3H 



NATURE 



\_Augiist 1 6, 1877 



bodies, was fully established Iby the researches of Black and 

 Wilke on latent and specific heat. This was at the time when 

 the idea of chemical composition was just taking its modern 

 shape through the recognition of aeriform bodies as possible 

 constituents of solids and liquids, and it was natural that the 

 new knowledge with regard to heat should be embodied in the 

 conception of a matter of heat, or caloric, capable of entering 

 into or separating from combination like fixed air or dephlo- 

 gisticated air. And in fact this conception not only took the 

 place of philosophical speculations upon the nature of heat such 

 as those of Bacon and Locke, but it withstood the experimental 

 onslaughts of Kumford and Davy, as well as the penetrating 

 scientific criticism of Thomas Young. It is to the steam-engine, 

 and to the attempt to find out the connection obviously existing 

 between the amount of heat supplied and the work done by the 

 engine, that we must trace the downfall of the idea of the 

 materiality of heat and the origin of our modern views." 



Probably it would be impossible to find a more remarkable 

 instance of what I referred to just now as the second way in 

 which practice may react upon science so as to promote its 

 advancement, than is presented to us in the case of electric 

 telegraphy. This is an example of an industrial undertaking 

 which is the direct offspring of scientific research, and could not 

 have co-existed in its actual state of development with a less 

 advanced condition of electrical science ; but if it were possible 

 to establish any common measure for such things, it may be 

 doubted whether it would not be found that telegraphy has 

 repaid to science benefits equal to those it has received. For 

 instance, the discovery of earth-currents was a direct result of 

 the large scale of the instrumental arrangements which are 

 needed for telegrajjhic purposes, and is one which would pro- 

 bably have long remained unmade in the absence of some 

 inducement to make experiments on a scale greater than that 

 indicated by the visible wants of scientific inquiry. The same 

 is true of the discovery of the influence of electro-static induction 

 upon the transmission of electric currents through metallic con- 

 ductors, and of the consequent additions to our knowledge of the 

 specific inductive capacity of insulators and of the whole subject of 

 electrostatic capacity. But by far the most important of the 

 benefits conferred by electric telegraphy upon electrical 

 science have resulted from the necessity under which the 

 practical electrician found himself, of not only being able to 

 produce certain results, but of producing them under definitely 

 ascertained conditions as to the expenditure of time and material. 

 When it was perceived that slight variations in the electrical con- 

 ductivity, insulating power, or specific inductive capacity of certain 

 materials might affect the pecuniary return upon investments 

 reckoned in millions of pounds sterling, measuring instruments 

 were devised which far surpassed in delicacy and accuracy those 

 that had been previously made for purely scientific purposes, or 

 the cost of which exceeded the means usually at the disposal of 

 scientific investigators. The multiplication and wide diffusion 

 of such instruments has led to the rapid accumulation of numerical 

 data of great scientific importance, and has largely contributed to 

 the spread of accurate conceptions as to the quantitative laws of 

 electrical phenomena. But the further necessity experienced by 

 practical electricians, that, besides being able to make accurate 

 measurements, they should be able mutually to communicate 

 and to understand each other's results, has probably done more 

 than anything else to hasten the introduction for scientific 

 purposes of so-called " absolute" measurements, instead of mere 

 comparisons of each quantity to be estimated witli a standard 

 magnitude of its own kind. The use of absolute measures 

 constitutes one of the most characteristic differences between the 

 physics of to-day and that of the time when the British Associa- 

 tion was instituted, and it may be even said to lie at the base of 

 the doctrine of the Conservation of Energy, which implies the 

 principle that every kind of energy can be reduced to the same 

 denomination. 



