Communication of electricity 1 1 5 



overcharged nor undercharged, nor will the electricity have any disposition 

 to run either in or out of it. 



209] If the overcharged body be now brought nearer, A will become 

 undercharged, and the electricity will run into it from the surrounding 

 air. If the overcharged body be not brought so near A will be overcharged, 

 and the electricity will run out of it. If an undercharged body be brought 

 near A it will become more overcharged than before, and the electricity 

 will run out stronger than before. 



COR. III. If the body A be negatively electrified, and an undercharged 

 body be brought near it till the electric fluid in the adjoining air is as 

 much compressed as that in the body A, the electricity will have no dis- 

 position to run either in or out of A , nor will it be either overcharged or 

 undercharged, as will appear from the same way of reasoning as was 

 used with regard to the 2nd Corollary. 



If the undercharged body be now brought nearer, A will become over- 

 charged, and the electricity will also run out of it. If the undercharged 

 body be removed farther off, A will become undercharged, and the elec- 

 tricity will also run into it. If an overcharged body be brought near to A, 

 it will become more undercharged than before, and the electricity will 

 also run in faster than before. 



On the whole, therefore, it appears that whenever a body is under- 

 charged the electricity will run into it, and whenever it is overcharged it 

 will run out. 



210] It has usually been supposed that two bodies, whenever the 

 electricity either runs into or out of both of them, repel each other ; but that 

 when it runs into one and out of the other, they attract. In the beginning 

 of this paper I laid down a different rule for the electric attraction and 

 repulsion, namely, that when the two bodies are both overcharged or both 

 undercharged they repel, but attract when one is overcharged and the 

 other undercharged. 



But by what has been just said it appears that these two rules agree 

 together, or at least if they do differ, they differ so little that there is no 

 reason to think my rule will agree less with experiment than the other. 



The reasoning here used would have been more satisfactory if the 

 bodies were capable of containing electricity only on one side, namely, 

 on that which is turned towards the other body. But I do not imagine, 

 however, that this will make much difference in the effect. 



211] What has been here said holds good only in cases where the size 

 of the body A is small in respect of the distance of the electrified body 

 from it, so that the influence of the electrified body may be nearly the 

 same on all parts of the body A as is the case in bits of cork held near an 

 excited tube; but when the size of the body A is such that the influence 



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