80 HISTORY OF GALVANISM. 



bility; and though they indicate the existence of 

 a peculiar agency, cannot be used to measure its 

 intensity and law. 



The various examples of the class of agents 

 which we here consider, magnetism, electricity, 

 galvanism, electro-magnetism, thermo-electricity, 

 differ from each other principally in the circum- 

 stances by which they are called into action ; and 

 these differences are in reality of a chemical nature, 

 and will have to be considered when we come to 

 treat of the inductive steps by which the general 

 principles of chemical theory are established. In 

 the present part of our task, therefore, we must 

 take for granted the chemical conditions on which 

 the excitation of these various kinds of action de- 

 pends, and trace the history of the discovery of 

 their mechanical laws only. This rule will much 

 abridge the account we have here to give of the 

 progress of discovery in the provinces to which I 

 have just referred. 



The first step in this career of discovery was 

 that made by Galvani, Professor of Anatomy at 

 Bologna. In 1 790, electricity, as an experimental 

 science, was nearly stationary. The impulse given 

 to its progress by the splendid phenomena of the 

 Leyden phial had almost died away ; Coulomb was 

 employed in systematizing the theory of the electric 

 fluid, as shown by its statical effects; but in all 

 the other parts of the subject, no great principle 

 or new result had for some time been detected. 



