Leyden Jar and Insulating Stand #10162 and 10552
The principle of the Leyden jar was discovered by Pieter Musschenbroek who received a severe electric shock from a jar of water that was charged. They were later made by applying foil to the inside and outside of a glass jar with an insulated knob on top connected to a chain that made contact with the inside foil. Some early lecturers demonstrated the power of electricity by electrocuting small animals with a battery of many charged Leyden jars.
References: Gerard L’E Turner, Nineteenth Century Scientific Instruments, Berkeley, 1983, p.190; David Wheatland, The Apparatus of Science at Harvard, 1765-1800, Cambridge, 1968, pp.141-42.
Battery of Leyden Jars #10248
Max Kohl, Chemnitz, Germany
These large, cylindrical capacitors were part of a Tesla apparatus and may have been used in a circuit to produce and detect Hertzian waves.
References: Max Kohl Catalogue No. 50 (c.1911) p.1035 and No. 100 (c.1927) p.1024.
Sir William Thomson’s Patent Electrostatic Voltmeter #10004
J. White, Glasgow
This instrument, devised by William Thomson (Lord Kelvin) in 1887, met a need in the growing electrical industry. It utilizes the force between two electrified bodies, in this case insulated parallel plates, one set fixed and the other moveable. Using the different weights supplied with the instrument one can measure potential differences of 50 to 10,000 volts. Electrostatic meters have the advantages that they use no current and can equally well be used with alternating and direct potential differences. The serial number on this example is 70.
Reference: George Green and John T. Lloyd, Kelvin’s Instruments and the Kelvin Museum, Glasgow, 1970, pp. VII and 25-27
Sir William Thomson’s Quadrant Electrometer #10560
J. White, Glasgow
Thomson invented the quadrant electrometer in 1853. As with the electrostatic voltmeter, the quadrant electrometer utilizes the electrical force between charged electrodes. A butterfly-shaped electrode composed of two quadrants of a circular disk is supported by a torsion fiber inside a stationary circular box composed of four quadrants, opposite pairs of which are electrically connected. The rotation of the suspended electrode depends on the potentials applied to the various electrodes. A beam of light reflected from a mirror attached to the fiber is shown on a scale and is deflected as the fiber is rotated. The serial number of this instrument is 152.
References: George Green and John T. Lloyd, Kelvin’s Instruments and the Kelvin Museum, Glasgow, 1970, pp. IV and 22-24; Gerard L’E Turner, Nineteenth Century Scientific Instruments, Berkeley, 1983, pp.199-200; James W. Queen, Electrical Testing Apparatus Catalogue I-66, 1887, p.20; Robert Bud and Deborah Jean Warner, Instruments of Science: An Historical Encyclopedia, New York, 1998, pp.208-11.
Lord Kelvin’s Patent Multicellular Voltmeter #10160
J. White, Glasgow
This instrument, patented in 1888 and bearing the serial number 574, is a form of quadrant electrometer modified for commercial use. Its sensitivity is greater because it uses several cells in place of the single cell in the quadrant electrometer. Instead of measuring the deflection, there is a provision for the operator to rotate the support of the torsion fiber so as to bring the mirror back to its rest position where it is in equilibrium between the torque of the fiber and the electrical attraction of the electrodes. The angle of rotation is then used with a calibration chart to obtain the potential difference to be measured.
Reference: George Green and John T. Lloyd, Kelvin’s Instruments and the Kelvin Museum, Glasgow, 1970, p.VIII and 27-28; Whipple Museum Catalogue 8: Electrical and Magnetic Instruments, 1991, No. 210.
Dolezalek Quadrant Electrometer #10561
The electrometer is an instrument for measuring potential differences utilizing electrical attraction or repulsion. Friedrich Dolezalek (1873-1920) invented this form of quadrant electrometer using a quartz fiber suspension. A slight rotation of the electrodes is registered as a motion of a light beam reflected from a small mirror mounted on the suspension fiber.
References: Gerard L’E. Turner, Nineteenth Century Scientific Instruments, Berkeley, 1983, p.200; Max Kohl Catalogue No. 50 (c.1911) p.842.
Capillary Galvanoscope #10411
Max Kohl, Chemnitz
A small drop of mercury in the horizontal capillary tube moves under the influence of an electric field applied to the two electrodes. The device is provided with a glass scale for projection.
Reference: Max Kohl Catalogue No.100 (c.1927) p.950.
String Electrometer #10174
Leeds & Northrup, Philadelphia
The "string" in this electrometer is a fine wire, connected to the potential to be measured, that passes through the electric field between a pair of electrodes connected to a battery. The deflection of the wire toward one or the other electrode is measured by a microscope and is approximately proportional to the potential on the wire. The sensitivity is varied by changing the tension on the wire and the strength of the field. This form of electrometer has the advantage of compactness, portability, and a wide range of sensitivity. This instrument, invented by Willem Einthoven, a Dutch Professor of physiology, is also used in electrocardiography.
References: Walter C. Michels, Advanced Electrical Measurements, Toronto, 1941, pp. 69-71; Robert Bud and Deborah Jean Warner, Instruments of Science An Historical Encyclopedia, New York, 1998, pp. 205-206.
Birdcage Quadrant Electrometer #10562
Nalder Bros. & Co., London
This is another example of a quadrant electrometer, this one shielded from air currents by a glass jar and against electrical effects by wire cages both inside and outside the glass.
Reference: Gerard L’E. Turner, Nineteenth Century Scientific Instruments, Berkeley, 1983, p.200; Robert Bud and Deborah Jean Warner, Instruments of Science: An Historical Encyclopedia, New York, 1998, pp.208-10; Whipple Museum Catalogue 8: Electrical and Magnetic Instruments, 1991, No.195.
Electrostatic Generator #10097
The contact of two dissimilar materials results in a transfer of electrons from one to the other. The effect is most pronounced when the contact areas are increased by rubbing. In electrostatic machines such as this one, a glass disk rubs against two leather pads when rotated by a crank. Charge builds up on the brass conductors and may be drawn off through a spark by means of a grounded discharger.
Reference: Max Kohl Price List No. 100 (c.1927), p. 830-31