ELECTRICITY OS 



there is no attraction. But if I rub the shellac with a piece 

 of flannel [rubbing the shellac, and then holding it near the 

 ball], look at the attraction which has arisen out of the shellac 

 simply by this friction, and which I may take away as easily 

 by drawing it gently through my hand. [The lecturer re- 

 peated the experiment of exciting the shellac, and then 

 removing the attractive power by drawing it through his 

 hand.] Again, you will see I can repeat this experiment 

 with another substance; for if I take a glass rod, and rub it 

 with a piece of silk covered with what we call amalgam, look 

 at the attraction which it has; how it draws the ball toward 

 it; and then, as before, by quietly rubbing it through the 

 hand, the attraction will be all removed again, to come back 

 by friction with this silk. 



But now we come to another fact. I will take this piece 

 of shellac, and make it attractive by friction ; and remember 

 that, whenever we get an attraction of gravity, chemical 

 affinity, adhesion, or electricity (as in this case), the body 

 which attracts is attracted also, and just as much as that 

 ball was attracted by the shellac, the shellac was attracted 

 by the ball. Now I will suspend this piece of excited shellac 

 in a little paper stirrup, in this way (FiG. 33), in order to 



FIG. 33 



make it move easily, and I will take another piece of shellac, 

 and, after rubbing it with flannel, will bring them near to- 

 gether : you will think that they ought to attract each other ; 

 but now what happens? It does not attract; on the con- 

 trary, it very strongly repels, and I can thus drive it round 



