The History of Things 55 



foundly disturbed by solar tides, and it was per- 

 haps a particularly high tide which made the earth 

 give birth to the moon. This marked the first 

 critical period in the history of our planet. *'At 

 the eventful time of parturition the earth was ro- 

 tating, with a period of from two to four hours, 

 about an axis inclined at some 11° or 12° to the 

 ecliptic. The time which has elapsed since the 

 moon occupied a position nine terrestrial radii 

 distant from the earth is at least fifty-six to fifty- 

 seven millions of years, but may have been much 

 more." ^ 



The moon thus arose as a sort of moult of the 

 outer envelope of the hot earth. It was charged 

 with steam and other gases under a pressure of 

 5,000 pounds to the square inch, but as it receded 

 from the earth and the pressure continuously dimin- 

 ished it became *^as explosive as a charged bomb, 

 and steam burst forth from numberless volcanoes." 

 The moon, in short, was only born to die. *' While 

 the face of the moon might thus have acquired its 

 existing features, the ejected material might possi- 

 bly have been shot so far away from its origin as to 

 have acquired an independent orbit "^ and some 

 of the meteorites which now descend upon the 

 earth may be returned portions of the early 



1 Prof. W. J. Sollas, Presidential Address, Section C, Brit- 

 ish Association, 1900. "Nature," September 13, p. 482. 

 a Prof. W. J. Sollas, loc. cit. 



