188 PROFESSOR FORBES ON THE VISCOUS THEORY OF GLACIER MOTION. 
estimate these more irregular causes is not so easy ; but some light is thrown upon 
them by a register of the weather and state of the snow, voluntarily kept for me 
at Chamouni by Auguste Balmat ; which forms a valuable supplement to the ther- 
mometrical register of Geneva and St. Bernard. Although the daily details would 
take up too much space, I will endeavour to give a faithful abstract of them so far 
as to give a general idea of the climate of Chamouni from October 1844 to November 
1845. This diary includes (at my request) occasional notes on the state of the source 
of the Arveiron, which are of considerable interest. 
Weather at Chamouni. 
1844. October. — A good deal of rain during the month, which on the 10th and 
16th fell as snow on the hills (nine inches at Montanvert), and subsequently to the 
latter day the glacier at the Montanvert was not clear of snow during the winter. 
14th. Source of the Arveiron diminished to one-fourth (of the summer volume). Ice- 
vault more than half closed. 
November. — Till 14th much rain and snow; fine with frost after. 20th. Source 
of the Arveiron very low ; has not shifted its usual position. 
December. — Weather generally fine throughout ; cold most severe from 7th to 12th. 
1845. January. — The weather continued splendid till the 20th; greatest cold from 
— 2° to —5° Reaumur. 19th. The vault has disappeared at the source of the 
Arveiron. 20th. The first snow fell which lay at Chamouni, and continued from this 
day, attaining a depth of 1^ foot in February. Up to this time all the secondary 
heights, even the Breven and Flegere, were clear of snow, and the weather suitable 
for Chamois hunting. Occasional snow till the end of the month. 
February. — Snow at intervals all the month. 13th. Greatest cold of the season; 
thermometer — 15°Reaum. followed by fine weather. 20th. Snow lies 2^ feet deep at 
the upper stations on the glaciers ; 1^ foot at Chamouni. The arch of the source of 
the Arveiron has wholly disappeared, but the water issues at the usual places as in 
summer. The water is reduced to a small amount and may easily be stepped across. 
It is still whitish and dirty , though less so than in summer; except when a change of 
weather is threatened (when it is as dirty as in summer) *. Same date. The glacier 
of Bossons has extended itself much. “ On ne s’y reconnait presque plus.” It is 
advancing towards the moraine of 1818; and the lower end is at least seventy 
feet high. 
March 1st — 3rd, mild, with rain; 3rd — 13th, cold; 15th, heavy rain. Alternate 
rain and fine till end of the month. 27th. Not half a foot of snow lying at Cha- 
mouni. The source of the Arveiron has not opened a vault. The quantity and 
muddiness of the water the same as at the last report. 
* This important remark proves that in the middle of winter a temporary rise of temperature of the air over 
the higher glacier regions (which is the precursor of bad weather) not only produces a thaw there, but finds 
the usual channels still open for transmitting the accumulated snow water. 
