diff options
Diffstat (limited to 'old/54897-h/54897-h.htm')
| -rw-r--r-- | old/54897-h/54897-h.htm | 13890 |
1 files changed, 0 insertions, 13890 deletions
diff --git a/old/54897-h/54897-h.htm b/old/54897-h/54897-h.htm deleted file mode 100644 index a9be346..0000000 --- a/old/54897-h/54897-h.htm +++ /dev/null @@ -1,13890 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" - "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> - <head> - <meta http-equiv="Content-Type" content="text/html;charset=utf-8" /> - <meta http-equiv="Content-Style-Type" content="text/css" /> - <title> - The Project Gutenberg eBook of Preliminary Discourse On the Study of Natural Philosophy, by Sir John F. W. Herschel. - </title> - <link rel="coverpage" href="images/cover.jpg" /> - <style type="text/css"> - -body {max-width: 40em; margin-left: auto; margin-right: auto;} - -h1,h2, h3 { - text-align: center; - clear: both; - margin-top: 2.5em; - margin-bottom: 1em; -} - -h1 {line-height: 1.8;} - -h2.chap {margin-bottom: 0;} -h2+p {margin-top: 1.5em;} - -.transnote h2 { - margin-top: .5em; - margin-bottom: 1em; -} - -.chapter+p, p.b2 {margin-bottom: 2em;} - -p { - text-indent: 1.75em; - margin-top: .51em; - margin-bottom: .24em; - text-align: justify; -} -.caption p {text-align: center; text-indent: 0;} -p.center {text-indent: 0;} - -.p1 {margin-top: 1em;} -.p2 {margin-top: 2em;} -.vspace {line-height: 1.5;} - -.in0 {text-indent: 0;} -.in2 {padding-left: 2em;} -.in4 {padding-left: 4em;} - -blockquote.hang2 p.ii, span.ii {text-indent: 0; padding-left: .6em;} -blockquote.hang2 p.iii, span.iii {text-indent: 0; padding-left: .3em;} -blockquote.hang2 p.iiii, span.iiii {text-indent: 0; padding-left: 0;} -blockquote.hang2 p.iiv, span.iiv {text-indent: 0; padding-left: .05em;} -blockquote.hang2 p.iv {text-indent: 0; padding-left: .4em;} -blockquote.hang2 p.ivi, span.ivi {text-indent: 0; padding-left: .05em;} - -.xxsmall {font-size: 50%;} -.small {font-size: 70%;} -.smaller {font-size: 85%;} -.larger {font-size: 125%;} -.large {font-size: 150%;} - -.center {text-align: center;} - -.smcap {font-variant: small-caps;} -.smcap.smaller {font-size: 75%;} - -.bold {font-weight: bold;} - -hr { - width: 33%; - margin-top: 4em; - margin-bottom: 4em; - margin-left: 33%; - margin-right: auto; - clear: both; -} -hr.narrow {width: 16%; margin-left: 42%;} - -table { - margin-left: auto; - margin-right: auto; - max-width: 80%; - border-collapse: collapse; -} - -.tdl { - text-align: left; - vertical-align: top; - padding-right: 1em; - padding-left: 1.5em; - text-indent: -1.5em; -} -.tdl.justify {text-align: justify;} - -.tdc {text-align: center;} -.tdc.chap, .tdc.part { - font-size: 110%; - padding-top: 1.5em; - padding-bottom: .5em; -} -.tdc.part {padding-top: 3em; padding-bottom: 1em; font-size: 133%;} -.tdc.part.nopad {padding-top: 0;} - -.tdr { - text-align: right; - vertical-align: bottom; - padding-left: .3em; - white-space: nowrap; -} - -.pagenum { - position: absolute; - right: 4px; - text-indent: 0em; - text-align: right; - font-size: 70%; - font-weight: normal; - font-variant: normal; - font-style: normal; - letter-spacing: normal; - line-height: normal; - color: #acacac; - border: 1px solid #acacac; - background: #ffffff; - padding: 1px 2px; -} - -.figcenter { - margin: 2em auto 2em auto; - text-align: center; - page-break-inside: avoid; - max-width: 100%; -} - -img { - padding: 1em 0 .5em 0; - max-width: 100%; - height: auto; -} - -.caption {text-align: center; margin-top: 0;} -.caption.floatl {float: left; font-size: 85%;} -.caption.floatr {float: right; font-size: 85%;} - -.footnotes { - border: thin dashed black; - margin: 4em 0 1em 0; - padding: .5em 1em .5em 1.5em; -} - -.footnote {font-size: .95em;} -.footnote p {text-indent: 1em;} -.footnote p.in0 {text-indent: 0;} -.footnote p.fn1 {text-indent: -.7em;} -.footnote p.fn2 {text-indent: -1.1em;} - -.fnanchor { - vertical-align: 80%; - line-height: .7; - font-size: .75em; - text-decoration: none; -} -.footnote .fnanchor {font-size: .8em;} - -/*INDEX as unordered list*/ -ul.index {padding-left: 0;} -li {list-style-type: none;} -li.indx, li.ifrst {list-style-type: none; padding-left: 3em; text-indent: -3em; padding-top: .2em;} -li.isub1 {padding-left: 3em; text-indent: -2em;} -li.isub2 {padding-left: 3em; text-indent: -1em;} -li.ifrst {padding-top: 1em;} -/*end Index*/ - -blockquote { - margin-left: 5%; - margin-right: 5%; -} - -blockquote.hang p {padding-left: 1.5em; text-indent: -1.5em; margin-bottom: 2em;} - -blockquote.hang2 p {padding-left: 3em; text-indent: -3em;} - -.transnote { - background-color: #EEE; - border: thin dotted; - font-family: sans-serif, serif; - color: #000; - margin-top: 4em; - margin-bottom: 2em; - padding: 1em; -} -.covernote {visibility: hidden; display: none;} - -.sigright { - margin-top: 0; - margin-right: 2em; - text-align: right;} - -.gesperrt { - letter-spacing: 0.2em; - margin-right: -0.2em; -} -.wspace {word-spacing: .3em;} - -span.locked {white-space:nowrap;} -.narrow_container {width: 70%; margin-left: 15%;} -.flet {font-size: 150%; font-weight: bold;} - -@media print, handheld -{ - h1, .chapter, .newpage {page-break-before: always;} - h1.nobreak, h2.nobreak, .nobreak {page-break-before: avoid; padding-top: 0;} - - p { - margin-top: .5em; - text-align: justify; - margin-bottom: .25em; - } - - table {width: 100%; max-width: 100%;} - - .tdl { - padding-left: 1em; - text-indent: -1em; - padding-right: 0; - } - -} - -@media handheld -{ - body {margin: 0; max-width: 100%;} - - hr { - margin-top: .1em; - margin-bottom: .1em; - visibility: hidden; - color: white; - width: .01em; - display: none; - } - - blockquote {margin: 1.5em 3% 1.5em 3%;} - - .hang {margin: .5em 3% 2em 3%;} - - .transnote { - page-break-inside: avoid; - margin-left: 2%; - margin-right: 2%; - margin-top: 1em; - margin-bottom: 1em; - padding: .5em; - } - - .index {margin-left: 0;} - - .covernote {visibility: visible; display: block; text-align: center;} - .narrow_container {width: 90%; margin-left: 5%;} -} - </style> - </head> - -<body> - - -<pre> - -The Project Gutenberg EBook of Preliminary Discourse on the Study of -Natural Philosophy, by John F. W. Herschel - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Preliminary Discourse on the Study of Natural Philosophy - -Author: John F. W. Herschel - -Release Date: June 12, 2017 [EBook #54897] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK PRELIMINARY DISCOURSE--NATURAL PHILOSOPHY *** - - - - -Produced by Sonya Schermann, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - -</pre> - - -<div class="transnote covernote"> -<p class="center">Transcriber’s Note: Cover created by Transcriber and placed in the Public Domain.</p> -</div> - -<h1 class="wspace"> -<i><span class="smcap">Preliminary discourse</span></i><br /> -<span class="smaller">on the Study of</span><br /> -<span class="larger">NATURAL PHILOSOPHY</span></h1> - -<p class="center large"><span class="small">BY</span><br /> -<span class="bold">SIR JOHN F. W. HERSCHEL, BART. K.H.</span><br /> -<span class="larger"><i>M.A.—D.C.L.—F.R.S.L&E.—M.R.I.A.—F.R.A.S.<br /> -F.G.S.—M.C.U.P.S.—&c. &c.</i></span></p> - -<p class="p1 center wspace">NEW EDITION.<br /> -1851. -</p> - -<div class="figcenter" style="max-width: 23em;"> -<img src="images/title.jpg" width="364" height="404" alt="Bacon" /> -<div class="caption floatl"><i>H. Corbould del.</i></div> -<div class="caption floatr"><i>E. Finden. sculp.</i></div> -</div> - -<p class="p2 center large"><span class="xxsmall">NATURÆ MINISTER ET INTERPRES.</span></p> - -<p class="p2 center vspace"> -<span class="bold">NEW EDITION.</span><br /> -London:<br /> -<span class="small">PRINTED FOR LONGMAN, BROWN, GREEN & LONGMANS, PATERNOSTER ROW</span> -</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_v">v</a></span></p> - -<div class="chapter"> -<h2><a id="CONTENTS"></a>CONTENTS.</h2> -</div> - -<table summary="Contents"> - <tr class="smaller"> - <td> </td> - <td class="tdr">Page</td></tr> - <tr> - <td class="tdc part nopad" colspan="2"><a href="#hdr_1">PART I.</a></td></tr> - <tr> - <td class="tdc" colspan="2">OF THE GENERAL NATURE AND ADVANTAGES OF THE STUDY OF THE PHYSICAL SCIENCES.</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_2">CHAP. I.</a></td></tr> - <tr> - <td class="tdl">Of Man regarded as a Creature of Instinct, of Reason, and Speculation.—General Influence of Scientific Pursuits on the Mind.</td> - <td class="tdr">1</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_3">CHAP. II.</a></td></tr> - <tr> - <td class="tdl">Of abstract Science as a Preparation for the Study of Physics.—A profound Acquaintance with it not indispensable for a clear Understanding of Physical Laws.—How a Conviction of their Truth may be obtained without it.—Instances.—Further Division of the Subject.</td> - <td class="tdr">18</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_4">CHAP. III.</a></td></tr> - <tr> - <td class="tdl">Of the Nature and Objects, immediate and collateral, of Physical Science, as regarded in itself, and in its Application to the practical Purposes of Life, and its Influence on the Well-being and Progress of Society.</td> - <td class="tdr">35</td></tr> - <tr> - <td class="tdc part" colspan="2"><a href="#hdr_5">PART II.</a><span class="pagenum"><a id="Page_vi">vi</a></span></td></tr> - <tr> - <td class="tdl justify" colspan="2">OF THE PRINCIPLES ON WHICH PHYSICAL SCIENCE RELIES FOR ITS SUCCESSFUL PROSECUTION, AND THE RULES BY WHICH A SYSTEMATIC EXAMINATION OF NATURE SHOULD BE CONDUCTED, WITH ILLUSTRATIONS OF THEIR INFLUENCE AS EXEMPLIFIED IN THE HISTORY OF ITS PROGRESS.</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_6">CHAP. I.</a></td></tr> - <tr> - <td class="tdl">Of Experience as the Source of our Knowledge.—Of the Dismissal of Prejudices.—Of the Evidence of our Senses.</td> - <td class="tdr">75</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_7">CHAP. II.</a></td></tr> - <tr> - <td class="tdl">Of the Analysis of Phenomena.</td> - <td class="tdr">85</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_8">CHAP. III.</a></td></tr> - <tr> - <td class="tdl">Of the State of Physical Science in General, previous to the Age of Galileo and Bacon.</td> - <td class="tdr">104</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_9">CHAP. IV.</a></td></tr> - <tr> - <td class="tdl">Of the Observation of Facts and the Collection of Instances.</td> - <td class="tdr">118</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_10">CHAP. V.</a></td></tr> - <tr> - <td class="tdl">Of the Classification of Natural Objects and Phenomena, and of Nomenclature.</td> - <td class="tdr">135</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_11">CHAP. VI.</a></td></tr> - <tr> - <td class="tdl">Of the First Stage of Induction.—The Discovery of Proximate Causes, and Laws of the lowest Degree of Generality, and their Verification.</td> - <td class="tdr">144</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_12">CHAP. VII.</a></td></tr> - <tr> - <td class="tdl">Of the higher Degrees of Inductive Generalization, and of the Formation and Verification of Theories.</td> - <td class="tdr">190</td></tr> - <tr> - <td class="tdc part" colspan="2"><a href="#hdr_13">PART III.</a><span class="pagenum"><a id="Page_vii">vii</a></span></td></tr> - <tr> - <td class="tdc" colspan="2">OF THE SUBDIVISION OF PHYSICS INTO DISTINCT BRANCHES, AND THEIR MUTUAL RELATIONS.</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_14">CHAP. I.</a></td></tr> - <tr> - <td class="tdl">Of the Phenomena of Force, and of the Constitution of Natural Bodies.</td> - <td class="tdr">221</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_15">CHAP. II.</a></td></tr> - <tr> - <td class="tdl">Of the Communication of Motion through Bodies.—Of Sound and Light.</td> - <td class="tdr">246</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_16">CHAP. III.</a></td></tr> - <tr> - <td class="tdl">Of Cosmical Phenomena.</td> - <td class="tdr">265</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_17">CHAP. IV.</a></td></tr> - <tr> - <td class="tdl">Of the Examination of the material Constituents of the World.</td> - <td class="tdr">290</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_18">CHAP. V.</a></td></tr> - <tr> - <td class="tdl">Of the Imponderable Forms of Matter.</td> - <td class="tdr">310</td></tr> - <tr> - <td class="tdc chap" colspan="2"><a href="#hdr_19">CHAP. VI.</a></td></tr> - <tr> - <td class="tdl">Of the Causes of the actual rapid Advance of the Physical Sciences compared with their Progress at an earlier Period.</td> - <td class="tdr">347</td></tr> -</table> - -<hr /> - -<p><span class="pagenum"><a id="Page_viii">viii</a></span></p> - -<div class="narrow_container"> -<p>“In primis, hominis est propria <span class="smcap smaller">VERI</span> inquisitio atque investigatio. Itaque -cum sumus negotiis necessariis, curisque vacui, tum avemus aliquid -videre, audire, ac dicere, cognitionemque rerum, aut occultarum aut admirabilium, -ad benè beatéque vivendum necessariam ducimus;—ex quo -intelligitur, quod <span class="smcap smaller">VERUM</span>, simplex, sincerumque sit, id esse naturæe hominis -aptissimum. Huic veri videndi cupiditati adjuncta est appetitio quædam -principatûs, ut nemini parere animus benè a naturâ informatus velit, -nisi præcipienti, aut docenti, aut utilitatis causa justè et legitimè imperanti: -ex quo animi magnitudo existit, et humanararum rerum contemtio.”</p> - -<p class="sigright"> -<span class="smcap">Cicero, de Officiis</span>, Lib. 1. § 13. -</p> - -<p>Before all other things, man is distinguished by his pursuit and investigation -of <span class="smcap smaller">TRUTH</span>. And hence, when free from needful business and cares, we -delight to see, to hear, and to communicate, and consider a knowledge of -many admirable and abstruse things necessary to the good conduct and -happiness of our lives: whence it is clear that whatsoever is <span class="smcap smaller">TRUE</span>, simple, -and direct, the same is most congenial to our nature as men. Closely allied -with this earnest longing to see and know the truth, is a kind of dignified -and princely sentiment which forbids a mind, naturally well constituted, to -submit its faculties to any but those who announce it in precept or in doctrine, -or to yield obedience to any orders but such as are at once just, -lawful, and founded on utility. From this source spring greatness of mind -and contempt of worldly advantages and troubles.</p> -</div> - -<hr /> - -<p><span class="pagenum"><a id="Page_1">1</a></span></p> - -<div class="chapter"> -<h2><span class="large wspace">PRELIMINARY DISCOURSE<br /> -ON<br /> -THE STUDY<br /> -OF<br /> -NATURAL PHILOSOPHY.</span></h2> -</div> - -<hr class="narrow" /> -<h2 id="hdr_1"><span class="larger">PART I.</span></h2> - -<p class="center">OF THE GENERAL NATURE AND ADVANTAGES OF -THE STUDY OF THE PHYSICAL SCIENCES</p> - -<hr class="narrow"/> -<h2 id="hdr_2">CHAPTER I.</h2> - -<blockquote class="hang"> - -<p>OF MAN REGARDED AS A CREATURE OF INSTINCT, OF -REASON, AND SPECULATION.—GENERAL INFLUENCE OF -SCIENTIFIC PURSUITS ON THE MIND.</p></blockquote> - -<p class="in0">(1.) <span class="smcap"><span class="flet">T</span>he</span> situation of man on the globe he inhabits, -and over which he has obtained the control, is in -many respects exceedingly remarkable. Compared -with its other denizens, he seems, if we regard only -his physical constitution, in almost every respect -their inferior, and equally unprovided for the supply -of his natural wants and his defence against the innumerable -enemies which surround him. No other -animal passes so large a portion of its existence in a<span class="pagenum"><a id="Page_2">2</a></span> -state of absolute helplessness, or falls in old age into -such protracted and lamentable imbecility. To no -other warm-blooded animal has nature denied that -indispensable covering without which the vicissitudes -of a temperate and the rigours of a cold climate are -equally insupportable; and to scarcely any has she -been so sparing in external weapons, whether for -attack or defence. Destitute alike of speed to avoid -and of arms to repel the aggressions of his voracious -foes; tenderly susceptible of atmospheric influences; -and unfitted for the coarse aliments which -the earth affords spontaneously during at least two -thirds of the year, even in temperate climates,—man, -if abandoned to mere instinct, would be of all -creatures the most destitute and miserable. Distracted -by terror and goaded by famine; driven to -the most abject expedients for concealment from his -enemies, and to the most cowardly devices for the -seizure and destruction of his nobler prey, his existence -would be one continued subterfuge or stratagem;—his -dwelling would be in dens of the earth, in clefts -of rocks, or in the hollows of trees; his food worms, -and the lower reptiles, or such few and crude productions -of the soil as his organs could be brought -to assimilate, varied with occasional relics, mangled -by more powerful beasts of prey, or contemned by -their more pampered choice. Remarkable only -for the absence of those powers and qualities -which obtain for other animals a degree of security -and respect, he would be disregarded by some, and -hunted down by others, till after a few generations -his species would become altogether extinct, or, at -best, would be restricted to a few islands in tropical<span class="pagenum"><a id="Page_3">3</a></span> -regions, where the warmth of the climate, the paucity -of enemies, and the abundance of vegetable food, -might permit it to linger.</p> - -<p>(2.) Yet man is the undisputed lord of the creation. -The strongest and fiercest of his fellow-creatures,—the -whale, the elephant, the eagle, and -the tiger,—are slaughtered by him to supply his most -capricious wants, or tamed to do him service, or imprisoned -to make him sport. The spoils of all nature -are in daily requisition for his most common uses, -yielded with more or less readiness, or wrested -with reluctance, from the mine, the forest, the -ocean, and the air. Such are the first fruits of -reason. Were they the only or the principal ones, -were the mere acquisition of power over the materials, -and the less gifted animals which surround -us, and the consequent increase of our external -comforts, and our means of preservation and sensual -enjoyment, the sum of the privileges which the possession -of this faculty conferred, we should after all -have little to plume ourselves upon. But this is so far -from being the case, that every one who passes his life -in tolerable ease and comfort, or rather whose whole -time is not anxiously consumed in providing the absolute -necessaries of existence, is conscious of wants -and cravings in which the senses have no part, of a -series of pains and pleasures totally distinct in kind -from any which the infliction of bodily misery or the -gratification of bodily appetites has ever afforded him; -and if he has experienced these pleasures and these -pains in any degree of intensity, he will readily admit -them to hold a much higher rank, and to deserve much -more attention, than the former class. Independent of<span class="pagenum"><a id="Page_4">4</a></span> -the pleasures of fancy and imagination, and social converse, -man is constituted a speculative being; he contemplates -the world, and the objects around him, not -with a passive, indifferent gaze, as a set of phenomena -in which he has no further interest than as -they affect his immediate situation, and can be rendered -subservient to his comfort, but as a system -disposed with order and design. He approves and -feels the highest admiration for the harmony of its -parts, the skill and efficiency of its contrivances. -Some of these which he can best trace and understand -he attempts to imitate, and finds that to a -certain extent, though rudely and imperfectly, he -can succeed,—in others, that although he can comprehend -the nature of the contrivance, he is totally -destitute of all means of imitation;—while in others, -again, and those evidently the most important, though -he sees the effect produced, yet the means by which -it is done are alike beyond his knowledge and his -control. Thus he is led to the conception of a -Power and an Intelligence superior to his own, and -adequate to the production and maintenance of all -that he sees in nature,—a Power and Intelligence -to which he may well apply the term infinite, since -he not only sees no actual limit to the instances in -which they are manifested, but finds, on the contrary, -that the farther he enquires, and the wider -his sphere of observation extends, they continually -open upon him in increasing abundance; and that -as the study of one prepares him to understand -and appreciate another, refinement follows on refinement, -wonder on wonder, till his faculties -become bewildered in admiration, and his intellect<span class="pagenum"><a id="Page_5">5</a></span> -falls back on itself in utter hopelessness of arriving -at an end.</p> - -<p>(3.) When from external objects he turns his view -upon himself, on his own vital and intellectual faculties, -he finds that he possesses a power of examining -and analysing his own nature to a certain -extent, but no farther. In his corporeal frame he is -sensible of a power to communicate a certain moderate -amount of motion to himself and other objects; -that this power depends on his will, and that its exertion -can be suspended or increased at pleasure -within certain limits; but <em>how</em> his will acts on his -limbs he has no consciousness: and whence he derives -the power he thus exercises, there is nothing to -assure him, however he may long to know. His -senses, too, inform him of a multitude of particulars -respecting the external world, and he perceives an -apparatus by which impressions from without may be -transmitted, as a sort of signals to the interior of his -person, and ultimately to his brain, wherein he is -obscurely sensible that the thinking, feeling, reasoning -being he calls <em>himself</em>, more especially resides; -but by what means he becomes conscious of these -impressions, and what is the nature of the immediate -communication between that inward sentient being, -and that machinery, his outward man, he has not -the slightest conception.</p> - -<p>(4.) Again, when he contemplates still more -attentively the thoughts, acts, and passions of this -his sentient intelligent self, he finds, indeed, that -he can remember, and by the aid of memory can -compare and discriminate, can judge and resolve, -and, above all, that he is irresistibly impelled, from<span class="pagenum"><a id="Page_6">6</a></span> -the perception of any phenomenon without or within -him, to infer the existence of something prior which -stands to it in the relation of a <em>cause</em>, without which -it would not be, and that this knowledge of causes -and their consequences is what, in almost every instance, -determines his choice and will, in cases where -he is nevertheless conscious of perfect freedom to -act or not to act. He finds, too, that it is in his -power to acquire more or less knowledge of causes -and effects according to the degree of attention he -bestows upon them, which attention is again in great -measure a voluntary act; and often when his choice -has been decided on imperfect knowledge or insufficient -attention, he finds reason to correct his judgment, -though perhaps too late to influence his decision -by after consideration. A world within him is -thus opened to his intellectual view, abounding with -phenomena and relations, and of the highest immediate -interest. But while he cannot help perceiving -that the insight he is enabled to obtain into this internal -sphere of thought and feeling is in reality the source -of all his power, the very fountain of his predominance -over external nature, he yet feels himself capable of -entering only very imperfectly into these recesses of -his own bosom, and analysing the operations of his -mind,—in this as in all other things, in short, “<em>a being -darkly wise</em>;” seeing that all the longest life and most -vigorous intellect can give him power to discover by -his own research, or time to know by availing himself -of that of others, serves only to place him on -the very frontier of knowledge, and afford a distant -glimpse of boundless realms beyond, where no human -thought has penetrated, but which yet he is sure<span class="pagenum"><a id="Page_7">7</a></span> -must be no less familiarly known to that Intelligence -which he traces throughout creation than the most -obvious truths which he himself daily applies to his -most trifling purposes. Is it wonderful that a being -so constituted should first encourage a hope, and by -degrees acknowledge an assurance, that his intellectual -existence will not terminate with the -dissolution of his corporeal frame, but rather that in -a future state of being, disencumbered of a thousand -obstructions which his present situation throws in -his way, endowed with acuter senses, and higher faculties, -he shall drink deep at that fountain of beneficent -wisdom for which the slight taste obtained on -earth has given him so keen a relish?</p> - -<p>(5.) Nothing, then, can be more unfounded than -the objection which has been taken, <i xml:lang="la" lang="la">in limine</i>, -by persons, well meaning perhaps, certainly narrow-minded, -against the study of natural philosophy, -and indeed against all science,—that it fosters in its -cultivators an undue and overweening self-conceit, -leads them to doubt the immortality of the soul, and -to scoff at revealed religion. Its natural effect, we -may confidently assert, on every well constituted -mind is and must be the direct contrary. No doubt, -the testimony of natural reason, on whatever exercised, -must of necessity stop short of those truths -which it is the object of revelation to make known; -but, while it places the existence and principal attributes -of a Deity on such grounds as to render doubt -impossible, it unquestionably opposes no natural or -necessary obstacle to further progress: on the contrary, -by cherishing as a vital principle an unbounded -spirit of enquiry, and ardency of expectation, it unfetters<span class="pagenum"><a id="Page_8">8</a></span> -the mind from prejudices of every kind, and -leaves it open and free to every impression of a higher -nature which it is susceptible of receiving, guarding -only against enthusiasm and self-deception by a -habit of strict investigation, but encouraging, rather -than suppressing, every thing that can offer a prospect -or a hope beyond the present obscure and -unsatisfactory state. The character of the true -philosopher is to hope all things not impossible, -and to believe all things not unreasonable. He -who has seen obscurities which appeared impenetrable -in physical and mathematical science suddenly -dispelled, and the most barren and unpromising -fields of enquiry converted, as if by inspiration, -into rich and inexhaustible springs of knowledge -and power on a simple change of our point of view, -or by merely bringing to bear on them some principle -which it never occurred before to try, will -surely be the very last to acquiesce in any dispiriting -prospects of either the present or future destinies -of mankind; while, on the other hand, the -boundless views of intellectual and moral as well as -material relations which open on him on all hands -in the course of these pursuits, the knowledge of -the trivial place he occupies in the scale of creation, -and the sense continually pressed upon him of his -own weakness and incapacity to suspend or modify -the slightest movement of the machinery he sees in -action around him, must effectually convince him -that humility of pretension, no less than confidence -of hope, is what best becomes his character.</p> - -<p>(6.) But while we thus vindicate the study of natural -philosophy from a charge at one time formidable,<span class="pagenum"><a id="Page_9">9</a></span> -owing to the pertinacity and acrimony with -which it was urged, and still occasionally brought -forward to the distress and disgust of every well -constituted mind, we must take care that the testimony -afforded by science to religion, be its extent or -value what it may, shall be at least independent, -unbiassed, and spontaneous. We do not here allude -to such reasoners as would make all nature bend to -their narrow interpretations of obscure and difficult -passages in the sacred writings: such a course might -well become the persecutors of Galileo and the other -bigots of the fifteenth and sixteenth centuries, but -can only be adopted by dreamers in the present age. -But, without going these lengths, it is no uncommon -thing to find persons, earnestly attached to science -and anxious for its promotion, who yet manifest a morbid -sensibility on points of this kind,—who exult and -applaud when any fact starts up explanatory (as they -suppose) of some scriptural allusion and who feel -pained and disappointed when the general course -of discovery in any department of science runs wide -of the notions with which particular passages in the -Bible may have impressed themselves. To persons -of such a frame of mind it ought to suffice to -remark, on the one hand, that truth can never be opposed -to truth, and, on the other, that error is only -to be effectually confounded by searching deep and -tracing it to its source. Nevertheless, it were much -to be wished that such persons, estimable and excellent -as many of them are, before they throw -the weight of their applause or discredit into -the scale of scientific opinion on such grounds, -would reflect, first, that the credit and respectability<span class="pagenum"><a id="Page_10">10</a></span> -of <em>any</em> evidence may be destroyed by -tampering with its <em>honesty</em>; and, secondly, that this -very disposition of mind implies a lurking mistrust -in its own principles, since the grand and indeed -only character of truth is its capability of enduring -the test of universal experience, and coming unchanged -out of every possible form of <em>fair</em> discussion.</p> - -<p>(7.) But if science may be vilified by representing -it as opposed to religion, or trammelled by mistaken -notions of the danger of free enquiry, there -is yet another mode by which it may be degraded -from its native dignity, and that is by placing it in -the light of a mere appendage to and caterer for our -pampered appetites. The question “<i xml:lang="la" lang="la">cui bono</i>” to -what practical end and advantage do your researches -tend? is one which the speculative philosopher who -loves knowledge for its own sake, and enjoys, as a -rational being should enjoy, the mere contemplation -of harmonious and mutually dependent truths, can -seldom hear without a sense of humiliation. He -feels that there is a lofty and disinterested pleasure -in his speculations which ought to exempt them -from such questioning; communicating as they do -to his own mind the purest happiness (after the -exercise of the benevolent and moral feelings) of -which human nature is susceptible, and tending to -the injury of no one, he might surely allege <em>this</em> as -a sufficient and direct reply to those who, having -themselves little capacity, and less relish for intellectual -pursuits, are constantly repeating upon him -this enquiry. But if he can bring himself to -descend from this high but fair ground, and justify<span class="pagenum"><a id="Page_11">11</a></span> -himself, his pursuits, and his pleasures in the eyes -of those around him, he has only to point to the -history of all science, where speculations, apparently -unprofitable, have, in innumerable instances, -been those from which great practical applications -have emanated. What, for instance, could be -more so than the dry speculations of the ancient -geometers on the properties of the conic sections, -or than the dreams of Kepler (as they would naturally -appear to his contemporaries) about the -numerical harmonies of the universe? Yet these -are the steps by which we have risen to a knowledge -of the elliptic motions of the planets and the -law of gravitation, with all its splendid theoretical -consequences, and its inestimable practical results. -The ridicule attached to “<em>Swing-swangs</em>” in -Hooke’s time<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">1</a> did not prevent him from reviving -the proposal of the <em>pendulum</em> as a standard of -measure, since so effectually wrought into practice -by the genius and perseverance of Captain Kater;—nor -did that which Boyle encountered in his -researches on the elasticity and pressure of the air -act as any obstacle to the train of discovery which -terminated in the steam-engine. The dreams of -the alchemists led them on in the path of experiment, -and drew attention to the wonders of -chemistry, while they brought their advocates (it -must be admitted) to merited contempt and ruin. -But in this case it was moral dereliction which gave -to ridicule a weight and power not necessarily or -naturally belonging to it: but among the alchemists<span class="pagenum"><a id="Page_12">12</a></span> -were men of superior minds, who reasoned while they -worked, and who, not content to grope always in the -dark, and blunder on their object, sought carefully -in the observed nature of their agents for guides in -their pursuit. To these we owe the creation of -experimental philosophy.</p> - -<p>(8.) Not that it is meant, by any thing above -said, to assert that there is no such thing as a great -or a little in speculative philosophy, or to place the -solution of an enigma on a level with the developement -of a law of nature, still less to adopt the -homely definition of Smith<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">2</a>, that a philosopher is -a person whose trade it is to do nothing, and speculate -on every thing. The speculations of the natural -philosopher, however remote they may for a -time lead him from beaten tracks and every-day -uses, being grounded in the realities of nature, have -all, of necessity, a practical application,—nay more, -such applications form the very criterions of their -truth, they afford the readiest and completest verifications -of his theories;—verifications which he -will no more neglect to test them by than an arithmetician -would omit to <em>prove</em> his sums, or a cautious -geometer to try his general theorems by particular -cases.<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">3</a></p> - -<p><span class="pagenum"><a id="Page_13">13</a></span> -(9.) After all, however, it must be confessed, -that to minds unacquainted with science, and unused -to consider the mutual dependencies of its various -branches, there is something neither unnatural nor -altogether blamable in the ready occurrence of this -question of direct advantage. It requires some -habit of abstraction, some penetration of the mind -with a tincture of scientific enquiry, some conviction -of the value of those estimable and treasured -principles which lie concealed in the most -common and homely facts,—some experience, in -fine, of success in developing and placing them in -evidence, announcing them in precise terms, and -applying them to the explanation of other facts of a -less familiar character, or to the accomplishment of -some obviously useful purpose:—to cure the mind -of this tendency to rush at once upon its object, -to undervalue the means in over-estimation of the -end, and while gazing too intently at the goal which -alone it has been accustomed to desire, to lose sight -of the richness and variety of the prospects that -offer themselves on either hand on the road.</p> - -<p>(10.) We must never forget that it is principles, -not phenomena,—the interpretation, not the mere<span class="pagenum"><a id="Page_14">14</a></span> -knowledge of facts,—which are the objects of enquiry -to the natural philosopher. As truth is single, -and consistent with itself, a principle may be as -completely and as plainly elucidated by the most -familiar and simple fact, as by the most imposing and -uncommon phenomenon. The colours which glitter -on a soap-bubble are the immediate consequence of -a principle the most important from the variety of -phenomena it explains, and the most beautiful, from -its simplicity and compendious neatness, in the whole -science of optics. If the nature of periodical colours -can be made intelligible by the contemplation of -such a trivial object, from that moment it becomes a -noble instrument in the eye of correct judgment; -and to blow a large, regular, and durable soap-bubble -may become the serious and praiseworthy endeavour -of a sage, while children stand round and scoff, or -children of a larger growth hold up their hands in -astonishment at such waste of time and trouble. -To the natural philosopher there is no natural -object unimportant or trifling. From the least of -nature’s works he may learn the greatest lessons. -The fall of an apple to the ground may raise his -thoughts to the laws which govern the revolutions -of the planets in their orbits; or the situation of a -pebble may afford him evidence of the state of the -globe he inhabits, myriads of ages ago, before his -species became its denizens.</p> - -<p>(11.) And this is, in fact, one of the great sources -of delight which the study of natural science imparts -to its votaries. A mind which has once imbibed a -taste for scientific enquiry, and has learnt the habit<span class="pagenum"><a id="Page_15">15</a></span> -of applying its principles readily to the cases which -occur, has within itself an inexhaustible source of -pure and exciting contemplations:—one would -think that Shakspeare had such a mind in view when -he describes a contemplative man as finding all nature -eloquent—the very trees, the brooks, and the -stones reading to him lessons of deep and serious import. -Accustomed to trace the operation of general -causes, and the exemplification of general laws, in -circumstances where the uninformed and unenquiring -eye perceives neither novelty nor beauty, he -walks in the midst of wonders: every object which -falls in his way elucidates some principle, affords -some instruction, and impresses him with a sense of -harmony and order. Nor is it a mere passive pleasure -which is thus communicated. A thousand -questions are continually arising in his mind, a -thousand subjects of enquiry presenting themselves, -which keep his faculties in constant exercise, and -his thoughts perpetually on the wing, so that lassitude -is excluded from his life, and that craving -after artificial excitement and dissipation of mind, -which leads so many into frivolous, unworthy, and -destructive pursuits, is altogether eradicated from -his bosom.</p> - -<p>(12.) It is not one of the least advantages of these -pursuits, which, however, they possess in common -with every class of intellectual pleasures, that they -are altogether independent of external circumstances, -and are to be enjoyed in every situation in -which a man can be placed in life. The highest degrees -of worldly prosperity are so far from being incompatible<span class="pagenum"><a id="Page_16">16</a></span> -with them, that they supply inestimable -advantages for their pursuit, and that sort of fresh -and renewed relish which arises partly from the -sense of contrast, partly from experience of the -peculiar pre-eminence they possess over the pleasures -of sense in their capability of unlimited increase -and continual repetition without satiety or -distaste. They may be enjoyed, too, in the intervals -of the most active business; and the calm -and dispassionate interest with which they fill the -mind renders them a most delightful retreat from -the agitations and dissensions of the world, and -from the conflict of passions, prejudices, and interests -in which the man of business finds himself involved. -There is something in the contemplation -of general laws which powerfully induces and persuades -us to merge individual feeling, and to commit -ourselves unreservedly to their disposal; while the -observation of the calm, energetic regularity of nature, -the immense scale of her operations, and the -certainty with which her ends are attained, tends, -irresistibly, to tranquillize and re-assure the mind, -and render it less accessible to repining, selfish, and -turbulent emotions. And this it does, not by debasing -our nature into weak compliances and abject -submission to circumstances, but by filling us, as -from an inward spring, with a sense of nobleness -and power which enables us to rise superior to them; -by showing us our strength and innate dignity, and -by calling upon us for the exercise of those powers -and faculties by which we are susceptible of the -comprehension of so much greatness, and which -form, as it were, a link between ourselves and the<span class="pagenum"><a id="Page_17">17</a></span> -best and noblest benefactors of our species, with -whom we hold communion in thoughts and participate -in discoveries which have raised them above -their fellow-mortals, and brought them nearer to -their Creator.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_18">18</a></span></p> - -<div class="chapter"> -<h2 id="hdr_3">CHAP. II.</h2> -</div> - -<blockquote class="hang"> - -<p class="b2">OF ABSTRACT SCIENCE AS A PREPARATION FOR THE -STUDY OF PHYSICS.—A PROFOUND ACQUAINTANCE -WITH IT NOT INDISPENSABLE FOR A CLEAR UNDERSTANDING -OF PHYSICAL LAWS.—HOW A CONVICTION -OF THEIR TRUTH MAY BE OBTAINED WITHOUT IT.—INSTANCES.—FURTHER -DIVISION OF THE SUBJECT.</p></blockquote> - -<p class="in0">(13.) <span class="smcap"><span class="flet">S</span>cience</span> is the knowledge of many, orderly -and methodically digested and arranged, so as to -become attainable by one. The knowledge of reasons -and their conclusions constitutes <em>abstract</em>, that of -causes and their effects, and of the laws of nature, -<em>natural science</em>.</p> - -<p>(14.) Abstract science is independent of a system -of nature,—of a creation,—of every thing, in short, -except memory, thought, and reason. Its objects -are, first, those primary existences and relations -which we cannot even conceive not to <em>be</em>, such as -space, time, number, order, &c.; and, secondly, -those artificial forms, or symbols, which thought -has the power of creating for itself at pleasure, -and substituting as representatives, by the aid of -memory, for combinations of those primary objects -and of its own conceptions,—either to facilitate the -act of reasoning respecting them, or as convenient -deposits of its own conclusions, or for their communication -to others. Such are, first, <em>language</em>, -oral or written; its conventional forms, which constitute -grammar, and the rules for its use in argument,<span class="pagenum"><a id="Page_19">19</a></span> -in which consists the logic of the schools; secondly, -<em>notation</em>, which, applied to <em>number</em>, is <em>arithmetic</em>,—and, -to the more general relations of abstract quantity -or order, is <em>algebra</em>; and, thirdly, that higher -kind of logic, which teaches us to use our reason in -the most advantageous manner for the discovery of -truth; which points out the criterions by which we -may be sure we have attained it; and which, by -detecting the sources of error, and exposing the -haunts where fallacies are apt to lurk, at once warns -us of their danger, and shows us how to avoid them. -This greater logic may be termed <em>rational</em><a id="FNanchor_4" href="#Footnote_4" class="fnanchor">4</a>; while, -to that inferior department which is conversant with -words alone, the epithet <em>verbal</em><a id="FNanchor_5" href="#Footnote_5" class="fnanchor">5</a> may, for distinction, -be applied.</p> - -<p>(15.) A certain moderate degree of acquaintance -with abstract science is highly desirable to every -one who would make any considerable progress in -physics. As the universe exists in time and place; -and as motion, velocity, quantity, number, and -order, are main elements of our knowledge of external -things and their changes, an acquaintance -with these, abstractedly considered, (that is to say, -independent of any consideration of the particular -things moved, measured, counted, or arranged,) -must evidently be a useful preparation for the more -complex study of nature. But there is yet another -recommendation of such sciences as a preparation -for the study of natural philosophy. Their objects -are so definite, and our notions of them so distinct, -that we can reason about them with an assurance,<span class="pagenum"><a id="Page_20">20</a></span> -that the words and signs used in our reasonings -are full and true representatives of the things signified; -and, consequently, that when we use language -or signs in argument, we neither, by their -use, introduce extraneous notions, nor exclude any -part of the case before us from consideration. For -example: the words space, square, circle, a hundred, -&c., convey to the mind notions so complete in -themselves, and so distinct from every thing else, -that we are sure when we use them we know and -have in view the whole of our own meaning. It is -widely different with words expressing natural objects -and mixed relations. Take, for instance, iron. -Different persons attach very different ideas to this -word. One who has never heard of magnetism has -a widely different notion of <em>iron</em> from one in the -contrary predicament. The vulgar, who regard this -metal as incombustible, and the chemist, who sees -it burn with the utmost fury, and who has other -reasons for regarding it as one of the most combustible -bodies in nature;—the poet, who uses it as -an emblem of rigidity; and the smith and engineer, -in whose hands it is plastic, and moulded like wax -into every form;—the jailer, who prizes it as an -obstruction, and the electrician, who sees in it only a -channel of open communication by which that most -impassable of obstacles, the air, may be traversed -by his imprisoned fluid, have all different, and all -imperfect, notions of the same word. The meaning -of such a term is like a rainbow—every body sees a -different one, and all maintain it to be the same. -So it is with nearly all our terms of sense. Some -are indefinite, as hard or soft, light or heavy (terms<span class="pagenum"><a id="Page_21">21</a></span> -which were at one time the sources of innumerable -mistakes and controversies); some excessively complex, -as man, life, instinct. But, what is worst of -all, some, nay most, have two or three meanings; -sufficiently distinct from each other to make a proposition -true in one sense and false in another, or -even false altogether; yet not distinct enough to -keep us from confounding them in the process by -which we arrived at it, or to enable us immediately -to recognise the fallacy when led to it by a train of -reasoning, each step of which we <em>think</em> we have -examined and approved. Surely those who thus -attach two senses to one word, or superadd a new -meaning to an old one, act as absurdly as colonists -who distribute themselves over the world, naming -every place they come to by the names of those -they have left, till all distinctions of geographical -nomenclature are confounded, and till we are unable -to decide whether an occurrence stated to have -happened at Windsor took place in Europe, America, -or Australia.<a id="FNanchor_6" href="#Footnote_6" class="fnanchor">6</a></p> - -<p>(16.) It is, in fact, in this double or incomplete sense -of words that we must look for the origin of a very -large portion of the errors into which we fall. Now, -the study of the abstract sciences, such as arithmetic, -geometry, algebra, &c., while they afford scope for -the exercise of reasoning about objects that are, or, -at least, may be conceived to be, external to us;<span class="pagenum"><a id="Page_22">22</a></span> -yet, being free from these sources of error and mistake, -accustom us to the strict use of language as -an instrument of reason, and by familiarizing us, in -our progress towards truth, to walk uprightly and -straight-forward on firm ground, give us that proper -and dignified carriage of mind which could never be -acquired by having always to pick our steps among -obstructions and loose fragments, or to steady them -in the reeling tempest of conflicting meanings.</p> - -<p id="p17">(17.) But there is yet another point of view under -which some acquaintance with abstract science may -be regarded as highly desirable in general education, -if not indispensably necessary, to impress -on us the distinction between strict and vague -reasoning, to show us what demonstration really -<em>is</em>, and to give us thereby a full and intimate sense -of the nature and strength of the evidence on -which our knowledge of the actual system of nature, -and the laws of natural phenomena, rests. For this -purpose, however, a very moderate acquaintance -with the more elementary branches of mathematics -may suffice. The chain is laid before us, and every -link is submitted to our unreserved examination, if -we have patience and inclination to enter on such -detail. Hundreds have gone through it, and will -continue to do so; but, for the generality of mankind, -it is enough to satisfy themselves of the solidity -and adamantine texture of its materials, and -the unreserved exposure of its weakest, as well as -its strongest, parts. If, however, we content ourselves -with this general view of the matter, we -must be content also to take on trust, that is, on -the authority of those who have examined deeper,<span class="pagenum"><a id="Page_23">23</a></span> -every conclusion which cannot be made apparent to -our senses. Now, among these there are many so -very surprising, indeed apparently so extravagant, -that it is quite impossible for any enquiring mind -to rest contented with a mere hearsay statement of -them,—we feel irresistibly impelled to enquire further -into their truth. What mere assertion will -make any man believe, that in one second of time, -in one beat of the pendulum of a clock, a ray of -light travels over 192,000 miles, and would therefore -perform the tour of the world in about the -same time that it requires to wink with our eyelids, -and in much less than a swift runner occupies in -taking a single stride? What mortal can be made -to believe, without demonstration, that the sun is -almost a million times larger than the earth? and -that, although so remote from us, that a cannon ball -shot directly towards it, and maintaining its full -speed, would be twenty years in reaching it, it yet -affects the earth by its attraction in an inappreciable -instant of time?—a closeness of union of which -we can form but a feeble, and totally inadequate, -idea, by comparing it to any material connection; -since the communication of an impulse to -such a distance, by any solid intermedium we are -acquainted with, would require, not moments, but -whole years. And when, with pain and difficulty -we have strained our imagination to conceive a distance -so vast, a force so intense and penetrating, if -we are told that the one dwindles to an insensible -point, and the other is unfelt at the nearest of the -fixed stars, from the mere effect of their remoteness, -while among those very stars are some whose actual<span class="pagenum"><a id="Page_24">24</a></span> -splendour exceeds by many hundred times that of the -sun itself, although we may not deny the truth of -the assertion, we cannot but feel the keenest curiosity -to know <em>how</em> such things were ever made out.</p> - -<p>(18.) The foregoing are among those results of -scientific research which, by their magnitude, seem -to transcend our powers of conception. There are -others, again, which, from their minuteness, would -appear to elude the grasp of thought, much more of -distinct and accurate measurement. Who would not -ask for demonstration, when told that a gnat’s wing, -in its ordinary flight, beats many hundred times in a -second? or that there exist animated and regularly -organized beings, many thousands of whose bodies -laid close together would not extend an inch? But -what are these to the astonishing truths which -modern optical enquiries have disclosed, which teach -us that every point of a medium through which a ray -of light passes is affected with a succession of periodical -movements, regularly recurring at equal intervals, -no less than five hundred millions of millions of times -in a single second! that it is by such movements, -communicated to the nerves of our eyes, that we -see:—nay more, that it is the <em>difference</em> in the frequency -of their recurrence which affects us with the -sense of the diversity of colour; that, for instance, -in acquiring the sensation of redness our eyes are -affected four hundred and eighty-two millions of -millions of times; of yellowness, five hundred and -forty-two millions of millions of times; and of violet, -seven hundred and seven millions of millions of times -per second.<a id="FNanchor_7" href="#Footnote_7" class="fnanchor">7</a> Do not such things sound more like<span class="pagenum"><a id="Page_25">25</a></span> -the ravings of madmen, than the sober conclusions of -people in their waking senses?</p> - -<p>(19.) They are, nevertheless, conclusions to which -any one may most certainly arrive, who will only -be at the trouble of examining the chain of reasoning -by which they have been deduced; but, in order to -do this, something beyond the mere elements of abstract -science is required. Waving, however, such -instances as these, which, after all, are rather calculated -to surprise and astound than for any other purpose, -it must be observed that it is not possible to -satisfy ourselves completely that we <em>have</em> arrived at -a true statement of any law of nature, until, setting -out from such statement, and making it a foundation -of reasoning, we can show, by strict argument, that -the facts observed must follow from it as necessary -logical consequences, and <em>this</em>, not vaguely and generally, -but with all possible precision in time, place, -weight, and measure.</p> - -<p>(20.) To do this, however, as we shall presently -see, requires in many cases a degree of knowledge of -mathematics and geometry altogether unattainable by -the generality of mankind, who have not the leisure, -even if they all had the capacity, to enter into such -enquiries, some of which are indeed of that degree of -difficulty that they can be only successfully prosecuted -by persons who devote to them their whole -attention, and make them the serious business of -their lives. But there is scarcely any person of -good ordinary understanding, however little exercised -in abstract enquiries, who may not be readily -made to comprehend at least the general train of -reasoning by which any of the great truths of physics<span class="pagenum"><a id="Page_26">26</a></span> -are deduced, and the essential bearings and connections -of the several parts of natural philosophy. -There are whole branches too and very extensive -and important ones, to which mathematical reasoning -has never been at all applied; such as chemistry, -geology, and natural history in general, and many -others, in which it plays a very subordinate part, and -of which the essential principles, and the grounds of -application to useful purposes, may be perfectly well -understood by a student who possesses no more -mathematical knowledge than the rules of arithmetic; -so that no one need be deterred from the -acquisition of knowledge, or even from active original -research in such subjects, by a want of mathematical -information. Even in those branches which, -like astronomy, optics, and dynamics, are almost exclusively -under the dominion of mathematics, and in -which no effectual progress can be made without -<em>some</em> acquaintance with geometry, the principal -<em>results</em> may be perfectly understood without it. To -one incapable of following out the intricacies of -mathematical demonstration, the conviction afforded -by verified predictions must stand in the place of -that purer and more satisfactory reliance which a -verification of every step in the process of reasoning -can alone afford, since every one will acknowledge -the validity of pretensions which he is in the daily -habit of seeing brought to the test of practice.</p> - -<p>(21.) Among the verifications of this practical -kind which abound in every department of physics, -there are none more imposing than the precise prediction -of the greater phenomena of astronomy; -none, certainly, which carry a broader conviction<span class="pagenum"><a id="Page_27">27</a></span> -home to every mind from their notoriety and unequivocal -character. The prediction of eclipses has -accordingly from the earliest ages excited the admiration -of mankind, and been one grand instrument -by which their allegiance (so to speak) to natural -science, and their respect for its professors, has been -maintained; and though strangely abused in unenlightened -ages by the supernatural pretensions of -astrologers, the credence given even to their absurdities -shows the force of this kind of evidence on -men’s minds. The predictions of astronomers are, -however, now far too familiar to endanger the just -equipoise of our judgment, since even the return of -comets, true to their paths and exact to the hour -of their appointment, has ceased to amaze, though -it must ever delight all who have souls capable of -being penetrated by such beautiful instances of accordance -between theory and facts. But the age of -mere wonder in such things is past, and men prefer -being guided and enlightened, to being astonished -and dazzled. Eclipses, comets, and the like, afford -but rare and transient displays of the powers of calculation, -and of the certainty of the principles on -which it is grounded. A page of “lunar distances” -from the Nautical Almanack is worth all the eclipses -that have ever happened for inspiring this necessary -confidence in the conclusions of science. That a -man, by merely measuring the moon’s apparent distance -from a star with a little portable instrument -held in his hand, and applied to his eye, even with -so unstable a footing as the deck of a ship, shall say -positively, within five miles, where he is, on a boundless -ocean, cannot but appear to persons ignorant of<span class="pagenum"><a id="Page_28">28</a></span> -physical astronomy an approach to the miraculous. -Yet, the alternatives of life and death, wealth and -ruin, are daily and hourly staked with perfect confidence -on these marvellous computations, which -might almost seem to have been devised on purpose -to show how closely the extremes of speculative -refinement and practical utility can be brought to -approximate. We have before us an anecdote communicated -to us by a naval officer<a id="FNanchor_8" href="#Footnote_8" class="fnanchor">8</a>, distinguished for -the extent and variety of his attainments, which -shows how impressive such results may become in -practice. He sailed from San Blas on the west -coast of Mexico, and after a voyage of 8000 miles, -occupying 89 days, arrived off Rio de Janeiro, having, -in this interval, passed through the Pacific -Ocean, rounded Cape Horn, and crossed the South -Atlantic, without making any land, or even seeing a -single sail, with the exception of an American whaler -off Cape Horn. Arrived within a week’s sail of Rio, -he set seriously about determining, by lunar observations, -the precise line of the ship’s course and its -situation in it at a determinate moment, and having -ascertained this within from five to ten miles, ran the -rest of the way by those more ready and compendious -methods, known to navigators, which can be -safely employed for short trips between one known -point and another, but which cannot be trusted in -long voyages, where the moon is the only sure guide. -The rest of the tale we are enabled by his kindness -to state in his own words:—“We steered towards -Rio de Janeiro for some days after taking the lunars<span class="pagenum"><a id="Page_29">29</a></span> -above described, and having arrived within fifteen or -twenty miles of the coast, I hove to at four in the -morning till the day should break, and then bore up; -for although it was very hazy, we could see before -us a couple of miles or so. About eight o’clock it -became so foggy that I did not like to stand in farther, -and was just bringing the ship to the wind -again before sending the people to breakfast, when -it suddenly cleared off, and I had the satisfaction of -seeing the great Sugar Loaf Rock, which stands on -one side of the harbour’s mouth, so nearly right -ahead that we had not to alter our course above a -point in order to hit the entrance of Rio. This was -the first land we had seen for three months, after -crossing so many seas and being set backwards and -forwards by innumerable currents and foul winds.” -The effect on all on board might well be conceived -to have been electric; and it is needless to remark -how essentially the authority of a commanding -officer over his crew may be strengthened by the -occurrence of such incidents, indicative of a degree -of knowledge and consequent power beyond their -reach.</p> - -<p>(22.) But even such results as these, striking as -they are, yet fall short of the force with which conviction -is urged upon us when, through the medium -of reasoning too abstract for common apprehension, -we arrive at conclusions which outrun experience, -and describe beforehand what will happen under -new combinations, or even correct imperfect experiments, -and lead us to a knowledge of facts contrary -to received analogies drawn from an experience -wrongly interpreted or overhastily generalised. To<span class="pagenum"><a id="Page_30">30</a></span> -give an example:—every body knows that objects -viewed through a transparent medium, such as water -or glass, appear distorted or displaced. Thus, a stick -in water appears bent, and an object seen through a -prism or wedge of glass seems to be thrown aside -from its true place. This effect is owing to what is -called the <em>refraction</em> of light; and a simple rule discovered -by Willebrod Snell enables any one to say -exactly <em>how much</em> the stick will be bent, and <em>how -far</em>, and in what <em>direction</em>, the apparent situation of -an object seen through the glass will deviate from the -real one. If a shilling be laid at the bottom of a -basin of water and viewed obliquely, it will appear -to be raised by the water; if instead of water spirits -of wine be used it will appear more raised; if oil, still -more:—but in none of these cases will it appear to -be thrown <em>aside</em> to the <em>right</em> or <em>left</em> of its true place, -however the eye be situated. The <em>plane</em>, in which -are contained the eye, the object, and the point in -the surface of the liquid at which the object is seen, -is an upright or <em>vertical</em> plane; and this is one of the -principal characters in the <em>ordinary refraction</em> of light, -viz. that the ray by which we see an object through a -refracting surface, although it undergoes a bending, -and is, as it were, broken at the surface, yet, in pursuing -its course to the eye, does not <em>quit a plane -perpendicular to the refracting surface</em>. But there -are again other substances, such as rock-crystal, and -especially Iceland spar, which possess the singular -property of <em>doubling</em> the image or appearance of an -object seen through them in certain directions; so -that instead of seeing one object we see two, side by -side, when such a crystal or spar is interposed between<span class="pagenum"><a id="Page_31">31</a></span> -the object and the eye; and if a ray or small -sunbeam be thrown upon a surface of either of these -substances, it will be split into two, making an angle -with each other, and each pursuing its own separate -course,—this is called <em>double refraction</em>. Now, of -these images or doubly refracted rays, one always -follows the same rule as if the substance were glass -or water: its deviation can be correctly calculated -by Snell’s law above mentioned, and it does not quit -the plane perpendicular to the refracting surface. -The other ray, on the contrary, (which is therefore -said to have undergone <em>extraordinary refraction</em>) <em>does</em> -quit that plane, and the amount of its deviation from -its former course requires for its determination a -much more complicated rule, which cannot be understood -or even stated without a pretty intimate -knowledge of geometry. Now, rock-crystal and -Iceland spar differ from glass in a very remarkable -circumstance. They affect naturally certain regular -figures, not being found in shapeless lumps, but in -determinate geometrical forms; and they are susceptible -of being cleft or split much easier in certain -directions than in others—they have a <em>grain</em> which -glass has not. When other substances having this -peculiarity (and which are called <em>crystallized</em> substances) -were examined, they were all, or by far the -greater part, found to possess this singular property -of <em>double refraction</em>; and it was very natural to conclude, -therefore, that the same thing took place in -all of them, viz. that of the two rays, into which any -beam of light falling on the surface of such a substance -was split, or of the two images of an object -seen through it, <em>one</em> only was turned aside out of its<span class="pagenum"><a id="Page_32">32</a></span> -<em>plane</em> and <em>extraordinarily</em> refracted, while the other -followed the <em>ordinary</em> rule. Accordingly this was -supposed to be the case; and not only so, but from -some trials and measurements purposely made by a -philosopher of great eminence, it was considered to -be a fact sufficiently established by experiment.</p> - -<p>(23.) Perhaps we might have remained long under -this impression, for the measurements are delicate, -and the subject very difficult. But it has lately -been demonstrated by an eminent French philosopher -and mathematician, M. Fresnel, that, granting certain -<em>principles</em> or postulates, all the phenomena of double -refraction, including perhaps the greatest variety of -facts that have ever yet been arranged under one -general head, may be satisfactorily explained and -deduced from them by strict mathematical calculation; -and <em>that</em>, when applied to the cases first mentioned, -these principles give a satisfactory account -of the <em>want</em> of the extraordinary image; <em>that</em> when -applied to such cases as those of rock-crystal or Iceland -spar, they also give a correct account of both -the images, and agree in their conclusions with the -rules before ascertained for them: but so far from -coinciding with that part of the previous statement, -which would make these conclusions extend to all -crystallised substances, M. Fresnel’s principles lead -to a conclusion quite opposite, and point to a <em>fact</em> -which had never been observed, viz. that in by far -the greater number of crystallized substances which -possess the property of double refraction, <em>neither</em> of -the images follows the ordinary law, but both undergo -a deviation from their original plane. Now -this had never been observed to be the case in any<span class="pagenum"><a id="Page_33">33</a></span> -previous trial, and all opinion was against it. But -when put to the test of experiment in a great variety -of new and ingenious methods, it was found to be -fully verified; and to complete the evidence, the substances -on whose imperfect examination the first -erroneous conclusion was founded, having been -lately subjected to a fresh and more scrupulous -examination, the result has shown the insufficiency -of the former measurements, and proved in perfect -accordance with the newly discovered laws. Now -it will be observed in this case, first, that, so far from -the principles assumed by M. Fresnel being at all -obvious, they are extremely remote from ordinary -observation; and, secondly, that the chain of reasoning -by which they are brought to the test is one -of such length and complexity, and the purely mathematical -difficulty of their application so great, that -no <em>mere</em> good common sense, no general tact or ordinary -practical reasoning, would afford the slightest -chance of threading their mazes. Cases like this -are the triumph of theories. They show at once -how large a part pure reason has to perform in our -examination of nature, and how implicit our reliance -ought to be on that powerful and methodical system -of rules and processes which constitute the modern -mathematical analysis, in all the more difficult applications -of exact calculation to her phenomena.</p> - -<p>(24.) To take an instance more within ordinary apprehension. -An eminent living geometer had proved -by calculations, founded on strict optical principles, -that in the <em>centre of the shadow</em> of a small circular -plate of metal, exposed in a dark room to a beam of -light emanating from a <em>very small brilliant point</em>,<span class="pagenum"><a id="Page_34">34</a></span> -there ought to be no darkness,—in fact, <em>no shadow</em> -at that place; but, on the contrary, a degree of illumination -precisely as bright as if the metal plate -were away. Strange and even impossible as this -conclusion may seem, it has been put to the trial, -and found perfectly correct.<a id="FNanchor_9" href="#Footnote_9" class="fnanchor">9</a></p> - -<p>(25.) We shall now proceed to consider more -particularly, and in <span class="locked">detail,—</span></p> - -<blockquote class="hang2"> - -<p> <span class="ii">I.</span> The nature and objects immediate and collateral -of physical science, as regarded in -itself, and in its application to the practical -purposes of life, and its influence on the -well-being and progress of society.</p> - -<p> <span class="iii">II.</span> The principles on which it relies for its successful -prosecution, and the rules by which -a systematic examination of nature should -be conducted, with examples illustrative of -their influence.</p> - -<p>III. The subdivision of physical science into distinct -branches, and their mutual relations.</p></blockquote> - -<hr /> - -<p><span class="pagenum"><a id="Page_35">35</a></span></p> - -<div class="chapter"> -<h2 id="hdr_4">CHAP. III.</h2> -</div> - -<blockquote class="hang"> - -<p>OF THE NATURE AND OBJECTS, IMMEDIATE AND COLLATERAL, -OF PHYSICAL SCIENCE, AS REGARDED IN -ITSELF, AND IN ITS APPLICATION TO THE PRACTICAL -PURPOSES OF LIFE, AND ITS INFLUENCE ON THE WELL-BEING -AND PROGRESS OF SOCIETY.</p></blockquote> - -<p class="in0">(26.) <span class="smcap"><span class="flet">T</span>he</span> first thing impressed on us from our -earliest infancy is, that events do not succeed one -another at random, but with a certain degree of order, -regularity, and connection;—some constantly, and, -as we are apt to think, immutably,—as the alternation -of day and night, summer and winter,—others -contingently, as the motion of a body from its place, -if pushed, or the burning of a stick if thrust into the -fire. The knowledge that the former class of events -<em>has</em> gone on, uninterruptedly, for ages beyond all -memory, impresses us with a strong expectation that -it will continue to do so in the same manner; and -thus our notion of an <em>order of nature</em> is originated -and confirmed. If every thing were equally regular -and periodical, and the succession of events liable to -no change depending on our own will, it may be -doubted whether we should ever think of looking for -causes. No one regards the night as the cause of the -day, or the day of night. They are alternate effects -of a common cause, which their regular succession -alone gives us no sufficient clue for determining. It<span class="pagenum"><a id="Page_36">36</a></span> -is chiefly, perhaps entirely, from the other or contingent -class of events that we gain our notions of -cause and effect. From them alone we gather that -there are such things as laws of nature. The very -idea of a law includes that of contingency. “<i xml:lang="la" lang="la">Si -quis mala carmina condidisset, fuste ferito</i>;” if such -a case arise, such a course shall be followed,—if the -match be applied to the gunpowder, it will explode. -Every law is a provision for cases which <em>may</em> occur, -and has relation to an infinite number of cases that -never have occurred, and never will. Now, it is -this provision, <i xml:lang="la" lang="la">à priori</i>, for contingencies, this contemplation -of possible occurrences, and predisposal -of what shall happen, that impresses us with -the notion of a <em>law</em> and a <em>cause</em>. Among all the -possible combinations of the fifty or sixty elements -which chemistry shows to exist on the earth, it is -likely, nay almost certain, that <em>some</em> have never been -formed; that some elements, in some proportions, -and under some circumstances, have never yet been -placed in relation with one another. Yet no chemist -can doubt that it is <em>already fixed</em> what they will do -when the case does occur. They will obey certain -laws, of which we know nothing at present, but -which must <em>be</em> already fixed, or they could not be -laws. It is not by habit, or by trial and failure, -that they will learn what to do. When the contingency -occurs, there will be no hesitation, no consultation;—their -course will at once be decided, and -will always be the same if it occur ever so often in -succession, or in ever so many places at one and the -same instant. This is the perfection of a law, that -it includes all possible contingencies, and ensures<span class="pagenum"><a id="Page_37">37</a></span> -implicit obedience,—and of this kind are the laws -of nature.</p> - -<p>(27.) This use of the word <em>law</em>, however, our -readers will of course perceive has relation to us as -understanding, rather than to the materials of which -the universe consists as obeying, certain rules. To -obey a law, to act in <em>compliance</em> with a rule, supposes -an understanding and a will, a power of complying -or not, in the being who obeys and complies, which -we do not admit as belonging to mere matter. The -Divine Author of the universe cannot be supposed -to have laid down particular laws, enumerating all -individual contingencies, which his materials have -understood and obey,—this would be to attribute -to him the imperfections of human legislation;—but -rather, by creating them, endued with certain -fixed qualities and powers, he has impressed them -in their origin with the <em>spirit</em>, not the <em>letter</em>, of his -law, and made all their subsequent combinations and -relations inevitable consequences of this first impression, -by which, however, we would no way be -understood to deny the constant exercise of his -direct power in maintaining the system of nature, or -the ultimate emanation of every energy which material -agents exert from his immediate will, acting in -conformity with his own laws.</p> - -<p>(28.) The discoveries of modern chemistry have -gone far to establish the truth of an opinion entertained -by some of the ancients, that the universe -consists of distinct, separate, indivisible <em>atoms</em>, or -individual beings so minute as to escape our senses, -except when united by millions, and by this aggregation -making up bodies of even the smallest visible<span class="pagenum"><a id="Page_38">38</a></span> -bulk; and we have the strongest evidence that, although -there exist great and essential differences in -individuals among these atoms, they may yet all be -arranged in a very limited number of groups or -classes, all the individuals of each of which are, to -all intents and purposes, <em>exactly alike</em> in all their -properties. Now, when we see a great number of -things precisely alike, we do not believe this similarity -to have originated except from a common -principle independent of them; and that we recognise -this likeness, chiefly by the identity of their deportment -under similar circumstances, strengthens -rather than weakens the conclusion. A line of spinning-jennies<a id="FNanchor_10" href="#Footnote_10" class="fnanchor">10</a>, -or a regiment of soldiers dressed -exactly alike, and going through precisely the same -evolutions, gives us no idea of independent existence: -we must see them act out of concert before -we can believe them to have independent wills and -properties, not impressed on them from without. -And this conclusion, which would be strong even -were there only two individuals precisely alike in -<em>all</em> respects and <em>for ever</em>, acquires irresistible force -when their number is multiplied beyond the power -of imagination to conceive. If we mistake not, then, -the discoveries alluded to effectually destroy the -idea of an <em>eternal self-existent matter</em>, by giving to -each of its atoms the essential characters, at once, -of a <em>manufactured article</em>, and a <em>subordinate agent</em>.</p> - -<p>(29.) But to ascend to the origin of things, and -speculate on the creation, is not the business of the -natural philosopher. An humbler field is sufficient<span class="pagenum"><a id="Page_39">39</a></span> -for him in the endeavour to discover, as far as our -faculties will permit, what <em>are</em> these primary qualities -originally and unalterably impressed on matter, and -to discover the <em>spirit</em> of the laws of nature, which -includes groups and classes of relations and facts -from the <em>letter</em> which, as before observed, is presented -to us by single phenomena: or if, after all, -this should prove impossible; if such a step be -beyond our faculties; and the essential qualities of -material agents be really <em>occult</em>, or incapable of -being expressed in any form intelligible to our understandings, -at least to approach as near to their -comprehension as the nature of the case will allow; -and devise such forms of words as shall include and -<em>represent</em> the greatest possible multitude and variety -of phenomena.</p> - -<p>(30.) Now, in this research there would seem one -great question to be disposed of before our enquiries -can even be commenced with any thing like a prospect -of success, which is, whether the laws of nature -themselves <em>have</em> that degree of permanence and -fixity which can render them subjects of systematic -discussion; or whether, on the other hand, the qualities -of natural agents are subject to mutation from -the lapse of time. To the ancients, who lived in -the infancy of the world, or rather, in the infancy -of man’s experience, this was a very rational subject -of question, and hence their distinctions between -corruptible and incorruptible matter. Thus, according -to some among them, the matter only of the -celestial spaces is pure, immutable, and incorruptible, -while all sublunary things are in a constant state -of lapse and change; the world becoming paralysed<span class="pagenum"><a id="Page_40">40</a></span> -and effete with age, and man himself deteriorating -in character, and diminishing at once in intellectual -and bodily stature. But to us, who have the experience -of some additional thousands of years, the -question of permanence is already, in a great measure, -decided in the affirmative. The refined speculations -of modern astronomy, grounding their conclusions -on observations made at very remote periods, have -proved to demonstration, that one at least of the -great powers of nature, the force of gravitation, -the main bond and support of the material universe, -has undergone no change in intensity from a high -antiquity. The stature of mankind is just what it -was three thousand years ago, as the specimens of -mummies which have been examined at various -times sufficiently show. The intellect of Newton, -Laplace, or Lagrange, may stand in fair competition -with that of Archimedes, Aristotle, or Plato; and -the virtues and patriotism of Washington with the -brightest examples of ancient history.</p> - -<p>(31.) Again, the researches of chemists have -shown that what the vulgar call corruption, destruction, -&c., is nothing but a change of arrangement of -the same ingredient elements, the disposition of the -same materials into other forms, without the loss -or actual destruction of a single atom; and thus any -doubts of the permanence of natural laws are discountenanced, -and the whole weight of <em>appearances</em> -thrown into the opposite scale. One of the most -obvious cases of apparent destruction is, when any -thing is ground to dust and scattered to the winds. -But it is one thing to grind a fabric to powder, and -another to annihilate its materials: scattered as they<span class="pagenum"><a id="Page_41">41</a></span> -may be, they must fall somewhere, and continue, -if only as ingredients of the soil, to perform their -humble but useful part in the economy of nature. -The destruction produced by fire is more striking: -in many cases, as in the burning of a piece of -charcoal or a taper, there is no smoke, nothing -visibly dissipated and carried away; the burning -body wastes and disappears, while nothing <em>seems</em> to -be produced but warmth and light, which we are -not in the habit of considering as substances; and -when all has disappeared, except perhaps some -trifling ashes, we naturally enough suppose it is -gone, lost, destroyed. But when the question is -examined more exactly, we detect, in the invisible -stream of heated air which ascends from the glowing -coal or flaming wax, the <em>whole</em> ponderable matter, -only united in a new combination with the air, -and dissolved in it. Yet, so far from being thereby -destroyed, it is only become again what it was -before it existed in the form of charcoal or wax, an -active agent in the business of the world, and a -main support of vegetable and animal life, and is -still susceptible of running again and again the same -round, as circumstances may determine; so that, -for aught we can see to the contrary, the same -identical atom may lie concealed for thousands of -centuries in a limestone rock; may at length be -quarried, set free in the limekiln, mix with the air, -be absorbed from it by plants, and, in succession, -become a part of the frames of myriads of living -beings, till some concurrence of events consigns it -once more to a long repose, which, however, no way -unfits it from again resuming its former activity.</p> - -<p><span class="pagenum"><a id="Page_42">42</a></span> -(32.) Now, this absolute indestructibility of the -ultimate materials of the world, in periods commensurate -to our experience, and their obstinate retention -of the same properties, under whatever variety -of circumstances we choose to place them, however -violent and seemingly contradictory to their natures, -is, of itself, enough to render it highly improbable -that time alone should have any influence over -them. All that age or decay can do seems to be -included in a wasting of parts which are only dissipated, -not destroyed, or in a change of sensible properties, -which chemistry demonstrates to arise only -from new combinations of the same ingredients. -But, after all, the question is one entirely of experience: -we cannot be sure, <i xml:lang="la" lang="la">à priori</i>, that the laws -of nature are <em>immutable</em>; but we can ascertain, by -enquiry, <em>whether they change or not</em>; and to this -enquiry all experience answers in the negative. It -is not, of course, intended here to deny that great -operations, productive of extensive changes in the -visible state of nature,—such as, for instance, those -contemplated by the geologists, and embracing for -their completion vast periods of time,—are constantly -going on; but these are consequences and -fulfilments of the laws of nature, not contradictions -or exceptions to them. No theorist regards such -changes as alterations in the fundamental principles -of nature; he only endeavours to reconcile them, -and show how they result from laws already known, -and judges of the correctness of his theory by -their ultimate agreement.</p> - -<p>(33.) But the laws of nature are not only permanent, -but consistent, intelligible, and discoverable<span class="pagenum"><a id="Page_43">43</a></span> -with such a moderate degree of research, as is calculated -rather to stimulate than to weary curiosity. -If we were set down, as creatures of another world, -in any existing society of mankind, and began to -speculate on their actions, we should find it difficult -at first to ascertain whether they were subject to -any laws at all: but when, by degrees, we had -found out that they did consider themselves to be -so; and would then proceed to ascertain, from their -conduct and its consequences, what these laws were, -and in what spirit conceived; though we might not -perhaps have much difficulty in discovering single -rules applicable to particular cases, yet, the moment -we came to generalize, and endeavour from these to -ascend, step by step, and discover any steady pervading -principle, the mass of incongruities, absurdities, -and contradictions, we should encounter, would -either dishearten us from further enquiry or satisfy -us that what we were in search of did not exist. -It is quite the contrary in nature; there we find -no contradictions, no incongruities, but all is harmony. -What once is learnt we never have to -unlearn. As rules advance in generality, apparent -exceptions become regular; and equivoque, in her -sublime legislation, is as unheard of as maladministration.</p> - -<p>(34.) Living, then, in a world where such laws -obtain, and under their immediate dominion, it is -manifestly of the utmost importance to know them, -were it for no other reason than to be sure, in all we -undertake, to have, at least, the law on our side, -so as not to struggle in vain against some insuperable -difficulty opposed to us by natural causes.<span class="pagenum"><a id="Page_44">44</a></span> -What pains and expense would not the alchemists, -for instance, have been spared by a knowledge of -those simple laws of composition and decomposition, -which now preclude all idea of the attainment of -their declared object! what an amount of ingenuity, -thrown away on the pursuit of the perpetual motion, -might have been turned to better use, if the simplest -laws of mechanics had been known and attended -to by the inventors of innumerable contrivances -destined to that end! What tortures, inflicted on -patients by imaginary cures of incurable diseases, -might have been dispensed with, had a few simple -principles of physiology been earlier recognised!</p> - -<p>(35.) But if the laws of nature, on the one hand, -are invincible opponents, on the other, they are -irresistible auxiliaries; and it will not be amiss if -we regard them in each of those characters, and consider -the great importance of a knowledge of them -to <span class="locked">mankind,—</span></p> - -<blockquote class="hang2"> - -<p><span class="ii">I.