CHAP, xii.] ELECTRICITY AND MAGNETISM. 397 



It may either be arranged as a "sounder" in which 

 case the operator who is receiving the message listens 

 to the clicks and notices whether the intervals between 

 them are long or short; or it may be arranged as an 

 " embosser" to print dots and dashes upon a strip of paper 

 drawn by clockwork through the instrument. In the 

 most modern form, however, the Morse instrument is 

 arranged as an "ink-writer" in which the attraction of 

 the armature downwards lifts a little inky wheel and 

 pushes it against a ribbon of paper. If the current is 

 momentary it prints a mere dot. If the current con- 

 tinues to flow for a longer time the ribbon of paper moves 

 on and the ink-wheel marks a dash. The Morse code, 

 or alphabet of dots and dashes, is as follows : 



A . K . U . . 



B . . . L . . . V . . . - 



C _ . _ . M W . - 



D . . N . x .... 



E . O - Y . - 



F . . . P . . Z - - . . 



G . Q - . - Full stop 



H . . . . R . . Repetition . . - - . . 



I . . S . . . Hyphen . . . . 



J . T Apostrophe . . 



426. Relay. In working over long lines, or where 

 there are a number of instruments on one circuit, the 

 currents are often not strong enough to work the 

 recording instrument directly. In such a case there is 

 interposed a relay or repeater. This instrument con- 

 sists of an electromagnet round which the line current 

 flows, and whose delicately poised armature, when 

 attracted, makes contact for a local circuit in which a 

 local battery and the receiving Morse instrument are 

 included. The principle of the relay is, then, that a 

 current too weak to do the work itself may set a strong 

 local current to do its work for it. 



