290 On the Glacial Theory^ 



opinion upon the merits of tlie theory, either to acknowledge 

 its truth or to expose its fallacy. The error which its oppo- 

 nents appear to labour under lies in not dealing with the esta- 

 blished properties of matter in the same manner as they would 

 have done, had another and more familiar subject been under 

 discussion, but in assuming that matter possesses exactly 

 those properties which are suitable for their preconceived 

 views. Such was the case with the reasons first assigned for 

 the motion of glaciers. Had De Saussure applied the laws 

 which regulate the descent of bodies down inclined planes 

 rigorously to the motion and condition of glaciers, he would 

 have found that the sliding theory was inapplicable ; and 

 had M. Agassiz considered the temperature to which water 

 must be reduced before it can freeze, he would not have advo- 

 cated the dilatation theory; nor would he have asserted with 

 so much confidence that the motion is suspended during win- 

 ter, had that not been essential to his theory. Professor 

 Forbes is the only one who has investigated the causes of the 

 motion of glaciers in a manner likely to lead to the truth, 

 and his exertions have accordingly been crowned with success. 

 We, however, paused until lately to subscribe to the viscous 

 theory, notwithstanding the many prima facie proofs he had 

 given in support of it, because we considered that the experi- 

 mentum crucis was still wanting — we mean the proof of the 

 power which glaciers were thought to possess of ejecting 

 upon their surface foreign bodies from their interior. A thou- 

 sand obvious facts prove, that a fluid in motion raises from 

 its bottom bodies having a greater specific gravity than itself; 

 and if the same property could be shown to exist in glaciers, 

 we deemed that the viscous theory was proved. Happily, 

 Professor Forbes has been fortunate in supplying this remain- 

 ing link of the chain, by the discovery last summer of a knap- 

 sack on the surface of the Mer de Glace of Chamouni, which 

 had been left in a crevass, the account of which he gave in the 

 last number of this Journal. We trust that the viscous theory 

 is now settled. 



We wish we could say as much for the glacial theory. 

 Believing in the former extension of glaciers, and that it was 



