14 ELEMENTARY LESSONS ON [CHAP. i. 



electricity of the paper to be of the same kind as that 

 with which the electroscope is charged, or positive. 



The Gold-Leaf Electroscope will also indicate roughly 

 the amount of electricity on a body placed in contact 

 with it, for the gold leaves open out more widely when 

 the quantity of electricity thus imparted to them is greater. 

 For exact measurement, however, of the amounts of 

 electricity thus present, recourse must be had to the instru- 

 ments known as Electrometers, described in Lesson XXI. 

 In another form of electroscope (Bohnenberger's) a 

 single gold leaf is used, and is suspended between two 

 metallic plates, one of which can be positively, the other 

 negatively electrified, by placing them in communication 

 >|th the poles of a "dry pile" (Art. 182). If the gold 

 leaf be charged with electricity of either kind it will be 

 attracted to one side and repelled from the other, 

 according to the law of attraction and repulsion men- 

 tioned in Art 4. 



14. Henley's Quadrant Electroscope. The 

 Quadrant Electroscope is sometimes employed as an 

 indicator for large charges of electricity. It consists of 

 a pith ball at the end of a light 

 arm fixed on a pivot to an upright. 

 When the whole is electrified the 

 pith-ball is repelled from the up- 

 right and flies out at an angle, 

 indicated on a graduated scale or 

 quadrant behind it. Its usual form 

 is shown in Fig. 8. This little 

 electroscope, which is seldom 

 used except to show whether an 

 electric machine or a Leyden 

 battery is charged, must on no 

 account be confused with the deli- 

 cate " Quadrant Electrometer" described in Lesson 

 XXL, whose object is to measure very small charges 

 of electricity not to indicate large ones. 



