253 



Sories A is a glow discbarge i-epreseiitilig tlie lo^Yest speed of tlie 

 Uiacliino. (Nothing ^A•as visil)lo l)elween the points in tlie darkened ttibe. 

 Each point showed a tiny bright specli. ) 



Series B is a brush discharge representing a liigher 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 .30 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, 3 then sliow 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 fi'ont 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 G show the current in a field of the second 

 direction, and Nos. 1 and 4 show it when the magnet v,-as 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 

 (j,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 tlie 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 



