It is conducted by glass but slowly, and still more slowly -by wood and charcoal. We receive some important intimations of the -molecular structure of matter, from those experiments which prove that -heat is conducted more readily along some lines than others. In some -planes, wood and other substances are better conductors than in others. -The metallic oxides or earths are bad conductors of heat, by which -provision the caloric absorbed by the sun’s rays is not carried away -from the surface of this planet so rapidly as it would have been had -it been of metal, but is retained in the superficial crust to produce -the due temperature for healthful germination and vegetable growth. The -wool and hair of animals are still inferior conductors, and thus, under -changes of climate and of seasons, the beasts of the field are secured -against those violent transitions from heat to cold which would be -fatal to them. Hair is a better conductor than wool: hence, by nature’s -alchemy, hair changed into wool in the animals of some countries on the -approach of winter, and feathers into down. - -It is therefore evident that the rate at which solar heat is conducted -into the crust of the earth must alter with the condition of the -surface upon which it falls. The conducting power of all the rocks -which have been examined is found to vary in some degree.[60] - -It follows, as a natural consequence of the position of the sun to -the earth, that the parts near the equator become more heated than -those remote from it. As this heat is conducted into the interior of -the mass, it has a tendency to move to the colder portions of it, and -thus the heat absorbed at the equator flows towards the poles, and -from these parts is carried off by the atmosphere, or radiated into -space. Owing to this, there is a certain depth beneath the surface of -our globe at which an equal temperature prevails, the depth increasing -as we travel north or south from the equator, and conforming to the -contour of the earth’s surface, the line sinking under the valleys and -rising under the hills.[61] - -A question of great interest, in a scientific point of view, is the -temperature of the centre of the earth. We are, of course, without the -means of solving this problem; but we advance a little way onwards -in the inquiry by a careful examination of subterranean temperature -at such depths as the enterprise of man enables us to reach. These -researches show us, that where the mean temperature of the climate -is 50°, the temperature of the rock at 59 fathoms from the surface -is 60°; at 132 fathoms it is 70°; at 239 fathoms it is 80°: being an -increase of 10° at 59 fathoms deep, or 1° in 35·4 feet; of 10° more at -73 fathoms deeper, or 1° in 43·8 feet; and of 10° more at 114 fathoms -still deeper, or 1° in 64·2 feet.[62] - -Although this would indicate an increase to a certain depth of about -one degree in every fifty feet, yet it would appear that the rate of -increase diminishes with the depth. It appears therefore probable, that -the heat of the earth, so far as man can examine it, is due to the -absorption of the solar rays by the surface. The evidences of intense -igneous action at a great depth cannot be denied, but the doctrine of -a cooling mass, and of the existence of an incandescent mass, at the -earth’s centre, remains but one of those guesses which active minds -delight in. The mean annual temperature of this planet is subject to -variations, which are probably dependent upon some physical changes in -the sun himself, or in the atmospheric envelope by which that orb is -surrounded. The variations over the earth’s surface are great. At the -equator we may regard the temperature as uniformly existing at 80°, -while at the poles it is below the freezing point of water; and as far -as observations have been made, the subterranean temperatures bear a -close relation to the thermic condition of the climate of the surface. -The circulation of water through faults or fissures in the strata is, -without doubt, one means of carrying heat downwards much quicker than -it would be conducted by the rocks themselves. It is not, however, -found that the quantity of water increases with the depth. In the mines -of Cornwall, unless where the ground is very loose, miners find that, -after about 150 fathoms (900 feet), the quantity of water rapidly -diminishes. That water must ascend from very much greater depths is -certain, from the high temperatures at which many springs flow out at -the surface. In the United Mines in Cornwall, water rises from one part -of the lode at 90°; and one of the levels in these workings is so hot -that, notwithstanding a stream of cold water is purposely brought into -it to reduce the temperature, the miners work nearly naked, and will -bathe in water at 80° to cool themselves. At the bottom of Tresavean -Mine, in the same county, about 320 fathoms from the surface, the -temperature is 100°. - -One cause of the great heat of many of our deep mines, which appears -to have been entirely lost sight of, is the chemical action going -on upon large masses of pyritic matter in their vicinity. The heat, -which is so oppressive in the United Mines, is, without doubt, due to -the decomposition of immense quantities of the sulphurets of iron and -copper known to be in this condition at a short distance from these -mineral works. - -The heat which man is enabled to measure beneath the earth’s surface, -appears to be alone due to the conducting powers of the rocks -themselves; it has been observed that the line of equal temperature -follows, as nearly as possible, the elevations and depressions which -prevail upon the surface, and the diminishing rate of increase beyond -this line, certainly is such as would arise, was all the heat so -measured, the result of the passage of the heat by conduction through -the crust of rocks. - -Whether or not the subterranean bands of equal heat have any strict -relation, upon a large scale, to the isothermic lines which have been -traced around most portions of our globe, is a point which has not yet -been so satisfactorily determined as to admit of any general deductions. - -The Oriental story-teller makes the inner world a place of rare -beauty--a cavern temple, bestudded with self-luminous gems, in which -reside the spiritual beings to whom the direction of the inorganic -world is confided. - -The Philosopher, in the height of his knowledge, has had dreams as -absurd as this; and amid the romances of science, there are not to be -found any more strange visions than those which relate to the centre -of our globe. At the same time it must be admitted, that many of the -peculiar phenomena which modern geological researches have brought to -light, are best explained on the hypothesis of a cooling sphere, which -necessarily involves the existence of a very high temperature towards -the centre. - -We have already noticed some remarkable differences between solar and -terrestrial heat; but a class of observations by Delaroche[63] still -requires our attention. Solar heat passes freely through colourless -glass, whereas the radiations from a bright fire or a mass of -incandescent metal are entirely obstructed by this medium. If we place -a lamp or a ball of glowing hot metal before a metallic reflector, the -focus of accumulated heat is soon discovered; but if a glass mirror -be used, the light is reflected, but not the heat; whereas, with the -solar rays, but little difference is detected, whether vitreous or -metallic reflectors are employed. It is well known that glass lenses -refract both the light and heat of the sun, and they are commonly known -as burning-glasses: the heat accumulated at their focal point being -of the highest intensity. If, instead of the solar beam, we employ, -in our experiments, an intense heat produced by artificial means, -the passage of it is obstructed, and the most delicate thermometers -remain undisturbed in the focus of the lens. Glass exposed in front -of a fire becomes warm, and by conduction the heat passes through it, -and a secondary radiation takes place from the opposite side.[64] It -has been found that glass is transcalescent, or _diathermic_, to some -rays of terrestrial heat, and _adiathemic_, or opaque for heat, to -others[65]--that the capability of permeating glass increases with the -temperature of the ignited body--and that rays which have passed one -screen traverse a second more readily. It would, however, appear that -something more than a mere elevation of temperature is necessary to -give terrestrial heat-radiations the power of passing through glass -screens, or, in other words, to acquire the properties of solar heat. - -To give an example. The heat of the oxy-hydrogen flame is most intense, -yet glass obstructs it, although it may be assisted by a parabolic -reflector. If this flame is made to play upon a ball of lime, by which -a most intense light is produced, the heat, which has not been actually -increased, acquires the power of being refracted by a glass lens, and -combustible bodies may be ignited in its focus. - -It certainly appears from these results, that the undulatory hypothesis -holds true, so far as the motion of the calorific power is concerned. -At a certain rate the vibrations are thrown back or stopped by the -opposing body, while in a state of higher excitation, moving with -increased rapidity, they permeate the screen.[66] This does not, -indeed, interfere with the refined theory of Prévost,[67] which -supposes a mutual and equal interchange of caloric between all bodies. - -The most general effect of heat is the expansion of matter; solids, -liquids, and airs, all expand under its influence. If a bar of metal -is exposed to calorific action, it increases in size, owing to its -particles being separated farther from each other: by continuing this -influence, after a certain time the cohesion of the mass is so reduced -that it melts, or becomes liquid, and, under the force of a still -higher temperature, this molten metal may be dissipated in vapour. It -would appear as if, under the agency of the heat applied to a body, its -atoms expanded, until at last, owing to the tenuity of the outer layer -or envelope of each atom, they were enabled to move freely over each -other, or to interpenetrate without difficulty. That heat does really -occasion a considerable disturbance in the corpuscular arrangement -of bodies, may be proved by a very interesting experiment. A bar of -heated metal is placed to cool, with one end supported upon a wedge -or a ring of a different metal the other resting on the ground. In -cooling, a distinct musical sound is given out, owing to the vibratory -action set up among the particles of matter moving as the temperature -declines.[68] - -Heat is diffused through all bodies in nature, and, as we shall -presently see, may be developed in many different ways. We may, -therefore, infer, that in converting a sphere of ice into water, and -that again into steam, we have done nothing more than interpenetrate -the mass with a larger quantity of heat, by which its atoms are more -widely separated, and that thus its molecules become free to move -about each other. Hence, from a solid state, the water becomes fluid; -and then, if the expansive force is continued, an invisible vapour. -If these limits are passed by the powers of any greatly increased -thermic action, the natural consequence, it must be seen, will be the -separation of the atoms from each other, to such an extent that the -molecule is destroyed, and chemical decomposition takes place. - -By the agency of the electricity of the voltaic battery, we are enabled -to produce the most intense heat with which we are acquainted, and by a -peculiarly ingenious arrangement Mr. Grove has succeeded in resolving -water by the mere action of heat into its constituent elements--oxygen -and hydrogen gases. That this decomposition is not due to the voltaic -current, but to the heat produced by it, was subsequently proved by -employing platina heated by the oxy-hydrogen flame.[69] - -This interesting question has been examined with great care by Dr. -Robinson of Armagh, who has shown that, as the temperature of water is -increased, the affinity of its elements is lessened, until at a certain -point it is eventually destroyed. This new and startling fact appears -scarcely consistent with our knowledge that a body heated so as to -be luminous has the power of causing the combination of the elements -of water with explosive violence.[70] But as this acute experimental -philosopher somewhat boldly but still most reasonably inquires: “Is -it not probable that, if not light, some other actinic power (like -that which accompanies light in the spectrum, and is revealed to us -by its chemical effects in the processes of photography) is evolved -by the heat, and, though invisible, determines, in conjunction with -the affinity, that atomic change which transforms the three volumes of -oxygen and hydrogen into two of steam?”[71] - -This speculation explains, in a very satisfactory manner, some -results which were obtained by Count Rumford, in 1798. In a series of -experiments instituted for the purpose of examining “those chemical -properties of light which have been attributed to it,” he has shown -that many cases of chemical decomposition occur in perfect darkness, -under the influence of heat, which are precisely similar to those -produced by exposure to the sun’s rays.[72] - -It must, however, be remembered, that both solar light and heat are -sometimes found in direct antagonism to actinic power, and that the -most decided chemical changes are produced by those rays in which -neither heat nor light can be detected. The most remarkable phenomena -of this class will be explained under the head of actinism. - -One of the most curious relations which as yet have been discovered -between light and heat is, that, the temperature at which all bodies -become incandescent, excepting such as are phosphorescent, is uniform. -The point on the thermometer (Fahrenheit’s scale) when the eye by -perfect repose is enabled to detect the first luminous influence, may -probably be regarded as, or very near, 1000°. Daniel has fixed this -point at 980°, Wedgwood at 947°, and Draper at 977°.[73] Dr. Robinson -and Dr. Draper, by independent observations, have both arrived at the -conclusion, that the first gleam of light which appears from heated -platina is not red, but of a lavender gray, the same in character of -colour as that detected by Sir John Herschel among the most refrangible -rays of the solar spectrum.[74] - -It must be admitted, that the question of the identity, or otherwise, -of light and radiant heat, is beset with difficulties. Many of their -phenomena are very similar--many of their modes of action are alike: -they are often found as allied agencies; but they as frequently exhibit -extreme diversity of action, and they may be separated from each other. - -We have now examined the physical conditions and properties of this -most important element, and we must proceed to learn something of the -means by which it may be developed, independently of its solar source. - -This extraordinary principle exists in a latent state in all bodies, -and may be pressed out of them. The blacksmith hammers a nail until it -becomes red hot, and from it he lights the match with which he kindles -the fire of his forge. The iron has by this process become more dense, -and percussion will not again produce incandescence until the bar has -been exposed in fire to a red heat. The only inference we can draw -from this result is, that by hammering the particles have been driven -closer together, and the heat driven out; now further hammering will -not force the atoms nearer, and consequently no additional quantity of -heat can be developed; the iron is made hot in a fire, it absorbs heat, -the particles are restored to their former state, and we can now again -by hammering develope both heat and light. The Indian produces a spark -by the attrition of two pieces of wood. By friction, two pieces of ice -may be made to melt each other; and could we, by mechanical pressure, -force water into a solid state, an immense quantity of heat would be -set free. By the condensation of hydrogen and oxygen gases, pulverulent -platinum will become glowing red-hot, and, with certain precautions, -even the compact metal, platinum, itself; the heat being derived from -the gases, the union of which it has effected. A body passing from the -solid to the fluid state absorbs heat from all surrounding substances, -and hence a degree of cold is produced. The heat which is thus removed -is not destroyed--it is held combined with the fluid; it exists in a -latent state. Fluids, in passing into a gaseous form, also rob all -surrounding bodies of an amount of heat necessary to maintain the -aëriform condition. From the air or from the fluid, this heat may, -as we have shown above, be again extracted. Locked in a pint measure -of air, there exists sufficient heat to raise several square inches -of metal to glowing redness. By the compression of atmospheric air -this may be shown, and with a small condensing syringe a sufficient -quantity of heat may be set free to fire the _Boletus igniarius_, -which, impregnated with nitre, is known as _amadou_. We are acquainted -with various sources from which heat may be developed for artificial -purposes: the flint-and-steel is an example of the production of heat -by mechanical force, and the modern lucifer-match, of the combined -action of friction and chemical affinity. These of themselves would -admit of a lengthened discourse; but it is necessary that we carefully -examine some of the less familiar phenomena of heat under the -influences of changes of chemical condition. - -If spirits of wine and water are mixed together, a considerable degree -of heat is given out, and by mixing sulphuric acid and water, an -infinitely larger quantity. If sulphuric acid (oil of vitriol) and -spirit of wine, or nitric acid (aquafortis) and spirits of turpentine, -at common temperatures, be suddenly mixed, so much heat is set free -as to ignite the spirit. In each of these instances there is a -condensation of the fluid. In nearly all cases of solution, cold is -produced by the absorption of the heat necessary to sustain the salt -in a liquid form; but when potash dissolves in water, heat is given -out, which is a fact we cannot yet explain. If potassium is placed on -water, it seizes the oxygen of the water and sets fire to the hydrogen -gas liberated by the heat produced in the change of form. Antimony -and many other metals thrown into chlorine gas ignite and burn with -brilliancy: the same phenomenon takes place in the vapours of iodine or -bromine. Many chemical combinations, as the chloride of potassium and -sulphur explode with a blow; whilst the slightest friction occasions -the detonation of the fulminating salts of silver, mercury, and -gold. Compounds of nitrogen and chlorine, or iodine, are still more -delicately combined--the former exploding with fearful violence on -the contact of any oleaginous body, and the latter by the smallest -elevation of temperature: both of them destroying the vessels in which -they may be contained. - -Gun cotton presents some peculiar phenomena which may merit brief -attention. This peculiar compound is prepared by the action of nitric -acid on cotton fibre. The general appearance of the cotton is not -altered, but a remarkable physical change has taken place. It is -now soluble in ether, and forms a gelatinous compound:--it explodes -violently at a temperature which is insufficient for the combustion -of gunpowder. Indeed, from, as it would appear, slight electrical -disturbances taking place in the gun cotton itself, it not unfrequently -explodes spontaneously. These fearful disturbances of the forces -which hold bodies in combination are explained with difficulty. May -it not be, that an enormous quantity of the calorific and chemical -principles is held in a state of extreme tension around the particles -of the compound, and that the equilibrium being destroyed, the whole is -developed in destructive rapidity? - -The fact of great heat being evolved during the conversion of a body -from a solid to a gaseous state, as in the explosion of gunpowder or -gun cotton, which is a striking exception to the law of latent heat, as -it prevails in most cases, admits of no more satisfactory explanation. - -As mechanical force produces calorific excitation, so we find that -every movement of sap in vegetables, and of the blood and fluids in -the animal economy, causes a sensible increase of heat. The chemical -processes constantly going on in plants and animals are another source -of heat, in addition to which nervous energy and muscular movement must -be regarded as producing the caloric which is essential to the health -and life of the latter. Digestion has been considered as a process -of combustion; and the action between the elements of food, and the -oxygen conveyed by the circulation of the blood to every part of the -body, regarded as the source of animal heat; and, without doubt, it -is one great source, although it can scarcely be regarded as the only -one.[75] - -The _vis vitæ_, or vital power, influences the delicate and beautiful -system of nerves; and as life (an essence of the rarest and most -subtile order, a diffusive influence) runs through them, from the brain -to the extremities of the members of the body, it sets those tender -threads in rapid vibration, and heat is developed. By this action, -the circulation of the blood is effected; the muscle is maintained -in an elastic condition, ready to perform the tasks of the will; and -through these agencies is the warm and fluid blood fitted to receive -its chemical restoratives in the lungs, and the stomach to support -changes for which it is designed--chemical also--by which more heat -is liberated. Was digestion--_Eremacausis_, as the slow combustion -produced by combination with oxygen is called--the only source of -animal heat, why should the injury of one filmy nerve place a member of -the body for ever in the condition of stony coldness? Or why, chemical -action being most actively continued after a violent death, by the -action of the gastric juices upon the animal tissues, should not animal -heat be maintained for a much longer period than it is found to be -after respiration has ceased?[76] - -In studying the influences of caloric upon the conditions of matter, -we must regard the effects of extreme heat, and also of the greatest -degrees of cold which have been obtained. - -There are a set of experiments by the Baron Cagniard de la Tour, which -appear to have a very important bearing on some conditions that may -be supposed to prevail in nature, particularly if we adopt the view of -a constantly increasing temperature towards the centre of our earth. -If water, alcohol, or ether, is put into a strong glass tube of small -bore, the ends hermetically sealed, and the whole exposed to a strong -heat, the fluid disappears, being converted into a transparent gas; -but, upon cooling, it is again condensed, without loss, into its -original fluid state.[77] In this experiment, fluid bodies have been -converted into elastic transparent gases with but small change of -volume, under the pressure of their own atmospheres. We can readily -conceive a similar result occurring upon a far more extensive scale. -In volcanic districts, at great depths, and consequently under the -pressure of the superincumbent mass, the siliceous rocks, or even -metals, may, from the action of intense heat, be brought into a fluid, -or even a gaseous condition, without any change of volume, since -the elastic force of heat is opposed by the rigid resistance of the -pressure of the surrounding rocks. Some beautiful experiments by Mr. -Hopkins, of Cambridge, have proved that the temperature necessary to -melt a body must be considerably elevated as the mechanical pressure to -which it is subjected is increased. - -Directly connected with the results of Cagniard de la Tour are a yet -more remarkable set of phenomena, which have been investigated by -M. Boutigny,[78] and generally known as the “spheroidal condition” -of bodies. If water is projected upon very hot metal it instantly -assumes a spheroidal form--an internal motion of its particles may -be observed--it revolves with rapidity, and evaporates very slowly. -If a silver or platinum capsule, when brought to a bright red heat, -is filled with cold water, the whole mass assumes the spheroidal -state, the temperature of the fluid remaining considerably below the -boiling point, so long as the red heat is maintained. If we allow the -vessel to cool below redness in the dark, the water then bursts into -active ebullition, and is dissipated into vapour with almost explosive -violence. An equal quantity of water being projected into two similar -vessels, over the fire, one cold and the other red hot, it will be -found that the water in the cold vessel will boil and evaporate long -before that in the one which is red hot. - -Another form of this experiment is exceedingly instructive. If a mass -of white hot metal is suddenly plunged into a vessel of cold water, the -incandescence is not quenched, the metal shines with a bright white -light, and the water is seen to circulate around, but at some distance -from the glowing mass, being actually repelled by calorific agency. At -length, when the metal cools, the water comes in contact with it, and -boils with energy. - -A result similar to this was observed by Perkins, but its correctness -most unjustly doubted. Having made an iron shell containing water, and -carefully plugged up, white hot, it was found that the steam never -exerted sufficient force to burst the vessel, as it was expected -it would do. He caused a hole to be drilled into the bottom of the -white-hot shell, and he was surprised to find that no water flowed -through the orifice, until the iron was considerably cooled, when it -issued forth with violence in the form of steam. Here we have the -_Cagniard de la Tour state_ first induced, and the calorific repulsion -of the spheroidal state supervenes. If water is poured upon an iron -sieve, the wires of which are made red hot, it will not percolate; -but on cooling, it runs through rapidly. M. Boutigny, pursuing this -curious inquiry, has recently proved that the moisture upon the skin -is sufficient to protect it from disorganization, if the arm is plunged -into baths of melted metal. The resistance of the surfaces is so great, -that little elevation of temperature is experienced.[79] Professor -Plücker, of Bonn, has stated that by washing the arm with ether -previously to plunging it into melted metal, the sensation produced, -while in the molten mass, is that of freezing coldness. - -We have now seen that heat at different degrees of intensity appears -to produce chemical composition--that it decomposes combined -elements--that it alters the conditions of bodies, and actually -maintains so powerfully a repellent force, that fluids cannot touch the -heated body. More than this, it exerts a most powerful antagonistic -influence over all chemical relations. If, to give one example, -the volatile element iodine is put into a glowing hot capsule, it -resolves itself immediately into a spheroid. Potash rapidly combines -with iodine; but if a piece of this alkali is thrown upon it in -the capsule, it also takes the spheroidal form, and both bodies -revolve independently of each other, their chemical affinities being -entirely suspended;--but allow the capsule to cool, and they combine -immediately. Science teaches us that a temperature so exalted as not to -burn organic bodies may be produced, and points to us this remarkable -fact, that the destructive limits of heat are measured between certain -degrees--beyond which a fire, by reason of its intensity, ceases to -develope heat. What is the radiant force into which this principle -changes? - -The experiments of Cagniard de la Tour and of Boutigny (d’Evreux), -connect themselves, in a striking manner, with those of Mr. Grove and -Dr. Robinson; and they teach us that but a very slight alteration in -the proportions of the calorific principle given to this planet would -completely change the character of every material substance of which it -is composed, unless there was an alteration in the physical condition -of the elements themselves. - -Supposing the ordeal of fiery purification to take place upon this -earth, these experiments appear to indicate the mighty changes which -would thence result. There would be no annihilation, but everything -would be transformed from the centre of the globe to the verge of its -atmosphere--old things would pass away, all things become new, and the -beautiful mythos of the phœnix be realized in the fresh creation. - -The deductions to be drawn from the results obtained by abstracting -heat from bodies are equally instructive. By taking advantage of the -cooling produced by the rapid solution of salts of several kinds in -water, an intense degree of coldness may be produced.[80] Indeed, the -absorption of heat by liquefaction may be shown by the use of metallic -bodies alone. If lead, tin, and bismuth, are melted together, and -reduced to a coarse powder by being poured into water, and the alloy -then dissolved in a large quantity of quicksilver, the thermometer will -sink nearly 50 degrees. An intense amount of cold will result from -the mixture of muriate of lime and snow, by which a temperature of -50° below the zero of Fahrenheit, or 82° below the freezing point of -water, is produced. By such a freezing mixture as this, mercury will -be rendered solid. A degree of cold, however, far exceeding it, has -lately been obtained by the use of solid carbonic acid and ether.[81] -Solid carbonic acid is itself procured from the gas liquefied by -pressure; which liquid, when allowed to escape into the air, evaporates -so rapidly that a large quantity of it is congealed by being robbed of -its combined heat by the vaporizing portion. When this solid acid is -united with ether, a bath is formed in which the carbonic acid will -remain solid for twenty or thirty minutes. By a mixture of this kind, -placed under the receiver of an air-pump, a good exhaustion being -sustained, a degree of cold 166° below zero is secured. By this intense -cold, many of the bodies which have hitherto been known to us only in -the gaseous state have been condensed into liquids and solids. Olefiant -gas, a compound of hydrogen and carbon, was brought into a liquid -form. Hydriodic and hydrobromic acids could be condensed into either a -liquid or a solid form. Phosphuretted hydrogen, a gas which inflames -spontaneously when brought into contact with the air or with oxygen, -became a transparent liquid at this great reduction of temperature. -Sulphurous acid may be condensed, by pressure and a reduction of -temperature, into a liquid which boils at 14° Fahrenheit, but by the -carbonic acid bath it is converted into a solid body, transparent and -without colour. Sulphuretted hydrogen gas solidifies at 122° below -zero, and forms a white substance resembling a mass of crystals of -sea-salt. - -A combination of the two gases, chlorine and oxygen, becomes solid at --75°, and the protoxide of nitrogen at -150°. Cyanogen, a compound -of carbon and nitrogen--the base of prussic acid--is solidified at -30° below the zero of our thermometric scale. The well-known pungent -compound, ammonia, so exceedingly volatile at common temperatures, -is converted into a crystalline, translucent, white substance at the -temperature of -103°. The difficulties which necessarily attend the -exposure of a body to extreme cold and great pressure at the same time, -appear to be the only obstacle to the condensation of oxygen, hydrogen, -and nitrogen gases. A sufficient amount of condensation was, however, -effected by Dr. Faraday, to lead him to the conclusion, arrived at -also by other evidences, that hydrogen, the lightest of the ponderable -bodies, partakes of the nature of a metal.[82] - -During the solidification of water by freezing, some remarkable facts -may be noticed. - -Water, in cooling, gradually condenses in volume until it arrives at -40° Fahr., which appears to be the point of greatest density. From this -temperature to that of 32°, the point at which it begins to solidify, -its volume remains unchanged,[82] as crystallisation (freezing) begins, -the bulk increases, the mass becomes specifically lighter, and it swims -on the surface of the fluid. From 40° to 32° the particles of water -must be taking up that new position which is essential to the formation -of the solid--ice; and while this is taking place, every substance held -in solution by the water is rejected. - -If we mix with water the deepest colouring matter--the strongest acid -or the most acrid poison--they are each and all rejected during the -process of freezing, and if the water has been kept in a state of -agitation during the process--so that the liberated particles may not -be mechanically entangled--the ice will be transparent, colourless, -tasteless, and inert--the substances rejected being gathered together -in the centre of the frozen mass in a state of intense concentration. -In like manner, even the atmospheric air, which is always held in -solution, is rejected, and hence the reason why all the ice which -forms upon still ponds is full of air-bubbles, while the ice which is -produced in agitated water is perfectly free from them. This in itself -is a remarkable condition, the entire bearing of which is not clearly -understood; but a still more singular fact has been discovered in -intimate connection with the rejection of all matter from a freezing -solution. Water, which in this way is freed entirely of air, will not -boil at 212° F., the ordinary boiling point of water. - -If a mass of ice formed in the manner described is placed in a vessel, -and being just covered with a film of oil, to prevent the absorption of -air, is melted over a lamp or fire, and the heat continued, it will, -so far from being converted into steam at 212°, continue to increase -in temperature up to 270° or more, and then burst into ebullition with -such explosive violence as to rend the vessel in which it is confined. - -From this experiment we learn that did water exist in any other -condition than that in which we find it--even with the apparently -simple difference of containing no air--it would not be safe to employ -it in any culinary or manufacturing operation, since its use would be -followed by explosions as dangerous as those of gunpowder. - -Such researches as these prove to us the admirable adaptation of all -things to their especial ends--the beautiful adjustment of the balance -of forces throughout creation. - -The refinements of Grecian philosophy saw, without the aids of -inductive science, that the outward vesture of nature covered a host -of mysterious agencies to which its characteristics were directly -due. In their dream of the four elements, fire, the external and -visible form of heat, was regarded as the cause of vitality, and the -disposer of every organised and unorganised condition of matter. Their -idealisations have assumed another form, but the researches of modern -science have only established their universality and truth. - -The great agents at work in nature--the mighty spirits bound to -never-ending tasks, which they pursue with unremitting toil, are of so -refined a character, that they will probably remain for ever unknown -to us. The arch-evocator, with the wand of induction, calls; but the -only answer to his evocation is the manifestation of power in startling -effects. Science pursues her inquiries with zeal and care: she tries -and tortures nature to compel her to reveal her secrets. Bounds are, -however, set to the powers of mortal search: we may not yet have -reached the limits within which we are free to exercise our mental -strength; but, those limits reached, we shall find an infinite region -beyond us, into which even conjecture wanders eyeless and aimless, as -the blind Cyclops groping in his melancholy cave.[83] - -All we know of heat is, that striking effects are produced which we -measure by sensation, and by instruments upon which we have observed -that given results will be produced under certain conditions: of -anything approaching to the cause of these we are totally ignorant. -The wonder-working mover of some of the grandest phenomena in -nature--giving health to the organic world, and form to the inorganic -mass--producing genial gales and dire tornadoes--earthquake strugglings -and volcanic eruptions--ministering to our comforts in the homely fire, -and to advancement in civilisation in the mighty furnace, and the -ingenious engine which drains our mines, or traverses our country with -bird-like speed,--will, in all probability, remain for ever unknown to -man. The immortal Newton, many of whose guesses have a prophetic value, -thus expresses himself:--“Heat consists in a minute vibratory motion in -the particles of bodies, and this motion is communicated through an -apparent vacuum by the undulations of a very subtile elastic medium, -which is also concerned in the phenomena of light.” - -Our experimental labours and our mathematical investigations have -considerably advanced our knowledge since the time of Newton; yet still -each theory of heat strangely resembles the mystic lamp which the -Rosicrucian regarded as a type of eternal life--a dim and flickering -symbol, in the tongue-like flame of which imagination, like a child, -can conjure many shapes. - -Modern theory regards heat as a manifestation of motion, and experiment -proves that a body falling through a certain space generates a definite -quantity of heat, while observation shows that the waters at the base -of the Falls of Niagara possess a temperature 1° higher than when they -first glide over the edge of the precipice. - -This increase of temperature is due to the mechanical force due to -the fall, and is no more an evidence of the conversion of motion into -heat, than is the old experiment of rubbing a button until it becomes -hot. At all events, the fact that a given amount of mechanical force -always produces an equivalent of heat is as applicable to the idea of -a “subtile elastic medium” which is diffused through all matter, as to -the, at present, favourite hypothesis. - -So far has this view been strained, that the temperature of the planets -has been referred to their motions, and speculation has aided the -mathematician in determining the cessation of planetary motion, by -the conversion of it into heat. It is true that other theorists have -supposed points in space upon which this heat might be concentrated and -reflected back again to produce motion. - -There may be much of the poetic element in such speculations, but it is -of that order which belongs rather to the romantic than to the real. - -A speculation which has more of truth, and which is, indeed, -demonstrable, cannot fail to impress every mind with its beauty, and -probable correctness. - -In the growth of a tree, its wood and all its products are the result -of certain external forces effecting chemical changes. Carbonic acid -is decomposed, the carbon is retained, and oxygen given off, and -assimilations of a complex character are in constant progress to -produce the various compounds of oxygen, hydrogen, nitrogen, and carbon. - -Every condition of organised forms is due to the external excitation -of light and heat, and in the chemical changes which take place, an -equivalent of these principles, or powers--it signifies but little -according to which view we may regard them--is absorbed, and retained -as essential to the condition of the matter formed. Let us confine -our attention to wood--although the position applies equally to every -organic product. A cubic foot of wood is formed by the decomposition -of a certain quantity of carbonic acid, by the vital function of the -plant, excited by the solar rays, which are involved in the mass which -nature by “her wondrous alchemy” has made. Eventually this cubic foot -of wood is subjected to a process of chemical change--combustion; by -the application of a single spark,--and in the disintegration of the -wood, its carbon combining with oxygen to form carbonic acid, its -hydrogen to form water, which is returned to the air, a large amount of -light and heat is produced. This is exactly equivalent to the amount -which was engaged in its formation. Indeed, the sunshine which fell -upon the leaves of the forest tree, of which the log formed a part, has -been hoarded up, and we again develope it in its original state of heat -and light. - -The vast coal beds of England were formed by the rapid growth and quick -decay of a peculiar class of plants under the influence of a tropical -sun. They have been buried myriads of ages, under hundreds of feet of -sandy rock. By the industry of the miner the coal is brought again -to the surface, and we develope from it those powers by which it was -formed. - -In the fire which gives comfort to our homes--in the furnace which -generates force for the purposes of manufacture, or to propel the -railway engine and its ponderous train--in the gas with which we -illumine our streets and gladden during the long winter nights our -apartments, we are developing that heat and light which fell upon -the earth with all its quickening influences millions of ages before -yet the Creator had called into existence the monarch Man, for whose -necessities these wondrous formations were designed. - - -FOOTNOTES: - -[43] The following table of the rays penetrating coloured glass has -been given by Melloni, in his memoir _On the Free Transmission of -Radiant Heat through Different Bodies_:-- - - Deep violet 53 - Yellowish red (flaked) 53 - Purple red (flaked) 51 - Vivid red 47 - Pale violet 45 - Orange red 44 - Clear blue 42 - Deep yellow 40 - Bright yellow 34 - Golden yellow 33 - Deep blue 33 - Apple green 26 - Mineral green 23 - Very deep blue 19 - -Translated in the Scientific Memoirs, vol. i. p. 30. - -[44] “The physical characters of this species of glass, which acts -so differently from the other species of coloured glass in all the -phenomena of calorific absorption, are, 1st, its intercepting almost -totally the rays which pass through alum; 2nd, its entirely absorbing -the red rays of the solar spectrum. I have already stated that their -colouration is produced almost entirely by the oxide of copper. - -“Thus, the colouring matters of the coloured glasses, while they -so powerfully affect the relations of quantity which the different -rays of ordinary light bear to each other, exercise no elective -action on the concomitant calorific rays. This curious phenomenon is -the more remarkable as the colouring matters absorb almost always -a very considerable portion of the heat _naturally transmitted by -the glass_. The following are, in fact, the calorific transmissions -of the seven coloured glasses referred to; the transmission of the -common glass being represented by 100; red glass, 82·5; orange, 72·5; -yellow, 55; bluish-green, 57·5; blue, 52·5; indigo, 30; violet, 85. -The quantity of heat absorbed through the action of the colouring -substances is, therefore, 17·5 in the red glass, 27·5 in the orange, -45 in the yellow, 42·5 in the green, 47·5 in the blue, 70 in the -indigo, and 15 in the violet. Now, as these absorptions extinguish a -proportional part of each of the rays which constitute the calorific -stream transmitted by common glass, they may be compared, as we said -before, with the absorbent action exercised on light by matters more -or less deeply brown or dark, when they are immersed in water, or some -other colourless liquid which dissolves, but does not affect them -chemically.”--_Annales de Chimie et de Physique_, tom. xl. p. 382. - -Guided by these principles, the author selected the glass employed in -glazing the Royal Palm-House, at Kew Botanical Gardens, where it was -desired to obstruct the passage of those rays which have a particular -scorching influence. Of this glass a description was given at the -meeting of the British Association at Oxford, which appears in the -Transactions for that year. The result has been all that could be -desired--not a single instance of scorching having occurred during the -three years which have elapsed. - -[45] In the _Philosophical Transactions_, vol. xc., the following -papers, by Sir William Herschel, may be consulted:-- - -_Investigation of the powers of the prismatic colours to heat -and illuminate objects; with remarks that prove the different -refrangibility of radiant heat. To which is added, an inquiry into the -method of viewing the sun advantageously, with telescopes of large -apertures and high magnifying powers_, p. 255. _Experiments on the -refrangibility of the invisible rays of the sun_, p. 284. _Experiments -on the solar and on the terrestrial rays that occasion heat; with a -comparative view of the laws to which light and heat, or rather the -rays which occasion them, are subject; in order to determine whether -they are the same or different_, pp. 293, 437. - -In connection with this inquiry, Sir William Herschel remarks, that -since a _red glass_ stops no less than 692 out of 1,000 such rays as -are of the refrangibility of red light, we have a direct and simple -proof, in the case of the red glass, that the rays of light are -transmitted, while those of heat are stopped, and that thus they have -nothing in common but a certain equal degree of refrangibility, which -by the power of the glass must occasion them to be thrown together into -the place which is pointed out to us by the visibility of the rays of -light. - -On the same subject, a Memoir, by Sir Henry Englefield, in the Journal -of the Royal Institution for 1802, p. 202, may be consulted; and -_Researches on Light_, by the Author. - -[46] Dr. Draper, _On the production of light by heat_, in the Phil. -Mag. for 1847. - -Sir Isaac Newton fixed the temperature at which bodies become -self-luminous at 635°; Sir Humphry Davy at 812°; Mr. Wedgewood at 947°; -and Mr. Daniell at 980°; whilst Dr. Draper from his experiments gives -977°; and Dr. Robinson 865°. - -In a review of the above paper by Melloni, entitled _Researches on the -Radiations of Incandescent Bodies, and on the Elementary Colours of the -Solar Spectrum_, translated for Silliman’s Journal for August, 1847, he -remarks:-- - -“I say that they conduct, as do others heretofore known on light and -radiant heat, to a perfect analogy between the general laws which -govern these two great agents of nature. I will add that I regard -the theory of their identity as the only one admissible by the rules -of philosophy; and that I consider myself obliged to adopt it, until -it shall have been proved to me that there is a necessity of having -recourse to two different principles, for the explanation of a series -of phenomena which at present appear to belong to a solitary agent.” - -Reference should also be made to a paper by Dr. Robinson, _On the -effects of Heat in lessening the Affinities of the Elements of Water_, -in the Transactions of the Royal Irish Academy, 1848, where he says -that “when a platinum wire is traversed by a current gradually -increased till it produces ignition, the first gleam that appears is -not red, but of a colour which, when I first saw it, I compared to -the ‘lavender ray’ discovered by Sir John Herschel beyond the violet, -though I was surprised at seeing the tint of that most refrangible ray -preceding the ray which is least so. It is quite conspicuous at about -865°; and as the mode in which it makes its appearance presents nothing -abrupt or discontinuous, it seems likely that it is merely a transition -from invisible rays excited at a lower temperature to ordinary -light.”--p. 310. - -[47] In the _Bakerian Lecture_ for 1842, _On the transparency of the -Atmosphere, and the law of extinction of the solar rays in passing -through it_, by James D. Forbes, Esq., F.R.S., &c., will be found a -most complete investigation of this subject. - -The experiments were, for the most part, made in Switzerland with Sir -John Herschel’s actinometer, and they prove satisfactorily,--“That -the absorption of the solar rays by the strata of air to which we -have immediate access, is considerable in amount for even moderate -thicknesses.” - -[48] After referring to several curious and instructive experiments, in -which peculiar chemical changes are produced under the influence of the -solar rays by their HEAT, Sir John Herschel says:-- - -“These rays are distinguished from those of Light by being invisible; -they are also distinguished from the pure calorific rays beyond the -spectrum, by their possessing properties (_of a peculiar character, -referred to in former papers_) either exclusively of the calorific -rays, or in a much higher degree. They may perhaps not improperly be -regarded as bearing the same relation to the calorific spectrum which -the photographic rays do to the luminous ones. If the restriction -to these rays of the term _thermic_, as distinct from _calorific_, -be not (as I think, in fact, it is not) a sufficient distinction, I -would propose the term _parathermic rays_ to designate them. These are -the rays which I conceive to be active in producing those singular -molecular affections which determine the precipitation of vapours in -the experiments of Messrs. Draper, Moser, and Hunt, and which will -probably lead to important discoveries as to the intimate nature of -those forces resident on the surfaces of bodies, to which M. Dutrochet -has given the name of epipolic forces.”--_On certain improvements in -Photographic Processes, described in a former communication_ (Phil. -Trans, vol. cxxxiii.); and _On the Parathermic Rays of the Solar -Spectrum_, Phil. Trans, vol. cxxxiv. - -The experiments of Mrs. Somerville, _On the Action of the Rays of the -Spectrum on Vegetable Juices_ (Phil. Transactions, vol. cxxxvii.), -appear to connect themselves with this particular class of rays in a -curious manner. - -[49] Experiments on the influence of heat on differently-coloured -bodies were first made by Dr. Hooke; and it was not until long after -that Franklin made his ingenious experiments. Davy exposed to sunshine -six equal pieces of copper, painted white, yellow, red, green, blue, -and black, in such a manner that one side only was illuminated. To -the dark side he attached a bit of cerate, ascertained by experiment -to melt at 700. The cerate attached to the black became fluid first, -the blue next, then the green and red, and lastly the yellow and -white.--Beddoes’s _Contributions to Physical Knowledge_, and collected -works of Sir Humphry Davy, vol. ii. p. 27. - -[50] By reference to the Treatise on Heat, in the _Encyclopædia -Metropolitana_, numerous suggestive experiments will be found, all -bearing on this subject. Peschel’s _Elements of Physics_ may also be -consulted with advantage. The fact is, however, simply proved, as -stated in the text, by placing the bulbs of delicate thermometers, -so as to be completely involved in the petals of flowers exposed to -sunshine, shading the upper portion of the stem of the instrument. - -[51] Moser, _On Vision, and on the Action of Light on Bodies_: and also -_On Latent Light_: Scientific Memoirs, vol. iii. Draper, _On certain -Spectral Appearances, and on the Discovery of Latent Light_: Phil. -Mag., Nov. 1842. - -[52] A particular examination of this curious question will be found in -the Author’s report _On the Influence of the Solar Rays on the Growth -of Plants_: Reports of the British Association for 1847. - -[53] Ammianus Marcellinus ascribes the longevity and robust health of -mountaineers to their exposure to the dews of night. Dew was employed -by the alchemists in their experiments on the solution of gold. The -ladies of old collected the “celestial wash,” which they imagined had -the virtue of preserving their fine forms, by exposing heaps of wool -to the influences of night radiation. It was supposed that the lean -features of the grasshopper arose from that insect feeding entirely on -dew: “Dumque thymo pascentur apes, dum rore cicadæ,” Virgil, Eclog. - -See some curious remarks by Boyle, _On the Power of Dew in Working on -Solid Bodies_: Works of the Honourable R. Boyle, vol. v. p. 121. 1744. - -[54] See the _Researches on Heat_, by Professor James Forbes, in the -Transactions of the Royal Society of Edinburgh; also Melloni’s papers -on the same subject in the _Annales de Chimie_, several of which have -been translated into the _Scientific Memoirs_, edited by Mr. Richard -Taylor. - -[55] The phenomena of dew have constantly engaged the attention of -man. Aristotle, in his book _De Mundo_, puts forth some just notions -on its nature. An opinion has almost always prevailed that dew falls. -Gersten appears to have been the first who opposed this motion. He was -followed by Musschenbroek, and then by Du Fay. The researches of Leslie -were of a far more exact character. Dr. Wilson, in the Transactions of -the Royal Society of Edinburgh, 1st vol., published a _Memoir on Hoar -Frost_ of much interest; but the questions involved remained unsettled -until the researches of Dr. Wells, which were published in his _Essay -on Dew_. - -[56] By far the most complete set of experiments on the radiation -of heat from the surface at night, which have been published since -Dr. Wells’s memoir _On Dew_, are those of Mr. Glaisher, of the Royal -Observatory at Greenwich. Instruments of the most perfect kind were -employed, and the observations made with sedulous care. The results -will be found in a memoir _On the Amount of the Radiation of Heat, at -night, from the Earth, and from various bodies placed on or near the -Surface of the Earth_, by James Glaisher, Esq., Philosophical Trans. -for 1847, part 2. - -[57] Dr. Wells noticed the practical fact that very light shades -protected delicate plants from frost, by preventing radiation. Mr. -Goldsworthy Gurney has made a series of interesting experiments, and -he imagines that by shading grasslands with boughs of trees, or any -light litter, a more abundant crop is produced. The subject has been -discussed in the journals of the Royal Agricultural Society. May not -the apparent increase be due entirely to the succulent condition in -which a plant always grows in the shade? - -[58] This paper of Melloni’s will be found in the _Bibliothèque -Universelle de Genève_, for 1843. The conclusions are highly ingenious, -but they rest entirely on the analogy supposed to be discovered -between the relations of heat, like light, to the coloured rays of the -spectrum. This, it must be remembered, is not the case, since even Sir -William Herschel showed that red light might exist with only a minimum -of calorific power, notwithstanding the fact, that the maximum heat-ray -of the spectrum coincides with the red rays. - -[59] Dr. Robinson, of Armagh, in his Memoir _On the Effects of Heat in -lessening the Affinities of the Elements of Water_.--Transactions of -the Royal Irish Academy, vol. xxi. part 2. - -[60] On this subject consult Robert Were Fox, _On the Temperature of -the Mines of Cornwall_.--Cornwall Geological Transactions, vol. ii.; W. -J. Henwood, on the same subject, _Ib._ vol. v.; Reports of the British -Association, 1840, p. 315; Edinburgh New Philosophical Journal, vol. -xxiv. p. 140. - -[61] _On the causes of the temperature of Hot and Thermal Springs; -and on the bearings of this subject as connected with the general -question regarding the internal temperature of the Earth_: by Professor -Gustav Bischoff, of Bonn.--Edinburgh New Philosophical Journal, vol. -xx. p. 376; vol. xxiii. p. 330. Some interesting information on -the temperature of the ground will be found in Erman’s _Travels in -Siberia_, translated by W. D. Cooley, vol. i. p. 339; vol. ii. p. -366. _Sur la Profondeur à laquelle se trouve la couche de Température -invariable entre les Tropiques_, by Boussingault: Annales de Chimie et -de Physique, 1833, p. 225. Reference may also be made to Humboldt’s -_Cosmos_, Otto’s translation; and to the excellent article on -_Meteorology_, by George Harvey, in the Encyclopædia Metropolitana. -These chthonisothermal lines, as they are called, have been traced by -Humboldt and others over extensive districts. - -[62] These results are obtained from the valuable observations -of Robert Were Fox, Esq., made with great care by that gentleman -in several of the Cornish mines: _Report on some observations on -Subterranean Temperature_.--British Association Reports, vol. ix. p. -309; Philosophical Magazine, 1837, vol. ii. p. 520. - -[63] From his experiments, the following conclusions were arrived at by -M. Delaroche:-- - -1. Invisible radiant heat may, in some circumstances, pass directly -through glass. - -2. The quantity of radiant heat which passes directly through glass -is so much greater, relative to the whole heat emitted in the same -direction, as the temperature of the source of heat is more elevated. - -3. The calorific rays which have already passed through a screen of -glass, experience, in passing through a second glass screen of a -similar nature, a much smaller diminution of their intensity than they -did in passing through the first screen. - -4. The rays emitted by a hot body differ from each other in their -faculty to pass through glass. - -5. A thick glass, though as much or more permeable to light than a thin -glass of worse quality, allows a much smaller quantity of radiant heat -to pass. The difference is so much the less as the temperature of the -radiating source is more elevated. - -6. The quantity of heat which a hot body yields in a given time, by -radiation to a cold body situate at a distance, increases, _cæteris -paribus_, in a greater ratio than the excess of temperature of the -first body above the second.--Journal de Physique, vol. lxxv. - -[64] Sir David Brewster differs from the conclusions arrived at by -Delaroche. He thus explains his views:--“The inability of radiant -heat to pass through glass, may be considered as a consequence of its -refusing to yield to the refractive force; for we can scarcely conceive -a particle of radiant matter freely permeating a solid body, without -suffering some change in its velocity and direction. The ingenious -experiments of M. Prévost, of Geneva, and the more recent ones of -M. Delaroche, have been considered as establishing the permeability -of glass to radiant heat. M. Prévost employed moveable screens of -glass, and renewed them continually, in order that the result which -he obtained might not be ascribed to the heating of the screen; but -such is the rapidity with which heat is propagated through a thin -plate of glass, that it is extremely difficult, if not impossible, to -observe the state of the thermometer before it has been affected by -the secondary radiation from the screen. The method employed by M. -Delaroche, of observing the difference of effect, when a blackened -glass screen and a transparent one were made successively to intercept -the radiant heat, is liable to an obvious error. The radiant heat would -find a quicker passage through the transparent screen; and, therefore, -the difference of effect was not due to the transmitted heat, but to -the heat radiated from the anterior surface. The truth contained in M. -Delaroche’s fifth proposition is almost a demonstration of the fallacy -of all those that precede it. He found that ‘a thick plate of glass, -though as much or more permeable to light than a thin glass of worse -quality, allowed a much smaller quantity of radiant heat to pass.’ If -he had employed very thick plates of the purest flint glass, or thick -masses of fluid that have the power of transmitting light copiously, -he would have found that not a single particle of heat was capable of -passing directly through transparent media.”--Sir D. Brewster, _On new -properties of heat as exhibited in its propagation along plates of -glass_. Philosophical Transactions, vol. cvi. p. 107. - -[65] _Proposal of a New Nomenclature for the Science of Calorific -Radiations_, by M. Melloni. Bibliothèque Universelle de Genève, No. -70. Scientific Memoirs, vol. iii. part 12. Many of the terms, as -_Diathermasy_, or transparency for heat; _Adiathermasy_, opacity for -heat; _Thermochroic_, coloured for heat, and others, are valuable -suggestions of forms of expression which are required in dealing with -these physical phenomena. - -[66] For a careful examination of the several theories of heat consult -Dr. Young’s Course of Lectures on Natural Philosophy, &c., Lecture 52, -_On the Measures and the Nature of Heat_; also Powell’s very excellent -_Reports on Radiant Heat_--Reports of the British Association, 1832, -1840. The transcendental view which the immaterial theory leads to, -cannot be better exemplified than by the following quotation from that -inexplicable dream of a talented man, _Elements of Physiophilosophy_, -by Lorenz Oken, M.D. (translated for the Ray Society, by Alfred Tulk):-- - -“Heat is not matter itself any more than light is; but it is only the -act of motion in the primary matter. In heat, as well as in light, -there certainly resides a material substratum; yet, this substratum -does not give out heat and light; but the _motion_ only of the -substratum gives out heat, and the _tension_ only of the substratum -light. There is no body of heat; nitrogen is the body of heat, just -as oxygen may be called the body of fire. Heat is real space; into it -all forms have been resolved, as all materiality has been resolved -into gravity, and all activity, all polarity, into light. Heat is the -universal form, consequently the want of form.” - -[67] Mémoires de la Société Physique, &c., de Genève, tom. ii. art. 2. - -[68] This curious phenomenon was first observed by Mr. Trevelyan, whose -_Notice regarding some Experiments on the Vibration of Heated Metals_ -will be found in the Transactions of the Royal Society of Edinburgh, -vol. xii., 1837. In a Memoir in the same volume, entitled _Experimental -Researches regarding certain vibrations which take place between -metallic masses having different temperatures_, Professor Forbes draws -the following conclusions:-- - -1. “The vibrations never take place between substances of the same -nature. - -2. “Both substances must be metallic. (This is now proved not to be -necessary.) - -3. “The vibrations take place with an intensity proportional (within -certain limits) to the difference of the conducting powers of the -metals for heat or electricity; the metal having the least conducting -power being necessarily the coldest. - -4. “The time of contact of two points of the metals must be longer than -that of the intermediate portions. - -5. “The impulse is received by a distinct and separate process at each -contact of the bar and block, and in no case is the metallic connection -of the bearing points in the bar, or those of the block, in any way -essential. - -6. “The intensity of the vibration is (under certain exceptions) -proportional to the difference of temperature of the -metals.”--Transactions of the Royal Society of Edinburgh, vol. xii. - -[69] The Bakerian Lecture. _On certain Phenomena of Voltaic Ignition, -and the Decomposition of Water into its Constituent Gases by Heat_: by -W. R. Grove, Esq.--Philosophical Transactions, 1847. Part 1. - -[70] Davy’s _Researches on Flame_. Works, vol. vi.--Philosophical -Transactions for 1817. - -[71] _On the Effect of Heat in lessening the affinities of the Elements -of Water_: by the Rev. Thomas Romney Robinson, D.D.--Transactions of -the Royal Irish Academy, vol. xxi. part 2. - -[72] _An Inquiry concerning the Chemical Properties that have been -attributed to Light_: by Benjamin, Count of Rumford.--Philosophical -Transactions, vol. lxxxviii. p. 449.--The results obtained by Count -Rumford were probably due to the non-luminous heat-rays--parathermic -rays--which are known to be given off by boiling water. - -[73] For Dr. Drapers paper, see Philosophical Magazine for May, 1847, -vol. xxx. 3rd series. - -[74] _On the Action of the Rays of the Solar Spectrum on Vegetable -Colours_: by Sir J. F. W. Herschel, Bart. - -The proof of the continuation of the visible prismatic spectrum beyond -the extreme violet may be witnessed in the following manner:--“Paper -stained with tincture of turmeric is of a yellow colour; and, in -consequence, the spectrum thrown in it, if exposed in open daylight, -is considerably affected in its apparent colours, the blue portion -appearing violet, and the violet very pale and faint; but beyond the -region occupied by the violet rays, is distinctly to be seen a faint -prolongation of the spectrum, terminated laterally, like the rest of -it, by straight and sharp outlines, and which, in this case, affects -the eye with the sensation of a pale yellow colour.”--Philosophical -Transactions, p. 133. - -[75] The most complete exposition of the theory that animal heat is -derived from chemical action only, will be found in _Animal Chemistry, -or Chemistry in its applications to Physiology and Pathology_, by -Justus Liebig: translated by Dr. Gregory. The conclusions arrived at -by the author, notwithstanding his high--and deservedly high--position -in chemical science, must, however, be received with great caution, -many of them being founded on most incorrect premises, and his -generalizations being of the most hasty and imperfect character. At -page 22 the following passage occurs:--“If we were to go naked, like -certain savage tribes, or if in hunting or fishing we were exposed -to the same degree of cold as the Samoiedes, we should be able, with -ease, to consume ten pounds of flesh, and, perhaps, a dozen of tallow -candles into the bargain, daily, as warmly clad travellers have related -with astonishment of these people. We should then also be able to take -the same quantity of brandy or train-oil without bad effects, because -the carbon and hydrogen of these substances would only suffice to keep -up the equilibrium between the external temperature and that of our -bodies.” - -A brief examination will exhibit the error of this. The analysis of -Beef, by D. Lyon Playfair, is as follows:-- - - Carbon 51·83 - Hydrogen 7·57 - Nitrogen 15·01 - Oxygen 21·37 - Ashes 4·23 - -And the following has been given by Chevreul as the composition of -mutton tallow:-- - - Carbon 96 - Hydrogen 16 - Nitrogen 16 - Oxygen 48 - -About three times the quantity of oxygen to the carbon eaten, is -required to convert it into carbonic acid; hence, the Samoiede, eating -more highly carbonized matter, must inspire 288 oz. of oxygen daily, -or nearly eight times as much as the “ordinary adult.” By the lungs -he must take into the body 2,304 cubic feet of air besides what will -be absorbed by the skin. His respirations must be so much quickened, -that at the lowest possible calculation he must have 500 pulsations a -minute. Under such conditions it is quite clear man could not exist. -There is no disputing the fact of the enormous appetites of these -people; but all the food is not removed from the system as carbonic -acid gas. - -[76] An interesting paper by Dr. Davy, _On the Temperature of Man_, -will be found in the Philosophical Transactions, vol. cxxxvi. p. -319.--Sir Humphry Davy, in his _Consolations in Travel, or the Last -Days of a Philosopher_, in his fourth dialogue, _The Proteus_, has -several ingenious speculations on this subject. - -[77] _Exposé de quelques résultats obtenus par l’action combinée de la -chaleur et de la compression sur certains liquides, tels que l’eau, -l’alcool, l’éther sulfurique, et l’essence de pétrole rectifiée_: par -M. le Baron Cagniard de la Tour. - -The three following conclusions are arrived at:-- - -1. Que l’alcool à 36 degrés, l’essence de pétrole rectifiée à 42 -degrés, et l’éther sulfurique soumis à l’action de la chaleur et de la -compression, sont susceptibles de se réduire complètement en vapeur -sous un volume un peu plus que double de celui de chaque liquide. - -2. Qu’une augmentation de pression, occasionnée par la présence de -l’air dans plusieurs des experiences qui viennent d’être citées, n’a -point apporté d’obstacle à l’évaporation du liquide dans le même -espace; qu’elle a seulement rendu sa dilatation plus calme et plus -facile à suivre jusqu’au moment où le liquide semble s’évanouir -tout-à-coup. - -3. Que l’eau, quoique susceptible sans doute d’être réduite en vapeur -très-comprimée, n’a pu être soumise à des experiences complètes, -faute de moyens suffisans pour assurer l’exacte fermeture de la -marmite de compression, non plus que dans les tubes de verre dont elle -altère la transparence en s’emparant de l’alcali qui entre dans leur -composition.--Annales de Chimie, vol. xxi. - -[78] _Sur les phénomènes qui présentent les corps projetés sur des -surfaces chaudes_: par M. Boutigny (d’Evreux).--Annales de Chimie et de -Physique, vol. xi. p. 16. _Congélation du mercure en trois secondes, -en vertu de l’état sphéroïdal dans un creuset incandescent_: by M. -Faraday.--Ibid., vol. xix. p. 383. - -_Spheroidal Condition of Bodies_ (Extrait d’une Note de M. Boutigny -d’Evreux). - -“Au nombre des propriétés des corps à l’état sphéroïdal, il en est cinq -qui me paraissent caractéristiques et fondamentales, et c’est sur ces -cinq propriétés que je base la définition que je soumets aujourd’hui au -jugement de l’Académie. Ces cinq propriétés sont:-- - -“1. La forme arrondie que prend la matière sur une surface chauffée à -une certaine température. - -“2. Le fait de la distance permanente qui existe entre le corps à -l’état sphéroïdal et le corps sphéroïdalisant. - -“3. La propriété de réfléchir le calorique rayonnant. - -“4. La suspension de l’action chimique. - -“5. La fixité de la température des corps à l’état sphéroïdal. - -“Cela posé, voici la définition que je propose: un corps projeté sur -une surface chaude est à l’état sphéroïdal quand il revêt la forme -arrondie et qu’il se maintient sur cette surface au delà du rayon de sa -sphère d’activité physique et chimique; alors il réfléchit le calorique -rayonnant, et ses molécules sont, quant à la chaleur, dans un état -d’équilibre stable; c’est-à-dire, à une température invariable, ou qui -ne varie que dans des limites étroites.”--Comptes Rendus, 6 Mars, 1848. - -[79] _Some Facts relative to the Spheroidal State of Bodies, Fire -Ordeal, Incombustible Man, &c._: by P. H. Boutigny (d’Evreux), -Philosophical Magazine, No. 233 (third, series), p. 80; Comptes Rendus, -May 14, 1849. - -[80] The theory of freezing mixtures is deduced from the doctrine of -latent caloric. These are mixtures of saline substances which, at the -common temperature, by their mutual chemical action, pass rapidly into -the fluid form, or are capable of being rapidly dissolved in water, -and, by this quick transition to fluidity, absorb caloric, and produce -degrees of cold more or less intense.--Rev. Francis Lunn, _On Heat_: -Encyclopædia Metropolitana. - -[81] _Propriétés de l’Acide Carbonique liquide_, par M. Thilorier, -Annales de Chimie, vol. lx. p. 427. _Solidification de l’Acide -Carbonique_: Ibid. p. 432. - -[82] _On the Liquefaction and Solidification of Bodies generally -existing as Gases_, by Michael Faraday, D.C.L., F.R.S., &c.; -Philosophical Transactions, vol. cxxxvi, p. 155. - -[83] Burns, in one of his most natural and pathetic letters. - - - - -CHAPTER VII. - -LIGHT. - - Theories of the Nature of Light--Hypotheses of Newton - and Huygens--Sources of Light--The Sun--Velocity of - Light--Transparency--Dark Lines of the Spectrum--Absorption - of Light--Colour--Prismatic Analysis--Rays of the - Spectrum--Rainbow--Diffraction--Interference--Goethe’s - Theory--Polarisation--Magnetisation of Light--Vision--The - Eye--Analogy--Sound and Light--Influence of Light on Animals and - Vegetables--Phosphorescence arising from several Causes--Artificial - Light--Its Colour dependent on Matter. - - -Light, the first creation, presents to the enquiring mind a series -of phenomena of the most exalted character. The glowing sunshine, -painting the earth with all the brilliancy of colour, and giving to the -landscape the inimitable charm of every degree of illumination, from -the grey shadow to the golden glow;--the calm of evening, when, weary -of the “excess of splendour,” the eye can repose in tranquillity upon -the “cloud-land” of the west, and watch the golden and the ruddy hues -fade slowly into the blue tincture of night;--and the pale refulgence -of the moon, with the quiet sparkle of the sun-lit stars,--all tend -to impress upon the soul, the great truth that, where there is light, -organisation and life are found, and beyond its influence death and -silence hold supreme dominion.[84] Through all time we have evidences -that this has been the prevailing feeling of the human race, derived, -of course, from their observation of the natural phenomena dependent -upon luminous agency. In the myths of every country, impersonations of -light prevail, and to these are referred the mysteries of the perpetual -renewal of life on the surface of the earth. - -This presentiment of a philosophic truth, in the instance of the poet -sages of intellectual Greece, was advanced to the highest degree of -refinement; and the sublime exclamation of Plato: “Light is truth, and -God is light,” approaches nearly to a divine revelation. - -As the medium of vision--as the cause of colour--as a power influencing -in a most striking manner all the forms of organisation around us, -light presented to the inquiring minds of all ages a subject of the -highest interest. - -The ancient philosophers, although they lost themselves in the -metaphysical subtleties of their schools, could not but discover in -light an element of the utmost importance in natural operations. The -alchemists regarded the luminous principle as a most subtile fluid, -capable of interpenetrating and mingling with gross matter: gold -being supposed to differ from the baser metals only in containing a -larger quantity of this ethereal essence.[85] Modern science, after -investigating most attentively a greater number of the phenomena of -light, has endeavoured to assist the inquiry by the aid of hypotheses. -Newton, in a theory, which exhibits the refined character of that -great philosopher’s mind, supposes luminous particles to dart from the -surfaces of bodies in all directions--that these infinitely minute -particles are influenced by the attracting and repelling forces of -matter, and thus turned back, or reflected, from their superficies in -some cases, and absorbed into their interstitial spaces in others. - -Huyghens, on the contrary, supposes light to be caused by the waves or -vibrations of an infinitely elastic medium--ETHER--diffused through all -space, which waves are propagated in every direction from the luminous -body. In the first theory, a luminous particle is supposed actually to -come from the sun to the earth; in the other, the sun only occasions a -disturbance of the _ether_, which extends with great rapidity, in the -same manner as a wave spreads itself over the surface of a lake. - -Nearly all the facts known in the time of Newton, and those discovered -by him, were explained most satisfactorily by his hypothesis; but -it was found they could be interpreted equally as the effects of -undulation, with the exception of the production of colour by prismatic -refraction. Although the labours of many gifted minds have been given, -with the utmost devotion, to the support of the vibratory theory, -this simple fact has never yet received any satisfactory explanation; -and there are numerous discoveries connected with the molecular and -chemical disturbances produced by the sun’s rays, which do not appear -to be explained by the hypothesis of emission or of undulation. - -In both theories a wave motion is admitted, and every fact renders -it probable that this mode of progression applies not only to light, -but to the so-called _imponderable forces_ in general. Admitting, -therefore, the undulatory movement of luminous rays, we shall not stop -to consider those points of the discussion which have been so ably -dealt with by Young, Laplace, Fresnel, Biot, Fraunhofer, Herschel, -Brewster, and others, but proceed at once to consider the sources of -light, and its more remarkable phenomena.[86] - -The sun is the greatest permanently luminous body we are acquainted -with, and that orb is continually pouring off light from its surface -in all directions at the rate, through the resisting medium of space -and of our own atmosphere, of 192,000 miles in a second of time. It has -been calculated, however, that light would move through a vacuum with -the speed of 192,500 miles in the same period. We, therefore, learn -that a ray of light requires eight minutes and thirteen seconds to -come from the sun to us. In travelling from the distant planet Uranus, -nearly three hours are exhausted; and from the nearest of the fixed -stars each ray of light requires more than six years to traverse the -intervening space between it and the earth. Allow the mind to advance -to the regions of nebulæ, and it will be found that hundreds of years -must glide away during the passage of their radiations. Consequently, -if one of those masses of matter, or even one of the remote fixed -stars, was “blotted out of heaven” to-day, several generations of -the finite inhabitants of this world would fade out of time before -the obliteration could be known to man. Here the immensity of space -assists us in our conception, limited though it be, of the for-ever of -eternity.[87] - -All the planets of our system shine with reflected light, and the -moon, our satellite, also owes her silvery lustre to the sun’s -radiations. The fixed stars are, in all probability, suns shining from -the far distance of space, with their own self-emitted lights. By the -photometric researches of Dr. Wollaston, we learn, however, that it -would take 20,000 millions of such orbs as Sirius, the brightest of the -fixed stars, to afford as much light as we derive from the sun. The -same observer has proved that the brightest effulgence of the full moon -is yet 801,072 times less than the luminous power of our solar centre. - -The cultivators of modern science are a bold race; not contented with -endeavouring to understand the physical earth, they are endeavouring -to comprehend the condition of the solar surface. The mind of man can -penetrate far into nature, and, as it were, feel out the mysteries of -untraversed space. The astronomer learns of a peculiar condition of -light, which is termed polarisation, and he learns by this, too, that -he can determine if from a bright luminous disc the light is derived -from a solid mass in a state of intense ignition, or from vapour in -an incandescent condition. He adds a polarising apparatus to his -telescopes, and he determines that the light we derive from the sun -is due to an envelope of vapour--burning, in all probability--only -with greater intensity, as the gas which we now employ. This -_Photosphere_--as it has been called by the late French philosopher -Arago, is found to be subjected to violent disturbances, and the dark -spots seen on the sun’s disc are now known to be openings through this -mysterious envelope of light, which enable us to look in upon the dark -body of the sun itself. - -Luminous phenomena may be produced by various means--chemical action -is a source of light; and, under several circumstances in which the -laws of affinity are strongly exerted, a very intense luminous effect -is produced. Under this head all the phenomena of combustion are -included. In the electric spark we have the development of light; -and the arc which is formed between charcoal points at the poles of -a powerful voltaic battery affords us the most intense artificial -illumination with which we are acquainted. In addition to these, we -have the peculiar phenomena of phosphorescence arising from chemical, -calorific, electrical, actinic, and vital excitation, all of which must -be particularly examined. - -From whatever source we procure light, it is the same in character, -differing only in intensity. In its action upon matter, we have the -phenomena of transmission, of reflection, of refraction, of colour, of -polarisation, and of vision, to engage our attention. - -A beam of white light falls upon a plate of colourless glass, and it -passes freely through it, losing but little of its intensity; the -largest portion being lost by reflection from the first surface upon -which the light impinges. If the glass is roughened by grinding, we -lose more light by absorption and by reflection from the asperities of -the roughened surface; but if we cover that face with any oleaginous -fluid, as, for instance, turpentine, its transparency is restored. We -have thus direct proof that transparency to light is due to molecular -condition. This may be most strikingly shown by an interesting -experiment of Sir David Brewster’s:-- - -If a glass tube is filled with nitrous acid vapour, which is of a dull -red colour, it admits freely the passage of the red and orange rays -with some of the others, and, if held upright in the sunshine, casts -a red shadow on the ground; by gently warming it with a spirit-lamp, -whilst in this position, it acquires a much deeper and blacker colour, -and becomes almost impervious to any of the rays of light; but upon -cooling it again recovers its transparency. - -It has also been stated by the same exact experimentalist, that having -brought a purple glass to a red heat, its transparency was improved, so -that it transmitted green, yellow, and red rays, which it previously -absorbed; but the glass recovered its absorptive powers as it cooled. -A piece of yellowish-green glass lost its transparency almost entirely -by being heated. Native yellow orpiment becomes blood-red upon being -warmed, when nearly all but the red rays are absorbed; and pure -phosphorus, which is of a pale yellow colour, and transmits freely all -the coloured rays upon being melted, becomes very dark, and transmits -no light. - -Chemistry affords numerous examples of a very slight change of -condition, producing absolute opacity in fluids which were previously -diaphanous.[88] - -Charcoal absorbs all the light which falls upon it, but in some -of its states of combination, and in the diamond, which is pure -carbon, it is highly transparent. Gold and silver beaten into thin -leaves are permeated by the green and blue rays, and the metals in -combination with acids are all of them more or less transparent. What -becomes of the light which falls upon and is absorbed by bodies, -is a question which we cannot yet, notwithstanding the extensive -observations that have been made by some of the most gifted of men, -answer satisfactorily. In all probability, as already stated, it -is permanently retained within their substances; and many of the -experiments of exciting light in bodies when in perfect darkness, by -the electric spark and other means, appear to support the idea of light -becoming latent or hidden. - -No body is absolutely transparent; some light is lost in passing even -through ethereal space, and still more in traversing our atmosphere. - -Amongst the most curious instances of absorption is that which is -uniformly discovered in the solar spectrum, particularly when we -examine it with a telescope. We then find that the coloured rays are -crossed by a great number of dark bands or lines, giving no light; -these are generally called Fraunhofer’s dark lines, as it was to the -indefatigable exertions of that experimentalist, and by the aid of his -beautiful instruments, that most of them were discovered and measured, -and enumerated, although they were previously noticed by Dr. Wollaston. -It is quite clear that those lines represent rays which have been -absorbed in their passage from the sun to the earth: although some -of them have no doubt undergone absorption within the limits of the -earth’s atmosphere, we have every reason to believe, with Sir John -Herschel, that the principal absorption takes place in the atmosphere -of the sun.[89] - -It has been proved by Dr. Miller, that the number of those dark -lines is continually varying with the alteration of atmospheric -conditions;[90] and the evidences which have been afforded, of peculiar -states of absorption by the gaseous envelope of the earth,--during the -prosecution of investigations on the chemical agencies of the sun’s -rays,--are of a sufficiently convincing character. - -It has been calculated by Bouguer, that if our atmosphere, in its -purest state, could be extended rather more than 700 miles from the -earth’s surface instead of nearly 40, as it is at present, the sun’s -rays could not penetrate it, and this globe would roll on in darkness -and silence, without a vestige of vegetable form or of animal life. In -the Hebrew version of the Mosaic History, the reading is, “Let light -appear:” may not this really mean that the earth’s atmosphere was so -cleared of obstructing vapours, that the solar rays were enabled to -reach the earth? The same calculation supposes that sea-water loses -all its transparency at the depth of 730 feet; but a dim twilight must -prevail much deeper in the ocean. - -The researches of Professor Edward Forbes have proved, that at the -depth of 230 fathoms in the Ægean sea, the few shelled animals that -exist are colourless: no plants are found within that zone; and that -industrious naturalist fixes the zero of animal life of those waters at -about 300 fathoms.[91] Since these zones mark the rapidly diminishing -light, it is evident that where life ceases to be must be beyond the -limits to which life can penetrate. - -Our atmosphere, charged with aqueous vapour, serves to shield us from -the intense action of the solar powers. By it we are protected from -the destructive influences of the sun’s light and heat; enjoy those -modified conditions which are most conducive to the healthful being of -organic forms; to it we owe “the blue sky bending over all,” and those -beauties of morning and evening twilight of which - - ---- Sound and motion own the potent sway. - Responding to the charm with its own mystery. - -To defective transparency, or rather to the different degrees of it, we -must attribute, in part, the colours of permeable media. Thus, a glass -or fluid appears yellow to the eye, because it has the property of -admitting the permeation of a larger quantity of the yellow rays than -of any others;--red, because the red rays pass it with the greatest -freedom; and so on for every other colour. In most cases the powers of -transmission and of reflection are similar; but it is not so in all; a -variety of fluor spar, which, while it transmits green light, reflects -blue, and the precious opal, are striking instances to the contrary. -Some glasses, which transmit yellow light have the singular power of -dispersing blue rays from one surface; and a solution of quinine in -water acidulated with sulphuric acid, although perfectly transparent -and colourless when held between the eye and the light, exhibits, if -viewed in a particular direction, a lively cerulean tint. These effects -being supposed to be due to the conditions of the surface, have been -called _epipolic_ phenomena.[92] - -The careful investigation of these phenomena has made us acquainted -with some very interesting facts, and indeed discovered to us a set -of luminous rays which were previously unknown. The dispersion of -blue light from the surface of some yellow glasses--such as have been -coloured by the oxide of silver--is of a different order from that -which takes place with the solution of sulphate of quinine, or with -the fluor spar. The first depends upon a peculiar condition of the -surface, while the latter phenomena are due to a dispersion which -takes place _within_ the solid or fluid. In addition to the sulphate -of quinine, and the fluor spar, we obtain the same results in a very -marked manner by a canary yellow glass, coloured with the oxide of -uranium, and by a decoction of the inner bark of the horse-chesnut -tree. Mr. Stokes, who has investigated this class of phenomena, and -proposes to call it _Fluorescence_, from its being naturally seen in -fluor-spar, has shown that the peculiar internal dispersion, and the -consequent alteration of the colour of the ray, is due to an alteration -in its refrangibility. Whether this hypothesis prove to be the correct -one or not, it is certain that there exists a set of rays of far higher -refrangibility than those seen in the ordinary Newtonian spectrum. This -may be shown in the following manner: taking either of the solutions -named, or a block of uranium glass, throw upon one face, by means of -a prism, a very pure spectrum. On looking _into_ the glass or fluid -there will be seen, commencing amidst the most refrangible rays, a -new set of spectral rays, struggling to make their way through the -absorbent medium. These are of a blue colour in the quinine or chesnut -solution, and green in the uranium glass, and are seen extending -themselves far beyond the most refrangible rays of the ordinary -Newtonian spectrum. This is the space over which those rays which -have the power of producing chemical changes, such as are rendered -familiar by the practice of Photography, are detected in their greatest -activity. It has, therefore, been supposed that these fluorescent rays -are the chemical rays rendered luminous by the alteration of their -refrangibility. This view has received much support from the fact that -the extra spectral rays are crossed with numerous dark lines, and that -in the chemical impressions these lines are marked by unchanged spaces -which exactly coincide with them. There is, however, much doubt of the -correctness of this, since, in the uranium glass of such a thickness -that these visible rays are quite absorbed, the chemical rays still -pass. - -However, the whole question requires, and is receiving, the most -searching investigation. The discovery of these phenomena, which are -included under the term of Fluorescence, is of that interesting and -important character, that it must be ranked as the most decided advance -which has been made in physical optics since the days of Newton. - -It is not improbable that those rays of such high refrangibility may, -although they are under ordinary circumstances invisible to the human -eye, be adapted to produce the necessary degree of excitement upon -which vision depends in the optic nerves of the night-roaming animals. -The bat, the owl, and the cat, may see in the gloom of night by the aid -of rays which are invisible to, or inactive on the eyes of man, or of -those animals which require the light of day for perfect vision. - -It is a general law of the radiant forces, that whenever they fall upon -any surface, a portion is thrown back or reflected at the same time -as other portions are absorbed or transmitted. Upon this peculiarity -appear to depend the phenomena of natural colour in bodies. - -The white light of the sun is well known to be composed of several -coloured rays. Or rather, according to the theory of undulations, when -the rate at which a ray vibrates is altered, a different sensation -is produced upon the optic nerve. The analytical examination of -this question shows, that to produce a red colour the ray of light -must give 37,640 undulations in an inch, and 458,000000,000000 in -a second. Yellow light requires 44,000 undulations in an inch, and -535,000000,000000 in a second; whilst the effect of blue results from -51,110 undulations within an inch, and 622,000000,000000 of waves in -a second of time.[93] The determination of such points as these is -among the highest refinements of science, and, when contrasted with the -most sublime efforts of the imagination, they must appear immeasurably -superior. - -If a body sends back white light unchanged, it appears white; if the -surface has the property of altering the vibration to that degree which -is calculated to produce redness, the result is a red colour: the -annihilation of the undulations produces blackness. By the other view, -or the corpuscular hypothesis, the beam of white light is supposed to -consist of certain coloured rays, each of which has physical properties -peculiar to itself, and thus is capable of producing different -physiological effects. These rays falling upon a transparent or an -opaque body suffer more or less absorption, and being thus dissevered, -we have the effect of colour. A red body absorbs all the rays but the -red; a blue surface, all but the blue; a yellow, all but the yellow; -and a black surface absorbs the whole of the light which falls upon it. - -That natural colours are the result of white light, and not innate -properties of the bodies themselves, is most conclusively shown by -placing coloured bodies in monochromatic light of another kind, when -they will appear either of the colour of that light, or, by absorbing -it, become black; whereas, when placed in light of their own character, -the intensity of colour is greatly increasing. - -Every surface has, therefore, a peculiar constitution, by which it -gives rise to the diversified hues of nature. The rich and lively -green, which so abundantly overspreads the surface of the earth, the -varied colours of the flowers, and the numberless tints of animals, -together with all those of the productions of the mineral kingdom, -and of the artificial combinations of chemical manufacture, result -from powers by which the relations of matter to light are rendered -permanent, until its physical conditions undergo some change. - -There is a remarkable correspondence between the geographical position -of a region and the colours of its plants and animals. Within the -tropics, where - - “The sun shines for ever unchangeably bright,” - -the darkest green prevails over the leaves of plants; the flowers -and fruits are tinctured with colours of the deepest dye, whilst the -plumage of the birds is of the most variegated description and of the -richest hues. In the people also of these climes there is manifested -a desire for the most striking colours, and their dresses have all -a distinguishing character, not of shape merely, but of chromatic -arrangement. In the temperate climates everything is of a more subdued -variety: the flowers are less bright of hue; the prevailing tint of the -winged tribes is a russet brown; and the dresses of the inhabitants of -these regions are of a sombre character. In the colder portions of the -earth there is but little colour; the flowers are generally white or -yellow, and the animals exhibit no other contrast than that which white -and black afford. A chromatic scale might be formed, its maximum point -being at the equator, and its minimum at the poles.[94] - -The influence of light on the colours of organized creation is well -shown in the sea. Near the shores we find sea-weeds of the most -beautiful hues, particularly on the rocks which are left dry by the -tides; and the rich tints of the actiniæ, which inhabit shallow water, -must have been often observed. The fishes which swim near the surface -are also distinguished by the variety of their colours, whereas those -which live at greater depths are grey, brown, or black. It has been -found that after a certain depth, where the quantity of light is so -reduced that a mere twilight prevails, the inhabitants of the ocean -become nearly colourless. That the sun’s ray alone gives to plants the -property of reflecting colour is proved by the process of blanching, or -_etiolation_, produced by artificially excluding the light. - -By a triangular piece of glass--a prism,--we are enabled to resolve -light into its ultimate rays. The white pencil of light which falls -on the first surface of the prism is bent from its path, and coloured -bands of different colours are obtained. These bands or rays observe a -curious constancy in their positions: the red ray is always the least -bent out of the straight path: the yellow class comes next in the -order of refrangibility; and the blue are the most diverted from the -vertex of the prism. The largest amount of illuminating power exists -in the yellow ray, and it diminishes towards either end.[95] It is not -uninteresting to observe something like the same variety of colour -occurring at each end of the prismatic spectrum. The strict order -in which the pure and mixed coloured rays present themselves is as -follows:-- - -1. The _extreme red_: a ray which can only be discovered when the eye -is protected from the glare of the other rays by a cobalt blue glass, -is of a crimson character--a mixture of the _red_ and the _blue_, red -predominating.[96] - -2. The _red_: the first ray visible under ordinary circumstances. - -3. The _orange_: red passing into and combining with yellow. - -4. The _yellow_: the most intensely luminous of the rays. - -5. The _green_: the yellow passing into and blending with the blue. - -6. The _blue_: in which the light very rapidly diminishes. - -7. The _indigo_: the dark intensity of blue. - -8. The _violet_: the _blue_ mingled again with the _red_--blue being in -excess. - -9. The _lavender grey_: a neutral tint, produced by the combination of -the red, blue, and yellow rays, which is discovered most easily when -the spectrum is thrown upon a sheet of turmeric paper. - -10. The fluorescent rays: which are either a _pure silvery blue_ or a -delicate _green_. - -Newton regarded the spectrum as consisting of seven colours of -definite and unvarying refrangibility. Brewster and others appear to -have detected a great diffusion of the colours over the spectrum, -and regard white light as consisting only of three rays, which in the -prismatic images overlap each other; and from these--red, yellow, -and blue--all the others can be formed by combination in varying -proportions. The truth will probably be found to be, that the ordinary -prismatic spectrum is a compound of two spectra:--that is, as we have -the ordinary rainbow, and a supplementary bow, the colours of which are -inverted, so the extraordinary may be somewhat masked by the intense -light of the ordinary spectrum; and yet by overlapping produce the -variations of colour in the rays. We have already examined the heating -power found in these coloured bands, which, although shown to be in a -remarkable manner in constant agreement with the colour of a particular -ray, is not directly connected with it; that is, not as the effect of a -cause, or the contrary. The chemical action of the solar rays, to which -from its important bearings we shall devote a separate chapter, has, in -like manner with heat, been confounded with the sun’s luminous power; -but although associated with light and heat, and modified by their -presence, it must be distinguished from them. - -We find the maximum of heat at one end of the spectrum, and that of -chemical excitation at the other--luminous power observing a mean point -between them. Without doubt we have these powers acting reciprocally, -modifying all the phenomena of each other, and thus giving rise to the -difficulties which beset the inquirer on every side. - -We have beautiful natural illustrations of luminous refraction in -the rainbow and in the halo: in both cases the rays of light being -separated by the refractive power of the falling rain drop, or the -vesicles which form the moisture constituting a fog. In the simple toy -of the child--the soap-bubble floating upon the air--the philosopher -finds subjects for his contemplation; and from the unrivalled play of -colours which he discovers in that attenuated film, he learns that the -varying thicknesses of surfaces influence, in a most remarkable manner, -the colours of the sunbeam. Films of oil floating upon water present -similar appearances; and the colours developed in tempering steel -are due entirely to the thickness of the oxidized surface produced -by heat. There have lately been introduced some beautiful specimens -of paper rendered richly iridescent by the following process:--A -solution of a gum resin in chloroform is floated upon water, where -it forms a film giving all the colours of Newton’s rings. A sheet of -paper which has been previously sunk in the water is carefully lifted, -and the film thus removed adheres with great firmness to the paper, -and produces this rich and curious play of colour. The rich tints -upon mother-of-pearl, in the feathers of many birds, the rings seen -in the cracks of rock-crystal, or between the unequal faces of two -pieces of glass, and produced by many chemical and indeed mechanical -operations--are all owing to the same cause;--the refraction of the -luminous pencil by the condition of the film or surface. If we take -one of those steel ornaments which are formed by being covered with -an immense number of fine lines, it will be evident that these striæ -present many different angles of reflection, and that, consequently, -the rays thrown back will, at some point or another, have a tendency -to cross each other. The result of this is, that the quantity of -light is augmented at some points of intersection, and annihilated at -others.[97] Out of the investigation of the phenomena of diffraction, -of the effects of thin and thick plates upon light, and the results of -interference, has arisen the discovery of one of the most remarkable -conditions within the range of physical science. - -_Two bright lights may be made to produce darkness._--If two pencils -of light radiate from two spots very close to each other in such a -manner that they cross each other at a given point, any object placed -at that line of interference will be illuminated with the sum of the -two luminous pencils. If we suppose those rays to move in waves, and -the elevation of the wave to represent the maximum of luminous effect, -then the two waves meeting, when they are both at the height of their -undulation, will necessarily produce a spot of greater intensity. If -now we so arrange the points of radiation, that the systems of luminous -waves proceed irregularly, and that one arrives at the screen half an -undulation before the other, the one in elevation falling into the -depression of the other, a mutual annihilation is the consequence. This -fact, paradoxical as it may appear, was broadly stated by Grimaldi, -in the description of his experiments on the inflection of light, and -has been observed by many others. The vibratory hypothesis, seizing -upon the analogy presented by two systems of waves in water, explains -this plausibly, and many similar phenomena of what is called the -_interference of light_; but still upon examination it does not appear -that the explanation is quite free from objection.[98] - -Another theory, not altogether new to us, it being indicated in Mayer’s -hypothesis of three primary colours (1775), and to be found as a -problem in some of the Encyclopædias of the last century, has been put -forth, in a very original manner, by that master-mind of intellectual -Germany, Goethe; and from the very comprehensive views which this -poet-philosopher has taken of both animal and vegetable physiology -(views which have been adopted by some of the first naturalists of -Europe), we are bound to receive his theory of colours with every -respect and attention. - -Goethe regards colour as the “thinning” of light; for example, by -obstructing a portion of white light, yellow is produced; by reducing -it still farther, red is supposed to result; and by yet farther -retarding the free passage of the beam, we procure a blue colour, which -is the next remove from blackness, or the absence of light. There is -truth in this; it bears about it a simplicity which will satisfy many -minds; by it many of the phenomena of colour may be explained: but it -is insufficient for any interpretation of several of those laws to -which the other theories do give us some insight. - -Newton may have allowed himself to be misled by the analogy presented -between the seven rays of the spectrum and the notes in an octave. -The mystic number, seven, may have clung like a fibre of the web of -superstition to the cloak of the great philosopher; but the attack made -by Goethe upon the Newtonian philosophy betrays the melancholy fact of -his being diseased with the lamentable weakness of too many exalted -minds--an overweening self-esteem. - -The polarization of light, as it has been unfortunately -called--unfortunately, as conveying an idea of determinate and -different points or poles, which only exists in hypothetical -analogy--presents to us a class of phenomena which promise to unclose -the mysterious doors of the molecular constitution of bodies. - -This remarkable condition, as produced by the reflection of light from -glass at a particular angle, was first observed by Malus, in 1808,[99] -when amusing himself by looking at the beams of the setting sun, -reflected from the windows of the Luxembourg Palace through a double -refracting prism. He observed that when the prism was in one position, -the windows with their golden rays were visible; but that turned -round a quarter of a circle from that position, the reflected rays -disappeared although the windows were still seen. - -The phenomenon of double refraction was noticed, in the first instance, -by Erasmus Bartholin, in Iceland-spar, a crystal the primary form of -which is a rhombohedron; who perceived that the two images produced by -this body were not in the same physical conditions.[100] It was also -studied by Huyghens and Sir Isaac Newton, and to our countryman we owe -the singular idea that a ray of light emerging from such a crystal -has _sides_. This breaking up of the beam of light into two,--which -is shown by looking through a pin-hole on a card through a crystal of -Iceland spar, when two holes become visible, is due to the different -states of tension in which the different layers constituting the -crystal exist. - -In thus separating the ray of light into two rays, the condition -called polarisation has been produced, and by experiment we discover -that the single ray has properties different from those of the compound -or ordinary ray. - -It is somewhat difficult to explain what is meant by, and what are the -conditions of, _polarised light_. In the first instance let us see by -what methods this peculiar state may be brought about. - -If we reflect a ray of light from the surface of any body, fluid or -solid, but not metallic, at an angle between 53° and 68° it undergoes -what has been called _plane polarisation_. It may also be produced by -the refraction of light from several refracting surfaces acting upon -the pencil of light in succession; as by a bundle of plates of glass. -Each surface polarises a portion of the pencil, and the number of -plates necessary to polarise a whole beam depends upon the intensity of -the beam and the angle of incidence. Thus, the light of a wax candle -is wholly polarised by forty-seven plates of glass at an angle of 40° -41'; while at an angle of 79° 11' it is polarised by eight plates. -Again, plane polarisation may be produced by the double refraction of -crystals. Each of the two pencils is polarised, like light reflected -from glass at an angle of 56° 45', but in opposite planes. - -Non-scientific readers will still ask,--What is this mysterious -condition of light which is produced by reflection and refraction at -peculiar angles to the incident ray. It is one of the most difficult of -problems to express in popular language. The conditions are, however, -these:-- - -An ordinary ray of light will be reflected from a reflecting surface at -whatever angle that surface may be placed in relation to the incident -beam. - -A polarised ray of light is not reflected in all positions of the -reflecting surface. - -An ordinary ray of light is freely transmitted through a transparent -medium, as glass, in whatever position it may be placed relative to the -source of light. - -A polarised ray of light is not transmitted in all the positions of the -permeable medium. - -Supposing a plate of glass is presented at the angle 56° to a polarised -ray, and the plane of incidence or reflexion is at right angles to the -plane of polarisation of the ray, _no light is reflected_. If we turn -the plate of glass round through 90°, when the plane of reflexion is -parallel to that of polarisation _the light is reflected_. If we turn -the plate round another 90°, so that the plane of reflexion and of -polarisation are parallel to each other, again _no light is reflected_; -and if we turn it through another 90° the reflection of the ray again -takes place. - -Precisely the same result takes place when, instead of being reflected, -the polarised ray is transmitted. - -Some substances have peculiar polarizing powers: _the tourmaline_ is a -familiar example. If a slice of tourmaline is taken, and we look at a -common pencil of light through it, we see it in whatever position we -may place the transparent medium. If, however, we look at a pencil of -polarised light, and turn the crystal round, it will be found that in -two positions the light is stopped, and that in two other positions it -passes freely through it to the eye. - -By way of endeavouring to conceive something of what may be the -conditions which determine this very mysterious state, let us suppose -each ray of light to vibrate in two planes at right angles to each -other: one wave being vertical and the other horizontal. We have many -examples of this compound motion. The mast of a ship, by the force with -which she is urged through the water, describes a vertical wave, while -by the roll of the billows across which she sails, a lateral undulation -is produced at the same time. We may sometimes observe the same thing -when a field of corn is agitated by a shifting wind on a gusty day. - -The hypothesis therefore is, that every ray of ordinary light consists -of two rays vibrating in different planes; and that these rays, -separated one from the other, have the physical conditions which we -call _polarized_. - -The most transparent bodies may be regarded as being made up of atoms -arranged in certain planes. Suppose the plane of lamination of any -substance to be vertical in position, it would appear that the ray -which has a vertical motion passes it freely, whereas if we turn the -body round so that the planes of lamination are at right angles to the -plane of vibration of the ray, it cannot pass. - -That some action similar to that which it is here endeavoured to -express in popular language does take place, is proved by the -correctness of the results deduced by rigid mathematical analyses -founded on this hypothesis. - -There are two other conditions of the polarization of light--called -_circular_ and _elliptical_ polarization. The first is produced by -light when it is twice reflected from the second surface of bodies at -their angle of maximum polarization, and the second by reflexions from -the surfaces of metals at angles varying from 70° 45' to 78° 30'. The -motion of the wave in the first is supposed to be circular, or to be -that which is represented by looking along the centre of a corkscrew -as it is turned round. At every turn of the medium effecting _circular -polarization_ the colour of the ray of light is changed after a uniform -order. If turned in one direction, they change through red, orange, -yellow, green, and violet; and if in the other direction, the colours -appear in the contrary order. - -The variety of striking effects produced by the polarization of light; -the unexpected results which have sprung from the investigation of the -laws by which it is regulated; and the singular beauty of many of its -phenomena, have made it one of the most attractive subjects of modern -science. - -Ordinary light passes through transparent bodies without producing any -very striking effects in its passage; but this _extraordinary_ beam -of light has the power of insinuating itself between the molecules -of bodies, and by illuminating them, and giving them every variety -of prismatic hue, of enabling the eye to detect something of the -structure of the mass. The chromatic phenomena of polarized light are -so striking, that no description can convey an adequate idea of their -character. - -Spectra more beautiful and intense than the prismatic image,--systems -of rings far excelling those of thin plates,--and forms of the most -symmetric order, are constantly presenting themselves, as the polarized -ray is passed through various transparent substances; the path of the -ray indicating whether the crystal has been formed round a single -nucleus or axis, or whether it has been produced by aggregation -around two axes. The coloured rings, and the dark or luminous crosses -which distinguish the path of the polarized ray, are respectively -due to different states of tension amongst the particles, although -those differences are so slight, that no other means is of sufficient -delicacy to detect the variation. - -The poetry which surrounds these, in every way, mysterious conditions -of the solar beam, is such, that it is with difficulty that imagination -is restrained by the stern features of truth. The uses of this peculiar -property in great natural phenomena are not yet made known to us; but, -since we find on every side of us the natural conditions for thus -separating the beam of light, and effecting its polarization, there -must certainly be some most important end for which it is designed by -Him who said, “Let there be Light.” - -It must not be forgotten that we have at command the means of showing -that the chromatic phenomena of polarized light are due to atomic -arrangement. By altering the molecular arrangement of transparent -bodies, either by heat or by mere mechanical pressure, the unequal -tension or strain of the particles is at once indicated by means of -the polarized ray of light and its rings of colour. Differences in the -chemical constitution of bodies, too slight to be discovered by any -other mode of analysis, can be most readily and certainly detected by -this luminous investigator of the molecular forces.[101] - -Although we cannot enter into an examination of all the conditions -involved in the polarization of, and the action of matter on, ordinary -light, it will be readily conceived, from what has been already stated, -that some most important properties are indicated, beyond those which -science has made known. - -Almost every substance in nature, in some definite position, appears -to have the power of producing this change upon the solar ray, as -may be satisfactorily shown by examining them with a polarizing -apparatus.[102] The sky at all times furnishes polarized light, which -is most intense where it is blue and unclouded, and the point of -maximum polarization is varied according to the relative position of -the sun and the observer. A knowledge of this fact has led to the -construction of a “Solar Clock,”[103] with which the hour can be -readily determined by examining the polarized condition of the sky. -It has been stated, that chemical change on the Daguerreotype plates -and on photographic papers is more readily produced by the polarized -than by the ordinary sunbeam.[104] If this fact be established by -future investigations, we advance a step towards the discovery so much -desiderated of the part it plays in natural operations. - -The refined and accurate investigations of Dr. Faraday stand -prominently forward amid those which will redeem the present age from -the charge of being superficial, and they will, through all time, be -referred to as illustrious examples of the influence of a love of truth -for truth’s sake, in entire independence of the marketable value, which -it has been unfortunately too much the fashion to regard. The searching -examination made by this “interpreter of nature” into the phenomena -of electricity in all its forms, has led him onward to trace what -connexion, if any, existed between this great natural agent and the -luminous principle. - -By employing that subtile analyzer, a polarized ray, Dr. Faraday -has been enabled to detect and exhibit effects of a most startling -character. He has proved magnetism to have the power of influencing a -ray of light in its passage through transparent bodies. A polarized ray -is passed through a piece of glass or a crystal, or along the length -of a tube filled with some transparent fluid, and the line of its path -carefully observed; if, when this is done, the solid or fluid body is -brought under powerful magnetic influence, such as we have at command -by making a very energetic voltaic current circulate around a bar of -soft iron, it will be found that the polarized light is disturbed; -that, indeed, it does not permeate the medium along the same line.[105] -This effect is most strikingly shown in bodies of the greatest density, -and diminished in fluids, the particles of which are easily moveable -over each other, and has not hitherto been observed in any gaseous -medium. The question, therefore, arises,--does magnetism act directly -upon the ray of light, or only indirectly, by producing a molecular -change in the body through which the ray is passing? This question, -so important in its bearings upon the connexion between the great -physical powers, will, no doubt, before long receive a satisfactory -reply. A medium is necessary to the production of the result, and, as -the density of the medium increases, the effect is enlarged: it would -therefore appear to be due to a disturbance by magnetic force of the -particles which constitute the medium employed. - -Without any desire to generalize too hastily, we cannot but express -a feeling,--amounting to a certainty in our own mind,--that those -manifestations of luminous power, connected with the phenomena of -terrestrial magnetism, which are so evident in all the circumstances -attendant upon the exhibition of Aurora Borealis, and those luminous -clouds which are often seen, independent of the Northern Lights, that -a very intimate, relation exists between the solar radiations and that -power which so strangely gives polarity to this globe of ours. - -In connexion with the mysterious subject of solar light, it is -important that we should occupy a brief space in these pages with the -phenomena of vision, which is so directly dependent upon luminous -radiation. - -The human eye has been rightly called the “masterpiece of divine -mechanism;” its structure is complicated, yet all the adjustments of -its parts are as simple as they are perfect. The eye-ball consists of -four coats. The cornea is the transparent coat in front of the globe; -it is the first optical surface, and this is attached to the sclerotic -membrane, filling up the circular aperture in the white of the eye; -the choroid coat is a very delicate membrane, lining the sclerotic, -and covered with a perfectly black pigment on the inside; and close to -this lies the most delicately reticulated membrane, the retina, which -is, indeed, an extension of the optic nerve. These coats enclose three -humours,--the aqueous, the vitreous, and the crystalline humours. - -The eye, in its more superficial mechanical arrangements, presents -exactly the same character as a camera obscura, the cornea and -crystalline lens receiving the images of objects refracting and -inverting them; but how infinitely more beautiful are all the -arrangements of the organ of vision than the dark chamber of Baptista -Porta![106] The humours of the eye are for the purpose of correcting -the aberrations of light, which are so evident in ordinary lenses, -and for giving to the whole an achromatic character. Both spherical -and chromatic aberration are corrected, the latter not entirely, and -by the agency of the cornea and the crystalline lens perfect images -are depicted on the retina, in a similar way to those very charming -pictures which present themselves in the table of the camera obscura. - -The seat of vision has been generally supposed to be the retina; -but Mariotte has shown that the base of the optic nerve, which is -immediately connected with the retina, is incapable of conveying an -impression to the brain. The choroid coat, which lies immediately -behind the retina, is regarded by Mariotte and Bernoulli as the more -probable seat of vision. The retina, being transparent, offers no -obstruction to the passage of the light onward to the black surface of -the choroid coat, from which the vibrations are, in all probability, -communicated to the retina and conveyed to the brain. Howbeit, upon one -or the other of these delicate coats a distinct image is impressed -by light, and the communication made with the brain possibly by a -vibratory action. We may trace up the phenomena of vision to this -point; we may conceive undulations of light, differing in velocity and -length of wave, occasioning corresponding tremors in the neuralgic -system of the eye; but how these vibrations are to communicate -correct impressions of length, breadth, and thickness, no one has yet -undertaken to explain. - -It has, however, been justly said by Herschel:-- - -“It is the boast of science to have been able to trace so far the -refined contrivances of this most admirable organ, not its shame to -find something still concealed from scrutiny; for, however anatomists -may differ on points of structure, or physiologists dispute on modes -of action, there is that in what we _do_ understand of the formation -of the eye, so similar, and yet so infinitely superior to a product -of human ingenuity; such thought, such care, such refinement, such -advantage taken of the properties of natural agents used as mere -instruments for accomplishing a given end, as force upon us a -conviction of deliberate choice and premeditated design, more strongly, -perhaps, than any single contrivance to be found whether in art or -nature, and renders its study an object of the greatest interest.”[107] - -Has the reader ever asked himself why it is, having two eyes, and -consequently two pictures produced upon the tablets of vision, that we -see only one object? According to the law of visible direction, all the -rays passing through the crystalline lenses converge to one point upon -the retina,--and as the two images are coincident and nearly identical, -they can only produce the sensation of one upon the brain. - -When we look at any round object, as the ornamented moderator lamp -before us, first with one eye, and then with the other, we discover -that, with the right eye, we see most of the right-hand side of the -lamp, and with the left eye more of the left-hand side. These two -images are combined, and we see an object which we know to be round. - -This is illustrated in a most interesting manner by the little optical -instrument, _the Stereoscope_. It consists either of two mirrors placed -each at an angle of 45°, or of two semi-lenses turned with their curved -sides towards each other. To view its phenomena, two pictures are -obtained by the camera obscura on photographic paper of any object in -two positions, corresponding with the conditions of viewing it with the -two eyes. By the mirrors or the lenses these dissimilar pictures are -combined within the eye, and the vision of an actually solid object is -produced from the pictures represented on a plane surface. Hence the -name of the instrument; which signifies, _Solid I see_. - -Analogy is often of great value in indicating the direction in which to -seek for a truth; but analogical evidence, unless where the resemblance -is very striking, should be received with caution. Mankind are so ready -to leap to conclusions without the labour necessary for a faithful -elucidation of the truth, that too often a few points of resemblance -are seized upon, and an inference is drawn which is calculated to -mislead. - -There is an idea that the phenomena of sound bear a relation to those -of light,--that there exists a resemblance between the chromatic -and the diatonic scales. Sound, we know, is conveyed by the beating -of material particles--the air--upon the auditory membrane of the -ear, which have been set in motion by some distant disturbance of -the medium through which it passes. Light has been supposed to act -on the optic nerve in the same manner. If we imagine colour to be -the result of vibrations of different velocities and lengths, we can -understand that under some of these tremors, first established on the -nerves, and through them conveyed to the brain, sensations of pain -or pleasure may result, in the same way as sharp or subdued sounds -are disagreeable or otherwise. Intensely coloured bodies do make an -impression upon perfectly blind men; and those who, being born blind, -know no condition of light or colour, will point out a difference -between strongly illuminated red and yellow media. When the eyes are -closed we are sensible to luminous influence, and even to differences -of colour. We must consequently infer that light produces some peculiar -action upon the system of nerves in general; this may or may not -be independent of the chemical agency of the solar radiations; but -certainly the excitement is not owing to any calorific influence. The -system of nerves in the eye is more delicately organized, and of course -peculiarly adapted to all the necessities of vision. - -Thus far some analogy does appear to exist between light and sound; -but the phenomena of the one are so much more refined than those of -the other--the impressions being all of them of a far more complicated -character, that we must not be led too far by the analogical evidence -in referring light, like sound, to mere material motion. - -It was a beautiful idea that real impressions of external objects -are made upon the seat of vision, and that they are viewed, as in a -picture, by something behind the screen,--that these pictures become -dormant, but are capable of being revived by the operations of the mind -in peculiar conditions; but we can only regard it as a philosophical -speculation of a poetic character, the truth or falsehood of which we -are never likely to be enabled to establish.[108] - -That which sees will never itself be visible. The secret principle -of sensation,--the mystery of the life that is in us,--will never be -unfolded to finite minds. - -Numerous experiments have been made from time to time on the influence -of light upon animal life. It has been proved that the excitement of -the solar rays is too great for the healthful growth of young animals; -but, at the same time, it appears probable that the development of -the functional organs of animals requires, in some way, the influence -of the solar rays. This might, indeed, have been inferred from the -discovery that animal life ceases in situations from which light is -absolutely excluded. The instance of the Proteus of the Illyrian lakes -may appear against this conclusion. This remarkable creature is found -in the deep and dark recesses of the calcareous rocks of Adelsburg, at -Sittich; and it is stated, also in Sicily, and in the Mammoth caves -of Kentucky. Sir Humphry Davy describes the Proteus anguinus as “an -animal to whom the presence of light is not essential, and who can -live indifferently in air and in water, on the surface of the rock, -or in the depths of the mud.” The geological character of rocks, -however, renders it extremely probable that these animals may have -descended with the water, percolating through fissures from very near -the surface of the ground. All the facts with which science has made us -acquainted--and both natural and physical science has been labouring -with most untiring industry in the pursuit of truth--go to prove -that light is absolutely necessary to organization. It is possible -the influence of the solar radiations may extend beyond the powers -of the human senses to detect luminous or thermic action, and that -consequently a development of animal and vegetable forms may occur -where the human eye can detect no light; and under such conditions -the Proteus may be produced in its cavernous abodes, and also those -creatures which live buried deep in mud. Some further consideration of -the probable agency of light will occupy us, when we come to examine -the phenomena of vital forces. - -Light is essentially necessary to vegetable life; and to it science -refers the powers which the plant possesses of separating carbon from -the air breathed by the leaves, and secreting it within its tissues for -the purpose of adding to its woody structure. As, however, we have, in -the growing plant, the action of several physical powers exerted to -different ends at the same time, the remarkable facts which connect -themselves with vegetable chemistry and physiology are deferred for a -separate examination. - -The power of the solar rays to produce in bodies that peculiar gleaming -light which we call phosphorescence, and the curious conditions under -which this phenomenon is sometimes apparent, independent of the sun’s -direct influence, present a very remarkable chapter in the science of -luminous powers. - -The phosphorescence of animals is amongst the most surprising of -nature’s phenomena, and it is not the less so from our almost entire -ignorance of the cause of it. Many very poetical fancies have been -applied in description of these luminous creations; and imagination -has found reason why they should be gifted with these extraordinary -powers. The glow-worm lights her lamp to lure her lover to her bower, -and the luminous animalcules of the ocean are employed in lighting up -the fathomless depths where the sun’s rays cannot penetrate, to aid its -monsters in their search for prey. “The lamp of love--the pharos--the -telegraph of the night,--which scintillates and marks, in the silence -of darkness, the spot appointed for the lover’s rendezvous,”[109] is -but a pretty fiction; for the glow-worm shines in its infant state, -in that of the larva, and when in its aurelian condition. Of the -dark depths of the ocean it may be safely affirmed that no organized -creation lives or moves in its grave-like silence to require this -fairy aid. Fiction has frequently borrowed her creations from science. -In these cases science appears to have made free with the rights of -fiction. - -The glow-worms (_lampyris noctiluca_), it is well known, have the -power of emitting from their bodies a beautiful pale bluish-white -light, shining during the hours of night in the hedge-row, like crystal -spheres. It appears, from the observations of naturalists, that these -insects never exhibit their light without some motion of the body or -legs;--from this it would seem that the phosphorescence was dependent -upon nervous action, regulated at pleasure by the insect; for they -certainly have the power of obscuring it entirely. If the glow-worm is -crushed, and the hands or face are rubbed with it, luminous streaks, -similar to those produced by phosphorus, appear. They shine with -greatly increased brilliancy in oxygen gas and in nitrous oxide. From -these facts may we not infer that the process by which this luminosity -is produced, whatever it may be, has a strong resemblance to that of -respiration? - -There are several varieties of flies, and three species of beetles of -the genus _Elater_, which have the power of emitting luminous rays. -The great lantern-fly of South America is one of the most brilliant, a -single insect giving sufficient light to enable a person to read. In -Surinam a very numerous class of these insects are found, which often -illuminate the air in a remarkable manner. In some of the bogs of -Ireland a worm exists which gives out a bright green light; and there -are many other kinds of creatures which, under certain circumstances, -become luminous in the dark. This is always dependent upon vitality; -for all these animals, when deprived of life, cease to shine. - -At the same time we have many very curious instances of phosphorescence -in dead animal and vegetable matter; the lobster among the Crustacea, -and the whiting among fishes, are striking examples; decayed wood -also emits much light under certain conditions of the atmosphere. -This development of light does not appear to be at all dependent upon -putrefaction; indeed, as this process progresses, the luminosity -diminishes. We cannot but imagine that this light is owing, in the -first place, to direct absorption by, and fixation within, the -corpuscular structure of those bodies, and that it is developed by the -decomposition of the particles under the influence of our oxygenous -atmosphere. - -The pale light emitted by phosphorus in the dark is well known; and -this is evidently only a species of slow combustion, a combination of -the phosphorus with the oxygen of the air. Where there is no oxygen, -phosphorus will not shine; its combustion in chlorine or iodine vapour -is a phenomenon of a totally different character from that which we are -now considering. This phosphorescence of animal and vegetable matter -has been regarded as something different from the slow combustion of -phosphorus; but, upon examination, all the chemical conditions are -found to be the same, and it is certainly due to a similar chemical -change. - -The luminous matter of the dead whiting or the mackerel may be -separated by a solution of common salt or of sulphate of magnesia; by -concentrating these solutions the light disappears; but it is again -emitted when the fluid is diluted. The entire subject is, however, -involved in the mystery of ignorance, although it is a matter quite -within the scope of any industrious observer. The self-emitted light -of the carbuncle of the romancer is realized in these remarkable -phenomena. - -The phosphorescence of some plants and flowers is not, perhaps, of -the same order as that which belongs to either of the conditions we -have been considering. It appears to be due rather to an absorption of -light and its subsequent liberation. If a nasturtium is plucked during -sunshine, and carried into a dark room, the eye, after it has reposed -for a short time, will discover the flower by a light emitted from its -leaves. - -The following remarkable example, and an explanation of it by the poet -Goethe, is instructive:-- - -“On the 19th of June, 1799, late in the evening, when the twilight was -deepening into a clear night, as I was walking up and down the garden -with a friend, we very distinctly observed a flame-like appearance -near the oriental poppy, the flowers of which are remarkable for their -powerful red colour. We approached the place, and looked attentively -at the flowers, but could perceive nothing further, till at last, by -passing and repassing repeatedly, while we looked side-ways on them, we -succeeded in renewing the appearance as often as we pleased. It proved -to be a physiological phenomenon, and the apparent corruscation was -nothing but the spectrum of the flower in the complementary blue-green -colour. The twilight accounts for the eye being in a perfect state -of repose, and thus very susceptible, and the colour of the poppy is -sufficiently powerful in the summer twilight of the longest days to act -with full effect, and produce a complementary image.”[110] - -The leaves of the _œnothera macrocarpa_ are said to exhibit phosphoric -light when the air is highly charged with electricity. The agarics -of the olive-grounds of Montpelier have been observed to be luminous -at night; but they are said to exhibit no light, even in darkness, -_during the day_. The subterranean passages of the coal mines near -Dresden are illuminated by the phosphorescent light of the _rhizomorpha -phosphoreus_, a peculiar fungus. On the leaves of the Pindoba palm, a -species of agaric grows which is exceedingly luminous at night; and -many varieties of the lichens, creeping along the roofs of caverns, -lend to them an air of enchantment by the soft and clear light which -they diffuse. In a small cave near Penryn, a luminous moss is abundant; -and it is also found in the mines of Hesse. According to Heinzmann, the -_rhizomorpha subterranea_ and _aidulæ_ are also phosphorescent. - -It is but lately that a plant which abounds in the jungles in the -Madura district of the East Indies was sent to this country, which, -although dead, was remarkably phosphorescent; and, when in the -living state, the light which it emitted was extraordinarily vivid, -illuminating the ground for some distance. Those remarkable effects -may be due, in some cases, to the separation of phosphuretted hydrogen -from decomposing matter, and, in others, to some peculiar electric -manifestation. - -The phosphorescence of the sea, or that condition called by fishermen -_brimy_, when the surface, being struck by an oar, or the paddle-wheels -of a steamer, gives out large quantities of light, has been attributed -to the presence of myriads of minute insects which have the power -of emitting light when irritated. The night-shining nereis (_Nereis -noctiluca_) emits a light of great brilliancy, as do several kinds of -the mollusca. The nereides attach themselves to the scales of fishes, -and thus frequently render them exceedingly luminous. Some of the -crustaceæ possess the same remarkable property;--twelve different -species of _cancer_ were taken up by the naturalists of the Zaire -in the Gulf of Guinea.[111] The _cancer fulgens_, discovered by Sir -Joseph Banks, is enabled to illuminate its whole body, and emits -vivid flashes of light. Many of the medusæ also exhibit powerful -phosphorescence.[112] These noctilucous creatures are, many of them, -exceedingly minute, several thousands being found in a tea-cup of sea -water. They float near the surface in countless myriads, and when -disturbed they give out brilliant scintillations, often leaving a train -of light behind them.[113] By microscopic examination no other fact has -been elicited than that these minute beings contain a fluid which, when -squeezed out, leaves a line of light upon the surface of water. The -appearance of these creatures is almost invariably on the eve of some -change of weather, which would lead us to suppose that their luminous -phenomena must be connected with electrical excitation; and of this, -the investigations of Mr. C. Peach, of Fowey, communicated to the -British Association at Birmingham, furnish the most satisfactory proofs -we have as yet obtained. - -Benvenuto Cellini gave a curious account of a carbuncle which shone -with great brilliancy in the dark.[114] The same thing has been stated -of the diamond; but it appears to be necessary to procure these -emissions of light, that the minerals should be first warmed near a -fire. From this it may be inferred that the luminous appearance is -of a similar character to that of fluor spar, and of numerous other -earthy minerals, which, when exposed to heat, phosphoresce with great -brilliancy. Phosphorescent glow can also be excited in similar bodies -by electricity, as was first pointed out by Father Beccaria, and -confirmed by Mr. Pearsall.[115] These effects, it must be remembered, -are distinct from the electric spark manifested upon breaking white -sugar in the dark, or scratching sulphuret of zinc. - -In the instances adduced there is not necessarily any exposure to the -sunshine required. It is probable that two, if not three, distinct -phenomena are concerned in the cases above quoted, and that all of them -are distinct from animal phosphorescence, or the luminous appearance -of vegetables. They, however, certainly prove, either that light is -capable of becoming latent, or that it is only a condition of matter, -in which it may be made manifest by any disturbance of the molecular -forces. We have, in answer to this, very distinct evidence that -some bodies do derive this property from the solar rays. Canton’s -phosphorus, which is a sulphuret of calcium, will, having been exposed -to the sun, continue luminous for some time after it is carried into -the dark; as will also the Bolognian stone,--a sulphuret of barium. -This result appears to be due to a particular class of the solar rays; -for it has been found, if these sulphurets, spread smoothly on paper, -are exposed to the influence of the solar spectrum for some little -time, and then examined in the dark, that luminous spaces appear, -exactly corresponding with the most refrangible rays, or those which -excite chemical change; and one very remarkable fact must not be -forgotten--the dark rays of the spectrum beyond the violet produce a -lively phosphorescence, which is _extinguished_ by the action of the -rays of least refrangibility, or the heat rays--whilst artificial heat, -such as a warm iron, produces a very considerable elevation of the -phosphorescent effect.[116] It is not improbable, that the fluorescent -rays of Mr. Stokes may be materially concerned in producing the -phenomena of phosphorescence: experiments are, however, required to -prove this. - -In these allied phenomena we have effects which are evidently dependent -upon several dissimilar causes. The phosphorescence of the living -animal is due, without doubt, to nervous excitation: that of the living -vegetable to solar luminous influence; and in the case of the mosses of -caverns, &c. to the chemical agency of the sun’s rays, which appears to -be capable of conduction. In the dead organic matter we have a purely -chemical action developing the light, and in the inorganic bodies we -have peculiar molecular constitution, by which an absorption of light -appears to take place. - -The subject is one of the greatest difficulty; the torch of science -is too dim to enable us to see the causes at work in producing these -marvellous effects. The investigation leads, to a certain extent, to -the elucidation of many of the secrets of luminous action; and the -determination of the question, whether light is an emanation from the -sun, or only a subtile principle diffused through all matter, which is -excited by solar influence, is intimately connected with the inquiry. - -It has been stated that matter is necessary to the development of -light; that no luminous effect would be produced if it were not for -the presence of matter. Of this we not only have no proof, but such -evidence as we have is against the position. There is no loss of light -in the most perfect vacuum we can produce by any artificial means, -which should be the case if matter was concerned in the phenomena of -light, as a cause. - -Colour is certainly a property regulated by material bodies; or -rather, the presence of matter is necessary to the production of -colour. Chlorine gas is a pale yellow, and nitrous vapour a yellowish -red. These and one or two other vapours, which are near the point of -condensation into fluids, are the only coloured gaseous or vaporiform -bodies. The sky is blue, because the material particles of the -atmosphere reflect back the blue rays. But we have more practical -illustrations than this. The flame of hydrogen burning with oxygen -gives scarcely any light; allow it to impinge on lime, a portion of -which is carried off by the heat of the flame, and the most intense -artificial light with which we are acquainted is produced. Hydrogen gas -alone gives a flame in which nearly all but the blue rays are wanting: -place a brush of steel or asbestos in it, and many of the other rays -are at once produced. An argand lamp, and more particularly the lamp -in which camphine--a purified turpentine,--is burnt, gives a flame -which emits most of the rays found in sunlight. Spirit of wine mixed -with water, warmed and ignited, gives only yellow rays; add nitrate -of strontian and they become red; but nitrate of barytes being mixed -with the fluid, they are changed to green and yellow; salts of copper -afford fine blue rays, and common salt intense yellow ones. Many of -these coloured rays and others can be produced in great power by the -use of various solid bodies introduced into flame. This has not been -sufficiently pointed out by authors; but it is clear from experiments -that light requires the presence of matter to enable it to diffuse its -coloured glories. How is it that the oxygen and hydrogen flame gives so -little light, and with a solid body present, pours forth such a flood -of brilliancy? - -The production of artificial light by electrical and chemical agencies -will necessarily find some consideration under their respective -heads. There are numerous phenomena which connect themselves with -luminous power, or appear to do so, which, in the present state of -our knowledge, cannot come immediately under our attention. We are -compelled to reserve our limited space for those branches of science -which we are enabled to connect with the great natural operations -constantly going on around us. Many of these more abstruse results -will, however, receive some incidental notice when we come to examine -the operation of the combined physical forces on matter. - -We see in light a principle which, if it has not its source in the -sun, is certainly dependent upon that luminary for its manifestations -and powers. From that “fountain of light” we find this principle -travelling to us at a speed which almost approaches the quickness of -thought itself; yet by the refinements of science we have been enabled -to measure its velocity with the utmost accuracy. The immortal poet of -our own land and language, in his creations of Ariel, that “tricksy -spirit,” who could creep like music upon the waters, and of the -fantastic Puck, who could girdle the earth in thirty minutes, appears -to have approached to the highest point to which mere imagination could -carry the human mind as to the powers of things ethereal. Science has, -since then, shown to man that this “spirit, fine spirit,” was a laggard -in his tasks, and a gross piece of matter, when compared with the -subtile essences which man, like a nobler Prospero, has now subdued to -do him service. - -Light is necessary to life; the world was a dead chaos before its -creation, and mute disorder would again be the consequence of its -annihilation. Every charm which spreads itself over this rolling globe -is directly dependent upon luminous power. Colours, and probably, -forms, are the result of light; certainly the consequence of solar -radiations. We know much of the mysterious influences of this great -agent, but we know nothing of the principle itself. The solar beam has -been tortured through prismatic glasses and natural crystals; every -chemical agent has been tried upon it, every electrical force in the -most excited state brought to bear upon its operations, with a view -to the discovery of the most refined of earthly agencies; but it has -passed through every trial without revealing its secrets, and even the -effects which it produces in its path are unexplained problems, still -to tax the intellect of man. - -Every animal and every plant alike proclaim that life and health are -due to light; and even the crystallizing forms of inorganic matter, by -bending towards it, confess its all-prevailing sway. From the sun to -each planet revolving around that orb, and to the remotest stars which -gleam through the vast immensity of heaven, we discover this power -still in its brightness, giving beauty and order to these unnumbered -creations; no less completely than to this small island of the universe -which we call our Earth. Through every form of matter we can mark -its power, and from all, we can, under certain conditions, evoke it -in lustre and activity. Over all and through all light spreads its -ethereal force, and manifests, in all its operations, powers which -might well exalt the mind of Plato to the idea of an omniscient and -omnipresent God. Science, with her Ithuriel wand, has, however, shown -that light is itself the effect of a yet more exalted cause, which we -cannot reach. - -Indeed, the attentive study of the fine abstractions of science lifts -the mind from the grossness of matter, step by step, to the refinements -of immateriality, and there appear, shadowed out beyond the physical -forces which man can test and try, other powers still ascending, until -they reach the Source of every good and every perfect gift. - - -FOOTNOTES: - -[84] “These--oxygen, hydrogen, nitrogen, and carbon--are the four -bodies, in fact, which, becoming animated at the fire of the sun, -the true torch of Prometheus, approve themselves upon the earth -the eternal agents of organisation, of sensation, of motion and of -thought.”--Dumas, _Leçons de Philosophie Chimique_, p. 100. Paris, 1837. - -[85] It will be found in examining any of the works of the -alchemists,--particularly those of Geber, _De inveniendi arte Auri et -Argenti_, and his _De Alchemiâ_; Roger Bacon’s _Opus Majus, or Alchymia -Major_; Helvetius’ _Brief of the Golden Calf_; or Basil Valentine’s -_Currus Triumphalis_,--that in the processes of transmutation the solar -light was supposed to be marvellously effective. In Boyle’s _Sceptical -Chemist_ the same idea will be found pervading it. - -Amid all their errors, the alchemists were assiduous workmen, and to -them we are indebted for numerous facts. Of them, and of their age, as -contrasted with our own, Gibbon remarks:--“Congenial to the avarice -of the human heart, it was studied in China, as in Europe, with equal -eagerness and equal success. The darkness of the middle ages ensured -a favourable reception to every tale of wonder; and the revival of -learning gave new vigour to hope, and suggested more specious arts -of deception. Philosophy, with the aid of experience, has at length -banished the study of alchemy; and the present age, however desirous of -riches, is content to seek them by the humbler means of commerce and -industry.”--_Decline and Fall_, vol. ii. p. 137. - -[86] On the two theories the following maybe consulted:--Young, -_Supplement to Encyclopædia Britannica_, article _Chromatics_; -Fresnel, _Supplément à la Traduction Française de la 5ième édition du -Traité de Chimie de Thomson_, par Riffault, Paris, 1822; Herschel’s -Article, _Light_, in the Encyclopædia Metropolitana, and the French -Translation of it by Quetelet and Verhulst; Airy’s _Tract on the -Undulatory Theory_, in his Tracts, 2nd edition, Cambridge, 1831; Powel, -_The Undulatory Theory applied to Dispersion_, &c. p. 184; Lloyd’s -_Lectures_, Dublin, 1836-41; Cauchy, _Sur le Mouvement des Corps -élastiques_, Mémoires de l’Institut, 1827, vol. ix. p. 114; _Théorie de -la Lumière_, Ibid. vol. x. p. 293; M’Cullagh, _On Double Refraction_, -Ibid., vol. xvi.; _Geometrical Propositions applied to the Wave Theory -of Light_, Ibid., vol. xvii.; Sir David Brewster’s papers in the -Transactions of the Royal Society of Edinburgh, and the Philosophical -Magazine. - -[87] _Results of Astronomical Observations made during the years -1834-38, at the Cape of Good Hope, &c._ By Sir John Herschel, Bart., -K.H., D.C.L., F.R.S.--“In the contemplation of the infinite, in number -and in magnitude, the mind ever fails us. We stand appalled before this -mighty spectre of boundless space, and faltering reason sinks under the -load of its bursting conceptions. But, placed as we are on the great -locomotive of our system, destined surely to complete at least one -round of its ethereal course, and learning that we can make no apparent -advance on our sidereal journey, we pant with new ardour for that -distant bourne which we constantly approach without the possibility -of reaching it. In feeling this disappointment, and patiently bearing -it, let us endeavour to realise the great truth from which it flows. -It cannot occupy our mind without exalting and improving it.”--_Sir D. -Brewster_: North British Review. - -[88] For examples of this, consult Graham’s _Elements of Chemistry_; -Brande’s _Manual of Chemistry_; or, indeed, any work treating of the -science. The formation of ink, by mixing two colourless solutions, -one of gallic acid and another of sulphate of iron, may be taken as a -familiar instance. - -[89] Sir John Herschel, in his paper _On the Chemical Action of the -Rays of the Solar Spectrum on Preparations of Silver_, remarks that, -“it may seem too hazardous to look for the cause of this very singular -phenomenon in a real difference between the chemical agencies of those -rays which issue from the central portion of the sun’s disc, and those -which, emanating from its borders, have undergone the absorptive -action of a much greater depth of its atmosphere; and yet I confess -myself somewhat at a loss what other cause to assign for it. It must -suffice, however, to have thrown out the hint; remarking only, that -I have other, and, I am disposed to think, decisive evidence (which -will find its place elsewhere) of the existence of an absorptive solar -atmosphere, extending beyond the luminous one. The breadth of the -border, I should observe, is small, not exceeding 0·5 or 1/7 part of -the sun’s radius, and this, from the circumstances of the experiment, -must necessarily err in excess.”--Philosophical Transactions, 1840. - -[90] _Experiments and Observations on some Cases of Lines in the -Prismatic Spectrum, produced by the passage of Light through Coloured -Vapours and Gases, and from certain Coloured Flames._ By W. A. -Miller, M.D., F.R.S., Professor of Chemistry in King’s College, -London.--Philosophical Magazine, vol. xxvii. - -[91] _Report on the Mollusca and Radiata of the Ægean Sea, and on their -distribution, considered as bearing on Geology._ By Edward Forbes, -F.R.S., &c.--Reports of the British Association, vol. xii. Professor -Forbes remarks:--“A comparison of the testacea, and other animals of -the lowest zones, with those of the higher, exhibits a very great -distinction in the hues of the species, those of the depths being, for -the most part, white or colourless, while those of the higher regions, -in a great number of instances, exhibit brilliant combinations of -colour. The results of an enquiry into this subject are as follows:-- - -“The majority of shells of the lowest zone are white or transparent; if -tinted rose is the hue, a very few exhibit markings of another colour. -In the seventh region, white species are also very abundant, though -by no means forming a proportion so great as the eighth. Brownish -red, the prevalent hue of the brachiopoda, also gives a character -of colour to the fauna of this zone; the crustacea found in it are -red. In the sixth zone the colours become brighter, reds and yellows -prevailing,--generally, however, uniformly colouring the shell. In -the fifth region many species are banded or clouded with various -combinations of colours, and the number of white species has greatly -diminished. In the fourth, purple hues are frequent, and contrasts of -colour common. In the second and third, green and blue tints are met -with, sometimes very vivid; but the gayest combinations of colour are -seen in the littoral zone, as well as the most brilliant whites. - -“The animals of Testacea, and the Radiata of the higher zones, are -much more brilliantly coloured than those of the lower, where they are -usually white, whatever the hue of the shell may be. Thus the genus -_Trochus_ is an example of a group of forms mostly presenting the -most brilliant hues both of shell and animal; but whilst the animals -of such species as inhabit the littoral zone are gaily chequered with -many vivid hues, those of the greater depth, though their shells are -almost as brightly covered as the coverings of their allies nearer the -surface, have their animals, for the most part, of a uniform yellow or -reddish hue, or else entirely white. The chief cause of this increase -of intensity of colour as we ascend is, doubtless, the increased amount -of light above a certain depth.”--p. 172. - -[92] Ἁμὁρφωτα. _On the Epipolic Dispersion of Light_, being a paper -entitled, _On a case of Superficial Colour presented, by a homogeneous -liquid internally colourless_. By Sir J. F. W. Herschel, Bart, K.H., -F.R.S., &c.--_An epipolized beam of light_ (meaning thereby a beam -which has once been transmitted through a quiniferous solution, and -undergone its dispersing action) _is incapable of further undergoing -epipolic dispersion_. In proof of this the following experiment may be -adduced,-- - -A glass jar being filled with a quiniferous solution, a piece of plate -glass was immersed in it vertically, so as to be entirely covered, and -to present one face directly to the incident light. In this situation, -when viewed by an eye almost perpendicularly over it, so as to graze -either surface very obliquely, neither the anterior nor posterior face -showed the slightest trace of epipolic colour. Now, the light, at its -egress from the immersed glass, entered the liquid under precisely the -same circumstances as that which, when traversing the anterior surface -of the glass jar, underwent epipolic dispersion on first entering -the liquid. It had, therefore, lost a property which it originally -possessed, and could not, therefore, be considered _qualitatively_ the -same light.--Philosophical Transactions, vol. cxxxvi. - -[93] In connection with this view, the Newtonian theory should be -consulted, for which see--_A Letter of_ Mr. Isaac Newton, _Professor -of the Mathematicks in the University of Cambridge; containing his new -Theory about Light and Colors: sent by the Author to the Publisher, -from Cambridge, Feb. 6, 1671-72, in order to be communicated to the -Royal Society._ - -[94] In that admirable work, _The Physical Atlas_ of Dr. Berghaus, of -which a very complete edition by Alexander Keith Johnstone is published -in this country, the following order of the distribution of plants is -given:-- - - 1. The region of palms and bananas Equatorial zone. - 2. Tree ferns and figs Tropical zone. - 3. Myrtles and laurels Sub-tropical zone. - 4. Evergreen trees Warm temperate zone. - 5. European trees Cold temperate zone. - 6. Pines Sub-arctic zone. - 7. Rhododendrons Arctic zone. - 8. Alpine plants Polar zone. - -Consult Humboldt, _Essai sur la Géographie des Plantes_, Paris, -1807; _De Distributione Geographicâ Plantarum_, Paris, 1817. Schouw, -_Grundzüge der Pflanzengeographie_. Also his _Earth, Plants, and Man_; -translated by Henfrey, in _Bohn’s Scientific Library_. Lamouroux, -_Géographie Physique_. _The Plant, a Biography_: by Schleiden; -translated by Henfrey. _Physical Geography_: by Mrs. Somerville. - -[95] Fraunhofer’s measure of illuminating power is as follows:-- - - At the 22nd degree of the red 0·032 - " 34th degree of the red 0·094 - " 22nd degree of the orange 0·640 - " 10th degree of the yellow 1·000 - " 42nd degree of the yellow 0·480 - " 2nd degree of the blue 0·170 - " 16th degree of the indigo 0·031 - " 43rd degree of the violet 0·0056 - -[96] Herschel, _On the Action of Crystallized Bodies on Homogeneous -Light, and on the causes of the deviation from Newtons scale in -the tints which many of them develope on exposure to a polarized -ray_.--Phil. Trans., vol. cx., p. 88. - -[97] _On the Nature of Light and Colours_: Lecture 39, in Young’s -_Lectures on Natural Philosophy_, Kelland’s Edition, p. 373, and the -authorities there quoted. - -[98] Brewster’s _Optics_: Lardner’s Cabinet Cyclopædia. Herschel, _On -Light_: Encyclopædia Metropolitana. - -[99] Malus, _Sur une Propriété de la Lumière Réfléchie_: Mémoires -d’Arcueil. Numerous memoirs by Sir David Brewster, in the Philosophical -Transactions. - -[100] Bartholin, _On Iceland Crystals_: Copenhagen, 1669. _An -Accompt of sundry Experiments made and communicated by that Learn’d -Mathematician_ Dr. Erasmus Bartholin, _upon a Chrystal like Body sent -to him out of Island_: in connection with which Dr. Matthias Paissenius -writes:--The observations of the excellent Bartholin upon the Island -Chrystal are, indeed, considerable, as well as painful. We have here, -also, made some tryals of it upon a piece he presented me with, which -confirm his observations. Mean time he found it somewhat scissile and -reducible by a knife into thin laminas or plates, which, when single, -shew’d the object single, but laid upon one another shew’d it double; -the two images appearing the more distant from one another, the -greater the number was of those thin plates laid on one another. With -submission to better judgements I think it to be a kind of Selenites. -Some of our curious men here were of opinion that the Rhomboid figure -proper to this stone was the cause of the appearances doubled thereby. -But having tryed whether in other transparent bodies of the like figure -the like would happen, we found no such thing in them, which made us -suspect some peculiarity in the very Body of the stone.--Phil. Trans. -for 1670, vol. v. - -[101] _On the Application of the Laws of Circular Polarization to the -Researches of Chemistry_: by M. Biot.--Nouvelles Annales du Muséum -d’Histoire Naturelle, vol. iii., and Scientific Memoirs, vol. i. -p. 600. _On Circular Polarization_: by Dr. Leeson.--Memoirs of the -Chemical Society. - -[102] In Sir David Brewster’s Treatise _On Optics_, chap, xviii., _On -Polarization_, the best arrangements for a polarizing apparatus will be -found described. - -[103] This beautiful application was recently made by Professor -Wheatstone, the particulars of which will be found in his interesting -communication.--_On a means of determining the apparent Solar Time -by the diurnal changes of the Plane of Polarization at the Northern -Pole of the Sky_: Report of the Eighteenth Meeting of the British -Association. - -[104] _On the Polarization of the Chemical Rays of Light_: by John -Sutherland, M.D., in which the author refers to the following -experiment of M. J. E. Bérard--“I received the chemical rays directed -into the plane of the meridian on an unsilvered glass, under an -incidence of 35° 61'. The rays reflected by the first glass were -received upon a second, under the same incidence. I found that when -this was turned towards the south, the muriate of silver exposed to -the invisible rays which it reflected was darkened in less than half -an hour; whereas, when it was turned towards the west, the muriate -of silver exposed in the place where the rays ought to have been -reflected, was not darkened, although it was left exposed for two -hours. It is consequently to be presumed that the chemical rays can -undergo double refraction in traversing certain diaphanous bodies; and -lastly, we may say that they enjoy the same physical properties as -light in general.”--Philosophical Magazine, vol. xx. - -Dr. Leeson has stated that Daguerreotype pictures can be taken more -readily under the influence of polarized light, than by ordinary -radiation. - -[105] _On the Magnetization of Light, and the Illumination of Magnetic -Lines of Force_: by Michael Faraday, D.C.L., F.R.S.--Philosophical -Transactions, vol. cxxxvii.--The following remarks are to the point -of doubt referred to in the text.--“The magnetic forces do not act -on the ray of light directly and without the intervention of matter, -but through the mediation of the substance in which they and the ray -have a simultaneous existence; the substances and the forces giving to -and receiving from each other the power of acting on the light. This -is shown by the non-action of a vacuum, of air or gases, and it is -also further shown by the special degree in which different matters -possess the property. That magnetic force acts upon the ray of light -always with the same character of manner, and in the same direction, -independent of the different varieties of substance, or their states -of solid or liquid, or their specific rotative force, shows that -the magnetic force and the light have a direct relation; but that -substances are necessary, and that these act in different degrees, -shows that the magnetism and the light act on each other through the -intervention of the matter. Recognising or perceiving _matter_ only by -its powers, and knowing nothing of any imaginary nucleus abstract from -the idea of these powers, the phenomena described must strengthen my -inclination to trust in the views I have advanced in reference to its -nature.”--Phil. Mag. vol. xxiv. - -[106] The invention of the camera obscura certainly belongs to -Giambattista Porta, and is described in his _Magiæ Naturalis, sive de -Miraculis Rerum Naturalium, Libri Viginti_; Antwerp, 1561. An English -translation made in 1658 exists, but I have not seen it. - -Hooke, in one of the earliest volumes of the Philosophical -Transactions, describes as new many of the phenomena mentioned by -Porta, and particularly the images of the dark chamber. - -[107] Herschel, _On Light_,--Encyclopædia Metropolitana. - -[108] “I would here observe that a consideration of many such -phenomena (the obliteration and revival of photographic drawings) has -led me to regard it as not impossible that the retina itself may be -_photographically_ impressed by strong light, and that some at least -of the phenomena of visual spectra and secondary colours may arise -from the sensorial perception of actual changes in progress in the -physical state of that organ itself subsequent to the cessation of the -direct stimulant.”--_On the action of the Rays of the Solar Spectrum on -Vegetable Colours, &c._: by Sir J. F. W. Herschel, Bart. - -[109] Dumeril. - -[110] _Theory of Colours_: by Goethe; translated by Eastlake. - -[111] See Tuckey’s Narrative of the Expedition of the Zaire. - -[112] The most complete examination of this subject will be found in -two Memoirs:-- - -1. _Experiments and observations on the light which is spontaneously -emitted with some degree, of permanency from various bodies._--Phil. -Trans., vol. xc. - -2. _A continuation of the above, with some experiments and observations -on solar light, when imbibed by Canton’s phosphorus_: by Nathaniel -Hulm, M.D.--Phil. Trans., vol. xci.; and in the _Monograph of the -British Naked-eyed Medusæ_, by Professor Edward Forbes (published -for the Ray Society). See Wilson’s note to the account of _Pennalata -phosphorea_ in Johnston’s Zoophytes, 2nd edition. - -[113] _A General Outline of the Animal Kingdom_: by Thomas Rymer Jones, -F.L.S.--Acalephæ, p. 64. _Lettre à M. Dumas sur la Phosphorescence des -Vers luisants_: par M. Ch. Matteucci.--Annales de Chimie, vol. ix. p. -71, 1843. - -[114] _Memoirs of Benvenuto Cellini--Bohn’s Standard Library._ See also -his Treatise on his Art as a Sculptor and Engraver. Florence, 1568. 4to. - -[115] _Phosphorescence of the Diamond_: by M. Reiss (Revue Scientifique -et Industrielle, vol. xxiii. p. 185).--“The diamond, phosphorescent -by insulation, lost rapidly its phosphorescence when submitted to the -action of the red rays of the solar spectrum. On the contrary, the -blue rays are those which render the diamond the most luminous in -the dark. It is probable that the phosphorescence produced by heat -is equally diminished by the action of the red rays of the solar -spectrum.” Giovanni Battista Beccaria published his experiments in -1769. See Priestley’s _History of Electricity_; and _On the Effects -of Electricity upon Minerals which are Phosphorescent by Heat_; and -_Further Experiments on the communication of Phosphorescence and Colour -to bodies of Electricity_; by Thomas J. Pearsall.--Journal of the -Royal Institution of Great Britain, Oct. 1830, Feb. 1831.--These two -memoirs contain the most complete set of experiments on this subject -which have yet been made; see _Placidus Heinrich_, _Phosphorescenz -der Körper_, vol. iv.; Gmelin’s _Handbuch der Chemie_, part 1.;--_On -the Phosphorescence of Minerals_, Brewster: Edinburgh Philosophical -Journal, vol. i. p. 137.;--_The Aërial Noctiluca, or some New -Phenomena, and a process of a factitious self shining substance_: -Boyle’s Works, vol. iv. - -[116] _Des Effets produits sur les corps par les Rayons Solaires_: par -M. Edmond Becquerel.--Annales de Chimie, vol. ix. p. 257. 1843. - -M. Becquerel has applied the term _phosphorogénique_ to those rays -producing phosphorescence. - - - - -CHAPTER VIII. - -ACTINISM--CHEMICAL RADIATIONS. - - The Sun-ray and its Powers--Darkening of Horn Silver--Niepce’s - Discovery--Prismatic Spectrum--Refrangibility of Light, Heat, and - Actinism--Daguerre’s Discovery--Photography--Chemical Effects - produced by Solar Radiations--Absorption of Actinism--Phenomena of - the Daguerreotype--Chemical Change produced upon all Bodies--Power - of Matter to restore its Condition--Light protects from Chemical - Change--Photographs taken in Darkness--Chemical Effects of Light - on organized Forms--Chemical Effects of Solar Heat--Influence - of Actinism on Electricity--Radiations in Darkness--Moser’s - Discoveries, &c. - - -Heat and light are derived from the sun, and we have attempted to show, -not only that the phenomena of these two principles are different, but -that they can scarcely, in the present condition of our knowledge, be -regarded as modified manifestations of _one_ superior power. Associated -with these two remarkable elements, others may exist in the solar rays. -Electrical phenomena are certainly developed by both heat and light, -and peculiar electric changes are produced by exposure to sunshine. -Electricity may be merely _excited_ by the solar rays, or it may -_flow_ like light from the sun. Chemical action may be only due to the -disturbance of some diffused principle; or it may be directly owing to -some agency which is radiated at once from the sun. - -A sun ray is a magical thing: we connect it in our fancy with the -most ethereal of possible creations. Yet in its action on matter it -produces colour; it separates the particles of solid masses farther -from each other, and it breaks up some of the strongest forces of -chemical affinity. To modern science is entirely due the knowledge -we have gained of the marvellous powers of the sunbeam; and it has -rendered us familiar with phenomena, to which the incantation scenes -of the Cornelius Agrippas of the dark ages were but ill-contrived -delusions, and their magic mirrors poor instruments. The silver tablets -of the photographic artist receiving fixed impressions of the objects -represented in the dark chamber by a lens, are far superior as examples -of natural magic. - -In the dark ages, or rather as the earliest gleams of the bright -morning of inductive research were dispelling the mists of that -phantom-peopled period, it was observed, for the first time, that the -sun’s rays turned a white compound black. Man must have witnessed, long -before, that change which is constantly taking place in all vegetable -colours: some darkening by exposure to sunlight, while others were -bleached by its influence. Yet those phenomena excited no attention, -and the world knew nothing of the mighty changes which were constantly -taking place around them. The alchemists--sublime pictures of credulous -humanity--toiling in the smoke of their secret laboratories, waiting -and watching for every change which could be produced by fire, or by -their “royal waters,” caught the first faint ray of an opening truth; -and their wild fancy, that light could change silver into gold, if they -but succeeded in getting its subtile beams to interpenetrate the metal, -was the clue afforded to the empirical philosopher to guide him through -a more than Cretan labyrinth.[117] - -The first fact recorded upon this, point was, that horn silver -blackened when exposed to the light. Without doubt many anxious -thoughts were given by these alchemists to that fact. Here was, as it -appeared, a mixing up of light and matter, and behold the striking -change! It was a step towards the realization of their dreams. Alas! -poor visionaries! in pursuing an ideality they lost the reality which -was within their grasp. - -Truths come slowly upon man, and long it is before these angel visits -are acknowledged by humanity. The world clings to its errors, and -avoids the truth, lest its light should betray their miserable follies. - -At length a man of genius announced that “_No substance can be -exposed to the sun’s rays without undergoing a chemical change_;” -but his words fell idly upon the ear. His friends looked upon his -light-produced pictures as singular; they preserved them in their -cabinets of curiosities; but the truths which he enunciated were soon -forgotten. Howbeit his words were recorded, and it is due to the -solitary experimentalist of Châlons on the Saône, to couple the name -of Niepce with the discovery of a fact which is scarcely second to -the development of the great law of universal gravitation.[118] But -an examination awaits us, which, for its novelty, has more charms -than most branches of science, and which, for the extensive views it -opens to the inquirer, has an interest in nowise inferior to any other -physical investigation. - -The prismatic spectrum affords us the means of examining the conditions -of the solar rays with great facility. In bending the ray of white -light out of its path, by means of a triangular piece of glass, we -divide it in a remarkable manner. We learn that heat is less refracted -by the glass than the other powers; we find the maximum point of the -calorific rays but slightly thrown out of the right line, which the -solar pencil would have taken, had it not been interrupted by the -prism; and the thermic action is found to diminish with much regularity -on either side of this line. We discover that the luminous power is -subject to greater refraction, and that its maximum lies considerably -above that of heat; and that, in like manner, on each side the light -diminishes, producing orange, red, and crimson colours below the -maximum point, and green, blue, and violet above it. Again, we find -that the radiations which produce chemical change are more refrangible -than either of the others, and the maximum of this power is found -at the point where light rapidly diminishes, and where scarcely any -heat can be detected: it extends in full activity, above its maximum, -to a considerable distance, where no trace of light under ordinary -conditions exists, and below that point, until light, appearing to -act as an interfering agent, quenches its peculiar properties. These -are strong evidences that _light_ and _actinism_--as this principle -has been named--are not identical: and we may separate them most -easily and effectually from each other. Certain glasses, stained dark -blue, with oxide of cobalt, admit scarcely any light; but they offer -no interruption to the passage of actinism or the chemical rays; on -the contrary, a pure yellow glass, or a yellow fluid, which does not -sensibly reduce the intensity of any one colour of the chromatic band -of luminous rays, completely cuts off this chemical principle, whatever -it may be. In addition to these, there are other results which we shall -have to describe, which prove that, although associated in the solar -beam, light and actinism are in constant antagonism. - -When Daguerre first published his great discovery, the European public -regarded his metal tablets with feelings of wonder: we have grown -accustomed to the beautiful phenomena of this art, and we have become -acquainted with a number of no less beautiful processes on paper, -all of which, if studied aright, must convince the most superficial -thinker, that a world of wonder lies a little beyond our knowledge, -but within the reach of industrious and patient research. Photography -is the name by which the art of sun-painting will be for ever known. -We regard this as unfortunate, conveying as it does a false idea,--the -pictures not being _light-drawn_. Could we adopt the name given -by Niepce to the process, the difficulty would be avoided, since -Heliography involves no hypothesis, and strictly tells the undeniable -truth, that our pictures are _sun-drawn_. That pictures can be produced -by the rays from artificial sources, presents no objection to this; -these rays were still originally derived from the sun. - -By whatever name we determine to convey our ideas of these phenomena, -it is certain that they involve a series of effects which are of the -highest interest to every lover of nature, and of the utmost importance -to the artist and the amateur. By easy manipulation we are now enabled -to give permanence to the charming pictures which are produced by means -of that pleasing invention of Baptista Porta, the _Camera Obscura_. Any -image, which being refracted by the lens of this instrument falls upon -the table in its dark chamber, may be secured with its most delicate -gradations of shadows, upon either a metallic or a paper tablet. - -But let us proceed to the examination of a few of the more striking -phenomena of these chemical changes. To commence with some of the more -simple but no less important results. - -Chlorine and hydrogen will not unite in darkness, nor will chlorine and -carbonic oxide; but, if either of those gaseous mixtures is exposed to -sunshine, they combine rapidly, and often with explosion. A solution of -the sulphate of iron in ordinary water may be preserved for a long time -in the dark without undergoing any change; expose it to the sunshine, -and a precipitation of oxide of iron is very rapidly produced. The -mineral chameleon, the _manganesiate of potash_ in solution, is -almost instantly decomposed in daylight; but it is a long time before -it undergoes any change in darkness. The same thing occurs with a -combination of platinum and lime: indeed, it appears that precipitation -is at all times, and under all circumstances, accelerated by the solar -rays. As these precipitations are in exact agreement with the quantity -of actinic radiation to which the solutions have been exposed, we may -actually weigh off the relative quantities, representing in grains the -equivalent numbers to the amount of actinism which has influenced the -chemical compound.[119] - -We have evidence which appears to prove that this chemical agent may -be absorbed by simple bodies, and that by this absorption an actual -change of condition, is produced, in many respects analogous to those -allotropic changes which we have previously considered. Chlorine, in -its ordinary state, does not combine with hydrogen in the dark. If we -employ the yellow medium of chlorine gas, for the purpose of analyzing -the sun’s rays previously to their falling upon some chemical compound -which is sensitive to actinic power, we shall find that the chlorine -obstructs all this actinism, and, however unstable the compound, -it remains unchanged. But the chlorine gas which has interrupted -this wonderful agent, appears to have absorbed it, and it is so far -altered in its constitution that _it will unite with hydrogen in the -dark_.[120] In like manner, if, of two portions of the same solution -of sulphate of iron, one is kept in the dark and the other exposed -to the sunshine, it will be found that the solution which has been -exposed will precipitate gold and silver from their combinations much -more speedily than that which has been preserved in darkness--the -temperature and every other condition being the same. - -The phenomena of the Daguerreotype involve many strange conditions. -A plate of silver, on which a slight chemical action has been -established by the use of iodine, is exposed to the lenticular image -in the camera obscura. If allowed to remain under the influence of -these radiations for a sufficient length of time, a faithful picture -of the illuminated objects is delineated on the plate, as shown by -the visible decomposition and darkening of the iodized surface. The -plate is not, however, in practice allowed to assume this condition; -after an exposure of a few seconds the radiant influence is cut off, -and the eye cannot detect any evidence of change upon the yellow -plate. It is now exposed to the vapour of mercury, and that metal in -a state of exceedingly fine division is condensed upon the plate; -but the condensation is not uniformly spread upon its face. The -deposit of mercurial vapour is in exact proportion to the amount of -chemical action produced. Is the change, by which this peculiar power -of condensation is effected, a chemical, calorific, electrical, or -merely a molecular one? The evidences, at present, are not sufficient -to determine the question. It has lately been suggested, that the -mercury acts chemically only, and effects the full decomposition of -the iodide of silver; and that the picture is due to this, and not to -the deposition actually of the mercury vapour. In all probability we -have the involved action of several forces. We have some experiments -which show, clearly enough, that mercury is deposited in proportions -which correspond with the intensity of solar action. A chemically -prepared surface is not necessary to exhibit this result. A polished -plate of metal, of glass, of marble, or a piece of painted wood, being -partially exposed, will, when breathed upon, or presented to the action -of mercurial vapour, show that a disturbance has been produced upon -the portions which were illuminated, whereas no change can be detected -upon the parts which were kept in the dark. It was thought, until -lately, that a few chemical compounds, such as the iodide of silver, -the material employed in the Daguerreotype and Calotype,--chloride of -silver, the ordinary photographic agent,--a few salts of gold, and one -or two of lead and iron, were the only materials upon which these very -remarkable changes were produced. We now know that it is impossible -to expose any body, simple or compound, to the sun’s rays, without -its being influenced by this chemical and molecular disturbing power. -To take our examples from inorganic nature, the granite rock which -presents its uplifted head in firmness to the driving storm, the stones -which genius has framed into forms of architectural beauty, or the -metal which is intended to commemorate the great acts of man, and which -in the human form proclaims the hero’s deeds and the artist’s talent, -are all alike destructively acted upon during the hours of sunshine, -and, but for provisions of nature no less wonderful, would soon perish -under the delicate touch of the most subtile of the agencies of the -universe. - -Niepce was the first to show that all bodies which underwent this -change during daylight possessed the power of restoring themselves -to their original conditions during the hours of night, when this -excitement was no longer influencing them. Resins, the Daguerreotype -plate, the unprepared metal tablet, and numerous photographic -preparations, prove this in a remarkable manner.[121] - -The picture which we receive to-day, unless we adopt some method of -securing its permanency, fades away before the morrow, and we try to -restore it in vain. With some of our chemical preparations this is -very remarkably shown, but by none in so striking a manner as by paper -prepared with the iodide of platinum, which, being impressed with an -image by heliographic power, which is represented by dark brown tints, -restores itself in the dark, in a few minutes, to its former state of -a yellow colour, and recovers its sensibility to sunshine.[122] The -inference we alone can draw from all the evidences which the study -of actino-chemistry affords, is, that the hours of darkness are as -necessary to the inorganic creation as we know night and sleep to be -to the organic kingdom. But we must not forget that there does exist -in the solar rays a balance of forces which materially modifies the -amount of disturbing influence exerted by them on matter. Not only do -we find that the chemical action is not extended over the whole length -of the prismatic spectrum, but we discover that over spaces, which -correspond with the maximum points of light and heat, a protective -action is exerted. That is, that highly sensitive photographic agents, -which blacken rapidly under exposure to diffused daylight, are entirely -protected from change in full sunshine, if at the same time as a strong -light is thrown upon them by reflection, the yellow and extra red rays -are brought to bear upon their surface. Not only so, but by employing -media which will cut off all the chemical rays of the spectrum, -admitting freely at the same time the luminous and calorific rays, we -find that a protected band, the length of the spectrum, remains white, -whilst every other portion has blackened.[123] - -Among the many curious instances of natural magic, none are more -remarkable than an experiment not long since proposed, by which -Daguerreotype pictures may be taken in absolute darkness to the human -eye. This is effected in the following manner:--A large prismatic -spectrum is thrown upon a lens fitted into one side of a dark chamber; -and as we know that the actinic power resides in great activity beyond -the violet ray, where there is no light, the only rays which we allow -to pass the lens into the chamber are those which are extra-spectral -and non-luminous. These are directed upon, any white object, and from -that object radiated upon a highly sensitive plate in a camera obscura. -Thus a copy of the subject will be obtained by the agency of radiations -which produce no sensible effect upon the optic nerve. This experiment -is the converse of those which show us that we may illuminate any -object with the strongest sunlight which has passed through yellow -glass, the yellow solution of sulphuret of calcium, or of the -bichromate of potash--these being non-transparent to the chemical -rays--and yet fail to secure any Daguerreotype copy of it, even upon -the most exquisitely sensitive plate. Indeed, the image of the sun -itself, when setting through an atmosphere which reduces its light to -a red or rich yellow colour, not only produces no chemical change, -but protects an iodized plate from it; and whilst every other part -of the tablet gives a picture of surrounding objects in the ordinary -character, the bright sun itself is represented by a spot upon which -no change has taken place.[124] In tropical climes, where a brilliant -sun is giving the utmost degree of illumination to all surrounding -objects, all photographic preparations are acted upon relatively more -slowly than in the climate of England, where the light is less intense. -As a remarkable instance of this fact, a circumstance may be mentioned, -which is curiously illustrative of the power of light to interfere with -actinism:-- - -A gentleman, well acquainted with the Daguerreotype process, obtained -in the city of Mexico all the necessary apparatus and chemicals, -expecting, under the bright light and cloudless skies of that climate, -to produce pictures of superior excellence. Failure upon failure was -the result; and although every care was used, and every precaution -adopted, it was not until the rainy season set in that he could secure -a good Daguerreotype of any of the buildings of that southern city. - -The first attempts, which were made at the instigation of M. Arago, -by order of the French Government, to copy the Egyptian tombs and -temples, and the remains of the Aztecs in Central America, were -failures. Although the photographers employed succeeded to admiration -in Paris, in producing pictures in a few minutes, they found often that -an exposure of an hour was insufficient under the bright and glowing -illumination of a southern sky. - -Experiments with the spectrum have been made in different latitudes, -and it is found, that, as we proceed towards the equator, a band which -is always left unchanged, corresponding exactly with the rays of -greatest illuminating power, regularly enlarges in size, thus proving -the increase of light over actinism--and the interfering power of the -former. - -By increasing the sensibility of the photographic preparation, this -difficulty is overcome, and particularly when any organic compound -enters into the preparation. So that we are now enabled to copy nature -in all her varying moods, whether we employ our photographic tablets in -temperate Europe, or in tropical Africa. - -The degree of sensibility which has been attained is remarkable. Mr. -Fox Talbot, by uniting a process devised by Dr. Woods, of Parsonstown, -and another which was first introduced by the author of this volume, -and combining them with an ether, obtains a most unstable compound, -which he thus employs. A glass plate is covered with albumen united -with the above solution, and then with nitrate of silver: this forms -the sensitive surface. The plate being placed in the dark, in a camera, -it is so adjusted that the image of a printed bill fixed upon a wheel -may fall upon it when uncovered, and the wheel illuminated. The wheel -is made to revolve with the utmost rapidity, in a perfectly dark -room, and the sensitive plate uncovered. Then the whirling bill is -illuminated for an inappreciably short space of time by the discharge -of a Leyden jar. Notwithstanding the rapid rate at which the pointed -paper is moving, and the instantaneous nature of the illumination--a -miniature flash of lightning--the bill is found to be copied with -unfailing fidelity upon the photographic plate. It unfortunately -happens, that the preparation by which this extraordinary degree of -sensibility is obtained, is very uncertain in its action--and hence it -is not generally useful; but here we have the evidence to show that -at a speed as rapid as that of a rifle-ball an impression may be made -upon a photographic plate. There are, however, some new processes which -promise eventually to rival the above for sensibility, and to be by no -means of difficult manipulation. Of this character is the collodion -process. The gun cotton dissolved in ether possesses some very great -accelerating properties, and in combination with the silver salts, and -one of the vegetable acids, it forms a sensitive surface upon which -pictures may be obtained in less than a second of time. - -Colour, natural colour too, has been very decidedly secured. The sun -has been solicited to display his palette, and the answer has been a -picture in which colour for colour in all their fidelity have been -impressed. The plate upon which this result has been obtained is of a -dark brown colour, and the chromatic variety is, as it were, eaten out -by the solar rays. These colours have not yet been permanently fixed -upon the plate employed, but from the temporary degree of fixedness -which has been obtained, we may fairly hope that in a short time colour -may be rendered as permanent on the productions of the photographer -as on those of the painter. It is a curious and striking fact, that -in the preparation of these plates, salts are used which give colours -to flame; and according to the colour which is produced by them when -burning, so, on the photographic plate, is that colour impressed -with greater intensity than the others. To what is this leading us? -Mysteries surround our advances on the domain of truth. We dare not -speculate upon them: the time of their full development will arrive. - -By the aid of this beautiful art, we are enabled to preserve the -lineaments of those who have benefited their race by their intellect, -or their heroism. We can hand down to future ages portraits of our own -Wellington, and the illustrious Arago, unerring in their truthfulness. -How great would be the joy of all, could we now obtain a daguerreotype -portrait of a Greek poet, or of a Roman philosopher, of a Sophocles, -or of a Seneca! How much discussion would be prevented did we possess -a calotype portrait of the Bard of Avon, or of the Philosopher of -Grantham! - -By the agency of those very rays which give life and brilliancy to the -laughing eye and the roseate cheek, we can at once correctly trace the -outline of the features we admire, with all those shadowy details which -give a reality to the “presentment.” The objects of our love may be for -ever present with us in these self-painted pictures. The vicious, whom -we would avoid, may be made known to us by this unerring painter. The -process which nature employs is perfect; the imperfections are those of -man, and these being few, he may soon learn to remedy. - -To the traveller, how valuable are the processes of photography! He -secures representations of those remains of temples which were in their -glory when Moses wrote. He copies by one operation a tomb at Karnac, -covered with myriads of hieroglyphics, or an inscribed stone in Arabia, -which it would occupy him days to trace. These he can carry to his home -and read at his leisure. The relics of hoar antiquity speaking to the -present of the past, and recording the histories of races which have -fleeted away like shadows, are thus preserved to tell their wondrous -tales. - -The admirer of nature may copy her arrangements with the utmost -fidelity. Every modulation of the landscape, each projecting rock or -beetling tor--the sinuous river in its rapid flow--the meandering -stream, “gliding like happiness away;” and the spreading plains -over which are scattered the homes of honest industry and domestic -peace, intermingled with the towers of those humble temples in which -simple-hearted piety delights to “bow the head and bend their knee;” -these, all of these, may, by the sunbeam which illuminates the whole, -be faithfully pencilled upon our chemical preparations. - -Our art enables us to do more even than this; we have but to present -our sensitive tablet to the moon, and she, by her own light, prints her -mountains and her valleys, and indicates with all truth the physical -conditions of her surface. - -Any reference to the _chemical agency_ of LIGHT--_the luminous rays_ as -distinguished from the _chemical and calorific rays_--has been avoided -until we came to the consideration of this particular question of -chemical change. - -Upon organic compounds, as, for instance, upon the colouring matter -of leaves and flowers, _light_ does exert a chemical power: and it -is found that vegetable colours are bleached, not by rays of their -own colour, but by those which are _complementary_ to them. A red dye -fades under the influence of a green ray, and a yellow under that of a -violet one, much more speedily than when exposed to rays of any other -colour; and this, it must be remembered, is due to the coloured ray -itself, and not to any _actinic_ power masked, as it were, behind the -colour, as is generally believed.[125] It was long a question whether -the decomposition of carbonic acid by plants was due to the luminous or -the chemical rays. It is now clearly established that the luminous rays -are the most active in producing this effect; which they do indirectly, -by exciting the vital powers of the organized structures. Therefore we -would refer this phenomenon of gaseous decomposition to a vital power -quickened by luminous excitement.[126] - -We have already noticed some chemical phenomena due to heat, -particularly those experiments of Count Rumford’s, which appeared to -him to prove that the chemical agency of the sun’s rays was due to its -calorific power. Certain chemical phenomena, we know, may be produced -by thermic action; but the only variety of thermo-chemical action which -connects itself immediately with the solar radiations, belongs to a -class of rays to which the name of _Parathermic_ has been given, and to -which the scorching, as it is called, of plants, the browning of the -autumnal leaves, and the ripening of fruits, appear to be due.[127] -When we come to the consideration of those physical phenomena which -belong to the growth of plants, all these peculiarities of solar action -must be attended to in detail. - -The manner in which we find the actinic power influencing electrical -action, also shows us that the equilibrium of forces is continued -through all the great principles of nature. If a galvanic arrangement -is made, by which small quantities of metals may be slowly precipitated -at one of the poles in the dark, and a similar arrangement be exposed -to sunshine, it will be found that no metal is deposited: the sun’s -rays have interfered with the decomposing power of the electrical -current. At the same time we learn, that by throwing a beam of light -upon a plate of copper which forms one of a galvanic pair, whilst -it is under the influence of an acidulated solution, an additional -excitation takes place, and the galvanometer will indicate the passage -of an increased current of electricity. These two dissimilar actions -appear enigmatical; but they may, there is no doubt, receive some -solution from the influence of different rays on the contrary poles -of the battery. One thing is quite evident,--electricity suffers a -disturbance of one order, by light; and an excitement of another by its -associated principles in the sunbeam. If a yellow glass is interposed -between the galvanic arrangement and the sun, the electro-chemical -precipitation goes on in the same manner as it would in perfect -darkness, and no extra excitement is produced upon the plates of the -battery. From this it would appear that actinism and not light is to be -regarded as the disturbing power.[128] It has already been shown that -yellow media possess the power of stopping back the chemical agent. - -We have already, detailed many of the peculiarities of the different -varieties of Phosphori, which would seem to be the result of light. -Phosphorescence is probably excited by those rays which produce -no direct effect upon the eye. If we spread sulphuret of calcium -upon paper, and expose it to the action of the solar spectrum, it -is found to glow (in the dark) only over those spaces occupied by -the violet rays and the ordinarily dark rays beyond them; proving -that the excitation necessary to the development of the phenomena -of phosphorescence is due to a class of rays distinct from the true -light-giving principle, and more nearly allied to that principle or -power which sets up chemical decomposition. Whether the fluorescent -rays, before mentioned, which are found so abundantly over the space -which produces the greatest phosphorescent effect, are active in -producing the phenomena, is as yet an unsolved problem. - -Vision and colour, calorific action, chemical change, molecular -disturbance, electrical phenomena, and phosphorescent excitation, all, -each one with a strange duality, are connected with the sunbeam. - -We find, when we receive solar spectra upon iodized plates, or on -several kinds of photographic paper, that a line, over which no action -takes place, is preserved at the top and bottom of the impressed image, -and in many cases along the sides also. The only way in which this can -be accounted for, as the spectrum represents the sun in a distorted -form, is by supposing that rays come from the edges of the sun of a -different character from those which proceed from the centre of that -orb.[129] - -Light from the centre of the solar disc is under different conditions -from that which comes from the edge of the sun: this is due to the -varying angle, which is presented to us by a circular body: calorific -action seems to be more strongly manifested when the envelope of -light, extending like an atmosphere to the sun, is thrown into great -agitation, and waves, and great hollows--solar spots--are produced. -There is some indication of the existence of a third condition on the -sun’s surface, to which probably belongs the mighty chemical power -which we call actinism. Electricity may be, as some have speculated, -the exciting agent; a constant and violent Aurora Borealis may exist on -the sun, and under the excitation of this force the others named may be -quickened into full activity. - -That actinism is one of the great powers of creation we have abundant -proof. Nearly all the phenomena of chemical change which have been -referred to light, are now proved to be dependent upon actinic power; -and beyond the influence which has been ascertained to be exerted by -it upon all inorganic bodies, we shall have occasion to show still -further the dependence of the vegetable and animal worlds upon its -agency. The influence of the solar beams on vegetation is proved by -common experience; the closer examination of its action on vegetable -life is reserved for the chapter devoted to its phenomena. Of its -influence on animals nothing is very correctly known; but some early -experiments prove that they, like other organised bodies, are subject -to all the radiant forces, as indeed, independent of experiment, every -observation must teach. Certain it is, that organisation can take place -only where the sun’s rays can penetrate: where there is unchanging -darkness, there we find all the silence of death. Prometheus stole -fire from heaven, and gave the sacred gift to man, as the most useful -to him of all things in his necessities: by the aid of it he could -temper the severities of climate, render his food more digestible and -agreeable, and illuminate the hours of darkness. So says the beautiful -fiction of the Grecian mind,--which appears as the poetic dream or -prophetic glance of a gifted race, who felt the mysterious truth -they were yet unable to describe. Pheaton and Apollo are only other -foreshadowings of the creative energies which dwell in the glorious -centre of our universe. The poetry of the Hellenic people ascended -above the littlenesses of merely human action, and sought to interpret -the great truths of creation. Reflective, they could not but see that -some mysterious powers were at work around them; imaginative, they gave -to fine idealisations the government of those inexplicable phenomena. -Modern science has shown what vastly important offices the solar rays -execute, and that the principles discovered in a sunbeam are indeed the -exciters of organic life, and the disposers of inorganic form. - -It must not be forgotten that we have already alluded to a speculation -which supposes this actinic influence to be diffused through all -nature, to be indeed the element to which chemical force in all its -forms is to be referred, and that it is merely excited by the solar -rays. This hypothesis receives some support from the very peculiar -manner in which chemical action once set up is carried on, independent -of all extraneous excitement, after the first disturbance has been -produced. If any of the salts of gold are exposed in connection with -organic matter, as on paper, to sunshine for a moment, an action is -begun, which goes on unceasingly in the dark, until the gold is reduced -to its most simple state.[130] The same thing occurs with chromate of -silver, some of the salts of mercury, argentine preparations combined -with protosulphate of iron or gallic acid, and some other chemical -combinations. These progressive influences point to some law not yet -discovered, which seems to link this radiant actinism with the chemical -agent existing in all matter. - -This problem also connects itself with another class of facts which, -although due, in all probability, to a great extent, to calorific -radiations, and hence known under the general term of Thermography, -appear to involve both chemical and electrical excitation. From the -investigations of Moser and of others, we learn the very extraordinary -fact, that even inanimate masses act and react upon each other by -the influence of some dark radiations, and seem to exchange some of -the peculiarities which they possess. This appears generally in the -curious experiments which have been referred to, as confined merely -to form or structure. Thus an engraved plate will give to a polished -surface of metal or glass placed near it, after a very little time, -a neat distinct image of itself; that is, produce such a structural -disturbance as will occasion the plate to receive vapour differently -over those spaces opposite to the parts in cameo or in intaglio, from -what it does over the opposite. If a piece of wood is used instead of a -metal, there will, by similar treatment, be produced a true picture of -the wood, even to the representation of its fibres.[131] - -It is also probable that chemical decomposition is produced by the -mere juxtaposition of different bodies. Iodide of gold or silver, -perfectly pure, has been placed upon a plate of glass, and a plate of -copper covered with mercury suspended over it: a gradual decomposition -of those salts is said to have been observed, iodide of mercury to -be formed, and the gold or silver salts reduced to a finely divided -metallic state.[132] - -A body whose powers of radiating heat are low, being brought near -another whose radiating powers are more extensive, will, in the course -of a short time, undergo such an amount of molecular disturbance as -will effect a complete change in the arrangement of its surface, and -an impression of the body having the highest radiating powers will be -made upon the other. This impression is dormant, but may be developed -under the influence of vapour, or of oxidation.[133] A body, such -as charcoal, of low conducting power, being placed near another, -such as copper, which is a good conductor, will, in a very short -time, produce, in like manner, an impression of itself upon the metal -plate. Thus any two bodies, whose conducting or radiating powers are -dissimilar, being brought near each other, will occasion a molecular -disturbance, or impress the one with the image of the other. However -small the difference may be, an effect is perceived, and that of the -most extraordinary kind, giving rise to the production of actual images -upon each surface exposed. It is thus that a print on paper may be -copied on metal, by merely suspending it near a well-polished plate of -silver or copper for a few days. The white and black lines radiate very -differently; consequently an effect is produced on the bright metal in -the parts corresponding to the black lines, dissimilar to that which -takes place opposite to the white portions of the paper; and, on the -application of vapour, a true image of the one is found impressed upon -the other.[134] - -Bodies which are in different electrical states act upon each other in -an analogous manner. Thus arsenic, which is highly electro-negative, -will, when placed near a piece of electro-positive copper, readily -impart to its surface an impression of itself, and so in like manner -will other bodies if in unlike conditions. Every substance physically -different (it signifies not whether as it regards colour, chemical -composition, mechanical structure, calorific condition, or electrical -state,) has a power of radiation by which a sensible change can be -produced in a body differently constituted. - -Fable has told us that the magicians of the East possessed mirrors in -which they could at will produce images of the absent. Science now -shows us that representations quite sufficient to deceive the credulous -can be produced on the surface of polished metals without difficulty. -A highly polished plate of steel may be impressed with images of any -kind, which would remain invisible, the polished surface not being in -the least degree affected, as it regards its reflecting powers; but -by breathing over it, the dormant images would develope themselves, -and fade away again as the condensed moisture evaporated from the -surface.[135] - -These, which are but a few selected from a series of results of an -equally striking character, serve to convince us that nature is -unceasingly at work, that every atom is possessed of properties by -which it influences every other atom in the universe, and that a most -important class of natural phenomena appear to connect themselves -directly with the radiant forces. - -The alchemists observed that a change took place in chloride of silver -exposed to sunshine. Wedgwood first took advantage of that discovery to -copy pictures. Niepce pursued a physical investigation of the curious -change, and found that all bodies were influenced by this principle -radiated from the sun. Daguerre produced effects from the solar pencil -which no artist could approach to; and Talbot and others extended the -application. Herschel took up the inquiry; and he, with his usual -power of inductive search and of philosophical deduction, presented -the world with a class of discoveries which showed how vast a field of -investigation was opening for the younger races of mankind,--a field -in which a true spirit may reap the highest reward in the discovery of -new facts, and to which we must look for a further development of those -great powers with which we have already some slight acquaintance, and -for the discovery of higher influences which are not yet dreamed of in -our philosophy. - - If music, with its mysteries of sound, - Gives to the human heart a heavenward feeling; - The beauty and the grandeur which are found - Spread like a vesture this fair earth around, - Creation’s wond’rous harmonies revealing, - And to the soul in truth’s strong tongue appealing, - With all the magic of those secret powers, - Which, mingling with the lovely band of light, - The sun in constant undulation showers - To mould the crystals, and to shape the flowers, - Or give to matter the immortal might - Of an embracing soul--should, from this sod, - Exalt our aspirations all to God. - - -FOOTNOTES: - -[117] See _Researches on Light_, by the Author.--Reference to any of -the works of the alchemists will prove the prevalence of the idea -expressed in the text. We find that gold was considered to be always -under the influence of light and solar heat.--“It is said of gold that -it waxeth cold towards daylight, insomuch that they who wear rings of -it may perceive when the day is ready to dawn.”--_Speculum Mundi, or a -Glass representing the face of the World_. Cambridge, 1643. - -[118] Daguerre’s Report to the Academy of Sciences: _La Daguerréotype -Historique, et description des procédés du Daguerréotype et du Diorama_ -(Paris, 1839); particularly the description of _Heliography_, by M. -Niepce. See also the letters by Niepce, published for the first time in -_Researches on Light_. - -[119] “If a solution of peroxalate of iron be kept in a dark place, -or if it be exposed to 212° of Fahr. for several hours, it does not -undergo any sensible change in its physical properties, nor does it -exhibit any phenomenon which may be considered as the result of any -elementary action. - -“If, however, it be exposed to the influence of solar light in a glass -vessel provided with a tube, the concentrated solution of oxalate -of iron soon presents a very interesting phenomenon: in a short -time the solution receiving the solar rays, developes an infinite -number of bubbles of gas, which rise in the liquor with increasing -rapidity, and give the solution the appearance of a syrup undergoing -strong fermentation. This ebullition always becomes stronger, and -almost tumultuous, when an unpolished glass tube is immersed in it -with a small piece of wood; the liquid itself is afterwards thrown -into ascending and descending currents, becomes gradually yellowish, -turbid, and eventually precipitates protoxalate of iron, in the form -of small brilliant crystals of a lemon-yellow colour, gas continuing -to evolve.” _Chemical action of light, and formation of Humboldtine -by it_; Phil. Mag., 1832, second series.--“When a solution of -platinum in nitro-muriatic acid, in which the excess of acid has been -neutralized by the addition of lime, and which has been well cleared -by filtration, is mixed with lime-water in the dark, no precipitation -to any considerable extent takes place for a long while,--indeed, none -whatever, though after very long standing a slight flocky sediment -is formed, after which the action is arrested entirely. But if the -mixture, either freshly made or when cleared by subsidence of this -sediment, is exposed to sunshine, it instantly becomes milky, and a -copious formation of a white precipitate (or a pale yellow one, if the -platinic solution be in excess) takes place, which subsides quickly -and is easily collected. The same takes place more slowly in cloudy -daylight.”--_On the action of light in determining the precipitation of -Muriate of Platinum by Lime water_; being an extract from a letter from -Sir John F. W. Herschel, K.H., F.R.S., &c., to Dr. Daubeny.--Phil. Mag. -1832. - -[120] _On a change produced by Exposure to the Beams of the Sun, in -the properties of an elementary substance_, by Professor Draper; -_On the changes which bodies undergo in the dark_, by Robert Hunt: -Report of the Thirteenth Meeting of the British Association, vol. -xii,--_Description of the Tithonometer, an instrument for measuring -the chemical force of the Indigo-tithonic rays_: by J. W. Draper, -M.D.--Philosophical Magazine, Dec. 1843, vol. xxiii. - -[121] For several illustrations of this remarkable phenomenon, see _On -the Action of the Rays of the Solar Spectrum on Vegetable Colours, -and on some new Photographic Processes_; by Sir John F. W. Herschel, -Bart., K.H., F.R.S.--Phil. Trans. June, 1842, vol. cxxxiii.; _On -certain improvements on Photographic Processes described in a former -communication, and on the Parathermic Rays of the Solar Spectrum_; -by Sir John F. W. Herschel, Bart., K.H., F.R.S., &c., in a letter -addressed to S. Hunter Christie.--Phil. Trans. 1843, vol. cxxxiv. - -[122] Sir J. F. W. Herschel; see also _Researches on Light_, by the -Author. - -[123] Attention has been directed to the protecting action of certain -rays of the spectrum by Sir John Herschel and others. See the -Eighteenth Report of the British Association for an experiment by -the Author, in which it was proved that all the LIGHT rays protected -photographic papers from chemical change, and, therefore, convincingly -show that light and actinism were not similar powers. - -[124] “Having noticed, one densely foggy day, that the disc of the sun -was of a deep red colour, I directed my apparatus towards it. After -ten seconds of exposure, I put the prepared plate in the mercury box, -and I obtained a round image perfectly black;--the sun had produced no -photogenic effect. In another experiment, I left the plate operating -for twenty minutes; the sun had passed over a certain space of the -plate, and there resulted an image seven or eight times the sun’s -diameter in length; it was black throughout, so that it was evident, -wherever the red disc of the sun had passed, not only was there a -want of photogenic action, but the red rays had destroyed the effect -produced previous to the sun’s passage. I repeated these experiments -during several days successively, operating with a sun of different -tints of red and yellow. These different tints produced nearly the same -effect; wherever the sun had passed, there existed a black band.”--Mr. -Claudet, _On different properties of Solar Radiation, modified by -coloured glass media, &c._: Phil. Trans. 1847. Part 2. - -[125] “It may also be observed that the rays effective in destroying -a given tint are, in a great many cases, those whose union produces a -colour complementary to the tint destroyed, or at least one belonging -to that class of colours to which such complementary tint may be -referred. For example, yellows tending towards orange are destroyed -with more energy by the blue rays; blue by the red, orange, and yellow -rays; purples and pinks by yellow and green rays.”--Sir J. F. W. -Herschel, _On the action of the rays of the Solar Spectrum on Vegetable -Colours_: Phil. Trans., vol. cxxxiii. 1842. - -[126] The following memoirs and works are necessary to a complete -history of the inquiry:--_Experiments and observations relating -to various branches of natural philosophy, with a continuation of -the observation on air_: by Dr. Priestley. London, 1779. _Mémoires -Physico-chimiques, &c._: by J. Senebier. _Expériences sur les -végétaux_, by De la Ville: Paris, 1782; and Phil. Trans. 