64 THE SUN. 



all be equally well warmed and lighted, and, then, that 

 is only in one plane ! But there is the whole sphere of 

 space above and below, unoccupied ; at any single point 

 of which if an earth were placed at the same distance, 

 it would receive the same amount of light and heat. 

 Take all the planets together, great and small ; the light 

 and heat they receive is only one 227 millionth part of 

 the whole quantity thrown out by the sun. All the rest 

 escapes into free space, and is lost among the stars ; or 

 does there some other work that we know nothing about. 

 Of the small fraction thus utilized in our system, the 

 earth takes for its share only one loth part, or less than 

 one 2000 millionth part of the whole supply. 



(22.) Now, then, bearing in mind this huge preliminary 

 fact to start with, let us see what amount of heat the 

 earth does receive from the sun. The earth is a globe ; 

 and therefore, taken on an average, it is constantly re- 

 ceiving as much, both of light and heat, as a flat circle 

 8000 miles in diameter, held perpendicularly to receive 

 it. Now, that section is 50,000,000 square miles, so that 

 there falls at every instant on the whole earth 50,000,000 

 times as much heat as falls on a square mile of the hottest 

 desert under the equator at noonday with a vertical sun 

 and with not a cloud in the sky and in fact nearly a 

 third more ; for more than a quarter of the sun's heat is 

 absorbed in the air in the clearest weather, and never 

 reaches the ground. Now, we all know that in those 

 countries it is much hotter than we like to keep our 

 rooms by fires. I have seen the thermometer four inches 

 deep in the sand in South Africa rise to 159 Fahrenheit 



