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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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