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Series A is a glow discharge representing the lowest speed of the 
machine. (Nothing was visible between the points in the darkened tube. 
Each point showed a tiny bright speck. ) 
Series B is a brush discharge representing a higher speed. (A violet 
stream extended about 0.8 cm. from the positive point. The negative point 
showed only a bright speck.) 
Series C is a visible spark discharge representing the lowest speed 
at which a visible spark is maintained. The spark was changed to brush 
when the magnet was excited. 
Series D is a visible spark discharge representing the highest speed of 
the machine. 
The six numbers of each series were taken in succession as rapidly 
as possible, it requiring 20 to 830 minutes to complete the series. In the 
photographs, the longer stream is the one from the positive terminal and 
the shorter one the stream from the negative electrode. If the positive 
stream is from right to left it is designated as the first direction; if from 
left to right as second direction. Nos. 1, 2, 8 then show current in the first 
direction, while Nos. 4, 5 and 6 show current in the second direction. If 
the magnet was excited so that the sense of the lines of force was from 
back to the front of the photograph (i. e., after correcting for the reversal 
in direction caused by printing from the plates), the magnetization is des- 
ignated as first direction and those with the lines of force from front to 
back of the page are designated as magnetized in the second direction. 
Following then this plan, Nos. 2 and 5 show the current in a field of the 
first direction, while Nos. 3 and 6 show the current in a field of the second 
direction, and Nos. 1 and 4 show it when the magnet was not excited. It 
may be observed from the photographs that the streams in series A, B, C 
and D are deflected as if they were flexible conductors bearing a current 
in so far as direction of deflection is concerned, thus indicating that the 
stream is one of charged particles. 
The magnetic field strength, measured by a bismuth spiral, was about 
6,400 lines per sq. cm. in the region of the points. The points were 18.05 
mm. apart. The potential of the points was the highest for series B and 
did not increase as the speed increased, as was suggested in the earlier 
work. The potential increased with the speed only until the sparks began 
passing, when it fell sometimes as much as 4,000 volts. When the speed 
was further increased, the current increased but the potential remained 
