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SCIENCE. 



[N. S. Vol.. XXI. No. 53.5. 



He begins by giving tbe physical properties 

 of ice with accounts of the experiments for 

 determining the plasticity and other constants. 

 The climate of glacial regions is consid- 

 ered, and then the forms of glaciers, which 

 leads to a study of the position of the neve 

 line; he gives the different methods for deter- 

 mining the height of this line, one of which, 

 due to Dr. Iless, depends upon the forms of 

 the contour lines above and below the neve 

 line and can be used when one has a good con- 

 tour map. Dr. Hess divides glaciers into two 

 general classes ; the Alpine type or the valley 

 glaciers and the inland ice type, and says that 

 these two are not separated by any definite 

 line but that they gradually grade into each 

 other through glaciers of intermediate type. 

 A description of the general distribution of 

 glaciers over the world completes the first part 

 of the work. 



The movement of glaciers is then discussed 

 and many determinations of velocity are given. 

 The very incomplete observations which we 

 have bearing on the changes of velocity in 

 passing from the surface to the bed, is sup- 

 plemented by the observations of Dr. Hess, in 

 which he shows by means of the theory given 

 further on, that the average velocity through a 

 particular section of the Hintereis glacier is 

 less than the average velocity of the surface. 

 The thickness of the ice was determined by 

 borings which completely pierced the glacier, 

 one of which was 153 meters deep. Dr. Hess 

 was convinced, as a result of his general ob- 

 servations, that the blue bands of glaciers were 

 merely modified strata, and by means of an 

 artificial glacier, made up of layers of different 

 colored wax, succeeded in making the original 

 layers take the forms which the bands assume. 

 In the chapter on ' Ice and Rock,' the phenom- 

 ena of moraines, superficial and internal, are 

 described, following the classification adopted 

 at the Rhone conference in 1899. He con- 

 siders that glaciers are strong erosive agents 

 and fortifies this view by a measurement of 

 the quantity of material being brought to the 

 surface by one of the internal moraines. The 

 origin of this moraine he follows to a snow- 

 covered jjeak in the region of the reservoir, 

 whose character is such that he thinks the 



material could not have fallen from its sur- 

 face and must therefore have been derived 

 from the glacier's bed. In the chapter on 

 ' The Ice Age ' he also shows how the valleys 

 have changed their shapes into the well-known 

 glacial troughs. 



A very interesting account is given of the 

 variations of glaciers. Beginning with the 

 seasonal changes, he goes on to describe the 

 larger variations which follow Brucknei-'s pe- 

 riod and he collects together the observations 

 that have been made on this subject. He con- 

 siders that the main cause of the glacial varia- 

 tions are variations of climate but that this 

 is greatly modified by topographic conditions. 

 Glaciers like the Vernagt, which have a large 

 basin-like reservoir and a narrow tongue, do 

 not begin to advance until there has been a 

 large collection of snow in the reservoir and 

 then the advance takes place very rapidly; 

 whereas another glacier, whose outlet from the 

 reservoir is broad and open, will probably re- 

 spond quickly to climatic changes. He de- 

 scribes very interesting changes that have 

 taken place in the Vernagt glacier since 1895, 

 when the accumulation in the reservoir began 

 to show itself; the end continued to re- 

 treat until 1897, after which came an advance. 

 This advance seems to have run its course as 

 the glacier is now about stationary. The 

 observations showed that the ice grew thicker 

 in the reservoir and that what might be called 

 a wave advanced along the glacier to its end. 

 very gi-eatly increasing the velocity of the ice 

 and itself moving still more rapidly. The 

 historical theories of the cause of glacial mo- 

 tion are described; Dr. Hess looks upon the 

 plastidty of ice as the property which allows 

 it to flow. It is only at this point that he 

 takes up the geometrical theory of glacial 

 motion, given simultaneously by Finsterwalder 

 and by Reid, and describes the lines of flow 

 and the relations existing between accumula- 

 tion, flow and melting. This theory is so 

 fundamental in its bearings on all glacial 

 phenomena that it might have been given with 

 advantage in an earlier part of the book. This 

 is followed by an account of Professor Finster- 

 walder's mathematical theory of glacier varia- 

 tions. In this theory. Professor Finsterwalder 



