HISTORY OF GALVANISM. 101 



tinated ; while ruby, sapphire,, quartz, and silex, 

 were not affected.* 



Since the experiments of Mr. Children, the only 

 addition which the science of galvanism has ac- 

 quired is from Dessaignes, who some time before 1! 

 had made a series of observations on the effects of 

 temperature upon the action of the pile, which he 

 now repeated and extended. He informs us, that 

 the instrument ceases to act if the whole of it be 

 heated to 2121: but that, on the contrary, its action 

 is doubled, if one half of it be heated, while the 

 other is cooled. He farther informs us, that two 

 pieces of metal of the same kind will act, if one of 

 them be heated, while the other is cooled ; and even 

 that the same effect will follow if different parts of 

 the same piece of metal be kept at different tem- 

 peratures. The result of these experiments is 

 probably what we should not previously have ex- 

 pected ; yet they may be explained either upon 

 electrical or chemical principles; as both the elec- 

 trical condition of bodies, and the effect of che- 

 mical re-agents, is materially affected by the degree 

 of temperature to which they are exposed.* 



These experiments will conclude the first part 

 of this essay, containing the history of galvanism. 

 Although it may be somewhat hazardous to form 

 predictions respecting the progress of science, I 



* Phil. Trans, for 1815, p. 363. 



f Journ. de Phys. Ixxiii. 230, 417; Ixxxii. 360 ; Ixxxiii. 194, 