1782. -_Observations sur les expériences de M. Ingenhousz_: by De la Ville; -Roz. obs. 23, 290. _Expériences propres à développer les effets de la -lumière sur certaines plantes_: by Tessier; Mém. de l’Ac. des Sc. de -Paris, 1783, p. 132; Licht. Mag. iv. 4, 146. _Sur la vertu de l’eau -impregnée d’air fixe pour en obtenir, par le moyen des plantes et de -la lumière du soleil, de l’air déphlogistiqué_: by Ingenhousz; Roz. -obs. 24, 337. _Expériences sur l’action de la lumière solaire dans la -végétation_: by Senebier; Genève et Paris, 1788, p. 61. _Extrait des -expériences de M. Senebier sur l’action de la lumière solaire dans la -végétation_: by Hasenfratz; Ann. Chim. iii. 2nd. ser. 266. _Expériences -relatives à l’influence de la lumière sur quelques végétaux_: by De -Candolle; Jour. de Ph. lii. 124: Voigt’s Mag. ii. 483; Gilb. Ann. -xiii. 372; Mém. des Sav. Etr. i. 329. _Recherches chimiques sur la -végétation_: by Saussure; Ann. Chim. l. 225; Jour. de Ph. lvii. p. -393; Gilb. Ann. xviii 208. _Recherches sur la respiration des plantes -exposées à la lumière du soleil_; by Ruhland; Ann. Ch. Ph. iii. 411; -Jour. de Ph. 1816. _On the action of light upon plants, and of plants -upon the atmosphere_: by Dr. Daubeny; Phil. Trans. cxxvii January, -1836. _On the action of yellow light in producing the green colour, and -of indigo light on the movements of plants_: by P. Gardner; Phil. Mag. -xxiv.; Bibl. Univ. xlix. p. 376, and lii. p. 381. _On the influence of -light on plants_: by R. Hunt; Phil. Mag. xxiv. p. 96; Bibl. Univ. xlix. -p. 383; Athen. 1844. _Note on the decomposition of carbonic acid by -the leaves of plants, under the influence of yellow light_: by Draper; -Phil. Mag. xxv. p. 169. _On the action of the yellow rays of light on -vegetation_: by Harkness; Phil. Mag. xxv. p. 339. _Influence des rayons -solaires sur la végétation_: by Zantedeschi; Inst. No. 541, p. 157. - -[127] Sir John Herschel’s Memoirs already referred to; and _Reports on -the influence of the Solar Rays on the growth of Plants_, by Robert -Hunt: Report of the British Association for the Advancement of Science, -for 1847. - -[128] _Memoir on the Constitution of the Solar Spectrum_, presented at -the meeting of the Academy of Sciences, 1842, by M. Edmond Becquerel; -_Des effets produits sur les corps par les rayons solaires_, par M. -Edmond Becquerel, aide au Muséum d’Histoire Naturelle: Mémoire présenté -à l’Académie des Sciences, le 23 Octobre, 1843.--“Dans le courant de -ce mémoire, j’ai employé les noms de rayons lumineux, chimiques, et -phosphorogéniques, pour désigner, dans chaque cas, la portion des -rayons solaires qui agit pour produire, en particulier, les effets -lumineux, chimiques, et phosphorogéniques; mais cela est sans préjudice -de l’opinion que je viens d’émettre touchant l’existence d’un seul et -même rayonnement.” - -“My reply is this,” says M. Arago, in his paper entitled -_Considerations relative to the action of Light_: “It is by no means -proved that the photogenic modifications of sensitive substances -result from the action of the solar light itself. The modifications -are, perhaps, engendered by invisible radiations mixed with light -properly so called, proceeding with it, and being similarly refracted. -In this case, the experiment would prove not only that the spectrum -formed by these invisible rays is not continuous, that there are -solutions of continuity as in the visible spectrum, but also that in -the two superposed spectra these solutions correspond exactly. This -would be one of the most curious, one of the most strange results of -physics.”--Taylor’s Scientific Memoirs. - -[129] The chemical evidence of this will be found in Sir John -Herschel’s Memoir _On the Solar Spectrum_, and particularly as -exemplified in the changes produced on the tartrate of silver. Similar -influences are described as observed on a Daguerreotype plate, in -a paper entitled _Experiments and Observations on Light which has -permeated coloured media, and on the Chemical Action of the Solar -Spectrum_; by Robert Hunt.--Philosophical Magazine, vol. xxvi. 1840. - -[130] This peculiar continuance of an effect has frequently been -observed in many of the photographic processes. In a note to a memoir -_On certain improvements in Photographic processes_, Sir John Herschel -thus refers to this property:--“The excitement is produced on such -paper by the ordinary moisture of the atmosphere, and goes on slowly -working its effect in the dark, apparently without other limit than is -afforded by the supply of ingredients present. In the case of silver it -ultimately produces a perfect _silvering_ of all the sunned portions. -Very singular and beautiful photographs, having much resemblance to -Daguerreotype pictures, are thus produced; the negative character -changing by keeping, and by quite insensible gradations to positive, -and the shades exhibiting a most singular _chatoyant_ change of colour -from ruddy-brown to black, when held more or less obliquely. No doubt, -also, gold pictures with the metallic lustre might be obtained by the -same process, though I have not tried the experiment.” - -[131] The details of this curious subject may be studied in the -following memoir and communications:--_On vision and the action of -light on all bodies_: by Professor Ludwig Moser, of Königsberg; from -Poggendorff’s Annalen, vol. lvi. p. 177, No. 6, 1845. _Some remarks -on Invisible Light_: by Professor Ludwig Moser, of Königsberg; from -Poggendorff’s Annalen, vol. lvi. p. 569, No. 8. _On the power which -light possesses of becoming latent_: by Professor Ludwig Moser, of -Königsberg; from Poggendorff’s Annalen, vol. lvii. No. 9, p. 1. 1842. -_On certain spectral appearances, and on the discovery of latent -light_: by J. W. Draper, M.D., Professor of Chemistry in the University -of New York; Phil. Mag. p. 348, Nov. 1842. _On a new imponderable -substance, and on a class of chemical rays analogous to the rays of -dark heat_: by Professor Draper; Phil. Mag., Dec. 1842. _On the action -of the rays of the solar spectrum on the Daguerreotype plate_; by Sir -J. F. W. Herschel, Bart.; Phil. Mag., Feb. 1843. See remarks in this -paper on the use which Moser has made of coloured glasses: also a -communication by Professor Draper, _On the rapid Detithonizing power of -certain gases and vapours, and on an instantaneous means of producing -spectral appearances_: Phil. Mag., March 1843; and _On the causes which -concur in the production of the images of Moser_: Comptes Rendus, Nov. -1842. See _Scientific Memoirs_, vol. iii. - -[132] This fact was first observed by myself, and described in the -paper already referred to, Philosophical Magazine, vol. xxii. p. 270. -It does not, however, appear to have attracted the attention of any -other observer. - -[133] _On Thermography, or the Art of copying Engravings or any printed -characters from paper or plates of metal, and on the recent discovery -of Moser, relative to the formation of images in the dark_, by Robert -Hunt: Reports of the Royal Cornwall Polytechnic Society for 1842, and -Philosophical Magazine, vol. xxi. p. 462.--_On the Spectral Images of -M. Moser_, by Robert Hunt: Philosophical Magazine, vol. xxiii. p. 415. - -[134] _Catalytic force, or attraction of surface concerned in the -diffusive power of gases: an occult energy or power in saturated saline -solutions_; Prater.--Mechanic’s Magazine, vol. xlv. p. 106. _Ueber -elektrische Abbildungen_; by G. Karsten.--Poggendorff’s Annalen, vol. -lvii. p. 402.--Melloni and Brewster may be consulted for much that is -most remarkable connected with radiation from coloured surfaces. - -[135] Cornelius Agrippa is said to have possessed such a mirror. -The Chinese make mirrors which, when placed in a particular light, -show upon their polished faces the pattern on the back of the metal, -although it is invisible in every other position. This is effected by -giving different degrees of hardness to the various parts of the metal. -In _Natural Magic_, by Sir David Brewster, several curious experiments -belonging to this class are named. - - - - -CHAPTER IX. - -ELECTRICITY. - - Discovery of Electrical Force--Diffused through all Matter--What - is Electricity?--Theories--Frictional Electricity--Conducting - Power of Bodies--Hypothesis of two Fluids--Electrical - Images--Galvanic Electricity--Effects on Animals--Chemistry of - Galvanic Battery--Electricity of a Drop of Water--Electro-chemical - Action--Electrical Currents--Thermo-Electricity--Animal - Electricity--Gymnotus--Torpedo--Atmospheric Electricity--Lightning - Conductors--Earth’s Magnetism due to Electrical Currents--Influence - on Vitality--Animal and Vegetable Development--Terrestrial - Currents--Electricity of Mineral Veins--Electrotype--Influence of - Heat, Light, and Actinism on Electrical Phenomena. - - -If a piece of amber, _electrum_, is briskly rubbed, it acquires the -property of attracting light bodies. This curious power excited the -attention of Thales of Miletus; and from the investigations of this -Grecian philosopher we must date our knowledge of one of the most -important of the natural forces--Electricity. - -If an inquiring mind had not been led to ask why does this curious -natural production attract a feather, the present age, in all -probability, would not have been in possession of the means by which it -is enabled to transmit intelligence with a rapidity which equals the -poet’s dream of the “swift-winged messengers of thought.” To this age -of application a striking lesson does this amber teach. Modern utility -would have regarded Thales as a madman. Holding a piece of yellow -resin in his hand, rubbing it, and then picking up bits of down, or -catching floating feathers, the old Greek would have appeared a very -imbecile, and the _cui bono_ generation would have laughed at his silly -labours. But when he announced to his school that this amber held a -soul or essence, which was awakened by friction, and went forth from -the body in which it previously lay dormant, and brought back the small -particles floating around it, he gave to the world the first hint of -a great truth which has advanced our knowledge of physical phenomena -in a marvellous manner, and ministered to the refinements and to the -necessities of civilisation. Each phenomenon which presents itself to -us, however simple it may appear to be, is an outward expression of -some internal truth, the interpretation of which is only to be arrived -at by assiduous study, but which, once discovered, directs the way to -new knowledge, and gives to man a great increase of power. There is no -truth so abstract that it will not find its useful application, and -every example of the ministration of Physical Science to the purposes -of humanity is an evidence of the value of abstract study, and a reply -to the utilitarian in his own language. - -Electricity appears to be diffused through all nature; and it is, -beyond all doubt, one of the most important of the physical forces, in -the great phenomena of creation. In the thunder-cloud, swelling with -destruction, it resides, ready to launch its darts and shake the earth -with its explosions: in the aërial undulations, silent and unseen, it -passes, giving the necessary excitement to the organisms around which -it floats. The rain-drop--the earth-girdling ocean--and the ringing -waters of the hill-born river, hold locked this mighty force. The -solid rocks--the tenacious clays which rest upon them--the superficial -soils--and the incoherent sands, give us evidence of the presence of -this agency; and in the organic world, whether animal or vegetable, the -excitement of electrical force is always to be detected. - -In the solar radiations we have perhaps the prime mover of this -power. In our atmosphere, when calm and cloudless, a great ocean of -light, or when sombre with the mighty aspect of the dire tornado, we -can constantly detect the struggle between the elements of matter to -maintain an equilibrium of electrical force. - -Diffused throughout matter, electricity is ever active; but it must -be remembered that although it is evidently a necessary agent in all -the operations of nature, that it is not the agent to which everything -unknown is to be referred. Doubtless the influence of this force is -more extensive than we have yet discovered; but that is an indolent -philosophy which refers, without examination, every mysterious -phenomenon to the influence of electricity. - -The question, what is electricity? has ever perplexed, and still -continues to agitate, the world of science. While one set of -experimentalists have endeavoured to explain the phenomena they have -witnessed, upon the theory that electricity is a peculiar subtile -fluid pervading matter, and possessing singular powers of attraction -and repulsion, another party find themselves compelled to regard -the phenomena as giving evidence of the action of two fluids which -are always in opposite states; while again, electricity has been -considered by others as, like the attraction of gravitation, a mere -property of matter.[136] Certain it is, that in the manifestations -of electrical phenomena we have, as it appears, the evidence of two -conditions of force; but of the states of _positive_ or _negative_, of -_vitreous_ or _resinous_ electricity, we have a familiar explanation -in the assumption of some current flowing into or out of the material -body,--of some principle which is ever active in maintaining its -equilibrium, which, consequently, must act in two directions, and -always exhibit that duality which is a striking characteristic of this -subtile agent. It is a curious, and it should be an instructive fact, -that each of the three theories of electricity is capable of proof, -and has, indeed, been most ably supported by the rigorous analysis -of mathematics. When we remember that some of the most enlightened -investigators of this and the past age have severally maintained, -in the most able manner, these dissimilar views, we should hesitate -before we pronounce an opinion upon the cause or causes of the very -complicated phenomena of electrical force. - -Although we discover, in all the processes of nature, the -manifestations of this principle or force in its characteristic -conditions, it will be necessary, before we regard the great phenomena, -to examine the known sources from which we can most readily evoke the -mighty power of electricity. If we rub a piece of glass or resin, we -readily render this agent active; these substances appear, by this -excitement, to become surrounded by an attractive or a repellent -atmosphere. Let us rub a strip of writing paper with Indian rubber, -or a strip of Gutta Percha with the fingers, in the dark, and we have -the manifestation of several curious phenomena. We have a peculiar -attracting power; we have a luminous discharge in the shape of a spark; -and we have very sensible evidence of muscular disturbance produced by -applying the knuckle to the surface of the material. In each case we -have the development of the same power. - -Every substance in nature is an electric, and, if so disposed that its -electricity may not fly off as it is developed, we may, by friction, -manifest its presence, and, indeed, measure its quantity or its force. -All bodies are not, however, equally good electrics; shell-lac, amber, -resins, sulphur, and glass, exhibiting more powerfully the phenomena -of frictional or mechanical electricity, than the metals, charcoal, -or plumbago. Solid bodies allow this peculiar principle to pass along -them also in very different degrees. Thus electricity travels readily -through copper and most other metals, platinum being the worst metallic -conductor. It also passes through living animals and vegetables, smoke, -vapour, rarified air, and moist earth; but it is obstructed by resins -and glass, paper when dry, oils, and dry metallic oxides, and in a very -powerful manner by Gutta Percha.[137] - -If, therefore, we place an electric upon any of those non-conducting -bodies, the air around being well dried, we are enabled to gather -a large quantity of the force for the production of any particular -effect. Taking advantage of this fact, arrangements are made for the -accumulation and liberation at pleasure of any amount of electricity. - -A Leyden phial,--so called from its inventor, Musschenbroek, having -resided at Leyden,--is merely a glass bottle lined within and without, -to within a few inches of the top, with a metal coating. If a wire or -chain, carrying an electric current, is allowed to dip to the bottom -of the bottle, the inner coat of the jar becomes charged, or gathers -an excess, whilst the outer one is in its natural condition--one is -said to be in a _positive_, and the other in a _negative_ state. If -the two coatings are now connected by a good conductor, as a piece of -copper wire, passing from one to the other, the outside to the inside, -a discharge, arising from the establishment of the equilibrium of the -two coatings, takes place; and, if the connection is made through the -medium of our bodies, we are sensible of a severe disturbance of the -nervous system. - -The cause of the conducting and non-conducting powers of bodies we know -not; they bear some relation to their conducting powers for caloric; -but they are not in exact obedience to the same laws. When we consider -that resin, a comparatively soft body, in which, consequently, -cohesive attraction is not very strong, is an imperfect conductor, -and that copper, in which cohesion is much more powerful, is a good -conductor, we may be disposed to consider that it is regulated by the -closer approximation of the particles of matter. But in platinum the -corpuscular arrangement must be much more dense than it is in copper, -and yet it is, compared with it, a very bad conductor.[138] - -We have now learnt that we may, by friction, excite the electricity -in a vitreous substance; but it must not be forgotten that we cannot -increase the quantity which is, under ordinary conditions, natural to -the electric; to do so, we must in some way establish a channel of -communication with the earth, from which, through the medium we excite, -we draw our supply. We have the means of confining this mighty force -within certain limits of quantity and of time. If we place bodies which -are susceptible of electrical excitation in a sensible degree upon -insulating ones, we may retain for a considerable time the evidences of -the excitement, in the same way as with the Leyden jar; but there is a -constant effort to maintain a balance of conditions, and the body in -which we have accumulated any extraordinary quantity by conduction soon -returns to its natural state. - -A very simple means may be adopted of showing what is thought to be -one of the many evidences in favour of two electricities. If the -wire carrying the current flowing from the machine, is passed over -paper covered with nitrate of silver, it produces no change upon it; -but if the wire which conveys the current to the instrument, when -it is excited, is passed over the same paper, the silver salt is -decomposed.[139] We may, however, explain this result in a satisfactory -manner, upon the hypothesis that the decomposition is produced by the -abstraction of electricity, rather than by any physical difference in -the fluid itself. By frictional electricity we may produce curious -molecular disturbances, and give rise to molecular re-arrangements, -which have been called “electrical images,” in glass, in stone, and in -the apparently less tractable metals: these images are rendered visible -by the manner in which, according to their electrical states, some -lines receive any particular powder, or vapour, which is repelled from -other spaces. Many of the great natural phenomena, such as Lightning -and Thunder, the Aurora Borealis, and Meteors, may be imitated in a -curiously exact manner by the electrical machine and a few familiar -arrangements.[140] - -Voltaic electricity, as the active force produced by chemical change -is commonly called, in honour of the illustrious Volta, is now to -be considered. It differs from frictional electricity in this:--the -electricity developed by friction of the glass plate or cylinder of -the electrical machine is a discharge with a sort of explosion. It -is electricity suddenly liberated from the highest state of tension, -whereas that which is generated by chemical action in the voltaic -battery is a steady flowing current. We may compare one to the ignition -of a mass of gunpowder at once, and the other to the slow burning of -the same quantity spread out into a very prolonged train. - -There are numerous ways in which we may excite the phenomena of -Voltaism, but in all of them the decomposition of one of the elements -employed appears to be necessary. This is the case in the arrangements -of batteries in which two dissimilar metals, zinc and copper, silver -and platinum, or the like, is immersed in fluids; the zinc or the -silver are gradually converted into soluble salts, which are dissolved, -whilst the copper or platinum is protected from any action. The most -simple manner of illustrating the development of this electricity is by -placing a piece of silver on the tongue, and a piece of zinc or lead -underneath it. No effect will be observed so long as the two metals -are kept asunder, but when their edges are brought together, a slight -tremulous sensation will pass through the tongue, a saline taste be -distinguished by the palate, and if in the dark, light will be observed -by the eye. - -This, the germ of the most remarkable of the sciences, was noticed by -Sulzar, fifty years before Galvani observed the convulsions in the -limbs of frogs, when excited by the action of dissimilar metals; but -the former paid little attention to the phenomenon, and the discovery -led to no results. - -When Galvani’s observant mind was directed to the remarkable fact that -the mere contact of two dissimilar metals with the moist surface of -living muscles produced convulsions, there was an awakening in the soul -of that philosopher to a great fundamental truth, which was nurtured -by him, tried and tested, and preserved to work its marvels for future -ages. - -Although the world of science looks back to Volta as the man who gave -the first true interpretation of this discovery, yet the ordinary world -will never disconnect this important branch of physical science from -the name of Galvani, and chemical electricity in all its forms will for -ever be known under the familiar name of Galvanism. And it must not be -forgotten, that the phenomena of the manifestation of electricity, in -connection with the conditions of vitality, are entirely due to Galvani. - -Let us examine the phenomena of Galvanism in its most simple phases:-- - -If we place a live flounder upon a plate of zinc, put a shilling on its -back, and then touch both metals with the ends of a metallic wire, the -fish will exhibit painful convulsions. The zinc becomes oxidized by -the separation of oxygen from the fluid on the surface with which it is -in contact, whilst hydrogen gas is liberated at that surface touched -by the other metal. Here we have, in the first place, a chemical -change effected, then a peculiar muscular disturbance. Each successive -combination or decomposition, like a pulsation, is transmitted along -the circuit from one extremity to the other. How the impulse which is -derived from the zinc is transmitted through the body of the animal, or -the tongue, to the silver or copper is the next consideration. - -We can only understand this upon the supposition that a series of -impulses are communicated in the most rapid manner along the connecting -line; the idea of a current, although the term is commonly employed, -tends to convey an imperfect impression to the mind. It would seem -rather that a disturbance throughout the entire circuit is at once set -up by a series of vibrations or impulses communicated from particle to -particle, and along the strange net-work of nerves. One set of chemical -elements have a tendency to develope themselves at that point where -vibration is first communicated to the mass from a better conductor -than it is, and another set at the point where it passes from the -body to a better conductor than itself. The cause of this is to be -sought for in the laws which regulate molecular constitution--by which -chemical affinity is disturbed,--and a new attractive force exerted, -in obedience to which the vital energy is itself agitated. We must -not, however, forget that it is probable after all, although not yet -susceptible of proof, that the electricity does nothing more than -disturb or quicken the unknown principles upon which chemical and vital -phenomena depend; being, indeed, a secondary agent.[141] - -Notwithstanding our long acquaintance with the phenomena of galvanism, -there are but few who entertain a correct idea of the enormous amount -of electricity which is necessary to the existing conditions of matter. -To Faraday we are indebted for the first clear set of deductions from a -series of inductive researches, which are of the most complete order. -He has proved, by a series of exceedingly conclusive experiments, that -if the electrical power which holds a grain of water in combination, -or which causes a grain of oxygen and hydrogen to unite in the right -proportions to form water, could be collected and thrown into the -condition of a voltaic current, it would be exactly the quantity -required to produce the decomposition of that grain of water, or the -liberation of its elements, hydrogen and oxygen.[142] - -By direct experiment it has been proved that one equivalent of zinc in -a voltaic arrangement evolves such a quantity of electricity in the -form of a current, as, passing through water, will decompose exactly -one equivalent of that fluid. The law has been thus expressed:--The -electricity which decomposes, and that which is evolved by the -decomposition of a certain quantity of matter, are alike. The -equivalent weights of bodies are those quantities of them which contain -equal quantities of electricity; electricity determining the equivalent -number, because it determines the combining force.[143] - -The same elegant and correct experimentalist has shown that zinc and -platinum wires, one-eighteenth of an inch in diameter, and about half -an inch long, dipped into water in which is mixed sulphuric acid so -weak that it is not sensibly sour to the tongue, will evolve more -electricity in one-twentieth of a minute than is given by thirty turns -of a large and powerful plate electrical machine in full action, a -quantity which, if passed through the head of a cat, is sufficient to -kill it as by a flash of lightning. Pursuing this interesting inquiry -yet further, it is found that a single grain of water contains as -much electricity as could be accumulated in 800,000 Leyden jars, each -requiring thirty turns of the large machine of the Royal Institution to -charge it,--a quantity equal to that which is developed from a charged -thunder-cloud. “Yet we have it under perfect command,--can evolve, -direct, and employ it at pleasure; and when it has performed its full -work of electrolisation, it has only separated the elements of a single -grain of water.” - -It has been argued by many that the realities of science will not admit -of anything like a poetic view without degrading its high office; that -poetry, being the imaginative side of nature, has nothing in common -with the facts of experimental research, or with the philosophy which -generalises the discoveries of severe induction. If our science was -perfect, and laid bare to our senses all the secrets of the inner -world; if our philosophy was infallible, and always connected one -fact with another through a long series up to the undoubted cause of -all--then poetry, in the sense we now use the term, would have little -business with the truth; it would, indeed, be lost or embodied, like -the stars of heaven, in the brightness of a meridian sun. But to take -our present fact as an example, how important a foundation does it -offer upon which to build a series of thoughts, capable of lifting -the human mind above the materialities by which it is surrounded,--of -exalting each common nature by the refinement of its fresh ideas to a -point higher in the scale of intelligence,--of quickening every impulse -of the soul,--and of giving to mankind the most holy longings. - -What does science tell us of the drop of water? Two gases, the one -exciting life and quickening combustion, the other a highly inflammable -air, are, by the influence of a combination of powers, brought into -a liquid globe. We can, from this crystal sphere, evoke heat, light, -electricity, and actinism in enormous quantities; and beyond these -we can see powers or forces, for which, in the poverty of our ideas -and our words, we have not names; and we learn that each one of these -principles is engaged in maintaining the conditions of the drop of -water which refreshes organic nature, and gives gladness to man’s -dwelling-place. - -Has poetry a nobler theme than this? Agencies are seen like winged -spirits of infinite power, each one working in its own peculiar way, -and all to a common end,--to produce, under the guidance of omnipotent -rule, the waters of the rivers and the seas. As the great ocean mirrors -the bright heaven which overspreads it, and reflects back the sunlight -and the sheen of the midnight stars in grandeur and loveliness; so -every drop of water, viewed with the knowledge which science has given -to us, sends back to the mind reflections of yet distant truths which, -rightly followed, will lead us upwards and onwards in the tract of -higher intelligences,-- - - “To the abodes where the eternals are.” - -In the discoveries connected with electricity, we have results of -a more tangible character than are as yet connected with the other -physical forces; and it does appear that this science has advanced -our knowledge of nature and of the mysteries of creation far more -extensively than any other department of purely experimental inquiry. - -The phenomena of electro-chemical action are so strange that we must -return for a moment to the consideration of the decomposition of -water, and the appearance of hydrogen at one pole, and of oxygen at -the other. It appears that some confusion of our ideas has arisen -from the views which have been received of the atomic constitution of -bodies. We have been accustomed to regard water,--to take that body as -an example of all,--as a compound of two gases, hydrogen and oxygen; -an equivalent, or one atom of the first, united to an equivalent or -one atom of the last, forming one atom of water. This atom of water we -regard as infinitely small; consequently a drop of water is made up of -many hundreds of these combined atoms, and a pint of water of not less -than 10,000 drops. Now, if this pint of water is connected with the -wires of a galvanic battery, although their extremities may be some -inches apart, for every atom of oxygen liberated at one pole, an atom -of hydrogen is set free at the other. It has been thought that an atom -has undergone decomposition at one point, its oxygen being torn from -it, and then there has arisen the difficulty of sending the atom of -hydrogen through all the combined atoms of water across to the other -pole. A series of decompositions and recompositions have been supposed -to take place, and the communication of effects from particle to -particle. - -An attracting power for one class of bodies has been found in one pole, -which is repellent to another class; and the reverse order has been -detected at the opposite pole of a galvanic arrangement.[144] That -is, the wire which carries the current from an excited zinc plate has -a relation to all bodies, which is directly opposite to that which -is exhibited by the wire conveying the current from, or completing -the circuit with, the copper plate. The one, for instance, collects -and carries acids and the like, the other the metallic bases. At the -extremity of one galvanic wire, placed into a drop of water, oxygen is -always liberated; and at the end of the other, necessary to complete -the circuit with the battery, hydrogen is set free. - -It appears necessary, to a clear understanding of what takes place in -this experiment, that we should regard each mass, howsoever large, as -the representative of a single atom. Nor is this difficult, as the -following illustration will show. - -Let us take one particle of common salt (_chloride_ of _sodium_) -weighing less than a grain, and put it into a hundred thousand grains -of distilled water. In a few minutes the salt has diffused itself -through the whole of the fluid, and in every drop we can detect -chlorine and soda. We cannot believe that this grain of salt has split -itself up into a hundred thousand parts; we conceive rather that the -phenomenon of solution is one of diffusion. One infinitely elastic body -has interpenetrated with another. - -Instead of an experiment with a pint of water, let us take our stand -on Dover heights, and, with a gigantic battery at our command, place -one wire into the ocean on our own shores, and convey the other through -the air across the channel, and let its extremity dip into the sea -off Calais pier--the experiment is a practicable one--we have now an -electrical circuit of which the British channel forms a part, and the -result will be exactly the same as that which we may observe in a -watch-glass with a drop of water. - -We cannot suppose that the instantaneous and simultaneous effect -which takes place in the water at Calais and at Dover, is due to -anything like what we have studied under the name of convection, when -considering Heat. - -A thousand balls are placed in a line touching each other; the first -ball receives a blow, and the last ball flies off with a force exactly -equal to the power applied to the first; none of the intermediate balls -being moved. - -We cannot conceive that the particle _A_ excites the particle _B_ next -it, and so on through the series between the two shores; but regarding -the channel as one large drop, charged with the electric principle as -we know it to be, it is excited by undulation or tremor throughout -its width, and we have an equivalent of oxygen thrown off on one side -of the line, and an exact equivalent of hydrogen at the other, the -electro-chemical influence being exerted only where the current or -motion is transferred from one medium to another.[145] The imperfect -character of this view is freely admitted; no other, consistent with -known facts, presents itself by which the effect can be explained. The -fact stands as a truth; the hypothesis by which it is attempted to -be interpreted is open to doubt, and it is opposed to some favourite -theories. - -Before we pass to the consideration of the other sources of -electricity, it is important we should understand that no chemical -or physical change, however slight it may be, can occur without the -development of electrical power. If we dissolve a salt in water, if -we mix two fluids together, if we condense a gas, or convert a fluid -into vapour, electricity is disturbed, and may be made manifest to our -senses.[146] - -It has been shown that this power may be excited by friction -(machine electricity) and by chemical action (voltaic electricity, -galvanism); it now remains to speak of the electricity developed by -heat (thermo-electricity), the electricity exhibited under nervous -excitement by the gymnotus and torpedo (animal electricity); magnetism -and its phenomena being reserved for a separate consideration. - -If a bar of metal is warmed at one end and kept cool at the other, -an electrical current circulates through the bar, and may be carried -off by connection with any good conductor, and shown to exhibit the -properties of ordinary electricity. The metals best suited for showing -the effects of thermo-electricity appear to be bismuth and antimony. By -binding two bars of these metals together at one end, and connecting -the other ends with a galvanometer, it will be discovered that an -electric current passes off through the instrument by the slightest -variation of temperature. Merely clasping the two metals, where bound -together, with the finger and thumb, is sufficient to exhibit the -phenomenon. By a series of such arrangements,--which form what have -been called thermo-electric multipliers,--we obtain the most delicate -measurers of heat with which philosophers are acquainted, by the aid of -which Melloni has been enabled to pursue his beautiful researches on -radiant caloric. - -That this electricity is identical with the other forms has been proved -by employing the current thus excited for the purpose of producing -chemical decomposition, magnetism, and electric light.[147] - -The phenomenon of thermo-electricity--the discovery of Seebeck, is -another proof of the very close connection of the physical forces. We -witness their being resolved as it were into each other, electricity -producing heat, and heat again electricity; and it is from these -curious results that the arguments in favour of their intimate -relations and actual identity have been drawn. It will, however, be -found to be the best philosophy to regard these forces as dissimilar, -until we are enabled to prove them to be only modified forms of one -principle or power. At the same time it must not be forgotten that -in natural operations we invariably find the combined action of -several forces producing a single phenomenon. The important fact to be -particularly regarded is, that we have evidence that every substance -which is unequally heated becomes the source of this very remarkable -form of electricity.[148] - -There exist a few fishes gifted with the very extraordinary power of -producing electrical phenomena by an effort of muscular or nervous -energy. - -The _Gymnotus electricus_, or electrical eel, and the _Raia torpedo_, -a species of ray, are the most remarkable. This power is, it would -appear, given to these curious creatures for purposes of defence, and -also for enabling them to secure their prey. The _Gymnotus_ of the -South America rivers, will, it is said, when in full vigour, send forth -a discharge of electricity sufficiently powerful to knock down a man, -or to stun a horse; while it can destroy fishes, through a considerable -space, by exerting its strange artillery.[149] - -Faraday’s description of a _Gymnotus_, paralyzing and seizing its -prey, is too graphic and important to be omitted. - -“The _Gymnotus_ can stun and kill fish which are in very various -positions to its own body; but on one day, when I saw it eat, its -action seemed to me to be peculiar. A live fish, about five inches in -length, caught not half a minute before, was dropped into the tub. -The _Gymnotus_ instantly turned round in such a manner as to form a -coil, inclosing the fish, the latter representing a diameter across -it; a shock passed, and there, in an instant, was the fish struck -motionless, as if by lightning, in the midst of the waters, its side -floating to the light. The _Gymnotus_ made a turn or two to look for -its prey, which, having found, he bolted, and then went about searching -for more. A second smaller fish was given him, which being hurt in the -conveyance, showed but little signs of life, and this he swallowed at -once, apparently without shocking it. The coiling of the _Gymnotus_ -round its prey had, in this case, every appearance of being intentional -on its part, to increase the force of the shock, and the action is -evidently well suited for that purpose, being in full accordance -with the well-known laws of the discharge of currents in masses of -conducting matter; and though the fish may not always put this artifice -in practice, it is very probable he is aware of its advantages, and may -resort to it in cases of need.”[150] - -Animal electricity has been proved to be of the same character as that -derived from other sources. The shock and the spark are like those -of the machine; and the current from the animal, circulating around -soft iron, like galvanic electricity, has the property of rendering it -magnetic. - -It is important that we should now review these conditions of -electrical force in connexion with the great physical phenomena of -nature. - -It is sufficiently evident, from the results which have been examined, -that all matter, whatever may be its form or condition, is for ever -under the operation of the physical forces, in a state of disturbance. -From the centre to the surface all is in an active condition: a state -of mutation prevails with every created thing; and science clearly -shows that influences are constantly in action which prevent the -possibility of absolute repose. - -Under the excitement of the several agencies of the solar beams, motion -is given to all bodies by the circulation of heat, and a full flow of -electricity is sent around the earth to perform its wondrous works. -The solar influences, which regulate, and possibly determine, every -physical force with which we are acquainted, are active in effecting -an actual change of state in matter. The sunbeam of the morning falls -on the solid earth, and its influence is felt to the very centre. -The mountain-top catches the first ray of light, and its base, still -wrapt in mists and darkness, is disturbed by the irradiating power. -The crystalline gems, hidden in the darkness of the solid rock, are -dependent, for that form which makes them valued by the proud and gay, -on the influence of those radiations which they are one day to refract -in beauty. The metals locked in the chasms of the rifted rocks are, for -all their physical peculiarities, as dependent on solar influence as is -the flower which lifts its head to the morning sun, or the bird which -sings “at heaven’s high gate.” - -Let us, then, examine how far electricity, as distinguished from the -other powers, acts in producing any of these effects. - -We find electricity in the atmosphere, which the electrical kite of Dr. -Franklin proved to be identical with that principle produced by the -friction of glass. In the grandeur and terror of a thunderstorm, many -see nothing but manifestations of Almighty wrath. When the volleys of -the bursting cloud are piercing the disturbed air, and the thunders -of the discharge are pealing their dreadful notes above our heads, -the chemical combinations of the noxious exhalations arising from the -putrefying animal and vegetable masses of this earth are effected, -elements fitted for the purposes of health and vegetation are formed, -and brought to the ground in the heavy rains which usually follow these -storms. Science has taught man this--has shown him that the “partial -evil” arising from the “winged bolt” is a “universal good;” and, more -than this, it has armed him with the means of protecting his life and -property from the influence of lightnings. So that, like Ajax, he can -defy the storm. By metallic rods, carried up a chimney, a tower, or a -mast, we may form a channel through which the whole of the electricity -of the most terrific thunder-cloud may be carried harmlessly into -the earth or the sea; and it is pleasing to observe that at length -prejudice has been overcome, and “conductors” are generally attached -to high buildings, and to most of the ships of our navy.[151] It was -discovered that the devastating hailstorms of the south of France -and Switzerland, so destructive to the vineyards and crops, were -accompanied by evidences of great electrical excitation, and it was -proposed to discharge the electricity from the air by means of pointed -metallic rods. These have been adopted, and, it is said, with real -advantage--each rod protecting an area of one hundred yards. Thus it -is that science ministers to our service; and how much more pleasing -is it to contemplate the lightning, with the philosopher, as an agent -destroying the elements of pestilence, and restoring the healthfulness -of the air we breathe, than with the romancer, to see in it only the -dreaded aspect of a demon of destruction. - -The laws which regulate the spread of a pestilence are unknown. The -difficulties of the investigation are great, but they are by no means -insurmountable. A plague passes from the east to the west across -the world--it spreads mourning over the gayest cities, and sorrow -sitteth in the streets. The black death rises in the Orient: it goes -on in unchecked strength, and only finishes its course when it has -made the circuit of the civilized world. The cholera spreads its -ebon wings--mankind trembles--watches its progress, and looks upon -the path which is marked by the myriads of the dead, who have fallen -before the dire fiend. The diseases pass away--the dead are buried, -and all is forgotten. The rush and the riot of life are pursued: and -until man is threatened with another advent, he cares not to trouble -himself. Accompanying the last visitation, there appear certain -peculiar meteorological conditions, which point a line of inquiry. It -may or may not be the path which leads to the truth, but certainly -its indications are worthy of careful examination. It may be asked, -can weak man stop a pestilence; can a mortal’s puny hand retard the -afflictions of the Almighty? The question asked--it must be answered in -reverence, yet without fear. No human power can produce a change in the -physical conditions of the earth, or of the air; and if our diseases -are connected with those changes, as beyond all doubt a number of them -are, they lie above man’s control. But when there are indications that -causes secondary to these are producing some dire effect, and when -we know that these secondary causes may be modified, it is sufficient -evidence to prove that man is permitted to control thus far the -afflictions which are sent to try his powers. - -We find a disease winging its way from lane to alley and closed court, -sweeping with destructive violence its way through damp cellars and -crowded attics; it is rife with mischief along the banks of reeking -ditches, and on the borders of filthy streams. Certain it is, -therefore, that some ultimate connexion exists between the conditions -of dirt and this speedy death. Can science tell of these? has it yet -searched out the connecting link? Let the question be answered by a few -facts. - -When the cholera first made its appearance, and subsequently, it has -been observed that the electrical intensity of the atmosphere was -unusually low. - -The disease has departed, and it is then found that the electricity of -the air has been restored to its ordinary condition. - -This appears to show some connexion; but how do these conditions link -this physical force with the ditch-seeking disease? - -From all stagnant places, from all the sinks of overcrowded humanity, -from fermenting vegetable and from putrefying animal matter, there -are constantly arising poisonous exhalations to do their work of -destruction. - -Where death and decay is a law, this must of necessity constantly -occur; but the poisonous reek may be diffused, or it may be -concentrated, and Nature has provided for this, and ordered the means -for rendering the poison harmless. - -By the agency of electricity,--probably, too, by the influence of -light,--the oxygen in the air undergoes a peculiar change, by which -it is rendered far more energetic than it is in its ordinary state. -This is the condition to which the name of _ozone_ has been applied. -Now, this ozone, or this peculiar oxygen, always exists in the air we -breathe; but its quantity is subject to great and rapid variations. It -is found that when electrical intensity is high the quantity of this -principle is great; when the electrical intensity is low, as in the -cholera years, the proportion of ozone is relatively low. - -This remarkable chemical agent possesses the power of instantly -combining with organic matter,--of removing with singular rapidity all -noxious odours; and it would appear to be the most active of all known -disinfectants. - -May we not infer from the facts stated that the pestilence we dread is -the result of organic poison, which from a deficiency of ozone,--its -natural antidote,--exerts its baneful influences on humanity. This -deficiency is due to alterations in the electrical character of the -air, possibly dependent upon phenomena taking place in the sun itself, -or it may be still more directly influenced by variations in the -character of solar light, which we have not yet detected, by which the -conditions of the electric power are determined. - -This may be a line along which it is fair to push enquiry. But such -an enquiry must be made in all the purity of the highest inductive -philosophy, and speculation must be held firmly in the controlling -chains of experiment and observation. In the truths, however, which are -known to us, there is so much harmony and consistence that even the -melancholy theme links itself--a tragedy--with the Poetry of Science. - -It has been thought, and much satisfactory evidence has been brought -forward to support the idea, that the earth’s magnetism is due to -currents of electricity circulating around the globe; as a great -natural current from east to west--that, indeed, it has an unvarying -reference to the motion of the earth in relation to the sun.[152] - -These terrestrial currents, as they have without doubt a very important -bearing on the structural conditions of the rock-formations and the -distribution of minerals, require an attentive consideration; but we -must, in the first place, examine, as far as we know, the influences -exerted, or supposed to be exerted, by electricity, in its varied forms. - -The phenomena of vitality have, by many, been considered as immediately -dependent upon its influence; and a rather extensive series of -experiments has been made in support of this hypothesis. The researches -of Philip on the action of the organs of digestion, when separated -from their connection with the brain, but united with a galvanic -battery, have been proved by Dr. Reid to be delusive;[153] since, as -the organ is not removed from the influence of the living principle, -it is quite evident that the electricity here is only secondary to -some more important power. Matteucci has endeavoured to show that -nervous action is intimately connected with electric excitation, and -that electricity may be made a measurer of nervous irritability.[154] -There can be no doubt that a peculiar susceptibility to excitement -exists in some systems, and this is very strikingly shown in the -disturbances produced by electric action; but in the experiments which -have been brought forward we have only the evidence that a certain -number of muscular contractions are exhibited in one animal by a -current of electricity, giving a measured effect by the voltameter, -which are different from those produced upon another by a current of -the same power. An attempt has recently been made by Mr. A. Smee to -reduce the electrical phenomena connected with vitality to a more -exact system than had hitherto been done. We cannot, however, regard -the attempt as successful. The author has trusted almost entirely -to analogical reasoning, which is in science always dangerous.[155] -In the development of electricity during the operation of the vital -force, we see only the phenomena produced by the action of any two -dissimilar chemical compounds upon each other. It has been thought -that the structure of the brain presents an analogy to that of the -galvanic battery, and the nerves represent the conducting wires. -Although, however, some of the conditions appear similar, there are -many which have no representatives in either the mechanical structure -or the physical properties of the brain, so far as we know it. That -the brain is the centre, the source, and termination of sensation is -very clearly proved by physiological investigations. That the nerves -are the media by which all sensation is conveyed to the brain, and -also the instruments by which the will exerts its power over the -muscles, is equally well established. But to say that we have any -evidence to support the idea that electricity has aught to do directly -with these great physiological phenomena, would be a bold assertion, -betraying a want of due caution on the part of the investigator. That -electric effects are developed during the operations of vitality is -most certain. Such must be the case, from the chemical changes taking -place during respiration and digestion, and the mechanical movements -by which, even during external repose, the necessary functions of the -body are carried on. Whether electricity is the cause of these, or an -effect arising from them, we need not stop to examine, as this is, -in the present state of our knowledge, a mere speculation. We have -no evidence that electricity is an exciting power, but rather that -it is one of those forces which tend to establish the equilibrium of -matter. When disturbed--when its equilibrium is overset--it does, in -its efforts to regain its stability, produce most remarkable effects. -An electrical machine must be rubbed to exhibit any force. In all -galvanic arrangements, even the most simple, dissimilar bodies are -brought together, and the latent electricity of both is disturbed; -and, even in the magnet, it is only when this takes place that its -electrical powers are developed. In the _Gymnotus_, electricity appears -to be dependent upon the power of the will of the animal; but even in -this extraordinary fish, it is only under peculiar conditions that the -electrical excitement takes place, and “what they inflict, they feel” -during the restoration of that equilibrium which is necessary to their -healthy state. In every case, therefore, we see that some power far -superior to this is the ultimate cause; indeed, light and heat, and -probably actinism, appear to stand superior to this principle; and on -these, in some combined mode of action, in all probability, sensible -electricity is dependent. Beyond even these elements, largely as they -are engaged in the organic and inorganic changes of this world, there -are occult powers which may never be understood by finite beings. -We advance step by step from the most solid to the most ethereal of -material creations, and we examine a series of extraordinary effects -produced by powers which we know not whether to regard as material or -immaterial, so subtile are they. On these, it appears, we may exhaust -our inductive investigations--we may discover the laws by which these -principles act upon the grosser elements, and develope phenomena of -a very remarkable kind which have been unobserved or misunderstood. -Whether light, heat, and electricity are modifications of one power, -or different powers very closely united in action, is a problem we may -possibly solve; but to know what they are, appears to be beyond the -hopes of science; and it were idle to dream of elucidating the causes -hidden beyond these forces, and by which they are regulated in all -their actions on dead or living matter. - -M. Du Bois Raymond, from a series of researches remarkable alike for -their difficulty and the delicacy with which they have been pursued, -draws the following, amongst many others, as his conclusions as to the -connection of electricity and vital phenomena. - -The muscles and nerves, including the brain and the spinal chord, are -endowed during life with an electromotive power, which acts according -to a definite law. - -The electromotive power _lasts after death_, or in dissected nerves and -muscles after separation from the body of the animal, as long as the -excitability of the nervous and muscular fibre; whether these fibres -are permitted to die gradually from the cessation of the conditions -necessary to the support of life, or whether they are suddenly deprived -of their vital properties by heat or chemical action. - -Let us not suppose for a moment that these conclusions indicate in the -remotest degree that electricity is life,--that vital power is due to -electricity. - -During life, with every motion, and, indeed, with every emotion, -whether we move a muscle or exert the mind, there is a change of state. -The result of this is chemical phenomena,--heat and electricity; but -these are not life. We excite them equally by giving motion to a dead -mass. - -Notwithstanding the assertions of those who have zealously followed -the path of Mesmer, and examined, or they have thought so, the -psychological effects dependent upon some strange physiological -conditions, there is not an experiment on record,--there is not an -observation worthy of credit, which shows that electricity has any -connection with their results. All around their subject is uncertainty: -doubt involves every experiment, and deception clouds a large number. -Some few grains of truth, and these are sufficiently strange, are mixed -up in an enormous mass of error. - -All the phenomena of life,--of the _vis vitæ_ or vitality, are beyond -human search. All the physical forces, or elements, we may examine by -the test of experiment: but the principle on which sensation depends, -the principle even upon which vegetable _life_ depends, cannot be -tested. Life is infinitely superior to every physical force; it holds -them all in control, but is not itself controlled by them; it keeps -its state sacred from human search,--the invisible hidden behind the -veil of mortality. - -During changes in the electrical conditions of the earth and -atmosphere, vegetables give indications of being in a peculiar manner -influenced by this power. It is proved by experiments that the leaves -of plants are among the best conductors of electricity, and it has -hence been inferred that it must necessarily be advantageous to -vegetation. That vegetable growth is, equally with animal growth, -subject to electricity, as one of its quickening powers, must be -admitted; but all experiments which have been fairly tried with the -view of stimulating the growth of plants by its agency, have given -results of a negative character.[156] That a galvanic arrangement may -produce chemical changes in the soil, which may be advantageous to the -plant, is probable; but that a plant can be brought to maturity sooner, -or be made to develope itself more completely, under the direct action -of electrical excitation, appears to be one of those dreams of science -which will have a place amongst the marvels of alchemy and the fictions -of astrology. An attentive examination of all the conditions necessary -for the satisfactory development of the plant, will render it evident, -that although the ordinary electrical state of the earth and atmosphere -must influence the processes of germination and vegetable growth, -yet that any additional excitement must be destructive to them. The -wonders wrought by electrical power are marvellous; a magic influence -is exerted by it, and naturally the inquiring mind is led at first to -believe that electricity is the all-powerful principle of creation; but -a little reflection will serve to convince us that it is a subordinate -agent, although a powerful one. - -In proceeding with our examination of the phenomena which present -themselves in connection with the terrestrial currents, we purposely -separate magnetism from those more distinct electro-chemical agencies -which play so important a part in the great cosmical operations. - -Electricity, we have already stated, flows through or involves all -bodies; but, like heat, it appears to undergo a very remarkable change -in becoming associated with some forms of matter. We have the phenomena -of magnetism when an electric current circulates through a metallic -wire, and it would appear that all other bodies acquire a peculiar -polar condition under the influence of this principle, which will be -explained in the next chapter. - -The rocks, taken as masses, will not conduct an electric current when -dry: granite, porphyry, slate, and limestone, obstructing its passage -even through the smallest spaces. But all the metallic formations admit -of its circulating with great freedom. This fact it must, however, -be remembered does not in any way interfere with the hypothesis of -the existence of electricity in all bodies, in what we must regard as -its latent state, from which, under prescribed conditions, it may be -readily liberated. Neither does it affect the question of circulation, -in relation to the great diffusion of electricity which we suppose to -exist through all nature, and to move in obedience to some fixed law. -We know that through the superficial strata electric currents circulate -freely, whether they are composed of clay, sand, or any mixture of -these with decomposed organic matter; indeed, that with any substance -in a moist state they suffer no interruption. - -The electricity of mineral veins has attracted much attention, and -numerous investigations into the phenomena which these metalliferous -formations present, have been made from time to time.[157] - -By inserting into the mass of a copper _lode_, or vein, in situ, a -metallic wire, which shall be connected with a measurer of galvanic -action, a wire also from the instrument being brought into contact with -another _lode_, an immediate effect is generally produced, showing -that a current is traversing through the wires from one _lode_ to the -other, and completing the circulation probably over the dark face of -the rock in which the fissures forming the mineral veins exist.[158] -The currents thus detected are often sufficiently active to deflect -a magnetic needle powerfully, to produce, slowly, electro-chemical -decomposition, and to render a bar of iron magnetic. These currents -must not be confounded with the great electrical movements around the -earth. They are only to be detected in those mineral formations in -which there is evidence of chemical action going on, and, the greater -the amount of this chemical operation, the more energetic are the -electrical currents.[159] We have, however, very good evidence that -these local currents have, of themselves, many peculiar influences. It -not unfrequently happens that owing to some great disturbance of the -crust of the earth, a mineral vein is dislocated, and one part either -sinks below, or is lifted above its original position; the fissures -formed between the two being usually filled in with clay or with -crystalline masses of more recent formation than the fissure itself. It -is frequently found that these “_cross courses_,” as they are called in -mining language, contain ores of a different character from those which -constitute the mineral vein; for instance, in them nickel, cobalt, and -silver are not unfrequently discovered. When these metals are so found, -they almost invariably occur between the ends of the dislocated lode, -and often take a curvilinear direction, as if they were deposited along -a line of electrical force.[160] - -In the laboratory such an arrangement has been imitated, and in a -mass of clay fixed between the galvanic plates, after a short period -a distinct formation of a mineral vein has taken place.[161] By the -action, too, of weak electrical currents, Becquerel, Crosse, and -others, have been successful in imitating nature so far as to produce -crystals of quartz and other minerals. In addition to this evidence, in -support of the electrical theory of the origin of mineral veins, it -can be experimentally shown that a schistose structure may be given to -clays and sandstone by voltaic action.[162] - -There is often a very remarkable regularity in the direction of mineral -veins: throughout Cornwall, for instance, they most commonly have a -bearing from the E. of N. to the W. of S. It has hence been inferred -that they observe some relation to the magnetic poles of the earth. -However this may be, it is certain that the ore in any lodes which -are in a direction at right angles, or nearly so, to this main line, -differs in character from that found in these, so called, east and west -lobes.[163] - -The sources of chemical action in the earth are numerous. Water -percolating through the soil, and finding its way to great depths -through fissures in the rocks, carries with it oxygen and various -salts in solution. Water again rising from below, whether infiltrated -from the ocean or derived from other sources, is usually of a high -temperature, and it always contains a large quantity of saline -matter.[164] By these causes alone chemical action must be set -up. Chemical change cannot take place without a development of -electricity: and it has been proved that the quantity of electricity -required for the production of any change is equal to that contained -in the substances undergoing such change. Thus a constant activity is -maintained within the caverns of the rock by the agency of the chemical -and electrical elements, and mutations on a scale of great grandeur are -constantly taking place under some directive force. - -The mysterious gnome, labouring--ever labouring--in the formation of -metals, and the mischievous Cobalus of the mine, are the poor creations -of superstition. A vague fear is spread amongst great masses of mankind -relative to the condition of the dark recesses of the earth; a certain -unacknowledged awe is experienced by many on entering a cavern, or -descending a mine: not the natural fear arising from the peculiarity of -the situation, but the result of a superstitious dread, the effect of a -depraved education, by which they have been taught to refer everything -a little beyond their immediate comprehension to supernatural causes. -The spirit of demon worship, as well as that of hero worship, has -passed from the early ages down to the present; and under its influence -the genii of the East and the demons of the West have preserved their -traditionary powers. - -Fiction has employed itself with the utmost license in giving glowing -pictures of treasures hidden in the earth’s recesses. The caverns -of Chilminar, the cave of Aladdin, the abodes of the spirits of the -Hartz, and the dwellings of the fairies of England, are gem-bespangled -and gold-glistening vaults, to which man has never reached. The -pictures are pleasing; but although they have the elements of poetry -in them, and delight the young mind, they want the sterling character -of scientific truth; and the wonderful researches of the plodding -mineralogist have developed more beauty in the caverns of the dark rock -than ever fancy painted in her happiest moments. - -In all probability the action of the sun’s rays upon the earth’s -surface, producing a constantly varying difference of temperature, -and also the temperature which has been observed as existing at great -depths, give rise to thermo-electrical currents, which may play an -important part in the results thus briefly described. - -In connection with these great natural operations, explaining them, -and being also, to some extent, explained by them, we have the very -beautiful application of electricity to the deposition of metals, -called the Electrotype. - -Applying the views we have adopted to this beautiful discovery,[165] -the whole process by which these metallic deposits are produced will -be yet more clearly understood. By the agency of the electric fluid, -liberated in the galvanic battery, a disturbance of the electricity of -the solution of copper, silver, or gold, is produced, and the metal is -deposited; but, instead of allowing the acid in combination to escape, -it has presented to it some of the same metal as that revived, and, -consequently, it combines with it, and this compound, being dissolved, -maintains the strength of the solution.[166] A system of revival, or -decomposition, is carried on at one pole, and one of abrasion, or more -correctly speaking, of composition and solution, at the other. By -taking advantage of this very extraordinary power of electricity, we -now form vessels for ornament or use, we gild or silver all kinds of -utensils, and give the imperishability of metal to the most delicate -productions of nature--her fruits, her flowers, and her insects;--and -over the finest labours of the loom we may throw coatings of gold or -silver to add to their elegance and durability. Nor need we employ the -somewhat complex arrangement of the battery: we may take the steel -magnet, and, by mechanically disturbing the electricity it contains, we -can produce a current through copper wires, which may be used, and is -extensively employed, for gilding and silvering.[167] The earth itself -may be made the battery, and, by connecting wires with its mineral -deposits, currents of electricity have been secured, and used for the -production of electrotype deposit.[168] - -The electrotype is but one of the applications of electricity to the -uses of man. This agent has been employed as the carrier of thought; -and with infinite rapidity, messages of importance, communications -involving life, and intelligences outstripping the speed of coward -crime, have been communicated. There will be no difficulty in -understanding the principle of this, although many of the nice -mechanical arrangements, to ensure precision, are of a somewhat -elaborate character. The entire action depends on the deflection of a -compass-needle by the passage of an electric current along its length. -If at a given point we place a galvanic battery, and at twenty or one -hundred miles distance from it a compass-needle, between a wire brought -from, and another returning to the battery, the needle will remain true -to its polar direction so long as the wires are unexcited; but the -moment connection is made, and the circuit is complete, the electricity -of the whole extent of wire is disturbed, and the needle is thrown at -right angles to the direction of the current. Provided a connection -between two points can be secured, however remote they are from each -other, we thus, almost instantaneously, convey any intelligence. The -effects of an electric current would appear at a distance of 576,000 -miles in a second of time; and to that distance, and with that speed, -it is possible, by Professor Wheatstone’s beautiful arrangements, to -convey whispers of love or messages of destruction. - -The enchanted horse of the Arabian magician, the magic carpet of the -German sorcerer, were poor contrivances, compared with the copper -wires of the electrician, by which all the difficulties of time and -the barriers of space appear to be overcome. In the Scandinavian -mythology we find certain spiritual powers of evil enabled to pass -with imperceptible speed from one remote point to another, sowing the -seeds of a common ruin amongst mankind. Such is the morbid creation -of a wild yet highly endowed imagination. The spirit of evil diffuses -itself in a remarkable manner, and, indeed, we might almost assign to -it the power of ubiquity; but in reality its advance is progressive, -and time enters as an element into any calculation on its diffusion. -Electricity is instantaneous in action; as a spirit of peace and -good-will it can overtake the spirit of evil, and divert it from its -designs. May we not hope that the electrical telegraph, making, as it -must do, the whole of the civilized world enter into a communion of -thought, and, through thought, of feeling with each other, will bind us -up in one common brotherhood, and that, instead of misunderstanding and -of misinterpreting the desires and the designs of each other, we shall -learn to know that such things as “natural enemies” do not exist? To -hope to break down the great barrier of language is perhaps too much; -but assuredly we may hope that, as we must do when closer and more -intimate relations are secured by the aids of science, the barrier of -prejudice may be razed to the ground, and not one stone left to stand -upon another? Our contentions, our sanguinary wars, consecrated to -history by the baptism of blood, have in every, or in nearly every, -instance sprung from the force of prejudice, or the mistakes of -politicians, whose minds were narrowed to the limits of a convention -formed for perpetuating the reign of ignorance. - -And can anything be more in accordance with the spirit of all that we -revere as holy, than the idea that the elements employed by the All -Infinite in the works of physical creation shall be made, even in the -hands of man, the ministering angels to the great moral redemption of -the world? Associate the distant nations of the earth, and they will -find some common ground on which they may unite. Mortality compels a -dependence; and there are charities which spring up alike in the breast -of the savage and the civilized man, which will not be controlled by -the cold usages of pride, but which, like all truths, though in a still -small voice, speak more forcibly to the heart than errors can, and -serve as links in the great chain which must bind mankind in a common -brotherhood. “None are all evil,” and the best have much to learn of -the amenities of life from him who yet lives in a “state of nature,” or -rather from him whose sensualities have prevailed over his intellectual -powers, but who still preserves many of the noblest instincts, to give -them no higher term, which other races, proud of their intelligence, -have thrown aside. Time and space have hitherto prevented the -accomplishment of this; electricity and mechanics promise to subdue -both; and we have every reason to hope those powers are destined to -accelerate the union of the vast human family. - -Electrical power has also been employed for the purpose of measuring -time, and by its means a great number of clocks can be kept in a state -of uniform correctness, which no other arrangement can effect. A -battery being united with the chief clock, which is itself connected -by wires with any number of clocks arranged at a distance from each -other, has the current continually and regularly interrupted by the -beating of the pendulum, which interruption is experienced by all the -clocks included in the electric circuit; and, in accordance with this -breaking and making contact, the indicators or hands move over the dial -with a constantly uniform rate. Instead of a battery the earth itself -has supplied the stream of electric fluid, with which the rate of its -revolutions has been registered with the utmost fidelity.[169] - -Electricity, which is now employed to register the march of time, -rushes far in advance of the sage who walks with measured tread, -watching the falling sands in the hour-glass. - -The earth is spanned and the ocean pierced by the wires of the electric -telegraph. Already, from the banks of the Thames to the shores of the -Adriatic, our electric messenger will do our bidding. The telegraph -is making its way through Italy, and it is dipping its wires in the -Mediterranean, soon to reach the coast of Africa. They will then run -along the African shores to Egypt and Turkey, and still onward until -they unite with the telegraphs of India, of which three thousand miles -are in progress. From Hindostan these wondrous wires will run from -island to island in the Indian Archipelago, and thus connect Australia -and New Zealand with Europe. - -In a few years we may expect to have an instantaneous report in London -of the extraordinary “nugget” discovered by some fortunate gold-digger; -and the exile from his native land in the Islands of the South Pacific -Ocean, may learn every hour, if he will, of the doings of his family -and friends in some village home of England. - - -FOOTNOTES: - -[136] _Traité de Physique_: M. Biot, vol. vii. Becquerel: Annales -de Chimie, vol. xlvi.-xlix. Faraday’s _Experimental Researches in -Electricity_, 2 vols., 1830-1844. _A Speculation touching Electric -Conduction and the Nature of Matter_: by Michael Faraday, D.C.L., -F.R.S.; Philosophical Magazine, vol. xxiv., 1836. _Objections to the -theories severally of Franklin, Dufay, and Ampère, with an attempt to -explain Electrical Phenomena by statical or undulatory polarization_: -by Robert Hare, M.D., Emeritus Professor of Chemistry in the University -of Pennsylvania. - -[137] “A good piece of gutta percha will insulate as well as an equal -piece of shell-lac, whether it be in the form of sheet, or rod, or -filament; but being tough and flexible when cold, as well as soft -when hot, it will serve better than shell-lac in many cases where the -brittleness of the latter is an inconvenience. Thus it makes very good -handles for carriers of electricity in experiments on induction; not -being liable to fracture in the form of thin band or string, it makes -an excellent insulating suspender; a piece of it in sheet makes a -most convenient insulating basis for anything placed on it. It forms -excellent insulating plugs for the stems of gold-leaf electrometers, -when they pass through sheltering tubes, and larger plugs form good -insulating feet for electrical arrangements; cylinders of it, half an -inch or more in diameter, have great stiffness, and form excellent -insulating pillars. In these and in other ways its power as an -insulator may be useful.”--_On the use of Gutta Percha in Electrical -Insulation_: by Dr. Faraday; Philosoph. Mag., March, 1848. - -The following deductions have been given by Faraday, in his _Researches -in Electricity_, a work of most extraordinary merit, being one of the -most perfect examples of fine inductive philosophy which we possess in -the English language:-- - -“All bodies conduct electricity in the same manner from metals to lacs -and gases, but in very different degrees. - -“Conducting power is in some bodies powerfully increased by heat, and -in others diminished, yet without one perceiving any accompanying -essential electrical difference, either in the bodies, or in the change -occasioned by the electricity conducted. - -“A numerous class of bodies insulating electricity of low intensity, -when solid, conduct it very freely when fluid, and are then decomposed -by it. - -“But there are many fluid bodies which do not sensibly conduct -electricity of this low intensity; there are some which conduct it and -are not decomposed; nor is fluidity essential to decomposition. - -“There are but two bodies (sulphuret of silver and fluoride of lead) -which, insulating a voltaic current when solid, and conducting it when -fluid, are not decomposed in the latter case. - -“There is no strict electrical distinction of conduction which can as -yet be drawn between bodies supposed to be elementary, and those known -to be compounds.” - -[138] Faraday’s _Speculation on the Nature of Matter_, already referred -to. - -[139] _Experimental Researches_: by Dr. Faraday. _Chemical -Decomposition_, p. 151. - -[140] Karsten; Poggendorff’s _Annalen_, vol. lvii. - -[141] _Traité Expérimental de l’Électricité et du Magnétisme_: -Becquerel, 1834, Priestley’s _Introduction to Electricity_. _On -Electricity in Equilibrium_: Dr. Young’s Lectures. - -[142] Faraday’s _Experimental Researches on Electricity_. This -philosopher has shown, by the most conclusive experiments, “that -the electricity which decomposes, and that which is evolved by the -decomposition of, a certain quantity of matter, are alike. What an -enormous quantity of electricity, therefore, is required for the -decomposition of a single grain of water! We have already seen that -it must be in quantity sufficient to sustain a platinum wire 1/104 -of an inch in thickness, red hot, in contact with the air, for three -minutes and three quarters. It would appear that 800,000 charges of a -Leyden battery, charged by thirty turns of a very large and powerful -plate machine, in full action--a quantity sufficient, if passed at once -through the head of a rat or cat, to have killed it as by a flash of -lightning--are necessary to supply electricity sufficient to decompose -a single grain of water; or, if I am right, to equal the quantity of -electricity which is naturally associated with the elements of that -grain of water, endowing them with their mutual chemical affinity.” - -[143] _Experimental Researches_: Faraday. - -[144] The appearance of acid and alkaline matter, in water acted on -by a current of electricity, at the opposite electrified metallic -surfaces, was observed in the first chemical experiments made with -the column of Volta--(see Nicholson’s Journal, vol. iv. p. 183, and -vol. iv. p. 261, for Mr. Cruickshank’s Experiments; and Annales de -Chimie, tom. xxxvii. p. 233, for those of M. Desormes): _On some -Chemical Agencies in Electricity_: by Sir Humphry Davy.--Philosophical -Transactions for 1807. The various theories of electro-chemical -decomposition are carefully stated by Faraday, in his fifth series -of _Experimental Researches on Electricity_, in which he thus states -his own views:--“It appears to me that the effect is produced by an -_internal corpuscular action_ exerted according to the direction of -the electric current, and that it is due to a force either _superadded -to_ or _giving direction to the ordinary chemical affinity_ of the -bodies present. The body under decomposition may be considered as a -mass of acting particles, all those which are included in the course -of the electric current contributing to the final effect; and it is -because the ordinary chemical affinity is relieved, weakened, or partly -neutralized by the influence of the electric current in one direction -parallel to the course of the latter, and strengthened or added to in -the opposite direction, that the combining particles have a tendency to -pass in opposite courses.” - -[145] “This capital discovery (chemical decomposition of electricity) -appears to have been made in the first instance by Messrs. Nicholson -and Carlisle, who observed the decomposition of water so produced. It -was speedily followed up by the still more important one of Berzelius -and Hisinger, who ascertained it as a general law, that, in all the -decompositions so effected, the acids and oxygen become transferred and -accumulated around the positive, and hydrogen, metals, and alkalies -around the negative, pole of a voltaic circuit; being transferred in -an invisible, and, as it were, a latent or torpid state, by the action -of the electric current, through considerable spaces, and even through -large quantities of water or other liquids, again to reappear with all -their properties at their appropriate resting-places.”--_Discourse on -the Study of Natural Philosophy_: by Sir John Herschel, Bart., F.R.S. - -[146] Numerous beautiful illustrations of this fact will be found in -Becquerel’s _Traité Expérimental de l’Électricité et du Magnétisme_. - -[147] See _Le Feu élémentaire_ of l’Abbé Nollet; Leçons de -Physique, tom. vi. p. 252; _Du Pouvoir thermo-électrique_, by M. -Becquerel--Annales de Chimie, vol. xli. p. 353; also a Memoir by -Nobili, Bibliothèque Universelle, vol. xxxvii. p. 15; _Experimental -Contributions towards the theory of Thermo-Electricity_ by Mr. J. -Prideaux--Philosophical Magazine, vol. iii., Third Series; _On the -Thermo-Magnetism of Homogeneous Bodies, with illustrative experiments_, -by Mr. William Sturgeon--Philosophical Magazine, vol. x. p. 1-116, -New Series. Botto made magnets and obtained chemical decomposition. -Antinori produced the spark. Mr. Watkins heated a wire in Harris’s -Thermo-Electrometer. - -[148] A very ingenious application of the knowledge of this fact -was suggested by Mr. Solly, by which the heat of a furnace could be -constantly registered at a very considerable distance from it. See -_Description of an Electric Thermometer_: by E. Solly, Jun., Esq. -Philosophical Magazine, vol. xx. p. 391. New Series. - -[149] Humboldt; _Personal Narrative_, Chap. xvii.--Annales de Chimie, -vol. xiv. p. 15. - -[150] _Experimental Researches on Electricity._ Series xv. -Consult Sir Humphry Davy: _An Account of some Experiments on the -Torpedo_.--Philosophical Transactions, 1829, p. 15. John Davy, M.D., -F.R.S.: _An Account of some Experiments and Observations on the -Torpedo_, ibid., 1832, p. 259; and the same author’s _Observations on -the Torpedo, with an Account of some Additional Experiments on its -Electricity_; and Matteucci, Bibliothèque Universelle, 1837, vol. xii. -p. 174. - -[151] _On Lightning Conductors_, by Sir William Snow Harris; -_Observations on the Action of Lightning Conductors_, by W. Snow -Harris, Esq., F.R.S.--London Electrical Society’s Transactions. -Numerous valuable papers _On Electricity_, by Sir William Harris, will -be found in the Philosophical Transactions. - -[152] Adopting, to a certain extent, this view, Faraday, in his -_Electrical Nomenclature_, proposed for the word pole to substitute -_anode_ (ανω, _upwards_, and ὁδος, _a way_), the way which the sun -rises; and _cathode_ (κατα, _downwards_, and ὁδος, _a way_), the way -which the sun sets. The hypothesis belongs essentially to Ampère. -_Objections to the Theories severally of Franklin, Dufay, and Ampère, -with an Effort to Explain Electrical Phenomena by Statical or -Undulatory Polarisation_, by Robert Hare, M.D., Pennsylvania, will well -repay an attentive perusal. - -[153] _Inquiry into the Laws of the Vital Functions._--Philosophical -Transactions, 1815, 1822; _Some Observations relating to the Functions -of Digestion_, ibid., 1829: _On the Powers on which the Functions of -Life in the more perfect animals depend, and on the manner in which -they are associated in the production of their more complicated -results_, by A. P. W. Philip, M.D., F.R.S., L. and E.--The following -extract from the last-quoted of Dr. Philip’s Memoirs, will give a -general view of the conclusions of that eminent physiologist:--“With -respect to the nature of the powers of the living animal which we have -been considering, the sensorial and muscular powers, and the powers -peculiar to living blood, we have found belong to the living animal -alone, all their peculiar properties being the properties of life. The -functions of life may be divided into two classes, those which are -affected by the properties of this principle alone, and those, by far -the most numerous class, which result from the co-operation of these -properties with those of the principles which operate in inanimate -nature. The nervous power we have found to be a modification of one -of the latter principles, because it can exist in other textures than -those to which it belongs in the living animal, and we can substitute -for it one of those principles without disturbing the functions of life. - -“Late discoveries have been gradually evincing how far more extensive -than was supposed, even a few years ago, is the dominion of -electricity. Magnetism, chemical affinity, and (I believe from the -facts stated in the foregoing paper, it will be impossible to avoid -the conclusion) the nervous influence, the leading power in the vital -functions of the animal frame, properly so called, appear all of them -to be modifications of this apparently universal agent; for I may add -we have already some glimpses of its still more extensive dominion.” - -Refer to Dr. Reid’s papers. - -[154] _Electro-physiological Researches_: by Signor Carlo Matteucci; -Phil. Trans. 1845, p. 293, and subsequent years. - -[155] Electro-Biology: by Alfred Smee, Esq. - -[156] _Observations of Electric Currents in Vegetable Structures_: by -Golding Bird, Esq., F.L.S.; Magazine of Natural History, vol. x. p. -240. In this paper Dr. Bird remarks that his experiments lead to the -conclusion that vegetables cannot become so charged with electricity -as to afford a spark; that electrical currents of feeble tension are -always circulating in vegetable tissues; and that electrical currents -are developed during germination from chemical action. - -[157] _On Mineral Veins_: by Robert Were Fox, Esq.; Fourth Report -of the Royal Cornwall Polytechnic Society. _On the Electro-magnetic -Properties of Metalliferous Veins in the mines of Cornwall_: by Robert -W. Fox, Esq.; Phil. Trans. 1830, p. 399. - -[158] _Experiments and Observations on the Electricity of Mineral -Veins_: by Robert Hunt and John Phillips; Reports of the Royal Cornwall -Polytechnic Society for 1841-42. _On the Electricity of Mineral Veins_: -by Mr. John Arthur Phillips; Ibid., 1843. - -[159] In the lead lodes of _Lagylas_ and _Frongoch_, electrical -currents were detected by Mr. Fox, but none in those of _South Mold_ -and _Milwr_, in Flintshire: Cornwall Geological Transactions, vol. iv. -In the lead veins of _Coldberry_ and _Skeers_, in Teasdale, Durham, the -currents detected were very feeble: Reports of the Bristol Association, -1838. Von Strombeck could detect no electric currents in the veins -worked in the clay slate near Saint Goar, on the Rhine: Archiv. für -Mineralogie, Geognosie, &c., von Dr. C. J. B Karsten, 1833. Professor -Reich, however, obtained very decided results at _Frisch Glück_, -_Neue Hoffnung_, _Gottlob_, and in other mineral veins in the mining -districts of Saxony: Edinburgh New Philosophical Journal, vol. xxviii. -1839. The irregularities are all to be explained by the presence or -absence of chemical excitation. - -[160] This was remarkably the case at _Huel Sparnon_, near Redruth, -where the cobalt was discovered between two portions of a dislocated -lode; and the same was observed by Mr. Percival Johnson in a small mine -worked for nickel, near St. Austell. - -[161] _On the process used for obtaining artificial veins in clay_: by -T. B. Jordan; Sixth Annual Report of the Royal Cornwall Polytechnic -Society. See also my memoir, already referred to, in the Memoirs of the -Geological Survey and Museum of Practical Geology, vol. i. - -[162] See Becquerel, _Traité Experimental de l’Electricité, &c. -Electrical Experiments on the formation of Artificial Crystals_: by -Andrew Crosse, Esq.; British Association Reports, vol. v., 1836. The -lamination of clay and other substances is described in my memoir -referred to, Note p. 226. - -[163] Report on the Geology of Cornwall, Devon, and West Somerset, by -Sir Henry T. De la Beche: _Theoretical observations on the formation -and filling of Mineral Veins and Common Faults_, p. 349. - -[164] The following analyses of waters from deep mines were made by me -in 1840, and, with many others, published in the Reports of the Royal -Cornwall Polytechnic Society. - - Consolidated Mines, Gwennap, - Cornwall. In 1,000 grains of water. - Muriate of soda 1·5 - Sulphate of lime ·5 - Sulphate of iron ·15 - Sulphate of copper 1·25 - Silica ·15 - Alumina ·3 - ---- - Total 3·7 - - United Mines, Gwennap. - Muriate of soda 1·10 - Muriate of lime ·15 - Sulphate of soda ·50 - Sulphate of lime 1·5 - Sulphate of iron ·75 - Alumina ·5 - Silica ·15 - ---- - Total 4·65 - - Great St. George. - Muriate of soda 1·35 - Sulphate of lime ·74 - Carbonate of iron ·70 - Alumina ·50 - Carbonate of lime ·10 - ---- - Total 3·4 - -[165] The discovery of the electrotype has been disputed, as all -valuable discoveries are. Without, however, at all disparaging the -merits of what had been done by Mr. Jordan, I am satisfied, after -the most careful search, that the first person who really employed -electro-chemical action for the precipitation of metals in an -ornamental form, was Mr. Spencer, of Liverpool. - -[166] See Spencer, _Instructions for the Multiplication of works of Art -in Metal by Voltaic Electricity. Novelties in Experimental Science_: -Griffin, Glasgow, _Elements of Electro-Metallurgy_: by Alfred Smee, Esq. - -[167] The magneto-electrical machine is employed in Birmingham for this -purpose; but I am informed by Messrs. Elkington that they do not find -it economical, or rather that the electro-precipitation is carried on -too slowly. - -[168] This has been done by Mr. Robert Were Fox, at a mine near -Falmouth. By connecting two copper wires with two lodes, and bringing -them, at the surface, into a cell containing a solution of sulphate -of copper, this gentleman obtained an electrotype copy of an engraved -copper-plate. - -[169] This has been most effectually accomplished by Mr. Bain. Mr. -Hobson has had an electric clock, thus excited, in action for several -years. - - - - -CHAPTER X. - -MAGNETISM. - - Magnetic Iron--Knowledge of, by the Ancients--Artificial - Magnets--Electro-Magnets--Electro-Magnetism--Magneto- - Electricity--Theories of Magnetism--The Magnetic Power of soft Iron - and Steel--Influence of Heat on Magnetism--Terrestrial - Magnetism--Declination of the Compass-needle--Variation of the - Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly - and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora - Borealis--Magnetic Storms--Magnetic conditions of - Matter--Diamagnetism, &c. - - -Agreeably with the view now generally received, that magnetism and -electricity are but modifications of one force, since they are found to -stand to each other in the relation of cause and effect, the separation -which is here adopted, of the consideration of their several phenomena, -may appear inappropriate. The importance, however, of all that is -connected with magnetism, and the very decided difference which is -presented by true magnetic action, and that of frictional or chemical -electricity, is so great that it has been thought advantageous to adopt -the present arrangement in reviewing the influence of terrestrial -magnetism with which science has made us acquainted. - -From a very early period a peculiar attractive force has been observed -in some specimens of iron ore. Masses of this kind were found in -Magnesia, and from that locality we derive the name given to iron in -its polar condition. This is confirmed by the following lines by -Lucretius:-- - - Quod superest agere incipiam, quo fœdere fiat - Natura lapis hic ut ferrum ducere possit, - Quem magnêta vocant patrio de nomine Graii - Magnêtum, quia sit patriis in finibus ortus. - -Again we find Pliny employing the term _magnetic_, to express this -singular power. It was known to the ancients that the magnetic power -of iron, and the electric property of amber, were not of the same -character, but they were both alike regarded as miraculous. The Chinese -and Arabians seem to have known Magnetism at a period long before -that at which Europeans became acquainted with either the natural -loadstone or the artificial magnet. Previously to A.D. 121, the magnet -is distinctly mentioned in a Chinese dictionary; and in A.D. 419 it -is stated in another of their books that ships were steered south by -it.[170] - -The earliest popularly received account of its use in Europe is, that -Vasco de Gama employed a compass in 1427, when that really adventurous -navigator first explored the Indian seas. It is highly probable, -however, that the knowledge of its important use was derived from some -of the Oriental nations at a much earlier period. - -We have some curious descriptions of the _leading stone_ or loadstone, -in the works of an Icelandic historian, who wrote in 1068. The -mariner’s compass is described in a French poem of the date of 1181; -and from Torfæus’s History of Norway, it appears to have been known to -the northern nations certainly in 1266. - -We have not to deal with the history of magnetic discovery, but so -far as it tells of the strange properties which magnets are found to -possess, and the application of this knowledge to the elucidation of -effects occurring in nature. - -A brown stone, in no respect presenting anything by which it shall be -distinguished from other rude stones around it, is found, upon close -examination, to possess the power of drawing light particles of iron -towards it. If this stone is placed upon a table, and iron filings -are thrown lightly around it, we discover that these filings arrange -themselves in symmetric curves, proceeding from some one point of the -mass to some other; and upon examining into this, we shall find that -the iron which has once clung to the one point will be rejected by the -other. If this stone is freely suspended, we shall learn also that -it always comes to rest in a certain position,--this position being -determined by these points, and some attractive force residing in the -earth itself. These points we call its poles; and it is now established -that this rude stone is but a small representative of our planet. Both -are magnetic: both are so in virtue of the circulation of currents -of electricity, or of lines of magnetic force, as seen in the curves -formed by the iron dust, and the north pole of the one attracts the -south pole of the other, and the contrary. By a confusion of terms we -speak of the north pole of a compass-needle, meaning that point which -is always opposite to the north pole of the earth: the truth being -that the pole of the compass-needle, which is so forcibly drawn to the -north, is a point in a contrary state, or, as we may express it, really -a south pole. - -There is a power of a peculiar kind, differing from gravitation, or any -other attracting or aggregating force with which we are acquainted, -which exists permanently in the magnetic iron stones, and also in the -earth. What is this power? - -Magnetism may be produced in any bar of steel, either by rubbing it -with a loadstone, or by placing it in a certain position in relation to -the magnetic currents of the earth, and, by a blow or any other means, -disturbing its molecular arrangement. This principle appears to involve -the iron as with an atmosphere, and to interpenetrate it. By one magnet -we may induce magnetism in any number of iron bars without its losing -any of its original force. As we have observed of the electrical forces -already considered, the magnet constantly presents two points in -which there is a difference manifested by the circumstance that they -are always drawn with considerable power towards the north or south -poles of the earth. That this power is of the same character as the -electricity which we have been considering, is now most satisfactorily -proved. By involving a bar of soft iron which, being without any -magnetic power, is incapable of sustaining even an ounce weight, with a -coil of copper wire, through which a galvanic current is passing, the -bar will receive, by induction from the current, an enormous accession -of power, and will, so long as the current flows around it, sustain -many hundred pounds weight, which, the moment the current is checked, -fall away from it in obedience to the law of gravity. Thus the mere -flow of this invisible agent around a mass of metal possessing no -magneto-attractive power, at once imparts this life-like influence to -it, and as long as the current is maintained, the iron is endowed with -this surprising energy. - -This discovery, which we owe to the genius of Oersted, and which has, -indeed, given rise to a new science, electro-magnetism, may be regarded -as one of the most important additions made to our knowledge. - -Current electricity is magnetic; iron is not necessary to the -production of magnetic phenomena, although by its presence we secure a -greater amount of power. The copper wires which complete the circuit -of a galvanic battery, will attract and hold up large quantities of -iron filings, and the wires of the electric telegraph will do the same, -while any signal is being conveyed along them. Again, all the phenomena -common to galvanic electricity can be produced by merely disturbing the -power permanently secured in the ordinary magnet. It was thought that -magnets would become weakened by this constant disturbance of their -magnetism; but, since its application to the purpose of manufacture, -and magneto-electricity has been employed in electro-plating, it has -been found that continued action for many years, during which enormous -quantities of electricity have been thus given out and employed in -producing chemical decomposition, has not, in the slightest degree, -altered their powers. Thus a small bar of metal is shown to be capable -of pouring out, for any number of years, the principle upon which the -phenomena of magnetism depend. - -There are, however, differences, and striking ones, between ordinary -and magnetic electricity. In the magnet we have a power at rest, and in -the electrical machine or galvanic battery, a power in motion. Ordinary -electricity is stopped in its passage by a plate of glass, of resin, -and many other substances; but magnetism passes these with freedom, and -influences magnetic bodies placed on the other side. It would appear, -though we cannot explain how, that magnetism is due to some lateral -influence of the electric currents. A magnetic bar is placed over a -copper wire, and it hangs steadily in the direction of its length; -an electric current is passed along it, and the magnet is at once -driven to place itself across the wire. Upon this experiment, in the -main, Ampère founds his theory of terrestrial magnetism. He supposes -electrical currents to be traversing our globe from east to west, and -thus, that the needle takes its direction, not from the terrestrial -action of any fixed magnetic poles, but from the repulsion of these -currents, as is the case with the wire. - -It has been found that wires, freely suspended, along which currents -were passing in opposite directions, revolve about each other, or have -an inclination to place themselves at right angles; thus exhibiting -the same phenomenon as the magnet and the conducting wire. So far the -hypothesis of Ampère leads us most satisfactorily. We see in the magnet -one form of electricity, and in the machine or battery another. But why -should not the electricity of the magnet, electricity at rest, exhibit -the same powers as this force in motion? - -Oersted, whose theory led him to the discovery of the fact of the -magnetic power of an electric current, of the establishment indeed of -the new science--ELECTRO-MAGNETISM, regards the phenomena of a current -passing a wire, and its action on a needle, as evidence of two fluids, -positive and negative, traversing in opposite directions, and mutually -attracting and repelling. He conceives that they pass the wires in a -series of spirals; that in the magnet, by some peculiar property of the -iron, this conflict of the currents is reduced to an equilibrium, and -its power becomes manifested in its attractive force.[171] This does -not, however, convey a clear idea to the mind. - -It is curious that iron becomes magnetic in a superior degree to any -other metal; that steel retains permanently any magnetism imparted -to it; but that soft iron rapidly loses its magnetic power. This -must be in virtue of some peculiar arrangement of the molecules, or -some unknown physical condition of the atoms of the mass, by which a -continued influence is retained by the steel, probably in a state of -constant internal circulation. It has, however, been shown that soft -iron, under certain circumstances, may be made to retain a large amount -of magnetic force.[172] - -If a horse-shoe shaped bar of soft iron is rendered magnetic by the -circulation of an electric current around it, while its two ends are -united by an armature of soft iron, so that it is capable of supporting -many hundred pounds weight; and we then, by breaking the circuit, stop -the current, taking care the armature is kept in contact, the iron will -not lose its magnetic property, but will retain this power for many -years. If the connecting piece of iron, the armature, is removed, the -bar immediately loses all its magnetism, and will not support even the -armature itself. This fact appears to confirm the idea that magnetism -is due to the retention of electricity, and that steel possesses -the property of equalizing the opposing forces, or of binding this -principle to itself like an atmosphere. - -The influence of heat on magnetism is so remarkable a proof of the -dependence of this power upon molecular arrangement, that it must not -escape our notice. To select but one of many experiments by Mr. Barlow, -it was found that in a bar of malleable iron, in which, when cold, the -magnetic effect was + 30° 0', all polarity ceased at a white heat, that -it was scarcely appreciable at a red heat, but that at a blood-red heat -it was equal to + 41° 0'.[173] - -The more closely we examine the peculiarities of the magnetic power, -and particularly as they are presented to us in its terrestrial action, -the more surprising will its influence appear to be. We have discovered -a natural cause which certainly exercises a very remarkable power -over matter, and we have advanced so far in our investigations as to -have learnt the secret of converting one form of force into another, -or of giving to a principle, produced by one agency, a new character -under new conditions; of changing, in fact, electricity into magnetism, -and from magnetism again evolving many of the effects of electrical -currents. - -If a magnetic bar is freely suspended above the earth, it takes, -in virtue of some terrestrial power, a given direction, which is -an indication of the earth’s magnetic force. Whether this is the -consequence of the currents of electricity, which Ampère supposes to -circulate around the globe, from east to west, or the result of points -of attraction in the earth itself, the phenomenon is equally wonderful. -To whatever cause we may refer the visible effects, it appears certain -that this earth is composed of particles in a magnetic state, the -character varying with physical conditions, and that terrestrial -magnetic force is the collective action of all the atoms of this -planetary mass.[174] - -The remarkable connexion which has been observed between the changes -in the physical condition of the surface of the sun and terrestrial -phenomena, must not escape our notice. Sir William Herschel thought -he perceived a link connecting the dark spots on the sun’s face with -the variations of the earth’s temperature. This has not, however, been -confirmed by the observations which have been made since the time -of Herschel. The careful examinations of the solar spots which have -been made by Schwabe,[175] prove a well-defined order of progress in -them. He has discovered that they move in cycles of ten years--from -the smallest number visible in a given year, they regularly increase -for five years, when they reach their maximum; they then as regularly -decrease, and at the end of another five years they are at their -maximum number. The magnetic observations which have been carried on by -the British and other governments for some years, over every part of -the world, have elicited the fact that the order of variation in the -earth’s magnetic intensity is in cycles of ten years, and the law of -increase and decrease which is found to prevail with the solar spots -distinctly marks the variations of terrestrial magnetism. Few more -interesting facts than this are within the range of our knowledge, -proving as it does the direct dependence of terrestrial phenomena on -solar force. - -The constancy with which a magnetised needle points along a certain -line which varies a little from the earth’s axial line, renders it one -of the most important instruments to the practical and the scientific -man. The wanderer of the ocean or of the desert is enabled, without -fear of error, to pursue his path, and in unknown regions to determine -the azimuth of objects. The miner or the surveyor finds in the -magnetic compass the surest guide in his labours, and the experiment is -for ever studying its indications. - - “True as the needle to the pole,” - -has passed into a proverb among mankind, but the searching inquiry -of modern observers has shown that the expression is correct only -with certain limitations. There are two lines on the surface of the -earth along which the needle points true north, or where the magnetic -and the geographical north correspond. These are called lines of _no -variation_, or, as they have also been designated, _agonic lines_, and -one is found in the eastern and the other in the western hemisphere. -The American line is singularly regular, passing in a south-east -direction from the latitude 60° to the west of Hudson’s Bay, across the -American lakes, till it reaches the South Atlantic ocean, and cuts the -meridian of Greenwich in about 65° south latitude. The Asiatic line -of _no variation_ is very irregular, owing, without doubt, to local -interferences; it begins below New Holland, in latitude 60° south, -it bends westward across the Indian ocean, and from Bombay has an -inflection eastward through China, and then northward across the sea -of Japan, till it reaches the latitude of 71° north, when it descends -again southward, with an immense semicircular bend, which terminates in -the White Sea. - -Hansteen has thought that there are two points in each hemisphere which -may be regarded as stronger and weaker poles on opposite sides of the -poles of revolution. These are called the magnetic poles of the earth, -or by Hansteen _magnetic points of convergence_. These four points are -considered to have a regular motion round the globe, the two northern -ones from west to east, and the two southern ones from east to west. By -the assistance of recorded observations, Hansteen has calculated the -periods of these revolutions to be as follows:-- - - The weakest north pole in 860 years. - The strongest north pole in 1746 years. - The weakest south pole in 1304 years. - The strongest south pole in 4609 years. - -There are some points of speculation on which Hansteen has ventured -which have been smiled at as fanciful; but they may rather indicate -an amount of knowledge in the Brahminical and Egyptian priesthood, -beyond what we are usually disposed to allow them, and prove that their -observations of nature had led them to an appreciation of some of the -most remarkable harmonies of this mysterious creation. - -The above terms are exceedingly near 864, 1246, 1728, 4320, and those -numbers are equal to the mystic number of the Indians, Greeks, and -Egyptians, 432 multiplied by 2, 3, 4, and 10. On these the ancients -believed a certain combination of natural events to depend, and, -according to Brahminical mythology, the duration of the world is -divided into four periods, each of 432,000 years. Again, the sun’s mean -distance from the earth is 216 radii of the sun, and the moon’s mean -distance 216 radii of the moon, each the half of 432. Proceeding with -this very curious examination, Hansteen says, 60 multiplied by 432 -equals 15,920, the smallest number divisible at once by all the four -periods of magnetic revolution, and hence the shortest time in which -the four poles can complete a cycle, and return to their present state, -and _which coincides exactly with the period in which the precession -of the equinoxes will amount to a complete circle_, reckoning the -precession at a degree in seventy-two years.[176] - -When we consider the phenomena of terrestrial magnetism carefully, it -appears to indicate the action of a power external to the earth itself, -and, as Hansteen conceives, having its origin from the action of the -sun, heating, illuminating, and producing a magnetic tension, in the -same manner as it produces electrical excitation and actino-chemical -action. - -The movements of these magnetic poles have been the subject of -extensive and most accurate observation in every quarter of the globe. -In London, during 1657-1662, there was no magnetic variation; the -agonic line passing through it. The variation steadily increased, -until, in 1815, it amounted to 24° 15' 17", since which time it has -been slowly diminishing. In addition to this great variation, we -have a regular annual change dependent on the position of the sun, -in reference to the equinoctial and solstitial points, which was -discovered by Cassini, and investigated by Arago and others. Also a -diurnal variation, which movement appears to commence early in the -morning, moving eastward until half-past seven, A.M., when it begins -to move westward until two, P.M., when it again returns to the east, -and in the course of the night reaches the point from which it started -twenty-four hours before. - -We have also remarkable variations in what is termed the _dip_ of -the needle. It is well known that a piece of unmagnetized steel, if -carefully suspended by its centre, will swing in a perfectly horizontal -position, but, if we magnetize this bar, it will immediately be drawn -downwards at one end. The force of the earth’s polarity, attracting the -dissimilar pole, has caused it to _dip_. - -There is, in the neighbourhood of the earth’s equator, and cutting it -at four points, an irregular curve, called the magnetic equator, or -_aclinic_ line, where the needle balances itself horizontally. As we -proceed from this line towards either pole the dip increases, until, -at the north and south poles, the needle takes a vertical position. -The _intensity_ of the earth’s magnetism is also found to vary with -the position, and to increase in a proportion which corresponds very -closely with the dip. But the _intensity_ is not a function of the -dip, and the lines of equal intensity, _isodynamic lines_, are not -parallel to those of equal dip. We have already remarked on the diurnal -variation of the declination of the needle; we know, also, that there -exists a regular monthly and daily change in the magnetic intensity. -The greatest monthly change appears when the earth is in its perihelion -and aphelion, in the months of December and June,--a maximum then -occurs; and about the time of the equinoxes a minimum is detected.[177] - -The daily variation of intensity is greatest in the summer, and least -in the winter. The magnetism is generally found to be at a minimum when -the sun is near the meridian; its intensity increasing until about six -o’clock, when it again diminishes.[178] - -What striking evidences all these well-ascertained facts give of the -dependence of terrestrial magnetism on solar influence! and in further -confirmation of this view, we find a very remarkable coincidence -between the lines of equal temperature--the isothermal lines, and those -of equal dip and magnetic intensity. - -Sir David Brewster first pointed out that there were in the northern -hemisphere two poles of maximum cold; these poles agree with the -magnetic points of convergence; and the line of maximum heat, which -does not run parallel to the earth’s equator, is nearly coincident with -that of magnetic power. Since Seebeck has shown us that electrical -and magneto-electrical phenomena can be produced by the action of heat -upon metallic bars, we have, perhaps, approached towards some faint -appreciation of the manner in which the solar calorific radiations may, -acting on the surface of our planet, produce electrical and magnetic -effects. If we suppose that the sun produces a disturbance of the -earth’s electricity along any given line, in all directions at right -angles to that line, we shall have magnetic polarity induced.[179] That -such a disturbance is regularly produced every time the sun rises, has -been sufficiently proved by many observers. - -In 1750, Wargentin noticed that a very remarkable display of _Aurora -borealis_ was the cause of a peculiar disturbance of the magnetic -needle; and Dr. Dalton[180] was the first to show that the luminous -rays of the Aurora are always parallel to the dipping-needle, -and that the Auroral arches cross the magnetic meridian at right -angles. Hansteen and Arago have attended with particular care to -these influences of the northern lights, and the results of their -observations are:-- - -That as the crown of the Aurora quits the usual place, the -dipping-needle moves several degrees forward:-- - -That the part of the sky where all the beams of the Aurora unite, is -that to which a magnetic needle directs itself, when suspended by its -centre of gravity:-- - -That the concentric circles, which show themselves previously to the -luminous beams, rest upon two points of the horizon equally distant -from the magnetic meridian; and that the most elevated points of each -arch are exactly in this meridian.[181] - -It does not appear that every Aurora disturbs the magnetic needle; as -Captains Foster and Back both describe very splendid displays of the -phenomenon, which did not appear to produce any tremor or deviation -upon their instruments.[182] - -Some sudden and violent movements have been from time to time observed -to take place in suspended magnets; and since the establishment of -magnetic observatories in almost every part of the globe, a very -remarkable coincidence in the time of these agitations has been -detected. They are frequently connected with the appearance of Aurora -borealis; but this is not constantly the case. These disturbances -have been called _magnetic storms_; and over the Asiatic and European -continent, the islands of the Atlantic and the western hemisphere, they -have been proved to be simultaneous. - -From observations made at Petersburg by Kupffer, and deductions drawn -from the observations obtained by the Magnetic Association, it appears -probable that these _storms_ arise from a sudden displacement in the -magnetic lines of the earth’s surface; but the cause to which this may -be due is still to be sought for. - -In the brief and hasty sketch which has been given of the phenomena -of terrestrial magnetism, enough has been stated to show the vast -importance of this very remarkable power in the great operations -of nature. We are gradually reducing the immense mass of recorded -observations, and arriving at certain laws which are found to prevail. -Still, the origin of the force, whether it is strictly electrical, -whether it is the circulation of a magnetic fluid, or whether it is -merely a peculiar excitation of some property of matter, are questions -which are open for investigation. - -In the beautiful Aurora borealis, with its trembling diffusive lights, -and its many-coloured rays, we have what may be regarded as a natural -exhibition of magnetism, and we appear to have within our grasp the -explanation we desire. But we know not the secret of even these -extraordinary meteorological displays. If we pass an electric spark -from a machine through a long cylinder, exhausted of air as far as -possible, we have a mimic representation of the Northern Lights--the -same attenuation of brightness, almost dwindling into phosphorescence; -and by the slightest change of temperature we may produce that play -of colours which is sometimes so remarkably manifested in Aurora. Dr. -Dalton considered Aurora borealis _as a magnetic phenomenon, and that -its beams are governed by the earth’s magnetism_. We know that the arc -of light produced between the poles of a powerful galvanic battery is -readily deflected by a good magnet; and we have lately learned that -every vapour obeys the magnetic force.[183] It is, therefore, yet a -question for our consideration, does the earth’s magnetism produce -the peculiar phenomena of Aurora by acting upon electricity in a -state of glow? or have we evidence in this display of the circulation -of the magnetic fluid around our globe, manifesting itself by its -action on the ferruginous and other metallic matter, which Fusinieri -has proved to exist in the upper regions of our atmosphere.[184] That -magnetic radiations do exist, has been proved by Faraday, and that they -form lines of force perpendicular to the earth’s surface, has been -experimentally shown. Parallelograms of wire moved upon a central axis, -and connected with a galvanometer, give at every revolution indication -of an electric disturbance in all respects analogous to the production -of a current by moving wires in front of a steel magnet. - -The alteration in the properties of heat, when it passes from the -radiant state into combination with matter, exhibits to us something -like what we may suppose occurs in the conversion of magnetism into -electricity or the contrary. We have a subtile agent, which evidently -is for ever busy in producing the necessary conditions of change in -this our earth: an element to which is due the development of many of -the most active powers of nature; performing its part by blending with -those principles which we have already examined; associating itself -with every form of matter; and giving, as we shall presently see, in -all probability, the first impulses to combination, and regulating the -forms of aggregating particles. - -As electricity has the power of altering the physical conditions of -the more adherent states of matter, thus giving rise to variations -of form and modes of combination, so gross matter appears to alter -the character of this agency, and thus disposes it to the several -modifications under which we have already detected its presence. -We have mechanical electricity and chemical electricity, each -performing its great work in nature; yet both manifesting conditions -so dissimilar, that tedious research was necessary before they could -be declared identical. Magnetic electricity is a third form; all its -characteristics are unlike the others, and the office it appears to -perform in the laboratory of creation is of a different order from -that of the other states of electrical force. In the first two we have -decomposing and recombining powers constantly manifested--in fact, -their influences are always of a chemical character; but in the last it -appears we have only a directive power. It was thought that evidence -had been detected of a chemical influence in magnetism; it did appear -that sometimes a retarding force was exerted, and often an accelerating -one. This has been again denied, and we have arrayed in opposition to -each other some of the first names among European experimentalists. -The question is not yet to be regarded as settled; but, from long and -tedious investigation, during which every old experiment has been -repeated, and numerous new ones tried, we incline to the conclusion -that chemical action is not directly affected by magnetic power. It -is highly probable that magnetism may, by altering the structural -arrangement of the surface, vary the rate of chemical action; but this -requires confirmation.[185] - -There is no substance to be found in nature existing independently of -magnetic power. But it influences bodies in different ways: one set -acting with relation to magnetism, like iron, and arranging themselves -along the line of magnetic force,--these are called magnetic bodies; -another set, of which bismuth may be taken as the representative, -always placing themselves at right angles to this line,--these are -called _diamagnetic bodies_.[186] This is strikingly shown by means of -powerful electro-magnets; but the magnetism of the earth is sufficient, -under proper care, to exhibit the phenomena. - -Every substance in nature is in one or other of these conditions. The -rocks, forming the crust of the earth, and the minerals which are -discovered in them; the surface soil, which is by nature prepared as -the fitting habitation of the vegetable world, and every tree, shrub, -and herb which finds root therein, with their carbonaceous matter, in -all its states of wood, leaf, flower, and fruit; the animal kingdom, -from the lowest monad through the entire series up to man,--have, all -of them, distinct magnetic or diamagnetic relations. - -“It is a curious sight,” says Dr. Faraday, “to see a piece of wood or -of beef, or an apple, or a bottle of water repelled by a magnet, or, -taking the leaf of a tree, and hanging it up between the poles, to -observe it take an equatorial position. Whether any similar effects -occur in nature among the myriads of forms which, upon all parts of its -surface, are surrounded by air, and are subject to the action of lines -of magnetic force, is a question which can only be answered by future -observation.”[187] - -At present, the bodies which are known to exhibit decided -ferro-magnetic properties are the following, which stand arranged in -the order of their intensity:-- - - Iron, Nickel, Cobalt, Manganese, - Chromium, Cerium, Titanium, - Palladium, Platinum, Osmium. - -It is interesting to know that there are evidences that two bodies -which, when separate, are not magnetic, as iron is, become so when -combined. Copper and zinc are both of the diamagnetic class, but many -kinds of brass are discovered to be magnetic. - -The salts of the above metals are, to a greater or less extent, -ferro-magnetic, but they may be rendered neutral by water, which is a -diamagnetic body, being repelled by the magnet. It will be unnecessary, -here, to enumerate the class of bodies which are diamagnetic; indeed, -all not included in the preceding list may be considered as belonging -to that class, with the exception of gases and vapours, which appear -to exist, relatively to each other, sometimes in the one, and sometimes -in the other condition.[188] - -To endeavour to reduce our knowledge of these facts to some practical -explanation, we must bear in mind that particular spaces around the -north and south geographical poles of the earth, are regarded as -circles to which all the magnetic lines of force converge. Under -circumstances which should prevent any interference with what is called -ferro-magnetic action, all bodies coming under that class would arrange -themselves according to the laws which would regulate the disposition -of an infinite number of magnets, free to move within the sphere of -each other’s influence. The north and south pole of one magnetic body -would attach itself to the south and north pole of another, until we -had a line of magnets of any extent; the two ends being in opposite -states, like the magnetic points of convergence of the earth. - -Every body, not ferro-magnetic, places itself across such a line of -magnetic force as we have conceived; and if the earth were made up of -separate layers of ferro-magnetic and diamagnetic bodies, the result -would be the formation of bands at right angles to each other. This -is not the case, by reason of the intermingling of the two classes -of substances. Out of the known chemical elements we find only about -ten which are actively ferro-magnetic; the others combining with -these give rise to either a weaker state, a neutral condition, or -the balance of action is turned to the diamagnetic side. Sulphate of -iron, for instance, is a magnetic salt; but in solution, water being -diamagnetic, it loses its property. The yellow prussiate of potash -dissolved in water is a diamagnetic body; but the red prussiate, which -contains an atom less of potassium, is magnetic: but in the solid state -they are both diamagnetic.[189] - -From this it would appear that the chemical composition of a body -regulated its relation to magnetism. The following facts will show, -however, that the molecular structure is more particularly concerned in -determining the molecular condition of substances. - -M. Plücker, being desirous of finding the extent to which the -_direction of the fibres_ in organic bodies might influence their -magnetic or diamagnetic properties, was led to inquire whether in -crystals the direction of the optic axes, which itself depends upon the -arrangement of the particles, might not also exercise some influence. -The first submitted to the action of the electro-magnet a thin plate -of tourmaline, such as is employed in experiments upon polarization, -having its optic axis parallel to its longest length. It was very -quickly perceived that the plate was magnetic, by the effect of the -iron that it contains; but it was suspended successively in three -ways,--first, so that its longest side was vertical, then as that the -shortest side was vertical, and finally so that the plate itself was -horizontal. In the first case it is directed between the two points -of the conical curvatures of the poles like a magnetic body; but, in -the other two cases, on the contrary, it took the direction assumed by -diamagnetic bodies--that is to say, a direction such that its longest -length was perpendicular to the line joining the poles. This direction -indicated that the optical axis was repelled by the two poles, and that -this repulsion outweighed the magnetic properties of the crystal.[190] - -The relation of structure to physical phenomena of essentially -different characters is remarkable. Savart, when making crystalline -plates of quartz and carbonate of lime vibrate, succeeded in -determining a relation between the acoustic figures that are -produced in them, and the particular mode of the crystallization of -the substance. He found that the direction of the optical axis is -constantly connected with that of the principal forms of the acoustic -figures. - -Mitscherlich has remarked that crystals do not expand uniformly by -heat, but that this dilatation is greater in one direction than in -another; and that this difference is connected with their crystalline -form. M. de Sénarmont has shown that conductibility for heat, -which is equal in all directions for the crystals of the regular -system, acquires in others a maximum or a minimum value, according -to directions parallel to the crystallographic axes; so that the -isothermic surfaces, which are spheres in the former case, are, in the -other, ellipsoids elongated or flattened in the same direction. The -optical axes do not altogether coincide with the principal axes of -conductibility for heat; but this appears to be due merely to slight -differences in the rate of progression, or the refrangibility of the -luminous and calorific rays. - -Wiedemann, by employing a fine point through which he made electricity -arrive upon a surface that he had powdered with licopodium or red lead, -succeeded in determining, by means of the form assumed by this light -powder, the conductibility of crystals in different directions. - -On a surface of glass, the powder which disperses itself around the -points, in consequence of electric repulsion, forms a circular -figure traversed by radii. When a plate of gypsum is used instead of -glass the figure is found to be elliptical, and the great axis of -the ellipse forms a right angle with the principal crystallographic -axis, which proves that the electricity distributes itself more -easily in a direction perpendicular to the axis than in any other. -M. Wiedemann comes to the conclusion that crystals which possess a -better conductibility in the direction of the principal axis, all -belong to the class of negative crystals: while those which have a -better conductibility in the direction perpendicular to the axis are -positive, which indicates that the direction of best conductibility -for electricity is also that according to which light is propagated -relatively with greater velocity. - -Tyndale has shown, that if gutta percha which has been rendered fibrous -in manufacture is cut so that the fibres are in the direction of this -greatest length, or in a direction perpendicular to this greatest -length, and placed under the influence of a magnet, they direct -themselves equatorially. Ivory cut in the same direction manifests the -same conditions, though both these substances are diamagnetic. - -The fibrous structure, and the planes of cleavage, thus determine the -magnetic condition of a substance. The special properties presented by -crystals, in regard to the action exercised upon them by magnets, is -due to a particular mode of grouping their particles. This is also the -cause of unequal dilatability, and of unequal conductibility for heat -and for electricity. - -How curiously, therefore, does molecular structure determine the -relation of a body to any of the forms of physical force! - -We still search in the dark, and see but dimly the evidences; yet it -becomes almost a certainty to us, that this stone of granite, with its -curious arrangement of felspar, mica, and quartz, presents its peculiar -condition in virtue of some law of magnetic force. The crystal, too, -of quartz, which we break out of the mass, and which presents to us a -beautifully regular figure, is, beyond a doubt, so formed, because the -atoms of silica are each one impelled in obedience to one of these two -conditions of magnetism to set themselves in a certain order to each -other, which cannot be altered by human force without destruction. - -All the laws which regulate the forms of crystals and amorphous bodies -are, to the greatest degree, simple. In nature the end is ever attained -by the easiest means; and the complexity of operation, which appears -sometimes to the observer, is only so because he cannot see the spring -by which the machine is moved. - -The gaseous envelope, our atmosphere, is in a neutral state. Oxygen is -strikingly magnetic in relation to hydrogen gas, whilst nitrogen is as -singularly the contrary; and the same contrasts present themselves when -these gases are examined in their relation to common air. Thus, oxygen -being magnetic, and nitrogen the contrary, we have an equilibrium -established, and the result is a compound neutral in its relations to -all matter. All gases and vapours are found to be diamagnetic, but in -different degrees.[191] This is shown by passing a stream of the gas, -rendered visible by a little smoke, within the influence of a powerful -magnet. - -These bodies are, however, found relatively to each other,--or even -to themselves, under different thermic conditions,--to change their -states, and pass from the magnetic to the diamagnetic class. Heat has a -very remarkable influence in altering these relations; and atmospheric -air at one temperature is magnetic to the same fluid at another: thus, -by thermic variations, attraction or repulsion may be alternately -maintained. By this it must be understood that a stream of air, at a -temperature elevated but a few degrees above that of an atmosphere of -the same kind into which it is passing, is deflected in one way by a -magnet; whereas, if the stream is colder than the bulk through which -it flows, it is bent in another way by the same force. In this respect -magnetism and diamagnetism show equally the influence of another -physical force, heat; and we may safely refer many meteorological -phenomena to similar alterations of condition in the atmosphere, -relative to the magnetic relations of the aërial currents. - -That magnetism has a directive power is satisfactorily shown by -the formation of crystals in the neighbourhood of the poles of -powerful magnets. The common iron salt, the protosulphate, ordinarily -crystallizes so that the crystals unite by their faces; but when -crystallizing under magnetic influence, they have a tendency to arrange -themselves with regard to each other so that the acute angle of one -crystal unites with one of the faces of another crystal, near to, but -never actually at, its obtuse angle. In addition to this, if a magnet -of sufficient power is employed, the crystals arrange themselves in -magnetic curves from one pole to the other, a larger crop of crystals -being always formed at the north than at the south pole. Here we have -evidence of an actual turning round of the crystal, in obedience to the -directive force of the magnet; and we have the curious circumstance of -a difference in some way, which is not clearly explained, between the -two opposite poles. If, instead of an iron or a ferro-magnetic salt, -we employ one which belongs to the other, or diamagnetic, class, we -have a curious difference in the result. If into a glass dish, fixed -on the poles of a strong electro-magnet, we pour a quantity of a -solution of nitrate of silver, and place in the fluid, over the poles -of the magnet, two globules of mercury (an arrangement by which that -arborescent crystallization, called the _Arbor Dianæ_, is produced,) we -have the long needle-shaped crystals of silver, arranging themselves in -curves which would cut the ordinary magnetic lines at right angles.[192] - -In the first example given we have an exhibition of magnetic force, -while in the last we have a striking display of the diamagnetic power. - -The large majority of natural formations appear to group themselves -under the class of diamagnetics. These bodies are thought to possess -poles of mutual repulsion among themselves, and which are equally -repelled by the magnetic points of convergence. Confining our ideas to -single particles in one condition or the other, we shall, to a certain -extent, comprehend the manifold results which must arise from the -exercise of these two modes of force. At present, our knowledge of the -laws of magnetism is too limited to allow of our making any general -deductions relative to the disposition of the molecules of matter; and -the amount of observation which has been given to the great natural -arrangements, is too confined to enable us to infer more than that it -is probable many of the structural conditions of our planet are due to -polarity. - -Mountain ranges observe a singular uniformity of direction, and -the cleavage planes of rock are evidently determined by some -all-pervading power. Mineral bodies are not distributed in all -rocks indiscriminately. The primary formations hold one class of -metalliferous ores, and the more recent ones another. This is not -to be regarded as in any way connected with their respective ages, -but with some peculiar condition of the stone itself. The granite -and slate rocks, at their junctions, present the required conditions -for the deposit of copper ore, while we find the limestones have the -characteristic physical state for accumulating lead ore. Again, on -examining any mineral vein, it will be at once apparent that every -particle of ore, and every crystal of quartz or limestone, is disposed -in a direction which indicates the exercise of some powerful directive -agency.[193] - -It appears, from all the results hitherto obtained, that the magnetic -and diamagnetic condition of bodies is equally due to some peculiar -property of matter in relation to the other forms of electricity. We -have not yet arrived at the connecting link, but it does not appear to -be far distant. - -We have already referred to the statement made by talented -experimentalists, that magnetism has a powerful influence in either -retarding or accelerating chemical combination. Beyond a doubt chemical -action weakens the power of a magnet; but the disturbance which it -occasions in soft iron, on the contrary, appears to tend to its -receiving magnetism more readily, and retaining it more permanently. -Further investigations are, however, required, before we can decide -satisfactorily either of these problems, both of which bear very -strongly upon the subject we have just been considering. - -We have seen that heat and electricity act strangely on magnetic force, -and that this statical power reacts upon them: and thus the question -naturally arises, Do light and magnetism in any way act upon each other? - -Morichini and Carpi on the continent, and Mrs. Somerville in England, -have stated that small bars of steel can be rendered magnetic by -exposing them to the influence of the violet rays of light. These -results have been denied by others, but again repeated and apparently -confirmed. In all probability, the rays to which the needles were -exposed, being those in which the maximum actinic power is found, -produced an actual chemical change; and then, if the position were -favourable, it is quite evident that magnetism would be imparted. -Indeed we have found this to be the case when the needles, exposed to -solar radiations, were placed in the direction of the dip. The supposed -magnetization of light by Faraday has already been mentioned. If the -influence in one case is determined, it will render the other more -probable.[194] - -“In seeking for a cause,” writes Sir David Brewster, “which is capable -of inducing magnetism on the ferruginous matter of our globe, whether -we place it within the earth, or in its atmosphere, we are limited to -the SUN, to which all the magnetic phenomena have a distinct reference; -but, whether it acts by its heat, or by its light, or by specific -rays, or influences of a magnetic nature, must be left to future -inquiry.”[195] - -We have learnt that magnetism is not limited to ferruginous matter; we -know that the ancient doctrine of the universality of the property is -true. Kircher, in his strange work on Magnetism, published in the early -part of the seventeenth century[196]--a curious exemplification of the -most unwearying industry and careful experiment, combined with the -influences of the credulity and superstitions of his age--attributes to -this power nearly all the cosmical phenomena with which, in his time, -men were acquainted. He curiously anticipates the use of the supposed -virtue of magnetic traction in the curative art; and as the titles of -his concluding chapters sufficiently show, he was a firm believer in -animal magnetism.[197] But it is not with any reference to these that -we refer to the work of _Athanasii Kircheri, Societatis Jesu, Magnes, -sive de Magnetivâ Arte_, but to show that two hundred years since, -man was near a great truth; but the time of its development being not -yet come, it was allowed to sleep for more than two centuries, and -the shadow of night had covered it. In speaking of the vegetable -world, and the remarkable processes by which the leaf, the flower, -and the fruit are produced, this sage brings forward the fact of the -diamagnetic character of the plant, which has been, within the last two -years, re-discovered; and he refers the motions of the Sun-flower, the -closing of the Convolvulus, and the directions of the spiral, formed by -twining plants, to this particular influence. - -This does not appear as a mere speculation, a random guess, but is -the result of deductions from experiment and observation. Kircher -doubtless leaped over a wide space to come to his conclusion; but the -result is valuable in a twofold sense. In the first it shows us that, -by neglecting a fact which is suggestive, we probably lose a truth -of great general application; and secondly, it proves to us, that by -stepping beyond the point to which inductive logic leads, and venturing -on the wide sea of hypothesis, we are liable to sacrifice the true to -the false, and thus to hinder the progress of human knowledge. - -Magnetism, in one or other of its forms, is now proved to be universal, -and to its power we are disposed to refer the structural conditions -of all material bodies, both organic and inorganic. This view has -scarcely yet been recognised by philosophers; but as we find a certain -law of polarity prevailing through every atom of created matter, in -whatever state it may be presented to our senses, it is evident that -every particle must have a polar and directing influence upon the mass, -and every coherent mass becomes thus only a larger and more powerful -representative of the magnetic unit. Thus we see the speculation of -Hansteen, that the sun is, to us, a magnetic centre, and that it -is equally influenced by the remoter suns of the universe,[198] is -supported by legitimate deductions from experiment. - -The great difficulty is not, however, got rid of by this speculation; -the cause by which the earth’s magnetism is induced is only removed -further off. - -The idea of a magnetic fluid is scarcely tenable; and the ferruginous -nature of the Aurora borealis receives no proof from any investigation; -indeed, we have procured evidence to show that iron is not at all -necessary for the production of magnetic phenomena. The leaf of a -tree, a flower, fruit, a piece of animal muscle, glass, paper, and a -variety of similar substances, have the power of repelling the bar of -iron which we call a magnet, and of placing it at right angles to the -direction of the force exerted by them. This is a point which must be -constantly borne in mind when we now consider the mysteries of magnetic -phenomena. - -Any two masses of matter act upon each other according to this law, -and although by the power of cohesion the force may be brought to an -equilibrium, or to its zero point, it is never lost, and may be readily -and rapidly manifested by any of the means employed for electrical -excitation. - -Reasoning by analogy, the question fairly suggests itself: If two -systems of inorganic atomic constitution are thus invested with a -power of influencing each other through a distance, why may not -two more highly developed organic systems equally, or to a greater -extent, produce an influence in like manner? Upon such reasoning as -this is founded the phenomenon known as Animal Magnetism. There is no -denying the fact that one mass of blood, muscle, nerves, and bone, -must, magnetically, influence another similar mass. This is, however, -something totally different from that abnormal condition which is -produced through some peculiar and, as yet, unexplained physiological -influences. - -With the mysterious operations of vital action, the forces which we -have been considering have nothing whatever in common. The powers -which are employed in the arrangements of matter are, notwithstanding -their subtile character, of far too gross a nature to influence the -psychological mysteries which present themselves to the observant -mind. It cannot be denied that, by placing a person of even moderate -nervous sensibility in a constrained position, and under an unnatural -influence of the mind, as acquired by the disciples of Mesmer, a torpor -affecting only certain senses is produced. The recognised and undoubted -phenomena are in the highest degree curious--but in these the marvels -of charlatanry and ignorance are not included;--and the explanation -must be sought for by the physiologist among those hidden principles -upon which depends all human sensation.[199] - -Man, like a magician, stands upon a promontory, and surveying the great -ocean of the physical forces which involve the material creation, -and produce that infinite variety of phenomena which is unceasingly -exhibited around him, he extends the wand of intelligence, and bids the -“spirits of the vasty deep” obey his evocation. - -The phenomena recur--the great processes of creation go on--the -external manifestations of omnipotent power proceed--effects are -again and again produced; but the current of force passes undulating -onwards;--and to the proud bidding of the evocator there is no reply -but the echo of his own vain voice, which is lost at last in the vast -immensity of the unknown which lies beyond him. - -We see how powerfully the physical forces, in their various modes of -action, stir and animate this planetary mass; and amongst these the -influence of magnetism appears as a great directing agent, though its -origin is unknown to us. - - That power which, like a potent spirit, guides - The sea-wide wanderers over distant tides, - Inspiring confidence where’er they roam, - By indicating still the pathway home;-- - Through nature, quicken’d by the solar beam, - Invests each atom with a force supreme, - Directs the cavern’d crystal in its birth, - And frames the mightiest mountains of the earth; - Each leaf and flower by its strong law restrains, - And binds the monarch Man within its mystic chains. - - -FOOTNOTES: - -[170] _Treatise on Magnetism_, by Sir David Brewster. _Cosmos: a -Sketch of a Physical description of the Universe_; by Alexander Von -Humboldt.--Otté’s Translation. - -[171] _Expérience Electro-Magnétique._ par M. Œrsted.--Annales de -Chimie, vol. xxii. p. 201. De la Rive, _Recherches sur la Distribution -de l’Electricité dyn. dans les Corps_.--Genève, 1825. - -[172] _On the Magnetic power of Soft Iron_: by Mr. -Watkins.--Philosophical Transactions, 1833. - -[173] Cavallo, _On Magnetism_.--Cavallo was the first who noticed the -influence of heat on Magnetism. Consult _On the anomalous Magnetic -Action of Hot Iron between the white and blood-red heat_: by Peter -Barlow, Esq.--Philosophical Transactions, 1822, p. 124. _Treatise on -Magnetism_: by Barlow.--Encyclopædia Metropolitana. - -[174] “The foundation of our researches is the assumption that the -terrestrial magnetic force is the collective action of all the -magnetised particles of the earth’s mass. We represent to ourselves -magnetisation as the separation of the magnetic fluids. Admitting the -representation, the mode of action of the fluids (repulsion of similar, -and attraction of dissimilar, particles inversely as the square of the -distance) belongs to the number of established truths. No alteration -in the results would be caused by changing this mode of representation -for that of Ampère, whereby, instead of magnetic fluids, magnetism is -held to consist in constant galvanic currents in the minutest particles -of bodies. Nor would it occasion a difference if the terrestrial -magnetism were ascribed to a mixed origin, as proceeding partly from -the separation of the magnetic fluids in the earth, and partly from -galvanic currents, in the same; inasmuch as it is known that for each -galvanic current may be substituted such a given distribution of the -magnetic fluids in a surface bounded by the current, as would exercise -in each point of external space precisely the same magnetic action as -would be produced by the galvanic current itself.”--_General Theory -of Terrestrial Magnetism_, by Professor Carl Friedrich Gauss, of the -University of Göttingen.--Scientific Memoirs, vol. ii. p. 188. - -[175] Humboldt’s _Cosmos_.--Otté’s translation. - -[176] Hansteen: _Untersuchungen über den Magnetismus der -Erde_, Christïana, 1819. Humboldt: _Exposé des Variations -Magnétiques_.--Gilbert’s Annales. Brewster’s Magnetism: Encyclopædia -Metropolitana. - -[177] Hansteen; as above. - -[178] _On the effects of temperature on the intensity of magnetic -forces, and on the diurnal variations of the terrestrial magnetic -intensity_; by Samuel Hunter Christie, Esq.--Philosophical -Transactions, vol. cxv. 1825. - -[179] It has been observed by Mr. Barlow, in England, and some eminent -observers in Austria, that an electric current constantly traverses -the wires of the electric telegraph wherever there are two earth -connections. - -[180] _Meteorological Observations and Essays_: by Dr. Dalton. _On the -Height of the Aurora Borealis above the surface of the Earth_: by John -Dalton, F.R.S.--Philosophical Transactions, vol. cxiv. p. 291. - -[181] Arago: Annales de Chimie, vol. xxxix. p. 369. _On the variable -Intensity of Terrestrial Magnetism and the Influence of the Aurora -Borealis upon it_; by Robert Were Fox.--Philosophical Transactions, -1831, p. 199. - -[182] “Brilliant and active coruscations of the Aurora Borealis,” says -Captain Back, “when seen through a hazy atmosphere, and exhibiting -the prismatic colours, almost invariably affected the needle. On the -contrary, a very bright Aurora, though attended by motion, and even -tinged with a dullish red and a yellow in a clear blue sky, seldom -produced any sensible change, beyond, at the most, a tremulous motion. -A dense haze or fog, in conjunction with an active Aurora, seemed -uniformly favourable to the disturbance of the needle, and a low -temperature was favourable to brilliant and active coruscations. On -no occasion during two winters was any sound heard to accompany the -motions. The Aurora was frequently seen at twilight, and as often to -the eastward as to the westward; clouds, also, were often perceived -in the day-time, in form and disposition very much resembling the -Aurora.”--_Narrative of the Arctic Land Expedition._ - -[183] Faraday: _On the Diamagnetic character of Flame and Gases_. - -[184] “The Aurora Borealis is certainly in some measure a magnetical -phenomenon; and if iron were the only substance capable of exhibiting -magnetic effects, it would follow that some ferruginous particles -must exist in the upper regions of the atmosphere. The light usually -attending this magnetical meteor may possibly be derived from -electricity, which may be the immediate cause of a change in the -distribution of the magnetic fluid, contained in the ferruginous -vapours which are imagined to float in the air.”--Lecture on Magnetism: -Young’s _Lectures on Natural Philosophy_, p. 533. - -[185] _On the supposed influence of Magnetism and Chemical Action_; by -Robert Hunt.--Philosophical Magazine, vol. xxxii. No. 215, 1849. - -[186] Those bodies which are attracted by a magnet, as iron is, are -called _magnetic bodies_. Those which are, on the contrary, repelled by -the same power, are termed _diamagnetic bodies_. On these Dr. Faraday -remarks:--“Of the substances which compose the crust of the earth, by -far the greater portion belong to the diamagnetic class; and though -ferruginous and other magnetic matters, being more energetic in their -action, are more striking in their phenomena, we should be hasty in -assuming that, therefore, they over rule entirely the effect of the -former bodies. As regards the ocean, lakes, rivers, and the atmosphere, -they will exert their peculiar effect almost uninfluenced by any -magnetic matter in them, and as respects the rocks and mountains, their -diamagnetic influence is perhaps greater than might be anticipated. -I mentioned that by adjusting water and a salt of iron together, I -obtained a solution inactive in air; that is, by a due association -of the forces of a body, from each class, water and a salt of iron, -the magnetic force of the latter was entirely counteracted by the -diamagnetic force of the former, and the mixture was neither attracted -nor repelled: To produce this effect, it required that more than 48·6 -grains of crystallised protosulphate of iron should be added to ten -cubic inches of water (for these proportions gave a solution which -would set equatorially), a quantity so large, that I was greatly -astonished on observing the power of the water to overcome it. It -is not, therefore, at all unlikely that many of the masses which -form the crust of this our globe, may have an excess of diamagnetic -power, and act accordingly.”--_On new magnetic actions, and on the -magnetic condition of all matter_; by Michael Faraday, D.C.L., F.R.S., -&c.--Philosophical Transactions, Jan. 1846, vol. cxxxvii. p. 41. - -[187] Ibid. - -[188] _On the Diamagnetic conditions of Flame and Gases_, by Michael -Faraday. F.R.S.; and _On the motions presented by Flame when under -Electro-Magnetic Influence_, by Professor Zantedeschi.--Philosophical -Magazine, 1847, pp. 401-421. - -[189] _On Diamagnetism_; by Professor Plücker, of Bonn.--Philosophical -Magazine, July, 1848. - -[190] For a detailed account of the experiments of Faraday, Plücker, -Becquerel, Tyndale, and Knoblauch, see De La Rive’s _Treatise on -Electricity in Theory and Practice_. - -[191] A few examples taken from Dr. Faraday’s paper will show this:-- - -Nitrogen being acted on was manifestly diamagnetic in relation to -common air when both were of the same temperature. Oxygen appears to -be magnetic in common air. Hydrogen proved to be clearly and even -strongly diamagnetic. Its diamagnetic state shows, in a striking -point of view, that gases, like solids, have peculiar and distinctive -degrees of diamagnetic force. Carbonic acid gas is diamagnetic in air. -Carbonic oxide was carefully freed from carbonic acid before it was -used, and it appears to be more diamagnetic than carbonic acid. Nitrous -oxide was moderately, but clearly, diamagnetic in air. Olefiant gas -was diamagnetic. The coal gas of London is very well diamagnetic, and -gives exceedingly good and distinct results. Sulphurous acid gas is -diamagnetic in air. Muriatic acid gas was decidedly diamagnetic in -air.--_On the Diamagnetic Conditions of Flame and Gases_: Philosophical -Magazine, 1847, p. 409. - -[192] For illustration of this I must refer to my own Memoir, -_Researches on the Influence of Magnetism and Voltaic Electricity on -Crystallization, and other conditions of matter_, in the Memoirs of the -Geological Survey of Great Britain, &c., vol. i. - -[193] In a work published by Mr. Evan Hopkins, entitled _On the -Connexion of Geology with Terrestrial Magnetism_, will be found many -valuable practical observations made in this country and the gold and -silver districts of America; but the views taken by the author are open -to many objections. - -[194] See a notice by Faraday of Morichini’s Experiments in _Relations -of Light to Magnetic Force_--Philosophical Transactions, vol. cxxxvii. -p. 15. See also Mr. Christie _On Magnetic Influence in the Solar -Rays_--Philosophical Transactions, vol. cvii. p. 219; vol. cxix. p. 379. - -[195] Sir David Brewster _On Magnetism_; republished from the -Encyclopædia Britannica. - -[196] The whole of the title of Kircher’s book will convey some idea -of the subjects embraced:--Athanasii Kircheri Societatis Jesu Magnes, -sive de Arte Magneticâ; opus tripartitum, quo Universa Magnetis Natura -ejusque in omnibus Scientiis et Artibus usus novâ methodo explicatur: -ac præterea e viribus et prodigiosis effectibus Magneticarum aliarumque -abditarum Naturæ Motionum in Elementis, Lapidibus, Plantis, Animalibus -elucescentium: multa hucusque incognita Naturæ Arcana, per Physica, -Medica, Chymica, et Mathematica omnis generis Experimenta recluduntur -Editio Tertia: ab ipso Authore recognita emendataque, ac multis novorum -Experimentorum Problematibus aucta. Romæ, 1654. - -[197] The following are the titles of the concluding chapters of -Kircher’s book:--_De magnetismo solis et lunæ in maria._ _De magneticâ -vi plantarum._ _De insitionis magneticis miraculis._ _De magnetismo -virgulæ auriferæ seu divinatoriæ._ _De plantis heliotropiis eorumque -magnetismo._ _De magnetismo rerum medicinalium._ _De vi attractivâ -potentiæ imaginativæ._ _De magnetismo musicæ._ _De magnetismo amoris._ - -[198] “For these reasons it appears most natural to seek their origin -in the sun, the source of all living activity, and our conjecture gains -probability from the preceding remarks on the daily oscillations of -the needle. Upon this principle the sun may be conceived as possessing -one or more magnetic axes, which, by distributing the force, occasion -a magnetic difference in the earth, in the moon, and all those planets -whose internal structure admits of such a difference. Yet, allowing -all this, the main difficulty seems not to be overcome, but merely -removed from the eyes to a greater distance; for the question may still -be asked, with equal justice, whence did the sun acquire its magnetic -force? And if from the sun we have recourse to a central sun, and from -that again to a general magnetic direction throughout the universe, -having the Milky Way for its equator, we but lengthen an unrestricted -chain, every link of which hangs on the preceding link, no one of them -on a point of support. All things considered, the following mode of -representing the subject appears to me most plausible. If a single -globe were left to move alone freely in the immensity of space, the -opposite forces existing in its material structure would soon arrive -at an equilibrium conformable to their nature, if they were not so at -first, and all activity would soon come to an end. But if we imagine -another globe to be introduced, a mutual relation will arise between -the two; and one of its results will be a reciprocal tendency to -unite, which is designated and sometimes thought to be explained by -the merely descriptive word Attraction. Now would this tendency be -the only consequence of this relation? Is it not more likely that the -fundamental forces, being drawn from their state of indifference or -rest, would exhibit their energy in all possible directions, giving -rise to all kinds of contrary action? The electric force is excited, -not by friction alone, but also by contact, and probably also, though -in smaller degrees, by the mutual action of two bodies at a distance; -for contact is nothing but the smallest possible distance, and that, -moreover, only for a few small particles. Is it not conceivable that -magnetic force may likewise originate in a similar manner? When the -natural philosopher and the mathematician pay regard to no other effect -of the reciprocal relation between two bodies at a distance, except -the tendency to unite, they proceed logically, if their investigations -require nothing more than a moving power; but should it be maintained -that no other energy can be developed between two such bodies, the -assertion will need proof and the proof will be hard to find.”--The -above is a translation from Hansteen’s work _On Magnetism_. - -[199] See article _Animal Magnetism_, Encyclopædia Britannica, and Mr. -Braid’s papers _On Hypnotism_, published in the “Medical Times.” - - - - -CHAPTER XI. - -CHEMICAL FORCES. - - Nature’s Chemistry--Changes produced by Chemical Combination--Atomic - Constitution of Bodies--Laws of Combination--Combining - Equivalents--Elective Affinity--Chemical Decomposition--Compound - Character of Chemical Phenomena--Catalysis or action - of Presence--Transformation of Organic Bodies--Organic - Chemistry--Constancy of Combining Proportions--The Law of Volumes, - the Law of Substitutions, Isomeric States, &c. - - -All things on the earth are the result of chemical combination. The -operations by which the commingling of molecules and the interchange -of atoms take place, we can imitate in our laboratories; but in nature -they proceed by slow degrees, and, in general, in our hands they are -distinguished by suddenness of action. In nature chemical power is -distributed over a long period of time, and the process of change is -scarcely to be observed. By art we concentrate chemical force, and -expend it in producing a change which occupies but a few hours at most. -Many of the more striking phenomena of nature are still mysterious to -us, and principally because we do not, or cannot, take the element time -into calculation. The geologist is compelled to do this to explain the -progress of the formation of the crust of the earth, but the chemist -rarely regards the effects of time in any of his operations. The -chemical change which within the fissure of the rock is slowly and -silently at work, displacing one element or molecule, and replacing it -by another, is in all probability the operation of a truly geological -period. Many, however, of the changes which are constantly going on -around us, are of a much more rapid character, and in these nature is -no slower in manipulating than the chemist. - -Had it been that the elements which are now found in combination -could exist in a free state, the most disastrous consequences would -necessarily ensue. There must have been a period when many of the -combinations known to us were not yet created. Their elements either -existed in other forms, or were uncombined. Our rocks are compounds of -oxygen with certain peculiar metals which unite with oxygen so rapidly -that incandescence is produced by their combination. Let us suppose -that any of these metals existed in purity, and that they were suddenly -brought into contact with water, the atmospheric air, or any body -containing oxygen, the result would be a convulsion of the most fearful -kind; the entire mass of metal would glow with intensity of heat, and -the impetuosity of the action would only be subdued when the whole -of the metal had become oxidized. Volcanic action has been referred -to some such cause as this, but there is not sufficient evidence to -support the hypothesis; indeed, it is contrary to the opinion of most -philosophers.[200] Such a condition may possibly have existed at one -time, during that period when darkness was upon the face of the deep, -when the earth was a chaos; but it is only adduced here as an example -of the violent nature of some chemical changes. Potassium thrown on -water bursts into flame, and sodium does so under certain conditions. -If these, or the metals proper in a state of fine division, are brought -into an atmosphere of chlorine, the intensity of chemical action is so -great that they become incandescent, many of them glowing with extreme -brilliancy. If hydrogen gas is mixed with this element (chlorine) -they unite, under the influence of light, with explosive violence, -giving rise to a compound, muriatic acid, which combines with water -in an almost equally energetic manner. Nitrogen, as it exists in the -atmosphere, mixed with oxygen, appears nearly inert; with hydrogen it -forms the pungent compound, ammonia; with carbon, the poisonous one, -cyanogen, the base of prussic acid; with chlorine it gives rise to a -fluid, oily in its appearance, but which, when merely touched by an -unctuous body, explodes more violently than any other known compound, -shivering whatever vessel it may be contained in, to atoms; with iodine -it is only slightly less violent; and in certain combinations with -silver, mercury, gold, or platinum, it produces fulminating compounds -of the most dangerous character.[201] Here we have elements harmless -when uncombined, exhibiting the most destructive effects if their -combinations are at all disturbed; and in the other case we have inert -masses produced from active and injurious agents. - -We regard a certain number of substances as _elementary_; that is to -say, not being able, in the present state of our knowledge, to reduce -them to any more simple condition, they are considered as the elements -which by combination produce the variety of substances found in the -three kingdoms of nature. - -We have already spoken of the atomic constitution of bodies. It remains -now to explain the simplicity and beauty which mark every variety of -combination under chemical force. As a prominent and striking example, -water is a compound of two gaseous bodies, oxygen and hydrogen:-- - -If we decompose water by means of galvanic electricity, or determine -its composition by direct chemical analysis, we shall find it consists -of two volumes of hydrogen gas, united to one volume of oxygen, or, by -weight, of one part of hydrogen combined with eight of oxygen. In 100 -parts, therefore, we should find-- - - Oxygen 88·9 - Hydrogen 11·0 - -It is found in the same way that the theoretical weight of the atom -of carbon is 6, and that of nitrogen 14; whilst the atom of iron is -28, that of silver 108, of gold 199, and that of platinum and iridium -each 98.[202] Now, as these are the relative weights of the ultimate -indivisible atom, it follows that all combinations must be either atom -to atom, or one to two, three, or four; but that in no case should -combination take place in any other than a multiple proportion of the -equivalent or atomic number. This is found to be the case. Oxygen, -for instance, combines as one, two, or three atoms; its combination -presenting some multiple of its equivalent number 8, as 16, or 24: -and in like manner the combining quantity of carbon is 6, or some -multiple of that number. Where this law is not found strictly to agree -with analytical results, of which some examples are afforded by the -sesquioxides, it may be attributed, without doubt, to some error of -analysis or in the method of calculation. - -Nothing can be more perfect than the manner in which nature regulates -the order of combination. We have no uncertain arrangement; but, -however great the number of the atoms of one element may be, over those -of another, those only combine which are required, according to this -great natural law, to form the compound, all the others still remaining -free and uncombined. These results certainly appear to prove that the -elementary particles of matter are not of the same specific gravities. -Do they not also indicate that any alteration in the specific gravity -of the atom would give rise to a new series of compounds, thus -apparently producing a new element? Surely there is nothing irrational -in the idea that the influences of heat or electricity, or of other -powers of which as yet we know nothing, may be sufficient to effect -such changes in the atomic constituents of this earth. - -The combination of elementary atoms takes place under the influence -of an unknown force which we are compelled to express by a figurative -term, _affinity_. In some cases it would appear that the disposition -of two bodies to unite, is determined by the electrical condition; but -a closer examination of the question than it is possible to enter into -in this place, clearly shows that some physical state, not electrical, -influences combining power. - -Chemical affinity or attraction is the peculiar disposition which one -body has to unite with another. To give some instances in illustration. -Water and spirit combine most readily: they have a strong affinity for -each other. Water and oil repel each other: they have no affinity; -they will not enter into combination. If carbonate of potash is added -to the spirit and water in sufficient quantity, the water is entirely -separated, and the pure spirit will float over the hydrated potash. If -potash is added to the oil and water, it combines with the oil, and, -forming soap, they all unite together; but, if we now add a little acid -to the mixture, the potash will quit the oil to combine with the acid, -and the oil will be repelled as before and float on the liquid. This -has been called single elective affinity. These elections were regarded -as constant, and chemists drew up tables for the purpose of showing the -order in which these decompositions occur.[203] Thus, ammonia, it was -shown, would separate sulphuric acid from magnesia, lime remove it from -ammonia, potash or soda from lime, and barytes from potash or soda. It -was thought the inverse of this order would not take place, but recent -researches have shown that the results are modified by quantity and -some other conditions. - -It often happens that we have a compound action of this kind in which -double election is indicated. Sulphate of lime and carbonate of ammonia -in solution are brought together, and there result a carbonate of lime -and a sulphate of ammonia. Now, in such cases nothing more than single -elective attraction most probably occurs, and the carbonic acid is -seized by the lime, by the great affinity of that earth for carbonic -acid, only after it has been set free from the ammonia, and then, by -the force of cohesion acting with the combining powers, the insoluble -salt is precipitated.[204] There is a curious fact in connection with -this decomposition. If carbonate of lime and sulphate of ammonia -are mixed together dry, and exposed, in a closed vessel, to a red -heat, sulphate of lime and carbonate of ammonia are formed. These -opposite effects are not very easily explained. The action of heat is -to set free the carbonic acid; and it can only be by supposing that -considerable differences of temperature reverse the laws of affinity, -that we can at all understand this phenomenon. That different effects -result at high temperatures from those which prevail at low ones, -recent experiments prove to us, particularly those of Boutigny, already -quoted when considering decomposition by calorific action. - -Under the term chemical affinity, which we regard as a power acting -at insensible distances, and producing a change in bodies, we are -content to allow ourselves to believe that we have explained the -great operations of nature. We find that the vegetable and animal -kingdoms are composed of carbon, hydrogen, oxygen, and nitrogen. The -granite mountains of the earth, and its limestone hills, and all its -other geological formations, are found to be metals and oxygen, and -carbon and sulphur, disposed to settle in harmonious union in their -proper places by chemical affinity. But what really is the power which -combines atom to atom, and unites molecule to molecule? Can we refer -the process to heat? The influence of caloric, although by changing -the form of bodies it sometimes assists combination, is to be regarded -rather as in antagonism to the power of cohesion. Can it be thought -that electricity is active in producing the result? During every change -of state, those phenomena which we term electrical are manifested; but -we thereby only prove the general diffusion of the electric principle, -and by no means show that electricity is the cause of the chemical -change. Can light determine these changes? It is evident, although -light may be a disturbing power, that it cannot be the effective one; -for many of these decompositions and recompositions are constantly -going on within the dark and silent depths of the earth, to which a -sunbeam cannot reach. That the excitation on the surface of the earth, -produced by solar influence, may modify those changes, is probable. It -is, however, certain that we must regard all manifestations of chemical -force as dependent upon some secret principles common to all matter, -diffused throughout the universe, but modified by the influences of the -known imponderable elements, and by the mechanical force of aggregative -attraction. - -Bodies undergo remarkable changes of form, and present very different -characters, by reactions, which are of several kinds. We suppose -that a permanent corpuscular arrangement is maintained so long as -the equilibrium of the molecular forces is undisturbed. Water, for -instance, remains unchanged so long as the balance of affinity is kept -up between the oxygen and hydrogen of which it is composed, or so long -as the oscillations of force between these combining elements are -equal; but disturb this force, or set up a new vibratory action, as by -passing an electric current through the water, or by presenting another -body, which has the power of reacting upon one of these corpuscular -systems, and the water is decomposed, the hydrogen and oxygen gases -being set free, or one alone is liberated, and the other combined with -the molecules of the agent employed, and a new compound produced. This -is chemistry, by which science we discover all the combinations of -matter. - -Having reason to conclude that atom combines with atom, according to -a system most harmoniously arranged, there can be no difficulty in -conceiving that molecule unites with molecule, in a manner regulated -by some equally well-marked law. It was, indeed, a discovery by -Wenzel, of Fribourg, that, in salts which decompose each other, the -acid which saturates one base will also saturate the other base; -and the subsequent observations of Richter, of Berlin, who attached -proportional numbers to the acids and bases, and who remarked that the -neutrality of metallic salts does not change during the precipitation -of metals by each other, which led the way to the atomic theory of Dr. -Dalton, to whom entirely belongs the observation, that the equivalent -of a compound body is the sum of the equivalents of its constituents, -and the discovery of combination in multiple proportions. - -The elements of a molecule can take a new arrangement amongst -themselves, without any alteration in the number of the atoms or of -their weight, and thus give rise to a body of a different form and -colour, although possessing the same chemical constitution. This is the -case with many of the organic compounds of carbon and hydrogen. - -The elements of a compound may be disassociated, and thus the -dissimilar substances of which it is composed set free. A piece -of chalk exposed to heat is, by the disturbance of its molecular -arrangement, changed in its nature; a gaseous body, carbonic acid, -is liberated, and quick-lime (oxide of calcium) is left behind. If -this carbonic acid is passed through red-hot metal tubes, or brought -in contact with heated potassium, it is resolved into oxygen and -charcoal--the oxygen combining with the metal employed. The oxide of -calcium (lime), if subjected to the action of a powerful galvanic -current, is converted into oxygen and a metal, calcium. Thus we learn -that chalk is a body consisting of two compound molecules,--carbonic -acid, which is formed by the combination of an atom of carbon with two -atoms of oxygen,--and lime, which results from the union of an atom of -calcium with one of oxygen. - -The condition requisite to the production of chemical action between -bodies is that they should be dissimilar. Two elementary atoms -are placed within the spheres of each other’s influences, and a -compound molecule results. Oxygen and hydrogen form water; oxygen -and carbon give rise to carbonic acid; nitrogen and hydrogen unite -to form ammonia; and chlorine and hydrogen to produce hydrochloric -acid. In all these cases an external force is required to bring the -atoms within the range of mutual affinity: flame,--the electrical -spark,--actinism,--or the interposition of a third body, is necessary -in each case. There are other examples in which no such influence is -required. Potassium and oxygen instantly unite: chlorine, iodine, and -bromine immediately, and with much violence, combine with the metals to -form chlorides, iodides, or bromides. - -With compound molecules the action is in many cases equally active, -and combination is readily effected, as in the cases of the acids and -the oxides of some metals, which are all instances of the most common -chemical attraction. - -An elementary or simple molecule and molecules of a compound and -different constitution are brought together, and a new compound -results from an interchange of their atoms, whilst an element is -liberated. These are essentially illustrations of analytical chemistry. -Sulphuretted hydrogen is mixed with chlorine; the chlorine combines -with the hydrogen, and sulphur is set free. Potassium is put into -water, and it combines with the oxygen of the water, whilst the -hydrogen is liberated. - -Two compound molecules being brought together may decompose each other, -and form two new compounds by an interchange of their elements. - -One element may be substituted for another under certain circumstances. -Gold may be replaced by mercury; copper will take the place of silver; -and iron will occasion the separation of copper from its solutions, -the iron itself being dissolved to supply its place; chlorine will -substitute hydrogen in the carburetted hydrogen gases; and many other -examples might be adduced. - -Chemical phenomena very frequently become of a complex character; -and one, two, or three of these cases may be occurring at the same -time in the decomposition of one compound by another. Such are the -general features of chemical science. Many peculiarities and remarkable -phenomena connected with chemical investigations will be named, as -the examination of the elementary composition of matter is proceeded -with; but, although the philosophy of chemical action is of the highest -interest, it must not be allowed to detain us with its details, which -are, indeed, more in accordance with a treatise on the science than -one which professes to do no more than sketch out those prevailing -and striking features which, whilst they elucidate the great truths -of nature, are capable of being employed as suggestive examples of -the tendency of scientific investigation to enlarge the boundaries of -thought, and give a greater elevation to the mind, leading us from -the merely mechanical process of analysis up to the great synthetical -operations, by which all that is found upon the earth for its ornament, -or our necessities, is created. - -Among the most remarkable phenomena within the range of physical -chemistry are those of _Catalysis_, or, as it has also been called, the -“_Action of presence_.”[205] There are a certain number of bodies known -to possess the power of resolving compounds into new forms, without -undergoing any change themselves. Kirchoff discovered that the presence -of an acid, at a certain temperature, converted starch into sugar and -gum, no combination with the acid taking place. Thenard found that -manganese, platinum, gold, and silver, and, indeed, almost any solid -organic body, had the power of decomposing the binoxide of hydrogen by -their presence merely, no action being detected on these bodies. Edmund -Davy found that powdered platinum, moistened with alcohol, became -red-hot, fired the spirit, and converted it into vinegar, without -undergoing, itself, any chemical change. Döbereiner next discovered -that spongy platinum fired a current of hydrogen gas directed upon -it, which, by combining with the oxygen of the air, formed water. -Dulong and Thenard traced the same property, differing only in degree, -through iridium, osmium, palladium, gold, silver, and even glass. -Further investigation has extended the number of instances; and it has -even been found that a polished plate of platinum has the power of -condensing hydrogen and oxygen so forcibly upon its surface, that these -gases are drawn into combination and form water, with a development of -heat sufficient to ignite the metal. - -This power, whatever it may be, is common in both organic and inorganic -nature, and on its important purposes Berzelius has the following -remarks:-- - -“This power gives rise to numerous applications in organic nature; -thus, it is only around the eyes of the potato that diastase exists: -it is by means of catalytic power that diastase, and that starch, -which are insoluble, are converted into sugar and into gum, which, -being soluble, form the sap that rises in the germs of the potato. -This evident example of the action of catalytic power in an organic -secretion, is not, probably, the only one in the animal and vegetable -kingdom, and it may hereafter be discovered that it is by an action -analogous to that of catalytic power, that the secretion of such -different bodies is produced, all which are supplied by the same -matter, the sap in plants, and the blood in animals.”[206] - -It is, without doubt, to this peculiar agency that we must attribute -the abnormal actions produced in the blood of living animals by the -addition of any gaseous miasma or putrid matter, of which we have, in -all probability, a fearful example in the progress of Asiatic cholera; -therefore the study of its phenomena becomes an important part of -public hygiène. - -Physical research has proved to us that all bodies have peculiar -powers, by which they condense with varying degrees of force gases -and vapours upon their surfaces; every body in nature may, indeed, be -regarded as forming its own peculiar atmosphere. To this power, in all -probability, does catalysis belong. Different views have, however, -prevailed on this subject, and Dr. Lyon Playfair[207] argues that the -catalytic force is merely a modified form of chemical affinity, exerted -under peculiar conditions. - -Whatever may be the power producing chemical change, it acts in -conformity with some fixed laws, and in all its transmutations, an -obedience to a most harmonious system is apparent. - -It is curious to observe the remarkable character of many of these -natural transmutations of matter, but we must content ourselves with a -few examples only. For instance:-- - -Sugar, oxalic acid, and citric acid are very unlike each other, yet -they are composed of the same elements; the first is used as a general -condiment, the second is a destructive poison, and the third a grateful -and healthful acid: sugar is readily converted into oxalic acid, and -in the process of ripening fruits nature herself converts citric acid -into sugar. Again, starch, sugar, and gum would scarcely be regarded -as alike, yet their only difference is in the mode in which carbon, -hydrogen, and oxygen combine. They are composed of the same principles, -in the following proportions:-- - - Carbon. Hydrogen. Oxygen. - Starch 12 10 10 - Sugar 12 11 11 - Gum 12 11 11 - -These _isomeric_ groups certainly indicate some law of affinity which -science has not yet discovered. Similar and even more remarkable -instances might be adduced of the same elements producing compounds -very unlike each other; but the above have been selected from their -well-known characters. Indeed, we may state with truth that all the -varieties of the vegetable world--their woody fibre--their acid or -alkaline juices--the various exudations of plants--their flowers, -fruit, and seeds, and the numerous products which, by art, they are -made to yield for the uses of man, are, all of them, compounds of these -three elements, differing only in the proportions in which they are -combined with nitrogen, or in some peculiar change of state in one -or other of the elementary principles. The chemist is now enabled by -simple processes, from the refuse of manufactories to produce fruit -essences which are equal in flavour to the natural production; and from -benzoic acid, which is obtained in great abundance from the houses in -which cows are kept, the most delicate essences are produced, which -are given to the world as the distillations of a thousand flowers. -By the impulse given to organic chemistry by Liebig, our knowledge -of the almost infinite variety of substances, in physical character -exceedingly dissimilar, which result from the combination of oxygen, -hydrogen, and carbon, in varying proportions, has been largely -increased. And the science is now in that state which almost causes -a regret that any new organic compounds should be discovered, until -some industrious mind has undertaken the task of reducing to a good -general classification the immense mass of valuable matter which has -been accumulated, but which, for all practical purposes, remains nearly -useless and unintelligible. - -These combinations, almost infinitely varied as they are, and so -readily produced and multiplied as to be nearly at the will of the -organic analyst, are not, any of them, accidental: they are the result -of certain laws, and atom has united with atom in direct obedience -to principles which have been through all time in active operation. -They are unknown; the researches of science have not yet developed -them, and the philosopher has not yet made his deductions. They are -to be referred to some secret fixed principles of action, to a force -which has impressed upon every atom of the universe its distinguishing -character. Chemistry makes us familiar with a system of order. The -researches of analysts have proved that every body has a particular -law of combination, to which it is bound by a mathematical precision; -but it is not proportional combination alone we have to consider. If -_allotrophy_ is evidenced in the mineral world, it is certainly far -more strikingly manifested in the vegetable and animal kingdoms. - -There are some cases in which bodies appear to combine without any -limitation, as spirit of wine and water, sulphuric acid and water; -but these must be considered as conditions of mixture rather than of -chemical combination. - -The composition of bodies is fixed and invariable, and a compound -substance, so long as it retains its characteristic properties, must -consist of the same elements united in the same proportions. Thus, -sulphuric acid is invariably composed of 16 parts of sulphur and 24 -parts of oxygen. Chalk, whether formed by nature or by the chemist, -yields 43·71 parts of carbonic acid, and 56·29 parts of lime. The rust -which forms upon the surface of iron by the action of the atmosphere, -is as invariable in its composition as if it had been formed by the -most delicate adjustment of weight by the most accurate manipulator, -being 28 parts of iron and 12 parts of oxygen. This law is the basis of -all chemical inquiry, all analytical investigations depending upon the -knowledge it affords us, that we can only produce certain undeviating -compounds as the results of our decompositions. We are not in a -position to offer any explanation which will account for these constant -quantities in combination. The forces of cohesion and elasticity -have been advanced in explanation, on the strength of the fact that -the solubility of a salt in water is regulated by cohesion, and that -of a gas by its elasticity. Although it may appear that some cases -of chemical combination are due to these powers,--as, for instance, -when the union of oxalic acid or sulphuric acid with lime produces -an insoluble salt,--we cannot thus explain the constant proportions -in which the metals, sulphur, oxygen, and similar bodies, unite. It -is quite certain there is a power or principle, which we have not -yet reached, upon which are dependent all the phenomena which we now -embrace under the term chemical affinity. - -Another law teaches us that when compound bodies combine in more than -one proportion, every additional union represents a multiple of the -combining proportion of the first. With the difficulty which arises -from the sub-multiple compounds we cannot deal:--further research may -render their laws less obscure. We have seen that 8 parts of oxygen -unite with 1 of hydrogen and 14 of nitrogen. It also unites with 110 of -silver, 96 of platinum, 40 of potassium, 36 of chlorine, and 200 parts -of mercury, giving rise to-- - - Water 9 - Nitrous oxide 22 - Oxide of silver 118 - Oxide of platinum 104 - Potash 48 - Oxide of chlorine 44 - Oxide of mercury 208 - -In these proportions, or in multiples of them, and in no others, will -these bodies unite with the acids or other compounds. It will, of -course, be understood that any other numbers may be adopted, provided -they stand in the same relation to each other.[208] - -From the discovery of these harmonious arrangements was deduced the -beautiful atomic theory to which allusion has been already made. -Indeed, there does not appear to be any other way of explaining these -phenomena than by the hypothesis that the ultimate atoms of bodies have -_relatively_ the weights which we arbitrarily assign to them, as their -combining quantities. These views are further confirmed by the fact, -that gaseous bodies unite together by volume in very simple definite -proportions:--100 measures of hydrogen and 200 measures of oxygen form -water; 100 measures of oxygen and 100 measures of vapour of sulphur -form sulphurous acid gas. Ammoniacal gas consists of 300 volumes of -hydrogen and 100 volumes of nitrogen, condensed by combination into 200 -volumes; consequently, we are enabled most readily to calculate the -specific gravity of ammoniacal gas. The specific gravity of nitrogen -is 0·9722, that of hydrogen 0·0694. Now, three volumes of hydrogen are -equal to 0·2082: this added to 0·9722 is equal to 1·1804, which is -exactly the specific gravity obtained by experiment. - -There is no doubt, from the generality with which this law of volumes -prevails, that it would be found to extend through all substances, -provided they could be rendered gaseous; in other words, there is -abundant proof to convince us that throughout nature the process of -combination, in the most simple ratio of volumes, is in operation to -produce all the forms of matter known to us. - -It has been shown, by the investigations of Dr. Dalton, in 1840, that -salts, containing water of crystallization, dissolve in water without -increasing the bulk of the fluid more than is due to the liquefaction -of the water which these salts contain; while Joule and Playfair -have shown that the anhydrous salts take up no space in solution. -From this we are naturally led to conclude that the volume occupied -by a salt in the solid state has a certain relation to the volume of -the same salt when in solution, and has also a fixed relation to the -volume occupied by any other salt. The law appears to be:--the atomic -volume of any salt whatever (anhydrous or hydrated) is a multiple of -11, or of a number near 11, or a multiple of 9·8 (the atomic volume -of ice), or the sum of a multiple of 11 or 9·8. Marignac, who has -also paid much attention to the subject, does not think these numbers -absolutely correct, but approximately so.[209] It would be a beautiful -exemplification of the simplicity of Nature’s operations, if it should -be clearly proved that the atomic volume of solid water (ice) regulated -the combining proportions by volume of all other bodies,--that it was -the standard by which chemical combination and ordinary solution were -determined. - -In addition to the laws already indicated, there appear to be some -others of which, as yet, we have a less satisfactory knowledge, and, -as a remarkable case, we may adduce the phenomena of _substitution_, -or that power which an elementary body, under certain conditions, -possesses, of turning out one of the elements of a compound, and of -taking its place.[210] Thus, the hydrogen of a compound radical, as -carburetted hydrogen, may be replaced by chlorine, equivalent for -equivalent, and form a chloride of carbon, which being constructed -on the same type as the original, will have the same general laws of -combination. - -Under the influence of these laws, all the combinations which we -discover in nature take place. The metals, and oxygen, and sulphur, -and phosphorus unite. The elements of the organic type, entering into -the closest relations, give rise to every form of vegetable life. The -acids, the gums, the resins, and the sugar which plants produce; and -those yet more complicated animal substances, bone, muscle, blood, and -bile; albumen, casein, milk, with those compounds which, under the -influence of vital power, resolve themselves into substances which are -essential to the existence, health, and beauty of the animal fabric, -are all dependent on these laws. But these metamorphoses must be -further considered in our examination of the more striking cases of -chemical action. The changes which result from organic combination are -so remarkable, and withal they show how completely the whole of the -material world is in subjection to chemical force, and every variety -of form the result of mysterious combination, that some particular -reference to these metamorphoses is demanded. - -In nearly all cases of decided chemical action, all trace of the -characters of the combining bodies disappear. We say decided chemical -action, because, although sulphuric acid and water combine, and -salts dissolve in water, we may always recognize their presence, and -therefore these and similar cases cannot be regarded as strict examples -of the phenomena under consideration. - -Hydrogen and oxygen, in combining, lose their gaseous forms, and are -condensed into a liquid--water. Sulphuric acid is intensely sour and -corrosive; potash is highly caustic; but united they form a salt -which is neither: they appear to have destroyed the distinguishing -characters of each other. Combined bodies frequently occupy less space -than they did previously to combination, of which numerous particular -instances might be adduced. Gases in many cases undergo a remarkable -condensation when chemically combined. In slaking lime, the water -becomes solid in the molecules of the hydrate of lime formed, and the -intense heat produced arises from the liberation of that caloric which -had been employed to keep the water liquid. When a solid passes into -the liquid state, cold is produced by the abstraction from surrounding -objects of the heat required to effect fluidity. An alteration of -temperature occurs whenever chemical change takes place, as we have -already shown, with a few trivial and uncertain exceptions. The -disturbance caused by the exercise of the force of affinity frequently -leads to the development of several physical powers. - -Changes of colour commonly arise; indeed, there does not appear to be -any relation between the colour of a compound and that of its elements. -Iodine is of a deep iron-grey colour; its vapour is violet; yet it -forms beautifully white salts with the alkalies, a splendid red salt -with mercury, and a yellow one with lead. The salts of iron vary from -white and yellow to green and dark brown. Those of copper, a red metal, -are of a beautiful blue and green colour, and the anhydrous sulphate is -white. - -Isomorphism, which appears in a very remarkable manner among the -organic compounds, has, under the head of crystallization, already had -our attention. There is also a class of bodies which are said to be -_isomeric_; that is, to have the same composition, although different -in their physical characters. But the idea that bodies exist, which, -although of a decidedly different external character, are of exactly -the same chemical composition and physical condition, is not tenable; -and in nearly all the examples which have been carefully examined, a -difference in the aggregate number of atoms, or in the mode in which -those atoms have respectively arranged themselves, or that peculiar -physical difference designated by the term _allotropy_, has been -detected. - -Oil of turpentine and oil of lemons have the same composition, each -being composed of five equivalents of carbon and four of hydrogen. -These substances form, from the striking difference perceptible in -their external characters, a good example of isomerism. - -The laws of organic chemistry are not, however, the same as those -applying to inorganic combinations. Organic chemistry is well defined -by Liebig, as the chemistry of compound radicals; and under the -influence of vitality, nature produces compounds which have all the -properties of simple elements.[211] - -When we reflect upon the conditions which prevail throughout nature, -with a few of which only has science made us acquainted, we cannot fail -to be struck with the various phases of being which are presented to -our observation, and the harmonious system upon which they all appear -to depend. - -When we discover that bodies are formed of certain determinate atoms, -which unite one with another, according to an arithmetical system, to -form molecules, which, combining with molecules, observe a similar law, -we see at once that all the harmonies of chemical combination--the -definite proportions, laws of volume, and the like--are but the -necessary consequences of these simple and guiding first principles. -In the pursuit of truth, investigators must discover still further -arrangements, which, from their perfection, may be compared to the -melodious interblending of sweet sounds, and many of the apparently -indeterminate combinations will, beyond a doubt, be shown to be as -definite as any others. But we cannot reflect upon the fact that these -atoms and these molecules are guided in their combinations by impulses, -which we can only explain by reference to human passions, as the term -_elective affinity_ implies, without feeling that an impenetrable -mystery of a grand and startling character in its manifestations -surrounds each grain of dust which is hurried along upon the wind. - -We now, habitually, speak of attraction and repulsion--of the affinity -and non-affinity of bodies. We are disposed, from the discovery of the -attractive and repelling poles of electrified substances, to regard -these powers in all cases as depending upon some electrical state, and -we write learnedly upon the laws of these forces. After all, it would -be more honest to admit, that we know no more of the secret impulses -which regulate the combinations of matter, than did those who satisfied -themselves by referring all phenomena of these kinds to sympathies -and antipathies: terms which have a poetic meaning, conveying to the -mind, with considerable distinctness, the fact, and giving the idea -of a feeling--a passion--involving and directing inanimate matter, -similar to that which stirs the human heart, and certainly calculated -to convey the impression that there is working within all things a -living principle, and pointing, indeed, to “the soul of the world.” The -animated marble of ancient story is far less wonderful than the fact, -proved by investigation, that every atom of matter is penetrated by a -principle which directs its movements and orders its positions, and -involved by an influence which extends, without limits, to all other -atoms, and which determines their union, or otherwise. - -We have gravitation, drawing all matter to a common centre, and -acting from all bodies throughout the wide regions of unmeasured -space upon all. We have cohesion, holding the particles of matter -enchained, operating only at distances too minute for the mathematician -to measure; and we have chemical attraction, different from either -of these, working no less mysteriously within absolutely insensible -distances, and, by the exercise of its occult power, giving determinate -and fixed forms to every kind of material creation. - -The spiritual beings, which the poet of untutored nature gave to the -forest, to the valley, and to the mountain, to the lake, to the river, -and to the ocean, working within their secret offices, and moulding -for man the beautiful or the sublime, are but the weak creations -of a finite mind, although they have for us a charm which all men -unconsciously obey, even when they refuse to confess it. They are like -the result of the labours of the statuary, who, in his high dreams of -love and sublimated beauty, creates from the marble block a figure -of the most exquisite moulding which mimics life. It charms us for a -season; we gaze and gaze again, and its first charms vanish; it is ever -and ever still the same dead heap of chiselled stone. It has not the -power of presenting to our wearying eyes the change which life alone -enables matter to give; and we admit the excellence of the artist, but -we cease to feel at his work. The creations of poetry are pleasing, but -they never affect the mind in the way in which the poetic realities -of nature do. The sylph moistening a lily is a sweet dream; but the -thoughts which rise when first we learn that its broad and beautiful -dark-green leaves, and its pure and delicate flower, are the results -of the alchemy which changes gross particles of matter into symmetric -forms,--of a power which is unceasingly at work under the guidance of -light, heat, and electrical force,--are, after our incredulity has -passed away--for it is too wonderful for the untutored to believe at -once--of an exalting character. - -The flower has grown under the impulse of principles which have -traversed to it on the solar beam, and mingled with its substance. A -stone is merely a stone to most men. But within the interstices of -the stone, and involving it like an atmosphere, are great and mighty -influences, powers which are fearful in their grander operations, and -wonderful in their gentler developments. The stone and the flower hold, -locked up in their recesses, the three great known forces--light, heat, -and electricity: and, in all probability, others of a more exalted -nature still, to which these powers are but subordinate agents. Such -are the facts of science, which, indeed, are the true “sermons in -stones,” and the most musical of “tongues in trees.” How weak are the -creations of romance, when viewed beside the discoveries of science! -One affords matter for meditation, and gives rise to thoughts of a most -ennobling character; the other excites for a moment, and leaves the -mind vacant or diseased. The former, like the atmosphere, furnishes -a constant supply of the most healthful matter; the latter gives -an unnatural stimulus, which compels a renewal of the same kind of -excitement, to maintain the continuation of its pleasurable sensations. - - -FOOTNOTES: - -[200] All the phenomena connected with volcanic action, and the -theories connected therewith, will be found in Dr. Daubeny’s work, _A -description of active and extinct Volcanoes, of Earthquakes, and of -Thermal Springs_. 1848. - -[201] Graham’s _Elements of Chemistry_. New Edition. - -[202] Graham’s _Elements of Chemistry_; and Brande’s _Manual_. - -[203] Of these _tables of attraction_ the following may be taken as a -specimen:-- - - SULPHURIC ACID. - Baryta. - Strontia. - Potassa. - Soda. - Lime. - Magnesia. - Ammonia. - -It thus appears that baryta separates sulphuric acid from its compounds -with all inferior substances, and that ammonia is separated from the -acid by all that are above it. - -[204] Berthollet: _Essai de Statique Chimique_, 1803. Sir Humphry Davy, -in his _Elements of Chemical Philosophy_, has given an excellent review -of the views of Berthollet. - -[205] _On certain combinations of a new acid, formed of Azote, Sulphur, -and Oxygen_; by J. Pelouze. Translated from Annales de Chimie, vol. -xvi., for Scientific Memoirs, vol. i. p. 470. _Some ideas of a new -force acting in the combinations of Organic Compounds_, by Berzelius: -Annales de Chimie, vol. lxi. The conclusion come to by this eminent -chemist is expressed in the following translation:--“This new power, -hitherto unknown, is common both in organic and inorganic nature. -I do not believe that it is a power which is entirely independent -of the electro-chemical affinities of the substance. I believe, on -the contrary, that it is merely a new form of it; but so long as we -do not see their connection and mutual dependence, it will be more -convenient to describe it by a separate name. I shall, therefore, call -it _catalytic power_: I shall also call _catalysis_, the decomposition -of bodies by this force--in the same way as the decomposition of bodies -by chemical affinity is termed analysis.” - -[206] Berzelius: _Annales de Chimie_, vol. lxi. - -[207] _On Transformations produced by Catalytic Bodies_: by Lyon -Playfair, Esq.; Phil. Mag., vol. xxxi. p. 191, 1847.--“Facts have been -brought forward to show that there is at least as much probability in -the view that the catalytic force is merely a modified form of chemical -affinity exerted under peculiar conditions, as there is in ascribing -it to an unknown power, or to the communication of an intestine motion -to the atoms of a complex molecule. Numerous cases have been cited, -in which the action results when the assisting or catalytic body is -not in a state of change; and attempts have been made to prove, by new -experiments, that the catalytic power exercises its peculiar power by -acting in the same direction as the body decomposing, or entering into -union, but under conditions in which its own affinity cannot always be -gratified.” - -[208] Consult Graham’s Chemistry, _On Combining Proportions_. - -[209] _Memoir on Atomic Volume and Specific Gravity._ Messrs. Lyon -Playfair and Joule.--Philosophical Magazine, vol. xxvii. p. 453, or -Transactions of Chemical Society of London. _Observations_ on the -above, by Professor de Marignac.--Bibliothèque Universelle, Feb. 1846. -_On the Relation of the Volumes of bodies in the solid state, to their -equivalents, or atomic weights_: by Professor Otto. _Studies on the -connection between the atomic weights, crystalline form, and density -of bodies_: by M. Filhol. Translated for the Cavendish Society, and -published in their Chemical Reports and Memoirs. - -[210] _Comptes Rendus de l’Académie des Sciences_, 1840, No. 5. A good -translation of Dumas’s Memoir appeared in the Philosophical Magazine, -from which I extract the following familiar exposition of the laws of -substitution:--“Let me make a comparison drawn from a familiar order of -ideas. Let us put ourselves in the place of a man overlooking a game at -chess without the slightest knowledge of the game. He would soon remark -that the pieces must be used according to positive rules. In chemistry, -the equivalents are our pieces, and the law of substitutions one of the -rules which preside over their moves. And as in the oblique move of the -pawns one pawn must be substituted for another, so in the phenomena -of substitution one element must take the place of another. But this -does not hinder the pawn from advancing without taking anything, as the -law of substitution does not hinder an element from acting on a body -without displacing or taking the place of any other element that it may -contain.”--_Memoir on the Law of Substitutions, and Theory of Chemical -Types._ - -[211] Liebig’s _Chemistry in its application to Agriculture and -Physiology_: translated by Lyon Playfair, Ph. D. _Animal Chemistry, or -Chemistry in its application to Physiology and Pathology_: by Justus -Liebig; translated by Wm. Gregory. - - - - -CHAPTER XII. - -CHEMICAL PHENOMENA. - - Water--Its Constituents--Oxygen--Hydrogen--Peroxide - of Hydrogen--Physical Property of Water--Ice--Sea - Water--Chlorine--Muriatic Acid--Iodine--Bromine--Compounds - of Hydrogen with Carbon--Combustion--Flame--Safety - Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic - Acid--Influence of Plants on the Air--Chemical Phenomena of - Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c. &c. - - -Without attempting anything which shall approach even to the character -of a sketch of chemical science, we may be allowed, in our search -after exalting truths, to select such examples of the results of -combination as may serve to elucidate any of the facts connected with -natural phenomena. In doing this, by associating our examination with -well-known natural objects or conditions, the interpretation afforded -by analysis will be more evident, and the operation of the creative -forces rendered more striking and familiar, particularly if at the same -time we examine such physical conditions as are allied in action, and -are sufficiently explanatory of important features. - -A large portion of this planet is covered by the waters of the ocean, -of lakes and rivers. Water forms the best means of communication -between remote parts of the earth. It is in every respect of the -utmost importance to the animal and vegetable kingdom; and, indeed, it -is indispensable in all the great phenomena of the inorganic world. -The peculiarities of saltness or freshness in water are dependent -upon its solvent powers. The waters of the ocean are saline from -holding dissolved various saline compounds, which are received in -part from, and imparted also to, the marine plants. Perfectly pure -water is without taste: even the pleasant character of freshly-drawn -spring-water is due to the admixture of atmospheric air and carbonic -acid. The manner in which water absorbs air is evidently due to a -peculiar physical attractive force, the value of which we do not at -present clearly perceive or correctly estimate. It is chemically -composed of two volumes of hydrogen gas--the lightest body known, and -at the same time a highly inflammable one--united with one volume of -oxygen, which excites combustion, and continues that action,--producing -heat and light,--with great energy. By weight, one part of hydrogen -is united with eight of oxygen, or in 100 parts of water we find 88·9 -oxygen, and 11·1 of hydrogen gas. That two such bodies should unite to -furnish the most refreshing beverage, and indeed the only natural drink -for man and animals, is one of the extraordinary facts of science. -Hydrogen will not support life--we cannot breathe it and live; and -oxygen would over-stimulate the organic system, and, producing a kind -of combustion, give rise to fever in the animal frame; but, united, -they form that drink, for a drop of which the fevered monarch would -yield his diadem, and the deprivation of which is one of the most -horrid calamities that can be inflicted upon any living thing. Water -appears as the antagonist principle to fire, and the ravages of the -latter are quenched by the assuaging powers of the former; yet a -mixture of oxygen and hydrogen gases, in the exact proportion in which -they form water, explodes with the utmost violence on the contact of -flame, and, when judiciously arranged, produces the most intense degree -of heat known;--such is the remarkable difference between a merely -mechanical mixture and a chemical combination. Beyond this, we have -already noticed the remarkable fact that water deprived of air is -explosive at a comparatively low temperature, less than 300°; gunpowder -requiring a temperature of nearly 1000° F. - -If we place in a globe, oxygen and hydrogen gases, in the exact -proportions in which they combine to form water, they remain without -change of state. They appear to mix intimately; and, notwithstanding -the difference in the specific gravities of the two gases, the lighter -one is diffused through the heavier in a curious manner, agreeably to -a law which has an important bearing on the conditions of atmospheric -phenomena.[212] The moment, however, that an incandescent body, or -the spark from an electric machine, is brought into contact with the -mixed gases, they ignite, explode violently, and combine to form water. -The discovery of the composition of water was thus synthetically made -by Cavendish--its constitution having been previously theoretically -announced by Watt.[213] - -If, instead of combining oxygen and hydrogen in the proportions in -which they form water, we compel the hydrogen to combine with an -additional equivalent of oxygen, we have a compound possessing many -properties strikingly different from water. This--peroxide of hydrogen, -as it is called--is a colourless liquid, less volatile than water, -having a metallic taste. It is decomposed at a low temperature, and, -at the boiling point, the oxygen escapes from it with such violence, -that something like an explosion ensues. All metals, except iron, tin, -antimony, and tellurium, have a tendency to decompose this compound, -and separate it into oxygen and water. Some metals are oxidized during -the decomposition, but gold, silver, platinum, and a few others, -still retain their metallic state. If either silver, lead, mercury, -gold, platinum, manganese, or cobalt, in their highest states of -oxidation, are put into a tube, containing this peroxide of hydrogen, -its oxygen is liberated with the rapidity of an explosion, and so -much heat is excited that the tube becomes red hot. These phenomena, -to which we have already referred in noticing catalysis, are by no -means satisfactorily explained, and the peculiar bleaching property -possessed by the peroxide of hydrogen sufficiently distinguishes it -from water. There are few combinations which show more strikingly than -this the difference arising from the chemical union of an additional -atom of one element. Similar instances are numerous in the range -of chemical science; but scarcely any two exhibit such dissimilar -properties. During the ordinary processes of combustion, it has been -long known that water is formed by the combination of the hydrogen of -the burning body with the oxygen of the air. The recent researches of -Schönbein have shown that a peculiar body, which has been regarded as -a peroxide of hydrogen, to which he has given the name of OZONE, is -produced at the same time, and that it is developed in a great many -ways, particularly during electrical changes of the atmosphere. Thus -we obtain evidence that this remarkable compound, which was considered -as a chemical curiosity merely, is diffused very generally through -nature, and produced under a great variety of circumstances. During -the excitation of an electrical machine, or the passage of a galvanic -current through water by the oxidation of phosphorus, and probably -in many similar processes--in particular those of combustion, and we -may therefore infer also of respiration--this body is formed. From -observations which have been made, it would appear that, during the -night, when the activity of plants is not excited by light, they act -upon the atmosphere in such a way as to produce this ozone; and its -presence is said to be indicated by its peculiar odour during the -early hours of morning. We are not yet acquainted with this body -sufficiently to speculate on its uses in nature: without doubt, they -are important, perhaps second to those of water only. It is probable, -as we have already had occasion to remark, that ozone may be the active -agent in removing from the atmosphere those organic poisons to which -many forms of pestilence are traceable; and it is a curious fact, that -a low electrical intensity, and a consequent deficiency of atmospheric -ozone, marks the prevalence of cholera, and an excess distinguishes the -reign of influenza.