ELECTRICAL MEASUREMENT. 451 



as now known, merely in some minor details ; the 

 moveable disc turns round with a micrometer 

 screw instead of moving up and down in a slide. 



Fig. 56. --Portable Electrometer, present form : full size. 



In all other respects it is the same, except the 

 awkward arrangement for placing the pumice, 

 which with my great care, did not lead to any 



G G 2 



