402 



NATURE 



{August 24, 1882 



Either the theory is upset, or the observations, if not altogether 

 faulty, are found susceptible of another interpretation. The 

 difficulty is greatest when the necessary conditions are uncertain, 

 and their fulfilment rare and uncontrollable. In many such 

 cases an attitude of reserve, in expectation of further evidence, 

 is the only wise one. Premature judgments err perhaps as much 

 on one side as on the other. Certainly in the past many extra- 

 ordinary observations have met with an excessive incredulity. I 

 may ins ance the fire-balls which sometimes occur during violent 

 thunderstorms. When the telephone was first invented, the 

 early reports of its performances were discredited by many on 

 quite insufficient grounds. 



It would be interesting, but too difficult and delicate a task, 

 to enumerate and examine the various important questions which 

 remain still undecided from the opposition of direct and indirect 

 evidence. Merely as illustrations I will mention one or two in 

 which I happen to have been interested. It has been sought to 

 remedy the inc 'nvenience caused by exce-sive reveberation of 

 sound in cathedral, and other large unfurnished buildings by 

 stre'ching wires overhead from one wall to another. In some 

 ca-es no difference has been perceived, but in others it is thought 

 that advantage has been gained. From a theoretical point of 

 view it is difficult to believe that the wires could be of service. 

 It is known that the vibrations of a wire do not communicate 

 themselves in any appreciable degree directly to the air, but 

 require the intervention of a sounding-board, from which we 

 may infer that vibrations in the air would not readily communi- 

 cate them elves to stretched wires. It seems more likely that 

 the advantage supposed to have been gained in a few cases is 

 imaginary than that the wires should really have played the 

 part attributed to them. 



The other subject on which, though with diffidence, I should 

 like to make a remark or two, is that of l'rout's law, according 

 to which the atomic weights of the elements, or at any rate of 

 many of them, stand in simple relation to that of hydrogen. 

 Some chemists have reprobated strongly the importation of 

 a priori views into the consideration of the question, and main- 

 tain that the only numbers worthy of recognition are the imme- 

 diate results of experiment. Others, more impressed by the 

 argument that the close approximations to simple numbers cannot 

 be merely fortuitous, and more alive to the inevitable imper- 

 fections of our measurements, consider that the experimental 

 evidence against the simple number 1 is of a very slender cha- 

 racter, balanced, if not outweighed, by the a priori argument in 

 favour of simplicity. The subject is eminently one for further 

 experiment ; and as it is now engaging the attention of chemists, 

 we may look forward to the settlement of the question by the 

 present generation. The time has perhaps come when a re- 

 determination of the densities of the principal gases may be 

 desirable — an undertaking for which I have made some pre- 

 parations. 



If there is any truth in the views that I have been endeavouring 

 to impress, our meetings in this section are amply justified. If 

 the progress of science demands the comparison of evidence 

 drawn from different sources, and fully appreciated only by 

 minds of different order, what may we not gain from the oppor- 

 tunities here given for public discussion, and, perhaps more 

 valuable still, private interchange of opinion? Let us endeavour, 

 one and all, to turn them to the best account. 



SECTION B 



CHEMICAL SCIENCE 



Opening Address by Prof. G. D. Liveing, M.A., F.R.S., 

 F.C.S., President of the Section 

 If I were asked in what direction chemical science had of 

 late been making the most impoitant advance, I should reply 

 that it was in the attempt to place the dynamics of chemistry on 

 a sati factory basi-, to render an account of the various pheno- 

 mena of chemical action on the same mechanical principles as 

 are acknowledged to be true in other branches of physics. I 

 cannot say that chemistry can yet be reckoned amongst what are 

 called the exact science-', that the results of bringing together 

 given matters under given circumstances can yet be deduced in 

 more than a few special cases by mere mathematical processes 

 from mechanical principles, but that some noteworthy advances 

 have in recent years been made which seem to bring such a 

 solution of chemical problems more nearly within our reach. 