[214] - -Some interesting researches appear to show the probability that ozone -is simply oxygen in a state of high activity. It has been found, -indeed, that perfectly dry oxygen, which will not bleach vegetable -colours in the dark, acquires, by exposure to sunshine, the power of -destroying them. Becquerel has proved that this ozonous state may be -produced in dry oxygen by passing a succession of electric sparks -through it. Fremy passed the electric sparks on the outside of a tube -which contained perfectly dry oxygen, and it was found to have acquired -the properties of ozone. In this case, and probably in the experiments -of Becquerel, the light of the spark, rather than the electricity, -appears to have been the active agent in producing this change. -Schönbein himself does not appear disposed to regard ozone as being -either peroxide of hydrogen, or an allotropic oxygen. He leans to his -first view of its being an entirely new chemical element. The energy -of this ozone is so great, that it has been found to destroy almost -instantaneously the Indian-rubber union joints of the apparatus in -which it is formed.[215] - -Water, from the consideration of which a digression has been indulged -in, to consider the curious character of one of its elements,--water is -one of the most powerful chemical agents, having a most extensive range -of affinities, entering directly into the composition of a great many -crystallizable bodies and organic compounds. In those cases where it is -not combined as water, its elements often exist in the proportions in -which water is formed. Gum, starch, and sugar, only differ from each -other in the proportions in which the elements of water are combined -with the carbon. - -In saline combinations, and also in many organic forms, we must regard -the water as condensed to the solid form; that is, to exist as ice. We -well know that, by the abstraction of heat, this condition is produced; -but, in chemical combinations, this change must be the result of the -mechanical force exerted by the power of the agency directing affinity. - -In the case of water passing from a liquid to a solid state, we have a -most beautiful exemplification of the perfection of natural operations. -Water conducts heat downwards but very slowly; a mass of ice will -remain undissolved but a few inches under water, on the surface of -which, ether, or any other inflammable body, is burning. If ice (solid -water) swam beneath the surface, the summer sun would scarcely have -power to thaw it; and thus our lakes and seas would be gradually -converted into solid masses at our ordinary winter temperatures. - -All similar bodies contract equally during the process of cooling, -from the highest to the lowest points to which the experiments have -been carried. It has been thought that if this applied to water, -the result would be the sudden consolidation of the whole mass. A -modification of the law has been supposed to take place to suit the -peculiar circumstances of water. Nature never modifies a law for a -particular purpose; we must, therefore, seek to explain the action of -the formation of ice, as we know it, by some more rational view. - -Water expands by heat, and contracts by cold; consequently, the -coldest portions of this body occupy the lower portions of the fluid; -but it must be remembered that these parts are warmed by the earth. -Ross, however, states that at the depth of 1,000 fathoms the sea -has a constant temperature of 39°. Water is said to be at its point -of greatest density at 40° of Fahrenheit’s thermometer; in cooling -further, this fluid appears to expand, in the same way as if heated: -and, consequently, water colder than this point, instead of being -heavier, is lighter, and floats on the surface of the warmer fluid. -It does not seem that any modification of the law is required to -account for this phenomenon. Water cooled to 40° still retains its -peculiar corpuscular arrangement; but immediately it passes below that -temperature, it begins to dispose itself in such a manner that visible -crystals may form the moment it reaches 32°. Now, if we conceive -the particles of water, at 39°, to arrange themselves in the manner -necessary for the assumption of the solid form, by the particular -grouping of molecules in an angular instead of a spheroidal shape, -it will be clear, from what we know of the arrangement of crystals -of water--ice--that they must occupy a larger space than when the -particles are disposed, side by side, in minute spheres. Even the -escape of air from the water in which it is dissolved is sufficient to -give an apparent lightness to the colder water. This expansion still -goes on increasing, from the same cause, during the formation of ice, -so that the specific gravity of a mass of frozen water is less than -that of water at any temperature below 40°. It must not be forgotten -that ice always contains a large quantity of air, by which it is -rendered buoyant. - -Water, at rest, may be cooled many degrees below the freezing point -without becoming solid. This is easily effected in a thin glass flask; -but the moment it is agitated, it becomes a firm mass. Here we have the -indication of another cause aiding in producing crystals of ice on the -surface of water, under the influence of the disturbance produced by -the wind, which does not extend to any depth. - -As oxygen and hydrogen gases enter largely into other chemical -compounds besides water, it is important to consider some of the forms -of matter into the composition of which these elements enter. To -examine this thoroughly, a complete essay on chemical philosophy would -be necessary; we must, therefore, be content with referring to a few of -the more remarkable instances. - -The waters of the ocean are salt: this arises from their holding, in -solution chloride of sodium (_muriate of soda_--_common culinary salt_) -and other saline bodies. Water being present, this becomes muriate of -soda,--that is, a compound of muriatic acid and soda: muriatic acid -is hydrogen, combined with a most remarkable gaseous body, called, -from its yellow colour, _chlorine_; and soda, oxygen in union with -the metal sodium,--therefore, when anhydrous, culinary salt is truly -a chloride of sodium. Chlorine in some respects resembles oxygen; it -attacks metallic bodies with great energy; and, in many cases, produces -the most vivid incandescence, during the process of combination. It -is a powerful bleaching agent, is destructive to animal life, and -rapidly changes all organic tissues. There are two other bodies in -many respects so similar to chlorine, although one is at the ordinary -temperatures solid, and the other fluid, and which are also discovered -in sea-water, or in the plants growing in it, that it is difficult to -consider them otherwise than as different forms of the same principle. -These are iodine and bromine, and they both unite with hydrogen to -form acids. The part which chlorine performs in nature is a great and -important one. Combined in muriate of soda, we may trace it in large -quantities through the three kingdoms of nature, and the universal -employment of salt as a condiment indicates the importance to the -animal economy of the elements composing it. Iodine has been traced -through the greater number of marine plants, existing, apparently as -an essential element of their constitution; in some land plants it has -also been found, particularly in the Armeria maritima, when this plant -grows near the sea:[216] it has been detected in some mineral springs, -and in small quantities in the mineral kingdom[217] combined as iodide -of silver, and in the aluminous slate of Latorp in Sweden.[218] Bromine -is found in sea-water, although in extremely minute quantities, in a -few saline springs, and in combination with silver; but we have no -evidence to show that its uses are important in nature. - -Hydrogen, again, unites with carbon in various proportions, producing -the most dissimilar compounds. The air evolved from stagnant water, -and the fire-damp of the coal mine, are both carburetted hydrogen; and -the gas which we employ so advantageously for illumination, is the -same, holding an additional quantity of carbon in suspension. Naphtha, -and a long list of organic bodies, are composed of these two chemical -elements. - -These combinations lead us, naturally, to the consideration of the -great chemical phenomena of combustion, which involve, indeed, the -influences of all the physical powers. By the application of heat, -we produce an intense action in a body said to be combustible; it -burns,--a chemical action of the most energetic character is in -progress, the elements which constitute the combustible body are -decomposed, they unite with some other elementary principles, and new -compounds are formed. A body burns--it is entirely dissipated, or it -leaves a very small quantity of ashes behind unconsumed, but nothing -is lost. Its volatile parts have entered into new arrangements, the -form of the body is changed, but its constituents are still playing an -important purpose in creation. - -The ancient notion that fire was an empyreal element, and the Stahlian -hypothesis of a phlogistic principle on which all the effects of -combustion depended,[219] have both given way to the philosophy of the -unfortunate Lavoisier--which has, indeed, been modified in our own -times--who showed that combustion is but the development of heat and -light under the influence of chemical combination. - -Combustion was, at one period, thought to be always due to the -combination of oxygen with the body burning, but research has shown -that vivid combustion may be produced where there is no oxygen. The -oxidizable metals burn most energetically in chlorine, and some of -them in the vapour of iodine and bromine, and many other unions take -place with manifestations of incandescence. Supporters of combustion -were, until lately, regarded as bodies distinct from those undergoing -combustion. For example, hydrogen was regarded as a combustible body, -and oxygen as a supporter of combustion. Such an arrangement is a -most illogical one, since we may _burn_ oxygen in an atmosphere of -hydrogen, in the same manner as we burn hydrogen in one of oxygen; and -so, in all the other cases, the supporter of combustion may be burnt -in an atmosphere formed of the, so called, combustible. The ordinary -phenomena of combustion are, however, due to the combination of oxygen -with the body burning; therefore every instance of oxidization may be -regarded as a condition of combustion, the difference being only one of -degree. - -Common iron, exposed to air and moisture, _rusts_; it combines with -oxygen. Pure iron, in a state of fine division, unites with oxygen so -eagerly, that it becomes incandescent, and in both cases oxide of iron -is formed. This last instance is certainly a case of combustion; but -in what does it differ from the first one, except in the intensity of -the action? The cases of spontaneous combustion which are continually -occurring are examples of an analogous character to the above. -Oxygen is absorbed, it enters more or less quickly, according to -atmospheric conditions, into chemical combination; heat is evolved, and -eventually,--the action continually increasing,--true combustion takes -place. In this way our cotton-ships, storehouses of flax, piles of -oiled-cloth, sawdust, &c., frequently ignite; and to such an influence -is to be attributed the destruction of two of our ships of war, a few -years since, in Devonport naval arsenal.[220] - -In the economic production of heat and light, we have the combination -of hydrogen and carbon with the oxygen of common air, forming water -and carbonic acid. In our domestic fires we employ coal, which is -essentially a compound of carbon and hydrogen containing a little -oxygen and some nitrogen, with some earthy matters which must be -regarded as impurities; the taper, whether of wax or tallow, is made up -of the same bodies, differing only in their combining proportions, and, -like coal gas, these burn as carburetted hydrogen. All these bodies -are very inflammable, having a tendency to combine energetically with -oxygen at a certain elevation of temperature. - -We are at a loss to know how heat can cause the combination of those -bodies. Sir Humphry Davy has shown that hydrogen will not burn, nor -a mixture of it with oxygen explode, unless directly influenced by a -body heated so as to _emit light_.[221] May we not, therefore, conclude -that the chemical action exhibited in a burning body is a development -of some latent force, with which we are unacquainted, produced by the -absorption of light;--that a repulsive action at first takes place, -by which the hydrogen and carbon are separated from each other;--and -that in the nascent state they are seized by the oxygen, and again -compelled, though in the new forms of water and carbonic acid, to -resume their chains of combining affinity? - -Every equivalent of carbon and of hydrogen in the burning body unites -with two equivalents of oxygen, in strict conformity with the laws -of combination. The flame of hydrogen, if pure, gives scarcely any -light, but combined with the solid particles of carbon, it increases -in brightness. The most brilliant of the illuminating gases is the -olefiant gas, produced by the decomposition of alcohol, and it is -only hydrogen charged with carbon to the point of saturation. Flame -is a cone of heated vapour, becoming incandescent at the points of -contact with the air; a mere superficial film only being luminous. It -is evident that all the particles of the gas are in a state of very -active repulsion over the surface, since flame will not pass through -wire gauze of moderate fineness. Upon this discovery is founded the -inimitable safety-lamp of Davy, by means of which the explosive gases -of a mine are harmlessly ignited within a cage of wire gauze. This -effect has been attributed to a cooling influence of the metal; but, -since the wires may be brought to a degree of heat but little below -redness without igniting the fire-damp, this does not appear to be the -cause. The conditions of the safety lamp may be regarded as presenting -examples exactly the converse of those already stated with reference to -the spheroidal state of water; and it affords additional evidence that -the condition of bodies at high temperatures is subject to important -physical changes. - -The principle upon which the safety lamp is constructed is, that a -mixture of the fire-damp and atmospheric air in certain proportions -explodes upon coming in contact with a flame. - -This mixture passes readily through a wire gauze, under all -circumstances, and it, of course, thus approaches the flame of the lamp -enclosed within such a material, and it explodes. But, notwithstanding -the mechanical force with which the exploding gas is thrown back -against the bars of its cage, it cannot pass them. Consequently, the -element of destruction is caught and caged; and notwithstanding its -fierceness and energy, it cannot impart to the explosive atmosphere -without, any of its force. No combustion can be communicated through -the wire gauze. - -The researches which led to the safety-lamp may be regarded as among -the most complete examples of correct inductive experiment in the range -of English science, and the result is certainly one of the proudest -achievements of physico-chemical research. By merely enveloping the -flame of a lamp with a metallic gauze, the labourer in the recesses of -the gloomy mine may feel himself secure from that outpouring current -of inflammable gas, which has been so often the minister of death; he -may walk unharmed through the explosive atmosphere, and examine the -intensity of its power, as it is wasted in trifling efforts within the -little cage he carries. Accidents have been attributed to the “Davy,” -as the lamp is called among the colliers; but they may in most cases be -traced to carelessness on the part of those whose duty it has been to -examine the lamps, or to the recklessness of the miners themselves. - -That curious metal, platinum, and also palladium, possesses a property -of maintaining a slow combustion, which the discoverer of the -safety-lamp proposed to render available to a very important purpose. -If we take a coil of platinum wire, and, having made it red-hot, plunge -it into an explosive atmosphere of carburetted hydrogen and common -air, it continues to glow with considerable brightness, producing, -by this very peculiar influence, a combination of the gases, which -is discovered by the escape of pungent acid vapours. Over the little -flame of the safety-lamp, it was proposed by Davy to suspend a coil -of platinum which would be thus kept constantly at a red heat. If the -miner became accidentally enveloped in an atmosphere of fire-damp, -although the flame of his lamp might be extinguished, the wire would -continue to glow with sufficient brightness to light him from his -danger, through the dark winding passages which have been worked in the -bed of fossil fuel. This very beautiful arrangement has not, however, -been adopted by our miners. - -It is thus that the discoveries of science, although they may appear -of an abstract character, constantly, sooner or later, are applied to -uses by which some branch of human labour is assisted, the necessities -of man’s condition relieved, and the amenities of life advanced. - -The respiration of animals is an instance of the same kind of chemical -phenomena as we discover in ordinary combustion. In the lungs the blood -becomes charged with oxygen, derived from the atmospheric air, with -which it passes through the system, performing its important offices, -and the blood is returned to the lungs with the carbonic acid formed -by the separation of carbon from the body which is thrown off at every -expiration. It will be quite evident that this process is similar to -that of ordinary combustion. In man or animals, as in the burning -taper,--which is aptly enough employed by poets as the symbol of -life,--we have hydrogen and carbon, with some nitrogen superadded; the -hydrogen and oxygen form water under the action of the vital forces; -the carbon with oxygen produces carbonic acid, and, by a curious -process, the nitrogen and hydrogen also combine, to form ammonia.[222] - -All the carbon which is taken into the animal economy passes, in -the process of time, again into the atmosphere, in combination with -oxygen, this being effected in the body, under the _catalytic_ power of -tissues, immediately influenced by the excitation of nervous forces, -which are the direct manifestations of vital energy. The quantity of -carbonic acid thus given out to the air is capable of calculation, -with only a small amount of error. It appears that upwards of fifty -ounces of carbonic acid must be given off from the body of a healthy -man in twenty-four hours. On the lowest calculation, the population of -London must add to the atmosphere daily 4,500,000 pounds of carbonic -acid. It must also be remembered that in every process for artificial -illumination, and in all the operations of the manufactures in which -fire is used, and also in our arrangements to secure domestic comfort, -immense quantities of this gas are formed. We may, indeed, fairly -estimate the amount, if we ascertain the quantity of wood and coal -consumed, of all the carbon which combines with oxygen while burning, -and escapes into the air, either as carbonic acid or carbonic oxide. -The former gas, the same as that which accumulates in deep wells -and in brewers’ vats, is highly destructive to life, producing very -distressing symptoms, even when mixed with atmospheric air, in but -slight excess over that proportion which it commonly contains. The -oppressive atmosphere of crowded rooms is in a great measure due to the -increased proportion of carbonic acid given off from the lungs of those -assembled, and collected in the almost stagnant air of badly ventilated -apartments. It will be evident to every one, that unless some provision -was made for removing this deleterious gas from the atmosphere as -speedily as it formed, consequences of the most injurious character to -the animal races would ensue. It is found, however, that the quantity -in the atmosphere is almost constantly about one per cent. The peculiar -properties of carbonic acid in part ensure its speedy removal. It is -among the heaviest of gaseous bodies, and it is readily absorbed by -water; consequently, floating within a short distance from the surface -of the earth, a large quantity is dissolved by the waters spread -over it. A considerable portion is removed by the vegetable kingdom; -indeed, the whole of that produced by animals, and by the processes -of combustion, eventually becomes part of the vegetable world, being -absorbed with water by the roots, and separated from the air by the -peculiar functions of the leaves. However, this heavy gas unites with -the lighter atmospheric fluid in obedience to that law which determines -the diffusion of different specific gravities through each other. - -The leaves of plants may be regarded as performing similar offices -to the lungs of animals. They are the breathing organs. In the animal -economy a certain quantity of carbon is necessarily retained, in -combination with nitrogen and other elements, to form muscle; but this -is constantly undergoing change; the entire system being renewed within -a comparatively limited period. The conditions with plants are somewhat -different. For instance, the carbon is fixed in a tree, and remains -as woody fibre until it decays, even though the life of the plant may -extend over centuries. - -Animals, then, are constantly supplying carbonic acid; plants are as -constantly feeding on it; thus is the balance for ever maintained -between the two kingdoms. Another condition is, however, required to -maintain for the uses of men and animals the necessary supply of oxygen -gas. This is effected by one of those wonderful operations of nature’s -chemistry which must strike every reflecting mind with admiration. -During the night plants absorb carbonic acid; but there is a condition -of repose prevailing then in their functions, and consequently their -powers of effecting the decomposition of this gas are reduced to their -minimum. The plant sleeps, and vital power reposes; its repose being as -necessary to the plant as to the animal. With the first gleam of the -morning sun the dormant energies of the plant are awakened into full -action; it decomposes this carbonic acid, secretes the carbon, to form -the rings of wood which constitute so large a part of its structure, -and pour out oxygen gas to the air. The plant is, therefore, an -essential element in the conditions necessary for the support of animal -life. - -The animal produces carbonic acid in an exact proportion to the -quantity of carbonaceous matter which it consumes. Fruit and herbage -contain a small quantity of carbon in comparison with muscle and fat. -But let us confine our attention to the human race. Man within the -Tropics, where the natural temperature is high, does not require so -great an amount of chemical action to go on within him for the purpose -of maintaining the requisite animal heat; consequently his Maker has -surrounded him with fruits and grains which constitute his food. - -As we advance to the colder regions of the earth man becomes a -flesh-eater, and his carnivorous appetite increases as the external -temperature diminishes. Eventually we reach the coldest zones, and the -human being there devours enormous quantities of fat to supply the -necessities of his condition. - -It must necessarily follow, that the inhabitants of the tropics do not -produce so much carbonic acid as those who dwell in colder regions. In -the first place, their habits of life are different, and they are not -under the necessity of maintaining animal heat by the use of artificial -combustion, as are the people of colder climes. The vegetation of -the regions of the tropics is much more luxuriant than that of the -temperate and arctic zones. Hence an additional supply of carbonic acid -is required between the torrid zones, and a less quantity is produced -by its animals. These cases are all met by the great aërial movements. -A current of warmed air, rich in oxygen, moves from the equator towards -the poles, whilst the cooler air, charged with the excess of carbonic -acid, sets in a constant stream towards the equator. By this means the -most perfect equalization of the atmospheric conditions is preserved. - -The carbonic acid poured out from the thousand mouths of our fiery -furnaces,--produced during the laborious toil of the hard-working -artizan,--and exhaled from every populous town of this our island -home,--is borne away by this our aërial currents to find its place -in the pines of the Pacific Islands, the spice-trees of the Eastern -Archipelago, and the cinchonas of Southern America. The plants of -the valley of the Caucasus, and those which flourish amongst the -Himalayas, equally with the less luxuriant vegetation of our temperate -climes, are directly dependent upon man and the lower animals for their -supply of food. - -If all plants were removed from the earth, animals could not exist. -How would it be if the animal kingdom was annihilated?--would it -be possible for vegetation to continue? This question is not quite -so easily answered; but, if we suppose all the carbon-producing -machines--the animals--to be extinct, from whence would the plants -draw their supply? It has been supposed that during the epoch of -the coal formation a luxuriant vegetation must have gone on over -the earth’s surface, when the existence of animal life was regarded -as problematical. It is supposed that the air was then charged with -carbonic acid, and that the calamites, lepidodendra, and sigilaria, -were employed to remove it, and fit the earth for the oxygen-breathing -races. The evidence upon these points is by no means satisfactory; and -although at one time quite disposed to acquiesce in a conjecture which -appears to account so beautifully for the observed geological phenomena -of carboniferous periods, we do not regard the necessities for such -a condition of the atmosphere as clearly made out.[223] Geological -research, too, has shown that the immense forests from which our coal -is formed teemed with life. A frog as large as an ox existed in the -swamps, and the existence of insects proves the high order of organic -creation at this epoch. - -In all probability the same mutual dependence which now exists between -the animal and vegetable kingdoms existed from the beginning of time, -and will continue to do so under varying circumstances through the -countless ages of the earth’s duration. - -There is yet another very important chain of circumstances which binds -these two great kingdoms together. This is the chain of the animal -necessities. A large number of races feed directly upon vegetables; -herbs and fruits are the only things from which they gain those -elements required to restore the waste of their systems. - -These herbivorous animals, which must necessarily form fat and muscle -from the elements of their vegetable diet, are preyed on by the -carnivorous races; and from these the carbon is again restored to the -vegetable world. Sweep off from the earth the food of the herbivora, -they must necessarily very soon perish, and with their dissolution, -the destruction of the carnivora is certainly ensured. To illustrate -this on a small scale, it may be mentioned that around the coasts of -Cornwall, pilchards were formerly caught in very great abundance, in -the shallow water within coves, where these fish are now but rarely -seen. From the investigations of the Messrs. Couch, whose very accurate -observations on the Cornish fauna have placed both father and son -amongst the most eminent of British naturalists,[224] it appears that -the absence of these fish is to be attributed entirely to the practice -of the farmers, who cut the sea-weed from the rocks for the purpose -of manuring their lands. By this they destroy all the small crustacea -inhabiting these immature marine forests feeding on the algæ, and as -these, the principal food of the pilchards, have perished they seek -for a substitute in more favourable situations. Mr. Darwin remarks, -that if the immense sea-weeds of the Southern Ocean were removed by any -cause, the whole fauna of these seas would be changed. - -We have seen that animals and vegetables are composed principally of -four elementary principles,--oxygen, hydrogen, nitrogen, and carbon. -We have examined the remarkable manner in which they pass from one -condition--from one kingdom of nature--into another. The animal, -perishing and dwindling by decomposition into the most simple forms of -matter, mingling with the atmosphere as mere gas, gradually becomes -part of the growing plant, and by like changes vegetable organism -progresses onward to form a portion of the animal structure. - -A plant exposed to the action of natural or artificial decomposition -passes into air, leaving but a few grains of solid matter behind it. -An animal, in like manner, is gradually resolved into “thin air.” -Muscle, and blood, and bones, having undergone the change, are found to -have escaped as gases, leaving only “a pinch of dust,” which belongs -to the more stable mineral world. Our dependency on the atmosphere -is therefore evident. We derive our substance from it--we are, after -death, resolved again into it. We are really but fleeting shadows. -Animal and vegetable forms are little more than consolidated masses of -the atmosphere. The sublime creations of the most gifted bard cannot -rival the beauty of this, the highest and the truest poetry of science. -Man has divined such changes by the unaided powers of reason, arguing -from the phenomena which science reveals in unceasing action around -him. The Grecian sage’s doubts of his own identity, were only an -extension of a great truth beyond the limits of our reason. Romance and -superstition resolve the spiritual man into a visible form of extreme -ethereality in the spectral creations, “clothed in their own horror,” -by which their reigns have been perpetuated. - -When Shakespeare made his charming Ariel sing-- - - “Full fathom five thy father lies, - Of his bones are coral made, - Those are pearls that were his eyes: - Nothing of him that doth fade, - But doth suffer a sea change - Into something rich and strange,” - -he painted, with considerable correctness, the chemical changes -by which decomposing animal matter is replaced by a siliceous or -calcareous formation. - -But the gifted have the power of looking through the veil of nature, -and they have revelations more wonderful than even those of the -philosopher, who evokes them by perpetual toil and brain-racking -struggle with the ever-changing elements around him. - -The mysteries of flowers have ever been the charm of the poet’s song. -Imagination has invested them with a magic influence, and fancy has -almost regarded them as spiritual things. In contemplating their -surpassing loveliness, the mind of every observer is improved, and -the sentiments which they inspire, by their mere external elegance, -are great and good. But in examining the real mysteries of their -conditions, their physical phenomena, the relations in which they stand -to the animal world, “stealing and giving odours” in the marvellous -interchange of carbonic acid and ammonia for the soul-inspiring -oxygen--all speaking of the powers of some unseen, in-dwelling -principle, directed by a supreme ruler--the philosopher finds subjects -for deep and soul-trying contemplation. Such studies lift the mind into -the truly sublime of nature. The poet’s dream is the dim reflection of -a distant star: the philosopher’s revelation is a strong telescopic -examination of its features. One is the mere echo of the remote whisper -of nature’s voice in the dim twilight; the other is the swelling music -of the harp of Memnon, awakened by the sun of truth, newly risen from -the night of ignorance. - -To return from our long, but somewhat natural digression, to a -consideration of the chemical phenomena connected with the atmosphere, -and its curious and important element, nitrogen, we must first examine -the evidence we have of the condition of the air itself. - -The mean pressure exerted upon the surface of the earth, as indicated -by the barometer, is equal to a column of mercury thirty inches -high; that is, the column of air from the surface of the ocean to -its highest limits exactly balances that quantity of mercury. If our -tube of mercury had the area of one square inch, the columns would -weigh fifteen pounds, which represents a pressure of fifteen pounds -upon every square inch of the earth’s surface. This pressure, it must -be remembered, is the compound weight of the gaseous envelope, and -the elastic force of the aqueous vapour contained in it.[225] If the -atmosphere were of uniform condition, its height, as inferred from -the barometer, would be about five miles and a half. The density of -the air, however, diminishes with the pressure upon it, so that at the -height of 11,556 feet, the atmosphere is of half density; or one volume -of air, as taken at the surface of the earth, is expanded into two at -that height. Thus the weight is continually diminishing; but this is -regularly opposed by the decreasing temperature, which diminishes the -rate of about one degree for every 352 feet of ascent, although in all -probability it is less rapid at great distances from the earth. - -It has been calculated from certain phenomena of refraction, that our -atmosphere must extend to about forty miles from the surface of the -earth. It may, in a state of extreme tenuity, extend still further; -but it is probable that the intense cold produced by rarefaction sets -limits to any extension much beyond this elevation. - -The uses of the atmosphere are many. It is the medium for regulating -the dispersion of watery vapours over the earth. If there were no -atmosphere, and that, as now, the equatorial climes were hot and the -poles cold, evaporation would be continually going on at the equator, -and condensation in the colder regions. The sky of the tropical climes -would be perpetually cloudless, whilst in the temperate and arctic -zones we should have constant rain and snow. By having a gaseous -atmosphere, a more uniform state of things is produced; the vapours -arising from the earth become intimately mixed with the air, and are -borne by it over large tracts of country, and only precipitated when -they enter some stratum much colder than that which involves them. -There are opposite tendencies in an atmosphere of air and one of -vapour. The air circulates from the colder to the warmer parts, and -the vapour from the warmer to the colder regions; and as the currents -of the air, from the distribution of land and sea--the land, from its -low conducting power, being more quickly heated than the sea--are -very complicated, and as some force is employed in keeping the vapour -suspended in the air, water is less suddenly deposited on the earth -than it would have been, had not these tendencies of the air and its -hygrometric peculiarities been such as we find them. - -The blue colour of the sky, which is so much more agreeable to the eye -than either red or yellow, is due to a tendency of the mixed gas and -vapour to reflect the blue rays rather than red or yellow. The white -light which falls upon the surface of the earth, without absorption or -decomposition in its passage from the sun, is partially absorbed by, -and in part reflected back from, the earth. The reflected rays pass -with tolerable freedom through this transparent medium, but a portion -of the blue rays are interrupted and rendered visible to us. That it -is reflected light, is proved by the fact of its being in a polarized -state.[226] Clouds of vapour reflect to us again, not isolated rays, -but the undecomposed beam, and consequently they appear white as snow -to our vision. - -The golden glories of sunset,--when, “like a dying dolphin,” heaven -puts on the most gorgeous hues, which are continually changing,--depend -entirely upon the quantity of watery vapour which is mixed with air, -and its state of condensation. It has been observed, that steam at -night, issuing into the atmosphere under a pressure of twenty or thirty -pounds to the square inch, transmits and reflects orange-red light. -This we may, therefore, conclude to be the property of such a condition -of mixed vapour and air, as prevails when the rising or the setting -sun is shedding over the eastern or the western horizon the glory of -its coloured rays.[227] - -Thus science points out to us the important uses of the air. We learn -that life and combustion are entirely dependent on it, and that it -is made the means for securing greater constancy in the climates -of the earth than could otherwise be obtained. The facts already -dwelt upon are sufficient to convince every thinking mind that the -beautiful system of order which is displayed in the composition of -the atmosphere, in which the all-exciting element, oxygen, is subdued -to a tranquil state by another element, nitrogen, (which, we shall -have presently to show, is itself, under certain conditions, one of -the most energetic agents with which we are acquainted,) indicates a -supreme power, omniscient in the adaptation of things to an especial -end. Oxygen and nitrogen are here _mixed_ for the benefit of man; -man _unites_ them by the aid of powers with which he is gifted, and -the consequences are of a fatal kind. The principles which the great -Chemist of Nature renders mild are transformed into sources of evil by -the chemist of art. - -Beyond all this, the atmosphere produces effects on light which add -infinitely to the beauty of the world. Were there no atmosphere, we -should only see those objects upon which the sun’s rays directly fell, -or from which they were reflected. A ray falling through a small hole -into a dark room, illuminating one object, which reflects some light -upon another, is an apt illustration of the effect of light upon -the earth, if it existed without its enveloping atmosphere. By the -dispersive powers of this medium, sunlight is converted into daylight; -and instead of unbearable, parallel rays illuminating brilliantly, -and scorching up with heat those parts upon which they directly -fall, leaving all other parts in the darkness of night, we enjoy the -blessings of a diffusion of its rays, and experience the beauties of -soft shades and slowly-deepening shadows. Without an atmosphere, the -sun of the morning would burst upon us with unbearable brilliancy, and -leave us suddenly, at the close of day, at once in utter darkness. With -an atmosphere we have the twilight with all its tempered loveliness,--a -“time for poets made.” - -In chemical character, atmospheric air is composed of twenty-one -volumes of oxygen, and seventy-nine volumes of nitrogen: or one hundred -grains of air consist of 23·1 grains of the former, and 76·9 grains -of the latter. Whether the air is taken from the greatest depths or -the most exalted heights to which man has ever reached, an invariable -proportion of the gases is maintained. The air of Chimborazo, of the -arid plains of Egypt, of the pestilential delta of the Niger, or -even of the infected atmosphere of an hospital, all give the same -proportions of these two gases as we find existing on the healthful -hills of Devonshire, or in the air of the city of London. This -constancy in constitution leads to the supposition that the oxygen -and nitrogen are chemically combined; but many eminent philosophers -have contended that they are merely mechanically mixed; and they have -shown that some peculiar properties prevail amongst gaseous bodies, -which very fully explain the equal admixture of two gases the specific -gravities of which are different. This is particularly exemplified in -the case of carbonic acid, of which gas one per cent. can be detected -in all regions of the air to which the investigations of man have -reached. This gas, although so heavy, is, by the law of diffusion, -mixed with great uniformity throughout the mass.[228] Every exhalation -from the earth, of course, passes into the air; but these are generally -either so light that they are carried into the upper regions, and -there perform their parts in the meteorological phenomena, or they -are otherwise very readily absorbed by water or growing plants, and -thus is the atmosphere preserved in a state of purity for the uses of -animals. Again, the quantity of oxygen contained in the air, and its -very peculiar character, ensures the oxidation of all the volatile -organic matters which are constantly passing off,--as the odoriferous -principles of plants, the miasmata of swamps, and the products of -animal putrefaction; these are rapidly converted into water, carbonic -acid, or nitric acid, and quickly enter into new and harmless -combinations. The elements of contagion we are unacquainted with; but -since the attention of inquirers has been of late directed to this -important and delicate subject, some light may possibly be thrown upon -it before long. - -Nothing, shows more strikingly the admirable adaptation of all things -for their intended uses than the atmosphere. In it we find the source -of life and health; and chemistry teaches us, most indisputably, -that it is composed of certain proportions of oxygen and nitrogen -gases; and experience informs us that it is on the oxygen that we -are dependent for all that we enjoy. So beautifully is the atomic or -molecular constitution ordered, that it is impossible to produce any -change in the air without rendering it injurious to the vegetable and -animal economy. It might be thought, from the well-known exhilirating -character of oxygen gas, that, if a larger quantity existed in the -atmosphere than that which we find there, the enjoyments of life would -be of a more exciting kind; but the consequences of any increase would -be exceedingly injurious; and, by quickening all the processes of life -to an unnatural extent, the animal fabric would soon decay: excited -into fever, it would be destroyed by its own fires. Chemistry has made -us acquainted with six other compounds of oxygen and nitrogen, neither -of them fitted for the purposes of vitality, of which the following are -the most remarkable:-- - -Nitrous oxide, or the, so called, _laughing gas_, which contains two -volumes of nitrogen to one of oxygen, would prove more destructive than -even pure oxygen, from the delirious intoxication which it produces. - -Nitric oxide is composed, according to Davy, of two volumes of nitrogen -and two of oxygen. It is of so irritating a nature, that the glottis -contracts spasmodically when any attempt is made to breathe it; and the -moment it escapes into the air it combines with more oxygen, and forms -the deep red fumes of nitrous acid. - -Nitrous acid and the peroxide of nitrogen each contains an additional -proportion of oxygen, and they are still more destructive to all -organization. - -Nitric acid contains five volumes of oxygen united to two of nitrogen; -and the well-known destructive properties of aqua fortis it is -unnecessary to describe. - -The atmosphere, and these chemically active compounds, contain the same -elements, but their mode of combining is different; and what is, in the -one case, poisonous to the highest degree, is, in the other, rendered -salubrious, and essential to all organized beings. - -Nitrogen gas may be regarded in the light of a diluent to the oxygen. -In its pure state it is only characterised by its negative properties. -It will not burn, or act as a supporter of combustion. Animals speedily -perish if confined in it; but they die rather through the absence -of oxygen than from any poisonous property of this gas. Yet, in -combination, we find nitrogen exhibiting powers of a most energetic -character. In addition to the fulminating compounds and the explosive -substances already named, which are among the most remarkable instances -of unstable affinity with which we are acquainted, we have also the -well-known pungent body, ammonia. From the analogous nature of this -volatile compound, and the fixed alkalies soda and potash, it was -inferred that it must, like them, be an oxide of a metallic base. Davy -exposed ammonia to the action of potassium, and to the influence of the -voltaic arc produced from 2,000 double plates, without at all changing -its character. From its slight tendency to combination, and from its -being found abundantly in the organs of animals feeding on substances -that do not contain it, it is, however, probably a compound body. A -phenomenon of an obscure and mysterious character is presented in the -formation of the “ammoniacal amalgam,” as it is called. - -Mercury, being mixed with an ammoniacal salt, is exposed to powerful -galvanic action; and a compound, maintaining its metallic appearance, -but of considerable lightness and very porous, presents itself.[229] -This preparation has been carefully examined by Davy, Berzelius, and -others. It is always resolved into ammonia and mercury; and, although -the latter chemist is strongly inclined to regard it as affording -evidence of the compound nature of nitrogen,--and he has, indeed, -proposed the name _nitricum_ for its hypothetical base,--yet, to the -present time, we have no satisfactory explanation of this apparent -metallization of ammonia. - -No attempt will be made to describe the various elementary substances -which come under the class of metallic bodies, much less to enumerate -their combinations. Many of the metals, as silver and copper, are found -sometimes in a native state, or nearly pure; but, for the most part, -they exist, in nature, in combination with oxygen or sulphur; gold -furnishing a remarkable exception. They are occasionally found combined -with other bodies,--as oxidized carbon, phosphorus, chlorine, &c.; but -these cases are by no means so common. Those substances called metals -are generally found embedded in the rocks, or deposited in fissures -formed through them; but it is one of the great discoveries of modern -science, that those rocks themselves are metallic oxides. With metals -we generally associate the idea of great density; but potassium and -sodium, the metallic bases of potash and soda, are lighter than water, -and they consequently float upon that fluid. We learn, therefore, from -the researches of science, that the crust of this earth is composed -entirely of metals, combined with gaseous elements; and there is -reason for believing that one, or perhaps two, of the gases we have -already named are also of a metallic character. Strange as it may -appear, there is nothing, as will be seen on attentive consideration, -irrational in this idea. Many of the metals proper, under the influence -of such heat as we can, by artificial means, command, are dissipated -in vapour, and may be maintained in this state perfectly invisible. -Indeed, the transparent space above the surface of the mercury in the -tube of a barometer, known as the Torricellian vacuum, is filled with -the vapour of mercury. There is, therefore, no reason why nitrogen, -or even hydrogen, should not be metallic molecules kept by the force -of the repulsive powers of heat, or some other influence, at a great -distance from each other. The peculiar manner in which nitrogen unites -with mercury, and the property which hydrogen possesses of combining -with antimony, zinc, arsenic, potassium, sodium, and possibly other -metals, besides its union with sulphur and carbon--in all which cases -there is no such change of character as occurs when they combine with -oxygen--appear to indicate bodies which, chemically, are not very -dissimilar to those metals themselves, although, physically, they have -not the most remote resemblance. - -“We know nothing,” says Davy, “of the true elements belonging to -nature; but, so far as we can reason from the relations of the -properties of matter, hydrogen is the substance which approaches -nearest to what the elements may be supposed to be. It has energetic -powers of combination, its parts are highly repulsive as to each -other, and attractive of the particles of other matter; it enters into -combination in a quantity very much smaller than any other substance, -and in this respect it is approached by no known body.”[230] - -Many of the elements are common to the three kingdoms of nature: -most of those found in one condition of organization are discovered -in another. The carbonates are an abundant mineral class. In the -vegetable kingdom we find carbon combining with oxygen, hydrogen, and -nitrogen: these elements, also, constitute the substance of animals, -the proportion of nitrogen being, however, much larger. If one element, -more than another, belongs especially to the animal economy, it is -phosphorus, although this is not wanting in the vegetable world; and -it is not uncommon in the mineral. Sulphur is common to the three -kingdoms: it is abundant in the mineral, being one of the products of -volcanic action; it is united with the metals, forming sulphurets; -and is found in our rocks in the state of sulphuric acid or oxidized -vapour, combined with the metallic bases of lime and other earths. In -the vegetable kingdom we discover sulphur in all plants of the onion -kind, in the mustard, and some others; it enters into the composition -of vegetable albumen, and appears always combined with albumen, -fibrine, and caseine, in the animal economy. - -Chlorine is found most abundantly in combination with sodium, as common -salt: in this state, in particular, we may trace it from the depths -of the earth, its waters, and its rocks, to the plants and animals -of the surface. Iodine is most abundant in marine plants; but it has -been found in the mineral world, traced to plants, and it is indicated -in the flesh of some animals. Bromine is known to us as a product of -certain saline waters, and a few specimens of natural bromide of silver -have been examined. Fluorine, the base of the acid which, combining -with lime, forms fluor-spar, is found to exist to some considerable -extent in bones; it has been discovered in milk and blood; and -investigations have proved its existence in the vegetable world. It -must not be forgotten that the earths, lime and magnesia, enter into -the composition of the more solid parts of plants and animals. Lime is -one of the principal constituents of animal bone and shells, and it is -found in nearly all vegetables. - -Silica, or the _earth_ of flints, is met with in beautiful transparent -crystals, in the depths of the mine; in all rock and soils we find it. -In the bark of many plants, particularly the grasses, it is discovered, -forming the hard supporting cuticle of the stalk, in wheat, the Dutch -rush, the sugar-cane, the bamboo, and many other plants. - -It is thus that we find the same elementary principle presenting itself -in every form of matter, under the most Protean shapes. Numerous -phenomena of even a more striking character than those selected, are -exhibited in every department of chemistry; but within the limits of -this essay it is impracticable to speak of any beyond those which -directly explain natural phenomena. - -The chemical elements, which actually exist in nature as simple -bodies, are probably but few. Most of the gases are in all probability -compounds of some ethereal ultimate principles; and with the advance of -science we may fairly hope to discover the means of reducing some of -them to a yet more simple state. - -Curious relations, which can be traced through certain bodies, lead us -to believe that they may be only modified conditions of one element. -Flint and charcoal do not at first appear allied; but carbon in some -of its states approaches very near to the condition of silicon, the -metallic base of flint. When we remember the differences which are -evident in three forms of one body--coke, graphite, and diamond--the -dissimilitude between flint, a quartz crystal, and carbon, will cease -to be a strong objection to the speculation. - -Phosphorus, sulphur, and selenium, have many properties in common. -Iodine, bromine, chlorine, and fluorine, appear to belong to the same -group. Iron and nickel, and cobalt, have a close relation. Silver and -lead are usually combined, and exhibit a strong relationship. Gold, -platinum, and the rarer metals, have so many properties in common, that -they may form a separate group from all the others. - -Indeed, a philosophical examination of the elements now supposed to -constitute the material world, enables us to divide them into about six -well-defined groups. Wide differences exist within these groups; but -still we find a sufficient number of common properties to warrant our -classing them in one family. - -The dream of the alchemists, in the vain endeavour to realise which -they exhausted their lives and dissipated their wealth, had its -foundation in a natural truth. The transmutation of one form of matter -into another may be beyond the power of man, but it is certainly -continually taking place in the laboratory of nature, under the -directing law of the great Creator of this beautiful earth. - -The speculations of men, through all ages, have leaned towards this -idea, as is shown by the theory of the four elements,--Air, Fire, -Earth, and Water,--of the ancients, the three,--Salt, Sulphur, and -Mercury,--of the alchemists, and the refined speculations of Newton -and Boscovich on the ultimate constitution of matter. All experimental -inquiry points towards a similar conclusion. It is true we have no -direct evidence of any elementary atom actually undergoing a change -of state; but when we regard the variations produced by electrical -influence, the changes of state which arise from the power of heat, and -the physical alterations produced by light, it will be difficult to -come to any other conclusion than that the particles of matter known -to us as ultimate are capable of change, and consequently must be far -removed from positively simple bodies, since the real elementary atom, -possessing fixed properties, cannot be supposed capable of undergoing -any transmutation. Allotropism could not occur in any absolutely simple -body. - -It will now be evident that in all chemical phenomena we have the -combined exercise of the great physical forces, and evidences of some -powers which are, as yet, shrouded in the mystery of our ignorance. The -formation of minerals within the clefts of the rocks, the decomposition -of metallic lodes, the germination of seeds, the growth of the plant, -the development of its fruit and its ultimate decay, the secret -processes of animal life, assimilation, digestion, and respiration, and -all the changes of external form, which take place around us, are the -result of the exercise of that principle which we call chemical. - -By chemical action plants take from the atmosphere the elements of -their growth; these they yield to animals, and from these they are -again returned to the air. The viewless atmosphere is gradually formed -into an organized being, the lordly tree upon whose branches the fowls -of the air have their homes, and the human animal, exalted by being -charged with a spiritual soul: yet the tree and the man alike are -gradually resolved again into thin air. The changes of the mineral -world are of an analogous character; but we cannot trace them so -clearly in all their phenomena. - -The planet on which we live began its course charged with a fixed -quantity of physical force, and this has remained constant to the -present moment, and will do so to the end of time. By influences -external to this earth the balance of these forces is continually -disturbed; and in the effort to restore the equilibrium, we have the -production of all the varied forms of matter, and the manifestation of -each particular physical principle or power. As motion and attraction, -balanced against each other, maintain the earth in her elliptical -orbit, so the opposition of forces determines the existence of the -amorphous rock, the light-refracting crystal, the fixed and flowering -plant, and the locomotive animal. - -An eternal round of chemical action is displayed in nature. Life and -death are but two phases of its influences. Growth and decay are -equally the result of its power. - - -FOOTNOTES: - -[212] Dr. Priestley appears to have been the first to observe the -peculiar property of the diffusion of gases. Dr. Dalton, however, -first drew attention to the important bearing of this fact on natural -phenomena, and he published his views on _The Miscibility of Gases_ in -the Manchester Memoirs, vol. v. The following extract from his memoir -_On the Constitution of the Atmosphere_ will exhibit its bearings:-- - -It may be worth while to contrast this view of the constitution of the -atmosphere with the only other one, as far as I know, that has been -entertained. - - According to one view, | According to the other view, - | - 1. The volumes of each gas | 1. The volume of each gas - found at the surface of the | found at the surface of - earth are proportional to | the earth, _multiplied by - the whole weights of the | its specific gravity_, is - respective atmospheres. | proportional to the whole - | weight of the respective - | atmospheres. - | - Azote 79 | Azote 76·6 - Oxygen 21 | Oxygen 23·4 - Aqueous vapour 1·33 | Aqueous vapour 0·83 - Carbonic acid 1·0 | Carbonic acid 0·15 - ------- | ------ - 101·43 | 100·88 - | - 2. The altitude of each | 2. The altitude of each - atmosphere differs from that | atmosphere is the same, and - of every other, and the | the proportion of each in the - proportions of each in the | compound atmosphere, is the - compound atmosphere gradually | same at all elevations. - vary in the ascent. | - | - 3. When two atmospheres are | 3. When two atmospheres - mixed, they take their places | are mixed, they continue - according to their specific | so without the heavier - gravity, not in separate | manifesting any disposition to - strata, but intermixedly. | separate and descend from the - There is, however, a separate | lighter. - stratum of the specifically | - lighter atmosphere at the | - summit over the other. | - -[213] The discussion of this question, commenced by Arago in his -_Eloge_, was continued by Lord Brougham in his _Lives of Watt and -Cavendish_, and by Mr. Vernon Harcourt, in his address as President -of the British Association, and more recently in his _Letter to Lord -Brougham_. Watt’s _Letters_ on the subject have been since published -under the superintendence of Mr. Muirhead. - -[214] See several papers _On Ozone_, by Professor Schönbein, in the -Philosophical Magazine, and in the Reports of the British Association. -Consult a paper by the Author: _Athenæum_, September, 1849. - -[215] Memoire _sur l’Ozone_; Bàle 1849. Poggendorff’s _Annalen_, -lxxvii., p. 592. Ibid, lxxviii. p. 162. - -[216] _Chemical Gazette_, 1849. - -[217] Iodide of silver has been found at Albarradon, near Mazapil, in -Mexico. Iodide of mercury, of a fine lemon-yellow colour, has been -discovered in the sandstone of Casas, Viegas, Mexico. Algers; Phillips’ -_Mineralogy_. - -[218] GENTELE’S Reports of the Stockholm Academy. - -[219] Stahl, taking up the obscure notions of Becher and Van Helmont, -supposed the phenomena of combustion to be due to phlogiston. He -imagined that by combination with phlogiston, a body was rendered -combustible, and that its disengagement occasioned combustion, and -after its evolution there remained either an acid or an earth: thus -sulphur was, by this theory, supposed to be composed of phlogiston and -sulphuric acid, and lead of the calx of lead and phlogiston, &c. - -[220] Being called upon by the Solicitor for the Admiralty to examine -into the causes of the fire which destroyed the _Imogene_ and -_Talavera_, in Devonport Arsenal, I discovered a bin under the roofing -which covered these ships, in which there had been accumulating for a -long period all the refuse of the wheelwrights’ and painters’ shop; and -it was quite evident that spontaneous combustion had taken place in the -mass of oiled oakum, sawdust, anti-attrition, and old sail-cloth, there -allowed to accumulate. - -[221] _Researches on Flame_: Sir H. Davy’s Collected Works. - -[222] See note, _ante_, _On the Chemical Theory of Respiration_. - -[223] At the request of the British Association, a committee undertook -the investigation of this subject. Experiments were carried on by Dr. -Daubeny, in the Botanic Gardens at Oxford, and by the Author, at his -residence, Stockwell. Dr. Daubeny, in his report made at the meeting -of the British Association at Birmingham, appears disposed to consider -ten per cent. of carbonic acid in excess as destructive to the growth -of ferns. I found, however, that, by gradually increasing the quantity, -the ferns would live in an atmosphere still more highly charged with -carbonic acid. - -[224] See memoir _On the Pilchard_, by Mr. Couch, in the Reports of the -Royal Cornwall Polytechnic Society. - -[225] “This scale, in which the humidity of the air is expressed, -is the simple natural scale in which air at its maximum of humidity -(_i.e._, when it is saturated with vapour) is reckoned as = 100, and -air absolutely deprived of moisture as = 0; the intermediate degrees -are given by the fraction 100 × actual tension of vapour ÷ tension -required for the saturation of the air at its existing temperature. -Thus, if the air at any temperature whatsoever contains vapour of half -the tension, which it would contain if saturated, the degree is 50; if -three-fourths, then 75; and so forth. Air of a higher temperature is -capable of containing a greater quantity of vapour than air of less -temperature; but it is the proportion of what it does contain, to what -it would contain if saturated, which constitutes the measure of its -dryness or humidity. The capacity of the air to contain moisture being -determined by its temperature, it was to be expected that an intimate -connection and dependence would be found to exist between the annual -and diurnal variations of the vapour and of the temperature.”--Sabine, -_On the Meteorology of Toronto_; Reports of the British Association, -vol. xiii. p. 47. _The Temperature Tables_: by Prof. W. H. Dove; -Reports for 1847 should be consulted. - -[226] Sir David Brewster’s _Optics_, and Memoirs in the Philosophical -Transactions. Sir John Herschel’s Treatise on _Light_, Encyclopædia -Metropolitana. - -[227] _On the Colour of Steam under certain circumstances_: by -Professor Forbes; Philosophical Magazine, vol. xiv. p. 121, vol. xv. -p. 25. In the first paper the following remarks occur:--“I cannot -doubt that the colour of watery vapour under certain circumstances -is the principal or only cause of the red colour observed in clouds. -The very fact that that colour chiefly appears in the presence of -clouds is a sufficient refutation of the only explanation of the -phenomena of sunset and sunrise, having the least plausibility, given -by optical writers. If the red light of the horizontal sky were simply -complementary to the blue of a pure atmosphere, the sun ought to set -red in the clearest weather, and then most of all; but experience shows -that a lurid sunrise or sunset is _always_ accompanied by clouds or -diffused vapours, and in a great majority of cases occurs when the -changing state of previously transparent and colourless vapour may be -inferred from the succeeding rain. In like manner, terrestrial lights -seen at a distance grow red and dim when the atmosphere is filled -with vapour soon to be precipitated. Analogy applied to the preceding -observations would certainly conduct to a solution of such appearances; -for I have remarked that the existence of vapour of high tension is -by no means essential to the production of colour, though of course -a proportionally greater thickness of the medium must be employed to -produce a similar effect when the elasticity is small.” - -[228] _On the Law of Diffusion of Gases_: by Thomas Graham, M.A., -F.R.S., &c.; Edinburgh Philosophical Transactions, 1832. _Sur l’Action -Capillaire des Fissures, &c._: by Döbereiner; Annales de Chimie, xxiv. -332. - -[229] _Electro-chemical Researches on the Decompositions of the Earths, -with observations on the Metals obtained from the Alkaline Earths, -and on the Amalgam procured from Ammonia_: by Sir Humphry Davy; -Philosophical Transactions, 1808, and collected works, vol. v. p. 102. - -[230] _Elements of Chemical Philosophy_: by Sir H. Davy. - - - - -CHAPTER XIII. - -TIME.--GEOLOGICAL PHENOMENA. - - Time, an element in Nature’s Operations--Geological - Science--Its Facts and Inferences--Nebular Hypothesis - applied--Primary Formations--Plutonic and Metamorphic - Rocks--Transition Series--Palæozoic Rocks--Commencement of - Organic Arrangements--Existence of Phosphoric Acid in Plutonic - Rocks--Fossil Remains--Coal Formation--Sandstones--Tertiary - Formations--Eocene, Miocene, and Pliocene Formations--Progressive - changes now apparent--General Conclusions--Physics applied in - explanation. - - -The influence of time, as an element, in producing certain structural -arrangements, by modifying the operations of physical force, under -whatever form it may be exerted, has scarcely been sufficiently -attended to in the examination of cosmical phenomena. Every particle -of matter is, as it were, suspended between the agencies to which -we have been directing our attention. Under the influences of the -physical powers, sometimes exerted in common, but often with a great -preponderance in favour of one of them, every accumulated heap of mud -or sand is slowly cohering, and assuming the form of a rock possessing -certain distinguishing features, as it regards lamination, cleavage, &c. - -The minute particles of matter are necessarily but slightly influenced -by the physical forces: their action in accordance with the laws which -determine physical condition is manifested in an exceedingly modified -degree. But in all the operations of nature, what is deficient in -power is made up in time, and effects are produced during myriads -of ages, by powers far too weak to give satisfactory results by any -experiments which might be extended even over a century. - -If, with the eye of a geologist, we take but a cursory glance over the -Earth, we shall discover that countless ages must have passed during -the progress of this planet to its present state. This is a fact -written by the finger of nature, in unmistakeable characters, upon the -mighty tablets of her mountains. - -The superficial crust of the earth,--by which is meant only that film, -compared with its diameter, which is represented by a few miles in -depth--is composed of distinct mineral masses, exhibiting peculiar -physical conditions and a certain order of arrangement. These rocks -appear to have resulted from two dissimilar causes; in one class the -action of heat is evident, and in the other we have either the slow -deposition of matter suspended in water, or crystallization from -solution; an aqueous origin is indicated by peculiarities of formation -in all the more recent rocks. - -There are few branches of science which admit of speculation to the -extent to which we find it carried in geology. The consequences of this -are shown in the popular character of the science. A few observations -are made over a limited area, and certain structural conditions are -ascertained, and at once the mind, “fancy free,” penetrates the -profound depths of the earth, and imagination, having “ample room -and verge enough,” creates causes by which every effect is to be -interpreted. Such students, generally ignorant of the first principles -of physics, knowing little of mineralogy, and less of chemistry, to -say nothing of palæontology, having none of the requisites for an -observer, boldly assume premises which are untenable, and think they -have explained a phenomenon,--given to the world a truth,--when they -have merely promulgated an unsubstantiated speculation, which may have -occasional marks of ingenuity, and but little else. - -The carefully-made observations of those who, with unwearying industry, -have traversed hill and valley, marked and measured the various -characters, thicknesses, inclinations, and positions of rocks; who have -watched the influences of heat in changing, of water in wearing, and -the results of precipitation in forming, strata; who have traced the -mechanical effects of earthquake strugglings and of volcanic eruptions, -and, reasoning from an immense mass of accumulated facts, deduced -certain general conclusions,--are, however, of a totally different -character; and it is such observers as these who induced Herschel to -say truly, that “geology, in the magnitude and sublimity of the objects -of which it treats, undoubtedly ranks, in the scale of the sciences, -next to astronomy.”[231] - -The origin of this planet is involved in great obscurity, which the -powers of the most gifted are unable to penetrate. It stands the work -of an Almighty and Eternal mind, the beginning of which we cannot -comprehend, nor can we define the period of its termination. - -It may, probably, be safe to speculate that there was a time when -this globe consisted of only one homogeneous stratum. Whether -this remains,--whether, in our plutonic rocks, our granites, or -our porphyries, we have any indications of the primitive state of -the world, or whether numerous changes took place before even our -unstratified formations had birth, are questions we cannot answer. The -geologist looks back into the vista of time, and reckons, by phenomena, -the progress of the world’s mutations. The stratified formations -must have occupied thousands of ages; but before these were, during -a period extending over countless thousands, the unstratified rocks -may have been variously metamorphosed. It matters not whether we admit -the nebular hypothesis or not,--a time must have been when all these -bodies which now form the mass of this globe existed in the most simple -state. We have already shown that very remarkable changes in external -character and in chemical relations are induced, in the same simple -element, by its having been exposed to some peculiar and different -conditions; and already have we speculated on the probability that -the advance of science will enable us to reduce the numerous elements -we now reckon, to two or three. It is, therefore, by no means an -irrational thought (which must, however, be held in the light of a -pure conjecture), to suppose that at the beginning a mighty mass of -matter, in the most attenuated state, was produced in space, and was -gradually, under the influence of gravitation, of cohesive force, and -of chemical aggregation, moulded into the form of a sphere. Ascending -to the utmost refinement of physics, we may suppose that this mass was -of one uniform character, and that it became in dissimilar parts--its -surfaces and towards its centre--differently constituted, under the -influences of the same powers which we now find producing, out of the -same body, charcoal and the diamond, and creating the multitudinous -forms of organized creations. These conditions being established, and -carried to an extent of which, as yet, science has afforded us no -evidence, chemical intermixture may have taken place, and a new series -of compounds have been formed, which, by again combining, gave rise to -another and more complex class of bodies. - -The foundation of the superficial crust of the earth appears to be -formed of a class of rocks which have resulted from the slow cooling -of an immense mass of heated matter. These rocks have been called -_igneous_; but are now more generally termed _Plutonic_ (such as -granites, syenites, &c.) Immediately above these, we find rocks which -have resulted by deposition from water. These masses, having been -exposed to the action of the heat below, have been considerably changed -in their character, and hence they are often called _metamorphic_; -but metamorphic rocks may, however, be of any age. The rocks formerly -termed the _transition_ series--from their forming the connecting link -between the earlier formations--are now, from the circumstance of their -being fossiliferous, classed under the general term of palæozoic rocks, -to distinguish them from the rocks in which no organic remains have -been found. Above these are found the secondary strata, and, still more -recently produced, we have a class now usually denominated the tertiary -formations. “Eternal as the hills” is a poetic expression, implying a -long duration; but these must, from the nature of things, eventually -pass away. The period of time necessary for the disintegration of a -granite hill is vastly beyond the powers of computation, according -to our conception of the ordinary bounds of finite things. But a -consideration of the results of a few years,--under the influence of -the atmosphere and the rains,--as shown in quantity of solid matter -carried off by the rivers, and deposited at their mouths, will tend to -carry conviction to every mind, that a degrading process is for ever in -action on the surface of the earth. The earth itself may be eternal, -but the surface is continually undergoing mutation, from various -causes, many of which we must briefly consider.[232] - -In regarding geological phenomena, the absence of any fossil remains -has often been supposed to indicate a period previous to any organic -formations. The inorganic constituents of matter are probably of -prior origin to the organic combinations; the vessel was constructed, -upon which the organic creation was to float in space before any -vital organisms were created. The supposed evidences in favour of the -assumption that there was no organic life during the formation of the -oldest rocks we know, are in some respects doubtful; and we can well -understand that changes may have been induced in the earlier rock -formations, by heat or by other powers, quite sufficient to destroy all -traces of organized forms. It was long thought that phosphoric acid was -not to be detected in rocks which are regarded as of igneous origin; -and since this acid is peculiarly a constituent of organic bodies, this -has been adduced as a proof that the plutonic rocks must have existed -previously to the appearance of vegetable or animal life upon the -surface of the globe. The researches of modern chemists have, however, -shown that phosphoric acid is to be found in formations of granitic -origin, in porphyry, basalt, and hornblende rocks.[233] If, therefore, -we are to regard this substance as of organic origin, the rational -inference is against the speculation; but there is no more necessity -for supposing phosphorus to be formed in the animal economy than in -the mineral kingdom, from which it will probably be found the animal -obtained it. - -Without attempting to enter into any account of the apparent progress -of life over the earth, it appears desirable that some description -should be given of the kinds of plants and animals which we know to -have existed at different epochs. We shall thus learn, at least, some -of the prevailing characteristics of the earth during its transitions, -and be in a better condition for applying our knowledge of physical -power to the explanation of the various geological phenomena. - -Among the earliest races we have those remarkable forms, the -trilobites, inhabiting the ancient ocean. - -These crustacea bear some resemblance, although a very remote one, to -the common wood-louse, and, like that animal, they had the power of -rolling themselves into a ball when attacked by an enemy. The eye of -the trilobite is a most remarkable organ; and in that of one species, -_Phacops caudatus_, not less than two hundred and fifty lenses have -been discovered. This remarkable optical instrument indicates that -these creatures lived under similar conditions to those which surround -the crustacea of the present day. - -At the period of the trilobites of the Silurian rocks, all the animals -contemporaneous with them had the organs necessary for the preservation -of life in the waters. - -Next in order of time to the trilobite, the most singular animals -inhabiting those ancient seas, whose remains have been preserved, -are the _Cephalopoda_, possessing some traces of organs which belong -to vertebrated animals. There are numerous arms for locomotion and -prehension, arranged in a centre round the head, which is furnished -with a pair of sharp, horny mandibles, embedded in powerful muscles. -These prehensile arms are provided with a double row of suckers, by -which the animal seized its prey. Of these cephalopodous animals there -are many varieties, but all of them appear to be furnished with powers -of rapid locomotion, and those with shells had an hydraulic arrangement -for sinking themselves to any depth of the seas in which, without -doubt, they reigned the tyrants. - -Passing by without notice the numerous fishes, which appear to have -exhibited a similar order of progression to the other animals, we must -proceed to the more remarkable period when the dry land first began to -appear. - -All the animals found in the strata we have mentioned are such as would -inhabit the seas; but we gradually arrive at distinct evidence of the -separation of the land from the water, and the “green tree yielding -seed” presents itself to our attention; not that the strata earlier -than this are entirely destitute of any remains indicating vegetable -growth, but those they exhibit are such as, in all probability, may be -referred to marine plants. - -Those plants, however, which are found in the carboniferous series -are most of them distinguished by all the characteristics of those -which grow upon the land; we, therefore, in the mutilated remains of -vegetation left us in our coal-formations, read the history of our -early world. - -Then the reed-like calamite bowed its hollow and fragile stems over -the edges of the lakes the tree-ferns grew luxuriantly in the shelter -of the hills, and gave a wild beauty to the humid valleys; the -lepidodendrons spread themselves in mighty forests along the plains, -which they covered with their curious cones; whilst the sigillariæ -extended their multitudinous branches, wreathing like serpents amongst -the luxurious vegetation, and embraced, with their roots (stigmariæ), a -most extensive space on every side.[234] - -The seas and lakes of this period abounded with minute animals nearly -allied to the coral animals, which are now so actively engaged in the -formation of islands in the tropical and southern seas. During the ages -which passed by without any remarkable disturbance of the surface of -the earth, the many bands of mountain limestone were formed by the -ceaseless activity of these minute architects. Encrinites (creatures -in some respects resembling star-fish) existed in vast numbers in the -oceans of this time; and the great variety of bivalve shells, and those -of a spiral character, discovered in the rocks of this period, show the -waters of the newer palæozoic period to have been instinct with life. - -In the world then, as it does now, water acting on the dry land -produced remarkable changes. We have evidence of extensive districts -over which the most luxuriant vegetation must have spread for -ages,--from the remains of plants in every state of decay,--which we -find went to form our great coal-fields. These, by some changes in the -relative levels of land and water, became covered with this fluid; -and over this mass of decaying organic matter, sand and mud were for -ages being deposited. At length, rising above the surface, it becomes -covered with vegetation, which is, after a period, submerged; the same -deposition of sand and mud again takes place, it is once more fitted -for vegetable growth, and thus, cycle after cycle, we see the dry land -and the water changing places with each other. This will be evident -to every one who will carefully contemplate a section of one of the -coal-fields of Great Britain. We find a stratum of coal lying upon -a bed of under clay, and above it an extensive stratum of shale or -sandstone, probably formed by the denudation of the neighbouring hills; -and in this manner we have many strata of coal, shale, clay, ironstone, -and sandstone alternating with each other; the coal-formations of the -South Wales coal-field having the extraordinary thickness of 1500 feet. -The lowest bed of this extensive series must at one time have been -exposed as the surface of the country. - -Ascending in the series, we have now formations of a more recent -character, in which fishes of a higher order of organization, creeping -and flying saurians, crocodiles and lizards, tortoises, serpents, and -frogs, are found. The lias formations (a term corrupted from _layers_), -consisting of strata in which an argillaceous character prevails, stand -next in series. In these we have animals preserved in a fossil state, -of a distinguishingly different character from those of the inferior -strata. We meet with extended beds of pentacrinites, some inches in -thickness; and their remains are often so very complete that every part -of the skeleton can be made out, although so complicated that it cannot -consist of less than 150,000 parts. In these formations we often find -the curiously beautiful remains of the ammonites, of which a great -variety have been discovered. Of the belemnites--animals furnished with -the shell and the ink-bag of the cuttle-fish, with which it darkened -the water to hide itself from enemies, numerous varieties have also -been disentombed, with the ink-bag so well preserved, that the story of -the remarkable fossil has been written with its own ink. In addition to -these we find nautili; and sixty species of extinct fishes have been -described by Agassiz from the lias of Lyme Regis alone. - -When these rocks were in the progress of formation, there existed the -ichthyosaurus, or fish-lizard, which appears, in many respects, to have -resembled the crocodile of the Nile. It was a predatory creature of -enormous power, and must have been the tyrant and terror of the seas -which it inhabited. Its alligator-like jaws, its powerful eye, its -fish-like fins, and turtle-like paddles, were all formed to facilitate -its progress as a destructive minister. The plesiosaurus was, if -possible, a still more extraordinary creation. To the head of a lizard -was united an enormously long neck, a small and fish-like body, and the -tail of a crocodile: it appears formed for existence in shallow waters, -so that, when moving at the bottom, it could lift its head above the -surface for air, or in search of its food. The flora of this period -must have been extensive; and it resembled the vegetation which exists -at present in Tropical regions. - -We pass now to a new epoch, which is well distinguished by its animals -from all that had preceded it. Races of reptiles still have place upon -the earth, and we have now the megalosaurian remains; these animals -possessing a strength and rapacity which would render them objects of -terror as well as astonishment, could they be restored to the world -which they once ravaged. An enormous bat-like creature also existed -at this time--the pterodactyl--which, in the language of Cuvier, was, -“undoubtedly, the most extraordinary of all the beings of whose former -existence a knowledge is granted to us, and that which, if seen alive, -would appear most unlike anything that exists in the present world.” -“You see before you,” says the same writer, “an animal which, in all -points of bony structure, from the teeth to the extremities of the -nails, presents the well-known saurian characteristics, and of which no -one can doubt that its integuments and soft parts, its scaly armour and -its organs of circulation and reproduction, are likewise analogous. But -it was, at the same time, an animal provided with the means of flying; -and, when stationary, its wings were probably folded back like those -of a bird, although, perhaps, by the claws attached to its fingers, it -might suspend itself from the branches of trees.”[235] - -From the disintegration of the older rocks have no doubt arisen those -formations which are known as the oolitic series. In these strata are -preserved the remains of plants and animals more resembling those which -now exist upon the earth; and, for the first time,--unless the evidence -of the footsteps of birds on the new red sandstone of America be -accepted,--we meet with the remains of the feathered tribes. - -In these formations we discover animals belonging to the class -Mammalia,--the amphitherium and the phascolotherium,--which appear -to have resembled, in many respects, the marsupial animals of New -Holland.[236] - -The wealden formations, which are the next in order of position, are a -series of clays and sands, with subordinate beds of limestone, grit, -and shale. These have, in some instances, been formed in the sea; but -they are usually regarded as fresh-water deposits. All the older rocks -bear evident marks of marine origin, unless some of the coal-measure -strata may be regarded as otherwise; but nearly all the wealden series -contain the remains of land, fresh-water, and estuary animals, and of -land vegetables. The creatures which we discover, preserved, to tell -the history of this period, are numerous, and have marked peculiarities -to distinguish them from those already described, or from any now -existing on the earth. We find land saurians of a large kind, and -animals of all sizes; even insects, of which a great variety are found -in the wealds. The remarkable iguanodon was an animal which, even by -the cautious measurement of Professor Owen, must have been at least -twenty-eight feet long; and this enormous creature was suspected, by -Cuvier, and has been proved by Owen, to have been an “herbivorous -saurian for terrestrial life.”[237] Dr. Mantell calculates that no -less than seventy individuals of the iguanodon of all ages have come -under his notice; and the bones of a vast number of others must have -been broken up by the workmen in the few quarries of Tilgate grit; -so that these creatures were by no means rare at the period of their -existence.[238] - -The uppermost of these secondary formations is the cretaceous or chalk -group, which spreads over a large portion of south-eastern England, and -is met with in all parts of Europe. This chalk, which is a carbonate -of lime, appears to have been slowly precipitated from tranquil water, -as, according to Sir Henry De la Beche, organic remains are beautifully -preserved in it. Substances of no greater solidity than common sponges -retain their forms, delicate shells remain unbroken, fish even are -frequently not flattened, and altogether we have the appearances -which justify us in concluding that, since these organic exuviæ were -entombed, they have been protected from pressure by the consolidation -of the rock around them.[239] - -Beneath the chalk exists what has been called, from its colour--derived -from a silicate of the protoxide of iron,--green sand, and was, no -doubt, formed by deposition from the same water in which the carbonate -of lime was suspended,--the green sand falling to the bottom more -readily from its greater specific gravity. “The tranquillity,” observes -Sir Henry De la Beche, “which seems to have prevailed during this great -accumulation of siliceo-calcareous matter, whether it may have been -a deposit from water, in which it was mechanically suspended, partly -the work of living creatures, or in a great measure chemical, is very -remarkable.”[240] - -In the chalk, the remains of the leaves of dicotyledonous plants -and fragments of wood are found more abundantly than in the earlier -strata, many of which are marked with the perforations of marine -worms, indicating that they had floated for some time in the ocean. -It should, however, be remembered, that these are not the first -indications of vegetable life,--leaves have been found in the new red -sandstone; and the flora of the coal formation must not be forgotten. -The manner in which silica has deposited itself on organic bodies--such -as the sponges--is curious; the whole of the organized tissue being -often removed, and flint having taken its place. Flints formed by -such a process as this abound in the upper chalk. The association -of carbon and silicon, combined with oxygen, as we find them in the -cretaceous formations, is most interesting, and naturally gives rise -to some speculation on the relation of these two elements. Both carbon -and silicon, as has been already shown, exist in several allotropic -conditions; and, although the statements made by Dr. Brown relative -to the conversion of carbon into silicon are proved to be grounded on -experimental error, it is not improbable that a very intimate relation -may exist between these elements.[241] The probability is, that the -sponge animal has the power of secreting silica to give strength -to its form. “Many species,” says Rymer Jones, speaking of recent -sponges, “exhibiting the same porous structure, have none of the -elasticity of the officinal sponge--a circumstance which is due to the -difference observable in the composition of their skeletons or ramified -frame-work. In such the living crust forms within its substance -not only tenacious bands of animal matter, but great quantities of -crystallized spicula, sometimes of a calcareous, at others of a -siliceous, nature.” Thus, a frame of siliceous matter being formed by -the living animal, a deposition of the same substance is continued -after death. - -Sea-urchins and star-fish, and numerous fossil shells, are found in -these beds, which, however, differ materially from the remains of the -same animals found in the earlier formations. A vast number of new -species and genera of fish are also discovered in the chalk. - -Nearly all the animals and plants which existed up to this period are -now extinct, although they have some imperfect representatives at the -present day. - -The uppermost group, which has been called the supercretaceous or -tertiary formation, appears in our island to have been formed during -four great eras, as we find fresh-water deposits alternating with -marine ones. The term _eocene_, which is the first or oldest deposit; -_miocene_, which is the second; _pliocene_, which is the third; and the -_newer pliocene_,--which is the fourth and last, have been applied to -these formations, the names referring to the respective proportions of -existing species found among their fossil shells.[242] - -All these formations show distinct evidence of their having been -deposited from still or slowly-flowing deep waters. Thus the eocene -appears in the Paris basin,--formed clearly at an estuary, in which -are mingled some interesting fresh-water deposits;--in the lacustrine -formations in Auvergne; also at Aix; and in the north of Italy. It -appears probable that, in the formations generally termed eocene, both -fresh-water and marine deposits have been confounded, and several -formations of widely-different eras regarded as the result of one. We -have not yet been furnished with any distinct and clear evidence to -show that the deposits of the Paris basin, and those of Auvergne, -are of the same age. At all events, it is sufficient for our present -purpose to know that they are the result of actions which are now as -general as they were when the plastic clay of Paris, and its sulphate -of lime, or the London clay, were slowly deposited. - -As a general conclusion, we may decide that, at the eocene period, -existing continents were the sites of vast lakes, rivers, and -estuaries, and were inhabited by quadrupeds, which lived upon -their thickly-wooded margins. Many remains, allied to those of the -hippopotamus, have been found in the subsidences of this period. - -Examples of the miocene or middle tertiary era are to be found in -Western France, over the whole of the great valley of Switzerland, and -the valley of the Danube. In these deposits we find the bones of the -rhinoceros, elephant, hippopotamus, and the dinotherium, an extinct -animal, possessing many very distinguishing features.[243] - -The pliocene period has been termed the age of elephants, and is most -remarkable for the great mastodons and gigantic elks, with other -animals not very unlike those which are contemporaneous with man. - -In the superficial layers of the earth, the diluvium, alluvium, peat -and vegetable soil, we have a continuation of the history of the -mutations of our globe and of its inhabitants, which has been here so -briefly sketched. They bring us up to the period when man appeared in -the world, since whose creation it is evident no very extensive change -has been produced upon the surface. We have viewed the phenomena of -each great epoch, marked as they are by new creations of organized -beings, and it would appear as if, through the whole series, from -the primary rocks up to the modern alluvial deposits, a progressive -improvement of the earth’s surface had been effected, to fit it at last -for the abode of the human race. - -Thus have we preserved for us, in a natural manner, evidences which, if -we read them aright, must convince us that the laws by which creation -has ever been regulated are as constant and unvarying as the Eternal -mind by which they are decreed. Our earth, we find, by the records -preserved in the foundation-stones of her mountains, has existed -through countless ages, and through them all exhibited the same active -energies that prevail at the present moment. By precisely similar -influences to those now in operation, have rocks been formed, which, -under like agencies, have been covered with vegetation, and sported -over by, to us, strange varieties of animal life. Every plant that -has grown upon the earliest rocks which presented their faces to the -life-giving sun, has had its influence on the subsequent changes of our -planet. Each trilobite, each saurian, and every one of the mammalia -which exist in the fossil state, have been small laboratories in which -the great work of eternal change has been carried forward, and, under -the compulsion of the strong laws of creation, they have been made -ministers to the great end of forming a world which might be fitting -for the presence of a creature endued with a spark taken from the -celestial flame of intellectual life. - -For a few moments we will return to a consideration of the operations -at present exhibiting their phenomena, and examine what bearing they -have upon our knowledge of geological formations. - -During periods of immense, but unknown, duration, the ocean and the dry -land are seen to have changed their places. Enormous deposits, formed -at the bottom of the sea, are lifted by some mechanical, probably -volcanic, force, above the waters, and the land, like the ocean -surrounding it, teems with life. This state of things lasts for ages; -but the time arrives when the ocean again floods the land, and a new -state of things, over a particular district, has a beginning. - -It must not be imagined that the changes which we have spoken of, as if -they were the result of slow decay and gradual deposit, were effected -without occasional violent convulsions. Many of the strata which -were evidently deposited at the bottom of the sea, and, of course, -as horizontal beds, are now found nearly vertical. We have evidence -of strata of immense thickness having been subjected to forces that -have twisted and contorted them in a most remarkable manner. Masses of -solid rock, many thousand feet deep, are frequently bent and fractured -throughout their whole extent. Mountains have been upheaved by internal -force, and immense districts have suddenly sunk far below their usual -level. By the expansive force due to that temperature which must be -required to melt basaltic and trap rocks, the whole of the superficial -crust of a country has been heaved to a great height, immense fissures -have been formed by the breaking of the mass, and the melted matter has -been forced through the opening, and overflowed extensive districts, or -volcanoes have been formed, and wide areas have been buried under the -ashes ejected from them. With the cause of these convulsions we are at -present unacquainted. - -We have evidence of the extent to which these forces may be exerted, in -the catastrophes which have occurred within historical times, and which -have happened even in our own day. Herculaneum and Pompeii, buried -under the lava and ashes of Vesuvius, in an hour when the inhabitants -of these cities were unprepared for such a fearful visitation,--the -frightful earthquakes which have, from time to time, occurred in South -America--are evidences of the existence of hidden forces which shake -the firm-set earth. Similar ravaging catastrophes may have often -occurred, and, involving cataclysms, swept the surface to produce the -changes we detect over every part of the earth, compared with which -the earthquakes and floods of history are but trivial things. Evidence -has been adduced, to show that the mountains of the Old World may -have approached in height the highest of the Andes or Himalayas, and -these have not been destroyed by any sudden effect, but by the slow -disintegrating action of the elements.[244] All these phenomena are -now in progress: the winds and the rains wear the faces of the exposed -rock; their _débris_, mixed with decayed vegetable and animal matter, -are washed off from the surface, and borne away by the rivers, to be -deposited in the seas. Thus it is that the great delta of the Ganges -is formed, and that a continual increase of matter is going on at the -mouths of rivers. The Amazon, the Mississippi, and other great rivers, -bear into the ocean, daily, thousands of tons of matter from the -surface of the earth.[245] This is, of course, deposited at the bottom -of the sea, and it must, in the process of time, alter the relative -levels of the ocean and the land. Islands have been lifted by volcanic -power from the bottom of the sea, and many districts in South America -have been depressed by the same causes. - -Changes as extensive have been, in all probability, effected by forces -“equally or more powerful, but acting with less irregularity, and so -distributed over time as to produce none of those interregnums of -chaotic anarchy which we are apt to think (perhaps erroneously) great -disfigurements of an order so beautiful and harmonious as that of -nature.”[246] These forces are, without doubt, even now in action. - -Had it not been for these convulsive disturbances of the surface, -the earth would have presented an almost uniform plain, and it would -have been ill-adapted for the abode of man. The hills raised by the -disturbances of nature, and the valleys worn by the storms of ages, -minister especially to his wants, and afford him the means of enjoyment -which he could not possess had the surface been otherwise formed. The -“iced mountain tops,” condensing the clouds which pass over them, send -down healthful streams to the valleys, and supply the springs of the -earth, thus securing the fertility and salubrity of the distant plains. -The severities of climate are mitigated by these conditions, and both -the people of the tropics and those dwelling near the poles are equally -benefited by them. - -Gravitation, cohesion, motion, chemical force, heat, and electricity, -must, from that hypothetical time when the earth floated a cloud of -nebulous vapour, in a state of gradual condensation up to the present -moment, have been exercising their powers, and regulating the mutations -of matter. - -When the dry land was beneath the waters, and when darkness was upon -the face of the deep, the same great operations as those which are -now in progress in the depths of the Atlantic, or in the still waters -of our inland lakes, were in full activity. At length the dry land -appears; and--mystery of mysteries--it soon becomes teeming with life -in all the forms of vegetable and animal beauty, under the aspect of -the beams of a glorious sun. - -Geology teaches us to regard our position upon the earth as one far -in advance of all former creations. It bids us look back through -the enormous vista of time, and see, shining still in the remotest -distance, the light which exposes to our vision many of nature’s holy -wonders. The elements which now make up this strangely beautiful fabric -of muscle, nerves, and bone, have passed through many ordeals, ere yet -it became fashioned to hold the human soul. No grain of matter has been -added to the planet, since it was weighed in a balance, and poised with -other worlds. No grain of matter can be removed from it. But in virtue -of those forces which seem to originate in the sun, “the soul of the -great earth,” a succession of new forms has been produced, as the old -things have passed away. - -Under the forces we have been considering, acting as so many contending -armies, matter passes from one condition to another, and what is now -a living and a breathing creature, or a delicate and sweetly-scented -flower, has been a portion of the amorphous mass which once lay in the -darkness of the deep ocean, and it will again, in the progress of time, -pass into that condition where no evidences of organization can be -found,--again, perhaps, to arise clothed with more exalted powers than -even man enjoys. - -When man places himself in contrast with the Intelligences beyond him, -he feels his weakness; and the extent of power which he can discover at -work, guided by a mysterious law, is such, that he is dwarfed by its -immensity. But looking on the past, surveying the progress of matter -through the inorganic forms up to the higher organizations, until at -length man stands revealed as the chief figure in the foreground of the -picture, the monarch of a world on which such elaborate care has been -bestowed, and the absolute ruler of all things around him, he rises -like a giant in the conscious strength of his far-searching mind. That -so great, so noble a being, should suffer himself to be degraded by the -sensualities of life to a level with the creeping things, upon which he -has the power to tread, is a lamentable spectacle, over which angels -must weep. - -The curious connection between the superstitions of races, the -traditionary tales of remote tribes, and the developments of the truths -of science, are often of a very marked character, and they cannot but -be regarded as instructive. In the wonders of “olden time” fiction has -ever delighted; and a thousand pictures have been produced of a period -when beings lived and breathed upon the earth which have no existence -now. - -Hydras, harpies, and sea-monsters, figure in the myths of antiquity. -In the mythology of the northern races of Europe we have fiery flying -dragons, and Poetry has placed these as the guardians of the “hoarded -spirit” and protectors of the enchanted gold. - -Through the whole of the romance period of European literature, -nothing figures but serpents, “white and red,” toiling and fighting -underground,--thus producing earthquakes, as in the story of Merlin -and the building of Stonehenge. Flying monsters, griffins and others, -which now live only in the meaningless embellishments of heraldry, -appear to have been conceived by the earlier races of men as the -representatives of power. Curious is it, too, to find the same class -of ideas prevailing in the East. The monster dragons of the Chinese, -blazoned on their standards and ornamenting their temples;--the -Buddaical superstition that the world is supported on a vast elephant, -which stands on the back of a tortoise, which again rests on a serpent, -whose movements produce earthquakes and violent convulsions;--the rude -decorations also of the temples of the Aztecs, which have been so -recently restored to our knowledge by the adventurous travellers of -Central America,--all give expression to the same mythological idea. - -Do not these indicate a faint and shadowy knowledge of a previous -state of organic existence? The process of communion between man of -the present, and the creations of a former world, we know not; it is -mysterious, and for ever lost to us. But even the most ignorant and -uncultivated races of mankind have figured for themselves the images -of creatures which, whilst they do really bear some resemblance to -things which have for ever passed away, do not, in the remotest degree, -partake of any of the peculiarities of existing creations. - -The ichthyosaurus, and the plesiosaurus, and the pterodactylus, are -preserved in the rude images of harpies, of dragons, and of griffins; -and, although the idea of an elephant standing on the back of a -tortoise was often laughed at as an absurdity, Captain Cautley and -Dr. Falconer at length discovered in the hills of Asia the remains of -a tortoise in a fossil state of such a size that an elephant could -easily have performed the feat.[247] - -Of the ammonites, we have more exact evidence; they were observed by -our forefathers, and called by them snake-stones. According to the -legends of Catholic saints they were considered as possessing a sacred -character:-- - - “Of these and snakes, each one - Was changed into a coil of stone - When holy Hilda prayed.” - -And in addition to this petrifying process, one of decapitation is said -to have been effected; hence the reason why these _snake-stones_ have -no heads. - -We also find, in the northern districts of our island, that the name of -“St. Cuthbert’s beads” is applied to the fossil remains of encrinites. - -Thus we learn that, to a great extent, fiction is dependent upon -truth for its creations; and we see that when we come to investigate -any wide-spread popular superstition, although much distorted by the -medium of error through which it has passed, it is frequently founded -upon some fragmentary truth. There are floating in the minds of men -certain ideas which are not the result of any associations drawn from -things around; we reckon them amongst the mysteries of our being. May -they not be the truths of a former world, of which we receive the dim -outshadowing in the present, like the faint lights of a distant Pharos, -seen through the mists of the wide ocean? - -Man treads upon the wreck of antiquity. In times which are so long -past, that the years between them cannot be numbered by the aids of -our science, geology teaches us that forms of life existed perfectly -fitted for the conditions of the period. These performed their offices -in the great work; they passed away, and others succeeded to carry -on the process of building a world for man. The past preaches to -the present, and from its marvellous discourses we venture to infer -something of the yet unveiled future. The forces which have worked -still labour: the phenomena which they have produced will be repeated. - - Ages on ages slowly pass away, - And nature marks their progress by decay. - The plant which decks the mountain with its bloom, - Finds in the earth, ere long, a damp dark tomb: - And man, earth’s monarch, howe’er great and brave-- - Toils on--to find at last a silent grave. - The chosen labours of his teeming mind - Fade by the light, and crumble ’neath the wind; - And e’en the hills, whose tops appear to shroud - Their granite peaks deep in the vapoury cloud, - Worn by tempests--wasted by the rains, - Sink slowly down to fill wide ocean’s plains. - The ocean’s breast new lands again display, - And life and beauty drink the light of day: - The powers which work at great creation’s wheel, - Will from the wrecks of matter still reveal - New forms of wondrous beauty--which will rise - Pure as the flame of love’s young sacrifice, - Beaming with all the pristine hues of youth, - Robed by the day, and crowned by holy truth. - - -FOOTNOTES: - -[231] _Preliminary Discourse_; Sir J. F. W. Herschel. Lardner’s Cabinet -Cyclopædia. - -[232] _Geological Researches_; by Sir Henry De la Beche, C.B. -(_Degradation of Mountains_, p. 167.) _Geological Manual_, p. 184. -_Principles of Geology_; by Sir Charles Lyell, 7th Edition, p. 150, -686. _On the Denudation of South Wales, and the adjacent countries of -England_; by Professor Andrew Ramsay; Memoirs of the Geological Survey -and Museum of Practical Geology, vol. i. p. 297. - -[233] Fownes, _On the Existence of Phosphoric Acid in Rocks of Igneous -Origin_; Phil. Trans. 1844, p. 53. Nesbitt, _Quarterly Journal of the -Chemical Society_. - -[234] _On the Vegetation of the Carboniferous Period as compared -with that of the present day; On some peculiarities in the structure -of Stigmaria; Remarks on the Structure and Affinities of some -Lepidostrobi_: by Dr. Hooker; Memoirs of the Geological Survey, &c., -vol. ii. pp. 387, 431, 440. - -[235] See Owen, Quarterly Journal of the Geological Society, No. 6, -p. 96. Dr. Buckland, Geological Transactions, vol. iii. p. 220. _The -Wonders of Geology_: by Dr. Mantell, vol. ii. p. 493. - -[236] _Report on British Fossil Mammalia_: by Richard Owen, Esq., -F.R.S.; British Association Reports, vols. xi. xii. - -[237] _Notice on the Iguanodon, a newly discovered fossil reptile from -the sandstone of Tilgate Forest, in Sussex_: by Gideon Mantell, Esq, -F.R.S., &c.; Philosophical Transactions, vol. cxv. p. 179. _On the -Structure of Teeth, &c._; by Professor Owen. - -[238] Dr. Mantell, _Wonders of Geology_. _Geology of the South-east of -England._ - -[239] _Geological Researches_; _Geological Manual_; by Sir Henry Thos. -De la Beche, C.B., &c. - -[240] Ibid. - -[241] _Experimental Researches on the production of Silicon from -Paracyanogen_: by Samuel Brown, M.D.; Transactions of the Royal Society -of Edinburgh, vol. xv. p. 229. _Experiments on the alleged conversion -of Carbon into Silicon_: by R. H. Brett, Ph.D., and J. Denham Smith, -Esq.; Philosophical Magazine, vol. xix. p. 295, New Series. See also -Dr. Brown’s reply to the above, ibid, p. 388. - -[242] _Geology, Introductory, Descriptive, and Practical_: by Prof. -Ansted, vol. ii. p. 22. - -[243] _The Wonders of Geology_: by Dr. Mantell, vol. i. p. 162. -_Bridgewater Treatise_: by Dr. Buckland. Dr. J. J. Kemp, and Dr. A. -V. Klipstein, _On the Dinotherium_; Darmstadt, 1836. Cuvier and De -Blainville have also carefully described the fossil remains of this -animal. - -[244] See Professor Ramsay’s memoir _On Denudation_: Memoirs of the -Geological Survey of Great Britain. - -[245] “The distances to which river water, more or less charged with -detritus, would flow over sea-water, will depend upon a variety -of obvious circumstances. Captain Sabine found discoloured water, -supposed to be that of the Amazons, three hundred miles distant in -the ocean from the embouchure of that river. It was about 126 feet -deep. Its specific gravity was = 1·0204, and the specific gravity of -the sea-water = 1·0262. This appears to be the greatest distance from -land at which river water has been detected on the surface of the -ocean. If rivers, containing mechanically suspended detritus, flowed -over sea-water in lines which, in general terms, might be called -straight, the deposit of transported matter which they carried out -would also be in straight lines. If, however, they be turned aside -by an ocean current, as was the case with that observed by Captain -Sabine, the detritus would be thrown, and cover an area corresponding -in a great degree with the sweep which the river has been compelled -to make out of the course, that its impulse, when discharged from its -embouchure, might lead it to take: supposing the velocity with which -this river-water was moving has been correctly estimated at about -three miles per hour, it is not a little curious to consider that the -agitation and resistance of its particles should be sufficient to keep -finely comminuted solid matter mechanically suspended, so that it -would not be disposed freely to part with it, except at its junction -with the sea-water over which it flows, and where, from friction, it -is sufficiently retarded. So that a river, if it can preserve a given -amount of velocity flowing over the sea, may deposit no very large -amount of mechanically suspended detritus in its course from the -embouchure, where it is ultimately stopped. Still, however, though the -deposit may not be so abundant as at first sight would appear probable, -the constant accumulation of matter, however inconsiderable at any -given time, must produce an appreciable effect during the lapse of -ages.”--Sir Henry De la Beche’s _Geological Researches_, p. 72. - -[246] Sir J. F. W. Herschel: _Preliminary Treatise_. - -[247] _Fauna Antiqua Sivalensis. Being the Fossil Zoology of the -Sewalik Hills in the North of India_: by Hugh Falconer and Proby T. -Cautley. 1844. - - - - -CHAPTER XIV. - -PHENOMENA OF VEGETABLE LIFE. - - Psychology of Flowers--Progress of Matter towards - Organization--Vital Force--Spontaneous Generation--The Vegetable - Cell--Simplest Development of Organization--The Crystal and - the Cell--Primitive Germ--Progress of Vegetation--Influence - of Light--Morphology--Germination--Production of Woody - Fibre--Leaves--Chlorophylle--Decomposition of Carbonic - Acid--Influence of Light, Heat, and Actinism on the Phenomena of - Vegetable Life--Flowers and Fruits--Etiolation--Changes in the - Sun’s Rays with the Seasons--Distribution of Plants--Electrical and - Combined Physical Powers - - -The variety of beautiful forms which cover the surface of this sphere, -serve, beyond the physical purposes to which we have already alluded, -to influence the mind, and give character to the inhabitants of every -locality. There are men who appear to be dead to the mild influences -of flowers; but these sweet blossoms--the stars of our earth--exert a -power as diffusive as their pervading odours. - -The poet tells us of a man to whom - - The primrose on the river’s brim - A yellow primrose was to him, - And it was nothing more. - -But it was something more. He, perhaps, attended not to the eloquent -teaching of its pure, pale leaves: he might not have been conscious -of the mysterious singing of that lowly flower: he might, perchance, -have crushed it beneath his rude foot rather than quaff the draught of -wisdom which it secreted in its cell; but the flower still ministered -to that mere sensualist, and in its strange, tongueless manner, -reproved his passions, and kept him “a wiser and a better man,“ than if -it had pleased God to have left the world without the lovely primrose. - -The psychology of flowers has found many students--than whom not one -read them more deeply than that mild spirit who sang of the Sensitive -Plant, and in wondrous music foreshadowed his own melancholy fate.[248] -That martyr to sensibility, Keats, who longed to feel the flowers -growing above him, drew the strong inspiration of his volant muse from -those delicate creations which exhibit the passage of inorganic matter -into life; and other poets will have their sensibilities awakened by -the æsthetics of flowers, and find a mirror of truth in the crystal -dew-drop which clings so lovingly to the purple violet, and draws fresh -beauties from its coloured petals. - -If we examine carefully all the conditions of matter which we have -made the subject of our studies, we cannot but perceive how gradual -is the progress of the involved action of the physical forces, as we -advance from the molecule--the mere particle of matter--up to the -organic combination. At first we detect only the action of cohesion in -forming the rude mass; then we have the influence of the crystallogenic -powers giving a remarkable regularity to bodies; we next discover the -influences of heat and electrical force in determining condition, and -of chemical action as controlled by them. Yet, still we have a body -without organization. Light exerts its mysterious powers, and the same -elements assume an organized form; and, in addition to the recognized -agencies, we dimly perceive others on which vitality evidently -depends. These empyreal influences become more and more complicated -to us: ascending in the scale, they rise beyond our science; and, at -length, we find them guiding the power of intelligence, while instinct -and reason are exhibited in immediate dependence upon them. - -Let it not be imagined that this view has any tendency to materialism. -The vital energy is regarded as a spiritualization, and reason as a -divine emanation; but they are connected with materialities, on which -they act, and by which they are themselves controlled. The organic -combinations, and the physical powers by which these unions of matter -are effected and retained, have a direct action over that ethereality -which is life, and the powers of life again control these more material -forces. The spirit, in whatever state, when connected with matter, is, -like Prometheus chained to his rock, in a constant struggle to escape -from its shackles, and assert the full power of its divine strength. - -We have seen variety enough in the substances which make up the -inorganic part of creation; but infinitely more varied are the forms -of organization. In the vegetable world which is immediately around -us, from the green slime of our marshes to the lustrous flowers of our -gardens and the lordly trees of our forests, what an extraordinary -diversity of form is apparent! From the infusoria of an hour, to the -gigantic elephant roaming in his greatness in the forests of Siam--the -noble lion of the caves of Senegal--the mighty condor of the Andes--and -onward to man, the monarch of them all, how vast are the differences, -and yet how complete are they in their respective conditions! In the -creation we have examined, we have had conclusive evidence, that from -the combination of _atoms_ every peculiar form has been produced. In -the creation we are about to examine, we shall discover that all the -immense diversity of form, of colour, and condition which is spread -over the world in the vegetable and animal kingdoms, results from the -combination of _cells_. The atom of inorganic nature becomes a cell in -organic creation. This cell must be regarded as the compound radical of -the chemist, and by decomposing it, we destroy the essential element of -organization. - -With the mysterious process by which the atom is converted into a -cell, or a compound radical, we are unacquainted; but we must regard -the cell as the organic atom. It is in vain that the chemist or the -physiologist attempts to examine this change of the inorganic elements -to an organized state; it is one of the mysteries of creation, which is -to be, in all probability, hid from our eyes, until this “mortal coil” -is shaken off, and we enjoy the full powers of that intelligence which -we are promised we shall enjoy in an immortal state. - -Again and again has the attention of men been attracted to the -_generatio æquivoca_; they have sometimes thought they have discovered -a _generatio primitiva_ or _spontanea_; but a more careful examination -of these organisms has shown that an embryo existed--a real germination -has taken place. - -Count Rumford[249] stated that threads of silk and wool had the power -of decomposing carbonic acid in water in the sunshine; and hence some -have referred organization to a mere chemical change produced by -luminous excitation; and we have heard of animal life resulting from -pounded siliceous matter. All such statements must be regarded as -evidences of imperfect investigation. - -Dr. Carus, alluding to the experiments of Gruithuisen, Priestley, and -Ingenhousz,[250] says:--“These show, more than any other experiments, -that, in the purest water, under the influence of air, light, and heat, -beings are formed, which, oscillating as it were between the animal -and the plant, exhibit the primitive germs of both kingdoms.”[251] -Treviranus[252] repeated, and appeared to confirm these results; but in -these experiments we have no evidence that the germ did not previously -exist in the spring-water which was employed. - -Some have regarded the cell as a crystal; they see the crystal forming, -by the accumulation of atoms, into a fixed form, under the influence -of an “inner life;” and, advancing but a step, they regard the cell as -the result of an increased exercise of the physical influences.[253] -We have referred crystalline form to certain magnetic conditions; and -it is evident that the atomic cell is influenced by similar forces; -but if we place a crystal in its natural fluid, though it increases in -size, it never alters in form: whereas, if we examine a cell in its -natural position, it gives indications of motion, it produces other -cells, and we have a development of organs which are in no respect -the same in form as the original. From a vesicle floating invisible -to the unaided human sense in its womb of fluid, is produced a plant -possessing strange powers, or an animal gifted with volition. The idea, -that two kinds of polarity--light on one side, and gravitation on the -other--produce the two peculiar developments of roots and branches, can -only be regarded as one of those fanciful analogies which prove more -imagination than philosophy.[254] - -The conditions are, however, most curious; they deserve very attentive -study; but in examining the phenomena, the safest course is to allow -the effects as they arise to interpret to us, and not admit the love -of hypothesis to lead us into bewildering analogies; or uncertain -phenomena to betray us to hasty inferences. It is of this evil that -Bacon speaks, in his “Advancement of Learning.” He says:-- - -“The root of this error, as of all others, is this, that men, in -their contemplations of nature, are accustomed to make too timely a -departure, and too remote a recess from experience and particulars, and -have yielded and resigned themselves over to the fumes of their own -fancies and popular argumentations.” - -Without venturing, therefore, to speculate on the origin of the -primitive cell, or unit of organic life, which involves the problem -of the metamorphosis of a rude mass--the primitive transformation -of the rudimentary atoms into organic form,--we must admit that the -highly organized plant or animal is but an aggregation of cells; their -arrangement being dependent upon certain properties peculiar to them, -and the exercise of forces such as we have been studying,--all of which -appear to act externally to the plant or animal itself. - -Experiments have been brought forward, in which it appeared that, after -all organization which could by any possibility have existed, had -been destroyed by the action of fire, solutions of flint and metallic -salts, have, under the influence of electric currents, exhibited -signs of organic formations, and that, indeed, insects--a species -of acari--have been developed in them. The experiments were said to -have been made with care, and many precautions taken to shut out -all chances of any error, but not all the precautions required in a -matter of such exceeding delicacy; and we are bound not to receive the -evidence afforded as the true expression of a fact without much further -investigation. All experience,--setting aside the experiment named,--is -against the supposition that pounded or dissolved flint could by any -artificial means be awakened into life. Ova may have been conveyed -into the vessels which contained the solutions under experiment; and -in due time, although possibly quickened by electric excitation, the -animals--the most common of insects--came into existence.[255] - -The rapid growth of confervæ upon water has often been brought forward -as evidence of a spontaneous generation, or the conversion of inorganic -elements into organic forms; but it has been most satisfactorily proved -that the germ must be present, otherwise no evidence of anything -like organization will be developed. All the conditions required for -the production of vegetable life appear to show, that it is quite -impossible for any kind of plant, even the very lowest in the scale, to -be formed in any other way than from an embryo in which are contained -the elements necessary for it, and the arrangements required for the -various processes which are connected with its vitality. - -The earth is now covered with vegetable life, but there must have -existed a time when “darkness was upon the face of the deep,” and -organization had not yet commenced tracing its lovely net-work of cells -upon the bare surface of the ocean-buried rock. At length the mystery -of organic creation began: into this science dares not penetrate, but -it is privileged to begin its search a little beyond this point, and -we are enabled to trace the progress of organic development through a -chain of interesting results which are constantly recurring. - -If we take some water, rising from a subterranean spring, and expose -it to sunshine, we shall see, after a few days, a curious formation -of bubbles, and the gradual accumulation of green matter. At first we -cannot detect any marks of organization--it appears a slimy cloud of -an irregular and undetermined form. It slowly aggregates, and forms a -sort of mat over the surface, which at the same time assumes a darker -green colour. Careful examination will now show the original corpuscles -involved in a net-work formed by slender threads, which are tubes of -circulation, and may be traced from small points which we must regard -as the compound atom, the vegetable unit. We must not forget, here, -that we have to deal with four chemical elements,--oxygen, hydrogen, -carbon, and nitrogen, which compose the world of organized forms, and -that the water affords us the two first as its constituents, gives us -carbon in the form of carbonic acid dissolved in it, and that nitrogen -is in the air surrounding it, and frequently mixed with it also. - -Under the influence of sunshine, we have now seen these elements -uniting into a mysterious bond, and the result is the formation of a -cellular tissue, which possesses many of the functions of the noblest -specimens of vegetable growth. But let us examine the progress. The -bare surface of a rock rises above the waters covered over with this -green slime, a mere veil of delicate net-work, which, drying off, -leaves no perceptible trace behind it; but the basis of a mighty growth -is there, and under solar influence, in the process of time, other -changes occur. - -After a period, if we examine the rock, we shall find upon its face -little coloured cups or lines with small hard discs. These, at first -sight, would not be taken for plants, but on close examination they -will be found to be lichens. These minute vegetables shed their seed -and die, and from their own remains a more numerous crop springs into -life. After a few of these changes, a sufficient depth of soil is -formed, upon which mosses begin to develope themselves, and give to -the stone a second time a faint tint of green, a mere film still, but -indicating the presence of a beautiful class of plants, which, under -the microscope, exhibit in their leaves and flowers many points of -singular elegance. These mosses, like the lichens, decaying, increase -the film of soil, and others of a larger growth supply their places, -and run themselves the same round of growth and decay. By and by, -funguses of various kinds mingle their little globes and umbrella-like -forms. Season after season plants, perish and add to the soil, which is -at the same time increased in depth by the disintegration of the rock -over which it is laid, the cohesion of particles being broken up by the -operations of vegetable life. The minute seeds of the ferns floating on -the breeze, now find a sufficient depth of earth for germination, and -their beautiful fronds, eventually, wave in loveliness to the passing -winds. - -Vegetable forms of a higher and a higher order gradually succeed each -other, each series perishing in due season, and giving to the soil -additional elements for the growth of plants of their own species or -those of others. Flowering herbs find a genial home on the once bare -rock; and the primrose pale, the purple foxglove, or the gaudy poppy, -open their flowers to the joy of light. The shrub, with its hardy roots -interlaced through the soil, and binding the very stones, grows rich -in its bright greenery. Eventually the tree springs from the soil, -and where once the tempest beat on the bare cold rock, is now the -lordly and branching monarch of the forest, with its thousand leaves, -affording shelter from the storm for bird and beast. - -Such are the conditions which prevail throughout nature in the progress -of vegetable growth; the green matter gathering on a pond, the mildew -accumulating on a shaded wall, being the commencement of a process -which is to end in the development of the giant trees of the forest, -and the beautifully tinted flower of nature’s most chosen spot. - -We must now consider closely the phenomena connected with the growth of -an individual plant, which will illustrate the operation of physical -influences throughout the vegetable world. The process by which the -embryo, secured in the seed, is developed, is our first inquiry. - -A seed is a highly carbonized body, consisting of integuments and -embryo: between these, in most seeds, lies a substance called the -_albumen_, or _perisperm_. The embryo contains the elements of the -future plant--the cotyledons, the plumule, and the radicle; the -former developing into stalk and leaves, the latter into roots. This -embryo hides the living principle, for the development of which it -is necessary that the starch and gluten undergo a chemical change, -and that an elevation of temperature is produced. The vital power -is dormant--it sleeps--in the seed until the proper conditions are -produced. It has been proved, that the powers of maintaining life -in the seed are very great; excessive cold, sufficiently intense to -freeze mercury, will not kill seed, and they resist a comparatively -high temperature. It is probable that heat only destroys seeds by -drying them too completely. The temperature at which seeds germinate is -exceedingly varied,--those belonging to our own clime will germinate -when the thermometer rises above 40° F., but the seeds of tropical -plants demand that a temperature of from 70° to 84°, or even to 90°, -be steadily applied to them. In some cases it has been found that -even boiling the seeds has been advantageous to the future process of -germination in the soil. But let us take the seed of some ordinary -plant, and trace its progress. - -An apparently dead grain is placed in the soil. If the temperature is a -few degrees above the freezing point, and the soil holds a due quantity -of water, the integument of the seed imbibes moisture and swells; the -tissue is softened, and the first effort of vital force begins. The -seed has now the power of decomposing water, the oxygen combines with -some of the carbon of the seed, and is expelled as carbonic acid. -Saussure’s experiments prove this. The air above the soil in which -a horse-bean was placed to germinate, gave, before the experiment, -nitrogen 210·26, and oxygen 56·29, and after germination, nitrogen -209·41, oxygen 44·38, and carbonic acid 11·27. This part of the process -is but little removed from the merely chemical changes which we have -already considered. We find the starch of the seed changed into gum and -sugar, which affords nutritive food for the developing embryo. The seed -now lengthens downwards by the radicle, and upwards by the cotyledons, -which, as they rise above the earth, acquire a green colour. Here the -first stage of vegetable life ends, the chemically exciting process is -at an end, and a new stimulus is required to continue in full activity -the vital powers. Carbonic acid is no longer given off. - -The cotyledons, which are two opposite roundish leaves, act as the -lungs; by them carbonic acid taken from the atmosphere is absorbed -and carried by a circulating process, now in full activity, through -the young plant. The carbonic acid, a compound of carbon and oxygen, -is decomposed; it is deprived of its carbon, which is retained by the -plant, and oxygen is exhaled. The plant at this period is little more -than an arrangement of cellular tissue, a very slight development -of vascular and fibrous tissue appearing as a cylinder lying in the -centre of the sheath. At this point, however, we begin more distinctly -to trace the operations of the new power; the impulses of life are -strikingly evident. - -The young root is now lengthening, and absorbing from the moisture in -the soil, which always contains some soluble salts, a portion of its -nutriment, which is impelled upwards by a force--probably capillary -attraction and endosmose action combined--to the point from which the -plumule springs. Capillary force raises the fluids through the tubes -in the stalk, and conveys them to the veins in the leaves, while -the endosmose force diffuses them through the vegetable tissues. -The plumule first ascends as a little twig, and, at the same time, -by exerting a more energetic action on the carbonic acid than the -cotyledons have done, the carbon retained by them being only so much -as is necessary to form chlorophylle, or the green colouring matter of -leaves, some wood is deposited in the centre of the radicle. From this -time the process of lignification goes on through all the fabric,--the -increase, and indeed the life, of the plant depending upon the -development of a true leaf from the plumule. - -It must not be imagined that the process consists, in the first place, -of a mere oxidation of the carbon in the seed,--a slow combustion by -which the spark of life is to be kindled;--the hydrogen of the water -plays an important part, and, combining also with the carbon, forms -necessary compounds, and by a secondary process gives rise again to -water by combination with oxygen in the cells of the germinating grain. -Nor must we regard the second class of phenomena as mere mechanical -processes for decomposing carbonic acid, but the result of the combined -influences of all the physical powers and life superadded. - -This elongating little twig, the plumule, at length unfolds itself, and -the branch is metamorphosed into a leaf. The leaf aërates the sap it -receives, effects the decomposition of the carbonic acid, the water, -and in all probability the ammonia which it derives from the air, -and thus returns to the pores, which communicate with the pneumatic -arrangements of the plant, the necessary secretions for the formation -of bark, wood, and the various proximate principles which it contains. - -After the first formation of a leaf, others successively appear, all -constructed alike, and performing similar functions. The leaf is the -principal organ to the tree; and, indeed, Linnæus divined, and Goethe -demonstrated, the beautiful fact, that the tree was developed from this -curiously-formed organ. - -“Keeping in view,” says the poet-philosopher, “the observations that -have been made, there will be no difficulty in discovering the leaf in -the seed-vessel, notwithstanding the variable structure of that part -and its peculiar combinations. Thus the pod is a leaf which is folded -up and grown together at its edges, and the capsules consist of several -leaves grown together, and the compound fruit is composed of several -leaves united round a common centre, their sides being opened so as to -form a communication between them, and their edges adhering together. -This is obvious from capsules which, when ripe, split asunder, at which -time each portion is a separate pod. It is also shown by different -species of one genus, in which modifications exist of the principle -on which their fruit is formed; for instance, the capsule of _nigella -orientalis_ consists of pods assembled round a centre, and partially -united; in _nigella damascena_ their union is complete.”[256] - -Professor Lindley thus explains the same view:--“Every flower, with -its peduncle and bracteolæ, being the development of a flower-bud, and -flower-buds being altogether analogous to leaf-buds, it follows as a -corollary that every flower, with its peduncle and bracteolæ, is a -metamorphosed branch. - -“And, further, the flowers being abortive branches, whatever the laws -are of the arrangement of branches with respect to each other, the same -will be the laws of the flowers with respect to each other. - -“In consequence of a flower and its peduncle being a branch in a -particular state, the rudimentary or metamorphosed leaves which -constitute bracteæ, floral envelopes, and sexes, are subject to exactly -the same laws of arrangement as regularly-formed leaves.”[257] - -The idea that the leaf is the principal organ of the plant, and that -from it all the other organs are probably developed, is worthy the -genius of the great German poet. - -Every leaf, a mystery in itself, is an individual gifted with peculiar -powers; they congregate in families, and each one ministers to the -formation of the branch on - -which it hangs, and to the main trunk of the tree of which it is a -member. The tree represents a world, every part exhibiting a mutual -dependence. - - “The one red leaf, the last of its clan, - That dances as often as dance it can; - Hanging so light and hanging so high, - On the topmost twig that looks up at the sky,” - -is influenced by, and influences, the lowest root which pierces -the humid soil. Like whispering voices, the trembling leaves sing -rejoicingly in the breeze and summer sunshine, and they tremble alike -with agony when the equinoctial gale rends them from the parent stalk. -The influences which pervade the whole, making up the sum of vital -force, are disturbed by every movement throughout the system; a wound -on a leaf is known to disturb the whole, and an injury inflicted on the -trunk interferes with the processes which are the functions of every -individual leaf.[258] - -The consideration of the physical circumstances necessary to -germination and vegetable growth, brings us acquainted with many -remarkable facts. At a temperature below the freezing point, seeds will -not germinate; at the boiling point of water, a chemical change is -produced in the grain, and its power of germinating is destroyed. Heat, -therefore, is necessary to the development of the embryo, but its power -must only be exerted within certain prescribed limits: these limits are -only constant for the same class of seeds, they vary with almost every -plant. This is apparent to every one, in the different periods required -for germination by the seeds of dissimilar vegetables. - -The seed is placed in the soil; shade is always--absolute darkness -sometimes--necessary for the success of the germinating process. We -have seen that the first operation of nature is purely a chemical one, -but this manifestation of affinity is due to an exertion of force, -which is directly dependent upon solar power. The seed is buried in the -soil, when the genial showers of spring, and the increasing temperature -of the earth, furnish the required conditions for this chemistry of -life, and the plant eventually springs into sunshine. Thus we obtain -evidence that even through some depth of soil the solar power, whatever -it may be, is efficient, and that under its excitement the first spring -of life, in the germ, is effected. - -The cotyledons and the plumule being formed, the plant undergoes a -remarkable change. The seed, like an animal, absorbed oxygen and -exhaled carbonic acid; the first leaves secrete carbon from carbonic -acid inspired, and send forth, as useless to the plant, an excess of -oxygen gas. - -This power of decomposing carbonic acid is a vital function which -belongs to the leaves and bark. It has been stated, on the authority -of Liebig, that during the night the plant acts only as a mere bundle -of fibres,--that it allows of the circulation of carbonic acid and -its evaporation, unchanged. In his eagerness to support his chemical -hypothesis of respiration, the able chemist neglected to inquire -if this was absolutely correct. The healthy plant never ceases to -decompose carbonic acid during one moment of its existence; but during -the night, when the excitement of light is removed, and the plant -reposes, its vital powers are at their minimum of action, and a much -less quantity is decomposed than when a stimulating sun, by the action -of its rays, is compelling the exertion of every vital function. - -During this process, we have another example of natural organic -chemistry. The four inorganic elements of which the vegetable kingdom -is composed--oxygen, hydrogen, nitrogen, and carbon--are absorbed as -air or moisture by the leaves and through the roots, and the great -phenomenon of vegetable life is the conversion of these to an organic -condition. Sugar and gum are constantly produced, and from these, by -combination with atmospheric nitrogen, a proteine compound is formed, -which is an essential element in the progress of development.[259] - -Plants growing in the light are beautifully green, the intensity of -colouring increasing with the brilliancy of the light. Those which are -grown in the dark are etiolated, their tissues are weak and succulent, -their leaves of a pale yellow. It is, therefore, evident that the -formation of this chlorophylle--as the green colouring matter of leaves -is called--results from some action determined by the sun’s rays. - -Chlorophylle is a carbonaceous compound formed in the leaves, serving, -it would appear, many purposes in the process of assimilation. In the -dark the plant still requires carbon for its further development, -and growing slowly, it removes it from the leaves, decomposing the -chlorophylle, and supports its weak existence by preying on parts of -its own structure, until at length, this being exhausted, it actually -perishes of starvation. - -Plants always turn towards the light: the guiding power we know not, -but the evidence of some impulsive or attracting force is strong; and -the purpose for which they are constituted to obey it, is proved to be -the dependence of vegetable existence upon luminous power. - -Light is not, however, alone sufficient to perfect the plant: another -agent is required to aid in the production of flowers and fruits, -and this power is proved to be heat--and heat, perhaps, in some -peculiar condition. Having reached that point of development when -the reproductive functions are, by another change in the chemical -operations going on within the vegetable structure, to be called forth, -it has been found that the heat rays become in a remarkable manner -effective. It has also been observed that plants bend from the red, -or calorific rays, instead of towards them, as they are found to do -to every other ray of the spectrum. From this we may argue that the -influence of these rays is to check the vegetation, and thus to ensure -the perfection of the reproductive processes. - -It has already been stated that we have the means of separating, to -a considerable extent, the three principles which we discover in the -sunbeam, from each other, by the use of absorbent media. - -By a peculiar yellow glass we cut off the chemical principle of the -sunbeam, and admit the passage of the _luminous rays_ only--LIGHT. - -By a cobalt blue glass we obstruct the _light_, but allow the chemical -agent to pass through freely, without, indeed, any loss--ACTINISM. - -By a glass coloured deep blood-red by oxide of gold we obstruct -the chemical principle and much of the light, but such a medium is -perfectly transparent to HEAT. - -Therefore, this gives us the means of experimenting with either of -these principles, and of examining the parts which they respectively -play in the work of organization. - -Some seeds being placed in the soil, in every respect in their natural -conditions, duly supplied with moisture, and a uniform and proper -temperature maintained, we place above the soil the three media -above named, and allow one portion to be exposed to all the ordinary -influences of the solar rays. - -The result will be, that the seeds under the blue glass will germinate -long before those which are exposed to the combined influences of the -sunshine: a few of the seeds will struggle into day under the red -glass, but the process of germination is entirely checked under the -yellow glass. Here we see that the chemical radiations have quickened -the chemical changes, and accelerated the process, under the red glass, -through which rays having some peculiar chemical action pass; the -germinating process, though checked, is not entirely stopped. Whereas, -it would appear that under the influences of light which has been -deprived of chemical power, this conversion of the starch into gum and -sugar, which appears to be necessary, is entirely prevented. - -If the experiment is continued, it will be found that under the -blue glass the plants grow rapidly, but weakly; and that instead of -producing leaves and wood they consist chiefly of stalk, upon which -will be seen here and there some abortive attempts to form leaves. -When the process of germination has terminated, if the young plant is -brought under the yellow glass, it grows most healthfully, and forms an -abundance of wood, the leaves having an unusually dark green colour, -from the formation of a large quantity of chlorophylle. Plants do not, -however, produce flowers with readiness under this medium; but if, at -the proper period, they are brought under the red glass, the flowering -and fruiting processes are most effectively completed.[260] - -These experiments, simple as they are, prove to us the importance of -light: the _luminous principle_ of the sunbeam is exciting the vital -powers of the plant to decompose carbonic acid and form wood; and the -calorific agent, possibly under those modifications which have already -been noticed as belonging to the parathermic rays, is essential to the -production of flower and fruit. - -Observations, which have been extended over many years, prove that -with the seasons these solar powers are, relatively to each other, -subject to an interesting change. In the spring, the actinic or -chemical power prevails, and during this period its agency is required -for the vitalization of the germ. As the summer comes on, the actinic -rays diminish, and those of light increase. Perhaps it would be more -strictly correct to say that the luminous intensity being increased, -the chemical power was retarded; the former expression implies a -variation in quantity, which may not be correct. We see the necessity -for this, since luminous power is required for the secretion of -the carbon, with which the woody fibre is formed, and also for the -elaboration of the proximate principles of the plant. Autumn, the -season of fruit, is characterized by an increase of the heat rays, and -a diminution of the others: this change being necessary, as science now -teaches us, for the due production of flower and fruit. - -The calorific rays of the solar beam, to which the autumnal phenomena -of vegetation appear particularly to belong, are of a peculiar -character. They have been called, the Parathermic rays, and exhibit a -curious compound nature. To these rays we may refer the ripening of -fruit and grain, and the browning of the leaf before its fall. May not -the rise of the sap in spring be traced to the excitement of either -light or actinism, and its recession, in the autumn, to that power -from which the plant is found to bend, and which appears to be their -modified form of heat? - -There can be no doubt that the varieties of climate and the -peculiarities of countries, as it regards their animal and vegetable -productions, are dependent on the same causes. The distribution of -species has been referred by some to specific centres of creation -around which the plants and animals have spread, without reference to -physical conditions. Although centres of creation may be admitted, -these centres themselves have been determined by the physical -fitness of each centre to the conditions of the creation, and in -like manner the migration of tribes is solely due to these physical -forces we have been considering. In every zone we find that vegetable -organization is peculiarly fitted for the considerations by which it -is surrounded. Under the equator we have the spice-bearing trees, the -nutmeg, the clove, the cinnamon, and the pepper-tree; there we have -also the odoriferous sandal, the ebony, the banyan, and the teak: we -have frankincense, and myrrh, and other incense-bearing plants; the -coffee-tree, the tea-plant, and the tamarind. - -A little further north we have the apricot, the citron, the peach, -and the walnut. In Spain, Sicily, and Italy, we have the orange and -lemon-tree blooming rich with perfume, and the pomegranate and the -myrtle growing wild upon the rocks. Beyond the Alps the vegetation -again changes; instead of the cypress, the chesnut, and the cork-tree, -which prevail to the south of them, we have the hardier oak, the beech, -and the elm. Still further north, we have the Scotch and spruce fir -and larch. On the northern shores of the Baltic, and in that line of -latitude, the hazel alone appears; and beyond this the hoary alder, -the sycamore, and the mountain ash. Within the Arctic circle we find -the mezereum, the water-lilies, and the globe-flowers; and, when the -weakness of the solar radiations becomes too great even for these, -the reindeer moss still lends an aspect of gladness to the otherwise -sterile soil. - -The cultivation of vegetables depends on the temperature of the clime. -The vine flourishes where the mean annual temperature ranges between -50° and 73°, and it is only cultivated profitably within 30° S. and 50° -N. of the equator. To the same limits is confined the cultivation of -maize and of olives. Cotton is grown profitably up to latitude 46° in -the Old World, but only up to 40° in the New. We have evidence derived -from photographic phenomena, that the constitution of the solar rays -varies with the latitude. The effects of the sun’s rays in France and -England in producing chemical change are infinitely more decided than, -with far greater splendour of light, they are found to be in the lands -under or near the equator. Indeed, the remarks made on the variations -in the character of the sunbeam with the changing seasons, may apply -equally to the variations in latitude. - -Fungals are among the lowest forms of vegetation, but in these we have -peculiarities which appear to link them with the animal kingdom. Marcet -found that mushrooms absorbed oxygen, and disengaged carbonic acid. -In all probability this is only a chemical phenomenon of a precisely -similar character to that which we know takes place with decaying -wood. In the conversion of wood into _humus_, oxygen is absorbed, and -combining with the carbon, it is evolved as carbonic acid. Of course we -have the peculiar condition of vitality to modify the effect, and we -have, too, in this class of plants, the existence of a larger quantity -of nitrogen than is found in any other vegetating substance. - -These few sketches of remarkable phenomena connected with vegetation -are intended to show merely the operations of the physical powers of -the universe, so far as we know them, upon these particular forms -of organization. During the process of germination, electricity is, -according to Pouillet, evolved; and again, in ripening fruits, there -appears to be some evidence of electrical currents. Vegetables are, -however, in the growing state, such good conductors of electricity, -that it is not, according to the laws of this force, possible that -they should accumulate it; so that the luminous phenomena stated to -have been observed cannot be due to this agency. We know, however, -that under every condition of change, whether induced by chemical or -calorific action, electricity is set in motion; and we have reasons -for believing that the excitation of light will also give rise to -electrical circulation. - -The question, whether plants possess sensation, whether they have -any disposition of parts at all analogous to the nervous system of -animals, has been often put forward, but as yet the answers have been -unsatisfactory. The point is one well worthy all the attention of -the vegetable physiologist; but regarding plants as the link between -the animal and the mineral kingdom,--looking upon phyto-chemistry, -as exhibited by them, as the means employed to produce those more -complex organizations which exist in animals,--we necessarily consider -plants as mere natural machines for effecting organic arrangements, -and, as such, that they cannot possess any nervous sensibility. -Muscular contraction may be represented in many of their marvellous -arrangements; and any disturbance produced by natural or artificial -means would consequently effect a change in the operations of those -forces which combine to produce vegetable life. Indeed, the experiments -of Carlo Matteucci, already referred to, prove that an incision across -a leaf, the fracture of a branch, or the mere bruising of any part of -the plant, interferes with the exercise of that power which, under the -operation of luminous agency, decomposes carbonic acid, and effects the -assimilation of the other elements. - -To recapitulate. A plant is an organized creation; it is so in virtue -of certain strange phyto-chemical operations, which are rendered active -by the solar influences involved in the great phenomena of light, and -by the excitation of caloric force mid electrical circulation. It is -a striking exemplification of the united action of certain empyreal -powers, which give rise to the combination, of inorganic principles -under such forms that they become capable of obeying the mysterious -impulses of life. - -The poet has imaged the agency of external powers in various shapes -of spiritualized beauty. From the goddess Flora, and her attendant -nymphs, to the romantic enchantress who called up flowers by the light -touch of her wand, we have, in all these creations, foreshadowings of -the discovery of those powers which science has shown are essential -to vegetable life. A power from without influences the plant; but the -animal is dependent upon a higher agency which is potent within him. - -The poet’s dream pleases the imaginative mind; and, associating in our -ideas all that is graceful and loveable in the female form, with that -diviner feeling which impresses the soul with the sense of some unseen -spirituality, we perceive in the goddess, the enchantress, or the -sylph, pure idealizations of the physical powers. The spirit floating -over these forms of beauty, and adorning them with all the richness -of colour--painting the rose, and giving perfume to the violet--is, -in the poet’s mind, one which ascends to nearly the highest point of -etherealization, and which becomes, indeed, to him a spirit of light; -they ride upon the zephyrs, and they float, in all the luxury of an -empyreal enjoyment, down to the earth upon a sunbeam. Such is the -work of the imagination. What is the result of the search of plodding -science after truth? The sunbeam has been torn into rays, and every ray -tasked to tell of its ministry. - -Nature has answered to some of the interrogations; and, passing over -all the earth, echoed from plant to plant, we have one universal cry -proclaiming that every function of vegetable life is due to the spirits -of the sun. - -The mighty Adansonia of Senegal, hoary with the mosses of five -thousand years,--the Pohon upas in their deadly valleys,--the climbing -lianas of the Guiana forests,--the contorted serpent-cactus on the -burning hills,--the oaks, which spread their branches in our tempered -climes,--the glorious flowers of the inter-tropical regions, and -those which gem our virent plains,--the reindeer lichen of northern -lands, and the confervæ of the silent pool,--the greatest and humblest -creations of the vegetable world,--all proclaim their direct -dependence upon the mysterious forces which are bound together in the -silver thread of Light. - -These undulations, pulsations too refined for mortal ears, which -quicken and guide these wonderful organisms, may be indeed regarded -as sphered music for ever repeating the Divine command, “_Let there -be Light_,” by the creation of which, a dark and dreary chaos was -moulded into a star of beauty, capable of radiating brightness to other -space-wandering worlds. - - -FOOTNOTES: - -[248] Percy Bysshe Shelley. - -[249] _Experiments on the production of dephlogisticated air from water -with various substances_: by Lieut.-General Sir Benjamin, Count of -Rumford; Phil. Trans., vol. lxxvii. p. 84. - -[250] _Experiments upon Vegetables, discovering their great power of -purifying the common air in the Sunshine, and of injuring it in the -Shade and at Night; to which is joined, A new method of examining the -accurate degrees of Salubrity of the Atmosphere_, by John Ingenhousz, -Councillor of the Court, and Body Physician to their Imperial and Royal -Majesties, F.R.S., &c. London: printed for P. Elmsley, in the Strand, -and H. Payne, Pall Mall, 1779. - -[251] _The Kingdoms of Nature, their life and affinity_: by Dr. C. G. -Carus; Scientific Memoirs, vol. i. p. 223. - -[252] In _Biologie_, by G. R. Treviranus, vol. ii. p. 302, the -following passage occurs:--“If we expose spring water to the sun in -open or even closed transparent vessels, after a few days bubbles -rise from the bottom, or from the sides of the vessel, and a green -crust is formed at the same time. Upon observing this crust through -a microscope, we discover a mass of green particles, generally of a -round or oval form, very minute, and overlaid with a transparent mucous -covering, some of them moving freely, whilst others, perfectly similar -to these, remain motionless and attached to the sides of the vessel. -This motion is sometimes greater than at others. The animalcules -frequently lie as if torpid, but soon recover their former activity.” - -[253] _On the Structure of the Vegetable Cell_: by Mohl.--Scientific -Memoirs, vol. iv. p. 113. _Outlines of Structural and Physical Botany_: -by Henfrey. - -[254] Dr. Carus, in the memoir already quoted, says:--“But since, in -the organization of the earth, light and air, as constituting a second -integrant part, stand opposed to gravitation, and since the plant -bears a relation, not only to gravitation, but to light also, when its -formation is complete it will necessarily present a second anatomical -system, namely, that of the spiral vessels, which have been very justly -considered, of late, as the organs that perform in plants the functions -of nerves.” - -[255] Mr. Crosse’s Experiments in the Journal of the London Electrical -Society, and Mr. Weekes in the Electrical Magazine, and a communication -appended to _Explanations: a Sequel to the Vestiges of the Natural -History of Creation_. - -[256] _Die Metamorphose der Pflanzen_: Goethe, sect. 78. - -[257] Lindley’s _Elements of Botany_. - -[258] See the very curious experiments of C. Matteucci. Traduit et -extrait du “_Cimento_.”--Archives des Sciences Physiques et Naturelles; -_Quelques Expériences sur la Respiration des Plantes_. Nov. 1846. - -[259] Consult _Rural Economy_, by J. B. Boussingault; _The Chemical and -Physiological Balance of Organic Nature_, by Dumas and Boussingault; -and _Agricultural Chemistry_, by Liebig. - -[260] The practical value of the discovery now described, will be best -understood from the following letter from Mr. Lawson, of Edinburgh:-- - -Edinburgh, 1, George the Fourth’s Bridge, Sept. 8, 1853. - -MY DEAR SIR,--I am favoured with yours of the 5th, relative to my -practical experience in the effect of the chemical agency of coloured -media on the germination of seeds and the growth of plants. - -I must first explain that it is our practice to test the germinating -powers of all seeds which come into our warehouses before we send -them out for sale; and, of course, it is an object to discover, with -as little delay as possible, the extent that the vital principle is -active, as the value comes to be depreciated in the ratio it is found -to be dormant. For instance, if we sow 100 seeds of any sort, and the -whole germinate, the seed will be the highest current value; but if -only 90 germinate, its value is 10 per cent. less; if 80, then its -value falls 20 per cent. - -I merely give this detail to show the practical value of this test, and -the influence it exerts on the fluctuation of prices. - -Our usual plan formerly was to sow the seeds to be tested in a hot-bed -or frame, and then watch the progress and note the results. It was -usually from eight to fourteen days before we were in a condition to -decide on the commercial value of the seed under trial. - -My attention was, however, directed to your excellent work, “On the -Physical Phenomena of Nature,” about five years ago, and I resolved to -put your theory to a practical test. I accordingly had a case made, -the sides of which were formed of glass coloured blue or indigo, which -case I attached to a small gas stove for engendering heat; in the case -shelves were fixed in the inside, on which were placed small pots -wherein the seeds to be tested were sown. - -The results were all that could be looked for: the seeds freely -germinated in from two to five days only, instead of from eight to -fourteen days as before. - -I have not carried our experiments beyond the germination of seeds, so -that I cannot afford practical information as to the effect of other -rays on the after culture of plants. - -I have, however, made some trials with the yellow ray in preventing the -germination of seeds, which have been successful; and I have always -found the violet ray prejudicial to the growth of the plant after -germination.--I remain, my dear Sir, - -Very faithfully yours, CHARLES LAWSON. - - - - -CHAPTER XV. - -PHENOMENA OF ANIMAL LIFE. - - Distinction between the Kingdoms of Nature--Progress of Animal - Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent - Animals--Annelidans--Myriapoda--Animal - Metamorphoses--Fishes--Birds--Mammalia--Nervous System--Animal - Electricity--Chemical Influences--Influence of Light on Animal - Life--Animal Heat--Mechanical Action--Nervous Excitement--Man and - the Animal Races, &c. - - -“A stone grows; plants grow and live; animals grow, live, and feel.” -Such were the distinctions made by Linnæus, between the conditions -of the three kingdoms of nature. We cannot, however, but regard them -as in all respects illogical. The stone--a solid mass of unorganized -particles--enlarges, if placed in suitable conditions, by the accretion -of other similar particles around it; but it does not, according to any -meaning in which we use the word, _grow_. Plants and animals grow; and -they differ, probably, only in the phenomena of sensation. Yet, the -trembling mimosa, and several other plants, appear to possess as much -feeling as sponges and some of the lower classes of animals. By this -definition, however, of the celebrated Swedish naturalist, we have a -popular and simple expression of a great fact. - -As we have only to examine the question of the agency of the physical -forces upon animal life, we must necessarily confine our attention to -the more striking phenomena with which science has made us acquainted; -and, having briefly traced the apparent order in which the advance of -organization proceeded, we must direct our few concluding remarks to -the physico-physiological influences, which we must confess to know but -too imperfectly. - -We learn that, during the states of progress which geology, looking -into the arcana of time, has made us acquainted with, a great variety -of animal forms were brought into existence. They lived their periods. -The conditions of the surface of the earth, the sea, or the atmosphere, -were altered; and, no longer fitted for the enjoyments of the new life, -these races passed away, and others occupied their places, which, in -turn, went through all the stages of growth, maturity, and decay; -until at length, the earth being constituted for the abode of the -highest order of animals, they were called into existence; and man, -the intellectual monarch of the world, was placed supreme amongst them -all. Types of nearly all those forms of life which are found in the -fossil state are now in existence; and if we examine the geographical -distribution of animals--the zones of elevation over the surface of -the earth, and the zones of depth in the ocean,--we shall find, now -existing, animal creations strikingly analogous to the primitive forms -and conditions of the earth’s inhabitants. From the depths of the ocean -we may even now study--as that most indefatigable naturalist, Professor -Edward Forbes, has done--the varying states of organization under the -circumstances of imperfect light and varying temperature.[261] - -The gradual advance of animal life in the ascending strata has led -to many speculations, ingenious and refined, on the progressive -development of animals. That the changes of the inorganic world have -impressed new conditions on the organic structures of animals, to meet -the necessities of their being, must be admitted. Comparative anatomy -has demonstrated that such supposed differences really existed between -the creatures of secondary formations--those of the tertiary and the -present periods. It has been imagined, but upon debatable foundations, -that the atmosphere, during the secondary periods, was highly charged -with carbonic acid; and, consequently, that though beneficial to the -growth of plants, and peculiarly fitted for the conditions required -by those which the fossil flora makes us acquainted with, it was not -adapted to support any animals above the slow-breathing, cold-blooded -fishes and reptiles. Under the action of the super-luxuriant vegetation -of these periods, this carbonic acid is supposed to have been removed, -an addition of oxygen furnished; and thus, consequently, the earth -gradually fitted for the abode of warm-blooded and quick-breathing -creatures. We do, indeed, find a very marked line between the fossil -remains of the lias formations which enclose the saurians, and the -wealden, in which birds make their appearance more numerously than in -any previous formation. - -Founded upon these facts, speculations have been put forth on the -gradual development of animals from the lowest up to the highest -orders. Between the polype and man a continuous series has been -imagined, every link of the chain being traced into connection with -the one immediately succeeding it; and, through all the divisions, -zoophytes, fishes, amphibia, reptiles, birds, and mammalia are seen, -according to this hypothesis, to be derived by gradual advancement from -the preceding orders. The first having given rise to amphibia,--the -amphibion gives birth to the reptile,--the reptile advances to -the bird,--and from this class is developed the mammal. A slight -investigation will convince us that this view has no foundation. -Although a certain relationship may be found between some of the -members of one class, and those of the other immediately joining it, -yet this is equally discovered to exist towards classes more remote -from each other; and in no one instance can we detect anything like -the passage of an animal of one class into an animal of another. Until -this is done, we cannot but regard the forms of animal life as distinct -creations, each one fitted for its state of being, springing from the -command of the great First Cause.[262] - -But it is time to quit these speculative questions, and proceed to the -examination of the general conditions of animal life at the present -time. - -Lowest in the scale of animals, and scarcely distinguishable from a -vegetable, we find the sponge, attached to and passing its life upon -a rock, exhibiting, indeed, less signs of feeling than many of the -vegetable tribes. The chemical differences between vegetables and -sponges are, however, very decided; and we find in the tissues of the -sponge a large quantity of nitrogen, a true animal element, which -exists, but in smaller quantities, in vegetables. - -These creations, standing between vegetable and animal life, possess -the singular power of decomposing carbonic acid, as plants do; and the -water in which they live always contains an excess of free oxygen. - -The polypes are a remarkably curious class. “Fixed in large arborescent -masses to the rocks of tropical seas, or in our own climate attached -to shells or other submarine substances, they throw but their -ramifications in a thousand beautiful and plant-like forms; or, -incrusting the rocks at the bottom of the ocean with calcareous earth, -separated from the water which bathes them, they silently build up -reefs and shoals, justly dreaded by the navigator; and sometimes giving -origin, as they rise to the surface of the sea, to islands, which -the lapse of ages clothes with luxuriant verdure, and peoples with -appropriate inhabitants.”[263] - -Most of the polypes are fixed and stationary; but the hydra and some -others have the power of changing their positions, which they do in -search of the light of the sun. They do not appear to have organs of -sight requiring light; but still they delight in the solar influences. -The most extraordinary fact connected with the hydra is its being -multiplied by division. If an incision be made in the side of a hydra, -a young polype soon developes itself; and if one of these creatures be -divided, it quickly restores the lost portion of its structure. The -varieties of the polypes are exceedingly numerous, and many of them are -in the highest degree curious, and often very beautiful. The actiniæ, -like flowers, appear to grow from the rocks, unfolding their tentacula -to the light; and, in the excitement due to their eagerness for prey, -they exhibit a beautiful play of colours and most interesting forms. -Microscopic zoophytes of the most curious shapes are found,--all of -which attest, under examination, the perfection of all created things. - -Infusoria and animalcula,--animals, many of them, appearing under the -microscope as little more than a transparent jelly,--must be recognized -as the most simple of the forms of life. They exist in all waters in -uncountable myriads; and, minute creatures as they are, it has been -demonstrated that many of the great limestone hills are composed -entirely of their remains. - -The acalephæ, or the phosphorescent animals of the ocean, are no less -curious. From creatures of the most minute size, they extend to a -considerable magnitude, yet they appear to be little more than animated -masses of sea-water. If any one of these sea-jellies, or jelly-fishes -as they are often called (even the largest varieties of them), is cast -upon the shore, it is soon, by the influence of the sun, converted into -a mere fibre no thicker than a cobweb: an animal weighing seven or -eight pounds is very soon reduced to as many grains. There are numerous -kinds of these singular creatures, most of which are remarkable for -the powerful phosphorescent light they emit. The _beroes_ and the -_pulmonigrade_ shine with an intense white light many feet below the -surface, whilst the _Cestum Veneris_, or girdle of Venus, gliding -rapidly along, presents, on the edge of the wave, an undulating riband -of flame of considerable length. There can be no doubt that this arises -from the emission of phosphorescent matter of an unknown kind from the -bodies of these animals. - -The microscope has made us familiar with the mysteries of a minute -creation which we should not otherwise have comprehended. These -creatures are found inhabiting the waters and the land, and they exist -in the intestinal structure of plants and animals, preying upon the -nutritive juices which pass through their systems. Although these -beings are so exceedingly small that even the most practised observer -cannot detect them with the naked eye, they are proved, by careful -examination under the microscope, to be in many cases elaborately -organized. Ehrenberg has discovered in them filamentary nerves and -nervous masses, and even vessels appropriated to the circulation -of fluids, showing that they belong really to a high condition of -existence. - -Passing over many links in that curious chain which appears to bind -the animal kingdom into a complete whole, we come to the articulata of -Cuvier--the homogangliata of Owen. - -All those creatures which we have been hitherto considering are too -imperfect in the construction of their simple organizations to maintain -a terrestrial existence; they are, therefore, confined to a watery -medium. In the articulata, we have evidences of higher attributes, -and indications of instincts developed in proportion to the increased -perfection of organization. Commencing with the annelidans, all of -which, except the earthworms, are inhabitants of the waters, we -proceed to the myriapoda, presenting a system intermediate in every -respect between that of worms and insects; we then find embraced in -the same order, the class insecta, which includes flies and beetles -of all kinds; and, as the fourth division of articulated beings, the -arachnidans or spiders; and, lastly, the marine tribe of crustaceans. - -The most remarkable phenomena connected with these animals are the -metamorphoses which they undergo. The female butterfly, for instance, -lays eggs, which, when hatched, produce caterpillars: these live in -this state for some time, feeding upon vegetables, and, after casting -their skins as they increase in size, at last assume an entirely -different state, and, dormant in their oblong case, they appear like -dead matter. This chrysalis, or pupa, is generally preserved from -injury by being embedded in the earth, from which, after a season, a -beautifully perfect insect escapes, and, floating on the breeze of -summer, enjoys its sunshine, and revels amidst its flowers. - -No less remarkable is the metamorphosis of the caducibranchiate -amphibia, passing through the true fish condition of the tadpole to the -perfect air-breathing and four-footed animal, the frog. - -A metamorphosis of the crustaceans, somewhat similar to that which -takes place in insects, has been of late years creating much discussion -amongst naturalists: but the question appears to be now settled by the -careful and long-continued observations of Mr. Thompson and Mr. R. C. -Couch. - -A wide line of demarcation marks the separation of the invertebrata -from the four great classes of vertebrate animals--fishes, reptiles, -birds, and mammalia. Every part of the globe,--the ocean and the inland -lake,--the wide and far-winding river, and the babbling stream,--the -mountain and the valley,--the forest with its depth of shade, and -the desert with its intensity of light,--the cold regions of the -frost-chained north, and the fervid clime within the tropics--presents -for our study innumerable animals, each fitted for the conditions to -which it is destined; and through the whole we find a gradual elevation -in the scale of intelligence, until at last, separated from all by -peculiar powers, we arrive at man himself. - -In each of these four classes the animals are furnished with a bony -skeleton, which is in the young animal little more than cartilage; -but, as growth increases, lime becomes deposited, and a sufficient -degree of hardness is thus produced to support the adult formation. -Some anatomists have endeavoured to show that even in the mechanical -structure of the bony fabrics of animals, we are enabled to trace a -gradual increase in the perfection of arrangement, from the fish until -the most perfect is found in man. Many of the mammalia, however, are -furnished with skeletons which really surpass that of man. These belong -to animals which depend for subsistence upon their muscular powers, and -with whom man is, in this particular, on no equality. What is the lord -of the creation, compared with the antelope for fleetness, or with the -elephant and many other animals for strength? - -As we ascend the scale of animal life we find a more perfectly -developed nervous system; and the relative size of the brain, compared -with that of the brute, is found progressively to increase, until it -arrives at the utmost perfection in man. On the system of nerves -depends sensation, and there can be no doubt that the more exalted the -order of intelligence displayed, the more exquisitely delicate is the -nervous system. Thus, in this world, refined genius must necessarily be -attended with a condition of sensibility which, too frequently, to the -possessor is a state of real disease. - -It must be evident to every reader that but very few of the striking -features of animal life have been mentioned in the rapid survey which -has been taken of the progress of animal organization. The subject -is so extensive that it would be quite impossible to embrace it -within any reasonable limits; and it furnishes matter so curious and -so instructive, that, having once entered on it, it would have been -difficult to have made any selection, and we must have devoted a volume -to the æsthetics of natural science. Passing it by, therefore, with the -mere outline which has been given, we must proceed to consider some of -the conditions of vitality. - -Bell has proved that one set of nerves is employed in conveying -sensation to the brain, and another set in transferring the desires of -the will to the muscles. By the separation of a main branch of one of -the nerves of sensation, although all the operations of life will still -proceed, the organ to which that nerve goes is dead to its particular -sense. In like manner, if one of the nerves of volition is divided, -the member will not obey the inclination of the brain. It is evident, -therefore, although many of the great phenomena of vital force are -dependent on the nervous system, and the paralysis of a member ensues -upon the separation or the disease of a nerve, that the nerves are but -the channels through which certain influences are carried. The _vis -vitæ_ or vital principle--for we are compelled by the imperfection of -our knowledge to associate under this one term the ultimate causes of -many of the phenomena of life--is a power which, although constantly -employed, has the capability of continually renewing itself by -some inexplicable connection existing between it and many external -influences. We know that certain conditions are necessary to the health -of animals. Diseased digestion, or any interruption in the circulation -of the blood, destroys the vital force, and death ensues. The processes -of digestion and of the circulation are perfectly understood, yet we -are no nearer the great secret of the living principle. - -Animals are dependent on several external agents for the support of -existence. The oxygen of the air is necessary for respiration. Animal -heat, as will be shown presently, is in a great measure dependent -upon it. The external heat is so regulated that animal existence is -comfortably supported. Electricity is without doubt an essential -element in the living processes; and, indeed, many physiologists have -been inclined to refer vital force to the development of electricity -by chemical action in the brain. This view has, however, no foundation -in experiment beyond that afforded by the appearance of electric -currents, when the brain is excited. This proves no more than that the -operations of mind develope physical power in the matter with which it -is mysteriously connected. - -The phenomena of the Torpedo and Gymnotus we have already noticed,[264] -and there are other creatures which certainly possess the power of -secreting and discharging electricity. Galvani’s experiments, and -those of Aldini, appear to show--and the more delicate researches of -Matteucci have satisfactorily determined--that currents of electricity -are always circulating in the animal frame;--that positive electricity -is constantly passing from the interior to the exterior of a muscle. -Matteucci, by arranging a series of muscles, has formed an electric -pile of some energy.[265] These currents have been detected in man, in -pigeons, fowls, eels, and frogs. - -In the human body it is evident a large quantity of electricity -exists in a state of equilibrium. Du Bois Raymond has shown that we -may by mere muscular motion give rise to electric currents which can -be measured by the galvanometer. This, however, may be said of every -substance. It is perhaps more easily disturbed in the human system; -indeed, the manifestation of sparks from the hair and other parts of -the body by friction is not uncommon. Every chemical action, it has -been already shown, gives rise to electrical manifestations; and the -animal body is a laboratory, beautifully fitted with apparatus, in -which nearly every chemical process is going on. It has been proved -that acid and alkaline principles are constantly acting upon each -other through the tissues of the animal frame; and we have the curious -phenomena of endosmose and exosmose in constant effort, and catalysis -or _surface force_, operating in a mysterious manner.[266] - -With the refined physiological questions connected with the phenomena -of sensation we cannot deal, nor will any argument be adduced for or -against the hypothesis which would refer these phenomena to some -extraordinary development of electric force in the brain. The entire -subject appears to stand beyond the true limits of science, and every -attempt to pass it is invariably found to lead to a confused mysticism, -in which the real and the ideal are strangely confounded. Science stops -short of the phenomena of vital action. - -We cannot, however, but refer to the idea entertained by many that the -brain is an electric battery, and the nerves a system of conductors. -On this view Sir John Herschel remarks:--“If the brain be an electric -pile constantly in action, it may be conceived to discharge itself -at regular intervals, when the tension of the electricity reaches a -certain point, along the nerves which communicate with the heart, and -thus excite the pulsation of that organ.” Priestley, however, appears -to have been the first to promulgate this idea. - -Light is an essential element in producing the grand phenomenon of -life, though its action is ill understood. Where there is light, -there is life, and any deprivation of this principle is rapidly -followed by disease of the animal frame, and the destruction of the -mental faculties. We have proof of this in the squalor of those whose -necessities compel them to labour in places to which the blessings -of sunshine never penetrate, as in our coal-mines, where men having -everything necessary for health, except light, exhibit a singularly -unhealthy appearance. The state of fatuity and wretchedness to which -those individuals have been reduced who have been subjected for -years to incarceration in dark dungeons, may be referred to the same -deprivation. Again, in the peculiar aspect of those people who inhabit -different regions of the earth under varying influences of light, we -see evidence of the powerful effects of solar action. Other forces, as -yet undiscovered, may, in all probability do, exert decided influences -on the animal economy; but, although we recognize many effects which we -cannot refer to any known causes, we are perfectly unable to imagine -the sources from which they spring. - -It will be interesting now to examine the phenomena of animal heat, the -consideration of which naturally leads us to consider the digestive -system, the circulatory processes, and the effects of nervous -excitation. - -The theory, which attributes animal heat to the combination of the -carbon of the food taken into the stomach with the oxygen of the air -inspired through the lungs, has become a very favourite one. It must, -however, be remembered that it is by no means new. The doctrines of -Brown, known as the Brunonian system, and set forth in his _Elementa -Medicinæ_, are founded upon similar hasty generalizations. Although, -without doubt, true in a certain degree, it is not so to the extent -to which its advocates would have us believe. That the carbonaceous -matter received into the stomach, after having undergone the process -of digestion, enters into combination with the oxygen breathed through -the lungs or absorbed by the skin, and is given off from the body in -the form of carbonic acid, and that, during the combination, heat is -produced, by a process similar to that of ordinary combustion, is an -established fact; but the idea of referring animal heat entirely to -this chemical source, when there are other well-known causes producing -calorific effects, is an example of the errors into which an ingenious -mind may be led, when eagerly seeking to establish a favourite -hypothesis. - -Animal and vegetable diet, which is composed largely of carbon and -hydrogen, passes into the digestive system, and becomes converted into -the various matters required for the support of the animal structure. -The blood is the principal fluid employed in distributing over the -system the necessary elements of health and vigour, and for restoring -the waste of the body. This fluid, in passing through the lungs, -undergoes a very remarkable change, and not merely assumes a different -colour, but really acquires new properties, from its exposure to the -air with which the cells of these organs are filled. By a true chemical -process, the oxygen is separated from the air, that oxygen is made to -combine with the carbon and hydrogen, and carbonic acid and water are -formed. These are liberated and thrown off from the body either through -the lungs or by the skin. In the processes of life, as far as we are -enabled to trace them, we see actions going on which are referred to -certain causes which we _appear_ to explain. Thus, the combination of -the oxygen of the air with the carbon of the blood is truly designated -a case of chemical affinity; and we find that in endeavouring to -imitate the processes of nature in the laboratory, we are, to a certain -extent, successful. We can combine carbon and oxygen to produce -carbonic acid; and we know that the result of that combination is the -development of certain definite quantities of heat. Let us examine the -conditions of this chemical phenomenon, and we shall find that in the -natural and artificial processes,--for we must be allowed to make that -distinction,--there are analogous circumstances. If we place a piece of -pure carbon, a lump of charcoal or a diamond, in a vessel of air, or -even of pure oxygen gas, no change will take place in either of these -elements, and, however long they may be kept together, they will still -be found as carbon or diamond, and oxygen gas. If we apply heat to the -carbon until it becomes incandescent, it immediately begins to combine -with the oxygen gas,--it burns;--after a little time all the carbon has -disappeared, and we shall find, if the experiment has been properly -made, that a gas is left behind which is distinguished by properties -in every respect the reverse of those of oxygen, supporting neither -life nor combustion, whereas oxygen gives increased vigour to both. -We have now, indeed, carbonic acid gas formed by the union of the two -principles. - -A dead mass of animal matter may be placed in oxygen gas, and, unless -some peculiar conditions are in some way brought about, no change will -take place; but, if it were possible to apply the _spark of life_ to -it, as we light up the spark in the other case, or if, as that is -beyond the power of man, we substitute a living creature, a combination -between the carbon of the animal and the gas will immediately begin, -and carbonic acid will be formed by the waste of animal matter, as in -the other case it is by the destruction of the carbon; and, if there is -not a fresh supply given, the animal must die, from the exhaustion of -its fabric. Now, in both these cases, it is clear that, although this -chemical union is a proximate cause of heat, there must be existing -some power superior to it, as the ultimate cause thereof. - -The slow combustion (_eremacausis_) of vegetable matter, decomposing -under the influence of moisture and the air, does not present similar -conditions to those of the human body, although it has been insisted -upon to be in every respect analogous. That the results resemble each -other is true, but we must carefully distinguish between effects and -causes; and the results of chemical decomposition in inert matter -differ from those in the living organism. The vegetable matter has lost -the principle of organic life, and, that gone, the tendency of all -things being to be resolved into their most simple forms, a disunion of -the elements commences: oxygen, hydrogen, and carbon pass off either -in the gaseous state or as water, whilst some carbon is liberated in -a very finely-divided condition, and enters slowly into combination -with oxygen supplied by the water or the air. Hydrogenous compounds -are at the same time formed, and, under all these circumstances, as in -all other chemical phenomena, an alteration of temperature results. -Heat results from the chemical changes, and eventually true combustion -begins. - -The animal tissue may act in the same way as platina has already -been shown to act in producing combination between gases; but of this -we have no proof. We know that electricity is capable of producing -the required conditions, and we also learn, from the beautiful -researches of Faraday, that the quantity of electricity developed -during decomposition is exactly equal to that required to effect the -combination of the same elements. Thus it is quite clear that, during -the combination of the carbon of the blood with the oxygen of the air, -a large amount of electricity must become latent in the compound. The -source of this we know not: it may be derived from some secret spring -within the living structure, or it may be gathered from the matter -surrounding it. There is much in nervous excitation which appears like -electrical phenomena, and attempts have been frequently made to refer -sensation to the agency of electricity. But these are the dreams of the -ingenious, for which there is but little waking reality. - -Every mechanical movement of the body occasions the development of -heat; every exertion of the muscles produces sensible warmth; and, -indeed, it can be shown by experiment that every expansion of muscular -fibre is attended with the escape of caloric, and its contraction -with the absorption of it. There are few operations of the mind which -do not excite the latent caloric of the body, and frequently we find -it manifested in a very remarkable manner by a suddenly-awakened -feeling. The poet, in the pleasure of creation, glows with the ardour -of his mind, and the blush of the innocent is but the exhibition -of the phenomenon under some nervous excitation, produced by a -spirit-disturbing thought. Thus we see that the processes of digestion -and respiration are not the only sources of animal heat, but that many -others exist to which much of the natural temperature of the body must -be referred. - -So much that is mysterious belongs to the phenomena of life, that -superstition has had a wide scope for the exercise of its influence; -and through all ages a powerful party of mankind have imagined that -the spirit of human curiosity must be checked before it advances to -remove the veil from any physiological causes. Hence it is that even at -the present day so much that stands between what, in our ignorance, we -call the real and the supernatural, remains uninvestigated. Even those -men whose minds are sceptical upon any development of the truths of -great natural phenomena,--who, at all events, will have proof before -they admit the evidence, are ready to give credit to the grossest -absurdities which may be palmed upon them by ingenious charlatans, -where the subject is man and his relations to the spiritual world. - -Man, and the races of animals by which he is surrounded, present a -very striking group, consider them in whatever light we please. The -gradual improvement of organic form, and the consequent increase of -sensibility, and eventually the development of reason, are the grandest -feature of animated creation. - -The conditions as to number even of the various classes are not the -least remarkable phenomena of life. In the lowest orders of animals, -creatures of imperfect organization,--consequently those to whom the -conditions of pain must be nearly unknown,--increase by countless -myriads. Of the infusoria and other beings, entire mountains have -been formed, although microscopes of the highest powers are required -to detect an individual. Higher in the scale, even among insects, the -same remarkable conditions of increase are observed. Some silkworms lay -from 1,000 to 2,000 eggs; the wasp deposits 3,000; the ant from 4,000 -to 5,000. The queen bee lays between 5,000 and 6,000 eggs according to -Burmeister; but Kirby and Spence state that in one season the number -may amount to 40,000 or 50,000. But, above all, the white ant (_Termes -fatalis_) produces 86,400 eggs each day, which, continuing for a -lunar month, gives the astonishing number of 2,419,200, a number far -exceeding that produced by any known animal. - -These may appear like the statements in which a fictionist might -indulge, but they are the sober truths discovered by the most -pains-taking and cautious observers. And it is necessary that such -conditions should prevail. These insects, and all the lower tribes of -the animal kingdom, furnish food for the more elevated races. Thousands -are born in an hour, and millions upon millions perish in a day. For -the support of organic life, like matter is required; and we find that -the creatures who are destined to become the prey of others are so -constituted that they pass from life with a perfect unconsciousness of -suffering. As the animal creation advances in size and strength, their -increase becomes limited; and thus they are prevented from maintaining -by numbers that dominion over the world which they would be enabled -from their powers to do, were their bands more numerous than we now -find them. - -The comparative strength, too, of the insect tribes has ever been a -subject of wonder and of admiration to the naturalist. The strength of -these minute creatures is enormous; their muscular power, in relation -to their size, far exceeds that of any other animal. The grasshopper -will spring two hundred times the length of its own body. The -dragonfly, by its strength of wing, will sustain itself in the air for -a long summer day with unabated speed. The house-fly makes six hundred -strokes with its wings, which will carry it five feet, every second. -The stag-beetle, were it the size of the elephant, would be able to -tear up the largest mountains. - -Such are the wonders of the natural world; from the zoophyte, growing -like a flowering plant[267] upon an axis filled with living pith--a -small remove from the conditions of vegetable life, upwards through the -myriads of breathing things--to man, we see the dependence of all upon -these physical powers which we have been considering. - -To trace the effects of those great causes through all their mysterious -phases is the work of inductive science; and the truths discovered tend -to fit us for the enjoyment of the eternal state of high intelligence -to which every human soul aspires. - -That which the ignorant man calls the supernatural, the philosopher -classes amongst natural phenomena. The ideal of the credulous man -becomes the real to him who will bend his mind to the task of inquiry. -Therefore to attempt to advance our knowledge of the unknown, to add -to the stores of truth, is an employment worthy the high destiny of -the human race. Remembering that the revelations of natural science -cannot in any way injure the revelation of eternal truth, but, on -the contrary, aid to establish in the minds of the doubting a firm -conviction of its Divine origin and of man’s high position, we need -never fear that we are proceeding too far with any inquiry, so long as -we are cautious to examine the conditions of our own minds, that they -be not made the dupe of the senses. - -In the fairies of the hills and valleys, in the gnomes of the caverns, -in the spirits of the elements, we have the attempts of the mind, when -the world was young, to give form to the dim outshadowings of something -which was then felt to be hidden behind external nature. - -In the Oread, the Dryad, and the Nereid, we have, in like manner, an -embodiment of powers which the poet-philosopher saw in his visions -presiding over the mountain, the forest, and the ocean. Content with -these, invested as they were with poetic beauty, man for ages held -them most religiously sacred; but the progress of natural science -has destroyed this class of creations. “Great Pan is dead,” but the -mountains are not voiceless; they speak in a more convincing tone; and, -instead of the ear catching the dying echo of an obscure truth, it is -gladdened with the full, clear note of nature in the sweetest voice -proclaiming secrets which were unknown to the dreams of superstition. - - -FOOTNOTES: - -[261] _Reports of the Fauna of the Ægean_: by Professor -Forbes.--Reports of the British Association. _On the Physical -Conditions affecting the Distribution of Life in the Sea and the -Atmosphere, &c._: by Dr. Williams. Swansea. - -[262] _The Vestiges of the Natural History of Creation._ - -[263] _General Outline of the Animal Kingdom_: by Professor Thomas -Rymer Jones, F.Z.S. - -[264] In addition to the memoirs already referred to, Note p. 211, -see Carlisle, _On the battery of the Torpedo, governed by a voluntary -muscle_.--Phil. Trans., vol. xcv. p. 11. Todd, _Experiments on the -Torpedo of the Cape of Good Hope_.--Ibid., vol. cvi. p. 120. Todd, -_Experiments on the Torpedo Electricus at La Rochelle_.--Ibid., vol. -cvii. p. 32. - -[265] For a concise account of these experiments see _Elements of -Natural Philosophy_: by Golding Bird, A.M., M.D., &c. 3rd Edition, -chap, xx p. 336. In this work all the most recent researches are given, -and the authorities referred to; see also Matteucci’s interesting -papers already quoted. - -[266] _On the laws according to which the mixing of fluids, and their -penetration into permeable substances, occurs, with special reference -to the processes in the Human and Animal Organism_, by Julius Vogel, of -Giessen: translated for the Cavendish Society. Liebig, _On the Motion -of the Juices in the Animal Body_. - -[267] _A General Outline of the Animal Kingdom_: by Thomas Rymer Jones, -p. 54, et seq. - - - - -CHAPTER XVI. - -GENERAL CONCLUSIONS. - - The Changes produced on Physical Phenomena by the Movement of - the Solar System considered--Exertion of the Physical Forces - through the Celestial Spaces--The Balance of Powers--Varieties - of Matter--Extension of Matter--Theory of Nonentity--A Material - Creation an indisputable fact--Advantages of the Study of - Science--Conclusion. - - -We have examined terrestrial phenomena under many of the harmonious -conditions which, with our limited intelligence, we can reach by the -aid of science. From the first exhibition of force, in the cohesion -of two atoms, onward to the full development of organic form in the -highest order of animals, we have observed strange influences. We -have seen the solitary molecule invested with peculiar properties, -and regulated by mighty forces; we have learned that the modes of -motion given to this beautiful sphere produce curious changes in the -operation of these powers; and we may with safety infer that every atom -constituting this globe is held in wonderful suspension against every -atom of every star, in the celestial spaces, even to that bright orb in -the centre of the Pleiades, around which the entire system of created -worlds is supposed to roll. - -As we move around our own sun--in the limited period of 365 days, and -round our own axis in 24 hours--we experience transitions from heat to -cold, dependent upon our position in regard to that luminary and the -laws which regulate the reception and retention of certain physical -forces. May we not therefore conclude, without being charged with -making any violent deduction, that in the great revolution of our -system around the centre of space, we are undergoing gradual changes -which are essential to the great scheme of creation, though at present -incomprehensible to us? - -In our consideration of the influence of time on the structure of -the earth as we find it, we discovered that, in ages long past, the -vegetation of the tropics existed upon these northern parts of the -globe; and geological research has also proved that over the same lands -the cold of an arctic winter must have long prevailed--the immense -glaciers of that period having left the marks of their movements upon -the face of the existing rocks.[268] We know that during 3,000 years -no change of temperature has taken place in the European climate. -The children of Israel found the date and the vine flourishing in -Canaan; and they exist there still. Arago has shown that a trifling -alteration of temperature would have destroyed one or the other of -these fruit-bearing trees, since the vine will not ripen where the mean -temperature of the year is higher than 84°, or the date flourish where -it sinks below that degree. - -How immense, then, the duration of time since these changes must have -taken place! The 432,000 years of Oriental mythology is a period -scarcely commensurable with these effects; yet, to the creature of -three-score years, that period appears an eternity. The thirty-three -millions of geographical miles which our solar system traverses -annually, if multiplied by three thousand years, during which we know -no change has taken place, give us 99,000,000,000 as the distance -passed over in that period. How wide, then, must have been the journey -of the system in space to produce the alteration in the physical -powers, by which these changes have been effected! - -We have an example, and a striking one, of the variations which may -be produced in all the physical conditions of a world, in those -disturbances of Uranus which led to the discovery of Neptune. For -thirty years or more certain perturbations were observed in this -distant planet, the discovery of Sir William Herschel, and calculation -pointed to some still more remote mass of matter as the cause, which -has been verified by its actual discovery. But now Uranus is at -rest;--quietly that star progresses in its appointed orbit,--Neptune -can no longer, for the present, cause it to move with greater or less -rapidity--they are too remote to produce any sensible influence upon -each other. Consequently, for thirty years, it is evident, phenomena -must have occurred on the surface of Uranus, which can be no longer -repeated until these two planets again arrive at the same positions -in their respective paths which they have occupied since 1812. These -considerations assist us in our attempts to comprehend infinite time -and space; but the human mind fails to advance far in the great -sublimity. - -Through every inch of space we have evidence of the exercise of such -forces as we have been considering. Gravitation chains world to world, -and holds them all suspended from the mystic centre. Cohesion binds -every mass of matter into a sphere, while motion exerts a constant -power, which tends to alter the form of the mass. The earth’s form--a -flattened spheroid--the rings of Saturn and of Neptune are the -consequences of motion in antagonism to cohesion. Heat, radiating -from one planet to another, does its work in all, giving variety to -matter. Light seeks out every world--each trembling star tells of the -mystery of its presence. Where light and heat are, chemical action, -as an associated power, must be present; and electricity must do its -wondrous duties amongst them all. Modified by peculiar properties of -matter, they may not manifest themselves in phenomena like those of our -terrestrial nature; but the evidence of light is a sufficient proof of -the presence of its kindred elements; and it is difficult to imagine -all these powers in action without producing some form of organization. -In the rounded pebble which we gather from the sea-shore, in the medusa -floating bright with all the beauty of prismatic colour in the sun-lit -sea,--in the animal, mighty in his strength, roaming the labyrinthine -forests, or, great in intelligence, looking from this to the mysteries -of other worlds,--in all created things around us, we see direct -evidence of a beautiful adjustment of the balance of forces, and the -harmonious arrangement of properties. - -One atom is removed from a mass and its character is changed; one -force being rendered more active than another, and the body, under its -influence, ceases to be the same in condition. The regulation which -disposes the arrangements of matter on this earth, must exist through -the celestial spaces, and every planet bears the same relation to every -other glittering mass in heaven’s o’erarching canopy, as one atom -bears to another in the pebble, the medusa, the lion, or the man. An -indissoluble bond unites them all, and the grain of sand which lies -buried in the depth of one of our primary formations, holds, chained -to it by these all-pervading forces, the uncounted worlds which, like -luminous sand, are sprinkled by the hand of the Creator through the -universe. Thus we advance to a conception of the oneness of creation. - -The vigorous mind of that immortal bard who sang “of man’s first -disobedience,” never, in the highest rapture, the holiest trance of -poetic conception, dreamed of any natural truths so sublime as those -which science has revealed to us. - -The dependence of all the systems of worlds upon each other, every -dust composing each individual globe being “weighed in a balance,” the -adjustment of the powers by which every physical condition is ordered, -the disposition of matter in the mass of the earth, and the close -relation of the kingdoms of nature,--are all revelations of natural -truths, exalting the mind to the divine conception of the universe. - -There is a remarkable antagonism displayed in the operation of many -of these forces. Gravitation and cohesion act in opposition to the -repellent influences of caloric. Light and heat are often associated -in a very remarkable manner; but they are certainly in their radiant -states in antagonism to chemical action, whether produced by the direct -agency of actinic force, or through the intermediate excitement of -the electrical current.[269] And in relation to chemical force, as -manifested in organic combinations, we have the all-powerful operation -of LIFE preventing any exercise of its decomposing power.[270] As world -is balanced against world in the universe, so in the human fabric, in -the vegetable structure, in the crystallized gem, or in the rude rock, -force is weighed against force, and the balance hangs in tranquillity. -Let but a slight disturbance occasion a vibration of the beam, and -electricity shakes the stoutest heart with terror, at the might of its -devastating power.[271] Heat melts the hardest rocks, and the earth -trembles with volcanic strugglings; and actinic agency, being freed -from its chains, speedily spreads decay over the beautiful, and renders -the lovely repulsive. - -We know matter in an infinite variety of forms, from the most ponderous -metal to the lightest gas; and we have it within our power to render -the most solid bodies invisible in the condition of vapour. Is it not -easy, then, to understand that matter may exist equally attenuated -in relation to hydrogen, as that gas itself is, when compared with -the metal platinum? A doubt has been raised against this view, from -the difficulty of accounting for the passage of the physical elements -through solid masses of matter. If we, however, remember that the known -gases have the power of transpiration through matter in a remarkable -degree,[272] and that the passage of water through a sieve may be -prevented by heat, it will be at once apparent that the permeation of -any radiant body through fixed solid matter is entirely a question of -conditions. - -We can form no idea of the size of the ultimate atom; we cannot -comprehend the degree of etherealization to which matter may be -extended. Our atmosphere, we have seen, is only another condition of -the same elements which compose all the organized forms of matter -upon the earth, and, at the height reached by man, it is in a state -of extreme attenuation. What must be its condition at the distance -of forty miles from the earth? According to known laws, certain -phenomena of refraction have led us to set these bounds to the matter -constituting our globe: but it may exist in such a state of tenuity, -that no philosophical instrument constructed by human hands could -measure its refracting power; and who shall declare with certainty that -matter itself may not be as far extended as we suppose its influences -to be? - -“Hast thou perceived the breadth of the earth? declare if thou knowest -it all. - -“Knowest thou the ordinances of heaven? Canst thou set the dominion -thereof in the earth?” - -A cheerless philosophy, derived from the transcendentalism of the -German schools, by an unhappy metaphysical subtlety, and grafted -upon what professes to be a positive philosophy, but which is not -so, is spreading amongst us, and would teach us to regard all things -as the mere exhibition of properties, a manifestation of powers; it -believes not in a material creation. The grandeur of the earth, and -the beautiful forms adorning it, are not entities. Yonder exquisite -specimen of the skill of man, in which mind appears to shine through -the marble,--that distant mountain which divides the clouds as they are -driven by the winds across it,--those trees, amid whose branches the -birds make most melodious music,--this flower, so redolent of perfume, -so bright in colour, and so symmetric in form,--and that lovely being -who, a model of beauty and grace, walks the earth an impersonation -of love and charity blended, making, indeed, “a sunshine in a shady -place,” are not realities. Certain forces combine to produce effects, -all of which unite to deceive poor man into the belief that he is a -material being, and the inhabitant of a material world. There may be -ingenuity in the philosophy of this school; its metaphysics may be of -a high order; but it evidently advances from the real to the ideal -with such rapidity, that every argument is based on an assumption -without a proof; every assumption being merely a type of the philosophy -itself,--a baseless fabric, a transcendental vision. - -A material creation surrounds us. This earth, all that it contains, and -the immense hosts of stellar worlds, are absolute entities, surrounded -with, and interpenetrated by, certain exhibitions of creative -intelligence, which perform, according to fixed laws, the mighty -labours upon which depend the infinite and eternal mutations of matter. -The origin of a grain of dust is hidden from our finite comprehensions; -but its existence should be a source of hope, that those minds which -are allowed the privilege of tracing out its marvellous properties,--of -examining the empyreal principles upon which its condition, as a grain -of dust, depends,--and even of reducing these giant elements to do our -human bidding,--may, after a period of probation, be admitted to the -enjoyment of that infinite power to which the great secrets of creation -will be unveiled. - -Every motion which the accurate search of the experimentalist has -traced, every principle or power which the physicist has discovered, -every combination which the chemist has detected, every form which the -naturalist has recorded, involves reflections of an exalting character, -which constitute the elements of the highest poetry. The philosophy of -physical science is a grand epic, the record of natural science a great -didactic poem. - -To study science for its useful applications merely, is to limit its -advantages to purely sensual ends. To pursue science for the sake of -the truths it may reveal, is an endeavour to advance the elements -of human happiness through the intelligence of the race. To avail -ourselves of facts for the improvement of art and manufactures, is -the duty of every nation moving in the advance of civilization. But -to draw from the great truths of science intelligible inferences and -masterly deductions, and from these to advance to new and beautiful -abstractions, is a mental exercise which tends to the refinement and -elevation of every human feeling. - -The mind thus exercised during the mid-day of life, will find in the -twilight of age a divine serenity; and, charmed by the music of nature, -which, like a vesper hymn poured forth from pious souls, proclaims -in devotion’s purest strain the departure of day, he will sink into -the repose of that mysterious night which awaits us all, tranquil in -the happy consciousness that the sun of truth will rise in unclouded -brilliancy, and place him in the enjoyment of that intellectual light, -which has ever been among the holiest aspirations of the human race. - -The task of wielding the wand of science,--of standing a scientific -evocator within the charmed circle of its powers, is one which leads -the mind through nature up to nature’s God. - -Experiment and observation instruct us in the discovery of a -fact;--that fact connects itself with natural phenomena,--the ultimate -cause of which we learn from Divine revelation, and receive in full -belief,--but the proximate causes are reserved as trials of man’s -intelligence; and every natural truth, discovered by induction, -enables the contemplative mind to deduce those perfect laws which are -exemplifications of the fresh-springing and all enduring POETRY OF -SCIENCE. - - -FOOTNOTES: - -[268] “As to the polishing and grooving of hard rocks, it has lately -been ascertained that glaciers give rise to these effects when pushing -forward sand, pebbles, and rocky fragments, and causing them to grate -along the bottom. Nor can there be any doubt that icebergs, when they -run aground on the floor of the ocean, imprint similar marks upon -it.”--_Principles of Geology, or the modern changes of the Earth and -its Inhabitants considered as illustrative of Geology_: by Charles -Lyell, M.A., F.R.S. _Travels through the Alps of Savoy, and other parts -of the Pennine Chain, with Observations on the Phenomena of Glaciers_: -by James D. Forbes, F.R.S. - -[269] This may be readily proved by the following simple but -instructive experiment:--Take two pairs of watch-glasses; into one pair -put a solution of nitrate of silver, into the other a weak solution -of iodide of potassium; connect the silver solution of each pair with -the potash one by a film of cotton, and carry a platina wire from one -glass into the other. Place one series in sunshine, and the other -in a dark place. After a few hours it will be found that the little -galvanic arrangement in the dark will exhibit, around the platina -wire, a very pretty crystallization of metallic silver, but no such -change is observable in the other exposed to light. If a yellow glass -is interposed between the glass and the sunshine, the action proceeds -as when in the dark. This experiment is naturally suggestive of many -others, and it involves some most important considerations. - -[270] In cases of violent death it is often found the gastric juice -has, in a few hours, dissolved portions of the stomach.