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[ 351 ] 
VI. The Ultra- Violet Band of Ammonia , and its Occurrence in the 
Solar Spectrum. 
By A. Fowler, F.R.S., Professor of Astrophysics, and C. C. L. Gregory, B.A., 
Research Student, Imperial College, South Kensington. 
Received December 15, 1917,—Read January 24, 1918. 
[Plate 2.] 
Introductory. 
A question of great interest in connection with the solar spectrum is that of the 
origin of the thousands of unidentified faint lines which were catalogued by Rowland 
in his “Preliminary Table of Solar Spectrum Wave-lengths.” Some of these lines 
may possibly be identical with faint lines in metallic spectra which have not yet been 
completely tabulated, but in view of the presence of bands of cyanogen, carbon and 
hydrocarbon, the possibility of the correspondence of most of them with band spectra 
of other substances should not be overlooked. 
As a contribution to this inquiry, the present investigation was undertaken 
primarily in order to determine whether Group P in the ultra-violet region of the 
solar spectrum might not be mainly due to the presence of ammonia in the 
absorbing atmosphere of the sun. Ammonia was already known to give a remark¬ 
able band in this region, having its position of maximum intensity near X 3360, but 
it had not been investigated in sufficient detail to permit of an adequate comparison 
with the solar tables. Photographs have accordingly been taken with spectrographs 
of high resolving power for the purpose of this comparison, and, as will appear from 
the details which follow, it has been established that the ammonia band is certainly 
represented in the solar spectrum, and accounts for a considerable number of faint 
lines for which no other origins have been suggested. 
In view of the unusual appearance of the band, an attempt has also been made 
to elucidate the chief features of its structure. 
Previous Observations. 
The characteristic ultra-violet band of ammonia, about X 3360, appears to have 
been first described by Eder, who observed it in the flame of ammonia burning in 
VOL. CCXVIII.-A 566. 3 a [Published June 5, 1919. 
