and the Inundations of the Val de Bagnes. 189 
ciit a subterraneous gallery for the purpose of effecting a gra^- 
dual discharge. With this^ view, the lower end of the gallery 
was sixty feet below the line of contact of the cone of ice with the 
flank of Mont Mauvoisin, and its upper extremity was fixed at 
the height to which the lake might be calculated to have risen 
when the gallery was finished. In this way, the water entering 
the upper extremity of the gallery, might be expected to deepen 
it by degrees, and thus permit the surface of the lake to de- 
scend gradually, till it was nearly emptied. This ingenious 
and bold scheme was begun on the 10th of May, and finished 
on the 13th of June,, under the direction of M.Venetz, an able 
engineer of the Valais. The gallery was sixty-eight feet long, 
and, during its formation, the workmen were exposed to the 
constant risk of being crushed to pieces by the falling blocks of 
ice,, or buried under the glacier itself. 
During the thirty-four days which were spent in the forma- 
tion of the gallery, the lake had risen sixty-two feet, but from 
particular causes, the upper entrance to the gaUery was still 
many feet above the surface of the lake. Without waiting for 
the farther rise of the waters, M. Venetz sunk the floor of the 
gallery several feet, and the water began to enter it on the 13th 
of J une. At this period, the length of the lake was from 10,000 
to 12,000 feet ; its average breadth, at the surface, about 700 
feet, and, at the bottom, about 100 feet. Its absolute average 
breadth was 400 feet ; its average depth 200 feet ; and its con- 
tents at least 800 millions of cubic feet. 
After the 14th of June, at 11 o’clock, the floor of the gal- 
lery began to wear down, and at 5 o’clock the lake was low- 
ered one foot. On the 15th of June, at 6 o’clock A. M. the 
height of the lake was diminished ten feet ; twenty-four hours 
afterwards, it was diminished thirty-six feet ; and on the 16th of 
June, at 6 o’clock P. M. the total diminution was forty-five 
feet. The effect of the gallery, therefore, had been to reduce 
the lake from 800 to 530 millions of cubic feet. 
As soon as the water flowed from the lower end of the 
gallery, the velocity of the cascade melted the ice, and 
thus wore away the gallery at its mouth. The water which 
had penetrated the crevices of the glacier, caused enormous 
fragments of ice to fall from the lower sides of it, so that owing to 
