652 
MR. W. CROOKES ON MOLECULAR PHYSICS IN HIGH VACUA. 
608. The coil being connected with an exhausted tube showing any of the phenomena 
I have already described, the negative terminal was thoroughly well connected with 
earth. This made no difference whatever in the phenomena observed in the tubes, 
which took place just as well as if the negative pole had not been connected with 
earth. 
609. It has been shown that the stream of molecules are shot off from the negative 
pole in a negatively charged condition, and their velocity is owing to the mutual repul¬ 
sion between the similarly electrified pole and molecules. It became of interest to 
ascertain whether lateral repulsion was exerted between the molecules themselves. 
If the stream of molecules coming from the negative pole carried an electric current, 
two parallel rays should exert mutual attraction; but if nothing of the nature of 
an electric current was carried by the stream, it was likely that the two parallel rays 
would act simply as negatively electrified bodies and exert lateral repulsion. This 
was not difficult to put to the test of experiment. 
610. A tube was made with two flat aluminium terminals, a b, close together at one 
end, and one terminal, c, at the other, as shown in fig. 11. Along the centre of the 
tube, cutting the axis obliquely, is a' screen of mica, painted over with a phospho¬ 
rescent powder, and between the screen and the double poles, a b, is a disc of mica 
crossing the axis of the tube, and therefore nearly at right angles to the phospho¬ 
rescent screen. In this mica disc are two slits—one opposite each pole a and b — 
running in such a direction that the molecular streams emanating from a and b when 
made negative shall pass through the slits, forming two horizontal sheets. These 
sheets striking against the oblique screen will be made evident as two horizontal lines 
of light. The poles a and b were somewhat bent, so that the lines of light were not 
quite parallel, but slightly converged. The tube being properly exhausted, the pole a 
was made negative, and c positive, the lower pole b being left idle. A sharp ray of 
phosphorescent light shot across the screen along the line cl f The negative wire was 
now transferred from a to b, when a ray of light shot along the screen from e to f 
The two poles a and b were now connected by a wire, and the two together were made 
the negative pole. Two lines of light now shone on the screen, but their positions, 
instead of being, as before, d f and e f, were now d g and e h, as shown by the dotted 
lines. The wire joining the poles a b was removed, and the pole a made negative; 
the ray from it followed the line cl f as before. While the coil was working, another 
wire hanging loose from the pole b was brought up to a, so as to make them both 
negative. Instantly the ray e h shot across the screen, and simultaneously the ray d f 
