Crystal Palace International Electric Exhibition 1881-82

15 [4.] 1838. COOKE & WHEATSTONE'S FOUR-NEEDLE TELEGRAPH. Since the sounds of C, Q, J, U, and Z need be very little used in the English language, it was found that the remaining letters of the alphabet could be formed by the deflection of four needles, and such. an. instrument was employed on the London and Blackwall Railway in 1840. In this instrument, the letters H and P ai’e formed by one needle only. [5.] 1842. COOKE & WHEATSTONE’S DOUBLE-NEEDLE TELEGRAPH. Owing to the frequent failure of one or two out of the four wires, it was soon found by the operators that an alphabet could "be formed by two needles only, if advantage were taken of repeated momentary movements, either separate or combined, instead of prolonged deflections. This identical instrument was fixed at Slough, in 1842. Kindly lent by Messrs. Reid Bi’os. [6.] 1850. COOKE & WHEATSTONE'S DOUBLE NEEDLE in a Gothic case made specially for the new Houses of Parliament. [7.] 1852. THE MODERN FORM OF DOUBLE NEEDLE modified by Messrs. Edwin and Latimer Clark, still used to a small extent on some railways in England. [8.] 1846. THE SINGLE-NEEDLE INSTRUMENT OF COOKE & WHEATSTONE. It was soon found that an alphabet could be foi’med by the movements of one needle only, by taking advantage of momen- tary deflections of the needle to one side or the other. At first an arbitrary alphabet was used, but in the [9.] 1869. MODERN FORM OF SINGLE NEEDLE, The German Union Morse Alphabet was adapted, and the form of the instrument much improved. The change of alphabet was made in 1855. [10.] 1843. BAIN'S I. AND V. TELEGRAPH. The alphabet is formed by the movements of two pointers, one moving to the right and the other to the left, according to the direction of the current. The pointers are attached to circular magnets moving inside coils. A code similar in principle to tnat of the single-needle instrument was Rm ploy nd for repre- senting the letters.