340 Professor Forbes’s Ninth Letter on Glaciers. 
in 24 hours ; and another, at an inclination of 20°, moved 1.8 
inches in the same time. This small result is quite confor- 
mable with the dry and powdery condition of such elevated 
glaciers, yielding little water, and capable of exerting, on 
their under parts, a very trifling hydrostatic pressure.* 
Exactly analogous results were obtained by M. Agassiz’s 
coadjutors at a somewhat later period of the same year. 
The experiments are fully detailed in the Comptes Rendus ;+ 
and the conclusions which are deducible from them, are (1), 
that the daily motions of these small glaciers, which, rested 
on beds so highly inclined as from 15° up to 33°, are included 
between 20 and 72 millimetres (0.79 to 2.84 English inches) 
per diem. (2.) The observers think that their observations 
go to prove that when these glaciers are prolonged far enough 
to meet the main glacier below, and to unite their streams, 
then the lower part of the tributary glacier, or that nearest 
the point of union, moves SLOWER than the upper part, or that 
nearest the origin of the little glacier ; but, on the contrary, 
if the glacier be pendant on the slope, and the lower end 
decays away without joining the principal, then the inferior 
extremity moves FASTER than the origin. Now the cause of 
this variation in the two cases (should the fact really appear 
to be general, as is not unlikely, provided the lower station 
be always chosen low enough), seems to be, that the main 
glacier resists the interference of its tributary with its 
course, and consequently represses its stream, causing a 
heaping up in front, such as mere friction on a low incli- 
nation alone produces, and is thus in conformity with the 
viscous theory. In the other case, that of the free glacier 
of the second order, the difference of velocity at the upper 
and lower station (one-seventh part only) is not more than 
the difference of slope (15° and 25°) will readily explain. 
VI. Movements of Bas-Névés or Snow-beds. One observation 
remains which completes my analysis of the measures of 
M. Agassiz’s coadjutors. Itis one of considerable interest, and 
I believe isnew. It is the establishment of the fact that the 
* This experiment is briefly mentioned at the close of my Highth Letter 
on Glaciers. 
t p. 1303 and two following pages. 
