MOLECULAR PRESSURE, AND THE TRAJECTORY OF MOLECULES. 159 
560. Exhaustion = 55 '2 M. Thickness of dark space =15 millims. The green 
phosphorescence is increasing in the bulb. The spot of light on the screen is better 
defined, but no image of the notch can be seen in it. The magnet brings the spot 
down to about the same position as in the last experiment. 
561. Exhaustion = 30'5 M. Thickness of dark space = 16 millims., but it is getting 
very faint. The spot of light on the screen is much more brilliant and is also sharply 
defined. The magnet brings the spot down to 6'8 on the scale, showing a deflection of 
11 *5 millims. The effect of greater exhaustion is therefore to flatten the trajectory 
of the molecules. 
562. Exhaustion = 26’3 M. Thickness of dark space about 25 millims., but it is too 
ill-defined to measure accurately. The bulb is very green, and only a little blue light 
is visible near the positive pole. The spot of light keeps steady at 18'3 on the scale ; 
it is very brilliant, but somewhat ill-defined in outline. When the magnet is put into 
position the spot sinks to 8'5, showing a deflection of 9'8 millims. 
When the spot of light is bent down to division 8‘5 on the scale, its position can be 
varied about 1 millim. by altering the intensity of the induction spark. 
563. Exhaustion = 9 - 7 M. The dark space has now disappeared, and the whole 
tube, except the parts in shadow, glows with a bright greenish-yellow light. The spot 
of fight is now no longer of any particular shape, but may be likened to a splash of 
green fight on the scale. It is also unsteady in position, the centre varying between 
18° and 20° on the scale. The magnet makes it more steady and brings it down to 
16°, giving a deflection of about 3 millims. 
Exhaustion =8*9 M. The spot of fight is too unsteady to enable its position to be 
determined with accuracy. The magnet brings it down between 2° and 3°. 
564. It being found difficult to get a higher vacuum than this in so large a bulb, 
carbonic acid was let in, and after exhausting and refilling several times with pure 
carbonic acid, the following experiments were tried. 
Exhaustion = 456’5 M. Thickness of dark space = 4’5 millims. No spot of light is 
to be seen on the scale, and no green phosphorescence in the bulb. 
565. Exhaustion = 264’4 M. Thickness of dark space = 6‘5 millims. Traces of 
green phosphorescence are visible, but there is no spot of light on the scale. 
566. Exhaustion = 206 - 6 M. Thickness of dark space = S'5 millims. The projected 
spot of light can just be detected with difficulty on the screen, at about 18° on the 
scale. 
567. Exhaustion = 59‘2 M. Thickness of dark space = 12 - 5 millims. Green light 
is appearing in the tube and the spot of fight on the screen is brighter. The magnet 
causes it to sink 14°. 
568. Exhaustion = 28‘4 M. Thickness of dark space = 13'5 millims. The spot of 
fight on the screen is brighter, and a well defined circle, no notch being seen on its 
edge. The magnet brings it down 11°. 
569. Exhaustion = 10'2m. Thickness of dark space is about 2 1 millims., but it is 
