CONGELATION OF INFILTRATED WATER DISCUSSED. xix 



times, and many of them during journeys, I believe that a sub- 

 stantial unity pervades the whole. 



On only one point of any importance was the original theory, 

 as delivered in the " Travels in the Alps," subsequently modi- 

 fied. In the earlier of my writings, I attributed the conversion 

 of the powdery neve into the perfect glacier (as I believe nearly 

 all preceding and contemporary authors had done), as well the 

 alternations of perfect and porous ice in the " veined structure" 

 of the latter (which at that time no one else had tried to ac- 

 count for), to the congelation by the winter's frost of water 

 percolating through their interstices. In the former case, the 

 interstitial spaces were those of the snowy granules ; in the 

 latter, the flaws due to the differential motion of the central 

 and lateral parts of the glacier. 



The congelation of infiltrated water was not a doctrine 

 which originated with me, but rather one which I had assisted 

 in banishing as much as possible from glacial speculations. 

 Having endeavoured to demonstrate that no efficient congela- 

 tion of this description can take place in summer when the 

 motion of the glacier is most rapid, I would gladly have dis- 

 pensed with it altogether. Still it was impossible to deny that 

 the winter's cold must penetrate to some depth in the glacier, 

 and at first I was willing to admit not only that it was the 

 efficient cause of the conversion of the neve into ice, and of the 

 glassy bands of the veined structure, but that it might by its 

 expansion restore the level of the glacier, during winter, to the 

 point from which it had fallen by the waste of the previous 

 summer. This was the idea I had in 1842.* But by the time 

 of the publication of the first edition of my Travels in the Alps 

 in 1843, I had already got rid of the necessity for allowing this 

 vertical dilatation, by including the ascent of the glacial surface 



* Fourth Letter on Glaciers (1842), p. 34 of this volume. 



