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Otto von Guericke (1602-1686), the Burgomeister of Magdeburg best known for his demonstration of the effect of atmospheric pressure on evacuated bodies (the Magdeburg Hemispheres), also showed the electrical effects were obtained by rubbing glass. Originally, he used a globe of sulphur mounted on a shaft, with the hand rubbing the rotating sphere. The sulphur was cast in a spherical shell of glass that was subsequently broken away; soon it was discovered that glass, and not sulphur, was the key ingredient of the demonstration. About 1700 Francis Hauksbee the Elder suggested that a glass cylinder be used in place of the sphere. |
| The form of cylinder electrostatic machine at the right was patented
by Edward Nairne (1726-1806) in 1782.
This example is on display at the Museum at St. Patrick's College, Maynooth, County Kildare, Ireland. The horsehair-covered leather pad that rubbed against the glass cylinder was placed atop the broken, vertical glass pillar. To promote the ready production of the electric fluid, the surface of the leather was smeared with a mixture of mercury and lard. Also missing is the toothed conductor that drew the charge from the surface of the glass and led it to a storage electrode or a Leiden Jar. This particular apparatus dates from the middle of the 19th century, according to Charles Mollan in The Scientific Apparatus of Nicholas Callan (Dublin, Samton Limited, 1994) pg 113. |
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This small, unmarked cylinder type electrostatic machine is in the collection at Dartmouth College. It is the only example of gearing, to increase the rotation rate of the glass cylinder, that I have seen. |
The small cylinder-type electrostatic machine at the right is marked "Prof. John Tyndall's Electric machine, Manufactured by Curt W. Meyer, .. New York". The 1886 Meyer catalogue devotes three and a half pages to the set of 58 pieces of apparatus designed to accompany Tyndall's "Lessons in Electricity", based on his lectures at the Royal Institution in 1875-76. The entire set cost $65, plus a dollar for the book. At $8.00, this electrical machine was the most expensive piece of apparatus. The machine is in the collection of Westminster College in New Wilmington, Pennsylvania. |
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| This unmarked, Ramsden-style electrostatic
machine is in the Garland Collection of Classic Physics Apparatus at Vanderbilt
University. It was bought ca. 1875 and, judging from other purchases made
by Chancellor Garland at the time, is probably of French manufacture. The
1853 Lerebours et Secretan shows a very similar machine with a glass disk
80 cm in diameter priced at 600 francs (about $120).
The design is due to Jesse Ramsden (1735-1800), the British designer and maker of scientific apparatus. In 1760 he suggested that the glass cylinder be replaced by a circular glass plate. |
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This electrostatic machine with a forty-inch
glass disk is in the collection of Vassar College in Poughkeepsie, New York.
It is unmarked, but it is almost certainly by Edward S. Ritchie of Boston. The 1854 catalogue electrical apparatus of Chamberlain & Ritchie lists a machine of this size, with the prime conductor at the right being sixty inches long. Originally this had a silk "pillow case" covering up the lower half of the glass disk to prevent the loss of the electrical charge; this may be seen in the picture above of the Vanderbilt machine. Vassar was founded in 1861. The 1860 Ritchie catalogue shows a similar machine with a forty-two inch diameter plate for $160. |
| The disk electrostatic machine at the right
is marked "Benjn Pike, Jr., No. 294 Broadway, New York."
The 1856 Pike catalogue lists this machine, with its sixteen-inch disk, at $20.00 and $25.00. This was the smallest machine in the series; the largest one, resembling the Vassar machine, sold for $200.00. The brass ball is the negative conductor, and the brass cylinder is the positive conductor. This beautiful little machine is in the collection of Richard Zitto. |
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When I photographed the Wightman disk electrostatic machine
in September 1979, in was on display at the physics department at Wittenberg
University in Springfield, Ohio.
The glass plate, which can be seen only dimly in this picture, is of the order of eighteen inches in diameter, and was sold by Joseph M. Wightman of Boston in 1846 for the order of $30.00. |
| Most American and European makers produced small
disk electrostatic machines with plates in the sixteen inch diameter range.
Here are three unmarked examples. From the top to the bottom they are at Benedictine College in Atchison, Kansas, Denison University in Granville, Ohio and the University of Glasgow in Scotland. |
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The pictures below show electrostatic machines of the type suggested by Georg K. Winter of Vienna ca. 1850. The example at the left at St. Patrick's College in Maynooth, County Kildare, Ireland is missing its signature plate, but was bought from Yeates of Dublin ca. 1877 as "Winter's Improved Plate Machine. It has a plate 91.5 cm in diameter. The smaller one at the right was at the antique shop of James Kennedy of Durham, North Carolina when I visited in April 2000, and the Winter signature plate can be seen at the front edge of the base.
The two characteristic items of the Winter design are the
rubber and the collector, which may be seen most clearly in the Maynooth example.
The rubbing mechanism has been dismounted and sits on the mahogany base-plate.
The rubbers are made of wood, covered with leather and stuffed with cotton.
The wooden rings have an inner surface lined with tin-foil from which fine
points extend. This mechanism is used to collect the charge generated by
the rubber, and is connected to the brass primary conductor at the right.
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This Winter-type electrostatic machine was on display
at the Royal Scottish Museum in Edinburgh when I photographed in in the summer
of 1978. It is a twin of the machine at the left-above in the Maynooth collection.
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