414 



Tlie following Donation to the Museum was presented — 



A Specimen of a Vegetable Impression from Burdie House. — Pre- 

 sented by D. Balfour, Esq. younger of Trenahy. 



The following Gentlemen were duly admitted Ordinary 

 Fellows of the Society : — 



Andrew Coventry, Esq., Advocate. 

 D. Balfour, Esq. younger of Trenaby. 



Monday, 20t/i March 1843. 



Sir DAVID BREWSTER, Vice-President, in the Chair. 



The following corammiication was read : — 



Papers on Glaciers. No. 3, On the Structure of Glaciers,, and 

 the cause of their motion. By Professor Forbes. 



With reference to his former paper of the 27th February, the 

 author stated, that he had received a most satisfactory confirmation 

 of his opinion respecting the motion of glaciers in winter. From 

 observations made by his direction on the Mer de Glace of Cha- 

 mouni, and in which he places entii'e confidence, it appears that the 

 ice moved no less than 76 feet between the 12th December 1842 

 and 17th February 1843, or at the rate of 13i inches per diem, 

 whilst its mean motion during the summer was 17^ inches. 



The author then explained the manner in which he conceives the 

 conoidal structure of glaciers to be due to the varying velocity of 

 different points of their section producing discontinuity by minute 

 fissures, which are infiltrated and ultimately frozen. He had before 

 satisfied himself that the forms of these surfaces are such as the mo- 

 tion of the particles of a viscid fluid, obstructed by the sides and bot- 

 tom of the canal in which it moves, would engender. But to make 

 this more palpable, he has endeavoured to imitate the motion of a 

 glacier, by causing a plastic fluid of difi'erent colours to mould itself 

 by the action of gravity in an inclined bed, and he has thus succeed- 

 ed in reproducing the forms of the structural surfaces of glaciers so 

 precisely that they cannot be cUstinguished from the curves which he 

 had drawn as representing the actual phenomena. — Sec Edinburgh 

 Philosophical Journal, Oct. 1842, pages 346, 347. 



