HISTORY AND PROGRESS. 115 



at rest, a spiral spring underneath the board keeps it in 

 contact with the point s x . This point is in constant com- 

 munication with the terminal 4, which leads to relay and 

 earth. The conditions under these circumstances are, there- 

 fore, precisely the same as when the line is brought into 

 communication with s lt by means of the switch I, in Fig. 60. 



While in this position it is impossible to press down the 

 knob d, the lever c resting upon a small elevated bed on the 

 bar g. 



To forward signals the lever must be turned to the left, by 

 which the contact at s l is broken ; that is to say, the relay is 

 cut out of circuit, and the little insulating buttons o, o, press 

 the spring s 2t which is fixed at the side of the bar k, against the 

 contact-point m, permanently connected to terminal 2, which 

 is in connection with the counteracting battery K. If the 

 key is pressed down now, the back contact is broken and the 

 front one n established, by which the circuit of the counter- 

 acting battery K is interrupted, and the main battery -|- K 

 brought into play. Consequently the same takes place as in 

 Fig. 60, when the line L is connected, by means of the arm 

 /, with the contact-point s 3 , and the key D pressed down. 



In order completely to discharge the line after finishing 

 the transmission of a despatch, a metal point, p, projecting 

 from one end of the base b of the bearings of the lever, rubs 

 against a contact-point, S 3 , connected with the terminal 5 and 

 earth, when the former returns to its position of rest at s x . 



75. De Sauty's Submarine Key. A submarine key has 

 been invented by Mr. C. Y. Sauty, with which the operator 

 in manipulating presses down a button in the middle of the 

 knob, and thus removes the line connection from the relay 

 to the battery-commutator. 



Fig. 62 represents a plan of this key. The lever is of 

 vulcanite, supported on- a pin, a a, in the bearings b b, on 

 the base c c. On each side of the lever at its fulcrum is a 

 plate of brass, p and p, insulated from the pin a and from 

 the bearings. At each end of the plate p, underneath, is a 

 platinum contact-point which presses upon one of the contact- 

 anvils c and 2" ; the underside of the plate p' carries a spring 



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