The Hawaiian gazette., 1872-01-10
The Mont Gents Tunnel.

IL may De rs well TO state that, though
called after Mont Gems, the tunnel really
pierces the Col de Freius, and is situated
at least fifteen miles to the Southwest OF
Mont Gents. 1t is 3,7O9 feet above the
level of the sea, and $50 feet above the
Mont Gems road at Modane The aver
age incline is one in forty-fve to a point
midway between the tive entrances. The
exact length, according TO a very interest
ing account in the Journal des DeJatS, is
1928 metres. 1t was calculated that the
distance would be 1920 metres, so that
the difference in the actual length is very
little. This wonderful tunnel of seven
and three-ffth miles, is said to be four and
a half miles longer than any railway tm-
mel ever made.
We now pass on to consider the ma
chimes by which this work has been ac-
complished The same power-water-
tunneled the rock, and supplied the air to
the workmen. The mountain streams of
the neighborhood, by hydraulic pressure,
compressed the air to six atmospheres,
and so worked the perforating machine.
The water was collected in large reser-
voir higher than the mouth of the tunnel,
and pressure obtained equal to twenty
six feet perpendicular. Ten air compress
sing machines and two aerometers were
placed near the mouth of the tunnel. The
compressors were worked by the aerome-
tiers, which in their turn had yielded to
the water-pressure. The air having been
condensed in the compressors, was forced
into the receivers to work the excavating
machine. The latter consisted of ten per-
forators and seven jumpers, which latter
bore into the rock, being worked by the
compressed air instead of steam. These
made a series of holes about yard deep,
which, when the jumpers had penetrated
as far as they would go, were filed with
gunpowder and exploded Before this
was done, however, the whole machine
and attendants retired to safe distance
behind stout wooden doors. The debris
had then to be carried away. According
to the nature of the rock, about two or
three yards could be accomplished in
twenty-four hours. The machine excavat-
ed an arc of twelve feet by eight; the
rest had to be done by hand and we have
seen it stated that operations would have
been conducted quickerif gun-cotton had
been used instead of gunpowder, owing
to the smoke made by the explosion of the
latter.
Light was wanted, of course; so the
Italian engineers manufactured their gas
Throughout the work, these engineers
have shown themselves indefatigable and
under their superintendent the whole |
was carried out,-France, on the annexa-
ton of Savoy, agreeing to pay half the
cost. The whole amount has been stated
at 65,OOO,OOO francs, or e2,6OO,OOO; but
from other statements / should think
f3, 100000 nearer the mark. In conse-
quence of the rapidity with which the
work was executed, France has to pay
100000 of the Italians share; for at
first it was thought it would take twenty
five years, and France had topay 100000
francs for every year less than the twenty
five, and 100000 francs for every year
less than fifteen. Imitators are springing
up. Already the st. Gothard is to be
pierced; and enterprising English engi-
neers even suggest tunnel from England
to France.
The old diligences took about nine hours
to cross the Alps by the Mont Gents route;
the Fell Railway did the same in four and
a half hours, and now the official " train
went through the tunnel in thirty-eight
and it is believed that when the
line is in full operation, only twenty min
utes will be occupied
The vertical distance of perforated stra-
tum is about 1000 metres. NJ Ellie de
Beaumont read a paper before the French
Academy of Sciences, Sept. 18th, to elicit |