—_ 
Professor Forbes’s Ninth Letter on Glaciers. 333 
particulars, especially if the observations have been made 
in circumstances at all different. In this respect, I find 
with pleasure, from a communication read at the Institute on 
the 9th December last, that M. Agassiz’s coadjutors on the 
glacier ofthe Aar, have obtained results so perfectly accord- 
ant with those which you have done me the favour of pub- 
lishing on former occasions, that they would have satis- 
factorily established, had earlier observations been awanting, 
the viscous theory of glacier motion with which alone they 
are reconcilable ; the single seeming antagonism to my own 
measurements being one which tells still more in favour of 
that view. . 
I propose to give a brief summary of these results, and to 
shew their correspondence with my own. This correspon- 
dence—amounting almost to coincidence—is, of course, éo 
me, a satisfactory guarantee for their accuracy, as far as 
they go. By others, the goodness of the instruments, and the 
expertness of the observers, must, in the mean time, be taken 
for granted. 
It is hardly necessary to premise that M. Agassiz and 
his friends now admit that all glaciers move fastest at the 
centre, and slowest at the sides. 
But a new fact still less reconcilable with the dilatation 
theory resulted from the first attempt to apply geometrical 
measurement to the motions of this glacier ; viz., 
I. The glacier of the Aar moves fastest in its middle 
region, and slower in its upper and lower regions (7. e. to- 
wards the origin and termination). The slowness in the 
upper region does not so plainly follow from the facts at pre- 
sent before us, but the retardation towards the termination of 
the glacier is undoubted. The following are the motions origi- 
nally ascertained, in $ of a year, or, more exactly, 289 days. 
We prefer retaining the original measures in Swiss feet ; the 
stations are in descending order, and a quarter of league 
(4000 feet) apart* (the second in order indicates the rock 
called Hotel des Neufchatelois.) 
* Bulletin de la Societé de Neufchatel, 8th Nov. 1843. 
