NO, 1865 OUR knowledge; of THD sun HALE 335 



Cooperation in Solar Research 



The widespread appreciation of the importance of solar investiga- 

 tions is ilkistrated by the formation of the International Union for 

 Cooperation in Solar Research, which counts among its members 

 astronomers and physicists in many parts of the world. In the es- 

 tablishment of the Union the initiative was taken by our National 

 Academy of Sciences, which invited various academies, as well as 

 astronomical and physical societies in Europe and America, to send 

 delegates to a preliminary meeting at Saint Louis in September, 

 1904. The favorable responses and the presence of delegates from 

 the academies of Paris, Stockholm, Saint Petersburg, and Vienna, 

 the Royal Society and the Royal Astronomical Society of London, 

 the physical societies of Paris and Berlin, and other leading scientific 

 bodies on both sides of the Atlantic promised well for the future 

 of the Union. The preliminary organization efifected at Saint Louis 

 was given more definite form at Oxford a year later, where coopera- 

 tive work was set on foot in the study of the spectra of Sun-spots, 

 solar photography with the spectroheliograph, and the measurement 

 of the solar radiation. It was also decided to adopt a new system 

 of standard wave-lengths, based upon Michelson's determination of 

 the length of the international meter in terms of the wave-length of 

 the cadmium lines. The high degree of precision attained by Row- 

 land in his Table of Solar Spectrum Wave-lengtJis no longer suffices 

 for the needs of spectroscopists. The new system, based upon stan- 

 dards measured with extraordinary accuracy by the interferometer 

 method, should provide a firm foundation for all spectroscopic in- 

 vestigations, whether of an astronomical or physical nature, for 

 many years to come. As the primary standards are being measured 

 by French, German, and American physicists, it will soon be possible 

 to prepare new tables of the wave-lengths of the lines in solar, me- 

 tallic, and gaseous spectra. A grant to assist in this work has been 

 made by the Bache Fund, and it is hoped that the publication of the 

 tables may be undertaken by the National Academy. 



The spectra of Sun-spots, as will be shown later, contain a great 

 number of lines, which require the most careful study. Hitherto 

 our knowledge of spot spectra has been derived almost exclusively 

 from the results of visual observations, made by individual observers 

 without the aid of a general plan. As a natural consequence cer- 

 tain regions of the spectrum have been altogether neglected, and the 

 time required for the identification of the lines has seriously limited 

 the amount of work accomplished. A committee of the Solar Union, 



