the life of thomas telford-第43章

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trough　of　cast　iron；　in　which　the　water　of　the　canal　was　to　be

carried　over　the　valleys；　instead　of　an　immense　puddled　trough；

in　accordance　with　the　practice　until　that　time　in　use；　and　he　adds；

〃the　immense　importance　of　this　improvement　on　the　old　practice　is

apt　to　be　lost　sight　of　at　the　present　day　by　those　who　overlook

the　enormous　size　and　strength　of　masonry　which　would　have　been

required　to　support　a　puddled　channel　at　the　height　of　120　feet。〃

Mr。　Hughes；　however；　claims　for　Mr。　Jessop　the　merit　of　having

suggested　the　employment　of　iron；　though；　in　our　opinion；　without

sufficient　reason。



Mr。　Jessop　was；　no　doubt；　consulted　by　Mr。　Telford　on　the　subject；

but　the　whole　details　of　the　design；　as　well　as　the　suggestion　of

the　use　of　iron　（as　admitted　by　Mr。　Hughes　himself）；　and　the

execution　of　the　entire　works；　rested　with　the　acting　engineer。

This　is　borne　out　by　the　report　published　by　the　Company

immediately　after　the　formal　opening　of　the　Canal　in　1805；　in　which

they　state：　〃Having　now　detailed　the　particulars　relative　to　the

Canal；　and　the　circumstances　of　the　concern；　the　committee；　in

concluding　their　report；　think　it　but　justice　due　to　Mr。　Telford　to

state　that　the　works　have　been　planned　with　great　skill　and

science；　and　executed　with　much　economy　and　stability；　doing　him；

as　well　as　those　employed　by　him；　infinite　credit。　　（Signed）

Bridgewater。〃



*＇7＇　Letter　to　Mr。　Andrew　Little；　Langholm；　dated　Shrewsbury；

16th　Sept。；　1794。



*＇8＇　lbid。



*＇9＇　Letter　to　Mr。　Andrew　Little；　Langholm；　dated　Salop；　20th　Aug。；

1797。





CHAPTER　VII。



IRON　AND　AND　OTHER　BRIDGES。



Shrewsbury　being　situated　in　the　immediate　neighbourhood　of　the

Black　Country；　of　which　coal　and　iron　are　the　principal　products；

Telford's　attention　was　naturally　directed；　at　a　very　early　period；

to　the　employment　of　cast　iron　in　bridge…building。　　The　strength　as

well　as　lightness　of　a　bridge　of　this　material；　compared　with　one

of　stone　and　lime；　is　of　great　moment　where　headway　is　ofimportance；

or　the　difficulties　of　defective　foundations　have　to　be　encountered。

The　metal　can　be　moulded　in　such　precise　forms　and　so　accurately

fitted　together　as　to　give　to　the　arching　the　greatest　possible

rigidity；　while　it　defies　the　destructive　influences　of　time　and

atmospheric　corrosion　with　nearly　as　much　certainty　as　stone　itself。



The　Italians　and　French；　who　took　the　lead　in　engineering　down　almost

to　the　end　of　last　century；　early　detected　the　value　of　this　material；

and　made　several　attempts　to　introduce　it　in　bridge…building；

but　their　efforts　proved　unsuccessful；　chiefly　because　of　the

inability　of　the　early　founders　to　cast　large　masses　of　iron；

and　also　because　the　metal　was　then　more　expensive　than　either　stone

or　timber。　　The　first　actual　attempt　to　build　a　cast　iron　bridge　was

made　at　Lyons　in　1755；　and　it　proceeded　so　far　that　one　of　the

arches　was　put　together　in　the　builder's　yard；　but　the　project　was

abandoned　as　too　costly；　and　timber　was　eventually　used。



It　was　reserved　for　English　manufacturers　to　triumph　over　the

difficulties　which　had　baffled　the　foreign　iron…founders。　　Shortly

after　the　above　ineffectual　attempt　had　been　made；　the　construction

of　a　bridge　over　the　Severn　near　Broseley　formed　the　subject　of

discussion　among　the　adjoining　owners。　　There　had　been　a　great

increase　in　the　coal；　iron；　brick；　and　pottery　trades　of　the

neighbourhood；　and　the　old　ferry　between　the　opposite　banks　of　the

river　was　found　altogether　inadequate　for　the　accommodation　of　the

traffic。　　The　necessity　for　a　bridge　had　long　been　felt；　and　the

project　of　constructing　one　was　actively　taken　up　in　1776　by

Mr。　Abraham　Darby；　the　principal　owner　of　the　extensive　iron　works

at　Coalbrookdale。　　Mr。　Pritchard；　a　Shrewsbury　architect；　prepared

the　design　of　a　stone　bridge　of　one　arch；　in　which　he　proposed　to

introduce　a　key…stone　of　cast　iron；　occupying　only　a　few　feet　at

