1883.] on Thoughts on Badlation, Theoretical and Practical. 265 



however, cleared the bank during the last two observations, and, 

 touching the air thermometer with its warmth, raised its temperature 

 from 26^ to 27^ and 29^. The very large difference of 18^ is in part 

 to be ascribed to this raising of the temperature of the air ther- 

 mometer. I will limit myself to citing one other case of a similar 

 kind. On the evening of the 31st of March, though the surface 

 temj^erature was far below the dew point, very little dew was 

 deposited. The air was obviously a dry air. The sky was perfectly 

 cloudless, while the barely perceptible movement of the air was from 

 the north-east. At 10 p.m. the temperature of the air thermometer 

 was 37°, that of the wool thermometer was 20*^, a refrigeration of 

 17° being therefore observed on this occasion. 



From the behaviour of a smooth ball when urged in succession over 

 short grass, over a gravel walk, over a boarded floor, and over ice, it 

 has been inferred that, were friction entirely withdrawn, we should have 

 no retardation. In a similar way, under atmospheric conditions 

 visibly the same, we observe that the refrigeration of the earth's 

 surface at night markedly increases with the dryness of the atmo- 

 sphere : we may infer what would occur if the invisible atmospheric 

 vapour were entirely withdrawn. I am far from saying that the 

 body of the atmosphere exerts no action whatever upon the waves of 

 terrestrial heat ; but only that its action is so small that, when due 

 precautions are taken to have the air pure and dry, laboratory experi- 

 ments fail to reveal any action. Without its vaporous screen, our 

 solid earth would practically be in the presence of stellar space ; and 

 with that space, so long as a difference existed between them, the 

 earth would continue to exchange temperatures. The final result of 

 such a process may be surmised. If carried far enough, it would 

 infallibly extinguish the life of our planet. 



[J. T.] 



