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D. H. MAHAN, M. A., 





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The New York Prihtinh Comfa 
New Vo«t:. 

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The present Edition of this Work, like the two 
preceding, has been compiled for the use of the ca- 
dets of the U. S. Mihtary Academy, and comprises 
that part of the Coarse of Civil Kngineering tauglit 
them which the Autlior deemed would prove tJie most 
useful to pupils in other seminaries, studying for ilie 
profession of the civil engineer. 

In preparing this Edition, the Author lias found ii 
necessary to recast and rewrite tlie greater portion 
of the work ; owing to the considerahle additions 
made to it, and called for by the vast accumulation 
of important facts since the pubhcation of the former 
editions, A new form has also been given to the 
work, in the substitution of wood-cuts in tlie, bodv 
of it for tlie plates in the former editions, as helte)' 
adapted to its main object as a text-book. From 
these additions and changes, the Author tmsts thai 
the work will be found to contain all of tln> essential 

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principles aiul facts respecting those branches of iho 
subject of which it treats; and that it will prove a 
serviceable aid to instructors and pupils, in opening 
tlie way to a more extensive prosecution ol ihfl 
studies coonected witn the engineer's art. 

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('la£HificatiDn of 


Clissifiiialiun of Stones 

Silieious Btcmcs 

Aimllaccous Sluiies .... , 

Oalcareoua Stones. 

Durability of Stones 

llanineBS of Sh.ncB 

1,1 MK. 

(;i:isaifi«aU«n of l.inii-s 

Uytliaulin liitncs anil Gcmenls 

I'liysical Characters anJ Tests of ilydrjuliu liii 

(^i^cination of Linicstiine > 54 . 

Lime-kilns 50 . 

Slaking Iiime 67 . 

Manner of reJucing llyclrjitili; CtiTicnt 78 . 

Artificial Hydranlii; Limes ami Cumenls 81 . 

Puzzolana, iSic 87 . 


CiassiDcalioii of Miiriars <M . 

Sand 100 . 

Hydraulic Moitar 107 . 

Mortars exposed to Wcatlicr 113 . 

Manipulations of Mortar 110 . 

Setting and Durability of Mortal 110 . 

Concrete Id9 . 

Beton I3:i . 

AdLercnee of Muvlar IT. . 

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Tiles 1G3 

ClaBEtficafion of Tinibei 169 

relling (if Timber 173 

Seasoning of Timber 175 

Pefcote of Timber :.. 181 

Preservation of Timber 184 

Durability of Timber 194 

Trees nbicli furnish Timber 198 


Cast Iron SOfl 

Wrougbi Irori 230 

. Durability of Iron 234 

, I'roservalion of Iron 346 

. Copper 355 

Zinc 256 

Tin 258 

Lead 259 

Compusitinns of 265 

Vaniish atid Paint for Zinoked Iron 267 

Rksui.ts o» Espehimental Ress. 


Ceiiural Remarks on ^70 

Strength of Stone 281 

J'raclical Dedacliona on the Strengtii of Stone 288 

Expansion of Stone by Heat 289 

::;lrength of Morlara 290 

Strength of Concrete atid lition 295 

Strength of Timber 298 

Slrene'h of Cast Iron 303 

. Strength of Wrought Irort 334 

Resistance to Torsion of Wrought and Cast Iron 333 

Strength of Copper 334 

Strwgth of otlier Meials 339 

Linear Dilatation of Metals by Heat 337 

Adhesion of Iron Spikes tJ Timber ^38 

J.'osBiiicatioii iif Masonry . 

Cut Stone 

Uubble Stona 


Brick Masonry, 383 . 

Foundations 868 . 

Precautions ag'ainst Lateral Yielding: in Foundations 393 . 

Fonndations in Water 304 . 

Oonatructlon of roundation Courses 408 . 

Component Paits of Struotures of Masonry 413 , 

Walls of Bnclosures 413 . . 

Vertical Supports 414 , 

Areas 415 . 

Retaining Walla 418 . 

Relieving: Arches 429 . 

Lintel 435 . 

Plate-baixde 48G . 

Arohea 437 . 

Precautions aifainEt Settling 479 . 

Pointing 480 . 

Repairs on Moaonry 483 . 

EHeots of Temperature 488 . 

General Principles of Framing' 400 . 

Friiinesof Timber 409 . 

Joints of Frames 520 . 

Fmmes of Iron 537 .. 

Flexible Supports for Frames 534 . 

Esperimenta on the Strengih of Frames 549 . 


CksaiGcatlou of Bridges 550 , 

Stone Bridges : 551 , 

Wooden Bridges 583 . 

Caat-iron Bridges , 606 . 

Effects of Temperature on Stone and Cast-jton Bridges 811 , 

Suspension Bribes 013 . 

Moveable Bridges S34 . 

Aqueduct Bridges 030 . 

Rcconniiissance C35 . 

Survey 036 . 

Map and Memoii' 837 . 

Locatkn of Common Roads 038 , 

Earth-worlt 646 , 

Drainage 053 . 

Road-coverings 054 . 

Pavements 6S5 . 

Broken etoue Eoad-covering 658 , 

Materials and Repairs 601 . 

Cross Dimensions of Roads GG3 . 





Chairs '. - . . 


flailways of Wouu and Iron 



Sidin(;s, &c 





Masonry of TunnHla 


[Classification of Canats 

IiBvel Canals 

Canals, not on the same Level 

Feeders and Reservoirs 

Lill of Locks 



Accessory Works 

General Dimensions of Cana^ls 


Natural Features of Rivers 734 . 

River 'Improvements 140 . 

Means for protecting River-banks 142 , 

Measures against Inundations 743 . 

Elbows... 744 . 

Bars ; 747 . 

Slack-water Navigatioii 753 . 


Chssifi gallon of, '^e 


If arbors 

V«a-wftUi •■>•••■ >•••• 

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1. A KNOWLEDGE of the properties of building matcriala i's one 
of llie niost important branches of Civil Engineering, An en- 
gineer, to be enabled to make a judicious selection of materials, 
and lo apply tliem so that the ends of sound economy and skilful 
workmanship shall be equally subserved, must know their or- 
dinary durability under the various circumstances in which they 
are employed, and the means of increasing it when desirable ; 
their capacity to sustain, witliout injury to tlieir physical quali- 
ties, permanent strains, whether exerted to crush them, tear them 
isunder, or lo break tiiem transversely ; their resistance to rup- 
iiire and wear, from percussion and attrition ; and, finally, the 
time and u.vpcnse necessary to convert them to the uses for which 
they may be required. 

2. The materials in general use for civil constructions may be 
arranged under the three foUovring heads : 

1st. Those which constitute the more solid components of 
structures, as Stone, Brick, Wood, and tlie Metals. 

2d, The cements in general, as Mortar, Mastics, Glue, &c., 
wliich are used to unite the more solid parts. 

3d. The various mixtures and chemical prepirations, as solu- 
tions of Salts, Paints, Bituminous Substances, &c., employed 
to coat the more solid parts, and protect them from tlie chemical 
and mechanical action of atmospheric changes, and other causes 
of destructibility. 


3 The term Stone, or Rock, is applied to any aggregation of 

several mineral substances. Stones, for the convenience of de« 

Bcription, may bo arranged under tiiree genera! heads — tlie silt- 

idous, the argillaceous, and the calcareous. 

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. SiLiciolis Stones. The stones arranged under this head 
. . ive ihcir appellation from silex, the prmcipal constituent of ths 
minerals ■whifch compose them. They are also frequer.tly desig- 
nated, either according to the mineral found most abundantly in 
them, or from the appearance of die stone, as feldspatkic, quart- 

5. The slUcious stones generally do not effervesce with acids, 
and emit spai'ks when Btnick willi a steel. They possess, in a 
high degree, the properties of strength, hardness, and durability ; 
and, although presenting great diversity iii tlie degree of these 
properties, as well as in their structure, they famish an < xtensive 
variety of tlie best stone for the various purposes of the engineer 
and architect. 

6. Sienite, Porphyry, and Green-stone, from the abundaJicc 
of feldspar which they contain, are often designatJ^d as feldspatiiie 
focks. For durability, strengtli, and hardness, lliey may be placed 
in the first rank of silicious stones. 

7. Sienite consists of a granular aggi^egation of feldspar, horn- 
blende, and quartz. It furnishes one of the most valuable building 
atones, particularly for structures which require great strengtli, 
or arc exposed to any very active causes of destructibihty, as 
Bca walls, lighthouses, and fortifications. Sienite occurs in exten- 
sive beds, and may be obtained, fron> the localities where it is 
quarried, in blocks of any requisite size. It does not yield easily 
to the cliisel, owing to its great hardness, and when coarse- 
grained it cannot be wrought to a smooth surface. Like all 
stones in which feldspar is found, the durabihty of sienite de- 
pends essentially upon the composition of this mineral, which, 
owing to the potash it contains, sometimes decomposes very lap- 
idly when exposed to the weather. The durability of feMspalhiC 
roclts, however, is very variable, even where their composition is 
the same ; no pains should therefore be spared to asceitain tins 
property in stone taken from new quarries, before using it foi 
important public works, 

8. Porphyry. This stone is usually composed of compact feld- 
spar, having crystals of the same, and sometiraes those of othei 
minerals, scattered through the mass. Porphyry furnishes stones 
of various colors and texture ; the usual color being reddish, ap 
proacliing to purple, from wluch the stone takes its name. One 
of the most beautiful varieties is a hrecciated porphyry, consii=t 
ing of angular fragments of tlie stone united bv a cement of com 
pact feldspar. Porphyry, from its rareness and extreme hardness 
13 seldom applied to any otiicr than ornamental purposes. Tin 
beat loiown lociiHtics of aicnile and porphyiy arc in llie nciglibut 
hood of Boston, 

9. Greenstone, This stone is a mixture of Iiornblciidc whl 

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KMiimoii ind coinp ict feldspar, presenting aomei.mes a Manular 
tliou^li usua hf a compact texture. Its ordinary coIor,'w1icn dry 
IS soioe ?haae of brown ; but, when wet, it becomes gi-een'sn^ 
from which it takea its name. Green-stone is very haj'd, and 
one of the mo'it duiable rocks ; bttt, occurring in small and 
uregulai blocks, its uses as. a building stone are very restricted 
When walla of this stone are built with very white mortar, they 
present a picturesque appearance, and it is on that account weli 
adapted to rural architecture. Green-stx)ne might also be used 
as a material for road-making ; large quantities of it are annually 
taken from the principal locality of this rock in the United States, 
so well Known as the Palisades, on the Hudson, for construct- 
ing wharves, as it is found to withstand well the action of sail 

10. Granite and Gneiss. The constituents of these two stones 
are tlie same ; being a granular aggregation of quartz, feldspar, 
and mica, in variable proportions. They differ only iij their 
structure ; gneiss being a stratified rock, tlic ingredients of 
wliich occur frequently in a more or less laminated state. Gneiis 
although less valuable than granite," owing to the effect of its 
structure on the size of the blocks which it yields, and from its 
not splitting as smoothly as granite across its beds of stratifici- 
tion, fumisncs a building stone suitable for most architectural 
purposes. It is also a good flagging material, when it can be ob- 
tained in tliin slabs. 

Granite varies greatly in quality, according to its texture and 
the relative proportions of its constituents. When tlie quartz in 
in excess, it renders the stone hard and brittle, and very difficuh 
to be worked with the chisel. An excess of mica usually malce? 
the stone friable. An excess of feldspar gives the stone a white 
hue, and makes it freer under the chisel. The best granites are 
those with a fine grain, in which the constituents seem uniformly 
disseminated tlirough the mass. The color of granite is usually 
some sliade of gray ; when it varies from this, it is owing to the 
color of the feldspar. One of its varieties, known as Oi-ienta) 
granite, has a iine reddish hue, and is chiefly used for ornamental 
purposes. Granite is sometimes mistaken for sienite, when i\ 
contains but little mica. 

The quality of granite is affected by the foreign minerals whicJj 
It may contain ; hornblende is said to render it tough, and schorl 
makes it quite brittle. The protoxide and sulphurets of iron are 
the most injurious in tlieir effects on granite ; the former by con 
version into a peroxide, and the latter by decomposing, destroying 
llie structure of llic stone, and causing it to break up and disin- 

Granite, gneiss, and sienite, differ so hltle in their cssenliai 

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qualilies, as a buOding material, that tliey may hi. used intUffei 
enlly for aU structures of a solid and durable character. Tiiej 
ure extensively quarried in most of the New England States, in 
iSfew York, and in some of the otlier States intersected by the 
great range of primitive rocks, where the quarries He couliguous 
to tide-water, 

H. Mica Slate. The constituents of this stone are quartz and 
mica ; the latter predominating. It is principally used as a flag 
ging stone, and as stone, or lining for furnaces. 

la. Buhr, or Millstone. This is a very hard, durable stone, 
presenting a peculiar, honeycomb appearance. It makes a good 
building material for common purposes, and is also suitable foi 
roai5 coverings. 

13. Horn-stone. This is a highly silicious and very liard 
stone. It resembles flint in its structure, and takes its name 
from its translucent, horn-like appearance. It furnishes a very 
good road material. 

14. Steatite, or Suap-stone. This stone is a partially indura- 
ted talc. It is a very soft stone, and not suitable for ordinary 
building purposes. It furnishes a good fire-stone, and is used 
for the lining of fireplaces. 

15. Talcose Slate. This stone resembles mica slate, being an 
aggregation of quartz and talc. It is applied to the same pur- 
poses as mica slate. 

16. Sand-stone. This stone consists of grains of silicious 
sand, arising from the disintegration of silicious rocks, which are 
united by some natural cement, generally of an argillaceous or a 
silicious character. 

The strength, hardness, and durability of sand-stone vary be- 
tween very wide limits. Some varieties being little inferior to 
good granite, as a building stone, others being very soft, friable, 
and disintegrating rapidly when exposed to die weather. Tiie 
least durable sand-stones are those which contain the most argil- 
laceous matter ; those of a feldspathic character are also found 
not to withstand well the action of weather. 

Sand-stone is used very extensively as a building stone, for 
flagging, for road materials, and some of its varieties furnish an 
35;cellent fire-stone. Most of the varieties of sand-stone yield 
readily under the chisel and saw, and split evenly, and, from 
these properties, have received from workmen the name oS free 
Stone. '1 he colors of sand-stone present also a variety of shades, 
principally of gray, brown, and red. 

The formations of sand-stone in the United States are very 
extensive, and a nrmibcr of quarries are worked in New England, 
New York, and the Middle States. These formations, and the 
character of the stone obtained from them, arc minutely des:'ribed 

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Ill liie Geological Reports of these States, which have hecn piib« 
lislicd witliin the last few years. 

Most of the stone used for the public huildlngs in Washingt<m, 
is a sand-stone ohtained from quarries on Acquia Creek and the 
Rappahannoclc. Much of this stone is feldapathic, possesses but 
litllc strength, and disintegrates rapidly. The red sand-stonea 
which are used in our large cities, are eidier from quarries in a 
formation extending from the Hudson to North Carolina, or from 
a separate deposite in the valley of the Connecticut. The most 
durable and hard porlions of tliese formations occur in the neigh 
borhood of trap dikes. The fine flagging-stone used in our cities 
is mostly oblained, either from the Connecticut quarries, or from 
others near the Hudson, hi the Calskill group of mouritains. 
Many quarries, which yield an excellent budding stone, arc 
worked in the extensive formations along the Appalachian, 
which extends through tlie interior, tlirough New York and Vir- 
ginia, and die intermediate States, 

17. Aegillaceous Stones, The stones arranged under this 
head are mostly composed of clay, in a more or less indui^ated 
state, and presenting a laminated structure. They vary greatly 
m strength, and are generally not durable, decomposing in some 
cases very rapidly, from changes in the metallic sulphurets and 
salts found in most of them. The uses of tins class of stones 
are restricted to roofing and flagging. 

18. Roofing Slate. This well-known stone is obtained from 
i hard, indurated clay, the surfeces of the lamina having a natu- 
ral polish. The best .kinds spht into thin, uniform, light slabs ; 
are free from sulphurets of iron ; give a clear ringing sound when 
BlrucJt ; and absorb but little water. Much of the roofing slate 
quarried in the United States is of a very inferior quality, and 
becomes rotten, or decomposes, after a few years' exposure. The 
durability of the best European slate is about one hundred years ; 
and it is stated that the material obtained from some of tiie quar- 
ries worked in the United States, is not apparently inferior to the 
best foreign slate brought into our markets. Several quarries of 
roofing slate are worked in the New England States, New'York, 
and Pennsylvania. 

19. • Graywaclce Slate. The composition of this stone is 
mostly indurated clay. It has a more earthy appearance than 
argillaceous slate, and is generally distinctly arenaceous. Its 
colors arc usually dark gi-ay, or red. It is quarried principally 
for ilagging-stone, 

20. tloTnilende Slate Tliis stone, known also as green-stone 
slate, properly belongs to the silicious class. It consists mostly 
of hornblende having a laminated structure. It » chiefly quarried 
for flagging-stone. 


21. Cjilcareous Stokes. Lime is the p,;'ncipal constituoD 
uf this class, the carbonates of which, known as limestone and 
marhle, furnish a large amount of ordinary b lilding stone, mosl 
of the ornamental stones, and the chief ingredient in the compo- 
siiion of the cements and mortars, used in stone and brick-work. 
Lime-stone effervesces copiously with acids ; its texture is dc 
stroycd by a strong heat, which also drives off its carbonic acid 
imd water, converting it into quick lime. By absorbing water, 
quick-lime is converted into a hydrate, or slaked lime ; consider- 
able heat is evolved during this chemical change, and the stone 
increases in bulk, and gradually crumbles down into a fine 

The lime-stones present great diversity in their physical prop- 
erties. Some of them seem as durable as the best silicious stones, 
and are but httle inferior to them in strength and hardness ; others 
decompose rapidly on exposure to the weather ; and some kinds 
are so soft that, when first quarried, tliey can be scratched with 
tlie nail, and broken between the fingers. The hme-stones are 
generally impure carbonates ; and we are indebted to these im- 
purities for some of the most beautiful, as well as the most inval- 
uable materials used for constructions. Those which are colored 
by metallic oxides, or by the presence of other minerals, furnish 
the large number of colored and variegated marbles ; while those 
which contain a certain proportion of clay, or of magnesia, yield, 
on calcination, those cements which, from their possessing the 
property of hardening under water, have received the various 
appellations of hydraulic lime, water lime, RoTnan cement, &c. 

Lime-stone is divided into two principal classes, granular 
lime-stone and coinpact lime-stone. Each of these furnishes both 
the marbles and oidinary building stone. The varieties not sus- 
ceptible of receiving a polish, are sometimes called common lime- 

The granular hme-stones are generally superior to the compact 
for building purposes. Those which have the finest grain are the 
best, both for marbles and ordinary building stone. The coarse 
grained varieties are frequently friable, and 'disintegrate rapidly 
when exposed to tlie weather. All the varieties, both of the com- 
pact and granular, work freely under the chisel and grit-saw, and 
may be obtained in: blocks of any suitable dimensions for the 
heaviest structures. 

The durability of lime-stone is very materially affected by the 
foreign minerals it may contain ; tlie presence of clay injures the 
stone, particularly when, as sometimes happens, it runs ihrougir 
the bed in vory minute veins : blocks of stone having this imjjer- 
lection, soon separate along these veins on exposure to moisture. 
The protoxide, tlie protocarbonate, and the sulphuret of iron, aK 

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also \'cry destructive in iJieir effects ; freqiionlly caiisinti, by llieit 
chemical changes, rapid disintegration. 

Among the varieties of in^jurc carbonates of lime, tiie magne 
nan lime-stones, called dolomites, merit to be particuliiily no- 
liced. They are regarded in Europe as a superior building 
ruaterial ; those being considered the best which are most crys- 
talline, and are composed of nearly equal proportions of the 
carbonates of lime and magnesia. Some of tiie quarries of this 
stone, which have been opened in New York and Massachusetts, 
have given a different result ; the stone obtained from them being, 
in some cases, extremely friable, 

22. Marbles. The term marble is now applied exclusively 
lo any lime-stone which will receive a polish. Owing lo llie cost 
of preparing marble, it is restricted in its uses to ornamentfil pur 
poses. The marbles present great variety, both in color and ap 
pearance, and have generally received some appropriate name 
descriptive of these accidents. 

23. Statuary Marble is of the purest while, iinest grain, and 
free from all foreign minerals. It receives that dehcate polish, 
without glare, which admirably adapts it to tho purposes of the 
sculptor, for whose uses it is mostly reserved, 

24. Conglomerate Marble. This consists of two varieties ; tlic 
one termed plodding stone, which is composed of rounded pebbles 
imbedded in compact lime-stone ; the other termed breccia, con- 
sisting of angular fragments united in a similar manner. The 
colors of these marbles are generally variegated, forming a very 
handsome ornamental material, 

25. Birds-eye Marble. The name of this stone is descriptive 
of its appearance, which arises from the cross sections of a pecu- 
liar fosEiil {fucoides demissus) contained iji the mass, made in 
sawing or splitting it. 

26. Lumackella MarUe. This is obtained from a lime-stone 
having shells imbedded in it, and takes its name from this cir- 

27. Verd Antique. Tiiis is a rare and costly variety, of a 
beautiful green color, caused by veins and blotclies of serpentine 
diffused through the lime-stone. 

28. Tho terms veined, golden, Italian, Irish, &c., given to 
tlie marbles found in our markets, are significant of tlieiv appeai- 
ance, or of tfie localities from which they are procured, 

29. Lime-stone is so extensively diffused throughout the Uni- 
tsd Slates, and is quarried, eitlier for buildmg Stone or to furnish 
hnie, in so many locaiities, thai it would be impracticable lo enu 
merale all witliin any moderate compass. One of the most re. 
markable formations of this stone extends, in an uninterrupted 
oed, from Canada, through llie States of Vcmioiit, Mass., Conn. 

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New York, New Jersey, Penn., and Virg., and, in all probaliihtj 
much farther south. 

Marbles arc quarried in various localities in the United States 
Among the most noted arc the quarries in Berkshire Co., Mass., 
which furnish both pure and variegated marbles ; those on the 
Potomac, from which the columns of conglomerate marbles were 
obtained that are seen in the interior of the Capitol at Washing- 
ton ; several in New York, which furnish white, the birds-eye, ana 
other variegated kinds; and some in Conn., which, among othei 
varieties, furnish a verd antique of handsome quality. 

Lime-stone is burned, either for building or agricultural pur- 
poses, in almost every locality where deposites of flie stone occur, 
fhomaston, in Maine, has supplied for some years most of the 
markets on the sea-board with a material which is considered aa 
a superior article for ordinary building purposes. One of the 
greatest additions to the building resources of our country, was 
made in the discovery of the hydrauhc or water lime-stones of 
New York. The preparation ot this material, so indispensable 
for all hydraulic works and heavy structures of stone, is carried 
on extensively at Roundout, on the Delaware and Hudson canal, 
in Madison Co., and is sent to every part of tlie United States, 
being in great demand for all the public works carried on undei 
the superintendence of our civil and military engineers A not 
less valuable addition to our building materials has been made by 
Prof. W. B. Rogers, who, a few years since, directed the atten- 
tion of engineers to the dolomites, for their good hydraulic prop- 
.3rties. IVom experiments made by Vicat, in France, who first 
there observed the same properties in the dolomite, and from 
those in our own country, it appears highly probable that the mag- 
iiesian lime-stones, containing a certain proportion of magnesia, 
will be fomid fully equal to the argillaceous, from which hydraulic 
lime has hitherto been solely obtained. 

Both of these lime-atones belong to very extensive formations, 
The %draulic lime-stones of New York occur in a deposite called 
the Water-lime Group, in the Geological Survey of New York 
corresponding to formation VI. of Prof. H. B. Rogers' arrange- 
ment of the rocks of Penn, This formation is co-extensive with 
the Helderberg Range as it crosses New York ; it is exposed in' 
many of llie valleys of Peim. and Virg., west of the Great Valley. 
It may be sought for just below or not far beneath the Oriskanj 
sanii-stones of the New York Survey, which correspond to form- 
ation VII. of Rogers. This sand-stone is easily recognised, bein^ 
of a yellowish white color, granular texture, with large cavities 
'.eft by decayed shells. The iime-stone is usually an eaithy 
drab-colored rock, somelimcs a greenish blue, which docs no 
ilake after being burned. 


The livclraiilic magnesian lime-stones belong to the furmatioiw 
[I. and Vl. of Rogers ; tlie first of these is the same as the Black 
Uiver, or Moliawk hme-stone of the New York Survey. It is tlic 
fjldsist fossiliferous Ume-stone in the United States, and occurs 
lliroughoul the whole bed, associated with the slates wliich occu- 
py formation III. of Rogers, and are called the Hudson River 
Group in the New York Survey. This extensive bed lies iii the 
great Appalachian Valley, known as the Valley of Lake Cham- 
nJain, V alley of the Hudson, as far as the Highlands, Ctunberland 
Valley, Valley of Virginia, and Valley of East Tennessee. The 
same stone is found in tlie deposites of some of the western val- 
leys of the mountain region of Perni. and Virginia. 

The important e of hydrauHc lime to the security of structures 
exposed to constant moisture, renders a knowledge of the geo- 
logical positions of those lime-stones from whicli it can be ob 
tained an object of great interest. From tlie results of the various 
geological surveys made in the United States, and in Europe, 
Bme-stone, possessing hydraulic properties when calcined, may 
be looked for among those beds which are found in connection 
with the shales, or other argillaceous deposites. The celebrated 
Roman, or Parker's cement, of England, which, from its prompt 
induration iu water, has become an important article of commerce, 
is manufactured from nodules of a concretionary argillaceous 
lime-stone, called septaria, from being traversed by veins of 
sparry carbonate of ume. Nodules of this chai'acter are found 
in Mass., and in some otJicr States ; and it is probable they wouiti 
yield, if suitably calcined and ground, an article in nowise itiferior 
to that imported. 

30. Gypsum, or Plaster of Paris. This stone is a sulpliate of 
lime, and has received its name from the extensive use made of 
it at Paris, and in its neighborhood, where it is quarried and sent to 
all parts of the world ; bemg of a superior quality, owing, it is stated, 
lo a certain portion of carbonate of lime which the stone contains. 
Gypsum is a very soft stone, and is not used as a building stone. 
Its chief utility is in furnishing a beautiful material for the orna- 
mental casts and mouldings in the interior of edifices. For tiiis 
puipose it is prepared by calcining, or, as ihe workmen term it, 
boiling the stone, until it is deprived of its water of crystallization, 
In this state it is made into a thin paste, and poured into moulds to 
form the cast, in which it hardens very promptly. Ca Icined plaster 
of Paris is also used as a cement for stone ; but it is einmently uiifil 
for this purpose \ for when exposed, in any situation, to moisture 
it absorbs it with avidity, swells, cracks, and exfoliates rapidly. 

Gypsum is found in various localities in the United States 
Large quantities of it arc quarried in New York, both for build 
ing and agricultural pirrposes. 

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31. UuRABiLiTY OF Stone. The moat impoi-tant propcittc" 
of stone, as a building material, are its durability under tbe or 
dinaxy circumstances of exposure to weather; ils capacity to 
eustain high degrees of temperature ; and its lesiitaiice to tlio 
destructive action of fresh aaid salt water. 

The wear of stone from ordinary exposure is very variable, 
depending, not only upon the texture and constituent elements of 
the stone, but also upon the locahty and the position it may oc- 
cupy in a structure, with respect to the prevailing driving rains. 
TJie chemist and geologist have not, thus far, laid down any in- 
livDible rules to guide tlie engineer in the selection of a material 
that may be pronounced durable for the ordinary period allotted 
to the works of idan. In truth, the subject admits of only gen- 
eral indications ; for stones having the same texture and chemical 
composition, from causes not fully ascertained, are found to pos- 
sess very different decrees of duration. This has been particu- 
larly noted in feldspatfiic rocks. As a "general rule, lliose stones 
which are fine-grained, absorb least water, and are of greatesl 
specific gravity-, are also most durable under ordinary exposures. 
The weight of a stone, however, may arise from a large propor- 
tion of iron in the state of a raotoside, a circumstance generally 
Qnfeivorable to its durabihty. Besides, the various chemical com 
binations of iron, potash and clay, when found in considenible 
quantities, both in the primary and sedimentary silicious rocks, 
greatly affect their durability. The potash contained in feldspar 
dissolves, and carrying off a considerable proportion of the silica, 
leaves nothing but aluminous matter behind. The clay, -on the 
other hand, absorbs water, becomes soft, and causes the utone to 
crumble to pieces. Iron in the form of protoxide, in soma cases 
only, discolors the stone by its conversion into a peroxide. This 
discoloration, while it greatly diminishes the value of some f.'.oncs, 
as in white marble, in others is not disagreeable to the eye, pro 
duciiig often a mottled appearance in buildings which sjidr, to tlit 
picturesque effect. 

32. Frost, or rather the alternate actions of fceczinj; r.ud thaw 
ing, is the most destnictive agent of Nature witli wiiich tlie en 
eineer has to contend. Its effects vary with the texture of stones , 
those of a fissile nature usually splitting, while the more porous 
kinds disintegrate, or exfoliate at uie surface. When stone from 
a new quarry is to be tried, the best indication of its resistance tc 
frost may be obtahied from an examination of ar.y rocks of the 
same kind, within its vicinity, which ai'e known to have becii 
exposed for a long period. Submitting tlie stone fresh from tlie 
i[uarry to the direct action of freezing would seem to be tlie mosl 
certain, test, were the stone destroyed by the espansive action 

one of frost : butbesides the, uncertainty of thii test, it is known 

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ihat some stones, ivliich, iviien first quarried, are much affecteii 
by frost, splitting mider its action, become impervious to it iifte 
they have lost tlie moisture of the quarry, as they do not re-absnib 
Eiear so large an amount as they bring from the quarry. 

33. M. Brard, a French chemist, has given a process for as- 
certaining the effects of frost on atone, which has met with the a-p- 
proval ofmaiiy Rrench architects and engineers of standing, as 'I 
corresponds with their experience. M. Brard directs that a smal! 
cubical blocli, about two inches on the edge, shal. ^le carefully 
sawed from the stone to be tested, A cold saturate- tolution of 
sulphate of soda is prepared, placed over a fire, and brought to 
llie boiling pomt. Tne stone, suspended from a string, is im- 
mersed in the boiling liquid, and kept there during thirty minutes; 
it is then carefully withdrawn ; the liquid is decanted, free fconi 
Bcdiment into a flat vessel, and the stone is suspended over it in 
a cool cellar. An efflorescence of ilie salt soon makes its appear- 
ance on tlie stone, when it must he again dipped into the liquid. 
This should be done once or more frequently during the day 
and the process be continued in this way for about a week. The 
earthy sediment, found at the end of this period in the vessel, is 
weighfed, and its quantity wiU give an indication of the like effect 
of frost. This process, with the official statement of a commission 
of engineers and architects, by whom it was tested, is minutely 
detailed in vol. 38, Annales de Chimie et de Physique, and tlie 
results are such as to commend it to the attention of engineers in 
submitting new stones to tiial. 

34. By the absorption of water, stones become softer and more 
friable. The materials for road coverings should be selected 
from those stones which absorb least water, and ate also hard 
and not brittle. Granite, and its varieties, lime-stone, and com- 
mon sand-stone, do not make good road materials of broken stone. 
All the hornblende rocks, porphyry, compact feldspar, and the 
quartzose rock associated with graywacke, furnish good, durable 
road coverings. The fine-grained granites which contain but a 
small proportion of mica, the fine-grained silicious sand-stones 
vvhicli are free from clay, and carbonate of lime, form a durable 
material when used in blocks for paving. Mica slate, talcose 
slate, hornblende slate, some varieties of gneiss, some varieties 
of sand-stone of a slaty structure, and graj-wacke slate, yield ex- 
cellent materials for flag-stone. 

35. The influence of locaHty on ihe durability of stone is very 
marked. Stone is observed to wear more rapidly in cities than 
m Uie country : aaid the stone in those parts of edifices exposed 
to the prcTan'mg I'ains and winds, soonest exhibits signs of decay. 
The disintegration of the stratified stones placed m a wall, is 
rnainlv affected by the position which the atvita or quarrv bed 

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receW3R, witli respect to tlie exposed s-'vfsce ; proceeding hstf.i 
when the faces of the strata are exposed, than in the contrary 

3fi. Stones which resist a liigh degree of heat without fusing 
are used for lining fnrnaccs, and are termed fire-stones, A gooa 
fire-stone should not only be infusihle, hut also not liable to crack 
or exfoliate from heat. Stones that contain lime, or magnesia, 
except in the form of silicates, are usually unsuitable for fire- 
stones. Some porous siUcious lime-stones, as well as some gyp 
Boua sUicious rocks, resist moderate degrees of htat Stones 
lliat contain much potash are very fusible under high tempera 
tures, running into a gl^sy substance. Quartz ind mica in 
\-arious combinations, furnish a good fire-stone as loi example 
finely granular quartz with tliin layers of mica, mica shte of tl c 
same structure, and some kinds of gneiss which contam a huge 
proportion of arenaceous quartz. Several varieties of sand-stono 
make a good hning for furnaces. They are usually those varie 
ties wliich are free from feldspar, somewhat porous, and are un 
crystallized in tlie mass. Tdcosc slate likewise furnishes a good 

37. Hardness is an essential quaUty in stone exposed to wear 
from the attrition of hard bodies. Stones selected for paving, flag- 
ging, and steps for stairs, should be hard, and of a grain siiffi 
ciently coarse not to admit of becoming very smooth under the 
action to which they arc submitted. As great hardness adds to 
tlie difficulty of working stone witli the chisel, and to the cost of 
the prepared material, builders prefer the softer or free-stones, 
such as tlie lime-stones and sand-stones, for most building pur- 
poses. Tiic following are some of the results, on this point, ob 
lained from experiment. 

Table showing the result, of experiments made under the direc 
tion of Mr. Walker, on the wear of different stones in the tram- 
waij on the Commercial Rood, London, from 27th March, 
1830, to August, 1831, being a period of seveiiteei. 
'nonilis. Transactions of Civil Engineers, vol. 1. 



on Sinai weigh 1. 





'7 1 19.75 




Hermef . . . 


r 3 94.25 




Budle .... 


S) 15.75 




Peterhead (blue) . 


4 1 7.50 





5 15.25 





1 9 11.50 




Diitlmoor . . . 


S 3 25,00 




Aheideen (blno) . 


6 a U 00 





The Coramercial Road stoueway consists of twc parallel 
of rectangular tramstones, 18 iiiclics wide by 12 inches decf, and 
jointed to each other endwise, for the wheels to travel on, witli a 
common street pavement between for the horses. 

The following table gives the results of some experiments on 
the wear of a mie-grained sand-stone pavement, by M. Coriolis, 
liming 8 years, upon the paved road from Paris to Toulouse, the 
carriage over which is about 500 tons daily, published in the 
Annales des Fonts et Chausies, for March and April, 1834 


moralon. compEuvd lo Ihat of 


158 lbs. 
154 " 
156 " 
150 " 
148 " 

Neglected as insensible. 

y's in volume. 

0.1023 inclj. 
0.1003 " 
0.1239 " 
0.213(1 " 
0.2677 " 

M. Coriolis remarks, that the weight of water absorbed afforils 
one of the best indications of the durability of tlie fine-grained 
sand-stones used in France for pavements. An equally good test 
of the relative durability of stones of the same kind, M. Coriolis 
states, is the more or less clearness of sound given out by striking 
the stone with a hammer. 

The following results are taken from an article by Mr. James 
Frost, Civ. Engineer, inserted in the Journal of the Franklin 
Institute for Oct. 1835, on the resistance of various substances 
to abrasion. The substances were abraded against a piece of 
white statuary marble, which was taken as a standard, repre- 
sented by 100, by means of fine emery and sand. The relative 
resistance was calculated from the weight lost by each substtnre 
during ihe operation. 

ue Resistance to Abrasion. 

Aberdeen granite ... . . 980 

Hard Yorkshire paving slone .... Z'it 

Italian blaclc marble 200 

Kilkenny black marble 110 

Statuary Marble 100 

Old Portland stotia T!) 

Roman cement stone G!) 

Fine-grainod Newcastle grindslono , , 53 

Stock hrick 34 

CoarsB-graineii Newcastle grindstone . , H 

Bath stone . 13 

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as. Ijime, considered , as a building materiul, is liow iisuall) 
divided into three principal classes ; Common, or Air lime, Hi/ 
draulic lime, and Hydraulic, or Water cement. 

39. Common, or air lime, is so called because the paste made 
from it with water will harden only in the air. 

40. Hydraulic lime and hydraulic cement both take their name 
from hardening under water. The former differs from the lattc! 
m two essential points. It slakes thoroughly, like common lime, 
when deprived of its carbonic acid, and it does not harden 
promptly under water. Hydraulic cement, on tlie contrary, docs 
not skke, and usually hardens very soon. 

41. Our nomenclature, with regard to these substances, is still 
quite defective for scientific arrangement. For the lime-stonea 
which yield hydraulic lime w^hen completely calcined, also give 
au hydraulic cement when deprived of a portion only of their 
carbonic acid ; and oilier hme-stones yield, on calcination, a result 
which can neither be termed Hme nor hydraulic cement, owing 
to its slaking very imperfectlji and not retaining the liardnesa 
wliicli it quickly tmes when first placed under water. 

M. Vicat, whose able researches into the properties of lime and 
mortars are so well Imown, has proposed to apply the term cement 
lims-stones (calcaires d ciment) to those stones which, when com- 
pletely calcined, yield hydraulic cement, and which under no de- 
gree of calcination, will give hydraulic lime. For the lime-stones 
which yield hydraulic lime when completely calcined, and which, 
when subjected to a degree of heat insufficient to drive oif all their 
carbonic acid, yield hydraulic cement, he proposes to retain the 
name hydrauhc lime-stones ; and to call tlie cement obtained 
from tlieir incomplete calcination, under-burnt hydraulic cement, 
{ciments d'incuits,) to distinguish it from that obtained from the 
cement stdne. With respect to those lime-stones which, by cal- 
cination, give a result that partakes partly of the properties both 
of hmes and cements, he proposes for them the name of dividing 
limes, {chatix limites.) 

The terms /af and meager are also applied to limes ; owing tc 
the difference in the quality of fhe paste obtained from them witli 
liie same quantity of water. The fat limes give a paste which is 
unctuous both to the sight and touch. The meager limes yield 
n thin paste. These names were of some importance when firsl 
introduced, as they served to distinguish common from hydraidic 
lime, tlie former being always fat, the latter meager ; but, late?, 
cspericnce having shown that all meager limes are not hydrau ic 
the terms are no longer of use, except to designate qualttiea ol' 
the paste of limes 

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43. Hydraulic Limes and Cements. The lime-slonts which 
yield these substances are either argillaceous, or magnesian, or 
argilo-magnesian. The products of their calcination van' con 
siderably in their hydraulic properties Some of tlie hydrauhc 
limes harden, or se( very slowly under water, while odiers set rap- 
idly. The hydraulic cements set in a very short lime. This 
diversity in the hydraulic energy of the argillaceous Ume-stones 
arises from the variable proportions in which the lime and ckv 
enter into their composition. 

43, M. Petot, a civil engineer in tlie French service, in an able 
work entitled Recherckes sur la Chauffoumerie, gives the follow- 
ing table, exhibiting these combinations, and the results obtained 
from their calcination. 




Diilliiellve cliaritetcrs of llie jiroducls. 





Very I at iime. 
Lime a little hydraulic, 
do. quite hjdraQlio. 
do. do. 
Plaslic, or hydraulic cement, 
Calcai-cous puEzolano (brick) 
do, do. 
do, do. 
Piizziilanoof pure cby do. 

Incapable of hardening in water. 
C Slakes like pure lime, when 
^ properly calcined, and hard- 
X ens under water. 
C Does not slake under any oir- 

< cunislances, and hardens un- 
{ der water with rapidity. 

i Does not slake nor harden un- 

< der water, unless mixed with 
( a fat, or an hydraulic lime. 
Same as the preceding. 

44. The most celebrated European hydraulic cements are ob- 
lained from argillaceous lime-stones, which vary but slightly in 
their constituent elements and properties. The following table 
^ves the results of analyses to determine tlic relative proportions 
of lime and clay in these cements. 

Table of Foreign Hydraulic Cements, showing the relative pro- 
portions of Clay and Lime contained in them. 




English, (commonly inown as Parker's, or Roman cement) 
Preaeh, (made from BmihgHe pe&btes) 

Do. (PouUIy) 

Bo. do, 

Do. (Ba,j4 

.55 40 
21 G9 



The livili 

: CQ'iicms used in England are obtained frou* 



rarious localities and differ bul little in the relative proportions 
of lime and clay found in them. Parker's cement, so called from 
tlie name of the person who first introduced it, is obtained by 
calcining nodules of septaria. The composition of these nodules 
IS the eaine as that of tlie Boulogne pebbles found on the opposite 
coast of France. The stones which furnish the English and 
French hydraulic cements, contain but a very small amount of 

45. The best known hydraulic cements of the United States, 
die manufactured in die State of New York. The following 
analyses of some of the hydraulic lime-stones, from the most 
noted localities, published in the Geological Report of the State 
of New York, 1839, are given by Dr. Beck. 

Analysis of the Munlius Hydraulic Limestone. 

Carbonic acid 30.80 

Lime 20,2.1 

Magnesia 18.80 

Slliea and alumina .... 13.50 

Oxide of iron 1.25 

Moisture and loss .... l.-ll 


Tills stone belongs to the same bed wliicli yields the hydraulic 
cement obtained near Kingston, in Upper Canada. 

Analysis of tlie CUttenango Hydraulic Limestone, hufore and 
after calcination. 


Carbonic acid and moisture 


Magnesia .... 


Alumina and oxide of iron 


Carbonic aciJ 
I.ime . . . 
Magnesia . . 
Silica . . 
Moist uro . 








Analysis of the Hydraulic Lime-slcne from Ulster Co., along 
the line of the Delaware and Hudson Canal, before and aftei 


Burnt ' 

JO, 65 



Oxide of iron 


a. 30 



'flic hydraulic cement from tliis last locality has become gen- 
erally well known, baring been successfuDy used for most of the 
military and civil public works on the sea-board. 

From the results of the analyses of all the above limestones, it 
appears that the proportions of lime and clay contained in them 
place them under the head of hydraulic cements, according to the 
classification of M. Petot. They do not slake, and they all set 
rapidly nnder water. 

46. The discovery of the hydraulic properties of certain mag 
nesian lime-stones is of recent ikte, and is due to M. Vicat, who 
first drew attention to tlie subject. M, Vicat inclines to the 
opinion, that magnesia alone, without the presence of some clay, 
will yield only a feeble hydraulic lime. He states, that he has 
never been able to obtain any other, from proceeding synthetically 
with common lime and magnesia ; and that he knows of no well- 
authenticated instance in which any of the dolomites, either of 
llie primitive or transition formations, have yielded a good hydrau 
lie lime. The stones from these formations, he states, are devoid 
of clay ; being very pure crystalline carbonates, or else contain 
silex only in the state of fijie sand. IVom M. Vicat's experi- 
ments, it is rendered certain that carbonate of ma^^nesia in combi- 
nation with carbonate of lime, in the proportion of 4if parts of the 
latter to from 30 to 40 of the fonner, will produce a feebly hy 
draulic lime, wSiich does not appear to increase in hardness aftei 
it has once set ; but that with ine same proportions, some hun 
diedths of clay are rec[iiisite to give hydraulic energy to t!ie com- 
pound. This proportion of clay M. Vicat supposes may caust 
the formation of ti'iple hydro-silicates of lime, alumir.a, and mag 
(lesia, having all tlie characteristic properties of good hydrauhc 

47. The hydraulic properties of the magncsian limo-sLoucs of 

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the United States were noticed by Professor W, B. Rogers, wh; , 
in his Report of the Geological Survey of Virginia, 1838, has 
given the following analyses of some of the stones from differcn' 

Carbonate of limo .... 



No. 3. 

No 4. 








24. IG 

Alumina and oxide of iron 





Silica and insoluble matter 


















The Kme-stone No. 1 of the above table is from Shcppardstown 
on the Potomac, in Virginia ; it is extensively manufactured for 
Iiydraulic cement. No. 2 is from the Natm^al Bridge, and banks 
of Cedar Creek, Virginia ; it makes a good hydraulic cement. 
No. 3 is from New York, and is extensively burnt for cement. 
No. 4 is from Louisville, Kentucky; said to make a good cement. 

48. M. Vicat states, tliat a magnesian lime-stone of France 
containing the following constituents, lime 40 parts, magaiesia 21, 
and silica SI, yields a good hydraulic cement ; and he gives the 
following analysis of a stone which gives a good hydrauhc lime. 

Carbonate of lime .... 50.00 

Carbonate of magnesia . . . 42.00 

Silica 5.00 

Alumina ...... 2,00 

Oxidoofiron .... 0.40 


By comparing the constlLucnts of these two last stones with the 
analyses of tlie cement-stones of New York, and the magnesian 
hydraulic lime-stones of Prof. Rogers, it will be seen that they 
consist, respectively, of nearly the same combmations t,f lime, 
magnesia, and silica, 

49. Physical Characters ami Tests of Hydraulic Limestones. 
The simple external characters of a lime-stone, as color, texture, 
fracture, and taste, are insufficient to enable a person to decide 
whether it belongs to the hydraulic class ; although they ass.'sl 
conjectuTe, particularly if the rock, from which the specimen is 
taken, is found in connection with the clay deposites, or if it he- 
long to a stratum whise general level and characteristics are tb-; 

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LIME. 19 

same as the argilo-magnesian rocks. Tliese rocks are generally 
some shade of drab, or of gray, or of a dark grayish blue ; have 
a compact texture ; fracture even or conchoidal ; with a clayey or 
earthy smell and taste. Although the hydraulic lime-stones are 
usuafly colored, stOl it may happen that tb j stone may be of a pure 
white, arising from the combination of lime with a pure clay. 

The difficulty of pronouncing upon the class to which a hmc- 
stone belongs, from its physical properties alone, renders it ncces 
sary to resort to a chemical andysis, and even to direct experiment 
to decide the question. 

50. In making a complete chemical analysis of alime-stone , more 
skill in chemical manipulations is requisite than engineers usually 
possess ; but a person who has the ordinary elenie'ntaiy know- 
ledge of chemistry, can readily ascertain the quantity of clay or 
of magnesia contained in a hme-stone, and from these two ele- 
ments can pronounce, with tolerable certainty, vipon its hydraulic 
properties. To arrive at this conclusion, a small portion of the 
stone to be tested — about five drachms — is taken and reduced to 
a powder ; this is placed in a capsule, or an ordinary watch 
crystal, and slightly diluted muriatic acid is poured over it until 
it ceases to effervesce. The capsule is then gently heated, and 
ihe liquor evaporated, until the residue in the capsule has acquired 
the coi^istence of thin paste. Tliis paste is thrown into a pint 
of pure water aiid well shaken up, and the mixtm:e is then fil- 
tered. The residue left on the filtering paper is thoroughly dried, 
by bringing it to a red heat ; this being weighed will give the 
clay, or insoluble matter, contained in the stone. It is important 
to ascertain the state of mechanical division of the insoluble mat 
ter thus obtained ; for if it be wholly granular, the stone wdl not 
yield hydraulic lime. The granular portion must therefore be 
carefully separated from the other before the latter is dried and 

51. If the sample tested contains magnesia, an indication of 
this will be given by the slowness with which tlie acid acts ; if 
the quantity of magnesia be but Httle, tlie solution will at iirsi 
proceed rapidly ana then become more sluggish. To ascertain 
the quantity of magnesia, clear Ume-water must be added to the 
filtered solution as long as any precipitate is formed, and this 
precipitate must be quickly gathered on filtering paper, and tlien 
be washed with pure water. The residue from this washing ia 
ihe magnesia. It must be thoroughly dried before being weighed, 
to ascertain its proportion to the day. 

52. Having ascertained, by the preceding analysis, the proba- 
ble hydraulic energy of the stone, a sample of it should ^so ba 
Bubmitted to direct experiment. Tliis may be hkcwise done on 
a small scale. A. sample of the stone mist be reduced to fraij 

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meiil.s about the size of a walnut. A crucible, perforated with 
holes for the free admission of air, is filled with the^e fragments, 
and placed over a fire sufficiently powerful to drive off the car 
bonic acid of the stone. The time for effecting this will depend 
on the intensity of the heat. When the heal has been applied 
for three or foin: hours, a small portion of the calcined stone niE^ 
be tried ivith an acid, and the degree of the calcination may be 
judged of by the more or less copiousness of the effervescence 
that ensues. If no effervescence takes place, the operation may 
be considered completed. The calcined stone should be tiicd 
soon after it has become cold ; otherwise, it should be kept in 
a glass jar made as air-tight as practicable until used. 

53. When the calcined stone is to be tried, it is first slaked 
by placing it in a small basket, wliich is immersed for five or sis 
seconds in pure water. The stone is emptied fi:6m the basket so 
soon as the water has drained off, and is allowed to stand until 
the slaking is terminated. This process will proceed more or 
less rapidly, according to the quality of the stone, and the degree 
of its calcmation. In some cases, it will be completed in a few 
minutes ; in others, portions only of the stone wOl fall to powder, 
the rest crumbling into lumps which slake very sluggislily ; while 
other varieties, as the true cement stones, give no evidence of slak- 
ing. If the stone slakes either completely or partially, it must bo 
converted into apaste of the consistence of soft putty, being groimd 
up thoroughly, if necessary, in an iron mortar. The paste is 
made into a cake, and placed on the bottom of an ordinary tum- 
bler, care being taken to make the diameter of the cake the same 
as that of the tumbler, which is filled with water, and the time of 
'mmersion noted. If the lime is only moderately hydraulic, it 
will have become bard enough at the end of fifteen or twenty 
days, to resist the pressure of the finger, and will continue to 
harden slowly,-more particularly from tlie sixth or eighth month 
after immersion ; and at the end of a year it will have acquired 
the consistency of hard soap, and will dissolve slowly m pure 
water. A fair hydraulic lime will have hardened so as to resisi 
the pressure of the finger, in about six or eight days after immer- 
sion, and wiU continue to grow harder until from six to twelve 
months after immersion ; it will then have acquired the hardness 
of the softest calcareous stones, and will be no longer soluble in 
pure water. When the stone is eminently hydraulic, it will have 
become hard in from two to four days after immersion, and in one 
monUi it will be quite hard and insoluble in pure water ; after sts 
months, its hardness will be about equal to the more absorbent 
calcareous stones ; will splinter from a blow, presenting a slaty 

As the hydraulic cements do not slake perceptibly, the luml 

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Blone must first be reduced to a fine powde before it is made 
into a pi^tc. The paste, when kneaded betweun the fingers, be- 
comes warm, and will generaUy set in a few minutes, either in the 
open air or in water. Hydramic cement is far more sparingly 
soluble in pure water ilian the hydraulic lime ; and the action of 
pure water upon them ceases, apparently, after a few weeks im- 
mersion in it. 

54. Calcination of Lime-stone. The effect of heat on lime- 
stones varies with the constituent elements of the stone. The 
pure lime-stones will stand a high degree of temperature with- 
out fusing, losing only their carbonic acid and water. The im- 
pure stones containing silica fiise completely under a great heat, 
and become more or less vitrified when the temperature much ex- 
ceeds a red heat. The action of heat on the impure lime-stones, 
besides driving off their carbonic acid and water, modifies the re- 
lations of tlieir other chemical constituents. The argillaceous 
stones, for example, yield an insoluble precipitate when acted on 
by an acid before calcination, but are perfectly soluble afterwards, 
unless the silex they contain happens to be in the form of grains. 

55. The calcination of tlie hydraulic lime-stones, from their 
fusible nature, requires to be conducted with great care ; for, if 
not pushed far enough, the under-burnt portions will not slake ; 
and, if carried too far, the stone becomes dead or sluggish ; slakes 
very slowly and imperfectly at first ; and, if used in this state for 
masonry, may do injury by the swelling which accompanies the 

56. The more or less facility with wliich the impure lune-stones 
can be burned, depends upon several causes ; as the compactness 
of the stone ; t!ie size of the fragments submitted to heat ; and 
the presence of a current of air, or of aqueous vapor. The more 
compact stones yield their carbonic acid less readily than those 
of an opposite texture. Stones which, when broken into very 
small lumps, can be calcined under tlie red heat of an ordinary 
fire m a few hours, will require a far greater degree of tempera- 
ture, and for a much longer period, when broken into fragments 
of six or eight inches in diameter. This is particularly the case 
with the impure lime-stones, which, wlien in large lumps, vitrify 
at the surface before the interior is thoroughly burnt. 

issed over tlie 

57. If a current of vapor is passed over tlie stone after it has 
commenced to give off its carbonic acid, the remaining portion of 
the gas which, under ordinary circumstances, is expelled witii 
great difiiculty, particulariy near the end of the process of calci- 
nation, will be carried ofi'^much sooner. This influence of an 
aqueous current is attributed, by M. Gay-Lussac, purely to a 
mechanical action, by removing liie gas as it is ' evolved, and hia 
experimf 'its go to show that a like clfecc is produced by an at 

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Biospheric current. In burning the impure lime-etones, liowevei 
an aqueous current produces the Jurtlier beneficial effect of pre 
venting the vilrification of the stone, when the temperature haa 
become too elevated ; but as the vapor, on coming in contacl 
with the heated stone, carries off a large portion of the heat, this 
together with the latent heat contained in it, may render its use- 
in some cases, far from economical. 

58. Wood, charcoal, peat, the bituminous and anthracite coals 
are used for fuel in lime-burning. M. Vicat states, that wood is 
the best fuel for burning hydraulic lime-stones ; that charcoal is 
inferior to bitmninous coal ; and that the results from this last are 
very uncertain. When wood is used, it should be dry ai ti spht 
up, to burn quickly and give a clear blaze. The commo op on 
among lime-buiners, that the greener the fuel the better a d that 
the lime-stone should be watered before it is placed in tl e k In ib 
wrong ;' as a large portion of the heat is consumed in co vert g 
the water in both cases into vapor. Coal is a more econo cal 
fuel than wood, and ia therefore generally preferred to it , but H 
requires particular care in ascertaining the proper quantity for use. 

59. Lime-liilns. Great diversity is met with in the iorms and 
proportions of lime-kilns. Wherever attention has been paid to 
economy in fuel, the cylindrical, ovoidal, or the inverted conical 
form has been adopted. The two first being prefeiTed foi- wood 
and the last for coal. 

60. The whole of the burnt lime is either drawn from the kib 
at once, or else the burning is so regulated, that fresh stone and 
fuel are added as the calcined portions are withdrawn. The lat- 
ter method, is usually followed when the fuel used is coal. The 
stone and coal, broken into proper sizes, (Fig. 1,) and in proper 

A, BoikI mBEOmy ol' the liilu, ichich Is built up on Uie extei^ra 
smiare tower, witli two atclied eatmnceEi at B, B on opj 

interior of the Mln, lined willi fire-brict or stone. 


;, openingaljetweonB.Baiiil tlie inlciioi'tlironsliwliichtlie 

lions determined by experiment, are placed in the kiln 1h alternate 
layers ; the coal is ignited at the bottom of the kiln, and fresh 
strata are added at the top, as the burnt mass settles down and is 
partially wi^drawn at the bottom. Kilns used in this way are 
called jjerpettial kilns ; they are more economical in tne con 
siiniption,of fuel than those in which the burning is jntbrmitted 
an.' wliich arc, on this account, termed intermittent kihts. Wood 


may also be used as fuel in perpetual kiin^ but not willi such 
economy as coal ; it moreover presents many mconvcniences, m 
supplying the kiln with fresh stone, and in regulating its dis- 
charge. The inverted conical-shaped idln is generally adcpted 
for coal, and the ovoidal-shappd for wood. 

61. Some care is requisite infilling the Idin with stone when a 
wood fire is used. A dome (Fig. 2) is formed of the largest blocks 

il ceDtra Jino of tile outranoe of A lime- 
A, solid masoniy of the itilii. 

itn and BUppljing fuel, 
i, shown by the doltal 

of the broken stone, which cither rests on Uie bottom of tlie luln or 
on the ash-grate. The lower diameter of the dome is a few feel 
less tlian that of the lain ; and its interior is made sufficiently capa- 
cious to receive the fuel which, cut into short lengths, is placed 
up endwise around the dome. The stone is placed over and 
around the courses which form the dome, the largest blocks in 
the centre of the Idln. The management of the fire is a matter 
of experiment. For the first eight or ten hours it should be care- 
fully regulated, in order to bring the stone gradually to a red heat. 
By applying a high heat at first, or by any sudden increase of it 
until the mass has reached a nearly uniform temperature, the 
stone is apt to shiver, and choke the kib, by stopping the voids 
between the courses of stone which form the dome. After the 
stone is brought to a red heat, the supply of fuel should be uni- 
form until the end of the calcination. The practice sometimes 
adopted, of abating the fire towards tlie end, is bad, as the last 
portions of carbonic acid retained by the stone, require a high de- 
gi-ee of heat for their expulsion. The indications of complete 
calcination are generally manifested by the duninution which 
gradually takes place in the mass, and which, at this stage, is 
about one sixth of the primitive volume ; by tlie broken appear- 
ance of the stone which forms the dome, the interstices bet^veen 
which being also choked up by fi:agments of the burnt stone ; and 
by the ease with which an iron bar may be forced down through 
the burnt stone in the kiln. When these indications of complete 
calcination are observed, the kiln should be closed for ter. or 
twelve hours, to confine the heat and. finish the burning of l!i& up- 



oe dtstormined only by careful experiment. If loo great heiglit 
be given to the mass, the lower portions may be overbnrned be 
fore the upper are burned enough. The proportions between the 
height and mean horizontal section, will depend on the texture of 
fhe stone ; the size of the fragmenjs into which it is broken for 
burning ; and the more or less facility with which it vitrifies. In 
the memoir of M. Petot, already cited, it is stated as the results 
of experiments made at Brest, tint large-sized kibis are more 
economical, both in the consumption of fuel and in the cost of 
attendance, than smali ones ; but that there is no notable econo- 
my in fuel when the mean horizontal secfion of the kiln exceeds 
sixty square feet. 

03. The circular seems the most suitable fonn for the horizon- 
tal sections of a kiln, both for strength and for economizing the 
heat. Were the section the same throughout, or the form of the , 
interior of the kiln cylindrical, the strata of stone, above a certain 
point, would be very imperfectly burned when the lower were 
enough so, owing to the rapidity with which the inflamed gases, 
arising from the combustion, axe cooled by coming into contact 
with the stone. To procure, therefore, a temperature throughout 
the heated mass whiai shall be nearly uiiiform,,the horizont J sec- 
tions of the kiln should gradually decrease from the point where 
the flame rises, which is near the top of the dome of broken stone, 
to the top of the Idln. This contraction of the horizontal section, 
■from the bottom upward, should not be made too rapidly, as the 
draft would he injured, and the capacity of tlie kiun too much 
diminished ; and in no case should the area of the top opening be 
less than about one fourth the area of the section taken near the 
top of the. dome. The best manner of arranghig the sides of the 
kiln, in the plane of the longitudinal section, is to connect the top 
opening willi the horizontal section through the top of tlie dome, 
by an arc of a circle whose tangent at the lower point shall be 

64. Lime^kilns are constructed either of brick, or of some of 
the more refractory stones. The walls of the kiln should be suf 
ficiently thick to confine the heat, and, when the locality admits 
of it, they are buCt into a side hill ; otherwise, it may be neces- 
sary to use iron hoops, and vertical bars of iron, to strengthen tho 
brick-worL The interior of the kiln should be faced eitlier with 
good lire-brick or with fire-stone. 

65, M. Petot prefers kilns arranged with fire-grates, and on 
ash-pit under the dome of broken stone, for tlie reason tliat they 
give the means of better regulating the heat, and of throwing tho 
flame more in the axis of the kiln than can be done in kilns with 
out them. The act'on of the flame is lh:ts more uniformly felt 
through the mass ol st'. nc above the top of the donic, while thai 

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of 1 e adia d I 
ui n 
66 M P 

pf dneh dob^^ 
f dp mg n h n o 1 

se kilns w h 

d I lomc, is a'.sc nioic 

m ss of stone tbove 

e tl an from ten to tliir- 

np ct texture of the 

w hwh ti^ifies. He pro- 

(}< ) for the piii^posn 


irai ofalimo-fciliiwithtv 

tuaBOiuT of the kiln. 

I sh wn Q7 the dotted line. 

II werstofT. 

ed ti n 

e to kilii. 

queous vapor. 
c dtawins kiln, &c., 
firs-proof door. 

vay for drawing kiln, &c 

ol ecL I 1 . ^ I , y ^ t B ^ 1 passes off from 

the top of the lower story, and would otherwise be lost, to heat 
the stone in the upper 'story; this story being arranged with a 
side-door, to introduce fuel under its dome of broken stone, and 
complete the calcination when that of the stone in the lower 
story is finished. 

M. Petot gives the following general directions for regulating 
the relative dimensions of the parts of the kiln. The greatest 
horizontal section of the kiln is placed rather below the top of the 
dome of broken stone ; the diameter of this section being 1 ,82, the 
diameter of the grate; The height of the dome above the grate 
is from 3 to 6 feet, according to the quantity of fuel to be con- 
sumed hourly. The bottom of the kiln, on which the piers of the 
dome rest, is from 4 to G inches above the top of the grate ; the 
diameter of the kiln at this point being about 2 feet 9 iucliea 
gi'eater than that of tlie grate. The diameter of the horizontal 
section at top is 0,63, the diameter of tiie greatest horizontal sec- 
lion. The horizontal seclions of the kiln diminish from the section 
near the top of the dome to the top and bottom of the kiln ; the 
sides of the kiln receiving the form shown in Fig, 3 : the object 
of contracting tlie Idln towards the bottom being to allow tlie slona 
near the bottom of the kiln to be thoroughly burned by tlie radiated 
iieat Tiie gi'ate is fonned of cast-iron bars of the usual form 

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the area of the spaces between the bars being one fourtla the tolai 
area of the grate. Tlie bottom of the ash-pit, wliich may be on 
the same level as the exterior ground, ia placed 18 inches below 
the grate ; and at the entrance to the ash-pit is place{l a reservoir 
for water, about 18 inches in depth, to furnish an aqueous cur 
rent. The draft through the grate is regulated by a lateral air 
cliainiel to the ash-pit, which can be tota% or partially shut by a 
valve ; the area of the cross section of this channel is one tenth 
the total area of the grate. A square opening 16 inches wide, 
the bottom of vfhich is on a level with the bottom of the kiln, 
leads to the dome for the supply of the fuel. This opening is 
closed with a fire-proof and air-tight door. 

In arranging a kiln with two stories, M. Petot states, that the 
grates of the upper story are so soon destroyed by the heat, that 
it is better to suppress them, and to place the fuel for completing 
the calcination of the stone of this story, on the top of ihe burnt 
Stone of the lower story. 

67. Slaking Lime. Quick-lime may be slaked in three dif- 
ferent ways. By pouring sufficient water on the burnt stone to 
convert the slaked lime into a thin paste, which is termed drown- 
ing the lime. By placing the burnt stone in a basket, and im 
mersing it for a few seconds in water, during which time it will 
imbibe enough water to cause it to fall, by slaking, into a dry 
powder ; or by sprinkling the burnt stone with a sufficient quaii 
tity of water to produce the same effect. By allowing the stone 
to slake spontaneously, from tlie moisture it hnbibes from the 
atmosphere, wliich is termed air-slaking. 

68. Opinion seems to be settled among engineers, that drown- 
ing is the worst method of slaking lime which is to be used for 
mortars. When properly done, however, it produces a finer paste 
than either of the other methods ; and it may therefore be resorted 
to whenever a paste of this character, or a whitewash is wanted. 
Some care, however, is requisite to produce this result. The 
stone should be fresh from the kiln., otherwise it is apt to slake 
into lumps or fine grit. All the water used should be poured 
over the stone at once, which should be arranged in a basin or 
vessel, so tliat the water surrounding it may be gradually imbibed 
as the slaking proceeds. If fresh water be added during the slak- 
ing, it checks the process, and causes a gritty paste to form. 

69. In slaking by immersion, or by sprinkhng with water, the 
stone should be reduced to small-sized fragments, otherwise the 
slaking will not proceed uniformly. The fat limes should be in 
lumps, about the sine of a walnut, for immersion ; and, when 
wiUidrawn from the water, should be placed immediately in bins 
or be covered with sand, to confine the heat and vapor. If lefi 
exposed to the air, the lime becomes chiUcd and separates into a 

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HME, 27 

coarse gnt, which takes aomo time ia slake [horouglily when 
mora water is added. Sprinkling the lime is a more convenienl 
process than immersion, and is equally good. To effect tbe slak 
ing in this way, the stone should be broken into fragmeuls of a 
suitable size, which experiment will determine, and be placed in 
small heaps, surrounded by sufficient sand to cover them up when 
the slaking is nearly completed. The stone is then sprinkled 
with about one fourth its bulk of water, poured through the rose 
of a watering-pot, those lumps which seem to slake moi t slug- 
gishly receiving the most water; when the process seems com- 
pleted, the heap is carefully covered over with the sand, and 
allowed to remain a day or two before it is used. 

70. Slaking either by immersion or by sprinkling is considered 
the best. The quantity of water imbibed by lime when slaked 
by immersion, varies with the nature of the lime ; 100 parts of 
fat lime will take up only 18 parts of water ; and the same quan- 
tity of meager lime will imbibe from 90 to 35 parts. One volume, 
in powder, of the burnt stone of rich lime yields from 1.50 to 
1.70 in volume of powder of slaked lime; while one volume 
of meager lime, under like circumstances, will yield from 1 .80 to 
2.18 in volume of slaked Hme. 

71. Quick lime, when exposed to the free action of the air in 
a dry locality, slakes slowly, by imbibing moisture from the at- 
mosphere, with a sHght disengagement of heat. Opinion seems 
to be divided with regai-d to the effect of this method of slaking 
on fet limes. Some assert, that the mortar made from them is 
better than that obtained from any other process, and attribute 
this result to the re-conversion of a portion of tiie slaked hme into 
"a carbonate ; others state the reverse to obtain, and assign the 
same cause for it. With regard to hydraulic limes, all agree thai 
they are greatly injured by air-slaking. 

72. Air-slaked fat limes increase two fifths in weight, and for 
one volume of quick lime yield 3.52 volumes of slaked lime. The 
meager limes increase one eighth in weight, and for one volume 
of quick lime yield from 1.75 to 2.35 volumes of slaked lime 

73. The dry hydrates of hme, when exposed to the atmosphere, 
gradually absorb carbonic acid and water. This process pro- 
ceeds very slowly, and the slaked lime never regains all the car- 
bonic acid which is driven off by the calcination of the hme-stone. 
When converted into a thick paste, and exposed to the air, the 
hydrates gradually absorb carbonic acid ; this action first taltcs 
place on the surface, and proceeds more slowly from year to 
year towards the interior of the exposed mass. The absoipxion 
of gas proceeds more rapidly in the meager tlian in the fat limes. 
Those hydrates which are most thoroughly slaked become hard 
est The hydrates of tlie piue fat linies become in time verj 

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hard, while those of the hydraulic limes hticome only moderately 

74. The fat limss, when slaked by drowning, may be pie> 
served for a long jeriod in the state of paste, if placed in a damp 
silualioa and kepi, from contact with the air. They may also be 
preserved for a long time without change, when slaked by im- 
mersion to a dry powder, if placed in covered vessels. Hydraulic 
limes, under similar circumstances, will harden if kept in the stale 
of paste, and will deteriorate when in powder, unless kept in 
perfectty air-tight vessels. 

75. The hydrates of fat lime, from air-slaking or immersion, 
require a smaller quantity of water to reduce them to the state of 
paste than the otliers ; but, when immersed in water, they grad- 
ually imbibe their full dose of water, the paste becoming tliicker, 
but remaining unchanged in volume.' Exposed in this way, the 
water will in time dissolve out all the lime of the hydrate which 
has not been re-converted into a sub-carbonate, by the absorption 
of carbonic acid before immersion ; and if the water contain car- 
bonic acid, it wiU also dissolve the carbonated portions. 

76. The hydrates of hydraulic lime, when immersed in water 
in the state of thin pastes, reject a portion of the water from the 
paste, and become hard in time ; if the paste be very stiff, they 
imbibe more water, set quickly, and acquire greater hardness in 
lime than the soft pastes. The pastes of the hydrates of hydrau- 
lic lime, which have hardened in the air, will retain their hai'dness 
when placed in water. 

77. The pastes of the fat limes shrink very unequally in drying, 
and die shrmkage increases with the purity of the lime ; on this 
account it is difficult to apply them alone to any building purposes, 
except in very thin layers. The pastes of the hydraulic limes 
can only he used with advantage under water, or where they are 
constantly exposed to humidity ; and in these situations they are 
never used alone, as they are found to succeed as well, and to 
present more economy, when mixed with a portion of sand 

78. Manner of Reducing Hydraulic Cement. As the cement 
stones will not sld'.e, they must be reduced to a fine powder by 
some mechanical process, before they can be converted into a 
hydrate. The methods usually employed for this purpose con- 
sist in first breaking the burnt stone into small fragments, eitlier 
under iron cylinders, or in mills suitably formed for this pur- 
pose, which are next ground between a pair of stones, or else 
crushed by an iron roller. The coarser particles are separated 
from tiie fine powder by the ordinary processes witli sieves. Tho 
powder is then carefully packed in air-tight casks, and kept for use 

79. Hydraulic cement, like hydrauhc Lime, deteriorates by 
exoosure to the air, and may in lime lose ;.'! its hydraulic prop- 

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onica. Oil this account it should bo used when fresh iVoii: the 
kiin ; for, however carefully packed, it cannot be well jireseTTcd 
wlien transported to any distance. 

80. The deterioration of hydraulic cements, from exposure to 
Ihe air, arises, probably, from a chemical disunion between the 
coikstituent elements of the burnt stone, occasioned by tlic ab- 
sorption of water 'and carbonic acid. When injured, their cnergif 
can be restored by submitting them to a mucli slighter degree ol 
heat than that which is requisite to calcine the stone suitably in 
t!ie first instance. TVom the experiments of M. Petot, it appears 
that a red heat, kept up for a short period, is sufficient to restore 
damaged hydrauhc cements. 

81. Arttjicial Hydraulic Limes and Cements. The discover) 
of the argillaceous character of the stones wliich yield hydraulic 
limes and cements, connected with the fact that brick reduced to 
a fine powder, as well as several substances of volcanic origin 
having nearly the same constituent elements as ordinary brick 
when mixed in suitable proportions with common lime, wiil yield 
a paste that hardens under water, has led, within a recent period, 
to artificial methods of producing compounds possessing tlie prop- 
erties of natural hydraulic lime-stones. 

82. M. Vicat was the first to ^oint out the metliod of forming 
an artificial hydraulic lime, by mixing common lime and unburnt 
clay, in suitable proportions, and then calcining them. The ex- 
periments of M. vicat have been repeated by several eminent 
engineers witli complete success, and among others by General 
Pasley, who, in a recent work by him, Observations on Limes, 
Calcareous Cements, &c., has given, witli minute detail, the results 
of his experiments ; fcom which it appears that an hydraulic ce- 
ment, fully equal in quality to that obtained fcom natural stones 
can be made by mixing common lime, either in the state of a 
carbonate or of a hydrate, with clay, and subjecting the mixture 
to a suitable degree of heat. In some parts of iSance, where 
chalk is found abundantly, the preparation of artificial hydrauhc 
lime has become a brancn of manufacture. 

83. Difi"erent methods have been pursued in preparing this 
material, the main object being to secure the finest mechanical 
divisionof the two ingredients, and their tlioroiigh mixture. For 
this purpose the lime-stone, if soft like chalk or tufa, may be re- 
duced in a wash-mill, or a rolling-mill, to the state of a soft pulp ; 
■t is then incorporated with the clay, by passing them through a 
[)ug-mjll. The mixture is next moulded into small blocks, or 
made up into balls between 2 and 3 inches diameter, by hand, 
and well dried. The balls arc placed in a kiln, — suitably calcined, 
and are finally slaked, or ground down iine for use. 

64. If the lime-stone be hard, it must be calcined and slaked 

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in the usual mmnerj before it can be mixed wim the clay. The 
process for mixing llie ingredients, their calcination, and farthet 
preparation for itse, arc the same as in the preceding case, 

85. Artificial hydraulic lime, prepared icam the hard limC' 
stones, is more expensive than that made from the soft ; but it is 
slated to be supenor in quality to the latter. 

86. As clays are seldom free from carbonate of lime, and as 
the lime-stones wliich yield common or fat lime may contain some 
portion of clay, the proper proportions of the two ingredients, to 
produce either an hydraulic lime or a cement, must be determmed 
by experiment in each case, guided by a previous analysis of tlic 
two ingredients to be tried. 

If the lime be pure, and the clay be free from lime, then the 
combinations in the proportions given in the table of M, Fetot will 
give, by calcination, like results with the same proportions when 
found natural^ combined. 

87. Puzzotana, &c. The practice of using brick or tile-dusl, 
or a volcanic substance known by the name of puzzolana, mixed 
with common lime, to form an hydraulic lime, was knovFn to the 
Romans, by whom mortars composed of these materials were 
extensively used in their hydraulic conslructions. This practice 
!ias been more or less foUowed by modern engineers, who, until 
witliin a few years, eitlier used the puzzolana of Italy, where it 
is obtained near Mount Vesuvius, in a pulverulent state, or a ma- 
terial termed Trass, manufactured in Holland, by grinding to a fine 
powder a volcanic stone obtained near Andemach on the Rhine. 

Experiments by several eminent chemists have extended the 
list of natural substances which, when properly burnt and reduced 
to powder, have the same properties as puzzolana. They mostly 
belong to the feldspathic and. schistose rocks, and are either fine 
sand, or clays more or less indurated. 

Tlie following Table gives the results of analyses of Puzzolana, 
Trass, a Basalt, and a Sckistus, tohich, when burnt and pow- 
dered, were found to possess the properties of puzzolana. 



















MagnoBia '. '. 



Oxide of iron 





Oxide of manganese 






Soda . 




Watei and loss 





1. 000 





88. All Qiiheii substances, when prepared artificially, areiow 
generally known by the name of artificial puzzolanas, in conira- 
dislinctipn to those which occur naturally. 

89. General Treussart, of the French Corps of Military Engi- 
neers, first attempted a systematic investigation of the properties 
of artificial puzzolanas made irom ordinary clay, and of the best 
manner of prepaimg them on a large scale. It appears from the 
results of his experiments, that the plastic clays used for tiles, or 
pottery, v/hich are unctuous to the touch, the alumina in them 
being in the proportion of one fifth to one lliird of the silica, fur- 
nish the best artificial puzzolanas when suitably burned. T)ie 
clays which are more meager, and harsher to the touch, yield an 
inferior article, but are in some cases preferable, from the greater 
case with which they can be reduced to a powder. 

90. As tlie clays mostly contain lime, magnesia, some of the 
metallic oxides, and alkahne salts. General Treussart endeavored 
to ascertain tlie influence of these substances upon the qualities of 
tlie artificial puzzolanas from clays in which they are found. He. 
states, that the carbonate of potash and the muriate of soda seem 
to act beneficially ; that magnesia seems to be passive, as well 
as the oxide of iron, except when the latter is found in a large 
proportion, when it acts huitfully ; and that the lime has a mate- 
rial influence on the degree of heat required to convert the clay 
into a good artificial puzzolana. 

91. The management of the heat, in the preparation of this 
material, seems of the first consequence ; and General Treussart 
recommends that direct experiment be resorted to, as the most 
certain means of ascertaining the proper point. For this purpose, 
specimens of the clay to be tried may be kneaded into balls as 
large as an egg, and Uie balls, when dry] be submitted to diiferent 
degrees of heat in a kiln, or furnace, mrough which a current of 
air must pass over the bails, as this last circumstance is essential 
to seciu-e a material possessing the best hydraulic qualities. Some 
of the baOs are withdrawn as soon as then- color indicates thai 
fhey are underbumt ; others when they have the appearance of 
weU-bm'nt brick ; and others when their color shows tliat they 
are overburnt, but before they become vitrified. The burnt balls 
are reduced to an impalpable powder, and this is mixed with a 
hydrate of fat lime, in the proportion of two parts of the powder 
to 5ne of lime in paste. Water is added, if necessary, to bring 
slie different mixtures to the consistence of a thick pulp ; and they 
are separately placed in glass vessels, covered with wafer, and 
allowed to remain imtil they harden. The compound which 
hardens most promptly wDl iniicale the most suitable degree of 
heat to be applied, 

93. As the arbonaies of It no, of potash, and of soda, act aa 

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fiuxes on silica, t!ie presence ot cither one of iliotn will inodift 
the degree of heat necessary to convert the clay into a good natu- 
ral puzzolana. Clay, containing about one tenth of lime, should 
be brought to about the state of sHghtly-burut brick. The ocJireoua 
clays require a higher degree of heat to convert them into a good 
material, and should be burnt until they assume the appearance 
of well-burnt brick. The more refractoiy clays will bear a still 
higher degree of heat ; but the calcination should in no case be 
can'ied to the point of incipient vitrification. 

93. The quantity of lime contained in the clay can be readily 
ascertained beforehand, by treating a small portion of the clay, 
diffused in water, with enough muriatic acid to dissolve out the 
lime ; and this last might serve as a guide in the preliminary 
stages of the experiments. 

94. General Treussart states, as the results of his experiments, 
that the misture of artificial puzzolana and fat hme form.s an hy 
draulic paste superior in quality to that obtained by M. Vicat's 
process for making artificial hydraulic lime. M. Curtois, a French 
civil engineer, in a memoir on these artificial compounds, pub- 
lished in the Annales des Fonts et Chauss&es, 1834, and General 
Pasley, more recently, adopt the conclusion of General Treussart. 
M. Vicat's process appears best adapted when chalk, or any very 
soft lime-stone, whicli can be readily conveited to a soft pulp, is 
ased, as offering more economy, and afibrding an hydraulic lime 
which is sufficiently strong for most building purposes. By it 
General Pasley has succeeded in obtaining an artificial hydraulic 
cement, which is but little, if at all, inferior to ihc best natural 
varieties ; a result which has not been obtained from any com- 
bination of fat lime with puzzolana, whether natural, or artificial. 

95. Ail tlie puzzolauas possess the important propeity of not 
rieteriori,>.ing by exposure to the air, which is not the case witli 
any of the hydraidic Umes, or cements. This properly may ren- 
der tliem very serviceable in many localities, where only common, 
or feebly hydraulic lime can be obtained. 

KG. Moiiar is any mixture of lime in paste with sand. It may 
be divided into two principal classes ; Hydraulic mortai; which is 
made of hydriiiilic lime, and- Common mortar, made of common 

97. The term Grmit is applied to any mortar in a thin or fluid 
state ; and the terms Concrete and Beton, to mortars incorporated 
wiili gravel and small fragments of stone or brick. 

98. Mortar is used for various purposes in building. It serv^a 
a3 a cement to unite blocks of stone, or bfick. In concrctL' and 

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MORTAIl. 33 

beton, whicli may be regarded as artificial conglomerate stones. 
it forms the matrix by which the gravel and broken stone are 
held together ; and it is the principal material with which the ex 
terior surfaces of walls and uie intenor of edifices are coated. 

99. The quality of mortars, whether used for structures ex- 
posed to the weather, or for those immersed in water, will depend 
upon the nature of IJie materials used ; — their proportion ; — t!ic 
manner in which the lime haB been converted into a paste to re 
ceive the sand ; — and the mode employed to mix the ingi-edients. 
Upon all of these points experiment is the only unerring guide for 
tlie engineer ; for the great diversity in the constituent elements 
of lime-stones, as well as in the oilier ingredients of mortars, must 
necessarily alone give rise to diversities in results ; ana when, to 
these causes of variation, are superadded those resulting from 
diiferent processes pursued in the manipulations of slaking the 
hme and mixing the ingredients, no surprise should he felt at the 
seemingly opposite conclusions at which writers, who have pur 
sued the subject experimentally, have arrived. From the great 
mass of facts, however, presented on this subject within a few 
years, some general rules may be laid down, which the engineer 
may safely follow, in the absence of the means of making direct 

100. Sand. Tliis material, which forms one of the ingredients 
of mortal', is the granular prwiuct arising from the disintegration 
(if rocks. It may, therefore, like the rocks from wliich it is de- 
rived, be divided into three principal varieties — the silicious, the 
calcareous, and the argillaceous. 

Sand is also named from the locality where it is obtained, as 
•pit-sand, which is procured from excavations in alluvial, or other 
deposites of disintegi-ated rock ; river sand and sea-sand, which 
are taken from the shores of tJie sea, or rivers. 

Builders again classify sarid according to the size of the giam. 
The term coarse sand is applied when the grain varies between 
Jth and y'jth of an inch in diameter; the tarcafine sand, when 
the grain is between y'jth and -j'jth of an mch in diameter ; and 
the term mixed sand is used for any mixture of tlie two prece- 
ding kinds. 

101. The silicious sands, arising from the quartzose rocks, are 
the most abundant, and are usually preferred by builders. The 
calcareous sands, from hard calcareous rocks, are more rare, but 
form a good ingredient for mortar. Some of the argillaceous sandi 
possess the properties of the less energetic puzzolanas, and dii 
therefore very valuable, as forming, with common lime, an arti- 
fit;ial hydraulic lime, 

lOS. The property which some argillaceous sands possess, of 
forming wilii common, or slightly hydraul'c hme a compound which 



will harden under water, has been long known in France, whera 
these sands are termed arenes. The sands of this nature are 
usually found in hillocks along river valleys. These hillocJcs 
sometimes rest on calcareous rocks, or argillaceous tufas, and are 
frequently formed of alternate beds of the sand and pebbles. The 
Kand is of various colors, such as yellow, red, and gi-een, and 
seems to have been formed from the disintegration of clay in a 
more or less iudnrated state. The arcnes are not as energetic as 
cither natural or artificial puzzolanas ; still they form, with com- 
mon lime, an excellent mortar for m.asonry exposed either to the 
open air, or to humid localities, as the foundations of edifices. 

103. Pit-sand has a rougher and more angular grain than river 
or sea sand ; and, on this account, is generally preferred by build- 
ers for mortar used for brick, or stone-work. Whether it forms a 
stronger mortar than the other two is not positively settled, al- 
though some experiments wordd lead to the conclusion that it 

104. River and sea sand are by some preferred for plastering, 
because they are whiter, and have a finer and more uniibrm grain 
tlian pit sand ; but as the sands from the shores of tidal waters 
contain salts, they should not be used, owing to their hygromelric 
properties, before the salts are dissolved out in fresh water by 
careful washing. 

105. Pit-sand is seldom obtained free from a mixture of dirt, 
or clay ; and these, when found in any notable quantity in it, give 
1 weak and bad mortar. Earthy sands should, therefore, be 
cleansed from dirt before using them for mortar ; this may be 
effected by washing the sand in shallow vats, and allowing the 
turbid water, in which the clay, dust, and otiier like impurities 
are held in suspension, to run .off. 

106. Sand, when pure or well cleansed, may be known by not 
soiling the fingers when nibbed between them 

107. Hydraulic mortar. This ma 1 ay b made from 
the naturd hydratdic limes ; from tho 1 h a p epared by 
M. Vicat's process; or from a mixture f mm feebly by- 
ilraulic lime, with a natural or artificia., p zz lai All writers, 
however, agree tliat it is better to use a natural 1 an an artificial 
liydraulic lime, when the foiraer can b addy p u ed. 

108. When the lime used is strongly hydraulic, M. Vicat is 
of opinion that sand alone should be used with it, to form a good 
hydraulic mortar. General Treussart has drawn the conclusion, 
from his experiments, that the mortar of all hydraulic limes ia 
improved by an addiUon of a natural or artificial puzzolana. The 
quantity of sand used may vary from 1 H" ^ pai'ts of the lime 
in bulk, when reduced to a thick pulp. 

109. For h; dra ihc m itira, made of common, feeble, or or 

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Jinary hydraulic limes, and artificial puzzolaiia, M. Vicat statei 
tlial llie puzzolana should be the wealier as the lime is more 
Bt.~ongly hydraulic ; using, for example, a very energetic j^uzzo- 
laJia with a fat, or a feebly hydraulic lime. The proportion of 
sand which can be incorporated with these ingredients, to form an 
iiydraulic mortar, is stated by General Treussart to be one vol- 
uine to one of puzzolana, and one of lime in paste. 

1 10. In proportioning the ingredients, the object to which the 
mortar is to be applied should be regarded. When it is to serve 
to unite stone, or brick work, it is better that the hydraulic lime 
should be rather in excess ; when it is used as a matrix for beton, 
no more lime should be used than is strictly required. No hann 
will arise from an excess of good hydraulic lime, in any case ; but 
an excess of common lime is injurious to the quality of the mortar, 

111. Common and ordinary hydraulic limes, when made into 
mortar with ardnes, give a good material for hydraulic purposes. 
The proportions in which tiiese have been found to succeed well, 
are one of hme to three of ar^nes. 

112. Hydraulic cement, from the promptitude with which il 
hardens, both in the air and under water, is an invaluable mate- 
rial where this property is essential. Any dose of sand injures 
its properties as a cement. But hydraulic cement may be added 
witli decided advantage to a mortar of common, or of feebly hy 
Jraulic lune and sand. It is in this way that it is generally used 
m our public works. The French engineers give the preference 
to a good hydraulic mortar over hydraulic cement, both for uniting 
stone, or brick work, and for plastering. They find, from their 
practice, that when used as a stucco, it does not withstand well 
the effects of weather ; that it swells and cracks in time ; and, 
when laid on in successive coats, that they become detached from 
each other. 

General Pasley, who lias paid great attention to the properties 
of natural and artificial hydraulic cements, does not agree witli 
the' French engineers- in his conclusions. He states that, when 
skilfully applied, hydraulic cement is superior to any hydrauhc 
mortar for masonry, but tliat it must be used only in thin joints ; 
and, when applied as a stucco, that it should be laid on in but one 
coat ; or, if it be laid on in two, the second must be added long 
before the first has set, so that, in feet, the two make but one 
coat. By attending to these precautious. General Pfisley states 
lliat a stucco of hydraulic cement and sand will withstand per- 
fectly tlie effects of frost, 

113. Mortars eccposed to weather. The French engineers, 
who have paid great attention to the subject of mortars, coincide 
in the opinion, that a mortar cannot be made of fat lime and any 
inert sands, like those of the silicious, or calcareous kinds which 

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will will stand the ordinary exposure of wcatlier ; and U;Eit, tc 
obtain a good mortar for this purpose, cither the hj:!raulic limes 
mixed with sand must be employed, or else common lime mised 
either with ardnes, or with a puzzolana and sand. 

1 14. Any pure sand mixed in proper propoilions with hydratilic 
.Ime, will give a good mortar for the open air ; but the nardnesa 
of the mortar will be affected by the size of the grain, particularly 
when hydraijlic lime is used. Fine sand yields the best mortar 
witli good hydraulic lime ; mixed sand with the feebly hydraulic 
limes ; and-coarse sand with fat lime. 

115. The proportion which the lime should bear to the sano 
seems to depend, in some measure, on the manner in which the 
lime is slaked. M. Vicat states, that the strength of mortar made 
of a stiff paste of fat lime, slaked in the ordinary way, increases 
from 0.50 to 2.40 to one of the paste in volume ; and tliat, when 
the lime is slaked by immersion, one volume of the like paste wiU 
give a mortar that increases in strength from 0.50 to 3.20 parts 
of sand. 

For one volume of a paste of hydraulic lime, slaked in the or- 
dmaiy way, the strength of the mortar increases from to 1.80' 

Earta of sand ; and, when slaked by immersion, the mortar of a 
ke paste increases in strength from to 1 .70 parts of lime. In 
every case, when the dose of sand was increased beyond these 
proportions, tlie strength of the resulting mortar was foiind to 

116. Manipiilations of Mortar. The quality of hydraulic mor- 
tar, which is to be immersed in water, is more affected by tlie 
mamier in wliich the lime is slaked, and the ingredients mixed, 
than that of mortar which is to be exposed to the weather ; al- 
though in both cases the increase of strength, by the best manipu- 
lations, is sufficient to make a study of tnem a matter of some 

117. Tlie results obtained from tlie ordinary method of slak- 
ing, by sprinkling, or by immersion, in the case of good hydraulic 
limes, are nearly the same. Spontaneous, or air-slaking, gives 
iaivariably the worst results. For common and slightly hydraulic 
iime, M. Vicat states that air-sIaklng yields the best results, and 
ordinary slaking the worst. 

118. The ingredients of mortar are incorporated either by 
manual labor, or by machinery : the latter method gives results 
superior to the former. The machines commonly used for mix- 
mg mortar are either the ordinary pug-mill (Fig. 4) employed by 
Dnckmakers for tempering ciay, or a grinding-mOl, (Fig. 5.) 
'i'he gi'inding-mill is the best machine, because it not only rc- 
Quces the lumps, which are found in the most carefully burnt 
Btonc, after the slaking is apparently complete, but it brings llie 



mic to tli6 state of a uniform stiff iiaste, wii'ch it shoiiii leee ve 
before the sand is incorporated it. Care slimild be taken 

repraseiilB a vertical eeetion through 

aiis of a pug-milt^ lor mixing of 

ig numar.— Ttua mM consists 

tempering m 

ofanoopediw „ 

nical fmshim, WMch leoelTeB ttie ia- 
gi^dients, and a vortical ehafl, to whicti 
arms with teeth, resembling an ordi- 
nary rake, are attached, tar toe purpose 
ormixui(i the iiigredienta. 

A, A, eeetion ofsidesof the vessel. 

D, vertical ^mft to which the aims C are 

D, hoiinmtal bar for giving a curcnlai mo- 
tion to the elialt B. 

E, siUs of timber enpporlinH the mil!. 

F, wroi^fht-iron suppart tnmngh v/liioh 
tiio nppOT part of the shaft passes. 

not to add too much water, particularly when the mortar is to be 
immersed in water. The mortar-mill, on this account, should be 
sheltered trom ram ; aiid the quantity of wafer with which it ia 

Fi;. 5 representa a part of a miS for crushing tlie 
iime and teiripering the mortar. 

A, heavy wheel of timber, or cast iron. 

B, iioi'iiontal bar posBiag through the wheel, which 
at one exij^init; is lixed to a vertical shaft, and 
is arranged at the other (C) wiHi tlie proper gear- 
ing for a horse. 

D, a oircnlar trough, with a trapezoidal cross sec- 
tion which receives Uie ingreoients to be mixed 
The tnii^h may be flumiM to 30 feet in diaraator ; 

BUpplied may vary with the state of the weather. Nothing seems 
to be gained by carrying the process of mixing, beyond obtaining 
a uniform mass of the consistence of plastic clay. Mortars of 
hydraulic lime are injured by long exposure to the air, and fre- 
quent turnings and misjngs with a shovel or spade ; those of 
common lime, under like circumstances, seem to be improved. 
Mortar, which has been set aside for a day or two, will become 
sensibly firmer ; if not allowed to stand too long, it may be again 
reduced Lo its clayey consistence, by simply pounding it with a 
beetle, without any iresh addition of water. 

119. Setting and Durability of Mortars. Morfai of common 
lime, without any addition of puzzolana, wOl not set in humid 
situations, like tlie foundations of edifices, until after a very long 
lapse of time. They set very soon when exposed to the air, oi 
o an ai.raospliere of carbonic acid gas. If, after having become 

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haid in tlie open air, tliey are placed undei water, lliey in tim^ 
'ose their cohesion and fall to pieces. 

120. Common mortars, wliich have had time to harden, resist 
tiie action of severe &osts very well, if they are made rather poor, 
or with an excess of sand. The sand should be over 2A0 parts-, 
in bulk, to one volume of the lime in paste ; and coarse sand is 
foimd to give better results than fine sand. 

191. Good hydraulic mortars set equally well in damp situa 
tions, and in the open air ; and those which have hardened in the 
uir will retain their hardness when immersed in water. They 
also resist well the action of frost, if they have had time to set 
before exposure to it ; but, hke common mortars, they require to 
be made with an excess of sand, to withstand well atmospheric 

122. The surface of a mass of hydrauHc mortar, whetlier made 
of a natural hydraulic lime or otherwise, when immersed in water, 
becomes more or less degraded by the action ofthe water upon the 
lime, particularly in a, current. "When the water is stagnant, a 
very thin crust of cai'bonatc of lirae forms on the surface of iJic 
mass, owing to the absorption by the lime of the carbonic acid 
gas in the water. This cnist, if the water be not agitated, will 
preserve the soft mortar beneath it from the farther action of the 
water, until it has had time to become hard, when the water will 
no longer act upon the lime in any perceptible degree. 

133. Hydraulic mortars set with more or less promptness, ac- 
cording to the character of the hydraulic lime, or of the puzzolana 
which enters into their composition. Artificial hydraulic mortars, 
with an excess of hme, set more slowly than when the lime is in 
a just proportion to the other ingredients. 

134; The quick-setting hydraulic limes are said to furnish a 
mortar which, in time, acquires neither as much strength nor 
hardness as that from the slower-setting hydraulic hmes. Ar- 
tificial hydrauhc mortars, on the contrary, which set quickly, 
gain, in time, more strength and hardness than those wliich set 

1 25. The time in which hydrauhc mortars, immersed in water, 
attain their greatest hardness, is not well ascertained. Mortars 
made of strong hydraulic limes do not show any appreciable in 
crease of hardness a£er the second year of their immersion ; while 
the best artificial hydraulic mortars continue to harden, in a sen. 
sible degree, during the third year after their immersion. 

126. Theory of Mortars. The paste of a hydrate, either of 
common or of hydraulic lime, when exposed to the air, absorbs 
carbonic acid gas from it ; passes to the state of sub-carbonate of 
hme ; without, however, rejeciing the water of the hydrate, and 
gradually hardens. The time required for the complete satuta 

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iicn of the mass exposed, will depend on its b. Ik. The absorp- 
tion of the gas commences at tlie suirace and proceeds more 
slowly towards the centre. The hardening of mortars exposed 
to tlie atmosphere, is generally attributed to this absorption of tlie 
gas, as no chemical action of hme upon quartzose sand, which is 
Uie usual kind employed for mortars, has hitherto been detected 
by the most careful experiments. 

127. Witli regard to hydraulic mortars, it is difficult to accouul 
for their hardening, except upon the effect which the silicate of 
lime may have upon the excess of 8im.ple hydrate of uncombined 
lime contained in the mass. M. Petot supposes, that the parti- 
cles of silicate of lime form so many centres, around whicn the 
uncombined hydrates group' themselves in a cn'stalline form ; 
becomii^ thus sufficiently hard to resist the solvent action of 
water. With respect to the action of quartzose sand in hydraulic 
mortars, M. Petot thinks that the grains produce the same me- 
chanical effect as the particles of the silicate of lime, in inducing 
the aggregation of the uncombined hydrate. 

1S8. Concrete. This term is applied, by English architects 
and engineers, to a mortar of finely-pulverized quick-lime, sand, 
and gravel. These materials are first thoroughly mixed in a dry 
s'tate, sufHcient water is added to bring the mass to the ordinary 
consistence of mortar, and it is then rapidly worked up by a 
shovel, or else passed through a pug-mill. The concrete is used 
immediately after tlic materials are well incoiporated, and while 
the mass is hot. 

129. The materials for concrete ai^e compounded in various 
proportions. The most approved are those in which the limo 
and sand are in the proper proportions to form a good mortaf 
and the gravel is twice the bulk of the sand. The gravel useO 
should be clean, and any pebbles contained in it larger than 
an egg, should be broken up before the materials are incorpo- 

130. Hot water has in some cases been used in making con 
Crete. It causes the mass to set more rapidly, but is not other- 
wise of any advantage. 

131. The bulk of a mass of concrete, when first made, is found 
to be about one iifth less tlian the total bulk of the dry materials 
But, as the lime slakes, the mass of concrete is found to exp 
about three eighths of an inch in height, for every foot of the n 
in depth. 

132. The use of concrete is at present mostly restricted to 
forming a sohd bed, in bad soils, for the foundations of edifices, 
U has also been used to form blocks of artificial stone, for the 
walls of buildings and. other like purposes ; but experience has 
shown, that it possesses neither the durability nor strenglh requi 

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site foi striictures of a, permanent character,, wlie.'. exposed to the 
action of water, or of the weather, 

133. Bcton. The term beton is appHed, by Frtnch engineers 
to any mixture of hydrauhc mortar with fragments of brick, stone 
or gravel ; and it is now also used by English engineers in tlio 
same sense. 

134. The proportions of the ingredients used for beton are va- 
riously stated by different authors. The sole object for whicl] 
the gravel, or the broken stone is used, being to obtain a more 
economical material than a like mass of hydrauhc mortar alom' 
would yield, the quantity of broken stone should be as great aa 
can be thoroughly united by the mortar. The smallest amount of 
mortar, therefore, tliat can be used for this purpose, will be ihat 
which wilt be just equal in volume to the void spaces in any given 
bulk of the broken stone, or gravel. The proportion which the 
volume occupied by the void spaces bears to any bulk of a loose 
material, like broken stone, or gravel, may be readily ascertiuned 
by filling a vessel of known capacity with the loose material, and 
pouring in as much water as the vessel will contain. The vol- 
ume of water thus found, wiU be the same as that of the void 

proportions of the ingredients were ascertained by the process' 
just detailed, has been found to give satisfactory results ; but, in 
order to obviate any defect arising from imperfect manipulation, 
it is usual to add an excess of mortar above that of the void 

The best and most economical beton is made of a mixture of 
broken stone, or brick, in fragments not larger than a hen's egg, 
and of coarse and fine gravel mixed in suitable proportions. 

136. In making beton, the mortar is first prepared, and then 
incorporated with the finer gravel ; the resulting mixture is spread 
out into a cake, 4 or 6 inches in thicltness, over which the coarser 
gravel and broken stone arc uniformly strewed and pressed down, 
the whole mass being finally brought to a homogeneous state with 
\he hoe and shovel. 

Beton is used for the same purposes aa concrete, to wMch it 
IS superior in every respect, but particularly so for foundations 
laid under water, or in htunid localities. 

137. Adherence of Mortar. The force with which mortars in 
general adhere to other materials, depends on the nature of the 
material, its texture, and the state of the surface to which the 
mortar is applied. 

138. Mortar adheres most strongly to briclt ; and more feebjj 
o wood than to any other material. Among stones, its adhesion 

to lime-stime is generally greatest ; and tobasaltandsand-s'.ones, 

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MiMir- 41 

'east, Among stonei of the same class, it adheres general!}' bel- 
ter 10 the porous and coarse-gramed, than to the compact and 
(ine -grained. Among surfaces, it adheies moie strongly to tlic- 
rough than to the smooth. 

139. The adhesion of common mortar lo brick and stone, for 
the first few years, is greater than the cohesion ol its own parti- 
cles. The force with which hydrauhc cement adheres to the same 
materials, is less than that of the cohesion between its own parti- 
cles : and. from some recent experiments of Colonel Pasley, on 
this- subject, it would seem that hydraulic cement adheres with 
nearly the same force lo polished suifaees of stone as to rough 

140. From experiments made by Rondelet, on llie adliesion o/ 
common mortar to stone, it appears that it required a force vai'j 
iiig from 1 5 to 30 pounds on the square inch, applied pcrpendicu 
lar to the plane of the joint, to separate the mortar and stone 
after six months union ; whereas, only 5 pounds to the square 
inch was required to separate the same surfaces, when applied 
parallel to the plane of the johit. 

From experiments made by Colonel Pasley, he concludes that 
the adhesive force of hydraulic cement to stone, may be taken as 
high as 125 pounds on the square inch, when the joint has had 
time to harden throughout; but, he remarks, that as in large 
joints the exterior part of the joint may have hardened while the 
interior still remains soft, it is not safe to estimate the adhesive 
force, in such cases, higher than from 30 to 40 pounds on the 
square inch. 

141 . The term Mastic is generally applied to artificial or naiu 
ral combinations' of bituminous or resinous substances with other 
ingredients. They are converted to various uses in ccmsD'uclions, 
eiuier as cements for other materials, or as coatings, to render them 
impervious to water. 

142. Bituminous Mastic. The knowledge of tliis material 
dates back to an early period ; but it is only within, compara- 
tively speaking, a few years that it has come into common use in 
Kurope and this country. The most usual form in which it ia 
now employed, is a combination of mineral tar and powdered 
bituminous lime-stone. 

143. The localities of each of these substances arc very nu- 
merous ; but they are chiefly brought into the market from several 
places in Switzerland and Irance, where these mir.erals are found 
m great abundance ; trihe most noted being Val-de-Travers in 
Switzerland, and Seyssel in France. 

144. Tl mineral tar is usually obtained by bo'ling in water a 

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Boft sand-slooe, called by the French molasse, which is sliongly 
impregnated with the tar. In this process, the tar is disengageii 
and rises to the surface of the water, or adheres to the sides oi 
tiie vessel, and the earthy matter remains at the boltom. An 
analysis of a rich specimen of thp Seyssel bituminous sand-stone 
gave the following results : — 

^oil . .OS^Uitum™ . .106 
CarboQ . . . .0^0 j 
Quartzy graina 600 

145. The bituminous lime-stone which, when reduced to a 

fiowdered state, is mixed with the mineral tar, is loiown at the 
ocalities mentioned by tl.e name of aspJialtum, an appellation 
which is now usually given to the mastic. This lime-stone occurs 
in the secondary formations, and is found to contain various pro- 
portions of bitumen, varying mostly from 3 to 15 per cent., with 
the other ordinary minerals, as argde, &c,, which arc met with 
in this formation. 

