ii8 ELEMENTS OF SCIENCE 



attracted (like the pieces of paper) and adhere either to 

 the sealing-wax or the glass rod. But after contact 

 with either, it will be repelled and will diverge in an 

 opposite direction, if that which before attracted it is 

 made to again approach it. But though it will be thus 

 repelled by whichever (wax or glass) was brought in 

 contact with it, it will be attracted by the other, till it 

 has come in contact with that other, which will then in 

 turn repel it. Thus the pith ball may be first attracted 

 by the wax and then repelled from it and attracted by 

 the glass ; then, in turn, it may be repelled from the 

 glass and attracted by the wax, and so on alternately 

 for any length of time, the friction of the flannel with 

 wax and of the silk with the glass being again and again 

 renewed. If two pith balls be similarly suspended side 

 by side, then, when both have simultaneously touched 

 either the wax or the glass, they will not only be repelled 

 by the approach of whichever of these they may have 

 touched, but they will also repel each other. Neverthe- 

 less this repulsion will gradually diminish, till they fall 

 together side by side, as they were at first, when it has 

 ceased altogether. 



Thus it is evident that some peculiar influence or energy 

 is excited by these frictions, and the force producing this 

 energy is called electricity. It is also sometimes spoken 

 of as if it were itself a substance of some kind and is 

 often popularly called the " electric fluid." 



Its real nature is as yet entirely unknown, but (like 

 light and heat) it is well to freely make use of any 

 hypothesis which may help us to elucidate and predict 

 electrical phenomena without pinning our faith to the 

 truth of any such hypothetical explanation. 



There are also evidently two kinds, or states, of elec- 

 tricity : (i) that produced on the glass which is rubbed 



