on Galvanometers. 



61 



passing through the instrument and with no controlling 

 magnet. For in that case the sensibility of the instrument 

 can be subsequently varied by simply raising or lowering the 



Fig. 1. 



controlling magnet parallel to itself ; whereas, if the galvano- 

 meter be fixed in any other position, it is necessary, when 

 raising or lowering the controlling magnet, to give it a care- 

 ful screwing motion to prevent the spot of light going off the 

 scale. 



