58 SCIENCE IN SHORT CHAPTERS. 



In thus venturing to question some of Professor 

 Langley's inferences I am far from underrating the interest 

 and importance of his researches. On the contrary, I re- 

 gard the quantitative results he has obtained as especially 

 valuable and opportune, in affording means of testing the 

 above-named and other speculations in solar physics. 

 Similar observations repeated at different elevations would 

 decide, so far as the lower regions are concerned, whether 

 or not there is any difference in the quantity of heat im- 

 parted by the bright and obscure portions of the Sun to 

 our atmosphere. If the differences already observed by 

 Professor Langley vary in ascending, a new means will be 

 afforded of studying the constitution of the interior of the 

 Sun and its relations to the photosphere. Direct evidence 

 of selective absorption by our atmosphere may thus be ob- 

 tained, which would go far towards solving one of the cru- 

 cial solar problems, viz., whether the darker regions are 

 hotter or cooler' than the photosphere. 



The obscure radiations from the moon must be absorbed 

 by our atmosphere like those from the sun-spot, and may be 

 sufficiently effective to account for the alleged dissipation of 

 clouds by the full moon. 



In both cases the climatic influence is greatly heightened 

 by the fact that all the heat thus absorbed is directly 

 effective in raising the temperature of the air. The action 

 of the absorbed heat in reference to cloud-formation is 

 directly opposite to that of the transmitted solar heat, as 

 this reaching the surface of the earth evaporates the super- 

 ficial water, and thereby produces the material of clouds. 

 On the other hand, the heat which is absorbed by the air 

 increases its vapor-holding capacity, and thus prevents the 

 formation of clouds, or even effects the dissolution of 

 clouds already formed. 



