RUMFOKD SPECTROHP:LI()()rvAPir OF THE YERKES 



OBSERVATORY." 



BV (iKORGE K. IIaI.K aiul FkKDINANI) ELLERMAN.& 



INTRODIKTION. 



The application of th(' s})ectr()scope in ISCxS to the observation of 

 solar prominences in full sunlight opened an extensiA^e field of 

 research and diivcted the attention of astronomers to the importance 

 of applying: tiie powerful 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 

 inijiortance of solar in\'estio-ation. 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 s})ectroscopic 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 prol)lems encountered in the study of stellar evolution 

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

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

 tion of the sun in 1(S:V,), has furnished an innnense amount of valuable 

 information, there appears to f)e an exceptional opportunity at the 

 present time to secure new and important results, especially through 

 the use of the large sj^ectroscopes and othei- powerful instruments 

 of the physical laboratory. For solar spectroscoj^y has by no means 

 kept pace with laboratory spectroscopy; few large grating spectro- 

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

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

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

 erally available are still awaiting application in solar reseai'ch. 



« Abstract, by permission, from tlie rublications of the Yerkes Observatory, 

 Vol. Ill, Fart I. 1904. 



6 Although this paper has been written by myself, for convonionce of refer- 

 ence to previous studies and opinions it belongs also to ;\Ir. Ellerman, because 

 of his important share iu the work. — G. E. H. 



131 



