DISCOVEEIES OF JOULE. 353 



current is diminished in a corresponding and fixed proportion. 

 He has further ascertained that by reversing the poles of a 

 magnetic bar a quantity of heat is produced proportional to 

 the square of the magnetic tension a fact which was also 

 discovered by myself, though at a later date. In particular, 

 Joule has likewise demonstrated, by means of numerous ex- 

 periments, that the heat evolved by friction under various cir- 

 cumstances stands in an unvarying proportion to the amount 

 of force expended. According to his most recent experiments 

 of this kind, he has fixed the mechanical equivalent of heat 

 at 423.* 



Joule has likewise investigated experimentally, in relation 

 to this question, the thermal behaviour of elastic fluids when 

 expanded, and has thereby confirmed the earlier results of 

 other physicists. 



The new subject soon began to excite the attention of 

 learned men ; but inasmuch as both at home and abroad the 

 subject has been exclusively treated as a foreign discovery, I 

 find myself compelled to make the claims to which priority en- 

 titles me ; for although the few investigations which I have 

 given to the public, and which have almost disappeared in the 

 flood of communications which every day sends forth without 

 leaving a trace behind, prove, by the very form of their pub- 

 lication, that I am not one who hankers after effect, it is not 

 therefore to be assumed that I am willing to be deprived of 

 intellectual property which documentary evidence proves to 

 be mine. 



By help of the mechanical equivalent of heat many prob- 

 lems can be solved which, without it, could not be attacked at 

 all : among them, the calculation of the thermal effect of the 

 falling together of cosmical masses may be especially men- 

 tioned. It will not be out of place to indicate here briefly a 

 few results of such calculations. 



* That is, 1 thermal unit =423 kilogrammetres. 



