ASTRONOMY — HALE. 'J'J 



ingly became of great interest to determine whether the observed changes 

 in spectra could be accounted for by variations in temperature alone, as 

 distinguished from the direct effect of any electrical or other conditions. 

 Mr. Gale found the results of the work with the short arc to be entirely 

 confirmed, in a comparison of the cooler flame of the arc with the 

 core. Since that time all doubt has been set at rest, as regards the 

 sufficiency of an hypothesis based upon change of temperature, by ex- 

 periments made within an electric furnace, where the vapors are inclosed 

 in a carbon tube, the outer walls of which are heated by an electric arc. 

 In the case of iron, for example, the same lines that are strengthened in 

 the synchronous arc at low phase, in the 2-ampere arc, and in the flame, 

 are strengthened in the electric furnace under low temperature condi- 

 tions. This fact, of course, does not preclude the possibility that other 

 causes, such as rapidly changing electromotive force, may operate in the 

 sun and stars, but it surely affords a firm basis for an hypothesis which 

 regards temperature as the most important variable. 



Relationship Between Soi.ar and Magnetic Phenomena. 



The investigations described above relate, for the most part, to the 

 study of the sun as a typical star. Of equal importance, however, is 

 the conception of the sun as the central body of the solar system, with 

 special reference to its effect upon terrestrial phenomena. The possible 

 variation of the intensity of the solar radiation, and its influence upon 

 climate, is the work to which the Smithsonian Institution is devoting 

 its attention. The measurement of the absorption of the sun's atmos- 

 phere, as related to any such variations of the solar radiation, is also 

 receiving attention in our holographic work v/ith the Snow telescope. 

 The variation in the solar activity, as recorded on the spectroheliograph 

 plates, may also prove to have an important bearing on this question of 

 the solar radiation. There stills remains to be considered the relation- 

 ship of the solar activity to terrestrial magnetism. In this department of 

 our vv'Ork we are fortunate in having the cooperation of Dr. L. A. Bauer, 

 Director of the Department of Terrestrial Magnetism of the Carnegie 

 Institution of Washington. 



In previous studies of the relationship between solar and magnetic 

 phenomena, the total area of the sun-spots has been taken as the index 

 of the solar activity. As already remarked, however, this total area may 

 not prove to be the most satisfactory index, in view of the comparatively 

 small size of the spot images and their absence from the disk during 

 long periods near the time of minimum. It seems probable that the 

 photographs of the calcium flocculi will furnish admirable data for the 

 purposes of this research, because of the great total area of the flocculi, 

 the fact that they are never altogether absent from the disk, and the 