146. The bituminous mastic is prepared from these two mate- 
rials by heating the mineral tar in cast-u:on or sheet-h-on boilers, 
and stirring in the proper proportion of the powdered lime- 
stone. This operation, although very simple in its kind, requires 
great attenlion and sldll on the part of the workmen in managing 
the fire, as the maslic may be injured by too low, or too high a 
degree of heat. The best plan appears to be, to apply a brisk 
liii until the boiling liquid commences to give out a thin whitish 
vapor. The fire is then moderated and kept at a uniform state, 
and the powdered stone is gradually added, and mixed in with the 
tar by stining the two well together. When the temperature has 
been raised too high, the heated mass gives out a yellowish or 
brownish vapor. In this state it should be stirred rapidly, and be 
removed at once from the fire. ' 

147. The asphaltic stone maybe reduced to powder, either by 
roasting it in vessels over a fire, or by grinding it down in the or- 
dinary mortar-mill. For roasting;, llie stone is first reduced to 
fragments the size of an egg. iTiese fragments are put into an 
'ion vessel ; heat is applied, and the stone is reduced to powder 
l)y stirring it and breaking it up with an iron instrument. This 
process is not only less economical than grinding, but the ma- 
terial loses a portion of its tar from evaporation, besides behig 
liable to injury from too great a degree o^ heat. For grinding, 
the stone is first broken as for roasting. Care should be taken, 
during ihe process, to stir the mass frequently, otlierwise it may 

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GLTTE. 43 

form into a cake. Cold dry weather is tlio bes season for ihi* 
operation; the stone, liowever, should not be esposed to tin 

148. Owing to the variable quantity of mineral tar in bitnmi 
nous lime-stone, the best proportions of the tar and powdered stonii 
for bituminous mastic, cannot be assigned beforehand. Three oi 
four per cent, too much of tar, is said to impair both the durability 
and tenacity of the mastic ; while too small a quantity is equally 
prejudicial. Generally, from eight to ten per cent, of the tar, bj 
weight, l^s been found to yield a favorable result. 

149. Mastics have been formed by mixing vegetable tar, pitch, 
aiid other resmous substances, with litharge, powdered brick, 
powdered lime-stone, &c, ; but the results obtained have gener- 
ally been inferior to those from bituminous mastic. 

150. Mineral tar is more durable than vegetable tar, and on tliis 
account it has been used alone as a coating for other materials, 
but not with the same success as mastic. Employed in this way 
the tar in time becomes dry and peels off; whereas, in tlie foric 
of mastic, the hard matter with wliich it is mixed prevents the 
evaporation of the oily portion of the tar, and thus promotes its 

151. The uses to which bituminous mastic is applied are daily 
mcreasing. It lias been used for paving in a variety of forms 
either as a cement for lai^e blocks of stone, or as the matiix of a 
concrete formed of small fragments of stone or gravel ; as a point 

ng, it is found to be more serviceable, for some purposes, thar 
fiydraulic cement ; it forms one of the best water-lignt coatings 
for cisterns, ceDars, the cappings of arches, terraces, and other 
similar roofings now in use ; and is a good preservative agent foi 
wood work exposed to wet or damp. 

152. The common animal glue is seldom used as a cement foi 
any other purpose llian for the work of the joiner. Although of 
considerable tenacity, it is weak, brittle, and readily impaired by 

153. Within a few years back, a material termed maj-ine^/we, 
ihe invention of Mr. Jeffery of England, has attracted attention in 
£ngiand and France, in both which countries its qualities as a 
cement, both for atone and wood, have been tested with die most 
satisfactory results. This composition is said to be made by first 
dissolving caoutchouc in coal naphtha, in the proportion of one 
pound of the former to five gallons of the latter ; to tliis solution 
an equal weight of shellac is added, and fiie composilion is tlien 
placed over a tire and thoroughly mixed by slirring 

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154. Owing to its insolubility in water, its remarkit.e tenacity 
and adhesion, and its powers of contraction and expansi:ii ihrough 
a very considerable range' of temperature, without becoming either 
very soft or brittle, the marine glue promises to be not only a val 
uable addition to tlie resources of the naval architect, bnt to the 
civil engineer. 

155. This material is properly an aitiiicial stone, formed by 
submitting common clay, which has undergone suitable prepara- 
tion, to a temperature sufficient to convert it into a semi-viljified 

156. Brick may be used for nearly all the purposes to which 
stone is applicable ; for when carefully made, its strength, hard 
ness, and durabihty, are bnt little inferior to the more ordinaij 
kinds of building stone. It remains unchanged under the ex- 
tremes of temperature ; resists the action of water ; sets firmly 
and promptly with mortar ; and being both cheaper and Hghter 
tlian stone, is preferable to it for many kinds of structures, as 
arches, the walls of houses, &c. 

1 57. The art of brick-maldng is a distinct branch of the useful 
arts, and does not properly belong to tliat of the engineer. But 
as the engineer is frequendy obliged to prepare this material him 
self, the following outline of the process may prove of service. 

158. The best brick earth is composed of a mixture of pure 
clay and sand, deprived of pebbles of every kind, but particularly 
of those which contain lime, and pyritous, or other metallic sub- 
stances ; as these substances, when in large quantities, and in the 
form of pebbles, act as fluxes, and destroy the shape of the brick, 
and weaken it by causing cavities and cracks ; but in small quan- 
tities, and equally dilFused tlnoughout the earth, they assist the 
verification, and give it a more uniform character. 

159. Good briclt earth is frequently fornid in a natural state, 
and requires no other preparation for the purposes of the brick- 
maker. When he is obliged to prepare the earth by mixing the 
pure clay and sand, direct experiments should, in all cases, be 
made, to ascertain Uie proper proportions of the two. If the clay' 
is in excess, the temperature required to semi-vitrify it, will cause 
it to warp, shrink, and crack ; and, if there is an excess of sand, 
complete vitrification will ensue, under similar circumstances. 

160. The quahty of the brick depends as much or. tin; care 
bos'.owed on its manufacture, as on tlic quality of the earth. The 
first stage of the process is to free the earth from pebbles, which 
is most effectually done by digging it out early in the autumn, 
and exposing it in small heaps to the wcatlier during the winter. 
[n the spring, the heaps are carefully riddled, if necessary, and 

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the earth is then in a proper state to be Itncaded or tempered , 
TfiC quantity of water required in tempering, will depend on the, 
quality of the earth ; no more should be used, than will be snffi 
cient to make the earth so plastic, as to admit of its being easily 
moulded by the workman. About half a cubic foot of water to 
one of the earth is, in most cases, a good proportion. If too much 
water be used, the brick will not only be very slow in drying, bu. 
it will, in moat cases, crack, owiu^ tcj the surface becoming com- 
pletely dry, before the moisture of the interior has had time to 
escape ; the consequence of which will be, that the brick, when 
burnt, will be either entirely unfit for use, or very weak. 

161 . Machinery is now coming into very general use in mould- 
ing brick : it is superior to manual labor, not only from the labor 
saved, but from its yielding a better quality of brick, by giving it 
great density, which adds to its strength. 

163. Great attention is requisite m drying the brick before it 
■umed. It should be placed, for this purpose, in a dry expo- 
sure, and be sheltered from the direct action of the wind and sun, 
in order that the moisture may be carried off slowly and uniformly 
from the entire surface. When this precaution is not taken, the 
brick will generally crack from the unequal shrinking, arismg 
from onepart drying more rapidly than the rest. 

163. The burning and cooling should be done with equal care. 
A very moderate fire should be applied under the arches of the 
kiln for about twenty-four hours, to expel any remaining moisture 
from the raw briclt; this is known to be completely effected, 
when the smoke from the kiln is no longer black. The fire is 
then increased until the bricks of the arches attain a white heat; 
it is then allowed to abate in some degree, in order to prevent 
complete vitrification ; and it is alternately raised and lowered in 
this way, until the burning is complete, which may be ascer- 
tained by examining the bricks at t!ie lop of the kihi. The 
cooling should be slowly eflected , o^erwise the bucks will not 
witlistand the eifects ol the weather It is done by closing 
ihe moutlis of the arches, and the top and sides of the kiln in 
tlic most tffettual manner with moist cKy and burnt brick, and 
allowing the kiln to lemam m this st ile until the waimlli has 

164. Brick of a good quality exhibits a fine, compact, iniifomi 
texture, when broken across ; gives a clear ringing sound, when 
strack ; and is of a cherry red, or brownish color. Three varie 
ties are found in the kiln ; those which form the arches, denom 
inated arch brick, arc always vitrified in part, and present a 
grayish glassy appearance at one end ; they axe very hai-d, but 
Brittle, of inferior strength, and set badly with mortar ; those from 
the interior of the kiluj usually denominated body, -hard, or cherry 

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16 BUILDi 

irich, are of the best quality ; those from near the top and sides. 
ai'e generaJly underbumt, and are denominated soft, pale or sa7n 
melbrich ; they have neither sufficient strength, nor durabihty 
for heavy masonry, nor the outside courses of walls, which nre 
exposed to the weather. 

165. The quality of good brick may be improved bv soaking 
it for some days in water, and re-burning it. This process in 
cieases both the strength and durability, and renders the brick 
more suitable for hydraulic constructions, as it is found not t( 
imbibe water so, readily after having undergone it. 

166. The size and form of bricks present but trifling variations. 
They are generaUy rectEmgular parallelopipeds, from eight to nine 
inches long, from four to four and a half wide, and from two to 
iwo and a quarter thick. Tliin brick is generally of a bcltci 
jjuahty than thick, because it can be dried and burned more 

167. Fire-brick. This material is used for the facing of fur 
naces, fireplaces, &c., where a high degree of temperature is to be 
sustained. It is made of a very refractory kind of pure clay, that 
remains unchanged bya degree of heatwhich would vitrify and com 
pletely destroy ordinary brick. A very remarkable bnck of this 
character has been made of agaric mineral; it remains un 
changed under tlie liighest tempei-ature, is one of the worst con- 
ductors of heat, and so light that it will float on water, 

168. Tiles. As a roof covering, tiles are, in many respects, 
superior to slate, or metallic coverings. They are strong and 
durable, and are very suitable for tlie covering of arches, as theii 
great weight is not so objectionable here, as in the case of roofs 
Formed of frames of timber. 

Tiles should be made of the best potter's clay, and be moulded 
with great care to give them the greatest density and strength. 
They are of very variable form and size ; the worst being tlie 
Hat square form, as, from the liability of the clay to warp in bum- 
bg, tliey do not make a perfectly water-tight covering. 

169. This material holds the next rank to stone, owing to its 
durability and strength, and the very gcncril use made of it in 
constructions. To suit it to the purposes of the ejigineer, the 
tree is felled after having attained its mature growth, and the 
Inmk, llie larger branches that spring from the trunk, and the 
main parts of the root, are cut into suitable dimensions, aid sea- 
Boned, in which state, the tei™ timber is applied to it. The 
crooked, or compass timber of the branches and roots, is mostiy 
applied to the purooscs of ship-building, for the knees and othcj 

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parts of the frame-work of Tcssels, crooked liniLei 
The trunk furnishes all the straight timber, 

170. Tlie trunk of a full-grown tree presents three distincl 
parts : llie bark, which forms the exterior coating ; the sap-wood, 
which is next to the bark ; the heart, or inner part, which is easily 
distinguishable from the sap-wood by its greater firmness and 
darker color. 

171. The heart forms the essential part of tlie tnmk, as ;■ 
building materia!. The sap-wood possesses but little slrengll' 
and is subject to rapid decay, owing to the great quantity of Tei 
mentable matter contained in it ; and the bark is not only wilJioui 
strength, but, if suffered to reinaiu on the tree after it is felled, it 
hastens the decay of the sap-wood and heart. 

172. Trees should not be feUed for timber until they have at- 
tained their mature growth, nor after they exhibit symptoms of. 
decline ; otherwise, the timber will be less strong, and far less 
durable. Most forest trees arrive at maturity between fifty and 
one hundred years, and commence to decline after one hundred 
and fifty or two hundred years. The age of the tree can, in- most 
cases, be ascertained either by its external appearances, or by 
cutting into the centre of the trunk, and counting the i-ings, or 
layers of the sap and heart, as a new ring is formed each year in 
the process of vegetation. When the tree commences to decline, 
the extremities ot the old branches, and particularly tlie top, ex- 
hibit sighs of decay. 

173. Trees should not be felled while the sap is in circulation ; 
for this svibstance is of apeculiarly fermentable nature, and, there 
fore, very productive of destruction to the wood. The winter 
months, and July, are the seasons in which trees arc felled for 
timber, as the sap is generally considered as dormant during these 
months ; this practice, however, is in part condemned by some 
writers ; and the recent experiments of M. Boucherie, in France, 
support this opinion, and indicate midsummer and autumn as the 
seasons in which the sap is least active, and therefore as most 
favorable for felling. 

174. As the sap-wood, in most tiees, forms a large portion of 
the trunk, experiments have been made, for the purpose of im- 
proving its strength and durabiUty. These experiments have been 
mostly directed towards the manner of preparing the tree, before 
felling it. One method consists in girdling, or malting an in 
cision with an ase arotmd the trunk, completely through the sap- 
wood, and suffering the tree to stand in this state until it is dead ; 
the oilier consists in harking, or stripping the entire trunk of its 
bark, without wounding the sap-wootf, early in the spring, and al- 
lowing tlie tree to stand until the new leaves have put forth aid 
fallen, before it is felled. The sap-wood of trees, tcated by both 

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of these methods, was found very much improved in hardneaa 
Btrength, and durability ; ihe results from girdling were, however 
irJerior to those from barking. 

175. The seasoning of timber isof the greatest importance, no) 
only to its durability, out to the solidity of the structure for which 
it may be used ; as a very slight shrinking of some of tlie pieces, 
arising from tlie seasoning of the wood, might, in many cases, 
cause material injury, if not complete destruction to the structure. 
Timber is considered as sufficiently seasoned, for the purposes 
of frame-work, when it has lost abou'. one fifth of the weight 
which it has in a green state. Several methods are in use for 
seasoning timber : they consist either in an exposure to the air 
for a certain period in a sheltered position, which is termed naiU' 
ral seasoning ; in immersion in water, terme'* water seasoning ; 
or in boiling, or steaming. 

176. For natural seasoning, it is usually recommended to strip 
the trunk of its branches and bark, immediately upon felhng, and 
to remove it to some dry position, until it can be sawed into suit- 
able scantling. From the experiments of M. Boucherie, just 
cited, it would seem tliat better results would ensue, from allow- 
ing the branches and bark to remain on tJie trunk for some days 
after felling. In this state, the vital action of the tre^ continuing 
in operation, the sap-vessels will be gradually exhausted of sap, 
and filled with ah, and the trunk thus better prepared for tlie pro- 
cess of seasoning. To complete the seasoning, the sawed timbei 
should be piled under drying sheds, where it will be freely ex- 
posed to the circulation of the air, but sheltered from the direct 
action of the wind, rain, and sun. By taking these precautions, 
an equable evaporation of the moisture will take place over tlie 
entire surface, which will prevent either warping or splitting, 
which necessarily ensues when one part dries more rapidly than 
another. It is farther recommended, instead of piling the pieces 
on each other in a horizontal position, that tliey be kid on cast- 
iron supports properly prepared, and with a sufficient inclination 
to facihtate the dripping of llic sap from one end ; and that heavy 
round timber be bored through the centre, to expose a greater 
sm'face to the air, as it has been found that it cracks mere in sea- 
soning than square timber. 

Natiu:al seasoning is preferable to any other, as timber seasoned 
in this way is, both sfronger and more durable than when prepared 
by any artiiicial process. Most timber will require, on pji aver- 
age, about two years to become fully seasoned in tlie natural 

j77. The process of seasoning by immersion in water, is slow 
and imperfect, as it takes years to saturate heavy timb-r ; and 
the soluble matter is discharged very slowly, and chiefly f-om (he 

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WOOD. 4t» 

extenor layers of the immersed wood. The practice of keeping 
limber in water, with a view to facilitate its seasoning, has been 
condemned as of doubtful utility ; particularly immersion in salt 
water, where the timber is liable to the inroads of those two very 
destructive inhabitants of our waters, the Limnoria Terebrans, 
and Teredo Navalis; the former of which rapidly destroys the 
heaviest logs, by gradually eating in between the annual rings ; 
and the latter, the well-kiiown ship-worm, by converting timber 
into a perfect honeycomb state by its numerous perforations. 

178 Steaming is mostly in use for ship-bnilding, where it is 
necessary to soften the fibres, for the purpose of bending large 
pieces of timber. This is effected by placing the timber in strong 
steam-light cylinders, where it is subjected to the action of steam 
long enough for the object in view ; the period usually allowed, 
is one hour to each inch in thickness. Steaming slightly impairs 
the strength of timber, but renders it less subject to decay, and 
less liable to warp and crack. 

179. "When timber is used for posts partly imbedded in the 
ground, it is usual to char the part imbedded, to preserve it from 
decay. This method is only serviceable when the timber has been 
previously well seasoned ; but for green timber it is highly inju- 
rious, as by closing the pores, it prevents the evaporation from the 
siuJace, and thus causes fermentation and rapid decay witliin, 

180. The most durable timber is procured from trees of a close 
compact texture, which, on analysis, yield the largest quantity of 
carbon. And those which grow in moist and shady localities, 
furnish timber wliich is weaker and less durable than that from 
trees growing in a dry open exposure. 

181. Timber is subject to defects, arising either from some 
peculiarity in the growUi of the tree, or from the effects of the 
weather. Straight-grained timber, free from knots, is superior 
in strength and quality^ as a building material, to that which is 
the reverse, 

182. The action of high winds, or of severe frosts, injures the 
tree while standing : the former separating the layers from each 
other, forming what is denominated roUed timber; the latter 
cracking the timber in several places, from th? surface to the 
centre. These defects, as well as those arising from worms, or 
age, are easily seen by examining a cross section of the trunk. 

183. The wet and dry rot ate the most serious, causes of the 
decay of timber ; as all the remedies thus far proposed to prevent 
them, are too expensive to admit of a very general application. 
Both of these causes have the same origin, fermentation, and 
consequent putrefaction. The wot rot takes place in wood ex- 
posed, aheniately, to moisture and dryness ; and the dry rot is 
occasioned by want of a free circulation of air, as in coniined 

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warm localities, like cellars and tlie more conliiied parts tf 

Trees of rapid growth, which contain a arge porlior of sap- 
wood, and timber of every description, wher. used green, whero 
there is a want of a free circulation of air, decay very rapidly with 
the rot. 

184, Numberless experiments have been made on the preser 
vation of timber, and many processes for this purpose liave been 
patented both in Europe and this country. Several of these 
processes have yielded tlie most satisfactoiy results ; and nearly 
all have proved more or less efficacious. The means mostly re- 
sorted to have been the saturation of the timber in the solution 
of some salt with a metallic, or earthy base, thus forming an in 
soluble compound with the soluble matter of the timber. The 
aalts which have been most generally tried, are the sulphate of 
iron, or copper, and the chloride of mercury, zinc, or calcium 
"The results obtained from the chlorides have been more satisfac 
tory than those from the sulphates ; the latter class of salts witli 
metallic bases possess undoubted antiseptic properties ; but it is 
stated that the freed sulphuric acid, arising from the chemical 
action of the salt on the wood, impairs the woody fibre, and 
changes it into a substance resembling carbon. 

185, The processes which have come into most general use, 
are those of Mr. Kyan, and of Sir W. Burnett, called after the 
patentees kyanizing and hurnetizing. Kyan's process is to sat- 
urate the timber with a solution of chloride of mercury ; uding, 
for the solution, one pound of the salt to five gallons of water 
Burnett uses a solution of chloride of zinc, in the proportion of 
one pound of the salt to ten gallons of water, for common pur- 
poses ; and a more highly concentrated solution when the olsject 
is also to render the wood incombustible. 

186. As timber under the ordinary circumstances of immer- 
sion imbibes the solutions very slowly, a more expeditious, as 
well as more perfect means of saturation has been used of late, 
wliich consists in placing the wood to be prepared in strong 
wrought-iron cylinders, lined with felt and boards, to protect the 
iron from the action of the solution, where, first by exhausting 
tlie cylinders of air, and then applying a slrong^ressure by means 
of a force-pump, the liquid is forced into the sap and air-vessels, 
and penetrates to the very centre of the timber. 

187. Among the patented processes in our countiy, that of Mr. 
Earle has received most notice. This consists in boiling the 
timber in a solution of the sulphates of copper ar.d iron. Opinion 
seems to be divided as to the efficacy of this method. It has been 
tried for the preservation of timber Mr artillery carriages, but i oi 
with satisfactory results 

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WOOD 51 

188. M. Boucherie j whose able researches on this subject 
reference has been made, noticing the slowness with which 
aqueous solutions were imbibed by wood, when simply im- 
mersed in them, conceived the ingenious idea of rendering the 
vital action of the sap-vessels subservient to a thorough impreg- 
nation of every part of the trunk where there was tnis vitality 
To effect this, ne first immersed the butt end of a freshly-fellei^ 
iree in a liquid, and found that it was diffused throughout all parts 
of the tree, in a few days, by the action in (question. But, find 
'ng it difficult to manage trees of some size when felled, M. 
Boucherie next attempts to saturate them before felling; for 
which purpose he bored an auger-hole through the trunk, and 
made a saw-cut from the auger-hole outwards, on each side, to 
within a few inches of the exterior, leaving enough of the fibres 
untouched to support the tree. One end of the auger-hole was 
then stopped, as well as all of the saw-cut on the exterior, and 
the liquid was introduced by a tube mserted into the open end of 
the auger-hole. This method was found equally efficacious with 
the first, and more convenient. 

189. After examining the action of the various neutral salts on 
the soluble matter contained in wood, M. Boucherie was led t{i 
try the impure pyrolignitQ of iron, both from its chemical compo- 
sition and its cheapness. The results of this experiment were 

"f satisfactory The pyroliimite of iron in the proportioi 

of one fiftieth in h f ! gr 
preserve the wood f m d y b 

190. Observin 1 ! pi bhy 
pended, in a grea m '^ 1 m 

f I only to 
a ry high 

ti y f ood de- 
n am d n it, M. 

Boucherie next d d 1 h proving 

these properties. For this purpose, he tried solutions of various 
deliquescent salts, which were found to answer the end proposed. 
Among these solutions, he gives the preference to that of chloride 
of calcium, which also, when concentrated, rendera the wood in- 
combustible. He also recommends for like purposes the mother 
water of salt-maishes, as cheaper than the solution of the chloride 
of calcium. Timtjer prepared in this way is not only improved 
in elasticity and pliability, but is prevented from warping am) 
cracking ; the timber, however, is subject to greater variations in 
weight than when seasoned naturally. 

191. M. Boucherie is of opinion that the earthy chlorides will 
also act as preservatives, but to ensure this he recommends thai 
they be mixed with one fifth of pyrolignite of iron. 

192. From other experiments of M. Boucherie, it afjpears thai 
the sap may be expelled, from any freshly-felled timber by the 
pressure of a liquid, and the timber be impregnated as thoroughly 

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as by ihe jireceiiiiig processes. To effect this, llie piece to bo 
saturated is pkced in an upright position, so that tlie sap may 
flow readily from the lower end ; a water-tight bag, containing 
the liquid, is affixed to the upper extremity which is surmounted 
by the Jlquid, the pressure from which expels the sap, and filU 
the sap-Tessels with the Kquid. The process is complete when 
the liquid is found to issue in a pure state from the lower end of 
the stick. 

193. Either of the above processes may be applied in impreg- 
nating Umber with coloring matter for ornamental purposes. The 
plan recommended by M. Boucberie, consists in introducing sep- 
arately the solutions by the chemical union of which the color 13 
to be formed. 

194. The effect of lime on the durability of timber, prepared 
by any of the various chemical processes which have just been 
detailed, remains to be seen ; although results of the most satis- 
factory nature may be looked for, considering the severe tests to 
which most of them have been submitted, by esposurc in situa- 
tions pecuharly favorable to the destruction of ligi^cous sub- 

195. The durability of timber, when not prepared by any of 
the above-mentioned processes, varies greatly under different cir- 
cumstances of esposurc. If placed in a sheltered position,' and 
exposed to a free circulation of air, limber will last for centuries, 
without showing any sensible changes in its physical proper- 
ties. An equal, if not superior, durability is observed when it 
is immersed in fresh water, or embedded in thick walls, or 
under ground, so as to be beyond the influence of atmospheric 

196. In salt water, however, particularly in warm climates, 
timber is rapidly destroyed by the two animals already noticed : 
the one, the limnoria terebrans, attacldng, it is said, only station- 
ary wood, while the attacks of the other, the tereSs navalis, are 
general. Various means have been tried to guard against the 
ravages of these destructive agents ; that of sheathing exposed 
timber with copper, or with a coating of hydrauHc cement, affixed 
to the wood by studding it thickly over with broad-headed nails to 
give a hold to the cement, has met with full success ; but the oxi- 
dation of the metal, and the hability to accident of tlie cement, 
limit their efficacy to cases where they can be renewed. The 
chemical processes for preserving timber from decay, do not ap- 
pear to guard them in salt water. A process, however, of pre- 
serving timber by impregnatmg it with coal tar, patented in this 
country by Professor Renwiclt, appears, from careful experi- 
nients, also to be efficacious against the attack of the snip-worm. 
A coatii\g of Jeffery's marine glue, when impregnated with some 

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WOOD. 63 

if iJie inaolable mineral poisons destructive to animal life, is said 
JO subserve tlie same end. 

197. The best seasoned timber wiL r ot withstand tlie effects 
of exposure to tlie weather for a much gi-eateT period than twenty 
five years, unless it is protected by a coating of paint or pitch, 
or of oil laid on hot, when the timber is partly charred over a Hghl 
blaze. Tliese substances themselves, being of a perishable na 
ture, require to be renewed, from' time to time, and will, there- 
fore, be serviceable only in situations which admit of their renewal. 
They are, moreover, more hurtful than serviceable, to unseasoned 
timber, as by closing the pores of the exterior surface, they pre- 
vent the moisture from escaping from within, and, therefore, pro- 
mote one of the chief causes of decay, 

198. The forests of our own country produce a great variety 
of the best timber for every purpose, and supply abundantly both 
our own and foreign markets. The following genera arc in most 
common use. 

199. Oak. Abont forty-four species of this tree arc enumera- 
ted by botanists, as found in our forests, and those of Mexico. 
The most of them afford a good building material, except the 
varieties of red oak, the timber of which is weak, and decays 

The "White Oak, {Quercus Alha,) so named from the color 
of its bark, is among the most valuable of the species, and is in 
very general use, but is mostly reserved for naval constructions ; 
Its trunk, which is large, serving for heavy frame-work, and the 
roots and larger branches affording the best compass timber. The 
wood is strong and durable, and of a slightly reddish tinge ; it is 
not suitable for boards, as it shrinks about ^V "^ seasoning, and 
is very subject to warp and crack. 

This tree is found most abundantly in the Middle States. It 
is seldom seen, in comparison with other forest trees, in the 
Eastern and Southern States, or in the rich valleys of the "West- 
ern States. 

Post Oak, (Quercus Ohtusiloba.) This tree seldom attains a 
greater diameter than about iifteen inches, and, on this account, 
is mostly used for posts, from which use it takes its name. The 
wood has a yellowish hue, and close grain ; is said to exceed 
white oak in strength and durability ; and is, therefore, an excel- 
lent building material for the lighter kinds of frame-work. This 
tree is found most abundantly in the forests of Maryland and Vir- 
ginia, and is there frequently called Box White Oak, and Iron 
Gale. It also grows in the forests of the Southern and Western 
States, but is rarely seen farther north than the moutli of the 
Hudson River, 

Chesnut 'While Oak, {Quercus Prinus Palustris.) The tun 

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oer of lliis tree j slrong and durable, but inferior to the two jro 
ceding species, Tlio tree is abundant from North Carolina M 

Rock Chcsnu Oak, {Querctis Prinus MonticoJa.) The timbei 
of this tree is mostly in use for naval constructions, for wiiich il 
13 esteemed inferior only to the white oak. The tree is ft and in 
the Middle States, and as far north as Vermont. 

Live Oak, {Quercus Virens.) The wood of tliis tree is of a 
yellowish tinge ; it is heavy, compaet, and of a fine grain ; it is 
stronger and more durable than any other species, and, on this 
account, it is considered invaluable for the purposes of ship 
building, for which it is exclusively reserved. 

The live oak is not found farther north tlian the neighborhood 
of Norfolk, Virginia, nor farther inland, than from fifteen to twenty 
miles from the seacoast. It is found in abundance along the 
coast south, and in the adjacent islands as far as the moulh of the 

900. Fine. This very interesting genus is considered inferior 
only to the oalc, from the excellent timber afforded by nearly all 
of its species. It is regarded as a most valuable building mate 
rial, owing to its strength and durability, the straightness of its 
fibre, the ease with which it is wrought, and its applicability to 
all the purposes of constructions in wood. 

Yellow Pine, {Pinus Mitts.) The heart-wood of this tree is 
fme-grained, moderately resinous, strong, and durable ; but the 
sap-wood is very inferior, decaying rapidly on exposure to the 
weather. The timber is in very general use for frame-work, &c. 

This tree is found throughout our country, but in the greatest 
^.bundance in the Middle States. In the Southern States, it is 
Imown as Spntce Pine and Short-leiwed Pine. 

Long-leaved Pine, or Southern Pine, (Pinus Australis.) This 
tree has but little sap-wood : and the resinous matter is uniformly 
distributed throughout the heart-wood, which presents a fine com- 
pact grain, having more hardness, strength, and durability, than 
any other species of the pine, owing to which quahties the timber 
is in very great demand. 

The tree is first met witli near Norfolk, Virginia, and from thla 
point south, it is abundantly found. 

White Pine, or Northern Pine, (Pinus Strobus.) This tree 
takes its name from the color of its wood, which is white, soft 
light, straight-grained, and durable. It is inferior in strength to 
the species just described, and has, moreover, the defect of swell- 
ing in damp weather. Its timber is, however, in great demand 
as a good building material, being almost the only kind in use iii 
ihe Eastern and Northern States, for the framc-wark and joinery 
of houses, &c. 

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Tiie Imest specimens of this tree grow in the fores /s of Maine 
.t is fcund in great abundance between the 43d and 47tii parol 
leis, N. L. 

201. Among the forest trees in less general use than the oa5i 
jind pine, the Locust, the Chesnut, the Red Cedar, ard the Larch, 
hola the first place for hardness, strength, and durability. They 
oie chiefly used for the frauiE-work of vessels. The chesnut, the 
locust, and the cedar, are preferred to all other trees for posts, 

202. The Black, or Double Spruce, {Ahies Nigra,) also af- 
fords an excellent material, its timber being strong, durable, and 

203. The Juniper or Whits Cedar, and the Cypress, are verj- 
celebrated for affording a material, which is very hght, and of 
great durabihty, when exposed to the weather ; owin^ to these 
qualities, it is almost exclusively used for shingles and other ex- 
terior coverings. These two trees are found, in great abundance, 
in the swamps of the Southern States. 

204. The melals in most common use in constructions s 
Iron, Copper, Zinc, Tin, and Lead. 

205. This metal is veiy exteusively used for the purposes of 
the engineer and architect, both in the state of Ccist Iron, and 
Wrought Iron. 

206. Cast Iron is one of the most valuable building materials, 
owing to its great strength, hardness, and durability, and the ease 
with which it can be cast, or moulded, into tlie best forms, for 
the purposes to which it is to be applied. 

S07. Cast iron is divided into two principal varieties, the Gray 
cast iron, and White cast iron. There exists a very marked dif 
ference between the properties of these two varieties. There 
are, besides, many intermediate varieties, which partake more or 
less of the properties of these two, as they approach, in tlieir ex- 
ternal appearances, nearer to the one or the other. 

208. Gray cast iron, when of a good quahty, is slightly malle- 
able in a cold state, and wiO ylola ieadily to the action of^the file, 
when the hard outside coating is removed. This variety is also 
sometimes termed soft gray cast iron ; it is softer and tougher 
than the white iron. When broken, the surface of the fiacturo 
presents a granular structure ; the color is gray ; and the liislre 
is what is termed metallic, resembling small brilliant particles of 
ead strewed over the surface. 

209. White cast iron is very hard and brittle ; when recent/ y 

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broken, the surface of the fracture presents a Jistiiictly ■marked 
crystalline structure ; the color is white ; and lustre vitieoiis, oi 
oearing a resemblance to the reflected light from an aggregation 
of smaO crystals. 

210. Mr. Mallet, in a very able Report made to the British 
Association for the Advancement of Science, remarking on the 
great want of uniformity, among manufacturers of iron, in tlie 
Eenns used to describe its different varieties, proposes the follow- 
ing nomenclature, as comprising every variety, witli their distinc- 
tive characters. 

Silvery. Least fusible ; thickens rapidly when fluid by a 
spontaneous puddling ; crystals vesicular, often crystalline ; in- 
capable of being cut by chisel or'file j ultimate cohesion a maxi- 
mum ; elastic range a minimum. 

Micaceous. Very soft ; greasy feel ; peculiar micaceous ap- 
pearance generally owing to excess of manganese ; soils the fin- 
gers strongly ; crystals large ; runs very fluid ; contraction large. 

Mottled. Tough and hard ; filed or cut with diiHculty ; crys- 
tals large and small mixed ; sometimes runs thick ; contraction in 

Bright Gray. Toughness and hardness most suitable for 
working ; ultimate cohesion and elastic range generally aie bal- 
anced most advantageously ; crystals uniform, very minute. 

Dull Gray. Less tougli than the preceding ; other characters 
alike ; contraction in cooling a minimum. 

Dark Gray. Most fnsible ; remains long fluid ; exudes graphite 
in cooling ; soils the fingers ; crystals large and lamellar ; ultimate 
cohesion a minimum, and elastic range a maximum. 

21 1 ■ The gray iron is most suitable where strength is required ; 
and the white, where hardness is the principal requisite. 

212. The color and lustre, presented by the surface of a recent 
fracture, are the best indications of the quality of iron. A uni- 
form dark gray color, and high metalhc lustre, are indications of the 
best and strongest. Willi me same color, but less lustre, the iron 
wiO be found to be softer and weaker, and to crumble readily, 
iron without lustre, of a dark and mottled color, is the softest and 
weakest of the gray varieties. 

Iron of a hght gray color and high metallic lustre, is usually 
very hard and tenacious. As the color approaches to white, and 
the metallic lustre changes to vitreous, hardness and brittleneas 
become more marked, until the extremes of a duU, or grayish white 
color, and a very high vitreous lustre, are attained, which are the 
indications of the hardest and most brittle of the white variety. 

213. The quality of cast iron may also be tested, by strildng a 
smart stroke with a hammer on the edge of a casting. If Ihe 
blow produces a slight indentation, without any appeavajice of 

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IRON. 67 

fracture, it sliows tliat tlie ii-oii is slightly malleabb, and, there- 
fore, of a good quahty ; if, on the contrary, the edge is broken, it 
indicates brittleness in the material, and a consequent want of 

314. Tlie strength of cast iron varies with its density ; and this 
element depends upon the temperature of the metal when drawa 
from the furnace ; the rate of cooling ; the head of metal under 
which the casting is made ; and the bulk of the casting. 

315. Tiie density of iron cast in vertical moulds increases, ac- 
cording to Mr. Mallet's experiments, very rapidly from the top 
downward, to a depth of about four feet below the top ; from this 
point to the bottom, the rate of increase is very nearly uniform. 
All other circumstances remaining the same, the density decreases 
with the bulk of the casting ; hence large are proportionally 
weaker than small castings. 

216. From all of these causes, by which the strength of iron 
may be influenced, it is very difficult to judge of the quality of a 
casting by its external characters ; in general, however, if the 
exterior presents a uniform appearance, devoid of marked ine- 
qualities of surface, it will be an indication of uniform strength. 

217. The economy in the manufacture of cast iron, arising 
from the use of the hot blast, has naturally directed attention to 
tlie comparative merits between iron produced by this process 
and that from the cold blast. This subject has been ably inves- 
tigated by Messrs. Fairbaim and Hodgkinson, and their results 
published in the Saventk Report of the British Association, 

Mr. Hodgkinson remarks on this subject, in reference to the 
results of his experiments : " It is rendered exceedingly probable 
that the introduction of a heated blast into the manufacture of 
cast iron, has injured the softer irons, while it has frequently 
molliiied and improved those of a harder nature ; and considering 
the small deterioration that" some " irons have sustained, and the 
amiarent benefit to those of" others, " togetherwith the great saving 
effected by the heated blast, there seems good reason for tlie pro- 
cess becoming as general as it has done." 

318. From a number of specific gravities given in these Re- 
ports, the mean specific gravity of cold blast iron is nearl}'- 7.09 1 , 
that of hot blast 7.021. 

2i9, Mr. Fairbairn concludes his Report with tliese observa 
tions, as the results of the investigations of himself and Mr. Hodg 
iiinson : " The xiltimEitum of our inquiries, made in tliis way, 
stands, therefore, in the ratio of strength, 1000 for the cold blast, 
to 1024.8 for the hot blast; leaving the small fractional difference 
of 24.8 in favor of tlie hot blast." 

"The relative powers to sustain impact, are hkewise in favo. 
of the liot blast, bein;; in the ratio of 1000 to 1826.3" 

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220. Wrought Iron. The color, lustre, and teituic of a recen 
fracture, present, also, lliG most certain indications of the qiialilV 
c-f wrought iron. The fracture submitted to examination, should 
be of bars at least one inch square ; or, if of flat bars, they should 
be at least half an inch thick ; otherwise, the texture will be so 
greatly changed, arising from the greater elongation of the fibres, 
m bars of smaUer dimensions, as to present none of those dis- 
tinctive diiferences observable in the fracture of large bars. 

221. The surface of a recent fracture of good iron, presents a 
clear gray'color, and high metaillic lustre ; the texture is granular, 
and the grains have an elongated shape, and are pointed and 
slightly crooked at their ends, giving the idea of a powerful force 
having been employed to produce the fracture. When a bar, 
presenting these appearances, is hammered, or drawn out into 
small bars, the surface of fr-acture of these bars will have a very 
marked fibrous appearance, the filaments being of a white color 
and veiy elongated. 

223. "When the texture is either laminated, or crystalline, it is 
an indication of some defect in the metal, arising either from the 
mixture of foreign ingredients, or else from some neglect in the 
process of forging. 

223. Burnt iron is of a clear gray color, with a shght shade 
of blue, and of a slaty texture. It is soft and brittle. 

224. Cold short iron, or iron that cannot be hammered wlier 
cold without breaking, presents nearly the same appearance as 
burnt iron, but its color inclines to white. It is very hard and 

225. Hot short iron, or tliat which breaks under the ham- 
mer when heated, is of a dark color without lustre. This de- 
fect is usually indicated in the bar by numerous cracks on the 

226. The fibrous textrire, which is developed oiily in smal. 
bars by hammering, is an inherent quality of^ good iron ; those 
varieties which are not susceptible of receiving this peculiar tex- 
ture, are of' an inferior quality, and should never be used for pur- 
poses requiring great strength : the filaments of bad varieties are 
Bhort, and the fracture is of a deep color, between lead gray and 
dark gray, 

227. The best wrought iron presents two varieties ; the Hard 
and Soft, The hard varietjf is very strong and ductile. It pre- 
serves its granular texture a long time under llie action of the 
hammer, and only developcs the fibrous texture when beaten, or 
drawn out into small rods : its fdamcnts then present a silvej 
white appearance. 

228. The soft variety is weaker than the hard ; it yields easily 
to the hammer; and ^t commeiiccs to esSibft, under ils action 


tlio fibrous lextui'e in tolerably large bars. The color of tlie 
fibres is between a silver white and lead gray. 

229. Iron may be naturally of a good quality, aic' stil., from 
being badly refined, not present the appearances winch are re- 
garded as sure indications of its excellence. Among the defects 
arising from this cause are blisters, Jlaws, and cinder-holes 
Generally, however, if the surface of firaclure presents a texture 
partly crystalline and partly fibrous, or a fine granular texture, ii 
whicli some of the grains seem pointed and crooJied at the points, 
together with a light gray color without lustre, it will indicate 
natural good qualities, which require only careful refining to be 
iblly developed. 

230. The strength of wrought iron is Tery variable, as it de- 
pends not only on the natural qualities of the metal, but also upon 
the care bestowed in forging, and the greater or less compres- 
sion of its fibres, when drawn or hammered into bai's of different 
SSI. In the Report made by the sub-committee, Messrs. John 

son and Reeves, on the strength of Boiler Iron, {Journal of Frank- 
lin Institute, vol, 20, New Series,) it is statedthat the following 
order of superiority obtains among the difi"erent kinds of pig 
metal, with respect to the malleable iron which tliey furnish : — ■ 
1 Lively gray ; 3 WJiite ; 3 Mottled gray ; 4 Dead gray ; 
5 Mixed metals. 

The Report states, " So far as these experiments may be con , 
sidered decisive of the question, tliey favor the lighter complexion 
of the cast metal, in preference to the darker and mottled varie 
ties; and they place the mixture of different sorts among the 
Worst modifications of the material to be used, where tlie object 
is mere tenacity." 

232. These experiments also show that pilmg iron of different 
degrees of fineness in the same plate is injurious to its quahty, 
owing to the consequent inequality of the welding. 

233. From these e^eriments, the mean specific gravity of 
boiler iron is 7,7344, and of bar iron 7.7254. 

234. Durability of Iron. The durabOity of iron, under the 
dilferent circumstances of exposure to which it may be submitted, 
depends on the manner in which the casting may have been made ; 
tlie bulk of the piece employed ; the more or fess homogeneous- 
ness of the mass ; its density and hardness, 

235. Among the most recent and able researches upon the ac 
tion of the ordinary conosive agents on iron, and the preservative 
means to be employed agamst them, those of Mr. Mallet, given in 
the Report already mentioned, hold the first rank. A briei re- 
capitulation of the most piomment conclusions at which ht 'Jas 
arrived, is all that can bo attempted in thi'^ place. 

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236. Wlien iron is only partly immersed ;a water, a wholly 
i.nmersed in water composed of strata of different densities, lika 
that of tidal rivers, a voltaic pile of one solid and twc fluid bodies 
is formed, wliich causes a more rapid corrosion than when ihe 
liquid is of uniform density. 

237. The corrosive action of the foul sea water of docks and 
harbors is far more powerful than that of clear sea, or fresh water, 
owing to the action of the hydro-sulphuric acid which, being dis- 
engaged from the mud, impregnates the water, and acts on the 

238. In clear fresh river water, the corrosive action is less than 
under any other circumstances of immersion ; owing to the ab- 
sence of corrosive agents, and the firm adherence of the oxide 
formed, which presents a hard coat that is not washed off as in 
sea water. 

239. In clear sea water, the rate of corrosion of iron bars, one 
inch thick, is from 3 to 4 tenths of an inch for cast iron in a cen- 
mry, and about 6 tenths of an inch for wrought iron. 

240. Wrought iron corrodes more rapidly in hot sea water than 
under any other circumstances of immersion. 

241. The same iron when chill cast corrodes more rapidly than 
when cast in green sand ; this arises from the chilled surface 
being less uniform, and therefore forming voltaic couples of iron 
of difierent densities, by which the rapidity of corrosion is in- 

242. Castings made in dry sand and loam arc more durable 
imder water tlian those made in green sand. 

243. Thin bars of fron corrode more rapidly than those of more 
buik. This difference in the rate of corrosion is more striking in 
the soft, or graphitic specimens of cast iron, than in the hard and 
silvery. It is caused by the more rapid rate of cooling in thin 
than m thick bars, by which the density of the surface of the for- 
mer becomes less uniform. These causes of destruclibility may, 
in some degree, be obviated in castings composed of ribbed 
pieces, by making the ribs of equal thickness with the main 
pieces, and causing them to be cooled in the sand, before strip- 
ping the moulds. 

244. The hai^d crust of cast iron promotes its durability ; when 
this is removed to ihe depth of one fourth of an inch, the u-on cor- 
rodes more rapidly in both air and water. 

245. Corrosion takes place tiie less rapidly in any variety of 
u'on, in propoition as it is more homogeneous, denser, harder, ana 
■-loser gramed, and the less graphitic. 

246. The more ordinary means uaed to protect iron againsl 
ihe action of corrosive agents, cons:".Bt of paints and varnishes. 
These, ul der the usual circumstances of atmospheric exposin^ff. 

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are oh but slight efficacy, and require to be frequently renewoil 
In water, they are all rapidly destroyed, with the exception of 
boiled coal-tar, which, when laid on hot iron, leaves a blight aiiq 
solid varnish of considerable duiability and protective power. 

247. The rapidly increasing purposes to which iron has been 
applied, within ^e last few years, has led to reseaiches tipon the 
agency of electro-chemical action, as a means of protecting it from 
t-orrosiou, both in air and water. Among the processes resorted 
to for tliis purpose, that of zincking, or as it is more commonly 
known, galvanizing iron has been most generally introduced. 
The experiments of Mr. Mallet, on this process, are decidedly 
against zinc as a permanent electro-chemical protector. Mr. 
Mallet states, as the result of his observations, that zinc applied in 
fusion, in the ordinaiy manner, over the whole surface of iron, 
will not preserve it longer than about two years ; and that, so 
soon as oxidation commences at any point of the iron, the protec- 
tive power of the zinc becomes considerably diminished, or even 
entirely null. Mr. Mallet concludes, " On the whole, it may be 
affirmed that, mider all circumstances, zinc has not yet been so 
applied to iron, as to rank as an electro-chemical protector to- 
wards it in the strict sense ; hitherto it has not become a preven- 
tive, but merely a more or less effective palliative to destruction." 

248. In extending his researches on this subject, with alloys 
oi copper and zinc, and copper and tin, Mr. Mallet found that the 
alloys of the last metals accelerate the corrosion of iron, when 
voltaically associated with it in sea water ; and that aji alloy of 
the two first, represented by 2SZn -}- 8Gu, in contact with iron, 
protects it as fully as zinc alone, and suffers but little loss from 
the electro-chemical action ; thus presenting a protective en- 
ergy more permanent and invariable than that of zinc, and giving 
a nearer approximation to the solution of the problem, " to obtain 
a mode of electro-chemical protection such, that while the iron 
sliall be preserved the protector shall not be acted on, and whose 
protection shall be mvariable." 

• 249. In the course of his experiments, Mr. Mallet ascertained 
that the softest gray cast iron bears such a voltaic relation to hard 
bright cast iron, when immersed in sea water and voltaically as- 
sociated with it, that although oxidation will not be prevented on 
either, it will stil! be greatly retarded on the hard, at the expense 
of the soft iron. 

250. In concluding the details of his important researches on 
this subject, Mr. Mallet makes the following judicious remarks : 
" The eneuieer of observant habit will soon have perceived, thai 
in exposed works in iron, equality or section or scantling, in all 
parts sustaining equal strain, is far from ensuring equal passive 
power of permanent resistance, imless, in addition to a general 



allowance for loss of substance by corrosion, this latter elemeiil 
be BO provided for, that it shall be equally balanced over the whole 
structure ; or, if not, shall be compelled to coniine itself to por- 
tions of the general structure, which may lose substance witboul 
injuring its stability." 

" The principles we have ah^eady estL'alished sufEcientiy g lide 
us in the modes of effecting this ; regard must not only be had to 
the contact Of dissimilar metals, or of the same in dissimilar fluids, 
but to the scantling of the casting and of its parts, and to the con- 
tact of cast iron with vnrought iron or steel, or of one sort of cast 
iron with another. Thus, in a suspension bridge, if the links of 
the chains be hammered, and tlie pins rolled, the latter, where 
equally exposed, will he eaten away long before the former. In 
marine steam-boilers, the rivets are hardened by hammering until 
cold ; the plates, therefore, are corroded through round the rivets 
oefore these have suiFered sensibly ; and in flie air-pumps and 
condensers of engines working with sea water, or in pit work, and 
pumps Hfting mmeraHzed or 'bad' water from mines, the cast 
iron perishes first round the holes through which wronght-iron 
bolts, &c., are inserted. And abundant other instances might be 
given, showing that llie effects here spoken of are in praclical 
operation to an extent that should press the means of counteract- 
ing them on the attention of the engineer." 

251. Since Mr. Mallet's Report to the British Association, he 
has invented two processes for the protection of iron from the ac- 
tion of the atmosphere and of water ; the one by means of a coat- 
ng formed of a triple alloy of zinc, mevcury, and sodium, or po- 
tassium ; the other by an amalgam of palladium and mercury. 

252. The first process consists of forming an alloy of the metals 
used, in llie following maimer. To 1 292 parts of zinc by weight, 
in a state of fusion, 202 parts of mercury are added, and tlie 
metals are well mixed, by stirring with a rod of dry wood, or one 
if iron coated with clay ; sodium, or potassium is next added, in 
small quantities at a time, in the proportion of one pound to every 
ton by weight of the other two metals. The iron to be coated 
with this alloy is first cleared of all adhering oxide, by immersing 
it in a warm dilute solution of sulphuric, of of hydro-chloric acid, 
vrashuig it in clear cold water, anddetacliing all scales, by strildng 
it with a hammer ; it is then scoured clean by the hand with sand, 
or emery, under a small stream of water, until a bright metallic 
histre is obtained ; while still wet, it is Immersed in a bath formed 
of equal parts of the cold saturated solutions of chloride of zinc 
and sal-ammoniac, to which as much more sohd sal-ammoniac is 
added as the solution will take up. The iron is allowed to re- 
main m this bath until it is covered by minute bubbles of gas ; il 
is then taken out, allowed to drain a few seconds, and plunged 

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uito ihe fused alloy, from ■whicli it is witlidrawn so soon as ii nas 
acquired the same temperatuie. When taken from the metallic 
baUi, the iron should be plunged in cold water and -well washed. 

253. Care must be taken that the iron bo not kept too long in 
the metallic bath, otherwise it may be fused, owing to the great 
afSnity of the alloy for iron. At the proper fusing temperature 
of ihe alloy, about 680° Tahr., it will dissolve plates of iron one 
eighth of an inch thick in a few seconds ; on this account, when- 
eyet small articles of iron have to be protected, Ihe affinity of the 
alloy for iron should be satisfied, by fusing some iron in it before 
immersing that to be coated. 

354. The other pi-ocess, which has been teimGd palladiumising, 
consists in coating the iron, prepared as in the first process for 
the reception of the metallic coat, with an amalgam of palladium 
and mercury. 

255. The most ordinary and useful application of this metal in 
constructions, is that of sheet copper, which is used for roof cov- 
erings, and like purposes. Its durability under the ordinary 
changes of atmosphere is very great. Sheet copper, when quite 
thin, is apt to be defective, from cracks arising from the process 
of drawing it out. These may be remedied, when sheet copper 
is to be used for a water-tight sheathing, by tinning the sheets on 
one side. Sheets prepared in this way have been found to be very 

The alloys of copper and zinc, known under the nimie of brass, 
and those of copper and tin, known as hronze, gun-metal, and 
hell-metal, are, in some cases, substituted for iron, owing to tlieir 
superior hardness to copper, and being less readily oxidized than 

256. Tills metal is used mostly in the form of sheets ; and foi 
water-tight sheathings it lias nearly displaced every otiier kind of 
sheet metal. The pure metallic surface of zinc soon becomes 
covered with a very thin, hard, transparent oxide, which is un 
changeable both in air and water, and preserves the metal bencatli 
it from farther oxidation. It is this property of the oxide of zinc, 
which renders this metal so valuable for sheathing purposes ; bul 
rts durability is dependent upon its not being brouglit into contact 
with iron in the presence of moisture, as the galvanic action which 
would then ensue, would soon destroy the zinc. On the same 
acc&unt zinc should be perfecdy free from the presence of iron 
as a very small quantity of the oxide of tliis last metal when con 
laincd in zinc, is found to occasion its rapid destruction. 

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257. Besides the alloys of zinc already mentioned, this ineta. 
alloyed widi copper forms one of the most useful solders ; and 
its alloy with lead has been proposed as a cramping metal foi 
uniting the parts of iron work together, or iron work to other ma- 
terials, in the place of lead, which is usually employed for this 
purpose, but which accelerates the desti'uction of iron in contact 
with it. 


358. The most useful apphcalion of tm is as a coating for 
sheet iron, or sheet copper i the alloy which it forms, in this way, 
upon tlie surfaces of tlie metals in question, preserves them for 
some lime from oxidation. Alloyed with lead it forms one of the 
most useful solders. 

259. Lead in sheets forms a very good and dmrable roof cover 
ing, but it is inferior to both copper and zinc in tenacity and 
dmBbihty ; and is very apt to tear asunder on inclined surfaces, 
particularly if covered with other materials, as in the case of the 
capping of water-tight arches. 


260. Paints are mixtures of certain fixed and volatile oils, 
chiefly tliose of hnseed and turpentine, with several of the metal 
lie salts and oxides, and other substances which are used either 
as pigments, or to give what is termed a body to the paint, and 
also to improve its drying properties. 

261. Paints are mainly used as protective agents to secure 
wood and metals from Uie destructive action of air and water. 
This they but imperfectly eiTect, owing to tlie unstable nature of 
the oils that enter into their composition, which are not only de- 
stroyed by the very agents against which they are used as pro- 
tectors, but by the chemical clianges which result from the action 
of tlie elements of the oil upon the metallic salts and oxides. 

262. Paints are more durable in air than in water. In the lat- 
ter element, whether fresh or salt, particularly if foul, paints are 
soon destroyed by the chemical changes which lake place, both 
from the action of tlie water upon the oils, and that otthe hydro 
sulphuric acid contained in foul water upon the metallic salts and 

263. However carefully made or applied, paints soon become 
permeable to water, owing to the, very minute pores which arise 
from the chemical changes in their constituents. These changes 
will have but little influence upon the preservative acticn of paints 
upon wood exposed to the efi'ects of the atmosphere, provided the 
wood be well seasoned before the paint is applied, and that the 



latter be renewed at suitable intervals of time. On metals these 
changes have a very important bearing. The permeability of the 
paint to moisture causes the surface of the metal under it to mst, 
and this cause of destruction is, in most cases, promoted by the 
chemical changes which the paint undergoes. 

S64. Varnishes are solutions of various resinous substances 
in solvents which possess the property of drying rapidly. They 
are used for the same purposes as paints, and have generally t]ie 
same defects. 

265. The following arc some of the more usual compositions 
of paints and varnishes. 

White Faint, (for exposed luood.) 
White lead, ground in oil ... 60 

Boiled oil 9 

Raw oil 9 

Spirits turpentine ■ . . . . 4 

The white lead to be ground in the oil, and the spirits of tin 
peutine added. 

Lamp-black . 
Japan varniali 
Linseed oil, boiled 
Spirits turpentine 

White lead, ground in oil 
Lamp-blaol: . 
Boiled linseed oil . 
Japan varnish 
Spirits turpentine , 

Gray, or Stone Color, (for buildings.') 

White lead ground in oil ... 78 

Boiled oil ..... O.n 

Raw oil 9.5 

Spirits of turpentine .... 3 

Turkey ombcr 0.£ 

Lamp-black . . . . . 0,S 

Lackers for Cast Iron. 
I —Black lead, pulverized .... 13 
Red lead .... .13 
LilUarge S 



9 — Anti-c< 

Grant's blaok, groand in oil . . 4 " 

Red lead, as a dryer . . . . 3 " 
Linseed oil ... , . .4 gala. 
Spirits turpentine ..... 1 pint. 

Copal Varnis'/i. 

Gum copal, (in clean lumps) . . . 30,5 
Boiled linseed oil . . . . . 43.5 
Spirits turpentine 31 

Japan Varnish. 

Lithirga .,,.,. 4 

Boiled oil 87 

Spirits turpentine ..... Q 

Red lead 8 

Umber ....... 1 

Gnm shellac 8 

Sugar of lead ..... 2 

White vitriol J. 

The proportions of the above compositicLiis are giver j' j 00 
parts, by weight, with the exception of lacker 2. 

The beautiful black pohsh on the Berlin castings for ornfin)<,iital 
purposes, is said to be produced by laying the following comiio- 
sition on the hot iron, and then baking it. 

Bitnmen of India ..... O.S 

Eesin 0,5 

Drying oil 1.0 

Copal, or amliei: varnish . . . .1.0 

Enough oil of turpentine is to be added to this mixture to make 
It spread. 

266. From experiments made by Mr. Mallet, on the preserva 
tiye properties of paints and varnishes for iron immersed in water, 
it appears that caoutchouc varnish is the best for iron m hot 
water, and asphaltum varnish under aU other circumstances ; b'.ii 
that boiled coal-tar, laid on hot iron, forms a superior coating to 
cither of the foregoing. 

267. Mr. Mallet recommends the following compositions for a 
paint, termed by him zoofagous paint, and a varnish to be used 
to preserve aincked iron both from corrosion and from fouling in 
sea water. 

Varnish far zmcked Iron. 

To £0 lbs. of foreign asphaltum, melted and boi.ed in an iro7t 
vessel for three or four hours, add 16 lbs. of red leac and litliargo 
ground to a fine powder, in equal proportions, with 10 gals, of 

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drying linseed oil, and bring the whole to a nearly boiling tem- 
perature. Melt, in a second vessel, 8 lbs, of gura-anim^ ; to 
which add 2 gals, of drj^ing linseed oil at a boiling heat, with 12 
lbs. of caoutchouc paitially dissolved in coal-tar naphtha. Pour 
the contents of the second vessel into the 6rst, and boil the whole 
gently, until the varnish, when taken up between two spatulas, is 
found to be tough and ropy. This composition, when quite cold, 
is to be thinned down for use with from 30 to 35 gals, of spirita 
of turpentine, or of coal naphtha. 

268, It is recommended that the iron should be heated before 
receiving this varnish, and that it should be applied with a spatula, 
or a flexible slip of horn, instead of the ordinary brush. 

When dry and haixJ, it is stated that this varnish is not acted 
upon by any moderately diluted acid, or alkali ; and, by long im- 
mersion in water, it does not form a partially soluble hydrate, as 
is the case with purely resinous varnishes and oil paints. It can 
with difficulty be removed by a sharp-pointed tool ; and is so 
clastic, that a plate of iron covered with it may be bent several 
times before it will become detached. 

Zoofagous Paint. 

269. To 100 lbs. of a mixture of drying linseed oil, red lead, 
sulphate of barytes, and a little spirits of turpentine, add 20 lbs. 
of the oxychloride of copper, and 3 lbs. of yellow soap and com- 
mori rosin, in equal proportions, with a little water. 

When zincked iron is exposed to the atmosphere alone, the var- 
nish is a sufficient protection for it; but when it is immersed in 
sea water, and it is desirable, as in iron ships, to prevent it from 
foulm^, by marine plants and animals attaching themselves to it, 
the pamt should be used, on account of its poisonous qualities. 
The paint is applied over the varnish, and is allowed to harden 
three or four days before immersion. 

^70. Whatever may be the physical structure if materials, 
.vhctlier fibrous or granular, experiment has shown that they all 
possess certain general properties, among the most important of 
which to the engineer are those of contraction, elongation, de- 
flection, torsion, and lateral adhesion, and the resistances which 
these olfer to the forces by which they are called into action.* 

* See Note !>., Appendix, 



271 All solid bodies, when submitted to strain^ by which anj 
ol' tliese properties are developed, have, within certain limits, 
termed llie hmits of elasticity, the property of wholly or partially 
resuming their original state, when the strain is taken oil'. This 
property is usually denominated the elastic force, and has for its 
measure, in the case of contraction, or elongation, the ratio be- 
tween the force which causes the one or the other of these statea 
and tlie fraction which measures the degree of contraction, oi 

272. To what extent bodies possess the property of tola! re- 
covery of form, when relieved from a strain, is still a matter of 
doubt. It lias been generally assumed, that the elasticity of a 
material does not undergo permanent injury by any strain less 
than about one third of that which would entirely destroy its force 
of cohesion, thereby causing rupture. But from the most recent 
cspeiiments on this point made by Mr. Hodgkinson on cast iron, 
it appears that the restoring power of this material is destroyed by 
very shght strains ; and it is rendered probable that this and most 
other materials receive a permanent change of form, or set, under 
any strain, however small. 

373. The extension, or contraction of a solid, may be effected 
either by a force acting in tlie direction in which the contraction, 
or elongation takesplace, or by one acting transversely, so as to 
bend the body. Esperiments have been made to ascertain, di- 
rectly, the proportion between the amount of contraction, or elou;- 
gation, and the forces by which they are produced. From these 
experiments, it results, that the contractions, or elongations are, 
within certain limits, proportional to the forces, but that an equal 
amount of contraction, or elong ' ' n p duced by the same 
amount of force. From the e penn f Mr, Hodgkinson and 

M. Duleau, it appears, that in as n 1 n 11 able iron the con- 
traction, or elongation, caused by h am mount of pressure, 
or tension, is nearly equal ; ^ ml n n b according to Mr. 
Hodgkinson, the amount of con n b t four fifths of the 

elongation for the same force. 

274. When a solid of any of the materials used in construc- 
tions is acted upon by a force so as to produce deflection, experi 
ment.has shown that the fibres towards the concave side of the 
bent solid are contracted, while those towards the convex side 
are elongated ; and tliat, between tlie fibres which are contracted 
ard tliose which are elongated, others are found which have not 
undergone any change oflength. The part of the solid occupied 
by tliese last fibres has received the name of the neutral line, oi 

375. The hypotliesis usually adopted, with respect to the cir- 
cumstances attending this kind of strain, is that the contraction? 

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Biid elongations of the iifares on each side of tlie neulia! axis are- 
proportional to their distances from this line ; and that, jor shght 
deflections, the neiitral asis passes through the centre of gravitj 
of the sectional area. From experiments, however, by Mr. Hodg- 
kinson and Mr, Barlow, it appears that the neutral axis, in forged 
ffon and cast iron, lies nearer to the coucave than to the convex 
surface of the bent solid, and, probably, shifts its position when 
the degree of deflection is so great as to cause rapture. In tim- 
ber, according to Mr. Barlow, the neutral axis lies nearest to the 
convex emface ; and, from his experiments on solids of forged 
iron and timber with a rectangular sectional figure, he places the 
neutral axis at about three eighths of the depth of the section from 
the convex side in timber, and between one third and one fifth of 
ilie depth of the section from the concave side in forged iron. 
, S76. When the strain to which a solid is subjected is sufB- 
ciently great to destroy the cohesion between its particles, and 
cause rupture, experiment has shown that tlte force producing 
this effect, whether it act by tension, so as to draw the fibres 
asunder, or by compression, to crush them, is proportional to the 
sectional area of the solid. Tiie measure, therefore, of the re- 
sistance offered by a solid to rupture, in either of these cases, is 
that force which will rupture a sectional area of tise solid repre 
sented by unity. 

277. From experiments made to ascertain the circumstances 
of rapture by a tensile force, it appears that the solid torn apart 
exhibits a surface of fracture more or less even, according to tlie 
nature of the material. 

278. Most of the experiments on the resistance to rupture 
by compression, have been made on small cubical blocks, and 
iiave given a measure of this resistance greater tlian can be de- 
pended upon in practical apphcations, when tiie height of the 
solid exceeds three times tlie radius of its base. This point has 
been very fully elucidated in tiie experiments of Mr. Hodg- 
kinson upon (lie rupture by compression of solids with circular 
and rectangular bases. These experiments go to prove, that tlie 
circumstances of rupture, and the resistance offered by tlie solid, 
vary in a constant manner with its height, tlie base remaining the 
same. In columns of cast iron, with circular sectional areas, it 
was found that tlie resistance remained constant for a height less 
than three times the radius of the base ; that, from this height to 
one equal to six times the radius of the base, the resistance still 
remained constant, but was less than hi the former case ; anri 
ihat, for any height greater than six tunes the radius of the base, 
tlie resistance decreased with the heiglit. In the two first cases 
dio solids were found to yield either by the upper portion slidiiiii 
off upon ihc lower, in the direction of a plane making a c 

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angle with llic axis of the solid; or else by separatuig imo coiii 
cal, or wedge-shaped blocks, having the upper and loiver suifaces 
of the solid as their bases, the angle at the apex being double tha' 
made by the plane and axis of the solid. With regaid to the re- 
sistances, it was fcund that they varied in the ratio of the area of 
the bases of the soliis. Where the height of the solid was greater 
than six times the ridius of the base, rupture generally took place 
by bending. 

379. From experiments by Mr, Hodgkinson, on wood and 

other substances, it would 


r that like circumstances a 

pany the rupture of all materials by compression ; that is, within 
certain limits, they all yield by an oblique surface of fracture, the 
angle of which with the axis of the solid is constant for the same 
material ; and that the resistances offered within these limits are 
proportional to the areas of the bases. 

280. Among the most interesting deductions drawn by Mr. 
Hodgkinson, from the wide range of his experiments upon ilic 
strength of materials, is the one which points to the existence 
of a constant relation between the resistances offered by materials 
of -the same kind to rupture from compression, tension, and a 
transverse strain. The following Table gives tliese relations, 
assuming the measure of the crushing force at 1000. 


sqoate Inch. 


Mean transverse force' 
and I fool lone. 

Timbec .... 
Cast iron .... 


Glass, {plate and crown) 




£81. Strength of Stone. The marked difference in tlie 
Ktructure, and in the proportions of the component elements fre- 
quently observed in atone from the same quarry, would lead to 
the conclusion that corresponding variations would be found in 
the strength of stones belonging to the same class ; a conclusion 
which experiment has confirmed. The experiments made by 
different individuals on this subject, from not having been con- 
ducted in the same manner, and from the omission in most cases 
of details respecting the structure and component elements of the 
niateria- tried, have, in some instances, led to contradictory re 
suits. A few facts, however, of a general character have been 
ascertained, which may serve as guides in ordinary cases ; bii 
in important structures, where heavy pressures are to be sus- 
tained direct experiment is the only safe course for the engineer 
to follow, in selecting a material from untiied quarries. 

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283, Owing to the ease with which sLor.cs generally break 
under a percussive force, and from the comparatively slight re- 
sistance they offer to a tensile force, and to a transverse strain, 
tliey are seldom submitted in structures to any other strain than 
one of compression ; and cases but rarely occur where this strain 
is not greatly beneath that ■which the better class of building 
Etones can sustain permanently, without undergoing any change 
m their physical properties. Where the durability of the stone, 
therefore, is well ascertained, it may be safely used vdthout a ro 
sort to any specific experiment upon its strength, whenever, in 
its structure and general appearance, it resembles a material of 
the same class known to be good. 

283. The following Table exhibits the principal results of ex- 
periments made by Mr. G. Rennie, and pubhshed in the Philo- 
sophical Transactions of 1818. The stones tried were in small 
cubes, measuring one and a half inches on the edge. The table 
gives the pressure, in tons, borne by each superficial inch of the 
stone at the moment of crushing. 

DiegniFTioM of srcNt. 

Spec. Eravily. 

Crushing n'eht. 


4.83 ! 







Derby, (red and friable) .... 


Marble, (juhke-veined Italian) 

Do. {white Brabant) .... 
Limerick, {black compact) .... 
Devonshira, [red marble) .... 
Poitland stone, {fine-grained oolite) 




The following results are taken from a series of experiments 
made under the direction of Messrs. Bramah & Sons, and pub- 
lished in Vol. 1, Transactions of the Institution of Civil. En- 
gineers. The first column of numbers gives theivcights, in tans, 
boiiio by each superficial inch when the stones commenced to 
fracture'; the second column gives the crushing weight, ir tons, 
(>n the same surface. 

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Herme . 
Aberdeen, {blue) 
Heytor . 
Peterhead, (red) 

Whitby . 

The following Table is taken from one published in Vol. 2, 
Civil Engineer and Architect's Journal, ■which forms a part of 
the Report on the subject of selecting stone for tlic New Houses 
of Parliament, The specimens submitted to experiment were 
cubical blocks measuring two inches on an edge. 


•Jpcdfic gmvlli 


Ctushiiig w'ehi. 

Sands tones. 
Craigleith .... 
Darley Dale .... 










Mansfield .... 
Magnesian Ltme-slones, 


Huddlestone .... 
Roach Abbey .... 
Park Nook' . . . . 

Ancaater ... 


2.1 S3 


Chilmark, (sLicicus) 


3.19 1 


Tha numbers of the first column give the specific gravil'es 

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those in the second column tho weight in tons on a sq.iai'c incli, 
when the stone commenced to fi-actuie ; and those in the thinl 
the crushing weight on a square inch. 

The following Table exliibits the results of experiments on the 
resistance of stone to a transverse strain, made by Colonel Pasley, 
on prisma 4 inches long, the cross section being a square of 2 
inches on a side ; the distance between the points of suppon 
3 inches. 


ATCr..^ bK^fcifif 


we'llhl la ibs. 

1, Kenlish Rag 



2. Yorkshire Landing 



3. Cornish granite . 



4. Portland . 





6. Bath . 



7. Well-bumed bticlis 



a. Inferior bricks . 


284. The conductors of the experiments on the stone for tlie 
New Houses of Parliament, Messrs. Daniell and Wheatstone, 
who also made a chemical analysis of the stones, and applied to 
(liem Brard's process for testing their resistance to frost, have 
appended the following conclusions from their experiments : — 
" If the stones be divided into classes, according to tneir chemical 
composition, it will be found that in all stones of the same class 
there exists generally a close relation between their various phy- 
sical qualities. Thus itwill be observed that the specimen wiiich 
has the greatest specific gravity possesses the greatest cohesive 
strength, absorbs the least quantitj of water, and dismtegrates 
!he least by the process which imitates the effects of weather. 
A comparison of all the experiments shows this to be the general 
niie, though it is liable to individual exceptions." 

" But this will not enable us to compare stones of different 
classes together. The sand-stones absorb llie least quantity of 
water, but they disintegrate more than the magncsian lime-stones, 
which, considering their compactness, absorb a great deal." 

285. Rondelet, from a numerous series of esperimcnts on the 
same subject, published in his wort, Art de B&tir, has arrived 
at hke conclusions with regard to the relations betv(een th<i 
specific gravity ai\d strengtli of stones belonging to tlie samo 

2S6. Among the results of tlie more recent experiments on this 

EUhjcct, those obtained by Mr. Hodgkinson, showing the relatios 


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between tbe crushing, the tensile, and tlie transverse strer.gth ol 
stone, have already been given. 

M. Vicat, in a memoir on the same subject, published in ths- 
Annahs des Fonts et CJumssies, 1833, lias arrived at an opposite 
conclusion from Mr. Hodgkinson, stating, as the results of his 
experiments, that no constant relation exists between the crush- 
ing and tensile strength of stone in general, and that there is no 
omer means of determining these two forces, but by direct ex- 
periinent in each case. 

287. The influence of form on the strenglli of stone, and tlie 
circumstances attending the rupture of hard and soft stones, have 
been made the subject of pai'ticular experiments by Rondelet and 
Vicat. Their experimenls agree in establishing the points that 
the crushing weight is in proportion to the area of the base. 
Vicat states, more generally, that the permanent weights borne 
by similar solids of stone, under like circumstances, will be as 
the squares of their homologous sides. These two authors agree 
on the point that the circular form of the base is the most favor- 
able to strength. They diiFcr on most other points, and pEffticu- 
larly on the manner in which the different kinds of stone yield by 

388. Practical Deductions. Were stones placed under the 
same circumstances in structures as in tlie experiments made to 
ascertain their strength, there would be no difficulty in assigning 
what fractional part of the weight which, in the comparatively 
short period usually given to an experiment, will crush them, 
could be bonie by them permanently with safety. But, in- 
dependently of the accidental causes of destruction to which 
structures are exposed, imperfections in the material itself, as 
well as careless worimianship, from which it is often placed 
in the most unfavorable circumstances of resistance, require to 
be guarded against. M- Vicat, in the memoir before -mentioned, 
states that a permanent strain of yVj of the crushing force of ex- 
periment, may be borne by stone without danger of impairing its 
cohesive strength, provided it be placed under the most favorable 
circumstances of resistance. This fraction of the crushing weight 
of experiment is greater than ordinary circumstances would jus- 
tify, and it is recommended in practice not to submit any stone 
To a greater permanent strain than one tenth of the crushing weight 
of experiments made on small cubes measuring about two inches 
on aa edge. 

The follomng Table shows the permanent strain, and crushinjj 
weight, for a square foot of the stones in some of the most re 
markable structures in Europe. 

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I Pillars of the dome of St. Peter's, (Rome) 

Do. St. PauI'E, {London) . 

I Do. St. Genevieve, (Paris) 

\ Do. Chuxeho^Toussaiat, (Angers) . 

Lower courses of the piers of the Bridge of ]Se 















The stone employed in all the structures eniimeralcd in the 
Table, is some variety of lime-stone. 

289. Expansion of Stone from Heat. Experiments have beca 
maiie in tliis country by Prof. Bartlett, and in England by Mr, 
Adie, to ascertain the expansion of stone for every degree o^ 
Fahrenheit. The experiments of Prof. Bartlett ^rive the follow- 
ing resuUs : 

Granite expands for every degre 
Marble " ■' 

Sand-stone " " 


Tahtfi-oftke Expansion of Stone, <^-c.,from the Experiments oj 
Alexander J. Adie,Civil Engineer, Edinburgh. 

— "- 



°^ t 

S. Sicilian while marble . 
3.»> . . 
4. Sanil-SIOIIB, (Craiglnlh) 
a.Sla.e.lW^cA). . . 
6.ReagnuuI«,(PelerA«id) J 

11. BBaialockliricE . . 
li-FiMhrick .... 

















One ejperJment, (moijt.) 

Hena oCitareo do. 

Mean of three do 
Mean of two do. 
Mean of two do. 
Meanoflivo do. 

290. Strength op Mortails. A very ■wide range of experi- 
ments has been made, within a fevir years back, by engineers both 
at home and abroad, upon the resistance offered by mortars to a 
transversa^ strain, witli a view to compare their qualities, both aa 
regards their constituent elements and the processes followed in 
their manipulation. As might naturally Iiave been anticipated 
diese experiments have presented very diversified, and, in many 
instances, contradictory results. The general conclusions, how- 
ever, drawn froin iliem, have been nearly tlic same in the majority 

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of cases ; and ihey fiirnisli the engineer witli the most tsliable 
guides I th s n portant branch of 1 s art. 

291 Tl e usual mell od of conducting these experiments has 
been to s Iject snail rectal gulai j sms of mortar, resting on 
points ot support at tl e r est emit es to a transversa strain ap- 
plied at tl e CG tre po t bet\veen tl e bearings. This, perhaps, 
is as uii xceptiondb ai d convenient a method as can be followed 
for testmg the comparative strength of mortars. 

292. M. Vicat, m the work already cited, gives the following 
as the average resistances on the square inch offered by mortars 
to a force oftraction ; the deductions being drawn from experi- 
ments on tlie resistance to a transversal strain. 

Mortars of Tery strong bydnulic lime 
" ordiDary di). 


These experiments were made upon prisms a year oid, which 
had been exposed to the ordinary cnanges of weather With re- 
gard to the best hydraulic mortars of the same age which had 
been, dming that same period e ihei immersed in water or 
buried in a damp position, M Viuat states tb-it their average 
tenacity may be estimated at 140 j ounds on the square inch 

293. Genera] Treussart, in his v, orL on hydrauhc and common 
mortars, has given in detail a large number of experiments on the 
transversal strength of artificial hydraulic mortars, made by sub- 
mitting small rectangular parallelopipeds of mortar six inclies in 
length, and two inches square, to a transversal strain applied at 
the centre point between the bearings, which were four inches 
apart. From these experiments he deduces the following prac- 
tical conclusions. 

That when the parallelopipeds sustain a transversal strain vary- 
ing between 220 and 330 pounds, the corresponding mortar will 
be suitable for common gross masonry ; but that for important 
hydraulic works the parallelopipeds should sustain, before yield 
ing, from 330 to 440 pounds. 

204. The only published experiments on this subject made in 
this country are those of Colonel Tottcn, appended to his transla- 
tion of General Treussart's work. The results of these experi- 
ments are of peculiar value to the American engineer, as they 
were made upon materials in very general use on the public 
works throughout the country. 

From these experiments Colonel Totten deduces the following 
general results : 

1st. That mortar of hydraulic cement and sand is ihe strongei 
and harder as the quantity of sand is less. 

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2d. That common mortar is tho stror.ger and harder as liis 
quantity of sand is leas. 

3d. That any addition of common lime to a mortar of hydimdic 
cement and sand weakens the mortar, but that a httle lime may 
be added without any considerable diminution of the strength of 
tlie mortar, and with a saving of expense, 

4th. The strength of common mortars is considembly improved 
by the addition of an artificial puzzolana, but more so by the ad 
dition of an hydraulic cement. 

5lh. Fine sand generally gives a stronger mortar than coars.* 

6th. Lime slalced by sprinlding gave better results than lime 
slaked by drowning. A few ezperiments made on air-slaked lime 
were unfavorable to that mode of slaking. 

7th. Both hydraulic and common mortar yielded better results 
when made with a small quantity of water than when made thin. 

8th. Mortar made in the mortar-mill was found to be superior 
to that mised in the usual way with a lioe. 

9th. Fresh water gave better results than salt water. 

295. Strength of Concuete and Beton. From experiments 
made on concrete, prepared according to the moat approved pro 
cess in England, by Colonel Paslcy, it appears that this material 
is very inferior in strength to good brick, and the weaker kinds 
of natural stones. 

From experiments made by Colonel Totten on betou, the fol- 
lowing conclusions are drawn : 

That beton made of a mortar composed of hydraulic cement- 
common lime, and sand, or of a mortar of hydraidic cement and 
sand, without lime, was the stronger as the quantilry of sand was 
the smaller. But there may be 0.50 of sand, and 0.S5 of com- 
mon lime, without sensible deterioration ; and as much as 1 .00 of 
sand, and 0.35 of lime, without great loss of strength. 

Beton made with just sufficient mortar to fill the void spaces 
between the fragments of stone was found to be leas strong than 
that made with double this bulk of mortar. But Colonel Totten 
remarks, that this result is perhaps attiubutable to the difficulty 
of causing so small a quantity of mortar to penetrate the voids, 
and unite all the fragments perfectly, in experiments made on a 
small scale. 

The strongest beton was obtained by using quite small frag- 
ments of brick, and the weakest from small, rounded, stone gravel. 

A beton formed by pouring grout among fragments of stone, oi 
brick, was inferior in strength to tliat made in the usual way with 

Comparing the strength of the belong on which the experi- 
ments were made, which were eight months old when tried, with 

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78 B¥ILD 

that of a sample of sound red sand stone of good quiHty, it ap 
pears that the strongest prisms of b;ton were only lialf as stiong 
as tlie sand-stone, 

296. Strength of Timber. A wide range of experimenls 
lias been made on the resistance of timber to compression, ex- 
tension, and a transverse strain, presenting very variable resulls. 
Among the most recent, and ■which command the greatest confi- 
dence from tSie ability of their authors, are tliose of Professor 
Barlow and Mr. Hodgkinson : the fonner oo the resistance t<i 
extension and a transverse strain ; the latter on Uiat to com- 

297. Resistance to Extension. T)ie following Table exhibits 
the specific gravity, and tlie mean sesislance per square inch of 
various kinds of timber, from the experiments of Prof. Barlow. 

Do. (Riga) . 

Bo. {Mar Forest) 
Larch, {Scotch) . 
Muliogany • 
Norway spars 
Oak, {Englisk) 

, Do. {African) . 

j Do. (Adriatic) . 
Do. (Canadian . 
Do. ipantzic) . 
Pear . 

Pine, ipitck) 
Do. {red) . 
Teak . 









298. But few direct experiments hwe been midi, upon the 
elongations of timber from a strain in the dnection cf the fibres 
From some made in France by MM Mmard and Desonries, il 
would apj>car that bars of oak having a sectionil area of one 
square i'lch, will be elongated .001176 of their length by a strain 

01 or.p [on. 

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299. Resistance to Compression. The following Table ei 
liibitB llie results obtained by Mr. Hodgkinson from exf crimeiits 
on short cvbnders of timber with flat ends. The diameter o. 
each cylinaer was one inch, and its height two inches. The re- 
sulte, in the first column, are a mean from about three experiments 
on timber moderately dry, being such as is used for maldng 
models for castings ; those in the second column were obtained, 
in a like manner, from similar specimens, winch were turned and 
kept dry in a warm place two months longer, A comparison of 
the results in the two columns, shows the effect of drying on tlie 
strength of timber ; wet timber not having half the strengtli of 
the same when dry. The circumstances of rupture were the 
same as already stated in the general observations under tliis 
head ; the height of the wedge which would slide off in tim- 
ber being about half the diameter, or thickness of the specimen 



Haywood .... 
■Beech .... 

Birch, (American) 
Do. {English) . 

Crab .'.'.'. \ 
Red deal .... 
White deal .... 



Fir, [spruce) 

Hornbeam .... 
Mahogany .... 
Oak, \Qaehec) . 
Do. {English) . 
Do, {Danish, very dry) 
Pine, (piteh) 

Bo. (ydlowJuU of turpentine) 
Do. (red) .... 
Poplar .... 
Plum, {wet) 
Do. {dry) 
Sycamore .... 


Larch, {fallen two months) . 

Willow '.'.'.'. 












































10 1049 










Resistance of Square Pillars. Mr. Hodgkinscn haa 



made a number of invaluable experiments on the slrene.'n ol 
pillars of timber, and of columns of iron and steel, and fioni 
them has deduced formulae for calculating the pressure which 
tliey will support before breaking. The experiments on timbeT 
were made on pillars with flat ends. The following are the for 
niul33 from which their strength may be estimated. 

Calling the brealdng weight in lbs. W. 

" the side of the square base in inches d. 
" the length of the pillar in feet I. 

Then for long columns of oak, in which the side of tlie squai 
base is less than j'^th the height of the column ; 

T^'= 24542 -jg-. 

and for red deal, 

For shorter pillars, where the ratio between their thickness and 
lieight is such that they still yield by bending, the strength is es- 
timated by the following formula : 

Calling the weight calculated from either of the preceding for- 
mula, W, 

Calling the crushing weight, as estimated from the preceding 
Table, W. 

Calling the breaking weight in lbs., W". 

Tiicn tJie formula for the strength is 

W" " — - 


In each of the preceding formula? d must be taken in inclies, 
and I ia feet. 

301. Resistance to Transverse Strains. As timber, from the 
purposes to which it is applied, is for the most part exposed to a 
transverse strain, llie far greater number of experiments nave been 
made to ascertain the relations between the strain, the deflection 
caused by it, and tire linear dimensions of the piece subjected 
to the strain. These relations have been made the subject of 
mathematical investigations, founded upon data derived from ex- 
periment, which will be given in the Appendix. The following 
Table exhibits the results of experiments made upon beams havmg 
a rectangular sectional area, which were laid horizontally upon 
supports at their ends, and subjected to a strain applied at the 
middle point between the supports, in a vertical direction. 

For a more convenient application of the formula to the results 
of die experiments, the notation adopted in the preceding Art 
will be here given. 

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Ca.1 the transverse force necessary to break ths beam iii lbs., W 
" the distance between the supports in inches, /. 
" the horizontal breadth of the sectional area in inches, b. 
" the vertical depth " " " d. 

" the deflection arising from a weight w in inches,/. 

Table of Experiments with the foregoing Notation. 









Oik, (English) . . . 
Do. (K,«ad,-™) . . 

0.k,'(E^K.i) . . . 
While =pJm:e,(a™««m) 
While pine. CAnsricaK). 

Bonlh^'Se, ^. '. 










Prof. Barlow. 


302. Resistance to Detrusion. From the experiments of Prof. 
Barlow, it appears that the resistance offered by the lateral adhe 
sion of the fibres of fir, to a force acting in a direction parallel to 
the fibres, may be estimated at 592 lbs. per square inch. 

Mr. Tredgold gives the following as the results of experiments 
on the resistance offered by adhesion to a force applied perpen- 
dicularly to the fibres to tear ihem asunder. 

Oak . . 
Poplar . . 
Larch, 970 to 1700 " 

303. Strength of Cast Iron. Tiie most recent experiments 
on the strengtli of this material are those of Mr. Hodgkinson. 
Those, particularly, made by him on the subject of the strength 
of columns, and the most suitable form of cast-iron beams to sus 
tain a transversal strain, have supplied the engineer and architect 
with the most valuable guide in adapting mis material to the 
various purposes of structures. 

304. Resistance to Extension. From a few experiments made 
by Mr. Rermie and Captain Brown, the tensile strength of cast 
iron varies from 7 to 9 tons per square inch. 

The experiments of Mr. Hodgkinson upon both hot and cold 
blast iron give the tensile Strengtli from 6 to 9| tons per square 

From some experiments made on American cast iron, imdei 
the direction of the Franklin Institute, tlie mean tensile strength 
IS 20834 lbs., or 9^ tons per square inch. 

305. Resistance to Compression. The general circumstances 
attending the rupture of this material by compression, drawn from 


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he p ■ t i 51 H dgkinson, have already been given 
riie gl f 1 V( Jg ulting from the rupture is about 55". 

Tl n n ! w ght derived from esperimenta upoE 
shoTt yl d f h bl ronvjas 121,685 lbs., or 54 tons GJ 
cwt. p q ar 1 

Th n 1 pn m f ho same, with square bases, 100,739 
lbs., 44 19 wt pe square inch 

That on short cylinders of cold blast iron ivas 135,403 lbs., oi 
55 tons 19i cwt. per square inch. 

That on short prisms of the same, lia^iiig other regular ligurea 
for their bases, was 100,631 lbs., or 44 tons ISj cwt. per square 

Mr. Hodgkinson remarks with respect to the forms of base 
differing from the circle : " In the other forms the difference of 
strength is but little ; and tlierefore we may perhaps admit that 
difference of form of section has no influence upon the power of 
a shoi-t prism to bear a crushing force." 

In remarking on the circumstances attending the rupture, Mr. 
Hodgkinson farther observes : " We may assume, therefore, 
without assignable error, that in the crushing of short iron prisms 
of various forms, longer than the wedge, the angle of fracture will 
be the same. This simple assumption, if admitted, would prove 
at once, not only in this material, but in others wliich break m the 
same manner, the proportionality of the crushing force in different 
forms to the area ; since the area of fracture would always be 
equal to the direct transverse area multiplied by a constant quan- . 
tity dependent upon the material." 

Table' exMhiting the Ratio of the Tensile to the Compressive 
Fences in Cast Iron, from Mr. Hodgkinson' s Experiments. 


.or ...... 



Devon iron, 

No. 3. Hot blast 



6.638 : 1 

Buffery iron, 

No, 1. Hoi blast 



6.431 : 1 


" Cold blast 



5.346 : 1 


,N"o.2. Hotbkst 



4.061 : 1 


" Cold bkst 



4.337 : 1 

Carron iron, 

No. 3. Hot blast 



8.037 : 1 ! 


" Cold blast 



6.376 : 1 

Carron iron, 

No. 3. Hot blast 



7.515 : I 


" Cold blast 



8.139 : 1 

30G. Resistance of Cjjlindrical Columns. The expcrimenis 
under ihis head were made upon solid and hollow columns, both 
ends of which were flat or rounded, fixed or loose, or ons 

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end Hut and the oilier rounded. In the case of columis with 
rounded ends, the pressure was applied in the direction of the 
axis of the column. 

Tiie foUow'ig extracts are made fcom Mr. Hodgkinson's paper 
an this subject, pubUshed in the Report of the British Association 

" ] St. In all long pillars of the same dimensions, tlie resistance 
to crashing by flesure is about three times greater when the ends 
of the pillars are flat, than when they are rounded. 

" 2d. The strength of a pillar, with one end rounded and the 
other flat, is the arithmetical mean between that of a pillar of the 
same dimensions with both ends round, and one with both enda 
flat. Thus, of three cylindrical pOlars, all of tlie same length 
:i.ud diameter, the first naving both its ends rounded, the second 
witli one end rounded and one flat, and the third with both ends 
flat, the strengths are as 1, 3, 3, nearly, 

"3d. A long, uniform, cast-iron pillar, with its ends fimily 
fised, whether by means of discs or otherwise, has the same 
power to resist breaking as a pillar of tlie same diameter, and 
iialf the length, with the ends rounded or turned so that the force 
would pass through the axis. 

" 4th. The experiments show that some additional strength ia 
given to a pillar by enlarging its diameter in llie middle part ; lliia 
increase does not, however, appear to be more than one seventh, 
or one eighth of the breaking weight. 

" 5th. The index of the power of the diameter to which tlie 
strength of long pillars with rounded ends is proportional, is 3.76 
nearly, and 3.55 in those with flat ends, as appeared from the re- 
iults of a great number of experiments ; or the strength of both 
may be taken as the 3.6 power of the diameter nearly. 

" 6th In pillars of tlie same thickness, the strength is inversely 
p oport onal to tl e 1 7 power of t' e lengtl nearly. 

Tl s the t e gtl of i sol d p U v,h\\ rounded ends, tlie 

d ameter of wl 1 </ a 1 tl e I pil / s as -r^." 

Tl e ibsolute stre j,t! of so Ij irs as appeared from ihe 
s^pen ne 1=! a e e ly as belo 
I ] 11a s tl roimde 1 end 

St e ad t =14 9-TJ5. 

In pillars willi flat ends, 

Strength in tons =44.16 jj. 

In holiow pillars nearly the same laws were found to ohtam 
thus, if D and d be the external and internal diameters of a pdiar 

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whose length is 1, llie strength of a hollow cylinder of whicli the 
ends were moveable (as in the connecting roa of a steam-engine) 
would be expressed by tlie fonxmla below. 

btrenglh m tons = 13 j^i • 

In hollow pillars, wliosc ends are flat, we had from experimsn 
as before, 

Strength in tons = 44.3 jp; 

The formula above apply to all pillars whose lengtli is not 
less than about thirty times the external diameter ; for piUars 
shorter than this, it is necessary to have recourse to the ' for- 
mula,' given under the head of Strength of Timbek, for short 
pillars of timber, substitutmg for W and TT" m that foimuh, the 
proper values applicable to cast iron " 

307, Similar Pillars "In simiHr pillars, or those whose 
length is to the diameter m a constint pioportion, the strength is 
nearly as the square ol the dumelei, or of any other bncar di- 
mension ; or, in otliei words, the strength is noaily as tlie arci 
of the transverse section " 

"In hollow pillars, of greater diamctei at one end th-m tlie 
other, or in the middle them 1 tho ends, it was not found that 
any additional strength ^\as obtained over that of cjlmdricil 

" The strength of a pilU" m the foim of ihc connecting rod of 
a steam-engine," (that la, the tnnsverse section prescntmg the 
figure of a cross +,) "was found to be very =imill, perhaps not 
hSf the strength tl^t the same metal would have given if cast in 
the form of a uniform hollow cyhndei " 

"A pillar irregularly fixed, so that the pretsuie would be in 
the direction of the diagonal, is reduced to one third of its strength. 
Pillars fixed at one end and moveable at the other, as in those flat 
at one end and rounded at the other, break at one third the length 
from the moveable end ; therefore, to economize the metal, they 
should he rendered stronger there than in other parts." 

308. Long-continued Pressure on Pillars. "To determine 
the effect of a load lying constantly on a pillar, Mr. Fairbairn had, 
at the writer's suggestion, four pillars cast, all of die same length 
and diameter.- The first was loaded with 4 cwt,, the second 
with 7 cwt., the third with 10 cwt., and the fourth with 13 cwt. ; 
this last load was yW of what had previously broken a pillar of 
the same dimensions, when the weight was carefully laid on with- 
out loss of time. The pillar loaded with 1 3 cwt. bore the weight 
between live and six months, and then broke." o 

309.. General Propertter of PiUars. "In pillars of wrough' 



iron, steel, and timber, the same laws, with respect to rounded 
and flat ends, were found to obtain, as had been showo to exist 
in cast iron," 

" Of rectangular pillars of timber, it was proved experimental 
y that the pillar of greatest strength of the same material is a 

310. Comparative Strengths of Cast Iron, Wrought Iron, 
Steel, and Timber. 

" It resulted from the experiments upon pillars of the same 
iiiiensions but of diiTerent materials, that if we call the strenglJi 
jf cast iron 1000, we shall have for wrought iron 1745, cast stee. 
2318, Dantzic oak 108,8, red deal 78.5." 

311. Resistanceto Transverse Strains. The following Tables 
and deductions are drawn from the experiments of Messrs. Hodg- 
kinson and Fairbairn, on hot and cold blast iron, as published in 
their Reports to the British Association in 1837. 

Table exhibiting the remits of earpenments by Mr. Hodgkinson 
on bars of hot blast iron 5 feet long, with a rectangular sec- 
tional area; the bars resting horizontally on props A feet 6 
inches apart; the weight being applied at the middle of the 

1,00 inch broaV 
Weight oflior, iribs. 3 oz. 


I.Da inches b™=J, 
WeUhl 78 lUs. 
















11 087 





UUun^.fe^clion 1 



Results of experiments, by tlie same, on the transverse strength of 
cold blast iron ; length of hars, and distance between the poin'.s 
of support the same as in the preceding Table. 



ReclfinBUlar liar, 












it bore 















312. The following remarks are extracted from the same Re 
port : " I had remarked, in some of the experiments^ that the 
elasticity of the bars was injured much earlier than is generally 
conceived ; and that instead of its remaining perfect tiD one third, 
or upwards, of the breaking weight was laid on, as is generally 
admitted by writers, it was evident that ^th, or less, produced in 
some cases a considerable set or defect of elasticity ; and judging 
from its slow increase afterwards, I was persuaded that it had not 
come on by a sudden change, but had existed, though in a less 
degree, from a very early period." 

"From what has been stated above, deduced from experiments 
made with great care, it is evident that tlie maxim of loading 
bodies witiiin the elastic limit, has no foundation in nature ; but 
.t win be considered as a compensating fact, that materials will 
bear for an indefinite period a much greater load tlian has hillicrto 
oeen conceived." 

313. "We may admit," from the mean results, "lint iha 
Btrength of rectangular bars is as the sqnars of the deptli." 

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314. Effects of time upon the deflections caused h^ a perma- 
nent load on the middle of horizontal bars. 

The following Table exhibits the results of Mr. Fairl airn's ex- 
periments on this point. The experiments were made on bars 
5 feet long, 1,05 inch deep; the one of cold blast iron, 1,03 inch 
.iroid ; the other of hot blast, 1.01 broad ; distance between tlie 
points of support 4 feet 6 inches. The constant weight sus- 
pended at the centre o':" the bars was 280 lbs. This weight re 
raained on from March lllh, 1837, to June 23d, 1838. 





,930 1 March lllli, 1837, 
.963 1 June 33d, 1838, 




.933 Increase, 



1000 : 1303 

ai5. Mr, Fairbairn in his Report remarks on tlie above and 
like results : " The hot blast bar in these experiments being more 
deflected than the cold blast, indicates that the particles are more 
extended and compressed in the former iron, with the same 
weight, tlian in the latter. This excess of deflection may in some 
degree account for the rapidity of increase, which it will be observed 
is considerably greater in the hot than in the cold blast bar." 

" It appears boto the present state of the bars, (which indicate 
a slow but progressive increase in the deflections,) that we must 
at some period arrive at a point beyond their bearing powers ; or 
otherwise to that position which indicates a correct adjustment 
of the particles in equihbrium with the load. Which of^ the two 
points we have in this instance attained is diflicult to determine ■ 
sufficient data, however, are adduced to show that tlie weights 
are considerably beyond the elastic limit, and that cast iron wil: 
support loads to an extent beyond what has usually been consid. 
ered safe, or beyond that point where a permanent set takes place." 

316. Effects of Temperature. Mr. Fairbairn remarks : "The 
infusion of heat into a metallic substance may render it more 
ductile, and probably less rigid in its nature ; and I apprehend it 
will be found weaker, and less secure under the effects of heavy 
strain. This is observable to a considerable extent in the experi- 
msnts" on transverse strength "ranging from 26° up to 190° Fahr," 
' The cold blast at 26" and 190°, is in strength as 874 : 743, 
The hot blast at 26" and 190", is in strength as 811 : 731, 
Duing a diminution in strength as 100 : 85 for the cold blast, and 
100 to 90 for the hot blast, or 15 per cent. loss of strength in iho 
Eold blast, and 10 per cent, in the hot blast." 

" A number of the experiments made on No. 3 iron have givet 

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extraordinary and not unffequent!y unexpected results. Gojier 
ally speaking, it is an iron of an irregular character, and presents 
less itniformity in its texture than either the first or second ntiali- 
lies ; in other respects it is more retentive, and is often used for 
giving strength a2id tenacity to the finer metals." 

" At 313° we have in the No. 3 a much greater weight sus- 
tained than what is indicated by the No. 2 at 190° ; and at 600" 
there appears in both hot and cold blast the anomaly of increased 
strength as the temperature is advanced from boiling vjater to 
melted lead, arising from the greater strength of the No. 3 iron.' 

317. Influence of Form in Cast Iron upon the Transversa 
Strength of Beams. Upon no point, respecting the strength of 
cast iron, have the experiments of Mr. Hodgkinson led to more 
valuable results to the engineer and architect, than upon the one 
under tliis head. The following Tables give the results of experi- 
ments on bars of a uniform cross section, (thus Xi) cast from hot 
and cold blast iron. The bars were 7 feet long, and placed, for 
breaking, on supports 6 feet 6 inches asunder. 

Table e:ehibiting the results of experiments on bars of hoi htasi 
iron of the form of cross section as above. 








liar broke 


as shown 

wiih Ihe rill dow 


Ihe rill ii|j 

















lot visible 





























































- .490 















ofle^Um 1 




le deflecli 



Note. Tlic annexed diagram shows the ■ 
lurm of tLe uniform cross section of llie 
bars. Tlie linear dimensions of tlie cross 
Bcction in the two experimcnls were as fol- 
lows : 

Length of parallelogram AB 5 inchea"! . . 5 inchi 

Depth " AB 0.30 » U 4 0-3" " 

Total depth of bar . CD 1.55" p^P'- *■ 1.5G " 

Breadth of rib , . . DE 0.36 " J . . 0.355' 

Table eathibiting results of experiments on bars of cold blast iron 
5 feet long, of the same form of cross section as in preceding 


B,tl.«>licn J^ >vUl. ,1b 




























it bore 



lIlUin:iIcdtlletUoii 36. 

Ultimate deflcelbn 1.03. 

Fr.iclure liy a wei?E6 broalilng 
unl ss in ExueiiiiieDt 5, Kui 

Note. The linear dimensions of the cross section of the bars 
in ihe above Table, were nearly the same as those in die [irecu 

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iliiig Table, wilh the exception of [he lolal depth CD, ivliirh. ia 
these last two experimeats, was 2.27 inches, or a little mori, 

318, The object had in view by Mr. Hodgkinson, in the ex 
pcriments recorded in the two preceding Tables, was twofold ; 
ihe one to ascertain the circumstances under which a permanent 
set, or injury to elasticity takes place ; the other to ascertain tlie 
effect of the form of cross section on ihe transverse strength of 
cast iron. The following extracts from the Report, give tlie 
principal deductions of Mr. Hodgkinson on these points. 

" In experiments 4 and 5," (on hot blast iron,) " which were 
on longer oars than the others, cast for this purpose, and for an- 
other mentioned further on, the elasticity {in Expt. 4) was sensi- 
bly injured with 7 lbs., and in the latter (Expt. 5) with 14 lbs., 
the breaking weights being 364 lbs., and 1120 lbs. In the for- 
mer of these cases a set was visible with ^'^, and in the other 
with j-V of l^he breaking weight, showing that there is no weight, 
however small, that will not injure the elasticity." 

" When a body is subjected to a transverse strain, some of its 
particles are extended and others compressed ; I w^ desirous to 
ascertain whether the above defect in elasticity axose from ten- 
sion or compression, or both. Experiments 4 and 5 show this ; in 
these a section of the casting, which was uniform throughout, had 

the form J.- During the experiments the broad part ah was laid 

horizojitally upon supports ; the vertical rib c in the latter experi- 
ment being upward, in tlie former downward. When it was 
downward the rib was extended, when upward the rib was com 
pressed. In both cases the part ah was the fulcrum ; it was thin 
and therefore easily flexible ; but its breadth was such that it was 
nearly inextensible and incompressible, comparatively, with the 
vertical rib. We may therefore assume, that nearly the whole 
flexure which talies place in a bar of this form, arises from the 
extension or compression of the rib, according as it is downward 
or upward. In Lxpt. 4 we have extension nearly without com- 
pression, and in Expt, 5 compression almost without extension. 
These experiments were made with great care. They show that 
there is but little difference in the quantity of set, whetlier il 
arises from tension or compression." 

" The set from compression, however, is usually less than tbiil 
from extension, as is seen in the commencement of the two ex- 
periments, and near the time of fracture in that stibmitted to ten 
Biqn. The deflections from equal weights are nearlv the same 
whether the rib be extended or compressed, but tte ultimate 
strengths, as appears from above, are widely different." 

S19. Form of Cast Iron Beam best adapted to resist a Tran» 

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verse Strain. The experiments of Mr. Hodgkbson on this sub. 
ject, published in the Memoirs of the Literary and Philosopiica] 
Society of Manchester, Second Series, vol, 5, are of equ&l in- 
terest with those just detailed, both in their general results and 
praclical bearing. From these experiments, tlie conclusion diawn 
la that the form of beam in the annexed diagrams is the most fa- 
vorable for resistance to transverse strains. 


Fig. a represents the plan, Fig b 
the elevation, and Fig. c the ciobs 
Bectioil (enl^ed) at llie middle oi 
tlie beam. From the Figs, it will 
be seen, that the beam consists of 
three pai'ts ; a bottom flanch of uni- 
form depth, but variable breadth, ta- 
pering from the centre towaids the 

extremities, where tlie points of &up- rp - — — ■ ■ "■ '-d 

port would be placed, so as to form i^ — ■■■ ■ ' "" 

a portion of the common parabola on each side of the d\i^> of the 
beam, the vertex of each parabola being at the centro of the beam 
The object of this form of flanch was to make it, according to 
llieory, the strongest, with the same amount of material, to bear 
a weight uniformly distributed oier it The top flanch is of a 
like form, hut of much smaHerbieadth and depth tliali the bottom 
one. The two are united by a vertical nb of urftform depth and 

The following are the relative dimensions of tliis form of beam 
wliich, from experiment, gave the most favorable residt. 

Distance of supporta 4 ft. 6 inclioe. 

Total depth of beam . 

Ureadth of top flanch at centre of 
" bottom flatioh " 

Uaiform depth of top flanch 

" bottom flanch . 

Thickness of vertical lib . 

