The largest Wimshurst machine ever built

What is probably the largest classical Wimshurst machine was constructed by J. Wimshurst in 1884. It had varnished glass disks with 7" (2.13 m) of diameter, 3/8" (9.5 mm) thick. In good conditions, it could produce sparks 14" (35.5 cm) long, and was designed to produce 30" (76 cm) sparks with suitable Leyden jars (apparently, it reached only 22"). It was first described in Engineering, January 16, 1885, page 60.

The machine was in the Science Museum of South Kensington, England, until 1931, when it was transferred to the Museum of Science and Industry, in Chicago, USA. By that time the plates were broken, and were replaced by new ones. One of the new disks broke again in 1941. It was repaired, but since then the machine was only rarely run. A disk broke again in 1991. By 2009-2010 it was restored again.

The machine, from the back side. Note that there are cranks on both sides, as seen in the old drawing.
A crank. Another view.
One of the supports that hold the main axle, charge collectors, and the neutralizers.
Another view of the support structure.
The charge collectors. Detail of the combs. Note that they are not directly opposite, what should increase the output current, but the machine is incorrectly assembled. The correct configuration is shown in the drawing, that shows the collectors that are out of the center plane moved in the direction of the nearest neutralizers, as suggested by Schaffers [26].
A neutralizer brush.
The broken disk.
Leyden jars.
Recent views of the machine, restored: Front, back. There is still something strange with the positions of the charge collectors.

After this machine, disk machines were rarely built with very large disks, as it was considered more practical to make multiple machines with smaller size, interconnected in parallel for larger current. A large machine is the only solution for high voltage output, what appears to have been the objective of this machine, with just 16 small sectors per disk.

A machine a bit larger than this, but with modern structure, can be seen at the Technorama science center, in Winterthur, Switzerland.

The largest multiple Wimshurst machine was the machine built by Archibald Campbell, Lord Blythswood, for his laboratory in Renfrew, Scotland, by 1892. The machine had 160 disks (some sources say 128) with 3 feet of diameter and 16 sectors, powered by a 1.5 hp electric motor. It was used in experiments about X-rays, and was the power source in a a curious experiment that apparently produced X-ray images without vacuum, before their discovery by Roentgen in 1895.

Thanks to Mark S. Rzeszotarski for most of the photos, to visitors that posted online [1][2] the recent pictures, and to the MSI staff for additional informations.

Created: 15 August 1999
Last update: 17 July 2011
By Antonio Carlos M. de Queiroz
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