1879*] Molecular Physics in High Vacua. 421 
This, then, is the kind of phenomenon we get in ordinary 
exhaustions. I will now try the same experiment with a 
tube that is highly exhausted, and, as before, will make 
the side pole (a') the negative, the top pole ( 6 ) being positive. 
Notice how widely different is the appearance from that 
shown by the last bulb. The negative pole is in the 
Fig. 6. 
form of a shallow cup. The bundle of rays from the cup 
crosses in the centre of the bulb, and thence diverging falls on 
the opposite side as a circular patch of green light. As I 
turn the bulb round you will all be able to see the faint 
blue focus and the green patch on the glass. Now observe, 
I remove the positive wire from the top, and connect it with 
the side pole (c). The green patch from the divergent negative 
focus is still there. I now make the lowest pole ( d ) posi- 
tive, and the green patch still remains where it was at 
•first, unchanged in position or intensity. 
This, then, gives us another faft which brings us a little 
nearer to the cause of this green phosphorescence. It is this — 