Total area of ciobs section ... 6.4 squats ir 

Weight cf beam tl lbs 



" This beam broke in the middle by compression with 260S4 
lbs., or U tons 13 cwt., a wedge separating from its uppei 

" Till; weights were laid gradually and slowly on, and the beam 
had borne within a little of its breaking weight a considerable time, 
perhaps half an hour." 

*' The form of the fracture and wedge is represented in tlie 
Fig. 6, where enf'is the wedge, ef = 5.1 inches, tn — 3.9 inches, 
angle ewf =82°.^' 

" It is extremely probable, from this fracture, that the neutral 
point was at n, '.he vertex of the wedge, and therefore at fths the 
depth of the beam, since 3.9 = | x 5|^ nearly." 

The relative dimensions above given were arrived at by " con- 
stantly making small additions" to the bottom flanch, until a point 
was reached where resistance to compression could no longer be 
sustained. The beams of this form, m all previous experiments, 
having yielded by the bottom flanch tearing asunder. 

" The great strength of this form of cross section is an indis- 
putable refutation of that theory which would make the top and 
bottom ribs of a cast iron beam equal." 

" The form of cross section" (as above) " is the best which we 
have arrived at for the beam to bear an ultimate strain. If we 
adopt tlie form of beam, (as above,) I think we may confidently 
expect to obtain the same strength with a saving of upwards of 
^tn of the metal." 

320. Rules for determining the ultimate Strength of Cast 
Iron Beams of the above forms. From the results of his experi- 
ments, Mr. Hodgkinson has deduced the following very simple 
formulffi, for determining the breaking weight, in tons, when ap- 
plied at tlie middle of abeam. 

Call the breaking weigh: in tons, W. 

Call the area of the cro^s section of the bottom flanch, taken 
ct the middle of the beam, a. 

Call the depth of the beam at the middle point, d. 
Call the distance between the supports, I. 

when the beam has been cast with the bottom flanch upward 

when the beam has been cast on its side. 

321. Effect of Horizontal Impact upon cast iron bars, and 

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Measure of the Resistance offered by cast iron to this force, Th e 
following fables of experiments on this subject, an* tlie rcKulis 
drawn from them, are taken from a paper by Mr. Hbdgkinscn, 
published in the Fifth Report of the British Association. 

The bars under experireient were impinged upon by a weigh 
suspended freely in such a position, that hanging vertically it was 
in contact with the side of Uie bar. The blow was given by al- 
lowing the weight to swing through different arcs. The bars 
were so confined agauist lateral supports, that they could take nc 
vertical motion. 

Table of experiments on a cast iron bar, Aft. 6 in. long, I in. 
broad, ^ in. thick, weigfdng 7^ lbs., placed with tlie broadside 
against lateral supports 4 ft. asunder, and impinged upon by 
cast iron and lead balls weighing 8^ lbs., swinging through 
arcs of the radius 12 feet. 








































\ ^ 












" Before the experiments on impact were made upon tliis btr, 
it was laid on two horizontal supports 4 feet asunder, and weiglils 
gently laid on the middle bent it (in the same direction that it was 
afterwards bent by impact) as below : 

28 Ihs, benl it .37 inch, 

5G lb* " .77 " Elaaticity a little injiued." 




Table of expei-iments on a cast iron har 7 ft. long, 1,08 m. 6 oad 
and 1.05 in. thick, weighing 23^ lbs., placed, as in preceding 
expeiiments, against supports 6 ft. 6 in. asunder, and bent by 
impacts in the middle. Impinging hall of cast iron weighing 
20| lbs. Radius of arcs 16 feet. 


ImpMtupnnlho 1 













• .63 

















I. S3 









'ITie results in the 3d and Ith columns of the above table were 
derived from allowing the ball to impinge against a weight of 56 
lbs., hung so as to be in contact with the bar. 

" Before the experiments on impact, the beam was laid on two 
supports 6 ft. 6 in. asunder, and was bent .78 in. by 123 lbs., 
(including the pressure from its own weight,) applied gently in 
ihe middle." 

ts on two cast iron bars, 4 ft, 6 in. long, full 

Tables of ^ 
inch square, weighing 14 lbs. 10 os. nearly, placed against 
supports 4: feet apart, and impinged upon by a cast iron ball 
weighing 44 lbs. Radius 16ft. 


Imiiact al one fonrth fto Icpglh from Ilia tnMdle 



Ctords of arcs 

Mean deiiocllons 
of Ihe two hara 
in inches. 

Moan mlo of the 
the two'iases. 









Ccoke in the 



Brolte at the 
point ofimjiact 


Tlie results in the Ist of the above Tables are from bars slnicli 

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in llie middle, tliosc in the 2d Tabic are from bars 5lnick at ihe 
middle point between the centre and extremity of the bar. 

322, From the above and other experiments the conclusion ia 
drawn, " that a uniform beam will bear the same blow, whetliei 
Struck in the middle or half way between that and one end." 

" Fi-om all the experiments it appears, that the deflection ia 
nearly as the chord of the arc fallen through, or as the velocity 
of impact." 

The following conclusions are drawn from the experiments. 

(I.) "If different bodies of equal weight, but diifering consider- 
ably in Iiardnesa and elastic force, be made to strike horizonlally 
against the middie of a heavy beam supported at its ends, all the 
bodies will recoil with velocities equal to one another," 

(2.) " If, as before, a beam supported at its ends be struck 
horizontally by bodies of the same weight, but different hardness 
and elastic force, the deflection of the beam will be the same 
whichever body be used." 

(3.) " The quantity of recoil in a body, after striking against a 
beam as above, ia nearly equal to (though somewhat below) what 
would arise from the full varying pressure of a perfectly elastic 
beam, as it recovered its form after deflection." 

Note. This last conclusion is drawn from a comparison of the 
results of experiment with those obtained from calculation, in 
which the beam is assumed as perfectly elastic. 

(4.) " The eflect of bodies of different natures striking against 
a hard, flexible beam, seems to be independent of the elasticities 
of the bodies, and may be calculated, with trifling error, on a sup- 
position that they are inelastic." 

(5.) " The power of a uniform beam to resist a blow given 
horizontally, is the same in whatever part it is struck." 

323. From the results of the experiments of Messrs. Fairbain] 
and Hodgkinson, on the properties of dold and hot blast iron, it ap- 
pears that the ratio of their resistances to impact is 1000 to 1226.3, 
the resistance of cold blast being represented by 1000 ; the re- 
sistance, or power of the beam to bear a horizontal impact, -being 
measured by the product of its breaking weight from a transverse 
strain at the middle of the beam and its ultimate deflection. Tliis 
measure, Mr. Hodgkinson remarks, " supposes that all cast iron 
bars of the same dimensions, in oiu- experiments, are of the same 
weight, and that the deflection of a beam up to the breaking 
weight, would be as the pressure. Neither of these is true; 
ihey are only approximations ; but the difference in the weights 
of cast iron bars of equal size is very little, and talcing them as 
the same, it may be inferred from my paper on Impact upon 
Beams, (Fifth Report of the British Association,) that the as- 
Buraption above gives results near enough for practice." 

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'4'2i Stubngth of Wrought Iron. This material, from its 
very extensive applications in structures where a considerable 
tensile force is to be resisted, as in suspension bridges, iron ties, 
&c., has been the subject of a very great number ofesperiments. 
Among the many may be cited those of Telford and Brown in 
England, Duleau in France, and the able and extensive series 
upon plate iron for steam boilers, made under the direction of the 
Frankliai Institute, and published in the 19th and 20th vols. {New 
Series) of the Journal of the Institute. 

Resistance to Extension. The following Tables exhibit the 
i.ensile strength of this material under ordinary temperatures, and 
in the different states in which it is used for structujes. 

Table exhibiting the Strength, of Square and Round bars of 
Wrought Iron. 


Xa>ml<,n u- 








UEkT 1 Inch squue, ITelih 






susrlisi . 

Roiind!iar,9in.d1sin. " 

Bar. 1.31 inch^squere ;_' 






EdoihI hnt. 1.31 in. aiiro., Bnislai 




Uat, 13i Inch sqiigia, WObIi . 


Eoi^.lh3r,tlln:dlan. " . 


Ban Tedncod in Ihe middle 1^ 



Bar, M!>,«iri . . 
l; (slit rods) . . . . 



1 InsHMW. 

■' sSSita^, Cmnalicsi 


Smdish' . . 


" GmlfB Co., Penit. 

" Ltaieailer Ct., Fenit. . 

: "-i-SsL,!.,..*:.* 


" ojse " 



" 0.10 - Ea^list 




Table exhibiting the Mean Strength of Boiler Iron, j)er square 
inch in lbs., cut from plates with shears. 

rroceas ofioanufaclnrc. 


EflB^s filed uni- 

Notchea filed inlo 

Piled iron .... 
Hammered plate 
Puddled iron . 




It is rem.arkcd in die Report of the Sub-committee, " that tlio 
iniicrent irregularities of tlic metal, evca in the best specimens, 



whether of roUedor hammered iron, seldom fall short of 10 or 15 
per cent, of the mean strength." 

From the same series of experiments, it appears thtt th 
strength of rolled plate lengthwise is about 6 per cent, greater 
than its strength crosswise. 

In the Tenth Report of the Biitish Association in 1840, Mr, 
Fairbaira has given the results of experiments on plate iron by 
Mr. Hodgkinson, from which it appears that the mean slrengtb 
jf iron plates lengthwise is 22.52 tons. 
Crosswise " 23.04 " 

Single-riveted plates " 18,590 lbs. 

Double-riveted plates " 22,358 " 

Representing the strength of the plate by 100. 

The double-riveted plates will be . .70 

The single " " . . 56. 

325. Professor Earlow, in his Report to the Directors of the 
London and Birmingham Railroad, (Journal of Franklin Insti- 
tute, July, 1835,) states, as the results of his experiments, that a 
bar of malleable iron one inch square is elongated the ipooth part 
of its length by a strain of one ton ; that good iron is elongated the 
■■(«th part by a sti^ain of 10 tons, and is injured by this strain, 
while indifferent, or bad iron is injured by a strain of 8 tons. 

, From the Report made to the Franklin Institute, it appears that 
the first set, or permanent elongation may take place under very 
different strains, varying widi the cliaracter of the material. The 
most ductile iron yields permanently to a low degree of strain. 
The extremes by which a permanent set is given vary between 
the 0.416 and 0.872 of the ultimate strength; the mcaji of tliir- 
teen comparisons being 0.641. 

336. Resistance to Compression. But few experiments have 
been published on the resistance of this material to compression. 
Rondelet states that it commences to yield under a pressure of 
about 70,800 lbs. per square inch, and that when the altitude of 
the specimen tried is greater than three times tiie diameter of 
the base it yields by bending. Mr. Hodgkinson states that the 
circumstances of its rupture from crushing indicate a law simi- 
lar to what obtains in cast iron. 

327. Resistance to a Transverse Strain. The following Ta- 
bles exhibit the circumstances of deflection from a transverse 
strain on bars laid on horizontal supports ; the weight being ap- 
plied at the middle of tlie bar. 

The Table I. gives the resuhs on bars 2 inches square, laid on 
supports 33 inches asunder; Table II. the results on bars 2 
inches -deep, 1.9 in. broad, bcaiing as in Table I. 

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Table I. Taule 1. . 

Dellocllona in 


cUoni b , 

Weight in Iods. 

WeigW in ton!. Incho 


half ion. 

































by Professor Barlow, and 
He remaika on the re- 

Tlie above experiments were made 
published in his Report already cited, 
suits in Table n., that the elasticity was injured by 2.50 Una 
and destroyed by 3.00 tons. 

328. Trials were made to ascertain mechanically the position 
of the neutral asis on the cross section. Professor Barlow re- 
marks on these trials, that " the measurements obtained in thtsse 
experiments being tension 1.6, compression 0.4, giying exactly 
the ratio of 1 to 4 in rectangular bars. These results seem the 
most positive of any hitherto obtained ; still there can be little 
douht this ratio varies in iron of different qualities ; but looking 
to the preceding experiments, it is probably always from 1 to 3, 
to 1 to 5." 

329. Effects of time on the elongation of Wrought Ironfrotn 
« constant strain of extension. M. Vicat naa given, in the An- 
nales de Ckimie et de Physique, vol. 54, some experiments on 
this point, made on iron wires which had not been annealed, by 
subjecting four wires, respectively, to strains amounting to the 
^-, the ^, the \, and 5 of their tensile strengtli, during a period of 
33 months. 

From the results of these experiments it appears, that each 
wire, immediately upon the appUcation of the strain to winch it 
was subjected, received a certain amount of extension. 

The first wire, which was subjected to a strain of 5th its ten- 
sile strength, was found at the end of the time in question not to 
liave acquired any increase of estension. 

The second, submitted to jd its tensile strength, was elongated 
0.027 in, per foot, independently of the elongation it at first rft- 

The third, subjected under hke circumstances to a strain ui 
jlii its tensile strength, was elongated 0.40 in. per foot, besides 
its first elongation. 

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The fourtn, similarly subjected to |ths the tensile sL'cnglh, was 
elongated 0.061, bLsides ils first elongatiou. 

From observations made dm:iiig the experiments, it was found 
'.hat, reckoning from the time when the first elongations took place, 
iJie rapidity of the subsequent elongations was nearly proportional 
to the times ; and that the elongations from strains greater than 
Jth the lenaile strength are, after equal times, nearly proportiona 
to I he strains. 

330. M. Vicat remarks ir. substance npon the results of these 
experiments, that iron wire, when not annealed, commences to 
exhibit a permanent set when subjected to a strain between the 
I and I- of its tensile strength, and that therefore it is rendered 
probable that the wire ropes of a suspension bridge, which should 
be subjected to a like sti^ain, would, when the vibratoiy motion to 
which such structures are liable is considered, yield constantly 
from year to year, until they entirely gave way. 

M. Vicat farther remarks, in substance, that the measure of tlie 
resistance offeredby materials to strains exerted only some minutes, 
or hours, is entirely relative to the duration of the experiments. 
To ascertain the absolute measure of this resistance, which should 
serve as a guide to the engineer, the materials ought to be sub- 
jected for some months to strains ; while observations should be 
made during this period, with accurate instruments, upon the 
manner in which they yield under these strains. 

331. Effects of Temperature on the Tensile Strength of 
Wrought Iron The^xperiments made under the direction of 
the Franklin Institute, already noticed, have developed some very 
curious facts of an anomalous character, with respect to the effect 
of an increase of temperature upon the strength of wrought iron. 
It was found that at high degrees of heat the tensile strength was 
greater up to a certam point than was exhibited by the same iron 
at ordinary temperatures. The fSub-conimittee in then: Report 
remark : " This circumstance was noted at 31 2°, 392", and 573", 
rising by steps of 180° each from 32", at which last point some 
trials have been made in melfing ice. At the highest of these 
points, however, it was perceived that some specimens of the 
metal exhibited but little, if any, superiority of strength ovtir that 
which they had possessed when cold, while others allowed of 
being heated nearly to the .boiling point of mercury, before they 
manifested any decided indications of a weakening effect from in- 
crease of temperature." 

"It hence became apparent that any law, tailing for a basis 
the strength of iron in its ordinary condition, and at common 
temperatures, must be liable to great uncertainty, in regard to its 
application to different specimens of the metal. It was evident 
.hat ihe anomaly above referred lo must be only apparent, and 

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that the tenacity actually exhibited at 573°, as well as that wnich 
prevails while the iron is in the state in which it was left by 
forging, or rolling, must be below its maximum tenacity." 

From the experiments made upon several bars of the saina 
iron, it appeared that their " maximum tenacity was 15 17 psr 
cent, greater than their mean strength when tried cold." 

Calculating tlie maximum tenacity in other experiments from 
this standard, the Sub-committee have drawn up the following 
Table exliibiting the relations between diminutions from the max- 
imum tenacity and the degrees of temperature by which they are 
caused, from which the curve representing the law of these rela- 
tions can be constructed. 



OlBeired teni- °'™ 


which represenu Hm 


peram^as-^. "^ 

alT«nt ""™"- 


















1 155 

































3.41 . 






Mean 3.58 

The Sub-committee remark on ths construction of the above 
Table . " As some of the experimen'.s which furnished the stand- 
ards of comparison for strength at ordinary temperatures, were 
made at 80°, and as at tht point small variations with respect to 
heat appear to affect but very slightly the tenacity of iron, it was 
conceived that for practical purposes, at least, the calculations 
might be commenced from that point." 

" It will be found that with the exception of a shght anomaly 
Between 520° and 570°, amounting to — .08, the numbers express- 
ng the ratios between the elevations of temperature, and the 
diminutions o£ tenacity, constantly increase until we reach 932°, 
at which it is 2.97, and that from tHs point the ratio of diminu- 
tion decreases to the limits of our range of trials, 1317°, where il 
is 2.14. It will also be observed, that the diminution of tenacity 
at 932°, where the law changes from an ir :reasjng to a decreasing 

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rate of diminution, is almost precisely one tliird of the total, oi 
maodmum strength of the iron at ordinary temperatures." 

From the mean of all the rates io the above Table tlic follow- 
ing rule is deduced : " the thirteenth power of the temperature 
above SQ" is proportionate to the fifth pOwer of the diminution 
from the maximum tenacity" 

Professor W. R. Johnson, a member of the sub -committee, 
has since applied the results developed in the preceding experi- 
ments to practical purposes, in increasing the tenacity of wrought 
iron by subjecting it to tension under a liigh degree of tempera- 
ture, before using it "for purposes in which it will have to undergo 
considerable strains, as, for example, in chain cables, &c. 

This subject was brought by Prof. Johnson before Uie Board 
of Navy Commissioners in 1841; subsequently, experiments were 
made by him under direction of the Navy Department, ilie results 
of which, as exhibited in the following Table, were published in 
the Senate Public Documents, {\) With Congress, Qd Session, 
p. 641. Dec; 3, 1844. 

Table of the ejects of Thertno-tension on the Tenacity anil 
Elongation of Wrought Iron. 


of cola. 



Gain of 

Tolal gain 

Tredegar, No. 1, round iron 

Do. do. 
Tredegar, square bar iron 
Tredegar, No. 3, round iron 
Salisbnry, round, (Ames') 
















Prof. Johnson in his letter rcmarJts : " It will be observed tliat 
in these experiments the temperature has, with a view to economy 
of time, been limited to 400", whereas the best effects of the pro- 
cess have generally been obtained heretofore when the heat has 
been as high as 575°." 

333. Resistance of Iron Wire to Impact. The following Ta- 
ble of experiments gives the results obtaine: by Mr. Hodekinson, 
. by suspending an iron ball at the end of a w", (diameter No, 17,) 
and letting another iron bail impinge upon it from different alti- 
tudes. The suspended and impinging balls had holes drilled 
througli them, tlirough which the wire passed. A disc of lead 
was placed on the suspended ball to receive the blow, and losser 
the recoil fro'ii olasticitv. 

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JVgllt ri.ll!.> I.hrnll£li bj iUikihs' 

""S i'^-ih. 







5 r' 


"_ " 

(replied wJlh fresh wire,) 1^ 

1 ^,„ n. 



i i 





a. 3, 4,5. 6 inches, 

ai a 




3 do. 


The following observations are made by Mr. Hodgkiiison : 
" To ascertain iSe strength aod extensibility of this wire, it was 
broken in a very careful experiment with 252^ lbs., suspended 
at its lower end, and laid gradually on. And to obtain the incre- 
ment of a portion of the wire (length 34 ft. 8 in.) when loaded by 
a certain weight, it had 139 lbs. hung at the bottom, and when 
89 lbs. were taken off the load, the wire decreased in length .39 

" Should it be suggested that the wire by being frequently im- 
pinged upon would perhaps be much weakened, the author would 
beg to refer to a paper of his on Chain Bridges, Manchestei- Me- 
moirs, 2d series, vol. 5, where it is shown that an iron wire broken 
by pressure several times in succession is very little weakened, 
and will nearly bear the same weight as at first." 

" The first of the preceding experiments on wires are the only 
ones from which the maximum can, with any approach to cer- 
tainty, be inferred ; and we see from them that the wire resisted 
the impulsion with the greatest effect when it was loaded at bot- 
tom with a weight, which, added to that of the strildng body, was 
a little more than one third of the weight tliat would break the 
wire by pressure." 

" From these experiments generally, it appears that the wire 
was weak to bear a blow when lightly loaded." 

" These last experiments and remarks, and some of the prece- 
ding ones," (on horizontal impact,) " show clearly the benefit of 
giving considerable weight to elast''; structures subject to impact 
and vibration." 

333. Resistance to Torsion of Wrought and Cast Iron. The 
following Table exhibits the results of experiment's made by 
Mr. Dunlop, at Glasgow, on round bars of wi-ought iron. The 
twisting weights were applied with an ami of lever 14 feet 2 

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Diameter of bars 

in inches. 























7'aUe of experiments made hy Mr. G. Rennie upcn Cast and 
Wrought Iron, Weight applied at an arm of level of 2 feet. 



Size of 

Mean break- 
ing walKl.1 

Iron ca; 


WtoQglit iron, (English) 







lb,. 0:1. 
9 15 
10 10 

7 3 
9 I 

8 8 
10 1 

S 9 

8 5 

9 13 
93 13 

10 3 
8 8 

334. Strength of Coppeh. The Tarious uses to wliicli cop- 
per is applied in constructions, render a luiowledgc of ils resist- 
ance under Tarious circumstances a matter of great interest to the 

Resistance to Extension. The resistance of cast copper on 
the square inch, from the experiments of Mr. G. Rennie, is 8.51 
tons, that of wrought copper reduced per hammer at 15.08 tons. 
Copper wire is stated to bear 27,30 tons on the square inch. 
From the experiments made under the direction of Uie Franklin 
Institute, already cited, the mean strength of rolled sheet copper 
is stated at 14.35 tons per square inch. 

Resistance to Compression. Mr. Ronnie's experiments on 
cubes of one fourth of an inch 011 the edge, give for the crushing 



weight of cube of cast copper 7318 lbs., and of wrought copjioi 
6440 lbs. 

335. Effects of Temperature on Tensile Strength. The tix- 
pcriments alreaiiy cited of the Franklin Institute, show that the 
difference in strength at the lower temperatures, as between 60* 
and 90", is scarcely greater than what arises from irregularities 
in tlie structure of the metal at ordinary temperatures. At; 550' 
I'alir. copper loses one fourth of its tenacity at ordinary tempera- 
tures, at 817° precisely one half, and at 1000° two thirds. 

Representing the results of experiments by a curve of which 
the ordinates represent the temperatures above 32°, and the ab- 
scissas the diminutions of tenacity arising from increase of tern 
pcralure, the relations between the two will be thus expressed : 
the squares of the diminutions are as the cubes of the tempera-, 

336. Strength of other Metals. Mr. Renrie states llie 
tenacity of cast tin at 2.11 tons per square inch; and the resist- 
ance to compression of a small "cube of \ of an inch on an edge 
at 966 lbs. 

In the same experiments, the tenacity of cast lead is stated at 
0.81 tons per square inch ; and the resistance of a small cube of 
same size as in preceding paragraph at 483 lbs. 

In tlie same experiments, the tenacity of hard gun-metal is 
stated at 16.23 tons; that of fine yellow brass at 8.01 tons. The 
resistance to compression of a cube of brass the same as before- 
mentioned, is stated at 10304 lbs. 

337. Linear Dilatation of Metals hy Heat. The following 
Table is taken from lesulf* of expeiimenis on ihe dilatation of 
solids, by Professor Darnell, published ui liic Philosophical 
Transactions, 1831. 

Table of Dimensions which a bar takes who; 

leiii'th at 62° 

Aiei2°, (ISO".) 

Al 0(3", (600°.) 


Iron, (woi-ght) . . 




Iron, (cast) 










1. 000347 





Tin . 



Brass, (zinc ) 




Bronze, (tin t) 



" I.OIG330 

Pevrter, (tin s) 






338. Adhesion, of Iron Spiles to Tirriber. The following 
Tables and results are tattii from an article, by Professor 
Walter R. Johnson, published in the Journal of the Franklin 
Institute, vol. 19, 1837, giving the details of esperiments made 
by him on spikes of various formsi diiven into different kinds of 

339. The first series of experiments was made with Burden's 
plain square spike, the fianched, grooved, and swell spike, and 
the grooved and dwelled spike. The timber v^aa seasoned Jersey 
yellow pine, and seasonea white oak. 

From these experiments it results, that the grooved and swelled 
form is about 5 per cent. less advantageous than the plain, in yel- 
low pine, and about 18^ per cent, superior to the plain in oak. 
The advantage of seasoned oak over the seasoned pine, for re- 
taining plain spikes, is as 1 to 1.9, and for grooved spikes as 1 to 

340. The second series of experiments, in which the timber 
was soaked in water after the spikes were driven, gave the fol- 
lowing results. 

For swelled and grooved spikes, the order of retentiveness was, 
I locust; 2 white oak; 3 hemlock; 4 unseasoned chcsnut; 5 
yellow pine. 

For grooved spike without swell, the like order is — 1 unsea- 
soned chesnut ; 2 yellow pine ; 3 hemloclc. 

The swelled and grooved spike was, in all cases, found to be 
inferior to the same spike with the swell filed off. 

341. The third series of experiments gave the following results. 
Thoroughly seasoned oak is tmce, and thoroughly seasonec 

locust Sj times as retentive as unseasoned chesnut. 

The forces required to extract spikes are more nearly propor 
tional to the breadths than to either the thickness or the weights 
of the spikes. And, in some cases, a diminution of thickness 
with the same breadth of spike afforded a gain in retentiveness. 

" In the softer and more spongy kinds of wood the fibres, in- 
stead of being forced back longitudinally and condensed upon 
diemselves, are, by driving a thick, and especially a rather ob 
[usely-pointed spike, folded in masses backward and downward so 
as to leave, in certain parts, the faces of the grain of the timber 
In contact with the surface of the metal." 

"Hence it appears to be necessary, m order to obtain the 
greatest effect, that the fibres of the wood should press the faopa 
as nearly as possible in their longitudinal direction, and with equal 
intensities throughout the whole length of the spike." 

The following is the order of superiority of the spikes front 
fhai of the ratio of their weights and extracting forces respec- 

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1. Narrow flat . . . 7.049 ratio of weight lo exlracling force 

2. Wide flat . . . 5.713 

3. Grooved hut not swelled 5,fi63 ■' " " 

4. Grooved and not notched 5.300 " " " 

5. Grooved aad swelled ■ 4.624 " " " 

6. Burden's patent . . 4.500 " ■' " 

7. Square hammered . . 4.13!) " " " 
e. Plain cylindriciLl . . 3.900 " " 

" All tlie experiments prove that when a spike is once starte,!, 
the force required for its final extraction is much less than llial 
which produced the first movement." 

" when a har of iron is spiked upon wood, if the spike he 
driven until the bar compresses the wood to a great degree, the 
recoil of the latter may become so great as to start back the spike 
for a short distance after the last blow has been given." 

342. From the fourth series of experiments it appears, that the 
spike tapering gradually towards the cutting edge, gives bettei 
results than mose with more obtuse ends. 

That beyond a certain limit the ratio of the weight of the spike 
to the extracting force begins to diminish ; " showing that it would 
be more economical to increase the number rather man the length 
of the spikes for producing a given effect," 

" That the absolute retaining power of unseasoned chesnut on 
square or flat spikes of from two to four inches in length, is a 
little more tlian 800 lbs. for every squcre inch of their two faces 
whicli condense longitudinally the fibres of the timber " 

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343. Masonry is tlie art of raising structures, iii stom;, bjicX 
«nd mortar. 

344. Masonry is classified either from the nature of the mate- 
rial, as stone masonrt/, brick masonry, and mixed, or that which 
is composed of stone and brick ; or from the manner in which 
the material is prepared, as cut stone or ashlar masonry, rubble 
stone or rough masonry, and hammered stone masonry; or, 
finally, from the form of the material, as regular masonry, and 
irregular masonry. 

345. Cut Stone. Masonry of cut stone, when carefully made, 
is stronger and more solid than that of any other class ; but, owing 
to the labor required in dressing, or preparing the stone, it is also 
the most expensive. It is, therefore, mostly restricted to those 
works where a certain architectural effect is to be produced by 
the regularity of the masses, or where great strength is indispen- 

346. Before explaining the means to be used to obtain the 
greatest strength in cut stone, it will be necessary to give a few 
definitions to render the subject clearer. 

In a wall of masonry, ihe t&iTnface is usually applied to the 
front of the wall, and the term back to the inside ; the stone 
which forms the front, is termed the facing ; that of the back, 
the backing ; and the interior, thejilling. If the front, or back 
of the wall, has a uniform slope from die top to the bottom, tliis 
slope is termed the batter, or b&tir. 

The term course is applied to each horizontal layer of stone 
in the wall : if the stones of each layer are of equal thicluiess 
throughout, it is termed regular coursing ; if the thicknesses are 
unequal, the term random, or in-egular coursing, is applied. 
The divisions between the stones, in the courses, are termed the 
Joints ; the upper surface of the stones of each course is also, 
sometimes, termed the bed, or build. 

The arrangement of llie different stones of each course, or of 
contiguous courses, is termed the bond. 

847. The strength of a mass of cut stone masonry will depend 
on the size of the blocks in each course ; on the accuracy of llip 
dressing ; and on the bond used. 

348, The size of the blocks varies with the kind of stone, and 
the nature of the quarry. From some quarries the stone may be 
obtained of any required dimensions ; others, owing to some pe- 
culiarity in the formation of the stone, only furnish blocks of small 

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gize. Again, Ite Blrengtli of some stones is so great as to adir,il 
of tlicir being used in blocks of any size, without danger to the 
stabihty of the structure, arising from their breaking ; others can 
only be used with safety, when the length, breadth, and thickness 
of the block bear certain relations to each other. No iixed rule 
can be laid down on this point : that usually followed by buildeis, 
is to make, with ordinary stone, the breadUi at least squsl to the 
thickness, and seldom greater than twice this dimension, and to 
limit the length to within three times the thickness. When the 
breadth or the length is considerable, in comparison with the 
thickness, there is danger that the block may break, if any un- 
equal setting, or unequal pressure should take place. As to the 
absolute dimensions, flie thickness is generally not less than one 
foot, nor greater than two ; stones of this thickness, with the rel- 
ative dimensions just laid do'wn, will weigh from 1000 to 8000 
pounds, allowing, on an average, 160 pounds to the cubic foot. 
With these dimensions, therefore, the weight of each block will 
require a very considerable power, both of machinery and men, 
to set it on its bed. 

349. For the coping and lop courses of a wall, the same ob- 
jections do not apply to excess ihlength : but this excess may, on 
the contrary, prove favorable ; because the niunber of top joints 
being thus diminished, the snass beneath the coping will bo better 
protected, bemg eXposedonlyattlie joints, which cannot be made 
water-tight, owing to the mortar being crushed by the expansion 
of the flocks in warm weather, and, when they contract, being 
washed out by the rain. 

350. The closeness with which tlie blocks fit is solely depen- 
dent on the accuracy with which the surfaces in contact, are 
wrought or dressed ; if this part of the work is done in a slovenly 
manner, the mass will not only present open joints from any in- 
equality in the settling ; but, from the courses not fitting accurately 
on their beds, the.blocks will be hable to crack from the unequal 
pressure on the different points of the block. 

351. The surfaces of one set of joints should, as a prime con- 
dition, be perpendicular to the direction of the pressure ; by this 
arrangement, there will be no tendency in any of the blocks to 
slip. In a vertical wall, for example, the pressure being down- 
ward, tJie surfaces of one set of joints, which are tlie beds, must 
be horizontal. The surfaces of the other set must be perpen- 
dicular to these, and, at the same time, perpendicular to the face, 
or to the back of tlie wall, according to tlie position of the stones 
in the mass ; two essential points will thus be attained ; the an- 
gles of the blocks, at the top and bottom of the course, and at the 
face or back, will be right angles, and the block will tlierefore bo 
as strong a'5 the nature of the stone will admit. Tlie principles 

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tieie applied to a vertical wall, are applicable, in all cases ivliat- 
cver may be the direction of the pressure and the form of the ex- 
terior surfaces, whether fiane or curved. 

353. A modification of this piinciple, however, may in some 
cases be requisite, arising from the strength of the stone. It is 
kid down as a rule, drawn from the experience of builders, that 
no stone work with angles less than 60° will offer sufficient 
strength and durability to resist accidents, and the effects of the 
weather. If, therefore, the batter of a wall should be gi-eater tlian 
60°, which is about 7 perpendicular to 4 base, the horizontal 
joints (Fig. 6) must not be carried out in tlie same plane, to the 

Fig. 0— Represents tlie arraiigemejit of stone with 
abutting, or elbov) joiiils lor voty ineliiioii but- 

A, face of tliB bloclc 

— f- D, buttma blocli, termed a 

face or back, but be broken off at right angles to it, so as to 
form a small abutting joint of about 4 inches in thickness. As 
the batter of walls is seldom so great as this, except in some cases 
of sustaining walls for the «ide slopes of earthen embanliments, 
this modification m the joints will not often occur ; for, in a 
greitcr batter it will generally be more economical, and the 
construction will be stronger to place the stones of the exterior in 
off'icts the exterior stone of one course, being placed within the 
extenor one of the course below it, so as to give the required 
general direction of the batter The arrangement with oifsets 
has thb farther advantage m its favor of not allowing the rain 
water to lodge m the lomt if the offset be slightly bevelled off. 

3j3 Workmen unless narrowlywatched, seldom take the pains 
npcessiiy to diess the beds and joints accurately; on the con- 
liary, to ubliin what aic tfimed close joints, they diess tlie iointa 


if - 


lace s of cut slona, wil 
th lined off, and tlio bac 

A aeGtionoffaceblocit. 

B rubble bacliins. 

Witli ^c 1 1 L ii s onlj from the outward surface, and 

u en chip m \ ill t le lowiHs the bacs, or tail, (Fig. 7,) so 

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lliat, ■when the Hock is set, it will be in contact with ihe adjacent 
stones, only ihroiighjut this very small extent of beaiing suiface 
This practice is objectionable under every point of view ; for, 
in the first place, it gives an extent of bearing surface, whiclv 
being generally inadequate to resist the pressure thrown on it, 
causes llie block to splinter off at the joint ; and in the se'cond 
place, to give the block its proper set, it has to be propped be- 
neath by small bits of stone, or wooden wedges, an operation 
teimei pinning-up, or under-pinning, and these props, causing 
the pressure on the block to be thrown oai a few points of the 
lower surface, instead of being equally diffused over it, expose 
the stone to crack, 

354, When the facing is of cut stone, and the backing of rub- 
ble, the method of thinning off the block may be allowed for the 
purpose of forming a better bond between the nibble and ashlar ; 
but, even in this case, the block should be dressed true on each 
ioint, to at least one foot back from the face. If there exists any 
cause, which would give a tendency to an outward thrust from 
the back, then, instead of thinning oif all the blocks towards the 
tail, it will be preferable to leave the tails of some tliicker than 
the parts which are dressed. 

355. Various methods are used by builders for the bond of cut 
stone. The system, termed headers and stretchers, in which the 
vertical joints of the blocks of each course alternate with the ver- 
tical joints of the courses above andbelowf it, or as it is termed 
break joints y/ilh. them, is the most simple, and offers, in most cases, 
all requisite solidity. In this system, (Fig. 8,) the blocks of each 
course are laid alternately with their greatest and least dimensions 
lo the face of the wall ; those which present the longest dimeu- 

1 1 « M 1 


! Is! 1 



M II 1 

III 1 



1, and plan C, of aw 
ra and stietcneis. 

el ^ , are termed stretchers; the others, headers 

\f the header reaches from the face to ihe back of the wall, it w 

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termed a through; if it only reaches part of ihc distance it is 
termed a hinder. Tlie vertical joints of one course are eiiliei 
just over the middle of t(ie blocks of the next course below, or 
else, at least four inches on one side or the other of the verticaJ 
joints of that course ; and the headers of one course rest as nearly 
as practicable on the middle of the stretchers of the course be- 
neath. If the backing is of rubble, and the facing of cut stone, a 
system of throughs or binders, similar to what has just been ex- 
plamed, must be used. 

By the arrangement here described, the facing and backing of 
each course are well connected; and, if any unequal settling 
fakes place, the vertical joints cannot open, as would be the case 
were Uiey in a continued line from the top to the bottom of the 
mass ; as each block of one course confines the ends of the two 
blocks on which it rests in the course beneath. 

356. In masses of cut stone exposed to violent shocks, as those 
of which light-houses, and sea-walls iii very exposed positions 
are formed, the blocks of each course require to be not only. very 
firmly united with each other, but also with the courses above 
and below them. To effect tliis, various means have been used. 
The beds of one course are sometimes arranged with projections 
(Fig. 9,) wliich fit into corresponding indentations of the next 
Iron cramps in the form of the letter S, or in any other 


' r. 

B r 

=== ' 


slwtpe that will answer the purpose of giving them a firm hold on 
the blocks, are let into the top of two blocks of the same course 
at a vortical joint, and are firmly set with melted lead, or with 
bolts, so as to confine the two blocks together. Holes are, in 
some cases, drilled through several courses, and the blocks of 
these courses are connected by strong iron bolls fitted to the 

1'he most noted examples of these methods of strengthening 
ilie bond of cut stone, are to be found in the works of tlicRomana 

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whicli have 'ueen preserved to our time, and in iwo celebrated 
modem structures, the Eddy-stone and Bell-rock ]ight-!iouses it 
Great Britain. (Fig. 10.) 

FiB. 10— Bepreaenls the manner of oiranging el 
Mtha same course by dove-lail Joints aiid jogg' 
taken from a horjraiital section of the maaonr 
the Bell-rock light-houee. 

357, The manner of dressing stone belongs to the stonecutLer'a . 
art, but the engineer should not be inattentive either to the accu- 
racy with ■which the dressing is performed, or the means employed 
to effect it. The tools chiefly used by the workman are the 
chisel, axe, and hammer for knotting. The usual manner of dress- 
ing a surface, is to cut draughts around and across the stone with 
the chisel, and then to use the chisel, the axe with a serrated edge, 
or the knotting hammer, to work down the intermediate portions 
into the same surface with the draughts. In performing this last 
operation, the chisel and axe should alone be used for soft stones, 
as the grooves on the surface of Uie hammer are liable to become 
choked by a soft material, and the stone may in consequence be 
materially injured by the repeated blows of the workman. In 
hard stones this need not be apprehended. 

In large blocks which require to be raised by machinery, o. 
hole, of the shape of an inverted trunt:aled wedge, is cut to receive 

-ixed 01 knotted, Biid lis tuckltnt! 

fur hoistms: also the comnuni 

iron tewu B with its taokling. 
I (Imnghlsannuid edgeofbloiok. 
b Imntted part between dieuEhts. 
c, iranbolls with, eyes let mtoDbliiiiia 

holes cat in the block. 
{ and «, chain and rope. tackling. 
_ ______ |,jgpg pj- \gyfjg (irith eye 


nhi-a. bolt. 

It small iron instrument Icimed 

rope IS atlichcd for " ispendm^ the blork , ci else 

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cut obliquely into tlie bloclc lo receive bolls with eyes for 'Jie 
same purpose, 

Wlien a block of cut stone is to be laid, the first point lo be 
attended to, is to examine the dressing, which is done by placing 
the block on its bed, and seeing that the joints fit close, and the 
face is in its proper plane. If it be found that the fit is not accu- 
"ate, the inaccuracies are marked, and the requisite changes made. 
The bed of the cotu^e, on which tlie block is to be laid, is then 
ihoroughly cleansed from dust, &c,, and well moistened, a bed 
of thin mortar is laid evenly over it, and the bloclt, the lower sur- 
face of which is first cleansed and mi- atened, is hid on the moi 
tar-bed, and well settled by «tnkiig it iMth a wooden mallet 
When the block is laid against another of the lame courae, the 
joint between them is prepared w th mortir ui tin, fame manm r 
as the bed. 

358. Rubble Stone Mast>u)/ With good moitar, jubble 
work, when carefully executed, possesses all tlie strength and 
durability required iii structures of an ordinary character ; and it 
is much less expensive than cut stone. 

359. The stone used for this work should be prepared simply 
by knocking off all the sharp, weak angles of the block ; it is then 
cleansed from dust, &c., and moistened, before placing it on iis 
bed. This bed is prepared by spreading over the top of the lower 
course an ample quantity of gowi ordinary-tempered mortar, inlo 
which the stone is firmly imbedded. The interstices between the 
larger masses of stone are filled in, by thrusting small fragments, 
or chippings of stone, into the mortar. Finally, the whole com'se 
may be carefully grouted before another is commenced, in order 
to fill up any voids left between the fuU mortar and stone. 

360. To connect the parts well together, and to strengthen the 
ri'eak points, fhroughs or binders should be used in all the courses ; 
and the angles should be constructed of cut or hammered stone. 
In heavy walls of rubble masonry, the precaution, moreover, 
should be observed, to lay the stones on their quarry-bed; that 
is, to give them the same position, in the mass of masonry, tliat 
they had in the quarry ; as stone is found to offer more resistance 
to pressure in a direction perpendicular to the nnarry-bed, than 
in any other. The directions of the lamina in sti'nlified stones, 
show the position of the quatry-bed. 

361. Hammered stone, or dressed rubble, is slone roughly 
fesliioned into regular masses with the hammer. The same pre 
cautions must be taken in laying this kind of masonry, as in the 
two preceding. 

363. Brick Masonry. With good brick and mortar, this ma 
sonry offers great strength and durability, arising from the stiong 
adhesion between the mortar and brick. 

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363. The bond used in brick work is very various, de(.er.Jing 
on ihc character of the structure. The most usual idnds are 
icnown as the English and Flemish. The first consists in ar- 
ranging the courses alternately, entirely as headers or stretchers, 
iha bricks through the course breaking joints. In the second the 
bricks are laid as headers and stretchers in each course. The 
first is stated to give -a stronger bond than the last, the bricks of 
which, owing to the difficulty of preventing continuous joints, 
cither in tlie same or different courses, are liable to separate, 
causing the face or the back to bulge outward. The Flemish 
bond presents the finer architectural appearance, and is therefore 
preferred for the fronts of edifices. 

364. Timber and iron have both been used to Elrengthen the 
bond of brick masonry. Among the most remarkable example? 
of their uses are the well, faced in brick, forming an entrance to 
the Thames Tunnel, the celebrated work of Mr. Brunei, and his 
experimental arch of brick, a description of which is given in the 
Civil Engineer and Architect's Journal, No. 6, vol. I. In both 
these Btructures Mr. Brunei used pantile laths and hoop iron, in 
the interior of tlie horizontal courses, to connect two contiguous 
courses throughout their length. The efficacy of this method 
has been farther fulSy tested by Mr, Brunei, in experiments made 
on the resistance to a transversal strain of a brick beam bonded 
with hoop iron, accounts of which, and of experiments of a Hkc 
itind, are given by Colonel Pasley in his work on Limes, Calca- 
reous Cements, &c. 

365. The mortar-bed of brick, may be either of ordinary, or 
thin-tempered mortar ; the last, however, is the best, as it makes 
closer joints, and, containing more water, does not dry so rapidly 
as the other. As brick has great avidity for water, it would al- 
ways be well not only to moisten it before laying it, but to allow 
it to soak in water several hours before it is used. By taking 
this precaution, the mortar between the joints will set more fii'mly 
than when it imparts its water to the dry brick, which it frequently 
does so rapidly as to render the mortar pulverulent when it has 


366. Tlie term foundation is used indifferently either for the 
lower courses of a structure of masonry, or for the artificial 
arrangement, of whatever character it may be, on which these 
courses rest. For more perspicuity, the term bed of the founda- 
tion wdl be used in this work when the latter is designated. 

367. The strength and durability of structures of masonry de- 
pend essentially up9n tlie bed of the foundation. In arranging 
Uiis, regard must be had not only to ihc permanent eiforts wliicL 

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ihe bed may have to support, but to those of an accidental clia* 
vacter. It should, in all cases, be placed so far below the surface 
of tiie aojl on which it rests, that it will not be liable to be un- 
covered, or exposed : and its surface should not only be normal 
to the resultant of the efforts which it sustains, but this resultant 
should intersect the base of the bed so far within it, that the por- 
tion of the soil between this point of intersection and the outward 
edge of the base shall be broad enough to prevent its yielding 
from the pressrae thrown on it. 

368. The first preparatory step to be taken, in determining the 
kind of bed required, is to,ascertain the nature of the subsDii on 
which the structure is to be raised. This roay be done, in or- 
dinary cases, by sinking a pit ; but where the subsoil is composed 
of various strata, and the structure demands extraordinary pre- 
caution, borings must be made with the tools usually employed 
for this purpose. 

369. With respect to foundations, soils are usually divided 
into three classes : 

The 1st class consists of soils which are incompressible, or, at 
least, so slightly compressible, as not to affect the stability of the 
heaviest masses laid upon (hem, and which, at the same time, do 
not yield in a lateral direction. Sohd rock, some tufas, compact 
stony soils, hard clay which yields only to the pick, or to blast-' 
ing, belong to this class. 

The 2d class consists of soils which are incompressible, but 
require to be coniined laterally, to prevent them from spreading 
out. Pure gravel and sand belong to this class. 

The 3d class consists of all the varieties of compressible soils ; 
under which head may be arranged ordinary clay, the common 
earths, and marshy soils. Some of this class are found in a more 
or less compact state, and are compressible only to a certain ex- 
tent, as most of the varieties of clay and common earth ; others 
LU'e found in an almost fluid state, and yield, with faciUty, in every 

370. To prepare the bed for a foundation on rock, the thiclt- 
ness of the stratum of rock should first be ascertained, if there are 
any doubts respecting it : and if tliere is any reason to suppose 
that tho stratum has not sufficient strength to bear the weight of 
the structure, it should be tested by a trial weight, at least twice 
as great as the one it will have to bear permanently. Tho rock 
U next properly prepared to receive the foundation courses, by 
levelling its surface, which is effected by' brealting down all pro- 
ecting points, and filling up cavities, either with rubble masonry 
or with beton , and by carefully removing any portions of the up 
per stratum which present indications of having been injured by 
'he weather. The surface, prepared in this manner, should, more 

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over, be perpendicular to the direction of the pressure ; if this ii 
vertical, the surface should be horizontal, and so for any othci 
direction of the pressure. Should there, however, bo any diffi- 
culty in so arranging the surface as to have it normal to the re- 
sultant of the pressure, it may receive a position such that one 
component of the resultant shall be perpendicular to it, and the 
other parallel ; the latter being counteracted by the friction and 
adhesion between the base of the bed and the surface of the rock. 
If, owing to a great dechvity of the surface, the whole cannot be 
brought to the same level, the rock must be broken into steps, in 
order that the bottom courses of the foundation throughout, may 
rest on a surface perpendicular to the direction of the pressure. 
If fissures or cavities are met with, of so great an extent as to 
render the filling them with masonry too expensive, an arch musi 
then be formed, resting on the two sides of the fissure, to support 
that part of the structure above it. 

The slaty rocks require most care in preparing them to receive 
a foundation, as tlieir top stratum will generally be found injured 
to a greater or less depth by tlie action of frost. 

371. In stony earths and hard clay, the bed is prepared by 
digging a Irencii wide enough to receive the foundation, and deep 
enough to reach the compact soil which has not been injured by 
the action of frost : a trench from 4 to 6 feet, will generally be 
deep enough for this purpose. 

373. In compact gravel, and sand, where there is no liability 
to lateral yielding, either from the action of rain or any other 
cause, the bed may be prepared as in the case of stony earths. 
If there is danger from lateral yielding, the part on which the 
foundation is to rest must be secured by confining it laterally hy 
means of sheeting piles, or in any other way that will offer suffi- 
cient security. 

373. In laying foundations on firm sand, a further precaution 
is sometimes resorted to, of placing a platform on the bottom of 
the trench, for the purpose of distributing the whole weight more 
uniformly over it. This, however, seems to be unnecessary ; for 
if the bottom courses of the masonry are well settled in their bed, 
there is no good reason to apprehend any unequal settling from the 
effect of the superincumbent weight : whereas, if the wooi of the 
platform should, by any accident, give way, it would leave a pari 
of the foundation witliout any support. 

When the sand under the bed is liable to injury from springs 
they must be cut off, and a platform, or, still better, an area of 
beton should compose the bed, and this should be confined on all 
sides between walla of stone, or beton sunk below the bottom of 
lt:e bed. 

374. If, in opening ". trench in sand, water is found at a eligli' 

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deplli, and ill sucii quantity as to impede tl.e labors of tlie work 
men aud the trench cannot be kept dry by the use of pumps oi 
Bcoops, a row of sheeting piles must be driven on each side of 
tbe space occupied by it, somewhat below the bottom of the bed, 
the sand on the outside of the sheeting piles be thrown out, and 
its place filled with a puddling of clay, to form a water-tight en- 
closure round the trench. The excavation for the bed is then 
commenced ; but if it be found that the water still makes rapidly 
at.the bottom, only a small portion of the trench must be opened, 
and after the lower courses are laid in this portion, the excavation 
will be gradually effected, as fast as the workmen can execute 
tlie work without diiEculty from the water. 

375. The beds of foundations incompressible soils require pe- 
culiar care particularly when tlie soil is not homogeneous, pre- 
senting more resistance to pressure in one point than in another ; 
for, in that case, it will be very difficult to guard against unequal 

376. In ordinary clay, or earth, a trench is dug of the proper 
width, and deep enough to reach a stratum, beyond the action of 
frost ; the bottom of the trench is then levelled off to receive the 
foundation. This may be laid immediately on the bottom, or 
else upon a grillage and. platform. In the first case, the stones 
forming the lowest com-se, should be firmly setded in iheir 
beds, by ramming them with a very heavy beetle. In the second 
a timber grating, termed a gi-illage (Fig, 12,) which is formed 
of a course of noavy beams laid lengthwise in the trench, an.: 
connected firmly by cross pieces into which they are notched, is 
firmly settled in the bed and the earth is solidly packed between 

e ong ud na and ; a flooring of thick planks, 

m d a p atf m h n n the gridage, to receive the 

lows u un n The object of the grillage, and 

platform, is to diffuse the weight more uniformly ov 
Face of the trench, to prevent any part from yielding. 

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lift MASOr-IIV. 

377. Repeated failures in grillages and platforms, arising eilliei 
from the compression of the woody fibre, or from a traiisvers;^ 
strain occasioned by the subsoil offering an unequal resistance, 
have impaired confidence in their efiicaCT. Engineers now pre 
fer beds formed of an area of beton, as offering more security Uian 
any bed of timber, either in a uniformly, or unequally compressi- 
ble soil. 

378. The preparation of an area of beton for the bed of a 
foundation, will depend on the circumstances of the case. lu 
ordinary cases the beton is thrown into the trench, and carefully 
rammed in layers of 6 or 9 inches, until the mortar collects in a 
semi-fluid state on the top of the layer. If the base of the bed is 
to be broader than the top, its sides must be confined by boards 
suitably arranged for this purpose. Whenever a layer is left in- 
complete at one end, and another is laid upon it, an olfset should 
be left at the unfinished extremity, for the purpose of connecting 
the two layers more firmly when the work on the unfinished pari 
is resumed. 

Considerable economy may be effected, in the quantity of be- 
ton required for the bed, by using large blocks of stone which 
should be so distributed throughout the layer, that the beetle will 
meet witli uo difficulty in settling the beton between and around 
tlie blocks. 

When springs rise through the soil ovet which the beton is to 
be spread, the water from tnem must either be conveyed off by 
artificial channels, which will prevent it rising througn the mas? 
of beton and washing out the hme ; or else strong cioili, prepared 
so as to be impermeable to water, may be laid over the surface 
of the soil to receive the bed of beton. 

The artificial channels for conveying off tlie water may be 
formed either of stone blocks with semi-cylindrical channels cut 
in them, or of semi-cylinders of iron, or tiles, as may be most 
convenient. .A sufficient number of these channels should be 
formed to give an outlet to the water as fast as it rises. 

An impermeable cloth may be formed of stout canvass, pre- 
pared with bituminous pitch and a drying oil. It is well to have 
the cloth doubled on each side with ordinary canvass to prevent 
accidents. The manner of settling the cloth on the surface of 
the soil must depend on the circumstances of the case. 

Each of tlie ioro^oing expedients for preventing the action of 
springs on an area of beton, has been tried with success. When 
artificial channels are used, they may be completely choked sub- 
seq\iently, by injecting into them a semi-fluid hydraulic cement, 
and the action of the springs be thus dostroyed. 

Foundation beds of beton are frequently made witliout exhaust- 
ing the water from tlie area on which thoy arc laid. For this 

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FOCNl;*.riO.\3. US 

purpose the beton is tlirov™ in layers over liie area, by using 
either a ■wooden conduit reaching nearly to tlie position of the 
layer, or else by placing the beton (Fig 13) in a box by which it 
is lowered to the position of the layer, and from which it is de 
posited so as not to permit the water to separate the lime from, 
iho other ingi'edients. 

!al box for lowe 

--aler.Biid E 

■of the box 1 

ea to let thfl 


ttie BBma 
beton fall 
icU tlia 

.. HTOUlvl W 

halves of tlie box _,,_.. 
, rope taclding for loweting 

Should it be found that springs boil up at the bottom, it must 
be covered witli an impermeable cloth. 

379. In marshy soils, the principal difficulty consists in form- 
mg a bed sufficiently firm to give stability to the structure, owing 
to the yielding nature of the soil in all directions. 

The following are some of the dispositions that have been tried 
with success in this case. Short piles from 6 to 13 feel long, 
and from 6 to 9 inches in diameter, are driven into the soil as 
close together as they can be crowded, over an area considerably 
greater than that which the structure is to occupy. The heads 
of the piles are accurately brought to a level to receive a grillage 
and platform ; or else a layer of clay, from 4 to 6 feet tliick, is 
laid over the area thus prepared with piles, and is either solidly 
rammed in layers of a foot thick, or submitted to a very heavy 
pressure for some time before commencing the foundations. The 
object of preparing the bed iu this manner, is to g e 1 e up 
per stratum of the soil all the firmness possible, by s hj ng 
it to a strong compression from the piles ; and wl e th Is 
been effected, to procure a firm bed for the lowest on s f 1 
foundation by the grillage, or clay bed ; by tliese a s 1 e 
whole pressure will be uniformly distributed throUp,hou he e 
Eire area. This case s also one in which a bed of 1 n uld 
replace, with great advantage, cither the one of clay, or the 



3 which the short piles are applied in this c 

is diffijrent from llic objecl to be attained u'sually in die employ 

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ment of piles for foundations ; which is to transmit the weight of 
l!ie structure that rests on the piles, to a firm incompressible soil, 
overlaid by a compressible one, that does not offer sufficieiil 
firmness for the bed of the foundation. 

380. When a firm soil is overlaid by one of a comjjressible 
character, and its distance below the surface is such tliat it can be 
reached by piles of ordinary dimensions, they should be used in 
preference to any other plan, when they can be rendered durable, 
on account of their economy and the security they afford. 

To prepare the bed to receive the foundations in tliis case, 
strong piles are driven at equal distances apart, oven- the entire 
area on which the structure is to rest. Tliese piles are driven, 
until they meet with a firm stratum below the compressible one, 
which offers sufficient resistance to prevent them from penetra- 
ting farther. 

381. Pdes are generally from 9 to 18 inches in diameter, witli 
a length not above 20 times the diameter, in order that they may 
not bend under tlie stroke of the ram. They are prepared for 
driving, by stripping them of their baik, and paring down the 
knots, so that the friction, in driving, may be reduced as much as 

Eossible. The head of the pile is usually encircled by a strong 
oop of wrought iron, to prevent the pile from being split by tlie 
action of the ram. The foot of the pile may receive a shoe 
formed of ordinary boiler iron, well fitted and spiked on ; or a 
cast-iron shoe of a suitable form for penetrating the soil may be 
cast around a wrought-iron bolt, by means of which it is fastened 
[o the pile. 

382 A machine, termed a pilp engine, is used for driving 
pdes It consist'^ essentially of two upnghts firmly connected 
at top by T cioss piece, and of a ?am, or monket/ of cast iron, for 
driving tlie pile by a force of percussion. Two kinds of en- 
gines are in use ; tlie one termed a crab engine, from the ma- 
chinery used to hoist the ram to the height from wliicli it is to 
fall on the pile ; t!ie other tlio ringing engine, from the monkey 
being raised by the sudden pull of several men upon a rope, 
by which the ram is drawn v.p a few feet to descend on the 

Tlic crab engine is' by far the more powerful machine, but on 

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ihis account is inapplicable in some cases, as in the drivi: g of 
cast-iron piles, where the force of the blow might destroy the 
pile ; also in long slender piles it may cause the pile to spring sa 
much as to prevent it from entering the subsoil. 

The luauner of driviag piles, and the extent to which they may 
be forced into the subsoil, will depend on local circumstances. It 
sometimes happens that a heavy blow will effect less than' sex eral 
slighter blows, and that piles after an interval between successive 
voSeys of blows, can with difficulty be started at first. In some 
cases the pile breaks below the surface, and continues to yield to 
the blows, by tlie fibres of the lower extremity being crushed. 
These difficulties require careful attention on the part of the en- 

fineer. Piles should be driven to an unyielding subsoil. The 
'rench civil engineers have, however, adopted a rule to stop 
the driving when the pile has arrived at its absolute stoppage, 
this being measured by the farther penetration into the subsoil 
of about /iths of an inch, caused by a volley of thirty blows 
from a ram of 800 lbs., falling from a height of 5 feet at each 

383. If the head of a pile has to be driven below the level to 
which the ram descends, another pile, termed a punch, is used 
for the purpose. A cast-iron socket of a suitable form embraces 
the head of the pile and the foot of the punch, and the effect of 
the blow is tims transmitted through the punch to the pile. 

384. When a pile from breaking, or any other cause, has to be 
drawn out, it is done by using a long beam as a lever for the pur- 
pose ; the pile being attached to the lever by a chain, or rope 
suitably adjusted. 

385. The number of piles required, will be regulated by the 
weight of tlie structure. An allowance of 1000 pounds on each 
square inch will ensure safety. The least distance apart, at 
which the pdes can be driven with ease, is about 2^ feet between 
their centres. If they are more crowded than tliis, they may 
force each other up, as they arc successively driven. When this 
is found to take place, the driving should be commenced at tlie 
centre of the irea, and the pile should be driven with the butt end 

386. From experiments carefully made in France, it appears 
that piles which resist only in virtue of the friction arising from 
the compression of the soil, cannot be subjected with safety to a 
load greater than one fifth of that which piles of the same dimen- 
sions will safely support when driven into a iirm soil. 

387. After the piles are driven, they are sawed off to a level, 
to receive a grillage and platform for the foundation. A large 
beam, termed a capping, is first placed on the heads of the out- 
side row of piles, to winch it is fastened by means of wooden 



pins, or Iree-naiis driven into an auger-hole, made through the 
cap into the liead of each pile. After llie cap is fitted, longitudi 
nal beams, termed string pieces, are laid lengthwise on the heads 
of each row, and rest at each extremity on the cap, to which thej 
are fastenod by a dove-tail joint and a wooden pin. Another series 
of beams, termed cross pieces, are laid crosswise on the string 
pieces, over the heads of^each row of piles. The cross and string 
pieces are connected by a notch cut into each, so that, when put 
tbgetlier, their upper surfaces may be on the same level, and tSey 
ai-e fastened to the heads of the piles in the same manner as tlie 
capping. The extremities of the cross pieces rest on the capping, 
and are connected with it, like the string pieces. 

The platform is of ihiclt planks laid over the grillage, -with 
the estremity of each plank resting on the capping, to which, 
and to tlie string and cross pieces, the planks are fastened by 

l"he capping is usually thicker tlian the cross and string pieces 
by the thickness of the plank ; when this is the case, a rabate, 
about foiu: inches wide, must be made on the inner edge of the 
capping, to receive the ends of the planks. 

388. An objection is made to the platform as a bed for the 
foundation, owing to the want of adhesion between wood and 
mortar ; from which, if any unequal settling should take place, 
the foundations would be exposed to slide oif the platform. I'o 
obviate this, it has been proposed to replace the grillage and plat- 
form by a layer of beton resting partly on the heads of the piles, 
and partly on the soil between iliem. This means would furnish 
a firm bed for the masonry of the foundations, devoid of the ob- 
jections made to the one of timber. 

To counteract any tendency to sliding, the platform may be 
inclined if there is a lateral pressure, as in the case, for example, 
of the abutments of an arch. 

389. In soils of alluvial formation, it is common to meet with 
a stratum of clay on the surface, underlaid with soft mud, in 
which case, the driving of short piles would be injurious, as the 
tenacity of the stratum of clay would ,be destroyed by the oper- 
ation. It would be better not to disturb the upper stratum 
in this case, but to give it as much firmness as possible, by 
lamming it with a heavy beetle, or by submitting it to a heavy 

390. Piles and sheeting piles of cast iron have been used with 
complete success in England, both for the ordinary purposes of 
cofferdams, and for permanent structures for wharfing. The 

C"es have been cast of a variety of forms ; in some cases lUey 
ve been cast hollow for the purpose of excavating the soli 
within the pile as it was driven, and thus facilitate its penetration 

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into ihe subsoil. Fig 15 i 
moio recent aiTangem°nls of 

s—Reproaenls a hur loiiWEectioii uf an Brrangempjit of p ies and sheeting 
Eting pilB with tt lap e lo coyer 11 e jo nt batween it and t! b next alieel ns 

h, piles with a lap on oach 5 do 
- aheeling pile lapped liy pile and ahooting pi 
rpilea and eheeling lules. 

i/, ribsofpiiei 

391. Sand has also been used with advantage to fonn a bed 
for fouiiditions in a \eiy compressible soil. For tliis purpose 
a trench is (Fig 16) e^cavited and filled with sand ; the sand 
being spiead in laye a of about 9 inches, and each layer being 
firmly settled b; 1 1 r i \ 1 c tip I efore laying the next. If water 

IG — Eei reeenb) a section of a aand fouii- 
1 bed and the masouiy upon it. 
' ' I in a trench. 

phould make rapidly in the liench it would not be practicable lo 
pick the sand m layers Instead therefore, of opening a trench, 

bales about 6 feet deep, and 6 mclieb 

(Fig. 17 ) 

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124 MAsomiY. 

should be made, by means of a short pile, as close together sa 
practicable ;, when the pile is withdrawn 'rom the hole, it la im- 
mediately filled with Ba-.d. To cause the sand to pack firmly, il 
should be slightly moistened before placing it m the holei, oi 

Sand, when used in this way, posscshea the valuable properly 
of assuming a new position of equilibnum and stdbiht\, sliould 
tlie soil oil which it is laid yield at any of its poinls Not only 
does this take place along the base of the sand bed, but also along 
the edges, or sides, when tiiese are enclosed by the sides of the 
trench made to receive the bed. This last point offers also some 
additional security against yielding in a lateral direction. The 
bed of sand must, in all cases, receive sufficient thickness to cause 
the pressure on its upper surface to be distributed over the entire 

392. When, from the fluidity of the soil, the vertical pressure 
of the structure causes the soil to rise around the bed, this action 
may be counteracted, either by scooping out the soil to some deptli 
around the bed and replacing it by another of a more compact 
nature, well ramiped in layers, or with any rubbish of a solid 
character ; or else a mass of loose stone may be placed over the 
surface exterior to the bed, whenever the character of the struc- 
ture will warrant the expense. 

393. Precautions against Lateral Yielding. Tlic soils which 
have been termed compressible, strictly speaking, yield only by 
the displacement of their particles either in a lateral direction, or 
upward around the structure laid upon them. Whei-e this action 
arises from the effect of a vertical weight, uniformly distributed 
over the base of the bed, the preceding methods for giving per- 
manent stability to structure, present all requisite security. But 
when tlie structure is subjected also to a lateral pressure, as for 
example, that which would arise from the action of a bank of 
earlh resting against the back of a wall, ad-dilional means of secu- 
rity are demanded. 

One of the most obvious expedients in this case, is to drive a 
row of strong square piles in juxtaposition immediately in contact 
with the exterior edges of the bed. This expedient is, however, 
only of service where the p'^es attain either an incompressible 
soil, or one at least firmer than that on which tlie bed imme- 
diately rests. For otherwise, as is obvious, the piles only serve 
to transmit the pressure to the yielding soil in contact with them. 
But where they are driven into a firm soil below, they gain a 
iised point of resistance, and the only insecurity they offer is 
either by t!ie rupture of the piles, from the cross strain upon 
them, or from the yielding of tlie firm subsoil, from the same 


rolIN DAT IONS. 125 

In caae the piles reach a firm subsoil, it will be beet to scoop 
out the upper yielding soil before driving the piles, ant! to fill in 
between and around them with loose broken stone, (Fig. 18.! 
This will give the piles greater stiffness, and effectually prevent 
tliem from spreading at top. 

Fig. 18— RepreBonla tlio mauner o 
looee stone to euslain piles and 
Uiem from yieliUiig latsrally. 

A, eeclioii of the masonry. 

B, looBs stone Uiromi aruiuid the V' 

When the piles cannot be secured by attaining a firm subsoil, 
it will be better to drive them around the area at some distance 
from the bed, and, as a farther precaution, to place horizontal 
buttresses of masonry at regular intervals from the bed to the 
piles. By this arrangement, some additional security is gained 
from the counter-pressure of tlie soil enclosed between the bed 
and the wall of piles. But it is obvious that unless the piles in 
this case are driven into a firmer soil thaa that on which the stnic- 
lure rests, there will still be danger of yielding. 

In using horizontal buttresses, the stone of which they are con- 
structed should be dressed with care ; their extremities near the 
wall of piles should be connected by horizontal arches, (Fig. 19,) 
to distribute the pressure more uniformly ; and where there is an 
upward pressure of the soil around the structure, arising from it? 
weight, the buttresses ought to be in the form of reversed arches. 

In buttresses of this kind, as likewise in broad areas resting on 
a very yielding soil, since as much danger is to be apprehended 
from their breaking by their own weight as from any other cause, 
it must he carefuUy guarded against. Something may be done 
for this ptirpose by ramming the earth around the Structure wilii 
a heavy beetle, when it can be made more compact by this means ; 
er else a part of the upper soil may be removed, and be repiacctl 
by one of a more compact nature which may be rammed in 
layers - 

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I the maimor of pre- 
las ^viill ftqm yielJiiiS 

T c fol 'v n tl d 1 e e ti cv can be resoitcd to, and 
eie th cl a a t it Btn ct re vill justify tlie expense, have 
been found to offer the best secmity m the case in question. 

When the bed can be buttressed in front with an embankment., 
a low counter-wall (Fig. 20) may be built parallel to the edge of 
the bed, and some 10 or 12 feet from it ; between ihis wall and 
the bed a reversed arch connecting the two miy be built, and a 
Biucharge of earth of a compact chiiacttr and well Tammed, may 
be placed against die counter wall to net by its> counter pressure 
against the lateral prcssuie upon the bed 

.id to the wall 
Bveraeu atoh, 
a secupu orEdEfaiiiiiig wall._ 

of embanktnenl d, 
aeclion of rerereed arch. 

ftom which couutei' preesum 

When the bed cannot be buttressed in front, as in quay walls, 
■t grillage and platform supported on p 'cs (Fig 21) maybe biiill 
to the rear from the back ot the wall, for the purpose of support- 
Hig the embankment against tlie back of tlie wall, and preventing 
the effect which its pressure on the subsoil might have in thrust 
lug forward the bed of the foundation. 

In adcliLion to these means, land ties of iron wili give great ad 

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ditional security, when a fived point in rear cf the ivall can lie 
found to attach them firmly. 


Tm ai— RoiTflseiilB liiB manii 
lievina a EislaininE wall i 
luleral action caused bj tlie 
or an embankment on the st 

Y, section of the wall. 
I !i, sertion of embankment. 
T pilas supporting tlie gtillaEe ar 

b, kKye stone formins it firm b 
der the platforms. 

c, piles supporting Uie platform 

394. Foundations in Water. In laying foundations in wate-, 
two difficulties have to be overcome, both of which require great 
resources and care on the part of the engineer. The first is found 
in the means to be used in prepaiing the bed of the foundation ; 
and the second, in securing the bed from the action of the water, 
to ensure the safety of the foundations. The last is, generally, 
the more difficult problem of the two ; for a current of water will 
gradually wear awavj not only every variety of loose soils, but 
also the more tender rocks, such as most varieties of sand-stone, 
and the calcareous and argillaceous rocks, particularly when they 
are stratified, or are of a loose texture. 

395. To prepare the bed of a foundation in stagnant water, 
the only difficulty that presents itself is to exclude t!ie water from 
the area on which the structure is to rest. If the deptli of water 
is not over 4 feet, this is done by surrounding the area witii an 
ordinary water-tight dam of clay, or of some other binding earth. 

, For this purpose, a shallow trench is formed around tlie area, by 
removing the soft, or loose stratum on the bottom ; the foundation 
of the dam is commenced by filling this trench with tlie clay, and 
the dam is made by spreading successive layers of clay about one 
foot ti.iick, and pressing each kyer as it is spread, to render it 
more compact. When the dam 's completed, the water is pumped 
out from the enclosed area, and die bed for the foundation is pre- 
pared as on dry land. 

396. When tlie depth of stagnant water is over 4 feet, and in 
ri-inning water, of any depth, the ordinary dam must be replaced 
by the coffer-dam. This construction consials of two rows of 

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plank, termed sheeting piles, driven jnlo the soil verticali}', form 
rng thus a coffer worlt, between which clay or binding eartli, 
termed the puddling, is filled in, to form a water-tight dam to ex- 
clude the water from the area enclosed. 

The arrangement, construction, and dimensions of coffer dams 
depend on their specific object, the depth of water, and the nature 
of the subsoil on which the colfer-dam rests. 

With regard to the fii-st point, the width of the dam between 
the sheeting piles should be so regulated as to serve as a scaffold- 
ing for the machinery and materials required about the work. 
This is pecuharly requisite where the coffer-dam encloses an isola- 
ted position removed from the shore. The interior space enclosed 
by the dam should have the requisite capacity for receiving the 
bed of the foundations, and such materials and machinery as may 
be required within the dam. 

The width, or thickness of the coffer-dam, by which is under- 
stood the distance between the sheeting piles, should be sufficienl 
not only to be impermeable to water, but to form, by llie weight 
of the puddling, in combination with the resistance of the timbe^ 
work, a wall of aufhcient strength to resist the horizontal pressure 
of the water on ti,e exterior, when the interior space is pumped 
dry. The lesistance offered by tlie weight of the puddling to the 
pressure of the watei can be easdy calculated ; that offered by 
ihe timber ^vork ■mil depend upon the manner in which the 
framing is arranged, and the mean? taken to stai/, or buttress the 
(lam fiom the enclobed space. 

The most -jimple and the usuil consliuclion of a coffer-dam 

b, wale, or siring pieces. 

rf, aheetmg piles. 

e, gaide stung piecee foi 


r apicB. 

driving a rov^ of onhnary straight piles 
o be enclosed, plarin^ their centre lines about 4 

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feet asunder, A second row ia driven parallel to tlie first, the 
respective piles being the same distance apart ; the distance be 
tween the centre lines of the two rows being so regulated as to 
leave the requisite thickness between the sheeting piles for the 
dam. The piles of each row are connected by a horizontal beam 
of square timber, termed a stnng or wale piece, placed a foot or 
two above the highest water line, and notched and bolted to each 
pile. The string pieces of the inner row of piles is placed on the 
side next to the area enclosed, and those of the outer row on the 
outside. Cross beams of square timber connect the string pieces 
of the two rows, upon which they are notched, serving both to 
prevent the rows of piles from spreading from the pressure that 
may be thrown on them, and as a joisting forilie scaffolding. On 
die opposite sides of the rows, interior string pieces are placed, 
about the same level with the exterior, for the purpose of serving 
both as guides and supports for the sheeting piles. The sheeting 
piles being well jointed, are driven in juxtaposition, and against 
the interior string pieces. A third course of striug, or ribbon 
pieces of smaller scantling confine, by means of large spikes, the 
sheeting piles against the interior string pieces. 

As has been stated, the thickness of the dam and the dimen- 
sions of the tin.ber of which the coffer work is made, will depend 
upon the pressure due to the head of water, when the interior 
space is pumped dry. For extraordinary depths, tlie engineer 
would not act prudently were he to neglect to verify by calcula- 
tion the equilibrium between the pressure and resistance ; but for 
ordinary depths under 10 feet, a rule followed is to make the 
thickness of the dam 10 feet ; and for depths over 10 feet to give 
an additional thickness of one foot for every additional depth of 
three feet. This rule will give every security against filtrations 
through the body of the dam, but it might not give sufiicient 
strength unless the scantling of the coffer work were suitably in- 
creased in dimensions. 

In very deep tidal water, coffer-danis have been made in off- 
sets, by using three rows of sheeting piles for the purpose of 
giving greater thickness to the dam below the low-water l.evel. 
In such cases strong square piles closely jointed and tongued and 
grooved, should be used in place of the ordinary sheeting piles. 

Besides providing against the pressure of the head of water, 
suitable dimensions must be given to the sheeting piles, in order 
that they may sustain the pressure aiising from the puddling when 
ihe interior space is emptied of water. This pressure against the 
interior sheeting piles may be farther increased by that of tl.e ex 
tenor water upon the exterior sheeting piles, should the pressure 
of the latter be greater than the former. To provide nsore se- 
curely against the effect of lhcse pressures, intermediate string 


pieces may be jjlaced against the interior row of piles tefore tlis 
sheeting piles are driven ; and the opposite sides of the dam on 
the interior may be buttressed by cross pieces reaching across the 
top string pieces, and by horizontal beams placed at intermediate 
points between the top and bottom of the dam. 

The main inconvenience met with in coffer-dams arises from 
llie difficulty of preventing leakage under the dam. In all cases 
the piles must be driven into a firm stratum, and tlie sheeting 
piles should equally have a firm footing in a tenacious compact 
sub-stratum. When an excavation is requisite on t!ie interior, to 
uncover the subsoil on which the bed of the foundation is to be 
laid, the sheeting piles should be driven at least as deep as this 
point, and somewhat betow it if the resistance offered to the 
driving does not prevent it. 

The puddling should be formed of a mixture of tenacious clay 
and sand, as this mixture settles better than pure clay alone. 
Before placing the puddling, all the soft mud and loose soil be- 
tween the sheeting piles should be carefuJly extracted ; the pud- 
dling should be placed in and compressed in layers, care being 
taken to agitate the water as little as practicable. 

With requisite care coffer-dams may be used for foundations in 
any depth of water, prov ded a water t ght bottoming can be found 
for the puddling. Sandy bottoms offer the greatest difficulty in 
this respect, and when tie leplh of water is over 5 feet, extraor- 
dinary precautions are e^ ste to j event leakage under the 

When the depth of ater s over 10 feet, particularly where 
the bottom is composed of suveral feet of soft mud, or of loose 
soil, beiow which it will be necessary to excavate to obtain a firm 
stratum for the bed of the foundation, additional precautions will 
be requisite to give sufficient support to the interior sheeting piles 
against the pressure of the puddling, to provide against lealtage 
under the puddhng, and to strengthen the dam against the pres- 
sure of the exterior water, when the interior space is pumped dry 
and excavated. The best means for these ends, when the local- 
ity will admit of their apphcation, is to form the exterior of the 
dam, as has already been described, by using piles and sheeting 
piles, giving to the latter additional points of support, by interme- 
diate string pieces between the one at top and the bottom of the 
water ; and to form a strong framing of timber for' a support to 
the interior sheeting piles, giving to it the dimensions of the area 
to be enclosed. The frame-work (Fig,"23) may be composed of 
upright square beams, placed at suitable distances apart, depend- 
nig on the strengtli required, upon which square string pieces are 
bolted at suitable distances from the top to the bottom, tlie bottom 
string res'jing on tlie surface of the mud. The sliing piece* 



s\:ivmg as supports for the sheeting piles, must be "on Jie sidds of 
the uprights towards the puddhng, and their faces in ll c sama— Keprostntsa 
eeolioii of ihe cof- 
fer-dam iiseil foi 
the Polomue aiiuo 

b, BlKing Kiuare 

e, ^eelius piles. 
d, to[> wale on ai: 

buUreE^ag opposite 


B, intecior. space. 

C, mud, &c. 

D, rock bottom. 

vertical plane. Between each pair of opposite uprights, horizon, 
tal shores may be placed at the points opposite the position of the 
string pieces, to increase the resistance of the dam to the pressure 
of the water ; the top shores extending entirely across the dam, 
and being notched on the top string pieces. The interior shores 
must be so arranged that they can be readily taken out as the 
masonry on the interior is built up, replacing them by other sliores 
resting against the masonry itself. 

397, When the bed of a river presents a rocky surface, or rock 
covered with but a few feet of mud, or loose soil, cases may occur 
in which it will be more economical and equally safe to lay a bed 
of beton without exhausting the water from the area to be built 
on ; enclosing the area, before throwing in the beton, by 3 simple 
coffer work formed of a strong frame work of uprights and hori- 
zontal beams and sheeting piles. The frame work (Fig. 24) in 
this case is composed of uprights connected by string pieces in 
pairs ; each pair is notched and bolted to the uprights, a suiBcJem 
interval being left between them for the insc I on of tf e b! c ^ 
piles. To secure the frame work to the rock t n y be e 
quisite to drill holes in the rock to rece e the foot of eicl \ 
riglit. The holes may be drilled by means of a long I a 
termed & jumper, which is used for this purpose or else t! e o 
dinary diving bell may be employed. Thia mad e s ve y c 
viceable in all similar constructions where an examination of work 
under water is requisite, or in cases where it is necessary to la) 

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masom^y under water. The frame work is put together mi land, 
floated to its position, and settled upon tl« rock; the sheetinj 

Fig. 34— Represenla a coffer work for confiuiii} 

A, aeclion of coffer work aiid be' 

B, plan of coffer work, 
a, a', Eguare uprighta oc — 

bolted lo them in pairs. 
c, <!, sheeting pUes inserted between the bcama b, a ai 
"' " uprights 0, -' 

nnected by horizontal beams b 

d, d; i 


to Bulea of colfei notk 

piles are then driven into close contact wilii the surface of the 

398. The convenience and economy resulting from the use of 
beton for the beds of structures raised in water, have led General 
Treussart to propose a' plan for laying beds of this material, and 
then to take advantage of their strength and impermeability to con- 
struct a coffer-dam upon them, in order to carry on the super- 
structure with more care. .To effect this, the space to be occupied 
by the bed (Fig- 25) is first enclosed by square piles, driven in 
juxtaposition and secured at lop by a string piece. The mud and 
loose soil are then scooped from the enclosed area to the ffrm soil 
on which the bed of beton is to be laid. The bed of briton is nexi 
iaid with the usual precautions, and while it is still soft a second 
rtw of square piles is driven into it, also in juxtaposition, and a 
a suitable distance from the first for the thickness of the dam 

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fol'ndati:ns. 133 

hese are also secured at top by a siring piece. Cross pieces aro 

I IT i —Repreaenis a ceclion of Gen 

il !ft«iisaBrt's dam. 

(lolche ! upon llicstrms; pieces, to "ii-Lurc ihc rows of piles and form 
a scaffolding. An oidnury puddling i-. placed in between tlie rows 
df piles, and the interior space is pumped dry. 

Should the soil under tlie bed of beton be permeable, ihe pros ■ 
sure of the water on the base of the bed may be sufficient to raise 
the bed and the dam upon it, when the water is taken from the 
interior space, A proper calculation will show whether this dan- 
ger is to be apprehended, and should it be, a provisional weight 
must be placed on the dam, or the bed of beton, before exhaust- 
ing the interior, 

399. When the depth of water is great, or when, from tlie 
permeability of the soil at the bottom, it is difficult to prevent 
leakage, a coffer-dam may be a less economical method of laying 
foundations than the caisson. The caisson (Fig. 36) is a strong 
water-tight vessel having a bottom of solid heavy timber, and 
vertical sides so an'anged that they can be readily detached from 
the bottom. The following is the usual arrangement of the cais- 
son, it, like the coffer-dam, being subject to changes to suit it to 
the locality. The bottom of the caisson, serving as a platform 
for the foundation course of the masonry, is made level and of 
heavy timber laid in juxtaposition, the ends of the beams being 
confined by tenons and screw-bolts to longitudinal capping pieces 
of larger dimensions. The sides of the Box are usually vertical. 
The sides are formed of upright pieces of scantling covered with 
Ibick plank, the seams being carefully calked to make the cais- 
son water-tight. The lower ends of llie uprights are inserted 
into shallow mortises made in tlie capping, Tlie arrangemeiu 

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for detacliing llie sides, is eiFecled in tlie following r 
Strong liooks of wioiight iron arc fixed to the bottom of iha 










t— „- -4 

acaiEaoa. The boatds m 
" repreaenfed b 

[1 at the sides of the cappinR piece, corresponding to the 
pouits wheie the uprights of the sides aie inserted into tliis piece 
Pieces ot strong scanlhng arc laid across the top of the caisson, 
resting on the opposite uprights, upon ■which they are notched. 
These cross pieces project beyond the sides, and the projecting 
parts are perforated by an auger-hole, large enough to receive a 
bolt of two inches in diameter. The object of these cross pieces , 
is twofold ; the first is to buttress the sides of the caisson at top 
against the exterior pressure of the water; and the second is to 
serve as a point of support for a long bolt, or rod of iron, with an 
eye at the lower end, into which the hook on the capping piece 
is inserted, and a screw at top, to which a nut, or female screw 
is fitted, and which, resting on the cross pieces as a point of sup- 
port, draws the bolt tight, and, in that way, attaches the sides 
and bottom of the caisson firmly together. 

A bed is prepared to receive the bottom of the caisson, by lev- 
elling the soil on which the structure is to rest, if it be of a suit- 
" ' d a 1 f 1 byd 

h pp mi 

1 Tl h d 

able d 
large p 1 

the fir 
on a le 

over i 
should b 


I Iding g 


f h 



Id b 


m 1 

d 1 


d f 

r, 1 


11 1 

of the caisson, for the purpose of filling it witli water at pier 

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By means of ihJs gate, the caisson can be filieil and grounded, 
and, by closing the gate and pumping out the water; it can be hei 

After the caisson is settled on its bed, and the masorry of the 
Btnicture is raised above the surface of the water, the sides are 
detached, by first unscrewing the nnts and detacliing tlie rods 
and then taking off the top cross pieces. By first filhng the cais- 
son with water, this operation of detaching the sides can be more 
easily perfonned. 

400. To adjust the piles before they are driven, and to prevent 
them from spreading outward by tlie operation of drivhig, a strong 
grating of heavy timber, formed by notching cross and longitudi- 
nal pieces on each oUier, and fastening them firmly together, may 
be resorted to. This grating is arranged in a similar manner to 
a grillage ; only the square compartments, between the cross and 
Btring pieces, are larger, so that they may enclose an area for 4 
or 9 piles ; and, instead of a single row of cross pieces, the 
grating is made with a double row, one at top, the other at the 
bottom, embracing the string pieces on which they are notched. 

The grating feed in its position at any depth under 
water, by a few provisional piles, to which it can be attached. 

401. Where the area occupied by a structure is very consider- 
able, and the depth of water great, the methods which have thus 
far been Cjtplained cannot be used. In such cases, a firm bed 
is made for the structure, bv forming an artificial island of loose 
heavy blocks of stone, which are spread over the area, and receive 
a batter of from one perpendicular to one base, to one perpen- 
dicular and six base, according to the exposure of the bed to the 
effects of waves. This bed is raised several feet above the sur- 
face of the water, according to the nature of the structure, and 
the foundation is commenced upon it. 

402. It is important to observe, that, where sucli heavy masses 
are laid upon an untried soil, the structure should not be com- 
menced before the bed appears entirely to have settled ; nor even 
then, if there be any danger of further settling taking place from 
tlie additional weight of the structure. Should any doubts arise 
on this point, the bed should be loaded with a provisional weight, 
somewhat greater than that of the contemplated structure, and 
this weight may be gradually removed, if^ composed of other 
materials than those required Jor the structure, as the work pro- 

403, To give perfect security to foundations in running water, 
(lie soil around the bed must be protected to some extent from* 
tlie action of the current. The most ordinary method of effect- 
ing this, is by throwing in loose masses of broken stone of suffi- 
cient size to resist the force of the current. This method will 

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give all required security, wliere the soil is not of a shifling cris 
racter, liiie sand and gravel. 'I'o secure a soil of this last nature, 
it will, ill some cases, be necessary to scoop out the bottom around 
the bed to a depth of from 3 to 6 feet, and to fill this excavated 
part with beton, the surface of which may be protected from the 
wear arising from the action of the pebbles carried over it by the 
current, by covering it with broad flat flagging stones. 

404. When the bottom is composed of soft mud to any great 
depth, it may be protected by enclosing the area with sheeting 
piles, and then, filling in the enclosed space with fragments ol 
loose stone. If the mud is very soft, it would be advisable, in 
the first place, to cover the area with a grillage, or with a layer 
of brushwood kid compactly, to serve as a bed for the loose 
stone, and thus form a more stable and solid mass, 


405. Under this head will be comprised whatever relates to the 
manner of determining llie forms and dimensions of the most im- 
poitant elementary components of structures of masonry, together 
with the practical details of their construction. 

406. Foundation Courses. As the object of the foundations is 
to give greater stability to the structure by diffusing its weight 
over a broad surface, ttieir breadth, or spread, should be propor- 
tioned both to the weight of the structure and to tlie resistance 
offered by the subsoil. In a perfectly unyielding soil, like hard 
rock, there would be no increase of stabihty by augmenting the 
base of the structure beyond what would be strictly necessary to 
its stability in a lateral direction ; whereas in a very compressible 
soil, like soft mud, it would be necessary to make the base of the 
foundation very broad, so that by diffusing the weight over a great 
surface, the subsoil may offer sufficient resistance, and any un- 
equal settling be obviated. 

407. The tliickness of the foundation course will depend on 
[he spread ; the base is made broader than the top from motives 
of ccononi)'. This diminution of the volume (Fig- 37) is made 

Tig. 27— Seclion of fo 

either in steps, termed offsets, or else by giving a uniform battel 
from the base to the top. The latter method is now generallj 



used ; '.t presents cqiial stability with Uie former wiili a smallei 

"Wlicn tlie foundation has to resist only a vertical pressure, ar 
tifiual batter is given to it on each side ; but if it has to resist also 
a lateral effort, the spread should be greater on the side opposea 
to this effort, in order to resist its tendency, which would be to 
cause a yielding on that side. 

408. The bottom course of the fouftdations is usually formed 
of the largest sized blocks, roughly dressed off with the hammer ; 
but if the bed is compressible, or the surfaces of the blocks are 
winding, it is preferable to use blocks of a small size for the bot- 
tom course ; because these small blocks can be firmly settled, by 
means of a heavy beetle, into close contact with the bed, ■which 
camiot be done with large sized blocks, particularly if their undeT 
surface is not perfectly plane. The next course above the bottoiij 
one should be of large blocks, to bind in a firm manner the smaller 
blocks of the bottom course, and to diffuse the weight more uni 
formly over them. 

409. When a foundation for a structure rests on isolated sup- 
ports, like tlie pillars, or columns of an edifice, an inverf.ed or 
counter-arch, (Fig. 28,) should connect the top course of tho 
foundation under the base of each isolated support, so that the 
pressure on any two adjacent ones may be distributed over the 
bed of the foundation in the interval between them. This precau- 
tion is obviouslv necessary only in compressible soils. In, incom 
pressible soils it would be alone requisite to carry up the courses 
immediately below each support with great care, to present a 
Btable bed for the base of tlie suppoit. 

levelled arcli 

A, reveiwd arch. 

B, vertical aii|iporta. 

The re^ rsed arch is "ilso used to gHC greater breadth to the 
foundations of 1 wall witii counterforts and in cases where an 
upward pressure from water or a semi fiuii soil requires to bo 
counteiacted In the foimei case the leiersed arclies are turned 
under tlie counterfirts m the lattei they foim the points of su[i- 
poit of the walls of the structure 

410. The angles of the foundations should be formed of tlia 

most massive blocks. The courses should be carried up uni 


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fbrmlv tliroiigliout the foundation, to p.-cYcnt iinequ^ lettlirg if 
th(! mass. 

Tlie stones of ihe top course of the foundation slioul 1 be sniV' 
cienlly large to allow toe course of the siiperstmcturc next abu- 
to rest on the exterior stones of the top course, 

411. Hydraulic mortar ehould be used for the foundations 
and the upper courses of the structure should not be commenC'SC 
unui the mortar has partially set throughout ihe entire found ■• 

413. Component parts of Structures of Mosonrij. These m). ' 
be divided into several classes, according to die efforts they su^ 
tain ; their forms and dimensions depending on these efforts. 

1st, Those which sustain only their own weight, and are rk, 
liable to any cross strain upon the blocks of which they ar 
formed, as tfie walls of enclosures. 

2d. Those which, besides their own weight, sustain a vortica 
pressure arising from a weight borne by them, as the walls of ed.' 
fices, columns, the piers of arches, &c. 

3d. Those which sustain lateral pressures, and cross strair 
upon tlie blocks, arising from the action of earth, water, frames 
or arches. 

4th. Those which sustain a vertical upward, or downward 
pressure, and a cross strain, as areas, lintels, &c. 

5th. Those which transfer the pressure they directly receive 
to lateral points of support, as arches. 

413. Walls of Enclosures. Walls for these purposes may te 
built of brick, rubble, or dry stone. 

Brick walls are usually built vertically upon the two faces ; 
their thickness cannot be less than that of one brick. A wall of 
one brick and a half thick will serve for any length, provided the 
height be not over 15 or 20 feet. 

Rubble stone walls should never receive a tliickness less than 
18 inches when the two iaces are vertical. Rondelet, in his work 
VArt de B&tir, lays down a nde tiiat the mean thickness of both 
nibble and brick walls should be yV of their height. 

Dry stone walls should not receive a less thickness than two 
feet. When their height exceeds 12 feet, their mean thickness 
should be I of the height. 

Stone walls are usually built with sloping faces. The batter 
should not be greater, when the stones are cemented with mor- 
tar, than one base to six perpendicular, in order that the rain may 
run rapidly from the surface, and that tlic wall be not too muth 
exposed to decay from the germination of seeds which may lodge 
in the joints. 

The batter s arranged either by building the wall in offsets 
from top to bottom, or by a uniform surface. In cither case, the 



thickness of llie wall at top should not be less iJian :'roni 8 to 12 

When a wall is built with an equal batter on each face, and ihe 
thickness at the top and the mean thickness are fixed, ike base of 
Ike wall, or its thickness at the bottom, will be found by subtract- 
ing tke thickness at top from twice ilm mean thickness. This 
rule evidently makes me batter of the wall depend npon the two 
preceding dimensions. 

The mean thickness of long walls may he advantageously 
diminished by placing counterforts, or buttresses, upon each face 
at equal distances along the hne of tlie wall. These are spurs 
of masonry projecting some length from the wall, and are iinnly 
connected with it by a suitable bond. Tlie horizontal section of 
tlie counterforts may be rectangular ; their height should be the 
game as that of the wall. 

In rubble wall the counterforts may be made of hamraergd, or 
cut stone. In addition to this means of strengthening walls,, hori- 
zontal courses, or chains of dressed stone may be advantageously 
used from distance to distance, from the bottom of the wall up- 

414. Vertical Supports. These consist of walls, columns, or 
pillars, according to circumstances. The dimensions of the 
courses of masoniy which compose the supports should be regu- 
lated by the weight borne. If, as in the walls of edifices, the 
resultant of the efforts sustained by the wall should not be verti- 
cal, it must not intersect the base of the wall so near the outer 
edge, that the stone forming the lowest course would be in danger 
of being crushed. 

In broad enclosed spaces covered at top, the dimensions of the 
wall may be calculated as in the case of ordinary enclosures, and 
the dimensions thus obtained be increased in proportion to the 
weight to be borne. 

Cross walls between the exterior walls, as the partition walls 
of edifices, should be regarded as counterforts which strengthen 
the main walls. 

415. Areas. The term area is applied to a mass of masonry, 
usually of a uniform thickness, laid over the ground enclosed by 
the foundations of walls. It seldom happens lliat areas have an 
upward pressure to sustain. Whenever this occurs, as in Uie 
case of the bottoms of cellars in communication witli a head of 
water which causes an upward pressure, the thickness and ar- 
rangement of tlie area should be regulated to resist this pressure. 
When the pressure is considerable, an area of uniform thickness 
may not be sufficiently strong to ensure safety ; in this case an 
iTiveyted arch must be used. 

416. Retaining, or Sustaining Walh. These terms are ap 



pliea lO wall vl cl us d a la e 1 pressure from an emoank 
menf, or a 1 ad of a e 

417. Rcl ng alls n ay J ell by sliding cilher along ihe 
base of tiic fou da n cour es o along one of the horizontal 
ioims, or by ro to abuut tl e exterior edge of some one of Vlie 
horizoalal jou ts 

418. 'The detem it of tl e form and dimensions of a re 
taining wall for a enb nkmen of earth is a problem of consider- 
able intricacy a d tl e n a i emit al solutions which have been 
given of it have genera y been confined to particular cases, for 
which approximate resuits alone have been obtained ; these, how- 
ever, present sufficient accuracy for all practical purposes within 
the hmits to which the solutions are apphcable. Among the many 
solutions of this problem,' those given oy M. Poncelet of the Corps 
of French Military Engineers, m a Memoir on tliis subject, pub- 
lished in tlic Memorial de VOfficier du Genie, No. 10, present 
a degree of research and completeness which peculiarly charac- 
terize all the writings of this gentleman, and have given to his 
productions a claim to the fullest confidence of practical men. 

The following formula, applicable to cases of rotation about the 
exterior edge of the lowest horizontal joint, are taken from the 
memoir above cited. 

Calling H, the height BC (Fig. 29) of a wall of uniform thick- 
ness, tlic face and back being vertical. 

20— Represents a seclion O of a 


h, the mein height CG of t!ie embankment, retained by the wall, 

above the top of the wall. 
, the heim DI, or distance between the foot of tlie embaiikir.eni 

and the outer edge of the top of the wall. 
«, ihe angle between the line of the natural slope BN of the earlli 

of the cmbinkment and the vertical BG. 
/= cot a, the co-efficient of friction of the earlli of the embank 


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ta, the weight of a cubic foot of the earth, 
w'j tlie weight of a cubic foot of the masonry of the wall. 
h, the base AB, or thickness of the wall at bottom 
Then, __ 

6^0,74 tan. iaV^(/i + 1.126H) + 0i0438;z-0.5Gc tan. R (4 

-0.6 5)4-0.25). 

The above formula gives the value of the base of a wall with 
vertical faces, within a near degree of approximation to the true 
result, only when the values of the quantities which enter into it 
are confined within certain limits. These limits are as follows : 
for Jt, between and H ; c, between and ^H ; /, between 0.6 
and 1.4, which correspond to values of a of 70° and 35°, hein^ 
in the one case the angle wliich the line of the natural slope of 
very fine dry sand assumes, and in the other of heavy clayey 
earth ; and for w, between w', and jw'. Besides these limits, 
the formula also rests on the assumption that the excess of stabil- 
ity of the wall over that of a strict equilibrium is represented by 
0.913 ; or, in other words, that the moment of the pressure agains; 
the wall is taken 0.912 greater tlian the moment of strict equi- 
librium between it and toe wall. This excess of stability given 
to the wall supposes an excess of resistance above the pressure 
against it equal to what obtains in the retaining walls of Vauban, 
ibr fortifications which have now stood the test of more than a 
century with security. 

419. Having by the preceding formula calculated the value of 
b for a vertic^l « ill the base b' of another wall, presenting equal 
slabilily, but hi'img a batter on the face, the back being vertical, 

which is the usual form of tlie cross section of retainuig i 
can be calculated from the following notation and formula. 
Calhng (Fig. SO) b' the base of the sjoping wall. 

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(12 rii.vSONRY. 

n = -:p~„ the baiter, or ratio of tiie base of ilic skpe to ihe pci 
Jjd ^ ' 

peudicnlar, or height of the ivail. 

420. Witli regard to sliding either on the base of the founda 
lion courses, or on tlie bed of any of the horizontal joints of the 
wall, M. Poncelet shows, in the memoir cited, by a comparison 
of the results obtained from calculations made under the suppo- 
sitions both of rotation and sliding, that no danger need be appre- 
hended from the latter, when the dimensions are calculated to 
conform to the former, so long as the limits of h are taken between 
and 4H ; particularly if the precaution be taken to allow the 
mortar of the masonry to set firmly before forming the embank- 
ment behind the wall. 

421. Form of Section of Retaining Walls. Retaining walls 
have been bi dt with a variety of forms of cross section. The more 
dsinl form of cross section is that in wliich the back of the wali 
is bmlt 1 ertically -md the face with a batter varying between one 
case to Bixpcipendiculai and one base to twenty-four perpen- 
dicular The foimer limit having been adopted, for the reasons 
akeady assigned to secure the joints from the effects of weather ; 
and the latter lec-iuse i will having a face more nearly veriical, 
is liable m t me to \ eld to the effects of the pressure, and lean 
forw aid 

422 The mo=t idvailageous form of cross section for econo- 
my oi miso rj a tl e it, (Fig. 31) termed a leaning retaining 

aco Al) anJ tlio bacC [MJ c 

al Tl c counter slope, or reversed batter of tlic back of the 
wil! si ould not be leas liian six perpendicular to one base. In 
th s case strength requires that the perpendicular let fall from the 
ce t e of gravity of the sectioFi upon the base, should fall so far 
vtl ll nnev edge of the base, that the stone of die bottom 

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riON op MASOMKir, 

timree of the foundation miy present sufficient surface to bear 
the pressure upon it 

423 Walls with a curved batter (Fig. 32) both upon the faco 
and bacK have been used in England, by some enginceis, for 
'juays Theypreaent no peculiar advantages in strength over 

32— Represeiila 

n elevation it of ilia 

wails witl pla e facets ind backs, and require paiticuiar care in 
11 ging the loud ani htting the stores or bricks of the face. 
434. Measures for increasing the Strength of Retaining 
Walls. These consist in the addilion of counterforts, in the use 
of relieving arches, and in the modes of forming the embank- 

425. Counterforts give additional strength to a retaining wall 
J!i several ways. By dividing the whole line of the wall into 
shorter lengths between each pair of counterforts, they prevent 
the horizontal courses of the wall from yielding to the pressure 
of the earth, and bulging outward between the extremities of the 
wails ; by receiving the pressure of the earth on the back of the 
counterfort, instead of on the corresponding portion of the back of 
the wall, its effect in producing rotation about the exterior foot of 
the wall is diminished ; the sides of the counterforts acting as 
abutments to the mass of earth between them may, in the case of 
sand, or like soil, cause the portion of the wall between tiie coun- 
terforts to be relieved from a part of the pressure of the earth 
oehind ilj owing to the manner in which the particles of sand be- 
come buttressed against each other when confined laterally, and 
offer a resistance to pressure, 

426. 1'iie horizontal section of counterforts may be either 
rectangular, or trapezoidal. Wher placed against the back of a 
wall, the rectangular form offers the greater stability in the case 
of rotation, and is more economical in construction ; the trape 

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Eoidal form giies a broader and therefore a finner connection be- 
twei'Ji the wall and counterfort than the rectangular, a point oi 
some consideration where, from the character of the inaf erials, tlic 
strength of this connection must mainly depend upon the strcngtii 
of the mortar used for the masonry. 

427 . Counterforts have been chiefly used by military engineera 
for the retaining walls of fortifications, termed rev^tements. In 
regulating their form and dimensions, the practice of Vauban has 
been generally followed, which is to rt.ake the horizontal section 
of the counterfort trapezoidal, making the height of the trapezoia 
ef, (Fig. 33,) which corresponds to the length of the counterfort, 
two tenths of the height of the loall added to two feet, the base of 
the trapezoid ub corresponding to the junction of the counterfort 
and back of the ^val! o}ie tenth of the height added to two feet, 
and the side cd which corresponds to the back of the counterfort 
equal o two thuds of the base ab. The counterforts are placed 

from 15 to 18 feet from centre to cciUrii along the back of the 
wall, according to tlie strength required. 

428. In adding counterfort;s to walls, the practice liaa generallv 
heen to regard them only as giving additional stability to the wall, 
and not as a means of diminishing its volume of masonry of 
which the addition of the counterforts ought to admit. Considered 
in this last point of view, the problem for determining both the 
suitable dimensions of the counterforts and the thickness of the 
corresponding wall, is (me of very considerable mathcmalical 
difficulty, who5C Boiu!io-i must vepohc upon assuraplions made a» 

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iCTiON OF MAso_viiy. 

CO tlie manner in wliich llie portions of the wall between the 
counterforts would be likely to yield to llic pressure upon tlicm, 
the support which they receive from tlie two counterforts at Oieir 
extremities, and the stability which the counterforts add to the 
flntire system in preventing rotation. 

429. Relieving Arches are so termed from their preventing a 
portion of the enibanlinienl from resting against the back of the 
wall, and thus relieving it from a part of the pressure. They 
consist (Fig. 34) of one or more tiers of brick arclies built upon 
counterforts, which act as the piers of the arches. 


yaUon N of a wall aiiJ relieving arches ii 
tlireo tieis. 
A, section of the wall. 

"ons ol' the arches through tlioiir 

r elcvatioHS of coimteiToila Berl- 

in irranging a combmation of relJeYiug arches and their piers, 
the Ktter liku ordinary counterforts, are placed about 18 feet 
apait between their centime lines ; their length should be so regu- 
lated that the earth behind them resting on the arches, and falling 
under them with the natural slope, shall not reach the wall be- 
tween thuaich and the foot of the back of the wall below the arch. 
The thickness of the arches, as well as that of the counterfoils, 
will depend upon the weight which the arches sustain. The 
dimensions of the wall will be regulated by the decreased pres 
sure against it caused by the action of the arches, and the point 
at which this pressure acts, 

430. Whenever it becomes necessaiy to form the embankment 
before the mortar of iJie retaining wall has had time to set firmly, 
various expedients may be employed to relieve the wall from the 
pressure which the embankment, if formed of loose earth, would 
throw upon it The portion of the embankment next to tlie wal! 
may he of a compact binding earth placed in layers inclining 
downward from the back of the wall, and well rammed ; or of a 
stiif mortal made either of clay, or sand, with about ^V^ ™ hxi]k 
of lime Instead of bringing the embankment directly against 
llie back of the wall, dry stone, or fascines may be laid in to a 
suitable depth bark from the wall for the same purpose. The 
precaution, however, of allowing the mortar to set firmly before 
orming the embankment, shoulaneverbe omitted except in casca 
of e'streme ujjpiicy, and then the Vind of the masonry should be 

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arranged wilh peculiar care, to prevent disjunction iiloi.g any ol 
the horizontal joints. 

