,,the ,,international ,,scientific ,,series4 ,,volume ,,vii4 ,,the ,,international ,,scientific ,,series4 ,works already ,published4 ,i4 ,,forms ,,of ,,water1 ,,in ,,clouds1 ,,rain1 ,,rivers1 ,,ice1 ,,and ,,glaciers4 ,by ,prof4 ,,john ,,tyndall1 ,,ll4 ,d41 ,f4 ,r4 ,s4 #a vol4 ,cloth4 ,price1 #a4ej4 ,,ii4 ,,physics ,,and ,,politics2 ,,or1 ,,thoughts ,,on ,,the ,,application ,,of ,,the ,,principles ,,of 8,,natural ,,selection0 ,,and 8,,inheritance0 ,,to ,,political ,,society4 ,by ,,walter ,,bagehot1 ,esq41 author of 8,the ,english ,constitution40 #a vol4 ,cloth4 ,price1 #a4ej4 ,,iii4 ,,foods4 ,by ,,edward ,,smith1 ,m4 ,d41 ,,ll4 ,b41 ,f4 ,r4 ,s4 #a vol4 ,cloth4 ,price1 #a4ge4 ,,iv4 ,,mind ,,and ,,body3 ,,the ,,theories ,,of ,,their ,,relations4 ,by ,,alex4 ,,bain1 ,,ll4 ,d41 ,professor of ,logic in the ,university of ,aberdeen1 #a vol41 #abmo4 ,cloth4 ,price1 #a4ej4 ,v4 ,,the ,,study ,,of ,,sociology4 ,by ,,herbert ,,spencer4 ,price1 #a4ej4 ,,vi4 ,,the ,,new ,,chemistry4 ,by ,prof4 ,,josiah ,p4 ,,cooke1 ,jr41 of ,harvard ,university4 #a vol41 #abmo4 ,cloth4 ,price1 #b4jj4 ,,vii4 ,,the ,,conservation ,,of ,,energy4 ,by ,prof4 ,,balfour ,,stewart1 ,,ll4 ,d41 ,f4 ,r4 ,s4 #a vol41 #abmo4 ,cloth4 ,price1 #a4ej4 ,,viii4 ,,animal ,,locomotion2 ,,or1 ,,walking1 ,,swimming1 ,,and ,,flying1 ,,with ,a ,,dissertation ,,on ,a,,ronautics4 ,by ,j4 ,,bell ,,pettigrew1 ,m4 ,d41 ,f4 ,r4 ,s4 ,e41 ,f4 ,r4 ,c4 ,p4 ,e4 #a vol41 #abmo4 ,fully illustrated4 ,price1 #a4ge4 ,,ix4 ,,responsibility ,,in ,,mental ,,disease4 ,by ,,henry ,,maudsley1 ,m4 ,d4 #a vol41 #abmo4 ,cloth4 ,price1 #a4ej4 ,x4 ,,the ,,science ,,of ,,law4 ,by ,prof4 ,,sheldon ,,amos4 #a vol41 #abmo4 ,cloth4 ,price1 #a4ge4 ,,xi4 ,,animal ,,mechanism4 ,a ,,treatise ,,on ,,terrestrial ,,and ,a,,rial ,,locomotion4 ,by ,e4 ,j4 ,,marey4 ,with #aag ,illustrations4 ,price1 #a4ge4 ,,xii4 ,,the ,,history ,,of ,,the ,,conflict ,,between ,,religion ,,and ,,science4 ,by ,,john ,,wm4 ,,draper1 ,m4 ,d41 ,,ll4 ,d41 author of 8,the ,intellectual ,development of ,europe40 ,price1 #a4ge4 ,,xiii4 ,,the ,,doctrine ,,of ,,descent1 ,,and ,,darwinism4 ,by ,prof4 ,,oscar ,,schmidt1 ,strasburg ,university4 ,price1 #a4ej4 ,,xiv4 ,,the ,,chemistry ,,of ,,light ,,and ,,photography4 ,,in ,,its ,,application ,,to ,,art1 ,,science1 ,,and ,,industry4 ,by ,dr4 ,,hermann ,,vogel4 #ajj ,illustrations4 ,price1 #b4jj4 ,,xv4 ,,fungi2 ,,their ,,nature1 ,,influence1 ,,and ,,uses4 ,by ,m4 ,c4 ,,cooke1 ,m4 ,a41 ,,ll4 ,d4 ,edited by ,rev4 ,m4 ,j4 ,,berkeley1 ,m4 ,a41 ,f4 ,l4 ,s4 ,with #aji ,illustrations4 ,price1 #a4ej4 ,,xvi4 ,,the ,,life ,,and ,,growth ,,of ,,language4 ,by ,prof4 ,w4 ,d4 ,,whitney1 of ,yale ,college4 ,price1 #a4ej4 ,,xvii4 ,,the ,,nature ,,of ,,light1 ,,with ,a ,,general ,,account ,,of ,,physical ,,optics4 ,by ,dr4 ,,eugene ,,lommel1 ,professor of ,physics in the ,university of ,erlangen4 ,with #ahh ,illustrations and a ,plate of ,spectra in ,chromo-lithography4 7,in press47 ,,the ,,international ,,scientific ,,series4 ,,the ,,conservation ,,of ,,energy4 ,,by ,,balfour ,,stewart1 ,,ll4 ,d41 ,f4,r4,s41 ,,professor ,,of ,,natural ,,philosophy ,,at ,,the ,,owens ,,college1 ,,manchester4 ,,with ,,an ,,appendix1 ,,treating ,,of ,,the ,,vital ,,and ,,mental ,,applications ,,of ,,the ,,doctrine ,,new ,,york3 ,d4 ,,appleton ,,and ,,company1 #edi #eea ,,broadway4 #ahge4 ,,entered1 according to ,act of ,congress1 in the year #ahgd1 by ,d4 ,,appleton ,,company1 ,in the ,office of the ,librarian of ,congress1 at ,washington4 ,,note ,,to ,,the ,,american ,,edition4 ,the great prominence which the modern doctrine of the ,conservation of ,energy or ,correlation of ,forces has lately assumed in the world of thought1 has made a simple and popular explanation of the subject very desirable4 ,the present work of ,dr4 ,balfour ,stewart1 contributed to the ,international ,scientific ,series1 fully meets this requirement1 as it is probably the clearest and most elementary statement of the question that has yet been attempted4 ,simple in language1 copious and familiar in illustration1 and remarkably lucid in the presentation of facts and principles1 his little treatise forms just the introduction to the great problem of the interaction of natural forces that is required by general readers4 ,but ,professor ,stewart having confined himself mainly to the physical aspects of the subject1 it was desirable that his views should be supplemented by a statement of the operation of the principle in the spheres of life and mind4 ,an ,appendix has1 accordingly1 been added to the ,american edition of ,dr4 ,stewart's work1 in which these applications of the law are considered4 ,professor ,joseph ,le ,conte published a very able essay fourteen years ago on the ,correlation of the ,physical and ,vital ,forces1 which was extensively reprinted abroad1 and placed the name of the author among the leading interpreters of the subject4 ,his mode of presenting it was regarded as peculiarly happy1 and was widely adopted by other writers4 ,after further investigations and more mature reflection1 he has recently restated his views1 and has kindly furnished the revised essay for insertion in this volume4 ,professor ,a4 ,bain1 the celebrated ,psychologist of ,aberdeen1 who has done so much to advance the study of mind in its physiological relations1 prepared an interesting lecture not long ago on the 8,correlation of the ,nervous and ,mental ,forces10 which was read with much interest at the time of its publication1 and is now reprinted as a suitable exposition of that branch of the subject4 ,these two essays1 by carrying out the principle in the field of vital and mental phenomena1 will serve to give completeness and much greater value to the present volume4 ,,new ,,york1 ,december1 #ahgc4 ,,preface4 ,we may regard the ,universe in the light of a vast physical machine1 and our knowledge of it may be conveniently divided into two branches4 ,the one of these embraces what we know regarding the structure of the machine itself1 and the other what we know regarding its method of working4 ,it has appeared to the author that1 in a treatise like this1 these two branches of knowledge ought as much as possible to be studied together1 and he has therefore endeavored to adopt this course in the following pages4 ,he has regarded a universe composed of atoms with some sort of medium between them as the machine1 and the laws of energy as the laws of working of this machine4 ,the first chapter embraces what we know regarding atoms1 and gives also a definition of ,energy4 ,the various forces and energies of ,nature are thereafter enumerated1 and the law of ,conservation is stated4 ,then follow the various transmutations of ,energy1 according to a list1 for which the author is indebted to ,prof4 ,tait4 ,the fifth chapter gives a short historical sketch of the subject1 ending with the law of ,dissipation2 while the sixth and last chapter gives some account of the position of living beings in this universe of ,energy4 ,b4 ,s4 ,the ,owens ,college1 ,manchester1 ,august1 #ahgc4 ,,contents4 ,,note ,,to ,,the ,,american ,,edition1 v ,,preface1 vii ,,chapter ,i4--,,what ,,is ,,energy8 #a ,,ii4--,,mechanical ,,energy ,,and ,,its ,,change ,,into ,,heat1 #bc ,,iii4--,,the ,,forces ,,and ,,energies ,,of ,,nature3 ,,the ,,law ,,of ,,conservation1 #dh ,,iv4--,,transmutations ,,of ,,energy1 #hg ,v4--,,historical ,,sketch3 ,,the ,,dissipation ,,of ,,energy1 #aca ,,vi4--,,the ,,position ,,of ,,life1 #aed ,,appendix ,i4--,,correlation ,,of ,,vital ,,with ,,chemical ,,and ,,physical ,,forces4 ,by ,,joseph ,,le ,,conte1 ,professor of ,geology and ,natural ,history in the ,university of ,california1 #aga ,,ii4--,,correlation ,,of ,,nervous ,,and ,,mental ,,forces4 ,by ,,alexander ,,bain1 ,professor of ,logic and ,mental ,philosophy in the ,university of ,aberdeen1 #bje ,,the ,,conservation ,,of ,,energy4 ,,chapter ,i4 ,,what ,,is ,,energy8 ,our ,ignorance of ,individuals4 #a4 ,very often we know little or nothing of individuals1 while we yet possess a definite knowledge of the laws which regulate communities4 ,the ,registrar-,general1 for example1 will tell us that the death-rate in ,london varies with the temperature in such a manner that a very low temperature is invariably accompanied by a very high death-rate4 ,but if we ask him to select some one individual1 and explain to us in what manner his death was caused by the low temperature1 he will1 most probably1 be unable to do so4 ,again1 we may be quite sure that after a bad harvest there will be a large importation of wheat into the country1 while1 at the same time1 we are quite ignorant of the individual journeys of the various particles of flour that go to make up a loaf of bread4 ,or yet again1 we know that there is a constant carriage of air from the poles to the equator1 as shown by the trade winds1 and yet no man is able to individualize a particle of this air1 and describe its various motions4 #b4 ,nor is our knowledge of individuals greater in the domains of physical science4 ,we know nothing1 or next to nothing1 of the ultimate structure and properties of matter1 whether organic or inorganic4 ,no doubt there are certain cases where a large number of particles are linked together1 so as to act as one individual1 and then we can predict its action--as1 for instance1 in the solar system1 where the physical astronomer is able to foretell with great exactness the positions of the various planets1 or of the moon4 ,and so1 in human affairs1 we find a large number of individuals acting together as one nation1 and the sagacious statesman taking very much the place of the sagacious astronomer1 with regard to the action and reaction of various nations upon one another4 ,but if we ask the astronomer or the statesman to select an individual particle and an individual human being1 and predict the motions of each1 we shall find that both will be completely at fault4 #c4 ,nor have we far to look for the cause of their ignorance4 ,a continuous and restless1 nay1 a very complicated1 activity is the order of nature throughout all her individuals1 whether these be living beings or inanimate particles of matter4 ,existence is1 in truth1 one continued fight1 and a great battle is always and everywhere raging1 although the field in which it is fought is often completely shrouded from our view4 #d4 ,nevertheless1 although we cannot trace the motions of individuals1 we may sometimes tell the result of the fight1 and even predict how the day will go1 as well as specify the causes that contribute to bring about the issue4 ,with great freedom of action and much complication of motion in the individual1 there are yet comparatively simple laws regulating the joint result attainable by the community4 ,but1 before proceeding to these1 it may not be out of place to take a very brief survey of the organic and inorganic worlds1 in order that our readers1 as well as ourselves1 may realize our common ignorance of the ultimate structure and properties of matter4 #e4 ,let us begin by referring to the causes which bring about disease4 ,it is only very recently that we have begun to suspect a large number of our diseases to be caused by organic germs4 ,now1 assuming that we are right in this1 it must nevertheless be confessed that our ignorance about these germs is most complete4 ,it is perhaps doubtful whether we ever saw one of these organisms1#a while it is certain that we are in profound ignorance of their properties and habits4 ,we are told by some writers#b that the very air we breathe is absolutely teeming with germs1 and that we are surrounded on all sides by an innumerable array of minute organic beings4 ,it has also been conjectured that they are at incessant warfare among themselves1 and that we form the spoil of the stronger party4 ,be this as it may1 we are at any rate intimately bound up with1 and1 so to speak1 at the mercy of1 a world of creatures1 of which we know as little as of the inhabitants of the planet ,mars4 #f4 ,yet1 even here1 with profound ignorance of the individual1 we are not altogether unacquainted with some of the habits of these powerful predatory communities4 ,thus we know that cholera is eminently a low level disease1 and that during its ravages we ought to pay particular attention to the water we drink4 ,this is a general law of cholera1 which is of the more importance to us because we cannot study the habits of the individual organisms that cause the disease4 ,could we but see these1 and experiment upon them1 we should soon acquire a much more extensive knowledge of their habits1 and perhaps find out the means of extirpating the disease1 and of preventing its recurrence4 ,again1 we know 7thanks to ,jenner7 that vaccination will prevent the ravages of small-pox1 but in this instance we are no better off than a band of captives who have found out in what manner to mutilate themselves1 so as to render them uninteresting to their victorious foe4 #g4 ,but if our knowledge of the nature and habits of organized molecules be so small1 our knowledge of the ultimate molecules of inorganic matter is1 if possible1 still smaller4 ,it is only very recently that the leading men of science have come to consider their very existence as a settled point4 ,in order to realize what is meant by an inorganic molecule1 let us take some sand and grind it into smaller and smaller particles1 and these again into still smaller4 ,in point of fact we shall never reach the superlative degree of smallness by this operation--yet in our imagination we may suppose the sub-division to be carried on continuously1 always making the particles smaller and smaller4 ,in this case we should1 at last1 come to an ultimate molecule of sand or oxide of silicon1 or1 in other words1 we should arrive at the smallest entity retaining all the properties of sand1 so that were it possible to divide the molecule further the only result would be to separate it into its chemical constituents1 consisting of silicon on the one side and oxygen on the other4 ,we have1 in truth1 much reason to believe that sand1 or any other substance1 is incapable of infinite sub-division1 and that all we can do in grinding down a solid lump of anything is to reduce it into lumps similar to the original1 but only less in size1 each of these small lumps containing probably a great number of individual molecules4 #h4 ,now1 a drop of water no less than a grain of sand is built up of a very great number of molecules1 attached to one another by the force of cohesion--a force which is much stronger in the sand than in the water1 but which nevertheless exists in both4 ,and1 moreover1 ,sir ,william ,thomson1 the distinguished physicist1 has recently arrived at the following conclusion with regard to the size of the molecules of water4 ,he imagines a single drop of water to be magnified until it becomes as large as the earth1 having a diameter of #hjjj miles1 and all the molecules to be magnified in the same proportion2 and he then concludes that a single molecule will appear1 under these circumstances1 as somewhat larger than a shot1 and somewhat smaller than a cricket ball4 #i4 ,whatever be the value of this conclusion1 it enables us to realize the exceedingly small size of the individual molecules of matter1 and renders it quite certain that we shall never1 by means of the most powerful microscope1 succeed in making visible these ultimate molecules4 ,for our knowledge of the sizes1 shapes1 and properties of such bodies1 we must always1 therefore1 be indebted to indirect evidence of a very complicated nature4 ,it thus appears that we know little or nothing about the shape or size of molecules1 or about the forces which actuate them2 and1 moreover1 the very largest masses of the universe share with the very smallest this property of being beyond the direct scrutiny of the human senses--the one set because they are so far away1 and the other because they are so small4 #aj4 ,again1 these molecules are not at rest1 but1 on the contrary1 they display an intense and ceaseless energy in their motions4 ,there is1 indeed1 an uninterrupted warfare going on--a constant clashing together of these minute bodies1 which are continually maimed1 and yet always recover themselves1 until1 perhaps1 some blow is struck sufficiently powerful to dissever the two or more simple atoms that go to form a compound molecule4 ,a new state of things thenceforward is the result4 ,but a simple elementary atom is truly an immortal being1 and enjoys the privilege of remaining unaltered and essentially unaffected amid the most powerful blows that can be dealt against it--it is probably in a state of ceaseless activity and change of form1 but it is nevertheless always the same4 #aa4 ,now1 a little reflection will convince us that we have in this ceaseless activity another barrier to an intimate acquaintance with molecules and atoms1 for even if we could see them they would not remain at rest sufficiently long to enable us to scrutinize them4 ,no doubt there are devices by means of which we can render visible1 for instance1 the pattern of a quickly revolving coloured disc1 for we may illuminate it by a flash of electricity1 and the disc may be supposed to be stationary during the extremely short time of the flash4 ,but we cannot say the same about molecules and atoms1 for1 could we see an atom1 and could we illuminate it by a flash of electricity1 the atom would most probably have vibrated many times during the exceedingly small time of the flash4 ,in fine1 the limits placed upon our senses1 with respect to space and time1 equally preclude the possibility of our ever becoming directly acquainted with these exceedingly minute bodies1 which are nevertheless the raw materials of which the whole universe is built4 ,action and ,reaction1 ,equal and ,opposite4 #ab4 ,but while an impenetrable veil is drawn over the individual in this warfare of clashing atoms1 yet we are not left in profound ignorance of the laws which determine the ultimate result of all these motions1 taken together as a whole4 ,in a ,vessel of ,goldfish4 ,let us suppose1 for instance1 that we have a glass globe containing numerous goldfish standing on the table1 and delicately poised on wheels1 so that the slightest push1 the one way or the other1 would make it move4 ,these goldfish are in active and irregular motion1 and he would be a very bold man who should venture to predict the movements of an individual fish4 ,but of one thing we may be quite certain3 we may rest assured that1 notwithstanding all the irregular motions of its living inhabitants1 the globe containing the goldfish will remain at rest upon its wheels4 ,even if the table were a lake of ice1 and the wheels were extremely delicate1 we should find that the globe would remain at rest4 ,indeed1 we should be exceedingly surprised if we found the globe going away of its own accord from the one side of the table to the other1 or from the one side of a sheet of ice to the other1 in consequence of the internal motions of its inhabitants4 ,whatever be the motions of these individual units1 yet we feel sure that the globe cannot move itself as a whole4 ,in such a system1 therefore1 and1 indeed1 in every system left to itself1 there may be strong internal forces acting between the various parts1 but these actions and reactions are equal and opposite1 so that while the small parts1 whether visible or invisible1 are in violent commotion among themselves1 yet the system as a whole will remain at rest4 ,in a ,rifle4 #ac4 ,now it is quite a legitimate step to pass from this instance of the goldfish to that of a rifle that has just been fired4 ,in the former case1 we imagined the globe1 together with its fishes1 to form one system2 and in the latter1 we must look upon the rifle1 with its powder and ball1 as forming one system also4 ,let us suppose that the explosion takes place through the application of a spark4 ,although this spark is an external agent1 yet if we reflect a little we shall see that its only office in this case is to summon up the internal forces already existing in the loaded rifle1 and bring them into vigorous action1 and that in virtue of these internal forces the explosion takes place4 ,the most prominent result of this explosion is the out-rush of the rifle ball with a velocity that may1 perhaps1 carry it for the best part of a mile before it comes to rest2 and here it would seem to us1 at first sight1 that the law of equal action and reaction is certainly broken1 for these internal forces present in the rifle have at least propelled part of the system1 namely1 the rifle ball1 with a most enormous velocity in one direction4 #ad4 ,but a little further reflection will bring to light another phenomenon besides the out-rush of the ball4 ,it is well known to all sportsmen that when a fowling-piece is discharged1 there is a kick or recoil of the piece itself against the shoulder of the sportsman1 which he would rather get rid of1 but which we most gladly welcome as the solution of our difficulty4 ,in plain terms1 while the ball is projected forwards1 the rifle stock 7if free to move7 is at the same moment projected backwards4 ,to fix our ideas1 let us suppose that the rifle stock weighs #ajj ounces1 and the ball one ounce1 and that the ball is projected forwards with the velocity of #ajjj feet per second2 then it is asserted1 by the law of action and reaction1 that the rifle stock is at the same time projected backwards with the velocity of #aj feet per second1 so that the mass of the stock1 multiplied by its velocity of recoil1 shall precisely equal the mass of the ball1 multiplied by its velocity of projection4 ,the one product forms a measure of the action in the one direction1 and the other of the reaction in the opposite direction1 and thus we see that in the case of a rifle1 as well as in that of the globe of fish1 action and reaction are equal and opposite4 ,in a ,falling ,stone4 #ae4 ,we may even extend the law to cases in which we do not perceive the recoil or reaction at all4 ,thus1 if ,i drop a stone from the top of a precipice to the earth1 the motion seems all to be in one direction1 while at the same time it is in truth the result of a mutual attraction between the earth and the stone4 ,does not the earth move also8 ,we cannot see it move1 but we are entitled to assert that it does in reality move upwards to meet the stone1 although quite to an imperceptible extent1 and that the law of action and reaction holds here as truly as in a rifle1 the only difference being that in the one case the two objects are rushing together1 while in the other they are rushing apart4 ,inasmuch1 however1 as the mass of the earth is very great compared with that of the stone1 it follows that its velocity must be extremely small1 in order that the mass of the earth1 multiplied into its velocity upwards1 shall equal the mass of the stone1 multiplied into its velocity downwards4 #af4 ,we have thus1 in spite of our ignorance of the ultimate atoms and molecules of matter1 arrived at a general law which regulates the action of internal forces4 ,we see that these forces are always mutually exerted1 and that if ,a attracts or repels ,b1 ,b in its turn attracts or repels ,a4 ,we have here1 in fact1 a very good instance of that kind of generalization1 which we may arrive at1 even in spite of our ignorance of individuals4 ,but having now arrived at this law of action and reaction1 do we know all that it is desirable to know8 have we got a complete understanding of what takes place in all such cases--for instance1 in that of the rifle which is just discharged8 ,let us consider this point a little further4 ,the ,rifle further considered4 #ag4 ,we define quantity of motion to mean the product of the mass by the velocity2 and since the velocity of recoil of the rifle stock1 multiplied by the mass of the stock1 is equal to the velocity of projection of the rifle ball1 multiplied by the mass of the ball1 we conceive ourselves entitled to say that the quantity of motion1 or momentum1 generated is equal in both directions1 so that the law of action and reaction holds here also4 ,nevertheless1 it cannot but occur to us that1 in some sense1 the motion of the rifle ball is a very different thing from that of the stock1 for it is one thing to allow the stock to recoil against your shoulder and discharge the ball into the air1 and a very different thing to discharge the ball against your shoulder and allow the stock to fly into the air4 ,and if any man should assert the absolute equality between the blow of the rifle stock and that of the rifle ball1 you might request him to put his assertion to this practical test1 with the absolute certainty that he would decline4 ,equality between the two6--,impossible6 ,why1 if this were the case1 a company of soldiers engaged in war would suffer much more than the enemy against whom they fired1 for the soldiers would certainly feel each recoil1 while the enemy would suffer from only a small proportion of the bullets4 ,the ,rifle ,ball possesses ,energy4 #ah4 ,now1 what is the meaning of this great difference between the two8 ,we have a vivid perception of a mighty difference1 and it only remains for us to clothe our naked impressions in a properly fitting scientific garb4 ,the something which the rifle ball possesses in contradistinction to the rifle stock is clearly the power of overcoming resistance4 ,it can penetrate through oak wood or through water1 or 7alas6 that it should be so often tried7 through the human body1 and this power of penetration is the distinguishing characteristic of a substance moving with very great velocity4 #ai4 ,let us define by the term energy this power which the rifle ball possesses of overcoming obstacles or of doing work4 ,of course we use the word work without reference to the moral character of the thing done1 and conceive ourselves entitled to sum up1 with perfect propriety and innocence1 the amount of work done in drilling a hole through a deal board or through a man4 #bj4 ,a body such as a rifle ball1 moving with very great velocity1 has1 therefore1 energy1 and it requires very little consideration to perceive that this energy will be proportional to its weight or mass1 for a ball of two ounces moving with the velocity of #ajjj feet per second will be the same as two balls of one ounce moving with this velocity1 but the energy of two similarly moving ounce balls will manifestly be double that of one1 so that the energy is proportional to the weight1 if we imagine that1 meanwhile1 the velocity remains the same4 #ba4 ,but1 on the other hand1 the energy is not simply proportional to the velocity1 for1 if it were1 the energy of the rifle stock and of the rifle ball would be the same1 inasmuch as the rifle stock would gain as much by its superior mass as it would lose by its inferior velocity4 ,therefore1 the energy of a moving body increases with the velocity more quickly than a simple proportion1 so that if the velocity be doubled1 the energy is more than doubled4 ,now1 in what manner does the energy increase with the velocity8 ,that is the question we have now to answer1 and1 in doing so1 we must appeal to the familiar facts of everyday observation and experience4 #bb4 ,in the first place1 it is well known to artillerymen1 that if a ball have a double velocity1 its penetrating power or energy is increased nearly fourfold1 so that it will pierce through four1 or nearly four1 times as many deal boards as the ball with only a single velocity--in other words1 they will tell us in mathematical language1 that the energy varies as the square of the velocity4 ,definition of ,work4 #bc4 ,and now1 before proceeding further1 it will be necessary to tell our readers how to measure work in a strictly scientific manner4 ,we have defined energy to be the power of doing work1 and although every one has a general notion of what is meant by work1 that notion may not be sufficiently precise for the purpose of this volume4 ,how1 then1 are we to measure work8 ,fortunately1 we have not far to go for a practical means of doing this4 ,indeed1 there is a force at hand which enables us to accomplish this measurement with the greatest precision1 and this force is gravity4 ,now1 the first operation in any kind of numerical estimate is to fix upon our unit or standard4 ,thus we say a rod is so many inches long1 or a road so many miles long4 ,here an inch and a mile are chosen as our standards4 ,in like manner1 we speak of so many seconds1 or minutes1 or hours1 or days1 or years1 choosing that standard of time or duration which is most convenient for our purpose4 ,so in like manner we must choose our unit of work1 but in order to do so we must first of all choose our units of weight and of length1 and for these we will take the kilogramme and the metre1 these being the units of the metrical system4 ,the kilogramme corresponds to about #ae1dcbce ,english grains1 being rather more than two pounds avoirdupois1 and the metre to about #cicga ,english inches4 ,now1 if we raise a kilogramme weight one metre in vertical height1 we are conscious of putting forth an effort to do so1 and of being resisted in the act by the force of gravity4 ,in other words1 we spend energy and do work in the process of raising this weight4 ,let us agree to consider the energy spent1 or the work done1 in this operation as one unit of work1 and let us call it the kilogrammetre4 #bd4 ,in the next place1 it is very obvious that if we raise the kilogramme two metres in height1 we do two units of work--if three metres1 three units1 and so on4 ,and again1 it is equally obvious that if we raise a weight of two kilogrammes one metre high1 we likewise do two units of work1 while if we raise it two metres high1 we do four units1 and so on4 ,from these examples we are entitled to derive the following rule3--,multiply the weight raised 7in kilogrammes7 by the vertical height 7in metres7 through which it is raised1 and the result will be the work done 7in kilogrammetres74 ,relation between ,velocity and ,energy4 #be4 ,having thus laid a numerical foundation for our superstructure1 let us next proceed to investigate the relation between velocity and energy4 ,but first let us say a few words about velocity4 ,this is one of the few cases in which everyday experience will aid1 rather than hinder1 us in our scientific conception4 ,indeed1 we have constantly before us the example of bodies moving with variable velocities4 ,thus a railway train is approaching a station and is just beginning to slacken its pace4 ,when we begin to observe1 it is moving at the rate of forty miles an hour4 ,a minute afterwards it is moving at the rate of twenty miles only1 and a minute after that it is at rest4 ,for no two consecutive moments has this train continued to move at the same rate1 and yet we may say1 with perfect propriety1 that at such a moment the train was moving1 say1 at the rate of thirty miles an hour4 ,we mean1 of course1 that had it continued to move for an hour with the speed which it had when we made the observation1 it would have gone over thirty miles4 ,we know that1 as a matter of fact1 it did not move for two seconds at that rate1 but this is of no consequence1 and hardly at all interferes with our mental grasp of the problem1 so accustomed are we all to cases of variable velocity4 #bf4 ,let us now imagine a kilogramme weight to be shot vertically upwards1 with a certain initial velocity--let us say1 with the velocity of #ih metres in one second4 ,gravity will1 of course1 act against the weight1 and continually diminish its upward speed1 just as in the railway train the break was constantly reducing the velocity4 ,but yet it is very easy to see what is meant by an initial velocity of #ih metres per second2 it means that if gravity did not interfere1 and if the air did not resist1 and1 in fine1 if no external influence of any kind were allowed to act upon the ascending mass1 it would be found to move over #ih metres in one second4 ,now1 it is well known to those who have studied the laws of motion1 that a body1 shot upwards with the velocity of #ih metres in one second1 will be brought to rest when it has risen #di metres in height4 ,if1 therefore1 it be a kilogramme1 its upward velocity will have enabled it to raise itself #di metres in height against the force of gravity1 or1 in other words1 it will have done #di units of work2 and we may imagine it1 when at the top of its ascent1 and just about to turn1 caught in the hand and lodged on the top of a house1 instead of being allowed to fall again to the ground4 ,we are1 therefore1 entitled to say that a kilogramme1 shot upwards with the velocity of #ih metres per second1 has energy equal to #di1 inasmuch as it can raise itself #di metres in height4 #bg4 ,let us next suppose that the velocity with which the kilogramme is shot upwards is that of #aif metres per second4 ,it is known to all who have studied dynamics that the kilogramme will now mount not only twice1 but four times as high as it did in the last instance--in other words1 it will now mount #aif metres in height4 ,evidently1 then1 in accordance with our principles of measurement1 the kilogramme has now four times as much energy as it had in the last instance1 because it can raise itself four times as high1 and therefore do four times as much work1 and thus we see that the energy is increased four times by doubling the velocity4 ,had the initial velocity been three times that of the first instance1 or #bid metres per second1 it might in like manner be shown that the height attained would have been #dda metres1 so that by tripling the velocity the energy is increased nine times4 #bh4 ,we thus see that whether we measure the energy of a moving body by the thickness of the planks through which it can pierce its way1 or by the height to which it can raise itself against gravity1 the result arrived at is the same4 ,we find the energy to be proportional to the square of the velocity1 and we may formularize our conclusion as follows3-- ,let v the initial velocity expressed in metres per second1 then the energy in kilogrammetres v_/#aif4 ,of course1 if the body shot upwards weighs two kilogrammes1 then everything is doubled1 if three kilogrammes1 tripled1 and so on2 so that finally1 if we denote by m the mass of the body in kilogrammes1 we shall have the energy in kilogrammetres mv_/#aif4 ,to test the truth of this formula1 we have only to apply it to the cases described in ,arts4 #bf and #bg4 #bi4 ,we may further illustrate it by one or two examples4 ,for instance1 let it be required to find the energy contained in a mass of five kilogrammes1 shot upwards with the velocity of #bj metres per second4 ,here we have m #e and v #bj1 hence-- ,energy #e7bj7_/7aif7 #bjjj_/7aif7 #ajbjd nearly4 ,again1 let it be required to find the height to which the mass of the last question will ascend before it stops4 ,we know that its energy is #ajbjd1 and that its mass is #e4 ,dividing #ajbjd by #e1 we obtain #bjdjh as the height to which this mass of five kilogrammes must ascend in order to do work equal to #ajbjd kilogrammetres4 #cj4 ,in what we have said we have taken no account either of the resistance or of the buoyancy of the atmosphere2 in fact1 we have supposed the experiments to be made in vacuo1 or1 if not in vacuo1 made by means of a heavy mass1 like lead1 which will be very little influenced either by the resistance or buoyancy of the air4 ,we must not1 however1 forget that if a sheet of paper1 or a feather1 be shot upwards with the velocities mentioned in our text1 they will certainly not rise in the air to nearly the height recorded1 but will be much sooner brought to a stop by the very great resistance which they encounter from the air1 on account of their great surface1 combined with their small mass4 ,on the other hand1 if the substance we make use of be a large light bag filled with hydrogen1 it will find its way upwards without any effort on our part1 and we shall certainly be doing no work by carrying it one or more metres in height--it will1 in reality1 help to pull us up1 instead of requiring help from us to cause it to ascend4 ,in fine1 what we have said is meant to refer to the force of gravity alone1 without taking into account a resisting medium such as the atmosphere1 the existence of which need not be considered in our present calculations4 #ca4 ,it should likewise be remembered1 that while the energy of a moving body depends upon its velocity1 it is independent of the direction in which the body is moving4 ,we have supposed the body to be shot upwards with a given velocity1 but it might be shot horizontally with the same velocity1 when it would have precisely the same energy as before4 ,a cannon ball1 if fired vertically upwards1 may either be made to spend its energy in raising itself1 or in piercing through a series of deal boards4 ,now1 if the same ball be fired horizontally with the same velocity it will pierce through the same number of deal boards4 ,in fine1 direction of motion is of no consequence1 and the only reason why we have chosen vertical motion is that1 in this case1 there is always the force of gravity steadily and constantly opposing the motion of the body1 and enabling us to obtain an accurate measure of the work which it does by piercing its way upwards against this force4 #cb4 ,but gravity is not the only force1 and we might measure the energy of a moving body by the extent to which it would bend a powerful spring or resist the attraction of a powerful magnet1 or1 in fine1 we might make use of the force which best suits our purpose4 ,if this force be a constant one1 we must measure the energy of the moving body by the space which it is able to traverse against the action of the force--just as1 in the case of gravity1 we measured the energy of the body by the space through which it was able to raise itself against its own weight4 #cc4 ,we must1 of course1 bear in mind that if this force be more powerful than gravity1 a body moved a short distance against it will represent the expenditure of as much energy as if it were moved a greater distance against gravity4 ,in fine1 we must take account both of the strength of the force and of the distance moved over by the body against it before we can estimate in an accurate matter the work which has been done4 ,,footnotes3 #a ,it is said that there are one or two instances where the microscope has enlarged them into visibility4 #b ,see ,dr4 ,angus ,smith on ,air and ,rain4 ,,chapter ,,ii4 ,,mechanical ,,energy ,,and ,,its ,,change ,,into ,,heat4 ,energy of ,position4 ,a ,stone high up4 #cd4 ,in the last chapter it was shown what is meant by energy1 and how it depends upon the velocity of a moving body2 and now let us state that this same energy or power of doing work may nevertheless be possessed by a body absolutely at rest4 ,it will be remembered 7,art4 #bf7 that in one case where a kilogramme was shot vertically upwards1 we supposed it to be caught at the summit of its flight and lodged on the top of a house4 ,here1 then1 it rests without motion1 but yet not without the power of doing work1 and hence not without energy4 ,for we know very well that if we let it fall it will strike the ground with as much velocity1 and1 therefore1 with as much energy1 as it had when it was originally projected upwards4 ,or we may1 if we choose1 make use of its energy to assist us in driving in a pile1 or utilize it in a multitude of ways4 ,in its lofty position it is1 therefore1 not without energy1 but this is of a quiet nature1 and not due in the least to motion4 ,to what1 then1 is it due8 ,we reply--to the position which the kilogramme occupies at the top of the house4 ,for just as a body in motion is a very different thing 7as regards energy7 from a body at rest1 so is a body at the top of a house a very different thing from a body at the bottom4 ,to illustrate this1 we may suppose that two men of equal activity and strength are fighting together1 each having his pile of stones with which he is about to belabour his adversary4 ,one man1 however1 has secured for himself and his pile an elevated position on the top of a house1 while his enemy has to remain content with a position at the bottom4 ,now1 under these circumstances1 you can at once tell which of the two will gain the day--evidently the man on the top of the house1 and yet not on account of his own superior energy1 but rather on account of the energy which he derives from the elevated position of his pile of stones4 ,we thus see that there is a kind of energy derived from position1 as well as a kind derived from velocity1 and we shall1 in future1 call the former energy of position1 and the latter energy of motion4 ,a ,head of ,water4 #ce4 ,in order to vary our illustration1 let us suppose there are two mills1 one with a large pond of water near it and at a high level1 while the other has also a pond1 but at a lower level than itself4 ,we need hardly ask which of the two is likely to work--clearly the one with the pond at a low level can derive from it no advantage whatever1 while the other may use the high level pond1 or head of water1 as this is sometimes called1 to drive its wheel1 and do its work4 ,there is1 thus1 a great deal of work