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Ganot calls this "Carré's dialectrical machine"
and includes the cut at the left. The device was introduced in 1868 and
was manufactured by Carré of Paris. The machine at the left, below,
was in storage at the Williston Northampton School in Easthaven, Massachusetts
when I visited in March 1996; the photograph is by Daniel Hayden. In the
1881 Ritchie catalogue it is listed at $75.00. This is the only example
I have seen in the United States. The machine at the right, below, is on
display at Birr Castle in County Offlay, Ireland. Charles Mollan, in the
Irish National Inventory of Historic Scientific Instruments, lists
five examples in Ireland alone.
The machine is a hybrid. The lower glass plate is electrified positively by friction by the rubber as the crank is turned. The upper plate is made of ebonite, and turns much more rapidly. Negative charges are induced on the upper plate, and are picked off by the sharp points. |
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