204 F. W. Very— On the Solar Constant. 



energy (in spite of a certain distinction which will be explained 

 presently), which is not entirely constant at all levels because 

 certain layers of air add their own radiation, while others 

 absorb more than they emit ; but the quantity which needs to 

 be considered in a comparison with the continuous ilux of 

 solar radiation is the average flux through the entire air 

 column, and not the sum of the fluxes through so many kilo- 

 meter layers ; that is to say, these sums should be taken, but 

 should be divided by the number of layers if the numbers are 

 to represent a flux of radiant energy measured in " gram cal./ 

 cm 2 min." 



Although the numbers given {pp. cit., p. 278) are in this 

 sense wrong, their ratios may be right, provided the arithmeti- 

 cal work of the similarly erroneous computations has always 

 been performed in the same way ; and thus it is of interest to 

 note that the thermal properties of the atmosphere as a whole, 

 derived from the thermodynamic equations, agree with those 

 of a black body computed by Stefan's law, although the atmos- 

 pheric selective radiation is only a little more than one-third 

 as great. This result is in general agreement with that which 

 I announced in my "Note on Atmospheric Radiation."** 



The form in which Bigelow states his radiant equation, 

 I + J a+ B = A, 

 is not unlike that which is introduced in my paper on " The 

 Solar Constant," f where, however, B stands for lost radiation, 

 either reflected from the atmosphere, or absorbed in lines too 

 fine to be discriminated by the bolometer, or in broad hazy 

 bands of such indefinite limits that they are not easily recog- 

 nized. In this case B increases from nothing at the outer 

 limit of the atmosphere to a value which may be greater than 

 I at sea-level. This represents a fact of nature. My measures 

 of the Earth's albedo J show that a fraction of the solar rays 

 which is equivalent to a thermal quantity of this order is 

 reflected back to space by the Earth, and chiefly by the atmos- 

 phere of the Earth ; but the losses by reflection can not pos- 

 sibly enter into any thermal equation of earth or air, and can 

 not possibly be determined from the equations of atmospheric 

 thermodynamics, which is Bigelow's proposition, because the 

 reflected radiation has never been absorbed by material sub- 

 stances and can not affect their temperature in the slightest. 



If Bigelow's B represented loss by reflection from succes- 

 sive layers of the air, it would increase gradually from zero at 



* This Journal (4), vol. xxxiv, pp. 533-538, December, 1912. 



f Monthly Weather Review for August, 1901 ; reprinted as Weather 

 Bureau Publication No. 254, cf. p. 26-27. 



% " The Earth's Albedo, " by Frank W. Very; Astronomische Nachrich- 

 ten, N r . 4696, excvi, 269-290, November, 1913. 