to be got out of water high up--real substantial work1 such as grinding corn or thrashing it1 or turning wood or sawing it4 ,on the other hand1 there is no work at all to be got from a pond of water that is low down4 ,a ,cross-bow bent4 ,a ,watch wound up4 #cf4 ,in both of the illustrations now given1 we have used the force of gravity as that force against which we are to do work1 and in virtue of which a stone high up1 or a head of water1 is in a position of advantage1 and has the power of doing work as it falls to a lower level4 ,but there are other forces besides gravity1 and1 with respect to these1 bodies may be in a position of advantage and be able to do work just as truly as the stone1 or the head of water1 in the case before mentioned4 ,let us take1 for instance1 the force of elasticity1 and consider what happens in a cross-bow4 ,when this is bent1 the bolt is evidently in a position of advantage with regard to the elastic force of the bow2 and when it is discharged1 this energy of position of the bolt is converted into energy of motion1 just as1 when a stone on the top of a house is allowed to fall1 its energy of position is converted into that of actual motion4 ,in like manner a watch wound up is in a position of advantage with respect to the elastic force of the mainspring1 and as the wheels of the watch move this is gradually converted into energy of motion4 ,advantage of ,position4 #cg4 ,it is1 in fact1 the fate of all kinds of energy of position to be ultimately converted into energy of motion4 ,the former may be compared to money in a bank1 or capital1 the latter to money which we are in the act of spending2 and just as1 when we have money in a bank1 we can draw it out whenever we want it1 so1 in the case of energy of position1 we can make use of it whenever we please4 ,to see this more clearly1 let us compare together a watermill driven by a head of water1 and a windmill driven by the wind4 ,in the one case we may turn on the water whenever it is most convenient for us1 but in the other we must wait until the wind happens to blow4 ,the former has all the independence of a rich man2 the latter1 all the obsequiousness of a poor one4 ,if we pursue the analogy a step further1 we shall see that the great capitalist1 or the man who has acquired a lofty position1 is respected because he has the disposal of a great quantity of energy2 and that whether he be a nobleman or a sovereign1 or a general in command1 he is powerful only from having something which enables him to make use of the services of others4 ,when the man of wealth pays a labouring man to work for him1 he is in truth converting so much of his energy of position into actual energy1 just as a miller lets out a portion of his head of water in order to do some work by its means4 ,transmutations of ,visible ,energy4--,a ,kilogramme shot upwards4 #ch4 ,we have thus endeavoured to show that there is an energy of repose as well as a living energy1 an energy of position as well as of motion2 and now let us trace the changes which take place in the energy of a weight1 shot vertically upwards1 as it continues to rise4 ,it starts with a certain amount of energy of motion1 but as it ascends1 this is by degrees changed into that of position1 until1 when it gets to the top of its flight1 its energy is entirely due to position4 ,to take an example1 let us suppose that a kilogramme is projected vertically upwards with the velocity of #aif metres in one second4 ,according to the formula of ,art4 #bh1 it contains #aif units of energy due to its actual velocity4 ,if we examine it at the end of one second1 we shall find that it has risen #adg metres in height1 and has now the velocity of #ih4 ,this velocity we know 7,art4 #bf7 denotes an amount of actual energy equal to #di1 while the height reached corresponds to an energy of position equal to #adg4 ,the kilogramme has1 therefore1 at this moment a total energy of #aif1 of which #adg units are due to position1 and #di to actual motion4 ,if we next examine it at the end of another second1 we shall find that it has just been brought to rest1 so that its energy of motion is nil2 nevertheless1 it has succeeded in raising itself #aif metres in height1 so that its energy of position is #aif4 ,there is1 therefore1 no disappearance of energy during the rise of the kilogramme1 but merely a gradual change from one kind to another4 ,it starts with actual energy1 and this is gradually changed into that of position2 but if1 at any stage of its ascent1 we add together the actual energy of the kilogramme1 and that due to its position1 we shall find that their sum always remains the same4 #ci4 ,precisely the reverse takes place when the kilogramme begins its descent4 ,it starts on its downward journey with no energy of motion whatever1 but with a certain amount of energy of position2 as it falls1 its energy of position becomes less1 and its actual energy greater1 the sum of the two remaining constant throughout1 until1 when it is about to strike the ground1 its energy of position has been entirely changed into that of actual motion1 and it now approaches the ground with the velocity1 and1 therefore1 with the energy1 which it had when it was originally projected upwards4 ,the ,inclined ,plane4 #dj4 ,we have thus traced the transmutations1 as regards energy1 of a kilogramme shot vertically upwards1 and allowed to fall again to the earth1 and we may now vary our hypothesis by making the kilogramme rise vertically1 but descend by means of a smooth inclined plane without friction--imagine in fact1 the kilogramme to be shaped like a ball or roller1 and the plane to be perfectly smooth4 ,now1 it is well known to all students of dynamics1 that in such a case the velocity which the kilogramme has when it has reached the bottom of the plane will be equal to that which it would have had if it had been dropped down vertically through the same height1 and thus1 by introducing a smooth inclined plane of this kind1 you neither gain nor lose anything as regards energy4 ,in the first place1 you do not gain1 for think what would happen if the kilogramme1 when it reached the bottom of the inclined plane1 should have a greater velocity than you gave it originally1 when you shot it up4 ,it would evidently be a profitable thing to shoot up the kilogramme vertically1 and bring it down by means of the plane1 for you would get back more energy than you originally spent upon it1 and in every sense you would be a gainer4 ,you might1 in fact1 by means of appropriate apparatus1 convert the arrangement into a perpetual motion machine1 and go on accumulating energy without limit--but this is not possible4 ,on the other hand1 the inclined plane1 unless it be rough and angular1 will not rob you of any of the energy of the kilogramme1 but will restore to you the full amount1 when once the bottom has been reached4 ,nor does it matter what be the length or shape of the plane1 or whether it be straight1 or curved1 or spiral1 for in all cases1 if it only be smooth and of the same vertical height1 you will get the same amount of energy by causing the kilogramme to fall from the top to the bottom4 #da4 ,but while the energy remains the same1 the time of descent will vary according to the length and shape of the plane1 for evidently the kilogramme will take a longer time to descend a very sloping plane than a very steep one4 ,in fact1 the sloping plane will take longer to generate the requisite velocity than the steep one1 but both will have produced the same result as regards energy1 when once the kilogramme has arrived at the bottom4 ,functions of a ,machine4 #db4 ,our readers are now beginning to perceive that energy cannot be created1 and that by no means can we coax or cozen ,dame ,nature into giving us back more than we are entitled to get4 ,to impress this fundamental principle still more strongly upon our minds1 let us consider in detail one or two mechanical contrivances1 and see what they amount to as regards energy4 ,illustration3 ,fig4 #a4 ,let us begin with the second system of pulleys4 ,here we have a power ,p attached to the one end of a thread1 which passes over all the pulleys1 and is ultimately attached1 by its other extremity1 to a hook in the upper or fixed block4 ,the weight ,w is1 on the other hand1 attached to the lower or moveable block1 and rises with it4 ,let us suppose that the pulleys are without weight and the cords without friction1 and that ,w is supported by six cords1 as in the figure4 ,now1 when there is equilibrium in this machine1 it is well known that ,w will be equal to six times ,p2 that is to say1 a power of one kilogramme will1 in such a machine1 balance or support a weight of six kilogrammes4 ,if ,p be increased a single grain more1 it will overbalance ,w1 and ,p will descend1 while ,w will begin to rise4 ,in such a case1 after ,p has descended1 say six metres1 its weight being1 say1 one kilogramme1 it has lost a quantity of energy of position equal to six units1 since it is at a lower level by six metres than it was before4 ,we have1 in fact1 expended upon our machine six units of energy4 ,now1 what return have we received for this expenditure8 ,our return is clearly the rise of ,w1 and mechanicians will tell us that in this case ,w will have risen one metre4 ,but the weight of ,w is six kilogrammes1 and this having been raised one metre represents an energy of position equal to six4 ,we have thus spent upon our machine1 in the fall of ,p1 an amount of energy equal to six units1 and obtained in the rise of ,w an equivalent amount equal to six units also4 ,we have1 in truth1 neither gained nor lost energy1 but simply changed it into a form more convenient for our use4 ,illustration3 ,fig4 #b4 #dc4 ,to impress this truth still more strongly1 let us take quite a different machine1 such as the hydrostatic press4 ,its mode of action will be perceived from ,fig4 #b4 ,here we have two cylinders1 a wide and a narrow one1 which are connected together at the bottom by means of a strong tube4 ,each of these cylinders is provided with a water-tight piston1 the space beneath being filled with water4 ,it is therefore manifest1 since the two cylinders are connected together1 and since water is incompressible1 that when we push down the one piston the other will be pushed up4 ,let us suppose that the area of the small piston is one square centimetre1#c and that of the large piston one hundred square centimetres1 and let us apply a weight of ten kilogrammes to the smaller piston4 ,now1 it is known1 from the laws of hydrostatics1 that every square centimetre of the larger piston will be pressed upwards with the force of ten kilogrammes1 so that the piston will altogether mount with the force of #ajjj kilogrammes--that is to say1 it will raise a weight of this amount as it ascends4 ,here1 then1 we have a machine in virtue of which a pressure of ten kilogrammes on the small piston enables the large piston to rise with the force of #ajjj kilogrammes4 ,but it is very easy to see that1 while the small piston falls one metre1 the large one will only rise one centimetre4 ,for the quantity of water under the pistons being always the same1 if this be pushed down one metre in the narrow cylinder1 it will only rise one centimetre in the wide one4 ,let us now consider what we gain by this machine4 ,the power of ten kilogrammes applied to the smaller piston is made to fall through one metre1 and this represents the amount of energy which we have expended upon our machine1 while1 as a return1 we obtain #ajjj kilogrammes raised through one single centimetre4 ,here1 then1 as in the case of the pulleys1 the return of energy is precisely the same as the expenditure1 and1 provided we ignore friction1 we neither gain nor lose anything by the machine4 ,all that we do is to transmute the energy into a more convenient form--what we gain in power we lose in space2 but we are willing to sacrifice space or quickness of motion in order to obtain the tremendous pressure or force which we get by means of the hydrostatic press4 ,principle of ,virtual ,velocities4 #dd4 ,these illustrations will have prepared our readers to perceive the true function of a machine4 ,this was first clearly defined by ,galileo1 who saw that in any machine1 no matter of what kind1 if we raise a large weight by means of a small one1 it will be found that the small weight1 multiplied into the space through which it is lowered1 will exactly equal the large weight1 multiplied into that through which it is raised4 ,this principle1 known as that of virtual velocities1 enables us to perceive at once our true position4 ,we see that the world of mechanism is not a manufactory1 in which energy is created1 but rather a mart1 into which we may bring energy of one kind and change or barter it for an equivalent of another kind1 that suits us better--but if we come with nothing in our hand1 with nothing we shall most assuredly return4 ,a machine1 in truth1 does not create1 but only transmutes1 and this principle will enable us to tell1 without further knowledge of mechanics1 what are the conditions of equilibrium of any arrangement4 ,for instance1 let it be required to find those of a lever1 of which the one arm is three times as long as the other4 ,here it is evident that if we overbalance the lever by a single grain1 so as to cause the long arm with its power to fall down while the short one with its weight rises up1 then the long arm will fall three inches for every inch through which the short arm rises2 and hence1 to make up for this1 a single kilogramme on the long arm will balance three kilogrammes on the short one1 or the power will be to the weight as one is to three4 ,illustration3 ,fig4 #c4 #de4 ,or1 again1 let us take the inclined plane as represented in ,fig4 #c4 ,here we have a smooth plane and a weight held upon it by means of a power ,p1 as in the figure4 ,now1 if we overbalance ,p by a single grain1 we shall bring the weight ,w from the bottom to the top of the plane4 ,but when this has taken place1 it is evident that ,p has fallen through a vertical distance equal to the length of the plane1 while on the other hand ,w has only risen through a vertical distance equal to the height4 ,hence1 in order that the principle of virtual velocities shall hold1 we must have ,p multiplied into its fall equal to ,w multiplied into its rise1 that is to say1 ,p ,length of plane ,w ,height of plane1 or ,p_/,w 7,height47_/7,length47 ,what ,friction does4 #df4 ,the two examples now given are quite sufficient to enable our readers to see the true function of a machine1 and they are now doubtless disposed to acknowledge that no machine will give back more energy than is spent upon it4 ,it is not1 however1 equally clear that it will not give back less2 indeed1 it is a well-known fact that it constantly does so4 ,for we have supposed our machine to be without friction--but no machine is without friction--and the consequence is that the available out-come of the machine is more or less diminished by this drawback4 ,now1 unless we are able to see clearly what part friction really plays1 we cannot prove the conservation of energy4 ,we see clearly enough that energy cannot be created1 but we are not equally sure that it cannot be destroyed2 indeed1 we may say we have apparent grounds for believing that it is destroyed--that is our present position4 ,now1 if the theory of the conservation of energy be true--that is to say1 if energy is in any sense indestructible--friction will prove itself to be1 not the destroyer of energy1 but merely the converter of it into some less apparent and perhaps less useful form4 #dg4 ,we must1 therefore1 prepare ourselves to study what friction really does1 and also to recognize energy in a form remote from that possessed by a body in visible motion1 or by a head of water4 ,to friction we may add percussion1 as a process by which energy is apparently destroyed2 and as we have 7,art4 #ci7 considered the case of a kilogramme shot vertically upwards1 demonstrating that it will ultimately reach the ground with an energy equal to that with which it was shot upwards1 we may pursue the experiment one step further1 and ask what becomes of its energy after it has struck the ground and come to rest8 ,we may vary the question by asking what becomes of the energy of the smith's blow after his hammer has struck the anvil1 or what of the energy of the cannon ball after it has struck the target1 or what of that of the railway train after it has been stopped by friction at the break-wheel8 ,all these are cases in which percussion or friction appears at first sight to have destroyed visible energy2 but before pronouncing upon this seeming destruction1 it clearly behoves us to ask if anything else makes its appearance at the moment when the visible energy is apparently destroyed4 ,for1 after all1 energy may be like the ,eastern magicians1 of whom we read that they had the power of changing themselves into a variety of forms1 but were nevertheless very careful not to disappear altogether4 ,when ,motion is destroyed1 ,heat appears4 #dh4 ,now1 in reply to the question we have put1 it may be confidently asserted that whenever visible energy is apparently destroyed by percussion or friction1 something else makes its appearance1 and that something is heat4 ,thus1 a piece of lead placed upon an anvil may be greatly heated by successive blows of a blacksmith's hammer4 ,the collision of flint and steel will produce heat1 and a rapidly-moving cannon ball1 when striking against an iron target1 may even be heated to redness4 ,again1 with regard to friction1 we know that on a dark night sparks are seen to issue from the break-wheel which is stopping a railway train1 and we know1 also1 that the axles of railway carriages get alarmingly hot1 if they are not well supplied with grease4 ,finally1 the schoolboy will tell us that he is in the habit of rubbing a brass button upon the desk1 and applying it to the back of his neighbour's hand1 and that when his own hand has been treated in this way1 he has found the button unmistakeably hot4 ,heat a species of ,motion4 #di4 ,for a long time this appearance of heat by friction or percussion was regarded as inexplicable1 because it was believed that heat was a kind of matter1 and it was difficult to understand where all this heat came from4 ,the partisans of the material hypothesis1 no doubt1 ventured to suggest that in such processes heat might be drawn from the neighbouring bodies1 so that the ,caloric 7which was the name given to the imaginary substance of heat7 was squeezed or rubbed out of them1 according as the process was percussion or friction4 ,but this was regarded by many as no explanation1 even before ,sir ,humphry ,davy1 about the end of last century1 clearly showed it to be untenable4 #ej4 ,davy's experiments consisted in rubbing together two pieces of ice until it was found that both were nearly melted1 and he varied the conditions of his experiments in such a manner as to show that the heat produced in this case could not be abstracted from the neighbouring bodies4 #ea4 ,let us pause to consider the alternatives to which we are driven by this experiment4 ,if we still choose to regard heat as a substance1 since this has not been taken from the surrounding bodies1 it must necessarily have been created in the process of friction4 ,but if we choose to regard heat as a species of motion1 we have a simpler alternative1 for1 inasmuch as the energy of visible motion has disappeared in the process of friction1 we may suppose that it has been transformed into a species of molecular motion1 which we call heat2 and this was the conclusion to which ,davy came4 #eb4 ,about the same time another philosopher was occupied with a similar experiment4 ,count ,rumford was superintending the boring of cannon at the arsenal at ,munich1 and was forcibly struck with the very great amount of heat caused by this process4 ,the source of this heat appeared to him to be absolutely inexhaustible1 and1 being unwilling to regard it as the creation of a species of matter1 he was led like ,davy to attribute it to motion4 #ec4 ,assuming1 therefore1 that heat is a species of motion1 the next point is to endeavour to comprehend what kind of motion it is1 and in what respects it is different from ordinary visible motion4 ,to do this1 let us imagine a railway carriage1 full of passengers1 to be whirling along at a great speed1 its occupants quietly at ease1 because1 although they are in rapid motion1 they are all moving at the same rate and in the same direction4 ,now1 suppose that the train meets with a sudden check2--a disaster is the consequence1 and the quiet placidity of the occupants of the carriage is instantly at an end4 ,even if we suppose that the carriage is not broken up and its occupants killed1 yet they are all in a violent state of excitement2 those fronting the engine are driven with force against their opposite neighbours1 and are1 no doubt1 as forcibly repelled1 each one taking care of himself in the general scramble4 ,now1 we have only to substitute particles for persons1 in order to obtain an idea of what takes place when percussion is converted into heat4 ,we have1 or suppose we have1 in this act the same violent collision of atoms1 the same thrusting forward of ,a upon ,b1 and the same violence in pushing back on the part of ,b--the same struggle1 confusion1 and excitement--the only difference being that particles are heated instead of human beings1 or their tempers4 #ed4 ,we are bound to acknowledge that the proof which we have now given is not a direct one2 indeed1 we have1 in our first chapter1 explained the impossibility of our ever seeing these individual particles1 or watching their movements2 and hence our proof of the assertion that heat consists in such movements cannot possibly be direct4 ,we cannot see that it does so consist1 but yet we may feel sure1 as reasonable beings1 that we are right in our conjecture4 ,in the argument now given1 we have only two alternatives to start with--either heat must consist of a motion of particles1 or1 when percussion or friction is converted into heat1 a peculiar substance called caloric must be created1 for if heat be not a species of motion it must necessarily be a species of matter4 ,now1 we have preferred to consider heat as a species of motion to the alternative of supposing the creation of a peculiar kind of matter4 #ee4 ,nevertheless1 it is desirable to have something to say to an opponent who1 rather than acknowledge heat to be a species of motion1 will allow the creation of matter4 ,to such an one we would say that innumerable experiments render it certain that a hot body is not sensibly heavier than a cold one1 so that if heat be a species of matter it is one that is not subject to the law of gravity4 ,if we burn iron wire in oxygen gas1 we are entitled to say that the iron combines with the oxygen1 because we know that the product is heavier than the original iron by the very amount which the gas has lost in weight4 ,but there is no such proof that during combustion the iron has combined with a substance called caloric1 and the absence of any such proof is enough to entitle us to consider heat to be a species of motion1 rather than a species of matter4 ,heat a ,backward and ,forward ,motion4 #ef4 ,we shall now suppose that our readers have assented to our proposition that heat is a species of motion4 ,it is almost unnecessary to add that it must be a species of backward and forward motion2 for nothing is more clear than that a heated substance is not in motion as a whole1 and will not1 if put upon a table1 push its way from the one end to the other4 ,mathematicians express this peculiarity by saying that1 although there is violent internal motion among the particles1 yet the centre of gravity of the substance remains at rest2 and since1 for most purposes1 we may suppose a body to act as if concentrated at its centre of gravity1 we may say that the body is at rest4 #eg4 ,let us here1 before proceeding further1 borrow an illustration from that branch of physics which treats of sound4 ,suppose1 for instance1 that a man is accurately balanced in a scale-pan1 and that some water enters his ear2 of course he will become heavier in consequence1 and if the balance be sufficiently delicate1 it will exhibit the difference4 ,but suppose a sound or a noise enters his ear1 he may say with truth that something has entered1 but yet that something is not matter1 nor will he become one whit heavier in consequence of its entrance1 and he will remain balanced as before4 ,now1 a man into whose ear sound has entered may be compared to a substance into which heat has entered2 we may therefore suppose a heated body to be similar in many respects to a sounding body1 and just as the particles of a sounding body move backwards and forwards1 so we may suppose that the particles of a heated body do the same4 ,we shall take another opportunity 7,art4 #afb7 to enlarge upon this likeness2 but1 meanwhile1 we shall suppose that our readers perceive the analogy4 ,mechanical ,equivalent of ,heat4 #eh4 ,we have thus come to the conclusion that when any heavy body1 say a kilogramme weight1 strikes the ground1 the visible energy of the kilogramme is changed into heat2 and now1 having established the fact of a relationship between these two forms of energy1 our next point is to ascertain according to what law the heating effect depends upon the height of fall4 ,let us1 for instance1 suppose that a kilogramme of water is allowed to drop from the height of #hdh metres1 and that we have the means of confining to its own particles and retaining there the heating effect produced4 ,now1 we may suppose that its descent is accomplished in two stages2 that1 first of all1 it falls upon a platform from the height of #dbd metres1 and gets heated in consequence1 and that then the heated mass is allowed to fall other #dbd metres4 ,it is clear that the water will now be doubly heated2 or1 in other words1 the heating effect in such a case will be proportional to the height through which the body falls--that is to say1 it will be proportional to the actual energy which the body possesses before the blow has changed this into heat4 ,in fact1 just as the actual energy represented by a fall from a height is proportional to the height1 so is the heating effect1 or molecular energy1 into which the actual energy is changed proportional to the height also4 ,having established this point1 we now wish to know through how many metres a kilogramme of water must fall in order to be heated one degree centigrade4 #ei4 ,for a precise determination of this important point1 we are indebted to ,dr4 ,joule1 of ,manchester1 who has1 perhaps1 done more than any one else to put the science of energy upon a sure foundation4 ,dr4 ,joule made numerous experiments1 with the view of arriving at the exact relation between mechanical energy and heat2 that is to say1 of determining the mechanical equivalent of heat4 ,in some of the most important of these he took advantage of the friction of fluids4 ,illustration3 ,fig4 #d4 #fj4 ,these experiments were conducted in the following manner4 ,a certain fixed weight was attached to a pulley1 as in the figure4 ,the weight had1 of course1 a tendency to descend1 and hence to turn the pulley round4 ,the pulley had its axle supported upon friction wheels1 at f and f1 by means of which the friction caused by the movement of the pulley was very much reduced4 ,a string1 passing over the circumference of the pulley1 was wrapped round r1 so that1 as the weight descended1 the pulley moved round1 and the string of the pulley caused r to rotate very rapidly4 ,now1 the motion of the axis r was conducted within the covered box ,b1 where there was attached to r a system of paddles1 of which a sketch is given in figure2 and therefore1 as r moved1 these paddles moved also4 ,there were1 altogether1 eight sets of these paddles revolving between four stationary vanes4 ,if1 therefore1 the box were full of liquid1 the paddles and the vanes together would churn it about1 for these stationary vanes would prevent the liquid being carried along by the paddles in the direction of rotation4 ,now1 in this experiment1 the weight was made to descend through a certain fixed distance1 which was accurately measured4 ,as it descended1 the paddles were set in motion1 and the energy of the descending weight was thus made to churn1 and hence to heat some water contained in the box ,b4 ,when the weight had descended a certain distance1 by undoing a small peg p1 it could be wound up again without moving the paddles in ,b1 and thus the heating effect of several falls of the weight could be accumulated until this became so great as to be capable of being accurately measured by a thermometer4 ,it ought to be mentioned that great care was taken in these experiments1 not only to reduce the friction of the axles of the pulley as much as possible1 but also to estimate and correct for this friction as accurately as possible2 in fact1 every precaution was taken to make the experiment successful4 #fa4 ,other experiments were made by ,joule1 in some of which a disc was made to rotate against another disc of cast-iron pressed against it1 the whole arrangement being immersed in a cast-iron vessel filled with mercury4 ,from all these experiments1 ,dr4 ,joule concluded that the quantity of heat produced by friction1 if we can preserve and accurately measure it1 will always be found proportional to the quantity of work expended4 ,he expressed this proportion by stating the number of units of work in kilogrammetres necessary to raise by #a ,c4 the temperature of one kilogramme of water4 ,this was #dbd1 as determined by his last and most complete experiments2 and hence we may conclude that if a kilogramme of water be allowed to fall through #dbd metres1 and if its motion be then suddenly stopped1 sufficient heat will be generated to raise the temperature of the water through #a ,c41 and so on1 in the same proportion4 #fb4 ,now1 if we take the kilogrammetre as our unit of work1 and the heat necessary to raise a kilogramme of water #a ,c4 as our unit of heat1 this proportion may be expressed by saying that one heat unit is equal to #dbd units of work4 ,this number is frequently spoken of as the mechanical equivalent of heat2 and in scientific treatises it is denoted by ,j41 the initial of ,dr4 ,joule's name4 #fc4 ,we have now stated the exact relationship that subsists between mechanical energy and heat1 and before proceeding further with proofs of the great law of conservation1 we shall endeavour to make our readers acquainted with other varieties of energy1 on the ground that it is necessary to penetrate the various disguises that our magician assumes before we can pretend to explain the principles that actuate him in his transformations4 ,,footnotes3 #c ,that is to say1 a square the side of which is one centimetre1 or the hundredth part of a metre4 ,,chapter ,,iii4 ,,the ,,forces ,,and ,,energies ,,of ,,nature3 ,,the ,,law ,,of ,,conservation4 #fd4 ,in the last chapter we introduced our readers to two varieties of energy1 one of them visible1 and the other invisible or molecular2 and it will now be our duty to search through the whole field of physical science for other varieties4 ,here it is well to bear in mind that all energy consists of two kinds1 that of position and that of actual motion1 and also that this distinction holds for invisible molecular energy just as truly as it does for that which is visible4 ,now1 energy of position implies a body in a position of advantage with respect to some force1 and hence we may with propriety begin our search by investigating the various forces of nature4 ,gravitation4 #fe4 ,the most general1 and perhaps the most important1 of these forces is gravitation1 and the law of action of this force may be enunciated as follows3--,every particle of the universe attracts every other particle with a force depending jointly upon the mass of the attracting and of the attracted particle1 and varying inversely as the square of distance between the two4 ,a little explanation will make this plain4 ,suppose a particle or system of particles of which the mass is unity to be placed at a distance equal to unity from another particle or system of particles of which the mass is also unity--the two will attract each other4 ,let us agree to consider the mutual attraction between them equal to unity also4 ,suppose1 now1 that we have on the one side two such systems with a mass represented by #b1 and on the other side the same system as before1 with a mass represented by unity1 the distance1 meanwhile1 remaining unaltered4 ,it is clear the double system will now attract the single system with a twofold force4 ,let us next suppose the mass of both systems to be doubled1 the distance always remaining the same4 ,it is clear that we shall now have a fourfold force1 each unit of the one system attracting each unit of the other4 ,in like manner1 if the mass of the one system is #b1 and that of the other #c1 the force will be #f4 ,we may1 for instance1 call the components of the one system ,a#a1 ,a1 and those of the other ,a#c1 ,a#d1 ,a#e1 and we shall have ,a#a pulled towards ,a#c1 ,a#d1 and ,a#e1 with a threefold force1 and ,a pulled towards ,a#c1 ,a#d1 and ,a#e1 with a threefold force1 making altogether a force equal to #f4 ,in the next place1 let the masses remain unaltered1 but let the distance between them be doubled1 then the force will be reduced fourfold4 ,let the distance be tripled1 then the force will be reduced ninefold1 and so on4 #ff4 ,gravitation may be described as a very weak force1 capable of acting at a distance1 or at least of appearing to do so4 ,it takes the mass of the whole earth to produce the force with which we are so familiar at its surface1 and the presence of a large mass of rock or mountain does not produce any appreciable difference in the weight of any substance4 ,it is the gravitation of the earth1 lessened of course by distance1 which acts upon the moon #bdj1jjj miles away1 and the gravitation of the sun influences in like manner the earth and the various other planets of our system4 ,elastic ,forces4 #fg4 ,elastic forces1 although in their mode of action very different from gravity1 are yet due to visible arrangements of matter2 thus1 when a cross-bow is bent1 there is a visible change produced in the bow1 which1 as a whole1 resists this bending1 and tends to resume its previous position4 ,it therefore requires energy to bend a bow1 just as truly and visibly as it does to raise a weight above the earth1 and elasticity is1 therefore1 as truly a species of force as gravity is4 ,we shall not here attempt to discuss the various ways in which this force may act1 or in which a solid elastic substance will resist all attempts to deform it2 but in all cases it is clearly manifest that work must be spent upon the body1 and the force of elasticity must be encountered and overcome throughout a certain space before any sensible deformation can take place4 ,force of ,cohesion4 #fh4 ,let us now leave the forces which animate large masses of matter1 and proceed to discuss those which subsist between the smaller particles of which these large masses are composed4 ,and here we must say one word more about molecules and atoms1 and the distinction we feel ourselves entitled to draw between these very small bodies1 even although we shall never be able to see either the one or the other4 ,in our first chapter 7,art4 #g7 we supposed the continual sub-division of a grain of sand until we had arrived at the smallest entity retaining all the properties of sand--this we called a molecule1 and nothing smaller than this is entitled to be called sand4 ,if we continue this sub-division further1 the molecule of sand separates itself into its chemical constituents1 consisting of silicon on the one side1 and oxygen on the other4 ,thus we arrive at last at the smallest body which can call itself silicon1 and the smallest which can call itself oxygen1 and we have no reason to suppose that either of these is capable of sub-division into something else1 since we regard oxygen and silicon as elementary or simple bodies4 ,now1 these constituents of the silicon molecule are called atoms1 so that we say the sand molecule is divisible into atoms of silicon and of oxygen4 ,furthermore1 we have strong reason for supposing that such molecules and atoms really exist1 but into the arguments for their existence we cannot now enter--it is one of those things that we must ask our readers to take for granted4 #fi4 ,let us now take two molecules of sand4 ,these1 when near together1 have a very strong attraction for each other4 ,it is1 in truth1 this attraction which renders it difficult to break up a crystalline particle of sand or rock crystal4 ,but it is only exerted when the molecules are near enough together to form a homogeneous crystalline structure1 for let the distance between them be somewhat increased1 and we find that all attraction entirely vanishes4 ,thus there is little or no attraction between different particles of sand1 even although they are very closely packed together4 ,in like manner1 the integrity of a piece of glass is due to the attraction between its molecules2 but let these be separated by a flaw1 and it will soon be found that this very small increase of distance greatly diminishes the attraction between the particles1 and that the structure will now fall to pieces from the slightest cause4 ,now1 these examples are sufficient to show that molecular attraction or cohesion1 as this is called1 is a force which acts very powerfully through a certain small distance1 but which vanishes altogether when this distance becomes perceptible4 ,cohesion is strongest in solids1 while in liquids it is much diminished1 and in gases it may be said to vanish altogether4 ,the molecules of gases are1 in truth1 so far away from one another1 as to have little or no mutual attraction1 a fact proved by ,dr4 ,joule1 whose name was mentioned in the last chapter4 ,force of ,chemical ,affinity4 #gj4 ,let us now consider the mutual forces between atoms4 ,these may be characterized as even stronger than the forces between molecules1 but as disappearing still more rapidly when the distance is increased4 ,let us1 for instance1 take carbon and oxygen--two substances which are ready to combine together to form carbonic acid1 whenever they have a suitable opportunity4 ,in this case1 each atom of carbon will unite with two of oxygen1 and the result will be something quite different from either4 ,yet under ordinary circumstances carbon1 or its representative1 coal1 will remain unchanged in the presence of oxygen1 or of atmospheric air containing oxygen4 ,there will be no tendency to combine together1 because although the particles of the oxygen would appear to be in immediate contact with those of the carbon1 yet the nearness is not sufficient to permit of chemical affinity acting with advantage4 ,when1 however1 the nearness becomes sufficient1 then chemical affinity begins to operate4 ,we have1 in fact1 the familiar act of combustion1 and1 as its consequence1 the chemical union of the carbon or coal with the oxygen of the air1 carbonic acid being the result4 ,here1 then1 we have a very powerful force acting only at a very small distance1 which we name chemical affinity1 inasmuch as it represents the attraction exerted between atoms of different bodies in contradistinction to cohesion1 which denotes the attraction between molecules of the same body4 #ga4 ,if we regard gravitation as the representative of forces that act or appear to act1 at a distance1 we may regard cohesion and chemical affinity as the representatives of those forces which1 although very powerful1 only act or appear to act through a very small interval of distance4 ,a little reflection will show us how inconvenient it would be if gravitation diminished very rapidly with the distance2 for then even supposing that the bond which retains us to the earth were to hold good1 that which retains the moon to the earth might vanish entirely1 as well as that which retains the earth to the sun1 and the consequences would be far from pleasant4 ,reflection will also show us how inconvenient it would be if chemical affinity existed at all distances2 if coal1 for instance1 were to combine with oxygen without the application of heat1 it would greatly alter the value of this fuel to mankind1 and would materially check the progress of human industry4 ,remarks on ,molecular and ,atomic ,forces4 #gb4 ,now1 it is important to remember that we must treat cohesion and chemical affinity exactly in the same way as gravity has been treated2 and just as we have energy of position with respect to gravity1 so may we have as truly a species of energy of position with respect to cohesion and chemical affinity4 ,let us begin with cohesion4 #gc4 ,we have hitherto regarded heat as a peculiar motion of the molecules of matter1 without any reference to the force which actuates these molecules4 ,but it is a well-known fact that bodies in general expand when heated1 so that1 in virtue of this expansion1 