162 feature's /BMracles, 



a little more than twenty-four hours, so that 

 the tidal day is a little longer than the solar 

 day. It corresponds to what we call the lunar 

 day. 



As all know, the moon goes through all its 

 phases once in twenty-eight days. The tvie 

 considered in its simplest aspect is a struggle 

 on the part of the water to follow the moon. 

 There is a mutual attraction of gravitation be- 

 tween the earth and ohe moon. Because the 

 water of the earth is mobile it tends to pile up 

 at a point nearest the moon. But the earth 

 as a whole also moves toward the moon, and 

 more than the water does, keeping its round 

 shape, while its movable water (practically 

 enveloping it) is piled up before it toward the 

 moon and left accumulated behind it away 

 from the moon. So that in a rough way it is 

 a solid sound earth, surrounded by an oval 

 body of water : the long axis of the oval repre- 

 senting the high tides, which, as they follow 

 the moon, slide completely around the earth 

 once in every twenty-four hours. Thus, there 

 are really two high tides and two low tides 

 moving around the earth at the same time; 

 and this accounts for the two daily tides. 



We have accounted for the time when they 

 occur in the fact that the water attempts to 

 follow the moon, but this does not account for 

 the gradual changes in the amount of fluctua- 

 tion from day to day. The problem is com- 



