5l6 PHILOSOPHICAL TRANSACTIONS. [aNNO 1774. 



as before observed, it appears by the best information, nearly at the same time ; 

 and in many other places, considerably distant from each other. 



I have observed, on another occasion, that if a round ball of metal, 2 inches 

 in diameter, was presented towards the large prime conductor to a good cylinder, 

 at the distance of 2 inches, it would continue to receive such strong sparks, as 

 would give the person who held it a sensible shock in both his legs ; but that if 

 the point of a lancet, or a wire 6 inches long, nicely tapered to a point, and 

 tipped with steel, were at the same time held towards the conductor, at the 

 distance of 2 feet, the point would draw off all its electricity silently, and not 

 suffer a spark to pass from it to the ball; and from this experiment I inferred, 

 that a sharp point might probably, in some measure, produce the same effect on 

 a cloud highly charged with electricity, or rather on the electric atmosphere 

 surrounding the cloud; and thus perhaps contribute to lessen a little, if not 

 actually prevent a stroke. I also observed, that if the point of the wire or lancet, 

 was brought nearly into contact with the prime conductor; yet no sensation 

 would be felt in the hand of the operator; and this I imagined was a kind of de- 

 monstration, that there could be no danger of inviting a stroke of lightning from 

 a cloud by a sharp-pointed conductor; as it could make no difference in the ex- 

 periment, whether the point moved towards the large prime conductor, or the 

 conductor moved towards the point. It having however been objected to this 

 experiment, that it was not analogous to the effect of nature operating by a 

 cloud; forasmuch as the cloud being a loose and floating body, it might accede 

 to, and strike on the point with its contents; which the conductor, being a 

 fixed body, was incapable of doing, I made the following experiment. 



Exp. 7. I procured a bullock's bladder, of the largest size, gilded with leaf 

 copper, and suspended it, by a silken string, at one end of an arm of wood, 

 placed horizontally, and turning freely on the point of a needle ; the needle 

 being stuck upright in another piece of wood, inserted in a firm base, and stand- 

 ing in a perpendicular direction to the floor. The bladder was balanced by a 

 leaden weight, at the other end of the wooden arm, as in fig. 8. The appa- 

 ratus being thus adjusted, I gave the bladder a strong spark from a knob of a 

 charged bottle; when, presenting towards it a brass rod, terminated by a ball, 

 2 inches in diameter, I observed, that the bladder would come towards it at the 

 distance of 3 inches ; it would even come back to it, when swinging in a con- 

 trary direction; and when it had got within 1 inch of it, it would throw off its 

 electricity in a full and strong spark: the bladder gave the spark nearly, if not 

 quite, as large as it received it. I then gave it another strong spark as before, 

 when, presenting towards it the pointed wire, I could never perceive that it ac- 

 ceded to that; and when it was brought nearly into contact with the bladder, 

 there was no spark at all, scarcely any sensible quantity of electricity remaining 



