the life of thomas telford-第36节

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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　direction；　upon　a　principle　entirely　new；　and

which　I　am　endeavouring　to　establish　with　regard　to　the　application

of　iron。〃*＇4＇



It　was　the　same　principle　which　he　applied　to　the　great　aqueducts

of　the　Ellesmere　Canal　now　under　consideration。　　He　had　a　model　made

of　part　of　the　proposed　aqueduct　for　Pont…Cysylltau；　showing　the

piers；　ribs；　towing…path；　and　side　railing；　with　a　cast　iron　trough

for　the　canal。　　The　model　being　approved；　the　design　was　completed；

the　ironwork　was　ordered　for　the　summit；　and　the　masonry　of　the

piers　then　proceeded。　　The　foundation…stone　was　laid　on　the　25th

July；　1795；　by　Richard　Myddelton；　Esq。；　of　Chirk　Castle；　M。P。；　and

the　work　was　not　finished　until　the　year　1803；thus　occupying　a

period　of　nearly　eight　years　in　construction。



The　aqueduct　is　approached　on　the　south　side　by　an　embankment　1500

feet　in　length；　extending　from　the　level　of　the　water…way　in　the

canal　until　its　perpendicular　height　at　the　〃tip〃　is　97　feet；

thence　it　is　carried　to　the　opposite　side　of　the　valley；　over　the

river　Dee；　upon　piers　supporting　nineteen　arches；　extending　to　the

length　of　1007　feet。　　The　height　of　the　piers　above　low　water　in　the

river　is　121　feet。　　The　lower　part　of　each　was　built　solid　for　70

feet；　all　above　being　hollow；　for　the　purpose　of　saving　masonry　as

well　as　ensuring　good　workmanship。　　The　outer　walls　of　the　hollow

portion　are　only　two　feet　thick；　with　cross　inner　walls。　　As　each

stone　was　exposed　to　inspection；　and　as　both　Telford　and　his

confidential　foreman；　Matthew　Davidson；*＇5＇　kept　a　vigilant　eye

upon　the　work；　scamping　was　rendered　impossible；　and　a　first…rate

piece　of　masonry　was　the　result。



＇Image＇　Pont…Cyslltau　Aqueduct



Upon　the　top　of　the　masonry　was　set　the　cast　iron　trough　for　the

canal；　with　its　towing…path　and　side…rails；　all　accurately　fitted

and　bolted　together；　forming　a　completely　water…tight　canal；　with　a

water…way　of　11　feet　10　inches；　of　which　the　towing…path；　standing

upon　iron　pillars　rising　from　the　bed　of　the　canal；　occupied　4　feet

8　inches；　leaving　a　space　of　7　feet　2　inches　for　the　boat。*＇6＇

The　whole　cost　of　this　part　of　the　canal　was　47；018L。；　which　was

considered　by　Telford　a　moderate　sum　compared　with　what　it　must

have　cost　if　executed　after　the　ordinary　manner。　　The　aqueduct　was

formally　opened　for　traffic　in　1805。　　〃And　thus；〃　said　Telford；　〃has

been　added　a　striking　feature　to　the　beautiful　vale　of　Llangollen；

where　formerly　was　the　fastness　of　Owen　Glendower；　but　which；　now

cleared　of　its　entangled　woods；　contains　a　useful　line　of

intercourse　between　England　and　Ireland；　and　the　water　drawn　from

the　once　sacred　Devon　furnishes　the　means　of　distributing

prosperity　over　the　adjacent　land　of　the　Saxons。〃



＇Image＇　Section　of　Top　of　Pont…Cyslltau　Aqueduct。



It　is　scarcely　necessary　to　refer　to　the　other　works　upon　this

canal；　some　of　which　were　of　considerable　magnitude；　though　they

may　now　seem　dwarfed　by　comparison　with　the　works　of　recent

engineers；　Thus；　there　were　two　difficult　tunnels　cut　through　hard

rock；　under　the　rugged　ground　which　separates　the　valleys　of　the

Dee　and　the　Ceriog。　　One　of　these　is　500　and　the　other　200　yards　in

length。　　To　ensure　a　supply　of　water　for　the　summit　of　the　canal；

the　lake　called　Bala　Pool　was　dammed　up　by　a　regulating　weir；　and

by　its　means　the　water　was　drawn　off　at　Llandisilio　when　required

for　the　purposes　of　the　navigation；　the　navigable　feeder　being　six

miles　long；　carried　along　the　bank　of　the　Llangollen　valley。

All　these　works　were　skilfully　executed；　and　when　the　undertaking

was　finished；　Mr。　Telford　may　be　said　to　have　fairly　established

his　reputation　as　an　engineer　of　first　rate　ability。



We　now　return　to　Telford's　personal　history　during　this　important

period　of　his　career。　　He　had　long　promised　himself　a　visit　to　his

dear　Eskdale；　and　the　many　friends　he　had　left　there；　but　more

especially　to　see　his　infirm　mother；　who　had　descended　far　into　the

vale　of