1 6 CARNEGIE INSTITUTION 



scopic, either visual or photographic ; spectroscopic, involving spec- 

 trum analysis in its various forms ; and bolometric analysis of heat 

 radiation. These may be likened to three senses by which solar 

 phenomena can be apprehended and described. One of these senses 

 may become aware of some passing and suggestive phenomenon in 

 regard to which the evidence of the other senses will be immediately 

 required. There would appear to be a strong likelihood that a 

 great gain will be experienced in the study of local developments 

 on the surface of the sun simultaneously from three points of view. 



The chief obstacle to progress, however, appears to reside in 

 atmospheric disturbances which prevent the full advantages that 

 otherwise might be realized from the use of powerful optical appli- 

 ances. There is scarcely any department of astronomical research 

 wherein this difficuly is more acutely felt. Very naturally nearly 

 all astronomical institutions founded by governments and universi- 

 ties have been located in or near capital cities or other great centers 

 of population, where the manifest advantages and stimulus of a 

 scientific atmosphere may be obtained. There is doubtless the 

 desire also to maintain the visible connection between them and the 

 power by which they were created. The observatories of Paris and 

 Berlin are in the heart of great cities. In the case of very few 

 existing observatories can it be said that the choice of site was 

 influenced in any marked degree by a consideration of superior 

 advantages in atmospheric conditions. 



But superior atmospheric conditions are precisely what solar re- 

 search most requires. Where these do not exist, small telescopes fre- 

 quently answer almost as well as large ones. The air is in an almost 

 continuous state of agitation, which prevents the employment of 

 high optical power. Dust and smoke absorb a portion of the solar 

 radiations, and these in an unequal degree. If we are to establish 

 a solar observatory in ideal conditions, we must seek to avoid these 

 disadvantages. While we shall not be able to accomplish this per- 

 fectly, we ought to inquire what gain may be fairly within reach. 



Although the Carnegie Institution is free to locate a solar observ- 

 atory anywhere in the world where this can be done to the best 

 advantage, we have still thought it likely that the proper balance 

 of advantages can be best secured within the United States. For 

 some purposes a subtropical station might offer peculiar advantages 

 for certain sections of this research. If the observatory had but 

 one thing to do, and if the methods of observation could be formu- 



