16 Anniversart/ Address of the 



the whole controversy turns, is the relative amount of work 

 done by mechanical force in given quantities of time, past and 

 present. Before we can determine the relative intensity of 

 the force emploj^ed, we must have some fixed standard by 

 which to measure the time expended in its development at 

 two distinct periods. Dr Whewell has justly observed, that 

 " mechanical power retains its amount, however much it be 

 distributed through time and divested of the character of 

 extraordinary violence,"* — a principle which should never 

 be lost sight of when we contrast the effects of the historical 

 with those of antecedent epochs. It is not the magnitude of 

 the effects, however gigantic their proportions, which can in- 

 form us in the slightest degree whether the operation was 

 sudden or gradual, insensible or paroxysmal. It must be 

 shewn, that a slow process could never in any series of ages 

 give rise to the same results. 



The advocate of paroxysmal energy might assume an uni- 

 form and fixed rate of variation in times past and present for 

 the animate world, that is to say, for the dying- out and 

 coming-in of species, and then endeavour to prove that the 

 changes of the inanimate world have not gone on in a cor- 

 responding ratio. But the adoption of such a standard of 

 comparison would lead, I suspect, to a theory by no means 

 favourable to the pristine intensity of natural causes. That 

 the present state of the organic world is not stationary can, 

 I think, be fairly inferred from the fact, that some species are 

 known to have become extinct in the course even of the last 

 three centuries, and that the exterminating causes always in 

 activity, both on the land and in the waters, are very nu- 

 merous ; also, because man himself is an extremely modern 

 creation ; and we may therefore reasonably suppose that 

 some of the mammalia now contemporary with man, as well 

 as a variety of species of inferior classes, may have been re- 

 cently introduced into the earth, to supply the places of 

 plants and animals which have from time to time disappeared. 

 But granting that some such secular variation in the zoolo- 

 gical and botanical worlds is going on, and is by no means 



* Quart. Journ. Geol. Soc, vol. iii. p. 231. 



