REPLY TO CRITICS. 21 



temperature of space the greater must be the decrease 

 of temperature resulting from an increase in the sun's 

 distance due to eccentricity. My opinion all along has 

 been that the temperature of .space is little above abso- 

 lute zero. 



As an argument against the conclusion that space 

 can have the high temperature assigned to it by 

 Pouillet and Herschel, he says : — " 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 incompar- 

 ably different in the two cases." This very argument 

 from the extreme smallness in the amount of light 

 derived from the stars in comparison to that from the 

 sun, intended by him to convince me of the absurdity 

 of supposing that space possesses a temperature as high 

 as — 239°, is just the argument advanced by myself 

 in the "Reader" for December 9, 1865, and after- 

 wards reproduced in ' Climate and Time,' at page 39, 

 from which I quote the following : — 



' We know that absolute zero is at least 493° below the 

 melting-point of ice. This is 222° below that of space. 

 Consequently, if the heat derived from the stars is able to 

 maintain a temperature of — 239°, or 222° of absolute tem- 

 perature, then nearly as much heat is derived from the stars 

 as from the sun. But if so, why do the stars give so much 

 heat and so very little light? If the radiation from the 

 stars could maintain a thermometer 222° above absolute 

 zero, then space must be far more transparent to heat-rays 

 than to light-rays, or else the stars give out a great amount 

 of heat, but very little light, neither of which suppositions 

 is probably true. The probability is, I venture to presume, 

 that the temperature of space is not very much above absolute 



