92 THE ELECTRIC TELEGRAPH. 



he wishes to telegraph. In doing so the circuit is closed 

 as soon as the point of the style touches any of the 

 metal pieces, and is broken again when it moves over the 

 ivory. 



The arrangement has never enjoyed an extensive employ- 

 ment, and is now, perhaps, entirely out of use. The reason 

 of this is probably to be found in the fact that the imperfect 

 appreciation of time which prevents some acquiring uni- 

 formity in manipulating the key renders them as unable to 

 move the style with an equal velocity over the plate, time 

 being a factor of velocity. 



63. Morse Apparatus with Relay. When the line con- 

 necting two stations is long, it is impossible sometimes, 

 even with very great battery power, to move the armature 

 of the electro-magnet with force enough to impress the 

 paper legibly. It was on this account that Morse employed 

 a relay in working his recording apparatus. The principle 

 of the relay has already been explained in conjunction with 

 Wheatstone's alarm. The form of relay used with the 

 Morse instrument differs, however, from that invented by 

 Wheatstone. Instead of the magnetic needle and mercury 

 cups, the local circuit is closed by the contact of the armature 

 of an electro- magnet, with a metal anvil, both being inserted 

 in the local circuit. A common form, known as the American 

 relay, from its general employment on the American lines, 

 is shown in Fig. 47. The electro-magnet M M is fixed 

 horizontally on a board, having before its poles the soft iron 

 armature a, supported by a tongue turning on the axis b. 

 The armature is held back by a spiral-spring f, stretched 

 between the tongue and an adjusting screw, g. The coils 

 M M of the electro-magnet terminate in the binding-screws 

 L' L", to which are brought respectively the line and earth 

 wires. The local battery and Morse apparatus are inserted 

 between the terminals L' L". The former of these is in per- 

 manent connection with the axis b by a wire, x, and the 

 latter with the body of the bracket k i, which carries two 

 screws, h d, with a platinum point, and c, whose point is 

 insulated with agate. 



