THE SIDEREAL UNIVERSE. 711 



" Let the sun/' says Camille Flammarion, " be considered 

 as a globe as large as 1,400,000 terrestrial globes, and com- 

 pletely covered with a layer of coal seven leagues in thick- 

 ness. Then the heat furnished by the combustion of all 

 this coal would be equal to what the sun annually projects 

 into space." 



And yet, great and incomprehensible as may be the heat 

 of this incandescent focus, which burns us at a distance of 

 91,328,600 miles, astronomers are so daring that they have 

 ventured to calculate the quantity of water necessary, if 

 not to extinguish it entirely, to put out, at any rate, the 

 surface conflagration. 



CHAPTER II. 



THE EARTH. 



WE have previously spoken at length of the earth in ref- 

 erence to geology ; here we only have to speak of its posi- 

 tion as a planetary body forming part of the solar system. 



The earth represents a sphere a little flattened towards 

 the poles. It is subject to two movements : one which takes 

 place round the sun in an orbit of which it traverses the 

 circuit in a year ; the other is performed in about twenty- 

 four hours round the axis which passes through its poles. 

 It is the latter movement which occasioned the belief that 

 the sun and the heavens turned round the earth in a direc- 

 tion from east to west, whilst on the contrary it is the ter- 

 restrial globe that turns from west to east. Copernicus was 

 the first to demonstrate this great astronomical fact, and 

 Galileo, with all the influence of his genius, confirmed it. 



