247 
AN INVESTIGATION oF A Point DiscHarGE IN MAGNETIC AND 
ELeEctrostatic ETELps. 
By Oscar WILLIAM SILVEY. 
A year ago the writer’ presented at the meeting 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 was 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 partiches composing the stream 
emitted from the points. 
The apparatus used in this and the previous work was that constructed 
by Professor Foley and Mr. Haseman®* 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 (KH, Figs. 
1 and 8) 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° are 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 come to rest, the cardboard was removed until the 
1 Proceedings of the Indiana Academy of Science, 1909. 
2 Not yet published. 
