The Sun.
London, England, 1847-07-10 00:00:00

THE TUNNEL OVER THE MENAI

• • STRAITS.
TO THE EDITOR OF THE SUN. ,
RESPECTED FRIEND,—I regret I was not in time to
get an opportunity of bringing my several subjects before
the Association in that form which appeared to me ad-
visable ; I, therefore, preferred to leave it to a future '
opportunity. I was much interested in hearing, at the
Mechanical Section, the description of Clarke and Var-
ley's atmospheric tube, which I think is the most effec-
tive plan of the kind I have yet seen. I was permitted
to exhibit my machine for proving the strain on beams,
bridges, &c., in the society's model room, where ii was
seen by many of the professors, &e., and its simplicity
and accuracy was admitted ly all. By a professor of
this section I was informed some of the particularsiot the
proposed iron tunnel, or tube, for conveying a railway
over the Menai Straits ; and though I was very much
surprised at the boldness olconstructing cast-iron beams,
or girders, 100 ft. long, and less than 4 ft. deep, I wa,
still more astonished to hear of the amazing boldness of
constructing a tunnel, or tube, of such mignitude, with
such comparatively alight materials. According to my
informant, its length is to be 460 ft., clear of the points
of bearing—so that I presume the entire length cannot
be far short of 470 ft., its diameter 30 ft., to be con-
structed with : wrought-iron plates, varying from in.
to 4 in. thick--therefore, supposing the average thick-
ness to be 4, and including the needful powerful ribs and
stays
.to .resist the i
vertical and literal pressures and
strains, tok,ether with the interior framing and rails, I
estimate its weight at upwards of 30 cwt. for
.
every foot of its length, or about 700 tons. Now the
depth of the tube is 30 ft., which is about 1-15th part
of its length ; theretore, according to my' machine, the
strain by Its own weight at the middle will be equal to
74 times its weight—viz., 5,250 tons • and suppose a
train, with the engine and load, to be 100 tons, equal to
750 tons—together 6,000 tons. According to Barlow's
theory, the sate capacity
to resist such a grain ought to
be equal to 18,000 tons, and to Tredgold's, 24,000 tons.
Now let us see what is the capacity of this projected
tunnel, or tube:—
The circumference is (say) 90 ft. ; the tension pro-
perty in the lower half, 45 ft. Suppose the plates average
5-Bths of an inch thick, it would give 74 square inches
on each toot ; say that each inch would sustain, before
breaking, 20 tons, this would make 150 tons to each foot
which, multiplied by 45, gives a capacity
of 6,750 tons !
—so that its own weight. and the load. would, according
to this calculation, produce a strain nearly equal to the
breaking point. Now, as wrought-iron will begin to
stretch at the strain of 10 or 12 tons to the inch, it must
be manifest that little more:-than half its
weight would
produce a permanent set, and render it perfectly unfit
and unsafe for the desired object'
If this projected tunnel, or tube, is actually in progress
of construction, or is seriously intended to be made, I
cannot but think it would be advisable for the parties
concerned to have the matter or subject investigated, so
as to prevent the probability of incurring great pecuniary
loss, as well as to guard against the P".sibility of a great
sacrifice of human life. The foregoing calculation is
upon the assumption that the entire support is intended
to be derived from the tension of the wrought-iron plates ;
and I do not see on what else they can depend, unless it
may be intended to sus consider it a most
suspend the tube from towers of
I
masonry. In that case, cannot but
expensive mode for obtaining the object—far greater than
the system of triangular bracing, or straight suspending
bars. T. MOTLEY, C.E.
Oxford, 7 mo., 1.

• __—'!--__ --- -- --
The following letter has been addressed by General
emigra loh. and to resume my
THE SPANISH EXILES.
Yriarte, one of the most distinguished followers of Es-
partero, to Lord Palmerston
hospitable country I
',Louden, July 1, 1847.
kindness from the
"My Lord,--I have just received the command of my
august Sovereign, Queen Isabellt", to return to my coun-
try, after three years of
rank of General in the Spanish army.
offering the tribute of
have the honour
have
elDi
English
During
(7. np ilye
theas residencewnel loist
markedin i s
as from the English Govern-
ment, and in fulfilment of the most sacred duty of man,
a whichand th ies
my earnest thanks, with every assurance of eternal gra-
titude.
"With these feelings I once more hp
g your Excellency
htiogphrosavteisftrnti.soenlfogfrattheufusl,l
will be pleased to accept my thanir.
. --, together with the
high consideration
assurance of my , and I remain
6, your Excellency's very obedient humble servant,
i• MARTIN JOSE YRIARTE."