Electric 'wind 75 



the redundant fluid is collected in much greater quantity near the ends of 

 the cylinders than near the middle. The same thing may be said, but I 

 believe in a less degree, of the edges of thin plates. 



What has been just said concerning the current of air, serves to explain 

 the reason of the revolving motion of Dr Hamilton's and Mr Kinnersley's 

 bent pointed wires, vide Philosophical Trans. Vol. LI., p. 905, and Vol. LIII., 

 p. 86; also Priestly, p. 429: for the same repulsion which impels the air 

 from the thick part of the wire towards the point, tends to impel the 

 wire in the contrary direction. 



126] It is well known, that if a body B is positively electrified, and 

 another body A, communicating with the ground, be then brought near 

 it, the electric fluid will escape faster from B, at that part of it which is 

 turned towards A, than before. This is plainly conformable to theory; 

 for as A is thereby rendered undercharged, B will in its turn be made 

 more overcharged, in that part of it which is turned towards A, than it 

 was before. But it is also well known that the fluid will escape faster 

 from B, if A be pointed, than if it be blunt; though B will be less over- 

 charged in this case than in the other ; for the broader the surface of A , 

 which is turned towards B, the more effect will it have in increasing the 

 overcharge of B. The cause of this phenomenon is as follows : 



If A is pointed, and the pointed end turned towards B, the air close 

 to the point will be very much undercharged, and therefore will be strongly 

 repelled by A, and attracted by B, which will cause a swift current of air 

 to flow from it towards B ; by which means a constant supply of under- 

 charged air will be brought in contact with B, which will accelerate the 

 discharge of electricity from it in a very great degree : and moreover, the 

 more pointed A is, the swifter will be this current. If, on the other hand, 

 that end of A which is turned towards B is so blunt, that the electricity 

 is not disposed to run into A faster than it is to run out of B, the air 

 adjoining to B may be as much overcharged as that adjoining to A is 

 undercharged; and therefore may by the joint repulsion of B and attrac- 

 tion of A , be impelled from B to A , with as much or more force than the 

 air adjoining to A is impelled in the contrary direction ; so that what little 

 current of air there is may flow in the contrary direction. 



It is easy applying" what has been here said to the case in which B is 

 negatively electrified. 



I2 7] 5- I n the paper of Mr Canton's, quoted in the second section, 

 and in a paper of Dr Franklin's Philosophical Transactions 1755, p. 300, 

 and Franklin's letters, p. 155, are some remarkable experiments, shewing 

 that when an overcharged body is brought near another body, some fluid 

 is driven to the further end of this body, and also some driven out of it, 

 if it is not insulated. The experiments are all strictly conformable to the 



