the life of thomas telford-第68章

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chain　was　carried　across；　an　incident　occurred　which　made　no　small

impression　on　my　mind　at　the　time。　　After　the　chain　had　reached　its

position；　a　cobbler　of　the　neighbourhood　crawled　to　the　centre　of

the　curve；　and　there　finished　a　pair　of　shoes；　when；　having

completed　his　task；　he　returned　in　safety　to　the　Caernarvon　side！

I　need　not　say　that　we　schoolboys　appreciated　his　feat　of

foolhardiness　far　more　than　Telford's　master　work。〃





CHAPTER　XIII。



DOCKS；　DRAINAGE；　AND　BRIDGES。



It　will　have　been　observed；　from　the　preceding　narrative；　how　much

had　already　been　accomplished　by　skill　and　industry　towards　opening

up　the　material　resources　of　the　kingdom。　　The　stages　of　improvement

which　we　have　recorded　indeed　exhibit　a　measure　of　the　vital　energy

which　has　from　time　to　time　existed　in　the　nation。　　In　the　earlier

periods　of　engineering　history；　the　war　of　man　was　with　nature。

The　sea　was　held　back　by　embankments。　　The　Thames；　instead　of　being

allowed　to　overspread　the　wide　marshes　on　either　bank；　was　confined

within　limited　bounds；　by　which　the　navigable　depth　of　its　channel

was　increased；　at　the　same　time　that　a　wide　extent　of　land　was

rendered　available　for　agriculture。



In　those　early　days；　the　great　object　was　to　render　the　land　more

habitable；　comfortable；　and　productive。　　Marshes　were　reclaimed；　and

wastes　subdued。　　But　so　long　as　the　country　remained　comparatively

closed　against　communication；　and　intercourse　was　restricted　by　the

want　of　bridges　and　roads；　improvement　was　extremely　slow。

For；　while　roads　are　the　consequence　of　civilisation；　they　are　also

among　its　most　influential　causes。　　We　have　seen　even　the　blind

Metcalf　acting　as　an　effective　instrument　of　progress　in　the

northern　counties　by　the　formation　of　long　lines　of　road。　　Brindley

and　the　Duke　of　Bridgewater　carried　on　the　work　in　the　same

districts；　and　conferred　upon　the　north　and　north…west　of　England

the　blessings　of　cheap　and　effective　water　communication。　　Smeaton

followed　and　carried　out　similar　undertakings　in　still　remoter

places；　joining　the　east　and　west　coasts　of　Scotland　by　the　Forth

and　Clyde　Canal；　and　building　bridges　in　the　far　north。　　Rennie　made

harbours；　built　bridges；　and　hewed　out　docks　for　shipping；　the

increase　in　which　had　kept　pace　with　the　growth　of　our　home　and

foreign　trade。　　He　was　followed　by　Telford；　whose　long　and　busy

life；　as　we　have　seen；　was　occupied　in　building　bridges　and　making

roads　in　all　directions；　in　districts　of　the　country　formerly

inaccessible；　and　therefore　comparatively　barbarous。　　At　length　the

wildest　districts　of　the　Highlands　and　the　most　rugged　mountain

valleys　of　North　Wales　were　rendered　as　easy　of　access　as　the

comparatively　level　counties　in　the　immediate　neighbourhood　of　the

metropolis。



During　all　this　while；　the　wealth　and　industry　of　the　country　had

been　advancing　with　rapid　strides。　　London　had　grown　in　population

and　importance。　　Many　improvements　had　been　effected　in　the　river；

But　the　dock　accommodation　was　still　found　insufficient；　and；　as

the　recognised　head　of　his　profession；　Mr。　Telford；　though　now

grown　old　and　fast　becoming　infirm；　was　called　upon　to　supply　the

requisite　plans。　　He　had　been　engaged　upon　great　works　for　upwards

of　thirty　years；　previous　to　which　he　had　led　the　life　of　a　working

mason。　　But　he　had　been　a　steady；　temperate　man　all　his　life；　and

though　nearly　seventy；　when　consulted　as　to　the　proposed　new　docks；

his　mind　was　as　able　to　deal　with　the　subject　in　all　its　bearings

as　it　had　ever　been；　and　he　undertook　the　work。



In　1824　a　new　Company　was　formed　to　provide　a　dock　nearer　to　the

heart　of　the　City　than　any　of　the　existing　ones。　　The　site　selected

was　the　space　between　the　Tower　and　the　London　Docks；　which

included　the　property　of　St。　Katherine's　Hospital。　　The　whole　extent

of　land　available　was　only　twenty…seven　acres　of　a　very　irregular

