the life of thomas telford-第35部分

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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　National

Convention；　as　representative　for　Calais。　　The　〃Friends　of　Man；〃

whose　cause　he　had　espoused；　treated　him　scurvily；　imprisoning　him

in　the　Luxembourg；　where　he　lay　for　eleven　months。　　Escaped　to

America；　we　find　him　in　1803　presenting　to　the　American　Congress　a

memoir　on　the　construction　of　Iron　Bridges；　accompanied　by　several

models。　　It　does　not　appear；　however；　that　Paine　ever　succeeded　in

erecting　an　iron　bridge。　　He　was　a　restless；　speculative；　unhappy

being；　and　it　would　have　been　well　for　his　memory　if；　instead　of

penning　shallow　infidelity；　he　had　devoted　himself　to　his　original

idea　of　improving　the　communications　of　his　adopted　country。

In　the　meantime；　however；　the　bridge　exhibited　at　Paddington　had

produced　important　results。　The　manufacturers　agreed　to　take　it

back　as　part　of　their　debt；　and　the　materials　were　afterwards　used

in　the　construction　of　the　noble　bridge　over　the　Wear　at　Sunderland；

which　was　erected　in　1796。



The　project　of　constructing　a　bridge　at　this　place；　where　the　rocky

banks　of　the　Wear　rise　to　a　great　height　oh　both　sides　of　the

river；　is　due　to　Rowland　Burdon；　Esq。；　of　Castle　Eden；　under　whom

Mr。　T。　Wilson　served　as　engineer　in　carrying　out　his　design。

The　details　differed　in　several　important　respects　from　the　proposed

bridge　of　Paine；　Mr。　Burdon　introducing　several　new　and　original

features；　more　particularly　as　regarded　the　framed　iron　panels

radiating　towards　the　centre　in　the　form　of　voussoirs；　for　the

purpose　of　resisting　compression。　　Mr。　Phipps；　C。E。；　in　a　report

prepared　by　him　at　the　instance　of　the　late　Robert　Stephenson；

under　whose　superintendence　the　bridge　was　recently　repaired；

observes；　with　respect　to　the　original　design；〃We　should　probably

make　a　fair　division　of　the　honour　connected　with　this　unique

bridge；　by　conceding　to　Burdon　all　that　belongs　to　a　careful

elaboration　and　improvement　upon　the　designs　of　another；　to　the

boldness　of　taking　upon　himself　the　great　responsibility　of

applying。　　this　idea　at　once　on　so　magnificent　a　scale；　and　to　his

liberality　and　public　spirit　in　furnishing　the　requisite　funds

＇to　the　amount　of　22；000L。＇；　but　we　must　not　deny　to　Paine　the　credit

of　conceiving　the　construction　of　iron　bridges　of　far　larger　span

than　had　been　made　before　his　time；　or　of　the　important　examples

both　as　models　and　large　constructions　which　he　caused　to　be　made

and　publicly　exhibited。　　In　whatever　shares　the　merit　of　this　great

work　may　be　apportioned；　it　must　be　admitted　to　be　one　of　the

earliest　and　greatest　triumphs　of　the　art　of　bridge　construction。〃

Its　span　exceeded　that　of　any　arch　then　known；　being　236　feet；　with

a　rise　of　34　feet；　the　springing　commencing　at　95　feet　above　the

bed　of　the　river；　and　its　height　was　such　as　to　allow　vessels　of

300　tons　burden　to　sail　underneath　without　striking　their　masts。

Mr。　Stephenson　characterised　the　bridge　as　〃a　structure　which；　as

regards　its　proportions　and　the　small　quantity　of　material　employed

in　its　construction；　will　probably　remain　unrivalled。〃



＇Image＇　Wear　Bridge；　at　Sunderland。



The　same　year　in　which　Burdon's　Bridge　was　erected　at　Sunderland；

Telford　was　building　his　first　iron　bridge　over　the　Severn　at

Buildwas；　at　a　point　about　midway　between　Shrewsbury　and　Bridgenorth。

An　unusually　high　flood　having　swept　away　the　old　bridge　in　the

Year　1795；　he　was　called　upon；　as　surveyor　for　the　county；　to

supply　the　plan　of　a　new　one。　　Having　carefully　examined　the　bridge

at　Coalbrookdale；　and　appreciated　its　remarkable　merits；　he

determined　to　build　the　proposed　bridge　at　Buildwas　of　iron；　and　as

the　waters　came　down　with　great　suddenness　from　the　Welsh　mountains；

he　further　resolved　to　construct　it　of　only　one　arch；　so　as　to

afford　the　largest　possible　water…way。



He　had　some　difficulty　in　inducing　the　Coalbrookdale　iron…masters；

who　undertook　the　casting　of　the　girders；　to　depart　from　the　plan

of　the　earlier　structure；　but　he　persisted　in　his　design；　which　was

eventually　carried　out。　　It　consisted　of　a　single　arch　of　130　feet

span；　the　segment　of　a　very　large　circle；　calculated　to　resist　the

tendency　of　the　abutments　to　slide　inwards；　which　had　been　a　defect

of　the　Coalbrookdale　bridge；　the　flat　arch　being　itself　sustained

and　strengthened　by　an　outer　ribbed　one　on　each　side；　springing

lower　than　the　former　and　also　rising　higher；　somewhat　after　the

manner　of　timber…trussing。　　Although　the　span　of　the　new　bridge　was

30　feet　wider　than　the　Coalbrookdale　bridge；　it　contained　less　than

half　the　quantity　of　iron；　Buildwas　bridge　containing　173；　whereas

the　other　contained　378　tons。　　The　new　structure　was；　besides；

extremely　elegant　in　form；　and　when　the　centres　were　struck；　the

arch　and　abutments　stood　perfectly　firm；　and　have　remained　so　to

this　day。　　But　the　ingenious　design　of　this　bridge　will　be　better

explained　by　the　following　representation　than　by　any　description

in　words。*＇4＇　　The　bridge　at　Buildwas；　however；　was　not　Telford's

first　employment　of　iron　in　bridge…building；　for；　the　year　before

its　erection；　we　find　him　writing　to　his　friend　at　Langholm　that　he

had　recommended　an　iron　aqueduct　for　the　Shrewsbury　Canal；

〃on　a　principle　entirely　new；〃　and　which　he　was　〃endeavouring　to

establish　with　regard　to　the　application　of　iron。〃*＇5＇　　This　iron

aqueduct　had　been　cast　and　fixed；　and　it　was　found　to　effect　so

great　a　saving　in　masonry　and　earthwork；　that　he　was　afterwards

induced　to　apply　the　same　principle；　as　we　have　already　seen；

in　different　forms；　in　the　magnificent　aqueducts　of　Chirk　and

Pont…Cysylltau。



The　uses　of　cast　iron　in　canal　construction　became　more　obvious

with　every　year's　successive　experience；　and　Telford　was　accustomed

to　introduce　it　in　many　cases　where　formerly　only　timber　or　stone

had　been　used。　　On　the　Ellesmere；　and　afterwards　on　the　Caledonial

Canal；　he　adopte