260 PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



a slender canal; and consequently, from what has been said before, it seems 

 reasonable to suppose that the waste of electricity from the end of the cone must 

 be very great in proportion to its surface ; though it does not appear from this 

 reasoning, whether the waste of electricity from the whole cone, should be 

 greater or less than from a cylinder of the same base and altitude. All that has 

 been here said relating to the flowing out of electricity from overcharged bodies, 

 holds equally true with regard to the flowing in of electricity into undercharged 

 bodies. 



But a circumstance which, he believes, contributes as much as any thing to 

 the quick, discharge of electricity from points, is the swift current of air caused 

 by them, and taken notice of by Mr. Wilson and Dr. Priestley (vide Priestley, 

 p. 117 and 591); and which is produced in this manner. If a globular body 

 ABD is overcharged, the air close to it, all round its surface, is rendered over- 

 charged, by the electric fluid, which flows into it from the body ; it will there- 

 fore be repelled by the body; but as the air all round the body is repelled with 

 the same force, it is in equilibrio, and has no tendency to fly off" from it. If 

 now the conical point acb be made to stand out from the globe, as the fluid will 

 escape much faster in proportion to the surface from the end of the point, than 

 from the rest of the body, the air close to it will be much more overcharged than 

 that close to the rest of the body; it will therefore be repelled with much more 

 force ; and consequently a current of air will flow along the sides of the cone, 

 from B towards c ; by which means there is a continual supply of fresh air, not 

 much overcharged, brought in contact with the point ; whereas otherwise the 

 air adjoining to it would be so much overcharged, that the electricity would have 

 but little disposition to flow from the point into it. 



The same current of air is produced in a less degree, without the help of the 

 point, if the body, instead of being globular, is oblong or flat, or has knobs on 

 it, or is otherwise formed in such manner as to make the electricity escape faster 

 from some parts of it than the rest. 



In like manner, if the body abd be undercharged, the air adjoining to it will 

 also be undercharged, and will therefore be repelled by it ; but as the air close 

 to the end of the point will be more undercharged than that close to the rest of 

 the body, it will be repelled with much more force ; which will cause exactly the 

 same current of air, flowing the same way, as if the body was overcharged; and 

 consequently the velocity with which the electric fluid flows into the body, will 

 be very much increased. Mr. C. believes indeed that it may be laid down as a 

 constant rule, that the faster the electric fluid escapes from any body when 

 overcharged, the faster will it run into that body when undercharged. 



Points are not the only bodies which cause a quick discharge of electricity ; in 

 particular, it escapes very fast from the ends of long slender cylinders ; and a 



