1895.] on Influence of Science on Mountaineering. 455 



it will often be powdery, as was found on the first ascent of 

 Chimborazo. This condition is rare in the Alps. In the latter, 

 indeed, the worst conditions of snow seldom in the summer months 

 turn back the mountaineer, but in higher regions, where time is of the 

 first consequence, it would be of the greatest moment to judge before- 

 hand in what condition the snow is likely to be found. The compass 

 bearings with regard to the sun of the slopes up which the track lies, 

 the prevailing winds and their temperature, the radiation from rocks 

 in the neighbourhood and such like factors must be taken into account. 

 With regard to the formation of crevasses Tyndall did much work, 

 though it was limited rather to the lower portion of the glacier, and 

 extended little above the ice-falls. He showed most clearly the 

 method of formation of crevasses, longitudinal, transverse and oblique. 

 Many years previously Besson had said " the ice of a glacier flows 

 like a torrent following fluid laws," probably not appreciating the 

 full truth of his own remark. Tyndall by careful measurement 

 showed the situation of the point of maximum motion and demon- 

 strated that when a glacier curved, the point of maximum motion lay 

 nearer the convex border of the glacier. Thus in a glacier whose 

 course is serpentine, the lines of maximum rate of motion crossed the 

 central line at each curve. From this a practical point in mountain- 

 eering can be deduced. In descending an unknown glacier, it is 

 generally best when the ice cannot be quitted to keep on the side of 

 the smaller curve of the glacier where the marginal crevasses will be 

 less numerous on this border. I can recall an occasion in the 

 Caucasus when inattention to this point led to our being benighted 

 on the glacier. 



On the so-called dirt-bands, first noticed by Professor Forbes in 

 1842, Tyndall made many observations. It is matter for regret that 

 a feature of glaciers so beautiful as these great curving stripes should 

 have received so unpoetic a name. Tyndall clearly demonstrated 

 their formation in the ice-falls. To the mountaineer much that is 

 practical may be gathered from their presence. Thus the existence 

 of dirt-bands shows conclusively that there must be an ice-fall at 

 some part of the glacier, and that there must be rocks in the neigh- 

 bourhood capable of yielding the grit of which the dirt-bands are 

 composed. Several glaciers may coalesce and form the main stream. 

 Thus the Mer de Glace has three tributaries ; on one, the Glacier du 

 Geant, the dirt-bands are strongly marked, on another, corresponding 

 to the Glacier de Talefre, they are but faintly indicated, while the 

 third, the central stream, has no dirt-bands at all. These several 

 streams can be distinguished one from another, to the very extremity 

 of the Mer de Glace, by the medial moraines. It is certain then that 

 on two of the glaciers higher up will be found ice-falls, and that the 

 third, the central, will lead by more or less gentle declivities to the 

 snow basins that feed it. Suppose the Mer de Glace were an unex- 

 plored field visited for the first time, such an observation might ob- 

 viously be of the highest value in determining the route to be taken. 



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