</span> <i>In showing us how to avoid attempting impossibilities.</i></p> - -<p><span class="iii">II.</span> <i>In securing us from important mistakes in attempting -what is, in itself, possible, by means -either inadequate, or actually opposed, to the -end in view.</i></p> - -<p>III. <i>In enabling us to accomplish our ends in the -easiest, shortest, most economical, and most -effectual manner.</i></p> - -<p><span class="iiv">IV.</span> <i>In inducing us to attempt, and enabling us to -accomplish, objects which, but for such knowledge, -we should never have thought of undertaking.</i></p></blockquote> - -<p class="in0"><span class="pagenum"><a id="Page_45">45</a></span> -We shall therefore proceed to illustrate by examples -the effect of physical knowledge under each of these -<span class="locked">heads:—</span></p> - -<p>(36.) Ex. 1. (35.) I. It is not many years since -an attempt was made to establish a colliery at -Bexhill, in Sussex. The appearance of thin seams -and sheets of fossil-wood and wood-coal, with some -other indications similar to what occur in the neighbourhood -of the great coal-beds in the north of -England, having led to the sinking of a shaft, and -the erection of machinery on a scale of vast expense, -not less than eighty thousand pounds are said to -have been laid out on this project, which, it is almost -needless to add, proved completely abortive, as every -geologist would have at once declared it must, the -whole assemblage of geological facts being adverse -to the existence of a regular coal-bed <em>in</em> the -Hastings’ <em>sand</em>; while this, on which Bexhill is -situated, is separated from the <em>coal-strata</em> by a -series of interposed beds of such enormous thickness -as to render all idea of penetrating <em>through</em> -them absurd. The history of mining operations is -full of similar cases, where a very moderate acquaintance -with the <em>usual order of nature</em>, to say -nothing of theoretical views, would have saved -many a sanguine adventurer from utter ruin.</p> - -<p>(37.) Ex. 2. (35.) II. The smelting of iron requires -the application of the most violent heat that -can be raised, and is commonly performed in tall furnaces, -urged by great iron bellows driven by steam-engines. -Instead of employing this power to force -<em>air</em> into the furnace through the intervention of<span class="pagenum"><a id="Page_46">46</a></span> -bellows, it was, on one occasion, attempted to employ -the steam itself in, apparently, a much less -circuitous manner; viz. by directing the current of -steam in a violent blast, from the boiler at once into -the fire. From one of the known ingredients of steam -being a highly inflammable body, and the other that -essential part of the air which supports combustion, -it was imagined that this would have the effect of -increasing the fire to tenfold fury, whereas it simply -<em>blew it out</em>; a result which a slight consideration -of the laws of chemical combination, and the -state in which the ingredient elements exist in -steam, would have enabled any one to predict -without a trial.</p> - -<p>(38.) Ex. 3. (35.) II. After the invention of -the diving-bell, and its success in subaqueous processes, -it was considered highly desirable to devise -some means of remaining for any length of time -under water, and rising at pleasure without assistance, -so as either to examine, at leisure, the bottom, -or perform, at ease, any work that might be required. -Some years ago, an ingenious individual proposed a -project by which this end was to be accomplished. -It consisted in sinking the hull of a ship made quite -water-tight, with the decks and sides strongly supported -by shores, and the only entry secured by a -stout trap-door, in such a manner, that by disengaging, -from within, the weights employed to sink it, -it might rise of itself to the surface. To render the -trial more satisfactory, and the result more striking, -the projector himself made the first essay. It was -agreed that he should sink in twenty fathoms water, -and rise again without assistance at the expiration of<span class="pagenum"><a id="Page_47">47</a></span> -twenty-four hours. Accordingly, making all secure, -fastening down his trap-door, and provided with all -necessaries, as well as with the means of making -signals to indicate his situation, this unhappy victim -of his own ingenuity entered and was sunk. No -signal was made, and the time appointed elapsed. -An immense concourse of people had assembled to -witness his rising, but in vain; for the vessel was -never seen more. The pressure of the water at so -great a depth had, no doubt, been completely under-estimated, -and the sides of the vessel being at once -crushed in, the unfortunate projector perished before -he could even make the signal concerted to indicate -his distress.</p> - -<p>(39.) Ex. 4. (35.) III. In the granite quarries -near Seringapatam the most enormous blocks are -separated from the solid rock by the following neat -and simple process. The workman having found a -portion of the rock sufficiently extensive, and situated -near the edge of the part already quarried, lays -bare the upper surface, and marks on it a line in the -direction of the intended separation, along which a -groove is cut with a chisel about a couple of inches -in depth. Above this groove a narrow line of fire -is then kindled, and maintained till the rock below is -thoroughly heated, immediately on which a line of -men and women, each provided with a pot full of -cold water, suddenly sweep off the ashes, and pour -the water into the heated groove, when the rock at -once splits with a clean fracture. Square blocks of -six feet in the side, and upwards of eighty feet in -length, are sometimes detached by this method, or -by another equally simple and efficacious, but not<span class="pagenum"><a id="Page_48">48</a></span> -easily explained without entering into particulars of -mineralogical detail.<a id="FNanchor_11" href="#Footnote_11" class="fnanchor">11</a></p> - -<p>(40.) Ex. 5. (35.) III. Hardly less simple and -efficacious is the process used in some parts of France, -where mill-stones are made. When a mass of stone -sufficiently large is found, it is cut into a cylinder -several feet high, and the question then arises how -to subdivide this into horizontal pieces so as to make -as many mill-stones. For this purpose horizontal -indentations or grooves are chiselled out quite round -the cylinder, at distances corresponding to the thickness -intended to be given to the mill-stones, into -which wedges of dried wood are driven. These are -then wetted, or exposed to the night dew, and next -morning the different pieces are found separated -from each other by the expansion of the wood, consequent -on its absorption of moisture; an irresistible -natural power thus accomplishing, almost without -any trouble, and at no expense, an operation which, -from the peculiar hardness and texture of the stone, -would otherwise be impracticable but by the most -powerful machinery or the most persevering labour.</p> - -<p>(41.) Ex. 6. (35.) III. To accomplish our ends -quickly is often of, at least, as much importance as -to accomplish them with little labour and expense. -There are innumerable processes which, if left to -themselves, <i>i. e.</i> to the ordinary operation of natural -causes, are done, and well done, but with extreme<span class="pagenum"><a id="Page_49">49</a></span> -slowness, and in such cases it is often of the highest -practical importance to accelerate them. The -bleaching of linen, for instance, performed in the -natural way by exposure to sun, rain, and wind, -requires many weeks or even months for its completion; -whereas, by the simple immersion of the -cloth in a liquid, chemically prepared, the same -effect is produced in a few hours. The whole circle -of the arts, indeed, is nothing but one continued -comment upon this head of our subject. The -instances above given are selected, not on account -of their superior importance, but for the simplicity -and <em>directness</em> of application of the principles on -which they depend, to the objects intended to be -attained.</p> - -<p>(42.) But so constituted is the mind of man, that -his views enlarge, and his desires and wants increase, -in the full proportion of the facilities afforded -to their gratification, and, indeed, with augmented -rapidity, so that no sooner has the successful exercise -of his powers accomplished any considerable -simplification or improvement of processes subservient -to his use or comfort, than his faculties are -again on the stretch to extend the limits of his -newly acquired power; and having once experienced -the advantages which are to be gathered by availing -himself of some of the powers of nature to accomplish -his ends, he is led thenceforward to regard -them all as a treasure placed at his disposal, if he -have only the art, the industry, or the good fortune, -to penetrate those recesses which conceal them from -immediate view. Having once learned to look on -knowledge as power, and to avail himself of it as<span class="pagenum"><a id="Page_50">50</a></span> -such, he is no longer content to limit his enterprises -to the beaten track of former usage, but is constantly -led onwards to contemplate objects which, in a previous -stage of his progress, he would have regarded -as unattainable and visionary, had he even thought -of them at all. It is here that the investigation of -the hidden powers of nature becomes a mine, every -vein of which is pregnant with inexhaustible wealth, -and whose ramifications appear to extend in all directions -wherever human wants or curiosity may lead -us to explore.</p> - -<p>(43.) Between the physical sciences and the arts of -life there subsists a constant mutual interchange of -good offices, and no considerable progress can be -made in the one without of necessity giving rise to -corresponding steps in the other. On the one hand, -every art is in some measure, and many entirely, -dependent on those very powers and qualities of the -material world which it is the object of physical -enquiry to investigate and explain; and, accordingly, -abundant examples might be cited of cases where -the remarks of experienced artists, or even ordinary -workmen, have led to the discovery of natural qualities, -elements, or combinations which have proved -of the highest importance in physics. Thus (to give -an instance), a soap-manufacturer remarks that the -residuum of his ley, when exhausted of the alkali for -which he employs it, produces a corrosion of his -copper boiler for which he cannot account. He -puts it into the hands of a scientific chemist for -analysis, and the result is the discovery of one of the -most singular and important chemical elements, -iodine. The properties of this, being studied, are<span class="pagenum"><a id="Page_51">51</a></span> -found to occur most appositely in illustration and -support of a variety of new, curious, and instructive -views then gaining ground in chemistry, and thus -exercise a marked influence over the whole body of -that science. Curiosity is excited: the origin of the -new substance is traced to the sea-plants from whose -ashes the principal ingredient of soap is obtained, -and ultimately to the sea-water itself. It is thence -hunted through nature, discovered in salt mines and -springs, and pursued into all bodies which have a -marine origin; among the rest, into sponge. A -medical practitioner<a id="FNanchor_12" href="#Footnote_12" class="fnanchor">12</a> then calls to mind a reputed -remedy for the cure of one of the most grievous and -unsightly disorders to which the human species is -subject—the <i xml:lang="la" lang="la">goître</i>—which infests the inhabitants -of mountainous districts to an extent that in this -favoured land we have happily no experience of, -and which was said to have been originally cured by -the ashes of burnt sponge. Led by this indication -he tries the effect of iodine on that complaint, and -the result establishes the extraordinary fact that -this singular substance, taken as a medicine, acts -with the utmost promptitude and energy on <i xml:lang="la" lang="la">goître</i>, -dissipating the largest and most inveterate in a short -time, and acting (of course, like all medicines, even -the most approved, with occasional failures,) as a -specific, or natural antagonist, against that odious -deformity. It is thus that any accession to our knowledge -of nature is sure, sooner or later, to make itself -felt in some practical application, and that a benefit -conferred on science by the casual observation or -shrewd remark of even an unscientific or illiterate<span class="pagenum"><a id="Page_52">52</a></span> -person infallibly repays itself with interest, though -often in a way that could never have been at first -contemplated.</p> - -<p>(44.) It is to such observation, reflected upon, however, -and matured into a rational and scientific form -by a mind deeply imbued with the best principles of -sound philosophy, that we owe the practice of vaccination; -a practice which has effectually subdued, in -every country where it has been introduced, one of -the most frightful scourges of the human race, and -in some extirpated it altogether. Happily for us -we know only by tradition the ravages of the small-pox, -as it existed among us hardly more than a century -ago, and as it would in a few years infallibly -exist again, were the barriers which this practice, -and that of inoculation, oppose to its progress -abandoned. Hardly inferior to this terrible scourge -on land was, within the last seventy or eighty years, -the scurvy at sea. The sufferings and destruction -produced by this horrid disorder on board our ships -when, as a matter of course, it broke out after a few -months’ voyage, seem now almost incredible. Deaths -to the amount of eight or ten a day in a moderate -ship’s company; bodies sewn up in hammocks and -washing about the decks for want of strength and -spirits on the part of the miserable survivors to cast -them overboard; and every form of loathsome and -excruciating misery of which the human frame is -susceptible:—such are the pictures which the narratives -of nautical adventure in those days continually -offer.<a id="FNanchor_13" href="#Footnote_13" class="fnanchor">13</a> At present the scurvy is almost<span class="pagenum"><a id="Page_53">53</a></span> -completely eradicated in the navy, partly, no doubt, -from increased and increasing attention to general -cleanliness, comfort, and diet; but mainly from the -constant use of a simple and palatable preventive, -the acid of the lemon, served out in daily rations. -If the gratitude of mankind be allowed on all hands -to be the just meed of the philosophic physician, to -whose discernment in seizing, and perseverance in -forcing it on public notice we owe the great safeguard -of infant life, it ought not to be denied to -those<a id="FNanchor_14" href="#Footnote_14" class="fnanchor">14</a> whose skill and discrimination have thus<span class="pagenum"><a id="Page_54">54</a></span> -strengthened the sinews of our most powerful arm, -and obliterated one of the darkest features in the -most glorious of all professions.</p> - -<p>(45.) These last, however, are instances of simple -observation, limited to the point immediately in view, -and assuming only so far the character of science as -a systematic adoption of good and rejection of evil, -when grounded on experience carefully weighed, -justly entitle it to do. They are not on that account -less appositely cited as instances of the importance<span class="pagenum"><a id="Page_55">55</a></span> -of a knowledge of nature and its laws to our well-being; -though, like the great inventions of the mariner’s -compass and of gunpowder, they may have -stood, in their origin, unconnected with more general -views. They are rather to be looked upon as -the spontaneous produce of a territory essentially -fertile, than as forming part of the succession of -harvests which the same bountiful soil, diligently -cultivated, is capable of yielding. The history of -iodine above related affords, however, a perfect -specimen of the manner in which a knowledge of -natural properties and laws, collected from facts -having no reference to the object to which they -have been subsequently applied, enables us to set in -array the resources of nature against herself; and -deliberately, of afore-thought, to devise remedies -against the dangers and inconveniences which beset -us. In this view we might instance, too, the <em>conductor</em>, -which, in countries where thunder-storms -are more frequent and violent than in our own, -and at sea (where they are attended with peculiar -danger, both from the greater probability of accident, -and its more terrible consequences when it -does occur,) forms a most real and efficient preservative -against the effects of lightning<a id="FNanchor_15" href="#Footnote_15" class="fnanchor">15</a>:—the <em>safety-lamp</em>, -which enables us to walk with light and<span class="pagenum"><a id="Page_56">56</a></span> -security while surrounded with an atmosphere more -explosive than gunpowder:—the <em>life-boat</em>, which -cannot be sunk, and which offers relief in circumstances -of all others the most distressing to humanity, -and of which a recent invention promises to -extend the principle to ships of the largest class:—the -<em>lighthouse</em>, with the capital improvements which -the lenses of Brewster and Fresnel, and the elegant -lamp of lieutenant Drummond, have conferred, and -promise yet to confer by their wonderful powers, -the one of producing the most intense light yet -known, the others of conveying it undispersed to -great distances:—the discovery of the disinfectant -powers of chlorine, and its application to the destruction -of miasma and contagion:—that of <em>quinine</em>, -the essential principle in which reside the febrifuge -qualities of the Peruvian bark, a discovery by which -posterity is yet to benefit in its full extent, but -which has already begun to diffuse <em>comparative</em> comfort -and health through regions almost desolated by -pestiferous exhalations<a id="FNanchor_16" href="#Footnote_16" class="fnanchor">16</a>;—and, if we desist, it is -not because the list is exhausted, but because a -sample, not a catalogue, is intended.</p> - -<p>(46.) One instance more, however, we will add, to -illustrate the manner in which a most familiar effect, -which seemed destined only to amuse children, or, -at best, to furnish a philosophic toy, may become a -safeguard of human life, and a remedy for a most<span class="pagenum"><a id="Page_57">57</a></span> -serious and distressing evil. In needle manufactories -the workmen who point the needles are -constantly exposed to excessively minute particles -of steel which fly from the grindstones, and mix, -though imperceptible to the eye, as the finest dust -in the air, and are inhaled with their breath. The -effect, though imperceptible on a short exposure, -yet, being constantly repeated from day to day, -produces a constitutional irritation dependent on -the tonic properties of the steel, which is sure to -terminate in pulmonary consumption; insomuch, -that persons employed in this kind of work used -scarcely ever to attain the age of forty years.<a id="FNanchor_17" href="#Footnote_17" class="fnanchor">17</a> In -vain was it attempted to purify the air before its -entry into the lungs by gauzes or linen guards; the -dust was too fine and penetrating to be obstructed -by such coarse expedients, till some ingenious person -bethought him of that wonderful power which -every child who searches for its mother’s needle -with a magnet, or admires the motions and arrangement -of a few steel filings on a sheet of paper held -above it, sees in exercise. Masks of magnetized -steel wire are now constructed and adapted to the -faces of the workmen. By these the air is not -merely <em>strained</em> but <em>searched</em> in its passage through -them, and each obnoxious atom arrested and removed.</p> - -<p>(47.) Perhaps there is no result which places in -a stronger light the advantages which are to be -derived from a mere knowledge of the <em>usual order -of nature</em>, without any attempt on our part to modify -it, and apart from all consideration of its causes,<span class="pagenum"><a id="Page_58">58</a></span> -than the institution of life-assurances. Nothing is -more uncertain than the life of a single individual; -and it is the sense of this insecurity which has given -rise to such institutions. They are, in their nature -and objects, the precise reverse of gambling speculations, -their object being to equalize vicissitude, -and to place the pecuniary relations of numerous -masses of mankind, in so far as they extend, on a -footing independent of individual casualty. To do -this with the greatest possible advantage, or indeed -with any advantage at all, it is necessary to know the -<em>laws of mortality</em>, or the average numbers of individuals, -out of a great multitude, who die at every -period of life from infancy to extreme old age. At -first sight this would seem a hopeless enquiry; to -some, perhaps, a presumptuous one. But it has been -made; and the result is, that, abating extraordinary -causes, such as wars, pestilence, and the like, a remarkable -regularity <em>does</em> obtain, quite sufficient -to afford grounds not only for general estimations, -but for nice calculations of risk and adventure, such -as infallibly to insure the success of any such institution -founded on good computations; and thus to -confer such stability on the fortunes of families dependent -on the exertions of one individual as to constitute -an important feature in modern civilization. -The only thing to be feared in such institutions is -their too great multiplication and consequent competition, -by which a spirit of gambling and underbidding -is liable to be generated among their conductors, -and the very mischief may be produced, -on a scale of frightful extent, which they are -especially intended to prevent.</p> - -<p><span class="pagenum"><a id="Page_59">59</a></span> -(48.) We have hitherto considered only cases in -which a knowledge of natural laws enables us to improve -our condition, by counteracting evils of which, -but for its possession, we must have remained forever -the helpless victims. Let us now take a similar view -of those in which we are enabled to call in nature -as an auxiliary to augment our actual power, and -capacitate us for undertakings, which without such -aid might seem to be hopeless. Now, to this end, it -is necessary that we should form a just conception -of what those hidden powers of nature <em>are</em>, which -we can at pleasure call into action;—how far they -transcend the measure of human force, and set at -naught the efforts not only of individuals but of -whole nations of men.</p> - -<p>(49.) It is well known to modern engineers, that -<em>there is virtue</em> in a bushel of coals properly consumed, -to raise seventy millions of pounds weight a -foot high. This is actually the <em>average</em> effect of an -engine at this moment working in Cornwall.<a id="FNanchor_18" href="#Footnote_18" class="fnanchor">18</a> Let -us pause a moment, and consider what this is -equivalent to in matters of practice.</p> - -<p>(50.) The ascent of Mont Blanc from the valley of -Chamouni is considered, and with justice, as the -most toilsome feat that a strong man can execute in -two days. The combustion of two pounds of coal -would place him on the summit.<a id="FNanchor_19" href="#Footnote_19" class="fnanchor">19</a></p> - -<p><span class="pagenum"><a id="Page_60">60</a></span> -(51.) The Menai Bridge, one of the most stupendous -works of art that has been raised by man in -modern ages, consists of a mass of iron, not less than -four millions of pounds in weight, suspended at a -medium height of about 120 feet above the sea. -The consumption of seven bushels of coal would -suffice to raise it to the place where it hangs.</p> - -<p>(52.) The great pyramid of Egypt is composed of -granite. It is 700 feet in the side of its base, and 500 -in perpendicular height, and stands on eleven acres -of ground. Its weight is, therefore, 12,760 millions -of pounds, at a medium height of 125 feet; consequently -it would be raised by the effort of about -630 chaldrons of coal, a quantity consumed in some -founderies in a week.</p> - -<p>(53.) The annual consumption of coal in London -is estimated at 1,500,000 chaldrons. The effort of -this quantity would suffice to raise a cubical block of -marble, 2200 feet in the side, through a space equal -to its own height, or to pile one such mountain upon -another. The Monte Nuovo, near Pozzuoli, (which -was erupted in a single night by volcanic fire,) -might have been raised by such an effort, from a -depth of 40,000 feet, or about eight miles.</p> - -<p>(54.) It will be observed, that, in the above statement, -the inherent power of fuel is, of necessity, -greatly under-rated. It is not pretended by engineers -that the economy of fuel is yet pushed to its utmost -limit, or that the whole effective power is obtained -in any application of fire yet devised; so that were<span class="pagenum"><a id="Page_61">61</a></span> -we to say 100 millions instead of 70, we should probably -be nearer the truth.</p> - -<p>(55.) The powers of wind and water, which we are -constantly impressing into our service, can scarcely -be called latent or hidden, yet it is not fully considered, -in general, what they <em>do</em> effect for us. -Those who would judge of what advantage may be -taken of the wind, for example, even on land (not -to speak of navigation), may turn their eyes on Holland. -A great portion of the most valuable and -populous tract of this country lies much below the -level of the sea, and is only preserved from inundation -by the maintenance of embankments. -Though these suffice to keep out the abrupt influx -of the ocean, they cannot oppose that law -of nature, by which fluids, in seeking their level, -insinuate themselves through the pores and subterraneous -channels of a loose sandy soil, and keep -the country in a constant state of infiltration -from below upwards. To counteract this tendency, -as well as to get rid of the rain water, which has no -natural outlet, pumps worked by windmills are established -in great numbers, on the dams and embankments, -which pour out the water, as from a leaky ship, -and in effect preserve the country from submersion, -by taking advantage of every wind that blows. To -drain the Haarlem lake<a id="FNanchor_20" href="#Footnote_20" class="fnanchor">20</a> would seem a hopeless -project to any speculators but those who had the -steam-engine at their command, or had learnt in<span class="pagenum"><a id="Page_62">62</a></span> -Holland what might be accomplished by the constant -agency of the desultory but unwearied powers -of wind. But the Dutch engineer measures his -surface, calculates the number of his pumps, and, -trusting to time and his experience of the operation -of the winds for the success of his undertaking, -boldly forms his plans to lay dry the bed of an inland -sea, of which those who stand on one shore -cannot see the other.<a id="FNanchor_21" href="#Footnote_21" class="fnanchor">21</a></p> - -<p>(56.) To gunpowder, as a source of mechanical -power, it seems hardly necessary to call attention; -yet it is only when we endeavour to <em>confine</em> it, that -we get a full conception of the immense energy of -that astonishing agent. In count Rumford’s experiments, -twenty-eight grains of powder confined in -a cylindrical space, <em>which it just filled</em>, tore asunder -a piece of iron which would have resisted a strain of -400,000 lbs.<a id="FNanchor_22" href="#Footnote_22" class="fnanchor">22</a>, applied at no greater mechanical disadvantage.</p> - -<p>(57.) But chemistry furnishes us with means of -calling into sudden action forces of a character infinitely -more tremendous than that of gunpowder. -The terrific violence of the different fulminating -compositions is such, that they can only be compared -to those untameable animals, whose ferocious<span class="pagenum"><a id="Page_63">63</a></span> -strength has hitherto defied all useful management, -or rather to spirits evoked by the spells of a -magician, manifesting a destructive and unapproachable -power, which makes him but too happy to close -his book, and break his wand, as the price of escaping: -unhurt from the storm he has raised. Such -powers are not yet subdued to our purposes, whatever -they may hereafter be; but, in the expansive -force of gases, liberated slowly and manageably from -chemical mixtures, we have a host of inferior, yet -still most powerful, energies, capable of being employed -in a variety of useful ways, according to -emergencies.<a id="FNanchor_23" href="#Footnote_23" class="fnanchor">23</a></p> - -<p>(58.) Such are the forces which nature lends us for -the accomplishment of our purposes, and which it is -the province of practical Mechanics to teach us to -combine and apply in the most advantageous manner; -without which the mere command of power -would amount to nothing. Practical Mechanics is, -in the most pre-eminent sense, a <em>scientific art</em>; and -it may be truly asserted, that almost all the great -combinations of modern mechanism, and many of its -refinements and nicer improvements, are creations of -pure intellect, grounding its exertion upon a moderate -number of very elementary propositions in -theoretical mechanics and geometry. On this head -we might dwell long, and find ample matter, both<span class="pagenum"><a id="Page_64">64</a></span> -for reflection and wonder; but it would require -not volumes merely, but libraries, to enumerate -and describe the prodigies of ingenuity which have -been lavished on every thing connected with machinery -and engineering. By these it is that we are -enabled to diffuse over the whole earth the productions -of any part of it; to fill every corner of -it with miracles of art and labour, in exchange for its -peculiar commodities; and to concentrate around -us, in our dwellings, apparel and utensils, the skill and -workmanship not of a few expert individuals, but -of all who, in the present and past generations, have -contributed their improvements to the processes of -our manufactures.</p> - -<p>(59.) The transformations of chemistry, by which -we are enabled to convert the most apparently useless -materials into important objects in the arts, are -opening up to us every day sources of wealth and -convenience of which former ages had no idea, and -which have been pure gifts of science to man. -Every department of art has felt their influence, and -new instances are continually starting forth of the -unlimited resources which this wonderful science -developes in the most sterile parts of nature. Not -to mention the impulse which its progress has given -to a host of other sciences, which will come more -particularly under consideration in another part of -this discourse, what strange and unexpected results -has it not brought to light in its application to some -of the most common objects! Who, for instance, -would have conceived that linen rags were capable -of producing <em>more than their own weight</em> of sugar, by -the simple agency of one of the cheapest and most<span class="pagenum"><a id="Page_65">65</a></span> -abundant acids?<a id="FNanchor_24" href="#Footnote_24" class="fnanchor">24</a>—that dry bones could be a magazine -of nutriment, capable of preservation for years, -and ready to yield up their sustenance in the form -best adapted to the support of life, on the application -of that powerful agent, steam, which enters so largely -into all our processes, or of an acid at once cheap -and durable?<a id="FNanchor_25" href="#Footnote_25" class="fnanchor">25</a>—that sawdust itself is susceptible -of conversion into a substance bearing no remote -analogy to bread; and though certainly less palatable -than that of flour, yet no way disagreeable, -and both wholesome and digestible as well as highly -nutritive?<a id="FNanchor_26" href="#Footnote_26" class="fnanchor">26</a> What economy, in all processes where -chemical agents are employed, is introduced by the -exact knowledge of the proportions in which natural -elements unite, and their mutual powers of displacing -each other! What perfection in all the arts -where fire is employed, either in its more violent -applications, (as, for instance, in the smelting of -metals by the introduction of well adapted fluxes, -whereby we obtain the whole produce of the ore in -its purest state,) or in its milder forms, as in sugar-refining -(the whole modern practice of which depends -on a curious and delicate remark of a late -eminent scientific chemist on the nice adjustment of -temperature at which the crystallization of syrup -takes place); and a thousand other arts which it -would be tedious to enumerate!</p> - -<p><span class="pagenum"><a id="Page_66">66</a></span> -(60.) Armed with such powers and resources, -it is no wonder if the enterprise of man should -lead him to form and execute projects which, to -one uninformed of their grounds, would seem altogether -disproportionate. Were they to have been -proposed at once, we should, no doubt, have rejected -them as such: but developed, as they have -been, in the slow succession of ages, they have -only taught us that things regarded impossible in -one generation may become easy in the next; and -that the power of man over nature is limited only -by the one condition, that it must be exercised in -conformity with the laws of nature. He must study -those laws as he would the disposition of a horse he -would ride, or the character of a nation he would -govern; and the moment he presumes either to -thwart her fundamental rules, or ventures to measure -his strength with hers, he is at once rendered -severely sensible of his imbecility, and meets the -deserved punishment of his rashness and folly. -But if, on the other hand, he will consent to use, -without abusing, the resources thus abundantly -placed at his disposal, and obey that he may command, -there seems scarcely any conceivable limit to -the degree in which the <em>average</em> physical condition -of great masses of mankind may be improved, their -wants supplied, and their conveniences and comforts -increased. Without adopting such an exaggerated -view, as to assert that the meanest inhabitant of a -civilized society is superior in physical condition to -the lordly savage, whose energy and uncultivated -ability gives him a natural predominance over his -fellow denizens of the forest,—at least, if we compare<span class="pagenum"><a id="Page_67">67</a></span> -like with like, and consider the multitude of human -beings who are enabled, in an advanced state of -society, to subsist in a degree of comfort and abundance, -which at best only a few of the most fortunate -in a less civilized state could command, we shall not -be at a loss to perceive the principle on which we -ought to rest our estimate of the advantages of civilization; -and which applies with hardly less force to -every degree of it, when contrasted with that next -inferior, than to the broad distinction between civilized -and barbarous life in general.</p> - -<p>(61.) The difference of the degrees in which the individuals -of a great community enjoy the good things -of life has been a theme of declamation and discontent -in all ages; and it is doubtless our paramount -duty, in every state of society, to alleviate the pressure -of the purely evil part of this distribution as much -as possible, and, by all the means we can devise, secure -the lower links in the chain of society from -dragging in dishonour and wretchedness: but there -is a point of view in which the picture is at least -materially altered in its expression. In comparing -society on its present immense scale, with its -infant or less developed state, we must at least -take care to enlarge every feature in the same -proportion. If, on comparing the <em>very</em> lowest states -in civilized and savage life, we admit a difficulty in -deciding to which the preference is due, at least -in every superior grade we cannot hesitate a moment; -and if we institute a similar comparison in -every different stage of its progress, we cannot fail -to be struck with the rapid <em>rate of dilatation</em> which -every degree upward of the scale, so to speak, exhibits,<span class="pagenum"><a id="Page_68">68</a></span> -and which, in an estimate of averages, gives -an immense preponderance to the present over -every former condition of mankind, and, for aught -we can see to the contrary, will place succeeding -generations in the same degree of superior relation -to the present that this holds to those passed away. -Or we may put the same proposition in other words, -and, admitting the existence of every inferior grade -of advantage in a higher state of civilization which -subsisted in the preceding, we shall find, first, that, -taking state for state, the proportional numbers of -those who enjoy the higher degrees of advantage -increases with a constantly accelerated rapidity as -society advances; and, secondly, that the superior -extremity of the scale is constantly enlarging by -the addition of new degrees. The condition of a -European prince is now as far superior, in the command -of real comforts and conveniences, to that of -one in the middle ages, as that to the condition of -one of his own dependants.</p> - -<p>(62.) The advantages conferred by the augmentation -of our physical resources through the medium -of increased knowledge and improved art have this -peculiar and remarkable property,—that they are -in their nature diffusive, and cannot be enjoyed in -any exclusive manner by a few. An eastern despot -may extort the riches and monopolize the art of -his subjects for his own personal use; he may -spread around him an unnatural splendour and -luxury, and stand in strange and preposterous contrast -with the general penury and discomfort of -his people; he may glitter in jewels of gold and -raiment of needlework; but the wonders of well<span class="pagenum"><a id="Page_69">69</a></span> -contrived and executed manufacture which we use -daily, and the comforts which have been invented, -tried, and improved upon by thousands, in every -form of domestic convenience, and for every ordinary -purpose of life, can never be enjoyed by him. -To produce a state of things in which the physical -advantages of civilized life can exist in a high degree, -the stimulus of increasing comforts and constantly -elevated desires, must have been felt by -millions; since it is not in the power of a few -individuals to create that wide demand for useful -and ingenious applications, which alone can lead to -great and rapid improvements, unless backed by -that arising from the speedy diffusion of the same -advantages among the mass of mankind.</p> - -<p>(63.) If this be true of physical advantages, it -applies with still greater force to intellectual. Knowledge -can neither be adequately cultivated nor -adequately enjoyed by a few; and although the -conditions of our existence on earth may be such as -to preclude an abundant supply of the physical necessities -of all who may be born, there is no such -law of nature in force against that of our intellectual -and moral wants. Knowledge is not, like food, destroyed -by use, but rather augmented and perfected. -It acquires not, perhaps, a greater certainty, -but at least a confirmed authority and a probable -duration, by universal assent; and there is no body -of knowledge so complete, but that it may acquire -accession, or so free from error but that it may -receive correction in passing through the minds of -millions. Those who admire and love knowledge for -its own sake ought to wish to see its elements made<span class="pagenum"><a id="Page_70">70</a></span> -accessible to all, were it only that they may be the -more thoroughly examined into, and more effectually -developed in their consequences, and receive that -ductility and plastic quality which the pressure of -minds of all descriptions, constantly moulding them -to their purposes, can alone bestow. But to this -end it is necessary that it should be divested, as far -as possible, of artificial difficulties, and stripped of -all such technicalities as tend to place it in the light -of a craft and a mystery, inaccessible without a -kind of apprenticeship. Science, of course, like -every thing else, has its own peculiar terms, and, -so to speak, its idioms of language; and these it -would be unwise, were it even possible, to relinquish: -but every thing that tends to clothe it in a strange -and repulsive garb, and especially every thing that, -to keep up an appearance of superiority in its professors -over the rest of mankind, assumes an unnecessary -guise of profundity and obscurity, should be sacrificed -without mercy. Not to do this, is to deliberately -reject the light which the natural unencumbered -good sense of mankind is capable of throwing on -every subject, even in the elucidation of principles: -but where principles are to be applied to practical -uses it becomes absolutely necessary; as all mankind -have then an interest in their being so familiarly -understood, that no mistakes shall arise in -their application.</p> - -<p>(64.) The same remark applies to arts. They cannot -be perfected till their whole processes are laid open, -and their language simplified and rendered universally -intelligible. Art is the application of knowledge -to a practical end. If the knowledge be merely<span class="pagenum"><a id="Page_71">71</a></span> -accumulated experience, the art is <em>empirical</em>; but -if it be experience reasoned upon and brought under -general principles, it assumes a higher character, -and becomes a <em>scientific art</em>. In the progress of -mankind from barbarism to civilised life, the arts -necessarily precede science. The wants and cravings -of our animal constitution must be satisfied; -the comforts, and some of the luxuries, of life must -exist. Something must be given to the vanity of -show, and more to the pride of power: the round -of baser pleasures must have been tried and found -insufficient, before intellectual ones can gain a footing; -and when they have obtained it, the delights -of poetry and its sister arts still take precedence of -contemplative enjoyments, and the severer pursuits -of thought; and when these in time begin to charm -from their novelty, and sciences begin to arise, they -will at first be those of pure speculation. The mind -delights to escape from the trammels which had -bound it to earth, and luxuriates in its newly found -powers. Hence, the abstractions of geometry—the -properties of numbers—the movements of the -celestial spheres—whatever is abstruse, remote, and -extramundane—become the first objects of infant -science. Applications come late: the arts continue -slowly progressive, but their realm remains separated -from that of science by a wide gulf which can only -be passed by a powerful spring. They form their own -language and their own conventions, which none but -artists can understand. The whole tendency of -empirical art, is to bury itself in technicalities, and -to place its pride in particular short cuts and mysteries -known only to adepts; to surprise and astonish<span class="pagenum"><a id="Page_72">72</a></span> -by results, but conceal processes. The character -of science is the direct contrary. It delights to -lay itself open to enquiry, and is not satisfied -with its conclusions, till it can make the road to -them broad and beaten: and in its applications it -preserves the same character; its whole aim being -to strip away all technical mystery, to illuminate -every dark recess, and to gain free access to all -processes, with a view to improve them on rational -principles. It would seem that a union of two qualities -almost opposite to each other—a going forth of -the thoughts in two directions, and a sudden transfer -of ideas from a remote station in one to an equally -distant one in the other—is required to start the first -idea of <em>applying science</em>. Among the Greeks, this -point was attained by Archimedes, but attained too -late, on the eve of that great eclipse of science -which was destined to continue for nearly eighteen -centuries, till Galileo in Italy, and Bacon in England, -at once dispelled the darkness: the one, by -his inventions and discoveries; the other, by the -irresistible force of his arguments and eloquence.</p> - -<p>(65.) Finally, the improvement effected in the condition -of mankind by advances in physical science -as applied to the useful purposes of life, is very far -from being limited to their direct consequences in -the more abundant supply of our physical wants, and -the increase of our comforts. Great as these benefits -are, they are yet but steps to others of a still higher -kind. The successful results of our experiments -and reasonings in natural philosophy, and the incalculable -advantages which experience, systematically -consulted and dispassionately reasoned on, has conferred<span class="pagenum"><a id="Page_73">73</a></span> -in matters purely physical, tend of necessity -to impress something of the well weighed and progressive -character of science on the more complicated -conduct of our social and moral relations. It -is thus that legislation and politics become gradually -regarded as experimental sciences; and history, not, -as formerly, the mere record of tyrannies and slaughters, -which, by immortalizing the execrable actions -of one age, perpetuates the ambition of committing -them in every succeeding one, but as the archive -of experiments, successful and unsuccessful, gradually -accumulating towards the solution of the -grand problem—how the advantages of government -are to be secured with the least possible inconvenience -to the governed. The celebrated apophthegm, -that nations never profit by experience, becomes -yearly more and more untrue. Political economy, -at least, is found to have sound principles, founded -in the moral and physical nature of man, which, -however lost sight of in particular measures—however -even temporarily controverted and borne down -by clamour—have yet a stronger and stronger testimony -borne to them in each succeeding generation, -by which they must, sooner or later, prevail. The -idea once conceived and verified, that great and -noble ends are to be achieved, by which the condition -of the whole human species shall be permanently -bettered, by bringing into exercise a sufficient quantity -of sober thought, and by a proper adaptation of -means, is of itself sufficient to set us earnestly on -reflecting what ends <em>are</em> truly great and noble, either -in themselves, or as conducive to others of a still -loftier character; because we are not now, as heretofore,<span class="pagenum"><a id="Page_74">74</a></span> -hopeless of attaining them. It is not now -equally harmless and insignificant, whether we are -right or wrong; since we are no longer supinely and -helplessly carried down the stream of events, but -feel ourselves capable of buffetting at least with its -waves, and perhaps of riding triumphantly over -them: for why should we despair that the reason -which has enabled us to subdue all nature to our -purposes, should (if permitted and assisted by the -providence of God) achieve a far more difficult conquest; -and ultimately find some means of enabling -the collective wisdom of mankind to bear down -those obstacles which individual short-sightedness, -selfishness, and passion, oppose to all improvements, -and by which the highest hopes are continually -blighted, and the fairest prospects marred.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_75">75</a></span></p> - -<div class="chapter"> -<h2 id="hdr_5"><span class="larger">PART II.</span></h2> -</div> - -<blockquote class="hang"> - -<p>OF THE PRINCIPLES ON WHICH PHYSICAL SCIENCE -RELIES FOR ITS SUCCESSFUL PROSECUTION, AND -THE RULES BY WHICH A SYSTEMATIC EXAMINATION -OF NATURE SHOULD BE CONDUCTED, -WITH ILLUSTRATIONS OF THEIR INFLUENCE -AS EXEMPLIFIED IN THE HISTORY OF ITS PROGRESS.</p></blockquote> - -<h2 id="hdr_6">CHAPTER I.</h2> - -<blockquote> - -<p class="center b2">OF EXPERIENCE AS THE SOURCE OF OUR KNOWLEDGE.—OF -THE DISMISSAL OF PREJUDICES.—OF THE EVIDENCE -OF OUR SENSES.</p></blockquote> - -<p class="in0">(66.) <span class="smcap"><span class="flet">I</span>nto</span> abstract science, as we have before observed, -the notion of cause does not enter. The -truths it is conversant with are <em>necessary</em> ones, and -exist independent of cause. There may be -no such real <em>thing</em> as a right-lined triangle -marked out in space; but the moment we conceive -one in our minds, we cannot refuse to admit the -sum of its three angles to be equal to two right -angles; and if in addition we conceive one of its -angles to be a right angle, we cannot thenceforth -refuse to admit that the sum of the squares on the -two sides, including the right angle, is equal to -the square on the side subtending it. To maintain -the contrary, would be, in effect, to deny its -being right angled. No one <em>causes</em> or <em>makes</em> all -the diameters of an ellipse to be bisected in its<span class="pagenum"><a id="Page_76">76</a></span> -centre. To assert the contrary, would not be to -rebel against a power, but to deny our own words. -But in natural science <em>cause</em> and <em>effect</em> are the ultimate -relations we contemplate; and <em>laws</em>, whether -imposed or maintained, which, for aught we can perceive, -might have been other than they are. This -distinction is very important. A clever man, shut -up alone and allowed unlimited time, might reason -out for himself all the truths of mathematics, by -proceeding from those simple notions of space and -number of which he cannot divest himself without -ceasing to think. But he could never tell, by any -effort of reasoning, what would become of a lump -of sugar if immersed in water, or what impression -would be produced on his eye by mixing the colours -yellow and blue.</p> - -<p>(67.) We have thus pointed out to us, as the great, -and indeed only ultimate source of our knowledge of -nature and its laws, <span class="smcap smaller">EXPERIENCE</span>; by which we -mean, not the experience of one man only, or of -one generation, but the accumulated experience of -all mankind in all ages, registered in books or recorded -by tradition. But experience may be acquired -in two ways: either, first, by noticing facts as -they occur, without any attempt to influence the -frequency of their occurrence, or to vary the circumstances -under which they occur; this is <span class="smcap smaller">OBSERVATION</span>: -or, secondly, by putting in action causes -and agents over which we have control, and purposely -varying their combinations, and noticing -what effects take place; this is <span class="smcap smaller">EXPERIMENT</span>. To -these two sources we must look as the fountains of -all natural science. It is not intended, however, by<span class="pagenum"><a id="Page_77">77</a></span> -thus distinguishing observation from experiment, -to place them in any kind of contrast. Essentially -they are much alike, and differ rather in degree -than in kind; so that, perhaps, the terms <em>passive</em> -and <em>active observation</em> might better express their -distinction; but it is, nevertheless, highly important -to mark the different states of mind in -inquiries carried on by their respective aids, as -well as their different effects in promoting the -progress of science. In the former, we sit still -and listen to a tale, told us, perhaps obscurely, -piecemeal, and at long intervals of time, with -our attention more or less awake. It is only by -after-rumination that we gather its full import; -and often, when the opportunity is gone by, we -have to regret that our attention was not more -particularly directed to some point which, at the -time, appeared of little moment, but of which we -at length appretiate the importance. In the latter, -on the other hand, we cross-examine our witness, -and by comparing one part of his evidence with -the other, while he is yet before us, and reasoning -upon it in his presence, are enabled to put pointed -and searching questions, the answer to which may -at once enable us to make up our minds. Accordingly -it has been found invariably, that in those -departments of physics where the phenomena are -beyond our control, or into which experimental -enquiry, from other causes, has not been carried, -the progress of knowledge has been slow, uncertain, -and irregular; while in such as admit of experiment, -and in which mankind have agreed to its -adoption, it has been rapid, sure, and steady. For<span class="pagenum"><a id="Page_78">78</a></span> -example, in our knowledge of the nature and causes -of volcanoes, earthquakes, the fall of stones from -the sky, the appearance of new stars and disappearance -of old ones, and other of those great -phenomena of nature which are altogether beyond -our command, and at the same time are of too rare -occurrence to permit any one to repeat and rectify -his impressions respecting them, we know little -more now than in the earliest times. Here our -tale is told us slowly, and in broken sentences. In -astronomy, again, we have at least an uninterrupted -narrative; the opportunity of observation is constantly -present, and makes up in some measure -for the impossibility of varying our point of view, -and calling for information at the precise moment -it is wanted. Accordingly, astronomy, regarded -as a science of mere observation, arrived, though -by very slow degrees, to a state of considerable -maturity. But the moment that it became a -branch of mechanics, a science essentially experimental, -(that is to say, one in which any -principle laid down can be subjected to immediate -and decisive <em>trial</em>, and where experience does -not require to be waited for,) its progress suddenly -acquired a tenfold acceleration; nay, to such a -degree, that it has been asserted, and we believe -with truth, that were the records of all observations -from the earliest ages annihilated, leaving -only those made in a single observatory<a id="FNanchor_27" href="#Footnote_27" class="fnanchor">27</a>, during -a single lifetime<a id="FNanchor_28" href="#Footnote_28" class="fnanchor">28</a>, the whole of this most perfect -of sciences might, from those data, and as to -the objects included in them, be at once reconstructed,<span class="pagenum"><a id="Page_79">79</a></span> -and appear precisely as it stood at their -conclusion. To take another instance: mineralogy, -till modern times, could hardly be said to exist. -The description of even the precious stones in -Theophrastus and Pliny are, in most cases, hardly -sufficient to identify them, and in many fall short -even of that humble object; more recent observers, -by attending more carefully to the obvious characters -of minerals, had formed a pretty extensive -catalogue of them, and made various attempts to -arrange and methodize the knowledge thus acquired, -and even to deduce some general conclusions -respecting the forms they habitually assume: -but from the moment that chemical analysis was -applied to resolve them into their constituent elements, -and that, led by a happy accident, the -genius of Bergmann discovered the general fact, that -they could be <em>cloven</em> or split in such directions as -to lay bare their peculiar primitive or fundamental -forms, (which lay concealed within them, as the -statue might be conceived encrusted in its marble -envelope,)—from that moment, mineralogy ceased -to be an unmeaning list of names, a mere laborious -cataloguing of stones and rubbish, and became, -what it now is, a regular, methodical, and most -important science, in which every year is bringing -to light new relations, new laws, and new practical -applications.</p> - -<p>(68.) Experience once recognized as the fountain -of all our knowledge of nature, it follows that, in the -study of nature and its laws, we ought at once to -make up our minds to dismiss as idle prejudices, or -at least suspend as premature, any preconceived<span class="pagenum"><a id="Page_80">80</a></span> -notion of what might or what ought to be the order -of nature in any proposed case, and content ourselves -with observing, as a plain matter of fact, what -<em>is</em>. To experience we refer, as the only ground of all -physical enquiry. But before experience itself can -be used with advantage, there is one preliminary -step to make, which depends wholly on ourselves: -it is the absolute dismissal and clearing the mind -of all prejudice, from whatever source arising, and -the determination to stand and fall by the result of -a direct appeal to facts in the first instance, and of -strict logical deduction from them afterwards. Now, -it is necessary to distinguish between two kinds of -prejudices, which exercise very different dominion -over the mind, and, moreover, differ extremely in -the difficulty of dispossessing them, and the process -to be gone through for that purpose. These <span class="locked">are,—</span></p> - -<p class="in0 in4"> -1. Prejudices of opinion.<br /> -2. Prejudices of sense. -</p> - -<p>(69.) By prejudices of opinion, we mean opinions -hastily taken up, either from the assertion of others, -from our own superficial views, or from vulgar observation, -and which, from being constantly admitted -without dispute, have obtained the strong -hold of habit on our minds. Such were the opinions -once maintained that the earth is the greatest body -in the universe, and placed immovable in its centre, -and all the rest of the universe created for its -sole use; that it is the nature of fire and of sounds -to ascend; that the moonlight is cold; that dews <em>fall</em> -from the air, &c.</p> - -<p>(70.) To combat and destroy such prejudices we -may proceed in two ways, either by demonstrating<span class="pagenum"><a id="Page_81">81</a></span> -the falsehood of the facts alleged in their support, -or by showing how the appearances, which seem to -countenance them, are more satisfactorily accounted -for without their admission. But it is unfortunately -the nature of prejudices of opinion to adhere, -in a certain degree, to every mind, and to some -with pertinacious obstinacy, <i xml:lang="la" lang="la">pigris radicibus</i>, after all -ground for their reasonable entertainment is destroyed. -Against such a disposition the student of -natural science must contend with all his power. Not -that we are so unreasonable as to demand of him an -instant and peremptory dismission of all his former -opinions and judgments; all we require is, that he -will hold them without bigotry, retain till he shall -see reason to question them, and be ready to resign -them when fairly proved untenable, and to doubt -them when the weight of probability is shown to lie -against them. If he refuse this, he is incapable of -science.</p> - -<p>(71.) Our resistance against the destruction of -the other class of prejudices, those of sense, is commonly -more violent at first, but less persistent, than -in the case of those of opinion. Not to trust the -evidence of our senses, seems, indeed, a hard condition, -and one which, if proposed, none would comply -with. But it is not the direct evidence of our -senses that we are in any case called upon to reject, -but only the erroneous judgments we unconsciously -form from them, and this only when they can be -shown to be so <em>by counter evidence of the same sort</em>; -when one sense is brought to testify against another, -for instance; or the same sense against itself, and -the obvious conclusions in the two cases disagree, so<span class="pagenum"><a id="Page_82">82</a></span> -as to compel us to acknowledge that one or other -must be wrong. For example, nothing at first can -seem a more rational, obvious, and incontrovertible -conclusion, than that the <em>colour</em> of an object is an -inherent quality, like its weight, hardness, &c. and -that to <em>see</em> the object, and see it <em>of its own colour</em>, -when nothing intervenes between our eyes and it, -are one and the same thing. Yet this is only a -prejudice; and that it is so, is shown by bringing forward -the same sense of vision which led to its adoption, -as evidence on the other side; for, when the -differently coloured prismatic rays are thrown, in a -dark room, in succession upon any object, whatever -be the colour we are in the habit of calling its own, -it will appear of the particular hue of the light which -falls upon it: a yellow paper, for instance, will appear -scarlet when illuminated by red rays, yellow -when by yellow, green by green, and blue by blue -rays; its own (so called) proper colour <em>not in the least -degree mixing with that it so exhibits</em>.</p> - -<p>(72.) To give one or two more examples of the -kind of illusion which the senses practise on us, or -rather which we practise on ourselves, by a misinterpretation -of their evidence: the moon at its -rising and setting appears much larger than when -high up in the sky. This is, however, a mere erroneous -judgment; for when we come to measure its -diameter, so far from finding our conclusion borne -out by fact, we actually find it to measure materially -less. Here is eyesight opposed to eyesight, with the -advantage of deliberate measurement. In ventriloquism -we have the hearing at variance with all the -other senses, and especially with the sight, which is<span class="pagenum"><a id="Page_83">83</a></span> -sometimes contradicted by it in a very extraordinary -and surprising manner, as when the voice is made to -seem to issue from an inanimate and motionless object. -If we plunge our hands, one into ice-cold water, and -the other into water as hot as can be borne, and, -after letting them stay awhile, suddenly transfer -them both to a vessel full of water at a blood heat, -the one will feel a sensation of heat, the other of -cold. And if we cross the two first fingers of one -hand, and place a pea in the fork between them, -moving and rolling it about on a table, we shall -(especially if we close our eyes) be fully persuaded -we have two peas. If the nose be held while we -are eating cinnamon, we shall perceive no difference -between its flavour and that of a deal shaving.</p> - -<p>(73.) These, and innumerable instances we might -cite, will convince us, that though we are never deceived -in the <em>sensible impression</em> made by external -objects on us, yet in forming our judgments of them -we are greatly at the mercy of circumstances, -which either modify the impressions actually received, -or combine them with adjuncts which have -become habitually associated with different judgments; -and, therefore, that, in estimating the degree -of confidence we are to place in our conclusions, -we must, of necessity, take into account these modifying -or accompanying circumstances, whatever they -may be. We do not, of course, here speak of deranged -organization; such as, for instance, a distortion of the -eye, producing double vision, and still less of mental -delusion, which absolutely perverts the meaning of -sensible impressions.</p> - -<p>(74.) As the mind exists not in the place of sensible<span class="pagenum"><a id="Page_84">84</a></span> -objects, and is not brought into immediate relation -with them, we can only regard sensible -impressions as signals conveyed from them by a -wonderful, and, to us, inexplicable mechanism, to our -minds, which receives and reviews them, and, by -habit and association, connects them with corresponding -qualities or affections in the objects; just as -a person writing down and comparing the signals of -a telegraph might interpret their meaning. As, for -instance, if he had constantly observed that the -exhibition of a certain signal was sure to be followed -next day by the announcement of the arrival of a -ship at Portsmouth, he would connect the two facts -by a link of the very same nature with that which -connects the notion of a large wooden building, filled -with sailors, with the impression of her outline on -the retina of a spectator on the beach.</p> - -<p>(75.) In captain Head’s amusing and vivid description -of his journey across the Pampas of South -America occurs an anecdote quite in point. His -guide one day suddenly stopped him, and, pointing -high into the air, cried out, “A lion!” Surprised at -such an exclamation, accompanied with such an act, -he turned up his eyes, and with difficulty perceived, -at an immeasurable height, a flight of condors -soaring in circles in a particular spot. Beneath -that spot, far out of sight of himself or guide, lay -the carcass of a horse, and over that carcass stood -(as the guide well knew) the lion, whom the condors -were eyeing with envy from their airy height. -The signal of the birds was to him what the sight -of the lion alone could have been to the traveller, -a full assurance of its existence.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_85">85</a></span></p> - -<div class="chapter"> -<h2 id="hdr_7">CHAP. II.</h2> -</div> - -<p class="center b2">OF THE ANALYSIS OF PHENOMENA</p> - -<p class="in0">(76.) <i><span class="smcap"><span class="flet">P</span>henomena</span></i>, then, or appearances, as the word -is literally rendered, are the sensible results of -processes and operations carried on among external -objects, or their constituent principles, of which they -are only signals, conveyed to our minds as aforesaid. -Now, these processes themselves may be in many instances -rendered <em>sensible</em>; that is to say, analysed, -and shown to consist in the motions or other affections -of sensible objects themselves. For instance, the phenomenon -of the sound produced by a musical string, -or a bell, when struck, may be shown to be the result -of a process consisting in the rapid vibratory motion -of its parts communicated to the air, and thence to -our ears; though the immediate effect on our organs -of hearing does not excite the least idea of such a -motion. On the other hand, there are innumerable -instances of sensible impressions which (at least at -present) we are incapable of tracing beyond the -mere sensation; for example, in the sensations of -bitterness, sweetness, &c. These, accordingly, if -we were inclined to form hasty decisions, might be -regarded as ultimate qualities; but the instance of -sounds, just adduced, alone would teach us caution -in such decisions, and incline us to believe them -mere results of some secret process going on in -our organs of taste, which is too subtle for us to<span class="pagenum"><a id="Page_86">86</a></span> -trace. A simple experiment will serve to set this -in a clearer light. A solution of the salt called by -chemists <em>nitrate of silver</em>, and another of the <em>hyposulphite -of soda</em>, have each of them separately, when -taken into the mouth, a disgustingly bitter taste; -but if they be mixed, or if one be tasted before the -mouth is thoroughly cleared of the other, the sensible -impression is that of intense sweetness. Again, -the salt called <em>tungstate of soda</em> when first tasted is -sweet, but speedily changes to an intense and pure -bitter, like quassia.<a id="FNanchor_29" href="#Footnote_29" class="fnanchor">29</a></p> - -<p>(77.) How far we may ever be enabled to attain a -knowledge of the ultimate and inward processes of -nature in the production of phenomena, we have no -means of knowing; but, to judge from the degree of -obscurity which hangs about the only case in which -we feel within ourselves a <em>direct</em> power to produce -any one, there seems no great hope of penetrating -so far. The case alluded to is the production of -motion by the exertion of force. We are conscious -of a power to move our limbs, and by their intervention -other bodies; and that this effect is the -result of a certain inexplicable process which we -are aware of, but can no way describe in words, by -which we exert <em>force</em>. And even when such exertion -produces no visible effect, (as when we press -our two hands violently together, so as just to oppose -each other’s effort,) we still perceive, by the -fatigue and exhaustion, and by the impossibility of -maintaining the effort long, that something is going -on within us, of which the mind is the agent, and -the will the determining cause. This impression<span class="pagenum"><a id="Page_87">87</a></span> -which we receive of the nature of force, from our -own effort and our sense of fatigue, is quite different -from that which we obtain of it from seeing the -effect of force exerted by others in producing <em>motion</em>. -Were there no such thing as motion, had -we been from infancy shut up in a dark dungeon, -and every limb encrusted with plaster, this internal -consciousness would give us a complete idea of -<em>force</em>; but when set at liberty, habit alone would -enable us to recognize its exertion by its <em>signal</em>, -motion, and <em>that</em> only by finding that the same -action of the mind which in our confined state enables -us to fatigue and exhaust ourselves by the -tension of our muscles, puts it in our power, when -at liberty, to move ourselves and other bodies. But -how obscure is our knowledge of the process going -on within us in the exercise of this important privilege, -in virtue of which alone we act as direct <em>causes</em>, -we may judge from this, that when we put any limb -in motion, the seat of the exertion seems to us to -be <em>in</em> the limb, whereas it is demonstrably no such -thing, but either in the brain or in the spinal -marrow; the proof of which is, that if a little fibre, -called a nerve, which forms a communication between -the limb and the brain, or spine, be divided in any -part of its course, however we may make the effort, -the limb will not move.</p> - -<p>(78.) This one instance of the obscurity which -hangs about the only act of direct <em>causation</em> of -which we have an immediate consciousness, will -suffice to show how little prospect there is that, -in our investigation of nature, we shall ever be able -to arrive at a knowledge of ultimate causes, and will<span class="pagenum"><a id="Page_88">88</a></span> -teach us to limit our views to that of <em>laws</em>, and to -the analysis of complex phenomena by which they -are resolved into simpler ones, which, appearing to -us incapable of further analysis, we must consent -to regard as causes. Nor let any one complain of -this as a limitation of his faculties. We have here -“ample room and verge enough” for the full exercise -of all the powers we possess; and, besides, it -does so happen, that we are actually able to trace -up a very large portion of the phenomena of the universe -to this one <em>cause</em>, viz. the exertion of mechanical -<em>force</em>; indeed, so large a portion, that it has -been made a matter of speculation whether this is -not the only one that is capable of acting on material -beings.</p> - -<p>(79.) What we mean by the analysis of complex -phenomena into simpler ones, will best be understood -by an instance. Let us, therefore, take the -phenomenon of sound, and, by considering the -various cases in which sounds of all kinds are produced, -we shall find that they all agree in these -points:—1st, The excitement of a motion in the -sounding body. 2dly, The communication of this -motion to the air or other intermedium which is -interposed between the sounding body and our -ears. 3dly, The propagation of such motion from -particle to particle of such intermedium in due -succession. 4thly, Its communication, from the particles -of the intermedium adjacent to the ear, to -the ear itself. 5thly, Its conveyance in the ear, by a -certain mechanism, to the auditory nerves. 6thly, The -excitement of sensation. Now, in this analysis, we -perceive that two principal matters must be understood,<span class="pagenum"><a id="Page_89">89</a></span> -before we can have a true and complete -knowledge of sound:—1st, The excitement and -propagation of motion. 2dly, The production of -sensation. These, then, are two other phenomena, -of a simpler, or, it would be more correct to say, of -a more general or elementary order, into which -the complex phenomenon of sound resolves itself. -But again, if we consider the communication of -motion from body to body, or from one part to -another of the same, we shall perceive that it is -again resolvable into several other phenomena. -1st, The original setting in motion of a material -body, or any part of one. 2dly, The behaviour -of a particle set in motion, when it meets another -lying in its way, or is otherwise impeded or influenced -by its connection with surrounding particles. -3dly, The behaviour of the particles so impeding -or influencing it under such circumstances; besides -which, the last two point out another phenomenon, -which it is necessary also to consider, viz. the phenomenon -of the connection of the parts of material -bodies in masses, by which they form aggregates, -and are enabled to influence each other’s motions.</p> - -<p>(80.) Thus, then, we see that an analysis of the -phenomenon of sound leads to the enquiry, 1st, of -two <em>causes</em>, viz. the cause of motion, and the cause -of sensation, these being phenomena which (at least -as human knowledge stands at present) we are -unable to analyse further; and, therefore, we set -them down as simple, elementary, and referable, -for any thing we can see to the contrary, to the -immediate action of their causes. 2dly, Of several -questions relating to the connection between the<span class="pagenum"><a id="Page_90">90</a></span> -motion of material bodies and its cause, such as, -<em>What will happen</em> when a moving body is surrounded -on all sides by others not in motion? <em>What -will happen</em> when a body not in motion is advanced -upon by a moving one? It is evident that the -answers to such questions as these can be no -other than <em>laws of motion</em>, in the sense we have -above attributed to laws of nature, viz. a statement -in words of what will happen in such and such -proposed general contingencies. Lastly, we are -led, by pursuing the analysis, and considering the -phenomenon of the aggregation of the parts of -material bodies, and the way in which they influence -each other, to two other general phenomena, -viz., the cohesion and elasticity of matter; -and these we have no means of analysing further, -and must, therefore, regard them (till we see -reasons to the contrary) as <em>ultimate phenomena</em>, -and referable to the direct action of causes, viz. -an attractive and a repulsive <em>force</em>.</p> - -<p>(81.) Of force, as counterbalanced by opposing -force, we have, as already said, an internal consciousness; -and though it may seem strange to us -that matter should be capable of exerting on matter -the same kind of effort, which, judging alone -from this consciousness, we might be led to regard -as a mental one; yet we cannot refuse the -direct evidence of our senses, which shows us -that when we keep a spring stretched with one -hand, we feel our effort opposed exactly in the same -way as if we had ourselves opposed it with the -other hand, or as it would be by that of another -person. The enquiry, therefore, into the aggregation<span class="pagenum"><a id="Page_91">91</a></span> -of matter resolves itself into the general -question, What will be the behaviour of material -particles under the mutual action of opposing -forces capable of counterbalancing each other? -and the answer to this question can be no other -than the announcement of the <em>law</em> of equilibrium, -whatever law that may be.</p> - -<p>(82.) With regard to the cause of sensation, it -must be regarded as much more obscure than that -of motion, inasmuch as we have no conscious knowledge -of it, <i>i. e.</i> we have no power, by any act of -our minds and will, to call up a sensation. It is -true, we are not destitute of an approach to it, -since, by an effort of memory and imagination, we can -produce in our minds an impression, or idea, of a -sensation which, in peculiar cases, may even approach -in vividness to actual reality. In dreams, too, -and, in some cases of disordered nerves, we have -sensations without objects. But if force, as a cause -of motion, is obscure to us, even while we are in the -act of exercising it, how much more so is this -other cause, whose exercise we can only imitate -imperfectly by any voluntary act, and of whose -purely internal action we are only fully conscious -when in a state that incapacitates us from reasoning, -and almost from observation!</p> - -<p>(83.) Dismissing, then, as beyond our reach, the -enquiry into causes, we must be content at present -to concentrate our attention on the laws which prevail -among phenomena, and which seem to be their -immediate results. From the instance we have just -given, we may perceive that every enquiry into the -intimate nature of a complex phenomenon branches<span class="pagenum"><a id="Page_92">92</a></span> -out into as many different and distinct enquiries as -there are simple or elementary phenomena into -which it may be analysed; and that, therefore, it -would greatly assist us in our study of nature, if we -could, by any means, ascertain what <em>are</em> the ultimate -phenomena into which all the composite ones -presented by it may be resolved. There is, however, -clearly no way by which this can be ascertained -<i xml:lang="la" lang="la">à priori</i>. We must go to nature itself, and be -guided by the same kind of rule as the chemist in -his analysis, who accounts every ingredient an <em>element</em> -till it can be decompounded and resolved into -others. So, in natural philosophy, we must account -every phenomenon an elementary or simple one till -we can analyse it, and show that it is the result of -others, which in their turn become elementary. -Thus, in a modified and relative sense, we may -still continue to speak of causes, not intending -thereby those ultimate principles of action on whose -exertion the whole frame of nature depends, but -of those proximate links which connect phenomena -with others of a simpler, higher, and more -general or elementary kind. For example: we -may regard the vibration of a musical string as -the proximate cause of the sound it yields, receiving -it, so far, as an ultimate fact, and waving or deferring -enquiry into the cause of vibrations, which -is of a higher and more general nature.</p> - -<p>(84.) Moreover, as in chemistry we are sometimes -compelled to acknowledge the existence of -elements different from those already identified and -known, though we cannot insulate them, and to -perceive that substances have the characters of<span class="pagenum"><a id="Page_93">93</a></span> -compounds, and must therefore be susceptible of -analysis, though we do not see how it is to be -set about; so, in physics, we may perceive the -complexity of a phenomenon, without being able -to perform its analysis. For example: in magnetism, -the agency of electricity is clearly made -out, and they are shown to stand to one another in -the relation of effect and cause. But the analysis -of magnetism, in its relation to particular metals, -is not yet quite satisfactorily performed; and -we are compelled to admit the existence of some -cause, whether proximate or ultimate, whose presence -in different metals, or in different states of -the same metal, determines that peculiar electric -condition which constitutes permanent magnetism. -Cases like these, of all which science presents, offer -the highest interest. They excite enquiry, like the -near approach to the solution of an enigma; they -show us that there is light, could only a certain veil -be drawn aside.</p> - -<p>(85.) In pursuing the analysis of any phenomenon, -the moment we find ourselves stopped by -one of which we perceive no analysis, and which, -therefore, we are forced to refer (at least provisionally) -to the class of ultimate facts, and to regard as -elementary, the study of that phenomenon and of -its laws becomes a separate branch of science. If -we encounter the same elementary phenomenon in -the analysis of several composite ones, it becomes -still more interesting, and assumes additional importance; -while at the same time we acquire information -respecting the phenomenon itself, by observing<span class="pagenum"><a id="Page_94">94</a></span> -those with which it is habitually associated, -that may help us at length to its analysis. It is -thus that sciences increase, and acquire a mutual -relation and dependency. It is thus, too, -that we are at length enabled to trace parallels -and analogies between great branches of science -themselves, which at length terminate in a perception -of their dependence on some common phenomenon -of a more general and elementary nature -than that which form the subject of either separately. -It was thus, for example, that, previous -to Oërsted’s great discovery of electro-magnetism, -a general resemblance between the two sciences of -electricity and magnetism was recognised, and -many of the chief phenomena in each were ascertained -to have their parallels, <i xml:lang="la" lang="la">mutatis mutandis</i>, in -the other. It was thus, too, that an analogy subsisting -between sound and light has been gradually -traced into a closeness of agreement, which can -hardly leave any reasonable doubt of their ultimate -coincidence in one common phenomenon, the -vibratory motion of an elastic medium. If it be -allowed to pursue our illustration from chemistry, -and to ground its application not on what has been, -but on what may one day be, done, it is thus that -the general family resemblance between certain -groups of bodies, now regarded as elementary, -(as nickel and cobalt, for instance, chlorine, iode, -and brome,) will, perhaps, lead us hereafter to perceive -relations between them of a more intimate -kind than we can at present trace.</p> - -<p>(86.) On those phenomena which are most frequently -encountered in an analysis of nature and<span class="pagenum"><a id="Page_95">95</a></span> -which most decidedly resist further decomposition, -it is evident that the greatest pains and attention -ought to be bestowed, not only because they furnish -a key to the greatest number of enquiries, and -serve to group and classify together the greatest -range of phenomena, but by reason of their higher -nature, and because it is in these that we must -look for the direct action of causes, and the most -extensive and general enunciation of the laws of -nature. These, once discovered, place in our power -the explanation of all particular facts, and become -grounds of reasoning, independent of particular -trial: thus playing the same part in natural philosophy -that axioms do in geometry; containing, in a -refined and condensed state, and as it were in a -quintessence, all that our reason has occasion to -draw from experience to enable it to follow out -the truths of physics by the mere application of -logical argument. Indeed, the axioms of geometry -themselves may be regarded as in some sort an -appeal to experience, not corporeal, but mental. -When we say, the whole is greater than its part, -we announce a general fact, which rests, it is -true, on our ideas of whole and part; but, in abstracting -these notions, we begin by considering -them as subsisting in space, and time, and body, -and again, in linear, and superficial, and solid space. -Again, when we say, the equals of equals are equal, -we mentally make comparisons, in equal spaces, -equal times, &c.; so that these axioms, however -self-evident, are still general propositions so far of -the inductive kind, that, independently of experience, -they would not present themselves to the mind.</p> - -<p><span class="pagenum"><a id="Page_96">96</a></span> -The only difference between these and axioms obtained -from extensive induction is this, that, in -raising the axioms of geometry, the instances offer -themselves spontaneously, and without the trouble -of search, and are few and simple; in raising -those of nature, they are infinitely numerous, complicated, -and remote; so that the most diligent -research and the utmost acuteness are required -to unravel their web, and place their meaning in -evidence.</p> - -<p>(87.) By far the most general phenomenon with -which we are acquainted, and that which occurs -most constantly, in every enquiry into which we -enter, is motion, and its communication. Dynamics, -then, or the science of force and motion, is thus -placed at the head of all the sciences; and, happily -for human knowledge, it is one in which -the highest certainty is attainable, a certainty no -way inferior to mathematical demonstration. As -its axioms are few, simple, and in the highest degree -distinct and definite, so they have at the same -time an immediate relation to geometrical quantity, -space, time, and direction, and thus accommodate -themselves with remarkable facility to geometrical -reasoning. Accordingly, their consequences may be -pursued, by arguments purely mathematical, to any -extent, insomuch that the limit of our knowledge -of dynamics is determined only by that of pure -mathematics, which is the case in no other branch of -physical science.</p> - -<p>(88.) But, it will now be asked, how we are to -proceed to analyse a composite phenomenon into -simpler ones, and whether any general rules can be<span class="pagenum"><a id="Page_97">97</a></span> -given for this important process? We answer, None; -any more than (to pursue the illustration we have -already had recourse to) general rules can be laid -down by the chemist for the analysis of substances -of which all the ingredients are unknown. Such -rules, could they be discovered, would include the -whole of natural science; but we are very far, indeed, -from being able to propound them. However, we -are to recollect that the analysis of phenomena, -philosophically speaking, is principally useful, as it -enables us to recognize, and mark for special investigation, -those which appear to us simple; to set methodically -about determining their laws, and thus to -facilitate the work of raising up general axioms, or -forms of words, which shall include the whole of -them; which shall, as it were, transplant them out of -the external into the intellectual world, render them -creatures of pure thought, and enable us to reason -them out <i xml:lang="la" lang="la">à priori</i>. And what renders the power of -doing this so eminently desirable is, that, in thus -reasoning back from generals to particulars, the propositions -at which we arrive apply to an immense -multitude of combinations and cases, which were -never individually contemplated in the mental process -by which our axioms were first discovered; and -that, consequently, when our reasonings are pushed -to the utmost limit of particularity, their results -appear in the form of <em>individual facts</em>, of which we -might have had no knowledge from immediate experience; -and thus we are not only furnished with the -explanation of all known facts, but with the actual -discovery of such as were before unknown. A remarkable -example of this has already been mentioned<span class="pagenum"><a id="Page_98">98</a></span> -in Fresnel’s <i xml:lang="la" lang="la">à priori</i> discovery of the extraordinary -refraction of both rays in a doubly refracting medium. -To give another example:—The law of gravitation -is a physical axiom of a very high and universal -kind, and has been raised by a succession of inductions -and abstractions drawn from the observation of -numerous facts and subordinate laws in the planetary -system. When this law is taken for granted, and -laid down as a basis of reasoning, and applied to -the actual condition of our own planet, one of the -consequences to which it leads is, that the earth, -instead of being an exact sphere, must be compressed -or flattened in the direction of its polar diameter, -the one diameter being about thirty miles shorter -than the other; and this conclusion, deduced at -first by mere reasoning, has been since found to be -true in fact. All astronomical predictions are -examples of the same thing.