246 CAMPBELL— CROCKER ECLIPSE EXPEDITION. 



graphs separated by the considerable intervals of time, with a view 

 to the detection of motion in coronal structure during the intervals. 

 Clouds prevented observation in Labrador; excellent photographs 

 were obtained through thin clouds in Spain, but the Egyptian photo- 

 graphs were not well-defined, owing to disturbances in the atmos- 

 phere, probably arising from the highly heated desert conditions of 

 the middle afternoon. Slide No. 14 compares an interesting region 

 of the corona as photographed in Spain and Egypt, with cameras of 

 identical dimensions, focal lengths forty feet. The great promi- 

 nence, it will be noticed, was sharply defined in Spain (on the left), 

 but the definition was poor in Egypt (on the right). IMany details 

 of prominence structure changed during the interval of approxi- 

 mately seventy minutes, but we are not concerned especially with 

 changes in prominences, as this is one of their w-ell-known charac- 

 teristics which may be and has been studied successfully on many 

 days of the year at home. A comparison of the coronal structure 

 in the region of the prominence is made difficult by the good defini- 

 tion in one case and the mediocre definition in the other, but there 

 is no doubt that many changes occurred in the coronal details while 

 the moon's shadow was passing from Spain to Egypt. Dr. Perrine 

 and I were unable to say, however, that the motion was outward or 

 inward, or that it was due to decrease of brightness for certain de- 

 tails and increase for others. Expressed dift'erently, there were 

 evident changes of detailed structure, but these changes were appar- 

 ently haphazard rather than due to motion of illuminated materials 

 systematically outward or inward. Nevertheless, that changes did 

 occur in the interval is certain. 



Dr. Moore has compared our 1918 coronal photographs ob- 

 tained in the State of Washington with copies of those obtained by 

 the Lowell Observatory Expedition, in Kansas, thanks to Director 

 Slipher's courtesy. The scales are different, and the atmospheric 

 conditions were poorer in Kansas, so that comparisons of our origi- 

 nals with copies of the Lowell photographs are difficult and unsatis- 

 factory. Nevertheless, many changes in details are noted to have 

 occurred in the interval of one half hour. Some of these seem to 

 be the result of motion outward and others of motion inward, but 

 we are not prepared to say that one or the other motion is the pre- 

 vailing tendency. 



