1 88 Prof. Henry on Electrical hidtiction 



the heavens. Also, from the great length of the conductor, 

 the more readily must the repulsive action of the free electri- 

 city of the cloud drive the natural electricity of the conductor 

 to the further end of the line, thus rendering move intense the 

 negative condition of the nearer part of the wire, and conse- 

 quently increasing the attraction of the metal for the free 

 electricity of the cloud. It is not hovi'ever probable that the 

 attraction, whatever may be its intensity, of so small a quantity 

 of matter as that of the wire of the telegraph, can of itself 

 produce an electrical discharge from the heavens; although, 

 if the discharge were started by some other cause, such as the 

 attraction of a large mass of conducting matter in the vicinity, 

 the attraction of the wire might be sufficient to change the 

 direction of the descending bolt, and draw it in part or whole 

 to itself. It should also be recollected that, on account of the 

 perfect conduction, a discharge on any part of the wire 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 researches on the lateral discharge of a conductor 

 transmitting a current 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 inti- 

 mately 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 ac- 

 cordance with the formula given by the French Institute, cor- 

 responding 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 phae- 

 nomenon to the fact, that during the transmission of a quan- 

 tity 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 immediately precedes its 

 position at any time; and hence but a part of the whole re- 



