On the Speed of the Electric Wave through Submarine Cables. 551 



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

 say, 225 miles of cable. The speed then obtained was 6'57. Through 

 four wires (t. 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 

 current ; and consequently, when the wires were so connected that 

 the current went up one wire and down the second, up the third and 

 down the fourth, as in experiment No. 4, the magneto-electric 

 action upon No. 2 wire is counterbalanced by the magneto-electric 

 action upon No. 3, and so on ; but in experiment No. 5 the mag- 

 neto-electric current was in full force on all the wires. The result, 

 however, did not show any appreciable difference in the speed of the 

 wave, as the machine then used could not be governed with sufficient 

 accuracy. 



Experiments were made to determine the effect of applying resist- 

 ance to one end of the cable. For instance, a telegraphic instrument, 

 when applied to the cable, augments the resistance of the circuit ; 

 and when a resistance equal to half that of the cable was applied at 

 one end, the rate of the electric wave through it was decreased to 

 three-quarters. When a resistance equal to the whole of the cable 

 was added at one end, so as to double the resistance of the whole 

 circuit, the speed was reduced to about three-fifths ; and when resist- 

 ance double that of the cable was added, the speed was reduced 

 rather more than one-half. 



Variations in the electromotive force produced no sensible varia- 

 tion in the speed of the waves. 



The second series of experiments were tried upon the Dunwich 

 and Zandvoort cable, after it was submerged, and consequently in a 

 straight line, and not, as in the previous experiment, in a coiled mass ; 

 it was therefore exposed to much less magneto-electric induction. 

 The insulation of this cable was very high indeed. 



The experiments on this cable, among other results, show that 

 doubling the length of the circuit reduced the speed nearly four 

 times. The experiments on the Mediterranean cable showed that 

 with three times the length, the speed was reduced nearly nine times. 

 With twice the length the speed was reduced nearly four times, or 

 inversely as the square of the distance nearly. 



The mean of the experiments through 270 miles of cable are 4*76 

 revolutions of the wheel per second, or 9*52 reversals of the current 

 per second. 

 . In the experiments through 540 miles, or twice the length of 



