Electrical Discharges
The nature of the electrical discharge, both in air and in a vacuum, is of considerable technical interest.
   This apparatus, in the collection at Hampden-Sydney College in Virginia,  is listed in the 1900 Max Kohl catalogue as "Apparatus for showing the difference of the two electricities" and cost 20 Marks. It has suffered somewhat over the years: the insulating columns were once straight, and the catalogue illustrations shows a point facing toward a disk, with one point on the left and one point on the right. 

   The apparatus was designed to illustrate the asymmetry of discharges from positive and negative points. The 1923 Leybold catalogue calls this "Gaugains's valve apparatus for showing that positive electricity passes more easily from a point to a plate, negative on the contrary passes more easily from a plate to a point."
   This unmarked apparatus is in the Dartmouth College collection. The electrical discharge can take place between the top plate and a sharp point, another plate, or a rounded point. The discharge can also be investigated as a function of the residual gas pressure in the system. 
 

 
   This unmarked device is in the collection of St. Mary's College in Notre Dame, Indiana. It is probably designed for the study of electrical discharges as a function of potential difference and gap length.
 
 


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