584 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



requiring better skilled clerks, but which offers in exchange the very 

 important advantage to lines where a telegraphic communication is 

 frequent, of being able to transmit about three times as fast as the 

 Morse. Hughes's system in fact requires only one transmission of 

 the current instead of three or four for each letter and sign. 



Hughes's system offers the peculiarity that when the manipulator 

 of a sending station is worked, the indicator of that station .works in 

 the same manner and at the same time as the indicator of the receiv- 

 ing station to which the message is sent, consequently the message is 

 printed at the same time at the two stations, so that a double control 

 is the result. If then we can give a clear explanation of the manner 

 in which this printing is accomplished in the sending apparatus we 



FIG. bSO. Itjlation between the type-shaft and pruning shaft. 



need do no more than show how the synchronism of the movements 

 at the receiving station is secured by the sending and interruption of 

 the successive line currents. 



Plate XIX. represents the complete apparatus in which the 

 manipulator and indicator are partly combined. Powerful clockwork 

 put in motion by a weight of at least fifty kilogrammes is arranged 

 on a table in front of which is seen the key board of the manipulator 

 composed of twenty-eight keys, of which twenty-six belong to letters, 

 figures, or other signs marked on their upper surface, and of the two 

 remaining, one is to produce the blanks or intervals between words, 

 and the other to print when required, the sign, figure or signal which 

 each key has marked on it above the alphabetical letter. 



