ON THE PHYSICAL VIEW OF NATURE. Ill 



A pupil of Dalton, Joule was early drawn into the 

 circle of ideas and investigations which are contained in 

 Faraday's experimental researches. With much ampler 

 means, and possibly also with a greater love for accurate 

 quantitative measurements, than Faraday 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 others 

 that force was indestructible, and that the different 

 forces of nature were mutually convertible. These 

 ideas had received popular circulation and current ex- 

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

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

 in whose mind they seem to have 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, 1 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 pi^iori 2 con- 



1 For details see Helm, ' Ener- 

 getik,' p. 34 ; also vol. i. p. 265, 

 note, of the present work. Joule's 

 equivalent varied from 742 to 890 

 foot-pounds, and was finally fixed 

 at 772 in 1850, this figure being 

 correct to ^ per cent (Joule's 

 ' Scientific Papers,' p. 328). 



2 Philosophical considerations are 

 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. 



A predisposition to believe that 

 some quantity besides matter could 

 not be lost or created, but only 

 preserved and transformed, existed 

 in the minds of Mohr, Se"guin, 

 Mayer, Colding, Joule, Hirn, and 

 has been traced variously back to 

 the writings of earlier thinkers, 

 such as Montgolfier, Faraday, Davy r 

 Oersted, Leibniz, &c. Prof. Mach 

 ('Warmelehre,' p. 238, &c.) dis- 

 cusses this point fully. The prin- 

 ciple gradually became firmly 



