Voss Machine
   Voss, Wimshurst and  Carré  machines are all electrostatic induction devices. In effect, they are all examples of a continuous electrophorous . In the latter, an initial charge on an insulated dielectric disk induces a charge of the opposite sign on an insulated conductor.

   In the Voss machine at the right a fixed plate of glass has two metallic foil sectors glued onto it. The slightly-larger rotating plate has six foil dots with raised studs glued to it; the foil sectors are large enough so that two of the studs are opposite each sector.
   In the middle is a horizontal ebonite rod, with collecting combs on the ends that are connected to Leiden jars. The vertical brass rod has metallic combs attached to its ends. In use, it is turned counterclockwise by about 30 degrees. At the northeast and southwest corners there are fixed metallic brushes that are in electrical contact with the foil sectors of the fixed disk

   Assume that when the disk starts to rotate in a clockwise direction there is a small amount of positive charge on the left-hand sector. This causes a separation of charge on the stud facing it, with negative charge being bound. Some of the positive charge is picked off by the comb attached to the upper end of the brass rod. The remaining net (negative) charge is picked off at the northeast corner, giving the right-hand sector a negative charge. This will now cause a separation of charge of the studs passing by the right-hand sector, with the net effect being the removal of a net positive charge from the studs to the left-hand sector as they pass by the brush on the south-west corner. And so it goes... 

   This machine, at Washington and Lee University in Lexington, Virginia, is unmarked, but it is an excellent match for a machine in the ca. 1900 Max Kohl catalogue. Its cost was about 70 Marks, depending on the diameter of the disk. The catalogue lists it as a Toepler machine, but it is clearly a Voss machine; the Toepler and Toepler-Hotlz machines had a somewhat different arrangements of plates and electrodes.
   This example of a Voss machine, at Denison University in Granville, Ohio, appears to be identical with the one above, apart from the darkening of the varnish used to damp-proof the disks. In this example, the southeastern brush has been broken off.
   This rather large Voss machine is at Benedictine College in Atchison, Kansas.

   The multiple-disk Voss machine at the right is in the collection of Transylvania College in Lexington, Kentucky. There are four stationary disks and four revolving disks, and they are made of ebonite. 

   This apparatus is unmarked, but, apart from its legs, it strongly resembles a machine that Kohl sold ca. 1900 for about 500 Marks, depending on the size of the disk.

   This enormous, multiple-disk Voss machine is at Fort Hayes State University in Hayes, Kansas. It was once used by a Kansas physician to furnish the high potential to run an X ray tube.

   This picture, from Huston's "Lessons on Electricity" (1903) shows a big Holtz machine being used for electric "therapy."
   The Milvay Toepler-Holtz Machine at the right was manufactured by the Chicago Apparatus Co. under the Milvay logo. It is listed in the 1929 catalogue at $38.50.

   The catalogue copy tells that "after a long series of tests we positively guarantee that the Milvay Static Machine will give a thick, energetic crashing spark three inches long, regardless of weather conditions... Under ideal conditions sparks six inches long have been obtained with ease.

    The machine is in the Jack Judson Collection at the Magic Lantern Collection in San Antonio, Texas.

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