306 SEC. 10. ELECTRICITY. 



1546. Theiler's " Step by Step" Type Printer, 1863-64. 



The type-wheel fixed cm the axle of the escapement is controlled by re- 

 versals, and the printing is performed by the wheelwork, which is brought 

 into action by an electro-magnet, the local batterj r circuit of the latter being 

 closed by a vibratory arrangement, which does not close the local circuit of 

 this magnet until the type-wheel is stopped at any particular letter. 



1547. Dujardin's Type Printer, 1865. 



A step-by-step instrument in which the escapement is controlled by reversals, 

 the electro-magnets acting on the anchor of the escapement being worked by 

 a polarised relay in the line circuit, and a local battery. 



The operation of printing is performed by an electro-magnet, the local 

 battery circuit of which is closed by the anchor of the escapement at the end 

 of each oscillation. 



When the apparatus is running, and no key is depressed, the short currents 

 passing through the printing magnet are insufficient to cause it to attract its 

 armature ; but when a key is depressed and the type-wheel stopped at any par- 

 ticular letter the printing magnet attracts its armature, and an impression is 

 made. 



An electro-magnetic "cut off" arrangement is used in connexion with the 

 printing magnet, by which the blow struck is always equal in duration 

 whether the key be held down for a longer or shorter time. 



The operation of printing is performed at both sending and receiving ends of 

 the line. 



This instrument was used for a short period on a wire between London and 

 Edinburgh in 1865, by the Electric Telegraph Company. 



1548. Cooke and Wheatstone's Revolving Disc Tele- 

 graph, 1840. 



A step-by-step instrument. The letters of the alphabet are arranged round a 

 paper disc fixed on the axle of an escapement wheel. 



The letters are presented at an opening in the front of the case. 



The escapement is similar to the " echappenient-a-cheville." and is con- 

 trolled by an electro-magnet. 



There are as many teeth in the escapement wheel as there are letters on 

 the revolving disc ; the latter moves from one letter to the following for each 

 current sent 



The train of wheel work is actuated by a mainspring. 



1549. Cooke and Wheatstone's Pointer Telegraph In- 

 strument, 1840. 



This instrument is similar in all respects to the revolving disc telegraph, 

 excepting that a pointer takes the place of the revolving disc. 



1550. Cooke and Wheatstone's Magneto-Electric Com- 

 municator, used with their revolving disc or pointer 

 alphabetical telegraph, 1840. 



This communicator is so arranged that a current is sent when its spoked 

 wheel is turned through a distance equal to that dividing the letters engraved 

 upon it. 



The commutator fixed on the axle of the revolving electro-magnet is so 

 constructed that the magneto-electric currents are all in the same direction. 



