244 CAMPBELI^CROCKER ECLIPSE EXPEDITION. 



Slide No. lo is an enlargement showing one of these sections on 

 a still greater scale. The division of this part of the corona into 

 three sections by the two intervening vacancies is clearly marked. 



The corona of 1893, at sunspot maximum, slide No. 11, does not 

 show this interesting phenomenon to have been present. Why it 

 should have been observed so much more conspicuously in 1918 

 than at other time remains unanswered. 



My colleague, Dr. Moore, had attempted to correlate the main 

 features of last year's corona with the prominences then visible and 

 with the positions of sunspots and faculse as they existed on the day 

 of the eclipse. The Mount Wilson Observatory has generously lent 

 its solar photographs secured on that day, and on several days pre- 

 ceding and following, for this purpose, and we gladly make due 

 acknowledgment of our indebtedness. Lantern slide No. 12 illus- 

 trates the position of coronal structure, prominences, sunspots, and 

 faculas, at the instant of the 1918 eclipse, as measured roughly, or 

 estimated, from the Mount Wilson observations obtained on the 

 several consecutive days. The features on the front side and near 

 the limb of the solar sphere are illustrated on the central circle of 

 the slide, and the features thought to be on the rear side of the sun 

 are set down on the right and left wings of the slide. The well- 

 defined symbols represent the spots and the poorly-defined markings 

 the faculse. It cannot be said from this sketch that the prominences 

 were situated above visible sunspots or f aculae. The hooded coronal 

 forms therefore appear not to have been controlled from centers of 

 disturbance coinciding with spots or faculas. The vacancy in the 

 coronal structure directly to the right of the sun is approximately 

 in a plane passing through the observer, the center of the sun, and 

 the group of spots and faculse visible in the sketch to the right of 

 the center, but, in view of the positions of the two principal promi- 

 nences on the right edge of the sun, occupying the central points of 

 their hooded structures, we seem not justified in looking further at 

 present for a relationship between the vacancy in the coronal struc- 

 ture and the group of spots and faculae. This group is really more 

 than 40° from the sun's east limb. 



Professor Perrine's coronal photographs of 1901, in Sumatra, 

 recorded what he called a " disturbed " volume of the corona. It is 