--Dr. Budd’s -Lecture before the College of Physicians. - -[271] Faraday’s _Experimental Researches_, vol. i.; from which a -quotation has already been made, showing the enormous quantity of -electricity which is latent in matter. - -[272] _On the Motion of Gases_: by Professor Graham, F.R.S.--Phil. -Trans., vol. cxxxvi. p. 573. - - - - -INDEX. - - - Absorption of heat by air, water, and earth, 74. - - ---- of light, 125. - - Acalephæ, or phosphorescent animals, 387. - - Actinism, 166. - - ---- producing chemical change, 174. - - ---- and light antagonistic, 177. - - ----, influence of, on plants, 372. - - Action of presence--_Catalysis_, 280. - - “Active principles” of Newton, 11. - - Adams on planet Neptune, 32. - - Adiathermic bodies, 95. - - Aërial currents dependent on heat, 80. - - ---- chemical, 274. - - Affinity, 292. - - Age of the world, 404. - - Aggregation, attraction of, 48. - - ----, crystalline, 58. - - Agonic lines, 244. - - Air, absorption of heat by, 74. - - ---- density of the, 319. - - Alchemy, Nature’s, 293. - - Aldini on animal electricity, 393. - - Allotropic conditions of atoms, 43. - - Allotropism, 330. - - Allotropy, 291. - - Alum, opacity to heat rays, 65. - - Alpinus’ theory of matter, 47. - - Ammonites of the lias, 341. - - Ammoniacal amalgam, 325. - - Ampère’s theory of magnetism, 239. - - Analogy, dangers of reasoning by, 152. - - Ancients’ knowledge of magnetism, 235. - - Animals, phosphorescence of, 154. - - ---- respiration of, 310. - - ---- articulated, 388. - - Animal magnetism, 267. - - ---- electricity, 211, 392. - - ---- life, progress of, 338. - - ----, phenomena of, 383. - - Arago on the surface of the sun, 123. - - ---- on copying the Egyptian temples, 177. - - ---- on magnetic variation, 246. - - _Arbor Dianæ_--silver tree, 261. - - Aristotle on motion, 10. - - Atmosphere, uses of the, 319. - - Atmospheric refraction, 322. - - Atomic theory, 278. - - ---- volumes, 287. - - Atoms, allotropic state of, 43. - - Atom, the organic, 360. - - ----, ultimate size of, 408. - - ----, the, and its powers, 3. - - Attraction, chemical, 275. - - Aurora of the sun, 186. - - - Back’s account of Aurora, 249. - - Balance of forces, 14. - - Bartholin on Iceland spar, 140. - - Beccaria, Father, on phosphorescence, 160. - - Becquerel’s experiments on electricity, 227. - - ---- on ozone, 300. - - Bell on the nerves, 391. - - Belemnites, 341. - - Berkeley, Bishop, on motion, 10. - - Berzelius on allotropy, 44. - - ---- on catalysis, 281. - - Biela’s comet, 26. - - Biot on polarization, 145. - - Bolognian stone, 161. - - Bouguer on the absorption of light by the atmosphere, 126. - - Boutigny on heat, 107. - - _Boletus igniarius_, 102. - - Boyle on motion, 9. - - Brain and nerves, 391. - - Brahminical philosophy, 245. - - Brewster, Sir D., refers magnetism to the sun, 263. - - ---- on magnetism, 247. - - Brown’s doctrines of life, 395. - - Butterfly, metamorphosis of, 389. - - - Cagniard de la Tour state, 106. - - Calorific transparency, 65. - - ---- influence on plants, 376. - - Calotype, the, 174. - - Canton’s phosphorus, 161. - - Carbon, allotropic state of, 43. - - Carboniferous plants, fossil, 339. - - Carbonic acid, solid, 111. - - ---- quantity in atmosphere, 311. - - Cassini on magnetic variation, 246. - - Catalysis, 280. - - Cell, organic, 361. - - Cellini, Benvenuto, on the carbuncle, 159. - - Central sun, doctrine of a, 27. - - Changes, physical, 290. - - Chemical phenomena developing heat, 42. - - ---- decomposition producing heat, 97. - - ---- combination by heat, 98. - - ---- affinity suspended by heat, 109. - - ---- radiations, 166. - - ---- power of solar rays in the Tropics, 177. - - ---- agency of luminous rays, 178. - - ---- action influenced by magnetism, 252. - - ---- forces, 270. - - ---- elements, 272. - - ---- proportions, 285. - - ---- metamorphoses, 289. - - ---- phenomena, 295. - - ---- composition of atmosphere, 322. - - ---- rays, action of, on germination, 375. - - Chemistry, Electro, 206. - - ---- of Nature, 270. - - ---- Animal, 396. - - Chinese knowledge of magnet, 236. - - Chlorophylle, formation of, 373. - - Chloride of sulphur, transparency of, to heat, 65. - - Chlorine and hydrogen combine by light, 171. - - Chlorine in the ocean, 303. - - Cholera and electricity, 215. - - Choroid coat, the, 149. - - Chromatic lines on the earth, 133. - - Clay converted into slate by electricity, 227. - - Climate of the earth, 350. - - Clock, Electrical, 233. - - Coal formation, theory of, 314. - - Cohesive force opposed to gravitation, 33. - - Cohesion and gravitation, 49. - - ---- distinguished from crystallization, 51. - - Cold, extreme, 110. - - Colour of bodies, 132. - - ---- changes of, in chemical combinations, 290. - - ---- blue, of sky, 320. - - ---- of steam, 321. - - Colours, Newton’s theory of, 135. - - Coloured heat rays, 85. - - Combining equivalents, 273. - - ---- forces, 292. - - Combination, laws of, 286. - - ---- of forces, 330. - - Combustion, 305. - - Comets, 26. - - Condensation of gases, 290. - - Conduction of heat, 69. - - Conducting power of bodies for heat, 89. - - Condition, change of chemical, 271. - - Conversion of motion, 16. - - Convection of heat, 69. - - Cotyledons, use of the, 368. - - Coulomb on repulsion of atoms, 47. - - Creation, oneness of, 406. - - Cretaceous formations, 344. - - Crosse on electricity, 227. - - Crustaceans, metamorphosis of, 389. - - Crust of the earth, 333. - - Crystals, pseudomorphous, 54. - - ----, size of, 56. - - Crystallogenic forces, 50. - - Crystalline bodies, magnetic influence of, 260. - - Cudworth’s “Plastic Nature,” 10. - - Current, electric, speed of, 231. - - ----, electricity, magnetic, 239. - - Crystallization, 50. - - Cultivation, limits of, 379. - - Currents of electricity around the earth, 224. - - Cyanite, a true magnet, 48. - - - Daguerre’s discovery, 170. - - Daguerreotype, the, 172. - - Dalton on Aurora Borealis, 248. - - ---- on liquefaction, 287. - - Dalton’s atomic theory, 278. - - Daniel on incandescence, 100. - - Dark lines of spectrum, 125. - - Darwin on sea-weeds of the Southern Ocean, 316. - - Davy, Sir H., on the elements, 328. - - ---- on flame, 307. - - ---- discovers the alkaline metals, 325. - - Decomposition, electro-chemical, 208. - - De la Tour, Cagniard’s experiments, 105. - - Delaroche on heat, 93. - - Density of the earth, 31. - - Development, animal, 384. - - Dew, formation of, 81. - - Diamond, allotropic carbon, 43. - - ----, phosphorescence of, 160. - - Diamagnetism, 253. - - Diamagnetic nature of gases, 259. - - Diathermic bodies, 94. - - Diffusion of gases, 323. - - Digestion a cause of heat, 105. - - Dip of magnetic needle, 247. - - Dimorphism in crystals, 55. - - Directive power of a magnet on crystals, 261. - - Distribution of elements, 328. - - Divisibility of matter, 38. - - Döbereiner’s lamp, 281. - - Dispersion of light, 129. - - Draper on incandescence, 100. - - Dumas on atoms, 39. - - Dust, a grain of, 2. - - - Earth, physical, the, 1. - - ---- density of, 31. - - ---- the revolution of the, 77. - - ----, geological formation of, 333. - - Earth’s, motion, 11. - - ---- temperature dependent on the sun, 63. - - Effects produced by loss of heat, 69. - - Eggs, number of, laid by insects, 399. - - Elective affinity, 292. - - Electricity, 193. - - Electricity and light influencing crystallization, 57. - - ----, kinds of, 195. - - ---- contained in water, 203. - - ---- developed by chemical action, 204. - - ----, velocity of, 231. - - ---- of plants, 380. - - Electric condition of matter, 5. - - ---- telegraph, the, 231. - - ---- affinity, 275. - - Electrical phosphorescence, 160. - - ---- action influenced by actinism, 183. - - ---- radiations, 190. - - ---- clock, 233. - - Electro-chemistry, 206. - - Electro culture, 223. - - Electrotype, the, 229. - - Electro-chemical decomposition, 208. - - Electro-magnetism, 240. - - Electrum, 193. - - Elements, chemical, 37, 272. - - ----, atmospheric, 325. - - ----, interchanges of, 319. - - Englefield on heat rays, 67. - - Eocene formations, 346. - - Equinoxes, precession of the, 244. - - ----, the vernal and autumnal, 77. - - Epicurus’ hooked atoms, 48. - - Epipolic phenomena, 129. - - Eremacausis, 105. - - Ether, hypothesis of an, 120. - - Examples of crystallization, 59. - - Expansion of bodies by heat, 96. - - Eye, mechanism of, 149. - - - Faraday on Magnetism of Crystals, 59. - - ---- on solidification of gases, 112. - - ---- on magnetization of light, 147. - - ---- on the gymnotus, 211. - - ---- on diamagnetism, 254. - - Ferro-magnetic bodies, 255. - - Fish Lizard, the, 341. - - Fixed stars, light of, 122. - - Flint glass, permeability to heat, 65. - - Flora, fossil, 345. - - Flowers, influences of, 317. - - Fluid, magnetic theory of, 252. - - Fluorescence of light, 130. - - Forbes, Prof. Jas., on vibrations of heated metals, 97. - - Forbes, Prof. Edward, on zones of life in the ocean, 127. - - Forbes on colour of steam, 321. - - Force producing motion, 9. - - ---- a cause of motion, 17. - - ----, molecular, 40. - - ---- of crystallization, 61. - - Forces, active, in matter, 3. - - ----, balance of, 14. - - ---- in antagonism, 407. - - Form, change of, 2. - - ---- of surface, influence of, on climate, 351. - - ----, variety of vegetable, 359. - - Foster describes Northern Lights, 249. - - Fox, R. W., on temperature of Cornish mines, 91. - - Franklin on atoms, 47. - - Franklin’s kite experiment, 214. - - Freezing mixtures, 110. - - Freezing, remarkable phenomena of, 112. - - ---- of water, 302. - - Friction, 17. - - Frictional electricity, 199. - - Fraunhofer’s dark lines, 125. - - Franklin’s experiment on heat, 75. - - Fusion influenced by pressure, 107. - - - Galvanism, 201. - - Galvani’s experiment, 201. - - Gases, condensation of, 111, 290. - - ----, magnetism of, 259. - - Gaseous constitution, 317. - - Gauss’s theory of magnetism, 243. - - Generation, spontaneous, 363. - - Geological phenomena, 332. - - Germ, Treviranus on the, 361. - - Germination of seeds, 367. - - Glass, coloured, transparency to heat, 65. - - Goethe’s theory of colour, 139. - - Goethe on phosphorescence, 157. - - ---- on the leaf, 369. - - Graham’s law of diffusion, 323. - - Gravitation, 21. - - Growth explained, 52. - - ----, progress of, 364. - - ---- defined, 383. - - Grove decomposes water by heat, 98. - - Gulf stream, the, 81. - - Gulielmini on crystallisation, 50. - - Gun cotton, 103. - - Gymnotus electricus, 211. - - Gyroscope, the, 14. - - - Hansteen and Arago on Northern Lights, 248. - - Hansteen on magnetism, 244. - - Heat, solar and terrestrial, 62. - - ----, conductors of, 90. - - ----, rays absorbed by atmosphere, 63, 73. - - ---- and light, their relations, 64. - - ----, radiation of, 82. - - ---- rays, coloured, 85. - - ---- lessens chemical affinity, 88. - - ----, latent, 101. - - ----, decomposition by, 109, 276. - - ----, scientific knowledge of, 114. - - ---- developed by combustion of wood equivalent to heat absorbed in - growth, 116. - - ----, influence of, on magnetism, 241. - - ----, action of, on water, 302. - - ----, influence of on plants, 371. - - ---- essential to life, 395. - - Heliography of M. Niepce, 170. - - Herbivorous animals, 315. - - Herschel on the nebulæ, 24. - - Herschel, Sir W., on heat rays, 67. - - Hobbes on the properties of matter, 8. - - Hopkins on the temperature of fusion, 107. - - Huyghens on double refraction, 140. - - Hydra, the, 387. - - Hydrogen, peroxide of, 298. - - ---- and oxygen, 289, 297. - - Hydro-carbons, 297. - - Hydro-carbon compounds, 308. - - Hypnotism, Mr. Braid on, 269. - - - Ice, 301. - - Ichthyosaurus, the, 341. - - Igneous rocks, 335. - - Ignition by chemical action, 102. - - Iguanodon, the, 343. - - Incandescence, temperature of, 69-100. - - Influences of matter on heat, 79. - - Infusoria and animalculæ, 387. - - Interference of light, 138. - - Intensity, magnetic, 247. - - Invisible light, Moser on, 188. - - Iodide of silver found natural, 304. - - Iodine, 304. - - Iridescent paper, 137. - - Iron, magnetic, 235. - - ----, soft, rendered magnetic, 241. - - ----, rusting, 306. - - Isomeric compounds, 291. - - Isomorphism, 290. - - Isothermic lines, 92. - - Isodynamic lines, 247. - - - Jones, Rymer, on sponges, 345. - - Joule on anhydrous salts, 287. - - ---- on heat and motion, 18. - - - Kircher’s Magnetism, 264. - - Kupffar on magnetic storms, 249. - - - Lamination of clay by electricity, 226. - - Land and sea, alternations of, 340. - - Laplace’s theory of the universe, 23. - - Latent heat, 101. - - Lavoisier’s theory of combustion, 305. - - Law of gravitation, 30. - - Lawson, letter from Mr., on germination of seeds, 375. - - Leaf, the functions of the, 369. - - Leaves of plants, action on air of, 311. - - Le Verrier on planet Neptune, 32. - - Leyden jar, the, 198. - - Lias formations, 341. - - Liebig and organic chemistry, 284. - - Life and light, 52. - - ----, influence of light on, 153. - - ---- dependent on light, 164. - - ----, vegetable, 362. - - ----, mysteries of, 398. - - Light, 118. - - ---- essential to life, 39. - - ---- of fixed stars, 122. - - ----, transparency to, 124. - - ----, transmission of, through different media, 128. - - ----, absorption of, 125. - - ----, interference of, 138. - - ----, polarized condition of, 141. - - ----, magnetization of, 146. - - ----, artificial, 162. - - ----, influence of, on plants, 373. - - ---- and heat, correlation of, 64. - - Lightning conductors, 215. - - Lindley on the leaf, 370. - - Lubbock, Sir J., on shooting stars, 22. - - Lodes, mineral, electricity of, 225. - - Luminous and actinic rays distinguished, 176. - - - Machine electricity, 209. - - Magellanic clouds, 25. - - Magnetic curves, 236. - - ---- iron ore, 237. - - ---- polarity, 237. - - ---- points of convergence, 244. - - ---- poles of the earth, 245. - - ---- intensity, 247 - - ---- storms, 249. - - ---- lines of no variation, 243. - - Magnetism, 235. - - ---- induced, 238. - - ---- influenced by heat, 242. - - ----, universality of, 253. - - ---- of gases, 259. - - ---- induced by solar rays 263. - - ---- and electricity, correlation of, 239. - - ---- and crystallisation, 57. - - Magneto-electrical decomposition, 230. - - Magnetisation of light, 146. - - Malus on polarisation, 139. - - Mammalia, fossil, 343. - - Man, temperature of, 105. - - Manganesiate of potash, 171. - - Mantell, Dr., on the iguanodon, 343. - - Mariotte on seat of vision, 149. - - Matter, its general conditions, 1. - - ----, forms of, 21. - - ----, transmutation of, 37. - - ----, divisibility of, 38. - - ----, solid, absorption of heat by, 75. - - ----, influence of, on light, 162. - - ----, polarity of, 265. - - ---- and its properties, 409. - - ----, entity of, 410. - - ----, varied condition of, 36. - - Mayer’s hypothesis of three colours, 138. - - Mechanical force and heat, 103. - - Mechanism of the eye, 149. - - Media, influence of, on light, 128. - - Medusæ, phosphorescence of, 159. - - Melloni on coloured heat rays, 85. - - ---- on new nomenclature for heat, 95. - - Mesmer and electricity, 222. - - Metamorphic rocks, 336. - - Metamorphoses of animals, 389. - - Mexico, Gulf of, warmth of the, 81. - - Mica, black, transparency to heat, 66. - - Miller, Dr., on dark lines of the spectrum, 126. - - Mineral veins, electricity of, 225. - - Mines, Cornish, temperature of, 91. - - Miocene formations, 346. - - Mirrors, magic, 191. - - Mitscherlich on expansion of crystals by heat, 257. - - Molecular forces, 35, 40. - - ----, compound action of, 279. - - Molecules, Dumas on, 39. - - ---- combination, 277. - - Morichini and Carpi on magnetism of violet rays of light, 263. - - Moser on invisible light, 189. - - Motion, 7. - - ---- a property of matter, 8. - - ----, principles of, 10. - - ---- of the earth, 12. - - ---- round an axis shows the earth’s motion, 18. - - ----, influence of, on form, 32. - - Mountain ranges probably determined by magnetic force, 262. - - Multiplication of life, 399. - - Musical notes produced by heat, 97. - - Muscular contraction by electricity, 202. - - Musschenbroek of Leyden, 198. - - Mythology, ancient, probable origin of, 353. - - - Natural polarization, 145. - - Nebulous state of matter, 23. - - Neptune, discovery of, 32. - - Newton on gravitating force, 49. - - Newton on motion, 9. - - Newton’s hypothesis of matter, 4. - - ---- theory of heat, 115. - - ---- theory of light, 120. - - ---- theory of colours, 135. - - Niepce on the chemical radiations, 168. - - Nitrogen, magnetic neutrality of, 259. - - ----, combinations of, 324. - - ----, supposed metallic nature of, 325. - - Nocturnal radiation, 83. - - Northern lights, the, 268. - - - Obsidian transparency to heat, 66. - - Ocean, waters of, 303. - - Oersted discovers electro-magnetism, 238. - - Orders of animals, 386. - - Organic creation, influence, 185. - - ---- compounds, 283. - - ---- compounds, influence of light on them, 181. - - ---- chemistry, 331. - - ---- cell, 360. - - ---- remains, 337. - - Organized forms, varieties of, 35. - - ---- bodies, heat of, 104. - - Organization, progress of, 385. - - Oxides, metallic, 326. - - Oxidizable metals, 305. - - Oxygen gas magnetic, 259. - - ---- and nitrogen, uses of, 321. - - ---- and carbon in animals, 396. - - Ozone, 299. - - ---- and electricity, 217. - - - Palladium maintaining slow combustion, 309. - - Parathermic rays, 74. - - ---- rays, influence in nature, 377. - - Particles, Dumas on, 39. - - Peach on phosphorescence of the sea, 159. - - Pearsall on phosphorescence, 160. - - Pendulum, oscillation of, indicates the earth’s motion, 13. - - Perkins on repulsion of heat, 108. - - Permeation of heat, 96. - - Perturbations of Uranus, 31. - - Pestilential diseases, 216. - - Phenomena of vision, 148. - - ----, natural, of electricity, 194. - - ----, recent geological, 349. - - Phosphorescence of animals, 154. - - ---- of plants, 156. - - Phosphorescent spectrum, 184. - - Phosphoric acid detected in the oldest rocks, 337. - - Photosphere of the sun, 123. - - Photography, 170. - - ----, its importance, 180. - - Physiological influences of electricity, 219. - - Physical forces, action of, 4, 45. - - ---- forces, modes of motion, 7. - - ---- properties of polarized light, 142. - - Physiological influences of magnetism, 268. - - Pilchard, on the, by Couch, 315. - - Plants, distribution of, dependent on light, 133. - - ----, phosphorescence of, 156. - - ----, respiration of, 312. - - ---- and animals, dependence of, 313. - - ----, growth of, 368. - - ---- bend to the light, 373. - - ----, distribution of, 378. - - ---- of the Tropics, 381. - - Plane polarization, 141. - - “Plastic nature” of Cudworth, 10. - - Plateau’s experiment on bodies relieved from gravitation, 33. - - Platinum maintaining slow combustion, 309. - - Plato on motion, 10. - - ---- on light, 119. - - Plesiosaurus, the, 341. - - Pliocene formations, 346. - - Plücker on crystallo-magnetic force, 57. - - ---- on diamagnetic bodies, 256. - - Plumule, use of, 369. - - Plutonic rocks, 334. - - Polarization, circular and elliptical, 143. - - Polarization of light, 139. - - Polar condition of matter, 265. - - Polypes and infusoria, 387. - - Porosity of matter, 41. - - Porta, Baptista--camera obscura, 149. - - Powers, active, in nature, 405. - - Prevost, theory of, on heat, 96. - - Primary origin of our planet, 334. - - Principles of motion, 10. - - Prismatic refraction, 121. - - ---- rays, heat of, 67. - - ---- analysis of sunbeam, 134. - - Principle of gravitation, 29. - - ----, elementary, 38. - - Properties, essential, of matter, 5. - - Pseudomorphism, 54. - - Psychology of flowers, 357. - - Pterodactyl, the, 342. - - Pythagorean doctrine of motion, 10. - - - Quinine, solution, influence of, on light, 129. - - - Radiant heat, 69. - - Radiation and absorption of heat, 77. - - ----, nocturnal, 83. - - Raia torpedo, 211. - - Raymond, Du Bois, on animal electricity, 221. - - Refrangibility, rays of high, 130. - - ---- of solar forces, 168. - - Refraction, prismatic, 121. - - Races, dependence of, 315. - - Repulsion of heat, 108. - - Respiration of animals, 310. - - ---- plants, 312. - - Rest, absolute and relative, 15. - - Respiration a cause of heat, 105. - - Retina, the, 149. - - Revelations of nature, 401. - - Revolution of magnetic poles, 246. - - Robinson on decomposition by heat, 98. - - Rock formations, 335. - - Rocks, conducting power of, 224. - - Rosse’s, Lord, telescopes, 25. - - Rumford, Count, experiments on heat, 18. - - ---- on chemical properties of light, 99. - - Rings, Newton’s, 137. - - - Safety lamp of Davy, 309. - - Salt rock, transparency to heat, 65. - - Saturn’s ring explained, 34. - - Savart on vibrating plates, 257. - - Seasons, influence of heat on the, 70. - - Sea, phosphorescence of, 158. - - Schönbein on ozone, 299. - - Schwabe on solar spots, 243. - - Seebeck on thermo-electricity, 211, 248. - - Selenite and alabaster, 60. - - Sénarmont on conducting power of crystals for heat, 257. - - Shooting stars, 21. - - Silicon, allotropic state of, 43. - - Silica, substitution of, 345. - - Simple bodies, chemical, 329. - - Sky of tropical climes, 319. - - Slow combustion in animals, 397. - - Smee on electricity and vitality, 219. - - Solar system, motion of, 11. - - ---- disc, light from, 185. - - ---- influence on magnetism, 263. - - Solidification of gases by Faraday, 112. - - Solstices, summer and winter, 77. - - Solar spots connected with magnetism, 243. - - Solar phosphori, 161. - - Somerville, Mrs., magnetises needles by light, 263. - - Sound and light, analogy of, 151. - - Spectra produced by polarization of light, 144. - - Spectrum, dark lines of, 125. - - Spheroidal condition of fluids, 107. - - Spontaneous ignition, 307. - - Stahl on phlogiston, 305. - - Stars, shooting, theories of, 21. - - Steel ornaments incandescent, 137. - - Stereoscope, the, 151. - - Stokes, Prof., on fluorescence, 130. - - Stratified formations, 334. - - Strength of animals, 400. - - Structure, influence of, on magnetism, 256. - - ----, relation of, to physical phenomena, 257. - - Struvé on motion of solar system, 12. - - Substitution, chemical, 279. - - ----, law of, 288. - - Substances, all, electric, 197. - - Subterranean temperature, 91. - - Sulphuric acid, permeability to heat, 65. - - Surfaces, action of, 282. - - Sulzar on galvanism, 201. - - Sulphuretted hydrogen, solid, 111. - - Sun, the central, 28. - - ----, the source of light, 121. - - ----, physical state of the, 123. - - ----, a magnetic centre, 265. - - - Tadpole, metamorphosis of, 389. - - Talbot’s sensitive photographic process, 178. - - Telegraph, electric, 231. - - Temperature of incandescence, 68. - - Temperature, subterranean, 91. - - Terrestrial currents of electricity, 224. - - ---- magnetism, 255. - - Thales of Miletus discovers electricity, 193. - - Theories of light, 86, 118. - - Thermography, 188. - - Thermometric examination of the temperature of flowers, 76. - - Thermo-electricity, 209. - - Theory of motion producing force, 15. - - Thilorier on solid carbonic acid, 111. - - Time, influence of, 332. - - Tissues, catalytic power of, 310. - - Tourmaline, action of, on light, 142. - - Trade winds, 81. - - Transition series of rocks, 336. - - Transparency, calorific, 67. - - ----, luminous, 124. - - Transmutation of matter, 37. - - Transmission of light, 128. - - Transcalescent bodies, 94. - - Trevelyan, Mr., on vibration of heated metals, 97. - - Tyndale proves the influence of structure on magnetism, 258. - - Type, elements of the organic, 289. - - - Undulations producing colour, 131. - - Undulatory theory of heat, 115. - - ---- theory of light, 121. - - Uranus, discovery of, 31. - - Uranium glass, influence of, on light, 129. - - - Vapour, elastic force of, 318. - - Variation, magnetic, 244. - - Vegetables conductors of electricity, 379. - - Vegetable life, phenomena of, 357. - - Vegetation of carboniferous epoch, 339. - - Velocity of electricity, 231. - - Vertebrate animals, 390. - - Vision, phenomena of, 148. - - Vis vitæ, vital principle, 391. - - Vision single with a pair of eyes, 150. - - Vitality superior to physical force, 53. - - Vision, seat of, 149. - - Volume, doctrine of, 287. - - Volcanic action referred to chemical action, 271. - - Volatilization of matter, 27. - - Voltaic electricity, 201. - - - Water, absorption of heat by, 74. - - ---- frozen free of air, 112. - - ---- free of air, peculiar state of, 113. - - ----, electricity in a drop of, 204. - - ----, composition of, 296. - - Wargentin’s notice of aurora, 248. - - Wave movement of heat and light, 68. - - Wealden formations, 343. - - Wedgwood on incandescence, 100. - - Wells, Dr., on dew, 84. - - Wiedemann on electrical vibrations, 257. - - Wenzel’s proportional numbers, 277. - - Winds dependent on heat, 80. - - Wollaston notices dark lines in spectrum, 125. - - World, its age, 404. - - - Young on molecular forces, 49. - - - Zodiacal light, 25. - - Zoophytes, microscopic, 387. - - -THE END. - - -Wilson and Ogilvy, 57, Skinner Street, Snowhill, London. - - - - -BOHN’S BOOKS. - - -BOHN’S STANDARD LIBRARY. - -_Post 8vo., Elegantly Printed, and bound in Cloth, at 3s. 6d. per Vol._ - - - =1. 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No attempt has been made -to correct these totals. - -In the original book, half of the publisher’s catalogue (Bohn’s Books) -was in the beginnig of the book. It was moved to immediately precede -the other half of the catalogue at the end of the book. - -Preface, Contents, Introduction, Index, Bohn’s Books and Transcriber’s -Note have been added to the table of contents. Only the chapters of -the book were in the table of contents in the original book. The title -"Bohn’s Books" was inserted into the beginning of the publisher’s book -catalogue. - -In the table below, the first line shows the text in this ebook, the -second line shows the text in the original book. - - Page vii.: conditions of Matter--Diamagnetism, &c. 235 - Originally: conditions of Matter--Dia-Magnetism, &c. 235 - - Page viii.: Time, an element in Nature’s Operations--Geological - Originally: Time, an element in Nature’s Operations==Geological - - Page viii.: Progress of Matter towards Organization - Originally: Progress of Matter rowards Organization - - Page xii.: of external nature, evoked beautiful spiritualizations - Originally: of external nature, evoked beautiful spirtualizations - - Footnote 1: Boscovich regarded the constitution of matter differently - Originally: Boscovitch regarded the constitution of matter differently - - Footnote 1: full explanation of the theory of Boscovich.) - Originally: full explanation of the theory of Boscovitch.) - - Page 8: The views of metaphysicians regarding motion involve - Originally: The views of metaphyscians regarding motion involve - - Page 14: tremulous gyration upon the deck of a vast aërial ship - Originally: tremulous gyration upon the deck of a vast aerial ship - - Page 27: agent of organisation and all manifestations of beauty? - Originally: agent of organisation and all manifestatious of beauty? - - Footnote 18: fixes, est déterminée par ce qui précède entre certaines - Originally: fixes, est determinée par ce qui précède entre certaines - - Footnote 18: est le groupe central de l’ensemble du système - Originally: est le groupe central l’ensemble du système - - Footnote 24: into a single mass at the bottom of the flask under - Originally: into a single mass at the bottom of the flask unde - - Page 42: with which the particles combined, from interstices, - Originally: with which the particles combined, from insterstices, - - Page 45: bromine, &c., are the results of different _allotropic_ - Originally: bromime, &c., are the results of different _allotropic_ - - Page 46: which,--from the imperfections of science,--resisting - Originally: which,--from the imperfectious of science,--resisting - - Page 46: The experiments of Faraday and of Plücker prove - Originally: The experiments of Faraday and of Plucker prove - - Footnote 25: Young’s _Natural Philosophy_; ed. by Rev. P. Kelland. - Originally: Young’s _Natural Philosophy_; ed. by Rev. P. Lelland. - - Footnote 35: Hence the origin of compound and visible bodies; hence - Originally: Hence the origin of compouud and visible bodies; hence - - Page 50: her operations, but the very processes themselves. - Originally: her operations, but the very processes themselvss. - - Paqe 59: combination appears to the eye in no respect different - Originally: combinatiou appears to the eye in no respect different - - Page 61: Those fissures formed by the first system of crystalline - Originally: Those fissures formed by the first sytsem of crystalline - - Page 68: luminous power are sufficiently striking to convince us - Originally: luminous power are sufficienlty striking to convince us - - Page 109: of temperature is experienced.[79] Professor Plücker, of - Originally: of temperature is experienced.[79] Professor Plucker, of - - Footnote 55: this motion. He was followed by Musschenbroek, and then - Originally: this motion. He was followed by Muschenbroek, and then - - Footnote 61: _regarding the internal temperature of the Earth_: by - Originally: _regarding the internal temperature of tha Earth_: by - - Footnote 78: _en vertu de l’état sphéroïdal dans un creuset_ - Originally: _en vertu de l’état sphérodïal dans un creuset_ - - Page 121: Fraunhofer, Herschel, Brewster, and others, but proceed - Originally: Frauenhofer, Herschel, Brewster, and others, but proceed - - Page 123: between charcoal points at the poles of a powerful voltaic - Originally: between charcoal points a the poles of a powerful voltaic - - Page 129: of quinine, and the fluor spar, we obtain the same results - Originally: of quinine, and the flour spar, we obtain the same results - - Page 140: the first instance, by Erasmus Bartholin, in Iceland-spar, - Originally: the first instance, by Erasmus Bartolin, in Iceland-spar, - - Page 145: from what has been already stated, that some - Originally: from what has beeen already stated, that some - - Page 153: to prove that light is absolutely necessary to - Originally: to prove that light is absolutely neccessary to - - Page 159: of light behind them.[113] By microscopic examination - Originally: of light behind them.[113] By miscroscopic examination - - Page 159: Benvenuto Cellini gave a curious account of a carbuncle - Originally: Benvenuto Cellini give a curious account of a carbuncle - - Page 160: near a fire. From this it may be inferred that the - Originally: near a a fire. From this it may be infered that the - - Footnote 88: Brande’s _Manual of Chemistry_; or, indeed, any work - Originally: Brande’s _Mannal of Chemistry_; or, indeed, any work - - Footnote 94: Schouw, _Grundzüge der Pflanzengeographie_. Also his - Originally: Schouw, _Grundüzge der Pflanzengeographie_. Also his - - Footnote 95: Fraunhofer’s measure of illuminating power is as - Originally: Frauenhofer’s measure of illuminating power is as - - Footnote 99: _Sur une Propriété de la Lumière Réfléchie_: Mémoires - Originally: _Sur une Propriété de la Lumière Réfléchie_: Memoires - - Page 176: the strongest sunlight which has passed through - Originally: the strongest sun-light which has passed through - - Page 179: productions of the photographer as on those of the - Originally: productions of the photograper as on those of the - - Page 180: preserve the lineaments of those who have benefited - Originally: preserve the lineaments of those who have benefitted - - Page 185: line, over which no action takes place, is preserved at - Originally: line, over which no action takes plates, is preserved at - - Page 185: presented to us by a circular body: calorific action seems - Originally: present to us by a circular body: calorific action seems - - Page 188: piece of wood is used instead of a metal, there will, by - Originally: piece of wood is used instead of a medal, there will, by - - Footnote 126: _dans la végétation_: by Senebier; Genève et Paris, 1788 - Originally: _dans la végetation_: by Senebier; Genève et Paris, 1788 - - Page 198: Leyden phial,--so called from its inventor, Musschenbroek, - Originally: Leyden phial,--so called from its inventor, Muschenbrock, - - Page 219: may be made a measurer of nervous irritability.[154] There - Originally: may be made a measurer of nervous iritability.[154] There - - Footnote 141: _Traité Expérimental de l’Électricité et du Magnétisme_: - Originally: _Traité Expérimental de l’Electricité et du Magnétisme_: - - Footnote 146: _Traité Expérimental de l’Électricité et du Magnétisme_. - Originally: _Traité Expérimental de l’Electricité et du Magnétisme_ - - Footnote 160: where the cobalt was discovered between two portions of - Originally: where the cobalt was discovered betweed two portions of - - Page 235: Storms--Magnetic conditions of Matter--Diamagnetism, - Originally: Storms--Magnetic conditions of Matter--Dia-Magnetism, - - Page 236: Magnêtum, quia sit patriis in finibus ortus. - Originally: Magnêtum, buia sit patriis in finibus ortus. - - Page 251: conditions of change in this our earth: an element to - Originally: conditions of change in this our earth: an elemeut to - - Page 257: Wiedemann, by employing a fine point through which - Originally: Wiedmann, by employing a fine point through which - - Page 258: than in any other. M. Wiedemann comes to the conclusion - Originally: than in any other. M. Wiedmann comes to the conclusion - - Page 260: salt, the protosulphate, ordinarily crystallizes so that - Originally: salt, the proto-sulphate, ordinarily crystallizes so that - - Footnote 176: Humboldt: _Exposé des Variations Magnétiques_. - Originally: Humboldt: _Exposé des Variations Magnetiques_. - - Footnote 188: _Electro-Magnetic Influence_, by Professor Zantedeschi. - Originally: _Electro-Magnetic Influence_, by Professor Zandeteschi. - - Footnote 190: detailed account of the experiments of Faraday, Plücker, - Originally: detailed account of the experiments of Faraday, Plucker, - - Page 276: light determine these changes? It is evident, although - Originally: light determine these change? It is evident, although - - Page 281: chemical change. Döbereiner next discovered that - Originally: chemical change. Dœbereiner next discovered that - - Page 282: a fearful example in the progress of Asiatic - Originally: a fearful example in the progress of Asatic - - Page 300: as being either peroxide of hydrogen, or an allotropic - Originally: as being either per-oxide of hydrogen, or an allotropic - - Page 304: the gas which we employ so advantageously for illumination - Originally: the gas which we emply so advantageously for illumination - - Page 306: increasing,--true combustion takes place. In this way - Originally: increasing,--true combustion takes plaee. In this way - - Page 306: sawdust, &c., frequently ignite; and to such an - Originally: saw-dust, &c., frequently ignite; and to such an - - Page 316: Mr. Darwin remarks, that if the immense sea-weeds of - Originally: Mr. Darwin remarks, that if the immense seaweeds of - - Page 317: When Shakespeare made his charming Ariel sing-- - Originally: When Shakspeare made his charming Ariel sing-- - - Footnote 212: (Redundant line removed before item 2 in table.) - Originally: According to one view, | According to the other view, - - Page 334: speculation, which may have occasional marks of ingenuity, - Originally: speculation, whieh may have occasional marks of ingenuity, - - Page 337: origin, the rational inference is against the speculation; - Originally: orgin, the rational inference is against the speculation; - - Page 370: capsule of _nigella orientalis_ consists of pods assembled - Originally: capsule of _nigilla orientalis_ consists of pods assembled - - Page 370: a centre, and partially united; in _nigella damascena_ - Originally: a centre, and partially united; in _nigilla damascena_ - - Page 399: whose minds are sceptical upon any development of the - Originally: whose mind are sceptical upon any development of the - - Page 406: evidence of a beautiful adjustment of the balance of - Originally: evidence of a beautifnl adjustment of the balance of - - Page 408: Let but a slight disturbance occasion a vibration - Originally: Let but a slight disturbance occcasion a vibration - - Page 409: A cheerless philosophy, derived from the transcendentalism - Originally: A cheerless philosophy, derived from the transendentalism - - Page 410: which are allowed the privilege of tracing out its - Originally: which are alowed the privilege of tracing out its - - Page 413: Aëreal currents dependent on heat, 80. - Originally: Æreal currents dependent on heat, 80. - - Page 413: Animal electricity, 211, 392. - Originally: Magnetic electricity, 211, 392. - - Page 413: Bartholin on Iceland spar, 140. - Originally: Bartolin on Iceland spar, 140. - - Page 414: Cagniard de la Tour state, 106. - Originally: Caignard de la Tour state, 106. - - Page 415: Döbereiner’s lamp, 281. - Originally: Doebereiner’s lamp, 281. - - Page 415: Eye, mechanism of, 149. - Originally: Eye, mechanism of, 491. - - Page 416: ---- on diamagnetism, 254. - Originally: ---- on dia-magnetism, 254. - - Page 418: Musschenbroek of Leyden, 198. - Originally: Muschenbrock of Leyden, 198. - - Page 421: Wiedemann on electrical vibrations, 257. - Originally: Wiedman on electrical vibrations, 257. - - Bohn’s Books: =LOUDON’S (MRS.) ENTERTAINING NATURALIST=, - Originally: =LOUDON’S (MRS.) ENTERTAING NATURALIST=, - - Bohn’s Books: Indexes of Scientific and Popular Names. _With_ - Originally: Indexes of Scientific and and Popular Names. _With_ - - Bohn’s Books: =18. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus, - Originally: =8. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus, - - Bohn’s Books: =35. JUVENAL, PERSIUS, &c.= By the REV. L. EVANS, M.A. - Originally: =34. JUVENAL, PERSIUS, &c.= By the REV. L. 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You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The Poetry of Science or, Studies of the Physical Phenomena of Nature - -Author: Robert Hunt - -Release Date: April 30, 2016 [EBook #51897] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE POETRY OF SCIENCE *** - - - - -Produced by Emmanuel Ackerman and the Online Distributed -Proofreading Team at http://www.pgdp.net (This file was -produced from images generously made available by The -Internet Archive/Canadian Libraries) - - - - - - -</pre> - - -<div class="chap"> - - -<h1><span class="normal-title">THE<br /></span> - -POETRY OF SCIENCE;</h1> - -<p class="center smaller-title">OR,</p> - -<p class="center bigger-title">STUDIES</p> - -<p class="center smaller-title">OF THE</p> - -<p class="center bigger-title">PHYSICAL PHENOMENA OF NATURE.</p> - -<p class="center p2">BY</p> - -<p class="center big-title">ROBERT HUNT,</p> - -<p class="center smaller-title">AUTHOR OF</p> - -<p class="center smaller-title">“RESEARCHES ON LIGHT;” “ELEMENTARY PHYSICS;” -“PANTHEA, OR THE SPIRIT OF NATURE,” ETC.</p> - -<p class="center smaller-title">PROFESSOR OF PHYSICS, METROPOLITAN SCHOOL OF SCIENCE, ETC., ETC.</p> - -<p class="center p2 smaller-title">THIRD EDITION, REVISED AND ENLARGED.</p> - -<p class="center p2 bigger-title">LONDON:</p> - -<p class="center">HENRY G. BOHN, YORK STREET, COVENT GARDEN.</p> - -<p class="center smaller-title">MDCCCLIV.</p> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p class="p4 hang">From Shakespeare to Plato—from the philosophic poet to the poetic philosopher—the -transition is easy, and the road is crowded with illustrations -of our present subject.</p> - -<hr class="tb" /> - -<p class="hang">Hast thou ever raised thy mind to the consideration of <span class="smcap">existence</span>, in and -by itself, as the mere act of existing?</p> - -<p class="hang">Hast thou ever said to thyself, thoughtfully, <span class="smcap">It is</span>!—heedless, in that -moment, whether it were a man before thee, or a flower, or a grain of -sand,—without reference, in short, to this or that particular mode or -form of existence? If thou hast, indeed, attained to this, thou wilt have -felt the presence of a mystery, which must have fixed thy spirit in awe -and wonder.</p> - -<p class="right"><i>Coleridge.</i></p> - -<p class="center p2"> -<span class="smcap">London</span>:<br /> -<span class="smcap">Wilson</span> and <span class="smcap">Ogilvy</span>,<br /> -57, Skinner Street. -</p> - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_iii" id="Page_iii"></a></span></p> - - -<h2><a name="PREFACE" id="PREFACE"></a>PREFACE.</h2> - - -<p>Since 1848, when the “Poetry of Science” was first -submitted to the public, two editions have been exhausted. -This, were proofs required, would of itself -show that there is a large circle of readers to whom -the deductions of science have an unfailing interest. -Beyond this, it conveys an assurance that every truth, -however abstract it may appear, has a large popular value -if studied in its relations to those generalities which -embrace great natural phenomena. With this persuasion -the third edition of the “Poetry of Science” -has been extended so as to include all the important -discoveries which have been made in Natural Philosophy -to the end of the year 1853. It is now presented -to the world in a new and cheaper form, in the -hope, that, with the extension of its circulation, there -may be awakened, in still larger circles, a deep and -healthful interest in the sciences of which the volume -treats.</p> - -<p class="right"> -R. H. -</p> - -<p>Edinburgh, March 7, 1854.</p> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_v" id="Page_v"></a></span></p> - - -<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h2> - -<table id="toc" summary="Table of Cotents"> -<tr><td></td><td class="page">Page</td></tr> -<tr><td class="chapter"><a href="#PREFACE">PREFACE.</a></td><td class="page"><a href="#Page_iii">iii</a></td></tr> -<tr><td class="chapter"><a href="#CONTENTS">CONTENTS.</a></td><td class="page"><a href="#Page_v">v</a></td></tr> -<tr><td class="chapter"><a href="#INTRODUCTION">INTRODUCTION.</a></td><td class="page"><a href="#Page_ix">ix</a></td></tr> - -<tr><td class="chapter"><a href="#CHAPTER_I">CHAPTER I.</a></td><td></td></tr> -<tr><td class="center">GENERAL CONDITIONS OF MATTER.</td><td></td></tr> -<tr><td class="hang"> -Its varied Characters, and constant change of -external Form—The Grain of Dust, its Properties and -Powers—Combinations in inorganic Masses and in organized -Creations—Our knowledge of Matter—Theory of Ultimate -Atoms—The Physical Forces acting on the Composition -of Masses—The certainty of the exercise of subtile -principles, which are beyond the reach of experimental -Science</td><td class="page"><a href="#Page_1">1</a></td></tr> - -<tr><td class="chapter"><a href="#CHAPTER_II">CHAPTER II.</a></td><td></td></tr> -<tr><td class="center">MOTION.</td><td></td></tr> -<tr><td class="hang"> -Are the Physical Forces modes of Motion?—Motion -defined—Philosophical Views of Motion, and the Principles -to which it has been referred—Motions of the Earth and -of the Solar System—Visible Proofs of the Earth’s Motion -on its Axis—Influence of the proper Motions of the Earth -on the Conditions of Matter—Theory of the Conversion of -Motion into Heat, &c.—The Physical Forces regarded as -principles independent of Motion, although the Cause and -often apparently the Effects of it</td><td class="page"><a href="#Page_7">7</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_III">CHAPTER III.</a></td><td></td></tr> -<tr><td class="center">GRAVITATION.</td><td></td></tr> -<tr><td class="hang"> -The Forms of Matter—Shape of the Earth—Probability -of the Mass forming this Planet having existed in a -Nebulous State—Zodiacal Lights—Comets—Volatilization -of Solid Matter by Artificial means—The principle -of Gravitation—Its Influence through Space and -within the smallest Limits—Gravitating powers of the -Planets—Density of the Earth—Certainty of Newton’s Law -of the Inverse Square—Discovery of Neptune—State of a -Body relieved from Gravitation—Experiment explaining -Saturn’s Ring, &c.—General inference</td><td class="page"><a href="#Page_21">21</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_IV">CHAPTER IV.</a></td><td></td></tr> -<tr><td class="center">MOLECULAR FORCES.</td><td></td></tr> -<tr><td class="hang"> -Conditions of Matter—Variety of organized -Forms—Inorganic Forms—All matter reducible to the -most simple conditions—Transmutation, a natural -operation—Chemical Elementary Principles—Divisibility -of Matter—Atom—Molecules—Particles—Molecular -Force includes several Agencies—Instanced -in the Action of Heat on Bodies—All Bodies -porous—Solution—Mixture—Combination—Centres -of Force—Different States of Matter (Allotropic -Conditions)—Theories of Franklin, Æpinus, and -Coulomb—Electrical and Magnetic Agencies—Ancient -<span class="pagenum"><a name="Page_vi" id="Page_vi"></a>[Pg vi]</span>Notions—Cohesive Attraction, &c.</td><td class="page"><a href="#Page_35">35</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_V">CHAPTER V.</a></td><td></td></tr> -<tr><td class="center">CRYSTALLOGENIC FORCES.</td><td></td></tr> -<tr><td class="hang"> -Crystallisation and Molecular Force -distinguished—Experimental Proof—Polarity of -Particles forming a Crystal—Difference between -Organic and Inorganic Forms—Decomposition of -Crystals in Nature—Substitution of Particles in -Crystals—Pseudomorphism—Crystalline Form not dependent -on Chemical Nature—Isomorphism—Dimorphism—Theories of -Crystallogenic Attraction—Influence of Electricity and -Magnetism—Phenomena during Crystallisation—Can a change -of Form take place in Primitive Atoms?—Illustrative -Example of Crystallisation</td><td class="page"><a href="#Page_50">50</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_VI">CHAPTER VI.</a></td><td></td></tr> -<tr><td class="center">HEAT—SOLAR AND TERRESTRIAL.</td><td></td></tr> -<tr><td class="hang"> -Solar and Terrestrial Heat—Position of the Earth -in the Solar System—Heat and Light associated in -the Sunbeam—Transparency of Bodies to Heat—Heating -Powers of the Coloured Rays of the Spectrum—Undulatory -Theory—Conducting Property of the Earth’s -Crust—Convection—Radiation—Action of the Atmosphere on -Heat Rays—Peculiar Heat Rays—Absorption and Radiation -of Heat by dissimilar Bodies—Changes in the Constitution -of Solar Beam—Differences between Transmitted and -Reflected Solar Heat—Phenomena of Dew—Action of -Solar Heat of the Ocean—Circulation of Heat by the -Atmosphere and the Ocean—Heat of the Earth—Mean -Temperature—Central Heat—Constant Radiation of Heat Rays -from all Bodies—Thermography—Action of Heat on Molecular -Arrangements—Sources of Terrestrial Heat—Latent Heat -of Bodies—Animal Heat—Eremacausis—Spheroidal State -Cold—Condensation—Freezing—Theories of Heat—Natural -Phenomena—and Philosophical Conclusion</td><td class="page"><a href="#Page_62">62</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_VII">CHAPTER VII.</a></td><td></td></tr> -<tr><td class="center">LIGHT.</td><td></td></tr> -<tr><td class="hang"> -Theories of the Nature of Light—Hypotheses -of Newton and Huygens—Sources of Light—The -Sun—Velocity of Light—Transparency—Dark -Lines of the Spectrum—Absorption of -Light—Colour—Prismatic Analysis—Rays of the -Spectrum—Rainbow—Diffraction—Interference—Goethe’s -Theory—Polarisation—Magnetisation of Light—Vision—The -Eye—Analogy—Sound and Light—Influence of Light on -Animals and Vegetables—Phosphorescence arising from -several Causes—Artificial Light—Its Colour dependent on -Matter</td><td class="page"><a href="#Page_118">118</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_VIII">CHAPTER VIII.</a></td><td></td></tr> -<tr><td class="center">ACTINISM—CHEMICAL RADIATIONS.</td><td></td></tr> -<tr><td class="hang"> -The Sun-ray and its Powers—Darkening of -Horn Silver—Niepce’s Discovery—Prismatic -Spectrum—Refrangibility of Light, Heat, and -<span class="pagenum"><a name="Page_vii" id="Page_vii"></a>[Pg vii]</span>Actinism—Daguerre’s Discovery—Photography—Chemical -Effects produced by Solar Radiations—Absorption of -Actinism—Phenomena of the Daguerreotype—Chemical -Change produced upon all Bodies—Power of Matter to -restore its Condition—Light protects from Chemical -Change—Photographs taken in Darkness—Chemical Effects -of Light on organized Forms—Chemical Effects of Solar -Heat—Influence of Actinism on Electricity—Radiations in -Darkness—Moser’s Discoveries, &c.</td><td class="page"><a href="#Page_166">166</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_IX">CHAPTER IX.</a></td><td></td></tr> -<tr><td class="center">ELECTRICITY.</td><td></td></tr> -<tr><td class="hang"> -Discovery of Electrical Force—Diffused through all -Matter—What is Electricity?—Theories—Frictional -Electricity—Conducting Power of Bodies—Hypothesis -of two Fluids—Electrical Images—Galvanic -Electricity—Effects on Animals—Chemistry of Galvanic -Battery—Electricity of a Drop of Water—Electro-chemical -Action—Electrical Currents—Thermo-Electricity—Animal -Electricity—Gymnotus—Torpedo—Atmospheric -Electricity—Lightning Conductors—Earth’s Magnetism due -to Electrical Currents—Influence on Vitality—Animal and -Vegetable Development—Terrestrial Currents—Electricity -of Mineral Veins—Electrotype—Influence of Heat, Light, -and Actinism on Electrical Phenomena</td><td class="page"><a href="#Page_193">193</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_X">CHAPTER X.</a></td><td></td></tr> -<tr><td class="center">MAGNETISM.</td><td></td></tr> -<tr><td class="hang"> -Magnetic Iron—Knowledge of, by the Ancients—Artificial -Magnets—Electro-Magnets—Electro-Magnetism—Magneto-Electricity—Theories -of Magnetism—The Magnetic -Power of soft Iron and Steel—Influence of Heat -on Magnetism—Terrestrial Magnetism—Declination -of the Compass-needle—Variation of the -Earth’s Magnetism—Magnetic Poles—Hansteen’s -Speculations—Monthly and Diurnal Variation—Dip and -Intensity—Thermo-Magnetism—Aurora Borealis—Magnetic -Storms—Magnetic conditions of Matter—<span class="correction" title="In the original book: Dia-magnetism">Diamagnetism</span>, &c.</td><td class="page"><a href="#Page_235">235</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_XI">CHAPTER XI.</a></td><td></td></tr> -<tr><td class="center">CHEMICAL FORCES.</td><td></td></tr> -<tr><td class="hang"> -Nature’s Chemistry—Changes produced by Chemical -Combination—Atomic Constitution of Bodies—Laws -of Combination—Combining Equivalents—Elective -Affinity—Chemical Decomposition—Compound Character -of Chemical Phenomena—Catalysis or action of -Presence—Transformation of Organic Bodies—Organic -Chemistry—Constancy of Combining Proportions—The Law of -Volumes, the Law of Substitutions, Isomeric States, &c.</td><td class="page"><a href="#Page_270">270</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_XII">CHAPTER XII.</a></td><td></td></tr> -<tr><td class="center">CHEMICAL PHENOMENA.</td><td></td></tr> -<tr><td class="hang"> -Water—Its Constituents—Oxygen—Hydrogen—Peroxide -of Hydrogen—Physical Property of Water—Ice—Sea -<span class="pagenum"><a name="Page_viii" id="Page_viii"></a>[Pg viii]</span>Water—Chlorine—Muriatic Acid—Iodine—Bromine—Compounds -of Hydrogen with Carbon—Combustion—Flame—Safety -Lamp—Respiration—Animal Heat—The Atmosphere—Carbonic -Acid—Influence of Plants on the Air—Chemical Phenomena -of Vegetation—Compounds of Nitrogen—Mineral Kingdom, &c. -&c.</td><td class="page"><a href="#Page_295">295</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_XIII">CHAPTER XIII.</a></td><td></td></tr> -<tr><td class="center">TIME.—GEOLOGICAL PHENOMENA.</td><td></td></tr> -<tr><td class="hang"> -Time, an element in Nature’s Operations<span class="correction" title="In the original book: ==">—</span>Geological -Science—Its Facts and Inferences—Nebular Hypothesis -applied—Primary Formations—Plutonic and Metamorphic -Rocks—Transition Series—Palæozoic Rocks—Commencement -of Organic Arrangements—Existence of Phosphoric -Acid in Plutonic Rocks—Fossil Remains—Coal -Formation—Sandstones—Tertiary Formations—Eocene, -Miocene, and Pliocene Formations—Progressive changes -now apparent—General Conclusions—Physics applied in -explanation</td><td class="page"><a href="#Page_332">332</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_XIV">CHAPTER XIV.</a></td><td></td></tr> -<tr><td class="center">PHENOMENA OF VEGETABLE LIFE.</td><td></td></tr> -<tr><td class="hang"> -Psychology of Flowers—Progress of Matter -<span class="correction" title="In the original book: rowards">towards</span> Organization—Vital Force—Spontaneous -Generation—The Vegetable Cell—Simplest Development -of Organization—The Crystal and the Cell—Primitive -Germ—Progress of Vegetation—Influence of -Light—Morphology—Germination—Production of Woody -Fibre—Leaves—Chlorophylle—Decomposition of -Carbonic Acid—Influence of Light, Heat, and Actinism -on the Phenomena of Vegetable Life—Flowers and -Fruits—Etiolation—Changes in the Sun’s Rays with the -Seasons—Distribution of Plants—Electrical and Combined -Physical Powers</td><td class="page"><a href="#Page_357">357</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_XV">CHAPTER XV.</a></td><td></td></tr> -<tr><td class="center">PHENOMENA OF ANIMAL LIFE.</td><td></td></tr> -<tr><td class="hang"> -Distinction between the Kingdoms -of Nature—Progress of Animal -Life—Sponges—Polypes—Infusoria—Animalcula—Phosphorescent -Animals—Annelidans—Myriapoda—Animal -Metamorphoses—Fishes—Birds—Mammalia—Nervous -System—Animal Electricity—Chemical Influences—Influence -of Light on Animal Life—Animal Heat—Mechanical -Action—Nervous Excitement—Man and the Animal Races, &c.</td><td class="page"><a href="#Page_383">383</a></td></tr> - - -<tr><td class="chapter"><a href="#CHAPTER_XVI">CHAPTER XVI.</a></td><td></td></tr> -<tr><td class="center">GENERAL CONCLUSIONS.</td><td></td></tr> -<tr><td class="hang"> -The Changes produced on Physical Phenomena by the Movement -of the Solar System considered—Exertion of the Physical -Forces through the Celestial Spaces—The Balance of -Powers—Varieties of Matter—Extension of Matter—Theory -of Nonentity—A Material Creation an indisputable -fact—Advantages of the Study of Science—Conclusion</td><td class="page"><a href="#Page_403">403</a></td></tr> -<tr><td class="chapter"><a href="#INDEX">INDEX.</a></td><td class="page"><a href="#Page_413">413</a></td></tr> -<tr><td class="chapter"><a href="#BOHNS_BOOKS">BOHN’S BOOKS.</a></td><td></td></tr> -<tr><td class="chapter"><a href="#TRANSCRIBERS_NOTE">TRANSCRIBER’S NOTE.</a></td><td></td></tr> - -</table> - -<hr class="chap" /> -</div> -<div class="chap"> - - -<p><span class="pagenum"><a name="Page_ix" id="Page_ix"></a>[Pg ix]</span></p> - - - - -<h2><a name="INTRODUCTION" id="INTRODUCTION"></a>INTRODUCTION.</h2> - - -<p>The True is the Beautiful. Whenever this becomes -evident to our senses, its influences are of a soul-elevating -character. The beautiful, whether it is perceived -in the external forms of matter, associated in the -harmonies of light and colour, appreciated in the -modulations of sweet sounds, or mingled with those -influences which are, as the inner life of creation, ever -appealing to the soul through the vesture which covers -all things, is the natural theme of the poet, and the -chosen study of the philosopher.</p> - -<p>But, it will be asked, where is the relation between -the stern labours of science and the ethereal system -which constitutes poetry? The fumes of the laboratory, -its alkalies and acids, the mechanical appliances of the -observatory, its specula and its lenses, do not appear -fitted for a place in the painted bowers of the Muses. -But, from the labours of the chemist in his cell,—from -the multitudinous observations of the astronomer on his -tower,—spring truths which the philosopher employs to -interpret nature’s mysteries, and which give to the soul -of the poet those realities to which he aspires in his high -imaginings.</p> - -<p>Science solicits from the material world, by the -persuasion of inductive search, a development of its -elementary principles, and of the laws which these obey. -Philosophy strives to apply the discovered facts to the<span class="pagenum"><a name="Page_x" id="Page_x"></a>[Pg x]</span> -great phenomena of being,—to deduce large generalities -from the fragmentary discoveries of severe induction,—and -thus to ascend from matter and its properties up to -those impulses which stir the whole, floating, as it were, -on the confines of sense, and indicating, though dimly, -those superior powers which, more nearly related to -infinity, mysteriously manifest themselves in the phenomena -of mind. Poetry seizes the facts of the one -and the theories of the other; unites them by a pleasing -thought, which appeals for truth to the most unthinking -soul, and leads the reflective intellect to higher and -higher exercises; it connects common phenomena with -exalted ideas; and, applying its holiest powers, it invests -the human mind with the sovereign strength of the -True.</p> - -<p>Truth is the soul of the poet’s thought;—truth is -the reward of the philosopher’s toil; and their works, -bearing this stamp, live among men through all time. -Science at present rejoices in her ministry to the requirements -of advancing civilization, and is content to receive -the reward given to applications which increase the -comforts of life, or add to its luxuries. Every improvement -in the arts or manufactures, beyond encreasing -utilities for society, has a tendency to elevate the race. -Science is ever useful in the working days of our week, -but it is not to be neglected on our Sabbath,—when, -resting from our labours, it becomes agreeable to contemplate -the few truths permitted to our knowledge, -and thus enter into communion as closely as is allowed -to finite beings, with those influences which involve and -interpenetrate the earth, giving to all things Life, -Beauty, and Divinity.</p> - -<p>The human mind naturally delights in the discovery -of truth; and even when perverted by the constant -operations of prevailing errors, a glimpse of the Real -comes upon it like the smile of daylight to the sorrowing -captive of some dark prison. The Psychean labours to<span class="pagenum"><a name="Page_xi" id="Page_xi"></a>[Pg xi]</span> -try man’s soul, and exalt it, are the search for truth -beneath the mysteries which surround creation,—to -gather amaranths, shining with the hues of heaven, -from plains upon which hang, dark and heavy, the mists -of earth. The poet may pay the debt of nature,—the -philosopher may return to the bosom of our common -mother,—even their names fade in the passage of time, -like planets blotted out of heaven but the truths -they have revealed to man burn on for ever with unextinguishable -brightness. Truth cannot die; it passes -from mind to mind, imparting light in its progress, and -constantly renewing its own brightness during its diffusion. -The True is the Beautiful; and the truths -revealed to the mind render us capable of perceiving -new beauties on the earth. The gladness of truth is like -the ringing voice of a joyous child, and the most remote -recesses echo with the cheerful sound. To be for ever -true is the Science of Poetry,—the revelation of truth -is the Poetry of Science.</p> - -<p>Man, a creation endued with mighty faculties, but a -mystery to himself, stands in the midst of a wonderful -world, and an infinite variety of phenomena arise around -him in strange form and magical disposition, like the -phantasma of a restless night.</p> - -<p>The solid rock obeys a power which brings its congeries -of atoms into a thousand shapes, each one geometrically -perfect. Its vegetable covering, in obedience -to some external excitation, developes itself in a curious -diversity of forms, from the exquisitely graceful to the -singularly grotesque, and exhibits properties still more -varied and opposed. The animal organism quickened -by higher impulses,—powers working within, and modifying -the influence of the external forces,—presents, -from the Monad to the Mammoth, and through every -phase of being up to Man, a yet more wonderful series -of combinations, and features still more strangely contrasted.</p> - -<p><span class="pagenum"><a name="Page_xii" id="Page_xii"></a>[Pg xii]</span></p> - -<p>Lifting our searching gaze into the measureless space -beyond our earth, we find planet bound to planet, and -system chained to system, all impelled by a universal -force to roll in regularity and order around a common -centre. The pendulations of the remotest star are communicated -through the unseen bond; and our rocking -world obeys the mysterious impulse throughout all those -forces which regulate the inorganic combinations of this -earth, and unto which its organic creation is irresistibly -compelled to bow.</p> - -<p>The glorious sun by day, and the moon and stars in -the silence and the mystery of night, are felt to influence -all material nature, holding the great Earth bound in a -many-stranded cord which cannot be broken. The -tidal flow of the vast ocean, with its variety of animal -and vegetable life, the atmosphere, bright with light, -obscured by the storm-cloud, spanned by the rainbow, -or rent with the explosions of electric fire,—attest to the -might of these elementary bonds.</p> - -<p>These are but a few of the great phenomena which -play their part around this globe of ours, exciting men -to wonder, or shaking them with terror.</p> - -<p>The mind of man, in its progress towards its higher -destiny, is tasked with the physical earth as a problem, -which, within the limits of a life, it must struggle to -solve. The intellectual spirit is capable of embracing -all finite things. Man is gifted with powers for studying -the entire circle of visible creation; and he is equal, -under proper training, to the task of examining much -of the secret machinery which stirs the whole.</p> - -<p>In dim outshadowing, earth’s first poets, from the -loveliness of external nature, evoked beautiful <span class="correction" title="In the original book: spirtualizations">spiritualizations</span>. -To them the shady forests teemed with aërial -beings,—the gushing springs rejoiced in fantastic sprites,—the -leaping cataracts gleamed with translucent shades,—the -cavernous hills were the abodes of genii,—and the -earth-girdling ocean was guarded by mysterious forms.<span class="pagenum"><a name="Page_xiii" id="Page_xiii"></a>[Pg xiii]</span> -Such were the creations of the far-searching mind in its -early consciousness of the existence of unseen powers. -The philosopher picked out his way through the dark -and labyrinthine path, between effects and causes, and -slowly approaching towards the light, he gathered -semblances of the great Reality, like a mirage, beautiful -and truthful, although still but a cloud-reflection of the -vast Unseen.</p> - -<p>It is thus that the human mind advances from the -Ideal to the Real, and that the poet becomes the philosopher, -and the philosopher rises into the poet; but at -the same time as we progress from fable to fact, much -of the soul-sentiment which made the romantic holy, -and gave a noble tone to every aspiration, is too -frequently merged in a cheerless philosophy which clings -to the earth, and reduces the mind to a mechanical -condition, delighting in the accumulation of facts, regardless -of the great laws by which these are regulated, -and the harmony of all Telluric combinations secured. -In science we find the elements of the most exalted -poetry; and in the mysterious workings of the physical -forces we discover connections with the illimitable world -of thought,—in which mighty minds delight to try their -powers,—as strangely complicated, and as marvellously -ordered, as in the psychological phenomena which have, -almost exclusively, been the objects of their studies.</p> - -<p>In the aspect of visible nature, with its wonderful -diversity of form and its charm of colour, we find the -Beautiful; and in the operations of these principles, -which are ever active in producing and maintaining the -existing conditions of matter, we discover the Sublime.</p> - -<p>The form and colour of a flower may excite our -admiration; but when we come to examine all the -phenomena which combine to produce that piece of -symmetry and that lovely hue,—to learn the physiological -arrangement of its structural parts,—the chemical<span class="pagenum"><a name="Page_xiv" id="Page_xiv"></a>[Pg xiv]</span> -actions by which its woody fibre and its juices are produced,—and -to investigate those laws by which is -regulated the power to throw back the white sunbeam -from its surface in coloured rays,—our admiration passes -to the higher feeling of deep astonishment at the perfection -of the processes, and of reverence for their great -Designer. There are, indeed, “tongues in trees;” but -science alone can interpret their mysterious whispers, -and in this consists its poetry.</p> - -<p>To rest content with the bare enunciation of a truth, -is to perform but one half of a task. As each atom of -matter is involved in an atmosphere of properties and -powers, which unites it to every mass of the universe, so -each truth, however common it may be, is surrounded -by impulses which, being awakened, pass from soul to -soul like musical undulations, and which will be repeated -through the echoes of space, and prolonged for all -eternity.</p> - -<p>The poetry which springs from the contemplation of -the agencies which are actively employed in producing -the transformation of matter, and which is founded upon -the truths developed by the aids of science, should be in -no respect inferior to that which has been inspired by -the beauty of the individual forms of matter, and the -pleasing character of their combinations.</p> - -<p>The imaginative view of man and his world—the -creations of the romantic mind—have been, and ever -will be, dwelt on with a soul-absorbing passion. The -mystery of our being, and the mystery of our ceasing to -be, acting upon intelligences which are for ever striving -to comprehend the enigma of themselves, leads by a -natural process to a love for the Ideal. The discovery -of those truths which advance the human mind towards -that point of knowledge to which all its secret longings -tend, should excite a higher feeling than any mere creation -of the fancy, how beautiful soever it may be. The<span class="pagenum"><a name="Page_xv" id="Page_xv"></a>[Pg xv]</span> -phenomena of Reality are more startling than the phantoms -of the Ideal. Truth is stranger than fiction. -Surely many of the discoveries of science which relate to -the combinations of matter, and exhibit results which -we could not by any previous efforts of reasoning dare -to reckon on, results which show the admirable balance -of the forces of nature, and the might of their uncontrolled -power, exhibit to our senses subjects for contemplation -truly poetic in their character.</p> - -<p>We tremble when the thunder-cloud bursts in fury -above our heads. The poet seizes on the terrors of the -storm to add to the interest of his verse. Fancy paints -a storm-king, and the genius of romance clothes his -demons in lightnings, and they are heralded by thunders. -These wild imaginings have been the delight of mankind; -there is subject for wonder in them: but is there -anything less wonderful in the well-authenticated fact, -the dew-drop which glistens on the flower, that the tear -which trembles on the eye-lid, holds locked in its transparent -cells an amount of electric fire equal to that -which is discharged during a storm from a thunder-cloud?</p> - -<p>In these studies of the effects which are continually -presenting themselves to the observing eye, and of the -phenomena of causes, as far as they are revealed by -Science in its search of the physical earth, it will be -shown that beneath the beautiful vesture of the external -world there exists, like its quickening soul, a pervading -power, assuming the most varied aspects, giving to the -whole its life and loveliness, and linking every portion -of this material mass in a common bond with some great -universal principle beyond our knowledge. Whether by -the improvement of the powers of the human mind, -man will ever be enabled to embrace within his knowledge -the laws which regulate these remote principles,<span class="pagenum"><a name="Page_xvi" id="Page_xvi"></a>[Pg xvi]</span> -we are not sufficiently advanced in intelligence to determine. -But if admitted even to a clear perception -of the theoretical Power which we regard as regulating -the known forces, we must still see an unknown agency -beyond us, which can only be referred to the Creator’s -will.</p> - -<hr class="chap" /> -</div> -<div class="chap"> - - -<p><span class="pagenum"><a name="Page_1" id="Page_1"></a>[Pg 1]</span></p> - - - - -<h2><a name="THE_POETRY_OF_SCIENCE" id="THE_POETRY_OF_SCIENCE"></a><span class="normal-title">THE<br /></span> POETRY OF SCIENCE.</h2> - - - -<hr class="chap" /> -<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.</h2> - -<p class="center">GENERAL CONDITIONS OF MATTER.</p> - - -<p class="chap-head">Its varied Characters, and constant change of external Form—The -Grain of Dust, its Properties and Powers—Combinations -in inorganic Masses and in organized Creations—Our -knowledge of Matter—Theory of Ultimate -Atoms—The Physical Forces acting on the Composition of -Masses—The certainty of the exercise of subtile principles, -which are beyond the reach of experimental Science.</p> - - -<p class="p2">The Physical Earth presents to us, in every form of -organic and inorganic matter, an infinite variety of -phenomena. If we select specimens of rocks, either -crystalline or stratified,—of metals in any of their -various combinations with oxygen, sulphur, and other -bodies,—of gems glistening with light and glowing with -colour,—if we examine the varied forms and hues of the -vegetable world, or the more mysterious animal creations, -we must inevitably come to the conclusion, long -since proclaimed, and admit that dust they are, and to -dust must they return. Whatever permanency may be -given to matter, it is certain that its form is ever in a -state of change. The surface of the<span class="pagenum"><a name="Page_2" id="Page_2"></a>[Pg 2]</span> “Eternal Hills” -is worn away by the soft rains which fall to fertilize, -and from their wrecks, borne by the waters to the -ocean, new continents are forming. The mutations of -the old earth may be read upon her rocks and mountains, -and these records of former changes tell us the infallible -truth, that as the present passes into the future, so will -the form of Earth undergo an important alteration. -The same forces which lifted the Andes and the Himalayas -are still at work, and from the particles of matter -carried from the present lands by the rivers into the sea, -where they subside in stratified masses, there will, in -the great future, be raised new worlds, upon which the -work of life will go forward, and over which will be -spread a vast Intelligence.</p> - -<p>If we regard the conditions of the beautiful and varied -organic covering of the Earth, the certainty, the constancy, -of change is ever before us. Vegetable life -passes into the animal form, and both perish to feed the -future plant. Man, moving to-day the monarch of a -mighty people, in a few years passes back to his primitive -clod, and that combination of elementary atoms, -which is dignified with the circle of sovereignty and the -robe of purple, after a period may be sought for in the -herbage of the fields, or in the humble flowers of the -valley.</p> - -<p>We have, then, this certain truth,—all things visible -around us are but aggregations of atoms. From particles -of dust, which under the microscope could scarcely -be distinguished one from the other, are all the varied -forms of nature created. This grain of dust, this particle -of sand, has strange properties and powers. Science has -discovered some truths, but still more are hidden within -this irregular molecule of matter which we now survey, -than have yet been shadowed in the dreams of our -philosophy. How strangely it obeys the impulses of -heat—mysterious are the influences of light upon it—electricity -wonderfully excites it—and still more curious<span class="pagenum"><a name="Page_3" id="Page_3"></a>[Pg 3]</span> -is the manner in which it obeys the magic of chemical -force. These are phenomena which we have seen; we -know them, and we can reproduce them at our pleasure. -We have advanced a little way into the secrets of nature, -and from the spot we have gained, we look forward -with a vision somewhat brightened by our task; but we -discover so much to be yet unknown, that we learn -another truth,—our vast ignorance of many things -relating to this grain of dust.</p> - -<p>It gathers around it other particles; they cling -together, and each acting upon every other one, and all -of them arranging themselves around the little centre -according to some law, a beautiful crystal results, the -geometric perfection of its form being a source of admiration.</p> - -<p>It exerts some other powers, and atom cohering to -atom, obeying the influences of many external radiant -forces, undergoes inexplicable changes, and the same -dust which we find forming the diamond, aggregates -into the lordly tree,—blends to produce the graceful, -scented, and richly painted flower,—and combines to -yield the luxury of fruit.</p> - -<p>It quickens with yet undiscovered energies; it moves -with life: dust is stirred by the mysterious excitement -of vital force; and blood and bone, nerve and muscle, -are the results. Forces, which we cannot by the utmost -refinements of our philosophy detect, direct the whole, -and from the same dust which formed the rock and -grew in the tree, is produced a living and a breathing -thing, capable of receiving a Divine illumination, of -bearing in its new state the gladness and the glory of a -Soul.</p> - -<p>These considerations lead us to reflect on the amount -of our knowledge. We are led to ask ourselves, what -do we know? We know that the world with all its -variety is composed of certain material atoms, which, -although presented to us in a great variety of forms, do<span class="pagenum"><a name="Page_4" id="Page_4"></a>[Pg 4]</span> -not in all probability differ very essentially from each -other.</p> - -<p>We know that those atoms obey certain conditions -which appear to be dependent upon the influences of -motion, gravitation, heat, light, electricity, and chemical -force. These powers are only known to us by their -effects; we only detect their action by their operations -upon matter; and although we regard the several -phenomena which we have discovered, as the manifestations -of different principles, it is possible they may be -but modifications of some one universal power, of which -these are but a few of its modes of action.</p> - -<p>In examining, therefore, the truths which science has -revealed to us, it is advantageous, for the purpose of -fixing the mind to the subject, that we assume certain -conditions as true. These may be stated in a few sentences, -and then, without wasting a thought upon those -metaphysical subtleties which have from time to time -perplexed science, and served to impede the progress of -truth, we shall proceed to examine our knowledge of -the phenomena which constantly occur around us.</p> - -<p>Every form, whether inorganic or organic, which we -can discover within the limits of human search, is composed -of atoms, which are capable of assuming, under -the influence of certain physical forces, conditions essential -to the physical state of that body of which they -constitute a part.<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> The known forces, active in pro<span class="pagenum"><a name="Page_5" id="Page_5"></a>[Pg 5]</span>ducing -these conditions, are modes of motion; gravitation -and aggregation, heat, light; and associated with -these, actinism or chemical radiation; electricity, under -all its conditions, whether static or dynamic; and -chemical affinity, regarded as the result of a separate -elementary principle.</p> - -<p>These forces must be considered as powers capable of -acting in perfect independence of each other. They are -possibly modifications of one principle; but this view -being an hypothesis, which, as yet, is only supported by -loose analogies, cannot, without danger, be received in -any explanation which attempts to deal only with the -truths of science.</p> - -<p>We cannot examine the varied phenomena of nature, -without feeling that there must be other and most active -principles of a higher order than any detected by science,<span class="pagenum"><a name="Page_6" id="Page_6"></a>[Pg 6]</span> -to which belong the important operations of vitality, -whether manifested in the plant or the animal. In -treating of these, although speculation cannot be entirely -avoided, it will be employed only so far as it gives any -assistance in linking phenomena together.</p> - -<p>We have to deal with the active agencies which give -form and feature to nature—which regulate the harmony -and beauty and vigour of life—and upon which depend -those grand changes in the conditions of matter, which -must convince us that death is but the commencement -of a new state of being.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> Sir Isaac Newton supposed matter to consist of hard, -impenetrable, perfectly inelastic atoms. -</p> -<p> -<span class="correction" title="In the original book: Boscovitch">Boscovich</span> regarded the constitution of matter differently. The -ultimate atom was with him a point surrounded by powers of infinite -elasticity. (See <i>Dr. Robisons Mechanical Philosophy</i>, for a -full explanation of the theory of <span class="correction" title="In the original book: Boscovitch">Boscovich</span>.) -</p> -<p> -The view entertained by Dr. Faraday, which will be comprehended -from one or two short extracts from his valuable and -suggestive paper, claims attention:— -</p> -<p> -“If the view of the constitution of matter already referred to be -assumed to be correct—and I may be allowed to speak of the -particles of matter, and the space between them (in water, or in -the vapour of water, for instance), as two different things—the -space must be taken as the only continuous part, for the particles -are considered as separated by space from each other. Space will -permeate all masses of matter in every direction like a net, except -that in the place of meshes it will form cells, isolating each atom -from its neighbours, and itself only being continuous.” -</p> -<p> -Examining the question of the conducting power of different -bodies, and observing that as space is the only continuous part, -so space, according to the received view of matter, must be at one -time a conductor, at others a non-conductor, it is remarked: -</p> -<p> -“It would seem, therefore, that, in accepting the ordinary -atomic theory, space may be proved to be a non-conductor in non-conducting -bodies, and a conductor in conducting bodies; but -the reasoning ends in this—a subversion of that theory altogether; -for, if space be an insulator, it cannot exist in conducting bodies; -and if it be a conductor, it cannot exist in insulating bodies.”—<i>A -Speculation touching Electric Conduction, and the Nature of -Matter</i>: by Michael Faraday, D.C.L., F.R.S., &c.: Philosophical -Magazine, vol. xxiv. Third Series. -</p> -<p> -See also Wollaston, <i>On the Finite Extent of the Atmosphere</i>.—Phil. -Trans. 1822. Young, <i>On the Essential Properties of -Matter</i>.—Lectures on Natural Philosophy. Mossotti, <i>On Molecular -Action</i>.—Scientific Memoirs, vol. i. p. 448.</p></div></div> - - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_7" id="Page_7"></a>[Pg 7]</span></p> - - -<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.</h2> - -<p class="center">MOTION.</p> - - -<p class="chap-head">Are the Physical Forces modes of Motion?—Motion defined—Philosophical -Views of Motion, and the Principles to which -it has been referred—Motions of the Earth and of the Solar -System—Visible Proofs of the Earth’s Motion on its Axis—Influence -of the proper Motions of the Earth on the Conditions -of Matter—Theory of the Conversion of Motion into -Heat, &c.—The Physical Forces regarded as principles independent -of Motion, although the Cause and often apparently -the Effects of it.</p> - - -<p class="p2">Many of the most eminent thinkers of the present time -are disposed to regard all the active principles of nature -as “modes of motion,”—to look upon light, heat, electricity, -and even vital force, as phenomena resulting from -“change of place” among the particles of matter; this -change, disturbance, or motion, being dependent upon -some undefined mover.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a></p> - -<p>The habit of leaving purely inductive examination for -the delusive charms of hypothesis—of viewing the<span class="pagenum"><a name="Page_8" id="Page_8"></a>[Pg 8]</span> -material world as a metaphysical bundle of essential -properties, and nothing more—has led some eminent -philosophers to struggle with the task of proving that -all the wonderful manifestations of the great physical -powers of the universe are but modifications of motion, -without the evidence of any antecedent force.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></p> - -<p>The views of <span class="correction" title="In the original book: metaphyscians">metaphysicians</span> regarding motion involve -many subtle considerations which need not at present -detain us. We can only consider motion as a change of -place in a given mass of matter. Now matter cannot -effect this of itself, no change of place being possible -without a mover; and, consequently, motion cannot be -a <i>property</i> of matter, in the strict sense in which that -term should be accepted.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a></p> -<p><span class="pagenum"><a name="Page_9" id="Page_9"></a>[Pg 9]</span></p> -<p>Motion depends upon certain external disturbing and -directing forces acting upon all matter; and, consequently, -as every mode of action is determined by some -excitement external to the body moved, motion cannot, -philosophically, be regarded otherwise than as a peculiar -affection of matter under determinable conditions. -“We find,” says Sir Isaac Newton, “but little motion -in the world, except what plainly flows from either the -active principles of nature, or from the command of the -willer.”<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a></p> -<p><span class="pagenum"><a name="Page_10" id="Page_10"></a>[Pg 10]</span></p> -<p>Plato, Aristotle, and the Pythagoreans, supposed that -throughout all nature an active principle was diffused, -upon which depended all the properties exhibited by -matter. This is the same as the “plastic nature” of -Cudworth,<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> the “intellectual and artificial fire” of -Bishop Berkeley;<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> and to these all modes of motion -were referred. Sir Isaac Newton also regards the<span class="pagenum"><a name="Page_11" id="Page_11"></a>[Pg 11]</span> -material universe and its phenomena as dependent upon -“<i>active principles</i>”—for instance, the cause of gravity—whereby -the planets and comets preserve their motions -in their orbits, and all bodies acquire a degree of motion -in falling; and the cause of fomentation—whereby the -heart and blood of animals preserve a perpetual warmth -and motion—the inner parts of the earth are kept constantly -warmed—many bodies burn and shine—and the -sun himself burns and shines, and with his light warms -and cheers all things.</p> - -<p>The earth turns on its axis at the rate of more than -1,000 miles an hour, and passes around the sun with -the speed of upwards of 68,000 miles in the same time.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> -The earth and the other planets of our system move in -ellipses around a common centre: therefore their motion -cannot have been originally communicated merely by -the impressed force of projection. Two forces, at least, -must have operated, one making the planets tend -directly to the centre, and the other impelling them to -fly off at a tangent to the curve described. Here we -have a system of spheres, held by some power to a great -central mass, around which they revolve with a fearful -velocity. Nor is this all; the Solar System itself, -bound by the same mystic chain to an undiscovered -centre, moves towards a point in space at the rate of -33,550,000 geographical miles, whilst our earth performs -one revolution around the sun.<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></p> - -<p><span class="pagenum"><a name="Page_12" id="Page_12"></a>[Pg 12]</span></p> - -<p>The evidence of the motion of the Earth around its -axis, as afforded by the swinging of a pendulum or the -rotation of a sphere, is too interesting to be omitted. -In mechanical philosophy, we have two terms of the -same general meaning—the conservation of the plane of -vibration—and the conservation of the axis of rotation. -For the non-scientific reader, these terms require -explanation, and in endeavouring to simplify this as -much as possible, we must ask the indulgence of the -Mechanical Philosopher. Let us fix in the centre of a -small round table an upright rod, having an arm extending -from its top, to which we can suspend a tolerably -heavy weight attached to a string. This is our piece of -apparatus: upon the table draw a chalk line, along -which line we intend our pendulum to swing, and continuing -this line upon the floor, or by a mark on the -wall, our arrangements are complete. Raise steadily -the bob of our pendulum, and set it free, so that its -plane of vibration is along the line which has been -marked. As the pendulum is swinging firmly along -this line, slowly and steadily turn the table round. It<span class="pagenum"><a name="Page_13" id="Page_13"></a>[Pg 13]</span> -will then be seen that the pendulum will still vibrate in the -direction of the line we have continued onward to the wall, -but that the line on the table is gradually withdrawn -from it. If we had no upright, we might turn the table -entirely round, without in the slightest degree altering -the line along which the pendulum performs its oscillations. -Now, if from some elevated spot, say, from the -centre of the dome of St. Paul’s, a long and heavy pendulum -is suspended, and if on the floor we mark the line -along which we set the pendulum free to vibrate, it will -be seen, as in the experiment with the table, that the -marked line moves away from under the pendulum. It -continues to vibrate in the plane it first described, -although the line on the earth’s surface continues to -move forward by the diurnal rotation around the axis. -Similar to this is the law of the conservation of the axis -of rotation. If a common humming-top, the spindle of -which is its axis of rotation, is set spinning obliquely, it -will be seen that the axis will continue to point along -the line it took at the commencement of motion. -By placing a heavy sphere in a lathe, resting its projecting -axial points on some moveable bearings, and then -getting the sphere into extremely rapid motion, one of the -bearings may be removed without the mass falling to -the ground. The rapidity of motion changes so constantly -and quickly the position of the particles which -have a tendency to fall, that we have motion balanced -against the force of gravitation in a striking manner; -and we learn, from this experiment, the explanation -of the planetary and stellar masses revolving on their -axis at a speed sufficient to maintain them without support -in space. A mass of matter, a sphere or a disc, -carefully balanced, is fixed in gymbals such as we employ -for fixing our compass needles, and it is set by some -mechanical contrivance in rapid rotation. The position -of the axis of rotation remains unaltered, although the -earth is moving; and thus, by this instrument,—called the<span class="pagenum"><a name="Page_14" id="Page_14"></a>[Pg 14]</span> -gyroscope,—we can determine, as with the pendulum, the -motion of the earth around its axis; and we learn why, -during its movement around the sun, its axis is undeviatingly -pointed towards one point in space, marked in -our Heavens as the Polar Star.</p> - -<p>In addition to these great rotations, the earth is subjected -to other motions, as the precession of the equinoxes -and the nutation of its axis. Rocking regularly -upon a point round which it rapidly revolves, whilst it -progresses onward in its orbit, like some huge top in -tremulous gyration upon the deck of a vast <span class="correction" title="In the original book: aerial">aërial</span> ship -gliding rapidly through space, is the earth performing -its part in the great law of motion.</p> - -<p>The rapidity of these impulses, supposing the powers -of the physical forces were for a moment suspended, -would be sufficient to scatter the mass of our planet -over space as a mere star-dust.</p> - -<p>Limiting, as much as possible, the view which opens -upon the mind as we contemplate the adjustments by -which this great machine, our system, is preserved in all -its order and beauty, let us forget the great movement -of the whole through space, and endeavour to consider -the effect of those motions which are directly related to -the earth, as a member of one small group of worlds.</p> - -<p>We cannot for a moment doubt, although we have not -any experimental proof of the fact, that the proper -motions of the earth materially influence the conditions -of the matter of which it is formed. Every pair of -atoms is, like a balance, delicately suspended, under -the constant struggle which arises from the tendency to -fly asunder, induced by one order of forces—centrifugal -force—and the efforts of others, gravitation and cohesion, -to chain them together. The spring is brought to -the highest state of tension—one tremor more, and it -would be destroyed.</p> - -<p>We cannot, by any comparison with the labours of -the most skilful human artisan, convey an idea of the<span class="pagenum"><a name="Page_15" id="Page_15"></a>[Pg 15]</span> -exquisite perfection of planetary mechanics, even so far -as they have been discovered by the labours of science; -and we must admit that our insight into the vast -machinery has been very limited.</p> - -<p>All we know is the fact that this planet moves in a -certain order, and at a fixed rate, and that the speed is -of itself sufficient to rend the hardest rocks; yet the -delicate down which rests so lightly upon the flower is -undisturbed. It is, therefore, evident that matter is -endued with powers, by which mass is bound to mass, -and atom to atom; these powers are not the results of -any of the motions which we have examined, but, -acting in antagonism to them, they sustain our globe in -its present form.</p> - -<p>Are there other motions to which these powers can be -referred? We know of none. That absolute rest may -not exist among the particles of matter is probable. -Electrical action, chemical power, crystalline aggregation, -the expansive force of heat, and many other known -agencies, are in constant operation to prevent it. It -must, however, be remembered, that each and every -atom constituting a mass may be so suspended between -the balanced forces, that it may be regarded as relatively -at rest.</p> - -<p>Theory imagines Motion as producing Force—a body -is moved, and its mere mechanical change of place is -regarded as generating heat; and hence the refinements -of modern science have advanced to the conclusion that -motion and heat are convertible. Admitting that the -material atoms of which this world is formed are never -in a state of quiescence, yet we cannot suppose any gross -ponderable particle as capable of moving itself; but -once set in motion, it may become the secondary cause -of motion in other particles.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> The difficulties of the<span class="pagenum"><a name="Page_16" id="Page_16"></a>[Pg 16]</span> -case would appear to have been as follows:—Are heat, -light, electricity, &c., material bodies? If they are -material bodies—and heat, for example, is the cause of -motion—must not the calorific matter move itself—or if -it be not self-moving, by what is it moved? If heat is -material, and the primary cause of motion, then matter -must have an innate power of moving; it can convert -itself into active force, or be at once a cause and an -effect, which can scarcely be regarded as a logical -deduction.</p> - -<p>We move a particle of matter, and heat is manifested; -the force being continued, light, electricity, and chemical -action result; all, as appears from a limited view of<span class="pagenum"><a name="Page_17" id="Page_17"></a>[Pg 17]</span> -the phenomena, arising out of the mechanical force -applied to the particle first moved.<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> This mechanical -force, it must be remembered, is external to the body -moved, and is, in all probability, set up by the movement -of a muscle, acted upon by nerves, under the -influence of a will.</p> - -<p>The series of phenomena we have supposed to arise -admit of an explanation free of the hypothesis of motion, -and we avoid the dangerous ground of metaphysical -speculation, and the subtleties of that logic which rests -upon the immateriality of all creation. This explanation, it -is freely admitted, is incomplete: we cannot distinctly -correlate each feature of the phenomena, combine link -to link, and thus form a perfect chain; but it is sufficiently -clear to exhibit what we do know, and leave the -unknown free for unbiassed investigation.</p> - -<p>Each particle, each atom of that which conveys to our -senses the only ideas we have of natural objects—ponderable -matter—is involved in, or interpenetrated by, -those principles which we call heat and electricity, with -probably many others which are unknown to us; and -although these principles or powers are, according to -some law, bound in statical equilibrium to inert matter, -they are freely developed by an external excitement, and -the disturbance of any one of them, upsetting the equilibrium, -leaves the other power equally free to be brought -under the cognizance of human sense by their effects.</p> - -<p>When we come to an examination of the influences -exerted by these powers upon the physical earth, the -position, that they must be regarded as the causes of -motion rather than the effects of it, will be further considered. -At present it is only necessary to state thus<span class="pagenum"><a name="Page_18" id="Page_18"></a>[Pg 18]</span> -generally the views we entertain of the conditions of -matter in connection with the imponderable forces and -mechanical powers. The conversion, as it has been -called, of motion into heat, in the experiments of Count -Rumford and Mr. Joule,<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> are only evidences that a<span class="pagenum"><a name="Page_19" id="Page_19"></a>[Pg 19]</span> -certain uniformity exists between the mechanical force -applied, and the amount of heat liberated. It does not -appear that we have any proof of the conversion of -motion into physical power.</p> - -<p>It is necessary, to a satisfactory contemplation of the -wonderful properties of matter, and of the forces regulating -the forms of the entire creation, that we should -be content with regarding the elementary bodies which -chemistry instructs us form our globe, as tangible, ponderable -atoms, having specific and distinguishing properties. -That we should, as far as it is possible for<span class="pagenum"><a name="Page_20" id="Page_20"></a>[Pg 20]</span> -finite minds to do so, endeavour to conceive the powers -or forces—gravitation, molecular attraction, electricity, -heat, light, and the principle which determines all -chemical phenomena—as manifestations of agencies -which hold a place between the most subtile form of -matter and the hidden principles of vitality, which is still -vastly inferior to the spiritual state, which reveals itself -dimly in psychological phenomena, and arrives at its -sublimity in the God of the universe.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> “Motion, therefore, is a change of rectilinear distance between -two points. Allowing the accuracy of this definition, it appears -that two points are necessary to constitute motion; that in all -cases, when we are inquiring whether or no any body or point is -in motion, we must recur to some other point which we can compare -with it; and that if a single atom existed alone in the universe, -it could neither be said to be in motion nor at rest. -</p> -<p> -“The space which we call quiescent is in general the earth’s -surface; yet we well know, from astronomical considerations, that -every point of the earth’s surface is perpetually in motion, and that -in very various directions: nor are any material objects accessible -to our senses which we can consider as absolutely motionless, or -even as motionless with regard to each other; since the continual -variation of temperature to which all bodies are liable, and the -minute agitations arising from the motion of other bodies with -which they are connected, will always tend to produce some imperceptible -changes in their distances.”—<i>Lectures on Natural -Philosophy, &c.</i>, by Thomas Young, M.D. Edited by the Rev. P. -Kelland. 1845.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> “The position which I seek to establish in this essay is, that -the various imponderable agencies, or the affections of matter -which constitute the main objects of experimental physics, viz., -heat, light, electricity, magnetism, chemical affinity, and motion, -are all correlative, or have a reciprocal dependence;—that neither, -taken abstractedly, can be said to be the essential or proximate -cause of the others; but that either may, as a force, produce, or be -convertible into, the other:—thus heat may mediately or immediately -produce electricity, electricity may produce heat, and so of -the rest.... Although strongly inclined to believe that the -five other affections of matter, which I have above named, are, and -will ultimately be, resolved into modes of motion, it would be -going too far at present to assume their identity with it: I, therefore, -use the term force, in reference to them, as meaning that -active force inseparable from matter, which induces its various -changes.”—<i>On the Correlation of Physical Forces</i>, by W. R. <span class="smcap">Grove</span>, -Esq., M.A., F.R.S.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> When discussing the hypothesis of Hobbes—<i>that no body can -possibly be moved but by a body contiguous and moved</i>—Boyle asks:— -</p> -<p> -“I demand how there comes to be local motion in the world? -For either all the portions of matter that compose the universe -have motion belonging to their natures, which the Epicureans -affirmed for their atoms, or some parts of matter have this motive -power, and some have not, or else none of them have it; but all -of them are naturally devoid of motion. If it be granted that -motion does naturally belong to all parts of matter, the dispute is -at an end, the concession quite overthrowing the hypothesis. -</p> -<p> -“If Mr. Hobbes should reply that the motion is impressed -upon any of the parts of matter by God, he will say that which -I most readily grant to be true, but will not serve his turn, if he -would speak congruously with his own hypothesis. For I demand -whether this Supreme Being that the assertion has recourse to, be -a corporeal or an incorporeal substance? If it be the latter, and -yet the efficient cause of motion in bodies, then it will not be universally -true that whatever body is moved is so by a body contiguous -and moved. For, in our supposition, the bodies that God -moves, either immediately or by the intervention of any other -immaterial being, are not moved by a body contiguous, but by an -incorporeal spirit.”—<i>Some Considerations about the Reconcileableness -of Reason and Religion</i>: Boyle, vol. iii. p. 520.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> Boyle has some ingenious speculations on this point:— -</p> -<p> -“That there is local motion in many parts of matter is manifest -to sense, but how matter came by this motion was of old, and is -still, hotly disputed of: for the ancient Corpuscularian philosophers -(whose doctrine in most other points, though not in all, we -are the most inclinable to), not acknowledging an author of the -universe, were thereby reduced to make motion congenite to -matter, and consequently coeval with it. But since local motion, -or an endeavour at it, is not included in the nature of matter, -which is as much matter when it rests as when it moves; and -since we see that the same portion of matter may from motion be -reduced to rest, and after it hath continued at rest, so long as other -bodies do not put it out of that state, may by external agents be -set a moving again; I, who am not wont to think a man the worse -naturalist for not being an atheist, shall not scruple to say with an -eminent philosopher of old, whom I find to have proposed among -the Greeks that opinion (for the main) that the excellent Des Cartes -has revived amongst us, that the origin of motion in matter is -from God; and not only so, but that thinking it very unfit to be -believed, that matter barely put into motion, and then left to -itself, should casually constitute this beautiful and orderly world; -I think also further, that the wise Author of things did, by establishing -the laws of motion among bodies, and by guiding the first -motions of the small parts of matter, bring them to convene after -the manner requisite to compose the world; and especially did -contrive those curious and elaborate engines, the bodies of living -creatures, endowing most of them with the power of propagating -their species.”—<i>Considerations and Experiments touching the Origin -of Forms and Qualities</i>: Boyle’s Works, vol. ii. p. 460. Edinburgh. -1744.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> Cudworth’s <i>Intellectual System</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> “According to the Pythagoreans and Platonists, there is a -life infused throughout all things ... an intellectual and -artificial fire—an inward principle, animal spirit, or natural life, -producing or forming within, as art doth without—regulating, -moderating, and reconciling the various motions, qualities, and -parts of the mundane system. By virtue of this life, the great -masses are held together in their ordinary courses, as well as the -minutest particles governed in their natural motions, according to -the several laws of attraction, gravity, electricity, magnetism, and -the rest. It is this gives instincts, teaches the spider her web, and -the bee her honey;—this it is that directs the roots of plants to -draw forth juice from the earth, and the leaves and the cortical -vessels to separate and attract such particles of air and elementary -fire as suit their respective natures.”—Bishop Berkeley, <i>Siris</i>, -No. 277.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> “The revolution of the earth is performed in a natural day, -or, more strictly speaking, once in 23h. 56' 4", and as its mean -circumference is 24,871 miles, it follows that any point in its equatorial -surface has a rotatory motion of more than 1,000 miles per -hour. This velocity must gradually diminish to nothing at either -pole. Whilst the earth is thus revolving on its axis, it has a progressive -motion in its orbit. If we take the length of the earth’s -orbit at 630,000,000, its motion through space must exceed 68,490 -miles in the hour.”—Enc. Brit. art. <i>Physical Geography</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> “Here then we have the splendid result of the united studies -of MM. Argelander, O. Struve, and Peters, grounded on observations -made at the three observatories of Dorpat, Abo, Pulkova, -and which is expressed in the following thesis:—The motion of -the solar system in space is directed to a point of the celestial -vault situated on the right line which joins the two stars π and μ -<i>Herculis</i>, at a quarter of the apparent distance of these stars, -reckoning from π <i>Herculis</i>. The velocity of this motion is such, -that the sun, with all the bodies which depend upon it, advances -annually in the above direction 1·623 times the radius of the -earth’s orbit, or 33,550,000 geographical miles. The possible -error of this last number amounts to 1,733,000 geographical miles, -or to a <i>seventh</i> of the whole value. We may then wager 400,000 -to 1 that the sun has a proper progressive motion, and 1 to 1 that -it is comprised between the limits of thirty-eight and twenty-nine -millions of geographical miles.”—<i>Etudes d’Astronomie Stellaire: -Sur la Voie Lactée et sur les Distances des Etoiles Fixes</i>: M. F. -W. G. Struve. [A report addressed to his Excellency M. Le -Comte Ouvaroff; Minister of Public Instruction and President of -the Imperial Academy of Sciences at St. Petersburg.]</p></div> - -<div class="footnote"> - -<p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> “The first great agent which the analysis of natural phenomena -offers to our consideration, more frequently and prominently -than any other, is force. Its effects are either, 1st, to counteract -the exertion of opposing force, and thereby to maintain <i>equilibrium</i>; -or, 2ndly, to produce <i>motion</i> in matter, -</p> -<p> -“Matter, or that whatever it be of which all the objects in nature -which manifest themselves directly to our senses consist, presents -us with two general qualities, which at first sight appear to -stand in contradiction to each other—activity and inertness. -Its activity is proved by its power of spontaneously setting other -matter in motion, and of itself obeying their mutual impulse, -and moving under the influence of its own and other force; -inertness, in refusing to move unless obliged to do so by a force -impressed externally, or mutually exerted between itself and -other matter, and by persisting in its state of motion or rest -unless disturbed by some external cause. Yet, in reality, this -contradiction is only apparent. Force being the cause, and -motion the effect produced by it on matter, to say that matter is -inert, or has <i>inertia</i>, as it is termed, is only to say that the cause -is expended in producing its effect, and that the same cause -cannot (without renewal) produce double or triple its own proper -effect. In this point of view, equilibrium may be conceived as a -continual production of two opposite effects, each, undoing at -every instant what the other has done,”?—See continuation of -the argument in <i>Herschel’s Discourse on the Study of Natural -Philosophy</i>, page 223. -</p> -<p> -In the Edinburgh New Philosophical Journal, vol. xlv., will be -found a paper by Dr Robert Brown—“<i>Of the sources of motions -upon the Earth, and of the means by which they are sustained</i>,” -which will well repay an attentive perusal, as pointing to a class -of investigation of the highest order, and containing deductions of -the most philosophic description.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> Friction, it is well known, generates heat; by rapidly rubbing -two sticks together, the Indian produces their ignition; heat and -light being both manifested. Under every mechanical disturbance -electrical changes can be detected, and the action of heat in -the combustion of the wood is a chemical phenomenon.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> Count Rumford’s experiment consisted in placing a mass of -metal in a box of water at a known temperature, and, by employing -a boring apparatus, ascertaining carefully the increase of -heat after a given number of revolutions. He thus describes his -most satisfactory experiment:— -</p> -<p> -“Everything being ready, I proceeded to make the experiment -I had projected, in the following manner. The hollow -cylinder having been previously cleaned out, and the inside of -its bore wiped with a clean towel till it was quite dry, the square -iron bar, with the blunt steel borer fixed to the end of it, was -put into its place; the mouth of the bore of the cylinder being -closed at the same time by means of the circular piston through -the centre of which the iron bar passed. -</p> -<p> -“This being done, the box was put in its place; and the joinings -of the iron rod, and of the neck of the cylinder with the -two ends of the box, having been made water-tight, by means of -collars of oiled leather, the box was filled with cold water (viz., at -the temperature of 60°) and the machine was put in motion. The -result of this beautiful experiment was very striking, and the -pleasure it afforded me amply repaid me for all the trouble I had -had, in contriving and arranging the complicated machinery used -in making it. The cylinder, revolving at the rate of about thirty-two -times in a minute, had been in motion but a short time, when -I perceived, by putting my hand into the water and touching the -outside of the cylinder, that heat was generated, and it was not -long before the water which surrounded the cylinder began to be -sensibly warm. At the end of one hour, I found, by plunging -a thermometer into the water in the box (the quantity of which -fluid amounted to 18·77 lbs. avoirdupois, or 2–1/4 wine gallons), -that its temperature had been raised no less than 47°; being -now 107° of Fahrenheit’s scale. When thirty minutes more -had elapsed, or one hour and thirty minutes after the machinery -had been put in motion, the heat of the water in the box was -142°. At the end of two hours, reckoning from the beginning -of the experiment, the temperature of the water was found to be -raised to 178°. At two hours twenty minutes it was at 200°; -and at two hours thirty minutes it <i>actually boiled</i>.”—<i>Inquiry -concerning the Source of the Heat excited by Friction</i>: Philosophical -Transactions, vol. lxxxviii. <span class="smcap">a.d.</span> 1798. -</p> -<p> -“Mr. Joule brought a communication on the same subject before -the British Association at Cambridge, which was afterwards -published in the Philosophical Magazine, and from that journal -the following notices are extracted:— -</p> -<p> -“The apparatus exhibited before the Association consisted of -a brass paddle-wheel, working horizontally in a can of water. -Motion could be communicated to this paddle by means of -weights, pulleys, &c. The paddle moved with great resistance -in the can of water, so that the weights (each of four pounds) -descended at the slow rate of about one foot per second. The -height of the pulleys from the ground was twelve yards, and -consequently when the weights had descended through that distance -they had to be wound up again in order to renew the -motion of the paddle. After this operation had been repeated -sixteen times, the increase of the temperature of the water was -ascertained by means of a very sensible and accurate thermometer. -</p> -<p> -“A series of nine experiments was performed in the above -manner, and nine experiments were made in order to eliminate -the cooling or heating effects of the atmosphere. After reducing -the result to the capacity for heat of a pound of water, it appeared -that for each degree of heat evolved by the friction of -water, a mechanical power equal to that which can raise a weight -of 890 lbs. to the height of one foot, had been expended. -</p> -<p> -“Any of your readers who are so fortunate as to reside amid -the romantic scenery of Wales or Scotland could, I doubt not, -confirm my experiments by trying the temperature of the water -at the top and at the bottom of a cascade. If my views be correct, -a fall of 817 feet will of course generate one degree of heat, -and the temperature of the river Niagara will be raised about -one fifth of a degree by its fall of 160 feet.”—<i>Relation between -Heat and Mechanical Power</i>: Philosoph. Mag. vol. xxvii. 1845.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_21" id="Page_21"></a>[Pg 21]</span></p> - - - -<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III.</h2> - -<p class="center">GRAVITATION.</p> - - -<p class="chap-head">The Forms of Matter—Shape of the Earth—Probability of the -Mass forming this Planet having existed in a Nebulous State—Zodiacal -Lights—Comets—Volatilization of Solid Matter -by Artificial means—The principle of Gravitation—Its Influence -through Space and within the smallest Limits—Gravitating -powers of the Planets—Density of the Earth—Certainty -of Newton’s Law of the Inverse Square—Discovery of -Neptune—State of a Body relieved from Gravitation—Experiment -explaining Saturn’s Ring, &c.—General inference.</p> - - -<p class="p2">Let us suppose the earth—consisting of three conditions -of matter; the solid, the fluid, and the aëriform—to be -set free from that power by which it is retained in its -present form of a spheroid flattened at the poles, but -still subject to the influences of its diurnal and annual -rotations. Agreeably to the law which regulates the -conditions of all bodies moving at high velocities, the -consequence of such a state of things would be, that our -planet would instantly spread itself over an enormous -area. The waters and even the solid masses of this -globe would, in all probability, present themselves amidst -the other phenomena of space in a highly attenuated -state, revolving in an orbit around the sun, as a band of -nebulous matter, which might sometimes be rendered -sensible to sight by still reflecting solar light, or by -condensation in the form of flights of shooting stars.<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a></p> -<p><span class="pagenum"><a name="Page_22" id="Page_22"></a>[Pg 22]</span></p> -<p>This may be illustrated by experiment. If upon a -rapidly revolving disc we place a ball of dust, it will be -almost immediately spread out, and its particles will -arrange themselves in a series of regular curves, varying<span class="pagenum"><a name="Page_23" id="Page_23"></a>[Pg 23]</span> -with the velocity of the motion. In addition to the disintegration -which would arise from the tendency of the -atoms to fly from the centre, the motion, in space, of -the planetary mass would naturally occasion a trailing -out, and the only degree of uniformity which this orb -could, under these imaginary conditions, possibly present, -would be derived from the combined effects of -motions in different directions.</p> - -<p>Amid the remoter stars, some remarkable cloud-like -appearances are discovered. These nebulæ, presenting -to the eye of the observer only a gleaming light, as from -some phosphorescent vapour, were long regarded as -indications of such a condition as that which we have -just been considering. Astronomers saw, in those mysterious -nebulæ, a confirmation of their views, which -regarded all the orbs of the firmament as having once -been thin sheets of vapour, which had gradually, from -irregular bodies traversing space, been slowly condensed -about a centre, and brought within the limits of aggregating -agencies, until, after the lapse of ages, they -become sphered stars, moving in harmony amid the -bright host of heaven.<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a> Geologists seized on those<span class="pagenum"><a name="Page_24" id="Page_24"></a>[Pg 24]</span> -views with eagerness, as confirming theoretical conclusions -deduced from an examination of the structure of -the earth itself, and explained by them the gradual -accretion of atoms into crystalline rocks from a cooling -mass.</p> -<p><span class="pagenum"><a name="Page_25" id="Page_25"></a>[Pg 25]</span></p> -<p>The researches of modern astronomers, aided by the -magnificent instruments of Lord Rosse,<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a> have, however, -shown that many of the most remarkable nebulæ are -only clusters of stars; so remote from us, that the light -from them appears blended into one diffused sheet or -luminous film. There are, however, the Magellanic -clouds, and other singular patches of light, exhibiting -changes which can only be explained on the theory of -their slow condensation. There is no evidence to disprove -the position that world-formation may still be -going on; that a slow and gradual aggregation of particles, -under the influence of laws with which we are -acquainted, may be constantly in progress, to end, eventually, -in the formation of a sphere.</p> - -<p>May we not regard the zodiacal light as the remains -of a solar luminiferous atmosphere, which once embraced -the entire system of which it is the centre?<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a href="#Footnote_16_16" class="fnanchor">[16]</a> Will not<span class="pagenum"><a name="Page_26" id="Page_26"></a>[Pg 26]</span> -the strange changes which have been <i>seen to take place</i> -in cometary bodies, even whilst they were passing near -the earth,—as the division of Biela’s comet and the -ultimate formation of a second nucleus from the detached -portion,—strongly tend to support the probability -of the idea that attenuated matter has, in the progress -of time, been condensed into solid masses, and -that nebulous clouds must still exist in every state of -tenuity in the regions of infinite space,<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a> which, in the<span class="pagenum"><a name="Page_27" id="Page_27"></a>[Pg 27]</span> -mysterious processes of world-formation, will, eventually, -become stars, and reflect across the blue immensity of -heaven, in brightness, that light which is the necessary -agent of organisation and all <span class="correction" title="In the original book: manifestatious">manifestations</span> of beauty?</p> - -<p>The inferences drawn from a careful study of the condition -of our own globe are in favour of the assumption -of the existence of nebulous matter. By the processes -of art and manufacture, by the operation of those powers -on which organisation and life depend, solid matter is -constantly poured off in such a state that it cannot be -detected, <i>as matter</i>, by any of the human senses. Yet -a thousand results, daily and hourly accumulating as -truths around us, prove that the solid metals, the gross -earths, and the constituents of animal and vegetable life, -all pass away invisible to us, and become “thin air.” -We know that, floating around us, these volatilized -bodies exist in some material form, and numerous experiments -in chemistry are calculated to convince us, -that the most attenuated air is capable, with a slight -change of circumstances, of being converted into the -condition of solid masses. Hydrogen gas, the lightest, -the most ethereal of the chemical elements, dissolves iron -and zinc, arsenic, sulphur, and carbon; and from the -transparent combinations thus formed, we can with -facility separate those ponderous bodies. Such substances -must exist in our own atmosphere; why not -in the regions of space? Whether this planet ever -floated a mass of nebulous matter, only known by its -dim and filmy light, or comet-like rushed through -space with widely eccentric orbit, are questions which -can only receive the reply of speculative minds. -Whether the earth and the other members of the Solar -System were ever parts of a Central Sun,<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a> and thrown<span class="pagenum"><a name="Page_28" id="Page_28"></a>[Pg 28]</span> -from it by some mighty convulsion, though now revolving -with all the other masses around that orb, chained -in their circuits by some infinite power, is beyond the -utmost refinements of science to discover. This hypothesis -is, however, in its sublime conception, worthy of -the master-mind that gave it birth.</p> - -<p>All we know is, that our earth is an oblate sphere, -which, by the effects of its rotation around an axis, is -somewhat enlarged at the equator and flattened at the -poles;—that it maintains its regular course around the -sun, in virtue of the operation of two forces, one of<span class="pagenum"><a name="Page_29" id="Page_29"></a>[Pg 29]</span> -which, acting constantly, would eventually draw it -into the body of the sun itself; but that it is opposed -by the other, centrifugal force, and the varying -momentum of the revolving mass;—that the same -force acting from the centre of the earth itself, and -from the centre of every particle of its substance, -resolves the whole into a globular form.</p> - -<p>The principle of Gravitation<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" class="fnanchor">[19]</a> is that force which -resides in every form of matter, by which particle is -attracted by particle, and mass by mass, the less -towards the greater. What this may be, we scarcely -dare to speculate. In the vast area of its action, which -opens before the eye of the mind, we see a power spanning -all space, and linking together every one of those -myriads of worlds which spangle the robe of the Infinite, -and we are compelled to pause. Is this principle -of gravitation a property of matter, or is it a power -higher than the more tangible forces, is the question -which presses on the mind. If we regard it as a subtile -principle pervading all space, we compel ourselves to -look beyond it for another power yet more refined; and -we cannot halt until, ascending from the limitable to -the illimitable, we resolve gravitation and its governing -influences to the centre of all power—the will of the -eternal Creator.</p> - -<p>Science has developed the grand truth, that it is by -the exercise of this all-pervading influence that the -earth is retained in its orbit—that the pellucid globe of -dew which glistens on the leaf is bound together—that -the débris which float upon the lake accumulate into -one mass—that the sea exhibits the phenomena of the -tides—and the aërial ocean its barometric changes. In -all things this force is active, and throughout nature it -is ever present. Our knowledge of the laws which it<span class="pagenum"><a name="Page_30" id="Page_30"></a>[Pg 30]</span> -obeys, enables us to conclude that the sun and distant -planets are consolidated masses like this earth. We -find that they have gravitating power, and by comparing -this influence with that exerted by the earth, we -are enabled to weigh the mass of one planet against -another. In the balance of the astronomer, it is as -easy to poise the remote star, as it is for the engineer -to calculate the weight of the iron tunnel of the Menai -Straits, or any other mechanical structure. Thus throughout -the universe the balance of gravitating force is unerringly -sustained. If one of the most remote of those -gems of light, which flicker at midnight in the dark -distance of the starry vault, was, by any power, removed -from its place, the disturbance of these delicately balanced -mysteries would be felt through all the created -systems of worlds.</p> - -<p>From the peculiarity of the laws which this power -called gravity obeys, it has been inferred that it acts -from centres of force; it is proved that its power diminishes -in the inverse ratio of the square of the distance, -and that the gravitating power of every material body -is in the direct proportion of its mass. In astronomical -calculations we have first to learn the mass of our -earth. Experiment informs us that the density of our -hardest rock is not above 2·8; but from the enormous -pressure to which matter must be subjected, at great -depths from the surface, the weight of the superincumbent -mass constantly increasing, it is quite certain -that the earth’s density must be far more than this. -Maskelyne determined the attraction of large masses -by a plummet and line on the mountain Schehallion.<span class="pagenum"><a name="Page_31" id="Page_31"></a>[Pg 31]</span><a name="FNanchor_20_20" id="FNanchor_20_20"></a><a href="#Footnote_20_20" class="fnanchor">[20]</a> -Cavendish, with exceedingly delicate apparatus, observed -the attraction of masses of known weight and size upon -each other. Applying the powers of arithmetical calculation, -and the data obtained from the small experiments -to the larger phenomena, Maskelyne determined -the earth’s mean density to be 4·71, whilst Cavendish -made it 5·48, but the more recent refined investigations -of Baily have determined it to be 5·67.<a name="FNanchor_21_21" id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a></p> - -<p>From data thus obtained by severe inductive experiments -and mathematical analyses, the astronomer, by -observing the deviations of a distant star, is enabled to -determine the influence of those stellar bodies near -which it passes, and, hence, to calculate the relative -magnitudes of each. The accuracy of the law is in this -way put to the severest test, and the precision of astronomical -prediction is the strongest proof of its universality -and truth.</p> - -<p>Rolling onward its lonely way, in the far immensity -of our system, the planet Uranus was discovered by -the elder Herschel,—so great its distance that its -diminished light could scarcely be detected by the -most powerful telescopes; but since its discovery its -path has been carefully watched, and some irregularities -noticed. Most of these disturbances were referable -to known causes; but a little alteration in its rate of -motion observed when the planet was in one portion -of its vast orbit was unexplained. Convinced of the -certainty of Newton’s law, and having determined -that the attraction of known masses was insufficient<span class="pagenum"><a name="Page_32" id="Page_32"></a>[Pg 32]</span> -to produce the disturbance observed, these deviations -were referred to the gravitating influence of a mass -beyond the known limits of our Solar System. By -the investigations of Adams in England,<a name="FNanchor_22_22" id="FNanchor_22_22"></a><a href="#Footnote_22_22" class="fnanchor">[22]</a> and Le Verrier -in France,<a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a> the place of the hypothetical mass was -determined, and its size computed. As a grand -confirmation of the great law, and to the glory of those -two far-searching minds, who do honour to their -respective countries and their age, the hypothesis -became a fact, in the discovery of the planet Neptune -in the place determined by rigorous calculation. Astronomy -affords other examples of the sublime truth of -the law of gravitation, than which science can afford no -more elevated poetry.</p> - -<p>So completely is all nature locked in the bonds of -this infinite power, that it is no poetic exaggeration to -declare, that the blow which rends any earthly mass -is conveyed by successive impulses to every one of the -myriads of orbs, which are even too remote for the -reach of telescopic vision.</p> - -<p>An illustrative experiment must close our consideration -of relative operations of rotation and gravitation. We well -know that a body in a fluid state would, if suspended above -the earth, it being at the same time free to take any form, -naturally assume that of a flattened spheroid, from the -action of the mass of the earth upon it: whereas the -force of cohesive attraction acting equally from all sides -of a centre, would, if uninfluenced, necessarily produce -a perfect sphere. The best method of showing that this -would be the case, is as follows:—</p> - -<p>Alcohol and water are to be mixed together until the<span class="pagenum"><a name="Page_33" id="Page_33"></a>[Pg 33]</span> -fluid is of the same specific gravity as olive oil. If, when -this is effected, we drop globules of the oil into the -mixed fluid, it will be seen that they take an orbicular -form;—and, of course, in this experiment the power of -the earth’s gravitating influence is neutralized. The -same drops of oil under any other conditions would be -flattened. Simple as this illustration is, it tells much of -the wondrous secret of those beautifully balanced forces -of cohesion and of gravitation; and from the prosaic -fact we rise to a great philosophical truth. Our experiment -may lead us yet farther in exemplification of -known phenomena. If we pass a steel wire through -one of those floating spheres of oil, and make it revolve -rapidly and steadily, thus imitating the motion of a -planet on its axis, the oil spreads out, and we have the -spheroidal form of our earth. Increase the rapidity of -this rotation, and when a certain rate is obtained the -oil widens into a disc, a ring separates itself from -a central globe, and at a distance from it still revolves -around it.<a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a> Here we have a miniature representation of<span class="pagenum"><a name="Page_34" id="Page_34"></a>[Pg 34]</span> -the ring of Saturn. This is a suggestive experiment, -the repetition of which, by reflective minds, cannot fail -to lead to important deductions. The phenomena of -cohesion, of motion, and gravitation, are all involved; -and we produce results resembling, in a striking manner, -the conditions which prevail in the planetary spaces, -under the influence of the same powers. If we take -a glass globe, and having filled it with a fluid of the -proper density, drop into it large and small globules of -oil, we may produce an instructive representation of -the stellar vault, with its beautiful spheres of light -revolving in their respective orbits; and though crossing -each other’s paths, still moving in obedience to -attracting and repelling forces—onward in perfect -harmony.</p> - -<p>From the centre of our earth to the utmost extremity -of the universe—from the infinitely small to the immensely -vast—gravitation exerts its force. It is met -on all sides by physical powers acting in antagonism to -it, but, like a ruling spirit, it restrains them in their -wildest moods.</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">The smallest dust which floats upon the wind</div> -<div class="verse">Bears this strong impress of the Eternal Mind.</div> -<div class="verse">In mystery round it, subtile forces roll;</div> -<div class="verse">And gravitation binds and guides the whole.</div> -<div class="verse">In every sand, before the tempest hurl’d,</div> -<div class="verse">Lie locked the powers which regulate a world,</div> -<div class="verse">And from each atom human thought may rise</div> -<div class="verse">With might to pierce the mysteries of the skies,—</div> -<div class="verse">To try each force which rules the mighty plan,</div> -<div class="verse">Of moving planets, or of breathing man;</div> -<div class="verse">And from the secret wonders of each sod,</div> -<div class="verse">Evoke the truths, and learn the power of God.</div> -</div></div></div> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> Three hypotheses may be used to account for this most curious -phenomenon. -</p> -<p> -1st. The body shines by its own light, and then explodes like a -sky-rocket, breaking into minute fragments too small to be any -longer visible to the naked eye. -</p> -<p> -2nd. Such a body, having shone by its own light, suddenly -ceases to be luminous. “The falling stars and other fiery meteors -which are frequently seen at a considerable height in the atmosphere, -and which have received different names according to the -variety of their figure and size, arise from the fermentation of the -effluvia of acid and alkaline bodies which float in the atmosphere. -When the more subtile parts of the effluvia are burned away, the -viscous and earthy parts become too heavy for the air to support, -and by their gravity fall to the earth.”—Keith’s <i>Use of the Globes</i>. -According to Sir Humphry Davy, in the Philosophical Transactions -for 1847, “the luminous appearances of shooting stars and -meteors cannot be owing to any inflammation of elastic fluids, but -must depend upon the ignition of solid bodies.” -</p> -<p> -3. The body shines by the reflected light of the sun, and ceases -to be visible by its passing into the earth’s shadow, or, in other -words, is eclipsed. Upon the two former suppositions the fact of -the star’s disappearance conveys to us no knowledge of its position, -or of its distance from the earth; and all that can be said is, that -if it be a satellite of the earth, the great rapidity of its motion involves -the necessity of its being at no great distance from the earth’s -surface—much nearer than the moon; while the resistance it -would encounter in traversing the air would be so great that it is -probably without the limits of our atmosphere. <i>Sir J. W. Lubbock -leans to the third hypothesis.</i>—Sir J. W. Lubbock, <i>On Shooting -Stars</i>: Phil. Mag. No. 213, p. 81. -</p> -<p> -Sir J. Lubbock also published a supplementary paper on the -same subject, in No. 214, p. 170. -</p> -<p> -Mr. J. P. Joule entertains an hypothesis with respect to Shooting -Stars similar to that advocated by Chladni to account for meteoric -stones, and he reckons the ignition of these miniature planetary -bodies by their violent collision with our atmosphere, to be a remarkable -illustration of the doctrine of the equivalency of heat to -mechanical power, or <i>vis viva</i>. -</p> -<p> -If we suppose a meteoric stone of the size of a six-inch cube to -enter our atmosphere at the rate of eighteen miles per second of -time, the atmosphere being 1/100 of its density at the earth’s surface, -the resistance offered to the motion of the stone will in this case -be at least 51,600 lbs.; and if the stone traverse twenty miles with -this amount of resistance, sufficient heat will thereby be developed -to give 1° Fahrenheit to 6,967,980 lbs. of water. Of course by far -the largest portion of this heat will be given to the displaced air, -every particle of which will sustain the shock, whilst only the surface -of the stone will be in violent collision with the atmosphere. -Hence the stone may be considered as placed in a blast of intensely -heated air, the heat being communicated from the surface to the -centre by conduction. Only a small portion of the heat evolved -will therefore be received by the stone; but if we estimate it at -only 1/100 it will still be equal to 1° Fahrenheit per 69,679 lbs. of -water, a quantity quite equal to the melting and dissipation of any -materials of which it may be composed.—Mr. J. P. Joule, <i>On Shooting -Stars</i>: Phil. Mag. No. 216, p. 348.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> “Laplace conjectures that in the original condition of the solar -system, the sun revolved upon his axis, surrounded by an atmosphere -which, in virtue of an excessive heat, extended far beyond -the orbits of all the planets, the planets as yet having no existence. -The heat gradually diminished, and as the solar atmosphere contracted -by cooling, the rapidity of its rotation increased by the laws -of rotatory motion; and an exterior zone of vapour was detached -from the rest, the central attraction being no longer able to overcome -the increased centrifugal force. This zone of vapour might -in some cases retain its form, as we see it in Saturn’s ring; but -more usually the ring of vapour would break into several masses, -and these would generally coalesce into one mass, which would revolve -about the sun,”—Whewell’s <i>Bridgewater Treatise</i>. -</p> -<p> -The following passage is translated by the same author from -Laplace:— -</p> -<p> -“The anterior state (a state of cloudy brightness) was itself preceded -by other states, in which the nebulous matter was more and -more diffuse, the nucleus being less and less luminous. We arrive -in this manner at a nebulosity so diffuse, that its existence could -scarce be suspected. Such is in fact the first state of the nebula -which Herschel carefully observed by means of his telescope.” -</p> -<p> -Sir William Herschel has the following observations on these -remarkable masses:— -</p> -<p> -“The nature of planetary nebulæ, which has hitherto been involved -in much darkness, may now be explained with some degree -of satisfaction, since the uniform and very considerable brightness -of their apparent disc accords remarkably well with a much condensed, -luminous fluid; whereas, to suppose them to consist of -clustering stars will not so completely account for the milkiness or -soft tint of their light, to produce which it would be required that -the condensation of the stars should be carried to an almost inconceivable -degree of accumulation. -</p> -<p> -“How far the light that is perpetually emitted from millions of -suns may be concerned in this shining fluid, it might be presumptuous -to attempt to determine; but notwithstanding the inconceivable -subtilty of the particles of light, when the number of the -emitting bodies is almost infinitely great, and the time of the continual -emission indefinitely long, the quantity of emitted particles -may well become adequate to the constitution of a shining fluid or -luminous matter, provided a cause can be found that may retain -them from <i>flying off, or reunite them</i>.”—<i>Observations on Nebulous -Stars</i>: Philosophical Transactions, vol. lxxxi. <span class="smcap">a.d.</span> 1791. -</p> -<p> -In addition, the following Memoirs on the same subject, by Sir -William Herschel, have been published in the Philosophical Transactions:—<i>Catalogue -of 1000 Nebulæ and Clusters of Stars</i>, vol. -lxxvi.; <i>Catalogue of another 1000, with remarks on the Heavens</i>, vol. -lxxix.; <i>Catalogue of 500 more, with remarks as above</i>, vol. xcii.; -<i>Of such as have a cometary appearance</i>, vol. ci.; <i>Of planetary -nebulæ</i>, ibid.; <i>Of stellar nebulæ</i>, ibid.; <i>On the sidereal part of -the heavens, and its connection with the nebulous</i>, vol. civ.; <i>On the -relative distances of clusters of nebulous stars</i>, vol. cviii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> Lord Rosse’s beautiful telescopes have been formed upon -principles which appear to embrace the best possible conditions -for obtaining a reflecting surface which should reflect the greatest -quantity of light, and retain that property little diminished for a -length of time. The alloy used for this purpose consists of tin and -copper in atomic proportions, namely, one atom of tin to four atoms -of copper, or by weight 58·9 to 126·4.—<i>On the Construction of -large Reflecting Telescopes</i>: by Lord Rosse. Report of the Fourteenth -Meeting of the British Association, 1844, p. 79.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_16_16" id="Footnote_16_16"></a><a href="#FNanchor_16_16"><span class="label">[16]</span></a> The best description of the Zodiacal Light occurs in a letter -furnished by Sir John Herschel to the <i>Times</i> newspaper in March, -1843:—“The zodiacal light, as its name imports, invariably appears -in the zodiac, or, to speak more precisely, in the plane of the -sun’s equator, which is 7° inclined to the zodiac, and which plane, -seen from the sun, intersects the ecliptic in longitude 78° and 258°, -or so much in advance of the equinoctial points: in consequence -it is seen to the best advantage at, or a little after, the equinoxes; -after sunset, at the spring, and before sunrise, at the autumnal -equinox; not only because the direction of its apparent axis lies -at those times more nearly perpendicular to the horizon, but also -because at those epochs we are approaching the situation when it -is seen most completely in section. -</p> -<p> -“At the vernal equinox the appearance of the zodiacal light is -that of a pretty broad pyramidal, or rather lenticular, body of light, -which begins to be visible as soon as the twilight decays. It is -very bright at its lower or broader part near the horizon, and, if -there be broken clouds about, often appears like the glow of a distant -conflagration, or of the rising moon, only less red, giving rise, -in short, to amorphous masses of light such as have been noticed -by one of your correspondents as possibly appertaining to the comet. -At higher altitudes, its light fades gradually, and is seldom traceable -much beyond the Pleiades, which it usually, however, attains -and involves, and (what is most to my present purpose) its axis at -the vernal equinox is always inclined (to the northward of the -equator) at an angle of between 60° and 70° to the horizon, and it -is most luminous at its base, resting on the horizon, where also it -is broadest, occupying, in fact, an angular breadth of somewhere -about 10° or 12° in ordinary clear weather.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_17_17" id="Footnote_17_17"></a><a href="#FNanchor_17_17"><span class="label">[17]</span></a> “The assumption that the extent of the starry firmament is -literally infinite has been made by one of the greatest of astronomers, -the late Dr. Olbers, the basis of a conclusion that the celestial -spaces are, in some slight degree, deficient in <i>transparency</i>; -so that all beyond a certain distance is, and must remain for ever, -unseen; the geometrical progression of the extinction of light far -outrunning the effect of any conceivable increase in the power of -our telescopes. Were it not so, it is argued, every part of the celestial -concave ought to shine with the brightness of the solar disc, -since no visual ray could be so directed as not, in some point or -other of its infinite length, to encounter such a disc.”—<i>Edinburgh -Review</i>, p. 185, for January, 1848; <i>Etudes d’Astronomie Stellaire</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a> In the <i>Astronomische Nachrichten</i> of July, 1846, appeared a -Memoir by M. Mädler, <i>Die Centralsonne</i>. The conclusions arrived -at by Mädler may be understood from the following quotation from -a French translation, made by M. A. Gautier, in the <i>Archives des -Sciences Physiques et Naturelles</i>, for October, 1846:—“Quoiqu’il -résulte de ce qui précède que la région du ciel que j’ai adoptée -satisfait à toutes les conditions posées plus haut, il n’en est pas -moins convenable de la soumettre à toutes les épreuves possibles. -Plusieurs essais de combinaisons différentes m’ont convaincu qu’on -ne pourrait trouver aucun autre point dans le ciel qui pût tenir -lieu, même d’une manière approchée, que celui que j’ai adopté. -On pourrait maintenant m’addresser l’objection que, si la région -du ciel où se trouve le centre de gravité de notre système d’étoiles -fixes, est <span class="correction" title="In the original book: determinée">déterminée</span> par ce qui précède entre certaines limites, il -n’en résulte pas la nécessité de choisir Alcyone pour ce centre, -attendu qu’il pourrait bien tomber sur quelqu’autre étoile située -dans le groupe ou dans son voisinage. Mais outre que c’est tout -près de là que se trouve le groupe le plus brillant et le plus riche -en étoiles de tout le ciel, et qu’il ne s’agit point ici d’un point -arbitraire situé dans le voisinage peu apparent et qui n’ait rien -qui le distingue, il ne se trouve nul part, même dans la région -voisine, une aussi exacte concordance des mouvements propres -qu’ici, et ces mouvements correspondent mieux que tous les autres -aux conditions établies plus haut. Or si l’on doit considérer ce -groupe central, entre les étoiles également éloignées, on peut présumer -que la plus brillante de beaucoup présente la plus grande -masse. Outre cela Alcyone, considérée optiquement, est au milieu -du groupe des Pleïades; et son mouvement propre, déterminé par -Bessel, est plus exactement en accord avec la moyenne de ceux -des autres Pleïades; ainsi que des étoiles de cette région jusqu’à -10° de distance. <i>Je puis donc établir comme conséquence de tout ce -qui précède, que le groupe des Pleïades est le groupe <span class="correction" title="In the original book: central l’ensemble">central de l’ensemble</span> -du système des étoiles fixes, jusqu’aux limites extérieures déterminées -par la Voie Lactée; et que Alcyone est l’étoile de ce groupe qui -paraît être, le plus vraisemblablement, le vrai Soleil central.</i>”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span class="label">[19]</span></a> See the article <i>On Gravitation</i>, Penny Cyclopædia, from the -pen of the Astronomer-Royal.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_20_20" id="Footnote_20_20"></a><a href="#FNanchor_20_20"><span class="label">[20]</span></a> Delambre dates the commencement of modern astronomical -observation in its most perfect form from Maskelyne, who was the -first who gave what is now called a standard catalogue (<span class="smcap">a.d.</span> 1790) -of stars; that is, a number of stars observed with such frequency -and accuracy, that their places serve as standard points of the -heavens. His suggestion of the <i>Nautical Almanack</i>, and his superintendence -of it to the end of his life, from its first publication -in 1767, are mentioned in the <i>Almanack</i> (vol. i. p. 364); his <i>Schehallion -Experiment on Attraction</i> in vol. iii. p. 69; and the character -of his <i>Greenwich Observations in Greenwich Observatory</i> in vol. -ii. p. 442.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_21_21" id="Footnote_21_21"></a><a href="#FNanchor_21_21"><span class="label">[21]</span></a> <i>Experiments to determine the Density of the Earth.</i> By Henry -Cavendish, Esq., F.R.S. and F.A.S.—Philosophical Transactions, -1798.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_22_22" id="Footnote_22_22"></a><a href="#FNanchor_22_22"><span class="label">[22]</span></a> Adams: <i>An Explanation of the observed irregularities in the -motion of Uranus, on the hypothesis of disturbance caused by a more -distant Planet</i>.—Appendix to Nautical Almanack for 1851.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_23_23" id="Footnote_23_23"></a><a href="#FNanchor_23_23"><span class="label">[23]</span></a> Le Verrier: <i>Premier Mémoire sur la théorie d’Uranus</i>, Comptes -Rendus, vol. xxi.; <i>Sur la planête qui produit les anomalies observées -dans le mouvement d’Uranus</i>.—<i>Ib.</i> vol. xxiii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_24_24" id="Footnote_24_24"></a><a href="#FNanchor_24_24"><span class="label">[24]</span></a> The experiment alluded to is one of a series by M. Plateau, -who thus describes his arrangement of the fluid:—“We begin by -making a mixture of alcohol and distilled water, containing a certain -excess of alcohol, so that when submitted to the trial of the -test tube it lets the small sphere of oil fall to the bottom rather -rapidly. When this point is obtained, the whole is thrown upon -filters, care being taken to cover the funnels containing these last -with plates of glass; this precaution is taken in order to prevent, -as much as possible, the evaporation of the alcohol. The alcoholic -liquor passes the first through the filters, ordinarily carrying -with it a certain number of very minute spherules of oil When -the greater part has thus passed, the spherules become more numerous; -what still remains in the first filters, namely, the oil and a -residue of alcoholic liquor, is then thrown into a single filter placed -on a new flask. This last filtration takes place much more slowly -than the first, on account of the viscosity of the oil; it is considerably -accelerated by renewing the filter once or twice during the -operation. If the funnel has been covered with sufficient care, the -oil will collect into a single mass at the bottom of the flask <span class="correction" title="In the original book: unde">under</span> -a layer of alcoholic liquor.”—<i>On the Phenomena presented by a free -Liquid Mass withdrawn from the action of Gravity.</i> By Professor -Plateau, of the University of Ghent. Translated from the <i>Memoirs -of the Royal Academy of Brussels</i>, vol. xvi.; in the <i>Scientific -Memoirs</i>, vol. iv. part 13.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_35" id="Page_35"></a>[Pg 35]</span></p> - - - -<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV.</h2> - -<p class="center">MOLECULAR FORCES.</p> - - -<p class="chap-head">Conditions of Matter—Variety of organized Forms—Inorganic -Forms—All matter reducible to the most simple conditions—Transmutation, -a natural operation—Chemical Elementary -Principles—Divisibility of Matter—Atoms—Molecules—Particles—Molecular -Force includes several Agencies—Instanced -in the Action of Heat on Bodies—All Bodies -porous—Solution—Mixture—Combination—Centres of -Force—Different States of Matter (Allotropic Conditions)—Theories -of Franklin, Æpinus, and Coulomb—Electrical -and Magnetic Agencies—Ancient Notions—Cohesive -Attraction, &c.</p> - - -<p class="p2">In contemplating the works of nature, we cannot but -regard, with feelings of religious admiration, the infinite -variety of forms under which matter is presented to our -senses. On every hand the utmost diversity is exhibited; -through all things we trace the most perfect -order; and over all is diffused the charm of beauty. It -is the uneducated or depraved alone who find deformities -in the creations by which we are surrounded.</p> - -<p>The three conditions of matter are—the solid, the -fluid, and the aëriform; and these belong equally to the -organic and the inorganic world.</p> - -<p>In organic nature we have an almost infinite variety -of animal form, presenting developments widely different -from each other, yet in every case suited to the circumstances -required by the position which the creature, -occupies in the scale of being. Through the entire -series, from the Polype to the higher order of animals, -even to man, we find a uniformity in the progress -towards perfection, and a continuity in the series, which<span class="pagenum"><a name="Page_36" id="Page_36"></a>[Pg 36]</span> -betrays the great secret, that the mystery of life is the -same in all,—a pervading spiritual essence associated -with matter, and modifying it by the master-mechanism -of an Infinite mind.</p> - -<p>In the vegetable clothing of the surface of the earth, -which fits it for the abode of man and animals—from -the confervæ of a stagnant pool, or the lichen of the -wind-beaten rocks, to the lordly oak or towering palm—a -singularly beautiful chain of being presents itself to -the contemplative mind, and we cannot but trace -the gradual elevation in the scale of organization.</p> - -<p>In the inorganic world, where the great phenomena -of life are wanting, we have constantly exhibited the -working of powers of a strangely complicated kind. -The symmetrical arrangement of crystals—the diversified -characters of mineral formations—the systematic -aggregations of particles to form masses possessing properties -of a peculiar and striking nature—all prove, that -agencies, which science, with all its refinements, has not -yet detected, are unceasingly at work. Heat, electricity, -chemical power—whatever that may be—and the forces -of cohesion, are known to be involved in the production -of the forms we see; but contemplation soon leads to -the conviction that these powers are subordinate to -others which we know not of. We know only the -things belonging to the surface of our planet, and these -but superficially. The geologist traces rock-formations -succeeding each other (from the primary strata -holding no traces of organized forms, through the Paleozoic -series, in which, step by step, the history of animal -life is recorded,) to the more recent formations, teeming -with relics, which, though allied to some animal types -still existing, are generally such as have passed away. -The naturalist searches the earth, the waters, and the -air, for their living things; and the diversity of form, -the variety of condition, and the perfection of organization -which he discovers as belonging to this our epoch—differing<span class="pagenum"><a name="Page_37" id="Page_37"></a>[Pg 37]</span> -from, indeed bearing but a slight relation to, -those which mark the earth’s mutations—exhibit, in a -most striking view, the endless variety of characters -which matter can assume.</p> - -<p>We are so accustomed to all these phenomena of -matter, that it is with some difficulty we can bend -ourselves to the study of the more simple conditions -in which it exists.</p> - -<p>The solid crusts of this telluric sphere—the waters -and the atmosphere—the diversified fabrics of the vegetable -kingdom—and the still more complicated structures -of men and animals—are, altogether, but the -aggregation of minute particles in accordance with -certain fixed laws. By mechanical means all kinds of -matter may be reduced to powder, the fine particles of -which would not appear very different from each other, -but each atom has been impressed with properties -peculiar to itself, which man has no power to change.</p> - -<p>To nature alone belongs the mysterious property of -transmutation. The enthusiastic alchemist, by the -agency of physical forces, dissipates a metal in vapour; -but it remains a metal, and the same metal still. By the -Hermetic art he breaks up the combination of masses; -but he cannot alter the principles of any one of the -elements which form the mass upon which his skill is -tried.</p> - -<p>Every atom is invested with properties peculiar to all -of its class; and each one possesses powers, to which in -mute obedience it is compelled, by which these properties -are modified, and the character of matter varied. -What are those properties? Do we know anything of -those powers?</p> - -<p>The earth, so far as we are acquainted with it, is -composed of about sixty principles, which we call -elementary. These are the most simple states to which -we can reduce matter, and from them all the forms of -creation yet examined by the chemist are produced.<span class="pagenum"><a name="Page_38" id="Page_38"></a>[Pg 38]</span> -These elementary principles are, some of them, permanently -gaseous under the ordinary temperature, and -others exist as solid masses; the difference between the -two conditions being regulated, as it appears, by the -opposing forces of heat and cohesive attraction.</p> - -<p>Matter has been regarded by some as infinitely divisible; -but the known conditions of chemical combinations -lead to the conclusion that there are limits beyond -which matter cannot be divided.<a name="FNanchor_25_25" id="FNanchor_25_25"></a><a href="#Footnote_25_25" class="fnanchor">[25]</a> The theory of atoms -having determinate characters, and possessing symmetric -forms, certainly has the advantage of presenting to the -human mind a starting point—a sort of standing ground,—from -which it can direct the survey of cosmical phenomena. -The metaphysical hypothesis, which resolves -all matter into properties, and refers all things to ideas,<span class="pagenum"><a name="Page_39" id="Page_39"></a>[Pg 39]</span> -leaves the mind in a state of uncertainty and bewilderment.</p> - -<p>Adapting the views of Dumas, with some modifications,<a name="FNanchor_26_26" id="FNanchor_26_26"></a><a href="#Footnote_26_26" class="fnanchor">[26]</a> -it will be found more satisfactory to regard the -<i>ultimate atoms</i> of matter as points beyond the reach of -our examination; which, according to a law, determined -by the influences of the so-called imponderable forces, -unite to form <i>molecules</i>. Again, these molecules combine -to form the <i>particles</i> of the mass which we may -regard as the limit of mechanical division. The particles -of solid bodies are solid, those of fluids fluid, and those of -gaseous bodies are themselves aëriform; but it does not -follow that the molecules of any body should be neces<span class="pagenum"><a name="Page_40" id="Page_40"></a>[Pg 40]</span>sarily -solid, fluid, or aëriform, from the circumstance of -their having formed the particles of a body in one of -these states.</p> - -<p>As this planet—a molecule in space—is formed of -aggregated atoms, and enveloped by its own physical -agencies—and as it is involved in the infinitely extending -influences of other planetary molecules, and thus forms -part of a system—so the molecules of any mass are -grouped into a system or particle, which possesses the -great characteristic features of the whole.</p> - -<p>In an aëriform body the particles are in a state of -extreme tenuity, the molecules being themselves, by the -influence of some repulsive force, just on the verge where -cohesion exerts its decaying power. In fluid bodies the -attenuation of the particles is less—the particles and -also the molecules are nearer together,—whereas, in the -solid body, the forces of cohesion are most strongly exerted, -and all the molecular conditions brought more -powerfully into action.</p> - -<p>Under the term molecular force, we include several -agencies,—not alike in the phenomena which they -exhibit, but which are all-powerful in producing the -general characteristics of bodies. These require a -somewhat close examination. All the particles of even -a solid mass may be brought under conditions on which -they are free to move. By heat we can increase the -length and thickness of a bar of iron, or any other -metal, and at length produce the fluid state,—a melted -metal flows as freely as water in a stream. Fluids, -and gases in like manner obey the dispersive influence -of caloric. From these and other analogous results we -learn that all bodies have a greater or less degree of -porosity. The distance at which the particles of fluid -bodies are maintained is strikingly proved by the fact, -that hydrated salts dissolved in water occupy no more -space than that which is equal to the water contained in -the crystalline body; while anhydrous salts dissolve<span class="pagenum"><a name="Page_41" id="Page_41"></a>[Pg 41]</span> -without at all increasing the bulk of the fluid. All the -solid matter of the salt must, in these cases, it would -appear, go to fill up the interstitial spaces which we -suppose to exist in the liquid.<a name="FNanchor_27_27" id="FNanchor_27_27"></a><a href="#Footnote_27_27" class="fnanchor">[27]</a></p> - -<p>The conditions which regulate the solubility of -bodies, and the power of solution, regarded either as a -mechanical or a chemical process, are very obscure. -We might be led to suppose, that those bodies possessing -the largest amount of unoccupied space were capable -of holding the greatest quantity of soluble matter dissolved. -This, however, is far from being the case, the -denser fluids generally having the greatest solvent -power.</p> - -<p>The peculiar manner in which hydrogen gas appears -to dissolve solid substances,—as iron, potassium, sodium, -sulphur, phosphorus, selenium, and arsenic, may be explained -by regarding the results as a manifestation -of the powers of chemical affinity over the forms of -bodies. In like manner, the solution of salt in water, -or the mixture of alcohol in that fluid, may be viewed as -chemical phenomena, although usually considered as -simple cases of solution or mixture: alterations of temperature -and other physical changes taking place in either. If -two masses of metal,—either tin and copper, for example,—are -melted and combined, the united mass will not -equal the bulk of the two masses. If a pint measure of -oil of vitriol and an equal quantity of water are mixed -together, the combined fluids will not fill a two pint -measure.<a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28" class="fnanchor">[28]</a></p> -<p><span class="pagenum"><a name="Page_42" id="Page_42"></a>[Pg 42]</span></p> -<p>In these instances a large quantity of heat is rendered -sensible, as if it had been squeezed out by the force -with which the particles combined, from <span class="correction" title="In the original book: insterstices">interstices</span>, -which were filled with, what we may be allowed to call, -an atmosphere of heat. Hence we conclude that, -amongst the influences determining the molecular constitution -of a body, heat performs an important part. -All these facts go to prove that the atoms which form -the compound body, whatever may be its character, are -disposed of as so many centres of force, which act by -influences of a peculiar character upon each other. That -these influences are dependent upon known physical -forces is certain; but the laws by which the powers of -the ultimate atom are altered remain still unknown.</p> - -<p>In the great operations of nature, changes are produced -which we cannot understand, and variations of -condition do certainly occur, which may be regarded as -instances of transmutation.</p> - -<p>Amongst others, we may adduce the different states -in which we know carbon to exist. We have the -diamond with its beautiful light-refracting property, its -hardness and high specific gravity, capable of being converted -into graphite and coke.<a name="FNanchor_29_29" id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a> Charcoal, graphite, and -the diamond, are totally unlike each other, yet we know -they are each composed of the same atoms. Charcoal -is a black irregular substance, light, and readily inflammable; -graphite is crystallizable; but the forms of its -crystals cannot be referred to those of the diamond, and -it burns with difficulty. The diamond occurs in the -most regular and beautifully transparent forms; and it -can be burned only at the highest artificial temperatures.<span class="pagenum"><a name="Page_43" id="Page_43"></a>[Pg 43]</span> -We are, however, convinced by experiment that the -brilliant and transparent gem is made up of the same -atoms as those which go to form the dull black mass of -charcoal. From diamonds, as is above stated, coke has -been formed by the heat of the voltaic battery, and recent -experiments have proved that the volatilized -carbon constantly passing off from one of the poles of a -sufficiently powerful battery, is deposited in a crystalline -powder, possessing most of the properties, as it -regards hardness, &c. of true diamond dust. What is -the mystery of this? We know not. The peculiar -conditions have been the subjects of anxious study; but -science has not yet let in a ray of light upon the -mystery. That a different state—it has been called -an <i>allotropic</i> condition—is often induced in the same -class of atoms is certain; and hence the variety of the -resulting compounds. To continue our illustrations -with carbon—may not its combinations, in uniform proportions -with oxygen and hydrogen,<a name="FNanchor_30_30" id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a> owe their differences -to some allotropic change in the ultimate atoms of -this element.</p> - -<p>We know that silicon—the metallic base of flint—is<span class="pagenum"><a name="Page_44" id="Page_44"></a>[Pg 44]</span> -capable of assuming two or more different states; and -that sulphur, selenium, phosphorus, and arsenic, are -susceptible of these remarkable changes in which, without -the slightest variation in the chemical character, a -complete change in the physical condition is produced. -Copper, iron, tin, and manganese, are known to exist in -at least two states of physical dissimilarity, and many of -the rarer metals exhibit the same peculiarity.<a name="FNanchor_31_31" id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a> Hence, -may we not infer that some of those substances, which -we now term elementary, are but altered conditions of -the same element? The resemblance between many of -those bodies strengthens the supposition. Iridium and -platinum,—iron and nickel,—chlorine, bromine, iodine, -and probably fluorine,—are good examples of these -similarities, although these bodies are all distinguished -by physical and chemical differences.</p> - -<p>The light-refracting gem, which glistens on the neck -of beauty, and is valued for its transparency, differs only -from the rude lump of coke in its molecular arrange<span class="pagenum"><a name="Page_45" id="Page_45"></a>[Pg 45]</span>ment. -Chemistry teaches us that we may, without producing -any disarrangement of the affinities, but by -merely setting up molecular disturbance, effect decided -changes, as is strikingly shown in the colour of iodide of -mercury changing from red to yellow under slight influences -of heat, and back again to red by a gentle -mechanical disturbance. By a slight change, merely -molecular, iron may be made to resemble platinum in -its physical properties.<a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32" class="fnanchor">[32]</a> An iron wire plunged into -nitric acid is attacked by the acid with violence; but if -one extremity of the wire is heated in the flame of -a spirit lamp, such a change of state is produced -throughout the entire length of the wire, that if it be -now plunged into nitric acid no effect is produced upon -it. On studying this question, we find good reason for -supposing that bodies which, though physically different, -resemble each other in some of their properties, iodine, -<span class="correction" title="In the original book: bromime">bromine</span>, &c., are the results of different <i>allotropic</i> conditions -which have been impressed upon the ultimate -atoms, similar to those observed in the substances -named. This hypothesis appears to be more in accordance -with the great principles which we must conceive<span class="pagenum"><a name="Page_46" id="Page_46"></a>[Pg 46]</span> -guided the labours of an Infinite Mind, than that which -supposes a vast number of individual creations. It will -be seen in the sequel that light, heat, electricity, and -chemical action, have the power of producing yet more -striking changes in the forms of bodies. Is it not -probable that, according to the operations of these -agents, either combined or separate, acting over different -spaces of time, and under varying circumstances, in -relation to the molecular forces, all those <i>allotropic</i> -states may be produced? Hence bodies may be discovered, -which,—from the <span class="correction" title="In the original book: imperfectious">imperfections</span> of science,—resisting -our means of analysis, must, for a time, be -regarded as new elements, whereas they are possibly -only altered states of the same substance.</p> - -<p>The experiments of Faraday and of <span class="correction" title="In the original book: Plucker">Plücker</span> prove -that all matter exists in certain polar conditions, having -powers of mutual attraction and repulsion.<a name="FNanchor_33_33" id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a> Are the -molecular forces, so called, to be referred to any of those -powers which are involved in the general term magnetic-polarity? -Are they not probably the result of some -ultimate principle of which these properties are but -the modified manifestations? These questions will -now be generally answered in favour of magnetism; -but in our ignorance we should pause; the next genera<span class="pagenum"><a name="Page_47" id="Page_47"></a>[Pg 47]</span>tion -will without doubt find another solution for -the problem.</p> - -<p>Franklin supposed the ultimate atoms of bodies to be -surrounded by a subtile fluid or ether, which they have -the power of condensing upon their surfaces with -great force—and we have experiments showing that -this is probable<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34" class="fnanchor">[34]</a>—whilst he regarded the atoms of the -ether itself as mutually repellent, thus establishing an -equilibrium of forces. Æpinus reduced the hypothesis -of Franklin to a mathematical theory; and Coulomb -<i>proved</i> that the force with which the repulsion of the -ethereal atoms and the attraction of the material molecules -are produced, is, like universal attraction,—to -whatever power that may be due,—regulated by the law -of the inverse ratio of the square of the distance. These -views are found, upon minute examination, to hold true -to the phenomena with which inductive science has -made us acquainted; and the striking manner in which, -when submitted to the rigorous investigations of geometers, -they agree with known conditions of electricity, -appears certainly to favour the opinion that this power -may be materially connected with these molecular -arrangements.</p> - -<p>Many of the phenomena which are connected with -the magnetic influences also bear in a remarkable -manner upon this inquiry. But, without the necessary -proof of direct experimental evidence, it were as unphilosophical -to refer the binding together of the -molecules of matter to the agency of electricity, as it -would be to adopt the theory of the hooked atoms of<span class="pagenum"><a name="Page_48" id="Page_48"></a>[Pg 48]</span> -Epicurus, or the astrological dream of the sympathies of -matter.<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35" class="fnanchor">[35]</a></p> - -<p>Science, however, enables us to infer with safety that -the mechanical powers which regulate the constitution -of a cube of marble, or a granite mountain, are of a -similar order to those which determine the earth’s relation -to the other planets in the solar system, and that -solar system itself a unit, in the immensity of space, to -the myriads of suns which spangle the stellar vault.</p> - -<p>In fine, cohesion, or the attraction of aggregation, is -a power employed in binding particle to particle. To -cohesion, we find we have heat opposed as a repellent -force; and the mysterious operations of those electrical -phenomena, generally referred to as polar forces, are -constantly, it is certain, interfering with its powers. In -addition, we have seen that in nature there exists an -agency which is capable of changing the constitution of -the ultimate atoms, and of thus giving variety to each -resulting mass. What this power may be, our science<span class="pagenum"><a name="Page_49" id="Page_49"></a>[Pg 49]</span> -cannot tell; but our reason leads us, with firm conviction, -to the belief that it is a principle which is, -beyond all others in its subtile influences which equally -universal with, appears to rise superior to gravitation; -and which, like a spirituality, shadows forth to our -dwarf conceptions the immensity of the divine power of -the omniscient Creator.</p> - -<p>The molecular forces involve a consideration of all the -known physical powers, the study of which, in their -operations on matter, will engage our attention. But it -is pleasant to learn, as we advance step by step in our -examination of the phenomena of creation, that we may -study the grand in what externally appears the simple, -and learn, in the mysteries of a particle, the high -truths which science has to tell of a planet.</p> - -<p>It may appear that the forces of gravitation and cohesion -are regarded as identical. Many phenomena, which -we are enabled to reach by the refinements of inductive -inquiry, certainly present to us a striking similarity in -the laws which regulate the operations of these powers; -but it must be remembered that their identity is not -established. So far from this, we know the law of gravitating -force. Newton determined with surprising -accuracy, that the action of this power diminishes with -the distance as the universe square, but cohesive force is -exerted only at such distances that it is impossible to -determine whether or not it is subjected to the same law. -To quote the words of Young: “The whole of our -inquiries respecting the intimate nature of forces of any -kind must be considered merely as speculative amusements, -which are of no further utility than as they -make our views more general, and assist our experimental -investigations.”<a name="FNanchor_36_36" id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a></p> -<hr class="chap" /> - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_25_25" id="Footnote_25_25"></a><a href="#FNanchor_25_25"><span class="label">[25]</span></a> “The divisibility of matter is great beyond the power of -imagination, but we have no reason for asserting that it is -infinite; for the demonstrations which have sometimes been -adduced in favour of this opinion are obviously applicable to -space only. The infinite divisibility of space seems to be essential -to the conception that we have of its nature, and it may be -strictly demonstrated that it is mathematically possible to draw -an infinite number of circles between any given circle and its -tangent, none of which shall touch either of them except at the -general point of contact; and that a ship following always the -same oblique course with respect to the meridian,—for example, -sailing north-eastwards,—would continue perpetually to approach -the pole without ever completely reaching it. But when we -inquire into the truth of the old maxim of the schools, that all -matter is infinitely divisible, we are by no means able to decide -so positively. Newton observes that it is doubtful whether any -human means may be sufficient to separate the particles of -matter beyond a certain limit; and it is not impossible that -there may be some constitution of atoms, or single corpuscles, -on which their properties, as matter, depend, and which would -be destroyed if the units were further divided; but it appears to -be more probable that there are no such atoms, and even if there -are, it is almost certain that matter is never thus annihilated in -the common course of matter.”—<i>The Essential Properties of -Matter</i>: Young’s <i>Natural Philosophy</i>; ed. by Rev. P. <span class="correction" title="In the original book: Lelland">Kelland</span>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_26_26" id="Footnote_26_26"></a><a href="#FNanchor_26_26"><span class="label">[26]</span></a> “Two very different hypotheses have been formed to explain -the nature of matter, or the mode of its formation; the -one known as the <i>atomic</i> theory, the other, the <i>dynamic</i>. The -founder of the former and earlier was Leucippus: he considered -the basis of all bodies to be extremely fine particles, -differing in form and nature, which he supposed to be dispersed -through space, and to which his follower Epicurus first gave -the name of atoms. To these atoms he attributed a rectilinear -motion, in consequence of which such as are homogeneous -united, whilst the lighter were dispersed through space. The -author of the second hypothesis was the famous Kant. He -imagined all matter existed, or was originated, by two antagonist -and mutually counteracting principles, which he called attraction -and repulsion, all the predicates of which he referred to motion. -Most modern philosophers, and foremost amongst them Ampère -and Poisson, have adopted an hypothesis combining the features -of both the preceding. They regarded the atoms as data, deriving -their origin from the Deity as the first cause, and consider their -innate attractive and repulsive force as a necessary condition to -their combination in bodies. The main features of this hypothesis -are borrowed from Aristotle, inasmuch as he supposed the basis -of all bodies to be the four elements known to the ancients, the -particles of which, endued with certain powers, constituted -bodies. According to Ampère, all bodies consist of equal particles, -and they again of molecules that, up to a certain distance, -attract each other. Their distance from each other he supposed -to be regulated by the intensity of the attractive and repulsive -forces, the latter of which preponderates.”—Peschel’s <i>Elements of -Physics</i>; translated by E. West, 1845.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_27_27" id="Footnote_27_27"></a><a href="#FNanchor_27_27"><span class="label">[27]</span></a> This was first proved by the researches of Dr. Dalton: the -subject will be again alluded to under the consideration of atomic -volumes.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_28_28" id="Footnote_28_28"></a><a href="#FNanchor_28_28"><span class="label">[28]</span></a> These peculiar phenomena may be studied advantageously in -the works of most of the eminent European chemists. In our -own language the reader is referred to Dr. Thompson’s <i>Outline of -the Sciences of Heat and Electricity</i>, 2nd edition; Brande’s -<i>Manual of Chemistry</i>—Art. <i>Specific Heat</i>; Graham’s <i>Elements of -Chemistry</i>; and Daniell’s <i>Introduction to the Study of Chemical -Philosophy</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_29_29" id="Footnote_29_29"></a><a href="#FNanchor_29_29"><span class="label">[29]</span></a> The conversion of the diamond into graphite and coke was -first effected by the agency of the galvanic arc of flame, by M. -Jaquelini, and communicated to the Academy of Sciences in 1847, -in a Memoir entitled, <i>De l’action calorifique de la pile de Bunsen, -du chalumeau à gaz oxygène et hydrogène sur le carbon pur, artificiel -et naturel</i>. See <i>Comptes Rendus</i>, 1847, vol. xxiv. p. 1050; also -<i>Report of the British Association</i>, for 1847, (<i>Transactions of Sections</i>) -p. 50.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_30_30" id="Footnote_30_30"></a><a href="#FNanchor_30_30"><span class="label">[30]</span></a> “In the annual report on the progress of chemistry, presented -to the Royal Academy of Stockholm, in March 1840, I have -proposed to designate by the term <i>allotropic state</i>, that dissimilar -condition which is observed in certain elements, and long known -examples of which are found in the different forms of carbon, as -graphite and diamond. -</p> -<p> -“Although these dissimilar conditions, which I have here called -allotropic, have long since attracted attention in one or two -elements, still they have been regarded as exceptions to the -general rule. It is at present my object to show that they are -not so rare; that it is probably rather a general property of the -elements to appear in different allotropic conditions; and that -although we have hitherto been unable to obtain several of the -elements when uncombined in their allotropic states, still their -compounds indicate the same with tolerable distinctness.”—<i>Berzelius -on the Allotropy of the Elementary Bodies</i>, <i>&c.</i>: Poggendorff’s -Annalen, 1844. Scientific Memoirs, vol. iv. p. 240.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_31_31" id="Footnote_31_31"></a><a href="#FNanchor_31_31"><span class="label">[31]</span></a> “Copper, when reduced by hydrogen at a heat below that of -redness, on exposure to air soon becomes converted throughout -its mass into protoxide; and when it is triturated for some time -with an equivalent quantity of sulphur, it combines with it -according to Böttcher’s experiments, producing flame, and forming -sulphuret of copper. If, however, the copper be reduced by -hydrogen at a red heat, still considerably below the temperature -at which it softens and begins to melt, it remains for years unchanged -by exposure to air, and cannot be made to combine -with sulphur without the application of heat. Iron, cobalt, and -nickel, when reduced by hydrogen below a red heat, inflame after -they have cooled, if exposed to the air; and if they are immediately -placed in water to avoid their taking fire, they inflame -when they are again removed, and have become nearly dry. If -we compare this behaviour with that of iron reduced by heat, -and with iron in that state in which it forms the conductor of -a galvanic current without becoming oxidized, it would appear -that these peculiarities depended upon something more than a -difference of mechanical condition.”—<i>Berzelius on the Allotropy -of Elementary Bodies.</i> See <i>On the Isomeric Conditions of the Peroxide -of Tin</i>: by Prof. H. Rose.—Chemical Gazette, Oct. 1848.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_32_32" id="Footnote_32_32"></a><a href="#FNanchor_32_32"><span class="label">[32]</span></a> On this curious subject, and its history, see Bergman’s -<i>Dissert. de Phlog. quantitate in Metallis</i>, 1764. Kirwan, <i>On the -Attractive Powers of Mineral Acids</i>: Philosophical Transactions. -Kier’s <i>Experiments and Observations on the Dissolution of Metals -in Acids</i>: Phil. Trans. 1790. -</p> -<p> -From these valuable papers it will be seen that the peculiar -states of iron had already attracted attention, particularly those -“inactive conditions” noticed in a “<i>Note sur la Manière d’agir -de l’Acide nitrique sur le Fer, par J. F. W. Herschel</i>,” Aug. 1833; -and previously indicated by M. H. Braconnot, <i>Sur quelques -Propriétés de l’Acide nitrique</i>, Annales de Chimie, vol. lii. p. 54. -Reference should also be made to the Memoirs of Sir John -Herschel, <i>On the Action of the Rays of the Solar Spectrum on -Vegetable Colours</i>, <i>&c.</i>: Phil. Trans. vol. cxxxiii. p. 221; and <i>On -the Separation of Iron from other Metals</i>: Phil. Trans. vol. cxi. p. -293; and several papers by Schönbein, in the Philosophical -Magazine, from 1837.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_33_33" id="Footnote_33_33"></a><a href="#FNanchor_33_33"><span class="label">[33]</span></a> Faraday, in his memoir <i>On new Magnetic Actions, and on the -Magnetic Conditions of all Matter</i>, says:—“By the exertion of -this new condition of force, the body moved may pass either along -the magnetic lines or across them, and it may move along or across -them in either or any direction, so that two portions of matter, -simultaneously subject to this power, may be made to approach -each other as if they were mutually attracted, or recede as if -mutually repelled. All the phenomena resolve themselves into -this, that a portion of such matter, when under magnetic action, -tends to move from stronger to weaker places or points of force. -When the substance is surrounded by lines of magnetic force of -equal power on all sides, it does not tend to move, and is then in -marked contradistinction with a linear current of electricity under -the same circumstances.”—Phil. Trans. for 1846, vol. cxxxvii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_34_34" id="Footnote_34_34"></a><a href="#FNanchor_34_34"><span class="label">[34]</span></a> <i>New Experiments and Observations on Electricity made at -Philadelphia, in America.</i>—Addressed to Mr. Collinson, from 1747 -to 1754. By Benjamin Franklin. Of these Priestley remarks:—“It -is not easy to say whether we are most pleased with the -simplicity and perspicuity with which the author proposes every -hypothesis of his own, or the noble frankness with which he -relates his mistakes, when they were corrected by subsequent -experiments.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_35_35" id="Footnote_35_35"></a><a href="#FNanchor_35_35"><span class="label">[35]</span></a> “The atomic philosophy of Epicurus, in its mere physical -contemplation, allows of nothing but matter and space, which are -equally infinite and unbounded, which have equally existed from -all eternity, and from different combinations of which every -visible form is created. These elementary principles have no -common property with each other; for whatever matter is, that -space is the reverse of; and whatever space is, matter is the contrary -to. The actual solid part of all bodies, therefore, are matter, -their actual pores space, and the parts which are not altogether -solid, but an intermixture of solidity and pore, are space and -matter combined. -</p> -<p> -“The infinite groups of atoms, flying through all time and -space in different directions and under different laws, have interchangeably -tried and exhibited every possible mode of rencounter: -sometimes repelled from each other by concussion, and -sometimes adhering to each other from their own jagged or -pointed construction, or from the casual interstices which two or -more connected atoms must produce, and which may be just -adapted to those of other figures,—as globular, oval, or square. -Hence the origin of <span class="correction" title="In the original book: compouud">compound</span> and visible bodies; hence the -origin of large masses of matter; hence, eventually, the origin of -the world itself.”—Dr. Good’s <i>Book of Nature</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_36_36" id="Footnote_36_36"></a><a href="#FNanchor_36_36"><span class="label">[36]</span></a> Young’s <i>Lectures on Natural Philosophy and the Mechanical -Arts</i>. Lecture 49, <i>On the Essential Properties of Matter</i>.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_50" id="Page_50"></a>[Pg 50]</span></p> - - -<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V.</h2> - -<p class="center">CRYSTALLOGENIC FORCES.</p> - - -<p class="chap-head">Crystallisation and Molecular Force distinguished—Experimental -Proof—Polarity of Particles forming a Crystal—Difference -between Organic and Inorganic Forms—Decomposition of -Crystals in Nature—Substitution of Particles in Crystals—Pseudomorphism—Crystalline -Form not dependent on Chemical -Nature—Isomorphism—Dimorphism—Theories of -Crystallogenic Attraction—Influence of Electricity and Magnetism—Phenomena -during Crystallisation—Can a change of -Form take place in Primitive Atoms?—Illustrative Example -of Crystallisation.</p> - - -<p class="p2">“Crystallisation is a peculiar and most admirable -work of nature’s geometry, worthy of being studied -by all the power of genius, and the whole energy of the -mind, not on account of the delight which always -attends the knowledge of wonders, but because of its -vast importance in revealing to us the secrets of nature; -for here she does, as it were, betray herself, and, laying -aside all disguise, permits us to behold, not merely the -results of her operations, but the very processes <span class="correction" title="In the original book: themselvss">themselves</span>.”—Such -is the language of an Italian philosopher, -Gulielmini; and it is the striking peculiarity of beholding -the process of the formation of the regular geometric -figures of crystals, the gradual accretion of particle to -particle, which induces us to separate crystallization from -mere molecular aggregation. Without doubt the formation -of a crystal and the production of an amorphous -block are due to powers which bear a close resemblance -in many points; but they present remarkable differences -in others.</p> - -<p><span class="pagenum"><a name="Page_51" id="Page_51"></a>[Pg 51]</span></p> - -<p>Let us take some simple case in illustration. In -quiet water we have very finely divided matter suspended, -and matter in a state of solution. The first is -slowly precipitated, and in process of time consolidates -into a hard mass at the bottom, presenting no particular -character, unless it has been placed in some peculiar -physical conditions; when, as in nature, we have a -regular bedding which is intersected by lines of lamination -or of cleavage, which we are, from experiment, -enabled to refer to the influence of current electricity. -The second—the matter in solution—is also slowly -deposited; but it is accumulated upon nuclei which -possess some peculiar disposing powers, and every particle -is united by some particular face, and an angular -figure of the most perfect character results. Many -pleasing experiments would appear to show that electricity -has much to do in the process of crystallization; -but it is evident that it must be under some peculiarly -modified conditions that this power is exerted, if, indeed, -it has any direct action.</p> - -<p>The same substances always crystallize in the same -forms, unless the conditions of the crystallizing body are -altered. It has been supposed that each particle of a -crystalline mass has certain points or poles which possess -definite properties, and that cohesion takes place only -along lines which have some relation to the attracting -or repelling powers of these poles. We shall have, -eventually, to consider results which appear to prove -that magnetism is universal in its influence, and that -this polarity of the particles of matter may be referred -to it.</p> - -<p>Be the cause of crystallisation what it may, it presents -to us in appearance a near approach in inorganic nature -to some of the peculiar conditions of growth in the -organised creation. In one, we have the gradual production -of parts and the formation of members due to -peculiar powers of assimilation, each individual pre<span class="pagenum"><a name="Page_52" id="Page_52"></a>[Pg 52]</span>serving -all its distinguishing features; and in the other, -we have a regular order of cohesion occurring under the -influence of a power which draws like to like, and -arranges the whole into a form of beauty.</p> - -<p>This appears to be the proper place for correcting an -error too prevalent, relative to the formation of crystals, -the development of cells, and the yet more fatal falsehood -of referring the great phenomena of Life to any -of the physical forces with which we are acquainted.</p> - -<p><span class="smcap">The Crystal</span> <i>forms</i>, by the accretion of particle to -particle, along lines determined by some yet unknown -power. There is no change in the character of any -particle—like coheres to like; the first atom and the -last of the series being identical in character.</p> - -<p><span class="smcap">The Plant</span> <i>grows</i>, not by the gathering together of -similar particles of matter, but by the absorption of a -compound particle—by that one which must be regarded -as the primary nuclear atom or cell. After this absorption—in -virtue of a power which we call <span class="smcap">life</span>, excited into -action by <span class="smcap">light</span>—the compound particle is decomposed, -and one constituent is retained to effect the formation -of a new cell, whilst the other is liberated as an invisible -air. Here we have a change of chemical constitution -effected; and this takes place through the whole period -of vegetable growth, from the development of the plumule -up to the formation of the latest leaf upon the -topmost branch of the most lordly tree.</p> - -<p>Life has been referred to electricity and to chemical -power—as the effect of a known cause. Without doubt, -during the operations of life the whole of the physical -powers are necessary to the production of all the phenomena -of growth in the vegetable and the animal world. -But these powers are ever subsidiary to vital force, and -are like attendant spirits chained to do an enchanter’s -bidding.</p> - -<p>Life is a force beyond the reach of human search, and -he who fancies he has a hold upon the principle which<span class="pagenum"><a name="Page_53" id="Page_53"></a>[Pg 53]</span> -produced biological phenomena, has committed himself -to as wild a pursuit as he who rashly endeavours to catch -a morass-meteor.</p> - -<p>Subtile as are the forces of light, heat, and electricity—that -of life, <i>vitality</i>, is infinitely more refined, and it -must for ever elude the search of the philosopher.</p> - -<p>Man is permitted to test and try all things which are -created, and to apply to useful ends the discoveries which -he may make. But man can never become a creator; -and he who would attempt to give sense to an inert mass -of matter, by electricity, heat, or light, will prove himself -as ignorant of nature’s truth as is the senseless mass -upon which he works.</p> - -<p>“So far shalt thou go, and no further,” was said -equally to the great tide-wave of human intellect, as to -the mighty surge of the earth-girdling ocean.</p> - -<p>It must not be forgotten that a striking difference -exists between the productions of the mineral and the -other kingdoms of nature. Animals and vegetables arrive -at maturity by successive developments, and increase by -the assimilation of substances, having the power of producing -the most important chemical changes upon such -matter as comes within the range of their influence; but -minerals are equally perfect in the earliest stages of their -formation, and increase only, as previously said, by the -accretion of particles without their undergoing any -change.</p> - -<p>The animal and vegetable tribes cease to continue the -functions of life: death ensues, and a complete disorganisation -takes place; but this is not the case in the -mineral world: the crystal being the result of a constantly -acting force is not necessarily liable to decomposition.</p> - -<p>Nevertheless, we sometimes find in nature that crystals, -after arriving at what may be regarded as, in some -sort, their maturity, are, owing to a change of the con<span class="pagenum"><a name="Page_54" id="Page_54"></a>[Pg 54]</span>ditions -under which they were formed, gradually decomposed. -In our mines we discover skeletons of crystals, -and within the hollow shell thus formed, other crystals -of a different constitution and figure find nuclei, and the -conditions required for their development. Again, to -give a striking instance, the felspar crystals of the -granitic formations are liable to decomposition in a -somewhat peculiar manner. In decomposing, these -crystals leave moulds of their own peculiar forms, and it -not unfrequently happens, in the stanniferous districts -of Cornwall, that oxide of tin gradually fills these moulds, -and we procure this metallic mineral in the form of the -earthy one. Then we have the curious instances of -bodies crystallising in a false form under change of circumstances. -We find, for example, Pseudomorphism, (or -<i>false-form</i>), as this class of phenomena is named, occurring -by the removal of the constituent atoms of one -crystal, while another set—which naturally assumes a -different form—takes their place, yet still preserving -the original shape. It often happens that copper pyrites -will, in this manner, exhibit the angles of an ordinary -variety of crystallised carbonate of iron. These curious -changes may be familiarised by supposing a beautiful -statue of gold, from which some skilful mechanic removes -particle by particle, and so skilfully substitutes a grain of -brass for every one of gold removed, that the loss of the -precious metal cannot be detected by any mere examination -of its form.</p> - -<p>Crystalline form is not strictly dependent upon the -chemical nature of the parts forming the crystal. The -same number of atoms, arranged in the same way, produce -the same form. Substances much unlike each -other will assume the same crystalline arrangement. -Magnesia, lime, oxide of cadmium, the protoxides of -iron, nickel, and cobalt, combined with the same acid, -present similarly formed bodies. These Isomorphic<span class="pagenum"><a name="Page_55" id="Page_55"></a>[Pg 55]</span> -(<i>like-form</i>)<a name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a> peculiarities are exceedingly common, and -the discoverer of the phenomena, Mitscherlich, announced -the above law. It cannot, however, be regarded -as a philosophical expression of the fact, and requires -reconsideration—chemical elements of a dissimilar character -may have the same law of aggregation, and thus -produce the same form, without having any relation to -the number of atoms.</p> - -<p>We also find compounds which have two distinct -systems of crystallisation. This property, Dimorphism, -is very strikingly shown in carbonate of lime, which -occurs in rhombohedrons, in calc spar, and in rhombic<span class="pagenum"><a name="Page_56" id="Page_56"></a>[Pg 56]</span> -prisms in arragonite. The molecular arrangements here -are not, however, of equal stability, and one form is -evidently forced upon the other, and is abandoned by it -on the slightest disturbance. When a prism of arragonite -is heated it breaks up into the rhombs of common -calc spar, at a temperature far below that at which the -carbonate of lime is decomposed; but no alteration of -temperature can convert calc spar into arragonite.</p> - -<p>Crystals are found in the most microscopic character, -and of an exceedingly large size. A crystal of quartz at -Milan is three feet and a quarter long, and five feet and -a half in circumference, and its weight is 870 pounds. -Beryls have been found in New Hampshire measuring -four feet in length.<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a href="#Footnote_38_38" class="fnanchor">[38]</a></p> - -<p>In the dark recesses of the earth, where the influences -which produce organisation and life cease to act, a -creative spirit still pursues its never-ending task of giving -form to matter.</p> - -<p>The science of crystallogeny,<a name="FNanchor_39_39" id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a> embracing the theoretical -and practical question of the causes producing these -geometric forms, has in various ways attempted to explain -the laws according to which molecules arrange -themselves on molecules in perfect order, giving rise to -a rigidly correct system of architecture. But it cannot -be said that any theory yet propounded is sufficiently -exact to embrace the whole of the known phenomena, -and the questions,—What is crystallogenic attraction, -and what is the physical nature of the ultimate particles -of matter,—are still open for the inquiries of that -genius which delights in wrestling with the secrets of -nature.</p> -<p><span class="pagenum"><a name="Page_57" id="Page_57"></a>[Pg 57]</span></p> -<p>The great Epicurus speculated on the “plastic nature” -of atoms, and attributed to this <i>nature</i> the power they -possess of arranging themselves into symmetric forms. -Modern philosophers satisfy themselves with attraction, -and, reasoning from analogy, imagine that each atom -has a polar system.</p> - -<p>Electricity, and light, and heat, exert remarkable -powers, and accelerate or retard crystallisation according -to the conditions under which these forces are brought -to bear on the crystallising mass. We have recently -obtained evidence which appears to prove that some form -of magnetism has an active influence in determining the -natural forms of crystals, and we discover that magnetism -exerts a peculiar influence in relation to the optic axes of -crystals, which is not exerted in lines at right angles to -these. Electricity appears to quicken the process of -crystalline aggregation—to collect more readily together -those atoms which seek to combine—to bring them all -within the limits of that influence by which their symmetrical -forms are determined; and strong evidence is -now afforded, in support of the theory of magnetic -polarity, by the refined investigations of Faraday and -Plücker, which prove that magnetism has a <i>directing</i> -influence upon crystalline bodies.<a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a></p> - -<p>It has been found that crystals of sulphate of iron, -slowly forming from a solution which has been placed -within the range of sufficiently powerful magnetic force, -dispose themselves along certain magnetic curves, such -as are formed around a magnet by steel filings; whereas -the crystals of the Arbor Dianæ, or silver tree, forming<span class="pagenum"><a name="Page_58" id="Page_58"></a>[Pg 58]</span> -under the same circumstances, take a position nearly at -right angles to these curves. Certain groups of crystals -have been found in nature, which appear to show, by -their positions, that terrestrial magnetism has been active -in producing the phenomena they exhibit; indeed, -nearly all our mineral formations indicate the influences -of this, or some similarly acting power.<a name="FNanchor_41_41" id="FNanchor_41_41"></a><a href="#Footnote_41_41" class="fnanchor">[41]</a></p> - -<p>During rapid crystallisation, some salts—as the sulphate -of soda, boracic acid, and arsenious acid crystallising -in muriatic acid—exhibit decided indications of -electrical excitement; light is given out in flashes. We -have evidence that crystals exhibit a tendency to move -towards the light, and that crystallisation takes place -more readily, and progresses with greater activity in the -sunshine than in the shade. Professor Plücker has -recently ascertained that certain crystals—in particular -the cyanite—“point very well to the north, by the magnetic -power of the earth only. It is a true compass -needle; and, more than that, you may obtain its declination.” -We must remember that this crystal, the -cyanite, is a compound of silica and alumina only. This -is the amount of experimental evidence which science has -afforded in explanation of the conditions under which -nature pursues her wondrous work of crystal formation. -We see just sufficient of the operation to be convinced -that the luminous star which shines in the brightness of<span class="pagenum"><a name="Page_59" id="Page_59"></a>[Pg 59]</span> -Heaven, and the cavern-secreted gem, are equally the -result of forces which are known to us in only a few of -their modifications.</p> - -<p>Every substance, when placed under circumstances -which allow of the free movement of its molecules, has -a tendency to crystallise. All the metals may, by slowly -cooling from the melting state, be exhibited with a crystalline -structure. Of the metallic and earthy minerals, -nature furnishes us with an almost infinite variety of -crystals, and, by a reduction of temperature, yet more -simple bodies assume the most symmetric forms. Water, -in the conditions of ice and snow, is a familiar and beautiful -example; and, by such extreme degrees of cold as -are artificially produced, many of the gases exhibit a -tendency to a crystalline condition.</p> - -<p>May not the solid elementary atoms be susceptible of -change of form under different influences? May not -the different states under which the same bodies are -found—as, for example, silica, carbon, and iron—be due -entirely to a change in the form of the primitive atom?</p> - -<p>Admitting the probability of this, we then easily see -that the central molecule, formed of an aggregation of -such atoms, uniting by particular faces, would present a -determinate form; and that the resulting crystal, a mass -of such molecules, cohering according to a given law, at -certain angles, would present such geometric figures as -we find in nature, or produce in our laboratories, when -we avail ourselves of processes which nature has taught -us.</p> - -<p>If we take a particle of marble, and place it in a large -quantity of water acidulated with sulphuric acid, it -dissolves, and a new compound results. The marble -disappears—the eye cannot detect it by form or colour: -the acid also has been disguised—the taste discovers -nothing sour in the fluid. We have, in combination -with the water, the lime and sulphuric acid; but that -<span class="correction" title="In the original book: combinatiou">combination</span> appears to the eye in no respect different<span class="pagenum"><a name="Page_60" id="Page_60"></a>[Pg 60]</span> -from the water itself. It is colourless and perfectly -transparent, although it holds a mass of solid matter -which previously would not allow of the permeation of -a ray of light. Let us expose this fluid to such circumstances -that the water will slowly evaporate, and we -shall find forming in it, after a time, microscopic particles -of solid, light-refracting matter. These particles -gradually increase in size, and we may watch their -growth until eventually we have a symmetric figure, -beautifully shaped, the primary form of which is a right -rhomboidal prism. Thus in nature, by the action, in -all probability, of vegetable matter on the sulphates held -in solution by the water of the great rivers and the -ocean—aided by our oxidizing atmosphere—sulphuric -acid is produced to do its work upon the limestone formations, -and from this combination would result the -well-known gypsum, or plaster of Paris, which ordinarily -exists as an amorphous mass, but is often found -in a crystalline form.<a name="FNanchor_42_42" id="FNanchor_42_42"></a><a href="#Footnote_42_42" class="fnanchor">[42]</a></p> - -<p>This is a very perfect illustration of the wonderful -process we have been considering, and in which, simple -though it appears to be, we have set to work a large -proportion of the known physical elements of the -universe. By studying aright the result which we have -it in our power to obtain in a watch-glass, we may -advance our knowledge of gigantic phenomena, which -are now progressing at the bottom of the ocean, or of<span class="pagenum"><a name="Page_61" id="Page_61"></a>[Pg 61]</span> -the wondrous agencies which are in operation, producing -light-refracting gems within the secret recesses of the -rocky crust of our globe.</p> - -<p>The force of crystallisation is a subject worthy of -much consideration. If we examine our slate rocks, -through which little veins filled with quartz crystals -are spread, we shall see that the mechanical force -exerted during the production of these crystals has -been capable of rending those rocks in every direction. -Those fissures formed by the first <span class="correction" title="In the original book: sytsem">system</span> of crystalline -veins, in order of time, are filled in by another set -of crystalline bodies, which equally exert their mechanical -power, and thus produce those curious intersections -and dislocations which were long a puzzle to the geologist. -The simplest power, slowly and constantly -acting through a long period of time, may become -sufficient, eventually, to rend the Andes from base to -summit, or to lift a new continent above the waters of -the ocean.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_37_37" id="Footnote_37_37"></a><a href="#FNanchor_37_37"><span class="label">[37]</span></a> “Gay Lussac first made the remark, that a crystal of potash -alum, transferred to a solution of ammonia alum, continued to increase -without its form being modified, and might thus be covered -with alternate layers of the two alums, preserving its regularity and -proper crystalline figure. M. Beudant afterwards observed that -other bodies, such as the sulphates of iron and copper, might present -themselves in crystals of the same form and angles, although -the form was not a simple one, like that of alum. But M. Mitscherlich -first recognised this correspondence in a sufficient number -of cases to prove that it was a general consequence of similarity of -composition in different bodies.”—Graham’s <i>Elements of Chemistry</i> -(1842), p. 136. -</p> -<p> -The following remarks are from a paper by Dr. Hermann Kopp, -<i>On the Atomic Volume and Crystalline Condition of Bodies, &c.</i>, -published in the Philosophical Magazine for 1841:—“The doctrine -of isomorphism shows us that there are many bodies which possess -an analogous constitution, and the same crystalline form. -Our idea of the volume (or, in other words, of the crystalline form) -of these bodies must therefore be the same. From this it follows -that their specific weight is connected with mass contained in the -same volume. From these considerations the following law may -be deduced: <i>The specific weight of isomorphous bodies is proportional -to their atomic weight, or isomorphous bodies possess the same -atomic volume</i>.”—page 255. A translation appears in the Cavendish -Society, from Dr. Otto’s Chemistry, <i>On Isomorphism</i>, which -may be advantageously consulted. See also a paper by M. Rose, -translated from the <i>Proceedings of the Royal Berlin Academy</i> for -the <i>Chemical Gazette</i>, Oct. 1848, entitled, <i>On the Isomeric Conditions -of the Peroxide of Tin</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_38_38" id="Footnote_38_38"></a><a href="#FNanchor_38_38"><span class="label">[38]</span></a> <i>A System of Mineralogy, comprising the most recent discoveries</i>, -by James D. Dana, A.M., New York, 1844.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_39_39" id="Footnote_39_39"></a><a href="#FNanchor_39_39"><span class="label">[39]</span></a> Crystallogeny, or the formation of crystals, is the term employed -by Dana, in his admirable work quoted above: whose -remarks on <i>Theoretical Crystallogeny</i>, p. 71, are well worthy of all -attention.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_40_40" id="Footnote_40_40"></a><a href="#FNanchor_40_40"><span class="label">[40]</span></a> <i>On the Magnetic Relations of the Positive and Negative Optic -Axes of Crystals</i>, by Professor Plücker, of Bonn.—Philosophical -Magazine, No. 231 (3rd Series), p. 450. <i>Experimental Researches -on Electricity; On the Crystalline Polarity of Bismuth and other -bodies, and on its Relation to the Magnetic form of Force</i>: by -Michael Faraday, Esq., F.R.S.—Transactions of the Royal Society -for 1848.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_41_41" id="Footnote_41_41"></a><a href="#FNanchor_41_41"><span class="label">[41]</span></a> In the <i>Memoirs of the Geological Survey of the United Kingdom, -and of the Museum of Economic Geology</i>, vol. i. 1846, will be -found a paper, by the author of this volume, <i>On the Influences of -Magnetism on Crystallisation, and other Conditions of Matter</i>, in -which the subject is examined with much care. See also <i>Magnétisme -polaire d’une montagne de Chlorite schisteuse et de Serpentine</i>: -Annales de Chimie, vol. xxv. p. 327; <i>Influence du Magnétisme sur -les actions chimiques</i>, by l’Abbé Rendus; and also a notice of the -experiments of Ritter and Hansteen, “Analysées par M. Œrsted;” -also <i>Effets du Magnétisme terrestre sur la précipitation de l’Argent, -observés par M. Muschman</i>: Annales de Chimie, vol. xxxviii. p. -196–201.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_42_42" id="Footnote_42_42"></a><a href="#FNanchor_42_42"><span class="label">[42]</span></a> The transparent varieties of sulphate of lime are distinguished -by the name <i>Selenite</i>; and the fine massive varieties are called -<i>Alabaster</i>. Gypsum forms very extensive beds in secondary -countries, and is found in tertiary deposits; occasionally, in -primitive rocks; it is also a product of volcanoes. The finest -foreign specimens are found in the salt mines of Bex, in Switzerland; -at Hall, in the Tyrol; in the sulphur-mines of Sicily; and -in the gypsum formation near Ocana, in Spain. In England, the -clay of Shotover Hill, near Oxford, yields the largest crystals.—See -Dana’s <i>Mineralogy</i>, second edition, p. 241.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_62" id="Page_62"></a>[Pg 62]</span></p> - - -<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI.</h2> - -<p class="center">HEAT—SOLAR AND TERRESTRIAL.</p> - - -<p class="chap-head">Solar and Terrestrial Heat—Position of the Earth in the Solar -System—Heat and Light associated in the Sunbeam—Transparency -of Bodies to Heat—Heating Powers of the -Coloured Rays of the Spectrum—Undulatory Theory—Conducting -Property of the Earth’s Crust—Convection—Radiation—Action -of the Atmosphere on Heat Rays—Peculiar -Heat Rays—Absorption and Radiation of Heat by -dissimilar Bodies—Changes in the Constitution of Solar -Beam—Differences between Transmitted and Reflected Solar -Heat—Phenomena of Dew—Action of Solar Heat on the -Ocean—Circulation of Heat by the Atmosphere and the -Ocean—Heat of the Earth—Mean Temperature—Central -Heat—Constant Radiation of Heat Rays from all Bodies—Thermography—Action -of Heat on Molecular Arrangements—Sources -of Terrestrial Heat—Latent Heat of Bodies—Animal -Heat—Eremacausis—Spheroidal State Cold—Condensation—Freezing—Theories -of Heat—Natural Phenomena—and -Philosophical Conclusion.</p> - - -<p class="p2">We receive heat from the sun, associated with light; and -we have the power of developing this important principle -by physical, mechanical, and chemical excitation, from -every kind of matter. Our convictions are, that the -calorific element, whether derived from a solar or a -terrestrial source, presents no essential difference in its -physical characters; but as there are some remarkable -peculiarities in the phenomena, as they arise from -either one or the other source, it will assist our comprehension -of this great principle, if we consider it under -the two heads.</p> - -<p>Untutored man finds health and gladness in the -warmth and light of the sun; he rears a rugged altar,<span class="pagenum"><a name="Page_63" id="Page_63"></a>[Pg 63]</span> -and bows his soul in prayer, to the principle of fire, -which in his ignorance he regards as the giver and the -supporter of life. The philosopher finds life and organization -dependent upon the powers combined in the -sunbeam; and, examining the phenomena of this -wonderful band of forces, he is compelled to acknowledge -that the flame upon the altar—on the Persian -hills,—was indeed a dim shadow of the infinite wisdom -which abides behind the veil.</p> - -<p>The present condition of our earth is directly dependent -upon the amount of heat we receive from the sun. -It has frequently been said, that if it were possible to -move this planet so much nearer that orb that the -quantity of heat would be increased, the circumstances -of life would necessarily be so far changed, that all the -present races of animals must perish; and that the -same result would happen from any alteration which -threw us yet further from our central luminary, when, -owing to the extremity of cold and the wretchedness of -gloom, all living creatures would equally fail to support -their organization.</p> - -<p>To move the earth nearer to, or more distant from -the sun, is an impossibility; but it has been argued -that those planets which are near to the sun must possess -a temperature which would melt our solid rocks, -and vaporize the ocean,—while Uranus and Neptune -must, from their distance from the source of heat, have -so small an amount, that water must become solid as -the rock, and such an atmosphere as that of the earth -exist as a dense liquid.</p> - -<p>It will be shown that according to the physical condition -of the material substances, so are their powers regulated -of absorbing and retaining the heat which falls as a -radiant power upon their surfaces. Heat rays, in passing -through the attenuated medium of planetary space, lose -none of their power—this we know from the fact that even -the less dense upper region of the earth’s atmosphere -takes from the solar rays but an exceedingly small<span class="pagenum"><a name="Page_64" id="Page_64"></a>[Pg 64]</span> -quantity of heat. Therefore, whether a solar heat ray -traverses through one million, or one hundred million -miles of space, it still retains its power equally of -imparting warmth to the solid matter by which it -is intercepted. There is no law of variation as the -inverse square of the distance of those radiating powers. -Consequently, there is no reason why the physical conditions, -alike of the nearest and the most remote -planetary bodies, should not be so adjusted that they all -enjoy that life promoting temperature which belongs to -the earth.</p> - -<p>All the objects around us are adapted to the circumstances -of the earth’s position in relation to the sun, to -which we are bound by the principle of gravitation; -opposed to that centrifugal force which tends constantly -to drive the moving planetary mass off from the centre -of power. The balance maintains its perfect equilibrium, -although we have one power constantly drawing the -earth towards the sun, and the other as constantly -exerting itself to move it off into space at a tangent to -the orbit in which the planet moves. In our examination -it will be found that one common system of harmony -runs through all the cosmical phenomena, by which -everything is produced that is so beautiful and joyous in -this world.