The Sun.
London, England, 1858-07-08 00:00:00

THE SUBALPINS TUNNEL.

An interesting communication on this important
subject has just been received by the Academy of
Sciences from M. Menabrea, one of the moat dis-
tinguished members of the Piedmontese Parlia-
ment. It was stated several months ago that the
immense work of boring a tunnel under the Alps
between Modane aud Bazdonece e ha.l coula,e:lt.;,d ;
but. we have now to recetu some interesting facts -
eicis night perhaps never have been discovered but
for the peculiar methods employed in this colossal
operation. Modane and Berdoneche are situated on
opposite sides of the Alpine chain dividing Pied-
mont
from France, precisely at a point where the
valleys of the Arc and the Dora, which lie nearly
on the same level, run parallel to each other, and
the mountain is narrowest. The thickness of the
intervening mountain is 13 kilometresin a straight
line ; the actual tunnel will be 12i kilometres. It
is designed in the same vertical plane, but, tofacili-
tate drainage, is somewhat higher in the middle
than at the orifices, so as to form gentle slopes
on both sides—one not exceeding an inclination
of five per thousand, aril the other being twenty-
three per thousand, in consequence of a differ-
ence
of level between the two• extremities, the
numbers being Bardoneche (southern mitt :e)
1,324 metres ; culminating point, 1,335 metres ;
Modane (northern orifice), 1,190 metres above the
level of the sea. The crest of the mountairebe ng
1,600 metres higher than the culminating point,
the sinking of shafts, which is the method gener-
ally employed in order to begin boring tunnels at
several points at once, was out of the question ;
hence the tunnel could only be worked at its ex-
tremities, so that the labour by the ordinary pro-
ces tes could not be accomplished in less than 36
years. Then, how was a depth of gallery of three
or four kilometres, and having but one orificeeto
be aired ? These were all serious obstacles. MM.
Elie do Beaumont and Angelo Simonds having
examined the mountain geologically, found it to
contain micaceous sandstone, micaceous eehists,
quartzite, gypsum, and limestone, all easy to blast,
the quattaite alone excepted ; but the stratum
of this is not likely to be very thick ; the
other elifficulties alone therefore remained,
and these were at length overcome by
three Sardinian engineer., MM. Sommeiller,
G:a,ttone, and Grandis, who proposed to turn the
ahundance of water for which the locality was re-
nrirkable to account, by applying it to a peculiar
system of perforation and ventilation, which we will
now endeavour to explain. The first apparatus
imagined by these gentlemen consists iu a hydraulic
air-condenser, which is a syphon turned with its
orifices upwards, and communicating by one ef
them with a stream of water, by the
other with a reservoir of air. The water,
descending into the first branch, enters the se-
cond, and by the pressure it exercises con-
denses the air, which is then forced into the reser-
voir. This done, a valve is opened, by which the
water contained in the syphon is let out, and the
operation recommences. The emission and intro-
duction valves are regulated by a small machine
operating by means of a column of water ; and the
air in tee reservoir is maintained at a constant
degree of pressure by a column of water communi-
cating with another reservoir above. Thus,
with a waterfall 2U metres in height, the air is
condensed to six atmospheres, equivalent to the
pressure of 62 metres of water. This condensed
air is used for two purposes ; first, as a motive
power, and then for ventilation. Two kinds of
perforators, worked by condensed air instead of
steam, are employed, one invented by Mr. Bartlett,
the other by M. Sommeiller ; and the manner in
which these machines perform their duty affords
the first practical demonstration of the possibility
of employing compressed air as a motive power
with advantage. By means of these perforators
holes for blasting may be bored through the hardest
sienite in one-twelfth of the time which would be
y means were employed. In
the importance of this result,
infdoe
understand
r
it may be stated that, in tunnelling, three-fourths
roerqdeurirte od u
of the time is employed in boring holes, and the
remainder in charging and blasting ; hence, accele-
rating the former operation is an immense advan-
tage. The perforators have another advantage ;
in a place where three couples of miners would
hardly find room, eighteen perforators may be set
to work, so that, by theta ingenious contrivances,
as well as by others for clearing away the
rubbish, the perforation of the tunnel may be
effected in six years, instead of 36. The air that
has been employed as a motive power is used to
feed the gallery, but when the latter. shall have
reached a considerable depth it will require 85,924
cubic metres of air per 24 hours to replace that
which has been vitiated by respiration, torches, and
gunpowder; and th is quautity, in the form of 14,320
cubic metres of air condensed to six atmospheres,
the reservoir can furnish. A new and curious fact
has been observed during these works—viz., that
when the air condensed to the degree above-
mentioned is shot into the gallery from the machine,
any.water happening to be near the latter suddenly
congeals, although the ambient temperature be
about 18 degrees centigrade (72 deg. Fahrenheit).
Hence, when a large mass of compressed air is
driven into a gallery situated at 1,600 metres below
the outer surface of the earth, and where conse-
quently the temperature must be about 160 deg.
Fahrenheit, the dilatation of the compressed air
produces a diminution of temperature sufficient to
counterbalance the excess alluded to. The pro-
gress now making per day in boring is three metres
on each side of the mountain, or six metres per day
'a all.

FATAL ACCIDENT.—As Major Hamilton, of the Sol:-
net, Chichester, late of the 10th Foot, was rowing his
children, a boy and gill, about Binstead, Isle of Wight,
on Tuesday evening, the little boat in wsicb he was
rowing was upset by the children climbing on the gun-
wale, and all were immersed in trio water. The major,
we regret ret to add,e
v wag
t drowned,l
la
lit deceased
ut the
was
sh. children et
the
• twereas
waved.
We believe b() ga
a guest of Lore Downoß.
STEAM BOILER ASSURANCE COMPANY.--A company
under this title has been established at Manohoster, and
tt is a singular fact that such a_ company Wan first
hug_
;ested by the late Mr. ThoinasForsytb, whose death by
'an explosion was announced last week. Mr. Forsyth
is said to have attended a meeting of the company os.ly
two days before hie death, when he adviied an assur-
Ince of lives against. boiler explosions in connection with'
the company. It is computed that within a radius of •
boilers, giving
round a
tManchestertotal
oi 1,
1,250,000 horse are
otereptohwanet .54re
requent and heavy losses occurring through the Vl'
plosion of boilers will, it is believed, induce manufac• -
turera throughout the country to avail thetaseltes Qt
such a means of insurance.