338 Professor Forbes' s Fourteenth Letter on Glaciers. 



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 ; li foot at Chamouni. The arch of the source of the Ar- 

 veiron 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 threat- 

 ened (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 lst-3d, Mild with rain ; 3d-13th, cold ; 15th, heavy rain. 

 Alternate rain and fine till the end of the month. 27th, Not half 

 a foot of snow lying at Chamouni. The source of the Arveiron has 

 not opened a vault. The quantity and muddiness of the water the 

 same as at the last report. 



April. — First week fine ; second week cold with snow ; change- 

 able to the end of the month. 16th, Source of Arveiron has not 

 much increased in water since the middle of March. In the end of 

 April the snow first disappeared from the lower part of both gla- 

 ciers. 



May. — The first half of the month fine, with occasional snow ; 

 the second half changeable, with rain. 17th, The source of the 

 Arveiron has increased three-fourths(m6a/^5 probably in the ratio of 

 four to one) since the middle of April, and is dirty. The ice- vault 

 is not yet formed. 26th, The Glacier des Bossons advances rapidly, 

 and is crumbling into pyramids. The end of the glacier is, at least, 

 eighty -five feet high, and advances considerably, particularly during 

 the month of May ; and widens greatly. 



June. — A changeable and wet month ; a very late season.f The 

 snow did not entirely disappear from the Mer de Glace, opposite the 

 Montanvert, till the beginning of July. 6th — 7th, The vault opened 

 at the source of the Arveiron. The quantity of water since the end 

 of May is the usual summer supply. 



July. — Commenced with warm weather. 5th, Thermometer 27° 

 Reaum. The snow has disappeared from the ice opposite Montan- 



* 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 pre- 

 cursor of bad weather) not only produces a thaw there, but finds the usual 

 channels still open for transmitting the accumulated snow water. 



t It will be seen from the temperature curves that the thermometer fell con- 

 siderably in the latter part of June, both at Geneva and St Bernard. 



