66 First published Paper on Electricity 



An attempt to explain some of the Principal Phenomena 

 of Electricity, by means of an Elastic Fluid Part II 



Containing a Comparison of the Foregoing Theory 

 with Experiment. 



98] I. It appears from experiment, that some bodies suffer the 

 electric fluid to pass with great readiness between their pores; while 

 others will not suffer it to do so without great difficulty ; and some hardly 

 suffer it to do so at all. The first sort of bodies are called conductors, 

 the others non-conductors. What this difference in bodies is owing to 

 I do not pretend to explain. 



It is evident that the electric fluid in conductors may be considered 

 as moveable, or answers to the definition given of that term in page 6. 

 As to the fluid contained in non-conducting substances, though it does 

 not absolutely answer to the definition of immoveable, as it is not abso- 

 lutely confined from moving, but only does so with great difficulty; yet 

 it may in most cases be looked upon as such without sensible error. 



99] Air does in some measure permit the electric fluid to pass through 

 it; though, if it is dry, it lets it pass but very slowly, and not without 

 difficulty; it is therefore to be called a non-conductor. 



It appears that conductors would readily suffer the fluid to run in and 

 out of them, were it not for the air which surrounds them: for if the end 

 of a conductor is inserted into a vacuum, the fluid runs in and out of it 

 with perfect readiness ; but when it is surrounded on all sides by the air, 

 as no fluid can run out of it without running into the air, the fluid will 

 not do so without difficulty. 



100] If any body is surrounded on all sides by the air, or other non- 

 conducting substances, it is said to be insulated: if on the other hand it 

 anywhere communicates with any conducting body, it is said to be not 

 insulated. When I say that a body communicates with the ground, or 

 any other body, I would be understood to mean that it does so by some 

 conducting substance. 



101] Though the terms positively and negatively electrified are much 

 used, yet the precise sense in which they are to be understood seems not 

 well ascertained; namely, whether they are to be understood in the same 

 sense in which I have used the words over or undercharged, or whether, 

 when any number of bodies, insulated and communicating with each other 

 by conducting substances, are electrified by means of excited glass, they 

 are all to be called positively electrified (supposing, according to the usual 



