Remarks on Glacier Theories. 341 



I may also refer to another passage in page 35, extracted 

 from the Edinburgh Review, in which he considers all sliding, 

 according to De Saussure's theory, as mechanically impos- 

 sible*. 



How far my own investigations on the interior temperature 

 of glaciers, and my experiments on the motion of ice down 

 inclined planes, may have anything of novelty, or how far they 

 may have met the objections above-stated, I leave to the judge- 

 ment of such of your readers as approach the subject in all 

 fairness and candour. I have only brought them forward as 

 iubsidiary to De Saussure's theory, and for the purpose of 

 elucidating it, and, I trust, in no spirit calculated to indispose 

 any one to allow to them such subordinate merit as may rea- 

 sonably attach to them. 



There is an observation introduced incidentally in Dr. 

 Whewell's second letter, to the effect that " Prof. Forbes's 

 theory, of course, includes what is true in that of De Saus- 

 sure." To this somewhat curious appropriation clause I would 

 suggest an amendment, that "De Saussure's theory, of course, 

 includes what is true in Prof. Forbes's." However much I 

 may think this the stronger claim, 1 am content now merely 

 to place it on record on behalf of De Saussure, and to await 

 the judgement which shall be passed upon it on the evidence 

 of further observation. 



Again, your correspondent observes, '• Since these views " 

 (I presume those of De Saussure and Professor Forbes) "are 

 thus combined, it may be asked. What is the principal cause 

 of glacial motion? Is it gravity? or the melting of the lower 

 surface? or the plasticity of the mass? But it is plain that if 

 this theory" (that, I presume, formed by a combination of the 

 two theories) " be adopted in fact, the question among these 

 forms of expression is quite unimportant." The question is 

 doubtless unimportant to those who only care to know whether 

 glaciers move or not, but to those who would know hotv they 

 move, this statement merges the primary question between the 

 sliding and plastic theories. If it were really of no import- 

 ance whether it be the state of the lower surface of the mass, 

 or its general plasticity, which renders gravity effective in pro- 

 ducing the motion of a glacier, what right would Prof. Forbes 

 have to give to glacial theory a new appellation, with which 

 his own name alone should be hereafter associated, to the ex- 

 clusion of the name of the distinguished traveller whose steps 



* The objection expressed in the passage referreil to would seem to rest 

 partly on the supposition that De Saussure regarded a glacier as a rigid 

 mass. I have already protested against an assumption which attributes 

 so glaring an absurdity to that distinguished and philosophic traveller. 



