|The electrometer at right was made starting
in 1845 by Watkins & Hill, instrument makers in London. The instrument
is supposed to measure the forces between small bodies charge with
electricity. A thin bar of insulating material, suspended from the
top with a silk filament holds horizontally an electrical conductive
ball balanced by a counterpoise. Electrified bodies were introduced
through the lateral hole and the degree of deflection was supposed
to measure the force between the two bodies.
The Watkins & Hill torsion balance was promoted
for many years to yields accurate estimates of the forces between
charged bodies. However, the proper functioning of such instrument
is highly questionable. The small diameter of the instrument (five
inches), the unshielded glass construction, the lack of moisture
prevention features makes the apparatus more a symbol of the inverse
square law of electrostatic force than a functional device.
The apparatus at right is of “Braun Electroscope”
type. It was created by Professor Ferdinand Braun of Tubingen Germany,
early in the early 1900. It is primarily used for classroom demonstrations
of electrostatic phenomena. The Braun's original version is housed
in a box.
Below is a standard Dolezalek quadrant electrometer of unknown
manufacture. Possibly German.
As is almost always the case, the quartz suspension fiber is missing.
The body is mostly stainless steel while the outer protective case
is painted brass. Four amber insulating posts support the polished
brass quadrants. The vane, not visible, is coated paper.
The electrical connections for the quadrants, not visible in the
photo, are on the bottom of the instrument.
Tne Lord Kelvin multicellular voltmeter in the right is made by Kelvin
Bottomey & Baird probably in the 1930s. The instrument has a removable
dashpot under it to house an oscilation dumping vane. Instructions
indicates that the Casor oil, provided in the carring box, should
be removed during transporation. No need to wory about this any more,
it will not splash, it hardened up! The green color probably should
be attributed to corrosion inside.
The instrument is a "modern" version of
the multicellular voltmeter developed by Thomson in 1887. The aparatus
at right is in Harvard Colection.
An instrument very similar with ours, with tag number 2900, Mfg:
Kelvin & James White, Ltd. is in Caltech collection.
The tho electrometers pictured above, are
very similar in shape to the Watkins & Hill instrument. Made
by Central Scientific. A major improvement: would be the methalic
body of the apaaratus. (shilding by Faraday effect). But
are those instruments electrometers? The only thing inside is a
heavy iron ring , most likely there to dumpen oscilation.