.158 
MR. W. CROOKES OK THE ILLUMINATION OF LINES OF 
557. The magnet used is a compound horseshoe magnet capable of supporting 
about 5 lbs. It is placed underneath the negative pole, as shown in fig. 18 at N S. 
The experiments already tried with the straight electro-magnet show that the mole¬ 
cular ray is deflected in a spiral to the right or to the left according to the pole 
presented to it. When two opposite poles, as in a horseshoe magnet, are placed 
in a line with the normal direction of movement of the molecules, one tends to 
twist it spirally to the right, and the other to the left (fig. 20, A, B). The resultant 
Fig. 20. 
direction is that the ray is bent in a curve, up or down, along a plane at right angles 
to the plane of the magnet, and the line joining the poles, according to whether the 
N pole is to the right or to the left. The magnet is so arranged that it can be put in 
position or moved away as often as necessary, with the certainty of always being 
replaced in exactly the same position. 
The first observations were taken with air at different pressures. Exhaustion 
= 411'7 millionths of an atmosphere. The thickness of the dark space in front of the 
negative pole, measured along the scale e, is 6*5 millims. The bulb is filled with blue 
and violet light; no green phosphorescence is visible. 
558. Exhaustion = 161'8 M. Thickness of dark space = 8'5 millims. Some green 
phosphorescence is seen near the negative pole, but no projection of an image is yet 
seen on the screen cl. 
559. Exhaustion = 102‘6 M. Thickness of dark space = 12 millims. A spot of 
green light is now seen projected on the scale d, bright in the centre and shading off at 
the edges. The spot is about 5 '5 millims. diameter. The centre of the spot, the 
magnet being away, is at 18'3 millims. on the scale. On placing the magnet in 
position, the spot of light is bent vertically down to 5 millims. on the scale, or a 
distance of 13'3 millims. 
The magnet would easily bend the light much more if brought nearer, but it was 
not thought advisable to get a greater deflection for fear of the light coming off 
the scale in other gases. 
