170 THE ELECTRIC TELEGRAPH. 



stage as in Fig. 91, so that the types A, B, c are all on the 

 right of the lever L, the arm L 1 will rest on the insulating 

 contact 1, and the beam of the polarised Morse, at the receiv- 

 ing station, on the upper screw, by which no mark is made 

 upon the paper. As soon as the hook L, however, touches the 

 first tooth of the type A, it will be pushed up, and L 1 thrown on 

 2. A positive current will instantly afterwards traverse the 

 line, and make a dot at the receiving instrument. A negative 

 current succeeds, which makes a space ; and then another 

 positive current, which re-attracts the armature. Before the 

 next following negative current is produced, the tooth has 

 passed by, and L dropped into the space which corresponds to 

 a whole revolution. The Morse-beam therefore prints a 

 dash which continues till the next tooth pushes L up in time 

 to complete the circuit for the negative current, which 

 draws up the armature again, and produces a space which 

 lasts until the first tooth of the letter B pushes up L, and 

 allows a positive current to go to the Morse. This tooth is 

 narrow, to break the circuit before the succeeding negative 

 current is developed, so that the Morse prints a dash until 

 the broad tooth of B pushes up L in time for the circulation 

 of a negative current, which begins a space. The tooth in 

 question is just so broad as to include three positive currents, 

 and ends at a negative current. Each letter of the alphabet 

 requires for its transmission an even number of waves. The 

 shortest letter is the single dot representing the letter e t 

 requiring two complete revolutions of the inductor-coil, 

 equivalent to two positive and two negative currents, of 

 which only one positive is used for marking. J, o, and Y 

 require each eight complete revolutions, or the time and 

 space of sixteen currents each, some of which are interrupted 

 at the proper places. 



Each of the types begins with a depression which cuts off 

 the first positive and negative currents, so that the first tooth 

 of a letter invariably sends a positive current into the line. 

 The types each end with a tooth after a negative current, so 

 that the printing-beam is always drawn off by the types 

 themselves before another type comes into play. 



