THE TIDES 91 



comes to rest. Hence it is that, though the tides are caused by the 

 moon, yet the energy they require is obtained by simply appro- 

 priating some of the vast supply available from the rotation of the 

 earth. 



It is quite true that many astronomers, without, how- 

 ever, making any pretense of logical demonstration, 

 hypothesize the existence of a statical tide, that is to say, 

 a tide on a non-rotating body. Standing by itself, this is 

 an eminently sensible idea ; but, taken in connection with 

 Newton's process of computing it, it is a wholly unwar- 

 ranted assumption. Besides, does not Young say, " In 

 fact the statical theory becomes utterly unsatisfactory in 

 regard to what actually takes place ' ' I 



Boiled down to its dregs, then, this is Newton's Tidal 

 Theory : 



1. The moon is the primary cause of the tides, and 

 the sun the secondary. 



2. The actual, or dynamical, cause of the tides is, 

 nevertheless, neither sun nor moon, but the centrifugal 

 force of the earth 's axial rotation. In fact, the moon even 

 feeds upon the energy of this rotation. 



3. The elevation known as the earth's equatorial 

 protuberance is the running effect of that centrifugal 

 force. 



4. The tides are likewise the running effect of this 

 same centrifugal force. 



5. This centrifugal force exists of itself without 

 any pre-existing cause. 



6. There is no way by which this force is replen- 

 ished. The earth is on the order of "a fly-wheel detached 

 from the engine," only that, in the earth's case, there 

 never was any engine so far as we know. 



7. To sustain in place the equatorial ring, this 

 centrifugal force continuously expends out of its stored 

 energy 1-289 of the power of gravity, and, to produce 

 the lunar tides, 289-2,811,400 of gravity. 



