ON THE PHYSICAL VIEW OF NATIKE. Ill 



A pupil of Daltou, Joule was early drawn into the 

 circle of ideas and iii\estigations winch are contained in 

 Faraday's experimental researches. With much ampler 

 means, and possibly also with a greater hne for accurate 

 quantitative measurements, than P'araday possessed, he 

 grasped the great importance of the law of electrolytic 

 equivalence as affording the means of accurately measur- 

 ing chemical processes, and of giving definite expression 

 to the vaguer ideas supported by Faraday and othei-s 

 that force was indestructible, and that the different 

 forces of nature w^ere mutually convertible. These 

 ideas had received popular circulation and current ex- 

 pression in Grove's celebrated lectures on the " Corre- 

 lation of riiysieal Forces" in 1842 and 1843. Joule, 

 in whose mind they seem to liave existed as axioms, 

 set himself to devise accurate instruments and methods 

 by which the convertibility of different forces, their 

 " mechanical duty," could be measured, and their equiv- 

 alence put into figures. The first numbers which Joule 

 found differed considerably,-^ so that the conclusion 

 arrived at that the mechanical duty or " value " of a 

 degree of heat is a constant quantity could only have 

 been drawn by one who had a strong a priori^ con- 



^ For details see Helm, ' Ener- A predisposition to believe that 

 getik,' p. 3-t ; also vol. i. p. 265, j some quantity besides matter could 

 note, of the present work. Joule's | not be lost or created, but onlj* 

 equivalent varied from 742 to 890 

 fuot-pounds, and was finally fixed 

 at 772 in 1850, this figure being 

 correct to h per cent (Joule's 

 'Scientific Papers,' p. 328). 



- Philosophical considerations arc 

 mixed up with all the early enun- 

 ciations of the principle of the in- 

 destructibility of force, or energy as 

 it was later more clearly termed. 



preserved and transformed, existed 

 in the mitids of ^lohr, iSeguin, 

 Mayer, Colding, Joule, Hirn, antl 

 has been traced variously back to 

 the wiitings of earlier thinkei-s, 

 such as Montgolfier, Faraday, Davy, 

 Oersted, Leibniz, &c. Prof. Mach 

 ('Wiirmelehre,' p. 238, &e.) dis- 

 cusses this jioint fully. The prin- 

 ciple gradually became firudy 



