Dr. J. R. Mayer on Celestial Dynamics. 245 



raise the temperature of one gramme of water 0-4408°. Not 

 much more than one-half of this quantity of heat, however, 

 reaches the solid surface of our globe, since a considerable 

 portion of it is absorbed by our atmosphere. The layer of ice 

 which, according to Pouillet, could be melted by the solar heat 

 which yearly reaches our globe would have a thickness of 

 30-89 metres. 



A square metre of our earth's surface receives, therefore, 

 according to Pouillet's results, which we shall adopt in the 

 following pages, on an average in one minute 4*408 units of 

 heat. The whole surface of the earth is =9,260,500 geographical 

 square miles*; consequently the earth receives in one minute 

 2247 billions of units of heat from the sun. 



In order to obtain smaller numbers, we shall call the quantity 

 of heat necessary to raise a cubic mile of water 1° C. in tempera- 

 ture, a cubic mile of heat. Since one cubic mile of water weighs 

 408-54 billions of kilogrammes, a cubic mile of heat contains 

 408*54 billions of units of heat. The effect produced by the 

 rays of the sun on the surface of the earth in one minute is 

 therefore 5*5 cubic miles of heat. 



Let us imagine the sun to be surrounded by a hollow sphere 

 whose radius is equal to the mean distance of the earth from 

 the sun, or 20,589,000 geographical miles * the surface of this 

 sphere would be equal to 5326 billions of square miles. The 

 surface obtained by the intersection of this hollow sphere and 

 our globe, or the base of the cone of solar light which reaches 

 our earth, stands to the whole surface of this hollow sphere as 

 9-^500 : 5326 billions, or as 1 to 2300 millions. This is the 

 ratio of the heat received by our globe to the whole amount 

 of heat sent forth from the sun, which latter in one minute 

 amounts to 12,650 millions of cubic miles of heat. 



This amazing radiation ought, unless the loss is by some 

 means made good, to cool considerably even a body of the 

 magnitude of the sun. 



If we assume the sun to be endowed with the same capacity 

 for heat as a mass of water of the same volume, and its loss of 

 heat by radiation to affect uniformly its whole mass, the tempe- 

 rature of the sun ought to decrease 1°*8 C. yearly, and for the 

 historic time of 5000 years this loss would consequently amount 

 to 9000° C. 



A uniform cooling of the whole of the suit's huge mass cannot, 

 however, take place; on the contrary, if the radiation were to occur 

 at the expense of a given store of heat or radiant power, the sun 



* The geographical mile =7420 metres, and one English mile =1G08 

 metres. 