431. Walla built to sustain a pressure of wtter should be regu- 
lated in form and dimensions like the retaining walls of embjmk- 
ments. The problem in this case is one of less difficulty than 
in the olher, from the greater simplicity of the mathematical 
formula for the pressure of water. The buoyant effort of the 
water must be taken into account in this calculation, whenever the 
masonrj- is so placed as to be partially immersed in the water. 

432. Heavy w^alls, and even those of ordinary dimensions, 
when exposed to moisture, should be laid in hydraulic mortar. 
Groat has been tried in laying heavy rubble walls, but with de- 
cided want of success, the successive drenchings of the stone 
causing the sand to separate from the lime, leaving when dry a 
weak porous mortar. When the stone is laid in full mortar, grout 
may be used with advantage over each course, to fill any void? 
left in the mass. 

433. Beton has frequently been used as a filling between ths 
back and facing of water-tight walls ; it presents no advantage 
over walls of cut, or rubble stone laid in hydraulic mortar, and 
causes unequal settling in the parts, unless great care is taken in 
the construction 

434. When a weight, arising from a mass of masonry or earth, 
rests upon two or more isolated supports, that portion of it which 
is distributed over the space, or hearing between any two of the 
supports, may be borne by a block of stone, termed a lintel, laid 
horizontally upon the supports, by a combination of blocks termed 
A plate-bande, so arranged as to resist, without disjunction, the 
pressure upon them ; or by an arch. 

435. Lintel. Owing to the slight resistance of stone to a cross 
strain, and to shocks, lintels of ordinary dimensions cannot be 
used alone with safety, for bearings over six feet. Por wider 
bearings, a slight brick arch is thrown across the bearing above 
the hntel, and thus relieves it from the pressm-e of the parts 

436. Plate-bande. The plate-bande is a combination of blocks 
cut in the form of truncated wedges. From tlie form of the 
blocks, the pressure thrown upon them causes a lateral pressure 
which must, be sustained either by the supports, or by some olher 
arrangement, (Fig. 35.) 

The plate-bande shoukl be used only for narrow hearings, as 
the upper edges of the blocks at the acute angles are liable to 
Bplinter from the pressure. If the bearing exceeds 10 feet, the 
plate-bande should be relieved from the pressure by a brick arch 
sbove it. Additional nseans of strengthening the plate-bande are 
ometimcs used by forming a broken joint between the blocks, or 

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by a projection made on ihe face of one block to fit iiitc a cor- 
responding mdiTt in lliParljarpnt i!'o 01 livronnectmgtlie blocks 

When, fi ' ■ . :)orts cannot be made suffi- 
ciently stro' j^._ 3ssm'e of the plate-bande, the 

extreme bloclcs must be united by an iron bar, termed a tie, suit- 
ably arranged to keep the blocks from yielding. 

437. Arckes. The arch is a combination of wedge-shaped 
blocks, termed arch stones or voussoirs, truncated towards tiie 
angle of the wedges bj a cnived suiface ^^hich ]s usually nonnal 
to the surfaces of tlie joinf between the blocks This mferior 
surface of the arch i=i termed the mtrado-., or soffit The upper, 
or outer smfacc of the dicli is term^'d the eiUado'!, or biick, 
;Fig. 36.) 

438. The extreme blocks of the arch rest against lateral sup- 
jorts, termed abutments, which sustain both the vertical pressure 
arisiug from the weight of the arch stones, and the weight of 
whatever lies upon them ; also the lateral pressure caused by tlie 
sction of the arch. 

4!)9. In a range, or series "f arches placed side by side, tlia 

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extreme supports arc termed the abutments, the inte:raediate a ip- 
porta which sustain the intermediate arches and the halves of the 
Iwo extreme ones are termed piers. "When tlie size of the arches 
is the same, and their springing lines arc in the same horizontal 
plane, the piers receive no other pressure but that arising from 
the weight of the arches. 

440. Arches are classified, from the form of tlie soiHt, into 
cylindrical, conical, conoidal, warped annular, gi-oined, clois- 
tered, and domes. They are also termed right, oblique, or asltew, 
and rampant, from their direction with respect to a vertical, or 
horizontal plane. 

441, Cylindrical Arch. This is the most usual and the sim- 
plest form of areh. The soffit consists of a portion of a cylindri- 
eal surfaee. When the section of tlie cylinder perpendicular to 
the' axis of the arch, termed a r^g/ii section, cuts from the emfacL. 
a semi-circle, the arch is termed ti full centie areh, when the 
section is an arc less thin a semi-circle, it is termed a segment 
arch; when tlie section gives a semi elhpst, it lu termed an 
elliptical arch, when the section gives % curve resembling a 
semi-ellipse, formed of arcs of circles tmgent to each other, the 
arch is termed an oval, (Fig 37,) or bailet handle, and is called 

centres, tl o arcb of w 1 1< 
t, span of tha curv&. 
B P, 6, a^d R, ccnfres of the w 

a curve of three, Jive, &c, centres, according to the number of 
arcs, which must be odd to obtain a curve symmetrical with 
respect to the vertical line bisecting it ; w)ieti tlie section is lliai 
of iwo arcs of circles intersecting at the middle point of the curve, 
it is termed a pointed, or an obtuse or surhased arch, (Figs. SS 
and 39,) according as the angle between the arcs at their intcr- 
fiectioii is acute, or obtuse. 

A cylindrical arch is denominated a right arch when it is ter- 
minated by two planes, termed the heaih of the arch, perpendicu 

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lar to the axis of tlie arch ; oblique, or askew, when tlie lieada 
are oblique to the axis ; and rampant when the axis of tlie aich 
is cblique to the horizontal plane. 

Fig. 38— Represeiifs tho half of a 

of four cenlree. 
ab, Jialf spun. 

Jnand n, cenlres of the half curve 

■-*. . 

Fig. 39-Represenla the 

Basert curve of four ccml 
ttb, lialf span. 

442. The chord of the curve of right section (see Fig. 36) la 
termed t!io span of the arch, its versed sine the rise of the arch. 
When the heads of the arch are oblique to the axis, the chord of 
the oblique section made by the plane of the heads is termed the 
span of the askew section. The lines of the soffit corresponding 
to the extremities of the span are termed the springing lines of 
the arch ; the top portion, or line of the soffit, is termed the 
crown. The tc » stone of the crown the key stone. The line 
drawn through tlie middle point of the span at the extremities of 
ihe arch, is termed the axis of the arch,* 

443. The form of right section will depend upon the purposes 
ivnich the arch is to serve, the locality, and the style of architec- 
ture employed. When tlie rise is less than half the span, t!io 
arch is weaker llian in either the full centre, or where lhe rise ii 

« See Note C, Aj/pnuiil. 



greater than half the span. The methods of t.escribiiig the varioui 
curves of right section will be explained in the Appenilix. 

444. The same general principle is followed in aiTanging tlit 
joints and bond of the masoiuy of arches, as in other structures 
of citt stone. The surfaces of"^the joints should be normal to the 
surface of the soffit, and the surfaces of any two systems of joints 
should be normal to each other at their lines of intersection. These 
conditions, with respect to the joints, will be satisfied by tracing 
upon the soffit its lines of least and greatest curvature, and taking 
the edges of one series of joints to correspond with one of these 
systems of lines, and the edges of the other series with the other 
system, the surfaces of the joints being formed by the surfaces 
normal to the soffit along the respective lines in question. When- 
ever the surface of the soffit belongs to any of the families ot 
geometrical surfaces, the joints will be thus either plane, or de- 
velopable surfaces. In the cylindrical arch, for example, the 
edges of one series of joints will correspond to the elements of 
the cylindrical surface, while those of the other will correspond 
to the curves of right section, the former answering to the lino 
of least, and the latter of greatest curvature. The surfaces of 
the joints will all be plane surfaces, and, being normal to the 
soffit along the lines in question,- will be normal also to each 

445. In full centre and segment arches, the voussoirs are 
usually made of the same breadth, estimated along the curve of 
right section. The planes of the joints of each course of vons 
soirs between the heads of the arch are made continuous, (sea 
Fig. 36,) each of these courses being termed a string course, and 
their joints coursing joints , The planes of the joints along the 
curves of right section are not continuous, but break joints ; the 
stones which correspond to two consecutive series of these joints 
being termed a ring cmirse, and its joints heading joints. By 
this combination of the ring and string courses, the fitting of the 
blocks, the settling of the courses, and the bond are arranged in 
the best manner. 

446. In the other forms of right section of cylindrical arches, 
it may not, in many cases, be practicable to give the voussoirs 
the same breadth, owing to the variable curvature of the right sec 
tioji; but the same arrangement is followed for the ring and string 

447. In oblique cylindrical ai^hes, when the obliquity is bul 
slight, no change will be required in the arrangement of the 
courses and joints ; but when the angle between the heads and 
the axia is considerably less than a right angle, the ring courses 
at the extremities of the arch would have what is termed a false 
bearing, that is, the pressure upon their coursing joints would 

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nJt be transmitted in the direction of the pressure to the fixed 
litteral supports, and therefore these pprtions of the anJi would 
be insecure. To obviate these defects, as well as the unetiual 
bearing upon the lateral supports in such case, arrangements of 
the coursing and heading joints have been devised, by v?hich a 
better bond is obtained, and the total pressure from the voussoira 
thrown upon the abutments. 

One method for this purpose has been mostly used in England, 
and consists in placing the edges of the heading and coursing 
joints along spira. lines of the cylindrical soffit which intersect 
each other at right angles. The directing spirals for the heading 
joints (Fig. 40) being taken parallel to the one which is drawn con. 

nectmg the c\lrcmc points of the askew curve of the head ; tliose 
for the coursmg bemg traced perpendicular to the former. The 
joints being normal to the soffit along the spirals, will be helicoi- 
dal surfaces. This method palhatea only to some extent the 
weakness of the bond in tlie courses near the heads, and giving 
a considerable dip to the coursing joints at the extremities of the 
abutments which make an acute angle with their faces, it presents 
here also a weak point. It possesses an important advantage, 
however, in permitting the soffit ends of the string courses to be 
of equal breadth throughout, and tlierefore allows the method to 
be adapted as well to brick as cut stone. To bring tlie coursing 
joints to correspond exactly with the divisions of the ring courses 
of the heads, it may be necessary, in some cases, to shift the 
spirals of the coursing joints slightly, in malting the drawings for 
the arch. The end blocks of the string courses which rest upon 
the abutment, or else the top course of the abutment, must be 
■niitably cut to correspond to the direction of the heading joints 
and that of the horizontal courses of the abutment. 

448. A second method, in use among the French engineers, 
consists in irking the heading joints plane surfaces and parallel 
to the heads of the arch, and in taldng for the edges of the coursing 
joints (Fig. 41) the trajectories traced on the soffit perijendicular 
to the ed^es of the heading joints. The surfaces of the coursing 

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joints, ar madi, iioninl to the soffit B\ liis plan sj nr, of the 
defects of the former dre iLmedit,d, but t haa tlie dibadvanlage 


head and a nortion 
ol the soffit of an 
obbqDB cjlindiiRBl 
arch with the 
edges of the coiira- 
ing loiiits forming 
timeclorieB at right 
BJialeslo [he edges 
■ lieadiug joints 

the aich. 

of giving in unequal bii--iJtJi to the soffit ends of llie voussoirs, 
ind therefoie is mapphcable to brick arches The cuitcs of the 
trajectone'i ind the cour'<ing jo nts aie of more diflicult construc- 
tion than in the first method 

449, Cyhndrical, groined, and cloistered arches are formed by 
the intersections of two or more cylindrical arches. The span 
of the arches may be different, but the rise is the same in each. 
The axes of the cylinders will be in the same plane, and they may 
intersect under any angle. 

The groined arch (Jig- 42) is formed by removing tl)ose por- 

Slg. 42— liepresenls the plazi of the soffit 
and (he right Beckons M Hud N oT the 
cylinders fonniug a gtoined arch. 

aa, pillaia snpportimi; the arch. 

be, groins of the somt. 

Dni.inn, edges of conialng .joints. 

A, key stone of the two arches formed of 
nne block. 
B, groin etonce of one block below the 
— ■—-; forming ajiart of each arch 

aons of each cylinder which lie under the other and between 
their common curves of intersection ; thus forming a projecting, 
or salient edge on the soffit along these curves. 

The cloistered arch (Fig. 43) is formed by removing those por- 
tions of each cylinder which are above the other and esterior to 
tlieii common intersection, forming thus re-entering angles along 
ihe same lines. 

450. The planes of the joints in both of tliese arches are placed 
in the same manner aa in the simple cylindrical arch. The innra 

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edges of tlie correspond' ng course of voussoirs in eacli arch aro 
placed in the same plane parallel to that of tlie axes of the cvlin- 

43— Represenls a aeclloii M oi Ihe > 
plevaHoii of tlie. Boflit ol' a cloialere 

ders. The portions of tlie so3it in each cylinder, corresponding 
to each course of voussoirs, which form either the groin in the 
one case, or the re-entering angle in the other, are cut from a 
single stone, to present no joint along the common intersection of 
the arches, and to give tlicm a firmer bond. 

451. Conical arches are of rare application. When used, the 
same general principles with respect to the joints and bond apply 
to them; The surfaces of one set of joints will be planes passed 
through the elements of the cone and normal to the soffit ; the 
other will be conical, or other surfaces, likewise normal to the 
soffit and passing through the cmres of least cur\'ature. 

453. When tlie spans at the two ends of an arch are unequal, 
hut the rise is the same, then the soffit of the arch is made of a 
ronoidaJ surface. The curves of right section at the two ends 
may be of any figure, but arfe usually talien from some variety 
of die elliptical, or oval curves. The soffit is formed by moving 
ft hne upon the two curves, and parallel to the plane containing 
their spans. 

nie conoidal arch belongs to t)ie class with warped soffits. A 
cariety of warped surfaces may be used for soffits according to 
circumstances ; tlie joints and the bond depending on the gener- 
ation of the surface. 

453. In arranging the joints in conoidal arches, the heading 
}oints are contained in planes perpendicular to the axis of the 
srch. The coursing joints are also formed of plane surfaces, so 

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arriiiiged lliat the porlioii of ihe joint corresponding ti each blcclt 
is formed by a pJaiie normal to the conoid at tlie midd.e point uf 
the lower edge of the block. In this way the joints of the string 
course will not be furmed of continuous surfaces. To malic 
them so, it wovild be necessary to give tliem the form of warped 
surfaces, which present more difficulty in their mechanical exe- 
cution, and not sufficient advantages over tlie method just ex- 
plained to compensate for having them continuous. 

454. The aniiular arch is formed by revolving the plane of a 
semi-circle, or semi-oval, or other curve, about a line drawn with- 
out the figure and parallel to the rise of ihc irch, (Fig. 44.) One 

aronnd whicli 
the Bection N 
ia tevolyed. 

series of j'oints in tliis arch will be formed by conical surfaces 
passing through the inner edges of the stones which correspond 
to -tlie string courses ; and the other series will be planes passed 
through the axis about which the semi-circle is revolved. This 
last series should break joints with each other. 

455. The soffit of a dome is usually formed by revolving the 
quadrant of one of the usual curves of cylindrical arches ai'ound 
the rise of the curve ; or else by revolving the semi-curve aboul 
the line of the span, and taking the half of the surface thus gen 
crated for the souit of tlie dome. In the first of these cases the 
horizontal section of the dome at the springing line will be a cir- 
cle ; in the second tlie entire curve of die semi-curve by which 
the soffit is generated. The plan of domes may also be of regu- 
ai' polygonal figures . ii- which case the soffit will be a polygoniii- 

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cloistered arcli formed of equal sections of cylinders, (Fig. 45 J 
The joints and the bond are determined in tlie same m'innor as 
in other arches. 


li III ill 

456 The voussoas which form tlie xing course of the heads, 
tn ordm^ry cylmdiicai arches, are usually tenninated by plane 
surfaces a! top and on the sides, for the purpose of connecting 
them with the horizontal courses of the head which lie above and 
on each side of the aich, (Figs, 46 and 47.) This connection 

icting tho 

maybe aiTanged in a variety of ways. The two points to be 
kept in view are, to form a good bond between the voussoirs and 
horizontal courses, and to give a pleasing architectural effect by 
the arrangemenL This connection should always give a sym- 
metrical appearance to the halves of the structure on each side 
of the crown. To effect these several objects it may be neces- 
sary, in cases of oval arches, to make the breadth of tlie voussoirs 
anequal, diminishing usually those near the springing hnes, 
. 457. In small arches the voussoirs near the springing line are 
so cut as to form a part also of the horizontal course, (see Fig, 
40,) forming what is termed an elhoio joint. This plan 'm' objeo 



lionable, botli because there is a waste of material in forming 
a joint of this kind, and the stone is liable to crack when the 
arcli settles. 

458. The forms and dimensions of tlie youssoirs should be de- 
termined both by geometiical drawings and numerical calcula 
tion, whenever the arch is importantj or presents any complication 
of form. The drawings should, in the first place, be made to a 
scale sufficiently large to determine the parts with accuracy, and 
ftom these, pattern drawings giving the parts in their true size 
may be made for the use cf the mason. To make the pattern 
drawings, the side of a vertical wall, or a firm horizontal area 
may be prepared, with a thin coating of mortar, to receive a thin 
smooth coat of plaster of Paris. The drawing may be made on 
this surface in the usual manner, by describing the curve either 
by points from its calculated abscissas and oi-dinates, or, where 
it is formed of circular arcs, by using the ordinary instrument for 
describing such arcs when the centres fall within the limits of the 
prepared surface. In ovals the positions of the extreme radi:. 
should be accurately drawn either from calculation, or construc- 
tion. To construct the intermediate normals, whenever the cen- 
tres of tlie arcs do not fall on the surface, an arc with a chord of 
about one foot, may be set off on each side of the point through 
which the normal is to be drawn, and the chord of the whole arc, 
thus set off, be bisected by a perpendicular. This construction 
will generally give a sufficiently accurate practical result for 
elliptical and other curves of a large size. 

459. The masonry of arches may be either of dressed stone, 
rubble, or briclt. 

In wide spans, particularly for oval and other flat archos, cut 
stone should alone be used. The joints should be dressed with 
extreme accuracy. As the voussoirs have to be supported by a 
framing of timber, termed a centre, untilthe arch is completed, 
and as this structare is liable to yield, both from, the elasticity pf 
the materials and the number of jomta in the frame, an allowance 
for the settling in the arch, arising from these causes, is some- 
times made, in cutting the joints of the voussoirs false, that is, 
not according to the true position of the normal, but from (he 
supposed position the joints will take when the arch has settled 
thoroughly. The object of this is to bring the surfaces of Hie 
joints into perfect contact when the arch has assumed its perma- 
nent state of equilibrium, and tlius prevent the voussoirs from 
hrealdng by unequal pressures on their coursing joints. This 
IS a problem of considerable difficulty, and it will generally bo 
better to cut the joints true, and guard against settling and its 
effects by giving great stiffness to the centres, and by placing be- 
tween the joints of those voussoirs, where the principal n 

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takes place in arches, sheets of lead suitably hamracred lo fit ihe 
joint andyield to any pressure. 

460. Iiie manner of laying the voussoirs demands peculiar 
care, particularly in those which form the heads of liie arch. 
The positions of the inner edges of the voussoirs are determined 
by fixed lines, marked on the abutments, or some other immovea 
ble object, and the calculated distances of the edges from these 
lines. These distances can be readily set off by means of the 
level and plumb-line. The angle of each joint can be fixed by a 
'Quadrant of a circle, connected wilh a plumb-line, on which the 
position of each joint is marked. 

461. Rubble stone is used only for very small arches which 
do not sustain much weight, or as a filling between a network of 
ring and strin^ courses in large arches which sustain only their 
own weight. In each case the blocks of rubble should be rougldy 
dressed with the hammer, and be laid in good hydraulic mortar, 

462. Brick may be used alone, or in combination with cut 
stone, for arches of considerable size. When the thicltness of a 
brick arch exceeds a brick and a half, the bond from ihe soffit 
outward presents some difficulties. If tlie bricks are laid in con 
centric layers, or shells, a continuous joint will be formed parallel 
to the smface of the soffit, which will probably yield wl\eu the 
arch settles, causing the shells to separate, (Fig- 48.) If the 

M repreEentB tho manner 

bricks are laid like ordinary string courses, forming continuous 
joints from the soffit outward, these joints, from the form of the 
bricks, will be vory open at the back, and, from the yielding of 
the mortar, the arch will be liable to injury in settling from ihis 
cause. To obviate both of these defects, the arcli may be built 
partly by the first plan and partly by the second, or as it is termed 
in shells and hlocks. The crown, or key of the arch should be 
laid in a block, increasing the breadth of the block by two bricks 
for each course from the soffit outward. These bricks should ba 



laid in hydraulic cement, and be well wedged willi })ieceH of lliia 
hard slate between the joints. 

463. When a combination of brick and cut stone is used., the 
ring courses of the heads, with some intermediate ring courses, 
the bottom string courses, the key-stone course, and a few inter- 
mediate slrmg courses, are made of cnt stone, (Fig. 49,) tho 

mlc h I ] i c mg filled m with bnck The brick poi 

tions ul the sofiit may, ifnecessary, be thrown wiliiin the stone 
portions, forming plain caissons. 

4:64. The centres of smaU arclies are not removed, or struck 
until the mortar has become bard ; in large ai-ches, the centres 
should not be struck until the whole of the mortar has set firmly. 
In the joints near the springing lines the mortar will have become 
hard, in the ordinary progress of building an arch, before that in 
the higher joints will liave had time to set, unless hydraulic mor- 
tar of a quick set be used. After the centres are struck, the arch 
is allowed to assume its permanent state of equilibrium, before 
any of the superstructure is laid. 

465. When the heads of the arch form a part of an exterior 
surface, as the faces of a wall, or the outer portions of a bridge, 
the voussoirs of the head ring courses are connected with the 
horizontal courses, as has been explained ; the top surface of the 
vouasoira of the intermediate ring courses are usually left in a 
roughly dressed state to receive the courses of masonry termed 
the capping, {see Fig. 49,) which rests upon the arch between 
the walls of the head. Before laying the capping, ihe joints of 
the voussoirs on the back of the arch should be carefully exam- 
ined, ^and, wherever they are found to be open from the settling 
of the arch, they should be filled. up with soft-tempered mortar, 
and by driving in pieces of hard slate. The capping may be va- 
riously formed of rubble, brick, or beton. Where the arches are 
exposed to the filti-ation of rain water, as in those used for bridges, 
and the casemates of fortifications, the capping should be of betou 

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(aid ill layers, and well rammed with ihe usual precaulioiiB for 
obtaining a solid homogeneous mass. 

466. The difficulty of forming water-tight cappings of mason- 
ry has led engineers, withm a few yeara back, to try a coating of 
asphalte upon the surface of beton. The surface of the beton 
capping is made uniform and smooth by ihe trowel, or float, and 
!he mass is allowed to become thoroughly :jy before the asphalte 
is laid, Asphalte is usually laid on in twc layei^. Before apply- 
ing the first, the surface of the beton should be thoroughly 
cleansed of dust, and receive a coating of mineral tar apphed hot 
with a swab. This application of hot mineral tar is said to pre- 
vent the formation of air bubbles in the layers of asphalte which, 
when present, permit the water to percolate tlirough the masonry, 
'i'he first layer of asphalte is laid on in squares, or thin blocks, 
care being taken to form a perfect union between the edges of 
the squares by pouring the hot liquid along them in forramg each 
new one. The surface of the first layer is made uniform, and 
rubbed until it becomes smooth and hard with an ordinary wooden 
float. In laying the second layer, the same precautions are taken 
as for the first, the squares breaking joints with those of the first. 
Fine sand is strewed over the surface of the top layer, and pressed 
into the asphalts before it becomes hard. 

Coverings of asphalte have been used both in Europe and in 
our military structures for some years back with decided success. 
There ha\e been taduies, in some instances, ai'ising in aJl prob- 
ability either from u-mg a bad material, or from some fault of 

4(>7 In a lan^e of aiches, like those of bndges, or casemates, 
the capping of eacli arch i'* shaped with two inclined surfaces, 
hke 1 common roof The bottom of these surfaces, by their 
junction, iorm gutters wheie the water collects, and from which 
It is conveyed oiF in conduits, formed either of iron pipes, or of 
vertical openings made through the masomy of the piers which 
communicate with honzontai covered drains. A small arch of 
sufficient width to admit a man to examine its interior, or a square 
culvert, is formed over the gutter. When the spaces between die 
head walls above the capping is filled in with eartli, a series of 
drains running from the top, or ridge of the cappmg, and leading 
into the main gutter drain, should be formed of brick. Thejy 
may be best made by using dry brick laid flat, and with intervals 
left for the drains, these being covered by other courses of dry 
brick with the joints in some degree open. The earth is filled in 
upon tlie upper course of brides, which should be so laid as to 
form a uniform surface. 

46S. When the space above the capping is not filled in with a 
uolid mass, for the purpose of receiving the 'veight borne by thfl 

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an,] e opea ngs h ougl 1 em o els sy stem of small right 
cv a "10 eda e maybeusGcl A of these methods are 

m use in bridge buddmg for sustaining the roadway, and also in 
roofing arched edifices. They throw less weight upon the abut- 
ments and piers of the arches than would a filling of solid ma- 

4C9. From observations taken on tlie manner in which large 
cjlindrical arches settle, and experiments made on a small scale, 
il appears that in all cases of arches where the rise is equal to 
or less than the half span they yield (Fig. 52) by the crown of 
llie arch falling inward, and ihruating outward the lower portions, 
presenting five joints of rupture, one at the key stone, one on each 
aide of it which limit the portions that fall inward, and one on 
each side near the springing lines which limit tlic parts ihrusl 

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outward. In pointed arcliee, or those in which the rise is greater 

^^ »i ^^"vi ^^'^- '>3-Koptc3Cnt! tho EQonnorin wMohllat nrclies jlolil 

H ^ o,]ointofruptareiitthokc7stflii8. 

^g Hn n,«, joints otruptnteot springing lines, 

than the half span, tlie tendency to yielding is, in some cases, 
different ; here the lower pai-ts may fall iaward, (Fig. 53,) and 
thrust upward and outward the parts near the crown. 

,63— Emrcsenlatli 

470. From tliis moyement in arches a pressure arises against 
the key stone, termed the JhoriBontal thrust of the ai'ch, the 
tendency of which is to crash the stone at the hey, and to over- 
turn tlie ahutments of tlie arch, causing them to rotate about 
the exterior edge of some one of their horizontal joints. 

471. Tlie joints of rupture below the key stone vaiy in arch- 
es of different forms, and in the same ai'ch with the weight it sus- 
tains. From experiments, it appears that in fuU centre arches 
the joints in question malce an angle of about 27° witli the 
horizon ; in segment arches of arcs Jess than 120° they are at 
tho springing fines ; and in oval arches of three centi'es they are 
found about the angle of 45° of the small arc which forms the 
extremity of the curve at the springing line. 

472. The calculation of the joints of rupture, tlie consequent 
hoi-izontal thntst, and its effects in cmsmng the stone at the 
key and in overtui'ning the abutment are problems of conside- 
rable mathematical intricacy. When the joints of iiiptureare 
given the problem assumes a more simple form, being one ,of 
statical equilibrium between tlie moments of the horizontal 
thrust and the weight of the arch and its abutments. 

The problem for finding the joints of rupture by calculation, 
and the consequent thicEaess of tlie ahatmente necessary to 
preserve the arch from yielding, has been solved by a number 
of writers on the theory of the equilibrinm of arches, and tables 
for effecting the necessary numerical calculations have been 
drawn up from their results to abridge the labor in each case. 

473. The connection between the top of tho abutment, term- 
ed the impost of the arch, and the bottom courses of the arch, 


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requires peeuliai' care in segmental, aaltew, and rampaat iircliea. 
In tlie first, the thrust of the aa'eh being very ^eat, it ■vpill bo 
well, in heavy arches, to make the joints of the interior coiu'ses 
of the abutment, for some courses at least below the impcst, ob- 
iique to the horizon to counteract any danger from sliding. The 
top stone of the abutment, termed the cushion stone of the arch, 
should be well bonded with the stones of the backing, and its bed, 
or bottom joint should be so fai- below the impost joint, that the 
Btone shall' offer sufficient sti-ength to resist the pressure on it 

In tiie askew ai'ch tlie abutments ai-e not umfoi-raly loaded, 
and the entire thrust of the arch will not be received by the 
ahutmente if the arch is constructed in the nsnal manner. Each 
of tliese points requires peculiar attention ; the first demanding 
the thickness of tlie abutment to be, suitably regulated ; the se- 
cond tiiat tlie arch be so built that the thi-ust may be thrown, as 
nearly as practicable, pai'allel to the planes of the heads. To 
effect this last point, the portion of the arch above the upper 
joints of rupture (Fig. 5i,) must be divided into several zones, each 
of these zones being built without any connection with the two 
adjacent to it, but with their ends so arranged that tliis connec- 
tion may be formed, and the arch made continuous after the 

without morfar. 
aeb, developmont of enrv< 
ce^ ona at tlio od^ea of thn 

ad, springing line of arch. 

(.I'nfres are struck By this plan the settling will take place 
lifter unceiitimg without causing cracks, and the tlirust will be 
thrown on the abutments m the direction d^ired. 

In rampant arches, the impost joint being oblique to the ho- 
rizon, care must he taken, if this obliquity be not less than the 
angle of friction of the stone used, either to cut the impostinto 
steps, or else to use some suitable bond, or ii-on cramps and 
bolts to prevent disjunction between, ihe arch and abutment. 

474. The abutments of right and of slightly oblique cylindri- 
cal arches are made of unitorm dimousiona ; but wlien the ob 

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Equity 19 considerable, it may be necessaty lo increase tlie thick 
ness of a portion of each abutment where, there is the giealea 

In conical and conoida! arches the abutments will in like man 
ner vary in dimensions with the span. 

475. In cloistered archei the abutments will be less llianin an 
ordinary cylindrical arch of the same length; and in groined 
arches, in calculating the resistance offered by the abutments, 
ihe counter resistance offered by the weight of one portion in 
resisting the thrust of the other, must be taken into consideration. 

476. When abutments, as in the case of edifices, require to be 
of considerable height, and therefore would demand extraordinary 
thickness, if used alone to sustain the thrust of the arch, they may 
be strengthened by the addition to their weight made in carrying 
them up above the imposts like the battlements and pinnacles in 
Gothic architecture ; by adding to them ordinary, full, or arched 
buttresses, termtd Jlying buttresses ; or by using ties of iron con- 
necting the voussoirs near the joints of rupture below the key 
stone. The employment of these different expedients, their forms 
and dimensions, will depend on the character of the structure 
and the kind of arch. The iron tie, for example, cannot be hid- 
den from view except in llie plate-bande, or in very ilat segment 
arches, and wherever its appearance would be unsightly some 
or-her expedient must be tried. 

Circular rings of iron have been used to strengthen the abut- 
ments of domes, by confining the lower courses of the dome and 
relieving the abutment from the thrust. 

477. ^Tien abutments sustain several arches above each other, 
like relieving arches in tiers, their dimensions' must be calculated 
to sustain the united thrusts of the arches ; and tiie several por- 
tions between each tier must be strong enough to resist the thrust 
of their corresponding arches. 

478. In a range of arches of unequal size, the piers will have 
to sustain a lateral pressure occasioned by t!ie unequal horizontal 
thrust of tlie arches. In arranging the form and dimensions of 
ihe piers this inequality of thrust nmst be estimated for, taking 
also into consideration the position of the imposts of the unequal 

479. Precautions against Settling. One of the most difficult 
nnd Important profelema in the construction of masonry, is that 
of preventing unequal settling In parts which require to be con- 
nected but sustain unequal weights, and the consequent ruptures 
ji the masses arising from this cause. To obviate this difficulty 
requires on the part of the engineer no small degree of practical 
tact. Several precautions must be taken to diminish as far as 
practicable the danger from unequal settling. Walls sustaining 

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Iieavy vertical pressu^'es should be built up uniformly, aid with 
great attention to the bond and correct fitting of the courses. The 
maleiiala should be uniform in quality and size ; hydraulic mor- 
tar should alone be used ; and the permanent -weight not be laid 
i:n tlie wall until the season after the masonry is laid. As a far- 
liier precaution, when practicable, a trial weight may be laid upon 
the wall before loading it with the permanent one. 

Where the heads of arches are i>uilt jnto a wall, particularly 
if they are designed to bear a heavy permanent weight, as an 
embankment of earth, the wall should not be carrried up higher 
than the imposts of the arches until the settling of the latter has 
reached its final term ; and as there will be danger of disjunction 
between the piers of the arches and the wall at tlie head, from 
the s^ne cause, these should be carried up independently, but sc 
arranged that their after-union may be conveniently effected. It 
would moreover be always well to suspend the building of the 
arches until the season following that in which, the piers are 
finished, and not to place the permanent weight upon the arches 
until the season following their completion. 

480. Pointing. The mortar in the joints near the surfaces of 
waUs exposed to the weather should be of the best hydraulic 
lime, or cement, and as this part of the joint always requires to 
be carefully attended to, it is usually filled, or as it is termed 
pointed, some time after the other work is finished. The period 
at which pointing should be done is a disputed subject among 
builders, some preferring to point while the mortar in the joint is 
still fresh, or green, and odrers not until it has become hard. 
The latter is the more usual and better plan. The mortar for 
pointing should be poor, that is, have rather an excess of sand ; 
the sand should be of a fine uniform grain, and but little water 
be used in tempering the mortar. Before applying the pointing, 
the joint should be well cleansed by scraping and bru^ing out 
the loose matter, and then be well moistened. The mortar is 
applied with a suitable tool for pressing it into the joint, and its 
surface is rubbed smooth with an iron tool. The practice among 
our military engineers is to use the ordinary tools for calking in 
applying pointing ; to calk the joint with the mortar in the usual 
way, and to rub the surface of the pointing until it becomes hard. 
To obtain pointing that will withstand the vicissitudes of our cli- 
mate is not the least of the difficulties of the builder's art. The 
contraction and expansion of the stone either causes the pointing 
to crack, or else to separate from the stone, and the surface water 
penetrating into the cracks thus made, when acted upon by frost, 
throws out the pointing. Some have tried to meet tiiis diificulfy 
by giving the surface of the pointing such a shape, and so ar 
ranging it with respect to the surfaces of the stones forming thf 

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joint, tliat the water shall trickle over the pointmg without enter 
mg ^e craclt which is usually between the bed of the stone and 
the pointing. 

48i. The term flash pointing is sometimes applied to a coat- 
ing of hydraulic mortar laid over the face, or back of a wall, tc 
preserve either the mortar joints, or tlie stone itself from the action 
of moisture, or the effects of the atmosphere. Mortar for flash 
pomting should also be made poor, and when it is used as a stucco 
to protect masonry from atmospheric action, it should be made of 
coarse sand, and be applied in a single unifomi coat over the sur- 
face, which should be prepared to receive the stucco by having 
the joints thoroughly cleansed from dust and loose mortar, and 
being well moistened. 

No pointing of mortar has been found to withstand the eifects 
of weather in our climate on a long line of coping. Within a few 
years a pointing of asphalte has been tried on some of our mili- 
tary works, and has given thus far promise of a successful issue. 

482. Stucco exposed to weather is sometimes covered with 
paint, or other mjstures, to give it dm^bility. Coal tar has been 
tried, hut without success in our chmate. M. Raucourt de 
Charleville, in his work Trait6 des Mortiers, gives the following 
compositions for protecting exposed stuccoes, which he states to 
succeed well in ail clunates. For important work, three parts of 
linseed oil boiled with one sixth of its weight of litharge, and one 
part of wax. For common works, one part of Hnseed oil, one 
tenth of its weight of litharge, and two or tluree parts of resin. 

The surfaces must be Sioroughly dry before applying the 
compositions, which should be laid on hot with a brush. 

483. Repairs of Masonry. In eifecting repaid in masonry, 
when new work is to be connected with old, the mortar of the old 
should be thoroughly cleaned dff wherever it is injured along the 
surface where the junction is effected. The bond and other ar- 
rangements will depend upon the circumstances of the case ; the 
surfaces connected should be fitted as accurately as pracficable, 
so that by using but little mortar, no disunion may take place 
from settling. 

484. An expedient, very fertile in its applications to hj-draulic 
constructions, has been for some years in use among the French 
engineers, for stopping leaks in walls and renewing the beds of 
foundations which have yielded, or have been otherwise removed 
by the action of water. It consists in injecting hydraulic cemenl 
ijito the parts to be tilled, tlu-ough holes drilled through the ma- 
sonry, by means of a strong syringe, The instruments used for 
(his purpose (Fig. 55) are usually cylinders of wood, or of cast 
iron ; the bore uniform, except at the end which is terminated 
wJlh a nozlc c f the usual conical form ; llic piston is of wood 

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and is diiven down by a heavy mallet. In uaiug the iyrbge it 
is adjusted to the hole ; l]ie hydraulic cement in a Bemi-fluit 

blate poured mto it a -n ad of f ow oi a di&l of k ilhcr being in- 
troduced on top before msertin^ the piston Tiie cement is 
forced m by repeated blows on the piston 

4b5 A mortii of hjdriulic lime and fine srnd his been used 
for the same purpose ; the Irnie being ground fresh from the kiln, 
and used, before slaking, in order that by the increase of Tolume 
which takes place from slaking, it might fill more compactly all 
interior voids. , The use of unslaked Ume has received several 
ingenious applications of this character ; its after expansion may 
prove injurious when confined. The use of sand in mortar for 
injections has by some engineers been condemned, as from the 
state of fluidity in which the mortar must be used, it settles to 
llic bottom of the syringe, and thus prevents the formation of a 
homogeneous mass. 

486. Effects of Temperature on Masonry. Frost is the most 
powerful destructive agent against which the engineer has to 
guard in constructions oi masonry. During severe winters in the 
northern, parts of our country, il lias been ascertained, by obser- 
vation, that the frost will penetrate earth in contact with walls to 
depths exceeding ten feet ; it therefore becomes a matter of the 
first importance to use every practicable means to drain thoroiighly 
all the ground in contact with masonry, to whatever depths the 
foundations may be sunk below the surface ; for if this precau- 
tion be not taken, accidents of the most serious nature may hap- 
pen to the foundations from the action of the frost. If watei 
collects in any quantity in the earth around the foundations, i 

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may be nei;essary to make small covered diaiiis under them ta 
convey it off, and to place a stratum of loose stone between tho 
eidca of tlie foundations and the suiTounding earth to give it a 
free downward passage. 

Tt may be laid down as a maxim in building, that mortar whicli 
[s exposed to the action of frost before it has set, will be so mncli 
dajnaged as to impair entirely its properties. This fact places in 
a stronger light what has already been remarked, on the necessity 
of laying the foundations and the structure resting on them in hy- 
draulic mortar, to a height of at least three feet above the ground , 
for, although the moitar of the foimdations might be piotected 
from the action of the fiost by the earth around them, the parts 
immediately above would be eipo&ed to it, and as those parts at- 
tract the moisture from the ground, the moitaa, if of commoi! 
lime, would not set m time to prevent the action of the fiosts of 

In heavy walls the moitai m the mteiior wdl usually be se- 
cured from the action of the frost, and masomy of this cliaracter 
might be carried on until freezing weather commences ; but stdl 
in all important works it will be by far the safer couise to sus- 
pend the construclion oi masonry s>everal wei-ks before the oi- 
dinary period of frost, 

During the heats of summer, the moitai is injured by a too 
rapid drying. To prevent this the slone, or brick, should be 
thoroughly moistened before being laid , and atteiwaids, if the 
weather is very hot, the masonry should be kept wet until the 
mortar gives indications of setting The top course should al- 
ways be well moistened by the workmen on quitting their work 
for any short period during very warm weather. 

The effects produced by a high or low temperature on morfai 
in a green state are similar. In the one case the freezing of the 
water prevents a union between the particles of the lime and 
sand ; and in the other the same arises from the water being 
rapidly evaporated. In both cases the moilar when it has set is 
weak ;md. polverulent. 



487. Fit.AMiNG is the art of arranging beams of solid matdriaif 
foi flic various purposes to which they are applied in strucluiea. 
A. frame is any artangement of beams made for sustaining slraina. 

488. That brsnch of framing which relates to the combinations 
of beams of timber is denominated Carpentry. 

489. Timber and iron are the only materials in common use 
for frames, as they are equally suitable to resist the various 
strains to be met with in structitres. Iron, independendy of 
oifering greater resistance to strains than timber, possesses the 
farther advantage of being susceptible of receiving the most suit- 
able forms for strength without injury to the material ; while tim- 
ber, if wrought into the best forms for the object in view may, in 
some cases, be greatly injured in strength. 

490. The object to be attained in framing is to give, by a suit- 
able combination of beams, the requisite degree of strength and 
stiffness demanded by the character of Ihe structure, imited with 
a lightness and an economy of material of which an arrangement 
of a massive kind is not susceptible. To attain this end, the 
beams of the frame must be of such forms, and be so combined 
that they shall not only offer the greatest resistance to the efforts 
they may have to sustain, but shall not cliange their relative po- 
sitions from the effect of these efforts. 

491. The forms of the beams will depend upon the kind oi 
material used, and the nature of the strain to which it may be 
subjected, wliether of tension, compression, or a cross strain. 

492. The general shape given to the frame, and the combiiia 
tions of the beams for this pimose, will depend upon the objcci 
of the frame and the directions m which the efforts act upon it. 

In frames of timber, for example, the cross sections of eacii 
beam are generally uniform throughout, these sections being 
either circular, or rectangular, as these are the only simple forms 
which a beam can receive without injury to its strength. In 
frames of cast iron, each beam may be cast into the most suitable 
■form for the strength required, and the economy of the materiaJ. 

493. In combining tlie beams, whatever may be the general 
shape of the frame, Uie parts which compose it must, as far as 
practicable, present triangular figures, each side of the triangles 
being formed of a single beam ; the connection of the beams at 
the angulai' points, termed the Joints, being so arranged that nc 
yielding can talse place. In all combinations, therefore, in which 

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lie principal beams form polygonal figures, secondary beams 
must be added, either in the directions of the diagonals of the 

polygon, or so as to connect each pair of beams forming an angle 
of UiB polygon, for llie purpose of preventing any change of form . 
of the figure, and of givmg the frame tlie requisite stiffness. 
These secondary pieces receive the general appellation of braces. 
When they sustain a strain of compression tliey are termed struts; 
when one of extension, ties, 

.494. As one of the objects of a frame is to transmit the sfrain 
It directly receives to firm points of support, the beams of which 
it is formed should be so combined that this may be done in the 
way which shall have the least tendency to change the shape of 
the frame, and to fracture the beams, ' These conditions will 
be best satisfied by giving the principal beams of the Irame a 
position such that the sti^ains they receive shall be transmitted 
through the axes, of the beams to the fixed supports ; in this man- 
ner there can be no tendency to change the shape of the frame, ex- 
cept so far as this may arise from the contractions, or elongations 
of the beams, caused by the strains ; and as all imnecessary 
transversal strains will in like manner be avoided, the resistances 
offered bv the beams will be the greatest practicable. 

495. Whenever these conditions cannot be satisfied, the strains 
on the frame should be so combined that those which are not 
transmitted to the points of support shall balance, or destroy each 
other ; and ^ose beams which, from being subjected to a cross 
strain, might be either in danger of rupture, or of being deflected 
to so great a degree as to injure the stability of the frame, should 
be supported by struts abutting either against fixed supports, or 
against points of the frame where the pressure thrown upon the 
strut would liave no effect in changing the shape of the frame, 

496. The points of support of a frame may be either above, or 
below it. In the first case, the frame will consist of a suspended 
system, in which the polygon will assume a position of stable 
equihbrium, its sides being subjected to a strain of extension. In 
the second case the frame, if of a polygonal form, must satisfy 
the essential conditions already enumerated, in order that its state 
of equilibrium shall be stable. 

497. The strength of the frame and that of its parts, and their 
consequent dimensions, must be i-egulated by the strains to which 
Ihey are subjected. When the form of the frame and die direc- 
lion and amount of the sti-ain borne by it are given, the direction 
and amount of the strain which the different parts sustain can be 
ascertained by the ordinary laws of statics, and, from these data, 
the requisite dimensions and forms of the parts, 

498. The object of the structure will necessarily decide the 
general shmpc of the frame, as well as the direction of ihe strains 

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to wliich it Will be subjected. An exaniinalion, therefore, of the 
frames adapted to some of tlie more usual structures will be the 
best course for illustrating both the preceding general principles 
and the more ordinary combinatioas of the beams and joints. 

499. Frames of Timber. These are composed either entirely 
of straight beams, or of a combination of straight beams and of 
ai-ches formed by bending straight beams. . 

Pieces of crooked timber are used either -where the form of tho 

Earts requires them, or else where a strong connection is necessary 
etween straight pieces that form an angle between them. 

500. As has already been stated, the cross section of each 
beam is generally uniform and rectangular. This will, in some 
cases, give more strength than the character of the strain resisted 
may demand ; and will, also, throw a greater amount of pressure 
on the points of support, than if beams of a form more strictly 
adapted to the object in view were used : but it avoids cutting 
the fibres across the grain, or making, as it is termed, graiiv-cut 
beams, and thereby materially injiuing the strength of the piece. 
This objection, however, is only applicable to the parts of a frame 
formed of single beams. Wherever several thicknesses of beams 
are required in the arrangement of any part, the advantage may 
be taken of giving the combination the most suitable form for 
strength and lightness combined. 

501. Frames for Cross Strains. The parts of a frame which 
receive a cross strain may be horizontal, as the beams, or joists of 
a floor; or inclined, as the beams, or rafters which form the inclined 
sides of the frame of a roof. The pressure producing the cross 
strain may either be uniformly distributed over the beams, as in 
the cases just cited, arising from the flooring boards in the one 
case, and the roof covering in the other ; or it may act only at one 
point, as in the case of a weight laid upon the beam. 

In all of these cases the extremities of the beam must be ikmly 
fixed against immoveable points of support ; the longer side of 
the rectangular section of Uie beam should be parallel to the di- 
rection of the strain, on account of placing the beam in the besl 
position for strength. 

If the distance between the points of support, or the hearing, 
be not great, the framing may consist simply of a rovi^ of paraOel 
beams of s'lch dimensions, and placed so iar asunder as the strain 
boiTic may require. When tho beams are narrow, or the depth 

I'ig. jO— Represents a 

of the rectangle considerably greater tlmn the breadth, CFig. ht',' 

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chert strutii of battens may be placed at intervals between each 
pair of beams, in a diagonal direction, uniting the bottom of the 
one with die top of the other, to prevent llie beams from twialinjj, 
or yielding laterally. 

When 3ie bearing and strain are so great t!\at a single beam 
will not present sufficient strength and stiffness, a combmation 
of beams, termed a built beam, which may be solid, consisting 
of several layers of timber laid in juxtaposition, and firmly con- 
nected together by iron bolts and straps, — or open, being formed 
of two beams, wilh an interval between them, so connected by 
cross and diagonal pieces, that a strain upon either the upper or 
lower beam will be transmitted to the other, and tiie whole system 
act under the effect of the strain like a solid beam. 

503. Solid, built Beams. In framing solid built beams, the 
pieces in each course (Fig, 57) are laid abutting end to end with 

n-— Repreeeiite a solid built beaei 
.. three coursea, the pieces of 
each CQUtsa breaking joiuts and 


a square joint between them, tlie courses brealdng joints to form 
a strong bond between them. The courses are firmly connected 
cither by iron bolts, formed with a screw and nut at one end to 
bring the courses into close contact, or else by iron bands driven 
on tight, or by iron stirrups (Fig. 58) suitably aiTanged with screw 
ends and nuts for the same purpose. 

•A A' 

screws c wliicli coalliiB tha cross piece of tho slirmp b 

When the strain is of such a character that the courses would 
be liable to work loose and slide along their joints, the beams of 
the different courses may be made with shallow indentations, 
(Figs. 59, 60,) accurately fitting into each other; or shallow rec- 

ig. 59— llopreseiits a Botid bulit 
beam of three ooiuEea amused 
with indeute anil coiifinod by irou 

ll? 00 -Represents asolid built beam, thofop part hBingoftwopiecesi & »1 ii-l nbu 
dgainst a broad flat irou bolt o, l«rmed a kins odl, 

unfihr notihes (Fig. 61) may be cut across each beam, boinj; 

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placed as tor e ebo ok of lard woo I 11 leys 

the purpose of causing lliem to fit tfic notches more closely, and 
to admit of bchig driven tight upon any shrinkage of the woody 

The joints between Uie courses may be lefi slightly open 
without impairing in an appreciable degree the strength of the 
combination. This is a good method in beams exposed to mois- 
ture, as it allows of evaporation from the free circulation of the 
air through the joints. Felt, or stout paper saturated with min- 
eral tar, has been recommended to secure the joints from the 
action of moisture. The prepared material is so placed as to 
occupy the entire surface of the joint, and the whole is well 
screwed together. 

503. Open built Beams. In framing open budt beams, the 
principal point to be kept in view is to form such a connection 
between the upper and lower solid beams, that they shall be 
strained uniformly by the action of a strain at any point between 
ilie bearings. This may be effected in various ways, (Fig. 63.) 

Fig. S3— Reprcaenls . 






built beam; A and B are 
tlie top and bottom lails or 
Etrings \ u, a, cixik pieces, 
either Giagle or in paits ; b, 
dii^onal Erocea in pairs ; c, 
eingie diagonal bracos. 

The upper and lower beams may consist either of single beams, 
or of solid built beams ; these are connected at regular intervals 
by pieces at right angles to them, between which diagonal pieces 
are placed. By this arrangement the relative position of all the 
parts of the frame will be preserved, and the strain at any point 
will be brought to bear upon the intermediate points. 

Two of Ihe best known applications of this combination, ivhen 
limber alone is used, are those of Colonel Long, of the XJ. S, 
Topogr£^hical Engineers, and of the late Mr. Town. 

504.- That of Colonel Long (Fig. 64) consists in forming btitli 
tlie upper and lower beams, termed by the inventor the sU-ingi. 

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■jI ihree parallel beams, sufficient space being left between tl.e, 
DTie in llie centre and the other two to insert the cross pieces. 

Kb. 84— ReprasentB a panel of Long's truss. 

A uul B, top and bottom strings of thise guuibgs 

C, C, posts m pairs. 

D, braces in puis. 

E, conntec brecfl single. 

a, a, mortiSBBWliBtBjLbs and teja are inserteil 

F, jib and key of tiard viood. 

leitned the posts ; the posts consist of beams in pairs p.aced al 
suitable intervals along the strings, with which they arc connected 
by wedge blocks, teimed jibs and keys, which are inserted into 
rectangular holes made through the strings, and fitting a corre- 
spondmgshallownotcb cut into each post. Adiagonalpiece,lermed 
a brace, connects the top of one post with the foot of the one ad- 
jacent by a suitable joint. Another diagonal piece, termed ihe 
counter-brace, is placed crosswise between the two braces axvl 
dieir posts, with its ends abutUng against the centre beam of the 
upper and lower strings. The counter-braces are connected 
with the posts and braces by wooden pins, termed tree-nails. 

In wide bearings, the strings will require to be made of several 
beams abutting end to end ; in tliis case the beams must break 

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■ointa, and short beams must be ioserled between the centre a;id 
exteiior beams wherever tlie joints occur, to strengtlien iheni. 

The beams in this combination are all of uniform cross section, 
t!ie joints and fastenings are of the simplest kind, and tlie parta 
are well distributed to call ioto plaj' tlie strength of the' strmg;:, 
and to produce imifonn stiffness and strain. 

505. The combination of Mr, Town (Fig. 05} consists in utD 

main strings, each formed of two or lliree parallel beams of twa 
thicknesses brealdng joints. Between the parallel beams are in- 
serted a series of diagonal beams crossing each other. These 
diagonals are connected with the strings and with each oliier by 
tree-nails. When the strings are formed of three parallel beams, 
diagonal pieces are placed between the centre and exterior beams, 
and two inteimediatc strings are placed between the two courses 
of diagonals. 

This combination, commonly known as the lattice truss, is of 
very easy mechanical execution, the beams being of a uniform 
cross section and length. The strains upon it are borne by the 
tree-nails, and when used for structures subjected to variable 
strains and jars, it loses its stiffness and sags between the points 
of support. It is more recommcndable for its simplicity tlian . 
scientific combination. 

506. A third method, called after the patentee, How's truio, 
has within a few years come into general, notice. It consists of 
(Fig, 66) an upper and lower string, each formed of several thick- 
nesses of beams placed side by side and breaking joints. On the 
upper side of the lower string and the lower side of the upper, 
blocks of hard wood are inserted into shallow notches ; the blocks 
are bevelled off on each side to form a suitable point of support, 
or step for the diagonal pieces. One series of the diagonal pieces 
are arranged in pairs, tlie others are single and placed between 
those in paira. Two strong bolts of iron, which pass through 
iho blocks, connect the upper and lower strings, and are arranged 
with II screw cut on one end and a nut to draw the parts closely 

I'his combination presents a judicious arrangement of the parts 
The blocks give abutting surfaces for the braces supericir to tlioae 

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obtained by the ordinary fonns of joint foi tbis purpose. The 
bolts replace advantageously the timber posts, and in case of tlie 

rrame working lOose and sagging, their irrangement for tightt-ii- 
ing up the parts is simple and efficicious The timber of each 
string is not combined to give is great strength as its cross tec 
tion is susceptible of, and the lower 'string, upon which a ''tiain 
of tension is brouglit, against which timber oifers the greatest 
resistance, ]ias received a greater cross section than thit of tue 

The preceding combinations have been applied gent,i dly m 
our country to bridges. In this application, the limber support 
ing the roadway ot the bridge is usuallv placed on ihp Ijwei 
strings ; two, three, or four built bcims bemg used, ao the case 
may require, for supporting the Irans^ei'-e beams under the roid- 
way, the centre beams leaving an equal \vidth of loadw ay between 
them and the eiterior beams 

507. Framing for intermrdiUf Supp07ts Beims of ordinaiT 
dimensions may be used for wide beanngs when intermediate 
Bupporls can be procured between the extreme points 

The simplest and most obvious method of effecting this i* to 
p;ace upright beams, termed ^jops, oi tltotes at suitible mtervils 
■-■nder the supported beam, 

"When the props would interfere with some other artaiigement, 
and points of^ support caa be procured at the extremities below 
ihose on which tlie beam rests, inclined struts (Fig- 67) may bt 
used. The struts must have a suitably formed step at Uie toot, 
ijA be connected at'top with the beam by a suitable joint. 

In some cases the bearing may be dimiiiislied by placing on 

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the points of support shoitpieces, termed corheh, (Fig. 68,} .ini 
Bupporting these near their ends by struts. 

In other cases a portion of the beam, at the middle, may be 
strengthened by placing under it a short beam, called a straining 
team, (Fig. 69,) against the ends of which the struts abut. 

Whenever the bearing may require it the two prcccdin 
rangements (Fig. 70) may be used in connection. 

In all combinations with struts, a lateral thrust will be thrown 
on the point of support wliere the foot of the strut rests. This 
strain must be provided for in arranging the strength of the sup- 

508. When intermediate supports can be procured only above 
the beam, an arrangement must be made which shall answer the 
purpose of sustaining the beam at its intermediate points by sus- 
pension. The combination will depend upon the number of in- 
lermsdiate points reauired. 

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When tho beam req^uires to Ije supported onlj ai thu aiiddle, 
it may te done by placing two inclmed pieces, resting on tlic 
beam at its extremitieB, and meeting under an angle above it, 
from which the middle of the beam canbe suspended by a rod of 
iron, or by another beam. Ifthe suspending piece he of iron, it 
must be an'anged at ono end with a screw and nut. When liio 
Bupportisof timber, a single beam, called ^Icingpost, (Fig. 71,) 

may be used, against the head of which the two inelined pieces 
may abut ; the foot of the post is connected with the beam by 
a holt, an iron stin-tip, or a suitable joint. Instead of tlie ordinary 
Idng post, two beams maybe used; these are placed opposite to 
each other and bolted together, embracing between them the sup- 
ported beam and the heads of the inchncd beams which fit into 
shallow notches cut into the supporting beams. Pieces arranged 
in this manner for Buspending poi-tions of a frame receive the 
name of suspension pieces, or bridle jpieecs. 

When two mtermediate points of snppoi-t are requiied, they may 
be obtained by two inelined pieces resting on the ends of the 
beam and abutting against the extremities of a elioi t horizontal 
straining beam, (Fig. 72.) The ST-ispension pieces in thi'* ease 

maybe either posts, tarmcAqutin posts, arranged like a king 
post, iron rods, or bridle pieces- This combinanon maybeused 
tor very wide bearings, (Fig. 73,) by suitably increasing the num- 
ber of inclined pieces and Btraining beams. 

Some of the preceding combinations maybe Tieed for support- 
ing one end of abeam subjected to a cross sti'ain when tho other 
bas a fixed point of support. This may be done either by an ui- 
clined stmt beneath^ or an inclined tie above the beam. When 
a wooden tie is used it should consist of two pieces bolted to- 
gether and embracing the beam, 

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509. The d asBifications tinder the two preceding headsrepi'e- 
sent tite principal coinl)inatiori8 of etraiglit beams applied ta the 
purposes of framing. The frame of an ordinary roof presents one 
of the simplest combinations by which the action of the different 
parts of a frame may be illustrated. 

A roof of the ordinary form consisto of two equally inclined 
Bides of metal, elate, or other material, which is attached to a 
covering of boai'ds tliat rests upon the frame of the roof. The 
frame consists of several vertical frames, termed the trusses of 
the roof, which ai-e placed parallel to and at suitable intervals 
from each other; these receive horizontal beams termed jwr^itw, 
■which rest upon them and are placed at suitable intervals apart, 
and upon the purlins are placed inclined pieces termed ihelcmg 
rcifiers, to which the boards are attached. 

Tlie truss of a roof, for ordinary bearings, consists (Fig. 74) 

ofa horizontalbeam termed the ilM Seam, witli which the inclined 
beams, termed thapHnoipal rafters, are connected by suitable 
joints. The principal raitei-smay either abut againstcach other 
at the top or vidge, or against a king post. IneUned struts are 
in some cases placed between the pnncipal rafters and tingpost, 
with which they are connected by suitable joints^ 

Tor wider bearings the aliort rafters (Fig. 75) abut against a 

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^training beam, at top. Queen posts connect these pieces with 
the tie-beam. A king post connects the stmining beam with the 

abuttlDg ngidost Uio s 

top of the short mftors ; and struts are placed at suitable pointa 
between the rafters and kiBg and qneen posts. 

In ea«h of these combinations the weight of the roof coveiing 
and the frames is supported by the points of support. The prin- 
cipalrafters are sabi ected to cross and longitudinal strains, arising 
from the weight of the roof covering and trom their reciprocal ac- 
tion on eachother. Thesestrainaaretransmittedtothetieheam, 
causing a strain of tension upon it. The struts resist Ihe cross 
strain upon the rafters and prevent them from sagging ; and the 
kingand qneenpostsprevent the tie andstrainingbeams from sag- 
ging and give points of support to the struts. The short rafters 
andstrainingbeam form pointa of support which resist the cross 
Strain on the principal rafters, andsupport the strain on the queen 

510. Wooden Arches. A wooden arch may be formed by 
bending a single beam (Kg. 76) and confining its extremities to 

prevent it from resuming its original shape. A beam in this 
state presents gi'eater resistance to a cross strain than when 
straight, andmay be used with advantage where great stiffness is 
required, provided tlie points ofsuppoi-tareofsuincient strength 
to r^ist the lateral thrust of the beam. Tliis method can be 
resorted to only in narrow bearings. 

For wide arches a curved built beam must be adopted ; and 
for this purpose a solid, (Figs. 77 and 78,) or an open built laeam 
may be used, depending on the bearing tp be spanned by the 
arch. In either case the curved beams are built in the same 
manner as straight beams, the pieces of which they are formed 
being suitably bent to coafoi'm to the curvature of the arch, which 
maybe done eitlier by steaming thepieces, hymechanical power, 
or by tliQ usual method of softening the woody fibres by keeping 
the pieces wet ^vhile subjected to the heat of a liglit blaze. 

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"Wooden arches may also te formed "by fastening together eov 
eral conrees of "boards, giving the frame a polygonal form, (Fig. 
79,) corresponding to the deshed curvatTire, and then shaping tlia 

^Eepresents on elevation A of n wooden 
ftrtned of sliott pieces a, 6 wMch abut 

outer and inner edges of the arch to tlie pi'oper curve. Eucli 
course is formed of boards cut intoshai-p lengths, depending on 
^e cnrvatore required ; these pieces ahut end to ena, the jomte 
being in the dh'ection of the radii of curvature, and the pieces 
composing the different conrseB treat joints ■with each othci'. 
The courses may be connected either by jibs and keys of hard 
■wood, or by iron bolts. This method ia very suitable for all 
light frame -work where the presure borne is not great. 

"Woodon arches are chiefly used for bridges and roofs. Thcj 

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EGrve as intermediate points of support for the framing on whieli 
the roadway rests in tiie one case, and tlie roof covering in the 
other. In bridges the roadway may lie either ahove the arch, 
or below it ; in either case vertical posts, iron rods, or bridles 
connect the horizontal beams with the arch. 

511. The greatest strain in wooden arches takes place between 
the crown and springing line ; this part should, therefore, when 
practicable, he relieved of the pressure that it would directly 
receive from the beams above it by inclined stmtfi, so an'anged 
as to throw this pressure upon the lateral supports of the arch. 

The pieces which compose a wooden ai'ch may be bent into 
any curve. The one, however, usually adopted is an ai'c of a 
circle, as the most simple for the mechanical construction of the 
framing, and presenting all desirable strength. 

612. Cent/res. The wooden frame with which the voussoirs 
of an arch are supported while the arch is in progress of con- 
straction is termed a centre. 

A centre, like the frame of a roof, consists of a number of 
vertical frames (Figs. 80, 81, 82, 83,) termed trusses, or ribs, 
upon which horizontal beams, termed bolsters, ai'c placed to re- 
ceive the YousBoirs of the arch. 

The cuiwed, or haa^ pieces of a centre on which the bolsters 
rest consist of beams cut into suitable lengths and shaped to the 
proper curvature ; these pieces abut end to end, the joints be- 
tween them being in the du'ection of the radii of curvature ; the 
ioints are usually secured by short pieces, or blocks placed un- 
der the abutting ends to which the back pieces are bolted. The 
blocks form abutting surfaces for shores, or inclined stinits seated 
E^ainst firm points of support below the back pieces. To pre- 
vent the shores, or the struts from bending, bi'aces, or bridles, 
whichareusuallyformedoftwopieces,eachwith shallow notches 
cat into them, are added, and embrace between them the 
shor^ or struts, the whole being firmly connected withironbolts. 

Thecombinationsusedfortheframesof centres will depend up- 
on the position of the points of support and the size of the arches. 

.'>i3. For small light ai'dies (Kg. 80) the ribs may be formed 

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of two or more thictnesses of short boards, firmly nai od togeth- 
er ; the boards in each coui'se abutting end to endby a jointin the 
direction of the radiua of curvature of the arch, and brealdng 
joints witli those of the other course. The riba are shaped to 
tho form of the intrados of the arch, to receive the bolsters, 
■\vhieh are of battens cut to suitable lengths and naUed tn the ribs, 
514. For heavy arches with wide spans, when firm intenne- 
diate points of support can be procm-ed between the abutments, 
the back pieces (Fig. 81) may be snpported by shores placed 

Fig. 61— ItEp'resenta Hio 

under the blocks in the direction of the radii of cui-vature of 
the arch, or of inclined struts (Fig. 82) resting on tho pomts of 

on sockets on tho Bup ■» 

e, folding woileM laid upon the tnok pif cos 5 of aacli ri 
YDUssolis Bie l^d. 

support. Tlie shores, or stmts, 
braces suitably placed for the " 

e prevented from bonding by 

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515. If intermediate points of support cannot be obtained, a 
1)road framed sapport must be made at eadi abutment to receive 
tlie extremities of the struts tliat sustain tlie back pieces. The 
framed Bupport (Fig. 83) consists of a lieavy boam laid either 

Fig. 88— Beproaants a part of a rib of W.ttorioo BcWjo over tlie Tliamoe. 

a, a, and 6, three beaTv beams, formine the rfriliflff plates, ivMoii with the ahores ft, ft, foi-m 

the framed support fbr the Btmts <ff the eentre. 
e, e, stmts abnttlng jigsinet ilie blocks ft? placed nnder the joints of the back pieces// 
1^ d, bridle or rndtal pieces In pairs which ai-e eonflnod at top uixd bottom belneen tliu horlzeat;i] 

ties m, n of the ribs, also In pairs. 

«, in,lJOlstera of Uio centre resting on the back pieces f. 

horizontally, or inclined, and is placed at that joint of t!ie arch, 
(the one which maltes an angle of about 30° with the horizon,) 
where the vou^oire, if TiUBvipported beneath, wovdd elide on 
their beds. Thig beam is borne by shores which find firm points 
of support on the foimdations of the abutment. 

The Dack pieces of the cenfci-e (Fig, 83) may be supported by 
inclined strata which rest immediately upon the framed support, 
one of the two efcrats under each block resting upon one of the 
framed supports, the other on the one on the opposite side, the two 
struts being so placed as to make equal angles with the radius of 
cnrrature of the arch drawn through the middle point of the 
block. Bridle pieces, placed in the direction of the radius of 
curvature, embrace the blocks and struts in the usual manner 

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and prevent tlie latter from sagging. Tliis combination j,jresente 
a figui-e of invariable form, as tlie strain at anj one point ia 
received by the stmts and ti-ansmitted directly to tlie fixed points 
of support. It has the disadvantage of reqniiing beams of gi'eat 
lengm when the span of the arch is considerable, and of present ■ 
ina frequent crossing of the stmts where notclies will bo re 
quisite, and the strength of the beams thereby diminished. 

The centre of Waterloo Bridge over the Thames (Fig. 83) 
was framed on this principle. To avoid the inconveniences re- 
sulting from the crossing of the struts, and of building beams 
of sufficient length where the stmts could not be procured from 
a single beam, the device was imagined in this work of receiv- 
ing the ends of several stmts at the points of crossing into a 
large east-iron socket suspended by a bridle piece. 

516. "When the preceding combination cannotbe employed, a 
strong tmss, (Fig. 8i,} consisting of two inclined stmts resting 

upon the framed supports, and abutting at top against a strain- 
ing beam, may be fonned to receive tiie ends of some of the 
sti'uts which support the back pieces. This combination, and 
all of a like chai'acter, require that the arch should not be 
consti-ucted more rapidly on one side of the centi'e than on the 
other, as any inequality of strain on the two halves of the 
centre would have a tendency to change the shape of the frame, 
thrusting it in the direction of the greater sti-ain. 

51T. Means used for sinking Vm.ti'es. "When the arch is 
completed the centres are detached from it, or stmck. To effect 
this m large centres an arrangement of wedge blocks is used, 
termed the striMng plates, by means of which the centime may be 
gradually lowered and detadied from the soffit of the arch. Ihis 
an-angement consiete (Fig. 83) in forming steps r.pon the upper 
Ein-face of the beam which forms the framed support to receive a 
wedge-shaped block, on which another beam, having its under 
Bm-face also aiTanged wili steps, rests. The stmts of the rib 
either abut against the upper surface of the top beam, or else are 
inserted into cast-iron sockets, tenned shoe-plates, fastened tc 

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tills eurfacc. The ccTitre is struck by driving "back tl.c ■nedgo 

518. "When the stiiits rest upon intermediate supports Tje- 
tw«en the abutments, double, or folding wedges may be placed 
nuder the struts, or else upon the back pieces of the riba under 
each bolster. The latter arrangement presents the advantage 
of allowing any part of the centre to be eased from the sofet, 
instead of detaching the whole at once as in the other methods 
of sti-iking wedges. This method was employed for the centres 
of Grosvenor Bridge, (Fig. 82,) over the river Dee at Chester, 
and was perfectly successM both in allowing a gradual settling 
of the ,arcli at various points, and in the operation of striking. 

519. Tim amd Braces for detaohed Frames. When a series 
of frames concur to one end, as, for example, tlie main beams 
of a bridge, the trass^ of a roof, ribs of a centre, &c., they 
require to be tied together and stiffened by other beams to 
prevent any displacement, and warjping of the frames. For this 
purpose beams are placed in a horizontal position and notched 
upon each frame at suitable pointB to connect the whole together ; 
wiile others are placed crossing each other, in a diagonal dh-ec- 
tion, between each pair of frames, with which they are united 
by suitable joints, to stiffen tJie frames and prevent tliem from 
yielding to any lateral effort. Both the ties and the diagonal 
braces may be either of single beams, or of beams in pairs, so 
an'Mged as to embrace between them tlie part of the frames 
with which they are connected. 

520. Joints. The form and aiTangement of joints will 
depend upon the relative position of tlie beams joined, and the 
object of the joint. 

Joints may bo required for various purposes, either to connect 
the ends of beams of which the axes are in the same right line, 
or make an angle between them ; or the end of one beam with 
the face of another; or where the face of one beam rests upon 
that of another. 

In all aiTangements of joints, the axes of the beams connected 
should lie in the same plane in which the strain upon the frame 
acts ; and the combination should be so arranged that the parts 
will accurately fit when the frame is put together, and that 
any portion may be displaced without disconnecting the rest. 
The simplest forms moat suitable to the object in view will 
usually be found to be the b^t, as offering the most facility in 
obtaining an accurate fit of the parts. 

In adjusting the surfaces of the joints an allowance should be 

made for any settling in the frame which may arise either from 

the shrinking of tlie timber in seasoning while in the frame, or 

from tlic fibres yielding to the action of tlie strain. Tins is don! 


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by leaving sufficient play in tlie joints when the frame is first set 
up, to admit of the parts coming into perfect contact when the 
frame has attained its final settling. Joints formed of plane sur- 
faces present more difficulty in ttia respect than curved joints, 
aa the bearing surfaces in the latter case will remain in contact 
shouJd any slight change take place in the relatiTe positions of 
the beams from settling ; whereas in the former a slight settling 
might cause the strains to be thrown upon a comer, or edge of 
the joint, by which the beai-ing surfaces might be crushed, and 
the parts of the frame work wrenched asunder from the leverage 
which such a circumstance might occasion. 

The surface of a joint subjected to pressure should be as 
gi'eat as practicable, to secure the parts in contact from being 
crushed by the strain ; and the suj'mce should be per]^)endicular 
to the direction of the sti'ain to prevent sliding. 

A thin sheet of wrought iron, or lead, may be inserted 
between tlie smfaces of joints where, from the magnitude of 
the strain, one of them is liable to be crushed by the other, as in 
the case of the end of one beam resting upon the face of another, 
521. Folding wedges, and pins, or tre&nadls, of hard wood 
are nsed to bring the surfaces of joints firmly to their bearings, 
and retain the parts of the frame in tlieir places. The wedges 
are inserted into square holes, and the pins into auger-holes 
made through the. parts connected. As the object of these 
accessories, is simply to bring the ;part8 connected into close 
contact, they should be carefully driven in order not to cause 
a strain that might crush the fibres. 

To secure joints subjected to a heavy strain, bolts, straps, and 
hoops of wrought iron are used. These should be placed in the 
best direction to counteract the strain and present the parts from 

^■---; and wherever the bolts are requisite they should 

. at those points which will least weaken the joint. 
nts of Beams wnUed end to end. When the axes of 
the beams are m the same right line, the form of the joint wiil 
depend upon tlie direction of the strain. If the sh-ain is one of 
compression, tlie ends of the beams may be united by a square 
joint perpendicular to their axes, the joint being secwred (Fig. 85) 


/ i • 1 H 


eecnred by side pieces < 

'and if bo 

by four short pieces so placed as to embrace the ends of the 
beams, and being fastoiied to tlie boamB and to each other by 

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bolts. This an-angemeutj termed fishing a 'beam, is used only 
for rough' work. It may also be used when the strain is one of 
extension ; in this case the short pieces (Fig. 86) may be notclion 



upon the beams, or else keys of hard wood, inserted into shallow 
notches made in the beams and sliort pieces, may be employed 
to give additional security to the joint. 

A joint termed a siai'f may he used for either of the foregoing 
pur[3oses. This j oint may be formed either by halving the beaiES 
011 each other neai- their ends, (Fig. 87,) and seeming the jointa 

ited by iron plntos e, e, keys ^ d, md Wfs. 

by bolts, or straps \ or else by so ai'ranging the ends of the two 
beams that each shall fit into shallow triangular notches cut 
into the other, the joint being secured by iron hoops. This last 
method is employed for round timber.. 

523. When beams united at their ends are subjected to a cross 
strain, a scarf joint is generally used, the under part of the joint 
being secured by an iron plate confined to the beams by bolts. 
The scarf for this purpose may be formed simply by halvingthe 
beams near their ends ; but a more usual and better fonn (Fig. 

88) is to make the poi-tiou of tlie joint at the top euifaoe of 
the beams peipendicular to their axes, and about one third of 
their depth ; the bottom portion being oblique to the axis, ae 
well as the portion joining these two. 

"Wlien the beams are subjected to a cross strain and to one of 
extension in the direction of their axes, the form of the ecaii' 
must be suitably arranged to resist each of these strains. The one 
showiiinFig. 89 is asmtableandusual form for these objects. A 
iolciing wedge key of hard wood is inserted into a space iefl 

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between the parts of the joint whicli catch when the "beame aio 
drawn apart. The key serves to hiiug the surfacea of the joints 

yLe bottom of tlio Joiot is 6C[;ured.%r nn Icon plato eonflned by bolta. TliB folding 
wedge key Inserted at o sarvce to bring oil tho BoifsceB of tbe joints to tliclt beailnga. 

to tlieir hear jnga, and to form an abutting snrface to resist tlie 
Btrain of extension. In thia fonn of scarf the surface of the 
joint which abuta against the key will be compressed ; the 
portions of the heama jnst above and below the Key will bo 
subjected to extension. These pai'ts should present the same 
amount of resistance, or have an equality of cross section. The 
length of tJie scarf should be regulated by the resistance with 
which the timber employed resists detfosion compared with 
its resistance to compression and extension. 

524. "When the axes of beams foi-m an angle between them, 
they may be connected at their ends either' by halving them 
on each other, or by cutting a mortise in the centime of one 
beam at the end, and taping the end of the other to iit into it. 

535. Jomtsfor oonnmtma tJie eiid of mie learn with the faee 
of (mother, 'flie joints used for this purpose are termed mortise 
amd terum joints. Their foi-m will depend upon the angle be- 
tween tho axes of the beams. When the axes ai'o perpendicular 
the mortise (Fig. 90)iscntinto the face of the beam, and the end 

of tbo beiinis oro pcrpcndJ- 

offho other beam is shaped into a tenon to fit the mortise. When 
the axes of the beams are obliq^ue to each otiier, a triangular 
notch (Fig. 91) is usually cut into the faee of one beam, the sides 
of ^e notch being perpendicular to each other, and a shallow 
mortise is cut into the lower surface of the notch ; t!ie end of 
the other beam is suitably shaped to fit tho notch and mortise. 


Tenon and mortise joints have receiyed a variety ( f focms, 
Ike direction of the strain and the effect it may prodiice upon 

tho joint must in all eases regulate this point. In some cases the 
circnlar joint may he more snitable than tliose forms which are 
piano Biirfacea ; in others a donhle tenon may be better than the 
simple joint, 

626. Tie joints. Itese joints are used to connect beams 
which cross, or lie on each other. Tlie simplest and strongest 
form of tie joint consists in cutting a notch in one, or both of the 
beams to connect them secnrely. But when tlio beams do not 
cross, but the end of one rests upon the other, a notch of a tra- 
pezoidal form (Fig. 93) maybe cntinthelowerbeam toreeeivo 

the end of the upper, which is suiiably shaped to fit the notch. 
This, ii'om its shape, is termed a dove-tail joint. It is of fre- 
quent use in joinery, but is not suitable for heavy frames where 
the joints are subjected to considerable eti-ains, as it soon becomes 
loose from the ehrinking of the timber. 

52T. Iron Frames. Cast and wi'onght iron are both usedfor The former is most suitable where great strength com- 
bined with stiffness is, required ; the latter for light frames and 
wlierever the strains act mainly as tensions. 

In iron frames the same general principles of combination 
are applicable as in those of timber, and they admit of the same 
classification as frames of the latter mateml. 

Cast iron is most easily wrought into the best forms for 
strength. The dimensions of the pieces imist, however, bo ro- 
fihicted within certain practical limits, both on account of the 

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tabor and expense attendant upon the casting and liandlmg ol 
heavy pieces, and the difficulty of procuring them of uiiiloim 
CLoalitywhenof lame size. In arranging the component parts of 
an iron frame, nnilormity in the shape and dimensions is requi- 
site both for economy and perfection of workmanship ; and asfai 
as practicable, the bulk of the different parts of each piece should 
be the same, in order to avoid the dangere arising from uneinaJ 
shrinking in cooling. 

Wrought iron may be hammered, or rolled into the most suit- 
able form for strength, but for frames bars of a rectangular sec- 
tion are mostly used. 

The joints in botli cast and wrought iron frames are made upon 
the same principles as in -those of timber, the forms being adapted 
to the nature of the material ; they are secured by wrought iron 
wedges,' keys, bolts, &c. 

528. 2''ramesfor Gross Strains. Solid beams of cast iron, 
moulded into the most suitable forms for strength and for adap- 
tation to the object in view, may be used for supporting a cross 
strain where the bearings are of a medium width. Solid wrought 
iron beams can be used with economy for the same piu'poses 
only for sliort bearings. 

529. Opencast iron beams are seldom used except in combina- 
tion with cast iron arches. Those of wrought iron ai'e frequently 
used in structures. They may be fonned of a top and bottom 
rail connected by diagonal pieces, foraiing the ordinaiy lattice 
an-angement ; or a piece bent into a curved foi-m may be placed 

d, e, and / rspi'esent the parte ol 
trusa of ft OTtVBd Ught roof, o, 
ceQtod nltli tlie opea beun; t 

J the rails, or any other suitable combination (Fig 

maybe used which combineslightncBS with strength andstitt 

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530. If on Arches. Cast iron arches may tensed for the samo 
Mljjects as those of timlaer. The frames for these purposoe con- 
eiet of several pai-allel ribs of uniform dimensions which are cast 
into an arch form, the ribs being connected by horizontal ties, 
and stiffened by diagonal braces. Tlie weight of the snperstnic- 
tnre is ti-anamitted to the curved ribs in a vaiiety of ways ; most 
usually by an open cast iron beam, thelowerpai'tof wnichiaao 
shaped as to rest upon the cuiwed rib, and the upper part suitably 
formed for the object in view. These beams are also connected 
by ties, and stiffened by diagonal braces. 

Each i-ib, except for naiTOW spans, is composed of several 
pieces, or segments, between each pair of which there is a joint 
m the direction of the radius of cuiwature. The forms and di- 
mensions of the segments are uniform. The segments areusually 
eithersolid, (Fig. 94,) or open plates of uniform thicliuf ' 

Plato Brch ivltli 

a ilanch of uniform breadth and depth at each end, and on the 
entradoH and intrados. Theilaiich seives both to give strengtli 
to the segment and to form the connection between tlie segments 
and the parts which rest upon tlie rib. 

The ribs are connected by tie plates which ai-e insci-ted be- 
tween the joints of the segments, audare fastened to the segments 
by iron screw bolts which pass through the end flanches of tlie 
segments and the tie plate between them. The tie plates-may be 
eiflier open, or solid ; the former being usually prefeiTed on ac- 
count of this superior lightne^ and cheapness. 

The frame work of the ribs is stiffened by diagonal pieces 
which are connected either with the ribs, or the tie plates. The 
diagonal braces are cast in one piece, tlie arms being ribbed, or 

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',, and tapenng from the centre towards llie ends in a 
sTiitable manner to give lightness combined with etrength, 

Tho open beams ^ig. 9i) ■which rest upon the curved ribs ai-e 
cast in a suitable number of panels ; the joint between each pair 
being either in the direction of the radii of the arch, or else verti- 
cal. These pieces are also cast with flanches, bywbieh they are 
connected together and with the other parts of the frame. The 
beams, lihe uie ribs, are tied together ard stiffened by ties and 
diagonal braces. 

Beams of suitable forms for the purposes of the structure are 
placed either lengthwise, or crosswise upon the open beams. 

531. CiUTed iTDS of a tubular form have, within a few yeai's 
back, been ti-ied with success, and bid fan- to supei^ede the or- 
dinary plate rib, as with the same amotint of metal they combine 
more strength than the flat rib. 

Tlie apphcation of tubular ribs was ilrst made in the United 

pig. yo— hepreBsnts n Me view A nmU crass BeeHon and und view B throu!;li n 

the tiibulur arch of llaior PelaBoifl. 
», a, <Fig A) n flida vLow, aid (Pig. B) Bn ead vlow of the elliptical floacllOB of 

6, b, sfioiildera, or ribs to atrengthen tho Dunclios agalDst lateral atridns. 

2 (PIrB) Bldo"vIow of'tho'riiE If the «e-plste flttod to tlie intotiot of tho tubo. 
<l, a, (Ffgs. A nnd B) safldle pisees to taceivo tho open boaioa of a torm similar t> 

saddle ptecBtJ 

Fig SJ, wliloli 

^ eross seeUon of the rlh through tlw sadaio place. 


Str-tes by Major Delafield of tlie U. S. Corps of Engineers, in 
an arcli for a bridge of 80 feet span. Each rib was formed of 
nine segmenta ; each seffment (Fie. 95) being cast in one piece, 
tlie cross section of which is an elhptical ring of nniform thiclc- 
ness, the ti-ansverse axis of the ellipse being in the direction of 
the radius of curvature of the rib. A broad elliptical fianch 
with ribs, or stays, is cast on each end of the segment, to connect 
tlie parts with eacli other; and three chaws, or sadcUs pi^-ces, 
with grooves in them, are cast upon the entrados of oacli seg- 
ment, and at equal intervals apart, to receive the open beam 
which rests on the curved rib. 

The ribs ai'e connected by an open tie plate, (Fig. 95.) Kaised 
elliptical projections axe cast on each face of the tie plate, where 
it is connected with tlie segments, which are adjusted accin-atcly 
to the interior surface of each pair of segments, between which 
the tie plate is embraced. The segments and plate are fastened 
by screw bolts passed through the end flanehes of tlie segments. 

The tie plates form the only connection between the curved 
ribs ; tlie broad ribbed flanehes of the seo;raents, and the raised 
rims of the tie plates inserted into Uie ends of the tubes, giving 
all the advantages and stiifiiess of diagonal pieces. 

532. Tubular ribs witli an elliptical cross section have been 
used in France for many of their bridges. They were first intro- 
duced bnt a few years back by M. Polonceau, after whose 



i / 

^ \ 

k ® 1 

rte. M— Bepraaonts a eWe view A .TJid « croas ei 
a, a, top flsnch, b, h boUoni fluncli of the Geml-sagn 
fTt, aiao Tlew of tho joint bol^^oon the DancliM 6, e i 

1 a-^i f nd visw B tlirousli i joLut of M. 
nritod along UievsrUoil joint ti tbionjrh 


\ the gi-eater part of tiese etruetnres have beer bnilt. 
AccordiBg to M. Poloiiceau's plan, each rib consists of two 
Bymmetiical parts divided lengtriwise by a vertical j oint. Each 
half of the rib is composed of a number of segments so distiibnt- 
ed as to break joints, in order that when the segments are pnt 
toffether there shall be no continnouB cross joint through the ribs. 

The segments (Fig. 96) are cast with a top and bottom flaiich 
and one also at each end. The halves of the rib are connected 
by bolts through the upper and lower flanchea, and the segments 
by bolts through the end flanchea. 

For the pm-poses of adjusting the segments and bringing the 
rib to a suitable degi-ee ol tension, flat pieces of wrought iron of 
a wedge shape are driven into the joints between the segments, 
and are confined in tlie joints by the bolts which fasten the 
segnents and which also pass tlirough these wedges. 

To connect the ribs with each other, iron tubular pieces are 

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placed between tliem, the ends of the tiibea Ijein^ saitaljly ad 
justed to the sides of the ribs. AVroughtiron rods whicli seiTe 
as ties pass thi-oiigh tlje tubes and ribs, being arranged witli 
ecrews andnuts to draw tlie rihs firmly against the tubular pieces. 
Diagonal pieces of a suitable fonn are placed between the ribs 
to give them the requisite degree of stiffness. 

In the bridges constructed by Mr. Poloncean according to 
this plan, he supports the longitudinal beams of the roadway by 
cast iron rings winch are fastened to the ribs and to each other, 
and bear a cnair of suitable form to receive the beams. 

533. Irmh roof Ti-usses. Frames of iron for roofe have been 
made either entirely of wrought iron, or of a combination of 
wrought and cast iron, or of these two last materials combined 
with timber. The combinations for the trusses of roofs of iron 
are in all respects the same as in those for timber trusses. The 
parts of the truss subjected to a cross strain, or to one of com 

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preaeioTi, are arranged to give tlie most suitable forms foi 
strength, and to adapt them to the object in view. The paiia 
subjected to a strain of extension, as the tie-beam and king and 
qneen posts, ave made either of wrought u-on or of timber, asmay 
befound best adapted to the particTilarendproposed._ The joints 
are in some cases arranged by inserting the ends of the beanis, 
or bare, in east iron sockets, or shoes of a suitable form ; in 
othei-s the beams are united by joints arranged like those for 
timber frames, tlie joints in all cases being secured by wrought 
iron bolts and keys. (Figs. 97, 98, and 99.) 

534. I^exihle Simportsjbr frames. Cliains and ropes may 
frequently bo substituted with advantage, for rigid materials, as 
intermediate points of support for fi'ames, forming systems of 
suspension in which tlie parts supported are suspended from 
the flexible supports, or else rest upon them either directly, or 
through the intermedium of rigid beams. 

535. All systems of suspension are based upon the property 
which the catenary cuito in a state of equilibrium possesses 
of converting vei'tical pressures upon it into tensions in the di- 
rection of the curve. These systems therefore offer the advan- 
tages of presenting the materials of which they are composed 
in the best manner for calling into action the gi-eatest amount 
of resistance of which they are capable, and of allowing the 
dimensions of the parts to be adapted to the strain thrown upon 
them more accurately than can be done in rigid systems ; thus 
avoiding much of the unproductive weight necessarily intro- 
duced into Btructures of stone, wood, and cast iron. They offer 
also the farther advantages that in their construction the parts 
ofwliichtheyareeomposedeanbereadily adjusted, put together 

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PE AMINO. 197 

and taken apart for repairs. They present tliedieadvaiitagesof 
changing both their form and dimcnsione from the action of the 
weather and variations of temperatm'e, and of being liable to 

frave accidents from undulations and vertical vibrations caused 
y high winds, or moveable loads. The require, therefore, that 
tie fixed points of support of the system should be very flrni 
and dm-able, and that constant attention should be given to 
keep the system in a thorough state of repair. 

536. A chain or rope, when fastened at each extremity to 
fixed points of support, will, from the action of gravity, assume 
the form of a catenary in a state of equiUbrium, whether the 
two exti-emities be on the same, or diflerent levels. The rela- 
tive height of the fixed supports may therefore be made to 
conform to the locality. 

537. Tlie ratio of the vei-aed sine of the arc to its chord, or 
span, will also depend, for the most part, on local cu'cumstances 
and the object of the suspended structure. The wider the span, 
or chord, for the same versed sine, tlie gi-eater will bo the 
tension along the curve, and the more sti'ength will therefore 
be required in all the parts. The rcvei'so will obtain for an 
increase of versed sine for the samo span ; but there will bo an 
increase in the length of the curve. 

538. The chains may either be attached at the exti-emities of 
the curve to the fixed supports, or piers; or they may rest upon 
them, (^Fig. 100, 101,) being fixed into anchoiing masses, or 

Fig; Ml- 

abutments, at some distance beyond the piers Locil circum 
stances will detennine which of tlie two methods i^ dl be the 
more suitable. The latter is generally adopted, particularly it 
the piers require to be high, since the strain upon them from 
the tension might, from the leverage, cause rupture in the pier 
near the bottom, and because, moreover it remedies in some 

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degree tlie inconvenieiiceB arising from variations of teiieict 
caused either by a moveable load, or clianges of temperatm-e, 
Piers of wood, or of east iron moveable around a joint at tlioir 
base, have been need instead of fixed piere, witn tlie object 
of remedying the same inconveniences. 

539. When the chains pass over the piers and are anchored 
at some distance beyond them, they may either rest upon 
saddle pieces of cast iron, or upon pulleys placed ou the piers, 

540. The position of the ancnoiing points will depend upon 
local circumstances. The two branches of the chain may either 
make equal angles witii the axis of the pier, thus assuming the 
Bame curvatui'e on each side of it, or else the extremity of the 
chain may be anchored at a point nearer to the base of the pier. 
In tlic former case the resultant of the tensions and weights will 
be vertical and in the direction of the axis of tlie pier, in the 
latter it will be oblique to the axis, and should pass so £ax 
within tlie base that the material will be secure from cmshing. 

541. The anchoring points are usually masses of masonry of 
a suitable foiTO to resist the strain to which they ai'e subjected. 
They may be placed either above or below the surface of the 
ground, as the locality may demand. The kind of resistance 
offered by them to tlie tension on the chain will depend upon 
the position of the chain. If the two branches of the chain malco 
equal angles with the axis of tiie pier, the resiatance offered 
by the abutments will mainly depend iipon the strength of the 
material of which they are formed. If the branches of the 
chain make unequal angles with tlie axis of the pier, the branch 
fixed to the anchoring mass is usually defiected in a vertical 
direction, and so secured that the weight of the abutment may 
act in resisting the tension on the chain. In this plan fixed 
pulleys placed on very iirm supports will be required at the point 
of deflection of tlie chain to resist the pressm'e arising from 
the tension at these points. 

"Wheneveritispracticable file abutmentand pier shouldbe suit- 
ably connected to increase the resistance offered by the former, 

Tlie connection between the chains and abntments should be 
so arranged that tho parts can be readily examined. The chaine 
at these points are sometimes imbedded in a paste of fat lime to 
preserve them from oxidation. 

543. Tlie chains may be placed either above or below the 
strocturo to be supported. The former gives a system of more 
stability than tlie latter, owing to the position of the centre of 
gi-avity, but it usually requires high piers, and the chain cannot 
generally be so well aiTanged as in the latter to subserve the re- 
quired purposes. The curves may consist of one or more chains, 
Several arc usually preferred to a single one, as for the sa 

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Binount of metal they offer more resistance, can be moic accu- 
rately manufactured, are lesa liable to accidents, and can Ija 
more easily put up and replaced tlian a single chain. The 
cliaina of the cui-ve may be placed either side by side, or above 
each otlier, according to circTimstances. 

543. The curves m ly he formed either of chains, of wire ca 
bles, or of bands of hoop iron. Each of tliese methods hai" 
found its respective advocates among engineers. Those who 
prefer wire cables to chains ui'ae that the latter are more liable 
to accideute tlian the fonner, that their strength is less unifonn 
and less in proportion to theii- weight than that of wire cables, 
that iron bars ai'e more liable to contain concealed defects than 
\rire, that the proofs to which cliaina ai-e subjected may increase 
without, in all cases, exjjosing these defects, and that the con- 
stmction and putting up of chains is more expensive and diffi- 
cult than for wire c^les. The opponents of wire cables state 
that they are open to tlie same objections as those m-ged against 
chains, that they offer a greater amount of surface to oxidation 
tlian the same volume of bar iron would, and that no precau- 
tion can prevent the moisture from penetrating into a wire 
cable and causing rapid oxidation. 

That in tliis, as in all like discussions, an exaggerated degi-ee 
of importance should have been attached to the objections urged 
on each side was but natui'al. Experience, however, derived 
&om existing works, has shown that each method may be ap- 
plied with eafety to sti'uctures of the boldest character, and that 
wherever failnres have been met with in either method, they 
were attributable to those faults of workmanship, or to defects 
in the material used, which can hardly be anticipated and 
avoided in any novel application of a Uke character. Time 
alone can definitively decide upon the comparative merits of the 
two methods, and how far either of them may be used witli 
advantage in the place of structures of more rigid materials. 

544. The ehaias of the curves may be formed of either round, 
sqiiare, or flat bare. Chains of flat bars have been most gene- 
rally used. Tliese are foi-med in long Hnts which are connected 
by short plates and bolts. Each link consists of several bars of 
the same lengthy each of which is perforated with a hole at 
each end to receive the connecting bolts. The bars of each 
link Ki-o placed side hy side, and the links are connected by 
iheplates which form a short link, and the bolts. 

The links of the portions of the chain wliicli rest upon tlie 
piere may either be bent, or else be made shorter than the 
others to accommodate the chain to the curved form of the sur- 
face on which it rests. 

545. The veriieal suspension bars may be citlier of round oj 

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square bare. Tliey iive uBually made with one or more articii 
latdons, to admit of their yielding -with less strain to the har tc 
any motion of vibration, or of oscillation. They may be siis- 
pended from the connecting bolts of the links, bnt the prefera- 
ble method is to attach them to a suitable saddle piece which 
is fitted to the top of tlie chain and thus distributes the sti-aiii 
npon the bar more nnifonnly over the bolts and links. The 
lower end of the bar is suitably arranged to connect it witli 
the pai-t suspended from it. 

546. The wire cables used for curves'are composed of wires 
laid side by side, which are brought to a cylindneal shape and 
confined by a spiral wrapping of wire. To form the cable seve- 
ral equal sized ropes, or yai'ns, aro iiret made. This may be 
done by cutting all the wires of the length reqtiked for the yam, 
or by uniting end to end the recLuisite number of wires for the 
yarn, and then winding them around two pieces of wrought or 
of cast u-on, of a horse-shoe shape, with a suitable gorge to re- 
ceive the wires, which are placed as far asunder as the requii'cd 
length of the yaxn. The yam is firmly attached at its two ends 
to WB iron pieces, or cru^ers, and the wires are temporarily eon- 
finedatintei-niediatepointsbyaspirallasliingofwii'e. Whichever 
of the two methods bo adopted, great cai-e must be taken to give 
to every wire oftheyani the same deereeof tension by a suitable 
mechanism. The cable is completed affcei- the yams are placed 
upon the piers and secured to the anchoring ropes or chains ; for. 
this purpose the temporaiy lashings of the yams are undone, and 
all the yarns are imited and brought to a cylindrical shape and 
secured tliroughout the extent of the cable, to within a short 
distance of each pier, by a continuous spiral lashing of wire. 

The part of the cable which rests upon the pier is not bound 
with wire, but is spi'ead over the saddle piece with a uniform 

54:7. The suspension ropes are foimed in the same way as the 
cables ; they are usually aiTanged witli a loop at each end, form- 
ed around an iron cmpper, to connect them witli tlie cables, 
to which they are attached, and to the pai-ts of the structure 
suspended from them by suitable saddle pieces. 

548. To secure the cables from oxidation tlie iron wires aro 
coated witli varnish before they are made into yams, and after 
the cables are completed they are either coated with the usual 
painte for securing iron fi'om the efi'ects of moisture, or else 
covered with some impermeable material. 

549. M^m'iments ontheStrerigth of IFrames. Experimental 
reseai'ches on this point have been mostly restricted to those 
made with models on a comparatively small scale, owing to the 
expense and difficulty attendant upon cxpcrinients on framea 

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having the form aiul diinensions of those emploj'ftd in ordinary 

Among the most remarkable experiments on a large scale 
are those made hy order of the French government at Lorient, 
under the direction of M. Eiebell, the superintending engineer 
of the port, and pahlished in the Ann<des Maritimea et Colo 
nicdes, Feb. imdKov., 1837. 

The experiments were made by first setting up the frame to 
he tried, and, after it had settled under tlie action of its own 
weight, suspending from the baclt of it, by ropes placed at 
equal intervals apart, equal weiglits to represent a load uni- 
tbrmly distributed over tlie hack of tlie frame. 

The results contained in the following table arc from experi- 
ments on a truss (Fig. 103) for the roof of a ship shed. The 
truss consisted of two rafters and a tic beam, witli suspension 

pieces in pairs, aud diagonal iron bolts which were added bcr 
cause it was necessary to scai-f the tie beam. The span of tlie 
truss was 65i^ feet ; the rafters had a slope of 1 pei-pendicular to 
4 base. The thickness of the beams, measm:ed honzontally, was 
about 2J inches, their depth about 18 inches. Tlie amount of 
the settling at each rope was ascertained by fixed graduated 
vertical rods, the measures being taken below a liorizontal line 
marked 0. 

—» ~— 

imonnt of setEling on tUe rlgbt of 1 
fan ridge beloir the hurlsuntol 0, 
in incbes. | 









Da io. lK4ibl:atiai3eSlba.,sij- 
S8BoT»^*T.»™™L™*rlbutoa°™d°13«3 lbs. Uom the 







The following table gives the results of experiments made on 
frames of the usual forms of straight and curved timber for roof 
trusses. The cur* ed pieces were made of two tliicknesses, each 

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Jf^indieB. The numbei-s in the fifth column give the ratioa 
between tho weight of the fi'ame and that of the weight horne 
by which tlie ehisticity was not impaired. 

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Framo fotmed of two mrtera nnd a tEo "boam * 
Do. do. do. 


Do. do. do. 

t i-^ma CI Hi aegmon't areu vnta i-jutere con' 
flned at their fiwt by a Ue piece, (Fir. 103) . 
Frame ot a foil senltc well conflned by a . 





3.1 to. 





with aiiapenalon i-ieces In pfjra 




550. TJndek thJs head will te comprised tliat elaes cf 8tnie= 
hires wliose object is to afford a line of commTiiiication above 
tlie general surface of a country, either by means of a roadway, 
or of a water-way, withoiit obstructing those comnmnicationa 
which lie upon tlie surface. 

"When the structure supports a roadway it is termed a viaduct y 
and when a water-way an aquedwct. 

If the structure is hmited to affording a communication over 
a water-course, it is termed' a lirldge when it supports a road- 
way, and an uqueduct^idge when it affords a water-way. 

For the convenience of description, bridges, &c., may be clas- 
sified either from the Idnd of material of wliicb they are con- 
structed, as a St<yn&-Bridge, a WoodmrBridge, &c., or from the 
character of the stnictui-e, aa a Pennanmt^Sridge, a Drww- 
Bridge, &c, 


551. A stone biidge coKSists of a roadway which rests upon 
one or more arches, usually of a cyhndrical form, the abutmonts 
and piers of the arches being of sufficient height and strength 
to secure them and tlie roadway from the eflects of an extraor- 
dinary rise in the wat^r-course. 

552. ZocaUty, Tlie point where a bridge may be required, 
as well as the direction of the axis, or centre line of tlie roadway 
over the bridge, usually depends Upon the position of a line of 
communication which traverses the water-course, and of which 
the bridge is a necessary lint. Wlien, however, the engineer is 
not restricted in the choice of a suitable locality by this condi- 
tion, he sliould endeavor to select one where the soil of the bed 
will afford a firm support for the foundations of the structure : 
where the approacltes, or avenues leading from the hanks of the 
watercourse to the bridge can be easily made, not requiring 
high embankments or deep excavations ; and one where the re- 
gimen of the water-course is uniform and not likely to he 
^changed in any hurtful degree by elbows, or otlier variations 
in the water-way near the bridge, or by the obstruction which 
the foundations, &c., of the structure may offer to the free dis- 
charge of the water. 

To avoid the difficulties which tiie construction of askew arches 

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presents, tlie axis of tlie bridge eliould be perpendicular tu the 
direction of the thread of tie current, since for me security of the 
foundations, the faces of the piers and abutments of the arches 
must be placed parallel to the thread of the cni-rent. 

553. Survey. With whatever considerations the loca.lity maj 
have been selected, a careful surrey must be made not only of 
it, but also of the wator-course and its environs for some distance 
above and below the point which tlie bndge will occupy, to en- 
able the engineer to judge of the probable effects wliich tlie 
bridge when erected may have upon the natural regimen of tlie 
water- coni'so. 

The object of tlie survey will be to ascertain thoroughly the 
natural features of the surface, the nature of the suLsoil of the 
bed and bants of the water-conrse, and the character of the 
water-coui-se at its different phases of high and low water, and 
of freshets. This information will bo embodied in atopographi 
cal map ; in cross and longitudinal sections of the water-courao 
and the substrata of its bed and banks, as ascertained by sound- 
ings andborings ; and in a descriptive memoir which, besides the 
usual state of the water-conrse, should exhibit an account of 
its changes, occasioned either by permanent or by accidental 
causes, as from the effects of extraordinary freshets, or from 
the construction of bridges, dams, and other artificial changes 
either in the bed or banks. 

654. Having obtained a thorougli knowledge botli of theposi- 
tion to be occupied bv the bridge and its environs, the two most 
essential points whicn will next demand the considei'ation of the 
engineer will be, in the first place, so to adapt his proposed struc- 
ture to the locality,that a sufticientwater-wayshallbe left bothfor 
navigable purposes and for the free discharge of tbe water accu- 
mulated during high freshets ; and, in the second, to adopt such 
a system of foundations as will be most likely to ensure the 
safety of the structure when exposed to this cause of danger. 