the molecules of a body are driven violently apart against the force of cohesion4 ,work has in truth been done against this force1 just as truly as1 when a kilogramme is raised from the earth1 work is done against the force of gravity4 ,when a substance is heated1 we may1 therefore1 suppose that the heat has a twofold office to perform1 part of it going to increase the actual motions of the molecules1 and part of it to separate these molecules from one another against the force of cohesion4 ,thus1 if ,i swing round horizontally a weight 7attached to my hand by an elastic thread of india-rubber71 my energy will be spent in two ways--first of all1 it will be spent in communicating a velocity to the weight2 and1 secondly1 in stretching the india-rubber string1 by means of the centrifugal tendency of the weight4 ,work will be done against the elastic force of the string1 as well as spent in increasing the motion of the weight4 ,now1 something of this kind may be taking place when a body is heated1 for we may very well suppose heat to consist of a vertical or circular motion1 the tendency of which would be to drive the particles asunder against the force of cohesion4 ,part1 therefore1 of the energy of heat will be spent in augmenting the motion1 and part in driving asunder the particles4 ,we may1 however1 suppose that1 in ordinary cases1 the great proportion of the energy of heat goes towards increasing the molecular motion1 rather than in doing work against the force of cohesion4 #gd ,in certain cases1 however1 it is probable that the greater part of the heat applied is spent in doing work against molecular forces1 instead of increasing the motions of molecules4 ,thus1 when a solid melts1 or when a liquid is rendered gaseous1 a considerable amount of heat is spent in the process1 which does not become sensible1 that is to say1 does not affect the thermometer4 ,thus1 in order to melt a kilogramme of ice1 heat is required sufficient to raise a kilogramme of water through #hj ,c41 and yet1 when melted1 the water is no warmer than the ice4 ,we express this fact by saying that the latent heat of water is #hj4 ,again1 if a kilogramme of water at #ajj be converted entirely into steam1 as much heat is required as would raise the water through #ecg ,c41 or #ecg kilogrammes of water through one degree2 but yet the steam is no hotter than the water1 and we express this fact by saying that the latent heat of steam is #ecg4 ,now1 in both of these instances it is at least extremely probable that a large portion of the heat is spent in doing work against the force of cohesion2 and1 more especially1 when a fluid is converted into a gas1 we know that the molecules are in that process separated so far from one another as to lose entirely any trace of mutual force4 ,we may1 therefore1 conclude that although in most cases the greater portion of the heat applied to a body is spent in increasing its molecular motion1 and only a small part in doing work against cohesion1 yet when a solid melts1 or a liquid vaporizes1 a large portion of the heat required is not improbably spent in doing work against molecular forces4 ,but the energy1 though spent1 is not lost1 for when the liquid again freezes1 or when the vapour again condenses1 this energy is once more transformed into the shape of sensible heat1 just as when a stone is dropped from the top of a house1 its energy of position is transformed once more into actual energy4 #ge4 ,a single instance will suffice to give our readers a notion of the strength of molecular forces4 ,if a bar of wrought iron1 whose temperature is #aj ,c4 above that of the surrounding medium1 be tightly secured at its extremities1 it will draw these together with a force of at least one ton for each square inch of section4 ,in some cases where a building has shown signs of bulging outwards1 iron bars have been placed across it1 and secured while in a heated state to the walls4 ,on cooling1 the iron contracted with great force1 and the walls were thereby pulled together4 #gf4 ,we are next brought to consider atomic forces1 or those which lead to chemical union1 and now let us see how these are influenced by heat4 ,we have seen that heat causes a separation between the molecules of a body1 that is to say1 it increases the distance between two contiguous molecules1 but we must not suppose that1 meanwhile1 the molecules themselves are left unaltered4 ,the tendency of heat to cause separation is not confined to increasing the distance between molecules1 but acts also1 no doubt1 in increasing the distance between parts of the same molecule3 in fact1 the energy of heat is spent in pulling the constituent atoms asunder against the force of chemical affinity1 as well as in pulling the molecules asunder against the force of cohesion1 so that1 at a very high temperature1 it is probable that most chemical compounds would be decomposed1 and many are so1 even at a very moderate heat4 ,thus the attraction between oxygen and silver is so slight that at a comparatively low temperature the oxide of silver is decomposed4 ,in like manner1 limestone1 or carbonate of lime1 is decomposed when subjected to the heat of a lime-kiln1 carbonic acid being given off1 while quick-lime remains behind4 ,now1 in separating heterogeneous atoms against the powerful force of chemical affinity1 work is done as truly as it is in separating molecules from one another against the force of cohesion1 or in separating a stone from the earth against the force of gravity4 #gg4 ,heat1 as we have seen1 is very frequently influential in performing this separation1 and its energy is spent in so doing2 but other energetic agents produce chemical decomposition as well as heat4 ,for instance1 certain rays of the sun decompose carbonic acid into carbon and oxygen in the leaves of plants1 and their energy is spent in the process2 that is to say1 it is spent in pulling asunder two such powerfully attracting substances against the affinity they have for one another4 ,and1 again1 the electric current is able to decompose certain substances1 and of course its energy is spent in the process4 ,therefore1 whenever two powerfully attracting atoms are separated1 energy is spent in causing this separation as truly as in separating a stone from the earth1 and when once the separation has been accomplished we have a species of energy of position just as truly as we have in a head of water1 or in a stone at the top of a house4 #gh4 ,it is this chemical separation that is meant when we speak of coal as a source of energy4 ,coal1 or carbon1 has a great attraction for oxygen1 and whenever heat is applied the two bodies unite together4 ,now oxygen1 as it exists in the atmosphere1 is the common inheritance of all1 and if1 in addition to this1 some of us possess coal in our cellars1 or in pits1 we have thus secured a store of energy of position which we can draw upon with more facility than if it were a head of water1 for1 although we can draw upon the energy of a head of water whenever we choose1 yet we cannot carry it about with us from place to place as we can with coal4 ,we thus perceive that it is not the coal1 by itself1 that forms the source of energy1 but this is due to the fact that we have coal1 or carbon1 in one place1 and oxygen in another1 while we have also the means of causing them to unite with each other whenever we wish4 ,if there were no oxygen in the air1 coal by itself would be of no value4 ,electricity3 its ,properties4 #gi4 ,our readers have now been told about the force of cohesion that exists between molecules of the same body1 and also about that of chemical affinity existing between atoms of different bodies4 ,now1 heterogeneity is an essential element of this latter force--there must be a difference of some kind before it can exhibit itself--and under these circumstances its exhibitions are frequently characterized by very extraordinary and interesting phenomena4 ,we allude to that peculiar exhibition arising out of the forces of heterogeneous bodies which we call electricity1 and1 before proceeding further1 it may not be out of place to give a short sketch of the mode of action of this very mysterious1 but most interesting1 agent4 #hj4 ,the science of electricity is of very ancient origin2 but its beginning was very small4 ,for a couple of thousand years it made little or no progress1 and then1 during the course of little more than a century1 developed into the giant which it now is4 ,the ancient ,greeks were aware that amber1 when rubbed with silk1 had the property of attracting light bodies2 and ,dr4 ,gilbert1 about three hundred years ago1 showed that many other things1 such as sulphur1 sealing-wax1 and glass1 have the same property as amber4 ,in the progress of the science it came to be known that certain substances are able to carry away the peculiar influence produced1 while others are unable to do so2 the former are called conductors1 and the latter non-conductors1 or insulators1 of electricity4 ,to make the distinction apparent1 let us take a metal rod1 having a glass stem attached to it1 and rub the glass stem with a piece of silk1 care being taken that both silk and glass are warm and dry4 ,we shall find that the glass has now acquired the property of attracting little bits of paper1 or elder pith2 but only where it has been rubbed1 for the peculiar influence acquired by the glass has not been able to spread itself over the surface4 ,if1 however1 we take hold of the glass stem1 and rub the metal rod1 we may1 perhaps1 produce the same property in the metal1 but it will spread over the whole1 not confining itself to the part rubbed4 ,thus we perceive that metal is a conductor1 while glass is an insulator1 or non-conductor1 of electricity4 ,illustration3 ,fig4 #e4 #ha4 ,we would next observe that this influence is of two kinds4 ,to prove this1 let us perform the following experiment4 ,let us suspend a small pith ball by a very slender silk thread1 as in ,fig4 #e4 ,next1 let us rub a stick of warm1 dry glass with a piece of warm silk1 and with this excited stick touch the pith ball4 ,the pith ball1 after being touched1 will be repelled by the excited glass4 ,let us next excite1 in a similar manner1 a stick of dry sealing-wax with a piece of warm1 dry flannel1 and on approaching this stick to the pith ball it will attract it1 although the ball1 in its present state1 is repelled by the excited glass4 ,thus a pith ball1 touched by excited glass1 is repelled by excited glass1 but attracted by excited sealing-wax4 ,in like manner1 it might be shown that a pith ball1 touched by excited sealing-wax1 will be afterwards repelled by excited sealing-wax1 but attracted by excited glass4 ,now1 what the excited glass did to the pith ball1 was to communicate to it part of its own influence1 after which the ball was repelled by the glass2 or1 in other words1 bodies charged with similar electricities repel one another4 ,again1 since the pith ball1 when charged with the electricity from glass1 was attracted to the electrified sealing-wax1 we conclude that bodies charged with unlike electricities attract one another4 ,the electricity from glass is sometimes called vitreous1 and that from sealing-wax resinous1 electricity1 but more frequently the former is known as positive1 and the latter as negative1 electricity--it being understood that these words do not imply the possession of a positive nature by the one influence1 or of a negative nature by the other1 but are merely terms employed to express the apparent antagonism which exists between the two kinds of electricity4 #hb4 ,the next point worthy of notice is that whenever one electricity is produced1 just as much is produced of an opposite description4 ,thus1 in the case of glass excited by silk1 we have positive electricity developed upon the glass1 while we have also negative electricity developed upon the silk to precisely the same extent4 ,and1 again1 when sealing-wax is rubbed with flannel1 we have negative electricity developed upon the sealing-wax1 and just as much positive upon the flannel4 #hc4 ,these facts have given rise to a theory of electricity1 or at least to a method of regarding it1 which1 if not absolutely correct1 seems yet to unite together the various phenomena4 ,according to this hypothesis1 a neutral1 unexcited body is supposed to contain a store of the two electricities combined together1 so that whenever such a body is excited1 a separation is produced between the two4 ,the phenomena which we have described are1 therefore1 due to this electrical separation1 and inasmuch as the two electricities have a great affinity for one another1 it requires the expenditure of energy to produce this separation1 just as truly as it does to separate a stone from the earth4 #hd4 ,now1 it is worthy of note that electrical separation is only produced when heterogeneous bodies are rubbed together4 ,thus1 if flannel be rubbed upon glass1 we have electricity2 but if flannel be rubbed upon glass covered with flannel1 we have none4 ,in like manner1 if silk be rubbed upon sealing-wax covered with silk1 or1 in fine1 if two portions of the same substance be rubbed together1 we have no electricity4 ,on the other hand1 a very slight difference of texture is sometimes sufficient to produce electrical separation4 ,thus1 if two pieces of the same silk ribbon be rubbed together lengthwise1 we have no electricity2 but if they be rubbed across each other1 the one is positively1 and the other negatively1 electrified4 ,in fact1 this element of heterogeneity is an all important one in electrical development1 and this leads us to conjecture that electrical attraction may probably be regarded as peculiarly allied to that force which we call chemical affinity4 ,at any rate1 electricity and chemical affinity are only manifested between bodies that are1 in some respects1 dissimilar4 #he4 ,the following is a list of bodies arranged according to the electricity which they develop when rubbed together1 each substance being positively electrified when rubbed with any substance beneath it in the list4 #a4 ,cat's skin4 #b4 ,flannel4 #c4 ,ivory4 #d4 ,glass4 #e4 ,silk4 #f4 ,wood4 #g4 ,shellac4 #h4 ,resin4 #i4 ,metals4 #aj4 ,sulphur4 #aa4 ,caoutchouc4 #ab4 ,gutta-percha4 #ac4 ,gun-cotton4 ,thus1 if resin be rubbed with cat's skin1 or with flannel1 the cat's skin or flannel will be positively1 and the resin negatively1 electrified2 while if glass be rubbed with silk1 the glass will be positively1 and the silk negatively1 electrified1 and so on4 #hf4 ,it is not our purpose here to describe at length the electrical machine1 but we may state that it consists of two parts1 one for generating electricity by means of the friction of a rubber against glass1 and another consisting of a system of brass tubes1 of considerable surface1 supported on glass stems1 for collecting and retaining the electricity so produced4 ,this latter part of the machine is called its prime conductor4 ,electric ,induction4 ,illustration3 ,fig4 #f4 #hg4 ,let us now suppose that we have set in action a machine of this kind1 and accumulated a considerable quantity of positive electricity in its prime conductor at ,a4 ,let us next take two vessels1 ,b and ,c1 made of brass1 supported on glass stems4 ,these two vessels are supposed to be in contact1 but at the same time to be capable of being separated from one another at their middle point1 where the line is drawn in ,fig4 #f4 ,now let us cause ,b and ,c to approach ,a together4 ,at first1 ,b and ,c are not electrified1 that is to say1 their two electricities are not separated from each other1 but are mixed together2 but mark what will happen as they are pushed towards ,a4 ,the positive electricity of ,a will decompose the two electricities of ,b and ,c1 attracting the negative towards itself1 and repelling the positive as far away as possible4 ,the disposition of electricities will1 therefore1 be as in the figure4 ,if we now pull ,c away from ,b1 we have obtained a quantity of positive electricity on ,c1 by help of the original electricity which was in ,a2 in fact1 we have made use of the original stock or electrical capital in ,a1 in order to obtain positive electricity in ,c1 without1 however1 diminishing the amount of our original stock4 ,now1 this distant action or help1 rendered by the original electricity in separating that of ,b and ,c1 is called electric induction4 #hh4 ,the experiment may1 however1 be performed in a somewhat different manner--we may allow ,b and ,c to remain together1 and gradually push them nearer to ,a4 ,as ,b and ,c approach ,a1 the separation of their electricities will become greater and greater1 until1 when ,a and ,b are only divided by a small thickness of air1 the two opposite electricities then accumulated will have sufficient strength to rush together through the air1 and unite with each other by means of a spark4 #hi4 ,the principle of induction may be used with advantage1 when it is wished to accumulate a large quantity of electricity4 ,illustration3 ,fig4 #g4 ,in this case1 an instrument called a ,leyden jar is very frequently employed4 ,it consists of a glass jar1 coated inside and outside with tin foil1 as in ,fig4 #g4 ,a brass rod1 having a knob at the end of it1 is connected metallically with the inside coating1 and is kept in its place by being passed through a cork1 which covers the mouth of the jar4 ,we have thus two metallic coatings which are not electrically connected with one another4 ,now1 in order to charge a jar of this kind1 let the outside coating be connected by a chain with the earth1 while at the same time positive electricity from the prime conductor of an electrical machine is communicated to the inside knob4 ,the positive electricity will accumulate on the inside coating with which the knob is connected4 ,it will then decompose the two electricities of the outside coating1 driving the positive electricity to the earth1 and there dissipating it1 but attracting the negative to itself4 ,there will thus be positive electricity on the inside1 and negative on the outside coating4 ,these two electricities may be compared to two hostile armies watching each other1 and very anxious to get together1 while1 however1 they are separated from one another by means of an insurmountable obstacle4 ,they will thus remain facing each other1 and at their posts1 while each side is1 meanwhile1 being recruited by the same operation as before4 ,we may by this means accumulate a vast quantity of opposite electricities on the two coatings of such a jar1 and they will remain there for a long time1 especially if the surrounding atmosphere and the glass surface of the jar be quite dry4 ,when1 however1 electric connection of any kind is made between the two coatings1 the electricities rush together and unite with one another in the shape of a spark1 while if the human body be the instrument of connecting them a severe shock will be felt4 #ij4 ,it would thus appear that1 when two bodies charged with opposite electricities are brought near each other1 the two electricities rush together1 forming a current1 and the ultimate result is a spark4 ,now1 this spark implies heat1 and is1 in truth1 nothing else than small particles of intensely heated matter of some kind4 ,we have here1 therefore1 first of all1 the conversion of electrical separation into a current of electricity1 and1 secondly1 the conversion of this current into heat4 ,in this case1 however1 the current lasts only a very small time2 the discharge1 as it is called1 of a ,leyden jar being probably accomplished in th of a second4 ,the ,electric ,current4 #ia4 ,in other cases we have electrical currents which1 although not so powerful as that produced by discharging a ,leyden jar1 yet last longer1 and are1 in fact1 continuous instead of momentary4 ,we may see a similar difference in the case of visible energy4 ,thus we might1 by means of gunpowder1 send up in a moment an enormous mass of water2 or we might1 by means of a fountain1 send up the same mass in the course of time1 and in a very much quieter manner4 ,we have the same sort of difference in electrical discharges1 and having spoken of the rushing together of two opposite electricities by means of an explosion and a spark1 let us now speak of the eminently quiet and effective voltaic current1 in which we have a continuous coming together of the same two agents4 ,illustration3 ,fig4 #h4 #ib4 ,it is not our object here to give a complete description1 either historical or scientific1 of the voltaic battery1 but rather to give such an account as will enable our readers to understand what the arrangement is1 and what sort of effect it produces2 and with this object we shall at once proceed to describe the battery of ,grove1 which is perhaps the most efficacious of all the various arrangements for the purpose of producing an electric current4 ,in this battery we have a number of cells connected together1 as in ,fig4 #h1 which shows a battery of three cells4 ,each cell consists of two vessels1 an outer and an inner one2 the outer vessel being made of glass or ordinary stone ware1 while the inner one is made of unglazed porcelain1 and is therefore porous4 ,the outer vessel is filled with dilute sulphuric acid1 and a plate of amalgamated zinc--that is to say1 of metallic zinc having its outer surface brightened with mercury1--is immersed in this acid4 ,again1 in the inner or porous vessel we have strong nitric acid1 in which a plate of platinum foil is immersed1 this being at the same time electrically connected with the zinc plate of the next outer vessel1 by means of a clamp1 as in the figure4 ,both metals must be clean where they are pressed together1 that is to say1 the true metallic surfaces of both must be in contact4 ,finally1 a wire is metallically connected with the platinum of the left-hand cell1 and a similar wire with the zinc of the right-hand cell1 and these connecting wires ought1 except at their extremities1 to be covered over with gutta-percha or thread4 ,the loose extremities of these wires are called the poles of the battery4 #ic4 ,let us now suppose that we have a battery containing a good many cells of this description1 and let the whole arrangement be insulated1 by being set upon glass supports1 or otherwise separated from the earth4 ,if now we test1 by appropriate methods1 the extremity of the wire connected with the left-hand platinum plate1 it will be found to be charged with positive electricity1 while the extremity of the other wire will be found charged with negative electricity4 #id4 ,in the next place1 if we connect these poles of the battery with one another1 the two electricities will rush together and unite1 or1 in other words1 there will be an electric current2 but it will not be a momentary but a continuous one1 and for some time1 provided these poles are kept together1 a current of electricity will pass through the wires1 and indeed through the whole arrangement1 including the cells4 ,the direction of the current will be such that positive electricity may be supposed to pass from the zinc to the platinum1 through the liquid2 and back again through the wire1 from the platinum at the left hand1 to the zinc at the right2 in fact1 to go in the direction indicated by the arrow-head4 #ie4 ,thus we have two things4 ,in the first place1 before the two terminals1 or poles1 have been brought together1 we have them charged with opposite electricities2 and1 secondly1 when once they have been brought together1 we have the production of a continuous current of electricity4 ,now1 this current is an energetic agent1 in proof of which we shall proceed to consider the various properties which it has1--the various things which it can do4 ,its ,magnetic ,effects4 #if4 ,in the first place1 it can deflect the magnetic needle4 ,for instance1 let a compass needle be swung freely1 and let a current of electricity circulate along a wire placed near this needle1 and in the direction of its length1 then the direction in which the needle points will be immediately altered4 ,this direction will now depend upon that of the current1 conveyed by the wire1 and the needle will endeavour to place itself at right angles to this wire4 ,in order to remember the connection between the direction of the current and that of the magnet1 imagine your body to form part of the positive current1 which may be supposed to enter in at your head1 and go out at your feet2 also imagine that your face is turned towards the magnet4 ,in this case1 the pole of the magnet1 which points to the north1 will always be deflected by the current towards your right hand4 ,the strength of a current may be measured by the amount of the deflection it produces upon a magnetic needle1 and the instrument by which this measurement is made is called a galvanometer4 #ig4 ,in the next place1 the current is able1 not merely to deflect a magnet1 but also to render soft iron magnetic4 ,let us take1 for instance1 the wire connected with the one pole of the battery1 and cover it with thread1 in order to insulate it1 and let us wrap this wire round a cylinder of soft iron1 as in ,fig4 #i4 ,if we now make a communication between the other extremity of the wire1 and the other pole of the battery1 so as to make the current pass1 it will be found that our cylinder of soft iron has become a powerful magnet1 and that if an iron keeper be attached to it as in the figure1 the keeper will be able to sustain a very great weight4 ,illustration3 ,fig4 #i4 ,its ,heating ,effect4 #ih4 ,the electric current has likewise the property of heating a wire through which it passes4 ,to prove this1 let us connect the two poles of a battery by means of a fine platinum wire1 when it will be found that the wire will1 in a few seconds1 become heated to redness4 ,in point of fact1 the current will heat a thick wire1 but not so much as a thin one1 for we may suppose it to rush with great violence through the limited section of the thin wire1 producing in its passage great heat4 ,its ,chemical ,effect4 #ii4 ,besides its magnetic and heating effects1 the current has also the power of decomposing compound substances1 under certain conditions4 ,suppose1 for instance1 that the poles of a battery1 instead of being brought together1 are plunged into a vessel of water1 decomposition will at once begin1 and small bubbles of oxygen will rise from the positive pole1 while small bubbles of hydrogen will make their appearance at the negative4 ,if the two gases are collected together in a vessel1 they may be exploded1 and if collected separately1 it may be proved by the ordinary tests1 that the one is oxygen and the other hydrogen4 ,attraction and ,repulsion of ,currents4 #ajj4 ,we have now described very shortly the magnetic1 the heating1 and the chemical effects of currents2 it remains for us to describe the effects of currents upon one another4 ,in the first place1 suppose that we have two wires which are parallel to one another1 and carry currents going in the same direction2 and let us further suppose that these wires are capable of moving1 then it is found that they will attract one another4 ,if1 however1 the wires1 although parallel1 convey currents going in opposite directions1 they will then repel one another4 ,a good way of showing this experimentally is to cause two circular currents to float on water4 ,if these currents both go either in the same direction as the hands of a watch1 or in the opposite direction1 then the two will attract one another2 but if the one goes in the one direction1 and the other in the other1 they will then repel one another4 ,attraction and ,repulsion of ,magnets4 #aja4 ,ampre1 who discovered this property of currents1 has likewise shown us that in very many respects a magnet may be likened to a collection of circular currents all parallel to one another1 their direction being such that1 if you look towards the north pole of a freely suspended cylindrical magnet facing it1 the positive current will descend on the east or left-hand side1 and ascend on the west or right-hand side4 ,if we adopt this method of viewing magnets1 we can easily account for the attraction between the unlike and the repulsion between the like poles of a magnet1 for when unlike poles are placed near each other1 the circular currents which face each other are then all going in the same direction1 and the two will1 therefore1 attract one another1 but if like poles are placed in this position1 the currents that face each other are going in opposite directions1 and the poles will1 therefore1 repel one another4 ,illustration3 ,fig4 #aj4 ,induction of ,currents4 #ajb4 ,before closing this short sketch of electrical phenomena1 we must allude to the inductive effect of currents upon each other4 ,let us suppose 7,fig4 #aj7 that we have two circular coils of wire1 covered with thread1 and placed near each other4 ,let both the extremities of the right-hand coil be connected with the poles of a battery1 so as to make a current of electricity circulate round the coil4 ,on the other hand1 let the left-hand coil be connected with a galvanometer1 thus enabling us to detect the smallest current of electricity which may pass through this coil4 ,now1 it is found that when we first connect the right-hand coil1 so as to pass the battery current through it1 a momentary current will pass through the left-hand coil1 and will deflect the needle of the galvanometer1 but this current will go in an opposite direction to that which circulates round the right-hand coil4 #ajc4 ,again1 as long as the current continues to flow through the right-hand coil there will be no current through the other1 but at the moment of breaking the contact between the right-hand coil and the battery there will again be a momentary current in the left-hand coil1 but this time in the same direction as that of the right-hand coil1 instead of being1 as before1 in the opposite direction4 ,in other words1 when contact is made in the right-hand coil1 there is a momentary current in the left-hand coil1 but in an opposite direction to that in the right1 while1 when contact is broken in the right-hand coil1 there is a momentary current in the left-hand coil in the same direction as that in the right4 #ajd4 ,in order to exemplify this induction of currents1 it is not even necessary to make and break the current in the right-hand coil1 for we may keep it constantly going and arrange so as to make the right-hand coil 7always retaining its connection with the battery7 alternately approach and recede from the other2 when it approaches the other1 the effect produced will be the same as when the contact was made in the above experiment--that is to say1 we shall have an induced current in an opposite direction to that of the primary1 while1 when it recedes from the other1 we shall have a current in the same direction as that of the primary4 #aje4 ,thus we see that whether we keep both coils stationary1 and suddenly produce a current in the right-hand coil1 or whether1 keeping this current constantly going1 we suddenly bring it near the other coil1 the inductive effect will be precisely the same1 for in both cases the left-hand coil is suddenly brought into the presence of a current4 ,and again1 it is the same1 whether we suddenly break the right-hand current1 or suddenly remove it from the left-hand coil1 for in both cases this coil is virtually removed from the presence of a current4 ,list of ,energies4 #ajf4 ,we are now in a position to enumerate the various kinds of energy which occur in nature2 but1 before doing so1 we must warn our readers that this enumeration has nothing absolute or complete about it1 representing1 as it does1 not so much the present state of our knowledge as of our want of knowledge1 or rather profound ignorance1 of the ultimate constitution of matter4 ,it is1 in truth1 only a convenient classification1 and nothing more4 #ajg4 ,to begin1 then1 with visible energy4 ,we have first of all-- ,energy of ,visible ,motion4 7,a47 ,visible energy of actual motion--in the planets1 in meteors1 in the cannon ball1 in the storm1 in the running stream1 and in other instances of bodies in actual visible motion1 too numerous to be mentioned4 ,visible ,energy of ,position4 7,b47 ,we have also visible energy of position--in a stone on the top of a cliff1 in a head of water1 in a rain cloud1 in a cross-bow bent1 in a clock or watch wound up1 and in various other instances4 #ajh4 ,then we have1 besides1 several cases in which there is an alternation between 7,a7 and 7,b74 ,a pendulum1 for instance1 when at its lowest point1 has only the energy 7,a71 or that of actual motion1 in virtue of which it ascends a certain distance against the force of gravity4 ,when1 however1 it has completed its ascent1 its energy is then of the variety 7,b71 being due to position1 and not to actual motion2 and so on it continues to oscillate1 alternately changing the nature of its energy from 7,a7 to 7,b71 and from 7,b7 back again to 7,a74 #aji4 ,a vibrating body is another instance of this alternation4 ,each particle of such a body may be compared to an exceedingly small pendulum oscillating backwards and forwards1 only very much quicker than an ordinary pendulum2 and just as the ordinary pendulum in passing its point of rest has its energy all of one kind1 while in passing its upper point it has it all of another1 so when a vibrating particle is passing its point of rest1 its energy is all of the variety 7,a71 and when it has reached its extreme displacement1 it is all of the variety 7,b74 ,heat ,motion4 #aaj4 7,c47 ,coming now to molecular or invisible energy1 we have1 in the first place1 that motion of the molecules of bodies which we term heat4 ,a better term would be absorbed heat1 to distinguish it from radiant heat1 which is a very different thing4 ,that peculiar motion which is imparted by heat when absorbed into a body is1 therefore1 one variety of molecular energy4 ,molecular ,separation4 7,d47 ,analogous to this is that effect of heat which represents position rather than actual motion4 ,for part of the energy of absorbed heat is spent in pulling asunder the molecules of the body under the attractive force which binds them together 7,art4 #gc71 and thus a store of energy of position is laid up1 which disappears again after the body is cooled4 ,atomic or ,chemical ,separation4 #aaa4 7,e47 ,the two previous varieties of energy may be viewed as associated with molecules rather than with atoms1 and with the force of cohesion rather than with that of chemical affinity4 ,proceeding now to atomic force1 we have a species of energy of position due to the separation of different atoms under the strong chemical attraction they have for one another4 ,thus1 when we possess coal or carbon and also oxygen in a state of separation from one another1 we are in possession of a source of energy which may be called that of chemical separation4 ,electrical ,separation4 #aab 7,f47 ,the attraction which heterogeneous atoms possess for one another1 sometimes1 however1 gives rise to a species of energy which manifests itself in a very peculiar form1 and appears as electrical separation1 which is thus another form of energy of position4 ,electricity in ,motion4 #aac 7,g47 ,but we have another species of energy connected with electricity1 for we have that due to electricity in motion1 or in other words1 an electric current which probably represents some form of actual motion4 ,radiant ,energy4 #aad 7,h47 ,it is well known that there is no ordinary matter1 or at least hardly any1 between the sun and the earth1 and yet we have a kind of energy which we may call radiant energy1 which proceeds to us from the sun1 and proceeds also with a definite1 though very great velocity1 taking about eight minutes to perform its journey4 ,now1 this radiant energy is known to consist of the vibrations of an elastic medium pervading all space1 which is called ether1 or the ethereal medium4 ,inasmuch1 therefore1 as it consists of vibrations1 it partakes of the character of pendulum motion1 that is to say1 the energy of any ethereal particle is alternately that of position and that of actual motion4 ,law of ,conservation4 #aae4 ,having thus endeavoured1 provisionally at least1 to catalogue our various energies1 we are in a position to state more definitely what is meant by the conservation of energy4 ,for this purpose1 let us take the universe as a whole1 or1 if this be too large1 let us conceive1 if possible1 a small portion of it to be isolated from the rest1 as far as force or energy is concerned1 forming a sort of microcosm1 to which we may conveniently direct our attention4 ,this portion1 then1 neither parts with any of its energy to the universe beyond1 nor receives any from it4 ,such an isolation is1 of course1 unnatural and impossible1 but it is conceivable1 and will1 at least1 tend to concentrate our thoughts4 ,now1 whether we regard the great universe1 or this small microcosm1 the principle of the conservation of energy asserts that the sum of all the various energies is a constant quantity1 that is to say1 adopting the language of ,algebra-- 7,a7 7,b7 7,c7 7,d7 7,e7 7,f7 7,g7 7,h7 a constant quantity4 #aaf4 ,this does not mean1 of course1 that 7,a7 is constant in itself1 or any other of the left-hand members of this equation1 for1 in truth1 they are always changing about into each other--now1 some visible energy being changed into heat or electricity2 and1 anon1 some heat or electricity being changed back again into visible energy--but it only means that the sum of all the energies taken together is constant4 ,we have1 in fact1 in the left hand1 eight variable quantities1 and we only assert that their sum is constant1 not by any means that they are constant themselves4 #aag4 ,now1 what evidence have we for this assertion8 ,it may be replied that we have the strongest possible evidence which the nature of the case admits of4 ,the assertion is1 in truth1 a peculiar one--peculiar in its magnitude1 in its universality1 in the subtle nature of the agents with which it deals4 ,if true1 its truth certainly cannot be proved after the manner in which we prove a proposition in ,euclid4 ,nor does it even admit of a proof so rigid as that of the somewhat analogous principle of the conservation of matter1 for in chemistry we may confine the products of our chemical combination so completely as to prove1 beyond a doubt1 that no heavy matter passes out of existence that--when coal1 for instance1 burns in oxygen gas--what we have is merely a change of condition4 ,but we cannot so easily prove that no energy is destroyed in this combination1 and that the only result is a change from the energy of chemical separation into that of absorbed heat1 for during the process it is impossible to isolate the energy--do what we may1 some of it will escape into the room in which we perform the experiment2 some of it will1 no doubt1 escape through the window1 while a little will leave the earth altogether1 and go out into space4 ,all that we can do in such a case is to estimate1 as completely as possible1 how much energy has gone away1 since we cannot possibly prevent its going4 ,but this is an operation involving great acquaintance with the laws of energy1 and very great exactness of observation3 in fine1 our readers will at once perceive that it is much more difficult to prove the truth of the conservation of energy than that of the conservation of matter4 #aah4 ,but if it be difficult to prove our principle in the most rigorous manner1 we are yet able to give the strongest possible indirect evidence of its truth4 ,our readers are no doubt familiar with a method which ,euclid frequently adopts in proving his propositions4 ,starting with the supposition that they are not true1 and reasoning upon this hypothesis1 he comes to an absurd conclusion--hence he concludes that they are true4 ,now1 we may adopt a method somewhat similar with regard to our principle1 only instead of supposing it untrue1 let us suppose it true4 ,it may then be shown that1 if it be true1 under certain test conditions we ought to obtain certain results--for instance1 if we increase the pressure1 we ought to lower the freezing point of water4 ,well1 we make the experiment1 and find that1 in point of fact1 the freezing point of water is lowered by increasing the pressure1 and we have thus derived an argument in favour of the conservation of energy4 #aai4 ,or again1 if the laws of energy are true1 it may be shown that1 whenever a substance contracts when heated1 it will become colder instead of hotter by compression4 ,now1 we know that ice-cold water1 or water just a little above its freezing point1 contracts instead of expanding up to #d ,c42 and ,sir ,william ,thomson has found1 by experiment1 that water at this temperature is cooled instead of heated by sudden compression4 ,india-rubber is another instance of this relation between these two properties1 for if we stretch a string of india-rubber it gets hotter instead of colder1 that is to say1 its temperature rises by extension1 and gets lower by contraction2 and again1 if we heat the string1 we find that it contracts in length instead of expanding like other substances as its temperature increases4 #abj4 ,numberless instances occur in which we are enabled to predict what will happen by assuming the truth of the laws of energy2 in other words1 these laws are proved to be true in all cases where we can put them to the test of rigorous experiment1 and probably we can have no better proof than this of the truth of such a principle4 ,we shall therefore proceed upon the assumption that the conservation of energy holds true in all cases1 and give our readers a list of the various transmutations of this subtle agent as it goes backwards and forwards from one abode to another1 making1 meanwhile1 sundry remarks that may tend1 we trust1 to convince our readers of the truth of our assumption4 ,,chapter ,,iv4 ,,transmutations ,,of ,,energy4 ,energy of ,visible ,motion4 #aba4 ,let us begin our list of transmutations with the energy of visible motion4 ,this is changed into energy of position when a stone is projected upwards above the earth1 or1 to take a case precisely similar1 when a planet or a comet goes from perihelion1 or its position nearest the sun1 to aphelion1 or its position furthest from the sun4 ,we thus see why a heavenly body should move fastest at perihelion1 and slowest at aphelion4 ,if1 however1 a planet were to move round the sun in an orbit exactly circular1 its velocity would be the same at all the various points of this orbit1 because there would be no change in its distance from the centre of attraction1 and therefore no transmutation of energy4 #abb4 ,we have already 7,arts4 #ajh1 #aji7 said that the energy in an oscillating or vibrating body is alternately that of actual motion1 and that of position4 ,in this respect1 therefore1 a pendulum is similar to a comet or heavenly body with an elliptical orbit4 ,nevertheless the change of energy is generally more complete in a pendulum or vibrating body than it is in a heavenly body2 for in a pendulum1 when at its lowest point1 the energy is entirely that of actual motion1 while at its upper point it is entirely that of position4 ,now1 in a heavenly body we have only a lessening1 but not an entire destruction1 of the velocity1 as the body passes from perihelion to aphelion--that is to say1 we have only a partial conversion of the one kind of energy into the other4 #abc4 ,let us next consider the change of actual visible energy into absorbed heat4 ,this takes place in all cases of friction1 percussion1 and resistance4 ,in friction1 for instance1 we have the conversion of work or energy into heat1 which is here produced through the rubbing of surfaces against each other2 and ,davy has shown that two pieces of ice1 both colder than the freezing point1 may be melted by friction4 ,in percussion1 again1 we have the energy of the blow converted into heat2 while1 in the case of a meteor or cannon ball passing through the air with great velocity1 we have the loss of energy of the meteor or cannon ball through its contact with the air1 and at the same time the production of heat on account of this resistance4 ,the resistance need not be atmospheric1 for we may set the cannon ball to pierce through wooden planks or through sand1 and there will equally be a production of heat on account of the resistance offered by the wooden planks or by the sand to the motion of the ball4 ,we may even generalize still further1 and assert that whenever the visible momentum of a body is transferred to a larger mass1 there is at the same time the conversion of visible energy into heat4 #abd4 ,a little explanation will be required to make this point clear4 ,the third law of motion tells us that action and reaction are equal and opposite1 so that when two bodies come into collision the forces at work generate equal and opposite quantities of momentum4 ,we shall best see the meaning of this law by a numerical example1 bearing in mind that momentum means the product of mass into velocity4 ,for instance1 let us suppose that an inelastic body of mass #aj and velocity #bj strikes directly another inelastic body of mass #ae and velocity #ae1 the direction of both motions being the same4 ,now1 it is well known that the united mass will1 after impact1 be moving with the velocity #ag4 ,what1 then1 has been the influence of the forces developed by collision8 ,the body of greater velocity had before impact a momentum #aj #bj #bjj1 while its momentum after impact is only #aj #ag #agj2 it has therefore suffered a loss of #cj units as regards momentum1 or we may consider that a momentum of #cj units has been impressed upon it in an opposite direction to its previous motion4 ,on the other hand1 the body of smaller velocity had before impact a momentum #ae #ae #bbe1 while after impact it has #ae #ag #bee units1 so that its momentum has been increased by #cj units in its previous direction4 ,the force of impact has therefore generated #cj units of momentum in two opposite directions1 so that1 taking account of direction1 the momentum of the system is the same before and after impact2 for before impact we had a momentum of #aj #bj #ae #ae #dbe1 while after it we have the united mass #be moving with the velocity #ag1 giving the momentum #dbe as before4 #abe4 ,but while the momentum is the same before and after impact1 the visible energy of the moving mass is undoubtedly less after impact than before it4 ,to see this we have only to turn to the expression of ,art4 #bh1 from which we find that the energy before impact was as follows3--,energy in kilogrammetres 7m v7_/7#ai #f7 7#aj #bj #ae #ae7_/aif #cgf nearly2 while that after impact 7#be #ag7_/aif #cfh nearly4 #abf4 ,the loss of energy will be still more manifest if we suppose an inelastic body in motion to strike against a similar body at rest4 ,thus if we have a body of mass #bj and velocity #bj striking against one of equal mass1 but at rest1 the velocity of the double mass after impact will obviously be only #aj2 but1 as regards energy1 that before impact will be 7#bj #bj7_/aif #f while that after impact will be 7#dj #aj7_/aif #f or only half the former4 #abg4 ,thus there is in all such cases an apparent loss of visible energy1 while at the same time there is the production of heat on account of the blow which takes place4 ,if1 however1 the substances that come together be perfectly elastic 7which no substance is71 the visible energy after impact will be the same as that before1 and in this case there will be no conversion into heat4 ,this1 however1 is an extreme supposition1 and inasmuch as no substance is perfectly elastic1 we have in all cases of collision a greater or less conversion of visible motion into heat4 #abh4 ,we have spoken 7,art4 #abb7 about the change of energy in an oscillating or vibrating body1 as if it were entirely one of actual energy into energy of position1 and the reverse4 ,but even here1 in each oscillation or vibration1 there is a greater or less conversion of visible energy into heat4 ,let us1 for instance1 take a pendulum1 and1 in order to make the circumstances as favourable as possible1 let it swing on a knife edge1 and in vacuo2 in this case there will be a slight but constant friction of the knife edge against the plane on which it rests1 and though the pendulum may continue to swing for hours1 yet it will ultimately come to rest4 ,and1 again1 it is impossible to make a vacuum so perfect that there is absolutely no air surrounding the pendulum1 so that part of the motion of the pendulum will always be carried off by the residual air of the vacuum in which it swings4 #abi4 ,now1 something similar happens in that vibratory motion which constitutes sound4 ,thus1 when a bell is in vibration1 part of the energy of the vibration is carried off by the surrounding air1 and it is in virtue of this that we hear the sound of the bell2 but1 even if there were no air1 the bell would not go on vibrating for ever4 ,for there is in all bodies a greater or less amount of internal viscosity1 a property which prevents perfect freedom of vibration1 and which ultimately converts vibrations into heat4 ,a vibrating bell is thus very much in the same position as an oscillating pendulum1 for in both part of the energy is given off to the air1 and in both there is unavoidable friction--in the one taking the shape of internal viscosity1 and in the other that of friction of the knife edge against the plane on which it rests4 #acj4 ,in both these cases1 too1 that portion of the energy which goes into the air takes ultimately the shape of heat4 ,the oscillating pendulum communicates a motion to the air1 and this motion ultimately heats the air4 ,the vibrating bell1 or musical instrument1 in like manner communicates part of its energy to the air4 ,this communicated energy first of all moves through the air with the well-known velocity of sound1 but during its progress it1 too1 no doubt becomes partly converted into heat4 ,ultimately1 it is transmitted by the air to other bodies1 and by means of their internal viscosity is sooner or later converted into heat4 ,thus we see that heat is the form of energy1 into which all visible terrestrial motion1 whether it be rectilinear1 or oscillatory1 or vibratory1 is ultimately changed4 #aca4 ,in the case of a body in visible rectilinear motion on the earth's surface1 this change takes place very soon--if the motion be rotatory1 such as that of a heavy revolving top1 it may1 perhaps1 continue longer before it is ultimately stopped1 by means of the surrounding air1 and by friction of the pivot2 if it be oscillatory1 as in the pendulum1 or vibratory1 as in a musical instrument1 we have seen that the air and internal friction are at work1 in one shape or another1 to carry it off1 and will ultimately succeed in converting it into heat4 #acb4 ,but1 it may be said1 why consider a body moving on the earth's surface8 why not consider the motion of the earth itself8 ,will this also ultimately take the shape of heat8 ,no doubt it is more difficult to trace the conversion in such a case1 inasmuch as it is not proceeding at a sensible rate before our eyes4 ,in other words1 the very conditions that make the earth habitable1 and a fit abode for intelligent beings like ourselves1 are those which unfit us to perceive this conversion of energy in the case of the earth4 ,yet we are not without indications that it is actually taking place4 ,for the purpose of exhibiting these1 we may divide the earth's motion into two--a motion of rotation1 and one of revolution4 #acc4 ,now1 with regard to the earth's rotation1 the conversion of the visible energy of this motion into heat is already well recognized4 ,to understand this we have only to study the nature of the moon's action upon the fluid portions of our globe4 ,in the following diagram 7,fig4 #aa7 we have an exaggerated representation of this1 by which we see that the spherical earth is converted into an elongated oval1 of which one extremity always points to the moon4 ,the solid body of the earth itself revolves as usual1 but1 nevertheless1 this fluid protuberance remains always pointing towards the moon1 as we see in the figure1 and hence the earth rubs against the protuberance as it revolves4 ,the friction produced by this action tends evidently to lessen the rotatory energy of the earth--in other words1 it acts like a break--and we have1 just as by a break-wheel1 the conversion of visible energy into heat4 ,this was first recognized by ,mayer and ,j4 ,thomson4 ,illustration3 ,fig4 #aa4 #acd4 ,but while there can be no doubt about the fact of such a conversion going on1 the only question is regarding its rate of progress1 and the time required before it can cause a perceptible impression upon the rotative energy of the earth4 ,now1 it is believed by astronomers that they have detected evidence of such a change1 for our knowledge of the motions of the sun and moon has become so exact1 that not only can we carry forward our calculations so as to predict an eclipse1 but also carry them backwards1 and thus fix the dates and even the very details of the ancient historical eclipses4 ,if1 however1 between those times and the present1 the earth has lost a little rotative energy on account of this peculiar action of the moon1 then it is evident that the calculated circumstances of the ancient total eclipse will not quite agree with those actually recorded2 and by a comparison of this nature it is believed that we have detected a very slight falling off in the rotative energy of our earth4 ,if we carry out the argument1 we shall be driven to the conclusion that the rotative energy of our globe will1 on account of the moon's action1 always get less and less1 until things are brought into such a state that the rotation comes to be performed in the same time as the revolution of the moon1 so that then the same portion of the terrestrial surface being always presented to the moon1 it is evident that there will be no effort made by the solid substance of the earth1 to glide from under the fluid protuberance1 and there will in consequence be no friction1 and no further loss of energy4 #ace4 ,if the fate of the earth be ultimately to turn the same face always to the moon1 we have abundant evidence that this very fate has long since overtaken the moon herself4 ,indeed1 the much stronger effect of our earth upon the moon has produced this result1 probably1 even in those remote periods when the moon was chiefly fluid2 and it is a fact well known1 not merely to astronomers1 but to all of us1 that the moon nowadays turns always the same face to the earth4#d ,no doubt this fate has long since overtaken the satellites of ,jupiter1 ,saturn1 and the other large planets2 and there are independent indications that1 at least in the case of ,jupiter1 the satellites turn always the same face to their primary4 #acf4 ,to come now to the energy of revolution of the earth1 in her orbit round the sun1 we cannot help believing that there is a material medium of some kind between the sun and the earth2 indeed1 the undulatory theory of light requires this belief4 ,but if we believe in such a medium1 it is difficult to imagine that its presence will not ultimately diminish the motion of revolution of the earth in her orbit2 indeed1 there is a strong scientific probability1 if not an absolute certainty1 that such will be the case4 ,there is even some reason to think that the energy of a comet of small period1 called ,encke's comet1 is gradually being stopped from this cause2 in fine1 there can be hardly any doubt that the cause is really in operation1 and will ultimately affect the motions of the planets and other heavenly bodies1 even although its rate of action may be so slow that we are not able to detect it4 ,we may perhaps generalize by saying1 that wherever in the universe there is a differential motion1 that is to say1 a motion of one part of it towards or from another1 then1 in virtue of the subtle medium1 or cement1 that binds the various parts of the universe together1 this motion is not unattended by something like friction1 in virtue of which the differential motion will ultimately disappear1 while the loss of energy caused by its disappearance will assume the form of heat4 #acg4 ,there are1 indeed1 obscure intimations that a conversion of this kind is not improbably taking place in the solar system2 for1 in the sun himself1 we have the matter near the equator1 by virtue of the rotation of our luminary1 carried alternately towards and from the various planets4 ,now1 it would seem that the sun-spots1 or atmospheric disturbances of the sun1 affect particularly his equatorial regions1 and have likewise a tendency to attain their maximum size in that position1 which is as far away as possible from the influential planets1 such as ,mercury or ,venus2#e so that if ,venus1 for instance1 were between the earth and the sun1 there would be few sun-spots in the middle of the sun's disc1 because that would be the part of the sun nearest ,venus4 ,but if the planets influence sun-spots1 the action is no doubt reciprocal1 and we have much reason to believe that sun-spots influence1 not only the magnetism1 but also the meteorology of our earth1 so that there are most displays of the ,aurora ,borealis1 as well as most cyclones1 in those years when there are most sun-spots4#f ,is it not then possible that1 in these strange1 mysterious phenomena1 we see traces of the machinery by means of which the differential motion of the solar system is gradually being changed into heat8 #ach4 ,we have thus seen that visible energy of actual motion is not unfrequently changed into visible energy of position1 and that it is also very often transformed into absorbed heat4 ,we have now to state that it may likewise be transformed into electrical separation4 ,thus1 when an ordinary electrical machine is in action1 considerable labour is spent in turning the handle2 it is1 in truth1 harder to turn than if no electricity were being produced--in other words1 part of the energy which is spent upon the machine goes to the production of electrical separation4 ,there are other ways of generating electricity besides the frictional method4 ,if1 for instance1 we bring an insulated conducting plate near the prime conductor of the electrical machine1 yet not near enough to cause a spark to pass1 and if we then touch the insulated plate1 we shall find it1 after contact1 to be charged with an electricity the opposite of that in the machine2 we may then remove it and make use of this electricity4 ,it requires a little thought to see what labour we have spent in this process4 ,we must bear in mind that1 by touching the plate1 we have carried off the electricity of the same name as that of the machine1 so that1 after touching the insulated plate it is more strongly attracted to the conductor than it was before4 ,when we begin to remove it1 therefore1 it will cost us an effort to do so1 and the mechanical energy which we spend in removing it will account for the energy of electrical separation which we then obtain4 #aci4 ,we may thus make use of a small nucleus of electricity1 to assist us in procuring an unlimited supply1 for in the above process the electricity of the prime conductor remains unaltered1 and we may repeat the operation as often as we like1 and gather together a very large quantity of electricity1 without finally altering the electricity of the prime conductor1 but not1 however1 without the expenditure of an equivalent amount of energy1 in the shape of actual work4 #adj4 ,while1 as we have seen1 there is a tendency in all motion to be changed into heat1 there is one instance where it is1 in the first place at least1 changed into a current of electricity4 ,we allude to the case where a conducting substance moves in the presence of an electric current1 or of a magnet4 ,in ,art4 #ajd we found that if one coil connected with a battery were quickly moved into the presence of another coil connected with a galvanometer1 an induced current would be generated in the latter coil1 and would affect the galvanometer1 its direction being the reverse of that passing in the other4 ,now1 an electric current implies energy1 and we may therefore conclude that some other form of energy must be spent1 or disappear1 in order to produce the current which is generated in the coil attached to the galvanometer4 ,again1 we learn from ,art4 #ajj that two currents going in opposite directions repel one another4 ,the current generated in the coil attached to the galvanometer or secondary current will1 therefore1 repel the primary current1 which is moving towards it2 this repulsion will either cause a stoppage of motion1 or render necessary the expenditure of energy1 in order to keep up the motion of this moving coil4 ,we thus find that two phenomena occur simultaneously4 ,in the first place1 there is the production of energy in the secondary coil1 in the shape of a current opposite in direction to that of the primary coil2 in the next case1 owing to the repulsion between this induced current and the primary current1 there is a stoppage or disappearance of the energy of actual motion of the moving coil4 ,we have1 in fact1 the creation of one species of energy1 and at the same time the disappearance of another1 and thus we see that the law of conservation is by no means broken4 #ada4 ,we see also the necessary connection between the two electrical laws described in ,arts4 #ajj and #ajd4 ,indeed1 had these laws been other than what they are1 the principle of conservation of energy would have been broken4 ,for instance1 had the induced current in the case now mentioned been in the same direction as that of the primary1 the two currents would have attracted each other1 and thus there would have been the creation of a secondary current1 implying energy1 in the coil attached to the galvanometer1 along with an increase of the visible energy of motion of the primary current--that is to say1 instead of the creation of one kind of energy1 accompanied with the disappearance of another1 we should have had the simultaneous creation of both2 and thus the law of conservation of energy would have been broken4 ,we thus see that the principle of conservation enables us to deduce the one electrical law from the other1 and this is one of the many instances which strengthen our belief in the truth of the great principle for which we are contending4 #adb4 ,let us next consider what will take place if we cause the primary current to move from the secondary coil instead of towards it4 ,in this case we know1 from ,art4 #ajd1 that the induced current will be in the same direction as the primary1 while we are told by ,art4 #ajj that the two currents will now attract each other4 ,the tendency of this attraction will be to stop the motion of the primary current from the secondary one1 or1 in other words1 there will be a disappearance of the energy of visible motion1 while at the same time there is the production of a current4 ,in both cases1 therefore1 one form of energy disappears while another takes its place1 and in both there will be a very perceptible resistance experienced in moving the primary coil1 whether towards the secondary or from it4 ,work will1 in fact1 have to be spent in both operations1 and the outcome of this work or energy will be the production of a current in the first place1 and of heat in the second2 for we learn from ,art4 #ih that when a current passes along a wire its energy is generally spent in heating the wire4 ,we have thus two phenomena occurring together4 ,in the first place1 in moving a current of electricity to and from a coil of wire1 or any other conductor1 or 7which is the same thing1 since action and reaction are equal and opposite7 in moving a coil of wire or any other conductor to and from a current of electricity1 a sense of resistance will be experienced1 and energy will have to be spent upon the process2 in the second place1 an electrical current will be generated in the conductor1 and the conductor will be heated in consequence4 #adc4 ,the result will be rendered very prominent if we cause a metallic top1 in rapid rotation1 to spin near two iron poles1 which1 by means of the battery1 we can suddenly convert into the poles of a powerful electro-magnet4 ,when this change is made1 and the poles become magnetic1 the motion of the top is very speedily brought to rest1 just as if it had to encounter a species of invisible friction4 ,this curious result can easily be explained4 ,we have seen from ,art4 #aja that a magnet resembles an assemblage of electric currents1 and in the metallic top we have a conductor alternately approaching these currents and receding from them2 and hence1 according to what has been said1 we shall have a series of secondary currents produced in the conducting top which will stop its motion1 and which will ultimately take the shape of heat4 ,in other words1 the visible energy of the top will be changed into heat just as truly as if it were stopped by ordinary friction4 #add4 ,the electricity induced in a metallic conductor1 moved in the presence of a powerful magnet1 has received the name of ,magneto-,electricity2 and ,dr4 ,joule has made use of it as a convenient means of enabling him to determine the mechanical equivalent of heat1 for it is into heat that the energy of motion of the conductor is ultimately transformed4 ,but1 besides all this1 these currents form1 perhaps1 the very best means of obtaining electricity2 and recently very powerful machines have been constructed by ,wild and others with this view4 #ade4 ,these machines1 when large1 are worked by a steam-engine1 and their mode of operation is as follows3--,the nucleus of the machine is a system of powerful permanent steel magnets1 and a conducting coil is made to revolve rapidly in presence of these magnets4 ,the current produced by this moving coil is then used in order to produce an extremely powerful electro-magnet1 and finally a coil is made to move with great rapidity in presence of this powerful electro-magnet1 thus causing induced currents of vast strength4 ,so powerful are these currents1 that when used to produce the electric light1 small print may be read on a dark night at the distance of two miles from the scene of operation6 ,it thus appears that in this machine a double use is made of magneto-electricity4 ,starting with a nucleus of permanent magnetism1 the magneto-electric currents are used1 in the first instance1 to form a powerful electro-magnet much stronger than the first1 and this powerful electro-magnet is again made use of in the same way as the first1 in order to give1 by means of magneto-electricity1 an induced current of very great strength4 #adf4 ,there is1 moreover1 a very great likeness between a magneto-electric machine like that of ,wild's for generating electric currents1 and the one which generates statical electricity by means of the method already described ,art4 #aci4 ,in both cases advantage is taken of a nucleus1 for in the magneto-electric machine we have the molecular currents of a set of permanent magnets1 which are made the means of generating enormous electric currents without any permanent alteration to themselves1 yet not without the expenditure of work4 ,again1 in an induction machine for generating statical electricity1 we have an electric nucleus1 such as we have supposed to reside in the prime conductor of a machine2 and advantage may be taken1 as we have seen1 of this nucleus in order to generate a vast quantity of statical electricity1 without any permanent alteration of the nucleus1 but not without the expenditure of work4 #adg4 ,we have now seen under what conditions the visible energy of actual motion may be changed--#astly1 into energy of position2 #bndly1 into the two energies which embrace absorbed heat2 #crdly1 into electrical separation2 and finally into electricity in motion4 ,as far as we know1 visible energy cannot directly be transformed into chemical separation1 or into radiant energy4 ,visible ,energy of ,position4 #adh4 ,having thus exhausted the transmutations of the energy of visible motion1 we next turn to that of position1 and find that it is transmuted into motion1 but not immediately into any other form of energy2 we may1 therefore1 dismiss this variety at once from our consideration4 ,absorbed ,heat4 #adj4 ,coming now to these two forms of energy which embrace absorbed heat1 we find that this may be converted into 7,a7 or actual visible energy in the case of the steam-engine1 the air-engine1 and all varieties of heat engines4 ,in the steam-engine1 for instance1 part of the heat which passes through it disappears as heat1 utterly and absolutely1 to reappear as mechanical effect4 ,there is1 however1 one condition which must be rigidly fulfilled1 whenever heat is changed into mechanical effect--there must be a difference of temperature1 and heat will only be changed into work1 while it passes from a body of high temperature to one of low4 ,carnot1 the celebrated ,french physicist1 has ingeniously likened the mechanical power of heat to that of water2 for just as you can get no work out of heat unless there be a flow of heat from a higher temperature level to a lower1 so neither can you get work out of water unless it be falling from a higher level to a lower4 #aej4 ,if we reflect that heat is essentially distributive in its nature1 we shall soon perceive the reason for this peculiar law2 for1 in virtue of its nature1 heat is always rushing from a body of high temperature to one of low1 and if left to itself it would distribute itself equally amongst all bodies1 so that they would ultimately become of the same temperature4 ,now1 if we are to coax work out of heat1 we must humour its nature1 for it may be compared to a pack of schoolboys1 who are always ready to run with sufficient violence out of the schoolroom into the open fields1 but who have frequently to be dragged back with a very considerable expenditure of energy4 ,so heat will not allow itself to be confined1 but will resist any attempt to accumulate it into a limited space4 ,work cannot1 therefore1 be gained by such an operation1 but must1 on the contrary1 be spent upon the process4 #aea4 ,let us now for a moment consider the case of an enclosure in which everything is of the same temperature4 ,here we have a dull dead level of heat1 out of which it will be impossible to obtain the faintest semblance of work4 ,the temperature may even be high1 and there may be immense stores of heat energy in the enclosure1 but not a trace of this is available in the shape of work4 ,taking up ,carnot's comparison1 the water has already fallen to the same level1 and lies there without any power of doing useful work--dead1 in a sense1 as far as visible energy is concerned4 #aeb4 ,we thus perceive that1 firstly1 we can get work out of heat when it passes from a higher to a lower temperature1 but that1 secondly1 we must spend work upon it in order to make it pass from a lower temperature to a higher one2 and that1 thirdly and finally1 nothing in the shape of work can be got out of heat which is all at the same temperature level4 ,what we have now said enables us to realize the conditions under which all heat engines work4 ,the essential point about such engines is1 not the possession of a cylinder1 or piston1 or fly wheels1 or valves1 but the possession of two chambers1 one of high and the other of low temperature1 while it performs work in the process of carrying heat from the chamber of high to that of low temperature4 ,let us take1 for example1 the low-pressure engine4 ,here we have the boiler or chamber of high1 and the condenser or chamber of low1 temperature1 and the engine works while heat is being carried from the boiler to the condenser--never while it is being carried from the condenser to the boiler4 ,in like manner in the locomotive we have the steam generated at a high temperature and pressure1 and cooled by injection into the atmosphere4 #aec4 ,but1 leaving formal engines1 let us take an ordinary fire1 which plays in truth the part of an engine1 as far as energy is concerned4 ,we have here the cold air streaming in over the floor of the room1 and rushing into the fire1 to be there united with carbon1 while the rarefied product is carried up the chimney4 ,dismissing from our thoughts at present the process of combustion1 except as a means of supplying heat1 we see that there is a continual in-draught of cold air1 which is heated by the fire1 and then sent to mingle with the air above4 ,heat is1 in fact1 distributed by this means1 or carried from a body of high temperature1 i4e4 the fire1 to a body of low temperature1 i4e4 the outer air1 and in this process of distribution mechanical effect is obtained in the up-rush of air through the chimney with considerable velocity4 #aed4 ,our own earth is another instance of such an engine1 having the equatorial regions as its boiler1 and the polar regions as its condensers2 for1 at the equator1 the air is heated by the direct rays of the sun1 and we have there an ascending current of air1 up a chimney as it were1 the place of which is supplied by an in-draught of colder air along the ground or floor of the world1 from the poles on both sides4 ,thus the heated air makes its way from the equator to the poles in the upper regions of the atmosphere1 while the cold air makes its way from the poles to the equator along the lower regions4 ,very often1 too1 aqueous vapour as well as air is carried up by means of the sun's heat to the upper and colder atmospheric regions1 and there deposited in the shape of rain1 or hail1 or snow1 which ultimately finds its way back again to the earth1 often displaying in its passage immense mechanical energy4 ,indeed1 the mariner who hoists his sail1 and the miller who grinds his corn 7whether he use the force of the wind or that of running water71 are both dependent upon this great earth-engine1 which is constantly at work producing mechanical effect1 but always in the act of carrying heat from its hotter to its colder regions4 #aee4 ,now1 if it be essential to an engine to have two chambers1 one hot and one cold1 it is equally important that there should be a considerable temperature difference between the two4 ,if ,nature insists upon a difference before she will give us work1 we shall not be able to pacify her1 or to meet her requirements by making this difference as small as possible4 ,and hence1 cteris paribus1 we shall obtain a greater proportion of work out of a certain amount of heat passing through our engine when the temperature difference between its boiler and condenser is as great as possible4 ,in a steam-engine this difference cannot be very great1 because if the water of the boiler were at a very high temperature the pressure of its steam would become dangerous2 but in an air-engine1 or engine that heats and cools air1 the temperature difference may be much larger4 ,there are1 however1 practical inconveniences in engines for which the temperature of the boiler is very high1 and it is possible that these may prove so formidable as to turn the scale against such engines1 although in theory they ought to be very economical4 #aef4 ,the principles now stated have been employed by ,professor ,j4 ,thomson1 in his suggestion that the application of pressure would be found to lower the freezing point of water2 and the truth of this suggestion was afterwards proved by ,professor ,sir ,w4 ,thomson4 ,the following was the reasoning employed by the former3-- ,suppose that we have a chamber kept constantly at the temperature #j ,c41 or the melting point of ice1 and that we have a cylinder1 of which the sectional area is one square metre1 filled one metre in height with water1 that is to say1 containing one cubic metre of water4 ,suppose1 next1 that a well-fitting piston is placed above the surface of the water in this cylinder1 and that a considerable weight is placed upon the piston4 ,let us now take the cylinder1 water and all1 and carry it into another room1 of which the temperature is just a trifle lower4 ,in course of time the water will freeze1 and1 as it expands in freezing1 it will push up the piston and weight about ths of a metre2 and we may suppose that the piston is kept fastened in this position by means of a peg4 ,now carry back the machine into the first room1 and in the course of time the ice will be melted1 and we shall have water once more in the cylinder1 but there will now be a void space of ths of a metre between the piston and the surface4 ,we have thus acquired a certain amount of energy of position1 and we have only to pull out the peg1 and allow the piston with its weight to fall down through the vacant space1 in order to utilize this energy1 after which the arrangement is ready to start afresh4 ,again1 if the weight be very great1 the energy thus gained will be very great2 in fact1 the energy will vary with the weight4 ,in fine1 the arrangement now described is a veritable heat engine1 of which the chamber at #j ,c4 corresponds to the boiler1 and the other chamber a trifle lower in temperature to the condenser1 while the amount of work we get out of the engine--or1 in other words1 its efficiency--will depend upon the weight which is raised through the space of ths of a metre1 so that1 by increasing this weight without limit1 we may increase the efficiency of our engine without limit4 ,it would thus at first sight appear that by this device of having two chambers1 one at #j ,c41 and the other a trifle lower1 we can get any amount of work out of our water engine2 and that1 consequently1 we have managed to overcome ,nature4 ,but here ,thomson's law come into operation1 showing that we cannot overcome ,nature by any such device1 but that if we have a large weight upon our piston1 we must have a proportionally large difference of temperature between our two chambers--that is to say1 the freezing point of water1 under great pressure1 will be lower in temperature than its freezing point1 if the pressure upon it be only small4 ,before leaving this subject we must call upon our readers to realize what takes place in all heat engines4 ,it is not merely that heat produces mechanical effect1 but that a given quantity of heat absolutely passes out of existence as heat in producing its equivalent of work4 ,if1 therefore1 we could measure the mere heat produced in an engine by the burning of a ton of coals1 we should find it to be less when the engine was doing work than when it was at rest4 ,in like manner1 when a gas expands suddenly its temperature falls1 because a certain amount of its heat passes out of existence in the act of producing mechanical effect4 #aeg4 ,we have thus endeavoured to show under what conditions absorbed heat may be converted into mechanical effect4 ,this absorbed heat embraces 7,art4 #aaj7 two varieties of energy1 one of these being molecular motion1 and the other molecular energy of position4 ,let us now1 therefore1 endeavour to ascertain under what circumstances the one of these varieties may be changed into the other4 ,it is well known that it takes a good deal of heat to convert a kilogramme of ice into water1 and that when the ice is melted the temperature of the water is not perceptibly higher than that of the ice4 ,it is equally well known that it takes a great deal of heat to convert a kilogramme of boiling water into steam1 and that when the transformation is accomplished1 the steam produced is not perceptibly hotter than the boiling water4 ,in such cases the heat is said to become latent4 ,now1 in both these cases1 but more obviously in the last1 we may suppose that the heat has not had its usual office to perform1 but that1 instead of increasing the motion of the molecules of water1 it has spent its energy in tearing them asunder from each other1 against the force of cohesion which binds them together4 ,indeed1 we know as a matter of fact that the force of cohesion which is perceptible in boiling water is apparently absent from steam1 or the vapour of water1 because its molecules are too remote from one another to allow of this force being appreciable4 ,we may1 therefore1 suppose that a large part1 at least1 of the heat necessary to convert boiling water into steam is spent in doing work against molecular forces4 ,when the steam is once more condensed into hot water1 the heat thus spent reassumes the form of molecular motion1 and the consequence is that we require to take away somehow all the latent heat of a kilogramme of steam before we can convert it into boiling water4 ,in fact1 if it is difficult and tedious to convert water into steam1 it is difficult and tedious to convert steam into water4 #aeh4 ,besides the case now mentioned1 there are other instances in which1 no doubt1 molecular separation becomes gradually changed into heat motion4 ,thus1 when a piece of glass has been suddenly cooled1 its particles have not had time to acquire their proper position1 and the consequence is that the whole structure is thrown into a state of constraint4 ,in the course of time such bodies tend to assume a more stable state1 and their particles gradually come closer together4 ,it is owing to this cause that the bulb of a thermometer recently blown gradually contracts1 and it is no doubt owing to the same cause that a ,prince ,rupert's drop1 formed by dropping melted glass into water1 when broken1 falls into powder with a kind of explosion4 ,it seems probable that in all such cases these changes are attended with heat1 and that they denote the conversion of the energy of molecular separation into that of molecular motion4 #aei4 ,having thus examined the transmutations of 7,c7 into 7,d71 and of 7,d7 back again into 7,c71 let us now proceed with our list1 and see under what circumstances absorbed heat is changed into chemical separation4 ,it is well known that when certain bodies are heated1 they are decomposed2 for instance1 if limestone or carbonate of lime be heated1 it is decomposed1 the carbonic acid being given out in the shape of gas1 while quick-lime remains behind4 ,now1 heat is consumed in this process1 that is to say1 a certain amount of heat energy absolutely passes out of existence as heat and is changed into the energy of chemical separation4 ,again1 if the lime so obtained be exposed1 under certain circumstances1 to an atmosphere of carbonic