IN CLOUDS AND RIVERS, ICE AND GLACIERS. 



125 



to, and which has entangled so many. So 

 natural was the association of ice and cold, 

 that even celebrated men assumed that all 

 that is needed to produce a great extension 

 of our glaciers is a diminution of the sun's 

 temperature. Had they gone through the 

 foregoing reflections and calculations, they 

 would probably have demanded more heat 

 instead of less for the production ot a " gla- 

 cial epoch." What they really needed were 

 condensers sufficiently powerful to 'congeal 

 the vapor generated by the heat of the sun. 



57. GLACIER THEORIES. 

 390. You have not forgotten, and hardly 

 ever can forget, our climbs to the Cleft Sta- 

 tion. Thoughts were then suggested which 

 we have not yet discussed. We saw the 

 branch glaciers coming down from, their 

 neves, welding themselves together, pushing 

 through Trelaporte, and afterward moving 

 through the sinuous valley of the Mer de 

 Glace. These appearances alone, without 

 taking into account subsequent observa- 

 tions, were sufficient to suggest the idea that 

 glacier ice, however hard and brittle it may 

 appear, is really a viscous substance, resem- 

 bling treacle, or honey, or tar, or lava. 



53. DILATATION AMD SLIDING THEORIES. 



891. Still this was not the notion expressed 

 by the majority of writers upon glaciers. 

 Scheuchzer of Zurich, a great naturalist, vis- 

 ited the glaciers in 1705, nnd propounded a 

 theory of their motion. Water, he knew, 

 expands in freezing, nnd the force of expan- 

 sion is so great that thick bomb-shells filled 

 with water, and permitted to freeze, are, as 

 we know (812), shattered to pieces by the ico 

 within. Scheuchzer supposed that the wa- 

 ter in the fissures of the irlacier-s, freezing 1 

 there and expanding with resistless force, 

 was the power which urged the glacier 

 downward. He added to this theory other 

 notions of a less scientific kind. 



392. Many years subsequently, De Char- 

 pentier of Bex renewed and developed this 

 theory with such ability and completeness 

 that it was long known as Ciiarpemier'a 

 Theory of Dilatation. M. Agassiz lor a time 

 espoused this theory, and it was aijo more or 

 less distinctly held by other wriieis. The 

 glacier, in fact, was considered to be a mag- 

 azine of cold, capable of freezing all water 

 percolating through it. The theory was 

 abandoned when this notion of glacier cold 

 was proved by M. Agassiz to be untenable. 



393. In 17b'0, Altmanu and Griiner pro- 

 pounded the view that glaciers moved by 

 sliding over their beds. Nearly lorty years 

 subsequently, this notion was revived by De 

 Saussure, and it has therefore been called 

 "De Saussure's Theory," or the "Sliding 

 Theory," of glacier motion. 



394. There was, however, but little reason 

 to connect the name of De Saussure with this 

 or any other theory of glaciers. Incessantly 

 occupied in observations of another kind, 

 this celebrated man devoted very little time 

 or thought to the question of glacier motion. 



What he has written upon the subject reads 

 less like the elaboration of a theory than the 

 expression of an opinion. 



59. PLASTIC THEORY. 



395. By none of these writers is the prop- 

 erty of viscosity or plasticity ascribed to gla- 

 cier ice ; the appearances of many glaciers 

 are, however, so suggestive of this idea that 

 we may be sure it would have found Ujore 

 frequent expression, were it not in such ap- 

 parent contradiction with our every day ex- 

 perience of ice. 



396. Still the idea found its advocates. In 

 a little book, published in 1773, and entitled 

 "Picturesque Journey to the Glaciers of 

 Savoy," Bordier of Geneva wrote thus : 

 " It is now time to look at all these objects 

 with the eyes of reason ; to study, in the 

 first place, the position and the progression 

 of glaciers, and to seek the solution rf their 

 principal phenomena. At the first aspect of 

 the ice-mountains an observation presents it- 

 self, which appears sufficient to explain all. 

 It is that the entire mass of ice is connected 

 together, and presses from above downward 

 after the manner of fluids. Let us then re- 

 gard the ice, not as a mass entirely rigid and 

 immobile, but as a heap of coagulated 

 matter, or as softened wax, flexible and duc- 

 tile to a certain point." Here probably for 

 the first time the quality of plasticity is as- 

 cribed to the ice of glaciers. 



397. To us, familiar with the aspect of tho 

 glaciers, it must seem strange that this idea 

 once expressed did not at once receive recog- 

 nition and development. But in those early 

 days explorers were few, and the " Pictur- 

 esque Journey" probably hut little known,, 

 so that the notion of plasticity lay dormant 

 for more than half a century. But Bordier 

 was at length succeeded by a man of far 

 greater scientific rapp and insight than him- 

 self. This was Rendu, a Catholic priest and, 

 canon when he wrote, and afterward Bishop < 

 of Annecy. In 1841 Rendu laid before the 

 Royal Academy of Sciences of Savoy his- 

 "Theory of the Glaciers of Savoy," a con- 

 tribution forever memorable in relation to; 

 this subject. 



398. Rendu seized the idea of glacier plas- 

 ticity with great power and clearness, and-; 

 followed it resolutely to its consequences. 

 It is not known that ho had ever seen the 

 work of Bordier ; probably not, as he never- 

 mentions it. Let me quote for you some of 

 Rendu's expressions, which, however, fail to 

 give an adequate idea of his insight and -pre- 

 cision of thought: "Between the Mer de 

 Glace and a river there is a resemblance BO 

 complete that it is imposiible to find in the. 

 glacier a circumstance which does not exist 

 in the river. In currents of water the mo- 

 tion is not uniform either throughout their 

 width or throughout their depth. The fric- 

 tion of the bottom and of the sides, with the 

 action of local hindrances, causes the motion 

 to vary, and only toward the middle of the 

 surface do we obtain the full motion." 



399. This reads like a prediction of what 



