XI. APPLICATIONS. 303 



[This apparatus was described by Gumming in 1827, in his "Electrodyna- 

 mics "; it is also mentioned in the Encyclopaedia Britannica, 7th ed., Art. 

 " Voltaic Electricity," and in the treatise on " Electromagnetism " in the 

 Library of Useful Knowledge, 1832.] 



1528. Plunger Signalling Key, used by the London District 

 Telegraph Company. 



This key is used instead of the drop handle key of Cooke and Wheatstone's 

 instrument, or the two-pedal key in Highton's instrument. An ordinary 

 single-needle indicator is used in connexion with it. 



1529. Keys used with Bain's and Morse Telegraphs, by the 

 Electric Telegraph Company. 



a. Simple spring key. 



6. Key for sending a short reversal after each signal, two sets of batteries 

 being required. When the key is up, the line wire is connected to the 

 receiving apparatus. 



c. Wheel key. A constant current is reported on the line, and signals are 

 made by depressing the key and thus reversing the current. A switch is used 

 for making the necessary alterations to the connexions for sending and 

 receiving. 



1530. Switches or Commutators for making Changes 

 of Wires in Circuits. Used by the Electric Telegraph Com- 

 pany. 



a. Earliest switch for double needle. Instruments fixed at Normanton. 



b. Tumbler switch. 



c. Umschalter or Universal switch. 



1531. Morse Embosser, about 1853. Used by the Electric 

 Telegraph Company. 



This superseded the Bain instrument and has in its turn been superseded by 

 the inkwriter. 



The dots and dashes of the Morse alphabet are made by a rounded steel 

 point fixed at one end of a lever, the other end being furnished with an 

 armature and attracted by an electro-magnet worked by a relay and local 

 battery. 



1532. Bain's Chemical Telegraph as used by the Electric 

 Telegraph Company in 1850 in place of the double needle. 



The paper ribbon was prepared with yellow prussiate of potash and nitrate 

 of ammonia ; the style is of iron. The Steinheil code, dots in two parallel 

 lines, was occasionally used, but was entirely superseded by the Morse code of 

 dots and dashes. 



1533. Various forms of Ink-writers. (Old.) 

 a.'Breguet's ink-writers. 



b. Ink-writer with inking pad and reservoir. 



c. Do. do. ink bottle. 



1534. Varley's Mill. 1855. Used by Electric Telegraph 

 Company. 



This contrivance was used in connexion with relays and translators. 

 When a current passes through the coils the armature is attracted rapidly 

 in the usual way, but when the current ceases the armature returns slowly to 



