the life of thomas telford-第61节

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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　chord；

with　only　13　feet　rise。　　〃This　complex　form；〃　says　Mr。　Telford；

〃converts　each　side　of　the　vault　of　the　arch　into　the　shape　of　the

entrance　of　a　pipe；　to　suit　the　contracted　passage　of　a　fluid；　thus

lessening　the　flat　surface　opposed　to　the　current　of　the　river

whenever　the　tide　or　upland　flood　rises　above　the　springing　of　the

middle　of　the　ellipse；　that　being　at　four　feet　above　low　water；

whereas　the　flood　of　1770　rose　twenty　feet　above　low　water　of　an

ordinary　spring…tide；　which；　when　there　is　no　upland　flood；　rises

only　eight　or　nine　feet。〃*＇1＇　　The　bridge　was　finished　and　opened　in

1828。



＇Image＇　Dean　Bridge；　Edinburgh。



The　last　structures　erected　after　our　engineer's　designs　were　at

Edinburgh　and　Glasgow：　his　Dean　Bridge　at　the　former　place；　and　his

Jamaica　Street　Bridge　at　the　latter；　being　regarded　as　among　his

most　successful　works。　　Since　his　employment　as　a　journeyman　mason

at　the　building　of　the　houses　in　Princes　Street；　Edinburgh；　the　New

Town　had　spread　in　all　directions。　　At　each　visit　to　it　on　his　way

to　or　from　the　Caledonian　Canal　or　the　northern　harbours；　he　had

been　no　less　surprised　than　delighted　at　the　architectural

improvements　which　he　found　going　forward。　　A　new　quarter　had　risen

up　during　his　lifetime；　and　had　extended　northward　and　westward　in

long　lines　of　magnificent　buildings　of　freestone；　until　in　1829　its

further　progress　was　checked　by　the　deep　ravine　running　along　the

back　of　the　New　Town；　in　the　bottom　of　which　runs　the　little　Water

of　Leith。　　It　was　determined　to　throw　a　stone　bridge　across　this

stream；　and　Telford　was　called　upon　to　supply　the　design。　　The　point

of　crossing　the　valley　was　immediately　behind　Moray　Place；　which

stands　almost　upon　its　verge；　the　sides　being　bold；　rocky；　and

finely　wooded。　　The　situation　was　well　adapted　for　a　picturesque

structure；　such　as　Telford　was　well　able　to　supply。　　The　depth　of

the　ravine　to　be　spanned　involved　great　height　in　the　piers；　the

roadway　being　106　feet　above　the　level　of　the　stream。　　The　bridge

was　of　four　arches　of　90　feet　span　each；　and　its　total　length　447

feet；　the　breadth　between　the　parapets　for　the　purposes　of　the

roadway　and　footpaths　being　39　feet。*＇2＇　　It　was　completed　and

opened　in　December；　1831。



But　the　most　important；　as　it　was　the　last；　of　Mr。　Telford's　stone

bridges　was　that　erected　across　the　Clyde　at　the　Broomielaw；

Glasgow。　　Little　more　than　fifty　years　since；　the　banks　of　the　river

at　that　place　were　literally　covered　with　broomand　hence　its

namewhile　the　stream　was　scarcely　deep　enough　to　float　a

herring…buss。　　Now；　the　Broomielaw　is　a　quay　frequented　by　ships　of

the　largest　burden；　and　bustling　with　trade　and　commerce。　　Skill　and

enterprise　have　deepened　the　Clyde；　dredged　away　its　shoals；　built

quays　and　wharves　along　its　banks；　and　rendered　it　one　of　the

busiest　streams　in　the　world；



It　has　become　a　great　river　thoroughfare；　worked　by　steam。　　On　its

waters　the　first　steamboat　ever　constructed　for　purposes　of　traffic

in　Europe　was　launched　by　Henry　Bell　in　1812；　and　the　Clyde　boats

to　this　day　enjoy　the　highest　prestige。



The　deepening　of　the　river　at　the　Broomielaw　had　led　to　a　gradual

undermining　of　the　foundations　of　the　old　bridge；　which　was

situated　close　to　the　principal　landing…place。　　A　little　above　it；

was　an　ancient　overfall　weir；　which　had　also　contributed　to　scour

away　the　foundations　of　the　piers。　　Besides；　the　bridge　was　felt　to

be　narrow；　inconvenient；　and　ill…adapted　for　accommodating　the

immense　traffic　passing　across　the　Clyde　at　that　point。　　It　was；

therefore；　determined　to　take　down　the　old　structure；　and　Build　a

new　one；　and　Mr。　Telford　was　called　upon　to　supply　the　design。

The　foundation　was　laid　with　great　ceremony　on　the　18th　of　March；　1833；

and　the　new　bridge　was　completed　and　opened　on　the　1st　of　January；

1836；　rather　more　than　a　year　after　the　engineer's　death。　　It　is　a

very　fine　work；　consisting　of　seven　arches；　segments　of　circles；

the　central　arch　being　58　feet　6　inches；　the　span　of　the　adjoining

arches　diminishing　to　57　feet　9　inches；　55　feet　6　inches；　and　52

feet　respectively。　　It　is　560　feet　in　length；　with　an　open　waterway

of　389　feet；　and　its　total　width　of　carriageway　and　footpath　is　60

feet；　or　wider；　at　the　time　it　was　built；　than　any　river　bridge　in

the　kingdom。



＇Image＇　Glasgow　Bridge



Like　most　previous　engineers　of　eminencelike　Perry；　Brindley；

Smeaton；　and　RennieMr。　Telford　was　in　the　course　of　his　life

extensively　employed　in　the　drainage　of　the　Fen　districts。　　He　had

been　jointly　concerned　with　Mr。　Rennie　in　carrying　out　the

important　works　of　the　Eau　Brink　Cut；　and　at　Mr。　Rennie's　death　he

succeeded　to　much　of　his　practice　as　consulting　engineer。



It　was　principally　in　designing　and　carrying　out　the　drainage　of

the　North　Level　that　Mr。　Telford　distinguished　himself　in　Fen

drainage。　　The　North　Level　includes　all　that　part　of　the　Great

Bedford　Level　situated