,,preliminary ,,discourse on the ,study of ,,natural ,,philosophy ,,by ,,sir ,,john ,f4 ,w4 ,,herschel1 ,,bart4 ,k4,h4 ,m4,a4--,d4,c4,l4--,f4,r4,s4,l,e4--,m4,r 4,i4,a4--,f4,r4,a4,s4 ,f4,g4,s4--,m4,c4,u4,p4,s4--c4 c4 ,,new ,,edition4 #ahea4 ,illustration3 ,h4 ,corbould del4 ,e4 ,finden4 sculp4 ,,natur ,,minister ,,et ,,interpres4 ,,new ,,edition4 ,london3 ,,printed ,,for ,,longman1 ,,brown1 ,,green ,,longmans1 ,,paternoster ,,row ,,contents4 ,page ,,part ,i4 ,,of ,,the ,,general ,,nature ,,and ,,advantages ,,of ,,the ,,study ,,of ,,the ,,physical ,,sciences4 ,,chap4 ,i4 ,of ,man regarded as a ,creature of ,instinct1 of ,reason1 and ,speculation4--,general ,influence of ,scientific ,pursuits on the ,mind4 #a ,,chap4 ,,ii4 ,of abstract ,science as a ,preparation for the ,study of ,physics4-- ,a profound ,acquaintance with it not indispensable for a clear ,understanding of ,physical ,laws4--,how a ,conviction of their ,truth may be obtained without it4--,instances4-- ,further ,division of the ,subject4 #ah ,,chap4 ,,iii4 ,of the ,nature and ,objects1 immediate and collateral1 of ,physical ,science1 as regarded in itself1 and in its ,application to the practical ,purposes of ,life1 and its ,influence on the ,well-being and ,progress of ,society4 #ce ,,part ,,ii4 ,,of ,,the ,,principles ,,on ,,which ,,physical ,,science ,,relies ,,for ,,its ,,successful ,,prosecution1 ,,and ,,the ,,rules ,,by ,,which ,a ,,systematic ,,examination ,,of ,,nature ,,should ,,be ,,conducted1 ,,with ,,illustrations ,,of ,,their ,,influence ,,as ,,exemplified ,,in ,,the ,,history ,,of ,,its ,,progress4 ,,chap4 ,i4 ,of ,experience as the ,source of our ,knowledge4--,of the ,dismissal of ,prejudices4--,of the ,evidence of our ,senses4 #ge ,,chap4 ,,ii4 ,of the ,analysis of ,phenomena4 #he ,,chap4 ,,iii4 ,of the ,state of ,physical ,science in ,general1 previous to the ,age of ,galileo and ,bacon4 #ajd ,,chap4 ,,iv4 ,of the ,observation of ,facts and the ,collection of ,instances4 #aah ,,chap4 ,v4 ,of the ,classification of ,natural ,objects and ,phenomena1 and of ,nomenclature4 #ace ,,chap4 ,,vi4 ,of the ,first ,stage of ,induction4--,the ,discovery of ,proximate ,causes1 and ,laws of the lowest ,degree of ,generality1 and their ,verification4 #add ,,chap4 ,,vii4 ,of the higher ,degrees of ,inductive ,generalization1 and of the ,formation and ,verification of ,theories4 #aij ,,part ,,iii4 ,,of ,,the ,,subdivision ,,of ,,physics ,,into ,,distinct ,,branches1 ,,and ,,their ,,mutual ,,relations4 ,,chap4 ,i4 ,of the ,phenomena of ,force1 and of the ,constitution of ,natural ,bodies4 #bba ,,chap4 ,,ii4 ,of the ,communication of ,motion through ,bodies4--,of ,sound and ,light4 #bdf ,,chap4 ,,iii4 ,of ,cosmical ,phenomena4 #bfe ,,chap4 ,,iv4 ,of the ,examination of the material ,constituents of the ,world4 #bij ,,chap4 ,v4 ,of the ,imponderable ,forms of ,matter4 #caj ,,chap4 ,,vi4 ,of the ,causes of the actual rapid ,advance of the ,physical ,sciences compared with their ,progress at an earlier ,period4 #cdg 8,in primis1 hominis est propria ,,veri inquisitio atque investigatio4 ,itaque cum sumus negotiis necessariis1 curisque vacui1 tum avemus aliquid videre1 audire1 ac dicere1 cognitionemque rerum1 aut occultarum aut admirabilium1 ad ben beatque vivendum necessariam ducimus2--ex quo intelligitur1 quod ,,verum1 simplex1 sincerumque sit1 id esse nature hominis aptissimum4 ,huic veri videndi cupiditati adjuncta est appetitio qudam principats1 ut nemini parere animus ben a natur informatus velit1 nisi prcipienti1 aut docenti1 aut utilitatis causa just et legitim imperanti3 ex quo animi magnitudo existit1 et humanararum rerum contemtio40 ,,cicero1 ,,de ,,officiis1 ,lib4 #a4 #ac4 ,before all other things1 man is distinguished by his pursuit and investigation of ,,truth4 ,and hence1 when free from needful business and cares1 we delight to see1 to hear1 and to communicate1 and consider a knowledge of many admirable and abstruse things necessary to the good conduct and happiness of our lives3 whence it is clear that whatsoever is ,,true1 simple1 and direct1 the same is most congenial to our nature as men4 ,closely allied with this earnest longing to see and know the truth1 is a kind of dignified and princely sentiment which forbids a mind1 naturally well constituted1 to submit its faculties to any but those who announce it in precept or in doctrine1 or to yield obedience to any orders but such as are at once just1 lawful1 and founded on utility4 ,from this source spring greatness of mind and contempt of worldly advantages and troubles4 ,,preliminary ,,discourse ,,on ,,the ,,study ,,of ,,natural ,,philosophy4 ,,part ,i4 ,,of ,,the ,,general ,,nature ,,and ,,advantages ,,of ,,the ,,study ,,of ,,the ,,physical ,,sciences ,,chapter ,i4 ,,of ,,man ,,regarded ,,as ,a ,,creature ,,of ,,instinct1 ,,of ,,reason1 ,,and ,,speculation4--,,general ,,influence ,,of ,,scientific ,,pursuits ,,on ,,the ,,mind4 7#a47 ,the situation of man on the globe he inhabits1 and over which he has obtained the control1 is in many respects exceedingly remarkable4 ,compared with its other denizens1 he seems1 if we regard only his physical constitution1 in almost every respect their inferior1 and equally unprovided for the supply of his natural wants and his defence against the innumerable enemies which surround him4 ,no other animal passes so large a portion of its existence in a state of absolute helplessness1 or falls in old age into such protracted and lamentable imbecility4 ,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 insupportable2 and to scarcely any has she been so sparing in external weapons1 whether for attack or defence4 ,destitute alike of speed to avoid and of arms to repel the aggressions of his voracious foes2 tenderly susceptible of atmospheric influences2 and unfitted for the coarse aliments which the earth affords spontaneously during at least two thirds of the year1 even in temperate climates1--man1 if abandoned to mere instinct1 would be of all creatures the most destitute and miserable4 ,distracted by terror and goaded by famine2 driven to the most abject expedients for concealment from his enemies1 and to the most cowardly devices for the seizure and destruction of his nobler prey1 his existence would be one continued subterfuge or stratagem2--his dwelling would be in dens of the earth1 in clefts of rocks1 or in the hollows of trees2 his food worms1 and the lower reptiles1 or such few and crude productions of the soil as his organs could be brought to assimilate1 varied with occasional relics1 mangled by more powerful beasts of prey1 or contemned by their more pampered choice4 ,remarkable only for the absence of those powers and qualities which obtain for other animals a degree of security and respect1 he would be disregarded by some1 and hunted down by others1 till after a few generations his species would become altogether extinct1 or1 at best1 would be restricted to a few islands in tropical regions1 where the warmth of the climate1 the paucity of enemies1 and the abundance of vegetable food1 might permit it to linger4 7#b47 ,yet man is the undisputed lord of the creation4 ,the strongest and fiercest of his fellow-creatures1--the whale1 the elephant1 the eagle1 and the tiger1--are slaughtered by him to supply his most capricious wants1 or tamed to do him service1 or imprisoned to make him sport4 ,the spoils of all nature are in daily requisition for his most common uses1 yielded with more or less readiness1 or wrested with reluctance1 from the mine1 the forest1 the ocean1 and the air4 ,such are the first fruits of reason4 ,were they the only or the principal ones1 were the mere acquisition of power over the materials1 and the less gifted animals which surround us1 and the consequent increase of our external comforts1 and our means of preservation and sensual enjoyment1 the sum of the privileges which the possession of this faculty conferred1 we should after all have little to plume ourselves upon4 ,but this is so far from being the case1 that every one who passes his life in tolerable ease and comfort1 or rather whose whole time is not anxiously consumed in providing the absolute necessaries of existence1 is conscious of wants and cravings in which the senses have no part1 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 him2 and if he has experienced these pleasures and these pains in any degree of intensity1 he will readily admit them to hold a much higher rank1 and to deserve much more attention1 than the former class4 ,independent of the pleasures of fancy and imagination1 and social converse1 man is constituted a speculative being2 he contemplates the world1 and the objects around him1 not with a passive1 indifferent gaze1 as a set of phenomena in which he has no further interest than as they affect his immediate situation1 and can be rendered subservient to his comfort1 but as a system disposed with order and design4 ,he approves and feels the highest admiration for the harmony of its parts1 the skill and efficiency of its contrivances4 ,some of these which he can best trace and understand he attempts to imitate1 and finds that to a certain extent1 though rudely and imperfectly1 he can succeed1--in others1 that although he can comprehend the nature of the contrivance1 he is totally destitute of all means of imitation2--while in others1 again1 and those evidently the most important1 though he sees the effect produced1 yet the means by which it is done are alike beyond his knowledge and his control4 ,thus he is led to the conception of a ,power and an ,intelligence superior to his own1 and adequate to the production and maintenance of all that he sees in nature1--a ,power and ,intelligence to which he may well apply the term infinite1 since he not only sees no actual limit to the instances in which they are manifested1 but finds1 on the contrary1 that the farther he enquires1 and the wider his sphere of observation extends1 they continually open upon him in increasing abundance2 and that as the study of one prepares him to understand and appreciate another1 refinement follows on refinement1 wonder on wonder1 till his faculties become bewildered in admiration1 and his intellect falls back on itself in utter hopelessness of arriving at an end4 7#c47 ,when from external objects he turns his view upon himself1 on his own vital and intellectual faculties1 he finds that he possesses a power of examining and analysing his own nature to a certain extent1 but no farther4 ,in his corporeal frame he is sensible of a power to communicate a certain moderate amount of motion to himself and other objects2 that this power depends on his will1 and that its exertion can be suspended or increased at pleasure within certain limits2 but how his will acts on his limbs he has no consciousness3 and whence he derives the power he thus exercises1 there is nothing to assure him1 however he may long to know4 ,his senses1 too1 inform him of a multitude of particulars respecting the external world1 and he perceives an apparatus by which impressions from without may be transmitted1 as a sort of signals to the interior of his person1 and ultimately to his brain1 wherein he is obscurely sensible that the thinking1 feeling1 reasoning being he calls himself1 more especially resides2 but by what means he becomes conscious of these impressions1 and what is the nature of the immediate communication between that inward sentient being1 and that machinery1 his outward man1 he has not the slightest conception4 7#d47 ,again1 when he contemplates still more attentively the thoughts1 acts1 and passions of this his sentient intelligent self1 he finds1 indeed1 that he can remember1 and by the aid of memory can compare and discriminate1 can judge and resolve1 and1 above all1 that he is irresistibly impelled1 from the perception of any phenomenon without or within him1 to infer the existence of something prior which stands to it in the relation of a cause1 without which it would not be1 and that this knowledge of causes and their consequences is what1 in almost every instance1 determines his choice and will1 in cases where he is nevertheless conscious of perfect freedom to act or not to act4 ,he finds1 too1 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 them1 which attention is again in great measure a voluntary act2 and often when his choice has been decided on imperfect knowledge or insufficient attention1 he finds reason to correct his judgment1 though perhaps too late to influence his decision by after consideration4 ,a world within him is thus opened to his intellectual view1 abounding with phenomena and relations1 and of the highest immediate interest4 ,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 power1 the very fountain of his predominance over external nature1 he yet feels himself capable of entering only very imperfectly into these recesses of his own bosom1 and analysing the operations of his mind1--in this as in all other things1 in short1 8a being darkly wise20 seeing that all the longest life and most vigorous intellect can give him power to discover by his own research1 or time to know by availing himself of that of others1 serves only to place him on the very frontier of knowledge1 and afford a distant glimpse of boundless realms beyond1 where no human thought has penetrated1 but which yet he is sure 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 purposes4 ,is it wonderful that a being so constituted should first encourage a hope1 and by degrees acknowledge an assurance1 that his intellectual existence will not terminate with the dissolution of his corporeal frame1 but rather that in a future state of being1 disencumbered of a thousand obstructions which his present situation throws in his way1 endowed with acuter senses1 and higher faculties1 he shall drink deep at that fountain of beneficent wisdom for which the slight taste obtained on earth has given him so keen a relish8 7#e47 ,nothing1 then1 can be more unfounded than the objection which has been taken1 in limine1 by persons1 well meaning perhaps1 certainly narrow-minded1 against the study of natural philosophy1 and indeed against all science1--that it fosters in its cultivators an undue and overweening self-conceit1 leads them to doubt the immortality of the soul1 and to scoff at revealed religion4 ,its natural effect1 we may confidently assert1 on every well constituted mind is and must be the direct contrary4 ,no doubt1 the testimony of natural reason1 on whatever exercised1 must of necessity stop short of those truths which it is the object of revelation to make known2 but1 while it places the existence and principal attributes of a ,deity on such grounds as to render doubt impossible1 it unquestionably opposes no natural or necessary obstacle to further progress3 on the contrary1 by cherishing as a vital principle an unbounded spirit of enquiry1 and ardency of expectation1 it unfetters the mind from prejudices of every kind1 and leaves it open and free to every impression of a higher nature which it is susceptible of receiving1 guarding only against enthusiasm and self-deception by a habit of strict investigation1 but encouraging1 rather than suppressing1 every thing that can offer a prospect or a hope beyond the present obscure and unsatisfactory state4 ,the character of the true philosopher is to hope all things not impossible1 and to believe all things not unreasonable4 ,he who has seen obscurities which appeared impenetrable in physical and mathematical science suddenly dispelled1 and the most barren and unpromising fields of enquiry converted1 as if by inspiration1 into rich and inexhaustible springs of knowledge and power on a simple change of our point of view1 or by merely bringing to bear on them some principle which it never occurred before to try1 will surely be the very last to acquiesce in any dispiriting prospects of either the present or future destinies of mankind2 while1 on the other hand1 the boundless views of intellectual and moral as well as material relations which open on him on all hands in the course of these pursuits1 the knowledge of the trivial place he occupies in the scale of creation1 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 him1 must effectually convince him that humility of pretension1 no less than confidence of hope1 is what best becomes his character4 7#f47 ,but while we thus vindicate the study of natural philosophy from a charge at one time formidable1 owing to the pertinacity and acrimony with which it was urged1 and still occasionally brought forward to the distress and disgust of every well constituted mind1 we must take care that the testimony afforded by science to religion1 be its extent or value what it may1 shall be at least independent1 unbiassed1 and spontaneous4 ,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 writings3 such a course might well become the persecutors of ,galileo and the other bigots of the fifteenth and sixteenth centuries1 but can only be adopted by dreamers in the present age4 ,but1 without going these lengths1 it is no uncommon thing to find persons1 earnestly attached to science and anxious for its promotion1 who yet manifest a morbid sensibility on points of this kind1--who exult and applaud when any fact starts up explanatory 7as they suppose7 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 themselves4 ,to persons of such a frame of mind it ought to suffice to remark1 on the one hand1 that truth can never be opposed to truth1 and1 on the other1 that error is only to be effectually confounded by searching deep and tracing it to its source4 ,nevertheless1 it were much to be wished that such persons1 estimable and excellent as many of them are1 before they throw the weight of their applause or discredit into the scale of scientific opinion on such grounds1 would reflect1 first1 that the credit and respectability of any evidence may be destroyed by tampering with its honesty2 and1 secondly1 that this very disposition of mind implies a lurking mistrust in its own principles1 since the grand and indeed only character of truth is its capability of enduring the test of universal experience1 and coming unchanged out of every possible form of fair discussion4 7#g47 ,but if science may be vilified by representing it as opposed to religion1 or trammelled by mistaken notions of the danger of free enquiry1 there is yet another mode by which it may be degraded from its native dignity1 and that is by placing it in the light of a mere appendage to and caterer for our pampered appetites4 ,the question 8cui bono0 to what practical end and advantage do your researches tend8 is one which the speculative philosopher who loves knowledge for its own sake1 and enjoys1 as a rational being should enjoy1 the mere contemplation of harmonious and mutually dependent truths1 can seldom hear without a sense of humiliation4 ,he feels that there is a lofty and disinterested pleasure in his speculations which ought to exempt them from such questioning2 communicating as they do to his own mind the purest happiness 7after the exercise of the benevolent and moral feelings7 of which human nature is susceptible1 and tending to the injury of no one1 he might surely allege this as a sufficient and direct reply to those who1 having themselves little capacity1 and less relish for intellectual pursuits1 are constantly repeating upon him this enquiry4 ,but if he can bring himself to descend from this high but fair ground1 and justify himself1 his pursuits1 and his pleasures in the eyes of those around him1 he has only to point to the history of all science1 where speculations1 apparently unprofitable1 have1 in innumerable instances1 been those from which great practical applications have emanated4 ,what1 for instance1 could be more so than the dry speculations of the ancient geometers on the properties of the conic sections1 or than the dreams of ,kepler 7as they would naturally appear to his contemporaries7 about the numerical harmonies of the universe8 ,yet these are the steps by which we have risen to a knowledge of the elliptic motions of the planets and the law of gravitation1 with all its splendid theoretical consequences1 and its inestimable practical results4 ,the ridicule attached to 8,swing-swangs0 in ,hooke's time#a did not prevent him from reviving the proposal of the pendulum as a standard of measure1 since so effectually wrought into practice by the genius and perseverance of ,captain ,kater2--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-engine4 ,the dreams of the alchemists led them on in the path of experiment1 and drew attention to the wonders of chemistry1 while they brought their advocates 7it must be admitted7 to merited contempt and ruin4 ,but in this case it was moral dereliction which gave to ridicule a weight and power not necessarily or naturally belonging to it3 but among the alchemists were men of superior minds1 who reasoned while they worked1 and who1 not content to grope always in the dark1 and blunder on their object1 sought carefully in the observed nature of their agents for guides in their pursuit4 ,to these we owe the creation of experimental philosophy4 7#h47 ,not that it is meant1 by any thing above said1 to assert that there is no such thing as a great or a little in speculative philosophy1 or to place the solution of an enigma on a level with the developement of a law of nature1 still less to adopt the homely definition of ,smith#b1 that a philosopher is a person whose trade it is to do nothing1 and speculate on every thing4 ,the speculations of the natural philosopher1 however remote they may for a time lead him from beaten tracks and every-day uses1 being grounded in the realities of nature1 have all1 of necessity1 a practical application1--nay more1 such applications form the very criterions of their truth1 they afford the readiest and completest verifications of his theories2--verifications which he will no more neglect to test them by than an arithmetician would omit to prove his sums1 or a cautious geometer to try his general theorems by particular cases4#c 7#i47 ,after all1 however1 it must be confessed1 that to minds unacquainted with science1 and unused to consider the mutual dependencies of its various branches1 there is something neither unnatural nor altogether blamable in the ready occurrence of this question of direct advantage4 ,it requires some habit of abstraction1 some penetration of the mind with a tincture of scientific enquiry1 some conviction of the value of those estimable and treasured principles which lie concealed in the most common and homely facts1--some experience1 in fine1 of success in developing and placing them in evidence1 announcing them in precise terms1 and applying them to the explanation of other facts of a less familiar character1 or to the accomplishment of some obviously useful purpose3--to cure the mind of this tendency to rush at once upon its object1 to undervalue the means in over-estimation of the end1 and while gazing too intently at the goal which alone it has been accustomed to desire1 to lose sight of the richness and variety of the prospects that offer themselves on either hand on the road4 7#aj47 ,we must never forget that it is principles1 not phenomena1--the interpretation1 not the mere knowledge of facts1--which are the objects of enquiry to the natural philosopher4 ,as truth is single1 and consistent with itself1 a principle may be as completely and as plainly elucidated by the most familiar and simple fact1 as by the most imposing and uncommon phenomenon4 ,the colours which glitter on a soap-bubble are the immediate consequence of a principle the most important from the variety of phenomena it explains1 and the most beautiful1 from its simplicity and compendious neatness1 in the whole science of optics4 ,if the nature of periodical colours can be made intelligible by the contemplation of such a trivial object1 from that moment it becomes a noble instrument in the eye of correct judgment2 and to blow a large1 regular1 and durable soap-bubble may become the serious and praiseworthy endeavour of a sage1 while children stand round and scoff1 or children of a larger growth hold up their hands in astonishment at such waste of time and trouble4 ,to the natural philosopher there is no natural object unimportant or trifling4 ,from the least of nature's works he may learn the greatest lessons4 ,the fall of an apple to the ground may raise his thoughts to the laws which govern the revolutions of the planets in their orbits2 or the situation of a pebble may afford him evidence of the state of the globe he inhabits1 myriads of ages ago1 before his species became its denizens4 7#aa47 ,and this is1 in fact1 one of the great sources of delight which the study of natural science imparts to its votaries4 ,a mind which has once imbibed a taste for scientific enquiry1 and has learnt the habit of applying its principles readily to the cases which occur1 has within itself an inexhaustible source of pure and exciting contemplations3--one would think that ,shakspeare had such a mind in view when he describes a contemplative man as finding all nature eloquent--the very trees1 the brooks1 and the stones reading to him lessons of deep and serious import4 ,accustomed to trace the operation of general causes1 and the exemplification of general laws1 in circumstances where the uninformed and unenquiring eye perceives neither novelty nor beauty1 he walks in the midst of wonders3 every object which falls in his way elucidates some principle1 affords some instruction1 and impresses him with a sense of harmony and order4 ,nor is it a mere passive pleasure which is thus communicated4 ,a thousand questions are continually arising in his mind1 a thousand subjects of enquiry presenting themselves1 which keep his faculties in constant exercise1 and his thoughts perpetually on the wing1 so that lassitude is excluded from his life1 and that craving after artificial excitement and dissipation of mind1 which leads so many into frivolous1 unworthy1 and destructive pursuits1 is altogether eradicated from his bosom4 7#ab47 ,it is not one of the least advantages of these pursuits1 which1 however1 they possess in common with every class of intellectual pleasures1 that they are altogether independent of external circumstances1 and are to be enjoyed in every situation in which a man can be placed in life4 ,the highest degrees of worldly prosperity are so far from being incompatible with them1 that they supply inestimable advantages for their pursuit1 and that sort of fresh and renewed relish which arises partly from the sense of contrast1 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 distaste4 ,they may be enjoyed1 too1 in the intervals of the most active business2 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 world1 and from the conflict of passions1 prejudices1 and interests in which the man of business finds himself involved4 ,there is something in the contemplation of general laws which powerfully induces and persuades us to merge individual feeling1 and to commit ourselves unreservedly to their disposal2 while the observation of the calm1 energetic regularity of nature1 the immense scale of her operations1 and the certainty with which her ends are attained1 tends1 irresistibly1 to tranquillize and re-assure the mind1 and render it less accessible to repining1 selfish1 and turbulent emotions4 ,and this it does1 not by debasing our nature into weak compliances and abject submission to circumstances1 but by filling us1 as from an inward spring1 with a sense of nobleness and power which enables us to rise superior to them2 by showing us our strength and innate dignity1 and by calling upon us for the exercise of those powers and faculties by which we are susceptible of the comprehension of so much greatness1 and which form1 as it were1 a link between ourselves and the best and noblest benefactors of our species1 with whom we hold communion in thoughts and participate in discoveries which have raised them above their fellow-mortals1 and brought them nearer to their ,creator4 ,,chap4 ,,ii4 ,,of ,,abstract ,,science ,,as ,a ,,preparation ,,for ,,the ,,study ,,of ,,physics4--,a ,,profound ,,acquaintance ,,with ,,it ,,not ,,indispensable ,,for ,a ,,clear ,,understanding ,,of ,,physical ,,laws4--,,how ,a ,,conviction ,,of ,,their ,,truth ,,may ,,be ,,obtained ,,without ,,it4--,,instances4--,,further ,,division ,,of ,,the ,,subject4 7#ac47 ,science is the knowledge of many1 orderly and methodically digested and arranged1 so as to become attainable by one4 ,the knowledge of reasons and their conclusions constitutes abstract1 that of causes and their effects1 and of the laws of nature1 natural science4 7#ad47 ,abstract science is independent of a system of nature1--of a creation1--of every thing1 in short1 except memory1 thought1 and reason4 ,its objects are1 first1 those primary existences and relations which we cannot even conceive not to be1 such as space1 time1 number1 order1 c42 and1 secondly1 those artificial forms1 or symbols1 which thought has the power of creating for itself at pleasure1 and substituting as representatives1 by the aid of memory1 for combinations of those primary objects and of its own conceptions1--either to facilitate the act of reasoning respecting them1 or as convenient deposits of its own conclusions1 or for their communication to others4 ,such are1 first1 language1 oral or written2 its conventional forms1 which constitute grammar1 and the rules for its use in argument1 in which consists the logic of the schools2 secondly1 notation1 which1 applied to number1 is arithmetic1--and1 to the more general relations of abstract quantity or order1 is algebra2 and1 thirdly1 that higher kind of logic1 which teaches us to use our reason in the most advantageous manner for the discovery of truth2 which points out the criterions by which we may be sure we have attained it2 and which1 by detecting the sources of error1 and exposing the haunts where fallacies are apt to lurk1 at once warns us of their danger1 and shows us how to avoid them4 ,this greater logic may be termed rational#d2 while1 to that inferior department which is conversant with words alone1 the epithet verbal#e may1 for distinction1 be applied4 7#ae47 ,a certain moderate degree of acquaintance with abstract science is highly desirable to every one who would make any considerable progress in physics4 ,as the universe exists in time and place2 and as motion1 velocity1 quantity1 number1 and order1 are main elements of our knowledge of external things and their changes1 an acquaintance with these1 abstractedly considered1 7that is to say1 independent of any consideration of the particular things moved1 measured1 counted1 or arranged17 must evidently be a useful preparation for the more complex study of nature4 ,but there is yet another recommendation of such sciences as a preparation for the study of natural philosophy4 ,their objects are so definite1 and our notions of them so distinct1 that we can reason about them with an assurance1 that the words and signs used in our reasonings are full and true representatives of the things signified2 and1 consequently1 that when we use language or signs in argument1 we neither1 by their use1 introduce extraneous notions1 nor exclude any part of the case before us from consideration4 ,for example3 the words space1 square1 circle1 a hundred1 c41 convey to the mind notions so complete in themselves1 and so distinct from every thing else1 that we are sure when we use them we know and have in view the whole of our own meaning4 ,it is widely different with words expressing natural objects and mixed relations4 ,take1 for instance1 iron4 ,different persons attach very different ideas to this word4 ,one who has never heard of magnetism has a widely different notion of iron from one in the contrary predicament4 ,the vulgar1 who regard this metal as incombustible1 and the chemist1 who sees it burn with the utmost fury1 and who has other reasons for regarding it as one of the most combustible bodies in nature2--the poet1 who uses it as an emblem of rigidity2 and the smith and engineer1 in whose hands it is plastic1 and moulded like wax into every form2--the jailer1 who prizes it as an obstruction1 and the electrician1 who sees in it only a channel of open communication by which that most impassable of obstacles1 the air1 may be traversed by his imprisoned fluid1 have all different1 and all imperfect1 notions of the same word4 ,the meaning of such a term is like a rainbow--every body sees a different one1 and all maintain it to be the same4 ,so it is with nearly all our terms of sense4 ,some are indefinite1 as hard or soft1 light or heavy 7terms which were at one time the sources of innumerable mistakes and controversies72 some excessively complex1 as man1 life1 instinct4 ,but1 what is worst of all1 some1 nay most1 have two or three meanings2 sufficiently distinct from each other to make a proposition true in one sense and false in another1 or even false altogether2 yet not distinct enough to keep us from confounding them in the process by which we arrived at it1 or to enable us immediately to recognise the fallacy when led to it by a train of reasoning1 each step of which we think we have examined and approved4 ,surely those who thus attach two senses to one word1 or superadd a new meaning to an old one1 act as absurdly as colonists who distribute themselves over the world1 naming every place they come to by the names of those they have left1 till all distinctions of geographical nomenclature are confounded1 and till we are unable to decide whether an occurrence stated to have happened at ,windsor took place in ,europe1 ,america1 or ,australia4#f 7#af47 ,it is1 in fact1 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 fall4 ,now1 the study of the abstract sciences1 such as arithmetic1 geometry1 algebra1 c41 while they afford scope for the exercise of reasoning about objects that are1 or1 at least1 may be conceived to be1 external to us2 yet1 being free from these sources of error and mistake1 accustom us to the strict use of language as an instrument of reason1 and by familiarizing us1 in our progress towards truth1 to walk uprightly and straight-forward on firm ground1 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 fragments1 or to steady them in the reeling tempest of conflicting meanings4 7#ag47 ,but there is yet another point of view under which some acquaintance with abstract science may be regarded as highly desirable in general education1 if not indispensably necessary1 to impress on us the distinction between strict and vague reasoning1 to show us what demonstration really is1 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 nature1 and the laws of natural phenomena1 rests4 ,for this purpose1 however1 a very moderate acquaintance with the more elementary branches of mathematics may suffice4 ,the chain is laid before us1 and every link is submitted to our unreserved examination1 if we have patience and inclination to enter on such detail4 ,hundreds have gone through it1 and will continue to do so2 but1 for the generality of mankind1 it is enough to satisfy themselves of the solidity and adamantine texture of its materials1 and the unreserved exposure of its weakest1 as well as its strongest1 parts4 ,if1 however1 we content ourselves with this general view of the matter1 we must be content also to take on trust1 that is1 on the authority of those who have examined deeper1 every conclusion which cannot be made apparent to our senses4 ,now1 among these there are many so very surprising1 indeed apparently so extravagant1 that it is quite impossible for any enquiring mind to rest contented with a mere hearsay statement of them1--we feel irresistibly impelled to enquire further into their truth4 ,what mere assertion will make any man believe1 that in one second of time1 in one beat of the pendulum of a clock1 a ray of light travels over #aib1jjj miles1 and would therefore perform the tour of the world in about the same time that it requires to wink with our eyelids1 and in much less than a swift runner occupies in taking a single stride8 ,what mortal can be made to believe1 without demonstration1 that the sun is almost a million times larger than the earth8 and that1 although so remote from us1 that a cannon ball shot directly towards it1 and maintaining its full speed1 would be twenty years in reaching it1 it yet affects the earth by its attraction in an inappreciable instant of time8--a closeness of union of which we can form but a feeble1 and totally inadequate1 idea1 by comparing it to any material connection2 since the communication of an impulse to such a distance1 by any solid intermedium we are acquainted with1 would require1 not moments1 but whole years4 ,and when1 with pain and difficulty we have strained our imagination to conceive a distance so vast1 a force so intense and penetrating1 if we are told that the one dwindles to an insensible point1 and the other is unfelt at the nearest of the fixed stars1 from the mere effect of their remoteness1 while among those very stars are some whose actual splendour exceeds by many hundred times that of the sun itself1 although we may not deny the truth of the assertion1 we cannot but feel the keenest curiosity to know how such things were ever made out4 7#ah47 ,the foregoing are among those results of scientific research which1 by their magnitude1 seem to transcend our powers of conception4 ,there are others1 again1 which1 from their minuteness1 would appear to elude the grasp of thought1 much more of distinct and accurate measurement4 ,who would not ask for demonstration1 when told that a gnat's wing1 in its ordinary flight1 beats many hundred times in a second8 or that there exist animated and regularly organized beings1 many thousands of whose bodies laid close together would not extend an inch8 ,but what are these to the astonishing truths which modern optical enquiries have disclosed1 which teach us that every point of a medium through which a ray of light passes is affected with a succession of periodical movements1 regularly recurring at equal intervals1 no less than five hundred millions of millions of times in a single second6 that it is by such movements1 communicated to the nerves of our eyes1 that we see3--nay more1 that it is the difference in the frequency of their recurrence which affects us with the sense of the diversity of colour2 that1 for instance1 in acquiring the sensation of redness our eyes are affected four hundred and eighty-two millions of millions of times2 of yellowness1 five hundred and forty-two millions of millions of times2 and of violet1 seven hundred and seven millions of millions of times per second4#g ,do not such things sound more like the ravings of madmen1 than the sober conclusions of people in their waking senses8 7#ai47 ,they are1 nevertheless1 conclusions to which any one may most certainly arrive1 who will only be at the trouble of examining the chain of reasoning by which they have been deduced2 but1 in order to do this1 something beyond the mere elements of abstract science is required4 ,waving1 however1 such instances as these1 which1 after all1 are rather calculated to surprise and astound than for any other purpose1 it must be observed that it is not possible to satisfy ourselves completely that we have arrived at a true statement of any law of nature1 until1 setting out from such statement1 and making it a foundation of reasoning1 we can show1 by strict argument1 that the facts observed must follow from it as necessary logical consequences1 and this1 not vaguely and generally1 but with all possible precision in time1 place1 weight1 and measure4 7#bj47 ,to do this1 however1 as we shall presently see1 requires in many cases a degree of knowledge of mathematics and geometry altogether unattainable by the generality of mankind1 who have not the leisure1 even if they all had the capacity1 to enter into such enquiries1 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 attention1 and make them the serious business of their lives4 ,but there is scarcely any person of good ordinary understanding1 however little exercised in abstract enquiries1 who may not be readily made to comprehend at least the general train of reasoning by which any of the great truths of physics are deduced1 and the essential bearings and connections of the several parts of natural philosophy4 ,there are whole branches too and very extensive and important ones1 to which mathematical reasoning has never been at all applied2 such as chemistry1 geology1 and natural history in general1 and many others1 in which it plays a very subordinate part1 and of which the essential principles1 and the grounds of application to useful purposes1 may be perfectly well understood by a student who possesses no more mathematical knowledge than the rules of arithmetic2 so that no one need be deterred from the acquisition of knowledge1 or even from active original research in such subjects1 by a want of mathematical information4 ,even in those branches which1 like astronomy1 optics1 and dynamics1 are almost exclusively under the dominion of mathematics1 and in which no effectual progress can be made without some acquaintance with geometry1 the principal results may be perfectly understood without it4 ,to one incapable of following out the intricacies of mathematical demonstration1 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 afford1 since every one will acknowledge the validity of pretensions which he is in the daily habit of seeing brought to the test of practice4 7#ba47 ,among the verifications of this practical kind which abound in every department of physics1 there are none more imposing than the precise prediction of the greater phenomena of astronomy2 none1 certainly1 which carry a broader conviction home to every mind from their notoriety and unequivocal character4 ,the prediction of eclipses has accordingly from the earliest ages excited the admiration of mankind1 and been one grand instrument by which their allegiance 7so to speak7 to natural science1 and their respect for its professors1 has been maintained2 and though strangely abused in unenlightened ages by the supernatural pretensions of astrologers1 the credence given even to their absurdities shows the force of this kind of evidence on men's minds4 ,the predictions of astronomers are1 however1 now far too familiar to endanger the just equipoise of our judgment1 since even the return of comets1 true to their paths and exact to the hour of their appointment1 has ceased to amaze1 though it must ever delight all who have souls capable of being penetrated by such beautiful instances of accordance between theory and facts4 ,but the age of mere wonder in such things is past1 and men prefer being guided and enlightened1 to being astonished and dazzled4 ,eclipses1 comets1 and the like1 afford but rare and transient displays of the powers of calculation1 and of the certainty of the principles on which it is grounded4 ,a page of 8lunar distances0 from the ,nautical ,almanack is worth all the eclipses that have ever happened for inspiring this necessary confidence in the conclusions of science4 ,that a man1 by merely measuring the moon's apparent distance from a star with a little portable instrument held in his hand1 and applied to his eye1 even with so unstable a footing as the deck of a ship1 shall say positively1 within five miles1 where he is1 on a boundless ocean1 cannot but appear to persons ignorant of physical astronomy an approach to the miraculous4 ,yet1 the alternatives of life and death1 wealth and ruin1 are daily and hourly staked with perfect confidence on these marvellous computations1 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 approximate4 ,we have before us an anecdote communicated to us by a naval officer#h1 distinguished for the extent and variety of his attainments1 which shows how impressive such results may become in practice4 ,he sailed from ,san ,blas on the west coast of ,mexico1 and after a voyage of #hjjj miles1 occupying #hi days1 arrived off ,rio de ,janeiro1 having1 in this interval1 passed through the ,pacific ,ocean1 rounded ,cape ,horn1 and crossed the ,south ,atlantic1 without making any land1 or even seeing a single sail1 with the exception of an ,american whaler off ,cape ,horn4 ,arrived within a week's sail of ,rio1 he set seriously about determining1 by lunar observations1 the precise line of the ship's course and its situation in it at a determinate moment1 and having ascertained this within from five to ten miles1 ran the rest of the way by those more ready and compendious methods1 known to navigators1 which can be safely employed for short trips between one known point and another1 but which cannot be trusted in long voyages1 where the moon is the only sure guide4 ,the rest of the tale we are enabled by his kindness to state in his own words3--8,we steered towards ,rio de ,janeiro for some days after taking the lunars above described1 and having arrived within fifteen or twenty miles of the coast1 ,i hove to at four in the morning till the day should break1 and then bore up2 for although it was very hazy1 we could see before us a couple of miles or so4 ,about eight o'clock it became so foggy that ,i did not like to stand in farther1 and was just bringing the ship to the wind again before sending the people to breakfast1 when it suddenly cleared off1 and ,i had the satisfaction of seeing the great ,sugar ,loaf ,rock1 which stands on one side of the harbour's mouth1 so nearly right ahead that we had not to alter our course above a point in order to hit the entrance of ,rio4 ,this was the first land we had seen for three months1 after crossing so many seas and being set backwards and forwards by innumerable currents and foul winds40 ,the effect on all on board might well be conceived to have been electric2 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 incidents1 indicative of a degree of knowledge and consequent power beyond their reach4 7#bb47 ,but even such results as these1 striking as they are1 yet fall short of the force with which conviction is urged upon us when1 through the medium of reasoning too abstract for common apprehension1 we arrive at conclusions which outrun experience1 and describe beforehand what will happen under new combinations1 or even correct imperfect experiments1 and lead us to a knowledge of facts contrary to received analogies drawn from an experience wrongly interpreted or overhastily generalised4 ,to give an example3--every body knows that objects viewed through a transparent medium1 such as water or glass1 appear distorted or displaced4 ,thus1 a stick in water appears bent1 and an object seen through a prism or wedge of glass seems to be thrown aside from its true place4 ,this effect is owing to what is called the refraction of light2 and a simple rule discovered by ,willebrod ,snell enables any one to say exactly how much the stick will be bent1 and how far1 and in what direction1 the apparent situation of an object seen through the glass will deviate from the real one4 ,if a shilling be laid at the bottom of a basin of water and viewed obliquely1 it will appear to be raised by the water2 if instead of water spirits of wine be used it will appear more raised2 if oil1 still more3--but in none of these cases will it appear to be thrown aside to the right or left of its true place1 however the eye be situated4 ,the plane1 in which are contained the eye1 the object1 and the point in the surface of the liquid at which the object is seen1 is an upright or vertical plane2 and this is one of the principal characters in the ordinary refraction of light1 viz4 that the ray by which we see an object through a refracting surface1 although it undergoes a bending1 and is1 as it were1 broken at the surface1 yet1 in pursuing its course to the eye1 does not quit a plane perpendicular to the refracting surface4 ,but there are again other substances1 such as rock-crystal1 and especially ,iceland spar1 which possess the singular property of doubling the image or appearance of an object seen through them in certain directions2 so that instead of seeing one object we see two1 side by side1 when such a crystal or spar is interposed between the object and the eye2 and if a ray or small sunbeam be thrown upon a surface of either of these substances1 it will be split into two1 making an angle with each other1 and each pursuing its own separate course1--this is called double refraction4 ,now1 of these images or doubly refracted rays1 one always follows the same rule as if the substance were glass or water3 its deviation can be correctly calculated by ,snell's law above mentioned1 and it does not quit the plane perpendicular to the refracting surface4 ,the other ray1 on the contrary1 7which is therefore said to have undergone extraordinary refraction7 does quit that plane1 and the amount of its deviation from its former course requires for its determination a much more complicated rule1 which cannot be understood or even stated without a pretty intimate knowledge of geometry4 ,now1 rock-crystal and ,iceland spar differ from glass in a very remarkable circumstance4 ,they affect naturally certain regular figures1 not being found in shapeless lumps1 but in determinate geometrical forms2 and they are susceptible of being cleft or split much easier in certain directions than in others--they have a grain which glass has not4 ,when other substances having this peculiarity 7and which are called crystallized substances7 were examined1 they were all1 or by far the greater part1 found to possess this singular property of double refraction2 and it was very natural to conclude1 therefore1 that the same thing took place in all of them1 viz4 that of the two rays1 into which any beam of light falling on the surface of such a substance was split1 or of the two images of an object seen through it1 one only was turned aside out of its plane and extraordinarily refracted1 while the other followed the ordinary rule4 ,accordingly this was supposed to be the case2 and not only so1 but from some trials and measurements purposely made by a philosopher of great eminence1 it was considered to be a fact sufficiently established by experiment4 7#bc47 ,perhaps we might have remained long under this impression1 for the measurements are delicate1 and the subject very difficult4 ,but it has lately been demonstrated by an eminent ,french philosopher and mathematician1 ,m4 ,fresnel1 that1 granting certain principles or postulates1 all the phenomena of double refraction1 including perhaps the greatest variety of facts that have ever yet been arranged under one general head1 may be satisfactorily explained and deduced from them by strict mathematical calculation2 and that1 when applied to the cases first mentioned1 these principles give a satisfactory account of the want of the extraordinary image2 that when applied to such cases as those of rock-crystal or ,iceland spar1 they also give a correct account of both the images1 and agree in their conclusions with the rules before ascertained for them3 but so far from coinciding with that part of the previous statement1 which would make these conclusions extend to all crystallised substances1 ,m4 ,fresnel's principles lead to a conclusion quite opposite1 and point to a fact which had never been observed1 viz4 that in by far the greater number of crystallized substances which possess the property of double refraction1 neither of the images follows the ordinary law1 but both undergo a deviation from their original plane4 ,now this had never been observed to be the case in any previous trial1 and all opinion was against it4 ,but when put to the test of experiment in a great variety of new and ingenious methods1 it was found to be fully verified2 and to complete the evidence1 the substances on whose imperfect examination the first erroneous conclusion was founded1 having been lately subjected to a fresh and more scrupulous examination1 the result has shown the insufficiency of the former measurements1 and proved in perfect accordance with the newly discovered laws4 ,now it will be observed in this case1 first1 that1 so far from the principles assumed by ,m4 ,fresnel being at all obvious1 they are extremely remote from ordinary observation2 and1 secondly1 that the chain of reasoning by which they are brought to the test is one of such length and complexity1 and the purely mathematical difficulty of their application so great1 that no mere good common sense1 no general tact or ordinary practical reasoning1 would afford the slightest chance of threading their mazes4 ,cases like this are the triumph of theories4 ,they show at once how large a part pure reason has to perform in our examination of nature1 and how implicit our reliance ought to be on that powerful and methodical system of rules and processes which constitute the modern mathematical analysis1 in all the more difficult applications of exact calculation to her phenomena4 7#bd47 ,to take an instance more within ordinary apprehension4 ,an eminent living geometer had proved by calculations1 founded on strict optical principles1 that in the centre of the shadow of a small circular plate of metal1 exposed in a dark room to a beam of light emanating from a very small brilliant point1 there ought to be no darkness1--in fact1 no shadow at that place2 but1 on the contrary1 a degree of illumination precisely as bright as if the metal plate were away4 ,strange and even impossible as this conclusion may seem1 it has been put to the trial1 and found perfectly correct4#i 7#be47 ,we shall now proceed to consider more particularly1 and in detail1-- ,i4 ,the nature and objects immediate and collateral of physical science1 as regarded in itself1 and in its application to the practical purposes of life1 and its influence on the well-being and progress of society4 ,,ii4 ,the principles on which it relies for its successful prosecution1 and the rules by which a systematic examination of nature should be conducted1 with examples illustrative of their influence4 ,,iii4 ,the subdivision of physical science into distinct branches1 and their mutual relations4 ,,chap4 ,,iii4 ,,of ,,the ,,nature ,,and ,,objects1 ,,immediate ,,and ,,collateral1 ,,of ,,physical ,,science1 ,,as ,,regarded ,,in ,,itself1 ,,and ,,in ,,its ,,application ,,to ,,the ,,practical ,,purposes ,,of ,,life1 ,,and ,,its ,,influence ,,on ,,the ,,well-,,being ,,and ,,progress ,,of ,,society4 7#bf47 ,the first thing impressed on us from our earliest infancy is1 that events do not succeed one another at random1 but with a certain degree of order1 regularity1 and connection2--some constantly1 and1 as we are apt to think1 immutably1--as the alternation of day and night1 summer and winter1--others contingently1 as the motion of a body from its place1 if pushed1 or the burning of a stick if thrust into the fire4 ,the knowledge that the former class of events has gone on1 uninterruptedly1 for ages beyond all memory1 impresses us with a strong expectation that it will continue to do so in the same manner2 and thus our notion of an order of nature is originated and confirmed4 ,if every thing were equally regular and periodical1 and the succession of events liable to no change depending on our own will1 it may be doubted whether we should ever think of looking for causes4 ,no one regards the night as the cause of the day1 or the day of night4 ,they are alternate effects of a common cause1 which their regular succession alone gives us no sufficient clue for determining4 ,it is chiefly1 perhaps entirely1 from the other or contingent class of events that we gain our notions of cause and effect4 ,from them alone we gather that there are such things as laws of nature4 ,the very idea of a law includes that of contingency4 8,si quis mala carmina condidisset1 fuste ferito20 if such a case arise1 such a course shall be followed1--if the match be applied to the gunpowder1 it will explode4 ,every law is a provision for cases which may occur1 and has relation to an infinite number of cases that never have occurred1 and never will4 ,now1 it is this provision1 priori1 for contingencies1 this contemplation of possible occurrences1 and predisposal of what shall happen1 that impresses us with the notion of a law and a cause4 ,among all the possible combinations of the fifty or sixty elements which chemistry shows to exist on the earth1 it is likely1 nay almost certain1 that some have never been formed2 that some elements1 in some proportions1 and under some circumstances1 have never yet been placed in relation with one another4 ,yet no chemist can doubt that it is already fixed what they will do when the case does occur4 ,they will obey certain laws1 of which we know nothing at present1 but which must be already fixed1 or they could not be laws4 ,it is not by habit1 or by trial and failure1 that they will learn what to do4 ,when the contingency occurs1 there will be no hesitation1 no consultation2--their course will at once be decided1 and will always be the same if it occur ever so often in succession1 or in ever so many places at one and the same instant4 ,this is the perfection of a law1 that it includes all possible contingencies1 and ensures implicit obedience1--and of this kind are the laws of nature4 7#bg47 ,this use of the word law1 however1 our readers will of course perceive has relation to us as understanding1 rather than to the materials of which the universe consists as obeying1 certain rules4 ,to obey a law1 to act in compliance with a rule1 supposes an understanding and a will1 a power of complying or not1 in the being who obeys and complies1 which we do not admit as belonging to mere matter4 ,the ,divine ,author of the universe cannot be supposed to have laid down particular laws1 enumerating all individual contingencies1 which his materials have understood and obey1--this would be to attribute to him the imperfections of human legislation2--but rather1 by creating them1 endued with certain fixed qualities and powers1 he has impressed them in their origin with the spirit1 not the letter1 of his law1 and made all their subsequent combinations and relations inevitable consequences of this first impression1 by which1 however1 we would no way be understood to deny the constant exercise of his direct power in maintaining the system of nature1 or the ultimate emanation of every energy which material agents exert from his immediate will1 acting in conformity with his own laws4 7#bh47 ,the discoveries of modern chemistry have gone far to establish the truth of an opinion entertained by some of the ancients1 that the universe consists of distinct1 separate1 indivisible atoms1 or individual beings so minute as to escape our senses1 except when united by millions1 and by this aggregation making up bodies of even the smallest visible bulk2 and we have the strongest evidence that1 although there exist great and essential differences in individuals among these atoms1 they may yet all be arranged in a very limited number of groups or classes1 all the individuals of each of which are1 to all intents and purposes1 exactly alike in all their properties4 ,now1 when we see a great number of things precisely alike1 we do not believe this similarity to have originated except from a common principle independent of them2 and that we recognise this likeness1 chiefly by the identity of their deportment under similar circumstances1 strengthens rather than weakens the conclusion4 ,a line of spinning-jennies#aj1 or a regiment of soldiers dressed exactly alike1 and going through precisely the same evolutions1 gives us no idea of independent existence3 we must see them act out of concert before we can believe them to have independent wills and properties1 not impressed on them from without4 ,and this conclusion1 which would be strong even were there only two individuals precisely alike in all respects and for ever1 acquires irresistible force when their number is multiplied beyond the power of imagination to conceive4 ,if we mistake not1 then1 the discoveries alluded to effectually destroy the idea of an eternal self-existent matter1 by giving to each of its atoms the essential characters1 at once1 of a manufactured article1 and a subordinate agent4 7#bi47 ,but to ascend to the origin of things1 and speculate on the creation1 is not the business of the natural philosopher4 ,an humbler field is sufficient for him in the endeavour to discover1 as far as our faculties will permit1 what are these primary qualities originally and unalterably impressed on matter1 and to discover the spirit of the laws of nature1 which includes groups and classes of relations and facts from the letter which1 as before observed1 is presented to us by single phenomena3 or if1 after all1 this should prove impossible2 if such a step be beyond our faculties2 and the essential qualities of material agents be really occult1 or incapable of being expressed in any form intelligible to our understandings1 at least to approach as near to their comprehension as the nature of the case will allow2 and devise such forms of words as shall include and represent the greatest possible multitude and variety of phenomena4 7#cj47 ,now1 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 success1 which is1 whether the laws of nature themselves have that degree of permanence and fixity which can render them subjects of systematic discussion2 or whether1 on the other hand1 the qualities of natural agents are subject to mutation from the lapse of time4 ,to the ancients1 who lived in the infancy of the world1 or rather1 in the infancy of man's experience1 this was a very rational subject of question1 and hence their distinctions between corruptible and incorruptible matter4 ,thus1 according to some among them1 the matter only of the celestial spaces is pure1 immutable1 and incorruptible1 while all sublunary things are in a constant state of lapse and change2 the world becoming paralysed and effete with age1 and man himself deteriorating in character1 and diminishing at once in intellectual and bodily stature4 ,but to us1 who have the experience of some additional thousands of years1 the question of permanence is already1 in a great measure1 decided in the affirmative4 ,the refined speculations of modern astronomy1 grounding their conclusions on observations made at very remote periods1 have proved to demonstration1 that one at least of the great powers of nature1 the force of gravitation1 the main bond and support of the material universe1 has undergone no change in intensity from a high antiquity4 ,the stature of mankind is just what it was three thousand years ago1 as the specimens of mummies which have been examined at various times sufficiently show4 ,the intellect of ,newton1 ,laplace1 or ,lagrange1 may stand in fair competition with that of ,archimedes1 ,aristotle1 or ,plato2 and the virtues and patriotism of ,washington with the brightest examples of ancient history4 7#ca47 ,again1 the researches of chemists have shown that what the vulgar call corruption1 destruction1 c41 is nothing but a change of arrangement of the same ingredient elements1 the disposition of the same materials into other forms1 without the loss or actual destruction of a single atom2 and thus any doubts of the permanence of natural laws are discountenanced1 and the whole weight of appearances thrown into the opposite scale4 ,one of the most obvious cases of apparent destruction is1 when any thing is ground to dust and scattered to the winds4 ,but it is one thing to grind a fabric to powder1 and another to annihilate its materials3 scattered as they may be1 they must fall somewhere1 and continue1 if only as ingredients of the soil1 to perform their humble but useful part in the economy of nature4 ,the destruction produced by fire is more striking3 in many cases1 as in the burning of a piece of charcoal or a taper1 there is no smoke1 nothing visibly dissipated and carried away2 the burning body wastes and disappears1 while nothing seems to be produced but warmth and light1 which we are not in the habit of considering as substances2 and when all has disappeared1 except perhaps some trifling ashes1 we naturally enough suppose it is gone1 lost1 destroyed4 ,but when the question is examined more exactly1 we detect1 in the invisible stream of heated air which ascends from the glowing coal or flaming wax1 the whole ponderable matter1 only united in a new combination with the air1 and dissolved in it4 ,yet1 so far from being thereby destroyed1 it is only become again what it was before it existed in the form of charcoal or wax1 an active agent in the business of the world1 and a main support of vegetable and animal life1 and is still susceptible of running again and again the same round1 as circumstances may determine2 so that1 for aught we can see to the contrary1 the same identical atom may lie concealed for thousands of centuries in a limestone rock2 may at length be quarried1 set free in the limekiln1 mix with the air1 be absorbed from it by plants1 and1 in succession1 become a part of the frames of myriads of living beings1 till some concurrence of events consigns it once more to a long repose1 which1 however1 no way unfits it from again resuming its former activity4 7#cb47 ,now1 this absolute indestructibility of the ultimate materials of the world1 in periods commensurate to our experience1 and their obstinate retention of the same properties1 under whatever variety of circumstances we choose to place them1 however violent and seemingly contradictory to their natures1 is1 of itself1 enough to render it highly improbable that time alone should have any influence over them4 ,all that age or decay can do seems to be included in a wasting of parts which are only dissipated1 not destroyed1 or in a change of sensible properties1 which chemistry demonstrates to arise only from new combinations of the same ingredients4 ,but1 after all1 the question is one entirely of experience3 we cannot be sure1 priori1 that the laws of nature are immutable2 but we can ascertain1 by enquiry1 whether they change or not2 and to this enquiry all experience answers in the negative4 ,it is not1 of course1 intended here to deny that great operations1 productive of extensive changes in the visible state of nature1--such as1 for instance1 those contemplated by the geologists1 and embracing for their completion vast periods of time1--are constantly going on2 but these are consequences and fulfilments of the laws of nature1 not contradictions or exceptions to them4 ,no theorist regards such changes as alterations in the fundamental principles of nature2 he only endeavours to reconcile them1 and show how they result from laws already known1 and judges of the correctness of his theory by their ultimate agreement4 7#cc47 ,but the laws of nature are not only permanent1 but consistent1 intelligible1 and discoverable with such a moderate degree of research1 as is calculated rather to stimulate than to weary curiosity4 ,if we were set down1 as creatures of another world1 in any existing society of mankind1 and began to speculate on their actions1 we should find it difficult at first to ascertain whether they were subject to any laws at all3 but when1 by degrees1 we had found out that they did consider themselves to be so2 and would then proceed to ascertain1 from their conduct and its consequences1 what these laws were1 and in what spirit conceived2 though we might not perhaps have much difficulty in discovering single rules applicable to particular cases1 yet1 the moment we came to generalize1 and endeavour from these to ascend1 step by step1 and discover any steady pervading principle1 the mass of incongruities1 absurdities1 and contradictions1 we should encounter1 would either dishearten us from further enquiry or satisfy us that what we were in search of did not exist4 ,it is quite the contrary in nature2 there we find no contradictions1 no incongruities1 but all is harmony4 ,what once is learnt we never have to unlearn4 ,as rules advance in generality1 apparent exceptions become regular2 and equivoque1 in her sublime legislation1 is as unheard of as maladministration4 7#cd47 ,living1 then1 in a world where such laws obtain1 and under their immediate dominion1 it is manifestly of the utmost importance to know them1 were it for no other reason than to be sure1 in all we undertake1 to have1 at least1 the law on our side1 so as not to struggle in vain against some insuperable difficulty opposed to us by natural causes4 ,what pains and expense would not the alchemists1 for instance1 have been spared by a knowledge of those simple laws of composition and decomposition1 which now preclude all idea of the attainment of their declared object6 what an amount of ingenuity1 thrown away on the pursuit of the perpetual motion1 might have been turned to better use1 if the simplest laws of mechanics had been known and attended to by the inventors of innumerable contrivances destined to that end6 ,what tortures1 inflicted on patients by imaginary cures of incurable diseases1 might have been dispensed with1 had a few simple principles of physiology been earlier recognised6 7#ce47 ,but if the laws of nature1 on the one hand1 are invincible opponents1 on the other1 they are irresistible auxiliaries2 and it will not be amiss if we regard them in each of those characters1 and consider the great importance of a knowledge of them to mankind1-- ,i4 ,in showing us how to avoid attempting impossibilities4 ,,ii4 ,in securing us from important mistakes in attempting what is1 in itself1 possible1 by means either inadequate1 or actually opposed1 to the end in view4 ,,iii4 ,in enabling us to accomplish our ends in the easiest1 shortest1 most economical1 and most effectual manner4 ,,iv4 ,in inducing us to attempt1 and enabling us to accomplish1 objects which1 but for such knowledge1 we should never have thought of undertaking4 ,we shall therefore proceed to illustrate by examples the effect of physical knowledge under each of these heads3-- 7#cf47 ,ex4 #a4 7#ce47 ,i4 ,it is not many years since an attempt was made to establish a colliery at ,bexhill1 in ,sussex4 ,the appearance of thin seams and sheets of fossil-wood and wood-coal1 with some other indications similar to what occur in the neighbourhood of the great coal-beds in the north of ,england1 having led to the sinking of a shaft1 and the erection of machinery on a scale of vast expense1 not less than eighty thousand pounds are said to have been laid out on this project1 which1 it is almost needless to add1 proved completely abortive1 as every geologist would have at once declared it must1 the whole assemblage of geological facts being adverse to the existence of a regular coal-bed in the ,hastings' sand2 while this1 on which ,bexhill is situated1 is separated from the coal-strata by a series of interposed beds of such enormous thickness as to render all idea of penetrating through them absurd4 ,the history of mining operations is full of similar cases1 where a very moderate acquaintance with the usual order of nature1 to say nothing of theoretical views1 would have saved many a sanguine adventurer from utter ruin4 7#cg47 ,ex4 #b4 7#ce47 ,,ii4 ,the smelting of iron requires the application of the most violent heat that can be raised1 and is commonly performed in tall furnaces1 urged by great iron bellows driven by steam-engines4 ,instead of employing this power to force air into the furnace through the intervention of bellows1 it was1 on one occasion1 attempted to employ the steam itself in1 apparently1 a much less circuitous manner2 viz4 by directing the current of steam in a violent blast1 from the boiler at once into the fire4 ,from one of the known ingredients of steam being a highly inflammable body1 and the other that essential part of the air which supports combustion1 it was imagined that this would have the effect of increasing the fire to tenfold fury1 whereas it simply blew it out2 a result which a slight consideration of the laws of chemical combination1 and the state in which the ingredient elements exist in steam1 would have enabled any one to predict without a trial4 7#ch47 ,ex4 #c4 7#ce47 ,,ii4 ,after the invention of the diving-bell1 and its success in subaqueous processes1 it was considered highly desirable to devise some means of remaining for any length of time under water1 and rising at pleasure without assistance1 so as either to examine1 at leisure1 the bottom1 or perform1 at ease1 any work that might be required4 ,some years ago1 an ingenious individual proposed a project by which this end was