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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



consists of a series of bright lines, and appears as an inversion of the 

 ordinary solar spectrum. This spectrum is of very great importance 

 for the study of the extreme layers of the sun, and it has been ob- 

 served very completely, especially by W. W. Campbell, of the Lick 

 Observatory, and by S. A. Mitchell, of the Leander McCormick Ob- 

 servatory. S. A. Mitchell, D. H. ISIenzel, and R. Wildt have drawn 

 elaborate conclusions as to the physical constitution of the sun's outer 

 layers from studies of the flash spectrum. In these studies spectra 

 of fairly large dispersion have been used. 



Partial Phase 



Inner contact 



Sharp edge 



Sharp edge 



FxGXJKE 1. — Scbematic picture of partial eclipse and of inner contact between the 

 limbs of the sun and moon. The centers of sun and moon are indicated by S 

 and M. The distribution of intensity along the radius of the solar disk is 

 indicated below. 



For a photometric study of the rapid change in the spectrum at 

 (lie beginning and end of a total eclipse considerably smaller disper- 

 sion may be used, and in this case it is of advantage to ]3hotogi-aph 

 the spectrum with a motion-picture camera. A rather successful 

 attempt at a cinematographic study of the flash spectrum was made 

 in Sweden by O. Wiberg and myself at the total eclipse in 1927. At 

 the same eclipse the Polish astronomer T. Banachiewicz developed 

 a method of determining very exactly the times of contact between 

 the limbs of the sun and moon by direct cinematography of the sun 

 at the beginning and end of the partial and total phases of the eclipse 

 and by a study of the details of the lunar limb which produce the 