figure；　so　that　when　the　quays　and　warehouses　were　laid　out；　it　was

found　that　only　about　ten　acres　remained　for　the　docks；　but　these；

from　the　nature　of　the　ground；　presented　an　unusual　amount　of　quay

room。　　The　necessary　Act　was　obtained　in　1825；　the　works　were　begun

in　the　following　year；　and　on　the　25th　of　October；　1828；　the　new

docks　were　completed　and　opened　for　business。



The　St。　Katherine　Docks　communicate　with　the　river　by　means　of　an

entrance　tide…lock；　180　feet　long　and　45　feet　wide；　with　three

pairs　of　gates；　admitting　either　one　very　large　or　two　small

vessels　at　a　time。　　The　lock…entrance　and　the　sills　under　the　two

middle　lock…gates　were　fixed　at　the　depth　of　ten　feet　under　the

level　of　low　water　of　ordinary　spring　tides。　　The　formation　of　these

dock…entrances　was　a　work　of　much　difficulty；　demanding　great　skill

on　the　part　of　the　engineer。　　It　was　necessary　to　excavate　the

ground　to　a　great　depth　below　low　water　for　the　purpose　of　getting

in　the　foundations；　and　the　cofferdams　were　therefore　of　great

strength；　to　enable　them；　when　pumped　out　by　the　steam…engine；　to

resist　the　lateral　pressure　of　forty　feet　of　water　at　high　tide。

The　difficulty　was；　however；　effectually　overcome；　and　the　wharf

walls；　locks；　sills　and　bridges　of　the　St。　Katherine　Docks　are

generally　regarded　as　a　master…piece　of　harbour　construction。

Alluding　to　the　rapidity　with　which　the　works　were　completed；

Mr。　Telford　says：　〃Seldom；　indeed　never　within　my　knowledge；　has　there

been　an　instance　of　an　undertaking；　of　this　magnitude；　in　a　very

confined　situation；　having　been　perfected　in　so　short　a　time；。。。。

but；　as　a　practical　engineer；　responsible　for　the　success　of

difficult　operations；　I　must　be　allowed　to　protest　against　such

haste；　pregnant　as　it　was；　and　ever　will　be；　with　risks；　which；　in

more　instances　than　one；　severely　taxed　all　my　experience　and

skill；　and　dangerously　involved　the　reputation　of　the　directors　as

well　as　of　their　engineer。〃



Among　the　remaining　bridges　executed　by　Mr。　Telford；　towards　the

close　of　his　professional　career；　may　be　mentioned　those　of

Tewkesbury　and　Gloucester。　　The　former　town　is　situated　on　the

Severn　at　its　confluence　with　the　river　Avon；　about　eleven　miles

above　Gloucester。　　The　surrounding　district　was　rich　and　populous；

but　being　intersected　by　a　large　river；　without　a　bridge；　the

inhabitants　applied　to　Parliament　for　powers　to　provide　so

necessary　a　convenience。　　The　design　first　proposed　by　a　local

architect　was　a　bridge　of　three　arches；　but　Mr。　Telford；　when

called　upon　to　advise　the　trustees；　recommended　that；　in　order　to

interrupt　the　navigation　as　little　as　possible；　the　river　should　be

spanned　by　a　single　arch；　and　he　submitted　a　design　of　such　a

character；　which　was　approved　and　subsequently　erected。　　It　was

finished　and　opened　in　April；　1826。



This　is　one　of　the　largest　as　well　as　most　graceful　of　Mr。　Telford's

numerous　cast　iron　bridges。　　It　has　a　single　span　of　170　feet；　with

a　rise　of　only　17　feet；　consisting　of　six　ribs　of　about　three　feet

three　inches　deep；　the　spandrels　being　filled　in　with　light

diagonal　work。　　The　narrow　Gothic　arches　in　the　masonry　of　the

abutments　give　the　bridge　a　very　light　and　graceful　appearance；

at　the　same　time　that　they　afford　an　enlarged　passage　for　the　high

river　floods。



The　bridge　at　Gloucester　consists　of　one　large　stone　arch　of　150

feet　span。　　It　replaced　a　structure　of　great　antiquity；　of　eight

arches；　which　had　stood　for　about　600　years。　　The　roadway　over　it

was　very　narrow；　and　the　number　of　piers　in　the　river　and　the　small

dimensions　of　the　arches　offered　considerable　obstruction　to　the

navigation。　　To　give　the　largest　amount　of　waterway；　and　at　the　same

time　reduce　the　gradient　of　the　road　over　the　bridge　to　the

greatest　extent；　Mr。　Telford　adopted　the　following　expedient。

He　made　the　general　body　of　the　arch　an　ellipse；　150　feet　on　the

chord…line　and　35　feet　rise；　while　the　voussoirs；　or　external

archstones；　being　in　the　form　of　a　segment；　have　the　same　chor