CHAP, iv.] ELECTRIC TELEGRAPHY. 587 



The clockwofk when put in motion turns with different velocities 

 three axes or shafts two of which are horizontal and the third vertical. 

 The first of these axes is the type shaft which carries on the outside 

 a wheel T (Figs. 380 and 381) on the circumference of which are 

 engraved in relief the letters of the alphabet, and in the intervals the 

 figures, stops, or other signals required in the composition of a message. 

 Behind the type shaft and on the same axis is the correcting wheel T', 

 whose function is to establish synchronism between the movements, 

 in case either of the indicators should gain or lose upon the other. 

 Two other toothed wheels transmit the motion to two other axes. 

 The second, the printing shaft, or cog shaft, turns with a much greater 

 velocity than the type shaft. It carries a series of four cogs, u iv x y 

 (Fig. 380), whose function we shall come to, one of them being princi- 

 pally for pressing the printing roller m against the paper, and the latter 

 against the letters of the type shaft inked by the ink pad K. The 

 second shaft is divided into two parts joined by a catch so that the part 

 whose movement causes the printing does not start till the key of the 

 manipulator key-board is pressed down, and the current produced, and 

 the consequent action of a particular portion of the mechanism affected 

 by the passage of the current. 



The third shaft a, which is vertical (Plate XIX.) derives its motion 

 from the type shaft by a bevel wheel, and in turning it makes a 

 chariot revolve on the horizontal disc G, so as to describe a complete 

 circumference in the same time that the type wheel makes a complete 

 revolution. The disc G is pierced with twenty-eight holes, that is as 

 many holes as there are keys on the key-board and letters on the 

 circumference of the type wheel. Now the motion of the different 

 parts of the mechanism is so arranged, that at the precise moment when 

 the chariot passes over a hole corresponding to a given letter, that 

 letter occurs on the type wheel situated at the lowest part, that is 

 over against the point of the printing roll which is being pressed against 

 it by the action of the printing shaft. But how does the position of 

 the chariot, or the pressing down the key determine the action of this 

 shaft ? Fig. 381 will help us to explain this. It is a section taken 

 through the apparatus in the plane which contains the type shaft 

 and the vertical shaft which carries the chariot. 



The vertical shaft is formed of two pieces of metal insulated by a 

 cylinder of ivory, and the arm of this shaft which constitutes the 



