6 REPORT — 1877. 



afforded by the idea of Work and the correlative one of Energy. These ideas, which 

 have been found to have a most far-reaching significance and to have exerted a trans- 

 forming effect upon every branch of physics, owe their recognition, not to the 

 spontaneous growth of the science, but to their having been forced on the atten- 

 tion of physicists by the cultivators of practical mechanics*. Very much the 

 same thing may also be said of the modern conceptions of the nature of heat 

 and of the relation between thermal phenomena and those of other branches of 

 physics. The notion of heat as a measurable magnitude, of which definite 

 quantities could be given to or taken away from bodies, was fully established by 

 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 consequently natural that the new knowledge of the laws of 

 heat should be embodied in the conception of a Matter of Heat or Caloric capable 

 of entering into and being separated from combination like fixed air or dephlogisti- 

 cated 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 Ivumford 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 nature of the connexion 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 t. 



Probably it would be impossible to find a more remarkable instance of what I 

 referred to j ust 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 coexisted 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 he 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 tele- 

 graphic purposes, and is one which would probably 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 may be said of the 

 discovery of the influence of electrostatic induction upon the transmission of elec- 

 tric currents through metallic conductors, 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 conductivity, 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 sur- 

 passed 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 instru- 

 ments have led to the rapid accumulation of numerical data of great scientific im- 

 portance, and have largely contributed to the spread of accurate conceptions as to 

 the quantitative laws of electrical phenomena. But the further necessity experi- 

 enced by practical electricians, that, besides being able to make accurate "measure- 

 ments, they should be able mutually to communicate and to understand each other's 

 results, has probably done more than any thing else to hasten the introduction, for 



* See on this point, Diihring, 'Kritische Gesehiehte dcr allgemeinen Prineipien der 

 Meehanik' (Berlin, 1573), pp. ^83-486. 

 t Conf. Diihring, foe. rit. 



