ON THE RETREAT OF THE EUROPEAN GLACIERS. 
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thus formed, arrives at the bottom of the glacier, where it melts. 
All this ice, therefore, represents the sum of the meteorological 
actions that have taken place during a very long period of time, 
perhaps more than a century. 
It would, therefore, he a mistake to seek in the last few 
years alone the cause of that retreat of the glaciers which we 
can now demonstrate. This would, no doubt, he the right course 
if the retreat were caused solely by a more rapid melting, hut 
it is quite otherwise if this cause ascends to the very origin of 
the glacier. Now the latter is probably the case, for meteoro- 
logical observations do not reveal to us any notable difference 
between the last quarter of a century and a preceding period. 
This is why the investigation of the great retreat of the 
glaciers that we now witness, must not be neglected ; it is right 
to watch and trace it to the end in all those countries where 
it has been demonstrated ; and the cause of this retreat, if we 
succeed in ascertaining it, will be an important factor among 
those which engage our attention in the study of the physics of 
the globe. 
Now, with regard to most glaciers, it is not difficult to 
appreciate the amount of the retreat. It is only necessary 
to draw a map of the lower extremity, as I have done several 
times with M. For el in the case of the Bhone glacier ; and in a 
question of this kind, with an element so variable as a glacier, 
it is not necessary to determine the position of each point 
within a centimetre or two. TJpon the moraine in front of 
the glacier we have established two fixed points, by means of 
two stakes firmly driven into the ground down to the level 
of its surface ; thence, with a small sextant, we determine the 
position of the most important points of the front of the 
glacier, which enables us to map it, and to see readily for each 
region of the glacier the amount of the retreat from year to 
year. 
