570 USE OF THE ELECTROSCOPE. 



ducing body is removed, the leaves drop again be- 

 cause the two separated electricities recombine, and 

 the electroscope is again in the neutral state A. If the 

 metal rod is touched with the finger, while the indu- 

 cing body is still near and the two electricities therefore 

 still separated, then, as shown at C, the free positive 

 electricity of the gold leaves escapes through the finger 

 and the leaves drop, while the negative electricity of 

 the knob remains bound as long as the, inducing body 

 is near the instrument. Now, while the inducing body 

 is still near, let the finger be removed first, and next 

 the inducing body ; then the negative electricity be- 

 comes free, and as it cannot now escape, it diffuses 

 itself over the metal portion of the instrument, and 

 the gold leaves diverge again, as in D. 



The electroscope is now charged by induction with 

 the opposite electricity to that of the inducing body, 

 that is, negatively, if the inducing body was, for 

 example, a positively charged glass rod, and positively 

 if the inducing body had been a negatively charged 

 stick of sealing-wax. The latter case is represented in 

 figures E, F, and 6r, which correspond to figures B, C, 

 and 77, respectively. 



An electroscope, charged with either electricity, may 

 be used not only for deciding whether a body is in the 

 electric state or not, but also with what kind of electricity 

 the body is charged. When a neutral body is brought into 

 the neighbourhood of a charged electroscope as shown in 

 A and B of fig. 309, no appreciable change takes place 

 in the divergence of the leaves. In reality the diver- 

 gence does diminish in that case slightly, because the 

 electroscope itself acts now like an inducing body, 



