32 ELEMENTARY LESSONS ON [CHAP. i. 



on the surface of an electrified body at any point, part 

 of the electricity flows into it, and it may be then re- 

 moved, and the sample thus obtained may be examined 

 with a Gold-leaf Electroscope in the ordinary way. For 

 some purposes a metallic bead, fastened to the end of a 

 glass rod, is more convenient than a flat disc. If such 



Fig. 18. 



a proof-plane be applied to the outside of our electrified 

 hollow ball, and then touched on the knob of an electro- 

 scope, the gold leaves will diverge, showing the presence 

 of a charge. But if the proof-plane be carefully inserted 

 through the opening, and touched against the inside of 



