XI. APPLICATIONS. 359 



act upon the centre punch, but in addition perforate large holes for the Morse 

 dot and dash. 



They are struck either by a small mallet or by pistons actuated by com- 

 pressed air. 



1556. The Transmitter. 



In Bain's and other automatic systems electrical contacts are made through 

 the holes in the paper. In Wheatstone's the holes act like the cards of a 

 jacquard loom, and control the movements of the mechanism by which the 

 contacts are made. 



The apparatus can be adjusted to produce signals in three ways. 



(a.) By persistent currents, the marking current lasting during the whole 

 time of the dot or dash ; the spacing or reverse current filling up the intervals 

 between them. It acts precisely in the same way as the double-current key. 

 (1562.) 



(6.) By intermittent currents, where a signal is commenced by a short 

 marking current, and ended by an equally short spacing current ; no current 

 whatever being sent in the interval, the line being disconnected. 



(c.) By compensated currents, where signals are commenced and ended as 

 in (&.), but instead of the line being disconnected in the interval a large 

 resistance is inserted, so that the last current sent continues to flow, but is 

 weakened. 



1557. Receiver, 1867. This is a very sensitive ink-writer. 



The electrical portion consists of two vertical electro-magnetic bobbins, the 

 iron cores of which are furnished with pole pieces, Two soft iron pieces 

 or tongues are fixed on a vertical axle, and are magnetised by induction from 

 a horseshoe magnet placed near them ; they play between the pole pieces of 

 the electro-magnet. The marking disc is in connexion with an arm attached 

 ta the vertical axle, and is pressed against or removed from the paper ribbon 

 according as the current passes in one direction or the other through the coils. 

 The tongues of the electro-magnets are set neutral, so that they remain on 

 the one side or the other after the current which has moved them has ceased 

 to act 



The speed of the wheelwork can be regulated at pleasure to suit the 

 rapidity of the signals. 



1568. Translator for relaying the signals of Wheatstone's 

 transmitter. (Post Office, 1876.) 



' It is somewhat similar to the double-current translator (1566). It differs 

 in that the currents are sent forward by the tongues of the line relays them- 

 selves, instead of by sounders in a local circuit. These tongues are set so as 

 to have no bias on either side. 



The automatic switch is similar in principle to 1566. 



15 7O. Regulator Clock and Apparatus for the distri- 

 bution of Greenwich time current at provincial stations. 



The current is sent on the wires used for message traffic, and it is there- 

 fore necessary to shift them from the telegraph apparatus to the time appa- 

 ratus. To ensure regularity, this must be done automatically by means of a 

 clock. 



The wire by which the signal is to be received from the central station, as 

 well as the wires on which the time signal is to be distributed, are connected to 

 the levers of an electro-magnetic switch (No. 1571). 



