246 



CARNEGIE INSTITUTION OF WASHINGTON. 



that the wave-length increased from morning to noon and decreased 

 from noon to evening, and referred this apparent change in wave- 

 length to a recession of the absorbing centers from the earth with a 

 velocity of 3.15 km. per second. Owing to the importance of atmos- 

 phere lines as standards in the solar spectrum, an extended series of 

 observations has been carried on by Messrs. St. John and Babcock 

 at Mount Wilson. 



On the B Band at X6800. 



Grating spectrograms of the sun's center were taken in February 

 1919 at sunrise, noon, and sunset, on which 8 oxygen lines were meas- 

 ured with the Rowland wave-length of the solar lines as standards. 

 After corrections for the motions of the earth, the mean, noon minus 

 morning and evening, is +0.002 a. To correspond with Perot's 

 results, the changes from morning and evening to noon should have 

 been +0.043 and +0.039 a. 



In June 1919, 28 lines of the B group were measured with the inter- 

 ferometer, using international wave-lengths of the solar lines as stan- 

 dards. The deviations from the mean for all observations are as 

 follows: 



Within the limits of error, the wave-lengths from these observations 

 of the 28 lines are independent of the altitude of the sun. To agree 

 with Perot's observations, the noon wave-lengths should exceed those 

 at 5 o'clock by +0.043 a. 



On the a Band at X6300. 



Grating spectrograms of the sun's center, with international solar 

 wave-lengths as standards, give for the mean of 8 lines in the a band: 



