265 



experiment no electricity passed through the floors from one conduc- 

 tor to the other; the effect was entirely due to the repulsive action of 

 the electricity in motion in the upper wire on the natural electricity of 

 the lower. In another experiment, two wires, about 400 feet long, 

 were stretched parallel to each other between two buildings; a spark 

 of electricity sent through one produced a current in the other, though 

 the two were separated to the distance of 300 feet ; and from all the 

 experiments, it was concluded that the distance might be indefinitely 

 increased, provided the wires were lengthened in a corresponding 

 ratio. 



That the same effect is produced by the repulsive action of the 

 electrical discharge in the heavens, is shown by the following modifi- 

 cation of the foregoing arrangement. One of the wires was removed, 

 and the other so lengthened at one end, as to pass into my study, and 

 thence through a cellar window into an adjacent well. With every 

 flash of lightning which took place in the heavens within at least a 

 circle of twenty miles around Princeton, needles were magnetized in 

 the study by the induced current developed in the wire. The same 

 effect was produced by soldering a wire to the metallic roof of the 

 house, and passing it down into the well ; at every flash of lightning 

 a series of currents in alternate directions was produced in the wire. 



I was also led, from these results, to infer that induced currents 

 must traverse the line of a rail-road, and this I found to be the case. 

 Sparks were seen at the breaks in the continuity of the rail, with 

 every flash of a distant thunder cloud. 



Similar effects, but in a greater degree, must be produced on the 

 wire of the telegraph, by every discharge in the heavens ; and the 

 phenomena which I witnessed on the 19th of June in the telegraph 

 office in Philadelphia, were, I am sure, of this kind. In the midst of 

 the hurry of the transmission of the congressional intelligence from 

 Washington to Philadelphia, and thence to New York, the apparatus 

 began to work irregularly. The operator at each end of the line an- 

 nounced at the same time a storm at Washington, and another at 

 Jersey City. The portion of the circuit of the telegraph which en- 

 tered the building, and was connected with one pole of the galvanic 

 battery, happened to pass within the distance of less than an inch of 

 the wire which served to form the connexion of the other pole with 

 the earth. Across this space, at an interval of every few minutes, a 

 series of sparks in rapid succession was observed to pass; and when 

 one of the storms arrived so near Philadelphia that the lightning 

 could be seen, each series of sparks was found to be simultaneous 



VOL. IV. — 2 M 



