ELECTRIC POTENTIAL. 17 



inch ill diameter projecting from its lower surface, as 

 shown in the enlarged section at D. 



To the lower end of the rod is attached a thin cross- 

 bar, about five-eighths of an inch long, which will pass 

 easily through the neck of the bottle. And from this 

 cross-bar are suspended two strips of imitation gold leaf, 

 each five-eighths of an inch wide by 2J inches long. A 

 small hole is drilled near the edge of the disc for con- 

 venience in attaching wires. 



The leaves in this instrument lie close together, and, 

 consequently, must always be electrified at the same 

 potential; but in some experiments it is desirable to 

 electrify them separately, and for this purpose .a bottle 

 with a wide neck is used, which will admit an ebonite 

 stopper through which two rods can be inserted about 

 an inch apart, and from the cross-bar of each a single 

 leaf is suspended, the surfaces being parallel to each 

 other. This style is represented at #, Fig. 4. The rods 

 can terminate above in balls, or be bent outward and 

 terminate in discs. 



Electroscopes may be constructed with thin metal 

 discs, attached to the glass opposite the leaves ; strips 

 of the same material extending down and connecting 

 with the earth. Brass rods surmounted with balls are 

 often used in the same way, as represented at (7, Fig. 4 ; 

 in which case a glass shade resting on a wooden base is 

 more convenient than the bottle form. 



The object in either case is to have conductors at zero 

 potential near the leaves, which renders them niore 

 sensitive, and discharges them in case of too great 

 divergence ; thus preventing their adhesion to the glass, 

 which is often troublesome. Annoyance from the latter 

 cause is also obviated by using a bottle of globular form, 