</p> - -<p>(89.) In the important business of raising these -axioms of nature, we are not, as in the analysis of -phenomena, left wholly without a guide. The nature -of abstract or general reasoning points out in -a great measure the course we must pursue. A -law of nature, being the statement of what will -happen in certain general contingencies, may be -regarded as the announcement, in the same words, -of a whole group or class of phenomena. Whenever, -therefore, we perceive that two or more phenomena -agree in so many or so remarkable points, as -to lead us to regard them as forming a class or group, -if we lay out of consideration, or <em>abstract</em>, all the circumstances -in which they disagree, and retain in -our minds those only in which they agree, and<span class="pagenum"><a id="Page_99">99</a></span> -then, under this kind of mental convention, frame a -definition or statement of one of them, in such words -that it shall apply equally to them all, such statement -will appear in the form of a general proposition, -having so far at least the character of a law of -nature.</p> - -<p>(90.) For example: a great number of transparent -substances, when exposed, in a certain particular -manner, to a beam of light which has been -prepared by undergoing certain reflexions or refractions, -(and has thereby acquired peculiar properties, -and is said to be “<em>polarized</em>,”) exhibit very vivid -and beautiful colours, disposed in streaks, bands, -&c. of great regularity, which seem to arise within -the substance, and which, from a certain regular -succession observed in their appearance, are called -“periodical colours.” Among the substances which -exhibit these periodical colours occur a great -variety of transparent solids, but no fluids and no -opake solids. Here, then, there seems to be sufficient -community of nature to enable us to use a -general term, and to state the proposition as a law, -viz. <em>transparent solids</em> exhibit periodical colours by -exposure to polarized light. However, this, though -true of many, does not apply to <em>all</em> transparent -solids, and therefore we cannot state it as a general -truth or law of nature in this form; although the -reverse proposition, that all solids which exhibit -such colours in such circumstances are <em>transparent</em>, -would be correct and general. It becomes -necessary, then, to make a list of those to which it -does apply; and thus a great number of substances -of all kinds become grouped together, in a class<span class="pagenum"><a id="Page_100">100</a></span> -linked by this common property. If we examine -the individuals of this group, we find among them -the utmost variety of colour, texture, weight, hardness, -form and composition; so that, in these respects, -we seem to have fallen upon an assemblage -of contraries. But when we come to examine -them closely, in all their properties, we find they -have all one point of agreement, in the property of -double refraction, (see page <a href="#Page_30">30</a>.) and therefore we -may describe them all truly as <em>doubly refracting -substances</em>. We may, therefore, state the fact in the -form, “Doubly refracting substances exhibit periodical -colours by exposure to polarized light;” -and in this form it is found, on further examination, -to be true, not only for those particular instances -which we had in view when we first propounded it, -but in all cases which have since occurred on further -enquiry, without a single exception; so that the -proposition is general, and entitled to be regarded -as a law of nature.</p> - -<p>(91.) We may therefore regard a law of nature -either, 1st, as a general proposition, announcing, in -abstract terms, a whole group of particular facts relating -to the behaviour of natural agents in proposed -circumstances; or, 2dly, as a proposition announcing -that a whole class of individuals agreeing in one -character agree also in another. For example: in -the case before us, the law arrived at includes, in -its general announcement, among others, the particular -facts, that rock crystal and saltpetre exhibit periodical -colours; for these are both of them doubly -refracting substances. Or, it may be regarded -as announcing a relation between the two phenomena<span class="pagenum"><a id="Page_101">101</a></span> -of double refraction, and the exhibition of -periodical colours; which in the actual case is one -of the most important, viz. the relation of <em>constant -association</em>, inasmuch as it asserts that in whatever -individual the one character is found, the other will -invariably be found also.</p> - -<p>(92.) These two lights, in which the announcement -of a general law may be regarded, though at -bottom they come to the same thing, yet differ -widely in their influence on our minds. The former -exhibits a law as little more than a kind of artificial -memory; but in the latter it becomes a step -in philosophical investigation, leading directly to the -consideration of a proximate, if not an ultimate, -cause; inasmuch as, whenever two phenomena are -observed to be invariably connected together, we -conclude them to be related to each other, either -as cause and effect, or as common effects of a single -cause.</p> - -<p>(93.) There is still another light in which we -may regard a law of the kind in question, viz. as a -proposition asserting the mutual connection, or in -some cases the entire identity, of two classes of individuals -(whether individual objects or individual -facts); and this is, perhaps, the simplest and most -instructive way in which it can be conceived, -and that which furnishes the readiest handle to -further generalization in the raising of yet higher -axioms. For example: in the case above mentioned, -if observation had enabled us to establish -the existence of a class of bodies possessing the -property of double refraction, and observations -of another kind had, independently of the former, led<span class="pagenum"><a id="Page_102">102</a></span> -as to recognize a class possessing that of the exhibition -of periodical colours in polarized light, a mere -comparison of lists would at once demonstrate the -identity of the two classes, or enable us to ascertain -whether one was or was not included in the other.</p> - -<p>(94.) It is thus we perceive the high importance -in physical science of just and accurate classifications -of particular facts, or individual objects, under -general well considered heads or points of agreement -(for which there are none better adapted -than the simple phenomena themselves into which -they can be analysed in the first instance); for by -so doing each of such phenomena, or heads of -classification, becomes not a particular but a general -fact; and when we have amassed a great store of -such <em>general facts</em>, they become the objects of another -and higher species of classification, and are -themselves included in laws which, as they dispose -of groups, not individuals, have a far superior -degree of generality, till at length, by continuing -the process, we arrive at <em>axioms</em> of the -highest degree of generality of which science is -capable.</p> - -<p>(95.) This process is what we mean by induction; -and, from what has been said, it appears that induction -may be carried on in two different ways,—either -by the simple juxta-position and comparison -of ascertained classes, and marking their agreements -and disagreements; or by considering the -individuals of a class, and casting about, as it were -to find in what particular they all agree, besides -that which serves as their principle of classification. -Either of these methods may be put in practice as<span class="pagenum"><a id="Page_103">103</a></span> -one or the other may afford facilities in any case; -but it will naturally happen that, where facts -are numerous, well observed, and methodically -arranged, the former will be more applicable than -in the contrary case: the one is better adapted to -the maturity, the other to the infancy, of science: -the one employs, as an engine, the division of -labour; the other mainly relies on individual penetration, -and requires a union of many branches of -knowledge in one person.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_104">104</a></span></p> - -<div class="chapter"> -<h2 id="hdr_8">CHAP. III.</h2> -</div> - -<p class="center">OF THE STATE OF PHYSICAL SCIENCE IN GENERAL, PREVIOUS -TO THE AGE OF GALILEO AND BACON.</p> - -<p class="in0">(96.) <span class="smcap"><span class="flet">I</span>t</span> is to our immortal countryman Bacon -that we owe the broad announcement of this grand -and fertile principle; and the developement of the -idea, that the whole of natural philosophy consists -entirely of a series of inductive generalizations, -commencing with the most circumstantially stated -particulars, and carried up to universal laws, or -axioms, which comprehend in their statements -every subordinate degree of generality, and of a -corresponding series of inverted reasoning from -generals to particulars, by which these axioms are -traced back into their remotest consequences, and -all particular propositions deduced from them; as -well those by whose immediate consideration we -rose to their discovery, as those of which we had -no previous knowledge. In the course of this -descent to particulars, we must of necessity encounter -all those facts on which the arts and works -that tend to the accommodation of human life -depend, and acquire thereby the command of an -unlimited practice, and a disposal of the powers -of nature co-extensive with those powers themselves. -A noble promise, indeed, and one which -ought, surely, to animate us to the highest exertion -of our faculties; especially since we have already -such convincing proof that it is neither vain nor -rash, but, on the contrary, has been, and continues<span class="pagenum"><a id="Page_105">105</a></span> -to be, fulfilled, with a promptness and liberality -which even its illustrious author in his most sanguine -mood would have hardly ventured to anticipate.</p> - -<p>(97.) Previous to the publication of the Novum -Organum of Bacon, natural philosophy, in any -legitimate and extensive sense of the word, could -hardly be said to exist. Among the Greek philosophers, -of whose attainments in science alone, -in the earlier ages of the world, we have any positive -knowledge, and that but a very limited one, -we are struck with the remarkable contrast between -their powers of acute and subtle disputation, -their extraordinary success in abstract reasoning, -and their intimate familiarity with subjects -purely intellectual, on the one hand; and, on the -other, with their loose and careless consideration -of external nature, their grossly illogical deductions -of principles of sweeping generality from -few and ill-observed facts, in some cases; and their -reckless assumption of abstract principles having -no foundation but in their own imaginations, in -others; mere forms of words, with nothing corresponding -to them in nature, from which, as from -mathematical definitions, postulates, and axioms, -they imagined that all phenomena could be derived, -all the laws of nature deduced. Thus, for -instance, having settled it in their own minds, that -a circle is the most perfect of figures, they concluded, -of course, that the movements of the heavenly -bodies must all be performed in exact circles, and -with uniform motions; and when the plainest observation -demonstrated the contrary, instead of -doubting the principle, they saw no better way of<span class="pagenum"><a id="Page_106">106</a></span> -getting out of the difficulty than by having recourse -to endless combinations of circular motions to preserve -their ideal perfection.</p> - -<p>(98.) Undoubtedly among the Greek philosophers -were many men of transcendent talents and virtues, -the ornaments of their species, and justly entitled to -the veneration of all posterity; but regarded as a body -they can hardly be considered otherwise than as a -knot of disputatious candidates for popular favour, -too busy in maintaining their ascendency over their -followers and admirers, by an ostentatious display of -superior knowledge, to have the leisure (had they -always the inclination) to base their pretensions on -a deep and sure foundation, and yet too sensible of -the disgrace and inconvenience of failure, not to -defend their dogmas, however shallow, when once -promulgated, against their keen and sagacious opponents, -by every art of sophism or appeal to passion. -Hence the crudities and chimerical views with -which their systems of philosophy, both natural and -moral, were overloaded; their endless disputes -about verbal subtleties, and, last and worst, the -proud assumption with which they sheltered ignorance -and indolence under the screen of unintelligible -jargon or dogmatical assertion. Perhaps, however, -this character applies rather to the later than -to the earlier of the Greek philosophers. The spirit -of rational enquiry into nature seems, if we can -judge from the uncertain and often contradictory -notices handed down to us of their tenets, to have -been far more alive, and less warped by this vain -and arrogant turn, then than at a later period. We -know not now what was the precise meaning<span class="pagenum"><a id="Page_107">107</a></span> -attached by Thales to his opinion, that water was -the origin of all things; but modern geologists will -not be at a loss to conceive how an observant traveller -might become impressed with this notion, -without having recourse to the mystic records of -Egypt or Chaldea. His ideas of eclipses and of the -nature of the moon were sound; and his prediction -of an eclipse of the sun, in particular, was attended -with circumstances so remarkable as to have made -it a matter of important investigation to modern astronomers. -Anaxagoras, among a number of crude -and imperfectly explained notions, speculated rationally -enough on the cause of the winds and of -the rainbow, and less absurdly on earthquakes than -many modern geologists have done, and appears generally -to have had his attention alive to nature, and -his mind open to just reasoning on its phenomena; -while Pythagoras, whether he reasoned it out for himself, -or borrowed the notion from Egypt or India, had -attained a just conception of the general disposition -of the parts of the solar system, and the place held -by the earth in it; nay, according to some accounts, -had even raised his views so far as to speculate on -the attraction of the sun as the bond of its union.</p> - -<p>(99.) But the successors of these <i xml:lang="la" lang="la">bonâ fide</i> enquirers -into nature debased the standard of truth; -and, taking advantage of the credit justly attached to -their discoveries, renounced the modest character of -learners, and erected themselves into teachers, and, to -maintain their pretensions to this character, adopted -the tone of men who had nothing further to learn. -Unfortunately for true science, the national character -gave every encouragement to pretensions of this<span class="pagenum"><a id="Page_108">108</a></span> -kind. That restless craving after novelty, which -distinguished the Greeks in their civil and political -relations, pursued them into their philosophy. Whatever -speculations were only ingenious and new had -irresistible charms; and the teacher who could embody -a clever thought in elegant language, or at -once save his followers and himself the trouble of -thinking or reasoning, by bold assertion, was too -often induced to acquire cheaply the reputation of -superior knowledge, snatch a few superficial notions -from the most ordinary and obvious facts, envelope -them in a parade of abstruse words, declare them -the primary and ultimate principles of all things, -and denounce as absurd and impious all opinions -opposed to his own.</p> - -<p>(100.) In this war of words the study of nature -was neglected, and an humble and patient enquiry -after facts altogether despised, as unworthy of the -high <i xml:lang="la" lang="la">priori</i> ground a true philosopher ought to take. -It was the radical error of the Greek philosophy to -imagine that the same method which proved so eminently -successful in mathematical, would be equally -so in physical, enquiries, and that, by setting out -from a few simple and almost self-evident notions, or -<em>axioms</em>, every thing could be reasoned out. Accordingly, -we find them constantly straining their invention -to discover these principles, which were to prove -so pregnant. One makes <em>fire</em> the essential matter -and origin of the universe; another, <em>air</em>; a third, -discovers the key to every difficulty, and the explanation -of all phenomena, in the “<span xml:lang="grc" lang="grc">το απειρον</span>” or -infinitude of things; a fourth, in the <span xml:lang="grc" lang="grc">το ὁν</span> and -the <span xml:lang="grc" lang="grc">το μη ὁν</span>, that is to say, in entity and nonentity;—<span class="pagenum"><a id="Page_109">109</a></span>till -at length an authority, which was destined to -command opinions for nearly two thousand years, -settled this important point, by deciding, that <em>matter</em>, -<em>form</em>, and <em>privation</em>, were to be considered the principles -of all things.</p> - -<p>(101.) It were to do injustice to Aristotle, however, -to judge of him by <em>such</em> a sample of his philosophy. -He, at least, saw the necessity of having recourse -to nature for something like principles of physical -science; and, as an observer, a collector -and recorder of facts and phenomena, stood without -an equal in his age. It was the fault of that -age, and of the perverse and flimsy style of verbal -disputation which had infected all learning, rather -than his own, that he allowed himself to be contented -with vague and loose notions drawn from -general and vulgar observation, in place of seeking -carefully, in well arranged and thoroughly considered -instances, for the true laws of nature. His -voluminous works, on every department of human -knowledge existing in his time, have nearly all -perished. From his work on animals, which has -descended to us, we are, however, enabled to appreciate -his powers of observation; and a parallel -drawn by an eminent Oxford professor between his -classifications and those of the most illustrious of -living naturalists, shows him to have attained a -view of animated nature in a remarkable degree -comprehensive, and which contrasts strikingly with -the confusion, vagueness, and assumption of his -physical opinions and dogmas. In these it is easy -to recognize a mind not at home, and an impression -of the necessity of saying something learned and<span class="pagenum"><a id="Page_110">110</a></span> -systematic, without knowing what to say. Thus -he divides motions into natural and unnatural; the -natural motion of fire and light bodies being upwards, -those of heavy downwards, each seeking its -kindred nature in the heavens and the earth. Thus, -too, the immediate impressions made on us by external -objects, such as hardness, colour, heat, &c. -are referred at once, in the Aristotelian philosophy, -to occult qualities, in virtue of which they are as -they are, and beyond which it is useless to enquire.<a id="FNanchor_30" href="#Footnote_30" class="fnanchor">30</a><span class="pagenum"><a id="Page_111">111</a></span> -Of course there will occur a limit beyond which -it <em>is</em> useless for merely human faculties to enquire; -but where that limit is placed, experience alone can -teach us; and at least to assert that we <em>have</em> attained -it, is now universally recognized as the sure criterion -of dogmatism.</p> - -<p>(102.) In the early ages of the church the writings -of Aristotle were condemned, as allowing too -much to reason and sense; and even so late as the -twelfth century they were sought out and burned, -and their readers excommunicated. By degrees, -however, the extreme injustice of this impeachment -of their character was acknowledged: they became -the favourite study of the schoolmen, and furnished -the keenest weapons of their controversy, being -appealed to in all disputes as of sovereign authority; -so that the slightest dissent from any opinion -of the “great master,” however absurd or unintelligible, -was at once drowned by clamour, or -silenced by the still more effectual argument of -bitter persecution. If the logic of that gloomy -period could be justly described as “the art of talking -unintelligibly on matters of which we are ignorant,” -its physics might, with equal truth, be summed up -in a deliberate preference of ignorance to knowledge, -in matters of every day’s experience and use.</p> - -<p>(103.) In “this opake of nature and of soul,” -the perverse activity of the alchemists from time -to time struck out a doubtful spark<a id="FNanchor_31" href="#Footnote_31" class="fnanchor">31</a>; and our<span class="pagenum"><a id="Page_112">112</a></span> -illustrious countryman, Roger Bacon, shone out at -the obscurest moment, like an early star predicting -dawn. It was not, however, till the sixteenth -century that the light of nature began to break -forth with a regular and progressive increase. The -vaunts of Paracelsus of the power of his chemical -remedies and elixirs, and his open condemnation of -the ancient pharmacy, backed as they were by many -surprising cures, convinced all rational physicians -that chemistry could furnish many excellent remedies, -unknown till that time<a id="FNanchor_32" href="#Footnote_32" class="fnanchor">32</a>, and a number of -valuable experiments began to be made by physicians -and chemists, desirous of discovering and -describing new chemical remedies. The chemical -and metallurgic arts, exercised by persons empirically -acquainted with their secrets, began to be -seriously studied with a view to the acquisition of -rational and useful knowledge, and regular treatises -on branches of natural science at length to -appear. George Agricola, in particular, devoted -himself with ardour to the study of mineralogy -and metallurgy in the mining districts of Bohemia -and Schemnitz, and published copious and methodical -accounts of all the facts within his knowledge: -and our countryman, Dr. Gilbert of Colchester, in<span class="pagenum"><a id="Page_113">113</a></span> -1590, published a treatise on magnetism, full of -valuable facts and experiments, ingeniously reasoned -on; and he likewise extended his enquiries -to a variety of other subjects, in particular to electricity.</p> - -<p>(104.) But, as the decisive mark of a great commencing -change in the direction of the human -faculties, astronomy, the only science in which the -ancients had made any real progress, and ascended -to any thing like large and general conceptions, -began once more to be studied in the best spirit -of a candid philosophy; and the Copernican or -Pythagorean system arose or revived, and rapidly -gained advocates. Galileo at length appeared, and -openly attacked and refuted the Aristotelian dogmas -respecting motion, by direct appeal to the evidence -of sense, and by experiments of the most -convincing kind. The persecutions which such a -step drew upon him, the record of his perseverance -and sufferings, and the ultimate triumph of his -opinions and reasonings, have been too lately and -too well related<a id="FNanchor_33" href="#Footnote_33" class="fnanchor">33</a> to require repetition here.</p> - -<p>(105.) By the discoveries of Copernicus, Kepler, -and Galileo, the errors of the Aristotelian philosophy -were effectually overturned on a plain appeal -to the facts of nature; but it remained to show on -broad and general principles, how and why Aristotle -was in the wrong; to set in evidence the peculiar -weakness of his method of philosophizing, and to -substitute in its place a stronger and better. This<span class="pagenum"><a id="Page_114">114</a></span> -important task was executed by Francis Bacon, Lord -Verulam, who will, therefore, justly be looked upon -in all future ages as the great reformer of philosophy, -though his own actual contributions to the -stock of physical truths were small, and his ideas -of particular points strongly tinctured with mistakes -and errors, which were the fault rather of the -general want of physical information of the age -than of any narrowness of view on his own part; -and of this he was fully aware. It has been attempted -by some to lessen the merit of this great -achievement, by showing that the inductive method -had been practised in many instances, both ancient -and modern, by the mere instinct of mankind; but -it is not the introduction of inductive reasoning, as -a new and hitherto untried process, which characterizes -the Baconian philosophy, but his keen perception, -and his broad and spirit-stirring, almost -enthusiastic, announcement of its paramount importance, -as the alpha and omega of science, as the -grand and only chain for the linking together of -physical truths, and the eventual key to every discovery -and every application. Those who would -deny him his just glory on such grounds would -refuse to Jenner or to Howard their civic crowns, -because a few farmers in a remote province had, -time out of mind, been acquainted with vaccination, -or philanthropists, in all ages, had occasionally -visited the prisoner in his dungeon.</p> - -<p>(106.) An immense impulse was now given to science, -and it seemed as if the genius of mankind, long -pent up, had at length rushed eagerly upon Nature,<span class="pagenum"><a id="Page_115">115</a></span> -and commenced, with one accord, the great work of -turning up her hitherto unbroken soil, and exposing -the treasures so long concealed. A general sense -now prevailed of the poverty and insufficiency of -existing knowledge in <em>matters of fact</em>; and, as information -flowed fast in, an era of excitement and wonder -commenced, to which the annals of mankind -had furnished nothing similar. It seemed, too, as -if Nature herself seconded the impulse; and, while -she supplied new and extraordinary aids to those -senses which were henceforth to be exercised in -her investigation,—while the telescope and the microscope -laid open <em>the infinite</em> in both directions,—as -if to call attention to her wonders, and signalize -the epoch, she displayed the rarest, the most splendid -and mysterious, of all astronomical phenomena, the -appearance and subsequent total extinction of a -new and brilliant fixed star twice within the lifetime -of Galileo himself.<a id="FNanchor_34" href="#Footnote_34" class="fnanchor">34</a></p> - -<p>(107.) The immediate followers of Bacon and -Galileo ransacked all nature for new and surprising -facts, with something of that craving for the marvellous, -which might be regarded as a remnant of -the age of alchemy and natural magic, but which, -under proper regulation, is a most powerful and -useful stimulus to experimental enquiry. Boyle, in -particular, seemed animated by an enthusiasm of -ardour, which hurried him from subject to subject,<span class="pagenum"><a id="Page_116">116</a></span> -and from experiment to experiment, without a -moment’s intermission, and with a sort of undistinguishing -appetite; while Hooke (the great contemporary, -and almost the worthy rival, of Newton) -carried a keener eye of scrutinizing reason into a -range of research even yet more extensive. As -facts multiplied, leading phenomena became prominent, -laws began to emerge, and generalizations -to commence; and so rapid was the career of discovery, -so signal the triumph of the inductive philosophy, -that a single generation and the efforts -of a single mind sufficed for the establishment of -the system of the universe, on a basis never after -to be shaken.</p> - -<p>(108.) We shall now endeavour to enumerate and -explain in detail the principal steps by which legitimate -and extensive inductions are arrived at, and -the processes by which the mind, in the investigation -of natural laws, purges itself by successive -degrees of the superfluities and incumbrances which -hang about particulars, and obscure the perception -of their points of resemblance and connection. We -shall state the helps which may be afforded us, in -a work of so much thought and labour, by a methodical -course of proceeding, and by a careful notice -of those means which have at any time been found -successful, with a view to their better understanding -and adaptation to other cases: a species of mental -induction of no mean utility and extent in itself; -inasmuch as by pursuing it alone we can attain a -more intimate knowledge than we actually possess -of the laws which regulate our discovery of truth,<span class="pagenum"><a id="Page_117">117</a></span> -and of the rules, so far as they extend, to which -invention is reducible. In doing this, we shall -commence at the beginning, with experience itself, -considered as the accumulation of the knowledge -of individual objects and facts.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_118">118</a></span></p> - -<div class="chapter"> -<h2 id="hdr_9">CHAP. IV.</h2> -</div> - -<p class="center">OF THE OBSERVATION OF FACTS AND THE COLLECTION -OF INSTANCES.</p> - -<p class="in0">(109.) <span class="smcap"><span class="flet">N</span>ature</span> offers us two sorts of subjects of -contemplation in the external world,—objects, and -their mutual actions. But, after what has been said -on the subject of sensation, the reader will be at no -loss to perceive that we know nothing of the objects -themselves which compose the universe, except -through the medium of the impressions they excite -in us, which impressions are the results of certain -actions and processes in which sensible objects -and the material parts of ourselves are directly -concerned. Thus, our observation of external nature -is limited to the mutual action of material objects -on one another; and to facts, that is, the associations -of phenomena or appearances. We gain no -information by perceiving merely that an object is -black; but if we also perceive it to be fluid, we -at least acquire the knowledge that blackness is -not incompatible with fluidity, and have thus made -a step, however trifling, to a knowledge of the more -intimate nature of these two qualities. Whenever, -therefore, we would either analyse a phenomenon into -simpler ones, or ascertain what is the course or law -of nature under any proposed general contingency, -the first step is to accumulate a sufficient quantity -of well ascertained facts or recorded instances,<span class="pagenum"><a id="Page_119">119</a></span> -bearing on the point in question. Common sense -dictates this, as affording us the means of examining -the same subject in several points of view; and it -would also dictate, that the more different these -collected facts are in all other circumstances but -that which forms the subject of enquiry, the better; -because they are then in some sort brought into -contrast with one another in their points of disagreement, -and thus tend to render those in which -they agree more prominent and striking.</p> - -<p>(110.) The only facts which can ever become useful -as grounds of physical enquiry are those which -happen uniformly and invariably under the same -circumstances. This is evident: for if they have -not this character they cannot be included in laws; -they want that universality which fits them to enter -as elementary particles into the constitution of those -universal axioms which we aim at discovering. If one -and the same result does not constantly happen under -a given combination of circumstances, apparently the -same, one of two things must be supposed,—caprice -(<i>i. e.</i> the arbitrary intervention of mental agency), or -differences in the circumstances themselves, really -existing, but unobserved by us. In either case, -though we may record such facts as curiosities, or -as awaiting explanation when the difference of circumstances -shall be understood, we can make no -use of them in scientific enquiry. Hence, whenever -we notice a remarkable effect of any kind, our -first question ought to be, Can it be reproduced? -What are the circumstances under which it has -happened? And will it <em>always</em> happen again if those<span class="pagenum"><a id="Page_120">120</a></span> -circumstances, so far as we have been able to collect -them, co-exist?</p> - -<p>(111.) The circumstances, then, which accompany -any observed fact, are main features in its observation, -at least until it is ascertained by sufficient -experience what circumstances have nothing to do -with it, and might therefore have been left unobserved -without sacrificing <em>the fact</em>. In observing and -recording a fact, therefore, altogether new, we ought -not to omit any circumstance capable of being noted, -lest some one of the omitted circumstances should -be essentially connected with the fact, and its -omission should, therefore, reduce the implied statement -of a <em>law of nature</em> to the mere record of an -<em>historical event</em>. For instance, in the fall of meteoric -stones, flashes of fire are seen proceeding from a -cloud, and a loud rattling noise like thunder is -heard. These circumstances, and the sudden stroke -and destruction ensuing, long caused them to be -confounded with an effect of lightning, and called -thunderbolts. But one circumstance is enough to -mark the difference: the flash and sound have -been perceived occasionally to emanate from a <em>very -small cloud</em> insulated in <em>a clear sky</em>; a combination -of circumstances which never happens in a thunder -storm, but which is undoubtedly intimately connected -with their real origin.</p> - -<p>(112.) Recorded observation consists of two distinct -parts: 1st, an exact notice of the thing -observed, and of all the particulars which may be -supposed to have any natural connection with it; -and, 2dly, a true and faithful record of them. As our -senses are the only inlets by which we receive impressions<span class="pagenum"><a id="Page_121">121</a></span> -of facts, we must take care, in observing, -to have them all in activity, and to let nothing escape -notice which affects any one of them. Thus, if -lightning were to strike the house we inhabit, we -ought to notice what kind of light we saw—whether -a sheet of flame, a darting spark, or a broken zig-zag; -in what direction moving, to what objects adhering, -its colour, its duration, &c.; what sounds were -heard—explosive, crashing, rattling, momentary, or -gradually increasing and fading, &c.; whether any -smell of fire was perceptible, and if sulphureous, -metallic, or such as would arise merely from substances -scorched by the flash, &c.; whether we felt -any shock, stroke, or peculiar sensation, or experienced -any strange taste in our mouths. Then, -besides detailing the effects of the stroke, all the -circumstances which might in any degree seem -likely to attract, produce, or modify it, such as -the presence of conductors, neighbouring objects, -the state of the atmosphere, the barometer, thermometer, -&c., and the disposition of the clouds, -should be noted; and after all this particularity, -the question <em>how</em> the house <em>came to be struck?</em> might -ultimately depend on the fact that a flash of lightning -twenty miles off passed at that particular -moment <em>from the ground to the clouds</em>, by an effect of -what has been termed the returning stroke.</p> - -<p>(113.) A writer in the Edinburgh Philosophical -Journal<a id="FNanchor_35" href="#Footnote_35" class="fnanchor">35</a> states himself to have been led into a series -of investigations on the chemical nature of a peculiar -acid, by noticing, accidentally, a bitter taste in a<span class="pagenum"><a id="Page_122">122</a></span> -liquid about to be thrown away. Chemistry is full -of such incidents.</p> - -<p>(114.) In transient phenomena, if the number of -particulars be great, and the time to observe them -short, we must consult our memory before they -have had time to fade, or refresh it by placing ourselves -as nearly as possible in the same circumstances -again; go back to the spot, for instance, and -try the words of our statement by appeal to all remaining -indications, &c. This is most especially -necessary where we have not observed ourselves, -but only collect and record the observations of others, -particularly of illiterate or prejudiced persons, on any -rare phenomenon, such as the passing of a great -meteor,—the fall of a stone from the sky,—the -shock of an earthquake,—an extraordinary hailstorm, -&c.</p> - -<p>(115.) In all cases which admit of numeration or -measurement, it is of the utmost consequence to -obtain precise numerical statements, whether in the -measure of time, space, or quantity of any kind. To -omit this, is, in the first place, to expose ourselves -to illusions of sense which may lead to the grossest -errors. Thus, in alpine countries, we are constantly -deceived in heights and distances; and when we have -overcome the first impression which leads us to -under-estimate them, we are then hardly less apt to -run into the opposite extreme. But it is not merely -in preserving us from exaggerated impressions that -numerical precision is desirable. It is the very soul -of science; and its attainment affords the only criterion, -or at least the best, of the truth of theories, -and the correctness of experiments. Thus, it was<span class="pagenum"><a id="Page_123">123</a></span> -entirely to the omission of exact numerical determinations -of quantity that the mistakes and confusion -of the Stahlian chemistry were attributable,—a -confusion which dissipated like a morning mist as -soon as precision, in this respect, came to be regarded -as essential. Chemistry is in the most pre-eminent -degree a science of quantity; and to enumerate the -discoveries which have arisen in it, from the mere -determination of weights and measures, would be -nearly to give a synopsis of this branch of knowledge. -We need only mention the law of definite -proportions, which fixes the composition of every -body in nature in determinate proportional weights -of its ingredients.</p> - -<p>(116.) Indeed, it is a character of all the higher laws -of nature to assume the form of precise <em>quantitative</em> -statement. Thus, the law of gravitation, the most -universal truth at which human reason has yet arrived, -expresses not merely the general fact of the -mutual attraction of all matter; not merely the -vague statement that its influence decreases as the -distance increases, but the exact numerical rate at -which that decrease takes place; so that when its -amount is known at any one distance it may be calculated -exactly for any other. Thus, too, the laws -of crystallography, which limit the forms assumed by -natural substances, when left to their own inherent -powers of aggregation, to precise geometrical figures, -with fixed angles and proportions, have the same -essential character of strict mathematical expression, -without which no exact particular conclusions could -ever be drawn from them.</p> - -<p>(117.) But, to arrive at laws of this description, it is<span class="pagenum"><a id="Page_124">124</a></span> -evident that every step of our enquiry must be perfectly -free from the slightest degree of looseness -and indecision, and carry with it the full force of -strict numerical announcement; and that, therefore, -the observations themselves on which all laws ultimately -rest ought to have the same property. None -of our senses, however, gives us direct information -for the exact comparison of quantity. Number, -indeed, that is to say, integer number, is an object -of sense, because we can count; but we can -neither weigh, measure, nor form any precise estimate -of fractional parts by the unassisted senses. -Scarcely any man could tell the difference between -twenty pounds and the same weight increased or -diminished by a few ounces; still less could he judge -of the proportion between an ounce of gold and a -hundred grains of cotton by balancing them in his -hands. To take another instance: the eye is no -judge of the proportion of different degrees of illumination, -even when seen side by side; and if an -interval elapses, and circumstances change, nothing -can be more vague than its judgments. When we -gaze with admiration at the gorgeous spectacle of -the golden clouds at sunset, which seem drenched -in light and glowing like flames of real fire, it is -hardly by any effort we can persuade ourselves -to regard them as the very same objects which at -noonday pass unnoticed as mere white clouds basking -in the sun, only participating, from their great horizontal -distance, in the ruddy tint which luminaries -acquire by shining through a great extent of the -vapours of the atmosphere, and thereby even losing -something of their light. So it is with our estimates<span class="pagenum"><a id="Page_125">125</a></span> -of time, velocity, and all other matters of -quantity; they are absolutely vague, and inadequate -to form a foundation for any exact conclusion.</p> - -<p>(118.) In this emergency we are obliged to have -recourse to instrumental aids, that is, to contrivances -which shall substitute for the vague impressions -of sense the precise one of number, and reduce all -measurement to counting. As a first preliminary -towards effecting this, we fix on convenient <em>standards</em> -of weight, dimension, time, &c., and invent contrivances -for readily and correctly repeating them as -often as we please, and counting how often such a -standard unit is contained in the thing, be it weight, -space, time, or angle, we wish to measure; and if -there be a fractional part over, we measure this -as a new quantity by aliquot parts of the former -standard.</p> - -<p>(119.) If every scientific enquirer observed only -for his own satisfaction, and reasoned only on his -own observations, it would be of little importance -what standards he used, or what contrivances (if -only just ones) he employed for this purpose; but if -it be intended (as it is most important they should) -that observations once made should remain as records -to all mankind, and to all posterity, it is evidently of -the highest consequence that all enquirers should -agree on the use of a common standard, and that -this should be one not liable to change by lapse -of time. The selection and verification of such -standards, however, will easily be understood to be -a matter of extreme difficulty, if only from the mere -circumstance that, to verify the permanence of one -standard, we must compare it with others, which it<span class="pagenum"><a id="Page_126">126</a></span> -is possible may be themselves inaccurate, or, at least, -stand in need of verification.</p> - -<p>(120.) Here we can only call to our assistance -the presumed permanence of the great laws of -Nature, with all experience in its favour, and the -strong impression we have of the general composure -and steadiness of every thing relating to the gigantic -mass we inhabit—“the great globe itself.” In its -uniform rotation on its axis, accordingly, we find a -standard of time, which nothing has ever given us -reason to regard as subject to change, and which, -compared with other periods which the revolutions -of the planets about the sun afford, has demonstrably -undergone none since the earliest history. In the -dimensions of the earth we find a natural unit -of the measure of space, which possesses in perfection -every quality that can be desired; and in -its attraction combined with its rotation the researches -of dynamical science have enabled us, -through the medium of the pendulum, to obtain -another invariable standard, more refined and less -obvious, it is true, in its origin, but possessing a -great advantage in its capability of ready verification, -and therefore easily made to serve as a check on -the other. The former, viz. direct measurement -of the dimensions of the earth, is the origin of -the <i xml:lang="fr" lang="fr">mètre</i>, the French unit of linear measure; the -latter, of the British yard. Theoretically speaking, -they are equally eligible; but when we consider that -the <em>quantity directly measured</em>, in the case of the -mètre, is a length a great many thousand times the -final unit, and in the pendulum or yard very nearly -the unit itself, there can be no hesitation in giving<span class="pagenum"><a id="Page_127">127</a></span> -the preference as an original measure to the former, -because any error committed in the process by -which that is determined becomes subdivided in -the final result; while, on the other hand, any minute -error committed in determining the length of -the pendulum becomes multiplied by the repetition -of the unit in all measurements of considerable -lengths performed in yards.</p> - -<p>(121.) The same admirable invention of the pendulum -affords a means of subdividing time to an -almost unlimited nicety. A clock is nothing more -than a piece of mechanism for counting the oscillations -of a pendulum; and by that peculiar property -of the pendulum, that one vibration commences -exactly where the last terminates, no part of time is -lost or gained in the juxta-position of the units so -counted, so that the precise fractional part of a day -can be ascertained which each such unit measures.</p> - -<p>(122.) It is owing to this peculiar property by -which the <em>juxta-position</em> of units of time and weight -can be performed <em>without error</em>, that the whole of -the accuracy with which time and weight can be -multiplied and subdivided is owing.<a id="FNanchor_36" href="#Footnote_36" class="fnanchor">36</a> The same -thing cannot be accomplished in <em>space</em>, by any method<span class="pagenum"><a id="Page_128">128</a></span> -we are yet acquainted with, so that our means of -subdividing space are much inferior in precision. -The beautiful principle of repetition, invented by -Borda, offers the nearest approach to it, but cannot -be said to be absolutely free from the source of error -in question. The method of “double weighing,” -which we owe to the same distinguished observer, -affords an instance of the direct comparison of two -equal weights independent of almost every source of -error which can affect the comparison of one object -with another. It has been remarked by Biot, that -previous to the invention of this elegant method, instruments -afforded no perfect means of ascertaining -the weight of a body.</p> - -<p>(123.) But it is not enough to possess a standard -of this abstract kind: a real material measure must -be constructed, and exact copies of it taken. This, -however, is not very difficult; the great difficulty is -to preserve it unaltered from age to age; for unless -we transmit to posterity the units of our measurements, -<em>such as we have ourselves used them</em>, we, in -fact, only half bequeath to them our observations. -This is a point too much lost sight of, and it were -much to be wished that some direct provision for -so important an object were made.<a id="FNanchor_37" href="#Footnote_37" class="fnanchor">37</a></p> - -<p><span class="pagenum"><a id="Page_129">129</a></span> -(124.) But, it may be asked, if our measurement of -quantity is thus unavoidably liable to error, how is -it possible that our observations can possess that -quality of numerical veracity which is requisite to -render them the foundation of laws, whose distinguishing -perfection consists in their strict mathematical -expression? To this the reply is twofold. -1st, that though we admit the necessary existence -of numerical error in every observation, we can -always assign a limit which such error cannot possibly -exceed; and the extent of this <em>latitude of error -of observation</em> is less in proportion to the perfection -of the instrumental means we possess, and the care -bestowed on their employment. In the greater part -of modern measurements it is, in point of fact, extremely -minute, and may be still further diminished, -almost to any required extent, by repeating the -measurements a great number of times, and under a -great variety of circumstances, and taking a mean -of the results, when errors of opposite kinds will, at -length, compensate each other. But, 2dly, there<span class="pagenum"><a id="Page_130">130</a></span> -exists a much more fundamental reply to this objection. -In reasoning upon our observations, the -existence and possible amount of quantitative error -is always to be allowed for; and the extent to which -theories may be affected by it is never to be lost -sight of. In reasoning upwards, from observations -confessedly imperfect to general laws, we must -take care always to regard our conclusions as conditional, -so far as they may be affected by such -unavoidable imperfections; and when at length we -shall have arrived at our highest point, and attained -to axioms which admit of general and deductive -reasoning, the question, whether they <em>are</em> vitiated -by the errors of observation or not, will still remain -to be decided, and must become the object of subsequent -verification. This point will be made the -subject of more distinct consideration hereafter, -when we come to speak of the verification of theories -and the laws of probability.</p> - -<p>(125.) With respect to our record of observations, -it should be not only circumstantial but <em>faithful</em>; by -which we mean, that it should contain all we did -<em>observe</em>, and nothing else. Without any intention of -falsifying our record, we may do so unperceived by -ourselves, owing to a mixture of the views and language -of an erroneous theory with that of simple fact. -Thus, for example, if, in describing the effect of -lightning, we should say, “The thunderbolt struck -with violence against the side of the house, and beat -in the wall,” a fact would be stated which we did -not see, and would lead our hearers to believe that a -solid or ponderable projectile was concerned. The -“strong smell of sulphur,” which is sometimes said<span class="pagenum"><a id="Page_131">131</a></span> -to accompany lightning, is a remnant of the theory -which made thunder and lightning the explosion of -a kind of aërial gunpowder, composed of sulphureous -and nitrous exhalations. There are some subjects -particularly infested with this mixture of theory in -the statement of observed fact. The older chemistry -was so overborne by this mischief, as quite -to confound and nullify the descriptions of innumerable -curious and laborious experiments. And in -geology, till a very recent period, it was often extremely -difficult, from this circumstance, to know -what <em>were</em> the facts observed. Thus, Faujas de St. -Fond, in his work on the volcanoes of central -France, describes with every appearance of minute -precision craters existing no where but in his own -imagination. There is no greater fault (direct falsification -of fact excepted) which can be committed -by an observer.</p> - -<p>(126.) When particular branches of science have -acquired that degree of consistency and generality, -which admits of an abstract statement of laws, and -legitimate deductive reasoning, the principle of the -division of labour tends to separate the province of -the observer from that of the theorist. There is no -accounting for the difference of minds or inclinations, -which leads one man to observe with interest -the developements of phenomena, another to -speculate on their causes; but were it not for this -happy disagreement, it may be doubted whether the -higher sciences could ever have attained even their -present degree of perfection. As laws acquire generality, -the influence of individual observations becomes -less, and a higher and higher degree of<span class="pagenum"><a id="Page_132">132</a></span> -refinement in their performance, as well as a great -multiplication in their number, becomes necessary -to give them importance. In astronomy, for instance, -the superior departments of theory are completely -disjoined from the routine of practical observation.</p> - -<p>(127.) To make a perfect observer, however, either -in astronomy or in any other department of science, -an extensive acquaintance is requisite, not only -with the particular science to which his observations -relate, but with every branch of knowledge which -may enable him to appretiate and neutralize the -effect of extraneous disturbing causes. Thus furnished, -he will be prepared to seize on any of those -minute indications, which (such is the subtlety of -nature) often connect phenomena which seem quite -remote from each other. He will have his eyes as -it were opened, that they may be struck at once with -any occurrence which, according to received theories, -ought not to happen; for these are the facts which -serve as clews to new discoveries. The deviation -of the magnetic needle, by the influence of an -electrified wire, must have happened a thousand -times to a perceptible amount, under the eyes of -persons engaged in galvanic experiments, with philosophical -apparatus of all kinds standing around them; -but it required the eye of a philosopher such as -Oërsted to seize the indication, refer it to its origin, -and thereby connect two great branches of science. -The grand discovery of Malus of the polarization -of light by reflection originated in his casual remark -of the disappearance of one of the images of a -window in the Luxembourg palace, one evening,<span class="pagenum"><a id="Page_133">133</a></span> -when strongly illuminated by the setting sun, viewed -through a doubly refracting prism.</p> - -<p>(128.) To avail ourselves as far as possible of the -advantages which a division of labour may afford -for the collection of facts, by the industry and activity -which the general diffusion of information, in -the present age, brings into exercise, is an object of -great importance. There is scarcely any well-informed -person, who, if he has but the will, has -not also the power to add something essential to -the general stock of knowledge, if he will only -observe regularly and methodically some particular -class of facts which may most excite his attention, -or which his situation may best enable him to study -with effect. To instance one or two subjects, -which can only be effectually improved by the -united observations of great numbers widely dispersed:—Meteorology, -one of the most complicated -but important branches of science, is at -the same time one in which any person who will -attend to plain rules, and bestow the necessary -degree of attention, may do effectual service. -What benefits has not Geology reaped from the -activity of industrious individuals, who, setting aside -all theoretical views, have been content to exercise -the useful and highly entertaining occupation of -collecting specimens from the countries which they -visit? In short, there is no branch of science whatever -in which, at least, if useful and sensible -queries were distinctly proposed, an immense mass -of valuable information might not be collected from -those who, in their various lines of life, at home or -abroad, stationary or in travel, would gladly avail<span class="pagenum"><a id="Page_134">134</a></span> -themselves of opportunities of being useful. Nothing -would tend better to attain this end than the -circulation of printed skeleton forms, on various subjects, -which should be so formed as, 1st, to ask distinct -and pertinent questions, admitting of short and -definite answers; 2dly, To call for exact numerical -statement on all principal points; 3dly, To point -out the attendant circumstances most likely to prove -influential, and which ought to be observed; 4thly, -To call for their transmission to a common centre.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_135">135</a></span></p> - -<div class="chapter"> -<h2 id="hdr_10">CHAP. V.</h2> -</div> - -<p class="center b2">OF THE CLASSIFICATION OF NATURAL OBJECTS AND -PHENOMENA, AND OF NOMENCLATURE.</p> - -<p class="in0">(129.) <span class="smcap"><span class="flet">T</span>he</span> number and variety of objects and relations -which the observation of nature brings before -us are so great as to distract the attention, unless -assisted and methodized by such judicious distribution -of them in classes as shall limit our view to -a few at a time, or to groups so bound together by -general resemblances that, for the immediate purpose -for which we consider them, they may be -regarded as individuals. Before we can enter into -any thing which deserves to be called a general and -systematic view of nature, it is necessary that we -should possess an enumeration, if not complete, -at least of considerable extent, of her materials -and combinations; and that those which appear -in any degree important should be distinguished -by names which may not only tend to fix them -in our recollection, but may constitute, as it were, -nuclei or centres, about which information may -collect into masses. The imposition of a name on -any subject of contemplation, be it a material object, -a phenomenon of nature, or a group of facts and relations, -looked upon in a peculiar point of view, is an -epoch in its history of great importance. It not only -enables us readily to refer to it in conversation or -writing, without circumlocution, but, what is of<span class="pagenum"><a id="Page_136">136</a></span> -more consequence, it gives it a recognized existence -in our own minds, as a matter for separate -and peculiar consideration; places it on a list for -examination; and renders it a head or title, under -which information of various descriptions may be -arranged; and, in consequence, fits it to perform the -office of a connecting link between all the subjects -to which such information may refer.</p> - -<p>(130.) For these purposes, however, a temporary -or provisional name, or one adapted for common -parlance, may suffice. But when a very great multitude -of objects come to be referred to one class, -especially of such as do not offer very obvious -and remarkable distinctions, a more systematic -and regular nomenclature becomes necessary, in -which the names shall recall the differences as well -as the resemblances between the individuals of a -class, and in which the direct relation between the -name and the object shall materially assist the solution -of the problem, “<em>given the one, to determine -the other</em>.” How necessary this may become, will -be at once seen, when we consider the immense -number of individual objects, or rather species, -presented by almost every branch of science of any -extent; which absolutely require to be distinguished -by names. Thus, the botanist is conversant with from -80,000 to 100,000 species of plants; the entomologist -with, perhaps, as many, of insects: the chemist -has to register the properties of combinations, by -twos, threes, fours, and upwards, in various doses -of upwards of fifty different elements, all distinguished -from each other by essential differences; -and of which though a great many thousands are<span class="pagenum"><a id="Page_137">137</a></span> -known, by far the greater part have never yet been -formed, although hundreds of new ones are coming -to light, in perpetual succession, as the science advances; -all of which are to be named as they -arise. The objects of astronomy are, literally, as -numerous as the stars of heaven; and although not -more than one or two thousand require to be expressed -by distinct names, yet the number, respecting -which particular information is required, is not -less than a hundred times that amount; and all these -must be registered in lists, (so as to be at once referred -to, and so that none shall escape,) if not by -actual names, at least by some equivalent means.</p> - -<p>(131.) Nomenclature, then, is, in itself, undoubtedly -an important part of science, as it prevents our -being lost in a wilderness of particulars, and involved -in inextricable confusion. Happily, in those great -branches of science where the objects of classification -are most numerous, and the necessity for a -clear and convenient nomenclature most pressing, -no very great difficulty in its establishment is felt. -The very multitude of the objects themselves -affords the power of grouping them in subordinate -classes, sufficiently well defined to admit of names, -and these again into others, whose names may become -attached to, or compounded with, the former, -till at length the particular species is identified. -The facility with which the botanist, the entomologist, -or the chemist, refers by name to any individual -object in his science shows what may be accomplished -in this way when characters are themselves -distinct. In other branches, however, considerable -difficulty is experienced. This arises<span class="pagenum"><a id="Page_138">138</a></span> -mostly where the species to be distinguished are -separated from each other chiefly by difference in -degree, of certain qualities common to all, and -where the degrees shade into each other insensibly. -Perhaps such subjects can hardly be considered -ripe for systematic nomenclature; and that the attempt -to apply it ought only to be partial, embracing -such groups and parcels of individuals as agree -in characters evidently natural and generic, and -leaving the remainder under trivial or provisional -denominations, till they shall be better known, and -capable of being scientifically grouped.</p> - -<p>(132.) Indeed, nomenclature, in a systematic point -of view, is as much, perhaps more, a consequence -than a cause of extended knowledge. Any one -may give an arbitrary name to a thing, merely to -be able to talk of it; but, to give a name which -shall at once refer it to a place in a system, we -must know its properties; and we must <em>have</em> a -system, large enough, and regular enough, to receive -it in a place which belongs to it, and to no other. -It appears, therefore, doubtful whether it is desirable, -for the essential purposes of science, that -extreme refinement in systematic nomenclature -should be insisted on. Were science perfect, indeed, -systems of classification might be agreed -on, which should assign to every object in nature -a place in some class, to which it more remarkably -and pre-eminently belonged than to any other, and -under which it might acquire a name, never afterwards -subject to change. But, so long as this is not -the case, and new relations are daily discovered, -we must be very cautious how we insist strongly<span class="pagenum"><a id="Page_139">139</a></span> -on the establishment and extension of classes -which have in them any thing artificial, as a basis -of a rigid nomenclature; and especially how we -mistake the means for the end, and sacrifice convenience -and distinctness to a rage for arrangement. -Every nomenclature dependent on artificial classifications -is necessarily subject to fluctuations; and -hardly any thing can counterbalance the evil of -disturbing well-established names, which have once -acquired a general circulation. In nature, one and -the same object makes a part of an infinite number -of different systems,—an individual in an infinite -number of groups, some of greater, some of less -importance, according to the different points of view -in which they may be considered. Hence, as many -different systems of nomenclature may be imagined -as there can be discovered different heads of -classification, while yet it is highly desirable that -each object should be universally spoken of under -one name, <em>if possible</em>. Consequently, in all subjects -where comprehensive heads of classification do not -prominently offer themselves, all nomenclature must -be a balance of difficulties, and a good, short, <em>unmeaning</em> -name, which has once obtained a footing in -usage, is preferable to almost any other.</p> - -<p>(133.) There is no science in which the evils resulting -from a rage for nomenclature have been felt -to such an extent as in mineralogy. The number -of simple minerals actually recognised by mineralogists -does not exceed a few hundreds, yet there -is scarcely one which has not four or five names -in different books. The consequence is most unhappy. -No name is suffered to endure long enough<span class="pagenum"><a id="Page_140">140</a></span> -to take root; and every new writer on this interesting -science begins, as a matter of course, by -making a <i xml:lang="la" lang="la">tabula rasa</i> of all former nomenclature, -and proposing a new one in its place. The climax -has at length been put to this most inconvenient -and bewildering state of things by the appearance -of a system supported by extraordinary merit in -other respects, and therefore carrying the highest -authority, in which names which had acquired -universal circulation, and had hitherto maintained -their ground in the midst of the general confusion, -and even worked their way into common language, -as denotive of <em>species</em> too definite to admit of mistake, -are actually rendered <em>generic</em>, and extended to -whole groups, comprising objects agreeing in nothing -but the arbitrary heads of a classification from which -the most important natural relations are professedly -and purposely rejected.<a id="FNanchor_38" href="#Footnote_38" class="fnanchor">38</a></p> - -<p>(134.) The classifications by which science is advanced, -however, are widely different from those -which serve as bases for artificial systems of nomenclature. -They cross and intersect one another, as it -were, in every possible way, and have for their very -aim to interweave all the objects of nature in a close -and compact web of mutual relations and dependence. -As soon, then, as any resemblance or analogy, any -point of agreement whatever, is perceived between -any two or more things,—be they what they will, -whether objects, or phenomena, or laws,—they immediately<span class="pagenum"><a id="Page_141">141</a></span> -and <i xml:lang="la" lang="la">ipso facto</i> constitute themselves into -a group or class, which may become enlarged to any -extent by the accession of such new objects, phenomena, -or laws, agreeing in the same point, as may -come to be subsequently ascertained. It is thus that -the materials of the world become grouped in natural -families, such as chemistry furnishes examples of, -in its various groups of acids, alkalies, sulphurets, &c.; -or botany, in its euphorbiaceæ, umbelliferæ, &c. -It is thus, too, that phenomena assume their places -under general points of resemblance; as, in optics, -those which refer themselves to the class of periodic -colours, double refraction, &c.; and that resemblances -themselves become traced, which it is the -business of induction to generalize and include in -abstract propositions.</p> - -<p>(135.) But every class formed on a positive resemblance -of characters, or on a distinct analogy, draws -with it the consideration of a negative class, in which -that resemblance either does not subsist at all, or the -contrary takes place; and again, there are classes in -which a given quality is possessed by the different -individuals in a descending scale of intensity. -Now, it is of consequence to distinguish between -cases in which there is a real opposition of quality, -or a mere diminution of intensity, in some quality -susceptible of degrees, till it becomes imperceptible. -For example, between transparency and -opacity there would at first sight appear a direct -opposition; but, on nearer consideration, when we -consider the gradations by which transparency diminishes -in natural substances, we shall see reason -to admit that the latter quality, instead of being the<span class="pagenum"><a id="Page_142">142</a></span> -<em>opposite</em> of the former, is only its <em>extreme lowest -degree</em>. Again, in the arrangement of natural objects -under the head of weight or specific gravity, the -scale extends through all nature, and we know of no -natural body in which the opposite of gravity, or -positive <em>levity</em>, subsists. On the other hand, the -opposite electricities; the north and south magnetic -polarities; the alkaline and acid qualities of -chemical agents; the positive and negative rotations -impressed by plates of rock crystal on the planes of -polarization of the rays of light, and many other -cases, exemplify not merely a negation, but an active -opposition of quality. Both these modes of classification -have their peculiar importance in the inductive -process: the one, as affording an opportunity of -tracing a relation between phenomena by the observation -of a correspondence in their scales of intensity; -the other, by that of contrast, as we shall show more -at large in the next section.</p> - -<p>(136.) There is a very wide distinction, too, to be -taken between such classes as turn upon a single -head of resemblance among individuals otherwise -very different, and such as bind together in natural -groups, by a great variety of analogies, objects -which yet differ in many remarkable particulars. -For example: if we make colourless transparency -a head of classification, the list of the class will -comprise objects differing most widely in their -nature, such as water, air, diamond, spirit of wine, -glass, &c. On the other hand, the chemical families -of alkalies, metals, &c. are instances of groups of -the other kind; which, with properties in many -respects different, still agree in a general resemblance<span class="pagenum"><a id="Page_143">143</a></span> -of several others, which at once decides -us in considering them as having a natural relation. -In the former cases, our ingenuity is exercised to determine -what can be the cause of their resemblance, -in the latter, of their difference; the former belong -to the province of inductive generalization, and -afford the most instructive cases for the investigation -of causes; the latter appertain to the more -secret recesses of nature; the very existence of such -families being in itself one of the great and complicated -phenomena of the universe, which we cannot -hope to unriddle without an intimate and extensive -acquaintance with the highest laws.<a id="FNanchor_39" href="#Footnote_39" class="fnanchor">39</a></p> - -<hr /> - -<p><span class="pagenum"><a id="Page_144">144</a></span></p> - -<div class="chapter"> -<h2 id="hdr_11">CHAP. VI.</h2> -</div> - -<blockquote class="hang"> - -<p class="center b2">OF THE FIRST STAGE OF INDUCTION.—THE DISCOVERY -OF PROXIMATE CAUSES, AND LAWS OF THE LOWEST -DEGREE OF GENERALITY, AND THEIR VERIFICATION.</p></blockquote> - -<p class="in0">(137.) <span class="smcap"><span class="flet">T</span>he</span> first thing that a philosophic mind -considers, when any new phenomenon presents -itself, is its <em>explanation</em>, or reference to an immediate -producing cause. If that cannot be ascertained, -the next is to <em>generalize</em> the phenomenon, -and include it, with others analogous to it, in the -expression of some law, in the hope that its consideration, -in a more advanced state of knowledge, -may lead to the discovery of an adequate proximate -cause.</p> - -<p>(138.) Experience having shown us the manner -in which one phenomenon depends on another in a -great variety of cases, we find ourselves provided, -as science extends, with a continually increasing -stock of such antecedent phenomena, or causes -(meaning at present merely proximate causes), -competent, under different modifications, to the -production of a great multitude of effects, besides -those which originally led to a knowledge of them. -To such causes Newton has applied the term <i xml:lang="la" lang="la">veræ -causæ</i>; that is, causes recognized as having a real existence -in nature, and not being mere hypotheses or -figments of the mind. To exemplify the distinction:—The -phenomenon of shells found in rocks, at<span class="pagenum"><a id="Page_145">145</a></span> -a great height above the sea, has been attributed -to several causes. By some it has been ascribed -to a plastic virtue in the soil; by some, to fermentation; -by some, to the influence of the celestial -bodies; by some, to the casual passage of pilgrims -with their scallops; by some, to birds feeding on -shell-fish; and by all modern geologists, with one -consent, to the life and death of real mollusca -at the bottom of the sea, and a subsequent -alteration of the relative level of the land and -sea. Of these, the plastic virtue and celestial -influence belong to the class of figments of fancy. -Casual transport by pilgrims is a real cause, and -might account for a few shells here and there -dropped on frequented passes, but is not extensive -enough for the purpose of explanation. Fermentation, -generally, is a real cause, so far as that -there <em>is such a thing</em>; but it is not a real cause -of the production of a shell in a rock, since no -such thing was ever witnessed as one of its effects, -and rocks and stones do not ferment. On the other -hand, for a shell-fish dying at the bottom of the -sea to leave his shell in the mud, where it becomes -silted over and imbedded, happens daily; and the -elevation of the bottom of the sea to become dry -land has really been witnessed so often, and on such -a scale, as to qualify it for a <i xml:lang="la" lang="la">vera causa</i> available in -sound philosophy.</p> - -<p>(139.) To take another instance, likewise drawn -from the same deservedly popular science:—The -fact of a great change in the general climate of -large tracts of the globe, if not of the whole earth, -and of a diminution of general temperature, having<span class="pagenum"><a id="Page_146">146</a></span> -been recognised by geologists, from their examination -of the remains of animals and vegetables of -former ages enclosed in the strata, various causes -for such diminution of temperature have been assigned. -Some consider the whole globe as having -gradually cooled from absolute fusion; some regard -the immensely superior activity of former volcanoes, -and consequent more copious communication of internal -heat to the surface, in former ages, as the -cause. Neither of these can be regarded as real -causes in the sense here intended; for we do not -<em>know</em> that the globe has so cooled from fusion, nor -are we sure that such supposed greater activity of -former than of present volcanoes really did exist. -A cause, possessing the essential requisites of a -<i xml:lang="la" lang="la">vera causa</i>, has, however, been brought forward<a id="FNanchor_40" href="#Footnote_40" class="fnanchor">40</a> -in the varying influence of the distribution of land<span class="pagenum"><a id="Page_147">147</a></span> -and sea over the surface of the globe: a change of -such distribution, in the lapse of ages, by the degradation -of the old continents, and the elevation of -new, being a demonstrated fact; and the influence -of such a change on the climates of particular regions, -if not of the whole globe, being a perfectly -fair conclusion, from what we know of continental, -insular, and oceanic climates by actual observation. -Here, then, we have, at least, a cause on which a -philosopher may consent to reason; though, whether -the changes actually going on are such as to warrant -the whole extent of the conclusion, or are even -taking place in the right direction, may be considered -as undecided till the matter has been more -thoroughly examined.</p> - -<p>(140.) To this we may add another, which -has likewise the essential characters of a <i xml:lang="la" lang="la">vera -causa</i>, in the astronomical <em>fact</em> of the actual slow -diminution of the eccentricity of the earth’s orbit -round the sun; and which, as a general one, affecting -the <em>mean temperature of the whole globe</em>, and -as one of which the effect is both inevitable, and -susceptible, to a certain degree, of exact estimation, -deserves consideration. It is evident that the -<em>mean</em> temperature of the whole surface of the -globe, in so far as it is maintained by the action -of the sun at a higher degree than it would have -were the sun extinguished, must depend on the -mean quantity of the sun’s rays which it receives, or, -which comes to the same thing, on the <em>total</em> quantity -received in a given invariable time: and the length -of the year being unchangeable in all the fluctuations -of the planetary system, it follows, that the<span class="pagenum"><a id="Page_148">148</a></span> -total <em>annual</em> amount of solar radiation will determine, -<i xml:lang="la" lang="la">cæteris paribus</i>, the general climate of the -earth. Now, it is not difficult to show that this -amount is inversely proportional to the minor axis -of the ellipse described by the earth about the -sun, regarded as slowly variable; and that, therefore, -the major axis remaining, as we know it to be, -constant, and the orbit being actually in a state of -approach to a circle, and, consequently, the minor -axis being on the <em>increase</em>, the mean annual amount -of solar radiation received by the whole earth must -be actually on the <em>decrease</em>. We have here, therefore, -an evident real cause, of sufficient universality, -and acting <em>in the right direction</em>, to account -for the phenomenon. Its adequacy is another -consideration.<a id="FNanchor_41" href="#Footnote_41" class="fnanchor">41</a></p> - -<p>(141.) Whenever, therefore, any phenomenon presents -itself for explanation, we naturally seek, in -the first instance, to refer it to some one or other -of those real causes which experience has shown to -exist, and to be efficacious in producing similar -phenomena. In this attempt our probability of -success will, of course, mainly depend, 1st, On the -number and variety of causes experience has placed -at our disposal; 2dly, On our habit of applying them -to the explanation of natural phenomena; and, 3dly, -On the number of analogous phenomena we can -collect, which have either been explained, or which -admit of explanation by some one or other of those -causes, and the closeness of their analogy with that -in question.</p> - -<p><span class="pagenum"><a id="Page_149">149</a></span> -(142.) Here, then, we see the great importance -of possessing a stock of analogous instances or phenomena -which class themselves with that under -consideration, the explanation of one among which -may naturally be expected to lead to that of all -the rest. If the analogy of two phenomena be -very close and striking, while, at the same time, the -cause of one is very obvious, it becomes scarcely -possible to refuse to admit the action of an analogous -cause in the other, though not so obvious in itself. -For instance, when we see a stone whirled round in -a sling, describing a circular orbit round the hand, -keeping the string stretched, and flying away the -moment it breaks, we never hesitate to regard it as -retained in its orbit by the tension of the string, -that is, by <em>a force</em> directed to the centre; for we -feel that we do really exert such a force. We have -here <em>the direct perception</em> of the cause. When, -therefore, we see a great body like the moon circulating -round the earth and not flying off, we -cannot help believing it to be prevented from so -doing, not indeed by a material tie, but by that -which operates in the other case through the intermedium -of the string,—a <em>force</em> directed constantly -to the centre. It is thus that we are continually -acquiring a knowledge of the existence -of causes acting under circumstances of such concealment -as effectually to prevent their direct discovery.</p> - -<p>(143.) In general we must observe that motion, -wherever produced or changed, invariably points -out the existence of <em>force</em> as its cause; and thus -the forces of nature become known and measured<span class="pagenum"><a id="Page_150">150</a></span> -by the motions they produce. Thus, the <em>force</em> of -magnetism becomes known by the deviation produced -by iron in a compass needle, or by a needle -leaping up to a magnet held over it, as certainly as -by that adhesion to it, when in contact and at rest, -which requires force to break the connection; and -thus the currents produced in the surface of a quantity -of quicksilver, electrified under a conducting -fluid, have pointed out the existence and direction -of forces of enormous intensity developed by the -electric circuit, of which we should not otherwise -have had the least suspicion.<a id="FNanchor_42" href="#Footnote_42" class="fnanchor">42</a></p> - -<p>(144.) But when the cause of a phenomenon neither -presents itself obviously on the consideration of -the phenomenon itself, nor is as it were forced on -our attention by a case of strong analogy, such as -above described, we have then no resource but in -a deliberate assemblage of all the parallel instances -we can muster; that is, to the formation of a class -of facts, having the phenomenon in question for a -head of classification; and to a search among the -individuals of this class for some other common -points of agreement, among which the cause will -of necessity be found. But if more than one cause -should appear, we must then endeavour to find, or, if -we cannot find, to <em>produce, new facts</em>, in which each of -these in succession shall be wanting, while yet they -agree in the general point in question. Here we -find the use of what Bacon terms “<em>crucial instances</em>,” -which are phenomena brought forward to decide -between two causes, each having the same analogies -in its favour. And here, too, we perceive the utility<span class="pagenum"><a id="Page_151">151</a></span> -of <em>experiment</em> as distinguished from mere passive -observation. We make an experiment of the crucial -kind when we form combinations, and put in -action causes from which some particular one shall -be deliberately excluded, and some other purposely -admitted; and by the agreement or disagreement -of the resulting phenomena with those of the class -under examination, we decide our judgment.</p> - -<p>(145.) When we would lay down general rules -for guiding and facilitating our search, among a -great mass of assembled facts, for their common -cause, we must have regard to the characters of -that relation which we intend by cause and effect. -Now, these <span class="locked">are,—</span></p> - -<blockquote class="hang"> - -<p>1st, Invariable connection, and, in particular, invariable -antecedence of the cause and consequence -of the effect, unless prevented by some -counteracting cause. But it must be observed, -that, in a great number of natural phenomena, -the effect is produced gradually, while the cause -often goes on increasing in intensity; so that -the antecedence of the one and consequence of -the other becomes difficult to trace, though it -really exists. On the other hand, the effect -often follows the cause so instantaneously, that -the interval cannot be perceived. In consequence -of this, it is sometimes difficult to decide, -of two phenomena constantly accompanying one -another, which is cause or which effect.</p> - -<p>2d, Invariable negation of the effect with absence -of the cause, unless some other cause be capable -of producing the same effect.</p> - -<p>3d, Increase or diminution of the effect, with<span class="pagenum"><a id="Page_152">152</a></span> -the increased or diminished intensity of the -cause, in cases which admit of increase and diminution.</p> - -<p>4th, Proportionality of the effect to its cause in -all cases of <em>direct unimpeded</em> action.</p> - -<p>5th, Reversal of the effect with that of the cause.</p></blockquote> - -<p>(146.) From these characters we are led to the -following observations, which may be considered as -so many propositions readily applicable to particular -cases, or rules of philosophizing: we conclude, -1st, That if in our group of facts there be one in -which any assigned peculiarity, or attendant circumstance, -is wanting or opposite, such peculiarity -cannot be the cause we seek.</p> - -<p>(147.) 2d, That any circumstance in which all -the facts without exception agree, <em>may</em> be the -cause in question, or, if not, at least a collateral -effect of the same cause: if there be but one -such point of agreement, this possibility becomes a -certainty; and, on the other hand, if there be more -than one, they may be concurrent causes.</p> - -<p id="p148">(148.) 3d, That we are not to deny the existence -of a cause in favour of which we have a unanimous -agreement of strong analogies, though it may not be -apparent how such a cause can produce the effect, -or even though it may be difficult to conceive its -existence under the circumstances of the case; in -such cases we should rather appeal to experience -when possible, than decide <i xml:lang="la" lang="la">à priori</i> against the cause, -and try whether it cannot be made apparent.</p> - -<p>(149.) For instance: seeing the sun vividly luminous, -every analogy leads us to conclude it intensely -hot. How heat can produce light, we know not;<span class="pagenum"><a id="Page_153">153</a></span> -and how such a heat can be maintained, we can -form no conception. Yet we are not, therefore, -entitled to deny the inference.</p> - -<p>(150.) 4th, That contrary or opposing facts are -equally instructive for the discovery of causes with -favourable ones.</p> - -<p>(151.) For instance: when air is confined with -moistened iron filings in a close vessel over water, -its bulk is diminished, by a certain portion of it -being abstracted and combining with the iron, producing -<em>rust</em>. And, if the remainder be examined, -it is found that it will <em>not</em> support flame or animal -life. This contrary fact shows that the cause of the -support of flame and animal life is to be looked for -in that part of the air which the iron abstracts, and -which rusts it.