acid1 it will gradually become changed into carbonate of lime2 and in this change 7which is a gradual one7 we may feel assured that the energy of chemical separation is once more converted into the energy of heat1 although we may not perceive any increment of temperature1 on account of the slow nature of the process4 ,at very high temperatures it is possible that most compounds are decomposed1 and the temperature at which this takes place1 for any compound1 has been termed its temperature of disassociation4 #afj4 ,heat energy is changed into electrical separation when tourmalines and certain other crystals are heated4 ,let us take1 for instance1 a crystal of tourmaline and raise its temperature1 and we shall find one end positively1 and the other negatively1 electrified4 ,again1 let us take the same crystal1 and suddenly cool it1 and we shall find an electrification of the opposite kind to the former1 so that the end of the axis1 which was then positive1 will now be negative4 ,now1 this separation of the electricities denotes energy2 and we have1 therefore1 in such crystals a case where the energy of heat has been changed into that of electrical separation4 ,in other words1 a certain amount of heat has passed out of existence as heat1 while in its place a certain amount of electrical separation has been obtained4 #afa4 ,let us next see under what circumstances heat is changed into electricity in motion4 ,this transmutation takes place in thermo-electricity4 ,suppose1 for instance1 that we have a bar of copper or antimony1 say copper1 soldered to a bar of bismuth1 as in ,fig4 #ab4 ,let us now heat one of the junctions1 while the other remains cool4 ,it will be found that a current of positive electricity circulates round the bar1 in the direction of the arrow-head1 going from the bismuth to the copper across the heated junction1 the existence of which may be detected by means of a compass needle1 as we see in the figure4 ,illustration3 ,fig4 #ab4 ,here1 then1 we have a case in which heat energy goes out of existence1 and is converted into that of an electric current1 and we may even arrange matters so as to make1 on this principle1 an instrument which shall be an extremely delicate test of the existence of heat4 ,by having a number of junctions of bismuth and antimony1 as in ,fig4 #ac1 and heating the upper set1 while the lower remain cool1 we get a strong current going from the bismuth to the antimony across the heated junctions1 and we may pass the current so produced round the wire of a galvanometer1 and thus1 by increasing the number of our junctions1 and also by using a very delicate galvanometer1 we may get a very perceptible effect for the smallest heating of the upper junctions4 ,this arrangement is called the thermopile1 and1 in conjunction with the reflecting galvanometer1 it affords the most delicate means known for detecting small quantities of heat4 ,illustration3 ,fig4 #ac4 #afb4 ,the last transmutation on our list with respect to absorbed heat is that in which this species of energy is transformed into radiant light and heat4 ,this takes place whenever a hot body cools in an open space--the sun1 for instance1 parts with a large quantity of his heat in this way2 and it is due1 in part at least1 to this process that a hot body cools in air1 and wholly to it that such a body cools in vacuo4 ,it is1 moreover1 due to the penetration of our eye by radiant energy that we are able to see hot bodies1 and thus the very fact that we see them implies that they are parting with their heat4 ,radiant energy moves through space with the enormous velocity of #ahh1jjj miles in one second4 ,it takes about eight minutes to come from the sun to our earth1 so that if our luminary were to be suddenly extinguished1 we should have eight minutes respite before the catastrophe overtook us4 ,besides the rays that affect the eye1 there are others which we cannot see1 and which may therefore be termed dark rays4 ,a body1 for instance1 may not be hot enough to be self-luminous1 and yet it may be rapidly cooling and changing its heat into radiant energy1 which is given off by the body1 even although neither the eye nor the touch may be competent to detect it4 ,it may nevertheless be detected by the thermopile1 which was described in ,art4 #afa4 ,we thus see how strong is the likeness between a heated body and a sounding one4 ,for just as a sounding body gives out part of its sound energy to the atmosphere around it1 so does a heated body give out part of its heat energy to the ethereal medium around it4 ,when1 however1 we consider the rates of motion of these energies through their respective media1 there is a mighty difference between the two1 sound travelling through the air with the velocity of #aajj feet a second1 while radiant energy moves over no less a space than #ahh1jjj miles in the same portion of time4 ,chemical ,separation4 #afc4 ,we now come to the energy denoted by chemical separation1 such as we possess when we have coal or carbon in one place1 and oxygen in another4 ,very evidently this form of energy of position is transmuted into heat when we burn the coal1 or cause it to combine with the oxygen of the air2 and generally1 whenever chemical combination takes place1 we have the production of heat1 even although other circumstances may interfere to prevent its recognition4 ,now1 in accordance with the principle of conservation1 it may be expected that1 if a definite quantity of carbon or of hydrogen be burned under given circumstances1 there will be a definite production of heat2 that is to say1 a ton of coals or of coke1 when burned1 will give us so many heat units1 and neither more or less4 ,we may1 no doubt1 burn our ton in such a way as to economize more or less of the heat produced2 but1 as far as the mere production of heat is concerned1 if the quantity and quality of the material burned and the circumstances of combustion be the same1 we expect the same amount of heat4 #afd4 ,the following table1 derived from the researches of ,andrews1 and those of ,favre and ,silbermann1 shows us how many units of heat we may get by burning a kilogramme of various substances4 ,,units of ,,heat developed by ,,combustion in ,,oxygen4 ,kilogrammes of ,water raised #a ,c4 ,substance by the combustion of one kilogramme ,burned4 of each substance4 ,hydrogen #cd1ace ,carbon #g1iij ,sulphur #b1bfc ,phosphorus #e1gdg ,zinc #a1cja ,iron #a1egf ,tin #a1bcc ,olefiant ,gas #aa1ijj ,alcohol #g1jaf #afe4 ,there are other methods1 besides combustion1 by which chemical combination takes place4 ,when1 for instance1 we plunge a piece of metallic iron into a solution of copper1 we find that when we take it out1 its surface is covered with copper4 ,part of the iron has been dissolved1 taking the place of the copper1 which has therefore been thrown1 in its metallic state1 upon the surface of the iron4 ,now1 in this operation heat is given out--we have in fact burned1 or oxidized1 the iron1 and we are thus furnished with a means of arranging the metals1 beginning with that which gives out most heat1 when used to displace the metal at the other extremity of the series4 #aff4 ,the following list has been formed1 on this principle1 by ,dr4 ,andrews3-- #a4 ,zinc #b4 ,iron #c4 ,lead #d4 ,copper #e4 ,mercury #f4 ,silver #g4 ,platinum --that is to say1 the metal platinum can be displaced by any other metal of the series1 but we shall get most heat if we use zinc to displace it4 ,we may therefore assume that if we displace a definite quantity of platinum by a definite quantity of zinc1 we shall get a definite amount of heat4 ,suppose1 however1 that instead of performing the operation in one step1 we make two of it4 ,let us1 for instance1 first of all displace copper by means of zinc1 and then platinum by means of copper4 ,is it not possible that the one of these processes may be more fruitful in heat giving than the other8 ,now1 ,andrews has shown us that we cannot gain an advantage over ,nature in this way1 and that if we use our zinc first of all to displace iron1 or copper1 or lead1 and then use this metal to displace platinum1 we shall obtain just the very same amount of heat as if we had used the zinc to displace the platinum at once4 #afg4 ,it ought here to be mentioned that1 very generally1 chemical action is accompanied with a change of molecular condition4 ,a solid1 for instance1 may be changed into a liquid1 or a gas into a liquid4 ,sometimes the one change counteracts the other as far as apparent heat is concerned2 but sometimes1 too1 they co-operate together to increase the result4 ,thus1 when a gas is absorbed by water1 much heat is evolved1 and we may suppose the result to be due in part to chemical combination1 and in part to the condensation of the gas into a liquid1 by which means its latent heat is rendered sensible4 ,on the other hand1 when a liquid unites with a solid1 or when two solids unite with one another1 and the product is a liquid1 we have very often the absorption of heat1 the heat rendered latent by the dissolution of the solid being more than that generated by combination4 ,freezing mixtures owe their cooling properties to this cause2 thus1 if snow and salt be mixed together1 they liquefy each other1 and the result is brine of a temperature much lower than that of either the ingredients4 #afh4 ,when heterogeneous metals1 such as zinc and copper1 are soldered together1 we have apparently a conversion of the energy of chemical separation into that of electrical separation4 ,this was first suggested by ,volta as the origin of the electrical separation which we see in the voltaic current1 and recently its existence has been distinctly proved by ,sir ,w4 ,thomson4 ,to render manifest this conversion of energy1 let us solder a piece of zinc and copper together--if we now test the bar by means of a delicate electrometer we shall find that the zinc is positively1 while the copper is negatively1 electrified4 ,we have here1 therefore1 an instance of the transmutation of one form of energy of position into another2 so much energy of chemical separation disappearing in order to produce so much electrical separation4 ,this explains the fact recorded in ,art4 #ic1 where we saw that if a battery be insulated and its poles kept apart1 the one will be charged with positive1 and the other with negative1 electricity4 #afi4 ,but further1 when such a voltaic battery is in action1 we have a transmutation of chemical separation into electricity in motion4 ,to see this1 let us consider what takes place in such a battery4 ,here no doubt the sources of electrical excitement are the points of contact of the zinc and platinum1 where1 as we see by our last article1 we have electrical separation produced4 ,but this of itself would not produce a current1 for an electrical current implies very considerable energy1 and must be fed by something4 ,now1 in the voltaic battery we have two things which accompany each other1 and which are manifestly connected together4 ,in the first place we have the combustion1 or at least the oxidation and dissolution1 of the zinc2 and we have1 secondly1 the production of a powerful current4 ,now1 evidently1 the first of these is that which feeds the second1 or1 in other words1 the energy of chemical separation of the metallic zinc is transmuted into that of an electrical current1 the zinc being virtually burned in the process of transmutation4 #agj4 ,finally1 as far as we are aware1 the energy of chemical separation is not directly transmuted into radiant light and heat4 ,electrical ,separation4 #aga4 ,in the first place the energy of electrical separation is obviously transmuted into that of visible motion1 when two oppositely electrified bodies approach each other4 #agb4 ,again1 it is transmuted into a current of electricity1 and ultimately into heat1 when a spark passes between two oppositely electrified bodies4 ,it ought1 therefore1 to be borne in mind that when the flash is seen there is no longer electricity1 what we see being merely air1 or some other material1 intensely heated by the discharge4 ,thus a man might be rendered insensible by a flash of lightning without his seeing the flash--for the effect of the discharge upon the man1 and its effect in heating the air1 might be phenomena so nearly simultaneous that the man might become insensible before he could perceive the flash4 ,electricity in ,motion4 #agc4 ,this energy is transmuted into that of visible motion when two wires conveying electrical currents in the same direction attract each other4 ,when1 for instance1 two circular currents float on water1 both going in the direction of the hands of a watch1 we have seen from ,art4 #ajj that they will move towards each other4 ,now1 here there is1 in truth1 a lessening of the intensity of each current when the motion is taking place1 for we know 7,art4 #ajd7 that when a circuit is moved into the presence of another circuit conveying a current1 there is produced by induction a current in the opposite direction2 and hence we perceive that1 when two similar currents approach each other1 each is diminished by means of this inductive influence--in fact1 a certain amount of current energy disappears from existence in order that an equivalent amount of the energy of visible motion may be produced4 #agd4 ,electricity in motion is transmuted into heat during the passage of a current along a thin wire1 or any badly conducting substance--the wire is heated in consequence1 and may even become white hot4 ,most frequently the energy of an electric current is spent in heating the wires and other materials that form the circuit4 ,now1 the energy of such a current is fed by the burning or oxidation of the metal 7generally zinc7 which is used in the circuit1 so that the ultimate effect of this combustion is the heating of the various wires and other materials through which the current passes4 #age4 ,we may1 in truth1 burn or oxidize zinc in two ways--we may oxidize it1 as we have just seen1 in the voltaic battery1 and we shall find that by the combustion of a kilogramme of zinc a definite amount of heat is produced4 ,or we may oxidize our zinc by dissolving it in acid in a single vessel1 when1 without going through the intermediate process of a current1 we shall get just as much heat out of a kilogramme of zinc as we did in the former case4 ,in fact1 whether we oxidize our zinc by the battery1 or in the ordinary way1 the quantity of heat produced will always bear the same relation to the quantity of zinc consumed2 the only difference being that1 in the ordinary way of oxidizing zinc1 the heat is generated in the vessel containing the zinc and acid1 while in the battery it may make its appearance a thousand miles away1 if we have a sufficiently long wire to convey our current4 #agf4 ,this is1 perhaps1 the right place for alluding to a discovery of ,peltier1 that a current of positive electricity passing across a junction of bismuth and antimony in the direction from the bismuth to the antimony appears to produce cold4 ,illustration3 ,fig4 #ad4 ,to understand the significance of this fact we must consider it in connection with the thermo-electric current1 which we have seen1 from ,art4 #afa1 is established in a circuit of bismuth and antimony1 of which one junction is hotter than the other4 ,suppose we have a circuit of this kind with both its junctions at the temperature of #ajj ,c4 to begin with4 ,suppose1 next1 that while we protect one junction1 we expose the other to the open air--it will1 of course1 lose heat1 so that the protected junction will now be hotter than the other4 ,the consequence will be 7,art4 #afa7 that a current of positive electricity will pass along the protected junction from the bismuth to the antimony4 ,now1 here we have an apparent anomaly1 for the circuit is cooling--that is to say1 it is losing energy--but at the very same time it is manifesting energy in another shape1 namely1 in that of an electric current1 which is circulating round it4 ,clearly1 then1 some of the heat of this circuit must be spent in generating this current2 in fact1 we should expect the circuit to act as a heat engine1 only producing current energy instead of mechanical energy1 and hence 7,art4 #aeb7 we should expect to see a conveyance of heat from the hotter to the colder parts of the circuit4 ,now1 this is precisely what the current does1 for1 passing along the hotter junction1 in the direction of the arrow-head1 it cools that junction1 and heats the colder one at ,c1--in other words1 it carries heat from the hotter to the colder parts of the circuit4 ,we should have been very much surprised had such a current cooled ,c and heated ,h1 for then we should have had a manifestation of current energy1 accompanied with the conveyance of heat from a colder to a hotter substance1 which is against the principle of ,art4 #aeb4 #agg4 ,finally1 the energy of electricity in motion is converted into that of chemical separation1 when a current of electricity is made to decompose a body4 ,part of the energy of the current is spent in this process1 and we shall get so much less heat from it in consequence4 ,suppose1 for instance1 that by oxidizing so much zinc in the battery we get1 under ordinary circumstances1 #ajj units of heat4 ,let us1 however1 set the battery to decompose water1 and we shall probably find that by oxidizing the same amount of zinc we get now only #hj units of heat4 ,clearly1 then1 the deficiency or #bj units have gone to decompose the water4 ,now1 if we explode the mixed gases which are the result of the decomposition1 we shall get back these #bj units of heat precisely1 and neither more nor less2 and thus we see that amid all such changes the quantity of energy remains the same4 ,radiant ,energy4 #agh4 ,this form of energy is converted into absorbed heat whenever it falls upon an opaque substance--some of it1 however1 is generally conveyed away by reflexion1 but the remainder is absorbed by the body1 and consequently heats it4 ,it is a curious question to ask what becomes of the radiant light from the sun that is not absorbed either by the planets of our system1 or by any of the stars4 ,we can only reply to such a question1 that as far as we can judge from our present knowledge1 the radiant energy that is not absorbed must be conceived to be traversing space at the rate of #ahh1jjj miles a second4 #agi4 ,there is only one more transmutation of radiant energy that we know of1 and that is when it promotes chemical separation4 ,thus1 certain rays of the sun are known to have the power of decomposing chloride of silver1 and other chemical compounds4 ,now1 in all such cases there is a transmutation of radiant energy into that of chemical separation4 ,the sun's rays1 too1 decompose carbonic acid in the leaves of plants1 the carbon going to form the woody fibre of the plant1 while the oxygen is set free into the air2 and of course a certain proportion of the energy of the solar rays is consumed in promoting this change1 and we have so much less heating effect in consequence4 ,but all the solar rays have not this power--for the property of promoting chemical change is confined to the blue and violet rays1 and some others which are not visible to the eye4 ,now1 these rays are entirely absent from the radiation of bodies at a comparatively low temperature1 such as an ordinary red heat1 so that a photographer would find it impossible to obtain the picture of a red-hot body1 whose only light was in itself4 #ahj4 ,the actinic1 or chemically active1 rays of the sun decompose carbonic acid in the leaves of plants1 and they disappear in consequence1 or are absorbed2 this may1 therefore1 be the reason why very few such rays are either reflected or transmitted from a sun-lit leaf1 in consequence of which the photographer finds it difficult to obtain an image of such a leaf2 in other words1 the rays which would have produced a chemical change on his photographic plate have all been used up by the leaf for peculiar purposes of its own4 #aha4 ,and here it is important to bear in mind that while animals in the act of breathing consume the oxygen of the air1 turning it into carbonic acid1 plants1 on the other hand1 restore the oxygen to the air2 thus the two kingdoms1 the animal and the vegetable1 work into each other's hands1 and the purity of the atmosphere is kept up4 ,,footnotes3 #d ,this explanation was first given by ,professors ,thomson and ,tait in their ,natural ,philosophy1 and by ,dr4 ,frankland in a lecture at the ,royal ,institution of ,london4 #e ,see ,de ,la ,rue1 ,stewart1 and ,loewy's researches on ,solar ,physics4 #f ,see the ,magnetic ,researches of ,sir ,e4 ,sabine1 also ,c4 ,meldrum on the ,periodicity of ,cyclones4 ,,chapter ,v4 ,,historical ,,sketch3 ,,the ,,dissipation ,,of ,,energy4 #ahb4 ,in the last chapter we have endeavoured to exhibit the various transmutations of energy1 and1 while doing so1 to bring forward evidence in favour of the theory of conservation1 showing that it enables us to couple together known laws1 and also to discover new ones--showing1 in fine1 that it bears about with it all the marks of a true hypothesis4 ,it may now1 perhaps1 be instructive1 to look back and endeavour to trace the progress of this great conception1 from its first beginning among the ancients1 up to its triumphant establishment by the labours of ,joule and his fellow-workers4 #ahc4 ,mathematicians inform us that if matter consists of atoms or small parts1 which are actuated by forces depending only upon the distances between these parts1 and not upon the velocity1 then it may be demonstrated that the law of conservation of energy will hold good4 ,thus we see that conceptions regarding atoms and their forces are allied to conceptions regarding energy4 ,a medium of some sort pervading space seems also necessary to our theory4 ,in fine1 a universe composed of atoms1 with some sort of medium between them1 is to be regarded as the machine1 and the laws of energy as the laws of working of this machine4 ,it may be that a theory of atoms of this sort1 with a medium between them1 is not after all the simplest1 but we are probably not yet prepared for any more general hypothesis4 ,now1 we have only to look to our own solar system1 in order to see on a large scale an illustration of this conception1 for there we have the various heavenly bodies attracting one another1 with forces depending only on the distances between them1 and independent of the velocities2 and we have likewise a medium of some sort1 in virtue of which radiant energy is conveyed from the sun to the earth4 ,perhaps we shall not greatly err if we regard a molecule as representing on a small scale something analogous to the solar system1 while the various atoms which constitute the molecule may be likened to the various bodies of the solar system4 ,the short historical sketch which we are about to give will embrace1 therefore1 along with energy1 the progress of thought and speculation with respect to atoms and also with respect to a medium1 inasmuch as these subjects are intimately connected with the doctrines of energy4 ,heraclitus on ,energy4 #ahd4 ,heraclitus1 who flourished at ,ephesus1 ,b4,c4 #ejj1 declared that fire was the great cause1 and that all things were in a perpetual flux4 ,such an expression will no doubt be regarded as very vague in these days of precise physical statements2 and yet it seems clear that ,heraclitus must have had a vivid conception of the innate restlessness and energy of the universe1 a conception allied in character to1 and only less precise than that of modern philosophers1 who regard matter as essentially dynamical4 ,democritus on ,atoms4 #ahe4 ,democritus1 who was born #dgj ,b4,c41 was the originator of the doctrine of atoms1 a doctrine which in the hands of ,john ,dalton has enabled the human mind to lay hold of the laws which regulate chemical changes1 as well as to picture to itself what is there taking place4 ,perhaps there is no doctrine that has nowadays a more intimate connection with the industries of life than this of atoms1 and it is probable that no intelligent director of chemical industry among civilized nations fails to picture to his own mind1 by means of this doctrine1 the inner nature of the changes which he sees with his eyes4 ,now1 it is a curious circumstance that ,bacon should have lighted upon this very doctrine of atoms1 in order to point one of his philosophical morals4 8,nor is it less an evil0 7says he71 8that in their philosophies and contemplations men spend their labour in investigating and treating of the first principles of things1 and the extreme limits of nature1 when all that is useful and of avail in operation is to be found in what is intermediate4 ,hence it happens that men continue to abstract ,nature till they arrive at potential and unformed matter2 and again they continue to divide ,nature1 until they have arrived at the atom2 things which1 even if true1 can be of little use in helping on the fortunes of men40 ,surely we ought to learn a lesson from these remarks of the great ,father of experimental science1 and be very cautious before we dismiss any branch of knowledge or train of thought as essentially unprofitable4 ,aristotle on a ,medium4 #ahf4 ,as regards the existence of a medium1 it is remarked by ,whewell that the ancients also caught a glimpse of the idea of a medium1 by which the qualities of bodies1 as colours and sounds are perceived1 and he quotes the following from ,aristotle3-- 8,in a void there could be no difference of up and down2 for1 as in nothing there are no differences1 so there are none in a privation or negation40 ,upon this the historian of science remarks1 8,it is easily seen that such a mode of reasoning elevates the familiar forms of language1 and the intellectual connexions of terms1 to a supremacy over facts40 ,nevertheless1 may it not be replied that our conceptions of matter are deduced from the familiar experience1 that certain portions of space affect us in a certain manner2 and1 consequently1 are we not entitled to say there must be something where we experience the difference of up or down8 ,is there1 after all1 a very great difference between this argument and that of modern physicists in favour of a plenum1 who tell us that matter cannot act where it is not8 ,aristotle seems also to have entertained the idea that light is not any body1 or the emanation of any body 7for that1 he says1 would be a kind of body71 and that therefore light is an energy or act4 ,the ,ideas of the ,ancients were not ,prolific4 #ahg4 ,these quotations render it evident that the ancients had1 in some way1 grasped the idea of the essential unrest and energy of things4 ,they had also the idea of small particles or atoms1 and1 finally1 of a medium of some sort4 ,and yet these ideas were not prolific--they gave rise to nothing new4 ,now1 while the historian of science is unquestionably right in his criticism of the ancients1 that their ideas were not distinct and appropriate to the facts1 yet we have seen that they were not wholly ignorant of the most profound and deeply-seated principles of the material universe4 ,in the great hymn chanted by ,nature1 the fundamental notes were early heard1 but yet it required long centuries of patient waiting for the practised ear of the skilled musician to appreciate the mighty harmony aright4 ,or1 perhaps1 the attempts of the ancients were as the sketches of a child who just contrives to exhibit1 in a rude way1 the leading outlines of a building2 while the conceptions of the practised physicist are more allied to those of the architect1 or1 at least1 of one who has realized1 to some extent1 the architect's views4 #ahh4 ,the ancients possessed great genius and intellectual power1 but they were deficient in physical conceptions1 and1 in consequence1 their ideas were not prolific4 ,it cannot indeed be said that we of the present age are deficient in such conceptions2 nevertheless1 it may be questioned whether there is not a tendency to rush into the opposite extreme1 and to work physical conceptions to an excess4 ,let us be cautious that in avoiding ,scylla1 we do not rush into ,charybdis4 ,for the universe has more than one point of view1 and there are possibly regions which will not yield their treasures to the most determined physicists1 armed only with kilogrammes and metres and standard clocks4 ,descartes1 ,newton1 and ,huyghens on a ,medium4 #ahi4 ,in modern times ,descartes1 author of the vertical hypothesis1 necessarily presupposed the existence of a medium in inter-planetary spaces1 but on the other hand he was one of the originators of that idea which regards light as a series of particles shot out from a luminous body4 ,newton likewise conceived the existence of a medium1 although he became an advocate of the theory of emission4 ,it is to ,huyghens that the credit belongs of having first conceived the undulatory theory of light with sufficient distinctness to account for double refraction4 ,after him1 ,young1 ,fresnel1 and their followers1 have greatly developed the theory1 enabling it to account for the most complicated and wonderful phenomena4 ,bacon on ,heat4 #aij4 ,with regard to the nature of heat1 ,bacon1 whatever may be thought of his arguments1 seems clearly to have recognized it as a species of motion4 ,he says1 8,from these instances1 viewed together and individually1 the nature of which heat is the limitation seems to be motion20 and again he says1 8,but when we say of motion that it stands in the place of a genus to heat1 we mean to convey1 not that heat generates motion or motion heat 7although even both may be true in some cases71 but that essential heat is motion and nothing else40 ,nevertheless it required nearly three centuries before the true theory of heat was sufficiently rooted to develop into a productive hypothesis4 ,principle of ,virtual ,velocities4 #aia4 ,in a previous chapter we have already detailed the labours in respect of heat of ,davy1 ,rumford1 and ,joule4 ,galileo and ,newton1 if they1 did not grasp the dynamical nature of heat1 had yet a clear conception of the functions of a machine4 ,the former saw that what we gain in power we lose in space2 while the latter went further1 and saw that a machine1 if left to itself1 is strictly limited in the amount of work which it can accomplish1 although its energy may vary from that of motion to that of position1 and back again1 according to the geometric laws of the machine4 ,rise of true ,conceptions regarding ,work4 #aib4 ,there can1 we think1 be no question that the great development of industrial operations in the present age has indirectly furthered our conceptions regarding work4 ,humanity invariably strives to escape as much as possible from hard work4 ,in the days of old those who had the power got slaves to work for them2 but even then the master had to give some kind of equivalent for the work done4 ,for at the very lowest a slave is a machine1 and must be fed1 and is moreover apt to prove a very troublesome machine if not properly dealt with4 ,the great improvements in the steam engine1 introduced by ,watt1 have done as much1 perhaps1 as the abolition of slavery to benefit the working man4 ,the hard work of the world has been put upon iron shoulders1 that do not smart2 and1 in consequence1 we have had an immense extension of industry1 and a great amelioration in the position of the lower classes of mankind4 ,but if we have transferred our hard work to machines1 it is necessary to know how to question a machine--how to say to it1 ,at what rate can you labour8 how much work can you turn out in a day8 ,it is necessary1 in fact1 to have the clearest possible idea of what work is4 ,our readers will see from all this that men are not likely to err in their method of measuring work4 ,the principles of measurement have been stamped as it were with a brand into the very heart and brain of humanity4 ,to the employer of machinery or of human labour1 a false method of measuring work simply means ruin2 he is likely1 therefore1 to take the greatest possible pains to arrive at accuracy in his determination4 ,perpetual ,motion4 #aic4 ,now1 amid the crowd of workers smarting from the curse of labour1 there rises up every now and then an enthusiast1 who seeks to escape by means of an artifice from this insupportable tyranny of work4 ,why not construct a machine that will go on giving you work without limit without the necessity of being fed in any way4 ,nature must have some weak point in her armour2 there must surely be some way of getting round her2 she is only tyrannous on the surface1 and in order to stimulate our ingenuity1 but will yield with pleasure to the persistence of genius4 ,now1 what can the man of science say to such an enthusiast8 ,he cannot tell him that he is intimately acquainted with all the forces of ,nature1 and can prove that perpetual motion is impossible2 for1 in truth1 he knows very little of these forces4 ,but he does think that he has entered into the spirit and design of ,nature1 and therefore he denies at once the possibility of such a machine4 ,but he denies it intelligently1 and works out this denial of his into a theory which enables him to discover numerous and valuable relations between the properties of matter--produces1 in fact1 the laws of energy and the great principle of conservation4 ,theory of ,conservation4 #aid4 ,we have thus endeavoured to give a short sketch of the history of energy1 including its allied problems1 up to the dawn of the strictly scientific period4 ,we have seen that the unfruitfulness of the earlier views was due to a want of scientific clearness in the conceptions entertained1 and we have now to say a few words regarding the theory of conservation4 ,here also the way was pointed out by two philosophers1 namely1 ,grove in this country1 and ,mayer on the continent1 who showed certain relations between the various forms of energy2 the name of ,sguin ought likewise to be mentioned4 ,nevertheless1 to ,joule belongs the honour of establishing the theory on an incontrovertible basis3 for1 indeed1 this is preeminently a case where speculation has to be tested by unimpeachable experimental evidence4 ,here the magnitude of the principle is so vast1 and its importance is so great1 that it requires the strong fire of genius1 joined to the patient labours of the scientific experimentalist1 to forge the rough ore into a good weapon that will cleave its way through all obstacles into the very citadel of ,nature1 and into her most secret recesses4 ,following closely upon the labours of ,joule1 we have those of ,william and ,james ,thomson1 ,helmholtz1 ,rankine1 ,clausius1 ,tait1 ,andrews1 ,maxwell1 who1 along with many others1 have advanced the subject2 and while ,joule gave his chief attention to the laws which regulate the transmutation of mechanical energy into heat1 ,thomson1 ,rankine1 and ,clausius gave theirs to the converse problem1 or that which relates to the transmutation of heat into mechanical energy4 ,thomson1 especially1 has pushed forward so resolutely from this point of view that he has succeeded in grasping a principle scarcely inferior in importance to that of the conservation of energy itself1 and of this principle it behoves us now to speak4 ,dissipation of ,energy4 #aie4 ,joule1 we have said1 proved the law according to which work may be changed into heat2 and ,thomson and others1 that according to which heat may be changed into work4 ,now1 it occurred to ,thomson that there was a very important and significant difference between these two laws1 consisting in the fact that1 while you can with the greatest ease transform work into heat1 you can by no method in your power transform all the heat back again into work4 ,in fact1 the process is not a reversible one2 and the consequence is that the mechanical energy of the universe is becoming every day more and more changed into heat4 ,it is easily seen that if the process were reversible1 one form of a perpetual motion would not be impossible4 ,for1 without attempting to create energy by a machine1 all that would be needed for a perpetual motion would be the means of utilizing the vast stores of heat that lie in all the substances around us1 and converting them into work4 ,the work would no doubt1 by means of friction and otherwise1 be ultimately reconverted into heat2 but if the process be reversible1 the heat could again be converted into work1 and so on for ever4 ,but the irreversibility of the process puts a stop to all this4 ,in fact1 ,i may convince myself by rubbing a metal button on a piece of wood how easily work can be converted into heat1 while the mind completely fails to suggest any method by which this heat can be reconverted into work4 ,now1 if this process goes on1 and always in one direction1 there can be no doubt about the issue4 ,the mechanical energy of the universe will be more and more transformed into universally diffused heat1 until the universe will no longer be a fit abode for living beings4 ,the conclusion is a startling one1 and1 in order to bring it more vividly before our readers1 let us now proceed to acquaint ourselves with the various forms of useful energy that are at present at our disposal1 and at the same time endeavour to trace the ultimate sources of these supplies4 ,natural ,energies and their ,sources4 #aif4 ,of energy in repose we have the following varieties3--7#a47 ,the energy of fuel4 7#b47 ,that of food4 7#c47 ,that of a head of water4 7#d47 ,that which may be derived from the tides4 7#e47 ,the energy of chemical separation implied in native sulphur1 native iron1 c4 ,then1 with regard to energy in action1 we have mainly the following varieties3-- 7#a47 ,the energy of air in motion4 7#b47 ,that of water in motion4 ,fuel4 #aig4 ,let us begin first with the energy implied in fuel4 ,we can1 of course1 burn fuel1 or cause it to combine with the oxygen of the air2 and we are thereby provided with large quantities of heat of high temperature1 by means of which we may not only warm ourselves and cook our food1 but also drive our heat-engines1 using it1 in fact1 as a source of mechanical power4 ,fuel is of two varieties--wood and coal4 ,now1 if we consider the origin of these we shall see that they are produced by the sun's rays4 ,certain of these rays1 as we have already remarked 7,art4 #ahj71 decompose carbonic acid in the leaves of plants1 setting free the oxygen1 while the carbon is used for the structure or wood of the plant4 ,now1 the energy of these rays is spent in this process1 and1 indeed1 there is not enough of such energy left to produce a good photographic impression of the leaf of a plant1 because it is all spent in making wood4 ,we thus see that the energy implied in wood is derived from the sun's rays1 and the same remark applies to coal4 ,indeed1 the only difference between wood and coal is one of age3 wood being recently turned out from ,nature's laboratory1 while thousands of years have elapsed since coal formed the leaves of living plants4 #aih4 ,we are1 therefore1 perfectly justified in saying that the energy of fuel is derived from the sun's rays2#g coal being the store which ,nature has laid up as a species of capital for us1 while wood is our precarious yearly income4 ,we are thus at present very much in the position of a young heir1 who has only recently come into his estate1 and who1 not content with the income1 is rapidly squandering his realized property4 ,this subject has been forcibly brought before us by ,professor ,jevons1 who has remarked that not only are we spending our capital1 but we are spending the most available and valuable part of it4 ,for we are now using the surface coal2 but a time will come when this will be exhausted1 and we shall be compelled to go deep down for our supplies4 ,now1 regarded as a source of energy1 such supplies1 if far down1 will be less effective1 for we have to deduct the amount of energy requisite in order to bring them to the surface4 ,the result is that we must contemplate a time1 however far distant1 when our supplies of coal will be exhausted1 and we shall be compelled to resort to other sources of energy4 ,food4 #aii4 ,the energy of food is analogous to that of fuel1 and serves similar purposes4 ,for just as fuel may be used either for producing heat or for doing work1 so food has a twofold office to perform4 ,in the first place1 by its gradual oxidation1 it keeps up the temperature of the body2 and in the next place it is used as a source of energy1 on which to draw for the performance of work4 ,thus a man or a horse that works a great deal requires to eat more food than if he does not work at all4 ,thus1 also1 a prisoner condemned to hard labour requires a better diet than one who does not work1 and a soldier during the fatigues of war finds it necessary to eat more than during a time of peace4 ,our food may be either of animal or vegetable origin--if it be the latter1 it is immediately derived1 like fuel1 from the energy of the sun's rays2 but if it be the former1 the only difference is that it has passed through the body of an animal before coming to us3 the animal has eaten grass1 and we have eaten the animal4 ,in fact1 we make use of the animal not only