THE VARIATIONS OF GLACIERS. 279 
floods which occurred at the time when the ice-sheet was at its 
maximum (2. ¢., when the melting area was greatest), were 
stronger than those which occurred later, we may infer that the 
retreat of the ice was due rather to a diminution of the snow-fall 
than to an increased rate of melting, brought about by a warmer 
climate; whereas, if the stronger floods occurred after the ice 
had retreated some distance (2. ¢., when its area was smaller), we 
may infer the opposite. 
How soon does a glacier respond to climatic influences? 
This is a question which cannot be answered directly ; usually we 
find some glaciers advancing and others retreating at the same 
time; for instance, a little before the middle of this century the 
Alpine glaciers were apparently all advancing; one after another 
ceased to advance and began to shorten, the number joining the 
retreating forces_ being greatest between 1850 and 1860; but it 
was not until 1870 that all were losing ground; for five years 
thereafter no glacier in the Alps was known to be advancing; in 
1875, the glacier des Bossons, on Mt. Blanc, led the beginning 
of a new advance; since then others have joined it, until now 
some fifty or sixty are advancing. Peculiarities show themselves 
in the changes; glaciers in the same mountain group, and even 
glaciers so closely related as the Findelen and Gorner, near 
Zermatt, whose névé regions adjoin, are sometimes moving in 
opposite phases at the same time. In general there seems to be 
a readier response on the part of the smaller glaciers; and the 
steeper ones also seem to start earlier than the others; but as 
far as I know variations have not been analyzed according to the 
size, slope, height, exposure of the glaciers, etc.; in fact, it would 
be extremely difficult to analyze them properly without the guid- 
ance of a mathematical theory, which would enable us, when 
glacier, to calculate the velocity in its 
5 
different parts. Material, however, is being collected which will 
given the dimensions of a 
form a basis for such a theory, in the general records of the 
movements of glaciers, and more particularly in the accurate 
observations which are annually made on the Rhone glacier under 
the auspices of the Swiss Alpine Club, and on some other glaciers. 