to be accomplished4 ,it consisted in sinking the hull of a ship made quite water-tight1 with the decks and sides strongly supported by shores1 and the only entry secured by a stout trap-door1 in such a manner1 that by disengaging1 from within1 the weights employed to sink it1 it might rise of itself to the surface4 ,to render the trial more satisfactory1 and the result more striking1 the projector himself made the first essay4 ,it was agreed that he should sink in twenty fathoms water1 and rise again without assistance at the expiration of twenty-four hours4 ,accordingly1 making all secure1 fastening down his trap-door1 and provided with all necessaries1 as well as with the means of making signals to indicate his situation1 this unhappy victim of his own ingenuity entered and was sunk4 ,no signal was made1 and the time appointed elapsed4 ,an immense concourse of people had assembled to witness his rising1 but in vain2 for the vessel was never seen more4 ,the pressure of the water at so great a depth had1 no doubt1 been completely under-estimated1 and the sides of the vessel being at once crushed in1 the unfortunate projector perished before he could even make the signal concerted to indicate his distress4 7#ci47 ,ex4 #d4 7#ce47 ,,iii4 ,in the granite quarries near ,seringapatam the most enormous blocks are separated from the solid rock by the following neat and simple process4 ,the workman having found a portion of the rock sufficiently extensive1 and situated near the edge of the part already quarried1 lays bare the upper surface1 and marks on it a line in the direction of the intended separation1 along which a groove is cut with a chisel about a couple of inches in depth4 ,above this groove a narrow line of fire is then kindled1 and maintained till the rock below is thoroughly heated1 immediately on which a line of men and women1 each provided with a pot full of cold water1 suddenly sweep off the ashes1 and pour the water into the heated groove1 when the rock at once splits with a clean fracture4 ,square blocks of six feet in the side1 and upwards of eighty feet in length1 are sometimes detached by this method1 or by another equally simple and efficacious1 but not easily explained without entering into particulars of mineralogical detail4#aa 7#dj47 ,ex4 #e4 7#ce47 ,,iii4 ,hardly less simple and efficacious is the process used in some parts of ,france1 where mill-stones are made4 ,when a mass of stone sufficiently large is found1 it is cut into a cylinder several feet high1 and the question then arises how to subdivide this into horizontal pieces so as to make as many mill-stones4 ,for this purpose horizontal indentations or grooves are chiselled out quite round the cylinder1 at distances corresponding to the thickness intended to be given to the mill-stones1 into which wedges of dried wood are driven4 ,these are then wetted1 or exposed to the night dew1 and next morning the different pieces are found separated from each other by the expansion of the wood1 consequent on its absorption of moisture2 an irresistible natural power thus accomplishing1 almost without any trouble1 and at no expense1 an operation which1 from the peculiar hardness and texture of the stone1 would otherwise be impracticable but by the most powerful machinery or the most persevering labour4 7#da47 ,ex4 #f4 7#ce47 ,,iii4 ,to accomplish our ends quickly is often of1 at least1 as much importance as to accomplish them with little labour and expense4 ,there are innumerable processes which1 if left to themselves1 i4 e4 to the ordinary operation of natural causes1 are done1 and well done1 but with extreme slowness1 and in such cases it is often of the highest practical importance to accelerate them4 ,the bleaching of linen1 for instance1 performed in the natural way by exposure to sun1 rain1 and wind1 requires many weeks or even months for its completion2 whereas1 by the simple immersion of the cloth in a liquid1 chemically prepared1 the same effect is produced in a few hours4 ,the whole circle of the arts1 indeed1 is nothing but one continued comment upon this head of our subject4 ,the instances above given are selected1 not on account of their superior importance1 but for the simplicity and directness of application of the principles on which they depend1 to the objects intended to be attained4 7#db47 ,but so constituted is the mind of man1 that his views enlarge1 and his desires and wants increase1 in the full proportion of the facilities afforded to their gratification1 and1 indeed1 with augmented rapidity1 so that no sooner has the successful exercise of his powers accomplished any considerable simplification or improvement of processes subservient to his use or comfort1 than his faculties are again on the stretch to extend the limits of his newly acquired power2 and having once experienced the advantages which are to be gathered by availing himself of some of the powers of nature to accomplish his ends1 he is led thenceforward to regard them all as a treasure placed at his disposal1 if he have only the art1 the industry1 or the good fortune1 to penetrate those recesses which conceal them from immediate view4 ,having once learned to look on knowledge as power1 and to avail himself of it as such1 he is no longer content to limit his enterprises to the beaten track of former usage1 but is constantly led onwards to contemplate objects which1 in a previous stage of his progress1 he would have regarded as unattainable and visionary1 had he even thought of them at all4 ,it is here that the investigation of the hidden powers of nature becomes a mine1 every vein of which is pregnant with inexhaustible wealth1 and whose ramifications appear to extend in all directions wherever human wants or curiosity may lead us to explore4 7#dc47 ,between the physical sciences and the arts of life there subsists a constant mutual interchange of good offices1 and no considerable progress can be made in the one without of necessity giving rise to corresponding steps in the other4 ,on the one hand1 every art is in some measure1 and many entirely1 dependent on those very powers and qualities of the material world which it is the object of physical enquiry to investigate and explain2 and1 accordingly1 abundant examples might be cited of cases where the remarks of experienced artists1 or even ordinary workmen1 have led to the discovery of natural qualities1 elements1 or combinations which have proved of the highest importance in physics4 ,thus 7to give an instance71 a soap-manufacturer remarks that the residuum of his ley1 when exhausted of the alkali for which he employs it1 produces a corrosion of his copper boiler for which he cannot account4 ,he puts it into the hands of a scientific chemist for analysis1 and the result is the discovery of one of the most singular and important chemical elements1 iodine4 ,the properties of this1 being studied1 are found to occur most appositely in illustration and support of a variety of new1 curious1 and instructive views then gaining ground in chemistry1 and thus exercise a marked influence over the whole body of that science4 ,curiosity is excited3 the origin of the new substance is traced to the sea-plants from whose ashes the principal ingredient of soap is obtained1 and ultimately to the sea-water itself4 ,it is thence hunted through nature1 discovered in salt mines and springs1 and pursued into all bodies which have a marine origin2 among the rest1 into sponge4 ,a medical practitioner#ab 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 gotre--which infests the inhabitants of mountainous districts to an extent that in this favoured land we have happily no experience of1 and which was said to have been originally cured by the ashes of burnt sponge4 ,led by this indication he tries the effect of iodine on that complaint1 and the result establishes the extraordinary fact that this singular substance1 taken as a medicine1 acts with the utmost promptitude and energy on gotre1 dissipating the largest and most inveterate in a short time1 and acting 7of course1 like all medicines1 even the most approved1 with occasional failures17 as a specific1 or natural antagonist1 against that odious deformity4 ,it is thus that any accession to our knowledge of nature is sure1 sooner or later1 to make itself felt in some practical application1 and that a benefit conferred on science by the casual observation or shrewd remark of even an unscientific or illiterate person infallibly repays itself with interest1 though often in a way that could never have been at first contemplated4 7#dd47 ,it is to such observation1 reflected upon1 however1 and matured into a rational and scientific form by a mind deeply imbued with the best principles of sound philosophy1 that we owe the practice of vaccination2 a practice which has effectually subdued1 in every country where it has been introduced1 one of the most frightful scourges of the human race1 and in some extirpated it altogether4 ,happily for us we know only by tradition the ravages of the small-pox1 as it existed among us hardly more than a century ago1 and as it would in a few years infallibly exist again1 were the barriers which this practice1 and that of inoculation1 oppose to its progress abandoned4 ,hardly inferior to this terrible scourge on land was1 within the last seventy or eighty years1 the scurvy at sea4 ,the sufferings and destruction produced by this horrid disorder on board our ships when1 as a matter of course1 it broke out after a few months' voyage1 seem now almost incredible4 ,deaths to the amount of eight or ten a day in a moderate ship's company2 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 overboard2 and every form of loathsome and excruciating misery of which the human frame is susceptible3--such are the pictures which the narratives of nautical adventure in those days continually offer4#ac ,at present the scurvy is almost completely eradicated in the navy1 partly1 no doubt1 from increased and increasing attention to general cleanliness1 comfort1 and diet2 but mainly from the constant use of a simple and palatable preventive1 the acid of the lemon1 served out in daily rations4 ,if the gratitude of mankind be allowed on all hands to be the just meed of the philosophic physician1 to whose discernment in seizing1 and perseverance in forcing it on public notice we owe the great safeguard of infant life1 it ought not to be denied to those#ad whose skill and discrimination have thus strengthened the sinews of our most powerful arm1 and obliterated one of the darkest features in the most glorious of all professions4 7#de47 ,these last1 however1 are instances of simple observation1 limited to the point immediately in view1 and assuming only so far the character of science as a systematic adoption of good and rejection of evil1 when grounded on experience carefully weighed1 justly entitle it to do4 ,they are not on that account less appositely cited as instances of the importance of a knowledge of nature and its laws to our well-being2 though1 like the great inventions of the mariner's compass and of gunpowder1 they may have stood1 in their origin1 unconnected with more general views4 ,they are rather to be looked upon as the spontaneous produce of a territory essentially fertile1 than as forming part of the succession of harvests which the same bountiful soil1 diligently cultivated1 is capable of yielding4 ,the history of iodine above related affords1 however1 a perfect specimen of the manner in which a knowledge of natural properties and laws1 collected from facts having no reference to the object to which they have been subsequently applied1 enables us to set in array the resources of nature against herself2 and deliberately1 of afore-thought1 to devise remedies against the dangers and inconveniences which beset us4 ,in this view we might instance1 too1 the conductor1 which1 in countries where thunder-storms are more frequent and violent than in our own1 and at sea 7where they are attended with peculiar danger1 both from the greater probability of accident1 and its more terrible consequences when it does occur17 forms a most real and efficient preservative against the effects of lightning#ae3--the safety-lamp1 which enables us to walk with light and security while surrounded with an atmosphere more explosive than gunpowder3--the life-boat1 which cannot be sunk1 and which offers relief in circumstances of all others the most distressing to humanity1 and of which a recent invention promises to extend the principle to ships of the largest class3--the lighthouse1 with the capital improvements which the lenses of ,brewster and ,fresnel1 and the elegant lamp of lieutenant ,drummond1 have conferred1 and promise yet to confer by their wonderful powers1 the one of producing the most intense light yet known1 the others of conveying it undispersed to great distances3--the discovery of the disinfectant powers of chlorine1 and its application to the destruction of miasma and contagion3--that of quinine1 the essential principle in which reside the febrifuge qualities of the ,peruvian bark1 a discovery by which posterity is yet to benefit in its full extent1 but which has already begun to diffuse comparative comfort and health through regions almost desolated by pestiferous exhalations#af2--;and1 if we desist1 it is not because the list is exhausted1 but because a sample1 not a catalogue1 is intended4 7#df47 ,one instance more1 however1 we will add1 to illustrate the manner in which a most familiar effect1 which seemed destined only to amuse children1 or1 at best1 to furnish a philosophic toy1 may become a safeguard of human life1 and a remedy for a most serious and distressing evil4 ,in needle manufactories the workmen who point the needles are constantly exposed to excessively minute particles of steel which fly from the grindstones1 and mix1 though imperceptible to the eye1 as the finest dust in the air1 and are inhaled with their breath4 ,the effect1 though imperceptible on a short exposure1 yet1 being constantly repeated from day to day1 produces a constitutional irritation dependent on the tonic properties of the steel1 which is sure to terminate in pulmonary consumption2 insomuch1 that persons employed in this kind of work used scarcely ever to attain the age of forty years4#ag ,in vain was it attempted to purify the air before its entry into the lungs by gauzes or linen guards2 the dust was too fine and penetrating to be obstructed by such coarse expedients1 till some ingenious person bethought him of that wonderful power which every child who searches for its mother's needle with a magnet1 or admires the motions and arrangement of a few steel filings on a sheet of paper held above it1 sees in exercise4 ,masks of magnetized steel wire are now constructed and adapted to the faces of the workmen4 ,by these the air is not merely strained but searched in its passage through them1 and each obnoxious atom arrested and removed4 7#dg47 ,perhaps there is no result which places in a stronger light the advantages which are to be derived from a mere knowledge of the usual order of nature1 without any attempt on our part to modify it1 and apart from all consideration of its causes1 than the institution of life-assurances4 ,nothing is more uncertain than the life of a single individual2 and it is the sense of this insecurity which has given rise to such institutions4 ,they are1 in their nature and objects1 the precise reverse of gambling speculations1 their object being to equalize vicissitude1 and to place the pecuniary relations of numerous masses of mankind1 in so far as they extend1 on a footing independent of individual casualty4 ,to do this with the greatest possible advantage1 or indeed with any advantage at all1 it is necessary to know the laws of mortality1 or the average numbers of individuals1 out of a great multitude1 who die at every period of life from infancy to extreme old age4 ,at first sight this would seem a hopeless enquiry2 to some1 perhaps1 a presumptuous one4 ,but it has been made2 and the result is1 that1 abating extraordinary causes1 such as wars1 pestilence1 and the like1 a remarkable regularity does obtain1 quite sufficient to afford grounds not only for general estimations1 but for nice calculations of risk and adventure1 such as infallibly to insure the success of any such institution founded on good computations2 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 civilization4 ,the only thing to be feared in such institutions is their too great multiplication and consequent competition1 by which a spirit of gambling and underbidding is liable to be generated among their conductors1 and the very mischief may be produced1 on a scale of frightful extent1 which they are especially intended to prevent4 7#dh47 ,we have hitherto considered only cases in which a knowledge of natural laws enables us to improve our condition1 by counteracting evils of which1 but for its possession1 we must have remained forever the helpless victims4 ,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 power1 and capacitate us for undertakings1 which without such aid might seem to be hopeless4 ,now1 to this end1 it is necessary that we should form a just conception of what those hidden powers of nature are1 which we can at pleasure call into action2--how far they transcend the measure of human force1 and set at naught the efforts not only of individuals but of whole nations of men4 7#di47 ,it is well known to modern engineers1 that there is virtue in a bushel of coals properly consumed1 to raise seventy millions of pounds weight a foot high4 ,this is actually the average effect of an engine at this moment working in ,cornwall4#ah ,let us pause a moment1 and consider what this is equivalent to in matters of practice4 7#ej47 ,the ascent of ,mont ,blanc from the valley of ,chamouni is considered1 and with justice1 as the most toilsome feat that a strong man can execute in two days4 ,the combustion of two pounds of coal would place him on the summit4#ai 7#ea47 ,the ,menai ,bridge1 one of the most stupendous works of art that has been raised by man in modern ages1 consists of a mass of iron1 not less than four millions of pounds in weight1 suspended at a medium height of about #abj feet above the sea4 ,the consumption of seven bushels of coal would suffice to raise it to the place where it hangs4 7#eb47 ,the great pyramid of ,egypt is composed of granite4 ,it is #gjj feet in the side of its base1 and #ejj in perpendicular height1 and stands on eleven acres of ground4 ,its weight is1 therefore1 #ab1gfj millions of pounds1 at a medium height of #abe feet2 consequently it would be raised by the effort of about #fcj chaldrons of coal1 a quantity consumed in some founderies in a week4 7#ec47 ,the annual consumption of coal in ,london is estimated at #a1ejj1jjj chaldrons4 ,the effort of this quantity would suffice to raise a cubical block of marble1 #bbjj feet in the side1 through a space equal to its own height1 or to pile one such mountain upon another4 ,the ,monte ,nuovo1 near ,pozzuoli1 7which was erupted in a single night by volcanic fire17 might have been raised by such an effort1 from a depth of #dj1jjj feet1 or about eight miles4 7#ed47 ,it will be observed1 that1 in the above statement1 the inherent power of fuel is1 of necessity1 greatly under-rated4 ,it is not pretended by engineers that the economy of fuel is yet pushed to its utmost limit1 or that the whole effective power is obtained in any application of fire yet devised2 so that were we to say #ajj millions instead of #gj1 we should probably be nearer the truth4 7#ee47 ,the powers of wind and water1 which we are constantly impressing into our service1 can scarcely be called latent or hidden1 yet it is not fully considered1 in general1 what they do effect for us4 ,those who would judge of what advantage may be taken of the wind1 for example1 even on land 7not to speak of navigation71 may turn their eyes on ,holland4 ,a great portion of the most valuable and populous tract of this country lies much below the level of the sea1 and is only preserved from inundation by the maintenance of embankments4 ,though these suffice to keep out the abrupt influx of the ocean1 they cannot oppose that law of nature1 by which fluids1 in seeking their level1 insinuate themselves through the pores and subterraneous channels of a loose sandy soil1 and keep the country in a constant state of infiltration from below upwards4 ,to counteract this tendency1 as well as to get rid of the rain water1 which has no natural outlet1 pumps worked by windmills are established in great numbers1 on the dams and embankments1 which pour out the water1 as from a leaky ship1 and in effect preserve the country from submersion1 by taking advantage of every wind that blows4 ,to drain the ,haarlem lake#bj would seem a hopeless project to any speculators but those who had the steam-engine at their command1 or had learnt in ,holland what might be accomplished by the constant agency of the desultory but unwearied powers of wind4 ,but the ,dutch engineer measures his surface1 calculates the number of his pumps1 and1 trusting to time and his experience of the operation of the winds for the success of his undertaking1 boldly forms his plans to lay dry the bed of an inland sea1 of which those who stand on one shore cannot see the other4#ba 7#ef47 ,to gunpowder1 as a source of mechanical power1 it seems hardly necessary to call attention2 yet it is only when we endeavour to confine it1 that we get a full conception of the immense energy of that astonishing agent4 ,in count ,rumford's experiments1 twenty-eight grains of powder confined in a cylindrical space1 which it just filled1 tore asunder a piece of iron which would have resisted a strain of #djj1jjj lbs4#bb1 applied at no greater mechanical disadvantage4 7#eg47 ,but chemistry furnishes us with means of calling into sudden action forces of a character infinitely more tremendous than that of gunpowder4 ,the terrific violence of the different fulminating compositions is such1 that they can only be compared to those untameable animals1 whose ferocious strength has hitherto defied all useful management1 or rather to spirits evoked by the spells of a magician1 manifesting a destructive and unapproachable power1 which makes him but too happy to close his book1 and break his wand1 as the price of escaping3 unhurt from the storm he has raised4 ,such powers are not yet subdued to our purposes1 whatever they may hereafter be2 but1 in the expansive force of gases1 liberated slowly and manageably from chemical mixtures1 we have a host of inferior1 yet still most powerful1 energies1 capable of being employed in a variety of useful ways1 according to emergencies4#bc 7#eh47 ,such are the forces which nature lends us for the accomplishment of our purposes1 and which it is the province of practical ,mechanics to teach us to combine and apply in the most advantageous manner2 without which the mere command of power would amount to nothing4 ,practical ,mechanics is1 in the most pre-eminent sense1 a scientific art2 and it may be truly asserted1 that almost all the great combinations of modern mechanism1 and many of its refinements and nicer improvements1 are creations of pure intellect1 grounding its exertion upon a moderate number of very elementary propositions in theoretical mechanics and geometry4 ,on this head we might dwell long1 and find ample matter1 both for reflection and wonder2 but it would require not volumes merely1 but libraries1 to enumerate and describe the prodigies of ingenuity which have been lavished on every thing connected with machinery and engineering4 ,by these it is that we are enabled to diffuse over the whole earth the productions of any part of it2 to fill every corner of it with miracles of art and labour1 in exchange for its peculiar commodities2 and to concentrate around us1 in our dwellings1 apparel and utensils1 the skill and workmanship not of a few expert individuals1 but of all who1 in the present and past generations1 have contributed their improvements to the processes of our manufactures4 7#ei47 ,the transformations of chemistry1 by which we are enabled to convert the most apparently useless materials into important objects in the arts1 are opening up to us every day sources of wealth and convenience of which former ages had no idea1 and which have been pure gifts of science to man4 ,every department of art has felt their influence1 and new instances are continually starting forth of the unlimited resources which this wonderful science developes in the most sterile parts of nature4 ,not to mention the impulse which its progress has given to a host of other sciences1 which will come more particularly under consideration in another part of this discourse1 what strange and unexpected results has it not brought to light in its application to some of the most common objects6 ,who1 for instance1 would have conceived that linen rags were capable of producing more than their own weight of sugar1 by the simple agency of one of the cheapest and most abundant acids8#bd--that dry bones could be a magazine of nutriment1 capable of preservation for years1 and ready to yield up their sustenance in the form best adapted to the support of life1 on the application of that powerful agent1 steam1 which enters so largely into all our processes1 or of an acid at once cheap and durable8#be--that sawdust itself is susceptible of conversion into a substance bearing no remote analogy to bread2 and though certainly less palatable than that of flour1 yet no way disagreeable1 and both wholesome and digestible as well as highly nutritive8#bf ,what economy1 in all processes where chemical agents are employed1 is introduced by the exact knowledge of the proportions in which natural elements unite1 and their mutual powers of displacing each other6 ,what perfection in all the arts where fire is employed1 either in its more violent applications1 7as1 for instance1 in the smelting of metals by the introduction of well adapted fluxes1 whereby we obtain the whole produce of the ore in its purest state17 or in its milder forms1 as in sugar-refining 7the 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 place72 and a thousand other arts which it would be tedious to enumerate6 7#fj47 ,armed with such powers and resources1 it is no wonder if the enterprise of man should lead him to form and execute projects which1 to one uninformed of their grounds1 would seem altogether disproportionate4 ,were they to have been proposed at once1 we should1 no doubt1 have rejected them as such3 but developed1 as they have been1 in the slow succession of ages1 they have only taught us that things regarded impossible in one generation may become easy in the next2 and that the power of man over nature is limited only by the one condition1 that it must be exercised in conformity with the laws of nature4 ,he must study those laws as he would the disposition of a horse he would ride1 or the character of a nation he would govern2 and the moment he presumes either to thwart her fundamental rules1 or ventures to measure his strength with hers1 he is at once rendered severely sensible of his imbecility1 and meets the deserved punishment of his rashness and folly4 ,but if1 on the other hand1 he will consent to use1 without abusing1 the resources thus abundantly placed at his disposal1 and obey that he may command1 there seems scarcely any conceivable limit to the degree in which the average physical condition of great masses of mankind may be improved1 their wants supplied1 and their conveniences and comforts increased4 ,without adopting such an exaggerated view1 as to assert that the meanest inhabitant of a civilized society is superior in physical condition to the lordly savage1 whose energy and uncultivated ability gives him a natural predominance over his fellow denizens of the forest1--at least1 if we compare like with like1 and consider the multitude of human beings who are enabled1 in an advanced state of society1 to subsist in a degree of comfort and abundance1 which at best only a few of the most fortunate in a less civilized state could command1 we shall not be at a loss to perceive the principle on which we ought to rest our estimate of the advantages of civilization2 and which applies with hardly less force to every degree of it1 when contrasted with that next inferior1 than to the broad distinction between civilized and barbarous life in general4 7#fa47 ,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 ages2 and it is doubtless our paramount duty1 in every state of society1 to alleviate the pressure of the purely evil part of this distribution as much as possible1 and1 by all the means we can devise1 secure the lower links in the chain of society from dragging in dishonour and wretchedness3 but there is a point of view in which the picture is at least materially altered in its expression4 ,in comparing society on its present immense scale1 with its infant or less developed state1 we must at least take care to enlarge every feature in the same proportion4 ,if1 on comparing the very lowest states in civilized and savage life1 we admit a difficulty in deciding to which the preference is due1 at least in every superior grade we cannot hesitate a moment2 and if we institute a similar comparison in every different stage of its progress1 we cannot fail to be struck with the rapid rate of dilatation which every degree upward of the scale1 so to speak1 exhibits1 and which1 in an estimate of averages1 gives an immense preponderance to the present over every former condition of mankind1 and1 for aught we can see to the contrary1 will place succeeding generations in the same degree of superior relation to the present that this holds to those passed away4 ,or we may put the same proposition in other words1 and1 admitting the existence of every inferior grade of advantage in a higher state of civilization which subsisted in the preceding1 we shall find1 first1 that1 taking state for state1 the proportional numbers of those who enjoy the higher degrees of advantage increases with a constantly accelerated rapidity as society advances2 and1 secondly1 that the superior extremity of the scale is constantly enlarging by the addition of new degrees4 ,the condition of a ,european prince is now as far superior1 in the command of real comforts and conveniences1 to that of one in the middle ages1 as that to the condition of one of his own dependants4 7#fb47 ,the advantages conferred by the augmentation of our physical resources through the medium of increased knowledge and improved art have this peculiar and remarkable property1--that they are in their nature diffusive1 and cannot be enjoyed in any exclusive manner by a few4 ,an eastern despot may extort the riches and monopolize the art of his subjects for his own personal use2 he may spread around him an unnatural splendour and luxury1 and stand in strange and preposterous contrast with the general penury and discomfort of his people2 he may glitter in jewels of gold and raiment of needlework2 but the wonders of well contrived and executed manufacture which we use daily1 and the comforts which have been invented1 tried1 and improved upon by thousands1 in every form of domestic convenience1 and for every ordinary purpose of life1 can never be enjoyed by him4 ,to produce a state of things in which the physical advantages of civilized life can exist in a high degree1 the stimulus of increasing comforts and constantly elevated desires1 must have been felt by millions2 since it is not in the power of a few individuals to create that wide demand for useful and ingenious applications1 which alone can lead to great and rapid improvements1 unless backed by that arising from the speedy diffusion of the same advantages among the mass of mankind4 7#fc47 ,if this be true of physical advantages1 it applies with still greater force to intellectual4 ,knowledge can neither be adequately cultivated nor adequately enjoyed by a few2 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 born1 there is no such law of nature in force against that of our intellectual and moral wants4 ,knowledge is not1 like food1 destroyed by use1 but rather augmented and perfected4 ,it acquires not1 perhaps1 a greater certainty1 but at least a confirmed authority and a probable duration1 by universal assent2 and there is no body of knowledge so complete1 but that it may acquire accession1 or so free from error but that it may receive correction in passing through the minds of millions4 ,those who admire and love knowledge for its own sake ought to wish to see its elements made accessible to all1 were it only that they may be the more thoroughly examined into1 and more effectually developed in their consequences1 and receive that ductility and plastic quality which the pressure of minds of all descriptions1 constantly moulding them to their purposes1 can alone bestow4 ,but to this end it is necessary that it should be divested1 as far as possible1 of artificial difficulties1 and stripped of all such technicalities as tend to place it in the light of a craft and a mystery1 inaccessible without a kind of apprenticeship4 ,science1 of course1 like every thing else1 has its own peculiar terms1 and1 so to speak1 its idioms of language2 and these it would be unwise1 were it even possible1 to relinquish3 but every thing that tends to clothe it in a strange and repulsive garb1 and especially every thing that1 to keep up an appearance of superiority in its professors over the rest of mankind1 assumes an unnecessary guise of profundity and obscurity1 should be sacrificed without mercy4 ,not to do this1 is to deliberately reject the light which the natural unencumbered good sense of mankind is capable of throwing on every subject1 even in the elucidation of principles3 but where principles are to be applied to practical uses it becomes absolutely necessary2 as all mankind have then an interest in their being so familiarly understood1 that no mistakes shall arise in their application4 7#fd47 ,the same remark applies to arts4 ,they cannot be perfected till their whole processes are laid open1 and their language simplified and rendered universally intelligible4 ,art is the application of knowledge to a practical end4 ,if the knowledge be merely accumulated experience1 the art is empirical2 but if it be experience reasoned upon and brought under general principles1 it assumes a higher character1 and becomes a scientific art4 ,in the progress of mankind from barbarism to civilised life1 the arts necessarily precede science4 ,the wants and cravings of our animal constitution must be satisfied2 the comforts1 and some of the luxuries1 of life must exist4 ,something must be given to the vanity of show1 and more to the pride of power3 the round of baser pleasures must have been tried and found insufficient1 before intellectual ones can gain a footing2 and when they have obtained it1 the delights of poetry and its sister arts still take precedence of contemplative enjoyments1 and the severer pursuits of thought2 and when these in time begin to charm from their novelty1 and sciences begin to arise1 they will at first be those of pure speculation4 ,the mind delights to escape from the trammels which had bound it to earth1 and luxuriates in its newly found powers4 ,hence1 the abstractions of geometry--the properties of numbers--the movements of the celestial spheres--whatever is abstruse1 remote1 and extramundane--become the first objects of infant science4 ,applications come late3 the arts continue slowly progressive1 but their realm remains separated from that of science by a wide gulf which can only be passed by a powerful spring4 ,they form their own language and their own conventions1 which none but artists can understand4 ,the whole tendency of empirical art1 is to bury itself in technicalities1 and to place its pride in particular short cuts and mysteries known only to adepts2 to surprise and astonish by results1 but conceal processes4 ,the character of science is the direct contrary4 ,it delights to lay itself open to enquiry1 and is not satisfied with its conclusions1 till it can make the road to them broad and beaten3 and in its applications it preserves the same character2 its whole aim being to strip away all technical mystery1 to illuminate every dark recess1 and to gain free access to all processes1 with a view to improve them on rational principles4 ,it would seem that a union of two qualities almost opposite to each other--a going forth of the thoughts in two directions1 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 applying science4 ,among the ,greeks1 this point was attained by ,archimedes1 but attained too late1 on the eve of that great eclipse of science which was destined to continue for nearly eighteen centuries1 till ,galileo in ,italy1 and ,bacon in ,england1 at once dispelled the darkness3 the one1 by his inventions and discoveries2 the other1 by the irresistible force of his arguments and eloquence4 7#fe47 ,finally1 the improvement effected in the condition of mankind by advances in physical science as applied to the useful purposes of life1 is very far from being limited to their direct consequences in the more abundant supply of our physical wants1 and the increase of our comforts4 ,great as these benefits are1 they are yet but steps to others of a still higher kind4 ,the successful results of our experiments and reasonings in natural philosophy1 and the incalculable advantages which experience1 systematically consulted and dispassionately reasoned on1 has conferred in matters purely physical1 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 relations4 ,it is thus that legislation and politics become gradually regarded as experimental sciences2 and history1 not1 as formerly1 the mere record of tyrannies and slaughters1 which1 by immortalizing the execrable actions of one age1 perpetuates the ambition of committing them in every succeeding one1 but as the archive of experiments1 successful and unsuccessful1 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 governed4 ,the celebrated apophthegm1 that nations never profit by experience1 becomes yearly more and more untrue4 ,political economy1 at least1 is found to have sound principles1 founded in the moral and physical nature of man1 which1 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 generation1 by which they must1 sooner or later1 prevail4 ,the idea once conceived and verified1 that great and noble ends are to be achieved1 by which the condition of the whole human species shall be permanently bettered1 by bringing into exercise a sufficient quantity of sober thought1 and by a proper adaptation of means1 is of itself sufficient to set us earnestly on reflecting what ends are truly great and noble1 either in themselves1 or as conducive to others of a still loftier character2 because we are not now1 as heretofore1 hopeless of attaining them4 ,it is not now equally harmless and insignificant1 whether we are right or wrong2 since we are no longer supinely and helplessly carried down the stream of events1 but feel ourselves capable of buffetting at least with its waves1 and perhaps of riding triumphantly over them3 for why should we despair that the reason which has enabled us to subdue all nature to our purposes1 should 7if permitted and assisted by the providence of ,god7 achieve a far more difficult conquest2 and ultimately find some means of enabling the collective wisdom of mankind to bear down those obstacles which individual short-sightedness1 selfishness1 and passion1 oppose to all improvements1 and by which the highest hopes are continually blighted1 and the fairest prospects marred4 ,,part ,,ii4 ,,of ,,the ,,principles ,,on ,,which ,,physical ,,science ,,relies ,,for ,,its ,,successful ,,prosecution1 ,,and ,,the ,,rules ,,by ,,which ,a ,,systematic ,,examination ,,of ,,nature ,,should ,,be ,,conducted1 ,,with ,,illustrations ,,of ,,their ,,influence ,,as ,,exemplified ,,in ,,the ,,history ,,of ,,its ,,progress4 ,,chapter ,i4 ,,of ,,experience ,,as ,,the ,,source ,,of ,,our ,,knowledge4--,,of ,,the ,,dismissal ,,of ,,prejudices4--,,of ,,the ,,evidence ,,of ,,our ,,senses4 7#ff47 ,into abstract science1 as we have before observed1 the notion of cause does not enter4 ,the truths it is conversant with are necessary ones1 and exist independent of cause4 ,there may be no such real thing as a right-lined triangle marked out in space2 but the moment we conceive one in our minds1 we cannot refuse to admit the sum of its three angles to be equal to two right angles2 and if in addition we conceive one of its angles to be a right angle1 we cannot thenceforth refuse to admit that the sum of the squares on the two sides1 including the right angle1 is equal to the square on the side subtending it4 ,to maintain the contrary1 would be1 in effect1 to deny its being right angled4 ,no one causes or makes all the diameters of an ellipse to be bisected in its centre4 ,to assert the contrary1 would not be to rebel against a power1 but to deny our own words4 ,but in natural science cause and effect are the ultimate relations we contemplate2 and laws1 whether imposed or maintained1 which1 for aught we can perceive1 might have been other than they are4 ,this distinction is very important4 ,a clever man1 shut up alone and allowed unlimited time1 might reason out for himself all the truths of mathematics1 by proceeding from those simple notions of space and number of which he cannot divest himself without ceasing to think4 ,but he could never tell1 by any effort of reasoning1 what would become of a lump of sugar if immersed in water1 or what impression would be produced on his eye by mixing the colours yellow and blue4 7#fg47 ,we have thus pointed out to us1 as the great1 and indeed only ultimate source of our knowledge of nature and its laws1 ,,experience2 by which we mean1 not the experience of one man only1 or of one generation1 but the accumulated experience of all mankind in all ages1 registered in books or recorded by tradition4 ,but experience may be acquired in two ways3 either1 first1 by noticing facts as they occur1 without any attempt to influence the frequency of their occurrence1 or to vary the circumstances under which they occur2 this is ,,observation3 or1 secondly1 by putting in action causes and agents over which we have control1 and purposely varying their combinations1 and noticing what effects take place2 this is ,,experiment4 ,to these two sources we must look as the fountains of all natural science4 ,it is not intended1 however1 by thus distinguishing observation from experiment1 to place them in any kind of contrast4 ,essentially they are much alike1 and differ rather in degree than in kind2 so that1 perhaps1 the terms passive and active observation might better express their distinction2 but it is1 nevertheless1 highly important to mark the different states of mind in inquiries carried on by their respective aids1 as well as their different effects in promoting the progress of science4 ,in the former1 we sit still and listen to a tale1 told us1 perhaps obscurely1 piecemeal1 and at long intervals of time1 with our attention more or less awake4 ,it is only by after-rumination that we gather its full import2 and often1 when the opportunity is gone by1 we have to regret that our attention was not more particularly directed to some point which1 at the time1 appeared of little moment1 but of which we at length appretiate the importance4 ,in the latter1 on the other hand1 we cross-examine our witness1 and by comparing one part of his evidence with the other1 while he is yet before us1 and reasoning upon it in his presence1 are enabled to put pointed and searching questions1 the answer to which may at once enable us to make up our minds4 ,accordingly it has been found invariably1 that in those departments of physics where the phenomena are beyond our control1 or into which experimental enquiry1 from other causes1 has not been carried1 the progress of knowledge has been slow1 uncertain1 and irregular2 while in such as admit of experiment1 and in which mankind have agreed to its adoption1 it has been rapid1 sure1 and steady4 ,for example1 in our knowledge of the nature and causes of volcanoes1 earthquakes1 the fall of stones from the sky1 the appearance of new stars and disappearance of old ones1 and other of those great phenomena of nature which are altogether beyond our command1 and at the same time are of too rare occurrence to permit any one to repeat and rectify his impressions respecting them1 we know little more now than in the earliest times4 ,here our tale is told us slowly1 and in broken sentences4 ,in astronomy1 again1 we have at least an uninterrupted narrative2 the opportunity of observation is constantly present1 and makes up in some measure for the impossibility of varying our point of view1 and calling for information at the precise moment it is wanted4 ,accordingly1 astronomy1 regarded as a science of mere observation1 arrived1 though by very slow degrees1 to a state of considerable maturity4 ,but the moment that it became a branch of mechanics1 a science essentially experimental1 7that is to say1 one in which any principle laid down can be subjected to immediate and decisive trial1 and where experience does not require to be waited for17 its progress suddenly acquired a tenfold acceleration2 nay1 to such a degree1 that it has been asserted1 and we believe with truth1 that were the records of all observations from the earliest ages annihilated1 leaving only those made in a single observatory#bg1 during a single lifetime#bh1 the whole of this most perfect of sciences might1 from those data1 and as to the objects included in them1 be at once reconstructed1 and appear precisely as it stood at their conclusion4 ,to take another instance3 mineralogy1 till modern times1 could hardly be said to exist4 ,the description of even the precious stones in ,theophrastus and ,pliny are1 in most cases1 hardly sufficient to identify them1 and in many fall short even of that humble object2 more recent observers1 by attending more carefully to the obvious characters of minerals1 had formed a pretty extensive catalogue of them1 and made various attempts to arrange and methodize the knowledge thus acquired1 and even to deduce some general conclusions respecting the forms they habitually assume3 but from the moment that chemical analysis was applied to resolve them into their constituent elements1 and that1 led by a happy accident1 the genius of ,bergmann discovered the general fact1 that they could be cloven or split in such directions as to lay bare their peculiar primitive or fundamental forms1 7which lay concealed within them1 as the statue might be conceived encrusted in its marble envelope17--from that moment1 mineralogy ceased to be an unmeaning list of names1 a mere laborious cataloguing of stones and rubbish1 and became1 what it now is1 a regular1 methodical1 and most important science1 in which every year is bringing to light new relations1 new laws1 and new practical applications4 7#fh47 ,experience once recognized as the fountain of all our knowledge of nature1 it follows that1 in the study of nature and its laws1 we ought at once to make up our minds to dismiss as idle prejudices1 or at least suspend as premature1 any preconceived notion of what might or what ought to be the order of nature in any proposed case1 and content ourselves with observing1 as a plain matter of fact1 what is4 ,to experience we refer1 as the only ground of all physical enquiry4 ,but before experience itself can be used with advantage1 there is one preliminary step to make1 which depends wholly on ourselves3 it is the absolute dismissal and clearing the mind of all prejudice1 from whatever source arising1 and the determination to stand and fall by the result of a direct appeal to facts in the first instance1 and of strict logical deduction from them afterwards4 ,now1 it is necessary to distinguish between two kinds of prejudices1 which exercise very different dominion over the mind1 and1 moreover1 differ extremely in the difficulty of dispossessing them1 and the process to be gone through for that purpose4 ,these are1-- #a4 ,prejudices of opinion4 #b4 ,prejudices of sense4 7#fi47 ,by prejudices of opinion1 we mean opinions hastily taken up1 either from the assertion of others1 from our own superficial views1 or from vulgar observation1 and which1 from being constantly admitted without dispute1 have obtained the strong hold of habit on our minds4 ,such were the opinions once maintained that the earth is the greatest body in the universe1 and placed immovable in its centre1 and all the rest of the universe created for its sole use2 that it is the nature of fire and of sounds to ascend2 that the moonlight is cold2 that dews fall from the air1 c4 7#gj47 ,to combat and destroy such prejudices we may proceed in two ways1 either by demonstrating the falsehood of the facts alleged in their support1 or by showing how the appearances1 which seem to countenance them1 are more satisfactorily accounted for without their admission4 ,but it is unfortunately the nature of prejudices of opinion to adhere1 in a certain degree1 to every mind1 and to some with pertinacious obstinacy1 pigris radicibus1 after all ground for their reasonable entertainment is destroyed4 ,against such a disposition the student of natural science must contend with all his power4 ,not that we are so unreasonable as to demand of him an instant and peremptory dismission of all his former opinions and judgments2 all we require is1 that he will hold them without bigotry1 retain till he shall see reason to question them1 and be ready to resign them when fairly proved untenable1 and to doubt them when the weight of probability is shown to lie against them4 ,if he refuse this1 he is incapable of science4 7#ga47 ,our resistance against the destruction of the other class of prejudices1 those of sense1 is commonly more violent at first1 but less persistent1 than in the case of those of opinion4 ,not to trust the evidence of our senses1 seems1 indeed1 a hard condition1 and one which1 if proposed1 none would comply with4 ,but it is not the direct evidence of our senses that we are in any case called upon to reject1 but only the erroneous judgments we unconsciously form from them1 and this only when they can be shown to be so by counter evidence of the same sort2 when one sense is brought to testify against another1 for instance2 or the same sense against itself1 and the obvious conclusions in the two cases disagree1 so as to compel us to acknowledge that one or other must be wrong4 ,for example1 nothing at first can seem a more rational1 obvious1 and incontrovertible conclusion1 than that the colour of an object is an inherent quality1 like its weight1 hardness1 c4 and that to see the object1 and see it of its own colour1 when nothing intervenes between our eyes and it1 are one and the same thing4 ,yet this is only a prejudice2 and that it is so1 is shown by bringing forward the same sense of vision which led to its adoption1 as evidence on the other side2 for1 when the differently coloured prismatic rays are thrown1 in a dark room1 in succession upon any object1 whatever be the colour we are in the habit of calling its own1 it will appear of the particular hue of the light which falls upon it3 a yellow paper1 for instance1 will appear scarlet when illuminated by red rays1 yellow when by yellow1 green by green1 and blue by blue rays2 its own 7so called7 proper colour not in the least degree mixing with that it so exhibits4 7#gb47 ,to give one or two more examples of the kind of illusion which the senses practise on us1 or rather which we practise on ourselves1 by a misinterpretation of their evidence3 the moon at its rising and setting appears much larger than when high up in the sky4 ,this is1 however1 a mere erroneous judgment2 for when we come to measure its diameter1 so far from finding our conclusion borne out by fact1 we actually find it to measure materially less4 ,here is eyesight opposed to eyesight1 with the advantage of deliberate measurement4 ,in ventriloquism we have the hearing at variance with all the other senses1 and especially with the sight1 which is sometimes contradicted by it in a very extraordinary and surprising manner1 as when the voice is made to seem to issue from an inanimate and motionless object4 ,if we plunge our hands1 one into ice-cold water1 and the other into water as hot as can be borne1 and1 after letting them stay awhile1 suddenly transfer them both to a vessel full of water at a blood heat1 the one will feel a sensation of heat1 the other of cold4 ,and if we cross the two first fingers of one hand1 and place a pea in the fork between them1 moving and rolling it about on a table1 we shall 7especially if we close our eyes7 be fully persuaded we have two peas4 ,if the nose be held while we are eating cinnamon1 we shall perceive no difference between its flavour and that of a deal shaving4 7#gc47 ,these1 and innumerable instances we might cite1 will convince us1 that though we are never deceived in the sensible impression made by external objects on us1 yet in forming our judgments of them we are greatly at the mercy of circumstances1 which either modify the impressions actually received1 or combine them with adjuncts which have become habitually associated with different judgments2 and1 therefore1 that1 in estimating the degree of confidence we are to place in our conclusions1 we must1 of necessity1 take into account these modifying or accompanying circumstances1 whatever they may be4 ,we do not1 of course1 here speak of deranged organization2 such as1 for instance1 a distortion of the eye1 producing double vision1 and still less of mental delusion1 which absolutely perverts the meaning of sensible impressions4 7#gd47 ,as the mind exists not in the place of sensible objects1 and is not brought into immediate relation with them1 we can only regard sensible impressions as signals conveyed from them by a wonderful1 and1 to us1 inexplicable mechanism1 to our minds1 which receives and reviews them1 and1 by habit and association1 connects them with corresponding qualities or affections in the objects2 just as a person writing down and comparing the signals of a telegraph might interpret their meaning4 ,as1 for instance1 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 ,portsmouth1 he would connect the two facts by a link of the very same nature with that which connects the notion of a large wooden building1 filled with sailors1 with the impression of her outline on the retina of a spectator on the beach4 7#ge47 ,in captain ,head's amusing and vivid description of his journey across the ,pampas of ,south ,america occurs an anecdote quite in point4 ,his guide one day suddenly stopped him1 and1 pointing high into the air1 cried out1 8,a lion60 ,surprised at such an exclamation1 accompanied with such an act1 he turned up his eyes1 and with difficulty perceived1 at an immeasurable height1 a flight of condors soaring in circles in a particular spot4 ,beneath that spot1 far out of sight of himself or guide1 lay the carcass of a horse1 and over that carcass stood 7as the guide well knew7 the lion1 whom the condors were eyeing with envy from their airy height4 ,the signal of the birds was to him what the sight of the lion alone could have been to the traveller1 a full assurance of its existence4 ,,chap4 ,,ii4 ,,of ,,the ,,analysis ,,of ,,phenomena 7#gf47 ,phenomena1 then1 or appearances1 as the word is literally rendered1 are the sensible results of processes and operations carried on among external objects1 or their constituent principles1 of which they are only signals1 conveyed to our minds as aforesaid4 ,now1 these processes themselves may be in many instances rendered sensible2 that is to say1 analysed1 and shown to consist in the motions or other affections of sensible objects themselves4 ,for instance1 the phenomenon of the sound produced by a musical string1 or a bell1 when struck1 may be shown to be the result of a process consisting in the rapid vibratory motion of its parts communicated to the air1 and thence to our ears2 though the immediate effect on our organs of hearing does not excite the least idea of such a motion4 ,on the other hand1 there are innumerable instances of sensible impressions which 7at least at present7 we are incapable of tracing beyond the mere sensation2 for example1 in the sensations of bitterness1 sweetness1 c4 ,these1 accordingly1 if we were inclined to form hasty decisions1 might be regarded as ultimate qualities2 but the instance of sounds1 just adduced1 alone would teach us caution in such decisions1 and incline us to believe them mere results of some secret process going on in our organs of taste1 which is too subtle for us to trace4 ,a simple experiment will serve to set this in a clearer light4 ,a solution of the salt called by chemists nitrate of silver1 and another of the hyposulphite of soda1 have each of them separately1 when taken into the mouth1 a disgustingly bitter taste2 but if they be mixed1 or if one be tasted before the mouth is thoroughly cleared of the other1 the sensible impression is that of intense sweetness4 ,again1 the salt called tungstate of soda when first tasted is sweet1 but speedily changes to an intense and pure bitter1 like quassia4#bi 7#gg47 ,how far we may ever be enabled to attain a knowledge of the ultimate and inward processes of nature in the production of phenomena1 we have no means of knowing2 but1 to judge from the degree of obscurity which hangs about the only case in which we feel within ourselves a direct power to produce any one1 there seems no great hope of penetrating so far4 ,the case alluded to is the production of motion by the exertion of force4 ,we are conscious of a power to move our limbs1 and by their intervention other bodies2 and that this effect is the result of a certain inexplicable process which we are aware of1 but can no way describe in words1 by which we exert force4 ,and even when such exertion produces no visible effect1 7as when we press our two hands violently together1 so as just to oppose each other's effort17 we still perceive1 by the fatigue and exhaustion1 and by the impossibility of maintaining the effort long1 that something is going on within us1 of which the mind is the agent1 and the will the determining cause4 ,this impression which we receive of the nature of force1 from our own effort and our sense of fatigue1 is quite different from that which we obtain of it from seeing the effect of force exerted by others in producing motion4 ,were there no such thing as motion1 had we been from infancy shut up in a dark dungeon1 and every limb encrusted with plaster1 this internal consciousness would give us a complete idea of force2 but when set at liberty1 habit alone would enable us to recognize its exertion by its signal1 motion1 and that 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 muscles1 puts it in our power1 when at liberty1 to move ourselves and other bodies4 ,but how obscure is our knowledge of the process going on within us in the exercise of this important privilege1 in virtue of which alone we act as direct causes1 we may judge from this1 that when we put any limb in motion1 the seat of the exertion seems to us to be in the limb1 whereas it is demonstrably no such thing1 but either in the brain or in the spinal marrow2 the proof of which is1 that if a little fibre1 called a nerve1 which forms a communication between the limb and the brain1 or spine1 be divided in any part of its course1 however we may make the effort1 the limb will not move4 7#gh47 ,this one instance of the obscurity which hangs about the only act of direct causation of which we have an immediate consciousness1 will suffice to show how little prospect there is that1 in our investigation of nature1 we shall ever be able to arrive at a knowledge of ultimate causes1 and will teach us to limit our views to that of laws1 and to the analysis of complex phenomena by which they are resolved into simpler ones1 which1 appearing to us incapable of further analysis1 we must consent to regard as causes4 ,nor let any one complain of this as a limitation of his faculties4 ,we have here 8ample room and verge enough0 for the full exercise of all the powers we possess2 and1 besides1 it does so happen1 that we are actually able to trace up a very large portion of the phenomena of the universe to this one cause1 viz4 the exertion of mechanical force2 indeed1 so large a portion1 that it has been made a matter of speculation whether this is not the only one that is capable of acting on material beings4 7#gi47 ,what we mean by the analysis of complex phenomena into simpler ones1 will best be understood by an instance4 ,let us1 therefore1 take the phenomenon of sound1 and1 by considering the various cases in which sounds of all kinds are produced1 we shall find that they all agree in these points3--#ast1 ,the excitement of a motion in the sounding body4 #b;dly1 ,the communication of this motion to the air or other intermedium which is interposed between the sounding body and our ears4 #c;dly1 ,the propagation of such motion from particle to particle of such intermedium in due succession4 #dthly1 ,its communication1 from the particles of the intermedium adjacent to the ear1 to the ear itself4 #ethly1 ,its conveyance in the ear1 by a certain mechanism1 to the auditory nerves4 #fthly1 ,the excitement of sensation4 ,now1 in this analysis1 we perceive that two principal matters must be understood1 before we can have a true and complete knowledge of sound3--#ast1 ,the excitement and propagation of motion4 #b;dly1 ,the production of sensation4 ,these1 then1 are two other phenomena1 of a simpler1 or1 it would be more correct to say1 of a more general or elementary order1 into which the complex phenomenon of sound resolves itself4 ,but again1 if we consider the communication of motion from body to body1 or from one part to another of the same1 we shall perceive that it is again resolvable into several other phenomena4 #ast1 ,the original setting in motion of a material body1 or any part of one4 #b;dly1 ,the behaviour of a particle set in motion1 when it meets another lying in its way1 or is otherwise impeded or influenced by its connection with surrounding particles4 #c;dly1 ,the behaviour of the particles so impeding or influencing it under such circumstances2 besides which1 the last two point out another phenomenon1 which it is necessary also to consider1 viz4 the phenomenon of the connection of the parts of material bodies in masses1 by which they form aggregates1 and are enabled to influence each other's motions4 7#hj47 ,thus1 then1 we see that an analysis of the phenomenon of sound leads to the enquiry1 #ast1 of two causes1 viz4 the cause of motion1 and the cause of sensation1 these being phenomena which 7at least as human knowledge stands at present7 we are unable to analyse further2 and1 therefore1 we set them down as simple1 elementary1 and referable1 for any thing we can see to the contrary1 to the immediate action of their causes4 #b;dly1 ,of several questions relating to the connection between the motion of material bodies and its cause1 such as1 ,what will happen when a moving body is surrounded on all sides by others not in motion8 ,what will happen when a body not in motion is advanced upon by a moving one8 ,it is evident that the answers to such questions as these can be no other than laws of motion1 in the sense we have above attributed to laws of nature1 viz4 a statement in words of what will happen in such and such proposed general contingencies4 ,lastly1 we are led1 by pursuing the analysis1 and considering the phenomenon of the aggregation of the parts of material bodies1 and the way in which they influence each other1 to two other general phenomena1 viz41 the cohesion and elasticity of matter2 and these we have no means of analysing further1 and must1 therefore1 regard them 7till we see reasons to the contrary7 as ultimate phenomena1 and referable to the direct action of causes1 viz4 an attractive and a repulsive force4 7#ha47 ,of force1 as counterbalanced by opposing force1 we have1 as already said1 an internal consciousness2 and though it may seem strange to us that matter should be capable of exerting on matter the same kind of effort1 which1 judging alone from this consciousness1 we might be led to regard as a mental one2 yet we cannot refuse the direct evidence of our senses1 which shows us that when we keep a spring stretched with one hand1 we feel our effort opposed exactly in the same way as if we had ourselves opposed it with the other hand1 or as it would be by that of another person4 ,the enquiry1 therefore1 into the aggregation of matter resolves itself into the general question1 ,what will be the behaviour of material particles under the mutual action of opposing forces capable of counterbalancing each other8 and the answer to this question can be no other than the announcement of the law of equilibrium1 whatever law that may be4 7#hb47 ,with regard to the cause of sensation1 it must be regarded as much more obscure than that of motion1 inasmuch as we have no conscious knowledge of it1 i4 e4 we have no power1 by any act of our minds and will1 to call up a sensation4 ,it is true1 we are not destitute of an approach to it1 since1 by an effort of memory and imagination1 we can produce in our minds an impression1 or idea1 of a sensation which1 in peculiar cases1 may even approach in vividness to actual reality4 ,in dreams1 too1 and1 in some cases of disordered nerves1 we have sensations without objects4 ,but if force1 as a cause of motion1 is obscure to us1 even while we are in the act of exercising it1 how much more so is this other cause1 whose exercise we can only imitate imperfectly by any voluntary act1 and of whose purely internal action we are only fully conscious when in a state that incapacitates us from reasoning1 and almost from observation6 7#hc47 ,dismissing1 then1 as beyond our reach1 the enquiry into causes1 we must be content at present to concentrate our attention on the laws which prevail among phenomena1 and which seem to be their immediate results4 ,from the instance we have just given1 we may perceive that every enquiry into the intimate nature of a complex phenomenon branches out into as many different and distinct enquiries as there are simple or elementary phenomena into which it may be analysed2 and that1 therefore1 it would greatly assist us in our study of nature1 if we could1 by any means1 ascertain what are the ultimate phenomena into which all the composite ones presented by it may be resolved4 ,there is1 however1 clearly no way by which this can be ascertained priori4 ,we must go to nature itself1 and be guided by the same kind of rule as the chemist in his analysis1 who accounts every ingredient an element till it can be decompounded and resolved into others4 ,so1 in natural philosophy1 we must account every phenomenon an elementary or simple one till we can analyse it1 and show that it is the result of others1 which in their turn become elementary4 ,thus1 in a modified and relative sense1 we may still continue to speak of causes1 not intending thereby those ultimate principles of action on whose exertion the whole frame of nature depends1 but of those proximate links which connect phenomena with others of a simpler1 higher1 and more general or elementary kind4 ,for example3 we may regard the vibration of a musical string as the proximate cause of the sound it yields1 receiving it1 so far1 as an ultimate fact1 and waving or deferring enquiry into the cause of vibrations1 which is of a higher and more general nature4 7#hd47 ,moreover1 as in chemistry we are sometimes compelled to acknowledge the existence of elements different from those already identified and known1 though we cannot insulate them1 and to perceive that substances have the characters of compounds1 and must therefore be susceptible of analysis1 though we do not see how it is to be set about2 so1 in physics1 we may perceive the complexity of a phenomenon1 without being able to perform its analysis4 ,for example3 in magnetism1 the agency of electricity is clearly made out1 and they are shown to stand to one another in the relation of effect and cause4 ,but the analysis of magnetism1 in its relation to particular metals1 is not yet quite satisfactorily performed2 and we are compelled to admit the existence of some cause1 whether proximate or ultimate1 whose presence in different metals1 or in different states of the same metal1 determines that peculiar electric condition which constitutes permanent magnetism4 ,cases like these1 of all which science presents1 offer the highest interest4 ,they excite enquiry1 like the near approach to the solution of an enigma2 they show us that there is light1 could only a certain veil be drawn aside4 7#he47 ,in pursuing the analysis of any phenomenon1 the moment we find ourselves stopped by one of which we perceive no analysis1 and which1 therefore1 we are forced to refer 7at least provisionally7 to the class of ultimate facts1 and to regard as elementary1 the study of that phenomenon and of its laws becomes a separate branch of science4 ,if we encounter the same elementary phenomenon in the analysis of several composite ones1 it becomes still more interesting1 and assumes additional importance2 while at the same time we acquire information respecting the phenomenon itself1 by observing those with which it is habitually associated1 that may help us at length to its analysis4 ,it is thus that sciences increase1 and acquire a mutual relation and dependency4 ,it is thus1 too1 that we are at length enabled to trace parallels and analogies between great branches of science themselves1 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 separately4 ,it was thus1 for example1 that1 previous to ,orsted's great discovery of electro-magnetism1 a general resemblance between the two sciences of electricity and magnetism was recognised1 and many of the chief phenomena in each were ascertained to have their parallels1 mutatis mutandis1 in the other4 ,it was thus1 too1 that an analogy subsisting between sound and light has been gradually traced into a closeness of agreement1 which can hardly leave any reasonable doubt of their ultimate coincidence in one common phenomenon1 the vibratory motion of an elastic medium4 ,if it be allowed to pursue our illustration from chemistry1 and to ground its application not on what has been1 but on what may one day be1 done1 it is thus that the general family resemblance between certain groups of bodies1 now regarded as elementary1 7as nickel and cobalt1 for instance1 chlorine1 iode1 and brome17 will1 perhaps1 lead us hereafter to perceive relations between them of a more intimate kind than we can at present trace4 7#hf47 ,on those phenomena which are most frequently encountered in an analysis of nature and which most decidedly resist further decomposition1 it is evident that the greatest pains and attention ought to be bestowed1 not only because they furnish a key to the greatest number of enquiries1 and serve to group and classify together the greatest range of phenomena1 but by reason of their higher nature1 and because it is in these that we must look for the direct action of causes1 and the most extensive and general enunciation of the laws of nature4 ,these1 once discovered1 place in our power the explanation of all particular facts1 and become grounds of reasoning1 independent of particular trial3 thus playing the same part in natural philosophy that axioms do in geometry2 containing1 in a refined and condensed state1 and as it were in a quintessence1 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 argument4 ,indeed1 the axioms of geometry themselves may be regarded as in some sort an appeal to experience1 not corporeal1 but mental4 ,when we say1 the whole is greater than its part1 we announce a general fact1 which rests1 it is true1 on our ideas of whole and part2 but1 in abstracting these notions1 we begin by considering them as subsisting in space1 and time1 and body1 and again1 in linear1 and superficial1 and solid space4 ,again1 when we say1 the equals of equals are equal1 we mentally make comparisons1 in equal spaces1 equal times1 c42 so that these axioms1 however self-evident1 are still general propositions so far of the inductive kind1 that1 independently of experience1 they would not present themselves to the mind4 ,the only difference between these and axioms obtained from extensive induction