42 THE ELECTRIC TELEGRAPH. 



One pole of the battery was connected to the front con- 

 tact, called the anvil, and the other pole to earth. The line 

 was connected through the supports with the lever, which 



Fig. 21. 



was kept on the back, or what has since been termed the 

 reposing contact, when not in use, by means of a steel spring 

 underneath the longer arm. The surfaces of the hammer 

 and anvil of the contact were faced with platinum, in order 

 to prevent oxidation by dampness from the atmosphere, or 

 by being burnt by the action of the current. 



42. Finding his instrument not sufficiently delicate for 

 great distances, by reason of the line- resistance and loss of 

 current by bad insulation, Morse had recourse to an expe- 

 dient of relays or repeating circuits. The arrangements 

 designed by him for this purpose were of a somewhat primi- 

 tive form, but in principle they are the same as that known 

 as translation, and used on all submarine lines at the present 

 day. 



43. In 1829, Edward Davy obtained a patent for an 

 electro-magnetic chemical telegraph, in which he had inge- 

 niously applied "Wheatstone's idea of combining an electro- 

 magnet with a clockwork, in the construction of a receiving 

 instrument. 



Davy's telegraph required at least four line wires, which, 

 independently of its complication, would be reason enough 

 to account for the fact that it never came into practice. 

 It has, however, the merit of having been the first system 

 in which the movements of a clockwork were governed by 



