CAMPBELL— CROCKER ECLIPSE EXPEDITION. 245 



shown in slide No. 13. Examining the photographs of the sun ob- 

 tained on and near the day of the echpse, he found that a prominent 

 sunspot, in fact the only conspicuous sunspot known to be on the 

 sun at that time, was situated very close to the sun's limb, and im- 

 mediately under the center of the disturbance in the corona. The 

 same slide shows a small prominence to the left of the sun — near 

 the lower left edge of the slide — with a faint hooded enclosure. 



This subject of relations between coronal structure and other 

 solar phenomena is a very interesting and important one for eclipse 

 observers of the future to hold in mind. 



The Forms of Coronal Streamers. 



The force which carries materials into the coronal region may be 

 volcanic, as Schaeberle and others have suggested, or it may be 

 chiefly radiation pressure, or a combination of these, or indeed a 

 force of quite unknown nature. The arrangement of the coronal 

 materials in the well-defined streamers may be a result of the sun's 

 magnetic properties, as Bigelow and others have thought, but if so 

 the principal features of the 1918 corona, especially to the east and 

 west of the sun, would require that merely local magnetic fields be 

 in control. The polar streamers certainly are very suggestive of 

 control by the sun's general magnetic forces, but this influence does 

 not seem to be the prevailing one in the remaining coronal structure. 



Motion within the Corona. 



Inasmuch as the corona of one eclipse is different in every detail 

 from that of the succeeding eclipse, we cannot doubt the existence 

 of motion and change within the corona. An interesting question 

 is, how rapidly do these changes occur ? Can they be detected from 

 a comparison of coronal photographs of the same eclipse, obtained 

 at two or more stations distributed along the path of totality ? This 

 is a problem which eclipse observers have held in mind during sev- 

 eral decades. The eclipse of 1905 seemed especially promising for 

 an attack upon this problem. Crocker expeditions from the Lick 

 Observatory were located in Labrador, in Spain, and in Upper 

 Egypt, with the principal motive the obtaining of coronal photo- 



