100 VISCOUS THEORY OF GLACIER MOTION. [1845 



If we feel surprise that a naturalist and observer so eminent 

 had not adverted to the difficulty of imagining a solid cake of 

 ice, even though perfectly detached from its bed, to disengage 

 itself from the obstacles and sinuosities of its rocky channel, we 

 should remember, first, that the explanation is given in the 

 most general terms, and there is no appearance that its author 

 looked more closely at its consequences and details than to 

 satisfy himself that a sliding motion in the abstract was ren- 

 dered possible by the action of the earth's proper heat, an 

 ingenious and philosophical element of the theory (however 

 inadequate), and that which being due principally to De Saussure, 

 renders the theory properly his, and connected it with his 

 ingenious inquiry into this curious part of physics as a distinct 

 and wholly independent investigation. Secondly. Every one 

 knows how an application of a principle so true and so ingenious 

 leads men of even the most exact habits of thought to overlook 

 difficulties in a subject almost unstudied. De Saussure did 

 much for our knowledge of glaciers, and he saw much which no 

 one had observed before him : we must not blame him if, 

 yielding to a true and natural analogy of sliding bodies, he 

 overlooked real and great difficulties inherent in the conception 

 of a glacier as a solid continuous mass and highly rigid. Thirdly. 

 In De Saussure's time no plan or map, worthy of the name, of 

 any glacier existed, and this was a blank which even De 

 Saussure did not attempt to supply. The popular notion of a 

 glacier, which it is certain he had in his mind when he penned 

 the passages which relate to their motion, is a mass of ice of 

 small depth and considerable but uniform breadth, sliding down 

 a uniform valley, or pouring from a narrow valley into a wider 

 one, as is the case with a vast majority of glaciers tolerably 

 accessible, and which alone were visited at the time of publica- 

 tion of the first edition of the Voyages dans les Alpes. In all 

 these cases the lateral resistance might easily be overlooked, and 

 the popular comparison to one solid body sliding on another and 

 lubricated by its own liquefaction, might be accepted as a com- 

 plete explanation ; as has even been done at a later period by 