is this1 that1 in raising the axioms of geometry1 the instances offer themselves spontaneously1 and without the trouble of search1 and are few and simple2 in raising those of nature1 they are infinitely numerous1 complicated1 and remote2 so that the most diligent research and the utmost acuteness are required to unravel their web1 and place their meaning in evidence4 7#hg47 ,by far the most general phenomenon with which we are acquainted1 and that which occurs most constantly1 in every enquiry into which we enter1 is motion1 and its communication4 ,dynamics1 then1 or the science of force and motion1 is thus placed at the head of all the sciences2 and1 happily for human knowledge1 it is one in which the highest certainty is attainable1 a certainty no way inferior to mathematical demonstration4 ,as its axioms are few1 simple1 and in the highest degree distinct and definite1 so they have at the same time an immediate relation to geometrical quantity1 space1 time1 and direction1 and thus accommodate themselves with remarkable facility to geometrical reasoning4 ,accordingly1 their consequences may be pursued1 by arguments purely mathematical1 to any extent1 insomuch that the limit of our knowledge of dynamics is determined only by that of pure mathematics1 which is the case in no other branch of physical science4 7#hh47 ,but1 it will now be asked1 how we are to proceed to analyse a composite phenomenon into simpler ones1 and whether any general rules can be given for this important process8 ,we answer1 ,none2 any more than 7to pursue the illustration we have already had recourse to7 general rules can be laid down by the chemist for the analysis of substances of which all the ingredients are unknown4 ,such rules1 could they be discovered1 would include the whole of natural science2 but we are very far1 indeed1 from being able to propound them4 ,however1 we are to recollect that the analysis of phenomena1 philosophically speaking1 is principally useful1 as it enables us to recognize1 and mark for special investigation1 those which appear to us simple2 to set methodically about determining their laws1 and thus to facilitate the work of raising up general axioms1 or forms of words1 which shall include the whole of them2 which shall1 as it were1 transplant them out of the external into the intellectual world1 render them creatures of pure thought1 and enable us to reason them out priori4 ,and what renders the power of doing this so eminently desirable is1 that1 in thus reasoning back from generals to particulars1 the propositions at which we arrive apply to an immense multitude of combinations and cases1 which were never individually contemplated in the mental process by which our axioms were first discovered2 and that1 consequently1 when our reasonings are pushed to the utmost limit of particularity1 their results appear in the form of individual facts1 of which we might have had no knowledge from immediate experience2 and thus we are not only furnished with the explanation of all known facts1 but with the actual discovery of such as were before unknown4 ,a remarkable example of this has already been mentioned in ,fresnel's priori discovery of the extraordinary refraction of both rays in a doubly refracting medium4 ,to give another example3--,the law of gravitation is a physical axiom of a very high and universal kind1 and has been raised by a succession of inductions and abstractions drawn from the observation of numerous facts and subordinate laws in the planetary system4 ,when this law is taken for granted1 and laid down as a basis of reasoning1 and applied to the actual condition of our own planet1 one of the consequences to which it leads is1 that the earth1 instead of being an exact sphere1 must be compressed or flattened in the direction of its polar diameter1 the one diameter being about thirty miles shorter than the other2 and this conclusion1 deduced at first by mere reasoning1 has been since found to be true in fact4 ,all astronomical predictions are examples of the same thing4 7#hi47 ,in the important business of raising these axioms of nature1 we are not1 as in the analysis of phenomena1 left wholly without a guide4 ,the nature of abstract or general reasoning points out in a great measure the course we must pursue4 ,a law of nature1 being the statement of what will happen in certain general contingencies1 may be regarded as the announcement1 in the same words1 of a whole group or class of phenomena4 ,whenever1 therefore1 we perceive that two or more phenomena agree in so many or so remarkable points1 as to lead us to regard them as forming a class or group1 if we lay out of consideration1 or abstract1 all the circumstances in which they disagree1 and retain in our minds those only in which they agree1 and then1 under this kind of mental convention1 frame a definition or statement of one of them1 in such words that it shall apply equally to them all1 such statement will appear in the form of a general proposition1 having so far at least the character of a law of nature4 7#ij47 ,for example3 a great number of transparent substances1 when exposed1 in a certain particular manner1 to a beam of light which has been prepared by undergoing certain reflexions or refractions1 7and has thereby acquired peculiar properties1 and is said to be 8polarized107 exhibit very vivid and beautiful colours1 disposed in streaks1 bands1 c4 of great regularity1 which seem to arise within the substance1 and which1 from a certain regular succession observed in their appearance1 are called 8periodical colours40 ,among the substances which exhibit these periodical colours occur a great variety of transparent solids1 but no fluids and no opake solids4 ,here1 then1 there seems to be sufficient community of nature to enable us to use a general term1 and to state the proposition as a law1 viz4 transparent solids exhibit periodical colours by exposure to polarized light4 ,however1 this1 though true of many1 does not apply to all transparent solids1 and therefore we cannot state it as a general truth or law of nature in this form2 although the reverse proposition1 that all solids which exhibit such colours in such circumstances are transparent1 would be correct and general4 ,it becomes necessary1 then1 to make a list of those to which it does apply2 and thus a great number of substances of all kinds become grouped together1 in a class linked by this common property4 ,if we examine the individuals of this group1 we find among them the utmost variety of colour1 texture1 weight1 hardness1 form and composition2 so that1 in these respects1 we seem to have fallen upon an assemblage of contraries4 ,but when we come to examine them closely1 in all their properties1 we find they have all one point of agreement1 in the property of double refraction1 7see page #cj47 and therefore we may describe them all truly as doubly refracting substances4 ,we may1 therefore1 state the fact in the form1 8,doubly refracting substances exhibit periodical colours by exposure to polarized light20 and in this form it is found1 on further examination1 to be true1 not only for those particular instances which we had in view when we first propounded it1 but in all cases which have since occurred on further enquiry1 without a single exception2 so that the proposition is general1 and entitled to be regarded as a law of nature4 7#ia47 ,we may therefore regard a law of nature either1 #ast1 as a general proposition1 announcing1 in abstract terms1 a whole group of particular facts relating to the behaviour of natural agents in proposed circumstances2 or1 #b;dly1 as a proposition announcing that a whole class of individuals agreeing in one character agree also in another4 ,for example3 in the case before us1 the law arrived at includes1 in its general announcement1 among others1 the particular facts1 that rock crystal and saltpetre exhibit periodical colours2 for these are both of them doubly refracting substances4 ,or1 it may be regarded as announcing a relation between the two phenomena of double refraction1 and the exhibition of periodical colours2 which in the actual case is one of the most important1 viz4 the relation of constant association1 inasmuch as it asserts that in whatever individual the one character is found1 the other will invariably be found also4 7#ib47 ,these two lights1 in which the announcement of a general law may be regarded1 though at bottom they come to the same thing1 yet differ widely in their influence on our minds4 ,the former exhibits a law as little more than a kind of artificial memory2 but in the latter it becomes a step in philosophical investigation1 leading directly to the consideration of a proximate1 if not an ultimate1 cause2 inasmuch as1 whenever two phenomena are observed to be invariably connected together1 we conclude them to be related to each other1 either as cause and effect1 or as common effects of a single cause4 7#ic47 ,there is still another light in which we may regard a law of the kind in question1 viz4 as a proposition asserting the mutual connection1 or in some cases the entire identity1 of two classes of individuals 7whether individual objects or individual facts72 and this is1 perhaps1 the simplest and most instructive way in which it can be conceived1 and that which furnishes the readiest handle to further generalization in the raising of yet higher axioms4 ,for example3 in the case above mentioned1 if observation had enabled us to establish the existence of a class of bodies possessing the property of double refraction1 and observations of another kind had1 independently of the former1 led as to recognize a class possessing that of the exhibition of periodical colours in polarized light1 a mere comparison of lists would at once demonstrate the identity of the two classes1 or enable us to ascertain whether one was or was not included in the other4 7#id47 ,it is thus we perceive the high importance in physical science of just and accurate classifications of particular facts1 or individual objects1 under general well considered heads or points of agreement 7for which there are none better adapted than the simple phenomena themselves into which they can be analysed in the first instance72 for by so doing each of such phenomena1 or heads of classification1 becomes not a particular but a general fact2 and when we have amassed a great store of such general facts1 they become the objects of another and higher species of classification1 and are themselves included in laws which1 as they dispose of groups1 not individuals1 have a far superior degree of generality1 till at length1 by continuing the process1 we arrive at axioms of the highest degree of generality of which science is capable4 7#ie47 ,this process is what we mean by induction2 and1 from what has been said1 it appears that induction may be carried on in two different ways1--either by the simple juxta-position and comparison of ascertained classes1 and marking their agreements and disagreements2 or by considering the individuals of a class1 and casting about1 as it were to find in what particular they all agree1 besides that which serves as their principle of classification4 ,either of these methods may be put in practice as one or the other may afford facilities in any case2 but it will naturally happen that1 where facts are numerous1 well observed1 and methodically arranged1 the former will be more applicable than in the contrary case3 the one is better adapted to the maturity1 the other to the infancy1 of science3 the one employs1 as an engine1 the division of labour2 the other mainly relies on individual penetration1 and requires a union of many branches of knowledge in one person4 ,,chap4 ,,iii4 ,,of ,,the ,,state ,,of ,,physical ,,science ,,in ,,general1 ,,previous ,,to ,,the ,,age ,,of ,,galileo ,,and ,,bacon4 7#if47 ,it is to our immortal countryman ,bacon that we owe the broad announcement of this grand and fertile principle2 and the developement of the idea1 that the whole of natural philosophy consists entirely of a series of inductive generalizations1 commencing with the most circumstantially stated particulars1 and carried up to universal laws1 or axioms1 which comprehend in their statements every subordinate degree of generality1 and of a corresponding series of inverted reasoning from generals to particulars1 by which these axioms are traced back into their remotest consequences1 and all particular propositions deduced from them2 as well those by whose immediate consideration we rose to their discovery1 as those of which we had no previous knowledge4 ,in the course of this descent to particulars1 we must of necessity encounter all those facts on which the arts and works that tend to the accommodation of human life depend1 and acquire thereby the command of an unlimited practice1 and a disposal of the powers of nature co-extensive with those powers themselves4 ,a noble promise1 indeed1 and one which ought1 surely1 to animate us to the highest exertion of our faculties2 especially since we have already such convincing proof that it is neither vain nor rash1 but1 on the contrary1 has been1 and continues to be1 fulfilled1 with a promptness and liberality which even its illustrious author in his most sanguine mood would have hardly ventured to anticipate4 7#ig47 ,previous to the publication of the ,novum ,organum of ,bacon1 natural philosophy1 in any legitimate and extensive sense of the word1 could hardly be said to exist4 ,among the ,greek philosophers1 of whose attainments in science alone1 in the earlier ages of the world1 we have any positive knowledge1 and that but a very limited one1 we are struck with the remarkable contrast between their powers of acute and subtle disputation1 their extraordinary success in abstract reasoning1 and their intimate familiarity with subjects purely intellectual1 on the one hand2 and1 on the other1 with their loose and careless consideration of external nature1 their grossly illogical deductions of principles of sweeping generality from few and ill-observed facts1 in some cases2 and their reckless assumption of abstract principles having no foundation but in their own imaginations1 in others2 mere forms of words1 with nothing corresponding to them in nature1 from which1 as from mathematical definitions1 postulates1 and axioms1 they imagined that all phenomena could be derived1 all the laws of nature deduced4 ,thus1 for instance1 having settled it in their own minds1 that a circle is the most perfect of figures1 they concluded1 of course1 that the movements of the heavenly bodies must all be performed in exact circles1 and with uniform motions2 and when the plainest observation demonstrated the contrary1 instead of doubting the principle1 they saw no better way of getting out of the difficulty than by having recourse to endless combinations of circular motions to preserve their ideal perfection4 7#ih47 ,undoubtedly among the ,greek philosophers were many men of transcendent talents and virtues1 the ornaments of their species1 and justly entitled to the veneration of all posterity2 but regarded as a body they can hardly be considered otherwise than as a knot of disputatious candidates for popular favour1 too busy in maintaining their ascendency over their followers and admirers1 by an ostentatious display of superior knowledge1 to have the leisure 7had they always the inclination7 to base their pretensions on a deep and sure foundation1 and yet too sensible of the disgrace and inconvenience of failure1 not to defend their dogmas1 however shallow1 when once promulgated1 against their keen and sagacious opponents1 by every art of sophism or appeal to passion4 ,hence the crudities and chimerical views with which their systems of philosophy1 both natural and moral1 were overloaded2 their endless disputes about verbal subtleties1 and1 last and worst1 the proud assumption with which they sheltered ignorance and indolence under the screen of unintelligible jargon or dogmatical assertion4 ,perhaps1 however1 this character applies rather to the later than to the earlier of the ,greek philosophers4 ,the spirit of rational enquiry into nature seems1 if we can judge from the uncertain and often contradictory notices handed down to us of their tenets1 to have been far more alive1 and less warped by this vain and arrogant turn1 then than at a later period4 ,we know not now what was the precise meaning attached by ,thales to his opinion1 that water was the origin of all things2 but modern geologists will not be at a loss to conceive how an observant traveller might become impressed with this notion1 without having recourse to the mystic records of ,egypt or ,chaldea4 ,his ideas of eclipses and of the nature of the moon were sound2 and his prediction of an eclipse of the sun1 in particular1 was attended with circumstances so remarkable as to have made it a matter of important investigation to modern astronomers4 ,anaxagoras1 among a number of crude and imperfectly explained notions1 speculated rationally enough on the cause of the winds and of the rainbow1 and less absurdly on earthquakes than many modern geologists have done1 and appears generally to have had his attention alive to nature1 and his mind open to just reasoning on its phenomena2 while ,pythagoras1 whether he reasoned it out for himself1 or borrowed the notion from ,egypt or ,india1 had attained a just conception of the general disposition of the parts of the solar system1 and the place held by the earth in it2 nay1 according to some accounts1 had even raised his views so far as to speculate on the attraction of the sun as the bond of its union4 7#ii47 ,but the successors of these bon fide enquirers into nature debased the standard of truth2 and1 taking advantage of the credit justly attached to their discoveries1 renounced the modest character of learners1 and erected themselves into teachers1 and1 to maintain their pretensions to this character1 adopted the tone of men who had nothing further to learn4 ,unfortunately for true science1 the national character gave every encouragement to pretensions of this kind4 ,that restless craving after novelty1 which distinguished the ,greeks in their civil and political relations1 pursued them into their philosophy4 ,whatever speculations were only ingenious and new had irresistible charms2 and the teacher who could embody a clever thought in elegant language1 or at once save his followers and himself the trouble of thinking or reasoning1 by bold assertion1 was too often induced to acquire cheaply the reputation of superior knowledge1 snatch a few superficial notions from the most ordinary and obvious facts1 envelope them in a parade of abstruse words1 declare them the primary and ultimate principles of all things1 and denounce as absurd and impious all opinions opposed to his own4 7#ajj47 ,in this war of words the study of nature was neglected1 and an humble and patient enquiry after facts altogether despised1 as unworthy of the high priori ground a true philosopher ought to take4 ,it was the radical error of the ,greek philosophy to imagine that the same method which proved so eminently successful in mathematical1 would be equally so in physical1 enquiries1 and that1 by setting out from a few simple and almost self-evident notions1 or axioms1 every thing could be reasoned out4 ,accordingly1 we find them constantly straining their invention to discover these principles1 which were to prove so pregnant4 ,one makes fire the essential matter and origin of the universe2 another1 air2 a third1 discovers the key to every difficulty1 and the explanation of all phenomena1 in the 8 0 or infinitude of things2 a fourth1 in the and the 1 that is to say1 in entity and nonentity2--till at length an authority1 which was destined to command opinions for nearly two thousand years1 settled this important point1 by deciding1 that matter1 form1 and privation1 were to be considered the principles of all things4 7#aja47 ,it were to do injustice to ,aristotle1 however1 to judge of him by such a sample of his philosophy4 ,he1 at least1 saw the necessity of having recourse to nature for something like principles of physical science2 and1 as an observer1 a collector and recorder of facts and phenomena1 stood without an equal in his age4 ,it was the fault of that age1 and of the perverse and flimsy style of verbal disputation which had infected all learning1 rather than his own1 that he allowed himself to be contented with vague and loose notions drawn from general and vulgar observation1 in place of seeking carefully1 in well arranged and thoroughly considered instances1 for the true laws of nature4 ,his voluminous works1 on every department of human knowledge existing in his time1 have nearly all perished4 ,from his work on animals1 which has descended to us1 we are1 however1 enabled to appreciate his powers of observation2 and a parallel drawn by an eminent ,oxford professor between his classifications and those of the most illustrious of living naturalists1 shows him to have attained a view of animated nature in a remarkable degree comprehensive1 and which contrasts strikingly with the confusion1 vagueness1 and assumption of his physical opinions and dogmas4 ,in these it is easy to recognize a mind not at home1 and an impression of the necessity of saying something learned and systematic1 without knowing what to say4 ,thus he divides motions into natural and unnatural2 the natural motion of fire and light bodies being upwards1 those of heavy downwards1 each seeking its kindred nature in the heavens and the earth4 ,thus1 too1 the immediate impressions made on us by external objects1 such as hardness1 colour1 heat1 c4 are referred at once1 in the ,aristotelian philosophy1 to occult qualities1 in virtue of which they are as they are1 and beyond which it is useless to enquire4#cj ,of course there will occur a limit beyond which it is useless for merely human faculties to enquire2 but where that limit is placed1 experience alone can teach us2 and at least to assert that we have attained it1 is now universally recognized as the sure criterion of dogmatism4 7#ajb47 ,in the early ages of the church the writings of ,aristotle were condemned1 as allowing too much to reason and sense2 and even so late as the twelfth century they were sought out and burned1 and their readers excommunicated4 ,by degrees1 however1 the extreme injustice of this impeachment of their character was acknowledged3 they became the favourite study of the schoolmen1 and furnished the keenest weapons of their controversy1 being appealed to in all disputes as of sovereign authority2 so that the slightest dissent from any opinion of the 8great master10 however absurd or unintelligible1 was at once drowned by clamour1 or silenced by the still more effectual argument of bitter persecution4 ,if the logic of that gloomy period could be justly described as 8the art of talking unintelligibly on matters of which we are ignorant10 its physics might1 with equal truth1 be summed up in a deliberate preference of ignorance to knowledge1 in matters of every day's experience and use4 7#ajc47 ,in 8this opake of nature and of soul10 the perverse activity of the alchemists from time to time struck out a doubtful spark#ca2 and our illustrious countryman1 ,roger ,bacon1 shone out at the obscurest moment1 like an early star predicting dawn4 ,it was not1 however1 till the sixteenth century that the light of nature began to break forth with a regular and progressive increase4 ,the vaunts of ,paracelsus of the power of his chemical remedies and elixirs1 and his open condemnation of the ancient pharmacy1 backed as they were by many surprising cures1 convinced all rational physicians that chemistry could furnish many excellent remedies1 unknown till that time#cb1 and a number of valuable experiments began to be made by physicians and chemists1 desirous of discovering and describing new chemical remedies4 ,the chemical and metallurgic arts1 exercised by persons empirically acquainted with their secrets1 began to be seriously studied with a view to the acquisition of rational and useful knowledge1 and regular treatises on branches of natural science at length to appear4 ,george ,agricola1 in particular1 devoted himself with ardour to the study of mineralogy and metallurgy in the mining districts of ,bohemia and ,schemnitz1 and published copious and methodical accounts of all the facts within his knowledge3 and our countryman1 ,dr4 ,gilbert of ,colchester1 in #aeij1 published a treatise on magnetism1 full of valuable facts and experiments1 ingeniously reasoned on2 and he likewise extended his enquiries to a variety of other subjects1 in particular to electricity4 7#ajd47 ,but1 as the decisive mark of a great commencing change in the direction of the human faculties1 astronomy1 the only science in which the ancients had made any real progress1 and ascended to any thing like large and general conceptions1 began once more to be studied in the best spirit of a candid philosophy2 and the ,copernican or ,pythagorean system arose or revived1 and rapidly gained advocates4 ,galileo at length appeared1 and openly attacked and refuted the ,aristotelian dogmas respecting motion1 by direct appeal to the evidence of sense1 and by experiments of the most convincing kind4 ,the persecutions which such a step drew upon him1 the record of his perseverance and sufferings1 and the ultimate triumph of his opinions and reasonings1 have been too lately and too well related#cc to require repetition here4 7#aje47 ,by the discoveries of ,copernicus1 ,kepler1 and ,galileo1 the errors of the ,aristotelian philosophy were effectually overturned on a plain appeal to the facts of nature2 but it remained to show on broad and general principles1 how and why ,aristotle was in the wrong2 to set in evidence the peculiar weakness of his method of philosophizing1 and to substitute in its place a stronger and better4 ,this important task was executed by ,francis ,bacon1 ,lord ,verulam1 who will1 therefore1 justly be looked upon in all future ages as the great reformer of philosophy1 though his own actual contributions to the stock of physical truths were small1 and his ideas of particular points strongly tinctured with mistakes and errors1 which were the fault rather of the general want of physical information of the age than of any narrowness of view on his own part2 and of this he was fully aware4 ,it has been attempted by some to lessen the merit of this great achievement1 by showing that the inductive method had been practised in many instances1 both ancient and modern1 by the mere instinct of mankind2 but it is not the introduction of inductive reasoning1 as a new and hitherto untried process1 which characterizes the ,baconian philosophy1 but his keen perception1 and his broad and spirit-stirring1 almost enthusiastic1 announcement of its paramount importance1 as the alpha and omega of science1 as the grand and only chain for the linking together of physical truths1 and the eventual key to every discovery and every application4 ,those who would deny him his just glory on such grounds would refuse to ,jenner or to ,howard their civic crowns1 because a few farmers in a remote province had1 time out of mind1 been acquainted with vaccination1 or philanthropists1 in all ages1 had occasionally visited the prisoner in his dungeon4 7#ajf47 ,an immense impulse was now given to science1 and it seemed as if the genius of mankind1 long pent up1 had at length rushed eagerly upon ,nature1 and commenced1 with one accord1 the great work of turning up her hitherto unbroken soil1 and exposing the treasures so long concealed4 ,a general sense now prevailed of the poverty and insufficiency of existing knowledge in matters of fact2 and1 as information flowed fast in1 an era of excitement and wonder commenced1 to which the annals of mankind had furnished nothing similar4 ,it seemed1 too1 as if ,nature herself seconded the impulse2 and1 while she supplied new and extraordinary aids to those senses which were henceforth to be exercised in her investigation1--while the telescope and the microscope laid open the infinite in both directions1--as if to call attention to her wonders1 and signalize the epoch1 she displayed the rarest1 the most splendid and mysterious1 of all astronomical phenomena1 the appearance and subsequent total extinction of a new and brilliant fixed star twice within the lifetime of ,galileo himself4#cd 7#ajg47 ,the immediate followers of ,bacon and ,galileo ransacked all nature for new and surprising facts1 with something of that craving for the marvellous1 which might be regarded as a remnant of the age of alchemy and natural magic1 but which1 under proper regulation1 is a most powerful and useful stimulus to experimental enquiry4 ,boyle1 in particular1 seemed animated by an enthusiasm of ardour1 which hurried him from subject to subject1 and from experiment to experiment1 without a moment's intermission1 and with a sort of undistinguishing appetite2 while ,hooke 7the great contemporary1 and almost the worthy rival1 of ,newton7 carried a keener eye of scrutinizing reason into a range of research even yet more extensive4 ,as facts multiplied1 leading phenomena became prominent1 laws began to emerge1 and generalizations to commence2 and so rapid was the career of discovery1 so signal the triumph of the inductive philosophy1 that a single generation and the efforts of a single mind sufficed for the establishment of the system of the universe1 on a basis never after to be shaken4 7#ajh47 ,we shall now endeavour to enumerate and explain in detail the principal steps by which legitimate and extensive inductions are arrived at1 and the processes by which the mind1 in the investigation of natural laws1 purges itself by successive degrees of the superfluities and incumbrances which hang about particulars1 and obscure the perception of their points of resemblance and connection4 ,we shall state the helps which may be afforded us1 in a work of so much thought and labour1 by a methodical course of proceeding1 and by a careful notice of those means which have at any time been found successful1 with a view to their better understanding and adaptation to other cases3 a species of mental induction of no mean utility and extent in itself2 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 truth1 and of the rules1 so far as they extend1 to which invention is reducible4 ,in doing this1 we shall commence at the beginning1 with experience itself1 considered as the accumulation of the knowledge of individual objects and facts4 ,,chap4 ,,iv4 ,,of ,,the ,,observation ,,of ,,facts ,,and ,,the ,,collection ,,of ,,instances4 7#aji47 ,nature offers us two sorts of subjects of contemplation in the external world1--objects1 and their mutual actions4 ,but1 after what has been said on the subject of sensation1 the reader will be at no loss to perceive that we know nothing of the objects themselves which compose the universe1 except through the medium of the impressions they excite in us1 which impressions are the results of certain actions and processes in which sensible objects and the material parts of ourselves are directly concerned4 ,thus1 our observation of external nature is limited to the mutual action of material objects on one another2 and to facts1 that is1 the associations of phenomena or appearances4 ,we gain no information by perceiving merely that an object is black2 but if we also perceive it to be fluid1 we at least acquire the knowledge that blackness is not incompatible with fluidity1 and have thus made a step1 however trifling1 to a knowledge of the more intimate nature of these two qualities4 ,whenever1 therefore1 we would either analyse a phenomenon into simpler ones1 or ascertain what is the course or law of nature under any proposed general contingency1 the first step is to accumulate a sufficient quantity of well ascertained facts or recorded instances1 bearing on the point in question4 ,common sense dictates this1 as affording us the means of examining the same subject in several points of view2 and it would also dictate1 that the more different these collected facts are in all other circumstances but that which forms the subject of enquiry1 the better2 because they are then in some sort brought into contrast with one another in their points of disagreement1 and thus tend to render those in which they agree more prominent and striking4 7#aaj47 ,the only facts which can ever become useful as grounds of physical enquiry are those which happen uniformly and invariably under the same circumstances4 ,this is evident3 for if they have not this character they cannot be included in laws2 they want that universality which fits them to enter as elementary particles into the constitution of those universal axioms which we aim at discovering4 ,if one and the same result does not constantly happen under a given combination of circumstances1 apparently the same1 one of two things must be supposed1--caprice 7i4 e4 the arbitrary intervention of mental agency71 or differences in the circumstances themselves1 really existing1 but unobserved by us4 ,in either case1 though we may record such facts as curiosities1 or as awaiting explanation when the difference of circumstances shall be understood1 we can make no use of them in scientific enquiry4 ,hence1 whenever we notice a remarkable effect of any kind1 our first question ought to be1 ,can it be reproduced8 ,what are the circumstances under which it has happened8 ,and will it always happen again if those circumstances1 so far as we have been able to collect them1 co-exist8 7#aaa47 ,the circumstances1 then1 which accompany any observed fact1 are main features in its observation1 at least until it is ascertained by sufficient experience what circumstances have nothing to do with it1 and might therefore have been left unobserved without sacrificing the fact4 ,in observing and recording a fact1 therefore1 altogether new1 we ought not to omit any circumstance capable of being noted1 lest some one of the omitted circumstances should be essentially connected with the fact1 and its omission should1 therefore1 reduce the implied statement of a law of nature to the mere record of an historical event4 ,for instance1 in the fall of meteoric stones1 flashes of fire are seen proceeding from a cloud1 and a loud rattling noise like thunder is heard4 ,these circumstances1 and the sudden stroke and destruction ensuing1 long caused them to be confounded with an effect of lightning1 and called thunderbolts4 ,but one circumstance is enough to mark the difference3 the flash and sound have been perceived occasionally to emanate from a very small cloud insulated in a clear sky2 a combination of circumstances which never happens in a thunder storm1 but which is undoubtedly intimately connected with their real origin4 7#aab47 ,recorded observation consists of two distinct parts3 #ast1 an exact notice of the thing observed1 and of all the particulars which may be supposed to have any natural connection with it2 and1 #b;dly1 a true and faithful record of them4 ,as our senses are the only inlets by which we receive impressions of facts1 we must take care1 in observing1 to have them all in activity1 and to let nothing escape notice which affects any one of them4 ,thus1 if lightning were to strike the house we inhabit1 we ought to notice what kind of light we saw--whether a sheet of flame1 a darting spark1 or a broken zig-zag2 in what direction moving1 to what objects adhering1 its colour1 its duration1 c42 what sounds were heard--explosive1 crashing1 rattling1 momentary1 or gradually increasing and fading1 c42 whether any smell of fire was perceptible1 and if sulphureous1 metallic1 or such as would arise merely from substances scorched by the flash1 c42 whether we felt any shock1 stroke1 or peculiar sensation1 or experienced any strange taste in our mouths4 ,then1 besides detailing the effects of the stroke1 all the circumstances which might in any degree seem likely to attract1 produce1 or modify it1 such as the presence of conductors1 neighbouring objects1 the state of the atmosphere1 the barometer1 thermometer1 c41 and the disposition of the clouds1 should be noted2 and after all this particularity1 the question how the house came to be struck8 might ultimately depend on the fact that a flash of lightning twenty miles off passed at that particular moment from the ground to the clouds1 by an effect of what has been termed the returning stroke4 7#aac47 ,a writer in the ,edinburgh ,philosophical ,journal#ce states himself to have been led into a series of investigations on the chemical nature of a peculiar acid1 by noticing1 accidentally1 a bitter taste in a liquid about to be thrown away4 ,chemistry is full of such incidents4 7#aad47 ,in transient phenomena1 if the number of particulars be great1 and the time to observe them short1 we must consult our memory before they have had time to fade1 or refresh it by placing ourselves as nearly as possible in the same circumstances again2 go back to the spot1 for instance1 and try the words of our statement by appeal to all remaining indications1 c4 ,this is most especially necessary where we have not observed ourselves1 but only collect and record the observations of others1 particularly of illiterate or prejudiced persons1 on any rare phenomenon1 such as the passing of a great meteor1--the fall of a stone from the sky1--the shock of an earthquake1--an extraordinary hailstorm1 c4 7#aae47 ,in all cases which admit of numeration or measurement1 it is of the utmost consequence to obtain precise numerical statements1 whether in the measure of time1 space1 or quantity of any kind4 ,to omit this1 is1 in the first place1 to expose ourselves to illusions of sense which may lead to the grossest errors4 ,thus1 in alpine countries1 we are constantly deceived in heights and distances2 and when we have overcome the first impression which leads us to under-estimate them1 we are then hardly less apt to run into the opposite extreme4 ,but it is not merely in preserving us from exaggerated impressions that numerical precision is desirable4 ,it is the very soul of science2 and its attainment affords the only criterion1 or at least the best1 of the truth of theories1 and the correctness of experiments4 ,thus1 it was entirely to the omission of exact numerical determinations of quantity that the mistakes and confusion of the ,stahlian chemistry were attributable1--a confusion which dissipated like a morning mist as soon as precision1 in this respect1 came to be regarded as essential4 ,chemistry is in the most pre-eminent degree a science of quantity2 and to enumerate the discoveries which have arisen in it1 from the mere determination of weights and measures1 would be nearly to give a synopsis of this branch of knowledge4 ,we need only mention the law of definite proportions1 which fixes the composition of every body in nature in determinate proportional weights of its ingredients4 7#aaf47 ,indeed1 it is a character of all the higher laws of nature to assume the form of precise quantitative statement4 ,thus1 the law of gravitation1 the most universal truth at which human reason has yet arrived1 expresses not merely the general fact of the mutual attraction of all matter2 not merely the vague statement that its influence decreases as the distance increases1 but the exact numerical rate at which that decrease takes place2 so that when its amount is known at any one distance it may be calculated exactly for any other4 ,thus1 too1 the laws of crystallography1 which limit the forms assumed by natural substances1 when left to their own inherent powers of aggregation1 to precise geometrical figures1 with fixed angles and proportions1 have the same essential character of strict mathematical expression1 without which no exact particular conclusions could ever be drawn from them4 7#aag47 ,but1 to arrive at laws of this description1 it is evident that every step of our enquiry must be perfectly free from the slightest degree of looseness and indecision1 and carry with it the full force of strict numerical announcement2 and that1 therefore1 the observations themselves on which all laws ultimately rest ought to have the same property4 ,none of our senses1 however1 gives us direct information for the exact comparison of quantity4 ,number1 indeed1 that is to say1 integer number1 is an object of sense1 because we can count2 but we can neither weigh1 measure1 nor form any precise estimate of fractional parts by the unassisted senses4 ,scarcely any man could tell the difference between twenty pounds and the same weight increased or diminished by a few ounces2 still less could he judge of the proportion between an ounce of gold and a hundred grains of cotton by balancing them in his hands4 ,to take another instance3 the eye is no judge of the proportion of different degrees of illumination1 even when seen side by side2 and if an interval elapses1 and circumstances change1 nothing can be more vague than its judgments4 ,when we gaze with admiration at the gorgeous spectacle of the golden clouds at sunset1 which seem drenched in light and glowing like flames of real fire1 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 sun1 only participating1 from their great horizontal distance1 in the ruddy tint which luminaries acquire by shining through a great extent of the vapours of the atmosphere1 and thereby even losing something of their light4 ,so it is with our estimates of time1 velocity1 and all other matters of quantity2 they are absolutely vague1 and inadequate to form a foundation for any exact conclusion4 7#aah47 ,in this emergency we are obliged to have recourse to instrumental aids1 that is1 to contrivances which shall substitute for the vague impressions of sense the precise one of number1 and reduce all measurement to counting4 ,as a first preliminary towards effecting this1 we fix on convenient standards of weight1 dimension1 time1 c41 and invent contrivances for readily and correctly repeating them as often as we please1 and counting how often such a standard unit is contained in the thing1 be it weight1 space1 time1 or angle1 we wish to measure2 and if there be a fractional part over1 we measure this as a new quantity by aliquot parts of the former standard4 7#aai47 ,if every scientific enquirer observed only for his own satisfaction1 and reasoned only on his own observations1 it would be of little importance what standards he used1 or what contrivances 7if only just ones7 he employed for this purpose2 but if it be intended 7as it is most important they should7 that observations once made should remain as records to all mankind1 and to all posterity1 it is evidently of the highest consequence that all enquirers should agree on the use of a common standard1 and that this should be one not liable to change by lapse of time4 ,the selection and verification of such standards1 however1 will easily be understood to be a matter of extreme difficulty1 if only from the mere circumstance that1 to verify the permanence of one standard1 we must compare it with others1 which it is possible may be themselves inaccurate1 or1 at least1 stand in need of verification4 7#abj47 ,here we can only call to our assistance the presumed permanence of the great laws of ,nature1 with all experience in its favour1 and the strong impression we have of the general composure and steadiness of every thing relating to the gigantic mass we inhabit--8the great globe itself40 ,in its uniform rotation on its axis1 accordingly1 we find a standard of time1 which nothing has ever given us reason to regard as subject to change1 and which1 compared with other periods which the revolutions of the planets about the sun afford1 has demonstrably undergone none since the earliest history4 ,in the dimensions of the earth we find a natural unit of the measure of space1 which possesses in perfection every quality that can be desired2 and in its attraction combined with its rotation the researches of dynamical science have enabled us1 through the medium of the pendulum1 to obtain another invariable standard1 more refined and less obvious1 it is true1 in its origin1 but possessing a great advantage in its capability of ready verification1 and therefore easily made to serve as a check on the other4 ,the former1 viz4 direct measurement of the dimensions of the earth1 is the origin of the mtre1 the ,french unit of linear measure2 the latter1 of the ,british yard4 ,theoretically speaking1 they are equally eligible2 but when we consider that the quantity directly measured1 in the case of the mtre1 is a length a great many thousand times the final unit1 and in the pendulum or yard very nearly the unit itself1 there can be no hesitation in giving the preference as an original measure to the former1 because any error committed in the process by which that is determined becomes subdivided in the final result2 while1 on the other hand1 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 yards4 7#aba47 ,the same admirable invention of the pendulum affords a means of subdividing time to an almost unlimited nicety4 ,a clock is nothing more than a piece of mechanism for counting the oscillations of a pendulum2 and by that peculiar property of the pendulum1 that one vibration commences exactly where the last terminates1 no part of time is lost or gained in the juxta-position of the units so counted1 so that the precise fractional part of a day can be ascertained which each such unit measures4 7#abb47 ,it is owing to this peculiar property by which the juxta-position of units of time and weight can be performed without error1 that the whole of the accuracy with which time and weight can be multiplied and subdivided is owing4#cf ,the same thing cannot be accomplished in space1 by any method we are yet acquainted with1 so that our means of subdividing space are much inferior in precision4 ,the beautiful principle of repetition1 invented by ,borda1 offers the nearest approach to it1 but cannot be said to be absolutely free from the source of error in question4 ,the method of 8double weighing10 which we owe to the same distinguished observer1 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 another4 ,it has been remarked by ,biot1 that previous to the invention of this elegant method1 instruments afforded no perfect means of ascertaining the weight of a body4 7#abc47 ,but it is not enough to possess a standard of this abstract kind3 a real material measure must be constructed1 and exact copies of it taken4 ,this1 however1 is not very difficult2 the great difficulty is to preserve it unaltered from age to age2 for unless we transmit to posterity the units of our measurements1 such as we have ourselves used them1 we1 in fact1 only half bequeath to them our observations4 ,this is a point too much lost sight of1 and it were much to be wished that some direct provision for so important an object were made4#cg 7#abd47 ,but1 it may be asked1 if our measurement of quantity is thus unavoidably liable to error1 how is it possible that our observations can possess that quality of numerical veracity which is requisite to render them the foundation of laws1 whose distinguishing perfection consists in their strict mathematical expression8 ,to this the reply is twofold4 #ast1 that though we admit the necessary existence of numerical error in every observation1 we can always assign a limit which such error cannot possibly exceed2 and the extent of this latitude of error of observation is less in proportion to the perfection of the instrumental means we possess1 and the care bestowed on their employment4 ,in the greater part of modern measurements it is1 in point of fact1 extremely minute1 and may be still further diminished1 almost to any required extent1 by repeating the measurements a great number of times1 and under a great variety of circumstances1 and taking a mean of the results1 when errors of opposite kinds will1 at length1 compensate each other4 ,but1 #b;dly1 there exists a much more fundamental reply to this objection4 ,in reasoning upon our observations1 the existence and possible amount of quantitative error is always to be allowed for2 and the extent to which theories may be affected by it is never to be lost sight of4 ,in reasoning upwards1 from observations confessedly imperfect to general laws1 we must take care always to regard our conclusions as conditional1 so far as they may be affected by such unavoidable imperfections2 and when at length we shall have arrived at our highest point1 and attained to axioms which admit of general and deductive reasoning1 the question1 whether they are vitiated by the errors of observation or not1 will still remain to be decided1 and must become the object of subsequent verification4 ,this point will be made the subject of more distinct consideration hereafter1 when we come to speak of the verification of theories and the laws of probability4 7#abe47 ,with respect to our record of observations1 it should be not only circumstantial but faithful2 by which we mean1 that it should contain all we did observe1 and nothing else4 ,without any intention of falsifying our record1 we may do so unperceived by ourselves1 owing to a mixture of the views and language of an erroneous theory with that of simple fact4 ,thus1 for example1 if1 in describing the effect of lightning1 we should say1 8,the thunderbolt struck with violence against the side of the house1 and beat in the wall10 a fact would be stated which we did not see1 and would lead our hearers to believe that a solid or ponderable projectile was concerned4 ,the 8strong smell of sulphur10 which is sometimes said to accompany lightning1 is a remnant of the theory which made thunder and lightning the explosion of a kind of arial gunpowder1 composed of sulphureous and nitrous exhalations4 ,there are some subjects particularly infested with this mixture of theory in the statement of observed fact4 ,the older chemistry was so overborne by this mischief1 as quite to confound and nullify the descriptions of innumerable curious and laborious experiments4 ,and in geology1 till a very recent period1 it was often extremely difficult1 from this circumstance1 to know what were the facts observed4 ,thus1 ,faujas de ,st4 ,fond1 in his work on the volcanoes of central ,france1 describes with every appearance of minute precision craters existing no where but in his own imagination4 ,there is no greater fault 7direct falsification of fact excepted7 which can be committed by an observer4 7#abf47 ,when particular branches of science have acquired that degree of consistency and generality1 which admits of an abstract statement of laws1 and legitimate deductive reasoning1 the principle of the division of labour tends to separate the province of the observer from that of the theorist4 ,there is no accounting for the difference of minds or inclinations1 which leads one man to observe with interest the developements of phenomena1 another to speculate on their causes2 but were it not for this happy disagreement1 it may be doubted whether the higher sciences could ever have attained even their present degree of perfection4 ,as laws acquire generality1 the influence of individual observations becomes less1 and a higher and higher degree of refinement in their performance1 as well as a great multiplication in their number1 becomes necessary to give them importance4 ,in astronomy1 for instance1 the superior departments of theory are completely disjoined from the routine of practical observation4 7#abg47 ,to make a perfect observer1 however1 either in astronomy or in any other department of science1 an extensive acquaintance is requisite1 not only with the particular science to which his observations relate1 but with every branch of knowledge which may enable him to appretiate and neutralize the effect of extraneous disturbing causes4 ,thus furnished1 he will be prepared to seize on any of those minute indications1 which 7such is the subtlety of nature7 often connect phenomena which seem quite remote from each other4 ,he will have his eyes as it were opened1 that they may be struck at once with any occurrence which1 according to received theories1 ought not to happen2 for these are the facts which serve as clews to new discoveries4 ,the deviation of the magnetic needle1 by the influence of an electrified wire1 must have happened a thousand times to a perceptible amount1 under the eyes of persons engaged in galvanic experiments1 with philosophical apparatus of all kinds standing around them2 but it required the eye of a philosopher such as ,orsted to seize the indication1 refer it to its origin1 and thereby connect two great branches of science4 ,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 palace1 one evening1 when strongly illuminated by the setting sun1 viewed through a doubly refracting prism4 7#abh47 ,to avail ourselves as far as possible of the advantages which a division of labour may afford for the collection of facts1 by the industry and activity which the general diffusion of information1 in the present age1 brings into exercise1 is an object of great importance4 ,there is scarcely any well-informed person1 who1 if he has but the will1 has not also the power to add something essential to the general stock of knowledge1 if he will only observe regularly and methodically some particular class of facts which may most excite his attention1 or which his situation may best enable him to study with effect4 ,to instance one or two subjects1 which can only be effectually improved by the united observations of great numbers widely dispersed3--,meteorology1 one of the most complicated but important branches of science1 is at the same time one in which any person who will attend to plain rules1 and bestow the necessary degree of attention1 may do effectual service4 ,what benefits has not ,geology reaped from the activity of industrious individuals1 who1 setting aside all theoretical views1 have been content to exercise the useful and highly entertaining occupation of collecting specimens from the countries which they visit8 ,in short1 there is no branch of science whatever in which1 at least1 if useful and sensible queries were distinctly proposed1 an immense mass of valuable information might not be collected from those who1 in their various lines of life1 at home or abroad1 stationary or in travel1 would gladly avail themselves of opportunities of being useful4 ,nothing would tend better to attain this end than the circulation of printed skeleton forms1 on various subjects1 which should be so formed as1 #ast1 to ask distinct and pertinent questions1 admitting of short and definite answers2 #b;dly1 ,to call for exact numerical statement on all principal points2 #c;dly1 ,to point out the attendant circumstances most likely to prove influential1 and which ought to be observed2 #dthly1 ,to call for their transmission to a common centre4 ,,chap4 ,v4 ,,of ,,the ,,classification ,,of ,,natural ,,objects ,,and ,,phenomena1 ,,and ,,of ,,nomenclature4 7#abi47 ,the number and variety of objects and relations which the observation of nature brings before us are so great as to distract the attention1 unless assisted and methodized by such judicious distribution of them in classes as shall limit our view to a few at a time1 or to groups so bound together by general resemblances that1 for the immediate purpose for which we consider them1 they may be regarded as individuals4 ,before we can enter into any thing which deserves to be called a general and systematic view of nature1 it is necessary that we should possess an enumeration1 if not complete1 at least of considerable extent1 of her materials and combinations2 and that those which appear in any degree important should be distinguished by names which may not only tend to fix them in our recollection1 but may constitute1 as it were1 nuclei or centres1 about which information may collect into masses4 ,the imposition of a name on any subject of contemplation1 be it a material object1 a phenomenon of nature1 or a group of facts and relations1 looked upon in a peculiar point of view1 is an epoch in its history of great importance4 ,it not only enables us readily to refer to it in conversation or writing1 without circumlocution1 but1 what is of more consequence1 it gives it a recognized existence in our own minds1 as a matter for separate and peculiar consideration2 places it on a list for examination2 and renders it a head or title1 under which information of various descriptions may be arranged2 and1 in consequence1 fits it to perform the office of a connecting link between all the subjects to which such information may refer4 7#acj47 ,for these purposes1 however1 a temporary or provisional name1 or one adapted for common parlance1 may suffice4 ,but when a very great multitude of objects come to be referred to one class1 especially of such as do not offer very obvious and remarkable distinctions1 a more systematic and regular nomenclature becomes necessary1 in which the names shall recall the differences as well as the resemblances between the individuals of a class1 and in which the direct relation between the name and the object shall materially assist the solution of the problem1 8given the one1 to determine the other40 ,how necessary this may become1 will be at once seen1 when we consider the immense number of individual objects1 or rather species1 presented by almost every branch of science of any extent2 which absolutely require to be distinguished by names4 ,thus1 the botanist is conversant with from #hj1jjj to #ajj1jjj species of plants2 the entomologist with1 perhaps1 as many1 of insects3 the chemist has to register the properties of combinations1 by twos1 threes1 fours1 and upwards1 in various doses of upwards of fifty different elements1 all distinguished from each other by essential differences2 and of which though a great many thousands are known1 by far the greater part have never yet been formed1 although hundreds of new ones are coming to light1 in perpetual succession1 as the science advances2 all of which are to be named as they arise4 ,the objects of astronomy are1 literally1 as numerous as the stars of heaven2 and although not more than one or two thousand require to be expressed by distinct names1 yet the number1 respecting which particular information is required1 is not less than a hundred times that amount2 and all these must be registered in lists1 7so as to be at once referred to1 and so that none shall escape17 if not by actual names1 at least by some equivalent means4 7#aca47 ,nomenclature1 then1 is1 in itself1 undoubtedly an important part of science1 as it prevents our being lost in a wilderness of particulars1 and involved in inextricable confusion4 ,happily1 in those great branches of science where the objects of classification are most numerous1 and the necessity for a clear and convenient nomenclature most pressing1 no very great difficulty in its establishment is felt4 ,the very multitude of the objects themselves affords the power of grouping them in subordinate classes1 sufficiently well defined to admit of names1 and these again into others1 whose names may become attached to1 or compounded with1 the former1 till at length the particular species is identified4 ,the facility with which the botanist1 the entomologist1 or the chemist1 refers by name to any individual object in his science shows what may be accomplished in this way when characters are themselves distinct4 ,in other branches1 however1 considerable difficulty is experienced4 ,this arises mostly where the species to be distinguished are separated from each other chiefly by difference in degree1 of certain qualities common to all1 and where the degrees shade into each other insensibly4 ,perhaps such subjects can hardly be considered ripe for systematic nomenclature2 and that the attempt to apply it ought only to be partial1 embracing such groups and parcels of individuals as agree in characters evidently natural and generic1 and leaving the remainder under trivial or provisional denominations1 till they shall be better known1 and capable of being scientifically grouped4 7#acb47 ,indeed1 nomenclature1 in a systematic point of view1 is as much1 perhaps more1 a consequence than a cause of extended knowledge4 ,any one may give an arbitrary name to a thing1 merely to be able to talk of it2 but1 to give a name which shall at once refer it to a place in a system1 we must know its properties2 and we must have a system1 large enough1 and regular enough1 to receive it in a place which belongs to it1 and to no other4 ,it appears1 therefore1 doubtful whether it is desirable1 for the essential purposes of science1 that extreme refinement in systematic nomenclature should be insisted on4 ,were science perfect1 indeed1 systems of classification might be agreed on1 which should assign to every object in nature a place in some class1 to which it more remarkably and pre-eminently belonged than to any other1 and under which it might acquire a name1 never afterwards subject to change4 ,but1 so long as this is not the case1 and new relations are daily discovered1 we must be very cautious how we insist strongly on the establishment and extension of classes which have in them any thing artificial1 as a basis of a rigid nomenclature2 and especially how we mistake the means for the end1 and sacrifice convenience and distinctness to a rage for arrangement4 ,every nomenclature dependent on artificial classifications is necessarily subject to fluctuations2 and hardly any thing can counterbalance the evil of disturbing well-established names1 which have once acquired a general circulation4 ,in nature1 one and the same object makes a part of an infinite number of different systems1--an individual in an infinite number of groups1 some of greater1 some of less importance1 according to the different points of view in which they may be considered4 ,hence1 as many different systems of nomenclature may be imagined as there can be discovered different heads of classification1 while yet it is highly desirable that each object should be universally spoken of under one name1 if possible4 ,consequently1 in all subjects where comprehensive heads of classification do not prominently offer themselves1 all nomenclature must be a balance of difficulties1 and a good1 short1 unmeaning name1 which has once obtained a footing in usage1 is preferable to almost any other4 7#acc47 ,there is no science in which the evils resulting from a rage for nomenclature have been felt to such an extent as in mineralogy4 ,the number of simple minerals actually recognised by mineralogists does not exceed a few hundreds1 yet there is scarcely one which has not four or five names in different books4 ,the consequence is most unhappy4 ,no name is suffered to endure long enough to take root2 and every new writer on this interesting science begins1 as a matter of course1 by making a tabula rasa of all former nomenclature1 and proposing a new one in its place4 ,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 respects1 and therefore carrying the highest authority1 in which names which had acquired universal circulation1 and had hitherto maintained their ground in the midst of the general confusion1 and even worked their way into common language1 as denotive of species too definite to admit of mistake1 are actually rendered generic1 and extended to whole groups1 comprising objects agreeing in nothing but the arbitrary heads of a classification from which the most important natural relations are professedly and purposely rejected4#ch 7#acd47 ,the classifications by which science is advanced1 however1 are widely different from those which serve as bases for artificial systems of nomenclature4 ,they cross and intersect one another1 as it were1 in every possible way1 and have for their very aim to interweave all the objects of nature in a close and compact web of mutual relations and dependence4 ,as soon1 then1 as any resemblance or analogy1 any point of agreement whatever1 is perceived between any two or more things1--be they what they will1 whether objects1 or phenomena1 or laws1--they immediately and ipso facto constitute themselves into a group or class1 which may become enlarged to any extent by the accession of such new objects1 phenomena1 or laws1 agreeing in the same point1 as may come to be subsequently ascertained4 ,it is thus that the materials of the world become grouped in natural families1 such as chemistry furnishes examples of1 in its various groups of acids1 alkalies1 sulphurets1 c42 or botany1 in its euphorbiace1 umbellifer1 c4 ,it is thus1 too1 that phenomena assume their places under general points of resemblance2 as1 in optics1 those which refer themselves to the class of periodic colours1 double refraction1 c42 and that resemblances themselves become traced1 which it is the business of induction to generalize and include in abstract propositions4 7#ace47 ,but every class formed on a positive resemblance of characters1 or on a distinct analogy1 draws with it the consideration of a negative class1 in which that resemblance either does not subsist at all1 or the contrary takes place2 and again1 there are classes in which a given quality is possessed by the different individuals in a descending scale of intensity4 ,now1 it is of consequence to distinguish between cases in which there is a real opposition of quality1 or a mere diminution of intensity1 in some quality susceptible of degrees1 till it becomes imperceptible4 ,for example1 between transparency and opacity there would at first sight appear a direct opposition2 but1 on nearer consideration1 when we consider the gradations by which transparency diminishes in natural substances1 we shall see reason to admit that the latter quality1 instead of being the opposite of the former1 is only its extreme lowest degree4 ,again1 in the arrangement of natural objects under the head of weight or specific gravity1 the scale extends through all nature1 and we know of no natural body in which the opposite of gravity1 or positive levity1 subsists4 ,on the other hand1 the opposite electricities2 the north and south magnetic polarities2 the alkaline and acid qualities of chemical agents2 the positive and negative rotations impressed by plates of rock crystal on the planes of polarization of the rays of light1 and many other cases1 exemplify not merely a negation1 but an active opposition of quality4 ,both these modes of classification have their peculiar importance in the inductive process3 the one1 as affording an opportunity of tracing a relation between phenomena by the observation of a correspondence in their scales of intensity2 the other1 by that of contrast1 as we shall show more at large in the next section4 7#acf47 ,there is a very wide distinction1 too1 to be taken between such classes as turn upon a single head of resemblance among individuals otherwise very different1 and such as bind together in natural groups1 by a great variety of analogies1 objects which yet differ in many remarkable particulars4 ,for example3 if we make colourless transparency a head of classification1 the list of the class will comprise objects differing most widely in their nature1 such as water1 air1 diamond1 spirit of wine1 glass1 c4 ,on the other hand1 the chemical families of alkalies1 metals1 c4 are instances of groups of the other kind2 which1 with properties in many respects different1 still agree in a general resemblance of several others1 which at once decides us in considering them as having a natural relation4 ,in the former cases1 our ingenuity is exercised to determine what can be the cause of their resemblance1 in the latter1 of their difference2 the former belong to the province of inductive generalization1 and afford the most instructive cases for the investigation of causes2 the latter appertain to the more secret recesses of nature2 the very existence of such families being in itself one of the great and complicated phenomena of the universe1 which we cannot hope to unriddle without an intimate and extensive acquaintance with the highest laws4#ci ,,chap4 ,,vi4 ,,of ,,the ,,first ,,stage ,,of ,,induction4--,,the ,,discovery ,,of ,,proximate ,,causes1 ,,and ,,laws ,,of ,,the ,,lowest ,,degree ,,of ,,generality1 ,,and ,,their ,,verification4 7#acg47 ,the first thing that a philosophic mind considers1 when any new phenomenon presents itself1 is its explanation1 or reference to an immediate producing cause4 ,if that cannot be ascertained1 the next is to generalize the phenomenon1 and include it1 with others analogous to it1 in the expression of some law1 in the hope that its consideration1 in a more advanced state of knowledge1 may lead to the discovery of an adequate proximate cause4 7#ach47 ,experience having shown us the manner in which one phenomenon depends on another in a great variety of cases1 we find ourselves provided1 as science extends1 with a continually increasing stock of such antecedent phenomena1 or causes 7meaning at present merely proximate causes71 competent1 under different modifications1 to the production of a great multitude of effects1 besides those which originally led to a knowledge of them4 ,to such causes ,newton has applied the term ver caus2 that is1 causes recognized as having a real existence in nature1 and not being mere hypotheses or figments of the mind4 ,to exemplify the distinction3--,the phenomenon of shells found in rocks1 at a great height above the sea1 has been attributed to several causes4 ,by some it has been ascribed to a plastic virtue in the soil2 by some1 to fermentation2 by some1 to the influence of the celestial bodies2 by some1 to the casual passage of pilgrims with their scallops2 by some1 to birds feeding on shell-fish2 and by all modern geologists1 with one consent1 to the life and death of real mollusca at the bottom of the sea1 and a subsequent alteration of the relative level of the land and sea4 ,of these1 the plastic virtue and celestial influence belong to the class of figments of fancy4 ,casual transport by pilgrims is a real cause1 and might account for a few shells here and there dropped on frequented passes1 but is not extensive enough for the purpose of explanation4 ,fermentation1 generally1 is a real cause1 so far as that there is such a thing2 but it is not a real cause of the production of a shell in a rock1 since no such thing was ever witnessed as one of its effects1 and rocks and stones do not ferment4 ,on the other hand1 for a shell-fish dying at the bottom of the sea to leave his shell in the mud1 where it becomes silted over and imbedded1 happens daily2 and the elevation of the bottom of the sea to become dry land has really been witnessed so often1 and on such a scale1 as to qualify it for a vera causa available in sound philosophy4 7#aci47 ,to take another instance1 likewise drawn from the same deservedly popular science3--,the fact of a great change in the general climate of large tracts of the globe1 if not of the whole earth1 and of a diminution of general temperature1 having been recognised by geologists1 from their examination of the remains of animals and vegetables of former ages enclosed in the strata1 various causes for such diminution of temperature have been assigned4 ,some consider the whole globe as having gradually cooled from absolute fusion2 some regard the immensely superior activity of former volcanoes1 and consequent more copious communication of internal heat to the surface1 in former ages1 as the cause4 ,neither of these can be regarded as real causes in the sense here intended2 for we do not know that the globe has so cooled from fusion1 nor are we sure that such supposed greater activity of former than of present volcanoes really did exist4 ,a cause1 possessing the essential requisites of a vera causa1 has1 however1 been brought forward#dj in the varying influence of the distribution of land and sea over the surface of the globe3 a change of such distribution1 in the lapse of ages1 by the degradation of the old continents1 and the elevation of new1 being a demonstrated fact2 and the influence of such a change on the climates of particular regions1 if not of the whole globe1 being a perfectly fair conclusion1 from what we know of continental1 insular1 and oceanic climates by actual observation4 ,here1 then1 we have1 at least1 a cause on which a philosopher may consent to reason2 though1 whether the changes actually going on are such as to warrant the whole extent of the conclusion1 or are even taking place in the right direction1 may be considered as undecided till the matter has been more thoroughly examined4 7#adj47 ,to this we may add another1 which has