330 GEOLOGICAL BEFOKM x 



be so is obvious, if one considers, roughly, that 

 the tides result from the pull which the sun 

 and the moon exert upon the sea, causing it 

 to act as a sort of break upon the rotating solid 

 earth. 



Kant, who was by no means a mere " abstract 

 philosopher," but a good mathematician and well 

 versed in the physical science of his time, not 

 only proved this in an essay of exquisite clear- 

 ness and intelligibility, now more than a century 

 old, l but deduced from it some of its more im- 

 portant consequences, such as the constant turn- 

 ing of one face of the moon towards the earth. 



But there is a long step from the demonstration 

 of a tendency to the estimation of the practical 

 value of that tendency, which is all with which 

 we are at present concerned. The facts bearing 

 on this point appear to stand as follows : 



It is a matter of observation that the moon's 

 mean motion is (and has for the last 3,000 years 

 been) undergoing an acceleration, relatively to 

 the rotation of the earth. Of course this may 

 result from one of two causes: the moon may 

 really have been moving more swiftly in its orbit ; 

 or the earth may have been rotating more slowly 

 on its axis. 



1 " Untersuchung der Frage ob die Erde in ihrer Umdrehung 

 um die Achse, wodurch sie die Abwechselung des Tages und der 

 Nacht hervorbringt, einige Veranderung seit den ersten Zeiten 

 ihres Ursprunges erlitten habe, &c." KANT'S Sdmmtliche 

 Werke, Bd. i. p. 178. 



