West London Scientific Apparatus Co. Ltd.
Resistance Bridge

Serial No.230

West London Scientific Apparatus Co. Ltd.(ex WD) Resistance Bridge in polished wood case with detachable lid with Ebonite panel wit brass plugs for resistance selection and brass terminals.Designed for line testing, two 10/100/1000 ohm arms and one variable 0-10000 ohm arm. Manganin BS ohms @ 150C working WEST LONDON SCIENTIFIC APPARATUS Co., Ltd., Premier Place, High Street, Putney, London. [The firm also manufactured "Surrey" motor cars in the 1920's and ceased to exist in 1931] UK 1914

The top is made of thick ebonite supporting undercut brass blocks shaped to accommodate sixteen interchangeable brass shorting plugs which have ebonite handles. The brass blocks are connected to resistance coils of thick wire to reduce the effect of heating when passing large currents. The coils are of manganin resistance wire, the resistivity of which does not change appreciably with small changes of temperature. The accuracy of such a resistance standard may be taken as 0.25%.

Resistance is inserted by removing a plug, which, when in place, short-circuits the resistance. This device is configured as a Wheatstone bridge, with terminals and key switches for a battery and galvanometer. I have a similar resistance bridge made by Pye.