as a variety of nutritious food1 but also to enable us indirectly to utilize those vegetable products1 such as grasses1 which we could not make use of directly with our present digestive organs4 ,head of ,water4 #bjj4 ,the energy of a head of water1 like that of fuel and food1 is brought about by the sun's rays4 ,for the sun vaporizes the water1 which1 condensed again in upland districts1 becomes available as a head of water4 ,there is1 however1 the difference that fuel and food are due to the actinic power of the sun's rays1 while the evaporation and condensation of water are caused rather by their heating effect4 ,tidal ,energy4 #bja4 ,the energy derived from the tides has1 however1 a different origin4 ,in ,art4 #acc we have endeavoured to show how the moon acts upon the fluid portions of our globe1 the result of this action being a very gradual stoppage of the energy of rotation of the earth4 ,it is1 therefore1 to this motion of rotation that we must look as the origin of any available energy derived from tidal mills4 ,native ,sulphur1 c4 #bjb4 ,the last variety of available energy of position in our list is that implied in native sulphur1 native iron1 c4 ,it has been remarked by ,professor ,tait1 to whom this method of reviewing our forces is due1 that this may be the primeval form of energy1 and that the interior of the earth may1 as far as we know1 be wholly composed of matter in its uncombined form4 ,as a source of available energy it is1 however1 of no practical importance4 ,air and ,water in ,motion4 #bjc4 ,we proceed next to those varieties of available energy which represent motion1 the chief of which are air in motion and water in motion4 ,it is owing to the former that the mariner spreads his sail1 and carries his vessel from one part of the earth's surface to another1 and it is likewise owing to the same influence that the windmill grinds our corn4 ,again1 water in motion is used perhaps even more frequently than air in motion as a source of motive power4 ,both these varieties of energy are due without doubt to the heating effect of the sun's rays4 ,we may1 therefore1 affirm that with the exception of the totally insignificant supply of native sulphur1 c41 and the small number of tidal mills which may be in operation1 all our available energy is due to the sun4 ,the ,sun--a ,source of ,high ,temperature ,heat4 #bjd4 ,let us1 therefore1 now for a moment direct our attention to that most wonderful source of energy1 the ,sun4 ,we have here a vast reservoir of high temperature heat2 now1 this is a kind of superior energy which has always been in much request4 ,numberless attempts have been made to construct a perpetual light1 just as similar attempts have been made to construct a perpetual motion1 with this difference1 that a perpetual light was supposed to result from magical powers1 while a perpetual motion was attributed to mechanical skill4 ,sir ,walter ,scott alludes to this belief in his description of the grave of ,michael ,scott1 which is made to contain a perpetual light4 ,thus the ,monk who buried the wizard tells ,william of ,deloraine-- 8,lo1 ,warrior6 now the ,cross of ,red ,points to the ,grave of the mighty dead2 ,within it burns a wondrous light1 ,to chase the spirits that love the night4 ,that lamp shall burn unquenchably ,until the eternal doom shall be40 ,and again1 when the tomb was opened1 we read-- 8,i would you had been there to see ,how the light broke forth so gloriously1 ,stream'd upward to the chancel roof1 ,and through the galleries far aloof6 ,no earthly flame blazed e'er so bright40 ,no earthly flame--there the poet was right--certainly not of this earth1 where light and all other forms of superior energy are essentially evanescent4 ,a ,perpetual ,light ,impossible4 #bje4 ,in truth1 our readers will at once perceive that a perpetual light is only another name for a perpetual motion1 because we can always derive visible energy out of high temperature heat--indeed1 we do so every day in our steam engines4 ,when1 therefore1 we burn coal1 and cause it to combine with the oxygen of the air1 we derive from the process a large amount of high temperature heat4 ,but is it not possible1 our readers may ask1 to take the carbonic acid which results from the combustion1 and by means of low temperature heat1 of which we have always abundance at our disposal1 change it back again into carbon and oxygen8 ,all this would be possible if what may be termed the temperature of disassociation--that is to say1 the temperature at which carbonic acid separates into its constituents--were a low temperature1 and it would also be possible if rays from a source of low temperature possessed sufficient actinic power to decompose carbonic acid4 ,but neither of these is the case4 ,nature will not be caught in a trap of this kind4 ,as if for the very purpose of stopping all such speculations1 the temperatures of disassociation for such substances as carbonic acid are very high1 and the actinic rays capable of causing their decomposition belong only to sources of exceedingly high temperature1 such as the sun4#h ,is the ,sun an ,exception8 #bjf4 ,we may1 therefore1 take it for granted that a perpetual light1 like a perpetual motion1 is an impossibility2 and we have then to inquire if the same argument applies to our sun1 or if an exception is to be made in his favour4 ,does the sun stand upon a footing of his own1 or is it merely a question of time with him1 as with all other instances of high temperature heat8 ,before attempting to answer this question let us inquire into the probable origin of the sun's heat4 ,origin of the ,sun's ,heat4 #bjg4 ,now1 some might be disposed to cut the ,gordian knot of such an inquiry by asserting that our luminary was at first created hot2 yet the scientific mind finds itself disinclined to repose upon such an assertion4 ,we pick up a round pebble from the beach1 and at once acknowledge there has been some physical cause for the shape into which it has been worn4 ,and so with regard to the heat of the sun1 we must ask ourselves if there be not some cause not wholly imaginary1 but one which we know1 or at least suspect1 to be perhaps still in operation1 which can account for the heat of the sun4 ,now1 here it is more easy to show what cannot account for the sun's heat than what can do so4 ,we may1 for instance1 be perfectly certain that it cannot have been caused by chemical action4 ,the most probable theory is that which was first worked out by ,helmholtz and ,thomson2#i and which attributes the heat of the sun to the primeval energy of position possessed by its particles4 ,in other words1 it is supposed that these particles originally existed at a great distance from each other1 and that1 being endowed with the force of gravitation1 they have since gradually come together1 while in this process heat has been generated just as it would be if a stone were dropped from the top of a cliff towards the earth4 #bjh4 ,nor is this case wholly imaginary1 but we have some reason for thinking that it may still be in operation in the case of certain nebul which1 both in their constitution as revealed by the spectroscope1 and in their general appearance1 impress the beholder with the idea that they are not yet fully condensed into their ultimate shape and size4 ,if we allow that by this means our luminary has obtained his wonderful store of high-class energy1 we have yet to inquire to what extent this operation is going on at the present moment4 ,is it only a thing of the past1 or is it a thing also of the present8 ,i think we may reply that the sun cannot be condensing very fast1 at least1 within historical times4 ,for if the sun were sensibly larger than at present his total eclipse by the moon would be impossible4 ,now1 such eclipses have taken place1 at any rate1 for several thousands of years4 ,doubtless a small army of meteors may be falling into our luminary1 which would by this fall tend to augment his heat2 yet the supply derived from this source must surely be insignificant4 ,but if the sun be not at present condensing so fast as to derive any sufficient heat from this process1 and if his energy be very sparingly recruited from without1 it necessarily follows that he is in the position of a man whose expenditure exceeds his income4 ,he is living upon his capital1 and is destined to share the fate of all who act in a similar manner4 ,we must1 therefore1 contemplate a future period when he will be poorer in energy than he is at present1 and a period still further in the future when he will altogether cease to shine4 ,probable ,fate of the ,universe4 #bji4 ,if this be the fate of the high temperature energy of the universe1 let us think for a moment what will happen to its visible energy4 ,we have spoken already about a medium pervading space1 the office of which appears to be to degrade and ultimately extinguish all differential motion1 just as it tends to reduce and ultimately equalize all difference of temperature4 ,thus the universe would ultimately become an equally heated mass1 utterly worthless as far as the production of work is concerned1 since such production depends upon difference of temperature4 ,although1 therefore1 in a strictly mechanical sense1 there is a conservation of energy1 yet1 as regards usefulness or fitness for living beings1 the energy of the universe is in process of deterioration4 ,universally diffused heat forms what we may call the great waste-heap of the universe1 and this is growing larger year by year4 ,at present it does not sensibly obtrude itself1 but who knows that the time may not arrive when we shall be practically conscious of its growing bigness8 #baj4 ,it will be seen that in this chapter we have regarded the universe1 not as a collection of matter1 but rather as an energetic agent--in fact1 as a lamp4 ,now1 it has been well pointed out by ,thomson1 that looked at in this light1 the universe is a system that had a beginning and must have an end2 for a process of degradation cannot be eternal4 ,if we could view the universe as a candle not lit1 then it is perhaps conceivable to regard it as having been always in existence2 but if we regard it rather as a candle that has been lit1 we become absolutely certain that it cannot have been burning from eternity1 and that a time will come when it will cease to burn4 ,we are led to look to a beginning in which the particles of matter were in a diffuse chaotic state1 but endowed with the power of gravitation1 and we are led to look to an end in which the whole universe will be one equally heated inert mass1 and from which everything like life or motion or beauty will have utterly gone away4 ,,footnotes3 #g ,this fact seems to have been known at a comparatively early period to ,herschel and the elder ,stephenson4 #h ,this remark is due to ,sir ,william ,thomson4 #i ,mayer and ,waterston seem first to have caught the rudiments of this idea4 ,,chapter ,,vi4 ,,the ,,position ,,of ,,life4 #baa4 ,we have hitherto confined ourselves almost entirely to a discussion of the laws of energy1 as these affect inanimate matter1 and have taken little or no account of the position of life4 ,we have been content very much to remain spectators of the contest1 apparently forgetful that we are at all concerned in the issue4 ,but the conflict is not one which admits of on-lookers1--it is a universal conflict in which we must all take our share4 ,it may not1 therefore1 be amiss if we endeavour to ascertain1 as well as we can1 our true position4 ,twofold nature of ,equilibrium4 #bab4 ,one of our earliest mechanical lessons is on the twofold nature of equilibrium4 ,we are told that this may be of two kinds1 stable and unstable1 and a very good illustration of these two kinds is furnished by an egg4 ,let us take a smooth level table1 and place an egg upon it2 we all know in what manner the egg will lie on the table4 ,it will remain at rest1 that is to say1 it will be in equilibrium2 and not only so1 but it will be in stable equilibrium4 ,to prove this1 let us try to displace it with our finger1 and we shall find that when we remove the pressure the egg will speedily return to its previous position1 and will come to rest after one or two oscillations4 ,furthermore1 it has required a sensible expenditure of energy to displace the egg4 ,all this we express by saying that the egg is in stable equilibrium4 ,mechanical ,instability4 #bac4 ,and now let us try to balance the egg upon its longer axis4 ,probably1 a sufficient amount of care will enable us to achieve this also4 ,but the operation is a difficult one1 and requires great delicacy of touch1 and even after we have succeeded we do not know how long our success may last4 ,the slightest impulse from without1 the merest breath of air1 may be sufficient to overturn the egg1 which is now most evidently in unstable equilibrium4 ,if the egg be thus balanced at the very edge of the table1 it is quite probable that in a few minutes it may topple over upon the floor2 it is what we may call an even chance whether it will do so1 or merely fall upon the table4 ,not that mere chance has anything to do with it1 or that its movements are without a cause1 but we mean that its movements are decided by some external impulse so exceedingly small as to be utterly beyond our powers of observation4 ,in fact1 before making the trial we have carefully removed everything like a current of air1 or want of level1 or external impulse of any kind1 so that when the egg falls we are completely unable to assign the origin of the impulse that has caused it to do so4 #bad4 ,now1 if the egg happens to fall over the table upon the floor1 there is a somewhat considerable transmutation of energy2 for the energy of position of the egg1 due to the height which it occupied on the table1 has all at once been changed into energy of motion1 in the first place1 and into heat in the second1 when the egg comes into contact with the floor4 ,if1 however1 the egg happens to fall upon the table1 the transmutation of energy is comparatively small4 ,it thus appears that it depends upon some external impulse1 so infinitesimally small as to elude our observation1 whether the egg shall fall upon the floor and give rise to a comparatively large transmutation of energy1 or whether it shall fall upon the table and give rise to a transmutation comparatively small4 ,chemical ,instability4 #bae4 ,we thus see that a body1 or system1 in unstable equilibrium may become subject to a very considerable transmutation of energy1 arising out of a very small cause1 or antecedent4 ,in the case now mentioned1 the force is that of gravitation1 the arrangement being one of visible mechanical instability4 ,but we may have a substance1 or system1 in which the force at work is not gravity1 but chemical affinity1 and the substance1 or system1 may1 under certain peculiar conditions1 become chemically unstable4 ,when a substance is chemically unstable1 it means that the slightest impulse of any kind may determine a chemical change1 just as in the case of the egg the slightest impulse from without occasioned a mechanical displacement4 ,in fine1 a substance1 or system1 chemically unstable bears a relation to chemical affinity somewhat similar to that which a mechanically unstable system bears to gravity4 ,gunpowder is a familiar instance of a chemically unstable substance4 ,here the slightest spark may prove the precursor of a sudden chemical change1 accompanied by the instantaneous and violent generation of a vast volume of heated gas4 ,the various explosive compounds1 such as gun-cotton1 nitro-glycerine1 the fulminates1 and many more1 are all instances of structures which are chemically unstable4 ,machines are of two kinds4 #baf4 ,when we speak of a structure1 or a machine1 or a system1 we simply mean a number of individual particles associated together in producing some definite result4 ,thus1 the solar system1 a timepiece1 a rifle1 are examples of inanimate machines2 while an animal1 a human being1 an army1 are examples of animated structures or machines4 ,now1 such machines or structures are of two kinds1 which differ from one another not only in the object sought1 but also in the means of attaining that object4 #bag4 ,in the first place1 we have structures or machines in which systematic action is the object aimed at1 and in which all the arrangements are of a conservative nature1 the element of instability being avoided as much as possible4 ,the solar system1 a timepiece1 a steam-engine at work1 are examples of such machines1 and the characteristic of all such is their calculability4 ,thus the skilled astronomer can tell1 with the utmost precision1 in what place the moon or the planet ,venus will be found this time next year4 ,or again1 the excellence of a timepiece consists in its various hands pointing accurately in a certain direction after a certain interval of time4 ,in like manner we may safely count upon a steamship making so many knots an hour1 at least while the outward conditions remain the same4 ,in all these cases we make our calculations1 and we are not deceived--the end sought is regularity of action1 and the means employed is a stable arrangement of the forces of nature4 #bah4 ,now1 the characteristics of the other class of machines are precisely the reverse4 ,here the object aimed at is not a regular1 but a sudden and violent transmutation of energy1 while the means employed are unstable arrangements of natural forces4 ,a rifle at full cock1 with a delicate hair-trigger1 is a very good instance of such a machine1 where the slightest touch from without may bring about the explosion of the gunpowder1 and the propulsion of the ball with a very great velocity4 ,now1 such machines are eminently characterized by their incalculability4 #bai4 ,to make our meaning clear1 let us suppose that two sportsmen go out hunting together1 each with a good rifle and a good pocket chronometer4 ,after a hard day's work1 the one turns to his companion and says3--8,it is now six o'clock by my watch2 we had better rest ourselves10 upon which the other looks at his watch1 and he would be very much surprised and exceedingly indignant with the maker1 if he did not find it six o'clock also4 ,their chronometers are evidently in the same state1 and have been doing the same thing2 but what about their rifles8 ,given the condition of the one rifle1 is it possible by any refinement of calculation to deduce that of the other8 ,we feel at once that the bare supposition is ridiculous4 #bbj4 ,it is thus apparent that1 as regards energy1 structures are of two kinds4 ,in one of these1 the object sought is regularity of action1 and the means employed1 a stable arrangement of natural forces3 while in the other1 the end sought is freedom of action1 and a sudden transmutation of energy1 the means employed being an unstable arrangement of natural forces4 ,the one set of machines are characterized by their calculability--the other by their incalculability4 ,the one set1 when at work1 are not easily put wrong1 while the other set are characterized by great delicacy of construction4 ,an ,animal is a delicately-constructed ,machine4 #bba4 ,but perhaps the reader may object to our use of the rifle as an illustration4 ,for although it is undoubtedly a delicately-constructed machine1 yet a rifle does not represent the same surpassing delicacy as that1 for instance1 which characterizes an egg balanced on its longer axis4 ,even if at full cock1 and with a hair trigger1 we may be perfectly certain it will not go off of its own accord4 ,although its object is to produce a sudden and violent transmutation of energy1 yet this requires to be preceded by the application of an amount of energy1 however small1 to the trigger1 and if this be not spent upon the rifle1 it will not go off4 ,there is1 no doubt1 delicacy of construction1 but this has not risen to the height of incalculability1 and it is only when in the hands of the sportsman that it becomes a machine upon the condition of which we cannot calculate4 ,now1 in making this remark1 we define the position of the sportsman himself in the ,universe of ,energy4 ,the rifle is delicately constructed1 but not surpassingly so2 but sportsman and rifle1 together1 form a machine of surpassing delicacy1 ergo the sportsman himself is such a machine4 ,we thus begin to perceive that a human being1 or indeed an animal of any kind1 is in truth a machine of a delicacy that is practically infinite1 the condition or motions of which we are utterly unable to predict4 ,in truth1 is there not a transparent absurdity in the very thought that a man may become able to calculate his own movements1 or even those of his fellow8 ,life is like the ,commander of an ,army4 #bbb4 ,let us now introduce another analogy--let us suppose that a war is being carried on by a vast army1 at the head of which there is a very great commander4 ,now1 this commander knows too well to expose his person2 in truth1 he is never seen by any of his subordinates4 ,he remains at work in a well-guarded room1 from which telegraphic wires lead to the headquarters of the various divisions4 ,he can thus1 by means of these wires1 transmit his orders to the generals of these divisions1 and by the same means receive back information as to the condition of each4 ,thus his headquarters become a centre1 into which all information is poured1 and out of which all commands are issued4 ,now1 that mysterious thing called life1 about the nature of which we know so little1 is probably not unlike such a commander4 ,life is not a bully1 who swaggers out into the open universe1 upsetting the laws of energy in all directions1 but rather a consummate strategist1 who1 sitting in his secret chamber1 before his wires1 directs the movements of a great army4#aj #bbc4 ,let us next suppose that our imaginary army is in rapid march1 and let us try to find out the cause of this movement4 ,we find that1 in the first place1 orders to march have been issued to the troops under them by the commanders of each regiment4 ,in the next place1 we learn that staff officers1 attached to the generals of the various divisions1 have conveyed these orders to the regimental commanders2 and1 finally1 we learn that the order to march has been telegraphed from headquarters to these various generals4 ,descending now to ourselves1 it is probably somewhere in the mysterious and well-guarded brain-chamber that the delicate directive touch is given which determines our movements4 ,this chamber forms1 as it were1 the headquarters of the general in command1 who is so well withdrawn as to be absolutely invisible to all his subordinates4 #bbd4 ,joule1 ,carpenter1 and ,mayer were at an early period aware of the restrictions under which animals are placed by the laws of energy1 and in virtue of which the power of an animal1 as far as energy is concerned1 is not creative1 but only directive4 ,it was seen that1 in order to do work1 an animal must be fed2 and1 even at a still earlier period1 ,count ,rumford remarked that a ton of hay will be administered more economically by feeding a horse with it1 and then getting work out of the horse1 than by burning it as fuel in an engine4 #bbe4 ,in this chapter1 the same line of thought has been carried out a little further4 ,we have seen that life is associated with delicately-constructed machines1 so that whenever a transmutation of energy is brought about by a living being1 could we trace the event back1 we should find that the physical antecedent was probably a much less transmutation1 while again the antecedent of this would probably be found still less1 and so on1 as far as we could trace it4 #bbf4 ,but with all this1 we do not pretend to have discovered the true nature of life itself1 or even the true nature of its relation to the material universe4 ,what we have ventured is the assertion that1 as far as we can judge1 life is always associated with machinery of a certain kind1 in virtue of which an extremely delicate directive touch is ultimately magnified into a very considerable transmutation of energy4 ,indeed1 we can hardly imagine the freedom of motion implied in life to exist apart from machinery possessed of very great delicacy of construction4 ,in fine1 we have not succeeded in solving the problem as to the true nature of life1 but have only driven the difficulty into a borderland of thick darkness1 into which the light of knowledge has not yet been able to penetrate4 ,organized ,tissues are subject to ,decay4 #bbg4 ,we have thus learned two things1 for1 in the first place1 we have learned that life is associated with delicacy of construction1 and in the next 7,art4 #bbj71 that delicacy of construction implies an unstable arrangement of natural forces4 ,we have now to remark that the particular force which is thus used by living beings is chemical affinity4 ,our bodies are1 in truth1 examples of an unstable arrangement of chemical forces1 and the materials which composed them1 if not liable to sudden explosion1 like fulminating powder1 are yet preeminently the subjects of decay4 #bbh4 ,now1 this is more than a mere general statement2 it is a truth that admits of degrees1 and in virtue of which those parts of our bodies which have1 during life1 the noblest and most delicate office to perform1 are the very first to perish when life is extinct4 8,oh6 o'er the eye death most exerts his might1 ,and hurls the spirit from her throne of light2 ,sinks those blue orbs in their long last eclipse1 ,but spares us yet the charm around the lips40 ,so speaks the poet1 and we have here an aspect of things in which the lament of the poet becomes the true interpretation of nature4 ,difference between ,animals and ,inanimate ,machines4 #bbi4 ,we are now able to recognize the difference between the relations to energy of a living being1 such as man1 and a machine1 such as a steam-engine4 ,there are many points in common between the two4 ,both require to be fed1 and in both there is the transmutation of the energy of chemical separation implied in fuel and food into that of heat and visible motion4 ,but while the one--the engine--requires for its maintenance only carbon1 or some other variety of chemical separation1 the other--the living being--demands to be supplied with organized tissue4 ,in fact1 that delicacy of construction which is so essential to our well-being1 is not something which we can elaborate internally in our own frames--all that we can do is to appropriate and assimilate that which comes to us from without2 it is already present in the food which we eat4 ,ultimate ,dependence of ,life upon the ,sun4 #bcj4 ,we have already 7,art4 #bjc7 been led to recognize the sun as the ultimate material source of all the energy which we possess1 and we must now regard him as the source likewise of all our delicacy of construction4 ,it requires the energy of his high temperature rays so to wield and manipulate the powerful forces of chemical affinity2 so to balance these various forces against each other1 as to produce in the vegetable something which will afford our frames1 not only energy1 but also delicacy of construction4 ,low temperature heat would be utterly unable to accomplish this2 it consists of ethereal vibrations which are not sufficiently rapid1 and of waves that are not sufficiently short1 for the purpose of shaking asunder the constituents of compound molecules4 #bca4 ,it thus appears that animals are1 in more ways than one1 pensioners upon the sun's bounty2 and those instances1 which at first sight appear to be exceptions1 will1 if studied sufficiently1 only serve to confirm the rule4 ,thus the recent researches of ,dr4 ,carpenter and ,professor ,wyville ,thomson have disclosed to us the existence of minute living beings in the deepest parts of the ocean1 into which we may be almost sure no solar ray can penetrate4 ,how1 then1 do these minute creatures obtain that energy and delicacy of construction without which they cannot live8 in other words1 how are they fed8 ,now1 the same naturalists who discovered the existence of these creatures1 have recently furnished us with a very probable explanation of the mystery4 ,they think it highly probable that the whole ocean contains in it organic matter to a very small but yet perceptible extent1 forming1 as they express it1 a sort of diluted soup1 which thus becomes the food of these minute creatures4 #bcb4 ,in conclusion1 we are dependent upon the sun and centre of our system1 not only for the mere energy of our frames1 but also for our delicacy of construction--the future of our race depends upon the sun's future4 ,but we have seen that the sun must have had a beginning1 and that he will have an end4 ,we are thus induced to generalize still further1 and regard1 not only our own system1 but the whole material universe when viewed with respect to serviceable energy1 as essentially evanescent1 and as embracing a succession of physical events which cannot go on for ever as they are4 ,but here at length we come to matters beyond our grasp2 for physical science cannot inform us what must have been before the beginning1 nor yet can it tell us what will take place after the end4 ,,footnotes3 #aj ,see an article on 8,the ,position of ,life10 by the author of this work1 in conjunction with ,mr4 ,j4 ,n4 ,lockyer1 8,macmillan's ,magazine10 ,september1 #ahfh2 also a lecture on 8,the ,recent ,developments of ,cosmical ,physics10 by the author of this work4 ,,appendix4 ,,correlation ,,of ,,vital ,,with ,,chemical ,,and ,,physical ,,forces4 ,,by ,,joseph ,,le ,,conte1 ,,professor ,,of ,,geology ,,and ,,natural ,,history ,,in ,,the ,,university ,,of ,,california4 ,,correlation ,,of ,,vital ,,with ,,chemical ,,and ,,physical ,,forces4 ,vital force2 whence is it derived8 ,what is its relation to the other forces of ,nature8 ,the answer of modern science to these questions is3 ,it is derived from the lower forces of ,nature2 it is related to other forces much as these are related to each other--it is correlated with chemical and physical forces4 ,at one time matter was supposed to be destructible4 ,by combustion or by evaporation matter seemed to be consumed--to pass out of existence2 but now we know it only changes its form from the solid or liquid to the gaseous condition--from the visible to the invisible--and that1 amid all these changes1 the same quantity of matter remains4 ,creation or destruction of matter1 increase or diminution of matter1 lies beyond the domain of ,science2 her domain is confined entirely to the changes of matter4 ,now1 it is the doctrine of modern science that the same is true of force4 ,force seems often to be annihilated4 ,two cannon-balls of equal size and velocity meet each other and fall motionless4 ,the immense energy of these moving bodies seems to pass out of existence4 ,but not so2 it is changed into heat1 and the exact amount of heat may be calculated2 moreover1 an equal amount of heat may be changed back again into an equal amount of momentum4 ,here1 therefore1 force is not lost1 but is changed from a visible to an invisible form4 ,motion is changed from bodily motion into molecular motion4 ,thus heat1 light1 electricity1 magnetism1 chemical affinity1 and mechanical force1 are transmutable into each other1 back and forth2 but1 amid all these changes1 the amount of force remains unchanged4 ,force is incapable of destruction1 except by the same power which created it4 ,the domain of ,science lies within the limits of these changes--creation and annihilation lie outside of her domain4 ,the mutual convertibility of forces into each other is called correlation of forces2 the persistence of the same amount1 amid all these protean forms1 is called conservation of force4#aa ,the correlation of physical forces with each other and with chemical force is now universally acknowledged and somewhat clearly conceived4 ,the correlation of vital force with these is not universally acknowledged1 and1 where acknowledged1 is only imperfectly conceived4 ,in #ahei ,i published a paper#ab in which ,i attempted to put the idea of correlation of vital force with chemical and physical forces in a more definite and scientific form4 ,the views expressed in that paper have been generally adopted by physiologists4 ,since the publication of the paper referred to1 the subject has lain in my mind1 and grown at least somewhat4 ,i propose1 therefore1 now to rembody my views in a more popular form1 with such additions as have occurred to me since4 ,there are four planes of material existence1 which may be represented as raised one above another4 ,these are3 #a4 ,the plane of elementary existence2 #b4 ,the plane of chemical compounds1 or mineral kingdom2 #c4 ,the plane of vegetable existence2 and1 #d4 ,the plane of animal existence4 ,their relations to each other are truly expressed by writing them one above the other1 thus3 ,i may sometimes use the word energy instead4 ,if any one should charge me with want of precision in language1 my answer is3 ,our language cannot be more precise until our ideas in this department are far clearer than now4 #d4 ,animal ,kingdom4 #c4 ,vegetable ,kingdom4 #b4 ,mineral ,kingdom4 #a4 ,elements4 ,now1 it is a remarkable fact that there is a special force1 whose function it is to raise matter from each plane to the plane above1 and to execute movements on the latter4 ,thus1 it is the function of chemical affinity alone to raise matter from ,no4 #a to ,no4 #b1 as well as to execute all the movements1 back and forth1 by action and reaction2 in a word1 to produce all the phenomena on ,no4 #b which together constitute the science of chemistry4 ,it is the prerogative of vegetable life-force alone to lift matter from ,no4 #b to ,no4 #c1 as well as to execute all the movements on that plane1 which together constitute the science of vegetable physiology4 ,it is the prerogative of animal life-force alone to lift matter from ,no4 #c to ,no4 #d1 and to preside over the movements on this plane1 which together constitute the science of animal physiology4 ,but there is no force in ,nature capable of raising matter at once from ,no4 #a to ,no4 #c1 or from ,no4 #b to ,no4 #d1 without stopping and receiving an accession of force1 of a different kind1 on the intermediate plane4 ,plants cannot feed upon elements1 but only on chemical compounds2 animals cannot feed on minerals1 but only on vegetables4 ,we shall see in the sequel that this is the necessary result of the principle of conservation of force in vital phenomena4 ,it is well known that atoms1 in a nascent state--i4 e41 at the moment of their separation from previous combination--are endowed with peculiar and powerful affinity4 ,oxygen and nitrogen1 nitrogen and hydrogen1 hydrogen and carbon1 which show no affinity for each other under ordinary circumstances1 readily unite when one or both are in a nascent condition4 ,the reason seems to be that1 when the elements of a compound are torn asunder1 the chemical affinity which previously bound them together is set free1 ready and eager to unite the nascent elements with whatever they come in contact with4 ,this state of exalted chemical energy is retained but a little while1 because it is liable to be changed into some other form of force1 probably heat1 and is therefore no longer chemical energy4 ,to illustrate by the planes3 matter falling down from ,no4 #b to ,no4 #a generates force by which matter is lifted from ,no4 #a to ,no4 #b4 ,decomposition generates the force by which combination is effected4 ,this principle underlies every thing ,i shall further say4 ,there are1 therefore1 two ideas or principles underlying this paper3 #a4 ,the correlation of vital with physical and chemical forces2 #b4 ,that in all cases vital force is produced by decomposition--is transformed nascent affinity4 ,neither of these is new4 ,grove1 many years ago1 brought out1 in a vague manner1 the idea that vital force was correlated with chemical and physical forces4#ac ,in #ahdh ,dr4 ,freke1 ,m4 ,r4 ,i4 ,a41 of ,dublin1 first advanced the idea that vital force of animal life was generated by decomposition4 ,in #ahea the same idea was brought out again by ,dr4 ,watters1 of ,st4 ,louis4 ,these papers were unknown to me when ,i wrote my article4 ,they have been sent to me in the last few years by their respective authors4 ,neither of these authors1 however1 extends this principle to vegetation1 the most fundamental and most important phenomenon of life4 ,in #aheg the same idea was again brought out by ,prof4 ,henry1 of the ,smithsonian ,institution1 and by him extended to vegetation4 ,i do not1 therefore1 now claim to have first advanced this idea1 but ,i do claim to have in some measure rescued it from vagueness1 and given it a clearer and more scientific form4 ,i wish now to apply these principles in the explanation of the most important phenomena of vegetable and animal life3 #a4 ,,vegetation4--,the most important phenomenon in the life-history of a plant--in fact1 the starting-point of all life1 both vegetable and animal--is the formation of organic matter in the leaves4 ,the necessary conditions for this wonderful change of mineral into organic matter seem to be1 sunlight1 chlorophyl1 and living protoplasm1 or bioplasm4 ,this is the phenomenon ,i wish now to discuss4 ,the plastic matters of which vegetable structure is built are of two kinds--amyloids and albuminoids4 ,the amyloids1 or starch and sugar groups1 consist of ,c1 ,h1 and ,o2 the albuminoids of ,c1 ,h1 ,o1 ,n1 and a little ,s and ,p4 ,the quantity of sulphur and phosphorus is very small1 and we will neglect them in this discussion4 ,the food out of which these substances are elaborated are1 ,,co1 ,h,o1 and ,h#c,n--carbonic acid1 water1 and ammonia4 ,now1 by the agency of sunlight in the presence of chlorophyl and bioplasm1 these chemical compounds 7,,co1 ,h,o1 and ,h#c,n7 are torn asunder1 or shaken asunder1 or decomposed2 the excess of ,o1 or of ,o and ,h1 is rejected1 and the remaining elements in a nascent condition combine to form organic matter4 ,to form the amyloids--starch1 dextrine1 sugar1 cellulose--only ,,co and ,h,o are decomposed1 and excess of ,o rejected4 ,to form albuminoids1 or protoplasm1 ,,co1 ,h,o1 and ,h#c,n1 are decomposed1 and excess of ,o and ,h rejected4 ,it would seem in this case1 therefore1 that physical force 7light7 is changed into nascent chemical force1 and this nascent chemical force1 under the peculiar conditions present1 forms organic matter1 and reappears as vital force4 ,light falling on living green leaves is destroyed or consumed in doing the work of decomposition2 disappears as light1 to reappear as nascent chemical energy2 and this in its turn disappears in forming organic matter1 to reappear as the vital force of the organic matter thus formed4 ,the light which disappears is proportioned to the ,o1 or the ,o and ,h rejected2 is proportioned also to the quantity of organic matter formed1 and also to the amount of vital force resulting4 ,to illustrate3 ,in the case of amyloids1 oxygen-excess falling or running down from plane ,no4 #b to plane ,no4 #a generates force to raise ,c1 ,h1 and ,o1 from plane ,no4 #b to plane ,no4 #c4 ,in the case of albuminoids1 oxygen-excess and hydrogen-excess running down from ,no4 #b to ,no4 #a generate force to raise ,c1 ,h1 ,o1 and ,n1 from ,no4 #b to ,no4 #c4 ,to illustrate again3 ,as sun-heat falling upon water disappears as heat1 to reappear as mechanical power1 raising the water into the clouds1 so sunlight falling upon green leaves disappears as light1 to reappear as vital force lifting matter from the mineral into the organic kingdom4 #b4 ,,germination4--,growing plants1 it is seen1 take their life-force from the sun2 but seeds germinate and commence to grow in the dark4 ,evidently there must be some other source from which they draw their supply of force4 ,they cannot draw force from the sun4 ,this fact is intimately connected with another fact1 viz41 that they do not draw their food from the mineral kingdom4 ,the seed in germination feeds entirely upon a supply of organic matter laid up for it by the mother-plant4 ,it is the decomposition of this organic matter which supplies the force of germination4 ,chemical compounds are comparatively stable--it requires sunlight to tear them asunder2 but organic matter is more easily decomposed--it is almost spontaneously decomposed4 ,it may be that heat 7a necessary condition of germination7 is the force which determines the decomposition4 ,however this may be1 it is certain that a portion of the organic matter laid up in the seed is decomposed1 burned up1 to form ,,co and ,h,o1 and that this combustion furnishes the force by which the mason-work of tissue-making is accomplished4 ,in other words1 of the food laid up in the form of starch1 dextrine1 protoplasm1 a portion is decomposed to furnish the force by which the remainder is organized4 ,hence the seed always loses weight in germination2 it cannot develop unless it is in part consumed2 8it is not quickened except it die40 ,this self-consumption continues until the leaves and roots are formed2 then it begins to draw force from the sun1 and food from the mineral kingdom4 ,to illustrate3 ,in germination1 matter running down from plane ,no4 #c to plane ,no4 #b generates force by which other similar matter is moved about and raised to a somewhat higher position on plane ,no4 #c4 ,as water raised by the sun may be stored in reservoirs1 and in running down from these may do work1 so matter raised by sun-force into the organic kingdom by one generation is stored as force to do the work of germination of the next generation4 ,again1 as1 in water running through an hydraulic ram1 a portion runs to waste1 in order to generate force to lift the remainder to a higher level1 so1 of organic matter stored in the seed1 a portion runs to waste to create force to organize the remainder4 ,thus1 then1 it will be seen that three things1 viz41 the absence of sunlight1 the use of organic food1 and the loss of weight1 are indissolubly connected in germination1 and all explained by the principle of conservation of force4 #c4 ,,starting ,,of ,,buds4--,deciduous trees are entirely destitute of leaves during the winter4 ,the buds must start to grow in the spring without leaves1 and therefore without drawing force from the sun4 ,hence1 also1 food in the organic form must be1 and is1 laid up from the previous year in the body of the tree4 ,a portion of this is consumed with the formation of ,,co and ,h,o1 in order to create force for the development of the buds4 ,so soon as by this means the leaves are formed1 the plant begins to draw force from the sun1 and food from the mineral kingdom4 #d4 ,,pale ,,plants4--,fungi and etiolated plants have no chlorophyl1 therefore cannot draw their force from the sun1 nor make organic matters from inorganic4 ,hence these also must feed on organic matter2 not1 indeed1 on starch1 dextrine1 and protoplasm1 but on decaying organic matter4 ,in these plants the organic matter is taken up in some form intermediate between the planes ,no4 #c and ,no4 #b4 ,the matter thus taken up is1 a portion of it1 consumed with the formation of ,,co and ,h,o1 in order to create force necessary to organize the remainder4 ,to illustrate3 ,matter falling from some intermediate point between ,no4 #b and ,no4 #c to ,no4 #b1 produces force sufficient to raise matter from the same intermediate point to ,no4 #c2 a portion runs to waste downward1 and creates force to push the remainder upward4 #e4 ,,growth ,,of ,,green ,,plants ,,at ,,night4--,it is well known that almost all plants grow at night as well as in the day4 ,it is also known that plants at night exhale ,,co4 ,these two facts have not1 however1 as far as ,i know1 been connected with one another1 and with the principle of conservation of force4 ,it is usually supposed that in the night the decomposition of ,,co and exhalation of oxygen are checked by withdrawal of sun light1 and some of the ,,co in the ascending sap is exhaled by a physical law4 ,but this does not account for the growth4 ,it is evident that1 in the absence of sun light1 the force required for the work of tissue-building can be derived only from the decomposition and combustion of organic matter4 ,there are two views as to the source of this organic matter1 either or both of which may be correct3 ,first4 ,there seems to be no doubt that most plants1 especially those grown in soils rich in humus1 take up a portion of their food in the form of semi-organic matter1 or soluble humus4 ,the combustion of a portion of this in every part of the plant1 by means of oxygen also absorbed by the roots1 and the formation of ,,co1 undoubtedly creates a supply of force night and day1 independently of sunlight4 ,the force thus produced by the combustion of a portion might be used to raise the remainder into starch1 dextrine1 etc41 or might be used in tissue-building4 ,during the day1 the ,,co thus produced would be again decomposed in the leaves by sunlight1 and thus create an additional supply of force4 ,during the night1 the ,,co would be exhaled4#ad ,again3 ,it is possible that more organic matter is made by sunlight during the day than is used up in tissue-building4 ,some of this excess is again consumed1 and forms ,,co and ,h,o1 in order to continue the tissue-building process during the night4 ,thus the plant during the day stores up sun-force sufficient to do its work during the night4 ,it has been suggested by ,dr4 ,j4 ,c4 ,draper1#ae though not proved1 or even rendered probable1 that the force of tissue-building 7force plastique7 is always derived from decomposition1 or combustion of organic matter4 ,in that case1 the force of organic-matter formation is derived from the sun1 while the force of tissue-building 7which is relatively small7 is derived from the combustion of organic matter thus previously formed4 #f4 ,,fermentation4--,the plastic matters out of which vegetable tissue is built1 and which are formed by sunlight in the leaves1 are of two kinds1 viz41 amyloids 7dextrine1 sugar1 starch1 cellulose71 and albuminoids1 or protoplasm4 ,now1 the amyloids are comparatively stable1 and do not spontaneously decompose2 but the albuminoids not only decompose spontaneously themselves1 but drag down the amyloids with which they are associated into concurrent decomposition--not only change themselves1 but propagate a change into amyloids4 ,albuminoids1 in various stages and kinds of decomposition1 are called ferments4 ,the propagated change in amyloids is called fermentation4 ,by various kinds of ferments1 amyloids are thus dragged down step by step to the mineral kingdom1 viz41 to ,,co and ,h,o4 ,the accompanying table exhibits the various stages of the descent of starch1 and the ferments by which they are effected3 #a4 ,starch #b4 ,dextrine ,diastase4 #c4 ,sugar #d4 ,alcohol and ,,co ,yeast4 #e4 ,acetic acid ,mother of vinegar4 #f4 ,,co and ,h,o ,mould4 ,by appropriate means1 the process of descent may be stopped on any one of these planes4 ,by far too much is1 unfortunately1 stopped on the fourth plane4 ,the manufacturer and chemist may determine the downward change through all the planes1 and the chemist has recently succeeded in ascending again to ,no4 #d2 but the plant ascends and descends the scale at pleasure 7avoiding1 however1 the fourth and fifth71 and even passes at one step from the lowest to the highest4 ,now1 it will be seen by the table that1 connected with each of these descensive changes1 there is a peculiar ferment associated4 ,diastase determines the change from starch to dextrine and sugar--saccharification2 yeast1 the change from sugar to alcohol--fermentation2 mother of vinegar1 the change from alcohol to acetic acid--acetification2 and a peculiar mould1 the change from acetic acid to ,,co and water4 ,but what is far more wonderful and significant is1 that1 associated with each of these ferments1 except diastase1 and therefore with each of these descensive changes1 except the change from starch to sugar1 or saccharification1 there is a peculiar form of life4 ,associated with alcoholic fermentation1 there is the yeast-plant2 with acetification1 the vinegar-plant2 and with the decomposition of vinegar1 a peculiar kind of mould4 ,we will take the one which is best understood1 viz41 yeast-plant 7saccharomyce71 and its relation to alcoholic fermentation4 ,it is well known that1 in connection with alcoholic fermentation1 there is a peculiar unicelled plant which grows and multiplies4 ,fermentation never takes place without the presence of this plant2 this plant never grows without producing fermentation1 and the rapidity of the fermentation is in exact proportion to the rapidity of the growth of the plant4 ,but1 as far as ,i know1 the fact has not been distinctly brought out that the decomposition of the sugar into alcohol and carbonic acid furnishes the force by which the plant grows and multiplies4 ,if the growing cells of the yeast-plant be observed under the microscope1 it will be seen that the carbonic-acid bubbles form1 and therefore probably the decomposition of sugar takes place only in contact with the surface of the yeast-cells4 ,the yeast-plant not only assimilates matter1 but also force4 ,it decomposes the sugar in order that it may assimilate the chemical force set free4 ,we have already said that the change from starch to sugar1 determined by diastase 7saccharification71 is the only one in connection with which there is no life4 ,now1 it is a most significant fact1 in this connection1 that this is also the only change which is not1 in a proper sense1 descensive1 or1 at least1 where there is no decomposition4 ,we now pass from the phenomena of vegetable to the phenomena of animal life4 #g4 ,,development ,,of ,,the ,,egg ,,in ,,incubation4--,the development of the egg in incubation is very similar to the germination of a seed4 ,an egg consists of albuminous and fatty matters1 so inclosed that1 while oxygen of the air is admitted1 nutrient matters are excluded4 ,during incubation the egg changes into an embryo2 it passes from an almost unorganized to a highly-organized condition1 from a lower to a higher condition4 ,there is work done3 there must be expenditure of force2 but1 as we have already seen1 vital force is always derived from decomposition4 ,but1 as the matters to be decomposed are not taken ab extra1 the egg must consume itself2 that it does so1 is proved by the fact that in incubation the egg absorbs oxygen1 eliminates ,,co and probably ,h,o1 and loses weight4 ,as in the seed1 a portion of the matters contained in the egg is consumed in order to create force to organize the remainder4 ,matter runs down from plane ,no4 #d to plane ,no4 #b1 and generates force to do the work of organization on plane ,no4 #d4 ,the amount of ,,co and ,h,o formed1 and therefore the loss of weight1 is a measure of the amount of plastic work done4 #h4 ,,development ,,within ,,the ,,chrysalis ,,shell4--,it is well known that many insects emerge from the egg not in their final form1 but in a wormlike form1 called a larva4 ,after this they pass into a second passive state1 in which they are again covered with a kind of shell--a sort of second egg-state1 called the chrysalis4 ,from this they again emerge as the perfect insect4 ,the butterfly is the most familiar1 as well as the best1 illustration of these changes4 ,the larva or caterpillar eats with enormous voracity1 and grows very rapidly4 ,when its growth is complete1 it covers itself with a shell1 and remains perfectly passive and almost immovable for many days or weeks4 ,during this period of quiescence of animal functions there are1 however1 the most important changes going on within4 ,the wings and legs are formed1 the muscles are aggregated in bundles for moving these appendages1 the nervous system is more highly developed1 the mouth-organs and alimentary canal are greatly changed and more highly organized1 the simple eyes are changed into compound eyes4 ,now1 all this requires expenditure of force1 and therefore decomposition of matter2 but no food is taken1 therefore the chrysalis must consume its own substance1 and therefore lose weight4 ,it does so2 the weight of the emerging butterfly is in many cases not one-tenth that of the caterpillar4 ,force is stored up in the form of organic matter only to be consumed in doing plastic work4 #i4 ,,mature ,,animals4--,whence do animals derive their vital force8 ,i answer1 from the decomposition of their food and the decomposition of their tissues4 ,plants1 as we have seen1 derive their vital force from the decomposition of their mineral food4 ,but the chemical compounds on which plants feed are very stable4 ,their decomposition requires a peculiar and complex contrivance for the reception and utilization of sunlight4 ,these conditions are wanting in animals4 ,animals1 therefore1 cannot feed on chemical compounds of the mineral kingdom2 they must have organic food which easily runs into decomposition2 they must feed on the vegetable kingdom4 ,animals are distinguished from vegetables by incessant decay in every tissue--a decay which is proportional to animal activity4 ,this incessant decay necessitates incessant repair1 so that the animal body has been likened to a temple on which two opposite forces are at work in every part1 the one tearing down1 the other repairing the breach as fast as made4 ,in vegetables no such incessant decay has ever been made out4 ,if it exists1 it must be very trifling in comparison4 ,protoplasm1 it is true1 is taken up from the older parts of vegetables1 and these parts die2 but the protoplasm does not seem to decompose1 but is used again for tissue-building4 ,thus the internal activity of animals is of two kinds1 tissue-destroying and tissue-building2 while that of plants seems to be1 principally1 at least1 of one kind1 tissue-building4 ,animals use food for force and repair and growth1 and in the mature animal only for force and repair4 ,plants1 except in reproduction1 use food almost wholly for growth--they never stop growing4 ,now1 the food of animals is of two kinds1 amyloids and albuminoids4 ,the carnivora feed entirely on albuminoids2 herbivora on both amyloids and albuminoids4 ,all this food comes from the vegetable kingdom1 directly in the case of herbivora1 indirectly in the case of carnivora4 ,animals cannot make organic matter4 ,now1 the tissues of animals are wholly albuminoid4 ,it is obvious1 therefore1 that for the repair of the tissues the food must be albuminoid4 ,the amyloid food1 therefore 7and1 as we shall see in carnivora1 much of the albuminoid71 must be used wholly for force4 ,as coal or wood1 burned in a steam-engine1 changes chemical into mechanical energy1 so food1 in excess of what is used for repair1 is burned up to produce animal activity4 ,let us trace more accurately the origin of animal force by examples4 #aj4 ,,carnivora4--,the food of carnivora is entirely albuminoid4 ,the idea of the older physiologists1 in regard to the use of this food1 seems to have been as follows3 ,albuminoid matter is exceedingly unstable2 it is matter raised1 with much difficulty and against chemical forces1 high1 and delicately balanced on a pinnacle1 in a state of unstable equilibrium1 for a brief time1 and then rushes down again into the mineral kingdom4 ,the animal tissues1 being formed of albuminoid matter1 are short-lived2 the parts are constantly dying and decomposing2 the law of death necessitates the law of reproduction2 decomposition necessitates repair1 and therefore food for repair4 ,but the force by which repair is effected was for them1 and for many physiologists now1 underived1 innate4 ,but the doctrine maintained by me in the paper referred to is1 that the decomposition of the tissues creates not only the necessity1 but also the force1 of repair4 ,suppose1 in the first place1 a carnivorous animal uses just enough food to repair the tissues1 and no more--say an ounce4 ,then ,i say the ounce of tissue decayed not only necessitates the ounce of albuminous food for repair1 but the decomposition sets free the force by which the repair is effected4 ,but it will be perhaps objected that the force would all be consumed in repair1 and none left for animal activity of all kinds4 ,i answer3 it would not all be used up in repair1 for1 the food being already albuminoid1 there is probably little expenditure of force necessary to change it into tissue2 while1 on the other hand1 the force generated by the decomposition of tissue into ,,co1 ,h,o1 and urea1 is very great--the ascensive change is small1 the descensive change is great4 ,the decomposition of one ounce of albuminous tissue into ,,co1 ,h,o1 and urea1 would therefore create force sufficient not only to change one ounce of albuminous matter into tissue1 but also leave a considerable amount for animal activities of all kinds4 ,a certain quantity of matter1 running down from plane ,no4 #d to plane ,no4 #b1 creates force enough not only to move the same quantity of matter about on plane ,no4 #d1 but also to do much other work besides4 ,it is probable1 however1 that the wants of animal activity are so immediate and urgent that1 under these conditions1 much food would be burned for this purpose1 and would not reach the tissues1 and the tissues would be imperfectly repaired1 and would therefore waste4 ,take1 next1 the carnivorous animal full fed4 ,in this case there can be no doubt that1 while a portion of the food goes to repair the tissues1 by far the larger portion is consumed in the blood1 and passes away partly as ,,co and ,h,o through the lungs1 and partly as urea through the kidneys4 ,this part is used1 and can be of use only1 to create force4 ,the food of carnivora1 therefore1 goes partly to tissue-building1 and partly to create heat and force4 ,the force of carnivorous animals is derived partly from decomposing tissues and partly from food-excess consumed in the blood4 #aa4 ,,herbivora4--,the food of herbivora and of man is mixed--partly albuminoid and partly amyloid4 ,in man1 doubtless1 the albuminoids are usually in excess of what is required for tissue-building2 but in herbivora1 probably1 the albuminoids are not in excess of the requirements of the decomposing tissues4 ,in this case1 therefore1 the whole of the albuminoids is used for tissue-making1 and the whole of the amyloids for force-making4 ,in this class1 therefore1 these two classes of food may be called tissue-food and force-food4 ,the force of these animals1 therefore1 is derived partly from the decomposition of the tissues1 but principally from the decomposition and combustion of the amyloids and fats4 ,some physiologists speak of the amyloid and fat food as being burned to keep up the animal heat2 but it is evident that the prime object in the body1 as in the steam-engine1 is not heat1 but force4 ,heat is a mere condition and perhaps a necessary concomitant of the change1 but evidently not the prime object4 ,in tropical regions the heat is not wanted4 ,in the steam-engine1 chemical energy is first changed into heat1 and heat into mechanical energy2 in the body the change is1 probably1 much of it direct1 and not through the intermediation of heat4 #ab4 ,we see at once1 from the above1 why it is that plants cannot feed on elements1 viz41 because their food must be decomposed in order to create the organic matter out of which all organisms are built4 ,this elevation of matter1 which takes place in the green leaves of plants1 is the starting-point of life2 upon it alone is based the possibility of the existence of the organic kingdom4 ,the running down of the matter there raised determines the vital phenomena of germination1 of pale plants1 and even of some of the vital phenomena of green plants1 and all the vital phenomena of the animal kingdom4 ,the stability of chemical compounds1 usable as plant-food1 is such that a peculiar contrivance and peculiar conditions found only in the green leaves of plants are necessary for their decomposition4 ,we see1 therefore1 also1 why animals as well as pale plants cannot feed on mineral matter4 ,we easily see also why the animal activity of carnivora is greater than that of herbivora1 for the amount of force necessary for the assimilation of their albuminoid food is small1 and therefore a larger amount is left over for animal activity4 ,their food is already on plane ,no4 #d2 assimilation1 therefore1 is little more than a shifting on the plane ,no4 #d from a liquid to a solid condition--from liquid albuminoid of the blood to solid albuminoid of the tissues4 ,we see also why the internal activity of plants may conceivably be only of one kind2 for1 drawing their force from the sun1 tissue-making is not necessarily dependent on tissue-decay4 ,while1 on the other hand1 the internal activity of animals must be of two kinds1 decay and repair2 for animals always draw a portion of their force1 and starving animals the whole of their force1 from decaying tissue4 #ac4 ,there are several general thoughts suggested by this subject1 which ,i wish to present in conclusion3 a4 ,we have said there are four planes of matter raised one above the other3 #a4 ,elements2 #b4 ,chemical compounds2 #c4 ,vegetables2 #d4 ,animals4 ,their relative position is truly represented thus3 #d4 ,animals4 #c4 ,plants4 #b4 ,chemical compounds4 #a4 ,elements4 ,now1 there are also four planes of force similarly related to each other1 viz41 physical force1 chemical force1 vitality1 and will4 ,on the first plane of matter operates physical force only2 for chemical force immediately raises matter into the second plane4 ,on the second plane operates1 in addition to physical1 also chemical force4 ,on the third plane operates1 in addition to physical and chemical1 also vital force4 ,on the fourth plane1 in addition to physical1 chemical1 and vital1 also the force characteristic of animals1 viz41 will4#af ,with each elevation there is a peculiar force added to the already existing1 and a peculiar group of phenomena is the result4 ,as matter only rises step by step from plane to plane1 and never two steps at a time1 so also force1 in its transformation into higher forms of force1 rises only step by step4 ,physical force does not become vital except through chemical force1 and chemical force does not become will except through vital force4 ,again1 we have compared the various grades of matter1 not to a gradually rising inclined plane1 but to successive planes raised one above the other4 ,there are1 no doubt1 some intermediate conditions2 but1 as a broad1 general fact1 the changes from plane to plane are sudden4 ,now1 the same is true also of the forces operating on these planes--of the different grades of force1 and their corresponding groups of phenomena4 ,the change from one grade to another1 as from physical to chemical1 or from chemical to vital1 is not1 as far as we can see1 by sliding scale1 but suddenly4 ,the groups of phenomena which we call physical1 chemical1 vital1 animal1 rational1 and moral1 do not merge into each other by insensible gradations4 ,in the ascensive scale of forces1 in the evolution of the higher forces from the lower1 there are places of rapid1 paroxysmal change4 b4 ,vital force is transformed into physical and chemical forces2 but it is not on that account identical with physical and chemical force1 and therefore we ought not1 as some would have us1 discard the term vital force4 ,there are two opposite errors on this subject3 one is the old error of regarding vital force as something innate1 underived1 having no relation to the other forces of ,nature2 the other is the new error of regarding the forces of the living body as nothing but ordinary physical and chemical forces1 and therefore insisting that the use of the term vital force is absurd and injurious to science4 ,the old error is still prevalent in the popular mind1 and still haunts the minds of many physiologists2 the new error is apparently a revulsion from the other1 and is therefore common among the most advanced scientific minds4 ,there are many of the best scientists who ridicule the use of the term vital force1 or vitality1 as a remnant of superstition2 and yet the same men use the words gravity1 magnetic force1 chemical force1 physical force1 etc4 ,vital force is not underived--is not unrelated to other forces--is1 in fact1 correlated with them2 but it is nevertheless a distinct form of force1 far more distinct than any other form1 unless it be still higher forms1 and therefore better entitled to a distinct name than any lower form4 ,each form of force gives rise to a peculiar group of phenomena1 and the study of these to a peculiar department of science4 ,now1 the group of phenomena called vital is more peculiar1 and more different from other groups1 than these are from each other2 and the science of physiology is a more distinct department than either physics or chemistry2 and therefore the form of force which determines these phenomena is more distinct1 and better entitled to a distinct name1 than either physical or chemical forces4 ,de ,candolle1 in a recent paper1#ag suggests the term vital movement instead of vital force2 but can we conceive of movement without force8 ,and1 if the movement is peculiar1 so also is the form of force4 c4 ,vital is transformed physical and chemical forces2 true1 but the necessary and very peculiar condition of this transformation is the previous existence then and there of living matter4 ,there is something so wonderful in this peculiarity of vital force that ,i must dwell on it a little4 ,elements brought in contact with each other under certain physical conditions--perhaps heat or electricity--unite and rise into the second plane1 i4 e41 of chemical compounds2 so also several elements1 ,c1 ,h1 ,o1 and ,n1 etc41 brought in contact with each other under certain physical or chemical conditions1 such as light1 nascency1 etc41 unite and rise into plane ,no4 #c1 i4 e41 form organic matter4 ,in both cases there is chemical union under certain physical conditions2 but in the latter there is one unique condition1 viz41 the previous existence then and there of organic matter1 under the guidance of which the transformation of matter takes place4 ,in a word1 organic matter is necessary to produce organic matter2 there is here a law of like producing like--there is an assimilation of matter4 ,again1 physical force changes into other forms of physical force1 or into chemical force1 under certain physical conditions2 so also physical and chemical forces are changed into vital force under certain physical conditions4 ,but1 in addition1 there is one altogether unique condition of the latter change1 viz41 the previous existence then and there of vital force4 ,here1 again1 like produces like--here1 again1 there is assimilation of force4 ,this law of like producing like--this law of assimilation of matter and force--runs throughout all vital phenomena1 even to the minutest details4 ,it is a universal law of generation1 and determines the existence of species2 it is the law of formation of organic matter and organic force2 it determines all the varieties of organic matter which we call tissues and organs1 and all the varieties of organic force which we call functions4 ,the same nutrient pabulum1 endowed with the same properties and powers1 carried to all parts of a complex organism by this wonderful law of like producing like1 is changed into the most various forms and endowed with the most various powers4 ,there are certainly limits and exceptions to this law1 however2 otherwise differentiation of tissues1 organs1 and functions1 could not take place in embryonic development2 but the limits and exceptions are themselves subject to a law even more wonderful than the law of like producing like itself1 viz41 the law of evolution4 ,there is in all organic nature1 whether organic kingdom1 organic individual1 or organic tissues1 a law of variation1 strongest in the early stages1 limited very strictly by another law--the law of inheritance1 of like producing like4 d4 ,we have seen that all development takes place at the expense of decay--all elevation of one thing1 in one place1 at the expense of corresponding running down of something else in another place4 ,force is only transferred and transformed4 ,the plant draws its force from the sun1 and therefore what the plant gains the sun loses4 ,animals draw from plants1 and therefore what the animal kingdom gains the vegetable kingdom loses4 ,again1 an egg1 a seed1 or a chrysalis1 developing to a higher condition1 and yet taking nothing ab extra1 must lose weight4 ,some part must run down1 in order that the remainder should be raised to a higher condition4 ,the amount of evolution is measured by the loss of weight4 ,by the law of conservation of force1 it is inconceivable that it should be otherwise4 ,evidently1 therefore1 in the universe1 taken as a whole1 evolution of one part must be at the expense of some other part4 ,the evolution or development of the whole cosmos--of the whole universe of matter--as a unit1 by forces within itself1 according to the doctrine of conservation of force1 is inconceivable4 ,if there be any such evolution1 at all comparable with any known form of evolution1 it can only take place by a constant increase of the whole sum of energy1 i4 e41 by a constant influx of divine energy--for the same quantity of matter in a higher condition must embody a greater amount of energy4 e4 ,finally1 as organic matter is so much matter taken from the common fund of matter of earth and air1 embodied for a brief space1 to be again by death and decomposition returned to that common fund1 so also it would seem that the organic forces of the living bodies of plants and animals may be regarded as so much force drawn from the common fund of physical and chemical forces1 to be again all refunded by death and decomposition4 ,yes1 by decomposition2 we can understand this4 ,but death6 can we detect any thing returned by simple death8 ,what is the nature of the difference between the living organism and a dead organism8 ,we can detect none1 physical or chemical4 ,all the physical and chemical forces withdrawn from the common fund of ,nature1 and embodied in the living organism1 seem to be still embodied in the dead until little by little it is returned by decomposition4 ,yet the difference is immense1 is inconceivably great4 ,what is the nature of this difference expressed in the formula of material science8 ,what is it that is gone1 and whither is it gone8 ,there is something here which science cannot yet understand4 ,yet it is just this loss which takes place in death1 and before decomposition1 which is in the highest sense vital force4 ,let no one from the above views1 or from similar views expressed by others1 draw hasty conclusions in favor of a pure materialism4 ,force and matter1 or spirit and matter1 or ,god and ,nature1 these are the opposite poles of philosophy--they are the opposite poles of thought4 ,there is no clear thinking without them4 ,not only religion and virtue1 but science and philosophy1 cannot even exist without them4 ,the belief in spirit1 like the belief in matter1 rests on its own basis of phenomena4 ,the true domain of philosophy is to reconcile these with each other4 ,,footnotes3 #aa ,in recent works the word energy is used to designate active or working force as distinguished from passive or non-working force4 ,it is in this working condition only that force is conserved1 and therefore conservation of energy is the proper expression4 ,nevertheless1 since the distinction between force and energy is imperfectly or not at all defined in the higher forms of force1 and especially in the domain of life1 ,i have preferred in this article to use the word force in the general sense usual until recently4 #ab ,american ,journal of ,science1 ,november1 #ahei4 ,philadelphia ,magazine1 vol4 xix41 p4 #acc4 #ac ,in #ahde ,dr4 ,j4 ,r4 ,mayer published a paper on 8,organic ,motion and ,nutrition40 ,i have not seen it4 #ad ,for more full account1 see my paper1 ,american ,journal of ,science1 ,november1 #ahei1 sixth and seventh heads4 #ae ,american ,journal of ,science1 ,november1 #ahgb4 ,the experiments of ,dr4 ,draper are inconclusive1 because they are made on seedlings1 which1 until their supply of organic food is exhausted1 are independent of sunlight4 #af ,i might add still another plane and another force1 viz41 the human plane1 on which operate1 in addition to all the lower forces1 also free-will and reason4 ,i do not speak of these1 only because they lie beyond the present ken of inductive science4 #ag ,archives des ,sciences1 vol4 xlv41 p4 #cde1 ,december1 #ahgb4 ,,correlation ,,of ,,nervous ,,and ,,mental ,,forces4 ,,by ,,alexander ,,bain1 ,,ll4 ,d41 ,,professor ,,of ,,logic ,,and ,,mental ,,philosophy ,,in ,,the ,,university ,,of ,,aberdeen4 ,,the ,,correlation ,,of ,,nervous ,,and ,,mental ,,forces4 ,the doctrine called the correlation1 persistence1 equivalence1 transmutability1 indestructibility of force1 or the conservation of energy1 is a generality of such compass that no single form of words seems capable of fully expressing it2 and different persons may prefer different statements of it4 ,my understanding of the doctrine is1 that there are five chief powers or forces in ,nature3 one mechanical1 or molar1 the momentum of moving matter2 the others molecular1 or embodied in the molecules1 also supposed in motion--these are1 heat1 light1 chemical force1 electricity4 ,to these powers1 which are unquestionable and distinct1 it is usual to add vital force1 of which1 however1 it is difficult to speak as a whole2 but one member of our vital energies1 the nerve-force1 allied to electricity1 fully deserves to rank in the correlation4 ,taking the one mechanical force1 and those three of the molecular named heat1 chemical force1 electricity1 there has now been established a definite rate of commutation1 or exchange1 when any one passes into any other4 ,the mechanical equivalent of heat1 the #ggb foot-pounds of ,joule1 expresses the rate of exchange between mechanical momentum and heat3 the equivalent or exchange of heat and chemical force is given 7through the researches of ,andrews and others7 in the figures expressing the heat of combinations2 for example1 one pound of carbon burnt evolves heat enough to raise #h1jhj pounds of water one degree1 ,c4 ,the combination of these to equivalents would show that the consumption of half a pound of carbon would raise a man of average weight to the highest summit of the ,himalayas4 ,it is an essential part of the doctrine1 that force is never absolutely created1 and never absolutely destroyed1 but merely transmuted in form or manifestation4 ,as applied to living bodies1 the following are the usual positions4 ,in the growth of plants1 the forces of the solar ray--heat and light--are expended in decomposing 7or deoxidizing7 carbonic acid and water1 and in building up the living tissues from the liberated carbon and the other elements2 all which force is given up when these tissues are consumed1 either as fuel in ordinary combustion1 or as food in animal combustion4 ,it is this animal combustion of the matter of plants1 and of animals 7fed on plants7--namely1 the reoxidation of carbon1 hydrogen1 etc4--that yields all the manifestations of power in the animal frame4 ,and1 in particular1 it maintains 7#a7 a certain warmth or temperature of the whole mass1 against the cooling power of surrounding space2 it maintains 7#b7 mechanical energy1 as muscular power2 and it maintains 7#c7 nervous power1 or a certain flow of the influence circulating through the nerves1 which circulation of influence1 besides reacting on the other animal processes--muscular1 glandular1 etc4--has for its distinguishing concomitant the ,,mind4 ,the extension of the correlation of force to mind1 if at all competent1 must be made through the nerve-force1 a genuine member of the correlated group4 ,very serious difficulties beset the proposal1 but they are not insuperable4 ,the history of the doctrines relating to mind1 as connected with body1 is in the highest degree curious and instructive1 but1 for the purpose of the present paper1 we shall notice only certain leading stages of the speculation4#ah ,not the least important position is the ,aristotelian2 a position in some respects sounder than what followed and grew out of it4 ,in ,aristotle1 we have a kind of gradation from the life of plants to the highest form of human intelligence4 ,in the following diagram1 the continuous lines may represent the material substance1 and the dotted lines the immaterial3 ,a4 ,soul of ,plants4 ---- ,without consciousness4 ,b4 ,animal ,soul4 ---- ,body and mind inseparable4 4444 ,c4 ,human ,soul--,,nous--,intellect4 ,i4 ,passive intellect4 ---- ,body and mind inseparable4 4444 ,,ii4 ,active intellect--cognition of the highest principles4 4444 ,pure form2 detached from matter2 the prime mover of all2 immortal4 ,all the phases of life and mind are inseparably interwoven with the body 7which inseparability is ,aristotle's definition of the soul7 except the last1 the active nous1 or intellect1 which is detached from corporeal matter1 self-subsisting1 the essence of ,deity1 and an immortal substance1 although the immortality is not personal to the individual4 7,the immateriality of this higher intellectual agent was net1 however1 that thorough-going negation of all material attributes which we now understand by the word 8immaterial407 ,how such a self-subsisting and purely spiritual soul could hold communication with the body-leagued souls1 ,aristotle was at a loss to say--the difficulty reappeared after him1 and has never been got over4 ,that there should be an agency totally apart from1 and entirely transcending1 any known powers of inert matter1 involves no difficulty--for who is to limit the possibilities of existence8 ,the perplexity arises only when this radically new and superior principle is made to be1 as it were1 off and on with the material principle2 performing some of its functions in pure isolation1 and others of an analogous kind by the aid of the lower principle4 ,the difference between the active and the passive reason of ,aristotle is a mere difference of gradation2 the supporting agencies assumed by him are a total contrast in kind--wide as the poles asunder4 ,there is no breach of continuity in the phenomena1 there is an impassable chasm between their respective foundations4 ,fifteen centuries after ,aristotle1 we reach what may be called the modern settlement of the relations of mind and body1 effected by ,thomas ,aquinas4 ,he extended the domain of the independent immaterial principle from the highest intellectual soul of ,aristotle to all the three souls recognized by him--the vegetable or plant soul 7without consciousness71 the animal soul 7with consciousness71 and the intellect throughout4 ,the two lower souls--the vegetable and the animal--need the coperation of the body in this life2 the intellect works without any bodily organ1 except that it makes use of the perceptions of the senses4 ,a4 ,vegetable or ,nutritive ,soul4 ---- ,incorporates an immaterial part1 although unconscious4 4444 ,b4 ,animal ,soul4 ---- ,has an immaterial part1 with consciousness4 4444 ,c4 ,intellect4 4444 ,purely immaterial4 ,the animal soul1 ,b1 contains sensation1 appetite1 and emotion1 and is a mixed or two-sided entity2 but the intellect1 ,c1 is a purely one-sided entity1 the immaterial4 ,this does not relieve our perplexities2 the phenomena are still generically allied and continuous--sensation passes into intellect without any breach of continuity2 but as regards the agencies1 the transition from a mixed or united material and immaterial substance to an immaterial substance apart1 is a transition to a differently constituted world1 to a transcendental sphere of existence4 ,the settlement of ,aquinas governed all the schools and all the religious creeds1 until quite recent times2 it is1 for example1 substantially the view of ,bishop ,butler4 ,at the instance of modern physiology1 however1 it has undergone modifications4 ,the dependence of purely intellectual operations1 as memory1 upon the material processes1 has been reluctantly admitted by the partisans of an immaterial principle2 an admission incompatible with the isolation of the intellect in ,aristotle and in ,aquinas4 ,this more thorough-going connection of the mental and the physical has led to a new form of expressing the relationship1 which is nearer the truth1 without being1 in my judgment1 quite accurate4 ,it is now often said the mind and the body act upon each other2 that neither is allowed1 so to speak1 to pursue its course alone--there is a constant interference1 a mutual influence between the two4 ,this view is liable to the following objections3 #a4 ,in the first place1 it assumes that we are entitled to speak of mind apart from body1 and to affirm its powers and properties in that separate capacity4 ,but of mind apart from body we have no direct experience1 and absolutely no knowledge4 ,the wind may act upon the sea1 and the waves may react upon the wind2 but the agents are known in separation--they are seen to exist apart before the shock of collision2 but we are not permitted to see a mind acting apart from its material companion4 #b4 ,in the second place1 we have every reason for believing that there is an unbroken material succession1 side by side with all our mental processes4 ,from the ingress of a sensation1 to the outgoing responses in action1 the mental succession is not for an instant dissevered from a physical succession4 ,a new prospect bursts upon the view2 there is a mental result of sensations1 emotion1 thought1 terminating in outward displays of speech or gesture4 ,parallel to this mental series is the physical series of facts1 the successive agitation of the physical organs1 called the eye1 the retina1 the optic nerve1 optic centres1 cerebral hemispheres1 outgoing nerves1 muscles1 etc4 ,there is an unbroken physical circle of effects1 maintained while we go the round of the mental circle of sensation1 emotion1 and thought4 ,it would be incompatible with every thing we know of the cerebral action to suppose that the physical chain ends abruptly in a physical void1 occupied by an immaterial substance2 which immaterial substance1 after working alone1 imparts its results to the other edge of the physical break1 and determines the active response--two shores of the material