262 



must affect every other part of the connected line, although it may 

 be hundreds of miles in length. 



That the wire should give off a discharge to a number of poles in 

 succession, is a fact I should have expected, from my previous re- 

 searches on the lateral discharge of a conductor transmitting a cur- 

 rent of free electricity. In a paper on this subject, presented to the 

 British Association in 1837, I showed that when electricity strikes a 

 conductor explosively, it tends to give off sparks to all bodies in the 

 vicinity, however intimately the conductor may be connected with 

 the earth. In an experiment in which sparks from a small machine 

 were thrown on the upper part of a lightning rod, erected in accord- 

 ance with the formula given by the French Institute, corresponding 

 sparks could be drawn from every part of the rod, even from that 

 near the ground. In a communication since made to this Society, I 

 have succeeded in referring this phenomenon to the fact, that during 

 the transmission of a quantity of electricity along a rod, the surface 

 of the conductor is charged in succession, as it were, by a wave 

 of the fluid, which, when it arrives opposite a given point, tends 

 to give off a spark to a neighbouring body, for the same reason that 

 the charged conductor of the machine gives off a spark under the 

 same circumstances. 



It might at first be supposed that the redundant electricity of the 

 conductor would exhaust itself in giving off the first spark, and that 

 a second discharge could not take place ; but it should be observed, 

 that the wave of free electricity, in its passage, is constantly attracted 

 to the wire by the portion of the uncharged conductor which imme- 

 diately precedes its position at any time; and hence but a part of the 

 whole redundant electricity is given off at one place; the velocity of 

 transmission of the wave as it passes the neighbouring body, and its 

 ;attraction for the wire, preventing a full discharge at any one place. 

 The intensity of the successive explosions is explained by referring to 

 the fact, that the discharge from the clouds does not generally consist 

 of a single wave of electricity, but of a number of discharges along 

 the same path in rapid succession, or of a continuous discharge which 

 tias an appreciable duration; and hence the wire of the telegraph is 

 <;apable of transmitting an immense quantity of the fluid thus distri- 

 buted over a great length of the conductor. 



The remarkable facts of the explosions of the electricity into the 

 air, and of the poles being struck in interrupted succession, find a 

 plausible explanation in another electrical principle which I have 

 established, namely, in all cases of the disturbance of the equili- 



