NO. 4 SOLAR RADIATION ABBOT, FOWLE, AND ALDRICH 3 1 



without the most careful consideration of the atmospheric transmis- 

 sion coefficients, as indeed Mr. Fowle's researches on the relations 

 of the transmission coefficients to Lord Rayleigh's theory of the sky 

 light have shown, still their effects will be eliminated in the same 

 manner as the infra-red bands were in the investigation just cited, 

 because the transmission coefficients in such spectrum regions will be 

 smaller than they would have been had the bands not been present 

 there. We feel satisfied that the existence of such bands, even if 

 there are any others than those which we know of, would hardly in 

 the slightest degree influence the value of the solar constant of 

 radiation. 



Sixth objection. — In regard to this matter, we think Mr. Very has 

 misinterpreted our procedure. We did not determine the quantity 

 of energy contained in the extreme infra-red part of the emission of 

 a " black body," of the size and distance of the sun, at 6,ooo° abso- 

 lute temperature, and add that to what we have found from our 

 spectro-bolometric observations. On the contrary, our procedure 

 has been to piece out the spectro-bolometric curve as we have found 

 it to be outside the atmosphere, by joining onto it, where our deter- 

 mination ends, a curve after the form of the distribution of energy 

 computed by the Wien-Planck formula for the " black body " at 

 6,ooo°. If, now, the condition of the sun is such that its distribution 

 of radiation in the infra-red corresponds to a " black body " at 7,000°, 

 or some still higher temperature, then the real rate of the falling off 

 of the curve in the infra-red, beyond the region that we observe, 

 would be more rapid than that which we have assumed it to be. 

 Accordingly the area included under such a curve would be less than 

 we have assumed it to be, and thus our value of the solar constant of 

 radiation will be too large on account of the error of our method of 

 extrapolating in the extreme infra-red, rather than too small, as Mr. 

 Very maintains. At all events, surely the difference so far down in 

 the spectrum as this is altogether trifling in amount. 



Seventh objection. — We agree with Mr. Kron that. the ultra-violet 

 spectrum may be a little more intense than we have supposed it to be. 

 However, when we consider the rapid falling off of solar energy in 

 the violet, and the reasonableness of it in view of the immense number 

 of solar absorption lines and other solar circumstances, we see no 

 probability at all that the part neglected would exceed 1 or 2 per cent, 

 at most, of the value of the solar constant of radiation. In confirma- 

 tion of this view, we point to the results of the balloon flights, which 

 we shall shortly describe. 



