160 PROFESSOR FORBES ON THE VISCOUS THEORY OF GLACIER MOTION. 
Studer’s account : 
“Die bisher fast allgemein herrschende Theorie erklarte die Bewegung der Glet- 
scher aus der Schvvere allein. Es soli die Gletschermasse als starrer Korper auf 
ihrer Felsgrundlage, wie auf einer schiefen Ebene, theils durch ihr eigenes Gewicht 
theils durch dem Druck der hoheren Eis- und Firnmasse herunter gleiten (Gruner, 
Ramond, Kuhn, De Saussure, Escher) 
This last testimony of the most exact and most learned of the living Swiss geologists 
as to the sense in which De Saussure’s theory has always been understood is so im- 
portant that I shall add a translation : “The hitherto generally prevailing theory ex- 
plains the movement of the glaciers by gravity alone. The glacier masses are con- 
sidered as rigid bodies, which slide down over their rocky beds partly by their own 
weight, partly under the pressure of the higher ice and n£vdT My interpretation of 
the views of De Saussure as regards the rigidity of the glacier ice is thus borne 
out by an independent authority, for M. Studer’s work and my own appeared 
simultaneously. It is further confirmed by private communication with another 
eminent Swiss naturalist nearly connected by relationship with De Saussure him 
self, who is more intimately acquainted with the opinions and writings of his illus- 
trious kinsman than any other person now alive, and who considers that De 
Saussure’s views were confined to the general analogy of the glaciers to solid masses 
sliding down inclined planes, and that the effects of the inequalities of the channels 
and forms of the ice-basins were not comprehended in his theory. 
If we feel surprise that a naturalist and observer so eminent had not adverted to 
the difficulty of imagining a solid cake of ice, even though perfectly detached from 
its bed, to disengage itself from the obstacles and sinuosities of its rocky channel, 
we should remember,— -first, that the explanation is given in the most general terms, 
and there is no appearance that its author looked more closely at its consequences 
and details than to satisfy himself that a sliding motion in the abstract was rendered 
possible by the action of the earth’s proper heat, an ingenious and philosophical 
element of the theory (however inadequate), and that which being due principally to 
De Saussure, renders the theory properly his, and connected it with his ingenious 
inquiry into this curious part of physics as a distinct and wholly independent investi- 
gation. Secondly. Every one knows how an application of a principle so true and so 
ingenious leads men of even the most exact habits of thought to overlook difficulties in 
a subject almost unstudied. De Saussure did much for our knowledge of glaciers, 
and he saw much which no one had observed before him : we must not blame him if, 
yielding to a true and natural analogy of sliding bodies, he overlooked real and great 
difficulties inherent in the conception of a glacier as a solid continuous mass and 
highly rigid. Thirdly. In De Saussure’s time no plan or map, worthy of the name, 
of any glacier existed, and this was a blank which even De Saussure did not attempt 
to supply. The popular notion of a glacier, which it is certain he had in his mind 
* Lehrbuch der physikalischen Geographic und Geologie, 1844. 