likewise the essential characters of a vera causa1 in the astronomical fact of the actual slow diminution of the eccentricity of the earth's orbit round the sun2 and which1 as a general one1 affecting the mean temperature of the whole globe1 and as one of which the effect is both inevitable1 and susceptible1 to a certain degree1 of exact estimation1 deserves consideration4 ,it is evident that the mean temperature of the whole surface of the globe1 in so far as it is maintained by the action of the sun at a higher degree than it would have were the sun extinguished1 must depend on the mean quantity of the sun's rays which it receives1 or1 which comes to the same thing1 on the total quantity received in a given invariable time3 and the length of the year being unchangeable in all the fluctuations of the planetary system1 it follows1 that the total annual amount of solar radiation will determine1 cteris paribus1 the general climate of the earth4 ,now1 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 sun1 regarded as slowly variable2 and that1 therefore1 the major axis remaining1 as we know it to be1 constant1 and the orbit being actually in a state of approach to a circle1 and1 consequently1 the minor axis being on the increase1 the mean annual amount of solar radiation received by the whole earth must be actually on the decrease4 ,we have here1 therefore1 an evident real cause1 of sufficient universality1 and acting in the right direction1 to account for the phenomenon4 ,its adequacy is another consideration4#da 7#ada47 ,whenever1 therefore1 any phenomenon presents itself for explanation1 we naturally seek1 in the first instance1 to refer it to some one or other of those real causes which experience has shown to exist1 and to be efficacious in producing similar phenomena4 ,in this attempt our probability of success will1 of course1 mainly depend1 #ast1 ,on the number and variety of causes experience has placed at our disposal2 #b;dly1 ,on our habit of applying them to the explanation of natural phenomena2 and1 #c;dly1 ,on the number of analogous phenomena we can collect1 which have either been explained1 or which admit of explanation by some one or other of those causes1 and the closeness of their analogy with that in question4 7#adb47 ,here1 then1 we see the great importance of possessing a stock of analogous instances or phenomena which class themselves with that under consideration1 the explanation of one among which may naturally be expected to lead to that of all the rest4 ,if the analogy of two phenomena be very close and striking1 while1 at the same time1 the cause of one is very obvious1 it becomes scarcely possible to refuse to admit the action of an analogous cause in the other1 though not so obvious in itself4 ,for instance1 when we see a stone whirled round in a sling1 describing a circular orbit round the hand1 keeping the string stretched1 and flying away the moment it breaks1 we never hesitate to regard it as retained in its orbit by the tension of the string1 that is1 by a force directed to the centre2 for we feel that we do really exert such a force4 ,we have here the direct perception of the cause4 ,when1 therefore1 we see a great body like the moon circulating round the earth and not flying off1 we cannot help believing it to be prevented from so doing1 not indeed by a material tie1 but by that which operates in the other case through the intermedium of the string1--a force directed constantly to the centre4 ,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 discovery4 7#adc47 ,in general we must observe that motion1 wherever produced or changed1 invariably points out the existence of force as its cause2 and thus the forces of nature become known and measured by the motions they produce4 ,thus1 the force of magnetism becomes known by the deviation produced by iron in a compass needle1 or by a needle leaping up to a magnet held over it1 as certainly as by that adhesion to it1 when in contact and at rest1 which requires force to break the connection2 and thus the currents produced in the surface of a quantity of quicksilver1 electrified under a conducting fluid1 have pointed out the existence and direction of forces of enormous intensity developed by the electric circuit1 of which we should not otherwise have had the least suspicion4#db 7#add47 ,but when the cause of a phenomenon neither presents itself obviously on the consideration of the phenomenon itself1 nor is as it were forced on our attention by a case of strong analogy1 such as above described1 we have then no resource but in a deliberate assemblage of all the parallel instances we can muster2 that is1 to the formation of a class of facts1 having the phenomenon in question for a head of classification2 and to a search among the individuals of this class for some other common points of agreement1 among which the cause will of necessity be found4 ,but if more than one cause should appear1 we must then endeavour to find1 or1 if we cannot find1 to produce1 new facts1 in which each of these in succession shall be wanting1 while yet they agree in the general point in question4 ,here we find the use of what ,bacon terms 8crucial instances10 which are phenomena brought forward to decide between two causes1 each having the same analogies in its favour4 ,and here1 too1 we perceive the utility of experiment as distinguished from mere passive observation4 ,we make an experiment of the crucial kind when we form combinations1 and put in action causes from which some particular one shall be deliberately excluded1 and some other purposely admitted2 and by the agreement or disagreement of the resulting phenomena with those of the class under examination1 we decide our judgment4 7#ade47 ,when we would lay down general rules for guiding and facilitating our search1 among a great mass of assembled facts1 for their common cause1 we must have regard to the characters of that relation which we intend by cause and effect4 ,now1 these are1-- #ast1 ,invariable connection1 and1 in particular1 invariable antecedence of the cause and consequence of the effect1 unless prevented by some counteracting cause4 ,but it must be observed1 that1 in a great number of natural phenomena1 the effect is produced gradually1 while the cause often goes on increasing in intensity2 so that the antecedence of the one and consequence of the other becomes difficult to trace1 though it really exists4 ,on the other hand1 the effect often follows the cause so instantaneously1 that the interval cannot be perceived4 ,in consequence of this1 it is sometimes difficult to decide1 of two phenomena constantly accompanying one another1 which is cause or which effect4 #b;d1 ,invariable negation of the effect with absence of the cause1 unless some other cause be capable of producing the same effect4 #c;d1 ,increase or diminution of the effect1 with the increased or diminished intensity of the cause1 in cases which admit of increase and diminution4 #dth1 ,proportionality of the effect to its cause in all cases of direct unimpeded action4 #eth1 ,reversal of the effect with that of the cause4 7#adf47 ,from these characters we are led to the following observations1 which may be considered as so many propositions readily applicable to particular cases1 or rules of philosophizing3 we conclude1 #ast1 ,that if in our group of facts there be one in which any assigned peculiarity1 or attendant circumstance1 is wanting or opposite1 such peculiarity cannot be the cause we seek4 7#adg47 #b;d1 ,that any circumstance in which all the facts without exception agree1 may be the cause in question1 or1 if not1 at least a collateral effect of the same cause3 if there be but one such point of agreement1 this possibility becomes a certainty2 and1 on the other hand1 if there be more than one1 they may be concurrent causes4 7#adh47 #c;d1 ,that we are not to deny the existence of a cause in favour of which we have a unanimous agreement of strong analogies1 though it may not be apparent how such a cause can produce the effect1 or even though it may be difficult to conceive its existence under the circumstances of the case2 in such cases we should rather appeal to experience when possible1 than decide priori against the cause1 and try whether it cannot be made apparent4 7#adi47 ,for instance3 seeing the sun vividly luminous1 every analogy leads us to conclude it intensely hot4 ,how heat can produce light1 we know not2 and how such a heat can be maintained1 we can form no conception4 ,yet we are not1 therefore1 entitled to deny the inference4 7#aej47 #dth1 ,that contrary or opposing facts are equally instructive for the discovery of causes with favourable ones4 7#aea47 ,for instance3 when air is confined with moistened iron filings in a close vessel over water1 its bulk is diminished1 by a certain portion of it being abstracted and combining with the iron1 producing rust4 ,and1 if the remainder be examined1 it is found that it will not support flame or animal life4 ,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 abstracts1 and which rusts it4 7#aeb47 #eth1 ,that causes will very frequently become obvious1 by a mere arrangement of our facts in the order of intensity in which some peculiar quality subsists2 though not of necessity1 because counteracting or modifying causes may be at the same time in action4 7#aec47 ,for example3 sound consists in impulses communicated to our ears by the air4 ,if a series of impulses of equal force be communicated to it at equal intervals of time1 at first in slow succession1 and by degrees more and more rapidly1 we hear at first a rattling noise1 then a low murmur1 and then a hum1 which by degrees acquires the character of a musical note1 rising higher and higher in acuteness1 till its pitch becomes too high for the ear to follow4 ,and from this correspondence between the pitch of the note and the rapidity of succession of the impulse1 we conclude that our sensation of the different pitches of musical notes originates in the different rapidities with which their impulses are communicated to our ears4 7#aed47 #fth1 ,that such counteracting or modifying causes may subsist unperceived1 and annul the effects of the cause we seek1 in instances which1 but for their action1 would have come into our class of favourable facts2 and that1 therefore1 exceptions may often be made to disappear by removing or allowing for such counteracting causes4 ,this remark becomes of the greatest importance1 when 7as is often the case7 a single striking exception stands out1 as it were1 against an otherwise unanimous array of facts in favour of a certain cause4 7#aee47 ,thus1 in chemistry1 the alkaline 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 metals4 ,ammonia is1 however1 a violent outstanding exception1 such as here alluded to1 being a compound of azote and hydrogen3 but there are almost certain indications that this exception is not a real one1 but assumes that appearance in consequence of some modifying cause not understood4 7#aef47 #gth1 ,if we can either find produced by nature1 or produce designedly for ourselves1 two instances which agree exactly in all but one particular1 and differ in that one1 its influence in producing the phenomenon1 if it have any1 must thereby be rendered sensible4 ,if that particular be present in one instance and wanting altogether in the other1 the production or non-production of the phenomenon will decide whether it be or be not the only cause3 still more evidently1 if it be present contrariwise in the two cases1 and the effect be thereby reversed4 ,but if its total presence or absence only produces a change in the degree or intensity of the phenomenon1 we can then only conclude that it acts as a concurrent cause or condition with some other to be sought elsewhere4 ,in nature1 it is comparatively rare to find instances pointedly differing in one circumstance and agreeing in every other2 but when we call experiment to our aid1 it is easy to produce them2 and this is1 in fact1 the grand application of experiments of enquiry in physical researches4 ,they become more valuable1 and their results clearer1 in proportion as they possess this quality 7of agreeing exactly in all their circumstances but one71 since the question put to nature becomes thereby more pointed1 and its answer more decisive4 7#aeg47 #hth1 ,if we cannot obtain a complete negative or opposition of the circumstance whose influence we would ascertain1 we must endeavour to find cases where it varies considerably in degree4 ,if this cannot be done1 we may perhaps be able to weaken or exalt its influence by the introduction of some fresh circumstance1 which1 abstractedly considered1 seems likely to produce this effect1 and thus obtain indirect evidence of its influence4 ,but then we are always to remember1 that the evidence so obtained is indirect1 and that the new circumstance introduced may have a direct influence of its own1 or may exercise a modifying one on some other circumstance4 7#aeh47 #ith1 ,complicated phenomena1 in which several causes concurring1 opposing1 or quite independent of each other1 operate at once1 so as to produce a compound effect1 may be simplified by subducting the effect of all the known causes1 as well as the nature of the case permits1 either by deductive reasoning or by appeal to experience1 and thus leaving1 as it were1 a residual phenomenon to be explained4 ,it is by this process1 in fact1 that science1 in its present advanced state1 is chiefly promoted4 ,most of the phenomena which nature presents are very complicated2 and when the effects of all known causes are estimated with exactness1 and subducted1 the residual facts are constantly appearing in the form of phenomena altogether new1 and leading to the most important conclusions4 7#aei47 ,for example3 the return of the comet predicted by professor ,encke1 a great many times in succession1 and the general good agreement of its calculated with its observed place during any one of its periods of visibility1 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 motion2 but when the effect of this cause is strictly calculated and subducted from the observed motion1 there is found to remain behind a residual phenomenon1 which would never have been otherwise ascertained to exist1 which is a small anticipation of the time of its reappearances or a diminution of its periodic time1 which cannot be accounted for by gravity1 and whose cause is therefore to be enquired into4 ,such an anticipation would be caused by the resistance of a medium disseminated through the celestial regions2 and as there are other good reasons for believing this to be a vera causa1 it has therefore been ascribed to such a resistance4 7#afj47 ,this #ith observation is of such importance in science1 that we shall exemplify it by another instance or two4 ,m4 ,arago1 having suspended a magnetic needle by a silk thread1 and set it in vibration1 observed1 that it came much sooner to a state of rest when suspended over a plate of copper1 than when no such plate was beneath it4 ,now1 in both cases there were two ver caus why it should come at length to rest1 viz4 the resistance of the air1 which opposes1 and at length destroys1 all motions performed in it2 and the want of perfect mobility in the silk thread4 ,but the effect of these causes being exactly known by the observation made in the absence of the copper1 and being thus allowed for and subducted1 a residual phenomenon appeared1 in the fact that a retarding influence was exerted by the copper itself2 and this fact1 once ascertained1 speedily led to the knowledge of an entirely new and unexpected class of relations4 ,to add one more instance4 ,if it be true 7as ,m4 ,fourrier considers it demonstrated to be7 that the celestial regions have a temperature independent of the sun1 not greatly inferior to that at which quicksilver congeals1 and much superior to some degrees of cold which have been artificially produced1 two causes suggest themselves3 one is that assigned by the author above mentioned2 the radiation of the stars2 another may be proposed in the ether or elastic medium mentioned in the last section1 which the phenomena of light and the resistance of comets give us reason to believe fills all space1 and which1 in analogy to all the elastic media known1 may be supposed to possess a temperature and a specific heat of its own1 which it is capable of communicating to bodies surrounded by it4 ,now1 if we consider that the heat radiated by the sun follows the same proportion as its light1 and regard it as reasonable to admit with respect to stellar heat what holds good of solar2 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 noon2 that is to say1 almost inconceivably smaller4 ,allowing1 then1 the full effect for this cause1 there would still remain a great residuum due to the presence of the ether4 7#afa47 ,many of the new elements of chemistry have been detected in the investigation of residual phenomena4 ,thus1 ,arfwedson discovered lithia by perceiving an excess of weight in the sulphate produced from a small portion of what he considered as magnesia present in a mineral he had analysed4 ,it is on this principle1 too1 that the small concentrated residues of great operations in the arts are almost sure to be the lurking places of new chemical ingredients3 witness iodine1 brome1 selenium1 and the new metals accompanying platina in the experiments of ,wollaston and ,tennant4 ,it was a happy thought of ,glauber to examine what every body else threw away4 7#afb47 ,finally1 we have to observe1 that the detection of a possible cause1 by the comparison of assembled cases1 must lead to one of two things3 either1 #ast1 ,the detection of a real cause1 and of its manner of acting1 so as to furnish a complete explanation of the facts2 or1 #b;dly1 ,the establishment of an abstract law of nature1 pointing out two phenomena of a general kind as invariably connected2 and asserting1 that where one is1 there the other will always be found4 ,such invariable connection is itself a phenomenon of a higher order than any particular fact2 and when many such are discovered1 we may again proceed to classify1 combine1 and examine them1 with a view to the detection of their causes1 or the discovery of still more general laws1 and so on without end4 7#afc47 ,let us now exemplify this inductive search for a cause by one general example3 suppose dew were the phenomenon proposed1 whose cause we would know4 ,in the first place1 we must separate dew from rain and the moisture of fogs1 and limit the application of the term to what is really meant1 which is1 the spontaneous appearance of moisture on substances exposed in the open air when no rain or visible wet is falling4 ,now1 here we have analogous phenomena in the moisture which bedews a cold metal or stone when we breathe upon it2 that which appears on a glass of water fresh from the well in hot weather2 that which appears on the inside of windows when sudden rain or hail chills the external air2 that which runs down our walls when1 after a long frost1 a warm moist thaw comes on3 all these instances agree in one point 7,rule #b4 #adg471 the coldness of the object dewed1 in comparison with the air in contact with it4 7#afd47 ,but1 in the case of the night dew1 is this a real cause--is it a fact that the object dewed is colder than the air8 ,certainly not1 one would at first be inclined to say2 for what is to make it so8 ,but the analogies are cogent and unanimous2 and1 therefore1 7pursuant to ,rule #c4 #adh47 we are not to discard their indications2 and1 besides1 the experiment is easy3 we have only to lay a thermometer in contact with the dewed substance1 and hang one at a little distance above it out of reach of its influence4 ,the experiment has been therefore made2 the question has been asked1 and the answer has been invariably in the affirmative4 ,whenever an object contracts dew1 it is colder than the air4 ,here1 then1 we have an invariable concomitant circumstance3 but is this chill an effect of dew1 or its cause8 ,that dews are accompanied with a chill is a common remark2 but vulgar prejudice would make the cold the effect rather than the cause4 ,we must1 therefore1 collect more facts1 or1 which comes to the same thing1 vary the circumstances2 since every instance in which the circumstances differ is a fresh fact2 and1 especially1 we must note the contrary or negative cases 7,rule #d4 #aej471 i4 e4 where no dew is produced4 7#afe47 ,now1 #ast1 no dew is produced on the surface of polished metals1 but it is very copiously on glass1 both exposed with their faces upwards1 and in some cases the under side of a horizontal plate of glass is also dewed2 which last circumstance 7by ,rule #a4 #adf47 excludes the fall of moisture from the sky in an invisible form1 which would naturally suggest itself as a cause4 ,in the cases of polished metal and polished glass1 the contrast shows evidently that the substance has much to do with the phenomenon2 therefore1 let the substance alone be diversified as much as possible1 by exposing polished surfaces of various kinds4 ,this done1 a scale of intensity becomes obvious 7,rule #e4 #aeb474 ,those polished substances are found to be most strongly dewed which conduct heat worst2 while those which conduct well resist dew most effectually4 ,here we encounter a law of the first degree of generality4 ,but1 if we expose rough surfaces1 instead of polished1 we sometimes find this law interfered with 7,rule #e4 #aeb474 ,thus1 roughened iron1 especially if painted over or blackened1 becomes dewed sooner than varnished paper3 the kind of surface therefore has a great influence4 ,expose1 then1 the same material in very diversified states as to surface 7,rule #g4 #aef471 and another scale of intensity becomes at once apparent2 those surfaces which part with their heat most readily by radiation are found to contract dew most copiously3 and thus we have detected another law of the same generality with the former1 by a comparison of two classes of facts1 one relating to dew1 the other to the radiation of heat from surfaces4 ,again1 the influence ascertained to exist of substance and surface leads us to consider that of texture3 and here1 again1 we are presented on trial with remarkable differences1 and with a third scale of intensity1 pointing out substances of a close firm texture1 such as stones1 metals1 c4 as unfavourable1 but those of a loose one1 as cloth1 wool1 velvet1 eiderdown1 cotton1 c4 as eminently favourable1 to the contraction of dew3 and these are precisely those which are best adapted for clothing1 or for impeding the free passage of heat from the skin into the air1 so as to allow their outer surfaces to be very cold while they remain warm within4 7#aff47 ,lastly1 among the negative instances1 7 #aej47 it is observed1 that dew is never copiously deposited in situations much screened from the open sky1 and not at all in a cloudy night2 but if the clouds withdraw1 even for a few minutes1 and leave a clear opening1 a deposition of dew presently begins1 and goes on increasing4 ,here1 then1 a cause is distinctly pointed out by its antecedence to the effect in question 7 #ade474 ,a clear view of the cloudless sky1 then1 is an essential condition1 or1 which comes to the same thing1 clouds or surrounding objects act as opposing causes4 ,this is so much the case1 that dew formed in clear intervals will often even evaporate again when the sky becomes thickly overcast 7,rule #d4 #aej474 7#afg47 ,when we now come to assemble these partial inductions so as to raise from them a general conclusion1 we consider1 #ast1 ,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 air4 ,those surfaces which part with their heat outwards most readily1 and have it supplied from within most slowly1 will1 of course1 become coldest if there be an opportunity for their heat to escape1 and not be restored to them from without4 ,now1 a clear sky affords such an opportunity4 ,it is a law well known to those who are conversant with the nature of heat1 that heat is constantly escaping from all bodies in rays1 or by radiation1 but is as constantly restored to them by the similar radiation of others surrounding them4 ,clouds and surrounding objects therefore act as opposing causes by replacing the whole or a great part of the heat so radiated away1 which can escape effectually1 without being replaced1 only through openings into infinite space4 ,thus1 at length1 we arrive at the general proximate cause of dew1 in the cooling of the dewed surface by radiation faster than its heat can be restored to it1 by communication with the ground1 or by counter-radiation2 so as to become colder than the air1 and thereby to cause a condensation of its moisture4 7#afh47 ,we have purposely selected this theory of dew1 first developed by the late ,dr4 ,wells1 as one of the most beautiful specimens we can call to mind of inductive experimental enquiry lying within a moderate compass4 ,it is not possible in so brief a space to do it justice2 but we earnestly recommend his work#dc 7a short and very entertaining one7 for perusal to the student of natural philosophy1 as a model with which he will do well to become familiar4 7#afi47 ,in the analysis above given1 the formation of dew is referred to two more general phenomena2 the radiation of heat1 and the condensation of invisible vapour by cold4 ,the cause of the former is a much higher enquiry1 and may be said1 indeed1 to be totally unknown2 that of the latter actually forms a most important branch of physical enquiry4 ,in such a case1 when we reason upwards till we reach an ultimate fact1 we regard a phenomenon as fully explained2 as we consider the branch of a tree to terminate when traced to its insertion in the trunk1 or a twig to its junction with the branch2 or rather1 as a rivulet retains its importance and its name till lost in some larger tributary1 or in the main river which delivers it into the ocean4 ,this1 however1 always supposes that1 on a reconsideration of the case1 we see clearly how the admission of such a fact1 with all its attendant laws1 will perfectly account for every particular--as well those which1 in the different stages of the induction1 have led us to a knowledge of it1 as those which we had neglected1 or considered less minutely than the rest4 ,but1 had we no previous knowledge of the radiation of heat1 this same induction would have made it known to us1 and1 duly considered1 might have led to the knowledge of many of its laws4 7#agj47 ,in the study of nature1 we must not1 therefore1 be scrupulous as to how we reach to a knowledge of such general facts3 provided only we verify them carefully when once detected1 we must be content to seize them wherever they are to be found4 ,and this brings us to consider the verification of inductions4 7#aga47 ,if1 in our induction1 every individual case has actually been present to our minds1 we are sure that it will find itself duly represented in our final conclusion3 but this is impossible for such cases as were unknown to us1 and hardly ever happens even with all the known cases2 for such is the tendency of the human mind to speculation1 that on the least idea of an analogy between a few phenomena1 it leaps forward1 as it were1 to a cause or law1 to the temporary neglect of all the rest2 so that1 in fact1 almost all our principal inductions must be regarded as a series of ascents and descents1 and of conclusions from a few cases1 verified by trial on many4 7#agb47 ,whenever1 therefore1 we think we have been led by induction to the knowledge of the proximate cause of a phenomenon or of a law of nature1 our next business is to examine deliberately and seriatim all the cases we have collected of its occurrence1 in order to satisfy ourselves that they are explicable by our cause1 or fairly included in the expression of our law3 and in case any exception occurs1 it must be carefully noted and set aside for re-examination at a more advanced period1 when1 possibly1 the cause of exception may appear1 and the exception itself1 by allowing for the effect of that cause1 be brought over to the side of our induction2 but should exceptions prove numerous and various in their features1 our faith in the conclusion will be proportionally shaken1 and at all events its importance lessened by the destruction of its universality4 7#agc47 ,in the conduct of this verification1 we are to consider whether the cause or law to which we are conducted be one already known and recognised as a more general one1 whose nature is well understood1 and of which the phenomenon in question is but one more case in addition to those already known1 or whether it be one less general1 less known1 or altogether new4 ,in the latter case1 our verification will suffice1 if it merely shows that all the cases considered are plainly cases in point4 ,but in the former1 the process of verification is of a much more severe and definite kind4 ,we must trace the action of our cause with distinctness and precision1 as modified by all the circumstances of each case2 we must estimate its effects1 and show that nothing unexplained remains behind2 at least1 in so far as the presence of unknown modifying causes is not concerned4 7#agd47 ,now1 this is precisely the sort of process in which residual phenomena 7such as spoken of in art4 #aeh47 may be expected to occur4 ,if our induction be really a valid and a comprehensive one1 whatever remains unexplained in the comparison of its conclusion with particular cases1 under all their circumstances1 is such a phenomenon1 and comes in its turn to be a subject of inductive reasoning to discover its cause or laws4 ,it is thus that we may be said to witness facts with the eyes of reason2 and it is thus that we are continually attaining a knowledge of new phenomena and new laws which lie beneath the surface of things1 and give rise to the creation of fresh branches of science more and more remote from common observation4 7#age47 ,physical astronomy affords numerous and splendid instances of this4 ,the law1 for example1 which asserts that the planets are retained in their orbits about the sun1 and satellites about their primaries1 by an attractive force1 decreasing as the square of the distances increases1 comes to be verified in each particular case by deducing from it the exact motions which1 under the circumstances1 ought to take place1 and comparing them with fact4 ,this comparison1 while it verifies in general the existence of the law of gravitation as supposed1 and its adequacy to explain all the principal motions of every body in the system1 yet leaves some small deviations in those of the planets1 and some very considerable ones in that of the moon and other satellites1 still unaccounted for2 residual phenomena1 which still remain to be traced up to causes4 ,by further examining these1 their causes have at length been ascertained1 and found to consist in the mutual actions of the planets on each other1 and the disturbing influence of the sun on the motions of the satellites4 7#agf47 ,but a law of nature has not that degree of generality which fits it for a stepping-stone to greater inductions1 unless it be universal in its application4 ,we cannot rely on its enabling us to extend our views beyond the circle of instances from which it was obtained1 unless we have already had experience of its power to do so2 unless it actually has enabled us before trial to say what will take place in cases analogous to those originally contemplated2 unless1 in short1 we have studiously placed ourselves in the situation of its antagonists1 and even perversely endeavoured to find exceptions to it without success4 ,it is in the precise proportion that a law once obtained endures this extreme severity of trial1 that its value and importance are to be estimated2 and our next step in the verification of an induction must therefore consist in extending its application to cases not originally contemplated2 in studiously varying the circumstances under which our causes act1 with a view to ascertain whether their effect is general2 and in pushing the application of our laws to extreme cases4 7#agg47 ,for example1 a fair induction from a great number of facts led ,galileo to conclude that the accelerating power of gravity is the same on all sorts of bodies1 and on great and small masses indifferently2 and this he exemplified by letting bodies of very different natures and weights fall at the same instant from a high tower1 when it was observed that they struck the ground at the same moment1 abating a certain trifling difference1 due1 as he justly believed it to be1 to the greater proportional resistance of the air to light than to heavy bodies4 ,the experiment could not1 at that time1 be fairly tried with extremely light substances1 such as cork1 feathers1 cotton1 c4 because of the great resistance experienced by these in their fall2 no means being then known of removing this cause of disturbance4 ,it was not1 therefore1 till after the invention of the air-pump that this law could be put to the severe test of an extreme case4 ,a guinea and a downy feather were let drop at once from the upper part of a tall exhausted glass1 and struck the bottom at the same moment4 ,let any one make the trial in the air1 and he will perceive the force of an extreme case4 7#agh47 ,in the verification of a law whose expression is quantitative1 not only must its generality be established by the trial of it in as various circumstances as possible1 but every such trial must be one of precise measurement4 ,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 7if any exist72 so that1 let it be ever so small1 it shall at last become sensible4 7#agi47 ,for instance1 let the law to be verified be1 that the gravity of every material body is in the direct proportion of its mass1 which is only another mode of expressing ,galileo's law above mentioned4 ,the time of falling from any moderate height cannot be measured with precision enough for our purpose3 but if it can be repeated a very great multitude of times without any loss or gain in the intervals1 and the whole amount of the times of fall so repeated measured by a clock2 and if at the same time the resistance of the air can be rendered exactly alike for all the bodies tried1 we have here ,galileo's trial in a much more refined state2 and it is evident that almost unlimited exactness may be obtained4 ,now1 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 respects1 as gold1 glass1 wood1 water1 wheat1 c4#dd1 and ascertaining the time required for the pendulum so charged to make a great number of oscillations2 in each of which it is clear the weights had to fall1 and be raised again successively1 without loss of time1 through the same identical spaces4 ,thus any difference1 however inconsiderable1 that might exist in the time of one such fall and rise would be multiplied and accumulated till they became sensible4 ,and none having been discovered by so delicate a process in any case1 the law was considered verified both in respect of generality and exactness4 ,this1 however1 is nothing to the verifications afforded by astronomical phenomena1 where the deviations1 if any1 accumulate for thousands of years instead of a few hours4 7#ahj47 ,the surest and best characteristic of a well-founded and extensive induction1 however1 is when verifications of it spring up1 as it were1 spontaneously1 into notice1 from quarters where they might be least expected1 or even among instances of that very kind which were at first considered hostile to them4 ,evidence of this kind is irresistible1 and compels assent with a weight which scarcely any other possesses4 ,to give an example3 ,m4 ,mitscherlich had announced a law to this effect--that the chemical elements of which all bodies consist are susceptible of being classified in distinct groups1 which he termed isomorphous groups2 and that these groups are so related1 that when similar combinations are formed of individuals belonging to two1 three1 or more of them1 such combinations will crystallize in the same geometrical forms4 ,to this curious and important law there appeared a remarkable exception4 ,according to professor ,mitscherlich1 the arsenic and phosphoric acids are similar combinations coming under the meaning of his law1 and their combinations with soda and water1 forming the salts known to chemists under the names of arseniate and phosphate of soda1 ought1 if the law were general1 to crystallize in identical shapes4 ,the fact1 however1 was understood to be otherwise4 ,but lately1 ,mr4 ,clarke1 a ,british chemist1 having examined the two salts attentively1 ascertained the fact that their compositions deviate essentially from that similarity which ,m4 ,mitscherlich's law requires2 and that1 therefore1 the exception in question disappears4 ,this was something3 but1 pursuing the subject further1 the same ingenious enquirer happily succeeded in producing a new phosphate of soda1 differing from that generally known in containing a different proportion of water1 and agreeing in composition exactly with the arseniate4 ,the crystals of this new salt1 when examined1 were found by him to be precisely identical in form with those of the arseniate3 thus verifying1 in a most striking and totally unexpected manner1 the law in question1 or1 as it is called1 the law of isomorphism4 7#aha47 ,unexpected and peculiarly striking confirmations of inductive laws frequently occur in the form of residual phenomena1 in the course of investigations of a widely different nature from those which gave rise to the inductions themselves4 ,a very elegant example may be cited in the unexpected confirmation of the law of the developement of heat in elastic fluids by compression1 which is afforded by the phenomena of sound4 ,the enquiry into the cause of sound had led to conclusions respecting its mode of propagation1 from which its velocity in the air could be precisely calculated4 ,the calculations were performed2 but1 when compared with fact1 though the agreement was quite sufficient to show the general correctness of the cause and mode of propagation assigned1 yet the whole velocity could not be shown to arise from this theory4 ,there was still a residual velocity to be accounted for1 which placed dynamical philosophers for a long time in a great dilemma4 ,at length ,laplace struck on the happy idea1 that this might arise from the heat developed in the act of that condensation which necessarily takes place at every vibration by which sound is conveyed4 ,the matter was subjected to exact calculation1 and the result was at once the complete explanation of the residual phenomenon1 and a striking confirmation of the general law of the developement of heat by compression1 under circumstances beyond artificial imitation4 7#ahb47 ,in extending our inductions to cases not originally contemplated1 there is one step which always strikes the mind with peculiar force1 and with such a sensation of novelty and surprise1 as often gives it a weight beyond its due philosophic value4 ,it is the transition from the little to the great1 and vice vers1 but especially the former4 ,it is so beautiful to see1 for instance1 an experiment performed in a watch-glass1 or before a blowpipe1 succeed1 in a great manufactory1 on many tons of matter1 or1 in the bosom of a volcano1 upon millions of cubic fathoms of lava1 that we almost forget that these great masses are made up of watch-glassfuls1 and blowpipe-beads4 ,we see the enormous intervals between the stars and planets of the heavens1 which afford room for innumerable processes to be carried on1 for light and heat to circulate1 and for curious and complicated motions to go forward among them3 we look more attentively1 and we see sidereal systems1 probably not less vast and complicated than our own1 crowded apparently into a small space 7from the effect of their distance from us71 and forming groups resembling bodies of a substantial appearance1 having form and outline3 yet we recoil with incredulous surprise when we are asked why we cannot conceive the atoms of a grain of sand to be as remote from each other 7proportionally to their sizes7 as the stars of the firmament2 and why there may not be going on1 in that little microcosm1 processes as complicated and wonderful as those of the great world around us4 ,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 for3 he will find1 for instance1 the phenomena of the propagation of winds referred to the same laws which regulate the propagation of motions through the smallest masses of air2 those of lightning assimilated to the mere communication of an electric spark1 and those of earthquakes to the tremors of a stretched wire3 in short1 he must lay his account to finding the distinction of great and little altogether annihilated in nature3 and it is well for man that such is the case1 and that the same laws1 which he can discover and verify in his own circumscribed sphere of power1 should prove available to him when he comes to apply them on the greatest scale2 since it is thus only that he is enabled to become an exciting cause in operations of any considerable magnitude1 and to vindicate his importance in creation4 7#ahc47 ,but the business of induction does not end here3 its final result must be followed out into all its consequences1 and applied to all those cases which seem even remotely to bear upon the subject of enquiry4 ,every new addition to our stock of causes becomes a means of fresh attack with new vantage ground upon all those unexplained parts of former phenomena which have resisted previous efforts4 ,it can hardly be pressed forcibly enough on the attention of the student of nature1 that there is scarcely any natural phenomenon which can be fully and completely explained in all its circumstances1 without a union of several1 perhaps of all1 the sciences4 ,the great phenomena of astronomy1 indeed1 may be considered exceptions2 but this is merely because their scale is so vast that one only of the most widely extending forces of nature takes the lead1 and all those agents whose sphere of action is limited to narrower bounds1 and which determine the production of phenomena nearer at hand1 are thrown into the back ground1 and become merged and lost in comparative insignificance4 ,but in the more intimate phenomena which surround us it is far otherwise4 ,into what a complication of different branches of science are we not led by the consideration of such a phenomenon as rain1 for instance1 or flame1 or a thousand others1 which are constantly going on before our eyes8 ,hence1 it is hardly possible to arrive at the knowledge of a law of any degree of generality in any branch of science1 but it immediately furnishes us with a means of extending our knowledge of innumerable others1 the most remote from the point we set out from2 so that1 when once embarked in any physical research1 it is impossible for any one to predict where it may ultimately lead him4 7#ahd47 ,this remark rather belongs to the inverse or deductive process1 by which we pursue laws into their remote consequences4 ,but it is very important to observe1 that the successful process of scientific enquiry demands continually the alternate use of both the inductive and deductive method4 ,the path by which we rise to knowledge must be made smooth and beaten in its lower steps1 and often ascended and descended1 before we can scale our way to any eminence1 much less climb to the summit4 ,the achievement is too great for a single effort2 stations must be established1 and communications kept open with all below4 ,to quit metaphor2 there is nothing so instructive1 or so likely to lead to the acquisition of general views1 as this pursuit of the consequences of a law once arrived at into every subject where it may seem likely to have an influence4 ,the discovery of a new law of nature1 a new ultimate fact1 or one that even temporarily puts on that appearance1 is like the discovery of a new element in chemistry4 ,thus1 selenium was hardly discovered by ,berzelius in the vitriol works of ,fahlun1 when it presently made its appearance in the sublimates of ,stromboli1 and the rare and curious products of the ,hungarian mines4 ,and thus it is with every new law1 or general fact4 ,it is hardly announced before its traces are found every where1 and every one is astonished at its having so long remained concealed4 ,and hence it happens that unexpected lights are shed at length over parts of science that had been abandoned in despair1 and given over to hopeless obscurity4 7#ahe47 ,the verification of quantitative laws has been already spoken of 7#agh472 but their importance in physical science is so very great1 inasmuch as they alone afford a handle to strict mathematical deductive application1 that something ought to be said of the nature of the inductions by which they are to be arrived at4 ,in their simplest or least general stages 7of which alone we speak at present7 they usually express some numerical relation between two quantities dependent on each other1 either as collateral effects of a common cause1 or as the amount of its effect under given numerical circumstances or data4 ,for example1 the law of refraction before noticed 7 #bb47 expresses1 by a very simple relation1 the amount of angular deviation of a ray of light from its course1 when the angle at which it is inclined to the refracting surface is known1 viz4 that the sine 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 perpendicular1 in a constant proportion1 so long as the refracting substance is the same4 ,to arrive inductively at laws of this kind1 where one quantity depends on or varies with another1 all that is required is a series of careful and exact measures in every different state of the datum and qusitum4 ,here1 however1 the mathematical form of the law being of the highest importance1 the greatest attention must be given to the extreme cases as well as to all those points where the one quantity changes rapidly with a small change of the other4#de ,the results must be set down in a table in which the datum gradually increases in magnitude from the lowest to the highest limit of which it is susceptible4 ,it will depend then entirely on our habit of treating mathematical subjects1 how far we may be able to include such a table in the distinct statement of a mathematical law4 ,the discovery of such laws is often remarkably facilitated by the contemplation of a class of phenomena to be noticed further on1 under the head of ,collective ,instances1 7see #aid47 in which the nature of the mathematical expression in which the law sought is comprehended1 is pointed out by the figure of some curve brought under inspection by a proper mode of experimenting4 7#ahf47 ,after all1 unless our induction embraces a series of cases which absolutely include the whole scale of variation of which the quantities in question admit1 the mathematical expression so obtained cannot be depended upon as the true one1 and if the scale actually embraced be small1 the extension of laws so derived to extreme cases will in all probability be exceedingly fallacious4 ,for example1 air is an elastic fluid1 and as such1 if enclosed in a confined space and squeezed1 its bulk diminishes3 now1 from a great number of trials made in cases where the air has been compressed into a half1 a third1 c4 even as far as a fiftieth of its bulk1 or less1 it has been concluded that 8the density of air is proportional to the compressing force10 or the bulk it occupies inversely as that force2 and when the air is rarefied by taking off part of its natural pressure1 the same is found to be the case1 within very extensive limits4 ,yet it is impossible that this should be1 strictly or mathematically speaking1 the true law2 for1 if it were so1 there could be no limit to the condensation of air1 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 liquid1 and even1 perhaps1 if pressed yet more violently1 into a solid form4 7#ahg47 ,laws thus derived1 by the direct process of including in mathematical formul the results of a greater or less number of measurements1 are called 8empirical laws40 ,a good example of such a law is that given by ,dr4 ,young 7,phil4 ,trans4 #ahbf17 for the decrement of life1 or the law of mortality4 ,empirical laws in this state are evidently unverified inductions1 and are to be received and reasoned on with the utmost reserve4 ,no confidence can ever be placed in them beyond the limits of the data from which they are derived2 and even within those limits they require a special and severe scrutiny to examine how nearly they do represent the observed facts2 that is to say1 whether1 in the comparison of their results with the observed quantities1 the differences are such as may fairly be attributed to error of observation4 ,when so carefully examined1 they become1 however1 most valuable2 and frequently1 when afterwards verified theoretically by a deductive process 7as will be explained in our next chapter71 turn out to be rigorous laws of nature1 and afford the noblest and most convincing supports of which theories themselves are susceptible4 ,the finest instances of this kind are the great laws of the planetary motions deduced by ,kepler1 entirely from a comparison of observations with each other1 with no assistance from theory4 ,these laws1 viz4 that the planets move in ellipses round the sun2 that each describes about the sun's centre equal areas in equal times2 and that in the orbits of different planets the squares of the periodical times are proportional to the cubes of the distances2 were the results of inconceivable labour of calculation and comparison3 but they amply repaid the labour bestowed on them1 by affording afterwards the most conclusive and unanswerable proofs of the ,newtonian system4 ,on the other hand1 when empirical laws are unduly relied on beyond the limits of the observations from which they were deduced1 there is no more fertile source of fatal mistakes4 ,the formul which have been empirically deduced for the elasticity of steam 7till very recently71 and those for the resistance of fluids1 and other similar subjects1 have almost invariably failed to support the theoretical structures which have been erected on them4 7#ahh47 ,it is a remarkable and happy fact1 that the shortest and most direct of all inductions should be that which has led at once1 or by very few steps1 to the highest of all natural laws1--we mean those of motion and force4 ,nothing can be more simple1 precise1 and general1 than the enunciation of these laws2 and1 as we have once before observed1 their application to particular facts in the descending or deductive method is limited by nothing but the limited extent of our mathematics4 ,it would seem1 then1 that dynamical science were taken thenceforward out of the pale of induction1 and transformed into a matter of absolute priori reasoning1 as much as geometry2 and so it would be1 were our mathematics perfect1 and all the data known4 ,unhappily1 the first is so far from being the case1 that in many of the most interesting branches of dynamical enquiry they leave us completely at a loss4 ,in what relates to the motions of fluids1 for instance1 this is severely felt4 ,we can include our problems1 it is true1 in algebraical equations1 and we can demonstrate that they contain the solutions2 but the equations themselves are so intractable1 and present such insuperable difficulties1 that they often leave us quite as much in the dark as before4 ,but even were these difficulties overcome1 recourse to experience must still be had1 to establish the data on which particular applications are to depend2 and although mathematical analysis affords very powerful means of representing in general terms the data of any proposed case1 and afterwards1 by comparison of its results with fact1 determining what those data must be to explain the observed phenomena1 still1 in any mode of considering the matter1 an appeal to experience in every particular instance of application is unavoidable1 even when the general principles are regarded as sufficiently established without it4 ,now1 in all such cases of difficulty we must recur to our inductive processes1 and regard the branches of dynamical science where this takes place as purely experimental4 ,by this we gain an immense advantage1 viz4 that in all those points of them where the abstract dynamical principles do afford distinct conclusions1 we obtain verifications for our inductions of the highest and finest possible kind4 ,when we work our way up inductively to one of these results1 we cannot help feeling the strongest assurance of the validity of the induction4 7#ahi47 ,the necessity of this appeal to experiment in every thing relating to the motions of fluids on the large scale has long been felt4 ,newton himself1 who laid the first foundations of hydrodynamical science 7so this branch of dynamics is called71 distinctly perceived it1 and set the example of laborious and exact experiments on their resistance to motion1 and other particulars4 ,venturi1 ,bernoulli1 and many others1 have applied the method of experiment to the motions of fluids in pipes and canals2 and recently the brothers ,weber have published an elaborate and excellent experimental enquiry into the phenomena of waves4 ,one of the greatest and most successful attempts1 however1 to bring an important1 and till then very obscure1 branch of dynamical enquiry back to the dominion of experiment1 has been made by ,chladni and ,savart in the case of sound and vibratory motion in general2 and it is greatly to be wished that the example may be followed in many others hardly less abstruse and impracticable when theoretically treated4 ,in such cases the inductive and deductive methods of enquiry may be said to go hand in hand1 the one verifying the conclusions deduced by the other2 and the combination of experiment and theory1 which may thus be brought to bear in such cases1 forms an engine of discovery infinitely more powerful than either taken separately4 ,this state of any department of science is perhaps of all others the most interesting1 and that which promises the most to research4 7#aij47 ,it can hardly be expected that we should terminate this division of our subject without some mention of the 8prerogatives of instances0 of ,bacon1 by which he understands characteristic phenomena1 selected from the great miscellaneous mass of facts which occur in nature1 and which1 by their number1 indistinctness1 and complication1 tend rather to confuse than to direct the mind in its search for causes and general heads of induction4 ,phenomena so selected on account of some peculiarly forcible way in which they strike the reason1 and impress us with a kind of sense of causation1 or a particular aptitude for generalization1 he considers1 and justly1 as holding a kind of prerogative dignity1 and claiming our first and especial attention in physical enquiries4 7#aia47 ,we have already observed that1 in forming inductions1 it will most commonly happen that we are led to our conclusions by the especial force of some two or three strongly impressive facts1 rather than by affording the whole mass of cases a regular consideration2 and hence the need of cautious verification4 ,indeed1 so strong is this propensity of the human mind1 that there is hardly a more common thing than to find persons ready to assign a cause for every thing they see1 and1 in so doing1 to join things the most incongruous1 by analogies the most fanciful4 ,this being the case1 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 inductions4 ,the misfortune1 however1 is1 in natural philosophy1 that the choice does not rest with us4 ,we must take the instances as nature presents them4 ,even if we are furnished with a list of them in tabular order1 we must understand and compare them with each other1 before we can tell which are the instances thus deservedly entitled to the highest consideration4 ,and1 after all1 after much labour in vain1 and groping in the dark1 accident or casual observation will present a case which strikes us at once with a full insight into a subject1 before we can even have time to determine to what class its prerogative belongs4 ,for example1 the laws of crystallography were obscure1 and its causes still more so1 till ,hay fortunately dropped a beautiful crystal of calcareous spar on a stone pavement1 and broke it4 ,in piecing together the fragments1 he observed their facets not to correspond with those of the crystal in its entire state1 but to belong to another form2 and1 following out the hint offered by a 8glaring instance0 thus casually obtruded on his notice1 he discovered the beautiful laws of the cleavage1 and the primitive forms of minerals4 7#aib47 ,it has always appeared to us1 we must confess1 that the help which the classification of instances1 under their different titles of prerogative1 affords to inductions1 however just such classification may be in itself1 is yet more apparent than real4 ,the force of the instance must be felt in the mind1 before it can be referred to its place in the system2 and1 before it can be either referred or appretiated1 it must be known2 and when it is appretiated1 we are ready enough to interweave it in our web of induction1 without greatly troubling ourselves with enquiring whence it derives the weight we acknowledge it to have in our decisions4 ,however1 since much importance is usually attached to this part of ,bacon's work1 we shall here give a few examples to illustrate the nature of some of his principal cases4 ,one1 of what he calls 8glaring instances10 has just been mentioned4 ,in these1 the nature or cause enquired into1 7which in this case is the cause of the assumption of a peculiar external form1 or the internal structure of a crystal17 8stands naked and alone1 and this in an eminent manner1 or in the highest degree of its power40 ,no doubt1 such instances as these are highly instructive2 but the difficulty in physics is to find such1 not to perceive their force when found4 7#aic47 ,the contrary of glaring are 8clandestine instances10 where 8the nature sought is exhibited in its weakest and most imperfect state40 ,of this1 ,bacon himself has given an admirable example in the cohesion of fluids1 as a clandestine instance of the 8nature or quality of consistence1 or solidity40 ,yet here1 again1 the same acute discrimination which enabled ,bacon to perceive the analogy which connects fluids with solids1 through the common property of cohesive attraction1 would1 at the same time1 have enabled him to draw from it1 if properly supported1 every consequence necessary to forming just notions of the cohesive force2 nor does its reference to the class of clandestine instances at all assist in bringing forward and maturing the final results4 ,when1 however1 the final result is obtained1--when our induction is complete1 and we would verify it1--this class of instances is of great use1 being1 in fact1 frequently no other than that of extreme cases1 such as we have already spoken of 7in #agg472 which1 by placing our conclusions1 as it were1 in violent circumstances1 try their temper1 and bring their vigour to the test4 7#aid47 ,bacon's 8collective instances0 7instanti unionis71 are no other than general facts1 or laws of some degree of generality1 and are themselves the results of induction4 ,but there is a species of collective instance which ,bacon does not seem to have contemplated1 of a peculiarly instructive character2 and that is1 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 inspection4 ,for example1 the parabolic form assumed by a jet of water spouted from a round hole1 is a collective instance of the velocities and directions of the motions of all the particles which compose it seen at once1 and which thus leads us1 without trouble1 to recognize the law of the motion of a projectile4 ,again1 the beautiful figures exhibited by sand strewed on regular plates of glass or metal set in vibration1 are collective instances of an infinite number of points which remain at rest while the remainder of the plate vibrates2 and in consequence afford us1 as it were1 a sight of the law which regulates their arrangement and sequence throughout the whole surface4 ,the beautifully coloured lemniscates seen around the optic axes of crystals exposed to polarized light afford a superb example of the same kind1 pointing at once to the general mathematical expression of the law which regulates their production4#df ,of such collective instances as these1 it is easy to see the importance1 and its reason4 ,they lead us to a general law by an induction which offers itself spontaneously1 and thus furnish advanced points in our enquiries2 and when we start from these1 already 8a thousand steps are lost40 7#aie47 ,a fine example of a collective instance is that of the system of ,jupiter or ,saturn with its satellites4 ,we have here1 in miniature1 and seen at one view1 a system similar to that of the planets about the sun2 of which1 from the circumstance of our being involved in it1 and unfavourably situated for seeing it otherwise than in detail1 we are incapacitated from forming a general idea but by slow progressive efforts of reason4 ,accordingly1 the contemplation of the circumjovial planets 7as they were called7 most materially assisted in securing the admission of the ,copernican system4 7#aif47 ,of 8,crucial instances0 we have also already spoken1 as affording the readiest and securest means of eliminating extraneous causes1 and deciding between rival hypotheses4 ,owing to the disposition of the mind to form hypotheses1 and to prejudge cases1 it constantly happens that1 among all the possible suppositions which may occur1 two or three principal ones occupy us1 to the exclusion of the rest2 or it may be that1 if we have been less precipitate1 out of a great multitude rejected for obvious inapplicability to some one or other case1 two or three of better claims remain for decision2 and this such instances enable us to do4 ,one of the instances cited by ,bacon in illustration of his crucial class is very remarkable1 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 in themselves1 or of the attraction of the earth 8by the corporeal mass thereof1 as by a collection of bodies of the same nature40 ,if it be so1 he says1 8it will follow that the nearer all bodies approach to the earth1 the stronger and with the greater force and velocity they will tend to it2 but the farther they are1 the weaker and slower30 and his experiment consists in comparing the effect of a spring and a weight in keeping up the motions of two 8clocks10 regulated together1 and removed alternately to the tops of high buildings and into the deepest mines4 ,by clocks he could not have meant pendulum clocks1 which were not then known1 7the first made in ,england was in #affb17 fly-clocks1 so that the comparison1 though too coarse1 was not contrary to sound mechanical principles4 ,in short1 its principle was the comparison of the effect of a spring with that of a weight1 in producing certain motions in certain times1 on heights and in mines4 ,now1 this is the very same thing that has really been done in the recent experiments of professors ,airy and ,whewell in ,dolcoath mine3 a pendulum 7a weight moved by gravity7 has been compared with a chronometer balance1 moved and regulated by a spring4 ,in his #cgth aphorism1 ,bacon also speaks of gravity as an incorporeal power1 acting at a distance1 and requiring time for its transmission2 a consideration which occurred at a later period to ,laplace1 in one of his most delicate investigations4 7#aig47 ,a well chosen and strongly marked crucial instance is1 sometimes1 of the highest importance2 when two theories1 which run parallel to each other 7as is sometimes the case7 in their explanation of great classes of phenomena1 at length come to be placed at issue upon a single fact4 ,a beautiful instance of this will be cited in the next section4 ,we may add to the examples above given of such instances1 that of the application of chemical tests1 which are almost universally crucial experiments4 7#aih47 ,bacon's 8travelling instances0 are those in which the nature or quality under investigation 8travels10 or varies in degree2 and thus 7according to #aeb47 afford an indication of a cause by a gradation of intensity in the effect4 ,one of his instances is very happy1 being that of 8paper1 which is white when dry1 but proves less so when wet1 and comes nearer to the state of transparency upon the exclusion of the air1 and admission of water40 ,in reading this1 and many other instances in the ,novum ,organum1 one would almost suppose 7had it been written7 that its author had taken them from ,newton's ,optics4 7#aii47 ,the travelling instances1 as well as what ,bacon terms 8frontier instances10 are cases in which we are enabled to trace that general law which seems to pervade all nature--the law1 as it is termed1 of continuity1 and which is expressed in the well known sentence1 8,natura non agit per saltum40 ,the pursuit of this law into cases where its application is not at first sight obvious1 has proved a fertile source of physical discovery1 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 any4 7#bjj47 ,for example1 the transparency of gold leaf1 which permits a bluish-green light to pass through it1 is a frontier instance between the transparency of pellucid bodies and the opacity of metals1 and it prevents a breach of the law of continuity between transparent and opake bodies1 by exhibiting a body of the class generally regarded the most opake in nature1 as still possessed of some slight degree of transparency4 ,it thus proves that the quality of opacity is not a contrary or antagonist quality to that of transparency1 but only its extreme lowest degree4 ,,chap4 ,,vii4 ,,of ,,the ,,higher ,,degrees ,,of ,,inductive ,,generalization1 ,,and ,,of ,,the ,,formation ,,and ,,verification ,,of ,,theories4 7#bja47 ,as particular inductions and laws of the first degree of generality are obtained from the consideration of individual facts1 so ,theories result from a consideration of these laws1 and of the proximate causes brought into view in the previous process1 regarded all together as constituting a new set of phenomena1 the creatures of reason rather than of sense1 and each representing under general language innumerable particular facts4 ,in raising these higher inductions1 therefore1 more scope is given to the exercise of pure reason than in slowly groping out our first results4 ,the mind is more disencumbered of matter1 and moves as it were in its own element4 ,what is now before it1 it perceives more intimately1 and less through the medium of sense1 or at least not in the same manner as when actually at work on the immediate objects of sense4 ,but it must not be therefore supposed that1 in the formation of theories1 we are abandoned to the unrestrained exercise of imagination1 or at liberty to lay down arbitrary principles1 or assume the existence of mere fanciful causes4 ,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 fetters1 but rather like that of the freeman who has learned the lessons of self-restraint in the school of just subordination4 ,the ultimate objects we pursue in the highest theories are the same as those of the lowest inductions2 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 cases4 7#bjb47 ,the immediate object we propose to ourselves in physical theories is the analysis of phenomena1 and the knowledge of the hidden processes of nature in their production1 so far as they can be traced by us4 ,an important part of this knowledge consists in a discovery of the actual structure or mechanism of the universe and its parts1 through which1 and by which1 those processes are executed2 and of the agents which are concerned in their performance4 ,now1 the mechanism of nature is for the most part either on too large or too small a scale to be immediately cognizable by our senses2 and her agents in like manner elude direct observation1 and become known to us only by their effects4 ,it is in vain therefore that we desire to become witnesses to the processes carried on with such means1 and to be admitted into the secret recesses and laboratories where they are effected4 ,microscopes have been constructed which magnify more than a thousand times in linear dimension1 so that the smallest visible grain of sand may be enlarged to the appearance of one a thousand million times more bulky2 yet the only impression we receive by viewing it through such a magnifier is1 that it reminds us of some vast fragment of a rock1 while the intimate structure on which depend its colour1 its hardness1 and its chemical properties1 remains still concealed3 we do not seem to have made even an approach to a closer analysis of it by any such scrutiny4 7#bjc47 ,on the other hand1 the mechanism of the great system of which our planet forms a part escapes immediate observation by the immensity of its scale1 nay1 even by the slowness of its evolutions4 ,the motion of the minute hand of a watch can hardly be perceived without the closest attention1 and that of the hour hand not at all4 ,but what are these1 in respect of the impression of slowness they produce in our minds1 compared with a revolving movement which takes a whole year1 or twelve1 thirty1 or eighty years to complete1 as is the case with the planets in their revolutions round the sun4 ,yet no sooner do we come to reflect on the linear dimensions of these orbs1 7which however we do not see1 nor can we measure them but by a long1 circuitous1 and difficult process17 than we are lost in astonishment at the swiftness of the very motions which before seemed so slow4#dg ,the motion of the sails of a windmill offers 7on a small scale7 an illustrative case4 ,at a distance the rotation seems slow and steady--but when we stand close to one of the sails in its sweep1 we are surprised at the swiftness with which it rushes by us4 7#bjd47 ,again1 the agents employed by nature to act on material structures are invisible1 and only to be traced by the effects they produce4 ,heat dilates matter with an irresistible force2 but what heat is1 remains yet a problem4 ,a current of electricity passing along a wire moves a magnetized needle at a distance2 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 stream3 and we apply the terms current1 or stream1 to the electricity only because in some of its relations it reminds us of something we have observed in a stream of air or water4 ,in like manner we see that the moon circulates about the earth2 and because we believe it to be a solid mass1 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 tie1 we conclude that there is a force1 and a mode of connection1 between the moon and the earth2 though1 what that mode can be1 we have no conception1 nor can imagine how such a force can be exerted at a distance1 and with empty space1 or at most an invisible fluid1 between4 7,see #adh47 7#bje47 ,yet are we not to despair1 since we see regular and beautiful results brought about in human works by means which nobody would1 at first sight1 think could have any thing to do with them4 ,a sheet of blank paper is placed upon a frame1 and shoved forwards1 and after winding its way successively over and under half a dozen rollers1 and performing many other strange evolutions1 comes out printed on both sides4 ,and1 after all1 the acting cause in this process is nothing more than a few gallons of water boiled in an iron vessel1 at a distance from the scene of operations4 ,but why the water so boiled should be capable of producing the active energy which sets the whole apparatus in motion is1 and will probably long remain1 a secret to us4 7#bjf47 ,this1 however1 does not at all prevent our having a very perfect comprehension of the whole subsequent process4 ,we might frequent printing-houses1 and form a theory of printing1 and having worked our way up to the point where the mechanical action commenced 7the boiler of the steam-engine71 and verified it by taking to pieces1 and putting together again1 the train of wheels and the presses1 and by sound theoretical examination of all the transfers of motion from one part to another2 we should1 at length1 pronounce our theory good1 and declare that we understood printing thoroughly4 ,nay1 we might even go away and apply the principles of mechanism we had learned in this enquiry to other widely different purposes2 construct other machines1 and put them in motion by the same moving power1 and all without arriving at any correct idea as to the ultimate source of the force employed4 ,but1 if we were inclined to theorize farther1 we might do so2 and it is easy to imagine how two theorists