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diameter and 5.2 cm. long. They were soldered into the ends of brass 

 rods 0.5 cm. in diameter. The rods were placed in glass tubes and held 

 firm by sealing wax at the two ends of the tubes. The points were charged 

 by means of a four-mica-plate Wagner static machine (the Leyden jars 

 had been removed), which was run by an electric motor with a rheostat 

 in circuit for regulating the speed. The rods extended through the sides 

 of the camera as shown by (P) Fig. 1, so that the points were near its 

 axis. The points were about 15.5 mm. apart for the first three series 

 of photographs and about 17 mm. apart for the last four series. 



For the first series of photographs the magnet extended through the 

 lower side of the tube directly below the points and was placed so that 

 the tops of the pole pieces were about 0.5 cm. below the points. When 

 the separable pole pieces, Fig. 7, were used they were covered with a layer 

 of sealing wax about 3 mm. thick on all sides except the one facing the 

 magnet cores, to prevent sparks passing to the magnet from the points. 



As a preparation for the experiment the simpler part of Precht's work 

 was repeated (i. e.. apparatus was set up containing one point and one 

 blunt electrode in the same position shown by the points in Fig. 6). The 

 deflection of spark, brush and glow discharge were easily observed in a 

 semi-darkened room when a transverse field was produced by exciting the 

 magnets. Some cases were observed in which the discharge was trans- 

 formed from one type into another, but no measurements were made of 

 the potential, nor determination made of the signs of the charge on the 

 points to see if they accorded with the results given by Precht. 



The magnets and points were then placed in the tube as described and 

 photographic records made of the discharge. The silent discharge was 

 first studied. To produce the magnetic field a permanent horseshoe mag- 

 net was first used, and although it was strong enough to blow out the arc 

 of an arc lamp, the photographs taken showed no deflection of the stream. 

 It was then replaced by an electro-magnet. Fig. 5, later pole pieces, Fig. 

 7, were placed as shown in Fig. 6, and finally two electro-magnets placed 

 in opposition, Fig. 8, in attempts to produce a field sufficiently strong to 

 deflect the stream. The magnets were weak compared with those used 

 by Precht and H. E. Schaeffer. The field measured only about 1,000 

 gausses as used in Figs. 5 and 6, and only about 1.500 gausses as used in 

 Fig. 8. None of the photographs taken of the silent discharge showed any 

 deflection when the magnets were excited. 