</p> - -<p>Heat, and the other elementary radiant principles, -are often combined as the common cause of effects -evident to our senses. The warmth of the solar rays, -and their luminous influence, are not, however, commonly -associated in the mind as the results of a -single cause. It is only when we come to examine the -physical phenomena connected with these radiations -that we discover the complexity of the inquiry. Yet it -is out of these very subtle researches that we draw the -most refined truths. The high inferences to which the -analysis of the subtile agencies of creation leads us, -render science, pursued in the spirit of truth, a great -system of religious instruction.</p> - -<p><span class="pagenum"><a name="Page_65" id="Page_65"></a>[Pg 65]</span></p> - -<p>Although we do not fear that heat and light can be -confounded in the mind, so different are their phenomena,—we -have heat rays, as from dark hot iron, -which give no light, while in the full flood of the lunar -rays the heat is scarcely appreciable by the most delicate -instruments;—yet it is important to show how far these -two principles have—been separated from each other. -Transparent bodies have varied powers of calorific transparency, -or transcalescence: some obstructing the heat -radiated from bodies of the highest temperatures almost -entirely even in the thinnest layers; whilst others will -allow the warmth of the hand to pass through a thickness -of several inches. Liquid chloride of sulphur, which is of -a deep red colour, will allow 63 out of 100 rays of heat -to pass, and a solution of carmine in ammonia, or glass -stained with oxides of gold, or copper, rather a greater -number; yet these transparent media obstruct a large -quantity of light. Colourless media obstructing scarcely -any light, will, on the contrary, prevent the passage of -calorific rays. Out of every hundred rays, oil of turpentine -will only transmit 31, sulphuric ether 21, sulphuric -acid 17, and distilled water only 11. Pure flint glass, -however, is permeated by 67 per cent. of the thermic rays, -and crown glass by 49 per cent. The body possessing -the most perfect transparency to the rays of heat is diaphanous -salt-rock, which transmits 92, while alum, equally -translucent, admits the passage of only 12 per cent.<a name="FNanchor_43_43" id="FNanchor_43_43"></a><a href="#Footnote_43_43" class="fnanchor">[43]</a></p> -<p><span class="pagenum"><a name="Page_66" id="Page_66"></a>[Pg 66]</span></p> -<p>Black mica, obsidian, and black glass, are nearly -opaque to light, but they allow 90 per cent. of radiant -heat to pass through them; whereas a pale green glass, -coloured by oxide of copper,<a name="FNanchor_44_44" id="FNanchor_44_44"></a><a href="#Footnote_44_44" class="fnanchor">[44]</a> covered with a layer of -water, or a very thin plate of alum, will, although -perfectly transparent to light, almost entirely obstruct -the permeation of heat rays.</p> -<p><span class="pagenum"><a name="Page_67" id="Page_67"></a>[Pg 67]</span></p> -<p>We thus arrive at the fact that heat and light may be -separated from each other; and if we examine the solar -beam by that analysis which the prism affords, we shall -find that there is no correspondence between intense -light and ardent heat. By careful observation, it has -been proved, when we have a temperature of 62° F. in the -yellow ray, which ray has the greatest illuminating power; -that below the red ray, out of the point of visible light, -the temperature is found to be 79°, while at the other end -of the spectrum, in the blue ray, it is 56°, and at the end -of the violet ray no thermic action can be detected.<a name="FNanchor_45_45" id="FNanchor_45_45"></a><a href="#Footnote_45_45" class="fnanchor">[45]</a></p> - -<p>From the circumstance, that as we, by artificial -means, raise the temperature of any body, and produce -intense heat, so after a certain point of thermic elevation<span class="pagenum"><a name="Page_68" id="Page_68"></a>[Pg 68]</span> -has been obtained, we occasion a manifestation of <i>light</i>.<a name="FNanchor_46_46" id="FNanchor_46_46"></a><a href="#Footnote_46_46" class="fnanchor">[46]</a> -It has been concluded, somewhat hastily, that heat and -light differ from each other only in the rapidity of the -undulations of an hypothetical ether.</p> - -<p>It must be admitted that the mathematical demonstrations -of many of the phenomena of calorific and -luminous power are <span class="correction" title="In the original book: sufficienlty">sufficiently</span> striking to convince us -that a wave-movement is common to both heat and -light. The undulatory theory, however, requires the<span class="pagenum"><a name="Page_69" id="Page_69"></a>[Pg 69]</span> -admission of so many premises of which we have no -proof; its postulates are, indeed, in many cases so -gratuitous, that notwithstanding the array of talent -which stands forward in its support, we must not allow -ourselves to be deceived by the deductions of its advocates, -or dazzled by the brilliancy of their displays of -learning.</p> - -<p>Radiant heat appears to move in waves; but that -calorific effects in material bodies are established by any -system of undulation, is a deduction without a proof; -and the thermic phenomena of matter are as easily explained -by the hypothesis of a diffusive subtile fluid.</p> - -<p>We have not, however, to prove the correctness of -either of the opposing views; indeed, it is acknowledged -that many phenomena require for their explanation -conditions which are not indicated by either theory.</p> - -<p>The earth receives its heat from the sun; a portion of -it is <i>conducted</i> from particle to particle into the interior -of the rocky crust. Another portion produces warmth -in the atmosphere around us, by <i>convection</i>, or the -circulation of particles; those warmed by contact with -the surface becoming lighter, and ascending to give -place to the colder and heavier ones. A third portion is -radiated off into space, according to laws which have -not been sufficiently investigated, but which are dependent -upon the colour, chemical composition, and mechanical -structure of the surface.</p> - -<p>It cannot but be instructive to contemplate the -indications which we have of the dependence of all that -is beautiful on earth, on the heat and light radiations -which we receive from the sun. Let us endeavour to -realise some of the effects which arise from even the -temporary deprivation of solar heat.</p> - -<p>It is winter, the vegetable world appears chilled to its -centre. The trees, except a few of the hardy evergreens, -are bare of leaves, and stretching forth their branches -into the cold air, they realise the condition of vegetable<span class="pagenum"><a name="Page_70" id="Page_70"></a>[Pg 70]</span> -skeletons. The lowly plants of the hedge-row, and the -grasses of the field, show that their vital power is subdued -to that minimum degree of action which is but a few -slight removes from death. The life of the running -stream is suspended, it is cased in the “thick-ribbed -ice,” and the waters beneath no longer send forth their -joyous music to the genial breeze. Even within the -temperate limits of our own land, the aspect of winter -convinces the ordinary observer, that the loss of heat -has been followed by diminished activity in the powers -of life; and the philosopher discovers that the lessened -energies of solar light, and the weaker action of the -radiant heat, have aided in producing that repose which -is a little more than sleep—a little less than death.</p> - -<p>It is night, and winter: the earth is parting with its -heat,—with the absence of light, there is a still greater -loss of vigour, a yet further diminution of the powers of -life. Even the animal races, sustained by vital influences -of a more exalted kind, sink under the temporary -deprivation of the solar rays to a monotonous, a melancholy -repose. All animals undergo different degrees of -hybernation, and each in his winter retreat supports -vitality by preying upon himself. The world is hung in -mourning black; there is no play of colours to harmonize -the human spirit by sending their ethereal pulsations to -the human eye, and it is only the consciousness that -when the night is at the darkest, the day is nearest, -that even man’s soul is sustained against the depressing -influences of the absence of the sun.</p> - -<p>The conditions which we must observe at our own -doors cannot fail to convey as a conviction to the least -imaginative mind, that a slightly prolonged continuance -of darkness, with its consequent increase of coldness, -would be fatal to the existence of the organic world.</p> - -<p>The sun has entered Aries: it is spring. The length -of the day and night are equal, the powers of light and -darkness are now exactly balanced against each other,<span class="pagenum"><a name="Page_71" id="Page_71"></a>[Pg 71]</span> -and light, like the Archangel, triumphs over the sombre -spirit. The organic world awakes. Chemical action -commences in the seed, the vital spark is kindled in the -embryo, and under the impulsive force of some solar -radiations the plant struggles into light and life. The -same invigorating force impels the circulation of the sap -through the capillary tubes of the forest tree, until the -topmost branch trembles with the new flow of life. The -buds burst forth into leaf, and a fresh and lively covering -spreads over those branches which, in their nakedness, -could scarcely be distinguished from the dead.</p> - -<p>The animal races are no less sensible of the new -influence which is diffused around. The birds float -joyously upon the breeze, and give to heaven their -trilling songs of praise. The beasts come forth from -the clefts of the rocks and the tangled shelters of the -forests, and gambol in the full luxury of their renewed -vigour. Man, even man, the inhabitant of cities, -trained and tempered to an artificial state, awakes of a -spring morning with a fuller consciousness of mind, and -a deeper and more pleased sense of his intelligence, -than when the fogs and gloom of winter hung like the -charmed robe upon the limbs of the giant. Now, the -dormant poetry of man seeks expression. As the -morning sun is said to have awakened the musical undulations -of the Memnonian statue, so the sun of the -vernal morning produces in the mind of the most -earthly, faint pulsations of that heaven-born music, which -neither sin nor sorrow can entirely destroy. The psychologist, -in studying the peculiar phenomena of the -human mind, must associate himself with the natural -philosopher, and learn to appreciate the influence of -physical causes in determining effects which our elder -philosophers and the poets of every age have attributed to -spiritual agencies.</p> - -<p>Summer, with its increased heat and light, reigns over<span class="pagenum"><a name="Page_72" id="Page_72"></a>[Pg 72]</span> -the land. The work of life is now at its maximum, and -every energy is quickened throughout the organic -creation. The laws of nature are arranged on the -principle of antagonistic forces, the constant struggle to -maintain them in equilibrium constituting the sensible -phenomena of existence. Heat and light, with chemical -power and electricity, have been quickening the unknown -principle of life, until it has become exhausted -in the production of new parts—in the strange phenomenon -of growth—the formation of organized matter -from the inorganic stores of creation.</p> - -<p>The autumn, with its tempered sunlight, comes, but in -the solar radiance we discover new powers, and under -the influence of these the flower and the fruit have -birth. The store of a new life is centered in the seed, -and though the leaf falls, and the flower fades, a new set -of organisms are produced, by which the continuance of -the species is secured.</p> - -<p>Let any man examine himself as the seasons change, -and he will soon be convinced that every alternation of -light and darkness, of heat and its absence, produces new -sets of influences equally on the mind and on the body, -showing the entire dependence of the animal and -vegetable kingdoms upon those causes which appear to -flow from the centre of our planetary system.</p> - -<p>The phenomena which connect themselves with the -changes of the seasons cannot fail to convince the most -superficial thinker that there is an intimate connection -between the sun and the earth which deserves our close -attention.</p> - -<p>Indeed, if we examine the most ancient of histories, -we find one great fact at the base of all their philosophies. -Moses connects darkness with a void and formless -earth, and light with the creation of harmony and life. -Menis sings of a fearful world by “many formed darkness -encircled,” and links the idea of a “life-breathing<span class="pagenum"><a name="Page_73" id="Page_73"></a>[Pg 73]</span> -divinity” with the awakening of light upon created -things. The Egyptian Isis, the Grecian Apollo, who,</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">The Lord of boundless light</div> -<div class="verse">Ascending calm o’er the empyrean sails,</div> -<div class="verse">And with ten-thousand beams his awful beauty veils,</div> -</div></div></div> - -<p>the fire-worshipper of the Persian hills and the sun-god -of the Peruvian mountains, exhibit, through time -and space, the full consciousness of man to the influences -of solar light and heat upon the organic creations of -which he is himself the chief exemplar.</p> - -<p>The investigations of modern philosophers have extended -these influences to the inorganic masses which -constitute the Planet <span class="smcap">Earth</span>:—and we now know that -the physical forces, ever active in determining the -chemical condition and the electrical relations of matter, -are directly influenced by the solar radiations.</p> - -<p>Few things within the range of our inquiry are more -striking than the phenomena of calorific radiation and -absorption. They display so perfectly the most refined -system of order, and exhibit so strikingly the admirable -adaptation of every formation to its particular conditions, -and for its part in the great economy of being, -that they claim most strongly the study of all who would -seek to discover a poetry in the inferences of science.</p> - -<p>Owing to the nature of our atmosphere, we are protected -from the influence of the full flood of solar heat. -The absorption of caloric by the air has been calculated -at about one-fifth of the whole in passing through a -column of 6,000 feet. This estimate is, of course, made -near the earth’s surface; but we are enabled, knowing -the increasing rarity of the upper regions of our gaseous -envelope in which the absorption is constantly diminishing, -to prove, that about one-third of the solar heat is -lost by vertical transmission through the whole extent of -our atmosphere.<a name="FNanchor_47_47" id="FNanchor_47_47"></a><a href="#Footnote_47_47" class="fnanchor">[47]</a></p> -<p><span class="pagenum"><a name="Page_74" id="Page_74"></a>[Pg 74]</span></p> -<p>Experience has proved that the conditions of the -sun’s rays are not always the same; and there are few -persons who have not observed that a more than usual -scorching influence prevails under some atmospheric -circumstances. This is also evidenced in the effects -produced on the foliage of trees, which, though often -attributed to electricity, is evidently due to heat. An -examination of the solar radiations, as exhibited in the -prismatic spectrum, has proved the existence of a class -of heat rays, which manifest themselves by a very peculiar -deoxidizing power quite independent of their caloric -properties, to which the name of <i>parathermic rays</i> -has been given.<a name="FNanchor_48_48" id="FNanchor_48_48"></a><a href="#Footnote_48_48" class="fnanchor">[48]</a> We are protected from the severe<span class="pagenum"><a name="Page_75" id="Page_75"></a>[Pg 75]</span> -effects of these rays by the ordinary state of the medium -through which the solar heat passes. Our atmosphere -is a mixture of gases and aqueous vapour; and it has -been found, as already stated, that even a thin film of -water, however transparent, prevents the passage of many -calorific radiations, and the rays retarded are, for the -most part, of that class which have this peculiar scorching -power. The air is, in this way, the great equaliser -of the solar heat, rendering the earth agreeable to all -animals, who, but for this peculiar absorbent medium, -would have to endure, even in our temperate clime, the -burning rays of a more than African sun.</p> - -<p>The surface of the earth during the sunshine—and, -though in a less degree, even when the sun is obscured -by clouds—is constantly receiving heat; but the rate of -its absorption varies. Benjamin Franklin showed, by a -set of simple but most conclusive experiments, that a -piece of black cloth was warmed much sooner than cloth -of a lighter colour;<a name="FNanchor_49_49" id="FNanchor_49_49"></a><a href="#Footnote_49_49" class="fnanchor">[49]</a> and we know, from observations -of a similar class, that the bare brown soil receives heat -more readily than the bright green grassy carpet of the -earth. Consequently, during the winter season, rela<span class="pagenum"><a name="Page_76" id="Page_76"></a>[Pg 76]</span>tively -to the quantity poured from its source, more heat -penetrates the uncovered soil, than during the spring -or summer.</p> - -<p>There is a constant tendency to an equilibrium; and, -during the night, the surface is robbed of more heat, by -the colder air, than by day; as, when the earth is not receiving -heat, it is constantly radiating it back into space. -Even in these processes of convection and radiation, a -similar law prevails to that which is discovered in examining -into the rate of calorific absorption.</p> - -<p>Every tree spreading its green leaves to the sunshine, -or exposing its brown branches to the air—every flower -which lends its beauty to the earth—possesses different -absorbing and radiating powers. The chalice-like cup -of the pure white lily floating on the lake—the variegated -tulip—the brilliant anemony—the delicate rose—and the -intensely coloured peony or dahlia—have each powers -peculiar to themselves for drinking in the warming life-stream -of the sun, and for radiating it back again to the -thirsting atmosphere. These are no conceits of a scientific -dreamer; they are the truths of direct induction; -and, by experiments of a simple character, they may be -put to a searching test.<a name="FNanchor_50_50" id="FNanchor_50_50"></a><a href="#Footnote_50_50" class="fnanchor">[50]</a></p> - -<p>A thermometric examination of the various coloured -flowers, by enclosing a delicate thermometer amongst -their leaves, will readily establish the correctness of the -one; and by a discovery of recent date, connected with -calorific radiation, which must be particularly described -presently, we can, with equal ease and certainty, test the<span class="pagenum"><a name="Page_77" id="Page_77"></a>[Pg 77]</span> -truth of the other;<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a href="#Footnote_51_51" class="fnanchor">[51]</a> the absorption and radiation of -heat being directly regulated by the colours of the surfaces -upon which the sun rays fall.</p> - -<p>It follows, as a natural consequence of the position of -the sun, as it regards any particular spot on the earth at -a given time, that the amount of heat is constantly varying -during the year. This variation regulates the -seasons.</p> - -<p>When it is remembered that the earth is, in the -winter, nearly three millions of miles nearer the sun -than in the summer, some explanation is required to -account for our suffering more cold when nearer the -source of heat, than when at the remotest distance.</p> - -<p>The earth in her path around the sun describes an -ellipse, the sun’s place being one of its foci. In obedience -to the law, already described, of the conservation -of the axis of rotation, the axis of the earth constantly -points towards the star in the constellation of the -Little Bear. Recollecting this, and also the two facts, -that a dense solid body absorbs heat more readily than -a fluid one, and that radiation from the surface is constantly -going on when absorption is not taking place, -let us follow the earth in her orbit.</p> - -<p>It is the time of the vernal equinox—we have equal -day and night—therefore the periods of absorption and -radiation of heat are alike. But at this time of the year -the southern hemisphere is opposite to the sun, consequently -the degree of absorption by the wide-spread -oceans small.</p> - -<p>It is the summer solstice—we have sixteen hours of -daylight, when the absorption of heat is going on—and -but eight hours of night, during which heat is passing<span class="pagenum"><a name="Page_78" id="Page_78"></a>[Pg 78]</span> -off. The northern hemisphere is now presented to the -sun, and as here we have the largest portion of dry land, -the powers of absorption are at their maximum.</p> - -<p>The autumnal equinox has arrived, with its equal day -and night, as in the spring, but now the whole northern -hemisphere is opposite the sun; hence, according to the -laws already explained, we see the causes of the increased -heat of the autumnal season.</p> - -<p>The winter solstice has come, with its long night and -shortened day. The time during which radiation is -going on is nearly twice that in which absorption takes -place, and the earth is in her worst position for receiving -heat, as that half which has the largest surface of -water is towards the sun.</p> - -<p>These are the causes which lead to the variations of -the seasons, and through these we learn why we are -colder when near the sun than when at a considerably -greater distance.</p> - -<p>An analysis of the spectrum shows us that there are -some changes regularly taking place in the state of the -solar beam, which cannot be referred to the mere alteration -of position. It may be inferred, from facts -by long-continued observations, that the three classes -of phenomena—light, heat, and chemical power, distinguished -by the term Actinism—which we detect in the -sun’s rays, are constantly changing their relative proportions. -In spring, the chemical agency prevails; in -summer, the luminous principle is the most powerful; -and in the autumn, the calorific forces are in a state of -the greatest activity.<a name="FNanchor_52_52" id="FNanchor_52_52"></a><a href="#Footnote_52_52" class="fnanchor">[52]</a> The importance of these variations, -to the great economy of vegetable life, will be -shown when we come to examine the phenomena connected -with organisation.</p> -<p><span class="pagenum"><a name="Page_79" id="Page_79"></a>[Pg 79]</span></p> -<p>A remarkable change takes place in the character of -heat in being reflected from material substances. In -nature we often see this fact curiously illustrated. Snow -which lies near the trunks of trees or wooden poles -melts much quicker than that which is at a distance -from them, the sun shining equally on both—the liquefaction -commencing on the side facing the sun, and -gradually extending. We see, therefore, that the direct -rays of solar heat produce less effect upon the snow than -those which are radiated from coloured surfaces. By -numerous experiments, it has been shown that these secondary -radiations are more abundantly absorbed by snow -or white bodies than the direct solar rays themselves. -Here is one of the many very curious evidences, which -science lays open to us, of the intimate connection between -the most ethereal and the grosser forms of matter. -Heat, by touching the earth, becomes more earth-like. -The subtile principle which, like the spirit of superstition, -has the power of passing, unfelt, through the -crystal mass, is robbed of its might by embracing the -things of earth; and although it still retains the evidences -of its refined origin, its movements are shackled as by a -clog of clay, and its wings are heavy with the dust of -this rolling ball. It has, however, acquired new properties, -which fit it for the requirements of creation, and -by which its great tasks are facilitated. Matter and -heat unite in a common bond, and, harmoniously pursuing -the necessities of some universal law, the result -is the extension of beautiful forms in every kingdom of -nature.</p> - -<p>An easy experiment pleasingly illustrates this remarkable -change. If a blackened card is placed upon snow -or ice in the sunshine, the frozen mass underneath it will -be gradually thawed, and the card sink into it, while -that by which it is surrounded, although exposed to the -full power of solar heat, is but little disturbed. If, how<span class="pagenum"><a name="Page_80" id="Page_80"></a>[Pg 80]</span>ever, -we reflect the sun’s rays from a metal surface, an -exactly contrary result takes place; the uncovered parts -are the first to melt, and the blackened card stands high -above the surrounding portion.</p> - -<p>The evidences of science all indicate the sun as the -source, not only of that heat which we receive directly -through our atmosphere, but even of that which has -been stored by our planet, and which we can, by several -methods, develope. We have not to inquire if the earth -was ever an intensely heated sphere;—this concerns not -our question; as we should, even were this admitted, -still have to speculate on the origin—the primitive source -of this caloric.</p> - -<p>Before, however, we proceed to the examination of -the phenomena of terrestrial heat, a few of the great -results of the laws of radiation and convection claim our -attention.</p> - -<p>Nearly all the heat which the sun pours upon the -ocean is employed in converting its water into vapour at -the very surface, or is radiated back from it, to perform -the important office of producing those disturbing influences -in the atmosphere, which are essential to the preservation -of the healthful condition of the great aërial -envelope in which we live.</p> - -<p>Currents of air are generally due to the unequal degrees -in which the atmosphere is warmed. Heat, by expanding, -increases the elasticity, and lessens the density, of a -given mass. Consequently, the air heated by the high -temperature of the tropics, ascends charged with aqueous -vapours, whilst the colder air of the temperate and the -frigid zones flows towards the equator to supply its place. -These great currents of the atmosphere are, independent -of the minor disturbances produced by local causes, in -constant flow, and by them a uniformity of temperature -is produced, which could not in any other way be accomplished. -By these currents, too, the equalisation of the<span class="pagenum"><a name="Page_81" id="Page_81"></a>[Pg 81]</span> -constituents of the “breath of life” is effected, and the -purer oxygen of the “land of the sunny south” is diffused -in healthful gales over the colder climes of the -north. The waters, too, evaporated from the great -central Atlantic Ocean, or the far Pacific, are thus carried -over the wide-spread continents, and poured in fertilising -showers upon distant lands.</p> - -<p>How magnificent are the operations of nature! The -air is not much warmed by the radiations of caloric passing -from the sun to the earth; but the surface soil is -heated by its power of absorbing these rays. The temperature -of the air next the earth is raised, and we thus -have the circulation of those beneficial currents which -are so remarkably regular in the Trade Winds. The air -heated within the tropics would ascend directly to the -poles, were the earth at rest, but being in motion, those -great aërial currents—the Trade Winds—are produced, -and the periodical monsoons are due to the same cause. -A similar circulation, quite independent of the ordinary -tidal movement, takes place also in the earth-girdling -ocean. The water, warmed, by convection, from the hot -surface of the tropical lands, sets across the Atlantic -from the Gulf of Mexico; and being under the influence -of the two forces—gravity and motion—it illustrates the -parallelogram of forces, and flowing along the diagonal, -reaches our own shores: the genial influences of -the gulf stream produce that tempered climate which -distinguishes our insular home. Here we have two immense -influences produced by one agency, rendering -those parts of the earth habitable and fertile, which but -for these great results would sorrow in the cheerless -aspect of an eternal winter.</p> - -<p>The beautiful phenomenon of the formation of dew is -also distinctly connected with the peculiar properties -which we have been studying. When from the bright blue -vault of heaven, the sparkling constellations shower their -mild light over the earth, the flowers of the garden and<span class="pagenum"><a name="Page_82" id="Page_82"></a>[Pg 82]</span> -the leaves of the forest become moist with a fluid of -the most translucid nature. Well might the ancients -imagine that the dews were actually shed from the stars; -and the alchemists and physicians of the middle ages -conceive that this pure distillation of the night possessed -subtile and penetrating powers beyond most other -things; and the ladies of those olden times endeavour -to preserve their charms in the perfection of their youthful -beauty through the influences of washes procured -from so pure a source.<a name="FNanchor_53_53" id="FNanchor_53_53"></a><a href="#Footnote_53_53" class="fnanchor">[53]</a></p> - -<p>Science has removed the veil of mystery with which -superstition had invested the formation of dew; and, in -showing to us that it is a condensation of vapour upon -bodies according to a fixed law of radiation, it has also -developed so many remarkable facts connected with the -characters of material creations, that a much higher -order of poetry is opened to the mind than that which, -though beautiful, sprang merely from the imagination.</p> - -<p>Upon the radiation of heat depends the formation of -dew, and bodies must become colder than the atmosphere -before it will be deposited upon them. At whatever -temperature the air may be, it is charged to -saturation with watery vapour, the quantity varying -uniformly with the temperature. Supposing the temperature -of the air to be 70° F., and that a bottle of -water at 60° is placed in it, the air around the bottle<span class="pagenum"><a name="Page_83" id="Page_83"></a>[Pg 83]</span> -will be cooled, and will deposit on the glass exactly that -quantity of moisture which is due to the difference between -the temperature of the two bodies. Different -substances, independent of colour, have the property of -parting with heat from their surfaces at different rates. -Rough and porous surfaces radiate heat more rapidly -than smooth ones, and are consequently reduced in temperature; -and, if exposed, are covered with dew sooner -than such as are smooth and dense. The grass parterre -glistens with dew, whilst the hard and stony walk is unmoistened.<a name="FNanchor_54_54" id="FNanchor_54_54"></a><a href="#Footnote_54_54" class="fnanchor">[54]</a></p> - -<p>Colourless glass is very readily suffused with dampness, -but polished metals are not so, even when dews are -heavily condensed on other bodies. To comprehend -fully the phenomena of the formation of dew, we must -remember that the entire surface of the earth is constantly -radiating heat into space; and that, as by night no absorption -is taking place, it naturally cools.<a name="FNanchor_55_55" id="FNanchor_55_55"></a><a href="#Footnote_55_55" class="fnanchor">[55]</a> As the -substances spread over the earth become colder than the -air, they acquire the power of condensing the vapour -with which the atmosphere is always charged. The -bodies which cover this globe are very differently constituted; -they possess dissimilar radiating powers, and con<span class="pagenum"><a name="Page_84" id="Page_84"></a>[Pg 84]</span>sequently -present, when examined by delicate thermometers, -varying degrees of temperature. By the researches -of Dr. Wells,<a name="FNanchor_56_56" id="FNanchor_56_56"></a><a href="#Footnote_56_56" class="fnanchor">[56]</a> which may be adduced as an example of -the best class of inductive experiments, we learn that the -following differences in sensible heat were observed at -seven o’clock in the evening:—</p> - -<table summary="Differences in heat in the evening"> -<tr><td>The air four feet above the grass</td><td class="tdpad">60–3/4</td></tr> -<tr><td>Wool on a raised board</td><td class="tdpad">54–1/2</td></tr> -<tr><td>Swandown on ditto</td><td class="tdpad">53</td></tr> -<tr><td>The surface of the raised board</td><td class="tdpad">57</td></tr> -<tr><td>Grass plat</td><td class="tdpad">51</td></tr> -</table> - -<p>Dew is most abundantly deposited on clear, calm -nights, during which the radiation from the surface of -the earth is uninterrupted. The increased cold of such -nights over those obscured by clouds is well known. The -clouds, it has been proved, act in the same way as the -screens used by gardeners to protect their young plants -from the frosts of the early spring, which obstruct the -radiation, and, in all probability, reflect a small quantity -of heat back to the earth.</p> - -<p>It is not improbable that the observed increase in -grass crops, when they have been strewn with branches -of trees or any slight shades, may be due to a similar -cause.<a name="FNanchor_57_57" id="FNanchor_57_57"></a><a href="#Footnote_57_57" class="fnanchor">[57]</a></p> -<p><span class="pagenum"><a name="Page_85" id="Page_85"></a>[Pg 85]</span></p> -<p>There are many remarkable results dependent entirely -on the colours of bodies, which are not explicable upon -the idea of difference in mechanical arrangement. We -know that different colours are regulated by the powers -which structures have of absorbing and reflecting light; -consequently a blue surface must have a different order -of molecular arrangement from a red one. But there -are some physical peculiarities which also influence heat -radiation, quite independently of this <i>surface</i> condition. -If we take pieces of red, black, green, and yellow glass, -and expose them when the dew is condensing, we shall -find that moisture will show itself first on the yellow, -then on the green glass, and last of all upon the black -or red glasses. The same thing takes place if we expose -coloured fluids in white glass bottles or troughs, in which -case the surfaces are all alike. If against a sheet of -glass, upon which moisture has been slightly frozen, we -place glasses similarly coloured to those already described, -it will be found that the earliest heat-rays will so warm -the red and the black glasses, that the ice will be melted -opposite to them, long before any change will be seen -upon the frozen film covered by the other colours.</p> - -<p>The order in which heat permeates coloured media, it -has already been shown, very nearly agrees with their -powers of radiation.</p> - -<p>These most curious results have engaged the attention -of Melloni, to whose investigations we owe so much; -and from the peculiar order of radiations, which present -phenomena of an analogous character to those of the -coloured rays of light, obtained by him from dissimilarly -coloured bodies, he has been led to imagine the existence<span class="pagenum"><a name="Page_86" id="Page_86"></a>[Pg 86]</span> -of a “heat-colouration.” That is, the heat-rays are -supposed to possess properties like luminous colour -although invisible; and, consequently, that a blue surface -has a strong affinity for the blue heat-rays, a red -surface for the red ones, and so on through the scale. -The ingenuity of this hypothesis has procured it much -attention; but now, when the Newtonian hypothesis of -the refrangibility of light is nearly overturned, we must -not, upon mere analogy, rush to the conclusion that the -rays of heat have different orders of refrangibility, which -Melloni’s hypothesis requires.<a name="FNanchor_58_58" id="FNanchor_58_58"></a><a href="#Footnote_58_58" class="fnanchor">[58]</a></p> - -<p>Can anything be more calculated to impress the mind -with the consciousness of the high perfection of natural -phenomena, than the fact, that the colour of a body -should powerfully influence the transmission of a principle -which is diffused through all nature, and also determine -the rate with which it is to pass off from its surface. -Some recent experiments have brought us acquainted -with other facts connected with these heat-radiations, -and the power of heat, as influenced by the calorific -rays, to produce molecular changes in bodies, which bear -most importantly on our subject.</p> - -<p>If we throw upon a plate of polished metal a prismatic -spectrum (deprived, as nearly as possible, of its chemical -power, by being passed through a deep yellow solution—which -possesses this property in a very remarkable -manner, as will be explained when we come to the examination -of the chemical action of the sun’s rays)—it -will be found, if we afterwards expose the plate to the<span class="pagenum"><a name="Page_87" id="Page_87"></a>[Pg 87]</span> -action of vapour, very slowly raised from mercury, that -the space occupied by the red rays, and those which lie -without the spectrum below it, will condense the vapour -thickly, while the portion corresponding with the other -rays will be left untouched. This affords us evidence of -the power of solar heat to produce, very readily, a change -in the molecular structure of solid bodies. If we allow -the sun’s rays to permeate coloured glasses, and then -fall upon a polished metallic surface, the result, on -exposing the plate to vapourisation, will be similar to -that just described. Under yellow and green glasses no -vapour will be condensed; but on the space on which -the rays permeating a red glass, or even a blackened one, -fall, a very copious deposit of vapour will mark with distinctness -the spaces these glasses covered. More remarkable -still, if these or any other coloured bodies are placed -in a box, and a polished metal plate is suspended a few -lines above them, the whole being kept <i>in perfect darkness</i> -for a few hours, precisely the same effect takes place -as when the arrangement is exposed to the full rays of -the sun. Here we have evidence of the radiating heat of -bodies, producing even in darkness the same phenomena -as the transmitted heat-rays of the sun. We must, -however, return to the examination of some of these and -other analogous influences under the head of actino-chemistry.</p> - -<p>From these curious discoveries of inductive research -we learn some high truths. Associated with light—obeying -many of the same laws—moving in a similar -manner—we receive a power which is essential to the -constitution of our planet. This power is often manifested -in such intimate combination with the luminous -principle of the solar rays, that it has been suspected to -be but another form of the same agency. While, however, -we are enabled to show the phenomena of one -without producing those which distinguish the other, -we are constrained to regard heat as something dis<span class="pagenum"><a name="Page_88" id="Page_88"></a>[Pg 88]</span>similar -to light. It is true that we appear to be tending -towards some point of proof on this problem; but we -are not in a position to declare them to be forms of one -common power, or “particular solutions of one great -physical equation.”<a name="FNanchor_59_59" id="FNanchor_59_59"></a><a href="#Footnote_59_59" class="fnanchor">[59]</a> In many instances it would certainly -appear that one of these forces was directly necessary -to the production of the other; but we have also -numerous examples in which they do not stand in any -such correlation.</p> - -<p>We learn, from the scientific facts which we have been -discussing, a few of the secrets of natural magic. In -their relations to heat, every flower, which adds to the -adornment of the wilds of nature or the carefully-tended -garden of the florist, possesses a power peculiar to itself;</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“Naiad-like lily of the vale,”</div> -</div></div></div> - -<p>and,</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“—— The pied wind-flowers, and the tulip tall,</div> -<div class="verse">And narcissi, the fairest among them all,”</div> -</div></div></div> - -<p>are, by their different colours, prevented from ever -having the same temperatures under the same -sunshine.</p> - -<p>Every plant bears within itself the measure of the -heat which is necessary for its well-being, and is endued -with functions which mutely determine the relative -amount of dew which shall wet its coloured leaves. -Some of the terrestrial phenomena of this remarkable -principle will still further illustrate the title of this -volume.</p> - -<p>To commence with the most familiar illustrations, let -us consider the consequences of change of temperature.<span class="pagenum"><a name="Page_89" id="Page_89"></a>[Pg 89]</span> -However slight the additional heat may be to which a -body is subjected, it expands under its influence; consequently, -every atom which goes to form the mass of -the earth moves under the excitation, and the first heat -ray of the morning which touches the earth’s surface, -sets up a vibration which is continued as a tremor to its -very centre. The differences between the temperature -of day and night are considerable; therefore all bodies -expand under the influence of the higher, and contract -under that of the lower temperature. During the day, -any cloud obscuring the sun produces, in every solid, -fluid, or aëriform body, within the range of solar influence, -a check: the particles which had been expanding -under the force of heat suddenly contract. Thus -there must of necessity be, during the hours of sunshine, -a tendency in all bodies to dilate, and during the hours -of night they must be resuming their original conditions.</p> - -<p>Not only do dissimilar bodies radiate heat in different -degrees, but they conduct it also with constantly varying -rates. Heat passes along silver or copper with readiness, -compared to its progress through platinum. It is -conducted by glass but slowly, and still more slowly by -wood and charcoal. We receive some important intimations -of the molecular structure of matter, from those -experiments which prove that heat is conducted more -readily along some lines than others. In some planes, -wood and other substances are better conductors than in -others. The metallic oxides or earths are bad conductors -of heat, by which provision the caloric absorbed by -the sun’s rays is not carried away from the surface of this -planet so rapidly as it would have been had it been of -metal, but is retained in the superficial crust to produce -the due temperature for healthful germination and -vegetable growth. The wool and hair of animals are still -inferior conductors, and thus, under changes of climate -and of seasons, the beasts of the field are secured against -those violent transitions from heat to cold which would<span class="pagenum"><a name="Page_90" id="Page_90"></a>[Pg 90]</span> -be fatal to them. Hair is a better conductor than wool: -hence, by nature’s alchemy, hair changed into wool in -the animals of some countries on the approach of winter, -and feathers into down.</p> - -<p>It is therefore evident that the rate at which solar -heat is conducted into the crust of the earth must alter -with the condition of the surface upon which it falls. -The conducting power of all the rocks which have been -examined is found to vary in some degree.<a name="FNanchor_60_60" id="FNanchor_60_60"></a><a href="#Footnote_60_60" class="fnanchor">[60]</a></p> - -<p>It follows, as a natural consequence of the position of -the sun to the earth, that the parts near the equator -become more heated than those remote from it. As this -heat is conducted into the interior of the mass, it has a -tendency to move to the colder portions of it, and thus -the heat absorbed at the equator flows towards the poles, -and from these parts is carried off by the atmosphere, or -radiated into space. Owing to this, there is a certain -depth beneath the surface of our globe at which an equal -temperature prevails, the depth increasing as we travel -north or south from the equator, and conforming to the -contour of the earth’s surface, the line sinking under -the valleys and rising under the hills.<a name="FNanchor_61_61" id="FNanchor_61_61"></a><a href="#Footnote_61_61" class="fnanchor">[61]</a></p> -<p><span class="pagenum"><a name="Page_91" id="Page_91"></a>[Pg 91]</span></p> -<p>A question of great interest, in a scientific point of -view, is the temperature of the centre of the earth. We -are, of course, without the means of solving this problem; -but we advance a little way onwards in the inquiry -by a careful examination of subterranean temperature at -such depths as the enterprise of man enables us to reach. -These researches show us, that where the mean temperature -of the climate is 50°, the temperature of the rock at -59 fathoms from the surface is 60°; at 132 fathoms it is -70°; at 239 fathoms it is 80°: being an increase of 10° -at 59 fathoms deep, or 1° in 35·4 feet; of 10° more at -73 fathoms deeper, or 1° in 43·8 feet; and of 10° more -at 114 fathoms still deeper, or 1° in 64·2 feet.<a name="FNanchor_62_62" id="FNanchor_62_62"></a><a href="#Footnote_62_62" class="fnanchor">[62]</a></p> - -<p>Although this would indicate an increase to a certain -depth of about one degree in every fifty feet, yet it would -appear that the rate of increase diminishes with the -depth. It appears therefore probable, that the heat of -the earth, so far as man can examine it, is due to the -absorption of the solar rays by the surface. The -evidences of intense igneous action at a great depth -cannot be denied, but the doctrine of a cooling mass, and -of the existence of an incandescent mass, at the earth’s -centre, remains but one of those guesses which active -minds delight in. The mean annual temperature of this -planet is subject to variations, which are probably -dependent upon some physical changes in the sun himself, -or in the atmospheric envelope by which that orb is -surrounded. The variations over the earth’s surface are -great. At the equator we may regard the temperature<span class="pagenum"><a name="Page_92" id="Page_92"></a>[Pg 92]</span> -as uniformly existing at 80°, while at the poles it is -below the freezing point of water; and as far as observations -have been made, the subterranean temperatures -bear a close relation to the thermic condition of the -climate of the surface. The circulation of water through -faults or fissures in the strata is, without doubt, one -means of carrying heat downwards much quicker than -it would be conducted by the rocks themselves. It is -not, however, found that the quantity of water increases -with the depth. In the mines of Cornwall, unless where -the ground is very loose, miners find that, after about -150 fathoms (900 feet), the quantity of water rapidly -diminishes. That water must ascend from very much -greater depths is certain, from the high temperatures at -which many springs flow out at the surface. In the -United Mines in Cornwall, water rises from one part of -the lode at 90°; and one of the levels in these workings -is so hot that, notwithstanding a stream of cold water is -purposely brought into it to reduce the temperature, the -miners work nearly naked, and will bathe in water at -80° to cool themselves. At the bottom of Tresavean -Mine, in the same county, about 320 fathoms from the -surface, the temperature is 100°.</p> - -<p>One cause of the great heat of many of our deep -mines, which appears to have been entirely lost sight of, -is the chemical action going on upon large masses of -pyritic matter in their vicinity. The heat, which is so -oppressive in the United Mines, is, without doubt, due -to the decomposition of immense quantities of the sulphurets -of iron and copper known to be in this condition -at a short distance from these mineral works.</p> - -<p>The heat which man is enabled to measure beneath the -earth’s surface, appears to be alone due to the conducting -powers of the rocks themselves; it has been observed -that the line of equal temperature follows, as nearly as -possible, the elevations and depressions which prevail -upon the surface, and the diminishing rate of increase<span class="pagenum"><a name="Page_93" id="Page_93"></a>[Pg 93]</span> -beyond this line, certainly is such as would arise, was all -the heat so measured, the result of the passage of the -heat by conduction through the crust of rocks.</p> - -<p>Whether or not the subterranean bands of equal heat -have any strict relation, upon a large scale, to the -isothermic lines which have been traced around most -portions of our globe, is a point which has not yet been -so satisfactorily determined as to admit of any general -deductions.</p> - -<p>The Oriental story-teller makes the inner world a -place of rare beauty—a cavern temple, bestudded with -self-luminous gems, in which reside the spiritual beings -to whom the direction of the inorganic world is confided.</p> - -<p>The Philosopher, in the height of his knowledge, has -had dreams as absurd as this; and amid the romances of -science, there are not to be found any more strange visions -than those which relate to the centre of our globe. At -the same time it must be admitted, that many of the -peculiar phenomena which modern geological researches -have brought to light, are best explained on the hypothesis -of a cooling sphere, which necessarily involves the -existence of a very high temperature towards the -centre.</p> - -<p>We have already noticed some remarkable differences -between solar and terrestrial heat; but a class of observations -by Delaroche<a name="FNanchor_63_63" id="FNanchor_63_63"></a><a href="#Footnote_63_63" class="fnanchor">[63]</a> still requires our attention. Solar -heat passes freely through colourless glass, whereas the<span class="pagenum"><a name="Page_94" id="Page_94"></a>[Pg 94]</span> -radiations from a bright fire or a mass of incandescent -metal are entirely obstructed by this medium. If we -place a lamp or a ball of glowing hot metal before a -metallic reflector, the focus of accumulated heat is soon -discovered; but if a glass mirror be used, the light is -reflected, but not the heat; whereas, with the solar rays, -but little difference is detected, whether vitreous or -metallic reflectors are employed. It is well known that -glass lenses refract both the light and heat of the sun, -and they are commonly known as burning-glasses: the -heat accumulated at their focal point being of the highest -intensity. If, instead of the solar beam, we employ, in -our experiments, an intense heat produced by artificial -means, the passage of it is obstructed, and the most -delicate thermometers remain undisturbed in the focus of -the lens. Glass exposed in front of a fire becomes -warm, and by conduction the heat passes through it, -and a secondary radiation takes place from the opposite -side.<a name="FNanchor_64_64" id="FNanchor_64_64"></a><a href="#Footnote_64_64" class="fnanchor">[64]</a> It has been found that glass is transcalescent, or -<i>diathermic</i>, to some rays of terrestrial heat, and <i>adia<span class="pagenum"><a name="Page_95" id="Page_95"></a>[Pg 95]</span>themic</i>, -or opaque for heat, to others<a name="FNanchor_65_65" id="FNanchor_65_65"></a><a href="#Footnote_65_65" class="fnanchor">[65]</a>—that the capability -of permeating glass increases with the temperature of -the ignited body—and that rays which have passed one -screen traverse a second more readily. It would, -however, appear that something more than a mere -elevation of temperature is necessary to give terrestrial -heat-radiations the power of passing through glass -screens, or, in other words, to acquire the properties of -solar heat.</p> - -<p>To give an example. The heat of the oxy-hydrogen -flame is most intense, yet glass obstructs it, although it -may be assisted by a parabolic reflector. If this flame<span class="pagenum"><a name="Page_96" id="Page_96"></a>[Pg 96]</span> -is made to play upon a ball of lime, by which a most -intense light is produced, the heat, which has not been -actually increased, acquires the power of being refracted -by a glass lens, and combustible bodies may be ignited -in its focus.</p> - -<p>It certainly appears from these results, that the -undulatory hypothesis holds true, so far as the motion of -the calorific power is concerned. At a certain rate the -vibrations are thrown back or stopped by the opposing -body, while in a state of higher excitation, moving with -increased rapidity, they permeate the screen.<a name="FNanchor_66_66" id="FNanchor_66_66"></a><a href="#Footnote_66_66" class="fnanchor">[66]</a> This -does not, indeed, interfere with the refined theory of -Prévost,<a name="FNanchor_67_67" id="FNanchor_67_67"></a><a href="#Footnote_67_67" class="fnanchor">[67]</a> which supposes a mutual and equal interchange -of caloric between all bodies.</p> - -<p>The most general effect of heat is the expansion of -matter; solids, liquids, and airs, all expand under its -influence. If a bar of metal is exposed to calorific -action, it increases in size, owing to its particles being<span class="pagenum"><a name="Page_97" id="Page_97"></a>[Pg 97]</span> -separated farther from each other: by continuing this -influence, after a certain time the cohesion of the mass is -so reduced that it melts, or becomes liquid, and, under -the force of a still higher temperature, this molten metal -may be dissipated in vapour. It would appear as if, -under the agency of the heat applied to a body, its atoms -expanded, until at last, owing to the tenuity of the outer -layer or envelope of each atom, they were enabled to -move freely over each other, or to interpenetrate without -difficulty. That heat does really occasion a considerable -disturbance in the corpuscular arrangement of bodies, -may be proved by a very interesting experiment. A -bar of heated metal is placed to cool, with one end supported -upon a wedge or a ring of a different metal the -other resting on the ground. In cooling, a distinct -musical sound is given out, owing to the vibratory action -set up among the particles of matter moving as the temperature -declines.<a name="FNanchor_68_68" id="FNanchor_68_68"></a><a href="#Footnote_68_68" class="fnanchor">[68]</a></p> -<p><span class="pagenum"><a name="Page_98" id="Page_98"></a>[Pg 98]</span></p> -<p>Heat is diffused through all bodies in nature, and, as -we shall presently see, may be developed in many different -ways. We may, therefore, infer, that in converting a -sphere of ice into water, and that again into steam, we -have done nothing more than interpenetrate the mass -with a larger quantity of heat, by which its atoms are -more widely separated, and that thus its molecules -become free to move about each other. Hence, from a -solid state, the water becomes fluid; and then, if the expansive -force is continued, an invisible vapour. If these -limits are passed by the powers of any greatly increased -thermic action, the natural consequence, it must be -seen, will be the separation of the atoms from each -other, to such an extent that the molecule is destroyed, -and chemical decomposition takes place.</p> - -<p>By the agency of the electricity of the voltaic battery, -we are enabled to produce the most intense heat with -which we are acquainted, and by a peculiarly ingenious -arrangement Mr. Grove has succeeded in resolving -water by the mere action of heat into its constituent -elements—oxygen and hydrogen gases. That this decomposition -is not due to the voltaic current, but to the heat -produced by it, was subsequently proved by employing -platina heated by the oxy-hydrogen flame.<a name="FNanchor_69_69" id="FNanchor_69_69"></a><a href="#Footnote_69_69" class="fnanchor">[69]</a></p> - -<p>This interesting question has been examined with -great care by Dr. Robinson of Armagh, who has shown -that, as the temperature of water is increased, the affinity -of its elements is lessened, until at a certain point it -is eventually destroyed. This new and startling fact -appears scarcely consistent with our knowledge that a<span class="pagenum"><a name="Page_99" id="Page_99"></a>[Pg 99]</span> -body heated so as to be luminous has the power of -causing the combination of the elements of water with -explosive violence.<a name="FNanchor_70_70" id="FNanchor_70_70"></a><a href="#Footnote_70_70" class="fnanchor">[70]</a> But as this acute experimental -philosopher somewhat boldly but still most reasonably -inquires: “Is it not probable that, if not light, some -other actinic power (like that which accompanies light in -the spectrum, and is revealed to us by its chemical -effects in the processes of photography) is evolved by the -heat, and, though invisible, determines, in conjunction -with the affinity, that atomic change which transforms -the three volumes of oxygen and hydrogen into two of -steam?”<a name="FNanchor_71_71" id="FNanchor_71_71"></a><a href="#Footnote_71_71" class="fnanchor">[71]</a></p> - -<p>This speculation explains, in a very satisfactory manner, -some results which were obtained by Count Rumford, in -1798. In a series of experiments instituted for the -purpose of examining “those chemical properties of -light which have been attributed to it,” he has shown -that many cases of chemical decomposition occur in -perfect darkness, under the influence of heat, which are -precisely similar to those produced by exposure to the -sun’s rays.<a name="FNanchor_72_72" id="FNanchor_72_72"></a><a href="#Footnote_72_72" class="fnanchor">[72]</a></p> - -<p>It must, however, be remembered, that both solar -light and heat are sometimes found in direct antagonism -to actinic power, and that the most decided chemical -changes are produced by those rays in which neither -heat nor light can be detected. The most remarkable -phenomena of this class will be explained under the -head of actinism.</p> - -<p><span class="pagenum"><a name="Page_100" id="Page_100"></a>[Pg 100]</span></p> - -<p>One of the most curious relations which as yet -have been discovered between light and heat is, that, the -temperature at which all bodies become incandescent, -excepting such as are phosphorescent, is uniform. The -point on the thermometer (Fahrenheit’s scale) when -the eye by perfect repose is enabled to detect the first -luminous influence, may probably be regarded as, or -very near, 1000°. Daniel has fixed this point at 980°, -Wedgwood at 947°, and Draper at 977°.<a name="FNanchor_73_73" id="FNanchor_73_73"></a><a href="#Footnote_73_73" class="fnanchor">[73]</a> Dr. Robinson -and Dr. Draper, by independent observations, have -both arrived at the conclusion, that the first gleam of -light which appears from heated platina is not red, but of -a lavender gray, the same in character of colour as that -detected by Sir John Herschel among the most refrangible -rays of the solar spectrum.<a name="FNanchor_74_74" id="FNanchor_74_74"></a><a href="#Footnote_74_74" class="fnanchor">[74]</a></p> - -<p>It must be admitted, that the question of the identity, -or otherwise, of light and radiant heat, is beset with -difficulties. Many of their phenomena are very similar—many -of their modes of action are alike: they are -often found as allied agencies; but they as frequently -exhibit extreme diversity of action, and they may be -separated from each other.</p> - -<p>We have now examined the physical conditions and<span class="pagenum"><a name="Page_101" id="Page_101"></a>[Pg 101]</span> -properties of this most important element, and we must -proceed to learn something of the means by which it -may be developed, independently of its solar source.</p> - -<p>This extraordinary principle exists in a latent state in -all bodies, and may be pressed out of them. The blacksmith -hammers a nail until it becomes red hot, and from -it he lights the match with which he kindles the fire of -his forge. The iron has by this process become more -dense, and percussion will not again produce incandescence -until the bar has been exposed in fire to a red -heat. The only inference we can draw from this result -is, that by hammering the particles have been driven -closer together, and the heat driven out; now further -hammering will not force the atoms nearer, and consequently -no additional quantity of heat can be developed; -the iron is made hot in a fire, it absorbs heat, the -particles are restored to their former state, and we can -now again by hammering develope both heat and light. -The Indian produces a spark by the attrition of two -pieces of wood. By friction, two pieces of ice may be -made to melt each other; and could we, by mechanical -pressure, force water into a solid state, an immense -quantity of heat would be set free. By the condensation -of hydrogen and oxygen gases, pulverulent platinum -will become glowing red-hot, and, with certain precautions, -even the compact metal, platinum, itself; -the heat being derived from the gases, the union of -which it has effected. A body passing from the solid to -the fluid state absorbs heat from all surrounding substances, -and hence a degree of cold is produced. The -heat which is thus removed is not destroyed—it is held -combined with the fluid; it exists in a latent state. -Fluids, in passing into a gaseous form, also rob all surrounding -bodies of an amount of heat necessary to -maintain the aëriform condition. From the air or from -the fluid, this heat may, as we have shown above, be -again extracted. Locked in a pint measure of air, there<span class="pagenum"><a name="Page_102" id="Page_102"></a>[Pg 102]</span> -exists sufficient heat to raise several square inches of -metal to glowing redness. By the compression of -atmospheric air this may be shown, and with a small -condensing syringe a sufficient quantity of heat may be -set free to fire the <i>Boletus igniarius</i>, which, impregnated -with nitre, is known as <i>amadou</i>. We are acquainted -with various sources from which heat may be developed -for artificial purposes: the flint-and-steel is an example -of the production of heat by mechanical force, and the -modern lucifer-match, of the combined action of friction -and chemical affinity. These of themselves would admit -of a lengthened discourse; but it is necessary that we -carefully examine some of the less familiar phenomena of -heat under the influences of changes of chemical condition.</p> - -<p>If spirits of wine and water are mixed together, a -considerable degree of heat is given out, and by mixing -sulphuric acid and water, an infinitely larger quantity. -If sulphuric acid (oil of vitriol) and spirit of wine, or -nitric acid (aquafortis) and spirits of turpentine, at common -temperatures, be suddenly mixed, so much heat is -set free as to ignite the spirit. In each of these instances -there is a condensation of the fluid. In nearly -all cases of solution, cold is produced by the absorption -of the heat necessary to sustain the salt in a liquid -form; but when potash dissolves in water, heat is given -out, which is a fact we cannot yet explain. If potassium -is placed on water, it seizes the oxygen of the water -and sets fire to the hydrogen gas liberated by the heat -produced in the change of form. Antimony and many -other metals thrown into chlorine gas ignite and burn -with brilliancy: the same phenomenon takes place in -the vapours of iodine or bromine. Many chemical combinations, -as the chloride of potassium and sulphur explode -with a blow; whilst the slightest friction occasions -the detonation of the fulminating salts of silver, mercury, -and gold. Compounds of nitrogen and chlorine, or -iodine, are still more delicately combined—the former<span class="pagenum"><a name="Page_103" id="Page_103"></a>[Pg 103]</span> -exploding with fearful violence on the contact of any -oleaginous body, and the latter by the smallest elevation -of temperature: both of them destroying the vessels in -which they may be contained.</p> - -<p>Gun cotton presents some peculiar phenomena -which may merit brief attention. This peculiar compound -is prepared by the action of nitric acid on -cotton fibre. The general appearance of the cotton -is not altered, but a remarkable physical change -has taken place. It is now soluble in ether, and -forms a gelatinous compound:—it explodes violently -at a temperature which is insufficient for the combustion -of gunpowder. Indeed, from, as it would appear, slight -electrical disturbances taking place in the gun cotton -itself, it not unfrequently explodes spontaneously. These -fearful disturbances of the forces which hold bodies in -combination are explained with difficulty. May it not -be, that an enormous quantity of the calorific and -chemical principles is held in a state of extreme tension -around the particles of the compound, and that the -equilibrium being destroyed, the whole is developed in -destructive rapidity?</p> - -<p>The fact of great heat being evolved during the conversion -of a body from a solid to a gaseous state, as in -the explosion of gunpowder or gun cotton, which is a -striking exception to the law of latent heat, as it prevails -in most cases, admits of no more satisfactory explanation.</p> - -<p>As mechanical force produces calorific excitation, so -we find that every movement of sap in vegetables, and -of the blood and fluids in the animal economy, causes a -sensible increase of heat. The chemical processes constantly -going on in plants and animals are another -source of heat, in addition to which nervous energy and -muscular movement must be regarded as producing the -caloric which is essential to the health and life of the latter. -Digestion has been considered as a process of combustion; -and the action between the elements of food, and<span class="pagenum"><a name="Page_104" id="Page_104"></a>[Pg 104]</span> -the oxygen conveyed by the circulation of the blood to -every part of the body, regarded as the source of animal -heat; and, without doubt, it is one great source, -although it can scarcely be regarded as the only one.<a name="FNanchor_75_75" id="FNanchor_75_75"></a><a href="#Footnote_75_75" class="fnanchor">[75]</a></p> -<p><span class="pagenum"><a name="Page_105" id="Page_105"></a>[Pg 105]</span></p> -<p>The <i>vis vitæ</i>, or vital power, influences the delicate -and beautiful system of nerves; and as life (an essence -of the rarest and most subtile order, a diffusive influence) -runs through them, from the brain to the extremities of -the members of the body, it sets those tender threads in -rapid vibration, and heat is developed. By this action, -the circulation of the blood is effected; the muscle is -maintained in an elastic condition, ready to perform the -tasks of the will; and through these agencies is the -warm and fluid blood fitted to receive its chemical -restoratives in the lungs, and the stomach to support -changes for which it is designed—chemical also—by -which more heat is liberated. Was digestion—<i>Eremacausis</i>, -as the slow combustion produced by combination -with oxygen is called—the only source of animal heat, -why should the injury of one filmy nerve place a member -of the body for ever in the condition of stony coldness? -Or why, chemical action being most actively continued -after a violent death, by the action of the gastric juices -upon the animal tissues, should not animal heat be -maintained for a much longer period than it is found to -be after respiration has ceased?<a name="FNanchor_76_76" id="FNanchor_76_76"></a><a href="#Footnote_76_76" class="fnanchor">[76]</a></p> - -<p>In studying the influences of caloric upon the conditions -of matter, we must regard the effects of extreme -heat, and also of the greatest degrees of cold which have -been obtained.</p> - -<p>There are a set of experiments by the Baron Cagniard -de la Tour, which appear to have a very important<span class="pagenum"><a name="Page_106" id="Page_106"></a>[Pg 106]</span> -bearing on some conditions that may be supposed to -prevail in nature, particularly if we adopt the view -of a constantly increasing temperature towards the -centre of our earth. If water, alcohol, or ether, is -put into a strong glass tube of small bore, the ends -hermetically sealed, and the whole exposed to a strong -heat, the fluid disappears, being converted into a transparent -gas; but, upon cooling, it is again condensed, -without loss, into its original fluid state.<a name="FNanchor_77_77" id="FNanchor_77_77"></a><a href="#Footnote_77_77" class="fnanchor">[77]</a> In this experiment, -fluid bodies have been converted into elastic -transparent gases with but small change of volume, -under the pressure of their own atmospheres. We can -readily conceive a similar result occurring upon a far -more extensive scale. In volcanic districts, at great -depths, and consequently under the pressure of the -superincumbent mass, the siliceous rocks, or even metals, -may, from the action of intense heat, be brought into a -fluid, or even a gaseous condition, without any change of<span class="pagenum"><a name="Page_107" id="Page_107"></a>[Pg 107]</span> -volume, since the elastic force of heat is opposed by the -rigid resistance of the pressure of the surrounding -rocks. Some beautiful experiments by Mr. Hopkins, of -Cambridge, have proved that the temperature necessary -to melt a body must be considerably elevated as -the mechanical pressure to which it is subjected is -increased.</p> - -<p>Directly connected with the results of Cagniard de la -Tour are a yet more remarkable set of phenomena, -which have been investigated by M. Boutigny,<a name="FNanchor_78_78" id="FNanchor_78_78"></a><a href="#Footnote_78_78" class="fnanchor">[78]</a> and -generally known as the “spheroidal condition” of bodies. -If water is projected upon very hot metal it instantly -assumes a spheroidal form—an internal motion of its -particles may be observed—it revolves with rapidity,<span class="pagenum"><a name="Page_108" id="Page_108"></a>[Pg 108]</span> -and evaporates very slowly. If a silver or platinum -capsule, when brought to a bright red heat, is filled with -cold water, the whole mass assumes the spheroidal -state, the temperature of the fluid remaining considerably -below the boiling point, so long as the red heat is -maintained. If we allow the vessel to cool below redness -in the dark, the water then bursts into active -ebullition, and is dissipated into vapour with almost explosive -violence. An equal quantity of water being -projected into two similar vessels, over the fire, one cold -and the other red hot, it will be found that the water in -the cold vessel will boil and evaporate long before that -in the one which is red hot.</p> - -<p>Another form of this experiment is exceedingly instructive. -If a mass of white hot metal is suddenly -plunged into a vessel of cold water, the incandescence is -not quenched, the metal shines with a bright white -light, and the water is seen to circulate around, but at -some distance from the glowing mass, being actually -repelled by calorific agency. At length, when the -metal cools, the water comes in contact with it, and -boils with energy.</p> - -<p>A result similar to this was observed by Perkins, but -its correctness most unjustly doubted. Having made an -iron shell containing water, and carefully plugged up, -white hot, it was found that the steam never exerted -sufficient force to burst the vessel, as it was expected it -would do. He caused a hole to be drilled into the -bottom of the white-hot shell, and he was surprised to -find that no water flowed through the orifice, until the -iron was considerably cooled, when it issued forth with -violence in the form of steam. Here we have the -<i>Cagniard de la Tour state</i> first induced, and the calorific -repulsion of the spheroidal state supervenes. If water is -poured upon an iron sieve, the wires of which are made -red hot, it will not percolate; but on cooling, it runs -through rapidly. M. Boutigny, pursuing this curious<span class="pagenum"><a name="Page_109" id="Page_109"></a>[Pg 109]</span> -inquiry, has recently proved that the moisture upon the -skin is sufficient to protect it from disorganization, if -the arm is plunged into baths of melted metal. The -resistance of the surfaces is so great, that little elevation -of temperature is experienced.<a name="FNanchor_79_79" id="FNanchor_79_79"></a><a href="#Footnote_79_79" class="fnanchor">[79]</a> Professor <span class="correction" title="In the original book: Plucker">Plücker</span>, of -Bonn, has stated that by washing the arm with ether -previously to plunging it into melted metal, the sensation -produced, while in the molten mass, is that of freezing -coldness.</p> - -<p>We have now seen that heat at different degrees of -intensity appears to produce chemical composition—that -it decomposes combined elements—that it alters -the conditions of bodies, and actually maintains so -powerfully a repellent force, that fluids cannot touch -the heated body. More than this, it exerts a most -powerful antagonistic influence over all chemical relations. -If, to give one example, the volatile element -iodine is put into a glowing hot capsule, it resolves itself -immediately into a spheroid. Potash rapidly combines -with iodine; but if a piece of this alkali is thrown upon -it in the capsule, it also takes the spheroidal form, and -both bodies revolve independently of each other, their -chemical affinities being entirely suspended;—but allow -the capsule to cool, and they combine immediately. -Science teaches us that a temperature so exalted as not -to burn organic bodies may be produced, and points to -us this remarkable fact, that the destructive limits of -heat are measured between certain degrees—beyond -which a fire, by reason of its intensity, ceases to -develope heat. What is the radiant force into which this -principle changes?</p> - -<p>The experiments of Cagniard de la Tour and of -Boutigny (d’Evreux), connect themselves, in a striking<span class="pagenum"><a name="Page_110" id="Page_110"></a>[Pg 110]</span> -manner, with those of Mr. Grove and Dr. Robinson; -and they teach us that but a very slight alteration in the -proportions of the calorific principle given to this planet -would completely change the character of every material -substance of which it is composed, unless there was an -alteration in the physical condition of the elements -themselves.</p> - -<p>Supposing the ordeal of fiery purification to take -place upon this earth, these experiments appear to indicate -the mighty changes which would thence result. -There would be no annihilation, but everything would -be transformed from the centre of the globe to the verge -of its atmosphere—old things would pass away, all -things become new, and the beautiful mythos of the -phœnix be realized in the fresh creation.</p> - -<p>The deductions to be drawn from the results obtained -by abstracting heat from bodies are equally instructive. -By taking advantage of the cooling produced by the -rapid solution of salts of several kinds in water, an -intense degree of coldness may be produced.<a name="FNanchor_80_80" id="FNanchor_80_80"></a><a href="#Footnote_80_80" class="fnanchor">[80]</a> Indeed, -the absorption of heat by liquefaction may be shown by -the use of metallic bodies alone. If lead, tin, and -bismuth, are melted together, and reduced to a coarse -powder by being poured into water, and the alloy then -dissolved in a large quantity of quicksilver, the thermometer -will sink nearly 50 degrees. An intense amount -of cold will result from the mixture of muriate of lime -and snow, by which a temperature of 50° below the zero -of Fahrenheit, or 82° below the freezing point of water, -is produced. By such a freezing mixture as this,<span class="pagenum"><a name="Page_111" id="Page_111"></a>[Pg 111]</span> -mercury will be rendered solid. A degree of cold, however, -far exceeding it, has lately been obtained by the -use of solid carbonic acid and ether.<a name="FNanchor_81_81" id="FNanchor_81_81"></a><a href="#Footnote_81_81" class="fnanchor">[81]</a> Solid carbonic -acid is itself procured from the gas liquefied by pressure; -which liquid, when allowed to escape into the air, -evaporates so rapidly that a large quantity of it is congealed -by being robbed of its combined heat by the -vaporizing portion. When this solid acid is united with -ether, a bath is formed in which the carbonic acid will -remain solid for twenty or thirty minutes. By a mixture -of this kind, placed under the receiver of an air-pump, -a good exhaustion being sustained, a degree of -cold 166° below zero is secured. By this intense cold, -many of the bodies which have hitherto been known to -us only in the gaseous state have been condensed into -liquids and solids. Olefiant gas, a compound of hydrogen -and carbon, was brought into a liquid form. Hydriodic -and hydrobromic acids could be condensed into -either a liquid or a solid form. Phosphuretted hydrogen, -a gas which inflames spontaneously when brought -into contact with the air or with oxygen, became a -transparent liquid at this great reduction of temperature. -Sulphurous acid may be condensed, by pressure and a -reduction of temperature, into a liquid which boils at 14° -Fahrenheit, but by the carbonic acid bath it is converted -into a solid body, transparent and without colour. Sulphuretted -hydrogen gas solidifies at 122° below zero, and -forms a white substance resembling a mass of crystals -of sea-salt.</p> - -<p>A combination of the two gases, chlorine and oxygen, -becomes solid at -75°, and the protoxide of nitrogen at -150°. -Cyanogen, a compound of carbon and nitrogen—the -base of prussic acid—is solidified at 30° below<span class="pagenum"><a name="Page_112" id="Page_112"></a>[Pg 112]</span> -the zero of our thermometric scale. The well-known -pungent compound, ammonia, so exceedingly volatile at -common temperatures, is converted into a crystalline, -translucent, white substance at the temperature of --103°. The difficulties which necessarily attend the -exposure of a body to extreme cold and great pressure -at the same time, appear to be the only obstacle to the -condensation of oxygen, hydrogen, and nitrogen gases. -A sufficient amount of condensation was, however, -effected by Dr. Faraday, to lead him to the conclusion, -arrived at also by other evidences, that hydrogen, the -lightest of the ponderable bodies, partakes of the nature -of a metal.[82]</p> - -<p>During the solidification of water by freezing, some -remarkable facts may be noticed.</p> - -<p>Water, in cooling, gradually condenses in volume -until it arrives at 40° Fahr., which appears to be the -point of greatest density. From this temperature to -that of 32°, the point at which it begins to solidify, its -volume remains unchanged,<a name="FNanchor_82_82" id="FNanchor_82_82"></a><a href="#Footnote_82_82" class="fnanchor">[82]</a> as crystallisation (freezing) -begins, the bulk increases, the mass becomes specifically -lighter, and it swims on the surface of the fluid. From -40° to 32° the particles of water must be taking up -that new position which is essential to the formation of -the solid—ice; and while this is taking place, every -substance held in solution by the water is rejected.</p> - -<p>If we mix with water the deepest colouring matter—the -strongest acid or the most acrid poison—they are -each and all rejected during the process of freezing, and -if the water has been kept in a state of agitation during -the process—so that the liberated particles may not be -mechanically entangled—the ice will be transparent, -colourless, tasteless, and inert—the substances rejected -being gathered together in the centre of the frozen mass<span class="pagenum"><a name="Page_113" id="Page_113"></a>[Pg 113]</span> -in a state of intense concentration. In like manner, -even the atmospheric air, which is always held in solution, -is rejected, and hence the reason why all the ice -which forms upon still ponds is full of air-bubbles, while -the ice which is produced in agitated water is perfectly -free from them. This in itself is a remarkable condition, -the entire bearing of which is not clearly understood; -but a still more singular fact has been discovered in -intimate connection with the rejection of all matter from -a freezing solution. Water, which in this way is freed -entirely of air, will not boil at 212° F., the ordinary -boiling point of water.</p> - -<p>If a mass of ice formed in the manner described is -placed in a vessel, and being just covered with a film of -oil, to prevent the absorption of air, is melted over a -lamp or fire, and the heat continued, it will, so far from -being converted into steam at 212°, continue to increase -in temperature up to 270° or more, and then burst into -ebullition with such explosive violence as to rend the -vessel in which it is confined.</p> - -<p>From this experiment we learn that did water exist -in any other condition than that in which we find it—even -with the apparently simple difference of containing -no air—it would not be safe to employ it in any culinary -or manufacturing operation, since its use would be followed -by explosions as dangerous as those of gunpowder.</p> - -<p>Such researches as these prove to us the admirable -adaptation of all things to their especial ends—the beautiful -adjustment of the balance of forces throughout -creation.</p> - -<p>The refinements of Grecian philosophy saw, without -the aids of inductive science, that the outward vesture of -nature covered a host of mysterious agencies to which -its characteristics were directly due. In their dream of -the four elements, fire, the external and visible form of -heat, was regarded as the cause of vitality, and the -disposer of every organised and unorganised condition<span class="pagenum"><a name="Page_114" id="Page_114"></a>[Pg 114]</span> -of matter. Their idealisations have assumed another -form, but the researches of modern science have only -established their universality and truth.</p> - -<p>The great agents at work in nature—the mighty -spirits bound to never-ending tasks, which they pursue -with unremitting toil, are of so refined a character, that -they will probably remain for ever unknown to us. The -arch-evocator, with the wand of induction, calls; but -the only answer to his evocation is the manifestation of -power in startling effects. Science pursues her inquiries -with zeal and care: she tries and tortures nature to -compel her to reveal her secrets. Bounds are, however, -set to the powers of mortal search: we may not yet -have reached the limits within which we are free to -exercise our mental strength; but, those limits reached, -we shall find an infinite region beyond us, into which -even conjecture wanders eyeless and aimless, as the blind -Cyclops groping in his melancholy cave.<a name="FNanchor_83_83" id="FNanchor_83_83"></a><a href="#Footnote_83_83" class="fnanchor">[83]</a></p> - -<p>All we know of heat is, that striking effects are produced -which we measure by sensation, and by instruments -upon which we have observed that given results -will be produced under certain conditions: of anything -approaching to the cause of these we are totally ignorant. -The wonder-working mover of some of the -grandest phenomena in nature—giving health to the -organic world, and form to the inorganic mass—producing -genial gales and dire tornadoes—earthquake -strugglings and volcanic eruptions—ministering to our -comforts in the homely fire, and to advancement in -civilisation in the mighty furnace, and the ingenious -engine which drains our mines, or traverses our country -with bird-like speed,—will, in all probability, remain for -ever unknown to man. The immortal Newton, many -of whose guesses have a prophetic value, thus expresses -himself:—“Heat consists in a minute vibratory motion -in the particles of bodies, and this motion is communi<span class="pagenum"><a name="Page_115" id="Page_115"></a>[Pg 115]</span>cated -through an apparent vacuum by the undulations -of a very subtile elastic medium, which is also concerned -in the phenomena of light.”</p> - -<p>Our experimental labours and our mathematical -investigations have considerably advanced our knowledge -since the time of Newton; yet still each theory of -heat strangely resembles the mystic lamp which the -Rosicrucian regarded as a type of eternal life—a dim -and flickering symbol, in the tongue-like flame of which -imagination, like a child, can conjure many shapes.</p> - -<p>Modern theory regards heat as a manifestation of -motion, and experiment proves that a body falling -through a certain space generates a definite quantity of -heat, while observation shows that the waters at the -base of the Falls of Niagara possess a temperature 1° -higher than when they first glide over the edge of the -precipice.</p> - -<p>This increase of temperature is due to the mechanical -force due to the fall, and is no more an evidence of the -conversion of motion into heat, than is the old experiment -of rubbing a button until it becomes hot. At all -events, the fact that a given amount of mechanical force -always produces an equivalent of heat is as applicable to -the idea of a “subtile elastic medium” which is diffused -through all matter, as to the, at present, favourite hypothesis.</p> - -<p>So far has this view been strained, that the temperature -of the planets has been referred to their motions, -and speculation has aided the mathematician in determining -the cessation of planetary motion, by the conversion -of it into heat. It is true that other theorists have -supposed points in space upon which this heat might be -concentrated and reflected back again to produce motion.</p> - -<p>There may be much of the poetic element in such -speculations, but it is of that order which belongs rather -to the romantic than to the real.</p> - -<p>A speculation which has more of truth, and which is,<span class="pagenum"><a name="Page_116" id="Page_116"></a>[Pg 116]</span> -indeed, demonstrable, cannot fail to impress every mind -with its beauty, and probable correctness.</p> - -<p>In the growth of a tree, its wood and all its products -are the result of certain external forces effecting chemical -changes. Carbonic acid is decomposed, the carbon -is retained, and oxygen given off, and assimilations of a -complex character are in constant progress to produce -the various compounds of oxygen, hydrogen, nitrogen, -and carbon.</p> - -<p>Every condition of organised forms is due to the external -excitation of light and heat, and in the chemical -changes which take place, an equivalent of these principles, -or powers—it signifies but little according to which -view we may regard them—is absorbed, and retained as -essential to the condition of the matter formed. Let us -confine our attention to wood—although the position -applies equally to every organic product. A cubic foot -of wood is formed by the decomposition of a certain -quantity of carbonic acid, by the vital function of the -plant, excited by the solar rays, which are involved in -the mass which nature by “her wondrous alchemy” has -made. Eventually this cubic foot of wood is subjected -to a process of chemical change—combustion; by the -application of a single spark,—and in the disintegration -of the wood, its carbon combining with oxygen to form -carbonic acid, its hydrogen to form water, which is returned -to the air, a large amount of light and heat is produced. -This is exactly equivalent to the amount which -was engaged in its formation. Indeed, the sunshine which -fell upon the leaves of the forest tree, of which the log -formed a part, has been hoarded up, and we again develope -it in its original state of heat and light.</p> - -<p>The vast coal beds of England were formed by the -rapid growth and quick decay of a peculiar class of -plants under the influence of a tropical sun. They have -been buried myriads of ages, under hundreds of feet of -sandy rock. By the industry of the miner the coal<span class="pagenum"><a name="Page_117" id="Page_117"></a>[Pg 117]</span> -is brought again to the surface, and we develope from -it those powers by which it was formed.</p> - -<p>In the fire which gives comfort to our homes—in the -furnace which generates force for the purposes of manufacture, -or to propel the railway engine and its ponderous -train—in the gas with which we illumine our streets -and gladden during the long winter nights our apartments, -we are developing that heat and light which fell -upon the earth with all its quickening influences millions -of ages before yet the Creator had called into -existence the monarch Man, for whose necessities these -wondrous formations were designed.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_43_43" id="Footnote_43_43"></a><a href="#FNanchor_43_43"><span class="label">[43]</span></a> The following table of the rays penetrating coloured glass has -been given by Melloni, in his memoir <i>On the Free Transmission of -Radiant Heat through Different Bodies</i>:— -</p> -<table summary="rays penetrating coloured glass"> -<tr><td>Deep violet</td><td class="tdpad">53</td></tr> -<tr><td>Yellowish red (flaked)</td><td class="tdpad">53</td></tr> -<tr><td>Purple red (flaked)</td><td class="tdpad">51</td></tr> -<tr><td>Vivid red</td><td class="tdpad">47</td></tr> -<tr><td>Pale violet</td><td class="tdpad">45</td></tr> -<tr><td>Orange red</td><td class="tdpad">44</td></tr> -<tr><td>Clear blue</td><td class="tdpad">42</td></tr> -<tr><td>Deep yellow</td><td class="tdpad">40</td></tr> -<tr><td>Bright yellow</td><td class="tdpad">34</td></tr> -<tr><td>Golden yellow</td><td class="tdpad">33</td></tr> -<tr><td>Deep blue</td><td class="tdpad">33</td></tr> -<tr><td>Apple green</td><td class="tdpad">26</td></tr> -<tr><td>Mineral green</td><td class="tdpad">23</td></tr> -<tr><td>Very deep blue</td><td class="tdpad">19</td></tr> -</table> -<p> -Translated in the Scientific Memoirs, vol. i. p. 30.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_44_44" id="Footnote_44_44"></a><a href="#FNanchor_44_44"><span class="label">[44]</span></a> “The physical characters of this species of glass, which -acts so differently from the other species of coloured glass in all -the phenomena of calorific absorption, are, 1st, its intercepting -almost totally the rays which pass through alum; 2nd, its entirely -absorbing the red rays of the solar spectrum. I have already -stated that their colouration is produced almost entirely by the -oxide of copper. -</p> -<p> -“Thus, the colouring matters of the coloured glasses, while -they so powerfully affect the relations of quantity which the different -rays of ordinary light bear to each other, exercise no elective -action on the concomitant calorific rays. This curious -phenomenon is the more remarkable as the colouring matters -absorb almost always a very considerable portion of the heat -<i>naturally transmitted by the glass</i>. The following are, in fact, the -calorific transmissions of the seven coloured glasses referred to; -the transmission of the common glass being represented by -100; red glass, 82·5; orange, 72·5; yellow, 55; bluish-green, -57·5; blue, 52·5; indigo, 30; violet, 85. The quantity of -heat absorbed through the action of the colouring substances is, -therefore, 17·5 in the red glass, 27·5 in the orange, 45 in the -yellow, 42·5 in the green, 47·5 in the blue, 70 in the indigo, -and 15 in the violet. Now, as these absorptions extinguish a -proportional part of each of the rays which constitute the calorific -stream transmitted by common glass, they may be compared, -as we said before, with the absorbent action exercised on light -by matters more or less deeply brown or dark, when they are -immersed in water, or some other colourless liquid which dissolves, -but does not affect them chemically.”—<i>Annales de Chimie -et de Physique</i>, tom. xl. p. 382. -</p> -<p> -Guided by these principles, the author selected the glass -employed in glazing the Royal Palm-House, at Kew Botanical -Gardens, where it was desired to obstruct the passage of those -rays which have a particular scorching influence. Of this glass -a description was given at the meeting of the British Association -at Oxford, which appears in the Transactions for that year. The -result has been all that could be desired—not a single instance of -scorching having occurred during the three years which have elapsed.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_45_45" id="Footnote_45_45"></a><a href="#FNanchor_45_45"><span class="label">[45]</span></a> In the <i>Philosophical Transactions</i>, vol. xc., the following -papers, by Sir William Herschel, may be consulted:— -</p> -<p> -<i>Investigation of the powers of the prismatic colours to heat and -illuminate objects; with remarks that prove the different refrangibility -of radiant heat. To which is added, an inquiry into -the method of viewing the sun advantageously, with telescopes of -large apertures and high magnifying powers</i>, p. 255. <i>Experiments -on the refrangibility of the invisible rays of the sun</i>, p. 284. -<i>Experiments on the solar and on the terrestrial rays that occasion -heat; with a comparative view of the laws to which light -and heat, or rather the rays which occasion them, are subject; in -order to determine whether they are the same or different</i>, -pp. 293, 437. -</p> -<p> -In connection with this inquiry, Sir William Herschel remarks, -that since a <i>red glass</i> stops no less than 692 out of 1,000 such -rays as are of the refrangibility of red light, we have a direct -and simple proof, in the case of the red glass, that the rays of -light are transmitted, while those of heat are stopped, and that -thus they have nothing in common but a certain equal degree of -refrangibility, which by the power of the glass must occasion -them to be thrown together into the place which is pointed out to -us by the visibility of the rays of light. -</p> -<p> -On the same subject, a Memoir, by Sir Henry Englefield, in -the Journal of the Royal Institution for 1802, p. 202, may -be consulted; and <i>Researches on Light</i>, by the Author.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_46_46" id="Footnote_46_46"></a><a href="#FNanchor_46_46"><span class="label">[46]</span></a> Dr. Draper, <i>On the production of light by heat</i>, in the Phil. -Mag. for 1847. -</p> -<p> -Sir Isaac Newton fixed the temperature at which bodies become -self-luminous at 635°; Sir Humphry Davy at 812°; Mr. -Wedgewood at 947°; and Mr. Daniell at 980°; whilst Dr. -Draper from his experiments gives 977°; and Dr. Robinson 865°. -</p> -<p> -In a review of the above paper by Melloni, entitled <i>Researches -on the Radiations of Incandescent Bodies, and on the Elementary -Colours of the Solar Spectrum</i>, translated for Silliman’s Journal -for August, 1847, he remarks:— -</p> -<p> -“I say that they conduct, as do others heretofore known on -light and radiant heat, to a perfect analogy between the general -laws which govern these two great agents of nature. I will add -that I regard the theory of their identity as the only one admissible -by the rules of philosophy; and that I consider myself -obliged to adopt it, until it shall have been proved to me that -there is a necessity of having recourse to two different principles, -for the explanation of a series of phenomena which at present -appear to belong to a solitary agent.” -</p> -<p> -Reference should also be made to a paper by Dr. Robinson, -<i>On the effects of Heat in lessening the Affinities of the Elements -of Water</i>, in the Transactions of the Royal Irish Academy, -1848, where he says that “when a platinum wire is traversed by -a current gradually increased till it produces ignition, the first -gleam that appears is not red, but of a colour which, when I -first saw it, I compared to the ‘lavender ray’ discovered by Sir -John Herschel beyond the violet, though I was surprised at -seeing the tint of that most refrangible ray preceding the ray -which is least so. It is quite conspicuous at about 865°; and -as the mode in which it makes its appearance presents nothing -abrupt or discontinuous, it seems likely that it is merely a -transition from invisible rays excited at a lower temperature -to ordinary light.”—p. 310.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_47_47" id="Footnote_47_47"></a><a href="#FNanchor_47_47"><span class="label">[47]</span></a> In the <i>Bakerian Lecture</i> for 1842, <i>On the transparency of the -Atmosphere, and the law of extinction of the solar rays in passing -through it</i>, by James D. Forbes, Esq., F.R.S., &c., will be found a -most complete investigation of this subject. -</p> -<p> -The experiments were, for the most part, made in Switzerland -with Sir John Herschel’s actinometer, and they prove satisfactorily,—“That -the absorption of the solar rays by the strata -of air to which we have immediate access, is considerable in -amount for even moderate thicknesses.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_48_48" id="Footnote_48_48"></a><a href="#FNanchor_48_48"><span class="label">[48]</span></a> After referring to several curious and instructive experiments, -in which peculiar chemical changes are produced under the influence -of the solar rays by their <span class="smcap">Heat</span>, Sir John Herschel says:— -</p> -<p> -“These rays are distinguished from those of Light by being -invisible; they are also distinguished from the pure calorific rays -beyond the spectrum, by their possessing properties (<i>of a peculiar -character, referred to in former papers</i>) either exclusively of the -calorific rays, or in a much higher degree. They may perhaps not -improperly be regarded as bearing the same relation to the calorific -spectrum which the photographic rays do to the luminous ones. -If the restriction to these rays of the term <i>thermic</i>, as distinct -from <i>calorific</i>, be not (as I think, in fact, it is not) a sufficient -distinction, I would propose the term <i>parathermic rays</i> to designate -them. These are the rays which I conceive to be active in producing -those singular molecular affections which determine the -precipitation of vapours in the experiments of Messrs. Draper, -Moser, and Hunt, and which will probably lead to important discoveries -as to the intimate nature of those forces resident on the -surfaces of bodies, to which M. Dutrochet has given the name of epipolic -forces.”—<i>On certain improvements in Photographic Processes, described -in a former communication</i> (Phil. Trans, vol. cxxxiii.); and -<i>On the Parathermic Rays of the Solar Spectrum</i>, Phil. Trans, vol. -cxxxiv. -</p> -<p> -The experiments of Mrs. Somerville, <i>On the Action of the Rays -of the Spectrum on Vegetable Juices</i> (Phil. Transactions, vol. -cxxxvii.), appear to connect themselves with this particular class -of rays in a curious manner.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_49_49" id="Footnote_49_49"></a><a href="#FNanchor_49_49"><span class="label">[49]</span></a> Experiments on the influence of heat on differently-coloured -bodies were first made by Dr. Hooke; and it was not until long -after that Franklin made his ingenious experiments. Davy exposed -to sunshine six equal pieces of copper, painted white, yellow, red, -green, blue, and black, in such a manner that one side only was -illuminated. To the dark side he attached a bit of cerate, ascertained -by experiment to melt at 700. The cerate attached to the -black became fluid first, the blue next, then the green and red, and -lastly the yellow and white.—Beddoes’s <i>Contributions to Physical -Knowledge</i>, and collected works of Sir Humphry Davy, vol. ii. p. 27.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_50_50" id="Footnote_50_50"></a><a href="#FNanchor_50_50"><span class="label">[50]</span></a> By reference to the Treatise on Heat, in the <i>Encyclopædia -Metropolitana</i>, numerous suggestive experiments will be found, all -bearing on this subject. Peschel’s <i>Elements of Physics</i> may also -be consulted with advantage. The fact is, however, simply proved, -as stated in the text, by placing the bulbs of delicate thermometers, -so as to be completely involved in the petals of flowers exposed to -sunshine, shading the upper portion of the stem of the instrument.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_51_51" id="Footnote_51_51"></a><a href="#FNanchor_51_51"><span class="label">[51]</span></a> Moser, <i>On Vision, and on the Action of Light on Bodies</i>: and -also <i>On Latent Light</i>: Scientific Memoirs, vol. iii. Draper, <i>On -certain Spectral Appearances, and on the Discovery of Latent Light</i>: -Phil. Mag., Nov. 1842.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_52_52" id="Footnote_52_52"></a><a href="#FNanchor_52_52"><span class="label">[52]</span></a> A particular examination of this curious question will be -found in the Author’s report <i>On the Influence of the Solar Rays on -the Growth of Plants</i>: Reports of the British Association for 1847.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_53_53" id="Footnote_53_53"></a><a href="#FNanchor_53_53"><span class="label">[53]</span></a> Ammianus Marcellinus ascribes the longevity and robust -health of mountaineers to their exposure to the dews of night. -Dew was employed by the alchemists in their experiments on the -solution of gold. The ladies of old collected the “celestial wash,” -which they imagined had the virtue of preserving their fine forms, -by exposing heaps of wool to the influences of night radiation. It -was supposed that the lean features of the grasshopper arose from -that insect feeding entirely on dew: “Dumque thymo pascentur -apes, dum rore cicadæ,” Virgil, Eclog. -</p> -<p> -See some curious remarks by Boyle, <i>On the Power of Dew in -Working on Solid Bodies</i>: Works of the Honourable R. Boyle, -vol. v. p. 121. 1744.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_54_54" id="Footnote_54_54"></a><a href="#FNanchor_54_54"><span class="label">[54]</span></a> See the <i>Researches on Heat</i>, by Professor James Forbes, in the -Transactions of the Royal Society of Edinburgh; also Melloni’s -papers on the same subject in the <i>Annales de Chimie</i>, several of -which have been translated into the <i>Scientific Memoirs</i>, edited by -Mr. Richard Taylor.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_55_55" id="Footnote_55_55"></a><a href="#FNanchor_55_55"><span class="label">[55]</span></a> The phenomena of dew have constantly engaged the attention -of man. Aristotle, in his book <i>De Mundo</i>, puts forth some just -notions on its nature. An opinion has almost always prevailed -that dew falls. Gersten appears to have been the first who opposed -this motion. He was followed by <span class="correction" title="In the original book: Muschenbroek">Musschenbroek</span>, and then by -Du Fay. The researches of Leslie were of a far more exact character. -Dr. Wilson, in the Transactions of the Royal Society of -Edinburgh, 1st vol., published a <i>Memoir on Hoar Frost</i> of much -interest; but the questions involved remained unsettled until the -researches of Dr. Wells, which were published in his <i>Essay on Dew</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_56_56" id="Footnote_56_56"></a><a href="#FNanchor_56_56"><span class="label">[56]</span></a> By far the most complete set of experiments on the radiation -of heat from the surface at night, which have been published since -Dr. Wells’s memoir <i>On Dew</i>, are those of Mr. Glaisher, of the Royal -Observatory at Greenwich. Instruments of the most perfect kind -were employed, and the observations made with sedulous care. -The results will be found in a memoir <i>On the Amount of the Radiation -of Heat, at night, from the Earth, and from various bodies -placed on or near the Surface of the Earth</i>, by James Glaisher, Esq., -Philosophical Trans. for 1847, part 2.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_57_57" id="Footnote_57_57"></a><a href="#FNanchor_57_57"><span class="label">[57]</span></a> Dr. Wells noticed the practical fact that very light shades protected -delicate plants from frost, by preventing radiation. Mr. -Goldsworthy Gurney has made a series of interesting experiments, -and he imagines that by shading grasslands with boughs of trees, -or any light litter, a more abundant crop is produced. The subject -has been discussed in the journals of the Royal Agricultural -Society. May not the apparent increase be due entirely to the -succulent condition in which a plant always grows in the shade?</p></div> - -<div class="footnote"> - -<p><a name="Footnote_58_58" id="Footnote_58_58"></a><a href="#FNanchor_58_58"><span class="label">[58]</span></a> This paper of Melloni’s will be found in the <i>Bibliothèque Universelle -de Genève</i>, for 1843. The conclusions are highly ingenious, -but they rest entirely on the analogy supposed to be discovered between -the relations of heat, like light, to the coloured rays of the -spectrum. This, it must be remembered, is not the case, since -even Sir William Herschel showed that red light might exist with -only a minimum of calorific power, notwithstanding the fact, that -the maximum heat-ray of the spectrum coincides with the red rays.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_59_59" id="Footnote_59_59"></a><a href="#FNanchor_59_59"><span class="label">[59]</span></a> Dr. Robinson, of Armagh, in his Memoir <i>On the Effects of -Heat in lessening the Affinities of the Elements of Water</i>.—Transactions -of the Royal Irish Academy, vol. xxi. part 2.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_60_60" id="Footnote_60_60"></a><a href="#FNanchor_60_60"><span class="label">[60]</span></a> On this subject consult Robert Were Fox, <i>On the Temperature -of the Mines of Cornwall</i>.—Cornwall Geological Transactions, -vol. ii.; W. J. Henwood, on the same subject, <i>Ib.</i> vol. v.; Reports -of the British Association, 1840, p. 315; Edinburgh New Philosophical -Journal, vol. xxiv. p. 140.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_61_61" id="Footnote_61_61"></a><a href="#FNanchor_61_61"><span class="label">[61]</span></a> <i>On the causes of the temperature of Hot and Thermal Springs; -and on the bearings of this subject as connected with the general -question regarding the internal temperature of <span class="correction" title="In the original book: tha">the</span> Earth</i>: by -Professor Gustav Bischoff, of Bonn.—Edinburgh New Philosophical -Journal, vol. xx. p. 376; vol. xxiii. p. 330. Some interesting -information on the temperature of the ground will be found in -Erman’s <i>Travels in Siberia</i>, translated by W. D. Cooley, vol. i. p. -339; vol. ii. p. 366. <i>Sur la Profondeur à laquelle se trouve la -couche de Température invariable entre les Tropiques</i>, by Boussingault: -Annales de Chimie et de Physique, 1833, p. 225. -Reference may also be made to Humboldt’s <i>Cosmos</i>, Otto’s -translation; and to the excellent article on <i>Meteorology</i>, by -George Harvey, in the Encyclopædia Metropolitana. These -chthonisothermal lines, as they are called, have been traced by -Humboldt and others over extensive districts.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_62_62" id="Footnote_62_62"></a><a href="#FNanchor_62_62"><span class="label">[62]</span></a> These results are obtained from the valuable observations of -Robert Were Fox, Esq., made with great care by that gentleman -in several of the Cornish mines: <i>Report on some observations on -Subterranean Temperature</i>.—British Association Reports, vol. ix. p. -309; Philosophical Magazine, 1837, vol. ii. p. 520.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_63_63" id="Footnote_63_63"></a><a href="#FNanchor_63_63"><span class="label">[63]</span></a> From his experiments, the following conclusions were arrived -at by M. Delaroche:— -</p> -<p> -1. Invisible radiant heat may, in some circumstances, pass -directly through glass. -</p> -<p> -2. The quantity of radiant heat which passes directly through -glass is so much greater, relative to the whole heat emitted in -the same direction, as the temperature of the source of heat is -more elevated. -</p> -<p> -3. The calorific rays which have already passed through a -screen of glass, experience, in passing through a second glass -screen of a similar nature, a much smaller diminution of their -intensity than they did in passing through the first screen. -</p> -<p> -4. The rays emitted by a hot body differ from each other in -their faculty to pass through glass. -</p> -<p> -5. A thick glass, though as much or more permeable to light -than a thin glass of worse quality, allows a much smaller quantity -of radiant heat to pass. The difference is so much the less as -the temperature of the radiating source is more elevated. -</p> -<p> -6. The quantity of heat which a hot body yields in a given -time, by radiation to a cold body situate at a distance, increases, -<i>cæteris paribus</i>, in a greater ratio than the excess of temperature of -the first body above the second.—Journal de Physique, vol. lxxv.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_64_64" id="Footnote_64_64"></a><a href="#FNanchor_64_64"><span class="label">[64]</span></a> Sir David Brewster differs from the conclusions arrived -at by Delaroche. He thus explains his views:—“The inability -of radiant heat to pass through glass, may be considered as a -consequence of its refusing to yield to the refractive force; -for we can scarcely conceive a particle of radiant matter freely -permeating a solid body, without suffering some change in its -velocity and direction. The ingenious experiments of M. Prévost, -of Geneva, and the more recent ones of M. Delaroche, have been -considered as establishing the permeability of glass to radiant -heat. M. Prévost employed moveable screens of glass, and renewed -them continually, in order that the result which he obtained -might not be ascribed to the heating of the screen; but -such is the rapidity with which heat is propagated through a -thin plate of glass, that it is extremely difficult, if not impossible, -to observe the state of the thermometer before it has been -affected by the secondary radiation from the screen. The method -employed by M. Delaroche, of observing the difference of effect, -when a blackened glass screen and a transparent one were made -successively to intercept the radiant heat, is liable to an obvious -error. The radiant heat would find a quicker passage through -the transparent screen; and, therefore, the difference of effect -was not due to the transmitted heat, but to the heat radiated -from the anterior surface. The truth contained in M. Delaroche’s -fifth proposition is almost a demonstration of the fallacy of all -those that precede it. He found that ‘a thick plate of glass, -though as much or more permeable to light than a thin glass of -worse quality, allowed a much smaller quantity of radiant heat -to pass.’ If he had employed very thick plates of the purest -flint glass, or thick masses of fluid that have the power of transmitting -light copiously, he would have found that not a single -particle of heat was capable of passing directly through transparent -media.”—Sir D. Brewster, <i>On new properties of heat as exhibited -in its propagation along plates of glass</i>. Philosophical -Transactions, vol. cvi. p. 107.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_65_65" id="Footnote_65_65"></a><a href="#FNanchor_65_65"><span class="label">[65]</span></a> <i>Proposal of a New Nomenclature for the Science of Calorific -Radiations</i>, by M. Melloni. Bibliothèque Universelle de Genève, -No. 70. Scientific Memoirs, vol. iii. part 12. Many of the terms, -as <i>Diathermasy</i>, or transparency for heat; <i>Adiathermasy</i>, opacity -for heat; <i>Thermochroic</i>, coloured for heat, and others, are valuable -suggestions of forms of expression which are required in dealing -with these physical phenomena.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_66_66" id="Footnote_66_66"></a><a href="#FNanchor_66_66"><span class="label">[66]</span></a> For a careful examination of the several theories of heat -consult Dr. Young’s Course of Lectures on Natural Philosophy, -&c., Lecture 52, <i>On the Measures and the Nature of Heat</i>; also -Powell’s very excellent <i>Reports on Radiant Heat</i>—Reports of the -British Association, 1832, 1840. The transcendental view which -the immaterial theory leads to, cannot be better exemplified than -by the following quotation from that inexplicable dream of a -talented man, <i>Elements of Physiophilosophy</i>, by Lorenz Oken, M.D. -(translated for the Ray Society, by Alfred Tulk):— -</p> -<p> -“Heat is not matter itself any more than light is; but it is -only the act of motion in the primary matter. In heat, as well -as in light, there certainly resides a material substratum; yet, -this substratum does not give out heat and light; but the <i>motion</i> -only of the substratum gives out heat, and the <i>tension</i> only of -the substratum light. There is no body of heat; nitrogen is -the body of heat, just as oxygen may be called the body of fire. -Heat is real space; into it all forms have been resolved, as all -materiality has been resolved into gravity, and all activity, all -polarity, into light. Heat is the universal form, consequently the -want of form.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_67_67" id="Footnote_67_67"></a><a href="#FNanchor_67_67"><span class="label">[67]</span></a> Mémoires de la Société Physique, &c., de Genève, tom. ii. -art. 2.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_68_68" id="Footnote_68_68"></a><a href="#FNanchor_68_68"><span class="label">[68]</span></a> This curious phenomenon was first observed by Mr. Trevelyan, -whose <i>Notice regarding some Experiments on the Vibration of Heated -Metals</i> will be found in the Transactions of the Royal Society of -Edinburgh, vol. xii., 1837. In a Memoir in the same volume, -entitled <i>Experimental Researches regarding certain vibrations which -take place between metallic masses having different temperatures</i>, -Professor Forbes draws the following conclusions:— -</p> -<p> -1. “The vibrations never take place between substances of the -same nature. -</p> -<p> -2. “Both substances must be metallic. (This is now proved -not to be necessary.) -</p> -<p> -3. “The vibrations take place with an intensity proportional -(within certain limits) to the difference of the conducting powers -of the metals for heat or electricity; the metal having the least -conducting power being necessarily the coldest. -</p> -<p> -4. “The time of contact of two points of the metals must be -longer than that of the intermediate portions. -</p> -<p> -5. “The impulse is received by a distinct and separate process -at each contact of the bar and block, and in no case is the -metallic connection of the bearing points in the bar, or those of -the block, in any way essential. -</p> -<p> -6. “The intensity of the vibration is (under certain exceptions) -proportional to the difference of temperature of the -metals.”—Transactions of the Royal Society of Edinburgh, -vol. xii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_69_69" id="Footnote_69_69"></a><a href="#FNanchor_69_69"><span class="label">[69]</span></a> The Bakerian Lecture. <i>On certain Phenomena of Voltaic -Ignition, and the Decomposition of Water into its Constituent Gases -by Heat</i>: by W. R. Grove, Esq.—Philosophical Transactions, -1847. Part 1.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_70_70" id="Footnote_70_70"></a><a href="#FNanchor_70_70"><span class="label">[70]</span></a> Davy’s <i>Researches on Flame</i>. Works, vol. vi.—Philosophical -Transactions for 1817.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_71_71" id="Footnote_71_71"></a><a href="#FNanchor_71_71"><span class="label">[71]</span></a> <i>On the Effect of Heat in lessening the affinities of the Elements -of Water</i>: by the Rev. Thomas Romney Robinson, D.D.—Transactions -of the Royal Irish Academy, vol. xxi. part 2.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_72_72" id="Footnote_72_72"></a><a href="#FNanchor_72_72"><span class="label">[72]</span></a> <i>An Inquiry concerning the Chemical Properties that have been -attributed to Light</i>: by Benjamin, Count of Rumford.—Philosophical -Transactions, vol. lxxxviii. p. 449.—The results obtained -by Count Rumford were probably due to the non-luminous heat-rays—parathermic -rays—which are known to be given off by -boiling water.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_73_73" id="Footnote_73_73"></a><a href="#FNanchor_73_73"><span class="label">[73]</span></a> For Dr. Drapers paper, see Philosophical Magazine for May, -1847, vol. xxx. 3rd series.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_74_74" id="Footnote_74_74"></a><a href="#FNanchor_74_74"><span class="label">[74]</span></a> <i>On the Action of the Rays of the Solar Spectrum on Vegetable -Colours</i>: by Sir J. F. W. Herschel, Bart. -</p> -<p> -The proof of the continuation of the visible prismatic spectrum -beyond the extreme violet may be witnessed in the following -manner:—“Paper stained with tincture of turmeric is of a yellow -colour; and, in consequence, the spectrum thrown in it, if exposed -in open daylight, is considerably affected in its apparent -colours, the blue portion appearing violet, and the violet very -pale and faint; but beyond the region occupied by the violet -rays, is distinctly to be seen a faint prolongation of the spectrum, -terminated laterally, like the rest of it, by straight and sharp outlines, -and which, in this case, affects the eye with the sensation of -a pale yellow colour.”—Philosophical Transactions, p. 133.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_75_75" id="Footnote_75_75"></a><a href="#FNanchor_75_75"><span class="label">[75]</span></a> The most complete exposition of the theory that animal heat -is derived from chemical action only, will be found in <i>Animal -Chemistry, or Chemistry in its applications to Physiology and -Pathology</i>, by Justus Liebig: translated by Dr. Gregory. The -conclusions arrived at by the author, notwithstanding his high—and -deservedly high—position in chemical science, must, however, -be received with great caution, many of them being founded on -most incorrect premises, and his generalizations being of the most -hasty and imperfect character. At page 22 the following passage -occurs:—“If we were to go naked, like certain savage tribes, or if -in hunting or fishing we were exposed to the same degree of cold -as the Samoiedes, we should be able, with ease, to consume ten -pounds of flesh, and, perhaps, a dozen of tallow candles into the -bargain, daily, as warmly clad travellers have related with astonishment -of these people. We should then also be able to take the -same quantity of brandy or train-oil without bad effects, because -the carbon and hydrogen of these substances would only suffice to -keep up the equilibrium between the external temperature and -that of our bodies.” -</p> -<p> -A brief examination will exhibit the error of this. The analysis -of Beef, by D. Lyon Playfair, is as follows:— -</p> -<table summary="Chemical analysis of beef"> -<tr><td>Carbon</td><td class="tdr tdpad">51·83</td></tr> -<tr><td>Hydrogen</td><td class="tdr tdpad">7·57</td></tr> -<tr><td>Nitrogen</td><td class="tdr tdpad">15·01</td></tr> -<tr><td>Oxygen</td><td class="tdr tdpad">21·37</td></tr> -<tr><td>Ashes</td><td class="tdr tdpad">4·23</td></tr> -</table> -<p> -And the following has been given by Chevreul as the composition -of mutton tallow:— -</p> -<table summary="Chemical analysis of mutton tallow"> -<tr><td>Carbon</td><td class="tdr tdpad">96</td></tr> -<tr><td>Hydrogen</td><td class="tdr tdpad">16</td></tr> -<tr><td>Nitrogen</td><td class="tdr tdpad">16</td></tr> -<tr><td>Oxygen</td><td class="tdr tdpad">48</td></tr> -</table> -<p> -About three times the quantity of oxygen to the carbon eaten, is -required to convert it into carbonic acid; hence, the Samoiede, -eating more highly carbonized matter, must inspire 288 oz. of -oxygen daily, or nearly eight times as much as the “ordinary -adult.” By the lungs he must take into the body 2,304 cubic -feet of air besides what will be absorbed by the skin. His -respirations must be so much quickened, that at the lowest possible -calculation he must have 500 pulsations a minute. Under -such conditions it is quite clear man could not exist. There is -no disputing the fact of the enormous appetites of these people; -but all the food is not removed from the system as carbonic -acid gas.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_76_76" id="Footnote_76_76"></a><a href="#FNanchor_76_76"><span class="label">[76]</span></a> An interesting paper by Dr. Davy, <i>On the Temperature of Man</i>, -will be found in the Philosophical Transactions, vol. cxxxvi. p. -319.—Sir Humphry Davy, in his <i>Consolations in Travel, or the Last -Days of a Philosopher</i>, in his fourth dialogue, <i>The Proteus</i>, has -several ingenious speculations on this subject.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_77_77" id="Footnote_77_77"></a><a href="#FNanchor_77_77"><span class="label">[77]</span></a> <i>Exposé de quelques résultats obtenus par l’action combinée de la -chaleur et de la compression sur certains liquides, tels que l’eau, -l’alcool, l’éther sulfurique, et l’essence de pétrole rectifiée</i>: par M. le -Baron Cagniard de la Tour. -</p> -<p> -The three following conclusions are arrived at:— -</p> -<p> -1. Que l’alcool à 36 degrés, l’essence de pétrole rectifiée à 42 -degrés, et l’éther sulfurique soumis à l’action de la chaleur et -de la compression, sont susceptibles de se réduire complètement -en vapeur sous un volume un peu plus que double de celui de -chaque liquide. -</p> -<p> -2. Qu’une augmentation de pression, occasionnée par la présence -de l’air dans plusieurs des experiences qui viennent d’être -citées, n’a point apporté d’obstacle à l’évaporation du liquide -dans le même espace; qu’elle a seulement rendu sa dilatation plus -calme et plus facile à suivre jusqu’au moment où le liquide -semble s’évanouir tout-à-coup. -</p> -<p> -3. Que l’eau, quoique susceptible sans doute d’être réduite -en vapeur très-comprimée, n’a pu être soumise à des experiences -complètes, faute de moyens suffisans pour assurer l’exacte fermeture -de la marmite de compression, non plus que dans les tubes -de verre dont elle altère la transparence en s’emparant de l’alcali -qui entre dans leur composition.—Annales de Chimie, vol. xxi.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_78_78" id="Footnote_78_78"></a><a href="#FNanchor_78_78"><span class="label">[78]</span></a> <i>Sur les phénomènes qui présentent les corps projetés sur des -surfaces chaudes</i>: par M. Boutigny (d’Evreux).—Annales de -Chimie et de Physique, vol. xi. p. 16. <i>Congélation du mercure en -trois secondes, en vertu de l’état <span class="correction" title="In the original book: sphérodïal">sphéroïdal</span> dans un creuset incandescent</i>: -by M. Faraday.—Ibid., vol. xix. p. 383. -</p> -<p> -<i>Spheroidal Condition of Bodies</i> (Extrait d’une Note de M. -Boutigny d’Evreux). -</p> -<p> -“Au nombre des propriétés des corps à l’état sphéroïdal, il en -est cinq qui me paraissent caractéristiques et fondamentales, et -c’est sur ces cinq propriétés que je base la définition que je -soumets aujourd’hui au jugement de l’Académie. Ces cinq propriétés -sont:— -</p> -<p> -“1. La forme arrondie que prend la matière sur une surface -chauffée à une certaine température. -</p> -<p> -“2. Le fait de la distance permanente qui existe entre le corps -à l’état sphéroïdal et le corps sphéroïdalisant. -</p> -<p> -“3. La propriété de réfléchir le calorique rayonnant. -</p> -<p> -“4. La suspension de l’action chimique. -</p> -<p> -“5. La fixité de la température des corps à l’état sphéroïdal. -</p> -<p> -“Cela posé, voici la définition que je propose: un corps projeté -sur une surface chaude est à l’état sphéroïdal quand il revêt la -forme arrondie et qu’il se maintient sur cette surface au delà du -rayon de sa sphère d’activité physique et chimique; alors il -réfléchit le calorique rayonnant, et ses molécules sont, quant à la -chaleur, dans un état d’équilibre stable; c’est-à-dire, à une température -invariable, ou qui ne varie que dans des limites étroites.”—Comptes -Rendus, 6 Mars, 1848.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_79_79" id="Footnote_79_79"></a><a href="#FNanchor_79_79"><span class="label">[79]</span></a> <i>Some Facts relative to the Spheroidal State of Bodies, Fire -Ordeal, Incombustible Man, &c.</i>: by P. H. Boutigny (d’Evreux), -Philosophical Magazine, No. 233 (third, series), p. 80; Comptes -Rendus, May 14, 1849.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_80_80" id="Footnote_80_80"></a><a href="#FNanchor_80_80"><span class="label">[80]</span></a> The theory of freezing mixtures is deduced from the doctrine -of latent caloric. These are mixtures of saline substances which, -at the common temperature, by their mutual chemical action, pass -rapidly into the fluid form, or are capable of being rapidly -dissolved in water, and, by this quick transition to fluidity, absorb -caloric, and produce degrees of cold more or less intense.—Rev. -Francis Lunn, <i>On Heat</i>: Encyclopædia Metropolitana.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_81_81" id="Footnote_81_81"></a><a href="#FNanchor_81_81"><span class="label">[81]</span></a> <i>Propriétés de l’Acide Carbonique liquide</i>, par M. Thilorier, -Annales de Chimie, vol. lx. p. 427. <i>Solidification de l’Acide Carbonique</i>: -Ibid. p. 432.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_82_82" id="Footnote_82_82"></a><a href="#FNanchor_82_82"><span class="label">[82]</span></a> <i>On the Liquefaction and Solidification of Bodies generally -existing as Gases</i>, by Michael Faraday, D.C.L., F.R.S., &c.; Philosophical -Transactions, vol. cxxxvi, p. 155.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_83_83" id="Footnote_83_83"></a><a href="#FNanchor_83_83"><span class="label">[83]</span></a> Burns, in one of his most natural and pathetic letters.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_118" id="Page_118"></a>[Pg 118]</span></p> - - -<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII.</h2> - -<p class="center">LIGHT.</p> - - -<p class="chap-head">Theories of the Nature of Light—Hypotheses of Newton and -Huygens—Sources of Light—The Sun—Velocity of Light—Transparency—Dark -Lines of the Spectrum—Absorption of -Light—Colour—Prismatic Analysis—Rays of the Spectrum—Rainbow—Diffraction—Interference—Goethe’s -Theory—Polarisation—Magnetisation -of Light—Vision—The Eye—Analogy—Sound -and Light—Influence of Light on -Animals and Vegetables—Phosphorescence arising from -several Causes—Artificial Light—Its Colour dependent on -Matter.</p> - - -<p class="p2">Light, the first creation, presents to the enquiring -mind a series of phenomena of the most exalted character. -The glowing sunshine, painting the earth with -all the brilliancy of colour, and giving to the landscape -the inimitable charm of every degree of illumination, -from the grey shadow to the golden glow;—the calm of -evening, when, weary of the “excess of splendour,” the -eye can repose in tranquillity upon the “cloud-land” -of the west, and watch the golden and the ruddy hues -fade slowly into the blue tincture of night;—and the -pale refulgence of the moon, with the quiet sparkle of -the sun-lit stars,—all tend to impress upon the soul, the -great truth that, where there is light, organisation and -life are found, and beyond its influence death and silence -hold supreme dominion.<a name="FNanchor_84_84" id="FNanchor_84_84"></a><a href="#Footnote_84_84" class="fnanchor">[84]</a> Through all time we have<span class="pagenum"><a name="Page_119" id="Page_119"></a>[Pg 119]</span> -evidences that this has been the prevailing feeling of the -human race, derived, of course, from their observation of -the natural phenomena dependent upon luminous agency. -In the myths of every country, impersonations of light -prevail, and to these are referred the mysteries of the -perpetual renewal of life on the surface of the earth.</p> - -<p>This presentiment of a philosophic truth, in the instance -of the poet sages of intellectual Greece, was advanced -to the highest degree of refinement; and the -sublime exclamation of Plato: “Light is truth, and God -is light,” approaches nearly to a divine revelation.</p> - -<p>As the medium of vision—as the cause of colour—as -a power influencing in a most striking manner all the -forms of organisation around us, light presented to the -inquiring minds of all ages a subject of the highest -interest.</p> - -<p>The ancient philosophers, although they lost themselves -in the metaphysical subtleties of their schools, -could not but discover in light an element of the utmost -importance in natural operations. The alchemists regarded -the luminous principle as a most subtile fluid, -capable of interpenetrating and mingling with gross -matter: gold being supposed to differ from the baser -metals only in containing a larger quantity of this ethereal -essence.<a name="FNanchor_85_85" id="FNanchor_85_85"></a><a href="#Footnote_85_85" class="fnanchor">[85]</a> Modern science, after investigating most<span class="pagenum"><a name="Page_120" id="Page_120"></a>[Pg 120]</span> -attentively a greater number of the phenomena of light, -has endeavoured to assist the inquiry by the aid of -hypotheses. Newton, in a theory, which exhibits the -refined character of that great philosopher’s mind, supposes -luminous particles to dart from the surfaces of -bodies in all directions—that these infinitely minute particles -are influenced by the attracting and repelling forces -of matter, and thus turned back, or reflected, from their -superficies in some cases, and absorbed into their interstitial -spaces in others.</p> - -<p>Huyghens, on the contrary, supposes light to be caused -by the waves or vibrations of an infinitely elastic medium—<span class="smcap">Ether</span>—diffused -through all space, which waves are -propagated in every direction from the luminous body. -In the first theory, a luminous particle is supposed actually -to come from the sun to the earth; in the other, -the sun only occasions a disturbance of the <i>ether</i>, which -extends with great rapidity, in the same manner as a -wave spreads itself over the surface of a lake.</p> - -<p>Nearly all the facts known in the time of Newton, -and those discovered by him, were explained most -satisfactorily by his hypothesis; but it was found they -could be interpreted equally as the effects of undulation, -with the exception of the production of colour by prismatic -refraction. Although the labours of many -gifted minds have been given, with the utmost devotion, -to the support of the vibratory theory, this simple fact -has never yet received any satisfactory explanation; and -there are numerous discoveries connected with the molecular -and chemical disturbances produced by the su<span class="pagenum"><a name="Page_121" id="Page_121"></a>[Pg 121]</span>n’s -rays, which do not appear to be explained by the hypothesis -of emission or of undulation.</p> - -<p>In both theories a wave motion is admitted, and every -fact renders it probable that this mode of progression -applies not only to light, but to the so-called <i>imponderable -forces</i> in general. Admitting, therefore, the undulatory -movement of luminous rays, we shall not stop to -consider those points of the discussion which have been -so ably dealt with by Young, Laplace, Fresnel, Biot, -<span class="correction" title="In the original book: Frauenhofer">Fraunhofer</span>, Herschel, Brewster, and others, but proceed -at once to consider the sources of light, and its -more remarkable phenomena.<a name="FNanchor_86_86" id="FNanchor_86_86"></a><a href="#Footnote_86_86" class="fnanchor">[86]</a></p> - -<p>The sun is the greatest permanently luminous body -we are acquainted with, and that orb is continually pouring -off light from its surface in all directions at the rate, -through the resisting medium of space and of our own -atmosphere, of 192,000 miles in a second of time. It has -been calculated, however, that light would move through -a vacuum with the speed of 192,500 miles in the same -period. We, therefore, learn that a ray of light requires -eight minutes and thirteen seconds to come from the sun -to us. In travelling from the distant planet Uranus, -nearly three hours are exhausted; and from the nearest<span class="pagenum"><a name="Page_122" id="Page_122"></a>[Pg 122]</span> -of the fixed stars each ray of light requires more than -six years to traverse the intervening space between it -and the earth. Allow the mind to advance to the -regions of nebulæ, and it will be found that hundreds of -years must glide away during the passage of their radiations. -Consequently, if one of those masses of matter, or -even one of the remote fixed stars, was “blotted out of -heaven” to-day, several generations of the finite inhabitants -of this world would fade out of time before the -obliteration could be known to man. Here the immensity -of space assists us in our conception, limited though -it be, of the for-ever of eternity.<a name="FNanchor_87_87" id="FNanchor_87_87"></a><a href="#Footnote_87_87" class="fnanchor">[87]</a></p> - -<p>All the planets of our system shine with reflected -light, and the moon, our satellite, also owes her silvery -lustre to the sun’s radiations. The fixed stars are, in -all probability, suns shining from the far distance of -space, with their own self-emitted lights. By the photometric -researches of Dr. Wollaston, we learn, however, -that it would take 20,000 millions of such orbs as Sirius, -the brightest of the fixed stars, to afford as much light -as we derive from the sun. The same observer has -proved that the brightest effulgence of the full moon is -yet 801,072 times less than the luminous power of our -solar centre.</p> - -<p><span class="pagenum"><a name="Page_123" id="Page_123"></a>[Pg 123]</span></p> - -<p>The cultivators of modern science are a bold race; not -contented with endeavouring to understand the physical -earth, they are endeavouring to comprehend the condition -of the solar surface. The mind of man can penetrate -far into nature, and, as it were, feel out the mysteries -of untraversed space. The astronomer learns of -a peculiar condition of light, which is termed polarisation, -and he learns by this, too, that he can determine if -from a bright luminous disc the light is derived from a -solid mass in a state of intense ignition, or from vapour -in an incandescent condition. He adds a polarising apparatus -to his telescopes, and he determines that the -light we derive from the sun is due to an envelope of -vapour—burning, in all probability—only with greater -intensity, as the gas which we now employ. This <i>Photosphere</i>—as -it has been called by the late French philosopher -Arago, is found to be subjected to violent disturbances, -and the dark spots seen on the sun’s disc are now -known to be openings through this mysterious envelope -of light, which enable us to look in upon the dark body -of the sun itself.</p> - -<p>Luminous phenomena may be produced by various -means—chemical action is a source of light; and, under -several circumstances in which the laws of affinity are -strongly exerted, a very intense luminous effect is produced. -Under this head all the phenomena of combustion -are included. In the electric spark we have the -development of light; and the arc which is formed -between charcoal points <span class="correction" title="In the original book: a">at</span> the poles of a powerful voltaic -battery affords us the most intense artificial illumination -with which we are acquainted. In addition to these, we -have the peculiar phenomena of phosphorescence arising -from chemical, calorific, electrical, actinic, and vital excitation, -all of which must be particularly examined.</p> - -<p>From whatever source we procure light, it is the same -in character, differing only in intensity. In its action<span class="pagenum"><a name="Page_124" id="Page_124"></a>[Pg 124]</span> -upon matter, we have the phenomena of transmission, of -reflection, of refraction, of colour, of polarisation, and of -vision, to engage our attention.</p> - -<p>A beam of white light falls upon a plate of colourless -glass, and it passes freely through it, losing but little of -its intensity; the largest portion being lost by reflection -from the first surface upon which the light impinges. If -the glass is roughened by grinding, we lose more light -by absorption and by reflection from the asperities of -the roughened surface; but if we cover that face with -any oleaginous fluid, as, for instance, turpentine, its -transparency is restored. We have thus direct proof -that transparency to light is due to molecular condition. -This may be most strikingly shown by an interesting -experiment of Sir David Brewster’s:—</p> - -<p>If a glass tube is filled with nitrous acid vapour, which -is of a dull red colour, it admits freely the passage of -the red and orange rays with some of the others, and, if -held upright in the sunshine, casts a red shadow on the -ground; by gently warming it with a spirit-lamp, whilst -in this position, it acquires a much deeper and blacker -colour, and becomes almost impervious to any of the -rays of light; but upon cooling it again recovers its -transparency.</p> - -<p>It has also been stated by the same exact experimentalist, -that having brought a purple glass to a red heat, -its transparency was improved, so that it transmitted -green, yellow, and red rays, which it previously absorbed; -but the glass recovered its absorptive powers as -it cooled. A piece of yellowish-green glass lost its -transparency almost entirely by being heated. Native -yellow orpiment becomes blood-red upon being warmed, -when nearly all but the red rays are absorbed; and pure -phosphorus, which is of a pale yellow colour, and transmits -freely all the coloured rays upon being melted, becomes -very dark, and transmits no light.</p> - -<p><span class="pagenum"><a name="Page_125" id="Page_125"></a>[Pg 125]</span></p> - -<p>Chemistry affords numerous examples of a very slight -change of condition, producing absolute opacity in fluids -which were previously diaphanous.<a name="FNanchor_88_88" id="FNanchor_88_88"></a><a href="#Footnote_88_88" class="fnanchor">[88]</a></p> - -<p>Charcoal absorbs all the light which falls upon it, but -in some of its states of combination, and in the diamond, -which is pure carbon, it is highly transparent. Gold -and silver beaten into thin leaves are permeated by the -green and blue rays, and the metals in combination with -acids are all of them more or less transparent. What -becomes of the light which falls upon and is absorbed -by bodies, is a question which we cannot yet, notwithstanding -the extensive observations that have been made -by some of the most gifted of men, answer satisfactorily. -In all probability, as already stated, it is permanently -retained within their substances; and many of the experiments -of exciting light in bodies when in perfect darkness, -by the electric spark and other means, appear to -support the idea of light becoming latent or hidden.</p> - -<p>No body is absolutely transparent; some light is lost -in passing even through ethereal space, and still more in -traversing our atmosphere.</p> - -<p>Amongst the most curious instances of absorption is -that which is uniformly discovered in the solar spectrum, -particularly when we examine it with a telescope. We -then find that the coloured rays are crossed by a great -number of dark bands or lines, giving no light; these -are generally called Fraunhofer’s dark lines, as it was to -the indefatigable exertions of that experimentalist, and -by the aid of his beautiful instruments, that most of them -were discovered and measured, and enumerated, although -they were previously noticed by Dr. Wollaston. It is -quite clear that those lines represent rays which have<span class="pagenum"><a name="Page_126" id="Page_126"></a>[Pg 126]</span> -been absorbed in their passage from the sun to the earth: -although some of them have no doubt undergone absorption -within the limits of the earth’s atmosphere, we -have every reason to believe, with Sir John Herschel, -that the principal absorption takes place in the atmosphere -of the sun.<a name="FNanchor_89_89" id="FNanchor_89_89"></a><a href="#Footnote_89_89" class="fnanchor">[89]</a></p> - -<p>It has been proved by Dr. Miller, that the number of -those dark lines is continually varying with the alteration -of atmospheric conditions;<a name="FNanchor_90_90" id="FNanchor_90_90"></a><a href="#Footnote_90_90" class="fnanchor">[90]</a> and the evidences -which have been afforded, of peculiar states of absorption -by the gaseous envelope of the earth,—during the -prosecution of investigations on the chemical agencies -of the sun’s rays,—are of a sufficiently convincing character.</p> - -<p>It has been calculated by Bouguer, that if our atmosphere, -in its purest state, could be extended rather more -than 700 miles from the earth’s surface instead of nearly -40, as it is at present, the sun’s rays could not penetrate<span class="pagenum"><a name="Page_127" id="Page_127"></a>[Pg 127]</span> -it, and this globe would roll on in darkness and silence, -without a vestige of vegetable form or of animal life. In -the Hebrew version of the Mosaic History, the reading -is, “Let light appear:” may not this really mean that -the earth’s atmosphere was so cleared of obstructing -vapours, that the solar rays were enabled to reach the -earth? The same calculation supposes that sea-water -loses all its transparency at the depth of 730 feet; but -a dim twilight must prevail much deeper in the ocean.</p> - -<p>The researches of Professor Edward Forbes have -proved, that at the depth of 230 fathoms in the Ægean -sea, the few shelled animals that exist are colourless: no -plants are found within that zone; and that industrious -naturalist fixes the zero of animal life of those waters at -about 300 fathoms.<a name="FNanchor_91_91" id="FNanchor_91_91"></a><a href="#Footnote_91_91" class="fnanchor">[91]</a> Since these zones mark the rapidly -diminishing light, it is evident that where life ceases to be -must be beyond the limits to which life can penetrate.</p> -<p><span class="pagenum"><a name="Page_128" id="Page_128"></a>[Pg 128]</span></p> -<p>Our atmosphere, charged with aqueous vapour, serves -to shield us from the intense action of the solar powers. -By it we are protected from the destructive influences -of the sun’s light and heat; enjoy those modified -conditions which are most conducive to the healthful -being of organic forms; to it we owe “the blue sky -bending over all,” and those beauties of morning and -evening twilight of which</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">—— Sound and motion own the potent sway.</div> -<div class="verse">Responding to the charm with its own mystery.</div> -</div></div></div> - -<p>To defective transparency, or rather to the different -degrees of it, we must attribute, in part, the colours of -permeable media. Thus, a glass or fluid appears yellow -to the eye, because it has the property of admitting the -permeation of a larger quantity of the yellow rays than -of any others;—red, because the red rays pass it with -the greatest freedom; and so on for every other colour. -In most cases the powers of transmission and of reflection -are similar; but it is not so in all; a variety of fluor -spar, which, while it transmits green light, reflects blue, -and the precious opal, are striking instances to the contrary. -Some glasses, which transmit yellow light have -the singular power of dispersing blue rays from one sur<span class="pagenum"><a name="Page_129" id="Page_129"></a>[Pg 129]</span>face; -and a solution of quinine in water acidulated with -sulphuric acid, although perfectly transparent and colourless -when held between the eye and the light, exhibits, -if viewed in a particular direction, a lively cerulean tint. -These effects being supposed to be due to the conditions -of the surface, have been called <i>epipolic</i> phenomena.<a name="FNanchor_92_92" id="FNanchor_92_92"></a><a href="#Footnote_92_92" class="fnanchor">[92]</a></p> - -<p>The careful investigation of these phenomena has -made us acquainted with some very interesting facts, and -indeed discovered to us a set of luminous rays which -were previously unknown. The dispersion of blue light -from the surface of some yellow glasses—such as have been -coloured by the oxide of silver—is of a different order -from that which takes place with the solution of sulphate -of quinine, or with the fluor spar. The first depends -upon a peculiar condition of the surface, while the latter -phenomena are due to a dispersion which takes place -<i>within</i> the solid or fluid. In addition to the sulphate -of quinine, and the <span class="correction" title="In the original book: flour">fluor</span> spar, we obtain the same results -in a very marked manner by a canary yellow glass,<span class="pagenum"><a name="Page_130" id="Page_130"></a>[Pg 130]</span> -coloured with the oxide of uranium, and by a decoction -of the inner bark of the horse-chesnut tree. Mr. -Stokes, who has investigated this class of phenomena, -and proposes to call it <i>Fluorescence</i>, from its being naturally -seen in fluor-spar, has shown that the peculiar internal -dispersion, and the consequent alteration of the colour -of the ray, is due to an alteration in its refrangibility. -Whether this hypothesis prove to be the correct one or -not, it is certain that there exists a set of rays of far -higher refrangibility than those seen in the ordinary -Newtonian spectrum. This may be shown in the following -manner: taking either of the solutions named, or a -block of uranium glass, throw upon one face, by means of -a prism, a very pure spectrum. On looking <i>into</i> the -glass or fluid there will be seen, commencing amidst the -most refrangible rays, a new set of spectral rays, struggling -to make their way through the absorbent medium. -These are of a blue colour in the quinine or chesnut -solution, and green in the uranium glass, and are seen -extending themselves far beyond the most refrangible -rays of the ordinary Newtonian spectrum. This is the -space over which those rays which have the power of producing -chemical changes, such as are rendered familiar -by the practice of Photography, are detected in their -greatest activity. It has, therefore, been supposed that -these fluorescent rays are the chemical rays rendered luminous -by the alteration of their refrangibility. This -view has received much support from the fact that the -extra spectral rays are crossed with numerous dark -lines, and that in the chemical impressions these -lines are marked by unchanged spaces which exactly -coincide with them. There is, however, much doubt of -the correctness of this, since, in the uranium glass of -such a thickness that these visible rays are quite absorbed, -the chemical rays still pass.</p> - -<p>However, the whole question requires, and is receiving, -the most searching investigation. The discovery of<span class="pagenum"><a name="Page_131" id="Page_131"></a>[Pg 131]</span> -these phenomena, which are included under the term of -Fluorescence, is of that interesting and important character, -that it must be ranked as the most decided advance -which has been made in physical optics since the -days of Newton.</p> - -<p>It is not improbable that those rays of such high -refrangibility may, although they are under ordinary -circumstances invisible to the human eye, be adapted -to produce the necessary degree of excitement upon -which vision depends in the optic nerves of the night-roaming -animals. The bat, the owl, and the cat, may -see in the gloom of night by the aid of rays which are -invisible to, or inactive on the eyes of man, or of those -animals which require the light of day for perfect vision.</p> - -<p>It is a general law of the radiant forces, that whenever -they fall upon any surface, a portion is thrown -back or reflected at the same time as other portions are -absorbed or transmitted. Upon this peculiarity appear -to depend the phenomena of natural colour in bodies.</p> - -<p>The white light of the sun is well known to be composed -of several coloured rays. Or rather, according to -the theory of undulations, when the rate at which a ray -vibrates is altered, a different sensation is produced upon -the optic nerve. The analytical examination of this -question shows, that to produce a red colour the ray of -light must give 37,640 undulations in an inch, and -458,000000,000000 in a second. Yellow light requires -44,000 undulations in an inch, and 535,000000,000000 -in a second; whilst the effect of blue results from 51,110 -undulations within an inch, and 622,000000,000000 of -waves in a second of time.<a name="FNanchor_93_93" id="FNanchor_93_93"></a><a href="#Footnote_93_93" class="fnanchor">[93]</a> The determination of such<span class="pagenum"><a name="Page_132" id="Page_132"></a>[Pg 132]</span> -points as these is among the highest refinements of -science, and, when contrasted with the most sublime -efforts of the imagination, they must appear immeasurably -superior.</p> - -<p>If a body sends back white light unchanged, it appears -white; if the surface has the property of altering the -vibration to that degree which is calculated to produce -redness, the result is a red colour: the annihilation of -the undulations produces blackness. By the other view, -or the corpuscular hypothesis, the beam of white light -is supposed to consist of certain coloured rays, each of -which has physical properties peculiar to itself, and thus -is capable of producing different physiological effects. -These rays falling upon a transparent or an opaque body -suffer more or less absorption, and being thus dissevered, -we have the effect of colour. A red body absorbs all -the rays but the red; a blue surface, all but the blue; -a yellow, all but the yellow; and a black surface absorbs -the whole of the light which falls upon it.</p> - -<p>That natural colours are the result of white light, and -not innate properties of the bodies themselves, is most -conclusively shown by placing coloured bodies in monochromatic -light of another kind, when they will appear -either of the colour of that light, or, by absorbing it, -become black; whereas, when placed in light of their -own character, the intensity of colour is greatly increasing.</p> - -<p>Every surface has, therefore, a peculiar constitution, -by which it gives rise to the diversified hues of nature. -The rich and lively green, which so abundantly overspreads -the surface of the earth, the varied colours of -the flowers, and the numberless tints of animals, together -with all those of the productions of the mineral -kingdom, and of the artificial combinations of chemical -manufacture, result from powers by which the relations -of matter to light are rendered permanent, until its physical -conditions undergo some change.</p> - -<p><span class="pagenum"><a name="Page_133" id="Page_133"></a>[Pg 133]</span></p> - -<p>There is a remarkable correspondence between the -geographical position of a region and the colours of its -plants and animals. Within the tropics, where</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“The sun shines for ever unchangeably bright,”</div> -</div></div></div> - -<p>the darkest green prevails over the leaves of plants; the -flowers and fruits are tinctured with colours of the -deepest dye, whilst the plumage of the birds is of the -most variegated description and of the richest hues. In -the people also of these climes there is manifested a -desire for the most striking colours, and their dresses -have all a distinguishing character, not of shape merely, -but of chromatic arrangement. In the temperate -climates everything is of a more subdued variety: the -flowers are less bright of hue; the prevailing tint of the -winged tribes is a russet brown; and the dresses of the -inhabitants of these regions are of a sombre character. -In the colder portions of the earth there is but little -colour; the flowers are generally white or yellow, and -the animals exhibit no other contrast than that which -white and black afford. A chromatic scale might be -formed, its maximum point being at the equator, and its -minimum at the poles.<a name="FNanchor_94_94" id="FNanchor_94_94"></a><a href="#Footnote_94_94" class="fnanchor">[94]</a></p> - -<p>The influence of light on the colours of organized<span class="pagenum"><a name="Page_134" id="Page_134"></a>[Pg 134]</span> -creation is well shown in the sea. Near the shores we -find sea-weeds of the most beautiful hues, particularly -on the rocks which are left dry by the tides; -and the rich tints of the actiniæ, which inhabit shallow -water, must have been often observed. The fishes which -swim near the surface are also distinguished by the -variety of their colours, whereas those which live at -greater depths are grey, brown, or black. It has been -found that after a certain depth, where the quantity of -light is so reduced that a mere twilight prevails, the -inhabitants of the ocean become nearly colourless. -That the sun’s ray alone gives to plants the property of -reflecting colour is proved by the process of blanching, -or <i>etiolation</i>, produced by artificially excluding the light.</p> - -<p>By a triangular piece of glass—a prism,—we are enabled -to resolve light into its ultimate rays. The white pencil -of light which falls on the first surface of the prism is -bent from its path, and coloured bands of different -colours are obtained. These bands or rays observe a -curious constancy in their positions: the red ray is -always the least bent out of the straight path: the -yellow class comes next in the order of refrangibility; -and the blue are the most diverted from the vertex of -the prism. The largest amount of illuminating power -exists in the yellow ray, and it diminishes towards either -end.<a name="FNanchor_95_95" id="FNanchor_95_95"></a><a href="#Footnote_95_95" class="fnanchor">[95]</a> It is not uninteresting to observe something like<span class="pagenum"><a name="Page_135" id="Page_135"></a>[Pg 135]</span> -the same variety of colour occurring at each end of the -prismatic spectrum. The strict order in which the pure -and mixed coloured rays present themselves is as -follows:—</p> - -<p>1. The <i>extreme red</i>: a ray which can only be discovered -when the eye is protected from the glare of the -other rays by a cobalt blue glass, is of a crimson -character—a mixture of the <i>red</i> and the <i>blue</i>, red -predominating.<a name="FNanchor_96_96" id="FNanchor_96_96"></a><a href="#Footnote_96_96" class="fnanchor">[96]</a></p> - -<p>2. The <i>red</i>: the first ray visible under ordinary circumstances.</p> - -<p>3. The <i>orange</i>: red passing into and combining with -yellow.</p> - -<p>4. The <i>yellow</i>: the most intensely luminous of the -rays.</p> - -<p>5. The <i>green</i>: the yellow passing into and blending -with the blue.</p> - -<p>6. The <i>blue</i>: in which the light very rapidly diminishes.</p> - -<p>7. The <i>indigo</i>: the dark intensity of blue.</p> - -<p>8. The <i>violet</i>: the <i>blue</i> mingled again with the <i>red</i>—blue -being in excess.</p> - -<p>9. The <i>lavender grey</i>: a neutral tint, produced by -the combination of the red, blue, and yellow rays, which -is discovered most easily when the spectrum is thrown -upon a sheet of turmeric paper.</p> - -<p>10. The fluorescent rays: which are either a <i>pure -silvery blue</i> or a delicate <i>green</i>.</p> - -<p>Newton regarded the spectrum as consisting of seven -colours of definite and unvarying refrangibility. Brewster -and others appear to have detected a great diffusion<span class="pagenum"><a name="Page_136" id="Page_136"></a>[Pg 136]</span> -of the colours over the spectrum, and regard white light as -consisting only of three rays, which in the prismatic images -overlap each other; and from these—red, yellow, and -blue—all the others can be formed by combination in -varying proportions. The truth will probably be found -to be, that the ordinary prismatic spectrum is a compound -of two spectra:—that is, as we have the ordinary -rainbow, and a supplementary bow, the colours of which -are inverted, so the extraordinary may be somewhat -masked by the intense light of the ordinary spectrum; -and yet by overlapping produce the variations of colour -in the rays. We have already examined the heating -power found in these coloured bands, which, although -shown to be in a remarkable manner in constant -agreement with the colour of a particular ray, is not -directly connected with it; that is, not as the effect -of a cause, or the contrary. The chemical action of the -solar rays, to which from its important bearings we shall -devote a separate chapter, has, in like manner with -heat, been confounded with the sun’s luminous power; -but although associated with light and heat, and modified -by their presence, it must be distinguished from -them.</p> - -<p>We find the maximum of heat at one end of the -spectrum, and that of chemical excitation at the other—luminous -power observing a mean point between them. -Without doubt we have these powers acting reciprocally, -modifying all the phenomena of each other, and -thus giving rise to the difficulties which beset the inquirer -on every side.</p> - -<p>We have beautiful natural illustrations of luminous -refraction in the rainbow and in the halo: in both cases -the rays of light being separated by the refractive power -of the falling rain drop, or the vesicles which form the -moisture constituting a fog. In the simple toy of the -child—the soap-bubble floating upon the air—the phi<span class="pagenum"><a name="Page_137" id="Page_137"></a>[Pg 137]</span>losopher -finds subjects for his contemplation; and from -the unrivalled play of colours which he discovers in -that attenuated film, he learns that the varying thicknesses -of surfaces influence, in a most remarkable -manner, the colours of the sunbeam. Films of oil -floating upon water present similar appearances; and -the colours developed in tempering steel are due entirely -to the thickness of the oxidized surface produced -by heat. There have lately been introduced some beautiful -specimens of paper rendered richly iridescent by the following -process:—A solution of a gum resin in chloroform -is floated upon water, where it forms a film giving all the -colours of Newton’s rings. A sheet of paper which -has been previously sunk in the water is carefully lifted, -and the film thus removed adheres with great firmness -to the paper, and produces this rich and curious play of -colour. The rich tints upon mother-of-pearl, in the -feathers of many birds, the rings seen in the cracks of -rock-crystal, or between the unequal faces of two pieces -of glass, and produced by many chemical and indeed -mechanical operations—are all owing to the same cause;—the -refraction of the luminous pencil by the condition -of the film or surface. If we take one of those steel -ornaments which are formed by being covered with an -immense number of fine lines, it will be evident that -these striæ present many different angles of reflection, -and that, consequently, the rays thrown back will, at -some point or another, have a tendency to cross each -other. The result of this is, that the quantity of light -is augmented at some points of intersection, and annihilated -at others.<a name="FNanchor_97_97" id="FNanchor_97_97"></a><a href="#Footnote_97_97" class="fnanchor">[97]</a> Out of the investigation of the phenomena -of diffraction, of the effects of thin and thick -plates upon light, and the results of interference, has<span class="pagenum"><a name="Page_138" id="Page_138"></a>[Pg 138]</span> -arisen the discovery of one of the most remarkable conditions -within the range of physical science.</p> - -<p><i>Two bright lights may be made to produce darkness.</i>—If -two pencils of light radiate from two spots very -close to each other in such a manner that they cross -each other at a given point, any object placed at that -line of interference will be illuminated with the sum -of the two luminous pencils. If we suppose those rays -to move in waves, and the elevation of the wave to -represent the maximum of luminous effect, then the -two waves meeting, when they are both at the height of -their undulation, will necessarily produce a spot of -greater intensity. If now we so arrange the points of -radiation, that the systems of luminous waves proceed -irregularly, and that one arrives at the screen -half an undulation before the other, the one in -elevation falling into the depression of the other, a -mutual annihilation is the consequence. This fact, -paradoxical as it may appear, was broadly stated by -Grimaldi, in the description of his experiments on the -inflection of light, and has been observed by many -others. The vibratory hypothesis, seizing upon the -analogy presented by two systems of waves in water, -explains this plausibly, and many similar phenomena of -what is called the <i>interference of light</i>; but still upon -examination it does not appear that the explanation is -quite free from objection.<a name="FNanchor_98_98" id="FNanchor_98_98"></a><a href="#Footnote_98_98" class="fnanchor">[98]</a></p> - -<p>Another theory, not altogether new to us, it being indicated -in Mayer’s hypothesis of three primary colours -(1775), and to be found as a problem in some of the -Encyclopædias of the last century, has been put forth, -in a very original manner, by that master-mind of intellectual -Germany, Goethe; and from the very comprehensive -views which this poet-philosopher has taken of<span class="pagenum"><a name="Page_139" id="Page_139"></a>[Pg 139]</span> -both animal and vegetable physiology (views which have -been adopted by some of the first naturalists of Europe), -we are bound to receive his theory of colours with every -respect and attention.</p> - -<p>Goethe regards colour as the “thinning” of light; -for example, by obstructing a portion of white light, yellow -is produced; by reducing it still farther, red is supposed -to result; and by yet farther retarding the free -passage of the beam, we procure a blue colour, which is -the next remove from blackness, or the absence of -light. There is truth in this; it bears about it a simplicity -which will satisfy many minds; by it many of -the phenomena of colour may be explained: but it is -insufficient for any interpretation of several of those -laws to which the other theories do give us some insight.</p> - -<p>Newton may have allowed himself to be misled by -the analogy presented between the seven rays of the -spectrum and the notes in an octave. The mystic -number, seven, may have clung like a fibre of the web -of superstition to the cloak of the great philosopher; -but the attack made by Goethe upon the Newtonian -philosophy betrays the melancholy fact of his being -diseased with the lamentable weakness of too many -exalted minds—an overweening self-esteem.</p> - -<p>The polarization of light, as it has been unfortunately -called—unfortunately, as conveying an idea of determinate -and different points or poles, which only exists -in hypothetical analogy—presents to us a class of phenomena -which promise to unclose the mysterious doors -of the molecular constitution of bodies.</p> - -<p>This remarkable condition, as produced by the reflection -of light from glass at a particular angle, was -first observed by Malus, in 1808,<a name="FNanchor_99_99" id="FNanchor_99_99"></a><a href="#Footnote_99_99" class="fnanchor">[99]</a> when amusing himself -by looking at the beams of the setting sun, reflected<span class="pagenum"><a name="Page_140" id="Page_140"></a>[Pg 140]</span> -from the windows of the Luxembourg Palace through -a double refracting prism. He observed that when the -prism was in one position, the windows with their golden -rays were visible; but that turned round a quarter of a -circle from that position, the reflected rays disappeared -although the windows were still seen.</p> - -<p>The phenomenon of double refraction was noticed, in -the first instance, by Erasmus <span class="correction" title="In the original book: Bartolin">Bartholin</span>, in Iceland-spar, -a crystal the primary form of which is a rhombohedron; -who perceived that the two images produced -by this body were not in the same physical conditions.<a name="FNanchor_100_100" id="FNanchor_100_100"></a><a href="#Footnote_100_100" class="fnanchor">[100]</a> -It was also studied by Huyghens and Sir Isaac Newton, -and to our countryman we owe the singular idea that a -ray of light emerging from such a crystal has <i>sides</i>. -This breaking up of the beam of light into two,—which -is shown by looking through a pin-hole on a card -through a crystal of Iceland spar, when two holes become -visible, is due to the different states of tension in -which the different layers constituting the crystal exist.</p> - -<p>In thus separating the ray of light into two rays, the<span class="pagenum"><a name="Page_141" id="Page_141"></a>[Pg 141]</span> -condition called polarisation has been produced, and -by experiment we discover that the single ray has -properties different from those of the compound or -ordinary ray.</p> - -<p>It is somewhat difficult to explain what is meant by, -and what are the conditions of, <i>polarised light</i>. In the -first instance let us see by what methods this peculiar -state may be brought about.</p> - -<p>If we reflect a ray of light from the surface of any -body, fluid or solid, but not metallic, at an angle between -53° and 68° it undergoes what has been called <i>plane -polarisation</i>. It may also be produced by the refraction -of light from several refracting surfaces acting upon the -pencil of light in succession; as by a bundle of plates -of glass. Each surface polarises a portion of the pencil, -and the number of plates necessary to polarise a whole -beam depends upon the intensity of the beam and the -angle of incidence. Thus, the light of a wax candle is -wholly polarised by forty-seven plates of glass at an -angle of 40° 41'; while at an angle of 79° 11' it is -polarised by eight plates. Again, plane polarisation -may be produced by the double refraction of crystals. -Each of the two pencils is polarised, like light reflected -from glass at an angle of 56° 45', but in opposite -planes.</p> - -<p>Non-scientific readers will still ask,—What is this -mysterious condition of light which is produced by reflection -and refraction at peculiar angles to the incident -ray. It is one of the most difficult of problems to -express in popular language. The conditions are, -however, these:—</p> - -<p>An ordinary ray of light will be reflected from a reflecting -surface at whatever angle that surface may be -placed in relation to the incident beam.</p> - -<p>A polarised ray of light is not reflected in all positions -of the reflecting surface.</p> - -<p>An ordinary ray of light is freely transmitted through<span class="pagenum"><a name="Page_142" id="Page_142"></a>[Pg 142]</span> -a transparent medium, as glass, in whatever position it -may be placed relative to the source of light.</p> - -<p>A polarised ray of light is not transmitted in all the -positions of the permeable medium.</p> - -<p>Supposing a plate of glass is presented at the angle -56° to a polarised ray, and the plane of incidence or -reflexion is at right angles to the plane of polarisation -of the ray, <i>no light is reflected</i>. If we turn the plate of -glass round through 90°, when the plane of reflexion is -parallel to that of polarisation <i>the light is reflected</i>. If -we turn the plate round another 90°, so that the plane -of reflexion and of polarisation are parallel to each other, -again <i>no light is reflected</i>; and if we turn it through -another 90° the reflection of the ray again takes place.</p> - -<p>Precisely the same result takes place when, instead of -being reflected, the polarised ray is transmitted.</p> - -<p>Some substances have peculiar polarizing powers: -<i>the tourmaline</i> is a familiar example. If a slice of -tourmaline is taken, and we look at a common pencil -of light through it, we see it in whatever position we -may place the transparent medium. If, however, we -look at a pencil of polarised light, and turn the crystal -round, it will be found that in two positions the light is -stopped, and that in two other positions it passes freely -through it to the eye.</p> - -<p>By way of endeavouring to conceive something of -what may be the conditions which determine this very -mysterious state, let us suppose each ray of light to -vibrate in two planes at right angles to each other: one -wave being vertical and the other horizontal. We have -many examples of this compound motion. The mast of -a ship, by the force with which she is urged through -the water, describes a vertical wave, while by the roll of -the billows across which she sails, a lateral undulation -is produced at the same time. We may sometimes -observe the same thing when a field of corn is agitated -by a shifting wind on a gusty day.</p> - -<p><span class="pagenum"><a name="Page_143" id="Page_143"></a>[Pg 143]</span></p> - -<p>The hypothesis therefore is, that every ray of ordinary -light consists of two rays vibrating in different -planes; and that these rays, separated one from the -other, have the physical conditions which we call -<i>polarized</i>.</p> - -<p>The most transparent bodies may be regarded as -being made up of atoms arranged in certain planes. -Suppose the plane of lamination of any substance to be -vertical in position, it would appear that the ray which -has a vertical motion passes it freely, whereas if we -turn the body round so that the planes of lamination -are at right angles to the plane of vibration of the ray, -it cannot pass.</p> - -<p>That some action similar to that which it is here -endeavoured to express in popular language does take -place, is proved by the correctness of the results deduced -by rigid mathematical analyses founded on this hypothesis.</p> - -<p>There are two other conditions of the polarization of -light—called <i>circular</i> and <i>elliptical</i> polarization. The -first is produced by light when it is twice reflected from -the second surface of bodies at their angle of maximum -polarization, and the second by reflexions from the surfaces -of metals at angles varying from 70° 45' to 78° 30'. -The motion of the wave in the first is supposed to be -circular, or to be that which is represented by looking -along the centre of a corkscrew as it is turned round. -At every turn of the medium effecting <i>circular polarization</i> -the colour of the ray of light is changed after a -uniform order. If turned in one direction, they change -through red, orange, yellow, green, and violet; and if -in the other direction, the colours appear in the contrary -order.</p> - -<p>The variety of striking effects produced by the polarization -of light; the unexpected results which have -sprung from the investigation of the laws by which it -is regulated; and the singular beauty of many of its<span class="pagenum"><a name="Page_144" id="Page_144"></a>[Pg 144]</span> -phenomena, have made it one of the most attractive -subjects of modern science.</p> - -<p>Ordinary light passes through transparent bodies -without producing any very striking effects in its passage; -but this <i>extraordinary</i> beam of light has the -power of insinuating itself between the molecules of -bodies, and by illuminating them, and giving them every -variety of prismatic hue, of enabling the eye to detect -something of the structure of the mass. The chromatic -phenomena of polarized light are so striking, that no -description can convey an adequate idea of their character.</p> - -<p>Spectra more beautiful and intense than the prismatic -image,—systems of rings far excelling those of -thin plates,—and forms of the most symmetric order, are -constantly presenting themselves, as the polarized ray is -passed through various transparent substances; the -path of the ray indicating whether the crystal has been -formed round a single nucleus or axis, or whether it -has been produced by aggregation around two axes. The -coloured rings, and the dark or luminous crosses which -distinguish the path of the polarized ray, are respectively -due to different states of tension amongst the particles, -although those differences are so slight, that no other -means is of sufficient delicacy to detect the variation.</p> - -<p>The poetry which surrounds these, in every way, mysterious -conditions of the solar beam, is such, that it is with -difficulty that imagination is restrained by the stern -features of truth. The uses of this peculiar property in -great natural phenomena are not yet made known to -us; but, since we find on every side of us the natural -conditions for thus separating the beam of light, and -effecting its polarization, there must certainly be some -most important end for which it is designed by Him -who said, “Let there be Light.”</p> - -<p>It must not be forgotten that we have at command -the means of showing that the chromatic phenomena of<span class="pagenum"><a name="Page_145" id="Page_145"></a>[Pg 145]</span> -polarized light are due to atomic arrangement. By -altering the molecular arrangement of transparent bodies, -either by heat or by mere mechanical pressure, the unequal -tension or strain of the particles is at once indicated -by means of the polarized ray of light and its -rings of colour. Differences in the chemical constitution -of bodies, too slight to be discovered by any other -mode of analysis, can be most readily and certainly -detected by this luminous investigator of the molecular -forces.<a name="FNanchor_101_101" id="FNanchor_101_101"></a><a href="#Footnote_101_101" class="fnanchor">[101]</a></p> - -<p>Although we cannot enter into an examination of all -the conditions involved in the polarization of, and the -action of matter on, ordinary light, it will be readily conceived, -from what has <span class="correction" title="In the original book: beeen">been</span> already stated, that some -most important properties are indicated, beyond those -which science has made known.</p> - -<p>Almost every substance in nature, in some definite -position, appears to have the power of producing this -change upon the solar ray, as may be satisfactorily shown -by examining them with a polarizing apparatus.<a name="FNanchor_102_102" id="FNanchor_102_102"></a><a href="#Footnote_102_102" class="fnanchor">[102]</a> The -sky at all times furnishes polarized light, which is most -intense where it is blue and unclouded, and the point of -maximum polarization is varied according to the relative -position of the sun and the observer. A knowledge of -this fact has led to the construction of a “Solar Clock,<span class="pagenum"><a name="Page_146" id="Page_146"></a>[Pg 146]</span>”<a name="FNanchor_103_103" id="FNanchor_103_103"></a><a href="#Footnote_103_103" class="fnanchor">[103]</a> -with which the hour can be readily determined by examining -the polarized condition of the sky. It has been stated, -that chemical change on the Daguerreotype plates and on -photographic papers is more readily produced by the -polarized than by the ordinary sunbeam.<a name="FNanchor_104_104" id="FNanchor_104_104"></a><a href="#Footnote_104_104" class="fnanchor">[104]</a> If this fact -be established by future investigations, we advance a -step towards the discovery so much desiderated of the -part it plays in natural operations.</p> - -<p>The refined and accurate investigations of Dr. Faraday -stand prominently forward amid those which will -redeem the present age from the charge of being superficial, -and they will, through all time, be referred to as -illustrious examples of the influence of a love of truth -for truth’s sake, in entire independence of the marketable -value, which it has been unfortunately too much -the fashion to regard. The searching examination made -by this “interpreter of nature” into the phenomena of -electricity in all its forms, has led him onward to trace -what connexion, if any, existed between this great -natural agent and the luminous principle.</p> - -<p>By employing that subtile analyzer, a polarized ray,<span class="pagenum"><a name="Page_147" id="Page_147"></a>[Pg 147]</span> -Dr. Faraday has been enabled to detect and exhibit -effects of a most startling character. He has proved -magnetism to have the power of influencing a ray of -light in its passage through transparent bodies. A -polarized ray is passed through a piece of glass or a -crystal, or along the length of a tube filled with some -transparent fluid, and the line of its path carefully -observed; if, when this is done, the solid or fluid body -is brought under powerful magnetic influence, such as -we have at command by making a very energetic voltaic -current circulate around a bar of soft iron, it will be -found that the polarized light is disturbed; that, indeed, it -does not permeate the medium along the same line.<a name="FNanchor_105_105" id="FNanchor_105_105"></a><a href="#Footnote_105_105" class="fnanchor">[105]</a> -This effect is most strikingly shown in bodies of the -greatest density, and diminished in fluids, the particles -of which are easily moveable over each other, and has -not hitherto been observed in any gaseous medium.<span class="pagenum"><a name="Page_148" id="Page_148"></a>[Pg 148]</span> -The question, therefore, arises,—does magnetism act -directly upon the ray of light, or only indirectly, by producing -a molecular change in the body through which -the ray is passing? This question, so important in its -bearings upon the connexion between the great physical -powers, will, no doubt, before long receive a satisfactory -reply. A medium is necessary to the production of the -result, and, as the density of the medium increases, the -effect is enlarged: it would therefore appear to be due -to a disturbance by magnetic force of the particles -which constitute the medium employed.</p> - -<p>Without any desire to generalize too hastily, we cannot -but express a feeling,—amounting to a certainty in -our own mind,—that those manifestations of luminous -power, connected with the phenomena of terrestrial -magnetism, which are so evident in all the circumstances -attendant upon the exhibition of Aurora Borealis, -and those luminous clouds which are often seen, -independent of the Northern Lights, that a very intimate, -relation exists between the solar radiations and -that power which so strangely gives polarity to this -globe of ours.</p> - -<p>In connexion with the mysterious subject of solar -light, it is important that we should occupy a brief -space in these pages with the phenomena of vision, which -is so directly dependent upon luminous radiation.</p> - -<p>The human eye has been rightly called the “masterpiece -of divine mechanism;” its structure is complicated, -yet all the adjustments of its parts are as simple as -they are perfect. The eye-ball consists of four coats. -The cornea is the transparent coat in front of the -globe; it is the first optical surface, and this is attached -to the sclerotic membrane, filling up the circular aperture -in the white of the eye; the choroid coat is a very -delicate membrane, lining the sclerotic, and covered -with a perfectly black pigment on the inside; and close -to this lies the most delicately reticulated membrane,<span class="pagenum"><a name="Page_149" id="Page_149"></a>[Pg 149]</span> -the retina, which is, indeed, an extension of the optic -nerve. These coats enclose three humours,—the aqueous, -the vitreous, and the crystalline humours.</p> - -<p>The eye, in its more superficial mechanical arrangements, -presents exactly the same character as a camera -obscura, the cornea and crystalline lens receiving the -images of objects refracting and inverting them; but -how infinitely more beautiful are all the arrangements of -the organ of vision than the dark chamber of Baptista -Porta!<a name="FNanchor_106_106" id="FNanchor_106_106"></a><a href="#Footnote_106_106" class="fnanchor">[106]</a> The humours of the eye are for the purpose -of correcting the aberrations of light, which are so -evident in ordinary lenses, and for giving to the whole -an achromatic character. Both spherical and chromatic -aberration are corrected, the latter not entirely, and by -the agency of the cornea and the crystalline lens perfect -images are depicted on the retina, in a similar way to -those very charming pictures which present themselves -in the table of the camera obscura.</p> - -<p>The seat of vision has been generally supposed to be -the retina; but Mariotte has shown that the base of the -optic nerve, which is immediately connected with the -retina, is incapable of conveying an impression to the -brain. The choroid coat, which lies immediately behind -the retina, is regarded by Mariotte and Bernoulli as the -more probable seat of vision. The retina, being transparent, -offers no obstruction to the passage of the light -onward to the black surface of the choroid coat, from -which the vibrations are, in all probability, communicated -to the retina and conveyed to the brain. Howbeit, upon -one or the other of these delicate coats a distinct image<span class="pagenum"><a name="Page_150" id="Page_150"></a>[Pg 150]</span> -is impressed by light, and the communication made -with the brain possibly by a vibratory action. We may -trace up the phenomena of vision to this point; we may -conceive undulations of light, differing in velocity and -length of wave, occasioning corresponding tremors in -the neuralgic system of the eye; but how these vibrations -are to communicate correct impressions of length, -breadth, and thickness, no one has yet undertaken to -explain.</p> - -<p>It has, however, been justly said by Herschel:—</p> - -<p>“It is the boast of science to have been able to trace -so far the refined contrivances of this most admirable -organ, not its shame to find something still concealed -from scrutiny; for, however anatomists may differ on -points of structure, or physiologists dispute on modes of -action, there is that in what we <i>do</i> understand of the -formation of the eye, so similar, and yet so infinitely -superior to a product of human ingenuity; such thought, -such care, such refinement, such advantage taken of the -properties of natural agents used as mere instruments -for accomplishing a given end, as force upon us a conviction -of deliberate choice and premeditated design, -more strongly, perhaps, than any single contrivance to -be found whether in art or nature, and renders its study -an object of the greatest interest.”<a name="FNanchor_107_107" id="FNanchor_107_107"></a><a href="#Footnote_107_107" class="fnanchor">[107]</a></p> - -<p>Has the reader ever asked himself why it is, having -two eyes, and consequently two pictures produced upon -the tablets of vision, that we see only one object? According -to the law of visible direction, all the rays passing -through the crystalline lenses converge to one point -upon the retina,—and as the two images are coincident -and nearly identical, they can only produce the sensation -of one upon the brain.</p> - -<p>When we look at any round object, as the ornamented -moderator lamp before us, first with one eye, and then -with the other, we discover that, with the right eye, we<span class="pagenum"><a name="Page_151" id="Page_151"></a>[Pg 151]</span> -see most of the right-hand side of the lamp, and with the -left eye more of the left-hand side. These two images -are combined, and we see an object which we know to -be round.</p> - -<p>This is illustrated in a most interesting manner by -the little optical instrument, <i>the Stereoscope</i>. It consists -either of two mirrors placed each at an angle of 45°, or -of two semi-lenses turned with their curved sides towards -each other. To view its phenomena, two pictures are -obtained by the camera obscura on photographic paper -of any object in two positions, corresponding with the -conditions of viewing it with the two eyes. By the -mirrors or the lenses these dissimilar pictures are combined -within the eye, and the vision of an actually solid -object is produced from the pictures represented on a -plane surface. Hence the name of the instrument; -which signifies, <i>Solid I see</i>.</p> - -<p>Analogy is often of great value in indicating the -direction in which to seek for a truth; but analogical -evidence, unless where the resemblance is very striking, -should be received with caution. Mankind are so ready -to leap to conclusions without the labour necessary for -a faithful elucidation of the truth, that too often a few -points of resemblance are seized upon, and an inference -is drawn which is calculated to mislead.</p> - -<p>There is an idea that the phenomena of sound bear a -relation to those of light,—that there exists a resemblance -between the chromatic and the diatonic scales. -Sound, we know, is conveyed by the beating of material -particles—the air—upon the auditory membrane of the -ear, which have been set in motion by some distant disturbance -of the medium through which it passes. Light -has been supposed to act on the optic nerve in the same -manner. If we imagine colour to be the result of vibrations -of different velocities and lengths, we can understand -that under some of these tremors, first established -on the nerves, and through them conveyed to the brain,<span class="pagenum"><a name="Page_152" id="Page_152"></a>[Pg 152]</span> -sensations of pain or pleasure may result, in the same -way as sharp or subdued sounds are disagreeable or -otherwise. Intensely coloured bodies do make an impression -upon perfectly blind men; and those who, -being born blind, know no condition of light or colour, -will point out a difference between strongly illuminated -red and yellow media. When the eyes are closed we -are sensible to luminous influence, and even to differences -of colour. We must consequently infer that light -produces some peculiar action upon the system of nerves -in general; this may or may not be independent of the -chemical agency of the solar radiations; but certainly -the excitement is not owing to any calorific influence. -The system of nerves in the eye is more delicately -organized, and of course peculiarly adapted to all the -necessities of vision.</p> - -<p>Thus far some analogy does appear to exist between -light and sound; but the phenomena of the one are so -much more refined than those of the other—the -impressions being all of them of a far more complicated -character, that we must not be led too far by the analogical -evidence in referring light, like sound, to mere -material motion.</p> - -<p>It was a beautiful idea that real impressions of external -objects are made upon the seat of vision, and that -they are viewed, as in a picture, by something behind -the screen,—that these pictures become dormant, but -are capable of being revived by the operations of the -mind in peculiar conditions; but we can only regard it -as a philosophical speculation of a poetic character, the -truth or falsehood of which we are never likely to be -enabled to establish.<a name="FNanchor_108_108" id="FNanchor_108_108"></a><a href="#Footnote_108_108" class="fnanchor">[108]</a></p> -<p><span class="pagenum"><a name="Page_153" id="Page_153"></a>[Pg 153]</span></p> -<p>That which sees will never itself be visible. The -secret principle of sensation,—the mystery of the life -that is in us,—will never be unfolded to finite minds.</p> - -<p>Numerous experiments have been made from time to -time on the influence of light upon animal life. It has -been proved that the excitement of the solar rays is too -great for the healthful growth of young animals; but, -at the same time, it appears probable that the development -of the functional organs of animals requires, in -some way, the influence of the solar rays. This might, -indeed, have been inferred from the discovery that -animal life ceases in situations from which light is -absolutely excluded. The instance of the Proteus of the -Illyrian lakes may appear against this conclusion. This -remarkable creature is found in the deep and dark -recesses of the calcareous rocks of Adelsburg, at Sittich; -and it is stated, also in Sicily, and in the Mammoth caves -of Kentucky. Sir Humphry Davy describes the Proteus -anguinus as “an animal to whom the presence of light -is not essential, and who can live indifferently in air and -in water, on the surface of the rock, or in the depths of -the mud.” The geological character of rocks, however, -renders it extremely probable that these animals may -have descended with the water, percolating through -fissures from very near the surface of the ground. All -the facts with which science has made us acquainted—and -both natural and physical science has been labouring -with most untiring industry in the pursuit of truth—go -to prove that light is absolutely <span class="correction" title="In the original book: neccessary">necessary</span> to -organization. It is possible the influence of the solar -radiations may extend beyond the powers of the human -senses to detect luminous or thermic action, and that<span class="pagenum"><a name="Page_154" id="Page_154"></a>[Pg 154]</span> -consequently a development of animal and vegetable -forms may occur where the human eye can detect no -light; and under such conditions the Proteus may be -produced in its cavernous abodes, and also those creatures -which live buried deep in mud. Some further consideration -of the probable agency of light will occupy us, -when we come to examine the phenomena of vital -forces.</p> - -<p>Light is essentially necessary to vegetable life; and -to it science refers the powers which the plant possesses -of separating carbon from the air breathed by the -leaves, and secreting it within its tissues for the purpose -of adding to its woody structure. As, however, -we have, in the growing plant, the action of several -physical powers exerted to different ends at the same -time, the remarkable facts which connect themselves -with vegetable chemistry and physiology are deferred for -a separate examination.</p> - -<p>The power of the solar rays to produce in bodies that -peculiar gleaming light which we call phosphorescence, -and the curious conditions under which this phenomenon -is sometimes apparent, independent of the sun’s -direct influence, present a very remarkable chapter in -the science of luminous powers.</p> - -<p>The phosphorescence of animals is amongst the most -surprising of nature’s phenomena, and it is not the -less so from our almost entire ignorance of the cause of -it. Many very poetical fancies have been applied in -description of these luminous creations; and imagination -has found reason why they should be gifted with -these extraordinary powers. The glow-worm lights her -lamp to lure her lover to her bower, and the luminous -animalcules of the ocean are employed in lighting up -the fathomless depths where the sun’s rays cannot -penetrate, to aid its monsters in their search for prey. -“The lamp of love—the pharos—the telegraph of the -night,—which scintillates and marks, in the silence of<span class="pagenum"><a name="Page_155" id="Page_155"></a>[Pg 155]</span> -darkness, the spot appointed for the lover’s rendezvous,”<a name="FNanchor_109_109" id="FNanchor_109_109"></a><a href="#Footnote_109_109" class="fnanchor">[109]</a> -is but a pretty fiction; for the glow-worm shines in its -infant state, in that of the larva, and when in its aurelian -condition. Of the dark depths of the ocean it may be -safely affirmed that no organized creation lives or -moves in its grave-like silence to require this fairy aid. -Fiction has frequently borrowed her creations from -science. In these cases science appears to have made -free with the rights of fiction.</p> - -<p>The glow-worms (<i>lampyris noctiluca</i>), it is well known, -have the power of emitting from their bodies a beautiful -pale bluish-white light, shining during the hours of -night in the hedge-row, like crystal spheres. It appears, -from the observations of naturalists, that these insects -never exhibit their light without some motion of the -body or legs;—from this it would seem that the -phosphorescence was dependent upon nervous action, -regulated at pleasure by the insect; for they certainly -have the power of obscuring it entirely. If the glow-worm -is crushed, and the hands or face are rubbed with -it, luminous streaks, similar to those produced by -phosphorus, appear. They shine with greatly increased -brilliancy in oxygen gas and in nitrous oxide. From -these facts may we not infer that the process by which -this luminosity is produced, whatever it may be, has a -strong resemblance to that of respiration?</p> - -<p>There are several varieties of flies, and three species of -beetles of the genus <i>Elater</i>, which have the power of -emitting luminous rays. The great lantern-fly of South -America is one of the most brilliant, a single insect -giving sufficient light to enable a person to read. In -Surinam a very numerous class of these insects are -found, which often illuminate the air in a remarkable -manner. In some of the bogs of Ireland a worm exists -which gives out a bright green light; and there are<span class="pagenum"><a name="Page_156" id="Page_156"></a>[Pg 156]</span> -many other kinds of creatures which, under certain -circumstances, become luminous in the dark. This is -always dependent upon vitality; for all these animals, -when deprived of life, cease to shine.</p> - -<p>At the same time we have many very curious -instances of phosphorescence in dead animal and -vegetable matter; the lobster among the Crustacea, and -the whiting among fishes, are striking examples; -decayed wood also emits much light under certain conditions -of the atmosphere. This development of light -does not appear to be at all dependent upon putrefaction; -indeed, as this process progresses, the luminosity -diminishes. We cannot but imagine that this light is -owing, in the first place, to direct absorption by, and -fixation within, the corpuscular structure of those bodies, -and that it is developed by the decomposition of the -particles under the influence of our oxygenous atmosphere.</p> - -<p>The pale light emitted by phosphorus in the dark is -well known; and this is evidently only a species of slow -combustion, a combination of the phosphorus with the -oxygen of the air. Where there is no oxygen, phosphorus -will not shine; its combustion in chlorine or iodine -vapour is a phenomenon of a totally different character -from that which we are now considering. This phosphorescence -of animal and vegetable matter has been -regarded as something different from the slow combustion -of phosphorus; but, upon examination, all the -chemical conditions are found to be the same, and it is -certainly due to a similar chemical change.</p> - -<p>The luminous matter of the dead whiting or the -mackerel may be separated by a solution of common -salt or of sulphate of magnesia; by concentrating these -solutions the light disappears; but it is again emitted -when the fluid is diluted. The entire subject is, however, -involved in the mystery of ignorance, although it -is a matter quite within the scope of any industrious<span class="pagenum"><a name="Page_157" id="Page_157"></a>[Pg 157]</span> -observer. The self-emitted light of the carbuncle of the -romancer is realized in these remarkable phenomena.</p> - -<p>The phosphorescence of some plants and flowers is -not, perhaps, of the same order as that which belongs to -either of the conditions we have been considering. It -appears to be due rather to an absorption of light and -its subsequent liberation. If a nasturtium is plucked -during sunshine, and carried into a dark room, the eye, -after it has reposed for a short time, will discover the -flower by a light emitted from its leaves.</p> - -<p>The following remarkable example, and an explanation -of it by the poet Goethe, is instructive:—</p> - -<p>“On the 19th of June, 1799, late in the evening, -when the twilight was deepening into a clear night, as I -was walking up and down the garden with a friend, we -very distinctly observed a flame-like appearance near -the oriental poppy, the flowers of which are remarkable -for their powerful red colour. We approached the place, -and looked attentively at the flowers, but could perceive -nothing further, till at last, by passing and repassing -repeatedly, while we looked side-ways on them, we succeeded -in renewing the appearance as often as we -pleased. It proved to be a physiological phenomenon, -and the apparent corruscation was nothing but the -spectrum of the flower in the complementary blue-green -colour. The twilight accounts for the eye being in a -perfect state of repose, and thus very susceptible, and -the colour of the poppy is sufficiently powerful in the -summer twilight of the longest days to act with full -effect, and produce a complementary image.”<a name="FNanchor_110_110" id="FNanchor_110_110"></a><a href="#Footnote_110_110" class="fnanchor">[110]</a></p> - -<p>The leaves of the <i>œnothera macrocarpa</i> are said to -exhibit phosphoric light when the air is highly charged -with electricity. The agarics of the olive-grounds of -Montpelier have been observed to be luminous at night; -but they are said to exhibit no light, even in darkness,<span class="pagenum"><a name="Page_158" id="Page_158"></a>[Pg 158]</span> -<i>during the day</i>. The subterranean passages of the coal -mines near Dresden are illuminated by the phosphorescent -light of the <i>rhizomorpha phosphoreus</i>, a peculiar -fungus. On the leaves of the Pindoba palm, a species -of agaric grows which is exceedingly luminous at night; -and many varieties of the lichens, creeping along the -roofs of caverns, lend to them an air of enchantment by -the soft and clear light which they diffuse. In a small -cave near Penryn, a luminous moss is abundant; and it -is also found in the mines of Hesse. According to -Heinzmann, the <i>rhizomorpha subterranea</i> and <i>aidulæ</i> -are also phosphorescent.</p> - -<p>It is but lately that a plant which abounds in the -jungles in the Madura district of the East Indies was -sent to this country, which, although dead, was -remarkably phosphorescent; and, when in the living -state, the light which it emitted was extraordinarily -vivid, illuminating the ground for some distance. -Those remarkable effects may be due, in some cases, to -the separation of phosphuretted hydrogen from decomposing -matter, and, in others, to some peculiar electric -manifestation.</p> - -<p>The phosphorescence of the sea, or that condition -called by fishermen <i>brimy</i>, when the surface, being struck -by an oar, or the paddle-wheels of a steamer, gives out -large quantities of light, has been attributed to the presence -of myriads of minute insects which have the power -of emitting light when irritated. The night-shining -nereis (<i>Nereis noctiluca</i>) emits a light of great brilliancy, -as do several kinds of the mollusca. The nereides -attach themselves to the scales of fishes, and thus -frequently render them exceedingly luminous. Some -of the crustaceæ possess the same remarkable property;—twelve -different species of <i>cancer</i> were taken up by -the naturalists of the Zaire in the Gulf of Guinea.<a name="FNanchor_111_111" id="FNanchor_111_111"></a><a href="#Footnote_111_111" class="fnanchor">[111]</a> The -<i>cancer fulgens</i>, discovered by Sir Joseph Banks, is<span class="pagenum"><a name="Page_159" id="Page_159"></a>[Pg 159]</span> -enabled to illuminate its whole body, and emits vivid -flashes of light. Many of the medusæ also exhibit -powerful phosphorescence.<a name="FNanchor_112_112" id="FNanchor_112_112"></a><a href="#Footnote_112_112" class="fnanchor">[112]</a> These noctilucous creatures -are, many of them, exceedingly minute, several thousands -being found in a tea-cup of sea water. They float -near the surface in countless myriads, and when disturbed -they give out brilliant scintillations, often leaving -a train of light behind them.<a name="FNanchor_113_113" id="FNanchor_113_113"></a><a href="#Footnote_113_113" class="fnanchor">[113]</a> By <span class="correction" title="In the original book: miscroscopic">microscopic</span> examination -no other fact has been elicited than that these -minute beings contain a fluid which, when squeezed out, -leaves a line of light upon the surface of water. The -appearance of these creatures is almost invariably on the -eve of some change of weather, which would lead us to -suppose that their luminous phenomena must be connected -with electrical excitation; and of this, the -investigations of Mr. C. Peach, of Fowey, communicated -to the British Association at Birmingham, furnish the -most satisfactory proofs we have as yet obtained.</p> - -<p>Benvenuto Cellini <span class="correction" title="In the original book: give">gave</span> a curious account of a carbuncle -which shone with great brilliancy in the dark.<a name="FNanchor_114_114" id="FNanchor_114_114"></a><a href="#Footnote_114_114" class="fnanchor">[114]</a> -The same thing has been stated of the diamond; but it -appears to be necessary to procure these emissions of<span class="pagenum"><a name="Page_160" id="Page_160"></a>[Pg 160]</span> -light, that the minerals should be first warmed <span class="correction" title="In the original book: near a a fire">near a -fire</span>. From this it may be <span class="correction" title="In the original book: infered">inferred</span> that the luminous -appearance is of a similar character to that of fluor -spar, and of numerous other earthy minerals, which, -when exposed to heat, phosphoresce with great brilliancy. -Phosphorescent glow can also be excited in similar -bodies by electricity, as was first pointed out by Father -Beccaria, and confirmed by Mr. Pearsall.<a name="FNanchor_115_115" id="FNanchor_115_115"></a><a href="#Footnote_115_115" class="fnanchor">[115]</a> These -effects, it must be remembered, are distinct from the -electric spark manifested upon breaking white sugar in -the dark, or scratching sulphuret of zinc.</p> - -<p>In the instances adduced there is not necessarily any -exposure to the sunshine required. It is probable that -two, if not three, distinct phenomena are concerned in -the cases above quoted, and that all of them are distinct -from animal phosphorescence, or the luminous appearance -of vegetables. They, however, certainly prove, -either that light is capable of becoming latent, or that it -is only a condition of matter, in which it may be made -manifest by any disturbance of the molecular forces.<span class="pagenum"><a name="Page_161" id="Page_161"></a>[Pg 161]</span> -We have, in answer to this, very distinct evidence that -some bodies do derive this property from the solar rays. -Canton’s phosphorus, which is a sulphuret of calcium, -will, having been exposed to the sun, continue luminous -for some time after it is carried into the dark; as will -also the Bolognian stone,—a sulphuret of barium. This -result appears to be due to a particular class of the solar -rays; for it has been found, if these sulphurets, spread -smoothly on paper, are exposed to the influence of the -solar spectrum for some little time, and then examined -in the dark, that luminous spaces appear, exactly corresponding -with the most refrangible rays, or those -which excite chemical change; and one very remarkable -fact must not be forgotten—the dark rays of the spectrum -beyond the violet produce a lively phosphorescence, -which is <i>extinguished</i> by the action of the rays of least -refrangibility, or the heat rays—whilst artificial heat, -such as a warm iron, produces a very considerable -elevation of the phosphorescent effect.<a name="FNanchor_116_116" id="FNanchor_116_116"></a><a href="#Footnote_116_116" class="fnanchor">[116]</a> It is not improbable, -that the fluorescent rays of Mr. Stokes may be -materially concerned in producing the phenomena of -phosphorescence: experiments are, however, required to -prove this.</p> - -<p>In these allied phenomena we have effects which are -evidently dependent upon several dissimilar causes. -The phosphorescence of the living animal is due, without -doubt, to nervous excitation: that of the living -vegetable to solar luminous influence; and in the case -of the mosses of caverns, &c. to the chemical agency of -the sun’s rays, which appears to be capable of conduction. -In the dead organic matter we have a purely -chemical action developing the light, and in the inor<span class="pagenum"><a name="Page_162" id="Page_162"></a>[Pg 162]</span>ganic -bodies we have peculiar molecular constitution, by -which an absorption of light appears to take place.</p> - -<p>The subject is one of the greatest difficulty; the -torch of science is too dim to enable us to see the causes -at work in producing these marvellous effects. The -investigation leads, to a certain extent, to the elucidation -of many of the secrets of luminous action; and the -determination of the question, whether light is an -emanation from the sun, or only a subtile principle -diffused through all matter, which is excited by solar -influence, is intimately connected with the inquiry.</p> - -<p>It has been stated that matter is necessary to the -development of light; that no luminous effect would be -produced if it were not for the presence of matter. Of -this we not only have no proof, but such evidence as we -have is against the position. There is no loss of light in -the most perfect vacuum we can produce by any artificial -means, which should be the case if matter was concerned -in the phenomena of light, as a cause.</p> - -<p>Colour is certainly a property regulated by material -bodies; or rather, the presence of matter is necessary to -the production of colour. Chlorine gas is a pale yellow, -and nitrous vapour a yellowish red. These and one or -two other vapours, which are near the point of condensation -into fluids, are the only coloured gaseous or -vaporiform bodies. The sky is blue, because the -material particles of the atmosphere reflect back the -blue rays. But we have more practical illustrations -than this. The flame of hydrogen burning with oxygen -gives scarcely any light; allow it to impinge on lime, a -portion of which is carried off by the heat of the flame, -and the most intense artificial light with which we are -acquainted is produced. Hydrogen gas alone gives a -flame in which nearly all but the blue rays are wanting: -place a brush of steel or asbestos in it, and many of the -other rays are at once produced. An argand lamp, and -more particularly the lamp in which camphine—a<span class="pagenum"><a name="Page_163" id="Page_163"></a>[Pg 163]</span> -purified turpentine,—is burnt, gives a flame which emits -most of the rays found in sunlight. Spirit of wine -mixed with water, warmed and ignited, gives only yellow -rays; add nitrate of strontian and they become red; but -nitrate of barytes being mixed with the fluid, they are -changed to green and yellow; salts of copper afford fine -blue rays, and common salt intense yellow ones. Many -of these coloured rays and others can be produced in -great power by the use of various solid bodies introduced -into flame. This has not been sufficiently pointed out -by authors; but it is clear from experiments that light -requires the presence of matter to enable it to diffuse its -coloured glories. How is it that the oxygen and -hydrogen flame gives so little light, and with a solid -body present, pours forth such a flood of brilliancy?</p> - -<p>The production of artificial light by electrical and -chemical agencies will necessarily find some consideration -under their respective heads. There are numerous -phenomena which connect themselves with luminous -power, or appear to do so, which, in the present state of -our knowledge, cannot come immediately under our -attention. We are compelled to reserve our limited -space for those branches of science which we are enabled -to connect with the great natural operations constantly -going on around us. Many of these more abstruse -results will, however, receive some incidental notice -when we come to examine the operation of the combined -physical forces on matter.</p> - -<p>We see in light a principle which, if it has not its -source in the sun, is certainly dependent upon that -luminary for its manifestations and powers. From that -“fountain of light” we find this principle travelling to -us at a speed which almost approaches the quickness of -thought itself; yet by the refinements of science we -have been enabled to measure its velocity with the -utmost accuracy. The immortal poet of our own land -and language, in his creations of Ariel, that “tricksy<span class="pagenum"><a name="Page_164" id="Page_164"></a>[Pg 164]</span> -spirit,” who could creep like music upon the waters, and -of the fantastic Puck, who could girdle the earth in -thirty minutes, appears to have approached to the -highest point to which mere imagination could carry the -human mind as to the powers of things ethereal. -Science has, since then, shown to man that this “spirit, -fine spirit,” was a laggard in his tasks, and a gross piece -of matter, when compared with the subtile essences -which man, like a nobler Prospero, has now subdued to -do him service.</p> - -<p>Light is necessary to life; the world was a dead -chaos before its creation, and mute disorder would again -be the consequence of its annihilation. Every charm -which spreads itself over this rolling globe is directly -dependent upon luminous power. Colours, and probably, -forms, are the result of light; certainly the consequence -of solar radiations. We know much of the -mysterious influences of this great agent, but we know -nothing of the principle itself. The solar beam has -been tortured through prismatic glasses and natural -crystals; every chemical agent has been tried upon it, -every electrical force in the most excited state brought -to bear upon its operations, with a view to the discovery -of the most refined of earthly agencies; but it has passed -through every trial without revealing its secrets, and -even the effects which it produces in its path are unexplained -problems, still to tax the intellect of man.</p> - -<p>Every animal and every plant alike proclaim that life -and health are due to light; and even the crystallizing -forms of inorganic matter, by bending towards it, confess -its all-prevailing sway. From the sun to each -planet revolving around that orb, and to the remotest -stars which gleam through the vast immensity of heaven, -we discover this power still in its brightness, giving -beauty and order to these unnumbered creations; no -less completely than to this small island of the universe -which we call our Earth. Through every form of matter<span class="pagenum"><a name="Page_165" id="Page_165"></a>[Pg 165]</span> -we can mark its power, and from all, we can, under certain -conditions, evoke it in lustre and activity. Over all -and through all light spreads its ethereal force, and manifests, -in all its operations, powers which might well exalt -the mind of Plato to the idea of an omniscient and omnipresent -God. Science, with her Ithuriel wand, has, however, -shown that light is itself the effect of a yet more -exalted cause, which we cannot reach.</p> - -<p>Indeed, the attentive study of the fine abstractions of -science lifts the mind from the grossness of matter, step -by step, to the refinements of immateriality, and there -appear, shadowed out beyond the physical forces which -man can test and try, other powers still ascending, until -they reach the Source of every good and every perfect -gift.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_84_84" id="Footnote_84_84"></a><a href="#FNanchor_84_84"><span class="label">[84]</span></a> “These—oxygen, hydrogen, nitrogen, and carbon—are the -four bodies, in fact, which, becoming animated at the fire of the -sun, the true torch of Prometheus, approve themselves upon the -earth the eternal agents of organisation, of sensation, of motion -and of thought.”—Dumas, <i>Leçons de Philosophie Chimique</i>, p. 100. -Paris, 1837.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_85_85" id="Footnote_85_85"></a><a href="#FNanchor_85_85"><span class="label">[85]</span></a> It will be found in examining any of the works of the alchemists,—particularly -those of Geber, <i>De inveniendi arte Auri et -Argenti</i>, and his <i>De Alchemiâ</i>; Roger Bacon’s <i>Opus Majus, or -Alchymia Major</i>; Helvetius’ <i>Brief of the Golden Calf</i>; or Basil -Valentine’s <i>Currus Triumphalis</i>,—that in the processes of transmutation -the solar light was supposed to be marvellously effective. -In Boyle’s <i>Sceptical Chemist</i> the same idea will be found pervading -it. -</p> -<p> -Amid all their errors, the alchemists were assiduous workmen, -and to them we are indebted for numerous facts. Of them, -and of their age, as contrasted with our own, Gibbon remarks:—“Congenial -to the avarice of the human heart, it was studied in -China, as in Europe, with equal eagerness and equal success. The -darkness of the middle ages ensured a favourable reception to -every tale of wonder; and the revival of learning gave new vigour -to hope, and suggested more specious arts of deception. Philosophy, -with the aid of experience, has at length banished the study -of alchemy; and the present age, however desirous of riches, is -content to seek them by the humbler means of commerce and industry.”—<i>Decline -and Fall</i>, vol. ii. p. 137.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_86_86" id="Footnote_86_86"></a><a href="#FNanchor_86_86"><span class="label">[86]</span></a> On the two theories the following maybe consulted:—Young, -<i>Supplement to Encyclopædia Britannica</i>, article <i>Chromatics</i>; Fresnel, -<i>Supplément à la Traduction Française de la 5ième édition du -Traité de Chimie de Thomson</i>, par Riffault, Paris, 1822; Herschel’s -Article, <i>Light</i>, in the Encyclopædia Metropolitana, and the French -Translation of it by Quetelet and Verhulst; Airy’s <i>Tract on the -Undulatory Theory</i>, in his Tracts, 2nd edition, Cambridge, 1831; -Powel, <i>The Undulatory Theory applied to Dispersion</i>, &c. p. 184; -Lloyd’s <i>Lectures</i>, Dublin, 1836–41; Cauchy, <i>Sur le Mouvement des -Corps élastiques</i>, Mémoires de l’Institut, 1827, vol. ix. p. 114; -<i>Théorie de la Lumière</i>, Ibid. vol. x. p. 293; M’Cullagh, <i>On Double -Refraction</i>, Ibid., vol. xvi.; <i>Geometrical Propositions applied to the -Wave Theory of Light</i>, Ibid., vol. xvii.; Sir David Brewster’s -papers in the Transactions of the Royal Society of Edinburgh, and -the Philosophical Magazine.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_87_87" id="Footnote_87_87"></a><a href="#FNanchor_87_87"><span class="label">[87]</span></a> <i>Results of Astronomical Observations made during the years -1834–38, at the Cape of Good Hope, &c.</i> By Sir John Herschel, -Bart., K.H., D.C.L., F.R.S.