with an intervening ocean of the immaterial4 ,there is1 in fact1 no rupture of nervous continuity4 ,the only tenable supposition is1 that mental and physical proceed together1 as individual twins4 ,when1 therefore1 we speak of a mental cause1 a mental agency1 we have always a two-sided cause2 the effect produced is not the effect of mind alone1 but of mind in company with body4 ,that mind should have operated on the body1 is as much as to say that a two-sided phenomenon1 one side being bodily1 can influence the body2 it is1 after all1 body acting upon body4 ,when a shock of fear paralyzes digestion1 it is not the emotion of fear1 in the abstract1 or as a pure mental existence1 that does the harm2 it is the emotion in company with a peculiarly excited condition of the brain and nervous system2 and it is this condition of the brain that deranges the stomach4 ,when physical nourishment1 or physical stimulant1 acting through the blood1 quiets the mental irritation1 and restores a cheerful tone1 it is not a bodily fact causing a mental fact by a direct line of causation3 the nourishment and the stimulus determine the circulation of blood to the brain1 give a new direction to the nerve-currents1 and the mental condition corresponding to this particular mode of cerebral action henceforth manifests itself4 ,the line of mental sequence is thus1 not mind causing body1 and body causing mind1 but mind-body giving birth to mind-body2 a much more intelligible position4 ,for this double or conjoint causation1 we can produce evidence2 for the single-handed causation we have no evidence4 ,if it were not my peculiar province to endeavor to clear up the specially metaphysical difficulties of the relationship of mind and body1 ,i would pass over what is to me the most puzzling circumstance of the relationship1 and indeed the only real difficulty in the question4 ,i say the real difficulty1 for factitious difficulties in abundance have been made out of the subject4 ,it is made a mystery how mental functions and bodily functions should be allied together at all4 ,that1 however1 is no business of ours2 we accept this alliance1 as we do any other alliance1 such as gravity with inert matter1 or light with heat4 ,as a fact of the universe1 the union is1 properly speaking1 just as acceptable1 and as intelligible1 as the separation would be1 if that were the fact4 ,the real difficulty is quite another thing4 ,what ,i have in view is this3 when ,i speak of mind as allied with body--with a brain and its nerve-currents--,i can scarcely avoid localizing the mind1 giving it a local habitation4 ,i am thereupon asked to explain what always puzzled the schoolmen1 namely1 whether the mind is all in every part1 or only all in the whole2 whether in tapping any point ,i may come at consciousness1 or whether the whole mechanism is wanted for the smallest portion of consciousness4 ,one might perhaps turn the question by the analogy of the telegraph wire1 or the electric circuit1 and say that a complete circle of action is necessary to any mental manifestation2 which is probably true4 ,but this does not meet the case4 ,the fact is that1 all this time we are speaking of nerves and wires1 we are not speaking of mind1 properly so called1 at all2 we are putting forward physical facts that go along with it1 but these physical facts are not the mental fact1 and they even preclude us from thinking of the mental fact4 ,we are in this fix3 mental states and bodily states are utterly contrasted2 they cannot be compared1 they have nothing in common except the most general of all attributes1 degree1 and order in time2 when engaged with one we must be oblivious of all that distinguishes the other4 ,when ,i am studying a brain and nerve communicating1 ,i am engrossed with properties exclusively belonging to the object or material world2 ,i am at that moment 7except by very rapid transitions or alternations7 unable to conceive a truly mental fact1 my truly mental consciousness4 ,our mental experience1 our feelings and thoughts1 have no extension1 no place1 no form or outline1 no mechanical division of parts2 and we are incapable of attending to any thing mental until we shut off the view of all that4 ,walking in the country in spring1 our mind is occupied with the foliage1 the bloom1 and the grassy meads1 all purely objective things2 we are suddenly and strongly arrested by the odor of the ,may-blossom2 we give way for a moment to the sensation of sweetness3 for that moment the objective regards cease2 we think of nothing extended2 we are in a state where extension has no footing2 there is1 to us1 place no longer4 ,such states are of short duration1 mere fits1 glimpses2 they are constantly shifted and alternated with object states1 but while they last and have their full power we are in a different world2 the material world is blotted out1 eclipsed1 for the instant unthinkable4 ,these subject-moments are studied to advantage in bursts of intense pleasure1 or intense pain1 in fits of engrossed reflection1 especially reflection upon mental facts2 but they are seldom sustained in purity beyond a very short interval2 we are constantly returning to the object-side of things--to the world where extension and place have their being4 ,this1 then1 as it appears to me1 is the only real difficulty of the physical and mental relationship4 ,there is an alliance with matter1 with the object1 or extended world2 but the thing allied1 the mind proper1 has itself no extension1 and cannot be joined in local union4 ,now1 we have no form of language1 no familiar analogy1 suited to this unique conjunction2 in comparison with all ordinary unions1 it is a paradox or a contradiction4 ,we understand union in the sense of local connection2 here is a union where local connection is irrelevant1 unsuitable1 contradictory1 for we cannot think of mind without putting ourselves out of the world of place4 ,when1 as in pure feeling--pleasure or pain--we change to the subject attitude from the object attitude1 we have undergone a change not to be expressed by place2 the fact is not properly described by the transition from the external to the internal1 for that is still a change in the region of the extended4 ,the only adequate expression is a change of state3 a change from the state of the extended cognition to a state of unextended cognition4 ,by various theologians1 heaven has been spoken of us not a place1 but a state2 and this is the only phrase that ,i can find suitable to describe the vast1 though familiar and easy1 transition from the material or extended1 to the immaterial or unextended side of the universe of being4 ,when1 therefore1 we talk of incorporating mind with brain1 we must be held as speaking under an important reserve or qualification4 ,asserting the union in the strongest manner1 we must yet deprive it of the almost invincible association of union in place4 ,an extended organism is the condition of our passing into a state where there is no extension4 ,a human being is an extended and material thing1 attached to which is the power of becoming alive to feeling and thought1 the extreme remove from all that is material2 a condition of trance wherein1 while it lasts1 the material drops out of view--so much so1 that we have not the power to represent the two extremes as lying side by side1 as container and contained1 or in any other mode of local conjunction4 ,the condition of our existing thoroughly in the one1 is the momentary eclipse or extinction of the other4 ,the only mode of union that is not contradictory is the union of close succession in time2 or of position in a continued thread of conscious life4 ,we are entitled to say that the same being is1 by alternate fits1 object and subject1 under extended and under unextended consciousness2 and that without the extended consciousness the unextended would not arise4 ,without certain peculiar modes of the extended--what we call a cerebral organization1 and so on--we could not have those times of trance1 our pleasures1 our pains1 and our ideas1 which at present we undergo fitfully and alternately with our extended consciousness4 ,having thus called attention to the metaphysical difficulty of assigning the relative position of mind and matter1 ,i will now state briefly what ,i think the mode of dealing with mind in correlation with the other forces4 ,that there is a definite equivalence between mental manifestations and physical forces1 the same as between the physical forces themselves1 is1 ,i think1 conformable to all the facts1 although liable to peculiar difficulties in the way of decisive proof3 ,i4 ,the mental manifestations are in exact proportion to their physical supports4 ,if the doctrine of the thorough-going connection of mind and body is good for any thing1 it must go this length4 ,there must be a numerically-proportioned rise and fall of the two together4 ,i believe that all the unequivocal facts bear out this proportion4 ,take first the more obvious illustrations4 ,in the employment of external agents1 as warmth and food1 all will admit that the sensation rises exactly as the stimulant rises1 until a certain point is reached1 when the agency changes its character2 too great heat destroying the tissues1 and too much food impeding digestion4 ,there is1 although we may not have the power to fix it1 a sensational equivalent of heat1 of food1 of exercise1 of sound1 of light2 there is a definite change of feeling1 an accession of pleasure or of pain1 corresponding to a rise of temperature in the air of #aj1 #bj1 or #cj4 ,and so with regard to every other agent operating upon the human sensibility3 there is1 in each set of circumstances1 a sensational equivalent of alcohol1 of odors1 of music1 of spectacle4 ,it is this definite relation between outward agents and the human feelings that renders it possible to discuss human interests from the objective side1 the only accessible side4 ,we cannot read the feelings of our fellows2 we merely presume that like agents will affect them all in nearly the same way4 ,it is thus that we measure men's fortunes and felicity by the numerical amount of certain agents1 as money1 and by the absence or low degree of certain other agents1 the causes of pain and the depressors of vitality4 ,and1 although the estimate is somewhat rough1 this is not owing to the indefiniteness of the sensational equivalent1 but to the complications of the human system1 and chiefly to the narrowness of the line that everywhere divides the wholesome from the unwholesome degrees of all stimulants4 ,let us next represent the equivalence under vital or physiological action4 ,the chief organ concerned is the brain2 of which we know that it is a system of myriads of connecting threads1 ramifying1 uniting1 and crossing at innumerable points2 that these threads are actuated or made alive with a current influence called the nerve force2 that this nerve-force is a member of the group of correlating forces2 that it is immediately derived from the changes in the blood1 and in the last resort from oxidation1 or combustion1 of the materials of the food1 of which combustion it is a definite equivalent4 ,we know1 further1 that there can be no feeling1 no volition1 no intellect1 without a proper supply of blood1 containing both oxygen and the material to be oxidized2 that1 as the blood is richer in quality in regard to these constituents1 and more abundant in quantity1 the mental processes are more intense1 more vivid4 ,we know also that there are means of increasing the circulation in one organ1 and drawing it off from another1 chiefly by calling the one into greater exercise1 as when we exert the muscles or convey food to the stomach2 and that1 when mental processes are more than usually intensified1 the blood is proportionally drawn to the brain2 the oxidizing process is there in excess1 with corresponding defect and detriment in other organs4 ,in high mental excitement1 digestion is stopped2 muscular vigor is abated except in the one form of giving vent to the feelings1 thoughts1 and purposes2 the general nutrition languishes2 and1 if the state were long continued or oft repeated1 the physical powers1 strictly so called1 would rapidly deteriorate4 ,we know1 on the other extreme1 that sleep is accompanied by reduced circulation in the brain2 there is in fact a reduced circulation generally2 while of that reduced amount more goes to the nutritive functions than to the cerebral4 ,in listening to ,dr4 ,frankland's lecture on 8,muscular ,power10 delivered at the ,royal ,institution of ,london1 ,i noticed that1 in accounting for the various items of expenditure of the food1 he gave 8mental work0 as one heading1 but declined to make an entry thereinunder4 ,i can imagine two reasons for this reserve1 the statement of which will further illustrate the general position4 ,in the first place1 it might be supposed that mind is a phenomenon so anomalous1 uncertain1 so remote from the chain of material cause and effect1 that it is not even to be mentioned in that connection4 ,to which ,i should say1 that mind is indeed1 as a phenomenon1 widely different from the physical forces1 but1 nevertheless1 rises and falls in strict numerical concomitance with these3 so that it still enters1 if not directly1 at least indirectly1 into the circle of the correlated forces4 ,or1 secondly1 the lecturer may have held that1 though a definite amount of the mental manifestations accompanies a definite amount of oxidation in the special organs of mind1 there is no means of reducing this to a measure1 even in an approximate way4 ,to this ,i answer1 that the thing is difficult but not entirely impracticable4 ,there is a possibility of giving1 approximately at least1 the amount of blood circulating in the brain1 in the ordinary waking state2 and1 as during a period of intense excitement we know that there is a general reduction1 almost to paralysis1 of the collective vital functions1 we could not be far mistaken in saying that1 in that case1 perhaps one-half or one-third of all the oxidation of the body was expended in keeping up the cerebral fires4 ,it is a very serious drawback in any department of knowledge1 where there are relations of quantity1 to be unable to reduce them to numerical precision4 ,this is the case with mind in a great degree1 although not with it alone2 many physical qualities are in the same state of unprecise measurement4 ,we cannot reduce to numbers the statement of a man's constitutional vigor1 so as to say how much he has lost by fatigue1 by disease1 by age1 or how much he has gained by a certain healthy regimen4 ,undoubtedly1 however1 it is in mind that the difficulties of attaining the numerical statement are greatest if not nearly insuperable4 ,when we say that one man is more courageous1 more loving1 more irascible than another1 we apply a scale of degree1 existing in our own mind1 but so vague that we may apply it differently at different times1 while we can hardly communicate it to others exactly as it stands to ourselves4 ,the consequence is1 that a great margin of allowance must always be made in those statements2 we can never run a close argument1 or contend for a nice shade of distinction4 ,between the extremes of timidity and courage of character the best observer could not entertain above seven or eight varieties of gradation1 while two different persons consulting together could hardly agree upon so minute a subdivision as that4 ,the phrenologists1 in their scale of qualities1 had the advantage of an external indication of size1 but they must have felt the uselessness of graduating this beyond the delicacy of discriminating the subjective side of character2 and their extreme scale included twenty steps or interpolations4 ,making allowance for this inevitable defect1 ,i will endeavor to present a series of illustrations of the principle of correlation as applied to mind1 in the manner explained4 ,i deal not with mind directly1 but with its material side1 with whose activity1 measured exactly as we measure the other physical forces1 true mental activity has a definite correspondence4 ,let us suppose1 then1 a human being with average physical constitution1 in respect of nutritive vigor1 and fairly supplied with food and with air1 or oxygen4 ,the result of the oxidation of the food is a definite total of force1 which may be variously distributed4 ,the demand made by the brain1 to sustain the purely mental functions1 may be below average1 or above average2 there will be a corresponding1 but inverse1 variation of the remainder available for the more strictly physical processes1 as muscular power1 digestive power1 animal heat1 and so on4 ,in the first case supposed1 the case of a small demand for mental work and excitement1 we look for1 and we find1 a better physique--greater muscular power and endurance1 more vigor of digestion1 rendering a coarser food sufficient for nourishment1 more resistance to excesses of cold and heat2 in short1 a constitution adapted to physical drudgery and physical hardship4 ,take1 now1 the other extreme4 ,let there be a great demand for mental work4 ,the oxidation must now be disproportionately expended in the brain2 less is given to the muscles1 the stomach1 the lungs1 the skin1 and secreting organs generally4 ,there is a reduction of the possible muscular work1 and of the ability to subsist on coarser food1 and to endure hardship4 ,experience confirms this inference2 the common observation of mankind has recognized the fact--although in a vague1 unsteady form--that the head-worker is not equally fitted to be a hand-worker4 ,the master1 mistress1 or overseer has each more delicacy of sense1 more management1 more resource1 than the manual operatives1 but to these belongs the superiority of muscular power and persistence4 ,there is nothing incompatible with the principle in allowing the possibility of combining1 under certain favorable conditions1 both physical and mental exertion in considerable amount4 ,in fact1 the principle teaches us exactly how the thing may be done4 ,improve the quality and increase the quantity of the food2 increase the supply of oxygen by healthy residence2 let the habitual muscular exertion be such as to strengthen and not impair the functions2 abate as much as possible all excesses and irregularities1 bodily and mental2 add the enormous economy of an educated disposal of the forces2 and you will develop a higher being1 a greater aggregate of power4 ,you will then have more to spare for all kinds of expenditure--for the physico-mental1 as well as for the strictly physical4 ,what other explanation is needed of the military superiority of the officer over the common soldier8 of the general efficiency of the man nourished1 but not enervated1 by worldly abundance8 ,it may be possible1 at some future stage of scientific inquiry1 to compute the comparative amount of oxidation in the brain during severe mental labor4 ,even now1 from obvious facts1 we must pronounce it to be a very considerable fraction of the entire work done in the system4 ,the privation of the other interests during mental exertion is so apparent1 so extensive1 that if the exertion should happen to be long continued1 a liberal atonement has to be made in order to stave off general insolvency4 ,mental excess counts as largely as muscular excess in the diversion of power2 it would be competent to suppose either the one or the other reducing the remaining forces of the system to one-half of their proper amount4 ,in both cases1 the work of restoration must be on the same simple plan of redressing the inequality1 of allowing more than the average flow of blood to the impoverished organs1 for a length of time corresponding to the period when their nourishment has been too small4 ,it is in this consideration that we seem to have the reasonable1 ,i may say the arithmetical1 basis of the constitutional treatment of chronic disease4 ,we repay the debt to ,nature by allowing the weakened organ to be better nourished and less taxed1 according to the degradation it has undergone by the opposite line of treatment4 ,in a large class of diseases we have obviously a species of insolvency1 to be dealt with according to the sound method of readjusting the relations of expenditure and income4 ,and1 if such be the true theory1 it seems to follow that medication is only an inferior adjunct4 ,drugs1 even in their happiest application1 can but guide and favor the restorative process2 just as the stirring of a fire may make it burn1 provided there be the needful fuel4 ,there is thus a definite1 although not numerically-statable relation1 between the total of the physico-mental forces and the total of the purely physical processes4 ,the grand aggregate of the oxidation of the system includes both2 and1 the more the force taken up by one1 the less is left to the other4 ,such is the statement of the correlation of mind to the other forces of ,nature4 ,we do not deal with pure mind--mind in the abstract2 we have no experience of an entity of that description4 ,we deal with a compound or two-sided phenomenon--mental on one side1 physical on the other2 there is a definite correspondence in degree1 although a difference of nature1 between the two sides2 and the physical side is itself in full correlation with the recognized physical forces of the world4 ,,ii4 ,there remains another application of the doctrine1 perhaps equally interesting to contemplate1 and more within my special line of study4 ,i mean the correlation of the mental forces among themselves 7still viewed in the conjoint arrangement74 ,just as we assign limits to mind as a whole1 by a reference to the grant of physical expenditure1 in oxidation1 etc41 for the department1 so we must assign limits to the different phases or modes of mental work--thought1 feeling1 and so on--according to the share allotted to each2 so that1 while the mind as a whole may be stinted by the demands of the non-mental functions1 each separate manifestation is bounded by the requirements of the others4 ,this is an inevitable consequence of the general principle1 and equally receives the confirmation of experience4 ,there is the same absence of numerical precision of estimate2 our scale of quantity can have but few divisions between the highest and the lowest degrees1 and these not well fixed4 ,what is required for this application of the principle is1 to ascertain the comparative cost1 in the physical point of view1 of the different functions of the mind4 ,the great divisions of the mind are--feeling1 will1 and thought2 feeling1 seen in our pleasures and pains2 will1 in our labors to attain the one and avoid the other2 thought1 in our sensations1 ideas1 recollections1 reasonings1 imaginings1 and so on4 ,now1 the forces of the mind1 with their physical supports1 may be evenly or unevenly distributed over the three functions4 ,they may go by preference either to feeling1 to action1 or to thinking2 and1 if more is given to one1 less must remain to the others1 the entire quantity being limited4 ,first1 as to the feelings4 ,every throb of pleasure costs something to the physical system2 and two throbs cost twice as much as one4 ,if we cannot fix a precise equivalent1 it is not because the relation is not definite1 but from the difficulties of reducing degrees of pleasure to a recognized standard4 ,of this1 however1 there can be no reasonable doubt--namely1 that a large amount of pleasure supposes a corresponding large expenditure of blood and nerve-tissue1 to the stinting1 perhaps1 of the active energies and the intellectual processes4 ,it is a matter of practical moment to ascertain what pleasures cost least1 for there are thrifty and unthrifty modes of spending our brain and heart's blood4 ,experience probably justifies us in saying that the narcotic stimulants are1 in general1 a more extravagant expenditure than the stimulation of food1 society1 and fine art4 ,one of the safest of delights1 if not very acute1 is the delight of abounding physical vigor2 for1 from the very supposition1 the supply to the brain is not such as to interfere with the general interests of the system4 ,but the theory of pleasure is incomplete without the theory of pain4 ,as a rule1 pain is a more costly experience than pleasure1 although sometimes economical as a check to the spendthrift pleasures4 ,pain is physically accompanied by an excess of blood in the brain1 from at least two causes--extreme intensity of nervous action1 and conflicting currents1 both being sources of waste4 ,the sleeplessness of the pained condition means that the circulation is never allowed to subside from the brain2 the irritation maintains energetic currents1 which bring the blood copiously to the parts affected4 ,there is a possibility of excitement1 of considerable amount1 without either pleasure or pain2 the cost here is simply as the excitement3 mere surprises may be of this nature4 ,such excitement has no value1 except intellectually2 it may detain the thoughts1 and impress the memory1 but it is not a final end of our being1 as pleasure is2 and it does not waste power to the extent that pain does4 ,the ideally best condition is a moderate surplus of pleasure--a gentle glow1 not rising into brilliancy or intensity1 except at considerable intervals 7say a small portion of every day71 falling down frequently to indifference1 but seldom sinking into pain4 ,attendant on strong feeling1 especially in constitutions young or robust1 there is usually a great amount of mere bodily vehemence1 as gesticulation1 play of countenance1 of voice1 and so on4 ,this counts as muscular work1 and is an addition to the brain-work4 ,properly speaking1 the cerebral currents discharge themselves in movements1 and are modified according to the scope given to those movements4 ,resistance to the movements is liable to increase the conscious activity of the brain1 although a continuing resistance may suppress the entire wave4 ,next as to the will1 or our voluntary labors and pursuits for the great ends of obtaining pleasure and warding off pain4 ,this part of our system is a compound experience of feeling and movement2 the properly mental fact being included under feeling--that is1 pleasure and pain1 present or imagined4 ,when our voluntary endeavors are successful1 a distinct throb of pleasure is the result1 which counts among our valuable enjoyments3 when they fail1 a painful and depressing state ensues4 ,the more complicated operations of the will1 as in adjusting many opposite interests1 bring in the element of conflict1 which is always painful and wasting4 ,two strong stimulants pointing opposite ways1 as when a miser has to pay a high fee to the surgeon that saves his eyesight1 occasion a fierce struggle and severe draft upon the physical supports of the feelings4 ,although the processes of feeling all involve a manifest1 and it may be a serious1 expenditure of physical power1 which of course is lost to the purely physical functions2 and although the extreme degrees of pleasure1 of pain1 or of neutral excitement1 must be adverse to the general vigor2 yet the presumption is1 that we can afford a certain moderate share of all these without too great inroads on the other interests4 ,it is the thinking or intellectual part of us that involves the heaviest item of expenditure in the physico-mental department4 ,any thing like a great or general cultivation of the powers of thought1 or any occupation that severely and continuously brings them into play1 will induce such a preponderance of cerebral activity1 in oxidation and in nerve-currents1 as to disturb the balance of life1 and to require special arrangements for redeeming that disturbance4 ,this is fully verified by all we know of the tendency of intellectual application to exhaust the physical powers1 and to bring on early decay4 ,a careful analysis of the operations of the intellect enables us to distinguish the kind of exercises that involve the greatest expenditure1 from the extent and the intensity of the cerebral occupation4 ,i can but make a rapid selection of leading points3 ,first4 ,the mere exercise of the senses1 in the way of attention1 with a view to watch1 to discriminate1 to identify1 belongs to the intellectual function1 and exhausts the powers according as it is long continued1 and according to the delicacy of the operation2 the meaning of delicacy being that an exaggerated activity of the organ is needed to make the required discernment4 ,to be all day on the qui vive for some very slight and barely perceptible indications to the eye or the ear1 as in catching an indistinct speaker1 is an exhausting labor of attention4 ,secondly4 ,the work of acquisition is necessarily a process of great nervous expenditure4 ,unintentional imitation costs least1 because there is no forcing of reluctant attention4 ,but a course of extensive and various acquisitions cannot be maintained without a large supply of blood to cement all the multifarious connections of the nerve-fibres1 constituting the physical side of acquisition4 ,an abated support of other mental functions1 as well as of the purely physical functions1 must accompany a life devoted to mental improvement1 whether arts1 languages1 sciences1 moral restraints1 or other culture4 ,of special acquisitions1 languages are the most apparently voluminous2 but the memory for visible or pictorial aspects1 if very high1 as in the painter and the picturesque poet1 makes a prodigious demand upon the plastic combinations of the brain4 ,the acquisition of science is severe1 rather than multifarious2 it glories in comprehending much in little1 but that little is made up of painful abstract elements1 every one of which1 in the last resort1 must have at its beck a host of explanatory particulars3 so that1 after all1 the burden lies in the multitude4 ,if science is easy to a select number of minds1 it is because there is a large spontaneous determination of force to the cerebral elements that support it2 which force is supplied by the limited common fund1 and leaves so much the less for other uses4 ,if we advert to the moral acquisitions and habits in a well-regulated mind1 we must admit the need of a large expenditure to build up the fabric4 ,the carefully-poised estimate of good and evil for self1 the ever-present sense of the interests of others1 and the ready obedience to all the special ordinances that make up the morality of the time1 however truly expressed in terms of high and abstract spirituality1 have their counterpart in the physical organism2 they have used up a large and definite amount of nutriment1 and1 had they been less developed1 there would have been a gain of power to some other department1 mental or physical4 ,refraining from further detail on this head1 ,i close the illustration by a brief reference to one other aspect of mental expenditure1 namely1 the department of intellectual production1 execution1 or creativeness1 to which in the end our acquired powers are ministerial4 ,of course1 the greater the mere continuance or amount of intellectual labor in business1 speculation1 fine art1 or any thing else1 the greater the demand on the physique4 ,but amount is not all4 ,there are notorious differences of severity or laboriousness1 which1 when closely examined1 are summed up in one comprehensive statement--namely1 the number1 the variety1 and the conflicting nature of the conditions that have to be fulfilled4 ,by this we explain the difficulty of work1 the toil of invention1 the harassment of adaptation1 the worry of leadership1 the responsibility of high office1 the severity of a lofty ideal1 the distraction of numerous sympathies1 the meritoriousness of sound judgment1 the arduousness of any great virtue4 ,the physical facts underlying the mental fact are a wide-spread agitation of the cerebral currents1 a tumultuous conflict1 a consumption of energy4 ,it is this compliance with numerous and opposing conditions that obtains the most scanty justice in our appreciation of character4 ,the unknown amount of painful suppression that a cautious thinker1 a careful writer1 or an artist of fine taste1 has gone through1 represents a great physico-mental expenditure4 ,the regard to evidence is a heavy drag on the wings of speculative daring4 ,the greater the number of interests that a political schemer can throw overboard1 the easier his work of construction4 ,the absence of restraints--of severe conditions--in fine art1 allows a flush and ebullience1 an opulence of production1 that is often called the highest genius4 ,the ,shakespearean profusion of images would have been reduced to one-half1 if not less1 by the self-imposed restraints of ,pope1 ,gray1 or ,tennyson4 ,so1 reckless assertion is fuel to eloquence4 ,a man of ordinary fairness of mind would be no match for the wit and epigram of ,swift4 ,and again4 ,the incompatibility of diverse attributes1 even in minds of the largest compass 7which supposes equally large physical resources71 belongs to the same fundamental law4 ,a great mind may be great in many things1 because the same kind of power may have numerous applications4 ,the scientific mind of a high order is also the practical mind2 it is the essence of reason in every mode of its manifestation--the true philosopher in conduct as well as in knowledge4 ,on such a mind also1 a certain amount of artistic culture may be superinduced2 its powers of acquisition may be extended so far4 ,but the spontaneous1 exuberant1 imaginative flow1 the artistic nature at the core1 never was1 cannot be1 included in the same individual4 ,aristotle could not be also a tragic poet2 nor ,newton a third-rate portrait-painter4 ,the cost of one of the two modes of intellectual greatness is all that can be borne by the most largely-endowed personality2 any appearances to the contrary are hollow and delusive4 ,other instances could be given4 ,great activity and great sensibility are extreme phases1 each using a large amount of power1 and therefore scarcely to be coupled in the same system4 ,the active1 energetic man1 loving activity for its own sake1 moving in every direction1 wants the delicate circumspection of another man who does not love activity for its own sake1 but is energetic only at the spur of his special ends4 ,and once more4 ,great intellect as a whole is not readily united with a large emotional nature4 ,the incompatibility is best seen by inquiring whether men of overflowing sociability are deep and original thinkers1 great discoverers1 accurate inquirers1 great organizers in affairs2 or whether their greatness is not limited to the spheres where feeling performs a part--poetry1 eloquence1 and social ascendency4 ,,the ,,end4 ,,footnotes3 #ah ,for the fuller elaboration of the point here referred to1 see ,chapter ,,vii41 ,professor ,bain's 8,mind and ,body0--an earlier volume in the present series4 ,,index4 ,absorbed heat changed into chemical separation1 #aad4 into actual visible energy1 #aje4 into light and heat1 #aag4 ,acquisition1 #bcb4 ,actinic rays1 #abi4 ,action and reaction equal and opposite1 #h4 ,affinity1 chemical1 #ec4 ,air and water in motion1 #adg4 ,albuminoids1 #agg1 #ahc4 ,amber1 #fa4 ,ampre1 #ge4 ,amyloids1 #agg1 #ahc4 ,ancients1 their ideas not prolific1 #ace4 ,andrews1 #ada4 ,animal heat1 #bjg4 ,animals1 how they live1 #ahh4 ,animals and inanimate machines1 #afe4 ,aristotle on a medium1 #acd4 on mind and body1 #bjg4 ,atmospheric circulation1 #aji4 ,atomic forces and heat1 #eh4 ,atomic or chemical separation1 #hj4 ,atoms and molecules1 #ea4 ,attention1 #bcb4 ,attraction1 molecular1 #eb4 mutual1 of atoms1 #ed4 and repulsion of magnets1 #ge4 of electric currents1 #ge4 ,bacon1 #acc1 #acg4 ,battery of ,grove1 #gj4 ,budding1 #ahj4 ,caloric1 #ch4 ,carnivora1 #ahi4 ,chemical affinity1 #ec4 and electrical attraction1 #fd4 and heat1 #eh4 ,chemical combination producing heat1 #aai4 ,chemical instability1 #aef4 ,chemical separation converted into electrical separation1 #abb4 into electricity in motion1 #abc4 ,chlorophyll1 #agg4 ,chrysalis1 #ahg4 ,circulation of the atmosphere1 #aji4 ,clausius1 #ada4 ,cohesion1 force of1 #ea4 ,cold apparently produced by the electric current1 #abf4 ,conduction of electricity1 #fa4 ,conservation1 laws of1 #hb4 theory of1 #adj4 ,crossbow and watch-spring1 #be4 ,current1 the electric1 #fi4 and magnetism1 #gb4 heating effect of1 #gc4 chemical effect of1 #gd4 ,currents1 electric1 attraction and repulsion of1 #gd4 induction of1 #ge4 ,dalton1 #acc4 ,davy1 ,sir ,humphrey1 #ch1 #acg4 ,democritus on atoms1 #acc4 ,descartes1 #acf4 ,diastase1 #ahd4 ,disease-germs1 #c4 ,dissipation of energy1 #ada4 ,dissociation1 #aae4 ,egg1 development of the1 #ahf4 ,electric current1 #fi4 and magnetism1 #gb4 heating effect of1 #gc4 chemical effect of1 #gd4 induction1 #fe4 ,electrical attraction and chemical affinity1 #fd4 ,electrical separation1 #ha4 when produced1 #fd4 transmuted into visible motion1 #abd4 into electric current1 #abd4 ,electro-magnetism1 #gb4 ,elastic forces1 #ej4 ,electricity1 #fj4 vitreous and resinous1 #fc4 negative and positive1 #fc4 theory of1 #fc4 in motion1 #ha4 transmuted into visible motion1 #abd4 into heat1 #abe4 into chemical separation1 #abg4 ,encke's comet1 #if4 ,energies1 list of1 #gh-hb4 natural1 and their sources1 #adc4 ,energy1 meaning of1 #a-bb4 of bodies in motion proportional to their weight or mass1 #ad4 proportional to the square of the velocity1 #ai4 of visible motion1 its transmutation1 #hg4 visible1 transformed into absorbed heat1 #hh4 dissipation of1 #ada4 transmutations of1 #bg4 varies as the square of the velocity1 #ae4 of motion1 #bd4 transformed into electrical separation1 #ih4 of position1 a sort of capital1 #bf4 ,equilibrium1 #aed4 ,etiolation1 #ahj4 ,fermentation1 #ahc4 ,food1 #ade4 ,force1 vital1 whence derived1 #aga4 physical1 #aid4 chemical1 #aid4 of chemical affinity1 #ec4 of cohesion1 #ea4 ,force1 mechanical or molar1 #bje4 molecular1 #bje4 ,friction1 #ce4 ,heat1 absorbed1 changed into chemical separation1 #aad4 into electrical separation1 #aae4 into electricity in motion1 #aaf4 ,heat-units of different substances1 #aai4 ,heat-motion1 #hj4 ,heat-engines1 their essential conditions1 #ajg4 ,helmholtz1 #ada4 ,heraclitus on energy1 #acc4 ,herbivora1 #aia4 ,heterogeneity essential in electrical development1 #fd4 ,huyghens1 #acg4 ,hydraulic press1 #cb4 ,inclined plane1 #bh4 ,incubation1 #ahf4 ,individuals1 our ignorance of1 #a4 ,induction1 electric1 #fe4 of electric currents1 #ge4 ,instability1 mechanical1 #aee4 chemical1 #aef4 ,intellectual labor1 #bcd4 ,joule1 #acg1 #adj1 #ada4 ,joule's experiments on work and heat1 #dd4 ,kilogrammetre1 #af4 ,larva1 #ahg4 ,latent heat1 #eg4 ,laws of conservation1 #hb4 ,life depends on the sun1 #afe4 ,light1 a perpetual1 impossible1 #adi4 ,lime1 carbonate1 easily decomposed1 #eh4 ,list of energies1 #gh-hb4 ,machines1 their true function1 #cc4 animated and inanimate1 #aeg4 ,magnets1 attachment and repulsion of1 #ge4 ,maxwell1 #ada4 ,mayor1 #adj4 ,mechanical energy changed into heat1 #bc4 equivalent of heat1 #dc4 force1 #bje4 instability1 #aee4 ,mental forces1 mutual correlations of1 #bbg-bcf4 ,mind1 its correlations to natural forces1 #bah-bbg4 and body1 #bjg1 #baa4 ,molar force1 #bje4 ,molecular attraction and heat1 #ee4 separation1 #hj4 ,molecules1 ultimate1 of matter1 #e4 their motions1 #g4 and atoms1 #ea4 ,motion changed into an electric current1 #ii4 ,muscular power1 #bjg4 ,narcotic stimulants1 #bbi4 ,negative and positive electricity1 #fc4 ,nerve power1 #bjg4 ,newton1 #acf1 #acg4 ,non-conductors of electricity1 #fa4 ,percussion1 #cf4 ,perpetual motion1 #aci4 ,physical force1 #aid4 ,plants growing at night1 #aha4 ,positive and negative electricity1 #fc4 ,protoplasm1 #agg4 ,pulleys1 their function1 #cj4 ,radiant energy1 #ha4 converted into absorbed heat1 #abc4 promoting chemical separation1 #abc4 ,rankine1 #ada4 ,resinous and vitreous electricity1 #fc4 ,rotation of earth retarded1 #ie4 ,rumford1 #ci1 #acg4 ,silver oxide readily decomposed1 #eh4 ,solar rays1 decomposition by1 #ei4 ,sulphur1 #adf4 ,sun--a source of high-temperature heat1 #adh4 ,sun's heat1 origin of1 #aej4 spots1 auroras1 and cyclones correlated1 #ih4 ,tait1 #ada4 ,temperature of dissociation1 #aae4 ,thermo-electricity1 #aaf4 ,thermopile1 #aag4 ,thomas ,aquinas1 #bji4 ,thomson1 ,william and ,james1 #adj4 ,tides1 #adf4 ,tissues1 decay of1 #afd4 ,universe1 its probable fate1 #aeb4 ,units of heat and work1 #df4 ,vegetation1 #agf4 ,velocity and energy1 relation between1 #af4 ,virtual velocities1 #cd4 principle of1 its history1 #acg4 ,vital force1 whence derived1 #aga4 ,vitality1 #aid4 ,vitreous and resinous electricity1 #fc4 ,voltaic current1 #fi4 and magnetism1 #gb4 heating effect of1 #gc4 chemical effect of1 #gd4 ,water at high level1 #bd4 ,watt1 #ach4 ,wild's electro-magnetic machine1 #ajc4 ,will1 #aid4 ,work1 definition of1 #ae4 unit of1 #ae4 rise of true conceptions regarding1 #ach4 ,yeast-plant1 #ahe4 ,,the ,,end4 ,transcriber's ,notes ,errors in punctuation have been fixed4 ,page #fj3 8heterogenous bodies0 changed to 8heterogeneous bodies0 ,page #hj3 8,analagous to this0 changed to 8,analogous to this0 ,page #hb3 8etherial medium0 changed to 8ethereal medium0 ,page #aeg3 8without occcasioned0 changed to 8without occasioned0