Literary and Philosophical Society of Liverpool. 233 
we owe to Professor Forbes the description of a very beautiful struc- 
ture in glaciers to which he has applied the term Conoidal, one 
aspect of which is the appearance of loops on the surface of the 
glacier, the apices of which point downwards in the direction of the 
glacier’s motion, and which Professor Forbes states “ give the idea 
of fluid motion, freest in the middle, obstructed by friction toward 
the sides and bottom.” 
B. Facts in regard to Motion.—lst. That glaciers do not pro- 
gress during winter. 2nd. That they progress during the warmer 
months at observed rates of 200 feet and upwards a year, according 
to circumstances of temperature, inclination of bed, &c. 3rd. That 
glaciers progress more rapidly in the centre than at the edges, and 
more rapidly at the lower than at the upper part of their bed. 4th. 
That glaciers progress more rapidly during the day than during 
the night, and that their motion is in proportion to the quantity of 
water supplied to their porous and capillary structure by the melting 
of their surface by atmospheric temperature and rains, so that their 
motion increases or diminishes according as the rise or fall of the 
atmospheric temperature increases or diminishes their supply of 
water. 5th. That the surfaces of glaciers are removed by melting 
and evaporation to the extent of several feet a year without any 
alteration in their level. 6th. That the peculiar conoidal structure 
already mentioned, as well as other facts observed by Professor 
Forbes, appear to establish the opinion entertained by him, that gla- 
ciers progress after the manner of semifluids. 
The author next proceeded to consider the theories which have 
been advanced to explain glacier-motion. Thesearetwoin number,— 
the Dilatation Theory and the Gravitation Theory. The first of 
these assumes that the water infiltrated into the glacier loses its 
caloric of fluidity, and in freezing expands longitudinally so as to 
force the glacier to advance, and vertically so as to maintain the 
thickness of the ice. Many objections were urged against this theory, 
two of the principal of which were the following :—I1st. That the 
temperature of the glacier had been proved by Agassiz to be32° Fahr. 
during its period of advance, and that it had never been proved 
that water proceeding from melted ice would freeze when brought 
in contact with ice at 32° Fahr. And it had besides been proved 
that the freezing point of water falls below 32° Fahr. under di- 
minished atmospheric pressure, which we know to exist at the al- 
titude of glacier regions. The occurrence of liquid water also at all 
depths in the glacier was shown to militate directly against the 
theory. 2nd. That in order to account for the ice always retaining 
its level, although the surface is constantly removed by melting and 
evaporation, the dilatation theory requires that al/ the water arising 
from this melting be refrozen in the substance of the glacier, whereas 
the greater part of it escapes by the crevices to the bed of the 
glacier, to form the glacier torrent, and only a small part enters the 
substance of the ice, and thus in one essential particular the theory 
is wholly inapplicable. 
The gravitation theory as promulgated by Saussure was shown 