might form very different hypotheses as to the origin of the power which alternately raised and depressed the piston-rod of the engine4 ,one1 for example1 might maintain that the boiler 7whose contents we will suppose that neither theorist has been permitted to examine7 was the den of some powerful unknown animal1 and he would not be without plausible analogies in the warmth1 the supply of fuel and water1 the breathing noises1 the smoke1 and above all1 the mechanical power exerted4 ,he would say 7not without a show of reason71 that where there is a positive and wonderful effect1 and many strong analogies1 such as materials consumed1 and all the usual signs of life maintained1 we are not to deny the existence of animal life because we know no animal that consumes such food4 ,nay1 he might observe with truth1 that the fuel actually consists of the chemical ingredients which constitute the chief food of all animals1 c42 while1 on the other hand1 his brother theorist1 who caught a glimpse of the fire1 and detected the peculiar sounds of ebullition1 might acquire a better notion of the case1 and form a theory more in consonance with fact4 7#bjg47 ,now1 nothing is more common in physics than to find two1 or even many1 theories maintained as to the origin of a natural phenomenon4 ,for instance1 in the case of heat itself1 one considers it as a really existing material fluid1 of such exceeding subtlety as to penetrate all bodies1 and even to be capable of combining with them chemically2 while another regards it as nothing but a rapid vibratory or rotatory motion in the ultimate particles of the bodies heated2 and produces a singularly ingenious train of mechanical reasoning to show1 that there is nothing contradictory to sound dynamical principles in such a doctrine4 ,thus1 again1 with light3 one considers it as consisting in actual particles darted forth from luminous bodies1 and acted upon in their progress by forces of extreme intensity residing in the substances on which they strike2 another1 in the vibratory motion of the particles of luminous bodies1 communicated to a peculiar subtle and highly elastic ethereal medium1 filling all space1 and conveyed through it into our eyes1 as sounds are to our ears1 by the undulations of the air4 7#bjh47 ,now1 are we to be deterred from framing hypotheses and constructing theories1 because we meet with such dilemmas1 and find ourselves frequently beyond our depth8 ,undoubtedly not4 ,est quodam prodire tenus si non datur ultra4 ,hypotheses1 with respect to theories1 are what presumed proximate causes are with respect to particular inductions3 they afford us motives for searching into analogies2 grounds of citation to bring before us all the cases which seem to bear upon them1 for examination4 ,a well imagined hypothesis1 if it have been suggested by a fair inductive consideration of general laws1 can hardly fail at least of enabling us to generalize a step farther1 and group together several such laws under a more universal expression4 ,but this is taking a very limited view of the value and importance of hypotheses3 it may happen 7and it has happened in the case of the undulatory doctrine of light7 that such a weight of analogy and probability may become accumulated on the side of an hypothesis1 that we are compelled to admit one of two things2 either that it is an actual statement of what really passes in nature1 or that the reality1 whatever it be1 must run so close a parallel with it1 as to admit of some mode of expression common to both1 at least in so far as the phenomena actually known are concerned4 ,now1 this is a very great step1 not only for its own sake1 as leading us to a high point in philosophical speculation1 but for its applications2 because whatever conclusions we deduce from an hypothesis so supported must have at least a strong presumption in their favour3 and we may be thus led to the trial of many curious experiments1 and to the imagining of many useful and important contrivances1 which we should never otherwise have thought of1 and which1 at all events1 if verified in practice1 are real additions to our stock of knowledge and to the arts of life4 7#bji47 ,in framing a theory which shall render a rational account of any natural phenomenon1 we have first to consider the agents on which it depends1 or the causes to which we regard it as ultimately referable4 ,these agents are not to be arbitrarily assumed2 they must be such as we have good inductive grounds to believe do exist in nature1 and do perform a part in phenomena analogous to those we would render an account of2 or such1 whose presence in the actual case can be demonstrated by unequivocal signs4 ,they must be ver caus1 in short1 which we can not only show to exist and to act1 but the laws of whose action we can derive independently1 by direct induction1 from experiments purposely instituted2 or at least make such suppositions respecting them as shall not be contrary to our experience1 and which will remain to be verified by the coincidence of the conclusions we shall deduce from them1 with facts4 ,for example1 in the theory of gravitation we suppose an agent1--viz4 force1 or mechanical power1--to act on any material body which is placed in the presence of any other1 and to urge the two mutually towards each other4 ,this is a vera causa2 for heavy bodies 7that is1 all bodies1 but some more1 some less17 tend to1 or endeavour to reach1 the earth1 and require the exertion of force to counteract this endeavour1 or to keep them up4 ,now1 that which opposes and neutralizes force is force4 ,and again1 a plumb-line1 which1 when allowed to hang freely1 always hangs perpendicularly2 is found to hang observably aside from the perpendicular when in the neighbourhood of a considerable mountain2 thereby proving that a force is exerted upon it1 which draws it towards the mountain4 ,moreover1 since it is a fact that the moon does circulate about the earth1 it must be drawn towards the earth by a force2 for if there were no force acting upon it1 it would go on in a straight line without turning aside to circulate in an orbit1 and would1 therefore1 soon go away and be lost in space4 ,this force1 then1 which we call the force of gravity1 is a real cause4 7#baj47 ,we have next to consider the laws which regulate the action of these our primary agents2 and these we can only arrive at in three ways3 #ast1 ,by inductive reasoning2 that is1 by examining all the cases in which we know them to be exercised1 inferring1 as well as circumstances will permit1 its amount or intensity in each particular case1 and then piecing together1 as it were1 these disjecta membra1 generalizing from them1 and so arriving at the laws desired2 #b;dly1 ,by forming at once a bold hypothesis1 particularizing the law1 and trying the truth of it by following out its consequences and comparing them with facts2 or1 #c;dly1 ,by a process partaking of both these1 and combining the advantages of both without their defects1 viz4 by assuming indeed the laws we would discover1 but so generally expressed1 that they shall include an unlimited variety of particular laws2--following out the consequences of this assumption1 by the application of such general principles as the case admits2--comparing them in succession with all the particular cases within our knowledge2 and1 lastly1 on this comparison1 so modifying and restricting the general enunciation of our laws as to make the results agree4 7#baa47 ,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 circumstances4 ,we might exemplify their successive application to the case of gravitation3 but as this would rather lead into a disquisition too particular for the objects of this discourse1 and carry us too much into the domain of technical mathematics1 we shall content ourselves with remarking1 that the method last mentioned is that which mathematicians 7especially such as have a considerable command of those general modes of representing and reasoning on quantity1 which constitute the higher analysis17 find the most universally applicable1 and the most efficacious2 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 mathematical expression4 ,such a case1 for instance1 is the elliptic motion of a planet1 which is a general proposition including the statement of an infinite number of particular places1 in which the laws of its motion allow it to be some time or other found1 and for which1 of course1 the law of force must be so assumed as to account4 7#bab47 ,with regard to the first process of the three above enumerated1 it is in fact an induction of the kind described in #ahe42 and all the remarks we there made on that kind of induction apply to it in this stage4 ,the direct assumption of a particular hypothesis has been occasionally practised very successfully4 ,as examples1 we may mention ,coulomb's and ,poisson's theories of electricity and magnetism1 in both which1 phenomena of a very complicated and interesting nature are referred to the actions of attractive and repulsive forces1 following a law similar in its expression to the law of gravitation4 ,but the difficulty and labour1 which1 in the greater theories1 always attends the pursuit of a fundamental law into its remote consequences1 effectually precludes this method from being commonly resorted to as a means of discovery1 unless we have some good reason1 from analogy or otherwise1 for believing that the attempt will prove successful1 or have been first led by partial inductions to particular laws which naturally point it out for trial4 7#bac47 ,in this case the law assumes all the characters of a general phenomenon resulting from an induction of particulars1 but not yet verified by comparison with all the particulars1 nor extended to all that it is capable of including4 7,see #aga47 ,it is the verification of such inductions which constitutes theory in its largest sense1 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 verify4 ,to return to our example3 particular inductions drawn from the motions of the several planets about the sun1 and of the satellites round their primaries1 c4 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 gravitation2 when we would verify this induction1 we must set out with assuming this law1 considering the whole system as subjected to its influence and implicitly obeying it1 and nothing interfering with its action2 we then1 for the first time1 perceive a train of modifying circumstances which had not occurred to us when reasoning upwards from particulars to obtain the fundamental law2 we perceive that all the planets must attract each other1 must therefore draw each other out of the orbits which they would have if acted on only by the sun2 and as this was never contemplated in the inductive process1 its validity becomes a question1 which can only be determined by ascertaining precisely how great a deviation this new class of mutual actions will produce4 ,to do this is no easy task1 or rather1 it is the most difficult task which the genius of man has ever yet accomplished3 still1 it has been accomplished by the mere application of the general laws of dynamics2 and the result 7undoubtedly a most beautiful and satisfactory one7 is1 that all those observed deviations in the motions of our system which stood out as exceptions 7 #aed471 or were noticed as residual phenomena and reserved for further enquiry 7 #aeh471 in that imperfect view of the subject which we got in the subordinate process by which we rose to our general conclusion1 prove to be the immediate consequences of the above-mentioned mutual actions4 ,as such1 they are neither exceptions nor residual facts1 but fulfilments of general rules1 and essential features in the statement of the case1 without which our induction would be invalid1 and the law of gravitation positively untrue4 7#bad47 ,in the theory of gravitation1 the law is all in all1 applying itself at once to the materials1 and directly producing the result4 ,but in many other cases we have to consider not merely the laws which regulate the actions of our ultimate causes1 but a system of mechanism1 or a structure of parts1 through the intervention of which their effects become sensible to us4 ,thus1 in the delicate and curious electro-dynamic theory of ,ampere1 the mutual attraction or repulsion of two magnets is referred to a more universal phenomenon1 the mutual action of electric currents1 according to a certain fundamental law4 ,but1 in order to bring the case of a magnet within the range of this law1 he is obliged to make a supposition of a peculiar structure or mechanism1 which constitutes a body a magnet1 viz4 that around each particle of the body there shall be constantly circulating1 in a certain stated direction1 a small current of electric fluid4 7#bae47 ,this1 we may say1 is too complex2 it is artificial1 and cannot be granted3 yet1 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 facts1--to make them a part of one system1 and enable us to reason from the known to the unknown1 and actually to predict facts before trial1--we would ask1 why should it not be granted8 ,when we examine those instances of nature's workmanship which we can take to pieces and understand1 we find them in the highest degree artificial in our own sense of the word4 ,take1 for example1 the structure of an eye1 or of the skeleton of an animal1--what complexity and what artifice6 ,in the one1 a pellucid muscle2 a lens formed with elliptical surfaces2 a circular aperture capable of enlargement or contraction without loss of form4 ,in the other1 a framework of the most curious carpentry2 in which occurs not a single straight line1 nor any known geometrical curve1 yet all evidently systematic1 and constructed by rules which defy our research4 ,or examine a crystallized mineral1 which we can in some measure dissect1 and thus obtain direct evidence of an internal structure4 ,neither artifice nor complication are here wanting2 and though it is easy to assert that these appearances are1 after all1 produced by something which would be very simple1 if we did but know it1 it is plain that the same might be said of a steam-engine executing the most complicated movements1 previous to any investigation of its nature1 or any knowledge of the source of its power4 7#baf47 ,in estimating1 however1 the value of a theory1 we are not to look1 in the first instance1 to the question1 whether it establishes satisfactorily1 or not1 a particular process or mechanism2 for of this1 after all1 we can never obtain more than that indirect evidence which consists in its leading to the same results4 ,what1 in the actual state of science1 is far more important for us to know1 is whether our theory truly represent all the facts1 and include all the laws1 to which observation and induction lead4 ,a theory which did this would1 no doubt1 go a great way to establish any hypothesis of mechanism or structure1 which might form an essential part of it3 but this is very far from being the case1 except in a few limited instances2 and1 till it is so1 to lay any great stress on hypotheses of the kind1 except in as much as they serve as a scaffold for the erection of general laws1 is to 8quite mistake the scaffold for the pile40 ,regarded in this light1 hypotheses have often an eminent use3 and a facility in framing them1 if attended with an equal facility in laying them aside when they have served their turn1 is one of the most valuable qualities a philosopher can possess2 while1 on the other hand1 a bigoted adherence to them1 or indeed to peculiar views of any kind1 in opposition to the tenor of facts as they arise1 is the bane of all philosophy4 7#bag47 ,there is no doubt1 however1 that the safest course1 when it can be followed1 is to rise by inductions carried on among laws1 as among facts1 from law to law1 perceiving1 as we go on1 how laws which we have looked upon as unconnected become particular cases1 either one of the other1 or all of one still more general1 and1 at length1 blend altogether in the point of view from which we learn to regard them4 ,an example will illustrate what we mean4 ,it is a general law1 that all hot bodies throw out or radiate heat in all directions1 7by which we mean1 not that heat is an actual substance darted out from hot bodies1 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 directions17 and that other colder bodies placed in their neighbourhood become hot1 as if they received the heat so radiated4 ,again1 all solid bodies which become heated in one part conduct1 or diffuse1 the heat from that part through their whole substance4 ,here we have two modes of communicating heat1--by radiation1 and by conduction2 and both these have their peculiar1 and1 to all appearance1 very different laws4 ,now1 let us bring a hot and a cold body 7of the same substance7 gradually nearer and nearer together1--as they approach1 the heat will be communicated from the hot to the cold one by the laws of radiation2 and from the nearer to the farther part of the colder one1 as it gradually grows warm1 by those of conduction4 ,let their distance be diminished till they just lightly touch4 ,how does the heat now pass from one to the other8 ,doubtless1 by radiation2 for it may be proved1 that in such a contact there is yet an interval4 ,let them then be forced together1 and it will seem clear that it must now be by conduction4 ,yet their interval must diminish gradually1 as the force by which they are pressed together increases1 till they actually cohere1 and form one4 ,the law of continuity1 then1 of which we have before spoken 7 #aii471 forbids us to suppose that the intimate nature of the process of communication is changed in this transition from light to violent contact1 and from that to actual union4 ,if so1 we might ask1 at what point does the change happen8 ,especially since it is also demonstrable1 that the particles of the most solid body are not1 really1 in contact4 ,therefore1 the laws of conduction and radiation have a mutual dependence1 and the former are only extreme cases of the latter4 ,if1 then1 we would rightly understand what passes1 or what is the process of nature in the slow communication of heat through the substance of a solid1 we must ground our enquiries upon what takes place at a distance1 and then urge the laws to which we have arrived1 up to their extreme case4 7#bah47 ,when two theories run parallel to each other1 and each explains a great many facts in common with the other1 any experiment which affords a crucial instance to decide between them1 or by which one or other must fall1 is of great importance4 ,in thus verifying theories1 since they are grounded on general laws1 we may appeal1 not merely to particular cases1 but to whole classes of facts2 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 wrong4 ,a curious example is given by ,m4 ,fresnel1 as decisive1 in his mind1 of the question between the two great opinions on the nature of light1 which1 since the time of ,newton and ,huyghens1 have divided philosophers4 7,see #bjg47 ,when two very clean glasses are laid one on the other1 if they be not perfectly flat1 but one or both in an almost imperceptible degree convex or prominent1 beautiful and vivid colours will be seen between them2 and if these be viewed through a red glass1 their appearance will be that of alternate dark and bright stripes4 ,these stripes are formed between the two surfaces in apparent contact1 as any one may satisfy himself by using1 instead of a flat plate of glass for the upper one1 a triangular-shaped piece1 called a prism1 like a three-cornered stick1 and looking through the inclined side of it next the eye1 by which arrangement the reflection of light from the upper surface is prevented from intermixing with that from the surfaces in contact4 ,now1 the coloured stripes thus produced are explicable on both theories1 and are appealed to by both as strong confirmatory facts2 but there is a difference in one circumstance according as one or the other theory is employed to explain them4 ,in the case of the ,huyghenian doctrine1 the intervals between the bright stripes ought to appear absolutely black2 in the other1 half bright1 when so viewed through a prism4 ,this curious case of difference was tried as soon as the opposing consequences of the two theories were noted by ,m4 ,fresnel1 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 medium4 7#bai47 ,theories are best arrived at by the consideration of general laws2 but most securely verified by comparing them with particular facts1 because this serves as a verification of the whole train of induction1 from the lowest term to the highest4 ,but then1 the comparison must be made with facts purposely selected so as to include every variety of case1 not omitting extreme ones1 and in sufficient number to afford every reasonable probability of detecting error4 ,a single numerical coincidence in a final conclusion1 however striking the coincidence or important the subject1 is not sufficient4 ,newton's theory of sound1 for example1 leads to a numerical expression for the actual velocity of sound1 differing but little from that afforded by the correct theory afterwards explained by ,lagrange1 and 7when certain considerations not contemplated by him are allowed for7 agreeing with fact2 yet this coincidence is no verification of ,newton's view of the general subject of sound1 which is defective in an essential point1 as the great geometer last named has very satisfactorily shown4 ,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 facts4 7#bbj47 ,but1 on the other hand1 when a theory will bear the test of such extensive comparison1 it matters little how it has been originally framed4 ,however strange and1 at first sight1 inadmissible its postulates may appear1 or however singular it may seem that such postulates should have been fixed upon1--if they only lead us1 by legitimate reasonings1 to conclusions in exact accordance with numerous 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 for1 we cannot refuse to admit them2 or if we still hesitate to regard them as demonstrated truths1 we cannot1 at least1 object to receive them as temporary substitutes for such truths1 until the latter shall become known4 ,if they suffice to explain all the phenomena known1 it becomes highly improbable that they will not explain more2 and if all their conclusions we have tried have proved correct1 it is probable that others yet untried will be found so too2 so that in rejecting them altogether1 we should reject all the discoveries to which they may lead4 7#bba47 ,in all theories which profess to give a true account of the process of nature in the production of any class of phenomena1 by referring them to general laws1 or to the action of general causes1 through a train of modifying circumstances2 before we can apply those laws1 or trace the action of those causes in any assigned case1 we require to know the circumstances3 we must have data whereon to ground their application4 ,now1 these can be learned only from observation2 and it may seem to be arguing in a vicious circle to have recourse to observation for any part of those theoretical conclusions1 by whose comparison with fact the theory itself is to be tried4 ,the consideration of an example will enable us to remove this difficulty4 ,the most general law which has yet been discovered in chemistry is this1 that all the elementary substances in nature are susceptible of entering into combination with each other only in fixed or definite proportions by weight1 and not arbitrarily2 so that when any two substances are put together with a view to unite them1 if their weights are not in some certain determinate proportion1 a complete combination will not take place1 but some part of one or the other ingredient will remain over and above1 and uncombined4 ,suppose1 now1 we have found a substance having all the outward characters of a homogeneous or unmixed body1 but which1 on analysis1 we discover to consist of sulphur1 and lead in the proportion of #bj parts of the former to #acj of the latter ingredient2 and we would know whether this is to be regarded as a verification of the law of definite proportions or an exception to it4 ,the question is reduced to this1 whether the proportion #bj to #acj be or be not that fixed and definite proportion1 7or one of them1 if there be more than one proportion possible17 in which1 according to the law in question1 sulphur and lead can combine2 now1 this can never be decided by merely looking at the law in all its generality4 ,it is clear1 that when particularized by restricting its expression to sulphur and lead1 the law should state what are those particular fixed proportions in which these bodies can combine4 ,that is to say1 there must be certain data or numbers1 by which these are distinguished from all other bodies in nature1 and which require to be known before we can apply the general law to the particular case4 ,to determine such data1 observation must be consulted2 and if we were to have recourse to that of the combination of the two substances in question with each other1 no doubt there would be ground for the logical objection of a vicious circle3 but this is not done2 the determination of these numerical data is derived from experiments purposely made on a great variety of different combinations1 among which that under consideration does not of necessity occur1 and all these being found1 independently of each other1 to agree in giving the same results1 they are therefore safely assumed as part of the system4 ,thus1 the law of definite proportions1 when applied to the actual state of nature1 requires two separate statements1 the one announcing the general law of combination1 the other particularizing the numbers appropriate to the several elements of which natural bodies consist1 or the data of nature4 ,among these data1 if arranged in a list1 there will be found opposite to the element sulphur the number #af1 and opposite to lead1 #ajddh2 and since #bj is to #acj in the exact proportion of #af to #ajd1 it appears that the combination in question affords a satisfactory verification of the law4 7#bbb47 ,the great importance of physical data of this description1 and the advantage of having them well determined1 will be obvious1 if we consider1 that a list of them1 when taken in combination with the general law1 affords the means of determining at once the exact proportion of the ingredients of all natural compounds1 if we only know the place they hold in the system4 ,in chemistry1 the number of admitted elements is between fifty and sixty1 and new ones are added continually as the science advances4 ,now1 the moment the number corresponding to any new substance added to the list is determined1 we have1 in fact1 ascertained all the proportions in which it can enter into combination with all the others1 so that a careful experiment made with the object of determining this number is1 in fact1 equivalent to as many different experiments as there are binary1 ternary1 or yet more complicated combinations capable of existing1 into which the new substance may enter1 as an ingredient4 7#bbc47 ,the importance of obtaining exact physical data can scarcely be too much insisted on1 for without them the most elaborate theories are little better than mere inapplicable forms of words4 ,it would be of little consequence to be informed1 abstractedly1 that the sun and planets attract each other1 with forces proportional to their masses1 and inversely as the squares of their distances3 but1 as soon as we know the data of our system1 as soon as we have an accurate statement 7no matter how obtained7 of the distances1 masses1 and actual motions of the several bodies which compose it1 we need no more to enable us to predict all the movements of its several parts1 and the changes that will happen in it for thousands of years to come2 and even to extend our views backwards into time1 and recover from the past1 phenomena1 which no observation has noted1 and no history recorded1 and which yet 7it is possible7 may have left indelible traces of their existence in their influence on the state of nature in our own globe1 and those of the other planets4 7#bbd47 ,the proof1 too1 that our data are correctly assumed1 is involved in the general verification of the whole theory1 of which1 when once assumed1 they form a part2 and the same comparison with observation which enables us to decide on the truth of the abstract principle1 enables us1 at the same time1 to ascertain whether we have fixed the values of our data in accordance with the actual state of nature4 ,if not1 it becomes an important question1 whether the assumed values can be corrected1 so as to bring the results of theory to agree with facts8 ,thus it happens1 that as theories approach to their perfection1 a more and more exact determination of data becomes requisite4 ,deviations from observed fact1 which1 in a first or approximative verification1 may be disregarded as trifling1 become important when a high degree of precision is attained4 ,a difference between the calculated and observed places of a planet1 which would have been disregarded by ,kepler in his verification of the law of elliptic motion1 would now be considered fatal to the theory of gravity1 unless it could be shown to arise from an erroneous assumption of some of the numerical data of our system4 7#bbe47 ,the observations most appropriate for the ready and exact determination of physical data are1 therefore1 those which it is most necessary to have performed with exactness and perseverance4 ,hence it is1 that their performance1 in many cases1 becomes a national concern1 and observatories are erected and maintained1 and expeditions despatched to distant regions1 at an expense which1 to a superficial view1 would appear most disproportioned to their objects4 ,but it may very reasonably be asked why the direct assistance afforded by governments to the execution of continued series of observations adapted to this especial end should continue to be1 as it has hitherto almost exclusively been1 confined to astronomy4 7#bbf47 ,physical data intended to be employed as elements of calculation in extensive theories1 require to be known with a much greater degree of exactness than any single observation possesses1 not only on account of their dignity and importance1 as affording the means of representing an indefinite multitude of facts2 but because1 in the variety of combinations that may arise1 or in the changes that circumstances may undergo1 cases will occur when any trifling error in one of the data may become enormously magnified in the final result to be compared with observation4 ,thus1 in the case of an eclipse of the sun1 when the moon enters very obliquely upon the sun's disc1 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 commence4 ,it ought to be remarked1 that these are1 of all others1 the conjunctures where observations are most available for the determination of data2 for1 by the same rule that a small change in the data will1 in such cases1 produce a great one in the thing to be observed2 so1 vice vers1 any moderate amount of error1 committed in an observation undertaken for ascertaining its value1 can produce but a very trifling one in the reverse calculation from which the data come to be determined by observation4 ,this remark extends to every description of physical data in every department of science1 and is never to be overlooked when the object in view is the determination of data with the last degree of precision4 7#bbg47 ,but how1 it may be asked1 are we to ascertain by observation1 data more precise than observation itself8 ,how are we to conclude the value of that which we do not see1 with greater certainty than that of quantities which we actually see and measure8 ,it is the number of observations which may be brought to bear on the determination of data that enables us to do this4 ,whatever error we may commit in a single determination1 it is highly improbable that we should always err the same way1 so that1 when we come to take an average of a great number of determinations1 7unless there be some constant cause which gives a bias one way or the other17 we cannot fail1 at length1 to obtain a very near approximation to the truth1 and1 even allowing a bias1 to come much nearer to it than can fairly be expected from any single observation1 liable to be influenced by the same bias4 7#bbh47 ,this useful and valuable property of the average of a great many observations1 that it brings us nearer to the truth than any single observation can be relied on as doing1 renders it the most constant resource in all physical enquiries where accuracy is desired4 ,and it is surprising what a rapid effect1 in equalizing fluctuations and destroying deviations1 a moderate multiplication of individual observations has4 ,a better example can hardly be taken than the average height of the quicksilver in the common barometer1 which measures the pressure of the air1 and whose fluctuations are proverbial4 ,nevertheless1 if we only observe it regularly every day1 and1 at the end of each month1 take an average of the observed heights1 we shall find the fluctuations surprisingly diminished in amount2 and if we go on for a whole year1 or for many years in succession1 the annual averages will be found to agree with still greater exactness4 ,this equalizing power of averages1 by destroying all such fluctuations as are irregular or accidental1 frequently enables us to obtain evidence of fluctuations really regular1 periodic in their recurrence1 and so much smaller in their amount than the accidental ones1 that1 but for this mode of proceeding1 they never would have become apparent4 ,thus1 if the height of the barometer be observed four times a day1 constantly1 for a few months1 and the averages taken1 it will be seen that a regular daily fluctuation1 of very small amount1 takes place1 the quicksilver rising and falling twice in the four-and-twenty hours4 ,it is by such observations that we are enabled to ascertain--what no single measure 7unless by a fortunate coincidence71 could give us any idea1 and never any certain knowledge of--the true sea level at any part of the coast1 or the height at which the water of the ocean would stand1 if perfectly undisturbed by winds1 waves1 or tides3 a subject of very great importance1 and upon which it would be highly desirable to possess an extensive series of observations1 at a great many points on the coasts of the principal continents and islands over the whole globe4 7#bbi47 ,in all cases where there is a direct and simple relation between the phenomenon observed and a single datum on which it depends1 every single observation will give a value of this quantity1 and the average of all 7under certain restrictions7 will be its exact value4 ,we say1 under certain restrictions2 for1 if the circumstances under which the observations are made be not alike1 they may not all be equally favourable to exactness1 and it would be doing injustice to those most advantageous1 to class them with the rest4 ,in such cases as these1 as well as in cases where the data are numerous and complicated together1 so as not to admit of single1 separate determination 7a thing of continual occurrence71 we have to enter into very nice1 and often not a little intricate1 considerations respecting the probable accuracy of our results1 or the limits of error within which it is probable they lie4 ,in so doing we are obliged to have recourse to a refined and curious branch of mathematical enquiry1 called the doctrine of probabilities1 the object of which 7as its name imports7 is to reduce our estimation of the probability of any conclusion to calculation1 so as to be able to give more than a mere guess at the degree of reliance which ought to be placed in it4 7#bcj47 ,to give some general idea of the considerations which such computations involve1 let us imagine a person firing with a pistol at a wafer on a wall ten yards distant3 we might1 in a general way1 take it for granted1 that he would hit the wall1 but not the wafer1 at the first shot2 but if we would form any thing like a probable conjecture of how near he would come to it1 we must first have an idea of his skill4 ,no better way of judging could be devised than by letting him fire a hundred shots at it1 and marking where they all struck4 ,suppose this done1--suppose the wafer has been hit once or twice1 that a certain number of balls have hit the wall within an inch of it1 a certain number between one and two inches1 and so on1 and that one or two have been some feet wide of the mark4 ,still the question arises1 what estimate are we thence to form of his skill8 how near 7or nearer7 may we1 after this experience1 safely1 or at least not unfairly1 bet that he will come to the mark the next subsequent shot8 ,this the laws of probability enable us on such data to say4 ,again1 suppose1 before we were allowed to measure the distances1 the wafer were to have been taken away1 and we were called upon1 on the mere evidence of the marks on the wall1 to say where it had been placed2 it is clear that no reasoning would enable any one to say with certainty2 yet there is assuredly one place which we may fix on with greater probability of being right than any other4 ,now1 this is a very similar case to that of an observer--an astronomer for example--who would determine the exact place of a heavenly body4 ,he points to it his telescope1 and obtains a series of results disagreeing among themselves1 but yet all agreeing within certain limits1 and only a comparatively small number of them deviating considerably from the mean of all2 and from these he is called upon to say1 definitively1 what he shall consider to have been the most probable place of his star at the moment4 ,just so in the calculation of physical data2 where no two results agree exactly1 and where all come within limits1 some wide1 some close1 what have we to guide us when we would make up our minds what to conclude respecting them8 ,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 valuable4 ,however1 as this doctrine is one of the most difficult and delicate among the applications of mathematics to natural philosophy1 this slight mention of it must suffice at present4 7#bca47 ,in the foregoing pages we have endeavoured to explain the spirit of the methods to which1 since the revival of philosophy1 natural science has been indebted for the great and splendid advances it has made4 ,what we have all along most earnestly desired to impress on the student is1 that natural philosophy is essentially united in all its departments1 through all which one spirit reigns and one method of enquiry applies4 ,it cannot1 however1 be studied as a whole1 without subdivision into parts2 and1 in the remainder of this discourse1 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 subdivided1 and endeavour to give a general idea of the nature of each1 and of its relations to the rest4 ,in the course of this1 we shall have frequent opportunity to point out the influence of those general principles we have above endeavoured to explain1 on the progress of discovery4 ,but this we shall only do as cases arise1 without entering into any regular analysis of the history of each department with that view4 ,such an analysis would1 indeed1 be a most useful and valuable work1 but would far exceed our present limits4 ,we are not1 however1 without a hope that this great desideratum in science will1 ere long1 be supplied from a quarter every way calculated to do it justice4 ,,part ,,iii4 ,,of ,,the ,,subdivision ,,of ,,physics ,,into ,,distinct ,,branches1 ,,and ,,their ,,mutual ,,relations4 ,,chapter ,i4 ,,of ,,the ,,phenomena ,,of ,,force1 ,,and ,,of ,,the ,,constitution ,,of ,,natural ,,bodies4 7#bcb47 ,natural ,history may be considered in two very different lights3 either1 #ast1 as a collection of facts and objects presented by nature1 from the examination1 analysis1 and combination of which we acquire whatever knowledge we are capable of attaining both of the order of nature1 and of the agents she employs for producing her ends1 and from which1 therefore1 all sciences arise2 or1 #b;dly1 as an assemblage of phenomena to be explained2 of effects to be deduced from causes2 and of materials prepared to our hands1 for the application of our principles to useful purposes4 ,natural history1 therefore1 considered in the one or the other of these points of view1 is either the beginning or the end of physical science4 ,as it offers to us1 in a confused and interwoven mass1 the elements of all our knowledge1 our business is to disentangle1 to arrange1 and to present them in a separate and distinct state3 and to this end we are called upon to resolve the important but complicated problem1--,given the effect1 or assemblage of effects1 to find the causes4 ,the principles on which this enquiry relies are those which constitute the relation of cause and effect1 as it exists with reference to our minds2 and their rules and mode of application have been attempted to be sketched out1 7though in far less detail than the intrinsic interest of the subject1 both in a logical and practical point of view1 would demand17 in the foregoing pages4 ,it remains now to bring together1 in a summary statement1 the results of the general examination of nature1 so far as it has been prosecuted to the discovery of natural agents1 and the mode in which they act4 7#bcc47 ,the first great agent which the analysis of natural phenomena offers to our consideration1 more frequently and prominently than any other1 is force4 ,its effects are either1 #ast1 to counteract the exertion of opposing force1 and thereby to maintain equilibrium2 or1 #b;dly1 to produce motion in matter4 7#bcd47 ,matter1 or that1 whatever it be1 of which all the objects in nature which manifest themselves directly to our senses consist1 presents us with two general qualities1 which at first sight appear to stand in contradiction to each other--activity and inertness4 ,its activity is proved by its power of spontaneously setting other matter in motion1 and of itself obeying their mutual impulse1 and moving under the influence of its own and other force2 inertness1 in refusing to move unless obliged to do so by a force impressed externally1 or mutually exerted between itself and other matter1 and by persisting in its state of motion or rest unless disturbed by some external cause4 ,yet in reality this contradiction is only apparent4 ,force being the cause1 and motion the effect produced by it on matter1 to say that matter is inert1 or has inertia1 as it is termed1 is only to say that the cause is expended in producing its effect1 and that the same cause cannot 7without renewal7 produce double or triple its own proper effect4 ,in this point of view1 equilibrium may be conceived as a continual production of two opposite effects1 each undoing at every instant what the other has done4 7#bce47 ,however1 if this should appear too metaphysical1 at all events this difference of effects gives rise to two great divisions of the science of force1 which are commonly known by the names of ,,statics and ,,dynamics2 the latter term1 which is general1 and has been used by us before in its general sense1 being usually confined to the doctrine of motion1 as produced and modified by force4 ,each of these great divisions again branches out into distinct subdivisions1 according as we consider the equilibrium or motion of matter in the three distinct states in which it is presented to us in nature1 the solid1 liquid1 and ariform state1 to which1 perhaps1 ought to be added the viscous1 as a state intermediate between that of solidity and fluidity1 the consideration of which1 though very obscure and difficult1 offers a high degree of interest on a variety of accounts4 ,statics and ,dynamics4 7#bcf47 ,the principles have been definitively fixed by ,galileo and his successors1 down to ,newton1 on a basis of sound induction2 and as they are perfectly general1 and apply to every case1 they are competent1 as we have already before observed1 to the solution of every problem that can occur in the deductive processes1 by which phenomena are to be explained1 or effects calculated4 ,hence1 they include every question that can arise respecting the motions and rest of the smallest particles of matter1 as well as of the largest masses4 ,but the mode of reasoning from these general principles differs materially1 whether we consider them as applied to masses of matter of a sensible size1 or to those excessively minute1 and perhaps indivisible1 molecules of which such masses are composed4 ,the investigations which relate to the latter subject are extremely intricate1 as they necessarily involve the consideration of the hypotheses we may form respecting the intimate constitution of the several sorts of bodies above enumerated4 7#bcg47 ,on the other hand1 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 structure4 ,thus1 in reasoning respecting the application of forces to a solid mass1 we suppose its parts indissolubly and unalterably connected2 it matters not by what tie1 provided this condition be satisfied1 that one point of it cannot be moved without setting all the rest in motion1 so that the relative situation of the parts one among another be not changed4 ,this is the abstract notion of a solid which the mechanician employs in his reasonings4 ,and their conclusions will apply to natural bodies1 of course1 only so far as they conform to such a definition4 ,in strictness of speaking1 however1 there are no bodies which absolutely conform to it4 ,no substance is known whose parts are absolutely incapable of yielding one among another2 but the amount by which they do yield is so excessively small as to be demonstrably incapable1 in most cases1 of having any influence on the results3 and in those where it has such influence1 an especial investigation of its amount can always be made4 ,this gives rise to two subdivisions of the application of mechanical reasonings to solid masses4 ,those which refer to the action of forces on flexible or elastic1 and on inflexible or rigid1 bodies1 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 error4 7#bch47 ,in like manner1 when we reason respecting the action of forces on a fluid mass1 all we have occasion to assume is1 that its parts are freely moveable one among the other4 ,if1 besides this1 we choose to regard a fluid as incompressible1 and deduce conclusions on this supposition1 they will hold good only so far as there may be found such fluids in nature4 ,now1 in strictness1 there are none such2 but1 practically speaking1 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 vitiated2 and1 in the remaining cases1 the same general principles enable us to enter on a special enquiry directed to this point3 and hence the division of fluids1 in mechanical language1 into compressible and incompressible1 the latter being only the extreme or limiting case of the former4 7#bci47 ,as we propose here1 however1 only to consider what is the actual constitution of nature1 we shall regard all bodies1 as they really are1 more or less flexible and yielding4 ,we know for certain1 that the space which any material body appears to occupy is not entirely filled by it2 because there is none which by the application of a sufficient force may not be compressed or forced into a smaller space1 and which1 either wholly1 as in air or liquids1 or in part1 as in the greater number of solids1 will not recover its former dimensions when the force is taken off4 ,in the case of air1 this condensation may be urged to almost any extent2 and not only does a mass of air so condensed completely recover its original bulk1 when the applied pressure is removed1 but if that ordinary pressure under which it exists at the earth's surface 7and which arises from the weight of the atmosphere7 be also removed by an air-pump1 it will still further dilate itself without limit so far as we have yet been able to try it4 ,hence we are led to the conclusion that the particles of air are mutually elastic1 and have a tendency to recede from one another1 which can only be counteracted by force1 and therefore is itself a force of the repulsive kind4 ,nevertheless1 as air is heavy1 and as gravitation is a universal property of matter1 there is no doubt that this repulsive tendency must have a limit1 and that there is a distance to which1 if the particles of the air could be removed from each other1 their mutual repulsion would cease1 and an attraction take its place4 ,this limit is probably attained at some very great height above the earth's surface1 beyond which1 of course1 its atmosphere cannot extend4 7#bdj47 ,what1 however1 we can only conclude by this or similar reasoning respecting air1 we see distinctly in liquids4 ,they are all1 though in a small degree1 compressible1 and recover their former dimensions completely when the pressure is removed2 but they cannot be dilated 7by mechanical means71 and have no tendency1 while they remain liquids1 to enlarge themselves beyond a certain limit1 and therefore they assume a determinate surface while at rest1 and their parts actually resist further separation with a considerable force1 thus giving rise to the phenomenon of the cohesion of liquids4 7#bda47 ,both in air and in liquids1 however1 the most perfect freedom of motion of the parts among each other subsists1 which could hardly be the case if they were not separate and independent of each other4 ,and from this1 combined with the foregoing considerations1 it has been concluded that they do not actually touch1 but are kept asunder at determinate distances from each other1 by the constant action of the two forces of attraction and repulsion1 which are supposed to balance and counteract each other at the ordinary distances of the particles1 but to prevail1 the one1 or the other1 according as they are forcibly urged together or pulled asunder4 7#bdb47 ,in solids1 however1 the case is very different4 ,the mutual free motion of their parts inter se is powerfully impeded1 and in some almost destroyed4 ,in some1 a slow and gradual change of figure may be produced to a great extent1 by pressure or blows1 as for instance in the metals1 clay1 butter1 c42 in others1 fracture is the consequence of any attempt to change the figure by violence beyond a certain very small limit4 ,in solids1 then1 it is evident1 that the consideration of their intimate structure has a 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 present2 yet the general facts that their parts cohere with a certain energy1 and that they resist displacement or intrusion on the part of other bodies1 are sufficient to demonstrate at least the existence of such forces1 whatever obscurity may subsist as to their mode of action4 7#bdc47 ,this division of bodies into airs1 liquids1 and solids1 gives rise1 then1 to three distinct branches of mechanical science1 in each of which the general principles of equilibrium and motion have their peculiar mode of application2 viz4 pneumatics1 hydrostatics1 and what might1 without impropriety1 be termed stereostatics4 ,pneumatics4 7#bdd47 ,pneumatics relates to the equilibrium or movements of arial fluids under all circumstances of pressure1 density1 and elasticity4 ,the weight of the air1 and its pressure on all the bodies on the earth's surface1 were quite unknown to the ancients1 and only first perceived by ,galileo1 on the occasion of a sucking-pump refusing to draw water above a certain height4 ,before his time it had always been supposed that water rose by suction in a pipe1 in consequence of a certain natural abhorrence of a vacuum or empty space1 which obliged the water to enter by way of supplying the place of the air sucked out4 ,but if any such abhorrence existed1 and had the force of an acting cause1 which could urge water a single foot into a pipe1 there is no reason why the same principle should not carry it up two1 three1 or any number of feet2 none why it should suddenly stop short at a certain height1 and refuse to rise higher1 however violent the suction might be1 nay1 even fall back1 if purposely forced up too high4 7#bde47 ,galileo1 however1 at first contented himself with the conclusion1 that the natural abhorrence of a vacuum was not strong enough to sustain the water more than about thirty-two feet above its level2 and1 although the true cause of the phenomenon at length occurred to him1 in the pressure of the air on the general surface1 it was not satisfactorily demonstrated till his pupil1 ,torricelli1 conceived the happy idea of instituting an experiment on a small scale by the use of a much heavier liquid1 mercury1 instead of water1 and1 in place of sucking out the air from above1 employing the much more effectual method of filling a long glass tube with mercury1 and inverting it into a basin of the same metal4 ,it was then at once seen1 as by a glaring instance1 that the maintenance of the mercury in the tube 7which is nothing else than the common barometer7 was the effect of a perfectly definite external cause1 while its fluctuations from day to day1 with the varying state of the atmosphere1 strongly corroborated the notion of its being due to the pressure of the external air on the surface of the mercury in the reservoir4 7#bdf47 ,the discovery of ,torricelli was1 however1 at first much misconceived1 and even disputed1 till the question was finally decided by appeal to a crucial instance1 one of the first1 if not the very first on record in physics1 and for which we are indebted to the celebrated ,pascal4 ,his acuteness perceived that if the weight of the incumbent air be the direct cause of the elevation of the mercury1 it must be measured by the amount of that elevation1 and therefore that1 by carrying a barometer up a high mountain1 and so ascending into the atmosphere above a large portion of the incumbent air1 the pressure1 as well as the length of the column sustained by it1 must be diminished2 while1 on the other hand1 if the phenomenon were due to the cause originally assigned1 no difference could be expected to take place1 whether the observation were made on a mountain or on the plain4 ,perhaps the decisive effect of the experiment which he caused to be instituted for the purpose1 on the ,puy de ,dme1 a high mountain in ,auvergne1 while it convinced every one of the truth of ,torricelli's views1 tended more powerfully than any thing which had previously been done in science to confirm1 in the minds of men1 that disposition to experimental verification which had scarcely yet taken full and secure root4 7#bdg47 ,immediately on this discovery followed that of the air-pump1 by ,otto von ,guericke of ,magdeburgh1 whose aim seems to have been to decide the question1 whether a vacuum could or could not exist1 by endeavouring to make one4 ,the imperfection of his mechanism enabled him only to diminish the arial contents of his receivers1 not entirely to empty them2 but the curious effects produced by even a partial exhaustion of air speedily excited attention1 and induced our illustrious countryman1 ,robert ,boyle1 to the prosecution of those experiments which terminated in his hands1 and in those of ,hauksbee1 ,hooke1 ,mariotte1 and others1 in a satisfactory knowledge of the general law of the equilibrium of the air under the influence of greater or less pressures4 ,these discoveries have since been extended to all the various descriptions of arial fluids which chemistry has shown to exist1 and to maintain their ariform state under artificial pressure1 and even to those which may be produced from liquids reduced to a state of vapour by heat1 so long as they retain that state4 7#bdh47 ,the manner in which the observed law of equilibrium of an elastic fluid1 like air1 may be considered to originate in the mutual repulsion of its particles1 has been investigated by ,newton1 and the actual statement of the law itself1 as announced by ,mariotte1 8that the density of the air1 or the quantity of it contained in the same space1 is1 cteris paribus1 proportional to the pressure it supports10 has recently been verified within very extensive limits by direct experiment1 by a committee of the ,royal ,academy of ,paris4 ,this law contains the principle of solution of every dynamical question that can occur relative to the equilibrium of elastic fluids1 and is therefore to be regarded as one of the highest axioms in the science of pneumatics4 ,hydrostatics4 7#bdi47 ,the principles of the equilibrium of liquids1 understanding by this word such fluids as do not1 though quite at liberty1 attempt to dilate themselves beyond a certain point1 are at once few and simple4 ,the first steps towards a knowledge of them were made by ,archimedes1 who established the general fact1 that a solid immersed in a liquid loses a portion of its weight equal to that of the liquid it displaces4 ,it seems very astonishing1 after this1 that it should not have been at once concluded that the weight thus said to be lost is only counteracted by the upward pressure of the liquid1 and that1 therefore1 a portion of any liquid1 surrounded on all sides by a liquid of the same kind1 does really exert its weight in keeping its place4 ,yet the prejudice that 8liquids do not gravitate in their natural place0 kept its ground1 and was only dispelled with the mass of error and absurdity which the introduction of a rational and experimental philosophy by ,galileo swept away4 7#bej47 ,the hydrostatical law of the equal pressure of liquids in all directions1 with its train of curious and important consequences1 is an immediate conclusion from the perfect mobility of their parts among one another1 in consequence of which each of them tends to recede from an excess of pressure on one side1 and thus bears upon the rest1 and distributes the pressure among its neighbours4 ,in this form it was laid down by ,newton1 and has proved one of the most useful and fertile principles of physico-mathematical reasoning on the equilibrium of fluid masses1 as affording a means of tracing the action of a force applied at any point of a liquid through its whole extent4 ,it applies1 too1 without any modification1 to expansible fluids as well as to liquids2 and1 in the applications of geometry to this subject1 enables us to dispense with any minute and intricate enquiries as to the mode in which individual particles act on each other4 7#bea47 ,in a practical point of view1 this law is remarkable for the directness of its application to useful purposes4 ,the immediate and perfect distribution of a pressure applied on any one part1 however small1 of a fluid surface through the whole mass1 enables us to communicate at one instant the same pressure to any number of such parts by merely increasing the surface of the fluid1 which may be done by enlarging the containing vessel2 and if the vessel be so constructed that a large portion of its surface shall be moveable together1 the pressures on all the similar parts of this portion will be united into one consentient force1 which may thus be increased to any extent we please4 ,the hydraulic press1 invented by ,bramah1 7or rather applied by him after a much more ancient inventor1 ,stevin17 is constructed on this principle4 ,a small quantity of water is driven by sufficient pressure into a vessel already full1 and provided with a moveable surface or piston of great size4 ,under such circumstances something must give way2 the great surface of the piston accumulates the pressure on it to such an extent that nothing can resist its violence4 ,thus1 trees are torn up by the roots2 piles extracted from the earth2 woollen and cotton goods compressed into the most portable dimensions2 and even hay1 for military service1 reduced to such a state of coercion as to be easily packed on board transports4 7#beb47 ,liquids differ from ariform fluids by their cohesion1 which may be regarded as a kind of approach to a solid state1 and was so regarded by ,bacon 7#aic474 ,indeed1 there can be little doubt that the solid1 liquid1 and ariform states of bodies are merely stages in a progress of gradual transition from one extreme to the other2 and that1 however strongly marked the distinctions between them may appear1 they will ultimately turn out to be separated by no sudden or violent line of demarcation1 but shade into each other by insensible gradations4 ,the late experiments of ,baron ,cagnard de la ,tour may be regarded as a first step towards the full demonstration of this 7#aii474 ,but the cohesion of liquids is not1 like that of solids1 so modified by their structure in other respects as to destroy the mobility of their parts one among another 7unless in those cases of nearer approach to the solid state which obtain in viscid or gummy liquids74 ,on the contrary1 the two qualities co-exist1 and give rise to a number of curious and intricate phenomena4 7#bec47 ,one of the most remarkable of these is capillary attraction1 or capillarity as it is sometimes called4 ,every body has remarked the adhesion of water to glass4 ,the elevation of the general surface of the liquid where it is in contact with the containing vessel2 the form of a drop suspended at the under side of a solid3 these are instances of capillary attraction4 ,if a small glass tube with a bore as fine as a hair be immersed in water1 the water will be observed to rise in it to a certain height1 and to assume a concave surface at its upper extremity4 ,the attraction of the glass on the water1 and the cohesion of the parts of the water to each other1 are no doubt the joint causes of this curious effect2 but the mode of action is at once obscure and complex2 and although the researches of ,laplace and ,young have thrown great light on it1 further investigation seems necessary before we can be said distinctly to understand it4 7#bed47 ,as the capillarity and cohesion of the parts of liquids shows them to possess the power of mutual attraction1 so their elasticity demonstrates that they also possess that of repulsion when forcibly brought nearer than their natural state4 ,from the extremely small extent to which the compression of liquids can be carried by any force we can employ1 compared with that of air1 we must conclude that this repulsion is much more violent in the former than in the latter1 but counteracted also by a more powerful force of attraction4 ,so much more powerful1 indeed1 is the resistance of liquids to compression1 that they were usually regarded as incompressible2 an opinion corroborated by a celebrated experiment made at ,florence1 in which water was forced through the pores 7as it was said7 of a golden ball4 ,more recent experiments by ,canton1 and since by ,perkins1 ,orsted1 and others1 have demonstrated however the contrary1 and assigned the amount of compression4 7#bee47 ,the consideration of the motions of fluids1 whether liquid or expansible1 is infinitely more complicated than that of their equilibrium4 ,when their motions are slow1 it is reasonable to suppose that the law of the equable distribution of pressure obtains2 but in very rapid displacements of their parts one among the other1 it is not easy to see how such an equable distribution can be accomplished1 and some phenomena exist which seem to indicate a contrary conclusion4 7#bef47 ,independent of this1 there are difficulties of an almost insuperable nature to the regular deductive application of the general principles of mechanics to this subject1 which arise from the excessive intricacy of the pure mathematical enquiries to which its investigation leads4 ,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 principles1 and thus laid the foundation of ,,hydrodynamics2 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 understood4 ,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 7#ahi47 is preferable4 ,such1 for example1 is that of the resistance of fluids to bodies moving through them2 a knowledge of which is of great importance in naval architecture and in gunnery1 where the resistance of the air acts to an enormous extent4 ,such1 too1 among the practical subjects which depend mainly on this branch of science1 are the use of sails in navigation2 the construction of windmills1 and water-wheels2 the transmission of water through pipes and channels2 the construction of docks and harbours1 c4 ,nature of ,solids in general4 7#beg47 ,the intimate constitution of solids is1 in all probability1 very complicated1 and we cannot be said to know much of it4 ,by some recent delicate experiments on the dimensions of wires violently strained1 it has been shown that they are to a certain small extent capable of being dilated by tension1 as they are also of being compressed by pressure1 but within limits even narrower than those of liquids4 ,usually1 when strained too far1 they break1 and refuse to re-unite2 or1 if compressed too forcibly1 take a permanent contraction of dimension4 ,thus1 wood may be indented by a blow1 and metals rendered denser and heavier by hammering or rolling4 ,there is a certain degree of confusion prevalent in ordinary language about the hardness1 elasticity1 and other similar qualities1 of solids1 which it may be well to remove4 ,hardness is that disposition of a solid which renders it difficult to displace its parts among themselves4 ,thus1 steel is harder than iron2 and diamond almost infinitely harder than any other substance in nature3 but the compressibility of steel1 or the extent to which it will yield to a given pressure and recover itself1 is not much less than that of soft iron1 and that of ice is very nearly the same with that of water4 7#beh47 ,again1 we call ,indian rubber a very elastic body1 and so it is2 but in a different sense from steel4 ,its parts admit of great mutual displacement without permanent dislocation2 however distorted1 it recovers its figure readily1 but with a small force4 ,yet1 if ,indian rubber were to be enclosed in a space that it just filled1 so as not to permit its parts to yield laterally1 doubtless it would resist actual compression with great violence4 ,here1 then1 we have an instance of two kinds of elasticity in one substance2 a feebler effort of recovery from distorted figure1 and a more violent one from a state of altered dimension4 ,both1 however1 originate in the same causes1 and are referable to the same principles2 the former being in fact only a modified case of the latter1 as the effort of a steel spring1 when bent1 to recover its former shape1 is referable to the same forces which give to steel its hardness and strength to resist actual compression and fracture4 7#bei47 ,the toughness of a solid1 or that quality by which it will endure heavy blows without breaking1 is again distinct from hardness though often confounded with it4 ,it consists in a certain yielding of parts with a powerful general cohesion1 and is compatible with various degrees of elasticity4 ,malleability is again another quality of solids1 especially metals1 quite distinct from toughness1 and depends on their capability of being deprived of their figure without an effort to recover it and without fracture4 7#bfj47 ,tenacity1 again1 is a property of solids more directly depending on the cohesion of their parts than toughness4 ,it consists in their power of resisting separation by a strain steadily applied1 while the quality of toughness is materially influenced by their disposition to communicate through their substance the jarring effect of a blow4 ,accordingly1 the tenacity of a solid is a direct measure of the cohesive attraction of its parts1 and is the best proof of the existence of such a power4 ,crystallography4 7#bfa47 ,it cannot be supposed that these and many other tangible qualities1 as they may be called1 should subsist in solids without a corresponding mechanism in their internal structure4 ,that they have such a mechanism1 and that a very curious and intricate one1 the phenomena of crystallography sufficiently show4 ,this interesting and beautiful department of natural science is of comparatively very modern date4 ,that many natural substances affected certain forms must have been known from the earliest times4 ,pliny appears to have been acquainted with this fact1 at least in some instances1 as he describes the forms of quartz and diamond4 ,but till the time of ,linnus no material attention seems to have been bestowed on the subject4 ,he1 however1 observed1 and described with care1 the crystalline forms of a variety of substances1 and even regarded them as so definite a character of the solids which assumed them1 that he supposed every particular form to be generated by a particular salt4 ,rom de l',isle pursued the study of the crystalline forms of bodies yet farther4 ,he first ascertained the important fact of the constancy of the angles at which their faces meet2 and observing further that many of them appear in several different shapes1 first conceived the idea that these shapes might be reducible to one1 appropriated in a peculiar manner to each substance1 and modified by strict geometrical laws4 ,bergmann1 reasoning on a fact imparted to him by his pupil ,gahn1 made a yet greater step1 and showed how at least one species of crystal might be built up of thin lamin ranged in a certain order1 and following certain rules of superposition4 ,he failed1 however1 in deducing just and general conclusions from this remark1 which1 correctly viewed1 is the foundation of the most important law of crystallography1 that which connects the primitive form with other forms capable of being exhibited by the same substance1 by a certain fixed relation4 ,an idea may be formed of what is meant by this sort of connection of one form with another1 by considering a pointed pyramid built up of cubic stones1 disposed in layers1 each of which separately is a square plate of the thickness of a single stone4 ,these layers1 laid horizontally one on the other1 and decreasing regularly in size from the bottom to the top1 produce a pyramidal form with a rough or channeled surface2 and if the layers are so extremely thin that the channels cease to be visible to the eye1 the pyramid will seem smooth and perfect4 7#bfb47 ,very shortly after this1 and without knowledge of what had been done by ,gahn and ,bergmann1 the ,abb ,hay1 instructed by the accidental fracture of a fine group of crystals1 made the remark noticed already 7in #fg471 and reasoning on it with more caution and success1 and pursuing it into all its detail1 developed the general laws which regulate the superposition of the layers of particles of which he supposes all crystals to be built up1 and which enable us1 from knowing their primitive forms1 to discover1 previous to trial1 what other forms they are capable of assuming2 and which1 according to this idea1 are called derivative or secondary forms4 ,mohs and others have since imagined processes and systems by which the derivation of forms from each other is facilitated1 and have corrected some errors of over-hasty generalization into which their predecessors had fallen1 as well as advanced1 by an extraordinary diligence of research1 our knowledge of the forms which the various substances which occur in nature and art actually do assume4 7#bfc47 ,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 composed1 may very readily be imagined by considering what would happen if the bricks of which an edifice is constructed had all a certain leaning or bias in one direction out of the perpendicular4 ,suppose every brick1 for instance1 when laid flat on its face1 with its longer edges north and south1 had its eastern and western faces upright1 but its northern and southern ones leaning southwards at a certain inclination the same for each brick2 a house built of such bricks would lean the same way1 if the bricks fitted well together4 ,if1 besides this1 the eastern and western faces of the bricks1 instead of being truly upright1 had an inclination eastward1 the house would have a similar one1 and all its four corners1 instead of being upright1 would lean to the south-east4 ,suppose1 instead of a house1 a pyramid were built of such oblique bricks1 with the sides of its base directed to the four points of the compass2 then its point1 instead of being situated vertically over the centre of its base1 would stand perpendicularly over some point to the south-east of that centre1 and the pyramid itself would have its sides facing the south and the east1 more highly inclined to the horizon than those towards the north and west4 7#bfd47 ,whatever conception we may form of the manner in which the particles of a crystal cohere and form masses1 it is next to impossible to divest ourselves of the idea of a determinate figure common to them all4 ,any other supposition1 indeed1 