the life of thomas telford-第40章

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construction。　　The　navigations　brought　lime；　coal；　manure；　and

merchandise；　almost　to　the　farmers'　doors；　and　provided　them　at　the

same　time　with　ready　means　of　conveyance　for　their　produce　to　good

markets。　　Farms　in　remote　situations　were　thus　placed　more　on　an

equality　with　those　in　the　neighbourhood　of　large　towns；　rents　rose

in　consequence；　and　the　owners　of　land　everywhere　became　the

advocates　and　projectors　of　canals。



The　dividends　paid　by　the　first　companies　were　very　high；　and　it

was　well　known　that　the　Duke's　property　was　bringing　him　in　immense

wealth。　　There　was；　therefore；　no　difficulty　in　getting　the　shares

in　new　projects　readily　subscribed　for：　indeed　Mr。　Telford　relates

that　at　the　first　meeting　of　the　Ellesmere　projectors；　so　eager

were　the　public；　that　four　times　the　estimated　expense　was

subscribed　without　hesitation。　　Yet　this　navigation　passed　through

a　difficult　country；　necessarily　involving　very　costly　works；　and

as　the　district　was　but　thinly　inhabited；　it　did　not　present　a　very

inviting　prospect　of　dividends。*＇1＇　　But　the　mania　had　fairly　set

in；　and　it　was　determined　that　the　canal　should　be　made。　　And

whether　the　investment　repaid　the　immediate　proprietors　or　not；　it

unquestionably　proved　of　immense　advantage　to　the　population　of　the

districts　through　which　it　passed；　and　contributed　to　enhance　the

value　of　most　of　the　adjoining　property。



The　Act　authorising　the　construction　of　the　canal　was　obtained　in

1793；　and　Telford　commenced　operations　very　shortly　after　his

appointment　in　October　of　the　same　year。　　His　first　business　was　to

go　carefully　over　the　whole　of　the　proposed　line；　and　make　a　careful

working　survey；　settling　the　levels　of　the　different　lengths；

and　the　position　of　the　locks；　embankments；　cuttings；　and　aqueducts。

In　all　matters　of　masonry　work　he　felt　himself　master　of　the

necessary　details；　but　having　had　comparatively　small　experience　of

earthwork；　and　none　of　canal…making；　he　determined　to　take　the

advice　of　Mr。　William　Jessop　on　that　part　of　the　subject；　and　he

cordially　acknowledges　the　obligations　he　was　under　to　that　eminent

engineer　for　the　kind　assistance　which　he　received　from　him　on　many

occasions。



The　heaviest　and　most　important　part　of　the　undertaking　was　in

carrying　the　canal　through　the　rugged　country　between　the　rivers

Dee　and　Ceriog；　in　the　vale　of　Llangollen。　　From　Nantwich　to

Whitchurch　the　distance　is　16　miles；　and　the　rise　132　feet；

involving　nineteen　locks；　and　from　thence　to　Ellesmere；　Chirk；

Pont…Cysylltau；　and　the　river　Dee；　1　3/4　mile　above　Llangollen；　the

distance　is　38　1/4　miles；　and　the　rise　13　feet；　involving　only　two

locks。　　The　latter　part　of　the　undertaking　presented　the　greatest

difficulties；　as；　in　order　to　avoid　the　expense　of　constructing

numerous　locks；　which　would　also　involve　serious　delay　and　heavy

expense　in　working　the　navigation；　it　became　necessary　to　contrive

means　for　carrying　the　canal　on　the　same　level　from　one　side　of　the

respective　valleys　of　the　Dee　and　the　Ceriog　to　the　other；　and

hence　the　magnificent　aqueducts　of　Chirk　and　Pont…Cysylltau；

characterised　by　Phillips　as　〃among　the　boldest　efforts　of　human

invention　in　modem　times。〃*＇2＇　　The　Chirk　Aqueduct　carries　the　canal

across　the　valley　of　the　Ceriog；　between　Chirk　Castle　and　the

village　of　that　name。　　At　this　point　the　valley　is　above　700　feet

wide；　the　banks　are　steep；　with　a　flat　alluvial　meadow　between

them；　through　which　the　river　flows。　The　country　is　finely

wooded。　　Chirk　Castle　stands　on　an　eminence　on　its　western　side；

with　the　Welsh　mountains　and　Glen　Ceriog　as　a　background；　the　whole

composing　a　landscape　of　great　beauty；　in　the　centre　of　which

Telford's　aqueduct　forms　a　highly　picturesque　object。



＇Image＇　Chirk　Aqueduct



The　aqueduct　consists　of　ten　arches　of　40　feet　span　each。

The　level　of　the　water　in　the　canal　is　65　feet　above　the　meadow；

