REPORT OF COMMITTEE ON OBSERVATORIES 6l 



The peculiar differences in the behavior of the various elements and 

 the characteristic parts they play in solar storms suggest questions 

 which are quite as important to the chemist or the physicist as to 

 the astronomer. The high temperature and the enormous masses 

 of material involved in these solar phenomena far surpass the possi- 

 bilities of laboratory experiments. If the elements can be broken 

 up into simpler forms by intense heat, as the tendency of modern 

 research seems to indicate, the best chance of detecting evidence of 

 such dissociation would appear to be in the sun. If calcium, for 

 example, can be separated by heat into several constituents, these 

 can be photographed with the spectroheliograph in solar storms, 

 where their difference in behavior should betray their separate ex- 

 istence. Results already obtained at the Yerkes Observatory point 

 to interesting possibilities in this direction ; but, in order to deal 

 with the problem successfully, apparatus much more powerful than 

 that now employed must be available for use under superior atmos- 

 pheric conditions. 



Problems without number relating to the solar constitution are 

 ready for solution and demand only a carefully planned attack under 

 suitable conditions. The peculiarities of the solar rotation, rapid 

 at the equator and decreasing toward the poles, have been but little 

 studied. The distribution of the elements in the lower chromo- 

 sphere and the explanation of the absorption which produces the 

 dark lines of the solar spectrum have been subjects of dispute for 

 many years. This problem is now studied only at eclipses, but a 

 large solar image, observed on any clear day with a powerful spec- 

 troscope in a good atmosphere, would permit important advances 

 to be made. The true cause of the darkness of sun spots is not 

 yet understood, and it is even uncertain whether they are cavities 

 or elevated regions. Their minute structure and the remarkable 

 phenomena of their chemical composition will afford indefinite 

 opportunity for research. 



All of these questions and many others are closely dependent upon 

 the sun spot period. As the spots increase in number and activity all 

 other solar phenomena vary in sympathy with them, increasing to- 

 ward the period of greatest intensity and then fading away toward the 

 time of calm. The investigation should therefore extend over a term 

 of at least eleven years, and preferably until after the maximum 

 which occurs about 1916. The advisability of continuing the work 

 longer may be left to be determined in the light of the results ob- 

 tained. 