would be incompatible with that exact similarity in all other respects which the phenomena of chemistry may be considered as having demonstrated4 ,however1 it must be borne in mind that this idea1 plausible as it may appear1 is yet in some degree hypothetical1 and that the laws of crystallography1 as determined from inductive observation1 are quite independent of any supposition of the kind1 or even of the existence of such things as ultimate particles or atoms at all4 7#bfe47 ,still1 that peculiar internal constitution of solid bodies1 whatever it be1 which is indicated by the assumption of determinate figures1 by their splitting easier in some directions than in others1 and by their presenting glittering plane surfaces when broken into fragments1 cannot but have an important influence on all their relations to external agents1 as well as to their internal movements and the mutual actions of their parts on one another4 ,accordingly1 the division of bodies into crystallized and uncrystallized1 or imperfectly crystallized1 is one of the most universal importance2 and almost all the phenomena produced by those more intimate natural causes which act within small limits1 and as it were on the immediate mechanism of solid substances1 are remarkably modified by their crystalline structure4 ,thus1 in transparent solids1 the course taken by the rays of light1 in traversing them1 as well as the properties impressed upon them in so doing1 are intimately connected with this structure4 ,the recent experiments of ,m4 ,savart1 too1 have proved that this is also the case with their power of resistance to external force1 on which depends their elasticity4 ,crystallized substances1 according to the results of these experiments1 resist compression with different degrees of elastic force1 according to the direction in which it is attempted to compress them2 and all the phenomena dependent on their elasticity are affected by this cause1 especially those which relate to their vibratory movements and their conveyance of sound4 7#bff47 ,there can be little doubt that modifications1 similarly depending on the internal structure of crystals1 will be traced through every department of physics4 ,in that interesting one which relates to the action of heat in expanding the dimensions of substances1 a beginning has already been made by ,professor ,mitscherlich4 ,it had long been known that all substances are dilated by heat1 and no exception to this law has been found1 so long as we regard the bulk of the heated body4 ,thus1 an iron rod when hot is both longer and thicker than when cold2 and the difference of dimension1 though but trifling in itself1 is yet capable of being made sensible1 and is of considerable consequence in engineering4 ,thus1 too1 the quicksilver in a common thermometer occupies a larger space when hot than when cold2 and being confined by the glass ball1 7which also expands1 but not so much in proportion17 it is forced to rise in the tube4 ,these and similar facts had long been known2 and accurate measures of the total amount of dilatation of a variety of different bodies1 under similar accessions of heat1 had been obtained and registered in tables4 ,but no one had suspected the important fact1 that this expansion in crystallized bodies takes place under totally different circumstances from what obtains in uncrystallized ones4 ,m4 ,mitscherlich has lately shown that such substances expand differently in different directions1 and has even produced a case in which expansion in one direction is actually accompanied with contraction in another4 ,this step1 the most important beyond a doubt which has yet been made in pyrometry1 can however only be regarded as the first in a series of researches which will occupy the next generation1 and which promises to afford an abundant harvest of new facts1 as well as the elucidation of some of the most obscure and interesting points in the doctrine of heat4 7#bfg47 ,from what has been said1 it is clear that if we look upon solid bodies as collections of particles or atoms1 held together and kept in their places by the perpetual action of attractive and repulsive forces1 we cannot suppose these forces1 at least in crystallized substances1 to act alike in all directions4 ,hence arises the conception of polarity1 of which we see an instance1 on a great scale1 in the magnetic needle1 but which1 under modified forms1 there is nothing to prevent us from conceiving to act among the ultimate atoms of solid or even fluid bodies1 and to produce all the phenomena which they exhibit in their crystallized state1 either when acting on each other1 or on light1 heat1 c4 ,it is not difficult1 if we give the reins to imagination1 to conceive how attractive and repulsive atoms1 bound together by some unknown tie1 may form little machines or compound particles1 which shall have many of the properties which we refer to polarity2 and accordingly many ingenious suppositions have been made to that effect3 but in the actual state of science it is certainly safest to wave these hypotheses1 without however absolutely rejecting them1 and regard the polarity of matter as one of the ultimate phenomena to which the analysis of nature leads us1 and of which it is our business fully to investigate the laws1 before we endeavour to ascertain its causes1 or trace the mechanism by which it is produced4 7#bfh47 ,the mutual attractions and repulsions of the particles of matter1 then1 and their polarity1 whether regarded as an original or a derivative property1 are the forces which1 acting with great energy1 and within very confined limits1 we must look to as the principles on which the intimate constitution of all bodies and many of their mutual actions depend4 ,these are what are understood by the general term of molecular forces4 ,molecular attraction has been attempted to be confounded by some with the general attraction of gravity1 which all matter exerts on all other matter2 but this idea is refuted by the plainest facts4 ,,chap4 ,,ii4 ,,of ,,the ,,communication ,,of ,,motion ,,through ,,bodies4--,,of ,,sound ,,and ,,light4 7#bfi47 ,the propagation of motion through all substances1 whether of a single impulse1 as a blow or thrust1 or of one frequently and regularly repeated1 such as a jarring or vibratory movement1 depends wholly on these molecular forces2 and it is on such propagation that sound and very probably light depend4 ,to conceive the manner in which a motion may be conveyed from one part of a substance to another1 whether solid or fluid1 we may attend to what takes place when a wave is made to run along a stretched string1 or the surface of still water4 ,every part of the string1 or water1 is in succession moved from its place1 and agitated with a motion similar to that of the original impulse1 leaving its place and returning to it1 and when one part ceases to move the next receives as it were the impression1 and forwards it onward4 ,this may seem a slow and circuitous process in description2 but when sound1 for example1 is conveyed through the air1 we are to consider1 #ast1 that the air1 the substance actually in motion1 is extremely light and acted upon by a very powerful elasticity1 so that the force which propagates the motion1 or by which the particles adjacent act on1 and urge forward1 each other1 is very great1 compared with the quantity of materials set in motion by it3 and the same is true1 even in a greater degree1 in liquids and solids2 for in these the elastic forces are even greater1 in proportion to the weight1 than in air4 7#bgj47 ,a general notion of the mode in which sounds are conveyed through the air was not altogether deficient among the ancients2 but it is to ,newton that we owe the first attempt to analyze the process1 and show correctly what takes place in the communication of motion from particle to particle4 ,reasoning on the properties of the air as an elastic body1 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 impulse1 which then1 re-acting by its spring1 drives back the portion which had advanced to its original place1 and at the same time urges forward the portion before it1 in the direction of the impulse1 so that every particle alternately advances and retreats4 ,but1 in pursuing this idea into its details1 ,newton fell into some errors which were pointed out by ,cramer1 though their origin was not traced1 nor the reasoning corrected1 till the subject was resumed by ,lagrange and ,euler2 nor is this any impeachment of the penetration of our immortal countryman4 ,the mathematical theory of the propagation of sound1 and of vibratory and undulatory motions in general1 is one of the utmost intricacy2 and1 in spite of every exertion on the part of the most expert geometers1 continues to this day to give continual occasion for fresh researches2 while phenomena are constantly presenting themselves1 which show how far we are from being able to deduce all the particulars1 even of cases comparatively simple1 by any direct reasoning from first principles4 7#bga47 ,whenever an impulse of any kind is conveyed by the air1 to our ears1 it produces the impression of sound2 but when such an impulse is regularly and uniformly repeated in extremely rapid succession1 it gives us that of a musical note1 the pitch of the note depending on the rapidity of the succession 7see art4 #aec474 ,the sense of harmony1 too1 depends on the periodical recurrence of coincident impulses on the ear1 and affords1 perhaps1 the only instance of a sensation for whose pleasing impression a distinct and intelligible reason can be assigned4 7#bgb47 ,acoustics1 then1 or the science of sound1 is a very considerable branch of physics1 and one which has been cultivated from the earliest ages4 ,even ,pythagoras and ,aristotle were not ignorant of the general mode of its transmission through the air1 and of the nature of harmony2 but as a branch of science1 independent of its delightful application in the art of music1 it could be hardly said to exist1 till its nature and laws became a matter of experimental enquiry to ,bacon and ,galileo1 ,mersenne and ,wallis2 and of mathematical investigation to ,newton1 and his illustrious successors1 ,lagrange and ,euler4 ,from that time its progress1 as a branch both of mathematical and experimental science1 has been constant and accelerated4 ,a curious and beautiful method of observation1 due to ,chladni1 consists in the happy device of strewing sand over the surfaces of bodies in a state of sonorous vibration1 and marking the figures it assumes4 ,this has made their motions susceptible of ocular examination1 and has been lately much improved on1 and varied in its application1 by ,m4 ,savart1 to whom we also owe a succession of instructive researches on every point connected with the subject of sound1 which may rank among the finest specimens of modern experimental enquiry4 ,but the subject is far from being exhausted2 and1 indeed1 there are few branches of physics which promise at once so much amusing interest1 and such important consequences1 in its bearings on other subjects1 and especially1 through the medium of strong analogies1 on that of light4 ,light and ,vision4 7#bgc47 ,the nature of light has always been involved in considerable doubt and mystery4 ,the ancients could scarcely be said to have any opinion on the subject1 unless1 indeed1 it could be considered such to affirm that distant bodies could not be put into communication without an intermedium2 and that1 therefore1 there must be something between the eye and the thing seen4 ,what that something is1 however1 they could only form crude and vague conjectures4 ,one supposed that the eyes themselves emit rays or emanations of some unknown kind1 by which distant objects are as it were felt2 a singularly unfortunate idea1 since it gives no reason why objects should not be equally well seen in the dark--no account1 in short1 of the part performed by light in vision4 ,others imagined that all visible objects are constantly throwing out from them1 in all directions1 some sort of resemblances or spectral forms of themselves1 which1 when received by the eyes1 produce an impression of the objects4 ,vague and clumsy as this hypothesis obviously is1 it assigns to the object a power1 and to light a diffusive propagation in all directions1 which are1 the one and the other1 independent of our eyes1 and therefore goes to separate the phenomena of light from those of vision4 7#bgd47 ,the hypothesis of ,newton is a refinement and improvement on this idea4 ,instead of spectra or resemblances1 he supposes luminous objects actually to dart out from them in all directions1 particles1 of inconceivable minuteness 7as indeed they must be1 having such an enormous velocity 7see #ag471 not to dash in pieces every thing they strike upon74 ,these particles he supposes to be acted upon by attractive and repulsive forces1 residing in all material bodies1 the latter extending to some very small distance beyond their surfaces2 and by the action of these forces to be turned aside from their natural straight-lined course1 without ever coming in actual contact with the particles themselves of the bodies on which they fall1 but either being turned back and reflected by the repulsive forces before they reach them1 or penetrating between their intervals1 as a bird may be supposed to fly through the branches of a forest1 and undergoing all their actions1 to take at quitting them a direction finally determined by the position of the surface at which they emerge with respect to their course4 7#bge47 ,this hypothesis1 which was discussed and reasoned upon by ,newton in a manner worthy of himself1 affords1 by the application of the same dynamical laws which he had applied with so much success to the explanation of the planetary motions1 not merely a plausible1 but a perfectly reasonable and fair explanation of all the usual phenomena of light known in his time4 ,his own beautiful discoveries1 too1 of the different refrangibilities of the differently coloured rays1 were perfectly well represented in this theory1 by simply admitting a difference of velocity in the particles1 which produce in the eye the sensations of different colours4 ,and had the properties of light remained confined to these1 there would have been no occasion to have resorted to any other mode of conceiving it4 7#bgf47 ,a very different hypothesis had1 however1 been suggested about the same period by ,huyghens1 who supposed light to be produced in the same manner with sound1 by the communication of a vibratory motion from the luminous body to a highly elastic fluid1 which he imagined as filling all space1 and as being less condensed within the limits of space occupied by matter1 and that to a greater or less extent1 according to the nature of the occupying substance4 ,thus1 in place of any thing actually thrown off1 he substituted waves1 or vibrations1 propagated in all directions from luminous bodies1 through this medium1 or ether1 as he called it4 ,huyghens1 being himself a consummate mathematician1 was enabled to trace many of the consequences of this hypothesis1 and to show that the ordinary laws of reflection and refraction were represented or accounted for by it1 as well as by ,newton's4 ,but the hypothesis of ,huyghens has not been fully successful in accounting for what may be considered the chief of all optical facts1 the production of colours in the ordinary refraction of light by a prism1 of which the theory of ,newton gives a complete and elegant explanation2 and the discovery of which by him marks one of the greatest epochs in the annals of experimental science4 ,this1 which has been often urged in objection to it1 remains still1 if not quite unanswered1 at least only imperfectly removed4 7#bgg47 ,other phenomena1 however1 were not wanting to afford a further trial of the explanatory powers of either hypothesis4 ,the diffraction or inflection of light1 discovered by ,grimaldi1 a ,jesuit of ,bologna1 seemed to indicate that the rays of light were turned aside from their straight course by merely passing near bodies of every description4 ,these phenomena1 which are very curious and beautiful1 were minutely examined by ,newton1 and referred by him to the action of repulsive forces extending to a sensible distance from the surfaces of bodies2 and his explanation1 so far as the facts known to him are concerned1 appears as satisfactory as could reasonably be then expected2 and much more so than any thing which could at that time be produced on the side of the hypothesis of ,huyghens1 which1 in fact1 seemed incapable of giving any account whatever of them4 7#bgh47 ,another class of delicate and splendid optical phenomena1 which had begun to attract attention somewhat previous to ,newton's time1 seemed to leave both hypotheses equally at a loss4 ,these were the colours exhibited by very thin films1 either of a liquid 7such as a soap-bubble71 or of air1 as when two glasses are laid together with only air between them4 ,these colours were examined by ,newton with a minuteness and care altogether unexampled in experimental philosophy at that time1 and with which few researches undertaken since will bear to stand in competition4 ,their result was a theory of a very singular nature1 which he grounded on an hypothesis of what he termed fits of easy transmission and reflection2 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 fall4 ,the simplest way in which the reader may conceive this hypothesis1 is to regard every particle of light as a sort of little magnet revolving rapidly about its own centre while it advances in its course1 and thus alternately presenting its attractive and repulsive pole1 so that when it arrives at the surface of a body with its repulsive pole foremost1 it is repelled and reflected2 and when the contrary1 attracted1 so as to enter the surface4 ,newton1 however1 very cautiously avoided announcing his theory in this or any similar form1 confining himself entirely to general language4 ,in consequence1 it has been confidently asserted by all his followers1 that the doctrine of fits of easy reflection and transmission1 as laid down by him1 is substantially nothing more than a statement of facts4 ,were it so1 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 ,newton4 ,but this1 as we shall presently see1 is not the case2 and this instance ought to serve to make us extremely cautious how we employ1 in stating physical laws derived from experiment1 language which involves any thing in the slightest degree theoretical1 if we would present the laws themselves in a form which no future research shall modify or subvert4 7#bgi47 ,a third class of optical phenomena1 which were likewise discovered while ,newton was yet engaged in his optical researches1 was that exhibited by doubly refracting crystals4 ,in what the phenomenon of double refraction consists1 we have already had occasion to explain4 ,the fact itself was first noticed by ,erasmus ,bartolin in the crystal called ,iceland spar2 and was studied with attention by ,huyghens1 who ascertained its laws1 and referred it with remarkable ingenuity and success to his theory of light1 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 another3 as if1 for example's sake1 we should suppose a sound conveyed through the air with different degrees of rapidity in a vertical and horizontal direction4 7#bhj47 ,some remarkable facts accompanying the double refraction produced by ,iceland spar1 which ,bartolin1 ,huyghens1 and ,newton1 had observed1 led the latter to conceive the singular idea that a ray of light after its emergence from such a crystal acquires sides1 that is to say1 distinct relations to surrounding space1 which it carries with it through its whole subsequent course1 and which give rise to all those curious and complicated phenomena which are now known under the name of the polarization of light4 ,these results1 however1 appeared so extraordinary1 and offered so little handle for further enquiry1 that their examination dropped1 as if by common consent2 ,newton himself resting content with urging strongly the apparent incompatibility of these properties with the ,huyghenian doctrine1 but without making any attempt to explain them by his own4 7#bha47 ,from the period of ,newton's optical discoveries to the commencement of the present century1 no great accession to our knowledge of the nature of light was made1 if we except one1 which1 from its invaluable practical application1 must ever hold a prominent place in the annals both of art and science3 we mean1 the discovery of the principle of the achromatic telescope1 which originated in a discussion between the celebrated geometer ,euler1 ,klingenstierna1 an eminent ,swedish philosopher1 and our own countryman1 the admirable optician ,dollond1 on the occasion of certain abstract theoretical investigations of the former1 which led him to speculate on its possibility1 and which ultimately terminated in its complete and happy execution by the latter2 a memorable case in science1 though not a singular one1 where the speculative geometer in his chamber1 apart from the world1 and existing among abstractions1 has originated views of the noblest practical application4#di 7#bhb47 ,the explanation which our knowledge of optical laws affords of the mechanism of the eye1 and the process by which vision is performed1 is as complete and satisfactory as that of hearing by the propagation of motion through the air4 ,the camera obscura1 invented by ,baptista ,porta in #aefj1 gave the first idea how the actual images of external objects might be conveyed into the eye1 but it was not till after a considerable interval that ,kepler1 the immortal discoverer of those great laws which regulate the periods and motions of the planets1 pointed out distinctly the offices performed by the several parts of the eye in the act of vision4 ,from this to the invention of the telescope and microscope there would seem but a small step1 but it is to accident rather than design that it is due2 and its re-invention by ,galileo1 on a mere description of its effects1 may serve1 among a thousand similar instances1 to show that inestimable practical applications lie open to us1 if we can only once bring ourselves to conceive their possibility1 a lesson which the invention of the achromatic telescope itself1 as we have above related it1 not less strongly exemplifies4 7#bhc47 ,the little instrument with which ,galileo's splendid discoveries were made was hardly superior in power to an ordinary finder of the present day2 but it was rapidly improved on1 and in the hands of ,huyghens attained to gigantic dimensions and very great power4 ,it was to obviate the necessity of the enormous length required for these telescopes1 and yet secure the same power1 that ,gregory and ,newton devised the reflecting telescope1 which has since become a much more powerful instrument than its original inventors probably ever contemplated4 7#bhd47 ,the telescope1 as it exists at present1 with the improvements in its structure and execution which modern artists have effected1 must assuredly be ranked among the highest and most refined productions of human art2 that in which man has been able to approximate most closely to the workmanship of nature1 and which has conferred upon him1 if not another sense1 at least an exaltation of one already possessed by him that merits almost to be regarded as a new one4 ,nor does it appear yet to have reached its ultimate perfection1 to which indeed it is difficult to assign any bounds1 when we take into consideration the wonderful progress which workmanship of every kind is making1 and the delicacy1 far superior to that of former times1 with which materials may now be wrought1 as well as the ingenious inventions and combinations which every year is bringing forth for accomplishing the same ends by means hitherto unattempted4#ej 7#bhe47 ,after a long torpor1 the knowledge of the properties of light began to make fresh progress about the end of the last century1 advancing with an accelerated rapidity1 which has continued unabated to the present time4 ,the example was set by our late admirable and lamented countryman1 ,dr4 ,wollaston1 who re-examined and verified the laws of double refraction in ,iceland spar announced by ,huyghens4 ,attention being thus drawn to the subject1 the geometry of ,laplace soon found a means of explaining at least one portion of the mystery of this singular phenomenon1 by the ,newtonian theory of light1 applied under certain supposed conditions2 and the reasoning which led him to the result 7at that time quite unexpected71 may justly be regarded as one of his happiest efforts4 ,the prosecution of the subject1 which had now acquired a high degree of interest1 was encouraged by the offer of a prize on the part of the ,french ,academy of ,sciences2 and it was in a memoir which received this honourable reward on that occasion1 in #ahaj1 that ,malus1 a retired officer of engineers in the ,french army1 announced the great discovery of the polarization of light by ordinary reflection at the surface of a transparent body4 7#bhf47 ,malus found that when a beam of light is reflected from the surface of such a body at a certain angle1 it acquires precisely the same singular property which is impressed upon it in the act of double refraction1 and which ,newton had before expressed by saying that it possessed sides4 ,this was the first circumstance which pointed out a connection between that hitherto mysterious phenomenon and any of the ordinary modifications of light2 and it proved ultimately the means of bringing the whole within the limits1 if not of a complete explanation1 at least of a highly plausible theoretical representation4 ,so true is1 in science1 the remark of ,bacon1 that no natural phenomenon can be adequately studied in itself alone1 but1 to be understood1 must be considered as it stands connected with all nature4 7#bhg47 ,the new class of phenomena thus disclosed were immediately studied with diligence and success1 both abroad by ,malus and ,arago1 and at home by our countryman ,dr4 ,brewster1 and their laws investigated with a care proportioned to their importance2 when another and apparently still more extraordinary class of phenomena presented itself in the production of the most vivid and beautiful colours 7every way resembling those observed by ,newton in thin films of air or liquids1 only infinitely more developed and striking17 in certain transparent crystallized substances1 when divided into flat plates in particular directions1 and exposed in a beam of polarized light4 ,the attentive examination of these colours by ,wollaston1 ,biot1 and ,arago1 but more especially by ,brewster1 speedily led to the disclosure of a series of optical phenomena so various1 so brilliant1 and evidently so closely connected with the most important points relating to the intimate structure of crystallized bodies1 as to excite the highest interest1--that sort of interest which is raised when we feel we are on the eve of some extraordinary discovery1 and expect every moment that some leading fact will turn up1 which will throw light on all that appears obscure1 and reduce into order all that seems anomalous4 7#bhh47 ,this expectation was not disappointed4 ,so long before the time we are speaking of as the first year of the present century1 our illustrious countryman1 the late ,dr4 ,thomas ,young1 had established a principle in optics1 which1 regarded as a physical law1 has hardly its equal for beauty1 simplicity1 and extent of application1 in the whole circle of science4 ,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 effects1 he was led to the idea that the same ought to hold good with light as with sound1 if the theory which makes light analogous to sound be the true one2 and that1 therefore1 two rays of light1 setting off from the same origin1 at the same instant1 and arriving at the same place by different routes1 ought to strengthen or wholly or partially destroy each other's effects according to the difference in length of the routes described by them4 ,that two lights should in any circumstances combine to produce darkness may be considered strange1 but is literally true2 and it had even been noticed long ago as a singular and unaccountable fact by ,grimaldi1 in his experiments on the inflection of light4 ,the experimental means by which ,dr4 ,young confirmed this principle1 which is known in optics by the name of the interference of the rays of light1 were as simple and satisfactory as the principle itself is beautiful2 but the verifications of it1 drawn from the explanation it affords of phenomena apparently the most remote1 are still more so4 ,newton's colours of thin films were the first phenomena to which its author applied it with full success4 ,its next remarkable application was to those of diffraction1 of which1 in the hands of ,m4 ,fresnel1 a late eminent ,french geometer1 it also furnished a complete explanation1 and that1 too1 in cases to which ,newton's hypothesis could not apparently be made to apply1 and through a complication of circumstances which might afford a very severe test of any hypothesis4 7#bhi47 ,a simple and beautiful experiment on the interferences of polarized light due to ,fresnel and ,arago enabled them to bring ,dr4 ,young's law to bear on the colours produced by crystallized plates in a polarized beam1 and by so doing afforded a key to all the intricacies of these magnificent but complex phenomena4 ,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 facts1 nor to the general laws of dynamics4 ,this essential idea1 without which every thing that had been before done would have been incomplete1 was also furnished by ,dr4 ,young1 who1 with a sagacity which would have done honour to ,newton himself1 had declared1 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 ether1 differently from that of a sonorous one through the air4 ,in the latter1 the particles of the air advance and recede2 in the former1 those of the ether must be supposed to tremble laterally4 7#bij47 ,taking this as the groundwork of his reasoning1 ,fresnel succeeded in erecting on it a theory of polarization and double refraction1 so happy in its adaptation to facts1 and in the coincidence with experience of results deduced from it by the most intricate analysis1 that it is difficult to conceive it unfounded4 ,if it be so1 it is at least the most curiously artificial system that science has yet witnessed2 and whether it be so or not1 so long as it serves to group together in one comprehensive point of view a mass of facts almost infinite in number and variety1 to reason from one to another1 and to establish analogies and relations between them2 on whatever hypothesis it may be founded1 or whatever arbitrary assumptions it may make respecting structures and modes of action1 it can never be regarded as other than a most real and important accession to our knowledge4 7#bia47 ,still1 it is by no means impossible that the ,newtonian theory of light1 if cultivated with equal diligence with the ,huyghenian1 might lead to an equally plausible explanation of phenomena now regarded as beyond its reach4 ,m4 ,biot is the author of the hypothesis we have already mentioned of a rotatory motion of the particles of light about their axes4 ,he has employed it only for a very limited purpose2 but it might doubtless be carried much farther2 and by admitting only the regular emission of the luminous particles at equal intervals of time1 and in similar states of motion from the shining body1 which does not seem a very forced supposition1 all the phenomena of interference at least would be readily enough explained without the admission of an ether4 7#bib47 ,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 other4 ,the indefatigable researches of ,dr4 ,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 themselves1 and thus become most valuable characters by which to recognise their internal constitution4 ,it was ,newton who first showed of what importance as a physical character1--as the indication of other properties1--the action of a body on light might become2 but the characters afforded by the use of polarized light as an instrument of experimental enquiry are so marked and intimate1 that they may almost be said to have furnished us with a kind of intellectual sense1 by which we are enabled to scrutinize the internal arrangement of those wonderful structures which ,nature builds up by her refined and invisible architecture1 with a delicacy eluding our conception1 yet with a symmetry and beauty which we are never weary of admiring4 ,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 telescope1 or to natural history by that of the microscope2 while the relations which have been discovered to exist between the optical properties of bodies and their crystalline forms1 and even their chemical habitudes1 have afforded numerous and beautiful instances of general laws concluded from laborious and painful induction1 and curiously exemplifying the simplicity of nature as it emerges slowly from an entangled mass of particulars in which1 at first1 neither order nor connection can be traced4 ,,chap4 ,,iii4 ,,of ,,cosmical ,,phenomena4 ,astronomy and ,celestial ,mechanics4 7#bic47 ,astronomy1 as has been observed in the former part of this discourse1 as a science of observation1 had made considerable progress among the ancients3 indeed1 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 success4 ,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 eclipses2 and some remarkable cycles1 or periods of years in which the lunar eclipses return in very nearly the same order1 had been ascertained by observation4 ,considering the extreme imperfection of their means of measuring time and space1 this was1 perhaps1 as much as could have been expected at that early period1 and it was followed up for a while in a philosophical spirit of just speculation1 which1 if continued1 could hardly have failed to lead to sound and important conclusions4 7#bid47 ,unfortunately1 however1 the philosophy of ,aristotle laid it down as a principle1 that the celestial motions were regulated by laws proper to themselves1 and bearing no affinity to those which prevail on earth4 ,by thus drawing a broad and impassable line of separation between celestial and terrestrial mechanics1 it placed the former altogether out of the pale of experimental research1 while it at the same time impeded the progress of the latter by the assumption of principles respecting natural and unnatural motions1 hastily adopted from the most superficial and cursory remark1 undeserving even the name of observation4 ,astronomy1 therefore1 continued for ages a science of mere record1 in which theory had no part1 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 mechanism4 ,hence arose an unwieldy1 if not self-contradictory1 mass of hypothetical motions of sun1 moon1 and planets1 in circles1 whose centres were carried round in other circles1 and these again in others without end1--8cycle on epicycle1 orb on orb10--till at length1 as observation grew more exact1 and fresh epicycles were continually added1 the absurdity of so cumbrous a mechanism became too palpable to be borne4 ,doubts were expressed1 to which the sarcasm of a monarch#ea gave a currency they might not have obtained in a period when men scarcely dared trust themselves to think2 and at length ,copernicus1 promulgating his own1 or reviving the ,pythagorean doctrine1 which places the sun in the centre of our system1 gave to astronomy a simplicity which1 contrasted with the complication of the preceding views1 at once commanded assent4 7#bie47 ,an elegant writer#eb1 whom we have before had occasion to quote1 has briefly and neatly accounted for the confused notions which so long prevailed respecting the constitution of our system1 and the difficulty experienced in acquiring a true notion of the disposition of its parts4 8,we see it10 he observes1 8not in plan1 but in section40 ,the reason of this is1 that our point of observation lies in its general plane1 but the notion we aim at forming of it is not that of its section1 but of its plan4 ,this is as if we should attempt to read a book1 or make out the countries on a map1 with the eye on a level with the paper4 ,we can only judge directly of the distances of objects by their sizes1 or rather of their change of distance by their change of size2 neither have we any means of ascertaining1 otherwise than indirectly1 even their positions1 one among the other1 from their apparent places as seen by us4 ,now1 the variations in apparent size of the sun and moon are too small to admit of exact measure without the use of the telescope1 and the bodies of the planets cannot even be distinguished as having any distinct size with the naked eye4 7#bif47 ,the ,copernican system once admitted1 however1 this difficulty of conception1 at least1 is effectually got over1 and it becomes a mere problem of geometry and calculation to determine1 from the observed places of a planet1 its real orbit about the sun1 and the other circumstances of its motion4 ,this ,kepler accomplished for the orbit of ,mars1 which he ascertained to be an ellipse having the sun in one of its foci2 and the same law1 being extended by inductive analogy to all the planets1 was found to be verified in the case of each4 ,this with the other remarkable laws which are usually cited in physical astronomy by the name of ,kepler's laws1 constitute undoubtedly the most important and beautiful system of geometrical relations which have ever been discovered by a mere inductive process1 independent of any consideration of a theoretical kind4 ,they comprise within them a compendium of the motions of all the planets1 and enable us to assign their places in their orbits at any instant of time past or to come 7disregarding their mutual perturbations71 provided certain purely geometrical problems can be numerically resolved4 7#big47 ,it was not1 however1 till long after ,kepler's time that the real importance of these laws could be felt4 ,regarded in themselves1 they offered1 it is true1 a fine example of regular and harmonious disposition in the greatest of all the works of creation1 and a striking contrast to the cumbersome mechanism of the cycles and epicycles which preceded them2 but there their utility seemed to terminate1 and1 indeed1 ,kepler was reproached1 and not without a semblance of reason1 with having rendered the actual calculation of the places of the planets more difficult than before1 the resources of geometry being then inadequate to resolve the problems to which the strict application of his laws gave rise4 7#bih47 ,the first result of the invention of the telescope and its application to astronomical purposes1 by ,galileo1 was the discovery of ,jupiter's disc and satellites1--of a system offering a beautiful miniature of that greater one of which it forms a portion1 and presenting to the eye of sense1 at a single glance1 that disposition of parts which in the planetary system itself is discerned only by the eye of reason and imagination 7see #aie474 ,kepler had the satisfaction of seeing it ascertained1 that the law which he had discovered to connect the times of revolution of the planets with their distances from the sun1 holds good also when applied to the periods of circulation of these little attendants round the centre of their principal2 thus demonstrating it to be something more than a mere empirical rule1 and to depend on the intimate nature of planetary motion itself4 7#bii47 ,it had been objected to the doctrine of ,copernicus1 that1 were it true1 ,venus should appear sometimes horned like the moon4 ,to this he answered by admitting the conclusion1 and averring that1 should we ever be able to see its actual shape1 it would appear so4 ,it is easy to imagine with what force the application would strike every mind when the telescope confirmed this prediction1 and showed the planet just as both the philosopher and his objectors had agreed it ought to appear4 ,the history of science affords perhaps only one instance analogous to this4 ,when ,dr4 ,hutton expounded his theory of the consolidation of rocks by the application of heat1 at a great depth below the bed of the ocean1 and especially of that of marble by actual fusion2 it was objected that1 whatever might be the case with others1 with calcareous or marble rocks1 at least1 it was impossible to grant such a cause of consolidation1 since heat decomposes their substance and converts it into quicklime1 by driving off the carbonic acid1 and leaving a substance perfectly infusible1 and incapable even of agglutination by heat4 ,to this he replied1 that the pressure under which the heat was applied would prevent the escape of the carbonic acid2 and that being retained1 it might be expected to give that fusibility to the compound which the simple quicklime wanted4 ,the next generation saw this anticipation converted into an observed fact1 and verified by the direct experiments of ,sir ,james ,hall1 who actually succeeded in melting marble1 by retaining its carbonic acid under violent pressure4 7#cjj47 ,kepler1 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 labour1 had obtained a glimpse of the general law of the inertia of matter1 as applicable to the great masses of the heavenly bodies as well as to those with which we are conversant on the earth4 ,after ,kepler1 ,galileo1 while he gave the finishing blow to the ,aristotelian dogmas which erected a barrier between the laws of celestial and terrestrial motion1 by his powerful argument and caustic ridicule1 contributed1 by his investigations of the laws of falling bodies and the motions of projectiles1 to lay the foundation of a true system of dynamics1 by which motions could be determined from a knowledge of the forces producing them1 and forces from the motions they produce4 ,hooke went yet farther1 and obtained a view so distinct of the mode in which the planets might be retained in their orbits by the sun's attraction1 that1 had his mathematical attainments been equal to his philosophical acumen1 and his scientific pursuits been less various and desultory1 it can hardly be doubted that he would have arrived at a knowledge of the law of gravitation4 7#cja47 ,but every thing which had been done towards this great end1 before ,newton1 could only be regarded as smoothing some first obstacles1 and preparing a state of knowledge1 in which powers like his could be effectually exerted4 ,his wonderful combination of mathematical skill with physical research enabled him to invent1 at pleasure1 new and unheard-of methods of investigating the effects of those causes which his clear and penetrating mind detected in operation4 ,whatever department of science he touched1 he may be said to have formed afresh4 ,ascending by a series of close-compacted inductive arguments to the highest axioms of dynamical science1 he succeeded in applying them to the complete explanation of all the great astronomical phenomena1 and many of the minuter and more enigmatical ones4 ,in doing this1 he had every thing to create3 the mathematics of his age proved totally inadequate to grapple with the numerous difficulties which were to be overcome2 but this1 so far from discouraging him1 served only to afford new opportunities for the exertion of his genius1 which1 in the invention of the method of fluxions1 or1 as it is now more generally called1 the differential calculus1 has supplied a means of discovery1 bearing the same proportion to the methods previously in use1 that the steam-engine does to the mechanical powers employed before its invention4 ,of the optical discoveries of ,newton we have already spoken2 and if the magnitude of the objects of his astronomical discoveries excite our admiration of the mental powers which could so familiarly grasp them1 the minuteness of the researches into which he there set the first example of entering1 is no less calculated to produce a corresponding impression4 ,whichever way we turn our view1 we find ourselves compelled to bow before his genius1 and to assign to the name of ,,newton a place in our veneration which belongs to no other in the annals of science4 ,his era marks the accomplished maturity of the human reason as applied to such objects4 ,every thing which went before might be more properly compared to the first imperfect attempts of childhood1 or the essays of inexpert1 though promising1 adolescence4 ,whatever has been since performed1 however great in itself1 and worthy of so splendid and auspicious a beginning1 has never1 in point of intellectual effort1 surpassed that astonishing one which produced the ,principia4 7#cjb47 ,in this great work1 ,newton shows all the celestial motions known in his time to be consequences of the simple law1 that every particle of matter attracts every other particle in the universe with a force proportional to the product of their masses directly1 and the square of their mutual distance inversely1 and is itself attracted with an equal force4 ,setting out from this1 he explains how an attraction arises between the great spherical masses of which our system consists1 regulated by a law precisely similar in its expression2 how the elliptic motions of planets about the sun1 and of satellites about their primaries1 according to the exact rules inductively arrived at by ,kepler1 result as necessary consequences from the same general law of force2 and how the orbits of comets themselves are only particular cases of planetary movements4 ,thence proceeding to applications of greater difficulty1 he explains how the perplexing inequalities of the moon's motion result from the sun's disturbing action2 how tides arise from the unequal attraction of the sun as well as of the moon on the earth1 and the ocean which surrounds it2 and1 lastly1 how the precession of the equinoxes is a necessary consequence of the very same law4 7#cjc47 ,the immediate successors of ,newton found full occupation in verifying his discoveries1 and in extending and improving the mathematical methods which it had now become manifest were to prove the keys to an inexhaustible treasure of knowledge4 ,the simultaneous but independent discovery of a method of mathematical investigation in every respect similar to that of ,newton1 by ,leibnitz1 while it created a degree of national jealousy which can now only be regretted1 had the effect of stimulating the continental geometers to its cultivation1 and impressing on it a character more entirely independent of the ancient geometry1 to which ,newton was peculiarly attached4 ,it was fortunate for science that it did so2 for it was speedily found that 7with one fine exception on the part of our countryman ,maclaurin1 followed up1 after a long interval1 by the late ,professor ,robison of ,edinburgh1 with equal elegance17 the geometry of ,newton was like the bow of ,ulysses1 which none but its master could bend2 and that1 to render his methods available beyond the points to which he himself carried them1 it was necessary to strip them of every vestige of that antique dress in which he had delighted to clothe them4 ,this1 however1 the countrymen of ,newton were very unwilling to do2 and they paid the penalty in finding themselves condemned to the situation of lookers on1 while their continental neighbours both in ,germany and ,france were pushing forward in the career of mathematico-physical discovery with emulous rapidity4 7#cjd47 ,the legacy of research which ,newton may be said to have left to his successors was truly immense4 ,to pursue1 through all its intricacies1 the consequences of the law of gravitation2 to account for all the inequalities of the planetary movements1 and the infinitely more complicated1 and to us more important ones1 of the moon2 and to give1 what ,newton himself certainly never entertained a conception of1 a demonstration of the stability and permanence of the system1 under all the accumulating influence of its internal perturbations2 this labour1 and this triumph1 were reserved for the succeeding age1 and have been shared in succession by ,clairaut1 ,d',alembert1 ,euler1 ,lagrange and ,laplace4 ,yet so extensive is the subject1 and so difficult and intricate the purely mathematical enquiries to which it leads1 that another century may yet be required to go through with the task4 ,the recent discoveries of astronomers have supplied matter for investigation1 to the geometers of this and the next generation1 of a difficulty far surpassing any thing that had before occurred4 ,five primary planets have been added to our system2 four of them since the commencement of the present century1 and these1 singularly deviating from the general analogy of the others1 and offering cases of difficulty in theory1 which no one had before contemplated4 ,yet even the intricate questions to which these bodies have given rise seem likely to be surpassed by those which have come into view1 with the discovery of several comets revolving in elliptic orbits1 like the planets1 round the sun1 in very moderate periods4 ,but the resources of modern geometry seem1 so far from being exhausted1 to increase with the difficulties they have to encounter1 and already1 among the successors of ,lagrange and ,laplace1 the present generation has to enumerate a powerful array of names1 which promise to render it not less celebrated in the annals of physico-mathematical research than that which has just passed away4 7#cje47 ,meanwhile the positions1 figures1 and dimensions of all the planetary orbits1 are now well known1 and their variations from century to century in great measure determined2 and it has been generally demonstrated1 that all the changes which the mutual actions of the planets on each other can produce in the course of indefinite ages1 are periodical1 that is to say1 increasing to a certain extent 7and that never a very great one71 and then again decreasing2 so that the system can never be destroyed or subverted by the mutual action of its parts1 but keeps constantly oscillating1 as it were1 round a certain mean state1 from which it can never deviate to any ruinous extent4 ,in particular the researches of ,laplace1 ,lagrange1 and ,poisson1 have shown the ultimate invariability of the mean distance of each planet from the sun1 and consequently of its periodic time4 ,relying on these grand discoveries1 we are enabled to look forward1 from the point of time which we now occupy1 many thousands of years into futurity1 and predict the state of our system without fear of material error1 but such as may arise from causes whose existence at present we have no reason to suppose1 or from interference which we have no right to anticipate4 7#cjf47 ,a correct enumeration and description of the fixed stars in catalogues1 and an exact knowledge of their position1 supply the only effectual means we can have of ascertaining what changes they are liable to1 and what motions1 too slow to deprive them of their usual epithet1 fixed1 yet sufficient to produce a sensible change in the lapse of ages1 may exist among them4 ,previous to the invention of the compass1 they served as guides to the navigator by night2 but for this purpose1 a very moderate knowledge of a few of the principal ones sufficed4 ,hipparchus was the first astronomer1 who1 excited by the appearance of a new star1 conceived the idea of forming a catalogue of the stars1 with a view to its use as an astronomical record1 8by which10 says ,pliny1 8posterity will be able to discover1 not only whether they are born and die1 but also whether they change their places1 and whether they increase or decrease40 ,his catalogue1 containing more than #ajjj stars1 was constructed about #abh years before ,christ4 ,it was in the course of the laborious discussion of his own and former observations of them1 undertaken with a view to the formation of this catalogue1 that he first recognised the fact of that slow1 general advance of all the stars eastward1 when compared with the place of the equinox1 which is known under the name of the precession of the equinoxes1 and which ,newton succeeded in referring to a motion in the earth's axis1 produced by the attraction of the sun and moon4 7#cjg47 ,since ,hipparchus1 at various periods in the history of astronomy1 catalogues of stars have been formed1 among which that of ,ulugh ,begh1 comprising about #ajjj stars1 constructed in #adcg1 is remarkable as the production of a sovereign prince1 working personally in conjunction with his astronomers2 and that of ,tycho ,brahe1 containing #ggg stars1 constructed in #afjj1 as having originated in a phenomenon similar to that which drew the attention of ,hipparchus4 ,in more recent times1 astronomers provided with the finest instruments their respective eras could supply1 and established in observatories1 munificently endowed by the sovereigns and governments of different ,european nations1 have vied and are still vying with each other1 in extending the number of registered stars1 and giving the utmost possible degree of accuracy to the determination of their places4 ,among these1 it would be ungrateful not to claim especial notice for the superb series of observations which1 under a succession of indefatigable and meritorious astronomers1 has1 for a very long period1 continued to emanate from our own national observatory of ,greenwich4 7#cjh47 ,the distance of the fixed stars is so immense1 that every attempt to assign a limit1 within which it must fall1 has hitherto failed4 ,the enquiries of astronomers of all ages have been directed to ascertain this distance1 by taking the dimensions of our own particular system of sun and planets1 or of the earth itself1 as the unit of a scale on which it might be measured4 ,but although many have imagined that their observations afforded grounds for the decision of this interesting point1 it has uniformly happened either that the phenomena on which they relied have proved to be referable to other causes not previously known1 and which the superior accuracy of their researches has for the first time brought to light2 or to errors arising from instrumental imperfections and unavoidable defects of the observations themselves4 7#cji47 ,the only indication we can expect to obtain of the actual distance of a star1 would consist in an annual change in its apparent place corresponding to the motion of the earth round the sun1 called its annual parallax1 and which is nothing more than the measure of the apparent size of the earth's orbit as seen from the star4 ,many observers have thought they have detected a measurable amount of this parallax2 but as astronomical instruments have advanced in perfection1 the quantity which they have successively assigned to it has been continually reduced within narrower and narrower limits1 and has invariably been commensurate with the errors to which the instruments used might fairly be considered liable4 ,the conclusion this strongly presses on us is1 that it is really a quantity too small to admit of distinct measurement in the present state of our means for that purpose2 and that1 therefore1 the distance of the stars must be a magnitude of such an order as the imagination almost shrinks from contemplating4 ,but this increase in our scale of dimension calls for a corresponding enlargement of conception in all other respects4 ,the same reasoning which places the stars at such immeasurable remoteness1 exalts them at the same time into glorious bodies1 similar to1 and even far surpassing1 our own sun1 the centres perhaps of other planetary systems1 or fulfilling purposes of which we can have no idea1 from any analogy in what passes immediately around us4 7#caj47 ,the comparison of catalogues1 published at different periods1 has given occasion to many curious remarks1 respecting changes both of place and brightness among the stars1 to the discovery of variable ones which lose and recover their lustre periodically1 and to that of the disappearance of several from the heavens so completely as to have left no vestige discernible even by powerful telescopes4 ,in proportion as the construction of astronomical and optical instruments has gone on improving1 our knowledge of the contents of the heavens has undergone a corresponding extension1 and1 at the same time1 attained a degree of precision which could not have been anticipated in former ages4 ,the places of all the principal stars in the northern hemisphere1 and of a great many in the southern1 are now known to a degree of nicety which must infallibly detect any real motions that may exist among them1 and has in fact done so1 in a great many instances1 some of them very remarkable ones4 7#caa47 ,it is only since a comparatively recent date1 however1 that any great attention has been bestowed on the smaller stars1 among which there can be no doubt of the most interesting and instructive phenomena being sooner or later brought to light4 ,the minute examination of them with powerful telescopes1 and with delicate instruments for the determination of their places1 has1 indeed1 already produced immense catalogues and masses of observations1 in which thousands of stars invisible to the naked eye are registered2 and has led to the discovery of innumerable important and curious facts1 and disclosed the existence of whole classes of celestial objects1 of a nature so wonderful as to give room for unbounded speculation on the extent and construction of the universe4 7#cab47 ,among these1 perhaps the most remarkable are the revolving double stars1 or stars which1 to the naked eye or to inferior telescopes1 appear single2 but1 if examined with high magnifying powers1 are found to consist of two individuals placed almost close together1 and which1 when carefully watched1 are 7many of them7 found to revolve in regular elliptic orbits about each other2 and so far as we have yet been able to ascertain1 to obey the same laws which regulate the planetary movements4 ,there is nothing calculated to give a grander idea of the scale on which the sidereal heavens are constructed than these beautiful systems4 ,when we see such magnificent bodies united in pairs1 undoubtedly by the same bond of mutual gravitation which holds together our own system1 and sweeping over their enormous orbits1 in periods comprehending many centuries1 we admit at once that they must be accomplishing ends in creation which will remain for ever unknown to man2 and that we have here attained a point in science where the human intellect is compelled to acknowledge its weakness1 and to feel that no conception the wildest imagination can form will bear the least comparison with the intrinsic greatness of the subject4 ,geology4 7#cac47 ,the researches of physical astronomy are confessedly incompetent to carry us back to the origin of our system1 or to a period when its state was1 in any great essential1 different from what it is at present4 ,so far as the causes now in action go1 and so far as our calculations will enable us to estimate their effects1 we are equally unable to perceive in the general phenomena of the planetary system either the evidence of a beginning1 or the prospect of an end4 ,geometers1 as already stated1 have demonstrated that1 in the midst of all the fluctuations which can possibly take place in the elements of the orbits of the planets1 by reason of their mutual attraction1 the general balance of the parts of the system will always be preserved1 and every departure from a mean state periodically compensated4 ,but neither the researches of the physical astronomer1 nor those of the geologist1 give us any ground for regarding our system1 or the globe we inhabit1 as of eternal duration4 ,on the contrary1 there are circumstances in the physical constitution of our own planet which at least obscurely point to an origin and a formation1 however remote1 since it has been found that the figure of the earth is not globular but elliptical1 and that its attraction is such as requires us to admit the interior to be more dense than the exterior1 and the density to increase with some degree of regularity from the surface towards the centre1 and that1 in layers arranged elliptically round the centre1 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 another1 even if we should hesitate to admit a state of primitive fluidity4 7#cad47 ,but from such indications nothing distinct can be concluded2 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 surface1 we must confine our views within limits far more restricted1 and to subjects much more within the reach of our capacity1 than either the creation of the world or its assumption of its present figure4 ,these1 indeed1 were favourite speculations with a race of geologists now extinct2 but the science itself has undergone a total change of character1 even within the last half century1 and is brought1 at length1 effectually within the list of the inductive sciences4 ,geologists now no longer bewilder their imaginations with wild theories of the formation of the globe from chaos1 or its passage through a series of hypothetical transformations1 but rather aim at a careful and accurate examination of the records of its former state1 which they find indelibly impressed on the great features of its actual surface1 and to the evidences of former life and habitation which organised remains imbedded and preserved in its strata indisputably afford4 7#cae47 ,records of this kind are neither few nor vague2 and though the obsoleteness of their language when we endeavour to interpret it too minutely1 may1 and no doubt often does1 lead to misapprehension1 still its general meaning is1 on the whole1 unequivocal and satisfactory4 ,such records teach us1 in terms too plain to be misunderstood1 that the whole or nearly the whole of our present lands and continents were formerly at the bottom of the sea1 where they received deposits of materials from the wearing and degradation of other lands not now existing1 and furnished receptacles for the remains of marine animals and plants inhabiting the ocean above them1 as well as for similar spoils of the land washed down into its bosom4 7#caf47 ,these remains are occasionally brought to light2 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 globe1 and of a period anterior to that in which it has been the habitation of man1 or rather1 indeed1 of a series of periods1 of unknown duration1 in which both land and sea teemed with forms of animal and vegetable life1 which have successively disappeared and given place to others1 and these again to new races approximating gradually more and more nearly to those which now inhabit them1 and at length comprehending species which have their counterparts existing4 7#cag47 ,these wrecks of a former state of nature1 thus wonderfully preserved 7like ancient medals and inscriptions in the ruins of an empire71 afford a sort of rude chronology1 by whose aid the successive depositions of the strata in which they are found may be marked out in epochs more or less definitely terminated1 and each characterized by some peculiarity which enables us to recognise the deposits of any period1 in whatever part of the world they may be found4 ,and1 so far as has been hitherto investigated1 the order of succession in which these deposits have been formed appears to have been the same in every part of the globe4 7#cah47 ,many of the strata which thus bear evident marks of having been deposited at the bottom of the sea1 and of course in a horizontal state1 are now found in a position highly inclined to the horizon1 and even occasionally vertical4 ,and they often bear no less evident marks of violence1 in their bending and fracture1 the dislocation of parts which were once contiguous1 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 place4 7#cai47 ,besides the rocks which carry this internal evidence of submarine deposition1 are many which exhibit no such proofs1 but on the contrary hold out every appearance of owing their origin to volcanoes or to some other mode of igneous action2 and in every part of the world1 and among strata of all ages1 there occur evidences of such action so abundant1 and on such a scale1 as to point out the volcano and the earthquake as agents which may have been instrumental in the production of those changes of level1 and those violent dislocations which we perceive to have taken place4 7#cbj47 ,at all events1 in accounting for those changes1 geologists have no longer recourse1 as formerly1 to causes purely hypothetical1 such as a shifting of the earth's axis of rotation1 bringing the sea to overflow the land1 by a change in the place of the longer and shorter diameters of the spheroidal figure1 nor to tides produced by the attraction of comets suddenly approaching very near the earth1 nor to any other fanciful and arbitrarily assumed hypotheses2 but rather endeavour to confine themselves to a careful consideration of causes evidently in action at present1 with a view to ascertain how far they1 in the first instance1 are capable of accounting for the facts observed1 and thus legitimately bringing into view1 as residual phenomena1 those effects which cannot be so accounted for4 ,when this shall have been in some measure accomplished1 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 cataclysms1--epochs of terrific confusion and violence which many geologists 7perhaps with justice7 regard as indispensable to the explanation of the existing features of the world4 ,we shall learn to distinguish between the effects which require for their production the sudden application of convulsive and fracturing efforts1 and those1 probably not less extensive1 changes which may have been produced by forces equally or more powerful1 but acting with less irregularity1 and so distributed over time as to produce none of those interregnums of chaotic anarchy which we are apt to think 7perhaps erroneously7 great disfigurements of an order so beautiful and harmonious as that of nature4 7#cba47 ,but to estimate justly the effects of causes now in action in geology is no easy task4 ,there is no priori or deductive process by which we can estimate the amount of the annual erosion1 for instance1 of a continent by the action of meteoric agents1 rain1 wind1 frost1 c41 nor the quantity of destruction produced on its coasts by the direct violence of the sea1 nor the quantity of lava thrown up per annum by volcanoes over the whole surface of the earth1 nor any similar effect4 ,and to consult experience on all such points is a slow and painful process if rightly gone into1 and a very fallible one if only partially executed4 ,much1 then1 at present must be left to opinion1 and to that sort of clear-judging tact which sometimes anticipates experience2 but this ought not to stand in the way of our making every possible effort to obtain accurate information on such points1 by which alone geology can be rendered1 if not an experimental science1 at least a science of that kind of active observation which forms the nearest approach to it1 where actual experiment is impossible4 7#cbb47 ,let us take1 for example1 the question1 8,what is the actual direction in which changes of relative level are taking place between the existing continents and seas80 ,if we consult partial experience1 that is1 all the information that we possess respecting ancient sea-marks1 soundings1 c41 we shall only find ourselves bewildered in a mass of conflicting1 because imperfect1 evidence4 ,it is obvious that the only way to decide the point is to ascertain1 by very precise and careful observations at proper stations on coasts1 selected at points where there exist natural marks not liable to change in the course of at least a century1 the true elevation of such marks above the mean level of the sea1 and to multiply these stations sufficiently over the whole globe to be capable of affording real available knowledge4 ,now1 this is not a very easy operation 7considering the accuracy required72 for the mean level of the sea can be determined by no single observation1 any more than the mean height of the barometer at a given station1 being affected both by periodical and accidental fluctuations due to tides1 winds1 waves1 and currents4 ,yet if an instrument adapted for the purpose were constructed1 and rendered easily attainable1 and rules for its use carefully drawn up1 there is little doubt we should soon 7by the industry of observers scattered over the world7 be in possession of a most valuable mass of information1 which could not fail to afford a point of departure for the next generation1 and furnish ground for the only kind of argument which ever can be conclusive on such subjects4 7#cbc47 ,geology1 in the magnitude and sublimity of the objects of which it treats1 undoubtedly ranks1 in the scale of the sciences1 next to astronomy2 like astronomy1 too1 its progress depends on the continual accumulation of observations carried on for ages4 ,but1 unlike astronomy1 the observations on which it depends1 when the whole extent of the subject to be explored is taken into consideration1 can hardly yet be said to be more than commenced4 ,yet1 to make up for this1 there is another important difference1 that while in the latter science it is impossible to recall the past or anticipate the future1 and observation is in consequence limited to a single fact in a single moment2 in the former1 the records of the past are always present2--they may be examined and re-examined as often as we please1 and require nothing but diligence and judgment to put us in possession of their whole contents4 ,only a very small part of the surface of our globe has1 however1 been accurately examined in detail1 and of that small portion we are only able to scratch the mere exterior1 for so we must consider those excavations which we are apt to regard as searching the bowels of the earth2 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 centre4 ,of course inductions founded on such limited examination can only be regarded as provisional1 except in those remarkable cases where the same great formations in the same order have been recognised in very distant quarters1 and without exception4 ,this1 however1 cannot long be the case4 ,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 discoveries1 and has carried the investigation of our island into such detail1 as to have excited a corresponding spirit among our continental neighbours2 while the same zeal which animates our countrymen on their native shore accompanies them in their sojourns abroad1 and has already begun to supply a fund of information respecting the geology of our ,indian possessions1 as well as of every other point where ,english intellect and research can penetrate4 7#cbd47 ,nothing can be more desirable than that every possible facility and encouragement should be afforded for such researches1 and indeed to the pursuits of the enlightened resident or traveller in every department of science1 by the representatives of our national authority wherever our power extends4 ,by these only can our knowledge of the actual state of the surface of the globe1 and that of the animals and vegetables of the ancient continents and seas1 be extended and perfected1 while more complete information than we at present possess of the habits of those actually existing1 and the influence of changes of climate1 food1 and circumstances1 on them1 may be expected to render material assistance to our speculations respecting those which have become extinct4 ,,chap4 ,,iv4 ,,of ,,the ,,examination ,,of ,,the ,,material ,,constituents ,,of ,,the ,,world4 ,mineralogy4 7#cbe47 ,the consideration of the history and structure of our globe1 and the examination of the fossil contents of its strata1 lead us naturally to consider the materials of which it consists4 ,the history of these materials1 their properties as objects of philosophical enquiry1 and their application to the useful arts and the embellishments of life1 with the characters by which they can be certainly distinguished one from another1 form the object of mineralogy1 taken in its most extended sense4 7#cbf47 ,there is no branch of science which presents so many points of contact with other departments of physical research1 and serves as a connecting link between so many distant points of philosophical speculation1 as this4 ,to the geologist1 the chemist1 the optician1 the crystallographer1 the physician1 it offers especially the very elements of their knowledge1 and a field for many of their most curious and important enquiries4 ,nor1 with the exception of chemistry1 is there any which has undergone more revolutions1 or been exhibited in a greater variety of forms4 ,to the ancients it could scarcely be said to be at all known1 and up