THE MOON'S HISTORY. 73 



stage is reached when the day is about fifty or sixty 

 times as long as our present day. 



All this time, in accordance with the general law of action 

 and reaction, the moon must be gradually retreating ; the 

 orbit of the moon is destined to grow ever wider and wider ; 

 the distance of our satellite from the earth becoming ever 

 greater and greater until at last the period is reached to 

 which we have already referred, when the day is some 

 fourteen hundred hours long. As the orbit of the moon 

 is gradually enlarging, the time that the moon takes to 

 revolve around the earth must be continually on the 

 increase ; from the present month of twenty-seven days 

 the length of the month will gradually augment as the 

 ages roll by until at last when the moon has reached a 

 certain distance the period of its rotation will have 

 become double what it is at present, or indeed rather more 

 than double, and we shall have the day and the month 

 equal, each being about fourteen hundred hours long. 

 When this state of things is reached, the earth will always 

 turn the same face towards the moon, just as the moon 

 at present always turns the same face towards the earth. 



We have already explained how the constant face of the 

 moon can be accounted for by the action of tides raised 

 in the moon by the attraction of the earth. Owing to the 

 small size of the moon the tides have already wrought 

 all that they were capable of doing, and have compelled 

 the moon to succumb to the conditions they imposed. 

 Owing to the great mass of the earth and the compara- 

 tively small mass of the moon the tides on the earth 

 raised by the moon have required a much longer period 

 wherein to accomplish their effects than was the case 



