THE CHILDHOOD OF THE EARTH 



haust the air), it will boil at a lower temperature than 

 this. If, on the other hand, we increase the pressure on 

 the surface of the water by any means, such, for ex- 

 ample, as by placing it in a chamber of compressed air, 

 the water can be heated to a higher temperature with- 

 out boiling away. In the bygone era of which we are 

 speaking the pressure of the atmosphere on the water's 

 surface was 700 Ib. or 800 Ib. to the square inch; and 

 therefore it could be heated up to a high temperature 

 without evaporating rapidly. 



Another thing began to happen in those days. All 

 bodies in space attract one another ; the Sun attracts 

 its planets ; the planets attract the Sun and their satel- 

 lites ; and the satellites in their turn attract the planets. 

 Ages before the earth had a moon these forces were at 

 work. But the attractions of solid bodies for one another 

 do not bring about any very perceptible alterations in 

 their shapes; though if the bodies are spinning they 

 effect slow changes in their speed of rotation. It is 

 different when the bodies are liquid, or if they have 

 liquid surfaces. Then the attractions of a sun or a 

 moon on a planet begin to draw up the waters of the 

 planet and produce tides. The attraction of the earth 

 would produce tides on the Moon if an ocean existed 

 there; and, it is suspected, do produce something re- 

 sembling tides on the present surface of the Sun. 1 As 

 soon, therefore, as oceans appeared on the earth the 



1 A paper read by Mr. E. W. Maunder before the Royal Astro- 

 nomical Society in 1907 gave reasons for believing that the earth 

 has perceptible effects on the movements of sun-spots. 



102 