to a comparatively recent period1 nothing could be more imperfect than its descriptions1 or more inartificial and unnatural than its classification4 ,the more important minerals in the arts1 indeed1 those used for economical purposes and those from which metals were extracted1 had a certain degree of attention paid to them1 for the sake of their utility and commercial value1 and the precious stones for that of ornament4 ,but until their crystalline forms were attentively observed and shown to be determinate characters on which dependence could be placed1 no mineralogist could give any correct account of the real distinction between one mineral and another4 7#cbg47 ,it was only1 however1 when chemical analysis had acquired a certain degree of precision and universal applicability that the importance of mineralogy as a science began to be recognized1 and the connection between the external characters of a stone and its ingredient constituents brought into distinct notice4 ,among these characters1 however1 none were found to possess that eminent distinctness which the crystalline form offers2 a character1 in the highest degree geometrical1 and affording1 as might be naturally supposed1 the strongest evidence of its necessary connection with the intimate constitution of the substance4 ,the full importance of this character was1 however1 not felt until its connection with the texture or cleavage of a mineral was pointed out1 and even then it required numerous and striking instances of the critical discernment of ,hay and other eminent mineralogists in predicting from the measurements of the angles of crystals which had been confounded together that differences would be found to exist in their chemical composition1 all which proved fully justified in their result before the essential value of this character was acknowledged4 ,this was no doubt in great measure owing to the high importance set by the ,german mineralogists on those external characters of touch1 sight1 weight1 colour1 and other sensible qualities1 which are little susceptible1 with the exception of weight1 of exact determination1 and which are subject to material variations in different specimens of the same mineral4 ,by degrees1 however1 the necessity of ascribing great weight to a character so definite was admitted1 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 type1 or primitive form1 and afforded grounds for an elegant theoretical account of the assumption of definite figures ab initio4 7#cbh47 ,a simple and elegant invention of ,dr4 ,wollaston1 the reflecting goniometer1 gave a fresh impulse to that view of mineralogy which makes the crystalline form the essential or leading character1 by putting it in the power of every one1 by the examination of even the smallest portion of a broken crystal1 to ascertain and verify that essential character on which the identity of a mineral in the system of ,hay was made to depend4 ,the application of so ready and exact a method speedily led to important results1 and to a still nicer discrimination of mineral species than could before be attained2 and the confirmation given to these results by chemical analysis stamped them with a scientific and decided character which they have retained ever since4 7#cbi47 ,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 form2 and the progress of optical science had shown that the fundamental crystalline form1 in the case at least of transparent bodies1 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 substances4 ,thus1 in every point of view1 additional importance became added to this character2 and the study of the crystalline forms of bodies in general assumed the form of a separate and independent branch of science1 of which the geometrical forms of the mineral world constituted only a particular case4 ,mineralogy1 however1 as a branch of natural history1 remains still distinct either from optics or crystallography4 ,the mineralogist is content1 and thinks he has performed his task1 if not as a natural historian at least as a classifier and arranger1 if he only gives such a characteristic description of a mineral as shall effectually distinguish it from every other1 and shall enable any one who may encounter such a body in any part of the world to impose on it its name1 assign it a place in his system1 and turn to his books for a further description of all that the chemist1 the optician1 the lapidary1 or the artist1 may require to know4 ,still this is no easy matter3 the laborious researches of the most eminent mineralogists can hardly yet be said to have effectually accomplished it2 and its difficulty may be appreciated by the small number of simple minerals1 or minerals of perfectly definite and well-marked characters1 which have been hitherto made out4 ,nor can this indeed be wondered at1 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 detritus of older rocks1 in which the fragments and powder of an infinite variety of substances are mingled together1 in all sorts of varying proportions1 and in such a way as to defy separation4 ,many of these rocks1 however1 so compounded1 occur with sufficient frequency and uniformity of character to have acquired names and to have been usefully applied2 indeed1 in the latter respect1 minerals of this description far surpass all the others4 ,as objects of natural history1 therefore1 they are well worthy of attention1 however difficult it may be to assign them a place in any artificial arrangement4 7#ccj47 ,this paucity of simple minerals1 however1 is probably rather apparent than real1 and in proportion as the researches of the chemist and crystallographer shall be extended throughout nature1 they will no doubt become much more numerous4 ,indeed1 in the great laboratories of nature it can hardly be doubted that almost every kind of chemical process is going forwards1 by which compounds of every description are continually forming4 ,accordingly1 it is remarked1 that the lavas and ejected scori of volcanoes are receptacles in which mineral products previously unknown are constantly discovered1 and that the primitive formations1 as they are called in geology1 which bear no marks of having been produced by the destruction of others1 are also remarkable for the beauty and distinctness of character of their minerals4 7#cca47 ,the great difficulty which has been experienced in attempts to classify mineral substances by their chemical constituents has arisen from the observed presence1 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 alike1 of ingredients foreign to the usual composition of the species1 and that occasionally in so large a proportion as to render it unjustifiable to refer their occurrence to accidental impurities4 ,these cases1 as well as some anomalies observed in the classification of minerals by their crystalline forms1 which seemed to show that the same substance might occasionally appear under two distinct forms1 as well as some remarkable coincidences between the forms of substances quite distinct from each other in a chemical point of view1 have within a recent period given rise to a branch of the science of crystallography of a very curious and important nature4 ,the isomorphism of certain groups of chemical elements has already afforded us an example illustrative of the manner in which inductions sometimes receive unexpected verifications 7see #ahj474 ,the laws and relations thus brought to light are among the most curious and interesting parts of modern science1 and seem likely in their further developement to afford ample scope for the exercise of chemical and mineralogical research4 ,they have already afforded innumerable fine examples of that important step in science by which anomalies disappear1 and occasional incongruities become reconciled under more general expressions of physical laws1 and thus unite in affording support to those very views which they promised1 when first observed1 to overset4 ,nothing1 indeed1 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 disregarding1 under any circumstances1 the plain results of direct experiment4 ,chemistry4 7#ccb47 ,the laws which concern the intimate constitution of bodies1 not as respects their structure or the manner in which their parts are put together1 but as regards their materials or the ingredients of which those parts are composed1 form the objects of chemistry4 ,a solid body may be regarded as a fabric1 more or less regularly and artificially constructed1 in which the materials and the workmanship may be separately considered1 and in which1 though the latter be ruined and confounded by violence1 the former remain unchanged in their nature1 though differently arranged4 ,in liquid or arial bodies1 too1 though there prevails a less degree of difference in point of structure1 and a greater facility of dispersion and dissipation1 than in solids1 yet an equal diversity of materials subsists1 giving to them properties differing extremely from each other4 7#ccc47 ,the inherent activity of matter is proved not only by the production of motion by the mutual attractions and repulsions of distant or contiguous masses1 but by the changes and apparent transformations which different substances undergo in their sensible qualities by mere mixture4 ,if water be added to water1 or salt to salt1 the effect is an increase of quantity1 but no change of quality4 ,in this case1 the mutual action of the particles is entirely mechanical4 ,again1 if a blue powder and a yellow one1 each perfectly dry1 be mixed and well shaken together1 a green powder will be produced2 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 each2 and the proof is had by examining the mixture with a microscope1 when the yellow and blue grains will be seen separate and each quite unaltered4 ,if the same experiment be tried with coloured liquids1 which are susceptible of mixing without chemical action1 a compound colour is likewise produced1 but no examination with magnifiers is in that case sufficient to detect the ingredients2 the reason obviously being1 the excessive minuteness of the parts1 and their perfect intermixture1 produced by agitating two liquids together4 ,from the mixture of two powders1 extreme patience would enable any one1 by picking out with a magnifier grain after grain1 to separate the ingredients4 ,but when liquids are mixed1 no mechanical separation is any longer practicable2 the particles are so minute as to elude all search4 ,yet this does not hinder us from regarding such a compound as still a mere mixture1 and its properties are accordingly intermediate between those of the liquids mixed4 ,but this is far from being the case with all liquids4 ,when a solution of potash1 for example1 and another of tartaric acid1 each perfectly liquid1 are mixed together in proper proportions1 a great quantity of a solid saline substance falls to the bottom of the containing vessel1 which is quite different from either potash or tartaric acid1 and the liquid from which it subsided offers no indications by its taste or other sensible qualities of the ingredients mixed1 but of something totally different from either4 ,it is evident that this is a phenomenon widely different from that of mere mixture2 there has taken place a great and radical change in the intimate nature of the ingredients1 by which a new substance is produced which had no existence before4 ,and it has been produced by the union of the ingredients presented to each other2 for when examined it is found that nothing has been lost1 the weight of the whole mixture being the sum of the weights mixed4 ,yet the potash and tartaric acid have disappeared entirely1 and the weight of the new product is found to be exactly equal to that of the tartaric acid and potash employed1 taken together1 abating a small portion held in solution in the liquid1 which may be obtained however by evaporation4 ,they have therefore combined1 and adhere to one another with a cohesive force sufficient to form a solid out of a liquid2 a force which has thus been called into action by merely presenting them to each other in a state of solution4 7#ccd47 ,it is the business of chemistry to investigate these and similar changes1 or the reverse of such changes1 where a single substance is resolved into two or more others1 having different properties from it1 and from each other1 and to enquire into all the circumstances which can influence them2 and either determine1 modify1 or suspend their accomplishment1 whether such influence be exercised by heat or cold1 by time and rest1 or by agitation or pressure1 or by any of those agents of which we have acquired a knowledge1 such as electricity1 light1 magnetism1 c4 7#cce47 ,the wonderful and sudden transformations with which chemistry is conversant1 the violent activity often assumed by substances usually considered the most inert and sluggish1 and1 above all1 the insight it gives into the nature of innumerable operations which we see daily carried on around us1 have contributed to render it the most popular1 as it is one of the most extensively useful1 of the sciences2 and we shall1 accordingly1 find none which have sprung forward1 during the last century1 with such extraordinary vigour1 and have had such extensive influence in promoting corresponding progress in others4 ,one of the chief causes of its popularity is1 perhaps1 to be sought for in this1 that it is1 of all the sciences1 perhaps1 the most completely an experimental one2 and even its theories are1 for the most part1 of that generally intelligible and readily applicable kind1 which demand no intense concentration of thought1 and lead to no profound mathematical researches4 ,the simple process of inductive generalization1 grounded on the examination of numerous facts1 all of them presenting considerable intrinsic interest1 has sufficed1 in most instances1 to lead1 by a clear and direct road1 to its highest laws yet known4 ,but1 on the other hand1 these laws1 when stated1 are not yet fully sufficient to lead us1 except in very limited cases1 to a deductive knowledge of particulars never before examined1 at least1 not without great caution1 and constant appeal to experiment as a check on our reasoning2 so that we are justified in regarding the axioms of chemistry1 the true handles of deductive reasoning1 as still unknown1 and1 perhaps1 likely long to remain so4 ,this is no fault of its cultivators1 who have comprised in their list the highest and most varied talents and industry1 but of the inherent complexity of the subject1 and the infinite multitude of causes which are concerned in the production of every1 even the simplest1 chemical phenomenon4 7#ccf47 ,the history of chemistry 7on which1 however1 we are not about to enlarge17 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 failures4 ,it may be divided1 #ast1 into the period of the alchemists1 a lamentable epoch in the annals of intellectual wandering2 #b;dly1 that of the phlogistic doctrines of ,beccher and ,stahl1 in which1 as if to prove the perversity of the human mind1 of two possible roads the wrong was chosen2 and a theory obtained universal credence on the strength of an induction1 valid as such1 but wrongly interpreted1 which is negatived1 in every instance1 by an appeal to the balance4 ,this1 too1 happened1 not by reason of unlucky coincidences1 or individual oversights1 but of necessity1 and from an inherent defect of the theory itself1 which thus impeded the progress of the science1 as far as a science of experiment can be impeded by a false theory1 by perplexing its cultivators with the appearance of contradictions in their experiments where none really subsisted1 by destroying all their confidence in the numerical exactness of their own results1 and by involving the subject in a mist of visionary and hypothetical causes in place of the true acting principles4 ,thus1 in the combustion of any substance which is incapable of flying away in fumes1 an increase of weight takes place1--the ashes are heavier than the fuel4 ,whenever this was observed1 however1 it was passed carelessly over as arising from the escape of phlogiston1 or the principle of inflammability1 which was considered as being either the element of fire itself1 or in some way combined with it1 and thus essentially light4 ,it is now known that the increase of weight is owing to the absorption of1 and combination with1 a quantity of a peculiar ingredient called oxygen1 from the air1 a principle essentially heavy4 ,so far as weight is concerned1 it makes no difference whether a body having weight enters1 or one having levity escapes2 but there is this plain difference in a philosophical point of view1 that oxygen is a real producible substance1 and phlogiston is no such thing3 the former is a vera causa1 the latter an hypothetical being1 introduced to account for what the other accounts for much better4 7#ccg47 ,the third age of chemistry--that which may be called emphatically modern chemistry--commenced 7in #aghf7 when ,lavoisier1 by a series of memorable experiments1 extinguished for ever this error1 and placed chemistry in the rank of one of the exact sciences1--a science of number1 weight1 and measure4 ,from that epoch to the present day it has constantly advanced with an accelerated progress1 and at this moment may be regarded as more progressive than ever4 ,the principal features in this progress may be comprised under the following general heads3-- #a4 ,the discovery of the proximate1 if not the ultimate1 elements of all bodies1 and the enlargement of the list of known elements to its present extent of between fifty and sixty substances4 #b4 ,the developement of the doctrine of latent heat by ,black1 with its train of important consequences1 including the scientific theory of the steam-engine4 #c4 ,the establishment of ,wenzel's law of definite proportions on his own experiments1 and those of ,richter1 a discovery subsequently merged in the more general wording and better development of ,dalton's atomic theory4 #d4 ,the precise determination of the atomic weights of the different chemical elements1 mainly due to the astonishing industry of ,berzelius1 and his unrivalled command of chemical resources1 as well as to the researches of the other chemists of the ,swedish and ,german school4 #e4 ,the assimilation of gases and vapours1 by which we are led to regard the former1 universally1 as particular cases of the latter1 a generalization resulting chiefly from the experiments of ,faraday on the condensation of the gases1 and those of ,gay-,lussac and ,dalton1 on the laws of their expansion by heat compared with that of vapours4 #f4 ,the establishment of the laws of the combination of gases and vapours by definite volumes1 by ,gay-,lussac4 #g4 ,the discovery of the chemical effects of electricity1 and the decomposing agency of the ,voltaic pile1 by ,nicholson and ,carlisle2 the investigation of the laws of such decompositions1 by ,berzelius and ,hisinger3 the decomposition of the alkalies by ,davy1 and the consequent introduction into chemistry of new and powerful agents in their metallic bases4 #h4 ,the application of chemical analysis to all the objects of organized and unorganized nature1 and the discovery of the ultimate constituents of all1 and the proximate ones of organic matter1 and the recognisance of the important distinctions which appear to divide these great classes of bodies from each other4 #i4 ,the applications of chemistry to innumerable processes in the arts1 and among other useful purposes to the discovery of the essential medical principles in vegetables1 and to important medicaments in the mineral kingdom4 #aj4 ,the establishment of the intimate connection between chemical composition and crystalline form1 by ,hay and ,vauquelin1 with the successive rectifications the statement of that connection has undergone in the hands of ,mitscherlich1 ,rose1 and others1 with the progress of chemical and crystallographical knowledge4 7#cch47 ,to pursue these several heads into detail would lead us into a treatise on chemistry2 but a few remarks on one or two of them1 as they bear upon the general principles of all scientific enquiry1 will not be irrelevant4 ,and first1 then1 with reference to the discovery of new elements1 it will be observed1 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 direction1 or geology at ascending to the creation of the earth4 ,there may be such an element4 ,some singular relations which have been pointed out in the atomic weights of bodies seem to suggest to minds fond of speculation that there is2 but philosophical chemistry is content to wait for some striking fact1 which may either occur unexpectedly or be led to by the slow progress of enlarged views1 to disclose to us its existence4 ,still1 the multiplication of so-considered elementary bodies has been considered by some as an inconvenience4 ,we confess we do not coincide with this view4 ,whatever they be1 the obstinacy with which they resist decomposition shows that they are ingredients of a very high and primary importance in the economy of nature2 and such as1 in any state of science1 it would be indispensably necessary to be perfectly familiar with4 ,like particular theorems in geometry1 which1 though not rising to the highest point of generality1 have yet their several scopes and ranges of extensive application1 they must be well and perfectly understood in all their bearings4 ,should we ever arrive at an analysis of these bodies1 the chemical properties of the new elements which will then come into view will be known only by our knowledge of these1 or of other compounds of the same class1 which they may be capable of forming4 ,not but that such an analysis would be a most important and indeed triumphant achievement1 and change the face of chemistry2 but it would undo nothing that has been done1 and render useless no point of knowledge which we have yet arrived at4 7#cci47 ,the atomic theory1 or the law of definite proportions1 which is the same thing presented in a form divested of all hypothesis1 after the laws of mechanics1 is1 perhaps1 the most important which the study of nature has yet disclosed4 ,the extreme simplicity which characterizes it1 and which is itself an indication1 not unequivocal1 of its elevated rank in the scale of physical truths1 had the effect of causing it to be announced at once by ,mr4 ,dalton1 in its most general terms1 on the contemplation of a few instances#ec1 without passing through subordinate stages of painful inductive ascent by the intermedium of subordinate laws1 such as1 had the contrary course been pursued by him1 would have been naturally preparatory to it1 and such as would have led others to it by the prosecution of ,wenzel's and ,richter's researches1 had they been duly attended to4 ,this is1 in fact1 an example1 and a most remarkable one1 of the effect of that natural propensity to generalize and simplify 7noticed in #aga471 which1 if it occasionally leads to over-hasty conclusions1 limited or disproved by further experience1 is yet the legitimate parent of many of our most valuable and soundest results4 ,instances like this1 where great and1 indeed1 immeasurable steps in our knowledge of nature are made at once1 and almost without intellectual effort1 are well calculated to raise our hopes of the future progress of science1 and1 by pointing out the simplest and most obvious combinations as those which are actually found to be agreeable to the harmony of creation1 to hold out the cheering prospect of difficulties diminishing as we advance1 instead of thickening around us in increasing complexity4 7#cdj47 ,a consequence of this immediate presentation of the law of definite proportions in its most general form is1 that its subordinate laws--those which limit its generality in particular cases1 which diminish the number of combinations abstractly possible1 and restrain the indiscriminate mixture of elements1--remain to be discovered4 ,some such limitations have1 in fact1 been traced to a certain extent1 but by no means so far as the importance of the subject requires2 and we have here abundant occupation for chemists for some time4 7#cda47 ,the determination of the atomic weights of the chemical elements1 like that of other standard physical data1 with the utmost exactness1 is in itself a branch of enquiry not only of the greatest importance1 but of extreme difficulty4 ,independent of the general reasons for desiring accuracy in this respect1 there is one peculiar to the subject4 ,it has been suggested 7by ,dr4 ,prout71 and strongly insisted on 7by ,dr4 ,thomson71 that all the numbers representing these weights1 constituting a scale of great extent1 in which the extremes already known are in proportion to each other1 as #a to upwards of #bjj1 are simple even multiples of the least of them4 ,if this be really the case1 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 one4 ,but in the actual state of chemical analysis1 with all deference to such high authority1 we confess it appears to us to stand in great need of further confirmation1 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 determined3 at least the results of the first experimenters1 obtained with the greatest care1 differ often by a greater amount2 and this degree of exactness1 at least1 would be required to verify the law satisfactorily in the higher parts of the scale4 7#cdb47 ,the mere agitation of such a question1 however1 points out a class of phenomena in physical science of a remote and singular kind1 and of a very high and refined order1 which could never become known but in an advanced state of science1 not only practical1 but theoretical1--we mean1 such as consist in observed relations among the data of physics1 which show them to be quantities not arbitrarily assumed1 but depending on laws and causes which they may be the means of at length disclosing4 ,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 orbits4 ,this law was interrupted between ,mars and ,jupiter1 so as to induce him to consider a planet as wanting in that interval2--a deficiency long afterwards strangely supplied by the discovery of four new planets in that very interval1 all of whose orbits conform in dimension to the law in question1 within such moderate limits of error as may be due to causes independent of those on which the law itself ultimately rests4#ed 7#cdc47 ,neither is it irrelevant to our subject to remark1 that the progress which has been made in this department of chemistry1 and the considerable exactness actually attainable in chemical analysis1 have been owing1 in great measure1 to a circumstance which might at first have been hardly considered likely to exercise much influence on the progress of a science1--the discovery of platina4 ,without the resources placed at the ready disposal of chemists by this invaluable metal1 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 performed4 ,this1 among many such lessons1 will teach us that the most important uses of natural objects are not those which offer themselves to us most obviously4 ,the chief use of the moon for man's immediate purposes remained unknown to him for five thousand years from his creation4 ,and1 since it cannot but be that innumerable and most important uses remain to be discovered among the materials and objects already known to us1 as well as among those which the progress of science must hereafter disclose1 we may hence conceive a well-grounded expectation1 not only of constant increase in the physical resources of mankind1 and the consequent improvement of their condition1 but of continual accessions to our power of penetrating into the arcana of nature1 and becoming acquainted with her highest laws4 ,,chap4 ,v4 ,,of ,,the ,,imponderable ,,forms ,,of ,,matter4 ,heat4 7#cdd47 ,one of the chief agents in chemistry1 on whose proper application and management the success of a great number of its enquiries depends1 and many of whose most important laws are disclosed to us by phenomena of a chemical nature1 is ,,heat4 ,although some of its effects are continually before our eyes as matters of the most common occurrence1 insomuch that there is scarcely any process in the useful arts and manufactures which does not call for its intervention1 and although1 independent of this high utility1 and the proportionate importance of a knowledge of its nature and laws1 it presents in itself a subject of the most curious speculation2 yet there is scarcely any physical agent of which we have so imperfect a knowledge1 whose intimate nature is more hidden1 or whose laws are of such delicate and difficult investigation4 7#cde47 ,the word heat generally implies the sensation which we experience on approaching a fire2 but1 in the sense it carries in physics1 it denotes the cause1 whatever it be1 of that sensation1 and of all the other phenomena which arise on the application of fire1 or of any other heating cause4 ,we should be greatly deceived if we referred only to sensation as an indication of the presence of this cause4 ,many of those things which excite in our organs1 and especially of those of taste1 a sensation of heat1 owe this property to chemical stimulants1 and not at all to their being actually hot4 ,this error of judgment has produced a corresponding confusion of language1 and hence had actually at one period#ee crept into physical philosophy a great many illogical and absurd conclusions4 ,again1 there are a number of chemical agents1 which1 from their corroding1 blackening1 and dissolving1 or drying up the parts of some descriptions of bodies1 and producing on them effects not generally unlike 7though intrinsically very different from7 those produced by heat1 are said1 in loose and vulgar language1 to burn them2 and this error has even become rooted into a prejudice1 by the fact that some of these agents are capable of becoming actually and truly hot during their action on moist substances1 by reason of their combination with the water the latter contain4 ,thus1 quicklime and oil of vitriol both exercise a powerful corrosive action on animal and vegetable substances1 and both become violently hot by their combination with water4 ,they are1 therefore1 set down in vulgar parlance as substances of a hot nature2 whereas1 in their relations to the physical cause of heat1 they agree with the generality of bodies similarly constituted4 7#cdf47 ,the nature of heat has hitherto been chiefly studied under the general heads of-- #ast1 ,its sources1 or the phenomena which it usually accompanies4 #b;d1 ,its communication from its sources to substances capable of receiving it1 and from these to others1 with a view to discover the laws which regulate its distribution through space or through the bodies which occupy it4 #c;d1 ,its effects1 on our senses1 and on the bodies to which it is communicated in its various degrees of intensity1 by which1 means are afforded us of measuring these degrees4 #dth1 ,its intimate relations to the atoms of matter1 as exhibited in its capability of acquiring a latent state under certain circumstances1 and of entering into something like chemical combinations4 7#cdg47 ,the most obvious sources of heat are1 the sun1 fire1 animal life1 fermentations1 violent chemical actions of all kinds1 friction1 percussion1 lightning1 or the electric discharge1 in whatever manner produced1 the sudden condensation of air1 and others1 so numerous1 and so varied1 as to show the extensive and important part it has to perform in the economy of nature4 ,the discoveries of chemists1 however1 have referred most of these to the general head of chemical combination4 ,thus1 fire1 or the combustion of inflammable bodies1 is nothing more than a violent chemical action attending the combination of their ingredients with the oxygen of the air4 ,animal heat is1 in like manner1 referable to a process bearing no remote analogy to a slow combustion1 by which a portion of carbon1 an inflammable principle existing in the blood1 is united with the oxygen of the air in respiration2 and thus carried off from the system3 fermentation is nothing more than a decomposition of chemical elements loosely united1 and their re-union in a more permanent state of combination4 ,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 principle4 ,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 optics1 so far from elucidating1 seems only to render more profound4 ,friction as a source of heat is well known3 we rub our hands to warm them1 and we grease the axles of carriage-wheels to prevent their setting fire to the wood2 an accident which1 in spite of this precaution1 does sometimes happen4 ,but the effect of friction1 as a means of producing heat with little or no consumption of materials1 was not fully understood till made the subject of direct experiment by count ,rumford1 whose results appear to have established the extraordinary fact1 that an unlimited supply of heat may be derived by friction from the same materials4 ,condensation1 whether of air by pressure1 or of metals by percussion1 is another powerful source of heat4 ,thus1 iron may be so dexterously hammered as to become red-hot1 and the rapid condensation of a confined portion of air will set tinder on fire4 7#cdh47 ,the most violent heats known are produced by the concentration of the solar rays by burning glasses1--by the combustion of oxygen and hydrogen gases mixed in the exact proportion in which they combine to produce water1--and by the discharge of a continued and copious current of electricity through a small conductor4 ,as these three sources of heat are independent of each other1 and each capable of being brought into action in a very confined space1 there seems no reason why they might not all three be applied at once at the same point1 by which means1 probably1 effects would be produced infinitely surpassing any hitherto witnessed4 7#cdi47 ,heat is communicated either by radiation between bodies at a distance1 or by conduction between bodies in contact1 or between the contiguous parts of one and the same body4 ,the laws of the radiation of heat have been studied with great attention1 and have been found to present strong analogies with that of light in some points1 and singular differences in others4 ,thus1 the heat which accompanies the sun's rays comports itself1 in all respects1 like light2 being subject to similar laws of reflection1 refraction1 and even of polarization1 as has been shown by ,berard4 ,yet they are not identical with each other2 ,sir ,william ,herschel having shown1 by decisive experiments1 verified by those of ,sir ,h4 ,englefield1 that there exist in a solar beam both rays of heat which are not luminous1 and rays of light which have no heating power4 7#cej47 ,the heat1 radiated by terrestrial fires1 and by bodies obscurely hot1 by whatever means they have acquired their heat 7even by exposure to the sun's rays71 differs very materially from solar heat in their power of penetrating transparent substances4 ,this singular and important difference was first noticed by ,mariotte1 and afterwards made the subject of many curious and interesting experiments by ,scheele1 who found that terrestrial heat1 or that radiated from fires or heated bodies1 is intercepted and detained by glass or other transparent bodies1 while solar heat is not2 and that1 being so detained1 it heats them3 which the latter1 as it passes freely through them1 is incapable of doing4 ,the more recent researches of ,delaroche1 however1 have shown that this detention is complete only when the temperature of the source of heat is low2 but that1 as that temperature is higher1 a portion of the heat radiated acquires a power of penetrating glass2 and that the quantity which does so bears continually a larger and larger proportion to the whole1 as the heat of the radiant body is more intense4 ,this discovery is very important1 as it establishes a community of nature between solar and terrestrial heat2 while at the same time it leads us to regard the actual temperature of the sun as far exceeding that of any earthly flame4 7#cea47 ,a variety of theories have been framed to account for these curious phenomena2 but the subject stands rather in need of further elucidation from experiment1 and is one which merits1 and will probably amply repay1 the labours of those who may hereafter devote their attention to it4 ,the theory of the radiation of heat1 in general1 which seems to agree best with the known phenomena1 is that of ,m4 ,prevost1 who considers all bodies as constantly radiating out heat in all directions1 and receiving it by a similar means of communication from others1 and thus tending1 in any space filled1 wholly or in part1 with bodies at various temperatures1 to establish an equilibrium or equality of heat in all parts4 ,the application of this idea to the explanation of the phenomenon of dew we have already seen 7see #afg474 ,the laws of such radiation1 under various circumstances1 have been lately investigated in a beautiful series of experiments on the cooling of bodies by their own radiation in vacuo1 by ,messrs4 ,dulong and ,petit1 which offer some of the best examples in science of the inductive investigation of quantitative laws4 7#ceb47 ,the communication of heat between bodies in contact1 or between the different parts of the same body1 is performed by a process called conduction4 ,it is1 in fact1 only a particular case of radiation1 as has been explained above 7#bag472 but a case so particular as to require a separate and independent investigation of its laws4 ,the most important consideration introduced into the enquiry by this peculiarity is that of time4 ,the communication of heat by conduction is performed1 for the most part1 with extreme slowness1 while that performed by direct radiation is probably not less rapid than the propagation of light itself4 ,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 ,fourrier1 whose recent lamented death has deprived science of an ornament it could ill spare1 thinned as its ranks have been within the last few years4 ,this acute philosopher and profound mathematician has developed1 in a series of elaborate memoirs presented to the ,french ,institute1 the laws of the communication of heat through the interior of solid masses1 placed under the influence of any external heating and cooling causes1 and has in particular applied his results to the conditions on which the maintenance of the actual observed temperature on the earth's surface depends2 to the possible influence of a supposed central heat on our climates2 and to the determination of the actual amount of the heat1 derived to us from the sun1 or at least that portion of it on which the difference of the seasons depends4 7#cec47 ,the principal effects of heat are the sensations of warmth or cold consequent on its entry or egress into or out of our bodies2 the dilatation it causes in the dimensions of all substances in which it is accumulated2 the changes of state it produces in the melting of solids1 and the conversion of them and of liquids into vapour2 and the chemical changes it performs by actual decompositions effected in the intimate molecules of various substances1 especially those of which vegetables and animals are composed2 to which we may add1 the production of electric phenomena under certain circumstances in the contact of metals1 and the developement of electric polarity in crystallised substances4 7#ced47 ,cold has been considered by some as a positive quality1 the effect of a cause antagonist to that of heat2 but this idea seems now 7with perhaps a single exception7 to be universally abandoned4 ,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 without2 and the experiments cited in proof of a radiation of cold are all perfectly explained by ,prevost's theory of reciprocal interchange4 ,it is remarkable1 however1 how very limited our means of producing intense cold are1 compared with those we possess of effecting the accumulation of heat in bodies4 ,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 altogether1 and leaving it in a state absolutely devoid of it4 ,but we ought to consider1 that the known methods of generating heat chiefly turn on the production of chemical combinations3 we may easily conceive1 therefore1 that1 to obtain equally powerful corresponding frigorific effects1 we ought to possess the means of effecting a disunion equally extensive and rapid between such elements1 actually combined1 as have already produced heat by their union4 ,this1 however1 we can only accomplish by engaging them in combinations still more energetic1 that is to say1 in which we may reasonably expect more heat to be produced by the new combination than would be destroyed or abstracted by the proposed decomposition4 ,chemistry1 however1 7unaided by electric agency17 affords no means of suddenly breaking the union of two elements1 and presenting both in an uncombined state4 ,a certain analogy to such disunion1 however1 and its consequences1 may be traced in the sudden expansion of condensed gases from a liquid state into vapour1 which is the most powerful source of cold known4 7#cee47 ,the dilatation of bodies by heat forms the subject of that branch of science called pyrometry4 ,there is no body but is capable of being penetrated by heat1 though some with greater1 others with less rapidity2 and being so penetrated1 all bodies 7with a very few exceptions1 and those depending on very peculiar circumstances17 are dilated by it in bulk1 though with a great diversity in the amount of dilatation produced by the same degree of heat4 ,of the several forms of natural bodies1 gases and vapours are observed to be most dilatable2 liquids next1 and solids least of all4 ,the dilatation of solids has been made a subject of repeated and careful measurement by several experimenters2 among whom1 ,smeaton1 ,lavoisier1 and ,laplace1 are the principal4 ,the remarkable discovery of the unequal dilatation of crystallised bodies by ,mitscherlich has already been spoken of4 7#bff47 ,that of gases and vapours was examined about the same time by ,dalton and ,gay-,lussac1 who both arrived independently at the conclusion of an equal dilatability subsisting in them all1 which constitutes one of the most remarkable points in their history4 7#cef47 ,the dilatation of air by heat affords1 perhaps1 the most unexceptionable means known of measuring degrees of heat4 ,the thermometer1 as originally constructed by ,cornelius ,drebell1 was an air thermometer4 ,those now in common use measure accessions of heat not by the degree of dilatation of air but of mercury4 ,it has been shown1 by the researches of ,dulong and ,petit1 that its indications coincide exactly with that of the air-thermometer in moderate temperatures2 though at very elevated ones they exhibit a sensible1 and even considerable1 deviation4 ,by this instrument1 which owes its present convenience and utility to the happy idea of ,newton1 who first thought of fixing determinate points on its scale1 we are enabled to estimate1 or at least identify1 the degrees of heat2 and thereby to investigate with accuracy the laws of its communication and its other properties4 ,were we sure that equal additions of heat produced equal increments of dimension in any substance1 the indications of a thermometer would afford a true and secure measure of the quantity present2 but this is so far from being the case1 that we are nearly in total ignorance on this important point2 a circumstance which throws the greatest difficulty in the way of all theoretical reasoning1 and even of experimental enquiry4 ,the laws of the dilatation of liquids1 in consequence of this deficiency of necessary preliminary knowledge1 are still involved in great obscurity1 notwithstanding the pains which have been bestowed on them by the elaborate experiments and calculations of ,gilpin1 ,blagden1 ,deluc1 ,dalton1 ,gay-,lussac1 and ,biot4 7#ceg47 ,the most striking and important of the effects of heat consist1 however1 in the liquefaction of solid substances1 and the conversion of the liquids so produced into vapour4 ,there is no solid substance known which1 by a sufficiently intense heat1 may not be melted1 and finally dissipated in vapour2 and this analogy is so extensive and cogent1 that we cannot but suppose that all those bodies which are liquid under ordinary circumstances1 owe their liquidity to heat1 and would freeze or become solid if their heat could be sufficiently reduced4 ,in many we see this to be the case in ordinary winters2 for some1 severe frosts are requisite2 others freeze only with the most intense artificial colds2 and some have hitherto resisted all our endeavours2 yet the number of these last is few1 and they will probably cease to be exceptions as our means of producing cold become enlarged4 7#ceh47 ,a similar analogy leads us to conclude that all ariform fluids are merely liquids kept in the state of vapour by heat4 ,many of them have been actually condensed into the liquid state by cold accompanied with violent pressure2 and as our means of applying these causes of condensation have improved1 more and more refractory ones have successively yielded4 ,hence we are fairly entitled to extend our conclusion to those which we have not yet been able to succeed with2 and thus we are led to regard it as a general fact1 that the liquid and ariform or vaporous states are entirely dependent on heat2 that were it not for this cause1 there would be nothing but solids in nature2 and that1 on the other hand1 nothing but a sufficient intensity of heat is requisite to destroy the cohesion of every substance1 and reduce all bodies1 first to liquids1 and then into vapour4 7#cei47 ,but solids1 themselves1 by the abstraction of heat shrink in dimension1 and at the same time become harder1 and more brittle2 yielding less to pressure1 and permitting less separation between their parts by tension4 ,these facts1 coupled with the greater compressibility of liquids1 and the still greater of gases1 strongly induce us to believe that it is heat1 and heat alone1 which holds the particles of all bodies at that distance from each other which is necessary to allow of compression2 which in fact gives them their elasticity1 and acts as the antagonist force to their mutual attraction1 which would otherwise draw them into actual contact1 and retain them in a state of absolute immobility and impenetrability4 ,thus we learn to regard heat as one of the great maintaining powers of the universe1 and to attach to all its laws and relations a degree of importance which may justly entitle them to the most assiduous enquiry4 7#cfj47 ,it was first ascertained by ,dr4 ,black that when heat produces the liquefaction of a solid1 or the conversion of a liquid into vapour1 the liquid or the vapour resulting is no hotter than the solid or liquid from which it was produced1 though a great deal of heat has been expended in producing this effect1 and has actually entered into the substance4 7#cfa47 ,hence he drew the conclusion that it has become latent1 and continues to exist in the product1 maintaining it in its new state1 without increasing its temperature4 ,he further proved1 that when the vapour condenses1 or the liquid freezes1 this latent heat is again given out from it4 ,this great discovery1 with its natural and hardly less important concomitant1 that of the difference of specific heats in different bodies1 or the different quantities of heat they require to raise their temperature equally1 are the chief reasons for regarding heat as a material substance in a more decided manner than light1 with which in its radiant state it holds so close an analogy4 7#cfb47 ,the subject of latent heat has been far less attentively studied than its great practical importance would appear to demand1 when we consider that it is to this part of physical science that the theory of the steam-engine is mainly referable1 and that material improvements may not unreasonably be expected in that wonderful instrument1 from a more extended knowledge than we possess of the latent heats of different vapours4 ,this is not the case1 however1 with the subject of specific heat1 which was followed up immediately after its first promulgation with diligence by ,irvine2 and1 after a brief interval1 by ,lavoisier and ,laplace1 as well as by our countryman ,crawfurd1 who determined the specific heats of many substances1 both solid and liquid4 ,after a considerable period of inactivity1 the subject was again resumed by ,delaroche and ,berard1 and subsequently by ,dulong and ,petit3 the result of whose investigations has been the inductive establishment of one of those simple and elegant physical laws which carry with them1 if not their own evidence1 at least their own recommendation to our belief1 as being in unison with every thing we know of the harmony of nature4 ,the law to which we allude is this3--that the atoms of all the simple chemical elements have exactly the same capacity for heat1 or are all equally heated or cooled by equal accessions or abstractions of heat4 ,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 heat1 and its relations to ponderable matter4 ,magnetism and ,electricity4 7#cfc47 ,these two subjects1 which had long maintained a distinct existence1 and been studied as separate branches of science1 are at length effectually blended4 ,this is1 perhaps1 the most satisfactory result which the experimental sciences have ever yet attained4 ,all the phenomena of magnetic polarity1 attraction1 and repulsion1 have at length been resolved into one general fact1 that two currents of electricity1 moving in the same direction repel1 and in contrary directions attract1 each other4 ,the phenomena of the communication of magnetism and what is called its induced state1 alone remain unaccounted for2 but the interesting theory which has been developed by ,m4 ,ampere1 under the name of ,electro-dynamics1 holds out a hope that this difficulty will also in its turn give way1 and the whole subject be at length completely merged1 as far as the consideration of the acting causes goes1 in the more general one of electricity4 ,this1 however1 does not prevent magnetism from maintaining its separate importance as a department of physical enquiry1 having its own peculiar laws and relations of the highest practical interest1 which are capable of being studied quite apart from all consideration of its electrical origin4 ,and not only so1 but to study them with advantage1 we must proceed as if that origin were totally unknown1 and1 at least up to a certain point1 and that a considerably advanced one1 conduct our enquiries into the subject on the same inductive principles as if this branch of physics were absolutely independent of all others4 7#cfd47 ,iron1 and its oxides and alloys1 were for a long time the only substances considered susceptible of magnetism4 ,the loadstone was even one of the examples produced by ,bacon of that class of physical instances to which he applies the term 8,instanti monodic0--singular instances4 ,and the history of magnetism affords a beautiful comment on his remark on instances of this sort4 8,nor should our enquiries10 he observes1 8into their nature be broken off1 till the properties and qualities found in such things as may be esteemed wonders in nature are reduced and comprehended under some certain law2 so that all irregularity or singularity may be found to depend upon some common form1 and the wonder only rest in the exact differences1 degrees1 or extraordinary concurrence1 and not in the species itself40 ,the discovery of the magnetism of nickel1 which though inferior to that of iron1 is still considerable2 that of cobalt1 yet feebler1 and that of titanium1 which is only barely perceptible1 have effectually broken down the imaginary limit between iron and the other materials of the world1 and established the existence of that general law of continuity which it is one chief business of philosophy to trace throughout nature4 ,the more recent discoveries of ,m4 ,arago 7mentioned in #afj47 have completed this generalization1 by showing that there is no substance but which1 under proper circumstances1 is capable of exhibiting unequivocal signs of the magnetic virtue4 ,and to obliterate all traces of that line of separation which was once so broad1 we are now enabled1 by the great discovery of ,orsted1 to communicate at and during pleasure to a coiled wire of any metal indifferently all the properties of a magnet2--its attraction1 repulsion1 and polarity2 and that even in a more intense degree than was previously thought to be possible in the best natural magnets4 ,in short1 in this case1 and in this case only1 perhaps1 in science1 have we arrived at that point which ,bacon seems to have understood by the discovery of 8forms40 8,the form of any nature10 says he1 8is such1 that where it is1 the given nature must infallibly be4 ,the form1 therefore1 is perpetually present when that nature is present2 ascertains it universally1 and accompanies it every where4 ,again1 this form is such1 that when removed1 the given nature infallibly vanishes4 ,lastly1 a true form is such as can deduce a given nature from some essential property1 which resides in many things40 7#cfe47 ,magnetism is remarkable in another important point of view4 ,it offers a prominent1 or 8glaring instance0 of that quality in nature which is termed polarity 7#bfg471 and that under circumstances which peculiarly adapt it for the study of this quality4 ,it does not appear that the ancients had any knowledge of this property of the magnet1 though its attraction of iron was well known to them4 ,the first mention of it in modern times cannot be traced earlier than #aahj1 though it was probably known to the ,chinese before that time4 ,the polarity of the magnet consists in this1 that if suspended freely1 one part of it will invariably direct itself towards a certain point in the horizon1 the other towards the opposite point2 and that1 if two magnets1 so suspended1 be brought near each other1 there will take place a mutual action1 in consequence of which1 the positions of both will be disturbed1 in the same manner as would happen if the corresponding parts of each repelled1 and those oppositely directed attracted1 each other2 and by properly varying the experiment1 it is found that they really do so4 ,if a small magnet1 freely suspended1 be brought into the neighbourhood of a larger one1 it will take a position depending on the position of the poles of the larger one1 with respect to its point of suspension4 ,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 magnets1 the one predominating at one end1 the other at the other2 and such that each particle shall attract those in which the opposite virtue to its own prevails1 and repel those in which a similar one resides with a force proportional to the inverse square of their mutual distance4 7#cff47 ,the direction in which a magnetic bar1 or needle of steel1 freely suspended1 places itself1 has been ascertained to be different at different points of the earth's surface4 ,in some places it points exactly north and south1 in others it deviates from this direction more or less1 and at some actually stands at right angles to it4 ,this remarkable phenomenon1 which is called the variation of the needle1 and which was discovered by ,sebastian ,cabot in the year #aejj1 is accompanied with another called the dip1 noticed by ,robert ,norman in #aegf4 ,it consists in a tendency of a needle1 nicely balanced on its centre1 when unmagnetized1 to dip or point downwards when rendered magnetic1 towards a point below the horizon1 and situated within the earth4 ,by tracing the variation and dip over the whole surface of the globe1 it has been found that these phenomena take place as they would do if the earth itself were a great magnet1 having its poles deeply situated below the surface1--and1 what is very remarkable1 possessing a slow motion within it1 in consequence of which neither the variation nor dip remain constantly the same at the same place4 ,the laws of this motion are at present unknown2 but the discovery of electro-magnetism1 by rendering it almost certain that the earth's magnetism is merely an effect of the continual circulation of great quantities of electricity round it1 in a direction generally corresponding with that of its rotation1 have dissipated the greater part of the mystery which hung over these phenomena2 since a variety of causes1 both geological and others1 may be imagined which may produce considerable deviations in the intensity1 and partial ones in the direction1 of such electric currents4 ,the unequal distribution of land and sea in the two hemispheres1 by affecting the operation of the sun's heat in producing evaporation from the latter1 which is probably one of the great sources of terrestrial electricity1 may easily be conceived to modify the general tendency of such currents1 and to produce irregularities in them1 which may render a satisfactory account of whatever still appears anomalous in the phenomena of terrestrial magnetism4 ,this branch of science thus becomes connected1 on a great scale1 with that of meteorology1 one of the most complicated and difficult1 but at the same time interesting1 subjects of physical research2 one1 however1 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 notion4 7#cfg47 ,the communication of magnetism from the earth to a magnetic body1 or from one magnetic body to another1 is performed by a process to which the name of induction has been given1 and the laws and properties of such induced magnetism have been studied with much perseverance and success1--practically1 by ,gilbert1 ,boyle1 ,knight1 ,whiston1 ,cavallo1 ,canton1 ,duhamel1 ,rittenhouse1 ,scoresby1 and others2 and theoretically1 by pinus1 ,coulomb1 and ,poisson1 and in our own country by ,messrs4 ,barlow and ,christie1 who have investigated with great care the curious phenomena which take place when masses of iron are presented successively1 in different positions1 by rotation on an axis1 to the influence of the earth's magnetism4 ,the magnetism of crystallized bodies 7partly from the extreme rarity of such as are susceptible of any considerable magnetic virtue7 has not hitherto been at all examined1 but would probably afford very curious results4 7#cfh47 ,to electricity the views of the physical enquirer now turn from almost every quarter1 as to one of those universal powers which ,nature seems to employ in her most important and secret operations4 ,this wonderful agent1 which we see in intense activity in lightning1 and in a feebler and more diffused form traversing the upper regions of the atmosphere in the northern lights1 is present1 probably in immense abundance1 in every form of matter which surrounds us1 but becomes sensible only when disturbed by excitements of peculiar kinds4 ,the most effectual of these is friction1 which we have already observed to be a powerful source of heat4 ,everybody is familiar with the crackling sparks which fly from a cat's back when stroked4 ,these1 by proper management1 may be accumulated in bodies suitably disposed to receive them1 and1 although then no longer visible1 give evidence of their existence by the exhibition of a vast variety of extraordinary phenomena1--producing attractions and repulsions in bodies at a distance1--admitting of being transferred by contact1 or by sudden and violent transilience of the interval of separation1 from one body to another1 under the form of sparks and flashes2--traversing with perfect facility the substance of the densest metals1 and a variety of other bodies called conductors1 but being detained by others1 such as glass1 and especially air1 which are thence called non-conductors1--producing painful shocks and convulsive motions1 and even death itself if in sufficient quantity1 in animals through which they pass1 and finally imitating1 on a small scale1 all the effects of lightning4 7#cfi47 ,the study of these phenomena and their laws until a comparatively recent period occupied the entire attention of electricians1 and constituted the whole of the science of electricity4 ,it appears1 as the result of their enquiries1 that all the phenomena in question are explicable on the supposition that electricity consists in a rare1 subtle1 and highly elastic fluid1 which in its tendency to expand and diffuse itself pervades with more or less facility the substance of conductors1 but is obstructed and detained from expansion more or less completely by non-conductors4 ,it is supposed1 moreover1 that this electric fluid possesses a power of attraction for the particles of all ponderable matter1 together with that of a repulsion for particles of its own kind4 ,whether it has weight1 or is rather to be regarded as a species of matter distinct from that of which ponderable bodies consist1 is a question of such delicacy1 that no direct experiments have yet enabled us to decide it2 but at all events its inertia compared with its elastic force must be conceived excessively small1 so that it is to be regarded as a fluid in the highest degree active1 obeying every impulse1 internal or external1 with the greatest promptitude2 in short1 a fluid whose energies can only be compared with those of the ethereal medium by which1 in the undulatory doctrine1 light is supposed to be conveyed4 ,the properties of hydrogen gas compared with those of the denser ariform fluids will1 in some slight degree1 aid our conception of the excessive mobility and penetrating activity of a fluid so constituted4 ,electricity1 however1 must be regarded as differing in some remarkable points from all those fluids to which we have hitherto been accustomed to apply the epithet elastic1 such as air1 gases1 and vapours4 ,in these1 the repulsive force of the particles on which their elasticity depends is considered as extending only to very small distances1 so as to affect only those in the immediate vicinity of each other1 while their attractive power1 by which they obey the general gravitation of all matter1 extends to any distance4 ,in electricity1 on the other hand1 the very reverse must be admitted4 ,the force by which its particles repel each other extends to great distances1 while its force of adhesion to ponderable matter must be regarded as limited in its extent to such minute intervals as escape observation4 7#cgj47 ,the conception of a single fluid of this kind1 which when accumulated in excess in bodies tends constantly to escape1 and seek a restoration of equilibrium by communicating itself to any others where there may be a deficiency1 is that which occurs most naturally to the mind1 and was accordingly maintained by ,franklin1 to whom the science of electricity is under great obligations for those decisive experiments which informed us respecting the true nature of lightning4 ,the same theory was afterwards advocated by pinus1 who first showed how the laws of equilibrium of such a fluid might be reduced to strict mathematical investigation4 ,but there are phenomena accompanying its transfer from body to body and the state of equilibrium it affects under various circumstances1 which appear to require the admission of two distinct fluids antagonist to each other1 each attracting the other1 and repelling itself2 but each1 alike1 susceptible of adhesion to material substances1 and of transfer more or less rapid from particle to particle of them4 ,these fluids in the natural undisturbed state are conceived to exist in a state of combination and mutual saturation2 but this combination may be broken1 and either of them separately accumulated in a body to any amount without the other1 provided its escape be properly obstructed by surrounding it with non-conductors4 ,when so accumulated1 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 them1 and to produce phenomena of a peculiar description1 which are termed induced electricity4 ,curious and artificial as this theory may appear1 there has hitherto been produced no phenomenon of which it will not afford at least a plausible1 and in by far the majority of cases a very satisfactory1 explanation4 ,it has one character which is extremely valuable in any theory1 that of admitting the application of strict mathematical reasoning to the conclusions we would draw from it4 ,without this1 indeed1 it is scarcely possible that any theory should ever be fairly brought to the test by a comparison with facts4 ,accordingly1 the mathematical theory of electrical equilibrium1 and the laws of the distribution of the electric fluids over the surfaces of bodies in which they are accumulated1 have been made the subject of elaborate geometrical investigation by the most expert mathematicians1 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 enquiry4 ,these researches are grounded on the assumption of a law of attraction and repulsion similar to those of gravity and magnetism1 and which by the general accordance of the results with facts1 as well as by experiments instituted for the express purpose of ascertaining the laws in question1 are regarded as sufficiently demonstrated4 7#cga47 ,the most obscure part of the subject is no doubt the original mode of disturbance of electrical equilibrium1 by which electricity is excited in the first instance1 either by friction or by any other of those causes which have been ascertained to produce such an effect3 analogies1 it is true1 are not wanting#ef2 but it must be allowed that hitherto nothing decisive has been offered on the subject2 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 us4 7#cgb47 ,philosophers had long been familiar with the effects of electricity above referred to1 and with those which it produces in its sudden and violent transfer from one body to another1 in rending and shattering the parts of the substances through which it passes1 and where in great quantity1 producing all the effect of intense heat1 igniting1 fusing1 and volatilizing metals1 and setting fire to inflammable bodies2 even its occasional influence in destroying or altering the polarity of the magnetic needle had been noticed3 but as heat was known to be produced by mechanical violence1 and as magnetism was also known to be greatly affected by the same cause1 these effects were referred rather to that cause than to any thing in the peculiar nature of the electric matter1 and regarded rather as an indirect consequence of its mode of action than as connected with its intimate nature4 ,in short1 electricity seemed destined to furnish another in addition to many instances of subjects insulated from the rest of philosophy1 and capable of being studied only in its own internal relations1 when the great discoveries of ,galvani and ,volta placed a new power at the command of the experimenter1 by whose means those effects which had before been crowded within an inappreciable instant could be developed in detail and studied at leisure2 and those forces which had previously exhibited themselves only in a state of uncontrollable intensity were tamed down1 as it were1 and made to distribute their efficacy over an indefinite time1 and to regulate their action at the will of the operator4 ,it was then soon ascertained that electricity in the act of its passage along conductors1 produces a variety of wonderful effects1 which had never been previously suspected2 and these of such a nature1 as to afford points of contact with several other branches of physical enquiry1 and to throw new and unexpected lights on some of the most obscure operations of nature4 7#cgc47 ,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 phenomenon1 however apparently trifling1 which may at the moment of observation appear inexplicable on received principles4 ,the convulsive motions of a dead frog in the neighbourhood of an electric discharge1 which originally drew ,galvani's attention to the subject1 had been noticed by others nearly a century before his time1 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 life4 ,galvani was not so satisfied4 ,he analysed the phenomenon2 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 parts1 a muscle1 a nerve1 and a metallic conductor1 each placed in contact with the other two1 and which was manifested by a convulsive motion produced in the muscle4 ,to this phenomenon he gave the name of animal electricity1 an unfortunate epithet1 since it tended to restrict enquiry into its nature to the class of phenomena in which it first became apparent4 ,but this circumstance1 which in a less enquiring age of science might have exercised a fatal influence on the progress of knowledge1 proved happily no obstacle to the further developement of its principles1 the subject being immediately taken up with a kind of prophetic ardour by ,volta1 who at once generalized the phenomena1 rejecting the physiological considerations introduced by ,galvani1 as foreign to the enquiry1 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 means4 ,it was thus that he arrived at the knowledge of a general fact1 that of the disturbance of electrical equilibrium by the mere contact of different bodies1 and the circulation of a current of electricity in one constant direction1 through a circuit composed of three different conductors4 ,to increase the intensity of the very minute and delicate effect thus observed became his next aim1 nor did his enquiry terminate till it had placed him in possession of that most wonderful of all human inventions1 the pile which bears his name1 through the medium of a series of well conducted and logically combined experiments1 which has rarely1 if ever1 been surpassed in the annals of physical research4 7#cgd47 ,though the original pile of ,volta was feeble compared to those gigantic combinations which were afterwards produced1 it sufficed1 however1 to exhibit electricity under a very different aspect from any thing which had gone before1 and to bring into view those peculiar modifications in its action which ,dr4 ,wollaston was the first to render a satisfactory account of1 by referring them to an increase of quantity1 accompanied with a diminution of intensity in the supply afforded4 ,the discovery had not long been made public1 and the instrument in the hands of chemists and electricians1 before it was ascertained that the electric current1 transmitted by it through conducting liquids1 produces in them chemical decompositions4 ,this capital discovery appears to have been made1 in the first instance1 by ,messrs4 ,nicholson and ,carlisle1 who observed the decomposition of water so produced4 ,it was speedily followed up by the still more important one of ,berzelius and ,hisinger1 who ascertained it as a general law1 that1 in all the decompositions so effected1 the acids and oxygen become transferred to1 and accumulated around1 the positive1--and hydrogen1 metals1 and alkalies round the negative1 pole of a ,voltaic circuit2 being transferred in an invisible1 and1 as it were1 a latent or torpid state1 by the action of the electric current1 through considerable spaces1 and even through large quantities of water or other liquids1 again to re-appear with all their properties at their appropriate resting-places4 7#cge47 ,it was in this state of things that the subject was taken up by ,davy1 who1 seeing that the strongest chemical affinities were thus readily subverted by the decomposing action of the pile1 conceived the happy idea of bringing to bear the intense power of the enormous batteries of the ,royal ,institution on those substances which1 though strongly suspected to be compounds1 had resisted all attempts to decompose them--the alkalies and earths4 ,they yielded to the force applied1 and a total revolution was thus effected in chemistry2 not so much by the introduction of the new elements thus brought to light1 as by the mode of conceiving the nature of chemical affinity1 which from that time has been regarded 7as ,davy broadly laid it down1 in a theory which was readily adopted by the most eminent chemists1 and by none more readily than by ,berzelius himself17 as entirely due to electric attractions and repulsions1 those bodies combining most intimately whose particles are habitually in a state of the most powerful electrical antagonism1 and dispossessing each other1 according to the amount of their difference in this respect4 7#cgf47 ,the connection of magnetism and electricity had long been suspected1 and innumerable fruitless trials had been made to determine1 in the affirmative or negative1 the question of such connection4 ,the phenomena of many crystallized minerals which become electric by heat1 and develope opposite electric poles at their two extremities1 offered an analogy so striking to the polarity of the magnet1 that it seemed hardly possible to doubt a closer connection of the two powers4 ,the developement