EVOLUTION THE MASTER-KEY 



the law of gravitation that the planetary system 

 will not endure forever. 



Charles Darwin was a foremost champion of 

 the theory of evolution in the realm of biology, 

 and George Darwin, his son, has greatly added 

 to our knowledge of evolution in the realm of 

 astronomy. By a study of the tides he has fore- 

 cast the future of the solar system. Even at this 

 hour the tides are acting as a brake upon our 

 earth as she rotates, and are lengthening the day 

 by about twenty-two seconds in each century. 

 The terrestrial tides are at present mainly pro- 

 duced, as we know, by the gravitational action of 

 the moon. The moon herself was almost certainly 

 formed by the breaking loose of the matter rolling 

 upon the earth some fifty million years ago, when 

 her surface was molten. The Atlantic and Pacific 

 oceans probably mark the scars left by the two 

 masses, detached from opposite points, which 

 later joined to form the moon. Now the present 

 effect of the tides is so to alter the relative lengths 

 of the month and the day that the moon and the 

 earth will eventually rotate together as if a solid 

 bar ran between them. There will then be no 

 moon-raised tides upon the earth. 



But to ignore the influence of the other planets 

 the earth will raise tides upon the sun, just as 

 Jupiter certainly does now. These solar tides act 

 as a brake upon his rotation just as the terrestrial 

 tides act upon the rotation of the earth. 



From these alterations in rate of rotation serious 

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