HISTORY AND PROGRESS. 



169 



in between the two, and are held, in some measure, tight by 

 the elasticity of the first piece. The rigid bar is cut at 

 regular intervals with vertical grooves or ribs, in which a 

 corresponding elevation at the back of each of the types fits, 

 to avoid shifting along the stick. 



When the arm L 1 is against the contact 2, or the hook L 

 lifted up, as in the figure, whilst T is revolving with the coil, 

 currents, alternately positive and negative, traverse the 

 line, and the polarised Morse at the receiving station gives 

 a series of dots. But when the contact L I with 2 is inter- 

 rupted, the armature of the printing magnet remains on 

 one of the contacts, upper or lower, until a reverse current 

 removes it. The last current before the interruption, positive 

 or negative, determines on which contact the printing beam 

 shall repose. On the upper contact a blank space, and on 

 the lower a line, is the result. 



It is the duty of the types, acting on the point of the lever 

 L 1 , L, to provide these interruptions after the different currents, 

 so as to produce the required 

 letters of the Morse alphabet at 

 the receiving station. 



Suppose a, b, Fig. 92, to re- 

 present a series of alternate posi- 

 tive and negative waves, produced 

 by the revolutions of the coil be- 

 tween the poles of the permanent 

 magnets, whilst L 1 , connected 

 with earth, completes the circuit. 

 During each complete revolution 

 a positive and a negative current 

 within the space c are developed, 

 each succeeding half-revolution 

 sending a different current into 

 the line. At the receiving station, whilst this continues, 

 the armature of the polarised Morse will vibrate up and 

 down, and print a series of short lines corresponding to the 

 intervals between the transmission of the positive currents 

 and the negative which follow them. 



If the composing-stick be not so far advanced along the 



Fig. 92. 



