32 



Mr. Ritchie on a Torsion Galvanometer. 



suspended by a single fibre of silk, the instrument becomes a 

 galvanoscope of extreme delicacy. The following experiment 

 affords a striking illustration of the extreme sensibility of the 

 instrument with this modification. 



EXPERIMENT I. 



File off a few grains from a piece of zinc and] copper by 

 means of a coarse file ; place two of these near each other in the 

 bottom of a clean watch glass ; bring the clean ends of two fine 

 copper wires, connected with the cups of the galvanometer, in 

 contact with them, and then drop over them a small quantity 

 of dilute acid, and the compound needle will be deflected several 

 degrees. 



