110 SCIENCE Itf SHORT CHAPTERS. 



terior of the Sun and its relations to the photosphere. Direct 

 evidence of selective absorption by our atmosphere may thus be 

 obtained, which would go far toward 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 suffi- 

 ciently 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 superficial water, and 

 thereby produces the material of clouds. On the other hand, 

 the heat which is absorbed by the air increases its vapor-hold- 

 ing capacity, and thus prevents the formation of clouds, or 

 even effects the dissolution of clouds already formed. 



CHAPTER XVI. 



THE PHILOSOPHY OF THE RADIOMETER AND ITS CO.JMI-2AL 



REVELATIONS. 



So much speculation, and not a little extravagant specula- 

 tion, has been devoted to the dynamics of the radiometer, 

 that I feel some compunction in adding another stone to the 

 heap, my only apology and justification for so doing being 

 that I propose to regard the subject from a very unsophisti- 

 cated point of view, and with somewhat heretical directness o! 

 vision i.e. quite irrespective of atoms, molecules, or ether, or 

 any other specific preconceptions concerning the essential 

 kinetics of radiant forces, beyond that of regarding such ford s 

 as affections or conditions of matter which arc transmitted 

 radially in constant qu?mtity, and therefore obey the necessMi-y 

 law of radial diffusion or inverse squares. 



The primary difficulty which appears to have generally been 

 suggested by the movements of the radiometer, is the case 



