VOL. LXVIII.J PHILOSOPHICAL TRANSACTIONS. 441 



position, but only to deny the universality of that asserted by Dr. Franklin, 

 which I apprehend to be sometimes true, and sometimes also false. Here it may 

 be of use to show, that sharp points having the most perfect communication with 

 the earth, are not wholly exempt from receiving them. My first authority shall 

 be Dr. Franklin himself. " Let a person," says he, p. 6o, " standing on the 

 floor, present the point of a needle at 12 or more inches from the prime con- 

 ductor, and while the needle is so presented, the conductor cannot be charged, 

 the point drawing off the fire as fast as it is thrown on by the electrical globe. 

 Let it be charged, and then present the point at the same distance, and it will 

 suddenly be discharged." The word suddenly means, I suppose, that it will 

 receive an explosion ; that being the most natural and obvious proof of the sud- 

 denness of the discharge. The same thing is more directly asserted by Mr. 

 Henly, in vol. 64 of the Phil. Trans, p. 138, where he says, that in discharging 

 3 of his large jars, to the coating of which he had connected a wire nicely 

 tapered to a point, the fire flew to the point, and the jars were discharged with 

 a full and loud explosion. A 3d, and equally decisive proof, is furnished by Mr. 

 Nairne's own experiments, though seemingly made with a contrary view. For 

 when the double or interrupted conductor was used, and the 2d conductor fixed 

 down by screws at about 3 inches distance from the first, the point presented to 

 the contrary end of the 2d conductor was found to receive a strong and loud ex- 

 plosion, with a while light at the distance of at least 3 inches. 



If we compare this experiment with another, very common one, exhibited at 

 the same time by Mr. Nairne, the comparison will perhaps lead us to the dis- 

 covery of a principle on which electrical explosions very frequently depend. 

 Though the point, in the circumstances above described, received so strong an 

 explosion, yet when it was presented directly to the prime conductor, it received 

 no explosion whatever at any distance, unless a succession of weak sparks, at the 

 distance of about a quarter of an inch, can be called so. To what must this 

 difference be attributed ? Plainly to the different quantity of electric fluid ac- 

 cumulated on the prime conductor in the one and the other case. Where the 

 point is presented to the prime conductor, from the time the machine begins to 

 work, the property attributed to them, and which, in some cases, they really 

 possess, of stealing away the electricity silently ; this property, I say, operating 

 from the very beginning, prevents the electric fluid from being accumulated in 

 the prime conductor, and of course the quantity of it will always be small. But 

 vv'hen a double or interrupted conductor is used, the 2d conductor receives no 

 electricity till the prime conductor is pretty highly charged, and, if put at the 

 greatest striking distance, not till it is fully charged, and consequently the sharp 

 point presented to the opposite end can carry away none of it till that time ; 

 when the whole quantity is thrown off at once. It should seem then, that the 



VOL. XIV. 3 L 



