the life of thomas telford-第67章
按键盘上方向键 ← 或 → 可快速上下翻页,按键盘上的 Enter 键可回到本书目录页,按键盘上方向键 ↑ 可回到本页顶部!
————未阅读完?加入书签已便下次继续阅读!
sides; until it seemed to die away along the shores in the distance。
Three foolhardy workmen; excited by the day's proceedings; had the
temerity to scramble along the upper surface of the chainwhich
was only nine inches wide and formed a curvature of 590 feetfrom
one side of the Strait to the other!*'2' Far different were the
feelings of the engineer who had planned this magnificent work。
Its failure had been predicted; and; like Brindley's Barton Viaduct;
it had been freely spoken of as a 〃castle in the air。〃 Telford had;
it is true; most carefully tested every part by repeated experiment;
and so conclusively proved the sufficiency of the iron chains to
bear the immense weight they would have to support; that he was
thoroughly convinced as to the soundness of his principles of
construction; and satisfied that; if rightly manufactured and
properly put together; the chains would hold; and that the piers
would sustain them。 Still there was necessarily an element of
uncertainty in the undertaking。 It was the largest structure of
the kind that had ever been attempted。 There was the contingency
of a flaw in the iron; some possible scamping in the manufacture;
some little point which; in the multiplicity of details to be
attended to; he might have overlooked; or which his subordinates
might have neglected。 It was; indeed; impossible but that he
should feel intensely anxious as to the result of the day's
operations。 Mr。 Telford afterwards stated to a friend; only a few
months before his death; that for some time previous to the opening
of the bridge; his anxiety was so great that he could scarcely
sleep; and that a continuance of that condition must have very soon
completely undermined his health。 We are not; therefore; surprised
to learn that when his friends rushed to congratulate him on the
result of the first day's experiment; which decisively proved the
strength and solidity of the bridge; they should have found the
engineer on his knees engaged in prayer。 A vast load had been
taken off his mind; the perilous enterprise of the day had been
accomplished without loss of life; and his spontaneous act was
thankfulness and gratitude。
'Image' Menai Bridge
The suspension of the remaining fifteen chains was accomplished
without difficulty。 The last was raised and fixed on the 9th of
July; 1825; when the entire line was completed。 On fixing the final
bolt; a band of music descended from the top of the suspension pier
on the Anglesea side to a scaffolding erected over the centre of
the curved part of the chains; and played the National Anthem
amidst the cheering of many thousand persons assembled along the
shores of the Strait: while the workmen marched in procession along
the bridge; on which a temporary platform had been laid; and the
St。 David steam…packet of Chester passed under the chains towards
the Smithy Rocks and back again; thus re…opening the navigation of
the Strait。
In August the road platform was commenced; and in September the
trussed bearing bars were all suspended。 The road was constructed
of timber in a substantial manner; the planking being spiked
together; with layers of patent felt between the planks; and the
carriage way being protected by oak guards placed seven feet and a
half apart。 Side railings were added; the toll…houses and
approach…roads were completed by the end of the year; and the
bridge was opened for public traffic on Monday; the 30th of January;
1826; when the London and Holyhead mailcoach passed over it for the
first time; followed by the Commissioners of the Holyhead roads;
the engineer; several stage…coaches; and a multitude of private
persons too numerous to mention。
We may briefly add a few facts as to the quantities of materials
used; and the dimensions of this remarkable structure。 The total
weight of iron was 2187 tons; in 33;265 pieces。 The total length of
the bridge is 1710 feet; or nearly a third of a mile; the distance
between the points of suspension of the main bridge being 579 feet。
The total sum expended by Government in its erection; including the
embankment and about half a mile of new line of road on the
Caernarvon side; together with the toll…houses; was 120;000L。
Notwithstanding the wonders of the Britannia Bridge subsequently
erected by Robert Stephenson for the passage across the same strait
of the Chester and Holyhead Railway; the Menai Bridge of Telford is
by far the most picturesque object。 〃Seen as I approached it;〃 says
Mr。 Roscoe; 〃in the clear light of an autumnal sunset; which threw
an autumnal splendour on the wide range of hills beyond; and the
sweep of richly variegated groves and plantations which covered
their basethe bright sun; the rocky picturesque foreground;
villas; spires; and towers here and there enlivening the prospect
the Menai Bridge appeared more like the work of some great magician
than the mere result of man's skill and industry。〃
'Image' Conway Suspension Bridge
Shortly after the Menai Bridge was begun; it was determined by the
Commissioners of the Holyhead road that a bridge of similar design
should be built over the estuary of the Conway; immediately
opposite the old castle at that place; and which had formerly been
crossed by an open ferry boat。 The first stone was laid on the
3rd of April; 1822; and the works having proceeded satisfactorily;
the bridge and embankment approaching it were completed by the summer
of 1826。 But the operations being of the same kind as those
connected with the larger structure above described; though of a
much less difficult character; it is unnecessary to enter into any
details as to the several stages of its construction。 In this
bridge the width between the centres of the supporting towers is
327 feet; and the height of the under side of the roadway above
high water of spring tides only 15 feet。 The heaviest work was an
embankment as its eastern approach; 2015 feet in length and about
300 feet in width at its highest part。
It will be seen; from the view of the bridge given on the opposite
page; that it is a highly picturesque structure; and combines;
with the estuary which it crosses; and the ancient castle of Conway;
in forming a landscape that is rarely equalled。
Footnotes for Chapter XII。
*'1' In an article in the 'Edinburgh Review;' No。 exli。; from the
pen of Sir David Brewster; the writer observes:〃Mr。 Telford's
principle of suspending and laying down from above the centering of
stone and iron bridges is; we think; a much more fertile one than
even he himself supposed。 With modifications; by no means
considerable; and certainly practicable; it appears to us that the
voussoirs or archstones might themselves be laid down from above;
and suspended by an appropriate mechanism till the keystone was
inserted。 If we suppose the centering in Mr。 Telford's plan to be
of iron; this centering itself becomes an iron bridge; each rib of
which is composed of ten pieces of fifty feet each; and by
increasing the number of suspending chains; these separate pieces
or voussoirs having been previously joined together; either
temporarily or permanently; by cement or by clamps; might be laid
into their place; and kept there by a single chain till the road
was completed。 The voussoirs; when united; might be suspended from
a general chain across the archway; and a platform could be added
to facilitate the operations。〃 This is as nearly as possible the
plan afterwards revived by Mr。 Brunel; and for the originality of
which; we believe; he has generally the credit; though it clearly
belongs to Telford。
*'2' A correspondent informs us of a still more foolhardy exploit
performed on the occasion。 He says; 〃Having been present; as a boy
from Bangor grammar school; on the 26th of April; when the first
chain was carried across; an incident occurred which made no small
impression on my mind at the time。 After the ch