Variation of Motion at different Seasons. 341 



depth. But this is undoubtedly the reason why the minimum and 

 maximum approach so near to one another in point of time in the 

 torrential glacier of Bossons, and it receives an important illustration 

 from the independent fact of the observed condition of the source of 

 the Arveiron, which (see the Meteorological Register), though very 

 small in February, was still whitish and dirty before a change of 

 weather, shewing that the bands of frost were not so strong as to 

 prevent a temporary relaxatioh of thaw throughout the mass of the 

 glacier even in winter ; and although the mean temperature of the 

 ail* had been rising ever since the middle of January, and the greatest 

 cold had occured early in February, we find that at the end of March 

 the source of the Arveiron was still as small as in February, and 

 that owing to the coldness of the spring, it had not even increased 

 very much till the middle of April, when it almost suddenly resumed 

 its summer volume. Now, during all this time the velocities of the 

 glaciers underwent but little change, — some oscillations backwards 

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

 and the tumultuous course of the Arveiron shewed 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 f^r a relation might be esta- 

 blished between the temperature of the air and the motion of the 

 glacier, independent of the irregularly acting causes above adverted 

 to, I projected the motions of the several points of the glaciers in 

 terms of the temperature of the air for the periods already men- 

 tioned. 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 circumstances 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 Montanvert and Chamouni) may represent pretty 

 fairly the climate ric conditions of the inferior parts of the Glaciers 

 des Bois and Bossons. Now, if we examine the curves in question, 

 they indicate an almost perfect uniformity of motion 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 tem- 

 perature, in a ratio which would appear to bo tolerably uniform if we 

 neglect the irregular inflections of the curves. 



IX. I am unwilling to multiply deductions which every intelli- 

 gent 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., 



VOL. XLII. NO. LXXXIV. — APRIL 1847- Z 



