462 THE POPULAR SCIENCE MONTHLY. 



theory of expansion it is difficult to see how it will explain the 

 greater motion of the glacier in precisely that part of the year and 

 of the day when the heat is the greatest, and the influence of expan- 

 sion by freezing must necessarily be least operative. 



The rapidity of the glacier's motion is much greater than we would 

 naturally expect. By a course of very careful observations and meas- 

 urements, Prof, Sexe found that, in the middle of July, 1868, the ice 

 on the surface of the glacier of Boium, near the centre of the glacier 

 and some distance from the lower end, moved 204|^ inches (Norwegian) 

 in 211 hours. This was about y^g- of an inch per hour, and, if kept up 

 during the entii'e year, would have given a total motion of about 707 

 feet. Here the motion was considerably greater by day than by 

 night ; in the former, exceeding 1^ inch per hour, and, in the latter, 

 being about |^ only. M. de Seue, however, coming later in the same 

 month, when the weather was less uniformly pleasant, found the aver- 

 age rate of progression of the same point very much diminished, viz., 

 to less than | of an inch per hour ; and there is every reason to be- 

 lieve that, had these gentlemen been able to resume their observa- 

 tions in winter, they would have found that the motion during the 

 cold weather is almost inappreciable. It is unnecessary to say that 

 the difficulty of taking observations during half the year, on account 

 of the temperature, and the glacier being covered over with deep snow, 

 can scarcely be exaggerated. 



It is not every part of the glacier which moves with even the 

 rapidity mentioned. Toward the sides (and undoubtedly we should 

 also find it so at the bottom, if we could get at it), the influence of 

 friction can be detected retarding the motion. Near the lower end, 

 also, the ice appeared to advance not more than one-third as fast as 

 further up. 



Of the numerous glaciers which M. de Seue describes as descending 

 from the snow-field of Justedal, a number seem to be objects of great 

 beauty. The photographic views which accompany his paper unfor- 

 tunately fail to convey a very satisfactory idea of their appearance. 

 The most considerable is the glacier of Trensbergdal, some nine miles 

 long, and from two-thirds of a mile to nearly a mile in width. In 

 several cases two or more glaciers meet, and, joining their contents, 

 merge so thoroughly that they can be distinguished only by the 

 moraines lines of detached blocks of stone, torn from the rocks 

 above in the downward course of the icy current, and which mark 

 their edges even after their junction. Several are instances of what 

 the French savants have called glaciers remanies, the internal struct- 

 ure being altogetlier changed in consequence of their having been pre- 

 cipitated over ledges of rocks of considerable height. One of the 

 smallest of the number is the glacier of Lunde, which is less than a 

 mile in length, and only 100 feet in breadth. The interest attaching 

 to it, however, lies in the suddenness with which it makes its spring 



