218 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 10 
decrease in the index between 500 and 650°C. is due to the decrease in density 
caused by the rapid increase in the expansivity of glass in this region. 
It is usually assumed that the index changes according to the relation 
w—l 
d 
between 20 and 500°C., while the density decreased. This increase in index 
must be due to the same influence that causes the ultra-violet absorption 
band to move toward the longer wave-length region when glass is heated. 
The effect of this cause must be the difference between the measured value 
for the index and the value computed from the density relation. This was 
found to increase at a constant rate even through the critical region between 
500 and 600°C. 
By invitation, Mr. C. C. Kiss presented a paper on Regularities in the 
sprectra of chromium and molybdenum. The paper was illustrated with 
lantern slides and was discussed by Messrs. Monier, HAwKESWORTH, 
Merceers, SosMAN, and HUMPHREYS. 
Author’s abstract: The elements in whose spectra series have been found 
fall, with a few exceptions, in the first three columns of the Periodic Table. 
The unravelling of series relationships in the spectra of the other elements 
has been delayed partly because of the complexity of their spectra but chiefly 
by the lack of reliable wave-length data in the spectral regions to the red of 
wave-length 6000 A. Recent studies of the are spectra of chromium and 
molybdenum at the Bureau of Standards have led to the discovery of series 
and other regularities in them. The same types of series exist in both spectra. 
In each spectrum, there are two systems of series whose members are widely 
separated triplets. ach system consists of a principal, sharp, and diffuse 
series, the members of which are separated from the homologous members 
of the second or parallel system by constant frequency differences. For 
chromium the characteristic triplet separations are Au. = 112.4, Au = 81.4 
and Av,’ = 115.1, Ave’ = 91.4; while for molybdenum the corresponding 
data are Ay, = 448.5, Ave = 257.5 and Any’ = 379.9, Ave’ = 233.4. In 
addition to the wide triplets, each spectrum contains narrow triplets of which 
the separations are Av; = 8.8, Av2 = 5.6 for chromium, and Ay; = 121.5, 
Av, = 87.0 formolybdenum. Besides the series regularities there exist in each 
spectrum other regularities known as multiplets. These consist of groups of 
nine or twelve lines linked together by constant frequency differences. Since 
more lines of the spectra of these elements have been assigned to multiplets 
than to series, it would seem to indicate that the multiplet rather than the 
series type of regularity is the predominant one in complex spectra. 
= Cor a similar relation. With glass, however, the index increased 
880TH MEETING 
The 880th meeting was a joint meeting with the Washington Academy 
of Sciences held in the Cosmos Club Auditorium on Saturday, March 10, 1923. 
President VAUGHAN of the Washington Academy of Sciences took the chair 
with 90 persons in attendance. 
Dr. Brices introduced Professor A. SOMMERFELD of Munich, who ad- 
dressed the joint meeting on the subject Evidence for the theory of relativity 
afforded by atomic physics. The address was illustrated with lantern slides 
and was discussed by Messrs. BAurR, Monter, HAWKESWoORTH, and Foore. 
On motion of Dr. Briaas, the joint meeting accorded Professor Sommerfeld 
a rising vote of thanks for his address. 
