CHAPTER XVI. 



THE TEMPEEATUEE OF SPACE AND ITS BEAEING ON 

 TEEEESTEIAL PHYSICS. 



The Importance of Knowing the Temperature of Space. — The 

 Researches of Pouillet and Herschel in reference to the Tem- 

 perature of Space. — A Defect in Dulong's and Petit's Formula. 

 — Professor Balfour Stewart on Radiation of Thin Plates. — 

 Radiation of Gases. 



Few questions bearing directly on terrestrial physics 

 have been so much overlooked as that of the tempera- 

 ture of stellar space ; that is to say, the temperature 

 which a thermometer would indicate if placed at the 

 outer limits of our atmosphere and exposed to no 

 other influence than that of radiation from the stars. 

 Were we asked what was probably the mid-winter 

 temperature of our island 11,700 years ago, when the 

 winter solstice was in aphelion, we could not tell 

 unless we knew the temperature of space. Again, 

 without a knowledge of the temperature of space, it 

 could not be ascertained how much the temperature 

 of the North Atlantic and the air over it were affected 

 by the Gulf Stream. We can determine the quantity 

 of heat conveyed into the Atlantic by the stream, and 

 compare it with the amount received by that area 

 directly from the sun, but this alone does not enable 

 us to say how much the temperature is raised by the 

 heat conveyed. We know that the basin of the North 

 Atlantic receives from the Gulf Stream a quantity of 

 heat equal to about one-fourth that received from the 



