FORMATION OF A GALVANIC CURRENT. 207 



SECTION XII. 



ON THE RELATION BETWEEN GALVANIC CURRENTS AND 

 MAGNETIC FORCES : AND ON THE REGISTER OF TER- 

 RESTRIAL GALVANIC CURRENTS: WITH SPECIAL RE- 

 FERENCE TO DISTURBANCES OF TERRESTRIAL MAG- 

 NETISM. 



88. Fundamental principles of the creation of a 

 galvanic current, and of its magnetic action : application 

 to the galvanometer and to the speaking -telegraph. 



The subject of galvanic action in general belongs so 

 completely to another science that we shall enter upon 

 it here no farther than is absolutely necessary for ex- 

 plaining the relations of which this Section treats. 



The simplest form of a galvanic battery is repre- 

 sented in Figure 63. A small vessel, of glass, or earth- 

 enware, or guttapercha, is nearly filled with dilute 

 sulphuric acid. In the acid are plunged two plates of 

 metal, selected principally for their difference of sus- 



