LOWELL. — TEMPERATURE OF MARS, 655 



This value of 1.180 i.s one which is probably about the average of 

 clear days in our latitude, the day in question being registered by 

 Crova as "very clear." 



From these several data we find the following values for the solar 

 radiation received at the respective posts, in calories in one column, in 

 percentage of that entering the atmosphere in another. 



Solar Radiation. 



Bar. Calories. Percentage. 



Outside the atmosphere . 0. 3.127 1.000 



Camp Whitney .... 500 mm. 1.89G .606 



Lone Pine 663 " 1.533 .490 



Montpellier 761 " 1.180 .377 



The loss in the visible spectrum is almost wholly from selective or 

 general reflection and from diffraction, that in the invisible one from 

 selective absorption. The absorptive loss by bands in the former is only 

 about 1 per cent of the whole, and the loss by reflection in the latter 

 probably not over 7 per cent of its depletion. 



In view of the fact that the absorption is known to take place high 

 up in the air. Very adopted the Alleghany amount for Lone Pine, 

 the diff"erence being insensible; but when it comes to Camp Whitney 

 it is clear from the above that 9 per cent of it is got rid of, between 

 X= 1.2 fj. and = 10 jU by rising the 11,700 ft. from sea-level. 



Depletion in Visible Rays. 



We may now find the depletion in the visible part of the spectrum 

 which is not in general the same as that for the invisible part, decreasing 

 relatively with the altitude and reversely increasing as the air envelope 

 becomes thicker. It does this at a greater rate than the increase of 

 the air mass, because the particles suspended in the air, dust, water 

 globules, and ice augment more rapidly than the air mass as one 

 approaches the ground. 



Drawing the curve for transmission at the sea-level on the same 

 principles as those for outside the atmosphere at Camp Whitney and 

 at Lone Pine, and then measuring the amounts of transmission of each 

 within the limits of the visual rays, from A = 0.393 ju the K line to 

 X = 0.76 /i the A band, we get the foUomng table : 



