Geology 



which prevents the Earth flying off at a tangent to its 

 orbit into space, and according to Newton's law the 

 Moon and the planets must also attract the Earth, and 

 it can readily be shown that these attractions actually 

 exist. 



Now, if we consider the attraction of, say, the Sun 

 on the waters of the ocean on the side of the Earth 

 nearest to it, it will be obvious that these will be drawn 

 more strongly towards the Sun than the solid Earth, 

 which is farther away, and that the solid Earth will be 

 pulled more strongly than the water on the far side. The 

 Moon produces a similar effect on the waters, but for 

 reasons presently to be explained, the tide-raising power 

 of the Moon is greater than that of the Sun, although 

 its total attraction is, of course, far less. 



In the diagram (Fig. 5) and the following calculation 

 the distances are measured in terrestrial radii, and the 

 masses of the Sun and Moon are expressed in terms of 

 the Earth's mass. 



The attraction of the Moon on the waters on 

 the side of the Earth nearest to it will be pro- 



*o 1 2 3 x i 

 portional to / ^ > while that on the waters on 



the far side will be , T~\r- The tide-raising power 



of the Moon will therefore be proportional to 



012 x i -0123 x i 



2 - (59 + 2 ) 2 = '0,000,002,279. Similarly the 



tide-raising power of the Sun will be proportional to 

 1 330,000x1 



- (23.481 +*r 



54 



