ON SOME MARVELS TN TELEGRAPHY. 255 



I have in the figure and description assumed that the 

 current from either station acts directly on th'e magnet 

 which works the recording style. Usually, in long-distance 

 telegraphy, the current is too weak for this, and the magnet 

 on which it acts is used only to complete the circuit of a 

 local battery, the current from which does the real work of 

 magnetizing M at A or M' at B, as the case may be. A local 

 battery thus employed is called a relay. 



The Morse instrument will serve to illustrate the principle 

 of the methods by which facsimiles are obtained. The 

 details of construction are altogether different from those 

 of the Morse instrument ; they also vary greatly in different 

 instruments, and are too complex to be conveniently de- 

 scribed here. But the principle, which is the essential point, 

 can be readily understood. 



In working the Morse instrument, the operator at B 

 depresses the handle H'. Suppose that this handle is kept 

 depressed by a spring, and that a long strip of paper pass- 

 ing uniformly between the two points at a prevents contact. 

 Then no current can pass. But if there is a hole in this 

 paper, then when the hole reaches a the two metal points 

 at a meet and the current passes. We have here the 

 principle of the Bain telegraph. A long strip of paper is 

 punched with round and long holes, corresponding to the 

 dots and marks of a message by the Morse alphabet As 

 it passes between a metal wheel and a spring, both forming 

 part of the circuit, it breaks the circuit until a hole allows 

 the spring to touch the wheel, either for a short or longer 

 time-interval, during which the current passes to the other 

 station, where it sets a relay at work. In Bain's system 

 the message is received on a chemically prepared strip of 

 paper, moving uniformly at the receiving station, and con- 

 nected with the negative pole of the relay battery. When 

 contact is made, the face of the paper is touched by a 

 steel pointer connected with the positive pole, and the 

 current which passes from the end of the pointer through 



