62 



ELECTRICITY. 



decree warrant such an inference. All 

 the mechanical effects that attend the 

 transfer of electricity are ultimately re- 

 solvable into the sudden action of a 

 repulsive power exerted among the par- 

 ticles of matter which are situated in the 

 line of its course. They are only parti- 

 ticular instances of the fundamental law 

 of electric action, that bodies charged 

 with the same kind of electricity repel 

 one another. Thus the particles of 

 air electrified by a pointed conductor 

 are repelled by that conductor, and 

 repel it also ; and, moreover, repel one 

 another: and the same, effect takes 

 place whether their electric state be of 

 the positive or negative kind. Hence 

 the stream of air which proceeds from 

 any electrified point is very naturally 

 accounted for. If the quantity of elec- 

 tricity which is transferred is consider- 

 able, it excites a more violent commo- 

 tion among the particles which it in- 

 fluences in its passage. The intense 

 energy of its repulsive action produces 

 the most sudden and forcible expansion 

 of that portion of the air which occupies 

 this line ; this air thus expanding must 

 be impelled laterally against the sur- 

 rounding particles, and must occasion 

 their sudden compression. The evolution 

 of heat and light is the necessary conse- 

 quence of this violent compression ; and 

 the vibratory impulse being propagated 

 in all directions is the source of the sound 

 which attends the electric explosion. The 

 sensation to which the passage of the elec- 

 tric shock through our bodies gives rise, is 

 also, evidently, referable to an impression 

 made on the nerves by the same repul- 

 sive action. In all this we can discern 

 no positive proof of the operation of a 

 material agent extraneous to the body 

 itself and acting by mechanical impulse. 

 The materiality of electricity, therefore, 

 must still rest upon a similar foundation 

 with that of heat, or of light. 



(230.) If the electric power, or fluid, 

 if we choose to consider it as such, does 

 not act by its mechanical momentum, the 

 arguments in favour of the motion of a 

 single fluid from the positive to the nega- 

 tive body, derived from the appearances 

 of the streams of electric light, ( 97, 98,) 

 the impulsion of a pith-ball, ( 225,) the 

 perforation of a card, ($ 159,) the rota- j 

 tion of a windmill, ( 226,) and the de- 

 termination of the flame of ataper ( 228) 

 in one constant direction, must fall to the 

 ground, and can evidently be of no avail 

 in deciding the great question, whether 

 there be two electric fluids or only one. 

 But, still, it is incumbent upon us to in- 



quire upon what principle these remark- 

 able differences in the phenomena of 

 positive and of negative electricity can 

 be accounted for, consistently with either 

 hypothesis. 



(231.) On an attentive examination of 

 the phenomena they appear to be expli- 

 cable on the supposition that the air, or 

 medium through which the electricity 

 passes, is, in the language of one theory, 

 more disposed to admit of the passage 

 of the vitreous than of the resinous elec- 

 tricity; or, to speak consistently with 

 the Franklinean theory, that it is ^ jre 

 disposed to receive the electric 

 from a conductor which is chare*, 

 it, than to part with it to an underch 

 conductor which absorbs it. Th: 

 sequences of this hypothesis are, tin 

 vitreous electricity meets with h 

 sistance in passing out from a body u- ^ 

 the air, and is therefore carried forward 

 more readily and more directly than the 

 resinous electricity. The latter, in con- 

 sequence of meeting with greater resist- 

 ance to its exit, is more diffused in the 

 surrounding space. 



On the Franklinean theory the same 

 effects will follow with reference to the 

 propulsion of the electric fluid from the 

 positive, and its absorption by the nega- 

 tive body. 



(232.) That the peculiarity of the me- 

 chanical effects of the different species 

 of electricity depends upon the proper- 

 ties of the air, which is the vehicle of 

 its agency, and not upon any specific 

 power in the agent itself, is shown by a 

 modification of the experiment described 

 in 159, in which a varnished card, 

 suspended between two conductors, 

 was perforated at the point where it was 

 touched by the negative wire. On re- 

 peating the same experiment under the 

 receiver of an air-pump, Mr. Tremery 

 found, that in proportion as the air is 

 exhausted, the place where the card is 

 perforated by the electric shock ap- 

 proaches nearer to the positive wire. 

 When the pressure of the air is reduced 

 to one-half, the hole is at the middle 

 point between the two wires. At every 

 discharge, a flash is seen to pass from 

 each conductor to the place of perfora- 

 tion. The curious appearances pre- 

 sented by the edges of the perforations 

 made in the leaves of a quire of paper, 

 already detailed ($ 160, 161,) are not 

 reconcileable with the supposition of 

 a mechanical impulse acting only in one 

 direction, but indicate the equal repul- 

 sive action of both kinds of electricity, 

 when the disturbing influence of the 



