164 Prof. P. Lowell on a Method for Evaluating 



a value for it got from taking spectral curves derived from 

 simultaneous actinometric and bolometric determinations at 

 Camp Whitney and Lone Pine; a notable improvement, since 

 simultaneity alone justifies comparison. From these curves 

 as bases he obtained one for outside the atmosphere by con- 

 sideration of both air and dust effects in selectively reflecting 

 and diffracting the energy waves. The air effect is propor- 

 tionate to the air- mass, but the dust-effect increases in greater 

 ratio as one nears the surface of the ground. The formulae 

 he used were adaptations of those of Rayleigh for the selective 

 reflexion and diffraction of small particles. (U.S . Department 

 of Agriculture, Weather Bureau, No. 254.) 



Energy of Invisible and Visible Spectrum. — Beginning with 

 his curve for outside our atmosphere, planimetric measure- 

 ment of the area included between it, limiting ordinates at 

 the side and the base — which integral gives the radiant 

 energy received between the limits — yields the following- 

 results : — 



Distribution of Heat in the Spectrum. 



Wave-lengths. Percentage. 



Invisible X= 0-2 yu, to 0*393 fi 2'5 



Visible =0-393/*,, 0-70 fi 32-0 



Invisible =0*76 fi „ 15*0 fi 65*5 



100-0 



giving for the 



Visible portion 32 per cent. 



Invisible portion 68 per cent, of the whole. 



Loss of Heat in traverse of the Air.- — Turning now from 

 the question of the initial heat for different parts of the 

 spectrum at the time the solar radiation enters the air, we 

 come next to consider the loss the several rays sustain in 

 their traverse of it. 



Taking Very's curves for the radiation at the confines of 

 the atmosphere at Camp Whitney and at Lone Pine from 

 X = to X=l*2/u,, and for beyond it using the absorption in 

 the red and infra-red from the Alleghany measures which he 

 considers the same as those of Lone Pine, we have, by plani- 

 metric measurement as before, calling the whole heat at the 

 confines of the atmosphere unity : — 



Transmission. 

 \ = 0-2 p to 1-2 ix X = 1-2 fi to 15 ^ 



Outside 0-50 0-50 



Camp Whitney ... 0*313 



Lone Pine 0-243 0-251 



