—— eS otis . 
mil a ee Aa 
get Mak 
_— 
-2479°1 
W. Crookes—Spectrum of Helium. 307 
Wave-length. Intensity. 
2944°9 8 A prominent line, only seen in “helium puriss.” 
and in “ broggerite, L.” 
2536°5 8 Seen in “helium puriss.” A mercury line occurs 
2536°72. 
4 Seen in ‘‘ helium puriss.” 
2446°4 2 Seen in “ helium puriss.” 
2419°8 2 Seen in “helium puriss.” 
Some of the more refrangible lines may possibly be due to 
the presence of a carbon compound with the helium. To 
photograph them a long exposure, extending over several hours, 
is necessary. The quartz window has to be cemented to the 
glass with an organic cement, and the long-continned action of 
the powerful induction current on the organic matter decom- 
poses it, and fills the more refrangible end of the spectrum 
with lines and bands in which some of the flutings of hydro- 
carbon, cyanogen, and carbonic anhydride are to be dis- 
tinguished. | 
There is a great difference in the relative intensities of the 
same lines in the gas.from different minerals. Besides the 
case mentioned by Professor Kayser of the yellow and green 
lines 5876 and 5016, which vary in strength to such a degree 
as to render it highly probable that they represent two dif- 
ferent elements, I have found many similar cases of lines 
which are relatively faint or absent in gas from one source and 
strong in that from another source. 
Noticing only the strongest lines which I have called 
“intensity 10,” “9,” or “8,” and taking no account of them 
when present in traces in other minerals, the following appear 
to be special to the gas from uraninite : 
4735°1 4424°0 4371°0 4189'9 3948°2 
4658°5 4399°0 4348°4 4181°5 3642°0 
4428-1 4378°8 4198°6 4157°6 
The following strong lines are present in all the samples of 
gas: 
7065°5 4922°6 4258'8 3885°5 
6678°1 4713°4 4012°9 3885'9 
5876°9 A4AT1°5 3962°3 3819°4 
5015°9 4386°3 3890°5 3705°4 
The distribution assigned to some of the lines in the above 
tables is subject to correction. The intensities are deduced 
from an examination of photographs, taken with very varied 
exposures ; some having been exposed long to bring out the 
fainter lines, and some a short time to give details of structure 
in the stronger lines. Unless all the photographs have been 
exposed for the same time, there is a liability of the relative 
