Royal Society. 2 1 9 



Jf~ n \ 2 U h dt* 

 to wit, u = <p (r t — p x), 



which he would not have been justified in doing if he had not 

 proved the general proposition. * * * * 

 Liverpool, February 10, 1846. 



XLIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



Jan. 15, " f\N the Viscous Theory of Glacier Motion." By 

 184-6. " James D. Forbes, Esq., F.R.S. &c. Part II*. " An 

 attempt to establish by observation the Plasticity of Glacier Ice." 



The two first sections of the present memoir are occupied with a 

 critical examination of the theory advanced by De Saussure to ac- 

 count for the progressive motion of glaciers, which he considered as 

 formed of masses of rigid and inflexible ice, and with the further 

 explanations of that theory given by Ramaud, BischofF, Agassiz, and 

 Studer. The author, on the other hand, regarding these masses as 

 possessing a considerable degree of plasticity, explains on that sup- 

 position the phenomena they present ; and, in the third section of 

 the paper, he relates a series of experiments which he carried on in 

 the Mer de Glace, near Chamouni, in the summer of 1844, with a 

 view to determine by direct measurement the relative motion of 

 different parts of the glacier. This he accomplished by selecting a 

 spot on the western side of the Mer de Glace, between Trelaporte 

 and 1* Angle, where the ice was compact and free from fissures, and 

 erecting on the surface a row of posts at short distances from one 

 another, in a line transverse to the general direction of the moving 

 mass. He was thus enabled to discover by trigonometrical observa- 

 tions the movements of different points in this line ; and he ascer- 

 tained that they advanced more and more rapidly in proportion as 

 they were distant from the sides of the glacier ; and that when not 

 under the influence of neighbouring crevasses, these motions were 

 gradual and uninterrupted ; as was shown by the lines carried 

 through the posts forming, after the lapse of a few days, a continuous 

 curve, of which the convexity was turned towards the lower end of 

 the glacier. 



" An Account of the Southern Magnetic Surveying Expedition." 

 By Lieut. H. Clerk, R.A., in a letter to Lieut.-Colonef Sabine, R.A., 

 F.R.S. Communicated by Lieut.-Colonel Sabine. 



The letter, which is dated from the Magnetical Observatory at the 

 Cape of Good Hope, June 28, 1845, reports the return to the Cape 

 of the Pagoda from her voyage to the high southern latitudes after 

 the successful completion of the magnetical service on which she had 

 been employed by direction of the Lords Commissioners of the Ad- 

 miralty, at the request of the President and Council of the Royal 

 Society. 



* An Abstract of Part I. will be found at p. 538, vol. xxvi., of this Journal. 



