Descriptive catalogue of magnetic, electro-magnetic, electro-dynamic, and magneto-electric inductive instruments and apparatus : constructed and sold by Watkins and Hill, 5 Charing Cross, London.

Watkins and Hill

Date:: [between 1837 and 1851]

Credit: Descriptive catalogue of magnetic, electro-magnetic, electro-dynamic, and magneto-electric inductive instruments and apparatus : constructed and sold by Watkins and Hill, 5 Charing Cross, London. Source: Wellcome Collection.

18/20 page 16

$123. mission of signals along wires by means of electrical currents. The communicator con¬ sists of a revolving wheel contact breaker, marked on the outer edge with letters cor¬ responding with those on the dial, and radial pins to turn the wheel round when com¬ municating signals, £7 7s. 121. Wheatstone’s Rheostat for adjusting and regulating an electric circuit so that any constant degree of force may be obtained. It consists of wood and metal cylinders with parallel axis and a fine metallic wire which can be coiled and uncoiled on to or off from either cylinder, by which means the electric current passes along the coils on the wood cylinder, but only from the two points of the wire which are in contact with the metal Cylinder, therefore the effective part of the length of the wire is the variable portion on the wood cylinder. A scale is placed to measure the number of coils unwound and the fractions of a coil are determined by an index which is fixed to the axis of one of the cylinders, and points to the division of a graduated circle, £3 13s. 6d. 122. Wheatstone’s Rheostat for regulating voltaic currents of comparatively small resistances. It consists of a wooden or slate cylinder, upon which a thick copper conducting wire is coiled, like the thread of a screw. A fixed metal bar arranged parallel to the axis of the cylinder carries a sliding spring piece constantly pressing against one of the coiled wires. By turning the handle the cylinder revolves, and according to the direction either lengthens or shortens the conducting portion of the copper wire coil, which produces a corre¬ sponding difference in the resistance of the electric current, £7 7s. to £9 9s. 123. Wheatstone’s differential Resistance Measurer of metal wires and other conductors of electricity. This apparatus is applicable to any galvanometer, and consists of a maho¬ gany base board, with an arrangement of four wires and brass binding screws, so that two galvanometer wires may be placed in the electric circuit. A contrivance is supplied for restoring the equilibrium produced by slight differences in the lengths of the wires, £1 11s. 6d., £2 2s. . E, TAYLOR, RED LION COURT, FLEET STREET. PRINTED BY R. AND J$