the life of thomas telford-第38节

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！



bridges　and　viaducts；　he　thus　kept　his　heart　open　to　the　influences

of　beauty　in　life　and　nature；　and；　at　all　events；　the　writing　of

verses；　indifferent　though　they　might　have　been；　proved　of　this

value　to　himthat　it　cultivated　in　him　the　art　of　writing　better

prose。



Footnotes　for　Chapter　VI。



*＇1＇　The　Ellesmere　Canal　now　pays　about　4　per　cent。　dividend。



*＇2＇　'A　General　History　of　Inland　Navigation；　Foreign　and

Domestic；'　&c。　By　J。　Phillips。　　Fourth　edition。　　London；　1803。



*＇3＇　＇Image＇　Section　of　Pier



Telford　himself　thus　modestly　describes　the　merit　of　this　original

contrivance：　〃Previously　to　this　time　such　canal　aqueducts　had　been

uniformly　made　to　retain　the　water　necessary　for　navigation　by

means　of　puddled　earth　retained　by　masonry；　and　in　order　to　obtain

sufficient　breadth　for　this　superstructure；　the　masonry　of　the

piers；　abutments；　and　arches　was　of　massive　strength；　and　after　all

this　expense；　and　every　imaginable　precaution；　the　frosts；　by

swelling　the　moist　puddle；　frequently　created　fissures；　which　burst

the　masonry；　and　suffered　the　water　to　escapenay；　sometimes

actually　threw　down　the　aqueducts；　instances　of　this　kind　having

occurred　even　in　the　works　of　the　justly　celebrated　Brindley。

It　was　evident　that　the　increased　pressure　of　the　puddled　earth　was

the　chief　cause　of　such　failures：　I　therefore　had　recourse　to　the

following　scheme　in　order　to　a　void　using　it。　　The　spandrels　of　the

stone　arches　were　constructed　with　longitudinal　walls；　instead　of

being　filled　in　with　earth　（as　at　Kirkcudbright　Bridge）；　and　across

these　the　canal　bottom　was　formed　by　cast　iron　plates　at　each　side；

infixed　in　square　stone　masonry。　　These　bottom　plates　had　flanches

on　their　edges；　and　were　secured　by　nuts　and　screws　at　every

juncture。　　　The　sides　of　the　canal　were　made　water…proof　by　ashlar

masonry；　backed　with　hard　burnt　bricks　laid　in　Parker's　cement；　on

the　outside　of　which　was　rubble　stone　work；　like　the　rest　of　the

aqueduct。　　The　towing　path　had　a　thin　bed　of　clay　under　the　gravel；

and　its　outer　edge　was　protected　by　an　iron　railing。　　The　width　of

the　water…way　is　11　feet；　of　the　masonry　on　each　side；　5　feet　6

inches；　and　the　depth　of　the　water　in　the　canal；　5　feet。　　By　this

mode　of　construction　the　quantity　of　masonry　is　much　diminished；

and　the　iron　bottom　plate　forms　a　continuous　tie；　preventing　the

side…walls　from　separation　by　lateral　pressure　of　the　contained

water。〃'Life　of　Telford；'　p。　40。



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

13th　March；　1795。



*＇5＇　Matthew　Davidson　had　been　Telford's　fellow　workman　at　Langholm；

and　was　reckoned　an　excellent　mason。　　He　died　at　Inverness；

where　he　had　a　situation　on　the　Caledonian　Canal。



*＇6＇　Mr。　Hughes；　C。E。；　in　his　'Memoir　of　William　Jessop；'　published

in　'Weale's　Quarterly　Papers　on　Engineering；'　points　out　the　bold

and　original　idea　here　adopted；　of　constructing　a　water…tight

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