TEMPERATURE OF SPACE, 263 



cause why the temperature of the air diminishes as we 

 ascend ? 



If the foregoing considerations be correct, it ought 

 to follow that a reduction in the amount of heat 

 received from the sun, owing to an increase of his 

 distance, should tend to produce a greater lowering 

 effect on the temperature of the air than it does on 

 the temperature of the solid ground. Taking, there- 

 fore, into consideration the fact that space has probably 

 a lower temperature than — 239°, and that the tempe- 

 rature of our climate is determined by the temperature 

 of the air, it will follow that the error of assuming 

 that the decrease of temperature is proportional to the 

 decrease in the intensity of the sun's heat may not be 

 great. 



In estimating the extent to which the winter tem- 

 perature is lowered by a great increase in the sun's 

 distance, there is another circumstance which must 

 be taken into account. The lowering of the tempera- 

 ture tends to diminish the amount of aqueous vapour 

 contained in the air, and this in turn tends to lower 

 the temperature by allowing the air to throw off its 

 heat more freely into space. 