</p> - -<p>(152.) 5th, That causes will very frequently become -obvious, by a mere arrangement of our facts in -the order of intensity in which some peculiar quality -subsists; though not of necessity, because counteracting -or modifying causes may be at the same -time in action.</p> - -<p id="p153">(153.) For example: sound consists in impulses -communicated to our ears by the air. If a series of -impulses of equal force be communicated to it at -equal intervals of time, at first in slow succession, -and by degrees more and more rapidly, we hear at -first a rattling noise, then a low murmur, and then a -hum, which by degrees acquires the character of a -musical note, rising higher and higher in acuteness, till -its pitch becomes too high for the ear to follow. And -from this correspondence between the pitch of the -note and the rapidity of succession of the impulse, we<span class="pagenum"><a id="Page_154">154</a></span> -conclude that our sensation of the different pitches -of musical notes originates in the different rapidities -with which their impulses are communicated to our -ears.</p> - -<p>(154.) 6th, That such counteracting or modifying -causes may subsist unperceived, and annul the -effects of the cause we seek, in instances which, -but for their action, would have come into our class -of favourable facts; and that, therefore, exceptions -may often be made to disappear by removing or -allowing for such counteracting causes. This remark -becomes of the greatest importance, when (as is -often the case) a single striking exception stands -out, as it were, against an otherwise unanimous array -of facts in favour of a certain cause.</p> - -<p>(155.) Thus, in chemistry, the <em>alkaline</em> quality of -the alkaline and earthy bases is found to be due to -the presence of oxygen combined with one or other -of a peculiar set of metals. Ammonia is, however, -a violent outstanding exception, such as here alluded -to, being a compound of azote and hydrogen: but -there are almost certain indications that this exception -is not a real one, but assumes that appearance -in consequence of some modifying cause not understood.</p> - -<p>(156.) 7th, If we can either find produced by -nature, or produce designedly for ourselves, two instances -which agree <em>exactly</em> in all but one particular, -and differ in that one, its influence in producing -the phenomenon, if it have any, <em>must</em> thereby be -rendered sensible. If that particular be present -in one instance and wanting altogether in the -other, the production or non-production of the phenomenon<span class="pagenum"><a id="Page_155">155</a></span> -will decide whether it be or be not the -only cause: still more evidently, if it be present -<em>contrariwise</em> in the two cases, and the effect be -thereby reversed. But if its total presence or -absence only produces a change in the <em>degree</em> or -intensity of the phenomenon, we can then only -conclude that it acts as a concurrent cause or -condition with some other to be sought elsewhere. -In nature, it is comparatively rare to find instances -pointedly differing in one circumstance and agreeing -in every other; but when we call experiment to -our aid, it is easy to produce them; and this is, in -fact, the grand application of <em>experiments of enquiry</em> -in physical researches. They become more valuable, -and their results clearer, in proportion as they possess -this quality (of agreeing exactly in all their -circumstances but one), since the question put to -nature becomes thereby more pointed, and its answer -more decisive.</p> - -<p>(157.) 8th, If we cannot obtain a complete negative -or opposition of the circumstance whose influence -we would ascertain, we must endeavour to -find cases where it varies considerably in degree. -If <em>this</em> cannot be done, we may perhaps be able to -weaken or exalt its influence by the introduction of -some fresh circumstance, which, abstractedly considered, -seems <em>likely</em> to produce this effect, and thus -obtain indirect evidence of its influence. But then -we are always to remember, that the evidence so -obtained <em>is</em> indirect, and that the new circumstance -introduced <em>may</em> have a direct influence of its own, -or may exercise a modifying one on some <em>other</em> -circumstance.</p> - -<p><span class="pagenum"><a id="Page_156">156</a></span> -(158.) 9th, Complicated phenomena, in which -several causes concurring, opposing, or quite independent -of each other, operate at once, so as -to produce a compound effect, may be simplified by -subducting the effect of all the known causes, as -well as the nature of the case permits, either by -deductive reasoning or by appeal to experience, and -thus leaving, as it were, a <em>residual phenomenon</em> to be -explained. It is by this process, in fact, that -science, in its present advanced state, is chiefly promoted. -Most of the phenomena which nature presents -are very complicated; and when the effects of -all known causes are estimated with exactness, and -subducted, the residual facts are constantly appearing -in the form of phenomena altogether new, and -leading to the most important conclusions.</p> - -<p>(159.) For example: the return of the comet predicted -by professor Encke, a great many times in -succession, and the general good agreement of its -calculated with its observed place during any one -of its periods of visibility, would lead us to say that its -gravitation towards the sun and planets is the sole -and sufficient cause of all the phenomena of its -orbitual motion; but when the effect of this cause -is strictly calculated and subducted from the observed -motion, there is found to remain behind a -<em>residual phenomenon</em>, which would never have been -otherwise ascertained to exist, which is a small -anticipation of the time of its reappearances or a -diminution of its periodic time, which cannot be -accounted for by gravity, and whose cause is therefore -to be enquired into. Such an anticipation -would be caused by the resistance of a medium disseminated<span class="pagenum"><a id="Page_157">157</a></span> -through the celestial regions; and as -there are other good reasons for believing this to -be a <i xml:lang="la" lang="la">vera causa</i>, it has therefore been ascribed to -such a resistance.</p> - -<p>(160.) This 9th observation is of such importance -in science, that we shall exemplify it by another -instance or two. M. Arago, having suspended -a magnetic needle by a silk thread, and set it -in vibration, observed, that it came much sooner -to a state of rest when suspended over a plate of -copper, than when no such plate was beneath -it. Now, in both cases there were two <i xml:lang="la" lang="la">veræ -causæ</i> why it <em>should</em> come at length to rest, viz. the -resistance of the air, which opposes, and at length -destroys, all motions performed in it; and the want -of perfect mobility in the silk thread. But the -effect of these causes being exactly known by the -observation made in the absence of the copper, and -being thus allowed for and subducted, a <em>residual</em> -phenomenon appeared, in the fact that a retarding -influence was exerted by the copper itself; and this -fact, once ascertained, speedily led to the knowledge -of an entirely new and unexpected class of relations. -To add one more instance. If it be true (as M. -Fourrier considers it demonstrated to be) that the -celestial regions have a temperature independent -of the sun, not greatly inferior to that at which -quicksilver congeals, and much superior to some degrees -of cold which have been artificially produced, -two causes suggest themselves: one is that assigned -by the author above mentioned; the radiation of the -stars; another may be proposed in the ether or elastic -medium mentioned in the last section, which the<span class="pagenum"><a id="Page_158">158</a></span> -phenomena of light and the resistance of comets -give us reason to believe fills all space, and which, -in analogy to all the elastic media known, may be -supposed to possess a temperature and a specific -heat of its own, which it is capable of communicating -to bodies surrounded by it. Now, if we -consider that the heat radiated by the sun follows -the same proportion as its light, and regard it as -reasonable to admit with respect to stellar heat -what holds good of solar; the effect of stellar radiation -in maintaining a temperature in space should -be as much inferior to that of the radiation of the -sun as the light of a moonless midnight is to that -of an equatorial noon; that is to say, almost inconceivably -smaller. Allowing, then, the full effect -for this cause, there would still remain a great -residuum due to the presence of the ether.</p> - -<p>(161.) Many of the new elements of chemistry -have been detected in the investigation of <em>residual -phenomena</em>. Thus, Arfwedson discovered lithia by -perceiving an <em>excess of weight</em> in the sulphate produced -from a small portion of what he considered as -magnesia present in a mineral he had analysed. It -is on this principle, too, that the <em>small concentrated -residues of great operations</em> in the arts are almost sure -to be the lurking places of new chemical ingredients: -witness iodine, brome, selenium, and the new metals -accompanying platina in the experiments of Wollaston -and Tennant. It was a happy thought of -Glauber to examine what every body else threw -away.</p> - -<p>(162.) Finally, we have to observe, that the detection -of a <em>possible</em> cause, by the comparison of<span class="pagenum"><a id="Page_159">159</a></span> -assembled cases, <em>must</em> lead to one of two things: -either, 1st, The detection of a real cause, and of its -manner of acting, so as to furnish a complete explanation -of the facts; or, 2dly, The establishment -of an abstract law of nature, pointing out two phenomena -of a general kind as invariably connected; -and asserting, that where one is, there the other -will always be found. Such invariable connection -is itself a phenomenon of a higher order than any -particular fact; and when many such are discovered, -we may again proceed to classify, combine, and -examine them, with a view to the detection of <em>their</em> -causes, or the discovery of still more general laws, -and so on without end.</p> - -<p>(163.) Let us now exemplify this inductive search -for a cause by one general example: suppose <em>dew</em> -were the phenomenon proposed, whose cause we -would know. In the first place, we must separate -dew from rain and the moisture of fogs, and limit the -application of the term to what is really meant, -which is, the spontaneous appearance of moisture on -substances exposed in the open air when no rain or -<em>visible</em> wet is falling. Now, here we have analogous -phenomena in the moisture which bedews a cold -metal or stone when we breathe upon it; that which -appears on a glass of water fresh from the well in hot -weather; that which appears on the <em>inside</em> of windows -when sudden rain or hail chills the external air; that -which runs down our walls when, after a long frost, a -warm moist thaw comes on: all these instances -agree in one point (Rule 2. § 147.), the coldness of -the object dewed, in comparison with the air in -contact with it.</p> - -<p><span class="pagenum"><a id="Page_160">160</a></span> -(164.) But, in the case of the night dew, is this a -<em>real cause</em>—is it a fact that the object dewed <em>is</em> colder -than the air? Certainly not, one would at first be -inclined to say; for what is to <em>make</em> it so? But the -analogies are cogent and unanimous; and, therefore, -(pursuant to Rule 3. § 148.) we are not to discard their -indications; and, besides, the experiment is easy: we -have only to lay a thermometer in contact with the -dewed substance, and hang one at a little distance -above it out of reach of its influence. The experiment -has been therefore made; the question has -been asked, and the answer has been invariably in the -<em>affirmative</em>. Whenever an object contracts dew, <em>it is</em> -colder than the air. Here, then, we have <em>an invariable -concomitant</em> circumstance: but is this chill an -effect of dew, or its cause? That dews are accompanied -with a chill is a common remark; but vulgar -prejudice would make the cold the <em>effect</em> rather -than the cause. We must, therefore, collect more -facts, or, which comes to the same thing, vary the -circumstances; since every instance in which the -circumstances differ is a fresh fact; and, especially, -we must note the contrary or negative cases (Rule -4. § 150.), <i xml:lang="la" lang="la">i. e.</i> where no dew is produced.</p> - -<p>(165.) Now, 1st, no dew is produced on the surface -of <em>polished metals</em>, but it is very copiously on -glass, both exposed with their faces upwards, and -in some cases the under side of a horizontal plate of -glass is also dewed; which last circumstance (by -Rule 1. § 146.) excludes the <em>fall</em> of moisture from -the sky in an invisible form, which would naturally -suggest itself as a cause. In the cases of -polished metal and polished glass, the contrast<span class="pagenum"><a id="Page_161">161</a></span> -shows evidently that the <em>substance</em> has much to do -with the phenomenon; therefore, let the substance -<em>alone</em> be diversified as much as possible, by exposing -polished surfaces of various kinds. This done, <em>a -scale of intensity</em> becomes obvious (Rule 5. § 152.). -Those polished substances are found to be most -strongly dewed which conduct heat worst; while -those which conduct well resist dew most effectually. -Here we encounter a <em>law</em> of the first degree of generality. -But, if we expose rough surfaces, instead of -polished, we sometimes find this law interfered with -(Rule 5. § 152.). Thus, roughened iron, especially if -painted over or blackened, becomes dewed sooner -than varnished paper: the kind of <em>surface</em> therefore -has a great influence. Expose, then, the <em>same</em> material -in very diversified states as to surface (Rule 7. -§ 156.), and another scale of intensity becomes at once -apparent; those <em>surfaces</em> which <em>part with their heat</em> -most readily by radiation are found to contract -dew most copiously: and thus we have detected -another law of the same generality with the former, -by a comparison of two classes of facts, one relating -to dew, the other to the radiation of heat from -surfaces. Again, the influence ascertained to exist -of <em>substance</em> and <em>surface</em> leads us to consider that of -<em>texture</em>: and here, again, we are presented on trial -with remarkable differences, and with a third <em>scale -of intensity</em>, pointing out substances of a close firm -texture, such as stones, metals, &c. as unfavourable, -but those of a loose one, as cloth, wool, velvet, -eiderdown, cotton, &c. as eminently favourable, to -the contraction of dew: and these are precisely those -which are best adapted for clothing, or for impeding<span class="pagenum"><a id="Page_162">162</a></span> -the free passage of heat from the skin into the air, -so as to allow their outer surfaces to be very cold -while they remain warm within.</p> - -<p>(166.) Lastly, among the negative instances, -(§ 150.) it is observed, that dew is never copiously -deposited in situations much screened from the open -sky, and not at all in <em>a cloudy night</em>; but if the -clouds withdraw, even for a few minutes, and leave -a clear opening, a deposition of dew presently begins, -and goes on increasing. Here, then, a cause is distinctly -pointed out by its antecedence to the effect -in question (§ 145.). A clear view of the cloudless -sky, then, is an essential condition, or, which comes -to the same thing, clouds or surrounding objects act -as <em>opposing causes</em>. This is so much the case, that -dew formed in clear intervals will often even evaporate -again when the sky becomes thickly overcast -(Rule 4. § 150.).</p> - -<p id="p167">(167.) When we now come to assemble these partial -inductions so as to raise from them a general conclusion, -we consider, 1st, That all the conclusions we -have come to have a reference to that first general -fact—the cooling of the exposed surface of the body -dewed below the temperature of the air. Those -surfaces which part with their heat outwards most -readily, and have it supplied from within most -slowly, will, of course, become coldest if there be an -opportunity for their heat to escape, and not be -restored to them from without. Now, a clear sky affords -such an opportunity. It is a law well known -to those who are conversant with the nature of heat, -that heat is constantly escaping from <em>all bodies</em> in -rays, or by <em>radiation</em>, but is as constantly restored<span class="pagenum"><a id="Page_163">163</a></span> -to them by the similar radiation of others surrounding -them. Clouds and surrounding objects therefore -act as opposing causes by replacing the whole or a -great part of the heat so radiated away, which can -escape effectually, without being replaced, only -through openings into infinite space. Thus, at -length, we arrive at the general proximate cause of -dew, in the cooling of the dewed surface by radiation -faster than its heat can be restored to it, -by communication with the ground, or by counter-radiation; -so as to become colder than the air, and -thereby to cause a condensation of its moisture.</p> - -<p>(168.) We have purposely selected this theory -of dew, first developed by the late Dr. Wells, as one -of the most beautiful specimens we can call to mind -of inductive experimental enquiry lying within a -moderate compass. It is not possible in so brief a -space to do it justice; but we earnestly recommend -his work<a id="FNanchor_43" href="#Footnote_43" class="fnanchor">43</a> (a short and very entertaining one) for -perusal to the student of natural philosophy, as a -model with which he will do well to become familiar.</p> - -<p>(169.) In the analysis above given, the formation -of dew is referred to two more general phenomena; -the radiation of heat, and the condensation of invisible -vapour by cold. The cause of the former -is a much higher enquiry, and may be said, indeed, -to be totally unknown; that of the latter actually -forms a most important branch of physical enquiry. -In such a case, when we reason upwards till we reach -an ultimate fact, we regard a phenomenon as fully explained; -as we consider the branch of a tree to<span class="pagenum"><a id="Page_164">164</a></span> -terminate when traced to its insertion in the trunk, -or a twig to its junction with the branch; or rather, -as a rivulet retains its importance and its name till -lost in some larger tributary, or in the main river -which delivers it into the ocean. This, however, always -supposes that, on a reconsideration of the case, -we see clearly how the admission of such a fact, -with all its attendant laws, will perfectly account -for <em>every particular</em>—as well those which, in the different -stages of the induction, have led us to a knowledge -of it, as those which we had neglected, or -considered less minutely than the rest. But, had -we no previous knowledge of the radiation of heat, -this same induction would have made it known to -us, and, duly considered, might have led to the -knowledge of many of its laws.</p> - -<p>(170.) In the study of nature, we must not, -therefore, be scrupulous as to <em>how</em> we reach to a -knowledge of such general facts: provided only -we verify them carefully when once detected, we -must be content to seize them wherever they are to -be found. And this brings us to consider the <em>verification</em> -of inductions.</p> - -<p id="p171">(171.) If, in our induction, every individual case -has actually been present to our minds, we are sure -that it will find itself duly <em>represented</em> in our final conclusion: -but this is impossible for such cases as -were <em>unknown</em> to us, and hardly ever happens even -with all the known cases; for such is the tendency -of the human mind to speculation, that on the least -idea of an analogy between a few phenomena, it -leaps forward, as it were, to a cause or law, to the -temporary neglect of all the rest; so that, in fact,<span class="pagenum"><a id="Page_165">165</a></span> -almost all our principal inductions must be regarded -as a series of ascents and descents, and of conclusions -from a few cases, verified by trial on many.</p> - -<p>(172.) Whenever, therefore, we think we have -been led by induction to the knowledge of the proximate -cause of a phenomenon or of a law of nature, our -next business is to examine deliberately and <i xml:lang="la" lang="la">seriatim</i> -all the cases we have collected of its occurrence, in -order to satisfy ourselves that they are explicable -by our cause, or fairly included in the expression -of our law: and in case any exception occurs, it must -be carefully noted and set aside for re-examination -at a more advanced period, when, possibly, the cause -of exception may appear, and the exception itself, -by allowing for the effect of that cause, be brought -over to the side of our induction; but should exceptions -prove numerous and various in their features, -our faith in the conclusion will be proportionally -shaken, and at all events its importance -lessened by the destruction of its universality.</p> - -<p>(173.) In the conduct of this verification, we are to -consider whether the cause or law to which we are -conducted be one already known and recognised as -a more general one, whose nature is well understood, -and of which the phenomenon in question is but one -more case in addition to those already known, or -whether it be one less general, less known, or altogether -new. In the latter case, our verification will -suffice, if it merely shows that all the cases considered -are plainly cases in point. But in the -former, the process of verification is of a much more -severe and definite kind. We must trace the action -of our cause with distinctness and precision, as modified<span class="pagenum"><a id="Page_166">166</a></span> -by all the circumstances of each case; we must -estimate its effects, and show that nothing unexplained -remains behind; at least, in so far as the -presence of unknown modifying causes is not concerned.</p> - -<p>(174.) Now, this is precisely the sort of process in -which <em>residual phenomena</em> (such as spoken of in art. -158.) may be expected to occur. If our induction -be really a valid and a comprehensive one, <em>whatever</em> -remains unexplained in the comparison of its conclusion -with particular cases, under all their circumstances, -<em>is</em> such a phenomenon, and comes in its -turn to be a subject of inductive reasoning to discover -its cause or laws. It is thus that we may be -said to witness facts with the eyes of reason; and it -is thus that we are continually attaining a knowledge -of new phenomena and new laws which lie -beneath the surface of things, and give rise to the -creation of fresh branches of science more and -more remote from common observation.</p> - -<p>(175.) Physical astronomy affords numerous and -splendid instances of this. The law, for example, -which asserts that the planets are retained in their -orbits about the sun, and satellites about their primaries, -by an attractive force, decreasing as the -square of the distances increases, comes to be verified -in each particular case by deducing from it -the exact motions which, under the circumstances, -ought to take place, and comparing them with fact. -This comparison, while it verifies in general the -existence of the law of gravitation as supposed, and -its adequacy to explain all the principal motions -of every body in the system, yet leaves some<span class="pagenum"><a id="Page_167">167</a></span> -small deviations in those of the planets, and some -very considerable ones in that of the moon and other -satellites, still unaccounted for; residual phenomena, -which still remain to be traced up to causes. By -further examining these, their causes have at length -been ascertained, and found to consist in the mutual -actions of the planets on each other, and the disturbing -influence of the sun on the motions of the -satellites.</p> - -<p>(176.) But a law of nature has not that degree of -generality which fits it for a stepping-stone to -greater inductions, unless it be <em>universal</em> in its application. -We cannot rely on its enabling us to -extend our views beyond the circle of instances -from which it was obtained, unless we have already -had experience of its power to do so; unless it -actually <em>has</em> enabled us before trial to say what will -take place in cases analogous to those originally -contemplated; unless, in short, we have studiously -placed ourselves in the situation of its antagonists, -and even perversely endeavoured to find exceptions -to it without success. It is in the precise proportion -that a law once obtained endures this -extreme severity of trial, that its value and importance -are to be estimated; and our next step in -the verification of an induction must therefore consist -in <em>extending</em> its application to cases not originally -contemplated; in studiously varying the circumstances -under which our causes act, with a view -to ascertain whether their effect is general; and in -pushing the application of our laws to extreme -cases.</p> - -<p>(177.) For example, a fair induction from a<span class="pagenum"><a id="Page_168">168</a></span> -great number of facts led Galileo to conclude that -the accelerating power of gravity is the same on all -sorts of bodies, and on great and small masses indifferently; -and this he exemplified by letting bodies -of very different natures and weights fall at the -same instant from a high tower, when it was observed -that they struck the ground at the same -moment, abating a certain trifling difference, due, as -he justly believed it to be, to the greater proportional -resistance of the air to light than to heavy -bodies. The experiment could not, at that time, -be fairly tried with extremely light substances, such -as cork, feathers, cotton, &c. because of the great resistance -experienced by these in their fall; no means -being then known of removing this cause of disturbance. -It was not, therefore, till after the invention -of the air-pump that this law could be put to the -severe test of an extreme case. A guinea and a -downy feather were let drop at once from the upper -part of a tall exhausted glass, and struck the bottom -at the same moment. Let any one make the -trial <em>in the air</em>, and he will perceive the force of an -<em>extreme case</em>.</p> - -<p>(178.) In the verification of a law whose expression -is <em>quantitative</em>, not only must its generality be established -by the trial of it in as various circumstances -as possible, but every such trial must be one of precise -measurement. And in such cases the means -taken for subjecting it to trial ought to be so devised -as to repeat and multiply a great number of -times any deviation (if any exist); so that, let it be -ever so small, it shall at last become sensible.</p> - -<p>(179.) For instance, let the law to be verified<span class="pagenum"><a id="Page_169">169</a></span> -be, that <em>the gravity of every material body is in the -direct proportion of its mass</em>, which is only another -mode of expressing Galileo’s law above mentioned. -The time of falling from any moderate height cannot -be measured with precision enough for our purpose: -but if it can be repeated a very great multitude of -times <em>without any loss or gain</em> in the intervals, and the -whole amount of the times of fall so repeated measured -by a clock; and if at the same time the resistance -of the air can be rendered <em>exactly alike</em> for all the -bodies tried, we have here Galileo’s trial in a much -more refined state; and it is evident that almost unlimited -exactness may be obtained. Now, all this -Newton accomplished by the simple and elegant -contrivance of enclosing in a hollow pendulum the -same weights of a great number of substances the -most different that could be found in all respects, as -gold, glass, wood, water, wheat, &c.<a id="FNanchor_44" href="#Footnote_44" class="fnanchor">44</a>, and ascertaining -the time required for the pendulum so charged -to make a great number of oscillations; in each of -which it is clear the weights had to fall, and be -raised again successively, without loss of time, -through the same <em>identical</em> spaces. Thus any difference, -however inconsiderable, that might exist in the -time of one such fall and rise would be multiplied and -accumulated till they became sensible. And none -having been discovered by so delicate a process in -any case, the law was considered verified both in respect -of generality and exactness. This, however, is -nothing to the verifications afforded by astronomical -phenomena, where the deviations, if any, accumulate -for thousands of years instead of a few hours.</p> - -<p><span class="pagenum"><a id="Page_170">170</a></span></p> - -<p id="p180">(180.) The surest and best characteristic of a -well-founded and extensive induction, however, is -when verifications of it spring up, as it were, -spontaneously, into notice, from quarters where -they might be least expected, or even among -instances of that very kind which were at first -considered hostile to them. Evidence of this kind -is irresistible, and compels assent with a weight -which scarcely any other possesses. To give an example: -M. Mitscherlich had announced a law to this -effect—<em>that</em> the chemical elements of which all -bodies consist are susceptible of being classified -in distinct groups, which he termed <i xml:lang="la" lang="la">isomorphous</i> -groups; and <em>that</em> these groups are so related, -that when similar combinations are formed of individuals -belonging to two, three, or more of them, -such combinations will crystallize in the same geometrical -forms. To this curious and important -law there appeared a remarkable exception. According -to professor Mitscherlich, the arsenic and -phosphoric acids <em>are</em> similar combinations coming -under the meaning of his law, and their combinations -with soda and water, forming the salts -known to chemists under the names of arseniate -and phosphate of soda, ought, if the law were -general, to crystallize in identical shapes. The -fact, however, was understood to be otherwise. -But lately, Mr. Clarke, a British chemist, having -examined the two salts attentively, ascertained -the fact that their compositions deviate essentially -from that similarity which M. Mitscherlich’s law -requires; and that, therefore, the exception in -question disappears. This was something: but,<span class="pagenum"><a id="Page_171">171</a></span> -pursuing the subject further, the same ingenious -enquirer happily succeeded in producing a <em>new</em> phosphate -of soda, differing from that generally known -in containing a different proportion of water, and -agreeing in composition exactly with the arseniate. -The crystals of this new salt, when examined, -were found by him to be precisely identical in form -with those of the arseniate: thus verifying, in a -most striking and totally unexpected manner, the -law in question, or, as it is called, the law of -isomorphism.</p> - -<p>(181.) Unexpected and peculiarly striking confirmations -of inductive laws frequently occur in the -form of residual phenomena, in the course of investigations -of a widely different nature from those -which gave rise to the inductions themselves. A -very elegant example may be cited in the unexpected -confirmation of the law of the developement -of heat in elastic fluids by compression, which is -afforded by the phenomena of sound. The enquiry -into the cause of sound had led to conclusions respecting -its mode of propagation, from which its -velocity in the air could be precisely calculated. -The calculations were performed; but, when compared -with fact, though the agreement was quite -sufficient to show the general correctness of the -cause and mode of propagation assigned, <em>yet</em> -the <em>whole</em> velocity could not be shown to arise -from this theory. There was still a <em>residual</em> velocity -to be accounted for, which placed dynamical -philosophers for a long time in a great dilemma. -At length Laplace struck on the happy idea, that -this might arise from the <em>heat</em> developed in the act<span class="pagenum"><a id="Page_172">172</a></span> -of that condensation which necessarily takes place at -every vibration by which sound is conveyed. The -matter was subjected to exact calculation, and the -result was at once the complete explanation of the -residual phenomenon, and a striking confirmation -of the general law of the developement of heat by -compression, under circumstances beyond artificial -imitation.</p> - -<p>(182.) In extending our inductions to cases not -originally contemplated, there is one step which -always strikes the mind with peculiar force, and with -such a sensation of novelty and surprise, as often -gives it a weight beyond its due philosophic value. -It is the transition from the little to the great, and -<i xml:lang="la" lang="la">vice versâ</i>, but especially the former. It is so beautiful -to see, for instance, an experiment performed -in a watch-glass, or before a blowpipe, succeed, in a -great manufactory, on many tons of matter, or, in the -bosom of a volcano, upon millions of cubic fathoms -of lava, that we almost forget that these great masses -are made up of watch-glassfuls, and blowpipe-beads. -We see the enormous intervals between the -stars and planets of the heavens, which afford room -for innumerable processes to be carried on, for -light and heat to circulate, and for curious and -complicated motions to go forward among them: -we look more attentively, and we see sidereal systems, -probably not less vast and complicated than our -own, crowded apparently into a small space (from -the effect of their distance from us), and forming -groups resembling bodies of a substantial appearance, -having form and outline: yet we recoil with -incredulous surprise when we are asked <em>why</em> we<span class="pagenum"><a id="Page_173">173</a></span> -cannot conceive the atoms of a grain of sand to be -as remote from each other (proportionally to their -sizes) as the stars of the firmament; and why -there may not be going on, in that little microcosm, -processes as complicated and wonderful as those of -the great world around us. Yet the student who -makes any progress in natural philosophy will encounter -numberless cases in which this transfer of -ideas from the one extreme of magnitude to the -other will be called for: he will find, for instance, -the phenomena of the propagation of winds referred -to the same laws which regulate the propagation -of motions through the smallest masses of air; those -of lightning assimilated to the mere communication -of an electric spark, and those of earthquakes to the -tremors of a stretched wire: in short, he must lay -his account to finding the distinction of great and -little altogether annihilated in nature: and it is well -for man that such is the case, and that the same -laws, which he can discover and verify in his own -circumscribed sphere of power, should prove available -to him when he comes to apply them on the -greatest scale; since it is thus only that he is enabled -to become an exciting cause in operations of -any considerable magnitude, and to vindicate his -importance in creation.</p> - -<p>(183.) But the business of induction does not -end here: its final result must be followed out into -all its consequences, and applied to all those cases -which seem even remotely to bear upon the subject -of enquiry. Every new addition to our stock -of causes becomes a means of fresh attack with new -vantage ground upon all those unexplained parts of<span class="pagenum"><a id="Page_174">174</a></span> -former phenomena which have resisted previous -efforts. It can hardly be pressed forcibly enough -on the attention of the student of nature, that there -is scarcely any natural phenomenon which can be -fully and completely explained in all its circumstances, -without a union of several, perhaps of all, -the sciences. The great phenomena of astronomy, -indeed, may be considered exceptions; but this is -merely because their scale is so vast that one only -of the most widely extending forces of nature takes -the lead, and all those agents whose sphere of action -is limited to narrower bounds, and which determine -the production of phenomena nearer at hand, are -thrown into the back ground, and become merged -and lost in comparative insignificance. But in the -more intimate phenomena which surround us it is -far otherwise. Into what a complication of different -branches of science are we not led by the consideration -of such a phenomenon as rain, for instance, -or flame, or a thousand others, which are constantly -going on before our eyes? Hence, it is hardly -possible to arrive at the knowledge of a law of -any degree of generality in any branch of science, -but it immediately furnishes us with a means of -extending our knowledge of innumerable others, -the most remote from the point we set out from; -so that, when once embarked in any physical research, -it is impossible for any one to predict where -it may ultimately lead him.</p> - -<p>(184.) This remark rather belongs to the inverse -or <em>deductive</em> process, by which we pursue laws into -their remote consequences. But it is very important -to observe, that the successful process of scientific<span class="pagenum"><a id="Page_175">175</a></span> -enquiry demands continually the alternate use of -both the <em>inductive</em> and <em>deductive</em> method. The path -by which we rise to knowledge must be made smooth -and beaten in its lower steps, and often ascended and -descended, before we can scale our way to any eminence, -much less climb to the summit. The achievement -is too great for a single effort; stations must -be established, and communications kept open with -all below. To quit metaphor; there is nothing so -instructive, or so likely to lead to the acquisition of -general views, as this pursuit of the consequences of -a law once arrived at into every subject where it -may seem likely to have an influence. The discovery -of a new law of nature, a new ultimate fact, -or one that even temporarily puts on that appearance, -is like the discovery of a new element in chemistry. -Thus, selenium was hardly discovered by -Berzelius in the vitriol works of Fahlun, when it -presently made its appearance in the sublimates of -Stromboli, and the rare and curious products of the -Hungarian mines. And thus it is with every new -law, or general fact. It is hardly announced before -its traces are found every where, and every one is -astonished at its having so long remained concealed. -And hence it happens that unexpected lights are -shed at length over parts of science that had been -abandoned in despair, and given over to hopeless -obscurity.</p> - -<p>(185.) The verification of <em>quantitative</em> laws has -been already spoken of (178.); but their importance in -physical science is so very great, inasmuch as they -alone afford a handle to strict mathematical deductive -application, that something ought to be said of<span class="pagenum"><a id="Page_176">176</a></span> -the nature of the inductions by which they are to -be arrived at. In their simplest or least general -stages (of which alone we speak at present) they -usually express some numerical relation between -two quantities dependent on each other, either as -collateral effects of a common cause, or as the -amount of its effect under given numerical circumstances -or <em>data</em>. For example, the law of refraction -before noticed (§ 22.) expresses, by a very -simple relation, the amount of angular deviation of a -ray of light from its course, when the <em>angle</em> at which -it is inclined to the refracting surface is known, -viz. that the <em>sine</em> of the angle which the incident -ray makes with a perpendicular to the surface is -always to that of the angle made by the refracted -ray with the same perpendicular, in a constant proportion, -so long as the refracting substance is the -same. To arrive inductively at laws of this kind, -where one quantity <em>depends</em> on or <em>varies with</em> another, -all that is required is a series of careful and exact -measures in every different state of the <em>datum</em> and -<i xml:lang="la" lang="la">quæsitum</i>. Here, however, the mathematical form -of the law being of the highest importance, the -greatest attention must be given to the <em>extreme cases</em> -as well as to all those points where the one quantity -changes rapidly with a small change of the other.<a id="FNanchor_45" href="#Footnote_45" class="fnanchor">45</a> -The results must be set down in a table in which -the <em>datum</em> gradually increases in magnitude from -the lowest to the highest limit of which it is susceptible.<span class="pagenum"><a id="Page_177">177</a></span> -It will depend then entirely on our habit -of treating mathematical subjects, how far we may -be able to include such a table in the distinct statement -of a mathematical law. The discovery of -such laws is often remarkably facilitated by the -contemplation of a class of phenomena to be noticed -further on, under the head of Collective Instances, -(see <a href="#p194">§ 194</a>.) in which the nature of the mathematical -expression in which the law sought is comprehended, -is pointed out by the figure of some -curve brought under inspection by a proper mode -of experimenting.</p> - -<p>(186.) After all, unless our induction embraces -a series of cases which absolutely include the -whole scale of variation of which the quantities -in question admit, the mathematical expression so -obtained cannot be depended upon as the true one, -and if the scale actually embraced be small, the -extension of laws so derived to extreme cases will -in all probability be exceedingly fallacious. For -example, air is an elastic fluid, and as such, if -enclosed in a confined space and squeezed, its bulk -diminishes: now, from a great number of trials made -in cases where the air has been compressed into a -half, a third, &c. even as far as a fiftieth of its bulk, -or less, it has been concluded that “the density of -air is proportional to the compressing force,” or the -bulk it occupies <em>inversely</em> as that force; and when -the air is rarefied by taking off part of its natural -pressure, the same is found to be the case, within -very extensive limits. Yet it is impossible that this -should be, strictly or mathematically speaking, the -true law; for, if it were so, there could be no limit<span class="pagenum"><a id="Page_178">178</a></span> -to the condensation of air, while yet we have the -strongest analogies to show that long before it had -reached any very enormous pitch the air would be -reduced into a liquid, and even, perhaps, if pressed -yet more violently, into a solid form.</p> - -<p>(187.) Laws thus derived, by the direct process -of including in mathematical formulæ the results -of a greater or less number of measurements, are -called “empirical laws.” A good example of such -a law is that given by Dr. Young (Phil. Trans. 1826,) -for the decrement of life, or the law of mortality. -Empirical laws in this state are evidently <em>unverified -inductions</em>, and are to be received and reasoned on -with the utmost reserve. No confidence can ever -be placed in them beyond the limits of the data from -which they are derived; and even within those limits -they require a special and severe scrutiny to -examine <em>how nearly</em> they do represent the observed -facts; that is to say, whether, in the comparison of -their results with the observed quantities, the differences -are such as may fairly be attributed to error -of observation. When so carefully examined, they -become, however, most valuable; and frequently, -when afterwards verified theoretically by a deductive -process (as will be explained in our next chapter), -turn out to be rigorous laws of nature, and afford -the noblest and most convincing supports of which -theories themselves are susceptible. The finest -instances of this kind are the great laws of the -planetary motions deduced by Kepler, entirely from -a comparison of observations with each other, with -no assistance from theory. These laws, viz. that -the planets move in ellipses round the sun; that<span class="pagenum"><a id="Page_179">179</a></span> -each describes about the sun’s centre equal areas in -equal times; and that in the orbits of different planets -the squares of the periodical times are proportional -to the cubes of the distances; were the results -of inconceivable labour of calculation and comparison: -but they amply repaid the labour bestowed -on them, by affording afterwards the most conclusive -and unanswerable proofs of the Newtonian system. -On the other hand, when empirical laws are unduly -relied on beyond the limits of the observations from -which they were deduced, there is no more fertile -source of fatal mistakes. The formulæ which have -been empirically deduced for the elasticity of steam -(till very recently), and those for the resistance of -fluids, and other similar subjects, have almost invariably -failed to support the theoretical structures -which have been erected on them.</p> - -<p>(188.) It is a remarkable and happy fact, that -the shortest and most direct of all inductions -should be that which has led at once, or by very -few steps, to the highest of all natural laws,—we -mean those of motion and force. Nothing can -be more simple, precise, and general, than the -enunciation of these laws; and, as we have once -before observed, their application to particular facts -in the descending or deductive method is limited -by nothing but the limited extent of our mathematics. -It would seem, then, that dynamical science -were taken thenceforward out of the pale of induction, -and transformed into a matter of absolute -<i xml:lang="la" lang="la">à priori</i> reasoning, as much as geometry; and so it -would be, were our mathematics perfect, and all the -<em>data</em> known. Unhappily, the first is so far from being<span class="pagenum"><a id="Page_180">180</a></span> -the case, that in many of the most interesting -branches of dynamical enquiry they leave us completely -at a loss. In what relates to the motions of -fluids, for instance, this is severely felt. We can -include our problems, it is true, in algebraical equations, -and we can demonstrate that they <em>contain</em> -the solutions; but the equations themselves are so -intractable, and present such insuperable difficulties, -that they often leave us quite as much in the dark -as before. But even were these difficulties overcome, -recourse to experience must still be had, to -establish the <em>data</em> on which particular applications -are to depend; and although mathematical analysis -affords very powerful means of <em>representing</em> in -general terms the data of any proposed case, and -<em>afterwards</em>, by comparison of its results with fact, -determining <em>what</em> those data must be to explain -the observed phenomena, still, in any mode of -considering the matter, an appeal to experience in -every particular instance of application is unavoidable, -even when the general principles are regarded -as sufficiently established without it. Now, in all -such cases of difficulty we must recur to our inductive -processes, and regard the branches of dynamical -science where this takes place as purely -experimental. By this we gain an immense advantage, -viz. that in all those points of them where -the abstract dynamical principles <em>do</em> afford distinct -conclusions, we obtain verifications for our inductions -of the highest and finest possible kind. When -we work our way up inductively to one of these -results, we cannot help feeling the strongest assurance -of the validity of the induction.</p> - -<p><span class="pagenum"><a id="Page_181">181</a></span> -(189.) The necessity of this appeal to experiment -in every thing relating to the motions of fluids on -the large scale has long been felt. Newton himself, -who laid the first foundations of hydrodynamical -science (so this branch of dynamics is called), distinctly -perceived it, and set the example of laborious -and exact experiments on their resistance to motion, -and other particulars. Venturi, Bernoulli, and -many others, have applied the method of experiment -to the motions of fluids in pipes and canals; and -recently the brothers Weber have published an elaborate -and excellent experimental enquiry into the -phenomena of waves. One of the greatest and most -successful attempts, however, to bring an important, -and till then very obscure, branch of dynamical -enquiry back to the dominion of experiment, has -been made by Chladni and Savart in the case of -sound and vibratory motion in general; and it is -greatly to be wished that the example may be followed -in many others hardly less abstruse and -impracticable when theoretically treated. In such -cases the inductive and deductive methods of enquiry -may be said to go hand in hand, the one verifying -the conclusions deduced by the other; and the -combination of experiment and theory, which may -thus be brought to bear in such cases, forms an engine -of discovery infinitely more powerful than either -taken separately. This state of any department of -science is perhaps of all others the most interesting, -and that which promises the most to research.</p> - -<p>(190.) It can hardly be expected that we -should terminate this division of our subject without -some mention of the “prerogatives of instances”<span class="pagenum"><a id="Page_182">182</a></span> -of Bacon, by which he understands characteristic -phenomena, selected from the great miscellaneous -mass of facts which occur in nature, and which, by -their number, indistinctness, and complication, tend -rather to confuse than to direct the mind in its -search for causes and general heads of induction. -Phenomena so selected on account of some peculiarly -forcible way in which they strike the reason, -and impress us with a kind of sense of causation, -or a particular aptitude for generalization, he considers, -and justly, as holding a kind of prerogative -dignity, and claiming our first and especial attention -in physical enquiries.</p> - -<p>(191.) We have already observed that, in forming -inductions, it will most commonly happen that -we are led to our conclusions by the especial -force of some two or three strongly impressive -facts, rather than by affording the whole mass of -cases a regular consideration; and hence the need -of cautious verification. Indeed, so strong is this -propensity of the human mind, that there is hardly -a more common thing than to find persons ready to -assign a cause for every thing they see, and, in so -doing, to join things the most incongruous, by analogies -the most fanciful. This being the case, it is -evidently of great importance that these first ready -impulses of the mind should be made on the contemplation -of the cases most likely to lead to good -inductions. The misfortune, however, is, in natural -philosophy, that the choice does not rest with us. -We must take the instances as nature presents -them. Even if we are furnished with a list of them -in tabular order, we must understand and compare<span class="pagenum"><a id="Page_183">183</a></span> -them with each other, before we can tell which <em>are</em> -the instances thus deservedly entitled to the highest -consideration. And, after all, after much labour in -vain, and groping in the dark, accident or casual -observation will present a case which strikes us at -once with a full insight into a subject, before we -can even have time to determine to what class its -<em>prerogative</em> belongs. For example, the laws of crystallography -were obscure, and its causes still more -so, till Haüy fortunately dropped a beautiful crystal -of calcareous spar on a stone pavement, and broke -it. In piecing together the fragments, he observed -their facets not to correspond with those of the -crystal in its entire state, but to belong to another -form; and, following out the hint offered by a -“<em>glaring instance</em>” thus casually obtruded on his -notice, he discovered the beautiful laws of the -cleavage, and the primitive forms of minerals.</p> - -<p>(192.) It has always appeared to us, we must -confess, that the help which the classification of instances, -under their different titles of prerogative, -affords to inductions, however just such classification -may be in itself, is yet more apparent than real. -The force of the instance must be felt in the mind, -before it can be referred to its place in the system; -and, before it can be either referred or appretiated, -it must be known; and when it <em>is</em> appretiated, we -are ready enough to interweave it in our web of induction, -without greatly troubling ourselves with -enquiring whence it derives the weight we acknowledge -it to have in our decisions. However, since -much importance is usually attached to this part of<span class="pagenum"><a id="Page_184">184</a></span> -Bacon’s work, we shall here give a few examples -to illustrate the nature of some of his principal cases. -One, of what he calls “glaring instances,” has just -been mentioned. In these, the <em>nature</em> or cause enquired -into, (which in this case is the cause of the -assumption of a peculiar external form, or the internal -<em>structure</em> of a crystal,) “stands naked and -alone, and this in an eminent manner, or in the -highest degree of its power.” No doubt, such instances -as these are highly instructive; but the -difficulty in physics is to find such, not to perceive -their force when found.</p> - -<p>(193.) The contrary of glaring are “clandestine -instances,” where “the nature sought is exhibited -in its weakest and most imperfect state.” Of -this, Bacon himself has given an admirable example -in the cohesion of fluids, as a <em>clandestine -instance</em> of the “<em>nature</em> or quality of consistence, -or solidity.” Yet here, again, the same acute discrimination -which enabled Bacon to perceive the analogy -which connects fluids with solids, through the -common property of cohesive attraction, would, at -the same time, have enabled him to draw from it, -if properly supported, every consequence necessary -to forming just notions of the cohesive force; nor -does its reference to the class of clandestine instances -at all assist in bringing forward and maturing -the final results. When, however, the final -result is obtained,—when our induction is complete, -and we would verify it,—this class of instances is of -great use, being, in fact, frequently no other than -that of <em>extreme cases</em>, such as we have already spoken -of (in § 177.); which, by placing our conclusions, as<span class="pagenum"><a id="Page_185">185</a></span> -it were, in violent circumstances, try their temper, -and bring their vigour to the test.</p> - -<p id="p194">(194.) Bacon’s “collective instances” (<i xml:lang="la" lang="la">instantiæ -unionis</i>), are no other than general facts, or laws of -some degree of generality, and are themselves the -results of induction. But there is a species of collective -instance which Bacon does not seem to have -contemplated, of a peculiarly instructive character; -and that is, where particular cases are offered to our -observation in such numbers at once as to make the -induction of their law a matter of ocular inspection. -For example, the parabolic form assumed by a jet of -water spouted from a round hole, is a <em>collective instance</em> -of the velocities and directions of the motions -of all the particles which compose it <em>seen at once</em>, -and which thus leads us, without trouble, to recognize -the law of the motion of a projectile. Again, -the beautiful figures exhibited by sand strewed on -regular plates of glass or metal set in vibration, -are <em>collective instances</em> of an infinite number of points -which remain at rest while the remainder of the -plate vibrates; and in consequence afford us, as it -were, a sight of the law which regulates their arrangement -and sequence throughout the whole -surface. The beautifully coloured lemniscates seen -around the optic axes of crystals exposed to polarized -light afford a superb example of the same -kind, pointing at once to the general mathematical -expression of the law which regulates their production.<a id="FNanchor_46" href="#Footnote_46" class="fnanchor">46</a> -Of such collective instances as these, it -is easy to see the importance, and its reason. They -lead us to a general law by an induction which<span class="pagenum"><a id="Page_186">186</a></span> -offers itself spontaneously, and thus furnish advanced -points in our enquiries; and when we start -from these, already “a thousand steps are lost.”</p> - -<p id="p195">(195.) A fine example of a collective instance is -that of the system of Jupiter or Saturn with its -satellites. We have here, in miniature, and seen -at one view, a system similar to that of the planets -about the sun; of which, from the circumstance of -our being involved in it, and unfavourably situated -for seeing it otherwise than in detail, we are incapacitated -from forming a general idea but by -slow progressive efforts of reason. Accordingly, the -contemplation of the <em>circumjovial planets</em> (as they -were called) most materially assisted in securing -the admission of the Copernican system.</p> - -<p>(196.) Of “Crucial instances” we have also already -spoken, as affording the readiest and securest -means of eliminating extraneous causes, and deciding -between rival hypotheses. Owing to the disposition -of the mind to form hypotheses, and to -prejudge cases, it constantly happens that, among -all the possible suppositions which may occur, two -or three principal ones occupy us, to the exclusion -of the rest; or it may be that, if we have been less -precipitate, out of a great multitude rejected for -obvious inapplicability to some one or other case, -two or three of better claims remain for decision; -and this such instances enable us to do. One of -the instances cited by Bacon in illustration of his -crucial class is very remarkable, being neither more -nor less than the proposal of a direct experiment to -determine whether the tendency of heavy bodies -downwards is a result of some peculiar mechanism<span class="pagenum"><a id="Page_187">187</a></span> -in themselves, or of the attraction of the earth “by -the corporeal mass thereof, as by a collection of -bodies of the same nature.” If it be so, he says, -“it will follow that the nearer all bodies approach -to the earth, the stronger and with the greater -force and velocity they will tend to it; but the -farther they are, the weaker and slower:” and his -experiment consists in comparing the effect of a -spring and a weight in keeping up the motions of -two “clocks,” regulated together, and removed alternately -to the tops of high buildings and into the -deepest mines. By <em>clocks</em> he could not have meant -pendulum clocks, which were not then known, (the -first made in England was in 1662,) <em>fly</em>-clocks, -so that the comparison, though too coarse, was not -contrary to sound mechanical principles. In short, -its principle was the comparison of the effect of a -spring with that of a weight, in producing certain -motions in certain times, on heights and in mines. -Now, this is the very same thing that has really been -done in the recent experiments of professors Airy -and Whewell in Dolcoath mine: a pendulum (a -weight moved by gravity) has been compared with -a chronometer balance, moved and regulated by a -spring. In his 37th aphorism, Bacon also speaks of -gravity as an incorporeal power, acting at a distance, -and <em>requiring time for its transmission</em>; a consideration -which occurred at a later period to Laplace, -in one of his most delicate investigations.</p> - -<p>(197.) A well chosen and strongly marked crucial -instance is, sometimes, of the highest importance; -when two theories, which run parallel to each -other (as is sometimes the case) in their explanation<span class="pagenum"><a id="Page_188">188</a></span> -of great classes of phenomena, at length -come to be placed at issue upon a single fact. A -beautiful instance of this will be cited in the next -section. We may add to the examples above given -of such instances, that of the application of chemical -tests, which are almost universally crucial experiments.</p> - -<p>(198.) Bacon’s “travelling instances” are those -in which the <em>nature</em> or quality under investigation -“travels,” or varies in degree; and thus (according -to § 152.) afford an indication of a cause by -a gradation of intensity in the effect. One of his -instances is very happy, being that of “paper, -which is white when dry, but proves less so when -wet, and comes nearer to the state of transparency -upon the exclusion of the air, and admission of -water.” In reading this, and many other instances -in the Novum Organum, one would almost suppose -(had it been written) that its author had taken -them from Newton’s Optics.</p> - -<p>(199.) The travelling instances, as well as what -Bacon terms “frontier instances,” are cases in which -we are enabled to trace that general law which -seems to pervade all nature—the law, as it is -termed, of continuity, and which is expressed in the -well known sentence, “Natura non agit per saltum.” -The pursuit of this law into cases where its -application is not at first sight obvious, has proved -a fertile source of physical discovery, and led us to -the knowledge of an analogy and intimate connection -of phenomena between which at first we should -never have expected to find any.</p> - -<p>(200.) For example, the transparency of gold leaf,<span class="pagenum"><a id="Page_189">189</a></span> -which permits a bluish-green light to pass through -it, is a frontier instance between the transparency -of pellucid bodies and the opacity of metals, and it -prevents a breach of the law of continuity between -transparent and opake bodies, by exhibiting a body -of the class generally regarded the most opake in -nature, as still possessed of some slight degree of -transparency. It thus proves that the quality of -opacity is not a <em>contrary</em> or <em>antagonist</em> quality to -that of transparency, but only its extreme lowest -degree.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_190">190</a></span></p> - -<div class="chapter"> -<h2 id="hdr_12">CHAP. VII.</h2> -</div> - -<blockquote class="hang"> - -<p class="center b2">OF THE HIGHER DEGREES OF INDUCTIVE GENERALIZATION, -AND OF THE FORMATION AND VERIFICATION -OF THEORIES.</p></blockquote> - -<p class="in0">(201.) <span class="smcap"><span class="flet">A</span>s</span> particular inductions and laws of the first -degree of generality are obtained from the consideration -of individual facts, so Theories result from a -consideration of these laws, and of the proximate -causes brought into view in the previous process, -regarded all together as constituting a new set of -phenomena, the creatures of reason rather than of -sense, and each representing under general language -innumerable particular facts. In raising these -higher inductions, therefore, more scope is given to -the exercise of pure reason than in slowly groping -out our first results. The mind is more disencumbered -of matter, and moves as it were in its own -element. What is now before it, it perceives more -intimately, and less through the medium of sense, -or at least not in the same manner as when actually -at work on the immediate objects of sense. But it -must not be therefore supposed that, in the formation -of theories, we are abandoned to the unrestrained -exercise of imagination, or at liberty to lay down -arbitrary principles, or assume the existence of mere -fanciful causes. The liberty of speculation which -we possess in the domains of theory is not like -the wild licence of the slave broke loose from his<span class="pagenum"><a id="Page_191">191</a></span> -fetters, but rather like that of the freeman who has -learned the lessons of self-restraint in the school of -just subordination. The ultimate objects we pursue -in the highest theories are the same as those of the -lowest inductions; and the means by which we can -most securely attain them bear a close analogy to -those which we have found successful in such inferior -cases.</p> - -<p>(202.) The immediate object we propose to ourselves -in physical theories is the analysis of phenomena, -and the knowledge of the hidden processes -of nature in their production, so far as they can be -traced by us. An important part of this knowledge -consists in a discovery of the actual structure or -mechanism of the universe and its parts, through -which, and by which, those processes are executed; -and of the agents which are concerned in their -performance. Now, the mechanism of nature is -for the most part either on too large or too small a -scale to be immediately cognizable by our senses; -and her agents in like manner elude direct observation, -and become known to us only by their effects. -It is in vain therefore that we desire to become -witnesses to the processes carried on with such -means, and to be admitted into the secret recesses -and laboratories where they are effected. Microscopes -have been constructed which magnify more -than a thousand times in <em>linear</em> dimension, so that -the smallest visible grain of sand may be enlarged -to the appearance of one a thousand million times -more bulky; yet the only impression we receive by -viewing it through such a magnifier is, that it reminds -us of some vast fragment of a rock, while the<span class="pagenum"><a id="Page_192">192</a></span> -intimate structure on which depend its colour, its -hardness, and its chemical properties, remains still -concealed: we do not seem to have made even an -approach to a closer analysis of it by any such -scrutiny.</p> - -<p>(203.) On the other hand, the mechanism of the -great system of which our planet forms a part -escapes immediate observation by the immensity of -its scale, nay, even by the slowness of its evolutions. -The motion of the minute hand of a watch can -hardly be perceived without the closest attention, -and that of the hour hand not at all. But what are -these, in respect of the impression of slowness they -produce in our minds, compared with a revolving -movement which takes a whole year, or twelve, -thirty, or eighty years to complete, as is the case -with the planets in their revolutions round the sun. -Yet no sooner do we come to reflect on the linear -dimensions of these orbs, (which however we do -not <em>see</em>, nor can we measure them but by a long, -circuitous, and difficult process,) than we are lost in -astonishment at the swiftness of the very motions -which before seemed so slow.<a id="FNanchor_47" href="#Footnote_47" class="fnanchor">47</a> The motion of the -sails of a windmill offers (on a small scale) an illustrative -case. At a distance the rotation seems slow -and steady—but when we stand close to one of the -sails in its sweep, we are surprised at the swiftness -with which it rushes by us.</p> - -<p><span class="pagenum"><a id="Page_193">193</a></span> -(204.) Again, the agents employed by nature to act -on material structures are invisible, and only to be -traced by the effects they produce. Heat dilates -matter with an irresistible force; but what heat is, -remains yet a problem. A current of electricity -passing along a wire moves a magnetized needle at a -distance; but except from this effect we perceive no -difference between the condition of the wire when it -conveys and when it does not convey the stream: -and we apply the terms current, or stream, to the -electricity only because in some of its relations -it reminds us of something we have observed in a -stream of air or water. In like manner we see -that the moon circulates about the earth; and because -we believe it to be a solid mass, and have -never seen one solid substance revolve round another -within our reach to handle and examine -unless retained by a force or united by a tie, we -conclude that there <em>is</em> a force, and a mode of connection, -between the moon and the earth; though, -what that mode can be, we have no conception, -nor can imagine <em>how</em> such a force can be exerted -at a distance, and with empty space, or at most an -invisible fluid, between. (See <a href="#p148">§ 148</a>.)</p> - -<p>(205.) Yet are we not to despair, since we -see regular and beautiful results brought about in -human works by means which nobody would, at -first sight, think could have any thing to do with -them. A sheet of blank paper is placed upon a -frame, and shoved forwards, and after winding its -way successively over and under half a dozen -rollers, and performing many other strange evolutions, -comes out printed on both sides. And,<span class="pagenum"><a id="Page_194">194</a></span> -after all, the acting cause in this process is nothing -more than a few gallons of water boiled in an iron -vessel, at a distance from the scene of operations. -But <em>why</em> the water so boiled should be capable of -producing the active energy which sets the whole -apparatus in motion is, and will probably long -remain, a secret to us.</p> - -<p>(206.) This, however, does not at all prevent our -having a very perfect comprehension of the whole -subsequent process. We might frequent printing-houses, -and form a theory of printing, and having -worked our way up to the point where the mechanical -action commenced (the boiler of the steam-engine), -and verified it by taking to pieces, and putting together -again, the train of wheels and the presses, and by -sound theoretical examination of all the transfers of -motion from one part to another; we should, at length, -pronounce our theory good, and declare that we -understood printing thoroughly. Nay, we might -even go away and apply the principles of mechanism -we had learned in this enquiry to other widely -different purposes; construct other machines, and -put them in motion by the same moving power, -and all without arriving at any correct idea as to -the ultimate source of the force employed. But, -if we were inclined to theorize farther, we might -do so; and it is easy to imagine how two theorists -might form very different <em>hypotheses</em> as to the origin -of the power which alternately raised and depressed -the piston-rod of the engine. One, for example, might -maintain that the boiler (whose contents we will suppose -that neither theorist has been permitted to -examine) was the den of some powerful unknown<span class="pagenum"><a id="Page_195">195</a></span> -animal, and he would not be without plausible -analogies in the warmth, the supply of fuel and -water, the breathing noises, the smoke, and above -all, the mechanical power exerted. He would say -(not without a show of reason), that where there is -a positive and wonderful effect, and many strong -analogies, such as materials consumed, and all the -usual signs of life maintained, we are not to deny -the existence of animal life because we know no -animal that consumes such food. Nay, he might -observe with truth, that the fuel actually consists -of the chemical ingredients which constitute the -chief food of all animals, &c.; while, on the other -hand, his brother theorist, who caught a glimpse -of the fire, and detected the peculiar sounds of -ebullition, might acquire a better notion of the -case, and form a theory more in consonance with -fact.</p> - -<p id="p207">(207.) Now, nothing is more common in physics -than to find two, or even many, <em>theories</em> maintained -as to the origin of a natural phenomenon. -For instance, in the case of heat itself, one considers -it as a really existing material fluid, of such -exceeding subtlety as to penetrate all bodies, and -even to be capable of combining with them chemically; -while another regards it as nothing but -a rapid vibratory or rotatory motion in the ultimate -particles of the bodies heated; and produces -a singularly ingenious train of mechanical reasoning -to show, that there is nothing contradictory to -sound dynamical principles in such a doctrine. -Thus, again, with light: one considers it as consisting -in actual particles darted forth from luminous<span class="pagenum"><a id="Page_196">196</a></span> -bodies, and acted upon in their progress by -forces of extreme intensity residing in the substances -on which they strike; another, in the vibratory -motion of the particles of luminous bodies, -communicated to a peculiar subtle and highly elastic -ethereal medium, filling all space, and conveyed -through it into our eyes, as sounds are to our ears, -by the undulations of the air.</p> - -<p>(208.) Now, are we to be deterred from framing -hypotheses and constructing theories, because -we meet with such dilemmas, and find ourselves -frequently beyond our depth? Undoubtedly not. -<i xml:lang="la" lang="la">Est quodam prodire tenus si non datur ultra.</i> -Hypotheses, with respect to theories, are what -presumed proximate causes are with respect to -particular inductions: they afford us motives for -searching into analogies; grounds of citation to -bring before us all the cases which seem to bear -upon them, for examination. A well imagined -hypothesis, if it have been suggested by a fair -inductive consideration of general laws, can hardly -fail at least of enabling us to generalize a step -farther, and group together several such laws under -a more universal expression. But this is taking a -very limited view of the value and importance of -hypotheses: it may happen (and it has happened -in the case of the undulatory doctrine of light) -that such a weight of analogy and probability may -become accumulated on the side of an hypothesis, -that we are compelled to admit one of two things; -either that it is an actual statement of what really -passes in nature, or that the reality, whatever it be, -must run so close a parallel with it, as to admit of<span class="pagenum"><a id="Page_197">197</a></span> -some mode of expression common to both, at least -in so far as the phenomena actually known are -concerned. Now, this is a very great step, not -only for its own sake, as leading us to a high point -in philosophical speculation, but for its applications; -because whatever conclusions we deduce from -an hypothesis so supported must have at least a -strong presumption in their favour: and we may -be thus led to the trial of many curious experiments, -and to the imagining of many useful and -important contrivances, which we should never -otherwise have thought of, and which, at all events, -if verified in practice, are real additions to our stock -of knowledge and to the arts of life.</p> - -<p>(209.) In framing a theory which shall render -a rational account of any natural phenomenon, we -have <em>first</em> to consider the agents on which it depends, -or the causes to which we regard it as -ultimately referable. These agents are not to be -arbitrarily assumed; they must be such as we have -good inductive grounds to believe do exist in nature, -and do perform a part in phenomena analogous to -those we would render an account of; or such, -whose presence in the actual case can be demonstrated -by unequivocal signs. They must be <i xml:lang="la" lang="la">veræ -causæ</i>, in short, which we can not only show to exist -and to act, but the laws of whose action we can derive -independently, by direct induction, from experiments -purposely instituted; or at least make such -suppositions respecting them as shall not be contrary -to our experience, and which will remain to be -verified by the coincidence of the conclusions we -shall deduce from them, with facts. For example, in<span class="pagenum"><a id="Page_198">198</a></span> -the theory of gravitation we suppose an agent,—<i>viz.</i> -force, or mechanical power,—to act on <em>any</em> material -body which is placed in the presence of <em>any</em> other, -and to urge the two mutually towards each other. -This is a <i xml:lang="la" lang="la">vera causa</i>; for heavy bodies (that is, -all bodies, but some more, some less,) tend to, or -endeavour to reach, the earth, and require the -exertion of force to counteract this endeavour, or -to keep them up. Now, that which opposes and -neutralizes force <em>is</em> force. And again, a plumb-line, -which, when allowed to hang freely, always hangs -perpendicularly; is found to hang observably aside -from the perpendicular when in the neighbourhood -of a considerable mountain; thereby proving that a -force is exerted upon it, which draws it towards the -mountain. Moreover, since it is a fact that the -moon does circulate about the earth, it must be -drawn towards the earth by a force; for if there -were no force acting upon it, it would go on in a -straight line without turning aside to circulate in an -orbit, and would, therefore, soon go away and be lost -in space. This force, then, which we call the <em>force</em> -of gravity, is a real cause.</p> - -<p>(210.) We have next to consider the laws which -regulate the action of these our primary agents; -and these we can only arrive at in three ways: 1st, By -inductive reasoning; that is, by examining all the cases -in which we know them to be exercised, inferring, -as well as circumstances will permit, its amount or -intensity in each particular case, and then piecing -together, as it were, these <i xml:lang="la" lang="la">disjecta membra</i>, generalizing -from them, and so arriving at the laws desired; -2dly, By forming at once a bold hypothesis, particularizing<span class="pagenum"><a id="Page_199">199</a></span> -the law, and trying the truth of it by -following out its consequences and comparing them -with facts; or, 3dly, By a process partaking of -both these, and combining the advantages of both -without their defects, viz. by assuming indeed the -laws we would discover, but so generally expressed, -that they shall include an unlimited variety of -particular laws;—following out the consequences -of this assumption, by the application of such general -principles as the case admits;—comparing them -in succession with all the particular cases within our -knowledge; and, lastly, <em>on this comparison</em>, so modifying -and restricting the general enunciation of our -laws as to <em>make the results agree</em>.</p> - -<p>(211.) All these three processes for the discovery -of those general elementary laws on which the -higher theories are grounded are applicable with -different advantage in different circumstances. We -might exemplify their successive application to -the case of gravitation: but as this would rather -lead into a disquisition too particular for the objects -of this discourse, and carry us too much -into the domain of technical mathematics, we shall -content ourselves with remarking, that the method -last mentioned is that which mathematicians (especially -such as have a considerable command of those -general modes of representing and reasoning on -quantity, which constitute the higher analysis,) find -the most universally applicable, and the most efficacious; -and that it is applicable with especial advantage -in cases where subordinate inductions of -the kind described in the last section have already -led to laws of a certain generality admitting of<span class="pagenum"><a id="Page_200">200</a></span> -mathematical expression. Such a case, for instance, -is the elliptic motion of a planet, which is a general -proposition including the statement of an infinite -number of particular <em>places</em>, in which the laws of its -motion allow it to be some time or other found, and -for which, of course, the law of force must be so -assumed as to account.</p> - -<p>(212.) With regard to the first process of the -three above enumerated, it is in fact an induction -of the kind described in § 185.; and all the remarks -we there made on that kind of induction -apply to it in this stage. The direct assumption -of a particular hypothesis has been occasionally -practised very successfully. As examples, we may -mention Coulomb’s and Poisson’s theories of electricity -and magnetism, in both which, phenomena -of a very complicated and interesting nature -are referred to the actions of attractive and repulsive -forces, following a law similar in its expression -to the law of gravitation. But the difficulty -and labour, which, in the greater theories, always -attends the pursuit of a fundamental law into its -remote consequences, effectually precludes this method -from being commonly resorted to as a means -of discovery, unless we have some good reason, -from analogy or otherwise, for believing that the -attempt will prove successful, or have been first -led by partial inductions to particular laws which -naturally point it out for trial.</p> - -<p>(213.) In this case the law assumes all the characters -of a general phenomenon resulting from an -induction of particulars, but not yet verified by comparison -with <em>all</em> the particulars, nor extended to all<span class="pagenum"><a id="Page_201">201</a></span> -that it is capable of including. (See <a href="#p171">§ 171</a>.) It -is the verification of such inductions which constitutes -theory in its largest sense, and which -embraces an estimation of the influence of all such -circumstances as may modify the effect of the -cause whose laws of action we have arrived at and -would verify. To return to our example: particular -inductions drawn from the motions of the several -planets about the sun, and of the satellites round -their primaries, &c. having led us to the general -conception of an attractive force exerted by every -particle of matter in the universe on every other -according to the law to which we attach the -name of gravitation; when we would verify this -induction, we must set out with assuming this law, -considering the whole system as subjected to its -influence and implicitly obeying it, and nothing interfering -with its action; we then, for the first time, -perceive a train of modifying circumstances which -had not occurred to us when reasoning upwards from -particulars to obtain the fundamental law; we perceive -that <em>all the planets</em> must attract <em>each other</em>, -must therefore draw each other out of the orbits -which they would have if acted on only by the sun; -and as this was never contemplated in the inductive -process, its validity becomes a question, which can -only be determined by ascertaining precisely how -great a deviation this new class of mutual actions -will produce. To do this is no easy task, or rather, -it is the most difficult task which the genius of man -has ever yet accomplished: still, it <em>has</em> been accomplished -by the mere application of the general laws -of dynamics; and the result (undoubtedly a most<span class="pagenum"><a id="Page_202">202</a></span> -beautiful and satisfactory one) is, that all those -observed deviations in the motions of our system -which stood out as exceptions (§ 154.), or were -noticed as residual phenomena and reserved for -further enquiry (§ 158.), in that imperfect view of -the subject which we got in the subordinate process -by which we rose to our general conclusion, prove -to be the immediate consequences of the above-mentioned -mutual actions. As such, they are neither -exceptions nor residual facts, but fulfilments of -general rules, and essential features in the statement -of the case, <em>without</em> which our induction would -be invalid, and the law of gravitation positively untrue.</p> - -<p>(214.) In the theory of gravitation, the law is all -in all, applying itself at once to the materials, and -directly producing the result. But in many other -cases we have to consider not merely the laws which -regulate the actions of our ultimate causes, but a -system of mechanism, or a structure of parts, through -the intervention of which their effects become -sensible to us. Thus, in the delicate and curious -electro-dynamic theory of Ampere, the mutual -attraction or repulsion of two magnets is referred -to a more universal phenomenon, the mutual action -of electric currents, according to a certain fundamental -law. But, in order to bring the case of a -magnet within the range of this law, he is obliged -to make a supposition of a peculiar structure or -mechanism, which constitutes a body a magnet, -viz. that around each particle of the body there -shall be constantly circulating, in a certain stated -direction, a small current of electric fluid.</p> - -<p><span class="pagenum"><a id="Page_203">203</a></span> -(215.) This, we may say, is too complex; it is -artificial, and cannot be granted: yet, if the admission -of this or any other structure tenfold more -artificial and complicated will enable any one to -present in a general point of view a great number -of particular facts,—to make them a part of one -system, and enable us to reason from the known -to the unknown, and actually to <em>predict facts before -trial</em>,—we would ask, why should it <em>not</em> be granted? -When we examine those instances of nature’s workmanship -which we can take to pieces and understand, -we find them in the highest degree artificial -in our own sense of the word. Take, for example, -the structure of an eye, or of the skeleton of an -animal,—what complexity and what artifice! In -the one, a <em>pellucid muscle</em>; a lens formed with elliptical -surfaces; a circular aperture capable of enlargement -or contraction without loss of form. In -the other, a framework of the most curious carpentry; -in which occurs not a single straight line, -nor any known geometrical curve, yet all evidently -systematic, and constructed by rules which defy our -research. Or examine a crystallized mineral, which -we can in some measure dissect, and thus obtain -direct evidence of an internal structure. Neither -artifice nor complication are here wanting; and -though it is easy to assert that these appearances -are, after all, produced by something which would -be very simple, if we did but know it, it is plain -that the same might be <em>said</em> of a steam-engine executing -the most complicated movements, previous -to any investigation of its nature, or any knowledge -of the source of its power.