—“In the contemplation of the infinite, -in number and in magnitude, the mind ever fails us. We -stand appalled before this mighty spectre of boundless space, and -faltering reason sinks under the load of its bursting conceptions. -But, placed as we are on the great locomotive of our system, destined -surely to complete at least one round of its ethereal course, -and learning that we can make no apparent advance on our sidereal -journey, we pant with new ardour for that distant bourne -which we constantly approach without the possibility of reaching -it. In feeling this disappointment, and patiently bearing it, let us -endeavour to realise the great truth from which it flows. It cannot -occupy our mind without exalting and improving it.”—<i>Sir D. -Brewster</i>: North British Review.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_88_88" id="Footnote_88_88"></a><a href="#FNanchor_88_88"><span class="label">[88]</span></a> For examples of this, consult Graham’s <i>Elements of Chemistry</i>; -Brande’s <i><span class="correction" title="In the original book: Mannal">Manual</span> of Chemistry</i>; or, indeed, any work -treating of the science. The formation of ink, by mixing two -colourless solutions, one of gallic acid and another of sulphate of -iron, may be taken as a familiar instance.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_89_89" id="Footnote_89_89"></a><a href="#FNanchor_89_89"><span class="label">[89]</span></a> Sir John Herschel, in his paper <i>On the Chemical Action of the -Rays of the Solar Spectrum on Preparations of Silver</i>, remarks that, -“it may seem too hazardous to look for the cause of this very singular -phenomenon in a real difference between the chemical agencies -of those rays which issue from the central portion of the sun’s -disc, and those which, emanating from its borders, have undergone -the absorptive action of a much greater depth of its atmosphere; -and yet I confess myself somewhat at a loss what other cause to -assign for it. It must suffice, however, to have thrown out the -hint; remarking only, that I have other, and, I am disposed to -think, decisive evidence (which will find its place elsewhere) of the -existence of an absorptive solar atmosphere, extending beyond the -luminous one. The breadth of the border, I should observe, is -small, not exceeding 0·5 or 1/7 part of the sun’s radius, and this, -from the circumstances of the experiment, must necessarily err in -excess.”—Philosophical Transactions, 1840.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_90_90" id="Footnote_90_90"></a><a href="#FNanchor_90_90"><span class="label">[90]</span></a> <i>Experiments and Observations on some Cases of Lines in the -Prismatic Spectrum, produced by the passage of Light through -Coloured Vapours and Gases, and from certain Coloured Flames.</i> -By W. A. Miller, M.D., F.R.S., Professor of Chemistry in King’s -College, London.—Philosophical Magazine, vol. xxvii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_91_91" id="Footnote_91_91"></a><a href="#FNanchor_91_91"><span class="label">[91]</span></a> <i>Report on the Mollusca and Radiata of the Ægean Sea, and -on their distribution, considered as bearing on Geology.</i> By Edward -Forbes, F.R.S., &c.—Reports of the British Association, vol. xii. Professor -Forbes remarks:—“A comparison of the testacea, and other -animals of the lowest zones, with those of the higher, exhibits a -very great distinction in the hues of the species, those of the -depths being, for the most part, white or colourless, while those of -the higher regions, in a great number of instances, exhibit brilliant -combinations of colour. The results of an enquiry into this subject -are as follows:— -</p> -<p> -“The majority of shells of the lowest zone are white or transparent; -if tinted rose is the hue, a very few exhibit markings of -another colour. In the seventh region, white species are also -very abundant, though by no means forming a proportion so great -as the eighth. Brownish red, the prevalent hue of the brachiopoda, -also gives a character of colour to the fauna of this zone; -the crustacea found in it are red. In the sixth zone the colours -become brighter, reds and yellows prevailing,—generally, however, -uniformly colouring the shell. In the fifth region many -species are banded or clouded with various combinations of colours, -and the number of white species has greatly diminished. In the -fourth, purple hues are frequent, and contrasts of colour common. -In the second and third, green and blue tints are met with, sometimes -very vivid; but the gayest combinations of colour are seen -in the littoral zone, as well as the most brilliant whites. -</p> -<p> -“The animals of Testacea, and the Radiata of the higher zones, -are much more brilliantly coloured than those of the lower, where -they are usually white, whatever the hue of the shell may be. -Thus the genus <i>Trochus</i> is an example of a group of forms mostly -presenting the most brilliant hues both of shell and animal; but -whilst the animals of such species as inhabit the littoral zone are -gaily chequered with many vivid hues, those of the greater depth, -though their shells are almost as brightly covered as the coverings -of their allies nearer the surface, have their animals, for the most -part, of a uniform yellow or reddish hue, or else entirely white. -The chief cause of this increase of intensity of colour as we ascend -is, doubtless, the increased amount of light above a certain depth.”—p. -172.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_92_92" id="Footnote_92_92"></a><a href="#FNanchor_92_92"><span class="label">[92]</span></a> Ἁμὁρφωτα. <i>On the Epipolic Dispersion of Light</i>, being a -paper entitled, <i>On a case of Superficial Colour presented, by a homogeneous -liquid internally colourless</i>. By Sir J. F. W. Herschel, -Bart, K.H., F.R.S., &c.—<i>An epipolized beam of light</i> (meaning -thereby a beam which has once been transmitted through a quiniferous -solution, and undergone its dispersing action) <i>is incapable -of further undergoing epipolic dispersion</i>. In proof of this the following -experiment may be adduced,— -</p> -<p> -A glass jar being filled with a quiniferous solution, a piece of -plate glass was immersed in it vertically, so as to be entirely -covered, and to present one face directly to the incident light. In -this situation, when viewed by an eye almost perpendicularly over -it, so as to graze either surface very obliquely, neither the anterior -nor posterior face showed the slightest trace of epipolic colour. -Now, the light, at its egress from the immersed glass, entered the -liquid under precisely the same circumstances as that which, when -traversing the anterior surface of the glass jar, underwent epipolic -dispersion on first entering the liquid. It had, therefore, lost a -property which it originally possessed, and could not, therefore, be -considered <i>qualitatively</i> the same light.—Philosophical Transactions, -vol. cxxxvi.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_93_93" id="Footnote_93_93"></a><a href="#FNanchor_93_93"><span class="label">[93]</span></a> In connection with this view, the Newtonian theory should -be consulted, for which see—<i>A Letter of</i> Mr. Isaac Newton, <i>Professor -of the Mathematicks in the University of Cambridge; containing -his new Theory about Light and Colors: sent by the Author -to the Publisher, from Cambridge, Feb. 6, 1671–72, in order to be -communicated to the Royal Society.</i></p></div> - -<div class="footnote"> - -<p><a name="Footnote_94_94" id="Footnote_94_94"></a><a href="#FNanchor_94_94"><span class="label">[94]</span></a> In that admirable work, <i>The Physical Atlas</i> of Dr. Berghaus, -of which a very complete edition by Alexander Keith Johnstone -is published in this country, the following order of the distribution -of plants is given:— -</p> -<table summary="distribution of plants"> -<tr><td>1. The region of palms and bananas</td><td class="tdpad">Equatorial zone.</td></tr> -<tr><td>2. Tree ferns and figs</td><td class="tdpad">Tropical zone.</td></tr> -<tr><td>3. Myrtles and laurels</td><td class="tdpad">Sub-tropical zone.</td></tr> -<tr><td>4. Evergreen trees</td><td class="tdpad">Warm temperate zone.</td></tr> -<tr><td>5. European trees</td><td class="tdpad">Cold temperate zone.</td></tr> -<tr><td>6. Pines</td><td class="tdpad">Sub-arctic zone.</td></tr> -<tr><td>7. Rhododendrons</td><td class="tdpad">Arctic zone.</td></tr> -<tr><td>8. Alpine plants</td><td class="tdpad">Polar zone.</td></tr> -</table> - -<p> -Consult Humboldt, <i>Essai sur la Géographie des Plantes</i>, Paris, -1807; <i>De Distributione Geographicâ Plantarum</i>, Paris, 1817. -Schouw, <i><span class="correction" title="In the original book: Grundüzge">Grundzüge</span> der Pflanzengeographie</i>. Also his <i>Earth, Plants, -and Man</i>; translated by Henfrey, in <i>Bohn’s Scientific Library</i>. -Lamouroux, <i>Géographie Physique</i>. <i>The Plant, a Biography</i>: by -Schleiden; translated by Henfrey. <i>Physical Geography</i>: by -Mrs. Somerville.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_95_95" id="Footnote_95_95"></a><a href="#FNanchor_95_95"><span class="label">[95]</span></a> <span class="correction" title="In the original book: Frauenhofer’s">Fraunhofer’s</span> measure of illuminating power is as follows:— -</p> -<table summary="Fraunhofer's measure of illuminating power"> -<tr><td>At the</td><td>22nd degree of the red</td><td class="tdpad">0·032</td></tr> -<tr><td class="tdc">"</td><td>34th degree of the red</td><td class="tdpad">0·094</td></tr> -<tr><td class="tdc">"</td><td>22nd degree of the orange</td><td class="tdpad">0·640</td></tr> -<tr><td class="tdc">"</td><td>10th degree of the yellow</td><td class="tdpad">1·000</td></tr> -<tr><td class="tdc">"</td><td>42nd degree of the yellow</td><td class="tdpad">0·480</td></tr> -<tr><td class="tdc">"</td><td>2nd degree of the blue</td><td class="tdpad">0·170</td></tr> -<tr><td class="tdc">"</td><td>16th degree of the indigo</td><td class="tdpad">0·031</td></tr> -<tr><td class="tdc">"</td><td>43rd degree of the violet</td><td class="tdpad">0·0056</td></tr> -</table> -</div> - -<div class="footnote"> - -<p><a name="Footnote_96_96" id="Footnote_96_96"></a><a href="#FNanchor_96_96"><span class="label">[96]</span></a> Herschel, <i>On the Action of Crystallized Bodies on Homogeneous -Light, and on the causes of the deviation from Newtons scale -in the tints which many of them develope on exposure to a polarized -ray</i>.—Phil. Trans., vol. cx., p. 88.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_97_97" id="Footnote_97_97"></a><a href="#FNanchor_97_97"><span class="label">[97]</span></a> <i>On the Nature of Light and Colours</i>: Lecture 39, in Young’s -<i>Lectures on Natural Philosophy</i>, Kelland’s Edition, p. 373, and the -authorities there quoted.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_98_98" id="Footnote_98_98"></a><a href="#FNanchor_98_98"><span class="label">[98]</span></a> Brewster’s <i>Optics</i>: Lardner’s Cabinet Cyclopædia. Herschel, -<i>On Light</i>: Encyclopædia Metropolitana.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_99_99" id="Footnote_99_99"></a><a href="#FNanchor_99_99"><span class="label">[99]</span></a> Malus, <i>Sur une Propriété de la Lumière Réfléchie</i>: <span class="correction" title="In the original book: Memoires">Mémoires</span> -d’Arcueil. Numerous memoirs by Sir David Brewster, in the -Philosophical Transactions.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_100_100" id="Footnote_100_100"></a><a href="#FNanchor_100_100"><span class="label">[100]</span></a> Bartholin, <i>On Iceland Crystals</i>: Copenhagen, 1669. <i>An Accompt -of sundry Experiments made and communicated by that Learn’d -Mathematician</i> Dr. Erasmus Bartholin, <i>upon a Chrystal like -Body sent to him out of Island</i>: in connection with which Dr. -Matthias Paissenius writes:—The observations of the excellent -Bartholin upon the Island Chrystal are, indeed, considerable, as -well as painful. We have here, also, made some tryals of it upon -a piece he presented me with, which confirm his observations. -Mean time he found it somewhat scissile and reducible by a knife -into thin laminas or plates, which, when single, shew’d the object -single, but laid upon one another shew’d it double; the two images -appearing the more distant from one another, the greater the number -was of those thin plates laid on one another. With submission -to better judgements I think it to be a kind of Selenites. Some -of our curious men here were of opinion that the Rhomboid figure -proper to this stone was the cause of the appearances doubled -thereby. But having tryed whether in other transparent bodies -of the like figure the like would happen, we found no such thing -in them, which made us suspect some peculiarity in the very Body -of the stone.—Phil. Trans. for 1670, vol. v.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_101_101" id="Footnote_101_101"></a><a href="#FNanchor_101_101"><span class="label">[101]</span></a> <i>On the Application of the Laws of Circular Polarization to the -Researches of Chemistry</i>: by M. Biot.—Nouvelles Annales du -Muséum d’Histoire Naturelle, vol. iii., and Scientific Memoirs, -vol. i. p. 600. <i>On Circular Polarization</i>: by Dr. Leeson.—Memoirs -of the Chemical Society.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_102_102" id="Footnote_102_102"></a><a href="#FNanchor_102_102"><span class="label">[102]</span></a> In Sir David Brewster’s Treatise <i>On Optics</i>, chap, xviii., <i>On -Polarization</i>, the best arrangements for a polarizing apparatus will -be found described.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_103_103" id="Footnote_103_103"></a><a href="#FNanchor_103_103"><span class="label">[103]</span></a> This beautiful application was recently made by Professor -Wheatstone, the particulars of which will be found in his interesting -communication.—<i>On a means of determining the apparent -Solar Time by the diurnal changes of the Plane of Polarization -at the Northern Pole of the Sky</i>: Report of the Eighteenth -Meeting of the British Association.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_104_104" id="Footnote_104_104"></a><a href="#FNanchor_104_104"><span class="label">[104]</span></a> <i>On the Polarization of the Chemical Rays of Light</i>: by -John Sutherland, M.D., in which the author refers to the following -experiment of M. J. E. Bérard—“I received the chemical -rays directed into the plane of the meridian on an unsilvered glass, -under an incidence of 35° 61'. The rays reflected by the first glass -were received upon a second, under the same incidence. I found -that when this was turned towards the south, the muriate of silver -exposed to the invisible rays which it reflected was darkened in -less than half an hour; whereas, when it was turned towards the -west, the muriate of silver exposed in the place where the rays -ought to have been reflected, was not darkened, although it was -left exposed for two hours. It is consequently to be presumed -that the chemical rays can undergo double refraction in traversing -certain diaphanous bodies; and lastly, we may say that they enjoy -the same physical properties as light in general.”—Philosophical -Magazine, vol. xx. -</p> -<p> -Dr. Leeson has stated that Daguerreotype pictures can be taken -more readily under the influence of polarized light, than by ordinary -radiation.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_105_105" id="Footnote_105_105"></a><a href="#FNanchor_105_105"><span class="label">[105]</span></a> <i>On the Magnetization of Light, and the Illumination of Magnetic -Lines of Force</i>: by Michael Faraday, D.C.L., F.R.S.—Philosophical -Transactions, vol. cxxxvii.—The following remarks are to the -point of doubt referred to in the text.—“The magnetic forces do -not act on the ray of light directly and without the intervention of -matter, but through the mediation of the substance in which they -and the ray have a simultaneous existence; the substances and -the forces giving to and receiving from each other the power of -acting on the light. This is shown by the non-action of a vacuum, -of air or gases, and it is also further shown by the special degree -in which different matters possess the property. That magnetic -force acts upon the ray of light always with the same character of -manner, and in the same direction, independent of the different -varieties of substance, or their states of solid or liquid, or their -specific rotative force, shows that the magnetic force and the light -have a direct relation; but that substances are necessary, and that -these act in different degrees, shows that the magnetism and the -light act on each other through the intervention of the matter. -Recognising or perceiving <i>matter</i> only by its powers, and knowing -nothing of any imaginary nucleus abstract from the idea of these -powers, the phenomena described must strengthen my inclination -to trust in the views I have advanced in reference to its nature.”—Phil. -Mag. vol. xxiv.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_106_106" id="Footnote_106_106"></a><a href="#FNanchor_106_106"><span class="label">[106]</span></a> The invention of the camera obscura certainly belongs to -Giambattista Porta, and is described in his <i>Magiæ Naturalis, sive -de Miraculis Rerum Naturalium, Libri Viginti</i>; Antwerp, 1561. -An English translation made in 1658 exists, but I have not seen -it. -</p> -<p> -Hooke, in one of the earliest volumes of the Philosophical Transactions, -describes as new many of the phenomena mentioned by -Porta, and particularly the images of the dark chamber.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_107_107" id="Footnote_107_107"></a><a href="#FNanchor_107_107"><span class="label">[107]</span></a> Herschel, <i>On Light</i>,—Encyclopædia Metropolitana.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_108_108" id="Footnote_108_108"></a><a href="#FNanchor_108_108"><span class="label">[108]</span></a> “I would here observe that a consideration of many such -phenomena (the obliteration and revival of photographic drawings) -has led me to regard it as not impossible that the retina itself may -be <i>photographically</i> impressed by strong light, and that some at -least of the phenomena of visual spectra and secondary colours -may arise from the sensorial perception of actual changes in progress -in the physical state of that organ itself subsequent to the -cessation of the direct stimulant.”—<i>On the action of the Rays of -the Solar Spectrum on Vegetable Colours, &c.</i>: by Sir J. F. W. -Herschel, Bart.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_109_109" id="Footnote_109_109"></a><a href="#FNanchor_109_109"><span class="label">[109]</span></a> Dumeril.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_110_110" id="Footnote_110_110"></a><a href="#FNanchor_110_110"><span class="label">[110]</span></a> <i>Theory of Colours</i>: by Goethe; translated by Eastlake.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_111_111" id="Footnote_111_111"></a><a href="#FNanchor_111_111"><span class="label">[111]</span></a> See Tuckey’s Narrative of the Expedition of the Zaire.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_112_112" id="Footnote_112_112"></a><a href="#FNanchor_112_112"><span class="label">[112]</span></a> The most complete examination of this subject will be found -in two Memoirs:— -</p> -<p> -1. <i>Experiments and observations on the light which is spontaneously -emitted with some degree, of permanency from various bodies.</i>—Phil. -Trans., vol. xc. -</p> -<p> -2. <i>A continuation of the above, with some experiments and observations -on solar light, when imbibed by Canton’s phosphorus</i>: by -Nathaniel Hulm, M.D.—Phil. Trans., vol. xci.; and in the <i>Monograph -of the British Naked-eyed Medusæ</i>, by Professor Edward -Forbes (published for the Ray Society). See Wilson’s note to the -account of <i>Pennalata phosphorea</i> in Johnston’s Zoophytes, 2nd -edition.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_113_113" id="Footnote_113_113"></a><a href="#FNanchor_113_113"><span class="label">[113]</span></a> <i>A General Outline of the Animal Kingdom</i>: by Thomas Rymer -Jones, F.L.S.—Acalephæ, p. 64. <i>Lettre à M. Dumas sur la Phosphorescence -des Vers luisants</i>: par M. Ch. Matteucci.—Annales de -Chimie, vol. ix. p. 71, 1843.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_114_114" id="Footnote_114_114"></a><a href="#FNanchor_114_114"><span class="label">[114]</span></a> <i>Memoirs of Benvenuto Cellini—Bohn’s Standard Library.</i> See -also his Treatise on his Art as a Sculptor and Engraver. Florence, -1568. 4to.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_115_115" id="Footnote_115_115"></a><a href="#FNanchor_115_115"><span class="label">[115]</span></a> <i>Phosphorescence of the Diamond</i>: by M. Reiss (Revue Scientifique -et Industrielle, vol. xxiii. p. 185).—“The diamond, phosphorescent -by insulation, lost rapidly its phosphorescence when -submitted to the action of the red rays of the solar spectrum. -On the contrary, the blue rays are those which render the diamond -the most luminous in the dark. It is probable that the phosphorescence -produced by heat is equally diminished by the action of -the red rays of the solar spectrum.” Giovanni Battista Beccaria -published his experiments in 1769. See Priestley’s <i>History of -Electricity</i>; and <i>On the Effects of Electricity upon Minerals which -are Phosphorescent by Heat</i>; and <i>Further Experiments on the communication -of Phosphorescence and Colour to bodies of Electricity</i>; -by Thomas J. Pearsall.—Journal of the Royal Institution of -Great Britain, Oct. 1830, Feb. 1831.—These two memoirs contain -the most complete set of experiments on this subject which have -yet been made; see <i>Placidus Heinrich</i>, <i>Phosphorescenz der Körper</i>, -vol. iv.; Gmelin’s <i>Handbuch der Chemie</i>, part 1.;—<i>On the Phosphorescence -of Minerals</i>, Brewster: Edinburgh Philosophical -Journal, vol. i. p. 137.;—<i>The Aërial Noctiluca, or some New -Phenomena, and a process of a factitious self shining substance</i>: -Boyle’s Works, vol. iv.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_116_116" id="Footnote_116_116"></a><a href="#FNanchor_116_116"><span class="label">[116]</span></a> <i>Des Effets produits sur les corps par les Rayons Solaires</i>: -par M. Edmond Becquerel.—Annales de Chimie, vol. ix. p. 257. -1843. -</p> -<p> -M. Becquerel has applied the term <i>phosphorogénique</i> to those -rays producing phosphorescence.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_166" id="Page_166"></a>[Pg 166]</span></p> - - - -<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII.</h2> - -<p class="center">ACTINISM—CHEMICAL RADIATIONS.</p> - - -<p class="chap-head">The Sun-ray and its Powers—Darkening of Horn Silver—Niepce’s -Discovery—Prismatic Spectrum—Refrangibility of -Light, Heat, and Actinism—Daguerre’s Discovery—Photography—Chemical -Effects produced by Solar Radiations—Absorption -of Actinism—Phenomena of the Daguerreotype—Chemical -Change produced upon all Bodies—Power of -Matter to restore its Condition—Light protects from Chemical -Change—Photographs taken in Darkness—Chemical -Effects of Light on organized Forms—Chemical Effects of -Solar Heat—Influence of Actinism on Electricity—Radiations -in Darkness—Moser’s Discoveries, &c.</p> - - -<p class="p2">Heat and light are derived from the sun, and we have -attempted to show, not only that the phenomena of -these two principles are different, but that they can -scarcely, in the present condition of our knowledge, be -regarded as modified manifestations of <i>one</i> superior -power. Associated with these two remarkable elements, -others may exist in the solar rays. Electrical phenomena -are certainly developed by both heat and light, -and peculiar electric changes are produced by exposure -to sunshine. Electricity may be merely <i>excited</i> by the -solar rays, or it may <i>flow</i> like light from the sun. -Chemical action may be only due to the disturbance of -some diffused principle; or it may be directly owing to -some agency which is radiated at once from the sun.</p> - -<p>A sun ray is a magical thing: we connect it in our -fancy with the most ethereal of possible creations. Yet -in its action on matter it produces colour; it separates -the particles of solid masses farther from each other,<span class="pagenum"><a name="Page_167" id="Page_167"></a>[Pg 167]</span> -and it breaks up some of the strongest forces of chemical -affinity. To modern science is entirely due the -knowledge we have gained of the marvellous powers of -the sunbeam; and it has rendered us familiar with -phenomena, to which the incantation scenes of the -Cornelius Agrippas of the dark ages were but ill-contrived -delusions, and their magic mirrors poor instruments. -The silver tablets of the photographic artist -receiving fixed impressions of the objects represented in -the dark chamber by a lens, are far superior as examples -of natural magic.</p> - -<p>In the dark ages, or rather as the earliest gleams of -the bright morning of inductive research were dispelling -the mists of that phantom-peopled period, it was -observed, for the first time, that the sun’s rays turned a -white compound black. Man must have witnessed, long -before, that change which is constantly taking place in -all vegetable colours: some darkening by exposure to -sunlight, while others were bleached by its influence. -Yet those phenomena excited no attention, and the -world knew nothing of the mighty changes which were -constantly taking place around them. The alchemists—sublime -pictures of credulous humanity—toiling in -the smoke of their secret laboratories, waiting and -watching for every change which could be produced by -fire, or by their “royal waters,” caught the first faint -ray of an opening truth; and their wild fancy, that -light could change silver into gold, if they but succeeded -in getting its subtile beams to interpenetrate the metal, -was the clue afforded to the empirical philosopher to -guide him through a more than Cretan labyrinth.<a name="FNanchor_117_117" id="FNanchor_117_117"></a><a href="#Footnote_117_117" class="fnanchor">[117]</a></p> -<p><span class="pagenum"><a name="Page_168" id="Page_168"></a>[Pg 168]</span></p> -<p>The first fact recorded upon this, point was, that horn -silver blackened when exposed to the light. Without -doubt many anxious thoughts were given by these -alchemists to that fact. Here was, as it appeared, a -mixing up of light and matter, and behold the -striking change! It was a step towards the realization -of their dreams. Alas! poor visionaries! in pursuing -an ideality they lost the reality which was within their -grasp.</p> - -<p>Truths come slowly upon man, and long it is before -these angel visits are acknowledged by humanity. The -world clings to its errors, and avoids the truth, lest its -light should betray their miserable follies.</p> - -<p>At length a man of genius announced that “<i>No substance -can be exposed to the sun’s rays without undergoing -a chemical change</i>;” but his words fell idly upon the -ear. His friends looked upon his light-produced pictures -as singular; they preserved them in their cabinets of -curiosities; but the truths which he enunciated were -soon forgotten. Howbeit his words were recorded, and -it is due to the solitary experimentalist of Châlons on -the Saône, to couple the name of Niepce with the discovery -of a fact which is scarcely second to the development -of the great law of universal gravitation.<a name="FNanchor_118_118" id="FNanchor_118_118"></a><a href="#Footnote_118_118" class="fnanchor">[118]</a> But -an examination awaits us, which, for its novelty, has -more charms than most branches of science, and which, -for the extensive views it opens to the inquirer, has an -interest in nowise inferior to any other physical investigation.</p> - -<p>The prismatic spectrum affords us the means of examining -the conditions of the solar rays with great<span class="pagenum"><a name="Page_169" id="Page_169"></a>[Pg 169]</span> -facility. In bending the ray of white light out of its -path, by means of a triangular piece of glass, we divide -it in a remarkable manner. We learn that heat is less -refracted by the glass than the other powers; we find -the maximum point of the calorific rays but slightly -thrown out of the right line, which the solar pencil would -have taken, had it not been interrupted by the prism; -and the thermic action is found to diminish with much -regularity on either side of this line. We discover that -the luminous power is subject to greater refraction, and -that its maximum lies considerably above that of heat; -and that, in like manner, on each side the light -diminishes, producing orange, red, and crimson colours -below the maximum point, and green, blue, and violet -above it. Again, we find that the radiations which -produce chemical change are more refrangible than -either of the others, and the maximum of this power is -found at the point where light rapidly diminishes, and -where scarcely any heat can be detected: it extends in -full activity, above its maximum, to a considerable distance, -where no trace of light under ordinary conditions -exists, and below that point, until light, appearing to -act as an interfering agent, quenches its peculiar properties. -These are strong evidences that <i>light</i> and -<i>actinism</i>—as this principle has been named—are not -identical: and we may separate them most easily and -effectually from each other. Certain glasses, stained -dark blue, with oxide of cobalt, admit scarcely any -light; but they offer no interruption to the passage of -actinism or the chemical rays; on the contrary, a pure -yellow glass, or a yellow fluid, which does not sensibly -reduce the intensity of any one colour of the chromatic -band of luminous rays, completely cuts off this chemical -principle, whatever it may be. In addition to these, -there are other results which we shall have to describe, -which prove that, although associated in the solar beam, -light and actinism are in constant antagonism.</p> - -<p><span class="pagenum"><a name="Page_170" id="Page_170"></a>[Pg 170]</span></p> - -<p>When Daguerre first published his great discovery, -the European public regarded his metal tablets with -feelings of wonder: we have grown accustomed to the -beautiful phenomena of this art, and we have become -acquainted with a number of no less beautiful processes -on paper, all of which, if studied aright, must convince -the most superficial thinker, that a world of wonder lies -a little beyond our knowledge, but within the reach of -industrious and patient research. Photography is the -name by which the art of sun-painting will be for ever -known. We regard this as unfortunate, conveying as it -does a false idea,—the pictures not being <i>light-drawn</i>. -Could we adopt the name given by Niepce to the process, -the difficulty would be avoided, since Heliography -involves no hypothesis, and strictly tells the undeniable -truth, that our pictures are <i>sun-drawn</i>. That pictures -can be produced by the rays from artificial sources, -presents no objection to this; these rays were still -originally derived from the sun.</p> - -<p>By whatever name we determine to convey our -ideas of these phenomena, it is certain that they involve -a series of effects which are of the highest interest to -every lover of nature, and of the utmost importance to -the artist and the amateur. By easy manipulation we -are now enabled to give permanence to the charming -pictures which are produced by means of that pleasing -invention of Baptista Porta, the <i>Camera Obscura</i>. Any -image, which being refracted by the lens of this instrument -falls upon the table in its dark chamber, may be -secured with its most delicate gradations of shadows, -upon either a metallic or a paper tablet.</p> - -<p>But let us proceed to the examination of a few of the -more striking phenomena of these chemical changes. -To commence with some of the more simple but no less -important results.</p> - -<p>Chlorine and hydrogen will not unite in darkness, -nor will chlorine and carbonic oxide; but, if either of<span class="pagenum"><a name="Page_171" id="Page_171"></a>[Pg 171]</span> -those gaseous mixtures is exposed to sunshine, they -combine rapidly, and often with explosion. A solution -of the sulphate of iron in ordinary water may be preserved -for a long time in the dark without undergoing -any change; expose it to the sunshine, and a precipitation -of oxide of iron is very rapidly produced. The -mineral chameleon, the <i>manganesiate of potash</i> in solution, -is almost instantly decomposed in daylight; but it -is a long time before it undergoes any change in darkness. -The same thing occurs with a combination of -platinum and lime: indeed, it appears that precipitation -is at all times, and under all circumstances, -accelerated by the solar rays. As these precipitations -are in exact agreement with the quantity of actinic -radiation to which the solutions have been exposed, we -may actually weigh off the relative quantities, representing -in grains the equivalent numbers to the amount of -actinism which has influenced the chemical compound.<a name="FNanchor_119_119" id="FNanchor_119_119"></a><a href="#Footnote_119_119" class="fnanchor">[119]</a></p> -<p><span class="pagenum"><a name="Page_172" id="Page_172"></a>[Pg 172]</span></p> -<p>We have evidence which appears to prove that this -chemical agent may be absorbed by simple bodies, and -that by this absorption an actual change of condition, is -produced, in many respects analogous to those allotropic -changes which we have previously considered. Chlorine, -in its ordinary state, does not combine with hydrogen in -the dark. If we employ the yellow medium of chlorine -gas, for the purpose of analyzing the sun’s rays previously -to their falling upon some chemical compound -which is sensitive to actinic power, we shall find that -the chlorine obstructs all this actinism, and, however -unstable the compound, it remains unchanged. But the -chlorine gas which has interrupted this wonderful agent, -appears to have absorbed it, and it is so far altered in its -constitution that <i>it will unite with hydrogen in the -dark</i>.<a name="FNanchor_120_120" id="FNanchor_120_120"></a><a href="#Footnote_120_120" class="fnanchor">[120]</a> In like manner, if, of two portions of the same -solution of sulphate of iron, one is kept in the dark and -the other exposed to the sunshine, it will be found that -the solution which has been exposed will precipitate -gold and silver from their combinations much more<span class="pagenum"><a name="Page_173" id="Page_173"></a>[Pg 173]</span> -speedily than that which has been preserved in darkness—the -temperature and every other condition being the -same.</p> - -<p>The phenomena of the Daguerreotype involve many -strange conditions. A plate of silver, on which a slight -chemical action has been established by the use of iodine, -is exposed to the lenticular image in the camera -obscura. If allowed to remain under the influence of -these radiations for a sufficient length of time, a faithful -picture of the illuminated objects is delineated on the -plate, as shown by the visible decomposition and darkening -of the iodized surface. The plate is not, however, -in practice allowed to assume this condition; after an -exposure of a few seconds the radiant influence is cut -off, and the eye cannot detect any evidence of change -upon the yellow plate. It is now exposed to the vapour -of mercury, and that metal in a state of exceedingly fine -division is condensed upon the plate; but the condensation -is not uniformly spread upon its face. The -deposit of mercurial vapour is in exact proportion to the -amount of chemical action produced. Is the change, -by which this peculiar power of condensation is effected, -a chemical, calorific, electrical, or merely a molecular -one? The evidences, at present, are not sufficient to -determine the question. It has lately been suggested, -that the mercury acts chemically only, and effects the -full decomposition of the iodide of silver; and that the -picture is due to this, and not to the deposition actually -of the mercury vapour. In all probability we have the -involved action of several forces. We have some experiments -which show, clearly enough, that mercury is -deposited in proportions which correspond with the -intensity of solar action. A chemically prepared surface -is not necessary to exhibit this result. A polished -plate of metal, of glass, of marble, or a piece of painted -wood, being partially exposed, will, when breathed upon, -or presented to the action of mercurial vapour, show<span class="pagenum"><a name="Page_174" id="Page_174"></a>[Pg 174]</span> -that a disturbance has been produced upon the portions -which were illuminated, whereas no change can be -detected upon the parts which were kept in the dark. -It was thought, until lately, that a few chemical compounds, -such as the iodide of silver, the material employed -in the Daguerreotype and Calotype,—chloride of -silver, the ordinary photographic agent,—a few salts of -gold, and one or two of lead and iron, were the only -materials upon which these very remarkable changes -were produced. We now know that it is impossible to -expose any body, simple or compound, to the sun’s rays, -without its being influenced by this chemical and molecular -disturbing power. To take our examples from -inorganic nature, the granite rock which presents its -uplifted head in firmness to the driving storm, the stones -which genius has framed into forms of architectural -beauty, or the metal which is intended to commemorate -the great acts of man, and which in the human form -proclaims the hero’s deeds and the artist’s talent, are -all alike destructively acted upon during the hours of -sunshine, and, but for provisions of nature no less -wonderful, would soon perish under the delicate touch -of the most subtile of the agencies of the universe.</p> - -<p>Niepce was the first to show that all bodies which -underwent this change during daylight possessed the -power of restoring themselves to their original conditions -during the hours of night, when this excitement -was no longer influencing them. Resins, the Daguerreotype -plate, the unprepared metal tablet, and numerous -photographic preparations, prove this in a remarkable -manner.<a name="FNanchor_121_121" id="FNanchor_121_121"></a><a href="#Footnote_121_121" class="fnanchor">[121]</a></p> -<p><span class="pagenum"><a name="Page_175" id="Page_175"></a>[Pg 175]</span></p> -<p>The picture which we receive to-day, unless we adopt -some method of securing its permanency, fades away -before the morrow, and we try to restore it in vain. -With some of our chemical preparations this is very -remarkably shown, but by none in so striking a manner -as by paper prepared with the iodide of platinum, which, -being impressed with an image by heliographic power, -which is represented by dark brown tints, restores itself -in the dark, in a few minutes, to its former state of a -yellow colour, and recovers its sensibility to sunshine.<a name="FNanchor_122_122" id="FNanchor_122_122"></a><a href="#Footnote_122_122" class="fnanchor">[122]</a> -The inference we alone can draw from all the evidences -which the study of actino-chemistry affords, is, that the -hours of darkness are as necessary to the inorganic -creation as we know night and sleep to be to the organic -kingdom. But we must not forget that there does exist -in the solar rays a balance of forces which materially -modifies the amount of disturbing influence exerted by -them on matter. Not only do we find that the chemical -action is not extended over the whole length of the -prismatic spectrum, but we discover that over spaces, -which correspond with the maximum points of light and -heat, a protective action is exerted. That is, that -highly sensitive photographic agents, which blacken -rapidly under exposure to diffused daylight, are entirely -protected from change in full sunshine, if at the same -time as a strong light is thrown upon them by reflection, -the yellow and extra red rays are brought to bear upon -their surface. Not only so, but by employing media -which will cut off all the chemical rays of the spectrum, -admitting freely at the same time the luminous and -calorific rays, we find that a protected band, the length<span class="pagenum"><a name="Page_176" id="Page_176"></a>[Pg 176]</span> -of the spectrum, remains white, whilst every other -portion has blackened.<a name="FNanchor_123_123" id="FNanchor_123_123"></a><a href="#Footnote_123_123" class="fnanchor">[123]</a></p> - -<p>Among the many curious instances of natural magic, -none are more remarkable than an experiment not long -since proposed, by which Daguerreotype pictures may -be taken in absolute darkness to the human eye. This -is effected in the following manner:—A large prismatic -spectrum is thrown upon a lens fitted into one side of a -dark chamber; and as we know that the actinic power -resides in great activity beyond the violet ray, where -there is no light, the only rays which we allow to pass -the lens into the chamber are those which are extra-spectral -and non-luminous. These are directed upon, -any white object, and from that object radiated upon a -highly sensitive plate in a camera obscura. Thus a -copy of the subject will be obtained by the agency of -radiations which produce no sensible effect upon the -optic nerve. This experiment is the converse of those -which show us that we may illuminate any object with -the strongest <span class="correction" title="In the original book: sun-light">sunlight</span> which has passed through -yellow glass, the yellow solution of sulphuret of calcium, -or of the bichromate of potash—these being non-transparent -to the chemical rays—and yet fail to -secure any Daguerreotype copy of it, even upon -the most exquisitely sensitive plate. Indeed, the -image of the sun itself, when setting through an -atmosphere which reduces its light to a red or rich -yellow colour, not only produces no chemical change, -but protects an iodized plate from it; and whilst every -other part of the tablet gives a picture of surrounding -objects in the ordinary character, the bright sun itself -is represented by a spot upon which no change has<span class="pagenum"><a name="Page_177" id="Page_177"></a>[Pg 177]</span> -taken place.<a name="FNanchor_124_124" id="FNanchor_124_124"></a><a href="#Footnote_124_124" class="fnanchor">[124]</a> In tropical climes, where a brilliant sun -is giving the utmost degree of illumination to all surrounding -objects, all photographic preparations are -acted upon relatively more slowly than in the climate of -England, where the light is less intense. As a remarkable -instance of this fact, a circumstance may be -mentioned, which is curiously illustrative of the power -of light to interfere with actinism:—</p> - -<p>A gentleman, well acquainted with the Daguerreotype -process, obtained in the city of Mexico all the -necessary apparatus and chemicals, expecting, under the -bright light and cloudless skies of that climate, to produce -pictures of superior excellence. Failure upon -failure was the result; and although every care was -used, and every precaution adopted, it was not until the -rainy season set in that he could secure a good Daguerreotype -of any of the buildings of that southern city.</p> - -<p>The first attempts, which were made at the instigation -of M. Arago, by order of the French Government, to -copy the Egyptian tombs and temples, and the remains -of the Aztecs in Central America, were failures. -Although the photographers employed succeeded to<span class="pagenum"><a name="Page_178" id="Page_178"></a>[Pg 178]</span> -admiration in Paris, in producing pictures in a few -minutes, they found often that an exposure of an hour -was insufficient under the bright and glowing illumination -of a southern sky.</p> - -<p>Experiments with the spectrum have been made in -different latitudes, and it is found, that, as we proceed -towards the equator, a band which is always left -unchanged, corresponding exactly with the rays of -greatest illuminating power, regularly enlarges in size, -thus proving the increase of light over actinism—and -the interfering power of the former.</p> - -<p>By increasing the sensibility of the photographic preparation, -this difficulty is overcome, and particularly -when any organic compound enters into the preparation. -So that we are now enabled to copy nature in all her -varying moods, whether we employ our photographic -tablets in temperate Europe, or in tropical Africa.</p> - -<p>The degree of sensibility which has been attained is -remarkable. Mr. Fox Talbot, by uniting a process -devised by Dr. Woods, of Parsonstown, and another -which was first introduced by the author of this volume, -and combining them with an ether, obtains a most -unstable compound, which he thus employs. A glass -plate is covered with albumen united with the above -solution, and then with nitrate of silver: this forms the -sensitive surface. The plate being placed in the dark, -in a camera, it is so adjusted that the image of a -printed bill fixed upon a wheel may fall upon it when -uncovered, and the wheel illuminated. The wheel is -made to revolve with the utmost rapidity, in a perfectly -dark room, and the sensitive plate uncovered. Then -the whirling bill is illuminated for an inappreciably short -space of time by the discharge of a Leyden jar. -Notwithstanding the rapid rate at which the pointed -paper is moving, and the instantaneous nature of the -illumination—a miniature flash of lightning—the bill is -found to be copied with unfailing fidelity upon the<span class="pagenum"><a name="Page_179" id="Page_179"></a>[Pg 179]</span> -photographic plate. It unfortunately happens, that the -preparation by which this extraordinary degree of -sensibility is obtained, is very uncertain in its action—and -hence it is not generally useful; but here we have -the evidence to show that at a speed as rapid as that of -a rifle-ball an impression may be made upon a photographic -plate. There are, however, some new processes -which promise eventually to rival the above for sensibility, -and to be by no means of difficult manipulation. -Of this character is the collodion process. The -gun cotton dissolved in ether possesses some very great -accelerating properties, and in combination with the -silver salts, and one of the vegetable acids, it forms a -sensitive surface upon which pictures may be obtained -in less than a second of time.</p> - -<p>Colour, natural colour too, has been very decidedly -secured. The sun has been solicited to display his -palette, and the answer has been a picture in which -colour for colour in all their fidelity have been impressed. -The plate upon which this result has been obtained is -of a dark brown colour, and the chromatic variety is, as -it were, eaten out by the solar rays. These colours -have not yet been permanently fixed upon the plate -employed, but from the temporary degree of fixedness -which has been obtained, we may fairly hope that in a -short time colour may be rendered as permanent on the -productions of the <span class="correction" title="In the original book: photograper">photographer</span> as on those of the -painter. It is a curious and striking fact, that in the -preparation of these plates, salts are used which give -colours to flame; and according to the colour which -is produced by them when burning, so, on the photographic -plate, is that colour impressed with greater -intensity than the others. To what is this leading us? -Mysteries surround our advances on the domain of -truth. We dare not speculate upon them: the time of -their full development will arrive.</p> - -<p>By the aid of this beautiful art, we are enabled to<span class="pagenum"><a name="Page_180" id="Page_180"></a>[Pg 180]</span> -preserve the lineaments of those who have <span class="correction" title="In the original book: benefitted">benefited</span> -their race by their intellect, or their heroism. We can -hand down to future ages portraits of our own Wellington, -and the illustrious Arago, unerring in their truthfulness. -How great would be the joy of all, could we -now obtain a daguerreotype portrait of a Greek poet, -or of a Roman philosopher, of a Sophocles, or of a -Seneca! How much discussion would be prevented did -we possess a calotype portrait of the Bard of Avon, or of -the Philosopher of Grantham!</p> - -<p>By the agency of those very rays which give life and -brilliancy to the laughing eye and the roseate cheek, -we can at once correctly trace the outline of the -features we admire, with all those shadowy details which -give a reality to the “presentment.” The objects of -our love may be for ever present with us in these self-painted -pictures. The vicious, whom we would avoid, -may be made known to us by this unerring painter. The -process which nature employs is perfect; the imperfections -are those of man, and these being few, he may soon -learn to remedy.</p> - -<p>To the traveller, how valuable are the processes -of photography! He secures representations of those -remains of temples which were in their glory when -Moses wrote. He copies by one operation a tomb at -Karnac, covered with myriads of hieroglyphics, or an -inscribed stone in Arabia, which it would occupy him -days to trace. These he can carry to his home and -read at his leisure. The relics of hoar antiquity speaking -to the present of the past, and recording the -histories of races which have fleeted away like shadows, -are thus preserved to tell their wondrous tales.</p> - -<p>The admirer of nature may copy her arrangements -with the utmost fidelity. Every modulation of the -landscape, each projecting rock or beetling tor—the -sinuous river in its rapid flow—the meandering stream, -“gliding like happiness away;” and the spreading<span class="pagenum"><a name="Page_181" id="Page_181"></a>[Pg 181]</span> -plains over which are scattered the homes of honest -industry and domestic peace, intermingled with the -towers of those humble temples in which simple-hearted -piety delights to “bow the head and bend their knee;” -these, all of these, may, by the sunbeam which illuminates -the whole, be faithfully pencilled upon our chemical -preparations.</p> - -<p>Our art enables us to do more even than this; we -have but to present our sensitive tablet to the moon, -and she, by her own light, prints her mountains and her -valleys, and indicates with all truth the physical conditions -of her surface.</p> - -<p>Any reference to the <i>chemical agency</i> of <span class="smcap">light</span>—<i>the -luminous rays</i> as distinguished from the <i>chemical -and calorific rays</i>—has been avoided until we came to -the consideration of this particular question of chemical -change.</p> - -<p>Upon organic compounds, as, for instance, upon the -colouring matter of leaves and flowers, <i>light</i> does exert -a chemical power: and it is found that vegetable -colours are bleached, not by rays of their own colour, -but by those which are <i>complementary</i> to them. A red -dye fades under the influence of a green ray, and a -yellow under that of a violet one, much more speedily -than when exposed to rays of any other colour; and this, -it must be remembered, is due to the coloured ray -itself, and not to any <i>actinic</i> power masked, as it were, -behind the colour, as is generally believed.<a name="FNanchor_125_125" id="FNanchor_125_125"></a><a href="#Footnote_125_125" class="fnanchor">[125]</a> It was<span class="pagenum"><a name="Page_182" id="Page_182"></a>[Pg 182]</span> -long a question whether the decomposition of carbonic -acid by plants was due to the luminous or the chemical -rays. It is now clearly established that the luminous -rays are the most active in producing this effect; which -they do indirectly, by exciting the vital powers of the -organized structures. Therefore we would refer this -phenomenon of gaseous decomposition to a vital power -quickened by luminous excitement.<a name="FNanchor_126_126" id="FNanchor_126_126"></a><a href="#Footnote_126_126" class="fnanchor">[126]</a></p> - -<p><span class="pagenum"><a name="Page_183" id="Page_183"></a>[Pg 183]</span></p> - -<p>We have already noticed some chemical phenomena -due to heat, particularly those experiments of Count -Rumford’s, which appeared to him to prove that the -chemical agency of the sun’s rays was due to its calorific -power. Certain chemical phenomena, we know, may be -produced by thermic action; but the only variety of -thermo-chemical action which connects itself immediately -with the solar radiations, belongs to a class of -rays to which the name of <i>Parathermic</i> has been given, -and to which the scorching, as it is called, of plants, the -browning of the autumnal leaves, and the ripening of -fruits, appear to be due.<a name="FNanchor_127_127" id="FNanchor_127_127"></a><a href="#Footnote_127_127" class="fnanchor">[127]</a> When we come to the consideration -of those physical phenomena which belong to -the growth of plants, all these peculiarities of solar -action must be attended to in detail.</p> - -<p>The manner in which we find the actinic power -influencing electrical action, also shows us that the -equilibrium of forces is continued through all the great -principles of nature. If a galvanic arrangement is made, -by which small quantities of metals may be slowly precipitated -at one of the poles in the dark, and a similar -arrangement be exposed to sunshine, it will be found -that no metal is deposited: the sun’s rays have interfered -with the decomposing power of the electrical -current. At the same time we learn, that by throwing -a beam of light upon a plate of copper which forms one -of a galvanic pair, whilst it is under the influence of an -acidulated solution, an additional excitation takes place, -and the galvanometer will indicate the passage of an -increased current of electricity. These two dissimilar -actions appear enigmatical; but they may, there is no -doubt, receive some solution from the influence of -different rays on the contrary poles of the battery. One<span class="pagenum"><a name="Page_184" id="Page_184"></a>[Pg 184]</span> -thing is quite evident,—electricity suffers a disturbance -of one order, by light; and an excitement of another by -its associated principles in the sunbeam. If a yellow -glass is interposed between the galvanic arrangement -and the sun, the electro-chemical precipitation goes on -in the same manner as it would in perfect darkness, -and no extra excitement is produced upon the plates of -the battery. From this it would appear that actinism -and not light is to be regarded as the disturbing power.<a name="FNanchor_128_128" id="FNanchor_128_128"></a><a href="#Footnote_128_128" class="fnanchor">[128]</a> -It has already been shown that yellow media possess the -power of stopping back the chemical agent.</p> - -<p>We have already, detailed many of the peculiarities of -the different varieties of Phosphori, which would seem -to be the result of light. Phosphorescence is probably -excited by those rays which produce no direct effect -upon the eye. If we spread sulphuret of calcium upon<span class="pagenum"><a name="Page_185" id="Page_185"></a>[Pg 185]</span> -paper, and expose it to the action of the solar spectrum, -it is found to glow (in the dark) only over those spaces -occupied by the violet rays and the ordinarily dark rays -beyond them; proving that the excitation necessary to -the development of the phenomena of phosphorescence -is due to a class of rays distinct from the true light-giving -principle, and more nearly allied to that principle -or power which sets up chemical decomposition. -Whether the fluorescent rays, before mentioned, which -are found so abundantly over the space which produces -the greatest phosphorescent effect, are active in producing -the phenomena, is as yet an unsolved problem.</p> - -<p>Vision and colour, calorific action, chemical change, -molecular disturbance, electrical phenomena, and phosphorescent -excitation, all, each one with a strange -duality, are connected with the sunbeam.</p> - -<p>We find, when we receive solar spectra upon iodized -plates, or on several kinds of photographic paper, that a -line, over which no action takes <span class="correction" title="In the original book: plates">place</span>, is preserved at -the top and bottom of the impressed image, and in many -cases along the sides also. The only way in which this -can be accounted for, as the spectrum represents the -sun in a distorted form, is by supposing that rays come -from the edges of the sun of a different character from -those which proceed from the centre of that orb.<a name="FNanchor_129_129" id="FNanchor_129_129"></a><a href="#Footnote_129_129" class="fnanchor">[129]</a></p> - -<p>Light from the centre of the solar disc is under different -conditions from that which comes from the edge -of the sun: this is due to the varying angle, which is -presented to us by a circular body: calorific action seems<span class="pagenum"><a name="Page_186" id="Page_186"></a>[Pg 186]</span> -to be more strongly manifested when the envelope of -light, extending like an atmosphere to the sun, is thrown -into great agitation, and waves, and great hollows—solar -spots—are produced. There is some indication of -the existence of a third condition on the sun’s surface, -to which probably belongs the mighty chemical power -which we call actinism. Electricity may be, as some -have speculated, the exciting agent; a constant and -violent Aurora Borealis may exist on the sun, and -under the excitation of this force the others named may -be quickened into full activity.</p> - -<p>That actinism is one of the great powers of creation -we have abundant proof. Nearly all the phenomena of -chemical change which have been referred to light, are -now proved to be dependent upon actinic power; and -beyond the influence which has been ascertained to be -exerted by it upon all inorganic bodies, we shall have -occasion to show still further the dependence of the -vegetable and animal worlds upon its agency. The influence -of the solar beams on vegetation is proved by -common experience; the closer examination of its -action on vegetable life is reserved for the chapter devoted -to its phenomena. Of its influence on animals -nothing is very correctly known; but some early experiments -prove that they, like other organised bodies, are -subject to all the radiant forces, as indeed, independent -of experiment, every observation must teach. Certain -it is, that organisation can take place only where -the sun’s rays can penetrate: where there is unchanging -darkness, there we find all the silence of death. Prometheus -stole fire from heaven, and gave the sacred gift -to man, as the most useful to him of all things in his -necessities: by the aid of it he could temper the severities -of climate, render his food more digestible and -agreeable, and illuminate the hours of darkness. So -says the beautiful fiction of the Grecian mind,—which -appears as the poetic dream or prophetic glance of a<span class="pagenum"><a name="Page_187" id="Page_187"></a>[Pg 187]</span> -gifted race, who felt the mysterious truth they were yet -unable to describe. Pheaton and Apollo are only other -foreshadowings of the creative energies which dwell in -the glorious centre of our universe. The poetry of the -Hellenic people ascended above the littlenesses of merely -human action, and sought to interpret the great truths -of creation. Reflective, they could not but see that -some mysterious powers were at work around them; -imaginative, they gave to fine idealisations the government -of those inexplicable phenomena. Modern science -has shown what vastly important offices the solar rays -execute, and that the principles discovered in a sunbeam -are indeed the exciters of organic life, and the disposers -of inorganic form.</p> - -<p>It must not be forgotten that we have already -alluded to a speculation which supposes this actinic influence -to be diffused through all nature, to be indeed -the element to which chemical force in all its forms is to -be referred, and that it is merely excited by the solar -rays. This hypothesis receives some support from the -very peculiar manner in which chemical action once set -up is carried on, independent of all extraneous excitement, -after the first disturbance has been produced. If -any of the salts of gold are exposed in connection with -organic matter, as on paper, to sunshine for a moment, -an action is begun, which goes on unceasingly in the -dark, until the gold is reduced to its most simple state.<span class="pagenum"><a name="Page_188" id="Page_188"></a>[Pg 188]</span><a name="FNanchor_130_130" id="FNanchor_130_130"></a><a href="#Footnote_130_130" class="fnanchor">[130]</a> -The same thing occurs with chromate of silver, some -of the salts of mercury, argentine preparations combined -with protosulphate of iron or gallic acid, and some other -chemical combinations. These progressive influences -point to some law not yet discovered, which seems to -link this radiant actinism with the chemical agent existing -in all matter.</p> - -<p>This problem also connects itself with another class of -facts which, although due, in all probability, to a great -extent, to calorific radiations, and hence known under -the general term of Thermography, appear to involve -both chemical and electrical excitation. From the investigations -of Moser and of others, we learn the very -extraordinary fact, that even inanimate masses act and -react upon each other by the influence of some dark -radiations, and seem to exchange some of the peculiarities -which they possess. This appears generally in the -curious experiments which have been referred to, as confined -merely to form or structure. Thus an engraved -plate will give to a polished surface of metal or glass -placed near it, after a very little time, a neat distinct -image of itself; that is, produce such a structural disturbance -as will occasion the plate to receive vapour differently -over those spaces opposite to the parts in cameo -or in intaglio, from what it does over the opposite. If a -piece of wood is used instead of a <span class="correction" title="In the original book: medal">metal</span>, there will, by -similar treatment, be produced a true picture of the wood, -even to the representation of its fibres.<a name="FNanchor_131_131" id="FNanchor_131_131"></a><a href="#Footnote_131_131" class="fnanchor">[131]</a></p> -<p><span class="pagenum"><a name="Page_189" id="Page_189"></a>[Pg 189]</span></p> -<p>It is also probable that chemical decomposition is produced -by the mere juxtaposition of different bodies. -Iodide of gold or silver, perfectly pure, has been placed -upon a plate of glass, and a plate of copper covered with -mercury suspended over it: a gradual decomposition -of those salts is said to have been observed, iodide of -mercury to be formed, and the gold or silver salts reduced -to a finely divided metallic state.<a name="FNanchor_132_132" id="FNanchor_132_132"></a><a href="#Footnote_132_132" class="fnanchor">[132]</a></p> - -<p>A body whose powers of radiating heat are low, being -brought near another whose radiating powers are more -extensive, will, in the course of a short time, undergo -such an amount of molecular disturbance as will effect -a complete change in the arrangement of its surface, -and an impression of the body having the highest radiating -powers will be made upon the other. This impression -is dormant, but may be developed under the -influence of vapour, or of oxidation.<a name="FNanchor_133_133" id="FNanchor_133_133"></a><a href="#Footnote_133_133" class="fnanchor">[133]</a> A body, such as<span class="pagenum"><a name="Page_190" id="Page_190"></a>[Pg 190]</span> -charcoal, of low conducting power, being placed near -another, such as copper, which is a good conductor, will, -in a very short time, produce, in like manner, an impression -of itself upon the metal plate. Thus any two -bodies, whose conducting or radiating powers are dissimilar, -being brought near each other, will occasion a -molecular disturbance, or impress the one with the image -of the other. However small the difference may be, an -effect is perceived, and that of the most extraordinary -kind, giving rise to the production of actual images upon -each surface exposed. It is thus that a print on paper -may be copied on metal, by merely suspending it near a -well-polished plate of silver or copper for a few days. -The white and black lines radiate very differently; consequently -an effect is produced on the bright metal in -the parts corresponding to the black lines, dissimilar to -that which takes place opposite to the white portions -of the paper; and, on the application of vapour, a -true image of the one is found impressed upon the -other.<a name="FNanchor_134_134" id="FNanchor_134_134"></a><a href="#Footnote_134_134" class="fnanchor">[134]</a></p> - -<p>Bodies which are in different electrical states act upon -each other in an analogous manner. Thus arsenic, which -is highly electro-negative, will, when placed near a piece -of electro-positive copper, readily impart to its surface -an impression of itself, and so in like manner will other -bodies if in unlike conditions. Every substance physically -different (it signifies not whether as it regards<span class="pagenum"><a name="Page_191" id="Page_191"></a>[Pg 191]</span> -colour, chemical composition, mechanical structure, calorific -condition, or electrical state,) has a power of radiation -by which a sensible change can be produced in a -body differently constituted.</p> - -<p>Fable has told us that the magicians of the East possessed -mirrors in which they could at will produce -images of the absent. Science now shows us that representations -quite sufficient to deceive the credulous can -be produced on the surface of polished metals without -difficulty. A highly polished plate of steel may be impressed -with images of any kind, which would remain -invisible, the polished surface not being in the least degree -affected, as it regards its reflecting powers; but by breathing -over it, the dormant images would develope themselves, -and fade away again as the condensed moisture -evaporated from the surface.<a name="FNanchor_135_135" id="FNanchor_135_135"></a><a href="#Footnote_135_135" class="fnanchor">[135]</a></p> - -<p>These, which are but a few selected from a series of -results of an equally striking character, serve to convince -us that nature is unceasingly at work, that every -atom is possessed of properties by which it influences -every other atom in the universe, and that a most important -class of natural phenomena appear to connect -themselves directly with the radiant forces.</p> - -<p>The alchemists observed that a change took place in -chloride of silver exposed to sunshine. Wedgwood first -took advantage of that discovery to copy pictures. -Niepce pursued a physical investigation of the curious -change, and found that all bodies were influenced by -this principle radiated from the sun. Daguerre produced -effects from the solar pencil which no artist could approach -to; and Talbot and others extended the applica<span class="pagenum"><a name="Page_192" id="Page_192"></a>[Pg 192]</span>tion. -Herschel took up the inquiry; and he, with his -usual power of inductive search and of philosophical -deduction, presented the world with a class of discoveries -which showed how vast a field of investigation was opening -for the younger races of mankind,—a field in which -a true spirit may reap the highest reward in the discovery -of new facts, and to which we must look for a further -development of those great powers with which we -have already some slight acquaintance, and for the discovery -of higher influences which are not yet dreamed -of in our philosophy.</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">If music, with its mysteries of sound,</div> -<div class="verse indent2">Gives to the human heart a heavenward feeling;</div> -<div class="verse">The beauty and the grandeur which are found</div> -<div class="verse">Spread like a vesture this fair earth around,</div> -<div class="verse indent2">Creation’s wond’rous harmonies revealing,</div> -<div class="verse indent2">And to the soul in truth’s strong tongue appealing,</div> -<div class="verse">With all the magic of those secret powers,</div> -<div class="verse indent2">Which, mingling with the lovely band of light,</div> -<div class="verse">The sun in constant undulation showers</div> -<div class="verse">To mould the crystals, and to shape the flowers,</div> -<div class="verse indent2">Or give to matter the immortal might</div> -<div class="verse">Of an embracing soul—should, from this sod,</div> -<div class="verse">Exalt our aspirations all to God.</div> -</div></div></div> -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_117_117" id="Footnote_117_117"></a><a href="#FNanchor_117_117"><span class="label">[117]</span></a> See <i>Researches on Light</i>, by the Author.—Reference to any of -the works of the alchemists will prove the prevalence of the idea -expressed in the text. We find that gold was considered to be -always under the influence of light and solar heat.—“It is said of -gold that it waxeth cold towards daylight, insomuch that they who -wear rings of it may perceive when the day is ready to dawn.”—<i>Speculum -Mundi, or a Glass representing the face of the World</i>. -Cambridge, 1643.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_118_118" id="Footnote_118_118"></a><a href="#FNanchor_118_118"><span class="label">[118]</span></a> Daguerre’s Report to the Academy of Sciences: <i>La Daguerréotype -Historique, et description des procédés du Daguerréotype et -du Diorama</i> (Paris, 1839); particularly the description of <i>Heliography</i>, -by M. Niepce. See also the letters by Niepce, published -for the first time in <i>Researches on Light</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_119_119" id="Footnote_119_119"></a><a href="#FNanchor_119_119"><span class="label">[119]</span></a> “If a solution of peroxalate of iron be kept in a dark place, -or if it be exposed to 212° of Fahr. for several hours, it does not -undergo any sensible change in its physical properties, nor does it -exhibit any phenomenon which may be considered as the result of -any elementary action. -</p> -<p> -“If, however, it be exposed to the influence of solar light in -a glass vessel provided with a tube, the concentrated solution of -oxalate of iron soon presents a very interesting phenomenon: in -a short time the solution receiving the solar rays, developes an -infinite number of bubbles of gas, which rise in the liquor with -increasing rapidity, and give the solution the appearance of a -syrup undergoing strong fermentation. This ebullition always -becomes stronger, and almost tumultuous, when an unpolished -glass tube is immersed in it with a small piece of wood; the -liquid itself is afterwards thrown into ascending and descending -currents, becomes gradually yellowish, turbid, and eventually -precipitates protoxalate of iron, in the form of small brilliant -crystals of a lemon-yellow colour, gas continuing to evolve.” -<i>Chemical action of light, and formation of Humboldtine by it</i>; -Phil. Mag., 1832, second series.—“When a solution of platinum -in nitro-muriatic acid, in which the excess of acid has been -neutralized by the addition of lime, and which has been well cleared -by filtration, is mixed with lime-water in the dark, no precipitation -to any considerable extent takes place for a long while,—indeed, -none whatever, though after very long standing a slight -flocky sediment is formed, after which the action is arrested -entirely. But if the mixture, either freshly made or when cleared -by subsidence of this sediment, is exposed to sunshine, it instantly -becomes milky, and a copious formation of a white precipitate -(or a pale yellow one, if the platinic solution be in excess) -takes place, which subsides quickly and is easily collected. The -same takes place more slowly in cloudy daylight.”—<i>On the action -of light in determining the precipitation of Muriate of Platinum by -Lime water</i>; being an extract from a letter from Sir John F. W. -Herschel, K.H., F.R.S., &c., to Dr. Daubeny.—Phil. Mag. 1832.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_120_120" id="Footnote_120_120"></a><a href="#FNanchor_120_120"><span class="label">[120]</span></a> <i>On a change produced by Exposure to the Beams of the Sun, -in the properties of an elementary substance</i>, by Professor Draper; -<i>On the changes which bodies undergo in the dark</i>, by Robert Hunt: -Report of the Thirteenth Meeting of the British Association, vol. -xii,—<i>Description of the Tithonometer, an instrument for measuring -the chemical force of the Indigo-tithonic rays</i>: by J. W. Draper, -M.D.—Philosophical Magazine, Dec. 1843, vol. xxiii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_121_121" id="Footnote_121_121"></a><a href="#FNanchor_121_121"><span class="label">[121]</span></a> For several illustrations of this remarkable phenomenon, see -<i>On the Action of the Rays of the Solar Spectrum on Vegetable -Colours, and on some new Photographic Processes</i>; by Sir John F. -W. Herschel, Bart., K.H., F.R.S.—Phil. Trans. June, 1842, vol. -cxxxiii.; <i>On certain improvements on Photographic Processes -described in a former communication, and on the Parathermic Rays -of the Solar Spectrum</i>; by Sir John F. W. Herschel, Bart., K.H., -F.R.S., &c., in a letter addressed to S. Hunter Christie.—Phil. -Trans. 1843, vol. cxxxiv.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_122_122" id="Footnote_122_122"></a><a href="#FNanchor_122_122"><span class="label">[122]</span></a> Sir J. F. W. Herschel; see also <i>Researches on Light</i>, by the -Author.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_123_123" id="Footnote_123_123"></a><a href="#FNanchor_123_123"><span class="label">[123]</span></a> Attention has been directed to the protecting action of certain -rays of the spectrum by Sir John Herschel and others. See the -Eighteenth Report of the British Association for an experiment -by the Author, in which it was proved that all the <span class="smcap">light</span> rays protected -photographic papers from chemical change, and, therefore, -convincingly show that light and actinism were not similar powers.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_124_124" id="Footnote_124_124"></a><a href="#FNanchor_124_124"><span class="label">[124]</span></a> “Having noticed, one densely foggy day, that the disc of the -sun was of a deep red colour, I directed my apparatus towards it. -After ten seconds of exposure, I put the prepared plate in the -mercury box, and I obtained a round image perfectly black;—the -sun had produced no photogenic effect. In another experiment, -I left the plate operating for twenty minutes; the sun had passed -over a certain space of the plate, and there resulted an image seven -or eight times the sun’s diameter in length; it was black throughout, -so that it was evident, wherever the red disc of the sun had -passed, not only was there a want of photogenic action, but the -red rays had destroyed the effect produced previous to the sun’s -passage. I repeated these experiments during several days -successively, operating with a sun of different tints of red and -yellow. These different tints produced nearly the same effect; -wherever the sun had passed, there existed a black band.”—Mr. -Claudet, <i>On different properties of Solar Radiation, modified by -coloured glass media, &c.</i>: Phil. Trans. 1847. Part 2.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_125_125" id="Footnote_125_125"></a><a href="#FNanchor_125_125"><span class="label">[125]</span></a> “It may also be observed that the rays effective in destroying -a given tint are, in a great many cases, those whose union produces -a colour complementary to the tint destroyed, or at least one -belonging to that class of colours to which such complementary -tint may be referred. For example, yellows tending towards -orange are destroyed with more energy by the blue rays; blue by -the red, orange, and yellow rays; purples and pinks by yellow and -green rays.”—Sir J. F. W. Herschel, <i>On the action of the rays of -the Solar Spectrum on Vegetable Colours</i>: Phil. Trans., vol. cxxxiii. -1842.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_126_126" id="Footnote_126_126"></a><a href="#FNanchor_126_126"><span class="label">[126]</span></a> The following memoirs and works are necessary to a complete -history of the inquiry:—<i>Experiments and observations relating to -various branches of natural philosophy, with a continuation of the -observation on air</i>: by Dr. Priestley. London, 1779. <i>Mémoires -Physico-chimiques, &c.</i>: by J. Senebier. <i>Expériences sur les végétaux</i>, -by De la Ville: Paris, 1782; and Phil. Trans. 1782. <i>Observations -sur les expériences de M. Ingenhousz</i>: by De la Ville; Roz. -obs. 23, 290. <i>Expériences propres à développer les effets de la -lumière sur certaines plantes</i>: by Tessier; Mém. de l’Ac. des Sc. -de Paris, 1783, p. 132; Licht. Mag. iv. 4, 146. <i>Sur la vertu de -l’eau impregnée d’air fixe pour en obtenir, par le moyen des plantes et -de la lumière du soleil, de l’air déphlogistiqué</i>: by Ingenhousz; -Roz. obs. 24, 337. <i>Expériences sur l’action de la lumière solaire -dans la <span class="correction" title="In the original book: végetation">végétation</span></i>: by Senebier; Genève et Paris, 1788, p. 61. -<i>Extrait des expériences de M. Senebier sur l’action de la lumière -solaire dans la végétation</i>: by Hasenfratz; Ann. Chim. iii. 2nd. -ser. 266. <i>Expériences relatives à l’influence de la lumière sur -quelques végétaux</i>: by De Candolle; Jour. de Ph. lii. 124: Voigt’s -Mag. ii. 483; Gilb. Ann. xiii. 372; Mém. des Sav. Etr. i. 329. -<i>Recherches chimiques sur la végétation</i>: by Saussure; Ann. Chim. -l. 225; Jour. de Ph. lvii. p. 393; Gilb. Ann. xviii 208. <i>Recherches -sur la respiration des plantes exposées à la lumière du soleil</i>; by -Ruhland; Ann. Ch. Ph. iii. 411; Jour. de Ph. 1816. <i>On the -action of light upon plants, and of plants upon the atmosphere</i>: by -Dr. Daubeny; Phil. Trans. cxxvii January, 1836. <i>On the action -of yellow light in producing the green colour, and of indigo light on -the movements of plants</i>: by P. Gardner; Phil. Mag. xxiv.; Bibl. -Univ. xlix. p. 376, and lii. p. 381. <i>On the influence of light on -plants</i>: by R. Hunt; Phil. Mag. xxiv. p. 96; Bibl. Univ. xlix. -p. 383; Athen. 1844. <i>Note on the decomposition of carbonic acid -by the leaves of plants, under the influence of yellow light</i>: by -Draper; Phil. Mag. xxv. p. 169. <i>On the action of the yellow rays -of light on vegetation</i>: by Harkness; Phil. Mag. xxv. p. 339. -<i>Influence des rayons solaires sur la végétation</i>: by Zantedeschi; -Inst. No. 541, p. 157.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_127_127" id="Footnote_127_127"></a><a href="#FNanchor_127_127"><span class="label">[127]</span></a> Sir John Herschel’s Memoirs already referred to; and <i>Reports -on the influence of the Solar Rays on the growth of Plants</i>, by Robert -Hunt: Report of the British Association for the Advancement of -Science, for 1847.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_128_128" id="Footnote_128_128"></a><a href="#FNanchor_128_128"><span class="label">[128]</span></a> <i>Memoir on the Constitution of the Solar Spectrum</i>, presented -at the meeting of the Academy of Sciences, 1842, by M. Edmond -Becquerel; <i>Des effets produits sur les corps par les rayons solaires</i>, -par M. Edmond Becquerel, aide au Muséum d’Histoire Naturelle: -Mémoire présenté à l’Académie des Sciences, le 23 Octobre, 1843.—“Dans -le courant de ce mémoire, j’ai employé les noms de -rayons lumineux, chimiques, et phosphorogéniques, pour désigner, -dans chaque cas, la portion des rayons solaires qui agit pour produire, -en particulier, les effets lumineux, chimiques, et phosphorogéniques; -mais cela est sans préjudice de l’opinion que je viens -d’émettre touchant l’existence d’un seul et même rayonnement.” -</p> -<p> -“My reply is this,” says M. Arago, in his paper entitled -<i>Considerations relative to the action of Light</i>: “It is by no means -proved that the photogenic modifications of sensitive substances -result from the action of the solar light itself. The modifications -are, perhaps, engendered by invisible radiations mixed with light -properly so called, proceeding with it, and being similarly refracted. -In this case, the experiment would prove not only that -the spectrum formed by these invisible rays is not continuous, -that there are solutions of continuity as in the visible spectrum, -but also that in the two superposed spectra these solutions correspond -exactly. This would be one of the most curious, one -of the most strange results of physics.”—Taylor’s Scientific -Memoirs.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_129_129" id="Footnote_129_129"></a><a href="#FNanchor_129_129"><span class="label">[129]</span></a> The chemical evidence of this will be found in Sir John -Herschel’s Memoir <i>On the Solar Spectrum</i>, and particularly as -exemplified in the changes produced on the tartrate of silver. -Similar influences are described as observed on a Daguerreotype -plate, in a paper entitled <i>Experiments and Observations on Light -which has permeated coloured media, and on the Chemical Action of -the Solar Spectrum</i>; by Robert Hunt.—Philosophical Magazine, -vol. xxvi. 1840.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_130_130" id="Footnote_130_130"></a><a href="#FNanchor_130_130"><span class="label">[130]</span></a> This peculiar continuance of an effect has frequently been -observed in many of the photographic processes. In a note to a -memoir <i>On certain improvements in Photographic processes</i>, -Sir John Herschel thus refers to this property:—“The excitement -is produced on such paper by the ordinary moisture of the atmosphere, -and goes on slowly working its effect in the dark, apparently -without other limit than is afforded by the supply of ingredients -present. In the case of silver it ultimately produces a perfect -<i>silvering</i> of all the sunned portions. Very singular and beautiful -photographs, having much resemblance to Daguerreotype pictures, -are thus produced; the negative character changing by keeping, -and by quite insensible gradations to positive, and the shades exhibiting -a most singular <i>chatoyant</i> change of colour from ruddy-brown -to black, when held more or less obliquely. No doubt, also, -gold pictures with the metallic lustre might be obtained by the -same process, though I have not tried the experiment.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_131_131" id="Footnote_131_131"></a><a href="#FNanchor_131_131"><span class="label">[131]</span></a> The details of this curious subject may be studied in the -following memoir and communications:—<i>On vision and the action -of light on all bodies</i>: by Professor Ludwig Moser, of Königsberg; -from Poggendorff’s Annalen, vol. lvi. p. 177, No. 6, 1845. <i>Some -remarks on Invisible Light</i>: by Professor Ludwig Moser, of -Königsberg; from Poggendorff’s Annalen, vol. lvi. p. 569, No. 8. -<i>On the power which light possesses of becoming latent</i>: by Professor -Ludwig Moser, of Königsberg; from Poggendorff’s Annalen, vol. -lvii. No. 9, p. 1. 1842. <i>On certain spectral appearances, and on the -discovery of latent light</i>: by J. W. Draper, M.D., Professor of -Chemistry in the University of New York; Phil. Mag. p. 348, -Nov. 1842. <i>On a new imponderable substance, and on a class of -chemical rays analogous to the rays of dark heat</i>: by Professor -Draper; Phil. Mag., Dec. 1842. <i>On the action of the rays of the -solar spectrum on the Daguerreotype plate</i>; by Sir J. F. W. -Herschel, Bart.; Phil. Mag., Feb. 1843. See remarks in this -paper on the use which Moser has made of coloured glasses: also -a communication by Professor Draper, <i>On the rapid Detithonizing -power of certain gases and vapours, and on an instantaneous means -of producing spectral appearances</i>: Phil. Mag., March 1843; and -<i>On the causes which concur in the production of the images of Moser</i>: -Comptes Rendus, Nov. 1842. See <i>Scientific Memoirs</i>, vol. iii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_132_132" id="Footnote_132_132"></a><a href="#FNanchor_132_132"><span class="label">[132]</span></a> This fact was first observed by myself, and described in the -paper already referred to, Philosophical Magazine, vol. xxii. p. 270. -It does not, however, appear to have attracted the attention of any -other observer.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_133_133" id="Footnote_133_133"></a><a href="#FNanchor_133_133"><span class="label">[133]</span></a> <i>On Thermography, or the Art of copying Engravings or any -printed characters from paper or plates of metal, and on the recent -discovery of Moser, relative to the formation of images in the dark</i>, -by Robert Hunt: Reports of the Royal Cornwall Polytechnic -Society for 1842, and Philosophical Magazine, vol. xxi. p. 462.—<i>On -the Spectral Images of M. Moser</i>, by Robert Hunt: Philosophical -Magazine, vol. xxiii. p. 415.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_134_134" id="Footnote_134_134"></a><a href="#FNanchor_134_134"><span class="label">[134]</span></a> <i>Catalytic force, or attraction of surface concerned in the -diffusive power of gases: an occult energy or power in saturated -saline solutions</i>; Prater.—Mechanic’s Magazine, vol. xlv. p. 106. -<i>Ueber elektrische Abbildungen</i>; by G. Karsten.—Poggendorff’s -Annalen, vol. lvii. p. 402.—Melloni and Brewster may be consulted -for much that is most remarkable connected with radiation -from coloured surfaces.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_135_135" id="Footnote_135_135"></a><a href="#FNanchor_135_135"><span class="label">[135]</span></a> Cornelius Agrippa is said to have possessed such a mirror. -The Chinese make mirrors which, when placed in a particular -light, show upon their polished faces the pattern on the back of the -metal, although it is invisible in every other position. This is -effected by giving different degrees of hardness to the various -parts of the metal. In <i>Natural Magic</i>, by Sir David Brewster, -several curious experiments belonging to this class are named.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_193" id="Page_193"></a>[Pg 193]</span></p> - - -<h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX.</h2> - -<p class="center">ELECTRICITY.</p> - - -<p class="chap-head">Discovery of Electrical Force—Diffused through all Matter—What -is Electricity?—Theories—Frictional Electricity—Conducting -Power of Bodies—Hypothesis of two Fluids—Electrical -Images—Galvanic Electricity—Effects on Animals—Chemistry -of Galvanic Battery—Electricity of a -Drop of Water—Electro-chemical Action—Electrical Currents—Thermo-Electricity—Animal -Electricity—Gymnotus—Torpedo—Atmospheric -Electricity—Lightning Conductors—Earth’s -Magnetism due to Electrical Currents—Influence on -Vitality—Animal and Vegetable Development—Terrestrial -Currents—Electricity of Mineral Veins—Electrotype—Influence -of Heat, Light, and Actinism on Electrical Phenomena.</p> - - -<p class="p2">If a piece of amber, <i>electrum</i>, is briskly rubbed, it -acquires the property of attracting light bodies. This -curious power excited the attention of Thales of Miletus; -and from the investigations of this Grecian philosopher -we must date our knowledge of one of the most important -of the natural forces—Electricity.</p> - -<p>If an inquiring mind had not been led to ask why -does this curious natural production attract a feather, the -present age, in all probability, would not have been in -possession of the means by which it is enabled to transmit -intelligence with a rapidity which equals the poet’s -dream of the “swift-winged messengers of thought.” -To this age of application a striking lesson does this -amber teach. Modern utility would have regarded -Thales as a madman. Holding a piece of yellow resin -in his hand, rubbing it, and then picking up bits of down, -or catching floating feathers, the old Greek would have<span class="pagenum"><a name="Page_194" id="Page_194"></a>[Pg 194]</span> -appeared a very imbecile, and the <i>cui bono</i> generation -would have laughed at his silly labours. But when he -announced to his school that this amber held a soul or -essence, which was awakened by friction, and went forth -from the body in which it previously lay dormant, and -brought back the small particles floating around it, he -gave to the world the first hint of a great truth which has -advanced our knowledge of physical phenomena in a marvellous -manner, and ministered to the refinements and to -the necessities of civilisation. Each phenomenon which -presents itself to us, however simple it may appear to be, -is an outward expression of some internal truth, the interpretation -of which is only to be arrived at by assiduous -study, but which, once discovered, directs the way to new -knowledge, and gives to man a great increase of power. -There is no truth so abstract that it will not find its useful -application, and every example of the ministration of -Physical Science to the purposes of humanity is an evidence -of the value of abstract study, and a reply to the -utilitarian in his own language.</p> - -<p>Electricity appears to be diffused through all nature; -and it is, beyond all doubt, one of the most important -of the physical forces, in the great phenomena of creation. -In the thunder-cloud, swelling with destruction, -it resides, ready to launch its darts and shake the earth -with its explosions: in the aërial undulations, silent -and unseen, it passes, giving the necessary excitement -to the organisms around which it floats. The rain-drop—the -earth-girdling ocean—and the ringing waters -of the hill-born river, hold locked this mighty force. -The solid rocks—the tenacious clays which rest upon -them—the superficial soils—and the incoherent sands, -give us evidence of the presence of this agency; and in -the organic world, whether animal or vegetable, the excitement -of electrical force is always to be detected.</p> - -<p>In the solar radiations we have perhaps the prime mover -of this power. In our atmosphere, when calm and cloud<span class="pagenum"><a name="Page_195" id="Page_195"></a>[Pg 195]</span>less, -a great ocean of light, or when sombre with the -mighty aspect of the dire tornado, we can constantly -detect the struggle between the elements of matter to -maintain an equilibrium of electrical force.</p> - -<p>Diffused throughout matter, electricity is ever active; -but it must be remembered that although it is evidently -a necessary agent in all the operations of nature, that it -is not the agent to which everything unknown is to be -referred. Doubtless the influence of this force is more -extensive than we have yet discovered; but that is an -indolent philosophy which refers, without examination, -every mysterious phenomenon to the influence of electricity.</p> - -<p>The question, what is electricity? has ever perplexed, -and still continues to agitate, the world of science. -While one set of experimentalists have endeavoured to -explain the phenomena they have witnessed, upon the -theory that electricity is a peculiar subtile fluid pervading -matter, and possessing singular powers of attraction -and repulsion, another party find themselves compelled -to regard the phenomena as giving evidence of the action -of two fluids which are always in opposite states; while -again, electricity has been considered by others as, like -the attraction of gravitation, a mere property of matter.<a name="FNanchor_136_136" id="FNanchor_136_136"></a><a href="#Footnote_136_136" class="fnanchor">[136]</a> -Certain it is, that in the manifestations of electrical phenomena -we have, as it appears, the evidence of two conditions -of force; but of the states of <i>positive</i> or <i>negative</i>, of -<i>vitreous</i> or <i>resinous</i> electricity, we have a familiar explanation -in the assumption of some current flowing into or<span class="pagenum"><a name="Page_196" id="Page_196"></a>[Pg 196]</span> -out of the material body,—of some principle which is -ever active in maintaining its equilibrium, which, consequently, -must act in two directions, and always exhibit -that duality which is a striking characteristic of this -subtile agent. It is a curious, and it should be an -instructive fact, that each of the three theories of electricity -is capable of proof, and has, indeed, been most -ably supported by the rigorous analysis of mathematics. -When we remember that some of the most enlightened -investigators of this and the past age have severally -maintained, in the most able manner, these dissimilar -views, we should hesitate before we pronounce an opinion -upon the cause or causes of the very complicated phenomena -of electrical force.</p> - -<p>Although we discover, in all the processes of nature, -the manifestations of this principle or force in its characteristic -conditions, it will be necessary, before we -regard the great phenomena, to examine the known -sources from which we can most readily evoke the -mighty power of electricity. If we rub a piece of glass -or resin, we readily render this agent active; these substances -appear, by this excitement, to become surrounded -by an attractive or a repellent atmosphere. Let us rub -a strip of writing paper with Indian rubber, or a strip -of Gutta Percha with the fingers, in the dark, and we -have the manifestation of several curious phenomena. -We have a peculiar attracting power; we have a luminous -discharge in the shape of a spark; and we have -very sensible evidence of muscular disturbance produced -by applying the knuckle to the surface of the material. -In each case we have the development of the same -power.</p> - -<p>Every substance in nature is an electric, and, if so -disposed that its electricity may not fly off as it is developed, -we may, by friction, manifest its presence, and, -indeed, measure its quantity or its force. All bodies -are not, however, equally good electrics; shell-lac,<span class="pagenum"><a name="Page_197" id="Page_197"></a>[Pg 197]</span> -amber, resins, sulphur, and glass, exhibiting more powerfully -the phenomena of frictional or mechanical electricity, -than the metals, charcoal, or plumbago. Solid -bodies allow this peculiar principle to pass along them -also in very different degrees. Thus electricity travels -readily through copper and most other metals, platinum -being the worst metallic conductor. It also passes -through living animals and vegetables, smoke, vapour, -rarified air, and moist earth; but it is obstructed by -resins and glass, paper when dry, oils, and dry metallic -oxides, and in a very powerful manner by Gutta Percha.<a name="FNanchor_137_137" id="FNanchor_137_137"></a><a href="#Footnote_137_137" class="fnanchor">[137]</a></p> -<p><span class="pagenum"><a name="Page_198" id="Page_198"></a>[Pg 198]</span></p> -<p>If, therefore, we place an electric upon any of those -non-conducting bodies, the air around being well dried, -we are enabled to gather a large quantity of the force -for the production of any particular effect. Taking advantage -of this fact, arrangements are made for the -accumulation and liberation at pleasure of any amount -of electricity.</p> - -<p>A Leyden phial,—so called from its inventor, <span class="correction" title="In the original book: Muschenbrock">Musschenbroek</span>, -having resided at Leyden,—is merely a glass bottle -lined within and without, to within a few inches of the -top, with a metal coating. If a wire or chain, carrying -an electric current, is allowed to dip to the bottom of -the bottle, the inner coat of the jar becomes charged, -or gathers an excess, whilst the outer one is in its natural -condition—one is said to be in a <i>positive</i>, and the other in -a <i>negative</i> state. If the two coatings are now connected -by a good conductor, as a piece of copper wire, passing -from one to the other, the outside to the inside, a discharge, -arising from the establishment of the equilibrium -of the two coatings, takes place; and, if the connection -is made through the medium of our bodies, -we are sensible of a severe disturbance of the nervous -system.</p> - -<p>The cause of the conducting and non-conducting -powers of bodies we know not; they bear some relation -to their conducting powers for caloric; but they are not -in exact obedience to the same laws. When we consider -that resin, a comparatively soft body, in which, conse<span class="pagenum"><a name="Page_199" id="Page_199"></a>[Pg 199]</span>quently, -cohesive attraction is not very strong, is an imperfect -conductor, and that copper, in which cohesion is -much more powerful, is a good conductor, we may be -disposed to consider that it is regulated by the closer approximation -of the particles of matter. But in platinum -the corpuscular arrangement must be much more dense -than it is in copper, and yet it is, compared with it, a -very bad conductor.<a name="FNanchor_138_138" id="FNanchor_138_138"></a><a href="#Footnote_138_138" class="fnanchor">[138]</a></p> - -<p>We have now learnt that we may, by friction, excite -the electricity in a vitreous substance; but it must not -be forgotten that we cannot increase the quantity which -is, under ordinary conditions, natural to the electric; to -do so, we must in some way establish a channel of communication -with the earth, from which, through the -medium we excite, we draw our supply. We have the -means of confining this mighty force within certain limits -of quantity and of time. If we place bodies which are -susceptible of electrical excitation in a sensible degree -upon insulating ones, we may retain for a considerable -time the evidences of the excitement, in the same way as -with the Leyden jar; but there is a constant effort to -maintain a balance of conditions, and the body in which -we have accumulated any extraordinary quantity by conduction -soon returns to its natural state.</p> - -<p>A very simple means may be adopted of showing what -is thought to be one of the many evidences in favour of -two electricities. If the wire carrying the current flowing -from the machine, is passed over paper covered with -nitrate of silver, it produces no change upon it; but if -the wire which conveys the current to the instrument, -when it is excited, is passed over the same paper, the -silver salt is decomposed.<a name="FNanchor_139_139" id="FNanchor_139_139"></a><a href="#Footnote_139_139" class="fnanchor">[139]</a> We may, however, explain -this result in a satisfactory manner, upon the hypothesis<span class="pagenum"><a name="Page_200" id="Page_200"></a>[Pg 200]</span> -that the decomposition is produced by the abstraction of -electricity, rather than by any physical difference in the -fluid itself. By frictional electricity we may produce -curious molecular disturbances, and give rise to molecular -re-arrangements, which have been called “electrical -images,” in glass, in stone, and in the apparently less -tractable metals: these images are rendered visible by -the manner in which, according to their electrical states, -some lines receive any particular powder, or vapour, -which is repelled from other spaces. Many of the great -natural phenomena, such as Lightning and Thunder, the -Aurora Borealis, and Meteors, may be imitated in a -curiously exact manner by the electrical machine and a -few familiar arrangements.<a name="FNanchor_140_140" id="FNanchor_140_140"></a><a href="#Footnote_140_140" class="fnanchor">[140]</a></p> - -<p>Voltaic electricity, as the active force produced by -chemical change is commonly called, in honour of the -illustrious Volta, is now to be considered. It differs -from frictional electricity in this:—the electricity developed -by friction of the glass plate or cylinder of the -electrical machine is a discharge with a sort of explosion. -It is electricity suddenly liberated from the highest state -of tension, whereas that which is generated by chemical -action in the voltaic battery is a steady flowing current. -We may compare one to the ignition of a mass of gunpowder -at once, and the other to the slow burning of -the same quantity spread out into a very prolonged -train.</p> - -<p>There are numerous ways in which we may excite the -phenomena of Voltaism, but in all of them the decomposition -of one of the elements employed appears to be -necessary. This is the case in the arrangements of batteries -in which two dissimilar metals, zinc and copper, -silver and platinum, or the like, is immersed in fluids; -the zinc or the silver are gradually converted into soluble -salts, which are dissolved, whilst the copper or platinum<span class="pagenum"><a name="Page_201" id="Page_201"></a>[Pg 201]</span> -is protected from any action. The most simple manner -of illustrating the development of this electricity is by -placing a piece of silver on the tongue, and a piece of -zinc or lead underneath it. No effect will be observed -so long as the two metals are kept asunder, but when -their edges are brought together, a slight tremulous sensation -will pass through the tongue, a saline taste be -distinguished by the palate, and if in the dark, light will -be observed by the eye.</p> - -<p>This, the germ of the most remarkable of the sciences, -was noticed by Sulzar, fifty years before Galvani observed -the convulsions in the limbs of frogs, when excited by -the action of dissimilar metals; but the former paid -little attention to the phenomenon, and the discovery -led to no results.</p> - -<p>When Galvani’s observant mind was directed to the -remarkable fact that the mere contact of two dissimilar -metals with the moist surface of living muscles produced -convulsions, there was an awakening in the soul of that -philosopher to a great fundamental truth, which was -nurtured by him, tried and tested, and preserved to work -its marvels for future ages.</p> - -<p>Although the world of science looks back to Volta as -the man who gave the first true interpretation of this -discovery, yet the ordinary world will never disconnect -this important branch of physical science from the -name of Galvani, and chemical electricity in all its -forms will for ever be known under the familiar name of -Galvanism. And it must not be forgotten, that the -phenomena of the manifestation of electricity, in connection -with the conditions of vitality, are entirely due to -Galvani.</p> - -<p>Let us examine the phenomena of Galvanism in its -most simple phases:—</p> - -<p>If we place a live flounder upon a plate of zinc, put a -shilling on its back, and then touch both metals with -the ends of a metallic wire, the fish will exhibit painful<span class="pagenum"><a name="Page_202" id="Page_202"></a>[Pg 202]</span> -convulsions. The zinc becomes oxidized by the separation -of oxygen from the fluid on the surface with which -it is in contact, whilst hydrogen gas is liberated at that -surface touched by the other metal. Here we have, in -the first place, a chemical change effected, then a peculiar -muscular disturbance. Each successive combination -or decomposition, like a pulsation, is transmitted along -the circuit from one extremity to the other. How the -impulse which is derived from the zinc is transmitted -through the body of the animal, or the tongue, to the -silver or copper is the next consideration.</p> - -<p>We can only understand this upon the supposition -that a series of impulses are communicated in the most -rapid manner along the connecting line; the idea of a -current, although the term is commonly employed, tends -to convey an imperfect impression to the mind. It -would seem rather that a disturbance throughout the -entire circuit is at once set up by a series of vibrations -or impulses communicated from particle to particle, and -along the strange net-work of nerves. One set of chemical -elements have a tendency to develope themselves -at that point where vibration is first communicated to -the mass from a better conductor than it is, and another -set at the point where it passes from the body to a better -conductor than itself. The cause of this is to be sought -for in the laws which regulate molecular constitution—by -which chemical affinity is disturbed,—and a new -attractive force exerted, in obedience to which the vital -energy is itself agitated. We must not, however, forget -that it is probable after all, although not yet susceptible -of proof, that the electricity does nothing more than disturb -or quicken the unknown principles upon which chemical -and vital phenomena depend; being, indeed, a -secondary agent.<a name="FNanchor_141_141" id="FNanchor_141_141"></a><a href="#Footnote_141_141" class="fnanchor">[141]</a></p> -<p><span class="pagenum"><a name="Page_203" id="Page_203"></a>[Pg 203]</span></p> -<p>Notwithstanding our long acquaintance with the phenomena -of galvanism, there are but few who entertain a -correct idea of the enormous amount of electricity which -is necessary to the existing conditions of matter. To -Faraday we are indebted for the first clear set of deductions -from a series of inductive researches, which are of -the most complete order. He has proved, by a series -of exceedingly conclusive experiments, that if the electrical -power which holds a grain of water in combination, -or which causes a grain of oxygen and hydrogen to unite -in the right proportions to form water, could be collected -and thrown into the condition of a voltaic current, it -would be exactly the quantity required to produce the -decomposition of that grain of water, or the liberation of -its elements, hydrogen and oxygen.<a name="FNanchor_142_142" id="FNanchor_142_142"></a><a href="#Footnote_142_142" class="fnanchor">[142]</a></p> - -<p>By direct experiment it has been proved that one equivalent -of zinc in a voltaic arrangement evolves such a -quantity of electricity in the form of a current, as, passing -through water, will decompose exactly one equivalent -of that fluid. The law has been thus expressed:—The -electricity which decomposes, and that which is evolved -by the decomposition of a certain quantity of matter, are<span class="pagenum"><a name="Page_204" id="Page_204"></a>[Pg 204]</span> -alike. The equivalent weights of bodies are those quantities -of them which contain equal quantities of electricity; -electricity determining the equivalent number, -because it determines the combining force.<a name="FNanchor_143_143" id="FNanchor_143_143"></a><a href="#Footnote_143_143" class="fnanchor">[143]</a></p> - -<p>The same elegant and correct experimentalist has -shown that zinc and platinum wires, one-eighteenth of -an inch in diameter, and about half an inch long, dipped -into water in which is mixed sulphuric acid so weak -that it is not sensibly sour to the tongue, will evolve -more electricity in one-twentieth of a minute than is -given by thirty turns of a large and powerful plate electrical -machine in full action, a quantity which, if passed -through the head of a cat, is sufficient to kill it as by a -flash of lightning. Pursuing this interesting inquiry -yet further, it is found that a single grain of water contains -as much electricity as could be accumulated in -800,000 Leyden jars, each requiring thirty turns of the -large machine of the Royal Institution to charge it,—a -quantity equal to that which is developed from a -charged thunder-cloud. “Yet we have it under perfect -command,—can evolve, direct, and employ it at pleasure; -and when it has performed its full work of electrolisation, -it has only separated the elements of a single -grain of water.”</p> - -<p>It has been argued by many that the realities of -science will not admit of anything like a poetic view -without degrading its high office; that poetry, being -the imaginative side of nature, has nothing in common -with the facts of experimental research, or with the -philosophy which generalises the discoveries of severe -induction. If our science was perfect, and laid bare to -our senses all the secrets of the inner world; if our -philosophy was infallible, and always connected one fact -with another through a long series up to the undoubted -cause of all—then poetry, in the sense we now use the<span class="pagenum"><a name="Page_205" id="Page_205"></a>[Pg 205]</span> -term, would have little business with the truth; it -would, indeed, be lost or embodied, like the stars of -heaven, in the brightness of a meridian sun. But to -take our present fact as an example, how important a -foundation does it offer upon which to build a series of -thoughts, capable of lifting the human mind above the -materialities by which it is surrounded,—of exalting -each common nature by the refinement of its fresh ideas -to a point higher in the scale of intelligence,—of quickening -every impulse of the soul,—and of giving to -mankind the most holy longings.</p> - -<p>What does science tell us of the drop of water? Two -gases, the one exciting life and quickening combustion, -the other a highly inflammable air, are, by the influence -of a combination of powers, brought into a liquid globe. -We can, from this crystal sphere, evoke heat, light, -electricity, and actinism in enormous quantities; and -beyond these we can see powers or forces, for which, in -the poverty of our ideas and our words, we have not -names; and we learn that each one of these principles -is engaged in maintaining the conditions of the drop of -water which refreshes organic nature, and gives gladness -to man’s dwelling-place.</p> - -<p>Has poetry a nobler theme than this? Agencies are -seen like winged spirits of infinite power, each one -working in its own peculiar way, and all to a common -end,—to produce, under the guidance of omnipotent -rule, the waters of the rivers and the seas. As the -great ocean mirrors the bright heaven which overspreads -it, and reflects back the sunlight and the sheen of the -midnight stars in grandeur and loveliness; so every -drop of water, viewed with the knowledge which science -has given to us, sends back to the mind reflections of -yet distant truths which, rightly followed, will lead us -upwards and onwards in the tract of higher intelligences,—</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“To the abodes where the eternals are.”</div> -</div></div></div> -<p><span class="pagenum"><a name="Page_206" id="Page_206"></a>[Pg 206]</span></p> - -<p>In the discoveries connected with electricity, we have -results of a more tangible character than are as yet connected -with the other physical forces; and it does appear -that this science has advanced our knowledge of nature -and of the mysteries of creation far more extensively -than any other department of purely experimental -inquiry.</p> - -<p>The phenomena of electro-chemical action are so -strange that we must return for a moment to the consideration -of the decomposition of water, and the -appearance of hydrogen at one pole, and of oxygen at -the other. It appears that some confusion of our ideas -has arisen from the views which have been received of -the atomic constitution of bodies. We have been -accustomed to regard water,—to take that body as an -example of all,—as a compound of two gases, hydrogen -and oxygen; an equivalent, or one atom of the first, -united to an equivalent or one atom of the last, -forming one atom of water. This atom of water we -regard as infinitely small; consequently a drop of water -is made up of many hundreds of these combined atoms, -and a pint of water of not less than 10,000 drops. Now, -if this pint of water is connected with the wires of -a galvanic battery, although their extremities may be -some inches apart, for every atom of oxygen liberated at -one pole, an atom of hydrogen is set free at the other. -It has been thought that an atom has undergone -decomposition at one point, its oxygen being torn from -it, and then there has arisen the difficulty of sending -the atom of hydrogen through all the combined atoms -of water across to the other pole. A series of decompositions -and recompositions have been supposed to take -place, and the communication of effects from particle to -particle.</p> - -<p>An attracting power for one class of bodies has been -found in one pole, which is repellent to another class; -and the reverse order has been detected at the opposite<span class="pagenum"><a name="Page_207" id="Page_207"></a>[Pg 207]</span> -pole of a galvanic arrangement.<a name="FNanchor_144_144" id="FNanchor_144_144"></a><a href="#Footnote_144_144" class="fnanchor">[144]</a> That is, the wire -which carries the current from an excited zinc plate -has a relation to all bodies, which is directly opposite to -that which is exhibited by the wire conveying the current -from, or completing the circuit with, the copper -plate. The one, for instance, collects and carries acids -and the like, the other the metallic bases. At the -extremity of one galvanic wire, placed into a drop of -water, oxygen is always liberated; and at the end of -the other, necessary to complete the circuit with the -battery, hydrogen is set free.</p> - -<p>It appears necessary, to a clear understanding of -what takes place in this experiment, that we should -regard each mass, howsoever large, as the representative -of a single atom. Nor is this difficult, as the following -illustration will show.</p> - -<p><span class="pagenum"><a name="Page_208" id="Page_208"></a>[Pg 208]</span></p> - -<p>Let us take one particle of common salt (<i>chloride</i> of -<i>sodium</i>) weighing less than a grain, and put it into a -hundred thousand grains of distilled water. In a few -minutes the salt has diffused itself through the whole of the -fluid, and in every drop we can detect chlorine and soda. -We cannot believe that this grain of salt has split itself -up into a hundred thousand parts; we conceive rather -that the phenomenon of solution is one of diffusion. -One infinitely elastic body has interpenetrated with -another.</p> - -<p>Instead of an experiment with a pint of water, let us -take our stand on Dover heights, and, with a gigantic -battery at our command, place one wire into the ocean -on our own shores, and convey the other through the -air across the channel, and let its extremity dip into the -sea off Calais pier—the experiment is a practicable one—we -have now an electrical circuit of which the British -channel forms a part, and the result will be exactly the -same as that which we may observe in a watch-glass -with a drop of water.</p> - -<p>We cannot suppose that the instantaneous and -simultaneous effect which takes place in the water at -Calais and at Dover, is due to anything like what we -have studied under the name of convection, when -considering Heat.</p> - -<p>A thousand balls are placed in a line touching each -other; the first ball receives a blow, and the last ball -flies off with a force exactly equal to the power applied -to the first; none of the intermediate balls being -moved.</p> - -<p>We cannot conceive that the particle <i>A</i> excites the -particle <i>B</i> next it, and so on through the series between -the two shores; but regarding the channel as one large -drop, charged with the electric principle as we know it -to be, it is excited by undulation or tremor throughout -its width, and we have an equivalent of oxygen thrown -off on one side of the line, and an exact equivalent of<span class="pagenum"><a name="Page_209" id="Page_209"></a>[Pg 209]</span> -hydrogen at the other, the electro-chemical influence -being exerted only where the current or motion is -transferred from one medium to another.<a name="FNanchor_145_145" id="FNanchor_145_145"></a><a href="#Footnote_145_145" class="fnanchor">[145]</a> The imperfect -character of this view is freely admitted; no -other, consistent with known facts, presents itself by -which the effect can be explained. The fact stands as a -truth; the hypothesis by which it is attempted to be -interpreted is open to doubt, and it is opposed to some -favourite theories.</p> - -<p>Before we pass to the consideration of the other -sources of electricity, it is important we should understand -that no chemical or physical change, however -slight it may be, can occur without the development of -electrical power. If we dissolve a salt in water, if we -mix two fluids together, if we condense a gas, or convert -a fluid into vapour, electricity is disturbed, and may be -made manifest to our senses.<a name="FNanchor_146_146" id="FNanchor_146_146"></a><a href="#Footnote_146_146" class="fnanchor">[146]</a></p> - -<p>It has been shown that this power may be excited by -friction (machine electricity) and by chemical action -(voltaic electricity, galvanism); it now remains to speak -of the electricity developed by heat (thermo-electricity), -the electricity exhibited under nervous excitement by<span class="pagenum"><a name="Page_210" id="Page_210"></a>[Pg 210]</span> -the gymnotus and torpedo (animal electricity); magnetism -and its phenomena being reserved for a separate -consideration.</p> - -<p>If a bar of metal is warmed at one end and kept cool -at the other, an electrical current circulates through the -bar, and may be carried off by connection with any -good conductor, and shown to exhibit the properties of -ordinary electricity. The metals best suited for showing -the effects of thermo-electricity appear to be bismuth -and antimony. By binding two bars of these metals -together at one end, and connecting the other ends with -a galvanometer, it will be discovered that an electric -current passes off through the instrument by the -slightest variation of temperature. Merely clasping -the two metals, where bound together, with the finger -and thumb, is sufficient to exhibit the phenomenon. -By a series of such arrangements,—which form what -have been called thermo-electric multipliers,—we -obtain the most delicate measurers of heat with which -philosophers are acquainted, by the aid of which -Melloni has been enabled to pursue his beautiful -researches on radiant caloric.</p> - -<p>That this electricity is identical with the other forms -has been proved by employing the current thus excited -for the purpose of producing chemical decomposition, -magnetism, and electric light.<a name="FNanchor_147_147" id="FNanchor_147_147"></a><a href="#Footnote_147_147" class="fnanchor">[147]</a></p> - -<p>The phenomenon of thermo-electricity—the discovery<span class="pagenum"><a name="Page_211" id="Page_211"></a>[Pg 211]</span> -of Seebeck, is another proof of the very close connection -of the physical forces. We witness their being resolved -as it were into each other, electricity producing heat, -and heat again electricity; and it is from these curious -results that the arguments in favour of their intimate -relations and actual identity have been drawn. It will, -however, be found to be the best philosophy to regard -these forces as dissimilar, until we are enabled to prove -them to be only modified forms of one principle or -power. At the same time it must not be forgotten that -in natural operations we invariably find the combined -action of several forces producing a single phenomenon. -The important fact to be particularly regarded is, that -we have evidence that every substance which is unequally -heated becomes the source of this very remarkable -form of electricity.<a name="FNanchor_148_148" id="FNanchor_148_148"></a><a href="#Footnote_148_148" class="fnanchor">[148]</a></p> - -<p>There exist a few fishes gifted with the very extraordinary -power of producing electrical phenomena -by an effort of muscular or nervous energy.</p> - -<p>The <i>Gymnotus electricus</i>, or electrical eel, and the -<i>Raia torpedo</i>, a species of ray, are the most remarkable. -This power is, it would appear, given to these curious -creatures for purposes of defence, and also for enabling -them to secure their prey. The <i>Gymnotus</i> of the South -America rivers, will, it is said, when in full vigour, send -forth a discharge of electricity sufficiently powerful to -knock down a man, or to stun a horse; while it can -destroy fishes, through a considerable space, by exerting -its strange artillery.<a name="FNanchor_149_149" id="FNanchor_149_149"></a><a href="#Footnote_149_149" class="fnanchor">[149]</a></p> - -<p>Faraday’s description of a <i>Gymnotus</i>, paralyzing and<span class="pagenum"><a name="Page_212" id="Page_212"></a>[Pg 212]</span> -seizing its prey, is too graphic and important to be -omitted.</p> - -<p>“The <i>Gymnotus</i> can stun and kill fish which are in -very various positions to its own body; but on one day, -when I saw it eat, its action seemed to me to be -peculiar. A live fish, about five inches in length, -caught not half a minute before, was dropped into the -tub. The <i>Gymnotus</i> instantly turned round in such a -manner as to form a coil, inclosing the fish, the latter -representing a diameter across it; a shock passed, and -there, in an instant, was the fish struck motionless, as -if by lightning, in the midst of the waters, its side -floating to the light. The <i>Gymnotus</i> made a turn or -two to look for its prey, which, having found, he bolted, -and then went about searching for more. A second -smaller fish was given him, which being hurt in the -conveyance, showed but little signs of life, and this he -swallowed at once, apparently without shocking it. The -coiling of the <i>Gymnotus</i> round its prey had, in this case, -every appearance of being intentional on its part, to -increase the force of the shock, and the action is evidently -well suited for that purpose, being in full -accordance with the well-known laws of the discharge -of currents in masses of conducting matter; and though -the fish may not always put this artifice in practice, it is -very probable he is aware of its advantages, and may -resort to it in cases of need.”<a name="FNanchor_150_150" id="FNanchor_150_150"></a><a href="#Footnote_150_150" class="fnanchor">[150]</a></p> - -<p>Animal electricity has been proved to be of the same -character as that derived from other sources. The -shock and the spark are like those of the machine; and<span class="pagenum"><a name="Page_213" id="Page_213"></a>[Pg 213]</span> -the current from the animal, circulating around soft -iron, like galvanic electricity, has the property of rendering -it magnetic.</p> - -<p>It is important that we should now review these -conditions of electrical force in connexion with the great -physical phenomena of nature.</p> - -<p>It is sufficiently evident, from the results which have -been examined, that all matter, whatever may be its -form or condition, is for ever under the operation of the -physical forces, in a state of disturbance. From the -centre to the surface all is in an active condition: a -state of mutation prevails with every created thing; and -science clearly shows that influences are constantly in -action which prevent the possibility of absolute repose.</p> - -<p>Under the excitement of the several agencies of the -solar beams, motion is given to all bodies by the circulation -of heat, and a full flow of electricity is sent -around the earth to perform its wondrous works. The solar -influences, which regulate, and possibly determine, every -physical force with which we are acquainted, are active -in effecting an actual change of state in matter. The -sunbeam of the morning falls on the solid earth, and its -influence is felt to the very centre. The mountain-top -catches the first ray of light, and its base, still wrapt in -mists and darkness, is disturbed by the irradiating -power. The crystalline gems, hidden in the darkness of -the solid rock, are dependent, for that form which -makes them valued by the proud and gay, on the -influence of those radiations which they are one day to -refract in beauty. The metals locked in the chasms of -the rifted rocks are, for all their physical peculiarities, -as dependent on solar influence as is the flower which -lifts its head to the morning sun, or the bird which sings -“at heaven’s high gate.”</p> - -<p>Let us, then, examine how far electricity, as distinguished -from the other powers, acts in producing any -of these effects.</p> - -<p><span class="pagenum"><a name="Page_214" id="Page_214"></a>[Pg 214]</span></p> - -<p>We find electricity in the atmosphere, which the -electrical kite of Dr. Franklin proved to be identical -with that principle produced by the friction of glass. In -the grandeur and terror of a thunderstorm, many see -nothing but manifestations of Almighty wrath. When -the volleys of the bursting cloud are piercing the -disturbed air, and the thunders of the discharge are -pealing their dreadful notes above our heads, the -chemical combinations of the noxious exhalations -arising from the putrefying animal and vegetable -masses of this earth are effected, elements fitted for the -purposes of health and vegetation are formed, and -brought to the ground in the heavy rains which usually -follow these storms. Science has taught man this—has -shown him that the “partial evil” arising from the -“winged bolt” is a “universal good;” and, more than -this, it has armed him with the means of protecting his -life and property from the influence of lightnings. So -that, like Ajax, he can defy the storm. By metallic -rods, carried up a chimney, a tower, or a mast, we may -form a channel through which the whole of the -electricity of the most terrific thunder-cloud may be -carried harmlessly into the earth or the sea; and it is -pleasing to observe that at length prejudice has been -overcome, and “conductors” are generally attached to -high buildings, and to most of the ships of our navy.<a name="FNanchor_151_151" id="FNanchor_151_151"></a><a href="#Footnote_151_151" class="fnanchor">[151]</a> -It was discovered that the devastating hailstorms of the -south of France and Switzerland, so destructive to the -vineyards and crops, were accompanied by evidences of -great electrical excitation, and it was proposed to discharge -the electricity from the air by means of pointed -metallic rods. These have been adopted, and, it is said,<span class="pagenum"><a name="Page_215" id="Page_215"></a>[Pg 215]</span> -with real advantage—each rod protecting an area of one -hundred yards. Thus it is that science ministers to our -service; and how much more pleasing is it to contemplate -the lightning, with the philosopher, as an agent -destroying the elements of pestilence, and restoring the -healthfulness of the air we breathe, than with the -romancer, to see in it only the dreaded aspect of a -demon of destruction.</p> - -<p>The laws which regulate the spread of a pestilence -are unknown. The difficulties of the investigation are -great, but they are by no means insurmountable. A -plague passes from the east to the west across the world—it -spreads mourning over the gayest cities, and sorrow -sitteth in the streets. The black death rises in the -Orient: it goes on in unchecked strength, and only -finishes its course when it has made the circuit of the -civilized world. The cholera spreads its ebon wings—mankind -trembles—watches its progress, and looks -upon the path which is marked by the myriads of the -dead, who have fallen before the dire fiend. The -diseases pass away—the dead are buried, and all is -forgotten. The rush and the riot of life are pursued: -and until man is threatened with another advent, he -cares not to trouble himself. Accompanying the last -visitation, there appear certain peculiar meteorological -conditions, which point a line of inquiry. It may or -may not be the path which leads to the truth, but -certainly its indications are worthy of careful examination. -It may be asked, can weak man stop a -pestilence; can a mortal’s puny hand retard the afflictions -of the Almighty? The question asked—it must -be answered in reverence, yet without fear. No -human power can produce a change in the physical conditions -of the earth, or of the air; and if our diseases -are connected with those changes, as beyond all doubt -a number of them are, they lie above man’s control. -But when there are indications that causes secondary to<span class="pagenum"><a name="Page_216" id="Page_216"></a>[Pg 216]</span> -these are producing some dire effect, and when we -know that these secondary causes may be modified, it is -sufficient evidence to prove that man is permitted to -control thus far the afflictions which are sent to try his -powers.</p> - -<p>We find a disease winging its way from lane to alley -and closed court, sweeping with destructive violence its -way through damp cellars and crowded attics; it is rife -with mischief along the banks of reeking ditches, and -on the borders of filthy streams. Certain it is, therefore, -that some ultimate connexion exists between the conditions -of dirt and this speedy death. Can science tell -of these? has it yet searched out the connecting link? -Let the question be answered by a few facts.</p> - -<p>When the cholera first made its appearance, and -subsequently, it has been observed that the electrical -intensity of the atmosphere was unusually low.</p> - -<p>The disease has departed, and it is then found that -the electricity of the air has been restored to its ordinary -condition.</p> - -<p>This appears to show some connexion; but how do -these conditions link this physical force with the ditch-seeking -disease?</p> - -<p>From all stagnant places, from all the sinks of overcrowded -humanity, from fermenting vegetable and from -putrefying animal matter, there are constantly arising -poisonous exhalations to do their work of destruction.</p> - -<p>Where death and decay is a law, this must of necessity -constantly occur; but the poisonous reek may be diffused, -or it may be concentrated, and Nature has provided -for this, and ordered the means for rendering the -poison harmless.</p> - -<p>By the agency of electricity,—probably, too, by the -influence of light,—the oxygen in the air undergoes a -peculiar change, by which it is rendered far more energetic -than it is in its ordinary state. This is the condition -to which the name of <i>ozone</i> has been applied.<span class="pagenum"><a name="Page_217" id="Page_217"></a>[Pg 217]</span> -Now, this ozone, or this peculiar oxygen, always exists -in the air we breathe; but its quantity is subject to great -and rapid variations. It is found that when electrical -intensity is high the quantity of this principle is great; -when the electrical intensity is low, as in the cholera -years, the proportion of ozone is relatively low.</p> - -<p>This remarkable chemical agent possesses the power -of instantly combining with organic matter,—of removing -with singular rapidity all noxious odours; and -it would appear to be the most active of all known -disinfectants.</p> - -<p>May we not infer from the facts stated that the pestilence -we dread is the result of organic poison, which -from a deficiency of ozone,—its natural antidote,—exerts -its baneful influences on humanity. This deficiency is -due to alterations in the electrical character of the air, -possibly dependent upon phenomena taking place in the -sun itself, or it may be still more directly influenced by -variations in the character of solar light, which we have -not yet detected, by which the conditions of the electric -power are determined.</p> - -<p>This may be a line along which it is fair to push enquiry. -But such an enquiry must be made in all the -purity of the highest inductive philosophy, and speculation -must be held firmly in the controlling chains of -experiment and observation. In the truths, however, -which are known to us, there is so much harmony and -consistence that even the melancholy theme links itself—a -tragedy—with the Poetry of Science.</p> - -<p>It has been thought, and much satisfactory evidence -has been brought forward to support the idea, that the -earth’s magnetism is due to currents of electricity -circulating around the globe; as a great natural current -from east to west—that, indeed, it has an unvarying -reference to the motion of the earth in relation to the sun.<a name="FNanchor_152_152" id="FNanchor_152_152"></a><a href="#Footnote_152_152" class="fnanchor">[152]</a></p> -<p><span class="pagenum"><a name="Page_218" id="Page_218"></a>[Pg 218]</span></p> -<p>These terrestrial currents, as they have without doubt -a very important bearing on the structural conditions -of the rock-formations and the distribution of minerals, -require an attentive consideration; but we must, in the -first place, examine, as far as we know, the influences -exerted, or supposed to be exerted, by electricity, in its -varied forms.</p> - -<p>The phenomena of vitality have, by many, been considered -as immediately dependent upon its influence; -and a rather extensive series of experiments has been -made in support of this hypothesis. The researches -of Philip on the action of the organs of digestion, when -separated from their connection with the brain, but -united with a galvanic battery, have been proved by -Dr. Reid to be delusive;<a name="FNanchor_153_153" id="FNanchor_153_153"></a><a href="#Footnote_153_153" class="fnanchor">[153]</a> since, as the organ is not<span class="pagenum"><a name="Page_219" id="Page_219"></a>[Pg 219]</span> -removed from the influence of the living principle, it is -quite evident that the electricity here is only secondary -to some more important power. Matteucci has endeavoured -to show that nervous action is intimately -connected with electric excitation, and that electricity -may be made a measurer of nervous <span class="correction" title="In the original book: iritability">irritability</span>.<a name="FNanchor_154_154" id="FNanchor_154_154"></a><a href="#Footnote_154_154" class="fnanchor">[154]</a> There -can be no doubt that a peculiar susceptibility to excitement -exists in some systems, and this is very strikingly -shown in the disturbances produced by electric action; -but in the experiments which have been brought forward -we have only the evidence that a certain number -of muscular contractions are exhibited in one animal by -a current of electricity, giving a measured effect by the -voltameter, which are different from those produced -upon another by a current of the same power. An -attempt has recently been made by Mr. A. Smee to -reduce the electrical phenomena connected with vitality -to a more exact system than had hitherto been done. -We cannot, however, regard the attempt as successful. -The author has trusted almost entirely to analogical -reasoning, which is in science always dangerous.<a name="FNanchor_155_155" id="FNanchor_155_155"></a><a href="#Footnote_155_155" class="fnanchor">[155]</a> In -the development of electricity during the operation of -the vital force, we see only the phenomena produced -by the action of any two dissimilar chemical compounds<span class="pagenum"><a name="Page_220" id="Page_220"></a>[Pg 220]</span> -upon each other. It has been thought that the structure -of the brain presents an analogy to that of the galvanic -battery, and the nerves represent the conducting wires. -Although, however, some of the conditions appear -similar, there are many which have no representatives -in either the mechanical structure or the physical -properties of the brain, so far as we know it. That the -brain is the centre, the source, and termination of sensation -is very clearly proved by physiological investigations. -That the nerves are the media by which all -sensation is conveyed to the brain, and also the instruments -by which the will exerts its power over the -muscles, is equally well established. But to say that we -have any evidence to support the idea that electricity -has aught to do directly with these great physiological -phenomena, would be a bold assertion, betraying a want -of due caution on the part of the investigator. That -electric effects are developed during the operations of -vitality is most certain. Such must be the case, from -the chemical changes taking place during respiration -and digestion, and the mechanical movements by which, -even during external repose, the necessary functions of -the body are carried on. Whether electricity is the -cause of these, or an effect arising from them, we need -not stop to examine, as this is, in the present state of -our knowledge, a mere speculation. We have no evidence -that electricity is an exciting power, but rather -that it is one of those forces which tend to establish -the equilibrium of matter. When disturbed—when its -equilibrium is overset—it does, in its efforts to regain -its stability, produce most remarkable effects. An -electrical machine must be rubbed to exhibit any force. -In all galvanic arrangements, even the most simple, -dissimilar bodies are brought together, and the latent -electricity of both is disturbed; and, even in the magnet, -it is only when this takes place that its electrical powers -are developed. In the <i>Gymnotus</i>, electricity appears to<span class="pagenum"><a name="Page_221" id="Page_221"></a>[Pg 221]</span> -be dependent upon the power of the will of the animal; -but even in this extraordinary fish, it is only under peculiar -conditions that the electrical excitement takes -place, and “what they inflict, they feel” during the -restoration of that equilibrium which is necessary to -their healthy state. In every case, therefore, we see -that some power far superior to this is the ultimate -cause; indeed, light and heat, and probably actinism, -appear to stand superior to this principle; and on these, -in some combined mode of action, in all probability, -sensible electricity is dependent. Beyond even these -elements, largely as they are engaged in the organic -and inorganic changes of this world, there are occult -powers which may never be understood by finite beings. -We advance step by step from the most solid to the -most ethereal of material creations, and we examine a -series of extraordinary effects produced by powers which -we know not whether to regard as material or immaterial, -so subtile are they. On these, it appears, we -may exhaust our inductive investigations—we may discover -the laws by which these principles act upon the -grosser elements, and develope phenomena of a very -remarkable kind which have been unobserved or misunderstood. -Whether light, heat, and electricity are -modifications of one power, or different powers very -closely united in action, is a problem we may possibly -solve; but to know what they are, appears to be beyond -the hopes of science; and it were idle to dream of -elucidating the causes hidden beyond these forces, and -by which they are regulated in all their actions on dead -or living matter.</p> - -<p>M. Du Bois Raymond, from a series of researches -remarkable alike for their difficulty and the delicacy -with which they have been pursued, draws the following, -amongst many others, as his conclusions as to the connection -of electricity and vital phenomena.</p> - -<p>The muscles and nerves, including the brain and the<span class="pagenum"><a name="Page_222" id="Page_222"></a>[Pg 222]</span> -spinal chord, are endowed during life with an electromotive -power, which acts according to a definite law.</p> - -<p>The electromotive power <i>lasts after death</i>, or in dissected -nerves and muscles after separation from the -body of the animal, as long as the excitability of the -nervous and muscular fibre; whether these fibres are -permitted to die gradually from the cessation of the -conditions necessary to the support of life, or whether -they are suddenly deprived of their vital properties by -heat or chemical action.</p> - -<p>Let us not suppose for a moment that these conclusions -indicate in the remotest degree that electricity -is life,—that vital power is due to electricity.</p> - -<p>During life, with every motion, and, indeed, with -every emotion, whether we move a muscle or exert the -mind, there is a change of state. The result of this is -chemical phenomena,—heat and electricity; but these are -not life. We excite them equally by giving motion to -a dead mass.</p> - -<p>Notwithstanding the assertions of those who have -zealously followed the path of Mesmer, and examined, -or they have thought so, the psychological effects dependent -upon some strange physiological conditions, -there is not an experiment on record,—there is not an -observation worthy of credit, which shows that electricity -has any connection with their results. All around -their subject is uncertainty: doubt involves every -experiment, and deception clouds a large number. -Some few grains of truth, and these are sufficiently -strange, are mixed up in an enormous mass of error.</p> - -<p>All the phenomena of life,—of the <i>vis vitæ</i> or vitality, -are beyond human search. All the physical forces, or -elements, we may examine by the test of experiment: -but the principle on which sensation depends, the principle -even upon which vegetable <i>life</i> depends, cannot -be tested. Life is infinitely superior to every physical -force; it holds them all in control, but is not itself<span class="pagenum"><a name="Page_223" id="Page_223"></a>[Pg 223]</span> -controlled by them; it keeps its state sacred from -human search,—the invisible hidden behind the veil of -mortality.</p> - -<p>During changes in the electrical conditions of the -earth and atmosphere, vegetables give indications of -being in a peculiar manner influenced by this power. -It is proved by experiments that the leaves of plants -are among the best conductors of electricity, and it -has hence been inferred that it must necessarily be -advantageous to vegetation. That vegetable growth -is, equally with animal growth, subject to electricity, -as one of its quickening powers, must be admitted; -but all experiments which have been fairly tried with -the view of stimulating the growth of plants by its -agency, have given results of a negative character.<a name="FNanchor_156_156" id="FNanchor_156_156"></a><a href="#Footnote_156_156" class="fnanchor">[156]</a> -That a galvanic arrangement may produce chemical -changes in the soil, which may be advantageous to the -plant, is probable; but that a plant can be brought to -maturity sooner, or be made to develope itself more -completely, under the direct action of electrical excitation, -appears to be one of those dreams of science -which will have a place amongst the marvels of alchemy -and the fictions of astrology. An attentive examination -of all the conditions necessary for the satisfactory development -of the plant, will render it evident, that -although the ordinary electrical state of the earth and -atmosphere must influence the processes of germination -and vegetable growth, yet that any additional excitement -must be destructive to them. The wonders wrought by -electrical power are marvellous; a magic influence is<span class="pagenum"><a name="Page_224" id="Page_224"></a>[Pg 224]</span> -exerted by it, and naturally the inquiring mind is led -at first to believe that electricity is the all-powerful -principle of creation; but a little reflection will serve -to convince us that it is a subordinate agent, although -a powerful one.</p> - -<p>In proceeding with our examination of the phenomena -which present themselves in connection with -the terrestrial currents, we purposely separate magnetism -from those more distinct electro-chemical agencies -which play so important a part in the great cosmical -operations.</p> - -<p>Electricity, we have already stated, flows through or -involves all bodies; but, like heat, it appears to undergo -a very remarkable change in becoming associated with -some forms of matter. We have the phenomena of -magnetism when an electric current circulates through -a metallic wire, and it would appear that all other bodies -acquire a peculiar polar condition under the influence of -this principle, which will be explained in the next chapter.</p> - -<p>The rocks, taken as masses, will not conduct an -electric current when dry: granite, porphyry, slate, and -limestone, obstructing its passage even through the -smallest spaces. But all the metallic formations admit -of its circulating with great freedom. This fact it must, -however, be remembered does not in any way interfere -with the hypothesis of the existence of electricity in all -bodies, in what we must regard as its latent state, from -which, under prescribed conditions, it may be readily -liberated. Neither does it affect the question of circulation, -in relation to the great diffusion of electricity -which we suppose to exist through all nature, and to -move in obedience to some fixed law. We know that -through the superficial strata electric currents circulate -freely, whether they are composed of clay, sand, or any -mixture of these with decomposed organic matter; -indeed, that with any substance in a moist state they -suffer no interruption.</p> - -<p><span class="pagenum"><a name="Page_225" id="Page_225"></a>[Pg 225]</span></p> - -<p>The electricity of mineral veins has attracted much -attention, and numerous investigations into the phenomena -which these metalliferous formations present, have -been made from time to time.<a name="FNanchor_157_157" id="FNanchor_157_157"></a><a href="#Footnote_157_157" class="fnanchor">[157]</a></p> - -<p>By inserting into the mass of a copper <i>lode</i>, or vein, in -situ, a metallic wire, which shall be connected with a measurer -of galvanic action, a wire also from the instrument -being brought into contact with another <i>lode</i>, an immediate -effect is generally produced, showing that a current is -traversing through the wires from one <i>lode</i> to the other, -and completing the circulation probably over the dark -face of the rock in which the fissures forming the -mineral veins exist.<a name="FNanchor_158_158" id="FNanchor_158_158"></a><a href="#Footnote_158_158" class="fnanchor">[158]</a> The currents thus detected are -often sufficiently active to deflect a magnetic needle -powerfully, to produce, slowly, electro-chemical decomposition, -and to render a bar of iron magnetic. These -currents must not be confounded with the great -electrical movements around the earth. They are -only to be detected in those mineral formations in which -there is evidence of chemical action going on, and, the -greater the amount of this chemical operation, the more -energetic are the electrical currents.<a name="FNanchor_159_159" id="FNanchor_159_159"></a><a href="#Footnote_159_159" class="fnanchor">[159]</a> We have, how<span class="pagenum"><a name="Page_226" id="Page_226"></a>[Pg 226]</span>ever, -very good evidence that these local currents have, -of themselves, many peculiar influences. It not unfrequently -happens that owing to some great disturbance -of the crust of the earth, a mineral vein is dislocated, -and one part either sinks below, or is lifted above its -original position; the fissures formed between the two -being usually filled in with clay or with crystalline -masses of more recent formation than the fissure itself. -It is frequently found that these “<i>cross courses</i>,” as -they are called in mining language, contain ores of a -different character from those which constitute the -mineral vein; for instance, in them nickel, cobalt, and -silver are not unfrequently discovered. When these -metals are so found, they almost invariably occur between -the ends of the dislocated lode, and often take a -curvilinear direction, as if they were deposited along a -line of electrical force.<a name="FNanchor_160_160" id="FNanchor_160_160"></a><a href="#Footnote_160_160" class="fnanchor">[160]</a></p> - -<p>In the laboratory such an arrangement has been -imitated, and in a mass of clay fixed between the galvanic -plates, after a short period a distinct formation of -a mineral vein has taken place.<a name="FNanchor_161_161" id="FNanchor_161_161"></a><a href="#Footnote_161_161" class="fnanchor">[161]</a> By the action, too, of -weak electrical currents, Becquerel, Crosse, and others, -have been successful in imitating nature so far as to -produce crystals of quartz and other minerals. In addition -to this evidence, in support of the electrical theory<span class="pagenum"><a name="Page_227" id="Page_227"></a>[Pg 227]</span> -of the origin of mineral veins, it can be experimentally -shown that a schistose structure may be given to clays -and sandstone by voltaic action.<a name="FNanchor_162_162" id="FNanchor_162_162"></a><a href="#Footnote_162_162" class="fnanchor">[162]</a></p> - -<p>There is often a very remarkable regularity in the -direction of mineral veins: throughout Cornwall, for -instance, they most commonly have a bearing from the -E. of N. to the W. of S. It has hence been inferred -that they observe some relation to the magnetic poles of -the earth. However this may be, it is certain that the -ore in any lodes which are in a direction at right angles, -or nearly so, to this main line, differs in character from -that found in these, so called, east and west lobes.<a name="FNanchor_163_163" id="FNanchor_163_163"></a><a href="#Footnote_163_163" class="fnanchor">[163]</a></p> - -<p>The sources of chemical action in the earth are numerous. -Water percolating through the soil, and finding -its way to great depths through fissures in the rocks, -carries with it oxygen and various salts in solution. -Water again rising from below, whether infiltrated from -the ocean or derived from other sources, is usually of a -high temperature, and it always contains a large quantity -of saline matter.<a name="FNanchor_164_164" id="FNanchor_164_164"></a><a href="#Footnote_164_164" class="fnanchor">[164]</a> By these causes alone chemical<span class="pagenum"><a name="Page_228" id="Page_228"></a>[Pg 228]</span> -action must be set up. Chemical change cannot take -place without a development of electricity: and it has -been proved that the quantity of electricity required for -the production of any change is equal to that contained -in the substances undergoing such change. Thus a -constant activity is maintained within the caverns of the -rock by the agency of the chemical and electrical -elements, and mutations on a scale of great grandeur -are constantly taking place under some directive force.</p> - -<p>The mysterious gnome, labouring—ever labouring—in -the formation of metals, and the mischievous Cobalus -of the mine, are the poor creations of superstition. A -vague fear is spread amongst great masses of mankind -relative to the condition of the dark recesses of the -earth; a certain unacknowledged awe is experienced by -many on entering a cavern, or descending a mine: not -the natural fear arising from the peculiarity of the situation, -but the result of a superstitious dread, the effect -of a depraved education, by which they have been taught -to refer everything a little beyond their immediate comprehension -to supernatural causes. The spirit of demon<span class="pagenum"><a name="Page_229" id="Page_229"></a>[Pg 229]</span> -worship, as well as that of hero worship, has passed -from the early ages down to the present; and under its -influence the genii of the East and the demons of the -West have preserved their traditionary powers.</p> - -<p>Fiction has employed itself with the utmost license in -giving glowing pictures of treasures hidden in the earth’s -recesses. The caverns of Chilminar, the cave of Aladdin, -the abodes of the spirits of the Hartz, and the -dwellings of the fairies of England, are gem-bespangled -and gold-glistening vaults, to which man has never -reached. The pictures are pleasing; but although they -have the elements of poetry in them, and delight the -young mind, they want the sterling character of scientific -truth; and the wonderful researches of the plodding -mineralogist have developed more beauty in the -caverns of the dark rock than ever fancy painted in her -happiest moments.</p> - -<p>In all probability the action of the sun’s rays upon -the earth’s surface, producing a constantly varying difference -of temperature, and also the temperature which -has been observed as existing at great depths, give rise -to thermo-electrical currents, which may play an important -part in the results thus briefly described.</p> - -<p>In connection with these great natural operations, explaining -them, and being also, to some extent, explained -by them, we have the very beautiful application of electricity -to the deposition of metals, called the Electrotype.</p> - -<p>Applying the views we have adopted to this beautiful -discovery,<a name="FNanchor_165_165" id="FNanchor_165_165"></a><a href="#Footnote_165_165" class="fnanchor">[165]</a> the whole process by which these metallic -deposits are produced will be yet more clearly understood. -By the agency of the electric fluid, liberated<span class="pagenum"><a name="Page_230" id="Page_230"></a>[Pg 230]</span> -in the galvanic battery, a disturbance of the electricity -of the solution of copper, silver, or gold, is produced, -and the metal is deposited; but, instead of allowing the -acid in combination to escape, it has presented to it -some of the same metal as that revived, and, consequently, -it combines with it, and this compound, being -dissolved, maintains the strength of the solution.<a name="FNanchor_166_166" id="FNanchor_166_166"></a><a href="#Footnote_166_166" class="fnanchor">[166]</a> A -system of revival, or decomposition, is carried on at one -pole, and one of abrasion, or more correctly speaking, of -composition and solution, at the other. By taking -advantage of this very extraordinary power of electricity, -we now form vessels for ornament or use, we gild or -silver all kinds of utensils, and give the imperishability -of metal to the most delicate productions of nature—her -fruits, her flowers, and her insects;—and over the -finest labours of the loom we may throw coatings of gold -or silver to add to their elegance and durability. Nor -need we employ the somewhat complex arrangement of -the battery: we may take the steel magnet, and, by -mechanically disturbing the electricity it contains, we -can produce a current through copper wires, which may -be used, and is extensively employed, for gilding and -silvering.<a name="FNanchor_167_167" id="FNanchor_167_167"></a><a href="#Footnote_167_167" class="fnanchor">[167]</a> The earth itself may be made the battery, -and, by connecting wires with its mineral deposits, currents -of electricity have been secured, and used for the -production of electrotype deposit.<a name="FNanchor_168_168" id="FNanchor_168_168"></a><a href="#Footnote_168_168" class="fnanchor">[168]</a></p> - -<p><span class="pagenum"><a name="Page_231" id="Page_231"></a>[Pg 231]</span></p> - -<p>The electrotype is but one of the applications of -electricity to the uses of man. This agent has been -employed as the carrier of thought; and with infinite -rapidity, messages of importance, communications involving -life, and intelligences outstripping the speed of -coward crime, have been communicated. There will be -no difficulty in understanding the principle of this, -although many of the nice mechanical arrangements, to -ensure precision, are of a somewhat elaborate character. -The entire action depends on the deflection of a compass-needle -by the passage of an electric current along -its length. If at a given point we place a galvanic battery, -and at twenty or one hundred miles distance from -it a compass-needle, between a wire brought from, and -another returning to the battery, the needle will remain -true to its polar direction so long as the wires are unexcited; -but the moment connection is made, and the -circuit is complete, the electricity of the whole extent of -wire is disturbed, and the needle is thrown at right -angles to the direction of the current. Provided a connection -between two points can be secured, however -remote they are from each other, we thus, almost -instantaneously, convey any intelligence. The effects -of an electric current would appear at a distance of -576,000 miles in a second of time; and to that distance, -and with that speed, it is possible, by Professor -Wheatstone’s beautiful arrangements, to convey whispers -of love or messages of destruction.</p> - -<p>The enchanted horse of the Arabian magician, the -magic carpet of the German sorcerer, were poor contrivances, -compared with the copper wires of the electrician, -by which all the difficulties of time and the -barriers of space appear to be overcome. In the Scandinavian -mythology we find certain spiritual powers of -evil enabled to pass with imperceptible speed from one -remote point to another, sowing the seeds of a common -ruin amongst mankind. Such is the morbid creation of<span class="pagenum"><a name="Page_232" id="Page_232"></a>[Pg 232]</span> -a wild yet highly endowed imagination. The spirit of -evil diffuses itself in a remarkable manner, and, indeed, -we might almost assign to it the power of ubiquity; -but in reality its advance is progressive, and time enters -as an element into any calculation on its diffusion. -Electricity is instantaneous in action; as a spirit of -peace and good-will it can overtake the spirit of evil, -and divert it from its designs. May we not hope that -the electrical telegraph, making, as it must do, the whole -of the civilized world enter into a communion of thought, -and, through thought, of feeling with each other, will -bind us up in one common brotherhood, and that, -instead of misunderstanding and of misinterpreting the -desires and the designs of each other, we shall learn to -know that such things as “natural enemies” do not -exist? To hope to break down the great barrier of -language is perhaps too much; but assuredly we may -hope that, as we must do when closer and more intimate -relations are secured by the aids of science, the barrier -of prejudice may be razed to the ground, and not one -stone left to stand upon another? Our contentions, -our sanguinary wars, consecrated to history by the baptism -of blood, have in every, or in nearly every, instance -sprung from the force of prejudice, or the mistakes of -politicians, whose minds were narrowed to the limits of -a convention formed for perpetuating the reign of -ignorance.</p> - -<p>And can anything be more in accordance with the -spirit of all that we revere as holy, than the idea that -the elements employed by the All Infinite in the works -of physical creation shall be made, even in the hands of -man, the ministering angels to the great moral redemption -of the world? Associate the distant nations -of the earth, and they will find some common ground -on which they may unite. Mortality compels a dependence; -and there are charities which spring up alike -in the breast of the savage and the civilized man, which<span class="pagenum"><a name="Page_233" id="Page_233"></a>[Pg 233]</span> -will not be controlled by the cold usages of pride, but -which, like all truths, though in a still small voice, -speak more forcibly to the heart than errors can, and -serve as links in the great chain which must bind mankind -in a common brotherhood. “None are all evil,” -and the best have much to learn of the amenities of -life from him who yet lives in a “state of nature,” or -rather from him whose sensualities have prevailed over -his intellectual powers, but who still preserves many -of the noblest instincts, to give them no higher term, -which other races, proud of their intelligence, have -thrown aside. Time and space have hitherto prevented -the accomplishment of this; electricity and mechanics -promise to subdue both; and we have every reason to -hope those powers are destined to accelerate the union -of the vast human family.</p> - -<p>Electrical power has also been employed for the purpose -of measuring time, and by its means a great number -of clocks can be kept in a state of uniform correctness, -which no other arrangement can effect. A battery being -united with the chief clock, which is itself connected by -wires with any number of clocks arranged at a distance -from each other, has the current continually and regularly -interrupted by the beating of the pendulum, which -interruption is experienced by all the clocks included -in the electric circuit; and, in accordance with this -breaking and making contact, the indicators or hands -move over the dial with a constantly uniform rate. -Instead of a battery the earth itself has supplied the -stream of electric fluid, with which the rate of its revolutions -has been registered with the utmost fidelity.<a name="FNanchor_169_169" id="FNanchor_169_169"></a><a href="#Footnote_169_169" class="fnanchor">[169]</a></p> - -<p>Electricity, which is now employed to register the -march of time, rushes far in advance of the sage who -walks with measured tread, watching the falling sands -in the hour-glass.</p> - -<p><span class="pagenum"><a name="Page_234" id="Page_234"></a>[Pg 234]</span></p> - -<p>The earth is spanned and the ocean pierced by -the wires of the electric telegraph. Already, from -the banks of the Thames to the shores of the -Adriatic, our electric messenger will do our bidding. -The telegraph is making its way through Italy, and -it is dipping its wires in the Mediterranean, soon to -reach the coast of Africa. They will then run along -the African shores to Egypt and Turkey, and still onward -until they unite with the telegraphs of India, of -which three thousand miles are in progress. From -Hindostan these wondrous wires will run from island to -island in the Indian Archipelago, and thus connect -Australia and New Zealand with Europe.</p> - -<p>In a few years we may expect to have an instantaneous -report in London of the extraordinary “nugget” discovered -by some fortunate gold-digger; and the exile -from his native land in the Islands of the South Pacific -Ocean, may learn every hour, if he will, of the doings -of his family and friends in some village home of -England.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_136_136" id="Footnote_136_136"></a><a href="#FNanchor_136_136"><span class="label">[136]</span></a> <i>Traité de Physique</i>: M. Biot, vol. vii. Becquerel: Annales -de Chimie, vol. xlvi.-xlix. Faraday’s <i>Experimental Researches in -Electricity</i>, 2 vols., 1830–1844. <i>A Speculation touching Electric -Conduction and the Nature of Matter</i>: by Michael Faraday, -D.C.L., F.R.S.; Philosophical Magazine, vol. xxiv., 1836. -<i>Objections to the theories severally of Franklin, Dufay, and Ampère, -with an attempt to explain Electrical Phenomena by statical or -undulatory polarization</i>: by Robert Hare, M.D., Emeritus Professor -of Chemistry in the University of Pennsylvania.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_137_137" id="Footnote_137_137"></a><a href="#FNanchor_137_137"><span class="label">[137]</span></a> “A good piece of gutta percha will insulate as well as an equal -piece of shell-lac, whether it be in the form of sheet, or rod, or filament; -but being tough and flexible when cold, as well as soft -when hot, it will serve better than shell-lac in many cases where -the brittleness of the latter is an inconvenience. Thus it makes -very good handles for carriers of electricity in experiments on -induction; not being liable to fracture in the form of thin band or -string, it makes an excellent insulating suspender; a piece of it in -sheet makes a most convenient insulating basis for anything -placed on it. It forms excellent insulating plugs for the stems of -gold-leaf electrometers, when they pass through sheltering tubes, -and larger plugs form good insulating feet for electrical arrangements; -cylinders of it, half an inch or more in diameter, have -great stiffness, and form excellent insulating pillars. In these -and in other ways its power as an insulator may be useful.”—<i>On -the use of Gutta Percha in Electrical Insulation</i>: by Dr. -Faraday; Philosoph. Mag., March, 1848. -</p> -<p> -The following deductions have been given by Faraday, in his -<i>Researches in Electricity</i>, a work of most extraordinary merit, -being one of the most perfect examples of fine inductive philosophy -which we possess in the English language:— -</p> -<p> -“All bodies conduct electricity in the same manner from -metals to lacs and gases, but in very different degrees. -</p> -<p> -“Conducting power is in some bodies powerfully increased by -heat, and in others diminished, yet without one perceiving any -accompanying essential electrical difference, either in the bodies, -or in the change occasioned by the electricity conducted. -</p> -<p> -“A numerous class of bodies insulating electricity of low -intensity, when solid, conduct it very freely when fluid, and are -then decomposed by it. -</p> -<p> -“But there are many fluid bodies which do not sensibly conduct -electricity of this low intensity; there are some which -conduct it and are not decomposed; nor is fluidity essential to -decomposition. -</p> -<p> -“There are but two bodies (sulphuret of silver and fluoride -of lead) which, insulating a voltaic current when solid, and conducting -it when fluid, are not decomposed in the latter case. -</p> -<p> -“There is no strict electrical distinction of conduction which -can as yet be drawn between bodies supposed to be elementary, -and those known to be compounds.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_138_138" id="Footnote_138_138"></a><a href="#FNanchor_138_138"><span class="label">[138]</span></a> Faraday’s <i>Speculation on the Nature of Matter</i>, already -referred to.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_139_139" id="Footnote_139_139"></a><a href="#FNanchor_139_139"><span class="label">[139]</span></a> <i>Experimental Researches</i>: by Dr. Faraday. <i>Chemical Decomposition</i>, -p. 151.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_140_140" id="Footnote_140_140"></a><a href="#FNanchor_140_140"><span class="label">[140]</span></a> Karsten; Poggendorff’s <i>Annalen</i>, vol. lvii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_141_141" id="Footnote_141_141"></a><a href="#FNanchor_141_141"><span class="label">[141]</span></a> <i>Traité Expérimental de <span class="correction" title="In the original book: l’Electricité">l’Électricité</span> et du Magnétisme</i>: -Becquerel, 1834, Priestley’s <i>Introduction to Electricity</i>. <i>On -Electricity in Equilibrium</i>: Dr. Young’s Lectures.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_142_142" id="Footnote_142_142"></a><a href="#FNanchor_142_142"><span class="label">[142]</span></a> Faraday’s <i>Experimental Researches on Electricity</i>. This -philosopher has shown, by the most conclusive experiments, -“that the electricity which decomposes, and that which is evolved -by the decomposition of, a certain quantity of matter, are alike. -What an enormous quantity of electricity, therefore, is required -for the decomposition of a single grain of water! We have -already seen that it must be in quantity sufficient to sustain a -platinum wire 1/104 of an inch in thickness, red hot, in contact -with the air, for three minutes and three quarters. It would -appear that 800,000 charges of a Leyden battery, charged by -thirty turns of a very large and powerful plate machine, in full -action—a quantity sufficient, if passed at once through the head -of a rat or cat, to have killed it as by a flash of lightning—are -necessary to supply electricity sufficient to decompose a single -grain of water; or, if I am right, to equal the quantity of electricity -which is naturally associated with the elements of that grain -of water, endowing them with their mutual chemical affinity.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_143_143" id="Footnote_143_143"></a><a href="#FNanchor_143_143"><span class="label">[143]</span></a> <i>Experimental Researches</i>: Faraday.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_144_144" id="Footnote_144_144"></a><a href="#FNanchor_144_144"><span class="label">[144]</span></a> The appearance of acid and alkaline matter, in water acted -on by a current of electricity, at the opposite electrified metallic -surfaces, was observed in the first chemical experiments made -with the column of Volta—(see Nicholson’s Journal, vol. iv. p. -183, and vol. iv. p. 261, for Mr. Cruickshank’s Experiments; and -Annales de Chimie, tom. xxxvii. p. 233, for those of M. Desormes): -<i>On some Chemical Agencies in Electricity</i>: by Sir Humphry Davy.—Philosophical -Transactions for 1807. The various theories of -electro-chemical decomposition are carefully stated by Faraday, in -his fifth series of <i>Experimental Researches on Electricity</i>, in which -he thus states his own views:—“It appears to me that the effect -is produced by an <i>internal corpuscular action</i> exerted according -to the direction of the electric current, and that it is due to a force -either <i>superadded to</i> or <i>giving direction to the ordinary chemical -affinity</i> of the bodies present. The body under decomposition -may be considered as a mass of acting particles, all those which -are included in the course of the electric current contributing to -the final effect; and it is because the ordinary chemical affinity -is relieved, weakened, or partly neutralized by the influence of the -electric current in one direction parallel to the course of the -latter, and strengthened or added to in the opposite direction, that -the combining particles have a tendency to pass in opposite -courses.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_145_145" id="Footnote_145_145"></a><a href="#FNanchor_145_145"><span class="label">[145]</span></a> “This capital discovery (chemical decomposition of electricity) -appears to have been made in the first instance by Messrs. -Nicholson and Carlisle, who observed the decomposition of water -so produced. It was speedily followed up by the still more important -one of Berzelius and Hisinger, who ascertained it as a general -law, that, in all the decompositions so effected, the acids and -oxygen become transferred and accumulated around the positive, -and hydrogen, metals, and alkalies around the negative, pole of a -voltaic circuit; being transferred in an invisible, and, as it were, -a latent or torpid state, by the action of the electric current, -through considerable spaces, and even through large quantities of -water or other liquids, again to reappear with all their properties -at their appropriate resting-places.”—<i>Discourse on the Study of -Natural Philosophy</i>: by Sir John Herschel, Bart., F.R.S.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_146_146" id="Footnote_146_146"></a><a href="#FNanchor_146_146"><span class="label">[146]</span></a> Numerous beautiful illustrations of this fact will be found in -Becquerel’s <i>Traité Expérimental de <span class="correction" title="In the original book: l’Electricité">l’Électricité</span> et du Magnétisme</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_147_147" id="Footnote_147_147"></a><a href="#FNanchor_147_147"><span class="label">[147]</span></a> See <i>Le Feu élémentaire</i> of l’Abbé Nollet; Leçons de Physique, -tom. vi. p. 252; <i>Du Pouvoir thermo-électrique</i>, by M. Becquerel—Annales -de Chimie, vol. xli. p. 353; also a Memoir by Nobili, -Bibliothèque Universelle, vol. xxxvii. p. 15; <i>Experimental Contributions -towards the theory of Thermo-Electricity</i> by Mr. J. -Prideaux—Philosophical Magazine, vol. iii., Third Series; <i>On the -Thermo-Magnetism of Homogeneous Bodies, with illustrative experiments</i>, -by Mr. William Sturgeon—Philosophical Magazine, vol. -x. p. 1–116, New Series. Botto made magnets and obtained -chemical decomposition. Antinori produced the spark. Mr. -Watkins heated a wire in Harris’s Thermo-Electrometer.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_148_148" id="Footnote_148_148"></a><a href="#FNanchor_148_148"><span class="label">[148]</span></a> A very ingenious application of the knowledge of this fact was -suggested by Mr. Solly, by which the heat of a furnace could be -constantly registered at a very considerable distance from it. See -<i>Description of an Electric Thermometer</i>: by E. Solly, Jun., -Esq. Philosophical Magazine, vol. xx. p. 391. New Series.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_149_149" id="Footnote_149_149"></a><a href="#FNanchor_149_149"><span class="label">[149]</span></a> Humboldt; <i>Personal Narrative</i>, Chap. xvii.—Annales de -Chimie, vol. xiv. p. 15.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_150_150" id="Footnote_150_150"></a><a href="#FNanchor_150_150"><span class="label">[150]</span></a> <i>Experimental Researches on Electricity.</i> Series xv. Consult -Sir Humphry Davy: <i>An Account of some Experiments on the Torpedo</i>.—Philosophical -Transactions, 1829, p. 15. John Davy, M.D., -F.R.S.: <i>An Account of some Experiments and Observations on the -Torpedo</i>, ibid., 1832, p. 259; and the same author’s <i>Observations -on the Torpedo, with an Account of some Additional Experiments on -its Electricity</i>; and Matteucci, Bibliothèque Universelle, 1837, -vol. xii. p. 174.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_151_151" id="Footnote_151_151"></a><a href="#FNanchor_151_151"><span class="label">[151]</span></a> <i>On Lightning Conductors</i>, by Sir William Snow Harris; -<i>Observations on the Action of Lightning Conductors</i>, by W. Snow -Harris, Esq., F.R.S.—London Electrical Society’s Transactions. -Numerous valuable papers <i>On Electricity</i>, by Sir William Harris, -will be found in the Philosophical Transactions.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_152_152" id="Footnote_152_152"></a><a href="#FNanchor_152_152"><span class="label">[152]</span></a> Adopting, to a certain extent, this view, Faraday, in his -<i>Electrical Nomenclature</i>, proposed for the word pole to substitute -<i>anode</i> (ανω, <i>upwards</i>, and ὁδος, <i>a way</i>), the way which the sun rises; -and <i>cathode</i> (κατα, <i>downwards</i>, and ὁδος, <i>a way</i>), the way which the -sun sets. The hypothesis belongs essentially to Ampère. <i>Objections -to the Theories severally of Franklin, Dufay, and Ampère, with -an Effort to Explain Electrical Phenomena by Statical or Undulatory -Polarisation</i>, by Robert Hare, M.D., Pennsylvania, will well repay -an attentive perusal.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_153_153" id="Footnote_153_153"></a><a href="#FNanchor_153_153"><span class="label">[153]</span></a> <i>Inquiry into the Laws of the Vital Functions.</i>—Philosophical -Transactions, 1815, 1822; <i>Some Observations relating to the Functions -of Digestion</i>, ibid., 1829: <i>On the Powers on which the Functions -of Life in the more perfect animals depend, and on the manner -in which they are associated in the production of their more complicated -results</i>, by A. P. W. Philip, M.D., F.R.S., L. and E.—The -following extract from the last-quoted of Dr. Philip’s Memoirs, -will give a general view of the conclusions of that eminent physiologist:—“With -respect to the nature of the powers of the living -animal which we have been considering, the sensorial and muscular -powers, and the powers peculiar to living blood, we have -found belong to the living animal alone, all their peculiar properties -being the properties of life. The functions of life may be -divided into two classes, those which are affected by the properties -of this principle alone, and those, by far the most numerous class, -which result from the co-operation of these properties with those -of the principles which operate in inanimate nature. The nervous -power we have found to be a modification of one of the latter principles, -because it can exist in other textures than those to which -it belongs in the living animal, and we can substitute for it one of -those principles without disturbing the functions of life. -</p> -<p> -“Late discoveries have been gradually evincing how far more -extensive than was supposed, even a few years ago, is the dominion -of electricity. Magnetism, chemical affinity, and (I believe -from the facts stated in the foregoing paper, it will be impossible -to avoid the conclusion) the nervous influence, the leading power -in the vital functions of the animal frame, properly so called, appear -all of them to be modifications of this apparently universal agent; -for I may add we have already some glimpses of its still more extensive -dominion.” -</p> -<p> -Refer to Dr. Reid’s papers.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_154_154" id="Footnote_154_154"></a><a href="#FNanchor_154_154"><span class="label">[154]</span></a> <i>Electro-physiological Researches</i>: by Signor Carlo Matteucci; -Phil. Trans. 1845, p. 293, and subsequent years.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_155_155" id="Footnote_155_155"></a><a href="#FNanchor_155_155"><span class="label">[155]</span></a> Electro-Biology: by Alfred Smee, Esq.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_156_156" id="Footnote_156_156"></a><a href="#FNanchor_156_156"><span class="label">[156]</span></a> <i>Observations of Electric Currents in Vegetable Structures</i>: by -Golding Bird, Esq., F.L.S.; Magazine of Natural History, vol. x. -p. 240. In this paper Dr. Bird remarks that his experiments lead -to the conclusion that vegetables cannot become so charged with -electricity as to afford a spark; that electrical currents of feeble -tension are always circulating in vegetable tissues; and that electrical -currents are developed during germination from chemical -action.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_157_157" id="Footnote_157_157"></a><a href="#FNanchor_157_157"><span class="label">[157]</span></a> <i>On Mineral Veins</i>: by Robert Were Fox, Esq.; Fourth Report -of the Royal Cornwall Polytechnic Society. <i>On the Electro-magnetic -Properties of Metalliferous Veins in the mines of Cornwall</i>: -by Robert W. Fox, Esq.; Phil. Trans. 1830, p. 399.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_158_158" id="Footnote_158_158"></a><a href="#FNanchor_158_158"><span class="label">[158]</span></a> <i>Experiments and Observations on the Electricity of Mineral -Veins</i>: by Robert Hunt and John Phillips; Reports of the Royal -Cornwall Polytechnic Society for 1841–42. <i>On the Electricity of -Mineral Veins</i>: by Mr. John Arthur Phillips; Ibid., 1843.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_159_159" id="Footnote_159_159"></a><a href="#FNanchor_159_159"><span class="label">[159]</span></a> In the lead lodes of <i>Lagylas</i> and <i>Frongoch</i>, electrical currents -were detected by Mr. Fox, but none in those of <i>South Mold</i> and -<i>Milwr</i>, in Flintshire: Cornwall Geological Transactions, vol. iv. -In the lead veins of <i>Coldberry</i> and <i>Skeers</i>, in Teasdale, Durham, -the currents detected were very feeble: Reports of the Bristol Association, -1838. Von Strombeck could detect no electric currents -in the veins worked in the clay slate near Saint Goar, on the -Rhine: Archiv. für Mineralogie, Geognosie, &c., von Dr. C. J. B -Karsten, 1833. Professor Reich, however, obtained very decided -results at <i>Frisch Glück</i>, <i>Neue Hoffnung</i>, <i>Gottlob</i>, and in other mineral -veins in the mining districts of Saxony: Edinburgh New -Philosophical Journal, vol. xxviii. 1839. The irregularities are all -to be explained by the presence or absence of chemical excitation.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_160_160" id="Footnote_160_160"></a><a href="#FNanchor_160_160"><span class="label">[160]</span></a> This was remarkably the case at <i>Huel Sparnon</i>, near Redruth, -where the cobalt was discovered <span class="correction" title="In the original book: betweed">between</span> two portions of a dislocated -lode; and the same was observed by Mr. Percival Johnson -in a small mine worked for nickel, near St. Austell.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_161_161" id="Footnote_161_161"></a><a href="#FNanchor_161_161"><span class="label">[161]</span></a> <i>On the process used for obtaining artificial veins in clay</i>: by -T. B. Jordan; Sixth Annual Report of the Royal Cornwall Polytechnic -Society. See also my memoir, already referred to, in the -Memoirs of the Geological Survey and Museum of Practical Geology, -vol. i.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_162_162" id="Footnote_162_162"></a><a href="#FNanchor_162_162"><span class="label">[162]</span></a> See Becquerel, <i>Traité Experimental de l’Electricité, &c. Electrical -Experiments on the formation of Artificial Crystals</i>: by -Andrew Crosse, Esq.; British Association Reports, vol. v., 1836. -The lamination of clay and other substances is described in my -memoir referred to, Note p. 226.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_163_163" id="Footnote_163_163"></a><a href="#FNanchor_163_163"><span class="label">[163]</span></a> Report on the Geology of Cornwall, Devon, and West Somerset, -by Sir Henry T. De la Beche: <i>Theoretical observations on the -formation and filling of Mineral Veins and Common Faults</i>, p. 349.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_164_164" id="Footnote_164_164"></a><a href="#FNanchor_164_164"><span class="label">[164]</span></a> The following analyses of waters from deep mines were made -by me in 1840, and, with many others, published in the Reports of -the Royal Cornwall Polytechnic Society. -</p> -<table id="water" summary="Analyses of water in mines"> - -<tr><th class="tdl">Consolidated Mines, Gwennap, Cornwall.</th><th class="tdpad1">In 1,000 grains of water.</th></tr> -<tr><td class="tdpad1">Muriate of soda</td><td class="tdr tdpadr">1·5 </td></tr> -<tr><td class="tdpad1">Sulphate of lime</td><td class="tdr tdpadr">·5 </td></tr> -<tr><td class="tdpad1">Sulphate of iron</td><td class="tdr tdpadr">·15</td></tr> -<tr><td class="tdpad1">Sulphate of copper</td><td class="tdr tdpadr">1·25</td></tr> -<tr><td class="tdpad1">Silica</td><td class="tdr tdpadr">·15</td></tr> -<tr><td class="tdpad1">Alumina</td><td class="tdr tdpadr">·3 </td></tr> -<tr><td></td><td class="tdr tdpadr">——</td></tr> -<tr><td class="tdpad2">Total</td><td class="tdr tdpadr">3·7 </td></tr> - -<tr><th class="tdtop tdl">United Mines, Gwennap.</th><th></th></tr> -<tr><td class="tdpad1">Muriate of soda</td><td class="tdr tdpadr">1·10</td></tr> -<tr><td class="tdpad1">Muriate of lime</td><td class="tdr tdpadr">·15</td></tr> -<tr><td class="tdpad1">Sulphate of soda</td><td class="tdr tdpadr">·50</td></tr> -<tr><td class="tdpad1">Sulphate of lime</td><td class="tdr tdpadr">1·5 </td></tr> -<tr><td class="tdpad1">Sulphate of iron</td><td class="tdr tdpadr">·75</td></tr> -<tr><td class="tdpad1">Alumina</td><td class="tdr tdpadr">·5 </td></tr> -<tr><td class="tdpad1">Silica</td><td class="tdr tdpadr">·15</td></tr> -<tr><td></td><td class="tdr tdpadr">——</td></tr> -<tr><td class="tdpad2">Total</td><td class="tdr tdpadr">4·65</td></tr> - -<tr><th class="tdtop tdl">Great St. George.</th><th></th></tr> -<tr><td class="tdpad1">Muriate of soda</td><td class="tdr tdpadr">1·35</td></tr> -<tr><td class="tdpad1">Sulphate of lime</td><td class="tdr tdpadr">·74</td></tr> -<tr><td class="tdpad1">Carbonate of iron</td><td class="tdr tdpadr">·70</td></tr> -<tr><td class="tdpad1">Alumina</td><td class="tdr tdpadr">·50</td></tr> -<tr><td class="tdpad1">Carbonate of lime</td><td class="tdr tdpadr">·10</td></tr> -<tr><td></td><td class="tdr tdpadr">——</td></tr> -<tr><td class="tdpad2">Total</td><td class="tdr tdpadr">3·4 </td></tr> -</table> -</div> - -<div class="footnote"> - -<p><a name="Footnote_165_165" id="Footnote_165_165"></a><a href="#FNanchor_165_165"><span class="label">[165]</span></a> The discovery of the electrotype has been disputed, as all valuable -discoveries are. Without, however, at all disparaging the -merits of what had been done by Mr. Jordan, I am satisfied, after -the most careful search, that the first person who really employed -electro-chemical action for the precipitation of metals in an ornamental -form, was Mr. Spencer, of Liverpool.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_166_166" id="Footnote_166_166"></a><a href="#FNanchor_166_166"><span class="label">[166]</span></a> See Spencer, <i>Instructions for the Multiplication of works of -Art in Metal by Voltaic Electricity. Novelties in Experimental -Science</i>: Griffin, Glasgow, <i>Elements of Electro-Metallurgy</i>: by -Alfred Smee, Esq.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_167_167" id="Footnote_167_167"></a><a href="#FNanchor_167_167"><span class="label">[167]</span></a> The magneto-electrical machine is employed in Birmingham -for this purpose; but I am informed by Messrs. Elkington that -they do not find it economical, or rather that the electro-precipitation -is carried on too slowly.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_168_168" id="Footnote_168_168"></a><a href="#FNanchor_168_168"><span class="label">[168]</span></a> This has been done by Mr. Robert Were Fox, at a mine near -Falmouth. By connecting two copper wires with two lodes, and -bringing them, at the surface, into a cell containing a solution of -sulphate of copper, this gentleman obtained an electrotype copy of -an engraved copper-plate.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_169_169" id="Footnote_169_169"></a><a href="#FNanchor_169_169"><span class="label">[169]</span></a> This has been most effectually accomplished by Mr. Bain. -Mr. Hobson has had an electric clock, thus excited, in action for -several years.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_235" id="Page_235"></a>[Pg 235]</span></p> - - -<h2><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X.</h2> - -<p class="center">MAGNETISM.</p> - - -<p class="chap-head">Magnetic Iron—Knowledge of, by the Ancients—Artificial -Magnets—Electro-Magnets—Electro-Magnetism—Magneto-Electricity—Theories -of Magnetism—The Magnetic Power -of soft Iron and Steel—Influence of Heat on Magnetism—Terrestrial -Magnetism—Declination of the Compass-needle—Variation -of the Earth’s Magnetism—Magnetic Poles—Hansteen’s -Speculations—Monthly and Diurnal Variation—Dip -and Intensity—Thermo-Magnetism—Aurora Borealis—Magnetic -Storms—Magnetic conditions of Matter—<span class="correction" title="In the original book: Dia-magnetism">Diamagnetism</span>, -&c.</p> - - -<p class="p2">Agreeably with the view now generally received, that -magnetism and electricity are but modifications of one -force, since they are found to stand to each other in the -relation of cause and effect, the separation which is here -adopted, of the consideration of their several phenomena, -may appear inappropriate. The importance, however, -of all that is connected with magnetism, and the very -decided difference which is presented by true magnetic -action, and that of frictional or chemical electricity, is -so great that it has been thought advantageous to adopt -the present arrangement in reviewing the influence of -terrestrial magnetism with which science has made us -acquainted.</p> - -<p>From a very early period a peculiar attractive force -has been observed in some specimens of iron ore. -Masses of this kind were found in Magnesia, and from -that locality we derive the name given to iron in its<span class="pagenum"><a name="Page_236" id="Page_236"></a>[Pg 236]</span> -polar condition. This is confirmed by the following -lines by Lucretius:—</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">Quod superest agere incipiam, quo fœdere fiat</div> -<div class="verse">Natura lapis hic ut ferrum ducere possit,</div> -<div class="verse">Quem magnêta vocant patrio de nomine Graii</div> -<div class="verse">Magnêtum, <span class="correction" title="In the original book: buia">quia</span> sit patriis in finibus ortus.</div> -</div></div></div> - -<p>Again we find Pliny employing the term <i>magnetic</i>, to -express this singular power. It was known to the -ancients that the magnetic power of iron, and the -electric property of amber, were not of the same -character, but they were both alike regarded as miraculous. -The Chinese and Arabians seem to have known -Magnetism at a period long before that at which Europeans -became acquainted with either the natural loadstone or -the artificial magnet. Previously to <span class="smcap">a.d.</span> 121, the -magnet is distinctly mentioned in a Chinese dictionary; -and in <span class="smcap">a.d.</span> 419 it is stated in another of their books -that ships were steered south by it.<a name="FNanchor_170_170" id="FNanchor_170_170"></a><a href="#Footnote_170_170" class="fnanchor">[170]</a></p> - -<p>The earliest popularly received account of its use in -Europe is, that Vasco de Gama employed a compass in -1427, when that really adventurous navigator first explored -the Indian seas. It is highly probable, however, -that the knowledge of its important use was derived -from some of the Oriental nations at a much earlier -period.</p> - -<p>We have some curious descriptions of the <i>leading -stone</i> or loadstone, in the works of an Icelandic -historian, who wrote in 1068. The mariner’s compass -is described in a French poem of the date of 1181; and -from Torfæus’s History of Norway, it appears to have -been known to the northern nations certainly in 1266.</p> - -<p><span class="pagenum"><a name="Page_237" id="Page_237"></a>[Pg 237]</span></p> - -<p>We have not to deal with the history of magnetic -discovery, but so far as it tells of the strange properties -which magnets are found to possess, and the -application of this knowledge to the elucidation of -effects occurring in nature.</p> - -<p>A brown stone, in no respect presenting anything by -which it shall be distinguished from other rude stones -around it, is found, upon close examination, to possess the -power of drawing light particles of iron towards it. If -this stone is placed upon a table, and iron filings are -thrown lightly around it, we discover that these filings -arrange themselves in symmetric curves, proceeding -from some one point of the mass to some other; and -upon examining into this, we shall find that the iron -which has once clung to the one point will be rejected -by the other. If this stone is freely suspended, we -shall learn also that it always comes to rest in a certain -position,—this position being determined by these -points, and some attractive force residing in the earth -itself. These points we call its poles; and it is now -established that this rude stone is but a small representative -of our planet. Both are magnetic: both are so -in virtue of the circulation of currents of electricity, or -of lines of magnetic force, as seen in the curves formed -by the iron dust, and the north pole of the one attracts -the south pole of the other, and the contrary. By a -confusion of terms we speak of the north pole of a compass-needle, -meaning that point which is always opposite -to the north pole of the earth: the truth being that -the pole of the compass-needle, which is so forcibly -drawn to the north, is a point in a contrary state, or, as -we may express it, really a south pole.</p> - -<p>There is a power of a peculiar kind, differing from -gravitation, or any other attracting or aggregating force -with which we are acquainted, which exists permanently -in the magnetic iron stones, and also in the earth. -What is this power?</p> - -<p><span class="pagenum"><a name="Page_238" id="Page_238"></a>[Pg 238]</span></p> - -<p>Magnetism may be produced in any bar of steel, -either by rubbing it with a loadstone, or by placing it in -a certain position in relation to the magnetic currents of -the earth, and, by a blow or any other means, disturbing -its molecular arrangement. This principle appears to -involve the iron as with an atmosphere, and to interpenetrate -it. By one magnet we may induce magnetism -in any number of iron bars without its losing any of its -original force. As we have observed of the electrical -forces already considered, the magnet constantly presents -two points in which there is a difference manifested by -the circumstance that they are always drawn with considerable -power towards the north or south poles of the -earth. That this power is of the same character as the -electricity which we have been considering, is now most -satisfactorily proved. By involving a bar of soft iron -which, being without any magnetic power, is incapable -of sustaining even an ounce weight, with a coil of -copper wire, through which a galvanic current is passing, -the bar will receive, by induction from the current, an -enormous accession of power, and will, so long as the -current flows around it, sustain many hundred pounds -weight, which, the moment the current is checked, fall -away from it in obedience to the law of gravity. Thus -the mere flow of this invisible agent around a mass of -metal possessing no magneto-attractive power, at once -imparts this life-like influence to it, and as long as the -current is maintained, the iron is endowed with this -surprising energy.</p> - -<p>This discovery, which we owe to the genius of -Oersted, and which has, indeed, given rise to a new -science, electro-magnetism, may be regarded as one of -the most important additions made to our knowledge.</p> - -<p>Current electricity is magnetic; iron is not necessary -to the production of magnetic phenomena, although by -its presence we secure a greater amount of power. The<span class="pagenum"><a name="Page_239" id="Page_239"></a>[Pg 239]</span> -copper wires which complete the circuit of a galvanic -battery, will attract and hold up large quantities of iron -filings, and the wires of the electric telegraph will do -the same, while any signal is being conveyed along -them. Again, all the phenomena common to galvanic -electricity can be produced by merely disturbing the -power permanently secured in the ordinary magnet. -It was thought that magnets would become weakened -by this constant disturbance of their magnetism; but, -since its application to the purpose of manufacture, and -magneto-electricity has been employed in electro-plating, -it has been found that continued action for many -years, during which enormous quantities of electricity -have been thus given out and employed in producing -chemical decomposition, has not, in the slightest degree, -altered their powers. Thus a small bar of metal is -shown to be capable of pouring out, for any number of -years, the principle upon which the phenomena of magnetism -depend.</p> - -<p>There are, however, differences, and striking ones, -between ordinary and magnetic electricity. In the -magnet we have a power at rest, and in the electrical -machine or galvanic battery, a power in motion. -Ordinary electricity is stopped in its passage by a plate -of glass, of resin, and many other substances; but magnetism -passes these with freedom, and influences magnetic -bodies placed on the other side. It would appear, -though we cannot explain how, that magnetism is due -to some lateral influence of the electric currents. A -magnetic bar is placed over a copper wire, and it hangs -steadily in the direction of its length; an electric current -is passed along it, and the magnet is at once driven to -place itself across the wire. Upon this experiment, in -the main, Ampère founds his theory of terrestrial magnetism. -He supposes electrical currents to be traversing -our globe from east to west, and thus, that the -needle takes its direction, not from the terrestrial action<span class="pagenum"><a name="Page_240" id="Page_240"></a>[Pg 240]</span> -of any fixed magnetic poles, but from the repulsion of -these currents, as is the case with the wire.</p> - -<p>It has been found that wires, freely suspended, along -which currents were passing in opposite directions, -revolve about each other, or have an inclination to -place themselves at right angles; thus exhibiting the -same phenomenon as the magnet and the conducting -wire. So far the hypothesis of Ampère leads us most -satisfactorily. We see in the magnet one form of -electricity, and in the machine or battery another. But -why should not the electricity of the magnet, electricity -at rest, exhibit the same powers as this force in -motion?</p> - -<p>Oersted, whose theory led him to the discovery of the -fact of the magnetic power of an electric current, of the -establishment indeed of the new science—<span class="smcap">Electro-Magnetism</span>, -regards the phenomena of a current passing -a wire, and its action on a needle, as evidence of two -fluids, positive and negative, traversing in opposite -directions, and mutually attracting and repelling. He -conceives that they pass the wires in a series of spirals; -that in the magnet, by some peculiar property of the -iron, this conflict of the currents is reduced to an equilibrium, -and its power becomes manifested in its attractive -force.<a name="FNanchor_171_171" id="FNanchor_171_171"></a><a href="#Footnote_171_171" class="fnanchor">[171]</a> This does not, however, convey a clear idea to -the mind.</p> - -<p>It is curious that iron becomes magnetic in a superior -degree to any other metal; that steel retains permanently -any magnetism imparted to it; but that soft -iron rapidly loses its magnetic power. This must be in -virtue of some peculiar arrangement of the molecules, -or some unknown physical condition of the atoms of the -mass, by which a continued influence is retained by the -steel, probably in a state of constant internal circulation.<span class="pagenum"><a name="Page_241" id="Page_241"></a>[Pg 241]</span> -It has, however, been shown that soft iron, under -certain circumstances, may be made to retain a large -amount of magnetic force.<a name="FNanchor_172_172" id="FNanchor_172_172"></a><a href="#Footnote_172_172" class="fnanchor">[172]</a></p> - -<p>If a horse-shoe shaped bar of soft iron is rendered -magnetic by the circulation of an electric current around -it, while its two ends are united by an armature of soft -iron, so that it is capable of supporting many hundred -pounds weight; and we then, by breaking the circuit, -stop the current, taking care the armature is kept in -contact, the iron will not lose its magnetic property, -but will retain this power for many years. If the connecting -piece of iron, the armature, is removed, the bar -immediately loses all its magnetism, and will not support -even the armature itself. This fact appears to confirm -the idea that magnetism is due to the retention of -electricity, and that steel possesses the property of -equalizing the opposing forces, or of binding this -principle to itself like an atmosphere.</p> - -<p>The influence of heat on magnetism is so remarkable -a proof of the dependence of this power upon molecular -arrangement, that it must not escape our notice. To -select but one of many experiments by Mr. Barlow, it -was found that in a bar of malleable iron, in which, -when cold, the magnetic effect was + 30° 0', all polarity -ceased at a white heat, that it was scarcely appreciable -at a red heat, but that at a blood-red heat it was equal -to + 41° 0'.<a name="FNanchor_173_173" id="FNanchor_173_173"></a><a href="#Footnote_173_173" class="fnanchor">[173]</a></p> - -<p>The more closely we examine the peculiarities of the -magnetic power, and particularly as they are presented -to us in its terrestrial action, the more surprising will -its influence appear to be. We have discovered a<span class="pagenum"><a name="Page_242" id="Page_242"></a>[Pg 242]</span> -natural cause which certainly exercises a very remarkable -power over matter, and we have advanced so far in -our investigations as to have learnt the secret of converting -one form of force into another, or of giving to a -principle, produced by one agency, a new character -under new conditions; of changing, in fact, electricity -into magnetism, and from magnetism again evolving -many of the effects of electrical currents.</p> - -<p>If a magnetic bar is freely suspended above the -earth, it takes, in virtue of some terrestrial power, a -given direction, which is an indication of the earth’s -magnetic force. Whether this is the consequence of -the currents of electricity, which Ampère supposes to -circulate around the globe, from east to west, or the -result of points of attraction in the earth itself, the -phenomenon is equally wonderful. To whatever cause -we may refer the visible effects, it appears certain that -this earth is composed of particles in a magnetic state, -the character varying with physical conditions, and that -terrestrial magnetic force is the collective action of all -the atoms of this planetary mass.<a name="FNanchor_174_174" id="FNanchor_174_174"></a><a href="#Footnote_174_174" class="fnanchor">[174]</a></p> -<p><span class="pagenum"><a name="Page_243" id="Page_243"></a>[Pg 243]</span></p> -<p>The remarkable connexion which has been observed -between the changes in the physical condition of the -surface of the sun and terrestrial phenomena, must not -escape our notice. Sir William Herschel thought he -perceived a link connecting the dark spots on the sun’s -face with the variations of the earth’s temperature. -This has not, however, been confirmed by the observations -which have been made since the time of Herschel. -The careful examinations of the solar spots which have -been made by Schwabe,<a name="FNanchor_175_175" id="FNanchor_175_175"></a><a href="#Footnote_175_175" class="fnanchor">[175]</a> prove a well-defined order of -progress in them. He has discovered that they move in -cycles of ten years—from the smallest number visible in -a given year, they regularly increase for five years, -when they reach their maximum; they then as regularly -decrease, and at the end of another five years they are -at their maximum number. The magnetic observations -which have been carried on by the British and other -governments for some years, over every part of the -world, have elicited the fact that the order of variation -in the earth’s magnetic intensity is in cycles of ten -years, and the law of increase and decrease which is found -to prevail with the solar spots distinctly marks the variations -of terrestrial magnetism. Few more interesting -facts than this are within the range of our knowledge, -proving as it does the direct dependence of terrestrial -phenomena on solar force.</p> - -<p>The constancy with which a magnetised needle points -along a certain line which varies a little from the earth’s -axial line, renders it one of the most important instruments -to the practical and the scientific man. The -wanderer of the ocean or of the desert is enabled, -without fear of error, to pursue his path, and in unknown -regions to determine the azimuth of objects.<span class="pagenum"><a name="Page_244" id="Page_244"></a>[Pg 244]</span> -The miner or the surveyor finds in the magnetic compass -the surest guide in his labours, and the experiment -is for ever studying its indications.</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“True as the needle to the pole,”</div> -</div></div></div> - -<p>has passed into a proverb among mankind, but the -searching inquiry of modern observers has shown that -the expression is correct only with certain limitations. -There are two lines on the surface of the earth along -which the needle points true north, or where the magnetic -and the geographical north correspond. These -are called lines of <i>no variation</i>, or, as they have also -been designated, <i>agonic lines</i>, and one is found in the -eastern and the other in the western hemisphere. The -American line is singularly regular, passing in a south-east -direction from the latitude 60° to the west of Hudson’s -Bay, across the American lakes, till it reaches the -South Atlantic ocean, and cuts the meridian of Greenwich -in about 65° south latitude. The Asiatic line of -<i>no variation</i> is very irregular, owing, without doubt, to -local interferences; it begins below New Holland, in -latitude 60° south, it bends westward across the Indian -ocean, and from Bombay has an inflection eastward -through China, and then northward across the sea of -Japan, till it reaches the latitude of 71° north, when it -descends again southward, with an immense semicircular -bend, which terminates in the White Sea.</p> - -<p>Hansteen has thought that there are two points in -each hemisphere which may be regarded as stronger -and weaker poles on opposite sides of the poles of revolution. -These are called the magnetic poles of the -earth, or by Hansteen <i>magnetic points of convergence</i>. -These four points are considered to have a regular -motion round the globe, the two northern ones from -west to east, and the two southern ones from east to -west. By the assistance of recorded observations,<span class="pagenum"><a name="Page_245" id="Page_245"></a>[Pg 245]</span> -Hansteen has calculated the periods of these revolutions -to be as follows:—</p> - -<ul class="no"> -<li>The weakest north pole in 860 years.</li> -<li>The strongest north pole in 1746 years.</li> -<li>The weakest south pole in 1304 years.</li> -<li>The strongest south pole in 4609 years.</li> -</ul> - -<p>There are some points of speculation on which -Hansteen has ventured which have been smiled at as -fanciful; but they may rather indicate an amount of -knowledge in the Brahminical and Egyptian priesthood, -beyond what we are usually disposed to allow them, and -prove that their observations of nature had led them to -an appreciation of some of the most remarkable harmonies -of this mysterious creation.</p> - -<p>The above terms are exceedingly near 864, 1246, -1728, 4320, and those numbers are equal to the mystic -number of the Indians, Greeks, and Egyptians, 432 -multiplied by 2, 3, 4, and 10. On these the ancients -believed a certain combination of natural events to -depend, and, according to Brahminical mythology, the -duration of the world is divided into four periods, each -of 432,000 years. Again, the sun’s mean distance from -the earth is 216 radii of the sun, and the moon’s mean -distance 216 radii of the moon, each the half of 432. -Proceeding with this very curious examination, Hansteen -says, 60 multiplied by 432 equals 15,920, the -smallest number divisible at once by all the four periods -of magnetic revolution, and hence the shortest time in -which the four poles can complete a cycle, and return to -their present state, and <i>which coincides exactly with the -period in which the precession of the equinoxes will -amount to a complete circle</i>, reckoning the precession at -a degree in seventy-two years.<a name="FNanchor_176_176" id="FNanchor_176_176"></a><a href="#Footnote_176_176" class="fnanchor">[176]</a></p> -<p><span class="pagenum"><a name="Page_246" id="Page_246"></a>[Pg 246]</span></p> -<p>When we consider the phenomena of terrestrial magnetism -carefully, it appears to indicate the action of a -power external to the earth itself, and, as Hansteen -conceives, having its origin from the action of the sun, -heating, illuminating, and producing a magnetic tension, -in the same manner as it produces electrical excitation -and actino-chemical action.</p> - -<p>The movements of these magnetic poles have been -the subject of extensive and most accurate observation -in every quarter of the globe. In London, during -1657–1662, there was no magnetic variation; the agonic -line passing through it. The variation steadily increased, -until, in 1815, it amounted to 24° 15' 17", since which -time it has been slowly diminishing. In addition to -this great variation, we have a regular annual change -dependent on the position of the sun, in reference to the -equinoctial and solstitial points, which was discovered -by Cassini, and investigated by Arago and others. -Also a diurnal variation, which movement appears to -commence early in the morning, moving eastward until -half-past seven, <span class="smcap">a.m.</span>, when it begins to move westward -until two, <span class="smcap">p.m.</span>, when it again returns to the east, and in -the course of the night reaches the point from which it -started twenty-four hours before.</p> - -<p>We have also remarkable variations in what is -termed the <i>dip</i> of the needle. It is well known that a -piece of unmagnetized steel, if carefully suspended by its -centre, will swing in a perfectly horizontal position, but, -if we magnetize this bar, it will immediately be drawn -downwards at one end. The force of the earth’s -polarity, attracting the dissimilar pole, has caused it to -<i>dip</i>.</p> - -<p>There is, in the neighbourhood of the earth’s equator, -and cutting it at four points, an irregular curve, called -the magnetic equator, or <i>aclinic</i> line, where the needle<span class="pagenum"><a name="Page_247" id="Page_247"></a>[Pg 247]</span> -balances itself horizontally. As we proceed from this -line towards either pole the dip increases, until, at the -north and south poles, the needle takes a vertical -position. The <i>intensity</i> of the earth’s magnetism is -also found to vary with the position, and to increase in -a proportion which corresponds very closely with the -dip. But the <i>intensity</i> is not a function of the dip, -and the lines of equal intensity, <i>isodynamic lines</i>, are not -parallel to those of equal dip. We have already remarked -on the diurnal variation of the declination of -the needle; we know, also, that there exists a regular -monthly and daily change in the magnetic intensity. -The greatest monthly change appears when the earth is -in its perihelion and aphelion, in the months of December -and June,—a maximum then occurs; and about -the time of the equinoxes a minimum is detected.<a name="FNanchor_177_177" id="FNanchor_177_177"></a><a href="#Footnote_177_177" class="fnanchor">[177]</a></p> - -<p>The daily variation of intensity is greatest in the -summer, and least in the winter. The magnetism is -generally found to be at a minimum when the sun is -near the meridian; its intensity increasing until about -six o’clock, when it again diminishes.<a name="FNanchor_178_178" id="FNanchor_178_178"></a><a href="#Footnote_178_178" class="fnanchor">[178]</a></p> - -<p>What striking evidences all these well-ascertained -facts give of the dependence of terrestrial magnetism on -solar influence! and in further confirmation of this -view, we find a very remarkable coincidence between -the lines of equal temperature—the isothermal lines, -and those of equal dip and magnetic intensity.</p> - -<p>Sir David Brewster first pointed out that there were -in the northern hemisphere two poles of maximum -cold; these poles agree with the magnetic points of -convergence; and the line of maximum heat, which -does not run parallel to the earth’s equator, is nearly -coincident with that of magnetic power. Since See<span class="pagenum"><a name="Page_248" id="Page_248"></a>[Pg 248]</span>beck -has shown us that electrical and magneto-electrical -phenomena can be produced by the action of heat -upon metallic bars, we have, perhaps, approached -towards some faint appreciation of the manner in which -the solar calorific radiations may, acting on the surface -of our planet, produce electrical and magnetic effects. -If we suppose that the sun produces a disturbance of -the earth’s electricity along any given line, in all directions -at right angles to that line, we shall have magnetic -polarity induced.<a name="FNanchor_179_179" id="FNanchor_179_179"></a><a href="#Footnote_179_179" class="fnanchor">[179]</a> That such a disturbance is -regularly produced every time the sun rises, has been -sufficiently proved by many observers.</p> - -<p>In 1750, Wargentin noticed that a very remarkable -display of <i>Aurora borealis</i> was the cause of a peculiar -disturbance of the magnetic needle; and Dr. Dalton<a name="FNanchor_180_180" id="FNanchor_180_180"></a><a href="#Footnote_180_180" class="fnanchor">[180]</a> -was the first to show that the luminous rays of the -Aurora are always parallel to the dipping-needle, and -that the Auroral arches cross the magnetic meridian at -right angles. Hansteen and Arago have attended with -particular care to these influences of the northern lights, -and the results of their observations are:—</p> - -<p>That as the crown of the Aurora quits the usual -place, the dipping-needle moves several degrees forward:—</p> - -<p>That the part of the sky where all the beams of the -Aurora unite, is that to which a magnetic needle -directs itself, when suspended by its centre of gravity:—</p> - -<p>That the concentric circles, which show themselves -previously to the luminous beams, rest upon two points -of the horizon equally distant from the magnetic meri<span class="pagenum"><a name="Page_249" id="Page_249"></a>[Pg 249]</span>dian; -and that the most elevated points of each arch -are exactly in this meridian.<a name="FNanchor_181_181" id="FNanchor_181_181"></a><a href="#Footnote_181_181" class="fnanchor">[181]</a></p> - -<p>It does not appear that every Aurora disturbs the -magnetic needle; as Captains Foster and Back both -describe very splendid displays of the phenomenon, which -did not appear to produce any tremor or deviation upon -their instruments.<a name="FNanchor_182_182" id="FNanchor_182_182"></a><a href="#Footnote_182_182" class="fnanchor">[182]</a></p> - -<p>Some sudden and violent movements have been from -time to time observed to take place in suspended -magnets; and since the establishment of magnetic -observatories in almost every part of the globe, a very -remarkable coincidence in the time of these agitations -has been detected. They are frequently connected with -the appearance of Aurora borealis; but this is not constantly -the case. These disturbances have been called -<i>magnetic storms</i>; and over the Asiatic and European -continent, the islands of the Atlantic and the western -hemisphere, they have been proved to be simultaneous.</p> - -<p>From observations made at Petersburg by Kupffer, -and deductions drawn from the observations obtained by -the Magnetic Association, it appears probable that these<span class="pagenum"><a name="Page_250" id="Page_250"></a>[Pg 250]</span> -<i>storms</i> arise from a sudden displacement in the magnetic -lines of the earth’s surface; but the cause to which this -may be due is still to be sought for.</p> - -<p>In the brief and hasty sketch which has been given -of the phenomena of terrestrial magnetism, enough has -been stated to show the vast importance of this very -remarkable power in the great operations of nature. We -are gradually reducing the immense mass of recorded -observations, and arriving at certain laws which are -found to prevail. Still, the origin of the force, whether -it is strictly electrical, whether it is the circulation of a -magnetic fluid, or whether it is merely a peculiar excitation -of some property of matter, are questions which are -open for investigation.</p> - -<p>In the beautiful Aurora borealis, with its trembling -diffusive lights, and its many-coloured rays, we have -what may be regarded as a natural exhibition of magnetism, -and we appear to have within our grasp the explanation -we desire. But we know not the secret of -even these extraordinary meteorological displays. If we -pass an electric spark from a machine through a long -cylinder, exhausted of air as far as possible, we have a -mimic representation of the Northern Lights—the same -attenuation of brightness, almost dwindling into phosphorescence; -and by the slightest change of temperature -we may produce that play of colours which is -sometimes so remarkably manifested in Aurora. Dr. -Dalton considered Aurora borealis <i>as a magnetic phenomenon, -and that its beams are governed by the earth’s -magnetism</i>. We know that the arc of light produced -between the poles of a powerful galvanic battery is -readily deflected by a good magnet; and we have lately -learned that every vapour obeys the magnetic force.