1846.] OSCILLATIONS OF GLACIERS THEIR CAUSES. 181 



feet to the eastward of the old larch seen in the views, Plate VII. 

 From this point, then (which cannot readily be mistaken), the 

 telescope of the theodolite was directed upon the steeple of the 

 little church of Entreves, the azimuth marked (286), and the 

 telescope was exactly levelled. It was then turned in azimuth 

 (tracing out the horizontal plane), until it cut the contour of the 



Horizon 



Fig. 20. Entries. 



glacier of La Brenva, which was at an azimuth of 1841. The 

 difference of azimuth 101|. It is plain that if the glacier 

 advances bodily into the valley, this angle will diminish ; if it 

 retreats, the angle will increase. Farther, from the same station, 

 B, the elevation of the highest part of the front of the glacier, 

 where it crosses the valley, was 11 37'. To fix the position of the 

 lowest point of the glacier in the valley, a line joining the vault of 

 ice from which the river Doire issues, and the door of the chapel 

 of Notre Dame (observed from below), runs S. 42 W. magnetic. 

 On the whole, the observations of this year on the sur- 

 prising extension of this glacier during the short space of four 

 years under the influence of meteorological circumstances, pecu- 

 liar, no doubt, but scarcely anomalous, confirm amply the 

 remarks which I formerly made (Travels, p. 205), on the great 

 extension which it underwent in 1818. Were the climate of 

 the years 1844 and 1845 to become permanent, the increase of 

 all glaciers would evidently be enormous. In* fact, a more 

 turbid and cloudy atmosphere, with an increase of the usual 

 precipitations, would suffice to increase glaciers to almost any 

 extent ; a great degree of dry cold would not produce the 

 desired effect (viz., an extension which would account for the 

 erratic phenomenon), a temperate climate being most favourable 

 to the growth, especially the. progression, of glaciers. 



