xlviii KANT'S UNIVERSAL NATURAL HISTORY 



Thus did Kant's ' really great discovery ' as Lord 

 Kelvin calls it advance on its way, ' per varios casus, 

 per tot discrimina rerum/ until it has now become all 

 but universally accepted by contemporary scientists. 

 Palmam qui meruit, ferat ! 



i. LORD KELVIN'S STATEMENT OF KANT'S DISCOVERY. 



We may here quote Lord Kelvin's most recent statement 

 (1897) concerning Kant's discovery. 'Kant pointed out in 

 the middle of last century, what had not previously been 

 discovered by mathematicians or physical astronomers, that 

 the frictional resistance against tidal currents on the earth's 

 surface must cause a diminution of the earth's rotational 

 speed. This really great discovery in Natural Philosophy 

 seems to have attracted very .little attention, indeed to 

 have passed quite unnoticed, among mathematicians, and 

 astronomers, and naturalists, until about 1840, when the 

 doctrine of energy began to be taken to heart. In 1866, 

 Delaunay suggested that tidal retardation of the earth's 

 rotation was probably the cause of an outstanding accelera- 

 tion of the moon's mean motion reckoned according to the 

 earth's rotation as a timekeeper found by Adams in 1853 by 

 correcting a calculation of Laplace which had seemed to 

 prove the earth's rotational speed to be uniform. Adopting 

 Delaunay's suggestion as true, Adams, in conjunction with 

 Professor Tait and myself, estimated the diminution of the 

 earth's rotational speed to be such that the earth as a time- 

 keeper, in the course of a century, would get 2z seconds 

 behind a thoroughly perfect watch or clock rated to agree 

 with it at the beginning of the century. According to this 

 rate of retardation the earth, 7,200 million years ago, would 

 have been rotating twice as fast as now : and the centrifugal 

 force in the equatorial regions would have been four times 