and　70　feet　above　the　level　of　the　river　Ceriog。　　The　proportions

of　this　work　far　exceeded　everything　of　the　kind　that　had　up　to

that　time　been　attempted　in　England。　　It　was　a　very　costly　structure；

but　Telford；　like　Brindley；　thought　it　better　to　incur　a　considerable

capital　outlay　in　maintaining　the　uniform　level　of　the　canal；　than

to　raise　and　lower　it　up　and　down　the　sides　of　the　valley　by　locks

at　a　heavy　expense　in　works；　and　a　still　greater　cost　in　time　and

water。　The　aqueduct　is　a　splendid　specimen　of　the　finest　class　of

masonry；　and　Telford　showed　himself　a　master　of　his　profession　by

the　manner　in　which　he　carried　out　the　whole　details　of　the

undertaking。　　The　piers　were　carried　up　solid　to　a　certain　height；

above　which　they　were　built　hollow；　with　cross　walls。　　The　spandrels

also；　above　the　springing　of　the　arches；　were　constructed　with

longitudinal　walls；　and　left　hollow。*＇3＇　　The　first　stone　was　laid

on　the　17th　of　June；　1796；　and　the　work　was　completed　in　the　year

1801；　the　whole　remaining　in　a　perfect　state　to　this　day。



The　other　great　aqueduct　on　the　Ellesmere　Canal；　named　Pont…Cysylltau；

is　of　even　greater　dimensions；　and　a　far　more　striking　object　in

the　landscape。　　Sir　Walter　Scott　spoke　of　it　to　Southey　as　〃the

most　impressive　work　of　art　he　had　ever　seen。〃　　It　is　situated　about

four　miles　to　the　north　of　Chirk；　at　the　crossing　of　the　Dee；　in

the　romantic　vale　of　Llangollen。　　The　north　bank　of　the　river　is

very　abrupt；　but　on　the　south　side　the　acclivity　is　more　gradual。

The　lowest　part　of　the　valley　in　which　the　river　runs　is　127　feet

beneath　the　water…level　of　the　canal；　and　it　became　a　question　with

the　engineer　whether　the　valley　was　to　be　crossed；　as　originally

intended；　by　locking　down　one　side　and　up　the　otherwhich　would

have　involved　seven　or　eight　locks　on　each　sideor　by　carrying　it

directly　across　by　means　of　an　aqueduct。



The　execution　of　the　proposed　locks　would　have　been　very　costly；

and　the　working　of　them　in　carrying　on　the　navigation　would

necessarily　have　involved　a　great　waste　of　water；　which　was　a

serious　objection；　inasmuch　as　the　supply　was　estimated　to　be　no

more　than　sufficient　to　provide　for　the　unavoidable　lockage　and

leakage　of　the　summit　level。　　Hence　Telford　was　strongly　in　favour

of　an　aqueduct；　but；　as　we　have　already　seen　in　the　case　of　that　at

Chirk；　the　height　of　the　work　was　such　as　to　render　it　impracticable

to　construct　it　in　the　usual　manner；　upon　masonry　piers　and　arches

of　sufficient　breadth　and　strength　to　afford　room　for　a　puddled

water…way；　which　would　have　been　extremely　hazardous　as　well　as

expensive。　　He　was　therefore　under　the　necessity　of　contriving　some

more　safe　and　economical　method　of　procedure；　and　he　again　resorted

to　the　practice　which　he　had　adopted　in　the　construction　of　the

Chirk　Aqueduct；　but　on　a　much　larger　scale。



＇Image＇　Pont…CyslltauSide　view　of　Cast　Iron　Trough



It　will　be　understood　that　many　years　elapsed　between　the　period　at

which　Telford　was　appointed　engineer　to　the　Ellesmere　Canal　and　the

designing　of　these　gigantic　works。　　He　had　in　the　meantime　been

carefully　gathering　experience　from　a　variety　of　similar

undertakings　on　which　he　was　employed；　and　bringing　his

observations　of　the　strength　of　materials　and　the　different　forms

of　construction　to　bear　upon　the　plans　under　his　consideration　for

the　great　aqueducts　of　Chirk　and　Pont…Cysylltau。　　In　1795　he　was

appointed　engineer　to　the　Shrewsbury　Canal；　which　extends　from　that

town　to　the　collieries　and　ironworks　in　the　neighbourhood　of

Wrekin；　crossing　the　rivers　Roden　and　Tern；　and　Ketley　Brook；　after

which　it　joins　the　Dorrington　and　Shropshire　Canals。　　Writing　to　his

Eskdale　friend；　Telford　said　：　〃Although　this　canal　is　only

eighteen　miles　long；　yet　there　are　many　important　works　in　its

courseseveral　locks；　a　tunnel　about　half　a　mile　long；　and　two

aqueducts。　　For　the　most　considerable　of　these　last；　I　have　just

recommended　an　aqueduct　of　iron。　　It　has　been　approved；　and　will　be

executed　under　my　direc