COSMIC PHILOSOPHY 



what larger now than they were originally. This 

 is an indirect consequence of the slow loss of 

 rotatory momentum due to tidal action. The 

 calculation by which Laplace thought he had 

 proved that the terrestrial day had not length- 

 ened since the time of Hipparchos, has been 

 shown by Professor Adams to be vitiated by the 

 inclusion of an erroneous datum ; and the the- 

 ory involved is no longer tenable. It has been 

 proved that the tidal wave which the moon 

 draws twice a day around the earth, in the op- 

 posite direction to the terrestrial rotation, acts 

 upon the earth like a brake on a carriage-wheel. 

 Owing to this circumstance, the day is now one 

 eighty-fourth part of a second longer than at 

 the beginning of the Christian era ; and it is 

 destined to continue lengthening until in the 

 remote future there will be from three to four 

 hundred hours between sunrise and sunset. But 

 the rotatory momentum thus lost by the earth 

 is not destroyed. In conformity with a well- 

 known principle of dynamics, it is added to the 

 tangential momentum of the moon, and thus 

 lengthens the radius of the moon's orbit. The 

 more slowly our planet rotates, the farther the 

 moon retires from us. A similar relation holds 

 good in the case of the planets and the sun. 

 Not only is it demonstrable a priori that the 

 planets must cause tides upon the surface of 

 the sun, but the tides caused by all the primary 

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