THE ELECTRIC TELEGRAPH. 



Fig. 85. 



FROMENT'S WHITING TELEGRAPH. 



207. This apparatus is represented in fig. 86 (p. 49), and the 

 principle on which it acts has been fully explained in (153). 



The paper upon which the telegraphic characters are written is 

 rolled upon the surface of a drum c. The pencil & is pressed by a 

 spring upon the paper. The drum is made to revolve by clock- 

 work in the usual manner contained in the case 7i. If the paper 

 be moved without moving the pencil, the latter will trace a 

 straight line ; but if the pencil be moved to and fro by the action 

 of the electro-magnet and recoil spring, a zigzag line will be 

 formed by the vibrations imparted to the pencil by the magnet, 

 or what is the same, by the pulsations of the current. 



To equalise the wear of the pencil, a slow motion of rotation is 

 imparted to it by wheels adapted for that purpose. 



The commutator by which the pulsations which determine the 

 signals are produced, is a wheel, at the circumference of which 

 are five metallic divisions with intermediate spaces vacant, so 

 that in each revolution the current is transmitted five times, and 

 suspended five times. If it be desired to produce a single pulsa- 

 tion, the wheel is moved through the fifth part of a revolution ; 

 if it be desired to produce three pulsations it is moved through 

 three-fifths of a revolution, and 'so on. For each pulsation, one 

 zigzag is made by the pencil at the station to which the despatch 

 is transmitted. 



The signs adopted in this telegraph to express the letters, are 

 various numbers and combinations of zigzag forms. 



BAIN'S ELECTRO-CHEMICAL TELEGRAPH. 



208. The manner in which the decomposing power of the 

 current is capable of producing written characters at a distance 

 from the hand of the writer has been already explained (170). 

 46 