555. Water-way. When the natural water-way of a river is 
obstraeted by any artificial means, the contraction, if eonsidei^ 
able, will cause the water, above the point where the obstruction 
is placed, to rise higher than the level of that below it, and pro- 
duce a f(dl, with an increased velocity due to it, in the eun-ent 
between the two levels. These causes during heavy freshets, 
may be productive ofseriousinjuryto agriculture, from the over- 
flowing of the bants of the water course ; — may endanger, if not 
entirely suspend navigation, during the seasons of freshets ; — and 
expose any structure which, like a bridge, forms the obstruction, 
to rain, from the increased action of the current upon the soil 
around its foondations. If, on the contrary, the natural water 
way is enlarged at the point where the structure is placed, witb 

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the view of preventing tliese consequences, the velocity of tde 
cuiTent, dui-ing tlie ordinaiy stages of the water, will be de- 
creased, and tiiie will occasion deposita to be foiined at the 
point, which, by gradually filling up the bed, might, on a siidden 
rise of the water, prove a more serious obstruction tlian the stinic- 
ture iteelf ; particularly if the main body of the water shonldhap- 
pen to be diverted by the deposit from its ordinary cbaanela, and 
torm new ones of greater depth aroiind the foundations of the 

The water-way left by the structure should, for the reaaong 
above, be eo regulated that no considerable change shall be oc- 
casioned in the velocity of the cun-ent through it during the 
moat unfavorable stages of the water. 

556. For the pui-pose of deciding upon the most suitable ve- 
locity for the eiirrent through the contracted water-way formed 
by the structure, the velocity of the current and its effects upon 
file soil of the banks and bed of thenatni-al water-way should be 
carefully noted at those seasons when the water is lughest ; se 
lecting, in preference, for these observations, those points above 
and below the one which the bridge is to occupy, where the 
natural water-way is most contracted. 

557. The velocity of the cmTcnt at any point may be ascer- 
tained by the simple process of allowing a lightball,or jZouiof 
some material, like white wax, or camphor, wnose specific grav- 
ity is somewhat less than that of water, to be earned along by 
the current of the middle tiiread of the water-eom-se, and noting 
the time of its passage between two fixed stations. 

558. IFrom tlie velocity at the surface, aBcertained in this 
way, the average, or mean- velooiiy of the water, which flows 
tlirotigh tlie cross-section of any water-way between the stations 
where the observations ai'e taken, may he found, by taking four 
fifths of the velocity at the surface. 

Having tlie mean velocity of the natural wat«r-way, that of 
the ai-tificial water-way will be obtained from the following ex- 

tn which s and v represent, respectively, the area and mean 
velocity of the artificial water-way ; b and v, the same data of 
the natural water-way ; and m a constant quantity, which, aa 
determined from various experimenta, may be represented by tha 
mixed number 1,09T. 

"With regard to the effect of the increased velocity on the bed, 
there are no experiments which directly apply fo the cases usually 
met wiUi. The following table is drawn up from experiments 

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made in a coiiiiiied chaiinel, tlielDottom and sides of the cliaimel 
being formed of rougli "boards. 


per Bceond. 

Hatm-e or tbe bottom whldi Just bears 
fineb YolotUcs. 


OtiHnray flooiis . 
Uniform tonots . 
OHding . . . 


GrayolofthoBiiaofgaraeabeans. , , 


559. BayB. With tKe data now before liim, the engineer can 
proceed to the arrangement of the I'orma and details of the TH- 
none part8 of the proposed etmctui'e. 

The fii'st point to be considered under tliis head will be tlie 
number of toys, or intervals into which the natui'al water-way 
must be divided, and the forma and dimensions of the archea 
which span the bays. 

As a general rule, there should be an odd number of bays, 
whenever tbe width of tlie water-way is too great to be spanned 
by a single arch. Local circumstances may rccjuire a departure 
from this canon ; but when departed from, it will be at the cost 
of architectural effect; since no secondary feature can occupy 
tlie central point in any architectural competition -without impair - 
ing the beauty of the sti-ucture to the eye ; and as tlie archea 
are the main features of a stone bridge, the central point ought 
to be occupied by one of them. 

The width of the bays will depend mainly upon the charac- 
ter of the cun'ent, the nature of the soil upon wliieh the founda- 
iaons rest, and the kind of material that can be obtained for the 

For streams with a gentle euri'ent, whicli are not subject to 
heavy freshets, naiTow bays, or those of a medium size maybe 
adopted, because, even a considerable diminution of the natural 
water-way will not gi-eatly affect the velocity under the bridge, 
and thefoundations therefore will notbeliableto be undermined. 
The difficulty, moreover, of laying the foundations instreamsof 
this chai-acter is generally inconsiderable. Tor streams with a 
rapid current, and which are moreover subject to great freshets, 
wide bays will be most suitable, in order, by procuring a wide 
water-way, to diminish the danger to tlie points of support, in 
placing as few in the sti'eam as practicable. 

If materials of the best quality canbeproem-edforthestruc- 
ture, wide bays witli bold ai'chcs can be adopted with safety ; 
but, if tlie materials are of an inferior quality, it will bo most 

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prudent to adopt bays of a small, or medium space, and a 
Btrong form of arch. 

560. Arches. Cylindrical arches with any of the usual forme 
of curve of intrados Biay be used tor bridges. The selection 
will be restricted by tlie width of the bay, the highest water- 
level during freshets, the approaehea to the bridge, and the 
architecture effect which may be produced by the stnicture, aa 
it is more or less exposed to view at the intennediate stages be- 
tween high and low water. 

Oval and segment arches are niostly preferred to tlie foil cen- 
tre arch, particularly for medium and widehays, forthe reasons 
that, for the same level of roadway, they afford a more ample 
water-way under them, and their heads and spandrels offer a 
smaller smface to the pressure of the water dunngfreshets than 
the full centi'6 ai'ch under like circumstances. 

The full centre arch, fromtlie intrinsic beauty of iteforra, the 
Bimplicity of its consfci-uction, and itsstrength, should be pi-eferred 
to any other arch for biidges over water-coui-ses of a uniformly 
moderate current, and which are not subjected to considerable 
changes in their water-levels, particularly wlien its adoption does 
not demand expensive embankments for the approacnes. 

If the bays spanned by the arches are of the same width, the 
curves of all th,e areli^ must be identical. If the bays are of 
unequal width, the widest should occupy tbe centre of the struc- 
ture, and those on each side of the centre should either be of 
equal width, or else decrease uniformly from the centre to each 
extremity of the bridge. In this case the cuiwes of the arches 
should be similar, ancF have their springing hues on the same 
level throughout the bridge. 

The level of the springmg lines will depend upon the rise of 
tlie arches, and the height of their crowns above tlie water-level 
of tlie highest freshets. The cro'wn of the arches should not, as 
a general m!e, be less than three feet above the highest known 
water-level, in order tliat a passage-way maybe left for floating 
bodies descending during freshets. Between this, the lowest 
position of the crown, and any other, the rise should besochosen 
that the approaches, on tlie one hand,maynotbeunnece8sai-ily 
raised, nor, on tlie other, the springing lines be placed so low 
as to mai- tlie architectural efiect of me structure during the 
ordinaiy stages of the water. 

Whenthearcheeai'eof the same size, the axis of the roadwaj 
and the principal architecturallineswliich nm'lengthwiBe along 
the heads of the bridge, as the top of the parapet, the cornice, 
&c., &e., will be horizontal, and the bridge, to use a common 
expression, te on a dead level throughout. This has for some 
time been a favorite feature in bridge architecture, few of the 

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more recent and celebi-ated bridges being withiiut it, aa it is 
thought to give a character of lightness and boldness to the struc- 
ture which ia wanting iu bndges built with a uniform declivity , 
from the centre to the extreme arches. "Witliout stopping to 
examine this claim of arcliitecturai beauty for level bridges, it 
is well to state that it may be purchased at too great a cost, par- 
ticulai'ly in localities where the relative level of the roadway 
and of the adjacent gi'ound would demand high embankments 
for the approaches, 

561. Style of AroMteoture. Tlie design and consti'uction of 
a bridge snould be governed by the same general principles as 
any other arehitectaral composition. As the object of a bridge 
is to bear heavy loads, and to withstand the effects of one of 
the moat destructive agents with which the engineer has to 
contend, the general character of its architecture should be that 
of strength. It should not only be secure, but to the apprehen- 
sion appear so. It should be eq^ually removed from Egyptian mas- 
siveness and Oorintbian lightne^; while, at the same time, if 
should conform to the features of tlie surrounding locality, being 
more oi-nate and carefully wi'ought in its minor details in a city, 
and near buildings of a sumptuous style, than iu more obscure 
quartei-s ; and assuming every shade of confonnity, from that 
whieli would be in keeping with the humblest hamlet and tamest 
landscape to the boldest features presented by IN^atnre and Art. 
Simplicity and strength are its natural characteristics ; all oma- 
ment of detail being rejected which is not of obvious utility, and 
suitable to the point of view from which it must be seen ; as well 
as all attempts at boldness of general design which might ^ve 
rise to a feeling of insecurity, however unfounded in reality. Tiie 
most, therefore, that can be tried in the way of mere ornament, 
even under the most favorable circumstances, will be to combine 
the voussoirs of the arches with the horizontal courses of the span- 
drels in a regular and suitable manner, — to add a projecting cor- 
nice, with supporting members if necessary, of an agreeable pro- 
lile, — and to give such a fonn to tlie ends of the piers, termedTthe 
starlings, or cuPuoaters, as shall heighten the general pleasing 
effect. The heads of the bridge, tlie cornice, and the parapet 
should also generally present an unbroken outline ; this, however, 
may be depai'ted from in bridges where it is desirable to place re- 
cesses for seats, so as not to interfere with the footpaths, mwhicli 
case a plain buttress may be built above each starling to support 
the recess andits seats, the utUitr? of which will be obvious, while 
it will give an appearance of additional sti-ength when the hoiglif 
of the parapet above tlie etarlings is at all considerablo. 

562. Qonstruoiion. Tiie metliods of laying the foundations 
af structures of stone, iSrc, described imder the article of Ma- 


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Bonry, beins alike applicable to all structures ivliich come under 
this denommation, there only remains to be added under this 
head whatever is peculiar to bridge-bnilding. Either of the 
methods referred to may be employed ia laying the foundations 
of the abutments and piera of a bridge, which, in the judgment 
of the engineer, may be most suited to the locahly, and wiU be 
least expensive. As the foundations and their beds of the pai'ts 
in question are greatly exposed, from the action of the ciu'rent 
both upon ^le soil around them and upon the materials used 
for their construction, the utmost precaution should be taken to 
secure them from damage, by giving to the foundation-bed an 
ample spread where the soil is at all yielding; by selecting the 
most durable materials for the masonry of mese parts ; and by 
employing some suitable means for securing the bed of the 
natural water-way around and between the piers from being 
removed by the current, 

563. Vai-ious expedients have been tried to effect tliis last 
object ; among the most simple and efficacious of which is that 
of covering the surface to bo protected by a bed of stone broken 
into fragments of sufficient bulk to resist the velocity of the 
current in the bays, if the soil is of an ordinary clayey mud ; 
but, if it be of loose sand or gi-avel, the surface should be first 
i covered by a bed of tenacious clay before the stone be thi-own 
in. The voids between the blocks of stone, in time, become 
filled with a deposite of mud, which, acting as a cement, gives 
to the mass a character of great durability. 

56i. The foundation courses of the piers should be fonned of 
heavy blocks of cut stone bonded in the most careful manner, 
and carried up in offsets. The faces of the piers should be of 
cut stone well bonded. They may be bmlt either verticaUy, or 
with a shght batter. Tlieir fliickness at the impost should be 
greater than what would be deemed sufficient undei- ordinary 
circumstances ; as tliey are exposed to the destractive action of 
thecm'rent, and of shocks from heavy floating-bodies; and from 
tlie loss of weight of the parts immersed, owing to the buoyant 
effort of the water, their resistance is decreased. The most siic- 
cessful bridge architects have adopted the practice of maJdng 
tlie thickness of the piers at the impost between one sixth and 
one eighth of the span of the arch. The thickness of tlie piers 
of tlie bridge of Neuilly, near Paris, bnilt by the celebrated 
Pcrronet, whose works form an epoch in modem bridge archi- 
tecture, is only one ninth of the span, its arches also being re- 
markable for the boldness of their cmwe. 

565. The usual practice is to give to all the piers tl e same 
proportional thickness. It has however been recomraer ded by 
eome engineers to give snffipieiit thiclaiess to a few of the piera 

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to reaist the horizontal dirust of the archea on either eide of 
tliem, and thns secure a part of tlie stnieture from niin, should 
an accident happen to any of the other piei-s. These masses, 
to which the name alutment piers has been appHed, would ho 
objectionable from the diminution of the natural watei'-way that 
would be caused by their bulk, and from the additional cost for 
their construction, besides impairing the architectural effect of 
the Btracture. They present the advantage, in addition to their 
main object, of iiermitting the bridge to be constnicted by 
sections, and thus procure an economy in the cost of the wooden 
centres for the arches. 

i>66. The projection of the starlings beyond tlie heads of the 
bridge, their form, and theheight given to them above ttie spring- 
ing lines, will depend upon local circumstancea. As the mam 
objects of the starhngs are to form a fendiyr, or gum-d, to secure 
the masonzy of the spandrels, &c., from being damaged by float- 
ing bodies, and to serve as a cut-water to tm^n the cmTent aside, 
and prevent the formation of whirls, and their action on the bed 
around the foundations, the form given to them should subserve 
both these purposes. Of the difiercnt forms of horizontal section 
Avhich hive bpen -iven to starlings {^i"-. 107 108, 109, 110,) 

F gs. IDT OS, and 110-KeprD- 
n hontontnl eocdoiu nl 
niUngB A ol ths more uinal 
nus imS jHui of the ^er Jl 
b lie Vtaadaaaa cunises. 
Fig. 109 reprasentB tbe plan cf 
tlie lood of a Blarllng li^a in 
umi-ses, the gcnecnl slinpe be- 

tho semi ellipse, from experiments cai-efully made, with tlieaa 
ends in view, appeal's best to satisfy both objects. 

The up and down sti-eam starlings, in tidal rivers not subject 
to freshets and ice, usually receive the same projections, which, 
^^'hon their plan is a semi-ellipse, must be somewhat gi-eater tlian 
iho eomi-width of the pier. Their general vertical outline is 

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colnirmar, being either straight or swelled , (Ilga. Ill, 113, ^.IS, 
114.) They should be built aa higli as the ordiuary highest 

Fig, 111— Eeprcsents In cloraKon stnrlinp A, their iooda B, tho roasaolra 0, the Bpnoflrela D 
nnd ttia uomtlnaUoD of lioii' conraa an-l jolnM wllh eicli other In OD ovol nreh ol tbn^t 

-" — £ ^ ■■ 

\ 1 

Fig. 113— Eeprcsonls In olcvnUon tlio M 
Titl^e of Heuillj-, and oval of clovei 

olemcnls us In Fig. 113, tiom lb- 

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r„ ll+-Iteprosoiitsncr,).5aB6iitloii 
of Fig. 118, siowlDg the arrange- 
J tba, pampat, and coi-Dkc' 

water-level. They are finislied at top with a coping stono to 
presei've the inaBoniy from the action of rain, &c, : this stone, 
termed the liood, may receive a conical, a spheroidal, or any 
other shape which will siibeerve the object in view, and produce 
a pleasing architectural effect, in keeping with the locahty. 

In sti-eams' subject to freshets and ice, the up stream starling 
should receive a greater projection thaa tlioso down stream, and, 
moreover, be hmlt in tlie form of an inclined plane (Fig. 115) 

ig. llS~KcriK!onta a ^da elevation M 
and plan if of a plot of tho Potomno 

, up-atteam Btaflins, Willi tho Inclin- 
ed Ice-brejikeT D wbfclt tLsea from 

:^ lop 01 pie 


to facilitate the breaking of the ice, and its passage throntrii 
the arches. 

567. Where the banks of a water-courBe spanned by a bridge 

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are so Btcep and difficult of access tJiat the roadwi. y r:.ust be 
raised to the same level with their crests, BecuritT for tlie founda- 
tion, and economy in tho construction demand that JioUow or 
open piers be used instead of a solid mass of masomy. A con- 
struction of tliis kind rec[u.ires gi'eat precaution. Xlie facing 
coui'ses of the piers i^nust be of heavy blocks dressed with ex- 
treme accui'acy. The starlings must be built solid, Tlie faces 
must be eonnected by one or more cross tie-walls of heavy, well- 
bonded blocks ; the tie-walls being connected from distance to 
distance vertically by strong tie-blocks ; or, if the width of the 
pier be considerable, by a tie-waU along its centre line. 

568. Tlie foundations, the dimensions, and the foi-m of the 
abutments of a bridge will be regulated upon the same principle 
as the like parts of other arched structures ; a judicious con- 
formity to the character of strength demanded by the structure, 
and to the requirements of die locality being obsei-ved. Tlie 
walls which at the extremities of the bridge form the con- 
tinuation of the heads, and sustain the embankments of the ap- 
proaches, — and which, from their widening oufclrom the general 
line of the heads, so as to form a gradual conti-action of the 
avenue by which (lie bridge isapproached, are termed the■w^)^5'- 
walls, — serve as fii-m buttresses to the abutments. In some cases 
the back of the abutment is terminated by a cylindrical arch, 
(Fig. 116,) placed on end, or having its right-line elements ver- 

in 110— Eeptcscnts a horlMmtal acctiun 

Fig. Ill— KcpresentellliorfzonM 

tical, which connects the two wiiig-walls. In others (Fig. 117) 

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a rectangular-sliaped biittress is "built back froa the centre line 
of the abiitment, and is connected -witb the wing walls oither by 
boriaontal arches, or by a vertical cross tie-wall, 

569. The -wing-walls may be either plane surface walls (Fig. 
118) arranged to make agiven angle with the lieadsoftbebridge, 

or they may be curved surface- walls presenting their concavity, 
(Fig. 136,} or their convexity to tlie exterior ; or of any other 
shape, whether presenting a continuous, or a broken surface, that 
the loealitj- may demand. Their dimensions and form of profile 
will be regelated like those of any other sustaining wall ; and 
they receive a suitable finish at top to connect tliem with the 
bridge, and make them conform to the outline of the embank- 
ments, or other approaches. 

570, The arches of bridges demand great care in proportion- 
ing the dimensions of the voussoirs, and procuring accumey in 
their forms, as the strength of the etructare, and the pennanenee 
of its flgnre, will chiefly depend upon the attention bestowed on 
these points. Peculiar cavo ehoiud be given in arranging the 
masonry above the piers which lies between the two adjacent 
arches. In some of tiie more recent bridges, (Fig, 120,) this pai't 
is built upsolid but a short distance above the imposts, generally 
not higher than a fourth of the rise, and is finished with a roversec? 

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arch tj give greater aeciirity against tlie effects ( f the pressure 
thrown upon it. 

a tbe atncliDge for senls 

The backs of the arches should bo covered wijli a water-tight 
capping of beton, and a coating of asphaltum. 

571. The entire spandi-el com-ses of the heads are usnally not 
laid Till til the arches have been iincentred, and have settJocl, in 
O.'derthat the joints of these courses maynot be subject to any 
Other cause of displacement than wliat may anse from the effects 
of vajiations of temperature upon the arcnee. The lihicltnesa of 

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BTO:S< ERIDGK8. 217 

(he head-walls will depend upon the method adopted for support- 
ing tlie roadway. If this he by a filling of earth between the 
liead-wallB, tlien their thickness must be calculated not only to 
resist the pressure of tlie earth which they sustain, but allowance 
must also be made for the effects of the shocks of floating bodies 
in weakening the bond, and separating the blocks from their mor 
tai^-bed. The more approved methods of supporting the roadway, 
and which ai-e now generally practised, except for very flat seg- 
ment arches, are to lay the road materials either npon broad flag- 
ging stones (Fig- 120, 191,) which rest upon thin brick walls bnut 

I II I 1 1 I 1 ] I I 1 ] icrs and arches; 

01 b) bmiU aichcs, (Ti^ 1^- ) 1 i "wl i h tlicsi, walls servo as 
pieis; or by a system oi "(mall groined aichea supported by 
piUais re='ting upon the pien, and mam arches when either 
of these memods is used, the head-walls may receive a mean 
thickness of one fifth of their height above the sohd spandrel. 

572. Svfperstruoture, The superatnictnre of a bridge consists 
of a cornice, the roadway and footpaths, &c., and a pai-apet. 

Tlie object of tlie cornice is to shelter the face ot the head- 
walls from rain. To subserve this puzpose, its projection beyond 
the smface to be sheltered should be the greater as the altitude 
of the sheltered part is the more considerable. Biis rale will 
require a cornice with supporting blocks, (Fig. 123,) teiraed 
modiUions, below it, whenever the projecting part would he 
actually, or might seem insecm-e from its weight. The height 
of the cornice, including its supports, should generally be equal 
to its projections ; this wiU often require more or less of detail 
in the profile of the cornice, in order tdat it may not appear 
lieavy. The top surface of the cornice Ehonld he a little above 

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that of tlie footpath, or roadway, and be sliglitly elcped oi^t- 
■ward ; the bottom should be aiTanged with iCsitrnMalarmicr^ 

Fla. laS-Ecpresfiil 

or drip, to prevent the water from finding a 
under surface to the face of the wall. 

573. Hie parapet snvmounts the coi'iiice, and sh mid he high 
enough to secure vehicles and foot-pass en gere from accidenis, 
without however intercepting the view from tire bridge. The 
parapet is Tieually a plain low wall of cut stone, surmounted by 
a coping Bh'gMy roxiuded on its top surface. In bridges which 

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liavo a character of lightness, like those with flat segmeat arches, 
the parapet may consist of alternate panels of plain wall and 
balustrades, provided this arrangemeTit be otlierwise in keeping 
with the locality. The exterior face of the parapet should not 
project beyond that of the heads. The blocks of which it is 
formed, and particnlai'ly tliose of tlie coping, should be fii-mly 
secured with copper or iron cramps. 

574. The width of the roadway and of the footpatlis will be 
regnhitedbytlielocaHty; being greatestwhere the thoroughfai-es 
connected by the bridge are most frequented. They are made 
either of broken, orof pavingstone, Tney should be so arranged 
that the surface-water from rain shall run quickly into the side 
channels left to receive it, and be conducted from thence by pipes 
which lead to vertical conduits (Fig. 121) in the piers that have 
their outlete in one of the faces of the piers, and below the 
lowest water-level. 

575. Strong and durable stone, di-essed witli the chisel, or 
hammer, should alone be used for the masonry of biidges where 
tlie span of die arch exceeds fifty feet. The interior of the 
piera, and the backing of the abutments and head-walls may, for 
economy, be of good nibble, providedgreat attention be bestowed 
upon the bond and workmanship. For medium and small spans 
a mixed masonry of dressed stone and rubble, or brick, may be 
used ; and, in some cases, brick alone. In all these cases (Figs.. 
132, 124) the starlings, — the foundation courses, — the impost 
stone, — ^me ring conrBes, at least of the heads, — and the key- 
stone, should be of good dressed stone. Tiie remainder may be 
of coui-sed rubble, or of the best brick, for the facing, with good 
rubble or biick for the fillings and backings. In amixed masonry 
of this character the courses of dressed stone mayproject slight- 
ly beyond the surfaces of the rest of the structure. The archi- 
tectural effect of this aiTangement is in some degree pleasing, 
particularly when the joints are chamfered ; and tlie method la 
obviously useful in structures of tliis kind, as protection is af- 
forded by it to the surfaces which, from the nature of the mate- 
rial, or the character of the work, offer the least resistance to the 
destructive action of floating bodies. Hydraulic mortal' should 
alone be used in eveiypart of the masonry of bridges. 

576. Approaches. The aiTangement ot the approaches will 
depend upon the number and direction of the avenues leading to 
the bridge, — the width of the avenues, and their position above 
or below the natural surface of the gi'ound, — and the locality. 
The principal poiuts to be kept in view in their arrangement are 
to procure an easy and safe access to the bridge for vehicles, and 
not to obstruct unnecessarily the ehaimels, for pui-poses of navi- 
gation, which may bo requisite under the extreme arches. 

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When the avenue to the bridge is, "by an embankment, in the 
eame line as its axis, and tlie roadway and bridge are of the same 
width, the head-walla of the bridge (Fig. 125) may be prolonged 
sufficiently far to allow tho foot of the Gmbantmcnt elope to fall 
within a few feet of the crest of the elope of the watei'-conree ; 
this portion of the embankment slope being shaped into the form 
of a quarter of a cone, and reveted with diy stone or sods, to pre- 
serve its surface from the action of rain. 

When several avenues meet at a bridge, or where the width 
of 'he roadway of a direct avenue is greater tlian that of the 

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bridge, tlie approacliRs are made by gi-adually w. deniiig the out 
let from the bridge, until it attains the requisite width, by means oi 

. . . _ . . lie eiaa alojjca of th« bant,. 

wing-walls bf any of tlie usual forms tliat may suit tlie locality. 
The form of wing-wall (Kg. 126) presenting a concave sm^face 
outward is usually preferred when suited to the locality, both 

Fiji. 128— EtiiroBeiit an elevation M anfl plia 
B, B', elope of cmbaokmcut 

fcr its architectunl effect and its strength. When made ol 
diessed stone it la ot more difficult constrnction and more ox- 
ponaivo than thfe plane sui-face wall. 

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In order that the approaches may not obstruct the com. 
mnniciitions along the haiiks for tlie purposes of navigatic ii, lui 
arched passage-way will, in most cases, be requisite under the 
roadway of the approach and behind tlie abutment of the ex- 
treme ai'ch, for hoi-s^, and, if necessary, vehicles. When the 
form of the arch will admit of it, as in flat segment arches, a 
roadway, projecting beyond the face of tie abutment, may be 
made under tlie ardi for the same purpose. 

577. Wat&i-^wings. To secure tlie natural banks near the 
bridge, and the foundations of the abutments from the action of 
the current, a facing of dry stone, or of masonry, should be laid 
upon the slope of the hanks, which should he properly prepared 
to receive it, and the foot of the facing must be secured by a 
mass of loose stone blocks spread over the bed around it, in ad- 
dition to which a line of square-jointed piles may be previously 
driven along the foot. "When the face of the abutment projects 
beyond tlie natural banks, an embankment faced witli stone 
should be formed connecting the face with points on the natural 
banks above and below the bridge. By this arrangement, 
termed the water-wings, the natural water-way will be gradu- 
ally contracted to confonn to that left by the bridge. 

578. ETilargement of Wider-way. In the full centre and oval 
arches, when the springing lines are placed low, the spandrels 
present a considerable surface and obstruction to the current 
during the higher stages of tlie water. This not only endaugei's 
the safety of tlie bridge, by the accumulation of diift-wood and 
ice which it occasions, but, during these epochs, gives a heavy 
appearance to the atructui-e. To remedy these detects the solid 
angle, formed by the heads and the soffit of the arch, may be 
truncated, the base of tlie cuneiform-shaped ma^ taken away 
being near the springing lines of the arch, and its apex near the 
crown. The foi-m of me detached mass may be variously ar- 
ranged. In the bridge of Ilfeuilly, which is oneof thefirst where 
this expedient was resorted to, the surface, marked F, (Figs. 113, 
114,) left by detaching the mass in question, is warped, and lies 
between two plane curves, the one an arc of a circle n o, ti'aced 
on the head of the bridge, the other an oval m o op, traced on 
the BoiBt of tlie arch. This affords a funnel-shaped water-waj 
to each aixh, and, during high water, gives a lignt appearance 
to the strnctui"e, as the voussoirs of tiie head ring-coiu'se have 
then the appearance of belonging to a flat segmental arch. 

579. Oenires. The framing of centres, and the arrangement 
for striking them, having been already folly explained under tlie 
article Framing, with illustrations taken from some of the most 
celebrated recent structures, nothing further need be here added 
than to point ont the necessity of great care both in the conibi- 

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nation of tlie frame, and in its mechanical execution, i- order 
to prevent any change in the fonn of the arch while nnder con- 
struction. The English engineers have generally been more 
successful in this respect than the Fi-ench. Hie latter, in several 
of their finest bridges, used a form of centre composed of seve 
ral polygonal frames, with short sides, so inscribed within each 
other ttiat the angles of tlie one corresponded to the middle of 
the sides of the ouier. The sides of each frame were united by 
joints, and the series of frames secured in their respective posi 
tions by radial pieces, in pairs, notched upon and bolted to the 
frames, which they clamped between them. A combiaation of 
this character can preserve its fonn only under an equablo 
pressure distiihuted over the back of the exterior polygon. 
When applied to the ordinaiy eircumstancea attending the con- 
struction 01 an arch, it is found to undergo successive changes 
of shape, as the voussoirs are laid on it ; risingfii-st at the crown, 
then yielding at the same point when the key-stone and the ad- 
jacent vousaoire are laid on. The English engineers have gen- 
erally selected those combinations in which, the pressures being 
transmitted directly to fixed points of support, no change of 
form can taJce place in the centre but what arises from the 
contraction or elongation of the parts of the frame. 

580. Q&aeral Remarks. The architecture ofstone bridges has, 
within a somewhat recent period, been cai-ried to a very high de- 
£free of perfection, both in draign and in mechanical execution. 
France, m this respect, has given an example to the world, andhas 
found worthy rivals in the, rest of Europe, and particularly iu 
Great Britain. Her territory is dotted over witJi innumerable 
fine moniiments of this character, which attest her solicitude ae 
well for the public welfare as for the advancement of the in- 
dustrial and liberal arts. Eor her progi'^s in this branch of 
architecture, France is mainly indebted to her School and her 
Corps of Fonts et Chmissies- institutions which, from the time 
of her celebrated engineer PeiTonet, have supplied her with a 
lo:ig line of names, ^ke eminent in the sciences and arts whicli 
pertain to the profession of the engineer. 

England, although on eoraepoints of mechanical skill pertain- 
ing to the engineer'sarttheeuperiorof France, holds thesecond 
rank to her in the science of her engineers, Witliout establish- 
ments for professional training corresponding to those of France, 
the English engineers, as ahody, have, until within a few years, 
iaborea under the disadvantage of having none of those institu- 
tions which, by creating a common bond of union, serve not only 
to diffase science tliroughont the whole body, but to raise ment 
to its proper level, and ffown down alike, throngli anenliglitened 
e&prit de cor^, the assumptions of ignoi'ant pretension, and the 

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malevolence of petty jealousies. Althotigli, as a body, lees ai! 
vaiitageously placed, in these respects, than theirmore thorough 
bred brethren of France, the engineers of England can point 
■with a jnst feeling of pride, not only to the monuments of their 
sldll, hat to individual names among them which, achieved 
nnder the peculiar obstacles ever attendant npon self-educatioi], 
yet stand in the &-et rank of thosebywhoso genius tlie industrial 
arts have been advanced and ennobled. 

The other European States have also contributed largely to 
bridge architeetui-e, although their efforts in tliis line are less 
widely known through their publications than those of France 
andEngland. Among the many bridges belonging to Italy, may 
be met^ cited the far-tamed MiaUo ; the bridge of oanta Trinita 
at Florence, the curve of whose intrados was so long a mathe- 
maticalpuzzle ; and the recent single arch over the DoraSi^a/ria 
near Turin. 

In the United States, the pressingimmediate wants of ayonng 
people, who ai'e still without that accumulated capital by which 
alone great and lasting pnbliemonuments can be raised, havepre- 
venteamnchbeingdone,iAbridge building, except of atemporary 
character. The bridges, viaducts, and aqued nets of stone in our 
country, almost without an exception, have been built of rustic 
work through economical considerations. The selection of thie 
kind of masonry,independently of its cheapness, has the merit of ap- 
propriateness, when taken in connection with iJie natural features 
ofthelocalities'wheremost of thesestmctures are placed. Among 
the works of this class, may be cited the riulroad bridge, called the 
"" ! Viad^lct, over the Patapsco, on the line of the Baltimore 

andWashingtonraih-oad, designed and built by l([r,B.H.Latrobe, 
the engineer of the road. This is one of the few existing bridge 
sti'ucturea with a curved axis. The engineer has very happily 
met the double difficulty before him, of beingobhged to adopt a 
curved axis, and of the want of workmen sufficiently conversant 
with the appKcation of working drawings of a rather compli- 
cated, feliaractcr, by placing full centre cylindi'ical arches upon 
Qiera with a tL-apezoidal horizontal section. Ttiis structure, with 
ute exception of some minor detfuls in rather questionable taste, 
as theslightiron parapet railing,for example,presents an impo- 
sing _aspect, and does great credit to the intelligence and skill of 
file engineer, at the time of its construction, but recently launched 
in a new career. The fine single arch, known as the Carrolton 

Viadmof, on the Baltimore and Ohio railroad, is also highly credit- 
able to the science andsltillof tlieengineer and mechanics under 
whom it was raisd. One of the largest bridges in the United 
States, designed and partly executed in stone, is the Potomaa 

Aqueduct at Georgeto \vii, where theChcsapeakoandOhio canal 

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intersects the Potomac river. This work, to wliich a wooden 
Buperstructuro lias been made, was built under the superintend- 
ence of Captain TurnbuU of the U. S. Topographical Engineers. 
In the published narrative of the progress of this work, a very fuU 
account is given of all tlie operations, in which, whxle the re- 
sources and skill of the engineer, in a very difficult and, to him, 
imtricd application of his art, are left to be gathered by tiie reader 
from the successful termination of the undertaldng. his failures 
are stated wiih a candor alike creditable to the man, and worthy 
of imitation by every engineer who prizes the advancement of his 
art above that personal reputation which a less trulliful course 
may place in prospect before him. 

581. The following table contains a summary of the principal 
details of some of the more noted stone bridges of Europe. 






Na™ off.^iieec. 

Vlellle'Srionda . 


3e lent 






cibik" 1 ; X 



Ke^l!y(A) . . 






47SI 1774 
- |1"5 


aalnl-MBiance (B) 



41,5 :i7&i 

Olpiac . . . . 



- 1793 


JeiiH[C) . . . 





43.7 !i3i: 




Si»(i)): : 


GlouMsleUE) . 


Lnadoo (F) . 


66 m 

Tl<rtn(G). . . 



GnBTsnoc (H) . 







(A.) This fine structure, designed and built by the celebrated 
Perronet, forms an epoch in bridge architecture,- from the bold- 
ness of its design, its skilful mechanical execution, and the simple 
but appropriate character of its architectural details. The curve 
of tlie intrados is an oval of eleven centres, the radius of the arc 
at the spring being 20.9 feet, and that of the arc at the crown 
159.1 feet. The engineer conceived the idea of giving to the 
soffit a funnel shape, by widening it at the heads, from the crown 
to the springing line. This he effected by connecting the soffit 
of each arcii and the heads by a warped surface, which passed, 
on the one hand, through a flat circular arc, described upon the 
heads through the points of the crown and the top of the two ad- 
jacent starlings, and, on the other, through two curves on Ihf 
soffit, cut out by two vertical planes, oblique to tlie axis, passea 
through the highest point of the curve on the heads, and through 
points on the two respective springing lines of the arch. The ob 
lect of this arrangement was twofold ; first, — as the springing Unea 
WPTC placed at the low-water level, tlic bridge, during the ecasona 

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of high water, would Jiave appeared ratJier heavy, as the grealei 
part of the sollit, at this period, would have been under water, — ■ 
it gave the bridge a lighter appearance during the epochs of high 
water ; and, second, as the obstruction to the free flow of die 
water from fJie spandrels would be very considerable at the same 
periods, the funnel form given to the sofHt at the heads partially 
femedied this inconvenience. 

The axis of the roadway, the coniice, and all the correspond- 
ing architectural lines were made horizontal, a feature in bridge 
architecture which the reputation of Perronet has since rendered 
classical ; and to obtain which points truly essential conditions 
have in some more recent structures been sacrificed. 

The abutments are 32 feet thick at the springing lines, and llie 
piers but 13.8 feet at the same point, giving an example of judi- 
cious boldness combined with adequate strength, on scientific 
principles, which had been partially lost sight of by preceding en- 
gineers in designing this part of bridges. 

The centres of the Neuilly bridge were designed upon the 
faulty principle of concentric polygonal frames. Perronet was 
aware of the inconveniences of this combination, and in no part 
of the construction of the bridge than in this was more sagacious 
forethought displayed by him, in providing for foreseen contingen- 
cies, nor greater resources and skill in remedying those wliich 
could not have been anticipated. An oversight, rather more 
serious in its consequences, was committed in widening the nalu- 
lal water-way of the river where the' bridge was erected; the 
eifect of this has been a gradual deposition near the bridge, and 
an obstruction of the navigable channcis. 

The bridge of Neuilly is a noble monument of the genius and 
practical skill of its engineer. The style of its architecture, both 
as a whole and in its several parts, is imposing and in tlie best 

(B) This bridge was built after the designs of Perronet. Se- 
duced by a thorough, knowledge of the capabilities of his art, tiic 
engineer was led, in planning this structure, into the error of 
sacrificing apparent strength, lor the purpose of producing great 
boldness and lightness of design. This he effected by placing 
very flat segment arches upon piers formed of four columns ; the 
two, forming the starlings, being united to the two adjacent by a 
connecting wall, an interval being left between the two centre 
columns. The diameters of the columns are 9.0 feet, with the 
same interval between tliem. 

The engineer who constructed the bridge, apprehensive appa 
renlly for its safety, introduced into the courses of tlie piers and 
of I le arches a large quantity of iron ties and cramping pieces, a 
mea5U'e oi precaution which, if necessary, ought to have con 

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ilemned the original designs, althougli supported by the high 
authodty oi Perronel, ana caused otliers lo be substituted tot 

(C) This bridge, now designated as the Pont de TEcole Mili 
taire, from its locality, and the bridge of Rouen, arc built upon 
nearly the same designs. The former is a model of architectural 
taste and of skilful workmanship. Its horizontal architectural 
lines, its fine cornice, copied from that of the temple of Mars the 
Avenger, and the sculptured wreath on its spandrels, form a 
whole of sii!gular beauty. 

(D) This bridge, designated when first built as the Strand 
Bridge, is worthy of the great metropolis in which it is placed. 
The engineer, influenced perhaps by other examples of the same 
character in the vicinity of this structure, has placed small col- 
umns upon tlie starlings, which support lecesses with seats for 
foot-passengers, and has thus m no inconside able degree, de- 
prived the bridge of that imposing character which its misiive- 
uess, and the excellent material of which it is built, could not 
otherwise have failed to produce 

(E) This fine elliptical arch is m 'iome respects built m imi 
tation of the Neuilly bridge, witli a funnel shaped soffit Its j,en 
oral architectural effect is heavy and its mere oraamenta' parts 
are m questionable taste The details of itf construct on aie 
alike monuments of the eminent piofessional skill, ind of the 
tnrthfulness of character of the great engineer whoplanned and 
superintended it In his nanativc of tlie work, Mr. Telford takes 
blame to himself foi OAei=iights and unanticipated results, in which 
the scrupulous care that he conscientiouiJy brought to every un- 
dertaking committed to him is unwittingly thrown into bolder 
relief, by tlie very confession of his failures ; and a lesson of in- 
struction is conveyed, more pregnant with important conseijuences 
to the advancement of his profession than the recording of hun- 
dreds of successful instances only could have furnished, 

(F) This noble work of Sir John Rennie must ever rank among 
the master-pieces of bridge architecture, in eveiy point by which 
this class of structiures should be distinguished. For boldness, 
strength, simpHcity, massiveness witliout heaviness, and a happy 
adaptation oi design to the locality, it stands unrivalled. Tlie 
beauty which is generally recognised in a level bridge has, in 
lliis, feeen judiciously sacrificed to a well-judged economy ; and 
the artificial approaches have thus been accommodated to the 
existing, by decreasing the dimensions of the arches from the 
centre to the two extremities. The square plain buttresses, 
which rise above the stailings and support the recesses for seats, 
Bre of fartlier obvious utility in strengthening the head-walls, 
rhich, at these points are of considerable height ; and ihey aW 

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prodice, in this case, a not unpleasing architectural effect, in 
separating the unequal arches, without impairing the unity of the 
general design. 

(G) Tliis is the boldest single arch of stone now standing, and 
!S a splendid example of architectural design and skilful workman 
ship. The soffit of the arch is made slighuy funnel-shaped, which 
gives (he bridge an air of almost too great boldness. The cornice, 
wiiich is copied from the same model as that of tlie bridge of 
Jena ; the convex cylindrical-shaped wing-walls, which give an 
approach of 144 feet between the parapets ; with the other archi- 
tectural accessories, have made this bndge a model of good taste 
for imitation under like circumstances. From the omission of a 
usual architectural member, there is perhaps a slight feeling of 
nakedness produced on the mind of the rigid connoisseur in art, 
on first seeing this structure, and its beauty is in some degree 
marred by this want. 

The abutments of this t)ridge are 40 feet thick at the founda- 
tions, and, besides the wing-walls, are strengthened by two coun- 
terforts 20 feet long and 10 feet wide. 

(H) The span of this arch is the widest on record. For 
architectural effect this bridge presents but little to the eye that 
is commendable ; for tliis the engineer who superintended it is 
liardly responsible, except so far as, from professional sympathy 
and respect for a deceased member of the profession, he was led 
to adopt the designs of another. The abutments form a continua- 
tion of the arch ; and the other details of the construction through 
out exhibit that thorough acquaintance with their art for which 
the Hartleys, father and s-^n, are well knovra to the profession. 

5S2, The practice of briage building is now generally the same 
throughout the civihzed world. In France, the method of laying 
tlie foundalions by caissons lias, in most of their later works, been 
preferred by her engineers, to that of coffer-dams ; and in the su- 
perstructure of their bridges the French engineers liave generally 
filled in, between the arches and the roadway, with solid material. 
In some of these bridges, as in that of Bordeaux, where appre- 
hension was felt for the stability of the piling, a mixed masonry 
of stone and brick was used, and the roadway was supported by 
a system of light-groined arclies of brick. Among the recent 
French bridges, presenting some intf.resting features in their con- 
struction, may be cited that of Souillac over the Dordogne. The 
river at tliis place having a torrent-like character, and the bed 
being of lime-stone rock with a very uneven surface, and occa 
siona! deep fissures filled with sand and gravel, the obstacle tt 
using either the caisson, or the ordinary coffer-dam for the foun- 
dations, was very great. ■ The engineer, M. Vicat, so well knowii 
»y liis researches upon mortar,. &.c., devised, to obviate these 

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difficulties, tlie plan of enclosing the area ot" each piei Dy a coffer 
work accurately fitted to the surface of the bed, and of filling this 
with beton to form a bed for the foundation courses. This he 
effected, by first forming a frame-work of heavy timber, so ar- 
ranged that thick sheeting-piles could be driven close to the bot- 
tom, between its horizontal pieces, and form a well-jointed vessel 
to contain the semi-fluid material for the bed. After this cofFer- 
■ work was placed, the loose sand and gravel was scooped from 
iJie bottom, the asperities of the surface levelled, and the fissures 
were voided, and refilled with fragments of a soft stone, which it 
was found could be more compactly settled, by rammuig, in the 
fissures, than a looser and rounder material like gravel. On this 
prepared surface, the bed of beton, which was from 13 to 15 feet 
in iliickness, was gradually raised, by successive layers, to with- 
in a few feet of the low-water level, and the stone superstructure 
then laid upon it, by using an ordinary coffer-dam tliat rested on 
the frame-work around the bed. In this bridge, as in that of 
Bordeaux, a provisional trial-weight, greater than tlie permanent 
load, was laid upon the bed, before commencing tlie superstruc- 

To give greatc; security to their foimdations, the French usually 
surround them with a mass of loose stone blocks thrown in and 
allowed to find tlieir own bed. Where piles are used and pro- 
ject some height above the bottom, they, in some cases, use, be- 
sides the loose stone, a grating of heavy timber, whicn lies between 
and encloses the piling, to give it gi'eater stifiness and prevent 
outward spreading. In streams of a torrent character, where the 
bed is liable to be worn away, or shifted, an artificial covering, 
or apron of stone laid in mortar, has, in some cases, been used, 
both under the arches and above and below the bridge, as far as 
tlie bed seemed to require this protection. At the bridge of Bor- 
deaux loose stone was spread over the river-bed between the 
aid's, and it has been found to answer perfectly iJie object of the 
engineer, the blocks having, in a few years, become united into a 
firm mass by the clayey sediment of tiie river deposited in their 
, interstices. At the elegant cast-iron bridge, built over the Lary 
near Plymouth, resort was had to a similar plan for securing the 
bed, which is of shifting sand. The engineer, Mr. Rendel, here 
laid, in the first place, a bed of compact clay upon the sand bed 
between the piers, and imbedded in it loose stone. This method, 
which for its economy is worthy of note, has iully answered tlici 
expectations of the engineer. 

The English engineers have greatly improved ilie method of 
centting, and, in their boldest arches, any settling approaching 
that which tiie French engineers usually counted upou, on striking 
their centres, would now be regarded as an evidence of great de 

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iect ill ihe design, or of very unskilful workmansliip. Thej 
have generally, in their recent bridges, supported their rsadway 
either upon flat stones, resting on light walls built parallel to the 
heads, or else upon light cylindrical arches laid upon piers having 
the same direction. In the preparation for laying the beds of their 
foundations, they have generally preferred the coffer-dam to any 
other plan, although in many localities Llie most expensive, on 
account of the greater facility and security offered by it for cany- 
ing on the work. They have not, until recently, made as exten- 
sive an application of beton as the French for hydraulic purposes, 
and, from naving mostly usee what is known as concrete among 
their architects, have met with some signal failures in its employ- 
ment for these purposes. 


583. A wooden bridge consists of three essentia] parts : 1st, 
the abutments and piers which form the points of support for 
thd bridge frame ; 2d, the bridge frame which supports the su- 
perstructure between the piers and abutment; 3d, the super- 
structure, consisting of the roadway, parapets, roofing, &c. 

584. The abutments and piers may be either of stone, or of 
limber. Stone supports are preferable to those of timber, both 
on account of the superior durability of stone, and of its offering 
morn security than frames of timber against the accidents to 
which the piers of bridges are liable from freshets, ice, &c. 

585. The forms, dimensions, and construction of stone abut- 
ments and piers for wooden bridges will depend, like those for 
stone bridges, upon local circumstances, and the kind of bridge- 
frame adopted. If the bridge-frame is so arranged that no lateral 
thrust is received from it by the piers, the dimensions of the latter 
should be regulated to support the weight of the bridge-frame 
and its superstructure, and to resist any action arising from acci- 
dental causes, as freshets, ice, &c. The forms and dimen- 
sions of the abutments, under the like circumstances, will be 
mainly regulated by the pressure upon tliem from the embank- 
ments of tJie approaches. 

586. If liic bridge-frame is of a form that exerts a lateral 
pressure, the dimensions of the abutments and piers must be suit 
ably adapted to resist tiiis action, and secure the supports from 
being oveiturned. Abuiment-picrs may be used witli advantage 
in tiiis case, as offering more security to the structure than sim- 
ple piers, when a frame between any two supports may require 
10 be taken out for repairs. The starlings should in all cases be 
carried above the line of the highest water-level, and the portior, 
of the pier above this line, which supports the roadway bearers 
may be built with plane faces and ends. 

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587. Wooden abutments may be formed by constructing what 
IS termed a crib-work, whicli consists of large pieces, of square 
timber laid horizontally upon each other, to form ihe upright, or 
sloping faces of the abutment. These pieces are halved into eacit 
other at the angles, and are otherwise fi.-mly connected togelhei 
by diagonal tiss and iron bolts. The space enclosed by the crib- 
work, which is usually built up in the manner just described, only 
oil three sides, is filled with earth carefully rammed, or with dry 
stone, as circumstances may seem to require. 

A wooden abutment of a more economical construclioii may 
be made, by partly imbedding large beams of timber placed in a 
vertical or an inclined position, at intervals of a few feet from 
each other, and forming a facing of thick plank to sustain the 
eariii behind the abutment. Wooden piers may also be made 
according to either of the methods here laid down, and be filled 
with loose stone, fo give them sufficient stability to resist the 
forces to which they may be exposed ; but the method is clumsy, 
and inferior, under every point of view to stone pier* or to the 
metliods which are about to be e\pldmej 

588. The simplest arrangement of a wooden pit,r coniista 
(Fig. 127) in driving heavy square or round piles m a i>mgle 
'ow, placing tlicm from two to four fei t ^part These upnght 

g. 127— novation of a wooclen pier- 

a, pAes of snbshiicture. 

b. cming of piles airant^ to receive Iho ciiJe cf llie ninigliU e, 
Tfiiidi suiqiort the string jiieces i, i. 

upper fender beam. 

lower fender twam. 

huizontal ties bolleii in paits an the upriglifs. 

1^, diasiuiBi bmces l>olt«d in paira on the upi-tgtiU. 

capping oftlie □priglils placM under Uie string piecer 

I roadivay 



pieces are sawed off level, and connected at ioji by i liorizontai 
Deani, termed a cap, wliich is either mortised to receive a tenon 
made in each upright, or else is fastened to the uprights by bolts 
or pins. Other pieces, which are notched and bolted in pairs on 
the sides of the uprights, are placed in an inclined, or diagonal 
position, to brace the whole system firmly. The several uprights 
of the pier are placed in the direction of the thread of the current 
If thought necessary, two horizontal beams, arranged like the 
diagonal pieces, may be added to the svstam just below the lowest 
water-level. In a pier of this kind, tlie place of the starlings ia 
supplied by two inclined beams on the satae line witli the up- 
rights, which are X&imiid. fender-heams. 

589. A strong objection to the system just described, arises 
from tne difficulty of replacing the uprights when in a state 
of decay. To remedy this defect, it has been proposed to drive 
large piles in the positions to be occupied by tne uprights, (Fig 
128,) to connect these piles below the low-water level by four 

oftlis foiuululion piles with the uprights. 

horizontal beams, firmly fastened to the heads of the piles, 
which are sawed off at a proper height to receive the horizontal 
beams. The two top beams nave large square mortises to re- 
ceive the ends of the uprights, which rest on those of the piles. 
The rest of the system may be constructed as in the former case. 
By this arrangement the uprights, when decayed, can be readily 
replaced, and they rest on a solid substructure not subject to de- 
cay ; shorter timber also can be used for the piers than when the 
uprights are driven into the bed of the stream. . 

590. In deep water, and especially in a rapid current, a sii igle 
row of piles might prove insufficient to give stability to the up 
tights; and it has therefore been proposed to give a sufficieiU 
epread to the substructure to admit of bracing the ujirights by struts 
on the two sides. To effect tiiis, three piles (rig. 129) should 
be driven for each upriglil ; one just under its position, and tlie 
other two on each side of this, on a line perpendicular to that of 
the pier. The distance between the three piles will depend or 
he inclination and cngth that it may be deemed necessary tu 



give the struts. The heads of the tlirce piles are sawed off Icvd 
and coni ected by two horizontal clamping p.'eces below llie low 

riC, latF— EloT 

foiindnticm fr 

i, b, piles I 

c, c, capping ui uiu piii^ij. 

d, d, Btruta to strengthen tlio upcigLls. 
I ■■ I *, e, clamping iiieees boiled lu iiaiis Ou mn ui^ 

u u w * 

est water, A square morlisc is left in these two pieces, over the 
micidle pile, to receive the uprights. The uprights are fastened 
together at the bottom by two clamping pieces, which rest on 
those that clamp tlie heads of the piles, and are rendered firmer 
by the two struts. 

591. In localities where piles cannot be driven, the uprights 
of the piers may be secured to the bottom by means of a grating, 
arranged in a suitable manner to receive the ends of the uprights. 
The bed, on which the grating is to rest, having been suitably 
prepared, it is floated to its position, and sunk cither before or 
after tlie uprights are fastened to it, as may be found most con- 
venient. The grating is retained in its place by loose stone. 
As a farther security Tor the piers, the uprights may be covered 
by a sheathing of boards, and the spaces betiveen tlie sheathing 
be filled in with gravel. Wooden piers may also be constmcted, 
if necessary, of two parallel rows of uprights placed a few feet 
apart, and connected by cross and diagonal lies and braces. 

593. As w ooden piers are not of a suitable form to resist heavy 
shocks, ice-bredkeis should be placed- in the stream, opposite to 
each piei, and at some distance torn it. In streams Willi a gen- 

rii llO— Elevation U and plan N of a i 

ir, a, loundation piles. 
b, b, capping of piles, 

(', mclinod fondor-bEam chod witli iron 

lie current, a simple inclined beam (Fig. 130) covered with thick 
Khcet iron, and supported by uprights and diagonal pieces, wjlj 

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be all that is necessary for an ice-breaker. But in rapid cunents 
a crib-worl(, liaving the form of a triangular pyramid, (Fig. 131, 

n tJ bi kcii loue 

llie op-8tveam edge of wliicb is covered willi iron, will be re- 
quired, to offer eufRcient resistance lo shocks. The crib-work 
may be filled in, if it be deemed advisable, with blocks of stone. 

593. The width of the bays in wooden bridges will depend on 
the local circumstances. As a genera! rule, the bays may be 
wider, and in bridge-frames of curved timber tlie rise less, than 
in stone bridges. In arranging this point, the engineer must take 
into consideration the fact that wooden bridges require more fre- 
quent repairs than those of stone, arising from tlie decay of the 
material, and from the effects of shrinking and vibrations upon 
llie joints of the frames, and tliat the difficulty of replacing de- 
cayed parts, and readjusting the frame-work, increases rapidly 
wiih the span. 

594. Bridge-frames may be divided into two general classes. 
To the one belong all lliose combinations, whether of straight or 
of curved timber, that exert a lateral pressure upon the abutments 
and piers, and in which the supersti-ucture is generally above the 
bridge-frame. To the other, those combinations which exert no 
lateral pressure upon the points of support, and in which the road 
way, &c. may be said to be suspended from the bridge-frarae. 

595. Any of tlie combinations, whether of straight, or of curved 
limber, described under the head of Framing, may be used foi 
bridges, according to the width of bay selected, A preterencC; 
witliin late years, has been generally given by engineers to com- 
binations of straight timber over curved frames, from the greater 
Bimpiicity and facility of their construction, as well as theif 
greater economy ; as curved frames require much moie iron in 

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WOOBEN liRl-UGES. 233 

She form of bolts, lies, &c., than frames of straight tin bur, ami 
laore cosily mechanical contrivances for putting the pacts together, 
find setting the frame upon ita supports. 

590. Tlie number of ribs in the bridge-frame will depend oi. 
the general strength required by the object cf the sti^ucture, and 
upon the class of frame adopted. In the first class, in which the 
roadway is usually above the frames, any requisite number of nha 
may be used, and they may be placed at equal intervals apart, 
or else be so placed as to give the best support to the loads wliich 
pass over the bridge. lu the second class, as the frame usually 
lies entirely, or projects partly above the roadway, &c., if more 
than two ribs are required, they are so arranged that one or two, 
as circumstances may demand, form each head of the bridge, and 
one or two more are placed midway between the heads, so as to 
leave a sufficient width of roadway between the centre and adja- 
cent ribs. The footpatlis are usually, in this case, eitlier placed 
between the two centre ribs, or, when there are two exterior ribs, 
between them. 

597. The manner of constructing tlie ribs, and of connecting 
them by cross lies and diagonal braces, is the same for bridge 
frames as for otiier wooden structures ; care being taken to ob- 
tain the strength and stiiFness which are peculiarly requisite in 
wooden bridges, to preserve them from the causes of destructi 
bility to which they are liable. In frames which exert a lateral 
pressure against the abutments and piers, the lowest points of 
the frame-work should be so placed as to be above the ordinary 
high-water level ; and plates of some metal should be inserted at 
those points, both of the frame and of the supports, where the 
effect of the pressure might cause injmy to the woody fibre. 

598. The roadway usually consists of a simple flooring formed 
of cross joists, termed tlie roadway-bearers, cc floor-girders, and 
flooring-boards, upon which a road-covering either of wood, or 
stone is laid. A more common and better arrangement of the 
roadway, now in use, consists in laying longitudinal joists of 
smaller scantling upon the roadway-bearers, to support the 
flooring-boards. This method preserves more effectually than 
the other the roadway-bearers from moisture. Besides, in 
bridges which, from the position of the ToaAyvay, do not admil 
of vertical diagonal braces to stiffen the irame-work, the only 
means, in most cases, of effecting tliis object is in placing hori 
zontal diagonal braces between each pair of roadway-bearers 
For like reasons, ston'? road-coverings for wooden bridges are 
generally rejected, and one of planlt used, which, for a horse 
track, should be of two tliicknesses, so that, in case of repairs, 
arising from the wear and tear of travel, the boards resting upon 
the flooring-joists may not require to be removed The footpath* 

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236 BlLmGESj ETC. 

consist filniply tf a slight flooring of suiEcient width, which ;« 
usuaUj detached from and raised a few inches above llie roadway 

599. When the bridge-frame is beneath the rcadway, a distinci 
parapet will be requisite for the safety of passengers. This may 
be formed either of wood, of iron, or of tlie two combined. It in 
most generally made of timber, and consists of a hand and fool 
rail connected by upright posts and stiffened by diagonal braces 
A wooden parapet, oesides the security it gives to passengers, 
may be made to add both to the strength and stiffness of the 
bridge, by constructing it of timber of a suitable size, and con 
necting it firmly with the exterior ribs. 

600. In brid;^e frames in which the ribs are above the roadway, 
a timber sheathing of thin boards will be requisite on the sides, 
and a roof above, to protect the structure from the weather. The 
lie-beams of the roof-trusses may serve also as ties for the ribs 
at top, and may receive horizontal diagonal braces to stiffen the 
structure, like those of the roadway-bearers. The rafters, in the 
case in which there is no centre rib, and tlie bearing, or distance 
between the exterior ribs, is so great that the roadway-bearers re- 
quire to be supported in tlie middle, may serve as points of sup- 
port for suspension pieces of wood, or of iron, to which the middle 
point of tbe road way -bearers may be attached. 

601. When the bridge-frame is beneath the roadway, tlie floor- 
ing, if sufficient projection be given it beyond the head, will pro- 
tect it from the weather, if the depth of the ribs be not very great. 
In the contrary case a side sheathing of boards may be requisite. 

602. The irame and other main timbers of a wooden bridge 
will not requhe to be coated with paint, or any like composition, 
to preserve them from decay when they are roofed and boarded 
in to keep them dry. When this is not the case, the ordinary 
preservatives against atmospheric action may be used for them. 
The under surface and joints of the planks of tlie roadway may 
lie coated with bituminous mastic when used for a horse-track ; 
in railroad bridges a metalhc covering may be suitably used 
when the bridge is not traversed by horses. 

603. Wooden bridges can produce but little, other architectural 
effect than that which naturally springs up in the mind of an 
educated spectator in regarding any judiciously-contrived struc- 
ture. When the roadway and parapet are ahovtj the bridge- 
fiame, a very simple cornice may be formed by a proper combi- 
nation of tlie roadway-timbers and flooring, which, with the para- 
pet, will present not only a pleasing appearance to the eye, but 
will be of obvious utility in covering tiie parts beneath from the 
wi^ather. In covered bridges, the most that can be done will be 
to paint them with a uniform coat of some subdued tint. A 


best, from their want of height as compared with then length, 
covered wooden bridges must, for the most part, be only uiisiglitly 
and also apparently insecure structures when looked at from sucb 
a point of view as to embrace all the parts in the field of vision : 
and any attempt, therefore, to disguise their true character, and la 
give them by painting the appearance of houses, or of stone arches, 
while it must fail to deceive even the most ignorant, v/iil only be- 
tray the bad taste; of the architect to the more enlightened judge. 

604. The art of erecting wooden bridges has been carried to 
great perfection in almost eveiy part of the world where timber 
has, at any period, been the principal building material at the 
disposal of the architect. The more modem wooden bridges of 
.Switzerland and Germany occupy in Europe the first rank, for 
boldness of design and scientific combination in their arrangemeni 
and construction. These fine foreign structures have been even 
surpassed in the United States, and our wooden bridges and the 
skill of our engineers and carpenters, as shown through them, 
have become deservedly celebrated throughout the scientific 
world. The more recent structures of this class are peculiarly 
characterized for simplicity of arrangement, perfection m the me- 
chanical execution, and boldness of design. If they are open to 
^e charge of any fault, it is to that of too groat boldness of de- 
sign, in spanning very wide bays with ribs of open-built beams 
either unsupported, or but imperfectly so, at intermediate points, 
by any combination of struts and corbels, or straining beams. 
The want of these additions is more oi less apparent m the gieat 
vibratory motion felt on some of the more recent ra Iroad and 
other bridges, and m a consc{iuent diaposilion in ihc frame to 
work loose at tlie jomts and sag 

605. The following Table contains the principal dnoensions 
of some of tlie most celebrated Ameiican and European w ooden 



Kiinilicr of 


Itiso or depth 

BridgeofSohafflmusen, (A) . . 


133 ft. 


Bridge of Kandel,(B) . . 


IGfl " 

Bridge of Bamberg, ) .p. 
Bridge of Freysingen, i^^> 


1G.9 ft. 


153 " 

II.G " 

EBBex bridge, (D) . . . 


250 " 

Upper SehuyUtill bridge, (E) 


3i0 " 

20 " 

Market-slreot bridge, (F) . 


185' ' 

Tcenioir bridge, (G) . . 
Columbia bridee, (H) ■ . . 


200 " 

27 ■' 

200 " 

Richmond bridge, (I) . . 


153 " 

15.4 '' 

Springfield bridge, (K) . . . . 


180 " 

18 " 


(A.) This celebrated Swiss bridge, built by John Ulrich Gia 
henmann, a carpenter, consisted of two bays, the one 193 and 
the other 172 feet. The bridge-frame was formed of two ribs 
with a roadway between them. Each rib was framed, in some 
respects, on lh"e same principle as an open-built beam, the uppei 
string being supported by a number of inclined struts wliict 
rested against the abutments and pier, and the lower string, upon 
which the roadway timbers were laid, being suspended from tht 
upper by suspension pieces. The whole structure was conso5i- 
dated and braced by bolts, stays, and straps of iron. Remarkable 
in its day, yet the drawings extant of the bridge of Schaff hausen, 
while they attest the ingenuity and practical skill of the builder, 
present it in singular contrast with Uie equally bold and less com- 
phcaled structures of the like nature recently erected in the 
United States. 

(B) This is also a Swiss bridge, built over the torrent of Kan- 
del in the canton of Berne. Its ribs are formed of solid-buill 
beams which gradually decrease in depth from the centre to the 
extremities ; this decrease being made by offsets, the built beams 

E resenting the appearance of a number of straining beams placed 
elow each other, against the ends of which abut inclined stmts 
that rest against the faces of the abutments. The roadway reste 
upon the built beams. 

(C) These two bridges are selected from among a number of 
the like character constructed in various parts of Germany by 
Wiebelung. The bridge-frame in all of them consists of several 
libs of curved solid-built beams upon which the roadway timbers 
are laid. This method of constructing bridge-fi'ames combines 
gi-eat strength and stiffness. It is more expensive than frames of 
straight timber, as it requires a larger amount of iron, and more 
complicated mechanical means for its construction than the latter, 
and the ribs, although stiffer, are impaired in strength by the 
operation of bending them. 

(D) This is a yery remarkable structure built over the river 
Merrimack near Newburyport. The ribs consist of curved open- 
built beams, each of which is composed of three concentric solid- 
Duilt beams, connected, at intervals along the rib, by two radial 
pieces of hard wood which fit into mortises made through the 
centre of each solid beam, and by a long wedge of hard wood in- 
serted, in the direction of the radius of curvature, between each 
pair of radial pieces. Each of the solid-built beams of the rib is 
fonned of two thicknesses of icantling, about 12 or 15 feet in 
lenglli, which abut end to end, breaking joints, and are connected 
by keys of hard wood inserted inio mortises made tiirough the two 
thicknesses. By these arrangements the architect has soughl 
to pi"esen'e bilh the curved shape and the parallelism of the solid 

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bcEims forming the nb, and also to connect all tlie parts firmly, 
The combination is an ingenious attempt at constructing an arch 
of wood on similar principles to one ot stone, but is inferior to 
the more simple and usual methods of forming curved open-built 
lieams by using radial and diagonal pieces. 

(E) This bridge, designed and built by L. Wernwag, has the 
widest span on record. The bridge-frame (Fig. 132) consists 

of Oio open cutvoil ril 

m, m, iron stays anchored in tha abutment C. 

ci five ribs. Each vib is an open-built beam formed of a bottom, 
curved solid-built beam and of a single top beam, wliicli are con- 
nected by radial pieces, diagonal braces, and inclined iron stays. 
The bottom curved beam is composed of three concentric solid- 
built beams slightly separated from each other, each of which 
has seven courses of curved scantling in it, each course 6 inches 
thick by 13 inches in breadth ; the courses, as well as the con- 
centiic beams, being firmly united by iron bolts, &c. A road 
■way that rests upon the bottom curved ribs is left on each side 
if the centre rib, and a footpath between each of the two exterior 
ribs. The bridge was covered in by a roof and a sheatliing on 
the sides. 

(F) This is also one of the many bridges designed and built 
hy Wernwag in the States of Pennsylvania and New Jersey. 
The bridge-frame consists of three ribs placed so far apart as to 
leave space between them for a carriage-way and a footpath or; 
each side of the centre rib. Each rib is an open-built beam, 
lonsifting of a bottom curved solid-built beam, with mortises at 
intervals to receive radial pieces, whicli are connected at top by 
a single beam, also mortised to receive tenons on the heads of tha 
radial pieces. A single diagonal brace a p' between each 

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pair of radial pieces. Longitudinal beams reach from tlie crown 
of the curved rib of one bay to that of the next, and on these the 
roadway-bearers are laid transversely. 

(G) In this fine structure, the roadway-bearers are suspended 
from curved solid-built beams by iron-bar chains and suspension 
rods. The span of the centre hay is SOO feet, that of tlie two 
adjacent 180 feet, and that of the extreme bays 160 feet. The 
bridge-frame (Fig. 133) consists of five ribs, having the same 

Fig. l:t3— Reptesenis a ofa o on 

A, solid curved beam. 

S'nlera suspended from A by tiie 'at 
d, a, diagonal braces. 
li, pottion or nier. 
C, iramB woti of roof-coveriiig over Hie pieis. 

ftrrangcment for the roadway and footpaths as in t!ie upper Schuyl- 
kill bridge. Each of the central ribs is formed of 8 courses of 
curved scanthng, each course being 4 inches tliick, and 13 inchea 
hroad. The two ctlcrior ribs have 9 courses of scantling of the 
same dimensions. Inclined limber braces connect the curved 
beam and roadway timbers. The ribs are tied at top by cross 
pieces, and stiffened by diagonal braces. The bridge-frame is 
braced on Uie exterior by vertical and horizontal timber-stays 
which abut against the top of Uie piers. The roadway is of 

Elank laid upon longitudinal joists that rest on the roadway 
carers. The roadway-bearers are stiffened by diagonal braces 
The abutments and piers are of stone, the latter being 20 feet 
thick at the impost, 

(H) This, lil;e most of tlie more recent bridges for railroads, 
aqueducts, &c., in Pennsylvania, is built upon Burr's plan, which 
'{Fig. 134) consists in forming each rib of an open-built beam of 
straight timber, and connecting with it a curved sohd-built bcaoj 
formed of two or nnore thicknesses of scantling, between wliick 
ihe frame-work of the open-built beam is clamped. The oper.- 
built beam consists of a horizontal bottom beam of two tliicknessei 
if scantling, termed ihc chords, which clamp uprights, termed tlig 

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queen posts, between them, — of a single top boam, termed theplaU 
of the side frame, which routs upon the uprights, with which it i; 

, e, plate of the sido fran'o. 
, 0, floor eirdf^is on wlii'.'li tlio flooring 
joists and flooring boards rest. 
, I?, check braces. 
, 1, (io beams ori'oof. 
L,iK>rtionof pier. 

connected by a mortise and tenon joint,— and of .diagonal braces 
and other smaller braces, termed check braces, placed between 
the uprights. The curved-built beam, termed the arch-timbers, 
is bolted upon the timbers of the open-built beam. The bridge- 
frame may consist of two or more ribs, which are connected and 
stiffened by cross ties and diagonal braces. The roadway-floor- 
ing {Fig, 135) is laid upon cross pieces, termed \hs floor girders, 
which may either rest upon the chords, or else be attached at any 
intermediate point between them ind the top bcim. The road 
wydfpl ylpld yp between the 




f 1 

] yb 

1 1 on adopted by 

b d f n J cribeo. The 


ppl by B rr of wlrAl be 

1 a d r an open-Buiii 

y b narl d fr IF 34 135, that the 

p bu i b a fly tl 1 e top beam, or 

ly f 1 d n n 1 n 1 b torn beam, or 

\ I by m and n er affords no 

h q p p 1 wl h act as aus- 

1 I 1 11 [ a f 1 p a which coniiLTies 

\ a F n } in whidi llie ai:<Ji- 

d d 111 pTT heopen-tiiiit 

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beam, they add but lilllc if any more strength and tiifness th 
would be given by straight timbers reaching from the springing 
point of tlic arch timbers to their crown ; and they are certainlv 

Fig. 135— Represents the half of a 

crass BBction of Fig. 131 throurfi 

the crown of the aicti liniben, in 

u'liich tlie letleni desiBuate Uii 

IB parts as in Uie preceding Fig. 

li agonal brQwa of bridge frame. 

Jess eiBcacious in subserving their end than would be imcliiied 
struts, occupying a like position at bottom, and abutting against a 
straining beam, placed either under the centre part of the chord, 
where uie locality would permit it, or under the centre portion of. 
the plate. In localities where fine timber is less abundant than in 
those in wliich the most of Burr's bridges have been built, a ju- 
dicious regard to economy would undoubtedly have suggested a . 
■ selection of forms for the secondary parts of the frame, wliich 
would have prevented these parts from being as' much cut to 
waste as the Figs, show theymust have been in the example 
taken to illustrate this system, 

(I) This structure, cojistructed under the superintendence of 
Moncure Robinson, Esq., is upon Town's plan. The width of 
the bays varies from 130 to 153 feet. It consists of two ribs, 
each of which is formed of a double lattice, with two chords at 
bottom and one at top. The roadway, for rails, rests on the top 
cirders. The ribs are braced by vertical diagonal braces, and bj 
horizontal diagonal braces between each pair of the top and bot- 
tom girders. The ^iers arc of rustic work; they are 40 feel 
above the low-water level,, and 4 feet thick at top. The esara- 
i)le here selected for illustration (Fig. 136) is taken from anoihei 
imdge, of nearly the same width of bay, erected subsequently 
vO the Richmond bridge, by the same engineer, in which the lop 

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(.hord also is doubled, as the former bridge was ft und to be ntitei 

IB. 130— Repreaenls a cross seclion of a riulroBil 
the road are placed ou a. flooring oii Uie lop of 

(K> This bridge is constiucted on Howe's plan. It consists 
(Fig. 137) of two ribs which are connected at top and bottom, in 
the usual manner, with cross ties and diagonal braces. The 
roadway flooring rests upon the cross girders at bottom. The 
bridge is not roofed, as is usually the case, the ribs being covered 
in on th<! isides and at top by a shcatliiiig of boards, and the 
flooring-bcatds by a metalhc coverimr 

The bridges constructed accord 
have been mostly applied to mediu p 
scription of the different improvem i i j p 

by Colonel Long, he very judicio ly d 

he terms arch braces, either below 1 p h b m 
as tlie locality may demand, for th p p f p 

ging, whicli mvist necessarily take pi m all Op n 

oeams of considerable span, if not . 1 d ! s way 

1 L 

1 P 



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606. Bridges of cast iron admit of even greater boldness of 
design than tliose of timber, owing to the superiority, both in 
strength and durability, of the former over the latter material ; 
and they may iherefore be resorted to under circumstances very 
nearly the same in which a ^yooden structure would be suitable. 

607. The abutments and piers of cast-iron bridges should be 
wtilt of stone, as the corrosive action of salt water, or even of 
fresh water when impure, would in time render iron supports of 
tliis character insecure ; and timber, when exposed to the same 
destructive agents, is alill les« lurable than cast iron. 

Tlie forms and dimensions ::{ the stone abutments and piers 
are regulated on the same principles as the like parts in wooden 
bridges with curved frames. The piers may be either built up 
high enough to receive the roadway-bearers, or else they may be 
termmalea just above the springing plates of ihc briiigc-framD 

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and form supports for casl-irdn standards upon which ll e roai'way 
bearers may bo laid. 

60S, Tiie curved ribs of cast-iron bridge-frames have under- 
gone various niodiiications and improvements. In the eailiei 
bridges, liiey were fonncd of several concentric arcs, or curved 
beams, placed at some dis3£.i.ce asunder, and united by radial 
pieces ; the spandrels being filled either by contiguous rings, oi 
by vertical pieces of cast iron upon which the roadway bearers 
were laid, 

In the next stage of progress towards improvement, ihe curved 
ribs were made less deep, and were each formed of several seg 
ments, or panels cast separately in one piece, each panel con 
sisting of three concentric arcs connected by ladiaJ pieces, and 
having flanches, with other suitable arrangements, for ccunecting 
them firmly by wrought-iron keys, screw-bolts, &c. ; the entire 
rib thus presenting the appearance of three concentric arcs con- 
nected by radial pieces. The spandrels were filled eillier with 
panels formed like those of the curved ribs, with iron rings, or 
with a lozenge-shaped reticulated combination. The ribs were 
connected by cast-iron plates and wrought-iron diagonal ties. 

In the more recent structures, the ribs have been composed of 
voussoir-shaped panels, each formed of a solid tliin plate with 
flanches around the edges ; or else of a curved tubular rib, fonned 
like tbose of Polonceau, or of Dclafield, described under the head 
of Framing. The spandrel-filling is either a reticulated combi- 
nation, or one of contiguous iron rings. The ribs are usually 
united by cast-iron tie-plates, and braced by diagonal ties of cast 
and wrought iron. 

609. The roadway-bcai'crs and flooring may be formed either 
of limber, or of cast iron. In the more recent structures in Eng- 
land, they have been made of the latter material ; the roadway- 
bearers being cast of a suitable form for strength, and for their 
connection witli the ribs ; and the flooring-plates being of cast 

The roadway and footpaths, formed in the usual manner, resi 
upon the flooring-plates. 

The parapet consists, in most cases, of a light combination of 
cast or wrought iron, in keeping with the general style of the 

610. The English engineers have taken the leadin this branch 
of architecture, and, in tlieir more recent structures, liave carried 
it to a high degree of mechanical perfection and arciiitectura' 
elegance, Among the more celebrated cast-iron bridges in Eng 
land, that of Coalbrookdale belongs to the first epoch above men 
tioned ; those of Staines and Sunderland to tlie second ; and to 
tlie llurd, the bridge of Southwark ai- London ; that of Tewkes 

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hury over the Severn ; that over die Larj near Plymoulli, and a 
number of others in various parts of the United Kijigdom. 

T.'ie French engineers have not only followed the lead set tliem 
by the English, but have taken a new step, in tlie tubular-shaped 
ribs of M. Polonccau. The Pont des Arts at Paris, a very ligh 
bridge for foot-passengers only, and which is, a combination ol 
cast and wrought iron, belongs to their earliest essays in lliis line ; 
the Pont d'Austerlitz, also at Paris, which is a combination simi- 
lar to those of Staines and Sunderland, belongs to their second 
epoch ; and the Pont die Carrousel, in the same city, built upon 
Polonceau's system, with several others on the same plan, belong 
to the last. 

In the United States a commencement can hardly be said to 
have been made in this brancli of bridge architecture ; the bridge 
of eighty feet span, with tubular ribs, constructed by Major Dela- 
lieid at Brownsville, stands almost alone, and is a slep contem- 
porary with that of Polonceau in France. 

Tiie following Table contains a summary description of some 
of tlic most noted European cast-iron bridges. 




£,.. In 




tests : 

Lary. (H) . . 
Canoiuel, (1) . 












(A) This is the first cast-iron bridge erected in England. The 
curved rib is nearly a semicircle in shape, and is composed of 
three concentric arcs, which are connected at intervals by short 
columnar pieces, in the direction of the radii of the curve. 

(B) This structure, which connects Wearmouth and Sunder- 
land, has a remarkably bold appearance, both from its great span, 
and its height, which is 1,00 feet between the high water-level 
and the intrados of the arch at the crown. The entire rib pre 
scnts the appearance of an open-built beam, composed of tnree 
concentric arcs united by radial pieces. The spandrel-filling is 
formed of contiguous iron rings, of increasing diameters from the 
crown to the springing line, which rest upon the back of the 
curved rih, and support the roadway-bearers. 

(C) Slaines bridge was designed on the same plan as Wear- 
mouth ; but from a defect in the strength of its abutments, they 
Buccessively yielded to the horizontal thrust, which in so flat sn 
aich was very considerable. 

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(D) The bridge of Auaterlitz is constructed on the .same jirin 
eiple as the two last, and produces a light and pleasmg architec 
tiiral effect. Each curved rib consists of 21 Toussoir-shapcd 
panels, about 4 feet in depth. The spandrel-fillings present the 
appearance of a continuation of the curved rib outwards, to form 
a support for the roadway-bearers. The piers are terminated al 
the springing lines of the curved rib, and are at this point 13 fee* 
thick; tlie roadway above them being supported by the ribs con 
tinned up to its level. The roadway is on a level, the roadway 
ncarers and flooring being of timber. 

(E) In this structure the cunred rib is formed of solid panels 
The spandrel-lillings consist of vertical shafts united by cross 
pieces. The piers are built up to support the roadway-bearers ; 
they are 13 feet thick at the springing line. The entire widtli 
of the bridge is 36 feet, the carriage-way occupying 25 feet. 

(F) In this bold structure, the width of each of the two extreme 
bays is 210 feet. The curved rib is composed of thirteen solid 
panels, each of which is 2| inches thick, and has a rim, or fianch 
around it about 4 inches broad. The rib is 6 feet deep at the 
crown and 8 feet at the spring. The spandrel-filling is composed 
of lozenge-shaped panels with vertical joints ; tliey are' secured 
lo the back of the curved rib and sujiport the roadway-plates. 
The curved ribs are connected by tie-plates inserted between the 
joints of the voussoirs ; and they are traced by feathered diago- 
nal braces. The piers are 24 ieet thick at the springing line, 
and are built up to the level of the roadway-plates. Ihe width 
of the carriage-way is 25 feet, and that of each of the footpaths 
7 feet. 

(G) This bridge presents a very light and elegant appearance ; 
die panels of the curved rib being cast with open curvilinear 
spaces, which divide the panel into several rectangular-shaped 
figures, with, solid sides and diagonals. Each rib consists of 
twelve panels. The depth of the ribs is 3 feet. The thickness 
of the two exterior ribs is 2^ inches, that of tlie four interior 
S inches. The ribs are connected by grated tie-plates between 
the panel-joints, and they abut against springing plates which 
are 3 feet wide and 4 inches thick. The roadway-bearers and 
road-plates are of cast iron. The spandrel-filling is composed 
of lozenge-shaped panels, the sides of tlie lozenges being fea- 
llicred, and tapering from the middle to the extremities. The 
ribs of the bridge-frame are connected and braced in the usual 
manner. The road-bearers are laid lengthwise upon the ribs, lO 
which they are firmly secured, and they are covered with iron 
;oad-plaIes, upon which the road-covering rests. The free road 
epace is 24 feet. 

(Hi In this structure, (Figs. .3^, 139,) the engineer has de 

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parted from lliG iTsual form of a circaiav segment aicr and 
adopted an elliptical segment. The following summ:i>Ttie! 

. 138— Repreeenta a .onailudi- 
nat section tliroiiuha pier sad its 
cast iron Etandatu of Lary bridge, 

CBBl-iioii fiamiiig aiiJ tlie £toue 

A, upiiel portion of pier 

B, slanilanl. 

C, panel of the curved rib. 

D, lozeiige epandrul-tiUiiig. 

lion is extracted from the engineer's publislied account of 
work : — " The arrangement of the design differs materially from 
other works of a similar nature : first, in the masonry of tiie piers 

8 takon tlirouBli llie aiis of (li< 

', b, road-plolea laiil on tlie ^oalin'ay-bDa^ 
braces of tlio standards. 

finishing at the a))ringing course of the arches ; secondly, in Uie 
curvOineai' forms of the piers and abutments ; and thirdly, in the 
employment of elliptical arches. 

" Tiie centre arch is 100 feet span, and rises 14 feet 6 inches 

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iKe tliickness of ihc piers, where smallest, being ID feel. The 
arches adjoining the centre are 95 feet span each, and rise IS 
feet 3 inches. The piers, taken as before, are each 9 feet 6 
inches thick. The estreine arches are each 81 feet span, and 
rise 10 feet 6 inches. The abutments axe, in their smallest di 
mcnsions, 13 feet thick, forming at the back a strong arch abutting 
against the return-walls to resist the horizontal thrust. The ends 
of the piers are seniicircular, having a curvilinear batter on the. 
sides and ends fomied with a radius of 35 feet, and extending 
upward from the level of high water to the springing course, and 
downward to the level of the water at the lowest ebb. The 
front of the abutments have a corresponding batter. 

" The roadway is 24 feet wide, supported by 5 cast-iron equi- 
distant ribs. Each rib is 3 feet 6 inches in depth at t!ie spring- 
ing, and 2 feet at the apex, by 2 inches thick, with a top and 
bottom flange of 6 inches wide by 2 inches thick, and is cast in 
5 pieces ; their joints (which are flanged for the purpose) are 
connected by screw-pins with tie-plates equal in length to the 
widtli of the roadway, and in depth and thickness to the ribs ; 
between these meeting-plates the ribs are connected by strong 
feathered crosses, or diagonal braces, 'with screw-pios passing 
thi'ongb their flanges and the main ribs. The springing-plates 
are 3 inches thick, with raised grooves to receive the ends of the 
libs, which have double shoulders. Tliese plates are sunk flush 
into the springing-oourse of the piers and abutments, which, with 
tiie cordon and springing course, are of gi'anite. The piei'- 
standarda and spandrel-fillings are feathered castings, connected 
transversely by diagonal braces and wrought-iron bars passing 
through cast-iron pipes, with bearing-shoulders for the several 
parts to abut agauist. The roadway-bearers are 7 inches in 
depth by H thicli, with a proportional top and bottom flange; 
they are fastened to the pier-atandards by screw-pins tlu'ough 
sliding mortises, whereby a due provision is made for eitiier ex 
pansion or contraction of the metal ; the roadway-plates are | of 
an inch thick by 3 feet wide, connected by flanges and screw- 
pins, and project 1 foot over the outer roadway-bearers, thus 
forming a cornice the whole length of the bridge. 

" The adoption of these forms for tlie piers and arches, in uni- 
son with the plan of iinishing the piers above the springing course 
with cast iron instead of masonry, has, as I had hoped, given u 
degree of uniform lightness combined with strength to the general 
effe<:t, unobtainable by the usual form of straight- sided p.ers cai- 
ried to the height of the roadway, witli flat segments of a circle 
for the arches." 

(I) The curved ribs of tliis bridge are tubular, tl e cross sec- 
tion of the tube being an clHpse, the transverse ax t of which is 

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2 feet 6 iuclies, and ihe conjugate about 1 foot 4 inches J!;ich 
rib consists of eleven pieces, wiiich are shaped and ronnected aa 
described under the head of Framing. Tlie apandrel-fiilings iiie 
formed of contiguous cast-iron rings which rest upon the ribs, 
and support the longitudinal roadway-bearers. Tlie ribs are Ued 
and braced nearly in the usual manner. The flooring upon which 
the road-covering is laid is of timber. The piers are built up to 
receiie the roadway-bearers. 

The system of M.Polonccau presents a very light and elegant 
form of cast-iron bridge. The inventor claims for it moie econo- 
my than by the ordinary combinations, and also more lightness 
combmed with adequate strength. It has been objected to this 
system tliat it is defective in rigidity ; this the inventor "■^ems 
disposed to regard as an advantage, and has preferred the span- 
drel-filling of rings partly on this account, because their elasticity 
is favorable to a gradual yielding and restoration of form in tht 

611. Effects of Temperature on stone and cast-iron Bridges 
The action of variations of temperature upon masses of masonry, 
particularly in the coping, has already been noticed. The effect 
. of tlie same action upon the equilibrium of arches was first ob- 
served by M. Vicat in the stone bridge built by him at Souillac, 
in the joints of which periodical changes were found to take place, 
not only from the ranges of temperature between the seasons, but 
even daily. Similar phenomena were also ver;^ accurately noted 
by Mr. George Rennie in a stone bridge at Staines. 

From these recorded observations the fact is conclusively es- 
tablished, that tlie joints of stone bridges, both in the arches and 
spandrels, are periodically aifected by this action, which must 
consequently at times throw an increased amount of pressure 
upon the abutments, but without, under ordinary circumstances, 
any danger to the permanent stability of the structure. 

When iron was first proposed to be employed for bridges, ob- 
jections were brought against it on the ground of the effect of 
changes of temperature upon this metal. The failure in the 
abutments of the iron bridge at Staines was imputed to tliis cause, 
and like objections were seriously urged against other stmcturea 
about to be erected in England. To put this matter at rest, ob- 
servations were very carefully made by Sir John Rennie upon 
tlie arches of Soudiwark bridge, built by his father. From these 
experiments it appears that the mean rise of the centre arch at 
the crown was about j\tii of an inch for each degree of Fahr,, 
or 1.25 inches for 50° Fahr. The change of form and increase 
if pressure arising from this cause do not appear to have affected 
■n any sensible degree the permanent stability either of this struc 
lure, or of any of a like character in Europe, 

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612. The use of flexible materials, as cordage and the hlte, to 
form a roadway over chasms, and narrow water- courses, dates 
from a very early period ; and structures of tliia character were 
probably among the first rude attempts of ingenuity, before tlie 
arts of the carpenter and mason were sufficiently advanced to be 
made subservient to the same ends. The idea of a suspended 
roadway, in its simplest form, is one that would naturally present 
itself to the mind, and its consequent construction would demand 
only obvious means and but little mechanical contrivance ; but 
the step from this stage to the one in which such structures are 
now found, supposes a very advanced state both of science and of 
its application to the industrial arts, and we accordingly find that 
bridge architecture, under every other guise, was brought to a 
high degree of perfection before the suspension bridge, as this 
structure is now understood, was attempted. 

Witfi the exception of some isolated cases which, hut in the 
material employed, differed little from the first rude structures, 
no recorded attempt had been made to reduce to systematic rules 
the means of suspending a roadway now in use, until about the 
year 1801, when a patent was taken out in this country for the 
purpose, by Mr. Finlay, in which the manner of hanging the 
chain supports, and suspending the roadway from it, are speci 
fically laid down, differing, in no very material point, from the- 
practice of the present day in this branch of bridge architecture. 
Since then, a number of structures of this character have been 
erected both in the United Stales and in Europe, and, in somi 
instances, valleys and water-courses have been spanned by them 
under circumstances which would have bafBed the engineer's art 
in the employment of any other means. 

A suspension bridge consists of the supports, termed piers, 
from which the suspension chains are hung ; of the anchoring 
masses, termed the abutments, to which the ends of the suspen- 
sion cliains are attached ; of the suspension chains, termed the 
main chains, from which the roadway is suspended ; of the verti- 
cal rods, or chains, termed the suspending-chains, &c., which 
connect the roadway with the main chains ; and of the roadway. 

013. As the general principles upon which flexible supports 
for structures should be arranged liave already been laid dcwn 
under the head of Framing, nothing more will be requisite, undci 
. the present head, than to add those modifications of the applica 
tioas of tliese principles called for .by the character of the stri"; 
tures in question. 

614. Bays. The natural water-way may be divided into any 
number of equal-sized bays, depending on local circumstances, 

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eb2 SRIDGEa, ETC. 

.iiid tlie comparative cost of high or low piers, and ihat of tl t 
main chains, and the suspending-rods. 

A bridge with a single bay of considerable width presents a 
bolder and more monumenial character, and its stabihtj-, all olher 
things being equal, is greater, the amplitude from undulationa 
caused by a moveable load heing'Jess than one of several bays. 

If two bays of equal span are preferred lo a single one with 
an equal versed sine, the chains may be supported either by a 
single central pier, or by three piers of the same height. With 
a single pier, the structure will present the appearance (Fig. 101, 
Art. 538) of two half curves. The tension on ilie chains and 
the horizontal strain at the top of the pier will, in tliis case, be 
the same as in that of the full curve of double the span and the 
same versed sine ; and twice as great as in the case of three 
piers with curves of equal span and the same versed Sine. 

If, instead of a central pier with two 'semi-arches, two entire 
arches be preferred for the bridge., then three piers will be neces- 
sary, whicQ need only be half uie height of those which a single 
bay would require. The tension on the chahis in this case will 
oe only one fourtli of that upon the chains of a bridge with a sin- 
gle bay of double width ; and the abutments may be made pro- 
portionally leas strong. 

615, Piers. These arc commonly masses of masonry in the 
shape of pillars, or columns, that rest on a common foundation, and 
are usually connected at top. Tlie form given to the ])ier, when 
of stone, will depend in some respects on the locality. Generally 
it is that of t!ie architectural monument known as the Triumphal 
Arch ; an arched opening being formed iii the centre of the mass 
for the roadway, and sometimes two others of smaller dimensions, 
on each side of the main one, for approaches lo tlie footpaths of 
the bridge. 

Piers of a columnar, or of an obelisk form, have in some in- 
stances been tried. They have generally been found to be want- 
ing in stiffness, being subject to vibrations from the action of the 
chains upon them, wliich in turn, from the reciprocal action upon 
the chains, tends very much to increase the amplitude of the vi- 
brations of the latter. These effects have been observed to be 
the more sensible as the columnar piers are the higher and more 

Cast-iron piers, in the form of columns connected at top by an 
entablature, have been tried with success, as also have been 
rr'.timnar piers of the same material so arranged, with a joint at 
iheir base, thai ihey can receive a pendulous motion at lop lo ac- 
commodate any increase of tension upon either branch of the chaic 
resting on them. 

'I'he dimensions of piers will depend upon their height and the 

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Strain upon th;m. When built of stone, the masonry shoiiltl be 
very carefully constructed of large blocks well bonded, and tied 
by metal cramps. The height of the piers will depend mostly 
on the locality. When of the usual forms, they should at least 
be high enough to admit the passage of vehicles under tlie arched 
way of tlie road. 

616. Abutments. The forms and dimensions of the abutments 
will depend upon the manner in which they may be connected 
with the chains. When the locality will admit the chains to be 
anciiored without deflecting them vertically, the abutments may 
be formed of any heavy mass of rough masonry, which, from its 
weight, and the manner in which it is imbedded, have sufficient 
strength to resist the tension in the direction of the chain. If it 
is found necessary to deflect the chains vertically to secure a good 
anchoring point it will ilso generally be necessiry to build ^mas3 

f m 

1 l3 ' ' 

Eu d by h 

i f 1 1 

w 11 b d d If 1 

f d f h p 

d g dd 1 
\ 1 M nCl ns Sc 

h d f m 

h d fl 

tr ngth 

i i; 

f 1 y bl k f 





f f 


n y b mad fh frmdffl d } 

sist of wire cables constructed in the usual mannei. 

The main chains of the earlier suspension bridges were fonned 
of long links of round iron made in the usual way ; but, indepen- 
dently of the greater expense of these chains, they were found to be 
liable to defects of welding, and the links, when long, were apt to 
become misshapen under a great strain, and required to be stayed 
to preserve their form. Chains formed of long links of flat bars, 
usually connected by shorter onei as couplincr links, have on 
tliese accounts superseded h f 1 d y oval-shaped 


The breadth of the chain \ lly 

but in some recent bridge d F 

the chains are made to incr f rmly 

ing tlie number of bars in a 1 1 f h 
suspension. In addition to hi 1 
chains, Mr. Dredge places J p 

plane parallel to the axis of 1 fad 
zon, inchning each way from I p 
the centre of the curve. F j 

very considerable increase f I 

material, is given by these m 1 ft li 

The number and disposit f h 

tde uniform , 

I y Mr, Dredge, 

d 1 , by increas- 

the points of 

h f of tlie main 

h in a vcrtica 

bl \ ly to the liori- 

f p sion towards 

ppcars that a 

1 e amount of 

w li d pend upon tne 

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strain to be borne and the arrangement of 1 e I vay a d fool 
paths. For a single carriage-way the n a n cl na e d spo ed 
Dn each side, leaving the requisite width of he ca age ay be- 
tween them. Should the weight to be b ne be so gr a la ha 
number of bars in a link would give su h b ead h i e ha as 
to require a considerable addition to the b 1 1 of 1 e p s vo 
or more chains must be employed, and h si Id be spe Id 
one immediately below the other. It has been suggested that 
their distance apart should be such tlial the shadow from the 
chain above upon that beneath should not prevent the action of 
the sun's rays, in evaporating any moisture that may lodge in the 
articulations of the links, and also to preserve an equable temper- 
ature in all the chauis. If there are two carriage-ways, with 
footpaths, any arrangement of the ciiains may be adopted, simi- 
lar 10 those already pointed out for the ribs of wooden bridges 
under like circumstances ; ,care being taken that the strength of 
th« chains be proportioned to the strain upon them, and tliat they 
be placed so far asunder, that in violent oscillations from high 
winds they may not come into collision. 

Some of the links of the main chains should be an'anged will, 
adjusting screws, or with keys, to bring tlie chains to the propei 
degree of curvature when set up. 

The chains may eitlier be attached to, or pass over a moveable 
cast-iron saddle, seated on rollers on the top of the piers, so thai 
it will allow of sufficient horizontal displacement to permit the 
chains to accommodate themselves to the effects of a moveable 
load on the roadway. The same ends may be attained by attach- 
ing the chains to a pendulum bar suspended from the top of the 

The chains are firmly connected with the abutments, by being 
altaciied to anchoring masses of cast iron, arranged in a suitable 
manner to receive and secure the ends of ilie chains, wliich are 
carefully imbedded in the masonry of the abutments. These 
points, when under ground, should be so placed that they can be 
visited and examined from time to time. 

618. Suspending Cliains. The susp ending-rods, or chains, 
should be attached to such points of tlie main chains and the 
roadway-bearers, as to distribute the load uniformly over ihe 
main chains, and to prevent their being broken or twisted oif 
oy the oscillations of the bridge from winds, or moveable loads. 
They should be connected by suitably-arranged articulations, with 
a saddle piece bearing upon the back of the main chain, and al 
bottom with the stirrup that embraces the roadway-bearors. 

The suspend ing-chains are usually hung vertically. In sotno 
recent bridges they have been inclined inward to give more Hl^ 
lices to the system. 

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619, Roadwaij. Transversal roadway-liearers are attached 
to the suspending- chains, upon which a flaoring of timber is laid 
for tiie roadway. The roadway-hearers, in some instances, have 
been made of wrought iron, but limber is now generally preferred 
for these pieces. Diagonal ties of wrought iron are placed hori 
zontally between the roadv/ay-bearers to brace the frame-work. 

The parapet may be formed in the visual style either of wrought 
iron, ur of timber, or of a combination of cast iron and timber 
Timber alone, or in combination with cast iron, is now preferred 
for the parapets ; as observation has shown that the stiffness given 
to the roadway by a strongly-trussed timber parapet limits the 
amplitude of the undulations caused by violent winds, and secures 
the structure from danger 

In some of the more recent suspension bridges, a trussed 
frame, similar to tlie parapet, has been continued below (lie level 
of the roadway, for tiie purpose of giving greater security to tlie 
structure against the action of high winds. 

When the roadway is above the chains, any requisite number 
of single chains may be placed for its support. Frames formed 
of vertical beams of timber, or of columns of cast iron united by 
diagonal braces, rest upon the chains, and support the roadway- 
bearers placed eitlier transversely, or lon^udinally, 

630. Vibrations. The undulatory or vibratory motions of 
suspension bridges, caused by the action of higli winds, or move- 
ble loads, should be reduced to the smallest practicable amount, 
by a suitable arrangement of bracing for the roadway-timbers and 
parapet, and by chain-stays attached to the roadway and to tlie 
basements of the piers, or to fixed points on Uie batilts whenever 
they can be obtained. 

Calculation and experience show that the vibrations caused by 
a moveable load decrease in amplitude as the span increases, 
and, for the same span, as the versed sine decreases. The 
heavier the roadway, also, all other things being the same, the 
smaller wOl be the amplitude of the vibrations caused by a move- 
able load, and the less will be tlieir effect in changing Uie form 
of the bridge. 

The vibrations caused by a moveable load seldom affciit the 
bridge in a hurtful degree, owing to the elasticity of the syslcm, 
unless they recur periodically, as in the passage of a body of 
soldiers with a cadenced march. Serious accidents have been 
occasioned in this way ; also by the passage of cattle, and by 
the sudden rush of a crowd from one side of the bridge to the 
other. Injuries of this character can on.y be guarded against by 
a proper system of police regulations. 

Cham-stays may either be attached to some point (jf tiie road 
way, and to fixed points beneatli it, or else they may be m tin 

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form of a reversed curve below the roadway. The foimi^r is the 
more efEcacious, but it causes the bridge to bend in a disagree- 
able manner at the point where the stay is attached, when the 
action of a moveable load causes the main chains to rise. The 
more oblique the stays, the longer, more expensive, and les* 
effective they become. Slays in the form of a reversed curvt 
preseive better the shape of the roadway under the action of a 
moveable load, but they are less effective in preventing vibrations 
than the simple stay. Neither of these methods is very service 
able, except in narrow spans. In wide spans, variations of lem 
perature cause considerable changes in the length of the stays, 
which makes them act unequally upon the roadway ; this is par- 
ticularly the case with the reversed curve. Both kinds should 
be arranged with adjusting screws, to accommodate their length 
to the more extreme variations of temperature. 

Engineers, at present, generally agree that the most efEcacious 
means of limiting the amplitude, and the consequent injurious 
effects of undulations, consists in a strong combination of the 
roadway-timbers and flooring, stiffened by a trussed parapet of 
limber above the roadway, and in some cases in extending the 
frame-work of the parapet below it. These combinations pre 
aent, in appearanc{:, and reality, two or more open-built beams, 
as circumstances may demand, placed parallel to each other, and 
strongly connected and braced by the frame-work cf the road- 
way, which are supported at intermediate points by the suspend- 
ing-rods, or chains. The method of placing the roadway-framing 
at the central line of the open-built beams presents the advantage 
of introducing vertical diagonal braces, or ties between the beams 
beneath the roadway-frame. The main objection to these com- 
binations is the increased tension thrown upon the chains from 
the greater weight of the frame-work. This increase of tension, 
however, provided it be kept within proper limits, so far from 
being injurious, adds to the stability and security of the bridge, 
both from the effects of undulations and of vibrations from shocks 

As a ferther security to the stability of the structure, the frame 
work of the roadway should be firmly attached at the two estre 
mitics to the basements of tlie piers. 

621, Presei-vative means. To preserve the chains from oxi 
dation on the surface, and from rain or dews which may lodge ii 
ihe articulations, they should receive several coats of minium, oi 
of some other preparation impervious to water, and ihis sbculd 
ho renewed from time to time, and the forms of all the parts 
should bo the most suitable to allow the free escape of moistuie. 

Wires for cables can be presei-ved from oxidation, until they 
are made into ropes, by keeping them immersed in some alkaline 
BolutioQ. Before making them into ropes they should be (iipped 

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several times in toiling linseed oi), prepared by previously boil- 
ing il with a small portion of litharge and lampblack. Tlie cables 
should receive a thick coating of the same preparation before 
they are put up, and finally be painted with white lead paint, both 
as a preservative means, and to show any incipient oxidation, as 
ihe rust will be detected by its discoloring the paint. 

622. Proofs of Stcspension Bridges. From the many grave 
accideniB, accompanied by serious loss of life, ■which have taken 
place in suspension bridges, it is highly desirable that some trial- 
proof should be made before opening such bridges to the public, 
and that, moreover, strict pohce regulations should be adopted 
and enforced, with reaped to them, to guard against the recur 
rence of such disasters as have several times taken place in Eng 
land, from the assemblage of a crowd upon the bridge. In 
France, and on the continent generally, where one of the impor- 
tant duties of the public pohce is to watch over the safety of life, 
under such circumstances, regulations of this character are rigidly 
enforced. The tiial-proof enacted in France for suspension 
bridges, before they are thrown open for travel, is about 40 lbs. 
to each superficial foot of roadway in addition to the permanent 
weight of the bridge. This proof is at first reduced to one half, 
m order not to injure the masonry of the points of support during 
the green condition of the mortar. It is made by distributing 
over the road surface any convenient weighty material, as bricks, 
pigs of iron, bags of earth, &c. Besides this after-trial, each 
element of liie main chains should be subjected to a special proof 
to prevent the introduction of unsound parts into the system. 
This precaution will not be necessary for the wire of a cable, as 
the process of drawing alone is a good test. Some of the coils 
tested will be a guarantee for the whole. 

From experiments made at Geneva by Colonel Dufotir, one of 
the earliest and most successful constructors of suspension bridges 
on the Continent, it appears that wrought bar iron can sustain 
without danger of rupture a shock arising from a weight of 44 
lbs. raised to a height of 3.28 feet on each, .OOlSdths of an inch 
of cross section, when the bar is strained by a weight equal to 
one third of its breaking weight ; and he concludes that no ap 
prehension need be entertained of injury to a bridge from shocks 
caused by the ordinary transit upon it, which has been subjected 
to the usual trial of a dead weight; and that the safely, m this 
respect, is the greater as the bridge is longer, since the elasticity 
of the system is the best preservative from accidents due to Guci 

023. Durehility. Time is the true test of the durability o . 

ilie structures under consideration. So far as experience goes 

there seems to be no reason to assign less durability to suspcn 


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sion diaii to cast-iron, or even stone bridges, if iheir repairs aniJ 
the proper means of preserving them from decay are attended to. 
Doubts have been expressed as to the durability of wire cables, 
but these seem to have been set at rest by the trials and exami- 
nations to which a bridge of this kind, erecte'd by Colonel Dufour, 
at Geneva, was subjected by him after twenty years service. It 
was found that the undulations were greater than when the bridge 
was first erected, owing to the shrinking of the roadway-frame ; 
but the main cables, and susp ending-ropes, even at the loops in 
contact with the timber, proved to be as sound as when first put 
■jp, and free from oxidation ; and the whole bridge stood another 
very severe proof ■without injury. 

624, Tlie following succinct descriptions of the principal ele- 
ments of some of the most celebrated suspension bridges of 
chains, and wire cables, of remarkable span, are taken from va- 
rious published accounts. 

