242 



SCIENTIFIC RECREATIONS. 



The various stops are also indicated in the same manner by combinations of 

 dots and lines. 



The Atlantic telegraph cables and similar enclosed wires between other 

 countries are too well known to need detailed description. There is a great 

 variety of telegraphic instruments. The dial, and other arrangements, are 

 very common, and the Wheatstone Key instrument is supplied to private 

 firms as being the most handy. It requires but a very short apprenticeship, 

 and any person who is handy can easily learn to work it in a few minutes. 

 The apparatus consists of a dial upon which the letters of the alphabet are 

 printed, each letter being supplied with a key or stop. A pointer is placed 

 in the centre, as in the wheel barometer, and there is a handle beneath. In 

 front, upon a sloping board, is another dial plate and pointer ; thus we 

 have the receiver and transmitter before us in a very small space. 



When it is necessary to work the instrument a bell is rung by turning 

 the handle rapidly. To speak by the instrument it is necessary to keep 



Fig. 254. Receiver. 



Dial Telegraph. 



Fig. 255. Manipulator. 



turning the handle with the right hand while the fingers of the left are 

 employed in pressing down in as rapid succession as practice will permit the 

 keys corresponding to the letters on the dial while the handle is kept turning. 

 When a word is completed the operator must stop at the + at the top, and 

 then begin again, stopping after each word. When all is said, a couple of 

 rapid turns of the dial will signify that you have ended. 



There are many other systems of telegraph, but all are dependent upon 

 the same principles. The accompanying illustrations (figs. 254, 255) show a 

 dial telegraph of a simple kind, which almost explains itself. 



The first figure is the receiver, on which is a pointer fixed to a dial- 

 plate having the letters of the alphabet inscribed around it. When the 

 manipulator is being worked the dart points to the letters in succession of 

 the words used, and they are separately spelt. The manipulator (fig. 255), 

 by closing and opening the circuit, works the needle. 



In the manipulator we have a wheel with an index point fixed above 

 it. In this wheel are thirteen teeth, with the openings between them filled 



