8 ON THE STRUCTURE AND MOTION OF GLACIERS 
we believe, a phenomenon of common occurrence. Professor Forbes 
calls the glacier a “crackling mass ;” he speaks of the ice “ cracking 
and straining forwards;” and in that concluding passage of his 
‘Travels’ which has excited such general admiration, he says of the 
glacier, “it yields groaning to its fate.” Other observers make use of 
similar expressions. M. Desor also speaks of the sudden change 
of the colour of the blue veins of the ice where a portion of the central 
moraine near the Abschwung is cleared away ; the observation is 
very remarkable. “Au moment,” says M. Desor,* ou on la met a 
découvert, la glace des bandes bleues est parfaitement transparente, 
ceil y plonge jusqu’a une profondeur de plusieurs pieds, mais cette 
pureté ne dure qu’un instant, et l’on voit bientét se former des petites 
félures d’abord superficielles, qui se combinent en réseau de maniére 
a enlever peu a peu a la glace bleue toute sa transparence. Ces 
félures propagent également dans les bandes blanches, et lorsqu’on 
approche l’oreille de la surface de la glace, en entend distinctement un 
léger bruit de crépitation qui les accompagnent au moment de leur 
formation.” These facts appear to be totally at variance with the idea 
of viscosity. 
In a chapter on the “ Appearance of the larger Glaciers,” in an 
interesting little work by M. Mousson of Ziirich, for which one of us ' 
has to thank the kindness of Professor Clausius, the phenomena which . 
they exhibit are thus described :—!“ The appearance of a large glacier © 
of the first order has been compared, not without reason, with that of 
a high swelled, and suddenly solidified stream. It winds itself in a 
similar manner through the curving of the valley, is deflected by 
obstacles, contracts its width, or spreads itself out... .. . In short, 
the form is modified in the most complete manner to suit the 
character and irregularities of its bed. To this capacity to change its 
form, the ice of glaciers unites another property, which reminds us of 
the fluid condition ; namely, the capability of joining and blending 
with other ice. Thus we see separate glacier branches perfectly 
uniting themselves to a single trunk; regenerated glaciers formed 
from crushed fragments ; fissures and chasms closed up, and other 
similar appearances. These phenomena evidently point to a slow 
movement of the particles of which the glacier consists; strange as 
the application of such an idea to a solid brittle mass such as glacier 
ice may appear to be. The solution of this enigma constitutes one of 
the most difficult points in the explanation of glaciers.” 
When the appearances here enumerated are considered with 
reference to the experiments on the regelation of ice above described, 
1 Die Gletscher des Jetztzeit, by Albert Mousson. Ziirich, 1854. 
