GG4 PROCEEDINGS OF THE AMERICAN ACADEMY. 



which gives not far from what we had before, since it lowers the re- 

 sulting temperature for Mars by only about 4° F. or 2° C. 



Albedo and Air, 



Some interesting conclusions follow on the investigation of plane- 

 tary albedo. 



If we classify the various planets according to their atmospheric 

 envelopes, we shall discover a significance in their several albedoes. 

 Three classes stand forth distinct : 1. those possessing no air ; 

 2. those with air but wholly or in part cloudless ; 3. those with a 

 cloud covering. Into these classes the planets fall in the manner 

 below, while the albedoes they respectively present are placed along- 

 side of them. 



I. Airless Bodies. Albedo. 



Mercury 17 



Moon 17 



II. Air-enveloped Bodies. 



Venus, Cloudless "I ht t • 92 



Earth, 50 % Cloudless r^^^™ ^^^ 77 



Mars, Cloudless, thin air 27 



III. Cloud-canopied Bodies. Albedo, 



Jupiter 75 



latest measures. 



c, , ^^ f or.78 by Struve's 



Saturn 88 j ^ 



Uranus 73 



Neptune 63 



The albedo of cloud is .72. Whence it is clear that cloud cannot 

 account for the albedo of Venus, but that it accords with the albedo 

 of the four major planets. That an air-envelope increases the albedo 

 of a planet is witnessed first by the greater brilliancy per unit of 

 disk of the earth, Venus, and Mars as compared with the airless bodies, 

 Mercury and the Moon, and secondly, by the relative specific bright- 

 ness of Venus and Mars, together with what has above been found as 

 to that of the earth. It appears that the denser the air surrounding 

 the planet the more dazzling the aspect the planet presents. This is 

 undoubtedly due not to the gases themselves, but to the solid or liquid 

 particles the gases support in the shape of dust, ice-particles, or drops 

 of water. 



This testimony of the albedo that Venus is not cloud-covered but 

 atmosphere-hid is corroborative of the observations made by me at 



