io6 Mr. H. H. Howorth on 



ones (id., 328). This most important generalization, which 

 has been amply confirmed since, was the first step in 

 a truly scientific theory of glaciers based upon experimental 

 and not upon a priori methods. 



M.Martins proposed another modification of DeSaussure's 

 theory. He states his theory thus : "In summer, immense 

 transverse crevasses divide the entire mass of the glacier 

 vertically into so many secondary wedge-shaped masses ; 

 consequently its surface is increased by the sum of all the 

 spaces which the crevices leave between them at their upper 

 part. The glacier resting firmly against the mountain 

 cannot be pushed backward ; it is, therefore at its lower 

 part when nothing arrests it, that it becomes displaced and 

 moves forward. The winter following, these crevices are 

 filled with snow, blown into them by the winds, or falling in 

 the form of avalanches. This snow becomes ice under the 

 alternate influences of melting and freezing during the 

 months of May, June, September, and October. In the 

 succeeding summer months new crevices are formed, the 

 glacier advances, and so on successively. This progression 

 is therefore neither a slipping nor a sinking (both of which 

 it is difficult to admit, since the ice must adhere to the 

 ground), but a successive dismemberment (^^. P>^27.yi^?/r.,, 

 30. 294). 



Besides the objection that we now know, that the move- 

 ment of glaciers is continuous and not by jerks, Forbes 

 adds, that it is universally admitted that the glacier proper 

 does not grow by the consolidation of snow in its fissures 

 {Theory of Glaciers, \o\). 



The views of De Saussure were revived and modified, as 

 I have mentioned, by a physicist of the first rank, in the 

 person of Mr. W. Hopkins. In his modification of the 

 theory, he got over the difficulty of the differential motion 

 by a somewhat ingenious argument. In his paper published 

 in the eighth volume of the Cmnbridge Transactions, he 



