Evaluating the Surface-Temperatures of the Planets. 751 



effect, and it is worth while to apply them to the Earth, 

 taking the best data at our command. 



At the surface let us take £ — 0*42 and a x — 0'5 as before. 

 For a we have no trustworthy observations, and I doubt 

 whether a calculation from Langley's observations is of any 

 more value than an estimate. Since a varies from perhaps 

 about 0°3 to 1, let us take a = 0'628 or 27r/10, a value 

 simplifying arithmetic. 



At the level of Camp Whitney 3550 metres above sea- 

 level, with barometer about 500 mm., and therefore with 

 about ^ of the atmosphere below it, we may take t = 0'6 and 

 «! — 0'4. For a we must take a value much smaller than 

 that at sea-level. Since the most absorbing third of the 

 atmosphere is below, I do not think it is far wrong to take a 

 as having half the value at the lower level, and I therefore 

 put a — 0*314. But I have also examined the consequences 

 of putting it equal to - 419, i. e. | of its value at the lower 

 level, and the results are given below to show how much the 

 figures are affected by the variation in the value taken. 



We have no data for n. I have therefore calculated the 

 values of R^ and R ?1 in terms of S for successive values of n 

 equal to 1, -J, i, |, 2; corresponding to D equal to A, f A, 

 J A, § A, and i A respectively. 



In the following tables the values of R rf /S and "R n /S are 



given, and also the mean R/S=^(R^ + R n )S. Then follow 

 the ratios of the day and night temperatures, d and n , to 

 the temperature 6 of a black surface radiating S, and the 



mean value 6/0. The last column gives the range 6 d — 6 n on 

 the supposition that £=300° A. 



Table I. - 

 At sea-level. £ = 0'42, ^ = 0-5, «^0'628. 



n. 



D/A. 



Erf/S. 



En/S. 



R. 



6d/0. 



e„/e. 



0/9. 



Range 



about 



300° A. 



1 



1 



103 



061 



083 



1-01 



0-88 



0-95 



41° 



5/4 



4/5 



0'83 



0-41 



062 



0-95 



0-80 



0-88 



51° 



4/3 



3/4 



0-79 



0-37 



58 



094 



0-78 



86 



56° 



3/2 



2/3 



072 



0-30 



051 



092 



0-74 



0-83 



65° 



2 



1/2 



62 



0-20 



041 



089 



0-67 



0-78 



85° 



Phil. Mag. S. 6. Vol. 14. No. 84. Dec. 1907, 



3E 



