160 abstracts: physics 



1910 and 1911 at Mount Wilson was caused almost wholly by molecular 

 scattering. From 0.36/z to 0.50^ the depletion is practically wholly 

 of this nature. Then come the great selective absorption l^ands, which 

 except near the D lines, have been eliminated from this discussion. 

 Even in the infra-red between these water-vapor bands, molecular 

 scattering accounts for the observed depletion of radiation bj^ the 

 atmosphere. 



The same analysis applied to atmospheric aqueous vapor shows 

 that the observed absorption is very much too great to be accounted 

 for by the number of water molecules present. The transmission 

 coefficients found by various observers for liquid water, however (0.2 1/x 

 to 0.50m), are such as would be expected from this amount of water 

 in vapor form. This leads to the inference that its absorption in liquid 

 form in this region results from molecular scattering. The number 

 of molecules, No, computed from the transmission coefficients of liquid 

 water is about 



A^o = 28 X 10^^ 



The increased absorption connected with atmospheric water-vapor 

 and the departure of the transmission coefficients from strict propor- 

 tionality to the inverse fourth power of the wave-length in the sense 

 that the coefficients for smaller wave-lengths are too high, leads to the 

 inference that the vapor is loaded with something greater in size than 

 molecules. This loading could be due to dust or iron, although there is 

 not definite evidence why these should be proportional to the amount of 

 water-vapor present. The presence of nuclei, formed by the action 

 of the ultra-violet light of the sun on the moisture present in the air, 

 seems perhaps the most satisfactory explanation. 



In the above study the amount of water-vapor present in the air was 

 measured by the depths of three calibrated selective absorption lines 

 in the infra-red. The effect of scattering, which varies slowly and 

 continuously with the wave-length, was eliminated. It has been shown 

 in an earlier paper {Astrophysical Journal, 37: 359. 1913) that the mean 

 results of such determinations of the amount of aqueous vapor in the 

 atmosphere agree with the mean results of estimates of it from obser- 

 vations with kites and balloons. F. E. F. 



PHYSICS. — Standard density and volumetric tables, 4th edition. Bureau 

 of Standards Circular No. 19. (In press.) 

 In this circular the following tables are included : Table 1 gives the den- 

 sity of water (according to P. Chappuis) at every tenth of a degree from 0° 



