208 CONTINUITY. 



the cold winter than the hot summer can melt, a result aided 

 by the shelter from the sun's rays produced by the vapour 

 suspended in consequence of aqueous evaporation ; hence we 

 should get glacial periods, when the orbit of the earth is at 

 its greatest eccentricity, at those parts of the earth's surface 

 where it is winter when the earth is in aphelion; carboni- 

 ferous or hot periods where it is winter in perihelion; and 

 normal or temperate periods when the eccentricity of orbit is 

 at a minimum; all these would gradually slide into each 

 other, and would produce at long distant periods alternations 

 of cold and heat, several of which we actually observe in 

 geological records. 



If this theory be borne out, we should approximate to a 

 test of the time which has elapsed between different geological 

 epochs. Mr. Croll's computation of this would make it cer- 

 tainly not less than 100,000 years since the last glacial epoch, 

 a time not very long in geological chronology probably it is 

 much more. 



When we compare with the old theories of the earth, by 

 which the apparent changes on its surface were accounted for 

 by convulsions and cataclysms, the modern view inaugurated 

 by Lyell, your former President, and now, if not wholly, at 

 all events to a great extent adopted, it seems strange that the 

 referring past changes to similar causes to those which are 

 now in operation should have remained uninvestigated until 

 the present century; but with this, as with other branches 

 of knowledge, the most simple is frequently the latest view 

 which occurs to the mind. It is much more easy to invent 

 a Deus ex machina than to trace out the influence of slow 

 continuous change; the love of the marvellous is so much 

 more attractive than the patient investigation of truth, that 

 we find it to have prevailed almost universally in the early 

 stages of science. 



In astronomy we had crystal spheres, cycles,. and epicycles ; 

 in chemistry the philosopher's stone, the elixir vitse, the archaeus 

 or stomach demon, and phlogiston ; in electricity the notion 

 that amber possessed a soul, and that a mysterious fluid could 

 knock down a steeple. In geology a deluge or a volcano was 

 supplied. In palaeontology a new race was created whenever 



