ELECTRIC POTENTIAL. 21 



Replacing this body, let the one from which energy 

 has been transferred be removed ; the potential of the 

 remaining body being positive, there is instantly a 

 transfer of energy from it to the disc and leaves, making 

 them positive also. Hence the leaves diverge as before, 

 from mutual repulsion, and the divergence is increased 

 by attraction from the lower potential of the glass and 

 surrounding objects. 



From this it will be seen that the effect on the electro- 

 scope is the same whether the potential of the electrified 

 body be positive or negative. In either case there is 

 mutual repulsion between- the leaves, from their being 

 at the same potential ; and mutual attraction between 

 them and surrounding objects, caused by difference of 

 potential. 



The indications of the electroscope furnish no means 

 of distinguishing between positive and negative poten- 

 tial, being the same for both. And as this is true of 

 most of the phenomena pertaining to these two states, 

 it is difficult, in static electricity especially, to determine 

 which phenomena are positive and which negative. 



There is no such well-marked distinction between 

 them as between the positive and negative states known 

 as heat and cold ; neither can we observe electric move- 

 ment as we can heat movement; since heat moves 

 slowly, while electricity moves with inconceivable ra- 

 pidity. 



But if we can show cause for an accumulation of elec- 

 tric energy at one point and for its absence at another, 

 and show effects following such difference of energy, we 

 then have proof of the positive and negative potential 

 of the different points, which may be accepted as 

 reliable. 



