ADVISORY COMMITTEE ON ASTRONOMY 1 47 



It has been surmised within recent years that the amount of ra- 

 diation of the Sun is variable, with an average period of approxi- 

 mately eleven years, corresponding with the period of maximum 

 frequency of Sun spots It has thus far been impossible to de- 

 termine this, and the possible change in the solar atmosphere, be- 

 cause of the variability of absorption of the terrestrial atmosphere. 

 This subject should form an important part of the investigations to 

 be undertaken by a supposed high-altitude observatory. The writer 

 has long believed and said that a variability of the absorption of the 

 solar envelope is a piobabie cause of the (probable) variabiHty of 

 the solar radiation, Investig-ation of the solar atmosphere should 

 therefore go on at the same time as that of the Earth, and this inci- 

 dentally gives another need for the Ingh station, for this part of the 

 work demands such a large and motionless solar image as can rarely 

 be obtained in our lower atmosphere. 



I have said little of the instrumental means for these principal 

 objects, but the:/ would be largely fitted to thermal studies. These 

 studies would be associated with daily photographic records of the 

 face of the Sun, and perhaps magnetic records and investigations 

 into the emanation of X-rays and others. The barest suggestions 

 of what may be done in the illimitable field are here given. 



To conclude, these studies are utilitarian in the highest sense, for 

 though we may never hope to af?ect the original source of solar ra- 

 diation by any human effort, there is every hope that we may learn 

 to forecast itsetlects upon the earth and provide for them.* 



S. P. Langley. 



Appendix E to Report of Committee on Astronomy. 



PRESENT vSTATK AND NEEDS OF ASTRONOMICAL 



RESEARCH. 



By Simon Nswcomb. 



Of the two great branches into which astronomical research is at 

 the present time divided, astronomy proper and astrophysics, the 

 latter has been so fully treated in the papers submitted by Professors 



*See letter of February ?8, 1902, addressed to Mr. C. D. Walcott, Secretary 

 of the Carnegie Institution, printed on page no. 



