Pneumatic electrostatic machines

By 1885, Walter Hempel [1][2] found that by enclosing an electrostatic machine in a pressurized vessel it was possible to increase its output current significantly, due to the increased breakdown voltage of pressurized gases. The machine used was of the Toepler type (not clear what structure), mounted under a glass cover for experiments at normal pressure (Fig. 1) and in an iron box for experiments at high pressure (Fig. 2). The machine was tried at several pressures and with different gases, and it was found that by increasing the pressure it was possible to obtain a consistent increase in the output current with the pressure. Experiments were reported with air, hydrogen, and carbon dioxide. The measurement method was to count the number of discharges of a Leyden jar for 400 turns of the machine. Presures up to 7 atm were used for air, with measured current increase of 2.7 times at 4 atm. The results with carbon dioxide were the best, with an increase of 5.9 times at 3 atm. It was also found that with less than 0.5 atm the machine would not work.


A Wimshurst machine enclosed in a pressure vessel was patented by Frederick Tudsbury [3][4] in 1900. He was an instrument maker, and built several models of the machine in the early 1900's. Advertisings showing these machines appear in publications from 1906.

Tudsbury, large   Tudsbury, small

A large machine with 60 disks was built by O. Leuner and O. Lehman [5][6], for the Institute of Physics in Karlsruhe, Germany.


Electrostatic machines operating in compressed gases continued to be developed in the XX century, with Van de Graaff generators and similar machines, some of great dimensions (1,2) , and the several rotating machines developed by N. Felici. More about these developments can be found in the site of Lyonel Baum.

Electrostatic machines operating in high vacuum are also possible. This thesis from J. G. Trump (MIT 1933) describes some of the first experiments.


[1] W. Hempel, "Die Hochdruck-Influenz-Electrisirmaschine," Annalen der Physik, 261, 7, pp. 487-493, 1885.
[2] W. Hempel, "A high-pressure influence electric machine", The telegraphic journal and electrical review, August 1, 1885, pp. 90-92.
[3] F. Tudsbury, "Improved means for increasing the efficiency of high tension electric influence machines," Patent #22731, 1900.
[4] J. A. Bergonié and G. H. Bécou, "Archives d´électricité médicale," Vol. 14, p. 56, 1906.
[5] J. Frick and O. Lehmann, "Dr. J. Fricks physikalische Technik, oder, Anleitung zu Experimentalvorträgen sowie zur selbstherstellung einfacher Demonstrationsapparate," Volume 2, F. Vieweg und Sohn, 1907.
[6] O. Lehman, "Beobachtungen über electrische Entladungen bei einer grossen Influenzmaschine," Annalen der Physik, 280, 12. pp. 642-653, 1891.

Created: 28/8/2011
Last update: 4/10/2012
By Antonio Carlos M. de Queiroz
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