To show how large a gap in our ideas of chem.cal dynamics 

 has been bridged over within the last quarter of a century, I 

 will quote the words of one of the largest-mindec philosophers 

 of his time, who was one of the earliest promoters of this Asso- 

 ciation, and its President in 1841 ; Whevvell, in a new and much 

 altered edition of his " Philosophy of the Induc'.ive Sciences," 

 published in 1858, says : — "Since Newton's time the use of the 

 word attraction as expressing the cause of the union of the 

 chemical elements of bodies has been familiarly continued ; 

 and has no doubt been accompanied in the minds of many per- 

 sons with an obscure notion that chemical attraction is in some 

 way a kind of mechanical attraction of the particles of bodies. 

 Yet the doctrine that chemical attraction and mechanical attrac- 

 tion are forces of the same kind, has never, so far as I am 

 aware, been worked out into a system of chemical theory ; nor 

 even applied with any distinctness as an explanation of any 

 particular chemical phenomena. Any such attempt, indeed, 

 could only tend to bring more clearly into view the entire in- 

 adequacy of such a mode of explanation. For the leading phe- 

 nomena of chemistry are all of such a nature that no mechanical 

 combination can serve to express them without an immense 

 accumulation of additional hypotheses." And further on he 

 says : — " We must consider the power which produces chemical 

 combination as a peculiar principle, a special relation of the 

 elements, not rightly expressed in mechanical terms." (Hist, 

 of Scientific Ideas, II., pp. 13, 14). 



The influence by which our ideas have gone round so as to be 

 now the very opposite of those of the illustrious thinker whom I 

 have just qu >ted, so that we should ridicule the thought of looking 

 for an explanation of chemical action on any but mechanical 

 principles, is undoubtedly the progre-s which has been made in 

 other branches of molecular physics. The indestructibility of 

 matter has long been a formula familiar to chemists, but that the 

 conservation of energy should be as universally true even in 

 regard to chemical actions, has only in recent years been fully 

 recognised. This is certainly no new principle, it was developed 

 math matically generations ago; but the realisation that it is 

 anything more than abstraction, that it is the keynote of every 

 rational explanation of physical phenomena, has been the 

 foundation of recent progress in physical science ; and if all 

 energy be one, there can be but one code of dynamical laws 

 which must apply to chemistry as well as all other branches of 

 physics. The development of the mechanical theory of heat, 

 and of the molecular theories which hive grownup in conse- 

 quence of it, have done much to set our minds free from pre- 

 conceived notions, and to induce us to build chemical theories 

 on something more thrn unverified conjectures. 



But how far can we say that mechanical principles are actually 

 recognised as the true basis of rational chemistry? So far as I 

 know no chemist denies that it is so, and yet how little do 

 our text-books, even the most recent and the most highly 

 reputed, show the predominance of this idea ! How very small 

 a portion of such books is taken up with it ; how much seems 

 utterly to ignore it, or io be couched in language which is anta 

 gonistic to it ! We still find chemical combinations described as 

 if they were statical phenomena, and expressions used which 

 imply that two perfectly elastic bidies can by their mutual action 

 alone bring each other into fixed relative positions. We still 

 find change of valency describe 1 as a suppression of "bonds of 

 affinity," as if a suppression of forces were the usual course of 

 nature, or as it it were possible that the same two forces, acting 

 at the same place and in the same direction, should at one time 

 neutralise one another, and at another time not neutralise one 

 another. We still find saturated compounds spoken of, as if the 

 stability of a compound were independent of circumstances, and 

 chemical combination no function of temperature and pressure. 

 Beginners are sometimes helped by the invention of intermediate 

 reactions in explanation of final results, without any reference to 

 the dynamical conditions of the problem, without any considera- 

 tion whether the fancied intermediate reactions imply a winding 

 up or a running down of energy. In fact our long familiar 

 chemical equations represent only the conservation of matter and 

 to keep always in mind the mechanical conditions of a reaction 

 is as difficult to some of us as it is to think in a foreign language. 

 Moreover we still find in many of our text-books the old statical 

 notion of chemical combination stereotyped in pictures of 

 molecules. I do not, of course, mean to accuse the distin- 

 guished inventors of graphic formula: of meaning to depict 

 molecules, fur I believe that they would agree with me in think- 

 ing that these diagrams do not any more nearly represent actual 



