CHAPTER VI. 



THE MOON'S HISTORY. 



THE doctrine which I shall here endeavour to set forth is 

 mainly due to the labours of Sir George H. Darwin of 

 Cambridge. I have mentioned how the tendency of the 

 tides on a tide-disturbed globe is to adjust the movements 

 of that globe in such a way that the tides shall no longer 

 ebb or flow, but that permanent high tide shall be estab- 

 lished in some places and permanent low tide in others. 

 If the rotation of the body be not fast enough the tide will 

 pull the body round in order to effect this object. If the 

 rotation of the body be too rapid then the influence of the 

 tide will tend to check the movement and bring down the 

 speed of rotation until the desired adjustment is obtained. 

 At present the earth is spinning too fast to permit the 

 high tides to remain at permanent localities, and con- 

 sequently tides are applied with the effect of checking the 

 rotation. The earth is, however, so vast, and the tides 

 generated by so small a body as the moon are relatively 

 so impotent, that their effects in reducing the speed of 

 the earth's rotation are insignificant. Nevertheless, small 

 though they are, they unquestionably exist, and there can- 