</p> - -<p><span class="pagenum"><a id="Page_204">204</a></span> -(216.) In estimating, however, the value of a -theory, we are not to look, <em>in the first instance</em>, -to the question, whether it establishes satisfactorily, -or not, a particular process or mechanism; for -of this, after all, we can never obtain more than -that indirect evidence which consists in its leading -to the same results. What, in the actual state of -science, is far more important for us to know, is -whether our theory truly represent <em>all</em> the facts, and -include <em>all</em> the laws, to which observation and induction -lead. A theory which did this would, no doubt, -go a great way to establish any hypothesis of mechanism -or structure, which might form an essential -part of it: but this is very far from being -the case, except in a few limited instances; and, -till it is so, to lay any great stress on hypotheses -of the kind, except in as much as they serve -as a scaffold for the erection of general laws, is -to “quite mistake the scaffold for the pile.” Regarded -in this light, hypotheses have often an eminent -use: and a facility in framing them, if attended -with an equal facility in laying them aside when -they have served their turn, is one of the most -valuable qualities a philosopher can possess; while, -on the other hand, a bigoted adherence to them, -or indeed to peculiar views of any kind, in opposition -to the tenor of facts as they arise, is the bane -of all philosophy.</p> - -<p>(217.) There is no doubt, however, that the -safest course, when it can be followed, is to rise by -inductions carried on among laws, as among facts, -from law to law, perceiving, as we go on, how laws -which we have looked upon as unconnected become<span class="pagenum"><a id="Page_205">205</a></span> -particular cases, either one of the other, -or all of one still more general, and, at length, blend -altogether in the point of view from which we learn -to regard them. An example will illustrate what we -mean. It is a general law, that all hot bodies -throw out or <em>radiate</em> heat in all directions, (by -which we mean, not that heat is an actual substance -darted out from hot bodies, but only that -the laws of the transmission of heat to distant objects -are similar to those which would regulate the distribution -of particles thrown forth in all directions,) -and that other colder bodies placed in their neighbourhood -become hot, <em>as if</em> they received the heat -so radiated. Again, all solid bodies which become -heated in one part <em>conduct</em>, or diffuse, the heat -from that part through their whole substance. -Here we have two modes of communicating heat,—by -radiation, and by conduction; and both these -have their peculiar, and, to all appearance, very different -laws. Now, let us bring a hot and a cold -body (of the same substance) gradually nearer -and nearer together,—as they approach, the heat -will be communicated from the hot to the cold -one by the <em>laws of radiation</em>; and from the nearer -to the farther part of the colder one, as it gradually -grows warm, by <em>those of conduction</em>. Let -their distance be diminished till they just lightly -touch. How does the heat <em>now</em> pass from one to -the other? Doubtless, by radiation; for it may -be proved, that in such a contact there is yet -an interval. Let them then be <em>forced</em> together, -and it will seem clear that it must now be by -<em>conduction</em>. Yet their <em>interval</em> must diminish gradually,<span class="pagenum"><a id="Page_206">206</a></span> -as the force by which they are pressed -together increases, till they actually cohere, and -form one. The law of continuity, then, of which -we have before spoken (§ 199.), forbids us to suppose -that the intimate nature of the process of -communication is changed in this transition from -light to violent contact, and from that to actual -union. If so, we might ask, at what point does the -change happen? Especially since it is also demonstrable, -that the particles of the most solid -body are not, really, in contact. <em>Therefore</em>, the -laws of conduction and radiation have a mutual -dependence, and the former are only extreme cases -of the latter. If, then, we would rightly understand -what passes, or what is the process of nature in -the slow communication of heat through the substance -of a solid, we must ground our enquiries -upon what takes place at a distance, and then urge -the laws to which we have arrived, up to their -extreme case.</p> - -<p>(218.) When two theories run parallel to each -other, and each explains a great many facts in common -with the other, any experiment which affords a -crucial instance to decide between them, or by -which one or other must fall, is of great importance. -In thus verifying theories, since they are grounded -on general laws, we may appeal, not merely to particular -cases, but to whole classes of facts; and we -therefore have a great range among the individuals -of these for the selection of some particular effect -which ought to take place oppositely in the event -of one of the two suppositions at issue being right -and the other wrong. A curious example is given<span class="pagenum"><a id="Page_207">207</a></span> -by M. Fresnel, as decisive, in his mind, of the question -between the two great opinions on the nature -of light, which, since the time of Newton and -Huyghens, have divided philosophers. (See <a href="#p207">§ 207</a>.) -When two very clean glasses are laid one on the -other, if they be not perfectly flat, but one or both -in an almost imperceptible degree convex or prominent, -beautiful and vivid colours will be seen between -them; and if these be viewed through a red glass, -their appearance will be that of alternate dark and -bright stripes. These stripes are formed <em>between</em> the -two surfaces in apparent contact, as any one may -satisfy himself by using, instead of a flat <em>plate</em> of -glass for the upper one, a triangular-shaped piece, -called a prism, like a three-cornered stick, and -looking through the inclined side of it next the -eye, by which arrangement the reflection of light -from the upper surface is prevented from intermixing -with that from the surfaces in contact. -Now, the coloured stripes thus produced are explicable -on both theories, and are appealed to by -both as strong confirmatory facts; but there is a -difference in one circumstance according as one or -the other theory is employed to explain them. In -the case of the Huyghenian doctrine, the intervals -between the bright stripes ought to appear <em>absolutely -black</em>; in the other, <em>half bright</em>, when so viewed -through a prism. This curious case of difference -was tried as soon as the opposing consequences of -the two theories were noted by M. Fresnel, and the -result is stated by him to be decisive in favour of -that theory which makes light to consist in the -vibrations of an elastic medium.</p> - -<p><span class="pagenum"><a id="Page_208">208</a></span> -(219.) Theories are best arrived at by the consideration -of general laws; but most securely verified -by comparing them with particular facts, because -this serves as a verification of the whole train of -induction, from the lowest term to the highest. -But then, the comparison must be made with facts -purposely selected so as to include every variety of -case, not omitting extreme ones, and in sufficient -number to afford every reasonable probability of -detecting error. A single numerical coincidence in -a final conclusion, however striking the coincidence -or important the subject, is not sufficient. Newton’s -theory of sound, for example, leads to a numerical -expression for the actual velocity of sound, differing -but little from that afforded by the correct theory -afterwards explained by Lagrange, and (when certain -considerations not contemplated by him are -allowed for) agreeing with fact; yet this coincidence -is no verification of Newton’s view of the general -subject of sound, which is defective in an essential -point, as the great geometer last named has very -satisfactorily shown. This example is sufficient to -inspire caution in resting the verification of theories -upon any thing but a very extensive comparison with -a great mass of observed facts.</p> - -<p>(220.) But, on the other hand, when a theory -will bear the test of such extensive comparison, -it matters little how it has been originally framed. -However strange and, at first sight, inadmissible its -postulates may appear, or however singular it may -seem that such postulates should have been fixed -upon,—if they only lead us, by legitimate reasonings, -to conclusions in exact accordance with numerous<span class="pagenum"><a id="Page_209">209</a></span> -observations purposely made under such a variety of -circumstances as fairly to embrace the whole range -of the phenomena which the theory is intended to -account for, we cannot refuse to admit them; or -if we still hesitate to regard them as demonstrated -truths, we cannot, at least, object to receive them -as temporary substitutes for such truths, until the -latter shall become known. If they suffice to explain -all the phenomena known, it becomes highly -improbable that they will not explain more; and if -all their conclusions we have tried have proved -correct, it is probable that others yet untried will -be found so too; so that <em>in rejecting them altogether, -we should reject all the discoveries to which they may -lead</em>.</p> - -<p>(221.) In all theories which profess to give a true -account of the process of nature in the production -of any class of phenomena, by referring them to -general laws, or to the action of general causes, -through a train of modifying circumstances; before -we can apply those laws, or trace the action of those -causes in any assigned case, we require to know the -circumstances: we must have data whereon to ground -their application. Now, these can be learned only -from observation; and it may seem to be arguing -in a vicious circle to have recourse to observation -for any part of those theoretical conclusions, by -whose comparison with fact the theory itself is to -be tried. The consideration of an example will -enable us to remove this difficulty. The most -general law which has yet been discovered in chemistry -is this, that all the elementary substances in -nature are susceptible of entering into combination<span class="pagenum"><a id="Page_210">210</a></span> -with each other only in fixed or <em>definite proportions</em> -by weight, and not arbitrarily; so that when any -two substances are put together with a view to -unite them, if their weights are not in some certain -determinate proportion, a complete combination will -not take place, but some part of one or the other -ingredient will remain over and above, and uncombined. -Suppose, now, we have found a substance -having all the outward characters of a homogeneous -or unmixed body, but which, on analysis, we -discover to consist of sulphur, and lead in the -proportion of 20 parts of the former to 130 of the -latter ingredient; and we would know whether this -is to be regarded as a verification of the law of -definite proportions or an exception to it. The -question is reduced to this, whether the proportion -20 to 130 be or be not <em>that</em> fixed and definite proportion, -(or one of them, if there be more than one -proportion possible,) in which, according to the law -in question, sulphur and lead can combine; now, -this can never be decided by merely looking at the -law in all its generality. It is clear, that when particularized -by restricting its expression to sulphur -and lead, the law should state <em>what are</em> those particular -fixed proportions in which these bodies can -combine. That is to say, there must be certain data -or numbers, by which these are distinguished from -all other bodies in nature, and which require to be -known before we can apply the general law to the -particular case. To determine such data, observation -must be consulted; and if we were to have -recourse to that of the combination of the two substances -in question with each other, no doubt there<span class="pagenum"><a id="Page_211">211</a></span> -would be ground for the logical objection of a vicious -circle: but this is not done; the determination of -these numerical data is derived from experiments -purposely made on a great variety of different -combinations, among which that under consideration -does not of necessity occur, and all these -being found, independently of each other, to agree in -giving the same results, they are therefore safely assumed -as part of the system. Thus, the law of definite -proportions, when applied to the actual state of -nature, requires two separate statements, the one -announcing the general law of combination, the -other particularizing the numbers appropriate to -the several elements of which natural bodies consist, -or the data of nature. Among these data, if -arranged in a list, there will be found opposite to the -element sulphur the number 16, and opposite to -lead, 104<a id="FNanchor_48" href="#Footnote_48" class="fnanchor">48</a>; and since 20 is to 130 in the exact -proportion of 16 to 104, it appears that the combination -in question affords a satisfactory verification -of the law.</p> - -<p>(222.) The great importance of physical data -of this description, and the advantage of having -them well determined, will be obvious, if we consider, -that a list of them, when taken in combination -with the general law, affords the means of -determining at once the exact proportion of the -ingredients of all natural compounds, if we only -know the place they hold in the system. In -chemistry, the number of admitted elements is -between fifty and sixty, and new ones are added -continually as the science advances. Now, the moment<span class="pagenum"><a id="Page_212">212</a></span> -the number corresponding to any new substance -added to the list is determined, we have, -in fact, ascertained all the proportions in which it -can enter into combination with all the others, so -that a careful experiment made with the object -of determining this number is, in fact, equivalent -to as many different experiments as there are -binary, ternary, or yet more complicated combinations -capable of existing, into which the new -substance may enter, as an ingredient.</p> - -<p>(223.) The importance of obtaining exact physical -data can scarcely be too much insisted on, for -without them the most elaborate theories are little -better than mere inapplicable forms of words. It -would be of little consequence to be informed, -abstractedly, that the sun and planets attract each -other, with forces proportional to their masses, -and inversely as the squares of their distances: -but, as soon as we know the data of our system, as -soon as we have an accurate statement (no matter -how obtained) of the distances, masses, and actual -motions of the several bodies which compose it, -we need no more to enable us to predict all the -movements of its several parts, and the changes -that will happen in it for thousands of years to -come; and even to extend our views backwards -into time, and recover from the past, phenomena, -which no observation has noted, and no history -recorded, and which yet (it is possible) may have -left indelible traces of their existence in their -influence on the state of nature in our own globe, -and those of the other planets.</p> - -<p>(224.) The proof, too, that our data <em>are</em> correctly<span class="pagenum"><a id="Page_213">213</a></span> -assumed, is involved in the general verification of the -whole theory, of which, when once assumed, they -form a part; and the same comparison with observation -which enables us to decide on the truth of -the abstract principle, enables us, at the same time, -to ascertain whether we have fixed the values of our -data in accordance with the actual state of nature. -If not, it becomes an important question, whether -the assumed values can be corrected, so as to bring -the results of theory to agree with facts? Thus it -happens, that as theories approach to their perfection, -a more and more exact determination of data -becomes requisite. Deviations from observed fact, -which, in a first or approximative verification, may -be disregarded as trifling, become important when -a high degree of precision is attained. A difference -between the calculated and observed places of a -planet, which would have been disregarded by -Kepler in his verification of the law of elliptic -motion, would now be considered fatal to the theory -of gravity, unless it could be shown to arise from an -erroneous assumption of some of the numerical data -of our system.</p> - -<p>(225.) The observations most appropriate for the -ready and exact determination of physical data are, -therefore, those which it is most necessary to have -performed with exactness and perseverance. Hence -it is, that their performance, in many cases, becomes -a national concern, and observatories are erected and -maintained, and expeditions despatched to distant -regions, at an expense which, to a superficial view, -would appear most disproportioned to their objects. -But it may very reasonably be asked why the direct<span class="pagenum"><a id="Page_214">214</a></span> -assistance afforded by governments to the execution -of continued series of observations adapted to this -especial end should continue to be, as it has hitherto -almost exclusively been, confined to astronomy.</p> - -<p>(226.) Physical data intended to be employed -as elements of calculation in extensive theories, -require to be known with a much greater degree -of exactness than any single observation possesses, -not only on account of their dignity and importance, -as affording the means of representing an -indefinite multitude of facts; but because, in the -variety of combinations that may arise, or in the -changes that circumstances may undergo, cases -will occur when any trifling error in one of the -data may become enormously magnified in the final -result to be compared with observation. Thus, in -the case of an eclipse of the sun, when the moon -enters very obliquely upon the sun’s disc, a trifling -error in the diameter of either the sun or moon -may make a great one in the time when the eclipse -shall be announced to commence. It ought to be -remarked, that these are, of all others, the conjunctures -where observations are most available for -the determination of data; for, by the same rule -that a small change in the data will, in such cases, -produce a great one in the thing to be observed; -so, <i xml:lang="la" lang="la">vice versâ</i>, any moderate amount of error, committed -in an observation undertaken for ascertaining -its value, can produce but a very trifling one in the -<em>reverse</em> calculation from which the data come to be -determined by observation. This remark extends -to every description of physical data in every department -of science, and is never to be overlooked<span class="pagenum"><a id="Page_215">215</a></span> -when the object in view is the determination of -data with the last degree of precision.</p> - -<p>(227.) But how, it may be asked, are we to -ascertain <em>by</em> observation, data more precise than -observation itself? How are we to conclude the -value of that which we do not see, with greater -certainty than that of quantities which we actually -see and measure? It is the number of observations -which may be brought to bear on the determination -of data that enables us to do this. Whatever -error we may commit in a single determination, -it is highly improbable that we should always err -the same way, so that, when we come to take an -average of a great number of determinations, (unless -there be some constant cause which gives a -bias one way or the other,) we cannot fail, at -length, to obtain a very near approximation to the -truth, and, even allowing a bias, to come much -nearer to it than can fairly be expected from any -single observation, liable to be influenced by the -same bias.</p> - -<p>(228.) This useful and valuable property of the -average of a great many observations, that it brings -us nearer to the truth than any single observation -can be relied on as doing, renders it the most constant -resource in all physical enquiries where accuracy -is desired. And it is surprising what a rapid -effect, in equalizing fluctuations and destroying -deviations, a moderate multiplication of individual -observations has. A better example can hardly -be taken than the average height of the quicksilver -in the common barometer, which measures the -pressure of the air, and whose fluctuations are proverbial.<span class="pagenum"><a id="Page_216">216</a></span> -Nevertheless, if we only observe it regularly -every day, and, at the end of each month, -take an average of the observed heights, we shall -find the fluctuations surprisingly diminished in -amount; and if we go on for a whole year, or -for many years in succession, the annual averages -will be found to agree with still greater exactness. -This equalizing power of averages, by destroying -all such fluctuations as are irregular or accidental, -frequently enables us to obtain evidence of fluctuations -really regular, periodic in their recurrence, -and so much smaller in their amount than the accidental -ones, that, but for this mode of proceeding, -they never would have become apparent. Thus, if -the height of the barometer be observed four times -a day, constantly, for a few months, and the -averages taken, it will be seen that a regular <em>daily</em> -fluctuation, of very small amount, takes place, the -quicksilver rising and falling twice in the four-and-twenty -hours. It is by such observations that -we are enabled to ascertain—what no single measure -(unless by a fortunate coincidence), could give -us any idea, and never any certain knowledge of—the -true <em>sea level</em> at any part of the coast, or the -height at which the water of the ocean would -stand, if perfectly undisturbed by winds, waves, -or tides: a subject of very great importance, and -upon which it would be highly desirable to possess -an extensive series of observations, at a great -many points on the coasts of the principal continents -and islands over the whole globe.</p> - -<p>(229.) In all cases where there is a direct and -simple relation between the phenomenon observed<span class="pagenum"><a id="Page_217">217</a></span> -and a single <em>datum</em> on which it depends, every -single observation will give a value of this quantity, -and the average of all (under certain restrictions) -will be its exact value. We say, under certain -restrictions; for, if the circumstances under which -the observations are made be not alike, they may -not all be equally favourable to exactness, and it -would be doing injustice to those most advantageous, -to class them with the rest. In such -cases as these, as well as in cases where the <em>data</em> -are numerous and complicated together, so as not -to admit of single, separate determination (a thing -of continual occurrence), we have to enter into -very nice, and often not a little intricate, considerations -respecting the <em>probable</em> accuracy of our -results, or the limits of error within which it is -<em>probable</em> they lie. In so doing we are obliged to -have recourse to a refined and curious branch -of mathematical enquiry, called the doctrine of -probabilities, the object of which (as its name -imports) is to reduce our estimation of the probability -of any conclusion to calculation, so as to -be able to give more than a mere guess at the -degree of reliance which ought to be placed in -it.</p> - -<p>(230.) To give some general idea of the considerations -which such computations involve, let us -imagine a person firing with a pistol at a wafer on a -wall ten yards distant: we might, in a general way, -take it for granted, that he would hit the wall, but -not the wafer, at the first shot; but if we would form -any thing like a probable conjecture of <em>how near</em> he -would come to it, we must first have an idea of his<span class="pagenum"><a id="Page_218">218</a></span> -skill. No better way of judging could be devised than -by letting him fire a hundred shots at it, and marking -where they all struck. Suppose this done,—suppose -the wafer has been hit once or twice, that a certain -number of balls have hit the wall within an inch of -it, a certain number between one and two inches, -and so on, and that one or two have been some feet -wide of the mark. Still the question arises, what -estimate are we thence to form of his skill? how -<em>near</em> (or nearer) may we, after this experience, -safely, or at least not unfairly, bet that he will come -to the mark the next subsequent shot? This the -laws of probability enable us on such data to say. -Again, suppose, <em>before</em> we were allowed to measure -the distances, the wafer were to have been taken -away, and we were called upon, on the mere evidence -of the marks on the wall, to say where it had -been placed; it is clear that no reasoning would enable -any one to say with certainty; yet there is assuredly -one place which we may fix on with greater -probability of being right than any other. Now, -this is a very similar case to that of an observer—an -astronomer for example—who would determine -the exact place of a heavenly body. He points -to it his telescope, and obtains a series of results -disagreeing among themselves, but yet all agreeing -within certain limits, and only a comparatively small -number of them deviating considerably from the -mean of all; and from these he is called upon to -say, definitively, what he shall consider to have -been the most probable place of his star at the -moment. Just so in the calculation of physical -<em>data</em>; where no two results agree exactly, and<span class="pagenum"><a id="Page_219">219</a></span> -where all come within limits, some wide, some -close, what have we to guide us when we would -make up our minds what to conclude respecting -them? It is evident that any system of calculation -that can be shown to lead of necessity to the -most probable conclusion where certainty is not -to be had must be valuable. However, as this doctrine -is one of the most difficult and delicate among -the applications of mathematics to natural philosophy, -this slight mention of it must suffice at -present.</p> - -<p>(231.) In the foregoing pages we have endeavoured -to explain the spirit of the methods to which, -since the revival of philosophy, natural science has -been indebted for the great and splendid advances -it has made. What we have all along most earnestly -desired to impress on the student is, that natural -philosophy is essentially united in all its departments, -through all which one spirit reigns and one -method of enquiry applies. It cannot, however, be -studied as a whole, without subdivision into parts; -and, in the remainder of this discourse, we shall -therefore take a summary view of the progress -which has been made in the different branches into -which it may be most advantageously so subdivided, -and endeavour to give a general idea of the nature -of each, and of its relations to the rest. In the -course of this, we shall have frequent opportunity -to point out the influence of those general principles -we have above endeavoured to explain, on the progress -of discovery. But this we shall only do as -cases arise, without entering into any regular -analysis of the history of each department with that<span class="pagenum"><a id="Page_220">220</a></span> -view. Such an analysis would, indeed, be a most -useful and valuable work, but would far exceed our -present limits. We are not, however, without a -hope that this great desideratum in science will, -ere long, be supplied from a quarter every way -calculated to do it justice.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_221">221</a></span></p> - -<div class="chapter"> -<h2 id="hdr_13"><span class="larger">PART III.</span></h2> -</div> - -<p class="center">OF THE SUBDIVISION OF PHYSICS INTO DISTINCT -BRANCHES, AND THEIR MUTUAL RELATIONS.</p> - -<h2 id="hdr_14">CHAPTER I.</h2> - -<p class="center b2">OF THE PHENOMENA OF FORCE, AND OF THE CONSTITUTION -OF NATURAL BODIES.</p> - -<p class="in0">(232.) <span class="smcap"><span class="flet">N</span>atural History</span> may be considered in -two very different lights: either, 1st, as a collection -of facts and objects presented by nature, from the -examination, analysis, and combination of which we -acquire whatever knowledge we are capable of attaining -both of the order of nature, and of the agents she -employs for producing her ends, and from which, -therefore, all sciences arise; or, 2dly, as an assemblage -of phenomena to be explained; of effects to -be deduced from causes; and of materials prepared -to our hands, for the application of our principles to -useful purposes. Natural history, therefore, considered -in the one or the other of these points -of view, is either the beginning or the end of physical -science. As it offers to us, in a confused and -interwoven mass, the elements of all our knowledge, -our business is to disentangle, to arrange, and to -present them in a separate and distinct state: and -to this end we are called upon to resolve the important -but complicated problem,—Given the effect, or assemblage<span class="pagenum"><a id="Page_222">222</a></span> -of effects, to find the causes. The principles -on which this enquiry relies are those which constitute -the relation of cause and effect, as it exists with -reference to our minds; and their rules and mode -of application have been attempted to be sketched -out, (though in far less detail than the intrinsic -interest of the subject, both in a logical and practical -point of view, would demand,) in the foregoing -pages. It remains now to bring together, in a -summary statement, the results of the general examination -of nature, so far as it has been prosecuted -to the discovery of natural agents, and the mode in -which they act.</p> - -<p>(233.) 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 -<em>equilibrium</em>; or, 2dly, to produce <em>motion</em> in matter.</p> - -<p>(234.) 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<span class="pagenum"><a id="Page_223">223</a></span> -by it on matter, to say that matter is inert, -or has <em>inertia</em>, 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.</p> - -<p>(235.) However, if this should appear too metaphysical, -at all events this difference of effects gives rise -to two great divisions of the science of force, which -are commonly known by the names of <span class="smcap">Statics</span> -and <span class="smcap">Dynamics</span>; the latter term, which is general, -and has been used by us before in its general sense, -being usually confined to the doctrine of motion, as -produced and modified by force. Each of these -great divisions again branches out into distinct subdivisions, -according as we consider the equilibrium -or motion of matter in the three distinct states in -which it is presented to us in nature, the solid, -liquid, and aëriform state, to which, perhaps, ought -to be added the <em>viscous</em>, as a state intermediate between -that of solidity and fluidity, the consideration -of which, though very obscure and difficult, offers a -high degree of interest on a variety of accounts.</p> - -<h3><i>Statics and Dynamics.</i></h3> - -<p>(236.) The principles have been definitively fixed -by Galileo and his successors, down to Newton, -on a basis of sound induction; and as they are -perfectly general, and apply to every case, they -are competent, as we have already before observed, -to the solution of every problem that can -occur in the deductive processes, by which phenomena<span class="pagenum"><a id="Page_224">224</a></span> -are to be explained, or effects calculated. -Hence, they include every question that can arise -respecting the motions and rest of the smallest particles -of matter, as well as of the largest masses. -But the mode of reasoning from these general principles -differs materially, whether we consider them -as applied to masses of matter of a sensible size, or -to those excessively minute, and perhaps indivisible, -molecules of which such masses are composed. -The investigations which relate to the latter subject -are extremely intricate, as they necessarily involve -the consideration of the hypotheses we may form -respecting the intimate constitution of the several -sorts of bodies above enumerated.</p> - -<p>(237.) On the other hand, those which respect the -equilibrium and motions of sensible masses of matter -are happily capable of being so managed as to render -unnecessary the adoption of any particular hypothesis -of structure. Thus, in reasoning respecting the application -of forces to a solid mass, we suppose its parts -indissolubly and unalterably connected; it matters -not by what tie, provided this condition be satisfied, -that one point of it cannot be moved without setting -all the rest in motion, so that the relative situation -of the parts one among another be not changed. -This is the abstract notion of a solid which the mechanician -employs in his reasonings. And their conclusions -will apply to natural bodies, of course, only -so far as they conform to such a definition. In strictness -of speaking, however, there are no bodies which -absolutely conform to it. No substance is known -whose parts are absolutely incapable of yielding one -among another; but the amount by which they do<span class="pagenum"><a id="Page_225">225</a></span> -yield is so excessively small as to be demonstrably -incapable, in most cases, of having any influence -on the results: and in those where it has such influence, -an especial investigation of its amount can -always be made. This gives rise to two subdivisions -of the application of mechanical reasonings to solid -masses. Those which refer to the action of forces -on flexible or elastic, and on inflexible or rigid, -bodies, comprehending under the latter all such -whose resistance to flexure or fracture is so very -great as to permit our adoption of the language and -ideas of the extreme case without fear of material -error.</p> - -<p>(238.) In like manner, when we reason respecting -the action of forces on a fluid mass, all we have -occasion to assume is, that its parts are freely moveable -one among the other. If, besides this, we -choose to regard a fluid as incompressible, and -deduce conclusions on this supposition, they will -hold good only so far as there may be found such -fluids in nature. Now, in strictness, there are none -such; but, practically speaking, in the greater number -of cases their resistance to compression is so very -great that the result of the reasoning so carried on -is not sensibly vitiated; and, in the remaining cases, -the same general principles enable us to enter on a -special enquiry directed to this point: and hence the -division of fluids, in mechanical language, into compressible -and incompressible, the latter being only -the extreme or limiting case of the former.</p> - -<p>(239.) As we propose here, however, only to -consider what is the actual constitution of nature, -we shall regard all bodies, as they really are, more<span class="pagenum"><a id="Page_226">226</a></span> -or less flexible and yielding. We know for certain, -that the space which any material body appears to -occupy is not entirely filled by it; because there is -none which by the application of a sufficient force -may not be <em>compressed</em> or forced into a smaller space, -and which, either wholly, as in air or liquids, or in -part, as in the greater number of solids, will not recover -its former dimensions when the force is taken -off. In the case of air, this condensation may be -urged to almost any extent; and not only does a -mass of air so condensed completely recover its original -bulk, when the applied pressure is removed, -but if that ordinary pressure under which it exists -at the earth’s surface (and which arises from the -weight of the atmosphere) be also removed by an air-pump, -it will still further dilate itself without limit -so far as we have yet been able to try it. Hence -we are led to the conclusion that the particles of air -are mutually elastic, and have a <em>tendency to recede -from one another</em>, which can only be counteracted by -<em>force</em>, and therefore is itself a force of the repulsive -kind. Nevertheless, as air is heavy, and as gravitation -is a universal property of matter, there is no -doubt that this repulsive tendency must have a -limit, and that there is a distance to which, if the -particles of the air could be removed from each -other, their mutual repulsion would cease, and an -attraction take its place. This limit is probably -attained at some very great height above the earth’s -surface, beyond which, of course, its atmosphere -cannot extend.</p> - -<p>(240.) What, however, we can only conclude by -this or similar reasoning respecting air, we see distinctly<span class="pagenum"><a id="Page_227">227</a></span> -in liquids. They are all, though in a small degree, -compressible, and recover their former dimensions -completely when the pressure is removed; but -they cannot be dilated (by mechanical means), and -have no tendency, while they remain liquids, to enlarge -themselves beyond a certain limit, and therefore -they assume a determinate <em>surface</em> while at -rest, and their parts actually resist further separation -with a considerable force, thus giving rise to -the phenomenon of the <em>cohesion of liquids</em>.</p> - -<p>(241.) Both in air and in liquids, however, the -most perfect freedom of motion of the parts among -each other subsists, which could hardly be the case -if they were not separate and independent of each -other. And from this, combined with the foregoing -considerations, it has been concluded that they do -not actually touch, but are kept asunder at determinate -distances from each other, by the constant -action of the two forces of attraction and repulsion, -which are supposed to balance and counteract each -other at the ordinary distances of the particles, but -to prevail, the one, or the other, according as they -are forcibly urged together or pulled asunder.</p> - -<p>(242.) In solids, however, the case is very different. -The mutual free motion of their parts <i xml:lang="la" lang="la">inter se</i> is -powerfully impeded, and in some almost destroyed. -In some, a slow and gradual change of figure may be -produced to a great extent, by pressure or blows, -as for instance in the metals, clay, butter, &c.; in -others, fracture is the consequence of any attempt -to change the figure by violence beyond a certain -very small limit. In solids, then, it is evident, that -the consideration of their intimate structure has a<span class="pagenum"><a id="Page_228">228</a></span> -very great influence in modifying the general results -of the action of such attractive and repulsive forces -as may be assumed to account for the phenomena -they present; yet the general facts that their parts -<em>cohere</em> with a certain energy, and that they resist displacement -or intrusion on the part of other bodies, -are sufficient to demonstrate at least the existence -of such forces, whatever obscurity may subsist as to -their mode of action.</p> - -<p>(243.) This division of bodies into airs, liquids, -and solids, gives rise, then, to three distinct branches -of mechanical science, in each of which the general -principles of equilibrium and motion have their peculiar -mode of application; viz. pneumatics, hydrostatics, -and what might, without impropriety, be -termed stereostatics.</p> - -<h3><i>Pneumatics.</i></h3> - -<p>(244.) Pneumatics relates to the equilibrium or -movements of aërial fluids under all circumstances -of pressure, density, and elasticity. The weight of -the air, and its pressure on all the bodies on the -earth’s surface, were quite unknown to the ancients, -and only first perceived by Galileo, on the occasion -of a sucking-pump refusing to draw water above a -certain height. Before his time it had always been -supposed that water rose by suction in a pipe, in -consequence of a certain natural <em>abhorrence of a -vacuum</em> or empty space, which obliged the water to -enter by way of supplying the place of the air sucked -out. But if any such abhorrence existed, and had -the force of an <em>acting cause</em>, which could urge water -a single foot into a pipe, there is no reason why the<span class="pagenum"><a id="Page_229">229</a></span> -same principle should not carry it up two, three, or -any number of feet; none why it should suddenly -stop short at a certain height, and refuse to rise -higher, however violent the suction might be, nay, -even fall back, if purposely forced up too high.</p> - -<p>(245.) Galileo, however, at first contented himself -with the conclusion, that the natural abhorrence of -a vacuum was not strong enough to sustain the -water more than about thirty-two feet above its -level; and, although the true cause of the phenomenon -at length occurred to him, in the pressure of -the air on the general surface, it was not satisfactorily -demonstrated till his pupil, Torricelli, conceived the -happy idea of instituting an experiment on a small -scale by the use of a much heavier liquid, mercury, -instead of water, and, in place of sucking out the -air from above, employing the much more effectual -method of filling a long glass tube with mercury, -and inverting it into a basin of the same metal. It -was then at once seen, as by a <em>glaring instance</em>, that -the maintenance of the mercury in the tube (which -is nothing else than the common barometer) was the -effect of a perfectly definite external cause, while its -fluctuations from day to day, with the varying state -of the atmosphere, strongly corroborated the notion -of its being due to the pressure of the external air -on the surface of the mercury in the reservoir.</p> - -<p>(246.) The discovery of Torricelli was, however, -at first much misconceived, and even disputed, till -the question was finally decided by appeal to a <em>crucial -instance</em>, one of the first, if not the very first -on record in physics, and for which we are indebted -to the celebrated Pascal. His acuteness perceived<span class="pagenum"><a id="Page_230">230</a></span> -that if the weight of the incumbent air be the direct -cause of the elevation of the mercury, it must be -measured by the amount of that elevation, and therefore -that, by carrying a barometer up a high mountain, -and so ascending into the atmosphere <em>above</em> a large -portion of the incumbent air, the pressure, as well -as the length of the column sustained by it, must be -diminished; while, on the other hand, if the phenomenon -were due to the cause originally assigned, no -difference could be expected to take place, whether -the observation were made on a mountain or on the -plain. Perhaps the decisive effect of the experiment -which he caused to be instituted for the purpose, on -the Puy de Dôme, a high mountain in Auvergne, -while it convinced every one of the truth of Torricelli’s -views, tended more powerfully than any thing -which had previously been done in science to confirm, -in the minds of men, that disposition to experimental -verification which had scarcely yet taken -full and secure root.</p> - -<p>(247.) Immediately on this discovery followed -that of the air-pump, by Otto von Guericke of Magdeburgh, -whose aim seems to have been to decide -the question, whether a vacuum could or could not -exist, by endeavouring to make one. The imperfection -of his mechanism enabled him only to diminish -the aërial contents of his receivers, not entirely -to empty them; but the curious effects produced by -even a partial exhaustion of air speedily excited attention, -and induced our illustrious countryman, -Robert Boyle, to the prosecution of those experiments -which terminated in his hands, and in those -of Hauksbee, Hooke, Mariotte, and others, in a satisfactory<span class="pagenum"><a id="Page_231">231</a></span> -knowledge of the general law of the equilibrium -of the air under the influence of greater or less -pressures. These discoveries have since been extended -to all the various descriptions of aërial fluids -which chemistry has shown to exist, and to maintain -their aëriform state under artificial pressure, -and even to those which may be produced from -liquids reduced to a state of vapour by heat, so long -as they retain that state.</p> - -<p>(248.) The manner in which the observed law of -equilibrium of an elastic fluid, like air, may be considered -to originate in the mutual repulsion of its -particles, has been investigated by Newton, and the -actual statement of the law itself, as announced by -Mariotte, “that the density of the air, or the quantity -of it contained in the same space, is, <i xml:lang="la" lang="la">cæteris -paribus</i>, proportional to the pressure it supports,” has -recently been verified within very extensive limits -by direct experiment, by a committee of the Royal -Academy of Paris. This law contains the principle -of solution of every dynamical question that can -occur relative to the equilibrium of elastic fluids, -and is therefore to be regarded as one of the highest -<em>axioms</em> in the science of pneumatics.</p> - -<h3><i>Hydrostatics.</i></h3> - -<p>(249.) The principles of the equilibrium of -liquids, understanding by this word such fluids as do -not, though quite at liberty, attempt to dilate themselves -beyond a certain point, are at once few and -simple. The first steps towards a knowledge of them -were made by Archimedes, who established the -general fact, that a solid immersed in a liquid loses<span class="pagenum"><a id="Page_232">232</a></span> -a portion of its weight equal to that of the liquid it -displaces. It seems very astonishing, after this, that -it should not have been at once concluded that the -weight thus said to be <em>lost</em> is only <em>counteracted</em> by -the upward pressure of the liquid, and that, therefore, -a portion of any liquid, surrounded on all sides -by a liquid of the same kind, does really exert its -weight in keeping its place. Yet the prejudice that -“liquids do not gravitate in their natural place” -kept its ground, and was only dispelled with the -mass of error and absurdity which the introduction -of a rational and experimental philosophy by Galileo -swept away.</p> - -<p>(250.) The hydrostatical law of <em>the equal pressure -of liquids in all directions</em>, with its train of -curious and important consequences, is an immediate -conclusion from the perfect mobility of their -parts among one another, in consequence of which -each of them tends to recede from an excess of -pressure on one side, and thus bears upon the rest, -and distributes the pressure among its neighbours. -In this form it was laid down by Newton, and has -proved one of the most useful and fertile principles -of physico-mathematical reasoning on the equilibrium -of fluid masses, as affording a means of -tracing the action of a force applied at any point -of a liquid through its whole extent. It applies, -too, without any modification, to expansible fluids -as well as to liquids; and, in the applications of -geometry to this subject, enables us to dispense -with any minute and intricate enquiries as to the -mode in which individual particles act on each other.</p> - -<p>(251.) In a practical point of view, this law is<span class="pagenum"><a id="Page_233">233</a></span> -remarkable for the directness of its application to -useful purposes. The immediate and perfect distribution -of a pressure applied on any one part, however -small, of a fluid surface through the whole mass, enables -us to communicate <em>at one instant</em> the same pressure -to any number of such parts by merely increasing -the surface of the fluid, which may be done by -enlarging the containing vessel; and if the vessel -be so constructed that a large portion of its surface -shall be moveable together, the pressures on all the -similar parts of this portion will be united into one -consentient force, which may thus be increased to -any extent we please. The hydraulic press, invented -by Bramah, (or rather applied by him after -a much more ancient inventor, Stevin,) is constructed -on this principle. A small quantity of -water is driven by sufficient pressure into a vessel -<em>already full</em>, and provided with a moveable surface -or piston of great size. Under such circumstances -something must give way; the great surface of the -piston accumulates the pressure on it to such an -extent that nothing can resist its violence. Thus, -trees are torn up by the roots; piles extracted from -the earth; woollen and cotton goods compressed -into the most portable dimensions; and even hay, -for military service, reduced to such a state of -coercion as to be easily packed on board transports.</p> - -<p>(252.) Liquids differ from aëriform fluids by -their <em>cohesion</em>, which may be regarded as a kind -of approach to a solid state, and was so regarded -by Bacon (193.). Indeed, there can be little doubt -that the solid, liquid, and aëriform states of bodies -are merely stages in a progress of gradual transition<span class="pagenum"><a id="Page_234">234</a></span> -from one extreme to the other; and that, -however strongly marked the distinctions between -them may appear, they will ultimately turn out to -be separated by no sudden or violent line of demarcation, -but shade into each other by insensible -gradations. The late experiments of Baron Cagnard -de la Tour may be regarded as a first step towards -the full demonstration of this (199.). But the -cohesion of liquids is not, like that of solids, so -modified by their structure in other respects as to -destroy the mobility of their parts one among another -(unless in those cases of nearer approach to -the solid state which obtain in viscid or gummy -liquids). On the contrary, the two qualities co-exist, -and give rise to a number of curious and intricate -phenomena.</p> - -<p>(253.) One of the most remarkable of these is -capillary attraction, or capillarity as it is sometimes -called. Every body has remarked the adhesion of -water to glass. The elevation of the general surface -of the liquid where it is in contact with the containing -vessel; the form of a drop suspended at the -under side of a solid: these are instances of capillary -attraction. If a small glass tube with a bore -as fine as a hair be immersed in water, the water -will be observed to rise in it to a certain height, -and to assume a concave surface at its upper extremity. -The attraction of the glass on the water, -and the cohesion of the parts of the water to each -other, are no doubt the joint causes of this curious -effect; but the mode of action is at once obscure -and complex; and although the researches of Laplace -and Young have thrown great light on it, further<span class="pagenum"><a id="Page_235">235</a></span> -investigation seems necessary before we can -be said distinctly to understand it.</p> - -<p>(254.) As the capillarity and cohesion of the parts -of liquids shows them to possess the power of -mutual attraction, so their elasticity demonstrates -that they also possess that of repulsion when forcibly -brought nearer than their natural state. From -the extremely small extent to which the compression -of liquids can be carried by any force we can -employ, compared with that of air, we must conclude -that this repulsion is much more violent in -the former than in the latter, but counteracted also -by a more powerful force of attraction. So much -more powerful, indeed, is the resistance of liquids -to compression, that they were usually regarded as -incompressible; an opinion corroborated by a celebrated -experiment made at Florence, in which -water was forced through the pores (as it was said) -of a golden ball. More recent experiments by Canton, -and since by Perkins, Oërsted, and others, have -demonstrated however the contrary, and assigned -the amount of compression.</p> - -<p>(255.) The consideration of the motions of fluids, -whether liquid or expansible, is infinitely more complicated -than that of their equilibrium. When their -motions are slow, it is reasonable to suppose that -the law of the equable distribution of pressure obtains; -but in very rapid displacements of their -parts one among the other, it is not easy to see how -such an equable distribution can be accomplished, -and some phenomena exist which seem to indicate -a contrary conclusion.</p> - -<p>(256.) Independent of this, there are difficulties<span class="pagenum"><a id="Page_236">236</a></span> -of an almost insuperable nature to the regular deductive -application of the general principles of -mechanics to this subject, which arise from the -excessive intricacy of the pure mathematical enquiries -to which its investigation leads. It was -Newton who set the example of a first attempt to -draw any conclusions respecting the motion of fluid -masses by direct reasoning from dynamical principles, -and thus laid the foundation of <span class="smcap">Hydrodynamics</span>; -but it was not till the time of D’Alembert -that the method of reducing any question -respecting the motions of fluids under the action -of forces to strict mathematical investigation could -be said to be completely understood. But the cases -even now in which this mode of treating such questions -can be applied with full satisfaction are few -in comparison of those in which the experimental -method of enquiry as already observed (189.) is -preferable. Such, for example, is that of the resistance -of fluids to bodies moving through them; -a knowledge of which is of great importance in -naval architecture and in gunnery, where the resistance -of the air acts to an enormous extent. -Such, too, among the practical subjects which depend -mainly on this branch of science, are the use -of sails in navigation; the construction of windmills, -and water-wheels; the transmission of water through -pipes and channels; the construction of docks and -harbours, &c.</p> - -<h3><i>Nature of Solids in general.</i></h3> - -<p>(257.) The intimate constitution of solids is, in all -probability, very complicated, and we cannot be said<span class="pagenum"><a id="Page_237">237</a></span> -to know much of it. By some recent delicate experiments -on the dimensions of wires violently -strained, it has been shown that they are to a -certain small extent capable of being dilated by -tension, as they are also of being compressed by -pressure, but within limits even narrower than those -of liquids. Usually, when strained too far, they -break, and refuse to re-unite; or, if compressed too -forcibly, take a permanent contraction of dimension. -Thus, wood may be indented by a blow, and metals -rendered denser and heavier by hammering or -rolling. There is a certain degree of confusion -prevalent in ordinary language about the hardness, -elasticity, and other similar qualities, of solids, which -it may be well to remove. Hardness is that disposition -of a solid which renders it difficult to -displace its parts among themselves. Thus, steel -is harder than iron; and diamond almost infinitely -harder than any other substance in nature: but the -compressibility of steel, or the extent to which it -will yield to a given pressure and recover itself, is -not much less than that of soft iron, and that of -ice is very nearly the same with that of water.</p> - -<p>(258.) Again, we call Indian rubber a very elastic -body, and so it is; but in a different sense from -steel. Its parts admit of great mutual displacement -without permanent dislocation; however distorted, -it recovers its figure readily, but with a -small force. Yet, if Indian rubber were to be enclosed -in a space that it just filled, so as not to -permit its parts to yield laterally, doubtless it would -resist actual compression with great violence. Here,<span class="pagenum"><a id="Page_238">238</a></span> -then, we have an instance of two kinds of elasticity -in one substance; a feebler effort of recovery -from distorted figure, and a more violent one from -a state of altered dimension. Both, however, originate -in the same causes, and are referable to the -same principles; the former being in fact only a -modified case of the latter, as the effort of a steel -spring, when bent, to recover its former shape, is -referable to the same forces which give to steel its -hardness and strength to resist actual compression -and fracture.</p> - -<p>(259.) The toughness of a solid, or that quality -by which it will endure heavy blows without breaking, -is again distinct from hardness though often -confounded with it. It consists in a certain yielding -of parts with a powerful general cohesion, and is -compatible with various degrees of elasticity. Malleability -is again another quality of solids, especially -metals, quite distinct from toughness, and depends -on their capability of being deprived of their figure -without an effort to recover it and without fracture.</p> - -<p>(260.) Tenacity, again, is a property of solids more -directly depending on the cohesion of their parts -than toughness. It consists in their power of resisting -separation by a strain steadily applied, while -the quality of toughness is materially influenced by -their disposition to communicate through their substance -the jarring effect of a blow. Accordingly, -the tenacity of a solid is a direct measure of the -cohesive attraction of its parts, and is the best -proof of the existence of such a power.</p> - -<p><span class="pagenum"><a id="Page_239">239</a></span></p> - -<h3><i>Crystallography.</i></h3> - -<p>(261.) It cannot be supposed that these and -many other tangible qualities, as they may be called, -should subsist in solids without a corresponding -mechanism in their internal structure. That they -have such a mechanism, and that a very curious and -intricate one, the phenomena of crystallography -sufficiently show. This interesting and beautiful -department of natural science is of comparatively -very modern date. That many natural substances -affected certain forms must have been known from -the earliest times. Pliny appears to have been acquainted -with this fact, at least in some instances, -as he describes the forms of quartz and diamond. -But till the time of Linnæus no material attention -seems to have been bestowed on the subject. He, -however, observed, and described with care, the -crystalline forms of a variety of substances, and even -regarded them as so definite a character of the -solids which assumed them, that he supposed every -particular form to be generated by a particular salt. -Romé de l’Isle pursued the study of the crystalline -forms of bodies yet farther. He first ascertained -the important fact of the constancy of the angles -at which their faces meet; and observing further -that many of them appear in several different shapes, -first conceived the idea that these shapes might -be reducible to one, appropriated in a peculiar -manner to each <em>substance</em>, and modified by strict -geometrical laws. Bergmann, reasoning on a fact -imparted to him by his pupil Gahn, made a yet -greater step, and showed how at least one species<span class="pagenum"><a id="Page_240">240</a></span> -of crystal might be built up of thin laminæ ranged -in a certain order, and following certain rules of -superposition. He failed, however, in deducing just -and general conclusions from this remark, which, -correctly viewed, is the foundation of the most important -law of crystallography, that which connects -the primitive form with other forms capable of being -exhibited by the same substance, by a certain -fixed relation. An idea may be formed of what is -meant by this sort of connection of one form with -another, by considering a pointed pyramid built -up of cubic stones, disposed in layers, each of -which separately is a square plate of the thickness -of a single stone. These layers, laid horizontally -one on the other, and decreasing regularly in size -from the bottom to the top, produce a pyramidal -form with a rough or channeled surface; and if the -layers are so extremely thin that the channels cease -to be visible to the eye, the pyramid will seem -smooth and perfect.</p> - -<p>(262.) Very shortly after this, and without -knowledge of what had been done by Gahn and -Bergmann, the Abbé Haüy, instructed by the accidental -fracture of a fine group of crystals, made -the remark noticed already (in 67.), and reasoning -on it with more caution and success, and pursuing -it into all its detail, developed the general -laws which regulate the superposition of the layers -of particles of which he supposes all crystals to -be built up, and which enable us, from knowing -their primitive forms, to discover, previous to trial, -what other forms they are capable of assuming; -and which, according to this idea, are called derivative<span class="pagenum"><a id="Page_241">241</a></span> -or secondary forms. Mohs and others have -since imagined processes and systems by which the -derivation of forms from each other is facilitated, -and have corrected some errors of over-hasty generalization -into which their predecessors had fallen, -as well as advanced, by an extraordinary diligence -of research, our knowledge of the forms which the -various substances which occur in nature and art -actually do assume.</p> - -<p>(263.) In what manner a variety in point of external -form may originate in a variety of figures -in the ultimate particles of which a solid is composed, -may very readily be imagined by considering -what would happen if the bricks of which an edifice -is constructed had all a certain <em>leaning</em> or bias in -one direction out of the perpendicular. Suppose -every brick, for instance, when laid flat on its face, -with its longer edges north and south, had its eastern -and western faces upright, but its northern and -southern ones leaning southwards at a certain inclination -the same for each brick; a house built -of such bricks would lean the same way, if the -bricks fitted well together. If, <em>besides this</em>, the -eastern and western faces of the bricks, instead of -being truly upright, had an inclination eastward, the -house would have a similar one, and all its four -corners, instead of being upright, would lean to the -south-east. Suppose, instead of a house, a pyramid -were built of such oblique bricks, with the sides of -its base directed to the four points of the compass; -then its point, instead of being situated vertically -over the centre of its base, would stand perpendicularly -over some point to the south-east of that<span class="pagenum"><a id="Page_242">242</a></span> -centre, and the pyramid itself would have its sides -facing the south and the east, more highly inclined -to the horizon than those towards the north and -west.</p> - -<p>(264.) Whatever conception we may form of the -manner in which the particles of a crystal cohere -and form masses, it is next to impossible to divest -ourselves of the idea of a determinate figure common -to them all. Any other supposition, indeed, -would be incompatible with that exact similarity in -all other respects which the phenomena of chemistry -may be considered as having demonstrated. However, -it must be borne in mind that this idea, plausible -as it may appear, is yet in some degree hypothetical, -and that the laws of crystallography, as -determined from inductive observation, are quite -independent of any supposition of the kind, or even -of the existence of such things as ultimate particles -or atoms at all.</p> - -<p>(265.) Still, that peculiar internal constitution of -solid bodies, whatever it be, which is indicated by -the assumption of determinate figures, by their -splitting easier in some directions than in others, -and by their presenting glittering plane surfaces -when broken into fragments, cannot but have an -important influence on all their relations to external -agents, as well as to their internal movements and -the mutual actions of their parts on one another. -Accordingly, the division of bodies into crystallized -and uncrystallized, or imperfectly crystallized, is -one of the most universal importance; and almost -all the phenomena produced by those more intimate -natural causes which act within small limits, and as<span class="pagenum"><a id="Page_243">243</a></span> -it were on the immediate mechanism of solid substances, -are remarkably modified by their crystalline -structure. Thus, in transparent solids, the course -taken by the rays of light, in traversing them, as -well as the properties impressed upon them in so -doing, are intimately connected with this structure. -The recent experiments of M. Savart, too, have -proved that this is also the case with their power -of resistance to external force, on which depends -their elasticity. Crystallized substances, according -to the results of these experiments, resist compression -with different degrees of elastic force, according -to the direction in which it is attempted to compress -them; and all the phenomena dependent on their -elasticity are affected by this cause, especially those -which relate to their vibratory movements and their -conveyance of sound.</p> - -<p>(266.) There can be little doubt that modifications, -similarly depending on the internal structure -of crystals, will be traced through every department -of physics. In that interesting one which -relates to the action of heat in expanding the -dimensions of substances, a beginning has already -been made by Professor Mitscherlich. It had long -been known that all substances are dilated by heat, -and no exception to this law has been found, so -long as we regard the <em>bulk</em> of the heated body. -Thus, an iron rod when hot is both longer and -thicker than when cold; and the difference of dimension, -though but trifling in itself, is yet capable -of being made sensible, and is of considerable consequence -in engineering. Thus, too, the quicksilver -in a common thermometer occupies a larger space<span class="pagenum"><a id="Page_244">244</a></span> -when hot than when cold; and being confined by -the glass ball, (which also expands, but <em>not so much -in proportion</em>,) it is forced to rise in the tube. These -and similar facts had long been known; and accurate -measures of the total amount of dilatation of -a variety of different bodies, under similar accessions -of heat, had been obtained and registered in tables. -But no one had suspected the important fact, that -this expansion in crystallized bodies takes place -under totally different circumstances from what -obtains in uncrystallized ones. M. Mitscherlich has -lately shown that such substances expand differently -in different directions, and has even produced a -case in which expansion in one direction is actually -accompanied with contraction in another. This -step, the most important beyond a doubt which -has yet been made in pyrometry, can however only -be regarded as the first in a series of researches -which will occupy the next generation, and which -promises to afford an abundant harvest of new -facts, as well as the elucidation of some of the -most obscure and interesting points in the doctrine -of heat.</p> - -<p>(267.) From what has been said, it is clear that if -we look upon solid bodies as collections of particles -or atoms, held together and kept in their places by -the perpetual action of attractive and repulsive -forces, we cannot suppose these forces, at least in -crystallized substances, to act alike in all directions. -Hence arises the conception of <em>polarity</em>, of which we -see an instance, on a great scale, in the magnetic -needle, but which, under modified forms, there is -nothing to prevent us from conceiving to act among<span class="pagenum"><a id="Page_245">245</a></span> -the ultimate atoms of solid or even fluid bodies, -and to produce all the phenomena which they -exhibit in their crystallized state, either when acting -on each other, or on light, heat, &c. It is not difficult, -if we give the reins to imagination, to conceive -how attractive and repulsive atoms, bound together -by some unknown tie, may form little machines or -compound particles, which shall have many of the -properties which we refer to polarity; and accordingly -many ingenious suppositions have been made -to that effect: but in the actual state of science it -is certainly safest to wave these hypotheses, without -however absolutely rejecting them, and regard the -<em>polarity of matter</em> as one of the ultimate phenomena -to which the analysis of nature leads us, and of -which it is our business fully to investigate the laws, -before we endeavour to ascertain its causes, or trace -the mechanism by which it is produced.</p> - -<p>(268.) The mutual attractions and repulsions of the -particles of matter, then, and their polarity, whether -regarded as an original or a derivative property, are -the forces which, acting with great energy, and -within very confined limits, we must look to as the -principles on which the intimate constitution of all -bodies and many of their mutual actions depend. -These are what are understood by the general term -of <em>molecular forces</em>. Molecular attraction has been -attempted to be confounded by some with the -general attraction of gravity, which all matter exerts -on all other matter; but this idea is refuted by the -plainest facts.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_246">246</a></span></p> - -<div class="chapter"> -<h2 id="hdr_15">CHAP. II.</h2> -</div> - -<p class="center b2">OF THE COMMUNICATION OF MOTION THROUGH -BODIES.—OF SOUND AND LIGHT.</p> - -<p class="in0">(269.) <span class="smcap"><span class="flet">T</span>he</span> propagation of motion through all substances, -whether of a single impulse, as a blow or -thrust, or of one frequently and regularly repeated, -such as a jarring or vibratory movement, depends -wholly on these molecular forces; and it is on such -propagation that sound and very probably light depend. -To conceive the manner in which a motion may -be conveyed from one part of a substance to another, -whether solid or fluid, we may attend to what takes -place when a wave is made to run along a stretched -string, or the surface of still water. Every part of -the string, or water, is in succession moved from its -place, and agitated with a motion similar to that of -the original impulse, leaving its place and returning -to it, and when one part ceases to move the next -receives as it were the impression, and forwards it -onward. This may seem a slow and circuitous process -in description; but when sound, for example, is -conveyed through the air, we are to consider, 1st, -that the air, the substance actually in motion, is extremely -light and acted upon by a very powerful -elasticity, so that the force which propagates the -motion, or by which the particles adjacent act on, -and urge forward, each other, is very great, compared -with the quantity of materials set in motion by it:<span class="pagenum"><a id="Page_247">247</a></span> -and the same is true, even in a greater degree, in -liquids and solids; for in these the elastic forces -are even greater, in proportion to the weight, than -in air.</p> - -<p>(270.) A general notion of the mode in which -sounds are conveyed through the air was not altogether -deficient among the ancients; but it is to -Newton that we owe the first attempt to analyze -the process, and show correctly what takes place in -the communication of motion from particle to particle. -Reasoning on the properties of the air as an -elastic body, he showed the effect of an impulse on -any portion of it to consist in a condensation of -the air immediately adjacent in the direction of the -impulse, which then, re-acting by its spring, drives -back the portion which had advanced to its original -place, and at the same time urges forward the portion -before it, in the direction of the impulse, so -that every particle alternately advances and retreats. -But, in pursuing this idea into its details, Newton -fell into some errors which were pointed out by -Cramer, though their origin was not traced, nor the -reasoning corrected, till the subject was resumed by -Lagrange and Euler; nor is this any impeachment -of the penetration of our immortal countryman. The -mathematical theory of the propagation of sound, -and of vibratory and undulatory motions in general, -is one of the utmost intricacy; and, in spite of every -exertion on the part of the most expert geometers, -continues to this day to give continual occasion for -fresh researches; while phenomena are constantly -presenting themselves, which show how far we are -from being able to deduce all the particulars, even<span class="pagenum"><a id="Page_248">248</a></span> -of cases comparatively simple, by any direct reasoning -from first principles.</p> - -<p>(271.) Whenever an impulse of any kind is conveyed -by the air, to our ears, it produces the impression -of sound; but when such an impulse is -regularly and uniformly repeated in extremely rapid -succession, it gives us that of a musical note, the -pitch of the note depending on the rapidity of the -succession (see <a href="#p153">art. 153</a>.). The sense of harmony, -too, depends on the periodical recurrence of coincident -impulses on the ear, and affords, perhaps, the -only instance of a sensation for whose pleasing impression -a distinct and intelligible reason can be -assigned.</p> - -<p>(272.) Acoustics, then, or the science of sound, -is a very considerable branch of physics, and one -which has been cultivated from the earliest ages. -Even Pythagoras and Aristotle were not ignorant of -the general mode of its transmission through the -air, and of the nature of harmony; but as a branch -of science, independent of its delightful application -in the art of music, it could be hardly said to exist, -till its nature and laws became a matter of experimental -enquiry to Bacon and Galileo, Mersenne and -Wallis; and of mathematical investigation to Newton, -and his illustrious successors, Lagrange and Euler. -From that time its progress, as a branch both of -mathematical and experimental science, has been -constant and accelerated. A curious and beautiful -method of observation, due to Chladni, consists in -the happy device of strewing sand over the surfaces -of bodies in a state of sonorous vibration, and marking -the figures it assumes. This has made their<span class="pagenum"><a id="Page_249">249</a></span> -motions susceptible of ocular examination, and has -been lately much improved on, and varied in its application, -by M. Savart, to whom we also owe a succession -of instructive researches on every point -connected with the subject of sound, which may -rank among the finest specimens of modern experimental -enquiry. But the subject is far from being -exhausted; and, indeed, there are few branches of -physics which promise at once so much amusing interest, -and such important consequences, in its -bearings on other subjects, and especially, through -the medium of strong analogies, on that of light.</p> - -<h3><i>Light and Vision.</i></h3> - -<p>(273.) The nature of light has always been involved -in considerable doubt and mystery. The ancients -could scarcely be said to have any opinion on the -subject, unless, indeed, it could be considered such -to affirm that distant bodies could not be put into -communication without an intermedium; and that, -therefore, there must be <em>something</em> between the eye -and the thing seen. What that something is, however, -they could only form crude and vague conjectures. -One supposed that the eyes themselves -emit rays or emanations of some unknown kind, by -which distant objects are as it were felt; a singularly -unfortunate idea, since it gives no reason why -objects should not be equally well seen in the dark—no -account, in short, of the part performed by <em>light</em> -in vision. Others imagined that all visible objects are -constantly throwing out from them, in all directions, -some sort of resemblances or spectral forms of -themselves, which, when received by the eyes,<span class="pagenum"><a id="Page_250">250</a></span> -produce an impression of the objects. Vague and -clumsy as this hypothesis obviously is, it assigns to -the object a power, and to light a diffusive propagation -in all directions, which are, the one and the -other, independent of our eyes, and therefore goes -to separate the phenomena of <em>light</em> from those of -<em>vision</em>.</p> - -<p>(274.) The hypothesis of Newton is a refinement -and improvement on this idea. Instead of spectra or -resemblances, he supposes luminous objects actually -to dart out from them in all directions, particles, of -inconceivable minuteness (as indeed they must be, -having such an enormous velocity (see <a href="#p17">17</a>.), not to -dash in pieces every thing they strike upon). These -particles he supposes to be acted upon by attractive -and repulsive forces, residing in all material bodies, -the latter extending to some very small distance -beyond their surfaces; and by the action of these -forces to be turned aside from their natural straight-lined -course, without ever coming in actual contact -with the particles themselves of the bodies on which -they fall, but either being turned back and <em>reflected</em> -by the repulsive forces before they reach them, or -penetrating between their intervals, as a bird may -be supposed to fly through the branches of a forest, -and undergoing all their actions, to take at quitting -them a direction finally determined by the position -of the surface at which they emerge with respect -to their course.</p> - -<p>(275.) This hypothesis, which was discussed and -reasoned upon by Newton in a manner worthy of -himself, affords, by the application of the same -dynamical laws which he had applied with so much<span class="pagenum"><a id="Page_251">251</a></span> -success to the explanation of the planetary motions, -not merely a plausible, but a perfectly reasonable -and fair explanation of all the <em>usual</em> phenomena of -light known in his time. His own beautiful discoveries, -too, of the different refrangibilities of -the differently coloured rays, were perfectly well -represented in this theory, by simply admitting a -difference of velocity in the particles, which produce -in the eye the sensations of different colours. And had -the properties of light remained confined to these, -there would have been no occasion to have resorted -to any other mode of conceiving it.</p> - -<p>(276.) A very different hypothesis had, however, -been suggested about the same period by Huyghens, -who supposed light to be produced in the same -manner with sound, by the communication of a -vibratory motion from the luminous body to a -highly elastic fluid, which he imagined as filling all -space, and as being less condensed within the limits -of space occupied by matter, and that to a greater or -less extent, according to the nature of the occupying -substance. Thus, in place of any thing actually -thrown off, he substituted waves, or vibrations, propagated -in all directions from luminous bodies, -through this medium, or ether, as he called it. -Huyghens, being himself a consummate mathematician, -was enabled to trace many of the consequences -of this hypothesis, and to show that the -ordinary laws of reflection and refraction were represented -or accounted for by it, as well as by Newton’s. -But the hypothesis of Huyghens has not been fully -successful in accounting for what may be considered -the chief of all optical facts, the production of<span class="pagenum"><a id="Page_252">252</a></span> -colours in the ordinary refraction of light by a prism, -of which the theory of Newton gives a complete -and elegant explanation; and the discovery of -which by him marks one of the greatest epochs in -the annals of experimental science. This, which has -been often urged in objection to it, remains still, -if not quite unanswered, at least only imperfectly -removed.</p> - -<p>(277.) Other phenomena, however, were not -wanting to afford a further trial of the <em>explanatory -powers</em> of either hypothesis. The diffraction or -inflection of light, discovered by Grimaldi, a Jesuit -of Bologna, seemed to indicate that the rays of -light were turned aside from their straight course -by merely passing near bodies of every description. -These phenomena, which are very curious -and beautiful, were minutely examined by Newton, -and referred by him to the action of repulsive forces -extending to a sensible distance from the surfaces -of bodies; and his explanation, so far as the facts -known to him are concerned, appears as satisfactory -as could reasonably be then expected; and much -more so than any thing which could at that time be -produced on the side of the hypothesis of Huyghens, -which, in fact, seemed incapable of giving -any account whatever of them.</p> - -<p>(278.) Another class of delicate and splendid -optical phenomena, which had begun to attract attention -somewhat previous to Newton’s time, seemed -to leave both hypotheses equally at a loss. These -were the colours exhibited by very thin films, -either of a liquid (such as a soap-bubble), or of air, -as when two glasses are laid together with only air<span class="pagenum"><a id="Page_253">253</a></span> -between them. These colours were examined by -Newton with a minuteness and care altogether unexampled -in experimental philosophy at that time, -and with which few researches undertaken since -will bear to stand in competition. Their result was -a theory of a very singular nature, which he -grounded on an hypothesis of what he termed <em>fits -of easy transmission and reflection</em>; and which supposed -each ray of light to pass in its progress -periodically through a succession of states such as -would alternately dispose it to penetrate or be -reflected back from the surface of a body on which -it might fall. The simplest way in which the reader -may conceive this hypothesis, is to regard every -particle of light as a sort of little magnet revolving -rapidly about its own centre while it advances in its -course, and thus alternately presenting its attractive -and repulsive pole, so that when it arrives at the -surface of a body with its repulsive pole foremost, -it is repelled and reflected; and when the contrary, -attracted, so as to enter the surface. Newton, -however, very cautiously avoided announcing his -theory in this or any similar form, confining himself -entirely to general language. In consequence, it -has been confidently asserted by all his followers, -that the doctrine of fits of easy reflection and transmission, -as laid down by him, is substantially nothing -more than a statement of facts. Were it so, it is -clear that any other theory which should offer a -just account of the same phenomena must ultimately -involve and coincide with that of Newton. But -this, as we shall presently see, is not the case; and -this instance ought to serve to make us extremely<span class="pagenum"><a id="Page_254">254</a></span> -cautious how we employ, in stating physical laws -derived from experiment, language which involves -any thing in the slightest degree theoretical, if we -would present the laws themselves in a form which -no future research shall modify or subvert.</p> - -<p>(279.) A third class of optical phenomena, which -were likewise discovered while Newton was yet -engaged in his optical researches, was that exhibited -by doubly refracting crystals. In what the phenomenon -of double refraction consists, we have already -had occasion to explain. The fact itself was first -noticed by Erasmus Bartolin in the crystal called -Iceland spar; and was studied with attention by -Huyghens, who ascertained its laws, and referred it -with remarkable ingenuity and success to his theory -of light, by the additional hypothesis of such a constitution -of his ethereal medium within the crystal -as should enable it to convey an impulse faster in -one direction than another: as if, for example’s -sake, we should suppose a sound conveyed through -the air with different degrees of rapidity in a vertical -and horizontal direction.</p> - -<p>(280.) Some remarkable facts accompanying the -double refraction produced by Iceland spar, which -Bartolin, Huyghens, and Newton, had observed, led -the latter to conceive the singular idea that a ray of -light after its emergence from such a crystal acquires -<em>sides</em>, that is to say, distinct relations to surrounding -space, which it carries with it through its whole -subsequent course, and which give rise to all those -curious and complicated phenomena which are now -known under the name of the <em>polarization of light</em>. -These results, however, appeared so extraordinary,<span class="pagenum"><a id="Page_255">255</a></span> -and offered so little handle for further enquiry, that -their examination dropped, as if by common consent; -Newton himself resting content with urging -strongly the apparent incompatibility of these properties -with the Huyghenian doctrine, but without -making any attempt to explain them by his own.</p> - -<p>(281.) From the period of Newton’s optical discoveries -to the commencement of the present century, -no great accession to our knowledge of the -nature of light was made, if we except one, -which, from its invaluable practical application, -must ever hold a prominent place in the annals both -of art and science: we mean, the discovery of the -principle of the achromatic telescope, which originated -in a discussion between the celebrated -geometer Euler, Klingenstierna, an eminent Swedish -philosopher, and our own countryman, the admirable -optician Dollond, on the occasion of certain abstract -theoretical investigations of the former, which led -him to speculate on its <em>possibility</em>, and which ultimately -terminated in its complete and happy <em>execution</em> -by the latter; a memorable case in science, -though not a singular one, where the speculative -geometer in his chamber, apart from the world, -and existing among abstractions, has originated -views of the noblest practical application.<a id="FNanchor_49" href="#Footnote_49" class="fnanchor">49</a></p> - -<p>(282.) The explanation which our knowledge of -optical laws affords of the mechanism of the eye, and -the process by which vision is performed, is as complete<span class="pagenum"><a id="Page_256">256</a></span> -and satisfactory as that of hearing by the propagation -of motion through the air. The camera obscura, -invented by Baptista Porta in 1560, gave the -first idea how the actual images of external objects -might be conveyed into the eye, but it was not till -after a considerable interval that Kepler, the immortal -discoverer of those great laws which regulate -the periods and motions of the planets, pointed -out distinctly the offices performed by the several -parts of the eye in the act of vision. From this to -the invention of the telescope and microscope -there would seem but a small step, but it is to accident -rather than design that it is due; and its re-invention -by Galileo, on a mere description of its -effects, may serve, among a thousand similar instances, -to show that inestimable practical applications -lie open to us, if we can only once bring -ourselves to conceive their possibility, a lesson -which the invention of the achromatic telescope itself, -as we have above related it, not less strongly -exemplifies.