VOL. LXVIII.] PHILOSOPHICAL TRANSACTIONS. 46Q 



electricity contrary to that of the electrified body. If the body plunged in this 

 atmosphere be of a small extent, it will be found so to all appearance, because 

 the two extremities of a small body cannot be separately examined ; whereas a 

 body of a certain extent exhibits in a very perceptible manner the two distinct 

 electricities. Tlie reason of this wonderful phenomenon is to be understood 

 from the principles adopted, and may without much attention be understood if 

 we suppose the excited body to be in a positive state of electricity ; for in this 

 case the atmosphere of electric fluid, surrounding the excited body, forces by its 

 repulsive quality the electric fluid of the neigiibouring body towards its farther 

 extremity, and thus accumulates or crowds it on that extremity, from whence it 

 is therefore ready to fly off on any other body, which is of a nature to receive it, 

 being brought near enough. 



If the excited body be in a state of negative electricity, the explanation is not 

 so obvious as in the positive case : it requires some more attention to conceive 

 what passes. The excited body, having lost a part of its natural share of elec- 

 tric fluid, a kind of vacuum, if I may call it so, takes place on this body. The 

 electric fluid of any other body being in its natural state, and therefore in a kind 

 of inactivity, confined as it were within its limits by the electric fluid of all the 

 surrounding bodies, is set at liberty, exerts its natural repulsive quality towards 

 that body, on which it does not find a similar quantity of electric fluid resisting 

 its spring, or its elastic and repulsive quality ; it therefore rushes towards that 

 kind of vacuum which exists on a body negatively electrified ; and thus the 

 electric fluid of this body, losing its natural state of equilibrium, and ac- 

 cumulating itself towards the vacuum, produces there a real positive electricity, 

 at the same time that the opposite extremity has a negative one. 



I must speak one word more of that particular quality of conducting bodies, 

 by which they receive, with a kind of reluctance, either state of electricity ; and, 

 after having received it, part with the same with as much seeming difficulty. 

 This quality, not unknown to attentive electricians, who must have observed it, 

 has commonly appeared somewhat extraordinary and diflicult to be believed by 

 many electricians, to whom I have happened to explain my theory of the elec- 

 trophore. As this quality is the foundation of this theory, I conceive it will not 

 be amiss to demonstrate it by facts. The first part of this inherent quality of 

 non-conducting bodies, receiving a state of electricity with more difficulty than 

 conducting bodies, is easily shown by the following simple experiment : a piece 

 of dry glass, held near a prime conductor, will receive no electricity, or almost 

 none, at the same distance as that at which a piece of metal or another conduct- 

 ing substance will have received a considerable degree of electricity, or even a 

 full spark. The 2d part of this inherent quality may be thus demonstrated : a 

 piece of metal insulated, as, for instance, the metal plate of an electrophore. 



