248 WRITINGS OP JOSEPH HENRY. [1846 



succession the several waves which make up the discharge 

 from the cloud. These waves will therefore interfere at cer- 

 tain 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 conductor. I do 

 not say that the effects observed were actually produced in 

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

 principles of electrical action might, under certain circum- 

 stances, lead us to anticipate such results. 



2. The state of the wire may be disturbed by the conduc- 

 tion of a current of electricity from one portion of space to 

 another, without the presence of a thunder-cloud ; and this 

 will liappen in case of a long line, when the electrical con- 

 dition of the atmosphere which surrounds 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, 

 elevated by means of a kite, gives sparks of positive electricity 

 on a perfectly clear day; hence, if the line of the telegraph 

 passes over an elevated mountain ridge, there will be con- 

 tinually, 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 precipitation of^ vapor, in the form of a fog, at one end, 

 while the air remains 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 began 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. On another 

 occasion a continued stream of electricity was observed to 

 pass between two points at a break in the wire, presenting 

 the appearance of a gaslight almost extinguished. A con- 



