454 Mr. Clinton T. Dent [Feb. 15, 



definition of a word. One feels almost inclined to echo John Hunter's 

 well-known condemnation of definitions. On one point there can be 

 little doubt; Tyndall's views fitted in admirably with practical 

 mountaineering. He rendered clear and precise the interpretation 

 of so many glacial phenomena that he almost made what is known as 

 snowcraft — the most intricate, and the most valuable branch of 

 mountaineering, for it is on excellence in snowcraft that the future 

 of mountain exploration chiefly depends. But the great influence he 

 had on mountaineering was through his brilliant writings and lectures. 

 Owing largely to these the glacial world began to attract the general 

 interest which before had been confined to the few who had frequented 

 and climbed the high Alps. This result was due to his admirable ex- 

 perimental methods and to the brilliancy with which he expounded his 

 views, and it was in this theatre mainly that the exposition was made. 

 T may throw on the screen a slide, a view of the Weisshorn by 

 Mr. Donkin, which almost epitomises the lectures on " Ice, Water, 

 Vapour and Air." Imagine that from the w 7 ater in the foreground 

 rises the vapour in solution. The warm air as it rises expands. The 

 expansion produces cooling ; as a result of the cooling the vapour is 

 condensed and the cloud is formed. Once formed, the band of cloud 

 may remain stationary and of uniform size for a long time, constantly 

 forming afresh on one surface, and as constantly diminishing on the 

 other. Or the cloud may increase in volume. Following it then 

 further in imagination till it becomes a rain cloud, the view shows 

 the light fresh snow which has fallen on the higher flanks of the 

 mountains. The snow sinks as the crystals part with their contained 

 air, and so the mass by its ow r n weight is pressed into firm snow, then 

 into neve, then again into pure ice, which melts and flows away as a 

 river. The circle is complete and the whole life history of a glacier 

 is shown in this one view — not the less notable in that it is the pre- 

 sentment of the mountain on which Tyndall's greatest climbing feat 

 was accomplished in 1861. 



Time forbids any endeavour to repeat the more striking of the 

 experiments shown to illustrate these processes, but I may bring 

 before your notice once again the simple experiment first made by 

 Faraday in 1850 to illustrate regelation. This simple observation 

 on the properties of regelation was applied by Tyndall to the inter- 

 pretation of many glacial phenomena. He showed that as the glacier 

 passed through any narrow channel or was torn and fissured as it 

 swept over the slopes or formed an ice-fall that the ice was subject 

 to crushing, and he demonstrated that pressure alone was sufficient 

 to account for the complete remoulding of the mass, the closing of 

 the crevasses, and the re-establishment of the purity of the ice. 

 Unless snow possess these properties all travel on the snowfields 

 would be impossible. When below the freezing-point regelation does 

 not take place. This fact, with regard to the highest ascents where 

 the cold may be extreme, is of obvious significance. Under con- 

 ditions of extreme cold, and where the snow contains little air, 



