RECENT PROGRESS IX ASTRONOMICAL RESEARCH. 



By C. G. Abbot. 



I. ACTIVITY IX SOLAK INVESTIGATION. 



Each periodic return of the time of maximum sun-spot occurrence 

 brings Avith it a freshened interest and renewed activity in sohir 

 observations. This revival of sohir research has been uncommonly 

 marked of late, and promises a steady and fruitful continuation of 

 work, even now that the sun-spot maximum has passed. Two impor- 

 tant international conferences to consider solar research have been 

 held, the first at St. Louis in 190-1, the second at Oxford, England, 

 in 1905, and an " International Union for Cooperation in Solar 

 Research " has been formed. The success of this promising move- 

 ment has been principally due to the efforts of Prof. George E. 

 Hale and Prof. Arthur Schuster, who by extensive correspondence 

 and personal intercourse with astronomers and physicists, and by 

 obtaining the support of the International Association of Academies, 

 secured a good attendance of men of ability at the two conferences 

 just mentioned. 



To understand the objects of the Union, it may be recalled that not- 

 w^ithstanding that the sun is the promoter of life on the earth, the 

 controller of climate, and the only star which is near enough to admit 

 of detailed study, j^et observation of this, the most important celes- 

 tial object, has hitherto been chiefly limited to eclipse observations, 

 estimations of sun-spot numbers, appearance of the prominences, 

 regulation of time, and occasional observations of peculiarities of 

 spectrum, time of rotation, and distribution of brightness. The 

 nature of sun-spots, the cause of their periodicity, their level as com- 

 pared with the photosphere, the cause of their drift over the surface 

 of the sun, the nature and thickness of the envelope which absorbs 

 the solar rays, the exact wave lengths of the lines in the solar 

 spectrum, the nature of the corona, the amount of the solar radiation 

 available to the earth, the question whether solar radiation is con- 

 stant or variable in amount, the connection between terrestrial mag- 

 netism and solar activity, the dependence of the earth's climate on 

 the solar radiation, the temperature of the sun's surface, the ques- 

 SM 190G 11 161 



