À POCKET GALVANOMETEK. 



289 



It will be seen that the system of magnets thus arranged is equi- 

 valent to Helmholfcz's galvanometer of two circular coils, if we imagine 

 the two coils to be deformed into two long rectangles of infinite 

 length, that is, reduced to four parallel currents. For if we adjust 

 these currents to proper positions, and replace each of them by a 

 magnet and the central magnet by a straight current, we have the 

 system just discussed. 



§ II. Flat Coil Pocket Galvanometer. 



I now pass to the description of the flat coil pocket galvanometer, 

 which may in virtue of its compactness and simplicity of construc- 

 tion be found useful for some purposes, although it can not of course 



