247 



An Investigation of a Point Discharge in Magnetic and 

 Electrostatic Fields. 



By Oscar William Silvey. 



A year ago the writer^ presented at the aieeting of the Indiana Acad- 

 emy of Science a report of an investigation of the electric point discharge 

 in a magnetic field of 1,500 gausses. In this work it was found that 

 the stream of air from the negative electrode was in no case deflected, and 

 if the glow discharge existed between the points neither positive nor 

 negative stream v/as deflected by a field of this strength. 



The purpose of the present investigation was to repeat with a stronger 

 magnetic field the work described in the previous report, to study the 

 effect of an electrostatic field upon the path of the spark, and to determine 

 if possible the nature and velocity of the particles composing the stream 

 emitted from the points. 



The apparatus used in this and the previous work was that constructed 

 by Professor Foley and Mr. Hasemau- for the investigation of interference 

 fringes about a point discharge, air streams, and vapor streams. It con- 

 sisted of a long wooden tube (Fig. 1), one part of which was made to 

 telescope over the other part. This provided a means of separating the two 

 parts for adjusting the points and magnet. Another portion (E, Figs. 

 1 and 3) containing a plate holder F was made to fit over the end. Black 

 screens (Fig. 4) were placed at intervals throughout the tube so that no 

 light would be reflected from the sides. The end of the tube was closed 

 by a cap (C), which shut out all light except from a pinhole, as shown 

 by Fig. 2. A circular disc with holes of various sizes provided a means 

 of regulating the amount of light. A is a 90° arc light, the center of 

 which is focused on the pinhole by means of the lens B. 



Light was shut out of the tube by placing a piece of plack cardboard 

 in front of the pinhole. When a photograph was to be taken, if the dis- 

 charge was a glow or a brush, the slide S was drawn from over the plate, 

 and after the tube had cdine to rest, the cardboard was removed until the 



' Proceedings of tlio lodiaua -Vcadcmy of Scionce, 1009. 

 ^ Not yet published. 



