Wimshurst Machine
   The Englishman, James Wimshurst (1832-1903),  spent most of his professional career working with the shipping industry as a surveyor and evaluator of ships, serving as the consulting engineer for the British Board of Trade.. At the same time he had a parallel career in science. We know him for his work with electrostatic generators in the early 1880s, when he improved Voss' electrostatic generator

   In Wimshurst design, the disks contra-rotate. The metal foil sectors on the disks induce charges on each other, which are picked off with metal brushes and stored in Leiden jars. 

   This is my favorite Wimshurst machine, for it is in my own collection. It bears the mark of the L. E. Knott Apparatus Co. of Boston, but my 1916 Knott catalogue shows an improved model with a gear drive and an openwork cast-iron base. Therefore, I suspect that it is somewhat older. The plates have been replaced; when I rescued it a two by four had just fallen across it. Despite being nearly one hundred years old, it still gives a good spark.

   The Wimshurst machine at the left, below, is in the Garland Collection of Classical Physics Apparatus at Vanderbilt University. The catalogue of Max Kohl of Chemnitz, Germany, published ca. 1900, shows this piece of apparatus at a cost ranging from 105 to 180 Marks, depending on the size of the plates. In 1916 the same machine, this time bearing the logo of the Chicago Laboratory Supply Company, was sold by C. H. Stoelting of Chicago for $40.00. At the right is an unmarked machine that I saw at James Kennedy Antiques in Durham, North Carolina in April 2000.
   This Wimshurst machine probably dates from the first quarter of the twentieth century. The cast iron base has "D. R. G. M. No. 29225" cast into the base. The ebonite plates are 20 cm in diameter. 

   It is at Hampden-Sydney College in Virginia.

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   The Wimshurst Machine at the right is in the Jack Judson Collection at the Magic Lantern Collection in San Antonio, Texas.

   The machine can be found in the 1912 catalogue of the "C.H. Stoelting Co., Chicago, Illinois, Successors to the Chicago Laboratory Supply and Scale Co."

   The catalogue notes that "the Wimshurst machine is not affected by moisture or atmospheric changes and works absolutely without changing the poles, making it desirable for X-Ray work. Less than one revolution of the crank is sufficient to charge the machine and set it in operation. ... The plates are of glass, 16 inches in diameter."

   The Wimshurst machine on the left is also in the Judson Collection in San Antonio. It is unmarked, and has the smallest collection of sectors that I have seen on one of these machines. The sectors are made of copper foil, also an unusual attribute.

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