THE VARIATIONS OF GLACIERS 47 



keep the record of the movements of some glaciers, but observations 

 there in the past have been very desultory. No systematic work has 

 been done by the government in the United States, although the maps 

 made by the Geological Survey and the Coast and Geodetic Survey 

 in glacial regions are of value in fixing the present positions of the 

 glaciers. Reports regarding the Antarctic and Arctic regions must 

 necessarily be irregular and must be obtained from exploratory expedi- 

 tions to those regions. 



Eleven annual reports have been pubhshed by the commission, 

 the first ten in the "Archives des sciences physiques et naturelles," 

 in Geneva. The eleventh report was pubhshed in the new Zeit- 

 schrijt fur Gletscherkunde, edited by Professor Eduard Briickner, of 

 Vienna, and future reports will appear there. A glance at these 

 reports will show that glaciers in all parts of the world are now retreat- 

 ing. The tendency to advance, which showed itself in the western 

 Alps about 1885 and which slowly passed on to the eastern Alps has 

 now practically disappeared. It did not extend to other glaciated 

 regions. 



Since the organization of the committee many theoretical and 

 observational studies of glaciers have been made. It has been shown 

 that when a glacier advances there is first an increase of thickness 

 and of velocity in the higher parts of the glacier and that a wave of 

 greater thickness and greater velocity travels down the glacier and 

 causes an advance of the end; this wave originates in an increased 

 accumulation in the reservoir, and in general the longer the glacier 

 the longer time will be needed for the wave to reach the end. It 

 has also been shown that the greatest thickness in the reservoir will 

 occur some time after the maximum snowfall; so that the advance of 

 the end may be many years after the period of maximum snowfall. If 

 the glacier itself advances sooner than this theory would lead us to 

 expect it must be due to diminished melting at the end, rather than to 

 increased accumulation in the reservoir. The application of the idea 

 of hydrodynamic lines of flow to the motion of glaciers has greatly 

 increased our understanding of glacial phenomena, and it is to the fur- 

 ther development and application of this idea that we must look for 

 the increase of our knowledge of glaciers in the near future. The long- 

 continued controversy as to the origin of the blue bands has been at 



