The ratio arms of the bridge are variable and controlled by the
single
switch below the meter which selects multiplying factors from .001 to
1000 (2000 ohms total). The rheostat arm consists of four decade
switches totalling 11,110 ohms in steps of 1 ohm. An internal battery
comprising two 1.5 volt cells can be used to power the bridge.
terminals with links enable th instrument to be used with an external
supply (including AC up to 10kHz) another galvanometer or indicating
device or standard resistor. The key operated switch on the left
enables the test set to be used for cable fault detection. It is suited
for Murray, Varley and Pomeroy's testing methods.
Alexander Muirhead founded Messrs Muirhead and Company in 1894.
He was a highly skilled electrical engineer, and his laboratory in
Downe had an international reputation for the design and construction
of telegraphic instruments of the very highest quality. Muirhead
established the technological supremacy of the company in
the fields of telegraphy and was the first man to make a recording of a
human heartbeat. Muirhead and Co. went on to supply the first X-rays to
Beckenham Hospital at the turn of the 20th century. The factory which
was situated in Elmers End, Beckenham, Kent was
demolished and replaced with a Tesco supermarket in the 1990's. Their
research department and offices were moved to an office block
which was built on the site of the Odeon Elmers End in the 1960s. When
the firm closed down Maunsell (now part of Aecom), a firm of
consulting engineers took it over and named it Maunsell House where I
worked for a short time in the early 1990's. It is now converted to
flats.
