RELATION BETWEEN RATE OF MOTION AND TEMPERATURE. 
191 
cidence with the curve of temperature is greater throughout than we could have 
expected, considering the important difference of circumstances which occur in 
autumn and in spring when the thermometer stands nearly alike, the first chill of 
autumn depriving the glacier of its fluid pressure more effectually than the severer 
cold of winter which is tempered by its snowy covering, whilst in spring the first re 
laxation of the bands of frost saturates the icy mass with the impetuous streams of 
melted snow, as effectually as theintensest heat of summer. In fact, the velocity would 
probably be greatest in spring, were it not that then the ice has attained, its greatest 
consolidation by the slow but continued effect of the winter’s cold penetrating its 
upper layers, though after all probably to no very great depth. But this is undoubt- 
edly 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 illus- 
tration 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, showing that the bands of 
frost were not so strong as to prevent a temporary relaxation of thaw throughout the 
mass of the glacier even in winter; and although the mean temperature of the air 
had been rising ever since the middle of January, and the greatest cold had occurred 
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 under- 
went 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 
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 XI. fig. 2, 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 circumstances of the whole 
glacier. Perhaps, therefore, the average of the observations at Geneva and St. Ber- 
nard (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 climateric 
conditions of the inferior parts of the Glaciers des Bois and Bossons. Now, if we 
examine the curves of fig. 2, 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. 
MDCCCXLVI. 2 C 
