THE TIDES 109 



Now, in Chapter II, if you remember, I computed the 

 energy value of the momentum of the moon, traveling as 

 she does at the rate of 3350 feet per second, to be 2,112 

 trillions of horse-power days (8.8 x 240 trillions). Multi- 

 plying this quantity, then, by 81 because of the earth 's 

 greater mass, but dividing the product by 9 (the square of 

 3, since the energy varies with the square of the velocity) 

 because of her slower (axial) speed, we obtain the sum of 

 20,000 trillions as the total number of horse-power days 

 " stored " in the earth's axial momentum at this given 

 instant. Compare this solitary energy asset now, if you 

 please, with our liabilities as previously appraised, and 

 you will be startled to find that were it to be applied 

 solely to the sustentation of the equatorial ring it would 

 exhaust itself in the brief space of less than a single hour, 

 or if applied wholly to the raising of the tides, in just 250 

 days ! What is the answer? How comes it that our asset 

 remains obviously intact in spite of these stupendous 

 drains 1 Can Sir Robert be right in likening the earth to 

 a fly-wheel detached from its engines? Did you ever see 

 a "fly-wheel detached from its engine, but still connected 

 with the machinery' 7 fail to betray signs of slowing up 

 almost immediately, and shortly come to a dead stop! 

 Furthermore, what sort of an engine was it to which the 

 terrestrial fly-wheel we call the earth was once attached, 

 and how did it become detached, and where is it now? 



Tide or no tide, equatorial ring or none, it is not true 

 that a great ball like ours, even were it the only one in ex- 

 istence, could, once started, continue to rotate forever 

 "because there would be nothing to stop it." There is 

 such a something gravity. It has been estimated that 

 the earth would have to rotate 17 times as fast as it does 

 before a loose rock, say, on its surface "would lose all its 

 weight and fly off to become a self-sustaining satellite." 

 Now, it seems quite plain that if the earth as a whole is to 

 keep on turning itself round and round forever, every 

 particle of it must be capable of doing its own carrying 

 and not depend for levitation or propulsion on its neigh- 

 bors, who have equal need of like help themselves. Ac- 

 cording to Newtonians, the rotation of the earth lightens 



