MILLER— SPROUL OBSERVATORY ECLIPSE EXPEDITION. 273 



determine the rotation of the corona, and a sHtless spectrograph 

 were mounted on another polar axis. 



The photographs secured show a moss of coronal detail. The 

 shorter exposures show the coronal arches that surround the great 

 number of prominences that are found on the rim of the sun. 

 These have been so well shown in the slides accompanying the pre- 

 ceding papers that it seems unnecessary to show them again and 

 for economy of time I shall show one only, a slide from the forty- 

 five second exposure with the sixty-two and one half feet focal 

 length. 



The problem that I had more specifically in mind was to secure 

 if possible some data that would contribute to a knowledge of the 

 origin of the corona, to see if we could from a study of the details 

 of its structure get a hint of the nature of the forces that produce it 

 and give it its shape. I shall limit myself to a brief statement of 

 our study of two things. 



1. To see if there was any indication of change of form in the 

 corona itself during the eclipse. 



2. To find if the general form of the streamers in the corona 

 gave any indication of the way in which it is formed. 



I. Change in the Corona. 



Director Campbell, of the Lick Observatory, and Professor J. 

 C. Hammond, Director of the Naval Observatory Station, most gen- 

 erously put at my disposal glass positives of short exposure photo- 

 graphs, made respectively at Goldendale, Washington, and Baker 

 City, Oregon. The Lick plate was made with a camera whose focal 

 length is forty feet. Totality at Goldendale lasted for one minute 

 and fifty-seven seconds. The plate loaned me by Director Camp- 

 bell was exposed from one minute fifty seconds to one minute fifty- 

 two seconds after the beginning of totality. This plate was com- 

 pared with two plates made by the Sproul Observatory expedition, 

 one exposed for two seconds just at the beginning of totality and 

 the other for three seconds just at the end of totality. The focal 

 length of the camera with which these plates are made is sixty-two 

 and one half feet, so that the pictures to be compared were of very 



PROC. AMER. PHIL. SOC, VOL. LVIH, R, AUG. I, IQlQ. 



