TELEGRAPH APPARATUS. 243 



with ivory. The axis of the wheel is in contact with the wire from the 

 positive pole, p, and a spring attached to the wire or by the binding-screw, /, 

 presses against the circumference of the wheel, and completes the circuit. 

 When the wheel is placed so that the arrow point is above the +, the needle 

 of the receiver is also at +. By turning the wheel to bring the needle to A, 

 the spring on the circumference is passed from an ivory "tooth" to a "metal" 

 one ; the circuit is closed, the point of the receiver also turns to A, and so on 

 through the word by successive closing and breaking of the circuit. 



As there are a great many other applications of electricity of which we 

 have to treat, the Electric Light, and Mr. Edison's other inventions, our 

 space will not permit a much more detailed account of the telegraph, but there 

 are some incidents connected with its progress which it would be as well to 

 mention. 



Alexander Bain, about 1840, attempted to produce a printing 

 telegraph, and in 1846 he actually accomplished a registering apparatus, 

 which was an application of the principles of Dyar and Davy. But although 

 Bain's system was good, Morse had the advantage of possession in the 



Fig. 256. Electric cable. Fig. 257. Ocean cable. 



United States, where it was tried, and Bain went out of fashion. Bain's 

 system was, in fact, the present chemical " automatic " telegraph, which has 

 been perfected for rapid transmission. 



Bakewell's instrument, which has been improved upon by later electri- 

 cians, is termed the fac-simile telegraph. The message to be sent is written 

 with a pen which has been dipped in varnish (for ink), and the characters are 

 inscribed upon prepared tinfoil. The message is then put upon a cylinder 

 covered with prepared paper, and has a pointer attached. There is a 

 precisely similar cylinder at the receiving station. When the cylinders are 

 simultaneously set going, the point at one will trace a spiral line as the 

 first (transmitting) point passes round its cylinder. However, as the latter 

 " stylus " meets the varnish letters a break occurs, and these spaces arc 

 exactly reproduced as blanks at the other end, and the form of the letters 

 can be seen. Coselli, in his adaptation, caused dark letters to be registered 

 on a white ground, and thus simplified matters. Since then we have had 

 printing telegraphs, and dials, and writing machines, one of which will be 

 described presently. 



Submarine telegraphs were, it is said, first suggested by Salva in 



