144 Mr. S. Newcomb on some 



stellar spaces at large can be made below the uppermost limits 

 of the earth's atmosphere, owing to the intervention in lower 

 regions of the radiation from the atmosphere itself. Mr. Croll 

 concludes, using Newton's law of radiation, that the heat 

 received from the stars is to that received from the sun as 222 

 to 299. I wonder that he did not see in this a reductio ad 

 absurdum either of the results of Pouillet and Herschel, or of 

 the law of radiation which he assumes. Photometry shows that 

 the combined light from all the stars visible in the most 

 powerful telescope is not a millionth of that received from the 

 sun, and there is no reason for believing that the ratio of light 

 to heat is incomparably different in the two cases. 



In considering the question of the heat conveyed by aerial 

 currents, Mr. Croll quotes from my former paper so fully and 

 fairly that I do not see any necessity to repeat my views at 

 length. I can only say that while I now see more plainly than 

 before some reason why a body at the upper region of the 

 earth's atmosphere should, on the average, be colder than at 

 the surface, I do not see that we have data for fixing the fall 

 of temperature at 5° or 100°. If the degree of cold is greater 

 than that due to expansion, then Mr. Croll is right in main- 

 taining that the aerial current would not carry to the poles all 

 the heat with which it left the equator. But, even granting 

 this condition, I see no ground for supposing the quantity of 

 heat conveyed insignificant. 



I shall now consider some of Mr. Croll's reasons why the 

 ocean should be warmer than the land. His assumed law that 

 a body transparent for heat-rays would become warmer under 

 solar radiation than an opaque body, I passed over in my 

 former criticism as too much opposed to the fundamental laws 

 of thermodynamics to need much consideration. He now 

 adduces, in support of his thesis, the fact that water is more 

 transparent to the solar rays than the rays which it would 

 itself radiate ; and that the upper layers of water would act 

 like the glass of a greenhouse, and thus allow the water to 

 stand at a higher temperature than it would otherwise do. 

 This addition to the modus operandi seems to me quite sound, 

 and therefore to show one true cause why water might rise to 

 a higher mean temperature than the land, though I am unable 

 to say whether the increase would be measurable with an 

 ordinary thermometer. But I am sorry to find that, notwith- 

 standing his addition of a sound cause, he adheres to views so 

 diametrically opposite to what I supposed to be the funda- 

 mental laws of thermodynamics, that I feel compelled to state 

 the case more fully. His first reason why the ocean should 

 be warmer than the land is in the following words: — 



