242 CAMPBELL— CROCKER ECLIPSE EXPEDITION. 



investigator who looks toward the understanding of the stars in 

 general. 



The Form of the Corona. 



Near the end of last century eclipse observers recognized that 

 the outline of the corona is a function of the sunspot phase. Our 

 first slide (No. i) illustrates well this general relationship. The 

 coronas here shown, proceeding from right to left, are, first, that 

 of 1889, at sunspot minimum ; second, the corona of 1893, at sun- 

 spot maximum; third, the minimum corona of 1900; and fourth, the 

 maximum corona of 1905. In all of these the sun's equator is 

 nearly vertical with reference to the slide, and the sun's rotation 

 axis is nearly horizontal. The phenomena in question are illus- 

 trated in a more interesting manner by the second and third slides 

 of the corona on a larger scale. The circular corona (No. 2) is 

 that of the 1893 eclipse, and the greatly elongated one (No. 3) is 

 of the year 1900. 



It is perhaps natural to expect that the polar streamers of the 

 corona should be more extensive at times of great solar activity, as 

 indicated by the maximum phase of spottedness, but that the equa- 

 torial streamers should be the longer at sunspot minimum would 

 scarcely have been predicted. 



It cannot be said, however, that the outline form of the corona 

 is accurately predictable from the known phase of the sunspot-cycle. 

 We photographed the corona (slide No. 4) with cameras of focal 

 lengths varying from four feet to forty feet on June 8, 1918, at 

 Goldendale, Washington. The spot phase was but a few months 

 past the maximum, and we expected the corona to be essentially 

 circular in outline. Our predictions were not fulfilled so satisfac- 

 torily as we had expected. Slide No. 5, an exposure of four sec- 

 onds with a camera whose focal length was four feet, shows stream- 

 ers extending out to approximately three solar diameters to the right 

 and to the left, that is, to the west and east of the sun, whereas the 

 streamers to the north and south (above and below) are very much 

 shorter. The sixth slide is one obtained with the forty-foot camera, 

 exposure four seconds ; the departure from circularity of outline is 

 very marked even for the inner corona. Does the circular type of 



