224 CARNEGIE INSTITUTION OF WASHINGTON. 



cessful of these is a tellurium-silver couple, used in vacuo, which has 

 given excellent preliminary results. Further studies will soon deter- 

 mine the best arrangement of this apparatus for the purposes in view 

 (p. 286). 



Closely connected with these problems is the question of the con- 

 stancy in position of the telluric lines, often used as standards in the 

 solar spectrum. A long series of very careful measures of oxygen and 

 water- vapor lines by Dr. St. John and Mr. Babcock has failed to con- 

 firm the large changes in wave-length found by Perot. They conclude 

 that these lines are practically constant in position, and are thus of 

 great value as standards (p. 245). Messrs. St. John and Nicholson, 

 using a dispersion of 3 angstroms per millimeter, have been able to 

 prove beyond question that both oxygen and water-vapor lines are 

 absent from the spectrum of Venus. With the high dispersion em- 

 ployed, the relative velocity of Venus and the earth was sufficient to 

 separate completely from the telluric lines any corresponding lines 

 originating in the atmosphere of Venus. The absence of oxygen 

 and water-vapor lines raises the question whether equal dispersion 

 would show them in the spectra of other planets (p. 248). Professor 

 Russell points out that St. John's proof of the absence of oxygen in 

 the atmosphere of Venus is in harmony with the slight indications of 

 oxygen in sun-spots, and the abundance of unoxidized material in 

 volcanic gases and in the earth's crust. A planet, if formed from the 

 outer layers of the sun, would contain little oxygen. This suggests 

 that the oxygen in the earth's atmosphere may be a product of vegeta- 

 tion in geological times (p. 241). 



From a discussion of 56 spectrograms of Venus and 41 of the sky, 

 Mr. Nicholson finds that the discrepancies between the wave-lengths of 

 Venus and sky lines may be attributed to the effect of atmospheric 

 refraction (p. 247). 



Another piece of related work is the investigation of the spectrum 

 of an iron arc on Mount Wilson by Dr. Anderson and Mr. Babcock, 

 as observed from the Pasadena laboratory at a distance of 7 miles, 

 equivalent to 1 .4 atmospheres. Under poor conditions of observation 

 the spectrum has been photographed as far as X2740, although the solar 

 spectrum ends at X2890. The work will be continued under better 

 atmospheric conditions (p. 292) . In this connection reference may also 

 be made to the identification by Dr. Merrill of additional air-lines in 

 the spark spectrum in pure oxygen (p. 292). 



The effective wave-length of sunlight has been determined with high 

 precision at Pasadena and on Mount Wilson by Mr. Anderson, with 

 results indicating that it is practically constant from the zenith down 

 to an altitude of 30°. By using this value it becomes possible to calcu- 

 late with sufficient accuracy from color indices the effective wave- 

 length of the light of any given star, as required in the reduction of 

 interferometer measures of its angular diameter (p. 245). 