</p> - -<p>(283.) The little instrument with which Galileo’s -splendid discoveries were made was hardly superior -in power to an ordinary finder of the present day; -but it was rapidly improved on, and in the hands of -Huyghens attained to gigantic dimensions and very -great power. It was to obviate the necessity of the -enormous length required for these telescopes, and -yet secure the same power, that Gregory and Newton -devised the reflecting telescope, which has since -become a much more powerful instrument than its -original inventors probably ever contemplated.</p> - -<p>(284.) The telescope, as it exists at present, with<span class="pagenum"><a id="Page_257">257</a></span> -the improvements in its structure and execution -which modern artists have effected, must assuredly -be ranked among the highest and most refined -productions of human art; that in which man has -been able to approximate most closely to the -workmanship of nature, and which has conferred -upon him, if not another sense, at least an exaltation -of one already possessed by him that merits -almost to be regarded as a new one. Nor does it -appear yet to have reached its ultimate perfection, -to which indeed it is difficult to assign any bounds, -when we take into consideration the wonderful -progress which workmanship of every kind is -making, and the delicacy, far superior to that of -former times, with which materials may now be -wrought, as well as the ingenious inventions and -combinations which every year is bringing forth -for accomplishing the same ends by means hitherto -unattempted.<a id="FNanchor_50" href="#Footnote_50" class="fnanchor">50</a></p> - -<p>(285.) After a long torpor, the knowledge of the -properties of light began to make fresh progress -about the end of the last century, advancing with -an accelerated rapidity, which has continued unabated -to the present time. The example was set -by our late admirable and lamented countryman,<span class="pagenum"><a id="Page_258">258</a></span> -Dr. Wollaston, who re-examined and verified the -laws of double refraction in Iceland spar announced -by Huyghens. Attention being thus drawn to the -subject, the geometry of Laplace soon found a means -of explaining at least one portion of the mystery -of this singular phenomenon, by the Newtonian -theory of light, applied under certain supposed conditions; -and the reasoning which led him to the result -(at that time quite unexpected), may justly be -regarded as one of his happiest efforts. The prosecution -of the subject, which had now acquired a -high degree of interest, was encouraged by the offer -of a prize on the part of the French Academy of -Sciences; and it was in a memoir which received this -honourable reward on that occasion, in 1810, that -Malus, a retired officer of engineers in the French -army, announced the great discovery of the <em>polarization -of light</em> by ordinary reflection at the surface of -a transparent body.</p> - -<p>(286.) Malus found that when a beam of light is -reflected from the surface of such a body at a certain -angle, it acquires precisely the same singular property -which is impressed upon it in the act of double -refraction, and which Newton had before expressed -by saying that it possessed <em>sides</em>. This was the first -circumstance which pointed out a connection between -that hitherto mysterious phenomenon and -any of the ordinary modifications of light; and it -proved ultimately the means of bringing the whole -within the limits, if not of a complete explanation, -at least of a highly plausible theoretical representation. -So true is, in science, the remark of Bacon,<span class="pagenum"><a id="Page_259">259</a></span> -that no natural phenomenon can be adequately -studied <em>in itself alone</em>, but, to be understood, must -be considered <em>as it stands connected with all nature</em>.</p> - -<p>(287.) The new class of phenomena thus disclosed -were immediately studied with diligence and success, -both abroad by Malus and Arago, and at -home by our countryman Dr. Brewster, and their -laws investigated with a care proportioned to their -importance; when another and apparently still more -extraordinary class of phenomena presented itself -in the production of the most vivid and beautiful -colours (every way resembling those observed by -Newton in thin films of air or liquids, only infinitely -more developed and striking,) in certain transparent -crystallized substances, when divided into flat plates -in particular directions, and exposed in a beam of -polarized light. The attentive examination of these -colours by Wollaston, Biot, and Arago, but more -especially by Brewster, speedily led to the disclosure -of a series of optical phenomena so various, so -brilliant, and evidently so closely connected with the -most important points relating to the intimate structure -of crystallized bodies, as to excite the highest -interest,—that sort of interest which is raised when -we feel we are on the eve of some extraordinary -discovery, and expect every moment that some leading -fact will turn up, which will throw light on all -that appears obscure, and reduce into order all that -seems anomalous.</p> - -<p>(288.) This expectation was not disappointed. -So long before the time we are speaking of as the -first year of the present century, our illustrious<span class="pagenum"><a id="Page_260">260</a></span> -countryman, the late Dr. Thomas Young, had established -a principle in optics, which, regarded as a -physical law, has hardly its equal for beauty, simplicity, -and extent of application, in the whole circle -of science. Considering the manner in which the -vibrations of two musical sounds arriving at once at -the ear affect the sense with an impression of sound -or silence according as they conspire or oppose -each other’s effects, he was led to the idea that -the same ought to hold good with light as with -sound, if the theory which makes light analogous to -sound be the true one; and that, therefore, two rays -of light, setting off from the same origin, at the same -instant, and arriving at the same place by different -routes, ought to strengthen or wholly or partially -destroy each other’s effects according to the difference -in length of the routes described by them. -That two lights should in any circumstances combine -to produce darkness may be considered strange, -but is <em>literally true</em>; and it had even been noticed -long ago as a singular and unaccountable fact by -Grimaldi, in his experiments on the inflection of -light. The experimental means by which Dr. Young -confirmed this principle, which is known in optics -by the name of the <em>interference</em> of the rays of light, -were as simple and satisfactory as the principle -itself is beautiful; but the verifications of it, drawn -from the explanation it affords of phenomena apparently -the most remote, are still more so. Newton’s -colours of thin films were the first phenomena to -which its author applied it with full success. Its -next remarkable application was to those of diffraction,<span class="pagenum"><a id="Page_261">261</a></span> -of which, in the hands of M. Fresnel, a late -eminent French geometer, it also furnished a complete -explanation, and that, too, in cases to which -Newton’s hypothesis could not apparently be made -to apply, and through a complication of circumstances -which might afford a very severe test of -any hypothesis.</p> - -<p>(289.) A simple and beautiful experiment on the -interferences of polarized light due to Fresnel and -Arago enabled them to bring Dr. Young’s law to -bear on the colours produced by crystallized plates -in a polarized beam, and by so doing afforded a -key to all the intricacies of these magnificent but -complex phenomena. Nothing now was wanting to -a rational theory of double refraction but to frame -an hypothesis of some mode in which light might -be conceived to be propagated through the elastic -medium supposed to convey it in such a way as not -to be contradictory to any of the facts, nor to -the general laws of dynamics. This essential idea, -without which every thing that had been before -done would have been incomplete, was also furnished -by Dr. Young, who, with a sagacity which -would have done honour to Newton himself, had -declared, that to accommodate the doctrine of -Huyghens to the phenomena of polarized light it is -necessary to conceive the mode of propagation of -a luminous impulse through the ether, differently -from that of a sonorous one through the air. In the -latter, the particles of the air <em>advance</em> and <em>recede</em>; -in the former, those of the ether must be supposed -to <em>tremble laterally</em>.</p> - -<p><span class="pagenum"><a id="Page_262">262</a></span> -(290.) Taking this as the groundwork of his -reasoning, Fresnel succeeded in erecting on it a -theory of polarization and double refraction, so -happy in its adaptation to facts, and in the coincidence -with experience of results deduced from it -by the most intricate analysis, that it is difficult to -conceive it unfounded. If it be so, it is at least the -most curiously artificial system that science has yet -witnessed; and whether it be so or not, so long as -it serves to group together in one comprehensive -point of view a mass of facts almost infinite in -number and variety, to reason from one to another, -and to establish analogies and relations between -them; on whatever hypothesis it may be founded, -or whatever arbitrary assumptions it may make -respecting structures and modes of action, it can -never be regarded as other than a most real and -important accession to our knowledge.</p> - -<p>(291.) Still, it is by no means impossible that the -Newtonian theory of light, if cultivated with equal -diligence with the Huyghenian, might lead to an -equally plausible explanation of phenomena now -regarded as beyond its reach. M. Biot is the author -of the hypothesis we have already mentioned -of a rotatory motion of the particles of light about -their axes. He has employed it only for a very -limited purpose; but it might doubtless be carried -much farther; and by admitting only the regular -emission of the luminous particles at equal intervals -of time, and in similar states of motion from the -shining body, which does not seem a very forced supposition, -all the phenomena of interference at least<span class="pagenum"><a id="Page_263">263</a></span> -would be readily enough explained without the admission -of an ether.</p> - -<p>(292.) The optical examination of crystallized -substances affords one among many fine examples -of the elucidation which every branch of science is -capable of affording to every other. The indefatigable -researches of Dr. Brewster and others have -shown that the phenomena exhibited by polarized -light in its transmission through crystals afford a -certain indication of the most important points -relating to the structure of the crystals themselves, -and thus become most valuable characters by which -to recognise their internal constitution. It was -Newton who first showed of what importance as a -physical character,—as the indication of other properties,—the -action of a body on light might become; -but the characters afforded by the use of polarized -light as an instrument of experimental enquiry are -so marked and intimate, that they may almost be -said to have furnished us with a kind of intellectual -sense, by which we are enabled to scrutinize the -internal arrangement of those wonderful structures -which Nature builds up by her refined and invisible -architecture, with a delicacy eluding our conception, -yet with a symmetry and beauty which we are never -weary of admiring. In this point of view the science -of optics has rendered to mineralogy and crystallography -services not less important than to astronomy -by the invention of the telescope, or to natural history -by that of the microscope; while the relations -which have been discovered to exist between the -optical properties of bodies and their crystalline forms,<span class="pagenum"><a id="Page_264">264</a></span> -and even their chemical habitudes, have afforded -numerous and beautiful instances of general laws -concluded from laborious and painful induction, and -curiously exemplifying the simplicity of nature as it -emerges slowly from an entangled mass of particulars -in which, at first, neither order nor connection can -be traced.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_265">265</a></span></p> - -<div class="chapter"> -<h2 id="hdr_16">CHAP. III.</h2> -</div> - -<p class="center b2">OF COSMICAL PHENOMENA.</p> - -<h3><i>Astronomy and Celestial Mechanics.</i></h3> - -<p class="in0">(293.) <span class="smcap"><span class="flet">A</span>stronomy,</span> as has been observed in the -former part of this discourse, as a science of observation, -had made considerable progress among the -ancients: indeed, it was the only branch of physical -science which could be regarded as having been cultivated -by them with any degree of assiduity or real -success. The Chaldean and Egyptian records had -furnished materials from which the motions of the -sun and moon could be calculated with sufficient exactness -for the prediction of eclipses; and some remarkable -cycles, or periods of years in which the -lunar eclipses return in very nearly the same order, -had been ascertained by observation. Considering -the extreme imperfection of their means of measuring -time and space, this was, perhaps, as much as could -have been expected at that early period, and it was -followed up for a while in a philosophical spirit of -just speculation, which, if continued, could hardly -have failed to lead to sound and important conclusions.</p> - -<p>(294.) Unfortunately, however, the philosophy of -Aristotle laid it down as a principle, that the celestial -motions were regulated by laws proper to themselves, -and bearing no affinity to those which prevail on<span class="pagenum"><a id="Page_266">266</a></span> -earth. By thus drawing a broad and impassable line -of separation between celestial and terrestrial mechanics, -it placed the former altogether out of the -pale of experimental research, while it at the same -time impeded the progress of the latter by the assumption -of principles respecting natural and unnatural -motions, hastily adopted from the most -superficial and cursory remark, undeserving even -the name of observation. Astronomy, therefore, continued -for ages a science of mere record, in which -theory had no part, except in so far as it attempted -to conciliate the inequalities of the celestial motions -with that assumed law of uniform circular revolution -which was alone considered consistent with the perfection -of the heavenly mechanism. Hence arose -an unwieldy, if not self-contradictory, mass of hypothetical -motions of sun, moon, and planets, in circles, -whose centres were carried round in other circles, -and these again in others without end,—“cycle on -epicycle, orb on orb,”—till at length, as observation -grew more exact, and fresh epicycles were continually -added, the absurdity of so cumbrous a mechanism -became too palpable to be borne. Doubts were expressed, -to which the sarcasm of a monarch<a id="FNanchor_51" href="#Footnote_51" class="fnanchor">51</a> gave a -currency they might not have obtained in a period -when men scarcely dared trust themselves to think; -and at length Copernicus, promulgating his own, or -reviving the Pythagorean doctrine, which places -the sun in the centre of our system, gave to astronomy -a simplicity which, contrasted with the complication -of the preceding views, at once commanded -assent.</p> - -<p><span class="pagenum"><a id="Page_267">267</a></span> -(295.) An elegant writer<a id="FNanchor_52" href="#Footnote_52" class="fnanchor">52</a>, whom we have before -had occasion to quote, has briefly and neatly accounted -for the confused notions which so long prevailed -respecting the constitution of our system, -and the difficulty experienced in acquiring a true -notion of the disposition of its parts. “We see it,” -he observes, “not in <em>plan</em>, but in <em>section</em>.” The -reason of this is, that our point of observation -lies in its general plane, but the notion we aim at -forming of it is not that of its section, but of its plan. -This is as if we should attempt to read a book, or -make out the countries on a map, with the eye on a -level with the paper. We can only judge directly -of the distances of objects by their sizes, or rather -of their change of distance by their change of size; -neither have we any means of ascertaining, otherwise -than indirectly, even their positions, one among the -other, from their apparent places as seen by us. Now, -the variations in apparent size of the sun and moon -are too small to admit of exact measure without the -use of the telescope, and the bodies of the planets -cannot even be distinguished as having any distinct -size with the naked eye.</p> - -<p>(296.) The Copernican system once admitted, however, -this difficulty of conception, at least, is effectually -got over, and it becomes a mere problem of geometry -and calculation to determine, from the observed -places of a planet, its real orbit about the sun, and -the other circumstances of its motion. This Kepler -accomplished for the orbit of Mars, which he ascertained -to be an ellipse having the sun in one of its -foci; and the same law, being extended by inductive<span class="pagenum"><a id="Page_268">268</a></span> -analogy to all the planets, was found to be verified in -the case of each. This with the other remarkable -laws which are usually cited in physical astronomy -by the name of Kepler’s laws, constitute undoubtedly -the most important and beautiful system of -geometrical relations which have ever been discovered -by a mere inductive process, independent of -any consideration of a theoretical kind. They comprise -within them a compendium of the motions of -all the planets, and enable us to assign their places -in their orbits at any instant of time past or to come -(disregarding their mutual perturbations), provided -certain purely geometrical problems can be numerically -resolved.</p> - -<p>(297.) It was not, however, till long after Kepler’s -time that the real importance of these laws could be -felt. Regarded in themselves, they offered, it is true, -a fine example of regular and harmonious disposition -in the greatest of all the works of creation, and a -striking contrast to the cumbersome mechanism of -the cycles and epicycles which preceded them; but -there their utility seemed to terminate, and, indeed, -Kepler was reproached, and not without a semblance -of reason, with having rendered the actual calculation -of the places of the planets more difficult -than before, the resources of geometry being then -inadequate to resolve the problems to which the -strict application of his laws gave rise.</p> - -<p>(298.) The first result of the invention of the -telescope and its application to astronomical purposes, -by Galileo, was the discovery of Jupiter’s -disc and satellites,—of a system offering a beautiful -miniature of that greater one of which it forms a<span class="pagenum"><a id="Page_269">269</a></span> -portion, and presenting to the eye of sense, at a -single glance, that disposition of parts which in the -planetary system itself is discerned only by the eye of -reason and imagination (see <a href="#p195">195</a>.). Kepler had the -satisfaction of seeing it ascertained, that the law which -he had discovered to connect the times of revolution -of the planets with their distances from the sun, holds -good also when applied to the periods of circulation -of these little attendants round the centre of their -principal; thus demonstrating it to be something -more than a mere empirical rule, and to depend on -the intimate nature of planetary motion itself.</p> - -<p>(299.) It had been objected to the doctrine of -Copernicus, that, were it true, Venus should appear -sometimes horned like the moon. To this he answered -by admitting the conclusion, and averring -that, should we ever be able to see its actual shape, -it <em>would</em> appear so. It is easy to imagine with what -force the application would strike every mind when -the telescope confirmed this prediction, and showed -the planet just as both the philosopher and his objectors -had agreed it ought to appear. The history -of science affords perhaps only one instance analogous -to this. When Dr. Hutton expounded his theory of -the consolidation of rocks by the application of heat, -at a great depth below the bed of the ocean, and -especially of that of marble by actual fusion; it was -objected that, whatever might be the case with -others, with calcareous or marble rocks, at least, it -was impossible to grant such a cause of consolidation, -since heat decomposes their substance and -converts it into quicklime, by driving off the carbonic -acid, and leaving a substance perfectly infusible,<span class="pagenum"><a id="Page_270">270</a></span> -and incapable even of agglutination by heat. -To this he replied, that the pressure under which -the heat was applied would prevent the escape of -the carbonic acid; and that being retained, it might -be expected to give that fusibility to the compound -which the simple quicklime wanted. The next -generation saw this anticipation converted into an -observed fact, and verified by the direct experiments -of Sir James Hall, who actually succeeded in melting -marble, by retaining its carbonic acid under -violent pressure.</p> - -<p>(300.) Kepler, among a number of vague and -even wild speculations on the causes of the motions -whose laws he had developed so beautifully and -with so much patient labour, had obtained a glimpse -of the general law of the inertia of matter, as applicable -to the great masses of the heavenly bodies -as well as to those with which we are conversant -on the earth. After Kepler, Galileo, while he gave -the finishing blow to the Aristotelian dogmas which -erected a barrier between the laws of celestial and -terrestrial motion, by his powerful argument and -caustic ridicule, contributed, by his investigations -of the laws of falling bodies and the motions of projectiles, -to lay the foundation of a true system of -dynamics, by which motions could be determined -from a knowledge of the forces producing them, -and forces from the motions they produce. Hooke -went yet farther, and obtained a view so distinct of -the mode in which the planets might be retained -in their orbits by the sun’s attraction, that, had his -mathematical attainments been equal to his philosophical -acumen, and his scientific pursuits been<span class="pagenum"><a id="Page_271">271</a></span> -less various and desultory, it can hardly be doubted -that he would have arrived at a knowledge of the -law of gravitation.</p> - -<p>(301.) But every thing which had been done towards -this great end, before Newton, could only be -regarded as smoothing some first obstacles, and -preparing a state of knowledge, in which powers -like his could be effectually exerted. His wonderful -combination of mathematical skill with physical -research enabled him to invent, at pleasure, new and -unheard-of methods of investigating the effects of -those causes which his clear and penetrating mind -detected in operation. Whatever department of -science he touched, he may be said to have formed -afresh. Ascending by a series of close-compacted -inductive arguments to the highest axioms of dynamical -science, he succeeded in applying them to -the complete explanation of all the great astronomical -phenomena, and many of the minuter and more -enigmatical ones. In doing this, he had every thing -to create: the mathematics of his age proved -totally inadequate to grapple with the numerous -difficulties which were to be overcome; but this, -so far from discouraging him, served only to afford -new opportunities for the exertion of his genius, -which, in the invention of the method of fluxions, -or, as it is now more generally called, the differential -calculus, has supplied a means of discovery, bearing -the same proportion to the methods previously in -use, that the steam-engine does to the mechanical -powers employed before its invention. Of the optical -discoveries of Newton we have already spoken; and -if the magnitude of the objects of his astronomical<span class="pagenum"><a id="Page_272">272</a></span> -discoveries excite our admiration of the mental -powers which could so familiarly grasp them, the -minuteness of the researches into which he there -set the first example of entering, is no less calculated -to produce a corresponding impression. -Whichever way we turn our view, we find ourselves -compelled to bow before his genius, and to assign -to the name of <span class="smcap">Newton</span> a place in our veneration -which belongs to no other in the annals of science. -His era marks the accomplished maturity of the -human reason as applied to such objects. Every -thing which went before might be more properly -compared to the first imperfect attempts of childhood, -or the essays of inexpert, though promising, -adolescence. Whatever has been since performed, -however great in itself, and worthy of so splendid -and auspicious a beginning, has never, in point of -intellectual effort, surpassed that astonishing one -which produced the Principia.</p> - -<p>(302.) In this great work, Newton shows all the -celestial motions known in his time to be consequences -of the simple law, that every particle of -matter attracts every other particle in the universe -with a force proportional to the product of their -masses directly, and the square of their mutual -distance inversely, and is itself attracted with an -equal force. Setting out from this, he explains how -an attraction arises between the great spherical -masses of which our system consists, regulated by -a law precisely similar in its expression; how the -elliptic motions of planets about the sun, and of -satellites about their primaries, according to the -exact rules inductively arrived at by Kepler, result<span class="pagenum"><a id="Page_273">273</a></span> -as necessary consequences from the same general -law of force; and how the orbits of comets themselves -are only particular cases of planetary movements. -Thence proceeding to applications of greater -difficulty, he explains how the perplexing inequalities -of the moon’s motion result from the sun’s -disturbing action; how tides arise from the unequal -attraction of the sun as well as of the moon on the -earth, and the ocean which surrounds it; and, lastly, -how the precession of the equinoxes is a necessary -consequence of the very same law.</p> - -<p>(303.) The immediate successors of Newton found -full occupation in verifying his discoveries, and in -extending and improving the mathematical methods -which it had now become manifest were to prove the -keys to an inexhaustible treasure of knowledge. The -simultaneous but independent discovery of a method -of mathematical investigation in every respect -similar to that of Newton, by Leibnitz, while it -created a degree of national jealousy which can now -only be regretted, had the effect of stimulating the -continental geometers to its cultivation, and impressing -on it a character more entirely independent -of the ancient geometry, to which Newton was -peculiarly attached. It was fortunate for science -that it did so; for it was speedily found that (with -one fine exception on the part of our countryman -Maclaurin, followed up, after a long interval, by the -late Professor Robison of Edinburgh, with equal -elegance,) the geometry of Newton was like the -bow of Ulysses, which none but its master could -bend; and that, to render his methods available -beyond the points to which he himself carried them,<span class="pagenum"><a id="Page_274">274</a></span> -it was necessary to strip them of every vestige of -that antique dress in which he had delighted to -clothe them. This, however, the countrymen of -Newton were very unwilling to do; and they paid -the penalty in finding themselves condemned to -the situation of lookers on, while their continental -neighbours both in Germany and France were pushing -forward in the career of mathematico-physical -discovery with emulous rapidity.</p> - -<p>(304.) The legacy of research which Newton may -be said to have left to his successors was truly immense. -To pursue, through all its intricacies, the -consequences of the law of gravitation; to account -for all the inequalities of the planetary movements, -and the infinitely more complicated, and to us more -important ones, of the moon; and to give, what -Newton himself certainly never entertained a conception -of, a demonstration of the stability and -permanence of the system, under all the accumulating -influence of its internal perturbations; this -labour, and this triumph, were reserved for the succeeding -age, and have been shared in succession by -Clairaut, D’Alembert, Euler, Lagrange and Laplace. -Yet so extensive is the subject, and so difficult and -intricate the purely mathematical enquiries to which -it leads, that another century may yet be required -to go through with the task. The recent discoveries -of astronomers have supplied matter for investigation, -to the geometers of this and the next generation, -of a difficulty far surpassing any thing that had -before occurred. Five primary planets have been -added to our system; four of them since the commencement -of the present century, and these, singularly<span class="pagenum"><a id="Page_275">275</a></span> -deviating from the general analogy of the -others, and offering <em>cases of difficulty</em> in theory, which -no one had before contemplated. Yet even the intricate -questions to which these bodies have given -rise seem likely to be surpassed by those which have -come into view, with the discovery of several comets -revolving in elliptic orbits, like the planets, round the -sun, in very moderate periods. But the resources -of modern geometry seem, so far from being exhausted, -to increase with the difficulties they have -to encounter, and already, among the successors of -Lagrange and Laplace, the present generation has to -enumerate a powerful array of names, which promise -to render it not less celebrated in the annals of -physico-mathematical research than that which has -just passed away.</p> - -<p>(305.) Meanwhile the positions, figures, and dimensions -of all the planetary orbits, are now well -known, and their variations from century to century -in great measure determined; and it has been generally -demonstrated, that all the changes which -the mutual actions of the planets on each other can -produce in the course of indefinite ages, are <em>periodical</em>, -that is to say, increasing to a certain extent -(and that never a very great one), and then -again decreasing; so that the system can never be -destroyed or subverted by the mutual action of its -parts, but keeps constantly oscillating, as it were, -round a certain mean state, from which it can never -deviate to any ruinous extent. In particular the -researches of Laplace, Lagrange, and Poisson, have -shown the ultimate invariability of the mean distance -of each planet from the sun, and consequently of its<span class="pagenum"><a id="Page_276">276</a></span> -periodic time. Relying on these grand discoveries, -we are enabled to look forward, from the point of -time which we now occupy, many thousands of years -into futurity, and predict the state of our system -without fear of material error, but such as may arise -from causes whose existence at present we have no -reason to suppose, or from interference which we -have no right to anticipate.</p> - -<p>(306.) A correct enumeration and description of -the fixed stars in catalogues, and an exact knowledge -of their position, supply the only effectual -means we can have of ascertaining what changes -they are liable to, and what motions, too slow to deprive -them of their usual epithet, <em>fixed</em>, yet sufficient -to produce a sensible change in the lapse of ages, -may exist among them. Previous to the invention -of the compass, they served as guides to the navigator -by night; but for this purpose, a very moderate -knowledge of a few of the principal ones -sufficed. Hipparchus was the first astronomer, who, -excited by the appearance of a new star, conceived -the idea of forming a catalogue of the stars, with a -view to its use as an astronomical record, “by -which,” says Pliny, “posterity will be able to discover, -not only whether they are born and die, but -also whether they change their places, and whether -they increase or decrease.” His catalogue, containing -more than 1000 stars, was constructed about 128 -years before Christ. It was in the course of the laborious -discussion of his own and former observations -of them, undertaken with a view to the formation of -this catalogue, that he first recognised the fact of that -slow, general advance of all the stars eastward, when<span class="pagenum"><a id="Page_277">277</a></span> -compared with the place of the equinox, which is -known under the name of the precession of the -equinoxes, and which Newton succeeded in referring -to a motion in the earth’s axis, produced by the -attraction of the sun and moon.</p> - -<p>(307.) Since Hipparchus, at various periods in the -history of astronomy, catalogues of stars have been -formed, among which that of Ulugh Begh, comprising -about 1000 stars, constructed in 1437, is remarkable -as the production of a sovereign prince, working personally -in conjunction with his astronomers; and that -of Tycho Brahe, containing 777 stars, constructed in -1600, as having originated in a phenomenon similar -to that which drew the attention of Hipparchus. -In more recent times, astronomers provided with -the finest instruments their respective eras could -supply, and established in observatories, munificently -endowed by the sovereigns and governments of -different European nations, have vied and are still -vying with each other, in extending the number of -registered stars, and giving the utmost possible -degree of accuracy to the determination of their -places. Among these, it would be ungrateful not to -claim especial notice for the superb series of observations -which, under a succession of indefatigable -and meritorious astronomers, has, for a very long -period, continued to emanate from our own national -observatory of Greenwich.</p> - -<p>(308.) The distance of the fixed stars is so immense, -that every attempt to assign a limit, <em>within -which</em> it <em>must</em> fall, has hitherto failed. The enquiries -of astronomers of all ages have been directed to ascertain -this distance, by taking the dimensions of our own<span class="pagenum"><a id="Page_278">278</a></span> -particular system of sun and planets, or of the earth -itself, as the unit of a scale on which it might be -measured. But although many have imagined that -their observations afforded grounds for the decision -of this interesting point, it has uniformly happened -either that the phenomena on which they relied -have proved to be referable to other causes not -previously known, and which the superior accuracy -of their researches has for the first time brought to -light; or to errors arising from instrumental imperfections -and unavoidable defects of the observations -themselves.</p> - -<p>(309.) The only indication we can expect to obtain -of the actual distance of a star, would consist -in an annual change in its apparent place corresponding -to the motion of the earth round the sun, -called its <em>annual parallax</em>, and which is nothing -more than the measure of the apparent size of the -earth’s orbit as seen from the star. Many observers -have thought they have detected a measurable -amount of this parallax; but as astronomical instruments -have advanced in perfection, the quantity -which they have successively assigned to it has -been continually reduced within narrower and narrower -limits, and has invariably been commensurate -with the errors to which the instruments used -might fairly be considered liable. The conclusion -this strongly presses on us is, that it is really a -quantity too small to admit of distinct measurement -in the present state of our means for that purpose; -and that, therefore, the distance of the stars must -be a magnitude of such an order as the imagination -almost shrinks from contemplating. But this increase<span class="pagenum"><a id="Page_279">279</a></span> -in our scale of dimension calls for a corresponding -enlargement of conception in all other -respects. The same reasoning which places the -stars at such immeasurable remoteness, exalts them -at the same time into glorious bodies, similar to, and -even far surpassing, our own sun, the centres perhaps -of other planetary systems, or fulfilling purposes -of which we can have no idea, from any analogy in -what passes immediately around us.</p> - -<p>(310.) The comparison of catalogues, published -at different periods, has given occasion to many -curious remarks, respecting changes both of place -and brightness among the stars, to the discovery of -variable ones which lose and recover their lustre -periodically, and to that of the disappearance of -several from the heavens so completely as to have -left no vestige discernible even by powerful telescopes. -In proportion as the construction of astronomical -and optical instruments has gone on improving, -our knowledge of the contents of the heavens -has undergone a corresponding extension, and, at -the same time, attained a degree of precision which -could not have been anticipated in former ages. -The places of all the principal stars in the northern -hemisphere, and of a great many in the southern, -are now known to a degree of nicety which must -infallibly detect any real motions that may exist -among them, and has in fact done so, in a great -many instances, some of them very remarkable -ones.</p> - -<p>(311.) It is only since a comparatively recent -date, however, that any great attention has been -bestowed on the smaller stars, among which there can<span class="pagenum"><a id="Page_280">280</a></span> -be no doubt of the most interesting and instructive -phenomena being sooner or later brought to light. -The minute examination of them with powerful -telescopes, and with delicate instruments for the -determination of their places, has, indeed, already -produced immense catalogues and masses of observations, -in which thousands of stars invisible to the -naked eye are registered; and has led to the discovery -of innumerable important and curious facts, -and disclosed the existence of whole classes of celestial -objects, of a nature so wonderful as to give -room for unbounded speculation on the extent and -construction of the universe.</p> - -<p>(312.) Among these, perhaps the most remarkable -are the revolving double stars, or stars which, to -the naked eye or to inferior telescopes, appear -single; but, if examined with high magnifying powers, -are found to consist of two individuals placed -almost close together, and which, when carefully -watched, are (many of them) found to revolve in -regular elliptic orbits about each other; and so far -as we have yet been able to ascertain, to obey the -same laws which regulate the planetary movements. -There is nothing calculated to give a grander idea -of the scale on which the sidereal heavens are -constructed than these beautiful systems. When we -see such magnificent bodies united in pairs, undoubtedly -by the same bond of mutual gravitation -which holds together our own system, and sweeping -over their enormous orbits, in periods comprehending -many centuries, we admit at once that they must -be accomplishing ends in creation which will remain -for ever unknown to man; and that we have here<span class="pagenum"><a id="Page_281">281</a></span> -attained a point in science where the human intellect -is compelled to acknowledge its weakness, and to feel -that no conception the wildest imagination can form -will bear the least comparison with the intrinsic -greatness of the subject.</p> - -<h3><i>Geology.</i></h3> - -<p>(313.) The researches of physical astronomy are -confessedly incompetent to carry us back to the -origin of our system, or to a period when its state -was, in any great essential, different from what it is at -present. So far as the causes now in action go, and -so far as our calculations will enable us to estimate -their effects, we are equally unable to perceive in -the general phenomena of the planetary system -either the evidence of a beginning, or the prospect -of an end. Geometers, as already stated, have demonstrated -that, in the midst of all the fluctuations -which can possibly take place in the elements of the -orbits of the planets, by reason of their mutual attraction, -the general balance of the parts of the -system will always be preserved, and every departure -from a mean state periodically compensated. -But neither the researches of the physical astronomer, -nor those of the geologist, give us any -ground for regarding our system, or the globe we -inhabit, as of eternal duration. On the contrary, -there are circumstances in the physical constitution -of our own planet which at least obscurely point to -an origin and a formation, however remote, since it -has been found that the figure of the earth is not<span class="pagenum"><a id="Page_282">282</a></span> -globular but elliptical, and that its attraction is such -as requires us to admit the interior to be more dense -than the exterior, and the density to increase with -some degree of regularity from the surface towards -the centre, and <em>that</em>, in layers arranged elliptically -round the centre, circumstances which could scarcely -happen without some such successive deposition of -materials as would enable pressure to be propagated -with a certain degree of freedom from one part of -the mass to another, even if we should hesitate to -admit a state of primitive fluidity.</p> - -<p>(314.) But from such indications nothing distinct -can be concluded; and if we would speculate to any -purpose on a former state of our globe and on the succession -of events which from time to time may have -changed the condition and form of its surface, we -must confine our views within limits far more -restricted, and to subjects much more within the -reach of our capacity, than either the creation of the -world or its assumption of its present figure. These, -indeed, were favourite speculations with a race of -geologists now extinct; but the science itself has -undergone a total change of character, even within -the last half century, and is brought, at length, -effectually within the list of the inductive sciences. -Geologists now no longer bewilder their imaginations -with wild theories of the formation of the globe -from chaos, or its passage through a series of hypothetical -transformations, but rather aim at a careful -and accurate examination of the records of its former -state, which they find indelibly impressed on the -great features of its actual surface, and to the<span class="pagenum"><a id="Page_283">283</a></span> -evidences of former life and habitation which organised -remains imbedded and preserved in its -strata indisputably afford.</p> - -<p>(315.) Records of this kind are neither few nor -vague; and though the obsoleteness of their language -when we endeavour to interpret it too minutely, may, -and no doubt often does, lead to misapprehension, -still its general meaning is, on the whole, unequivocal -and satisfactory. Such records teach us, in -terms too plain to be misunderstood, that the whole -or nearly the whole of our present lands and continents -were formerly at the bottom of the sea, -where they received deposits of materials from the -wearing and degradation of other lands not now -existing, and furnished receptacles for the remains -of marine animals and plants inhabiting the ocean -above them, as well as for similar spoils of the land -washed down into its bosom.</p> - -<p>(316.) These remains are occasionally brought -to light; and their examination has afforded indubitable -evidence of the former existence of a state of -animated nature widely different from what now -obtains on the globe, and of a period anterior to that -in which it has been the habitation of man, or -rather, indeed, of a series of periods, of unknown -duration, in which both land and sea teemed with -forms of animal and vegetable life, which have successively -disappeared and given place to others, -and these again to new races approximating gradually -more and more nearly to those which now inhabit -them, and at length comprehending species -which have their counterparts existing.</p> - -<p>(317.) These wrecks of a former state of nature,<span class="pagenum"><a id="Page_284">284</a></span> -thus wonderfully preserved (like ancient medals and -inscriptions in the ruins of an empire), afford a sort -of rude chronology, by whose aid the successive depositions -of the strata in which they are found may -be marked out in epochs more or less definitely -terminated, and each characterized by some peculiarity -which enables us to recognise the deposits -of any period, in whatever part of the world they -may be found. And, so far as has been hitherto -investigated, the <em>order</em> of succession in which these -deposits have been formed appears to have been -the same in every part of the globe.</p> - -<p>(318.) Many of the strata which thus bear evident -marks of having been deposited at the bottom -of the sea, and of course in a horizontal state, are -now found in a position highly inclined to the horizon, -and even occasionally vertical. And they -often bear no less evident marks of violence, in -their bending and fracture, the dislocation of parts -which were once contiguous, and the existence of -vast collections of broken fragments which afford -every proof of great violence having been used in -accomplishing some at least of the changes which -have taken place.</p> - -<p>(319.) Besides the rocks which carry this internal -evidence of submarine deposition, are many -which exhibit no such proofs, but on the contrary -hold out every appearance of owing their origin to -volcanoes or to some other mode of igneous action; -and in every part of the world, and among strata -of all ages, there occur evidences of such action so -abundant, and on such a scale, as to point out the -volcano and the earthquake as agents which may<span class="pagenum"><a id="Page_285">285</a></span> -have been instrumental in the production of those -changes of level, and those violent dislocations -which we perceive to have taken place.</p> - -<p>(320.) At all events, in accounting for those -changes, geologists have no longer recourse, as formerly, -to causes purely hypothetical, such as -a shifting of the earth’s axis of rotation, bringing -the sea to overflow the land, by a change in the -place of the longer and shorter diameters of the -spheroidal figure, nor to tides produced by the attraction -of comets suddenly approaching very near -the earth, nor to any other fanciful and arbitrarily -assumed hypotheses; but rather endeavour to confine -themselves to a careful consideration of causes -evidently in action at present, with a view to ascertain -how far they, in the first instance, are capable -of accounting for the facts observed, and thus legitimately -bringing into view, as residual phenomena, -those effects which cannot be so accounted for. -When this shall have been in some measure accomplished, -we shall be able to pronounce with greater -security than at present respecting the necessity of -admitting a long succession of tremendous and -ravaging catastrophes and cataclysms,—epochs of -terrific confusion and violence which many geologists -(perhaps with justice) regard as indispensable -to the explanation of the existing features of -the world. We shall learn to distinguish between -the effects which require for their production the -sudden application of convulsive and fracturing -efforts, and those, probably not less extensive, -changes which may have been produced by forces -equally or more powerful, but acting with less irregularity,<span class="pagenum"><a id="Page_286">286</a></span> -and so distributed over time as to produce -none of those <em>interregnums</em> of chaotic anarchy which -we are apt to think (perhaps erroneously) great disfigurements -of an order so beautiful and harmonious -as that of nature.</p> - -<p>(321.) But to estimate justly the effects of -causes now in action in geology is no easy task. -There is no <i xml:lang="la" lang="la">à priori</i> or deductive process by which -we can estimate the amount of the annual erosion, -for instance, of a continent by the action of meteoric -agents, rain, wind, frost, &c., nor the quantity of -destruction produced on its coasts by the direct -violence of the sea, nor the quantity of lava thrown -up <i xml:lang="la" lang="la">per annum</i> by volcanoes over the whole surface -of the earth, nor any similar effect. And to consult -experience on all such points is a slow and -painful process if rightly gone into, and a very fallible -one if only partially executed. Much, then, -at present must be left to opinion, and to that sort -of clear-judging tact which sometimes anticipates -experience; but this ought not to stand in the way -of our making every possible effort to obtain accurate -information on such points, by which alone -geology can be rendered, if not an experimental -science, at least a science of that kind of active -observation which forms the nearest approach to it, -where actual experiment is impossible.</p> - -<p>(322.) Let us take, for example, the question, -“What is the actual direction in which changes of -relative level are taking place between the existing -continents and seas?” If we consult partial experience, -that is, <em>all</em> the information that we possess -respecting ancient sea-marks, soundings, &c., we<span class="pagenum"><a id="Page_287">287</a></span> -shall only find ourselves bewildered in a mass of -conflicting, because imperfect, evidence. It is obvious -that the only way to decide the point is to ascertain, -by very precise and careful observations at -proper stations on coasts, selected at points where -there exist natural marks not liable to change in -the course of at least a century, the true elevation -of such marks above the <em>mean</em> level of the sea, and -to multiply these stations sufficiently over the whole -globe to be capable of affording real available knowledge. -Now, this is not a very easy operation (considering -the accuracy required); for the <em>mean</em> level -of the sea can be determined by no single observation, -any more than the mean height of the barometer -at a given station, being affected both by -periodical and accidental fluctuations due to tides, -winds, waves, and currents. Yet if an instrument -adapted for the purpose were constructed, and rendered -easily attainable, and rules for its use carefully -drawn up, there is little doubt we should soon -(by the industry of observers scattered over the -world) be in possession of a most valuable mass of -information, which could not fail to afford a point of -departure for the next generation, and furnish -ground for the only kind of argument which ever -can be conclusive on such subjects.</p> - -<p>(323.) Geology, in the magnitude and sublimity -of the objects of which it treats, undoubtedly ranks, -in the scale of the sciences, next to astronomy; -like astronomy, too, its progress depends on the -continual accumulation of observations carried on -for ages. But, unlike astronomy, the observations -on which it depends, when the whole extent of the<span class="pagenum"><a id="Page_288">288</a></span> -subject to be explored is taken into consideration, -can hardly yet be said to be more than commenced. -Yet, to make up for this, there is another important -difference, that while in the latter science it is impossible -to recall the past or anticipate the future, -and observation is in consequence limited to a single -fact in a single moment; in the former, the records -of the past are always present;—they may be examined -and re-examined as often as we please, and -require nothing but diligence and judgment to put us -in possession of their whole contents. Only a very -small part of the surface of our globe has, however, -been accurately examined in detail, and of that small -portion we are only able to scratch the mere exterior, -for so we must consider those excavations -which we are apt to regard as searching the bowels -of the earth; since the deepest mines which have -been sunk penetrate to a depth hardly surpassing the -ten thousandth part of the distance between its surface -and its centre. Of course inductions founded -on such limited examination can only be regarded -as provisional, except in those remarkable cases where -the same great formations in the same order have been -recognised in very distant quarters, and without exception. -This, however, cannot long be the case. The -spirit with which the subject has been prosecuted for -many years in our own country has been rewarded -with so rich a harvest of surprising and unexpected -discoveries, and has carried the investigation of our -island into such detail, as to have excited a corresponding -spirit among our continental neighbours; -while the same zeal which animates our countrymen -on their native shore accompanies them in their sojourns<span class="pagenum"><a id="Page_289">289</a></span> -abroad, and has already begun to supply a -fund of information respecting the geology of our -Indian possessions, as well as of every other point -where English intellect and research can penetrate.</p> - -<p>(324.) Nothing can be more desirable than that -every possible facility and encouragement should be -afforded for such researches, and indeed to the pursuits -of the enlightened resident or traveller in every -department of science, by the representatives of our -national authority wherever our power extends. By -these only can our knowledge of the actual state -of the surface of the globe, and that of the animals -and vegetables of the ancient continents and seas, be -extended and perfected, while more complete information -than we at present possess of the habits of -those actually existing, and the influence of changes -of climate, food, and circumstances, on them, may -be expected to render material assistance to our -speculations respecting those which have become -extinct.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_290">290</a></span></p> - -<div class="chapter"> -<h2 id="hdr_17">CHAP. IV.</h2> -</div> - -<p class="center b2">OF THE EXAMINATION OF THE MATERIAL CONSTITUENTS -OF THE WORLD.</p> - -<h3><i>Mineralogy.</i></h3> - -<p class="in0">(325.) <span class="smcap"><span class="flet">T</span>he</span> consideration of the history and structure -of our globe, and the examination of the fossil -contents of its strata, lead us naturally to consider -the materials of which it consists. The history of -these materials, their properties as objects of philosophical -enquiry, and their application to the useful -arts and the embellishments of life, with the characters -by which they can be certainly distinguished -one from another, form the object of mineralogy, -taken in its most extended sense.</p> - -<p>(326.) There is no branch of science which presents -so many points of contact with other departments -of physical research, and serves as a connecting -link between so many distant points of philosophical -speculation, as this. To the geologist, -the chemist, the optician, the crystallographer, -the physician, it offers especially the very elements -of their knowledge, and a field for many of -their most curious and important enquiries. Nor, -with the exception of chemistry, is there any which -has undergone more revolutions, or been exhibited -in a greater variety of forms. To the ancients it -could scarcely be said to be at all known, and up to -a comparatively recent period, nothing could be<span class="pagenum"><a id="Page_291">291</a></span> -more imperfect than its descriptions, or more inartificial -and unnatural than its classification. The -more important minerals in the arts, indeed, those -used for economical purposes and those from which -metals were extracted, had a certain degree of -attention paid to them, for the sake of their utility -and commercial value, and the precious stones for -that of ornament. But until their crystalline forms -were attentively observed and shown to be determinate -characters on which dependence could be -placed, no mineralogist could give any correct account -of the real distinction between one mineral -and another.</p> - -<p>(327.) It was only, however, when chemical -analysis had acquired a certain degree of precision -and universal applicability that the importance of -mineralogy as a science began to be recognized, and -the connection between the external characters of -a stone and its ingredient constituents brought into -distinct notice. Among these characters, however, -none were found to possess that eminent distinctness -which the crystalline form offers; a character, -in the highest degree geometrical, and affording, as -might be naturally supposed, the strongest evidence -of its necessary connection with the intimate constitution -of the substance. The full importance of -this character was, however, not felt until its connection -with the texture or cleavage of a mineral -was pointed out, and even then it required numerous -and striking instances of the critical discernment of -Haüy and other eminent mineralogists in predicting -from the measurements of the angles of crystals -which had been confounded together that differences<span class="pagenum"><a id="Page_292">292</a></span> -would be found to exist in their chemical -composition, all which proved fully justified in their -result before the essential value of this character was -acknowledged. This was no doubt in great measure -owing to the high importance set by the German -mineralogists on those external characters of touch, -sight, weight, colour, and other sensible qualities, -which are little susceptible, with the exception of -weight, of exact determination, and which are subject -to material variations in different specimens of -the same mineral. By degrees, however, the necessity -of ascribing great weight to a character so definite -was admitted, especially when it was considered -that the same step which pointed out the intimate -connection of external form with internal structure -furnished the mineralogist with the means of reducing -all the forms of which a mineral is susceptible -under one general type, or primitive form, and afforded -grounds for an elegant theoretical account of -the assumption of definite figures <i xml:lang="la" lang="la">ab initio</i>.</p> - -<p>(328.) A simple and elegant invention of Dr. Wollaston, -the reflecting goniometer, gave a fresh impulse -to that view of mineralogy which makes the -crystalline form the essential or leading character, -by putting it in the power of every one, by the examination -of even the smallest portion of a broken -crystal, to ascertain and verify that essential character -on which the identity of a mineral in the -system of Haüy was made to depend. The application -of so ready and exact a method speedily led -to important results, and to a still nicer discrimination -of mineral species than could before be attained; -and the confirmation given to these results<span class="pagenum"><a id="Page_293">293</a></span> -by chemical analysis stamped them with a scientific -and decided character which they have retained ever -since.</p> - -<p>(329.) Meanwhile the progress made in chemical -analysis had led to the important conclusion that -every chemical compound susceptible of assuming -the solid state assumed with it a determinate crystalline -form; and the progress of optical science -had shown that the fundamental crystalline form, in -the case at least of transparent bodies, drew with it -a series of optical properties no less curious than important -in relation to the affections of light in its passage -through such substances. Thus, in every point -of view, additional importance became added to this -character; and the study of the crystalline forms -of bodies in general assumed the form of a separate -and independent branch of science, of which the -geometrical forms of the mineral world constituted -only a particular case. Mineralogy, however, as a -branch of natural history, remains still distinct either -from optics or crystallography. The mineralogist -is content, and thinks he has performed his task, if -not as a natural historian at least as a classifier -and arranger, if he only gives such a characteristic -description of a mineral as shall effectually distinguish -it from every other, and shall enable any one -who may encounter such a body in any part of the -world to impose on it its name, assign it a place in -his system, and turn to his books for a further description -of all that the chemist, the optician, the -lapidary, or the artist, may require to know. Still -this is no easy matter: the laborious researches of -the most eminent mineralogists can hardly yet be<span class="pagenum"><a id="Page_294">294</a></span> -said to have effectually accomplished it; and its -difficulty may be appreciated by the small number of -simple minerals, or minerals of perfectly definite and -well-marked characters, which have been hitherto -made out. Nor can this indeed be wondered at, -when we consider that by far the greater portion -of the rocks and stones which compose the external -crust of the globe consists of nothing more than -the accumulated <em>detritus</em> of older rocks, in which the -fragments and powder of an infinite variety of substances -are mingled together, in all sorts of varying -proportions, and in such a way as to defy separation. -Many of these rocks, however, so compounded, -occur with sufficient frequency and uniformity -of character to have acquired names and to -have been usefully applied; indeed, in the latter -respect, minerals of this description far surpass all -the others. As objects of natural history, therefore, -they are well worthy of attention, however -difficult it may be to assign them a place in any -artificial arrangement.</p> - -<p>(330.) This paucity of simple minerals, however, -is probably rather apparent than real, and in proportion -as the researches of the chemist and crystallographer -shall be extended throughout nature, -they will no doubt become much more numerous. -Indeed, in the great laboratories of nature it can -hardly be doubted that almost every kind of chemical -process is going forwards, by which compounds -of every description are continually forming. -Accordingly, it is remarked, that the lavas and -ejected scoriæ of volcanoes are receptacles in which -mineral products previously unknown are constantly<span class="pagenum"><a id="Page_295">295</a></span> -discovered, and that the primitive formations, as -they are called in geology, which bear no marks of -having been produced by the destruction of others, -are also remarkable for the beauty and distinctness -of character of their minerals.</p> - -<p>(331.) The great difficulty which has been experienced -in attempts to classify mineral substances -by their chemical constituents has arisen from the -observed presence, in some specimens of minerals -bearing that general resemblance in other respects -as well as agreement in form which would seem to -entitle them to be considered as alike, of ingredients -foreign to the usual composition of the species, and -that occasionally in so large a proportion as to render -it unjustifiable to refer their occurrence to accidental -impurities. These cases, as well as some -anomalies observed in the classification of minerals -by their crystalline forms, which seemed to show -that the same substance might occasionally appear -under two distinct forms, as well as some remarkable -coincidences between the forms of substances -quite distinct from each other in a chemical point of -view, have within a recent period given rise to a -branch of the science of crystallography of a very -curious and important nature. The <em>isomorphism</em> -of certain groups of chemical elements has already -afforded us an example illustrative of the manner in -which inductions sometimes receive unexpected -verifications (see <a href="#p180">180</a>.). The laws and relations -thus brought to light are among the most curious -and interesting parts of modern science, and -seem likely in their further developement to afford -ample scope for the exercise of chemical and<span class="pagenum"><a id="Page_296">296</a></span> -mineralogical research. They have already afforded -innumerable fine examples of that important step in -science by which anomalies disappear, and occasional -incongruities become reconciled under more general -expressions of physical laws, and thus unite in -affording support to those very views which they promised, -when first observed, to overset. Nothing, indeed, -can be more striking than to see the very ingredient -which every previous chemist and mineralogist -would agree to disregard and reject as a mere -casual impurity brought forward and appealed to in -support of a theory expressly directed to the object -of rescuing science from the imputation of disregarding, -under any circumstances, the plain results -of direct experiment.</p> - -<h3><i>Chemistry.</i></h3> - -<p>(332.) The laws which concern the intimate constitution -of bodies, not as respects their <em>structure</em> or -the manner in which their parts are put together, -but as regards their <em>materials</em> or the ingredients of -which those parts are composed, form the objects of -chemistry. A solid body may be regarded as a -fabric, more or less regularly and artificially constructed, -in which the materials and the workmanship -may be separately considered, and in which, -though the latter be ruined and confounded by -violence, the former remain unchanged in their -nature, though differently arranged. In liquid or -aërial bodies, too, though there prevails a less -degree of difference in point of structure, and a -greater facility of dispersion and dissipation, than in -solids, yet an equal diversity of <em>materials</em> subsists,<span class="pagenum"><a id="Page_297">297</a></span> -giving to them properties differing extremely from -each other.</p> - -<p>(333.) The inherent activity of matter is proved -not only by the production of motion by the mutual -attractions and repulsions of distant or contiguous -masses, but by the changes and apparent transformations -which different substances undergo in -their sensible qualities by mere mixture. If water -be added to water, or salt to salt, the effect is an -increase of quantity, but no change of quality. In this -case, the mutual action of the particles is entirely mechanical. -Again, if a blue powder and a yellow one, -each perfectly dry, be mixed and well shaken together, -a green powder will be produced; but this is a mere -effect arising in the eye from the intimate mixture -of the yellow and blue light separately and independently -reflected from the minute particles of -each; and the proof is had by examining the mixture -with a microscope, when the yellow and blue -grains will be seen separate and each quite unaltered. -If the same experiment be tried with coloured -liquids, which are susceptible of mixing without -chemical action, a compound colour is likewise produced, -but no examination with magnifiers is in that -case sufficient to detect the ingredients; the reason -obviously being, the excessive minuteness of the -parts, and their perfect intermixture, produced by -agitating two liquids together. From the mixture -of two powders, extreme patience would enable any -one, by picking out with a magnifier grain after grain, -to separate the ingredients. But when liquids are -mixed, no mechanical separation is any longer practicable; -the particles are so minute as to elude all<span class="pagenum"><a id="Page_298">298</a></span> -search. Yet this does not hinder us from regarding -such a compound as still a mere mixture, and its -properties are accordingly intermediate between -those of the liquids mixed. But this is far from -being the case with all liquids. When a solution of -potash, for example, and another of tartaric acid, -each perfectly liquid, are mixed together in proper -proportions, a great quantity of a solid saline substance -falls to the bottom of the containing vessel, -which is quite different from either potash or tartaric -acid, and the liquid from which it subsided -offers no indications by its taste or other sensible -qualities of the ingredients mixed, but of something -totally different from either. It is evident that this -is a phenomenon widely different from that of mere -mixture; there has taken place a great and radical -change in the intimate nature of the ingredients, by -which a new substance is produced which had no -existence before. And it has been produced by the -<em>union</em> of the ingredients presented to each other; for -when examined it is found that nothing has been -<em>lost</em>, the weight of the whole mixture being the -sum of the weights mixed. Yet the potash and -tartaric acid have disappeared entirely, and the -weight of the new product is found to be exactly -equal to that of the tartaric acid and potash employed, -taken together, abating a small portion held -in solution in the liquid, which may be obtained -however by evaporation. They have therefore combined, -and adhere to one another with a cohesive -force sufficient to form a solid out of a liquid; a force -which has thus been called into action by merely -presenting them to each other in a state of solution.</p> - -<p><span class="pagenum"><a id="Page_299">299</a></span> -(334.) It is the business of chemistry to investigate -these and similar changes, or the reverse of such -changes, where a single substance is resolved into -two or more others, having different properties from -it, and from each other, and to enquire into all the -circumstances which can influence them; and either -determine, modify, or suspend their accomplishment, -whether such influence be exercised by heat -or cold, by time and rest, or by agitation or pressure, -or by any of those agents of which we have -acquired a knowledge, such as electricity, light, -magnetism, &c.</p> - -<p>(335.) The wonderful and sudden transformations -with which chemistry is conversant, the violent activity -often assumed by substances usually considered -the most inert and sluggish, and, above all, the insight -it gives into the nature of innumerable operations -which we see daily carried on around us, have contributed -to render it the most popular, as it is one of -the most extensively useful, of the sciences; and we -shall, accordingly, find none which have sprung -forward, during the last century, with such extraordinary -vigour, and have had such extensive influence -in promoting corresponding progress in -others. One of the chief causes of its popularity is, -perhaps, to be sought for in this, that it is, of all the -sciences, perhaps, the most completely an experimental -one; and even its theories are, for the -most part, of that generally intelligible and readily -applicable kind, which demand no intense concentration -of thought, and lead to no profound mathematical -researches. The simple process of inductive -generalization, grounded on the examination of numerous<span class="pagenum"><a id="Page_300">300</a></span> -facts, all of them presenting considerable -intrinsic interest, has sufficed, in most instances, to -lead, by a clear and direct road, to its highest laws -yet known. But, on the other hand, these laws, -when stated, are not yet fully sufficient to lead us, -except in very limited cases, to a deductive knowledge -of particulars never before examined, at least, -not without great caution, and constant appeal to -experiment as a check on our reasoning; so that we -are justified in regarding the <em>axioms</em> of chemistry, -the true handles of deductive reasoning, as still unknown, -and, perhaps, likely long to remain so. This -is no fault of its cultivators, who have comprised in -their list the highest and most varied talents and -industry, but of the inherent complexity of the -subject, and the infinite multitude of causes which -are concerned in the production of every, even the -simplest, chemical phenomenon.</p> - -<p>(336.) The history of chemistry (on which, however, -we are not about to enlarge,) is one of great interest -to those who delight to trace the steps by which -mankind advance to the discovery of truth through -a series of mistakes and failures. It may be divided, -1st, into the period of the alchemists, a lamentable -epoch in the annals of intellectual wandering; 2dly, -that of the phlogistic doctrines of Beccher and Stahl, -in which, as if to prove the perversity of the human -mind, of two possible roads the wrong was chosen; -and a theory obtained universal credence on the -strength of an induction, valid as such, but wrongly -interpreted, which is negatived, <em>in every instance</em>, -by an appeal to the balance. This, too, happened, -not by reason of unlucky coincidences, or individual<span class="pagenum"><a id="Page_301">301</a></span> -oversights, but of necessity, and from an inherent -defect of the theory itself, which thus impeded the -progress of the science, as far as a science of experiment -can be impeded by a false theory, by perplexing -its cultivators with the appearance of -contradictions in their experiments where none -really subsisted, by destroying all their confidence -in the numerical exactness of their own results, -and by involving the subject in a mist of visionary -and hypothetical causes in place of the true -acting principles. Thus, in the combustion of any -substance which is incapable of flying away in fumes, -an increase of weight takes place,—the ashes are -heavier than the fuel. Whenever this was observed, -however, it was passed carelessly over as arising -from the escape of phlogiston, or the principle of inflammability, -which was considered as being either -the element of fire itself, or in some way combined -with it, and thus essentially <em>light</em>. It is now known -that the increase of weight is owing to the absorption -of, and combination with, a quantity of a peculiar -ingredient called <em>oxygen</em>, from the air, a principle -essentially <em>heavy</em>. So far as weight is concerned, it -makes no difference whether a body having weight -enters, or one having levity escapes; but there is -this plain difference in a philosophical point of view, -that oxygen is a real producible substance, and -phlogiston is no such thing: the former is a <i xml:lang="la" lang="la">vera -causa</i>, the latter an hypothetical being, introduced -to account for what the other accounts for much -better.</p> - -<p>(337.) The third age of chemistry—that which -may be called emphatically modern chemistry—<span class="pagenum"><a id="Page_302">302</a></span>commenced -(in 1786) when Lavoisier, by a series of -memorable experiments, extinguished for ever this -error, and placed chemistry in the rank of one of the -exact sciences,—a science of number, weight, and -measure. From that epoch to the present day it has -constantly advanced with an accelerated progress, -and at this moment may be regarded as more progressive -than ever. The principal features in this -progress may be comprised under the following -general <span class="locked">heads:—</span></p> - -<blockquote class="hang2"> - -<p> 1. The discovery of the proximate, if not the -ultimate, elements of all bodies, and the enlargement -of the list of known elements to -its present extent of between fifty and sixty -substances.</p> - -<p> 2. The developement of the doctrine of latent -heat by Black, with its train of important -consequences, including the scientific theory -of the steam-engine.</p> - -<p> 3. The establishment of Wenzel’s law of definite -proportions on his own experiments, and -those of Richter, a discovery subsequently -merged in the more general wording and -better development of Dalton’s atomic -theory.</p> - -<p> 4. The precise determination of the atomic weights -of the different chemical elements, mainly -due to the astonishing industry of Berzelius, -and his unrivalled command of chemical resources, -as well as to the researches of the -other chemists of the Swedish and German -school.</p> - -<p> 5. The assimilation of gases and vapours, by which<span class="pagenum"><a id="Page_303">303</a></span> -we are led to regard the former, universally, -as particular cases of the latter, a generalization -resulting chiefly from the experiments -of Faraday on the condensation of the gases, -and those of Gay-Lussac and Dalton, on the -laws of their expansion by heat compared -with that of vapours.</p> - -<p> 6. The establishment of the laws of the combination -of gases and vapours by definite volumes, -by Gay-Lussac.</p> - -<p> 7. The discovery of the chemical effects of electricity, -and the decomposing agency of the -Voltaic pile, by Nicholson and Carlisle; the -investigation of the laws of such decompositions, -by Berzelius and Hisinger: the decomposition -of the alkalies by Davy, and the -consequent introduction into chemistry of -new and powerful agents in their metallic -bases.</p> - -<p> 8. The application of chemical analysis to all the -objects of organized and unorganized nature, -and the discovery of the ultimate constituents -of all, and the proximate ones of organic -matter, and the recognisance of the important -distinctions which appear to divide these -great classes of bodies from each other.</p> - -<p> 9. The applications of chemistry to innumerable -processes in the arts, and among other useful -purposes to the discovery of the essential -medical principles in vegetables, and to important -medicaments in the mineral kingdom.</p> - -<p>10. The establishment of the intimate connection<span class="pagenum"><a id="Page_304">304</a></span> -between chemical composition and crystalline -form, by Haüy and Vauquelin, with the -successive rectifications the statement of that -connection has undergone in the hands of -Mitscherlich, Rose, and others, with the progress -of chemical and crystallographical -knowledge.</p></blockquote> - -<p>(338.) To pursue these several heads into detail -would lead us into a treatise on chemistry; but a -few remarks on one or two of them, as they bear -upon the general principles of all scientific enquiry, -will not be irrelevant. And first, then, with reference -to the discovery of new elements, it will be -observed, that philosophical chemistry no more aims -at determining the one essential element out of which -all matter is framed—the one ultimate principle of -the universe—than astronomy at discovering the -origin of the planetary movements in the application -of a determinate projectile force in a determinate -direction, or geology at ascending to the creation -of the earth. There may be such an element. Some -singular relations which have been pointed out in -the atomic weights of bodies seem to suggest to -minds fond of speculation that there is; but philosophical -chemistry is content to wait for some striking -fact, which may either occur unexpectedly or be led -to by the slow progress of enlarged views, to disclose -to us its existence. Still, the multiplication of so-considered -elementary bodies has been considered -by some as an inconvenience. We confess we do -not coincide with this view. Whatever they be, the -obstinacy with which they resist decomposition -shows that they are ingredients of a very high and<span class="pagenum"><a id="Page_305">305</a></span> -primary importance in the economy of nature; and -such as, in any state of science, it would be indispensably -necessary to be perfectly familiar with. -Like particular theorems in geometry, which, -though not rising to the highest point of generality, -have yet their several scopes and ranges of extensive -application, they must be well and perfectly -understood in all their bearings. Should we ever -arrive at an analysis of these bodies, the chemical -properties of the new elements which will then -come into view will be known only by our knowledge -of these, or of other compounds of the same -class, which they may be capable of forming. Not but -that such an analysis would be a most important and -indeed triumphant achievement, and change the -face of chemistry; but it would undo nothing that -has been done, and render useless no point of knowledge -which we have yet arrived at.</p> - -<p>(339.) The atomic theory, or the law of definite -proportions, which is the same thing presented in a -form divested of all hypothesis, after the laws of -mechanics, is, perhaps, the most important which -the study of nature has yet disclosed. The extreme -simplicity which characterizes it, and which is -itself an indication, not unequivocal, of its elevated -rank in the scale of physical truths, had the effect -of causing it to be announced at once by Mr. -Dalton, in its most general terms, on the contemplation -of a few instances<a id="FNanchor_53" href="#Footnote_53" class="fnanchor">53</a>, without passing through -subordinate stages of painful inductive ascent by -the intermedium of subordinate laws, such as, had -the contrary course been pursued by him, would<span class="pagenum"><a id="Page_306">306</a></span> -have been naturally preparatory to it, and such as -would have led others to it by the prosecution of -Wenzel’s and Richter’s researches, had they been -duly attended to. This is, in fact, an example, and -a most remarkable one, of the effect of that natural -propensity to generalize and simplify (noticed in -171.), which, if it occasionally leads to over-hasty -conclusions, limited or disproved by further experience, -is yet the legitimate parent of many of our -most valuable and soundest results. Instances like -this, where great and, indeed, immeasurable steps -in our knowledge of nature are made at once, and -almost without intellectual effort, are well calculated -to raise our hopes of the future progress of science, -and, by pointing out the simplest and most obvious -combinations as those which are actually found to -be agreeable to the harmony of creation, to hold -out the cheering prospect of difficulties diminishing -as we advance, instead of thickening around us in -increasing complexity.</p> - -<p>(340.) A consequence of this immediate presentation -of the law of definite proportions in its most -general form is, that its subordinate laws—those -which limit its generality in particular cases, which -diminish the number of combinations abstractly -possible, and restrain the indiscriminate mixture of -elements,—remain to be discovered. Some such -limitations have, in fact, been traced to a certain -extent, but by no means so far as the importance of -the subject requires; and we have here abundant -occupation for chemists for some time.</p> - -<p>(341.) The determination of the atomic weights -of the chemical elements, like that of other standard<span class="pagenum"><a id="Page_307">307</a></span> -physical data, with the utmost exactness, is in itself -a branch of enquiry not only of the greatest importance, -but of extreme difficulty. Independent -of the general reasons for desiring accuracy in this -respect, there is one peculiar to the subject. It -has been suggested (by Dr. Prout), and strongly -insisted on (by Dr. Thomson), that all the numbers -representing these weights, constituting a scale of -great extent, in which the extremes already known -are in proportion to each other, as 1 to upwards of -200, are simple even multiples of the least of them. -If this be really the case, it opens views of such -importance as to justify any degree of labour and -pains in the verification of the law as a purely inductive -one. But in the actual state of chemical -analysis, with all deference to such high authority, -we confess it appears to us to stand in great need -of further confirmation, since it seems doubtful -whether such accuracy has yet been attained as to -enable us to answer positively for a fraction not -exceeding the three or four hundredth part of the -whole quantity to be determined: at least the results -of the first experimenters, obtained with the -greatest care, differ often by a greater amount; and -this degree of exactness, at least, would be required -to verify the law satisfactorily in the higher parts -of the scale.</p> - -<p>(342.) The mere agitation of such a question, -however, points out a class of phenomena in physical -science of a remote and singular kind, and of a very -high and refined order, which could never become -known but in an advanced state of science, not only -practical, but theoretical,—we mean, such as consist<span class="pagenum"><a id="Page_308">308</a></span> -in observed relations among the <em>data</em> of physics, -which show them to be quantities not <em>arbitrarily</em> -assumed, but depending on laws and causes which -they may be the means of at length disclosing. -A remarkable instance of such a relation is the -curious law which Bode observed to obtain in the -progression of the magnitudes of the several planetary -orbits. This law was interrupted between Mars -and Jupiter, so as to induce him to consider a -planet as wanting in that interval;—a deficiency -long afterwards strangely supplied by the discovery -of <em>four</em> new planets in that very interval, all of -whose orbits conform in dimension to the law in -question, within such moderate limits of error as -may be due to causes independent of those on which -the law itself ultimately rests.