1846] WRITINGS OF JOSEPH HENRY. 247 



that the charged conductor of the machine gives off a spark 

 under the same circumstances. 



It miglit 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 wliich immediately 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 neighboring 

 body, and its attraction for the wire, preventing a full dis 

 charge at any one place. The intensity of the successive 

 explosions is explained by referring to the fact, that the dis- 

 charge 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 has an appreciable duration ; and hence the wire of 

 the telegraph is capable of transmitting an immense quantity 

 of the fluid thus distributed over a great length of the con- 

 ductor. 



The remarkable facts of the explosions of the electricity 

 into the air, and of the poles being struck in interrupted suc- 

 cession, find a plausible explanation in another electrical 

 principle which I have established, namely, in all cases of 

 the disturbance of the equilibrium of the electrical plenum 

 which we must suppose to exist throughout all terrestrial 

 space, the state of rest is attained by a series of diminishing 

 oscillations. Thus, in a discharge of a Leyden jar, I have 

 shown that the phenomena exhibited cannot be explained 

 by merel}' supposing the transfer of a quantity of fluid 

 from the inner to the outer side of the jar; but in addition 

 to this we are obliged to admit the existence of several waves, 

 backwards and forwards, until the equilibrium is attained. 

 In the case of the discharge from the cloud, a wave of the 

 natural electricity of the metal is repelled each way from 

 the point on which the discharge falls, to either end of the 

 wire, is then reflected, and in its reverse passage meets in 



