248 W. Crookes—Radiant Matter. 
I have here a tube (fig. 4) which will serve to illustrate the 
dependence of the phosphorescence of the glass on the degree 
of exhaustion. The two poles are at a and 3, and at the end 
(c) is a small supplementary tube connected with the other by 
abe gy J fainter and the vacuum becoming non-conducting ; 
ut I should detain you too long, as time is required for the 
duced a change in the electric light from to blue, from blue to indigo, 
and so on to violet and purple, till the medium has at length become so dense 
as no longer to be a conductor of electricity. I think there can be little 
oe ee the above experiments, of the non-conducting power of a perfect 
“This seems to prove that there is a limit even in the rarefaction of air, which 
sets bounds to its conducting power; or, in other words, that the icles of ait 
See ear seperated. from each other as no longer to be able to transmit the 
power and continually increases till their approach also 
