266 PHILOSOPHICAL TRANSACTIONS* [aNNO 1771. 



strongly disposed to part with its electricity to the air, and the other is strongly 

 disposed to receive it. 



In like manner, when the electric fluid is made to pass through water, in the 

 form of a spark, as in Signor Beccaria's* and Mr. Lane's -|- experiments, Mr. 

 C. imagines that the water, by the rapid motion of the electric fluid through it, 

 is turned into an elastic fluid, and so much rarefied as to make very little oppo- 

 sition to its motion ; and when stones are burst or thrown out from buildings 

 struck by lightning, in all probability that effect is caused by the moisture in the 

 stone, or some of the stone itself, being turned into an elastic fluid. 



It appears plainly, from the sudden rising of the water in Mr. Kinnersley's 

 electrical air thermometer, + that when the electric fluid passes through the air, 

 in the form of a spark, the air in its passage is either very much rarefied, or 

 entirely displaced: and the bursting of the glass vessels, in Beccaria's and Lane's 

 experiments, shows that the same thing happens with regard to the water, when 

 the electric fluid passes through it in the form of a spark. Now, Mr. C. saw 

 no means by which the displacing of the air or water can be brought about, but 

 by supposing its elasticity to be increased, by the motion of the electric fluid 

 through it, unless you suppose it to be actually pushed aside, by the force with 

 which the electric fluid endeavours to issue from the overcharged body: but he 

 can by no means think that the force with which the fluid endeavours to issue, 

 in the ordinary cases in which electric sparks are produced, is sufficient to over- 

 come the pressure of the atmosphere, much less that it is sufficient to burst the 

 glass vessels in Beccaria's and Lane's experiments. 



• The truth of this is confirmed by prop. l6. For, let an undercharged body 

 be brought near to, and opposite to the end of a long cylindrical body, commu- 

 nicating with the ground ; by that proposition the pressure of the electric fluid 

 against the base of the cylinder, is scarcely greater than the force with which the 

 two bodies attract each other, provided that no part of the cylinder is under- 

 charged; which is very unlikely to be the case, if the electric repulsion is in- 

 versely as the square of the distance, as he has great reason to believe it is; and 

 consequently, if the spark was profluced by the air being pushed aside, by the 

 force with which the fluid endeavours to issue from the cylinder, no sparks should 

 be produced, unless the electricity was so strong, that the force with which the 

 bodies attracted each other was as great as the pressure of the atmosphere against 

 the base of the cylinder; whereas it is well known, that a spark may be pVoduced, 

 when the force, with which the bodies attract, is very trifling in respect of that. 



* Elettricismo artificiale e naturale, p. tlO. Priestley, p. 209. 



+ PhU. Trans. 1767, p. 451. 



X Phil.Tr^ns. 1763, p, 84. Priestley, p. 2l6. 



