138 VISCOUS THEORY OF GLACIER MOTION. [1846. 



but took no real start until the frost had given way, and the 

 tumultuous course of the Arveiron showed that its veins were 

 again filled with the circulating medium to which the glacier, 

 like the organic frame, owes its moving energy. 



VIII. Being curious to see how far a relation might be 

 established between the temperature of the air and the motion 

 of the glacier, independent of the irregularly acting causes 

 above adverted to, I projected, in Plate V., the motions of the 

 several points of the glaciers in terms of the temperature of the 

 air for the periods already mentioned.* It is to be recollected, 

 however, that the observations of the thermometer were not 

 made on the spot, and, indeed, it would have been difficult to 

 have fixed upon a spot which should represent the mean cir- 

 cumstances of the whole glacier. Perhaps, therefore, the 

 average of the observations at Geneva and St. Bernard (the 

 mean of whose elevations is 4750 English feet above the sea, 

 and therefore between that of Montarivert and Chamouni) may 

 represent pretty fairly the climateric conditions of the inferior 

 parts of the Glaciers des Bois and Bossons. NoW, if we examine 

 the curves of Plate V., we are struck with their almost perfect 

 flatness until zero of the centigrade scale of temperature is reached ; 

 but, the thawing point of ice past, the velocity manifestly goes on 

 increasing with the temperature, in a ratio which would appear 

 to be tolerably uniform if we neglect the irregular inflections of 

 the curves. 



IX. I am unwilling to multiply deductions which every 

 intelligent reader will draw for himself; but one more I must 

 add. It very clearly appears that the variations of velocity due 

 to season are greatest where the variations of temperature of 

 the air are greatest, as in the lower valleys ; but it also appears 

 from Remark VIII. , that variations of temperature below 

 centigrade, or 32 Fahrenheit, produce almost inappreciable 

 changes in the rate of motion of the ice. Hence, from this 

 circumstance alone, we should deduce that in the higher parts 



* [This diagram has been rendered a somewhat more complete and accurate 

 representation of the numbers given in pages 128 and 131, than the original figure 

 in the Philosophical Transactions] 



