251 
When a photograph of the discharge parallel with the lines of force 
was desired, the magnet was turned with its axis perpendicular to the axis 
of the tube, and the glass tubes, held in position by corks in the hollow 
cores, provided insulation for the rods holding the points. In this case 
also an auxiliary tube 12.5 cm. square and 1 meter long was placed between 
the coils and telescoped into the two portions of the longer tube which 
were too large to fit between the coils. This small tube had a circular hole 
in each of two sides to receive the pole pieces of the magnet, and another 
in the upper side similar to the one in the first auxiliary tube described. 
In all cases the magnet was electrically connected to earth and the 
wires bearing the current were separated from the walls of the room 
and from the camera by means of glass tubing, when they were too near 
for the air to insulate them. All metal parts used in the magnetic field. 
such as screws in the auxiliary tubes, were of brass. 
When studying the deflection of the discharge due to electrostatic 
deflection, the tube was used as shown in Fig. 1. Two brass plates 
8 by 5 cm. were placed one above the other below the points. They were 
held in position by brass rods soldered perpendicularly to them at the 
center. The reds were firmly fitted into glass tubes which passed through 
the upper and lower sides of the tube. For part of the work the plates 
were connected electrically in multiple circuit with the points, while for 
the other part they were charged by means of a small Holtz machine. 
The points were charged by a four-mica plate Wagner electrostatic machine, 
from which the Leyden jars had been removed. Both the Wagner and the 
Holtz machines were run by electric motors with rheostats in circuit for 
yarying the speed. Sixteen different speeds were possible with the 
Wagner, and eight with the Holtz machine. 
The points were made of brass pins 1.15 mm. in diameter and 4 cm. 
long. They were put in a4 lathe, sharply pointed by means of a carborundum 
stone, and made to slope 2.5 cm. from the end. They were soldered into 
the ends of brass rods 5.57 mi. in diameter. 
TRANSVERSE MAGNETIC FIELD. 
The apparatus was first adjusted with the points at right angles to 
the direction of the magnetic lines of force and the photographs of series 
A, B, C and D were taken. 
