136 Sioux City Academy of Science and Letters. 



Professor Young suggests that it may be similar to 

 Eoentgen and cathode rays due to ions driven off from 

 the molecules of the solar gases and controlled in their 

 motions by electric and magnetic forces emanating from 

 the sun/^"^ 



Sir Wm. Huggins considers the corona to be a halo 

 of "incandescent fog." Professor Newcomb suggests 

 detached particles, wholly or partially vaporized, while 

 Bigelow presents an electro-magnetic theory, based on 

 a study of the coronal structure as discussed by spheri- 

 cal harmonics; all these theories seem to have some 

 points which can be accepted as true, but the whole 

 problem is still baffling and must await the results of 

 future investigation. 



In concluding this review of the progress of solar 

 physics since the advent of the spectroscope and photo- 

 graphic plate and their application to the study of the 

 sun's consitution, a short account of the problems yet 

 remaining partially or wholly unsolved, the solution of 

 which will so materially assist us in solving some of 

 the great problems of life and energy on our earth, may 

 be of interest. 



Perhaps the most important problems connected 

 with the nature of the sun are, according to Miss 

 Gierke's admirable discussion of the sun as a whole,^'^^ 

 its rotation and its periodicity; regarding the former 

 little more is known at present than before the spectro- 

 scope was applied to the telescope; true it has told us 

 much more about the peculiarities of the sun's rotational 

 motion than could have been deduced from a study of 

 sunspots alone as was done by Carrington and others, 

 but as to the underlying cause of the anomalies of rota- 

 tion nothing is known. Duner has summed up his 

 conclusion thus: "I must confess that this difference 

 betAveen the rotation periods in the different solar lati- 

 tudes appears to me incomprehensible, and constitutes 

 one of the most difficult problems of Astrophysics." ^^^ 



The solar periodicity is another intricate problem 

 awaiting solution by astronomer or physicist. No satis- 

 factory theory has yet been advanced to account for the 

 eleven year cycle first discovered by Schwabe in 1851. 



