Professor Forbes’s Ninth Letter on Glaciers. 339) 
was but 3 inches in the same time ; and close to the side it 
had nearly, if not entirely, vanished.”* Now this observa- 
tion, 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 ques- 
tion 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 oc- 
cupancy, 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 con- 
tribution to the magnificent glacier which often fills the 
valley immediately below them.+ Their isolated position, their 
great absolute height, and their usually very steep declivity 
and small surface, give considerable interest to the determi- 
nation of their rate of motion, at least approximately. Ac- 
cordingly I seized the occasion of spending some days in 
July 1844, at the Hospice of the Simplon (already at a 
height of 6600 feet above the sea), to examine and measure 
the progress of the small glacier which hangs from the slope 
of the Schénhorn, immediately behind it, and 1400 feet 
higher. I intend to give elsewhere a minute account of this 
glacier, and my observations upon it; but in the mean time 
I may state that one of the marks observed, at a point 
having an inclination of 10°, moved at the rate of 1.4 inches 
* Eighth Letter on Glaciers, Edin. Phil. Journal, Oct. 1844. 
t See a Plate, giving a correct idea of a glacier of the second order, in 
my Travels, plate ix. 
