T 



[ 300 ] 

 XXXVIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 226.] 

 June 14, 1855. — The Lord Wrottesley, President, in the Chair. 

 HE followina: communications were read : — 



" Remarks on the Rev. H. Moseley's Theory of the Descent of 

 Glaciers." By James I). Forbes, D.C.L., F.R.S. 



In a paper "On the Descent of Glaciers," communicated to the 

 Royal Society on the 19th of April, 1855, and printed in their Pro- 

 ceedings, the Rev. Henry Moseley has proposed an explanation of 

 that phenomenon. 



The first part of his paper contains a lucid description of the 

 gradual motion of a sheet of lead covering the roof of Bristol Cathe- 

 dral, which he ascribes (I have no doubt justly) to the successive 

 expansions and contractions of the lead by atmospheric temperature. 

 He explains the influence of the slojie of the roof and of the measure 

 of friction upon the motion with his customary precision and clear- 

 ness. He also finds for the probable measure of the effect or creep- 

 ing motion of the lead, a quantity which, considering the imperfect 

 nature of the data with regard to temperature, agrees sufficiently 

 well with observation. 



In the latter and shorter part of the paper is a transition to the 

 case of glaciers, whose motion over their beds may, he thinks, be 

 accounted for in the same way, namely, by the alternate contraction 

 and expansion of the ice by diurnal changes of temperature, and he 

 then enters into certain calculations founded principally on data 

 contained in my 'Travels in the Alps of Savoy' in confirmation of 

 this view. 



Entertaining as I do the highest respect for Mr. Moseley's emi- 

 nent attainments as a theoretical mechanician, it is with extreme 

 regret that I find it necessary, in maintenance of the views regarding 

 glacier motion which I have elsewhere advanced, and in the interest 

 of scientific truth, to show (as I believe I can) that Mr. Moseley 

 has been led, apparently by a sudden inadvertency, to uphold an 

 opinion completely indefensible. 



I must first object to Mr. Moseley's descrij)tion or definition of 

 a glacier, as calculated to mislead the inquirer : he says (p. 339), 

 " glaciers are, on an increased scale" [compared to the sheet lead 

 covering of a roof], " sheets of ice placed upon the slopes of moun- 

 tains." There are certainly some inconsiderable glaciers of the 

 second order to which this description might possibly apply, with 

 the exception of the small thickness inferred by the word " sheet ;" 

 but the true glaciers, whose theory has been so often discussed 

 (which theory must evidently likewise include that of glaciers of the 

 second order), cannot fairly be called either sheets of ice or be 

 accurately described as lying o?i the slopes of mountains. They are 

 vast icy accumulations whose depth bears a considerable proportion 

 to their breadth, and which fill mountain ravines or valleys. 



