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diameter and 5.2 em. long. They were soldered into the ends of brass 
rods 0.5 em. 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 em. 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 cne 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 
photographie 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 are 
of an are 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. BH. 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. 
