RUMFOiU) spectrohelioOraph of the yerkes 



OBSERVATORY." 



By (JEORtiE E. IIalk aiul Fkrdinand Ki.lekman.6 



INTRODUCTION. 



The application of the spectroscope in 1S(J8 to the observation of 

 sohir prominences in full sunlight opened an extensive field of 

 research and directed the attention of astronomers to the importance 

 of applying the poAverful instruments and methods of the physical 

 laboratory to the study of the sun. Since that time the rise and 

 development of stellar spectroscopy have further emphasized the 

 imi^ortance of solar investigation. For it can not be too often 

 repeated that the sun is the only star whose phenomena can be 

 studied in detail; in interpreting the spectroscopic phenomena of 

 all the other stars we must therefore return in every instance to the 

 sun. If its infinitely varied and complex activities were well under- 

 stood, the problems encountered in the study of stellar evolution 

 would be greatly simplified. But although the constant use of the 

 spectroscope, dating back to the discovery of the chemical constitu- 

 tion of the sun in 1859, has furnished an immense amount of valuable 

 information, there appeal's to be an exceptional opportunity at the 

 ])resent time to secure new and important results, especially through 

 the use of the large spectroscopes and other powerful instruments 

 of the physical laboratory. For solar spectroscopy has b}^ no means 

 kept pace with laboratory spectroscopy; few largo grating spectro- 

 scopes, such as are foinid in every physical laboratory, have ever 

 been employed to study a large image of the sun. This being true, 

 it is less renuirkable that other laboratory instruments not so gen- 

 erally available are still awaiting application in solar research. 



" Abstract, by pennission, Iroiu the Publications of the Yerkes Observatory, 

 Vol. Ill, Part I, 1904. 



''Altbough this paper has been wrirtcn by myself, for coiivcnicnco of refer- 

 once to previous studies and o[)inions it belongs also to Mr. Ellernian, because 

 of. his important share iu the work.— G. E. U, 



131 