of a similar polarity in the ,voltaic pile pointed strongly to the same conclusion2 and experiments had even been made with a view to ascertain whether a pile in a state of excitement might not manifest a disposition to place itself in the magnetic meridian2 but the essential condition had been omitted1 that of allowing the pile to discharge itself freely1 a condition which assuredly never would have occurred of itself to any experimenter4 ,of all the philosophers who had speculated on this subject1 none had so pertinaciously adhered to the idea of a necessary connection between the phenomena as ,orsted4 ,baffled often1 he returned to the attack2 and his perseverance was at length rewarded by the complete disclosure of the wonderful phenomena of electro-magnetism4 ,there is something in this which reminds us of the obstinate adherence of ,columbus to his notion of the necessary existence of the ,new ,world2 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 another1 though no direct connection appears2 as an indication not to be neglected of a community of origin4 7#cgg47 ,it is highly probable that we are still ignorant of many interesting features in electrical science1 which the study of the ,voltaic circuit will one day disclose4 ,the violent mechanical effects produced by it on mercury1 placed under conducting liquids which have been referred by ,professor ,erman to a modified form of capillary attraction1 but which a careful and extended view of the phenomena have led others#eg to regard in a very different light1 as pointing out a primary action of a dynamical rather than a statical character1 deserve1 in this point of view1 a further investigation2 and the curious relations of electricity to heat1 as exhibited in the phenomena of what has been called thermo-electricity1 promise an ample supply of new information4 7#cgh47 ,among the remarkable effects of electricity disclosed by the researches of ,galvani and ,volta1 perhaps the most so consisted in its influence on the nervous system of animals4 ,the origin of muscular motion is one of those profound mysteries of nature which we can scarcely venture to hope will ever be fully explained4 ,physiologists1 however1 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 nerves2 and the discovery of the rapid transmission of electricity along conductors1 with the violent effects produced by shocks1 transmitted through the body1 on the nervous system1 would very naturally lead to the idea that this nervous fluid1 if it had any real existence1 might be no other than the electrical4 ,but until the discoveries of ,galvani and ,volta1 this could only be looked upon as a vague conjecture4 ,the character of a vera causa was wanting to give it any degree of rational plausibility1 since no reason could be imagined for the disturbance of the electrical equilibrium in the animal frame1 composed as it is entirely of conductors1 or rather1 it seemed contrary to the then known laws of electrical communication to suppose any such4 ,yet one strange and surprising phenomenon might be adduced indicative of the possibility of such disturbance1 viz4 the powerful shock given by the torpedo and other fishes of the same kind1 which presented so many analogies with those arising from electricity1 that they could hardly be referred to a different source1 though besides the shock neither spark nor any other indication of electrical tension could be detected in them4 7#cgi47 ,the benumbing effect of the torpedo had been ascertained to depend on certain singularly constructed organs composed of membranous columns1 filled from end to end with lamin1 separated from each other by a fluid3 but of its mode of action no satisfactory account could be given2 nor was there any thing in its construction1 and still less in the nature of its materials1 to give the least ground for supposing it an electrical apparatus4 ,but the pile of ,volta supplied at once the analogies both of structure and of effect1 so as to leave little doubt of the electrical nature of the apparatus1 or of the power1 a most wonderful one certainly1 of the animal1 to determine1 by an effort of its will1 that concurrence of conditions on which its activity depends4 ,this remained1 as it probably ever will remain1 mysterious and inexplicable2 but the principle once established1 that there exists in the animal economy a power of determining the developement of electric excitement1 capable of being transmitted along the nerves1 and it being ascertained1 by numerous and decisive experiments1 that the transmission of ,voltaic electricity along the nerves of even a dead animal is sufficient to produce the most violent muscular action1 it became an easy step to refer the origin of muscular motion in the living frame to a similar cause2 and to look to the brain1 a wonderfully constituted organ1 for which no mode of action possessing the least plausibility had ever been devised1 as the source of the required electrical power4#eh 7#chj47 ,it is not our intention1 however1 to enter into any further consideration of physiological subjects4 ,they form1 it is true1 a most important and deeply interesting province of philosophical enquiry2 but the view that we have taken of physical science has rather been directed to the study of inanimate nature1 than to that of the mysterious phenomena of organization and life1 which constitute the object of physiology4 ,the history of the animal and vegetable productions of the globe1 as affording objects and materials for the convenience and use of man1 and as dependent on and indicative of the general laws which determine the distribution of heat1 moisture1 and other natural agents1 over its surface1 and the revolutions it has undergone1 are of course intimately connected with our subject1 and will1 therefore1 naturally afford room for some remarks1 but not such as will long detain the reader's attention4 7#cha47 ,in zoology1 the connection of peculiar modes of life and food1 with peculiarities of structure1 has given rise to systems of classification at once obvious and natural2 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 being2 a scale not without its intervals1 but which every successive discovery of animals heretofore unknown has tended to fill up4 ,the wonders disclosed by microscopic observation have opened to us a new world1 in which we discover1 with astonishment1 the extremes of minuteness and complexity of structure united2 while1 on the other hand1 the examination of the fossil remains of a former state of creation has demonstrated the existence of animals far surpassing in magnitude those now living1 and brought to light many forms of being which have nothing analogous to them at present1 and many others which afford important connecting links between existing genera4 ,and1 on the other hand1 the researches of the comparative anatomist and conchologist have thrown the greatest light on the studies of the geologist1 and enabled him to discern1 through the obscure medium of a few relics1 scattered here and there through a stratum1 circumstances connected with the formation of the stratum itself which he could have recognised by no other indication4 ,this is one among many striking instances of the unexpected lights which sciences1 however apparently remote1 may throw upon each other4 7#chb47 ,to botany many of the same remarks apply4 ,its artificial systems of classification1 however convenient1 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 system2 a community of character extending over the whole habit and properties of the individuals compared4 ,the important chemical discoveries which have been lately made of peculiar proximate principles which1 in an especial manner1 characterize certain families of plants1 hold out the prospect of a greatly increased field of interesting knowledge in this direction1 and not only interesting1 but in a high degree important1 when it is considered that the principles thus brought into view are1 for the most part1 very powerful medicines1 and are1 in fact1 the essential ingredients on which the medical virtues of the plants depend4 ,the law of the distribution of the generic forms of plants over the globe1 too1 has1 within a comparatively recent period1 become an object of study to the naturalist2 and its connection with the laws of climate constitutes one of the most interesting and important branches of natural-historical enquiry1 and one on which great light remains to be thrown by future researches4 ,it is this which constitutes the chief connecting link between botany and geology1 and renders a knowledge of the vegetable fossils1 of any portion of the earth's surface1 indispensable to the formation of a correct judgment of the circumstances under which it existed in its ancient state4 ,fossil botany is accordingly cultivated with great and increasing ardour2 and the subterraneous 8,flora0 of a geological formation is1 in many instances1 studied with a degree of care and precision little inferior to that which its surface exhibits4 ,,chap4 ,,vi4 ,,of ,,the ,,causes ,,of ,,the ,,actual ,,rapid ,,advance ,,of ,,the ,,physical ,,sciences ,,compared ,,with ,,their ,,progress ,,at ,,an ,,earlier ,,period4 7#chc47 ,there is no more extraordinary contrast than that presented by the slow progress of the physical sciences1 from the earliest ages of the world to the close of the sixteenth century1 and the rapid developement they have since experienced4 ,in the former period of their history1 we find only small additions to the stock of knowledge1 made at long intervals of time2 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 discoveries1 or1 at best1 permitted them to linger on record1 rather as literary curiosities1 than as possessing1 in themselves1 any intrinsic interest and importance4 ,a few enquiring individuals1 from age to age1 might perceive their value1 and might feel that irrepressible thirst after knowledge which1 in minds of the highest order1 supplies the absence both of external stimulus and opportunity4 ,but the total want of a right direction given to enquiry1 and of a clear perception of the objects to be aimed at1 and the advantages to be gained by systematic and connected research1 together with the general apathy of society to speculations remote from the ordinary affairs of life1 and studiously kept involved in learned mystery1 effectually prevented these occasional impulses from overcoming the inertia of ignorance1 and impressing any regular and steady progress on science4 ,its objects1 indeed1 were confined in a region too sublime for vulgar comprehension4 ,an earthquake1 a comet1 or a fiery meteor1 would now and then call the attention of the whole world1 and produce from all quarters a plentiful supply of crude and fanciful conjectures on their causes2 but it was never supposed that sciences could exist among common objects1 have a place among mechanical arts1 or find worthy matter of speculation in the mine or the laboratory4 ,yet it cannot be supposed1 that all the indications of nature continually passed unremarked1 or that much good observation and shrewd reasoning on it failed to perish unrecorded1 before the invention of printing enabled every one to make his ideas known to all the world4 ,the moment this took place1 however1 the sparks of information from time to time struck out1 instead of glimmering for a moment1 and dying away in oblivion1 began to accumulate into a genial glow1 and the flame was at length kindled which was speedily to acquire the strength and rapid spread of a conflagration4 ,the universal excitement in the minds of men throughout ,europe1 which the first out-break of modern science produced1 has been already spoken of4 ,but even the most sanguine anticipators could scarcely have looked forward to that steady1 unintermitted progress which it has since maintained1 nor to that rapid succession of great discoveries which has kept up the interest of the first impulse still vigorous and undiminished4 ,it may truly1 indeed1 be said1 that there is scarcely a single branch of physical enquiry which is either stationary1 or which has not been1 for many years past1 in a constant state of advance1 and in which the progress is not1 at this moment1 going on with accelerated rapidity4 7#chd47 ,among the causes of this happy and desirable state of things1 no doubt we are to look1 in the first instance1 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 mankind1 which have long been and still continue steadily progressive in every principal ,european state1 and which the increase and fresh establishment of civilized communities in every distant region are rapidly spreading over the whole globe4 ,it is not1 however1 merely the increased number of cultivators of science1 but their enlarged opportunities1 that we have here to consider1 which1 in all those numerous departments of natural research that require local information1 is in fact the most important consideration of all4 ,to this cause we must trace the great extension which has of late years been conferred on every branch of natural history1 and the immense contributions which have been made1 and are daily making1 to the departments of zoology and botany1 in all their ramifications4 ,it is obvious1 too1 that all the information that can possibly be procured1 and reported1 by the most enlightened and active travellers1 must fall infinitely short of what is to be obtained by individuals actually resident upon the spot4 ,travellers1 indeed1 may make collections1 may snatch a few hasty observations1 may note1 for instance1 the distribution of geological formations in a few detached points1 and now and then witness remarkable local phenomena2 but the resident alone can make continued series of regular observations1 such as the scientific determination of climates1 tides1 magnetic variations1 and innumerable other objects of that kind1 requires2 can alone mark all the details of geological structure1 and refer each stratum1 by a careful and long continued observation of its fossil contents1 to its true epoch2 can alone note the habits of the animals of his country1 and the limits of its vegetation1 or obtain a satisfactory knowledge of its mineral contents1 with a thousand other particulars essential to that complete acquaintance with our globe as a whole1 which is beginning to be understood by the extensive designation of physical geography4 ,besides which1 ought not to be omitted multiplied opportunities of observing and recording those extraordinary phenomena of nature which offer an intense interest1 from the rarity of their occurrence as well as the instruction they are calculated to afford4 ,to what1 then1 may we not look forward1 when a spirit of scientific enquiry shall have spread through those vast regions in which the process of civilization1 its sure precursor1 is actually commenced and in active progress8 ,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 world1 and over an extent of territory far surpassing that which has hitherto produced the whole harvest of human intellect8 ,in proportion as the number of those who are engaged on each department of physical enquiry increases1 and the geographical extent over which they are spread is enlarged1 a proportionately increased facility of communication and interchange of knowledge becomes essential to the prosecution of their researches with full advantage4 ,not only is this desirable1 to prevent a number of individuals from making the same discoveries at the same moment1 which 7besides the waste of valuable time7 has always been a fertile source of jealousies and misunderstandings1 by which great evils have been entailed on science2 but because methods of observation are continually undergoing new improvements1 or acquiring new facilities1 a knowledge of which1 it is for the general interest of science1 should be diffused as widely and as rapidly as possible4 ,by this means1 too1 a sense of common interest1 of mutual assistance1 and a feeling of sympathy in a common pursuit1 are generated1 which proves a powerful stimulus to exertion2 and1 on the other hand1 means are thereby afforded of detecting and pointing out mistakes before it is too late for their rectification4 7#che47 ,perhaps it may be truly remarked1 that1 next to the establishment of institutions having either the promotion of science in general1 or1 what is still more practically efficacious in its present advanced state1 that of particular departments of physical enquiry1 for their express objects1 nothing has exercised so powerful an influence on the progress of modern science as the publication of monthly and quarterly scientific journals1 of which there is now scarcely a nation in ,europe which does not produce several4 ,the quick and universal circulation of these1 places observers of all countries on the same level of perfect intimacy with each other's objects and methods1 while the abstracts they from time to time 7if well conducted7 contain of the most important researches of the day consigned to the more ponderous tomes of academical collections1 serve to direct the course of general observation1 as well as to hold out1 in the most conspicuous manner1 models for emulative imitation4 ,in looking forward to what may hereafter be expected from this cause of improvement1 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 science4 ,nothing can be more discouraging to one engaged in active research1 than the impression that all he is doing may1 very likely1 be labour taken in vain2 that it may1 perhaps1 have been already done1 and much better done1 than1 with his opportunities1 or his resources1 he can hope to perform it2 and1 on the other hand1 nothing can be more exciting than the contrary impression4 ,thus1 by giving a connected view of what has been done1 and what remains to be accomplished in every branch1 those digests and bodies of science1 which from time to time appear1 have1 in fact1 a very important weight in determining its future progress1 quite independent of the quantity of information they communicate4 ,with respect to elementary treatises1 it is needless to point out their utility1 or to dwell on the influence which their actual abundance1 contrasted with their past remarkable deficiency1 is likely to exercise over the future4 ,it is only by condensing1 simplifying1 and arranging1 in the most lucid possible manner1 the acquired knowledge of past generations1 that those to come can be enabled to avail themselves to the full of the advanced point from which they will start4 7#chf47 ,one of the means by which an advanced state of physical science contributes greatly to accelerate and secure its further progress1 is the exact knowledge acquired of physical data1 or those normal quantities which we have more than once spoken of in the preceding pages 7#bbb472 a knowledge which enables us not only to appretiate the accuracy of experiments1 but even to correct their results4 ,as there is no surer criterion of the state of science in any age than the degree of care bestowed1 and discernment exhibited1 in the choice of such data1 so as to afford the simplest possible grounds for the application of theories1 and the degree of accuracy attained in their determination1 so there is scarcely any thing by which science can be more truly benefited than by researches directed expressly to this object1 and to the construction of tables exhibiting the true numerical relations of the elements of theories1 and the actual state of nature1 in all its different branches4 ,it is only by such determinations that we can ascertain what changes are slowly and imperceptibly taking place in the existing order of things2 and the more accurate they are1 the sooner will this knowledge be acquired4 ,what might we not now have known of the motions of the 7so-called7 fixed stars1 had the ancients possessed the means of observation we now possess1 and employed them as we employ them now8 7#chg47 ,in any enumeration of causes which have contributed to the recent rapid advancement of science1 we must not forget the very important one of improved and constantly improving means of observation1 both in instruments adapted for the exact measurement of quantity1 and in the general convenience and well-judged adaptation to its purposes1 of every description of scientific apparatus4 ,in the actual state of science there are few observations which can be productive of any great advantage but such as afford accurate measurement2 and an increased refinement in this respect is constantly called for4 ,the degree of delicacy actually attained1 we will not say in the most elaborate works of the highest art1 but in such ordinary apparatus as every observer may now command1 is such as could not have been arrived at unless in a state of the mechanical arts1 which in its turn 7such is the mutual re-action of cause and effect7 requires for its existence a very advanced state of science4 ,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 measurement1 and the construction and common introduction of an instrument adapted for it cannot be better exemplified than by the instance of the reflecting goniometer4 ,this simple1 cheap1 and portable little instrument1 has changed the face of mineralogy1 and given it all the characters of one of the exact sciences4 7#chh47 ,our means of perceiving and measuring minute quantities1 in the important relations of weight1 space1 and time1 seem already to have been carried to a point which it is hardly conceivable they should surpass4 ,balances have been constructed which have rendered sensible the millionth part of the whole quantity weighed2 and to turn with the thousandth part of a grain is the performance of balances pretending to no very extraordinary degree of merit4 ,the elegant invention of the sphrometer1 by substituting the sense of touch for that of sight in the measurement of minute objects1 permits the determination of their dimensions with a degree of precision which is fully adequate to the nicest purposes of scientific enquiry4 ,by its aid an inch may be readily subdivided into ten or even twenty thousand parts2 and the lever of contact1 an instrument in use among the ,german opticians1 enables us to appretiate quantities of space even yet smaller4 ,for the subdivision of time1 too1 the perfection of modern mechanism has furnished resources which leave very little to be desired4 ,by the aid of clocks and chronometers1 as they are now constructed1 a few tenths of a second is all the error that need be apprehended in the subdivision of a day2 and for the further subdivision of smaller portions of time1 instruments have been imagined which admit of almost unlimited precision1 and permit us to appreciate intervals to the nicety of the hundredth1 or even the thousandth part of a single second4#ei ,when the precision attainable by such means is contrasted with what could be procured a few generations ago1 by the rude and clumsy workmanship of even the early part of the last century1 it will be no matter of astonishment that the sciences which depend on exact measurements should have made a proportional progress4 ,nor will any degree of nicety in physical determinations appear beyond our reach1 if we consider the inexhaustible resources which science itself furnishes1 in rendering the quantities actually to be determined by measure great multiples of the elements required for the purposes of theory1 so as to diminish in the same proportion the influence of any errors which may be committed on the final results4 7#chi47 ,great1 indeed1 as have been of late the improvements in the construction of instruments1 both as to what regards convenience and accuracy1 it is to the discovery of improved methods of observation that the chief progress of those parts of science which depend on exact determinations is owing4 ,the balance of torsion1 the ingenious invention of ,cavendish and ,coulomb1 may be cited as an example of what we mean4 ,by its aid we are enabled not merely to render sensible1 but to subject to precise measurement and subdivision1 degrees of force infinitely too feeble to affect the nicest balance of the usual construction1 even were it possible to bring them to act on it4 ,the galvanometer1 too1 affords another example of the same kind1 in an instrument whose range of utility lies among electric forces which we have no other means of rendering sensible1 much less of estimating with exactness4 ,in determinations of quantities less minute in themselves1 the methods devised by ,messrs4 ,arago and ,fresnel1 for the measurement of the refractive powers of transparent media by means of the phenomenon of diffraction1 may be cited as affording a degree of precision limited only by the wishes of the observer1 and the time and patience he is willing to devote to his observation4 ,and in respect of the direction of observations to points from which real information is to be obtained1 and positive conclusions drawn1 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 arbitrary4 7#cij47 ,in speculating on the future prospects of physical science1 we should not be justified in leaving out of consideration the probability1 or rather certainty1 of the occasional occurrence of those happy accidents which have had so powerful an influence on the past2 occasions1 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 notice4 ,boyle has entitled one of his essays thus remarkably1--8,of ,man's great ,ignorance of the ,uses of natural ,things2 or that there is no one ,thing in ,nature whereof the ,uses to human ,life are yet thoroughly understood40#fj ,the whole history of the arts since ,boyle's time has been one continued comment on this text2 and if we regard among the uses of the works of nature1 that1 assuredly the noblest of all1 which leads us to a knowledge of the ,author of nature through the contemplation of the wonderful means by which he has wrought out his purposes in his works1 the sciences have not been behind hand in affording their testimony to its truth4 ,nor are we to suppose that the field is in the slightest degree narrowed1 or the chances in favour of such fortunate discoveries at all decreased1 by those which have already taken place3 on the contrary1 they have been incalculably extended4 ,it is true that the ordinary phenomena which pass before our eyes have been minutely examined1 and those more striking and obvious principles which occur to superficial observation have been noticed and embodied in our systems of science2 but1 not to mention that by far the greater part of natural phenomena remain yet unexplained1 every new discovery in science brings into view whole classes of facts which would never otherwise have fallen under our notice at all1 and establishes relations which afford to the philosophic mind a constantly extending field of speculation1 in ranging over which it is next to impossible that he should not encounter new and unexpected principles4 ,how infinitely greater1 for instance1 are the mere chances of discovery in chemistry among the innumerable combinations with which the modern chemist is familiar1 than at a period when two or three imaginary elements1 and some ten or twenty substances1 whose properties were known with an approach to distinctness1 formed the narrow circle within which his ideas had to revolve8 ,how many are the instances where a new substance1 or a new property1 introduced into familiar use1 by being thus brought into relation with all our actual elements of knowledge1 has become the means of developing properties and principles among the most common objects1 which could never have otherwise been discovered8 ,had not platina 7to take an instance7 been an object of the most ordinary occurrence in a laboratory1 would a suspicion have ever occurred that a lamp could be constructed to burn without flame2 and should we have ever arrived at a knowledge of those curious phenomena and products of semi-combustion which this beautiful experiment discloses8 7#cia47 ,finally1 when we look back on what has been accomplished in science1 and compare it with what remains to be done1 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 profit4#fa ,in a few instances only have we arrived at those general axiomatic laws which admit of direct deductive inference1 and place the solutions of physical phenomena before us as so many problems1 whose principles of solution we fully possess1 and which require nothing but acuteness of reasoning to pursue even into their farthest recesses4 ,in fewer still have we reached that command of abstract reasoning itself which is necessary for the accomplishment of so arduous a task4 ,science1 therefore1 in relation to our faculties1 still remains boundless and unexplored1 and1 after the lapse of a century and a half from the ra of ,newton's discoveries1 during which every department of it has been cultivated with a zeal and energy which have assuredly met their full return1 we remain in the situation in which he figured himself1--standing on the shore of a wide ocean1 from whose beach we may have culled some of those innumerable beautiful productions it casts up with lavish prodigality1 but whose acquisition can be regarded as no diminution of the treasures that remain4 7#cib47 ,but this consideration1 so far from repressing our efforts1 or rendering us hopeless of attaining any thing intrinsically great1 ought rather to excite us to fresh enterprise1 by the prospect of assured and ample recompense from that inexhaustible store which only awaits our continued endeavours4 8,it is no detraction from human capacity to suppose it incapable of infinite exertion1 or of exhausting an infinite subject40#fb ,in whatever state of knowledge we may conceive man to be placed1 his progress towards a yet higher state need never fear a check1 but must continue till the last existence of society4 7#cic47 ,it is in this respect an advantageous view of science1 which refers all its advances to the discovery of general laws1 and to the inclusion of what is already known in generalizations of still higher orders2 inasmuch as this view of the subject represents it1 as it really is1 essentially incomplete1 and incapable of being fully embodied in any system1 or embraced by any single mind4 ,yet it must be recollected that1 so far as our experience has hitherto gone1 every advance towards generality has at the same time been a step towards simplification4 ,it is only when we are wandering and lost in the mazes of particulars1 or entangled in fruitless attempts to work our way downwards in the thorny paths of applications1 to which our reasoning powers are incompetent1 that nature appears complicated3--the moment we contemplate it as it is1 and attain a position from which we can take a commanding view1 though but of a small part of its plan1 we never fail to recognise that sublime simplicity on which the mind rests satisfied that it has attained the truth4 ,,index4 ,acoustics cultivated by ,pythagoras and ,aristotle1 page #bdh4 pinus1 his laws of equilibrium of electricity1 #ccb4 ,ariform fluids1 liquids kept in a state of vapour1 #cba4 ,agricola1 ,george1 his knowledge of mineralogy and metallurgy1 #aab4 ,air1 compressibility and elasticity of2 limitation to the repulsive tendency of1 #bbf4 ,weight of1 unknown to the ancients1 #bbh4 ,first perceived by ,galileo1 #bbh4 ,proved by a crucial instance1 #bbi4 ,equilibrium of1 established1 #bca4 ,dilatation of1 by heat1 #cai4 ,air-pump1 discovery of1 #bcj4 ,airy1 his experiments in ,dolcoath mine1 #ahg4 ,alchemists1 advantages derived from1 #aa4 ,algebra1 #ai4 ,ampere1 his electro-dynamic theory1 #bjb4 ,utility of1 #bjc1 #cbd4 ,analysis of force1 #hf4 ,of motion1 #hg4 ,of complex phenomena1 #hh4 ,anaxagoras1 philosophy of1 #ajg4 ,animal electricity1 #ccg4 ,arago1 ,m41 his experiment with a magnetic needle and a plate of copper1 #aeg4 ,archimedes1 his practical application of science1 #gb4 ,his knowledge of hydrostatics1 #bca4 ,arfwedson1 his discovery of lithia1 #aeh4 ,aristotle1 his knowledge of natural history1 #aji4 ,his works condemned1 and subsequently studied with avidity1 #aaa4 ,his philosophy overturned by the discoveries of ,copernicus1 ,kepler1 and ,galileo1 #aac4 ,arithmetic1 #ai4 ,art1 empirical and scientific1 differences between1 #ga4 ,remarks on the language1 terms1 or signs1 used in treating of it1 #gj4 ,assurances1 life1 utility and abuses of1 #eh4 ,astronomy1 cause of the slow progress of our knowledge of1 #gh4 ,theory and practical observations distinct in1 #acb4 ,an extensive acquaintance with science and every branch of knowledge necessary to make a perfect observer in1 #acb4 ,five primary planets added to our system1 #bgd4 ,positions1 figures1 and dimensions of all the planetary orbits now well known1 #bge4 ,atomic theory1 #cje4 ,advantage of1 #cjf4 ,atomic weights of chemical elements1 #cjf4 ,attraction1 capillary1 or capillarity1 investigated by ,laplace and ,young1 #bcd4 ,bacon1 celebrated in ,england for his knowledge of science1 #gb4 ,benefits conferred on ,natural ,philosophy by him1 #ajd4 ,his ,novum ,organum1 #aje4 ,his reform in philosophy proves the paramount importance of induction1 #aad4 ,his prerogative of facts1 #aha4 ,illustrated by the fracture of a crystallized substance1 #ahc4 ,his collective instances1 #ahd4 ,importance of1 #ahe4 ,his experiment on the weight of bodies1 #ahf4 ,travelling instances of1 frontier instances of1 #ahh4 ,his difference between liquids and ariform fluids1 #bcc4 ,bartolin1 ,erasmus1 first discovers the phenomena exhibited by doubly refracting crystals1 #bed4 ,beccher1 phlogistic doctrines of1 #cjj4 ,bergmann1 his advancement in crystallography1 #bci4 ,bernoulli1 experiments of1 in hydrodynamical science1 #aha4 ,biot1 his hypothesis of a rotatory motion of the particles of light about their axes1 #bfb4 ,black1 ,dr41 his discovery of latent heat1 #cbb4 ,bode1 his curious law observed in the progression of the magnitudes of the several planetary orbits1 #cjh4 ,bodies1 natural constitution of1 #bba4 ,division of1 into crystallized and uncrystallized1 #bdb4 ,bones1 dry1 a magazine of nutriment1 #fe4 ,borda1 his invention for subdivision1 #abh4 ,botany1 general utility of1 #cde4 ,boyle1 ,robert1 his enthusiasm in the pursuit of science1 #aae4 ,his improvement on the air-pump1 #bcj4 ,brain1 hypothesis of its being an electric pile1 #cdc4 ,bramah's press1 principle and utility of1 #bcc4 ,brewster1 ,dr41 his improvement on lenses for lighthouses1 #ef4 ,his researches prove that the phenomena exhibited by polarized light1 in its transmission through crystals1 afford a certain indication of the most important points relating to the structure of crystals themselves1 #bfc4 ,cabot1 ,sebastian1 his discovery of the variation of the needle1 #cbg4 ,cagnard1 ,baron de la ,tour1 utility of his experiments1 #bcd4 ,causes and consequences directors of the will of man1 #f4 ,causes1 proximate1 discovery of1 called by ,newton ver caus1 #add4 ,celestial mechanics1 #bfe4 ,chaldean records1 #bfe4 ,chemistry furnishes causes of sudden action1 also fulminating compositions1 #fb4 ,analogy of the complex phenomena of1 with those of physics1 #ib4 ,benefits arising from the analysis of1 #id4 ,axioms of1 analogous to those of geometry1 #ie4 ,many of the new elements of1 detected in the investigation of residual phenomena1 #aeh4 ,the most general law of1 #bji4 ,illustration of1 #baj4 ,between fifty and sixty elements in1 #baa4 ,objects of1 #bif4 ,general heads of the principal improvements in1 #cjb4 ,remarks on those general heads1 #cjd4 ,chemistry1 ,stahlian1 cause of the mistakes and confusions of1 #abc4 ,chladni1 experiments of1 in dynamical science1 #aha4 ,chlorine1 disinfectant powers of1 #ef4 ,clarke1 ,dr41 his experiments on the arseniate and phosphate of soda1 #agj4 ,his success in producing a new phosphate of soda1 #aga4 ,climate1 change of1 in large tracts of the globe1 alleged cause of1 #ade4 ,coals1 power of a bushel of1 properly consumed1 #ei4 ,quantity consumed in ,london1 #fj4 ,cohesion1 an ultimate phenomenon1 #ij4 ,cold1 qualities of1 #cah4 ,compass1 mariner's1 #ee4 ,condensation1 a source of heat1 #cac4 ,conduction of heat1 laws of1 #bje4 ,copernicus1 effect of his discoveries on the ,aristotelian philosophy1 #aac4 ,objections to his astronomical doctrines1 #bfi4 ,crystallography1 laws of1 #abc1 #bci4 ,a determinate figure supposed to be common to all the particles of a crystal1 #bdb4 ,d',alembert1 his improvements in hydrodynamics1 #bcf4 ,dalton1 his announcement of the atomic theory1 #cje4 ,his examination of gases and vapours1 #cai4 ,davy1 ,sir ,h41 brings the voltaic pile to bear upon the earths and alkalies1 #cci4 ,deduction1 utility of1 #agd4 ,de l',isle1 ,rom1 his study of crystalline bodies1 #bci4 ,dew1 causes of1 investigated1 #aei4 ,effects of1 on different substances1 #afj4 ,objects capable of contracting it1 #afa4 ,a cloudless sky favourable to its production1 #afb4 ,general proximate cause of1 #afc4 ,drummond1 lieutenant1 his improvement on lenses for lamps of lighthouses1 #ef4 ,dynamics1 importance of1 #if1 #bbc4 ,earth1 the orbit of1--diminution of its eccentricity round the sun1 #adg4 ,economy1 political1 #gc4 ,egypt1 great pyramid of1 height1 weight1 and ground occupied by it1 #fj4 ,accuracy of the astronomical records of1 #bfe4 ,elasticity1 an ultimate phenomenon1 #ij4 ,electricity may be the cause of magnetism1 #ic4 ,universality of1 #cbi4 ,effects of1 #ccj4 ,activity of1 #cca4 ,equilibrium of1 #ccb4 ,productive of chemical decomposition1 #cch4 ,empirical laws1 #agh4 ,evils resulting from1 #agi4 ,encke1 professor1 his prediction of the return of the comet so many times in succession1 #aef4 ,englefield1 sir ,h41 his analysis of a solar beam1 #cad4 ,equilibrium maintained by force1 #bbb4 ,erman1 professor1 his opinion of the effects of the voltaic circuit1 #cdj4 ,euler1 his improvement on ,newton's theory of sound1 #bdg4 ,experience1 source of our knowledge of nature's laws1 #gf4 ,experiment1 a means of acquiring experience1 #gf4 ,utility of1 #aea4 ,facts1 the observation of1 #aah4 ,faujas de ,st4 ,fond1 imaginary craters of1 #aca4 ,fluids1 laws of the motion of1 #aha4 ,compressibility of1 #bbe4 ,consideration of the motions of1 more complicated than that of equilibrium1 #bce4 ,force1 analysis of1 #hf4 ,the cause of motion1 #adi4 ,phenomena of1 #bba4 ,molecular forces1 #bde4 ,fourier1 baron1 his opinion that the celestial regions have a temperature1 independent of the sun1 not greatly inferior to that at which quicksilver congeals1 #aeg4 ,his analysis of the laws of conduction and radiation of heat1 #cag4 ,franklin1 ,dr41 his experiments on electricity1 #ccb4 ,fresnel1 ,m41 his mathematical explanation of the phenomena of double refraction1 #cb4 ,his improvement on lenses for lamps of lighthouses1 #ef4 ,his opinions on the nature of light1 #bjg4 ,his experiments on the interference of polarized light1 #bfa4 ,his theory of polarization1 #bfb4 ,friction1 a source of heat1 #cac4 ,galileo1 celebrity of1 for his knowledge of science1 #gb4 ,his exposition of the ,aristotelian philosophy1 #aaj4 ,his refutation of ,aristotle's dogmas respecting motion1 his persecution in consequence of it1 #aac4 ,his knowledge of the accelerating power of gravity1 #afh4 ,his knowledge of the weight of the atmosphere1 #bbh4 ,galvani1 utility of his discoveries in electricity1 #cce4 ,his application of it to animals1 #ccf4 ,gay-,lussac1 his examination of gases and vapours1 #cai4 ,generalization1 inductive1 #a1 #ij4 ,geology1 #bha4 ,its rank as a science1 #bhg4 ,geometry1 axioms of1 an appeal to experience1 not corporeal1 but mental1 #ie4 ,gilbert1 ,dr41 of ,colchester1 his knowledge of magnetism and electricity1 #aab4 ,gravitation1 law of1 a physical axiom of a very high and universal kind1 #ih4 ,influence of1 decreases in the inverse ratio of the square of the distance1 #abc4 ,greece1 philosophers of1 their extraordinary success in abstract reasoning1 and their careless consideration of external nature1 #aje4 ,their general character1 #ajf4 ,philosophy of1 #ajh4 ,grimaldi1 a jesuit of ,bologna1 his discovery of diffraction1 or inflection of light1 #beb4 ,guinea and feather experiment1 #afh4 ,gunpowder1 invention of1 #ee4 ,a mechanical agent1 #fb4 ,haarlem lake1 draining of1 #fa4 ,harmony1 sense of1 #bdh4 ,head1 captain1 anecdote of1 #hd4 ,heat1 #aic4 ,radiation and conduction of1 #bje4 ,one of the chief agents in chemistry1 #caj4 ,our ignorance of the nature of1 #caj4 ,abuse of the sense of the term1 #caa4 ,the general heads under which it is studied1 #cab4 ,its most obvious sources1 #cab4 ,animal heat1 to what process referable1 #cac4 ,radiation and conduction of1 #cad4 ,solar heat differs from terrestrial fires1 or hot bodies1 #cae4 ,principal effects of1 #cag4 ,the antagonist to mutual attraction1 #cbb4 ,latent heat1 #cbb4 ,specific heat1 #cbc4 ,herschel1 sir ,william1 his analysis of a solar beam1 #cad4 ,hipparchus1 his catalogue of stars1 #bgf4 ,holland drained of water by windmills1 #fa4 ,hooke almost the rival of ,newton1 #aaf4 ,huel ,towan1 steam-engine at1 #ei4 ,huyghens1 his doctrine of light1 #bjg4 ,ascertains the laws of double refraction1 #bed4 ,hydrostatics1 first step towards a knowledge of1 made by ,archimedes1 #bca4 ,law of the equal pressure of liquids1 #bcb4 ,general applicability of1 #bcb4 ,hypothesis1 not to be deterred from framing them1 #aif4 ,conditions on which they should be framed1 #aig4 ,illustrated by the laws of gravitation1 #aih4 ,use and abuse of1 #bjd4 ,induction1 different ways of carrying it on1 #ajb4 ,steps by which it is arrived at on a legitimate and extensive scale1 #aah4 ,first stage of1 #add4 ,verification of1 #afd4 ,instanced in astronomy1 #aff4 ,must be followed into all its consequences1 and applied to all those cases which seem even remotely to bear upon the subject of enquiry1 #agc4 ,nature of the inductions by which quantitative laws are arrived at1 #agf4 ,necessity of induction embracing a series of cases which absolutely include the whole scale of variation of which the quantities in question admit1 #agg4 ,induced electricity1 #ccc4 ,inertia1 #bbc4 ,iodine1 discovery of1 #ej4 ,efficacy of1 in curing gotre1 #ea4 ,isomorphism1 law of1 #agj4 ,kepler1 effect of his discoveries on the ,aristotelian philosophy1 #aac4 ,nature of his laws of the planetary system1 #agh4 ,proofs of the ,newtonian system1 #agi4 ,knowledge1 physical facts illustrative of the utility of1 #de4 ,diffusion of1 how to take advantage of in the investigation of nature1 #ach4 ,lagrange1 his improvements on ,newton's theory of sound1 #bdg4 ,his astronomical researches1 #bge4 ,lamp1 safety1 #ee4 ,laplace1 his explanation of the residual velocity of sound and confirmation of the general law of the developement of heat by compression1 #agb4 ,his astronomical research1 #bge4 ,his experiments on the dilatation of bodies by heat1 #cai4 ,his study of specific heat1 #cbc4 ,latent heat1 #cbc4 ,laws1 inductive1 #aga4 ,general1 #aih4 ,how applicable1 #aii4 ,illustrated by the planetary system1 #bja4 ,empirical laws1 #agh4 ,lavoisier1 his improvements in chemical science1 #cjb4 ,experiments on dilatation of bodies by heat1 #cai4 ,his investigation on specific heat1 #cbc4 ,light1 refraction of1 #cj4 ,double refraction of1 #ca4 ,polarization of1 #bed4 ,light and vision1 ignorance of the ancients respecting1 #bdi4 ,lighthouse1 #ef4 ,lightning1 how to judge philosophically of it1 #abj4 ,returning stroke of1 #aba4 ,liquids1 cohesion1 attraction and repulsion of the particles of1 #bbg4 ,differ from ariform fluids by their cohesion1 #bcc4 ,the ,florentine experiment on2 experiments by ,canton1 ,perkins1 ,orsted1 and others on1 #bce4 ,obscurity of the laws of dilatation of1 #cbj4 ,linnus1 his knowledge of crystalline substances1 #bci4 ,logic1 #ai4 ,lyell's ,principles of ,geology1 extract from1 #adf4 ,magnetism may be caused by electricity1 #ic4 ,offers a 8glaring instance0 of polarity1 #cbf4 ,experiments illustrative of1 #cbg4 ,malus1 a ,french officer of engineers1 discovers the polarization of light1 #acb1 #beh4 ,man1 regarded as a creature of instinct1 #a4 ,of reason and speculation1 #c4 ,his will determined by causes and consequences1 #f4 ,advantages to1 from the study of science1 #g4 ,his necessity to study the laws of nature illustrated1 #ff4 ,happiness and the opposite state of man in the aggregate1 #fg4 ,advantages conferred on1 by the augmentation of physical resources1 #fh4 ,advantages from intellectual resources1 #fi4 ,mariotte1 his law of equilibrium of an elastic fluid recently verified by the ,royal ,academy of ,paris1 #bca4 ,his difference between solar and other heat1 #cae4 ,matter1 indestructibility of2 ,divided by grinding1 #dj4 ,by fire1 #da4 ,dilated by heat1 #aic4 ,inertia of1 #bjb4 ,polarity of1 one of the ultimate phenomena to which the analysis of nature leads us1 #bde4 ,inherent activity of1 #big4 ,causes of the polarity of1 #bii4 ,imponderable forms of1 #caj4 ,measure1 the standard1 difficulty of preserving it unaltered1 #abh4 ,how to be assisted in measurement1 #abi4 ,our conclusions from1 should be conditional1 #acj4 ,menai ,bridge1 weight and height of1 #fj4 ,mechanics1 practical1 #fc4 ,mtre1 the ,french1 #abf4 ,microscopes1 power of1 #aia4 ,millstones1 method of making in ,france1 #dh4 ,mind1 its transition from the little to the great1 and vice vers1 illustrated1 #agb4 ,mineralogy unknown to the ancients1 #gi4 ,prejudiced by the rage for nomenclature1 #aci4 ,benefited by the progress of chemical analysis1 #bic4 ,minerals1 simple1 apparent paucity of1 #bid4 ,difficulty in classing them1 #bie4 ,mitscherlich1 his law of isomorphism1 #agj4 ,his experiments on the expansion of substances by heat1 #bdc4 ,motion1 #hg4 ,simplicity and precision of the laws of1 #agi4 ,nature1 laws of1 #cg4 ,immutability of1 #db4 ,harmony of1 and advantage of studying them1 #dc4 ,prove the impossibility of attaining the declared object of the alchemist4 ,how they serve mankind generally1 #dd4 ,illustrated by mining1 #de4 ,economy derived from a knowledge of1 #fe4 ,how to be regarded1 #ajj1 #aja4 ,nature1 objects of1 an enumeration and nomenclature of1 useful in the study of1 #ace4 ,mechanism of1 on too large or too small a scale to be immediately cognisable by our senses1 #aia4 ,newton1 his proof of ,galileo's laws of gravitation by an experiment with a hollow glass pendulum1 #afj4 ,his foundation to hydrodynamical science1 #aha4 ,fixes the division between statics and dynamics1 #bbc4 ,his investigation of the law of equilibrium of elastic fluids1 #bca4 ,his law of hydrostatics1 #bcb4 ,his foundation of hydrodynamics #bcf4 ,his analysis of sound1 #bdg4 ,hypothesis of light1 #bej4 ,examination of a soap-bubble1 #beb4 ,his hypothesis of fits of easy transmission and reflection1 #bec4 ,his combination of mathematical skill with physical research1 #bga4 ,his ,principia1 #bgb4 ,his successors2 his geometry1 #bgc4 ,nomenclature1 importance of1 to science1 #acf4 ,more a consequence than a cause of extended knowledge1 #ach4 ,prejudicial to mineralogy1 #aci4 ,norman1 ,robert1 his discovery of the dip of the needle1 #cbg4 ,numerical precision1 necessity of1 in science1 #abb4 ,objects1 and their mutual actions1 subjects of contemplation1 #aah4 ,observation1 a means of acquiring experience1 #gf4 ,passive and active1 #gg4 ,recorded observation1 #abj4 ,necessity of1 to acquire precise physical data1 #bae4 ,illustrated by the barometer1 #baf4 ,orsted1 his discoveries in electricity and magnetism1 #acb4 ,of electro-magnetism1 #cdj4 ,opacity1 #ahi4 ,otto von ,guericke of ,magdeburgh1 his invention of the air-pump1 #bcj4 ,paracelsus1 power of his chemical remedies2 his use of mercury1 opium1 and tartar1 #aab4 ,pascal1 his crucial instances proving the weight of air1 #bbi4 ,pendulum1 #abf4 ,phenomena1 analysis of1 illustrated by musical sounds1 the sensation of taste1 #he4 ,the ultimate and inward process of nature in the production of1 #hf4 ,analysis of complex phenomena1 #hh4 ,ultimate phenomena1 #ij4 ,how the analysis of1 is useful1 #ig4 ,a transient phenomenon1 how to judge of1 #abb4 ,method of explaining one when it presents itself1 #adh4 ,how to discover the cause of one1 #aej4 ,two1 or many1 theories1 maintained as the origin of1 in physics1 #aie4 ,cosmical phenomena1 #bfe4 ,philosophy1 natural1 unfounded objections to the study of1 #g4 ,advantages derivable from the study of1 #aj4 ,pleasure and happiness1 the consequences of the study of1 #ae4 ,phlogistic doctrines of ,beccher and ,stahl1 #cjj4 ,physical data1 necessity of1 #bji4 ,great importance of1 #baa4 ,illustrated by the erection of observatories1 #bac4 ,necessity of an exact knowledge of1 #bad4 ,more precise than the observations by which we acquire them1 #bae4 ,physics1 axioms of2 analysis of1 #ajb4 ,planets1 circumjovial1 #ahf4 ,platina1 discovery of1 #cjh4 ,pliny1 his knowledge of quartz and diamond1 #bci4 ,pneumatics1 #bbh4 ,political economy1 #gc4 ,prejudices of opinion and sense1 #hj4 ,conditions on which such are injurious1 #ha4 ,illustrated by the division of the rays of light1 by the moon at the horizon1 and by ventriloquism1 #hb4 ,by the transition of the hand from heat to cold1 #hc4 ,prevost1 ,m41 his theory of heat1 #caf4 ,his theory of reciprocal interchanges1 a proof of the radiation of cold1 #cah4 ,printing1 the art of1 #aic4 ,performed by steam1 #aid4 ,probabilities1 doctrine of1 #bag4 ,illustrated by shooting at a wafer1 #bah4 ,prout1 ,dr41 his opinion of the atomic weights1 #cjg4 ,pyrometry1 #cai4 ,pythagoras1 philosophy of1 #ajg4 ,quinine1 sulphate of1 comparative comfort and health resulting from the use of1 #ef4 ,radiation of heat1 laws of1 #bje4 ,repulsion in fluids and solids1 #bbg4 ,rules1 general1 for guiding and facilitating our search among a great mass of assembled facts1 #aea4 ,rumford1 count1 experiments of1 on gunpowder1 #fb4 ,savart1 ,m41 his experiments on solids1 #bdc4 ,his researches on sound1 #bdi4 ,science1 abstract1 a preparation for the study of physics1 #ai4 ,not indispensable to the study of physical laws1 #be4 ,instances illustrative of1 #bg4 ,science1 physical1 nature and objects1 immediate and collateral1 as regarded in itself and in its application to the practical purposes of life1 and its influence on society1 #ce4 ,state of1 previous to the age of ,galileo and ,bacon1 #ajd4 ,causes of the rapid advance of1 compared with the progress at an earlier period1 #cdg4 ,science1 natural1 cause and effect1 the ultimate relations of1 #gf4 ,sciences and ,arts1 remarks on the language1 terms1 or signs used in treating of them1 #gj4 ,receive an impulse by the ,baconian philosophy1 #aad4 ,sensation1 cause of1 #ia4 ,senses1 inadequate to give us direct information for the exact comparison of quantity1 #abd4 ,substitutes for the inefficiency of1 #abe4 ,seringapatam1 method of breaking blocks from the quarries of1 #dg4 ,shells found in rocks at a great height above the sea1 supposed cause of1 #ade4 ,smeaton1 his experiments on bodies dilated by heat1 #cai4 ,solids1 transparent1 exhibit periodical colours when exposed to polarized light1 #ii4 ,influence of1 on the ,mind1 #aja4 ,solids in general1 nature of1 #bcf4 ,constitution of1 complicated1 #bcg4 ,toughness of1 distinct from hardness2 tenacity of1 #bch4 ,become liquefied by the addition of heat1 #cba4 ,sounds1 musical1 illustrative of the analysis of phenomena1 #he4 ,means of having a knowledge of1 #hi4 ,propagation of1 through the air1 #bdf4 ,newton's analysis of1 #bdg4 ,standard measurement1 necessity of1 #abe4 ,laws of nature used as such1 illustrated by the rotation of the earth1 #abf4 ,substances all subject to dilatation by the addition of heat1 #bdc4 ,sun1 the character of the heat of1 #cae4 ,thales1 philosophy of1 #ajg4 ,theories1 how to estimate the value of1 #bjd4 ,best arrived at by the consideration of general laws1 #bjh4 ,explanatory of the phenomena of nature2 on what their application ought to be grounded1 #bji4 ,thomson1 ,dr41 his opinion of the atomic weights1 #cjg4 ,thermometer1 air1 #cai4 ,thermo-electricity1 #cda4 ,time1 division of1 #abf1 #abg4 ,torricelli1 pupil of ,galileo1 his experiments proving the weight of atmosphere1 #bbi4 ,torpedo1 shock of1 #cda1 #cdb4 ,ulugh ,begh1 his catalogue of stars1 #bgg4 ,vaccination1 success of1 as a preventive to small-pox1 #eb4 ,vision and light1 ignorance of the ancients respecting1 #bdi4 ,volta1 his discoveries in electricity1 #cce4 ,electric pile of1 #ccg4 ,voltaic circuit1 #cch4 ,water1 effects of the power of1 #fa4 ,whewell1 his experiments1 #ahg4 ,wells1 ,dr41 his theory of dew1 #afc4 ,wind1 effects of the power of1 #fa4 ,wire steel1 magnetized masks of1 used by needle-makers1 #eg4 ,wollaston1 ,dr41 his verification of the laws of double refraction in ,iceland spar1 #beh4 ,his invention of the goniometer1 #bib4 ,world1 the materials of the1 #bij4 ,young1 ,dr41 his experiments on the interference of the rays of light1 #bfj4 ,zoology1 fossil1 #cdd4 ,,the ,,end4 ,,london ,,printed ,,by ,,spottiswoode ,,and ,,co4 ,,new-,,street ,,square4 ,,footnotes #a ,hooke's ,posthumous ,works4 ,lond4 #agje4--p4 #dgb and p4 #deh4 #b ,wealth of ,nations1 book i4 chap4 i4 p4 #ae4 #c ,on this subject1 we cannot forbear citing a passage from one of the most profound but at the same time popular writers of our time1 on a subject unconnected it is true with our own1 but bearing strongly on the point before us4 8,but1 if science be manifestly incomplete1 and yet of the highest importance1 it would surely be most unwise to restrain enquiry1 conducted on just principles1 even where the immediate practical utility of it was not visible4 ,in mathematics1 chemistry1 and every branch of natural philosophy1 how many are the enquiries necessary for their improvement and completion1 which1 taken separately1 do not appear to lead to any specifically advantageous purpose6 how many useful inventions1 and how much valuable and improving knowledge1 would have been lost1 if a rational curiosity1 and a mere love of information1 had not generally been allowed to be a sufficient motive for the search after truth60--,malthus's ,principles of ,political ,economy1 p4 #af4 #d 1 ratio1 reason4 #e 1 verbum1 a word4 #f ,it were much to be wished that navigators would be more cautious in laying themselves open to a similar censure4 ,on looking hastily over a map of the world we see three ,melville ,islands1 two ,king ,george's ,sounds1 and ,cape ,blancos innumerable4 #g ,young4 ,lectures on ,nat4 ,phil4 ii4 #fbg4 ,see also ,phil4 ,trans4 #ahja-b4 #h ,captain ,basil ,hall1 ,r4 ,n4 #i ,we must caution our readers who would assure themselves of it by trial1 that it is an experiment of some delicacy1 and not to be made without several precautions to ensure success4 ,for these we must refer to our original authority 7,fresnel4 ,mmoire sur la ,diffraction de la ,lumiere1 p4 #abd472 and the principles on which they depend will of course be detailed in that volume of the ,cabinet ,cyclopdia which is devoted to the subject of ,,light4 #aj ,little reels used in cotton mills to twist the thread4 #aa ,such a block would weigh between four and five hundred thousand pounds4 ,see ,dr4 ,kennedy's 8,account of the ,erection of a ,granite ,obelisk of a ,single ,stone about ,seventy ,feet high1 at ,seringapatam40--,ed4 ,phil4 ,trans4 vol4 ix1 p4 #cab4 #ab ,dr4 ,coindet of ,geneva4 #ac ,journal of a ,voyage to the ,south ,seas1 c4 c4 under the ,command of ,commodore ,george ,anson1 in #agdj-agdd1 by ,pascoe ,thomas1 ,lond4 #agde1 ,so tremendous were the ravages of scurvy1 that1 in the year #agbf1 admiral ,hosier sailed with seven ships of the line to the ,west ,indies1 and buried his ships' companies twice1 and died himself in consequence of a broken heart4 ,dr4 ,johnson1 in the year #aggh1 could describe a sea-life in such terms as these3--8,as to the sailor1 when you look down from the quarter deck to the space below1 you see the utmost extremity of human misery1 such crowding1 such filth1 such stench60--8,a ship is a prison with the chance of being drowned--it is worse--worse in every respect--worse room1 worse air1 worse food--worse company60 ,smollet1 who had personal experience of the horrors of a seafaring life in those days1 gives a lively picture of them in his ,roderick ,random4 #ad ,lemon juice was known to be a remedy for scurvy far superior to all others #bjj years ago1 as appears by the writings of ,woodall4 ,his work is entitled 8,the ,surgeon's ,mate1 or ,military and ,domestic ,medicine4 ,by ,john ,woodall1 ,master in ,surgery ,london1 #afcf10 p4 #afe4 ,in #afjj1 ,commodore ,lancaster sailed from ,england with three other ships for the ,cape of ,good ,hope1 on the #b;d of ,april1 and arrived in ,saldanha ,bay on the #ast of ,august1 the commodore's own ship being in perfect health1 from the administration of three table-spoonsfull of lemon juice every morning to each of his men1 whereas the other ships were so sickly as to be unmanageable for want of hands1 and the commander was obliged to send men on board to take in their sails and hoist out their boats4 7,purchas's ,pilgrim1 vol4 i4 p4 #adi47 ,a ,fellow of the college1 and an eminent practitioner1 in #agec published a tract on sea scurvy1 in which he adverts to the superior virtue of this medicine2 and ,mr4 ,a4 ,baird1 surgeon of the ,hector sloop of war1 states1 that from what he had seen of its effects on board of that ship1 he 8thinks he shall not be accused of presumption in pronouncing it1 if properly administered1 a most infallible remedy1 both in the cure and prevention of scurvy40 7,vide ,trotter's ,medicina ,nautica47 ,the precautions adopted by captain ,cook in his celebrated voyages1 had fully demonstrated by their complete success the practicability of keeping scurvy under in the longest voyages1 but a uniform system of prevention throughout the service was still deficient4 ,it is to the representations of ,dr4 ,blair and sir ,gilbert ,blane1 in their capacity of commissioners of the board for sick and wounded seamen1 in #agie1 we believe1 that its systematic introduction into nautical diet1 by a general order of the admiralty1 is owing4 ,the effect of this wise measure 7taken1 of course1 in conjunction with the general causes of improved health17 may be estimated from the following facts3--,in #aghj1 the number of cases of scurvy received into ,haslar hospital was #adeg2 in #ahjf one only1 and in #ahjg one4 ,there are now many surgeons in the navy who have never seen the disease4 #ae ,throughout ,france the conductor is recognised as a most valuable and useful instrument2 and in those parts of ,germany where thunder-storms are still more common and tremendous they are become nearly universal4 ,in ,munich there is hardly a modern house unprovided with them1 and of a much better construction than ours--several copper wires twisted into a rope4 #af ,we have been informed by an eminent physician in ,rome1 7,dr4 ,morichini7 that a vast quantity of the sulphate of quinine is manufactured there and consumed in the ,campagna1 with an evident effect in mitigating the severity of the malarious complaints which affect its inhabitants4 #ag ,dr4 ,johnson1 ,memoirs of the ,medical ,society1 vol4 v4 #ah ,the engine at ,huel ,towan4 ,see ,mr4 ,henwood's ,statement 8of the performance of steam-engines in ,cornwall for ,april1 ,may1 and ,june1 #ahbi40 ,brewster's ,journal1 ,oct4 #ahbi4--,the highest monthly average of this engine extends to #gi millions of pounds4 #ai ,however1 this is not quite a fair statement2 a man's daily labour is about #d lbs4 of coals4 ,the extreme toil of this ascent arises from other obvious causes than the mere height4 #bj ,its surface is about #dj1jjj acres1 and medium depth about #bj feet4 ,it was proposed to drain it by running embankments across it1 and thus cutting it up into more manageable portions to be drained by windmills4 #ba ,no one doubts the practicability of the undertaking4 ,eight or nine thousand chaldrons of coals duly burnt would evacuate the whole contents4 ,but many doubt whether it would be profitable1 and some1 considering that a few hundreds of fishermen who gain their livelihood on its waters would be dispossessed1 deny that it would be desirable4 #bb 8,experiments to determine the ,force of fired ,gunpowder40 ,phil4 ,trans4 vol4 lxxxvii4 p4 #bed4 et seq4 #bc ,see a very ingenious application of this kind in ,mr4 ,babbage's article on ,diving in the ,encyc4 ,metrop4--,others will readily suggest themselves4 ,for instance1 the ballast in reserve of a balloon might consist of materials capable of evolving great quantities of hydrogen gas in proportion to their weight1 should such be found4 #bd ,the sulphuric4 ,bracconot1 ,annales de ,chimie1 vol4 xii4 p4 #ahd4 #be ,d',arcet1 ,annales de l',industrie1 ,fevrier1 #ahbi4 #bf ,see ,dr4 ,prout's account of the experiments of professor ,autenrieth of ,tubingen4 ,phil4 ,trans4 #ahbg1 p4 #cha4 ,this discovery1 which renders famine next to impossible1 deserves a higher degree of celebrity than it has obtained4 #bg ,greenwich4 #bh ,maskelyne's4 #bi ,thomson's ,first ,principles of ,chemistry1 vol4 ii4 p4 #fh4 #cj ,galileo exposes unsparingly the ,aristotelian style of reasoning4 ,the reader may take the following from him as a specimen of its quality4 ,the object is to prove the immutability and incorruptibility of the heavens2 and thus it is done3-- ,i4 ,mutation is either generation or corruption4 ,,ii4 ,generation and corruption only happen between contraries4 ,,iii4 ,the motions of contraries are contrary4 ,,iv4 ,the celestial motions are circular4 ,v4 ,circular motions have no contraries4 4 ,because there can be but three simple motions4 #a4 ,to a centre4 #b4 ,round a centre4 #c4 ,from a centre4 4 ,of three things1 one only can be contrary to one4 4 ,but a motion to a centre is manifestly the contrary to a motion from a centre4 4 ,therefore a motion round a centre 7i4 e4 a circular motion7 remains without a contrary4 ,,vi4 ,therefore celestial motions have no contraries--therefore among celestial things there are no contraries--therefore the heavens are eternal1 immutable1 incorruptible1 and so forth4 ,it is evident that all this string of nonsense depends on the excessive vagueness of the notions of generation1 corruption1 contrariety1 c4 on which the changes are rung4--,see ,,galileo1 ,systema ,cosmicum1 ,dial4 i4 p4 #cj4 #ca ,macquer justly observes1 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 successful4--,macquer's ,dictionary of ,chemistry1 i4 x4 #cb ,paracelsus performed most of these cures by mercury and opium1 the use of which latter drug he had learned in ,turkey4 ,of mercurial preparations the physicians of his time were ignorant1 and of opium they were afraid1 as being 8cold in the fourth degree40 ,tartar was likewise a great favourite of ,paracelsus1 who imposed on it that name1 8because it contains the water1 the salt1 the oil1 and the acid1 which burn the patient as hell does30 in short1 a kind of counterbalance to his opium4 #cc ,see the ,life of ,galileo ,galilei1 by ,mr4 ,drinkwater1 with ,illustrations of the ,advancement of ,experimental ,philosophy4 #cd ,the temporary star in ,cassiopeia observed by ,cornelius ,gemma1 in #aegb1 was so bright as to be seen at noon-day4 ,that in ,serpentarius1 first seen by ,kepler in #afjd1 exceeded in brilliancy all the other stars and planets4 #ce ,edinburgh ,phil4 ,journ4 #ahai1 vol4 i4 p4 #h4 #cf ,the abstract principle of repetition in matters of measurement 7viz4 juxta-position of units without error7 is applicable to a great variety of cases in which quantities are required to be determined to minute nicety4 ,in chemistry1 in determining the standard atomic weights of bodies1 it seems easily and completely applicable1 by a process which will suggest itself at once to every chemist1 and seems the only thing wanting to place the exactness of chemical determinations on a par with astronomical measurements4 #cg ,accurate and perfectly authentic copies of the yard and pound1 executed in platina1 and hermetically sealed in glass1 should be deposited deep in the interior of the massive stone-work of some great public building1 whence they could only be rescued with a degree of difficulty sufficient to preclude their being disturbed unless on some very high and urgent occasion4 ,the fact should be publicly recorded1 and its memory preserved by an inscription4 ,indeed1 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 distinct1 tangible1 and imperishable form1 if1 instead of the absurd and useless deposition of a few coins and medals under the foundations of buildings1 specimens of ingenious implements or condensed statements of scientific truths1 or processes in arts and manufactures1 were substituted4 ,will books infallibly preserve to a remote posterity all that we may desire should be hereafter known of ourselves and our discoveries1 or all that posterity would wish to know8 and may not a useless ceremony be thus transformed into an act of enrolment in a perpetual archive of what we most prize1 and acknowledge to be most valuable8 #ch ,in the system alluded to1 the name of quartz is assigned to iolite and obsidian2 that of mica to plumbago1 chlorite1 and uranite2 sulphur1 to orpiment and realgar1 c4 ,see ,mohs's ,system of ,mineralogy1 translated by ,haidinger4 #ci ,the following passage1 from ,lindley's ,synopsis of the ,british ,flora1 characterises justly the respective merits1 in a philosophical point of view1 of natural and artificial systems of classification in general1 though limited in its expression to his own immediate science3--8,after all that has been effected1 or is likely to be accomplished hereafter1 there will always be more difficulty in acquiring a knowledge of the natural system of botany than of the ,linnan4 ,the latter skims only the surface of things1 and leaves the student in the fancied possession of a sort of information which it is easy enough to obtain1 but which is of little value when acquired3 the former requires a minute investigation of every part and every property known to exist in plants2 but when understood has conveyed to the mind a store of real information1 of the utmost use to man in every station of life4 ,whatever the difficulties may be of becoming acquainted with plants according to this method1 they are inseparable from botany1 which cannot be usefully studied without encountering them40 ,schiller has some beautiful lines on this1 entitled 8,menschliches ,wissen0 7or ,human ,knowledge72 ,gedichte1 vol4 i4 p4 #gb4 ,leipzig1 #ahjj4 #dj ,lyell's ,principles of ,geology1 vol4 i4 ,fourrier1 ,mm4 de l',acad4 des ,sciences1 tom4 vii4 p4 #eib4 8,l'tablissement et le progrs des socits humaines1 l'action des forces naturelles1 peuvent changer notablement1 et dans de vastes contres1 l'tat de la surface du sol1 la distribution des eaux1 et les grands mouvemens de l'air4 ,de tels effets sont propres faire varier1 dans le cours de plusieurs sicles1 le dgr de la chaleur moyenne2 car les expressions analytiques comprennent des coefficiens qui se rapportent l'tat superficiel1 et qui influent beaucoup sur la valeur de la temprature40 ,in this enumeration1 by ,m4 ,fourrier1 of causes which may vary the general relation of the surface of extensive continents to heat1 it is but justice to ,mr4 ,lyell to observe1 that the gradual shifting of the places of the continents themselves on the surface of the globe1 by the abrading action of the sea on the one hand1 and the elevating agency of subterranean forces on the other1 does not expressly occur and cannot be fairly included in the general sense of the passage1 which confines itself to the consideration of such changes as may take place on the existing surface of the land4 #da ,the reader will find this subject further developed in a paper lately communicated to the ,geological ,society4 #db ,phil4 ,trans4 #ahbd4 #dc ,wells on ,dew4 #dd ,principia1 book iii4 prop4 #f4 #de ,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 obliquities4 ,optics1 book ii4 part i4 obs4 #g4 #df ,see ,phil4 ,trans4 #ahai4 #dg 8,when we are told that ,saturn moves in his orbit more than #bb1jjj miles an hour1 we fancy the motion to be swift2 but when we find that he is more than three hours moving his own diameter1 we must then think it1 as it really is1 slow40 ,thirty ,letters on various ,subjects1 by ,william ,jackson1 #agie4 #dh ,thomson's ,first ,principles of ,chemistry4 #di ,there seems no doubt1 however1 that an achromatic telescope had been constructed by a private amateur1 a ,mr4 ,hall1 some time before either ,euler or ,dollond ever thought of it4 #ej ,we allude to the recently invented achromatic combinations of ,messrs4 ,barlow and ,rogers1 and the dense glasses of which ,mr4 ,faraday has recently explained the manufacture in a memoir full of the most beautiful examples of delicate and successful chemical manipulation1 and which promise to give rise to a new era in optical practice1 by which the next generation at least may benefit4 ,see ,phil4 ,trans4 #ahcj4 #ea ,alphonso of ,castile1 #abeb4 #eb ,jackson1 ,letters on ,various ,subjects1 c4 #ec ,thomson's ,first ,principles of ,chemistry1 ,introduction4 #ed ,the progress of astronomical discovery has since shown that this law cannot be relied on 7#ahea74 #ee ,novum ,organum1 part ii4 table #b4 7#bd71 7#cj71 c4 on the form or nature of heat4 #ef ,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 mechanical1 and by a process depending entirely on a certain order and sequence of events1 and the operation of known causes4 ,suppose a quantity of air enclosed in a metallic reservoir1 of some good conductor of heat1 and suddenly compressed by a piston4 ,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 above the surrounding atmosphere1 let the piston be suddenly retracted and the air restored to its original volume in an instant4 ,the whole apparatus is now precisely in its initial situation1 as to the disposition of its material parts1 and the whole quantity of heat it contains remains unchanged4 ,but it is evident that the distribution of this heat within it is now very different from what it was before2 for the air in its sudden expansion cannot re-absorb in an instant of time all the heat it had parted with to the metal3 it will1 therefore1 have a temperature below that of the general atmosphere1 while the metal yet retains one above it4 ,thus1 a subversion of the equilibrium of temperature has been bon fide effected4 ,heat has been driven from the air into the metal1 while every thing else remains unchanged4 ,we have here a means by which1 it is evident1 heat may be obtained1 to any extent1 from the air1 without fuel4 ,for if1 in place of withdrawing the piston and letting the same air expand1 within the reservoir1 it be allowed to escape so suddenly as not to re-absorb the heat given off1 and fresh air be then admitted and the process repeated1 any quantity of air may thus be drained of its heat4 #eg ,see ,phil4 ,trans4 #ahbd4 #eh ,if the brain be an electric pile1 constantly in action1 it may be conceived to discharge itself at regular intervals1 when the tension of the electricity developed reaches a certain point1 along the nerves which communicate with the heart1 and thus to excite the pulsations of that organ4 ,this idea is forcibly suggested by a view of that elegant apparatus1 the dry pile of ,deluc2 in which the successive accumulations of electricity are carried off by a suspended ball1 which is kept by the discharges in a state of regular pulsation for any length of time4 ,we have witnessed the action of such a pile maintained in this way for whole years in the study of the above-named eminent philosopher4 ,the same idea of the cause of the pulsation of the heart appears to have occurred to ,dr4 ,arnott2 and is mentioned in his useful and excellent work on physics1 to which however1 we are not indebted for the suggestion1 it having occurred to us independently many years ago4 #ei ,see a description of a contrivance of this kind by ,dr4 ,young1 ,lectures1 vol4 i4 p4 #aia4 #fj ,boyle's ,works1 folio1 vol4 iii4 ,essay x4 p4 #ahe4 #fa ,jackson1 ,the ,four ,ages1 p4 #eb4 ,london3 ,cadell and ,davies1 #agih4 #hvo4 #fb ,jackson1 ,the ,four ,ages1 p4 #ij4 ,transcriber's ,notes ,cover created by ,transcriber and placed in the ,public ,domain4 ,punctuation1 hyphenation1 and spelling were made consistent when a predominant preference was found in this book2 otherwise they were not changed4 ,simple typographical errors were corrected2 occasional unbalanced quotation marks retained4 ,ambiguous hyphens at the ends of lines were retained4 ,spelling of non-,english words was not reviewed4 ,text uses both 8appreciate0 and 8appretiate02 both retained4 ,index not checked for proper alphabetization or correct page references4