<a name="FNanchor_183_183" id="FNanchor_183_183"></a><a href="#Footnote_183_183" class="fnanchor">[183]</a> -It is, therefore, yet a question for our consideration, -does the earth’s magnetism produce the peculiar pheno<span class="pagenum"><a name="Page_251" id="Page_251"></a>[Pg 251]</span>mena -of Aurora by acting upon electricity in a state of -glow? or have we evidence in this display of the circulation -of the magnetic fluid around our globe, manifesting -itself by its action on the ferruginous and other -metallic matter, which Fusinieri has proved to exist in -the upper regions of our atmosphere.<a name="FNanchor_184_184" id="FNanchor_184_184"></a><a href="#Footnote_184_184" class="fnanchor">[184]</a> That magnetic -radiations do exist, has been proved by Faraday, and -that they form lines of force perpendicular to the earth’s -surface, has been experimentally shown. Parallelograms -of wire moved upon a central axis, and connected with -a galvanometer, give at every revolution indication of an -electric disturbance in all respects analogous to the -production of a current by moving wires in front of a -steel magnet.</p> - -<p>The alteration in the properties of heat, when it -passes from the radiant state into combination with -matter, exhibits to us something like what we may suppose -occurs in the conversion of magnetism into electricity -or the contrary. We have a subtile agent, which -evidently is for ever busy in producing the necessary -conditions of change in this our earth: an <span class="correction" title="In the original book: elemeut">element</span> to -which is due the development of many of the most active -powers of nature; performing its part by blending with -those principles which we have already examined; -associating itself with every form of matter; and giving, -as we shall presently see, in all probability, the first -impulses to combination, and regulating the forms of -aggregating particles.</p> - -<p><span class="pagenum"><a name="Page_252" id="Page_252"></a>[Pg 252]</span></p> - -<p>As electricity has the power of altering the physical -conditions of the more adherent states of matter, thus -giving rise to variations of form and modes of combination, -so gross matter appears to alter the character of -this agency, and thus disposes it to the several modifications -under which we have already detected its presence. -We have mechanical electricity and chemical electricity, -each performing its great work in nature; yet both -manifesting conditions so dissimilar, that tedious research -was necessary before they could be declared -identical. Magnetic electricity is a third form; all its -characteristics are unlike the others, and the office it -appears to perform in the laboratory of creation is of a -different order from that of the other states of electrical -force. In the first two we have decomposing and recombining -powers constantly manifested—in fact, their -influences are always of a chemical character; but in -the last it appears we have only a directive power. It -was thought that evidence had been detected of a -chemical influence in magnetism; it did appear that -sometimes a retarding force was exerted, and often an -accelerating one. This has been again denied, and we -have arrayed in opposition to each other some of the -first names among European experimentalists. The -question is not yet to be regarded as settled; but, from -long and tedious investigation, during which every old -experiment has been repeated, and numerous new ones -tried, we incline to the conclusion that chemical action -is not directly affected by magnetic power. It is highly -probable that magnetism may, by altering the structural -arrangement of the surface, vary the rate of chemical -action; but this requires confirmation.<a name="FNanchor_185_185" id="FNanchor_185_185"></a><a href="#Footnote_185_185" class="fnanchor">[185]</a></p> - -<p>There is no substance to be found in nature existing -independently of magnetic power. But it influences<span class="pagenum"><a name="Page_253" id="Page_253"></a>[Pg 253]</span> -bodies in different ways: one set acting with relation to -magnetism, like iron, and arranging themselves along -the line of magnetic force,—these are called magnetic -bodies; another set, of which bismuth may be taken as -the representative, always placing themselves at right -angles to this line,—these are called <i>diamagnetic -bodies</i>.<a name="FNanchor_186_186" id="FNanchor_186_186"></a><a href="#Footnote_186_186" class="fnanchor">[186]</a> This is strikingly shown by means of powerful -electro-magnets; but the magnetism of the earth is -sufficient, under proper care, to exhibit the phenomena.</p> - -<p>Every substance in nature is in one or other of these -conditions. The rocks, forming the crust of the earth, -and the minerals which are discovered in them; the -surface soil, which is by nature prepared as the fitting -habitation of the vegetable world, and every tree, shrub, -and herb which finds root therein, with their carbonaceous -matter, in all its states of wood, leaf, flower, and -fruit; the animal kingdom, from the lowest monad<span class="pagenum"><a name="Page_254" id="Page_254"></a>[Pg 254]</span> -through the entire series up to man,—have, all of them, -distinct magnetic or diamagnetic relations.</p> - -<p>“It is a curious sight,” says Dr. Faraday, “to see a -piece of wood or of beef, or an apple, or a bottle of water -repelled by a magnet, or, taking the leaf of a tree, and -hanging it up between the poles, to observe it take an -equatorial position. Whether any similar effects occur -in nature among the myriads of forms which, upon all -parts of its surface, are surrounded by air, and are subject -to the action of lines of magnetic force, is a question -which can only be answered by future observation.”<a name="FNanchor_187_187" id="FNanchor_187_187"></a><a href="#Footnote_187_187" class="fnanchor">[187]</a></p> - -<p>At present, the bodies which are known to exhibit -decided ferro-magnetic properties are the following, -which stand arranged in the order of their intensity:—</p> - -<ul class="no"> -<li>Iron, Nickel, Cobalt, Manganese,</li> -<li>Chromium, Cerium, Titanium,</li> -<li>Palladium, Platinum, Osmium.</li> -</ul> - -<p>It is interesting to know that there are evidences -that two bodies which, when separate, are not magnetic, -as iron is, become so when combined. Copper and -zinc are both of the diamagnetic class, but many kinds -of brass are discovered to be magnetic.</p> - -<p>The salts of the above metals are, to a greater or less -extent, ferro-magnetic, but they may be rendered neutral -by water, which is a diamagnetic body, being repelled -by the magnet. It will be unnecessary, here, to enumerate -the class of bodies which are diamagnetic; indeed, -all not included in the preceding list may be considered -as belonging to that class, with the exception of gases<span class="pagenum"><a name="Page_255" id="Page_255"></a>[Pg 255]</span> -and vapours, which appear to exist, relatively to each -other, sometimes in the one, and sometimes in the other -condition.<a name="FNanchor_188_188" id="FNanchor_188_188"></a><a href="#Footnote_188_188" class="fnanchor">[188]</a></p> - -<p>To endeavour to reduce our knowledge of these facts -to some practical explanation, we must bear in mind -that particular spaces around the north and south geographical -poles of the earth, are regarded as circles to -which all the magnetic lines of force converge. Under -circumstances which should prevent any interference -with what is called ferro-magnetic action, all bodies -coming under that class would arrange themselves according -to the laws which would regulate the disposition -of an infinite number of magnets, free to move -within the sphere of each other’s influence. The north -and south pole of one magnetic body would attach itself -to the south and north pole of another, until we had a -line of magnets of any extent; the two ends being in -opposite states, like the magnetic points of convergence -of the earth.</p> - -<p>Every body, not ferro-magnetic, places itself across -such a line of magnetic force as we have conceived; and -if the earth were made up of separate layers of ferro-magnetic -and diamagnetic bodies, the result would be -the formation of bands at right angles to each other. -This is not the case, by reason of the intermingling of -the two classes of substances. Out of the known chemical -elements we find only about ten which are actively -ferro-magnetic; the others combining with these give -rise to either a weaker state, a neutral condition, or the -balance of action is turned to the diamagnetic side. -Sulphate of iron, for instance, is a magnetic salt; but<span class="pagenum"><a name="Page_256" id="Page_256"></a>[Pg 256]</span> -in solution, water being diamagnetic, it loses its -property. The yellow prussiate of potash dissolved -in water is a diamagnetic body; but the red -prussiate, which contains an atom less of potassium, -is magnetic: but in the solid state they are both -diamagnetic.<a name="FNanchor_189_189" id="FNanchor_189_189"></a><a href="#Footnote_189_189" class="fnanchor">[189]</a></p> - -<p>From this it would appear that the chemical composition -of a body regulated its relation to magnetism. -The following facts will show, however, that the molecular -structure is more particularly concerned in determining -the molecular condition of substances.</p> - -<p>M. Plücker, being desirous of finding the extent to -which the <i>direction of the fibres</i> in organic bodies might -influence their magnetic or diamagnetic properties, was -led to inquire whether in crystals the direction of the -optic axes, which itself depends upon the arrangement -of the particles, might not also exercise some influence. -The first submitted to the action of the electro-magnet -a thin plate of tourmaline, such as is employed in experiments -upon polarization, having its optic axis parallel to -its longest length. It was very quickly perceived that -the plate was magnetic, by the effect of the iron that it -contains; but it was suspended successively in three -ways,—first, so that its longest side was vertical, then as -that the shortest side was vertical, and finally so that -the plate itself was horizontal. In the first case it is -directed between the two points of the conical curvatures -of the poles like a magnetic body; but, in the other -two cases, on the contrary, it took the direction assumed -by diamagnetic bodies—that is to say, a direction such -that its longest length was perpendicular to the line -joining the poles. This direction indicated that the -optical axis was repelled by the two poles, and that this<span class="pagenum"><a name="Page_257" id="Page_257"></a>[Pg 257]</span> -repulsion outweighed the magnetic properties of the -crystal.<a name="FNanchor_190_190" id="FNanchor_190_190"></a><a href="#Footnote_190_190" class="fnanchor">[190]</a></p> - -<p>The relation of structure to physical phenomena of -essentially different characters is remarkable. Savart, -when making crystalline plates of quartz and carbonate -of lime vibrate, succeeded in determining a relation -between the acoustic figures that are produced in them, -and the particular mode of the crystallization of the -substance. He found that the direction of the optical -axis is constantly connected with that of the principal -forms of the acoustic figures.</p> - -<p>Mitscherlich has remarked that crystals do not expand -uniformly by heat, but that this dilatation is greater in -one direction than in another; and that this difference -is connected with their crystalline form. M. de Sénarmont -has shown that conductibility for heat, which is -equal in all directions for the crystals of the regular -system, acquires in others a maximum or a minimum -value, according to directions parallel to the crystallographic -axes; so that the isothermic surfaces, which are -spheres in the former case, are, in the other, ellipsoids -elongated or flattened in the same direction. The optical -axes do not altogether coincide with the principal axes -of conductibility for heat; but this appears to be due -merely to slight differences in the rate of progression, -or the refrangibility of the luminous and calorific rays.</p> - -<p><span class="correction" title="In the original book: Wiedmann">Wiedemann</span>, by employing a fine point through which -he made electricity arrive upon a surface that he had -powdered with licopodium or red lead, succeeded in determining, -by means of the form assumed by this light -powder, the conductibility of crystals in different directions.</p> - -<p>On a surface of glass, the powder which disperses -itself around the points, in consequence of electric re<span class="pagenum"><a name="Page_258" id="Page_258"></a>[Pg 258]</span>pulsion, -forms a circular figure traversed by radii. -When a plate of gypsum is used instead of glass the -figure is found to be elliptical, and the great axis of the -ellipse forms a right angle with the principal crystallographic -axis, which proves that the electricity distributes -itself more easily in a direction perpendicular to the axis -than in any other. M. <span class="correction" title="In the original book: Wiedmann">Wiedemann</span> comes to the conclusion -that crystals which possess a better conductibility -in the direction of the principal axis, all belong to the -class of negative crystals: while those which have a -better conductibility in the direction perpendicular to -the axis are positive, which indicates that the direction -of best conductibility for electricity is also that according -to which light is propagated relatively with greater -velocity.</p> - -<p>Tyndale has shown, that if gutta percha which has -been rendered fibrous in manufacture is cut so that the -fibres are in the direction of this greatest length, or in -a direction perpendicular to this greatest length, and -placed under the influence of a magnet, they direct -themselves equatorially. Ivory cut in the same direction -manifests the same conditions, though both these -substances are diamagnetic.</p> - -<p>The fibrous structure, and the planes of cleavage, thus -determine the magnetic condition of a substance. The -special properties presented by crystals, in regard to -the action exercised upon them by magnets, is due to -a particular mode of grouping their particles. This is -also the cause of unequal dilatability, and of unequal -conductibility for heat and for electricity.</p> - -<p>How curiously, therefore, does molecular structure -determine the relation of a body to any of the forms of -physical force!</p> - -<p>We still search in the dark, and see but dimly the -evidences; yet it becomes almost a certainty to us, that -this stone of granite, with its curious arrangement of -felspar, mica, and quartz, presents its peculiar condition<span class="pagenum"><a name="Page_259" id="Page_259"></a>[Pg 259]</span> -in virtue of some law of magnetic force. The crystal, -too, of quartz, which we break out of the mass, and -which presents to us a beautifully regular figure, is, beyond -a doubt, so formed, because the atoms of silica are -each one impelled in obedience to one of these two conditions -of magnetism to set themselves in a certain order -to each other, which cannot be altered by human force -without destruction.</p> - -<p>All the laws which regulate the forms of crystals and -amorphous bodies are, to the greatest degree, simple. -In nature the end is ever attained by the easiest means; -and the complexity of operation, which appears sometimes -to the observer, is only so because he cannot see -the spring by which the machine is moved.</p> - -<p>The gaseous envelope, our atmosphere, is in a neutral -state. Oxygen is strikingly magnetic in relation to -hydrogen gas, whilst nitrogen is as singularly the contrary; -and the same contrasts present themselves when -these gases are examined in their relation to common -air. Thus, oxygen being magnetic, and nitrogen the -contrary, we have an equilibrium established, and the -result is a compound neutral in its relations to all -matter. All gases and vapours are found to be diamagnetic, -but in different degrees.<a name="FNanchor_191_191" id="FNanchor_191_191"></a><a href="#Footnote_191_191" class="fnanchor">[191]</a> This is shown by -passing a stream of the gas, rendered visible by a little -smoke, within the influence of a powerful magnet.</p> -<p><span class="pagenum"><a name="Page_260" id="Page_260"></a>[Pg 260]</span></p> -<p>These bodies are, however, found relatively to each -other,—or even to themselves, under different thermic -conditions,—to change their states, and pass from the -magnetic to the diamagnetic class. Heat has a very -remarkable influence in altering these relations; and -atmospheric air at one temperature is magnetic to the -same fluid at another: thus, by thermic variations, -attraction or repulsion may be alternately maintained. -By this it must be understood that a stream of air, at a -temperature elevated but a few degrees above that of an -atmosphere of the same kind into which it is passing, is -deflected in one way by a magnet; whereas, if the -stream is colder than the bulk through which it flows, -it is bent in another way by the same force. In -this respect magnetism and diamagnetism show equally -the influence of another physical force, heat; and -we may safely refer many meteorological phenomena -to similar alterations of condition in the atmosphere, -relative to the magnetic relations of the aërial currents.</p> - -<p>That magnetism has a directive power is satisfactorily -shown by the formation of crystals in the neighbourhood -of the poles of powerful magnets. The common iron -salt, the <span class="correction" title="In the original book: proto-sulphate">protosulphate</span>, ordinarily crystallizes so that -the crystals unite by their faces; but when crystallizing -under magnetic influence, they have a tendency to -arrange themselves with regard to each other so that -the acute angle of one crystal unites with one of the -faces of another crystal, near to, but never actually at, -its obtuse angle. In addition to this, if a magnet of -sufficient power is employed, the crystals arrange themselves -in magnetic curves from one pole to the other, a -larger crop of crystals being always formed at the north<span class="pagenum"><a name="Page_261" id="Page_261"></a>[Pg 261]</span> -than at the south pole. Here we have evidence of an -actual turning round of the crystal, in obedience to the -directive force of the magnet; and we have the curious -circumstance of a difference in some way, which is not -clearly explained, between the two opposite poles. If, -instead of an iron or a ferro-magnetic salt, we employ -one which belongs to the other, or diamagnetic, class, -we have a curious difference in the result. If into a -glass dish, fixed on the poles of a strong electro-magnet, -we pour a quantity of a solution of nitrate of silver, and -place in the fluid, over the poles of the magnet, two -globules of mercury (an arrangement by which that -arborescent crystallization, called the <i>Arbor Dianæ</i>, is -produced,) we have the long needle-shaped crystals of -silver, arranging themselves in curves which would cut -the ordinary magnetic lines at right angles.<a name="FNanchor_192_192" id="FNanchor_192_192"></a><a href="#Footnote_192_192" class="fnanchor">[192]</a></p> - -<p>In the first example given we have an exhibition of -magnetic force, while in the last we have a striking -display of the diamagnetic power.</p> - -<p>The large majority of natural formations appear to -group themselves under the class of diamagnetics. -These bodies are thought to possess poles of mutual -repulsion among themselves, and which are equally -repelled by the magnetic points of convergence. Confining -our ideas to single particles in one condition or -the other, we shall, to a certain extent, comprehend the -manifold results which must arise from the exercise of -these two modes of force. At present, our knowledge -of the laws of magnetism is too limited to allow of our -making any general deductions relative to the disposition -of the molecules of matter; and the amount of -observation which has been given to the great natural -arrangements, is too confined to enable us to infer more<span class="pagenum"><a name="Page_262" id="Page_262"></a>[Pg 262]</span> -than that it is probable many of the structural conditions -of our planet are due to polarity.</p> - -<p>Mountain ranges observe a singular uniformity of -direction, and the cleavage planes of rock are evidently -determined by some all-pervading power. Mineral -bodies are not distributed in all rocks indiscriminately. -The primary formations hold one class of metalliferous -ores, and the more recent ones another. This is not -to be regarded as in any way connected with their -respective ages, but with some peculiar condition of -the stone itself. The granite and slate rocks, at their -junctions, present the required conditions for the deposit -of copper ore, while we find the limestones have -the characteristic physical state for accumulating lead -ore. Again, on examining any mineral vein, it will be -at once apparent that every particle of ore, and every crystal -of quartz or limestone, is disposed in a direction which -indicates the exercise of some powerful directive agency.<a name="FNanchor_193_193" id="FNanchor_193_193"></a><a href="#Footnote_193_193" class="fnanchor">[193]</a></p> - -<p>It appears, from all the results hitherto obtained, that -the magnetic and diamagnetic condition of bodies is -equally due to some peculiar property of matter in relation -to the other forms of electricity. We have not -yet arrived at the connecting link, but it does not appear -to be far distant.</p> - -<p>We have already referred to the statement made by -talented experimentalists, that magnetism has a powerful -influence in either retarding or accelerating chemical -combination. Beyond a doubt chemical action weakens -the power of a magnet; but the disturbance which it -occasions in soft iron, on the contrary, appears to tend -to its receiving magnetism more readily, and retaining -it more permanently. Further investigations are, how<span class="pagenum"><a name="Page_263" id="Page_263"></a>[Pg 263]</span>ever, -required, before we can decide satisfactorily either -of these problems, both of which bear very strongly -upon the subject we have just been considering.</p> - -<p>We have seen that heat and electricity act strangely on -magnetic force, and that this statical power reacts upon -them: and thus the question naturally arises, Do light -and magnetism in any way act upon each other?</p> - -<p>Morichini and Carpi on the continent, and Mrs. -Somerville in England, have stated that small bars of -steel can be rendered magnetic by exposing them to -the influence of the violet rays of light. These results -have been denied by others, but again repeated and -apparently confirmed. In all probability, the rays to -which the needles were exposed, being those in which -the maximum actinic power is found, produced an -actual chemical change; and then, if the position were -favourable, it is quite evident that magnetism would be -imparted. Indeed we have found this to be the case -when the needles, exposed to solar radiations, were placed -in the direction of the dip. The supposed magnetization -of light by Faraday has already been mentioned. If -the influence in one case is determined, it will render -the other more probable.<a name="FNanchor_194_194" id="FNanchor_194_194"></a><a href="#Footnote_194_194" class="fnanchor">[194]</a></p> - -<p>“In seeking for a cause,” writes Sir David Brewster, -“which is capable of inducing magnetism on the ferruginous -matter of our globe, whether we place it within -the earth, or in its atmosphere, we are limited to the -<span class="smcap">sun</span>, to which all the magnetic phenomena have a distinct -reference; but, whether it acts by its heat, or by -its light, or by specific rays, or influences of a magnetic -nature, must be left to future inquiry.”<a name="FNanchor_195_195" id="FNanchor_195_195"></a><a href="#Footnote_195_195" class="fnanchor">[195]</a></p> -<p><span class="pagenum"><a name="Page_264" id="Page_264"></a>[Pg 264]</span></p> -<p>We have learnt that magnetism is not limited to ferruginous -matter; we know that the ancient doctrine of -the universality of the property is true. Kircher, in -his strange work on Magnetism, published in the early -part of the seventeenth century<a name="FNanchor_196_196" id="FNanchor_196_196"></a><a href="#Footnote_196_196" class="fnanchor">[196]</a>—a curious exemplification -of the most unwearying industry and careful -experiment, combined with the influences of the credulity -and superstitions of his age—attributes to this power -nearly all the cosmical phenomena with which, in his -time, men were acquainted. He curiously anticipates -the use of the supposed virtue of magnetic traction -in the curative art; and as the titles of his concluding -chapters sufficiently show, he was a firm believer -in animal magnetism.<a name="FNanchor_197_197" id="FNanchor_197_197"></a><a href="#Footnote_197_197" class="fnanchor">[197]</a> But it is not with -any reference to these that we refer to the work of -<i>Athanasii Kircheri, Societatis Jesu, Magnes, sive de -Magnetivâ Arte</i>, but to show that two hundred years -since, man was near a great truth; but the time of its -development being not yet come, it was allowed to sleep -for more than two centuries, and the shadow of night<span class="pagenum"><a name="Page_265" id="Page_265"></a>[Pg 265]</span> -had covered it. In speaking of the vegetable world, -and the remarkable processes by which the leaf, the -flower, and the fruit are produced, this sage brings forward -the fact of the diamagnetic character of the plant, -which has been, within the last two years, re-discovered; -and he refers the motions of the Sun-flower, the closing -of the Convolvulus, and the directions of the spiral, -formed by twining plants, to this particular influence.</p> - -<p>This does not appear as a mere speculation, a random -guess, but is the result of deductions from experiment -and observation. Kircher doubtless leaped over a wide -space to come to his conclusion; but the result is valuable -in a twofold sense. In the first it shows us that, -by neglecting a fact which is suggestive, we probably -lose a truth of great general application; and secondly, -it proves to us, that by stepping beyond the point to -which inductive logic leads, and venturing on the wide -sea of hypothesis, we are liable to sacrifice the true to -the false, and thus to hinder the progress of human -knowledge.</p> - -<p>Magnetism, in one or other of its forms, is now proved -to be universal, and to its power we are disposed to refer -the structural conditions of all material bodies, both -organic and inorganic. This view has scarcely yet been -recognised by philosophers; but as we find a certain -law of polarity prevailing through every atom of created -matter, in whatever state it may be presented to our -senses, it is evident that every particle must have a polar -and directing influence upon the mass, and every coherent -mass becomes thus only a larger and more -powerful representative of the magnetic unit. Thus we -see the speculation of Hansteen, that the sun is, to us, -a magnetic centre, and that it is equally influenced by -the remoter suns of the universe,<a name="FNanchor_198_198" id="FNanchor_198_198"></a><a href="#Footnote_198_198" class="fnanchor">[198]</a> is supported by -legitimate deductions from experiment.</p> -<p><span class="pagenum"><a name="Page_266" id="Page_266"></a>[Pg 266]</span></p> -<p>The great difficulty is not, however, got rid of by -this speculation; the cause by which the earth’s magnetism -is induced is only removed further off.</p> - -<p><span class="pagenum"><a name="Page_267" id="Page_267"></a>[Pg 267]</span></p> - -<p>The idea of a magnetic fluid is scarcely tenable; and -the ferruginous nature of the Aurora borealis receives -no proof from any investigation; indeed, we have procured -evidence to show that iron is not at all necessary for -the production of magnetic phenomena. The leaf of a -tree, a flower, fruit, a piece of animal muscle, glass, paper, -and a variety of similar substances, have the power of -repelling the bar of iron which we call a magnet, and -of placing it at right angles to the direction of the force -exerted by them. This is a point which must be constantly -borne in mind when we now consider the -mysteries of magnetic phenomena.</p> - -<p>Any two masses of matter act upon each other -according to this law, and although by the power of -cohesion the force may be brought to an equilibrium, or -to its zero point, it is never lost, and may be readily and -rapidly manifested by any of the means employed for -electrical excitation.</p> - -<p>Reasoning by analogy, the question fairly suggests -itself: If two systems of inorganic atomic constitution -are thus invested with a power of influencing each other -through a distance, why may not two more highly -developed organic systems equally, or to a greater extent, -produce an influence in like manner? Upon such -reasoning as this is founded the phenomenon known as -Animal Magnetism. There is no denying the fact that -one mass of blood, muscle, nerves, and bone, must, -magnetically, influence another similar mass. This is, -however, something totally different from that abnormal -condition which is produced through some peculiar and, -as yet, unexplained physiological influences.</p> - -<p>With the mysterious operations of vital action, the -forces which we have been considering have nothing<span class="pagenum"><a name="Page_268" id="Page_268"></a>[Pg 268]</span> -whatever in common. The powers which are employed -in the arrangements of matter are, notwithstanding their -subtile character, of far too gross a nature to influence -the psychological mysteries which present themselves to -the observant mind. It cannot be denied that, by -placing a person of even moderate nervous sensibility -in a constrained position, and under an unnatural -influence of the mind, as acquired by the disciples of -Mesmer, a torpor affecting only certain senses is produced. -The recognised and undoubted phenomena are -in the highest degree curious—but in these the marvels -of charlatanry and ignorance are not included;—and -the explanation must be sought for by the physiologist -among those hidden principles upon which depends all -human sensation.<a name="FNanchor_199_199" id="FNanchor_199_199"></a><a href="#Footnote_199_199" class="fnanchor">[199]</a></p> - -<p>Man, like a magician, stands upon a promontory, and -surveying the great ocean of the physical forces which -involve the material creation, and produce that infinite -variety of phenomena which is unceasingly exhibited -around him, he extends the wand of intelligence, and -bids the “spirits of the vasty deep” obey his evocation.</p> - -<p>The phenomena recur—the great processes of creation -go on—the external manifestations of omnipotent -power proceed—effects are again and again produced; -but the current of force passes undulating onwards;—and -to the proud bidding of the evocator there is no -reply but the echo of his own vain voice, which is lost at -last in the vast immensity of the unknown which lies -beyond him.</p> - -<p>We see how powerfully the physical forces, in their -various modes of action, stir and animate this planetary -mass; and amongst these the influence of magnetism<span class="pagenum"><a name="Page_269" id="Page_269"></a>[Pg 269]</span> -appears as a great directing agent, though its origin is -unknown to us.</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">That power which, like a potent spirit, guides</div> -<div class="verse">The sea-wide wanderers over distant tides,</div> -<div class="verse">Inspiring confidence where’er they roam,</div> -<div class="verse">By indicating still the pathway home;—</div> -<div class="verse">Through nature, quicken’d by the solar beam,</div> -<div class="verse">Invests each atom with a force supreme,</div> -<div class="verse">Directs the cavern’d crystal in its birth,</div> -<div class="verse">And frames the mightiest mountains of the earth;</div> -<div class="verse">Each leaf and flower by its strong law restrains,</div> -<div class="verse">And binds the monarch Man within its mystic chains.</div> -</div></div></div> -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_170_170" id="Footnote_170_170"></a><a href="#FNanchor_170_170"><span class="label">[170]</span></a> <i>Treatise on Magnetism</i>, by Sir David Brewster. <i>Cosmos: a -Sketch of a Physical description of the Universe</i>; by Alexander -Von Humboldt.—Otté’s Translation.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_171_171" id="Footnote_171_171"></a><a href="#FNanchor_171_171"><span class="label">[171]</span></a> <i>Expérience Electro-Magnétique.</i> par M. Œrsted.—Annales -de Chimie, vol. xxii. p. 201. De la Rive, <i>Recherches sur la Distribution -de l’Electricité dyn. dans les Corps</i>.—Genève, 1825.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_172_172" id="Footnote_172_172"></a><a href="#FNanchor_172_172"><span class="label">[172]</span></a> <i>On the Magnetic power of Soft Iron</i>: by Mr. Watkins.—Philosophical -Transactions, 1833.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_173_173" id="Footnote_173_173"></a><a href="#FNanchor_173_173"><span class="label">[173]</span></a> Cavallo, <i>On Magnetism</i>.—Cavallo was the first who noticed -the influence of heat on Magnetism. Consult <i>On the anomalous -Magnetic Action of Hot Iron between the white and blood-red heat</i>: -by Peter Barlow, Esq.—Philosophical Transactions, 1822, p. 124. -<i>Treatise on Magnetism</i>: by Barlow.—Encyclopædia Metropolitana.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_174_174" id="Footnote_174_174"></a><a href="#FNanchor_174_174"><span class="label">[174]</span></a> “The foundation of our researches is the assumption that the -terrestrial magnetic force is the collective action of all the magnetised -particles of the earth’s mass. We represent to ourselves magnetisation -as the separation of the magnetic fluids. Admitting -the representation, the mode of action of the fluids (repulsion of -similar, and attraction of dissimilar, particles inversely as the -square of the distance) belongs to the number of established -truths. No alteration in the results would be caused by changing -this mode of representation for that of Ampère, whereby, instead -of magnetic fluids, magnetism is held to consist in constant galvanic -currents in the minutest particles of bodies. Nor would it -occasion a difference if the terrestrial magnetism were ascribed to -a mixed origin, as proceeding partly from the separation of the -magnetic fluids in the earth, and partly from galvanic currents, -in the same; inasmuch as it is known that for each galvanic -current may be substituted such a given distribution of the magnetic -fluids in a surface bounded by the current, as would exercise -in each point of external space precisely the same magnetic action -as would be produced by the galvanic current itself.”—<i>General -Theory of Terrestrial Magnetism</i>, by Professor Carl Friedrich -Gauss, of the University of Göttingen.—Scientific Memoirs, -vol. ii. p. 188.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_175_175" id="Footnote_175_175"></a><a href="#FNanchor_175_175"><span class="label">[175]</span></a> Humboldt’s <i>Cosmos</i>.—Otté’s translation.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_176_176" id="Footnote_176_176"></a><a href="#FNanchor_176_176"><span class="label">[176]</span></a> Hansteen: <i>Untersuchungen über den Magnetismus der Erde</i>, -Christïana, 1819. Humboldt: <i>Exposé des Variations <span class="correction" title="In the original book: Magnetiques">Magnétiques</span></i>.—Gilbert’s -Annales. Brewster’s Magnetism: Encyclopædia Metropolitana.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_177_177" id="Footnote_177_177"></a><a href="#FNanchor_177_177"><span class="label">[177]</span></a> Hansteen; as above.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_178_178" id="Footnote_178_178"></a><a href="#FNanchor_178_178"><span class="label">[178]</span></a> <i>On the effects of temperature on the intensity of magnetic forces, -and on the diurnal variations of the terrestrial magnetic intensity</i>; -by Samuel Hunter Christie, Esq.—Philosophical Transactions, -vol. cxv. 1825.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_179_179" id="Footnote_179_179"></a><a href="#FNanchor_179_179"><span class="label">[179]</span></a> It has been observed by Mr. Barlow, in England, and some -eminent observers in Austria, that an electric current constantly -traverses the wires of the electric telegraph wherever there are two -earth connections.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_180_180" id="Footnote_180_180"></a><a href="#FNanchor_180_180"><span class="label">[180]</span></a> <i>Meteorological Observations and Essays</i>: by Dr. Dalton. <i>On -the Height of the Aurora Borealis above the surface of the Earth</i>: -by John Dalton, F.R.S.—Philosophical Transactions, vol. cxiv. -p. 291.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_181_181" id="Footnote_181_181"></a><a href="#FNanchor_181_181"><span class="label">[181]</span></a> Arago: Annales de Chimie, vol. xxxix. p. 369. <i>On the variable -Intensity of Terrestrial Magnetism and the Influence of the -Aurora Borealis upon it</i>; by Robert Were Fox.—Philosophical -Transactions, 1831, p. 199.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_182_182" id="Footnote_182_182"></a><a href="#FNanchor_182_182"><span class="label">[182]</span></a> “Brilliant and active coruscations of the Aurora Borealis,” -says Captain Back, “when seen through a hazy atmosphere, and -exhibiting the prismatic colours, almost invariably affected the -needle. On the contrary, a very bright Aurora, though attended -by motion, and even tinged with a dullish red and a yellow in a -clear blue sky, seldom produced any sensible change, beyond, at -the most, a tremulous motion. A dense haze or fog, in conjunction -with an active Aurora, seemed uniformly favourable to the -disturbance of the needle, and a low temperature was favourable -to brilliant and active coruscations. On no occasion during two -winters was any sound heard to accompany the motions. The -Aurora was frequently seen at twilight, and as often to the eastward -as to the westward; clouds, also, were often perceived in -the day-time, in form and disposition very much resembling the -Aurora.”—<i>Narrative of the Arctic Land Expedition.</i></p></div> - -<div class="footnote"> - -<p><a name="Footnote_183_183" id="Footnote_183_183"></a><a href="#FNanchor_183_183"><span class="label">[183]</span></a> Faraday: <i>On the Diamagnetic character of Flame and Gases</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_184_184" id="Footnote_184_184"></a><a href="#FNanchor_184_184"><span class="label">[184]</span></a> “The Aurora Borealis is certainly in some measure a magnetical -phenomenon; and if iron were the only substance capable -of exhibiting magnetic effects, it would follow that some ferruginous -particles must exist in the upper regions of the atmosphere. -The light usually attending this magnetical meteor may -possibly be derived from electricity, which may be the immediate -cause of a change in the distribution of the magnetic fluid, contained -in the ferruginous vapours which are imagined to float in -the air.”—Lecture on Magnetism: Young’s <i>Lectures on Natural -Philosophy</i>, p. 533.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_185_185" id="Footnote_185_185"></a><a href="#FNanchor_185_185"><span class="label">[185]</span></a> <i>On the supposed influence of Magnetism and Chemical Action</i>; -by Robert Hunt.—Philosophical Magazine, vol. xxxii. No. 215, -1849.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_186_186" id="Footnote_186_186"></a><a href="#FNanchor_186_186"><span class="label">[186]</span></a> Those bodies which are attracted by a magnet, as iron is, are -called <i>magnetic bodies</i>. Those which are, on the contrary, repelled -by the same power, are termed <i>diamagnetic bodies</i>. On these Dr. -Faraday remarks:—“Of the substances which compose the crust -of the earth, by far the greater portion belong to the diamagnetic -class; and though ferruginous and other magnetic matters, being -more energetic in their action, are more striking in their phenomena, -we should be hasty in assuming that, therefore, they over -rule entirely the effect of the former bodies. As regards the ocean, -lakes, rivers, and the atmosphere, they will exert their peculiar -effect almost uninfluenced by any magnetic matter in them, and -as respects the rocks and mountains, their diamagnetic influence -is perhaps greater than might be anticipated. I mentioned that -by adjusting water and a salt of iron together, I obtained a solution -inactive in air; that is, by a due association of the forces of a body, -from each class, water and a salt of iron, the magnetic force of the -latter was entirely counteracted by the diamagnetic force of the -former, and the mixture was neither attracted nor repelled: To -produce this effect, it required that more than 48·6 grains of crystallised -protosulphate of iron should be added to ten cubic inches -of water (for these proportions gave a solution which would set -equatorially), a quantity so large, that I was greatly astonished on -observing the power of the water to overcome it. It is not, therefore, -at all unlikely that many of the masses which form the crust -of this our globe, may have an excess of diamagnetic power, and -act accordingly.”—<i>On new magnetic actions, and on the magnetic -condition of all matter</i>; by Michael Faraday, D.C.L., F.R.S., &c.—Philosophical -Transactions, Jan. 1846, vol. cxxxvii. p. 41.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_187_187" id="Footnote_187_187"></a><a href="#FNanchor_187_187"><span class="label">[187]</span></a> Ibid.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_188_188" id="Footnote_188_188"></a><a href="#FNanchor_188_188"><span class="label">[188]</span></a> <i>On the Diamagnetic conditions of Flame and Gases</i>, by Michael -Faraday. F.R.S.; and <i>On the motions presented by Flame when -under Electro-Magnetic Influence</i>, by Professor <span class="correction" title="In the original book: Zandeteschi">Zantedeschi</span>.—Philosophical -Magazine, 1847, pp. 401–421.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_189_189" id="Footnote_189_189"></a><a href="#FNanchor_189_189"><span class="label">[189]</span></a> <i>On Diamagnetism</i>; by Professor Plücker, of Bonn.—Philosophical -Magazine, July, 1848.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_190_190" id="Footnote_190_190"></a><a href="#FNanchor_190_190"><span class="label">[190]</span></a> For a detailed account of the experiments of Faraday, <span class="correction" title="In the original book: Plucker">Plücker</span>, -Becquerel, Tyndale, and Knoblauch, see De La Rive’s <i>Treatise on -Electricity in Theory and Practice</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_191_191" id="Footnote_191_191"></a><a href="#FNanchor_191_191"><span class="label">[191]</span></a> A few examples taken from Dr. Faraday’s paper will show -this:— -</p> -<p> -Nitrogen being acted on was manifestly diamagnetic in relation -to common air when both were of the same temperature. Oxygen -appears to be magnetic in common air. Hydrogen proved to be -clearly and even strongly diamagnetic. Its diamagnetic state shows, -in a striking point of view, that gases, like solids, have peculiar -and distinctive degrees of diamagnetic force. Carbonic acid gas -is diamagnetic in air. Carbonic oxide was carefully freed from -carbonic acid before it was used, and it appears to be more diamagnetic -than carbonic acid. Nitrous oxide was moderately, but -clearly, diamagnetic in air. Olefiant gas was diamagnetic. The -coal gas of London is very well diamagnetic, and gives exceedingly -good and distinct results. Sulphurous acid gas is diamagnetic -in air. Muriatic acid gas was decidedly diamagnetic in air.—<i>On -the Diamagnetic Conditions of Flame and Gases</i>: Philosophical -Magazine, 1847, p. 409.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_192_192" id="Footnote_192_192"></a><a href="#FNanchor_192_192"><span class="label">[192]</span></a> For illustration of this I must refer to my own Memoir, <i>Researches -on the Influence of Magnetism and Voltaic Electricity on -Crystallization, and other conditions of matter</i>, in the Memoirs of -the Geological Survey of Great Britain, &c., vol. i.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_193_193" id="Footnote_193_193"></a><a href="#FNanchor_193_193"><span class="label">[193]</span></a> In a work published by Mr. Evan Hopkins, entitled <i>On the -Connexion of Geology with Terrestrial Magnetism</i>, will be found -many valuable practical observations made in this country and -the gold and silver districts of America; but the views taken by -the author are open to many objections.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_194_194" id="Footnote_194_194"></a><a href="#FNanchor_194_194"><span class="label">[194]</span></a> See a notice by Faraday of Morichini’s Experiments in -<i>Relations of Light to Magnetic Force</i>—Philosophical Transactions, -vol. cxxxvii. p. 15. See also Mr. Christie <i>On Magnetic Influence -in the Solar Rays</i>—Philosophical Transactions, vol. cvii. p. 219; -vol. cxix. p. 379.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_195_195" id="Footnote_195_195"></a><a href="#FNanchor_195_195"><span class="label">[195]</span></a> Sir David Brewster <i>On Magnetism</i>; republished from the -Encyclopædia Britannica.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_196_196" id="Footnote_196_196"></a><a href="#FNanchor_196_196"><span class="label">[196]</span></a> The whole of the title of Kircher’s book will convey some idea -of the subjects embraced:—Athanasii Kircheri Societatis Jesu -Magnes, sive de Arte Magneticâ; opus tripartitum, quo Universa -Magnetis Natura ejusque in omnibus Scientiis et Artibus usus -novâ methodo explicatur: ac præterea e viribus et prodigiosis -effectibus Magneticarum aliarumque abditarum Naturæ Motionum -in Elementis, Lapidibus, Plantis, Animalibus elucescentium: -multa hucusque incognita Naturæ Arcana, per Physica, Medica, -Chymica, et Mathematica omnis generis Experimenta recluduntur -Editio Tertia: ab ipso Authore recognita emendataque, ac multis -novorum Experimentorum Problematibus aucta. Romæ, 1654.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_197_197" id="Footnote_197_197"></a><a href="#FNanchor_197_197"><span class="label">[197]</span></a> The following are the titles of the concluding chapters of -Kircher’s book:—<i>De magnetismo solis et lunæ in maria.</i> <i>De magneticâ -vi plantarum.</i> <i>De insitionis magneticis miraculis.</i> <i>De magnetismo -virgulæ auriferæ seu divinatoriæ.</i> <i>De plantis heliotropiis -eorumque magnetismo.</i> <i>De magnetismo rerum medicinalium.</i> <i>De vi -attractivâ potentiæ imaginativæ.</i> <i>De magnetismo musicæ.</i> <i>De -magnetismo amoris.</i></p></div> - -<div class="footnote"> - -<p><a name="Footnote_198_198" id="Footnote_198_198"></a><a href="#FNanchor_198_198"><span class="label">[198]</span></a> “For these reasons it appears most natural to seek their -origin in the sun, the source of all living activity, and our conjecture -gains probability from the preceding remarks on the -daily oscillations of the needle. Upon this principle the sun -may be conceived as possessing one or more magnetic axes, -which, by distributing the force, occasion a magnetic difference -in the earth, in the moon, and all those planets whose -internal structure admits of such a difference. Yet, allowing -all this, the main difficulty seems not to be overcome, but -merely removed from the eyes to a greater distance; for the -question may still be asked, with equal justice, whence did -the sun acquire its magnetic force? And if from the sun we -have recourse to a central sun, and from that again to a general -magnetic direction throughout the universe, having the Milky -Way for its equator, we but lengthen an unrestricted chain, -every link of which hangs on the preceding link, no one of -them on a point of support. All things considered, the following -mode of representing the subject appears to me most -plausible. If a single globe were left to move alone freely in the -immensity of space, the opposite forces existing in its material -structure would soon arrive at an equilibrium conformable to their -nature, if they were not so at first, and all activity would soon -come to an end. But if we imagine another globe to be introduced, -a mutual relation will arise between the two; and one of its -results will be a reciprocal tendency to unite, which is designated -and sometimes thought to be explained by the merely descriptive -word Attraction. Now would this tendency be the only consequence -of this relation? Is it not more likely that the fundamental -forces, being drawn from their state of indifference or rest, -would exhibit their energy in all possible directions, giving rise to -all kinds of contrary action? The electric force is excited, not by -friction alone, but also by contact, and probably also, though in -smaller degrees, by the mutual action of two bodies at a distance; -for contact is nothing but the smallest possible distance, and that, -moreover, only for a few small particles. Is it not conceivable -that magnetic force may likewise originate in a similar manner? -When the natural philosopher and the mathematician pay regard -to no other effect of the reciprocal relation between two bodies at -a distance, except the tendency to unite, they proceed logically, if -their investigations require nothing more than a moving power; -but should it be maintained that no other energy can be developed -between two such bodies, the assertion will need proof and the -proof will be hard to find.”—The above is a translation from -Hansteen’s work <i>On Magnetism</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_199_199" id="Footnote_199_199"></a><a href="#FNanchor_199_199"><span class="label">[199]</span></a> See article <i>Animal Magnetism</i>, Encyclopædia Britannica, and -Mr. Braid’s papers <i>On Hypnotism</i>, published in the “Medical -Times.”</p></div></div> - - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_270" id="Page_270"></a>[Pg 270]</span></p> - -<h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI.</h2> - -<p class="center">CHEMICAL FORCES.</p> - - -<p class="chap-head">Nature’s Chemistry—Changes produced by Chemical Combination—Atomic -Constitution of Bodies—Laws of Combination—Combining -Equivalents—Elective Affinity—Chemical -Decomposition—Compound Character of Chemical Phenomena—Catalysis -or action of Presence—Transformation -of Organic Bodies—Organic Chemistry—Constancy of -Combining Proportions—The Law of Volumes, the Law of -Substitutions, Isomeric States, &c.</p> - - -<p class="p2">All things on the earth are the result of chemical combination. -The operations by which the commingling of -molecules and the interchange of atoms take place, we -can imitate in our laboratories; but in nature they -proceed by slow degrees, and, in general, in our hands -they are distinguished by suddenness of action. In -nature chemical power is distributed over a long period -of time, and the process of change is scarcely to be -observed. By art we concentrate chemical force, and -expend it in producing a change which occupies but a -few hours at most. Many of the more striking phenomena -of nature are still mysterious to us, and principally -because we do not, or cannot, take the element time -into calculation. The geologist is compelled to do this -to explain the progress of the formation of the crust of -the earth, but the chemist rarely regards the effects of -time in any of his operations. The chemical change -which within the fissure of the rock is slowly and -silently at work, displacing one element or molecule,<span class="pagenum"><a name="Page_271" id="Page_271"></a>[Pg 271]</span> -and replacing it by another, is in all probability the -operation of a truly geological period. Many, however, -of the changes which are constantly going on around us, -are of a much more rapid character, and in these nature -is no slower in manipulating than the chemist.</p> - -<p>Had it been that the elements which are now found -in combination could exist in a free state, the most -disastrous consequences would necessarily ensue. There -must have been a period when many of the combinations -known to us were not yet created. Their elements -either existed in other forms, or were uncombined. -Our rocks are compounds of oxygen with certain peculiar -metals which unite with oxygen so rapidly that -incandescence is produced by their combination. Let us -suppose that any of these metals existed in purity, and -that they were suddenly brought into contact with -water, the atmospheric air, or any body containing -oxygen, the result would be a convulsion of the most -fearful kind; the entire mass of metal would glow with -intensity of heat, and the impetuosity of the action would -only be subdued when the whole of the metal had -become oxidized. Volcanic action has been referred to -some such cause as this, but there is not sufficient -evidence to support the hypothesis; indeed, it is contrary -to the opinion of most philosophers.<a name="FNanchor_200_200" id="FNanchor_200_200"></a><a href="#Footnote_200_200" class="fnanchor">[200]</a> Such a -condition may possibly have existed at one time, during -that period when darkness was upon the face of the -deep, when the earth was a chaos; but it is only adduced -here as an example of the violent nature of some -chemical changes. Potassium thrown on water bursts -into flame, and sodium does so under certain conditions. -If these, or the metals proper in a state of fine division, -are brought into an atmosphere of chlorine, the intensity<span class="pagenum"><a name="Page_272" id="Page_272"></a>[Pg 272]</span> -of chemical action is so great that they become incandescent, -many of them glowing with extreme brilliancy. -If hydrogen gas is mixed with this element (chlorine) -they unite, under the influence of light, with explosive -violence, giving rise to a compound, muriatic acid, which -combines with water in an almost equally energetic -manner. Nitrogen, as it exists in the atmosphere, -mixed with oxygen, appears nearly inert; with hydrogen -it forms the pungent compound, ammonia; with carbon, -the poisonous one, cyanogen, the base of prussic acid; -with chlorine it gives rise to a fluid, oily in its appearance, -but which, when merely touched by an unctuous body, -explodes more violently than any other known compound, -shivering whatever vessel it may be contained in, -to atoms; with iodine it is only slightly less violent; -and in certain combinations with silver, mercury, gold, -or platinum, it produces fulminating compounds of the -most dangerous character.<a name="FNanchor_201_201" id="FNanchor_201_201"></a><a href="#Footnote_201_201" class="fnanchor">[201]</a> Here we have elements -harmless when uncombined, exhibiting the most destructive -effects if their combinations are at all disturbed; -and in the other case we have inert masses produced -from active and injurious agents.</p> - -<p>We regard a certain number of substances as <i>elementary</i>; -that is to say, not being able, in the present -state of our knowledge, to reduce them to any more -simple condition, they are considered as the elements -which by combination produce the variety of substances -found in the three kingdoms of nature.</p> - -<p>We have already spoken of the atomic constitution of -bodies. It remains now to explain the simplicity and -beauty which mark every variety of combination under -chemical force. As a prominent and striking example, -water is a compound of two gaseous bodies, oxygen and -hydrogen:—</p> - -<p>If we decompose water by means of galvanic elec<span class="pagenum"><a name="Page_273" id="Page_273"></a>[Pg 273]</span>tricity, -or determine its composition by direct chemical -analysis, we shall find it consists of two volumes of hydrogen -gas, united to one volume of oxygen, or, by weight, of -one part of hydrogen combined with eight of oxygen. -In 100 parts, therefore, we should find—</p> - -<table summary="chemical analysis of water"> -<tr><td>Oxygen</td><td class="tdpad">88·9</td></tr> -<tr><td>Hydrogen</td><td class="tdpad">11·0</td></tr> -</table> - -<p>It is found in the same way that the theoretical weight -of the atom of carbon is 6, and that of nitrogen 14; -whilst the atom of iron is 28, that of silver 108, of gold -199, and that of platinum and iridium each 98.<a name="FNanchor_202_202" id="FNanchor_202_202"></a><a href="#Footnote_202_202" class="fnanchor">[202]</a> Now, -as these are the relative weights of the ultimate indivisible -atom, it follows that all combinations must be -either atom to atom, or one to two, three, or four; but -that in no case should combination take place in any -other than a multiple proportion of the equivalent or -atomic number. This is found to be the case. Oxygen, -for instance, combines as one, two, or three -atoms; its combination presenting some multiple of its -equivalent number 8, as 16, or 24: and in like manner -the combining quantity of carbon is 6, or some multiple -of that number. Where this law is not found strictly -to agree with analytical results, of which some examples -are afforded by the sesquioxides, it may be -attributed, without doubt, to some error of analysis or -in the method of calculation.</p> - -<p>Nothing can be more perfect than the manner in -which nature regulates the order of combination. We -have no uncertain arrangement; but, however great the -number of the atoms of one element may be, over those -of another, those only combine which are required, -according to this great natural law, to form the compound, -all the others still remaining free and uncom<span class="pagenum"><a name="Page_274" id="Page_274"></a>[Pg 274]</span>bined. -These results certainly appear to prove that the -elementary particles of matter are not of the same -specific gravities. Do they not also indicate that any -alteration in the specific gravity of the atom would give -rise to a new series of compounds, thus apparently producing -a new element? Surely there is nothing -irrational in the idea that the influences of heat or -electricity, or of other powers of which as yet we know -nothing, may be sufficient to effect such changes in the -atomic constituents of this earth.</p> - -<p>The combination of elementary atoms takes place -under the influence of an unknown force which we are -compelled to express by a figurative term, <i>affinity</i>. -In some cases it would appear that the disposition of -two bodies to unite, is determined by the electrical condition; -but a closer examination of the question than -it is possible to enter into in this place, clearly shows -that some physical state, not electrical, influences combining -power.</p> - -<p>Chemical affinity or attraction is the peculiar disposition -which one body has to unite with another. To -give some instances in illustration. Water and spirit -combine most readily: they have a strong affinity for -each other. Water and oil repel each other: they have -no affinity; they will not enter into combination. If -carbonate of potash is added to the spirit and water in -sufficient quantity, the water is entirely separated, and -the pure spirit will float over the hydrated potash. If -potash is added to the oil and water, it combines with -the oil, and, forming soap, they all unite together; but, -if we now add a little acid to the mixture, the potash -will quit the oil to combine with the acid, and the oil -will be repelled as before and float on the liquid. This -has been called single elective affinity. These elections -were regarded as constant, and chemists drew up tables -for the purpose of showing the order in which these<span class="pagenum"><a name="Page_275" id="Page_275"></a>[Pg 275]</span> -decompositions occur.<a name="FNanchor_203_203" id="FNanchor_203_203"></a><a href="#Footnote_203_203" class="fnanchor">[203]</a> Thus, ammonia, it was shown, -would separate sulphuric acid from magnesia, lime -remove it from ammonia, potash or soda from lime, and -barytes from potash or soda. It was thought the -inverse of this order would not take place, but recent -researches have shown that the results are modified by -quantity and some other conditions.</p> - -<p>It often happens that we have a compound action of -this kind in which double election is indicated. Sulphate -of lime and carbonate of ammonia in solution are -brought together, and there result a carbonate of lime -and a sulphate of ammonia. Now, in such cases -nothing more than single elective attraction most -probably occurs, and the carbonic acid is seized by the -lime, by the great affinity of that earth for carbonic -acid, only after it has been set free from the ammonia, -and then, by the force of cohesion acting with the combining -powers, the insoluble salt is precipitated.<a name="FNanchor_204_204" id="FNanchor_204_204"></a><a href="#Footnote_204_204" class="fnanchor">[204]</a> There -is a curious fact in connection with this decomposition. -If carbonate of lime and sulphate of ammonia are mixed -together dry, and exposed, in a closed vessel, to a red -heat, sulphate of lime and carbonate of ammonia are<span class="pagenum"><a name="Page_276" id="Page_276"></a>[Pg 276]</span> -formed. These opposite effects are not very easily explained. -The action of heat is to set free the carbonic -acid; and it can only be by supposing that considerable -differences of temperature reverse the laws of affinity, -that we can at all understand this phenomenon. That -different effects result at high temperatures from those -which prevail at low ones, recent experiments prove to -us, particularly those of Boutigny, already quoted when -considering decomposition by calorific action.</p> - -<p>Under the term chemical affinity, which we regard as -a power acting at insensible distances, and producing a -change in bodies, we are content to allow ourselves to -believe that we have explained the great operations of -nature. We find that the vegetable and animal kingdoms -are composed of carbon, hydrogen, oxygen, and -nitrogen. The granite mountains of the earth, and its -limestone hills, and all its other geological formations, -are found to be metals and oxygen, and carbon and -sulphur, disposed to settle in harmonious union in their -proper places by chemical affinity. But what really is -the power which combines atom to atom, and unites -molecule to molecule? Can we refer the process to -heat? The influence of caloric, although by changing -the form of bodies it sometimes assists combination, is -to be regarded rather as in antagonism to the power of -cohesion. Can it be thought that electricity is active in -producing the result? During every change of state, -those phenomena which we term electrical are manifested; -but we thereby only prove the general diffusion -of the electric principle, and by no means show that -electricity is the cause of the chemical change. Can -light determine these <span class="correction" title="In the original book: change">changes</span>? It is evident, although -light may be a disturbing power, that it cannot be the -effective one; for many of these decompositions and recompositions -are constantly going on within the dark -and silent depths of the earth, to which a sunbeam -cannot reach. That the excitation on the surface of the<span class="pagenum"><a name="Page_277" id="Page_277"></a>[Pg 277]</span> -earth, produced by solar influence, may modify those -changes, is probable. It is, however, certain that we -must regard all manifestations of chemical force as -dependent upon some secret principles common to all -matter, diffused throughout the universe, but modified -by the influences of the known imponderable elements, -and by the mechanical force of aggregative attraction.</p> - -<p>Bodies undergo remarkable changes of form, and -present very different characters, by reactions, which -are of several kinds. We suppose that a permanent -corpuscular arrangement is maintained so long as the -equilibrium of the molecular forces is undisturbed. -Water, for instance, remains unchanged so long as the -balance of affinity is kept up between the oxygen and -hydrogen of which it is composed, or so long as the -oscillations of force between these combining elements -are equal; but disturb this force, or set up a new -vibratory action, as by passing an electric current -through the water, or by presenting another body, which -has the power of reacting upon one of these corpuscular -systems, and the water is decomposed, the hydrogen and -oxygen gases being set free, or one alone is liberated, -and the other combined with the molecules of the agent -employed, and a new compound produced. This is -chemistry, by which science we discover all the combinations -of matter.</p> - -<p>Having reason to conclude that atom combines with -atom, according to a system most harmoniously arranged, -there can be no difficulty in conceiving that molecule -unites with molecule, in a manner regulated by some -equally well-marked law. It was, indeed, a discovery -by Wenzel, of Fribourg, that, in salts which decompose -each other, the acid which saturates one base will also -saturate the other base; and the subsequent observations -of Richter, of Berlin, who attached proportional numbers -to the acids and bases, and who remarked that the -neutrality of metallic salts does not change during the<span class="pagenum"><a name="Page_278" id="Page_278"></a>[Pg 278]</span> -precipitation of metals by each other, which led the way -to the atomic theory of Dr. Dalton, to whom entirely -belongs the observation, that the equivalent of a compound -body is the sum of the equivalents of its constituents, -and the discovery of combination in multiple -proportions.</p> - -<p>The elements of a molecule can take a new arrangement -amongst themselves, without any alteration in the -number of the atoms or of their weight, and thus give -rise to a body of a different form and colour, although -possessing the same chemical constitution. This is the -case with many of the organic compounds of carbon and -hydrogen.</p> - -<p>The elements of a compound may be disassociated, -and thus the dissimilar substances of which it is composed -set free. A piece of chalk exposed to heat is, by -the disturbance of its molecular arrangement, changed -in its nature; a gaseous body, carbonic acid, is liberated, -and quick-lime (oxide of calcium) is left behind. If -this carbonic acid is passed through red-hot metal tubes, -or brought in contact with heated potassium, it is resolved -into oxygen and charcoal—the oxygen combining -with the metal employed. The oxide of calcium -(lime), if subjected to the action of a powerful galvanic -current, is converted into oxygen and a metal, calcium. -Thus we learn that chalk is a body consisting of two -compound molecules,—carbonic acid, which is formed -by the combination of an atom of carbon with two atoms -of oxygen,—and lime, which results from the union of -an atom of calcium with one of oxygen.</p> - -<p>The condition requisite to the production of chemical -action between bodies is that they should be dissimilar. -Two elementary atoms are placed within the spheres of -each other’s influences, and a compound molecule -results. Oxygen and hydrogen form water; oxygen -and carbon give rise to carbonic acid; nitrogen and -hydrogen unite to form ammonia; and chlorine and<span class="pagenum"><a name="Page_279" id="Page_279"></a>[Pg 279]</span> -hydrogen to produce hydrochloric acid. In all these -cases an external force is required to bring the atoms -within the range of mutual affinity: flame,—the electrical -spark,—actinism,—or the interposition of a third body, -is necessary in each case. There are other examples in -which no such influence is required. Potassium and -oxygen instantly unite: chlorine, iodine, and bromine -immediately, and with much violence, combine with the -metals to form chlorides, iodides, or bromides.</p> - -<p>With compound molecules the action is in many -cases equally active, and combination is readily effected, -as in the cases of the acids and the oxides of some -metals, which are all instances of the most common -chemical attraction.</p> - -<p>An elementary or simple molecule and molecules of a -compound and different constitution are brought -together, and a new compound results from an interchange -of their atoms, whilst an element is liberated. -These are essentially illustrations of analytical chemistry. -Sulphuretted hydrogen is mixed with chlorine; -the chlorine combines with the hydrogen, and sulphur -is set free. Potassium is put into water, and it combines -with the oxygen of the water, whilst the hydrogen -is liberated.</p> - -<p>Two compound molecules being brought together -may decompose each other, and form two new compounds -by an interchange of their elements.</p> - -<p>One element may be substituted for another under -certain circumstances. Gold may be replaced by -mercury; copper will take the place of silver; and iron -will occasion the separation of copper from its solutions, -the iron itself being dissolved to supply its place; -chlorine will substitute hydrogen in the carburetted -hydrogen gases; and many other examples might be -adduced.</p> - -<p>Chemical phenomena very frequently become of a -complex character; and one, two, or three of these cases<span class="pagenum"><a name="Page_280" id="Page_280"></a>[Pg 280]</span> -may be occurring at the same time in the decomposition -of one compound by another. Such are the general -features of chemical science. Many peculiarities and -remarkable phenomena connected with chemical investigations -will be named, as the examination of the elementary -composition of matter is proceeded with; but, -although the philosophy of chemical action is of the -highest interest, it must not be allowed to detain us -with its details, which are, indeed, more in accordance -with a treatise on the science than one which professes -to do no more than sketch out those prevailing and -striking features which, whilst they elucidate the great -truths of nature, are capable of being employed as suggestive -examples of the tendency of scientific investigation -to enlarge the boundaries of thought, and give a -greater elevation to the mind, leading us from the -merely mechanical process of analysis up to the great -synthetical operations, by which all that is found upon -the earth for its ornament, or our necessities, is created.</p> - -<p>Among the most remarkable phenomena within the -range of physical chemistry are those of <i>Catalysis</i>, or, as -it has also been called, the “<i>Action of presence</i>.”<a name="FNanchor_205_205" id="FNanchor_205_205"></a><a href="#Footnote_205_205" class="fnanchor">[205]</a> -There are a certain number of bodies known to possess<span class="pagenum"><a name="Page_281" id="Page_281"></a>[Pg 281]</span> -the power of resolving compounds into new forms, -without undergoing any change themselves. Kirchoff -discovered that the presence of an acid, at a certain -temperature, converted starch into sugar and gum, no -combination with the acid taking place. Thenard found -that manganese, platinum, gold, and silver, and, indeed, -almost any solid organic body, had the power of decomposing -the binoxide of hydrogen by their presence -merely, no action being detected on these bodies. -Edmund Davy found that powdered platinum, moistened -with alcohol, became red-hot, fired the spirit, and converted -it into vinegar, without undergoing, itself, any -chemical change. <span class="correction" title="In the original book: Dœbereiner">Döbereiner</span> next discovered that -spongy platinum fired a current of hydrogen gas -directed upon it, which, by combining with the oxygen -of the air, formed water. Dulong and Thenard traced -the same property, differing only in degree, through -iridium, osmium, palladium, gold, silver, and even glass. -Further investigation has extended the number of -instances; and it has even been found that a polished -plate of platinum has the power of condensing hydrogen -and oxygen so forcibly upon its surface, that these gases -are drawn into combination and form water, with a -development of heat sufficient to ignite the metal.</p> - -<p>This power, whatever it may be, is common in both -organic and inorganic nature, and on its important purposes -Berzelius has the following remarks:—</p> - -<p>“This power gives rise to numerous applications in -organic nature; thus, it is only around the eyes of the -potato that diastase exists: it is by means of catalytic -power that diastase, and that starch, which are insoluble, -are converted into sugar and into gum, which, being -soluble, form the sap that rises in the germs of the -potato. This evident example of the action of catalytic -power in an organic secretion, is not, probably, the only -one in the animal and vegetable kingdom, and it may -hereafter be discovered that it is by an action analogous<span class="pagenum"><a name="Page_282" id="Page_282"></a>[Pg 282]</span> -to that of catalytic power, that the secretion of such -different bodies is produced, all which are supplied by -the same matter, the sap in plants, and the blood in -animals.”<a name="FNanchor_206_206" id="FNanchor_206_206"></a><a href="#Footnote_206_206" class="fnanchor">[206]</a></p> - -<p>It is, without doubt, to this peculiar agency that we -must attribute the abnormal actions produced in the -blood of living animals by the addition of any gaseous -miasma or putrid matter, of which we have, in all probability, -a fearful example in the progress of <span class="correction" title="In the original book: Asatic">Asiatic</span> -cholera; therefore the study of its phenomena becomes -an important part of public hygiène.</p> - -<p>Physical research has proved to us that all bodies -have peculiar powers, by which they condense with -varying degrees of force gases and vapours upon their -surfaces; every body in nature may, indeed, be regarded -as forming its own peculiar atmosphere. To this power, -in all probability, does catalysis belong. Different -views have, however, prevailed on this subject, and Dr. -Lyon Playfair<a name="FNanchor_207_207" id="FNanchor_207_207"></a><a href="#Footnote_207_207" class="fnanchor">[207]</a> argues that the catalytic force is merely -a modified form of chemical affinity, exerted under -peculiar conditions.</p> - -<p>Whatever may be the power producing chemical -change, it acts in conformity with some fixed laws, and<span class="pagenum"><a name="Page_283" id="Page_283"></a>[Pg 283]</span> -in all its transmutations, an obedience to a most harmonious -system is apparent.</p> - -<p>It is curious to observe the remarkable character -of many of these natural transmutations of matter, but -we must content ourselves with a few examples only. -For instance:—</p> - -<p>Sugar, oxalic acid, and citric acid are very unlike -each other, yet they are composed of the same elements; -the first is used as a general condiment, the second is a -destructive poison, and the third a grateful and healthful -acid: sugar is readily converted into oxalic acid, and in -the process of ripening fruits nature herself converts -citric acid into sugar. Again, starch, sugar, and gum -would scarcely be regarded as alike, yet their only difference -is in the mode in which carbon, hydrogen, and -oxygen combine. They are composed of the same principles, -in the following proportions:—</p> - -<table summary="chemical analyses of starch, sugar and gum"> -<tr><th></th><th class="tdpad">Carbon.</th><th class="tdpad">Hydrogen.</th><th class="tdpad">Oxygen.</th></tr> -<tr><td>Starch</td><td class="tdc">12</td><td class="tdc">10</td><td class="tdc">10</td></tr> -<tr><td>Sugar</td><td class="tdc">12</td><td class="tdc">11</td><td class="tdc">11</td></tr> -<tr><td>Gum</td><td class="tdc">12</td><td class="tdc">11</td><td class="tdc">11</td></tr> -</table> - -<p>These <i>isomeric</i> groups certainly indicate some law -of affinity which science has not yet discovered. -Similar and even more remarkable instances might be -adduced of the same elements producing compounds -very unlike each other; but the above have been -selected from their well-known characters. Indeed, we -may state with truth that all the varieties of the vegetable -world—their woody fibre—their acid or alkaline -juices—the various exudations of plants—their flowers, -fruit, and seeds, and the numerous products which, by -art, they are made to yield for the uses of man, are, all -of them, compounds of these three elements, differing -only in the proportions in which they are combined -with nitrogen, or in some peculiar change of state in<span class="pagenum"><a name="Page_284" id="Page_284"></a>[Pg 284]</span> -one or other of the elementary principles. The chemist -is now enabled by simple processes, from the refuse of -manufactories to produce fruit essences which are -equal in flavour to the natural production; and from -benzoic acid, which is obtained in great abundance from -the houses in which cows are kept, the most delicate -essences are produced, which are given to the world as -the distillations of a thousand flowers. By the impulse -given to organic chemistry by Liebig, our knowledge of -the almost infinite variety of substances, in physical -character exceedingly dissimilar, which result from the -combination of oxygen, hydrogen, and carbon, in varying -proportions, has been largely increased. And the -science is now in that state which almost causes a regret -that any new organic compounds should be discovered, -until some industrious mind has undertaken the task of -reducing to a good general classification the immense -mass of valuable matter which has been accumulated, -but which, for all practical purposes, remains nearly useless -and unintelligible.</p> - -<p>These combinations, almost infinitely varied as they -are, and so readily produced and multiplied as to be -nearly at the will of the organic analyst, are not, any of -them, accidental: they are the result of certain laws, -and atom has united with atom in direct obedience to -principles which have been through all time in active -operation. They are unknown; the researches of -science have not yet developed them, and the philosopher -has not yet made his deductions. They are to be referred -to some secret fixed principles of action, to a force -which has impressed upon every atom of the universe its -distinguishing character. Chemistry makes us familiar -with a system of order. The researches of analysts -have proved that every body has a particular law of combination, -to which it is bound by a mathematical precision; -but it is not proportional combination alone we<span class="pagenum"><a name="Page_285" id="Page_285"></a>[Pg 285]</span> -have to consider. If <i>allotrophy</i> is evidenced in the -mineral world, it is certainly far more strikingly manifested -in the vegetable and animal kingdoms.</p> - -<p>There are some cases in which bodies appear to combine -without any limitation, as spirit of wine and water, -sulphuric acid and water; but these must be considered -as conditions of mixture rather than of chemical -combination.</p> - -<p>The composition of bodies is fixed and invariable, -and a compound substance, so long as it retains its -characteristic properties, must consist of the same -elements united in the same proportions. Thus, sulphuric -acid is invariably composed of 16 parts of sulphur -and 24 parts of oxygen. Chalk, whether formed by -nature or by the chemist, yields 43·71 parts of carbonic -acid, and 56·29 parts of lime. The rust which forms -upon the surface of iron by the action of the atmosphere, -is as invariable in its composition as if it had been -formed by the most delicate adjustment of weight by -the most accurate manipulator, being 28 parts of iron -and 12 parts of oxygen. This law is the basis of all -chemical inquiry, all analytical investigations depending -upon the knowledge it affords us, that we can only produce -certain undeviating compounds as the results of -our decompositions. We are not in a position to offer -any explanation which will account for these constant -quantities in combination. The forces of cohesion and -elasticity have been advanced in explanation, on the -strength of the fact that the solubility of a salt in water -is regulated by cohesion, and that of a gas by its -elasticity. Although it may appear that some cases of -chemical combination are due to these powers,—as, for -instance, when the union of oxalic acid or sulphuric -acid with lime produces an insoluble salt,—we cannot -thus explain the constant proportions in which the -metals, sulphur, oxygen, and similar bodies, unite. It -is quite certain there is a power or principle, which we<span class="pagenum"><a name="Page_286" id="Page_286"></a>[Pg 286]</span> -have not yet reached, upon which are dependent all the -phenomena which we now embrace under the term -chemical affinity.</p> - -<p>Another law teaches us that when compound bodies -combine in more than one proportion, every additional -union represents a multiple of the combining proportion -of the first. With the difficulty which arises from the -sub-multiple compounds we cannot deal:—further research -may render their laws less obscure. We have -seen that 8 parts of oxygen unite with 1 of hydrogen -and 14 of nitrogen. It also unites with 110 of silver, -96 of platinum, 40 of potassium, 36 of chlorine, and -200 parts of mercury, giving rise to—</p> - -<table summary="results of combining chemicals mentioned above"> -<tr><td>Water</td><td class="tdr tdpad">9</td></tr> -<tr><td>Nitrous oxide</td><td class="tdr tdpad">22</td></tr> -<tr><td>Oxide of silver</td><td class="tdr tdpad">118</td></tr> -<tr><td>Oxide of platinum</td><td class="tdr tdpad">104</td></tr> -<tr><td>Potash</td><td class="tdr tdpad">48</td></tr> -<tr><td>Oxide of chlorine</td><td class="tdr tdpad">44</td></tr> -<tr><td>Oxide of mercury</td><td class="tdr tdpad">208</td></tr> -</table> - -<p>In these proportions, or in multiples of them, and in -no others, will these bodies unite with the acids or other -compounds. It will, of course, be understood that any -other numbers may be adopted, provided they stand in -the same relation to each other.<a name="FNanchor_208_208" id="FNanchor_208_208"></a><a href="#Footnote_208_208" class="fnanchor">[208]</a></p> - -<p>From the discovery of these harmonious arrangements -was deduced the beautiful atomic theory to which allusion -has been already made. Indeed, there does not -appear to be any other way of explaining these phenomena -than by the hypothesis that the ultimate atoms -of bodies have <i>relatively</i> the weights which we arbitrarily -assign to them, as their combining quantities. -These views are further confirmed by the fact, that -gaseous bodies unite together by volume in very simple -definite proportions:—100 measures of hydrogen and<span class="pagenum"><a name="Page_287" id="Page_287"></a>[Pg 287]</span> -200 measures of oxygen form water; 100 measures of -oxygen and 100 measures of vapour of sulphur form -sulphurous acid gas. Ammoniacal gas consists of 300 -volumes of hydrogen and 100 volumes of nitrogen, condensed -by combination into 200 volumes; consequently, -we are enabled most readily to calculate the specific -gravity of ammoniacal gas. The specific gravity of -nitrogen is 0·9722, that of hydrogen 0·0694. Now, -three volumes of hydrogen are equal to 0·2082: this -added to 0·9722 is equal to 1·1804, which is exactly the -specific gravity obtained by experiment.</p> - -<p>There is no doubt, from the generality with which -this law of volumes prevails, that it would be found to -extend through all substances, provided they could be -rendered gaseous; in other words, there is abundant -proof to convince us that throughout nature the process -of combination, in the most simple ratio of volumes, is -in operation to produce all the forms of matter known -to us.</p> - -<p>It has been shown, by the investigations of Dr. Dalton, -in 1840, that salts, containing water of crystallization, -dissolve in water without increasing the bulk of -the fluid more than is due to the liquefaction of the -water which these salts contain; while Joule and Playfair -have shown that the anhydrous salts take up no -space in solution. From this we are naturally led to -conclude that the volume occupied by a salt in the solid -state has a certain relation to the volume of the same -salt when in solution, and has also a fixed relation to -the volume occupied by any other salt. The law appears -to be:—the atomic volume of any salt whatever (anhydrous -or hydrated) is a multiple of 11, or of a number -near 11, or a multiple of 9·8 (the atomic volume of ice), -or the sum of a multiple of 11 or 9·8. Marignac, who -has also paid much attention to the subject, does not -think these numbers absolutely correct, but approxi<span class="pagenum"><a name="Page_288" id="Page_288"></a>[Pg 288]</span>mately -so.<a name="FNanchor_209_209" id="FNanchor_209_209"></a><a href="#Footnote_209_209" class="fnanchor">[209]</a> It would be a beautiful exemplification of -the simplicity of Nature’s operations, if it should be -clearly proved that the atomic volume of solid water -(ice) regulated the combining proportions by volume of -all other bodies,—that it was the standard by which -chemical combination and ordinary solution were -determined.</p> - -<p>In addition to the laws already indicated, there appear -to be some others of which, as yet, we have a less satisfactory -knowledge, and, as a remarkable case, we may -adduce the phenomena of <i>substitution</i>, or that power -which an elementary body, under certain conditions, -possesses, of turning out one of the elements of a compound, -and of taking its place.<a name="FNanchor_210_210" id="FNanchor_210_210"></a><a href="#Footnote_210_210" class="fnanchor">[210]</a> Thus, the hydrogen<span class="pagenum"><a name="Page_289" id="Page_289"></a>[Pg 289]</span> -of a compound radical, as carburetted hydrogen, may be -replaced by chlorine, equivalent for equivalent, and -form a chloride of carbon, which being constructed on -the same type as the original, will have the same general -laws of combination.</p> - -<p>Under the influence of these laws, all the combinations -which we discover in nature take place. The metals, -and oxygen, and sulphur, and phosphorus unite. The -elements of the organic type, entering into the closest -relations, give rise to every form of vegetable life. The -acids, the gums, the resins, and the sugar which plants -produce; and those yet more complicated animal substances, -bone, muscle, blood, and bile; albumen, casein, -milk, with those compounds which, under the influence -of vital power, resolve themselves into substances which -are essential to the existence, health, and beauty of the -animal fabric, are all dependent on these laws. But -these metamorphoses must be further considered in our -examination of the more striking cases of chemical -action. The changes which result from organic combination -are so remarkable, and withal they show how -completely the whole of the material world is in subjection -to chemical force, and every variety of form the -result of mysterious combination, that some particular -reference to these metamorphoses is demanded.</p> - -<p>In nearly all cases of decided chemical action, all -trace of the characters of the combining bodies disappear. -We say decided chemical action, because, -although sulphuric acid and water combine, and salts -dissolve in water, we may always recognize their -presence, and therefore these and similar cases cannot -be regarded as strict examples of the phenomena under -consideration.</p> - -<p>Hydrogen and oxygen, in combining, lose their gaseous -forms, and are condensed into a liquid—water. Sulphuric -acid is intensely sour and corrosive; potash is -highly caustic; but united they form a salt which is<span class="pagenum"><a name="Page_290" id="Page_290"></a>[Pg 290]</span> -neither: they appear to have destroyed the distinguishing -characters of each other. Combined bodies frequently -occupy less space than they did previously to combination, -of which numerous particular instances might be adduced. -Gases in many cases undergo a remarkable condensation -when chemically combined. In slaking lime, the water -becomes solid in the molecules of the hydrate of lime -formed, and the intense heat produced arises from the -liberation of that caloric which had been employed to -keep the water liquid. When a solid passes into the -liquid state, cold is produced by the abstraction from -surrounding objects of the heat required to effect fluidity. -An alteration of temperature occurs whenever chemical -change takes place, as we have already shown, with a -few trivial and uncertain exceptions. The disturbance -caused by the exercise of the force of affinity frequently -leads to the development of several physical powers.</p> - -<p>Changes of colour commonly arise; indeed, there -does not appear to be any relation between the colour of -a compound and that of its elements. Iodine is of a -deep iron-grey colour; its vapour is violet; yet it forms -beautifully white salts with the alkalies, a splendid red -salt with mercury, and a yellow one with lead. The -salts of iron vary from white and yellow to green and -dark brown. Those of copper, a red metal, are of a -beautiful blue and green colour, and the anhydrous -sulphate is white.</p> - -<p>Isomorphism, which appears in a very remarkable -manner among the organic compounds, has, under the -head of crystallization, already had our attention. There -is also a class of bodies which are said to be <i>isomeric</i>; -that is, to have the same composition, although different -in their physical characters. But the idea that bodies -exist, which, although of a decidedly different external -character, are of exactly the same chemical composition -and physical condition, is not tenable; and in nearly all -the examples which have been carefully examined, a<span class="pagenum"><a name="Page_291" id="Page_291"></a>[Pg 291]</span> -difference in the aggregate number of atoms, or in the -mode in which those atoms have respectively arranged -themselves, or that peculiar physical difference designated -by the term <i>allotropy</i>, has been detected.</p> - -<p>Oil of turpentine and oil of lemons have the same -composition, each being composed of five equivalents of -carbon and four of hydrogen. These substances form, -from the striking difference perceptible in their external -characters, a good example of isomerism.</p> - -<p>The laws of organic chemistry are not, however, the -same as those applying to inorganic combinations. Organic -chemistry is well defined by Liebig, as the chemistry -of compound radicals; and under the influence -of vitality, nature produces compounds which have all -the properties of simple elements.<a name="FNanchor_211_211" id="FNanchor_211_211"></a><a href="#Footnote_211_211" class="fnanchor">[211]</a></p> - -<p>When we reflect upon the conditions which prevail -throughout nature, with a few of which only has science -made us acquainted, we cannot fail to be struck with -the various phases of being which are presented to our -observation, and the harmonious system upon which -they all appear to depend.</p> - -<p>When we discover that bodies are formed of certain -determinate atoms, which unite one with another, according -to an arithmetical system, to form molecules, -which, combining with molecules, observe a similar law, -we see at once that all the harmonies of chemical combination—the -definite proportions, laws of volume, and -the like—are but the necessary consequences of these -simple and guiding first principles. In the pursuit of -truth, investigators must discover still further arrangements, -which, from their perfection, may be compared -to the melodious interblending of sweet sounds, and<span class="pagenum"><a name="Page_292" id="Page_292"></a>[Pg 292]</span> -many of the apparently indeterminate combinations will, -beyond a doubt, be shown to be as definite as any others. -But we cannot reflect upon the fact that these atoms -and these molecules are guided in their combinations by -impulses, which we can only explain by reference to -human passions, as the term <i>elective affinity</i> implies, -without feeling that an impenetrable mystery of a grand -and startling character in its manifestations surrounds -each grain of dust which is hurried along upon the -wind.</p> - -<p>We now, habitually, speak of attraction and repulsion—of -the affinity and non-affinity of bodies. We are -disposed, from the discovery of the attractive and repelling -poles of electrified substances, to regard these -powers in all cases as depending upon some electrical -state, and we write learnedly upon the laws of these -forces. After all, it would be more honest to admit, -that we know no more of the secret impulses which -regulate the combinations of matter, than did those -who satisfied themselves by referring all phenomena of -these kinds to sympathies and antipathies: terms which -have a poetic meaning, conveying to the mind, with -considerable distinctness, the fact, and giving the idea -of a feeling—a passion—involving and directing inanimate -matter, similar to that which stirs the human -heart, and certainly calculated to convey the impression -that there is working within all things a living principle, -and pointing, indeed, to “the soul of the world.” The -animated marble of ancient story is far less wonderful -than the fact, proved by investigation, that every atom -of matter is penetrated by a principle which directs its -movements and orders its positions, and involved by an -influence which extends, without limits, to all other -atoms, and which determines their union, or otherwise.</p> - -<p>We have gravitation, drawing all matter to a common -centre, and acting from all bodies throughout the wide<span class="pagenum"><a name="Page_293" id="Page_293"></a>[Pg 293]</span> -regions of unmeasured space upon all. We have cohesion, -holding the particles of matter enchained, operating -only at distances too minute for the mathematician -to measure; and we have chemical attraction, different -from either of these, working no less mysteriously within -absolutely insensible distances, and, by the exercise of -its occult power, giving determinate and fixed forms to -every kind of material creation.</p> - -<p>The spiritual beings, which the poet of untutored -nature gave to the forest, to the valley, and to the -mountain, to the lake, to the river, and to the ocean, -working within their secret offices, and moulding for -man the beautiful or the sublime, are but the weak -creations of a finite mind, although they have for us a -charm which all men unconsciously obey, even when -they refuse to confess it. They are like the result of -the labours of the statuary, who, in his high dreams of -love and sublimated beauty, creates from the marble -block a figure of the most exquisite moulding which -mimics life. It charms us for a season; we gaze and -gaze again, and its first charms vanish; it is ever and -ever still the same dead heap of chiselled stone. It has not -the power of presenting to our wearying eyes the change -which life alone enables matter to give; and we admit -the excellence of the artist, but we cease to feel at his -work. The creations of poetry are pleasing, but they -never affect the mind in the way in which the poetic -realities of nature do. The sylph moistening a lily is -a sweet dream; but the thoughts which rise when first -we learn that its broad and beautiful dark-green leaves, -and its pure and delicate flower, are the results of the -alchemy which changes gross particles of matter into -symmetric forms,—of a power which is unceasingly at -work under the guidance of light, heat, and electrical -force,—are, after our incredulity has passed away—for -it is too wonderful for the untutored to believe at once—of -an exalting character.</p> - -<p><span class="pagenum"><a name="Page_294" id="Page_294"></a>[Pg 294]</span></p> - -<p>The flower has grown under the impulse of principles -which have traversed to it on the solar beam, and mingled -with its substance. A stone is merely a stone to -most men. But within the interstices of the stone, and -involving it like an atmosphere, are great and mighty -influences, powers which are fearful in their grander -operations, and wonderful in their gentler developments. -The stone and the flower hold, locked up in their recesses, -the three great known forces—light, heat, and -electricity: and, in all probability, others of a more -exalted nature still, to which these powers are but subordinate -agents. Such are the facts of science, which, -indeed, are the true “sermons in stones,” and the most -musical of “tongues in trees.” How weak are the creations -of romance, when viewed beside the discoveries of -science! One affords matter for meditation, and gives -rise to thoughts of a most ennobling character; the other -excites for a moment, and leaves the mind vacant or diseased. -The former, like the atmosphere, furnishes a -constant supply of the most healthful matter; the latter -gives an unnatural stimulus, which compels a renewal -of the same kind of excitement, to maintain the continuation -of its pleasurable sensations.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_200_200" id="Footnote_200_200"></a><a href="#FNanchor_200_200"><span class="label">[200]</span></a> All the phenomena connected with volcanic action, and the -theories connected therewith, will be found in Dr. Daubeny’s -work, <i>A description of active and extinct Volcanoes, of Earthquakes, -and of Thermal Springs</i>. 1848.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_201_201" id="Footnote_201_201"></a><a href="#FNanchor_201_201"><span class="label">[201]</span></a> Graham’s <i>Elements of Chemistry</i>. New Edition.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_202_202" id="Footnote_202_202"></a><a href="#FNanchor_202_202"><span class="label">[202]</span></a> Graham’s <i>Elements of Chemistry</i>; and Brande’s <i>Manual</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_203_203" id="Footnote_203_203"></a><a href="#FNanchor_203_203"><span class="label">[203]</span></a> Of these <i>tables of attraction</i> the following may be taken as a -specimen:— -</p> - -<ul class="no"> -<li><span class="smcap">Sulphuric Acid.</span></li> -<li class="sub1">Baryta.</li> -<li class="sub1">Strontia.</li> -<li class="sub1">Potassa.</li> -<li class="sub1">Soda.</li> -<li class="sub1">Lime.</li> -<li class="sub1">Magnesia.</li> -<li class="sub1">Ammonia.</li> -</ul> - -<p> -It thus appears that baryta separates sulphuric acid from its -compounds with all inferior substances, and that ammonia is -separated from the acid by all that are above it.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_204_204" id="Footnote_204_204"></a><a href="#FNanchor_204_204"><span class="label">[204]</span></a> Berthollet: <i>Essai de Statique Chimique</i>, 1803. Sir Humphry -Davy, in his <i>Elements of Chemical Philosophy</i>, has given an excellent -review of the views of Berthollet.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_205_205" id="Footnote_205_205"></a><a href="#FNanchor_205_205"><span class="label">[205]</span></a> <i>On certain combinations of a new acid, formed of Azote, Sulphur, -and Oxygen</i>; by J. Pelouze. Translated from Annales de Chimie, vol. -xvi., for Scientific Memoirs, vol. i. p. 470. <i>Some ideas of a new -force acting in the combinations of Organic Compounds</i>, by Berzelius: -Annales de Chimie, vol. lxi. The conclusion come to by -this eminent chemist is expressed in the following translation:—“This -new power, hitherto unknown, is common both in organic -and inorganic nature. I do not believe that it is a power which -is entirely independent of the electro-chemical affinities of the -substance. I believe, on the contrary, that it is merely a new -form of it; but so long as we do not see their connection and -mutual dependence, it will be more convenient to describe it by a -separate name. I shall, therefore, call it <i>catalytic power</i>: I shall -also call <i>catalysis</i>, the decomposition of bodies by this force—in -the same way as the decomposition of bodies by chemical affinity -is termed analysis.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_206_206" id="Footnote_206_206"></a><a href="#FNanchor_206_206"><span class="label">[206]</span></a> Berzelius: <i>Annales de Chimie</i>, vol. lxi.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_207_207" id="Footnote_207_207"></a><a href="#FNanchor_207_207"><span class="label">[207]</span></a> <i>On Transformations produced by Catalytic Bodies</i>: by Lyon -Playfair, Esq.; Phil. Mag., vol. xxxi. p. 191, 1847.—“Facts have -been brought forward to show that there is at least as much probability -in the view that the catalytic force is merely a modified -form of chemical affinity exerted under peculiar conditions, as -there is in ascribing it to an unknown power, or to the communication -of an intestine motion to the atoms of a complex molecule. -Numerous cases have been cited, in which the action -results when the assisting or catalytic body is not in a state of -change; and attempts have been made to prove, by new experiments, -that the catalytic power exercises its peculiar power by -acting in the same direction as the body decomposing, or entering -into union, but under conditions in which its own affinity cannot -always be gratified.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_208_208" id="Footnote_208_208"></a><a href="#FNanchor_208_208"><span class="label">[208]</span></a> Consult Graham’s Chemistry, <i>On Combining Proportions</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_209_209" id="Footnote_209_209"></a><a href="#FNanchor_209_209"><span class="label">[209]</span></a> <i>Memoir on Atomic Volume and Specific Gravity.</i> Messrs. -Lyon Playfair and Joule.—Philosophical Magazine, vol. xxvii. p. -453, or Transactions of Chemical Society of London. <i>Observations</i> -on the above, by Professor de Marignac.—Bibliothèque Universelle, -Feb. 1846. <i>On the Relation of the Volumes of bodies in the -solid state, to their equivalents, or atomic weights</i>: by Professor -Otto. <i>Studies on the connection between the atomic weights, -crystalline form, and density of bodies</i>: by M. Filhol. Translated -for the Cavendish Society, and published in their Chemical -Reports and Memoirs.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_210_210" id="Footnote_210_210"></a><a href="#FNanchor_210_210"><span class="label">[210]</span></a> <i>Comptes Rendus de l’Académie des Sciences</i>, 1840, No. -5. A good translation of Dumas’s Memoir appeared in the Philosophical -Magazine, from which I extract the following familiar exposition -of the laws of substitution:—“Let me make a comparison -drawn from a familiar order of ideas. Let us put ourselves in the -place of a man overlooking a game at chess without the slightest -knowledge of the game. He would soon remark that the pieces -must be used according to positive rules. In chemistry, the -equivalents are our pieces, and the law of substitutions one of the -rules which preside over their moves. And as in the oblique -move of the pawns one pawn must be substituted for another, so -in the phenomena of substitution one element must take the place -of another. But this does not hinder the pawn from advancing -without taking anything, as the law of substitution does not hinder -an element from acting on a body without displacing or taking -the place of any other element that it may contain.”—<i>Memoir on -the Law of Substitutions, and Theory of Chemical Types.</i></p></div> - -<div class="footnote"> - -<p><a name="Footnote_211_211" id="Footnote_211_211"></a><a href="#FNanchor_211_211"><span class="label">[211]</span></a> Liebig’s <i>Chemistry in its application to Agriculture and -Physiology</i>: translated by Lyon Playfair, Ph. D. <i>Animal -Chemistry, or Chemistry in its application to Physiology and -Pathology</i>: by Justus Liebig; translated by Wm. Gregory.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_295" id="Page_295"></a>[Pg 295]</span></p> - - - -<h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII.</h2> - -<p class="center">CHEMICAL PHENOMENA.</p> - - -<p class="chap-head">Water—Its Constituents—Oxygen—Hydrogen—Peroxide of Hydrogen—Physical -Property of Water—Ice—Sea Water—Chlorine—Muriatic -Acid—Iodine—Bromine—Compounds of -Hydrogen with Carbon—Combustion—Flame—Safety Lamp—Respiration—Animal -Heat—The Atmosphere—Carbonic -Acid—Influence of Plants on the Air—Chemical Phenomena -of Vegetation—Compounds of Nitrogen—Mineral Kingdom, -&c. &c.</p> - - -<p class="p2">Without attempting anything which shall approach -even to the character of a sketch of chemical science, -we may be allowed, in our search after exalting truths, -to select such examples of the results of combination as -may serve to elucidate any of the facts connected with -natural phenomena. In doing this, by associating our -examination with well-known natural objects or conditions, -the interpretation afforded by analysis will be -more evident, and the operation of the creative forces -rendered more striking and familiar, particularly if at -the same time we examine such physical conditions as -are allied in action, and are sufficiently explanatory of -important features.</p> - -<p>A large portion of this planet is covered by the waters -of the ocean, of lakes and rivers. Water forms the best -means of communication between remote parts of the -earth. It is in every respect of the utmost importance -to the animal and vegetable kingdom; and, indeed, it -is indispensable in all the great phenomena of the inorganic -world. The peculiarities of saltness or freshness<span class="pagenum"><a name="Page_296" id="Page_296"></a>[Pg 296]</span> -in water are dependent upon its solvent powers. The -waters of the ocean are saline from holding dissolved -various saline compounds, which are received in part -from, and imparted also to, the marine plants. Perfectly -pure water is without taste: even the pleasant character -of freshly-drawn spring-water is due to the admixture -of atmospheric air and carbonic acid. The manner in -which water absorbs air is evidently due to a peculiar -physical attractive force, the value of which we do not -at present clearly perceive or correctly estimate. It is -chemically composed of two volumes of hydrogen gas—the -lightest body known, and at the same time a highly -inflammable one—united with one volume of oxygen, -which excites combustion, and continues that action,—producing -heat and light,—with great energy. By weight, -one part of hydrogen is united with eight of oxygen, or -in 100 parts of water we find 88·9 oxygen, and 11·1 of -hydrogen gas. That two such bodies should unite to -furnish the most refreshing beverage, and indeed the -only natural drink for man and animals, is one of the -extraordinary facts of science. Hydrogen will not support -life—we cannot breathe it and live; and oxygen -would over-stimulate the organic system, and, producing -a kind of combustion, give rise to fever in the animal -frame; but, united, they form that drink, for a drop of -which the fevered monarch would yield his diadem, and -the deprivation of which is one of the most horrid calamities -that can be inflicted upon any living thing. Water -appears as the antagonist principle to fire, and the -ravages of the latter are quenched by the assuaging -powers of the former; yet a mixture of oxygen and -hydrogen gases, in the exact proportion in which they -form water, explodes with the utmost violence on the -contact of flame, and, when judiciously arranged, produces -the most intense degree of heat known;—such is the -remarkable difference between a merely mechanical -mixture and a chemical combination. Beyond this, we<span class="pagenum"><a name="Page_297" id="Page_297"></a>[Pg 297]</span> -have already noticed the remarkable fact that water -deprived of air is explosive at a comparatively low temperature, -less than 300°; gunpowder requiring a temperature -of nearly 1000° F.</p> - -<p>If we place in a globe, oxygen and hydrogen gases, -in the exact proportions in which they combine to form -water, they remain without change of state. They -appear to mix intimately; and, notwithstanding the -difference in the specific gravities of the two gases, the -lighter one is diffused through the heavier in a curious -manner, agreeably to a law which has an important -bearing on the conditions of atmospheric phenomena.<a name="FNanchor_212_212" id="FNanchor_212_212"></a><a href="#Footnote_212_212" class="fnanchor">[212]</a> -The moment, however, that an incandescent body, or<span class="pagenum"><a name="Page_298" id="Page_298"></a>[Pg 298]</span> -the spark from an electric machine, is brought into -contact with the mixed gases, they ignite, explode violently, -and combine to form water. The discovery of -the composition of water was thus synthetically made -by Cavendish—its constitution having been previously -theoretically announced by Watt.<a name="FNanchor_213_213" id="FNanchor_213_213"></a><a href="#Footnote_213_213" class="fnanchor">[213]</a></p> - -<p>If, instead of combining oxygen and hydrogen in the -proportions in which they form water, we compel the -hydrogen to combine with an additional equivalent of -oxygen, we have a compound possessing many properties -strikingly different from water. This—peroxide of hydrogen, -as it is called—is a colourless liquid, less -volatile than water, having a metallic taste. It is -decomposed at a low temperature, and, at the boiling -point, the oxygen escapes from it with such violence, -that something like an explosion ensues. All metals, -except iron, tin, antimony, and tellurium, have a tendency -to decompose this compound, and separate it into -oxygen and water. Some metals are oxidized during -the decomposition, but gold, silver, platinum, and a few -others, still retain their metallic state. If either silver, -lead, mercury, gold, platinum, manganese, or cobalt, in<span class="pagenum"><a name="Page_299" id="Page_299"></a>[Pg 299]</span> -their highest states of oxidation, are put into a tube, -containing this peroxide of hydrogen, its oxygen is -liberated with the rapidity of an explosion, and so much -heat is excited that the tube becomes red hot. These -phenomena, to which we have already referred in -noticing catalysis, are by no means satisfactorily explained, -and the peculiar bleaching property possessed -by the peroxide of hydrogen sufficiently distinguishes -it from water. There are few combinations which show -more strikingly than this the difference arising from -the chemical union of an additional atom of one element. -Similar instances are numerous in the range of chemical -science; but scarcely any two exhibit such dissimilar -properties. During the ordinary processes of combustion, -it has been long known that water is formed by -the combination of the hydrogen of the burning body -with the oxygen of the air. The recent researches of -Schönbein have shown that a peculiar body, which has -been regarded as a peroxide of hydrogen, to which he -has given the name of <span class="smcap">Ozone</span>, is produced at the same -time, and that it is developed in a great many ways, -particularly during electrical changes of the atmosphere. -Thus we obtain evidence that this remarkable compound, -which was considered as a chemical curiosity -merely, is diffused very generally through nature, and -produced under a great variety of circumstances. -During the excitation of an electrical machine, or the -passage of a galvanic current through water by the -oxidation of phosphorus, and probably in many similar -processes—in particular those of combustion, and we -may therefore infer also of respiration—this body is -formed. From observations which have been made, it -would appear that, during the night, when the activity -of plants is not excited by light, they act upon the -atmosphere in such a way as to produce this ozone; and -its presence is said to be indicated by its peculiar odour -during the early hours of morning. We are not yet<span class="pagenum"><a name="Page_300" id="Page_300"></a>[Pg 300]</span> -acquainted with this body sufficiently to speculate on its -uses in nature: without doubt, they are important, -perhaps second to those of water only. It is probable, -as we have already had occasion to remark, that ozone -may be the active agent in removing from the atmosphere -those organic poisons to which many forms of -pestilence are traceable; and it is a curious fact, that a -low electrical intensity, and a consequent deficiency of -atmospheric ozone, marks the prevalence of cholera, and -an excess distinguishes the reign of influenza.<a name="FNanchor_214_214" id="FNanchor_214_214"></a><a href="#Footnote_214_214" class="fnanchor">[214]</a></p> - -<p>Some interesting researches appear to show the probability -that ozone is simply oxygen in a state of high -activity. It has been found, indeed, that perfectly dry -oxygen, which will not bleach vegetable colours in the -dark, acquires, by exposure to sunshine, the power of -destroying them. Becquerel has proved that this -ozonous state may be produced in dry oxygen by passing -a succession of electric sparks through it. Fremy -passed the electric sparks on the outside of a tube which -contained perfectly dry oxygen, and it was found to -have acquired the properties of ozone. In this case, and -probably in the experiments of Becquerel, the light of -the spark, rather than the electricity, appears to have -been the active agent in producing this change. Schönbein -himself does not appear disposed to regard ozone -as being either <span class="correction" title="In the original book: per-oxide">peroxide</span> of hydrogen, or an allotropic -oxygen. He leans to his first view of its being an -entirely new chemical element. The energy of this -ozone is so great, that it has been found to destroy -almost instantaneously the Indian-rubber union joints -of the apparatus in which it is formed.<a name="FNanchor_215_215" id="FNanchor_215_215"></a><a href="#Footnote_215_215" class="fnanchor">[215]</a></p> -<p><span class="pagenum"><a name="Page_301" id="Page_301"></a>[Pg 301]</span></p> -<p>Water, from the consideration of which a digression -has been indulged in, to consider the curious character -of one of its elements,—water is one of the most -powerful chemical agents, having a most extensive -range of affinities, entering directly into the composition -of a great many crystallizable bodies and organic compounds. -In those cases where it is not combined as -water, its elements often exist in the proportions in -which water is formed. Gum, starch, and sugar, only -differ from each other in the proportions in which the -elements of water are combined with the carbon.</p> - -<p>In saline combinations, and also in many organic -forms, we must regard the water as condensed to the -solid form; that is, to exist as ice. We well know that, -by the abstraction of heat, this condition is produced; -but, in chemical combinations, this change must be the -result of the mechanical force exerted by the power of -the agency directing affinity.</p> - -<p>In the case of water passing from a liquid to a solid -state, we have a most beautiful exemplification of the -perfection of natural operations. Water conducts heat -downwards but very slowly; a mass of ice will remain -undissolved but a few inches under water, on the surface -of which, ether, or any other inflammable body, is -burning. If ice (solid water) swam beneath the surface, -the summer sun would scarcely have power to thaw it; -and thus our lakes and seas would be gradually converted -into solid masses at our ordinary winter temperatures.</p> - -<p>All similar bodies contract equally during the process -of cooling, from the highest to the lowest points to -which the experiments have been carried. It has been -thought that if this applied to water, the result would be -the sudden consolidation of the whole mass. A modification -of the law has been supposed to take place to -suit the peculiar circumstances of water. Nature -never modifies a law for a particular purpose; we must,<span class="pagenum"><a name="Page_302" id="Page_302"></a>[Pg 302]</span> -therefore, seek to explain the action of the formation -of ice, as we know it, by some more rational view.</p> - -<p>Water expands by heat, and contracts by cold; consequently, -the coldest portions of this body occupy the -lower portions of the fluid; but it must be remembered -that these parts are warmed by the earth. Ross, however, -states that at the depth of 1,000 fathoms the sea -has a constant temperature of 39°. Water is said to be -at its point of greatest density at 40° of Fahrenheit’s -thermometer; in cooling further, this fluid appears to -expand, in the same way as if heated: and, consequently, -water colder than this point, instead of being heavier, is -lighter, and floats on the surface of the warmer fluid. -It does not seem that any modification of the law is required -to account for this phenomenon. Water cooled -to 40° still retains its peculiar corpuscular arrangement; -but immediately it passes below that temperature, it -begins to dispose itself in such a manner that visible -crystals may form the moment it reaches 32°. Now, if -we conceive the particles of water, at 39°, to arrange -themselves in the manner necessary for the assumption -of the solid form, by the particular grouping of molecules -in an angular instead of a spheroidal shape, it will -be clear, from what we know of the arrangement of -crystals of water—ice—that they must occupy a larger -space than when the particles are disposed, side by -side, in minute spheres. Even the escape of air from -the water in which it is dissolved is sufficient to give an -apparent lightness to the colder water. This expansion -still goes on increasing, from the same cause, during the -formation of ice, so that the specific gravity of a mass of -frozen water is less than that of water at any temperature -below 40°. It must not be forgotten that ice -always contains a large quantity of air, by which it is -rendered buoyant.</p> - -<p>Water, at rest, may be cooled many degrees below -the freezing point without becoming solid. This is<span class="pagenum"><a name="Page_303" id="Page_303"></a>[Pg 303]</span> -easily effected in a thin glass flask; but the moment it -is agitated, it becomes a firm mass. Here we have the -indication of another cause aiding in producing crystals -of ice on the surface of water, under the influence of the -disturbance produced by the wind, which does not extend -to any depth.</p> - -<p>As oxygen and hydrogen gases enter largely into -other chemical compounds besides water, it is important -to consider some of the forms of matter into the -composition of which these elements enter. To examine -this thoroughly, a complete essay on chemical philosophy -would be necessary; we must, therefore, be content -with referring to a few of the more remarkable -instances.</p> - -<p>The waters of the ocean are salt: this arises from -their holding, in solution chloride of sodium (<i>muriate -of soda</i>—<i>common culinary salt</i>) and other saline bodies. -Water being present, this becomes muriate of soda,—that -is, a compound of muriatic acid and soda: muriatic -acid is hydrogen, combined with a most remarkable -gaseous body, called, from its yellow colour, <i>chlorine</i>; -and soda, oxygen in union with the metal sodium,—therefore, -when anhydrous, culinary salt is truly a -chloride of sodium. Chlorine in some respects resembles -oxygen; it attacks metallic bodies with great -energy; and, in many cases, produces the most vivid -incandescence, during the process of combination. -It is a powerful bleaching agent, is destructive to -animal life, and rapidly changes all organic tissues. -There are two other bodies in many respects so similar -to chlorine, although one is at the ordinary temperatures -solid, and the other fluid, and which are -also discovered in sea-water, or in the plants growing -in it, that it is difficult to consider them otherwise -than as different forms of the same principle. -These are iodine and bromine, and they both unite -with hydrogen to form acids. The part which<span class="pagenum"><a name="Page_304" id="Page_304"></a>[Pg 304]</span> -chlorine performs in nature is a great and important -one. Combined in muriate of soda, we may -trace it in large quantities through the three kingdoms -of nature, and the universal employment of salt as a condiment -indicates the importance to the animal economy -of the elements composing it. Iodine has been traced -through the greater number of marine plants, existing, -apparently as an essential element of their constitution; -in some land plants it has also been found, particularly -in the Armeria maritima, when this plant grows near -the sea:<a name="FNanchor_216_216" id="FNanchor_216_216"></a><a href="#Footnote_216_216" class="fnanchor">[216]</a> it has been detected in some mineral springs, -and in small quantities in the mineral kingdom<a name="FNanchor_217_217" id="FNanchor_217_217"></a><a href="#Footnote_217_217" class="fnanchor">[217]</a> combined -as iodide of silver, and in the aluminous slate -of Latorp in Sweden.<a name="FNanchor_218_218" id="FNanchor_218_218"></a><a href="#Footnote_218_218" class="fnanchor">[218]</a> Bromine is found in sea-water, -although in extremely minute quantities, in a few -saline springs, and in combination with silver; but we -have no evidence to show that its uses are important in -nature.</p> - -<p>Hydrogen, again, unites with carbon in various proportions, -producing the most dissimilar compounds. -The air evolved from stagnant water, and the fire-damp -of the coal mine, are both carburetted hydrogen; and -the gas which we <span class="correction" title="In the original book: emply">employ</span> so advantageously for illumination, -is the same, holding an additional quantity of -carbon in suspension. Naphtha, and a long list of -organic bodies, are composed of these two chemical -elements.</p> - -<p>These combinations lead us, naturally, to the consideration -of the great chemical phenomena of combustion, -which involve, indeed, the influences of all the -physical powers. By the application of heat, we pro<span class="pagenum"><a name="Page_305" id="Page_305"></a>[Pg 305]</span>duce -an intense action in a body said to be combustible; -it burns,—a chemical action of the most energetic -character is in progress, the elements which constitute -the combustible body are decomposed, they unite with -some other elementary principles, and new compounds -are formed. A body burns—it is entirely dissipated, or -it leaves a very small quantity of ashes behind unconsumed, -but nothing is lost. Its volatile parts have -entered into new arrangements, the form of the body is -changed, but its constituents are still playing an -important purpose in creation.</p> - -<p>The ancient notion that fire was an empyreal element, -and the Stahlian hypothesis of a phlogistic principle on -which all the effects of combustion depended,<a name="FNanchor_219_219" id="FNanchor_219_219"></a><a href="#Footnote_219_219" class="fnanchor">[219]</a> have -both given way to the philosophy of the unfortunate -Lavoisier—which has, indeed, been modified in our own -times—who showed that combustion is but the development -of heat and light under the influence of chemical -combination.</p> - -<p>Combustion was, at one period, thought to be always -due to the combination of oxygen with the body burning, -but research has shown that vivid combustion may -be produced where there is no oxygen. The oxidizable -metals burn most energetically in chlorine, and some of -them in the vapour of iodine and bromine, and many -other unions take place with manifestations of incandescence. -Supporters of combustion were, until lately, -regarded as bodies distinct from those undergoing combustion. -For example, hydrogen was regarded as a<span class="pagenum"><a name="Page_306" id="Page_306"></a>[Pg 306]</span> -combustible body, and oxygen as a supporter of combustion. -Such an arrangement is a most illogical one, -since we may <i>burn</i> oxygen in an atmosphere of hydrogen, -in the same manner as we burn hydrogen in -one of oxygen; and so, in all the other cases, the supporter -of combustion may be burnt in an atmosphere -formed of the, so called, combustible. The ordinary -phenomena of combustion are, however, due to the -combination of oxygen with the body burning; therefore -every instance of oxidization may be regarded as a condition -of combustion, the difference being only one of -degree.</p> - -<p>Common iron, exposed to air and moisture, <i>rusts</i>; it -combines with oxygen. Pure iron, in a state of fine -division, unites with oxygen so eagerly, that it becomes -incandescent, and in both cases oxide of iron is formed. -This last instance is certainly a case of combustion; but -in what does it differ from the first one, except in the -intensity of the action? The cases of spontaneous -combustion which are continually occurring are examples -of an analogous character to the above. Oxygen -is absorbed, it enters more or less quickly, according to -atmospheric conditions, into chemical combination; heat -is evolved, and eventually,—the action continually -increasing,—true combustion takes <span class="correction" title="In the original book: plaee">place</span>. In this way -our cotton-ships, storehouses of flax, piles of oiled-cloth, -sawdust, &c., frequently ignite; and to such an -influence is to be attributed the destruction of two of -our ships of war, a few years since, in Devonport naval -arsenal.<a name="FNanchor_220_220" id="FNanchor_220_220"></a><a href="#Footnote_220_220" class="fnanchor">[220]</a></p> -<p><span class="pagenum"><a name="Page_307" id="Page_307"></a>[Pg 307]</span></p> -<p>In the economic production of heat and light, we -have the combination of hydrogen and carbon with the -oxygen of common air, forming water and carbonic -acid. In our domestic fires we employ coal, which is -essentially a compound of carbon and hydrogen containing -a little oxygen and some nitrogen, with some earthy -matters which must be regarded as impurities; the -taper, whether of wax or tallow, is made up of the same -bodies, differing only in their combining proportions, -and, like coal gas, these burn as carburetted hydrogen. -All these bodies are very inflammable, having a tendency -to combine energetically with oxygen at a certain -elevation of temperature.</p> - -<p>We are at a loss to know how heat can cause the -combination of those bodies. Sir Humphry Davy has -shown that hydrogen will not burn, nor a mixture of it -with oxygen explode, unless directly influenced by a -body heated so as to <i>emit light</i>.<a name="FNanchor_221_221" id="FNanchor_221_221"></a><a href="#Footnote_221_221" class="fnanchor">[221]</a> May we not, therefore, -conclude that the chemical action exhibited in a -burning body is a development of some latent force, -with which we are unacquainted, produced by the absorption -of light;—that a repulsive action at first takes -place, by which the hydrogen and carbon are separated -from each other;—and that in the nascent state they -are seized by the oxygen, and again compelled, though -in the new forms of water and carbonic acid, to resume -their chains of combining affinity?</p> - -<p>Every equivalent of carbon and of hydrogen in the -burning body unites with two equivalents of oxygen, in -strict conformity with the laws of combination. The -flame of hydrogen, if pure, gives scarcely any light, but -combined with the solid particles of carbon, it increases -in brightness. The most brilliant of the illuminating -gases is the olefiant gas, produced by the decomposition -of alcohol, and it is only hydrogen charged with carbon<span class="pagenum"><a name="Page_308" id="Page_308"></a>[Pg 308]</span> -to the point of saturation. Flame is a cone of heated -vapour, becoming incandescent at the points of contact -with the air; a mere superficial film only being luminous. -It is evident that all the particles of the gas are in a -state of very active repulsion over the surface, since -flame will not pass through wire gauze of moderate -fineness. Upon this discovery is founded the inimitable -safety-lamp of Davy, by means of which the explosive -gases of a mine are harmlessly ignited within a cage of -wire gauze. This effect has been attributed to a cooling -influence of the metal; but, since the wires may be -brought to a degree of heat but little below redness -without igniting the fire-damp, this does not appear to -be the cause. The conditions of the safety lamp may -be regarded as presenting examples exactly the converse -of those already stated with reference to the spheroidal -state of water; and it affords additional evidence that -the condition of bodies at high temperatures is subject -to important physical changes.</p> - -<p>The principle upon which the safety lamp is constructed -is, that a mixture of the fire-damp and -atmospheric air in certain proportions explodes upon -coming in contact with a flame.</p> - -<p>This mixture passes readily through a wire gauze, -under all circumstances, and it, of course, thus approaches -the flame of the lamp enclosed within such a -material, and it explodes. But, notwithstanding the -mechanical force with which the exploding gas is thrown -back against the bars of its cage, it cannot pass them. -Consequently, the element of destruction is caught and -caged; and notwithstanding its fierceness and energy, it -cannot impart to the explosive atmosphere without, any -of its force. No combustion can be communicated -through the wire gauze.</p> - -<p>The researches which led to the safety-lamp may be -regarded as among the most complete examples of -correct inductive experiment in the range of English<span class="pagenum"><a name="Page_309" id="Page_309"></a>[Pg 309]</span> -science, and the result is certainly one of the proudest -achievements of physico-chemical research. By merely -enveloping the flame of a lamp with a metallic gauze, the -labourer in the recesses of the gloomy mine may feel -himself secure from that outpouring current of inflammable -gas, which has been so often the minister of -death; he may walk unharmed through the explosive -atmosphere, and examine the intensity of its power, as -it is wasted in trifling efforts within the little cage he -carries. Accidents have been attributed to the “Davy,” -as the lamp is called among the colliers; but they may -in most cases be traced to carelessness on the part of -those whose duty it has been to examine the lamps, or -to the recklessness of the miners themselves.</p> - -<p>That curious metal, platinum, and also palladium, -possesses a property of maintaining a slow combustion, -which the discoverer of the safety-lamp proposed to -render available to a very important purpose. If we -take a coil of platinum wire, and, having made it red-hot, -plunge it into an explosive atmosphere of carburetted -hydrogen and common air, it continues to -glow with considerable brightness, producing, by this -very peculiar influence, a combination of the gases, -which is discovered by the escape of pungent acid -vapours. Over the little flame of the safety-lamp, it was -proposed by Davy to suspend a coil of platinum which -would be thus kept constantly at a red heat. If the -miner became accidentally enveloped in an atmosphere -of fire-damp, although the flame of his lamp might be -extinguished, the wire would continue to glow with -sufficient brightness to light him from his danger, -through the dark winding passages which have been -worked in the bed of fossil fuel. This very beautiful -arrangement has not, however, been adopted by our -miners.</p> - -<p>It is thus that the discoveries of science, although they -may appear of an abstract character, constantly, sooner<span class="pagenum"><a name="Page_310" id="Page_310"></a>[Pg 310]</span> -or later, are applied to uses by which some branch of -human labour is assisted, the necessities of man’s condition -relieved, and the amenities of life advanced.</p> - -<p>The respiration of animals is an instance of the same -kind of chemical phenomena as we discover in ordinary -combustion. In the lungs the blood becomes charged -with oxygen, derived from the atmospheric air, with which -it passes through the system, performing its important -offices, and the blood is returned to the lungs with the -carbonic acid formed by the separation of carbon from -the body which is thrown off at every expiration. It -will be quite evident that this process is similar to that -of ordinary combustion. In man or animals, as in the -burning taper,—which is aptly enough employed by -poets as the symbol of life,—we have hydrogen and -carbon, with some nitrogen superadded; the hydrogen -and oxygen form water under the action of the vital -forces; the carbon with oxygen produces carbonic acid, -and, by a curious process, the nitrogen and hydrogen -also combine, to form ammonia.<a name="FNanchor_222_222" id="FNanchor_222_222"></a><a href="#Footnote_222_222" class="fnanchor">[222]</a></p> - -<p>All the carbon which is taken into the animal economy -passes, in the process of time, again into the atmosphere, -in combination with oxygen, this being effected in the -body, under the <i>catalytic</i> power of tissues, immediately -influenced by the excitation of nervous forces, which are -the direct manifestations of vital energy. The quantity -of carbonic acid thus given out to the air is capable of -calculation, with only a small amount of error. It -appears that upwards of fifty ounces of carbonic acid -must be given off from the body of a healthy man in -twenty-four hours. On the lowest calculation, the population -of London must add to the atmosphere daily -4,500,000 pounds of carbonic acid. It must also be remembered -that in every process for artificial illumination, -and in all the operations of the manufactures in which<span class="pagenum"><a name="Page_311" id="Page_311"></a>[Pg 311]</span> -fire is used, and also in our arrangements to secure domestic -comfort, immense quantities of this gas are -formed. We may, indeed, fairly estimate the amount, -if we ascertain the quantity of wood and coal consumed, -of all the carbon which combines with oxygen while -burning, and escapes into the air, either as carbonic acid -or carbonic oxide. The former gas, the same as that -which accumulates in deep wells and in brewers’ vats, -is highly destructive to life, producing very distressing -symptoms, even when mixed with atmospheric air, in -but slight excess over that proportion which it commonly -contains. The oppressive atmosphere of crowded -rooms is in a great measure due to the increased proportion -of carbonic acid given off from the lungs of those assembled, -and collected in the almost stagnant air of badly -ventilated apartments. It will be evident to every one, that -unless some provision was made for removing this deleterious -gas from the atmosphere as speedily as it formed, -consequences of the most injurious character to the -animal races would ensue. It is found, however, that -the quantity in the atmosphere is almost constantly -about one per cent. The peculiar properties of carbonic -acid in part ensure its speedy removal. It is among -the heaviest of gaseous bodies, and it is readily absorbed -by water; consequently, floating within a short distance -from the surface of the earth, a large quantity is dissolved -by the waters spread over it. A considerable -portion is removed by the vegetable kingdom; indeed, -the whole of that produced by animals, and by the -processes of combustion, eventually becomes part of -the vegetable world, being absorbed with water by the -roots, and separated from the air by the peculiar functions -of the leaves. However, this heavy gas unites -with the lighter atmospheric fluid in obedience to that -law which determines the diffusion of different specific -gravities through each other.</p> - -<p>The leaves of plants may be regarded as performing<span class="pagenum"><a name="Page_312" id="Page_312"></a>[Pg 312]</span> -similar offices to the lungs of animals. They are the -breathing organs. In the animal economy a certain -quantity of carbon is necessarily retained, in combination -with nitrogen and other elements, to form muscle; but -this is constantly undergoing change; the entire system -being renewed within a comparatively limited period. -The conditions with plants are somewhat different. For -instance, the carbon is fixed in a tree, and remains -as woody fibre until it decays, even though the life of -the plant may extend over centuries.</p> - -<p>Animals, then, are constantly supplying carbonic -acid; plants are as constantly feeding on it; thus is the -balance for ever maintained between the two kingdoms. -Another condition is, however, required to maintain for -the uses of men and animals the necessary supply of -oxygen gas. This is effected by one of those wonderful -operations of nature’s chemistry which must strike -every reflecting mind with admiration. During the -night plants absorb carbonic acid; but there is a condition -of repose prevailing then in their functions, and -consequently their powers of effecting the decomposition -of this gas are reduced to their minimum. The plant -sleeps, and vital power reposes; its repose being as -necessary to the plant as to the animal. With the first -gleam of the morning sun the dormant energies of the -plant are awakened into full action; it decomposes this -carbonic acid, secretes the carbon, to form the rings of -wood which constitute so large a part of its structure, -and pour out oxygen gas to the air. The plant -is, therefore, an essential element in the conditions -necessary for the support of animal life.</p> - -<p>The animal produces carbonic acid in an exact proportion -to the quantity of carbonaceous matter which -it consumes. Fruit and herbage contain a small quantity -of carbon in comparison with muscle and fat. But -let us confine our attention to the human race. Man -within the Tropics, where the natural temperature is<span class="pagenum"><a name="Page_313" id="Page_313"></a>[Pg 313]</span> -high, does not require so great an amount of chemical -action to go on within him for the purpose of maintaining -the requisite animal heat; consequently his -Maker has surrounded him with fruits and grains which -constitute his food.</p> - -<p>As we advance to the colder regions of the earth -man becomes a flesh-eater, and his carnivorous appetite -increases as the external temperature diminishes. -Eventually we reach the coldest zones, and the human -being there devours enormous quantities of fat to -supply the necessities of his condition.</p> - -<p>It must necessarily follow, that the inhabitants of the -tropics do not produce so much carbonic acid as those -who dwell in colder regions. In the first place, their -habits of life are different, and they are not under the -necessity of maintaining animal heat by the use of artificial -combustion, as are the people of colder climes. -The vegetation of the regions of the tropics is much -more luxuriant than that of the temperate and arctic -zones. Hence an additional supply of carbonic acid is -required between the torrid zones, and a less quantity -is produced by its animals. These cases are all met by -the great aërial movements. A current of warmed air, -rich in oxygen, moves from the equator towards the -poles, whilst the cooler air, charged with the excess of -carbonic acid, sets in a constant stream towards the -equator. By this means the most perfect equalization -of the atmospheric conditions is preserved.</p> - -<p>The carbonic acid poured out from the thousand -mouths of our fiery furnaces,—produced during the -laborious toil of the hard-working artizan,—and exhaled -from every populous town of this our island -home,—is borne away by this our aërial currents to -find its place in the pines of the Pacific Islands, the -spice-trees of the Eastern Archipelago, and the cinchonas -of Southern America. The plants of the valley -of the Caucasus, and those which flourish amongst<span class="pagenum"><a name="Page_314" id="Page_314"></a>[Pg 314]</span> -the Himalayas, equally with the less luxuriant vegetation -of our temperate climes, are directly dependent -upon man and the lower animals for their supply of -food.</p> - -<p>If all plants were removed from the earth, animals -could not exist. How would it be if the animal kingdom -was annihilated?—would it be possible for vegetation -to continue? This question is not quite so -easily answered; but, if we suppose all the carbon-producing -machines—the animals—to be extinct, from -whence would the plants draw their supply? It has -been supposed that during the epoch of the coal formation -a luxuriant vegetation must have gone on over -the earth’s surface, when the existence of animal life was -regarded as problematical. It is supposed that the air was -then charged with carbonic acid, and that the calamites, -lepidodendra, and sigilaria, were employed to remove it, -and fit the earth for the oxygen-breathing races. The -evidence upon these points is by no means satisfactory; -and although at one time quite disposed to acquiesce in -a conjecture which appears to account so beautifully for -the observed geological phenomena of carboniferous -periods, we do not regard the necessities for such a -condition of the atmosphere as clearly made out.<a name="FNanchor_223_223" id="FNanchor_223_223"></a><a href="#Footnote_223_223" class="fnanchor">[223]</a> -Geological research, too, has shown that the immense -forests from which our coal is formed teemed with life. -A frog as large as an ox existed in the swamps, and the -existence of insects proves the high order of organic -creation at this epoch.</p> -<p><span class="pagenum"><a name="Page_315" id="Page_315"></a>[Pg 315]</span></p> -<p>In all probability the same mutual dependence which -now exists between the animal and vegetable kingdoms -existed from the beginning of time, and will continue to -do so under varying circumstances through the countless -ages of the earth’s duration.</p> - -<p>There is yet another very important chain of circumstances -which binds these two great kingdoms together. -This is the chain of the animal necessities. A large -number of races feed directly upon vegetables; herbs -and fruits are the only things from which they gain -those elements required to restore the waste of their -systems.</p> - -<p>These herbivorous animals, which must necessarily -form fat and muscle from the elements of their vegetable -diet, are preyed on by the carnivorous races; and from -these the carbon is again restored to the vegetable world. -Sweep off from the earth the food of the herbivora, they -must necessarily very soon perish, and with their dissolution, -the destruction of the carnivora is certainly -ensured. To illustrate this on a small scale, it may be -mentioned that around the coasts of Cornwall, pilchards -were formerly caught in very great abundance, in the -shallow water within coves, where these fish are now but -rarely seen. From the investigations of the Messrs. -Couch, whose very accurate observations on the Cornish -fauna have placed both father and son amongst the most -eminent of British naturalists,<a name="FNanchor_224_224" id="FNanchor_224_224"></a><a href="#Footnote_224_224" class="fnanchor">[224]</a> it appears that the -absence of these fish is to be attributed entirely to the -practice of the farmers, who cut the sea-weed from the -rocks for the purpose of manuring their lands. By this -they destroy all the small crustacea inhabiting these -immature marine forests feeding on the algæ, and as -these, the principal food of the pilchards, have perished -they seek for a substitute in more favourable situations.<span class="pagenum"><a name="Page_316" id="Page_316"></a>[Pg 316]</span> -Mr. Darwin remarks, that if the immense <span class="correction" title="In the original book: seaweeds">sea-weeds</span> of -the Southern Ocean were removed by any cause, the -whole fauna of these seas would be changed.</p> - -<p>We have seen that animals and vegetables are composed -principally of four elementary principles,—oxygen, -hydrogen, nitrogen, and carbon. We have examined -the remarkable manner in which they pass from one -condition—from one kingdom of nature—into another. -The animal, perishing and dwindling by decomposition -into the most simple forms of matter, mingling with the -atmosphere as mere gas, gradually becomes part of the -growing plant, and by like changes vegetable organism -progresses onward to form a portion of the animal -structure.</p> - -<p>A plant exposed to the action of natural or artificial -decomposition passes into air, leaving but a few grains -of solid matter behind it. An animal, in like manner, -is gradually resolved into “thin air.” Muscle, and -blood, and bones, having undergone the change, are -found to have escaped as gases, leaving only “a pinch -of dust,” which belongs to the more stable mineral -world. Our dependency on the atmosphere is therefore -evident. We derive our substance from it—we are, -after death, resolved again into it. We are really but -fleeting shadows. Animal and vegetable forms are little -more than consolidated masses of the atmosphere. The -sublime creations of the most gifted bard cannot rival -the beauty of this, the highest and the truest poetry of -science. Man has divined such changes by the unaided -powers of reason, arguing from the phenomena which -science reveals in unceasing action around him. The -Grecian sage’s doubts of his own identity, were only an -extension of a great truth beyond the limits of our -reason. Romance and superstition resolve the spiritual -man into a visible form of extreme ethereality in the -spectral creations, “clothed in their own horror,” by -which their reigns have been perpetuated.</p> - -<p><span class="pagenum"><a name="Page_317" id="Page_317"></a>[Pg 317]</span></p> - -<p>When <span class="correction" title="In the original book: Shakspeare">Shakespeare</span> made his charming Ariel sing—</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“Full fathom five thy father lies,</div> -<div class="verse indent2">Of his bones are coral made,</div> -<div class="verse">Those are pearls that were his eyes:</div> -<div class="verse indent2">Nothing of him that doth fade,</div> -<div class="verse">But doth suffer a sea change</div> -<div class="verse">Into something rich and strange,”</div> -</div></div></div> - -<p>he painted, with considerable correctness, the chemical -changes by which decomposing animal matter is replaced -by a siliceous or calcareous formation.</p> - -<p>But the gifted have the power of looking through the -veil of nature, and they have revelations more wonderful -than even those of the philosopher, who evokes them -by perpetual toil and brain-racking struggle with the -ever-changing elements around him.</p> - -<p>The mysteries of flowers have ever been the charm of -the poet’s song. Imagination has invested them with -a magic influence, and fancy has almost regarded them -as spiritual things. In contemplating their surpassing -loveliness, the mind of every observer is improved, and -the sentiments which they inspire, by their mere external -elegance, are great and good. But in examining -the real mysteries of their conditions, their physical -phenomena, the relations in which they stand to the -animal world, “stealing and giving odours” in the marvellous -interchange of carbonic acid and ammonia for -the soul-inspiring oxygen—all speaking of the powers of -some unseen, in-dwelling principle, directed by a supreme -ruler—the philosopher finds subjects for deep and soul-trying -contemplation. Such studies lift the mind into -the truly sublime of nature. The poet’s dream is the -dim reflection of a distant star: the philosopher’s revelation -is a strong telescopic examination of its features. -One is the mere echo of the remote whisper of nature’s -voice in the dim twilight; the other is the swelling<span class="pagenum"><a name="Page_318" id="Page_318"></a>[Pg 318]</span> -music of the harp of Memnon, awakened by the sun of -truth, newly risen from the night of ignorance.</p> - -<p>To return from our long, but somewhat natural -digression, to a consideration of the chemical phenomena -connected with the atmosphere, and its curious and -important element, nitrogen, we must first examine the -evidence we have of the condition of the air itself.</p> - -<p>The mean pressure exerted upon the surface of the -earth, as indicated by the barometer, is equal to a column -of mercury thirty inches high; that is, the column of -air from the surface of the ocean to its highest limits -exactly balances that quantity of mercury. If our -tube of mercury had the area of one square inch, -the columns would weigh fifteen pounds, which represents -a pressure of fifteen pounds upon every square -inch of the earth’s surface. This pressure, it must be -remembered, is the compound weight of the gaseous -envelope, and the elastic force of the aqueous vapour -contained in it.<a name="FNanchor_225_225" id="FNanchor_225_225"></a><a href="#Footnote_225_225" class="fnanchor">[225]</a> If the atmosphere were of uniform<span class="pagenum"><a name="Page_319" id="Page_319"></a>[Pg 319]</span> -condition, its height, as inferred from the barometer, -would be about five miles and a half. The density of -the air, however, diminishes with the pressure upon it, -so that at the height of 11,556 feet, the atmosphere is -of half density; or one volume of air, as taken at the -surface of the earth, is expanded into two at that height. -Thus the weight is continually diminishing; but this is -regularly opposed by the decreasing temperature, which -diminishes the rate of about one degree for every 352 -feet of ascent, although in all probability it is less -rapid at great distances from the earth.</p> - -<p>It has been calculated from certain phenomena of -refraction, that our atmosphere must extend to about -forty miles from the surface of the earth. It may, in -a state of extreme tenuity, extend still further; but -it is probable that the intense cold produced by rarefaction -sets limits to any extension much beyond this -elevation.</p> - -<p>The uses of the atmosphere are many. It is the -medium for regulating the dispersion of watery vapours -over the earth. If there were no atmosphere, and -that, as now, the equatorial climes were hot and the -poles cold, evaporation would be continually going on -at the equator, and condensation in the colder regions. -The sky of the tropical climes would be perpetually -cloudless, whilst in the temperate and arctic zones we -should have constant rain and snow. By having a -gaseous atmosphere, a more uniform state of things is -produced; the vapours arising from the earth become -intimately mixed with the air, and are borne by it -over large tracts of country, and only precipitated -when they enter some stratum much colder than that -which involves them. There are opposite tendencies in -an atmosphere of air and one of vapour. The air circulates -from the colder to the warmer parts, and the -vapour from the warmer to the colder regions; and as<span class="pagenum"><a name="Page_320" id="Page_320"></a>[Pg 320]</span> -the currents of the air, from the distribution of land and -sea—the land, from its low conducting power, being -more quickly heated than the sea—are very complicated, -and as some force is employed in keeping the vapour -suspended in the air, water is less suddenly deposited on -the earth than it would have been, had not these tendencies -of the air and its hygrometric peculiarities been -such as we find them.</p> - -<p>The blue colour of the sky, which is so much more -agreeable to the eye than either red or yellow, is due to -a tendency of the mixed gas and vapour to reflect the -blue rays rather than red or yellow. The white light -which falls upon the surface of the earth, without absorption -or decomposition in its passage from the sun, -is partially absorbed by, and in part reflected back from, -the earth. The reflected rays pass with tolerable freedom -through this transparent medium, but a portion of -the blue rays are interrupted and rendered visible to us. -That it is reflected light, is proved by the fact of its being -in a polarized state.<a name="FNanchor_226_226" id="FNanchor_226_226"></a><a href="#Footnote_226_226" class="fnanchor">[226]</a> Clouds of vapour reflect to us -again, not isolated rays, but the undecomposed beam, -and consequently they appear white as snow to our -vision.</p> - -<p>The golden glories of sunset,—when, “like a dying -dolphin,” heaven puts on the most gorgeous hues, which -are continually changing,—depend entirely upon the -quantity of watery vapour which is mixed with air, and -its state of condensation. It has been observed, that -steam at night, issuing into the atmosphere under a -pressure of twenty or thirty pounds to the square inch, -transmits and reflects orange-red light. This we may, -therefore, conclude to be the property of such a condition -of mixed vapour and air, as prevails when the<span class="pagenum"><a name="Page_321" id="Page_321"></a>[Pg 321]</span> -rising or the setting sun is shedding over the eastern -or the western horizon the glory of its coloured rays.<a name="FNanchor_227_227" id="FNanchor_227_227"></a><a href="#Footnote_227_227" class="fnanchor">[227]</a></p> - -<p>Thus science points out to us the important uses of -the air. We learn that life and combustion are entirely -dependent on it, and that it is made the means for -securing greater constancy in the climates of the earth -than could otherwise be obtained. The facts already -dwelt upon are sufficient to convince every thinking -mind that the beautiful system of order which is displayed -in the composition of the atmosphere, in which -the all-exciting element, oxygen, is subdued to a tranquil -state by another element, nitrogen, (which, we shall -have presently to show, is itself, under certain conditions, -one of the most energetic agents with which we -are acquainted,) indicates a supreme power, omniscient -in the adaptation of things to an especial end. Oxygen -and nitrogen are here <i>mixed</i> for the benefit of man;<span class="pagenum"><a name="Page_322" id="Page_322"></a>[Pg 322]</span> -man <i>unites</i> them by the aid of powers with which he is -gifted, and the consequences are of a fatal kind. The -principles which the great Chemist of Nature renders -mild are transformed into sources of evil by the chemist -of art.</p> - -<p>Beyond all this, the atmosphere produces effects on -light which add infinitely to the beauty of the world. -Were there no atmosphere, we should only see those objects -upon which the sun’s rays directly fell, or from which -they were reflected. A ray falling through a small hole -into a dark room, illuminating one object, which reflects -some light upon another, is an apt illustration of the -effect of light upon the earth, if it existed without its -enveloping atmosphere. By the dispersive powers of -this medium, sunlight is converted into daylight; and -instead of unbearable, parallel rays illuminating brilliantly, -and scorching up with heat those parts upon -which they directly fall, leaving all other parts in the -darkness of night, we enjoy the blessings of a diffusion -of its rays, and experience the beauties of soft shades -and slowly-deepening shadows. Without an atmosphere, -the sun of the morning would burst upon us with unbearable -brilliancy, and leave us suddenly, at the close -of day, at once in utter darkness. With an atmosphere -we have the twilight with all its tempered loveliness,—a -“time for poets made.”</p> - -<p>In chemical character, atmospheric air is composed of -twenty-one volumes of oxygen, and seventy-nine volumes -of nitrogen: or one hundred grains of air consist of 23·1 -grains of the former, and 76·9 grains of the latter. -Whether the air is taken from the greatest depths or the -most exalted heights to which man has ever reached, an -invariable proportion of the gases is maintained. The -air of Chimborazo, of the arid plains of Egypt, of the -pestilential delta of the Niger, or even of the infected -atmosphere of an hospital, all give the same proportions -of these two gases as we find existing on the healthful hills<span class="pagenum"><a name="Page_323" id="Page_323"></a>[Pg 323]</span> -of Devonshire, or in the air of the city of London. This -constancy in constitution leads to the supposition that -the oxygen and nitrogen are chemically combined; but -many eminent philosophers have contended that they -are merely mechanically mixed; and they have shown -that some peculiar properties prevail amongst gaseous -bodies, which very fully explain the equal admixture of -two gases the specific gravities of which are different. -This is particularly exemplified in the case of carbonic -acid, of which gas one per cent. can be detected in all -regions of the air to which the investigations of man -have reached. This gas, although so heavy, is, by the -law of diffusion, mixed with great uniformity throughout -the mass.<a name="FNanchor_228_228" id="FNanchor_228_228"></a><a href="#Footnote_228_228" class="fnanchor">[228]</a> Every exhalation from the earth, of course, -passes into the air; but these are generally either so -light that they are carried into the upper regions, and -there perform their parts in the meteorological phenomena, -or they are otherwise very readily absorbed by -water or growing plants, and thus is the atmosphere -preserved in a state of purity for the uses of animals. -Again, the quantity of oxygen contained in the air, and -its very peculiar character, ensures the oxidation of all -the volatile organic matters which are constantly passing -off,—as the odoriferous principles of plants, the miasmata -of swamps, and the products of animal putrefaction; -these are rapidly converted into water, carbonic -acid, or nitric acid, and quickly enter into new and harmless -combinations. The elements of contagion we are -unacquainted with; but since the attention of inquirers -has been of late directed to this important and delicate -subject, some light may possibly be thrown upon it -before long.</p> - -<p>Nothing, shows more strikingly the admirable adaptation<span class="pagenum"><a name="Page_324" id="Page_324"></a>[Pg 324]</span> -of all things for their intended uses than the atmosphere. -In it we find the source of life and health; and chemistry -teaches us, most indisputably, that it is composed of -certain proportions of oxygen and nitrogen gases; and -experience informs us that it is on the oxygen that we are -dependent for all that we enjoy. So beautifully is the -atomic or molecular constitution ordered, that it is impossible -to produce any change in the air without rendering it -injurious to the vegetable and animal economy. It might -be thought, from the well-known exhilirating character -of oxygen gas, that, if a larger quantity existed in the -atmosphere than that which we find there, the enjoyments -of life would be of a more exciting kind; but the -consequences of any increase would be exceedingly injurious; -and, by quickening all the processes of life to an -unnatural extent, the animal fabric would soon decay: -excited into fever, it would be destroyed by its own fires. -Chemistry has made us acquainted with six other compounds -of oxygen and nitrogen, neither of them fitted -for the purposes of vitality, of which the following are -the most remarkable:—</p> - -<p>Nitrous oxide, or the, so called, <i>laughing gas</i>, which -contains two volumes of nitrogen to one of oxygen, -would prove more destructive than even pure oxygen, -from the delirious intoxication which it produces.</p> - -<p>Nitric oxide is composed, according to Davy, of two -volumes of nitrogen and two of oxygen. It is of so -irritating a nature, that the glottis contracts spasmodically -when any attempt is made to breathe it; and -the moment it escapes into the air it combines with -more oxygen, and forms the deep red fumes of nitrous -acid.</p> - -<p>Nitrous acid and the peroxide of nitrogen each contains -an additional proportion of oxygen, and they are -still more destructive to all organization.</p> - -<p>Nitric acid contains five volumes of oxygen united to -two of nitrogen; and the well-known destructive properties -of aqua fortis it is unnecessary to describe.</p> - -<p><span class="pagenum"><a name="Page_325" id="Page_325"></a>[Pg 325]</span></p> - -<p>The atmosphere, and these chemically active compounds, -contain the same elements, but their mode of -combining is different; and what is, in the one case, -poisonous to the highest degree, is, in the other, rendered -salubrious, and essential to all organized beings.</p> - -<p>Nitrogen gas may be regarded in the light of a diluent -to the oxygen. In its pure state it is only characterised -by its negative properties. It will not burn, or act as -a supporter of combustion. Animals speedily perish if -confined in it; but they die rather through the absence -of oxygen than from any poisonous property of this gas. -Yet, in combination, we find nitrogen exhibiting powers -of a most energetic character. In addition to the fulminating -compounds and the explosive substances -already named, which are among the most remarkable -instances of unstable affinity with which we are acquainted, -we have also the well-known pungent body, -ammonia. From the analogous nature of this volatile -compound, and the fixed alkalies soda and potash, it -was inferred that it must, like them, be an oxide of a -metallic base. Davy exposed ammonia to the action of -potassium, and to the influence of the voltaic arc produced -from 2,000 double plates, without at all changing -its character. From its slight tendency to combination, -and from its being found abundantly in the organs of -animals feeding on substances that do not contain it, it -is, however, probably a compound body. A phenomenon -of an obscure and mysterious character is presented in -the formation of the “ammoniacal amalgam,” as it is -called.</p> - -<p>Mercury, being mixed with an ammoniacal salt, is -exposed to powerful galvanic action; and a compound, -maintaining its metallic appearance, but of considerable -lightness and very porous, presents itself.<a name="FNanchor_229_229" id="FNanchor_229_229"></a><a href="#Footnote_229_229" class="fnanchor">[229]</a> This prepa<span class="pagenum"><a name="Page_326" id="Page_326"></a>[Pg 326]</span>ration -has been carefully examined by Davy, Berzelius, -and others. It is always resolved into ammonia and -mercury; and, although the latter chemist is strongly -inclined to regard it as affording evidence of the compound -nature of nitrogen,—and he has, indeed, proposed -the name <i>nitricum</i> for its hypothetical base,—yet, to the -present time, we have no satisfactory explanation of this -apparent metallization of ammonia.</p> - -<p>No attempt will be made to describe the various elementary -substances which come under the class of -metallic bodies, much less to enumerate their combinations. -Many of the metals, as silver and copper, are -found sometimes in a native state, or nearly pure; but, -for the most part, they exist, in nature, in combination -with oxygen or sulphur; gold furnishing a remarkable -exception. They are occasionally found combined with -other bodies,—as oxidized carbon, phosphorus, chlorine, -&c.; but these cases are by no means so common. -Those substances called metals are generally found embedded -in the rocks, or deposited in fissures formed -through them; but it is one of the great discoveries of -modern science, that those rocks themselves are metallic -oxides. With metals we generally associate the idea of -great density; but potassium and sodium, the metallic -bases of potash and soda, are lighter than water, and -they consequently float upon that fluid. We learn, -therefore, from the researches of science, that the crust -of this earth is composed entirely of metals, combined -with gaseous elements; and there is reason for believing -that one, or perhaps two, of the gases we have already -named are also of a metallic character. Strange as it -may appear, there is nothing, as will be seen on attentive -consideration, irrational in this idea. Many of the -metals proper, under the influence of such heat as we -can, by artificial means, command, are dissipated in vapour, -and may be maintained in this state perfectly invisible. -Indeed, the transparent space above the surface<span class="pagenum"><a name="Page_327" id="Page_327"></a>[Pg 327]</span> -of the mercury in the tube of a barometer, known as the -Torricellian vacuum, is filled with the vapour of mercury. -There is, therefore, no reason why nitrogen, or -even hydrogen, should not be metallic molecules kept -by the force of the repulsive powers of heat, or some -other influence, at a great distance from each other. -The peculiar manner in which nitrogen unites with mercury, -and the property which hydrogen possesses of -combining with antimony, zinc, arsenic, potassium, -sodium, and possibly other metals, besides its union with -sulphur and carbon—in all which cases there is no such -change of character as occurs when they combine with -oxygen—appear to indicate bodies which, chemically, are -not very dissimilar to those metals themselves, although, -physically, they have not the most remote resemblance.</p> - -<p>“We know nothing,” says Davy, “of the true elements -belonging to nature; but, so far as we can reason -from the relations of the properties of matter, hydrogen -is the substance which approaches nearest to what the -elements may be supposed to be. It has energetic powers -of combination, its parts are highly repulsive as to each -other, and attractive of the particles of other matter; it -enters into combination in a quantity very much smaller -than any other substance, and in this respect it is -approached by no known body.”<a name="FNanchor_230_230" id="FNanchor_230_230"></a><a href="#Footnote_230_230" class="fnanchor">[230]</a></p> - -<p>Many of the elements are common to the three kingdoms -of nature: most of those found in one condition of -organization are discovered in another. The carbonates -are an abundant mineral class. In the vegetable kingdom -we find carbon combining with oxygen, hydrogen, and -nitrogen: these elements, also, constitute the substance -of animals, the proportion of nitrogen being, however, -much larger. If one element, more than another, belongs -especially to the animal economy, it is phosphorus, -although this is not wanting in the vegetable world;<span class="pagenum"><a name="Page_328" id="Page_328"></a>[Pg 328]</span> -and it is not uncommon in the mineral. Sulphur is -common to the three kingdoms: it is abundant in the -mineral, being one of the products of volcanic action; -it is united with the metals, forming sulphurets; and is -found in our rocks in the state of sulphuric acid or -oxidized vapour, combined with the metallic bases of -lime and other earths. In the vegetable kingdom we -discover sulphur in all plants of the onion kind, in the -mustard, and some others; it enters into the composition -of vegetable albumen, and appears always combined with -albumen, fibrine, and caseine, in the animal economy.</p> - -<p>Chlorine is found most abundantly in combination -with sodium, as common salt: in this state, in particular, -we may trace it from the depths of the earth, its -waters, and its rocks, to the plants and animals of the -surface. Iodine is most abundant in marine plants; -but it has been found in the mineral world, traced to -plants, and it is indicated in the flesh of some animals. -Bromine is known to us as a product of certain saline -waters, and a few specimens of natural bromide of silver -have been examined. Fluorine, the base of the acid -which, combining with lime, forms fluor-spar, is found -to exist to some considerable extent in bones; it has -been discovered in milk and blood; and investigations -have proved its existence in the vegetable world. It -must not be forgotten that the earths, lime and magnesia, -enter into the composition of the more solid parts -of plants and animals. Lime is one of the principal -constituents of animal bone and shells, and it is found -in nearly all vegetables.</p> - -<p>Silica, or the <i>earth</i> of flints, is met with in beautiful -transparent crystals, in the depths of the mine; in all -rock and soils we find it. In the bark of many plants, -particularly the grasses, it is discovered, forming the -hard supporting cuticle of the stalk, in wheat, the Dutch -rush, the sugar-cane, the bamboo, and many other -plants.</p> - -<p><span class="pagenum"><a name="Page_329" id="Page_329"></a>[Pg 329]</span></p> - -<p>It is thus that we find the same elementary principle -presenting itself in every form of matter, under -the most Protean shapes. Numerous phenomena of -even a more striking character than those selected, are -exhibited in every department of chemistry; but within -the limits of this essay it is impracticable to speak -of any beyond those which directly explain natural -phenomena.</p> - -<p>The chemical elements, which actually exist in nature -as simple bodies, are probably but few. Most of the -gases are in all probability compounds of some ethereal -ultimate principles; and with the advance of science we -may fairly hope to discover the means of reducing some -of them to a yet more simple state.</p> - -<p>Curious relations, which can be traced through certain -bodies, lead us to believe that they may be only modified -conditions of one element. Flint and charcoal do not at -first appear allied; but carbon in some of its states -approaches very near to the condition of silicon, the -metallic base of flint. When we remember the differences -which are evident in three forms of one body—coke, -graphite, and diamond—the dissimilitude between flint, -a quartz crystal, and carbon, will cease to be a strong -objection to the speculation.</p> - -<p>Phosphorus, sulphur, and selenium, have many properties -in common. Iodine, bromine, chlorine, and -fluorine, appear to belong to the same group. Iron and -nickel, and cobalt, have a close relation. Silver and -lead are usually combined, and exhibit a strong relationship. -Gold, platinum, and the rarer metals, have so -many properties in common, that they may form a -separate group from all the others.</p> - -<p>Indeed, a philosophical examination of the elements -now supposed to constitute the material world, enables -us to divide them into about six well-defined groups. -Wide differences exist within these groups; but still we<span class="pagenum"><a name="Page_330" id="Page_330"></a>[Pg 330]</span> -find a sufficient number of common properties to warrant -our classing them in one family.</p> - -<p>The dream of the alchemists, in the vain endeavour -to realise which they exhausted their lives and dissipated -their wealth, had its foundation in a natural truth. The -transmutation of one form of matter into another may -be beyond the power of man, but it is certainly continually -taking place in the laboratory of nature, under -the directing law of the great Creator of this beautiful -earth.</p> - -<p>The speculations of men, through all ages, have leaned -towards this idea, as is shown by the theory of the four -elements,—Air, Fire, Earth, and Water,—of the ancients, -the three,—Salt, Sulphur, and Mercury,—of the alchemists, -and the refined speculations of Newton and -Boscovich on the ultimate constitution of matter. All -experimental inquiry points towards a similar conclusion. -It is true we have no direct evidence of any -elementary atom actually undergoing a change of state; -but when we regard the variations produced by electrical -influence, the changes of state which arise from the -power of heat, and the physical alterations produced by -light, it will be difficult to come to any other conclusion -than that the particles of matter known to us as ultimate -are capable of change, and consequently must be far -removed from positively simple bodies, since the real -elementary atom, possessing fixed properties, cannot be -supposed capable of undergoing any transmutation. -Allotropism could not occur in any absolutely simple -body.</p> - -<p>It will now be evident that in all chemical phenomena -we have the combined exercise of the great physical -forces, and evidences of some powers which are, as yet, -shrouded in the mystery of our ignorance. The formation -of minerals within the clefts of the rocks, the -decomposition of metallic lodes, the germination of<span class="pagenum"><a name="Page_331" id="Page_331"></a>[Pg 331]</span> -seeds, the growth of the plant, the development of its -fruit and its ultimate decay, the secret processes of -animal life, assimilation, digestion, and respiration, and -all the changes of external form, which take place around -us, are the result of the exercise of that principle which -we call chemical.</p> - -<p>By chemical action plants take from the atmosphere -the elements of their growth; these they yield to -animals, and from these they are again returned to the -air. The viewless atmosphere is gradually formed into -an organized being, the lordly tree upon whose branches -the fowls of the air have their homes, and the human -animal, exalted by being charged with a spiritual soul: -yet the tree and the man alike are gradually resolved -again into thin air. The changes of the mineral world -are of an analogous character; but we cannot trace them -so clearly in all their phenomena.</p> - -<p>The planet on which we live began its course charged -with a fixed quantity of physical force, and this has -remained constant to the present moment, and will do -so to the end of time. By influences external to this -earth the balance of these forces is continually disturbed; -and in the effort to restore the equilibrium, -we have the production of all the varied forms of -matter, and the manifestation of each particular physical -principle or power. As motion and attraction, balanced -against each other, maintain the earth in her elliptical -orbit, so the opposition of forces determines the existence -of the amorphous rock, the light-refracting crystal, the -fixed and flowering plant, and the locomotive animal.</p> - -<p>An eternal round of chemical action is displayed in -nature. Life and death are but two phases of its influences. -Growth and decay are equally the result of -its power.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_212_212" id="Footnote_212_212"></a><a href="#FNanchor_212_212"><span class="label">[212]</span></a> Dr. Priestley appears to have been the first to observe the -peculiar property of the diffusion of gases. Dr. Dalton, however, -first drew attention to the important bearing of this fact on natural -phenomena, and he published his views on <i>The Miscibility of -Gases</i> in the Manchester Memoirs, vol. v. The following extract -from his memoir <i>On the Constitution of the Atmosphere</i> will exhibit -its bearings:— -</p> -<p> -It may be worth while to contrast this view of the constitution -of the atmosphere with the only other one, as far as I know, that -has been entertained. -</p> - -<table id="two_views" summary="two views"> -<tr><td colspan="2" class="br cell">According to one view,</td> -<td colspan="2" class="bl cell">According to the other view,</td></tr> - -<tr><td colspan="2" class="tdvtop br cell">1. The volumes of each gas found at the surface of the -earth are proportional to the whole weights of the respective atmospheres.</td> -<td colspan="2" class="tdvtop bl cell">1. The volume of each gas found at the surface of the earth, <i>multiplied by -its specific gravity</i>, is proportional to the whole weight of the respective atmospheres.</td></tr> - -<tr><td class="sub_tab tdtop">Azote</td><td class="sub_tab tdtop tdr br">79 </td> -<td class="bl sub_tab tdpad tdtop">Azote</td><td class="sub_tab tdr tdtop">76·6 </td></tr> -<tr><td class="sub_tab">Oxygen</td><td class="sub_tab tdr br">21 </td> -<td class="bl sub_tab tdpad">Oxygen</td><td class="sub_tab tdr">23·4 </td></tr> -<tr><td class="sub_tab">Aqueous vapour</td><td class="sub_tab tdr br">1·33</td> -<td class="bl sub_tab">Aqueous vapour</td><td class="sub_tab tdr">0·83</td></tr> -<tr><td class="sub_tab">Carbonic acid</td><td class="sub_tab tdr br">1·0 </td> -<td class="bl sub_tab">Carbonic acid</td><td class="sub_tab tdr">0·15</td></tr> -<tr><td></td><td class="sub_tab tdr br">———</td> -<td class="bl"></td><td class="sub_tab tdr">———</td></tr> -<tr><td></td><td class="sub_tab tdr br">101·43</td> -<td class="bl"></td><td class="sub_tab tdr">100·88</td></tr> - -<tr><td colspan="2" class="tdvtop br cell">2. The altitude of each atmosphere differs from that -of every other, and the proportions of each in the compound atmosphere gradually vary in the ascent.</td> -<td colspan="2" class="tdvtop bl cell">2. The altitude of each atmosphere is the same, and -the proportion of each in the compound atmosphere, is the same at all elevations.</td></tr> - -<tr><td colspan="2" class="tdvtop br cell">3. When two atmospheres are mixed, they take their places -according to their specific gravity, not in separate strata, but intermixedly. There is, however, a separate -stratum of the specifically lighter atmosphere at the summit over the other.</td> -<td colspan="2" class="tdvtop bl cell">3. When two atmospheres are mixed, they continue -so without the heavier manifesting any disposition to separate and descend from the lighter.</td></tr> -</table> -</div> - -<div class="footnote"> - -<p><a name="Footnote_213_213" id="Footnote_213_213"></a><a href="#FNanchor_213_213"><span class="label">[213]</span></a> The discussion of this question, commenced by Arago in his -<i>Eloge</i>, was continued by Lord Brougham in his <i>Lives of Watt and -Cavendish</i>, and by Mr. Vernon Harcourt, in his address as President -of the British Association, and more recently in his <i>Letter to -Lord Brougham</i>. Watt’s <i>Letters</i> on the subject have been since -published under the superintendence of Mr. Muirhead.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_214_214" id="Footnote_214_214"></a><a href="#FNanchor_214_214"><span class="label">[214]</span></a> See several papers <i>On Ozone</i>, by Professor Schönbein, in the -Philosophical Magazine, and in the Reports of the British -Association. Consult a paper by the Author: <i>Athenæum</i>, September, -1849.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_215_215" id="Footnote_215_215"></a><a href="#FNanchor_215_215"><span class="label">[215]</span></a> Memoire <i>sur l’Ozone</i>; Bàle 1849. Poggendorff’s <i>Annalen</i>, -lxxvii., p. 592. Ibid, lxxviii. p. 162.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_216_216" id="Footnote_216_216"></a><a href="#FNanchor_216_216"><span class="label">[216]</span></a> <i>Chemical Gazette</i>, 1849.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_217_217" id="Footnote_217_217"></a><a href="#FNanchor_217_217"><span class="label">[217]</span></a> Iodide of silver has been found at Albarradon, near Mazapil, -in Mexico. Iodide of mercury, of a fine lemon-yellow colour, has -been discovered in the sandstone of Casas, Viegas, Mexico. -Algers; Phillips’ <i>Mineralogy</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_218_218" id="Footnote_218_218"></a><a href="#FNanchor_218_218"><span class="label">[218]</span></a> <span class="smcap">Gentele’s</span> Reports of the Stockholm Academy.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_219_219" id="Footnote_219_219"></a><a href="#FNanchor_219_219"><span class="label">[219]</span></a> Stahl, taking up the obscure notions of Becher and Van Helmont, -supposed the phenomena of combustion to be due to -phlogiston. He imagined that by combination with phlogiston, a -body was rendered combustible, and that its disengagement -occasioned combustion, and after its evolution there remained -either an acid or an earth: thus sulphur was, by this theory, supposed -to be composed of phlogiston and sulphuric acid, and lead -of the calx of lead and phlogiston, &c.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_220_220" id="Footnote_220_220"></a><a href="#FNanchor_220_220"><span class="label">[220]</span></a> Being called upon by the Solicitor for the Admiralty to examine -into the causes of the fire which destroyed the <i>Imogene</i> -and <i>Talavera</i>, in Devonport Arsenal, I discovered a bin under the -roofing which covered these ships, in which there had been accumulating -for a long period all the refuse of the wheelwrights’ and -painters’ shop; and it was quite evident that spontaneous combustion -had taken place in the mass of oiled oakum, sawdust, anti-attrition, -and old sail-cloth, there allowed to accumulate.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_221_221" id="Footnote_221_221"></a><a href="#FNanchor_221_221"><span class="label">[221]</span></a> <i>Researches on Flame</i>: Sir H. Davy’s Collected Works.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_222_222" id="Footnote_222_222"></a><a href="#FNanchor_222_222"><span class="label">[222]</span></a> See note, <i>ante</i>, <i>On the Chemical Theory of Respiration</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_223_223" id="Footnote_223_223"></a><a href="#FNanchor_223_223"><span class="label">[223]</span></a> At the request of the British Association, a committee undertook -the investigation of this subject. Experiments were carried -on by Dr. Daubeny, in the Botanic Gardens at Oxford, and by the -Author, at his residence, Stockwell. Dr. Daubeny, in his report -made at the meeting of the British Association at Birmingham, -appears disposed to consider ten per cent. of carbonic acid in excess -as destructive to the growth of ferns. I found, however, that, -by gradually increasing the quantity, the ferns would live in an -atmosphere still more highly charged with carbonic acid.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_224_224" id="Footnote_224_224"></a><a href="#FNanchor_224_224"><span class="label">[224]</span></a> See memoir <i>On the Pilchard</i>, by Mr. Couch, in the Reports of -the Royal Cornwall Polytechnic Society.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_225_225" id="Footnote_225_225"></a><a href="#FNanchor_225_225"><span class="label">[225]</span></a> “This scale, in which the humidity of the air is expressed, is -the simple natural scale in which air at its maximum of humidity -(<i>i.e.</i>, when it is saturated with vapour) is reckoned as = 100, and -air absolutely deprived of moisture as = 0; the intermediate degrees -are given by the fraction 100 × actual tension of vapour ÷ -tension required for the saturation of the air at its existing temperature. -Thus, if the air at any temperature whatsoever contains -vapour of half the tension, which it would contain if saturated, -the degree is 50; if three-fourths, then 75; and so forth. Air -of a higher temperature is capable of containing a greater quantity -of vapour than air of less temperature; but it is the proportion of -what it does contain, to what it would contain if saturated, which -constitutes the measure of its dryness or humidity. The capacity -of the air to contain moisture being determined by its temperature, -it was to be expected that an intimate connection and dependence -would be found to exist between the annual and diurnal variations -of the vapour and of the temperature.”—Sabine, <i>On the Meteorology -of Toronto</i>; Reports of the British Association, vol. xiii. p. -47. <i>The Temperature Tables</i>: by Prof. W. H. Dove; Reports for -1847 should be consulted.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_226_226" id="Footnote_226_226"></a><a href="#FNanchor_226_226"><span class="label">[226]</span></a> Sir David Brewster’s <i>Optics</i>, and Memoirs in the Philosophical -Transactions. Sir John Herschel’s Treatise on <i>Light</i>, Encyclopædia -Metropolitana.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_227_227" id="Footnote_227_227"></a><a href="#FNanchor_227_227"><span class="label">[227]</span></a> <i>On the Colour of Steam under certain circumstances</i>: by Professor -Forbes; Philosophical Magazine, vol. xiv. p. 121, vol. xv. -p. 25. In the first paper the following remarks occur:—“I cannot -doubt that the colour of watery vapour under certain circumstances -is the principal or only cause of the red colour observed in -clouds. The very fact that that colour chiefly appears in the presence -of clouds is a sufficient refutation of the only explanation -of the phenomena of sunset and sunrise, having the least plausibility, -given by optical writers. If the red light of the horizontal -sky were simply complementary to the blue of a pure atmosphere, -the sun ought to set red in the clearest weather, and then most of -all; but experience shows that a lurid sunrise or sunset is <i>always</i> -accompanied by clouds or diffused vapours, and in a great -majority of cases occurs when the changing state of previously -transparent and colourless vapour may be inferred from the succeeding -rain. In like manner, terrestrial lights seen at a distance -grow red and dim when the atmosphere is filled with vapour soon -to be precipitated. Analogy applied to the preceding observations -would certainly conduct to a solution of such appearances; for I -have remarked that the existence of vapour of high tension is by -no means essential to the production of colour, though of course a -proportionally greater thickness of the medium must be employed -to produce a similar effect when the elasticity is small.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_228_228" id="Footnote_228_228"></a><a href="#FNanchor_228_228"><span class="label">[228]</span></a> <i>On the Law of Diffusion of Gases</i>: by Thomas Graham, M.A., -F.R.S., &c.; Edinburgh Philosophical Transactions, 1832. <i>Sur -l’Action Capillaire des Fissures, &c.</i>: by Döbereiner; Annales de -Chimie, xxiv. 332.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_229_229" id="Footnote_229_229"></a><a href="#FNanchor_229_229"><span class="label">[229]</span></a> <i>Electro-chemical Researches on the Decompositions of the Earths, -with observations on the Metals obtained from the Alkaline Earths, -and on the Amalgam procured from Ammonia</i>: by Sir Humphry -Davy; Philosophical Transactions, 1808, and collected works, -vol. v. p. 102.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_230_230" id="Footnote_230_230"></a><a href="#FNanchor_230_230"><span class="label">[230]</span></a> <i>Elements of Chemical Philosophy</i>: by Sir H. Davy.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_332" id="Page_332"></a>[Pg 332]</span></p> - - -<h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII.</h2> - -<p class="center">TIME.—GEOLOGICAL PHENOMENA.</p> - - -<p class="chap-head">Time, an element in Nature’s Operations—Geological Science—Its -Facts and Inferences—Nebular Hypothesis applied—Primary -Formations—Plutonic and Metamorphic Rocks—Transition -Series—Palæozoic Rocks—Commencement of -Organic Arrangements—Existence of Phosphoric Acid in -Plutonic Rocks—Fossil Remains—Coal Formation—Sandstones—Tertiary -Formations—Eocene, Miocene, and Pliocene -Formations—Progressive changes now apparent—General -Conclusions—Physics applied in explanation.</p> - - -<p class="p2">The influence of time, as an element, in producing -certain structural arrangements, by modifying the operations -of physical force, under whatever form it may be -exerted, has scarcely been sufficiently attended to in the -examination of cosmical phenomena. Every particle of -matter is, as it were, suspended between the agencies to -which we have been directing our attention. Under the -influences of the physical powers, sometimes exerted in -common, but often with a great preponderance in favour -of one of them, every accumulated heap of mud or sand -is slowly cohering, and assuming the form of a rock -possessing certain distinguishing features, as it regards -lamination, cleavage, &c.</p> - -<p>The minute particles of matter are necessarily but -slightly influenced by the physical forces: their action -in accordance with the laws which determine physical -condition is manifested in an exceedingly modified -degree. But in all the operations of nature, what is<span class="pagenum"><a name="Page_333" id="Page_333"></a>[Pg 333]</span> -deficient in power is made up in time, and effects are -produced during myriads of ages, by powers far too weak -to give satisfactory results by any experiments which -might be extended even over a century.</p> - -<p>If, with the eye of a geologist, we take but a cursory -glance over the Earth, we shall discover that countless -ages must have passed during the progress of this planet -to its present state. This is a fact written by the finger -of nature, in unmistakeable characters, upon the mighty -tablets of her mountains.</p> - -<p>The superficial crust of the earth,—by which is meant -only that film, compared with its diameter, which is -represented by a few miles in depth—is composed of distinct -mineral masses, exhibiting peculiar physical conditions -and a certain order of arrangement. These rocks -appear to have resulted from two dissimilar causes; in -one class the action of heat is evident, and in the other -we have either the slow deposition of matter suspended -in water, or crystallization from solution; an aqueous -origin is indicated by peculiarities of formation in all the -more recent rocks.</p> - -<p>There are few branches of science which admit of -speculation to the extent to which we find it carried in -geology. The consequences of this are shown in the -popular character of the science. A few observations -are made over a limited area, and certain structural conditions -are ascertained, and at once the mind, “fancy -free,” penetrates the profound depths of the earth, and -imagination, having “ample room and verge enough,” -creates causes by which every effect is to be interpreted. -Such students, generally ignorant of the first principles -of physics, knowing little of mineralogy, and less of -chemistry, to say nothing of palæontology, having none -of the requisites for an observer, boldly assume premises -which are untenable, and think they have explained a -phenomenon,—given to the world a truth,—when they -have merely promulgated an unsubstantiated specula<span class="pagenum"><a name="Page_334" id="Page_334"></a>[Pg 334]</span>tion, -<span class="correction" title="In the original book: whieh">which</span> may have occasional marks of ingenuity, and -but little else.</p> - -<p>The carefully-made observations of those who, with -unwearying industry, have traversed hill and valley, -marked and measured the various characters, thicknesses, -inclinations, and positions of rocks; who have watched -the influences of heat in changing, of water in wearing, -and the results of precipitation in forming, strata; who -have traced the mechanical effects of earthquake strugglings -and of volcanic eruptions, and, reasoning from an -immense mass of accumulated facts, deduced certain -general conclusions,—are, however, of a totally different -character; and it is such observers as these who induced -Herschel to say truly, that “geology, in the magnitude -and sublimity of the objects of which it treats, undoubtedly -ranks, in the scale of the sciences, next to -astronomy.”<a name="FNanchor_231_231" id="FNanchor_231_231"></a><a href="#Footnote_231_231" class="fnanchor">[231]</a></p> - -<p>The origin of this planet is involved in great obscurity, -which the powers of the most gifted are unable to penetrate. -It stands the work of an Almighty and Eternal -mind, the beginning of which we cannot comprehend, -nor can we define the period of its termination.</p> - -<p>It may, probably, be safe to speculate that there was -a time when this globe consisted of only one homogeneous -stratum. Whether this remains,—whether, in -our plutonic rocks, our granites, or our porphyries, we -have any indications of the primitive state of the world, -or whether numerous changes took place before even our -unstratified formations had birth, are questions we -cannot answer. The geologist looks back into the vista -of time, and reckons, by phenomena, the progress of the -world’s mutations. The stratified formations must -have occupied thousands of ages; but before these were, -during a period extending over countless thousands, the<span class="pagenum"><a name="Page_335" id="Page_335"></a>[Pg 335]</span> -unstratified rocks may have been variously metamorphosed. -It matters not whether we admit the nebular -hypothesis or not,—a time must have been when all these -bodies which now form the mass of this globe existed in -the most simple state. We have already shown that -very remarkable changes in external character and in -chemical relations are induced, in the same simple -element, by its having been exposed to some peculiar -and different conditions; and already have we speculated -on the probability that the advance of science will enable -us to reduce the numerous elements we now reckon, to -two or three. It is, therefore, by no means an irrational -thought (which must, however, be held in the light of a -pure conjecture), to suppose that at the beginning a -mighty mass of matter, in the most attenuated state, was -produced in space, and was gradually, under the influence -of gravitation, of cohesive force, and of chemical -aggregation, moulded into the form of a sphere. -Ascending to the utmost refinement of physics, we may -suppose that this mass was of one uniform character, -and that it became in dissimilar parts—its surfaces and -towards its centre—differently constituted, under the -influences of the same powers which we now find producing, -out of the same body, charcoal and the diamond, -and creating the multitudinous forms of organized -creations. These conditions being established, and -carried to an extent of which, as yet, science has -afforded us no evidence, chemical intermixture may have -taken place, and a new series of compounds have been -formed, which, by again combining, gave rise to another -and more complex class of bodies.</p> - -<p>The foundation of the superficial crust of the earth -appears to be formed of a class of rocks which have -resulted from the slow cooling of an immense mass of -heated matter. These rocks have been called <i>igneous</i>; -but are now more generally termed <i>Plutonic</i> (such as -granites, syenites, &c.) Immediately above these, we<span class="pagenum"><a name="Page_336" id="Page_336"></a>[Pg 336]</span> -find rocks which have resulted by deposition from -water. These masses, having been exposed to the action -of the heat below, have been considerably changed in -their character, and hence they are often called <i>metamorphic</i>; -but metamorphic rocks may, however, be of -any age. The rocks formerly termed the <i>transition</i> -series—from their forming the connecting link between -the earlier formations—are now, from the circumstance -of their being fossiliferous, classed under the general -term of palæozoic rocks, to distinguish them from the -rocks in which no organic remains have been found. -Above these are found the secondary strata, and, still -more recently produced, we have a class now usually -denominated the tertiary formations. “Eternal as the -hills” is a poetic expression, implying a long duration; -but these must, from the nature of things, eventually -pass away. The period of time necessary for the disintegration -of a granite hill is vastly beyond the powers -of computation, according to our conception of the -ordinary bounds of finite things. But a consideration -of the results of a few years,—under the influence of -the atmosphere and the rains,—as shown in quantity of -solid matter carried off by the rivers, and deposited at -their mouths, will tend to carry conviction to every -mind, that a degrading process is for ever in action on -the surface of the earth. The earth itself may be -eternal, but the surface is continually undergoing mutation, -from various causes, many of which we must -briefly consider.<a name="FNanchor_232_232" id="FNanchor_232_232"></a><a href="#Footnote_232_232" class="fnanchor">[232]</a></p> - -<p>In regarding geological phenomena, the absence of<span class="pagenum"><a name="Page_337" id="Page_337"></a>[Pg 337]</span> -any fossil remains has often been supposed to indicate a -period previous to any organic formations. The inorganic -constituents of matter are probably of prior origin -to the organic combinations; the vessel was constructed, -upon which the organic creation was to float in space -before any vital organisms were created. The supposed -evidences in favour of the assumption that there was no -organic life during the formation of the oldest rocks we -know, are in some respects doubtful; and we can well -understand that changes may have been induced in the -earlier rock formations, by heat or by other powers, quite -sufficient to destroy all traces of organized forms. It -was long thought that phosphoric acid was not to be -detected in rocks which are regarded as of igneous origin; -and since this acid is peculiarly a constituent of organic -bodies, this has been adduced as a proof that the plutonic -rocks must have existed previously to the appearance of -vegetable or animal life upon the surface of the globe. The -researches of modern chemists have, however, shown that -phosphoric acid is to be found in formations of granitic -origin, in porphyry, basalt, and hornblende rocks.<a name="FNanchor_233_233" id="FNanchor_233_233"></a><a href="#Footnote_233_233" class="fnanchor">[233]</a> If, -therefore, we are to regard this substance as of organic -<span class="correction" title="In the original book: orgin">origin</span>, the rational inference is against the speculation; -but there is no more necessity for supposing phosphorus -to be formed in the animal economy than in the mineral -kingdom, from which it will probably be found the -animal obtained it.</p> - -<p>Without attempting to enter into any account of the -apparent progress of life over the earth, it appears -desirable that some description should be given of the -kinds of plants and animals which we know to have -existed at different epochs. We shall thus learn, at least, -some of the prevailing characteristics of the earth during<span class="pagenum"><a name="Page_338" id="Page_338"></a>[Pg 338]</span> -its transitions, and be in a better condition for applying -our knowledge of physical power to the explanation of -the various geological phenomena.</p> - -<p>Among the earliest races we have those remarkable -forms, the trilobites, inhabiting the ancient ocean.</p> - -<p>These crustacea bear some resemblance, although a -very remote one, to the common wood-louse, and, like -that animal, they had the power of rolling themselves -into a ball when attacked by an enemy. The eye of the -trilobite is a most remarkable organ; and in that of one -species, <i>Phacops caudatus</i>, not less than two hundred and -fifty lenses have been discovered. This remarkable -optical instrument indicates that these creatures lived -under similar conditions to those which surround the -crustacea of the present day.</p> - -<p>At the period of the trilobites of the Silurian rocks, -all the animals contemporaneous with them had the -organs necessary for the preservation of life in the -waters.</p> - -<p>Next in order of time to the trilobite, the most singular -animals inhabiting those ancient seas, whose remains -have been preserved, are the <i>Cephalopoda</i>, possessing -some traces of organs which belong to vertebrated -animals. There are numerous arms for locomotion and -prehension, arranged in a centre round the head, which -is furnished with a pair of sharp, horny mandibles, -embedded in powerful muscles. These prehensile arms -are provided with a double row of suckers, by which the -animal seized its prey. Of these cephalopodous animals -there are many varieties, but all of them appear to be -furnished with powers of rapid locomotion, and those -with shells had an hydraulic arrangement for sinking -themselves to any depth of the seas in which, without -doubt, they reigned the tyrants.</p> - -<p>Passing by without notice the numerous fishes, which -appear to have exhibited a similar order of progression -to the other animals, we must proceed to the more<span class="pagenum"><a name="Page_339" id="Page_339"></a>[Pg 339]</span> -remarkable period when the dry land first began to -appear.</p> - -<p>All the animals found in the strata we have mentioned -are such as would inhabit the seas; but we gradually -arrive at distinct evidence of the separation of the land -from the water, and the “green tree yielding seed” -presents itself to our attention; not that the strata -earlier than this are entirely destitute of any remains -indicating vegetable growth, but those they exhibit are -such as, in all probability, may be referred to marine -plants.</p> - -<p>Those plants, however, which are found in the carboniferous -series are most of them distinguished by all -the characteristics of those which grow upon the land; -we, therefore, in the mutilated remains of vegetation left -us in our coal-formations, read the history of our early -world.</p> - -<p>Then the reed-like calamite bowed its hollow and -fragile stems over the edges of the lakes the tree-ferns -grew luxuriantly in the shelter of the hills, and gave a -wild beauty to the humid valleys; the lepidodendrons -spread themselves in mighty forests along the plains, -which they covered with their curious cones; whilst the -sigillariæ extended their multitudinous branches, wreathing -like serpents amongst the luxurious vegetation, and embraced, -with their roots (stigmariæ), a most extensive -space on every side.<a name="FNanchor_234_234" id="FNanchor_234_234"></a><a href="#Footnote_234_234" class="fnanchor">[234]</a></p> - -<p>The seas and lakes of this period abounded with -minute animals nearly allied to the coral animals, which -are now so actively engaged in the formation of islands -in the tropical and southern seas. During the ages -which passed by without any remarkable disturbance of<span class="pagenum"><a name="Page_340" id="Page_340"></a>[Pg 340]</span> -the surface of the earth, the many bands of mountain -limestone were formed by the ceaseless activity of these -minute architects. Encrinites (creatures in some respects -resembling star-fish) existed in vast numbers in the -oceans of this time; and the great variety of bivalve -shells, and those of a spiral character, discovered in the -rocks of this period, show the waters of the newer palæozoic -period to have been instinct with life.</p> - -<p>In the world then, as it does now, water acting on -the dry land produced remarkable changes. We have -evidence of extensive districts over which the most -luxuriant vegetation must have spread for ages,—from -the remains of plants in every state of decay,—which we -find went to form our great coal-fields. These, by some -changes in the relative levels of land and water, became -covered with this fluid; and over this mass of decaying -organic matter, sand and mud were for ages being deposited. -At length, rising above the surface, it becomes -covered with vegetation, which is, after a period, submerged; -the same deposition of sand and mud again -takes place, it is once more fitted for vegetable growth, -and thus, cycle after cycle, we see the dry land and the -water changing places with each other. This will be -evident to every one who will carefully contemplate a -section of one of the coal-fields of Great Britain. We -find a stratum of coal lying upon a bed of under clay, and -above it an extensive stratum of shale or sandstone, probably -formed by the denudation of the neighbouring -hills; and in this manner we have many strata of coal, -shale, clay, ironstone, and sandstone alternating with -each other; the coal-formations of the South Wales coal-field -having the extraordinary thickness of 1500 feet. -The lowest bed of this extensive series must at one time -have been exposed as the surface of the country.</p> - -<p>Ascending in the series, we have now formations of a -more recent character, in which fishes of a higher order -of organization, creeping and flying saurians, crocodiles<span class="pagenum"><a name="Page_341" id="Page_341"></a>[Pg 341]</span> -and lizards, tortoises, serpents, and frogs, are found. -The lias formations (a term corrupted from <i>layers</i>), consisting -of strata in which an argillaceous character -prevails, stand next in series. In these we have animals -preserved in a fossil state, of a distinguishingly different -character from those of the inferior strata. We meet -with extended beds of pentacrinites, some inches in -thickness; and their remains are often so very complete -that every part of the skeleton can be made out, although -so complicated that it cannot consist of less than 150,000 -parts. In these formations we often find the curiously -beautiful remains of the ammonites, of which a great -variety have been discovered. Of the belemnites—animals -furnished with the shell and the ink-bag of the -cuttle-fish, with which it darkened the water to hide -itself from enemies, numerous varieties have also been -disentombed, with the ink-bag so well preserved, that -the story of the remarkable fossil has been written with -its own ink. In addition to these we find nautili; and -sixty species of extinct fishes have been described by -Agassiz from the lias of Lyme Regis alone.</p> - -<p>When these rocks were in the progress of formation, -there existed the ichthyosaurus, or fish-lizard, which -appears, in many respects, to have resembled the crocodile -of the Nile. It was a predatory creature of enormous -power, and must have been the tyrant and terror -of the seas which it inhabited. Its alligator-like jaws, -its powerful eye, its fish-like fins, and turtle-like paddles, -were all formed to facilitate its progress as a destructive -minister. The plesiosaurus was, if possible, a still more -extraordinary creation. To the head of a lizard was -united an enormously long neck, a small and fish-like -body, and the tail of a crocodile: it appears formed for -existence in shallow waters, so that, when moving at -the bottom, it could lift its head above the surface for -air, or in search of its food. The flora of this period<span class="pagenum"><a name="Page_342" id="Page_342"></a>[Pg 342]</span> -must have been extensive; and it resembled the vegetation -which exists at present in Tropical regions.</p> - -<p>We pass now to a new epoch, which is well distinguished -by its animals from all that had preceded -it. Races of reptiles still have place upon the earth, -and we have now the megalosaurian remains; these -animals possessing a strength and rapacity which would -render them objects of terror as well as astonishment, -could they be restored to the world which they once -ravaged. An enormous bat-like creature also existed -at this time—the pterodactyl—which, in the language -of Cuvier, was, “undoubtedly, the most extraordinary -of all the beings of whose former existence a knowledge -is granted to us, and that which, if seen alive, would -appear most unlike anything that exists in the present -world.” “You see before you,” says the same writer, -“an animal which, in all points of bony structure, from -the teeth to the extremities of the nails, presents the -well-known saurian characteristics, and of which no one -can doubt that its integuments and soft parts, its scaly -armour and its organs of circulation and reproduction, -are likewise analogous. But it was, at the same time, -an animal provided with the means of flying; and, when -stationary, its wings were probably folded back like -those of a bird, although, perhaps, by the claws attached -to its fingers, it might suspend itself from the branches -of trees.”<a name="FNanchor_235_235" id="FNanchor_235_235"></a><a href="#Footnote_235_235" class="fnanchor">[235]</a></p> - -<p>From the disintegration of the older rocks have no -doubt arisen those formations which are known as the -oolitic series. In these strata are preserved the remains -of plants and animals more resembling those which now -exist upon the earth; and, for the first time,—unless -the evidence of the footsteps of birds on the new red<span class="pagenum"><a name="Page_343" id="Page_343"></a>[Pg 343]</span> -sandstone of America be accepted,—we meet with the -remains of the feathered tribes.</p> - -<p>In these formations we discover animals belonging to -the class Mammalia,—the amphitherium and the phascolotherium,—which -appear to have resembled, in many -respects, the marsupial animals of New Holland.<a name="FNanchor_236_236" id="FNanchor_236_236"></a><a href="#Footnote_236_236" class="fnanchor">[236]</a></p> - -<p>The wealden formations, which are the next in order -of position, are a series of clays and sands, with subordinate -beds of limestone, grit, and shale. These have, -in some instances, been formed in the sea; but they are -usually regarded as fresh-water deposits. All the older -rocks bear evident marks of marine origin, unless some -of the coal-measure strata may be regarded as otherwise; -but nearly all the wealden series contain the -remains of land, fresh-water, and estuary animals, and -of land vegetables. The creatures which we discover, -preserved, to tell the history of this period, are numerous, -and have marked peculiarities to distinguish them -from those already described, or from any now existing -on the earth. We find land saurians of a large kind, -and animals of all sizes; even insects, of which a great -variety are found in the wealds. The remarkable -iguanodon was an animal which, even by the cautious -measurement of Professor Owen, must have been at -least twenty-eight feet long; and this enormous creature -was suspected, by Cuvier, and has been proved by Owen, -to have been an “herbivorous saurian for terrestrial -life.”<a name="FNanchor_237_237" id="FNanchor_237_237"></a><a href="#Footnote_237_237" class="fnanchor">[237]</a> Dr. Mantell calculates that no less than seventy -individuals of the iguanodon of all ages have come -under his notice; and the bones of a vast number of -others must have been broken up by the workmen in<span class="pagenum"><a name="Page_344" id="Page_344"></a>[Pg 344]</span> -the few quarries of Tilgate grit; so that these creatures -were by no means rare at the period of their existence.<a name="FNanchor_238_238" id="FNanchor_238_238"></a><a href="#Footnote_238_238" class="fnanchor">[238]</a></p> - -<p>The uppermost of these secondary formations is the -cretaceous or chalk group, which spreads over a large -portion of south-eastern England, and is met with in all -parts of Europe. This chalk, which is a carbonate of -lime, appears to have been slowly precipitated from -tranquil water, as, according to Sir Henry De la Beche, -organic remains are beautifully preserved in it. Substances -of no greater solidity than common sponges -retain their forms, delicate shells remain unbroken, fish -even are frequently not flattened, and altogether we -have the appearances which justify us in concluding -that, since these organic exuviæ were entombed, they -have been protected from pressure by the consolidation -of the rock around them.<a name="FNanchor_239_239" id="FNanchor_239_239"></a><a href="#Footnote_239_239" class="fnanchor">[239]</a></p> - -<p>Beneath the chalk exists what has been called, from -its colour—derived from a silicate of the protoxide of -iron,—green sand, and was, no doubt, formed by deposition -from the same water in which the carbonate of -lime was suspended,—the green sand falling to the -bottom more readily from its greater specific gravity. -“The tranquillity,” observes Sir Henry De la Beche, -“which seems to have prevailed during this great -accumulation of siliceo-calcareous matter, whether it -may have been a deposit from water, in which it was -mechanically suspended, partly the work of living -creatures, or in a great measure chemical, is very -remarkable.”<a name="FNanchor_240_240" id="FNanchor_240_240"></a><a href="#Footnote_240_240" class="fnanchor">[240]</a></p> - -<p>In the chalk, the remains of the leaves of dicotyledonous -plants and fragments of wood are found more -abundantly than in the earlier strata, many of which<span class="pagenum"><a name="Page_345" id="Page_345"></a>[Pg 345]</span> -are marked with the perforations of marine worms, -indicating that they had floated for some time in the -ocean. It should, however, be remembered, that these -are not the first indications of vegetable life,—leaves -have been found in the new red sandstone; and the -flora of the coal formation must not be forgotten. The -manner in which silica has deposited itself on organic -bodies—such as the sponges—is curious; the whole of -the organized tissue being often removed, and flint -having taken its place. Flints formed by such a process -as this abound in the upper chalk. The association of -carbon and silicon, combined with oxygen, as we find -them in the cretaceous formations, is most interesting, -and naturally gives rise to some speculation on the -relation of these two elements. Both carbon and -silicon, as has been already shown, exist in several allotropic -conditions; and, although the statements -made by Dr. Brown relative to the conversion of carbon -into silicon are proved to be grounded on experimental -error, it is not improbable that a very intimate relation -may exist between these elements.<a name="FNanchor_241_241" id="FNanchor_241_241"></a><a href="#Footnote_241_241" class="fnanchor">[241]</a> The probability is, -that the sponge animal has the power of secreting silica -to give strength to its form. “Many species,” says -Rymer Jones, speaking of recent sponges, “exhibiting -the same porous structure, have none of the elasticity of -the officinal sponge—a circumstance which is due to the -difference observable in the composition of their -skeletons or ramified frame-work. In such the living -crust forms within its substance not only tenacious -bands of animal matter, but great quantities of crystal<span class="pagenum"><a name="Page_346" id="Page_346"></a>[Pg 346]</span>lized -spicula, sometimes of a calcareous, at others of a -siliceous, nature.” Thus, a frame of siliceous matter -being formed by the living animal, a deposition of the -same substance is continued after death.</p> - -<p>Sea-urchins and star-fish, and numerous fossil shells, -are found in these beds, which, however, differ materially -from the remains of the same animals found in the -earlier formations. A vast number of new species and -genera of fish are also discovered in the chalk.