80 First published Paper on Electricity 



fluid is apt to fly through the air from B to A, in the form of a spark: 

 the way by which this is brought about seems to be this. The fluid placed 

 anywhere between the two bodies, is repelled from B towards A , and will 

 consequently move slowly through the air from one to the other: how it 

 seems as if this motion increased the elasticity of the air, and made it 

 rarer: this will enable Ihe fluid to flow in a swifter current, which will 

 still further increase the elasticity of the air, till at last it is so much 

 ratified, as to form very little opposition to the motion of the electric fluid, 

 upon which it flies in an uninterrupted mass from one body to the other. 

 In the same manner may the electric fluid pass from one body to 

 another, in the form of a spark, if the first body communicates with the 

 ground, and the other body is negatively electrified, or in any other case 

 in which one body is strongly disposed to part with its electricity to the 

 air, and the other is strongly disposed to receive it. 



136] 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 f 

 experiments, I imagine that the water, by the rapid motion of the electric 

 fluid through it, is turned into an elastic fluid, and so much ratified as to 

 make very little opposition 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. 



137] It appears plainly, from the sudden rising of the water in Mr 

 Kinnersley's electrical air thermometer J, that when the electric fluid 

 passes through the air, in the form of a spark, the air in its passage is 

 either very much rarified, or intirely displaced: and the bursting of the 

 glass vessels, in Beccaria's and Lane's experiments, shews that the same 

 thing happens with regard to the water, when the electric fluid passes 

 through it in the form of a spark. Now, I see 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 I 

 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 overcome the pressure of the atmosphere, much less that it 

 is sufficient to burst the glass vessels in Beccaria's and Lane's experiments. 



138] The truth of this is confirmed by Prop. XVI. For, let an under- 

 charged body be brought near to, and opposite to the end of a long 

 cylindrical body communicating with the ground, by that proposition the 



* Elettricismo artificial e naturale, p. no. Priestly, p. 209. 



f Phil. Trans. 1767, p. 451. 



{ Phil. Trans. 1763, p. 84. Priestly, p. 216. 



