218 CARNEGIE INSTITUTION OF WASHINGTON. 



the astronomer, but have attacked our problems with the general 

 interests of research in mind, without endeavoring to draw any boun- 

 dary line between astronomy and physics. 



Attractive as the fundamental physical aspects of these problems 

 may be, it is nevertheless plain that their unlimited pursuit by the 

 Observatory staff would result in a scattering of effort and in too great 

 a departure from the paths leading to our primary objectives. It is 

 opportune to consider in the present connection the nature of these 

 objectives and the best means of developing the work of the Obser- 

 vatory in its broader aspect. 



At the outset, as the original name of the Observatory indicated, 

 our plan was to base a general study of stellar evolution on an intensive 

 investigation of the sun, the results of which were expected to guide our 

 attack on other celestial objects. The belief that increased knowledge 

 of our nearest neighbor among the stars would aid in the comprehen- 

 sion of remote stellar objects has not been disappointed, as previous 

 reports have shown. But in one important respect it has become 

 necessary to enlarge the scope of our plan. The relationship between 

 physical development, defining the successive stages in stellar life, 

 and the various elements that determine a star's place in the struc- 

 ture of the universe has proved to be much more intimate than the 

 knowledge then available had led us to recognize. Moreover, the 

 various data, such as radial velocity, parallax, absolute luminosity, 

 etc., thus rendered necessary for the interpretation of stellar spectra, 

 were at hand only in the case of a few of the brighter stars. As our 

 work progressed outward toward the remote stars, the importance of 

 including in our scheme an investigation of the structure of the stellar 

 universe, involving observations of stellar parallaxes, radial velocities, 

 etc., became manifest. The results described in the present report 

 are sufficient evidence of the necessity of this policy. 



Two great problems of astronomy— the evolution of stars and the 

 structure of the universe— have thus been attacked, but an equally 

 important one has hitherto played only a minor part in the scheme of 

 the Observatory. This is the constitution of matter, which in many 

 cases may be approached even more effectively by the astrophysicist 

 than by the physicist or chemist. Helium, rare on the earth but con- 

 spicuous in the solar atmosphere, was first detected there in 1868 and 

 found in a terrestrial source in 1896. The influence of a magnetic 

 field on radiation was visible forty years ago in the spectra of sun- 

 spots, where a great physical experiment, open to observation with the 

 best instruments of that time, was in progress in every spot. Faraday's 

 last experiment, frustrated by inadequate instrumental means, was an 

 attempt to detect the very effect that the magnetic field in spots shows 

 so plainly. To go farther back, the complete Balmer series of hydrogen 

 lines, known in the laboratory only through its four less refrangible mem- 