</p> - -<p>Nearly all the animals and plants which existed up to -this period are now extinct, although they have some -imperfect representatives at the present day.</p> - -<p>The uppermost group, which has been called the -supercretaceous or tertiary formation, appears in our -island to have been formed during four great eras, as -we find fresh-water deposits alternating with marine -ones. The term <i>eocene</i>, which is the first or oldest -deposit; <i>miocene</i>, which is the second; <i>pliocene</i>, which -is the third; and the <i>newer pliocene</i>,—which is the fourth -and last, have been applied to these formations, the -names referring to the respective proportions of existing -species found among their fossil shells.<a name="FNanchor_242_242" id="FNanchor_242_242"></a><a href="#Footnote_242_242" class="fnanchor">[242]</a></p> - -<p>All these formations show distinct evidence of their -having been deposited from still or slowly-flowing deep -waters. Thus the eocene appears in the Paris basin,—formed -clearly at an estuary, in which are mingled some -interesting fresh-water deposits;—in the lacustrine -formations in Auvergne; also at Aix; and in the north -of Italy. It appears probable that, in the formations -generally termed eocene, both fresh-water and marine -deposits have been confounded, and several formations -of widely-different eras regarded as the result of one. -We have not yet been furnished with any distinct and -clear evidence to show that the deposits of the Paris<span class="pagenum"><a name="Page_347" id="Page_347"></a>[Pg 347]</span> -basin, and those of Auvergne, are of the same age. -At all events, it is sufficient for our present purpose to -know that they are the result of actions which are now -as general as they were when the plastic clay of Paris, -and its sulphate of lime, or the London clay, were slowly -deposited.</p> - -<p>As a general conclusion, we may decide that, at the -eocene period, existing continents were the sites of vast -lakes, rivers, and estuaries, and were inhabited by quadrupeds, -which lived upon their thickly-wooded margins. -Many remains, allied to those of the hippopotamus, have -been found in the subsidences of this period.</p> - -<p>Examples of the miocene or middle tertiary era are -to be found in Western France, over the whole of the -great valley of Switzerland, and the valley of the Danube. -In these deposits we find the bones of the rhinoceros, -elephant, hippopotamus, and the dinotherium, an extinct -animal, possessing many very distinguishing features.<a name="FNanchor_243_243" id="FNanchor_243_243"></a><a href="#Footnote_243_243" class="fnanchor">[243]</a></p> - -<p>The pliocene period has been termed the age of -elephants, and is most remarkable for the great mastodons -and gigantic elks, with other animals not very -unlike those which are contemporaneous with man.</p> - -<p>In the superficial layers of the earth, the diluvium, -alluvium, peat and vegetable soil, we have a continuation -of the history of the mutations of our globe and of its -inhabitants, which has been here so briefly sketched. They -bring us up to the period when man appeared in the -world, since whose creation it is evident no very extensive -change has been produced upon the surface. We -have viewed the phenomena of each great epoch, marked -as they are by new creations of organized beings, and it -would appear as if, through the whole series, from the<span class="pagenum"><a name="Page_348" id="Page_348"></a>[Pg 348]</span> -primary rocks up to the modern alluvial deposits, a progressive -improvement of the earth’s surface had been -effected, to fit it at last for the abode of the human -race.</p> - -<p>Thus have we preserved for us, in a natural manner, -evidences which, if we read them aright, must convince -us that the laws by which creation has ever been regulated -are as constant and unvarying as the Eternal mind -by which they are decreed. Our earth, we find, by the -records preserved in the foundation-stones of her mountains, -has existed through countless ages, and through -them all exhibited the same active energies that prevail -at the present moment. By precisely similar influences -to those now in operation, have rocks been formed, -which, under like agencies, have been covered with -vegetation, and sported over by, to us, strange varieties -of animal life. Every plant that has grown upon the -earliest rocks which presented their faces to the life-giving -sun, has had its influence on the subsequent -changes of our planet. Each trilobite, each saurian, -and every one of the mammalia which exist in the fossil -state, have been small laboratories in which the great -work of eternal change has been carried forward, and, -under the compulsion of the strong laws of creation, -they have been made ministers to the great end of forming -a world which might be fitting for the presence of a -creature endued with a spark taken from the celestial -flame of intellectual life.</p> - -<p>For a few moments we will return to a consideration -of the operations at present exhibiting their phenomena, -and examine what bearing they have upon our knowledge -of geological formations.</p> - -<p>During periods of immense, but unknown, duration, -the ocean and the dry land are seen to have changed -their places. Enormous deposits, formed at the bottom -of the sea, are lifted by some mechanical, probably -volcanic, force, above the waters, and the land, like the<span class="pagenum"><a name="Page_349" id="Page_349"></a>[Pg 349]</span> -ocean surrounding it, teems with life. This state of -things lasts for ages; but the time arrives when the -ocean again floods the land, and a new state of things, -over a particular district, has a beginning.</p> - -<p>It must not be imagined that the changes which we have -spoken of, as if they were the result of slow decay and -gradual deposit, were effected without occasional violent -convulsions. Many of the strata which were evidently -deposited at the bottom of the sea, and, of course, as -horizontal beds, are now found nearly vertical. We -have evidence of strata of immense thickness having -been subjected to forces that have twisted and contorted -them in a most remarkable manner. Masses of solid -rock, many thousand feet deep, are frequently bent and -fractured throughout their whole extent. Mountains -have been upheaved by internal force, and immense -districts have suddenly sunk far below their usual level. -By the expansive force due to that temperature which -must be required to melt basaltic and trap rocks, the -whole of the superficial crust of a country has been -heaved to a great height, immense fissures have been -formed by the breaking of the mass, and the melted -matter has been forced through the opening, and overflowed -extensive districts, or volcanoes have been formed, -and wide areas have been buried under the ashes ejected -from them. With the cause of these convulsions we -are at present unacquainted.</p> - -<p>We have evidence of the extent to which these forces -may be exerted, in the catastrophes which have occurred -within historical times, and which have happened even -in our own day. Herculaneum and Pompeii, buried -under the lava and ashes of Vesuvius, in an hour when -the inhabitants of these cities were unprepared for such -a fearful visitation,—the frightful earthquakes which -have, from time to time, occurred in South America—are -evidences of the existence of hidden forces which -shake the firm-set earth. Similar ravaging catastrophes<span class="pagenum"><a name="Page_350" id="Page_350"></a>[Pg 350]</span> -may have often occurred, and, involving cataclysms, -swept the surface to produce the changes we detect over -every part of the earth, compared with which the earthquakes -and floods of history are but trivial things. -Evidence has been adduced, to show that the mountains -of the Old World may have approached in height the -highest of the Andes or Himalayas, and these have not -been destroyed by any sudden effect, but by the slow -disintegrating action of the elements.<a name="FNanchor_244_244" id="FNanchor_244_244"></a><a href="#Footnote_244_244" class="fnanchor">[244]</a> All these -phenomena are now in progress: the winds and the -rains wear the faces of the exposed rock; their <i>débris</i>, -mixed with decayed vegetable and animal matter, are -washed off from the surface, and borne away by the -rivers, to be deposited in the seas. Thus it is that the -great delta of the Ganges is formed, and that a continual -increase of matter is going on at the mouths of rivers. -The Amazon, the Mississippi, and other great rivers, -bear into the ocean, daily, thousands of tons of matter -from the surface of the earth.<a name="FNanchor_245_245" id="FNanchor_245_245"></a><a href="#Footnote_245_245" class="fnanchor">[245]</a> This is, of course, de<span class="pagenum"><a name="Page_351" id="Page_351"></a>[Pg 351]</span>posited -at the bottom of the sea, and it must, in the -process of time, alter the relative levels of the ocean -and the land. Islands have been lifted by volcanic -power from the bottom of the sea, and many districts -in South America have been depressed by the same -causes.</p> - -<p>Changes as extensive have been, in all probability, -effected by forces “equally or more powerful, but acting -with less irregularity, and so distributed over time as to -produce none of those interregnums of chaotic anarchy -which we are apt to think (perhaps erroneously) great -disfigurements of an order so beautiful and harmonious -as that of nature.”<a name="FNanchor_246_246" id="FNanchor_246_246"></a><a href="#Footnote_246_246" class="fnanchor">[246]</a> These forces are, without doubt, -even now in action.</p> - -<p>Had it not been for these convulsive disturbances of the -surface, the earth would have presented an almost uniform -plain, and it would have been ill-adapted for the -abode of man. The hills raised by the disturbances of -nature, and the valleys worn by the storms of ages, -minister especially to his wants, and afford him the -means of enjoyment which he could not possess had the -surface been otherwise formed. The “iced mountain -tops,” condensing the clouds which pass over them, send -down healthful streams to the valleys, and supply the<span class="pagenum"><a name="Page_352" id="Page_352"></a>[Pg 352]</span> -springs of the earth, thus securing the fertility and -salubrity of the distant plains. The severities of climate -are mitigated by these conditions, and both the people -of the tropics and those dwelling near the poles are -equally benefited by them.</p> - -<p>Gravitation, cohesion, motion, chemical force, heat, -and electricity, must, from that hypothetical time when -the earth floated a cloud of nebulous vapour, in a state -of gradual condensation up to the present moment, have -been exercising their powers, and regulating the mutations -of matter.</p> - -<p>When the dry land was beneath the waters, and when -darkness was upon the face of the deep, the same great -operations as those which are now in progress in the -depths of the Atlantic, or in the still waters of our -inland lakes, were in full activity. At length the dry -land appears; and—mystery of mysteries—it soon -becomes teeming with life in all the forms of vegetable -and animal beauty, under the aspect of the beams of a -glorious sun.</p> - -<p>Geology teaches us to regard our position upon the -earth as one far in advance of all former creations. It -bids us look back through the enormous vista of time, -and see, shining still in the remotest distance, the light -which exposes to our vision many of nature’s holy -wonders. The elements which now make up this -strangely beautiful fabric of muscle, nerves, and bone, -have passed through many ordeals, ere yet it became -fashioned to hold the human soul. No grain of matter -has been added to the planet, since it was weighed in a -balance, and poised with other worlds. No grain of -matter can be removed from it. But in virtue of those -forces which seem to originate in the sun, “the soul of -the great earth,” a succession of new forms has been -produced, as the old things have passed away.</p> - -<p>Under the forces we have been considering, acting as -so many contending armies, matter passes from one<span class="pagenum"><a name="Page_353" id="Page_353"></a>[Pg 353]</span> -condition to another, and what is now a living and a -breathing creature, or a delicate and sweetly-scented -flower, has been a portion of the amorphous mass which -once lay in the darkness of the deep ocean, and it will -again, in the progress of time, pass into that condition -where no evidences of organization can be found,—again, -perhaps, to arise clothed with more exalted powers than -even man enjoys.</p> - -<p>When man places himself in contrast with the Intelligences -beyond him, he feels his weakness; and the -extent of power which he can discover at work, guided -by a mysterious law, is such, that he is dwarfed by its -immensity. But looking on the past, surveying the -progress of matter through the inorganic forms up to -the higher organizations, until at length man stands -revealed as the chief figure in the foreground of the -picture, the monarch of a world on which such elaborate -care has been bestowed, and the absolute ruler of all -things around him, he rises like a giant in the conscious -strength of his far-searching mind. That so great, -so noble a being, should suffer himself to be degraded by -the sensualities of life to a level with the creeping things, -upon which he has the power to tread, is a lamentable -spectacle, over which angels must weep.</p> - -<p>The curious connection between the superstitions of -races, the traditionary tales of remote tribes, and the -developments of the truths of science, are often of a -very marked character, and they cannot but be regarded -as instructive. In the wonders of “olden time” fiction -has ever delighted; and a thousand pictures have been -produced of a period when beings lived and breathed -upon the earth which have no existence now.</p> - -<p>Hydras, harpies, and sea-monsters, figure in the myths -of antiquity. In the mythology of the northern races -of Europe we have fiery flying dragons, and Poetry has -placed these as the guardians of the “hoarded spirit” -and protectors of the enchanted gold.</p> - -<p><span class="pagenum"><a name="Page_354" id="Page_354"></a>[Pg 354]</span></p> - -<p>Through the whole of the romance period of European -literature, nothing figures but serpents, “white and -red,” toiling and fighting underground,—thus producing -earthquakes, as in the story of Merlin and the building -of Stonehenge. Flying monsters, griffins and others, -which now live only in the meaningless embellishments -of heraldry, appear to have been conceived by the earlier -races of men as the representatives of power. Curious -is it, too, to find the same class of ideas prevailing in -the East. The monster dragons of the Chinese, blazoned -on their standards and ornamenting their temples;—the -Buddaical superstition that the world is supported -on a vast elephant, which stands on the back of a tortoise, -which again rests on a serpent, whose movements -produce earthquakes and violent convulsions;—the rude -decorations also of the temples of the Aztecs, which -have been so recently restored to our knowledge by the -adventurous travellers of Central America,—all give -expression to the same mythological idea.</p> - -<p>Do not these indicate a faint and shadowy knowledge -of a previous state of organic existence? The process -of communion between man of the present, and the -creations of a former world, we know not; it is -mysterious, and for ever lost to us. But even the most -ignorant and uncultivated races of mankind have figured -for themselves the images of creatures which, whilst -they do really bear some resemblance to things which -have for ever passed away, do not, in the remotest -degree, partake of any of the peculiarities of existing -creations.</p> - -<p>The ichthyosaurus, and the plesiosaurus, and the -pterodactylus, are preserved in the rude images of -harpies, of dragons, and of griffins; and, although the -idea of an elephant standing on the back of a tortoise -was often laughed at as an absurdity, Captain Cautley -and Dr. Falconer at length discovered in the hills of -Asia the remains of a tortoise in a fossil state of such a<span class="pagenum"><a name="Page_355" id="Page_355"></a>[Pg 355]</span> -size that an elephant could easily have performed the -feat.<a name="FNanchor_247_247" id="FNanchor_247_247"></a><a href="#Footnote_247_247" class="fnanchor">[247]</a></p> - -<p>Of the ammonites, we have more exact evidence; -they were observed by our forefathers, and called by -them snake-stones. According to the legends of Catholic -saints they were considered as possessing a sacred -character:—</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“Of these and snakes, each one</div> -<div class="verse">Was changed into a coil of stone</div> -<div class="verse">When holy Hilda prayed.”</div> -</div></div></div> - -<p>And in addition to this petrifying process, one of -decapitation is said to have been effected; hence the -reason why these <i>snake-stones</i> have no heads.</p> - -<p>We also find, in the northern districts of our island, -that the name of “St. Cuthbert’s beads” is applied to -the fossil remains of encrinites.</p> - -<p>Thus we learn that, to a great extent, fiction is -dependent upon truth for its creations; and we see that -when we come to investigate any wide-spread popular -superstition, although much distorted by the medium of -error through which it has passed, it is frequently -founded upon some fragmentary truth. There are floating -in the minds of men certain ideas which are not the -result of any associations drawn from things around; -we reckon them amongst the mysteries of our being. -May they not be the truths of a former world, of which -we receive the dim outshadowing in the present, like the -faint lights of a distant Pharos, seen through the mists -of the wide ocean?</p> - -<p>Man treads upon the wreck of antiquity. In times -which are so long past, that the years between them -cannot be numbered by the aids of our science, geology<span class="pagenum"><a name="Page_356" id="Page_356"></a>[Pg 356]</span> -teaches us that forms of life existed perfectly fitted for -the conditions of the period. These performed their -offices in the great work; they passed away, and others -succeeded to carry on the process of building a world -for man. The past preaches to the present, and from -its marvellous discourses we venture to infer something -of the yet unveiled future. The forces which have -worked still labour: the phenomena which they have -produced will be repeated.</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">Ages on ages slowly pass away,</div> -<div class="verse">And nature marks their progress by decay.</div> -<div class="verse">The plant which decks the mountain with its bloom,</div> -<div class="verse">Finds in the earth, ere long, a damp dark tomb:</div> -<div class="verse">And man, earth’s monarch, howe’er great and brave—</div> -<div class="verse">Toils on—to find at last a silent grave.</div> -<div class="verse">The chosen labours of his teeming mind</div> -<div class="verse">Fade by the light, and crumble ’neath the wind;</div> -<div class="verse">And e’en the hills, whose tops appear to shroud</div> -<div class="verse">Their granite peaks deep in the vapoury cloud,</div> -<div class="verse">Worn by tempests—wasted by the rains,</div> -<div class="verse">Sink slowly down to fill wide ocean’s plains.</div> -<div class="verse">The ocean’s breast new lands again display,</div> -<div class="verse">And life and beauty drink the light of day:</div> -<div class="verse">The powers which work at great creation’s wheel,</div> -<div class="verse">Will from the wrecks of matter still reveal</div> -<div class="verse">New forms of wondrous beauty—which will rise</div> -<div class="verse">Pure as the flame of love’s young sacrifice,</div> -<div class="verse">Beaming with all the pristine hues of youth,</div> -<div class="verse">Robed by the day, and crowned by holy truth.</div> -</div></div></div> -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_231_231" id="Footnote_231_231"></a><a href="#FNanchor_231_231"><span class="label">[231]</span></a> <i>Preliminary Discourse</i>; Sir J. F. W. Herschel. Lardner’s -Cabinet Cyclopædia.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_232_232" id="Footnote_232_232"></a><a href="#FNanchor_232_232"><span class="label">[232]</span></a> <i>Geological Researches</i>; by Sir Henry De la Beche, C.B. -(<i>Degradation of Mountains</i>, p. 167.) <i>Geological Manual</i>, p. 184. -<i>Principles of Geology</i>; by Sir Charles Lyell, 7th Edition, p. -150, 686. <i>On the Denudation of South Wales, and the adjacent -countries of England</i>; by Professor Andrew Ramsay; Memoirs -of the Geological Survey and Museum of Practical Geology, -vol. i. p. 297.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_233_233" id="Footnote_233_233"></a><a href="#FNanchor_233_233"><span class="label">[233]</span></a> Fownes, <i>On the Existence of Phosphoric Acid in Rocks of -Igneous Origin</i>; Phil. Trans. 1844, p. 53. Nesbitt, <i>Quarterly -Journal of the Chemical Society</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_234_234" id="Footnote_234_234"></a><a href="#FNanchor_234_234"><span class="label">[234]</span></a> <i>On the Vegetation of the Carboniferous Period as compared with -that of the present day; On some peculiarities in the structure of -Stigmaria; Remarks on the Structure and Affinities of some Lepidostrobi</i>: -by Dr. Hooker; Memoirs of the Geological Survey, -&c., vol. ii. pp. 387, 431, 440.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_235_235" id="Footnote_235_235"></a><a href="#FNanchor_235_235"><span class="label">[235]</span></a> See Owen, Quarterly Journal of the Geological Society, No. 6, -p. 96. Dr. Buckland, Geological Transactions, vol. iii. p. 220. -<i>The Wonders of Geology</i>: by Dr. Mantell, vol. ii. p. 493.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_236_236" id="Footnote_236_236"></a><a href="#FNanchor_236_236"><span class="label">[236]</span></a> <i>Report on British Fossil Mammalia</i>: by Richard Owen, Esq., -F.R.S.; British Association Reports, vols. xi. xii.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_237_237" id="Footnote_237_237"></a><a href="#FNanchor_237_237"><span class="label">[237]</span></a> <i>Notice on the Iguanodon, a newly discovered fossil reptile from -the sandstone of Tilgate Forest, in Sussex</i>: by Gideon Mantell, -Esq, F.R.S., &c.; Philosophical Transactions, vol. cxv. p. 179. -<i>On the Structure of Teeth, &c.</i>; by Professor Owen.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_238_238" id="Footnote_238_238"></a><a href="#FNanchor_238_238"><span class="label">[238]</span></a> Dr. Mantell, <i>Wonders of Geology</i>. <i>Geology of the South-east -of England.</i></p></div> - -<div class="footnote"> - -<p><a name="Footnote_239_239" id="Footnote_239_239"></a><a href="#FNanchor_239_239"><span class="label">[239]</span></a> <i>Geological Researches</i>; <i>Geological Manual</i>; by Sir Henry -Thos. De la Beche, C.B., &c.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_240_240" id="Footnote_240_240"></a><a href="#FNanchor_240_240"><span class="label">[240]</span></a> Ibid.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_241_241" id="Footnote_241_241"></a><a href="#FNanchor_241_241"><span class="label">[241]</span></a> <i>Experimental Researches on the production of Silicon from -Paracyanogen</i>: by Samuel Brown, M.D.; Transactions of the -Royal Society of Edinburgh, vol. xv. p. 229. <i>Experiments on the -alleged conversion of Carbon into Silicon</i>: by R. H. Brett, Ph.D., -and J. Denham Smith, Esq.; Philosophical Magazine, vol. xix. -p. 295, New Series. See also Dr. Brown’s reply to the above, -ibid, p. 388.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_242_242" id="Footnote_242_242"></a><a href="#FNanchor_242_242"><span class="label">[242]</span></a> <i>Geology, Introductory, Descriptive, and Practical</i>: by Prof. -Ansted, vol. ii. p. 22.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_243_243" id="Footnote_243_243"></a><a href="#FNanchor_243_243"><span class="label">[243]</span></a> <i>The Wonders of Geology</i>: by Dr. Mantell, vol. i. p. 162. -<i>Bridgewater Treatise</i>: by Dr. Buckland. Dr. J. J. Kemp, and -Dr. A. V. Klipstein, <i>On the Dinotherium</i>; Darmstadt, 1836. -Cuvier and De Blainville have also carefully described the fossil -remains of this animal.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_244_244" id="Footnote_244_244"></a><a href="#FNanchor_244_244"><span class="label">[244]</span></a> See Professor Ramsay’s memoir <i>On Denudation</i>: Memoirs -of the Geological Survey of Great Britain.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_245_245" id="Footnote_245_245"></a><a href="#FNanchor_245_245"><span class="label">[245]</span></a> “The distances to which river water, more or less charged -with detritus, would flow over sea-water, will depend upon a variety -of obvious circumstances. Captain Sabine found discoloured water, -supposed to be that of the Amazons, three hundred miles distant -in the ocean from the embouchure of that river. It was about -126 feet deep. Its specific gravity was = 1·0204, and the specific -gravity of the sea-water = 1·0262. This appears to be the -greatest distance from land at which river water has been detected -on the surface of the ocean. If rivers, containing mechanically -suspended detritus, flowed over sea-water in lines which, in general -terms, might be called straight, the deposit of transported matter -which they carried out would also be in straight lines. If, -however, they be turned aside by an ocean current, as was the -case with that observed by Captain Sabine, the detritus would be -thrown, and cover an area corresponding in a great degree with -the sweep which the river has been compelled to make out of the -course, that its impulse, when discharged from its embouchure, -might lead it to take: supposing the velocity with which this river-water -was moving has been correctly estimated at about three -miles per hour, it is not a little curious to consider that the agitation -and resistance of its particles should be sufficient to keep -finely comminuted solid matter mechanically suspended, so that it -would not be disposed freely to part with it, except at its junction -with the sea-water over which it flows, and where, from friction, -it is sufficiently retarded. So that a river, if it can preserve a -given amount of velocity flowing over the sea, may deposit no -very large amount of mechanically suspended detritus in its course -from the embouchure, where it is ultimately stopped. Still, however, -though the deposit may not be so abundant as at first sight -would appear probable, the constant accumulation of matter, however -inconsiderable at any given time, must produce an appreciable -effect during the lapse of ages.”—Sir Henry De la Beche’s <i>Geological -Researches</i>, p. 72.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_246_246" id="Footnote_246_246"></a><a href="#FNanchor_246_246"><span class="label">[246]</span></a> Sir J. F. W. Herschel: <i>Preliminary Treatise</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_247_247" id="Footnote_247_247"></a><a href="#FNanchor_247_247"><span class="label">[247]</span></a> <i>Fauna Antiqua Sivalensis. Being the Fossil Zoology of the -Sewalik Hills in the North of India</i>: by Hugh Falconer and Proby -T. Cautley. 1844.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_357" id="Page_357"></a>[Pg 357]</span></p> - - -<h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV.</h2> - -<p class="center">PHENOMENA OF VEGETABLE LIFE.</p> - - -<p class="chap-head">Psychology of Flowers—Progress of Matter towards Organization—Vital -Force—Spontaneous Generation—The Vegetable -Cell—Simplest Development of Organization—The -Crystal and the Cell—Primitive Germ—Progress of Vegetation—Influence -of Light—Morphology—Germination—Production -of Woody Fibre—Leaves—Chlorophylle—Decomposition -of Carbonic Acid—Influence of Light, Heat, -and Actinism on the Phenomena of Vegetable Life—Flowers -and Fruits—Etiolation—Changes in the Sun’s Rays with the -Seasons—Distribution of Plants—Electrical and Combined -Physical Powers</p> - - -<p class="p2">The variety of beautiful forms which cover the surface -of this sphere, serve, beyond the physical purposes to -which we have already alluded, to influence the mind, -and give character to the inhabitants of every locality. -There are men who appear to be dead to the mild -influences of flowers; but these sweet blossoms—the -stars of our earth—exert a power as diffusive as their -pervading odours.</p> - -<p>The poet tells us of a man to whom</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">The primrose on the river’s brim</div> -<div class="verse">A yellow primrose was to him,</div> -<div class="verse">And it was nothing more.</div> -</div></div></div> - -<p>But it was something more. He, perhaps, attended not -to the eloquent teaching of its pure, pale leaves: he -might not have been conscious of the mysterious singing -of that lowly flower: he might, perchance, have crushed<span class="pagenum"><a name="Page_358" id="Page_358"></a>[Pg 358]</span> -it beneath his rude foot rather than quaff the draught -of wisdom which it secreted in its cell; but the flower -still ministered to that mere sensualist, and in its -strange, tongueless manner, reproved his passions, and -kept him “a wiser and a better man,“ than if it -had pleased God to have left the world without the -lovely primrose.</p> - -<p>The psychology of flowers has found many students—than -whom not one read them more deeply than that -mild spirit who sang of the Sensitive Plant, and in -wondrous music foreshadowed his own melancholy -fate.<a name="FNanchor_248_248" id="FNanchor_248_248"></a><a href="#Footnote_248_248" class="fnanchor">[248]</a> That martyr to sensibility, Keats, who longed to -feel the flowers growing above him, drew the strong -inspiration of his volant muse from those delicate -creations which exhibit the passage of inorganic matter -into life; and other poets will have their sensibilities -awakened by the æsthetics of flowers, and find a mirror -of truth in the crystal dew-drop which clings so lovingly -to the purple violet, and draws fresh beauties from its -coloured petals.</p> - -<p>If we examine carefully all the conditions of matter -which we have made the subject of our studies, we -cannot but perceive how gradual is the progress of the -involved action of the physical forces, as we advance -from the molecule—the mere particle of matter—up to -the organic combination. At first we detect only the -action of cohesion in forming the rude mass; then we -have the influence of the crystallogenic powers giving -a remarkable regularity to bodies; we next discover the -influences of heat and electrical force in determining -condition, and of chemical action as controlled by them. -Yet, still we have a body without organization. Light -exerts its mysterious powers, and the same elements -assume an organized form; and, in addition to the -recognized agencies, we dimly perceive others on which<span class="pagenum"><a name="Page_359" id="Page_359"></a>[Pg 359]</span> -vitality evidently depends. These empyreal influences -become more and more complicated to us: ascending in -the scale, they rise beyond our science; and, at length, -we find them guiding the power of intelligence, while -instinct and reason are exhibited in immediate dependence -upon them.</p> - -<p>Let it not be imagined that this view has any tendency -to materialism. The vital energy is regarded as a -spiritualization, and reason as a divine emanation; but -they are connected with materialities, on which they -act, and by which they are themselves controlled. The -organic combinations, and the physical powers by which -these unions of matter are effected and retained, have a -direct action over that ethereality which is life, and the -powers of life again control these more material forces. -The spirit, in whatever state, when connected with matter, -is, like Prometheus chained to his rock, in a constant -struggle to escape from its shackles, and assert the full -power of its divine strength.</p> - -<p>We have seen variety enough in the substances which -make up the inorganic part of creation; but infinitely -more varied are the forms of organization. In the -vegetable world which is immediately around us, from -the green slime of our marshes to the lustrous flowers -of our gardens and the lordly trees of our forests, what -an extraordinary diversity of form is apparent! From -the infusoria of an hour, to the gigantic elephant roaming -in his greatness in the forests of Siam—the noble -lion of the caves of Senegal—the mighty condor of the -Andes—and onward to man, the monarch of them all, -how vast are the differences, and yet how complete are -they in their respective conditions! In the creation we -have examined, we have had conclusive evidence, that -from the combination of <i>atoms</i> every peculiar form has -been produced. In the creation we are about to -examine, we shall discover that all the immense diversity -of form, of colour, and condition which is spread over<span class="pagenum"><a name="Page_360" id="Page_360"></a>[Pg 360]</span> -the world in the vegetable and animal kingdoms, results -from the combination of <i>cells</i>. The atom of inorganic -nature becomes a cell in organic creation. This cell -must be regarded as the compound radical of the chemist, -and by decomposing it, we destroy the essential element -of organization.</p> - -<p>With the mysterious process by which the atom is -converted into a cell, or a compound radical, we are unacquainted; -but we must regard the cell as the organic -atom. It is in vain that the chemist or the physiologist -attempts to examine this change of the inorganic elements -to an organized state; it is one of the mysteries of -creation, which is to be, in all probability, hid from our -eyes, until this “mortal coil” is shaken off, and we -enjoy the full powers of that intelligence which we -are promised we shall enjoy in an immortal state.</p> - -<p>Again and again has the attention of men been -attracted to the <i>generatio æquivoca</i>; they have sometimes -thought they have discovered a <i>generatio primitiva</i> -or <i>spontanea</i>; but a more careful examination of these -organisms has shown that an embryo existed—a real -germination has taken place.</p> - -<p>Count Rumford<a name="FNanchor_249_249" id="FNanchor_249_249"></a><a href="#Footnote_249_249" class="fnanchor">[249]</a> stated that threads of silk and -wool had the power of decomposing carbonic acid -in water in the sunshine; and hence some have referred -organization to a mere chemical change produced -by luminous excitation; and we have heard of -animal life resulting from pounded siliceous matter. All -such statements must be regarded as evidences of imperfect -investigation.</p> - -<p>Dr. Carus, alluding to the experiments of Gruithuisen, -Priestley, and Ingenhousz,<a name="FNanchor_250_250" id="FNanchor_250_250"></a><a href="#Footnote_250_250" class="fnanchor">[250]</a> says:—“These show, more<span class="pagenum"><a name="Page_361" id="Page_361"></a>[Pg 361]</span> -than any other experiments, that, in the purest water, -under the influence of air, light, and heat, beings are -formed, which, oscillating as it were between the animal -and the plant, exhibit the primitive germs of both kingdoms.”<a name="FNanchor_251_251" id="FNanchor_251_251"></a><a href="#Footnote_251_251" class="fnanchor">[251]</a> -Treviranus<a name="FNanchor_252_252" id="FNanchor_252_252"></a><a href="#Footnote_252_252" class="fnanchor">[252]</a> repeated, and appeared to confirm -these results; but in these experiments we have no -evidence that the germ did not previously exist in the -spring-water which was employed.</p> - -<p>Some have regarded the cell as a crystal; they see -the crystal forming, by the accumulation of atoms, into -a fixed form, under the influence of an “inner life;” -and, advancing but a step, they regard the cell as the -result of an increased exercise of the physical influences.<a name="FNanchor_253_253" id="FNanchor_253_253"></a><a href="#Footnote_253_253" class="fnanchor">[253]</a> -We have referred crystalline form to certain -magnetic conditions; and it is evident that the atomic -cell is influenced by similar forces; but if we place a -crystal in its natural fluid, though it increases in size, it -never alters in form: whereas, if we examine a cell in<span class="pagenum"><a name="Page_362" id="Page_362"></a>[Pg 362]</span> -its natural position, it gives indications of motion, it -produces other cells, and we have a development of -organs which are in no respect the same in form as -the original. From a vesicle floating invisible to -the unaided human sense in its womb of fluid, is produced -a plant possessing strange powers, or an animal -gifted with volition. The idea, that two kinds of -polarity—light on one side, and gravitation on the -other—produce the two peculiar developments of roots -and branches, can only be regarded as one of those -fanciful analogies which prove more imagination than -philosophy.<a name="FNanchor_254_254" id="FNanchor_254_254"></a><a href="#Footnote_254_254" class="fnanchor">[254]</a></p> - -<p>The conditions are, however, most curious; they deserve -very attentive study; but in examining the phenomena, -the safest course is to allow the effects as they -arise to interpret to us, and not admit the love of hypothesis -to lead us into bewildering analogies; or uncertain -phenomena to betray us to hasty inferences. It is of this -evil that Bacon speaks, in his “Advancement of Learning.” -He says:—</p> - -<p>“The root of this error, as of all others, is this, -that men, in their contemplations of nature, are -accustomed to make too timely a departure, and too -remote a recess from experience and particulars, -and have yielded and resigned themselves over to -the fumes of their own fancies and popular argumentations.”</p> - -<p>Without venturing, therefore, to speculate on the -origin of the primitive cell, or unit of organic life, which -involves the problem of the metamorphosis of a rude<span class="pagenum"><a name="Page_363" id="Page_363"></a>[Pg 363]</span> -mass—the primitive transformation of the rudimentary -atoms into organic form,—we must admit that the -highly organized plant or animal is but an aggregation -of cells; their arrangement being dependent upon -certain properties peculiar to them, and the exercise of -forces such as we have been studying,—all of which -appear to act externally to the plant or animal itself.</p> - -<p>Experiments have been brought forward, in which -it appeared that, after all organization which could by -any possibility have existed, had been destroyed by the -action of fire, solutions of flint and metallic salts, -have, under the influence of electric currents, exhibited -signs of organic formations, and that, indeed, insects—a -species of acari—have been developed in them. The -experiments were said to have been made with care, and -many precautions taken to shut out all chances of any -error, but not all the precautions required in a matter of -such exceeding delicacy; and we are bound not to -receive the evidence afforded as the true expression of a -fact without much further investigation. All experience,—setting -aside the experiment named,—is against the -supposition that pounded or dissolved flint could by any -artificial means be awakened into life. Ova may -have been conveyed into the vessels which contained -the solutions under experiment; and in due time, -although possibly quickened by electric excitation, -the animals—the most common of insects—came into -existence.<a name="FNanchor_255_255" id="FNanchor_255_255"></a><a href="#Footnote_255_255" class="fnanchor">[255]</a></p> - -<p>The rapid growth of confervæ upon water has often -been brought forward as evidence of a spontaneous -generation, or the conversion of inorganic elements into -organic forms; but it has been most satisfactorily proved -that the germ must be present, otherwise no evidence of<span class="pagenum"><a name="Page_364" id="Page_364"></a>[Pg 364]</span> -anything like organization will be developed. All the -conditions required for the production of vegetable life -appear to show, that it is quite impossible for any kind -of plant, even the very lowest in the scale, to be formed -in any other way than from an embryo in which are -contained the elements necessary for it, and the arrangements -required for the various processes which are connected -with its vitality.</p> - -<p>The earth is now covered with vegetable life, but -there must have existed a time when “darkness was -upon the face of the deep,” and organization had not -yet commenced tracing its lovely net-work of cells upon -the bare surface of the ocean-buried rock. At length -the mystery of organic creation began: into this -science dares not penetrate, but it is privileged to begin -its search a little beyond this point, and we are -enabled to trace the progress of organic development -through a chain of interesting results which are constantly -recurring.</p> - -<p>If we take some water, rising from a subterranean -spring, and expose it to sunshine, we shall see, after a -few days, a curious formation of bubbles, and the -gradual accumulation of green matter. At first we -cannot detect any marks of organization—it appears a -slimy cloud of an irregular and undetermined form. -It slowly aggregates, and forms a sort of mat over the -surface, which at the same time assumes a darker green -colour. Careful examination will now show the original -corpuscles involved in a net-work formed by slender -threads, which are tubes of circulation, and may be -traced from small points which we must regard as the -compound atom, the vegetable unit. We must not -forget, here, that we have to deal with four chemical -elements,—oxygen, hydrogen, carbon, and nitrogen, -which compose the world of organized forms, and that -the water affords us the two first as its constituents, -gives us carbon in the form of carbonic acid dissolved<span class="pagenum"><a name="Page_365" id="Page_365"></a>[Pg 365]</span> -in it, and that nitrogen is in the air surrounding it, and -frequently mixed with it also.</p> - -<p>Under the influence of sunshine, we have now seen -these elements uniting into a mysterious bond, and the -result is the formation of a cellular tissue, which possesses -many of the functions of the noblest specimens of -vegetable growth. But let us examine the progress. -The bare surface of a rock rises above the waters -covered over with this green slime, a mere veil of delicate -net-work, which, drying off, leaves no perceptible -trace behind it; but the basis of a mighty growth is -there, and under solar influence, in the process of time, -other changes occur.</p> - -<p>After a period, if we examine the rock, we shall find -upon its face little coloured cups or lines with small -hard discs. These, at first sight, would not be taken for -plants, but on close examination they will be found to be -lichens. These minute vegetables shed their seed and -die, and from their own remains a more numerous crop -springs into life. After a few of these changes, a sufficient -depth of soil is formed, upon which mosses begin to -develope themselves, and give to the stone a second -time a faint tint of green, a mere film still, but indicating -the presence of a beautiful class of plants, which, under -the microscope, exhibit in their leaves and flowers many -points of singular elegance. These mosses, like the -lichens, decaying, increase the film of soil, and others of -a larger growth supply their places, and run themselves -the same round of growth and decay. By and by, -funguses of various kinds mingle their little globes and -umbrella-like forms. Season after season plants, perish -and add to the soil, which is at the same time increased -in depth by the disintegration of the rock over which -it is laid, the cohesion of particles being broken up by -the operations of vegetable life. The minute seeds of -the ferns floating on the breeze, now find a sufficient -depth of earth for germination, and their beautiful<span class="pagenum"><a name="Page_366" id="Page_366"></a>[Pg 366]</span> -fronds, eventually, wave in loveliness to the passing -winds.</p> - -<p>Vegetable forms of a higher and a higher order -gradually succeed each other, each series perishing in -due season, and giving to the soil additional elements -for the growth of plants of their own species or those of -others. Flowering herbs find a genial home on the -once bare rock; and the primrose pale, the purple foxglove, -or the gaudy poppy, open their flowers to the joy -of light. The shrub, with its hardy roots interlaced -through the soil, and binding the very stones, grows -rich in its bright greenery. Eventually the tree springs -from the soil, and where once the tempest beat on the -bare cold rock, is now the lordly and branching monarch -of the forest, with its thousand leaves, affording shelter -from the storm for bird and beast.</p> - -<p>Such are the conditions which prevail throughout -nature in the progress of vegetable growth; the green -matter gathering on a pond, the mildew accumulating -on a shaded wall, being the commencement of a process -which is to end in the development of the giant trees of -the forest, and the beautifully tinted flower of nature’s -most chosen spot.</p> - -<p>We must now consider closely the phenomena connected -with the growth of an individual plant, which -will illustrate the operation of physical influences -throughout the vegetable world. The process by which -the embryo, secured in the seed, is developed, is our -first inquiry.</p> - -<p>A seed is a highly carbonized body, consisting of -integuments and embryo: between these, in most seeds, -lies a substance called the <i>albumen</i>, or <i>perisperm</i>. The -embryo contains the elements of the future plant—the -cotyledons, the plumule, and the radicle; the former -developing into stalk and leaves, the latter into roots. -This embryo hides the living principle, for the development -of which it is necessary that the starch and gluten<span class="pagenum"><a name="Page_367" id="Page_367"></a>[Pg 367]</span> -undergo a chemical change, and that an elevation of -temperature is produced. The vital power is dormant—it -sleeps—in the seed until the proper conditions are -produced. It has been proved, that the powers of -maintaining life in the seed are very great; excessive -cold, sufficiently intense to freeze mercury, will not kill -seed, and they resist a comparatively high temperature. -It is probable that heat only destroys seeds by drying -them too completely. The temperature at which -seeds germinate is exceedingly varied,—those belonging -to our own clime will germinate when the thermometer -rises above 40° F., but the seeds of tropical plants -demand that a temperature of from 70° to 84°, or even -to 90°, be steadily applied to them. In some cases it -has been found that even boiling the seeds has been -advantageous to the future process of germination in -the soil. But let us take the seed of some ordinary -plant, and trace its progress.</p> - -<p>An apparently dead grain is placed in the soil. If -the temperature is a few degrees above the freezing point, -and the soil holds a due quantity of water, the integument -of the seed imbibes moisture and swells; the tissue is -softened, and the first effort of vital force begins. The -seed has now the power of decomposing water, the -oxygen combines with some of the carbon of the seed, -and is expelled as carbonic acid. Saussure’s experiments -prove this. The air above the soil in which a horse-bean -was placed to germinate, gave, before the experiment, -nitrogen 210·26, and oxygen 56·29, and after -germination, nitrogen 209·41, oxygen 44·38, and carbonic -acid 11·27. This part of the process is but little -removed from the merely chemical changes which we -have already considered. We find the starch of the -seed changed into gum and sugar, which affords nutritive -food for the developing embryo. The seed now -lengthens downwards by the radicle, and upwards by<span class="pagenum"><a name="Page_368" id="Page_368"></a>[Pg 368]</span> -the cotyledons, which, as they rise above the earth, -acquire a green colour. Here the first stage of vegetable -life ends, the chemically exciting process is at an -end, and a new stimulus is required to continue in full -activity the vital powers. Carbonic acid is no longer -given off.</p> - -<p>The cotyledons, which are two opposite roundish -leaves, act as the lungs; by them carbonic acid taken -from the atmosphere is absorbed and carried by a circulating -process, now in full activity, through the young -plant. The carbonic acid, a compound of carbon and -oxygen, is decomposed; it is deprived of its carbon, which -is retained by the plant, and oxygen is exhaled. The -plant at this period is little more than an arrangement -of cellular tissue, a very slight development of vascular -and fibrous tissue appearing as a cylinder lying in the -centre of the sheath. At this point, however, we begin -more distinctly to trace the operations of the new -power; the impulses of life are strikingly evident.</p> - -<p>The young root is now lengthening, and absorbing -from the moisture in the soil, which always contains -some soluble salts, a portion of its nutriment, which is -impelled upwards by a force—probably capillary attraction -and endosmose action combined—to the point from -which the plumule springs. Capillary force raises the -fluids through the tubes in the stalk, and conveys -them to the veins in the leaves, while the endosmose -force diffuses them through the vegetable tissues. The -plumule first ascends as a little twig, and, at the same time, -by exerting a more energetic action on the carbonic -acid than the cotyledons have done, the carbon retained -by them being only so much as is necessary to form -chlorophylle, or the green colouring matter of leaves, -some wood is deposited in the centre of the radicle. -From this time the process of lignification goes on -through all the fabric,—the increase, and indeed the<span class="pagenum"><a name="Page_369" id="Page_369"></a>[Pg 369]</span> -life, of the plant depending upon the development of a -true leaf from the plumule.</p> - -<p>It must not be imagined that the process consists, in -the first place, of a mere oxidation of the carbon in the -seed,—a slow combustion by which the spark of life is -to be kindled;—the hydrogen of the water plays an -important part, and, combining also with the carbon, -forms necessary compounds, and by a secondary process -gives rise again to water by combination with -oxygen in the cells of the germinating grain. Nor -must we regard the second class of phenomena as mere -mechanical processes for decomposing carbonic acid, but -the result of the combined influences of all the physical -powers and life superadded.</p> - -<p>This elongating little twig, the plumule, at length -unfolds itself, and the branch is metamorphosed into a -leaf. The leaf aërates the sap it receives, effects the -decomposition of the carbonic acid, the water, and in all -probability the ammonia which it derives from the air, -and thus returns to the pores, which communicate with -the pneumatic arrangements of the plant, the necessary -secretions for the formation of bark, wood, and the -various proximate principles which it contains.</p> - -<p>After the first formation of a leaf, others successively -appear, all constructed alike, and performing similar -functions. The leaf is the principal organ to the tree; -and, indeed, Linnæus divined, and Goethe demonstrated, -the beautiful fact, that the tree was developed from this -curiously-formed organ.</p> - -<p>“Keeping in view,” says the poet-philosopher, “the -observations that have been made, there will be no -difficulty in discovering the leaf in the seed-vessel, notwithstanding -the variable structure of that part and its -peculiar combinations. Thus the pod is a leaf which is -folded up and grown together at its edges, and the capsules -consist of several leaves grown together, and the com<span class="pagenum"><a name="Page_370" id="Page_370"></a>[Pg 370]</span>pound -fruit is composed of several leaves united round -a common centre, their sides being opened so as to -form a communication between them, and their edges -adhering together. This is obvious from capsules which, -when ripe, split asunder, at which time each portion is -a separate pod. It is also shown by different species -of one genus, in which modifications exist of the principle -on which their fruit is formed; for instance, the -capsule of <i><span class="correction" title="In the original book: nigilla">nigella</span> orientalis</i> consists of pods assembled -round a centre, and partially united; in <i><span class="correction" title="In the original book: nigilla">nigella</span> damascena</i> -their union is complete.”<a name="FNanchor_256_256" id="FNanchor_256_256"></a><a href="#Footnote_256_256" class="fnanchor">[256]</a></p> - -<p>Professor Lindley thus explains the same view:—“Every -flower, with its peduncle and bracteolæ, being -the development of a flower-bud, and flower-buds being -altogether analogous to leaf-buds, it follows as a corollary -that every flower, with its peduncle and bracteolæ, -is a metamorphosed branch.</p> - -<p>“And, further, the flowers being abortive branches, -whatever the laws are of the arrangement of branches -with respect to each other, the same will be the laws of -the flowers with respect to each other.</p> - -<p>“In consequence of a flower and its peduncle being -a branch in a particular state, the rudimentary or metamorphosed -leaves which constitute bracteæ, floral envelopes, -and sexes, are subject to exactly the same laws -of arrangement as regularly-formed leaves.”<a name="FNanchor_257_257" id="FNanchor_257_257"></a><a href="#Footnote_257_257" class="fnanchor">[257]</a></p> - -<p>The idea that the leaf is the principal organ of the -plant, and that from it all the other organs are probably -developed, is worthy the genius of the great German -poet.</p> - -<p>Every leaf, a mystery in itself, is an individual gifted -with peculiar powers; they congregate in families, and -each one ministers to the formation of the branch on</p> - -<p><span class="pagenum"><a name="Page_371" id="Page_371"></a>[Pg 371]</span></p> - -<p>which it hangs, and to the main trunk of the tree of -which it is a member. The tree represents a world, -every part exhibiting a mutual dependence.</p> - -<div class="poetry-container"><div class="poem"><div class="stanza"> -<div class="verse">“The one red leaf, the last of its clan,</div> -<div class="verse">That dances as often as dance it can;</div> -<div class="verse">Hanging so light and hanging so high,</div> -<div class="verse">On the topmost twig that looks up at the sky,”</div> -</div></div></div> - -<p>is influenced by, and influences, the lowest root which -pierces the humid soil. Like whispering voices, the -trembling leaves sing rejoicingly in the breeze and -summer sunshine, and they tremble alike with agony -when the equinoctial gale rends them from the parent -stalk. The influences which pervade the whole, making -up the sum of vital force, are disturbed by every movement -throughout the system; a wound on a leaf is -known to disturb the whole, and an injury inflicted on -the trunk interferes with the processes which are the -functions of every individual leaf.<a name="FNanchor_258_258" id="FNanchor_258_258"></a><a href="#Footnote_258_258" class="fnanchor">[258]</a></p> - -<p>The consideration of the physical circumstances -necessary to germination and vegetable growth, brings -us acquainted with many remarkable facts. At a temperature -below the freezing point, seeds will not germinate; -at the boiling point of water, a chemical change -is produced in the grain, and its power of germinating -is destroyed. Heat, therefore, is necessary to the development -of the embryo, but its power must only be -exerted within certain prescribed limits: these limits -are only constant for the same class of seeds, they vary -with almost every plant. This is apparent to every one, -in the different periods required for germination by the -seeds of dissimilar vegetables.</p> - -<p>The seed is placed in the soil; shade is always—<span class="pagenum"><a name="Page_372" id="Page_372"></a>[Pg 372]</span>absolute -darkness sometimes—necessary for the success -of the germinating process. We have seen that the -first operation of nature is purely a chemical one, but -this manifestation of affinity is due to an exertion of -force, which is directly dependent upon solar power. The -seed is buried in the soil, when the genial showers of -spring, and the increasing temperature of the earth, -furnish the required conditions for this chemistry of -life, and the plant eventually springs into sunshine. -Thus we obtain evidence that even through some depth -of soil the solar power, whatever it may be, is efficient, -and that under its excitement the first spring of life, -in the germ, is effected.</p> - -<p>The cotyledons and the plumule being formed, the -plant undergoes a remarkable change. The seed, like -an animal, absorbed oxygen and exhaled carbonic acid; -the first leaves secrete carbon from carbonic acid inspired, -and send forth, as useless to the plant, an excess -of oxygen gas.</p> - -<p>This power of decomposing carbonic acid is a vital -function which belongs to the leaves and bark. It -has been stated, on the authority of Liebig, that during -the night the plant acts only as a mere bundle of fibres,—that -it allows of the circulation of carbonic acid and -its evaporation, unchanged. In his eagerness to support -his chemical hypothesis of respiration, the able chemist -neglected to inquire if this was absolutely correct. The -healthy plant never ceases to decompose carbonic acid -during one moment of its existence; but during the -night, when the excitement of light is removed, and the -plant reposes, its vital powers are at their minimum of -action, and a much less quantity is decomposed than -when a stimulating sun, by the action of its rays, is -compelling the exertion of every vital function.</p> - -<p>During this process, we have another example of -natural organic chemistry. The four inorganic elements -of which the vegetable kingdom is composed—oxygen,<span class="pagenum"><a name="Page_373" id="Page_373"></a>[Pg 373]</span> -hydrogen, nitrogen, and carbon—are absorbed as air or -moisture by the leaves and through the roots, and the -great phenomenon of vegetable life is the conversion of -these to an organic condition. Sugar and gum are -constantly produced, and from these, by combination -with atmospheric nitrogen, a proteine compound is -formed, which is an essential element in the progress of -development.<a name="FNanchor_259_259" id="FNanchor_259_259"></a><a href="#Footnote_259_259" class="fnanchor">[259]</a></p> - -<p>Plants growing in the light are beautifully green, the -intensity of colouring increasing with the brilliancy of -the light. Those which are grown in the dark are etiolated, -their tissues are weak and succulent, their leaves -of a pale yellow. It is, therefore, evident that the formation -of this chlorophylle—as the green colouring -matter of leaves is called—results from some action -determined by the sun’s rays.</p> - -<p>Chlorophylle is a carbonaceous compound formed in -the leaves, serving, it would appear, many purposes in -the process of assimilation. In the dark the plant still -requires carbon for its further development, and growing -slowly, it removes it from the leaves, decomposing the -chlorophylle, and supports its weak existence by preying -on parts of its own structure, until at length, this being -exhausted, it actually perishes of starvation.</p> - -<p>Plants always turn towards the light: the guiding power -we know not, but the evidence of some impulsive or attracting -force is strong; and the purpose for which they -are constituted to obey it, is proved to be the dependence -of vegetable existence upon luminous power.</p> - -<p>Light is not, however, alone sufficient to perfect the -plant: another agent is required to aid in the production -of flowers and fruits, and this power is proved to be -heat—and heat, perhaps, in some peculiar condition. -Having reached that point of development when the<span class="pagenum"><a name="Page_374" id="Page_374"></a>[Pg 374]</span> -reproductive functions are, by another change in the -chemical operations going on within the vegetable -structure, to be called forth, it has been found that the -heat rays become in a remarkable manner effective. It -has also been observed that plants bend from the red, -or calorific rays, instead of towards them, as they are -found to do to every other ray of the spectrum. From -this we may argue that the influence of these rays is to -check the vegetation, and thus to ensure the perfection -of the reproductive processes.</p> - -<p>It has already been stated that we have the means of -separating, to a considerable extent, the three principles -which we discover in the sunbeam, from each other, by -the use of absorbent media.</p> - -<p>By a peculiar yellow glass we cut off the chemical -principle of the sunbeam, and admit the passage of the -<i>luminous rays</i> only—<span class="smcap">Light</span>.</p> - -<p>By a cobalt blue glass we obstruct the <i>light</i>, but -allow the chemical agent to pass through freely, without, -indeed, any loss—<span class="smcap">Actinism</span>.</p> - -<p>By a glass coloured deep blood-red by oxide of gold -we obstruct the chemical principle and much of the -light, but such a medium is perfectly transparent to -<span class="smcap">Heat</span>.</p> - -<p>Therefore, this gives us the means of experimenting -with either of these principles, and of examining the -parts which they respectively play in the work of -organization.</p> - -<p>Some seeds being placed in the soil, in every respect -in their natural conditions, duly supplied with moisture, -and a uniform and proper temperature maintained, we -place above the soil the three media above named, and -allow one portion to be exposed to all the ordinary -influences of the solar rays.</p> - -<p>The result will be, that the seeds under the blue glass -will germinate long before those which are exposed to -the combined influences of the sunshine: a few of the<span class="pagenum"><a name="Page_375" id="Page_375"></a>[Pg 375]</span> -seeds will struggle into day under the red glass, but the -process of germination is entirely checked under the -yellow glass. Here we see that the chemical radiations -have quickened the chemical changes, and accelerated -the process, under the red glass, through which rays -having some peculiar chemical action pass; the germinating -process, though checked, is not entirely stopped. -Whereas, it would appear that under the influences of -light which has been deprived of chemical power, this -conversion of the starch into gum and sugar, which -appears to be necessary, is entirely prevented.</p> - -<p>If the experiment is continued, it will be found that -under the blue glass the plants grow rapidly, but weakly; -and that instead of producing leaves and wood they -consist chiefly of stalk, upon which will be seen here -and there some abortive attempts to form leaves. -When the process of germination has terminated, if the -young plant is brought under the yellow glass, it grows -most healthfully, and forms an abundance of wood, the -leaves having an unusually dark green colour, from the -formation of a large quantity of chlorophylle. Plants -do not, however, produce flowers with readiness under -this medium; but if, at the proper period, they are -brought under the red glass, the flowering and fruiting -processes are most effectively completed.<a name="FNanchor_260_260" id="FNanchor_260_260"></a><a href="#Footnote_260_260" class="fnanchor">[260]</a></p> -<p><span class="pagenum"><a name="Page_376" id="Page_376"></a>[Pg 376]</span></p> -<p>These experiments, simple as they are, prove to us -the importance of light: the <i>luminous principle</i> of the -sunbeam is exciting the vital powers of the plant to -decompose carbonic acid and form wood; and the -calorific agent, possibly under those modifications which -have already been noticed as belonging to the parathermic -rays, is essential to the production of flower and -fruit.</p> - -<p>Observations, which have been extended over many -years, prove that with the seasons these solar powers are,<span class="pagenum"><a name="Page_377" id="Page_377"></a>[Pg 377]</span> -relatively to each other, subject to an interesting change. -In the spring, the actinic or chemical power prevails, -and during this period its agency is required for the -vitalization of the germ. As the summer comes on, -the actinic rays diminish, and those of light increase. -Perhaps it would be more strictly correct to say that -the luminous intensity being increased, the chemical -power was retarded; the former expression implies a -variation in quantity, which may not be correct. We -see the necessity for this, since luminous power is required -for the secretion of the carbon, with which the -woody fibre is formed, and also for the elaboration of -the proximate principles of the plant. Autumn, the -season of fruit, is characterized by an increase of the -heat rays, and a diminution of the others: this change -being necessary, as science now teaches us, for the due -production of flower and fruit.</p> - -<p>The calorific rays of the solar beam, to which the -autumnal phenomena of vegetation appear particularly -to belong, are of a peculiar character. They have been -called, the Parathermic rays, and exhibit a curious -compound nature. To these rays we may refer the -ripening of fruit and grain, and the browning of the leaf -before its fall. May not the rise of the sap in spring -be traced to the excitement of either light or actinism, -and its recession, in the autumn, to that power from -which the plant is found to bend, and which appears to -be their modified form of heat?</p> - -<p>There can be no doubt that the varieties of climate -and the peculiarities of countries, as it regards their -animal and vegetable productions, are dependent on the -same causes. The distribution of species has been -referred by some to specific centres of creation around -which the plants and animals have spread, without -reference to physical conditions. Although centres of -creation may be admitted, these centres themselves -have been determined by the physical fitness of each<span class="pagenum"><a name="Page_378" id="Page_378"></a>[Pg 378]</span> -centre to the conditions of the creation, and in like manner -the migration of tribes is solely due to these -physical forces we have been considering. In every -zone we find that vegetable organization is peculiarly -fitted for the considerations by which it is surrounded. -Under the equator we have the spice-bearing trees, the -nutmeg, the clove, the cinnamon, and the pepper-tree; -there we have also the odoriferous sandal, the ebony, -the banyan, and the teak: we have frankincense, and -myrrh, and other incense-bearing plants; the coffee-tree, -the tea-plant, and the tamarind.</p> - -<p>A little further north we have the apricot, the citron, -the peach, and the walnut. In Spain, Sicily, and Italy, -we have the orange and lemon-tree blooming rich with -perfume, and the pomegranate and the myrtle growing -wild upon the rocks. Beyond the Alps the vegetation -again changes; instead of the cypress, the chesnut, and -the cork-tree, which prevail to the south of them, we -have the hardier oak, the beech, and the elm. Still further -north, we have the Scotch and spruce fir and larch. -On the northern shores of the Baltic, and in that line of -latitude, the hazel alone appears; and beyond this the -hoary alder, the sycamore, and the mountain ash. -Within the Arctic circle we find the mezereum, the -water-lilies, and the globe-flowers; and, when the -weakness of the solar radiations becomes too great even -for these, the reindeer moss still lends an aspect of -gladness to the otherwise sterile soil.</p> - -<p>The cultivation of vegetables depends on the temperature -of the clime. The vine flourishes where the -mean annual temperature ranges between 50° and 73°, -and it is only cultivated profitably within 30° S. and 50° -N. of the equator. To the same limits is confined -the cultivation of maize and of olives. Cotton is grown -profitably up to latitude 46° in the Old World, but only -up to 40° in the New. We have evidence derived from -photographic phenomena, that the constitution of the<span class="pagenum"><a name="Page_379" id="Page_379"></a>[Pg 379]</span> -solar rays varies with the latitude. The effects of the -sun’s rays in France and England in producing chemical -change are infinitely more decided than, with far greater -splendour of light, they are found to be in the lands -under or near the equator. Indeed, the remarks made -on the variations in the character of the sunbeam with -the changing seasons, may apply equally to the variations -in latitude.</p> - -<p>Fungals are among the lowest forms of vegetation, but -in these we have peculiarities which appear to link them -with the animal kingdom. Marcet found that mushrooms -absorbed oxygen, and disengaged carbonic acid. -In all probability this is only a chemical phenomenon -of a precisely similar character to that which we know -takes place with decaying wood. In the conversion of -wood into <i>humus</i>, oxygen is absorbed, and combining with -the carbon, it is evolved as carbonic acid. Of course we -have the peculiar condition of vitality to modify the -effect, and we have, too, in this class of plants, the existence -of a larger quantity of nitrogen than is found in -any other vegetating substance.</p> - -<p>These few sketches of remarkable phenomena connected -with vegetation are intended to show merely the -operations of the physical powers of the universe, so far -as we know them, upon these particular forms of -organization. During the process of germination, -electricity is, according to Pouillet, evolved; and again, -in ripening fruits, there appears to be some evidence of -electrical currents. Vegetables are, however, in the -growing state, such good conductors of electricity, that -it is not, according to the laws of this force, possible -that they should accumulate it; so that the luminous -phenomena stated to have been observed cannot be due -to this agency. We know, however, that under every -condition of change, whether induced by chemical or -calorific action, electricity is set in motion; and we -have reasons for believing that the excitation of light -will also give rise to electrical circulation.</p> - -<p><span class="pagenum"><a name="Page_380" id="Page_380"></a>[Pg 380]</span></p> - -<p>The question, whether plants possess sensation, -whether they have any disposition of parts at all -analogous to the nervous system of animals, has been -often put forward, but as yet the answers have been -unsatisfactory. The point is one well worthy all the -attention of the vegetable physiologist; but regarding -plants as the link between the animal and the mineral -kingdom,—looking upon phyto-chemistry, as exhibited -by them, as the means employed to produce those more -complex organizations which exist in animals,—we -necessarily consider plants as mere natural machines -for effecting organic arrangements, and, as such, that -they cannot possess any nervous sensibility. Muscular -contraction may be represented in many of their marvellous -arrangements; and any disturbance produced by -natural or artificial means would consequently effect a -change in the operations of those forces which combine -to produce vegetable life. Indeed, the experiments of -Carlo Matteucci, already referred to, prove that an -incision across a leaf, the fracture of a branch, or the -mere bruising of any part of the plant, interferes with -the exercise of that power which, under the operation of -luminous agency, decomposes carbonic acid, and effects -the assimilation of the other elements.</p> - -<p>To recapitulate. A plant is an organized creation; it is -so in virtue of certain strange phyto-chemical operations, -which are rendered active by the solar influences -involved in the great phenomena of light, and by the -excitation of caloric force mid electrical circulation. It -is a striking exemplification of the united action of -certain empyreal powers, which give rise to the combination, -of inorganic principles under such forms that -they become capable of obeying the mysterious impulses -of life.</p> - -<p>The poet has imaged the agency of external powers in -various shapes of spiritualized beauty. From the goddess -Flora, and her attendant nymphs, to the romantic -enchantress who called up flowers by the light touch of<span class="pagenum"><a name="Page_381" id="Page_381"></a>[Pg 381]</span> -her wand, we have, in all these creations, foreshadowings -of the discovery of those powers which science has shown -are essential to vegetable life. A power from without -influences the plant; but the animal is dependent upon -a higher agency which is potent within him.</p> - -<p>The poet’s dream pleases the imaginative mind; and, -associating in our ideas all that is graceful and loveable -in the female form, with that diviner feeling which -impresses the soul with the sense of some unseen -spirituality, we perceive in the goddess, the enchantress, -or the sylph, pure idealizations of the physical powers. -The spirit floating over these forms of beauty, and -adorning them with all the richness of colour—painting -the rose, and giving perfume to the violet—is, in the -poet’s mind, one which ascends to nearly the highest -point of etherealization, and which becomes, indeed, to -him a spirit of light; they ride upon the zephyrs, and -they float, in all the luxury of an empyreal enjoyment, -down to the earth upon a sunbeam. Such is the work -of the imagination. What is the result of the search of -plodding science after truth? The sunbeam has been -torn into rays, and every ray tasked to tell of its -ministry.</p> - -<p>Nature has answered to some of the interrogations; -and, passing over all the earth, echoed from plant to -plant, we have one universal cry proclaiming that every -function of vegetable life is due to the spirits of the -sun.</p> - -<p>The mighty Adansonia of Senegal, hoary with the -mosses of five thousand years,—the Pohon upas in their -deadly valleys,—the climbing lianas of the Guiana -forests,—the contorted serpent-cactus on the burning -hills,—the oaks, which spread their branches in our -tempered climes,—the glorious flowers of the inter-tropical -regions, and those which gem our virent plains,—the -reindeer lichen of northern lands, and the confervæ -of the silent pool,—the greatest and humblest creations<span class="pagenum"><a name="Page_382" id="Page_382"></a>[Pg 382]</span> -of the vegetable world,—all proclaim their direct -dependence upon the mysterious forces which are bound -together in the silver thread of Light.</p> - -<p>These undulations, pulsations too refined for mortal -ears, which quicken and guide these wonderful organisms, -may be indeed regarded as sphered music for ever -repeating the Divine command, “<i>Let there be Light</i>,” -by the creation of which, a dark and dreary chaos was -moulded into a star of beauty, capable of radiating brightness -to other space-wandering worlds.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_248_248" id="Footnote_248_248"></a><a href="#FNanchor_248_248"><span class="label">[248]</span></a> Percy Bysshe Shelley.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_249_249" id="Footnote_249_249"></a><a href="#FNanchor_249_249"><span class="label">[249]</span></a> <i>Experiments on the production of dephlogisticated air from -water with various substances</i>: by Lieut.-General Sir Benjamin, -Count of Rumford; Phil. Trans., vol. lxxvii. p. 84.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_250_250" id="Footnote_250_250"></a><a href="#FNanchor_250_250"><span class="label">[250]</span></a> <i>Experiments upon Vegetables, discovering their great power of -purifying the common air in the Sunshine, and of injuring it in the -Shade and at Night; to which is joined, A new method of examining -the accurate degrees of Salubrity of the Atmosphere</i>, by John Ingenhousz, -Councillor of the Court, and Body Physician to their Imperial -and Royal Majesties, F.R.S., &c. London: printed for P. -Elmsley, in the Strand, and H. Payne, Pall Mall, 1779.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_251_251" id="Footnote_251_251"></a><a href="#FNanchor_251_251"><span class="label">[251]</span></a> <i>The Kingdoms of Nature, their life and affinity</i>: by Dr. C. G. -Carus; Scientific Memoirs, vol. i. p. 223.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_252_252" id="Footnote_252_252"></a><a href="#FNanchor_252_252"><span class="label">[252]</span></a> In <i>Biologie</i>, by G. R. Treviranus, vol. ii. p. 302, the following -passage occurs:—“If we expose spring water to the sun in open -or even closed transparent vessels, after a few days bubbles rise -from the bottom, or from the sides of the vessel, and a green crust -is formed at the same time. Upon observing this crust through -a microscope, we discover a mass of green particles, generally of a -round or oval form, very minute, and overlaid with a transparent -mucous covering, some of them moving freely, whilst others, perfectly -similar to these, remain motionless and attached to the sides -of the vessel. This motion is sometimes greater than at others. -The animalcules frequently lie as if torpid, but soon recover their -former activity.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_253_253" id="Footnote_253_253"></a><a href="#FNanchor_253_253"><span class="label">[253]</span></a> <i>On the Structure of the Vegetable Cell</i>: by Mohl.—Scientific -Memoirs, vol. iv. p. 113. <i>Outlines of Structural and Physical -Botany</i>: by Henfrey.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_254_254" id="Footnote_254_254"></a><a href="#FNanchor_254_254"><span class="label">[254]</span></a> Dr. Carus, in the memoir already quoted, says:—“But since, -in the organization of the earth, light and air, as constituting a -second integrant part, stand opposed to gravitation, and since -the plant bears a relation, not only to gravitation, but to light also, -when its formation is complete it will necessarily present a second -anatomical system, namely, that of the spiral vessels, which have -been very justly considered, of late, as the organs that perform in -plants the functions of nerves.”</p></div> - -<div class="footnote"> - -<p><a name="Footnote_255_255" id="Footnote_255_255"></a><a href="#FNanchor_255_255"><span class="label">[255]</span></a> Mr. Crosse’s Experiments in the Journal of the London -Electrical Society, and Mr. Weekes in the Electrical Magazine, -and a communication appended to <i>Explanations: a Sequel to the -Vestiges of the Natural History of Creation</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_256_256" id="Footnote_256_256"></a><a href="#FNanchor_256_256"><span class="label">[256]</span></a> <i>Die Metamorphose der Pflanzen</i>: Goethe, sect. 78.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_257_257" id="Footnote_257_257"></a><a href="#FNanchor_257_257"><span class="label">[257]</span></a> Lindley’s <i>Elements of Botany</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_258_258" id="Footnote_258_258"></a><a href="#FNanchor_258_258"><span class="label">[258]</span></a> See the very curious experiments of C. Matteucci. Traduit -et extrait du “<i>Cimento</i>.”—Archives des Sciences Physiques et -Naturelles; <i>Quelques Expériences sur la Respiration des Plantes</i>. -Nov. 1846.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_259_259" id="Footnote_259_259"></a><a href="#FNanchor_259_259"><span class="label">[259]</span></a> Consult <i>Rural Economy</i>, by J. B. Boussingault; <i>The Chemical -and Physiological Balance of Organic Nature</i>, by Dumas and -Boussingault; and <i>Agricultural Chemistry</i>, by Liebig.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_260_260" id="Footnote_260_260"></a><a href="#FNanchor_260_260"><span class="label">[260]</span></a> The practical value of the discovery now described, will be -best understood from the following letter from Mr. Lawson, of -Edinburgh:— -</p> -<blockquote> -<div class="correspondence-head-container"> -<div class="correspondence-head"> -Edinburgh, 1, George the Fourth’s Bridge,<br /> -Sept. 8, 1853.</div> -</div> - -<p> -<span class="smcap">My dear Sir</span>,—I am favoured with yours of the 5th, relative -to my practical experience in the effect of the chemical agency of -coloured media on the germination of seeds and the growth of -plants. -</p> -<p> -I must first explain that it is our practice to test the germinating -powers of all seeds which come into our warehouses before -we send them out for sale; and, of course, it is an object to discover, -with as little delay as possible, the extent that the vital -principle is active, as the value comes to be depreciated in the -ratio it is found to be dormant. For instance, if we sow 100 -seeds of any sort, and the whole germinate, the seed will be the -highest current value; but if only 90 germinate, its value is 10 -per cent. less; if 80, then its value falls 20 per cent. -</p> -<p> -I merely give this detail to show the practical value of this -test, and the influence it exerts on the fluctuation of prices. -</p> -<p> -Our usual plan formerly was to sow the seeds to be tested in a -hot-bed or frame, and then watch the progress and note the results. -It was usually from eight to fourteen days before we were in a -condition to decide on the commercial value of the seed under -trial. -</p> -<p> -My attention was, however, directed to your excellent work, -“On the Physical Phenomena of Nature,” about five years ago, -and I resolved to put your theory to a practical test. I accordingly -had a case made, the sides of which were formed of glass coloured -blue or indigo, which case I attached to a small gas stove for -engendering heat; in the case shelves were fixed in the inside, on -which were placed small pots wherein the seeds to be tested were -sown. -</p> -<p> -The results were all that could be looked for: the seeds freely -germinated in from two to five days only, instead of from eight to -fourteen days as before. -</p> -<p> -I have not carried our experiments beyond the germination of -seeds, so that I cannot afford practical information as to the effect -of other rays on the after culture of plants. -</p> -<p> -I have, however, made some trials with the yellow ray in preventing -the germination of seeds, which have been successful; -and I have always found the violet ray prejudicial to the growth -of the plant after germination.—I remain, my dear Sir, -</p> -<p class="center">Very faithfully yours,</p> -<p class="right"><span class="smcap">Charles Lawson</span>.</p></blockquote> -</div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_383" id="Page_383"></a>[Pg 383]</span></p> - - -<h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV.</h2> - -<p class="center">PHENOMENA OF ANIMAL LIFE.</p> - - -<p class="chap-head">Distinction between the Kingdoms of Nature—Progress of Animal -Life—Sponges—Polypes—Infusoria—Animalcula—Phosphorescent -Animals—Annelidans—Myriapoda—Animal -Metamorphoses—Fishes—Birds—Mammalia—Nervous -System—Animal Electricity—Chemical Influences—Influence -of Light on Animal Life—Animal Heat—Mechanical -Action—Nervous Excitement—Man and the Animal -Races, &c.</p> - - -<p class="p2">“A stone grows; plants grow and live; animals grow, -live, and feel.” Such were the distinctions made by -Linnæus, between the conditions of the three kingdoms -of nature. We cannot, however, but regard them as -in all respects illogical. The stone—a solid mass of -unorganized particles—enlarges, if placed in suitable -conditions, by the accretion of other similar particles -around it; but it does not, according to any meaning -in which we use the word, <i>grow</i>. Plants and animals -grow; and they differ, probably, only in the phenomena -of sensation. Yet, the trembling mimosa, and several -other plants, appear to possess as much feeling as -sponges and some of the lower classes of animals. By -this definition, however, of the celebrated Swedish -naturalist, we have a popular and simple expression of a -great fact.</p> - -<p>As we have only to examine the question of the -agency of the physical forces upon animal life, we must -necessarily confine our attention to the more striking -phenomena with which science has made us acquainted;<span class="pagenum"><a name="Page_384" id="Page_384"></a>[Pg 384]</span> -and, having briefly traced the apparent order in which -the advance of organization proceeded, we must direct -our few concluding remarks to the physico-physiological -influences, which we must confess to know but too -imperfectly.</p> - -<p>We learn that, during the states of progress which -geology, looking into the arcana of time, has made us -acquainted with, a great variety of animal forms were -brought into existence. They lived their periods. The -conditions of the surface of the earth, the sea, or the -atmosphere, were altered; and, no longer fitted for the -enjoyments of the new life, these races passed away, and -others occupied their places, which, in turn, went -through all the stages of growth, maturity, and decay; -until at length, the earth being constituted for the -abode of the highest order of animals, they were called -into existence; and man, the intellectual monarch of -the world, was placed supreme amongst them all. Types -of nearly all those forms of life which are found in the -fossil state are now in existence; and if we examine the -geographical distribution of animals—the zones of -elevation over the surface of the earth, and the zones of -depth in the ocean,—we shall find, now existing, animal -creations strikingly analogous to the primitive forms -and conditions of the earth’s inhabitants. From the -depths of the ocean we may even now study—as that -most indefatigable naturalist, Professor Edward Forbes, -has done—the varying states of organization under the -circumstances of imperfect light and varying temperature.<a name="FNanchor_261_261" id="FNanchor_261_261"></a><a href="#Footnote_261_261" class="fnanchor">[261]</a></p> - -<p>The gradual advance of animal life in the ascending -strata has led to many speculations, ingenious and<span class="pagenum"><a name="Page_385" id="Page_385"></a>[Pg 385]</span> -refined, on the progressive development of animals. -That the changes of the inorganic world have impressed -new conditions on the organic structures of animals, to -meet the necessities of their being, must be admitted. -Comparative anatomy has demonstrated that such supposed -differences really existed between the creatures of -secondary formations—those of the tertiary and the -present periods. It has been imagined, but upon debatable -foundations, that the atmosphere, during the -secondary periods, was highly charged with carbonic -acid; and, consequently, that though beneficial to the -growth of plants, and peculiarly fitted for the conditions -required by those which the fossil flora makes us acquainted -with, it was not adapted to support any animals -above the slow-breathing, cold-blooded fishes and reptiles. -Under the action of the super-luxuriant vegetation of -these periods, this carbonic acid is supposed to have been -removed, an addition of oxygen furnished; and thus, -consequently, the earth gradually fitted for the abode of -warm-blooded and quick-breathing creatures. We do, -indeed, find a very marked line between the fossil -remains of the lias formations which enclose the -saurians, and the wealden, in which birds make their -appearance more numerously than in any previous formation.</p> - -<p>Founded upon these facts, speculations have been put -forth on the gradual development of animals from the -lowest up to the highest orders. Between the polype -and man a continuous series has been imagined, every -link of the chain being traced into connection with the -one immediately succeeding it; and, through all the -divisions, zoophytes, fishes, amphibia, reptiles, birds, and -mammalia are seen, according to this hypothesis, to be -derived by gradual advancement from the preceding -orders. The first having given rise to amphibia,—the -amphibion gives birth to the reptile,—the reptile advances -to the bird,—and from this class is developed the<span class="pagenum"><a name="Page_386" id="Page_386"></a>[Pg 386]</span> -mammal. A slight investigation will convince us that -this view has no foundation. Although a certain relationship -may be found between some of the members -of one class, and those of the other immediately joining -it, yet this is equally discovered to exist towards -classes more remote from each other; and in no one -instance can we detect anything like the passage of an -animal of one class into an animal of another. Until -this is done, we cannot but regard the forms of animal -life as distinct creations, each one fitted for its state of -being, springing from the command of the great First -Cause.<a name="FNanchor_262_262" id="FNanchor_262_262"></a><a href="#Footnote_262_262" class="fnanchor">[262]</a></p> - -<p>But it is time to quit these speculative questions, and -proceed to the examination of the general conditions of -animal life at the present time.</p> - -<p>Lowest in the scale of animals, and scarcely distinguishable -from a vegetable, we find the sponge, attached -to and passing its life upon a rock, exhibiting, indeed, -less signs of feeling than many of the vegetable tribes. -The chemical differences between vegetables and sponges -are, however, very decided; and we find in the tissues -of the sponge a large quantity of nitrogen, a true animal -element, which exists, but in smaller quantities, in -vegetables.</p> - -<p>These creations, standing between vegetable and -animal life, possess the singular power of decomposing -carbonic acid, as plants do; and the water in which they -live always contains an excess of free oxygen.</p> - -<p>The polypes are a remarkably curious class. “Fixed -in large arborescent masses to the rocks of tropical seas, -or in our own climate attached to shells or other submarine -substances, they throw but their ramifications in -a thousand beautiful and plant-like forms; or, incrusting -the rocks at the bottom of the ocean with calcareous -earth, separated from the water which bathes them, they<span class="pagenum"><a name="Page_387" id="Page_387"></a>[Pg 387]</span> -silently build up reefs and shoals, justly dreaded by the -navigator; and sometimes giving origin, as they rise -to the surface of the sea, to islands, which the lapse of -ages clothes with luxuriant verdure, and peoples with -appropriate inhabitants.”<a name="FNanchor_263_263" id="FNanchor_263_263"></a><a href="#Footnote_263_263" class="fnanchor">[263]</a></p> - -<p>Most of the polypes are fixed and stationary; but the -hydra and some others have the power of changing their -positions, which they do in search of the light of the -sun. They do not appear to have organs of sight requiring -light; but still they delight in the solar influences. -The most extraordinary fact connected with the hydra -is its being multiplied by division. If an incision be -made in the side of a hydra, a young polype soon developes -itself; and if one of these creatures be divided, -it quickly restores the lost portion of its structure. The -varieties of the polypes are exceedingly numerous, and -many of them are in the highest degree curious, and -often very beautiful. The actiniæ, like flowers, appear -to grow from the rocks, unfolding their tentacula to the -light; and, in the excitement due to their eagerness for -prey, they exhibit a beautiful play of colours and most -interesting forms. Microscopic zoophytes of the most -curious shapes are found,—all of which attest, under -examination, the perfection of all created things.</p> - -<p>Infusoria and animalcula,—animals, many of them, -appearing under the microscope as little more than a -transparent jelly,—must be recognized as the most -simple of the forms of life. They exist in all waters -in uncountable myriads; and, minute creatures as -they are, it has been demonstrated that many of the -great limestone hills are composed entirely of their -remains.</p> - -<p>The acalephæ, or the phosphorescent animals of the -ocean, are no less curious. From creatures of the most<span class="pagenum"><a name="Page_388" id="Page_388"></a>[Pg 388]</span> -minute size, they extend to a considerable magnitude, -yet they appear to be little more than animated masses -of sea-water. If any one of these sea-jellies, or jelly-fishes -as they are often called (even the largest varieties -of them), is cast upon the shore, it is soon, by the influence -of the sun, converted into a mere fibre no thicker -than a cobweb: an animal weighing seven or eight -pounds is very soon reduced to as many grains. There -are numerous kinds of these singular creatures, most of -which are remarkable for the powerful phosphorescent -light they emit. The <i>beroes</i> and the <i>pulmonigrade</i> shine -with an intense white light many feet below the surface, -whilst the <i>Cestum Veneris</i>, or girdle of Venus, gliding -rapidly along, presents, on the edge of the wave, an undulating -riband of flame of considerable length. There -can be no doubt that this arises from the emission of -phosphorescent matter of an unknown kind from the -bodies of these animals.</p> - -<p>The microscope has made us familiar with the mysteries -of a minute creation which we should not otherwise -have comprehended. These creatures are found -inhabiting the waters and the land, and they exist in -the intestinal structure of plants and animals, preying -upon the nutritive juices which pass through their -systems. Although these beings are so exceedingly -small that even the most practised observer cannot -detect them with the naked eye, they are proved, by -careful examination under the microscope, to be in many -cases elaborately organized. Ehrenberg has discovered -in them filamentary nerves and nervous masses, and -even vessels appropriated to the circulation of fluids, -showing that they belong really to a high condition of -existence.</p> - -<p>Passing over many links in that curious chain which -appears to bind the animal kingdom into a complete -whole, we come to the articulata of Cuvier—the homogangliata -of Owen.</p> - -<p><span class="pagenum"><a name="Page_389" id="Page_389"></a>[Pg 389]</span></p> - -<p>All those creatures which we have been hitherto considering -are too imperfect in the construction of their -simple organizations to maintain a terrestrial existence; -they are, therefore, confined to a watery medium. In -the articulata, we have evidences of higher attributes, -and indications of instincts developed in proportion to -the increased perfection of organization. Commencing -with the annelidans, all of which, except the earthworms, -are inhabitants of the waters, we proceed to the -myriapoda, presenting a system intermediate in every -respect between that of worms and insects; we then -find embraced in the same order, the class insecta, -which includes flies and beetles of all kinds; and, -as the fourth division of articulated beings, the arachnidans -or spiders; and, lastly, the marine tribe of crustaceans.</p> - -<p>The most remarkable phenomena connected with -these animals are the metamorphoses which they -undergo. The female butterfly, for instance, lays eggs, -which, when hatched, produce caterpillars: these live -in this state for some time, feeding upon vegetables, -and, after casting their skins as they increase in size, -at last assume an entirely different state, and, dormant -in their oblong case, they appear like dead matter. -This chrysalis, or pupa, is generally preserved from -injury by being embedded in the earth, from which, -after a season, a beautifully perfect insect escapes, and, -floating on the breeze of summer, enjoys its sunshine, -and revels amidst its flowers.</p> - -<p>No less remarkable is the metamorphosis of the caducibranchiate -amphibia, passing through the true fish -condition of the tadpole to the perfect air-breathing -and four-footed animal, the frog.</p> - -<p>A metamorphosis of the crustaceans, somewhat similar -to that which takes place in insects, has been of late -years creating much discussion amongst naturalists: -but the question appears to be now settled by the<span class="pagenum"><a name="Page_390" id="Page_390"></a>[Pg 390]</span> -careful and long-continued observations of Mr. Thompson -and Mr. R. C. Couch.</p> - -<p>A wide line of demarcation marks the separation of -the invertebrata from the four great classes of vertebrate -animals—fishes, reptiles, birds, and mammalia. Every -part of the globe,—the ocean and the inland lake,—the -wide and far-winding river, and the babbling stream,—the -mountain and the valley,—the forest with its depth -of shade, and the desert with its intensity of light,—the -cold regions of the frost-chained north, and the -fervid clime within the tropics—presents for our study -innumerable animals, each fitted for the conditions to -which it is destined; and through the whole we find a -gradual elevation in the scale of intelligence, until at -last, separated from all by peculiar powers, we arrive at -man himself.</p> - -<p>In each of these four classes the animals are furnished -with a bony skeleton, which is in the young -animal little more than cartilage; but, as growth increases, -lime becomes deposited, and a sufficient degree -of hardness is thus produced to support the adult formation. -Some anatomists have endeavoured to show -that even in the mechanical structure of the bony fabrics -of animals, we are enabled to trace a gradual increase -in the perfection of arrangement, from the fish until the -most perfect is found in man. Many of the mammalia, -however, are furnished with skeletons which really -surpass that of man. These belong to animals which -depend for subsistence upon their muscular powers, and -with whom man is, in this particular, on no equality. -What is the lord of the creation, compared with the -antelope for fleetness, or with the elephant and many -other animals for strength?</p> - -<p>As we ascend the scale of animal life we find a more -perfectly developed nervous system; and the relative -size of the brain, compared with that of the brute, is -found progressively to increase, until it arrives at the<span class="pagenum"><a name="Page_391" id="Page_391"></a>[Pg 391]</span> -utmost perfection in man. On the system of nerves -depends sensation, and there can be no doubt that the -more exalted the order of intelligence displayed, the -more exquisitely delicate is the nervous system. Thus, -in this world, refined genius must necessarily be attended -with a condition of sensibility which, too frequently, -to the possessor is a state of real disease.</p> - -<p>It must be evident to every reader that but very few -of the striking features of animal life have been mentioned -in the rapid survey which has been taken of the -progress of animal organization. The subject is so -extensive that it would be quite impossible to embrace -it within any reasonable limits; and it furnishes -matter so curious and so instructive, that, having once -entered on it, it would have been difficult to have made -any selection, and we must have devoted a volume to -the æsthetics of natural science. Passing it by, therefore, -with the mere outline which has been given, we -must proceed to consider some of the conditions of -vitality.</p> - -<p>Bell has proved that one set of nerves is employed in -conveying sensation to the brain, and another set in -transferring the desires of the will to the muscles. By -the separation of a main branch of one of the nerves -of sensation, although all the operations of life will still -proceed, the organ to which that nerve goes is dead to -its particular sense. In like manner, if one of the -nerves of volition is divided, the member will not obey -the inclination of the brain. It is evident, therefore, -although many of the great phenomena of vital force -are dependent on the nervous system, and the paralysis -of a member ensues upon the separation or the disease -of a nerve, that the nerves are but the channels through -which certain influences are carried. The <i>vis vitæ</i> or -vital principle—for we are compelled by the imperfection -of our knowledge to associate under this one term the -ultimate causes of many of the phenomena of life—is a<span class="pagenum"><a name="Page_392" id="Page_392"></a>[Pg 392]</span> -power which, although constantly employed, has the -capability of continually renewing itself by some inexplicable -connection existing between it and many -external influences. We know that certain conditions -are necessary to the health of animals. Diseased digestion, -or any interruption in the circulation of the blood, -destroys the vital force, and death ensues. The processes -of digestion and of the circulation are perfectly -understood, yet we are no nearer the great secret of the -living principle.</p> - -<p>Animals are dependent on several external agents for -the support of existence. The oxygen of the air is -necessary for respiration. Animal heat, as will be -shown presently, is in a great measure dependent upon -it. The external heat is so regulated that animal -existence is comfortably supported. Electricity is -without doubt an essential element in the living processes; -and, indeed, many physiologists have been -inclined to refer vital force to the development of electricity -by chemical action in the brain. This view has, -however, no foundation in experiment beyond that -afforded by the appearance of electric currents, when -the brain is excited. This proves no more than that -the operations of mind develope physical power in the -matter with which it is mysteriously connected.</p> - -<p>The phenomena of the Torpedo and Gymnotus we -have already noticed,<a name="FNanchor_264_264" id="FNanchor_264_264"></a><a href="#Footnote_264_264" class="fnanchor">[264]</a> and there are other creatures -which certainly possess the power of secreting and discharging -electricity. Galvani’s experiments, and those -of Aldini, appear to show—and the more delicate -researches of Matteucci have satisfactorily determined<span class="pagenum"><a name="Page_393" id="Page_393"></a>[Pg 393]</span>—that -currents of electricity are always circulating in -the animal frame;—that positive electricity is constantly -passing from the interior to the exterior of a muscle. -Matteucci, by arranging a series of muscles, has formed -an electric pile of some energy.<a name="FNanchor_265_265" id="FNanchor_265_265"></a><a href="#Footnote_265_265" class="fnanchor">[265]</a> These currents -have been detected in man, in pigeons, fowls, eels, and -frogs.</p> - -<p>In the human body it is evident a large quantity of -electricity exists in a state of equilibrium. Du Bois -Raymond has shown that we may by mere muscular -motion give rise to electric currents which can be -measured by the galvanometer. This, however, may be -said of every substance. It is perhaps more easily disturbed -in the human system; indeed, the manifestation -of sparks from the hair and other parts of the body by -friction is not uncommon. Every chemical action, it -has been already shown, gives rise to electrical manifestations; -and the animal body is a laboratory, beautifully -fitted with apparatus, in which nearly every -chemical process is going on. It has been proved that -acid and alkaline principles are constantly acting upon -each other through the tissues of the animal frame; -and we have the curious phenomena of endosmose and -exosmose in constant effort, and catalysis or <i>surface force</i>, -operating in a mysterious manner.<a name="FNanchor_266_266" id="FNanchor_266_266"></a><a href="#Footnote_266_266" class="fnanchor">[266]</a></p> - -<p>With the refined physiological questions connected -with the phenomena of sensation we cannot deal, nor -will any argument be adduced for or against the hy<span class="pagenum"><a name="Page_394" id="Page_394"></a>[Pg 394]</span>pothesis -which would refer these phenomena to some -extraordinary development of electric force in the brain. -The entire subject appears to stand beyond the true -limits of science, and every attempt to pass it is invariably -found to lead to a confused mysticism, in which -the real and the ideal are strangely confounded. Science -stops short of the phenomena of vital action.</p> - -<p>We cannot, however, but refer to the idea entertained -by many that the brain is an electric battery, and the -nerves a system of conductors. On this view Sir John -Herschel remarks:—“If the brain be an electric pile -constantly in action, it may be conceived to discharge -itself at regular intervals, when the tension of the electricity -reaches a certain point, along the nerves which -communicate with the heart, and thus excite the pulsation -of that organ.” Priestley, however, appears to -have been the first to promulgate this idea.</p> - -<p>Light is an essential element in producing the grand -phenomenon of life, though its action is ill understood. -Where there is light, there is life, and any deprivation -of this principle is rapidly followed by disease of the -animal frame, and the destruction of the mental faculties. -We have proof of this in the squalor of those whose necessities -compel them to labour in places to which the -blessings of sunshine never penetrate, as in our coal-mines, -where men having everything necessary for health, -except light, exhibit a singularly unhealthy appearance. -The state of fatuity and wretchedness to which those -individuals have been reduced who have been subjected -for years to incarceration in dark dungeons, may be referred -to the same deprivation. Again, in the peculiar -aspect of those people who inhabit different regions of -the earth under varying influences of light, we see evidence -of the powerful effects of solar action. Other -forces, as yet undiscovered, may, in all probability do, -exert decided influences on the animal economy; but, -although we recognize many effects which we cannot<span class="pagenum"><a name="Page_395" id="Page_395"></a>[Pg 395]</span> -refer to any known causes, we are perfectly unable to -imagine the sources from which they spring.</p> - -<p>It will be interesting now to examine the phenomena -of animal heat, the consideration of which naturally leads -us to consider the digestive system, the circulatory processes, -and the effects of nervous excitation.</p> - -<p>The theory, which attributes animal heat to the -combination of the carbon of the food taken into the -stomach with the oxygen of the air inspired through -the lungs, has become a very favourite one. It must, -however, be remembered that it is by no means new. -The doctrines of Brown, known as the Brunonian -system, and set forth in his <i>Elementa Medicinæ</i>, are -founded upon similar hasty generalizations. Although, -without doubt, true in a certain degree, it is not so to -the extent to which its advocates would have us believe. -That the carbonaceous matter received into the stomach, -after having undergone the process of digestion, enters -into combination with the oxygen breathed through the -lungs or absorbed by the skin, and is given off from -the body in the form of carbonic acid, and that, during the -combination, heat is produced, by a process similar to -that of ordinary combustion, is an established fact; but -the idea of referring animal heat entirely to this chemical -source, when there are other well-known causes producing -calorific effects, is an example of the errors into -which an ingenious mind may be led, when eagerly -seeking to establish a favourite hypothesis.</p> - -<p>Animal and vegetable diet, which is composed largely -of carbon and hydrogen, passes into the digestive -system, and becomes converted into the various matters -required for the support of the animal structure. The -blood is the principal fluid employed in distributing over -the system the necessary elements of health and vigour, -and for restoring the waste of the body. This fluid, in -passing through the lungs, undergoes a very remarkable -change, and not merely assumes a different colour, but<span class="pagenum"><a name="Page_396" id="Page_396"></a>[Pg 396]</span> -really acquires new properties, from its exposure to the -air with which the cells of these organs are filled. By -a true chemical process, the oxygen is separated from -the air, that oxygen is made to combine with the carbon -and hydrogen, and carbonic acid and water are formed. -These are liberated and thrown off from the body either -through the lungs or by the skin. In the processes of -life, as far as we are enabled to trace them, we see -actions going on which are referred to certain causes -which we <i>appear</i> to explain. Thus, the combination of -the oxygen of the air with the carbon of the blood is -truly designated a case of chemical affinity; and we -find that in endeavouring to imitate the processes of -nature in the laboratory, we are, to a certain extent, -successful. We can combine carbon and oxygen to -produce carbonic acid; and we know that the result of -that combination is the development of certain definite -quantities of heat. Let us examine the conditions of -this chemical phenomenon, and we shall find that in the -natural and artificial processes,—for we must be allowed -to make that distinction,—there are analogous circumstances. -If we place a piece of pure carbon, a lump of -charcoal or a diamond, in a vessel of air, or even of pure -oxygen gas, no change will take place in either of these -elements, and, however long they may be kept together, -they will still be found as carbon or diamond, and -oxygen gas. If we apply heat to the carbon until it -becomes incandescent, it immediately begins to combine -with the oxygen gas,—it burns;—after a little -time all the carbon has disappeared, and we shall find, -if the experiment has been properly made, that a gas is -left behind which is distinguished by properties in every -respect the reverse of those of oxygen, supporting neither -life nor combustion, whereas oxygen gives increased -vigour to both. We have now, indeed, carbonic acid -gas formed by the union of the two principles.</p> - -<p>A dead mass of animal matter may be placed in<span class="pagenum"><a name="Page_397" id="Page_397"></a>[Pg 397]</span> -oxygen gas, and, unless some peculiar conditions are in -some way brought about, no change will take place; -but, if it were possible to apply the <i>spark of life</i> to it, -as we light up the spark in the other case, or if, as that -is beyond the power of man, we substitute a living -creature, a combination between the carbon of the -animal and the gas will immediately begin, and carbonic -acid will be formed by the waste of animal matter, as -in the other case it is by the destruction of the carbon; -and, if there is not a fresh supply given, the animal -must die, from the exhaustion of its fabric. Now, in -both these cases, it is clear that, although this chemical -union is a proximate cause of heat, there must be -existing some power superior to it, as the ultimate cause -thereof.</p> - -<p>The slow combustion (<i>eremacausis</i>) of vegetable -matter, decomposing under the influence of moisture -and the air, does not present similar conditions to those -of the human body, although it has been insisted upon -to be in every respect analogous. That the results -resemble each other is true, but we must carefully distinguish -between effects and causes; and the results of -chemical decomposition in inert matter differ from those -in the living organism. The vegetable matter has lost -the principle of organic life, and, that gone, the tendency -of all things being to be resolved into their most simple -forms, a disunion of the elements commences: oxygen, -hydrogen, and carbon pass off either in the gaseous -state or as water, whilst some carbon is liberated in a -very finely-divided condition, and enters slowly into -combination with oxygen supplied by the water or the -air. Hydrogenous compounds are at the same time -formed, and, under all these circumstances, as in all -other chemical phenomena, an alteration of temperature -results. Heat results from the chemical changes, and -eventually true combustion begins.</p> - -<p>The animal tissue may act in the same way as platina<span class="pagenum"><a name="Page_398" id="Page_398"></a>[Pg 398]</span> -has already been shown to act in producing combination -between gases; but of this we have no proof. We -know that electricity is capable of producing the -required conditions, and we also learn, from the beautiful -researches of Faraday, that the quantity of electricity -developed during decomposition is exactly equal -to that required to effect the combination of the same -elements. Thus it is quite clear that, during the combination -of the carbon of the blood with the oxygen of -the air, a large amount of electricity must become -latent in the compound. The source of this we know -not: it may be derived from some secret spring within -the living structure, or it may be gathered from the -matter surrounding it. There is much in nervous excitation -which appears like electrical phenomena, and -attempts have been frequently made to refer sensation -to the agency of electricity. But these are the dreams -of the ingenious, for which there is but little waking -reality.</p> - -<p>Every mechanical movement of the body occasions -the development of heat; every exertion of the muscles -produces sensible warmth; and, indeed, it can be shown -by experiment that every expansion of muscular fibre is -attended with the escape of caloric, and its contraction -with the absorption of it. There are few operations of -the mind which do not excite the latent caloric of the -body, and frequently we find it manifested in a very remarkable -manner by a suddenly-awakened feeling. The -poet, in the pleasure of creation, glows with the ardour -of his mind, and the blush of the innocent is but the -exhibition of the phenomenon under some nervous excitation, -produced by a spirit-disturbing thought. Thus -we see that the processes of digestion and respiration -are not the only sources of animal heat, but that many -others exist to which much of the natural temperature -of the body must be referred.</p> - -<p>So much that is mysterious belongs to the phenomena<span class="pagenum"><a name="Page_399" id="Page_399"></a>[Pg 399]</span> -of life, that superstition has had a wide scope for the -exercise of its influence; and through all ages a powerful -party of mankind have imagined that the spirit of -human curiosity must be checked before it advances to -remove the veil from any physiological causes. Hence -it is that even at the present day so much that stands -between what, in our ignorance, we call the real and the -supernatural, remains uninvestigated. Even those men -whose <span class="correction" title="In the original book: mind">minds</span> are sceptical upon any development of the -truths of great natural phenomena,—who, at all events, -will have proof before they admit the evidence, are -ready to give credit to the grossest absurdities which -may be palmed upon them by ingenious charlatans, -where the subject is man and his relations to the -spiritual world.</p> - -<p>Man, and the races of animals by which he is surrounded, -present a very striking group, consider them -in whatever light we please. The gradual improvement -of organic form, and the consequent increase of sensibility, -and eventually the development of reason, are -the grandest feature of animated creation.</p> - -<p>The conditions as to number even of the various -classes are not the least remarkable phenomena of life. -In the lowest orders of animals, creatures of imperfect -organization,—consequently those to whom the conditions -of pain must be nearly unknown,—increase by -countless myriads. Of the infusoria and other beings, -entire mountains have been formed, although microscopes -of the highest powers are required to detect an -individual. Higher in the scale, even among insects, -the same remarkable conditions of increase are observed. -Some silkworms lay from 1,000 to 2,000 eggs; the -wasp deposits 3,000; the ant from 4,000 to 5,000. -The queen bee lays between 5,000 and 6,000 eggs -according to Burmeister; but Kirby and Spence state -that in one season the number may amount to 40,000 or<span class="pagenum"><a name="Page_400" id="Page_400"></a>[Pg 400]</span> -50,000. But, above all, the white ant (<i>Termes fatalis</i>) -produces 86,400 eggs each day, which, continuing for a -lunar month, gives the astonishing number of 2,419,200, -a number far exceeding that produced by any known -animal.</p> - -<p>These may appear like the statements in which a -fictionist might indulge, but they are the sober truths -discovered by the most pains-taking and cautious -observers. And it is necessary that such conditions -should prevail. These insects, and all the lower tribes -of the animal kingdom, furnish food for the more -elevated races. Thousands are born in an hour, and -millions upon millions perish in a day. For the support -of organic life, like matter is required; and we -find that the creatures who are destined to become the -prey of others are so constituted that they pass from -life with a perfect unconsciousness of suffering. As the -animal creation advances in size and strength, their -increase becomes limited; and thus they are prevented -from maintaining by numbers that dominion over the -world which they would be enabled from their powers -to do, were their bands more numerous than we now -find them.</p> - -<p>The comparative strength, too, of the insect tribes has -ever been a subject of wonder and of admiration to the -naturalist. The strength of these minute creatures is -enormous; their muscular power, in relation to their -size, far exceeds that of any other animal. The grasshopper -will spring two hundred times the length of its -own body. The dragonfly, by its strength of wing, will -sustain itself in the air for a long summer day with -unabated speed. The house-fly makes six hundred -strokes with its wings, which will carry it five feet, -every second. The stag-beetle, were it the size of the -elephant, would be able to tear up the largest mountains.</p> - -<p>Such are the wonders of the natural world; from the<span class="pagenum"><a name="Page_401" id="Page_401"></a>[Pg 401]</span> -zoophyte, growing like a flowering plant<a name="FNanchor_267_267" id="FNanchor_267_267"></a><a href="#Footnote_267_267" class="fnanchor">[267]</a> upon an -axis filled with living pith—a small remove from the -conditions of vegetable life, upwards through the myriads -of breathing things—to man, we see the dependence -of all upon these physical powers which we have been -considering.</p> - -<p>To trace the effects of those great causes through all -their mysterious phases is the work of inductive science; -and the truths discovered tend to fit us for the enjoyment -of the eternal state of high intelligence to which -every human soul aspires.</p> - -<p>That which the ignorant man calls the supernatural, -the philosopher classes amongst natural phenomena. -The ideal of the credulous man becomes the real to him -who will bend his mind to the task of inquiry. Therefore -to attempt to advance our knowledge of the unknown, -to add to the stores of truth, is an employment -worthy the high destiny of the human race. Remembering -that the revelations of natural science cannot in -any way injure the revelation of eternal truth, but, on -the contrary, aid to establish in the minds of the doubting -a firm conviction of its Divine origin and of man’s -high position, we need never fear that we are proceeding -too far with any inquiry, so long as we are cautious to -examine the conditions of our own minds, that they -be not made the dupe of the senses.</p> - -<p>In the fairies of the hills and valleys, in the gnomes -of the caverns, in the spirits of the elements, we have -the attempts of the mind, when the world was young, -to give form to the dim outshadowings of something -which was then felt to be hidden behind external -nature.</p> - -<p>In the Oread, the Dryad, and the Nereid, we have, in -like manner, an embodiment of powers which the poet-philosopher -saw in his visions presiding over the moun<span class="pagenum"><a name="Page_402" id="Page_402"></a>[Pg 402]</span>tain, -the forest, and the ocean. Content with these, -invested as they were with poetic beauty, man for ages -held them most religiously sacred; but the progress of -natural science has destroyed this class of creations. -“Great Pan is dead,” but the mountains are not voiceless; -they speak in a more convincing tone; and, -instead of the ear catching the dying echo of an obscure -truth, it is gladdened with the full, clear note of nature -in the sweetest voice proclaiming secrets which were -unknown to the dreams of superstition.</p> - -<hr class="chap" /> - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_261_261" id="Footnote_261_261"></a><a href="#FNanchor_261_261"><span class="label">[261]</span></a> <i>Reports of the Fauna of the Ægean</i>: by Professor Forbes.—Reports -of the British Association. <i>On the Physical Conditions -affecting the Distribution of Life in the Sea and the Atmosphere, &c.</i>: -by Dr. Williams. Swansea.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_262_262" id="Footnote_262_262"></a><a href="#FNanchor_262_262"><span class="label">[262]</span></a> <i>The Vestiges of the Natural History of Creation.</i></p></div> - -<div class="footnote"> - -<p><a name="Footnote_263_263" id="Footnote_263_263"></a><a href="#FNanchor_263_263"><span class="label">[263]</span></a> <i>General Outline of the Animal Kingdom</i>: by Professor Thomas -Rymer Jones, F.Z.S.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_264_264" id="Footnote_264_264"></a><a href="#FNanchor_264_264"><span class="label">[264]</span></a> In addition to the memoirs already referred to, Note p. 211, -see Carlisle, <i>On the battery of the Torpedo, governed by a voluntary -muscle</i>.—Phil. Trans., vol. xcv. p. 11. Todd, <i>Experiments on the -Torpedo of the Cape of Good Hope</i>.—Ibid., vol. cvi. p. 120. Todd, -<i>Experiments on the Torpedo Electricus at La Rochelle</i>.—Ibid., -vol. cvii. p. 32.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_265_265" id="Footnote_265_265"></a><a href="#FNanchor_265_265"><span class="label">[265]</span></a> For a concise account of these experiments see <i>Elements of -Natural Philosophy</i>: by Golding Bird, A.M., M.D., &c. 3rd Edition, -chap, xx p. 336. In this work all the most recent researches -are given, and the authorities referred to; see also Matteucci’s -interesting papers already quoted.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_266_266" id="Footnote_266_266"></a><a href="#FNanchor_266_266"><span class="label">[266]</span></a> <i>On the laws according to which the mixing of fluids, and their -penetration into permeable substances, occurs, with special reference -to the processes in the Human and Animal Organism</i>, by Julius -Vogel, of Giessen: translated for the Cavendish Society. Liebig, -<i>On the Motion of the Juices in the Animal Body</i>.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_267_267" id="Footnote_267_267"></a><a href="#FNanchor_267_267"><span class="label">[267]</span></a> <i>A General Outline of the Animal Kingdom</i>: by Thomas Rymer -Jones, p. 54, et seq.</p></div></div> - -<hr class="chap" /> -</div> -<div class="chap"> - -<p><span class="pagenum"><a name="Page_403" id="Page_403"></a>[Pg 403]</span></p> - - -<h2><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI.</h2> - -<p class="center">GENERAL CONCLUSIONS.</p> - - -<p class="chap-head">The Changes produced on Physical Phenomena by the Movement -of the Solar System considered—Exertion of the -Physical Forces through the Celestial Spaces—The Balance -of Powers—Varieties of Matter—Extension of Matter—Theory -of Nonentity—A Material Creation an indisputable -fact—Advantages of the Study of Science—Conclusion.</p> - - -<p class="p2">We have examined terrestrial phenomena under many -of the harmonious conditions which, with our limited -intelligence, we can reach by the aid of science. From -the first exhibition of force, in the cohesion of two -atoms, onward to the full development of organic form -in the highest order of animals, we have observed -strange influences. We have seen the solitary molecule -invested with peculiar properties, and regulated by -mighty forces; we have learned that the modes of -motion given to this beautiful sphere produce curious -changes in the operation of these powers; and we may -with safety infer that every atom constituting this globe -is held in wonderful suspension against every atom of -every star, in the celestial spaces, even to that bright -orb in the centre of the Pleiades, around which the -entire system of created worlds is supposed to roll.</p> - -<p>As we move around our own sun—in the limited -period of 365 days, and round our own axis in 24 hours—we -experience transitions from heat to cold, dependent -upon our position in regard to that luminary and -the laws which regulate the reception and retention of -certain physical forces. May we not therefore conclude,<span class="pagenum"><a name="Page_404" id="Page_404"></a>[Pg 404]</span> -without being charged with making any violent deduction, -that in the great revolution of our system around -the centre of space, we are undergoing gradual changes -which are essential to the great scheme of creation, -though at present incomprehensible to us?</p> - -<p>In our consideration of the influence of time on the -structure of the earth as we find it, we discovered that, -in ages long past, the vegetation of the tropics existed -upon these northern parts of the globe; and geological -research has also proved that over the same lands the -cold of an arctic winter must have long prevailed—the -immense glaciers of that period having left the marks of -their movements upon the face of the existing rocks.<a name="FNanchor_268_268" id="FNanchor_268_268"></a><a href="#Footnote_268_268" class="fnanchor">[268]</a> -We know that during 3,000 years no change of temperature -has taken place in the European climate. -The children of Israel found the date and the vine -flourishing in Canaan; and they exist there still. -Arago has shown that a trifling alteration of temperature -would have destroyed one or the other of these -fruit-bearing trees, since the vine will not ripen where -the mean temperature of the year is higher than 84°, or -the date flourish where it sinks below that degree.</p> - -<p>How immense, then, the duration of time since these -changes must have taken place! The 432,000 years of -Oriental mythology is a period scarcely commensurable -with these effects; yet, to the creature of three-score -years, that period appears an eternity. The thirty-three -millions of geographical miles which our solar system<span class="pagenum"><a name="Page_405" id="Page_405"></a>[Pg 405]</span> -traverses annually, if multiplied by three thousand years, -during which we know no change has taken place, give -us 99,000,000,000 as the distance passed over in that -period. How wide, then, must have been the journey -of the system in space to produce the alteration in the -physical powers, by which these changes have been -effected!</p> - -<p>We have an example, and a striking one, of the variations -which may be produced in all the physical conditions -of a world, in those disturbances of Uranus which -led to the discovery of Neptune. For thirty years or -more certain perturbations were observed in this distant -planet, the discovery of Sir William Herschel, and -calculation pointed to some still more remote mass of -matter as the cause, which has been verified by its actual -discovery. But now Uranus is at rest;—quietly that -star progresses in its appointed orbit,—Neptune can no -longer, for the present, cause it to move with greater or -less rapidity—they are too remote to produce any sensible -influence upon each other. Consequently, for thirty years, -it is evident, phenomena must have occurred on the surface -of Uranus, which can be no longer repeated until these -two planets again arrive at the same positions in their -respective paths which they have occupied since 1812. -These considerations assist us in our attempts to comprehend -infinite time and space; but the human mind -fails to advance far in the great sublimity.</p> - -<p>Through every inch of space we have evidence of the -exercise of such forces as we have been considering. -Gravitation chains world to world, and holds them all -suspended from the mystic centre. Cohesion binds -every mass of matter into a sphere, while motion exerts -a constant power, which tends to alter the form of the -mass. The earth’s form—a flattened spheroid—the -rings of Saturn and of Neptune are the consequences -of motion in antagonism to cohesion. Heat, radiating -from one planet to another, does its work in all, giving<span class="pagenum"><a name="Page_406" id="Page_406"></a>[Pg 406]</span> -variety to matter. Light seeks out every world—each -trembling star tells of the mystery of its presence. -Where light and heat are, chemical action, as an -associated power, must be present; and electricity -must do its wondrous duties amongst them all. Modified -by peculiar properties of matter, they may not -manifest themselves in phenomena like those of our -terrestrial nature; but the evidence of light is a sufficient -proof of the presence of its kindred elements; and it is -difficult to imagine all these powers in action without -producing some form of organization. In the rounded -pebble which we gather from the sea-shore, in the medusa -floating bright with all the beauty of prismatic -colour in the sun-lit sea,—in the animal, mighty in his -strength, roaming the labyrinthine forests, or, great in -intelligence, looking from this to the mysteries of other -worlds,—in all created things around us, we see direct -evidence of a <span class="correction" title="In the original book: beautifnl">beautiful</span> adjustment of the balance of -forces, and the harmonious arrangement of properties.</p> - -<p>One atom is removed from a mass and its character -is changed; one force being rendered more active than -another, and the body, under its influence, ceases to be -the same in condition. The regulation which disposes -the arrangements of matter on this earth, must exist -through the celestial spaces, and every planet bears the -same relation to every other glittering mass in heaven’s -o’erarching canopy, as one atom bears to another in the -pebble, the medusa, the lion, or the man. An indissoluble -bond unites them all, and the grain of sand -which lies buried in the depth of one of our primary formations, -holds, chained to it by these all-pervading -forces, the uncounted worlds which, like luminous sand, -are sprinkled by the hand of the Creator through the -universe. Thus we advance to a conception of the oneness -of creation.</p> - -<p>The vigorous mind of that immortal bard who sang -“of man’s first disobedience,” never, in the highest<span class="pagenum"><a name="Page_407" id="Page_407"></a>[Pg 407]</span> -rapture, the holiest trance of poetic conception, dreamed -of any natural truths so sublime as those which science -has revealed to us.</p> - -<p>The dependence of all the systems of worlds upon -each other, every dust composing each individual globe -being “weighed in a balance,” the adjustment of the -powers by which every physical condition is ordered, the -disposition of matter in the mass of the earth, and the -close relation of the kingdoms of nature,—are all revelations -of natural truths, exalting the mind to the divine -conception of the universe.</p> - -<p>There is a remarkable antagonism displayed in the -operation of many of these forces. Gravitation and -cohesion act in opposition to the repellent influences of -caloric. Light and heat are often associated in a very -remarkable manner; but they are certainly in their -radiant states in antagonism to chemical action, whether -produced by the direct agency of actinic force, or through -the intermediate excitement of the electrical current.<a name="FNanchor_269_269" id="FNanchor_269_269"></a><a href="#Footnote_269_269" class="fnanchor">[269]</a> -And in relation to chemical force, as manifested in organic -combinations, we have the all-powerful operation -of <span class="smcap">life</span> preventing any exercise of its decomposing -power.<a name="FNanchor_270_270" id="FNanchor_270_270"></a><a href="#Footnote_270_270" class="fnanchor">[270]</a> As world is balanced against world in the<span class="pagenum"><a name="Page_408" id="Page_408"></a>[Pg 408]</span> -universe, so in the human fabric, in the vegetable structure, -in the crystallized gem, or in the rude rock, force -is weighed against force, and the balance hangs in tranquillity. -Let but a slight disturbance <span class="correction" title="In the original book: occcasion">occasion</span> a vibration -of the beam, and electricity shakes the stoutest -heart with terror, at the might of its devastating power.<a name="FNanchor_271_271" id="FNanchor_271_271"></a><a href="#Footnote_271_271" class="fnanchor">[271]</a> -Heat melts the hardest rocks, and the earth trembles -with volcanic strugglings; and actinic agency, being -freed from its chains, speedily spreads decay over the -beautiful, and renders the lovely repulsive.</p> - -<p>We know matter in an infinite variety of forms, from -the most ponderous metal to the lightest gas; and we -have it within our power to render the most solid bodies -invisible in the condition of vapour. Is it not easy, then, -to understand that matter may exist equally attenuated -in relation to hydrogen, as that gas itself is, when compared -with the metal platinum? A doubt has been -raised against this view, from the difficulty of accounting -for the passage of the physical elements through solid -masses of matter. If we, however, remember that the -known gases have the power of transpiration through -matter in a remarkable degree,<a name="FNanchor_272_272" id="FNanchor_272_272"></a><a href="#Footnote_272_272" class="fnanchor">[272]</a> and that the passage of -water through a sieve may be prevented by heat, it will -be at once apparent that the permeation of any radiant -body through fixed solid matter is entirely a question -of conditions.</p> - -<p>We can form no idea of the size of the ultimate atom; -we cannot comprehend the degree of etherealization to -which matter may be extended. Our atmosphere, -we have seen, is only another condition of the same -elements which compose all the organized forms of -matter upon the earth, and, at the height reached by -man, it is in a state of extreme attenuation. What<span class="pagenum"><a name="Page_409" id="Page_409"></a>[Pg 409]</span> -must be its condition at the distance of forty miles from -the earth? According to known laws, certain phenomena -of refraction have led us to set these bounds to -the matter constituting our globe: but it may exist in -such a state of tenuity, that no philosophical instrument -constructed by human hands could measure its refracting -power; and who shall declare with certainty that matter -itself may not be as far extended as we suppose its -influences to be?</p> - -<p>“Hast thou perceived the breadth of the earth? declare -if thou knowest it all.</p> - -<p>“Knowest thou the ordinances of heaven? Canst -thou set the dominion thereof in the earth?”</p> - -<p>A cheerless philosophy, derived from the <span class="correction" title="In the original book: transendentalism">transcendentalism</span> -of the German schools, by an unhappy metaphysical -subtlety, and grafted upon what professes to be a -positive philosophy, but which is not so, is spreading -amongst us, and would teach us to regard all things -as the mere exhibition of properties, a manifestation -of powers; it believes not in a material creation. -The grandeur of the earth, and the beautiful forms -adorning it, are not entities. Yonder exquisite specimen -of the skill of man, in which mind appears to shine -through the marble,—that distant mountain which -divides the clouds as they are driven by the winds across -it,—those trees, amid whose branches the birds make -most melodious music,—this flower, so redolent of perfume, -so bright in colour, and so symmetric in form,—and -that lovely being who, a model of beauty and -grace, walks the earth an impersonation of love and -charity blended, making, indeed, “a sunshine in a -shady place,” are not realities. Certain forces combine -to produce effects, all of which unite to deceive poor -man into the belief that he is a material being, and -the inhabitant of a material world. There may be -ingenuity in the philosophy of this school; its metaphysics -may be of a high order; but it evidently<span class="pagenum"><a name="Page_410" id="Page_410"></a>[Pg 410]</span> -advances from the real to the ideal with such rapidity, -that every argument is based on an assumption without -a proof; every assumption being merely a type of the -philosophy itself,—a baseless fabric, a transcendental -vision.</p> - -<p>A material creation surrounds us. This earth, -all that it contains, and the immense hosts of stellar -worlds, are absolute entities, surrounded with, and interpenetrated -by, certain exhibitions of creative intelligence, -which perform, according to fixed laws, the -mighty labours upon which depend the infinite and -eternal mutations of matter. The origin of a grain of -dust is hidden from our finite comprehensions; but its -existence should be a source of hope, that those minds -which are <span class="correction" title="In the original book: alowed">allowed</span> the privilege of tracing out its marvellous -properties,—of examining the empyreal principles -upon which its condition, as a grain of dust, -depends,—and even of reducing these giant elements to -do our human bidding,—may, after a period of probation, -be admitted to the enjoyment of that infinite -power to which the great secrets of creation will be -unveiled.</p> - -<p>Every motion which the accurate search of the experimentalist -has traced, every principle or power which the -physicist has discovered, every combination which the -chemist has detected, every form which the naturalist -has recorded, involves reflections of an exalting character, -which constitute the elements of the highest poetry. The -philosophy of physical science is a grand epic, the record -of natural science a great didactic poem.</p> - -<p>To study science for its useful applications merely, is -to limit its advantages to purely sensual ends. To -pursue science for the sake of the truths it may reveal, -is an endeavour to advance the elements of human -happiness through the intelligence of the race. To -avail ourselves of facts for the improvement of art and -manufactures, is the duty of every nation moving in the<span class="pagenum"><a name="Page_411" id="Page_411"></a>[Pg 411]</span> -advance of civilization. But to draw from the great -truths of science intelligible inferences and masterly -deductions, and from these to advance to new and beautiful -abstractions, is a mental exercise which tends to -the refinement and elevation of every human feeling.</p> - -<p>The mind thus exercised during the mid-day of life, -will find in the twilight of age a divine serenity; and, -charmed by the music of nature, which, like a vesper -hymn poured forth from pious souls, proclaims in devotion’s -purest strain the departure of day, he will sink -into the repose of that mysterious night which awaits -us all, tranquil in the happy consciousness that the sun -of truth will rise in unclouded brilliancy, and place him -in the enjoyment of that intellectual light, which has -ever been among the holiest aspirations of the human -race.</p> - -<p>The task of wielding the wand of science,—of standing -a scientific evocator within the charmed circle of its -powers, is one which leads the mind through nature up -to nature’s God.</p> - -<p>Experiment and observation instruct us in the discovery -of a fact;—that fact connects itself with natural -phenomena,—the ultimate cause of which we learn from -Divine revelation, and receive in full belief,—but the -proximate causes are reserved as trials of man’s intelligence; -and every natural truth, discovered by induction, -enables the contemplative mind to deduce those perfect -laws which are exemplifications of the fresh-springing -and all enduring <span class="smcap">Poetry of Science</span>.</p> - -<hr class="chap" /> - - - -<div class="footnotes"><p class="center">FOOTNOTES:</p> - -<div class="footnote"> - -<p><a name="Footnote_268_268" id="Footnote_268_268"></a><a href="#FNanchor_268_268"><span class="label">[268]</span></a> “As to the polishing and grooving of hard rocks, it has lately -been ascertained that glaciers give rise to these effects when -pushing forward sand, pebbles, and rocky fragments, and causing -them to grate along the bottom. Nor can there be any doubt that -icebergs, when they run aground on the floor of the ocean, imprint -similar marks upon it.”—<i>Principles of Geology, or the modern -changes of the Earth and its Inhabitants considered as illustrative -of Geology</i>: by Charles Lyell, M.A., F.R.S. <i>Travels through the -Alps of Savoy, and other parts of the Pennine Chain, with Observations -on the Phenomena of Glaciers</i>: by James D. Forbes, F.R.S.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_269_269" id="Footnote_269_269"></a><a href="#FNanchor_269_269"><span class="label">[269]</span></a> This may be readily proved by the following simple but instructive -experiment:—Take two pairs of watch-glasses; into one -pair put a solution of nitrate of silver, into the other a weak solution -of iodide of potassium; connect the silver solution of each -pair with the potash one by a film of cotton, and carry a platina -wire from one glass into the other. Place one series in sunshine, -and the other in a dark place. After a few hours it will be found -that the little galvanic arrangement in the dark will exhibit, around -the platina wire, a very pretty crystallization of metallic silver, -but no such change is observable in the other exposed to light. -If a yellow glass is interposed between the glass and the sunshine, -the action proceeds as when in the dark. This experiment is -naturally suggestive of many others, and it involves some most -important considerations.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_270_270" id="Footnote_270_270"></a><a href="#FNanchor_270_270"><span class="label">[270]</span></a> In cases of violent death it is often found the gastric juice -has, in a few hours, dissolved portions of the stomach.—Dr. Budd’s -Lecture before the College of Physicians.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_271_271" id="Footnote_271_271"></a><a href="#FNanchor_271_271"><span class="label">[271]</span></a> Faraday’s <i>Experimental Researches</i>, vol. i.; from which a -quotation has already been made, showing the enormous quantity -of electricity which is latent in matter.</p></div> - -<div class="footnote"> - -<p><a name="Footnote_272_272" id="Footnote_272_272"></a><a href="#FNanchor_272_272"><span class="label">[272]</span></a> <i>On the Motion of Gases</i>: by Professor Graham, F.R.S.—Phil. -Trans., vol. cxxxvi. p. 573.</p></div></div> - - -<hr class="chap" /> -</div> -<div class="chap"> -<p><span class="pagenum"><a name="Page_413" id="Page_413"></a>[Pg 413]</span></p> - - -<h2><a name="INDEX" id="INDEX"></a>INDEX.</h2> - - -<ul id="indx"> -<li>Absorption of heat by air, water, and earth, <a href="#Page_74">74</a>.</li> -<li>—— of light, <a href="#Page_125">125</a>.</li> -<li>Acalephæ, or phosphorescent animals, <a href="#Page_387">387</a>.</li> -<li>Actinism, <a href="#Page_166">166</a>.</li> -<li>—— producing chemical change, <a href="#Page_174">174</a>.</li> -<li>—— and light antagonistic, <a href="#Page_177">177</a>.</li> -<li>——, influence of, on plants, <a href="#Page_372">372</a>.</li> -<li>Action of presence—<i>Catalysis</i>, <a href="#Page_280">280</a>.</li> -<li>“Active principles” of Newton, <a href="#Page_11">11</a>.</li> -<li>Adams on planet Neptune, <a href="#Page_32">32</a>.</li> -<li>Adiathermic bodies, <a href="#Page_95">95</a>.</li> -<li><span class="correction" title="In the original book: Ærial">Aërial</span> currents dependent on heat, <a href="#Page_80">80</a>.</li> -<li>—— chemical, <a href="#Page_274">274</a>.</li> -<li>Affinity, <a href="#Page_292">292</a>.</li> -<li>Age of the world, <a href="#Page_404">404</a>.</li> -<li>Aggregation, attraction of, <a href="#Page_48">48</a>.</li> -<li>——, crystalline, <a href="#Page_58">58</a>.</li> -<li>Agonic lines, <a href="#Page_244">244</a>.</li> -<li>Air, absorption of heat by, <a href="#Page_74">74</a>.</li> -<li>—— density of the, <a href="#Page_319">319</a>.</li> -<li>Alchemy, Nature’s, <a href="#Page_293">293</a>.</li> -<li>Aldini on animal electricity, <a href="#Page_393">393</a>.</li> -<li>Allotropic conditions of atoms, <a href="#Page_43">43</a>.</li> -<li>Allotropism, <a href="#Page_330">330</a>.</li> -<li>Allotropy, <a href="#Page_291">291</a>.</li> -<li>Alum, opacity to heat rays, <a href="#Page_65">65</a>.</li> -<li>Alpinus’ theory of matter, <a href="#Page_47">47</a>.</li> -<li>Ammonites of the lias, <a href="#Page_341">341</a>.</li> -<li>Ammoniacal amalgam, <a href="#Page_325">325</a>.</li> -<li>Ampère’s theory of magnetism, <a href="#Page_239">239</a>.</li> -<li>Analogy, dangers of reasoning by, <a href="#Page_152">152</a>.</li> -<li>Ancients’ knowledge of magnetism, <a href="#Page_235">235</a>.</li> -<li>Animals, phosphorescence of, <a href="#Page_154">154</a>.</li> -<li>—— respiration of, <a href="#Page_310">310</a>.</li> -<li>—— articulated, <a href="#Page_388">388</a>.</li> -<li>Animal magnetism, <a href="#Page_267">267</a>.</li> -<li><span class="correction" title="In the original book: Magnetic electricity">—— electricity</span>, <a href="#Page_211">211</a>, <a href="#Page_392">392</a>.</li> -<li>—— life, progress of, <a href="#Page_338">338</a>.</li> -<li>——, phenomena of, <a href="#Page_383">383</a>.</li> -<li>Arago on the surface of the sun, <a href="#Page_123">123</a>.</li> -<li>—— on copying the Egyptian temples, <a href="#Page_177">177</a>.</li> -<li>—— on magnetic variation, <a href="#Page_246">246</a>.</li> -<li><i>Arbor Dianæ</i>—silver tree, <a href="#Page_261">261</a>.</li> -<li>Aristotle on motion, <a href="#Page_10">10</a>.</li> -<li>Atmosphere, uses of the, <a href="#Page_319">319</a>.</li> -<li>Atmospheric refraction, <a href="#Page_322">322</a>.</li> -<li>Atomic theory, <a href="#Page_278">278</a>.</li> -<li>—— volumes, <a href="#Page_287">287</a>.</li> -<li>Atoms, allotropic state of, <a href="#Page_43">43</a>.</li> -<li>Atom, the organic, <a href="#Page_360">360</a>.</li> -<li>——, ultimate size of, <a href="#Page_408">408</a>.</li> -<li>——, the, and its powers, <a href="#Page_3">3</a>.</li> -<li>Attraction, chemical, <a href="#Page_275">275</a>.</li> -<li>Aurora of the sun, <a href="#Page_186">186</a>.</li> - -<li class="ifrst">Back’s account of Aurora, <a href="#Page_249">249</a>.</li> -<li>Balance of forces, <a href="#Page_14">14</a>.</li> -<li>Bartholin on Iceland spar, <a href="#Page_140">140</a>.</li> -<li>Beccaria, Father, on phosphorescence, <a href="#Page_160">160</a>.</li> -<li>Becquerel’s experiments on electricity, <a href="#Page_227">227</a>.</li> -<li>—— on ozone, <a href="#Page_300">300</a>.</li> -<li>Bell on the nerves, <a href="#Page_391">391</a>.</li> -<li>Belemnites, <a href="#Page_341">341</a>.</li> -<li>Berkeley, Bishop, on motion, <a href="#Page_10">10</a>.</li> -<li>Berzelius on allotropy, <a href="#Page_44">44</a>.</li> -<li>—— on catalysis, <a href="#Page_281">281</a>.</li> -<li>Biela’s comet, <a href="#Page_26">26</a>.</li> -<li>Biot on polarization, <a href="#Page_145">145</a>.</li> -<li>Bolognian stone, <a href="#Page_161">161</a>.</li> -<li>Bouguer on the absorption of light by the atmosphere, <a href="#Page_126">126</a>.</li> -<li><span class="pagenum"><a name="Page_414" id="Page_414"></a>[Pg 414]</span>Boutigny on heat, <a href="#Page_107">107</a>.</li> -<li><i>Boletus igniarius</i>, <a href="#Page_102">102</a>.</li> -<li>Boyle on motion, <a href="#Page_9">9</a>.</li> -<li>Brain and nerves, <a href="#Page_391">391</a>.</li> -<li>Brahminical philosophy, <a href="#Page_245">245</a>.</li> -<li>Brewster, Sir D., refers magnetism to the sun, <a href="#Page_263">263</a>.</li> -<li>—— on magnetism, <a href="#Page_247">247</a>.</li> -<li>Brown’s doctrines of life, <a href="#Page_395">395</a>.</li> -<li>Butterfly, metamorphosis of, <a href="#Page_389">389</a>.</li> - -<li class="ifrst"><span class="correction" title="In the original book: Caignard">Cagniard</span> de la Tour state, <a href="#Page_106">106</a>.</li> -<li>Calorific transparency, <a href="#Page_65">65</a>.</li> -<li>—— influence on plants, <a href="#Page_376">376</a>.</li> -<li>Calotype, the, <a href="#Page_174">174</a>.</li> -<li>Canton’s phosphorus, <a href="#Page_161">161</a>.</li> -<li>Carbon, allotropic state of, <a href="#Page_43">43</a>.</li> -<li>Carboniferous plants, fossil, <a href="#Page_339">339</a>.</li> -<li>Carbonic acid, solid, <a href="#Page_111">111</a>.</li> -<li>—— quantity in atmosphere, <a href="#Page_311">311</a>.</li> -<li>Cassini on magnetic variation, <a href="#Page_246">246</a>.</li> -<li>Catalysis, <a href="#Page_280">280</a>.</li> -<li>Cell, organic, <a href="#Page_361">361</a>.</li> -<li>Cellini, Benvenuto, on the carbuncle, <a href="#Page_159">159</a>.</li> -<li>Central sun, doctrine of a, <a href="#Page_27">27</a>.</li> -<li>Changes, physical, <a href="#Page_290">290</a>.</li> -<li>Chemical phenomena developing heat, <a href="#Page_42">42</a>.</li> -<li>—— decomposition producing heat, <a href="#Page_97">97</a>.</li> -<li>—— combination by heat, <a href="#Page_98">98</a>.</li> -<li>—— affinity suspended by heat, <a href="#Page_109">109</a>.</li> -<li>—— radiations, <a href="#Page_166">166</a>.</li> -<li>—— power of solar rays in the Tropics, <a href="#Page_177">177</a>.</li> -<li>—— agency of luminous rays, <a href="#Page_178">178</a>.</li> -<li>—— action influenced by magnetism, <a href="#Page_252">252</a>.</li> -<li>—— forces, <a href="#Page_270">270</a>.</li> -<li>—— elements, <a href="#Page_272">272</a>.</li> -<li>—— proportions, <a href="#Page_285">285</a>.</li> -<li>—— metamorphoses, <a href="#Page_289">289</a>.</li> -<li>—— phenomena, <a href="#Page_295">295</a>.</li> -<li>—— composition of atmosphere, <a href="#Page_322">322</a>.</li> -<li>—— rays, action of, on germination, <a href="#Page_375">375</a>.</li> -<li>Chemistry, Electro, <a href="#Page_206">206</a>.</li> -<li>—— of Nature, <a href="#Page_270">270</a>.</li> -<li>—— Animal, <a href="#Page_396">396</a>.</li> -<li>Chinese knowledge of magnet, <a href="#Page_236">236</a>.</li> -<li>Chlorophylle, formation of, <a href="#Page_373">373</a>.</li> -<li>Chloride of sulphur, transparency of, to heat, <a href="#Page_65">65</a>.</li> -<li>Chlorine and hydrogen combine by light, <a href="#Page_171">171</a>.</li> -<li>Chlorine in the ocean, <a href="#Page_303">303</a>.</li> -<li>Cholera and electricity, <a href="#Page_215">215</a>.</li> -<li>Choroid coat, the, <a href="#Page_149">149</a>.</li> -<li>Chromatic lines on the earth, <a href="#Page_133">133</a>.</li> -<li>Clay converted into slate by electricity, <a href="#Page_227">227</a>.</li> -<li>Climate of the earth, <a href="#Page_350">350</a>.</li> -<li>Clock, Electrical, <a href="#Page_233">233</a>.</li> -<li>Coal formation, theory of, <a href="#Page_314">314</a>.</li> -<li>Cohesive force opposed to gravitation, <a href="#Page_33">33</a>.</li> -<li>Cohesion and gravitation, <a href="#Page_49">49</a>.</li> -<li>—— distinguished from crystallization, <a href="#Page_51">51</a>.</li> -<li>Cold, extreme, <a href="#Page_110">110</a>.</li> -<li>Colour of bodies, <a href="#Page_132">132</a>.</li> -<li>—— changes of, in chemical combinations, <a href="#Page_290">290</a>.</li> -<li>—— blue, of sky, <a href="#Page_320">320</a>.</li> -<li>—— of steam, <a href="#Page_321">321</a>.</li> -<li>Colours, Newton’s theory of, <a href="#Page_135">135</a>.</li> -<li>Coloured heat rays, <a href="#Page_85">85</a>.</li> -<li>Combining equivalents, <a href="#Page_273">273</a>.</li> -<li>—— forces, <a href="#Page_292">292</a>.</li> -<li>Combination, laws of, <a href="#Page_286">286</a>.</li> -<li>—— of forces, <a href="#Page_330">330</a>.</li> -<li>Combustion, <a href="#Page_305">305</a>.</li> -<li>Comets, <a href="#Page_26">26</a>.</li> -<li>Condensation of gases, <a href="#Page_290">290</a>.</li> -<li>Conduction of heat, <a href="#Page_69">69</a>.</li> -<li>Conducting power of bodies for heat, <a href="#Page_89">89</a>.</li> -<li>Condition, change of chemical, <a href="#Page_271">271</a>.</li> -<li>Conversion of motion, <a href="#Page_16">16</a>.</li> -<li>Convection of heat, <a href="#Page_69">69</a>.</li> -<li>Cotyledons, use of the, <a href="#Page_368">368</a>.</li> -<li>Coulomb on repulsion of atoms, <a href="#Page_47">47</a>.</li> -<li>Creation, oneness of, <a href="#Page_406">406</a>.</li> -<li>Cretaceous formations, <a href="#Page_344">344</a>.</li> -<li>Crosse on electricity, <a href="#Page_227">227</a>.</li> -<li>Crustaceans, metamorphosis of, <a href="#Page_389">389</a>.</li> -<li>Crust of the earth, <a href="#Page_333">333</a>.</li> -<li><span class="pagenum"><a name="Page_415" id="Page_415"></a>[Pg 415]</span>Crystals, pseudomorphous, <a href="#Page_54">54</a>.</li> -<li>——, size of, <a href="#Page_56">56</a>.</li> -<li>Crystallogenic forces, <a href="#Page_50">50</a>.</li> -<li>Crystalline bodies, magnetic influence of, <a href="#Page_260">260</a>.</li> -<li>Cudworth’s “Plastic Nature,” <a href="#Page_10">10</a>.</li> -<li>Current, electric, speed of, <a href="#Page_231">231</a>.</li> -<li>——, electricity, magnetic, <a href="#Page_239">239</a>.</li> -<li>Crystallization, <a href="#Page_50">50</a>.</li> -<li>Cultivation, limits of, <a href="#Page_379">379</a>.</li> -<li>Currents of electricity around the earth, <a href="#Page_224">224</a>.</li> -<li>Cyanite, a true magnet, <a href="#Page_48">48</a>.</li> - -<li class="ifrst">Daguerre’s discovery, <a href="#Page_170">170</a>.</li> -<li>Daguerreotype, the, <a href="#Page_172">172</a>.</li> -<li>Dalton on Aurora Borealis, <a href="#Page_248">248</a>.</li> -<li>—— on liquefaction, <a href="#Page_287">287</a>.</li> -<li>Dalton’s atomic theory, <a href="#Page_278">278</a>.</li> -<li>Daniel on incandescence, <a href="#Page_100">100</a>.</li> -<li>Dark lines of spectrum, <a href="#Page_125">125</a>.</li> -<li>Darwin on sea-weeds of the Southern Ocean, <a href="#Page_316">316</a>.</li> -<li>Davy, Sir H., on the elements, <a href="#Page_328">328</a>.</li> -<li>—— on flame, <a href="#Page_307">307</a>.</li> -<li>—— discovers the alkaline metals, <a href="#Page_325">325</a>.</li> -<li>Decomposition, electro-chemical, <a href="#Page_208">208</a>.</li> -<li>De la Tour, Cagniard’s experiments, <a href="#Page_105">105</a>.</li> -<li>Delaroche on heat, <a href="#Page_93">93</a>.</li> -<li>Density of the earth, <a href="#Page_31">31</a>.</li> -<li>Development, animal, <a href="#Page_384">384</a>.</li> -<li>Dew, formation of, <a href="#Page_81">81</a>.</li> -<li>Diamond, allotropic carbon, <a href="#Page_43">43</a>.</li> -<li>——, phosphorescence of, <a href="#Page_160">160</a>.</li> -<li>Diamagnetism, <a href="#Page_253">253</a>.</li> -<li>Diamagnetic nature of gases, <a href="#Page_259">259</a>.</li> -<li>Diathermic bodies, <a href="#Page_94">94</a>.</li> -<li>Diffusion of gases, <a href="#Page_323">323</a>.</li> -<li>Digestion a cause of heat, <a href="#Page_105">105</a>.</li> -<li>Dip of magnetic needle, <a href="#Page_247">247</a>.</li> -<li>Dimorphism in crystals, <a href="#Page_55">55</a>.</li> -<li>Directive power of a magnet on crystals, <a href="#Page_261">261</a>.</li> -<li>Distribution of elements, <a href="#Page_328">328</a>.</li> -<li>Divisibility of matter, <a href="#Page_38">38</a>.</li> -<li><span class="correction" title="In the original book: Doebereiner’s">Döbereiner’s</span> lamp, <a href="#Page_281">281</a>.</li> -<li>Dispersion of light, <a href="#Page_129">129</a>.</li> -<li>Draper on incandescence, <a href="#Page_100">100</a>.</li> -<li>Dumas on atoms, <a href="#Page_39">39</a>.</li> -<li>Dust, a grain of, <a href="#Page_2">2</a>.</li> - -<li class="ifrst">Earth, physical, the, <a href="#Page_1">1</a>.</li> -<li>—— density of, <a href="#Page_31">31</a>.</li> -<li>—— the revolution of the, <a href="#Page_77">77</a>.</li> -<li>——, geological formation of, <a href="#Page_333">333</a>.</li> -<li>Earth’s, motion, <a href="#Page_11">11</a>.</li> -<li>—— temperature dependent on the sun, <a href="#Page_63">63</a>.</li> -<li>Effects produced by loss of heat, <a href="#Page_69">69</a>.</li> -<li>Eggs, number of, laid by insects, <a href="#Page_399">399</a>.</li> -<li>Elective affinity, <a href="#Page_292">292</a>.</li> -<li>Electricity, <a href="#Page_193">193</a>.</li> -<li>Electricity and light influencing crystallization, <a href="#Page_57">57</a>.</li> -<li>——, kinds of, <a href="#Page_195">195</a>.</li> -<li>—— contained in water, <a href="#Page_203">203</a>.</li> -<li>—— developed by chemical action, <a href="#Page_204">204</a>.</li> -<li>——, velocity of, <a href="#Page_231">231</a>.</li> -<li>—— of plants, <a href="#Page_380">380</a>.</li> -<li>Electric condition of matter, <a href="#Page_5">5</a>.</li> -<li>—— telegraph, the, <a href="#Page_231">231</a>.</li> -<li>—— affinity, <a href="#Page_275">275</a>.</li> -<li>Electrical phosphorescence, <a href="#Page_160">160</a>.</li> -<li>—— action influenced by actinism, <a href="#Page_183">183</a>.</li> -<li>—— radiations, <a href="#Page_190">190</a>.</li> -<li>—— clock, <a href="#Page_233">233</a>.</li> -<li>Electro-chemistry, <a href="#Page_206">206</a>.</li> -<li>Electro culture, <a href="#Page_223">223</a>.</li> -<li>Electrotype, the, <a href="#Page_229">229</a>.</li> -<li>Electro-chemical decomposition, <a href="#Page_208">208</a>.</li> -<li>Electro-magnetism, <a href="#Page_240">240</a>.</li> -<li>Electrum, <a href="#Page_193">193</a>.</li> -<li>Elements, chemical, <a href="#Page_37">37</a>, <a href="#Page_272">272</a>.</li> -<li>——, atmospheric, <a href="#Page_325">325</a>.</li> -<li>——, interchanges of, <a href="#Page_319">319</a>.</li> -<li>Englefield on heat rays, <a href="#Page_67">67</a>.</li> -<li>Eocene formations, <a href="#Page_346">346</a>.</li> -<li>Equinoxes, precession of the, <a href="#Page_244">244</a>.</li> -<li>——, the vernal and autumnal, <a href="#Page_77">77</a>.</li> -<li>Epicurus’ hooked atoms, <a href="#Page_48">48</a>.</li> -<li>Epipolic phenomena, <a href="#Page_129">129</a>.</li> -<li>Eremacausis, <a href="#Page_105">105</a>.</li> -<li>Ether, hypothesis of an, <a href="#Page_120">120</a>.</li> -<li>Examples of crystallization, <a href="#Page_59">59</a>.</li> -<li>Expansion of bodies by heat, <a href="#Page_96">96</a>.</li> -<li><span class="pagenum"><a name="Page_416" id="Page_416"></a>[Pg 416]</span>Eye, mechanism of, <span class="correction" title="In the original book: 491"><a href="#Page_149">149</a></span>.</li> - -<li class="ifrst">Faraday on Magnetism of Crystals, <a href="#Page_59">59</a>.</li> -<li>—— on solidification of gases, <a href="#Page_112">112</a>.</li> -<li>—— on magnetization of light, <a href="#Page_147">147</a>.</li> -<li>—— on the gymnotus, <a href="#Page_211">211</a>.</li> -<li>—— on <span class="correction" title="In the original book: dia-magnetism">diamagnetism</span>, <a href="#Page_254">254</a>.</li> -<li>Ferro-magnetic bodies, <a href="#Page_255">255</a>.</li> -<li>Fish Lizard, the, <a href="#Page_341">341</a>.</li> -<li>Fixed stars, light of, <a href="#Page_122">122</a>.</li> -<li>Flint glass, permeability to heat, <a href="#Page_65">65</a>.</li> -<li>Flora, fossil, <a href="#Page_345">345</a>.</li> -<li>Flowers, influences of, <a href="#Page_317">317</a>.</li> -<li>Fluid, magnetic theory of, <a href="#Page_252">252</a>.</li> -<li>Fluorescence of light, <a href="#Page_130">130</a>.</li> -<li>Forbes, Prof. Jas., on vibrations of heated metals, <a href="#Page_97">97</a>.</li> -<li>Forbes, Prof. Edward, on zones of life in the ocean, <a href="#Page_127">127</a>.</li> -<li>Forbes on colour of steam, <a href="#Page_321">321</a>.</li> -<li>Force producing motion, <a href="#Page_9">9</a>.</li> -<li>—— a cause of motion, <a href="#Page_17">17</a>.</li> -<li>——, molecular, <a href="#Page_40">40</a>.</li> -<li>—— of crystallization, <a href="#Page_61">61</a>.</li> -<li>Forces, active, in matter, <a href="#Page_3">3</a>.</li> -<li>——, balance of, <a href="#Page_14">14</a>.</li> -<li>—— in antagonism, <a href="#Page_407">407</a>.</li> -<li>Form, change of, <a href="#Page_2">2</a>.</li> -<li>—— of surface, influence of, on climate, <a href="#Page_351">351</a>.</li> -<li>——, variety of vegetable, <a href="#Page_359">359</a>.</li> -<li>Foster describes Northern Lights, <a href="#Page_249">249</a>.</li> -<li>Fox, R. W., on temperature of Cornish mines, <a href="#Page_91">91</a>.</li> -<li>Franklin on atoms, <a href="#Page_47">47</a>.</li> -<li>Franklin’s kite experiment, <a href="#Page_214">214</a>.</li> -<li>Freezing mixtures, <a href="#Page_110">110</a>.</li> -<li>Freezing, remarkable phenomena of, <a href="#Page_112">112</a>.</li> -<li>—— of water, <a href="#Page_302">302</a>.</li> -<li>Friction, <a href="#Page_17">17</a>.</li> -<li>Frictional electricity, <a href="#Page_199">199</a>.</li> -<li>Fraunhofer’s dark lines, <a href="#Page_125">125</a>.</li> -<li>Franklin’s experiment on heat, <a href="#Page_75">75</a>.</li> -<li>Fusion influenced by pressure, <a href="#Page_107">107</a>.</li> - -<li class="ifrst">Galvanism, <a href="#Page_201">201</a>.</li> -<li>Galvani’s experiment, <a href="#Page_201">201</a>.</li> -<li>Gases, condensation of, <a href="#Page_111">111</a>, <a href="#Page_290">290</a>.</li> -<li>——, magnetism of, <a href="#Page_259">259</a>.</li> -<li>Gaseous constitution, <a href="#Page_317">317</a>.</li> -<li>Gauss’s theory of magnetism, <a href="#Page_243">243</a>.</li> -<li>Generation, spontaneous, <a href="#Page_363">363</a>.</li> -<li>Geological phenomena, <a href="#Page_332">332</a>.</li> -<li>Germ, Treviranus on the, <a href="#Page_361">361</a>.</li> -<li>Germination of seeds, <a href="#Page_367">367</a>.</li> -<li>Glass, coloured, transparency to heat, <a href="#Page_65">65</a>.</li> -<li>Goethe’s theory of colour, <a href="#Page_139">139</a>.</li> -<li>Goethe on phosphorescence, <a href="#Page_157">157</a>.</li> -<li>—— on the leaf, <a href="#Page_369">369</a>.</li> -<li>Graham’s law of diffusion, <a href="#Page_323">323</a>.</li> -<li>Gravitation, <a href="#Page_21">21</a>.</li> -<li>Growth explained, <a href="#Page_52">52</a>.</li> -<li>——, progress of, <a href="#Page_364">364</a>.</li> -<li>—— defined, <a href="#Page_383">383</a>.</li> -<li>Grove decomposes water by heat, <a href="#Page_98">98</a>.</li> -<li>Gulf stream, the, <a href="#Page_81">81</a>.</li> -<li>Gulielmini on crystallisation, <a href="#Page_50">50</a>.</li> -<li>Gun cotton, <a href="#Page_103">103</a>.</li> -<li>Gymnotus electricus, <a href="#Page_211">211</a>.</li> -<li>Gyroscope, the, <a href="#Page_14">14</a>.</li> - -<li class="ifrst">Hansteen and Arago on Northern Lights, <a href="#Page_248">248</a>.</li> -<li>Hansteen on magnetism, <a href="#Page_244">244</a>.</li> -<li>Heat, solar and terrestrial, <a href="#Page_62">62</a>.</li> -<li>——, conductors of, <a href="#Page_90">90</a>.</li> -<li>——, rays absorbed by atmosphere, <a href="#Page_63">63</a>, <a href="#Page_73">73</a>.</li> -<li>—— and light, their relations, <a href="#Page_64">64</a>.</li> -<li>——, radiation of, <a href="#Page_82">82</a>.</li> -<li>—— rays, coloured, <a href="#Page_85">85</a>.</li> -<li>—— lessens chemical affinity, <a href="#Page_88">88</a>.</li> -<li>——, latent, <a href="#Page_101">101</a>.</li> -<li>——, decomposition by, <a href="#Page_109">109</a>, <a href="#Page_276">276</a>.</li> -<li>——, scientific knowledge of, <a href="#Page_114">114</a>.</li> -<li>—— developed by combustion of wood equivalent to heat absorbed in growth, <a href="#Page_116">116</a>.</li> -<li>——, influence of, on magnetism, <a href="#Page_241">241</a>.</li> -<li>——, action of, on water, <a href="#Page_302">302</a>.</li> -<li>——, influence of on plants, <a href="#Page_371">371</a>.</li> -<li>—— essential to life, <a href="#Page_395">395</a>.</li> -<li>Heliography of M. Niepce, <a href="#Page_170">170</a>.</li> -<li>Herbivorous animals, <a href="#Page_315">315</a>.</li> -<li>Herschel on the nebulæ, <a href="#Page_24">24</a>.</li> -<li><span class="pagenum"><a name="Page_417" id="Page_417"></a>[Pg 417]</span>Herschel, Sir W., on heat rays, <a href="#Page_67">67</a>.</li> -<li>Hobbes on the properties of matter, <a href="#Page_8">8</a>.</li> -<li>Hopkins on the temperature of fusion, <a href="#Page_107">107</a>.</li> -<li>Huyghens on double refraction, <a href="#Page_140">140</a>.</li> -<li>Hydra, the, <a href="#Page_387">387</a>.</li> -<li>Hydrogen, peroxide of, <a href="#Page_298">298</a>.</li> -<li>—— and oxygen, <a href="#Page_289">289</a>, <a href="#Page_297">297</a>.</li> -<li>Hydro-carbons, <a href="#Page_297">297</a>.</li> -<li>Hydro-carbon compounds, <a href="#Page_308">308</a>.</li> -<li>Hypnotism, Mr. Braid on, <a href="#Page_269">269</a>.</li> - -<li class="ifrst">Ice, <a href="#Page_301">301</a>.</li> -<li>Ichthyosaurus, the, <a href="#Page_341">341</a>.</li> -<li>Igneous rocks, <a href="#Page_335">335</a>.</li> -<li>Ignition by chemical action, <a href="#Page_102">102</a>.</li> -<li>Iguanodon, the, <a href="#Page_343">343</a>.</li> -<li>Incandescence, temperature of, 69–100.</li> -<li>Influences of matter on heat, <a href="#Page_79">79</a>.</li> -<li>Infusoria and animalculæ, <a href="#Page_387">387</a>.</li> -<li>Interference of light, <a href="#Page_138">138</a>.</li> -<li>Intensity, magnetic, <a href="#Page_247">247</a>.</li> -<li>Invisible light, Moser on, <a href="#Page_188">188</a>.</li> -<li>Iodide of silver found natural, <a href="#Page_304">304</a>.</li> -<li>Iodine, <a href="#Page_304">304</a>.</li> -<li>Iridescent paper, <a href="#Page_137">137</a>.</li> -<li>Iron, magnetic, <a href="#Page_235">235</a>.</li> -<li>——, soft, rendered magnetic, <a href="#Page_241">241</a>.</li> -<li>——, rusting, <a href="#Page_306">306</a>.</li> -<li>Isomeric compounds, <a href="#Page_291">291</a>.</li> -<li>Isomorphism, <a href="#Page_290">290</a>.</li> -<li>Isothermic lines, <a href="#Page_92">92</a>.</li> -<li>Isodynamic lines, <a href="#Page_247">247</a>.</li> - -<li class="ifrst">Jones, Rymer, on sponges, <a href="#Page_345">345</a>.</li> -<li>Joule on anhydrous salts, <a href="#Page_287">287</a>.</li> -<li>—— on heat and motion, <a href="#Page_18">18</a>.</li> - -<li class="ifrst">Kircher’s Magnetism, <a href="#Page_264">264</a>.</li> -<li>Kupffar on magnetic storms, <a href="#Page_249">249</a>.</li> - -<li class="ifrst">Lamination of clay by electricity, <a href="#Page_226">226</a>.</li> -<li>Land and sea, alternations of, <a href="#Page_340">340</a>.</li> -<li>Laplace’s theory of the universe, <a href="#Page_23">23</a>.</li> -<li>Latent heat, <a href="#Page_101">101</a>.</li> -<li>Lavoisier’s theory of combustion, <a href="#Page_305">305</a>.</li> -<li>Law of gravitation, <a href="#Page_30">30</a>.</li> -<li>Lawson, letter from Mr., on germination of seeds, <a href="#Page_375">375</a>.</li> -<li>Leaf, the functions of the, <a href="#Page_369">369</a>.</li> -<li>Leaves of plants, action on air of, <a href="#Page_311">311</a>.</li> -<li>Le Verrier on planet Neptune, <a href="#Page_32">32</a>.</li> -<li>Leyden jar, the, <a href="#Page_198">198</a>.</li> -<li>Lias formations, <a href="#Page_341">341</a>.</li> -<li>Liebig and organic chemistry, <a href="#Page_284">284</a>.</li> -<li>Life and light, <a href="#Page_52">52</a>.</li> -<li>——, influence of light on, <a href="#Page_153">153</a>.</li> -<li>—— dependent on light, <a href="#Page_164">164</a>.</li> -<li>——, vegetable, <a href="#Page_362">362</a>.</li> -<li>——, mysteries of, <a href="#Page_398">398</a>.</li> -<li>Light, <a href="#Page_118">118</a>.</li> -<li>—— essential to life, <a href="#Page_39">39</a>.</li> -<li>—— of fixed stars, <a href="#Page_122">122</a>.</li> -<li>——, transparency to, <a href="#Page_124">124</a>.</li> -<li>——, transmission of, through different media, <a href="#Page_128">128</a>.</li> -<li>——, absorption of, <a href="#Page_125">125</a>.</li> -<li>——, interference of, <a href="#Page_138">138</a>.</li> -<li>——, polarized condition of, <a href="#Page_141">141</a>.</li> -<li>——, magnetization of, <a href="#Page_146">146</a>.</li> -<li>——, artificial, <a href="#Page_162">162</a>.</li> -<li>——, influence of, on plants, <a href="#Page_373">373</a>.</li> -<li>—— and heat, correlation of, <a href="#Page_64">64</a>.</li> -<li>Lightning conductors, <a href="#Page_215">215</a>.</li> -<li>Lindley on the leaf, <a href="#Page_370">370</a>.</li> -<li>Lubbock, Sir J., on shooting stars, <a href="#Page_22">22</a>.</li> -<li>Lodes, mineral, electricity of, <a href="#Page_225">225</a>.</li> -<li>Luminous and actinic rays distinguished, <a href="#Page_176">176</a>.</li> - -<li class="ifrst">Machine electricity, <a href="#Page_209">209</a>.</li> -<li>Magellanic clouds, <a href="#Page_25">25</a>.</li> -<li>Magnetic curves, <a href="#Page_236">236</a>.</li> -<li>—— iron ore, <a href="#Page_237">237</a>.</li> -<li>—— polarity, <a href="#Page_237">237</a>.</li> -<li>—— points of convergence, <a href="#Page_244">244</a>.</li> -<li>—— poles of the earth, <a href="#Page_245">245</a>.</li> -<li>—— intensity, 247</li> -<li>—— storms, <a href="#Page_249">249</a>.</li> -<li>—— lines of no variation, <a href="#Page_243">243</a>.</li> -<li>Magnetism, <a href="#Page_235">235</a>.</li> -<li>—— induced, <a href="#Page_238">238</a>.</li> -<li>—— influenced by heat, <a href="#Page_242">242</a>.</li> -<li>——, universality of, <a href="#Page_253">253</a>.</li> -<li>—— of gases, <a href="#Page_259">259</a>.</li> -<li><span class="pagenum"><a name="Page_418" id="Page_418"></a>[Pg 418]</span>—— induced by solar rays <a href="#Page_263">263</a>.</li> -<li>—— and electricity, correlation of, <a href="#Page_239">239</a>.</li> -<li>—— and crystallisation, <a href="#Page_57">57</a>.</li> -<li>Magneto-electrical decomposition, <a href="#Page_230">230</a>.</li> -<li>Magnetisation of light, <a href="#Page_146">146</a>.</li> -<li>Malus on polarisation, <a href="#Page_139">139</a>.</li> -<li>Mammalia, fossil, <a href="#Page_343">343</a>.</li> -<li>Man, temperature of, <a href="#Page_105">105</a>.</li> -<li>Manganesiate of potash, <a href="#Page_171">171</a>.</li> -<li>Mantell, Dr., on the iguanodon, <a href="#Page_343">343</a>.</li> -<li>Mariotte on seat of vision, <a href="#Page_149">149</a>.</li> -<li>Matter, its general conditions, <a href="#Page_1">1</a>.</li> -<li>——, forms of, <a href="#Page_21">21</a>.</li> -<li>——, transmutation of, <a href="#Page_37">37</a>.</li> -<li>——, divisibility of, <a href="#Page_38">38</a>.</li> -<li>——, solid, absorption of heat by, <a href="#Page_75">75</a>.</li> -<li>——, influence of, on light, <a href="#Page_162">162</a>.</li> -<li>——, polarity of, <a href="#Page_265">265</a>.</li> -<li>—— and its properties, <a href="#Page_409">409</a>.</li> -<li>——, entity of, <a href="#Page_410">410</a>.</li> -<li>——, varied condition of, <a href="#Page_36">36</a>.</li> -<li>Mayer’s hypothesis of three colours, <a href="#Page_138">138</a>.</li> -<li>Mechanical force and heat, <a href="#Page_103">103</a>.</li> -<li>Mechanism of the eye, <a href="#Page_149">149</a>.</li> -<li>Media, influence of, on light, <a href="#Page_128">128</a>.</li> -<li>Medusæ, phosphorescence of, <a href="#Page_159">159</a>.</li> -<li>Melloni on coloured heat rays, <a href="#Page_85">85</a>.</li> -<li>—— on new nomenclature for heat, <a href="#Page_95">95</a>.</li> -<li>Mesmer and electricity, <a href="#Page_222">222</a>.</li> -<li>Metamorphic rocks, <a href="#Page_336">336</a>.</li> -<li>Metamorphoses of animals, <a href="#Page_389">389</a>.</li> -<li>Mexico, Gulf of, warmth of the, <a href="#Page_81">81</a>.</li> -<li>Mica, black, transparency to heat, <a href="#Page_66">66</a>.</li> -<li>Miller, Dr., on dark lines of the spectrum, <a href="#Page_126">126</a>.</li> -<li>Mineral veins, electricity of, <a href="#Page_225">225</a>.</li> -<li>Mines, Cornish, temperature of, <a href="#Page_91">91</a>.</li> -<li>Miocene formations, <a href="#Page_346">346</a>.</li> -<li>Mirrors, magic, <a href="#Page_191">191</a>.</li> -<li>Mitscherlich on expansion of crystals by heat, <a href="#Page_257">257</a>.</li> -<li>Molecular forces, <a href="#Page_35">35</a>, <a href="#Page_40">40</a>.</li> -<li>——, compound action of, <a href="#Page_279">279</a>.</li> -<li>Molecules, Dumas on, <a href="#Page_39">39</a>.</li> -<li>—— combination, <a href="#Page_277">277</a>.</li> -<li>Morichini and Carpi on magnetism of violet rays of light, <a href="#Page_263">263</a>.</li> -<li>Moser on invisible light, <a href="#Page_189">189</a>.</li> -<li>Motion, <a href="#Page_7">7</a>.</li> -<li>—— a property of matter, <a href="#Page_8">8</a>.</li> -<li>——, principles of, <a href="#Page_10">10</a>.</li> -<li>—— of the earth, <a href="#Page_12">12</a>.</li> -<li>—— round an axis shows the earth’s motion, <a href="#Page_18">18</a>.</li> -<li>——, influence of, on form, <a href="#Page_32">32</a>.</li> -<li>Mountain ranges probably determined by magnetic force, <a href="#Page_262">262</a>.</li> -<li>Multiplication of life, <a href="#Page_399">399</a>.</li> -<li>Musical notes produced by heat, <a href="#Page_97">97</a>.</li> -<li>Muscular contraction by electricity, <a href="#Page_202">202</a>.</li> -<li><span class="correction" title="In the original book: Muschenbrock">Musschenbroek</span> of Leyden, <a href="#Page_198">198</a>.</li> -<li>Mythology, ancient, probable origin of, <a href="#Page_353">353</a>.</li> - -<li class="ifrst">Natural polarization, <a href="#Page_145">145</a>.</li> -<li>Nebulous state of matter, <a href="#Page_23">23</a>.</li> -<li>Neptune, discovery of, <a href="#Page_32">32</a>.</li> -<li>Newton on gravitating force, <a href="#Page_49">49</a>.</li> -<li>Newton on motion, <a href="#Page_9">9</a>.</li> -<li>Newton’s hypothesis of matter, <a href="#Page_4">4</a>.</li> -<li>—— theory of heat, <a href="#Page_115">115</a>.</li> -<li>—— theory of light, <a href="#Page_120">120</a>.</li> -<li>—— theory of colours, <a href="#Page_135">135</a>.</li> -<li>Niepce on the chemical radiations, <a href="#Page_168">168</a>.</li> -<li>Nitrogen, magnetic neutrality of, <a href="#Page_259">259</a>.</li> -<li>——, combinations of, <a href="#Page_324">324</a>.</li> -<li>——, supposed metallic nature of, <a href="#Page_325">325</a>.</li> -<li>Nocturnal radiation, <a href="#Page_83">83</a>.</li> -<li>Northern lights, the, <a href="#Page_268">268</a>.</li> - -<li class="ifrst">Obsidian transparency to heat, <a href="#Page_66">66</a>.</li> -<li>Ocean, waters of, <a href="#Page_303">303</a>.</li> -<li>Oersted discovers electro-magnetism, <a href="#Page_238">238</a>.</li> -<li>Orders of animals, <a href="#Page_386">386</a>.</li> -<li>Organic creation, influence, <a href="#Page_185">185</a>.</li> -<li>—— compounds, <a href="#Page_283">283</a>.</li> -<li>—— compounds, influence of light on them, <a href="#Page_181">181</a>.</li> -<li>—— chemistry, <a href="#Page_331">331</a>.</li> -<li>—— cell, <a href="#Page_360">360</a>.</li> -<li>—— remains, <a href="#Page_337">337</a>.</li> -<li>Organized forms, varieties of, <a href="#Page_35">35</a>.</li> -<li>—— bodies, heat of, <a href="#Page_104">104</a>.</li> -<li><span class="pagenum"><a name="Page_419" id="Page_419"></a>[Pg 419]</span>Organization, progress of, <a href="#Page_385">385</a>.</li> -<li>Oxides, metallic, <a href="#Page_326">326</a>.</li> -<li>Oxidizable metals, <a href="#Page_305">305</a>.</li> -<li>Oxygen gas magnetic, <a href="#Page_259">259</a>.</li> -<li>—— and nitrogen, uses of, <a href="#Page_321">321</a>.</li> -<li>—— and carbon in animals, <a href="#Page_396">396</a>.</li> -<li>Ozone, <a href="#Page_299">299</a>.</li> -<li>—— and electricity, <a href="#Page_217">217</a>.</li> - -<li class="ifrst">Palladium maintaining slow combustion, <a href="#Page_309">309</a>.</li> -<li>Parathermic rays, <a href="#Page_74">74</a>.</li> -<li>—— rays, influence in nature, <a href="#Page_377">377</a>.</li> -<li>Particles, Dumas on, <a href="#Page_39">39</a>.</li> -<li>Peach on phosphorescence of the sea, <a href="#Page_159">159</a>.</li> -<li>Pearsall on phosphorescence, <a href="#Page_160">160</a>.</li> -<li>Pendulum, oscillation of, indicates the earth’s motion, <a href="#Page_13">13</a>.</li> -<li>Perkins on repulsion of heat, <a href="#Page_108">108</a>.</li> -<li>Permeation of heat, <a href="#Page_96">96</a>.</li> -<li>Perturbations of Uranus, <a href="#Page_31">31</a>.</li> -<li>Pestilential diseases, <a href="#Page_216">216</a>.</li> -<li>Phenomena of vision, <a href="#Page_148">148</a>.</li> -<li>——, natural, of electricity, <a href="#Page_194">194</a>.</li> -<li>——, recent geological, <a href="#Page_349">349</a>.</li> -<li>Phosphorescence of animals, <a href="#Page_154">154</a>.</li> -<li>—— of plants, <a href="#Page_156">156</a>.</li> -<li>Phosphorescent spectrum, <a href="#Page_184">184</a>.</li> -<li>Phosphoric acid detected in the oldest rocks, <a href="#Page_337">337</a>.</li> -<li>Photosphere of the sun, <a href="#Page_123">123</a>.</li> -<li>Photography, <a href="#Page_170">170</a>.</li> -<li>——, its importance, <a href="#Page_180">180</a>.</li> -<li>Physiological influences of electricity, <a href="#Page_219">219</a>.</li> -<li>Physical forces, action of, <a href="#Page_4">4</a>, <a href="#Page_45">45</a>.</li> -<li>—— forces, modes of motion, <a href="#Page_7">7</a>.</li> -<li>—— properties of polarized light, <a href="#Page_142">142</a>.</li> -<li>Physiological influences of magnetism, <a href="#Page_268">268</a>.</li> -<li>Pilchard, on the, by Couch, <a href="#Page_315">315</a>.</li> -<li>Plants, distribution of, dependent on light, <a href="#Page_133">133</a>.</li> -<li>——, phosphorescence of, <a href="#Page_156">156</a>.</li> -<li>——, respiration of, <a href="#Page_312">312</a>.</li> -<li>—— and animals, dependence of, <a href="#Page_313">313</a>.</li> -<li>——, growth of, <a href="#Page_368">368</a>.</li> -<li>—— bend to the light, <a href="#Page_373">373</a>.</li> -<li>——, distribution of, <a href="#Page_378">378</a>.</li> -<li>—— of the Tropics, <a href="#Page_381">381</a>.</li> -<li>Plane polarization, <a href="#Page_141">141</a>.</li> -<li>“Plastic nature” of Cudworth, <a href="#Page_10">10</a>.</li> -<li>Plateau’s experiment on bodies relieved from gravitation, <a href="#Page_33">33</a>.</li> -<li>Platinum maintaining slow combustion, <a href="#Page_309">309</a>.</li> -<li>Plato on motion, <a href="#Page_10">10</a>.</li> -<li>—— on light, <a href="#Page_119">119</a>.</li> -<li>Plesiosaurus, the, <a href="#Page_341">341</a>.</li> -<li>Pliocene formations, <a href="#Page_346">346</a>.</li> -<li>Plücker on crystallo-magnetic force, <a href="#Page_57">57</a>.</li> -<li>—— on diamagnetic bodies, <a href="#Page_256">256</a>.</li> -<li>Plumule, use of, <a href="#Page_369">369</a>.</li> -<li>Plutonic rocks, <a href="#Page_334">334</a>.</li> -<li>Polarization, circular and elliptical, <a href="#Page_143">143</a>.</li> -<li>Polarization of light, <a href="#Page_139">139</a>.</li> -<li>Polar condition of matter, <a href="#Page_265">265</a>.</li> -<li>Polypes and infusoria, <a href="#Page_387">387</a>.</li> -<li>Porosity of matter, <a href="#Page_41">41</a>.</li> -<li>Porta, Baptista—camera obscura, <a href="#Page_149">149</a>.</li> -<li>Powers, active, in nature, <a href="#Page_405">405</a>.</li> -<li>Prevost, theory of, on heat, <a href="#Page_96">96</a>.</li> -<li>Primary origin of our planet, <a href="#Page_334">334</a>.</li> -<li>Principles of motion, <a href="#Page_10">10</a>.</li> -<li>Prismatic refraction, <a href="#Page_121">121</a>.</li> -<li>—— rays, heat of, <a href="#Page_67">67</a>.</li> -<li>—— analysis of sunbeam, <a href="#Page_134">134</a>.</li> -<li>Principle of gravitation, <a href="#Page_29">29</a>.</li> -<li>——, elementary, <a href="#Page_38">38</a>.</li> -<li>Properties, essential, of matter, <a href="#Page_5">5</a>.</li> -<li>Pseudomorphism, <a href="#Page_54">54</a>.</li> -<li>Psychology of flowers, <a href="#Page_357">357</a>.</li> -<li>Pterodactyl, the, <a href="#Page_342">342</a>.</li> -<li>Pythagorean doctrine of motion, <a href="#Page_10">10</a>.</li> - -<li class="ifrst">Quinine, solution, influence of, on light, <a href="#Page_129">129</a>.</li> - -<li class="ifrst">Radiant heat, <a href="#Page_69">69</a>.</li> -<li>Radiation and absorption of heat, <a href="#Page_77">77</a>.</li> -<li>——, nocturnal, <a href="#Page_83">83</a>.</li> -<li>Raia torpedo, <a href="#Page_211">211</a>.</li> -<li>Raymond, Du Bois, on animal electricity, <a href="#Page_221">221</a>.</li> -<li>Refrangibility, rays of high, <a href="#Page_130">130</a>.</li> -<li>—— of solar forces, <a href="#Page_168">168</a>.</li> -<li><span class="pagenum"><a name="Page_420" id="Page_420"></a>[Pg 420]</span>Refraction, prismatic, <a href="#Page_121">121</a>.</li> -<li>Races, dependence of, <a href="#Page_315">315</a>.</li> -<li>Repulsion of heat, <a href="#Page_108">108</a>.</li> -<li>Respiration of animals, <a href="#Page_310">310</a>.</li> -<li>—— plants, <a href="#Page_312">312</a>.</li> -<li>Rest, absolute and relative, <a href="#Page_15">15</a>.</li> -<li>Respiration a cause of heat, <a href="#Page_105">105</a>.</li> -<li>Retina, the, <a href="#Page_149">149</a>.</li> -<li>Revelations of nature, <a href="#Page_401">401</a>.</li> -<li>Revolution of magnetic poles, <a href="#Page_246">246</a>.</li> -<li>Robinson on decomposition by heat, <a href="#Page_98">98</a>.</li> -<li>Rock formations, <a href="#Page_335">335</a>.</li> -<li>Rocks, conducting power of, <a href="#Page_224">224</a>.</li> -<li>Rosse’s, Lord, telescopes, <a href="#Page_25">25</a>.</li> -<li>Rumford, Count, experiments on heat, <a href="#Page_18">18</a>.</li> -<li>—— on chemical properties of light, <a href="#Page_99">99</a>.</li> -<li>Rings, Newton’s, <a href="#Page_137">137</a>.</li> - -<li class="ifrst">Safety lamp of Davy, <a href="#Page_309">309</a>.</li> -<li>Salt rock, transparency to heat, <a href="#Page_65">65</a>.</li> -<li>Saturn’s ring explained, <a href="#Page_34">34</a>.</li> -<li>Savart on vibrating plates, <a href="#Page_257">257</a>.</li> -<li>Seasons, influence of heat on the, <a href="#Page_70">70</a>.</li> -<li>Sea, phosphorescence of, <a href="#Page_158">158</a>.</li> -<li>Schönbein on ozone, <a href="#Page_299">299</a>.</li> -<li>Schwabe on solar spots, <a href="#Page_243">243</a>.</li> -<li>Seebeck on thermo-electricity, <a href="#Page_211">211</a>, <a href="#Page_248">248</a>.</li> -<li>Selenite and alabaster, <a href="#Page_60">60</a>.</li> -<li>Sénarmont on conducting power of crystals for heat, <a href="#Page_257">257</a>.</li> -<li>Shooting stars, <a href="#Page_21">21</a>.</li> -<li>Silicon, allotropic state of, <a href="#Page_43">43</a>.</li> -<li>Silica, substitution of, <a href="#Page_345">345</a>.</li> -<li>Simple bodies, chemical, <a href="#Page_329">329</a>.</li> -<li>Sky of tropical climes, <a href="#Page_319">319</a>.</li> -<li>Slow combustion in animals, <a href="#Page_397">397</a>.</li> -<li>Smee on electricity and vitality, <a href="#Page_219">219</a>.</li> -<li>Solar system, motion of, <a href="#Page_11">11</a>.</li> -<li>—— disc, light from, <a href="#Page_185">185</a>.</li> -<li>—— influence on magnetism, <a href="#Page_263">263</a>.</li> -<li>Solidification of gases by Faraday, <a href="#Page_112">112</a>.</li> -<li>Solstices, summer and winter, <a href="#Page_77">77</a>.</li> -<li>Solar spots connected with magnetism, <a href="#Page_243">243</a>.</li> -<li>Solar phosphori, <a href="#Page_161">161</a>.</li> -<li>Somerville, Mrs., magnetises needles by light, <a href="#Page_263">263</a>.</li> -<li>Sound and light, analogy of, <a href="#Page_151">151</a>.</li> -<li>Spectra produced by polarization of light, <a href="#Page_144">144</a>.</li> -<li>Spectrum, dark lines of, <a href="#Page_125">125</a>.</li> -<li>Spheroidal condition of fluids, <a href="#Page_107">107</a>.</li> -<li>Spontaneous ignition, <a href="#Page_307">307</a>.</li> -<li>Stahl on phlogiston, <a href="#Page_305">305</a>.</li> -<li>Stars, shooting, theories of, <a href="#Page_21">21</a>.</li> -<li>Steel ornaments incandescent, <a href="#Page_137">137</a>.</li> -<li>Stereoscope, the, <a href="#Page_151">151</a>.</li> -<li>Stokes, Prof., on fluorescence, <a href="#Page_130">130</a>.</li> -<li>Stratified formations, <a href="#Page_334">334</a>.</li> -<li>Strength of animals, <a href="#Page_400">400</a>.</li> -<li>Structure, influence of, on magnetism, <a href="#Page_256">256</a>.</li> -<li>——, relation of, to physical phenomena, <a href="#Page_257">257</a>.</li> -<li>Struvé on motion of solar system, <a href="#Page_12">12</a>.</li> -<li>Substitution, chemical, <a href="#Page_279">279</a>.</li> -<li>——, law of, <a href="#Page_288">288</a>.</li> -<li>Substances, all, electric, <a href="#Page_197">197</a>.</li> -<li>Subterranean temperature, <a href="#Page_91">91</a>.</li> -<li>Sulphuric acid, permeability to heat, <a href="#Page_65">65</a>.</li> -<li>Surfaces, action of, <a href="#Page_282">282</a>.</li> -<li>Sulzar on galvanism, <a href="#Page_201">201</a>.</li> -<li>Sulphuretted hydrogen, solid, <a href="#Page_111">111</a>.</li> -<li>Sun, the central, <a href="#Page_28">28</a>.</li> -<li>——, the source of light, <a href="#Page_121">121</a>.</li> -<li>——, physical state of the, <a href="#Page_123">123</a>.</li> -<li>——, a magnetic centre, <a href="#Page_265">265</a>.</li> - -<li class="ifrst">Tadpole, metamorphosis of, <a href="#Page_389">389</a>.</li> -<li>Talbot’s sensitive photographic process, <a href="#Page_178">178</a>.</li> -<li>Telegraph, electric, <a href="#Page_231">231</a>.</li> -<li>Temperature of incandescence, <a href="#Page_68">68</a>.</li> -<li>Temperature, subterranean, <a href="#Page_91">91</a>.</li> -<li>Terrestrial currents of electricity, <a href="#Page_224">224</a>.</li> -<li>—— magnetism, <a href="#Page_255">255</a>.</li> -<li>Thales of Miletus discovers electricity, <a href="#Page_193">193</a>.</li> -<li>Theories of light, <a href="#Page_86">86</a>, <a href="#Page_118">118</a>.</li> -<li>Thermography, <a href="#Page_188">188</a>.</li> -<li><span class="pagenum"><a name="Page_421" id="Page_421"></a>[Pg 421]</span>Thermometric examination of the temperature of flowers, <a href="#Page_76">76</a>.</li> -<li>Thermo-electricity, <a href="#Page_209">209</a>.</li> -<li>Theory of motion producing force, <a href="#Page_15">15</a>.</li> -<li>Thilorier on solid carbonic acid, <a href="#Page_111">111</a>.</li> -<li>Time, influence of, <a href="#Page_332">332</a>.</li> -<li>Tissues, catalytic power of, <a href="#Page_310">310</a>.</li> -<li>Tourmaline, action of, on light, <a href="#Page_142">142</a>.</li> -<li>Trade winds, <a href="#Page_81">81</a>.</li> -<li>Transition series of rocks, <a href="#Page_336">336</a>.</li> -<li>Transparency, calorific, <a href="#Page_67">67</a>.</li> -<li>——, luminous, <a href="#Page_124">124</a>.</li> -<li>Transmutation of matter, <a href="#Page_37">37</a>.</li> -<li>Transmission of light, <a href="#Page_128">128</a>.</li> -<li>Transcalescent bodies, <a href="#Page_94">94</a>.</li> -<li>Trevelyan, Mr., on vibration of heated metals, <a href="#Page_97">97</a>.</li> -<li>Tyndale proves the influence of structure on magnetism, <a href="#Page_258">258</a>.</li> -<li>Type, elements of the organic, <a href="#Page_289">289</a>.</li> - -<li class="ifrst">Undulations producing colour, <a href="#Page_131">131</a>.</li> -<li>Undulatory theory of heat, <a href="#Page_115">115</a>.</li> -<li>—— theory of light, <a href="#Page_121">121</a>.</li> -<li>Uranus, discovery of, <a href="#Page_31">31</a>.</li> -<li>Uranium glass, influence of, on light, <a href="#Page_129">129</a>.</li> - -<li class="ifrst">Vapour, elastic force of, <a href="#Page_318">318</a>.</li> -<li>Variation, magnetic, <a href="#Page_244">244</a>.</li> -<li>Vegetables conductors of electricity, <a href="#Page_379">379</a>.</li> -<li>Vegetable life, phenomena of, <a href="#Page_357">357</a>.</li> -<li>Vegetation of carboniferous epoch, <a href="#Page_339">339</a>.</li> -<li>Velocity of electricity, <a href="#Page_231">231</a>.</li> -<li>Vertebrate animals, <a href="#Page_390">390</a>.</li> -<li>Vision, phenomena of, <a href="#Page_148">148</a>.</li> -<li>Vis vitæ, vital principle, <a href="#Page_391">391</a>.</li> -<li>Vision single with a pair of eyes, <a href="#Page_150">150</a>.</li> -<li>Vitality superior to physical force, <a href="#Page_53">53</a>.</li> -<li>Vision, seat of, <a href="#Page_149">149</a>.</li> -<li>Volume, doctrine of, <a href="#Page_287">287</a>.</li> -<li>Volcanic action referred to chemical action, <a href="#Page_271">271</a>.</li> -<li>Volatilization of matter, <a href="#Page_27">27</a>.</li> -<li>Voltaic electricity, <a href="#Page_201">201</a>.</li> - -<li class="ifrst">Water, absorption of heat by, <a href="#Page_74">74</a>.</li> -<li>—— frozen free of air, <a href="#Page_112">112</a>.</li> -<li>—— free of air, peculiar state of, <a href="#Page_113">113</a>.</li> -<li>——, electricity in a drop of, <a href="#Page_204">204</a>.</li> -<li>——, composition of, <a href="#Page_296">296</a>.</li> -<li>Wargentin’s notice of aurora, <a href="#Page_248">248</a>.</li> -<li>Wave movement of heat and light, <a href="#Page_68">68</a>.</li> -<li>Wealden formations, <a href="#Page_343">343</a>.</li> -<li>Wedgwood on incandescence, <a href="#Page_100">100</a>.</li> -<li>Wells, Dr., on dew, <a href="#Page_84">84</a>.</li> -<li><span class="correction" title="In the original book: Wiedman">Wiedemann</span> on electrical vibrations, <a href="#Page_257">257</a>.</li> -<li>Wenzel’s proportional numbers, <a href="#Page_277">277</a>.</li> -<li>Winds dependent on heat, <a href="#Page_80">80</a>.</li> -<li>Wollaston notices dark lines in spectrum, <a href="#Page_125">125</a>.</li> -<li>World, its age, <a href="#Page_404">404</a>.</li> - -<li class="ifrst">Young on molecular forces, <a href="#Page_49">49</a>.</li> - -<li class="ifrst">Zodiacal light, <a href="#Page_25">25</a>.</li> -<li>Zoophytes, microscopic, <a href="#Page_387">387</a>.</li> -</ul> - - -<p class="p2 center">THE END.</p> - - -<p class="p2 center">Wilson and Ogilvy, 57, Skinner Street, Snowhill, London.</p> - -<hr class="chap" /> -</div> -<div class="chap"> - - -<h2><a name="BOHNS_BOOKS" id="BOHNS_BOOKS"></a>BOHN’S BOOKS.</h2> - -<h3>BOHN’S STANDARD LIBRARY.</h3> - -<p class="bohn1"><i>Post 8vo., Elegantly Printed, and bound in Cloth, at 3s. 6d. per Vol.</i></p> - -<ul class="bohn-books"> -<li><b>1. 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Changes are indicated below and in the text <span class="not-hh">with -a mouse-over</span> like <span class="correction" title="In the original book: that">this</span>. -<span class="hh-only"> The cover was developed at pgdp.net and is in the -public domain.</span></p> - - -<p>Some entries in the index were out of alphabetical order in the original book. They have been moved without -noting them in the details below.</p> - -<p>The totals in the various tables are not equal to the sum of the column -above them. I assume this is due to round off error, or details in the -original data which are not represented here. No attempt has been made -to correct these totals.</p> - -<p>In the original book, half of the publisher’s catalogue (Bohn’s Books) was in the beginnig of the book. -It was moved to immediately precede the other half of the catalogue at the end of the book.</p> - -<p>Preface, Contents, Introduction, Index, Bohn’s Books and Transcriber’s Note have been added to -the table of contents. Only the chapters of the book were in the table of contents in the original book. The title -"Bohn’s Books" was inserted into the beginning of the publisher’s book catalogue.</p> - -<p>In the table below, the first line shows the text in this ebook, the second line shows the text in the original -book.</p> - -<table id="details" summary="details of the transcribing changes"> -<tr><td class="dfrst">Page <a href="#Page_vii">vii</a>.:</td><td class="dfrst">conditions of Matter—Diamagnetism, &c. 235</td></tr> -<tr><td>Originally:</td><td>conditions of Matter—Dia-Magnetism, &c. 235</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_viii">viii</a>.:</td><td class="dfrst">Time, an element in Nature’s Operations—Geological</td></tr> -<tr><td>Originally:</td><td>Time, an element in Nature’s Operations==Geological</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_viii">viii</a>.:</td><td class="dfrst">Progress of Matter towards Organization</td></tr> -<tr><td>Originally:</td><td>Progress of Matter rowards Organization</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_xii">xii</a>.:</td><td class="dfrst">of external nature, evoked beautiful spiritualizations</td></tr> -<tr><td>Originally:</td><td>of external nature, evoked beautiful spirtualizations</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_1_1">1</a>:</td><td class="dfrst">Boscovich regarded the constitution of matter differently</td></tr> -<tr><td>Originally:</td><td>Boscovitch regarded the constitution of matter differently</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_1_1">1</a>:</td><td class="dfrst">full explanation of the theory of Boscovich.)</td></tr> -<tr><td>Originally:</td><td>full explanation of the theory of Boscovitch.)</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_8">8</a>:</td><td class="dfrst">The views of metaphysicians regarding motion involve</td></tr> -<tr><td>Originally:</td><td>The views of metaphyscians regarding motion involve</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_14">14</a>:</td><td class="dfrst">tremulous gyration upon the deck of a vast aërial ship</td></tr> -<tr><td>Originally:</td><td>tremulous gyration upon the deck of a vast aerial ship</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_27">27</a>:</td><td class="dfrst">agent of organisation and all manifestations of beauty?</td></tr> -<tr><td>Originally:</td><td>agent of organisation and all manifestatious of beauty?</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_18_18">18</a>:</td><td class="dfrst">fixes, est déterminée par ce qui précède entre certaines</td></tr> -<tr><td>Originally:</td><td>fixes, est determinée par ce qui précède entre certaines</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_18_18">18</a>:</td><td class="dfrst">est le groupe central de l’ensemble du système</td></tr> -<tr><td>Originally:</td><td>est le groupe central l’ensemble du système</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_24_24">24</a>:</td><td class="dfrst">into a single mass at the bottom of the flask under</td></tr> -<tr><td>Originally:</td><td>into a single mass at the bottom of the flask unde</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_42">42</a>:</td><td class="dfrst">with which the particles combined, from interstices,</td></tr> -<tr><td>Originally:</td><td>with which the particles combined, from insterstices,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_45">45</a>:</td><td class="dfrst">bromine, &c., are the results of different <i>allotropic</i></td></tr> -<tr><td>Originally:</td><td>bromime, &c., are the results of different <i>allotropic</i></td></tr> - -<tr><td class="dfrst">Page <a href="#Page_46">46</a>:</td><td class="dfrst">which,—from the imperfections of science,—resisting</td></tr> -<tr><td>Originally:</td><td>which,—from the imperfectious of science,—resisting</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_46">46</a>:</td><td class="dfrst">The experiments of Faraday and of Plücker prove</td></tr> -<tr><td>Originally:</td><td>The experiments of Faraday and of Plucker prove</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_25_25">25</a>:</td><td class="dfrst">Young’s <i>Natural Philosophy</i>; ed. by Rev. P. Kelland.</td></tr> -<tr><td>Originally:</td><td>Young’s <i>Natural Philosophy</i>; ed. by Rev. P. Lelland.</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_35_35">35</a>:</td><td class="dfrst">Hence the origin of compound and visible bodies; hence</td></tr> -<tr><td>Originally:</td><td>Hence the origin of compouud and visible bodies; hence</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_50">50</a>:</td><td class="dfrst">her operations, but the very processes themselves.</td></tr> -<tr><td>Originally:</td><td>her operations, but the very processes themselvss.</td></tr> - -<tr><td class="dfrst">Paqe <a href="#Page_59">59</a>:</td><td class="dfrst">combination appears to the eye in no respect different</td></tr> -<tr><td>Originally:</td><td>combinatiou appears to the eye in no respect different</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_61">61</a>:</td><td class="dfrst">Those fissures formed by the first system of crystalline</td></tr> -<tr><td>Originally:</td><td>Those fissures formed by the first sytsem of crystalline</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_68">68</a>:</td><td class="dfrst">luminous power are sufficiently striking to convince us</td></tr> -<tr><td>Originally:</td><td>luminous power are sufficienlty striking to convince us</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_109">109</a>:</td><td class="dfrst">of temperature is experienced.[79] Professor Plücker, of</td></tr> -<tr><td>Originally:</td><td>of temperature is experienced.[79] Professor Plucker, of</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_55_55">55</a>:</td><td class="dfrst">this motion. He was followed by Musschenbroek, and then</td></tr> -<tr><td>Originally:</td><td>this motion. He was followed by Muschenbroek, and then</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_61_61">61</a>:</td><td class="dfrst"><i>regarding the internal temperature of the Earth</i>: by</td></tr> -<tr><td>Originally:</td><td><i>regarding the internal temperature of tha Earth</i>: by</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_78_78">78</a>:</td><td class="dfrst"><i>en vertu de l’état sphéroïdal dans un creuset</i></td></tr> -<tr><td>Originally:</td><td><i>en vertu de l’état sphérodïal dans un creuset</i></td></tr> - -<tr><td class="dfrst">Page <a href="#Page_121">121</a>:</td><td class="dfrst">Fraunhofer, Herschel, Brewster, and others, but proceed</td></tr> -<tr><td>Originally:</td><td>Frauenhofer, Herschel, Brewster, and others, but proceed</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_123">123</a>:</td><td class="dfrst">between charcoal points at the poles of a powerful voltaic</td></tr> -<tr><td>Originally:</td><td>between charcoal points a the poles of a powerful voltaic</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_129">129</a>:</td><td class="dfrst">of quinine, and the fluor spar, we obtain the same results</td></tr> -<tr><td>Originally:</td><td>of quinine, and the flour spar, we obtain the same results</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_140">140</a>:</td><td class="dfrst">the first instance, by Erasmus Bartholin, in Iceland-spar,</td></tr> -<tr><td>Originally:</td><td>the first instance, by Erasmus Bartolin, in Iceland-spar,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_145">145</a>:</td><td class="dfrst">from what has been already stated, that some</td></tr> -<tr><td>Originally:</td><td>from what has beeen already stated, that some</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_153">153</a>:</td><td class="dfrst">to prove that light is absolutely necessary to</td></tr> -<tr><td>Originally:</td><td>to prove that light is absolutely neccessary to</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_159">159</a>:</td><td class="dfrst">of light behind them.[113] By microscopic examination</td></tr> -<tr><td>Originally:</td><td>of light behind them.[113] By miscroscopic examination</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_159">159</a>:</td><td class="dfrst">Benvenuto Cellini gave a curious account of a carbuncle</td></tr> -<tr><td>Originally:</td><td>Benvenuto Cellini give a curious account of a carbuncle</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_160">160</a>:</td><td class="dfrst">near a fire. From this it may be inferred that the</td></tr> -<tr><td>Originally:</td><td>near a a fire. From this it may be infered that the</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_88_88">88</a>:</td><td class="dfrst">Brande’s <i>Manual of Chemistry</i>; or, indeed, any work</td></tr> -<tr><td>Originally:</td><td>Brande’s <i>Mannal of Chemistry</i>; or, indeed, any work</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_94_94">94</a>:</td><td class="dfrst">Schouw, <i>Grundzüge der Pflanzengeographie</i>. Also his</td></tr> -<tr><td>Originally:</td><td>Schouw, <i>Grundüzge der Pflanzengeographie</i>. Also his</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_95_95">95</a>:</td><td class="dfrst">Fraunhofer’s measure of illuminating power is as</td></tr> -<tr><td>Originally:</td><td>Frauenhofer’s measure of illuminating power is as</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_99_99">99</a>:</td><td class="dfrst"><i>Sur une Propriété de la Lumière Réfléchie</i>: Mémoires</td></tr> -<tr><td>Originally:</td><td><i>Sur une Propriété de la Lumière Réfléchie</i>: Memoires</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_176">176</a>:</td><td class="dfrst">the strongest sunlight which has passed through</td></tr> -<tr><td>Originally:</td><td>the strongest sun-light which has passed through</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_179">179</a>:</td><td class="dfrst">productions of the photographer as on those of the</td></tr> -<tr><td>Originally:</td><td>productions of the photograper as on those of the</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_180">180</a>:</td><td class="dfrst">preserve the lineaments of those who have benefited</td></tr> -<tr><td>Originally:</td><td>preserve the lineaments of those who have benefitted</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_185">185</a>:</td><td class="dfrst">line, over which no action takes place, is preserved at</td></tr> -<tr><td>Originally:</td><td>line, over which no action takes plates, is preserved at</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_185">185</a>:</td><td class="dfrst">presented to us by a circular body: calorific action seems</td></tr> -<tr><td>Originally:</td><td>present to us by a circular body: calorific action seems</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_188">188</a>:</td><td class="dfrst">piece of wood is used instead of a metal, there will, by</td></tr> -<tr><td>Originally:</td><td>piece of wood is used instead of a medal, there will, by</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_126_126">126</a>:</td><td class="dfrst"><i>dans la végétation</i>: by Senebier; Genève et Paris, 1788</td></tr> -<tr><td>Originally:</td><td><i>dans la végetation</i>: by Senebier; Genève et Paris, 1788</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_198">198</a>:</td><td class="dfrst">Leyden phial,—so called from its inventor, Musschenbroek,</td></tr> -<tr><td>Originally:</td><td>Leyden phial,—so called from its inventor, Muschenbrock,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_219">219</a>:</td><td class="dfrst">may be made a measurer of nervous irritability.[154] There</td></tr> -<tr><td>Originally:</td><td>may be made a measurer of nervous iritability.[154] There</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_141_141">141</a>:</td><td class="dfrst"><i>Traité Expérimental de l’Électricité et du Magnétisme</i>:</td></tr> -<tr><td>Originally:</td><td><i>Traité Expérimental de l’Electricité et du Magnétisme</i>:</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_146_146">146</a>:</td><td class="dfrst"><i>Traité Expérimental de l’Électricité et du Magnétisme</i>.</td></tr> -<tr><td>Originally:</td><td><i>Traité Expérimental de l’Electricité et du Magnétisme</i></td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_160_160">160</a>:</td><td class="dfrst">where the cobalt was discovered between two portions of</td></tr> -<tr><td>Originally:</td><td>where the cobalt was discovered betweed two portions of</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_235">235</a>:</td><td class="dfrst">Storms—Magnetic conditions of Matter—Diamagnetism,</td></tr> -<tr><td>Originally:</td><td>Storms—Magnetic conditions of Matter—Dia-Magnetism,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_236">236</a>:</td><td class="dfrst">Magnêtum, quia sit patriis in finibus ortus.</td></tr> -<tr><td>Originally:</td><td>Magnêtum, buia sit patriis in finibus ortus.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_251">251</a>:</td><td class="dfrst">conditions of change in this our earth: an element to</td></tr> -<tr><td>Originally:</td><td>conditions of change in this our earth: an elemeut to</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_257">257</a>:</td><td class="dfrst">Wiedemann, by employing a fine point through which</td></tr> -<tr><td>Originally:</td><td>Wiedmann, by employing a fine point through which</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_258">258</a>:</td><td class="dfrst">than in any other. M. Wiedemann comes to the conclusion</td></tr> -<tr><td>Originally:</td><td>than in any other. M. Wiedmann comes to the conclusion</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_260">260</a>:</td><td class="dfrst">salt, the protosulphate, ordinarily crystallizes so that</td></tr> -<tr><td>Originally:</td><td>salt, the proto-sulphate, ordinarily crystallizes so that</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_176_176">176</a>:</td><td class="dfrst">Humboldt: <i>Exposé des Variations Magnétiques</i>.</td></tr> -<tr><td>Originally:</td><td>Humboldt: <i>Exposé des Variations Magnetiques</i>.</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_188_188">188</a>:</td><td class="dfrst"><i>Electro-Magnetic Influence</i>, by Professor Zantedeschi.</td></tr> -<tr><td>Originally:</td><td><i>Electro-Magnetic Influence</i>, by Professor Zandeteschi.</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_190_190">190</a>:</td><td class="dfrst">detailed account of the experiments of Faraday, Plücker,</td></tr> -<tr><td>Originally:</td><td>detailed account of the experiments of Faraday, Plucker,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_276">276</a>:</td><td class="dfrst">light determine these changes? It is evident, although</td></tr> -<tr><td>Originally:</td><td>light determine these change? It is evident, although</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_281">281</a>:</td><td class="dfrst">chemical change. Döbereiner next discovered that</td></tr> -<tr><td>Originally:</td><td>chemical change. Dœbereiner next discovered that</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_282">282</a>:</td><td class="dfrst">a fearful example in the progress of Asiatic</td></tr> -<tr><td>Originally:</td><td>a fearful example in the progress of Asatic</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_300">300</a>:</td><td class="dfrst">as being either peroxide of hydrogen, or an allotropic</td></tr> -<tr><td>Originally:</td><td>as being either per-oxide of hydrogen, or an allotropic</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_304">304</a>:</td><td class="dfrst">the gas which we employ so advantageously for illumination</td></tr> -<tr><td>Originally:</td><td>the gas which we emply so advantageously for illumination</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_306">306</a>:</td><td class="dfrst">increasing,—true combustion takes place. In this way</td></tr> -<tr><td>Originally:</td><td>increasing,—true combustion takes plaee. In this way</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_306">306</a>:</td><td class="dfrst">sawdust, &c., frequently ignite; and to such an</td></tr> -<tr><td>Originally:</td><td>saw-dust, &c., frequently ignite; and to such an</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_316">316</a>:</td><td class="dfrst">Mr. Darwin remarks, that if the immense sea-weeds of</td></tr> -<tr><td>Originally:</td><td>Mr. Darwin remarks, that if the immense seaweeds of</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_317">317</a>:</td><td class="dfrst">When Shakespeare made his charming Ariel sing—</td></tr> -<tr><td>Originally:</td><td>When Shakspeare made his charming Ariel sing—</td></tr> - -<tr><td class="dfrst">Footnote <a href="#Footnote_212_212">212</a>:</td><td class="dfrst">(Redundant line removed before item 2 in table.)</td></tr> -<tr><td>Originally:</td><td>According to one view, | According to the other view,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_334">334</a>:</td><td class="dfrst">speculation, which may have occasional marks of ingenuity,</td></tr> -<tr><td>Originally:</td><td>speculation, whieh may have occasional marks of ingenuity,</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_337">337</a>:</td><td class="dfrst">origin, the rational inference is against the speculation;</td></tr> -<tr><td>Originally:</td><td>orgin, the rational inference is against the speculation;</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_370">370</a>:</td><td class="dfrst">capsule of <i>nigella orientalis</i> consists of pods assembled</td></tr> -<tr><td>Originally:</td><td>capsule of <i>nigilla orientalis</i> consists of pods assembled</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_370">370</a>:</td><td class="dfrst">a centre, and partially united; in <i>nigella damascena</i></td></tr> -<tr><td>Originally:</td><td>a centre, and partially united; in <i>nigilla damascena</i></td></tr> - -<tr><td class="dfrst">Page <a href="#Page_399">399</a>:</td><td class="dfrst">whose minds are sceptical upon any development of the</td></tr> -<tr><td>Originally:</td><td>whose mind are sceptical upon any development of the</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_406">406</a>:</td><td class="dfrst">evidence of a beautiful adjustment of the balance of</td></tr> -<tr><td>Originally:</td><td>evidence of a beautifnl adjustment of the balance of</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_408">408</a>:</td><td class="dfrst">Let but a slight disturbance occasion a vibration</td></tr> -<tr><td>Originally:</td><td>Let but a slight disturbance occcasion a vibration</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_409">409</a>:</td><td class="dfrst">A cheerless philosophy, derived from the transcendentalism</td></tr> -<tr><td>Originally:</td><td>A cheerless philosophy, derived from the transendentalism</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_410">410</a>:</td><td class="dfrst">which are allowed the privilege of tracing out its</td></tr> -<tr><td>Originally:</td><td>which are alowed the privilege of tracing out its</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_413">413</a>:</td><td class="dfrst">Aëreal currents dependent on heat, 80.</td></tr> -<tr><td>Originally:</td><td>Æreal currents dependent on heat, 80.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_413">413</a>:</td><td class="dfrst">Animal electricity, 211, 392.</td></tr> -<tr><td>Originally:</td><td>Magnetic electricity, 211, 392.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_413">413</a>:</td><td class="dfrst">Bartholin on Iceland spar, 140.</td></tr> -<tr><td>Originally:</td><td>Bartolin on Iceland spar, 140.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_414">414</a>:</td><td class="dfrst">Cagniard de la Tour state, 106.</td></tr> -<tr><td>Originally:</td><td>Caignard de la Tour state, 106.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_415">415</a>:</td><td class="dfrst">Döbereiner’s lamp, 281.</td></tr> -<tr><td>Originally:</td><td>Doebereiner’s lamp, 281.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_415">415</a>:</td><td class="dfrst">Eye, mechanism of, 149.</td></tr> -<tr><td>Originally:</td><td>Eye, mechanism of, 491.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_416">416</a>:</td><td class="dfrst">—— on diamagnetism, 254.</td></tr> -<tr><td>Originally:</td><td>—— on dia-magnetism, 254.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_418">418</a>:</td><td class="dfrst">Musschenbroek of Leyden, 198.</td></tr> -<tr><td>Originally:</td><td>Muschenbrock of Leyden, 198.</td></tr> - -<tr><td class="dfrst">Page <a href="#Page_421">421</a>:</td><td class="dfrst">Wiedemann on electrical vibrations, 257.</td></tr> -<tr><td>Originally:</td><td>Wiedman on electrical vibrations, 257.</td></tr> - -<tr><td class="dfrst"><a href="#BOHNS_BOOKS">Bohn’s Books</a>:</td><td class="dfrst"><b>LOUDON’S (MRS.) ENTERTAINING NATURALIST</b>,</td></tr> -<tr><td>Originally:</td><td><b>LOUDON’S (MRS.) ENTERTAING NATURALIST</b>,</td></tr> - -<tr><td class="dfrst"><a href="#BOHNS_BOOKS">Bohn’s Books</a>:</td><td class="dfrst">Indexes of Scientific and Popular Names. _With_</td></tr> -<tr><td>Originally:</td><td>Indexes of Scientific and and Popular Names. _With_</td></tr> - -<tr><td class="dfrst"><a href="#BOHNS_BOOKS">Bohn’s Books</a>:</td><td class="dfrst"><b>18. PLATO.</b> Vol. III. By <span class="smcap">G. Burges</span>, M.A. [Euthydemus,</td></tr> -<tr><td>Originally:</td><td><b>8. PLATO.</b> Vol. III. By <span class="smcap">G. Burges</span>, M.A. [Euthydemus,</td></tr> - -<tr><td class="dfrst"><a href="#BOHNS_BOOKS">Bohn’s Books</a>:</td><td class="dfrst"><b>24, 25, & 32. OVID.</b> By <span class="smcap">H. T. Riley</span>, B.A. Complete in 3</td></tr> -<tr><td>Originally:</td><td><b>24, 25, & 32. OVID.</b> By H. T. RILEY, B.A. Complete in 3</td></tr> - -<tr><td class="dfrst"><a href="#BOHNS_BOOKS">Bohn’s Books</a>:</td><td class="dfrst"><b>35. JUVENAL, PERSIUS, &c.</b> By the <span class="smcap">Rev. L. Evans</span>, M.A.</td></tr> -<tr><td>Originally:</td><td><b>34. JUVENAL, PERSIUS, &c.</b> By the <span class="smcap">Rev. L. Evans</span>, M.A.</td></tr> -</table> - -<hr class="chap" /> -</div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of The Poetry of Science or, Studies of -the Physical Phenomena of Nature, by Robert Hunt - -*** END OF THIS PROJECT GUTENBERG EBOOK THE POETRY OF SCIENCE *** - -***** This file should be named 51897-h.htm or 51897-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/1/8/9/51897/ - -Produced by Emmanuel Ackerman and the Online Distributed -Proofreading Team at http://www.pgdp.net (This file was -produced from images generously made available by The -Internet Archive/Canadian Libraries) - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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