PLANETARY EVOLUTION 



planets, save Mars, Uranus, and Neptune, have 

 been actually detected by a minute comparison 

 of the variations in the solar spots. These tidal 

 waves are drawn around the sun in the direc- 

 tion opposite to that of his rotation, and must 

 therefore exert a retarding effect. And the ro- 

 tatory momentum thus stolen from the sun is 

 added, in accordance with a pro rata princi- 

 ple of distribution, to the tangential momenta 

 of the various planets concerned in the theft. 

 There can be little doubt, therefore, that all 

 the planetary orbits, both primary and second- 

 ary, are steadily enlarging, and that this pro- 

 cess must go on until that synchrony between 

 revolution and rotation now witnessed in our 

 moon becomes universal, unless it is previously 

 checked by the cessation of tidal phenomena. 

 As between the earth and moon, for example, 

 the ultimate result of the whole process must 

 be the lengthening of the terrestrial day until 

 it corresponds with a lunar month, so that the 

 earth and moon will move in relation to each 

 other just as if joined together by a rigid rod. 

 This result will actually be realized unless fore- 

 stalled by the completed refrigeration of the 

 earth, which will put an end to the tidal friction. 

 In like manner the sun's rotation must dimin- 

 ish until equilibrated with the motions of the 

 planets, unless this result is forestalled by the 

 completed refrigeration of the sun. And in all 



vol. n. 3^5 



