©N ELECTRICITY IN EQUILIBRIUM. 665 



usually in a contrary state, and therefore renders them still more capable of 

 returning, when they have touched it, to the first substance, in conseciuence 

 of an increased attraction, assisted also by a new repulsion. This alternation- 

 has been applied to the construction of severalelectrical toys ; a little hammeiv 

 for example, has been made to play between two bells; and this instrument has 

 been employed for giving notice of any change of the electrical state of the 

 atmosphere. The repulsion, which takes'place between two bodies, in a similar 

 state of electricity, is> the cause of the currents of air which always accompany 

 the discharge of electricity, whether negative or positive, from pointed sub- 

 stances; each particle of air, as soon as it has received its electricity from the 

 point, being immediately repelled by it ; and this current has also been supposed 

 to facilitate the escape of the electricity, by bringing a continual succession of 

 particles not already overcharged. 



If two bodies approach each other, electrified either positively or negatively 

 in different degrees, they will either repel or attract each other, according to- 

 their distance: when they are very remote, they exhibit a repulsive force,, 

 but when they are within a certain distance, the effects of induced electricity 

 overcome the repulsion, which would necessarily take place, if the distribution! 

 of the fluid remained unaltered by their mutual influence. 



When a quantity of the electric fluid is accumulated on one side of a non- 

 conducting substance, it tends to drive off the fluid from the other side; and 

 if this fluid is suffered to escape, the remaining matter exerts its attrac- 

 tion on the fluid which has been imparted to the first side, and allows it to be 

 accumulated in a much greater quantity than could have existed in an equal 

 surface of a conducting substance. In this state, the body is said "to 

 be charged; and for producing it the more readily, each surface is usually 

 coated with a conducting substance, which serves to convey the fluid to and 

 from its different parts with convenience. The thinner any substance is, the 

 greater quantity of the fluid is required for charging it in this manner, so as 

 to produce a given tension, or tendency to escape: but if it be made too thiti, 

 it will be liable to break, the attractive force of the fluid, for the matter on the 

 opposite side overcoming the cohesion of the substance, and perhaps forcing; 

 its way through the temporary vacuum which is formed. 



