132 REPORTS ON THE STATE OF SCIENCE. 
Some Properties of Light of very Short Wave Lengths. ° 
By Professor THEODORE LyMAN. 
[Ordered by the General Committee to be printed in extenso.] 
THE most refrangible region of the spectrum discovered by Schumann! 
is interesting from two points of view. On the one hand, it affords a 
new field for the investigation of pure spectroscopy, and, on the other, it 
offers opportunities for the extension of the study of photo-chemical and 
photo-electric phenomena. 
In the realm of spectrum analysis something has already been accom- 
plished. Absorption and emission of light by hydrogen, oxygen, 
nitrogen, carbon monoxide, carbon dioxide, argon, and helium have been 
investigated and the absorption of a considerable number of solids has 
been studied. 
The absorption of gases is perhaps the most striking phenomenon to 
be found in this region. One millimetre of air at atmospheric pressure 
is quite sufficient to absorb most of the light of shorter wave length than 
1700 Angstrém units. The oxygen of the air is the chief agent in pro- 
ducing the effect, for this gas possesses a strong absorption band extend- 
ing from nearA 1800 to the neighbourhood of A 1300. The discovery 
of the more refrangible limit of this band is one of the recent results in 
this subject.? 
Hydrogen, argon, and helium when examined in short columns all 
prove perfectly transparent, while the absorption produced by nitrogen 
is extremely slight. | Carbon monoxide and carbon dioxide, however, 
each possess absorption spectra characterised by narrow bands. 
The behaviour of oxygen is obviously different from that of other 
simple gases. This difference may be attributed to a photo-chemical 
reaction typical of this gas. 
From the point of view of the emission of light, hydrogen is the most 
important of the gases examined.* It possesses a strong spectrum, very 
rich in lines extending from » 1650 to 4 1030. This spectrum is much 
weakened when capacity is introduced in the discharge circuit ; it seems 
to correspond to the ‘secondary’ or ‘many line’ spectrum of 
hydrogen in the less refrangible region, but it is not continuous with 
it. Lines of the ‘ primary’ or Balmer type do not appear to exist 
in the region between A 2000 and 41250. This is to be expected from 
theoretical considerations, for the chief series as given by Rydberg‘ 
lies on the less refrangible side of A 2000, and the chief series as given 
by Ritz * lies on the more refrangible side of \ 1250. It seems prob- 
able that the first line of the series predicted by Ritz does exist, but 
so far experimental difficulties have prevented its identification. 
Next in importance is the spectrum produced by carbon monoxide; 
exactly the same spectrum is given by carbon dioxide. It consists of 
a large number of bands, whose heads point toward the violet and whose 
1 Smithsonian Contributions to Knowledge, No. 1413. 
2 Astrophysical Journal, vol. xxvii. No. 2. 
8 Tbid., vol. xxiii. No. 3. 4 Tbid., vol, vi. p. 233. 
5 Ann. d. Physik, v. 25, 1908, p. €67. 
