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brium of the electrical plenum, which we must suppose to exist 

 throughout all terrestrial space, the state of rest is attained by a se- 

 ries of diminishing oscillations. Thus, in the discharge of a Leyden 

 jar, I have shown that the phenomena exhibited cannot be explained 

 by merely 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 equih brium 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 succession 

 the several waves which make up the discharge from the cloud. 

 These waves will therefore interfere at certain points along the wire, 

 producing, for a moment, waves of double magnitude, and will thus 

 enhance the tendency of the fluid at these points to fly from the con- 

 ductor. I do not say that the effects observed were actually pro- 

 duced in this way; I merely wish to convey the idea that known 

 principles of electrical action might, under certain circumstances, 

 lead us to anticipate such results. 



2. The state of the wire may be disturbed by the conduction of a 

 current of electricity from one portion of space to another, without 

 the presence of a thunder cloud; and this will happen in case of a 

 long line, when the electrical condition of the atmosphere which sur- 

 rounds the wire at one place is different from that at another. Now 

 it is well known that a mere difference in elevation is attended with a 

 change in the electrical state of the atmosphere. A conductor, ele- 

 vated by means of a kite, gives sparks of positive electricity in a per- 

 fectly clear day; hence, if the line of the telegraph passes over an 

 elevated mountain ridge, there will be continually, during clear 

 weather, a current from the more elevated to the lower points of the 

 conductor. 



A current may also be produced in a long level line, by the pre- 

 cipitation of vapour in the form of fog at one end, while the air re- 

 mains clear at the other ; or by the existence of a storm of rain or 

 snow at any point along the line, while the other parts of the wire are 

 not subjected to the same influence. 



Currents of sufficient power to set in motion the marking machine 

 of the telegraph have been observed, which must have been produced 

 by some of these causes. In one case the machine spontaneously be- 

 gan to operate without the aid of the battery, while a snow storm was 

 falling at one end of the line, and clear weather existed at the other. 