<a id="FNanchor_54" href="#Footnote_54" class="fnanchor">54</a></p> - -<p>(343.) Neither is it irrelevant to our subject to -remark, that the progress which has been made in -this department of chemistry, and the considerable -exactness actually attainable in chemical analysis, -have been owing, in great measure, to a circumstance -which might at first have been hardly considered -likely to exercise much influence on the -progress of a science,—the discovery of platina. -Without the resources placed at the ready disposal -of chemists by this invaluable metal, it is difficult to -conceive that the multitude of delicate analytical -experiments which have been required to construct -the fabric of existing knowledge could have ever -been performed. This, among many such lessons,<span class="pagenum"><a id="Page_309">309</a></span> -will teach us that the most important uses of natural -objects are not those which offer themselves -to us most obviously. The chief use of the moon -for man’s immediate purposes remained unknown -to him for five thousand years from his creation. -And, since it cannot but be that innumerable and -most important uses remain to be discovered among -the materials and objects already known to us, as -well as among those which the progress of science -must hereafter disclose, we may hence conceive a -well-grounded expectation, not only of constant increase -in the physical resources of mankind, and the -consequent improvement of their condition, but of -continual accessions to our power of penetrating -into the arcana of nature, and becoming acquainted -with her highest laws.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_310">310</a></span></p> - -<div class="chapter"> -<h2 id="hdr_18">CHAP. V.</h2> -</div> - -<p class="center b2">OF THE IMPONDERABLE FORMS OF MATTER.</p> - -<h3><i>Heat.</i></h3> - -<p class="in0">(344.) <span class="smcap"><span class="flet">O</span>ne</span> of the chief agents in chemistry, on -whose proper application and management the -success of a great number of its enquiries depends, -and many of whose most important laws are disclosed -to us by phenomena of a chemical nature, -is <span class="smcap smaller">HEAT</span>. Although some of its effects are continually -before our eyes as matters of the most -common occurrence, insomuch that there is scarcely -any process in the useful arts and manufactures -which does not call for its intervention, and although, -independent of this high utility, and the -proportionate importance of a knowledge of its -nature and laws, it presents in itself a subject of -the most curious speculation; yet there is scarcely -any physical agent of which we have so imperfect -a knowledge, whose intimate nature is more hidden, -or whose laws are of such delicate and difficult investigation.</p> - -<p>(345.) The word heat generally implies the sensation -which we experience on approaching a fire; -but, in the sense it carries in physics, it denotes the -cause, whatever it be, of that sensation, and of all<span class="pagenum"><a id="Page_311">311</a></span> -the other phenomena which arise on the application -of fire, or of any other heating cause. We should -be greatly deceived if we referred only to sensation -as an indication of the presence of this cause. -Many of those things which excite in our organs, -and especially of those of taste, a sensation of heat, -owe this property to chemical stimulants, and not -at all to their being actually <em>hot</em>. This error of -judgment has produced a corresponding confusion -of language, and hence had actually at one period<a id="FNanchor_55" href="#Footnote_55" class="fnanchor">55</a> -crept into physical philosophy a great many illogical -and absurd conclusions. Again, there are a number -of chemical agents, which, from their corroding, -blackening, and dissolving, or drying up the parts -of some descriptions of bodies, and producing on -them effects not generally unlike (though intrinsically -very different from) those produced by heat, -are said, in loose and vulgar language, to burn -them; and this error has even become rooted into -a prejudice, by the fact that some of these agents -are capable of becoming actually and truly <em>hot</em> -during their action on moist substances, by reason -of their combination with the water the latter contain. -Thus, quicklime and oil of vitriol both exercise -a powerful corrosive action on animal and -vegetable substances, and both become violently -hot by their combination with water. They are, -therefore, set down in vulgar parlance as substances -of a hot nature; whereas, in their relations to the -physical cause of heat, they agree with the generality -of bodies similarly constituted.</p> - -<p><span class="pagenum"><a id="Page_312">312</a></span> -(346.) The nature of heat has hitherto been -chiefly studied under the general heads <span class="locked">of—</span></p> - -<blockquote class="hang2"> - -<p>1st, Its sources, or the phenomena which it usually -accompanies.</p> - -<p>2d, Its communication from its sources to substances -capable of receiving it, and from these -to others, with a view to discover the laws -which regulate its distribution through space -or through the bodies which occupy it.</p> - -<p>3d, Its effects, on our senses, and on the bodies to -which it is communicated in its various degrees -of intensity, by which, means are afforded -us of measuring these degrees.</p> - -<p>4th, Its intimate relations to the atoms of matter, -as exhibited in its capability of acquiring a -latent state under certain circumstances, and -of entering into something like chemical combinations.</p></blockquote> - -<p>(347.) The most obvious sources of heat are, the -sun, fire, animal life, fermentations, violent chemical -actions of all kinds, friction, percussion, lightning, -or the electric discharge, in whatever manner produced, -the sudden condensation of air, and others, -so numerous, and so varied, as to show the extensive -and important part it has to perform in the -economy of nature. The discoveries of chemists, -however, have referred most of these to the general -head of chemical combination. Thus, fire, or the -combustion of inflammable bodies, is nothing more -than a violent chemical action attending the combination -of their ingredients with the oxygen of the -air. Animal heat is, in like manner, referable to a -process bearing no remote analogy to a slow combustion,<span class="pagenum"><a id="Page_313">313</a></span> -by which a portion of carbon, an inflammable -principle existing in the blood, is united with -the oxygen of the air in respiration; and thus carried -off from the system: fermentation is nothing -more than a decomposition of chemical elements -loosely united, and their re-union in a more permanent -state of combination. The analogy between -the sun and terrestrial fire is so natural as to have -been chosen by Newton to exemplify the irresistible -force of an inference derived from that principle. -But the nature of the sun and the mode in which -its wonderful supply of light and heat is maintained -are involved in a mystery which every discovery that -has been made either in chemistry or optics, so far -from elucidating, seems only to render more profound. -Friction as a source of heat is well known: -we rub our hands to warm them, and we grease -the axles of carriage-wheels to prevent their setting -fire to the wood; an accident which, in spite of -this precaution, does sometimes happen. But the -effect of friction, as a means of producing heat with -little or no consumption of materials, was not fully -understood till made the subject of direct experiment -by count Rumford, whose results appear to -have established the extraordinary fact, that an -unlimited supply of heat may be derived by friction -from the same materials. Condensation, whether -of air by pressure, or of metals by percussion, is -another powerful source of heat. Thus, iron may -be so dexterously hammered as to become red-hot, -and the rapid condensation of a confined portion of -air will set tinder on fire.</p> - -<p>(348.) The most violent heats known are produced<span class="pagenum"><a id="Page_314">314</a></span> -by the concentration of the solar rays by -burning glasses,—by the combustion of oxygen and -hydrogen gases mixed in the exact proportion in -which they combine to produce water,—and by the -discharge of a continued and copious current of -electricity through a small conductor. As these -three sources of heat are independent of each -other, and each capable of being brought into -action in a very confined space, there seems no -reason why they might not all three be applied at -once at the same point, by which means, probably, -effects would be produced infinitely surpassing any -hitherto witnessed.</p> - -<p>(349.) Heat is communicated either by <em>radiation</em> -between bodies at a distance, or by <em>conduction</em> -between bodies in contact, or between the contiguous -parts of one and the same body. The laws -of the radiation of heat have been studied with -great attention, and have been found to present -strong analogies with that of light in some points, -and singular differences in others. Thus, the heat -which accompanies the sun’s rays comports itself, -in all respects, like light; being subject to similar -laws of reflection, refraction, and even of polarization, -as has been shown by Berard. Yet they are -not identical with each other; Sir William Herschel -having shown, by decisive experiments, verified by -those of Sir H. Englefield, that there exist in a -solar beam both rays of heat which are not luminous, -and rays of light which have no heating power.</p> - -<p>(350.) The heat, radiated by terrestrial fires, and -by bodies <em>obscurely</em> hot, by whatever means they -have acquired their heat (even by exposure to the<span class="pagenum"><a id="Page_315">315</a></span> -sun’s rays), differs very materially from solar heat -in their power of penetrating transparent substances. -This singular and important difference was first -noticed by Mariotte, and afterwards made the subject -of many curious and interesting experiments -by Scheele, who found that terrestrial heat, or that -radiated from fires or heated bodies, is intercepted -and detained by glass or other transparent bodies, -while solar heat is not; and that, being so detained, -it heats them: which the latter, as it passes freely -through them, is incapable of doing. The more -recent researches of Delaroche, however, have -shown that this detention is complete only when -the temperature of the source of heat is low; but -that, as that temperature is higher, a portion of the -heat radiated acquires a power of penetrating glass; -and that the quantity which does so bears continually -a larger and larger proportion to the whole, -as the heat of the radiant body is more intense. -This discovery is very important, as it establishes -a community of nature between solar and terrestrial -heat; while at the same time it leads us to regard -the actual temperature of the sun as far exceeding -that of any earthly flame.</p> - -<p>(351.) A variety of theories have been framed to -account for these curious phenomena; but the subject -stands rather in need of further elucidation -from experiment, and is one which merits, and will -probably amply repay, the labours of those who may -hereafter devote their attention to it. The theory -of the radiation of heat, in general, which seems to -agree best with the known phenomena, is that of -M. Prevost, who considers all bodies as constantly<span class="pagenum"><a id="Page_316">316</a></span> -radiating out heat in all directions, and receiving it -by a similar means of communication from others, -and thus tending, in any space filled, wholly or in -part, with bodies at various temperatures, to establish -an equilibrium or equality of heat in all parts. -The application of this idea to the explanation of -the phenomenon of dew we have already seen (see -<a href="#p167">167</a>.). The laws of such radiation, under various -circumstances, have been lately investigated in a -beautiful series of experiments on the cooling of -bodies by their own radiation in vacuo, by Messrs. -Dulong and Petit, which offer some of the best examples -in science of the inductive investigation of -quantitative laws.</p> - -<p>(352.) The communication of heat between bodies -in contact, or between the different parts of the -same body, is performed by a process called conduction. -It is, in fact, only a particular case of -radiation, as has been explained above (217.); but -a case <em>so</em> particular as to require a separate and -independent investigation of its laws. The most -important consideration introduced into the enquiry -by this peculiarity is that of time. The communication -of heat by conduction is performed, for -the most part, with extreme slowness, while that -performed by direct radiation is probably not less -rapid than the propagation of light itself. The -analysis of the delicate and difficult points which -arise in the investigation of this subject in its -reduction to direct geometrical treatment has been -executed with admirable success by the late Baron -Fourrier, whose recent lamented death has deprived -science of an ornament it could ill spare, thinned<span class="pagenum"><a id="Page_317">317</a></span> -as its ranks have been within the last few years. -This acute philosopher and profound mathematician -has developed, in a series of elaborate -memoirs presented to the French Institute, the -laws of the communication of heat through the -interior of solid masses, placed under the influence -of any external heating and cooling causes, and has -in particular applied his results to the conditions on -which the maintenance of the actual observed -temperature on the earth’s surface depends; to the -possible influence of a supposed central heat on our -climates; and to the determination of the actual -amount of the heat, derived to us from the sun, or -at least that portion of it on which the difference of -the seasons depends.</p> - -<p>(353.) The principal effects of heat are the sensations -of warmth or cold consequent on its entry -or egress into or out of our bodies; the dilatation it -causes in the dimensions of all substances in which -it is accumulated; the changes of state it produces -in the melting of solids, and the conversion of -them and of liquids into vapour; and the chemical -changes it performs by actual decompositions -effected in the intimate molecules of various substances, -especially those of which vegetables and -animals are composed; to which we may add, the -production of electric phenomena under certain -circumstances in the contact of metals, and the -developement of electric polarity in crystallised substances.</p> - -<p>(354.) Cold has been considered by some as a -positive quality, the effect of a cause antagonist to -that of heat; but this idea seems now (with perhaps<span class="pagenum"><a id="Page_318">318</a></span> -a single exception) to be universally abandoned. -The sensation of cold is as easily explicable by the -passage of heat outwards through the surface of the -body as that of heat by its ingress from without; -and the experiments cited in proof of a radiation of -cold are all perfectly explained by Prevost’s theory -of reciprocal interchange. It is remarkable, however, -how very limited our means of producing intense -cold are, compared with those we possess of -effecting the accumulation of heat in bodies. This -is one of the strongest arguments adducible in favour -of the doctrines of those who maintain the possibility -of exhausting the heat of a body altogether, and -leaving it in a state absolutely devoid of it. But we -ought to consider, that the known methods of generating -heat chiefly turn on the production of chemical -combinations: we may easily conceive, therefore, -that, to obtain equally powerful corresponding -frigorific effects, we ought to possess the means of -effecting a disunion equally extensive and rapid between -such elements, actually combined, as have -already produced heat by their union. This, however, -we can only accomplish by engaging them in -combinations still more energetic, that is to say, in -which we may reasonably expect more heat to be -produced by the new combination than would be -destroyed or abstracted by the proposed decomposition. -Chemistry, however, (unaided by electric -agency,) affords no means of suddenly breaking the -union of two elements, and presenting <em>both</em> in an uncombined -state. A certain analogy to such disunion, -however, and its consequences, may be traced in the -sudden expansion of condensed gases from a liquid<span class="pagenum"><a id="Page_319">319</a></span> -state into vapour, which is the most powerful source -of cold known.</p> - -<p>(355.) The dilatation of bodies by heat forms the -subject of that branch of science called pyrometry. -There is no body but is capable of being penetrated -by heat, though some with greater, others with less -rapidity; and being so penetrated, all bodies (with a -very few exceptions, and those depending on very peculiar -circumstances,) are dilated by it in bulk, though -with a great diversity in the amount of dilatation -produced by the same degree of heat. Of the several -forms of natural bodies, gases and vapours are observed -to be most dilatable; liquids next, and solids -least of all. The dilatation of solids has been made -a subject of repeated and careful measurement by -several experimenters; among whom, Smeaton, -Lavoisier, and Laplace, are the principal. The -remarkable discovery of the unequal dilatation of -crystallised bodies by Mitscherlich has already -been spoken of. (266.) That of gases and vapours -was examined about the same time by Dalton and -Gay-Lussac, who both arrived independently at the -conclusion of an equal dilatability subsisting in -them all, which constitutes one of the most remarkable -points in their history.</p> - -<p>(356.) The dilatation of air by heat affords, perhaps, -the most unexceptionable means known of -measuring degrees of heat. The thermometer, as -originally constructed by Cornelius Drebell, was an -air thermometer. Those now in common use -measure accessions of heat not by the degree of -dilatation of air but of mercury. It has been shown, -by the researches of Dulong and Petit, that its indications<span class="pagenum"><a id="Page_320">320</a></span> -coincide exactly with that of the air-thermometer -in moderate temperatures; though at very -elevated ones they exhibit a sensible, and even -considerable, deviation. By this instrument, which -owes its present convenience and utility to the -happy idea of Newton, who first thought of fixing -determinate points on its scale, we are enabled to -estimate, or at least identify, the degrees of heat; -and thereby to investigate with accuracy the laws -of its communication and its other properties. Were -we sure that equal additions of heat produced equal -increments of dimension in any substance, the indications -of a thermometer would afford a true and -secure <em>measure</em> of the quantity present; but this is -so far from being the case, that we are nearly in -total ignorance on this important point; a circumstance -which throws the greatest difficulty in the way -of all theoretical reasoning, and even of experimental -enquiry. The laws of the dilatation of liquids, -in consequence of this deficiency of necessary preliminary -knowledge, are still involved in great obscurity, -notwithstanding the pains which have been -bestowed on them by the elaborate experiments and -calculations of Gilpin, Blagden, Deluc, Dalton, Gay-Lussac, -and Biot.</p> - -<p>(357.) The most striking and important of the -effects of heat consist, however, in the liquefaction of -solid substances, and the conversion of the liquids -so produced into vapour. There is no solid substance -known which, by a sufficiently intense heat, may -not be melted, and finally dissipated in vapour; and -this analogy is so extensive and cogent, that we cannot -but suppose that all those bodies which are<span class="pagenum"><a id="Page_321">321</a></span> -liquid under ordinary circumstances, owe their liquidity -to heat, and would freeze or become solid if -their heat could be sufficiently reduced. In many -we see this to be the case in ordinary winters; for -some, severe frosts are requisite; others freeze only -with the most intense artificial colds; and some -have hitherto resisted all our endeavours; yet the -number of these last is few, and they will probably -cease to be exceptions as our means of producing -cold become enlarged.</p> - -<p>(358.) A similar analogy leads us to conclude that -all aëriform fluids are merely liquids kept in the -state of vapour by heat. Many of them have been -actually condensed into the liquid state by cold accompanied -with violent pressure; and as our means -of applying these causes of condensation have improved, -more and more refractory ones have successively -yielded. Hence we are fairly entitled to -extend our conclusion to those which we have not -yet been able to succeed with; and thus we are led -to regard it as a general fact, that the liquid and -aëriform or vaporous states are entirely dependent -on <em>heat</em>; that were it not for this cause, there -would be nothing but solids in nature; and that, on -the other hand, nothing but a sufficient intensity of -heat is requisite to destroy the cohesion of every -substance, and reduce all bodies, first to liquids, and -then into vapour.</p> - -<p>(359.) But solids, themselves, by the abstraction -of heat shrink in dimension, and at the same time -become harder, and more brittle; yielding less to -pressure, and permitting less separation between -their parts by tension. These facts, coupled with<span class="pagenum"><a id="Page_322">322</a></span> -the greater compressibility of liquids, and the still -greater of gases, strongly induce us to believe that -it is heat, and heat alone, which holds the particles -of all bodies at that distance from each other which -is necessary to allow of compression; which in fact -gives them their elasticity, and acts as the antagonist -force to their mutual attraction, which would -otherwise draw them into actual contact, and retain -them in a state of absolute immobility and impenetrability. -Thus we learn to regard heat as one of -the great maintaining powers of the universe, and to -attach to all its laws and relations a degree of importance -which may justly entitle them to the most -assiduous enquiry.</p> - -<p>(360.) It was first ascertained by Dr. Black that -when heat produces the liquefaction of a solid, or -the conversion of a liquid into vapour, the liquid or -the vapour resulting is no <em>hotter</em> than the solid or -liquid from which it was produced, though a great -deal of heat has been expended in producing this -effect, and has actually entered into the substance.</p> - -<p>(361.) Hence he drew the conclusion that it has -become <em>latent</em>, and continues to exist in the product, -maintaining it in its new state, without increasing -its temperature. He further proved, that when the -vapour condenses, or the liquid freezes, this latent -heat is again given out from it. This great discovery, -with its natural and hardly less important -concomitant, that of the difference of specific heats -in different bodies, or the different quantities of heat -they require to raise their temperature equally, are -the chief reasons for regarding heat as a material -substance in a more decided manner than light,<span class="pagenum"><a id="Page_323">323</a></span> -with which in its radiant state it holds so close an -analogy.</p> - -<p>(362.) The subject of latent heat has been far less -attentively studied than its great practical importance -would appear to demand, when we consider -that it is to this part of physical science that the -theory of the steam-engine is mainly referable, and -that material improvements may not unreasonably -be expected in that wonderful instrument, from a -more extended knowledge than we possess of the -latent heats of different vapours. This is not the -case, however, with the subject of specific heat, -which was followed up immediately after its first -promulgation with diligence by Irvine; and, after a -brief interval, by Lavoisier and Laplace, as well as -by our countryman Crawfurd, who determined the -specific heats of many substances, both solid and -liquid. After a considerable period of inactivity, the -subject was again resumed by Delaroche and Berard, -and subsequently by Dulong and Petit: the result of -whose investigations has been the inductive establishment -of one of those simple and elegant physical -laws which carry with them, if not their own -evidence, at least their own recommendation to our -belief, as being in unison with every thing we know -of the harmony of nature. The law to which we -allude is this:—that the atoms of all the simple -chemical elements have exactly the same capacity -for heat, or are all equally heated or cooled by equal -accessions or abstractions of heat. It is only among -laws like this that we can expect to find a clew capable -of guiding us to a knowledge of the true nature -of heat, and its relations to ponderable matter.</p> - -<p><span class="pagenum"><a id="Page_324">324</a></span></p> - -<h3><i>Magnetism and Electricity.</i></h3> - -<p>(363.) These two subjects, which had long maintained -a distinct existence, and been studied as -separate branches of science, are at length effectually -blended. This is, perhaps, the most satisfactory -result which the experimental sciences have ever -yet attained. All the phenomena of magnetic polarity, -attraction, and repulsion, have at length been -resolved into one general fact, that two currents of -electricity, moving in the same direction repel, and -in contrary directions attract, each other. The -phenomena of the communication of magnetism and -what is called its induced state, alone remain unaccounted -for; but the interesting theory which has -been developed by M. Ampere, under the name of -Electro-dynamics, holds out a hope that this difficulty -will also in its turn give way, and the whole -subject be at length completely merged, as far as the -consideration of the acting causes goes, in the more -general one of electricity. This, however, does not -prevent magnetism from maintaining its separate -importance as a department of physical enquiry, -having its own peculiar laws and relations of the -highest practical interest, which are capable of -being studied quite apart from all consideration of its -electrical origin. And not only so, but to study them -with advantage, we must proceed as if that origin -were totally unknown, and, at least up to a certain -point, and that a considerably advanced one, conduct -our enquiries into the subject on the same inductive -principles as if this branch of physics were absolutely -independent of all others.</p> - -<p><span class="pagenum"><a id="Page_325">325</a></span> -(364.) Iron, and its oxides and alloys, were for a -long time the only substances considered susceptible -of magnetism. The loadstone was even one of the -examples produced by Bacon of that class of physical -instances to which he applies the term “Instantiæ -monodicæ”—<em>singular instances</em>. And the -history of magnetism affords a beautiful comment on -his remark on instances of this sort. “Nor should -our enquiries,” he observes, “into their nature be -broken off, till the properties and qualities found in -such things as may be esteemed wonders in nature -are reduced and comprehended under some certain -law; so that all irregularity or singularity may be -found to depend upon some common form, and the -wonder only rest in the exact differences, degrees, -or extraordinary concurrence, and not in the species -itself.” The discovery of the magnetism of nickel, -which though inferior to that of iron, is still considerable; -that of cobalt, yet feebler, and that of -titanium, which is only barely perceptible, have -effectually broken down the imaginary limit between -iron and the other materials of the world, and established -the existence of that general law of continuity -which it is one chief business of philosophy -to trace throughout nature. The more recent discoveries -of M. Arago (mentioned in 160.) have -completed this generalization, by showing that there -is no substance but which, under proper circumstances, -is capable of exhibiting unequivocal signs of -the magnetic virtue. And to obliterate all traces of -that line of separation which was once so broad, we -are now enabled, by the great discovery of Oërsted, -to communicate at and during pleasure to a coiled<span class="pagenum"><a id="Page_326">326</a></span> -wire of any metal indifferently all the properties of -a magnet;—its attraction, repulsion, and polarity; -and <em>that</em> even in a more intense degree than was previously -thought to be possible in the best natural -magnets. In short, in this case, and in this case -only, perhaps, in science, have we arrived at that -point which Bacon seems to have understood by the -discovery of “forms.” “The <em>form</em> of any nature,” -says he, “is such, that where it is, the given nature -must infallibly be. The form, therefore, is perpetually -present when that nature is present; ascertains -it universally, and accompanies it every where. -Again, this form is such, that when removed, the -given nature infallibly vanishes. Lastly, a true form -is such as can deduce a given nature from some -essential property, which resides in many things.”</p> - -<p>(365.) Magnetism is remarkable in another important -point of view. It offers a prominent, or -“<em>glaring instance</em>” of that quality in nature which -is termed <em>polarity</em> (267.), and that under circumstances -which peculiarly adapt it for the study of -this quality. It does not appear that the ancients -had any knowledge of this property of the magnet, -though its attraction of iron was well known to them. -The first mention of it in modern times cannot be -traced earlier than 1180, though it was probably -known to the Chinese before that time. The polarity -of the magnet consists in this, that if suspended -freely, one part of it will invariably direct -itself towards a certain point in the horizon, the -other towards the opposite point; and that, if two -magnets, so suspended, be brought near each other, -there will take place a mutual action, in consequence<span class="pagenum"><a id="Page_327">327</a></span> -of which, the positions of both will be disturbed, in -the same manner as would happen if the corresponding -parts of each repelled, and those oppositely -directed attracted, each other; and by properly -varying the experiment, it is found that they really -do so. If a small magnet, freely suspended, be -brought into the neighbourhood of a larger one, it -will take a position depending on the position of the -<em>poles</em> of the larger one, with respect to its point of -suspension. And it has been ascertained that these -and all other phenomena exhibited by magnets in -their mutual attractions and repulsions are explicable -on the supposition of two forces or virtues -lodged in the particles of the magnets, the one -predominating at one end, the other at the other; -and such that each particle shall attract those in -which the <em>opposite</em> virtue to its own prevails, and -repel those in which a <em>similar</em> one resides with a -force proportional to the inverse square of their -mutual distance.</p> - -<p>(366.) The direction in which a magnetic bar, or -needle of steel, freely suspended, places itself, has been -ascertained to be different at different points of the -earth’s surface. In some places it points exactly north -and south, in others it deviates from this direction more -or less, and at some actually stands at right angles -to it. This remarkable phenomenon, which is called -the variation of the needle, and which was discovered -by Sebastian Cabot in the year 1500, is accompanied -with another called the dip, noticed by Robert Norman -in 1576. It consists in a tendency of a needle, -nicely balanced on its centre, when unmagnetized, -to <em>dip</em> or point downwards when rendered magnetic,<span class="pagenum"><a id="Page_328">328</a></span> -towards a point below the horizon, and situated -within the earth. By tracing the variation and dip -over the whole surface of the globe, it has been -found that these phenomena take place as they -would do if the earth itself were a great magnet, -having its poles deeply situated below the surface,—and, -what is very remarkable, possessing a slow -motion within it, in consequence of which neither -the variation nor dip remain constantly the same at -the same place. The laws of this motion are at -present unknown; but the discovery of electro-magnetism, -by rendering it almost certain that the -earth’s magnetism is merely an effect of the continual -circulation of great quantities of electricity -round it, in a direction generally corresponding with -that of its rotation, have dissipated the greater part -of the mystery which hung over these phenomena; -since a variety of causes, both geological and others, -may be imagined which may produce considerable -deviations in the intensity, and partial ones in the -direction, of such electric currents. The unequal -distribution of land and sea in the two hemispheres, -by affecting the operation of the sun’s heat in producing -evaporation from the latter, which is probably -one of the great sources of terrestrial electricity, -may easily be conceived to modify the general tendency -of such currents, and to produce irregularities -in them, which may render a satisfactory account of -whatever still appears anomalous in the phenomena -of terrestrial magnetism. This branch of science -thus becomes connected, on a great scale, with that -of meteorology, one of the most complicated and -difficult, but at the same time interesting, subjects of<span class="pagenum"><a id="Page_329">329</a></span> -physical research; one, however, which has of late -begun to be studied with a diligence which promises -the speedy disclosure of relations and laws of which -at present we can form but a very imperfect notion.</p> - -<p>(367.) The communication of magnetism from the -earth to a magnetic body, or from one magnetic body -to another, is performed by a process to which the -name of induction has been given, and the laws and -properties of such induced magnetism have been -studied with much perseverance and success,—practically, -by Gilbert, Boyle, Knight, Whiston, Cavallo, -Canton, Duhamel, Rittenhouse, Scoresby, and others; -and theoretically, by Æpinus, Coulomb, and Poisson, -and in our own country by Messrs. Barlow and -Christie, who have investigated with great care the -curious phenomena which take place when masses -of iron are presented successively, in different positions, -by rotation on an axis, to the influence of the -earth’s magnetism. The magnetism of crystallized -bodies (partly from the extreme rarity of such as are -susceptible of any considerable magnetic virtue) has -not hitherto been at all examined, but would probably -afford very curious results.</p> - -<p>(368.) To electricity the views of the physical -enquirer now turn from almost every quarter, as to -one of those universal powers which Nature seems -to employ in her most important and secret operations. -This wonderful agent, which we see in -intense activity in lightning, and in a feebler and -more diffused form traversing the upper regions of -the atmosphere in the northern lights, is present, -probably in immense abundance, in every form of -matter which surrounds us, but becomes sensible<span class="pagenum"><a id="Page_330">330</a></span> -only when disturbed by excitements of peculiar -kinds. The most effectual of these is friction, -which we have already observed to be a powerful -source of heat. Everybody is familiar with the -crackling sparks which fly from a cat’s back when -stroked. These, by proper management, may be -accumulated in bodies suitably disposed to receive -them, and, although then no longer visible, give -evidence of their existence by the exhibition of a vast -variety of extraordinary phenomena,—producing -attractions and repulsions in bodies at a distance,—admitting -of being transferred by contact, or by -sudden and violent transilience of the interval of -separation, from one body to another, under the -form of sparks and flashes;—traversing with perfect -facility the substance of the densest metals, and a -variety of other bodies called conductors, but being -detained by others, such as glass, and especially -<em>air</em>, which are thence called non-conductors,—producing -painful shocks and convulsive motions, and -even death itself if in sufficient quantity, in animals -through which they pass, and finally imitating, on a -small scale, all the effects of lightning.</p> - -<p>(369.) The study of these phenomena and their -laws until a comparatively recent period occupied -the entire attention of electricians, and constituted -the whole of the science of electricity. It appears, -as the result of their enquiries, that all the phenomena -in question are explicable on the supposition -that electricity consists in a rare, subtle, and highly -elastic fluid, which in its tendency to expand and -diffuse itself pervades with more or less facility the -substance of conductors, but is obstructed and detained<span class="pagenum"><a id="Page_331">331</a></span> -from expansion more or less completely by -non-conductors. It is supposed, moreover, that this -electric fluid possesses a power of attraction for the -particles of all ponderable matter, together with -that of a repulsion for particles of its own kind. -Whether it has weight, or is rather to be regarded as -a species of matter distinct from that of which ponderable -bodies consist, is a question of such delicacy, -that no direct experiments have yet enabled us to -decide it; but at all events its <em>inertia</em> compared -with its elastic force must be conceived excessively -small, so that it is to be regarded as a fluid in the -highest degree <em>active</em>, obeying every impulse, internal -or external, with the greatest promptitude; -in short, a fluid whose energies can only be compared -with those of the ethereal medium by which, -in the undulatory doctrine, light is supposed to be -conveyed. The properties of hydrogen gas compared -with those of the denser aëriform fluids will, -in some slight degree, aid our conception of the -excessive mobility and penetrating activity of a -fluid so constituted. Electricity, however, must be -regarded as differing in some remarkable points from -all those fluids to which we have hitherto been accustomed -to apply the epithet elastic, such as air, -gases, and vapours. In these, the repulsive force -of the particles on which their elasticity depends is -considered as extending only to very small distances, -so as to affect only those in the immediate vicinity -of each other, while their attractive power, by -which they obey the general gravitation of all -matter, extends to any distance. In electricity, on -the other hand, the very reverse must be admitted.<span class="pagenum"><a id="Page_332">332</a></span> -The force by which its particles repel each other -extends to great distances, while its force of adhesion -to ponderable matter must be regarded as -limited in its extent to such minute intervals as -escape observation.</p> - -<p>(370.) The conception of a single fluid of this -kind, which when accumulated in excess in bodies -tends constantly to escape, and seek a restoration -of equilibrium by communicating itself to any others -where there may be a deficiency, is that which -occurs most naturally to the mind, and was accordingly -maintained by Franklin, to whom the science -of electricity is under great obligations for those -decisive experiments which informed us respecting -the true nature of lightning. The same theory was -afterwards advocated by Æpinus, who first showed -how the laws of equilibrium of such a fluid might -be reduced to strict mathematical investigation. -But there are phenomena accompanying its transfer -from body to body and the state of equilibrium -it affects under various circumstances, which appear -to require the admission of <em>two distinct fluids</em> -antagonist to each other, each attracting the other, -and repelling itself; but each, alike, susceptible of -adhesion to material substances, and of transfer -more or less rapid from particle to particle of them. -These fluids in the natural undisturbed state are -conceived to exist in a state of combination and -mutual saturation; but this combination may be -broken, and either of them separately accumulated -in a body to any amount without the other, provided -its escape be properly obstructed by surrounding -it with non-conductors. When so accumulated,<span class="pagenum"><a id="Page_333">333</a></span> -its repulsion for its own kind and attraction -of the opposite species in neighbouring bodies tends -to disturb the natural equilibrium of the two fluids -present in them, and to produce phenomena of a -peculiar description, which are termed <em>induced</em> electricity. -Curious and artificial as this theory may -appear, there has hitherto been produced no phenomenon -of which it will not afford at least a plausible, -and in by far the majority of cases a very -satisfactory, explanation. It has one character -which is extremely valuable in any theory, that of -admitting the application of strict mathematical -reasoning to the conclusions we would draw from -it. Without this, indeed, it is scarcely possible -that any theory should ever be fairly brought to -the test by a comparison with facts. Accordingly, -the mathematical theory of electrical equilibrium, -and the laws of the distribution of the electric -fluids over the surfaces of bodies in which they -are accumulated, have been made the subject of -elaborate geometrical investigation by the most -expert mathematicians, and have attained a degree -of extent and elegance which places this branch of -science in a very high rank in the scale of mathematico-physical -enquiry. These researches are -grounded on the assumption of a law of attraction -and repulsion similar to those of gravity and magnetism, -and which by the general accordance of -the results with facts, as well as by experiments -instituted for the express purpose of ascertaining -the laws in question, are regarded as sufficiently -demonstrated.</p> - -<p>(371.) The most obscure part of the subject is no<span class="pagenum"><a id="Page_334">334</a></span> -doubt the original mode of disturbance of electrical -equilibrium, by which electricity is excited in the -first instance, either by friction or by any other of -those causes which have been ascertained to produce -such an effect: analogies, it is true, are not -wanting<a id="FNanchor_56" href="#Footnote_56" class="fnanchor">56</a>; but it must be allowed that hitherto<span class="pagenum"><a id="Page_335">335</a></span> -nothing decisive has been offered on the subject; -and that conjectural modes of action have in this -instance too often usurped the place of those to -which a careful examination of facts alone can -lead us.</p> - -<p>(372.) Philosophers had long been familiar with -the effects of electricity above referred to, and with -those which it produces in its sudden and violent -transfer from one body to another, in rending and -shattering the parts of the substances through which -it passes, and where in great quantity, producing all -the effect of intense heat, igniting, fusing, and volatilizing -metals, and setting fire to inflammable -bodies; even its occasional influence in destroying -or altering the polarity of the magnetic needle -had been noticed: but as heat was known to be -produced by mechanical violence, and as magnetism -was also known to be greatly affected by the -same cause, these effects were referred rather to -that cause than to any thing in the peculiar nature -of the electric matter, and regarded rather as an -indirect consequence of its mode of action than as -connected with its intimate nature. In short, electricity -seemed destined to furnish another in addition -to many instances of subjects insulated from -the rest of philosophy, and capable of being studied -only in its own internal relations, when the great -discoveries of Galvani and Volta placed a new -power at the command of the experimenter, by -whose means those effects which had before been -crowded within an inappreciable instant could be -developed in detail and studied at leisure; and those -forces which had previously exhibited themselves<span class="pagenum"><a id="Page_336">336</a></span> -only in a state of uncontrollable intensity were -tamed down, as it were, and made to distribute -their efficacy over an indefinite time, and to regulate -their action at the will of the operator. It was -then soon ascertained that electricity in the act of -its passage along conductors, produces a variety of -wonderful effects, which had never been previously -suspected; and these of such a nature, as to afford -points of contact with several other branches of -physical enquiry, and to throw new and unexpected -lights on some of the most obscure operations of -nature.</p> - -<p>(373.) The history of this grand discovery affords -a fine illustration of the advantage to be derived in -physical enquiry from a close and careful attention -to any phenomenon, however apparently trifling, -which may at the moment of observation appear inexplicable -on received principles. The convulsive -motions of a dead frog in the neighbourhood of an -electric discharge, which originally drew Galvani’s -attention to the subject, had been noticed by others -nearly a century before his time, but attracted no -further remark than as indicating a peculiar sensibility -to electrical excitement depending on that -remnant of vitality which is not extinguished in the -organic frame of an animal by the deprivation of -actual life. Galvani was not so satisfied. He analysed -the phenomenon; and in investigating all the -circumstances connected with it was led to the observation -of a peculiar electrical excitement which -took place when a circuit was formed of three distinct -parts, a muscle, a nerve, and a metallic conductor, -each placed in contact with the other two,<span class="pagenum"><a id="Page_337">337</a></span> -and which was manifested by a convulsive motion -produced in the muscle. To this phenomenon he -gave the name of animal electricity, an unfortunate -epithet, since it tended to restrict enquiry into its -nature to the class of phenomena in which it first -became apparent. But this circumstance, which -in a less enquiring age of science might have exercised -a fatal influence on the progress of knowledge, -proved happily no obstacle to the further developement -of its principles, the subject being immediately -taken up with a kind of prophetic ardour by -Volta, who at once generalized the phenomena, rejecting -the physiological considerations introduced -by Galvani, as foreign to the enquiry, and regarding -the contraction of the muscles as merely a delicate -means of detecting the production of electrical excitements -too feeble to be rendered sensible by any -other means. It was thus that he arrived at the -knowledge of a general fact, that of the disturbance -of electrical equilibrium by the mere contact of different -bodies, and the circulation of a current of -electricity in one constant direction, through a circuit -composed of three different conductors. To -increase the intensity of the very minute and delicate -effect thus observed became his next aim, nor -did his enquiry terminate till it had placed him in -possession of that most wonderful of all human inventions, -the pile which bears his name, through -the medium of a series of well conducted and logically -combined experiments, which has rarely, if -ever, been surpassed in the annals of physical -research.</p> - -<p>(374.) Though the original pile of Volta was feeble<span class="pagenum"><a id="Page_338">338</a></span> -compared to those gigantic combinations which were -afterwards produced, it sufficed, however, to exhibit -electricity under a very different aspect from -any thing which had gone before, and to bring into -view those peculiar modifications in its action which -Dr. Wollaston was the first to render a satisfactory -account of, by referring them to an increase of -<em>quantity</em>, accompanied with a diminution of <em>intensity</em> -in the supply afforded. The discovery had not -long been made public, and the instrument in -the hands of chemists and electricians, before it -was ascertained that the electric current, transmitted -by it through conducting liquids, produces -in them chemical decompositions. This capital discovery -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 to, -and accumulated around, the positive,—and hydrogen, -metals, and alkalies round 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 re-appear with all their properties -at their appropriate resting-places.</p> - -<p>(375.) It was in this state of things that the subject -was taken up by Davy, who, seeing that the strongest -chemical affinities were thus readily subverted by -the decomposing action of the pile, conceived the<span class="pagenum"><a id="Page_339">339</a></span> -happy idea of bringing to bear the intense power of -the enormous batteries of the Royal Institution on -those substances which, though strongly suspected -to be compounds, had resisted all attempts to decompose -them—the alkalies and earths. They -yielded to the force applied, and a total revolution -was thus effected in chemistry; not so much by the -introduction of the new elements thus brought to -light, as by the mode of conceiving the nature of -chemical affinity, which from that time has been regarded -(as Davy broadly laid it down, in a theory -which was readily adopted by the most eminent -chemists, and by none more readily than by Berzelius -himself,) as entirely due to electric attractions -and repulsions, those bodies combining most intimately -whose particles are habitually in a state of -the most powerful electrical antagonism, and dispossessing -each other, according to the amount of -their difference in this respect.</p> - -<p>(376.) The connection of magnetism and electricity -had long been suspected, and innumerable fruitless -trials had been made to determine, in the affirmative -or negative, the question of such connection. The -phenomena of many crystallized minerals which -become electric by heat, and develope opposite -electric poles at their two extremities, offered an -analogy so striking to the polarity of the magnet, -that it seemed hardly possible to doubt a closer -connection of the two powers. The developement -of a similar polarity in the Voltaic pile pointed -strongly to the same conclusion; and experiments -had even been made with a view to ascertain whether -a pile in a state of excitement might not manifest a<span class="pagenum"><a id="Page_340">340</a></span> -disposition to place itself in the magnetic meridian; -but the essential condition had been omitted, that of -allowing the pile to discharge itself freely, a condition -which assuredly never would have occurred of itself -to any experimenter. Of all the philosophers who -had speculated on this subject, none had so pertinaciously -adhered to the idea of a necessary connection -between the phenomena as Oërsted. Baffled often, -he returned to the attack; and his perseverance was -at length rewarded by the complete disclosure of the -wonderful phenomena of electro-magnetism. There -is something in this which reminds us of the obstinate -adherence of Columbus to his notion of the -necessary existence of the New World; and the -whole history of this beautiful discovery may serve -to teach us reliance on those general analogies and -parallels between great branches of science by which -one strongly reminds us of another, though no direct -connection appears; as an indication not to be neglected -of a community of origin.</p> - -<p>(377.) It is highly probable that we are still -ignorant of many interesting features in electrical -science, which the study of the Voltaic circuit will -one day disclose. The violent mechanical effects -produced by it on mercury, placed under conducting -liquids which have been referred by Professor -Erman to a modified form of capillary attraction, -but which a careful and extended view of the phenomena -have led others<a id="FNanchor_57" href="#Footnote_57" class="fnanchor">57</a> to regard in a very different -light, as pointing out a primary action of a -dynamical rather than a statical character, deserve, -in this point of view, a further investigation; and<span class="pagenum"><a id="Page_341">341</a></span> -the curious relations of electricity to heat, as exhibited -in the phenomena of what has been called -thermo-electricity, promise an ample supply of new -information.</p> - -<p>(378.) Among the remarkable effects of electricity -disclosed by the researches of Galvani and Volta, -perhaps the most so consisted in its influence on -the nervous system of animals. The origin of muscular -motion is one of those profound mysteries of -nature which we can scarcely venture to hope will -ever be fully explained. Physiologists, however, -had long entertained a general conception of the -conveyance of some subtle fluid or spirit from the -brain to the muscles of animals along the nerves; -and the discovery of the rapid transmission of electricity -along conductors, with the violent effects -produced by shocks, transmitted through the body, -on the nervous system, would very naturally lead to -the idea that this nervous fluid, if it had any real -existence, might be no other than the electrical. -But until the discoveries of Galvani and Volta, this -could only be looked upon as a vague conjecture. -The character of a <i xml:lang="la" lang="la">vera causa</i> was wanting to give it -any degree of rational plausibility, since no reason -could be imagined for the disturbance of the electrical -equilibrium in the animal frame, composed as it is -entirely of conductors, or rather, it seemed contrary -to the then known laws of electrical communication -to suppose any such. Yet one strange and surprising -phenomenon might be adduced indicative of the -possibility of such disturbance, viz. the powerful -shock given by the torpedo and other fishes of the -same kind, which presented so many analogies with<span class="pagenum"><a id="Page_342">342</a></span> -those arising from electricity, that they could hardly -be referred to a different source, though <em>besides</em> the -shock neither spark nor any other indication of electrical -tension could be detected in them.</p> - -<p>(379.) The benumbing effect of the torpedo had -been ascertained to depend on certain singularly constructed -organs composed of membranous columns, -filled from end to end with laminæ, separated -from each other by a fluid: but of its mode of -action no satisfactory account could be given; -nor was there any thing in its construction, and -still less in the nature of its materials, to give -the least ground for supposing it an electrical apparatus. -But the pile of Volta supplied at once the -analogies both of structure and of effect, so as to -leave little doubt of the electrical nature of the apparatus, -or of the power, a most wonderful one -certainly, of the animal, to determine, by an effort -of its will, that concurrence of conditions on which -its activity depends. This remained, as it probably -ever will remain, mysterious and inexplicable; but -the principle once established, that there exists in -the animal economy a power of determining the -developement of electric excitement, capable of being -transmitted along the nerves, and it being ascertained, -by numerous and decisive experiments, -that the transmission of Voltaic electricity along the -nerves of even a dead animal is sufficient to produce -the most violent muscular action, it became an easy -step to refer the origin of muscular motion in the living -frame to a similar cause; and to look to the brain, -a wonderfully constituted organ, for which no mode -of action possessing the least plausibility had ever<span class="pagenum"><a id="Page_343">343</a></span> -been devised, as the source of the required electrical -power.<a id="FNanchor_58" href="#Footnote_58" class="fnanchor">58</a></p> - -<p>(380.) It is not our intention, however, to enter -into any further consideration of physiological subjects. -They form, it is true, a most important and -deeply interesting province of philosophical enquiry; -but the view that we have taken of physical science -has rather been directed to the study of inanimate -nature, than to that of the mysterious phenomena -of organization and life, which constitute the object -of physiology. The history of the animal and -vegetable productions of the globe, as affording -objects and materials for the convenience and use -of man, and as dependent on and indicative of the -general laws which determine the distribution of -heat, moisture, and other natural agents, over its -surface, and the revolutions it has undergone, are of -course intimately connected with our subject, and -will, therefore, naturally afford room for some remarks,<span class="pagenum"><a id="Page_344">344</a></span> -but not such as will long detain the reader’s -attention.</p> - -<p>(381.) In <em>zoology</em>, the connection of peculiar modes -of life and food, with peculiarities of structure, has -given rise to systems of classification at once obvious -and natural; and the great progress which -has been made in comparative anatomy has enabled -us to trace a graduated scale of organization almost -through the whole chain of animal being; a scale -not without its intervals, but which every successive -discovery of animals heretofore unknown has tended -to fill up. The wonders disclosed by microscopic -observation have opened to us a new world, in -which we discover, with astonishment, the extremes -of minuteness and complexity of structure united; -while, on the other hand, the examination of the -fossil remains of a former state of creation has -demonstrated the existence of animals far surpassing -in magnitude those now living, and brought to light -many forms of being which have nothing analogous -to them at present, and many others which afford -important connecting links between existing genera. -And, on the other hand, the researches of the comparative -anatomist and conchologist have thrown -the greatest light on the studies of the geologist, -and enabled him to discern, through the obscure -medium of a few relics, scattered here and there -through a stratum, circumstances connected with -the formation of the stratum itself which he could -have recognised by no other indication. This is one -among many striking instances of the unexpected -lights which sciences, however apparently remote, -may throw upon each other.</p> - -<p><span class="pagenum"><a id="Page_345">345</a></span> -(382.) To <em>botany</em> many of the same remarks apply. -Its artificial systems of classification, however convenient, -have not prevented botanists from endeavouring -to group together the objects of their -science in natural classes having a community of -character more intimate than those which determine -their place in the Linnean or any similar -system; a community of character extending over -the whole habit and properties of the individuals -compared. The important chemical discoveries -which have been lately made of peculiar proximate -principles which, in an especial manner, characterize -certain families of plants, hold out the prospect of a -greatly increased field of interesting knowledge in -this direction, and not only interesting, but in a -high degree important, when it is considered that -the principles thus brought into view are, for the -most part, very powerful medicines, and are, in fact, -the essential ingredients on which the medical -virtues of the plants depend. The law of the distribution -of the generic forms of plants over the -globe, too, has, within a comparatively recent period, -become an object of study to the naturalist; and its -connection with the laws of climate constitutes one -of the most interesting and important branches of -natural-historical enquiry, and one on which great -light remains to be thrown by future researches. -It is this which constitutes the chief connecting -link between botany and geology, and renders a -knowledge of the vegetable fossils, of any portion of -the earth’s surface, indispensable to the formation -of a correct judgment of the circumstances under -which it existed in its ancient state. Fossil botany<span class="pagenum"><a id="Page_346">346</a></span> -is accordingly cultivated with great and increasing -ardour; and the subterraneous “Flora” of a geological -formation is, in many instances, studied with -a degree of care and precision little inferior to that -which its surface exhibits.</p> - -<hr /> - -<p><span class="pagenum"><a id="Page_347">347</a></span></p> - -<div class="chapter"> -<h2 id="hdr_19">CHAP. VI.</h2> -</div> - -<blockquote class="hang"> - -<p class="center b2">OF THE CAUSES OF THE ACTUAL RAPID ADVANCE OF THE -PHYSICAL SCIENCES COMPARED WITH THEIR PROGRESS -AT AN EARLIER PERIOD.</p></blockquote> - -<p class="in0">(383.) <span class="smcap"><span class="flet">T</span>here</span> is no more extraordinary contrast than -that presented by the slow progress of the physical -sciences, from the earliest ages of the world to the -close of the sixteenth century, and the rapid developement -they have since experienced. In the -former period of their history, we find only small -additions to the stock of knowledge, made at long -intervals of time; during which a total indifference -on the part of the mass of mankind to the study of -nature operated to effect an almost complete oblivion -of former discoveries, or, at best, permitted them to -linger on record, rather as literary curiosities, than -as possessing, in themselves, any intrinsic interest -and importance. A few enquiring individuals, from -age to age, might perceive their value, and might -feel that irrepressible thirst after knowledge which, -in minds of the highest order, supplies the absence -both of external stimulus and opportunity. But the -total want of a right direction given to enquiry, and -of a clear perception of the objects to be aimed -at, and the advantages to be gained by systematic -and connected research, together with the general -apathy of society to speculations remote from the<span class="pagenum"><a id="Page_348">348</a></span> -ordinary affairs of life, and studiously kept involved -in learned mystery, effectually prevented these occasional -impulses from overcoming the inertia of -ignorance, and impressing any regular and steady -progress on science. Its objects, indeed, were confined -in a region too sublime for vulgar comprehension. -An earthquake, a comet, or a fiery meteor, -would now and then call the attention of the whole -world, and produce from all quarters a plentiful -supply of crude and fanciful conjectures on their -causes; but it was never supposed that sciences -could exist among common objects, have a place -among mechanical arts, or find worthy matter of -speculation in the mine or the laboratory. Yet it -cannot be supposed, that all the indications of nature -continually passed unremarked, or that much good -observation and shrewd reasoning on it failed to -perish unrecorded, before the invention of printing -enabled every one to make his ideas known to all -the world. The moment this took place, however, -the sparks of information from time to time struck -out, instead of glimmering for a moment, and dying -away in oblivion, began to accumulate into a genial -glow, and the flame was at length kindled which -was speedily to acquire the strength and rapid spread -of a conflagration. The universal excitement in the -minds of men throughout Europe, which the first -out-break of modern science produced, has been -already spoken of. But even the most sanguine -anticipators could scarcely have looked forward to -that steady, unintermitted progress which it has -since maintained, nor to that rapid succession of -great discoveries which has kept up the interest of<span class="pagenum"><a id="Page_349">349</a></span> -the first impulse still vigorous and undiminished. It -may truly, indeed, be said, that there is scarcely a -single branch of physical enquiry which is either -stationary, or which has not been, for many years -past, in a constant state of advance, and in which -the progress is not, at this moment, going on with -accelerated rapidity.</p> - -<p>(384.) Among the causes of this happy and desirable -state of things, no doubt we are to look, in the -first instance, to that great increase in wealth and civilization -which has at once afforded the necessary -leisure and diffused the taste for intellectual pursuits -among numbers of mankind, which have long been -and still continue steadily progressive in every principal -European state, and which the increase and fresh -establishment of civilized communities in every distant -region are rapidly spreading over the whole -globe. It is not, however, merely the increased -number of cultivators of science, but their enlarged -opportunities, that we have here to consider, which, -in all those numerous departments of natural research -that require local information, is in fact the -most important consideration of all. To this cause -we must trace the great extension which has of late -years been conferred on every branch of natural -history, and the immense contributions which have -been made, and are daily making, to the departments -of zoology and botany, in all their ramifications. -It is obvious, too, that all the information -that can possibly be procured, and reported, by the -most enlightened and active travellers, must fall -infinitely short of what is to be obtained by individuals -actually resident upon the spot. Travellers,<span class="pagenum"><a id="Page_350">350</a></span> -indeed, may make collections, may snatch a few -hasty observations, may note, for instance, the distribution -of geological formations in a few detached -points, and now and then witness remarkable local -phenomena; but the resident alone can make continued -series of regular observations, such as the -scientific determination of climates, tides, magnetic -variations, and innumerable other objects of that -kind, requires; can alone mark all the details of -geological structure, and refer each stratum, by a -careful and long continued observation of its fossil -contents, to its true epoch; can alone note the habits -of the animals of his country, and the limits of its -vegetation, or obtain a satisfactory knowledge of its -mineral contents, with a thousand other particulars -essential to that complete acquaintance with our -globe as a whole, which is beginning to be understood -by the extensive designation of physical geography. -Besides which, ought not to be omitted -multiplied opportunities of observing and recording -those extraordinary phenomena of nature which -offer an intense interest, from the rarity of their occurrence -as well as the instruction they are calculated -to afford. To what, then, may we not look -forward, when a spirit of scientific enquiry shall have -spread through those vast regions in which the process -of civilization, its sure precursor, is actually -commenced and in active progress? And what may -we not expect from the exertions of powerful minds -called into action under circumstances totally different -from any which have yet existed in the world, -and over an extent of territory far surpassing that -which has hitherto produced the whole harvest of<span class="pagenum"><a id="Page_351">351</a></span> -human intellect? In proportion as the number of -those who are engaged on each department of physical -enquiry increases, and the geographical extent -over which they are spread is enlarged, a proportionately -increased facility of communication and -interchange of knowledge becomes essential to the -prosecution of their researches with full advantage. -Not only is this desirable, to prevent a number of -individuals from making the same discoveries at the -same moment, which (besides the waste of valuable -time) has always been a fertile source of jealousies -and misunderstandings, by which great evils have -been entailed on science; but because methods of -observation are continually undergoing new improvements, -or acquiring new facilities, a knowledge -of which, it is for the general interest of science, -should be diffused as widely and as rapidly as possible. -By this means, too, a sense of common interest, of -mutual assistance, and a feeling of sympathy in a -common pursuit, are generated, which proves a -powerful stimulus to exertion; and, on the other -hand, means are thereby afforded of detecting and -pointing out mistakes before it is too late for their -rectification.</p> - -<p>(385.) Perhaps it may be truly remarked, that, next -to the establishment of institutions having either the -promotion of science in general, or, what is still more -practically efficacious in its present advanced state, -that of particular departments of physical enquiry, -for their express objects, nothing has exercised so -powerful an influence on the progress of modern -science as the publication of monthly and quarterly -scientific journals, of which there is now scarcely a<span class="pagenum"><a id="Page_352">352</a></span> -nation in Europe which does not produce several. -The quick and universal circulation of these, places -observers of all countries on the same level of perfect -intimacy with each other’s objects and methods, -while the abstracts they from time to time (if well -conducted) contain of the most important researches -of the day consigned to the more ponderous tomes -of academical collections, serve to direct the course -of general observation, as well as to hold out, in the -most conspicuous manner, models for emulative -imitation. In looking forward to what may hereafter -be expected from this cause of improvement, we are -not to forget the powerful effect which must in -future be produced by the spread of elementary -works and digests of what is actually known in each -particular branch of science. Nothing can be more -discouraging to one engaged in active research, than -the impression that all he is doing may, very likely, -be labour taken in vain; that it may, perhaps, have -been already done, and much better done, than, with -his opportunities, or his resources, he can hope to -perform it; and, on the other hand, nothing can be -more exciting than the contrary impression. Thus, -by giving a connected view of what has been done, -and what remains to be accomplished in every -branch, those digests and bodies of science, which -from time to time appear, have, in fact, a very important -weight in determining its future progress, quite -independent of the quantity of information they -communicate. With respect to elementary treatises, -it is needless to point out their utility, or to dwell -on the influence which their actual abundance, contrasted -with their past remarkable deficiency, is<span class="pagenum"><a id="Page_353">353</a></span> -likely to exercise over the future. It is only by -condensing, simplifying, and arranging, in the most -lucid possible manner, the acquired knowledge of -past generations, that those to come can be enabled -to avail themselves to the full of the advanced point -from which they will start.</p> - -<p>(386.) One of the means by which an advanced state -of physical science contributes greatly to accelerate -and secure its further progress, is the exact knowledge -acquired of physical data, or those normal -quantities which we have more than once spoken -of in the preceding pages (222.); a knowledge -which enables us not only to appretiate the accuracy -of experiments, but even to correct their results. -As there is no surer criterion of the state of science -in any age than the degree of care bestowed, and -discernment exhibited, in the choice of such data, so -as to afford the simplest possible grounds for the application -of theories, and the degree of accuracy -attained in their determination, so there is scarcely -any thing by which science can be more truly benefited -than by researches directed expressly to this -object, and to the construction of tables exhibiting -the true numerical relations of the elements of -theories, and the actual state of nature, in all its different -branches. It is only by such determinations -that we can ascertain what changes are slowly and -imperceptibly taking place in the existing order -of things; and the more accurate they are, the <em>sooner</em> -will this knowledge be acquired. What might we -not now have known of the motions of the (so-called) -fixed stars, had the ancients possessed the means of<span class="pagenum"><a id="Page_354">354</a></span> -observation we now possess, and employed them as -we employ them now?</p> - -<p>(387.) In any enumeration of causes which have -contributed to the recent rapid advancement of -science, we must not forget the very important one -of improved and constantly improving means of -observation, both in instruments adapted for the -exact measurement of quantity, and in the general -convenience and well-judged adaptation to its purposes, -of every description of scientific apparatus. -In the actual state of science there are few observations -which can be productive of any great advantage -but such as afford accurate measurement; and an -increased refinement in this respect is constantly -called for. The degree of delicacy actually attained, -we will not say in the most elaborate works of the -highest art, but in such ordinary apparatus as every -observer may now command, is such as could not -have been arrived at unless in a state of the mechanical -arts, which in its turn (such is the mutual -re-action of cause and effect) requires for its existence -a very advanced state of science. What an important -influence may be exercised over the progress -of a single branch of science by the invention of a -ready and convenient mode of executing a definite -measurement, and the construction and common -introduction of an instrument adapted for it cannot -be better exemplified than by the instance of the -reflecting goniometer. This simple, cheap, and -portable little instrument, has changed the face of -mineralogy, and given it all the characters of one -of the exact sciences.</p> - -<p><span class="pagenum"><a id="Page_355">355</a></span> -(388.) Our means of perceiving and measuring minute -quantities, in the important relations of weight, -space, and time, seem already to have been carried -to a point which it is hardly conceivable they should -surpass. Balances have been constructed which -have rendered sensible the millionth part of the -whole quantity weighed; and to turn with the -thousandth part of a grain is the performance of balances -pretending to no very extraordinary degree of -merit. The elegant invention of the sphærometer, -by substituting the sense of touch for that of sight in -the measurement of minute objects, permits the -determination of their dimensions with a degree of -precision which is fully adequate to the nicest purposes -of scientific enquiry. By its aid an inch may -be readily subdivided into ten or even twenty thousand -parts; and the lever of contact, an instrument -in use among the German opticians, enables us to -appretiate quantities of space even yet smaller. -For the subdivision of time, too, the perfection of -modern mechanism has furnished resources which -leave very little to be desired. By the aid of clocks -and chronometers, as they are now constructed, a -few tenths of a second is all the error that need -be apprehended in the subdivision of a day; and -for the further subdivision of smaller portions of -time, instruments have been imagined which admit -of almost unlimited precision, and permit us to appreciate -intervals to the nicety of the hundredth, or -even the thousandth part of a single second.<a id="FNanchor_59" href="#Footnote_59" class="fnanchor">59</a> -When the precision attainable by such means is<span class="pagenum"><a id="Page_356">356</a></span> -contrasted with what could be procured a few generations -ago, by the rude and clumsy workmanship -of even the early part of the last century, it will be -no matter of astonishment that the sciences which -depend on exact measurements should have made -a proportional progress. Nor will any degree of -nicety in physical determinations appear beyond our -reach, if we consider the inexhaustible resources -which science itself furnishes, in rendering the -quantities actually to be determined by measure -great multiples of the elements required for the -purposes of theory, so as to diminish in the same -proportion the influence of any errors which may be -committed on the final results.</p> - -<p>(389.) Great, indeed, as have been of late the improvements -in the construction of instruments, both -as to what regards convenience and accuracy, it is to -the discovery of improved <em>methods</em> of observation that -the chief progress of those parts of science which depend -on exact determinations is owing. The balance -of torsion, the ingenious invention of Cavendish and -Coulomb, may be cited as an example of what we -mean. By its aid we are enabled not merely to render -sensible, but to subject to precise measurement and -subdivision, degrees of force infinitely too feeble -to affect the nicest balance of the usual construction, -even were it possible to bring them to act on it. -The galvanometer, too, affords another example of -the same kind, in an instrument whose range of -utility lies among electric forces which we have no -other means of rendering sensible, much less of -estimating with exactness. In determinations of -quantities less minute in themselves, the methods<span class="pagenum"><a id="Page_357">357</a></span> -devised by Messrs. Arago and Fresnel, for the -measurement of the refractive powers of transparent -media by means of the phenomenon of diffraction, -may be cited as affording a degree of precision -limited only by the wishes of the observer, and the -time and patience he is willing to devote to his -observation. And in respect of the direction of -observations to points from which real information -is to be obtained, and positive conclusions drawn, -the hygrometer of Daniell may be cited as an -elegant example of the introduction into general use -of an instrument substituting an indication founded -on strict principles for one perfectly arbitrary.</p> - -<p>(390.) In speculating on the future prospects of -physical science, we should not be justified in leaving -out of consideration the probability, or rather -certainty, of the occasional occurrence of those happy -accidents which have had so powerful an influence -on the past; occasions, where a fortunate combination -opportunely noticed may admit us in an instant -to the knowledge of principles of which no -suspicion might occur but for some such casual -notice. Boyle has entitled one of his essays thus remarkably,—“<cite>Of -Man’s great Ignorance of the Uses of -natural Things; or that there is no one Thing in Nature -whereof the Uses to human Life are yet thoroughly -understood</cite>.”<a id="FNanchor_60" href="#Footnote_60" class="fnanchor">60</a> The whole history of the arts since -Boyle’s time has been one continued comment on -this text; and if we regard among the uses of the -works of nature, <em>that</em>, assuredly the noblest of all, -which leads us to a knowledge of the Author of -nature through the contemplation of the wonderful<span class="pagenum"><a id="Page_358">358</a></span> -means by which he has wrought out his purposes -in his works, the sciences have not been behind -hand in affording their testimony to its truth. -Nor are we to suppose that the field is in the -slightest degree narrowed, or the chances in favour -of such fortunate discoveries at all decreased, by -those which have already taken place: on the -contrary, they have been incalculably extended. -It is true that the ordinary phenomena which pass -before our eyes have been minutely examined, and -those more striking and obvious principles which -occur to superficial observation have been noticed -and embodied in our systems of science; but, not -to mention that by far the greater part of natural -phenomena remain yet unexplained, every -new discovery in science brings into view whole -classes of facts which would never otherwise have -fallen under our notice at all, and establishes relations -which afford to the philosophic mind a constantly -extending field of speculation, in ranging -over which it is next to impossible that he should -not encounter new and unexpected principles. How -infinitely greater, for instance, are the mere chances -of discovery in chemistry among the innumerable -combinations with which the modern chemist is -familiar, than at a period when two or three imaginary -elements, and some ten or twenty substances, -whose properties were known with an approach to -distinctness, formed the narrow circle within which -his ideas had to revolve? How many are the instances -where a new substance, or a new property, -introduced into familiar use, by being thus brought -into relation with all our actual elements of knowledge,<span class="pagenum"><a id="Page_359">359</a></span> -has become the means of developing properties -and principles among the most common objects, -which could never have otherwise been discovered? -Had not platina (to take an instance) been an object -of the most ordinary occurrence in a laboratory, would -a suspicion have ever occurred that a lamp could be -constructed to burn without flame; and should we -have ever arrived at a knowledge of those curious -phenomena and products of semi-combustion which -this beautiful experiment discloses?</p> - -<p>(391.) Finally, when we look back on what has been -accomplished in science, and compare it with what -remains to be done, it is hardly possible to avoid -being strongly impressed with the idea that we have -been and are still executing the labour by which -succeeding generations are to profit.<a id="FNanchor_61" href="#Footnote_61" class="fnanchor">61</a> In a few instances -only have we arrived at those general -axiomatic laws which admit of direct deductive -inference, and place the solutions of physical phenomena -before us as so many problems, whose principles -of solution we fully possess, and which require -nothing but acuteness of reasoning to pursue even -into their farthest recesses. In fewer still have we -reached that command of abstract reasoning itself -which is necessary for the accomplishment of so -arduous a task. Science, therefore, in relation to -our faculties, still remains boundless and unexplored, -and, after the lapse of a century and a half from the -æra of Newton’s discoveries, during which every -department of it has been cultivated with a zeal and -energy which have assuredly met their full return,<span class="pagenum"><a id="Page_360">360</a></span> -we remain in the situation in which he figured himself,—standing -on the shore of a wide ocean, from -whose beach we may have culled some of those innumerable -beautiful productions it casts up with lavish -prodigality, but whose acquisition can be regarded as -no diminution of the treasures that remain.</p> - -<p>(392.) But this consideration, so far from repressing -our efforts, or rendering us hopeless of attaining any -thing intrinsically great, ought rather to excite us to -fresh enterprise, by the prospect of assured and ample -recompense from that inexhaustible store which only -awaits our continued endeavours. “It is no detraction -from human capacity to suppose it incapable of -infinite exertion, or of exhausting an infinite subject.”<a id="FNanchor_62" href="#Footnote_62" class="fnanchor">62</a> -In whatever state of knowledge we may conceive -man to be placed, his progress towards a -yet higher state need never fear a check, but must -continue till the last existence of society.</p> - -<p>(393.) It is in this respect an advantageous view -of science, which refers all its advances to the discovery -of general laws, and to the inclusion of what -is already known in generalizations of still higher -orders; inasmuch as this view of the subject represents -it, as it really is, essentially incomplete, and -incapable of being fully embodied in any system, or -embraced by any single mind. Yet it must be recollected -that, so far as our experience has hitherto -gone, every advance towards generality has at the -same time been a step towards simplification. It is -only when we are wandering and lost in the mazes -of particulars, or entangled in fruitless attempts to -work our way downwards in the thorny paths of<span class="pagenum"><a id="Page_361">361</a></span> -applications, to which our reasoning powers are incompetent, -that nature appears complicated:—the -moment we contemplate it as it is, and attain a position -from which we can take a commanding view, -though but of a small part of its plan, we never fail to -recognise that sublime simplicity on which the mind -rests satisfied that it has attained the truth.</p> - -<p><span class="pagenum"><a id="Page_363">363</a></span></p> - -<hr /> - -<div class="chapter"><div class="index"> -<h2 class="nobreak"><a id="INDEX">INDEX.</a></h2> - -<ul class="index"> -<li class="ifrst">Acoustics cultivated by Pythagoras and Aristotle, page <a href="#Page_248">248</a>.</li> - -<li class="indx">Æpinus, his laws of equilibrium of electricity, <a href="#Page_332">332</a>.</li> - -<li class="indx">Aëriform fluids, liquids kept in a state of vapour, <a href="#Page_321">321</a>.</li> - -<li class="indx">Agricola, George, his knowledge of mineralogy and metallurgy, <a href="#Page_112">112</a>.</li> - -<li class="indx">Air, compressibility and elasticity of; limitation to the repulsive tendency of, <a href="#Page_226">226</a>.</li> -<li class="isub1">Weight of, unknown to the ancients, <a href="#Page_228">228</a>.</li> -<li class="isub1">First perceived by Galileo, <a href="#Page_228">228</a>.</li> -<li class="isub1">Proved by a crucial instance, <a href="#Page_229">229</a>.</li> -<li class="isub1">Equilibrium of, established, <a href="#Page_231">231</a>.</li> -<li class="isub1">Dilatation of, by heat, <a href="#Page_319">319</a>.</li> - -<li class="indx">Air-pump, discovery of, <a href="#Page_230">230</a>.</li> - -<li class="indx">Airy, his experiments in Dolcoath mine, <a href="#Page_187">187</a>.</li> - -<li class="indx">Alchemists, advantages derived from, <a href="#Page_11">11</a>.</li> - -<li class="indx">Algebra, <a href="#Page_19">19</a>.</li> - -<li class="indx">Ampere, his electro-dynamic theory, <a href="#Page_202">202</a>.</li> -<li class="isub1">Utility of, <a href="#Page_203">203</a>, <a href="#Page_324">324</a>.</li> - -<li class="indx">Analysis of force, <a href="#Page_86">86</a>.</li> -<li class="isub1">Of motion, <a href="#Page_87">87</a>.</li> -<li class="isub1">Of complex phenomena, <a href="#Page_88">88</a>.</li> - -<li class="indx">Anaxagoras, philosophy of, <a href="#Page_107">107</a>.