52 CARXEGIE IN.STITUTION 



physical laboratory and require laboratory conditions for their suc- 

 cessful use. No existing organization proposes to do this work 

 under these conditions, and there is no prospect that it will be 

 undertaken unless b^' the Carnegie Institution. 



Advantages to be Gained Through Improved Atmospheric Conditions. 



Up to the present time practically all observations of the sun have 

 been made from the lower regions of the atmosphere. This surrounds 

 the observ^er in a vast fluctuating mass, which reduces the brightness 

 of the heavenly bodies by nearly one half, and transforms their 

 images, which should be sharp and clearly defined, into boiling and 

 confused objects, in which the delicate details of the originals are 

 almost wholly concealed. At rare moments of comparative calm, 

 glimpses may be had of structure of indescribable delicacj^ but if 

 partially rev^ealed for a moment it is instantly swallowed up by dis- 

 turbances in the atmosphere. It is as though the astronomer were 

 forced to make his observations from the bottom of an ocean, whose 

 constant storms are not confined to its surface, but penetrate the 

 utmost depths, churning them into a seething mass, through which 

 all external objects .seem vague and ill defined. It is evident that 

 such disturbances in our atmosphere must prevent not onl}' a clear 

 and perfect understanding of the solar structure, but in no less 

 degree an accurate and reliable measure of the intensity of the solar 

 radiation, which will seem to vary with the fluctuations in the 

 atmospheric absorption. 



A sharp distinction must here be drawn between two very different 

 kinds of disturbances which the atmosphere produces. 



(i) In the measurement of the sun's heat radiation, to determine 

 whether it varies from year to year, the absorption of the atmosphere 

 is the principal obstacle. No solar image is required, and local dis- 

 turbances due to irregular refraction are of little consequence. The 

 absorption may evidently be obviated in large part by making obser- 

 vations from the summit of a very high mountain, at a point well 

 above the denser portion of the atmosphere where most of the ab- 

 sorption occurs. 



(2) The detailed study of the various phenomena of the sun's 

 surface, on the other hand, is impossible without a large and well- 

 defined image, free from disturbances caused by local inequalities of 

 temperature in our atmosphere. Currents of warm and cold air, 

 especially if they are in the neighborhood of the instruments, are 

 fatal to successful work. 



