130 CARNEGIE INSTITUTION 



showing the gradual changes from star to star, which rr.ark the 

 steps in their evolution from nebulas. 



Every research bearing on stellar evolution is certain to raise 

 questions of great interest, to answer which additional stellar, solar, 

 or laboratory researches will be required. The spectra of red stars, 

 for example, have been found to resemble in a most interesting way 

 the spectra of Sun spots. On the strength of this one might be 

 tempted to conclude that these siars, which probably represent the 

 last stage of stellar evolution, are covered with spots like those on 

 the Sun. Such a conclusion would have an important bearing on 

 theories of the Sun, and perhaps on theories of variable stars. But 

 with existing instruments the question cannot be settled. What is 

 needed is a powerful grating spectroscope, such as Rowland used in 

 his work on the Sun, mounted immovably in a constant temperature 

 laborator}', and supplied with starlight by a special form of reflect- 

 ing telescope. The special conditions thus realized would permit 

 the exposure of a photograph to be continued from night to night, 

 thus compensating for the faintuess of the highly dispersed star- 

 light. Even with very long exposures, hov/ever, onlj' a few of the 

 brightest red stars could be investigated in this way. For this rea- 

 son the reflecting telescope employed should be of the greatest pos- 

 sible aperture. Many other astrophysical researches, such as the 

 determination of the amount of heat radiated by the stars, could be 

 made vv'ith such apparatus. 



Thus one of the first questions raised by this study of stellar evo- 

 lution suggests a new combination of instruments, which should 

 render possible many important advances. Another question illus- 

 trates the urgent need for solar research. Available information 

 regarding the spectra of Sun spots is wholly inadequate for tiie pur- 

 po.ses of this investigation of the red stars, or for any s3/stematic 

 study of the spots themselves. It is remarkable that so many appli- 

 cations of the best spectro.scopic methods to solar investigations are 

 still to be made. Here, as in the case of the red stars, the nature 

 of the work to be done is such as to require the use of instruments 

 now employed only in the physical laboratory. If a small fraction 

 of the enthusiasm so admirably shov.m on the occ:^sion of total 

 eclipses with a moderate share of the funds could be devoted to solar 

 research at homiC our knowledge of the Sun would lose nothing by 

 the exchange. 



But even the simultaneous study of the Sun and stars with instru- 

 jueuts much better adapted for the purpose than those now employed 