</li> - -<li class="indx">Animal electricity, <a href="#Page_337">337</a>.</li> - -<li class="indx">Arago, M., his experiment with a magnetic needle and a plate of copper, <a href="#Page_157">157</a>.</li> - -<li class="indx">Archimedes, his practical application of science, <a href="#Page_72">72</a>.</li> -<li class="isub1">His knowledge of hydrostatics, <a href="#Page_231">231</a>.</li> - -<li class="indx">Arfwedson, his discovery of lithia, <a href="#Page_158">158</a>.</li> - -<li class="indx">Aristotle, his knowledge of natural history, <a href="#Page_109">109</a>.</li> -<li class="isub1">His works condemned, and subsequently studied with avidity, <a href="#Page_111">111</a>.</li> -<li class="isub1">His philosophy overturned by the discoveries of Copernicus, Kepler, and Galileo, <a href="#Page_113">113</a>.</li> - -<li class="indx">Arithmetic, <a href="#Page_19">19</a>.</li> - -<li class="indx">Art, empirical and scientific, differences between, <a href="#Page_71">71</a>.</li> -<li class="isub1">Remarks on the language, terms, or signs, used in treating of it, <a href="#Page_70">70</a>.</li> - -<li class="indx">Assurances, life, utility and abuses of, <a href="#Page_58">58</a>.</li> - -<li class="indx">Astronomy, cause of the slow progress of our knowledge of, <a href="#Page_78">78</a>.</li> -<li class="isub1">Theory and practical observations distinct in, <a href="#Page_132">132</a>.</li> -<li class="isub1">An extensive acquaintance with science and every branch of knowledge necessary to make a perfect observer in, <a href="#Page_132">132</a>.</li> -<li class="isub1">Five primary planets added to our system, <a href="#Page_274">274</a>.</li> -<li class="isub1">Positions, figures, and dimensions of all the planetary orbits now well known, <a href="#Page_275">275</a>.</li> - -<li class="indx">Atomic theory, <a href="#Page_305">305</a>.</li> -<li class="isub1">Advantage of, <a href="#Page_306">306</a>.</li> - -<li class="indx">Atomic weights of chemical elements, <a href="#Page_306">306</a>.</li> - -<li class="indx">Attraction, capillary, or capillarity, investigated by Laplace and Young, <a href="#Page_234">234</a>.</li> - -<li class="ifrst">Bacon, celebrated in England for his knowledge of science, <a href="#Page_72">72</a>.<span class="pagenum"><a id="Page_364">364</a></span></li> -<li class="isub1">Benefits conferred on Natural Philosophy by him, <a href="#Page_104">104</a>.</li> -<li class="isub1">His Novum Organum, <a href="#Page_105">105</a>.</li> -<li class="isub1">His reform in philosophy proves the paramount importance of induction, <a href="#Page_114">114</a>.</li> -<li class="isub1">His prerogative of facts, <a href="#Page_181">181</a>.</li> -<li class="isub1">Illustrated by the fracture of a crystallized substance, <a href="#Page_183">183</a>.</li> -<li class="isub1">His collective instances, <a href="#Page_184">184</a>.</li> -<li class="isub1">Importance of, <a href="#Page_185">185</a>.</li> -<li class="isub1">His experiment on the weight of bodies, <a href="#Page_186">186</a>.</li> -<li class="isub1">Travelling instances of, frontier instances of, <a href="#Page_188">188</a>.</li> -<li class="isub1">His difference between liquids and aëriform fluids, <a href="#Page_233">233</a>.</li> - -<li class="indx">Bartolin, Erasmus, first discovers the phenomena exhibited by doubly refracting crystals, <a href="#Page_254">254</a>.</li> - -<li class="indx">Beccher, phlogistic doctrines of, <a href="#Page_300">300</a>.</li> - -<li class="indx">Bergmann, his advancement in crystallography, <a href="#Page_239">239</a>.</li> - -<li class="indx">Bernoulli, experiments of, in hydrodynamical science, <a href="#Page_181">181</a>.</li> - -<li class="indx">Biot, his hypothesis of a rotatory motion of the particles of light about their axes, <a href="#Page_262">262</a>.</li> - -<li class="indx">Black, Dr., his discovery of latent heat, <a href="#Page_322">322</a>.</li> - -<li class="indx">Bode, his curious law observed in the progression of the magnitudes of the several planetary orbits, <a href="#Page_308">308</a>.</li> - -<li class="indx">Bodies, natural constitution of, <a href="#Page_221">221</a>.</li> -<li class="isub1">Division of, into crystallized and uncrystallized, <a href="#Page_242">242</a>.</li> - -<li class="indx">Bones, dry, a magazine of nutriment, <a href="#Page_65">65</a>.</li> - -<li class="indx">Borda, his invention for subdivision, <a href="#Page_128">128</a>.</li> - -<li class="indx">Botany, general utility of, <a href="#Page_345">345</a>.</li> - -<li class="indx">Boyle, Robert, his enthusiasm in the pursuit of science, <a href="#Page_115">115</a>.</li> -<li class="isub1">His improvement on the air-pump, <a href="#Page_230">230</a>.</li> - -<li class="indx">Brain, hypothesis of its being an electric pile, <a href="#Page_343">343</a>.</li> - -<li class="indx">Bramah’s press, principle and utility of, <a href="#Page_233">233</a>.</li> - -<li class="indx">Brewster, Dr., his improvement on lenses for lighthouses, <a href="#Page_56">56</a>.</li> -<li class="isub1">His researches prove that the phenomena exhibited by polarized light, in its transmission through crystals, afford a certain indication of the most important points relating to the structure of crystals themselves, <a href="#Page_263">263</a>.</li> - -<li class="ifrst">Cabot, Sebastian, his discovery of the variation of the needle, <a href="#Page_327">327</a>.</li> - -<li class="indx">Cagnard, Baron de la Tour, utility of his experiments, <a href="#Page_234">234</a>.</li> - -<li class="indx">Causes and consequences directors of the will of man, <a href="#Page_6">6</a>.</li> - -<li class="indx">Causes, proximate, discovery of, called by Newton <i xml:lang="la" lang="la">veræ causæ</i>, <a href="#Page_144">144</a>.</li> - -<li class="indx">Celestial mechanics, <a href="#Page_265">265</a>.</li> - -<li class="indx">Chaldean records, <a href="#Page_265">265</a>.</li> - -<li class="indx">Chemistry furnishes causes of sudden action, also fulminating compositions, <a href="#Page_62">62</a>.</li> -<li class="isub1">Analogy of the complex phenomena of, with those of physics, <a href="#Page_92">92</a>.</li> -<li class="isub1">Benefits arising from the analysis of, <a href="#Page_94">94</a>.<span class="pagenum"><a id="Page_365">365</a></span></li> -<li class="isub1">Axioms of, analogous to those of geometry, <a href="#Page_95">95</a>.</li> -<li class="isub1">Many of the new elements of, detected in the investigation of residual phenomena, <a href="#Page_158">158</a>.</li> -<li class="isub1">The most general law of, <a href="#Page_209">209</a>.</li> -<li class="isub1">Illustration of, <a href="#Page_210">210</a>.</li> -<li class="isub1">Between fifty and sixty elements in, <a href="#Page_211">211</a>.</li> -<li class="isub1">Objects of, <a href="#Page_296">296</a>.</li> -<li class="isub1">General heads of the principal improvements in, <a href="#Page_302">302</a>.</li> -<li class="isub1">Remarks on those general heads, <a href="#Page_304">304</a>.</li> - -<li class="indx">Chemistry, Stahlian, cause of the mistakes and confusions of, <a href="#Page_123">123</a>.</li> - -<li class="indx">Chladni, experiments of, in dynamical science, <a href="#Page_181">181</a>.</li> - -<li class="indx">Chlorine, disinfectant powers of, <a href="#Page_56">56</a>.</li> - -<li class="indx">Clarke, Dr., his experiments on the arseniate and phosphate of soda, <a href="#Page_170">170</a>.</li> -<li class="isub1">His success in producing a new phosphate of soda, <a href="#Page_171">171</a>.</li> - -<li class="indx">Climate, change of, in large tracts of the globe, alleged cause of, <a href="#Page_145">145</a>.</li> - -<li class="indx">Coals, power of a bushel of, properly consumed, <a href="#Page_59">59</a>.</li> -<li class="isub1">Quantity consumed in London, <a href="#Page_60">60</a>.</li> - -<li class="indx">Cohesion, an ultimate phenomenon, <a href="#Page_90">90</a>.</li> - -<li class="indx">Cold, qualities of, <a href="#Page_318">318</a>.</li> - -<li class="indx">Compass, mariner’s, <a href="#Page_55">55</a>.</li> - -<li class="indx">Condensation, a source of heat, <a href="#Page_313">313</a>.</li> - -<li class="indx">Conduction of heat, laws of, <a href="#Page_205">205</a>.</li> - -<li class="indx">Copernicus, effect of his discoveries on the Aristotelian philosophy, <a href="#Page_113">113</a>.</li> -<li class="isub1">Objections to his astronomical doctrines, <a href="#Page_269">269</a>.</li> - -<li class="indx">Crystallography, laws of, <a href="#Page_123">123</a>, <a href="#Page_239">239</a>.</li> -<li class="isub1">A determinate figure supposed to be common to all the particles of a crystal, <a href="#Page_242">242</a>.</li> - -<li class="ifrst">D’Alembert, his improvements in hydrodynamics, <a href="#Page_236">236</a>.</li> - -<li class="indx">Dalton, his announcement of the atomic theory, <a href="#Page_305">305</a>.</li> -<li class="isub1">His examination of gases and vapours, <a href="#Page_319">319</a>.</li> - -<li class="indx">Davy, Sir H., brings the voltaic pile to bear upon the earths and alkalies, <a href="#Page_339">339</a>.</li> - -<li class="indx">Deduction, utility of, <a href="#Page_174">174</a>.</li> - -<li class="indx">De l’Isle, Romé, his study of crystalline bodies, <a href="#Page_239">239</a>.</li> - -<li class="indx">Dew, causes of, investigated, <a href="#Page_159">159</a>.</li> -<li class="isub1">Effects of, on different substances, <a href="#Page_160">160</a>.</li> -<li class="isub1">Objects capable of contracting it, <a href="#Page_161">161</a>.</li> -<li class="isub1">A cloudless sky favourable to its production, <a href="#Page_162">162</a>.</li> -<li class="isub1">General proximate cause of, <a href="#Page_163">163</a>.</li> - -<li class="indx">Drummond, lieutenant, his improvement on lenses for lamps of lighthouses, <a href="#Page_56">56</a>.</li> - -<li class="indx">Dynamics, importance of, <a href="#Page_96">96</a>, <a href="#Page_223">223</a>.</li> - -<li class="ifrst">Earth, the orbit of,—diminution of its eccentricity round the sun, <a href="#Page_147">147</a>.</li> - -<li class="indx">Economy, political, <a href="#Page_73">73</a>.</li> - -<li class="indx">Egypt, great pyramid of, height, weight, and ground occupied by it, <a href="#Page_60">60</a>.</li> -<li class="isub1">Accuracy of the astronomical records of, <a href="#Page_265">265</a>.</li> - -<li class="indx">Elasticity, an ultimate phenomenon, <a href="#Page_90">90</a>.</li> - -<li class="indx">Electricity may be the cause of magnetism, <a href="#Page_93">93</a>.</li> -<li class="isub1">Universality of, <a href="#Page_329">329</a>.<span class="pagenum"><a id="Page_366">366</a></span></li> -<li class="isub1">Effects of, <a href="#Page_330">330</a>.</li> -<li class="isub1">Activity of, <a href="#Page_331">331</a>.</li> -<li class="isub1">Equilibrium of, <a href="#Page_332">332</a>.</li> -<li class="isub1">Productive of chemical decomposition, <a href="#Page_338">338</a>.</li> - -<li class="indx">Empirical laws, <a href="#Page_178">178</a>.</li> -<li class="isub1">Evils resulting from, <a href="#Page_179">179</a>.</li> - -<li class="indx">Encke, professor, his prediction of the return of the comet so many times in succession, <a href="#Page_156">156</a>.</li> - -<li class="indx">Englefield, sir H., his analysis of a solar beam, <a href="#Page_314">314</a>.</li> - -<li class="indx">Equilibrium maintained by force, <a href="#Page_222">222</a>.</li> - -<li class="indx">Erman, professor, his opinion of the effects of the voltaic circuit, <a href="#Page_340">340</a>.</li> - -<li class="indx">Euler, his improvement on Newton’s theory of sound, <a href="#Page_247">247</a>.</li> - -<li class="indx">Experience, source of our knowledge of nature’s laws, <a href="#Page_76">76</a>.</li> - -<li class="indx">Experiment, a means of acquiring experience, <a href="#Page_76">76</a>.</li> -<li class="isub1">Utility of, <a href="#Page_151">151</a>.</li> - -<li class="ifrst">Facts, the observation of, <a href="#Page_118">118</a>.</li> - -<li class="indx">Faujas de St. Fond, imaginary craters of, <a href="#Page_131">131</a>.</li> - -<li class="indx">Fluids, laws of the motion of, <a href="#Page_181">181</a>.</li> -<li class="isub1">Compressibility of, <a href="#Page_225">225</a>.</li> -<li class="isub1">Consideration of the motions of, more complicated than that of equilibrium, <a href="#Page_235">235</a>.</li> - -<li class="indx">Force, analysis of, <a href="#Page_86">86</a>.</li> -<li class="isub1">The cause of motion, <a href="#Page_149">149</a>.</li> -<li class="isub1">Phenomena of, <a href="#Page_221">221</a>.</li> -<li class="isub1">Molecular forces, <a href="#Page_245">245</a>.</li> - -<li class="indx">Fourier, baron, his opinion that the celestial regions have a temperature, independent of the sun, not greatly inferior to that at which quicksilver congeals, <a href="#Page_157">157</a>.</li> -<li class="isub1">His analysis of the laws of conduction and radiation of heat, <a href="#Page_317">317</a>.</li> - -<li class="indx">Franklin, Dr., his experiments on electricity, <a href="#Page_332">332</a>.</li> - -<li class="indx">Fresnel, M., his mathematical explanation of the phenomena of double refraction, <a href="#Page_32">32</a>.</li> -<li class="isub1">His improvement on lenses for lamps of lighthouses, <a href="#Page_56">56</a>.</li> -<li class="isub1">His opinions on the nature of light, <a href="#Page_207">207</a>.</li> -<li class="isub1">His experiments on the interference of polarized light, <a href="#Page_261">261</a>.</li> -<li class="isub1">His theory of polarization, <a href="#Page_262">262</a>.</li> - -<li class="indx">Friction, a source of heat, <a href="#Page_313">313</a>.</li> - -<li class="ifrst">Galileo, celebrity of, for his knowledge of science, <a href="#Page_72">72</a>.</li> -<li class="isub1">His exposition of the Aristotelian philosophy, <a href="#Page_110">110</a>.</li> -<li class="isub1">His refutation of Aristotle’s dogmas respecting motion, his persecution in consequence of it, <a href="#Page_113">113</a>.</li> -<li class="isub1">His knowledge of the accelerating power of gravity, <a href="#Page_168">168</a>.</li> -<li class="isub1">His knowledge of the weight of the atmosphere, <a href="#Page_228">228</a>.</li> - -<li class="indx">Galvani, utility of his discoveries in electricity, <a href="#Page_335">335</a>.</li> -<li class="isub1">His application of it to animals, <a href="#Page_336">336</a>.</li> - -<li class="indx">Gay-Lussac, his examination of gases and vapours, <a href="#Page_319">319</a>.</li> - -<li class="indx">Generalization, inductive, <a href="#Page_1">1</a>, <a href="#Page_90">90</a>.</li> - -<li class="indx">Geology, <a href="#Page_281">281</a>.</li> -<li class="isub1">Its rank as a science, <a href="#Page_287">287</a>.</li> - -<li class="indx">Geometry, axioms of, an appeal to experience, not corporeal, but mental, <a href="#Page_95">95</a>.</li> - -<li class="indx">Gilbert, Dr., of Colchester, his knowledge of magnetism and electricity, <a href="#Page_112">112</a>.<span class="pagenum"><a id="Page_367">367</a></span></li> - -<li class="indx">Gravitation, law of, a physical axiom of a very high and universal kind, <a href="#Page_98">98</a>.</li> -<li class="isub1">Influence of, decreases in the inverse ratio of the square of the distance, <a href="#Page_123">123</a>.</li> - -<li class="indx">Greece, philosophers of, their extraordinary success in abstract reasoning, and their careless consideration of external nature, <a href="#Page_105">105</a>.</li> -<li class="isub1">Their general character, <a href="#Page_106">106</a>.</li> -<li class="isub1">Philosophy of, <a href="#Page_108">108</a>.</li> - -<li class="indx">Grimaldi, a jesuit of Bologna, his discovery of diffraction, or inflection of light, <a href="#Page_252">252</a>.</li> - -<li class="indx">Guinea and feather experiment, <a href="#Page_168">168</a>.</li> - -<li class="indx">Gunpowder, invention of, <a href="#Page_55">55</a>.</li> -<li class="isub1">A mechanical agent, <a href="#Page_62">62</a>.</li> - -<li class="ifrst">Haarlem lake, draining of, <a href="#Page_61">61</a>.</li> - -<li class="indx">Harmony, sense of, <a href="#Page_248">248</a>.</li> - -<li class="indx">Head, captain, anecdote of, <a href="#Page_84">84</a>.</li> - -<li class="indx">Heat, <a href="#Page_193">193</a>.</li> -<li class="isub1">Radiation and conduction of, <a href="#Page_205">205</a>.</li> -<li class="isub1">One of the chief agents in chemistry, <a href="#Page_310">310</a>.</li> -<li class="isub1">Our ignorance of the nature of, <a href="#Page_310">310</a>.</li> -<li class="isub1">Abuse of the sense of the term, <a href="#Page_311">311</a>.</li> -<li class="isub1">The general heads under which it is studied, <a href="#Page_312">312</a>.</li> -<li class="isub1">Its most obvious sources, <a href="#Page_312">312</a>.</li> -<li class="isub1">Animal heat, to what process referable, <a href="#Page_313">313</a>.</li> -<li class="isub1">Radiation and conduction of, <a href="#Page_314">314</a>.</li> -<li class="isub1">Solar heat differs from terrestrial fires, or hot bodies, <a href="#Page_315">315</a>.</li> -<li class="isub1">Principal effects of, <a href="#Page_317">317</a>.</li> -<li class="isub1">The antagonist to mutual attraction, <a href="#Page_322">322</a>.</li> -<li class="isub1">Latent heat, <a href="#Page_322">322</a>.</li> -<li class="isub1">Specific heat, <a href="#Page_323">323</a>.</li> - -<li class="indx">Herschel, sir William, his analysis of a solar beam, <a href="#Page_314">314</a>.</li> - -<li class="indx">Hipparchus, his catalogue of stars, <a href="#Page_276">276</a>.</li> - -<li class="indx">Holland drained of water by windmills, <a href="#Page_61">61</a>.</li> - -<li class="indx">Hooke almost the rival of Newton, <a href="#Page_116">116</a>.</li> - -<li class="indx">Huel Towan, steam-engine at, <a href="#Page_59">59</a>.</li> - -<li class="indx">Huyghens, his doctrine of light, <a href="#Page_207">207</a>.</li> -<li class="isub1">Ascertains the laws of double refraction, <a href="#Page_254">254</a>.</li> - -<li class="indx">Hydrostatics, first step towards a knowledge of, made by Archimedes, <a href="#Page_231">231</a>.</li> -<li class="isub1">Law of the equal pressure of liquids, <a href="#Page_232">232</a>.</li> -<li class="isub1">General applicability of, <a href="#Page_232">232</a>.</li> - -<li class="indx">Hypothesis, not to be deterred from framing them, <a href="#Page_196">196</a>.</li> -<li class="isub1">Conditions on which they should be framed, <a href="#Page_197">197</a>.</li> -<li class="isub1">Illustrated by the laws of gravitation, <a href="#Page_198">198</a>.</li> -<li class="isub1">Use and abuse of, <a href="#Page_204">204</a>.</li> - -<li class="ifrst">Induction, different ways of carrying it on, <a href="#Page_102">102</a>.</li> -<li class="isub1">Steps by which it is arrived at on a legitimate and extensive scale, <a href="#Page_118">118</a>.</li> -<li class="isub1">First stage of, <a href="#Page_144">144</a>.</li> -<li class="isub1">Verification of, <a href="#Page_164">164</a>.</li> -<li class="isub1">Instanced in astronomy, <a href="#Page_166">166</a>.</li> -<li class="isub1">Must be followed into all its consequences, and applied to all those cases which seem even remotely to bear upon the subject of enquiry, <a href="#Page_173">173</a>.</li> -<li class="isub1">Nature of the inductions by which quantitative laws are arrived at, <a href="#Page_176">176</a>.</li> -<li class="isub1">Necessity of induction embracing a series of cases which absolutely include the whole scale of variation of which the quantities in question admit, <a href="#Page_177">177</a>.</li> - -<li class="indx">Induced electricity, <a href="#Page_333">333</a>.<span class="pagenum"><a id="Page_368">368</a></span></li> - -<li class="indx">Inertia, <a href="#Page_223">223</a>.</li> - -<li class="indx">Iodine, discovery of, <a href="#Page_50">50</a>.</li> -<li class="isub1">Efficacy of, in curing goître, <a href="#Page_51">51</a>.</li> - -<li class="indx">Isomorphism, law of, <a href="#Page_170">170</a>.</li> - -<li class="ifrst">Kepler, effect of his discoveries on the Aristotelian philosophy, <a href="#Page_113">113</a>.</li> -<li class="isub1">Nature of his laws of the planetary system, <a href="#Page_178">178</a>.</li> -<li class="isub1">Proofs of the Newtonian system, <a href="#Page_179">179</a>.</li> - -<li class="indx">Knowledge, physical facts illustrative of the utility of, <a href="#Page_45">45</a>.</li> -<li class="isub1">Diffusion of, how to take advantage of in the investigation of nature, <a href="#Page_138">138</a>.</li> - -<li class="ifrst">Lagrange, his improvements on Newton’s theory of sound, <a href="#Page_247">247</a>.</li> -<li class="isub1">His astronomical researches, <a href="#Page_275">275</a>.</li> - -<li class="indx">Lamp, safety, <a href="#Page_55">55</a>.</li> - -<li class="indx">Laplace, his explanation of the residual velocity of sound and confirmation of the general law of the developement of heat by compression, <a href="#Page_172">172</a>.</li> -<li class="isub1">His astronomical research, <a href="#Page_275">275</a>.</li> -<li class="isub1">His experiments on the dilatation of bodies by heat, <a href="#Page_319">319</a>.</li> -<li class="isub1">His study of specific heat, <a href="#Page_323">323</a>.</li> -<li class="isub1">Latent heat, <a href="#Page_323">323</a>.</li> - -<li class="indx">Laws, inductive, <a href="#Page_171">171</a>.</li> -<li class="isub1">General, <a href="#Page_198">198</a>.</li> -<li class="isub1">How applicable, <a href="#Page_199">199</a>.</li> -<li class="isub1">Illustrated by the planetary system, <a href="#Page_201">201</a>.</li> -<li class="isub1">Empirical laws, <a href="#Page_178">178</a>.</li> - -<li class="indx">Lavoisier, his improvements in chemical science, <a href="#Page_302">302</a>.</li> -<li class="isub1">Experiments on dilatation of bodies by heat, <a href="#Page_319">319</a>.</li> -<li class="isub1">His investigation on specific heat, <a href="#Page_323">323</a>.</li> - -<li class="indx">Light, refraction of, <a href="#Page_30">30</a>.</li> -<li class="isub1">Double refraction of, <a href="#Page_31">31</a>.</li> -<li class="isub1">Polarization of, <a href="#Page_254">254</a>.</li> - -<li class="indx">Light and vision, ignorance of the ancients respecting, <a href="#Page_249">249</a>.</li> - -<li class="indx">Lighthouse, <a href="#Page_56">56</a>.</li> - -<li class="indx">Lightning, how to judge philosophically of it, <a href="#Page_120">120</a>.</li> -<li class="isub1">Returning stroke of, <a href="#Page_121">121</a>.</li> - -<li class="indx">Liquids, cohesion, attraction and repulsion of the particles of, <a href="#Page_227">227</a>.</li> -<li class="isub1">Differ from aëriform fluids by their cohesion, <a href="#Page_233">233</a>.</li> -<li class="isub1">The Florentine experiment on; experiments by Canton, Perkins, Oërsted, and others on, <a href="#Page_235">235</a>.</li> -<li class="isub1">Obscurity of the laws of dilatation of, <a href="#Page_320">320</a>.</li> - -<li class="indx">Linnæus, his knowledge of crystalline substances, <a href="#Page_239">239</a>.</li> - -<li class="indx">Logic, <a href="#Page_19">19</a>.</li> - -<li class="indx">Lyell’s Principles of Geology, extract from, <a href="#Page_146">146</a>.</li> - -<li class="ifrst">Magnetism may be caused by electricity, <a href="#Page_93">93</a>.</li> -<li class="isub1">Offers a “glaring instance” of polarity, <a href="#Page_326">326</a>.</li> -<li class="isub1">Experiments illustrative of, <a href="#Page_327">327</a>.</li> - -<li class="indx">Malus, a French officer of engineers, discovers the polarization of light, <a href="#Page_132">132</a>, <a href="#Page_258">258</a>.</li> - -<li class="indx">Man, regarded as a creature of instinct, <a href="#Page_1">1</a>.</li> -<li class="isub1">Of reason and speculation, <a href="#Page_3">3</a>.</li> -<li class="isub1">His will determined by causes and consequences, <a href="#Page_6">6</a>.</li> -<li class="isub1">Advantages to, from the study of science, <a href="#Page_7">7</a>.</li> -<li class="isub1">His necessity to study the laws of nature illustrated, <a href="#Page_66">66</a>.</li> -<li class="isub1">Happiness and the opposite state of man in the aggregate, <a href="#Page_67">67</a>.</li> -<li class="isub1">Advantages conferred on, by the augmentation of physical resources, <a href="#Page_68">68</a>.<span class="pagenum"><a id="Page_369">369</a></span></li> -<li class="isub1">Advantages from intellectual resources, <a href="#Page_69">69</a>.</li> - -<li class="indx">Mariotte, his law of equilibrium of an elastic fluid recently verified by the Royal Academy of Paris, <a href="#Page_231">231</a>.</li> -<li class="isub1">His difference between solar and other heat, <a href="#Page_315">315</a>.</li> - -<li class="indx">Matter, indestructibility of; Divided by grinding, <a href="#Page_40">40</a>.</li> -<li class="isub1">By fire, <a href="#Page_41">41</a>.</li> -<li class="isub1">Dilated by heat, <a href="#Page_193">193</a>.</li> -<li class="isub1">Inertia of, <a href="#Page_202">202</a>.</li> -<li class="isub1">Polarity of, one of the ultimate phenomena to which the analysis of nature leads us, <a href="#Page_245">245</a>.</li> -<li class="isub1">Inherent activity of, <a href="#Page_297">297</a>.</li> -<li class="isub1">Causes of the polarity of, <a href="#Page_299">299</a>.</li> -<li class="isub1">Imponderable forms of, <a href="#Page_310">310</a>.</li> - -<li class="indx">Measure, the standard, difficulty of preserving it unaltered, <a href="#Page_128">128</a>.</li> -<li class="isub1">How to be assisted in measurement, <a href="#Page_129">129</a>.</li> -<li class="isub1">Our conclusions from, should be conditional, <a href="#Page_130">130</a>.</li> - -<li class="indx">Menai Bridge, weight and height of, <a href="#Page_60">60</a>.</li> - -<li class="indx">Mechanics, practical, <a href="#Page_63">63</a>.</li> - -<li class="indx">Mètre, the French, <a href="#Page_126">126</a>.</li> - -<li class="indx">Microscopes, power of, <a href="#Page_191">191</a>.</li> - -<li class="indx">Millstones, method of making in France, <a href="#Page_48">48</a>.</li> - -<li class="indx">Mind, its transition from the little to the great, and <i xml:lang="la" lang="la">vice versâ</i>, illustrated, <a href="#Page_172">172</a>.</li> - -<li class="indx">Mineralogy unknown to the ancients, <a href="#Page_79">79</a>.</li> -<li class="isub1">Prejudiced by the rage for nomenclature, <a href="#Page_139">139</a>.</li> -<li class="isub1">Benefited by the progress of chemical analysis, <a href="#Page_293">293</a>.</li> - -<li class="indx">Minerals, simple, apparent paucity of, <a href="#Page_294">294</a>.</li> -<li class="isub1">Difficulty in classing them, <a href="#Page_295">295</a>.</li> - -<li class="indx">Mitscherlich, his law of isomorphism, <a href="#Page_170">170</a>.</li> -<li class="isub1">His experiments on the expansion of substances by heat, <a href="#Page_243">243</a>.</li> - -<li class="indx">Motion, <a href="#Page_87">87</a>.</li> -<li class="isub1">Simplicity and precision of the laws of, <a href="#Page_179">179</a>.</li> - -<li class="ifrst">Nature, laws of, <a href="#Page_37">37</a>.</li> -<li class="isub1">Immutability of, <a href="#Page_42">42</a>.</li> -<li class="isub1">Harmony of, and advantage of studying them, <a href="#Page_43">43</a>.</li> -<li class="isub1">Prove the impossibility of attaining the declared object of the alchemist. How they serve mankind generally, <a href="#Page_44">44</a>.</li> -<li class="isub1">Illustrated by mining, <a href="#Page_45">45</a>.</li> -<li class="isub1">Economy derived from a knowledge of, <a href="#Page_65">65</a>.</li> -<li class="isub1">How to be regarded, <a href="#Page_100">100</a>, <a href="#Page_101">101</a>.</li> - -<li class="indx">Nature, objects of, an enumeration and nomenclature of, useful in the study of, <a href="#Page_135">135</a>.</li> -<li class="isub1">Mechanism of, on too large or too small a scale to be immediately cognisable by our senses, <a href="#Page_191">191</a>.</li> - -<li class="indx">Newton, his proof of Galileo’s laws of gravitation by an experiment with a hollow glass pendulum, <a href="#Page_160">160</a>.</li> -<li class="isub1">His foundation to hydrodynamical science, <a href="#Page_181">181</a>.</li> -<li class="isub1">Fixes the division between statics and dynamics, <a href="#Page_223">223</a>.</li> -<li class="isub1">His investigation of the law of equilibrium of elastic fluids, <a href="#Page_231">231</a>.</li> -<li class="isub1">His law of hydrostatics, <a href="#Page_232">232</a>.</li> -<li class="isub1">His foundation of hydrodynamics <a href="#Page_236">236</a>.</li> -<li class="isub1">His analysis of sound, <a href="#Page_247">247</a>.<span class="pagenum"><a id="Page_370">370</a></span></li> -<li class="isub1">Hypothesis of light, <a href="#Page_250">250</a>.</li> -<li class="isub1">Examination of a soap-bubble, <a href="#Page_252">252</a>.</li> -<li class="isub1">His hypothesis of fits of easy transmission and reflection, <a href="#Page_253">253</a>.</li> -<li class="isub1">His combination of mathematical skill with physical research, <a href="#Page_271">271</a>.</li> -<li class="isub1">His Principia, <a href="#Page_272">272</a>.</li> -<li class="isub1">His successors; his geometry, <a href="#Page_273">273</a>.</li> - -<li class="indx">Nomenclature, importance of, to science, <a href="#Page_136">136</a>.</li> -<li class="isub1">More a consequence than a cause of extended knowledge, <a href="#Page_138">138</a>.</li> -<li class="isub1">Prejudicial to mineralogy, <a href="#Page_139">139</a>.</li> - -<li class="indx">Norman, Robert, his discovery of the dip of the needle, <a href="#Page_327">327</a>.</li> - -<li class="indx">Numerical precision, necessity of, in science, <a href="#Page_122">122</a>.</li> - -<li class="ifrst">Objects, and their mutual actions, subjects of contemplation, <a href="#Page_118">118</a>.</li> - -<li class="indx">Observation, a means of acquiring experience, <a href="#Page_76">76</a>.</li> -<li class="isub1">Passive and active, <a href="#Page_77">77</a>.</li> -<li class="isub1">Recorded observation, <a href="#Page_120">120</a>.</li> -<li class="isub1">Necessity of, to acquire precise physical data, <a href="#Page_215">215</a>.</li> -<li class="isub1">Illustrated by the barometer, <a href="#Page_216">216</a>.</li> - -<li class="indx">Oërsted, his discoveries in electricity and magnetism, <a href="#Page_132">132</a>.</li> -<li class="isub1">Of electro-magnetism, <a href="#Page_340">340</a>.</li> - -<li class="indx">Opacity, <a href="#Page_189">189</a>.</li> - -<li class="indx">Otto von Guericke of Magdeburgh, his invention of the air-pump, <a href="#Page_230">230</a>.</li> - -<li class="ifrst">Paracelsus, power of his chemical remedies; his use of mercury, opium, and tartar, <a href="#Page_112">112</a>.</li> - -<li class="indx">Pascal, his crucial instances proving the weight of air, <a href="#Page_229">229</a>.</li> - -<li class="indx">Pendulum, <a href="#Page_126">126</a>.</li> - -<li class="indx">Phenomena, analysis of, illustrated by musical sounds, the sensation of taste, <a href="#Page_85">85</a>.</li> -<li class="isub1">The ultimate and inward process of nature in the production of, <a href="#Page_86">86</a>.</li> -<li class="isub1">Analysis of complex phenomena, <a href="#Page_88">88</a>.</li> -<li class="isub1">Ultimate phenomena, <a href="#Page_90">90</a>.</li> -<li class="isub1">How the analysis of, is useful, <a href="#Page_97">97</a>.</li> -<li class="isub1">A transient phenomenon, how to judge of, <a href="#Page_122">122</a>.</li> -<li class="isub1">Method of explaining one when it presents itself, <a href="#Page_148">148</a>.</li> -<li class="isub1">How to discover the cause of one, <a href="#Page_150">150</a>.</li> -<li class="isub1">Two, or many, theories, maintained as the origin of, in physics, <a href="#Page_195">195</a>.</li> -<li class="isub1">Cosmical phenomena, <a href="#Page_265">265</a>.</li> - -<li class="indx">Philosophy, natural, unfounded objections to the study of, <a href="#Page_7">7</a>.</li> -<li class="isub1">Advantages derivable from the study of, <a href="#Page_10">10</a>.</li> -<li class="isub1">Pleasure and happiness, the consequences of the study of, <a href="#Page_15">15</a>.</li> - -<li class="indx">Phlogistic doctrines of Beccher and Stahl, <a href="#Page_300">300</a>.</li> - -<li class="indx">Physical data, necessity of, <a href="#Page_209">209</a>.</li> -<li class="isub1">Great importance of, <a href="#Page_211">211</a>.</li> -<li class="isub1">Illustrated by the erection of observatories, <a href="#Page_213">213</a>.</li> -<li class="isub1">Necessity of an exact knowledge of, <a href="#Page_214">214</a>.</li> -<li class="isub1">More precise than the observations by which we acquire them, <a href="#Page_215">215</a>.</li> - -<li class="indx">Physics, axioms of; analysis of, <a href="#Page_102">102</a>.</li> - -<li class="indx">Planets, circumjovial, <a href="#Page_186">186</a>.</li> - -<li class="indx">Platina, discovery of, <a href="#Page_308">308</a>.</li> - -<li class="indx">Pliny, his knowledge of quartz and diamond, <a href="#Page_239">239</a>.<span class="pagenum"><a id="Page_371">371</a></span></li> - -<li class="indx">Pneumatics, <a href="#Page_228">228</a>.</li> - -<li class="indx">Political economy, <a href="#Page_73">73</a>.</li> - -<li class="indx">Prejudices of opinion and sense, <a href="#Page_80">80</a>.</li> -<li class="isub1">Conditions on which such are injurious, <a href="#Page_81">81</a>.</li> -<li class="isub1">Illustrated by the division of the rays of light, by the moon at the horizon, and by ventriloquism, <a href="#Page_82">82</a>.</li> -<li class="isub1">By the transition of the hand from heat to cold, <a href="#Page_83">83</a>.</li> - -<li class="indx">Prevost, M., his theory of heat, <a href="#Page_316">316</a>.</li> -<li class="isub1">His theory of reciprocal interchanges, a proof of the radiation of cold, <a href="#Page_318">318</a>.</li> - -<li class="indx">Printing, the art of, <a href="#Page_193">193</a>.</li> -<li class="isub1">Performed by steam, <a href="#Page_194">194</a>.</li> - -<li class="indx">Probabilities, doctrine of, <a href="#Page_217">217</a>.</li> -<li class="isub1">Illustrated by shooting at a wafer, <a href="#Page_218">218</a>.</li> - -<li class="indx">Prout, Dr., his opinion of the atomic weights, <a href="#Page_307">307</a>.</li> - -<li class="indx">Pyrometry, <a href="#Page_319">319</a>.</li> - -<li class="indx">Pythagoras, philosophy of, <a href="#Page_107">107</a>.</li> - -<li class="ifrst">Quinine, sulphate of, comparative comfort and health resulting from the use of, <a href="#Page_56">56</a>.</li> - -<li class="ifrst">Radiation of heat, laws of, <a href="#Page_205">205</a>.</li> - -<li class="indx">Repulsion in fluids and solids, <a href="#Page_227">227</a>.</li> - -<li class="indx">Rules, general, for guiding and facilitating our search among a great mass of assembled facts, <a href="#Page_151">151</a>.</li> - -<li class="indx">Rumford, count, experiments of, on gunpowder, <a href="#Page_62">62</a>.</li> - -<li class="ifrst">Savart, M., his experiments on solids, <a href="#Page_243">243</a>.</li> -<li class="isub1">His researches on sound, <a href="#Page_249">249</a>.</li> - -<li class="indx">Science, abstract, a preparation for the study of physics, <a href="#Page_19">19</a>.</li> -<li class="isub1">Not indispensable to the study of physical laws, <a href="#Page_25">25</a>.</li> -<li class="isub1">Instances illustrative of, <a href="#Page_27">27</a>.</li> - -<li class="indx">Science, physical, nature and objects, immediate and collateral, as regarded in itself and in its application to the practical purposes of life, and its influence on society, <a href="#Page_35">35</a>.</li> -<li class="isub1">State of, previous to the age of Galileo and Bacon, <a href="#Page_104">104</a>.</li> -<li class="isub1">Causes of the rapid advance of, compared with the progress at an earlier period, <a href="#Page_347">347</a>.</li> - -<li class="indx">Science, natural, cause and effect, the ultimate relations of, <a href="#Page_76">76</a>.</li> - -<li class="indx">Sciences and Arts, remarks on the language, terms, or signs used in treating of them, <a href="#Page_70">70</a>.</li> -<li class="isub1">Receive an impulse by the Baconian philosophy, <a href="#Page_114">114</a>.</li> - -<li class="indx">Sensation, cause of, <a href="#Page_91">91</a>.</li> - -<li class="indx">Senses, inadequate to give us direct information for the exact comparison of quantity, <a href="#Page_124">124</a>.</li> -<li class="isub1">Substitutes for the inefficiency of, <a href="#Page_125">125</a>.</li> - -<li class="indx">Seringapatam, method of breaking blocks from the quarries of, <a href="#Page_47">47</a>.</li> - -<li class="indx">Shells found in rocks at a great height above the sea, supposed cause of, <a href="#Page_145">145</a>.</li> - -<li class="indx">Smeaton, his experiments on bodies dilated by heat, <a href="#Page_319">319</a>.</li> - -<li class="indx">Solids, transparent, exhibit periodical colours when exposed to polarized light, <a href="#Page_99">99</a>.</li> -<li class="isub1">Influence of, on the Mind, <a href="#Page_101">101</a>.</li> - -<li class="indx">Solids in general, nature of, <a href="#Page_236">236</a>.</li> -<li class="isub1">Constitution of, complicated, <a href="#Page_237">237</a>.<span class="pagenum"><a id="Page_372">372</a></span></li> -<li class="isub1">Toughness of, distinct from hardness; tenacity of, <a href="#Page_238">238</a>.</li> -<li class="isub1">Become liquefied by the addition of heat, <a href="#Page_321">321</a>.</li> - -<li class="indx">Sounds, musical, illustrative of the analysis of phenomena, <a href="#Page_85">85</a>.</li> -<li class="isub1">Means of having a knowledge of, <a href="#Page_89">89</a>.</li> -<li class="isub1">Propagation of, through the air, <a href="#Page_246">246</a>.</li> -<li class="isub1">Newton’s analysis of, <a href="#Page_247">247</a>.</li> - -<li class="indx">Standard measurement, necessity of, <a href="#Page_125">125</a>.</li> -<li class="isub1">Laws of nature used as such, illustrated by the rotation of the earth, <a href="#Page_126">126</a>.</li> - -<li class="indx">Substances all subject to dilatation by the addition of heat, <a href="#Page_243">243</a>.</li> - -<li class="indx">Sun, the character of the heat of, <a href="#Page_315">315</a>.</li> - -<li class="ifrst">Thales, philosophy of, <a href="#Page_107">107</a>.</li> - -<li class="indx">Theories, how to estimate the value of, <a href="#Page_204">204</a>.</li> -<li class="isub1">Best arrived at by the consideration of general laws, <a href="#Page_208">208</a>.</li> -<li class="isub1">Explanatory of the phenomena of nature; on what their application ought to be grounded, <a href="#Page_209">209</a>.</li> - -<li class="indx">Thomson, Dr., his opinion of the atomic weights, <a href="#Page_307">307</a>.</li> - -<li class="indx">Thermometer, air, <a href="#Page_319">319</a>.</li> - -<li class="indx">Thermo-electricity, <a href="#Page_341">341</a>.</li> - -<li class="indx">Time, division of, <a href="#Page_126">126</a>, <a href="#Page_127">127</a>.</li> - -<li class="indx">Torricelli, pupil of Galileo, his experiments proving the weight of atmosphere, <a href="#Page_229">229</a>.</li> - -<li class="indx">Torpedo, shock of, <a href="#Page_341">341</a>, <a href="#Page_342">342</a>.</li> - -<li class="ifrst">Ulugh Begh, his catalogue of stars, <a href="#Page_277">277</a>.</li> - -<li class="ifrst">Vaccination, success of, as a preventive to small-pox, <a href="#Page_52">52</a>.</li> - -<li class="indx">Vision and light, ignorance of the ancients respecting, <a href="#Page_249">249</a>.</li> - -<li class="indx">Volta, his discoveries in electricity, <a href="#Page_335">335</a>.</li> -<li class="isub1">Electric pile of, <a href="#Page_337">337</a>.</li> - -<li class="indx">Voltaic circuit, <a href="#Page_338">338</a>.</li> - -<li class="ifrst">Water, effects of the power of, <a href="#Page_61">61</a>.</li> - -<li class="indx">Whewell, his experiments, <a href="#Page_187">187</a>.</li> - -<li class="indx">Wells, Dr., his theory of dew, <a href="#Page_163">163</a>.</li> - -<li class="indx">Wind, effects of the power of, <a href="#Page_61">61</a>.</li> - -<li class="indx">Wire steel, magnetized masks of, used by needle-makers, <a href="#Page_57">57</a>.</li> - -<li class="indx">Wollaston, Dr., his verification of the laws of double refraction in Iceland spar, <a href="#Page_258">258</a>.</li> -<li class="isub1">His invention of the goniometer, <a href="#Page_292">292</a>.</li> - -<li class="indx">World, the materials of the, <a href="#Page_290">290</a>.</li> - -<li class="ifrst">Young, Dr., his experiments on the interference of the rays of light, <a href="#Page_260">260</a>.</li> - -<li class="ifrst">Zoology, fossil, <a href="#Page_344">344</a>.</li> -</ul> -</div></div> - -<p class="p2 center smaller">THE END.</p> - -<p class="p2 center vspace"> -<span class="small">LONDON<br /> -PRINTED BY SPOTTISWOODE AND CO.<br /> -NEW-STREET SQUARE.</span> -</p> - -<div class="chapter"><div class="footnotes"> -<h2 class="nobreak p1"><a id="FOOTNOTES"></a>FOOTNOTES</h2> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_1" href="#FNanchor_1" class="fnanchor">1</a> Hooke’s Posthumous Works. Lond. 1705.—p. 472 -and p. 458.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_2" href="#FNanchor_2" class="fnanchor">2</a> Wealth of Nations, book i. chap. i. p. 15.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_3" href="#FNanchor_3" class="fnanchor">3</a> On this subject, we cannot forbear citing a passage from -one of the most profound but at the same time popular writers -of our time, on a subject unconnected it is true with our own, -but bearing strongly on the point before us. “But, if science -be manifestly incomplete, and yet of the highest importance, -it would surely be most unwise to restrain enquiry, conducted -on just principles, even where the immediate practical utility -of it was not visible. In mathematics, chemistry, and every -branch of natural philosophy, how many are the enquiries -necessary for their improvement and completion, which, taken -separately, do not appear to lead to any specifically advantageous -purpose! how many useful inventions, and how much -valuable and improving knowledge, would have been lost, if a -rational curiosity, and a mere love of information, had not -generally been allowed to be a sufficient motive for the search -after truth!”—Malthus’s Principles of Political Economy, -p. 16.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_4" href="#FNanchor_4" class="fnanchor">4</a> <span xml:lang="grc" lang="grc">Λογος</span>, <em>ratio</em>, reason.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_5" href="#FNanchor_5" class="fnanchor">5</a> <span xml:lang="grc" lang="grc">Λογος</span>, <i xml:lang="la" lang="la">verbum</i>, a word.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_6" href="#FNanchor_6" class="fnanchor">6</a> It were much to be wished that navigators would be more -cautious in laying themselves open to a similar censure. On -looking hastily over a map of the world we see three Melville -Islands, two King George’s Sounds, and Cape Blancos innumerable.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_7" href="#FNanchor_7" class="fnanchor">7</a> Young. Lectures on Nat. Phil. ii. 627. See also Phil. -Trans. 1801–2.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_8" href="#FNanchor_8" class="fnanchor">8</a> Captain Basil Hall, R. N.</p></div> - -<div class="footnote"> - -<p class="fn1"><a id="Footnote_9" href="#FNanchor_9" class="fnanchor">9</a> We must caution our readers who would assure themselves -of it by trial, that it is an experiment of some delicacy, and not -to be made without several precautions to ensure success. For -these we must refer to our original authority (Fresnel. Mémoire -sur la Diffraction de la Lumiere, p. 124.); and the principles -on which they depend will of course be detailed in that -volume of the Cabinet Cyclopædia which is devoted to the -subject of <span class="smcap">Light</span>.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_10" href="#FNanchor_10" class="fnanchor">10</a> Little reels used in cotton mills to twist the thread.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_11" href="#FNanchor_11" class="fnanchor">11</a> Such a block would weigh between four and five hundred -thousand pounds. See Dr. Kennedy’s “Account of the -Erection of a Granite Obelisk of a Single Stone about Seventy -Feet high, at Seringapatam.”—<cite>Ed. Phil. Trans.</cite> vol. ix, -p. 312.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_12" href="#FNanchor_12" class="fnanchor">12</a> Dr. Coindet of Geneva.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_13" href="#FNanchor_13" class="fnanchor">13</a> Journal of a Voyage to the South Seas, &c. &c. under the -Command of Commodore George Anson, in 1740–1744, by -Pascoe Thomas, Lond. 1745, So tremendous were the ravages -of scurvy, that, in the year 1726, admiral Hosier sailed with -seven ships of the line to the West Indies, and buried his ships’ -companies twice, and died himself in consequence of a broken -heart. Dr. Johnson, in the year 1778, could describe a sea-life -in such terms as these:—“As to the sailor, when you look -down from the quarter deck to the space below, you see the -utmost extremity of human misery, such crowding, such filth, -such stench!”—“A ship is a prison with the chance of being -drowned—it is worse—worse in every respect—worse room, -worse air, worse food—worse company!” Smollet, who had -personal experience of the horrors of a seafaring life in those -days, gives a lively picture of them in his Roderick Random.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_14" href="#FNanchor_14" class="fnanchor">14</a> Lemon juice was known to be a remedy for scurvy far -superior to all others 200 years ago, as appears by the -writings of Woodall. His work is entitled “The Surgeon’s -Mate, or Military and Domestic Medicine. By John Woodall, -Master in Surgery London, 1636,” p. 165. In 1600, Commodore -Lancaster sailed from England with three other ships -for the Cape of Good Hope, on the 2d of April, and arrived -in Saldanha Bay on the 1st of August, the commodore’s own -ship being in perfect health, from the administration of three -table-spoonsfull of lemon juice every morning to each of his -men, whereas the other ships were so sickly as to be unmanageable -for want of hands, and the commander was obliged -to send men on board to take in their sails and hoist out their -boats. (Purchas’s Pilgrim, vol. i. p. 149.) A Fellow of the -college, and an eminent practitioner, in 1753 published a tract -on sea scurvy, in which he adverts to the superior virtue of this -medicine; and Mr. A. Baird, surgeon of the Hector sloop of -war, states, that from what he had seen of its effects on -board of that ship, he “thinks he shall not be accused of -presumption in pronouncing it, if properly administered, a -<em>most infallible remedy</em>, both in the cure and prevention of -scurvy.” (Vide Trotter’s Medicina Nautica.) The precautions -adopted by captain Cook in his celebrated voyages, had fully -demonstrated by their complete success the practicability of -keeping scurvy under in the longest voyages, but a uniform -system of prevention throughout the service was still deficient. -</p> -<p> -It is to the representations of Dr. Blair and sir Gilbert -Blane, in their capacity of commissioners of the board for sick -and wounded seamen, in 1795, we believe, that its <em>systematic -introduction into nautical diet</em>, by a general order of the admiralty, -is owing. The effect of this wise measure (taken, of -course, in conjunction with the general causes of improved -health,) may be estimated from the following facts:—In -1780, the number of cases of scurvy received into Haslar -hospital was 1457; in 1806 <em>one</em> only, and in 1807 <em>one</em>. There -are now many surgeons in the navy who have never seen the -disease.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_15" href="#FNanchor_15" class="fnanchor">15</a> Throughout France the conductor is recognised as a most -valuable and useful instrument; and in those parts of Germany -where thunder-storms are still more common and tremendous -they are become nearly universal. In Munich there is hardly -a modern house unprovided with them, and of a much better -construction than ours—several copper wires twisted into a -rope.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_16" href="#FNanchor_16" class="fnanchor">16</a> We have been informed by an eminent physician in Rome, -(Dr. Morichini) that a vast quantity of the sulphate of quinine -is manufactured there and consumed in the Campagna, with -an evident effect in mitigating the severity of the malarious -complaints which affect its inhabitants.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_17" href="#FNanchor_17" class="fnanchor">17</a> Dr. Johnson, Memoirs of the Medical Society, vol. v.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_18" href="#FNanchor_18" class="fnanchor">18</a> The engine at Huel Towan. See Mr. Henwood’s Statement -“of the performance of steam-engines in Cornwall for -April, May, and June, 1829.” Brewster’s Journal, Oct. 1829.—The -<em>highest</em> monthly average of this engine extends to 79 -millions of pounds.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_19" href="#FNanchor_19" class="fnanchor">19</a> However, this is not quite a fair statement; a man’s daily -labour is about 4 lbs. of coals. The extreme toil of this ascent -arises from other obvious causes than the mere height.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_20" href="#FNanchor_20" class="fnanchor">20</a> Its surface is about 40,000 acres, and medium depth -about 20 feet. It was proposed to drain it by running embankments -across it, and thus cutting it up into more manageable -portions to be drained by windmills.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_21" href="#FNanchor_21" class="fnanchor">21</a> No one doubts the <em>practicability</em> of the undertaking. -Eight or nine thousand chaldrons of coals duly burnt would -evacuate the whole contents. But many doubt whether it would -be profitable, and some, considering that a few hundreds of -fishermen who gain their livelihood on its waters would be -dispossessed, deny that it would be <em>desirable</em>.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_22" href="#FNanchor_22" class="fnanchor">22</a> “Experiments to determine the Force of fired Gunpowder.” -Phil. Trans. vol. lxxxvii. p. 254. et seq.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_23" href="#FNanchor_23" class="fnanchor">23</a> See a very ingenious application of this kind in Mr. Babbage’s -article on Diving in the Encyc. Metrop.—Others -will readily suggest themselves. For instance, the ballast in -reserve of a balloon might consist of materials capable of evolving -great quantities of hydrogen gas in proportion to their -weight, should such be found.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_24" href="#FNanchor_24" class="fnanchor">24</a> The sulphuric. Bracconot, Annales de Chimie, vol. xii. -p. 184.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_25" href="#FNanchor_25" class="fnanchor">25</a> D’Arcet, Annales de l’Industrie, Fevrier, 1829.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_26" href="#FNanchor_26" class="fnanchor">26</a> See Dr. Prout’s account of the experiments of professor -Autenrieth of Tubingen. Phil. Trans. 1827, p. 381. This discovery, -which renders famine next to <em>impossible</em>, deserves a -higher degree of celebrity than it has obtained.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_27" href="#FNanchor_27" class="fnanchor">27</a> Greenwich.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_28" href="#FNanchor_28" class="fnanchor">28</a> Maskelyne’s.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_29" href="#FNanchor_29" class="fnanchor">29</a> Thomson’s First Principles of Chemistry, vol. ii. p. 68.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_30" href="#FNanchor_30" class="fnanchor">30</a> Galileo exposes unsparingly the Aristotelian style of reasoning. -The reader may take the following from him as a specimen -of its quality. The object is to prove the immutability -and incorruptibility of the heavens; and thus it is done:— -</p> - -<blockquote class="hang2"> - -<p class="ii">I. Mutation is either generation or corruption.</p> -<p class="iii">II. Generation and corruption only happen between contraries.</p> -<p class="iiii">III. The motions of contraries are contrary.</p> -<p class="iiv">IV. The celestial motions are circular.</p> -<p class="iv">V. Circular motions have no contraries.</p> -<div class="in2"> -<p class="in2"><span xml:lang="grc" lang="grc">α</span>. Because there can be but three simple motions.</p> -<p class="in0 in4">1. To a centre.<br /> -2. Round a centre.<br /> -3. From a centre.</p> -<p class="in2"><span xml:lang="grc" lang="grc">β</span>. Of three things, one only can be contrary to one.</p> -<p class="in2"><span xml:lang="grc" lang="grc">γ</span>. But a motion to a centre is manifestly the contrary to a motion from a centre.</p> -<p class="in2"><span xml:lang="grc" lang="grc">δ</span>. Therefore a motion <em>round</em> a centre (<i>i. e.</i> a circular motion) remains without a contrary.</p> -</div> -<p class="ivi"> -VI. <em>Therefore</em> celestial motions have no contraries—<em>therefore</em> -among celestial <em>things</em> there are no contraries—<em>therefore</em> -the heavens are eternal, immutable, incorruptible, and so forth.</p></blockquote> - -<p> -It is evident that all this string of nonsense depends on the -excessive vagueness of the notions of generation, corruption, -contrariety, &c. on which the changes are rung.—<i>See</i> <span class="smcap">Galileo</span>, -<cite>Systema Cosmicum</cite>, Dial. i. p. 30.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_31" href="#FNanchor_31" class="fnanchor">31</a> Macquer justly observes, that the alchemists would have -rendered essential service to chemistry had they only related -their unsuccessful experiments as clearly as they have obscurely -related those which they pretend to have been successful.—<cite>Macquer’s -Dictionary of Chemistry</cite>, i. x.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_32" href="#FNanchor_32" class="fnanchor">32</a> Paracelsus performed most of these cures by mercury and -opium, the use of which latter drug he had learned in Turkey. -Of mercurial preparations the physicians of his time were ignorant, -and of opium they were afraid, as being “cold in the fourth -degree.” Tartar was likewise a great favourite of Paracelsus, -who imposed on it that name, “because it contains the water, -the salt, the oil, and the acid, which burn the patient as hell -does:” in short, a kind of counterbalance to his opium.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_33" href="#FNanchor_33" class="fnanchor">33</a> See the Life of Galileo Galilei, by Mr. Drinkwater, with -Illustrations of the Advancement of Experimental Philosophy.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_34" href="#FNanchor_34" class="fnanchor">34</a> The temporary star in Cassiopeia observed by Cornelius -Gemma, in 1572, was so bright as to be seen at noon-day. That -in Serpentarius, first seen by Kepler in 1604, exceeded in -brilliancy all the other stars and planets.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_35" href="#FNanchor_35" class="fnanchor">35</a> Edinburgh Phil. Journ. 1819, vol. i. p. 8.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_36" href="#FNanchor_36" class="fnanchor">36</a> The abstract principle of repetition in matters of measurement -(viz. juxta-position of units without error) is applicable -to a great variety of cases in which quantities are required to be -determined to minute nicety. In chemistry, in determining -the standard atomic weights of bodies, it seems easily and completely -applicable, by a process which will suggest itself at once -to every chemist, and seems the only thing wanting to place -the exactness of chemical determinations on a par with astronomical -measurements.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_37" href="#FNanchor_37" class="fnanchor">37</a> Accurate and <em>perfectly</em> authentic copies of the yard and -pound, executed in platina, and hermetically sealed in glass, -should be deposited deep in the interior of the massive stone-work -of some great public building, whence they could only be rescued -with a degree of difficulty sufficient to preclude their being disturbed -unless on some very high and urgent occasion. The -fact should be publicly recorded, and its memory preserved by an -inscription. Indeed, how much valuable and useful information -of the actual existing state of arts and knowledge at any -period might be transmitted to posterity in a distinct, tangible, -and imperishable form, if, instead of the absurd and useless -deposition of a few coins and medals under the foundations -of buildings, specimens of ingenious implements or -condensed statements of scientific truths, or processes in arts -and manufactures, were substituted. Will books infallibly -preserve to a remote posterity all that we may desire should be -hereafter known of ourselves and our discoveries, or all that -posterity would wish to know? and may not a useless ceremony -be thus transformed into an act of enrolment in a perpetual -archive of what we most prize, and acknowledge to be most -valuable?</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_38" href="#FNanchor_38" class="fnanchor">38</a> In the system alluded to, the name of quartz is assigned -to iolite and obsidian; that of mica to plumbago, chlorite, and -uranite; sulphur, to orpiment and realgar, &c. See Mohs’s -System of Mineralogy, translated by Haidinger.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_39" href="#FNanchor_39" class="fnanchor">39</a> The following passage, from Lindley’s Synopsis of the -British Flora, characterises justly the respective merits, -in a philosophical point of view, of natural and artificial -systems of classification in general, though limited in its -expression to his own immediate science:—“After all that -has been effected, or is likely to be accomplished hereafter, -there will always be more difficulty in acquiring a knowledge -of the natural system of botany than of the Linnæan. The -latter skims only the surface of things, and leaves the student -in the fancied possession of a sort of information which it is -easy enough to obtain, but which is of little value when acquired: -the former requires a minute investigation of every -part and every property known to exist in plants; but when -understood has conveyed to the mind a store of real information, -of the utmost use to man in every station of life. Whatever -the difficulties may be of becoming acquainted with plants -according to this method, they are inseparable from botany, -which cannot be usefully studied without encountering them.” -Schiller has some beautiful lines on this, entitled “Menschliches -Wissen” (or Human Knowledge); Gedichte, vol. i. -p. 72. Leipzig, 1800.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_40" href="#FNanchor_40" class="fnanchor">40</a> Lyell’s Principles of Geology, vol. i. Fourrier, Mém. de -l’Acad. des Sciences, tom. vii. p. 592. “L’établissement et -le progrès des sociétés humaines, l’action des forces naturelles, -peuvent changer notablement, et dans de vastes contrées, l’état de -la surface du sol, la distribution des eaux, et les grands mouvemens -de l’air. De tels effets sont propres à faire varier, dans -le cours de plusieurs siècles, le dégré de la chaleur moyenne; -car les expressions analytiques comprennent des coefficiens qui -se rapportent à l’état superficiel, et qui influent beaucoup sur -la valeur de la température.” In this enumeration, by M. -Fourrier, of causes which may vary the general relation of the -surface of extensive continents to heat, it is but justice to Mr. -Lyell to observe, that the gradual shifting of the <em>places</em> of the -continents themselves on the surface of the globe, by the abrading -action of the sea on the one hand, and the elevating agency -of subterranean forces on the other, does not expressly occur -and cannot be fairly included in the general sense of the passage, -which confines itself to the consideration of such changes as -may take place on the existing surface of the land.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_41" href="#FNanchor_41" class="fnanchor">41</a> The reader will find this subject further developed in a -paper lately communicated to the Geological Society.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_42" href="#FNanchor_42" class="fnanchor">42</a> Phil. Trans. 1824.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_43" href="#FNanchor_43" class="fnanchor">43</a> Wells on Dew.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_44" href="#FNanchor_44" class="fnanchor">44</a> Principia, book iii. prop. 6.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_45" href="#FNanchor_45" class="fnanchor">45</a> A very curious instance of the pursuit of a law completely -empirical into an extreme case is to be found in Newton’s rule for -the dilatation of his coloured rings seen between glasses at great -obliquities. Optics, book ii. part i. obs. 7.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_46" href="#FNanchor_46" class="fnanchor">46</a> See Phil. Trans. 1819.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_47" href="#FNanchor_47" class="fnanchor">47</a> “When we are told that Saturn moves in his orbit more -than 22,000 miles an hour, we fancy the motion to be swift; but -when we find that he is more than three hours moving his own -diameter, we must then think it, as it really is, slow.” Thirty -Letters on various Subjects, by William Jackson, 1795.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_48" href="#FNanchor_48" class="fnanchor">48</a> Thomson’s First Principles of Chemistry.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_49" href="#FNanchor_49" class="fnanchor">49</a> There seems no doubt, however, that an achromatic -telescope had been constructed by a private amateur, a Mr. -Hall, some time before either Euler or Dollond ever thought -of it.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_50" href="#FNanchor_50" class="fnanchor">50</a> We allude to the recently invented achromatic combinations -of Messrs. Barlow and Rogers, and the dense glasses of -which Mr. Faraday has recently explained the manufacture in -a memoir full of the most beautiful examples of delicate and -successful chemical manipulation, and which promise to give -rise to a new era in optical practice, by which the next generation -at least may benefit. See Phil. Trans. 1830.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_51" href="#FNanchor_51" class="fnanchor">51</a> Alphonso of Castile, 1252.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_52" href="#FNanchor_52" class="fnanchor">52</a> Jackson, Letters on Various Subjects, &c.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_53" href="#FNanchor_53" class="fnanchor">53</a> Thomson’s First Principles of Chemistry, Introduction.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_54" href="#FNanchor_54" class="fnanchor">54</a> The progress of astronomical discovery has since shown -that this law cannot be relied on (1851).</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_55" href="#FNanchor_55" class="fnanchor">55</a> Novum Organum, part ii. table 2. (24), (30), &c. on the -form or nature of heat.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_56" href="#FNanchor_56" class="fnanchor">56</a> We will mention one which we do not remember to have -seen noticed elsewhere in the case of a disturbance of the equilibrium -of heat produced by means purely mechanical, and by -a process depending entirely on a certain order and sequence -of events, and the operation of known causes. Suppose a quantity -of air enclosed in a metallic reservoir, of some good conductor -of heat, and suddenly compressed by a piston. After -giving time for the heat developed by the condensation to be -communicated from the air to the metal which will be thereby -more or less raised in temperature <em>above</em> the surrounding atmosphere, -let the piston be suddenly retracted and the air restored -to its original volume in an instant. The whole apparatus is -now precisely in its initial situation, as to the disposition of its -material parts, and the whole quantity of heat it contains remains -unchanged. But it is evident that the distribution of -this heat within it is now very different from what it was before; -for the air in its sudden expansion cannot re-absorb in an instant -of time all the heat it had parted with to the metal: it -will, therefore, have a temperature <em>below</em> that of the general -atmosphere, while the metal yet retains one above it. Thus, -a subversion of the equilibrium of temperature has been <i xml:lang="la" lang="la">bonâ -fide</i> effected. Heat has been driven from the air into the -metal, while every thing else remains unchanged. -</p> -<p> -We have here a means by which, it is evident, heat may be -obtained, to any extent, from the air, without fuel. For if, in -place of withdrawing the piston and letting the <em>same</em> air expand, -within the reservoir, it be allowed to escape so suddenly -as not to re-absorb the heat given off, and fresh air be then admitted -and the process repeated, any quantity of air may thus -be <em>drained</em> of its heat.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_57" href="#FNanchor_57" class="fnanchor">57</a> See Phil. Trans. 1824.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_58" href="#FNanchor_58" class="fnanchor">58</a> 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 developed reaches a certain point, -along the nerves which communicate with the heart, and thus -to excite the pulsations of that organ. This idea is forcibly -suggested by a view of that elegant apparatus, the dry pile of -Deluc; in which the successive accumulations of electricity -are carried off by a suspended ball, which is kept by the discharges -in a state of regular pulsation for any length of time. -We have witnessed the action of such a pile maintained in this -way for whole years in the study of the above-named eminent -philosopher. The same idea of the cause of the pulsation of -the heart appears to have occurred to Dr. Arnott; and is mentioned -in his useful and excellent work on physics, to which -however, we are not indebted for the suggestion, it having -occurred to us independently many years ago.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_59" href="#FNanchor_59" class="fnanchor">59</a> See a description of a contrivance of this kind by Dr. -Young, Lectures, vol. i. p. 191.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_60" href="#FNanchor_60" class="fnanchor">60</a> Boyle’s Works, folio, vol. iii. Essay x. p. 185.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_61" href="#FNanchor_61" class="fnanchor">61</a> Jackson, The Four Ages, p. 52. London: Cadell and -Davies, 1798. 8vo.</p></div> - -<div class="footnote"> - -<p class="fn2"><a id="Footnote_62" href="#FNanchor_62" class="fnanchor">62</a> Jackson, The Four Ages, p. 90.</p></div> -</div></div> - -<div class="chapter"><div class="transnote"> -<h2 class="nobreak p1"><a id="Transcribers_Notes">Transcriber’s Notes</a></h2> - -<p>Cover created by Transcriber and placed in the Public Domain.</p> - -<p>Punctuation, hyphenation, and spelling were made consistent when a predominant -preference was found in this book; otherwise they were not changed.</p> - -<p>Simple typographical errors were corrected; occasional unbalanced -quotation marks retained.</p> - -<p>Ambiguous hyphens at the ends of lines were retained.</p> - -<p>Spelling of non-English words was not reviewed.</p> - -<p>Text uses both “appreciate” and “appretiate”; both retained.</p> - -<p>Index not checked for proper alphabetization or correct page references.</p> -</div></div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of Preliminary Discourse on the Study of -Natural Philosophy, by John F. W. Herschel - -*** END OF THIS PROJECT GUTENBERG EBOOK PRELIMINARY DISCOURSE--NATURAL PHILOSOPHY *** - -***** This file should be named 54897-h.htm or 54897-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/4/8/9/54897/ - -Produced by Sonya Schermann, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. Special rules, set forth in the General Terms of Use part -of this license, apply to copying and distributing Project -Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm -concept and trademark. Project Gutenberg is a registered trademark, -and may not be used if you charge for the eBooks, unless you receive -specific permission. If you do not charge anything for copies of this -eBook, complying with the rules is very easy. You may use this eBook -for nearly any purpose such as creation of derivative works, reports, -performances and research. They may be modified and printed and given -away--you may do practically ANYTHING in the United States with eBooks -not protected by U.S. copyright law. Redistribution is subject to the -trademark license, especially commercial redistribution. - -START: FULL LICENSE - -THE FULL PROJECT GUTENBERG LICENSE -PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK - -To protect the Project Gutenberg-tm mission of promoting the free -distribution of electronic works, by using or distributing this work -(or any other work associated in any way with the phrase "Project -Gutenberg"), you agree to comply with all the terms of the Full -Project Gutenberg-tm License available with this file or online at -www.gutenberg.org/license. - -Section 1. General Terms of Use and Redistributing Project -Gutenberg-tm electronic works - -1.A. By reading or using any part of this Project Gutenberg-tm -electronic work, you indicate that you have read, understand, agree to -and accept all the terms of this license and intellectual property -(trademark/copyright) agreement. If you do not agree to abide by all -the terms of this agreement, you must cease using and return or -destroy all copies of Project Gutenberg-tm electronic works in your -possession. If you paid a fee for obtaining a copy of or access to a -Project Gutenberg-tm electronic work and you do not agree to be bound -by the terms of this agreement, you may obtain a refund from the -person or entity to whom you paid the fee as set forth in paragraph -1.E.8. - -1.B. "Project Gutenberg" is a registered trademark. It may only be -used on or associated in any way with an electronic work by people who -agree to be bound by the terms of this agreement. There are a few -things that you can do with most Project Gutenberg-tm electronic works -even without complying with the full terms of this agreement. See -paragraph 1.C below. There are a lot of things you can do with Project -Gutenberg-tm electronic works if you follow the terms of this -agreement and help preserve free future access to Project Gutenberg-tm -electronic works. See paragraph 1.E below. - -1.C. The Project Gutenberg Literary Archive Foundation ("the -Foundation" or PGLAF), owns a compilation copyright in the collection -of Project Gutenberg-tm electronic works. Nearly all the individual -works in the collection are in the public domain in the United -States. If an individual work is unprotected by copyright law in the -United States and you are located in the United States, we do not -claim a right to prevent you from copying, distributing, performing, -displaying or creating derivative works based on the work as long as -all references to Project Gutenberg are removed. Of course, we hope -that you will support the Project Gutenberg-tm mission of promoting -free access to electronic works by freely sharing Project Gutenberg-tm -works in compliance with the terms of this agreement for keeping the -Project Gutenberg-tm name associated with the work. You can easily -comply with the terms of this agreement by keeping this work in the -same format with its attached full Project Gutenberg-tm License when -you share it without charge with others. - -1.D. The copyright laws of the place where you are located also govern -what you can do with this work. Copyright laws in most countries are -in a constant state of change. If you are outside the United States, -check the laws of your country in addition to the terms of this -agreement before downloading, copying, displaying, performing, -distributing or creating derivative works based on this work or any -other Project Gutenberg-tm work. The Foundation makes no -representations concerning the copyright status of any work in any -country outside the United States. - -1.E. Unless you have removed all references to Project Gutenberg: - -1.E.1. The following sentence, with active links to, or other -immediate access to, the full Project Gutenberg-tm License must appear -prominently whenever any copy of a Project Gutenberg-tm work (any work -on which the phrase "Project Gutenberg" appears, or with which the -phrase "Project Gutenberg" is associated) is accessed, displayed, -performed, viewed, copied or distributed: - - This eBook is for the use of anyone anywhere in the United States and - most other parts of the world at no cost and with almost no - restrictions whatsoever. You may copy it, give it away or re-use it - under the terms of the Project Gutenberg License included with this - eBook or online at www.gutenberg.org. If you are not located in the - United States, you'll have to check the laws of the country where you - are located before using this ebook. - -1.E.2. If an individual Project Gutenberg-tm electronic work is -derived from texts not protected by U.S. copyright law (does not -contain a notice indicating that it is posted with permission of the -copyright holder), the work can be copied and distributed to anyone in -the United States without paying any fees or charges. If you are -redistributing or providing access to a work with the phrase "Project -Gutenberg" associated with or appearing on the work, you must comply -either with the requirements of paragraphs 1.E.1 through 1.E.7 or -obtain permission for the use of the work and the Project Gutenberg-tm -trademark as set forth in paragraphs 1.E.8 or 1.E.9. - -1.E.3. If an individual Project Gutenberg-tm electronic work is posted -with the permission of the copyright holder, your use and distribution -must comply with both paragraphs 1.E.1 through 1.E.7 and any -additional terms imposed by the copyright holder. Additional terms -will be linked to the Project Gutenberg-tm License for all works -posted with the permission of the copyright holder found at the -beginning of this work. - -1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm -License terms from this work, or any files containing a part of this -work or any other work associated with Project Gutenberg-tm. - -1.E.5. Do not copy, display, perform, distribute or redistribute this -electronic work, or any part of this electronic work, without -prominently displaying the sentence set forth in paragraph 1.E.1 with -active links or immediate access to the full terms of the Project -Gutenberg-tm License. - -1.E.6. You may convert to and distribute this work in any binary, -compressed, marked up, nonproprietary or proprietary form, including -any word processing or hypertext form. However, if you provide access -to or distribute copies of a Project Gutenberg-tm work in a format -other than "Plain Vanilla ASCII" or other format used in the official -version posted on the official Project Gutenberg-tm web site -(www.gutenberg.org), you must, at no additional cost, fee or expense -to the user, provide a copy, a means of exporting a copy, or a means -of obtaining a copy upon request, of the work in its original "Plain -Vanilla ASCII" or other form. Any alternate format must include the -full Project Gutenberg-tm License as specified in paragraph 1.E.1. - -1.E.7. Do not charge a fee for access to, viewing, displaying, -performing, copying or distributing any Project Gutenberg-tm works -unless you comply with paragraph 1.E.8 or 1.E.9. - -1.E.8. You may charge a reasonable fee for copies of or providing -access to or distributing Project Gutenberg-tm electronic works -provided that - -* You pay a royalty fee of 20% of the gross profits you derive from - the use of Project Gutenberg-tm works calculated using the method - you already use to calculate your applicable taxes. The fee is owed - to the owner of the Project Gutenberg-tm trademark, but he has - agreed to donate royalties under this paragraph to the Project - Gutenberg Literary Archive Foundation. Royalty payments must be paid - within 60 days following each date on which you prepare (or are - legally required to prepare) your periodic tax returns. Royalty - payments should be clearly marked as such and sent to the Project - Gutenberg Literary Archive Foundation at the address specified in - Section 4, "Information about donations to the Project Gutenberg - Literary Archive Foundation." - -* You provide a full refund of any money paid by a user who notifies - you in writing (or by e-mail) within 30 days of receipt that s/he - does not agree to the terms of the full Project Gutenberg-tm - License. You must require such a user to return or destroy all - copies of the works possessed in a physical medium and discontinue - all use of and all access to other copies of Project Gutenberg-tm - works. - -* You provide, in accordance with paragraph 1.F.3, a full refund of - any money paid for a work or a replacement copy, if a defect in the - electronic work is discovered and reported to you within 90 days of - receipt of the work. - -* You comply with all other terms of this agreement for free - distribution of Project Gutenberg-tm works. - -1.E.9. If you wish to charge a fee or distribute a Project -Gutenberg-tm electronic work or group of works on different terms than -are set forth in this agreement, you must obtain permission in writing -from both the Project Gutenberg Literary Archive Foundation and The -Project Gutenberg Trademark LLC, the owner of the Project Gutenberg-tm -trademark. Contact the Foundation as set forth in Section 3 below. - -1.F. - -1.F.1. Project Gutenberg volunteers and employees expend considerable -effort to identify, do copyright research on, transcribe and proofread -works not protected by U.S. copyright law in creating the Project -Gutenberg-tm collection. Despite these efforts, Project Gutenberg-tm -electronic works, and the medium on which they may be stored, may -contain "Defects," such as, but not limited to, incomplete, inaccurate -or corrupt data, transcription errors, a copyright or other -intellectual property infringement, a defective or damaged disk or -other medium, a computer virus, or computer codes that damage or -cannot be read by your equipment. - -1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right -of Replacement or Refund" described in paragraph 1.F.3, the Project -Gutenberg Literary Archive Foundation, the owner of the Project -Gutenberg-tm trademark, and any other party distributing a Project -Gutenberg-tm electronic work under this agreement, disclaim all -liability to you for damages, costs and expenses, including legal -fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT -LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE -PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE -TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE -LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR -INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH -DAMAGE. - -1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a -defect in this electronic work within 90 days of receiving it, you can -receive a refund of the money (if any) you paid for it by sending a -written explanation to the person you received the work from. If you -received the work on a physical medium, you must return the medium -with your written explanation. The person or entity that provided you -with the defective work may elect to provide a replacement copy in -lieu of a refund. If you received the work electronically, the person -or entity providing it to you may choose to give you a second -opportunity to receive the work electronically in lieu of a refund. If -the second copy is also defective, you may demand a refund in writing -without further opportunities to fix the problem. - -1.F.4. Except for the limited right of replacement or refund set forth -in paragraph 1.F.3, this work is provided to you 'AS-IS', WITH NO -OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT -LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE. - -1.F.5. Some states do not allow disclaimers of certain implied -warranties or the exclusion or limitation of certain types of -damages. If any disclaimer or limitation set forth in this agreement -violates the law of the state applicable to this agreement, the -agreement shall be interpreted to make the maximum disclaimer or -limitation permitted by the applicable state law. The invalidity or -unenforceability of any provision of this agreement shall not void the -remaining provisions. - -1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the -trademark owner, any agent or employee of the Foundation, anyone -providing copies of Project Gutenberg-tm electronic works in -accordance with this agreement, and any volunteers associated with the -production, promotion and distribution of Project Gutenberg-tm -electronic works, harmless from all liability, costs and expenses, -including legal fees, that arise directly or indirectly from any of -the following which you do or cause to occur: (a) distribution of this -or any Project Gutenberg-tm work, (b) alteration, modification, or -additions or deletions to any Project Gutenberg-tm work, and (c) any -Defect you cause. - -Section 2. Information about the Mission of Project Gutenberg-tm - -Project Gutenberg-tm is synonymous with the free distribution of -electronic works in formats readable by the widest variety of -computers including obsolete, old, middle-aged and new computers. It -exists because of the efforts of hundreds of volunteers and donations -from people in all walks of life. - -Volunteers and financial support to provide volunteers with the -assistance they need are critical to reaching Project Gutenberg-tm's -goals and ensuring that the Project Gutenberg-tm collection will -remain freely available for generations to come. In 2001, the Project -Gutenberg Literary Archive Foundation was created to provide a secure -and permanent future for Project Gutenberg-tm and future -generations. To learn more about the Project Gutenberg Literary -Archive Foundation and how your efforts and donations can help, see -Sections 3 and 4 and the Foundation information page at -www.gutenberg.org - - - -Section 3. Information about the Project Gutenberg Literary Archive Foundation - -The Project Gutenberg Literary Archive Foundation is a non profit -501(c)(3) educational corporation organized under the laws of the -state of Mississippi and granted tax exempt status by the Internal -Revenue Service. The Foundation's EIN or federal tax identification -number is 64-6221541. Contributions to the Project Gutenberg Literary -Archive Foundation are tax deductible to the full extent permitted by -U.S. federal laws and your state's laws. - -The Foundation's principal office is in Fairbanks, Alaska, with the -mailing address: PO Box 750175, Fairbanks, AK 99775, but its -volunteers and employees are scattered throughout numerous -locations. Its business office is located at 809 North 1500 West, Salt -Lake City, UT 84116, (801) 596-1887. Email contact links and up to -date contact information can be found at the Foundation's web site and -official page at www.gutenberg.org/contact - -For additional contact information: - - Dr. Gregory B. Newby - Chief Executive and Director - gbnewby@pglaf.org - -Section 4. Information about Donations to the Project Gutenberg -Literary Archive Foundation - -Project Gutenberg-tm depends upon and cannot survive without wide -spread public support and donations to carry out its mission of -increasing the number of public domain and licensed works that can be -freely distributed in machine readable form accessible by the widest -array of equipment including outdated equipment. Many small donations -($1 to $5,000) are particularly important to maintaining tax exempt -status with the IRS. - -The Foundation is committed to complying with the laws regulating -charities and charitable donations in all 50 states of the United -States. Compliance requirements are not uniform and it takes a -considerable effort, much paperwork and many fees to meet and keep up -with these requirements. We do not solicit donations in locations -where we have not received written confirmation of compliance. To SEND -DONATIONS or determine the status of compliance for any particular -state visit www.gutenberg.org/donate - -While we cannot and do not solicit contributions from states where we -have not met the solicitation requirements, we know of no prohibition -against accepting unsolicited donations from donors in such states who -approach us with offers to donate. - -International donations are gratefully accepted, but we cannot make -any statements concerning tax treatment of donations received from -outside the United States. U.S. laws alone swamp our small staff. - -Please check the Project Gutenberg Web pages for current donation -methods and addresses. Donations are accepted in a number of other -ways including checks, online payments and credit card donations. To -donate, please visit: www.gutenberg.org/donate - -Section 5. General Information About Project Gutenberg-tm electronic works. - -Professor Michael S. Hart was the originator of the Project -Gutenberg-tm concept of a library of electronic works that could be -freely shared with anyone. For forty years, he produced and -distributed Project Gutenberg-tm eBooks with only a loose network of -volunteer support. - -Project Gutenberg-tm eBooks are often created from several printed -editions, all of which are confirmed as not protected by copyright in -the U.S. unless a copyright notice is included. Thus, we do not -necessarily keep eBooks in compliance with any particular paper -edition. - -Most people start at our Web site which has the main PG search -facility: www.gutenberg.org - -This Web site includes information about Project Gutenberg-tm, -including how to make donations to the Project Gutenberg Literary -Archive Foundation, how to help produce our new eBooks, and how to -subscribe to our email newsletter to hear about new eBooks. - - - -</pre> - -</body> -</html> |