644 MR. W. CROOKES OK MOLECULAR PHYSICS IN HIGH VACUA. 
as portions of ellipses formed by the intersection of the several sheets of molecular 
rays with the cylindrical tube. Fig. 3 shows this appearance. 
Fig. 3. 
When the other pole was made negative, and the exhaustion was such that the dark 
space extended about 8 millims. from the pole, the first appearance noticed was 
that of a ray of dark blue light issuing through the hole in the mica screen, and 
shooting upwards towards the side of the tube, but not reaching it. Fig. 4 shows the 
dark space round the pole, and the ray of blue light. On increasing the exhaustion 
this blue line of light, and the luminous boundary to the dark space, disappeared, and 
presently a green oval spot appeared on the side of the tube, exactly on the place 
previously marked where the rays issuing normal from the surface of the pole should 
fall. 
Fig. 4. 
592. It happened that this oval spot fell on a portion of the tube where one of the 
elliptical projections from the opposite (corrugated) pole also fell when that was made 
negative. Thus by reversing the commutator I could get a narrow band of green 
phosphorescent light from one pole, or a wider oval of green light from the other pole, 
to fall alternately on the same portion of the glass. Fig. 5 shows these effects, which, 
however, did not occur together as represented in the figure, but alternately. 
The narrow band shone very brightly with green phosphorescence, but on reversing 
the commutator and obtaining the oval spot, this was seen to be cut across the middle 
by a darker band where the phosphorescence was much less intense. The fight of the 
band was always more intense than that from the spot; the impacts from the one being 
more concentrated than from the other, owing to the shape and position of the poles; 
moreover the experiments had been first tried with the corrugated pole negative. The 
glass along the band gradually becomes deadened by repeated impacts, and will not 
readily phosphoresce in reply to the weaker blows from the flat plate, although it still 
