﻿2 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 47 



INTRODUCTION 



The region of the solar spectrum observed at the Smithsonian 

 Astrophysical Observatory, under the direction of Mr. Langley, is 

 particularly adapted to this study of the spectroscopic absorption of 

 atmospheric water vapor between wavelengths O.68// and 2.0ti. At 

 the time of the publication of the first volume of the Annals of this 

 Observatory, although some attempts had been made at quantitative 

 measures in the atmospheric bands and other places in this region of 

 the solar spectrum, the results were very meager. 1 The holograms 

 then taken, made for the determination of the deviations and wave- 

 lengths of the various absorption lines and bands, were not adapted 

 to measures of the ordinates or intensities. The plates were taken at 

 insufficient speed, and no determinations of the zero of ordinates were 

 made except at the beginning and the end of an hour's run. A 

 subsequent trial proved but little more fertile. 



Within the last two years, in the holographic study of the general 

 atmospheric absorption- and the solar constant of radiation, holo- 

 grams have been taken at twenty times the speed formerly employed, 

 and the zero of ordinates is now determined nearly every minute 

 during the run. Moreover, owing to the improved bolometric appa- 

 ratus, the drift has been reduced to such an extent that no more now 

 may occur in a week than formerly often occurred in an hour. Con- 

 sequently these recent holograms are far better suited to the present 

 discussion of the ordinates, although unfortunately the effective 

 dispersion used is much too small for the best results. 



This paper, then, is devoted to the application of Bouguer's for- 

 mula to measures of the transmission of our atmosphere in the 

 various absorption bands between B (0.687 /x) an d w 2 ( 2 -°5/ Lt )- 

 These various bands are indicated in plate 1, which consists, in figure 

 1, of two superposed holograms, one of February 19, 1903, of very 

 small water vapor absorption, the other of September 14, 1903, and 

 nf -real water-vapor absorption. The bands may be tabulated as 

 foil »ws : 



Table I 



B, atmospheric oxygen, wavelength 0.687// 



a, " water vapor, " 0.718 



A, oxygen, " 0.760 



1 Chapter vn, p. 205, vol. 1. Annals of the Astrophysical Observatory of the 

 Smithsonian Institution, 1900. 



2 Smithsonian Reports for 1902 and 1903. S. P. Langley, Astrophysical 

 Journal, xvn, p. 89, 1903. and XIX, p. 305, 1904. C. G. Abbot, Smithsonian 

 Miscellaneous Collections (Quarterly Issue), vol. 45. i>. 74, 1903. 