Bridge over the Tweed near Beitoick. This is the first large 
suspension bridge erected in Great Britain. It was constructed 
■ upon the plans of Capt. Brown, who took out a patent for the 
principles of its construction. 

Span .... 449 feet- 
Versed sine . . , 30 " 
Number of main chains 12, six being placed on each side of the 

roadway, in three ranges, of two chains each, above each 


The chains are composed of long links of round iron, 2 inches 
in diameter, and are 1 5 feet long. They are connected by coupling 
links of round iron, 1 -J- inch diameter, and about 7 inches long, by 
means of coupling bolts. 

The roadway is korne by suspcnding-rods of round iron, which 
are attached alternately to the three ranges of chains. The road- 
way-bearers are of timber, and are laid upon longitudinal bars 
of wrought iron, which are attached to the suspension rods. 

Menai Bridge, erected after the designs of Mr. Telford. 
Opened in 1826. 

Span .... 579.8 feel. 

Versed sine . . 43 " 

Number of main chains IG, arranged in sets of 4 e a! :li, vertically 

above each other. 
Number of bars in each link 5. 
Length of links 10 feet. 

Brcadtli of each bar 3-J inches ; depth 1 incii. 
Coupling links 16 inches long, 8 inches broad, and 1 inch dtcp 
Coupling bolts 3 inches in diameter. 
Total area of cross section of the main chain, 260 square inches 

'I'he main chains are fastened to iheir abutments hy anchoring 



[toita 9 feet long and G inches in diameter, which are secure! iti 
tast-iron grooves. The abutments, which are underground and 
reached by suitable tunnels, are the solid rock. 

Upon the tops of the piers are cast-iron saddles, upon which 
the main chains rest. The base of the saddle, which is fitted 
with grooves to receive them, rests upon iron rollers placed on a 
convex cylindrical bed of cast iron, shaped like the bottom of the 
base of the saddle, to admit of a slight displacement of the chains 
from moveable loads, or changes of temperature. 

The roadway is divided into two carriage-ways, each 12 feel 
wide, and a footpath 4 feet wide between them. The roadway- 
framing consists of 444 wrought-iron roadway-bearers, 3^ inches 
Jeep and ^ inch thick, which are supported at the centre points 
of each of the carriage-ways by an inverted truss, consisting 
of two hent iron ties which support a vertical bar placed under 
the roadway-bars at the points just mentioned. The platform 
of the roadway is formed of two thicknesses of plank. The 
first, 3 inches thick, is laid on the roadway-bearers and fastened 
to them. This is cohered by a coating of patent felt soalted in 
boiling tar. Tlie second is two inches thick and spiked to the 

The roadway is suspended by articulated rods attached to 
stirrups on the roadway-bearers and to tlie coupling bolts of the 
main chains. 

The piers are 152 feet high above the high-water level. They 
have an arched opening leading to the roadway, and the masses 
on the sides of t!ie arch are built hollow, witli a cross-tie partition 
wall between the exterior main walls. 

The parapet is of wrought-iron vertical and parallel bars con- 
nected by a network. 

This bridge was seriously injured by a violent gale, which gave 
so great an oscillation to the main chains that they were dashed 
against each other, and the rivet-heads of the bolts were broken 
off. To provide against similar accidents, a frame-work of cast 
iron tubes, connected by diagonal pieces, was fastened at inter- 
vals between the main chains, by cross ties of wrought-iron lods, 
which passed through the tubes, and were firmly connected mtli 
the exterior chains. Subsequently to this addition, a number of 
strong timber roadway-beaiers were fastened at intervals to those 
of iron, as llie iron roadway-bearers were found to have been 
bent, and in some instances broken, by the undulatory motion of 
the bridge in heavy gales. 

The total suspending weight of this bridge, including the main 
chains, roadway, and all accessories, is stated at 643 tons 1 5J 

The Fribourg of wire thrown across the valley ci ihe 

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Sarine, opposite Fribourg, was erected in 1832 l)y M. OhaUy, a 
French engineer. 

Span . . 870.32 feet, 

versed sine . . 63.26 " 

Tliere are 4 main cables, two on each side of the roaj, of the 
same elevation, and about 1^ inch asunder. Each cable is com* 
posed of 1056 wires, each about 0.118 inch in diameter, which 
are firmly connected and brought to a cylindrical shape by a spiral 
wire wrapping. The diameter of the cable Taries from 5 to 5i 
inches. The cables pass over 3 fixed pulleys on the top of the 
piers, upon which they are spread out without ligatures, and are 
each attached to two other cables of half their diameter which 
are anchored at some distance from the piers, in vertical pits, 
passing over a fixed pulley where they enter the mouth of tlifl 

The suspending-ropes are of wire a size smaller than that used 
for the cables. Their diameter is nearly 1 inch. They are 
formed with a loop at each end, fastened around a crupper-shaped 
piece of cast iron, that forms an eye to connect the rope with the 
hook of the stirrup affixed to the roadway-bearers, and to a saddle- 
piece of wrought iron, for each rope, that rests on the two main 

The roadway-bearers are of timber, being deeper in the centre 
than at the two ends, the top surface being curved to conform to 
a slight transverse curvature given to the surface of the carriage- 
way ; they are placed about 5 feet between their centre lines, 
every fourth one projecting about 3 feet beyond the ends of the 
others, to receive an oblique wrought-iron stay to maintain the 
parapet in its vertical position. The carriage-way, which is about 
15^ feet wide, is formed of two thicknesses of plank. The foot- 
paths, which are 6 feet wide, are raised above ftie surface of the 
carriage-way, and rest upon longitudinal beams of large dimen- 
sions, the inner one of which is firmly secured to the roadway 
bearers by stirrups which embrace them, and the exterior one is 
fastened to the same pieces by long screw-bolts, which pass 
through the top rail of the parapet. The roadway has a slight 
curvature from the centre to the two extremities, along the axis ; 
the centre point being irom 18 inches to about 3 feet higher than 
the ends, according to the variations of temperature. The main 
eables at the centre ai"e brought dowi nearly in contact with the ■ 
roadway- timbers. 

The parapet is an open-built beam, consisting of a top rail, the 
bottom rail being the longitudinal exterior beam of the footpath, 
and of diagonal pieces which are mortised into the two rails ; the 
whole being secured by the iron bolts that pass through the road 
waj-bearers and the op rail. This combination of the parapet 

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With the inclination towards tJie axis of the loadway given lo the 
BUspending-ropes, gives gi eat stiffness to the roadway, and coun- 
teracts botli lateral oscillafions and longitudinal undulations. 

The piers consist of two pillars of solid masoniy, about 66 fee . 
high above the level of the roadway, which are united, at aboul 
33 feet above the same level, by a full centre arch, having a span 
of nearly 20 feet, and which forms the top of the gateway leading 
to the bridge. 

Hungeijord and Lambeth bridge, erected over the Tiiamea 
upon the plans of Mr. Brunei, 

This bridge, designed for foot-passengers only, has the widest 
span of any chain bridge erected up to Uiis period. 
Span . . . 676i feet. 

Versed sine . , 50 " 

The main chains are 4 in number, two being placed on each 
side f f tlie bridge, one above the other. These chains are formed 
entirely of long links of flat bars ; the hnks near the centre of the 
curve having alternately ten and eleven bars in each, and those 
near the piers alternatdy eleven and twelve bars. The bars are 
24 feet long, 7 inches in depth, and 1 inch thick. They are 
connected by coupling-bolls, 4f inches in diameter, which are 
secured at each end by cast-iron nuts, 8 inches in diameter, and 
2f inches thick. The extremity of each chain is connected with 
1 cast-iron saddle-piece, by bolts which pass through the vertical 
ribs of the saddle-piece, of which theTe are 15. The bottom of 
the saddle rests on 50 friction-rollers, which are laid on a firm 
horizontal bed of cast iron. The saddle can move 18 inches 
horizontally, either way from the centre, and thus compensate 
for any inequality of strain on tlie main chains, either from a load, 
or from variations of temperature. 

The side main-chains are attached in like manner to the sad- 
dle, and anchored at the other exlremilv in an abutment of brick- 
woik The and or ^e {F^, 140) ringed by passing the 

I— =lhowa the manner in which tliB 

Fia n citains are anchored. 

iQGil shaft for the chains ieading to 

1 BaiohedchamherBof thflanehorage. 

a »o main-chain9, paffied through tha 

cast ran holding-plate b and faste:i«il 

beh tid t Iiy keys. 

chains llirough a strong cast-iron plate, and si 

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he bars oy keys. T 1 o pes reta tied la place 

Dy two strong cast-iron beuns aga n 1 c he tr pon the 
plate is thrown. 

Tlie suspendiiig-rods (i ^ 1 1 ) a e com ec e 1 bo he 

, a, a, upper main-chiiin. 
\o h, b, joint of lower main- 

E, suependina-rod willi a 
forked head to receive thw 
plate d, hting by stirnli' 
straps e and/, respectivu- 
]y, to tlie coupling-bait of 
the links and lo the Iwt 
boltss-, fastened to the Gttd- 
dle A on top of lheupix:i 

upper and lower main-chains ; to the upper by a saddle-piece 
and bolts, and to the coupling-bolt of the lower by an arrange- 
ment of articulations, which allows an easy play to the rods ; at 
bottom (Fig. 142) they are connected by a joint willi a bolt thai 
fastens firmly the road way- timbers. 

d, (op longitudinal beam forming the bottom rail of tlie para- 

)lt, with a forked head to receive the end of the suspending 
roil, which ie keyed benealli and secures the beams, &o. 
fi, wrought-iron iioriimulal diagonal ties. 

The roadway-timbers consist of a strong longitudinal botton: 
beam, upon which the roadway-bearers are notched ; these last 
pieces are in pairs, tlie two being so far apart that the bolts con- 
necting with tlie suspending-rods bj^ a forked head can pass be 
iween them ; the flooring-plank is laid upon llic roadway-bearers ; 
and a top longitudinal beam, which forms the bottom rail of the 
parapet, is secured to the bottom beam by the connecting bolt. 
Wrought-iron diagonal ties are placed horizontally below the 
flooring, to brace the whole of the timbers beneath. 

The loadway is 14 feet wide. It slopes from the centre poiii 

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atoiig llie axis to the extremities, being 4 feet higlifj in the cc ntie 
iban at the two last points. 

The piers are in the form of towers, resembUiig tlie Italian 
lielfry. They are of brick, 80 feet high, and so conairucted and 
combined with the top saddles, that they have to sustain no othei 
strain than the vertical pressure from the main-chains. 

The whole weight of tlie structure, with an additional load of 
100 lbs. per square foot of the roadway, would throw about lOOC 
Ions on each pier. The tension on the chains from this load is 
calculated at about 1480 tons; while the strain they can bcai- 
witfiout impmring their strength is about 5000 tons. 

Monongaliela wire Bridge. This bridge, erected at Pittsburgfi. 
Penn., upon plans, and under the superintendence of Mr. Roe 
bling, has 8 bays, varying between 188 and 190 feet in width. Il 
is one of the more recent of these structures in the United States. 

The roadway of each bay is supported by two wire cables, of 
4| inches in diameter, and by diagonal stays of wire rope, at 
tached to the same point of suspension as the cables, and con 
necting with diiferent points of the roadway- timbers. The ends 
of the cables of each bay are attached to pendulum-bars, by 
means of two oblique arms, which are united by joints to the 
pendulum-bars. These bars are suspended from the top of 4 
cast-iron columns, inclining inwards at top, which are there iirmly 
united to each other ; and, at bottom, anch6red to the top of a 
stone pier built up to the level of the roadway-timbers. The 
side columns of each frame are connected throughout by an open 
lozenge-work of cast iron. The front columns have a like con- 
nection, leaving a sufficient height of passage-way for foot-pas- 
,, sen Iters. 

The frame-work of 4 columns on each side is firmly connected 
at top by cast-iron beams, in the form of an entablature. A'car- 
riage-way is left between the two frames, and a footpath between 
(he two columns forming the fronts of each frame. 

The points of suspension of the cables are over the centre line 
of the footpaths ; and the cables are inclined so far inward thai 
the centre point of the curve is attached just outside of the car- 
riage-way. The suspending-ropes have a like inward inclination, 
the object in both cases being to add stiffness to the system, and 
diminish lateral oscillations. 

The roadway consists of a carriage-way 22 feet wide, and two 
footpaths each 5 feet wide. The roadway-bearers are transversal 
beams in pairs, 35 feet long, 15 inches deep, and 4^ inches wide 
They are attached to the suspending-ropes. The flooring con 
sists of Sj inch plank, laid longitudinally over the entire roadway- 
surface ; and of a second thickness of 2^ inch oak plank laid 
transversely o'cr the carriage-way. 

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864 ER1HGES, ETC. 

The parapet, wiiich is on ihe principle of Town's lattice, ci 
ends so far below tlie roadway-bearers that lliey rest and ara 
notched on the lowest chord of the lattice. A second chord em 
braces them on top, and finally a third chord completes the lattice 
at top. The object of adopting this fonn of parapet was to in 
crease the resistance of the roadway to \indulations. 


624. The tenn moveable bridge is cominonly aoplicd to a 

Elatform supported by a frame-work of limber, or of cast iron, 
y means of which a communication can be formed or inter 
rupted at pleasure, between any two points of a fised bridge, oi 
over any narrow water-way. These bridges are generally de- 
nominated draw-bridges, but this term is now, for the most part, 
confined to those moveable bridges which can be raised or low- 
ered by means of a horizontal axis, placed either at one extremity 
of the platform, or at some intermediate point between the two 
ends, and a counterpoise which is so connected with the platform 
, in either case, that the bridge can be easily manceuvred by a 
small power acting through the intermedium of some suitable 
mechanism applied to the counterpoise. The term turning- or 
swinging brmge is used when the bridge is arranged to turr. 
horizontally around'a vertical axis placed at a point between its 
two ends, so that the parts on each side of the axis balance each 
other ; and tire term rolling bridge is applied when the bridge 
resting upon rollers can be shoved forward or backward horizon- 
tally, to open or interrupt the passage. 

To the above may be added another class of moveable bridges 
used for the same purpose, which consist of a platform supported 
by a boat, or other buoyant body, which can be placed in or 
withdrawn from the water-way, as ckcumstances may require. 

625. Loca! circumstances will, in all cases, determine wliat 
description of moveable bridge will be best. If the vridth of the 
water-way is not over 34 feet, a single bridge may be used ; but 
for greater widths the bridge must consist of two symmetrical 

626. Draw-bridges. "When the horizontal axis of this de 
scription of bridge is placed at the extremity of the platform, the 
bridge is manceuvred by attaching a chain to the other extremity, 
which is connected with a counterpoise and a suitable mechanism, 
by wliich the slight additional power required for raismg the 
bridge can be applied, 

A number of ingenious contrivances have been put in practice 
for il'.ese purposes. They consist usually either of a counter, 
piijsff of iuvai-iablc weight, connected with additional animal mo 

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tive power, which acts wilh constant intensity but with a variab.e 
arm of lever ; or of a counterpoise of variable weight, which is 
assisted by animal motive power acting with an invariable aim of 
lever. In some cases the bridge is worked with a less compli- 
cated combination, by dispensing with a counterpoise, ant! ap- 
plying animal motive power, of variable intensity, acting with a 
constant or a variable arm of lever. 

Among the combinations of the first kind, the most simple 
consists in placing a framed lever (Fig. 143) revolving on a hori 

Fig. 143— Shows the man- 
ner of maiiiBuvring a ilra»- 
bridge eitlier by a framed 
lever, or by a oouiite/poisa 
-lapendeil ftom a Epiral 

moveabls arounit 

113 lower end. 
!, bar wiUi an BrticulBlion 
at each eud that confines 
tlio platform. 

wi h the com erpoiae 

arn'r. " ' 

zontal axis above tl e platform TI e nter o pa of tl e fianie 
is connected with tl e irjo\ cable ex em y of 1 ] ^'i fof '^ by two 
chains. The poste or port o h cl fo n & tl e coun crpoise. 
lias chains attached to it by vh ch the 1 ve can be n o 1 ed by 

When the local y doc not adm t of iV s arra ^ nen , the 
chain attached to tl e moveable c d of 1 e pi for n nay I e con 
iiected with a horizontal axle a ovc tl e pU for n to nl cl s also 
attached a fixed ecce tr c ot a sp al si aj e (F g Hn ) connected 
witli a chain that passes over its gorge and sustains a counter- 
poise of invariable weight. Upon the same axle an ordinary 
wheel is hung, over the gorge of which passes an endless chain 
cr manosuvre the bridge by animal power. 

Of the combinations of variable counterpoises the raechanisni 

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of M. Poncelet, which has been successfully aj^plied ir jnaiiT 
instances in France for ihe draw-bridges ot military works, la 
one of the most simple in its arrangement and construction. The 
moveable end of the platform (Fig. 144} is coimected by a com- 

ranaemcntof a draw- 


to the M • 

wheel k died a 

horizontal Bhofl, tc 
which Is also aUaoli- 
ed the wheel m aiul 
the eudleea chain n 
for mancenvring tho 

mon (.hain, that passes o\ er the gorge of a wheel hung upon e 
hoiizontal shaft above theplatform, with another chain of variable 
breadth, fomsed of flit bar links, which forms the counterpoise, 
Ihc cliam counterpoise is tttached at its other extremity to a 
fiiced point in such a w ay, that when the platform ascends, a por- 
tion of the w eight of the chain is borne by this fixed point ; and 
thus the weight of the counterpoise decreases as the platform 
iiaci The sjitem is manteuvrcd by an endless chain passed 
over the gorge of a wheel hung upon the horizontal shaft 

For hght platforms a counterpoise may be dispensed with, and 
tlie bridge may be manceuvied by connecting the chain attached 
to the moveable end of the platform to a horizontil shaft, which 
is turned by the usual tooth-work combinations 

When the locality does not admit of mTnceuvimg the bml^c b^ 

F>s 14..— Sliowa Iho ar 
ransemeiil ot a di-an 
biidge where the couii 
ternoise is formed by 
pmougiug back the 

a chain connected w 
platform, Fig 145 i 

h some point abo\c the fiimo woik of the 
Lontnmcil bick, from two [huds. to thrt-e 

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fifths its length, from the face of the abutment, to form a couo' 
terpoise for the platform of llie bridge. The horizontal axis of 
the bridge is placed near the face of the abutment, and a well of a 
suitable shape to receive the posterior portion of the platform that 
forms the counterpoise is formed behind the abutment. 

The mechanism for working the bridge may consist of i chain 
and capstan below the platform-counterpoise, or of a suitable 
combination of tooth-work. 

In bridges of a single plalforni, the moveable extremity, when 
the bridge is lowered, rests on the opposite abutment, and no 
intermediate support will be required for the structure if the 
frame-work be of sufficient strength ; but when a double bridge, 
consisting of two platforms, is used, the platforms (Fig. 143) 
should be supported near their moveable ends, when the bridge 
is down, by struts moveable around the joint by which they are 
connected with the face of the abutments. These struts are 
BO connected with the bridge that ihey are detached from it 
and drawn up when it is raised, and fall back into their places, 
abutting against blocks near the moveable end of the pktfonn, 
when the bridge is down. By these arrangements the chains for 
working the bridge are relieved from a portion of the strain when 
the bridge is down, and it is also rendered more firm. 

When the counterpoise is formed by llie rear part of the plat 
form, additional security may be given to the bridge when down 
by attaching two chains beneath the platform, and securing them 
to anchoring-points at the bottom of the well. In some cases a 
heavy bar, fitted to staples beneath connected witli the timbers 
of the platform, is used for the same purpose. 

In double bridges the two platforms when lowered should abut 
against each other, giving a slight elevation to the centre of the 
bridge. This not only gives greater stiffness, but is favorable to 
detaching the platforms when the bridge is to be raised. 

For draw, and every kind of moveable bridge, temporary bar- 
riers should be erected on each side at the entrance upon the 
bridge, to prevent accidents by persons attempting to cross the 
!)ridge before it is properly secured when lowered. 

637. Turning-bridges. These bridges revolve horizontally 
upon a vertical shaft, or gudgeon below the platform, which is 
usually thrown far enough back from the face of the abutment tc 
place the side of the briogei when brought round, just within this 
face. The weights of the parts of the bridge around the shaft 
fihould balance each other. 

To support and manoeuvre the bridge (Fig. 146) a circulai 
ring of iron, or roller-way, of less diameter than the breadth of 
.he bridge, and concentric with the ver;ical shaft, is firmly im- 
Dedded in masonry. Fi?ed rollers, in the shane of truncated 

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cones, are allached at equal distances apart to tlic frame-wcrk of 
ihc plalfonn beneath, and rest upon the roller-way. The bridge 

(s Ihe atraiigeraent of a tummg-bnilKe. 
-e itttacheil. 
0, 0, conical raUoit 

is worked by a suitably arranged tooth-work, or by a chain ami 
capstan. In some cases cast-iron balls, resting on a grooved 
rolier-way and fitting into one of corresponding shape fixed, be- 
neath the platform, have been used for manceuvring the bridge. 

The ends of the bridge are cut in the sliape of circular arcs to 
fit recesses of a corresponding form in the abutments, so arranged 
as not to impede the play of the bridge. 

In double turning-bridges the two ends of the platforms which 
come together should be of a curved shape. The platforms 
should be sustained from beneath by struts, like those used for 
draw-bridges, which can be detached and drawn into recesses 
when tlie passage is interrupted ; or else they may be arranged 
with a ball-and-socket joint at their lower extremity, so as to be 
brought round with the bridge. For the purpose of giving addi- 
tionod strengtii and security to the bridge, iron stays are, in some 
cases, attached on each side of the platform near the extremities, 
and connected with vertical posts placed in a line with the verti 
cal shaft. 

Turning-bridges may be made either of timber, or of cast iron ; 
the latter material is the more suitable, as admitting of more ac- 
curacy of workmanship, and not being liable to the derangements 
caused by the shrinking or warping of frame-work of timber. 

628. Rolling-bridges. These bridges are placed upon fixed 
rollers, so tliat they can be moved forward or backward, to inter- 
rupt, or open the communication across tlie water-way. The 
part of tlie bridge that rests upon the rollers, when tlie passage 
is closed, must form a counterpoise to the other. The mechan- 
ism usually employed for manceuvring these bridges consists of 
tooth-work, and may be so arranged that it can be worked by 
one or more persons standing on the bridge. Instead of fixed 
rollers turning on asl ;s, iron balls resting in a grooved roller-waj 

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intybe jacd, a similar roller-way being affixed to thefi^me-worlt 

629. Boat-bridge. A moveable bridge of this kind may be 
made by placing a platform to form a roadway upon a boat, or a 
water-tight box of a suitable shape. This bridge is placed in, oi 
withdrawn from the water-way, as circumstances may require, n 
suitable recess or mooring being arranged for it near the water 
way when it is left open. 

A bridge of this character cannot be conveniently used in tidal 
waters, escept at certain stages of the water. It may be em 
ployed with advantage on canals in positions where a fixed bridge 
could not be placed. 


630. In aqueducts and aqueduct-bridges of masonry, for sup- 
plying reservoirs for the wants of a city, or for any other purpose, 
tlie volume of water conveyed being, generally speaking, small, 
the structure will present no peculiar difficulties beyond affording 
a water-tight channel. This may be made either of masonry, oi 
of cast-iron pipes, according to the quantity of water to be deliv- 
ered. If formed of masonry, the sides and bottom of the channel 
should be laid in the most careful manner with hydraulic cement, 
and the surface in contact with tlie water should receive a coating 
of the same material, particularly if the stone or brick used be 
of a porous nature. This part of the structure should not be 
commenced until the arches nave been uncentred and the lieavier 
parts of the structure have been carried up and have had time to 
settle. The interior spandrel-filling, to the level of the masonry 
which forms the bottom of the water-way, may either be formed 
of solid material, of good rubble laid in hydraulic cement, or of 
beton well settled in layers ; or a system of interior walls, like 
those used in common bridges for the support of the roadway, 
may be used in this case for the masonry of the water-way to 
rest on. 

631. In canal aqueduct-bridges of masonry, as the volume of 
water required for the purposes of navigation is much greater 
than in the case of ordinary aqueducts, and as the sti'ucture has 
to be traversed by horses, every precaution should be taken t& 
procure great solidity, and secure the work from accidents. 

Segment arcries of medium span will generally be found mosi 
suitable for works of this character. The section of the water- 
way is generally of a trapezoidal form, the bottom line being 
horizontS, and the two sides receiving a slight batir ; its dimen 
sions are usually restricted to allow the passage of a single boat 
at a time. On one side of the water-way a horse or tow path w 


270 BRIDGES, Eli:. 

placed, and on llie other a narrow footpath. The water-way 
should be faced with a hard, cut-stone masoniy, well bonded to 
secure it from damage from tlie passage of the boats. The space 
between the facing of the water-way, termed the trunlc of the 
aqueduct, and the head-walls, is filled .in with solid material, either 
of rubble or of beton. 

A parapet-wali of llie ordinary form and dimensions surmounts 
the tow and footpaths. 

The approach to an aqueduct-bridge from a canal is made by 
gradually increasing the width of the trunk between the wings, 
Thich. for this purpose, usually receives a curved shape, and 
narrowing the water-way of the canal so as to form a convenient 
access to the aqueduct. Great care should be taken to form a 
perfectly water-tight junction between the two works. 

632. \yhen cast iron or timber is used for the trunk of an 
aqueduct-bridge, the abutments and piers should be built of stone. 
The trunk, which, if of cast iron, is formed of plates with flanches 
to connect them, or, if of timber, consists of one or two thick- 
nesses of plank supported on the outside by a framing of scant- 
hng, may be supported by a bridge-frame of cast iron, or of tim- 
ber, or be suspended from chains or wire cables. 

The tow-path may be placed either within the water-way, or, 
as is most usually done, without. It generally consists of a sim- 
ple flooring of plarik laid on cross-joists supported from beneath 
by suitably arranged frame-work. 

633. The following succinct descriptions of some of the ague 
duct-bridges of the United States and of Europe are derived from 
authentic sources. 

Chirlc Aqueduct-bridge over the Ceriog. This work, built by 
Telford, consists of 10 full centre arches of masonry, of 40 feet 
span each. The water-way is only 1 1 feet wide and 5 feet deep, 
I'he tow-path 6 feet wide. 

The piers of this work, which in some places are over 1 00 feci 
iu height, are built hollow for some distance below the top ; tlie 
facing being connected by cross-walls upon which tiie bottom 
of the water-way, formed of broad iron-nanched plates, and tho 
masonry of the sides rest. 

Pont-y-Cystile A(jv.educl-brtdgc over the Dee. This is also 
one of Telford's early works. The trunk is of cast-iron plates 
connected by flanches. These rest upon stone piers and upon a 
bridge-frame of cast iron consisting of four ribs of aoHd panels. 
The span of the ribs is 45 feet and the rise 7i feet. 

The breadth of the water-way is 11 foet 10 inches. The tow- 
path is 4 feet S inches wide, and is plated within the watc way, 
reBting upon cast-iron uprights. 

The canal aqueduct-bridges at Gultin over the AlUer, and a 

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Digom Upon the Loire, are among the more recent siruclures oi 
this character in France. They are both built upon the saiim 
plan, and of mixed masonry. The first has eighteen arches ; 
the second eleven. The span of each arch is 52i feet, and tlia 
rise about S3 feet. The piers are about 10 feet tiiick at the im 
post. The breadth of the aqueduct between the heads is 31 feet, 
and that of the water-way about Ifi feet. 

Rochester Canal Aqueduct-bridge. This is the most recent 
and the largest aqueduct^bridge built entirely of masonry in the 
United Stales. It consists of seven segment arches. Its water 
way is of sufficient width for the passage of two boats, and is 
adapted to the enlaraement of the Erie canal. The span of each 
arch is 52 feet; the rise 10 feet. The key-stone is 3 feel 
6 inches in depth, and the top of it is on a level with the bottom 
of the trunk. The piers are 10 feet thick at the impost. The 
water-way is 9 feet in depth, the masonry of the sides receiving 
a batir of 2 inches in one foot. The deplh of water is 7 feet, 
and the width at the water-hne 45 feet. The sides of the water- 
way, the top surface of which forms the tow-paths, are 1 1 feet in 
width at top, including the projection of the coping. The trunk 
at each extremity is gradually enlarged, in a cun'cd shape, to the 
width of 55 feet, where it unites witli the slopes of the water-way 
of the canal. 

This work is built throughout in a very strong and superior 
manner, of heavy blocks of gray lime-stone laid in hydraii.'ic 

Potomac Canal Aqueduct-bridge. This work, originally in- 
tended to be of stone throughout, was to have consisted of twelve 
oval arches of eleven centres, the span of each being 100 feet, 
and the rise 25 feet. Every third pier forms an abutment-pier, 
and is 21 feet thick at the impost ; the others are only 12 feet 
thick at the same level. The piers have been built upon the 
original design, but a wooden superstructure, consisting of the 
trunk of the aqueduct, a tow-path, and the frame-work for their 
support, has been substituted for the stone arches. 

The trunk (Fig. 147) is formed of a frame consisting of two 
parallel open-built beams, connected at bottom by parallel cross- 
joists and horizontal diagonal braces, which are sheathed on the 
interior with plank to form the water-way. 

Each of the open-built beams is composed of a top and bottom 
string connected by uprights that project above and below tlie 
strings, and by single diagoral braces placed between each pair 
of uprights. 

The tow-path is placed on the outside of the trunk, and con 
iisls of a flooring laid upon cross-joists placed between one of tfao 
built beams of the trunk and a thiic' parallel to it. 

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The exterior-built beam of the tow-path is framed of &ni?iijci 
scantling than the other two. It is connected with, the bunt 

Fig. Hl—Ropresonla a cross section of the tninl: ai 
Potomac canal aqueduct-bridge. 

A, interioi of trunk. 

B, tow-imtli. 

a, a, nforishfs of Ihe open-built beams on Ihe aideaof tiie 

*, uprighfof the open-bni)t beam of Dis low-patli. 

c, lower sUingH of the built beama. 

a, upper string. 

e, crosB-joists oa which the sheathing of the bottom of tli 

n, eross-joiBta of the tow-palh. 

beam of the trunk by every fourth cross-joist of the trunk, by tha 
top cross-joists of the flooring, and by vertical diagonal bracea 
placed between each pair of top and bottom cross-joists. 

The uprights of the exterior-built beam of tlie tow-path pro- 
ject sufficiently high above the flooring to form a parapet. 

The frame-work of the trunk and tow-path is supported al 
intermediate points from beneath by inclined stmts which abut 
against the faces of the piers at a point above the high-watei 

The section of the water-way is rectangular. The interior 
Width is 17 feet; Ihe height of the sheathing 8 feet 4 inches 
within ; and the depth of water 4 feet 4 inches. 

The surface of the tow-path is 6 feet wide between the uprig-hts 
of the built beams, and is on a level with the lop of the sheathing. 
The exterior parapet is 3 feet ] inches above the level of the 
tow-path, and an interior parapet, 2 feet above the same level, is 
formed by a capping on the uprights of the built beam, making 
the height of the capping on each side of the trank 10 feet 4 
mches above the sheathing of the bottom. 

The frame-work of this structure is simple in its combinations 
and well arranged both for strength and stiffness. 

Wire Suspension Canal AqueducuJyi-idge over the Alleghany 
river at Pillshurgh, This novel work (Fig. 148) was planned 

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Bj Supports of niasomy on tlie piers for llie wire catilea. 

C, interior of a portion of the tranlt. 

a, cros^'ioials suspuudod from ttie cables m by Via bent euspbnding-bats n» 

on which the bottom e of trank rests. 
6, inclined stmtB in pairs connected with tlio pieces c lo support the aides d 

of the trunk. 

D, tow-path. 

e, croBs-joistsof the tow-patli. 

r, inclined supports of a. 

t and D, parapets. 

ft, sleepers on topof Uia piers on which the cross-joisls a rest. 

anl constructed by Mr. Roebling, through whom the followiig 
deailed description was obtained : 

"This work is formed of seven spans of 160 feet each from 
centre to centre of pier. The tronit is ot wood and 1140 fet. 
long, 14 feet wide at bottom, 16^ feet wide on top ; the sides 8^ 
feet deep. These as well as the bottom are composed of a 
double course of 2^ inch wliite-pine plank laid diagonally, the 
two courses crossing each other at right angles, so as lo form a 
solid lattice-work of great strength and stiffness, sufficient to bear 
its own weight and resist the effects of the most violent storms, 
The bottom of the trunk rests upon transverse beams, arranged 
in pairs 4 feet apart ; between tliese the posts which support the 
sides of the trunk are let io with dove-tailed tenons, secured by 
bohs. The outside posts which support tlie side-walk and tow- 
path incline outwards and arc connected with the beams in a 
similar wanner. Each trunk-post is held by two braces 2^x10 
inches, and connected with the outside posts by a double joist of 
ZJXlO. The trunk-posts are 7 inches square af the top und 

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2^4 JJBlDilES ETC 

7X14 at the heel. The transverse beams are 1J7 feet long 10 
inches deep, and 6 inches wide ; the S|)aee between the two ad- 
joining is 4 inches. It will be observed that all parts of the 
frame, with the exception of the posts, are double, so as to admit 
the suspension-rods. Each pair of beams is supported on each 
side of the trunk by double suspending-rods of 1|- inch round 
bar-iron, bent in the shape of a stirrup, and mounted on a small 
cast-iron saddle, which rests on the cable. These saddles are on 
lop of tlie cables connected by links, which diminish in size from 
Ihe pier towards the centre. The sides of the trunk rest solid 
.against the bodies of masonry, which are erected on each piei 
and abutment as bases for the pyramids wliich support the cables 
These pyramids, which are constructed of three blocks or coursee 
of a durable coarse-grained hai'd mountain sand-stone, rise 5 feel 
above the level of the side-walk and tow-path, and measure 3x5 
feet on top, and 4 x6J feet in base. The side-walk and tow-path 
being 7 feet wide, leave 3 feet space outside for the passage of 
lie pyramids ; the ample width of the low and footpath is there- 
''ore contracted on every pier ; but tliis arrangement proves no 
inconvenience, and was necessary for the suspension of the 
ne.Kt to the trunk. 

" As the caps which cover the saddles and cables on the pyra- 
mids rise 3 feet above the inside, or trunk-railing, they would 
obstruct the passage of the tow-line ; this however is obviated 
by a slide-rod of round iron, wliich passes over the top of the cap 
and forms a gradual slope down to the railing on each side of the 

" The wire cables, which are the main support of the structure, 
are suspended next to Uie trunk, one on each side. Each of 
these two cables is exactly 7 inches in diameter, perfectly sohd 
and compact, and constructed in one piece from shore to shore, 
1175 feet long; it is composed of 1900 wires of ^ inch diameter, 
which are laid parallel to each other. Great care has been taken 
to insure an equal tension of tlie wires. The oxidation of the 
wires is guarded against by a varnish applied to each separately. 
The preservation of the cables is insured by a close, compact, 
and continuous wrapping, made of annealed wire and laid on by 
machinery in the most perfect manner 

" The extremities of the cables on the aqueduct do not extend 
below ground, but connect with anchor-chains, which in a curved 
Ihie pass through large masses of masoniy, the last links occupy- 
ing a vertical position. The bars composing these chn'ns aver- 
age 1^X4 inches, and are from 4 to 12 feet long; they are 
manufactured of boiler-scrap, and forged in one piece will, out a 
weld. The extreme links are anchored to heavy cast-iron plates 
•f (i feel square, which are held down by the foundations, upor 

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ivliich the weight of 700 perches of masonry rests. The stabilitj 
cT this part of the structuie is fully insured, as the resistance of 
die anchorage is twice as great as the greatest strain to which the 
:;hains can ever be subjected, 

■' The plan of anchorage adopted on the aqueduct varies mate- 
rially from those methods usually applied to suspension bridges, 
where an open channel is formed under ground for the passage 
of the chains. The chains below ground are imbedded and com- 
pletely surrounded by cement. In the construction of the ma- 
sonry this n;Laterial and common lime-mortar liave been abundantly 
applied. The bars are painted with red lead : their preservation 
is rendered certain by the known quality of calcareous cements to 
prevent oxidation. If moisture should find its way to the chains, 
it will be saturated with lime, and add another calcareous coat- 
ing to the iron. This portion of the work has been executed 
with scrupulous care, so as to render it unnecessary, on the part 
of those who exercise a surveillance over the structure, to examine 
it. The repainting of the cables every two or three years will 
insure their duration for a long ppjiod. 

" Where the cables rest on the saddles, their size is increased 
at two points, by introducing short wires and forming swells 
which fit into corresponding recesses of the casting. Between 
these swells the cable is forcibly held down by three sets of 
strong iron wedges, driven through openings which are cast in 
the sides of the saddle. During the raising of the frame-work, 
the several arches were frequenUy subjected to very unequal and 
considerable forces, which never disturbed the balance, and proved 
the correctness of previous calculations. The woodwork in any 
of the arches, separately, may be removed and substituted by new 
material, without aiFecting the equilibrium of the next one. 

" The original idea upon which the plan has been perfected, 
was to form a wooden trunk, strong enough to support its own 
weight, and stiff enough for an aqueduct, or bridge, and to com- 
bine this structure wi3i wire cables, of a sufficient strength tc 
bear safely the great weight of water. 

" Tahle of Quantities on Aqueduct. 

Length of aqueduct without extensions . 

Length of cables 

length of cables and chains .... 
Diameter of cables ..... 

Aggregate weight of both cables 
Section of 4 feet of water in trunk . 
Total weight of water ill aqueduct , 



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Aggregate solid sectiot of both cables 

Do. do. ' anchor-ubains 

Deflection of cables .... 

Elevation from top of pyramids to top of piers 

WeigKt of n^tei' L one span between pler^ 
Tension of cablea resulting from lliie weiglit 
Tension of one single nire 
Average ultimate strength of one wi 
Ultimate strength of cables 
Tension lesulting from weight of «■! 

square inch of wire cable 
Tension lesalting from weight of water upon 

inch of anchor-chains 
Pressure resulting froni water upon a pyramid 
Do. upon ^ne superficial foot 


53 supcrf. incli 

14 feet G incl 
16 " 6 ' 
ers tons. 

392 " 
SOB lbs. 
1 100 " 

aOOO ions, 
naoo lbs. 

11000 " 

I37i tonB 
18*00 Iba." 

Se: >roteA,, App^iidi-^ 



634. In establisliing a line of internal communication (if any 
:iiaractcr, whether it be an ordinary road, raihroad, or canal, the 
main considerations to which the attentioii of the engineer must 
he directed in the outset arc— 1, ihe probable character and 
amount of traffic over the line ; 2, the wants of the community 
in the neighborhood of the line ; 3, the natural features of the 
country, between the points of arrival and departure, as regards 
their adaptation to the proposed communication. 

As the last point alone comes exclusively within the province 
of the engineer's art, and within the limits prescribed to this work, 
attention will be confined solely to its consideratiou. 

633. Reconnaissance. A thorough examination and study of 
the ground by the eye, termed a reconncdssance, is an indis- 
pensable preliminary to any more accurate and minute survey 
fay instruments, to avoid loss of time, as by this more rapid ope-^ 
ration any ground unsuitable for the proposed Hue will be as cer- 
tainly detected by a person of some experience, as it could be by 
the slow process of an instrumental survey. Before however pro- 
ceeding to make a reconnaissance, a careful inspection of the 
general maps of that portion of the country through which the 
communication is to pass, will faciUtate, and may considerably 
abridge, the labors of the engineer ; as from the natural features 
laid down upon them, particularly the direction of the water- 
courses, he will at once be able to detect those points which will 
be favorable, or otherwise, to the general direction selected for 
the line. Tliis will be sufficiently evident when it is considered 
— 1, that the water-courses are necessarily the lowest lines of 
the valleys through whicii they flow, and that their direction must 
also be that of the lines of greatest declivity of their respective 
valleys ; 2, that from the position of the water-courses the position 
also of the high grounds by which they are separated iiajurally 
follows, as well as the approximate position at least of the ridges, 
or highest lines of the hi^i grounds, which separate their opposite 
slopes, and which are at the same time the lines of greatest de- 
chvity common to these slopes, as the water-courses are the cor 
responding lines of the slopes that form the valleys. 

Keeping these facts (which are susceptible of rigid mathemati 
Cal demonstration) in view, it will be practicable, from a careful 
examination of an ordinary general map, if accurately cor structed. 
jot only to trace, wilb considerasle accuracy, the general diiec 



lion of the ridges from having that of the water-courses, but also 
to detect those depressions in them which will be favorable to the 
passage of a communication intended to connect tvfo main oi two 
secondary valleys. The following illustrations may serve to place 
this subject in a clearer aspect. 

]f, for example, it be found that on any portion of a map the 
water-courses seem to diverge from or converge towards one point, 
it will be evident that the ground in tlie first case must be the 
common source or supply of the water- courses, and therefore the 
highest ; and in the second case that it is the lowest, and forma 
their common recipient. 

If two water-courses flow in opposite directions from a common 
point, it will show that this is tlie point from which they derive 
their common supply, at the head of their respective valleys, and 
that it must be fed by the slopes of high grounds above this point ; 
or, in other words, that the valleys of the two water-courses are 
separated by a chain of high grounds, which, at the point where 
it crosses them, presents a depression in its ridge, wliich would 
be tlie natural position for a communication connecting the two 

If two water-courses flow in the same direction and parallel lo 
each other, it will simply indicate a general inclination of the 
ridge between ihem, in the same direction as tliat of the water- 
courses. The ridge, however, may present in its course eleva- 
tions and depressions, which will be indicated by the points in 
which the water-courses of the secondary valleys, on each side 
of it, intersect each other on it ; and these will be the lowest 
points at which lines of communication, tlirough the secondary 
valleys, connecting the main water-courses, would cross the divi- 
ding ridge. 

If two water-courses flow in the same direction, and parallel 
to each other, and then at a certain point assume divergent direc- 
tions, it will indicate that this is the lowest point of the ridge be- 
tweeen them. 

If two water-courses flow in parallel but opposite directions, 
depressions in tlie ridge between them will be shown by the 
meeting of the water-courses of the secondary valleys on the 
ridge ; or by an approach towards each other, a any point, of 
the two principal water-courses. 

Furnished with the data obtained from tlie maps, the charactei 
of the ground should be carefully studied both ways by the en 
gineer, first from tlie point of departure to that of arrival, and then 
returning from the latter tc^ the former, as without this double 
craverse natural features of essential importance might escape 
lie eye. 

636. Suitcys. From the results of the reconnaissance, iha 

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Boiss. 370 

engineer ■will be able to direct undergtanomgly the rci^uieite aur 
veya, wIkcIi consist in measuiiii^ ihe lengths, deffirraining the 
directions, and ascertaining both iTie longitudinal and cross levels 
of tKe different routes, or, as they are termed, trial lines, willi 
suflicieEt accuracy to enable him to make a comparative estimate 
both of their practicability and cost. As the expense of making 
the requisite surveys is usually but a small item compared wim 
that of constructing the communication, no labor should be spared 
m running every practicable line, as otherwise natural features 
might be overlooked which might have an important influence on 
the cost of construction. 

637. Map and Memoir. The results of the surveys are ac- 
curately embodied in a map exhibiting minutely the topographical 
features and sections of the different trial lines, and in a memoit 
which should contain a particular description of those features of 
the ground that cannot be shown on a map, with all such infor- 
mation on other points that may be regarded as favorable, or 
otherwise, to the proposed communication ; as, for example, the 
nature of the soil, that of tlie water-courses met with, &c., &;c. 

638. Location of common Roads. In selecting among the 
different trial-lines of the survey the one most suitable to a com- 
mon road, the engineer is less restricted, from the nature of the 
conveyance used, than in any other kind of communication. The 
main points to which his attention should be confined are — 1, to 
connect the points of arrival and departure by the most direct, or 
shortest line ; 2, to avoid unnecessary ascents and descents, or,, 
in other words, to reduce the ascents and descents to the smallesl 
practicable Hmit ; 3, to adopt such suitable slopes, or gradients, 
for the axis, or centre line of the road, as the nature of the con- 
veyance may demand ; 4, to give the axis such a position, with re- 
gard to the surface of llie ground and the natural obstacles to be 
overcome, that the cost of construction for the excavations and 
embankments required by the gradients, and for the bridges and 
other accessories, shall be reduced to the lowest amount. 

639. Deviations from the right line drawn on the map, between 
the points of arrival and departure, will be often demanded by the 
natural features of the ground. In passing the dividing ridges 
of main, or secondary valleys, for example, it will frequently be 
found more advantageous, both for the most suitable gradients, 
and to diminish the amount of excavation and embankment, tc 
cross the ridge at a lower point than tiie one in which it is inter- 
sected by the right line, deviating from the right hne cither 
towai'ds the head, or upper part of the valley, or towards its out- 
let, accord^ing Iq the advantages presented by the natural features 
of the ground, both for reducing the gradients and the anrouot of 
excavation and embankment 

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"Where the right hne intersects either a marsh, or water-cou/se 
it may be found les'i expensive to change the direction, avoiding 
tlie marsh, or intersecting the water-course at a point where the 
cost of construction of a bridge, or of the approaches to it, wil 
be more favorable than the one in wliich it is intersected by thp 
right hne. 

Chaises from the direction of the right hne may also be fa 
vorable tor the purpose of aioidiiig the intersection of secondary 
water-courses , of gainmg a better soil for the roadway ; of giv- 
ing a better esposuie of its surface to the sun and wind ; or of 
procuring better materials for the road-covering. 

By a careful comparison of the advantages presented by these 
different features, the ei gineer will bo enabled to decide how far 
the genera! direction of the right line may be departed from with 
advantage to the location By choosing a more sinuous course llio 
length of the hne will often not be increased to any very consider 
able degree, while the cost of construction may be greatly re- 
duced, either m obtammg moie favorable gradients, or in lessening 
the amount of excavation and embankment. 

640. "When the points of arrival and departure are upon dif- 
ferent levels, as is usually the case, it vrill seldom be practicable 
to connect them by a continual ascent. The most that can be 
done will be to cross the dividing ridges at their lowest points, 
and to avoid, as far as practicable, Uie intersection of considerable 
secondai^ valleys which might require any considerable ascent 
,on one side and descent on the other, 

641. The gradients upon common roads will depend upon the 
kind of material Used for the road-covering, and upon the stale 
in which the road-surface is kept. The gradient in all cases 
should be less than the angle of repose, or of that inclination of 
the axis of the road in which the ordinary vehicles for Iransporta 
tion would remain at a state of rest, or, if placed in motion, would 
descend by the action of gravity with uniform velocity. 

The gradients corresponding to the angle of repose have been 
ascertained by experiments made upon the various road-coverings 
in ordinary use, by allowing a vehicle to descend along a road 
of variable inclination until it was brought to a state of rest by 
the retarding force of friction ; also, by ascertaining the amount of 
force, termed the force of traction, requisite to put in motion a 
vehicle with a given load on a level road. 

The following are the results of experiments made by Mr 
Macneill, in England, to determine the iorce of traction for one 
ton upon level roads. 
No. 1. Good pavement, the force of traction is . 33 Iba 

" 2. Broken stone surface laid on '^n old flint road 65 " 

" 3. Gravel road 14f '' 

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B0AO9. 2SI 

No. 4. Broken-stone surface on a rough pave.nent 

bottom IG lbs. 

*' 5. Eroken-stone surface on a bottom of beton . 46 " 
From this it appears that the angle of repose in the first casa 
13 represented by ^Hz, or j'-g nearly; and that the slope of 
the road should therefore not be greater than one perpendicular 
to sixty-eight in length ; or that the height to be overcome must 
not he greater than one sixty-eighth of the distance between the 
two points measured along the roid, ni older that the force of 
friction may counteract that of gr^iity m the direction of the 

A similar calculation will show tint the in_Ie of repoHO in the 
other cases will be as follows : 

No, 2, . . . . 1 to . .35 nearly. 

"3, 1 to . . 15 " 

" 4 and 5, . . . 1 to . . . 49 " 
These numbers, which give the angle of repose between -^j 
and jV for the kinds of road-covering Nos, 2 and 4 in most or- 
dinary use, and corresponding to a road-surface in good order 
may be somewhat increased, to from jV to ^'g, for the ordinary 
state of the surface of a well-kept road, without there being any 
necessity for applying a brake to the wheels in descending, or 
going out of a trot in. ascending. The steepest gradient that can 
be allowed on roads with a broken-stone covering is about ^Vi ^s 
this, from experience, is found to be about the angle of repose 
upon roads of this character in the state in which they are usually 
kept. Upon a road with this inclination, a horse can draw at a 
walk his usual load for a level without requiring the assistance 
of an extra horse ; and experience has farther shown that a horse 
at the usual walkmg pace will attain, with less apparent fatigue, 
the summit of a gradient of -^^ in nearly the same time that he 
would require to reach the same point on a trot over a gradient 
of jV- 

A road on a dead level, or one with a continued and uniform 
ascent between the points of arrival and departure where they lie 
d ff 1 1 1 m f bl he draft of the 

! E h f 1 n f g i m tlian a line of 

ts d d f 1 gl g d as, for exam- 

] II I w as heavy a 

! 1 I. 

b d i far as prac- 
1 p forth ill ovcr- 

ngh grd y dblly should as a 

g I 1 ! f b k p 1 1 a'ai wherever 

Jie ground will admit of it. This can generally be ciiccled, even 
ill ascending steep hill-sides, by giving the axis of the roai a zig- 

s <i 

f ui 


Iw 1 h 

P 1 


Tl g d 

1 uld 


M 1 




zag direction, connecting the straight portions of the zigzags ^^ 
circulai arcs. The grad'ents of tlie curved portions of the zig- 
zags should be reduced, and the roadway also at these points be 
widened, for the safety of Tehicles descending rapidly. The 
width of the roadway may be increased about one fourth, when 
the angle between the straight portions of the zigzags is from 
120° to 90°; and the increase should be nearly one half where 
the angle is from 90° to 60°. 

642. Having laid down upon the map the approximate location 
of the axis of the road, a comparison can theiioe made between 
the solid contents of the excavations and embankments, which 
should be so adjusted that ihey shall balance each other, or, in 
other words, the necessary excavations shall furnish sufficient 
earth to form tlie embankments. To effect tliis, it will frequently 
be necessary to alter the first location, by shifting the position of 
the axis to the right or left of the position first assumed, and alsa 
by changing the gradients within the prescribed limits. This 
is a problem of very considerable intricacy, whose solution can 
only be arrived at by successive approximations. For this pur 
pose, the line must be subdivided mto several portions, in each 
of which the equalization should be attempted independently of 
the rest, instead of trying a general equaHzation for the whole 
line at once. 

In the calculations of solid contents required in balancing the 
excavations and embankments, the most accurate method consists 
in subdividing the different solids into others of the most simple 
geometrical forms, as prisms, prisraoids, wedges, and pyramids, 
whose solidities are readily determined by the ordinary rules for 
the mensuration of solids. As this process, however, is frequently 
long and tedious, other methods requiring less time but not so 
accurate, are generally preferred, as their results give an approx- 
imation sufEciently near the true for most practical purposes. 
They consist in taking a number of equidistant profiles, and cal- 
culating the solid contents between each pair, either by multiply- 
ing the half sum of their areas by the distance between them, or 
else by taking the profile at the middle point between each pair, 
and, multiplying its area by the same length as before. Pho 
latter method is the more expeditious ; it gives less than the trae 
solid contents, but a nearer approximation than the former, which 
gives more than the true sohd contents, whatever may be the 
form of the ground between each pair of cross profiles. 

In calculating the solid contents, allowance must be made for 
the difference in bulk between the different kinds of earth when 
occupying their natural bed and when made into enibanlanent 
From some careful experiments on this point made by Mr. Ehvood 
Morris, a civil ei'gineer, and published in t!»' Frankhn Joumal 

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ROADS. 28a 

t appea.'s ihat light smdy earth occupies the same space both in 
excavation and embankment ; clayey earth about one tenth less 
in embankment than in its natural bed ; gravelly earth also aboul 
one twelfth less ; rock in large fragments about five twelfths 
more, and. in small fragments about six tenths more. 

, 643. Another problem connected with the one in question, is 
that of determining the lead, or the mean distance to which the 
earth taken from Die excavations must be carried to form the 
'embankments. From the manner in which the earth is usually 
transported from the one to the other, this distance is usually that 
between the centre of gravity of the solid of excavation and 
that of its corresponding embankment. Whatever disposition 
may be made of the solids of excavation, it is important, so far 
as the cost of their removal is concerned, that the lead should be 
the least possible. The solution of the problem under this point 
of view will frequently be extremely intricate, and demand the 
appUcation of all the resources of the higher analysis. One gen- 
eral principle however is to be observed in all cases, in order to 
obtain an approximate solution, which is, that in the removal of 
the different portions of the solid of excavation to their corre- 
sponding positions on that of the embankment, the paths passed 
over by their respective centres of gravity shall not cross each 
other either in a horizontal, or vertical direction, , This may in 
most cases be effected by intersecting the solids of excavation 
and embankment by vertical planes in the direction of the re- 
moval, and, by removing the partial solids between the planes 
within the boundaries marked out by them. 

644. The definitive location having been settled by again going 
over the line, and comparing the features of the ground with iho 
results furnished by the preceding operations, general and de- 
tailed maps of the different divisions of the definitive location are 
prepared, which should give, with the utmost accuracy,\^e lon- 
gitudinal and cross sections of the natural ground, and of the ex- 
cavations and embankments, with the horizontal and vertical 
measurements carefully written upon them, so that the superin- 
tending engineer may have no difficulty in setting out the work 
from them on the ground. 

In addition to these maps, which are mainly intended to guide 
the engineer in regulating the earth-work, detailed drawings of tlic 
road-covering, of the masonry and carpentry of the bridges, cul- 
verts, &c., accompanied by written specifications of the mannei 
in which the various kind of worit is to be performed, should be 
prepared for the guidance both of the engineer and workmen. 

645. With the data furnished by the maps and drawings, iht. 
engineer can proceed to set out the line on the ground. The 
axis of the road fe determined by placing stout stakes, or picket^ 

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at equal intervals apart, which are nuir.-borud to coiTCPpond wii ^ 
the same poinis on the map. Tlie widOi of the roadway and the 
hnes on the ground correspoiiding to the side slopes of the exca- 
vations and embankments, are laid out in the same manner, by 
stakes placed along the lines of the cross profiles. 

Besides the numbers marked on the stakes, to indicate tlieii 
position on the map, other numbers, showing the depth of the 
excavations, or the height of the embankments from the surface 
of the ground, accompanied by the letters Cut. Fill to indicate a 
cuttmg, or B.Jilling, as the case may be, are also added to guide 
the workmen in their operations. The positions of the stakes on 
the ground, which show the principal points of the axis of the 
road, should, moreover, be laid down on the map with great ac- 
.curacy, by ascertaining their bearings and distances from any fixed 
and marked objects in their vicinity, in order that the poinis may 
be readily found should the stakes be subsequently misplaced. 

046. Earth-work. This term is applied to whatever relates to 
the construction of the excavations and embankments, to prepare 
them for receiving the road-covering. 

647. In forming the excavations, the inclmadon of the side 
slopes demands peculiar attention. This inclination will depend 
on the nature of the soil, and the action of the atmosphere and 
internal moisture upon it. In common sods, as ordmaiy garden 
earth formed of a mixture of clay and sand, compact clay, and 
compact stony soils, although the side dopes would withstand 
very .well the effects of the weather with a greater mclmation, it 
is best to give them two base to one perpendicular ; as the sur- 
face of the roadway will, by this arrangement, be well exposed 
to the action of the sun and air, which will cause a rapid evapo- 
ration of the moisture on the surface. Pure sand and gravel may 
require a greater slope, according to circumstances. In all cases 
where the depth of tlie excavation is great, the base of the slope 
should be increased. It is not usual to use any artiiicial means 
to protect the surface of the side slopes from the action of the 
weather ; but it is a precaution which, in the end, wilt save much 
labor and expense in keeping the roadway in good order. The 
simplest means which can be used for this purpose, consist in cov- 
ering the slopes with good sods, (Fig. 149,) or else with a layer 

'ig. 149— Cross EEclion o( a roac 

of vegetable mould about four mchos thick, carefully laid and 
sown with grass seed. These means will be amply sufficient to 
protect the side slopes from injury when iJicy are not exposed tc 

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mj other causes of deterioration than the wash of the rain, and 
ihe action of frost on the ordinary moisture retained by the soil. 

The side slopes form usually an unbroken surface from the 
foot to the top. But in deep excavations, and particularly in soils 
liable to slips, they are sometimes formed with horizontal offsets, 
termed benches, which are made a few feet wide and have a ditch 
on the inner side to receive tlie surface-water from the portion of 
ihe side slope above them. These benches catch and retain the 
earth that may fall from the portion of the side slope above. 

When the side slopes are not protected, it will be well, in lo- 
calities where stone is plenty, to raise a small wall of dry stone 
at the foot of the slopes, to prevent tlie wash of the slopes from 
being carried into the roadway. 

A covering of brush wood, or a thatch of straw, may also be 
used with good effect ; but, from their perishable nature, they 
will require frequent renewal and repairs. 

In excavations through solid rock, w.hich does not disintegrate 
on exposure to the atmosphere, the side slopes might be made 
perpendicular ; but as this would exclude, in a great degree, the 
action of the sun and air, which is essential to keeping the road- 
surface dry and in good order, it will be necessary to make the 
side slopes with an inclination, varying from one base to one 
perpendicular, to one base to two perpendicular, or even greater, 
according to the locality ; the inclination of the slope on the 
south side in northern latitudes being greatest, to expose belter 
the road-surface to the sun's rays. 

The slaty rocks generally decompose rapidly on the surface, 
when exposed to moisture and the action of frost. Tlie side 
slopes in rocks of this character may be cut into steps, (Fig. 150,) 

and then bo covered by a layer of vegetable monld sown in grass 
seed, or else the earth may be sodded in the usual way. 

648. The stratified soils and rocks, in which tlie strata have a 
dip, or inciinatioi. to the horizon, are liable to slij>s, or to give 
way by one stratum becoming detached and sliding on another 
which is caused either from the action of frost, or from the pres- . 
sure of water, which insinuates itself between the strata. The worst 
roils of tills character are those formed of alternate strata of clay 
and sand ; particularly if the clay is of a nature to become semi- 
fluid when mixed with water. The best preventives iliat can ha 

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resorted to in these cases, are to adopt a tliorougli system ol 
drainage, to prevent the surface-water of the ground from run 
ning down the side slopes, and to cut off all springs which rur, 
towards the roadway from the side slopes. The surface-walei 
may be cut off by means of a single ditch (Fig. 149) made on 
the up-hill side of the road, to catch the water before it reaches 
the slope of the excavation, and convey it off to the natural 
water-courses most convenient ; as, in almost every case, it wiP 
be found that the side slope on the down-hill side is, compara- 
tively speaking, but slightly affected by the surface-water. 

Where slips occm: from the action of springs, it frequently 
becomes a very difficult task to secure the side slopes. If the 
sources can be easily reached by excavating into the side slopes, 
drains formed of layers of fascines, or brush-wood, may be placed 
to give an outlet to the water, and prevent its action upon the 
side slopes. The foscines may be covered on top with good 
Mods laid with the grass side beneath, and the excavation made 
to place the drain be filled in with good earth well rammed. 
Drains formed of broken stone, covered in like manner on top 
with a layer of sod to prevent the drain from becoming choked 
with earth, may be used under the same circumstances as fascine 
drains. "Where the sources are not isolated, and the whole mass 
of the soil formmg the side slopes appears saturated, the drainage 
may be effected by excavating trenches a few feet wide at inter- 
vals to the deptli of some feet into the side slopes, and filling 
them with broken stone, or else a general drain of broken stone 
may be made throughout the whole extent of the side slope by 
excavating into it. When this is deemed necessary, it will be 
well to arrange the drain Hke an inclined retaining- wal!, with 
buttresses at intervals projecting into the earth farther than the 
general mass of the dram. The front face of the drain should, in 
this case, also be covered with a layer of sods with the grass side 
beneath, and upon this a layer of good earth should be compactly 
laid to form the face of the side slopes. The drain need only be 
carried high enough above the foot of the side slope to tap all the 
sources ; and it should be sunk sufficiently below the roadway- 
surface to give it a secure fooling. 

The drainage has been effected, in some cases, by sinkmg 
wells or shafts at some distance behind the side slopes, from the 
top surface to the level of the bottom of the excavation, and lead- 
ing the water which collects in them By pipes into drains at the 
foot of the side slopes. In others a narrow trench has been ex- 
cavated, parallel to the axis of tlie road, from the top surface to 
a sufficient deptli to tap aO the sources which flow towards the 
side slope, and a drain formed either by filling the trench wholly 
with broken stone, or else by arranging an cpen conduit at llie 

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RCAH 281 

BoilOiti to receive the water collected, over w'nich a layer of 
bmsliwood is laid, the remainder of the trench being filled vi-iil: 
broken sfoae. 

In sorcie recent instances in England, the side slopes of vei'j 
bad soils have been secured by a facing of brick arranged in a 
manner very similar to the metliod resorted to for securing the 
]Derpendicular sides of narrow deep trenches by a timber-facing. 
The plan pursued is to place, at intervals along the excavation, 
strong buttresses of brick on each side, opposite to each other, 
and to connect them at bottom by a reyersed arch. Between 
these buttresses are placed, at suitable heights, one or more brick 
beams, formed at bottom with a flat segment arch and it top 
with a like inverted arch The buttresses, seemed m this way, 
serve as piers for veitioil cylmducal arches which lorra the 
facing and support the pies^uic ot the eirth between the but- 

649. In foimingthe embi.nkra<nls, (Fig 151,) the '!ide slopea 

sliould be made with a less inclmalion tlian that which the earth 
naturally asfcume^ , for the purpose of givmg them greater dura- 
bility, and to prevent the width ol the top surface along which 
the roadway is made, irom diminishing by every change m the 
side slopes, as it would weie they made with tlie natural slope 
To protect the side "slopes more effectuailj , ihey should be sod 
ded, or sown m gia^s seed, and the surtice-water of the top 
should not be allowed to nm down them, as it would soon wash 
them into guihes, and destroy the embankment In locihties 
where stone is plenty, a sustiining wall of dry &tone may be ad- 
vantageously substituted tor the iide slopes 

To present, as fir as possible, the settling which takes plati. 
in erahankments, they should be formed with great care , thi. 
eartli being laid in successive layers of about four feet in thick- 
ness, and each layer well settled with rammers. As this method 
is very expensive, it is seldom resorted to except in works which 
require great care, and are of trifling extent. For extensive 
works, the method- usually followed on account of economy, is 
to embank out from one end, carrying forward the work on a 
level with the top surface. In this case, as tliere must be a wani 
of compactness in the mass, it would be best to form the outsidea 
of the embankment first, and to gradually fill in towards tlic cen- 
tre, in onier that the earth may arrange itself in layers with a dip 
from the Fides inwards : this will in a great mcasuic counteiacl 

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S&8 RGAliS. 

any tendency to slips outward. The foot ■:•{ the slopes sJjfttiU 
be secured by buttressing them either by a low stone wall, oi 
by forming a slight excavation for the same purpose, 

650. When the axis of the roadway is laid out on the side 
slope of a hill, and the road-surface is formed partly by excava- 
ting and partly by embanking out, the usual and most simple 
nietliod is to extend out the embankment gradually aloiig the 
whole line of excavation. This method is insecure, and no pains 
therefore should be spared to give the embankment a good foot- 
ing on the natural surface upon which it rests, particularly at the 
foot of the slope. For this purpose the natural surface (Fig. 152) 

should 1 p 

eecu d by b 
terra f ar f lly 

In d f mmg 1 g 
the m d f ru 

secu m g wall 

both f 1 

made mply f dry 
block f ffi 
BuiSc 1 y 

when ! 1 1 f 

ff ts d th f fie slope be 

i 11 >r a small 
d 1 

1 rf f gi nclination, 

J pi d 11 b ufficiently 

b b d f 1 ide slopes, 

d bankm Th Us may be 

11 an b procured in 

1 1 k d f ruction of 

h p f 1 rth. But 

d 11 1 J they must 

oe laid m mfrt ir, (Fig. 153,) and hydi'aulic mortar is the orJy 


Kind which will form a safe construction. The wall which sup 
plies the slope of the excavation should be carried up as high aa 
the natural surface of the ground ; the one that sustains the em- 
bankment should be built up to the surface of the roadway ; and 
a parapet-wall should be raised upon it, to secure vehicles from 
accidents in deviating from the line of the roadway. 

A road may be constructed partly in excavation and partly in 
embankment along a rocky ledge, by blasting the rock, when the 
inclination of the natural surface is not greater than one perpen- 
dicular to two base ; but with a greater inclination than this, the 
whole should be in excavation. 

651. There are examples of road constructions, ii .ocalities 
like the last, supported on a frame-work, consisting of horizontal 
pieces, which are firmly fixed at one end by being let into holes 
drilled in the rock, and are sustained at the other by an inclined 
5triit underneath, which rests against the rock in a shoulder 
formed to receive it. 

C53, When the excavations do not furnish sufficient earth for 
the embankments, it is obtained from excavations, termed side- 
cuttings, made some place in the vicinity of the emhankmenr, 
from which the earth can be obtained with the most economy. 

If the excavations furnish more earth than is required for the 
embankment, it is deposited in what is termed spoil-bank, on the 
side of the excavation. The spoil-bank should be made at some 
distance back from the side slope of the excavation, and on the 
iown-hiil side of the top surface ; and suitable drains should br 
arranged to carry off any water that might collect near it and ai 
feet the side slope of the excavation. 

The forms to be given to side-cuttings and spoil-banks wih 
depend, in a great degree, upon the locality : they should, as far 
as practicable, be such that the cost of removal of the eailh ahal' 
oe east possible 

653. Drainage. A system of thorough drainage, by whicn 
.lie water that filters through the ground will be cut off Irom the 
Boil beneath the roadway, to a depth of at least three feet below 
^e bottom of the road-covering, and by which that which falls 
upon the surface will be speedily conveyed off, before it can filter 
through the road-covering, is essential to the good condition of a 

The surface-water is conveyed off hv giving the surface of the 
roadwav a sUght transverse convexity, trom the middle i<> the 
sides, where the water is received into the gutters, or side chan- 
nels, from wliich it is conveyed by underground aqueducts, termeji 
culveris. built of stone or brick and usually arched at top, into 
he main drains that communicate with the natural water-courses. 
This convexity is regulated by making the figure of the profde 

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an ellipse, of which the scmi-traiiBverss axis is 15 feet, and tbe 
semi conjugate axis 9 inches ; thus placing the middle of the 
roadway nine inches above the bottom of the side channels. This 
convexity, which is as great as should be given, will not be suffi 
cient in a flat counliy to keep the road-suiface dry ; and in such 
loca.Jlies, if a sligrit longitudinal slope cannot be given to the 
road, it should be raised, when practicable, three or four feet 
above the general level ; both on account of conveying off speedily 
the surface-water, and exposing the surface better to the action 
of the wind. 

To drain the soil beneath the roadway in a level country, 
ditches, termed open side diains (Fig 154) are niiJi pirillel 

from aido channels to the side drains t. 

to the road, and at some feet from it on each side. The bottom 
of the side drains should be at least three feel below the road- 
covering ; their size will depend on the nature of the soil to be 
drained. In a cultivated country the side drains should be on the 
field side of the fences. 

As open drains would be soon tilled along the parts of a road 
in excavation, by the washings from the side slopes, covered 
drains, built either of brick or stone, must be substituted for 
them. These drains (Fig. 155} consist simply of a flooring of 

iaggmg stone, or of bnck, with two side walls of nibble, or brck 
masonry, v. hich 'support a top covering of fiat stones, or of brick, 
with open joints, of about half an inch, to give a free passage 
waV to the water into the drain. The top is covered with a layer 
ot straw or brushwood ; and clean gravel, or broken stone, in 
Binall fragments, is laid over this, for the purpose of allowing i!;^ 

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water to filter freely tliroiigh to llie drain, without carrying with il 
.my earth or sediment, which might in time accumulate and choke 
it. The width and height of covered drarr.s will depend on the 
materials of which they are built, and the quantity of water to 
which they yield a passage. 

Besides the longitudinal covered drains in cuttings, other drains 
are made under the roadway which, from their form, are termed 
cross mitre drains. Their plan is in shape like the letter V, the 
angular point being at the centre of the road, and pointing in the 
direction of its ascent. The angle should be so regulated that 
the bottom of the drain shall not have a greater slope along either 
of its branches, than one perpendicular to one himdred base, to pre- 
serve the masonry from damage by the current T!ie construc- 
tion of mitre drains is the same as the covered longitudinal drains. 
They should be placed at intervals of about 60 yards from each 

In some cases surface drains, termed catch-water drains, are 
made on the side slopes of cuttings. They are run up obliquely 
ilong the surface, and empty directly into the cross drains which 
convey the water into the natural water-courses. 

When the roadway is in side-forming, cross drains of the or- 
dinary form of culverts are made, to convey the water from the 
side channels and the covered drains into the natural water- 
courses. They should be of sufficient dimensions to convey off 
a lajge volume of water, and to admit a man to pass through 
ihem so that they may be readily cleared out, or even repaired, 
without breaking up the roadway over them. 

The only drains required for embankments are the ordinary 
side channels of the roadway, with occasional culverts, to convey 
die water from them into the natural water- courses. Great care 
should be talsen to prevent the surface-water from n.nning down 
the side slopes, as they would soon be washed into gullies by it. 

Very wet and marshy soils require to be thoroualdy dmined 
before the roadway can be made with safety. The best system 
that Can be followed in such cases, is to cut a wide and deep open 
main-drain on each side of the road, to conVey the water to the 
natural water-courses. Covered cross drains should be made at . 
frequent intervals, to drain the soil under the roadway. They 
should be sunk as low as will admit of the water running from 
them into the main drains, by giving a slight slope to the bottom 
each way from the centre of the road to facilitate its flow 

Independently of the drainage for marshy soils, they wdl re- 
quire, when the subsoil is of a spongy, elastic nature, an artificial 
bed for the road-covering. This bed may, in some cases, be 
formed by simply removing the upper stratum to a depth of sev- 
era. feet, and supplying its place with well-jiacked gravel, or any 

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29i! uoAUs 

soil of a finTi cliuracter. In otlier cases, when the subso 1 yields 
readily to the ordinary pressure that the road-surface must bear, 
a bed of bmshwood, from 9 to 13 inches in thickness, must be 
formed to receive the soil on which the road-covering is to rest 
The brushwood should be carefully selected from the long straight 
slender shoots of the branches or undergrowth, and be tied up in 
bundles, termed fascines, from 9 to 12 inches in diameter, and 
from 10 to 20 feet long. The fascines are laid in alternate layers 
crosswise and lengthwise, and the layers are either connected by 
pickets, or else the withes, with which the fascines are bound, 
are cut to allow the brushwood to form a uniform and compact 

This method of securing a good bed for structures on a weak 
wet soil has been long practised in Holland, and experience' has 
fully tested its excellence. 

654. Road-coverings. The object of a road-covering being 
to diminish the resistances arising from collision and friction, 
and thereby to reduce the force of traction to the least prac- 
ticable amount, it should be composed of hard and durable ma- 
terials, laid on a firm foundation, and present a uniform even 

The material in ordinary use for road-coverings is stone, eithei 
in the shape of blocks of a regular form, or of large round peb- 
bles, termed a ^nuemeMt,' or broken into small angular masses ; 
or in the form of gravel. 

655. Pavements. The pavements in most general use in our 
country are consti^ucled of^ rounded pebbles, known as paving 
stones, varying from 3 to 8 inches in diameter, which are set in a 
form, or bed of clean sand or gravel, a foot or two in thickness, 
which is laid upon the natural soil excavated to receive the form. 
The largest stones are placed in tiie centre of tlie roadway. The 
stones are carefully set in the form, in close contact wilh each 
other, and are then firmly settled by a heavy rammer until their 
tops are even with the general surface of the roadway, which 
should be of a sKghtly convex shape, having a slope of about ^'j 
from the centre each way to the sides. After the stones are 
driven, the road-surface is covered with a layer of clean sand, or 
fine gravel, two or three inches in thickness, which is gradually 
worked in between the stones by the combined action of the 
travel over the pavement and of the weather 

The defects of pebble pavements are obvious, and confirmed 
by experience. The form of sand or gravel, as usually made, is 
not sufficiently firm ; it should be made in separate layers of 
about 4 inches, each layer being moistened and well settled either 
by ramming, or passing a heavy roller over it. Upon the form 
prepared in this way a layer of loose material of two or three 

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:jicliea in thickness maybe placed, to rect, ve tlie ends of the 
paving stones. From the form of the pebbles, the resistance lo 
traction arising from colhsion and friction is very great. 

Pavements termed stone tramways have been tried in some cf 
t!ie cities of Europe, both for light and heavy trafiic. They are 
formed by laying two lines of long stone blocks for the wheels to 
run on, with a pavement of pebble for the horac-track between 
the wheel-tracks. In crowded tliorough fares tramways offer but 
few if any advantages, as it is impracticable to confine the vehicles 
to them, and when exposed to heavy traffic they wear into ruta. 
The stone blocks should be carefully laid on a very firm bottoming, 
and particular attention is requisite to prevent ruts from forming 
between the blocks and the pebble pavement. 

Stone suitable for pavements should be hard and tough, and 
not wear smooth under the action to which it is exposed. Some 
varieties of granite have been found in England to furnish the 
best paving blocks. In Franco, a very fine-grained compact gray 
sandstone of a bluish cast is mostly in use ior the same purpose, 
but it wears quite smooth. 

The sand used for forms should be clean and free from peb- 
bles and gravel of a larger grain than about two tenths of an inch. 
The form should be made by moistening the sand, and com- 
pressing it in layers of about four inches in thickness, cither by 
ramming, or by passing over each layer several times a heavy 
iron roller. Upon the top layer about an inch of loose sand may 
be spread to receive the blocks ; the Joints between which, after 
they are placed, should be carefully filled with sand. 

The sand form, when carefully made, presents a very firm and 
stable foundation for the pavement. 

Wooden pavements, formed of blocks of wood of various 
shapes, have been tried in England and several of our cities 
within the last few years, but are now for the most part aban- 
doned, as the material has been found to decay very rapidly, 
even when prepared with some of the preservatives of timber 
against the rot. 

Asphaltic pavements have undergone a like trial, and have also 
been found to fail after a few years service. This material is 
farther objectionable as a pavement in cities where the pave- 
ments and sidewalks have frequently to be disturbed for the 
purposes of repairing, or laying down sewei-s, water-pipes, and 
other necessary conveniences for a city. 

The best system of pavement is that which has been partially 
put in practice in some of the commercial cities of England, the 
idea of^ which seems to have been taken from the excellent mili 
Eary roads of the Romans, vestiges ni which remain at the prcaeiU 
4ay in a good state. 

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In constructing this pavement, a bed {Fig. i;6)is first pre 
pared, by removing the siirl ice of the soil to the dejith of a foo 
ormoiL, to obtain a firm stratum, the surfice of this bed re 

Fig 15B— Paysd road-coverai' 

A, pavement. 

B, flagging of side-walk. 

ceives a very slight convexity, of about two inches to ten feet, 
from the centre to the sides of the roadway. If tlie soil is of a 
. soft clayey nature, into which small fragments of broken stone 
would be easily worked by the wheels of vehicles, it should be 
excavated a foot or two deeper to receive a form of sand, or of 
clean fine gravel. On the surface of the bed thus prepared, a 
layer of small broken stone, four inches thick, is laid ; the di- 
mensions of these fragments should not be greater than two and 
a half inches in any direction ; the road is then opened to vehicles 
until this first layer becomes perfectly compact ; care being taken 
10 fill up any ruts with fresh stone, in order to obtain a uniform 
surface, A second layer of stone, of the same thickness as the 
first, is then laid on, and treated in the same manner ; and finally 
a third layer. When the third layer has become perfectly com- 
pact, and is of a uniform surface, a layer of fine clean gravel, 
two and a half inches thick, is spread evenly over it to receive 
the paving stones. The blocks of stone are of a square shape, 
and of different sizes, according to the nature of tlie travelling 
over the pavement. The largest size are ten inches thick, nine 
inches broad, and twelve inches long ; the smallest are six inches 
thick, five inches broad, and ten inches long. Each block is 
carefully settled in the form, by means of a heavy beetle ; it is 
then removed in order to cover the side of the one against which 
it is to rest with hydraulic mortar ; this being done, the block is 
replaced, and properly adjusted. The blocks of the different 
courses across the roadway should breakjoints. The surface of 
the road is convex ; the convexity being determined by making 
the outer edges six inciies lower than the middle, for a width of 
thirty feet. 

Tjiis system of pavement fulfils in the best manner all the re- 
quisites of a good road-covering, presenting a hard even surface 
to the action of the wheels, and reposing on a firm bed formed 
by the broken-stone bottoming. The mortar-joints, so long aa 
they remain tight, will efiectually prevent the penetration of watei 
beneath the pavement ; but it is probable, fiom the effect of iho 
transit of heavily-laden vehicles, and from the expansion am} 

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conlractioii of the stone, whicli in our climate is found to be \erj 
considerable, that the mortar would soon be crushed and waslied 

In France, and in many of the large cities of the continent, thp. 
pavements are made ivith blocks of rough stone of a cubical form 
measuring between eight and nine inches along the edge of the 
cube. These are laid on a form of sand of only a few inches thick 
when the soil beneath is iinn ; but in bad soils the ihicltness is 
increased to from six to twelve inches. The transversal joints 
are usually continuous, and those in the direction of the axis of 
the road break joints. In some cases the blocks are so laid thai 
the joints make an angle of 45° with the axis of the roadway, one 
set being continuous, the other breaking joints with them. By 
this arrangement of the joints, it is said that tlie wear upon the 
edges of tlie blocks, by which the upper surface soon assumes a 
convex shape, is diminished. It has been ascertained by expe- 
rience, that the wear upon the edges of the blocks is greatest at 
the joints which run transversely to the axis when the blocks are 
laid in the usual manner. From the experiments of M. Morin, to 
ascertain t!ie influence of the shape of stone blocks on the force 
of traction, it was found that the resistance offered by a pavement 
of blocks averaging from five to six inches in breadth, measured 
in the direction of the axis of the roadway, and about nine incliea 
in length, was less than in one of cubical blocks of the ordinary 

Pavements m cities must be accompanied by sidcwaliis, and 
crossing-places, for foot passengers The sidewalks are made 
of large flat flagging-stone, at least t\\o inches thick, laid on a 
form of clean gravel well rammed and =!etlled. The width of 
the sidewalks will depend on the stieet being more or less fre 
quented by a crowd. It would, m all cases, be well to have them 
at least twelve feet wide ; they receive a slope, or pitch, of one 
inch to ten feet, towards the pavement, to convey the surface- 
water to the side channels. The pavement is separated from the 
sidewalk by a row of lon^ slabs set on their edges, termed curi- 
stones, which confine both the flagging and paving stones. The 
curb-stones form the sides of the side channels, and should for 
this purpose project six inches above the outside pavmg stones, 
and »e sunk at least four inches below their top surface ; they 
should, moreover, be flush with the upper surface of the side. 
walks, to allow the water to run over into the aide channels, and 
to prevent accidents which might otherwiHe happen from their 

The crossings should be from four to six feet wide, and ba 
slightly raised above the general surface of the pavement, to keep 
thtid tre& from mud. 


296 ROADS. 

65G. Broken-stone road-covering. The or(3inary ro,ji-covei 
ing for common roads, in use in this country and Europe, ia 
formed of a coating of stone broken into small fragments, whicl- 
is laid either upon the natural soil, or upon a paved bottoming 
of small irregular blocks of stone. In England these two systems 
liave their respective partisans ; tiie one claiming the superiority 
for road-coverings of stone broken into small fragments, a method 
brought into vogue some years since by Mr. McAdam, from whom 
these roads have been termed macadamized ; the other being the 
plan pursued by Mr. Telford in the great national roads con- 
structed in Great Britain within about the same period. 

The subject of road-maJking has within the last few years ex- 
cited renewed interest and discussion -among engineers in France ; 
the conclusion, drawn from experience, there generally adopted 
is, that a covering alone of stone broken into small fragments ia 
sufficient under the heaviest traffic and most frequented roads. 
Some of the French engineers recommend, in very yielding 
clayey soils, that either a paved bottoming after Telford's method 
be resorted to, or that the soil be well compressed at the surface 
before placing the road-covering. 

The paved bottom road-covering on Telford's plan (Fig. 155) 
IS foraied by excavating the surface of the ground to a suitable 
depth, and preparing the form for the pavement with the precau- 
tions as for a common pavement. Blocks of stone of an irregu- 
lar pyramidal shape are selected for the pavement, which, for a 
roadway 30 feet in width, should be seven inches thick for the 
centre of the road, and three inches thick at the sides. The base 
of each block should not measure more than five inches, and the 
top not Jess than four inches. 

The blocks are set by the hand, with great care, as closely in 
contact at their bases as practicable ; and blocks of a suitable 
size are selected to give the surface of the pavement a slightly 
convex shape from the centre outwards. The spaces between 
the blocks are filled with cbippings of stone compactly set with 
1 small hammer. 

A layer of broken stone, four inches thick, is laid over this 
pavement, for a width of nine feet on each side of the centre ; no 
Iragment of this layer should measure over two and a half inches 
in any direction. A layer of broken stone of smaller dimensions, 
or of clean coarse gravel, is spread over the wings to the same 
depth as the centre layer. 

The road-covering, thus prepared, is thrown open to vehicles 
until the upper layer has become perfectly compact ; care having 
beer, taken to fill in the ruts with fresK stone, in order to obtain 
a uniform siuface. A second layer, about two niches in depth 
*.s then laid over the centre of the roadway ; and the wings re 

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RC...DS. 291 

ceive also a layer of new material laid on to a sufficient tiiicknesa 
to make the outside of the roadway nine inches lower than the 
centre, by giving a slight convexity to the surface from the centre 
outwards. A coating of clean coarse gravel, one inch and a half 
thick, termed a binding, is spread over the surface, and the road- 
covering is then ready to be thrown open to "travelling. 

The stone used for the pavement may be of an inferior quality, 
in hardness and strength, to that placed at the surface, as it is bai 
little esposed to the wear and tear occasioned by travelling. The 
suiface-stone should be of the hardest kind that can be procured 
The grivel binding is laid over the surface to facilitate the trav- 
elling, whilst the under stratum of stone is still loose ; it is, how- 
e\er, hurtful, as, by working in between the broken stones, il 
pi events them fiom setting as compactly as they would otherwise 

If the roadway cannot be paved the entire width, it should, 
it least, recene a pavement for the width of nine feet on each 
side of the centre. The wings, in this case, may be formed 
entirely of clean gravel, or of cnippings of stone. 

For loads which ai-e not much travelled, like the ordinary cross 
roads of the country, the pavement will not demand so much 
care ; bnt may be made of any stone at hand, broken into frag- 
ments of such dimensions that no stone shall weigh over four 
pounds. The surface-coating may be formed in tlie manner just 

657. In fonning a ro^yl- covering of broken stone alone, the 
bed for the covering is arranged in the same manner as for the 
paved, bottoming : a layer of the stone, four inches in thickness, 
is carefully spread over the bed, and the road is thrown open to 
vehicles, care being taken to fill the ruts, and preserve the sur- 
face in a uniform state until the layer has become compact ; 
successive layers are laid on and treated in the same manner as 
the first, until the covering has received a thickness of about 
twelve inches in the centre, with the ordinary convexity at the 

658. Where good gravel can be procured the road-covering 
may be made of tliis material, which should be well screened, 
and all pebbles found in it over two and a half inches in diame- 
ter should be broken into fragtnents of not greater dimensions 
(Jian ihese, A firm level form having been prepared, a layer of 
gravel, four inches in thickness, is laid on, and, when this has 
Become compact from the travel, successive layers of about tliree 
inches in thickness are laid on and treated like the first, until the 
covering has received a thickness of sixteen inches in the centre 
and the ordinary convexity. 

059. As has been ah-cady stated, the French civil cngineera 

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(!o not regard a paved bottoming as sseotlal for Lrokeii-stODfi 
road-coverings, except ia cases of a veiy heavy traffic, or wherf. 
the substratum of the road is of a. very yielding character. 
They also give Jess thickness to the road-covering than the 
I'liglish engineers of Telford's school deem necessary ; allowing 
not more than six to eight inches to road-coverings for light 
traffic, and about ten inches only for the heaviest traffic. 

660. If the soil upon which the road-covering is to be placed 
is not dry and firm, they compress it by rolhng, vfliich is dona 
by passing over it several times an iron cylinder, about six feet 
in diameter, and four feet in length, the weight of which can be 
increased, by additional weights, from six thousand to about 
twenty thousand pounds. The road material is placed upon the 
bed, when well compressed and levelled, in layers of about four 
inches, each layer being compressed by passing the cylinder 
several times over it before a new one is laid on. If the opera- 
tion of rolling is performed in dry weather, the layer of stone is 
watered, and some add a thin layer of clean sand, from four to 
eight tenths of an inch in thickness, over each layer before it is 
rolled, for the purpose of consolidating the surface of the layer, 
by filling the voids between the broken-stone fragments. After 
the surface has been well consolidated by rolling, the road is 
thrown open for travel, and aU ruts and other displacement of 
the stone on the surface are carefully repaired, by adding fresh 
material, and levelling the ridges by ramming. 

Great importance is attached by the French engineers to the 
use of the iron cylinder for compressing the materials of a new 
road, and to minute attention to daily repairs. It is stated that 
by the use of the cyhnder the road is presented at once in a 
good traveiling Condition ; the wear of the materials is less than 
by the old method of gradually consohdating them by the travel ; 
liie cost of repairs during the first years is diminished ; it gives 
to the road-covering a more uniform thickness, and admits of its 
being thinner than in the usual method. 

661. Materials and Repairs. The materials for broken-stone 
roads should be hard and durable. For the bottom layer a soft 
stone, or a mixture of hard and soft may be used, hut on the 
surface none but the hardest stone will withstand tlie action of 
the wheels, _ The stone should he carefully broken into frag- 
ments of nearly as cubical a form as practicable, and be cleansed 
from dirt and of all very small fragments. Tfie broken stone 
should be kept in depots at convenient points along the line of 
ihe road for repairs. 

Too great attention cannot be hcstowed upon keeping tha 
road-surface free from an accumulation of mud and even of diisi. 
It shcvild be constantly cleaned by scraping and sweeping. Tfc* 

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ROADS. 299 

topairs should be daily made by adding fresh materiai iijuin al 
points where hollows or ruts commence to form. It is iticom 
mended by some lliat when fresh material is added, the surface 
on which it is spread should be broken witii a pick to the depth 
of half an inch to an inch, and the fresh material be well settled 
by ramming, a small quantity of clean sand beiag added to make 
the stone pack better. When not daily repaired by persons 
whose sole business it is to keep the road in good order, genera* 
repairs should be made in the months of October and April, 
by removing all accumulations of mud, cleaning out the aide 
channels and other drains, and adding fresh material where re- 

The importance of keeping the road-surface at all times free 
from an accumulation of mud and dust, and of preserving the 
surface in a uniform state of evenness, by the daily addition of 
fresh material wherever the wear is sufficient to call for it, can- 
not be too strongly insisted upon. Without this constant super- 
vision, the best constructed road will, in a short time, be uufit 
for travel, and with it the weakest may at all lime's be kept in a 
tolerably fair state 

662. Cross dimensions of roads. A road thirty feet in width 
IS amply sufficient for the carriage-way of the most firequented 
thoroughfares between cities. A width of forty, or even sixty 
feet, may be given near cities, where the greater part of the 
transportation is effected by land. For cross roads, and others 
of minor importance, the v/idth may be reduced according to the 
nature of the case. The width should be at least sufficient to 
allow two of the ordinary carriages of the country to pass each 
other with safety. In all cases, it should be borne irf mind, that 
any unnecessary width increases both the first cost of construc- 
tion, and the expense of annual repairs. 

Very wide roads have, in some cases, been used, the centre 
part only receiving a road-covering, and the wings, termed sum- 
mer roads, being formed on the natural surface of the subsoil. 
The object of this system is to relieve the road-covering from 
the wear and tear occasioned by the lighter kind of vehicles du- 
ring the summer, as the wings present a more pleasant surface 
for travelling in that season. But httle is gained by this system 
under this point of view ; and it has the inconvenience of fonn- 
' ing during the winter a large quantity of mud which is very in- 
jurious to the road-covering. ■■ 

There should be at least one foot-path, from five to six feet 
wide, and not more than nine inches higher than the bottom of 
Jie side channels. The surface of the foot-path should have a 
pitch of two inches, towards the side channels, to convey its 
surface watei into them, When thn. natural scil is firm and 

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sandy, or grarelly, its surfucc will serve for the foot-patli ; l'\rt 
in other cases the natural soil must be thrown out to a depth of 
six inches, and the excavation be filled with fine clean gravel. 

ng damaged by the current 
ide slope, next to the side 
'ng of good sods, or of Ji-y 

To prevent the foot-path from bein 
of water in the side channels, its sid 
channel, must be protected by a facin, 

As it is of the first importance, in keeping the road-way in a 
good travelling state, lliat its surface should be kept dry, it will 
DO necessary to remove from it, as far as practicable, aU objects 
that might obstruct the action of the wind and the sun on its 
surface. Fences and hedges along the road should not be higher 
than five feet ; and no trees should be suffered to stand on the 
load-side of the side drains, for independently of shading the 
road-way, their roots would in time throw up the road-cov 

See Aliic B,, Appendix. 



663. Tub gieat resistance ofibred to tha force of i 
common roads, where the traffic is of a heavy character, natu 
rally suggested the idea of trying other means, which would 
afford a more even and durable track for the wheels than llie 
road-coverings in ordinary use. Various methods have been re- 
sorted to, with greater or less success, lo accomplish tliis object : 
in some instances tracks have been formed of long narrow stone 
blocks ; in others, heavy beams of timber, covered on the sur- 
face with sheet iron to protect them from wear, have been used ; 
and iinally, both the stone and wooden ways were replaced by 
iron places and bars, and that system of road-covering, now so 
well known as the railway, or railroad, has been the result. 

For these successive stages of improvement, by which, in tlie 
short period of less than a quarter of a centuiy, so great a revo- 
lution has been made both in the speed and the amount of trans- 
portation on land, by means which bid fair to supersede evei^ 
other, the civilized world is indebted to England, in whose mi- 
ning districts die railway system first sprung up. 

664. Kiailway, or railroad, is a track for the wheels of ve- 
hicles to run on, nhich is formed of iron bars placed in two 
parallel lines and restmg on firm supports. 

665. Rails The iron ways first hiid down, and termed tram- 
ways were made of narrow iron plates, cast in short lengths, 
with an upright flanch on the exterior to coniine the wheel within 
the tiack The plates were found to be deficient in strength, 
and were replaced by others to which a vertical rib was added 
undei the plate This rib was of uniform breadth, and of the 
shape of i semi ellipse m elevttion. This form of tramway, 
although sipenor m strength to the first, was still found not to 
work well as the mud which accumulated between the ilanch 
and the surface of the plate piesented a considerable resiatance 
to the foice of triction To obviate this defect, iron bars of a 
eemi cUipl c d shape m elevation, whic)i received the UEime of 

a V V> —Represents a croaa Boction a, of the fish-bet- 

-^-^ »d a 1 of the LiTerpool and Maacfiesler Railway 

id tha method in which It is Recuced to its chair 
formed witli a shght wgectkni at hoc 

cros^> sectiD 

E de of the cliair li. An iron wedss c v hwateA 
aia a notch on the opiutsito Bide of the chair, and 
couflnes (tie rail in its place. 

■ were substituted for the plates of the tramway. 1 ho 
of theae iii\= were of the form shown in Fig. 157, 

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huZ KAir. iVAYb. 

the top surface being slightly convex, and sufficiently broad Ic 
preserve the tire of the wheel from wearing \inevenly. Tliia 
change in the form of the rail introduced a corresponding one ir 
the tires of the wheels, which were made with a flanch on tht 
Ulterior to confine them with'.n the rails of the track. 

The cast-iron edge-rail was found upon trial to he subject to 
many defects, arising from the nature of the material. As it 
was necessary to cast the rails in short lengths of three or four 
feet, the track presented a number of joints, which rendered it 
extremely difficult to preserve a uniform surface. The rails 
were found to break readily, and the surface upon which the 
wheels ran wore unevenly. These imperfections finally led to 
the substitution of wrought-iron for cast-iron. 

666. The wrought-iron rails first brought into use received 
nearly the same shape in cross section and elevation us the cast 
iron rail. They were formed by rolling them out m a rolUng- 
mill so arranged as to give the rail its proper shape. The lengm 
of the rail was usually fifteen feet, the bottom of it (Fig, 158) 

presenting an undulating outline so disposed as to give the rail a 
bearing point on supports placed three feet apart between their 
centres. This form, known as the fish-belly I'ail, was adopted 
as presenting the greatest strength for the saiae amount of metal. 
It has been fo nd o tnal to be 1 able to some inconveniences. 
The r^ 1 b e k at bo t nme cl es fro i the supports, or one 
fourth of led tance be een the I ar g po its, and from the 
curved fo i of tl e botto n ot the ra I tl ey do ot admit of being 
suppor ed I ro gl o t tl e r le gtl 

667 Tl e fo i of a 1 at present n nost general use is 
known by the ne of 1 e pa ullel or si a ght rail, the top and 
bottom of 1 e ail b pa all 1 or as tl e T o ■ H rail, from tha 
form of tl e cro s sec o 

A var e y of forn s o c o s s on a to be met with in the 
parallel r 1 Tl e n re u uil f tl t (F g. 159) in which 

D — RepreaMita a < 
n ft & p^oilel ri 
Q g n rally adopted 

ihe top IS sh ped Ikelesnep tie fish-belly rail, the 

uottom be ng w dened out to g ve the ra 1 a more stable seat on 

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Its sujipurts In some C3«es the top and bottom are made ilike 
to admit of turning tlid rail The greatest deviation from the 
u^ual form IS m the rail of the Great Western Railway in Etig 
land, (Fig 160 ) 

'ig 1611— Ropresente a crosa section of Ihe rait of the 
Orraat Western Railway in England. This rail is laiJ 
on a CDntinuouB sapport, and is fastened to it byssrewa 
on eacli side of tlie rail, A piece of tarred felt was 
inserted between tlio base of iFie rail and its support. 

The dimensions of the cross section of a rail should bo eiich 
that the deflection m the centre between any two points of sup- 
port, caused by the heaviest loads upon the track, should not be 
so great a^ to ciuse any very appreciable increase of resistance 
lo the forLe of traction The greatest deflection, as laid down 
by some writers, should not exceed three hundredtiis of an inch, 
tor the usual beanng of three feet between the points of sup- 
port The top of the nil is usually about two and a half inches 
liroad, and an inch in depth This has been found to present a 
gocd bearing surface for the wheels, and sufficient strength to 
prevent the top fiom being crushed by the weight upon the rail. 
The breadth of the nb vanes between three fourths of an inch to 
an inch , and the total depth of the rail from three to five inches. 
The thickness and breadth of the bottom have been varied ac- 
cording to the strength and stability demanded by the tratHc. 

668. Supports. The rails are laid upon supports of timber, 
or atone. The supports should present a firm unyielding bed to 
the rails, so as to prevent all displacement, either in a lateral or 
a vertical direction, from the pressure thrown upon tliem. 

Considerable diversilv is to be met with in tlie practice of 
engineers on this poinl On the earlier roads, heavy stone 
blocks were mostly used for supports, but these were, found to 
require great precautions to render them firm, and they were, 
moreover, liable to split from the means taken to confine the 
rails to them. Timber has, ■within !ate years, been generally 
preferred to stone. It affords a more agreeable road i'or travel 
and gives a belter lateral support to the rails than stono blocks. 

The usual method of placing timber supports is transversely 
to the track. Each support, termed a sleeper, or cross-lie, being 
formed of a piece of timber six or eight inches square. The or- 
dinary distance between the centre lines of the supports, is three 
feet for rails of the usual dimensions. With a greater bearing, 
rails of the ordinary dimensions do not present sufficient stiffness. 
The sleepers, when formed of round timber, should be Si^uared 
on the upper and lower surface. On some of the recent railways 
in England., sleepers presenting in cross section a right-angled 
iriangle have been used, the right angle being at the bottom. 
They »re represented to bo more convenient in setting, and to 

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offer a more stable support thin tho e of the usuil f cm. Tlif 
sleepers are placed either upon the ball i n^, of tl e roadway, c. 
upon longitudinal beams laid be eatl 1 e alo g tl e line of the 
rails. The latter is now the more usual practice w th us, and is 
indispensable upon new embankments to prevent the ends of 
tiie keepers from settling unequally. Thick planlt, about eight 
inches broad and lluree or four inches thick, is usually employed 
for the longifadinal supports of the sleepers. 

On some of the more recent railways in England, the rails 
ha¥P, been laid upon longitudinal beams, presenting a continuous 
support to llie rail, the beams resting upon cross-ties. 

669. Chairs. The rails are firmly fastened to their supports by 
cast-iron chairs, (Figs. 157, 159,) wrought-iron spiltes, or screws. 
The chair is cast in one piece, and consists of a bottom-plate, upon 
which the rail rests, and two side pieces between which the rail is 
confined by wedges of iron, or of wood. The chairs are fastened 
to the supports by iron bolts, or wooden pins. A variety of 
forms have been given to the chairs, and different methods adopt- 
ed for confining the rail firmly withm ihem. Iron wedges having 
been found to work loose, wooden wedges, or keys, have been 
substituted for them. They are made of laln-dried timber, and 
are forced through cutters, by which they receive the proper 
shape, and are at the same lime strongly compressed. The key, 
prepared in this manner, gradually swells by imbibing moisture 
after being inserted, and forms a very strong fastening. Chairs 
ai^e generally placed upon each support. In some cases they 
are only placed at the points of junction of the rails ; iron spikes 
with a bent head being driven into the supports, to confine the 
rails at tiie intermediate points between the chairs. 

A joint of sufficient width is left between the ends of the rails, 
to allow for the expansion of the bars. Various methods of 
forming this joint have been tried ; the more usual forms are the 
square joint, and the oblique joint. 

070. Ballast. A covering of broken stone, of clean coarse 
gravel, or of any other material that will allow the water lo 
drain off freely, is laid upon the natural surface of the excavations 
and embankments, to form a firm foundation for the supports. 
This has received the appellation of the ballast. Its thickness 
is from nine to eighteen inches. Open or broken-stone drains 
should be placed beneath the ballasting to convey off the surface 
water. The parts of the ballasting upon which ^le supports 
rest should be well rammed, or rolled ; and it should be wel. 

flacked beneath and around tlie s'jipporta. After the rails aru 
aid, another layer of broken stone or gravel should be added 
the siuface of whic)i should be sfightly convex and about three 
inches below the top of the rails. 

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671. Tempmary railways of wood and iron. On ihe first 
introduction of railways into the United States, the tracks weic 
formed of flat iron bars laid upon longitudinal beams. ■ The iron 
bars wei'e about two and a half inches in breadth, and from one 
iialf to three fourtlis of an inch in thickness, the top surface 
being slightly convex. They were placed on the longiiudina, 
beams, a little back from the inner edge, the side of the beam 
near the top being bevelled off, and were fastened to the beam 
by screws or spikes, which passed through elliptical holes with 
a countersink to receive the heads of the spikes ; the holes re . 
ceiving this shape to allow of the contraction and expansion of 
the bar, without disjilacing the fastenings. The longitudinal 
beams were supported by cross sleepers, witli which they were 
connected by wedges that confined the beams in notches cut 
into the sleepers to receive them. The longitudinal beams were 
usually about six inches in breadth, and nine inclies in depth, 
and in as long lengths as they could be procured. The joints 
between the bais were eiilier square or oblique, and a piece of 
iron or zinc was inserted -nto the beams at the joint, to prevent 
the end of llie rail from oeing crushed into the wood by the 

In some instances the bars were fastened to long stone blocks, 
but tins method was soon abandoned, as the stone was rapidly 
destroyed by tlie action of the wheels ; besides which, the rigid 
nature of tlie stone rendered the travelling upon it excessively 

This system of railway, whose chief recouimendalion is eco- 
nomy in the first cost, lias gradually given place to the solid rail. 
Besides the want of durability of tlie structure, it does not pos- 
sess sufficient strength for a heavy traiSc. 

673. Gauge. Ine distance between the two lines of rails of 
a track, termed the gauge, which has been adopted for the great 
majority of the railways in England, and also with us, is 4 feet 
8^ inches. Tiiis gauge appears to have been the result of 
chance, and it has been followed in the great majority of cases 
up to the present lime, owing to the inconvenience tJiat would 
arise from the adoption of a different gauge upon new lines. 
The greatest deviation yet made from the established gauge is in 
that of the Great Western Railway, in which the gauge is seven 
feet. Engineers are generally agreed that a wider gauge is de- 
sirable, as with it the wheels of railway cars could be made of 
greater , diameter than they now receive, and be placed outside 
of the cars instead of under them as at present j the centre of 
gravity of the load might be placed lower, and more steadi 
ness of motion and greater security at high velocities be it 

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III a double track the distance between the two tracks is geo- 
erallv tlic same as the gauge; and tbe distance between the 
outside rail of a track, and the sides of tiie escavatioiii or em- 
bankment, is seldom made greater than six feet, as this is deemed 
sufficient to prevent the cars from going over an emfaankment 
were they to run off the rails. 

