186 THIRTEENTH LETTER ON GLACIERS. [1846. 



the rotatory motion acquired by any floating patches of foam, 

 which is always in a direction forwards and towards the side of 

 the stream to which it is nearest ; thus, in the preceding figure, 

 it would be in the direction of the hands of a watch; I re- 

 main, etc. 



EDINBURGH, 24th October 1846. 



XVI. THIRTEENTH LETTER ON GLACIERS. 



Addressed to Professor JAMESON.* 



Acceleration of the Surface Motion of Glaciers confirmed Velocity of the Mer de 

 Glace in the Summer of 1846 at Stations C, D, P, and R Velocity of the 

 Glacier of Talefre, near its point of discharge Discovery of a Knapsack ten 

 years buried in the Ice, and deduction of the motion The Glacier of Nant 

 Blanc visited, and its Motion determined The Glacier of Miage revisited, and 

 motion measured On the Conversion of the Neve into Ice Congelation of 

 Infiltrated Water not necessary to produce the Veined Structure An Attempt 

 to explain the apparent rejection of Stones from the Glacier Ridges of Ice in 

 certain parts of Glaciers due to the bruising effect of intense Pressure Three 

 Orders of discontinuity, Ridges, Crevasses, Veined Structure. 



My dear Sir Since the completion of my Twelfth Letter, 

 I have observed, in the Comptes Rendus for 26th October, an 

 account of a communication made to the Academy of Sciences 

 by M. Martins, of an experiment on the relative motion of the 

 surface and inferior part of a glacier, on which I have also made 

 the experiments detailed in my Eleventh Letter (dated 16th 

 September), and published on 1st October in The New Edin- 

 burgh Philosophical Journal. My experiments, it will be recol- 

 lected, were made at three points of the terminal face of the 

 Glacier des Bois, and proved, as I had long ago anticipated, that 

 the superficial ice has by much the most rapid motion. MM. 

 Dollfuss and Martins arrive at the same result, establishing the 

 desired identity with the motion of rivers ; but their experiment 

 being made, not on the terminal face, but only on the steep 



* Read before the Royal Society of Edinburgh, 21 st December 1846. Published 

 in Edinburgh Philosophical Journal, January 1847. 



