Crystal Palace International Electric Exhibition 1881-82

18 [20.] 1840. COOKE & WHEATSTONE'S ABC INSTRU- MENT. 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 appear at an opening in the front of the case. The escapement is similar to the “ échappement-å- cheville,” and is controlled 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 other for each current sent. The train of clockwork is actuated by a main-spring. The 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. [21.] 1840. SIMILAR APPARATUS to No. 20, but a pointer is used instead of a revolving card. [22.] 1858. MODERN FORM OF WHEATSTONE’S ABC INSTRUMENT. A magneto-electric instrument. The currents for working the same being generated by the revolution of an armature in front of polarized electro-magnets. The depression of a key- opposite a letter arrests the motion of the pointer and cuts off the currents going out to line. [23.] COLLECTION OF KEYS. a. 1852. Simple Spring Key used with Bain’s chemical recording telegraph. b. 1854. 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. 1854. Varley’s Wheel Key. A constant current is main- tained 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 connections for sending and receiving. d. 1870. Stroh’s Key. Similar in general principle to Varley’s key, but the contacts are made by springs, and the switch, action is attained by moving the lever of the key to the right or left as required. When the lever is at the “ receive ” position it cannot be depressed. e. J 882. Single Current Key. f. 1882. Double Current Key.