CELESTIAL EVOLUTION. 233 



supported by Duner, and is distinctly confirmed 

 by Hale's observations with the Yerkes telescope. 

 Vogel's views, in fact, are generally accepted 

 among astronomers. The nebular theory, modi- 

 fied by subsequent research, seems destined to 

 hold its own against all attacks. 



Distinctly supplementary to the nebular theory 

 are the remarkable researches, commenced in 

 1879, by Sir George Howard Darwin (born 

 1845), son of Charles Darwin the great biologist. 

 George Howard Darwin was born in 1845, at 

 Downe in Kent, was educated at Cambridge, and 

 studied for the law; but in 1873 he returned to 

 Cambridge, where he became Plumian Professor 

 of Astronomy in 1883. In 1879 he communicated 

 to the Royal Society the first of his papers on 

 tidal friction, which were summed up in his book 

 on 'The Tides/ published in 1898. He finds 

 that the tides act upon the Earth as a brake 

 does upon a machine, they tend to retard its 

 rotation. Consequently, the day is growing 

 longer, the Moon's orbit is becoming enlarged, 

 and its period of revolution is being lengthened. 



At present the day is about twenty-four hours 

 long, and the month about twenty-seven days. 

 The day, however, will be lengthened at a more 

 rapid rate than the month, and in the remote 

 future the day and month will both last fifty-five 



