280 LTE OWKINAL, OF 8GOLEOGN A 
M. Forel has collected and discussed the records of variations 
of glaciers in a series of most interesting reports to the Swiss 
Alpine Club.*. He finds that glaciers go through periodic changes 
of from thirty-five to fifty years’ duration.” Beginning with a 
glacier at its minimum the changes occur in the following order: 
First comes an increased velocity due to increased snow-fall, and 
the glacier advances rather rapidly ; later the velocity diminishes, 
the glacier reaches its maximum, and then begins to retreat. 
During this whole period the rate of melting may not have 
changed at all markedly. The advance is rapid, taking about a 
third as long as the retreat, which is merely a time of melting, 
during a diminished flow, until a new advance, produced by 
increased snow-fall, begins again. The average for quite a num- 
ber of glaciers observed during this century gives a complete 
period of thirty-eight years or more. But the subject is much 
complicated by the fact that different glaciers begin and end 
their advance at widely different times; so different indeed, that 
we can frequently in a given year find different glaciers represent- 
ing all phases of advance and retreat. This makes the task of 
comparing variations of climate with variations of glaciers very 
difficult, for one does not know what to consider the time of 
maximum or minimum advance. 
Some progress has however been made; Professor Brickner? 
starting with the fact that glaciers have periodic changes, made 
an exhaustive study of the variations in the heights of lakes, of 
interior seas; of the inundations of rivers, and the duration of 
their winter freezing; of agricultural matters, such as the times 
of vintage, etc., and found a similar period in them all. He 
then took up meteorological observations proper and found the 
same thing. His researches reach back to 1700. He was able 
tJahrbuch des Schw, Alp. Club, from 1881 to date. I am indebted to Professor 
Forel and Professor Richter (cited below) for almost all the material of this paper. 
2 American glaciers are in general retreating, but observations have not been fre- 
quent enough to show a periodicity in their movements. 
3 Klima-Schwankungen seit 1700. Geog. Abhand. von Dr. Penck, 1890, IV. 
(cited by Professor Forel). 
