406 



THE POPULAR SCIENCE MONTHLY. 



place. In the Morse alphabet, which is now the telegraphic alphabet 

 of all nations, the shortest signs are allotted to those letters which 

 occur most frequently. This was not the case with the old needle- 

 alphabet, which was rather planned with the view of assisting the 

 memory ; and experience has shown that such assistance is quite un- 

 necessary. The needle instrument is also, to a great extent, being su- 

 perseded by Morse's instrument. 



Telegraphs in which the ordinary letters of the alphabet are ranged 

 round the circumference of a dial, and are pointed at by a revolving 

 hand, are specially convenient for those who are not professional teleg- 

 raphists. They are constructed on the principle of step-by-step mo- 

 tion, the hand being advanced by successive steps, each representing 

 one current sent or stopped. 



One of the simplest instruments of this class is Breguet's, which 

 is extensively used on the French railways. Fig. 4 represents the ex- 

 terior of the receiving instrument. The dial is inscribed with the 25 

 letters of the French alphabet and a cross, making 26 signals in all. 

 The hand (as in other step-by-step telegraphs) advances only in one 

 direction, which is the same as that of the hands of a clock, stopping 

 before each letter which is to be indicated, and pointing to the cross 

 at the end of each word. Fig. 5 shows the mechanism by which the 



Fig. 5. 



Mechanism of Indicator. 



motion is produced. A is the armature of an electro-magnet, the mag- 

 net itself being removed in the figure to allow the other parts to be 

 better seen. The two dotted circles traced on the armature represent 

 vertical sections of the two coils, which rest on the bottom of the box, 

 and have their axes horizontal. If introduced, they would nearly con- 



