THE CROCKER ECLIPSE EXPEDITION FROM THE LICK 

 OBSERVATORY, JUNE 8, 1918. 



Some Eclipse Problems. 



By W. W. CAMPBELL. 

 (Read April 25, 1919.) 



Eclipse observers have always before them two principal ques- 

 tions : 



What is the solar corona? 



Why does the sun have a corona ? 



It must be confessed that the best answers at present available 

 are far from satisfactory and complete. We have established many 

 important facts, especially as to the nature of the corona, but these 

 are more or less isolated facts, with suggestions here and there as 

 to the relations of the facts to each other. That the progress made 

 has not been greater is due to the tantalizingly short time available 

 for observation. In the past twenty-one years I have had a total 

 of twelve minutes in which to secure observations of the corona, 

 and during four of those minutes — in Spain — the observations were 

 made through thin clouds. 



It is not a narrow interest which directs our efiforts. The corona 

 is a part of the sun, and we can never claim to know what the sun 

 is until w^e understand all parts of it, including the corona, and the 

 reasons for the corona's existence. The sunspots, the faculse, the 

 flocculi, and the prominences are undoubted evidence of great activ- 

 ity of movement in the sun's outer strata. It seems not too much to 

 hope that a thorough understanding of the corona will contribute 

 greatly to an. understanding of the sun's circulatory system. 



Again, it is not alone the more thorough understanding of our 

 own sun which supplies the motive for eclipse study. Is there a 

 corona around every sun? There may be; solar coronas may be 

 plentiful throughout the universe, but we do not know. A complete 

 understanding of our own star is certainly a pressing duty to the 



PROC. AMER. PHIL. SOC, VOL. LVIII, P, JULY 30, IQip. 241 



