CHAP, v.] TELEGRAPHIC LINES. 619 



a message is sent, puts hi.s commutator in the position for 

 receiving. Then he fixes his eye on the divided scale of the dark 

 chamber, noting all the signals indicated by the successive oscil- 

 lations of the luminous image, which correspond as we have said 

 to the conventional vocabulary of Morse's system. There is 

 nothing then left but to translate the message and write it in 

 ordinary characters. 



The syphon recorder, an instrument recently introduced by Sir 

 William Thomson to supersede the use of the galvanometer, consists 

 of two parts, the motor or mechanical power and the recorder for 

 registering the signals. 



The motor or mechanical part of the instrument consists of a very 

 light and delicate insulated wire coil suspended in a very powerful 

 magnetic field produced by permanent or electro-magnets ; these, 

 acting with great exciting force upon the suspended coil, cause it to 

 deflect or vibrate when a current passes through it. The second or 

 recording mechanism of the apparatus consists in imparting the 

 motion of the receiving coil to a light capillary tube or syphon of 

 glass suspended and adjusted to the coil by means of the torsional 

 elasticity of a helical wire. The long leg of this syphon acts as the 

 " marker," the short end dipping into a reservoir of ink, which is 

 continuously ejected from the long end of the syphon by electrical 

 agency on to a moving paper ribbon mechanically drawn forward 

 over a metal plate electrified in an opposite way to that of the ink 

 within the syphon. Thus a powerful difference of electrical potential 

 is constantly maintained between the ink in the tube and the metal 

 plate, ti.e tendency to produce equilibrium resulting in a succession 

 of sparks between the syphon and the metal plate, producing a 

 fine stream of ink or a succession of minute dots upon the moving 

 paper ribbon. Thus if the syphon remains in a neutral position, 

 a continuous line will be drawn over the paper ; but when by reason 

 of the motion of the receiving coil the syphon is drawn either to 

 the right or to the left, a corresponding deviation from the straight 

 line will be indicated ; thus a record is maintained on paper of the 

 movements of the coil, without that movement being in the least 

 degree impeded by friction or any other mechanical defects. 