673. On aJi straight portions of a track, tlie supports should 
be on a level transversely, and jjarallel to tlie plane of the track 
longitudinally. The top surface of the rail should incline' in- 
ward,- to conform to tlie conical form of the wheels; this ia 
now usually effected by giving the chair the requisite pitch, or 
by forming the top surface v/ith the requisite bevel for this pur- 

674. Cwvcs. In the curved portions of a track the centri- 
fugal force tends to force the carriage towards the outside rail 
of the curve. This action of t!ie centrifugal force is counter- 
acted, to a certain extent, by the conical form of the wheels, 
which, by causing them to run on unequal diameters so soon as 
[hey enter ,a curve, inclines the car inward. Within certain 
limits of the radius of curvature, the amount of this force by 
which the car is impelled towards the centre of the curve, by 
this change in ibe diameter of the interior and exterior wheels, 
will be sufficient to counteract the centrifugal force which urges 
it outward. With wheels of the diameter and shape at present 
in general use, the usual gauge of track, and play between the 
flanch of each wheel and the side of the rail, the least radius of 
curvature which will prevent the flanch of the exterior wheel 
from being brought into contact witSi the side of the rail, is found 
to be about 600 feet. To prevent actual contact and offer per- 
fect security, the radius allowed should not be less than 1000 feet, 
when the exterior and interior rails are on the same level trans- 
versely. As on curves with a smaller radius than 1000 feet, 
the fianch of the wheel might be driven against the rail, and tlie 
car be forced from the track, it will be requisite to provide 
against this by raising tlie exterior rail higher than the interior, 
so that by thus placing the wheels on an inclined plane, the 
component of gravity, opposed to the centrifugal force, added to 
the force which impels the car inward when running on wheels 
of unequal diameter, may balance the centrifugal force. From 
ihe above conditions of equilibrium, the elevation whicli the ex- 
terior rail should receive above the interior can be readily tal- 
culated. The method more usually adopted, however, is to 
neglect the effect of the conical form of the wheel, incoiuitor 
acting the action of the centrifugal force within certain limits, 
and to give the exterior rail an elevation sufEcient to prevent the 
fianch of the wheel from being driven against the side of tiie rail 

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wlicn the car ismoving at the highest supposed velocity ; or, in 
otlicr words, to give the inclined plane across the track, on which 
the whefels' rest, an inclination such that the tendency of the 
wheels, to shde towards tiie interior rail shall alone coimteracl 
the centrifugal force. 

675. Simngs, ^c. On single lines of railways short portions 
of a track, termed sidings, are placed at convenient intervals 
along the main track, to enable cars going in opposite directiona 
to cross each otlier, one train passing into the sidfng and stop- 
ping while the other proceeds oo the main track. On double 
tinea arrangements, termed crossings, are made to enable trains 
to pass from one track into the other, as circumstances may re- 
, quire. The position of sidings and their length will depend 
entirely on local circumstances, as the lengtii of the trains, the 
number daily, &c. 

The manner generally adopted, of connecting tlie main track 
with a siding, or a crossing, is very simple. It consists (Fig. 
101) in having two short lengths of the opposite rails of the mair 

lis of siding. 

M:ack, where tlte siding or crossing joins it, moveable around one 
of their ends, so that the other can be displaced from the line of 
the main track, and be joined with that of ihe siding, or crossing, 
fln tiie passage of a car out of the main trrtck. These moveable' 
portions of rails are connected and kept parallel by a long cross 


fig. IffiJ— Represenfs a plan M, and eectfou K, of a fixed cnHsina plats. The p]ata A, 
fi of cast-iron, with verlioal ribs e, c, on the bottom, to ftive il the wqaifflte etrengtlu 
Wmucl It-iron haa a, a, placed in Iho lines or tlie Iwo Intersenlins iu.'ji d, d. En 
firmly Enrewi'd ti tlie plufe ; a nulficient tpaee being left between tlieni and tlie ladf 
roc Uie l^KlMli of tlie wlieel to oass. 



bolt, lo the cud of which a vertical lever is attai^hcd to dravi 
them forward, or shove them bacli. 

At the point where the rails of the two traclts intersect, a east 
iron plate, termed a crossing-plate (Fig. 162} is placed lo con 
nect the rails. The surface of the plate is arranged either with 
grooves in the lines of llie rails to admit ihe flaoch of the wheel 
in passing, the tire running upon the suiface of the plate ; or 
wrought-iron bars are affixed to the surface of the pkte for the 
same purpose. 

The angle between the rails of tlio main tiacUs and those oi a 
siding or crossing, termed the angle of deflection, should not be 
greater than 2" or 3°. The connecting rails between the straight 
portions of the tracks should be of the shape of an & cuive, m 
order that the passage may be gradually effected. 

676, Turn-plates. "Where one track intersects another under 
a considerable angle, it will be necessary lo substitute for the 
ordinary method of connecting them, what is termed a tmn-plaie, 
or turn-table. This consists of a strong circular platform of 
wood or cast-iron, moveable around its centre by means of coni- 
cal rollers beneath it running upon iron roller-ways Two lails 
are laid upon the platform to receive the car, which is tiansferred 
from one track to the other by turning the platform sufficiently 
to place the rails upon it in the same line as those of tlie track 
to be passed into. 

677, Street-crossings. When a tiacv mtersecta a roid, or 
street, upon the same level witli it, the riil must be guirded by 
cast-iron plates laid on each side of it, sufhcicnt sp-ici- being Iclt 
between them and the rail for the play of the flanch The toi 
of the plates should be on a level nith the top of the idJl 
Wherever it is practicable i dram should be placed beneath, to 
receive the mud and dust which accumulating butween tlie plates 
and rail, might interfere with the passing of the cais along the 

678, Gradients. From vaiiou^ expeiiments upon the fiiction 
of cars upon railways it appears that the angle of repose is 
abou bu h d d n gi idients much steeper, the 
veloc y lue 1 a 1 f ce ot gravity soon attains it* 
grea 1 n a d ua from the lesialance caused 
bv lea 

Tl I n f h 1 J ! u aincd upon gradients of -im 
deg 1 h 1 tr d n Is ly the action of giavity alone 

or by the combined action of the motive power of the engine 
and gravity, can be readily determined for any given load. Froin 
calculation and experiment it appears that heavy trains may de- 
scend gradients or j^-^, without attaining a greater velocity than 
about 40 or 50 miles an hour, by allowing them to run freely 

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ivitlurat applyiig the brake to check tlie speed. By tlie apph* 
cation of the brake, the velocity may be kept within any limit 
of safety upon much steeper gradients. The only question, then, 
in comparing the advantages of different gradients, is one of the 
comparative cost between the loss of power and speed, on the 
one hand, for ascending trains on steep gradien's, and that of the 
heavy excavations, tunnels, and embankments, on the other, 
which may be required by lighter gradients. 

In distributing the gradients along a line, engineers arc gener- 
ally agreed that it is more advantageous to have steep gradients 
upon short portions of the hne, than to overcome the same dif- 
ference of level by gradients less sleep upon longer develop- 

679. In steep gradients, where locomotive power cannot be 
employed, stationary power is used, the trains being dragged up, 
or lowered, by ropes connected with a suitable mechanism, 
worked by stationary power placed at the top of the plane. 
The inchned planes, with stationary power, generally receive a 
uniform slope throughout. The portion of the track at the top 
and bottom of the plane, should be level for a sufficient distance 
back, to receive the ascending or descending trains. The axes 
of the level portions should, when practicable, be in the same 
vertical plane as that of the axis of the inclined plane. 

Small rollers, or sheeves, are placed at suitable distances along 
the axis of the inclined plane, upon which the rope rests. 

Within a few years back flexible bands of rolled hoop-iron 
have been substituted for ropes on some of the inchned planes 
of the United States, and have been found to work well, pre- 
senting more durability and being less expensive than ropes, 

6S0. Tunnels. The great consumption of power by gravity, 
and the necessity therefore of either employing additional power, 
or of diminishing the load of locomotives in ascending steep gra- 
dients, have caused engineers to resort to excavations and em- 
bankments frequently of excessive dimensions, to obtain gradients 
upon which the ordinary loads on a level can be transported with 
a suitable degree of speed. The diJhcnlty and cost of forming 
these works become in some cases so great, that it is found 
preferable to obtain the requisite gradient by carrying the road 
under ground by an excavation termed a tunnel. 

The choice between deep cutting and tunnelling, will depend 
ujKJn the relative cost of the two, and the nature of the ground. 
Wlien the cost of the two methods would be about equal, ana 
the slopes of the deep cut are not liable to slips, it is usually 
more advantageous to resort to deep cutting tlvui to tunnelling. 
So much, however, will depend upon local circumstances, tlial 
llie compiv.'ative advantages of the two mctiiods can only be de 

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cided upon understEindingly wlien these are known Whtre any 
lalilude of choice of locality is allowed, the natuie oi' the soil, 
the length of the tunnel, that of the deep cuts by which it musl 
be approached, and also the depths of the working and air ahafla, 
must all be well studied before any definitive location is decided 
upon. In some cases it may be founds that a longer tunnel wit'i 
snorter deep cuts will be more advantageous in one position, 
than a shorter tunnel with longer deep cuts in another. In otli- 
ers, the greater depth of working shafts may be more than com- 
pensated by obtaining a safer soil, or a shorter tunnel. 

■681. The operations in tunneHing will depend upon the nature 
of the soil. The work is commenced by setting out, in the first 
place, with great accuracy upon the surface of the ground, the 
profile line contained in the vertical plane of the axis of the tun- 
nel. At suitable intervals along this line vertical pits, termed 
working shafts, are sunk to a level with the top, or crown of the 
tunnel. The shafts and the excavations, which form the en- 
nances to the tunnel, are connected, when the soil will admit of 
it, by a small excavation termed a heading, or drift, usually five 
or six feet in width, and seven or eisht ieet in height, which is 
made along the crown of the tuuEel. After the drift is com- 
pleted, the excavation for the tunnel is gradually enlarged ; the 
excavated earth is raised tliroagh the working shafts, and at the 
same time caraed out at tiie ends. The dimensions and form 
of the cross section of the excavation, will depend lipon the na- 
ture of the soil, and the object of the tunne! as a communi- 
cation. In solid roclt the sides of the excavation are usually 
vertical ; the top receives an arched form ; and the bottom is 
horizontal. In soils which require to be sustained by an arch, 
the excavation should confprnQ as nearly as practicable to the 
form of cross section of the arch. 

In tunnels through uustratified rocks, the sides and roof may 
be safely left unsupported ; but in stratified rocks tiiere is dan- 
ger of blocks becoming detached and falling : wherever this ia 
to be apprehended, the top of the tunnel should be supported bj 
an arch. 

Tunnelling in loose soils is one of the most hazardous opera 
tions of the miner's art, requiring the greatest precautions ir 
supporting the sides of the excavations by strong rough frame 
work, covered by a sheathing of boards, to secure the workmeii 
from danger. When in such cases the drift cannot be extended 
throughout the line of the tunnel, the excavation is advanced 
only a few feet in each direction from the bottom of the working 
shafts, and is gradually widened and deepened to the propei 
form and dimensions to receive the masonry of the tunnel, which 
is immediately commenced below each working shaft, and ia 

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carried fi/iward in botli directions towards tlie two ends of tlif. 

GH'-l. Masonry of tunnels. Tlie cross seclion of llie arch of ? 
r.unnel {Fig. 163) is usually an oval segment, formed of arcs of 

the bottom invetl«d 

circles for the sides and lop, resting on an inverted arch at hot 
lorn. The tunnels on some of the recent railways in England 
are from 24 to 30 feet wide, and of the same height frona the 
level of tlie rails to the crown of the arch. The usual thickness 
of the arch is eighteen inches. Brick laid in hydraulic cement 
is generally used for the masonry, an askew back course of stone 
being placed at the junction of the sides and the inverted arch. 
The masonry is constructed in short lengths of ab'out twenty 
feet, depending, however, upon the precautions necessary to se- 
cure the sides of the excavation. As the sides of the arch are 
carried up, the frame-work supporting the earth behind is grad- 
ually removed, and the space between the back of the ma- 
sonry and the sides of the excavation is filled in with earth 
well rammed. This operation should be carefully attended to 
throughout the whole of the backing of tlie arch, so that the 
masonry may not be exposed to the elfects of any sudden yield 
ing of the' earth around it. 

683. The frame-work of the centres should be so arrangec 
. that they may be taken apart and bo set up with facihty. The 

combination adopted will depend upon the size of the arch, and 
the necessity of snpportr'ng the sides as well as the top of the 
arch by the centre, during the process of the work. 

684. The earth at the ends of t!ie tunnel is supported by o 
retaining wall, usually faced with stone. These wal'-s, terme.i 
\h.n fronts of the tunnel, are generally finished with the usua' 

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arcliilectural designs for gateways. To secure the ends of the 
arcli from the pressure of the earth above them, cast-iron plates 
of the same shape and depth as the top of the arch, are inscrten 
wilhin the masonry, a short distance from the ends, and arc so 
cured by wrought-iron rods finnly ancliored to tho masonry at 
some distance from each end. 

685. The working shafts, which are generally made cylindri- 
cal and faced with brick, rest upon sti-ong curbs of cast-iron, 
inserted into the masonry of the arch. The diameter of the shafi 
within is ordinarily nine feet. 

- Small shafts, about three feet in diameter, termed air shafts, 
are in some cases required at intermediate points between the 
working shafts, for the pmrposes of ventilation- 

686. The ordinary difficulties of tunnelling are greatly increased 
by the presence of water in the soil through which the work is 
driven. Pumps, or other suitable machinery for raising water, 
placed in the working shafts, will in some cases be requisite to 
keep them and the drift free from water until an outlet can be 
obtained for it at the ends, by a drain along the bottom of the 
drift. Sometimes, when the water is found to gain upon the 
pumps at some distance above the level of the crown of the 
lunnel, an outlet may be obtained for it by driving above the 
tunnel a drift-way between the shafts, giving it a suitable slope 
from the centre to the two extremities to convey the water oH" 

In tunnels for railways, a drain should be Jaid under the bal- 
astiisg along the axis, upon the inverted arch of the bottom. 

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687. Canals na aiiificid channels for water, applitd to t]i« 
purpose of inland navigatioa ; for the supply of cities wiih wa 
ter ; for dvaining ; for irrigation, &c. &c, 

688. Navigmie canals are divided into two classes : 1st. C;i 
nala which are on the same level throughout their entire length, 
as those which are found in low level countries. 3d. Canals 
which connect two points of different levels, which lie either in 
the same valley, or on opposite sides of a dividing ridge. This 
class is found in broken countries, in which it is necessary to 
divide the entire length of the canal into several level portions, 
the communication between which is effected by some artificial 
means. When the points to be connected lie on opposite sides 
of a dividing ridge, the highest reach, which crosses the ridge, 
is termed the summit level. 

689. 1st Class. The surveying and laying out a canal in a 
level country, are operations of such extreme simplicity as to 
require no particular notice in tliis place ; since tliese operations 
have bean fully explained in the subject of Common Heads. 
The line of tlie canal should be run in a direct line between the 
two points to be connected, unless it be found necessary to de- 
flect it at any intermediate points ; in which case, the straight 
portions will be connected by arcs of circles of sufficient curva- 
ture to allow the boats used in the navigation to pass each othei 
at the curves, without any diminution of their ordinary rate of 

The cros>- ^oLtion of tins class (Fig 164) pit^ents usually a 

vjater-Tvajj, or channel of a trapezoidal form, with an embank- 
ment on each side, raised above the general level of the country, 
and formed of the excavation for the water-way. The level, oi 

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814 CANALS. 

Bui-fiice of the wafer, is usually above the natnial surface, suffi- 
cient thickness being given to the embanhmcnts to prevent the 
filtration of the water through them, and to lesisl its- piessuie. 
This arrangement has in its, favoi the advantage of economy ni 
the labor of excavating and embanking, since ilie cross secUon 
of the cutting may be so calculated as to furmsh the necessary 
earth for the embankment ; but it exposes the surrounding cnun- 
tty to injury, from accidents happening to the embank men Is. 

The relative dimensions of the paru of the cro^s section may 
be ffeuerally stated as follows ; subject to suih modifications as 
eacn particular case may seem to demand 

The width of the water-way, at bottom, should he at least 
twice the width of the boats used m navigating the canal ; so 
that two boats, in passing each othei, may, by bheering towards 
the sides, avoid being brought into contact 

The depth of the water-way should be at least eighteen 
inches greater than the draft ol tho boat, to facilitate the motion 
of the hoat, particularly if tlieie are water-plants growing on 
the bottom. 

The side slopes of the water-way, zn compact soils, should 
receive a base at least once-and-a-halt the altitude, and propo: 
lionally more as the soi! is less compact 

The thickness of the embankmento, at top, is seldom regu 
■ lated by the pressure of the water agamat ihcm, as this, m most 
cases, is inconsiderable, but to pievent filtration, which, were it 
Lo take place, would soon cause their destruction A thickncs 
from four to six feet, at top, with the additional thickness gii t,n 
oy the side slopes at the water suiface, wdl, in most cases, be 
amply sufficient to prevent filtrations A pathway for the hoises 
attached to the boats, termed a tow-path, which is made on one 
of the embankments, and a foot-path on the other, which should 
be wide enough to serve as an occasional tow-path, gne a su- 
perabundance of strength to the embankments 

The tow-path should be from ten to twehe feet wide, to allow 
the horses to pass each other w^th ease ; and the fool-path at 
least six feet wide. The height ol the surfaces of these patls, 
above the water surface, should not be less tlian t\\o feet, to 
avoid the wash of llie ripple, nor greater than foui feet and a 
half, for the facility of the draft of the horses in towing. The 
surface of the tow-path should incline slightly outward, botli 
to convey off the surface water in wet weather, and to give 
a firmer footing to the horses, which naturally draw from the 

The side slopes of the embankment vary with the characiei 
of the soil : towards the water-way they should seldom be less 
than two base lo one peqicndicular ; froin it, they may, if it be 

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CANALS. 315 

thought necessary, be less. The interior slope is usuiiHy not 
carried up Unbroken from the bottom to the top ; but a Jiorizon- 
tal space, termed a bench, or berm, about one or two feet wide, 
is left, about one foot above the water surface, between the side 

■ slope of the water-way and' the foot of the embankment above 
ihe berm. This space serves to protect the upper part of the 
interior side slope, and is, in some cases, planted with such 
shrubbery as grows most luxuriantly in aquatic localities, to pro 
tect more efficaciously the banks, by the support which its roots 
give to the soil. The side slopes are better protected by a re- 

■ veiement of dry stone. Aquatic plants of the bulrush kind 
have been used, with success, for the same purpose ; being 
planted on the bottom, at the foot of the side slope, they serve 
to break the ripple, and preserve the slopes from its effects. 

The earth of which the embankments are formed should be 
of a good binding character, and perfectly free from vegetable 
mould, and all vegetable matter, as the roots of plants, &c. In 
forming the embankments, the vegetable mould should be care- 
fully removed from the surface on which they are to rest ; and 
',hey should be carried up in uniform layers, from nine to twelve 
inches thick, and be well'rammed. If the character of the earth, 
of which the embankments are formed, is such as not to present 
entire security against filtration, a puddling ,of clay, or fine sand, 
two or three feet thick, may be laid in the interior of the mass, 
penetrating a foot below the natural surface. Sand is useful in 
preventing filtration caused by the holes made in the embank- 
ments near the water surface by insects, moles, rats, &c. 

Side drains must be made, on each side, a foot or two from 
the embanltments, to prevent the surface water of the natural 
surface from injuring the embankments. 

690. 2d Class. This class will admit of two subdivisions . 
1st, Canals which he throughout in the same valley ; 2d, Canals 
with a summit level. 

Location. In laying out canals, belonging to the first sub- 
division, the line of direction of the canal should be as direct as 
f)racticable between the two points. As the different levels, 
lowever, must be laid ouf on one of the side slopes of the val- 
. ley, their lines of direction will be nearly the same as the hori 
zontal curved line in which the natural surface of the ground 
would be intersected by the water surface of the canal pro- 
duced ; the variations in direction from this curve depending on 
tlie cliaracter of the cuttings and fillings, botli as to the advan- 
tages which the one may present over the other as regards filtra 
tton, and the economy of construction. 

With respect to the side slope of the valley along vvhicK the 
canal is to be run, the engineer must be guided in his choice by 

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316 CANALS. 

the rehtive e\pense of coiisfiuctioii on llic two siles; which 
will depend (ii the quai tity of cutt ng and filhng tl e masoniy 
foi the culverts, &.c , and tne ndture of the "o 1 as adapted tt 
holding watei All other things bei ig equal the side on which 
the fewest sccond'\ry watercourses ire fuind will, generally 
spea! mg offer the creileat idiantagi- as fo expense , but, it may 
happen that the secoiiday water couises will 1 1- lequired to feed 
the canal with water in which case it wili be necessary to lay 
out the line on the side wheie the\ aie found mobt convenient, 
an 1 in moit abundance 

As to the points m which the h e of dneciion shoi Id cross the 
secoidary valley'! the ensrinee will be guided by the same con- 
sideiat ons as for any other lini. of communication; crossing 
them by following the nati al burfjce or else by a filling in a 
right line as may be most economical 

691 Cross section The side formations of excavations and 
embankments lequ rt- peculiar care parucularly the latter, aa 
any crevices, when they are firat formed, or which may take 
place by settling, might prove destructive to the work. In most 
cases, a stratum of good binding eartli, lining the water-way 
throughout to the thickness of about four feet, if compactly 
rammed, will be found to offer sufficient security, if the sub- 
structure is of a firm character, and not liable to settle. Fine 
sand has been applied with success to stop the leakage in canals. 
The sand for this purpose is sprinkled, in small quantities at a 
time, over the surface of the water, and gradually fills up the 
outlets in the bottom and sides of the canal. Bui neither this 
nor puddhiig has been found to answer in all cases, particularly 
where the substructure is formed of fragments of rocks offenng 
large crevices to filtrations, or is of a marly nature. In such 
cases it has been found necessary to line the water-way thiough- 
out with stone, laid in hydraulic mortar. A lining of this cha- 
racter, (Fig. 165,) both at the bottom and sides, fonned of flai 

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stones, about four inches thick, laid on a bed of hydraulic mar- 
tar, one inch thick, and covered by a similar coat of. monar, 
making the entire thickness of the lining sis inches, has been 
found to answer all the required purposes. This lining should 
be covered, both at bottom and on the sides, by a layer of good 
earth, at least three feet tliick, to protect it from ihe shock of the 
boats striking either of those parts. 

The cross section of the canal and its tow-paths in deep cut 
ting (Fig. 16S) should be regulated in the same way as in canal.' 

ot the first class ; but when the cuttings are of considerable 
depth, it has been recommended to reduce both to the dimen- 
sions strictly ■ necessary for the passage of a single boat. By 
this reduction there would be some economy in the excavations ; 
but this advantage would, generally, be of too trifling a charac- 
ter to be placed as an offset to. the iuconveniences resulting to 
the navigation, particularly where an active trade was to be car- 
ried on. 

692. Summit level. As the water for the supply of the sum- 
mit ievel of a canal must be collected from the ground that lie& 
above it, the position selected for the summit level should be al 
the lowest point practicable of the dividing ridge, between the 
two branches of the canal. In selecting this point, and the di. 
rection of the two branches of the canal, the ejigineer will be 
guided by the considerations with regard to the natural features 
of the surface, which have already been dwelt upon. 

693. Suppli/ of water. The quantity of water required fo- 
canals with a summit level, may be divided into two portions 
1st. That which is required for the summit level, and those lev. 
els which draw from it their supply, 2d, That which is wanted 
for the levels below those, and which is famished from other 

The supply of the first portion, which must be collected al 
the summit level, may be divided into several elements: 1st. 
The quantity required to fill the summit level, and the levels 
which draw their supply from it, Sd. The quantity required te 
supply losses, arising from accidents ; as breaches in the banks, 

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al6 CArfALS. 

nnd llie emijtying cif ihe levels for repairs, 3d. The supplici 
for from surface evaporation, from leakage tlirougli tlie 
Boil, and through the lock gates. A. The quantity required for 
the service, of the navigation, arising from the passage of the 
boats from one level to another. Owing to the want of sufficient 
data, founded on accurate observations, no precise amount can 
be assigned to these various elements which will serve the engi- 
neer as data for rigorous calculation. 

The quantity required, in the first place, to fii'l the summit 
level and its dependent levels, will depend on thei; size, an ele- 
ment which can be readily calculated ; and upon the quantity 
which would soak into the soil, wliich is an element of a very 
indeterminate character, depending on the nature of the soil in 
the different levels. 

The supplies for accidental losses are of a still less deteimi- 
nate cliM'acter. 

To calculate the supply for losses from surface evaporation, 
correct observations must be made, on the yearly amount of 
evaporation, and the quantity of rain that falls on the surface ; as 
tbe loss to be supplied will be the difference between these two 

"With rega'd to the leakage through the soil, it will depend on 
'the greater or less capacity which the soil has for holding water. 
This element varies not only with the nature of the soil, out also 
witli the shorter or longer tune that the canal may have been in 
use ; it having been found to decrease with time, and to be, 
comparatively, but trifling in old canals. In ordinary Soils it 
may be estimated at about two incJies in depth every twenty-four 
hours, for some lime after the canal is first opened. The leak- 
age through the gates will depend on tbe workmanship of these 
parts. . From experiments by Mr, Fisk, on the Chesapeake and 
Ohio canal, the leakage through the locks at the summit level, 
which are 100 feet long, 15 feet wide, and have a lift of 8 feet, 
amounts to twelve locks full daily, or about 62 cubic feet per 
minute. The monthly loss upon the same canal, from evapora- 
tion and filu-ation, is about twice the quantity of water contained 
in il. From experiments made by Mr. J. B. Jervis, on the Erie 
tanal; tne total loss, Irom evaporation, filtration, and leakage 
.iirougb the gates, is about 100 cubic feet per minute, for eacli 

tn estimating the quantity of water expended for ihe service 
of the navigation, in passing the boats from one level to another, 
two distinct cases require examination: — 1st. Where there is but 
one lock between two levels, or in Other words, when the locks 
are isolated. 2d. When there are several contiguous locks, or 
IS it is Icnilcd, ^fligli' of locks' between two levels. 

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CANALS. 319 

694 A lock i~, a small bisin just hrgc cnouch to receive a 
boat, in wl jch the water is usually confined on the sides by two 
upright \va Is of masonry, and at the ends bv two gates, which 
open and shut, both for tlie purpo'ie of allowing the beat to pass, 
nnd to cut off liie water of the upper level fiom the lower, as 
well as fiom the lock while the boat is in it To pass a boat 
from one let el to the othnr — from the lower to the upper end, 
tor e\ample — the lower gates are opened, and the boat having 
entered the lock they arc shu*, and witcr is drnwn from the up- 
per le\ el, by means of vah ei to till the lock and raise the boat , 
when this operation is &iished, the upper gates are opened, and 
the boat is passed out To descend fiom the upper level, the 
lock IS first filled , the upper gates are tlien opened, and the boat 
passed m , these gates aie iitxt shut and tl e water is drawn 
fiom the lock, by calves, until the boat is luwered to the lower 
le\el, when the lower gates are opened and the boat is passed 

In the two operations jubt described, it is evident, that for tlie 
passage of a boat, up or down, a quantity of water must be 
diawn from the uppeT level to ^lU the lock to a iieight which is 
equal to the difierence of level between the surface of the water 
in the two ; this height is termed the lift of the lock, and the 
volume of water required to pass a boat up or down is termea 
the prism of lift. The calculation, therefore, for the quantity 
of water requisite for the service of the navigalion, wiH be sim- 
ply that of the number of prisms of lift which each boat will 
draw from the summit level in passing up or down. 

695. Let a boat, on its way up, be supposed to have arrived 
at the lowest level supplied from the summit level ;' it will re- 
quire a prism of lift to ascend the next level above, and so on in 
succession, until it reaches ihe summit level, from which one 
prism of lift must be drawn to enable the boat to enter it. From 
this it appears that but one prism of lift is drawn from tlie sum- 
mit level for the passage of a boat up. Now, in descending on 
iie other side, the boat will require one prism of lift to take it to 
the nest level, and this prisni of lift will carrV it tlirough all the 
successive locks, if their lifts are the same. Tor the entire pas- 
sage of one boat, then, two prisms of lift must be drawn from 
t!ie summit level. 

This boat will thus leave all tlie locks full on the side of the 
' ascent, and empty on the sido of the descent. Now the next boat 
may be going in the same, or in an opposite direction, with re- 
spect to the first. ' If it follows the first, it will evidently require 
two prisms of lift for its entire passage, and will leave the locks 
ill the same state as they were. If it proceeds in an opposite 
direclion, i* will require a prism of lift to ascend to the sumiiii 

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320 CANALS. 

fevel ; but, in descending, it will take advantage of tfie full loc* 
ieft by the preceding boat, and will therefore not draw from the 
summit level for its descent to the next ; tlie same will lake 
place "at every level until the last, wl ere it will carry out with it 
the prism of lift, which was drawn from the summit level for the 
preceding boat, so that in this case it will draw but one prism 
of lift from the summit level. If the two boats had met on the 
summit level, the same would have taken place : therefore, wlien 
the boats alternate regularly, each will require but one pnsm of 
hft for its entire passage. But as this regularity of alternation 
cannot be practically carried into effect, an allowance of two 
prisms of hft must be made for the entire passage of each boat- 
In calculating the expenditure for locks in flights, a new ele- 
ment, termed liie prism of draught, must be taken into account. 
This prism is the quantity of water required to float the boat in 
the lock when tlie prism of lift is drawn off; and is evidently 
equal in depth to tne water in the canal, unless it should be 
deemed advisable to make it just sufficient for thp draught of the 
boat, by which a small saving of water mjght be effected. 

696. Locks in flights may be considered under two points of 
view, witli regard to the expenditure of water : the first, where 
both the prism of lift, and that of draught, are drawn off for the 
passage of a boat ; or second, where the prisms of draught are 
always retained in the locks. The expenditure, of course, will 
be different for the two cases. 

To ascertain what wiH take place in the two cases, let a case 
be supposed, in which there is a flight of locks on each side of 
the summit level, to connect it with the two next lower levels. 
In the first case, a boat, aiTiviug at the foot of the fli^f, finds 
all the locks of the flight empty, except the lowest, which must 
contain a prism of draught to float the boat in. To raise the 
boat, tlien, to the upper level, all the locks of the flight must be 
filled from the summit level, which will require as many prisms 
of lift as there are locks, and as many prisms of draught as ther& 
are locks less one ; or, representing by l the prism of lift, d the 
prism of draught, and n the number of locks in the flight, the 
total quantity of water, for the ascent of the boat, will he repre- 

sented by 

nL4-(ji— 1)d; . . . (1). 

In descending, on the opposite side, the boat will require a prism 
of lift and one of draught at the lirst lock ; but to enter tiie sec- 
ond another prism of draught in addition will be required, and 
this entire quantity will be suiFiciont to take it through all the 
remaining locks of the flight : this quantity will therefore be rep- 
resented b^' 

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CiNALS. 321 

■0 tliat for the entire pissan'e of ihe bo^t the lotil expenditure 
will be rep ese te(i y 

(n + l)L+( +I)d (3) 

I he fl ght one s de s ti Ub lef f 11 af er t! e pas ge of 
the fi st boat ado tl e oti er i !e empty If i second boat 
the folio V8 d Qc ly ifter tl e fi t tl e p sm o-f I ft n ust be 
dra V fron the lowest lock to ad n t 1 e boit tl s j r &n s ll en 
suppl ed fro ll e o 1 e t above ai d so o to the sumn t lev 
el ""O tl it but one pr sm of 1 ft wdl be d a vn off for tl e ascent 
of tt s boa an 1 t 1 req re on of 1 f and two of dra p,ht 
to carry t do vn the oppos te fi gi t If ti erefore ll e to al 
nu nber of boats wh c! fol o v n th s o d r clud g tl e first, 
be I c ed l^ tl e o 1 esj en!l e wll be ejreae t 
cd hy 

(?i + l)L + (« + l)D + (m-i)2L + {ni-I)2D. . (4). 

If the second boat, instead of following the firs!, arrives in 
the opposite direction, or alternates with it, the expenditure for 
its ascent will be represented by the formula ( 1 ), and for its de- 
scent it will be iiotliing, since it finds the opposite flight filled, 
as left by the first boat ; but if the locks had oeen emptied, then 
the passage of llie second boat would have taken place under 
the same circumstances as that of the first. 

It will be unnecessary here to go farther into these calcula- 
tions for the various cases that may occur, under the different 
circumstances ef passage of tiie boats or of empty or full flights ; 
the preceding gives the spirit of the method, and will give the 
means for entering upon a calculation to allow for the loss or 
gain by the passage of freighted or of empty boats, following 
any prescribed order of passage. These refinementa are, for 
the most part, more curious tljan useful; and the eng-ineer should 
confine himself to making an ample allowance for the most un- 
favorable cases, both as regards ilie order of passage and the 
number of boats. 

697. Feeders and Reservoirs. Having ascertained, from the 
preceding considerations, the probable supply which should be 
collected at the summit level, the engineer will nest direct his 
attention to the sources from which it may be procured. Theo- 
retically considered, all the water that drains from the ground 
adjacent to the summit level, and above it, might bo collected for 
its supply ; but it is foimd in practice that channels for the con- 
veyance of water must have certain slopes, and tliat these slope? 
moreover, will regulate the supply furnished in a certain tim6, 
all other things being equal. In making, however, the .survey 
of the country, from which the water is to be supplied to tha 
smnmit level, alt the ground above it should bo examined, lejiv- 

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ing t!ie detcrminatioa of the slopes for after consiileraiiona. TJie 
survey for this object consists in making an accurate dcVueation 
of all the water-courses above the summit level, and in ascer- 
taining the quantity of water which can be furnished by each in 
a given time. This survey, aa well as ihc" measurement of the 
quantity of water fiimished bv each stream; which is termed the 
gauging, should be made in tlie driest season of the year, in or- 
der to ascertain the minimum Bupply, 

698. The u 1 ra 1 od f 11 g I f ! 
and conveyin„ h n 1 J b f d i 
voirs. The / i 1 f m il 1 h a 
traced on tlie f I g d 1 bl 1 ( c 
convey the wa 1 n 1 d he 
summit level Tl d f 1 I he 
longitudinal si ] f 1 d 1 Id 1 1 o 
each other, ii d 1 h 11 d 1 ppl a 
given lime. Ti !) h 1 pe g 1 f d II r 
will be the po h h w 11 h f pply. 
and therefore the greater will be the quantity of water which it 
will receive. This slope, however, has a practical limit, which 
is laid down at four inches in 1000 yards, or nine thousand base 
to one altitude ; and the greatest slope should not exceed that 
which would give the current a greater mean velocity than tliir 
teen inches per second, in order that the bed of the feeder may 
not be injured. Feeders are furnished, like ordinary canals, 
with contrivances to let off a part, or the whole, of the water in 
them, in cases of heavy rains, or for making repairs. 

But a small proportion of the w^ter collected by the feeders 
is delivered at the reservoir ; the loss from various causes being 
much greater in them than in canals. From observations made 
on some of the feeders of canals in France, which have been in 
use for a long period, it appears that the feeder of the Briare 
canal delivers only about one fourth of the water it gathers from 
its sources of supply ; and tliat the annua! loss of the two feed- 
ers of the Languedoc canal, amounts to 100 times the quantity 
of water which they can contain. 

699. A reservoir is a large pond, or body of water, held in 
resei ve for the necessary supply of the siunmit level. A reser- 
voir is usually formed by choosing a suitable site in a deep and 
joarrow valley, which lies above the summit level, and erecting u 
dam of earth, or of masonry, across the outlet of the valley, or 
ftt some more suitable point, to confine the water to be collected 
The object to be attained, in this case, is to embody the greatest 
voiunie of water, and at the same time present the smallcai 
evaporating suiface, at the smallest cost for the construction ol 
the dam 

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CANALS. 323 

It 19 generally deemed best to have two reservoirs for tKe sup- 
ply, one to contain the greater quantity of water, and liie otiier 
ivnich is termed the distributing reservoir, to regulate the sup* 
ply to the summit level. Jf, however, the summit level is very 
capacious, it rnay be used as the distributing reseiTroir. 

The proportion between the quantity of water that falls \ipon 
a given surface, and that which can be collected from it for the 
auppfy of a reservoir, varies considerably with the latitude, the 
season of tlie year, and the natural features of the locality. The 
drainage is greatest in high latitudes, and in the winter and spring 
seasons ; with respect to the natural features, a wooded surface 
with narrow and deep valleys will yield a larger amount llian an 
open flat country. 

But few observations have been made on this point by engi- 
neers. From some by Mr. J. B. Jervis, in reference to the 
reservoirs for the Chenango canal, in the slate of New York, it 
appears that in that locality about two fiftlis of the quantity of 
ain may be collected for the supply of a reservoir. The pro- 
'lortion usually adopted by engineers is one third. 

.The loss of water from the reservoir by evaporation, iiliration, 
and other causes, will depend upon the nature of the soil, and 
the exposure of the water surface. From observations made 
upon some of the old reservoirs in England and France, it ap- 
pears that the daily loss averages about half an inch in depth. 

700. The dams of reservoirs have been variously constructed: 
in some cases they have been made entirely of earth, (Fig. 167;) 

A, body 01 

B, (WikI. 

_,_,„, A wilh valves al llieirinlels, which diEeharge i to the vertical wtll i. 

r.e.cHTOOVcB.inthelaeeaor t!iosiae-watls,whcl foiin tl e e IraaCB to t^e culveit), 

li, fllop-plank tlsra acrosa (he outlet of lii; bollom culvert, to dam back the water into 

the fBitical well, 
f , parapet wall on top of Uib darn. 

m others, entirely of masonry ; and in otliers, of earth packed in 
between several parallel stone walls. It is now thoiigiit bestU 

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use either earth or niasanry alone, according to the circwm 
stances of the case ; the comparative expense of the two melh 
ods being carefully considered. 

Earthen dams should je made witli extreme care, of tiiebesl 
binding earth, well freed from every thing that might cause fil- 
trations. A wide trench should be excavated to the firm soil, tc 
receive the base of the dam ; and the earth should be carefully 
spread and rammed in layers not over a foot thick. As a farthei 
precaution, it has in some instances been thought necessary to 
place a stratum of the best clay puddling in the centre of the 
dam, reaching from the top to three or four feet below the base. 
The dam may be from fifteen to twenty feet thick at top. The 
slope of the dam towards the pond should be from three to six 
base to one perpendicular; the reverse slope need only be some- 
what greater than the natural slope of the earth. 

The slope of dams exposed to the water is usually faced 
witli dry stone, to protect the dam from the action of the surface 
ripple. This kind of facing has not been found to withstand 
well the action of the water when agitated by high winds. Upon 
some of the more recent earthen dams erected in France, a facing 
of stone laid in hydraulic mortar has been substituted for the one 
of dry stone 1 he plan adopted for this facing {Fig. 168) con- 

Fis. I6B— Represents the melhoil 
of faoii^ tJie pond slope of a 
d4m, with low walls plucDd in 

A balyDfthoilam. 

o a, a, low walls, the fncea of 
which nre built in ofTaets. 

b b top surfitce ortlieotlseta bo 

stoae slabs laid in mortar. 
c lop of dam laced hbe the ofT- 

d parapet wall. 

sists m placing a scries of Ion walK in ofi'sets above each other, 
along tl e slope of the dim, co\ erin^ the exposed surface of each 
offset, between the top of one wall and the foot of the next, with 
a coating of slab-stone laid in mortar. The walls are from five 
to six feet high. They are carried up in small offsets upon the 
face, and are made either vertical, or leaning, on the back. The- 
width of the ofi'sets of the dam, between the lop of one wall and 
the foot of the next, is from two to three feet. 

An arciied culvert, or a large cast-iron pipe, placed at some 
suitable point of the base of the dam, which can be closed or 
opened by a valve, will serve for drawing off the requisite 
supply of water, and for draining the reservoir in case of re- 

'J'hc culvert should be strongly constructed, and tne cartb 

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CANALS. 323 

around it be well puddled and rammed, to prevent iiitrationa 
lis size should be sufficient for a man to enter it with ease. 
Tlie valves may be placed either at the entrance of the culvert, 
or at some intemiediate point between the two ends. Great 
care should be taken in their arrangement, to secure them from 
accid Mits. 

Winn the depth of water in a reservoir is considerable, several 
culver Is should be constructed, (Fig. 167,)to draw offthe water at 
different levels, as the pressure upon the lower valves in this case 
would be very great when the reservoir is full. They may be 
placed at intervals of about twelve feet above each other, and be 
arranged to discharge their water in a common vertical shaft. 
In this case it will be well to place a dam of timber at the outlet 
of the bottom culvert, in order to keep it filled with water, to 
prevent the injure which the bottom of it might receive from the 
water discharged from the upper culverts. 

The side walls which retain the earth at the entrance to the 
culverts, should be arranged witli grooves to receive pieces of 
scantling laid horizontally between the walls, termed stop-planks, 
to ^orm a temporary dam, and cut off the water of me reser- 
voir, in case of repairs to the culverts, or to the face of the 

The valves arc small sliding gates, which are raised and low- 
ered by a rack and pinion, or by a square screw. The cross 
section of the culvert is contracted by a partition, either of ma- 
sonry or timber, at the point where the valve is placed. 

701. Dains of masonry are water-tight walls, of suitable forms 
and dimensions to prevent filtration, and resist the pressure of 
water in the reservoir. The most suitable cross section is that 
of a trapezoid, the face towards the water being vertical, and 
the exterior face inclined with a suitable batter to give the wall 
sufficient stability. The wall should be at least four feet thick 
at the water line, to prevent filtration, and this thickness may be 
increased as circumstances may seem to require. Buttresses 
should be added to the exterior facing, to give the wall greater 

702. Suitable dispositions should be made to relieve tlie dam 
from all surplus water during wet seasons. For this purpose 
arrangements should be made for cutting off the sources of sup- 
ply from the reservoir ; and a cut, termed a waste-weir, (Fig. 
169,) of suitable width a.ui depth should be made at some point 
along the lop of the dam, and be faced with stone, or wood, to 
give an outlet to the water over the dam. In high dams the 
total fall of the water should he divided into several partial falls, 
by dividing the exterior surface over which the water runs into 
offsets. '1 o break the shock of the water upon llie horizoiita 

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surface of tlie offset it "hould be kept covered witli a slieet ti' 
watt-r retained by a dam placed across ita outlet. 

A body of If e clam 
a lop of the waste vie r 
b iiool foimed by a stop plan 
d covering of loose stone to b 

703. In extensive reservoirs, in which a large surface is ex- 
posed to the action of the wind.s, waves might be forced over 
the top of the dam, and subject it to danger ; in such cases the 
precaution should be taken of placing a parapet wall towards 
the outer edge of the top of the dam, and facing the top through- 
out with flat stones laid in mortar. 

704. Lift of locks. From the preceding observations on the 
expenditure of water for the service of the navigation, it appears 
tliat isolated locks are more favorable under this point of view 
than locks in flights. The engineer is not, however, always left 
free to select between the two sisteni for the form of the 
natural surface of the ground rav^ compel hun to adopt a flight 
of locks at certain points. As to the comparative e-jpense of the 

. two methods, a flight is in moat ca=es cheiper than the same 
number of single locks, as thi,re %ro certain parts of the masonry 
which can be suppressed, fhtre is also an economy in the 
suppression of the small gates ■which ire not needud in flights. 
It is, however, more difficult to secure the foundations of com- 
bined than of single locks from the cfi'i-cts of the i^sater, which 
forces its way from the upper to tlic lower level undei tlie locks. 
Where an active trade is earned on, a double fl ght is sometimes 
arranged ; one for the ascending the other foi the descending 
boats. In this case the water which fills one flight may, after 
'.he passage of the boat, be partly used foi the other, by an 
arrangement of valves made m tl e side waU sepirating the 

The lift of locks ia a subject of miportance both as regards 
die consumption of witer for the na^ igdtion ai d the economy 
f)f construction. Locks with great hfta as may be seen from 
the remarks on the passage of boats consume more water than 
those with small lifts. They requite ilso moie cire in their 

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constiMiction to preserve tliem frOm accidents owing to the grcvi 
pressure ot witer igau sttersJs fie expe e of ro struc- 
tion is other \ se n tl e r favor that is 1 e e\pense w 11 ncreaae 
wild liie total mber of lock tl e 1 e ^,1 1 I be a&cended being 
llie samp. The smallest 1 fts are soldo i less ll a f ve feet, and 
the grealc t f r o J nar\ canal not o er twelve n ed m lifts 
of seven o e ght feet are cons dcrcd tl e best unJer e ery point 
cf view. 11 s is a po t loveve wl cl can ot be settled 
arbitrarily as the nat r of tl e fou dat o s tl e i cr als nsed, 
the embaakme s ar un 1 1 loci led dnges tl e uection 
of the canil caused by va y g tlie 1 f s a e so a y n odifying 
causes, wh ch slo H be car f Ily wegied before adopting a 
definitive pai 

The lifts of a fl t,bt si o Id be ll e sa e througl out but in 
isolated loci s t! e 1 fts may vary according to c re n s a ces. If 
the supply of water from the si u t level requ res to be econo- 
mized with care he 1 f s of locks wl cl are fur she 1 from it 
may be less than those lower down. 

705. Levels. Theposition and the dimensions of the levels 
must be mainly determined by the form of the natural surface. 
Those points are naturally chosen to pass from one level to 
another, or as the positions for the locks, where there is an ab 
rupt change in the surface. 

A level, by a suitable modification of its cross section, can be 
inade as short as may be deemed desirable ; there being but one 
point to be attended to in this, winch is, that a boat passing be- 
tween the two locks, at the ends of the level, will have time to 
enter either lock before it can ground, on the supposition, that 
the water drawn off to fill the lower lock, while tne^boat is tra- 
versing tlie level, will just reduce the depth to the draught of the 

706. Locks. A lock {Fig, 170) may be divided into three 
distinct pails : — 1st. The part included between the two gates, 
which is termed t!ie chamber. 2d. The part above the upper 
gates, termed the fore, or head-bay. 3d. The part below the 
lower gales, termed the aft, or tail-bay. 

707. The lock chamber must be wide enough to aOow an 
easy ingress and egress to the boats commonly used on the ca- 
nal; a auvplus widtfi of one foot over the width of the boat across 
the beam is usually deemed sufficient for this purpose. The 
length of the chamber should be also regulated by that of the 
boats ; it should be such, that when the boat enters the lock 
from the lower level, the tail-gates may be sliut without requiring 
the boat to unship its rudder. 

The plan of the chamber is usually rectangular, as this form 
B, ifl every respct:t, superior to all others. lu tlie cross section 



CANiLS. 326 

cf ihe chamber (Fig 171 ) llic sides receive generally a sliglil 

70, iluungb 
h bottom 

ba er as when so a an die} fiund to give greater fa- 
cility to the passage of the boat than when vertical. The bot- 
tom of the chamber is cither flat or curved ; more water will be 
requued lo fill the flat bottomed chamber than the curved, but il 
will require less masonry in it? construction. 

708 The chambei is t m d j 1 1 1 d bj 

a vertical wall, the plan f wh h lly "1 1 

wall senirates the uppe f 11 1 

lift-wall , It la usually of h m h 1 
els The top of the lift- all f m d f I ! 

jomts of which are noim I h d f f 1 11 h 

lop course projects from n h b 1 1 

the upper levpl, presentii g 1 P f ^ l^ m f 

the head-<Tites, when ehi t, gai Tl d ! 

imtie-sill Vaiioui degr f j h 1 h 

dngle between the two bnnchesj of the mitre-sill ; it is, howevci", 
geuenlly so detcrmmcd, that the perpendicular of the isosceles 
Intngle, formed by the two blanches, shall vary between onf. 
fif h ind jne si\th of the base 

As stcne mitie-sills ire Inble to injury from llie shock of the 
gate, ihty aie now usually constructed of timber, (Fig. 173,) bv 

d 1 
1 If ftl I 

Fip. 172— Represents apian of a wooJcn milte- 
sill, and a horizontBl section of a. lock-gala 
(Fig, 173) closed. 

a, o, milre-Bill IVamed with thn pioecs h and c, 
and firnilv faetaned to the Kide walls A, A. 

d Bectiou of quoin posts of lock-gal«. 

(raming two strong beams with the proper angle for the gate 
when closed, and securing them firtnly upon the top of the lift- 
ivall. It will be well to place the top of the raitre-sill on the 
iift-wall a little lower than the bottom of the canal, to preserve 
it from being struck by the keel of the boat on entering, at 
leaving the lock. 

709. The cross section of the chamber walls is usually trape- 

Eoidai i the fucing receives a slight baiter. The chamber walls 


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lie exposed to twj opposite efforts ; the watev in the Iock m 
one side, and the embankment against the wall on the other 
The pressure of the embanlcment is the greater as well as the 
more permanent effort of tlie two. The dimensions of the wall 
must be regulated by this pressure. The usual manner of doing 
tliis, is to make the wall four feet thick at the water line of the 
upper level, to secure it against filtration ; and then to determine 
tlie base of the batter, so that the mass of masonry shall present 
sufficient stability to counteract the tendency of the pressure. 
The spread, and other dimensions of the foundations, will be 
regulated according to the nature of the soil, in tlie same way 
as in other structures. 

710. The bottom of the chamber, as has been slated, may be 
either flat or curved. The flat bottom is suitable to very fimi 
soils, which will neither yield to llie vertical pressure of the 
chamber walls, nor admit the water to filter from the upper level 
under the bottom of the lock. In either of the contrary cases, 
the bottom should be made with an inverted arch as this form 
will oppose greater resistance to the upward pressuie of the 
water under .the bottom, and will serve to dibtiibute the weight 
of the walls' over the portion of the foundati n ui der the arch. 
The thickness of the masonry of the bottom will depend on the 
width of tlie chamber, and the nature of the soil Were the 
soil a solid rock, no bottoming would be reqnis te , if it is of soft 
mud, a very solid bottoming, from ihrce to six feet Jii thickness, 
might be requisite. 

711. The principal danger to the foundations arises from the 
water which may niter from the upper to the lower level, under 
the bottom of the lock. One preventive for this, but not an ef- 
fectual one, is to drive sheeting piles across the canal at the end 
of the head-bay ; another, which is more expensive, but more 
certain in its efi'ects, consists in forming a deep trench of two or 
three feet in width, just under the head-bay, and filling it with 
beton, which unites at top with the masonry of the head-bay. 
Similar trenches might be placed under the chamber were it 
considered necessary. 

712. The lift-wall usually receives the same thickness as the 
chamber walls ; but, unless the soil is very, firm, it would be 
more prudent to form a general mass of masonry under the en- 
tire head-bay, to a level with the base of the chahiber founda- 
tions, of which mass the lift-wall should form a part. 

713. The head-bay is enclosed between two parallel waUs| 
which form a part of the side walls of the lock. They are ter 
minatcd by two wing walls, which it will be found most ecc 
comical to run back at riffbt angles with the side walls. A rie- 
Ci,s8, termed the gnte-chaviber, is made in the wall of the hea«l 

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CANALS. 331 

!)av •; the depth of this recess should be sufficient to allow tlis 
gate, when open, to fall two or three inches within the facing of 
the wall, BO that it may be out of the way when a boat is pass 
ing ; the length of the recess should be a few inches more than 
ihe width of the gate. That part of the recess where the gate 
tnrns on its pivot is termed the hollow quoin ; it receives whal 
is termed the heel, or quoin-post of the gate, which is made of a 
suitable form to fit the hollow quoin The distance between the 
hollow quoins and the fice of the lift wall will depend on the 
pressure aijainst the mitre sdl, and the strength of the stone 
eiditeen inches will geneialSy be found amply sufiicant 

Ihe side walls need not extend moie than twelve inches be 
yond the other end of the gale chamber The wing walU miy 
be extenJed back to the total width of the caml, but it will be 
moie economical to na row the canal neir the lock, and to ex- 
tend the wing walla only about two teel into the banks, or sidts 
The dimensions of the side and wing walls of the head-bay are 
regulated in the same wav as the chamber v,alls 

1 lit bottom of the head bay la flat, and on the same level with 
the bottom of the canal , the citenor course of stones at the en- 
trance to the lock should be so jointed as not to work loose. 

714. The gate-chambers for the lower gates are made in the 
chamber walls ; and it is to be observed, that the bottom of the 
chamber, where the gates swing back, should be flat, or be oth- 
erwise arranged not to impede the play of the gates. 

715. The side walls of the tail-bay are also a pai't of the gen- 
eral side walls, and their thickness is regulated as in the prece- 
ding cases. Their length will depend chiefly on the pressure 
which the lower gatss throw against them when the lock is full ; 
and partly on the space required by tlie lock-men in opening and 
shutting gates inanteuvred by the balance beam. A calculation 
must be made for each particular case, to ascertain the most 
suitable length. The side walls are also terminated by wing 
walls, similarly arranged to those of the head-bay. The points 
of junction between the wing and side walls should, in both 
cases, either be cuiTed, or the stones at the angles be rounded 
off. One or two perpendicular grooves are sometimes made in 
the side walls of the tail-bay, to receive stop planks when a 
temporary dam is needed, to shut oif tin- w iter of the lower \^.^ el 
from the chamber, in case of repairs &c Similar airangements 
might be made al the head-bay, but they nie not indifpenbable 
in eitlier case. 

The strain on the walls at the holl w quon s i« greater tlnn ai 
Bnv other points, owinjr to the prea'uri, at those poi its from tl e 
gates, when they are shut, and to tlie action of the gitcs when 
in motion; lo counteract this, and oticngthen tin, walls, bu 


832 CANALS. 

tresses sliould be placed at tlie back of the walls in the hkhI 
favorable posilion behind the quoins to subserve the object ia 

The bottom of tlie tail-bay is arranged, in all respects, like 
that of tlie head-bay. 

716. The top of the side walls of the lock may be from one 
to two feet above the general level of the water in the upper 
reach ; the top course of the masonry being of heavy large 
blocks of cut stone, although this kind of coping is not indis-, 
penaable, as aiKallcr masses have been found to suit the same 
purpose, but they are less durable. As to the masonry of the 
lock, in general, it is only necessary to observe, that those parts 
alone need be of cut stone where there is great wear and tear 
from any cause, as at the angles generally ; or where an accu- 
rate finish is indispensable, as at the hollow quoins. The other 

Earts may be of brick, rubble, beton, &c., but every part should 
e laid in the best hydraulic mortar. 

717. The filling and emptying the lock chamber have given 
rise to various discussions and experiments, all of which have 
been reduced to the comparative advantages of letting the watei 
in and oif by valves made in the gates themselves, or by culverts 
in die side walls, which are opened and shut by valves. When 
the water is let in tlirough valves in the gates, its eifects on the 
sides and bottom of the chamber are found to be very injurious, 
particularly in high lift-walls ; besides the inconvenience result- 
mg from tiie agitation of the boat in the lock. To obviate this, 
in some degree, it has been proposed to give ihe lift-wall the 
form of an inclined curved surface, along which the water might 
descend without producing a shock on the bottom. 

718. The side culverts are small arched conduits, of a circu- 
lar, or an elliptical cross section, which are made in tlio mass 
of masonry of the side-walls, to convey the water from ihc up- 
per level to the cliamber. These culverts, in some cases, run 
the entire length of the side walls, on a level with the bottom 
of the chamber, from the lift-wall to the end of the lail-wall, and 
liave several outlets leading to the chamber. They arc arranged 
with two valves, one to close the mouth of the culvert, al; the 
upper level, the other to close the outlet from iJie chamber, to 
tlie lower level. This is, perhaps, one of the best arrangements 
for side culverts. They all present the same difficulty in making 
repairs when out of oi der, and they are moreover very subject 
to acc'dents. They are therefore on these accounts inferior to 
valves in the gates. 

719. It has also been proposed, to avoid the incofivcniencea 
of culvcrls, and the disadvantages of lift-walls, by suppressing 
the latter, and gradually increasing the depth of the upper level; 

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Co the bottom of the chamber. This method presents a saving 
ill the mass of masonr}', but the g.itcs will cost more, as the 
head and lail gates must be of the same height. It would en- 
tirely remove the objection to valves in the gates, as the ciirrcnt 
through thera, iri this case, would not be sufficiently strong tc 
injure the masonry. 

720. The bottom of the canal below the lock should be pro- 
tected by what is termed an apron, which is a covering of plank 
laid on a grillage, or else one of brush-wood and dry stone. The 
sides should also be faced with timber or dry stone. The length 
of this facing will depend on the strength of the current ; gene- 
rally not more thati from fifteen to thirty feet from the lock will 
require it. The entrance to the head-bay is, in some cases, 
Bimilarly protected, but this is unnecessary, as the current has 
but a very slight effect at that point. 

721. Locks constructed of timber and dry stcne, termed conv- 
posite-locks, are to be met with on several of the canals of the 
United States. The side walls are formed of dry stone carefully 
laid ; the sides of the chamber being faced with plank nailed to 
horizontal and upright timbers, which are firmly secured to the 
dry stone walls. The walls rest upon a platform laid upon heavy 
beams placed transversely to the axis of the lock. The bottom 
of the chamber usually receives a double thickness of plank 
1"he qiioin-posts and mitre-sills are formed of heavy beams. 

72'i. Lock Gates. A lock gate (Fig. 173) is composed of two 

leaves, each leaf consisting of a solid frame-work covered on 
the side towards the water with thick plank made water-tigliL 
The frame usually consists of two uprights, of several horizon- 
tal cross pieces let into the uprights, and sometimes a diagonal 
niece, oi brace, intended to keep the frame of an invariable 

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334 GANALC. 

form, is added. The upright, around which the leaf turns, te/iiisd 
the ^leozM or heel-post, is rounded off on the back to fit in tiie 
hollow quoin ; it is made slightly eccentric with it, so that it may 
turn easily without rubbing against the quoin ; its lower end rests 
on an iron gudgeon, to which it is fitted by a corresponding in 
dentation in an iron socket on the end ; the upper exti-emily is 
secured to the side walls by an iron collar, within which t!ie posi 
turns. The collar is so arranged that it can be easily fastened 
to, or. loosened from two iron bars, termed anchor-irons, which 
are firmly attached by bolts, or a lead sealing, to tlie top course 
of the walls. One of the anchor-irons is placed in a line with . 
the leaf when shu«, the other in a line with it when open, to re ■ 
sist most effectually the strain in those two positions of the gate. 
The oppncite upright, termed the mitre-post, has one edge bev- 
elled oft', to fit against the mitre-post of the other leaf of the 

723. A long heavy beam, termed a balance beam, from its 
partially balancing toe weight of the leaf, rests on the quoin 
posl^ to which it is secured, and is mortised with the mitre post. 
The balance beam should be about four feet above the top of the 
lock, lo be readily manoeuvred ; its principal use being to open 
and shut the leaf. 

724. The top cross piece of the gate should be about on a 
level wilh the top of the lock ; the bottom cross piece should 
swing clear of the bottom of the lock. The position of the in- 
termediate cross pieces may be made to depend on their dimen- 
sions ; if they are of the same dimensions, tiiey should be placed 
learer together at the bottom, as the pressure of the water is 
there greatest ; but, by making them of unequal dimensions, 
they may be placed at equal distances apail ; this, however, is 
not of much importance except for large gates, and considerable 
depths of water. 

The plank may be arranged either parallel to the uprights, or 
parallel lo the diagonal brace ; in the latter position they will act 
with the brace to preserve the form of the frame. 

725. A wide board supported on brackets, is often affixed to 
the gates, both for the manceuvre of the machinery of the valves, 
and to serve as a foot bridge across the lock. The valves are 
small gates which are arranged to close tlie openings made in 
the gales for letting in, or drawing oif the water. They are ar- 
ranged to slide up and down in grooves, by the aid ol a rack and 
pinion, or a square screw ; or they may be made to open or shut 
bv turning on a vertical axis, in wliich case they are termed pad- 
dle gales. The openings in the upper gales are made becwe(!ii 
the two lowest cross pieces. In the lower gales the openinga 
are placed just below ihc surface of tlie water in'thc rea'^n. The 

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liss of the opening will depend on the lime in which t is n 
quired lo fill the lock. 

726. Accessory Works. Under this head are classed tliosa 
construclioibs which are not a part of the canal proper, although 
generally found necessary on all canals ; as the culverts for coii- 
vcymg off tiie water courses which intersect the line of the canal; 
the inlets of feeders for the supply of water ; aquciiucl bridj^cs, 
&c &c. 

727. Culverts. The disposition to be made of water courses 
intersecting the line of the canal will depend on their size, the 
character of their current, end the relative positions of the canal 
and stream. 

Small biooks which lio lower than the canal may be conveyed 
under it ihrOL-gb' an ordinary culvert. If the level of the canal 
and brook is naarly the same, it will then be necessary to make 
the culvert in the shape of an inverted syphon, and it is therefore 
termed a broken-back culvert. If the water of the' brook is 
generally limpici, and its current gentle, it may, in the last case, 
be received into the canal. The communication of the brook, or 
feeder, with the canal, should be so arranged that the water may 
be shut off, or let in at pleasure, in any qiiantity desired. For 
this purpose a cut is made through the side of the canal, and the 
sides and bottom of the cut are faced witii masonry laid in hy- 
draulic mortar. A sliding gate, iitted irto two grooves made in 
the side walls, is mano>uvred by a rack end pinion, so as to reg- 
ulate the quantity of walei to be let in. The water of iJie feeder, 
or brook, shoula first be received in a basin, or reservoir, near 
the canal, where it may deposite its sediment before it is drawn 
off. In cases where the line of the canal is cossed by a torrent, 
which brings down a large quantity of sand, pebbles, &c., it may 
be necessary to make a permanent structure over the canal, form- 
ing a channel for the torrent ; but if the discharge of the torrent 
is only periodical, a moveable chrnnsl may be arranged, for tlie 
same purpose, by constructing a boat with a deck and sides to 
form the water-way of the torrent. The boat is kept in a recess 
in the near the point where it i^ used, and is floated lo its 
posilion, and sunk when wanted. 

728. Aqueducts, ^c. When the lir.e of the canal is inlersect- 
ed by a wide water-course, the communication between the two 
shores must be effected cither by a canal pqueduct bridge, or by 
tlic boats descending from the canal inio the stream. As the 
construction of aqueduct bridges has airosdy been considered 
nothing farther on this point need here be iu^'ded. The expe- 
dient of crossing the stream by the boats may be attended with 
manv grave inconveniences in water courses liable to fi'e.ihets, 
or to considerable variations of 'evel at different seasons. In 


tliese cases 'ooks. must be so iiringed on each sioe, wliere the 
canal enltis ihe stream that boits may pass fiom the onu to the 
other under til circumitances of difieience of level between the 
two Tlic locks and the poilions of the canal which join the 
stream must be secured against damage from freshets by snita- 
ble embankments. , and, when the summer water of the stream 
IS so low ll at the navigation w ouM he impeded % dam across 
the stream will be requisite losecire an adequate depth of water 
during this epoch 

729 Crnnl Biilges Bridges for roo. Is ovei a ca lal termed 
canal hitdges, are constructed like other stiuctuies oi tlie same 
kind. In planning them the engineer should endeavor to give 
sufficient height to the bridge to prevent those accidents, of bul 
too frequent occurrence, from persons standing upright on tlie 
deck of the passage-boat while passing under a bridge. 

730. Waste'Wier. Waste-wiers must bs made along the 
levels to let off the surplus water. The best position for them 
is at points where they can dischai'ge into natural water courses. 
The best arrangement for a wasfe-wier is to make a cut through 
the side of the canal to a level with the bottom of it, so that, in 
case of necessity, the waste-wier may also serve for draining the 
level. The sides and bottom of the cut must be faced with ma- 
sonry, and have grooves left in them to receive stop-plank, or a 
sliding gate, over which the surplus water is allowed to flow, 
under die usual circumstances, but which can be removed, if il 
be found necessary, either to let off a larger amount of water, oi 
to draiu the level completely. 

731. Temporary Dams. In long levels an accident happen- 
ing at any one point might cause serious .injury to the navigation, 
besides a great loss of water. To prevent this, in some meas- 
ure, the width of the cana! may be diminished, at several points 
of a long level, to the width of a lock, and the sides, at these 
points, may be faced with masonry, arranged with grooves and 
atop-planlts, to form a temporary dam for shutting off the water 
on either side. 

732. Tide, or Guard Lock. The point at which a canal en- 
ters a river requires to be selected with judgment. Generally 
speaking, a bar will be found in the principal water couras at, 
or below, tlie points where it receives its affluents. When the 
canal, therefore, follows the valley of an affluent, its outlet 
should be placed below the bar, to render its navigation perma 
iiently secure from obstruction. A large basin is usually formed 
at the outlet, for the convenience of comm_erce : and the entrance 
from this basin to the canal, or from the river to the basin, is ef- 
fected by means of a lock with double gates, so arranged that a 
boat can be passed either way, according a'j the level in the onp 

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rANALS. 337 

IS higlier or lower tlian thai in the oilier, A lock so arranged ia 
termed a tide, or guard lock, from its uses. The position of 
llie tail of this lock is not indifferent in all cases where it fonns 
the outlet to the river ; for were the tail placed up stream, it 
would be more difilciilt to pass in or out, than if it were down 

733. The general dimensions of canals and their locks in this 
country and in Europe, with occasional exceptions, do not differ 
in Jtnv considerable degree. 

English Canals. Two classes of canals are to be met with in 
England, differing materially in their dimensions. The following 
are the usual dimensions of the cross section of the largest size, 
and those of tlieir locks : — 

Width of section at the water level, from 36 to 40 feet. 
Width at bottom, .... 24 " 

Depth, 5 " 

Length of lock between mitre-sills, 75 to S5 '■ 

Width of chamber, . . . . 15 " 

Tlie Caledonian canal, in Scotland, wliich connects Loch-Eil 
on the Western sea with Murray Firth on the Eastern, is re- 
markable for its size, which will admit of the passage of frigates 
of the second class. The following are the principal dimensions 
of the cross section of the canal and its locks : — 

Width of canal at the water level, . 110 feet. 

Width at bottom, . . . . 60 " 

■ Depth of water, .... 20 " 

Width of berm, 6 " 

Length of lock between mitre-slllii, . 180 " 

Width of chamber at top, . . . 40 '' 

Lift of lock, 8 " 

The side walls of the locks are bnilt with a curved batter, 
they are of the uniform thickness of 6 feet, and are strengthened 
by counterforts, placed about 15 feet apart, which are 4 feet wide 
and of the same thickness. The bottom of the chamber is form 
ed with an inverted arch. 

French Canals. In Franco the following uni^'^rm system has 
been eslabhshed for the dimensions of canals and their locks ■— - 
Width of canal at water level, . . 53 feet. 

Width at bottom, . . . . 33 to 3f> " 

Depth of water, 5 '* 

Length of lock between mitre-sills, . 115 " 

Width of lock, 17 " 

The boats adapted to these dimensions are from 105 to 108 
feet long, IGj feet across the beam, and have a draught of 4 feet. 

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The English and Frencli canals usually have but one tow-path 
which is from 9 lo 12 feet wide, and about 3 feet above the wa 
ter level. The side of the tow-path embankment next to tht 
waler-way is uaually faced either with dry stone, masonry, oi 
planlis retained by snort piles. 

Canals of the United States and Canada. The originiil di 
mensions of the New- York Erie canal and its lacks, have been 
generally adopted for similar works subsequently constnicled in 
most of tlic other states. The dimensions of this canal and it 
locks are as follows :— 

Width of canal at top, .... 40 feet. 
Width at bottom, .... 28 " 

Depth of water, -4 

Width of tow-paUi 9 to 12 

Length of locks between mitrc-sills, . 90 

Width of locks, .... 10 

For the enlargement of the Erie canal, tlie following dimen- 
sions have been adopted : — 

Width of canal at top, .... 70 feet. 

Width at bottom 42 " 

Depth of water, 7 " 

Width of tow-path, . . . . , 14 " 

Length of locks between milrc-sills, . 110 " 

Width of lock at top, . . . 18.8" 

Width of lock at bottom, . , . 14.0 " 

Lift of locks, 8 " 

Between the double locks a culvert is placed, which allowa 
the water to flow from the level above the lock to the one below, 
when there is a surplus of water in the former. 

A well, or pit, is left between the lift-wall of the lock and the 
cross wall which retains llie earth at the head of the lock to the 
level of the bottom of the canal. This pit, receiving the deposite 
of sand and gravel brought down by the current, prevents it from 
obstrucUng the play of the gates. 

On the Chesapeake and Oliio canal, the cross seclion of the 
canal below Harper's Ferry lias received the following dimen- 

Widih of canal at top, .... 60 feel. 

' Width at bottom, .... 42 " 

Depth of water, fl " 

Length of locks between mitre-sills, . 00 " 

Width of locks, 15 " 

The following dimensions have been adopted on the JamBi 
river canal, in Virginia : — 

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Width of canal at top, .... 50 feet. 
Width at bottom, .... 30 " 

Depth of water, 5 " 

Length of locks, .... 100 " 

Width of locks 16 " 

The Rideau canal, wliich connects Lake Ontario- with the 
River Ottawa, is arranged for steam navigation. A considerable 
portion of tiiis line consists of slack-water navigation, formed by 
connecting the natural water-courses between the outlets of the 
canal. The length of the locks on this canal is 1 34 feet between 
the mitre-sills, and their widtli 33 feet. 

The Welland canal, between lakes Erie and Ontario, as origin- 
ally constructed, received the following dimensions : — 

Width of canal at top, .... 56 feet. 
Width at bottom, .... 24 " 

Depth of water, 8 " 

Length of locks betwen mitre-sills, . 110 " 

Width of locks 22 " . 

The canals and locks made to avoid the dangerous rapids ol 

the St. Lawrence are in all respects among the largest in tiie 

world. The following arc the dimensions of the portion of the 

canal and the locks between Long Sault and Cornwall : — 

Width of canal at top, .... 132 feet. 

Width at bottom, .... 100 " 

Depth of water, 8 " 

Widlh of tow-path, . . . . 13 *' 

Length of locks between mitre-sills, . 200 " 

Width of locks at top, . . . 5fi.6 " 

Width of locks at bottom, . . . 43 " 

A berm of 5 feet is left on each side between the water way 

aiid tiie foot of the interior slope of the tow-path. Tiie height 

of the tow-path is 6 feet above the berm. By increasing the 

depth of water in t!ie canal to 10 feet, the water line at top can 

be increased tc 150 feet. 

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73'i. N itural features of Rivers, All rivers present ihe sama 
natural features and phenomena, which are more or less strongly 
marked and diversified by the character of the region througn 
which they flow. Taking their rise in the highlands, and gradu- 
ally descending thence to some lake, or sea, their beds are mod- 
ified by the nature of the soil of the valleys in which they lie, 
and tlic velocities of their currents are affected by the same 
causes. Near their sources, their beds are usually rocky, irregular, 
narrow, and steep, and their currents are rapid. Approaching 
their outlets, the oeds become wider and more regular, the de- 
clivity less, and tlie current more genUe and uniform. In the 
upper portions of the beds, their direction is more direct, and the 
obstructions met with are usually of a permanent chai'acter, aris- 
ing from the inequalities of the bottom. In the lower portions, 
the beds assume a more tortuous course, winding tlirough theit 
valleys, and forming those abrupt bends, termed elbows, which 
seem subject to no lixed laws ; and here are found those ob- 
structions, of a more changeable character, termed bars, wliich 
are caused by deposites in the bed, arising from the wear of the 
banks by the current. 

735. The relations which are found to exist between the cross 
section of a river, its longitudinal slope, the nature of its bed, 
and its volume of water, are termed tJie. regimen of the river. 
When these relations remain permanently invariable, or change 
insensibly with time, the river is said to have &fixed regimen. 

736. Most rivers acquire in time a fixed regimen, although 
periodically, and sometimes accidentally, subject to changes 
from freshets caused by the melting of snow, and heavy falls of 
rain. These variations in the volume of water thrown into the 
bed, cause corresponding changes in the velocity of the curreiil, 
and in the form and dimensions of the bed. These changes wil^ 
depend on the character of the soil, and the width of the valley. 
In narrow I'alleys, where the banks do not readily yield to the 
action of the current, the effects of any variation of velocity will 
only be temporarily to deepen the bed. In wide valleys, where 
the soil of the banks is more easily wor-n by the current than the 
bottom, any increase in the volume of water will widen the bed ; 
and if one bank yields more than the other, an elbow will be 
formed, and the position of the bed will be gradually shifted to- 
ivarils the concave side of the elbow 

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nivsRS. 341 

797. Tiio formation, of elbows occasions also variations in the 
iepth and velocity of the water. The greatest depth is found 
at the concave side. At tlie straight portions which connect two 
elbowa, the depth is found to decrease, and the velocity «f the 
current to increase. Tlie bottom of the bed thus presents a se- 
ries of undulations, forming shallows and deep pools, with rapid 
*nd gentle currents, 

738. Bars are. formed at those points, whore from any cause 
the velocity of the current receives a sudden check. The 
particles suspended in the water, or borne along over the bottom 
of the bed by the current, are deposited at these points, and con- 
tinue to accumulate, until, by the gradual filling of the bed, the 
Water acquires sufficieot velocity to bear farther on the particles 
that reach the bar, when the river at this point acquires and re- 
tains a fixed regimen, until disturbed by some new cause. 

739. The points at which these. changes of velocity usually 
take place, and near wliich bars are found, are at the junction of 
a river with its affluents, at those points where the bed of the river 
receives a considerable increase in width, at the straight portions 
of the bed between elbows, and at the outlet of the river to the 
sea. The character of the bars will depend upon that of the soi, 
of the banks, and the velocity of the current. Generally speak- 
ing, the bars in the upper portions of the bed will be composed 
of particles which are larger ttian those by which they are formed 
lower down. These accumulations at the mouths of large rivers 
form in time exl a e s! Hows and great obstructions to the 
disciiarge of the wa e d g h seasons of freshets. The river 
then, not finding a suffic ou let by the ordinary channel, ex- 
cavates for itself o he s log! the most yielding parts of the 
deposites. In thi ma n a e med tliose features which char- 
acterize the outle f ma y la ^e rivers, and which are termed 
delta, after .the nan eg he peculiar shape of the outlets 
of the Nile. 

740. River Imp Tl ere is no subject lliat falls witli- 
in the province of 1 e n art, that presents greater diffi- 
culties and more un an u than the improvement of rivers. 
Ever subject to'i p rtant hanges in their regimen, as tiie re- 
gions by which 1 y e f e 1 are cleared of tiieir forests and 
Drought under cul a on o e entury sees them deep, flowing 
with an equable cu en a d 1 able only to a gradual increase iu 
rolume during the a a ns f f hets ; while the next finds their 
beds a prey to sudden and great fresliets, which leave them, after 
their violent passage, obstructed by ever shifting bars and elbows. 
Besides these revolutions brought about in the course of j'ears, 
every obstruction temporarily placed in the way of the current 
every attempt to guard one point from its action by any artificial 

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means, inevi:ablv pioduces some coiresponding change at another, 
which can ssldom lie foreseen, and for which ihe rcmody applied 
may prove but a new cause of harm. Thus, a bar remOTed fiom 
one point is foiirid gradually to form lower down ; one bank pro- 
tected from the current's force transfers its action to the opposite 
one, on any increase of volume from freshets, widening the bed 
and frequently giving a new direction to the channel. OwJng te 
these ever varying causes of change, the best weighed plans of 
river improvement sometimes result in complete failure. 

741. In forming a plan for a river improvement, the principal 
objects to be considered by the engmeer, are, Ist, The means to 
be taken to protect the banks from the action of the current. 
2(i, Those to prevent inundations of the surrounding country. 
3d, The removal of bars, elbows, and other natural obstructions 
to navigation. 4th, The means to be resorted to for obtaining a 
suitable 'depth of water for [ oats, of a proper tonnage, for the 
trade on the river. 

742. Means for protecting the banks. To protect the banks, 
either the velocity of the cui-rent in-shore must be decreased so 
as to icBsen its action on the soil ; or else a facing of some ma- 
terial sufficiently durable to resist its action must be employed. 
The former method may be used when the banks are low and 
have a gentle declivity. The simplest plan for this purpose con- 
sists eitiicr in planting such shrubbery on the declivity as will 
thrive near water ; or by driving down short pickets and interla- 
cing them witli twigs, forming a kind of wicker-work. These con- 
stnictions break tlie force of the current, and diminish its velocity 
near the shore, and thus cause the water to deposite it'3 finer par- 
ticles, which gradually fill out and strengthen the banks. If the 
banks are high, and are subject to cave in from the action of the 
current on their base, they may be either cut down to a gentle 
dechvily, as in the last case ; or else they may receive a slope 
of nearly 45°, and be faced with dry stone, care being taken to 
secure the base by blocks of loose stone, or by a facing of brush 
and stone laid in alternate layers. 

743. Measures against inundations. At the points in the 
course of a river where inundations are to be apprehended, the 
water-way, if practicable, should be increased ; all obstructions 
to the free discharge of the water below the point should be re- 
moved ; aad dikes of earth, usually termed levees, should be 
raised on each side of the river. By increasing the water-way a 
'emporary improvement only will be effected ; for, except in the 
aeason of freshets, the velocity of the current at this point will be 
eo much decreased as to form deposites, which, at some future 
day, may prove a cause of damage. In confining the water be- 
tween levees, two methods have been tried ; the one consists io 

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leaving a water wiiy strictly necessary for tin discharge of freslt- 
ets the otber in giving the stream a wide bed. The Po in Itaiy 
and [he Mississippi present examples of the 'ormer method; the 
effect of whicu m both cases has been to laise the bed of the 
stream <!o much that in many parts tlie water is habitually above 
tiie natural surface of the country, leaving it exposed to seriona 
nunditiona siiould the levees give way. The other method 
flds been tried on the Loire in France, and observation haa 
proied that the general level of the bed has not sensibly risen 
foi t long scries ut years ; but it haa been found that tlie bars, 
which aie formed after each freshet, are shifted constantly by 
;lie next, so that when ihe waters have subsided to their ordinary 
state, ilio navigation is extremely intricate from this cause. Other 
means have been tried, such as opening new channels at the ex- 
posed points, or building dams above thorn to keep the water 
back; but they have all been found to afford only a temporary 

744. Elbows. The constant wear of the bank, and shifting 
of the channel towards the concave side of elbows, have led to 
various plans for removing tiie inconveniences which they pre- 
sent to navigation. The method which has been most generally 
tried for this purpose consists in building out dikes, termed losng"- 
Jams, from the concave side into the stream, placing them either 
at right angles to the thread of iho cnnant. of obfiqiiQly down 
Ktf^p.iR, so as to deflect the current towards the opposite shorfi 

ffe. 174- -Iteprewnfs a eeotion of the timber wine-damson tiie P< 

on the inolined pieces of the iit». 
ti ami 1 1, iuolioed ttuxa of tlia ilaiii, tlie flrat maklug an augl 

of S3" ffiththeliorizou. 

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Wing-dams are usually constructed either of blocks of slono 
rjf crib-work formed of heavy timbers filled in with broken stone 
or of alternate layers of gravel and fascines. Within a few years 
back, wing-dams, consisting simply of a series of vertical frames, 
or ribs, (Fig. 174,) strongly connected together, and covered on 
the up-stream side by thick plank, which present a broken in- 
clined plane to the current, the lower part )f which is less steep 
than the upper, have been used upon the Po, with, it is stated, 
complete success, for arresting the wear of a bank by tlie cur- 
rent. These dams are placed at some di&tance above the point 
to be protected, and their plan is slightly convex on the up-strei.m 

Wing-dams of the oixlmary form and construction are now 
regarded, from the experience of a long series of years on the 
Rhine, and some other rivers in Europe, as little serviceable, if 
not. positively hurlful, as a river improvement, and the abandon- , 
ment of theiruae has been strongly urged by engineers in France, 

The action of the current against (he side of the dam causes 
whirls and counter-currents, which are found to undermine the 
base of the dam, and the bank adjacent to it. Shallows and bars 
are formed in tlie bed of the stream, near the dam, by the debris 
borne along by the current after it passes the dam, giving very 
frequently a more tortuous course to the channel than it had na- 
turally assumed in the elbow. The best method yet found of 
arresting the pregress of an elbow is to protect tlie concave bank 
by a facing of dry stone, formed by throwing in loose blocks of 
stone along the foot of the bank, and giving them the slope they 
naturally assume when thus thrown in, 

745. Elbows upon most rivers finally reach that state of de- 
velopment in which the wear upon the concave side, from the 
action of the current, will be entirely suspended, and the regi- 
men of the river at these points will remain stable. This state 
will depend upon the nature of the soil of the banks and bed, 
and the character of the freshets. From observations made upon 
the Rhine, it is stated that elbows, with a radius of curvature of 
nearly 3000 yards, preserve a fixed regimen ; and that the banks 
of those which have a radius of about 1500 yards are seldom 
injured if properly faced. 

746. Attempts have, in some cases, been raadc to shorten and 
straighten the course of a river, by cutting across the tongue of. 
land that forms the convex bank of the elbow, and turning the 
water into a new channel. It has generally been found that the 
stream in time forms for itself a new bed of nearly the same cliar 
KCter as it originally had 

747. Bars. To obtain a suilicient depth of water over bars, 
Ihe deposite musl either be scoojiod up by machinery, and b« 

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RIVERS. 345 

conveyed away, or be removed by giving an increased velccily 
to the current. When the latter plan is preferred, an artificial 
channel ia furmed, by contracting the natural way, confining il 
between two low dikes, which should rise only a little above the 
ordinaiy level of low water, so that a sufficient outlet maybe left 
for tlie water during tlie season of freshets, by allowing it to flow 
over the dams. 

If the river separates into several channels at the bar, dams 
shouJd be built across all except the main channel, so that by 
throwing the whole of the water into it the effects of the current 
may be greater upon the bed. 

The longitudinal dikes, between which the main channel is 
confined, should be placed as nearly as practicable in ike direc 
tion which the channel has naturally assumed. If it be deemed 
advisable to change the position of the channel, it should be shift- 
ed to that side of the bed which will yield most readily to the 
action of tlie current. 

748. In situations where large reservoirs can be formed near 
ihe bar, the water from them may be used for removing it. Foi 
this purpose an outlet is made from the reservoir, in the direction 
of tlie bar, which is closed by a gate that turns upon a vertical 
axis, and is so arranged tliat il can be suddenly thrown open to 
let off the water. The chase of water formed in this way sweep- 
ing over the bar will prevent the accumulalion of deposites upon 
it. This plan is frequently resorted to in Europe for the removal 
of deposites that accumulate at the mouth of harbors in those lo- 
calities where, from the height to which the tide rises, a great 
head of water can be obtained in the reservoirs. 

749. In the improvement of the mouths of rivers which empty 
into the sea through several channels, no obstruction should ha 
placed to the free ingress of the tides through all the channels. 
If the main channel is subject to obstiuctions from deposites, 
dams should be built across the secondary channels, which may 
be so arranged with cuts through them closed by gates, that the 
flood-tide will meet with no obstruction from the gates, while the 
ebb-tide, causing the gales to close, will be forced to recede 
ihrough the main channel, which, in this way, will be daily 
scoured, and freed from deposites by the ebb current. The same 
object may be effected by building dams without inlets across 
the secondary channels, giving them such a height that at a cer- 
tain stage of the flood-tide, the water will flow over them, and 
fill the channels above the dams. The portion of water thus 
dammed m will be forced ihrough the main channel at the ebb. 

750. When the bed is obstructed by rocks, it may be deepaned 
liy blasting the rocks, and removing the fragments with the as< 
gistancc 111 ihe diving-bell, and other machinery. 


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843 RiVEES. 

75i. In some of our rivers, obstructions of a very dangerous 
tfl2,racter to boats are met with, in the trunks of iirgc trees 
which arc imbedded in the bottom at one end, wliile the other ia 
near the surface ; they are termed snags and sawyers by the 
boatmen. These obstructions have been very successfully re 
moved, within late years, by means of machinery, and by pro- 
pelling two heavy boats, moved by steam, which are connected 
by a Etrong beam across their bows, so that the beam will strike 
tUe snag, and either break it oflf near the bottom, or uproot it 
Other obstructions, termed rafts, formed by the accumulation of 
drift wood at points of a river's course, are also found in somt* 
of our western T! 1 P f ' ^J 

cutting through 1 m 1 y 1 h I b f d 


752. Shck-W N g VI 1 1 d p I f 

water in a rive & fid 1 f b f 1 

slack-water, oil ] dd m g d Tl 

consisU hi div d h 1 bl p d bj 

forming dams 1 j 1 w h p d Id 

and by passing P ^ 1 b 1 k 1 d f 

the dams. 

753. The po f 1 I m d 1 1 11 

depend upon tl 1 1 I bj 1 ! 

it will generally be advisable to place the dams at the widest 
parts of the bed, to obtain tJie greatest outlet for the water over 
the dam. The dams may be built either in a straight line be- 
tween the banks and perpendicular to the thread of the current, 
or they may be in a straight line oblique to the current, or their 
plan may be conves, the convex surface being up stream, or it 
may be a broken line presenting an angle up stream. The three 
last forms offer a greater outlet the first to the water that 
flows over the dam, but are more liable to cause injuiy to the 
bed below llie stream, from the oblique direction which the cur- 
rent mjv receive, arising from the form of the dam at top. 

75 1 . The cross section of a dam is usually tr^apezoidal, the 
face up-stream being inclined, and the one down-stream either 
veilicai or inclined. When the down stream face is vertical, the 
velocity of the water which flows over the dam is destroyed by 
the shock against the water of the pond below the dam, but 
whirls are formed which are more destructive to the bed than 
would be the action of the currentiipon it along the inclined face 
of a dam. In all cases the sides and bed of the stream, for some 
distance below the dam, should be protected from the action of 
llie current by a facing of dry stone, timber, or any other con< 
Btruction of sufficient durability for the object in view. 

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RIVERS. 847 

755. The dams should receive a sufEcient height only ts 
maintain the requisite depth of water in the ponds for the pui 
Boses of nai'igation. Any material at hand, offering sufficient 
durability against the action of the water, may be resorted to in 
their construction. Dams of alternate layers of brush and gravel, 
!vith a facing of plank, fascine.s, or dry stone, answer very well 
:n gentle currents. If the dam is exposed to heavy freshets, to 
shocks of ice, and other heavy floating bodies, as drift-wood, it 
would be more prudent to form it of dry stone entirely, or of 
crib-work filled with stone ; or, if the last material cannot be ob- 
tained, of a solid crib-work alone. If the dam is to be made 
water-tight, sand" and gravel in sufficient quantity may he thrown 
in against it in the upper pond. The points where the dam joina 
the banks, which are termed the roots of the dam, require par- 
ticular attention to prevent the water from filtering around them. 
The ordinary precaution for this is to build the dam some dis ■ 
tance back into the banks. 

756. The safest means of communication between the ponda 
is by an ordinary lock. It should be placed at one extremity of 
the dam, an excavation in the bank being made for it, to secure 
it from damage by floating bodies brought down by the current. 
The sides of the lock and a portion of the dam near it should be 

aised sufficiently high to prevent iheni from being overflowed 
by the heaviest freshets. When the height to which the freshets 
rise is great, the leaves of the head gates should be formed of 
two parts, as a single leaf would, from its size, be too unwieldy ; 
the lower portion being of a suitable height for the ordinary man 
ceuvres of the lock ; the upper, being used only during the fresh- 
ets, are so arranged that their bottom cross pieces shall rest, 
when the gates are closed, against the top of the lower portions. 
All arrangement somewhat similar to this may be made for the 
tail gates, when the lifts of the locks are great, to avoid the diffi 
culty of manosuvring very high gates, by permanently closing 
the upper part of the entrance to tiie lock at the tail gates, either 
by a wall built between the side walls, or by a permanent frame- 
work, below which a sufficient height is left for the boats to pass. 

757. A common, but unsafe method of passing from one pond 
to another, is that which is termed fiasfiing ; it consists of a 
sluice in the dam, which is opened and cldsed by means of a 
gate revolving on a vertical axis, which is so arranged that it can 
be manceuvred with ease. One plan for this purpose is to divide 
the gale into two unequal parts by an axis, and to place a valve 
of such dimensions in the greater, that when opened the surface 
against which the water presses shall be less than that of the 
smaller part. The play of the gate is thus rendered very simple ; 
when the valve is shut, the pressure of water on the larger but. 

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848 RIVEKS. 

face closes it against the sides of the sluice ; when the valve u 
opened, the gate swings ro\ind and takes a position in the dirct- 
lion of the current. Various other plans for flashing, on sirr.Qsjr 
principles, are to be met with. 

758. When the obstruction in a river cannot be overcome bj 
any of the preceding means, as for example in those considerable 
descents in the bed known as rapids, wliere the water acquires 
a velocity so great that a boat can neither ascend nor descend 
with safety, resort must be had to a canal for the purpose of 
uniting its navigable parts above and below the obstruction. 

The general direction of the canal will be parallel to the bed 
of the river. In some cases it may occupy a part of the bed by 
forming a dike in the bed parallel to the bank, and sufficiently far 
from it to give the requisite width to the canal. Whatever posi- 
tion the canal may occupy, every precaution should be taken to 
secure it from damage by freshets. 

759. A lock will usually be necessary at each extremity of the 
canal where it joins the river. The positions for the extreme locks 
should be carefully chosen, so that tbe boats can at all limes en- 
ter tliem with ease and safety. The locks should be secured by 
guard gates and other suitable means from freshets ; and if they 
are liable to be obstructed by deposites, arrangements should be 
made for their removal cither by a chase of water, or by ma- 

If the river should not present a sufficient depth of water at 
all seasons for entering the canal from it, a dam will be required 
at some point near the lock to obtain the depth requisite. 

It may be advisable m some cases, mstead of placing the ex. 
tremc locks at the outlets of the canal to the river, to form a ca- 
pacious basin at each ex.tremity of the canal between the lock 
and river, where the boats can he in safety. The outlets from 
the basins to the rivers may either be left open at all limes, or 
else guard gates may be placed at tliem to shut off the wate? 
during freshets. 

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760. The following subdivisions may be made of tlie works 
belonging lo this class of improvements. 1st. Arlificial Road- 
steads. 2d. The worlcs required for natural and artificial Har- 
■bors. 3d. The works for the protection of tlie seacoast against 
the action of the sea. 

761. Before adopting any definitive plan for the improveraoni 
of the seacoast at any point, the action of the tides, currents, and 
waves at that point must be ascertained. 

703. The theory of tides is well understood ; their rise and 
duration, caused by the attraction of the sun and moon, are also de- 
pendent on the strength and direction of the wind, and the confor- 
mation of the shore. Along our own seaboard, the highest tides 
vary greatly between the most southern and northern parts. At 
Eastport, Me,, the highest tides, when not affected by the wind, 
vary between twenty-five and thirty feet above the ordinary low 
water. At Boston they rise from eleven to twelve feet above 
the same point, under similar circumstances ; and from New- 
York, following the line of the seaboard to Florida, they seldom 
rise above five feet. 

763. Currents arc principally caused by the tides, assisted, in 
some cases, by the wind. The theorj' of their action is simple. 
From the main current, which sweeps along the coast, secondary 
currents proceed into the hays, or indentations, in a line more or 
less direct, until they strike some point of the shore, from which 
they are deflected, and frequently separate into several others, 
the main branch following the general direction wliicli it had 
when it struck the shore, and the others not unfrequently taking 
an opposite direction, forming what are termed counter currents, 
and, at points where the opposite currents meet, that rotary mo- 
tion of the water known as whirlpools. The action of currents 
on the coast is to wear it away at those points against which 
they directly impinge, and lo transport the debris to other points, 
thus forming, and sometimes removing, natural obstructions to 
navigation. These continual changes, caused by cun-ents, make 
it extremely difficult to foresee their effects, and to foretell the 
consequences which will arise from any change in the directioot 
or the intensity, of a current, occasioned by artificial obstacles. 

764. A good theory of waves, wiiich shall satisfactorily ex- 
plain all their phenomena, is still a desideratum in science. It 
IS known that they are produced by 'vinds acting on the surface 



of ths sea ; biit how far ihis action extends below the surface 
and what are its effects at various depths, are questions that re- 
main to be answered. The most commonly received theory is^ 
that a wave is a simple oscillation of the water, in which each 
partidle rises and falls, in a vertical line, a certain distance during 
each o3ciliation, without receiving any motion of translation in a 
horizontal direction. It has been objected to this theory that it 
tails to explain many phenomena observed in connection with 

In a recent French work on this subject, its author. Colonel 
Emy, an engineer of high standmg, combats the received llieory ; 
and contends that the particles of water receive also a motion 
of translation horizontally, which, witli that of ascension, causes 
the particles to assume an orbicular motion, each particle de- 
scribmg an orbit, which he supposes to be elliptical. He farther 
contends, that in this manner the particles at the surface com- 
municate their motion to those just below them, and these again 
to the next, and so on downward, the intensity decreasing from 
the surface, without however becoming insensible at even very 
considerable depths ; and that, in this way, owing to the reaction 
from the bottom, an immense volume of water is propelled along 
the bottom itself, with a motion of translation so powerful as to 
overtiirow obstacles of the greatest strenglli if directly opposed 
to it. From this he argues that walls built to resist the shock of 
the waves should receive a very great batir at the base, and that 
this batir should be grsidually decreased upward, until, towards 
the top, the wall shouJd project over, thus presenting a concave 
surface at top to throw ilie water back. By adopting this form, 
he contends that the mass of water, which is roiled forward, as 
it were, on the bottom, when it strikes the face of the wall, will 
ascend along it, and thus gradually lose its momentum. These 
views of Colonel Emy have been attacked by other engineers, 
who have had opportunities to observe the same phenomena, on 
the ground that they are not supported by facts ; and the question 
still remains undecided. It is certain, from experiments made 
by the author quoted upon walls of the form here described, that 
they seem to answer fully their mtended purpose, 

765. Roadsteads. The term j oadstead la applied to an in- 
dentation of tlie coast, where 1 m y 1 1 n- 
chor under ali circumstances of w I If ! d s 
covered by natural projections f I 5 (5 p 1 e 
action of the winds and waves d h I d J k d n 
tlie contrary case, it is termed a p n d d 

The anchorage of open road d f n n a 

violent winds setting into them f 1 d ng 

high waves, wliich nre very 1 Ti c 

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remeJy applied in ihis case is to place an obstruclicn, near ihe 
entrance of the roadstead, to break t!ie force of the waves froir 
the sea. These obstruclions, termed breakwaters, are artificial 
islands of greater or less extent, and of variable fonn, according 
to the nature of the case, made by throwing heavy blocks of 
fltone into the sea, and allowing them to take their own bed. 

The first great work of this kind undertaken in modern limes, 
was the one at Cherbourg in France, to cover tlie roadstead it: 
front of that town. After some trials to break the effects of the 
waves on the roadstead by placing large conical shaped Struc- 
tures of timber filled with stones across it, whjch resulted in 
failure, as these vessels were completely destroyed by subsequent 
storms, the plan was adopted of forming a breakwater by throw- 
ing ill loose blocks of stone, and allowing the mass to assume the 
form produced by the action of the waves upon its surface. The 
subsequent experience of many years, during which this work 
has been exposed to the most violent tempests, has shown that 
the action of the sea on the exposed surface is not very sensible 
at this locality at a depth of about 20 feet below the water level 
of the lowest tides, as the blocks of stone forming this part 
of the breakwater, some of which do not average over 40 lbs. 
in weight, have not been displaced from the slope the mass 
first assumed, which was somewhat less than one perpendicular 
to one base. From this point upwards, and particularly between 
the levels of high and low water, the action of the waves has 
been very powerful at times, during violent gales, displacing 
blocks of several tons weight, tlirowiog them over the top of the 
breakwater upon the slope towards the shore. Wherever this 
part of the surface has been exposed the blocks of stone have 
been gradually worn down by the action of tlie waves, and tlie 
slope has become less and less steep, from year to year, until 
finallv the surface assumed a shghtly concave slope, which, at 
Bom£ points, was as great as ten base to one perpendicular. 

The experience acquired at this work has conclusively shown 
that breakwaters, formed of the heaviest blocks of loose stone, 
are always liable to damage in heavy gales when the sea breaks 
over tliem, and that the only means of securing them is by cov 
ering the exposed surface with a facing of heavy blocks of ham 
mered stone carefully set in hydraulic cement. 

As the Cherbourg breakwater is intended also as a military 
construction, for the protection of the roadstead against an ene- 
my's fleet, the cross section shown in (Fig. 175) has been adopt- 
ed for it. Profiting by the experience of many years' observation, 
t was decided to construct the work that forms the cannon battery 
of solid masonry laid on a thick and broad bed of belon. The 
top surface of the breakwater is covered with heitvv loose block* 

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of stone, and the foot of the wall on the face is protected by 
large blocks of irtificial stone formed of beton. The top of tlia 
battery is about 13 feet aboie the highest water level. 

The next work of the Itind was built to cover the roadstead of 
Plymouth in England. Its cross section was, at first, made with 
an interior slope of one and a half base to one perpendicular, and 
an exterior slope of only three base to one perpendicular ; but 
from the damage it sustained in the severe tempests in the 
winter of 1816-17, it is thought that its exterior slope was too 

A work of the same kind is still in process of construction on 
our coast, off the mouth of the Delaware, Tbe same cross sec- 
tion has been adopted for it as in the one at Cherbourg. 

All of these works were made in the same way, discharging 
the stone on the spot, from vessels, and allowing it to take its 
own bed, except for the facing, where, when practicable, the 
blocks were carefully laid, so as to present a uniform surface to 
the waves. The interior of the mass, in each case, has been 
formed of stone in small blocks, and the facing of very large 
blocks. It is thought, however, that it would be more prudent 
to form the whole of large blocks, because, were the exterior to 
suffer damage, and experience shows that the heaviest blocks yet 
used have at times been displaced by the shock of the waves, tha 
interior would still present a great obstacle. 

From the foregoing details, respecting (he cross sections of 
breakwaters, wliich from experiment have been found to answer, 
the proper form and dimensions of the cross section in similar 
cases may be arranged. As to tlie plan of such works, it must 
depend on tbe locality. The position of the breakwater should 
be chosen vnlh regard to the direction of the heaviest swells from 
the sea, Mo the roadstead, — the action of the current, and that 
of the waves. The part of the roadstead which it covers should 
afford a proper depth of water, and secure, anchorage for vessels 
of the largest class, during the moat severe storms ; and vessels 
should be able to double the breakwater under all circumstances 

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ol Wind and tide. Such a position should, moreover, be chosen 
[hat there will be no liability to obstructions being formed within 
■.he roadstead, or at any of its outlets, from the change in the 
■:uiTent which may be made by the breakwater. 

766. The dilEculty of obtaining very heavy blocks of atone, 
aS well as iheir great cost, has led to the suggestion of aubstitu 
ting for them blocks of artificial stone, formed of concrete, which 
can be made of any shape and size desirable. This plan lias 
been tried with success in several instances, particularly in a 
jetty or mole, at Algiers, constructed by the French government 
The beton for a portion of this work was placed in large boxes, 
the sides of which were of wood, shaped at bottom to correspond 
to the irregularities of the bottom on which the beton was to be 
spread. The bottom of the box was made of strong canvass tar 
red. These boxes were first sunk in the position for which they 
were constructed, and then filled with the beton. 

767. Harbors. The term harbor is applied to a secure an- 
chorage of a more limited capacity than a roadstead, and there- 
fore offering a safer refuge during boisterous weather. Harbors 
are either natural, or artificial. 

768. An artificial harbor is usually formed by enclosing a 
space on the coast between two aims, or dikes of stone, or of 
wood, termed _7'e files, which project into the sea from the shore, 
m such a way as to cover the harbor from the action of the wind 
and waves. 

769. Tlic plan of each jetty is curved, and the space enclosed 
by the two will depend on the number of vessels which it may 
be supposed will be in the harbor at the same time. The dis- 
tance between the ends, or heads, of the jetties, which forms the 
mouth of the harbor, will also depend on local circumstances ; 
it should seldom be less than one hundred yards, and generally 
need not be more than five hundred. There are certain winds 
at every point of a coast which are more unfavorable than others 
to vessels entering and quitting the liarbor, and to the tranquil- 
lity of its water. One of the jetties should, on this account, be 
longer than the other, and be so placed that it will both break 
the force of the heaviest swells from the sea into the mouth o* 
*he harbor, and facilitate the ingress and egress of vessels, by 
preventing them from being driven by the winds on the other 
jetty, just as they are entering or quitting the mouth. 

770. The cross section, and construction of a stone jetty differ 
m nothing flrom those of a breakwater, except that the jetty is 
usually wider on top, thirty feet being allowed, as it serves foi 
a wharf in unloading vessels. The head of tlie jetty is usually 
■nade circular, and considerably broader than the other parts, as 
!t, in some instances, receives a lighthouse, an.d a battery of ca»- 

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.154 SEACOAST im 

non. It 'should lie made with great care, of large blocks of slonfi 
well united by iron, or copper cramps, and the exterior courses 
should moreover be protected by fender beams of heavy timber 
to receive the shock of floating bodies. 

771. Wooden jetties are formed of an open framework of 
heavy timber, the sides of which are covered on the interior by 
a strong sheeting of thick plank. Each rib of the frame 
(Fig. 176) consists of two inclined pieces, which form the sides 

^of an upright centre piece, — and of horizontal clamping pieces, 
which are notched and bolted in pairs on the inclined and uprighl 
pieces ; the inclined pieces are farther strei^hened by struts, 
which abut against them and the upright. The ribs are con- 
nected by large string-pieces, laid horizontally, which are notched 
and bolted on tlie inclined jtieces, the uprights, and the clamping 
pieces, at their points of junction. The foundation, on which 
this framework rests, consists usually of three rows of large 
piles driven under the foot of the inclined pieces and the uprights. 
The rows of piles are firmly connected by cross and longitudinal 
beams notched and bolted on them ; and they are, moreover, 
firmly united to the framework in a similar manner. The inte- 
rior sheeting does not, in all cases, extend the entire length of 
the sides, but open spaces, termed clear-ways, are often left, te 

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me a fiee passage and spread lo tlie waves confined between 
3ia jetties, for the purpose of forming smooth water in the chan 
nel. If the jetties are covered at their back with earth, the cleai 
ways receive the form of inclined planes. 

I'he foundation of the jetties requires particular care, espe- 
cir.lly when llie channel between them is very nan-ow. Loose 
stone thrown around the piles is the ordinary construction used 
lor this purpose ; and, if it be deemed necessary, the bottom of 
the entire channel may be protected by an apron of brush and 
loose stone. 

The top of the jetties is covered witli a flooring of thick plank, 
which serves as a wharf. A strong hand railing should be 
placed on each side of the flooring as a protection against acci- 
dents. The sides of jetties have been variously inclined ; the 
more usual inclination varies between three and four perpendicu- 
lar to one base. 

