288 Chronicles of Science. [April, 



A long telegraphic cable is a long Leyden jar of great resist- 

 ance — so great that, instead of electrical charges rushing in and 

 out almost instantaneously, as is the case with ordinary Leyden 

 jars, an appreciable time is necessary to convey a decided charge 

 through so long a conductor to the distant end. The artificial 

 representative consisted of eleven resistances and ten immense 

 condensers, or Leyden jars, connected between the resistances and 

 the earth. By moving a handle the condenser could be applied on 

 or removed from, these junctions. 



On depressing an ordinary commutation key, the cable was 

 removed from its connection with the earth, and a positive current 

 allowed to flow into the line. On depressing a second key, a 

 negative current rushed in ; whilst when both the keys were at 

 rest, the cable was simply connected with the earth. * The ten 

 reflecting galvanometers were placed one above the other, and a 

 bundle of rays from the electric lamp was thrown upon the ten 

 mirrors, each of which reflected a little sun-like spot upon a large 

 white screen, forming, when no current was passing through the 

 cable, a straight vertical line of luminous points. On pressing 

 the right-hand or positive key, the upper spot, which was named 

 Gibraltar, almost immediately responded ; and when it had travelled 

 about thirteen inches over the screen, the second spot, Malta, began 

 visibly to move; the third spot, Suez, following later still. It 

 was. however, fifteen or sixteen seconds before any decided motion 

 or current was noticed at the Australian end of the line. After 

 the lapse of a minute, a powerful cur-rent was rushing out at the 

 Australian end. The English end was then removed from the bat- 

 tery and connected with the earth, and quickly after the Gibraltar 

 spot rushed across to the other side of the screen, indicating the 

 rushing back of a powerful current to the earth. This was 

 followed shortly afterwards by Malta, Suez, and Aden. Bombay 

 came only as far as the zero line. The currents in the different 

 parts of the cable were flowing out at each end, leaving Bombay 

 neutral. It was some minutes before the cable discharged itself 

 sufficiently to allow the ten spots to come near enough to the zero 

 line to admit of a second experiment. 



In 1863-64 Mr. Yarley found, by experiments on his artificial 

 line, that by using a succession of four or five currents, all of the 

 same strength but varying in direction, greater rapidity could be 

 secured. For example : — First, a positive current, followed by a 

 negative of longer duration ; followed again by a positive current of 

 much less duration ; then a shorter negative current ; and that 

 again by a very short positive current, produced a succession of 

 positive and negative waves throughout the line : the result of all 

 of which was at the Australian end one very small positive wave 



