336 SMITHSONIAN MISCELIvANEOUS C0LL1;CTI0NS VOL. 52 



numbering among its members most of the active observers in this 

 field, has now divided the spectrum into Hmited regions, one of v^hich 

 is selected by each observer. With the aid of the photographic map 

 mentioned below, an observer may easily make an exhaustive study 

 of the lines he has chosen. Although it will be shown that pho- 

 tographic observations are far superior to visual ones in most work 

 on spot spectra, there are various phenomena in which the eye still 

 has the advantage of the sensitive plate. The Solar Union has al- 

 ready secured valuable results through this cooperation, and many 

 more may be expected in the future. 



In accordance with a plan prepared by another committee of the 

 Solar Union, the Sun is photographed almost every hour of the 

 twenty-four with spectroheliographs in India, Sicily, Germany, 

 France, Spain, England, Wisconsin, and California. This nearly 

 continuous record of the calcium flocculi will soon be supplemented 

 by similar work in Mexico, and there is some reason to hope that 

 the Japanese and Australian governments will assist in overcoming 

 the breaks in the record due to the absence of spectroheliographs 

 between California and India. 



Other committees are formulating plans for a cooperative attack 

 on the problem of the solar rotation, securing greater uniformity 

 in the methods of recording observations of the solar prominences 

 and inquiring as to the advisability of coordinating the plans of 

 eclipse expeditions. In every phase of the work the results to be 

 derived from personal initiative and individual effort are recognized 

 as likely to transcend in importance any that may follow from 

 routine cooperation. From this standpoint the best accomplishment 

 of the Solar Union is the creation of a renewed interest in solar re- 

 search and in related problems of physics and astronomy. Every 

 member is strongly encouraged to develop and extend his own ideas 

 and methods, an aim by no means incompatible with the prosecution 

 of cooperative work in fields where routine observations are essential. 

 It is hoped that the large attendance and hearty interest which char- 

 acterized the recent meeting of the Solar Union in Paris may not be 

 lacking when the members again come together on Mount Wilson 

 in 1910. 



The Mount Wilson Solar Observatory 



The Carnegie Institution was not slow to recognize the exceptional 

 opportunities which, through a fortunate combination of circum- 

 stances, lay open to its proposed solar observatory. These included : 



I. The application to the study of the Snn and stars of powerful 



