HISTORY AND PROGRESS. 



51 



W Y or 



Both needles deflected at the same time, 

 E or 8 U or 9 S T 



X Y Q Z 



/////#// /\ \/ 



The same rules are observed with regard to the short and 

 long strokes, as with the single needle instrument. 



The employment of two needles in receiving the signs 

 renders this telegraph very expeditious ; the rate at which 

 it is worked being about double that of the common Morse 

 telegraph. The necessity of two lines, however, prevents it 

 taking any prominent place amongst the existing systems of 

 useful telegraphs. 



49. Principle of self-acting Make-and-break. A considerable 

 step in advance of then existing systems was made by Dr. 

 Werner Siemens, of Berlin, by the invention of his first 

 beautiful step-by-step motion telegraph. 



The principle of this apparatus was that of the automatic 



Fig. 25. 



transmission of currents, or what has been called the self- 

 acting make-and^break* 



Suppose the soft iron armature A A, Fig. 25, of the electro- 

 magnet E, is supported on an axis, B, at one end, and by 

 the spiral spring s in the middle, by which it is pressed 



E 2 



