Usage/History: Instruments such as this were used
by trained technical/scientific staff for precision laboratory
measurements of voltage, and as secondary standards for calibrating
other meters. The mirrored scale makes it easier to read the
instrument to a given accuracy by enabling the operator to avoid
parallax errors. Note that this particular instrument has been
standardized at the factory and was certified accurate to ±0.5%
of full scale, or in this case ±0.075 volts.
Some contemporary/early descriptions of the DC Voltmeter
and its use are provided below:
DC Voltmeter Kimball, A
College Text-Book of Physics (1923)
Description: The instrument in housed in a 7.75 x
7.75 x 4.5" oak case with a leather handle. All hardware
is nickel-plated brass. The front panel and meter face plate
are of heavy cast iron with a fine diamond pattern on the casting.
Iron parts have a "japanned" black enamel finish. The
binding posts are of black Bakelite. The meter has a mirrored
scale. The serial number is hand written on the white scale behind
the face plate. The top screw holding the face plate in place
is sealed with sealing wax(?) and stamped with a "W."
There is a brass plate finished in black and nickel plating attached
to the front of the cabinet below the door:
MADE BY THE
WESTON ELECTRICAL INSTRUMENT CO.
NEWARK, N.J., U.S.A
PATENTED
NOV. 6, 1888 MAY 14, 1889 APR. 29,
1890
FEB. 17, 1891 DEC. 19, 1893 OCT.
4, 1898
JUL. 18, 1901
MODEL 45 NO 31789
Beneath this plate is a brass escutcheon labeled "0 CORRECTION" giving access to the zero
correction screw.
There is a calibration sheet
held under acetate in a black painted brass frame inside the
door. It is signed and dated: June 15, 1926. There is an oval
brass tag attached with brass brads left side of instrument stamped
HUMBOLDT S-T-C / 2100.
The oak case has been stripped and refinished with "Watco
Danish Oil," all exposed metal parts have been acid cleaned
and lightly polished. Bakelite, painted metal, and rubber parts
have been cleaned and polished with furniture polish, and the
leather handle has been treated with neatsfoot oil.
