74 NINTH LETTER ON GLACIERS. [1845. 



former being more or less fissured by rents. But the contrary 

 is the case on the great glaciers which move on small slopes, 

 and with smaller velocities ; and the discovery of this fact 

 rewarded me for the labour of a short visit which I made the 

 Great Aletsch glacier, in July 1844, when I ascertained, not 

 merely the small daily progress of the mass of the glacier, but 

 the astonishing retardation produced by the sides, whilst the 

 surface remained compact and wholly undivided by longitudinal 

 crevasses. In that case, I found that, " whilst the velocity of 

 the ice at 1300 feet, or about a quarter of a mile from the side, 

 is 14 inches in 24 hours, at 300 feet distant from the side it 

 was but 3 inches in the same time ; and close to the side it had 

 nearly, if not entirely, vanished."* Now this observation, a 

 hasty one, and which, therefore, I am happy to have confirmed, 

 is more than borne out by the observations on the glacier of 

 the Aar, detailed in the Comptes Rendus, and which were 

 made shortly after. The movement of the centre of the glacier 

 is to that of a point 5 metres from the edge as FOURTEEN to 

 ONE ; such is the effect of plasticity ! Thirteen-fourteenths of the 

 motion of the glacier of the Aar are due to the sliding of the ice over 

 its own particles, and one-fourteenth only to its motion over the soil. 

 V. Motion of Glaciers of the Second Order. It is a question 

 of considerable interest to know how those small glaciers, called by 

 De Saussure glaciers of the second order, advance, compared to 

 the great ice masses which fill the bottoms of valleys. These 

 little glaciers, on the contrary, are usually isolated, extending 

 but a small way, occupying a nook or niche in a mountain side, 

 and though persisting in their occupancy, and shewing signs of 

 motion and activity, like other glaciers, yet stretch forward but 

 a small way, then cease abruptly, as if foiled in the struggle to 

 join their icy contribution to the magnificent glacier which often 

 fills the valley immediately below them.f Their isolated 



* Eighth Letter on Glaciers, Edin. Phil. Journal, Oct. 1844 [p. 62 of this 

 volume]. 



f See a plate, giving a correct idea of a glacier of the second order, in my 

 Travels, Plate ix. 



