246 ^ai| Sermons, (Sssags, Hnir gebrcfos. [xr. 



which asks for so much time that the succession of 

 life demands vast intervals ; but this appears to me to 

 be reasoning in a circle. Biology takes her time from 

 geology. The only reason we have for believing in the 

 slow rate of the change in living forms is the fact that 

 they persist through a series of deposits which, geology 

 informs us, have taken a long while to make. If the 

 geological clock is wrong, all the naturalist will have to 

 do is to modify his notions of the rapidity of change 

 accordingly. And I venture to point out that, when we 

 are told that the limitation of the period during which 

 living beings have inhabited this planet to one, two, or 

 three hundred million years requires a complete revolu- 

 tion in geological speculation, the onus probandi rests 

 on the maker of the assertion, who brings forward not 

 a shadow of evidence in its support. 



Thus, if we accept the limitation of time placed before 

 us by Sir W. Thomson, it is not obvious, on the face 

 of the matter, that we shall have to alter, or reform, 

 our ways in any appreciable degree ; and we may there- 

 fore proceed with much calmness, and indeed much 

 indifference, as to the result, to inquire whether that 

 limitation is justified by the arguments employed in its 

 support. 



These arguments are three in number : 



I. The first is based upon the undoubted fact that the 

 tides tend to retard the rate of the earth's rotation upon 

 its axis. That this must be so is obvious, if one con- 

 siders, 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 philo- 

 sopher," but a good mathematician and well versed in 

 the physical science of his time, not only proved this in 

 an essay of exquisite clearness and intelligibility, now 