the　crown　of　the　arch。　　This　plan　was；　however；　given　up　as

unsuitable；　and　another；　with　the　entire　arch　of　cast　iron；　was

designed　under　the　superintendence　of　Mr。　Darby。　　The　castings　were

made　in　the　works　at　Coalbrookdale；　and　the　bridge　was　erected　at　a

point　where　the　banks　were　of　considerable　height　on　both　sides　of

the　river。　　It　was　opened　for　traffic　in　1779；　and　continues　a　most

serviceable　structure　to　this　day；　giving　the　name　to　the　town　of

Ironbridge；　which　has　sprung　up　in　its　immediate　vicinity。　　The

bridge　consists　of　one　semicircular　arch；　of　100　feet　span；　each　of

the　great　ribs　consisting　of　two　pieces　only。　　Mr。　Robert　Stephenson

has　said　of　the　structure〃If　we　consider　that　the　manipulation　of

cast　iron　was　then　completely　in　its　infancy；　a　bridge　of　such

dimensions　was　doubtless　a　bold　as　well　as　an　original　undertaking；

and　the　efficiency　of　the　details　is　worthy　of　the　boldness　of　the

conception。〃*＇1＇



＇Image＇　The　first　Iron　Bridge；　Coalbrookdale。



It　is　a　curious　circumstance　that　the　next　projector　of　an　iron

bridgeand　that　of　a　very　bold　designwas　the　celebrated；　or

rather　the　notorious；　Tom　Paine；　whose　political　writings　Telford

had　so　much　admired。　　The　son　of　a　decent　Quaker　of　Thetford；　who

trained　him　to　his　own　trade　of　a　staymaker；　Paine　seems　early　to

have　contracted　a　dislike　for　the　sect　to　which　his　father

belonged。　　Arrived　at　manhood；　he　gave　up　staymaking　to　embrace　the

wild　life　of　a　privateersman；　and　served　in　two　successive

adventures。　　Leaving　the　sea；　he　became　an　exciseman；　but　retained

his　commission　for　only　a　year。　　Then　he　became　an　usher　in　a

school；　during　which　he　studied　mechanics　and　mathematics。　　Again

appointed　an　exciseman；　he　was　stationed　at　Lewes　in　Sussex；　where

he　wrote　poetry　and　acquired　some　local　celebrity　as　a　writer。

He　was　accordingly　selected　by　his　brother　excisemen　to　prepare　their

petition　to　Government　for　an　increase　of　pay；　*＇2＇　　the　document

which　he　drew　up　procuring　him　introductions　to　Goldsmith　and

Franklin；　and　dismissal　from　his　post。　　Franklin　persuaded　him　to　go

to　America；　and　there　the　quondam　staymaker；　privateersman；　usher；

poet；　an　a　exciseman；　took　an　active　part　in　the　revolutionary

discussions　of　the　time；　besides　holding　the　important　office　of

Secretary　to　the　Committee　for　Foreign　Affairs。　　Paine　afterwards

settled　for　a　time　at　Philadelphia；　where　he　occupied　himself　with

the　study　of　mechanical　philosophy；　electricity；　mineralogy；　and

the　use　of　iron　in　bridge…building。　　In　1787；　when　a　bridge　over

the　Schnylkill　was　proposed；　without　any　river　piers；　as　the　stream

was　apt　to　be　choked　with　ice　in　the　spring　freshets；　Paine　boldly

offered　to　build　an　iron　bridge　with　a　single　arch　of　400　feet

span。　　In　the　course　of　the　same　year；　he　submitted　his　design　of

the　proposed　bridge　to　the　Academy　of　Sciences　at　Paris；　he　also

sent　a　copy　of　his　plan　to　Sir　Joseph　Banks　for　submission　to　the

Royal　Society；　and；　encouraged　by　the　favourable　opinions　of

scientific　men；　he　proceeded　to　Rotherham；　in　Yorkshire；　to　have

his　bridge　cast。*＇3＇　　An　American　gentleman；　named　Whiteside；　having

advanced　money　to　Paine　on　security　of　his　property　in　the　States；

to　enable　the　bridge　to　be　completed；　the　castings　were　duly　made；

and　shipped　off　to　London；　where　they　were　put　together　and

exhibited　to　the　public　on　a　bowling…green　at　Paddington。

The　bridge　was　there　visited　by　a　large　number　of　persons；　and　was

considered　to　be　a　highly　creditable　work。　Suddenly　Paine's　attention

was　withdrawn　from　its　further　prosecution　by　the　publication　of

Mr。　Burke's　celebrated　'Thoughts　on　the　French　Revolution；'　which

he　undertook　to　answer。　　Whiteside　having　in　the　meantime　become

bankrupt；　Paine　was　arrested　by　his　assignees；　but　was　liberated　by

the　assistance　of　two　other　Americans；　who　became　bound　for　him。

Paine；　however；　was　by　this　time　carried　away　by　the　fervour　of　the

French　Revolution；　having　become　a　member　of　the　Nation