ADVISORY committe;e; on astronomy 131 



will not suffice in a thorough investigation of stellar evolution. 

 Constant appeal must be made to laboratory experiments for the 

 elucidation of celestial phenomena. The fact that some of the in- 

 formation required may be obtained at a future date in some physical 

 laboratory by no means meets the need for immediate results. Cases 

 are constantly arising in which much time could be saved if a good 

 collection of physical apparatus, especially designed for radiation 

 experiments, were at hand. But it is not only for incidental re- 

 searches that such apparatus is needed. The advantage of carrying 

 on extended physical investigations in direct connection with solar 

 and stellar work is frequently very great. Evidence of this, based 

 upon the peculiar radiation phenomena of hydrogen in certain stars 

 and of carbon in others, the lack of extensive information regarding 

 the effect of pressure on radiation, etc., might be multiplied indefi- 

 nitely. The bearing of this on the importance of laboratory work 

 in observatories and incidentally on the nature of astrophysics and 

 its needs is sufficiently obvious. 



This illustration of the intimate relationship of solar, stellar, and 

 laboratory phenomena, drawn from a single research on the evolu- 

 tion of the red stars, is intended to give an idea of the variety of the 

 questions which present themselves in astrophysical investigations 

 and the necessit)'- of providing new instruments to answer them. 

 Consideration of such questions as these has led to the following 

 conclusions, which seem likely to have some bearing on the progress 

 of astrophysics. 



1 . In many investigations it is desirable that stellar, solar, and 

 laboratory researches should be planned and executed from a single 

 point of view, and, if possible, in a single institution. For this 

 reason observatories in which astrophysical work is done should be 

 well equipped with physical apparatus in order that special labora- 

 tory researches can be made when necessary. 



2. Solar researches in great variety are urgently needed. Few 

 fields of investigation offer such opportunities for important advances. 



3. I^aboratory conditions should be more completely realized in 

 stellar and solar research. In this connection it is worth while to 

 recall the fact that the spectroscope, even more truly than the tele- 

 scope, is the chief instrument of the spectroscopist, and hence that 

 provision should be made for its use under the most favorable con- 

 ditions. 



4. Much attention should be devoted to the improvement of pho- 

 tographic plates and processes. A comparatively small advance in 

 this direction may double the power of a telescope. 



