1845.] DE SAUSSURE'S THEORY OF GLACIER MOTION. 95 



XII. ILLUSTRATIONS OF THE VISCOUS THEORY 

 OF GLACIER MOTION. PART II. AN ATTEMPT TO 

 ESTABLISH BY OBSERVATION THE PLASTICITY OF GLACIER 

 ICE.* 



3. De Saussures Theory. 4. Modifications of De 

 Saussures Theory. 5. Experiments at Chamouni on the 

 Plasticity of j.ce. 



3. DE SAUSSURE'S THEORY. 



When Gruner proposed the explanation of glacier motion 

 by the sliding of the ice over its bed, and De Saussure illus- 

 trated and confirmed it by considerations drawn from the lubri- 

 cating action of the earth's heat melting the ice in contact with 

 the soil,f there is no reason to suppose that either of them 

 thought it necessary to take into account the varying form of 

 the channel through which the glacier had to pass, and the 

 consequently invincible barrier presented to the passage of a 

 rigid cake of ice through a strait or narrow aperture when it 

 occurred. This is the more remarkable, because he [De Saus- 

 sure] conceives that the inequalities of the bed or bottom may be 

 overcome by the hydrostatic pressure of the water, which he 

 supposes may be imprisoned between the rock and the ice, so 

 as absolutely to heave the latter over the resisting obstacles. 



I believe that in no part of De Saussure's writings will there 

 be found any, the slightest reference to the possibility of the 

 glacier, when fairly formed, moulding itself to the inequalities of 

 the surfaces over which gravity urges it ; nor is there any trace 



* Philosophical Transactions, 1846, p. 137. Received July 28, 1845. Read 

 January 15, 1846. 



f To do Gruner justice, he appears to have heen aware of the effects of the 

 earth's heat and the lubricating action of the water thawed from the glacier : 

 " Lorsque les cotes de 1'amas [de glace] qui touchent la montagne, fondent en entier, 

 toute la masse entrainee par son poids glisse sur son fond et s'avance dans la vallee," 

 French translation, p. 333 . . . " il est vraisemblahle que leur surface, inferieure 

 [i. e. des glaciers] se liquefie autant, et peut-etre plus que la superieure," ib. p. 289. 



