Crystal Palace International Electric Exhibition 1881-82

13 [11.] HUGHES' INDUCTION BALANCE. An extremely delicate apparatus by which impurities in metals and alloys are detected. [12.] WATER LEVEL INDICATOR. For indicating the height of the water level in a reservoir. The “ transmitter” sends intermittent currents in one direction or the other, according as a float in the reservoir rises or falls. The “ receiver ” is worked by a polarised armature, with an escapement, which, is propelled in one direction or the other, according as positive or negative currents are received from the (C transmitter.” INSTRUMENTS, fyc., IN OPERATION. [1.] SET OF WHEATSTONE’S ABC INSTRUMENTS. [2.] SINGLE NEEDLE INSTRUMENTS, each with Com- mutators, and one with Tin Sounder. [3.] DUPLEX DIRECT INKERS. [4.] DUPLEX DOUBLE-CURRENT SOUNDER SET. [5.] WHEATSTONE'S AUTOMATIC APPARATUS. HISTORICAL TELEGRAPHIC APPARATUS. [1.] 1816. RONALDS' ELECTRIC TELEGRAPH (lent bv Mr. Latimer Clark). Tins was o> Dial Telegrapli, Two dials (scparatecl by a, wir©) were rotated synchronously by clockwork. When a letter which it was desired to transmit appeared at the opening in the dial at the sending end, a charge of statical electricity from a Leyden jar was sent into the wire, which caused two pith, balls at both the sending and receiving ends to diverge simultaneously, and thus to indicate the letter. Words were thus spelt out. Sir Francis Ronalds used copper wire insulated in glass tubes pro- tected by a trough of wood well tarred. A portion of this experimental line laid down in his garden in Hammersmith on the