44 THE ELECTRIC TELEGRAPH. 



several modifications in the course of a year or so. The 

 principle remained, however, unaltered in all of them ; it was 

 that of sending, from the transmitting station, a series of 

 alternate currents through the line, which, passing round the 

 soft iron of an electro-magnet, moved an armature, and regu- 

 lated the motion of an escapement similar to that of a clock. 

 It consisted of two parts : 



1. The transmitter, and 



2. The receiving instrument. 



The transmitting portion of the original apparatus con- 

 sisted of a commutator, to direct the current of a battery 

 alternately through two electro-magnets at the receiving 

 station. The direction of the current was effected by means 

 of a tooth- wheel, supported by a metal upright. The teeth 

 of this wheel, to the number of fifteen, were so arranged 

 that the teeth and the spaces in rotation represented thirty 

 letters of the alphabet, numerals, &c. On each side of 

 the wheel was a spring contact, only one of which made 

 contact with the wheel at the same time; when the one 

 pressed against a tooth the other was always opposite to a 

 space. These springs were connected to two line wires, and 

 a battery was inserted between the tooth- wheel and earth. 

 From the circumference of the wheel protruded thirty spokes, 

 and on the base of the upright was a bar, used as a stop 

 for the hand of the operator when turning the spoke wheel, 

 and it was wished to signal the letter opposite the spoke 

 taken hold of. 



The receiving instrument or indicator was formed by a 

 dial having 30 divisions corresponding to the letters, nume- 

 rals, &c., of the transmitter. The index which moved over 

 the dial was driven by a clockwork, the escapement of which 

 was fixed in the axis of a beam supporting two armatures 

 of soft iron, over the poles of two electro-magnets, in the 

 circuits of the two line wires. As the tooth- wheel of the 

 transmitter was turned round, currents were alternately sent 

 through the side contacts, through the lines, and round the 

 cores of the escapement magnet. Whenever, therefore, the 

 tooth- wheel of the transmitter rested at any place, a current 



