172 Prof. P. Lowell on a Method for Evaluating 



If we assume clouds to transmit less heat than 20 per cent, 

 we diminish y and increase (1 — *35 ^)^ so that the ultimate 

 result is not greatly altered. 



Albedo and Air. — Some interesting conclusions follow on 

 the investigation of planetary albedo. If we classify the 

 various planets according to their atmospheric envelopes, we 



The values for these quantities found bolometrically for a clear sky 

 are : — 



cc = -50, 



A = l— -79 X •32 = 747= whole spectrum — albedo of the air into 

 |8= approximately oc. visible portion, 



„=l--ll=-89. 



For the Earth in its entirety M = and N = (), since what is lost by 

 convection in one place is gained in another. 



Applying this same formula to the case of Mars, we have similarly : — 



^ = •40 approx. 



A 1 = 1 — -^— „(! — '17x'32) = whole spectrum —albedo of its air 

 t'°^± . into visible portion 



= ' 9 i 6 

 1-524 2 ' 



fi l =cc. l approx. 

 „, = !- -13= -87. 

 Whence for the Earth under a clear sky 



rni_ A(l+i>— vsc) # 

 ~~ y{l + v-Pvj ' 



and similarly for Mars, substituting its values for A, as and /3. Since in 

 both «=j8 and y x =7 approx., we have T\ for Mars, which gives 



T 4 A ' 



But the Earth is -50 cloud-covered and the transmission of cloud being' 

 not more than "20 (the value he takes), we have finally 



IV _ A,-99 

 T 4 " A-60' 

 whence 



T L = -974T, 



and T being 519° '4 abs. on the Fahrenheit scale, 



T = 505°-7, that is 46°-3 F. or 8° C, 



a result substantially the same as we have deduced. 



Had we assumed /3 to be *70 and to be in the like proportion to a for 

 Mars, we should have had » 



r,vi IT .,, A 



and 



T 4 =l-140 



7 



M01 A ' ; 



which gives not far from what we had before, since it loweis the resulting 

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



