60'2 PHILOSOPHICAL TBANSACTIONS. [aNNO 17 69. 



the explosion of a battery made ever so near to a brass rod did not so much as 

 disturb the equilibrium of the electric fluid in the body itself: for when he had 

 insulated the rod, and hung a pair of pith balls on the end opposite to that near 

 which the explosion passed, he found that the balls were not in the least moved 

 at the time of explosion, which they would have been, if part of the electric 

 fluid, natural to the body, had been driven, though but for a moment, towards 

 the opposite end. He also observed, that the effect was the same, when the ex- 

 plosion was made to pass through one of the knobs of the insulated rod. This 

 lateral force was evident through thin substances of various kinds interposed 

 between the explosion and the bodies removed by it, as paper, tin-foil, and even 

 glass ; for when some grains of gunpowder were put into a thin phial, close 

 stopped, and held near the explosion of a battery, they were thrown into mani- 

 fest agitation. 



Dr. P. therefore thinks it most probable, that this lateral force is produced by 

 the expulsion of the air from the place where the explosion is made. For the 

 electric matter makes a vacuum of air in its passage ; and this air, being dis- 

 placed suddenly, gives a concussion to all the bodies that happen to be near it. 

 Hence the removal of the light bodies, and the agitation communicated to the 

 thin substances, and to the air, and the light bodies placed beyond them. The 

 only objection to this hypothesis is, that this lateral force is not so much less in 

 vacuo as might be expected, when the air is supposed to receive the concussion 

 first, and to communicate it to other bodies ; but it must be considered, that the 

 most perfect vacuum we can make with a pump is not free from air. Dr. P. 

 tried to make this experiment in a Torricellian vacuum, but could not succeed at 

 that time. Besides, as the electric matter, of which an explosion consists, must 

 take a wider path in vacuo, if not equally fill the whole space, it may affect a 

 body in its passage, without the intervention of any air. In condensed air, 

 this lateral force was not, as far as he could perceive, much increased. 



Willing to feel what kind of an impulse it was that acted on bodies, when 

 they were driven away by this lateral force of electricity ; Dr. P. held his finger 

 near the path of an explosion of the battery, passing over the surface of a green 

 leaf, when he felt a stroke, as of something pushing against his finger. Several 

 corks, placed in the same situation, were driven to a considerable distance by the 

 same explosion. Recollecting that this power, which he now calls the lateral 

 force of electrical explosions, must be the same with that which gives the con- 

 cussion to water, mentioned in his experiments to imitate an earthquake, and to 

 vegetable and animal substances, over the surface of which it passes; and being 

 determined to make a more satisfactory trial of it than he had ventured to 

 do before, he laid a green leaf on the palm of his hand, intending to make the 

 explosion pass over the leaf; but the leaf was burst, and torn to pieces, and the 