Perhaps, aiter speaking as I have done of the necessity for the 

 co-operation of mathematics in tlie advancement of physics, it is 

 not inappropriate that I should, in conclusion, refer to the 

 possibility tliat, by a too implicit reliance upon mathematical 

 guidance, the physicist may be led away from the discovery of 

 fresh truth, or even into actual error. Mathematics is seen to 

 be so indispensable and usually so powerful an aid in physical 

 investigation, that there is a danger of forgetting that there are 

 after all limits to its power. Partly from want of sufficient 

 knowledge of the physical data on which mathematical discussion 

 * Conf. Diihring, loc, cit. 



must be based, and partly from the imperfection of mathematical 

 methods themselves, it happens that it is not possible to give a 

 thoroughly complete mathematical account of even the simplest 

 physical phenomenon. In all real cases, although some one 

 effect may often predominate so greatly as alone to attract 

 attention on a cursory view, the actual complexity is so great that 

 it is only by deliberately leaving out of consideration what we 

 believe to be the accidental accompaniments of a phenomenon, 

 and confining our attention to what seems to be its essential and 

 characteristic part that it is possible to make it the subject of 

 mathematical calculation. The consequence is that the problems 

 treated of in mathematical physics are not the problems pre- 

 sented by nature, but are problems suggested by these, and 

 derived from them by a process of ideal simplification. There Is, 

 therefore, always a possibility that, in this simplifying process, 

 some apparently trivial but really important feature of the actual 

 phenomenon, to which the ideal one is meant to correspond, 

 may have been overlooked. When this is the case, the tact will 

 reveal itself sooner or later by the occurrence of discrepancies 

 between the results of mathematical theory and those of experi- 

 mental investigation. Such discrepancies are the finger-posts, 

 pointing to new discoveries ; but the experimenter who forgets 

 the inevitable limitation of the authority of theoretical conclu- 

 sions, arising from the conditions I have alluded to, is apt to 

 disregard them, and, perhaps conscious of laziness and want of 

 care in his method of working, or sometimes from a want of 

 proper self-confidence, he attributes all anomalous results to " the 

 unavoidable errors of observaiion." 



Two classes of experimenters are safe from falling into this 

 danger. There are first, those who, the first time they observe 

 anything that is not provided for in their text-books, conclude 

 that the law of gravitation ought to be reconsidered. Secondly, 

 there are those who, with scrupulous care, take account of all 

 the conditions which are known to be able to aftect the pheno- 

 menon they are investigating, and are thus able to say, with 

 well-founded confidence, when they meet with some unforeseen 

 result, that it must indicate the operation of some unrecognised 

 cause. 



A brilliant example of this latter mode of working and of the 

 discoveries to which it may lead has recently been afforded to us 

 by the researches of Mr. Crookes, some of whose results, as 

 embodied in the now well-known instrument which he has called 

 the radiomdrr, have attracted much attention. It has appeared 

 to me liowever, that the surprising nature of these results has to 

 some extent called off attention from the remarkable character of 

 the scientific investigation which led to them, and it was at one 

 time my intention to take advantage of the present opportunity 

 for the purpose of trying, on the one hand, to render to Mr. 

 Crookes the credit which I think his researches deserve, and, on 

 the other hand, to give a connected account of the further 

 investigations, both experimental and theoretical, to which these 

 researches have given rise. There seemed to be the more reason 

 for endeavouring to carry out the former part of my intention, 

 inasmuch as an eminent and accomphshed scientific man had 

 published, within the last few months, an account of the dis- 

 covery of the radiometer, the unmistakable tendency of which 

 was, either intentionally or unintentionally, to depreciate Mr. 

 Crookes's merits, and to make it appear that he had put a wrong 

 interpretation upon his own results. I found, however, that the 

 time at my disposal would not enable me to make myself suffi- 

 ciently master of the whole subject to treat it in the way that I 

 wished, and I have therefore been obliged to content myself with 

 merely making this allusion to it as an illustration of the more 

 general considerations to which I have ventured to ask your 

 attention. 



SECTION B. 



chemical science. 

 Opening Address by the President, Prof. Ab«l, F.R.S. 

 The subject which my predecessor in the honourable position 

 of President of this Section, made the chief topic of his in- 

 teresting and instructive address, affords excellent illustrations of 

 the operation of purely scientific research in creating and de- 

 veloping important branches of industry. Mr. Perkin, whose 

 name has from the very commencement of the history of coal- 

 tar colours been identified with their discovery and their scientific 

 and technical history, referred to several series of researches, 

 each one of which formed a link in a chain of discoveries in 



