214 [June 19, 



maximum (the first maximum being that obtained when the wheel 

 is not rotating at all) ; and by augmenting the speed still more, until 

 the wave is three-quarters of a revolution behind, the wave is again 

 bisected and a second zero is obtained, and so on. 



The great variation of speed necessary to give these and other re- 

 sults was such that the means then at the author's disposal in the 

 first experiments were not sufficiently regular to admit of very ac- 

 curate readings. 



The experiments now communicated were made upon two cables, 

 one containing six conducting wires, a portion of which was laid in 

 the Mediterranean. This cable had been lying exposed to sun and 

 weather in the East India Docks for some years, and the gutta percha 

 had become deteriorated to a considerable extent ; its exact length 

 was not known ; and from these combined causes it could not be used 

 for determining the rate at which the wave travels through given 

 lengths, but it has served to demonstrate that Thomson's "law of the 

 squares " is substantially correct in practice. 



In the experiments made on this cable, the resistance of the galva- 

 nometer was equal to one mile of the cable. The battery power 

 used averaged from 12 to 36 cells of DanielPs battery, each cell 

 offering a resistance of one-sixth of a mile of the cable. 



The first experiment was made upon two wires forming a loop of 

 about 150 miles in length ; and when the currents were reversed at 

 the rate of 15' 16 per second, the needle came to zero. 



The second experiment was made through three wires, that is to 

 say, 225 miles of cable. The speed then obtained was 6 '5 7. Through 

 four wires (*. e. double the length of first experiment) 3*78 reversals 

 per second were obtained. 



Through six wires, or three times the length of the first experi- 

 ment, 1*75 per second were obtained, or inversely as the square of 

 the length. 



In the foregoing experiments the current was made to pass up 

 one wire and down the second, up the third and down the fourth, 

 and so on ; but in experiment No. 5, the current was made to pass 

 through all the six wires, one after the other, in the same direction, 

 the object being to determine, if possible, what amount of retarda- 

 tion was attributable to the magnetization of the iron covering. On 

 the current through the first wire ceasing, a magneto- electric current 

 is produced in the opposite direction to the first magneto-electric 



