50 CARNEGIE INSTITUTION 



we may hope immeasurably to strengthen and deepen the founda- 

 tions on which investigations of stellar phenomena are laid. 



Conversely the only means of studying the origin and develop- 

 ment of the sun and of determining what it will become in the 

 future is afforded by the phenomena of stars and nebulae, for we 

 find in the heavens stars in all stages of growth, illustrating every 

 step in the process of evolution by which the sun has been devel- 

 oped from a nebula. Solar research should thus begin with the 

 nebulae, proceed with a physical investigation of those celestial 

 objects which represent the earlier stages of stellar growth, culmi- 

 nate in a study of the solar structure and radiation, and conclude 

 with an examination of the red stars, one of which the sun will 

 some day become. The study of the sun, with the inseparably 

 connected question of stellar evolution, thus presents a single great 

 problem, important alike to the philosopher, the astronomer, the 

 physicist, the chemist, the geologist, and indeed to everj^ one inter- 

 ested in the study of nature. 



Purpose of a SoIvAr Observatory. 



After full and careful consideration of the recommendations of the 

 Advisory Committee on Astronomy* and an extended examination 

 of the various questions involved, we respectfully recommend the 

 establishment by the Carnegie Institution of a Solar Observatory, so 

 situated and equipped as to permit the accomplishment of three 

 principal objects : 



(i) To measure the intensity of the solar heat radiation, and to 

 determine whether it varies from perfect constancy during at least 

 one sun spot period of eleven years. In connection with this inves- 

 tigation, to measure the absorption of sunlight in its transmission 

 through the atmosphere of the earth and that of the sun, and also 

 the radiation of different portions of the sun's image, such as spots, 

 faculae, and prominences. 



(2) To bring to bear upon the solution of solar problems various 

 modern methods of research, principally of a spectroscopic nature, 

 which have not hitherto been applied with adequate facilities. More 

 specificall}^ to provide for the investigation of various solar phe- 

 nomena with the spectroheliograph, the visual and photographic 

 study, with powerful spectroscopes, of the spectra of the chromo- 

 sphere, sun spots, and for other researches of a similar nature. 



*Carnegie Institution Year Book No. i, Appendix A, p. 96. 