772. Jetties are sometimes built out to form a passage to a 
natural harbor, which is either very much exposed, or subject to 
bars at its mouth. By narrowing the passage to the harbor be- 
tween tlie jetties, great velocity is given to the current caused 
by the tide, and this alone will free the greater part of ihe chan- 
nel from deposites. But at the head of the jetties a bar will, in 
ilmost every case, bo found to accumulate, from the current 
along shore, which is broken by tlie jetties, and from the dimin- 
ished velocity of the ebbing tides at this point. To remove these 
bars resort may be had, in localities where they are left nearly 
dry at low water, to reservoirs, ajid sluices, arranged with turn- 
ing gates, like those adverted to for river improvements. The 
reservoirs are formed by excavating a large, basin in-shore, at 
some suitable point from which the collected water can be di- 
rected, with its full force, on the bar. The basin wiil be filled 
at flood-tide, and when the ebb commences the sluice gales will 
be kept closed until dead low water, when they should all be 
opened at once to give a strong water chase, 

773. In harbors where vessels caiuiot be safely and conve- 
niently moored alongside of the quays, large basins, termed wei' 
docks, are formed, in which the water can be kept at a constant 
level. A wet-dock may be made either by an in-shore excavation, 
or by enclosing a part of the harbor with strong water-tight walls ; 
the first is the more usual plan. The entrance to llie basin may 
be by a simple sluice, closed by ordinary lock gates, or by means 
of an ordinary lock. With the first msthod vessels can cntet 
the baain only at high tide ; by the last they may be entered oi 
passed out at any period of the tide. The outlet of the iock 
should be provided with a pair of guard gates, to be shut againsi 
very high tides, or in cases of danger from storms. 

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774. Tlio construction of tlie locks for basins differs in notltirg 
in principle, from that pursued in canal locks. The greatest 
care wCl necessarily be taken to form a strong mass free from all 
' iger of accidents. The gates of a basin-lock are made convex 

towards the head of w 

gi I m m strength to resisi 

the great pressure up 

T g and mantEuvred 

differently from ordinary 

q n-post is attached 

to the side walls in th 

b foot of the mitre- 

post an iron or brass 

fa h runs on an iron 

roller way, and thus s 

leaf, relieving the 

collar of the quoin-po 

ra vould be otherwise 

thrown on it, besides g 

play. Chains are 

attached to each mitr 

f pressure of the 

water, and tlie gate is 

d means of windlasses 

to which the other end 


775. The quays of 
Both brick and stone 

ir y built of masonry, 
f ing at least should 

be of dressed stone. L 

m nay be attached to 

the face of the wall, t p 

brought in contact 

with the sides of the 

T tion of quay-walls 

should be fixed on the 

of other sustaining 

walla. It might be prudent to add buttresses to tlie back of the 
waL to strengthen it against the shocks of the vessels. 

770. Quay-walls with us are ordinarily made either by form- 
ing a facing of heavy round or square piles driven in juxtaposition, 
which are connected by 1 or zo tal p eces and see re 1 from the 
pressure of the earth hJIed in bel d them by It d t eg ; or, by 
placing the pieces h zontally j o each other a d securing 
them by iron bolts. La d ties a e se 1 to courteract the pres- 
sure of the earth or ri bb si wh c! s tl own behind them to 
form the surface of tie quaj A otler mode of co istruction, 
which is found to be strong and durable, is in use m our Eastern 
seaports. It consists in making a kind of crib-work of large 
blocks of granite, and filling in with eartli and stone rubbisn. 
The bottom course of the crib may be laid on the bed of the 
river, if it is firm and horizontal ; in the contrary case a strong 
grillage, termed a cradle, must be made, and be sunk to receive 
the stone work. The top of the cradle should be horizontal, and 
the bottom should receive the same slope as that of the bed, in 
order that when the stones are laid they may settle horizontally. 

777. Dikes. To protect the lowlands bordering the ocean from 
inundations, dikes, constructed of ordinary earth, and faced to- 
wards the sea with some material which will resist the action of 
the current, are usually resorted to. 

The Dutch dikes, by means of which a large extent of countrj- 
has been reclaimed and protected from the sea, are the moat re 

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niarkable structi les of tliis kind in existence. The cross section 
of those dikes is of a trapezoidal fonn, the width at top averaging 
from four to six feet, the interior slope being the same as the na- 
tural slope of the earth, and the exterior slope T&rying, according 
to circumstances, between three and twelve base to one perpendic- 
ular. The top of the dike, for perfect safety, should be about 
si's feet above the level of the hJD-hest spring tides although, in 

y places, they are only 
The earth for these dik 
t«een which and the foot I 
feet IS left, which aniweis f 
nou'ly faced, according to 1 
of the current and waves 1 
straw thatch is put on, and fi 
means ; in others, a layer f f 
and is strongly picketed to \ 
lowed to project out abou ! 
ceive a wicker-work form d by n 
the spaces between this i ' 
stone ; this forms a very d 

h ab 

h 1 1 

d h 

] 1 m 

ly d by p k 

/'h p k 
1 ! 

In h m 
k b ng fill d V 
bl 1 f 

e, be- 
1 is va- 
1 racter 

not only the action of the current, but, by its elasticity, the shocks 
of the heaviest waves. 

The foot of the exterior slope requires peculiar care for il» 
protection ; the shore, for this purpose, is in some places cover 
ed witli a thick apron of brush and gravel in alternate layers, to 
a distance of one hundred yards into the water from the foot of 
the slope. 

On some parts of the coast of France, where it has been found 
necessary to protect it from encroachments of the sea, a cross 
section has been given to the dikes towards the sea, of the same 
form as tlie one which the shore naturally takes from the action of 
the waves. The dikes in other respects are constructed and faced 
after the manner which has been so long in practice in HollaJid. 

778. Groins. Constructions, termed groins, are used when- 
ever it becomes necessary to check the effect of the current 
along the shore, and cause deposites to be formed. These are 
artificial ridges which rise a few feet only above the surface of 
the beach, and are built out in a direction either perpendicular 
lo that of the shore, or oblique to it. They are constructed ei- 
ther of clay, which is well rammed and protected on the surface 
by a facing of fascines or stones ; or of layers of fascines ; or of 
one or two rows of short piles driven in juxtaposition ; or any 
9ther moans that the locality may fumish may be resorted to ; 
the object being to interpose an obstacle, which, breaking tlie 
force of the current, will occasion a dcposite near it, and thtig 
gradually cause the sliore to gain upon tlie sea. 

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779, Sea-walls. When the sea encroaches upon llic lanJ 
forming a steep bluff, the face of which is gradually worn away 
a wall of masonrj' is the only meaus that will afford, a permanent 
protection against this action of the w^aves. Walls made for thia 
object are termed sea-walls. The face of a sea-wall should be 
constructed of the most durable stane in large blocks. The 
bacldng may be of rubble or of be ;o \. The whole work sho^ i.d 
be laid with hydraulic mortar. 

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Note A to Arts. Framing and Bridges , 

Tubular Frames qf Wrought Iron. — Except for the obvious applit^ition fo 
steam boilers, sheet iron had not been considered as suitable for etnicturea 
deiijanding great eirongtl:, from its apparent deficiency in rigidity; and 
allJiough tlie principle of gaining strength by a proper distribution of the 
material, and of giving any desirable rigidity by eonibinalJons adapted to the 
object in view, were at every moment acted upon, from the ever-increasing 
demands of the art, engineers seem not to have loolied upon sheet iron as 
suited to such purposes, until an extraordinary case occurred which seemed 
about to batfle all tho means hitherto employed. The occasion arose when it 
became a queslion to throw a bridge of rigid material, for a railroad, across 
the Menai Straite; suspension systems, from their llexibility, and some actual 
fiulures, being, in the opinion of Iho ablest European engineers, unsuitable for 
this kind of communication, 

Robert Stephenson, who for some years back has held tho highest rank 
among. Engli^ engineers, appears, from undisputed testimony, to have been 
the first to entertjtin the novel and bold idea of spanning the Strait by a tabe 
of sheet iron, supported on piers, of sufficient dimensions for the passage 
within it of the usual trdns of riuiroads, Tho preliminary experiments for 
testing the practicability of this conception, and tho working out the details of 
its eneontiou, were left chiefly in the hands of Mr. William Fau' whom 
the profession owes many valuable papers and facts on professional topics. 
TliJs gentleman, who, to a thorough aequMntance witb the mode of eenducling 
such experiments, united great zeal and judgment, carried through the task 
committed to him ; proceeding step by step, until conviction so firm took the 
place of apprehension, that he rejected all suggestions for tho use of any 
auxiliary means, and urged, from his crowning experiment, reliance upon the 
tnbe alone aa equal to the end to bo attained. 

Numerous experiments were miide by him upon tubes of circular, elliptical, 
Knd rectangular cross section. The object chiefly kept in view in these 
eapcrinients w.t3, to detarmine the form of cross section which, when the tube 



vaa snbmitfed to a cross strain, wonld present an equalitj' of rciistance II tin 
parts bronglit into compression and extension. It was shown, at an earlj 
stage of the operations, that the circular and elliptical forms were too weak ir 
ihe parts submitted to compression, but that the elliptical was the stronger of 
he two; and that, whatever form might beadopted,e2traordinary means would 
be reqniMte to prerent the parts submitted to compression from yielding, by 
" puckering " and doubling. To meet this last difScuIty, the fortunate espedienl 
was hit upon of mailing the part of the main tube, upon wlilch the strain of 
compres^on was brought, of a series of snmllep tubes, or cells of a curved o( 
a. rectangjilai' crosa section. Tlie latter form of section was adopted definitivoly 
for ihe main tube, aa having yielded the moat satisfactory lesults as to resist- 
ance; and iilso for the smaller tnbes, or cells, as most easy of construction and 

As a detail of each of these experiments would occupy more space than can 
be given in this work, that alone of the tube which gave results that led to the 
forms and dimensions adopted for tho tubular bridges subsequently constructed, 
will be given in this place. 

Model Tu6e.— The total length of the tube was 78 ft. The distance, oi 
bearing between the points of support, on which it was placed to test its 
sliength, was 76 ft. Total depth of the tube at the middle, 4 ft. 6J in. Depth 
at each extremity, 4 ft. Breadth, 2 ft. 8 in. 

The top of the tube was composed of a top and bottom plate, formed of 
pieces of sheet inin, abutting end to end, and connected by narrow strips 
riveted to them over the joints. These plates were 2 ft. 11} in. wide. They 
were Qi in. apai't, and connected by two vertical side plates, and five interior 
division plates, with which they were strongly joined by angle irons, riveted- 
to the division plates, and to the top and bottom plates where they joined. 
Each cell, between two dividon plates and the top and bottom plates, was 
nearly 6 in. wide. The sides of the tube were made of plates of sheet iron 
similarly connected ; their depth was 3 ft. 6f in. A atrip of angle iron, bent 
lO a curved shape, and running from the bottom of each end of tlie tube to tho 
top just below ihe cellular part, was riveted to each side to give it stiffness. 
Beades this, precautions were finally taken to stilTen the tube by diagonal 
■braces within it The bottom of the tube was formed of sheets, abutting end 
to enO, and secured to each ofiier lilre the top plates; a continuous joint, 
■ running the entire length of the tube along the centre line of the bottom, waa 
secured by a continuous strip of iron on the under side, riveted to the plates 
on each side of the joint. The entu^ width of the bottom was 3 ft. 11 in. 

The sheet iron composing the top cellular portion was 0-147 in. thick ; that 
of the sudes 0099 in. thick. The bottom of the tuba at the final experiments, 
to a oiatance of 20 ft. on each side of the centre, was composed of two thiokr 
nesses of sheet iron, each 0'35 in, thick, the joints being secured by strips 
abi>ve and below them riveted to the sheets ; the rcmamder, to the end of Hia 
tube, was formed of sheets 0'15e in. thick 

The total area of sheets composing tiie top cellular portion was 34-034 in. ; 
that of the bottom plates at the centre portion, 23-450 in. 


The general dimenaions of the tube were one aixtli tliose ol tlie propoied 
Btructure. Ita weight at the final experiment, 13,020 lbs. 

The experiments, as already stated, were conducted with a view to obtain 
Oil equality between the reaistancea of the parts strained by compression and 
thoao extended; with this object, at the end of e!ieh experiment, the parta 
torn asunder at the bottom were replaced by additional pieces of increased 

The following table exhibits the results of llie final esperlmonts. 

No. ofEiperiinenl 

Velgbt In lbs. Dcfleuioa in 



35,776 . 
















138,060 . 













. 3-98 















The tube bro!;e with tlie weight in the 25l,!i expGriment; tjio cellular top 
yielding by puckering at nbont 2 ft. from the point wliere tJio weight wai 
applied. The bottom and wdea remained uninjured. 

The ultimate deflection was 4*89 in. 

Brilannja 7V6uJar Bridge. — Nothing further tiiaii a succhlct deaeription of 
this marvel of engineering wiE be attempted here, and only with a view of 
showing the arrangement of the parts for the attainment of the proposed end, 
It differs in its genera! structm'e from the model tube, chiefly in liaving tjia 
bottom formed like (he top, of rectiingular cells, and in tlif means taken fot 
giving stitfness to the mdes. 


The total djatance spanned by the biiilge is 1489 ft. This is, lii d?d inta 
four Lays, the two in the centre being each 460 ft., aad the one at uoeh end 
230 ft. each. 

The tub© is 1524 ft. long. Its bearing on tha centre pier is 45 ft.; that (u 
(he two infermedlate 32 ft, ; and that on efloh abutment n ft. 6 m, The 
height of the tuhe at the centre pier is 30 ft. ; at the intermediate piers 37 ft.; 
and at the ends 23 ft. This gives to the top of tlie tube the shnpo of s 
parabolic cun'C. 

C, colli of bauomcellulirb 

nnglea of Jl, mi etieDiUsg 


The celliiliir (op (Fig. 1) i^ dividecl into eight cells B, by division plates c, 
connected with the top a, and bottom Zi,by angle irons o, riveted to the plates 
cunnecfed. Tlie different sheets composing the pbtoa a and i abut end t« 
end lergtiiwiae the tube; Und tJie joints are secured by the strips iJ and e^ 
riveted to the sheets by rivets that pass through the infei'ior angle 

The sheets of which tJiis portion i^ composed are each 6 fL long, and 
1 ft. 9 in, wide ; those at the centre of the tube are ]Jths of an inch tjii;'ic ; 
they decrease in thickness towards (he piers, where they are JJtlis of an inch 
tliieit. The division plates ace of the same thickness at the centre, and 
decrease in Uie same manner towards the piers. The rivets are 1 in. thick, 
and are placed 3 in. apart from centre fo centre. The cells are 1 ft. 9 in. by 
1 ft. 9 in., so as to admit a man for painting and repairs. 

The cellular bottom is divided into six cells C, each of which is 2 fl. 4 in. 
wide by 1 ft. 9 in. in height To diminish, as far as praetjcable, the number 
of joints, the sheets for the ades of the cells were made 12 ft. long. To ^ve 
sufficient alrongth to resist the great tensile strain, the top and bottom platea 
of this part are composed of two thicknesses of sheet iron, the one layer 
breaking joint with the other. The joints over the division plates are secwed 
by angle irons o, in the same manner as in the cellular top. The Joints 
between the sheets are secured by sheets 2 ft. 8 in. long placed over them, 
which are fastened by rivets that pass through the triple thickness of sheets 
at these points. The rivets, for attaining greater strength at these points, are 
in lines lengthwise of the cell. The sheets forming the top and bottom plates 
of the cells are i',ths of an inch at Hie centre of the tube, and decrease to ^tha 
at the ends. The division plates are Sths in the middle, and Sths at the ends 
of tlie tube. The rivets of ths top and bottom plates are IJ in. in diameter. 

Tig. 2. 

Fig 3— Iteptcsenls a honionlal cio^s soclioii of Iho T In 

g, plalfls of Ui8 alOes. 
*, exietior T Irons. 

The aides of the tube (Fig'. 3) between the cellular top and bottom are 
formed of sheets g,2ft. wide ; the lengths of which are so arranged that 
tnero are alternately three and four plates in each pannel, the sheets of each 
pannel abutdng end to end, and forming a contiruoua vortical joint between 
the adjacent paanela. These vertical joints are secured by strips of iron, 
■4 a™! t, of the T cross section, placed over each aide of the joint, and 


clamping tho s.:eets of the adjacent pannels between ti em. ITio T ircna 
within aiid without ai'e fireily riveted together with 1 in. rivets, pla:ed at 
3 in. between their centres. Over tho jointa, between tbo ends of the sheota 
in each paanel, pieces of sheet iron are placed on each side, and connected by 
rivets. The sheets of the paraiels at the cenlre of the tube are Jllia of aji 
inch thick; they increase to IJtlis to within about 10 ft. of the piers, where 
ttirir thickness is again increased; and the T irons are hero also increased in 
thickness, being composed of a strip of thick slieet iron, chitnped between 
strips of angle iro wh h te d f ni the top to the bottom of the joints. 
The object of this as f th kness, in the pannels and T ii 


piei^i, is to give sum 
these points. 

The T irons on tl 
far as tlie third cell f 
projecting rib of each in ihe 

d ty d strength to resist the cmdiing strsdn at 

bent at top and bottom, and extended aa 
t top, and to the second at bottom. The 
la clamped between two pieces, n, of sheet 
to which it is secured by rivets, to give greater stiffness at the angles of 
the tube. 

The nvriingeraent of the ordinary "T irons and sheets of tlie pannels is 
shown in cross section by D, Fig. 2 ; and that of the like parts near the piers 
by E, same Fig. 

For the purpose of giving greater stiffness to the bottom, and to secure 
fastenings for the wooden cross sleepers that support the longitudinal beams 
on which the nuts lie, ecosB plates of sheet iron, half an inch thick, and 10 in. 
in deptii, are laid on the bottom of the tube, from side to side, at every fourth 
rib of tho T iron, or 6 ft. apart These cross plates are secured to the bottom 
by angle iron, and are riveted also to the T iron. 

The tube ia Urmly fixed to the central pier, but at the intermediate piers an^ 
the abutments it rests upon saddles supported on rollers and balls, to allow 
of the play from contratstion and expansion by changes of temperature. 

The following tabular statements give tho details of the dimensions, weights, 
fee,, of the Brirannia Bridge. 



















" II 1 tube over pier 32ft.'ionB 
Fmmes and beams 









Formi;'-a for reducing Ihe Breaking WeigU of WroitgU Iron Tubes. 

Bei>tesenting by A, the total area in inohes of the cross aottion of the metal. 
" " d, tho totfll depth in inchea of the lube. 

" " ], tlie length in inchea between the points of support. 

" " C, a constant to be determined by experiment. 

" " W, the breaking weight in tons. 

Then the relations between these elenionts, in tubes of cylindrical, elliptica 
and reotiingulnr cross section, will be expressed by 

Tlio mean value for C for cylindrical tubes, deduced from SGVQr:d cxperi- 
tnents, was found to be 13'03; that for elliptical tubes, 15'3; and that for 
'ectaugukr tubes, 21'6. 


i\o(e B to Ail Rtfiis 

Plank-Roads. — A loid coiermg, consi-ting of tliii-k boird^ or planus, 
resting on longitnd nal bewna, or elcepeis, and known is P!anJ Roads, has, 
within the past few yeirs, been introduced among us, and from jts adaptation 
to our uncleared foiest distncta, 1I3 eaperior economy to the ordinary road 
eoverings in each localities, and its inttinsn. merit"', na fulfill ng the leqnisitBS 
of a good road covonng, ia rapidly coming into extensive use throughout all 
parts of our country 

Pig A 


The metliod rnost generally adopted in constructing plank-roads consists ic 
laying a flooring, or track, eight feet wide, composed of boai'ds from nina to 
twelve inches in width, and three inches in Ihickness, which rest upon two 
parallel rows of sleepers, or sills, laid lengthwise of the road, and having their 
centre lines aliout four feet apart, or two. feet from tlie axis of the road. Sills 
of various sized scantling have been used, but experience seems in fovor o( 
Bcantling about twelve inches in width, four inches in Ihickness. and in lengths 
of not leas Ihan fifteen to twenty feet. Sills of these dimensions, laid flatwise, 
and firmly embedded, present n firm and uniform bearing to the boards, nnd 
dUtiibute the presgnre they iT^elve over so great a surface, that, if the soil 
upon which thify rest ia compiet and kept well drained, there can fao but little 


s^tfli ]g T A displicement of the ro'id surfico from the usual londa passing 
over it The better to bLCure thia unitorm d stributjon of the pressure, the 
sills of one row are so kid as fo break jcints with the other, nnd t« 
prevent the ends of the iills from jieldingthe usua prcLiution a taken to 
pla,.B short siHb ■it the joints, either beneath the mui sills or on the samn 
lei el with them 

Thi, boirda aie laid pei'ptnd enlii to the i" s of the lOiid experience havinj; 
shown thnt this position is as favoiaVle to their wear nnd teir is any other 
and is otherwise (he most eeonomicaj. Tlieir ends are not in an unbroken 
Sine, but so arranged that the ends of every three or four project alternately, 
on each side of the axis of the road, three or four inches beyond those next to 
them, for the purpose of presenting a short shoulder to the wheels o! 
vehicles, to facilitate their coming upon the plank surface, when from any 
cause they may have turned aside. On some roads the boards liave been 
spiked to the slHs; but this is, at present, regarded as unnecessary, the 
stability of the boards being- best secured by well packing the earth between 
and around the sills, so as to present, with them, a uniform bearing surface to 
the boards, and by adopting the usual precnutJons for keeping the subsoil well 
di'aiaed, and preventing any acdurauUtion of rain water on the surface. 

The hoards for plank-roads should b lect dfmtmb t fmth 
usual defects, such as knots, shakes, & wl I uld d t U u tahl 
fi!i ordinary building purposes; as dur bil fy t 1 i m nt tl 

economy of this class of structures. Si p nh fnlddt. 

hoards of three inches in thickness ofi li th qu t ft th d 
durability that can be obtained from timb 1 d n y at te, 1 1 t a 

used for plank-roads. 

Besides the wooden track of eight feet, an earthen ti'atk of twelve feet in 
width is made, which serves as a summer road for light veliieles, and as a turn 
out for loaded ones ; thia, with the wooden track, gives a clear road surKice o( 
twenty feet, the least that can be well allowed for a frequented road. It is 
recommended to lay the wooden track on the right hand aide of the approach 
of a road to a town, or village, for the proper convenience of the rural trafBo, 
aa the heavy trade is to the town. The surface of fliis (rack receives a cross 
slope from the side towai'ds the axis of the road outwards of 1 in 32. The 
surface of the summer road receives a cross slope in the opposite direction .of 
1 in 16. Tiicse slopes are given for tlie purpose of facilitating a rapid surface 
drainage. The side drains are placed for this purpose parallel to the asis of 
;he road, and connected with the road surface in a auitahle slope. 

Where, from the character of the soil, good anmmer roads cannot he had, 
it will be necessary to make wooden turn oats, from space to space, to 
prevent the inconvenience and delay of miry roads. Tliis it is proposed to 
do by laying, at these points, a wooden traek of double width, to enable 
rehieles meeting to pass each otfer. It is recommended to lay these turn 
outs on four or five sills, to spring ihe boards slightly at the eeiitrp, and epika 
their ends to Ihe exterior ail la. 

The angle of repose, bj which the gr^ida of plank-roads sliould bt^ regu- 

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Iflted, has not yet been determined by exporiiaent; but as the wooden surface 
is covered with a layer of elenn sand, fine grEivel, or tnn bark, before it ia 
thrown open to vehicles, and aa it in time becomes covered witli a permanenl 
stratum of dust, &c., it is probable tliat this angle will not materially diffci 
from that on a road with a broken stone EHrface, like the one of McAdam, o, 
of Telford, when kept ia a Ihorough state of rcpinr. 

In some of the earlier plank-roads made in Canada, a width of sixteen feet 
was given to the wooden track, the bonrda of which were Idd upon four or 
five rows of sills ; experience soon demonstrated that this was by no means 
an economical plan, as it was found that vehicles kept the centre of ihe wooden 
surface, which was soon worn into a beaten track, whilst the remainder was 
but slightly impaired. This led to the abandonment of ihe wide track for tha 
oncnowusually adopted, which answers all Ihoends of the wants of travel, and 
is mach more economical, both in the first outlay and for subsequent renewals. 

The great advanlflges of pinnk-roads over every other kind, in o densely 
wooded country, for Uie lural traffic, are so obvious, that, did not- experience 
teach ua by what mere accidents, apparently, improvements of the most 
important kind have been suggested and carried into effect, it might be a 
subject of astonishment that they had not been among the first to be intro- 
duced, after a trial of the old corduroy road, so generally resorted to in it* 
early stages of road-making in this country. 


Note C la Arls. 441 and 442. 

Methods of describing Curves composed (f Arcs of C if des. — Ti i span mid 
TOO of an arch being given, together with the directions of the tangents to the 
eorve at the springing linei; and crown, na inflnite number of curves, composed 
of arcs of circles, can be determined, which shall satisfy the conditions of form- 
ing a coniJnuons curve, or one in which tho arcs shall be consecutively 
tengent to each other, and snch that those at the Epiinging lines and the 
erown shall be tangent to the assnmed directions of the tangents to the curve 
at those points. To give a determinHte character to the problem, in each 
paiUcular case, certain other conditions must be imposed, npon which the 
solution vrill depend. 

Wiien the tangents to the curve at tho springing lines and crown aw 
respectively perpendiculnr to the span and rise, the curve srvtisfying the above 
general conditions will belong to tho class of oval or basket-handle curves; 
when the tangents at the springing lines are perpendicular to the span, and 
those at tho crown are oblique to the rise, the curves will belong lo the class 
of pointed or obtuse curves. 

In the ciasa of ovals, when the rise ia not less than one third of the span, 
the oval of three centres will generally give a carve of ft more pleasing form 
to tho eye than one ofagreafernumberof centres; when the rise is less tiian 
a third of the spar, a curve of five, seven, or ft greater odd number of centres 
will give, under this point of view, a more satisfactory solution. In tho 
pointed and obtuso curves tlie number of centres is even, and is usually 
restricted to four. 

Three Centre Curves. To obtain a determinate solution in tliis case it will 
he necessary to impose one more condition, which shall be compatible wilJi 
the two general ones of having the directions of llie tangents at the springing 
lines and crown fi.Yed. Ono of the most simple, and at the same time 
admitting of a greater voilely of curves to choose from, is (o assnme the radius 
of the curve at the springing lines. In order that this condition shall be com- 
oatible with tiio other two, the length assumed for this must lie between zero 
and the rise of the arch ; for were it zero there would be hut one centre, and 
If taken equal to the rise the radius of the curve at the erown would be 

Let A J? (fig. A) be the half span, and A C the rise, Hsving prolonged C .4 
indefinitely, take any distance less than A C, and set it ffffrom D to JR, along 
AD ; and from C to F, along A C Join R and P, which distance bisect by a 
perpendicular. Prolong Uie perpendicular, to intersect the indefinite proioDg- 
ation of C A. Through this point of intersection 8, and the poiat R, draw an 
indefinite line. Troin R, as a centre, with tho radius R D, describe an arc, 
which prolong to Q to intersect SR prolonged. Fcom S, as a centre, withtllB 
radius S Q, describe an arc, which, from the conatruction, must pass throngk 

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the point C, and be tangent lo the Gist arc at Q, The centres R and S, thni 
determined, and the curve -7) J9 C deduced fromthcm, will satisfy tlie imposed 

The two foJIowing constructions, from tlieir dtnplloity and the a_ 
form of carve which tliey produce, are in frequent use. The first consists in 
imposing Hie condition that each of the three ores shall be of 60°; the second, 

that the ratio — between the radii of the arcs at the crown and spiinging line 

shall be a minimum. 

To construct the curve aaiiafying the former condition, let d B be Uio 
half span, and A C the rise. With the radius A B describe A a of 90°, — set 
off on it S S = 60°,— draw the lines a i, b B b.M A 6,— from C draw a 
parallel to a b, and mark its intersection c with 6 B, — from o draw a parallel to 
A 6, and mark its intersections iVand O with A B, and C A prolonged. From 
JV with the radius N B describe the are B c, — from O with the radius O e 
describe the arc O c. The curve U c C will be the half of tlie one satisfying 
the given conditions ; and N and O two of the centres. 

To construct the curve satisfying the second condition, or d i — l = o. Let 

A D be the h«!f span,— A C the rise. Draw D C, and from C set off on it 
C d=^ C a, eqnal to the difierence between tlie half span and rise. Bisect 
(he distance J9 d by a perpendicular, which prolong to intersect D A, and 
C A prolonged, at R and S, — from these points, as centres, with the radii 
R D and S Q, describe the area D Q and Q C; and the curve D QC wil! 
be the half of the one required. 

The analysis, from which the aluve result is obtained, is of t. very simple 
character ; for designating hy R ■^ S C the greater radius, by r =: JI D th* 


CEHcr, — by a =°A D the half span, and hy 6 ^ jl 
from the right angled triangle SAR, 

8R' = IS' + AR', 

from which i 

( Ji _ r')' = ili — by + (« - r}\ 

R a' f o' - Siir 


r (26 — 2r)r 
'h.c tins expression, and placing its llrst differential 

efficient eqlia 

to zero, or mating — , — = 0, iliere results, siftec (ho t 

are reduced, 

a' + J» 

- (a — I) v"a' + 6'_ ^/a' + //' V"' + b'' — (a — h\ 


), but 

Va^ + 6' = DC, and ^'a" + i' — (a — b) = Dii, hence the given construc- 
tion for the centres required. 

By comparing the two methods just explained, for the same span and rise 
it will be seen that the former gives a curve in which the lengths of the .ires 
differ less than in the latter, and which is therefore more agreeable to the 

Obtuse aTid Pointed Curves of Font 
Centres. — Ijbt 4 B be the liaK 
span,— A C the rise of the required 
curve, — and C D the direcUon of the 
tangent to it at the crown. At C 
draw a perpendicular to C D. Talte 
any point it on A B,. such that R B 
eliall be less than tlie perpendicular 
R b, from R upon the tnngent C D. 
From C, on tlie perpendicular to 
C D, set off C d, equal to the 
assumed distance R B,— draw R d, 
and bisect it by a perpendicular, — 
which prolong to intersect the one 
from C at the point S, — through S 
and R draw a line,— from R, with tlie 
radius R B, describe an me, which 
prolong to Q, to intersect tlie line 
through S and R, — from S with the 
radius S Q, describe an arc, which 
wU. be tangent to "the first at Q, and pass through C. The curve B Q 
«tll be the half of the one required to satisfy the given conditions. 
The analogy between this lonslraetion and the one first ^ven for tiiros 

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( tLe tWB 

centre curves will be readily seen by comp ng the construct oi 
Five Centre Oval Ctirves, ^c When ti e r ae s leaa tl an one h d of the 
Bpaa, it is found that oval currea of a pie ng si po e nn t be obtui ed by 
using only three centres, and five, or a gro te oddnunbe ofee ramuBtba 
resorted to. Besides the two general conditiona common to all ovals, a 
greater number of particular ones must be impoae-i, hs the number of centrea 
is inereased, restviciing them within the limits of conipatjbillty with each other 
and with tiie two common to ail. By imposing, for example, on the oval ol 
five centres, the conditiona that the radii of the two conaecuiive area from the 
sprin^ng line shall be assumed as the parficular conditiona, a very simple 
eonatructJoD, analogous to the one for ovals of three centres, will show the 
limks within which these must be reatiijted, not to interfere with the others 
that are common to all. Without stopping t3 ilbstrate this by an example, 
which will present no difficulty to any one tolerably conversant- with the 
elementa of geometry to make out alone, a mora general nethod will be given, 
■ 'e alike to all curves of this cIt-s 

The half span and n« being given, let it 
be required to determine an oval of five 
leitres-Bith the partii-nlar conditions, thit 
the radii of the consecutive "(rts, from the 
springing Ihie towards tho cro^\o, shall be 
in anincceasiDg geometncal progression — 
in which case the corvaturcs of the area 
will bo in a decreasing geometrical pic 
grcaaion — and the lengths of the consecutive 
irca shall increase in a gnen ratio Desig- 
nate the half span AB by p (Fig, C), the 
rise by q, — the ratio of tho radii by m, — 
the ratio of the arcs by n, and the number ' 
of degrees in the am at the springing line 
by a. Suppose the centres 0, P and Q 
found, and draw PS perpendicular to AB, 
— and PR porpendicular to BC produced. 

The radii OA, PE and Qfl will be re- 
presented respectively by r, rm, and mf, — 
and tlie angles AOE, EPD, and DqC 
between them by 

now, from the properties of the figure, ths 
following equationa are obtained 




From the right angle ti'Iangle OPS, niid PQR, there resulfa, 
0S= OP COS. a = irm — r) COS. a ; 
PS = OP sin. a = (i-oi— !■) sin. a ; 

QS = PQ sill, (a + "^) = irm-- m) am. (a + a—) 

by Buliatituting these values in equations (B) and (C), there results, 
p = r J 1 + im-1) COS. a+ (m'-m) cos. (^) a | (E) 

„ = r5»«'-C^-l)sin.a-Cm"-m)sIn. (^")«ji (F) 
and by reduction, equation (A) b 

■-—-^^-^90"; <G) 

The equations (E), (F) and (G) express, therefore, the relations which sub 
sist between the six quantities p, q,r,a,m and n when the imposed conditions 
nre satisfied. Let three of these quantities as m, re and r be assumed, the 
otiiera will be found from the three equations in question; that is tiie span, 
rise, and number of degrees in the ai'c at the springing line, which correspond 
to the given values. 

Ftoin the solution jiere given, the ratio of p to q or — is found ; but as the 

rise and sj),in are usually a part of the data, this ratio — may be different 

from that — of the given half span b, and rise c; in which case it will be 
necessary to assume new values for the quantities nt, n, and r, and find tha 
corresponding values of y, q, and a, until the ratio — is equal to, or nearly the 

Bame as — . When a suitable approximation has been obtained, it will bo 

easy to find a cnrve which shall differ but little from the required one, and 

whose half span and rise shall have the required ratio — . 

To effect this, let s: bo the quantify which must be added to p and i, 
respectively, to make their ratio tiie same as that of 6 to c; this coudilion will 
be expressed by the eqnnlion, 


C q + x' 

.Vcm whicli there results 

pe — qb _ 


if now tills quantity be set off from A to M (Fig. C), and from C to /V, ana 
& new curve AN be described from the same centres O, P and Q, It will be 
parallel to ihe curve A C, whose half span and rise are p and 5, and the half 
epan BM, and Tise BN, will have the same ratio as b to e. To pass from this 
curve to a similar one, described on the given half span b, and rise c, it will bo 
only necessary to multiply each line of the figure QPOMNXiy the ratio 

or, substituting for x its value, as determined in equation (11), by 


since the figures being similar, their homologous lines are proportional, or, for 

p + !c:b::OM:-^OM; 

which will give the lino, corresponding tfl OM, in the figure of which b is tho 
lialf span, and c the rise. 

The method here explained may be applied to any number of centres, but 
where the rise ia less than one-fourth of the span, an oval of five centres will 
be found to answer fully all the required conditions. 

There are other methods of describing the oval of five, or a greater number 
of centres, which are ratlier more simple for calculation tlie general 
method just given. 

By assuming, for example, the greatest and smallest radii within suitable 
limits, the intermediate radius may receive the condition of being a mean 
proporUonal between these two ; or designating it by a, there will result 
x^^RXt; — ii being the gi'eatest radius, and rtheleast. Having found a:, 
the position of the intermediate centre P m found, by describing an arc from 
Q with a radiasK — x, and another from O with a radius a; — r, and taking 
their point of intersection P. 

A similar process might be followed for an oval of seven cenfrca, by finding 
the two intermediate terms of a geomef r'lal progression, of which rand Ji are 
the two extremes. 

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Noil D to AH. 612. 

Niagara Jlailroad and Eighinaij Suspension Bridge. — This remarkable atruoture, 
l[ke the Aqueduct suspension bridge at Pittaburgli, was coastructed byEoebliog; 
aud, for bolduess of plan, and skill in fiieeieeutionof its details, is every way worthy 
of tlie profesaonal ability of this distinguished engineer. 

Designed to afford apassage-wsy over the Niagara river, both forrailroad and oora- 
ffion Toad traffic, it consists caaeatially of two platforms (Fig. A) one above the other, 

Ftg. A— Cfoee aeclioa of magi 
A ndltriy tiook unQ beams. C. ^°"<''i 

B lower pblfotni for 

C, fllQEona! truss. 

D, pMflpet. - 
A, lower roaaway tmiirers. 


A', upper 

way bearera. 

C', nppm midn cables. 

D, BUBpension rapes. 

E, wroDg-tt-iron braces. 
P, 1100301 braces. 
G, beams of longltmllnal ■ 
H, 101lgitnlH]lalb^lceabct■ 
^I, hoi-iioDti • 


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and a!bou6 fifteen feet Epnrt; tlie upperaerving as the railroad tracts, and the lower 
for ordinary veliidea ; the two being connected by a lattice girder on eacli side ; and 
the whole bridge-frame being suspoadad from four main wiro cables, twoofwliieliare 
connected with the upper platform, and two witli the lower, by suspension rods and 
wire ropes atlaobed to the roadway bearers, or joists of the platforms. 

Each platform consists of a aeries of roadway bearera in pairs; the lower covered 
by two thicknesses of flooring-planlt, the upper by one thickness; the portion of 
the latter immediately under the railroad trECkhaTinga thickness of four inclieg, an'' 
the remaiijder on each side bnt two inches. 

M posts In pairs. 

t) aiosonalironbvaee-rods. 

The lattice-girders consist of vertical posts in pairs, the ondgofwliicli areciampod 
between the roadway bearers; and of diagonal iron-wrought rods with screws at each 
end, which pass through cast-iron plates fastened abOTB tho roadway bearers of tha 
upper platfonn, and below those of the lower, and are brought to a proper bearing 
by nuts on each end. A tiorizoatal rail of timber is placed between the posts of 
the lattice at their middio points, to prevent flexure. 

The roadway bearers and flooring of the upper platform are solidly clamped ba- 


1 each aide of tlie 


tween four solid built beams or ^rders ; two abOTO the flooring, which rest on cross 
supports; and two, corresponding to tliose above, below tlie roadway bearers; the 
uppor audlowor corresponding beams, ivitli longitudinal braces in pairs between the 
roadway bearers and resting on tha lower beama, being firmly connected by screw- 
bolts. Tlie rails are laid upon the top beams. 

A strong parapet, on the plan of Howe's truss, is 
upper platform. 
■Wrouglit-iron and wooden bracos connect tfio posts and tho two 
Tl:e piers (Fig. C.) consist of four olielisk-shaped pillars, which ar 
the Ijaae of each being a aqnare of fifteen feet si 

Fig. 0.— End olovaeon «f piers nm 
ing arch of bridge. 

A, BbeJt of the plei. 

B, pedestnl. 

D, nrdiea Way tor common road. 

Bides. Tlio pedestal of each pillar is a squavo of about seventeen tfeet side at top, 
and having a bfttir of one foot verlically to one horizontally, or —. on each of ila 
faces. The height of tho pedestals on tlie United States aide of tho ri 

w being 
n arch-way below the 

twenty-eiglit feet, and on the Canadian side eiglitee 
level of the railroad connects the two pedestals. 

Tbe main cables pass over saddles placed on rollers, on the tops of the piers, and 
they are listened at their ends (Fig. D) to chains formed of links of wrouglit-iron 
bars, which, passing through abutments of masoniy, and down into shafts made into 
the solid rock below, are there each flrmly attached to an anchoring plate of cast-iron. 

Besides the usual suspeudlng-rods of the bridge, a number of wire ropes, termed 
over-Jloor stays, connect the portions of tho upper platform adjacent to the piers with 
the saddles at the top of tho piers ; and the lower platform is in like manner con. 
cected with the rocky banks of the river, by a number of lilce Bta.ya. The object 
of both being to resist tha action of high winds upon the platform, and to give tho 
bridge more rigidity. 

Each of tho main cables is formed of seven Emaller ones or slrands. Thowliole 

,dt>y Google 

bound ti^ether in tlie nsual manner lay a wire wrapping, 
wires in its cross-seotion, ^xty of whicli make an area of i 

ach Btrani oontamB520 
e sijuars iucli. 

The main cables to wliich the roadway bearers of the upper plaL^ria are attached, 
are deflected laterally twoarda the axis of tho bridge, and thus limit the range of 
lateral oscillationa. This provision, the lattice structure of the sides and tho parapotj 
llie oyer and under floor slays, the deep longitudinal girdera of the railway track, 
the aliglit camber or longitudinal curvature from the ends of the bridge to the centre, 
and its own weight, giTo to the whole structure that degree of rigidity and stability 
which ore its marked charaoteristioa, as contraatod with suspension bridges usually. 

Some of the principal dimensions of the means of suspension are given in the fol- 
lowing statement: 

Span of boll] cables between axis of piers, 821t feet 

Versed sine of cables of lower platforra, G4 feet. 

Versed sine of cables of upper platform, 54 feet. 

Diameter of each cable, 10 inehea. 

Area of cross-section of each cable, G0.4 squaro inches. 

Area of croas-section of upper links of anchor chains, 372 square iochesL 

Ultimale slrength of anchor chains, 11,904 tons. 

Number of wires in the four cables, 14,650. 


Average Btrengtli of one wire, I,G48 Iba. 

Ultimata slrengtii of tho four cables, 12,000 tons. 

Permanent weight borne by the caWes, 1,000 tons. 

Length of auohor obains, GG feet. 

Length of upper cables, 1,261 foeK 

Length of lower cables, 1,193 feot. 

Huniber of Buspendera, 624. 

Number of OTer-floor stajs, G4. 

Number of uuder-floor stayH, 56. 

Length of platforms between piers, SOO feet. 

Height of railway traclt above middle stapte of water, 245 foot 


Foie aioArl.Z9i. 

Caisson and GrU/mrh Coffa--dams. — In tbe construction of the ronndatiuns for Ui« 
piers aod abatmeuta of tlie Tietoria tubular iron railroad bridge orer Uie river Saint 
Lawrence, at Moatreal, the englneei'S had to contend against unusual difficulties ; 
in a rooliy bottom covered with holders, whioli prevented liie use of piles ; and in a 
Bwift ciirrontj bringmg down in the spring of the year enormous fields of ice, the 
effects of which none of the ordinary methods of caisson or eoffer-damg could have 

These diiHoulties were successfully met, in some cases by the use of a larpo n atcr- 
tight caisson, sho^n in plan (Fig. A), and in cross-section (Fig. B), of such a lorm 
and dimenaona as to leave a suflioient interior area, between ils interinr sides, for a 
coffer-dam, and for the ground to be occupied for the construction of the foundations 
of tbe pier. In others (Eg. C), where, from the velocity of the curreoi, the caissons, 
from their great bulk, proved unmanageable, by enclosing the area to be occupied by 
crib-work, sunk upon the bottom and heavily laden with stone; and exterior to this 
forming a second similar enclosure i and then, by means of sheeting piles, Bnpported 
against the opposite sides of these two encloeures, forming a colTcr-dam lietween 

in (Fig. A) consisted of two parts, the two sides and up-stream wedged- 
shaped bead, and a reotangnlar-shaped porrion B, which fitted in between the two 


adca, forming the down-alreani end, and wli 1 Id 
when it became necessaij to remore the eall ea es i 

The caisaoc (Fig. B) was Bat-bottomed, wi h rt 
with a strong flat deck, to reoeiwe the works! p m 
ing, dredging, and tha construction of tlie masonry. 

Ho-. B 

;d in position, it vraa moored to a loaded, sanlten cribwork np-st 
and, besidea the exterior guiae-pilea, long two-inch iron bolts were inserted into lioleg 
drilled into the solid rock, through Tertioal holes Ijored througti the piles. In this 
way, througli the bearing of the pOes on tha bottom, the foothold given by Iho 
bolts and the mooring-taokle, the caiaaon, when sunt, was solidly secured against 
accidents from rafts, or other floating bodies. 

Tha interior sides of the oofTer-dara. were strongly buttressed by horizontal beama, 
to withstand the pressure of the water. These Ijeama were removed, and their places 
supplied by shorter buttresses placed between, tlie sides of the ooffer-dam and pier as 
the masonry was carried up. 

The cribwork dams were constructed of a numher of ciibs, each about forty feet 
in length, whlcli were placed end to end to form the sides of the enclosures, and 
strongly conneotod with each other. Some of these were constructed on shore, and 
towed to their positions. Soma were constructed in tho water behind mooring-oribs, 
and others upon the ice during the winter, &ni sunk in position. 

A flooring (Pig. C) was made, about midway betwoea tho top and bottom of the 
cribs, to receive the block of stone with which tlie cribs were loaded, tosecuro them 
from the effects of the pre.^^ure of the ice in its spring movement, and the collision 
of floating bodies. 


to bo pumped 
Tiio cribs wen 

. were not of adeqaate Etrengtli to resist tlie crush of tfio ice, and imd 
)ut and removed tor. securo position bofors the closing of tlie river, 
planked ovei- at top, and remained in place as long as required for the 

Pneumalic Piks. — Tliia appellation bas 1:>een given to oylindora of cast-ir 
in the place of ordinary piles to reach a firta subsoil below the bed of a river, suit- 
able for the chareotcr of the superstructure to rest upon it, which, being made au-tight 
on the odes and fop, but left opon at the bottom, are sunk to the required depth, by 
rapidlj withdrawing the air within tliem, by methods to be described, and thus 
causing the water to rush in through the opon bottom, removing in its flow the snb- 
soil in contact with the lower end of the cylinder, and allowing it to siak by its 
own weight. 

The cylinders are eaet and put together very much ia the aamo manner as ordinary 
water-pipes ; being composed of lengths of from sis to ten feet, each of which has 
aa interior flange at each end, with holes for screw-bolts, by means of wliioh and a 
disk of india-rubber, inserted between the connecting flanges, tbe joints are made 
air and water tight. 

In the first essays at tins mode of foundation, the cylinders were BUuk by Mmply 
oxhausKng the internal air, in the ordinary way, above the water-level. Theresults, 
however, were not satisfactory, as the pile sunk very slowly. 

The nest step (Fig. A) was to connect an air-tight cylindrical vessel, p, by means 
of a tube, A, with a stop-oock, with the interior of the pile Ai fi°^ also with the air- 
pump, by another tube leading to the pump from the other end. In order to sink 
the pile, the communioaljon between it and the exhaust chamber Q was first closed, 

ttom D until a auDlcient vacuum waa produced, when the oommunication with the 
pump waa closed, and that with the pile opened, allowing the air to flow from it into 
the chamber with considerable velocity. Tliis sudden disturbance of the equilibrium 
between the external and internal pressures on the pile caused it to descend iostan- 


taneoudy and rapidly, asif Btruck on tha top by a heavy blow, thedi 
ing frequently many feet antil an eqwlibriura among the forces was ri 

mg. A.— LOBsituiUnal socOon 


A, exiiiniBt tulo toliTCcn A 

B, irater djscliarg«-tab9- 

C, equilibrium tubs ictwecn 

the look and dmiuber o! 
the pile. 
D flqnllibriDro tolie between 


When the resistance to the further descent of the pile was found to be too great, 
cither from some obstrnotioa mot with at the hottom, or from tlie tanacity of the soil 
itself, the ingeniotis expedient was hit upon to force the water from within the piia, 
by pumping air into it, and thus enable workmen to descend to the bottom and re- 
mo e tho soil or other obstruction to the descents Tlie plan devised for this purpose 
w fi ootlier air-tight iron cylindrical veeselC *<> t''^ fopof thepile, of sufEcieut 
d te d height to hold several workmen, and a windlass, W, arranged with an 
d pe and buekela for riiisingthe excavated soil into the chamber C. 

Th hamber, which has received the name of an air-lock from its fanctions, was 
p d d With an upper man-hole M at top for entering the loclt, and one N ia tho 
ttom entering tha pile. Each man-hole had two air-tight valves, one openmg 
w ho other inwards. Two tabea C and D, with Btop-eocka, furniahed an air- 

's g ween the air of the pile and that of the lock, and between the latter and 
st 1 air. A syphon-shnped water-discharge tube B, with a stop-cocJt, leads 


from telow t!ia level of tlio inner water surface tlirougli the bottom and side of the 

The operation of sinking the pile by tlfst exhausting the air from tba eshaust 
chamber P, was the same in this case sa in tha preceding ; tho upper valves of 
either man-hola being dosed, and all eoramunioatioii between tho external air and 
the ictBrior of the pile being cut off by means of tlie Btop-cocka. 

When it became necesaary to descend to the bottom of the pile, to remove the 
soil or any obstniotioc, the Inwor valre of the lower wan-hole, with tlie tube C, 
were closed; the discharge tube, B, leil open ; ami the air forced into the pilo,hythe 
pumpa, through the tube A; the increased pressure upon tlie water aarfaee caused 
the water to rise in tlio tubo B, and Sow Ont at tho otiier end. 

When all the water was discharged in this way, the lower valve of the upper man- 
hole, and tlie tubes A, B, and D were closed | the tube C was tlien opened, through 
which the eoadenaed air in tha pile flowed iuto tho lock, until the doualty of the air 
in it and in the pile became the same; the lower valve of tlie lower man-hole waa 
then opened, to allow tho workmen to descend, and the e■>:ca^ ated soil to be raiaed 
into tho lock-ohamber. 

To take tha excavated material out of the lock, tho luwo: man-hole under valve 
and the tube C are closed, and ilie tube D opened the cuadi,n3ed au' of the loci! 
flows out, and the upper man-hole lower valve is opened 

In some of the more recent cases of Uie application of pneumatic piles, the exhaust 
chamber and the disehai^o- water-pipe have been suppressed, condensed air being 
. alone used, hotli to force the internal water out through the open bottom of the pile, 
to allow the workman to excavate within, and also to produce a scour below tha 
lower end,. from the rush of the water baclt into the pile, by allowmg the condensed 
air to escape rapidly from it. For this purpose a tube leads from the air-pumps, 
through the side and bottom of the air-lock, iuto tha pile, to supply the compressed 
air. Another pipe with a stop-cock leads through tho aide and bottom of the loclc, 
from the external ah' to the interior of the pile, through which the condensed air in 
the pile can be discharged. The upper and lower roan-holes have each ao under 
valve. Two equilibrium-tubes with stop-cocks, one forming a connection between 
the interior of the pile and the au'-lock, the other leading Uirough tlie side of the loclt 
to the external air, furnish the means of bringing the air of the lock to the same 
density aa that within the pile, or that of the atmosphere. 

To force out the water, the lower man-hole, the condensed air discharge-pipe, and 
the condensed air equilibrium-tube are closed, and the air then forced into the pile 
by tho pumps. 

To excavate the internal soil, the workmen enter tho look, close the upper man- 
hole and tho upper equilibrium-tube, and open the lower equilibrium-tube. This 
establishes an equilibrium between the air of the lock and that of the pile, and tha 
workmen can then descend into the pile and excavate the soiL 

To remove the excavated soil which has been raised into Iho look, the lower man- 
hola and lower equilibrium-tube ore closed, and the upper equilibrium-tuba opened, 
which eetablisheB au equilibrium between the air of tho lock and that of the atmos- 
pliero. The upper man-hole then being opened, Ibe material in tho loci; can be car« 


woduce a aoonr undor the pile to allow it to sink, the iTorkmen leave the pilo 
" 1 then opened, and by the rush of the 
anient of the pile ia teraoved from ila 

und lock; the condensed air discharge-pipe 
water into the pile all obstruction to the mc 
lower end. 

DaMe Air-LocH. — In some of tho more 
Europe, air-looks in pain have been used 

Tig. B.— LoEgltuJlnnl aeclion of pile A, 
iell or working-chamber B, ""S nir- 
loeka C, D, uBod ut tlio briaga at 


A, ivatcrdEschnrg«-p1po. 

B, equlHbtlum tnliea of nir-Iock. 
■ C, elevation of nlr-loet. 

D, longitndiDBl section ot nlr-Iock. 
M, hoiellng-genr In Uio bell, 

Vlf , comttecpolsij to compresieil air. 

:b case (Fig. E) consist of a working cliamber, B, termed tbe 
lell, which ia a large air-tight Iroa ojlindrical vessel fastened to the bead of the pilo, 
in which there is sufficient room for a hoisting-apparatus, M, and several workmen, 
to raise tho eieavated soil to the level of the air-loeks; of two small air-loeka, and 
C, which are inserted into the hell about two-thirds of their length; of a sjphon- 
shaped wafer diacliai^e-pipe A ; and of a windlass N to raise the excavated soil oat 
of the locka. 

Each lock has a mau-hole, witli an undervHlve on top, for entering the lock, and a 

vertical iloor on tho side for entering the boll. Each is provided with two sets of 

equilibrium valves, so arranged Ihat they can be opened Ijy a person from within the 


,dhy Google 

boll or tbo look, to eBtflblisb an equilibrium between the air in tliem ; or from tho 
outside of the lock, or the inside, to estahlisli an equilibrium between the e:;t«rnal air 
and tliat of the lock. 

The air in the pile is condecaed by air-pumps in the uannl way. 

The hoisting-eBgine in tlio boll has lis gearing so arranged tliat the filled buckets 
can be delivered alternately into tlie loekB, and from there be taken by the gearing 
of the wiodlaas above. In the example represented by !Flg. B a weight, W, formed 
of east-iron bars, resting on brackets caat on the outside of the bell, forma a counter- 
pressure to the interior condensed air. 

The pile la sunk by opening a condensod air-pipe loBdlng to tbn citernal air, 
Ihe lower portions of water discbarge-pipe having been vemoved ind with the tools 
vaei in excayating, pla«od within the boU. 

Tbe descent of the pile at eac-hdisoliarge of the condensed ■iir depenis upon the 
nature of the strata met with. In very compact clay the descent will, m some in- 
stances, be only a few inches in several discharges; whilst m sandy or gravelly 
strata it will descend as ranch, at times, as twelve or more feet. This is owing to 
the difforenoe botwoon the effect of tlie sconr, and tbe resistance offered by tbe fric- 
tion on tho exterior surface of the pile. Tho resistances in sand and gravel being 
much less than in stiff clay. It has been found, in some cases, that two or three feet 
of a compact clay soil left within the piles at the bottom would prevent thn scour, 
and the farther descant of Ilia pile when the condenscci air was discharged. 

Tlia piles are placed in portion by a suitable hoisting-gearing raised upon a strong 
scaffolding; and in their descent are kept in a vertical position by guides placed in 
connection with the scaffolding. Great precautions have to be taken in managing 
the descent of the pile, when it is approaching the depth to which it is wished lo 
»nk it, so t L tl to surface of eicli on the some level 

concrete ca od 

were driven within the cyhnder some diotanci 
thrown in to rest upon the heads of the piles, 
over the Harlom river, Kew York, the engineer, Mr. W. J. McAlpine, formed a con- 
ienl-shaped exoavatlon, E, (Fig. A), around and below the bottom of the pile, 
extending it beyond the exterior surface of the pile a distance of two fcet^ by means 
of plank thrust outwards and downwards, under the lower edge of the pile, forminga 
kind of conical roof, covering a hed of hydraulic concrete, upon which the pile and 
body of concrete within it rested, thus Increasing considerably the bearing surface of 
the stratum upon which the suprstructure bore. 

Au opicion has obtained, from tha condition in which the hydraulic concrete vraa 
found in a pile accidentally fractured, in which it had lain for some time, that this 
material did not harden when subjected to the great pressure of the water from tha 
bottom. A remedy, it la stated, has been found tor this, by using a portion of. 
tsof aporous brick in a dry state instead of stone, in the oomposiUoQ of tho 


aa done in tlie case of the piera of the bridge at SMgodia, in Hun- 
gaiy; and byiuserting- in the body of the concrete balf-Lnch gas-pipes, tlirough which 
the compressed air was diffused throughout the maBs, as practised at the Harlem 
Bridge by Mr. McAlpine. 

Aa large quantities of hydraulic concrete are required for filling the piles, the 
method pursued in (Jemiatiy, and as practised at the bridge at Szegedin, for mixing 
the mortar andiragments of bi'Iel^ or stone, commonda itself foe its economy, and the 
thorouglmosa with which the mBterlals are incorporated. A wooden C3'linder about 
twelve feet long, and four feet diameter, made and boopod like a barrel, and lined with 

. an inclined position of — to the horizc 

to revolve by 

a hand set in motion by a steam-engine, from fiHeen to twenty revolutions in a minute. 
The cjlinder \vas fed by a hopper at the upper end, into which the materials wore 
thrown, and they were discharged thoroughly mixed and ready for use into wheel- 
barrows at the lower end. It is stated that this simple machine delivered from 280 
to 350 cubic feet in ten hours. 

The concrete ia usually throivn down into the pile from the hell or lock. At Iha 
bridge at Szegedin the double locks were, aitomntely, nearly fllled with the concrete, 
audit was raked cat from them and thrown Into the pile; care being taken to work 
it in well by band, around the flanges and joints. 


Flj;. O.— LongitDdinai section of tbe oilrai 
and maaonryof nplcrofarallroodbriai 
0Terth8ScMir,fltL'0rieDt Franco 

FLg. D.— Plan. 

A, wurWnE-ohiunber for excayatlBs enll 

B, interior elevation of eaiaaon 

C, C, elevaUon of the balls contalaJng t] 

Fneamalic Caissons. — The application of corapreaaed air for lajing foundations 
has been further extended in some of the raJroid bridges recently constructed in 
Europe; by using wrought-iron oaisaons of snEBcient dimensions to serve as an 
envelope, or jacket, for the masonry of «n entire pier; and gradually sinking the 
■whole to the requisite depth, by excavating the soil within the pier to the desired 

The calsaona (Figs. C, D) for this purpose were divided into tivo compartments. 


The lower, A (Fig. 0), wliieU aerred as a chamber for the workmen, Tot exeftyating 
tlio soil, was sirongly roored at top, with iron bars and iron sheeting, to beac the 
weight of the maaoDry that rested upoa it ; and waa securely buttreaaed. on the sidea 
to reaist the inwurd pressure of the soil on the oulalde. Tiie upper charaher, B, 
served as an oTdiaary caisson, flttiag closely to the masonry on the sides, and rising 
BufBoiently above it to exclude the water during the construction of the masonry; 
the body of which, composed of beton with a facing of atone, waa gradually raised 
as the caiaaon was suni through the earth overlying a bed of roclc upon which the 
pier was Hnally to rest 

The working-chamber A waa connected with two bells C, C, by two vortical iron 
CjlLndera D, D (Fig. 0), for each bell ; these cylinders serving aa a communicfltlon 
between the working-chamber and hells, for the paasage of the workmen from one 
to, the other, for raising tlia excavated soil, and as a pasaage for the compressed air 
forced in by the air-pumpg. 

Each bell contained two air-locks for communicating between it and the exterior; 
and a, hoisting-gearing for the excavated soil ; the fill I b k ta a ding through 
one cylinder, and the enipty onea descending throu h the oth 

The lower chamber, the bottom of which was pen was kept filled with com- 
pressed air of sufflciont density to exclude the wate and enable the workmen to 
excavate the soil 

The caisson was gradually sunk, by the weight of tl e superincumbent mass, as the 
Boil below waa removed. 

So soon as the roct-bed was reached, (he surface was thoroughly cleaned off, and 
levelled ander the edges of the bottom of the caisson, and the ohambor A was gra- 
dually flUod in with masonry closely up to its roof. J^inally the cylinders D were 
cemored, and the wells occupied by them in the body of the pier, filled with bcton. 

As a matter of interest, on the subject of laying ibundations by means of pneu- 
maUo piles and oalasona, a few additional facta in connection with the examploa abovo 
ciled will not be out of place here. 

Bridge over the Thetss.—Tho soil below the bed of the river Thcisa, at Saegedin, 
is alluvial, and found in alternate strata of compact clay and Hand to an indefinite 
depth. The current throughout its course ia sluggish, having a surface velocity at 
Szegedin, during the highest stage of the waters, of from three to three and a half feet. 
The rise and fall of the water are both very gradual; the higheat stage being about 
twenly-Eix feet, and the mean level about axteen feet. The arched ribs and other 
superstructure of the bridge were of wrougbt-iron platea. Each pier was formed of 
two piles, or columns, filled with beton, aa above described ; and each supporting one 
track of the railroad. They were cast in lengths of ax feet, and ten feet in diameter, 
and one inch and one-tenth in thickness. The piles were sunk to tlie depth of about 
thirty feet below the surface of the bed; and about forty feet below the ordinary 
low-water level. Their height corresponded to the highest water level, or nearly 
Ibittj-three feet aboro the presumed acour of the bed. 

The interior escavatlon of the soil was carried down lo the first Joint, or eiz feet 
troia the bottom of the column. To compress the soil below the column to sustain 
better the super! tioumbent weight, twelve piles of pine were driven within ll-e col« 
umn to a depth of twenty feet below the bottom. 



The air-locks were eacli about six feet sis inelies in height, and two feet nine 
inches in diameter. 

To provide againat the scour of the current, tlie entire pier was encloeed by a row 
of square slieeling-piles, driven to the level of the bottom of tho columaa, and about 
two feet from them. Tiie space between these piles and columns, to tho depth of 
ten feet below tho bed level, waa filled with hydraulic concrete ; and Hie piles were 
surrounded by loose stone with a spread of aliout tea feet from the piles. 

iTorfeM Bridge.— la the Harlem Bridge, the piles were sis feet in diameter, and 
cast in lengths or ten feet. The air-locic was of the same diameter as tlie piles, and 
six feet high ; the valves or man-holea twenty inches in diameter. The moat notice- 
able future in this part of the structure. Is the expedient of using an underpinning 
of plank and concrete, to obtain la wider spread of tile foundation bed, and a greater 
bearing surikoe for the anperstructure tq rest on. For thla parpoae, plank Hve feet 
]ong, three inches wide, end one inch and a quarter Uiick, were forced under the bot- 
tom of the pile, in sections of thsee feet wide on opposite aidos, and hi an inclined 
direction, so as to gain an additional spread of foundation base of two feet around 
and beyond the pile. These formed a temporary roofing, fram beneath which the 
soil was rapidly removed, and the excavated space filled in with concrete. Finding 
great inconvenience in this process, from tlie rapiditywitli which the water and sancl 
came in on the sides, an additional condensation was given to the compressed air of 
six to ten feet extra water pressure ; tbis was found to counteract the external pres- 
sure, BO as to allow the ejroavations to be carried on with facility. 

The refuse gas-pipes, which were used to convey tbe compressed air down between 
'.he bottom of tho concrete and the underlying soil, as well as giving it a pafsage be- 
tween the outside of the pipes andthobodyof the concrete, were distributed llirough 
tbe concrete about a foot apart 

The bottom of the foundation in this example was thirty feet below the surface of river-bed, and fifty feet below tide. 

Siidge ever Sie Scarff. — In the example of the bridge at L'Orient over tlie Scorff, 
the tliBr-bcd is a stratum of mud, forty-six feet in depth, resting upon a surface of 
hard schiaicae ^'ock more or less inclined and uneven. The level of mean tide is 
about sixty fei,; above tbe rock surface ; tliat of the highest IJde sevenlj feet. 

The caissons Ui.;u in this example were designed for the piers of a alone bridge, 
and were aboui, 'uru/ ioot long and twelve feet broad. The bells, or upper working- 
chambers, were ten fet,' high and eight feet in diameter; the lower working-chamber 
ten feet high ; and the iryhnuJis, for eommunicatjon between them, two feet and a 
half in diameter. 

The caissons were built of si'.eet-iron, in zones decreasing in thickness from the top 
to the bottom; but not haying been buttressed within against the pressure of tlio 
water, as the lower working-chamber was, tliey yielded and got out of shape. 

In a subsequent structure of nearly the same dimensions, for a railroad bridge at 
HantaB, the same fuiluro took place, and precautions were then taken against It by 
the insertion of oroaa-stays, which mere removed as tlie masonry was carried up. 
In tbe caissons used in this case, the beila and air-locks were made larger. Each 
air-lock had three separate compartmenls; one for the passage of the workmen 
which could contain four men; one for the barrows by which the excavated soil was 
removed, and one for the concrete to fill up tlie lower working-obamber, when tho 
excavation was completed. 



ition o( the well-known device of the di/ingi 
The main difficulty In their use is iii prevents 
than another duriug their deacent, and of 

These caiasons are, in fact, a comhiii: 
bell and t^e ordinary floatjcig caisson, 
iug them from settling on one side mo: 
rectilying any accident of this kind. 

The diving-bell ia seldom oaed except for examining tlio condition of works under 
water, and for setting blocks of masonry, or laying a bed of concrete. Within a few 
years back, the water-tight and air-tight dress, to enable the workman to move about 
under water as on land, known as submarine armor, has also been BuccessTully used 
for like porposee. 

The chief objection to the employment of all these expedienia arises from tha 
great pressure to which tho workman is subjected from the condensed air in which 
lie labors. This, however disagreeable and inconvenient for the time, seems to pro- 
duce notliing more than a temporary effcet upon men of good constitution, evenunder 
a pressure of three atmospheres, when ordinary precautions are taken in passing 
from the free air into tiie condensed, or the reverse, Tho great success In the use of 
the pneumatic piles and caissons, and the recent improvements in them, have inclined 
professional opinion more and more in favor of their employment, particularly for 
depths of foundations beyond thirty feet below the water level. 

Screie-PUes. — Tn localises where it has been found irapract cable to resort to any 
of tho usual means of foundations, as on sandspits, or on beds of a soft oongbm- 
erato formed of shells, clay, and the oxide of iron such as are found on our 
Southern coasts, iron screw-pilea have been used w tl " cccsa part cularly for light- 

The Eorew (Fig. A) conajsts of a broad disk spiral thread A, the newel of which, 
B, ia prolonged and HIted to receive tlie end of tho pile, to which it ia fastened by a 
bolt. A horizontal lever is attached to the end of the pile, and tlie screw driven by 
men aoliug against the arms of the lever. 

The diameter of the screw on top has been made from two to four feet 


Hole E to Arts. 210, ifc«,, and Arts. 168, S:e. 

ii. Classijkaiion of Strains. — Any rod, or bar of liomogenoiis slrueturo and 
uniforra cross-section g, may be regarded as a prism, composed of an inflpito 
number of CHires, each of which raaj-, in lata, be considerefl as a right prism, hav- 
ing an infinitely ainall area for ita base, and its edges parallel to those of the 

If a priam so composed be Intersected by an infiDite number of planes, each per- 
pendicular to ila edges, tliese planes will divide the fibres into iuflnitelj- small Bolids, 
each of which may be considered as the element of a flbre ; and if those elementary 
solids, or fibres, be referred, in the oeual manner, to three rectangular axes, two of 
which, as X, and Y, are contained in a plane perpendicular to the edges of the prism, 
and the tbifd, Z,' parallel to them, then the area of the base of any elementary fibre 
will be eaipreased by ds: dy, and its length by ^. 

b. In considering tlie elementary fibres contained between any two ot those con- 
secutivo planes, it will bo readily seen that^ although the relative poaitioas of tlio 
planes may be varied in an infinity of ways, tboy admit of four simple relative 
3, which, either singly or combined, will cover all the cases of change of 
a the elementary fibres between tliem, arising from tl-.eso cbaagca of positions. 






O. As on iUosh^oii of tJiia, let (Fig. A) be the longitudinal, and (Fig. B) the 
crosa-sectionofany sacb prism, and A B, and C D, be two of the consecutive planes 
in question. 

1st. The plane, C D, may be moTed parallel to A B, cither from or towards it. 
In the former case, the elementary fibres between the planes will be knghheaed, 
nnd ia the latter sliortenod ; and the strains to which they are aubjooted will arlsa 
from a force of extension in the first case, and one of compression in the second, act- 
ing parallel to the fibres. 


Sd. The plane, C D, maj take the position, C D', by turning aronnd some IIqb, 
0, in it aa an axis, in which ease the elementary fibres on one side of this axis, in 
conforming to the new position of C D, will be deflected and iengtliened, undergo- 
ing a strain of tension; whilst those on the opposite aide will bo deflected and 
shortened, undergoing a strain of compression ; and those, as 0', io tlio plane 
of the axis of the prism and of the aslsO of rotation, will bo simply deflected, with- 
out any change in their original lengtli ; the piano, C D, in ila new position C D', 
continuing normal to all tlio elementary Qbrea in their new position of deflection. 

I. TliB plane, C D, (Fig C) may rt 

C D, parallel to / 

a b, will take a 

original position. 

4th. Or the pli 

around sor 

ra of translation in the direction 
, in whicli any elementary fibre, as 
,r position, aa a b', oblique to its 

!, C D, may re 

a motion of ro- 
to it, in which 
of any elementary fibre, as b, in the 
C D (Fg B^ w'll lak a new position desorib 

pi CD 

d tl 

d d th t 

y 1 m t ry fib 




mb i 

th It g t 



V t 

m L 

t f th 

pi es q t 
t d by th m 

1 f 

^ J 



p W m 

from tl 



1 "■ 

f t al m h 

c« d d 



1 fl d h 

pp! I th 




the forces 

to which they ar 

e subjected from the 

vo the mode of solving som 

of the B 



Aa these relative h g t p 
exterior to the prism and th 
into play by tho str th £.b 

ment, for their solnt 
the solid portions of at 
form and design of the at 

The object of this M>le is 
problems which fall under this head. 

d. Relation, Jiehoeea the Ehngaiion and the fbrce iy vihkli H is produced, in Ute case 
of a rod or bar of a given cross-section, Ihe force ading in the diredion of the aais of 
ifte iar. 

From experiments made upon homogeneous bars of small area of cross-section, 
and within the limits of elasticity of the material of which tho bar is composed, it 
n shown that the elongation, from any force acting in the direction of the 
axis of the bar, is directly proportional to the length of tho bar, and 
,0 the force itself and inversely aa the ai 



Represent (Fig. D) by 

L, the original length of tho bar. 

"W, the force applied to lengthen it, 

I, the elongation due to W. 

A, tho area of the ctoaa-seetion. 

E, a constant to be determined by experiment. 


i aljove, obtained from'esperiment, there obtoica til 

Equation (A) ffves the relation botwoen the foroa and its o 
tion; Biid Eq. (B) showa lliat tlie ratio of the strain on ' 

by -J—, and the elongation of the unit of length expressed hj —^ ' 

vahie of the oonatant depending on the nature of the material. 

Mailing A = 1 and -^^ = 1, in E<i. (B), there obtainu 
B = W, 
(hat 1^, B 13 the force which, applied to a bar, the croBa-seolion of whicb is a super- 
ficnl unit, -would produce an elongation equal to the original length of the bar, 
auppo'iing its elosticitj' perfect up to this limit. The quantity, E, thus defined ia 
termed the mod^as, or coeJiderU of elaslicili;. 

Sq,iiation (A) may be stated aa the fundamental proposition in this subject upon 
which the solution of all the others depends. 

e, Tajind the relaiions Mweea the EtoagalioK and tJie Forces producing U, w!uai (he 
11 eijhi of the Mr is laken into consideralioii. 

In Eq (A), the only foree actmg is W, the weight of the bar itaelf being neglected. 
To determine the elongation, the latter being taken into aeooanl, 

Eepresent (Fig. D) by 

L, the total orighial length of the bar j 

A, the area of the eross-seotion ; 

a, tho original length of any portion as AC ; 

die, the lengto of an elemeatarj" portion of AC ; 

W, the force applied at the end B ; 

to, the weight of a unit of volume of the bar. 

The volume of the porlJonAC will be expressed by (L-a) A J and its we^t by 

Tho total force acting to elongate the portion A C will be expressed by 
■W + (L-s) Aw, 

The relations, therefore, between this force and tho elongation produced by it on 
aoy elementary portion cJ;e, will be obtained by suhatitntJag<!a:for L, andW+(E — ss) 


A 10 for W, in Eq. A. Making tliose substitutlong, and fiadiag the oorraapcndin? 
elongation, there obtains 

' rho total length of dx after eloEgatloa will, therefore, be 

Integrating tliia between the limits ic = 

x = L, tliei 

E A 

for the total length of the Ijar after elongation. 

£. It will bo readily seen, frorn the preceding discussion, that the greatest straia 
on the bar will be at tlie top, and that it will arise from the force, W, and Its own 
weight, or from "W-j- L A«/. The strains on tlie other sections Taryingmith a;, wlli, 
thereroro, decrease aa x inoreasoa. Consequently, the strain on each unit of area of 
the bar will bo yariable; and, representing by a any variable lengtli, asB C, estimated 
from B upwards, the force acting on the unit of area at any point to produce this 
strain will, iroro Eq. (A) be expressed by, 

in which X is tho elongation correspouding to a ; and In order that tlie strain shall 
bo tho same on the unit of area of every seotioa, aud therefore equally strong at 

- must bo constant. 

g. To apply this, let the cross-section of the bar (Kg E) at every point bs a 
circle, and let tlie radius of any one of these circles be repre- 
Mited by r. 
The area of the circle will bo 

and tho weight of this elementary volume by 

Substituting those values, in Eq. (0), for A, and a: A «f, and mak- 
ing — z=e, there obtains 


to r^resent the Btrain on the unit oE arei on 
Differontiating Eq. (D) there oblaing, 

ju I f' rfj; = 'Ec2 ^r dr, 

dr w , 

wbicli integrated givc3 

which shows that tlio hno cut from the bar, by a aectioQ through tbo asis, h a log- 
nritlimic curve. 
Making TT 1-' == A, and E c — m, in Eq. (D), there ohtaina 

W+W f'j^dx = mA; (E) 

lienoe, bj ilificrentialion, 

w A. dx = m, d A, 

-^ = — (fc. 

Integrating this expression betwcon the Hmita of a = o, and » = L, and repre- 
senting by A', and A", ttie corresponding values of A, and in whicli r will take the 
corresponding valuea r' = 6n, and r" = am, ihore obtaina 

benae, passing to the equivalent numbers, 

— L 
A" = A' e ,(E) 

But, from Eqa. (D) and (E), the quantity E ;;=: m, is evidonlly the welghtor forcoor 
tension, on the unit of area at any cross-section of the bar; so that, at the lowest 
point, where the strain arises fvoni tlie force W alone, the total atrniu on A' will be 
expressed by m A' ; hence 

mA' = W, BcdA' ~ -^. 

Substiluting tlJs value of A, in Eq. (E), tlier© ohtaiofl 
f(T the value of tlie area at the upper end. 


h, Jielaiicms beUeeen a fm'MViMch prodiices simple dejkdkiti and the ehtigatiom and 
compressions ef the JibrM of a iar, the cross-section being miiform and eymmeirkalniiih 
respect to the plane in vihich the force acts. 

In tho problem here proposed for aolution, the circumstanoea are the same as those 
that UBuallj ohlam in all Btruutures subjected to farces which act; either obliquelj or 
perpendicularly to the fibres of the material of wliicb the parts are composed; as, for 
example, in the various kind of frames. 

In all such cases, the cross-seatious of the parts ai 
vary by Inaoneible degrees, by a law of continuity fr 

bat regarded aa the eame betwoon hdj two stK^tions 1 

Ithaa been stated, in the illastraUon already given, thal^ 
fiection, the hypotheses geaerally adopted are : 1st, that the plani 
perpendicular to the fibres of any bar, taken at distances infinitely near each other, 
wilt remain normal to the fibres ailer deflection ; 2d, that these planes will rotate 
aronnd 6ome line drawa aeroas the figure of the cross-section ; 3d, that the Sbrea 
lyhig on one side of this Ime will be extended, and those on the other coTopreaaed; 
4th, that the elongation or compression of any fibre will bo proportional to its distance 
from this line; and 5th, that ail the fibres contained in a plane passed through liiia 
line and parallel to the a:s:is of the bar, will not bo changed in length by the defieo- 
tiou undergone. The central fihre in this plana is termed the mean, or nmtti-aljihe. 

nitely m 

iniform, or else they 
>int to anolher; the 
apart, being siraUar, 


!f - I 

"1 CO 


Let (Fig. A) bo the longitudinal section, and (Fig B) the figure of tl.o uniform 
cross- section, taken at any point as A B (Fig. A), Bud which ia symmetrical with tha 
line A B (Fig. B) cut from the plane of cross-aectiou by the piano paaaod through 
the axis of the bar, and ia which a force, W, acta at the point F, to cause deflection 
in the bar, which may be supposed to be fixed in any manner at the point E, Let 
E F be tlio mean fibre cut out by the plane of longitudinal section; and P the 
line of the fibres, cut by the plane of cross-Bection, which are not changed m. length 
by the deflection ; and which may be termed the neu/rol axis of the oross-section. 
Let X aadO Y be two rectangular coordinate axes to which oil points of the cross- 


Aif EXDix, 897 

Represent by 

L, tlis original length of an elementair fibre as R B, a b, (Fig. A) 

a=dse dy the area or ila cross-secUon ; 

x aa3 y, the coordioates of a; 

0, the mflnitoly small angle which tlie plane C D' makes with its original poM- 
ti^n, C D aiter defiedjoo. 

Now, from thehypothesiaadopted, any fibre, aa a b (Fig. A), contained between two 
consecutive planes, will, after defieetion, be lengtheneii by an amount equal to b C in 
the relative change of poaition of the plane C D; and as the diatanco of this fibre 

from the oeutral 33:13 ia y, this increase of length will he 


in like manner, the doccenao in length of any filjre at the same diatanoe from Iho 
neutral axis, oq the other ^de of it^ will also he expressed by y 0. 

Resuming now Eq, (A), and Bubstituljng in ita aecond member dxdy~a for A, 
aod ^ n for ^ there obtains 

which expresses the relation between the strain, and the corresponding elongation 
for any elementary fibre. 
Therefore the total strain on theflbrea elongated will be eipresaed Ijy 


In lilte manner the strains on the compressed fibres will bo expressed by 

the negative sign being used to denote the contrary direction of the olaatlo resist- 

As these strains are caused by the force "W acting to deflect the har, aud tlierefora 
to produce rotation about any neutral axis, aa P, with an arm of lever S=z, 
there will obtain, to cxpreaa the conditions of equlllbriuni of the aystom of forces, 

^jySil^dyy - ■~JJ'Ed:cdyy = o;[G) 

~J'C-Edxdyy'> + -^ jy "E di: dy y'' ~ Ws = 0. (H) 

]Jq. (G), which expresses the condition that the algebraic sum of the strains 
on all the fibres, parallel to the mean fibre E F, and perpendicular to the plane C D', 
is equal to zero, shows that the neutral axis, P, passes through the centre of 
gravity of the figure of the cross-section ; and Eq. (H) that the sum of tlie momenta 
of the Btrains and of the force W is also equal to zero. 

When the centre ofgraWty coincides with the centre of figure, or tlie neutral aiia 
divides the cross-section symmetrically, Eq. (H) becomes. 

~jy-Edxdyy''-W^ = o. (I) 

,dhy Google 


n 13 analogous to the general expreasion for tlie movcent of inertia of a 
Tolume of uniform denmty, in which E ia constant and depends only on thephygical 

properties of the material, and / / lit dy y' depends entirely for its value on the 
figure of the oross-seotion. To apply this to any particular figure, the integral must 
be taken betivcoa ic=o, and x,='b, in which h is the breadth of the figure eatiaiated 
along the neutral axis ; and between y=e, and y=: -i li, in which d ia the length of 
the flguro, estimated along the line drawn through ila centre, and perpendicular to 
the ceutral axis. 

Tbe expression 2 / / Vi dx dy y^ liaa received the appellation of the momenl of 
jl&dbilily; and Wz that of the bending moment 

k. Forliimlar moments of JtedMity. — The value of the moment of flexibility, which 
is a mere problem of calculus, is easily found, for any geometrical figure, from the 

double integral / / dady y'. 

For examples, when the cross-section of the figure is a reclatigJe 
(Fig. F), in which & is the breadth, and d tho depth, the integral, taken 
within the Jimits'a;=9, and x=i ; y=o, and 1^=^ d, becomes 

2jy'dxdyy^ = -^bd'. 

1 (Fig G), like that of a hollow girder, m 
which 6 is the entire breadth, d the total depth, 6' the breadth of the 
r, (f its depth, the limits become, a = 6- 6' ; ondff =irf— J<f ; and 
ttie moment of flexibility, 

2_£r*-*»' = i^("'-w) 

The expression will he of the same form iu tiie case of the cross- 

sootion of the I girder (Fig. H) in which 5 ia the breadth of the 

flanges; 6' tho sum of breadths of tho two shoulders; (£ tlie depth of 

tho girder, and if the depth between the flanges. 

3. When tho cross-section ia a circle, and the axes of coordinates 

e taken Oirough tho centra, the limits of a will be -H r, — r ; 

and those of y= tJ t' 

;' will be the sf 



= i^r"' 

iS\ i. For a hollow cylinder, in which i' is tl:e exterior andr' thein- 

il terior radius, the iotegral ia J ?r ( r* — r''). 

X 5. When the croas-aeotion is an ellipse, and the neutral asis coin- 

1 cidcfl wiih tho conjugate axis, if the transverse axis be represented 

\ by d, and tho conjugate by 6, and the limits of x and y be taJten as 

II, in the drole, tlien, 


-l,l»j,p.atl; ■ 

,dhy Google 

1 Hirain oit the imit of area, — Retamicg to the general expression Eq. (I), by ro- 
pr;seii;i.>g 2 / / dxdi/y'bYJ, it becomes 

L EI '^ ' 
miiltipljing eacli member of this equation by y, thero obtaiiia, 

But I/O is the elongation of the elementary 5bre L at the dlstaneo y from tlie neutral 

axis, therefore, Eq, (A), a: 

is the strain on tlie unit of area, so E-^|:~ '^ — t"!/ '^ ^^^ strain referred to the atut 
of urea caused by the deSectioa on the elementary fibre at the distance y from the 
Doutral axia. 

Taking, for example, a bar having a uniform vectaagular crosa-section of tlie depth 
d and breadth b ; and represen^ng by R the limit of the strain on the unit of area 
of the fibres at the distance -Jd from tha neutral axis, and for y, substituting ^d, and 
for lies value -^biPi there obtains, from Eq. (K), 

which expresses the relations that rauEt exist between 6, d, W and a to satisfy this 

m. The quantity J- B 6 iP reeeives the name of the moineat of ncpkire, when E is 
the strain on the unit of surface at the instant that rupture takes place; and its value 
has been determined by direct experiment as stated in the subject of the Resists 
anoB of Materials. But it is to bo noted that as tho proportionality of the elonga- 
tions or compressions of the fibres to the forces causing tbem is truo only within 
certain limits, and that it fails when the strain approadies that of rupture, the resulla 
obtained from Eq. (L) will be found to accord with experiment only within these 

n. Solids of Egual Eesislance. — A like problem presentaitael^ in strains caused by 
deflection, to the one in which the strains are caused by a force acting in the direc- 
tion of tho fibres; in which, the crosa-section s, varying from point to point, but 
being similar flgurea, it is proposed so to determino the longitudinal section, tbat the 
greatest strain on the unit of area for each cross-section shall be constant 

EepresenUng this constant strain by H', and supposing the cro^-seotions to be rec- 
tangles, Eq. {!.) becomes 

Saw Bq. {L') may bo HatisGed in various ways; by making W either constant, oi 
variable with z; by making either & or d constant, or variable; or by making any 
one of these quantities to vary with tho other. 


too AfFEHVIS. 

The following caaea may be taken aa examples of tlie applications of Eq. (L), 

C 1 i '^ pp b (Fg I\ tbs 

oas- t fwliht ryit a 

t gl w th t t I d i 1 t ri- 

tl d ptl t b Hi 1 t d any 

d tra d by osta t f roe 





this fibre. Por a 

tanco 2 from the poiut of application of W, 

representing the variable depth by y, Eq. (L) 

' bR' ' 

which !a the equation of a parabola, the vertex of wliicb is at Uie point B. Assum- 
ing the liae A B of the longitudinal section to be a straight lice, the line B D which 
boocda the figure on the opposite side will bo the parabola given hy the equation. 
Case 2d. If the strain arises from a weight 
uniformly distributed clong the line A B (Fig E) 
and that for a unit of length of the n e 
reapouding woijt''t ^ represented lyu h n 
for any distance a frona B, the weg wi be 
VJZ, and ila arm of lever, for the cro s-sec n at 
the distance z Iram B, will be J^ If tlien ha 
breadth remains constaat and depth ab e E 
(L) will take the form, 



-. .-. y' = 

R6 ■ 

which ia the equation of a right line B D of which B is the origiu of coordinates. 
Case si Taking W aa in tlie first case, let the ratio of 6 to i^ be constant, or 
S = dm, then Eq. (L') will become 

which ia the equation of a cubic parabola for tbo curve between B and D (Fig. K). 
Cass 4i/t Taking W aa in the flrst caao, lot Oie 
depth d, (Fig. L), be constant, and the breadth 
vatiable. Eepreaenting this variable breadth by 
X, Eq. (L-) becomes 

, _ Wb _ sw 

•^ "iad"- ■'•"" R'd'"' 
which ia tho equation of a right line having the 
origin of coordmatca at B, The figure of the 
longitudinal section perpendicular to the line of 
action of W will be an iBOSoelM triangle, C B D. 


,dhy Google 

Cose 5lh. Snpposing', as in the second ca=e an 
equal weight vi on each unit of length to be d g 
U-ibated along the ceiitro line A B (Fig. M) and 
the depth to be conalaat and breadth viir ible 
Then for any croaa-section at the distance 
B, Eq. (I/) becomes, 

R' = 

ixd" ' 

■ E'cP 

which is the equation of a parabola having its lei 

ihereforebebouiidedby the two equal and eym metrical paratolio area B C and B D. 

Cose 6!ft. Supposing a bar to rest horizontally on two supporba. A, B (Pig. If), at 
its two extramities, and to be strained 
hy a weight W acting at any point D, 
and that its depth is VBliable and 
bread tli ooustant. Eepresent the 
length A B by 2 i, and the distance C D 
between the middle point of A B and 
Ihe croas-section where W acts bj z. 

From the theorem of parallel force 


lei components of W acting 

- .~f -"W, and for B by 
the neutral 
for any cros 

A and B, and conHeqacntlj tli 
llieso points, and 

Fig. K. 
1- read ion, are the paral- 
for the point A, by 

imd their respecti 

h regard to' 
W, Eq. (L'), therefore 

''• ^ —Ti — ■ iw' ■■ ■' = R^! ^' ~'^: 

which la the equation of an ellipse referred, to its centre and axis. The llne.A 
therefore, being a right line, tlie outline of the longitudinal section of the bar oa t 
opposite side will be the semi-eliipse A E D ; the semi-conjugate asia of whidi c 
bo foand from the equation of the curve hy making z=o. 
"Were the weight W to act at the point D alone, then the problem would fall ir 

the Case 1, and the longitudinal 
ares A E and B E. 

t'oselUi. Supposing a bar 
to rest, aa in the preceding 
«ise, on two supports, A, B 
(Fig. 0), and a weight w to bo 
distributed over encli unit of 
length of the contre lino A B ; 
the depth o! the bar d to he 
constant, and the breadth vari- 
able. Ropreaenting by 2 Z the 
length A B, and by z, the distance C D of any 

would ha bounded by the 


then, from the Iheorem of parallel forces, aa 2 w J ia tha total weight diatribuled otot 
A B, the pressure on each support scd consequent reaction will be w i. But ths 
weight diatributod over the portion D B is espreaaod by ui(! — z). Tbe oroEa-seotioii 
at D will therefore be strained by the two forces w I acting at B upwards ; and 
w (I — z) acting through the middle of the diatanco D B downwards, Ec[. (L') to con- 
form to these circumstances will become 

^~ Roi- ■ 

which istliecquatioD of aparahoiareferred to thecoordijiate axes C B, C E. Tiiolon- 
^tudinal section perpendicular to the line of action of the force 2 w I will be bound 
ed by two parabolic arcs A EB, and A F B, the vertices of n 
E F bisecting A B. 

ofWa A B pe 

^ to the rs D 

of flsxibiiity at this section. This case therefore is the aame as os 4, 

line of the loDgitudinal section will be two isosceles triang a, h g mm n 

base E F, and their vertices at A and B. 

If, as in Case 6lh, the weight may act at any point, then t b w 

parabolic arcs, having their vertices on the perpendicular to g A B 

Ca3e 1th. 

O. Effed ef Uie figure of Ike crost-sectkn on tlie resisttma tosii-airtscattseAbydeJkction. 

From Eq. (K) which gives the strain on the unit of area for any fibre at the dia- 
tanee y tVom the neutral axis, or 

R = 


From this it ia scon, that, for any conetant value of the bending moment Wa, the the distance^ from the neutral axis, will 

be tbe smaller a 

I . 

B the greater. Dut fc* any tw 

same area A, iu which ^ =: -^ d js the distance of tbe xt 
tral axis I will be the greater as J J ia the greater Th 
give a very simple means of comparing the relati\ 
by cross-sections .of equivalent areas, but of differ t 6g 


APPENDIX. 403 ■ 

Taking, for examples, the eiiuivalenl crosa-seotJons in the rectangle (Pig. F), the 

elUpse,aBd the x ^rder (Fig, H), the respective values of j-r are, for the rectangle, 

for tlie ellipse, the area of which ia J ir 5 rf, there obtams, 




tor the X cross-section, if the breadth b—V of the web conneoting the two flangca 
be so small that its area may bo neglected ia estimating tlie qnaatity I, and in 
like manner the thiokness d—d' of itheflaogesbe algo so small, as compared with^ 
tiiat it may also bo neglected in the same way, then the value of I will nearly op- 
proach lo the quantity J A iT, in which A is the area of the ili 

id~ id 

Comparing the three valves above of — , it is apparent, tbiit, A being the same 
in each, the crosa-seotion of greatest resistance is that of the x form; and that of 
the reetaogle is greater than in the ellipse. And that ia each, A remaining tho 

= iXd. 

3, but 6 varying inveraely a 


rfill inc 

e witli d. Tliis shows that the 

mass of tlio flbres should be tlirown as far from tlie neutral axij^ which in .each of 
those cases is taken to Tjiaeet the distance d, as the limits of practice will allow. 
Hence is seen the advantage presented in the crosa-soctions of Figs. G and II. 

p. Shearing Strain. — This tfirm is applied to the resistance offered by the flbres 
to a force acting in a plane perpendicular to them, as illustrated by Pig, ; and tho 
force producing tho strain ia termed a sheariag farce. 

The result of tho action of such a force would be auoh, for example, as would be 
seen in the distortion that would take place in a very short bar of great relative 
stiffness, lilie a nail or peg, which firmly fixed at one end, should be strained by. a 
force acting on the projecting part perpendicular to its axis. ■ 

Comparatively few experiments have been made to determine the amount of re- 
astance oflered to this kind of strain. But from the evident analogy of (he phe- 
nomena in this caae to those in the case of the duect elongation of the fibres, writers 
on the subject have proposed to- express the relations between the distortions of tho 
fibres and the forces producing them by formulas anali^ous lo those for the drees 
13 in the cases of direct elongations. 
It (Fig C) by 

L, the original length of any fibre a b between the 

two consecutive planes A B and C D. 
y, the distance & 6' which every point of the plane 
C D has moved in the direction of C D, relatively to 
Iho plane A B, owing to the force cauring this dis- 

I, the stram on any libre. 
a, tho area of the cross-section of any fibre. 
R, a constant. 


Kow, in tlie displacement of a S from the posiUon ah to ah', it may be assumed 
from aanlogy, tliat tlie reaislanee to tliia displacement is, oa the one liand, propor- 
tional to a ; and on Ihe other, to -j- , ivliith ia the measure of tiiia displacement 
referred to the unit of length. To express tliB hypothesis there oMalaa 

which eapreasea the ratio between the straia on the unit of area of any Gbre and 
the displacement of this area corresponding to a unit of length. 
1 Eepresenting by T the entire resistance to this displacement of C D ; by A' its 
area; and assuming G aa constant throughout its area, there obtains from Eq. (M) 

T = G A -|-. (0) 

It has been proposed to call the quantity B, in the preceding analogous expression, 
modulus of longiludinal elaslidty, and the quantity 6 in this modvius of lalsral 

So far as determined by experiment, tho ratio of the two ([uan titles, or — ^, differs 
but little from 3. 

From the preceding discussions it will b0 9een,frora thehjpothesisadoptcd, that tlie 
reeullant of the resistances offered by thelongitudmal and lateral elasticities of any 
malcrial to a atrain, caused by any force which calls into action these two rcsiatanoes, 
passes through the centre of gravity of the resisting section, this point ia termed 
the centre of ehsiicily. 

H. lAmits of ihe resistance im the unii of a/rea to a loiigitudinal, or lateral strain. 

By means of the liindamental formulas (A), (L), and (0) tho limit of the strain on 
iba unit of area, at the fibre where the strain is grealest, caused by a force acting iu. 
Uie plane of symmetry of the crosa-aection, whether perpendicular or oblique to the 
direction of the mean fibre, can be readily determined. 

, Supposing the force to be oblique to tho mean fibre, it can be resolved into two 
components, one P perpendicular to the direction of tbe fibre, the other Q parallel to 
it . The component P will produce a deflection, which will give rise to a certain 
^rqoant of compression, or cstension in tho estraniBfii^re, tlie value of which, for the 
unit of area, can be found from formula (L). In lilie manner the component Q wil} 
CaUSO a certain amount of oompreasion, or estenaion, the valne of which, for the 
unit of area, can be found from tho formula (A), Now" these strains being iatliodireii- 
lion of tho fibres, their amount on tlie unit of area for tho extreme libre, will bo equal 
to the sumof the two calculated from rorraulas(A)and(L); and should not he greater 


tiian tlio resistance E that can be offered with safety to tlie 

m which — - is the diatanco of Ihe extreinB fibre Iroiii the neutral axis ; and A ia tho 

The component P is also tlio amauat of tha sheariDg forca on any cross-seclion ; 
and the reeistaace to it on tha unit of area can be found from formala (OJ, denoting 
by E' lis limit there obtains 

far this limit. 

If the strain, therefore, ou Uie unit of area k in tlja one case leas tlian B, and in 
the other less tliau E', the change which tlie fibres will undergo under the action of 
the force will be witbin the limitB of safoty. 

It ia important to remark, that the values of R and R', when tha sign of equality 
ia uaed in the two preceding esprossiona, cannot always be aatiaSed in practice for 
any assumed area of croaa-section, although for economy of material it is desir- 
able they should be. Taking, for example, a beam of a lectaogular crosa-sectioo, 
tho area of which ia expressed by Ii d, which is deflected by a pressure W, acting 
with the arm of lever t, the two preceding expresaiona, in thiscase, taken as equali- 
ties, become 

„ GWi ,„, W 
~ TW ' ~ Td' 

Aa "W, !, E and E' are given, the values of 6 ^ and 6 t^ as determined from thera 
can b« represented by the equalities 

6 d' = 511, and 6 d = n ; 

hecee, dividing tlio ono by the other, there olitaina iJ = — , and 1 = — . KflW 
these values may be such as to make if so much greater than 6 as to be beyond the 
limits of practice; in which case a value should be given to d, such, that the value 
of 6, determined from the equality 6 iP = m, shall be within the rules of practice, as 
the strain from deflection is more to be guarded against tlian tliat from the shearing 
force. Whilst tbe limit from deflection should not be exeeedoS, neither should that 
from shearing be dangerously BO. 

r. Eslalions lelmeen ihe strains and tlie forces prodacmg Oiem in Ihe case of straight 
Seams, or girders of anifbnn cross-sedion, resting oa two points of sz^port, in tehich 
Die farces act ^nsversely to Vie meimfibre, 

The case here given finds a number of applications in the combinations of straight 
beams of timber or iron in framing ; in. wbioh it may be necessaiy to find the reac- 
tiona of tha pojnla of support (Vom the forces acting on tha beam, tha changes caaaed 
by the strains on the fibres, the amounts of Ihe bending moment and the shearing 
force, with tlie view of so proportioning the figure and area of tha cross-seclion as to 
resist the greatest strain to which the unit of area can be subjected at any point. 


The straii 
der the circ 
niay arise either from a weight 
or preasura acting atone point 
botween tlie supports; or from 
weights, or pressures Of equal 
intensity uniformly distributed 
along the entire length of the 
beam ] or from both of thesa 



weighta or pressures must bo 
applied perpendicularly to the 
mean fibre of the beam, and the reaclioa of tlio supports taken vertical. 

Case 1. (Pig. Q) Beam resting hariaordaily on mpporls al each end, and aUnUned 
hyaforceadingperpendkitlario Sm mean fi'iro al its middle point. 

Eepresent by 
2 I, tiie diataDce A B between the points of support. 
a W, the fiirce applied at C the middle point. 
a and y, the coordinatoa of anypoint of the curve A D B, assumed by the m^aa 

fibre under the action of 2 W, referred to the axis X and Y, through C. 
t ^ E I, the moment of flexibility, Bq. (I'). 
{, the radius of curvature at any point. 

Ti'om the theorem of parallel forces, each point of support will furnish a reaction, 
expressed by -W, equal and contrary to the components W of 2 W. Then, from 
Eq. {!'), there obttuns, to express the relations hetween the bending momontaud the 
moment of fiezibility, by substituting W (f — a) for W^, and for L, ife = Jo 
_^_ W(l-x) „ 1 _ W(i-i 



snd substituting- For tlie radiu; 

.Hegarding thedefleotion as very small, --rVt which is the square of the tangent to 
curve at the point <c, y, may be omitted, and Eq. (2) becomes 

Integrating Eq. (3), end noting that, for x~o, tho tangent bocomea parallel fo tha 

axis of X, and -^-- = o, there obtains 


Integrating Eq, (4), and noting tha^ for i=I, y=o, there obtains 

»='-fC--^ + f + -=^^=~('-=')Pl'+2l«-«')!(0) 

iviiicli 13 the equation of the curve D B of llie meau fibre. The greatest ordinate 
of tbe curve C D, ropreaented l)y_/j is obtained by mating a; = o, Eq. (5) ; hence 

Case 3. (Fig. Q) Sb-ain arising from a tveirjlit or prcsswe iv, imfornily disiri^uied 
over eacli unit of length of 2 1 

In tliia case tlie reaction at each support will be — la I, and ia equal and coutrary 
to either of the two parallel componeuta of 2 lo i, the total weight. 

Tor any distance l—x from B, the weiglit will be a (I— a;) acting downward; the 
Cbrofl therefore at the cross-section at the point, a, y, will have a strain caused by 
— w I acting upwards, and a (i—"^) acting downwards. The moment of the force of 
reaction will be— vil(l—s:); unci that of lu (?—»:) will be w {l-~x) i (l—v) = -i 
Ki(i_3;)'. The hendhig moment therefore will be the algebraic sum of these two. 
Eq. (3) tiieit beoomea 

Hence, by the same processes of integration as in Case 1, 

= i-^(P-s1 (!!•-«■). (9) 

A comparison of the value obtained for f, the groatest ordinate, from Eq. (9), and 
for/ obtained from the following equation, 

which is the equation of a parabola, obtained by omitting x' in Eq. (9), the greatest 
value of which is P, as small with respect to 5 J°, will show that the latter equa- 
tion may be substituted for the former, aa that of the curve A D B. 
From either of the two preceding Bqa. there obtains, for/ corresponding to i =: o, 

To ascertain the position of the 
strain on the unit of area obtains, i 

" "'^°""""' -Wy-«),and-i«.y"-a:'), 

!n the two preceding cases. Each of these will be greatest for a: = o. Having this 

greatest value, its relation to the limit B can bo found by the process already given. 

The shearing force, which is W in the one case, and via ia the other, for any 


croaa-seetion at the aistaaoe x from D, it ia aeen will be coualant throughout in Cast 
1, but yariable in Case 2, Hating- !t3 greatest ralue for x = l,'m the latter. 

Taking the value ol f, or the greatest nmount of deflection in tlia two oaaes, il 
, will be seen thai;, supposing/ the same ia both, W = |- w I, or that the value of/ 
obtained from the force 2 lo/, uniformly distributed, would be obtained by J lu acting 
Bt the middle point C. 

If it were desired that the greatest longitudinal tenalou on the unit of area should 
in each case bo the aamo, then the groatest values of the two bending n 
Wy-ic), and f VI {i'-x'% must he equal, o 

Wi--i«jr'. hen 

I W = 


which shows that the greatest longitudinal tension on the unit of area when the 
weight 19 uniformly distributed is the same as what would arise from half this weight 
acting at the middle point C. 

It is easy to spply the Eqs. io the preceding cases to the one in which there is 
weight 2 W acting at the middle point, and one 2 wl uniformly distributed, by re- 
membering that tha forces of reaction at A and B will be represented in this case 
by W and w I; and that the bending moment for any cross-section will bo the al- 
gebraic sum of tha bending moments given in tha two preceding cases. 

Case 3. (Kg E) Beam haviiig its two endsjlrmly kelddtnon, on Us stipporls; as, far 
example, a beam having iu ends embedded in any manner in two parallel viaUs. 

In this case, the strains 

areprodiicedhyaforce2 W 

acting, as in Case 1, at the 

, middle point, and one 2 w ( 

uniformly distributed as in 

Case 2. The circumstances 

didferlng from the other two, 

in that the ends of the 

beams are supposed to be 

hold in a horizontal posiljon 

by being firmly embedded. 

aW Thia condition may be sup- 

poaed to arise from forces 

acting vertioally upon the embedded ends beyond tha points of support A B, 

"With respect to either of these forces, as the one at the end towards B, which may 
be repreaented by T, it can be transferred to the point B by substituting a couple, 
in the usual manner, the moment of which being unknown may be represented hy 
(I. With respect to T, it will bo determined by the consideration that the reaction 
at each support will be W-)-io I. 

Adopting the same notation as in Cases 1 and 2, the relation between Uio momonl 
of flexibility, for any oross-saotion at the distance a; from E, tlie bending mcments, and 
the moment of the couple ;■, ■will be expressed by, 

= -W(I-l) -',«(!•-.■) + ,, (10) 



Integratjng between tlio limits of x, anfl j; = o, there obtains, 

.-|- = -^("-tH«('--t)+"<"i 

But as tlio tangents to the curve, bolTi at B and C, are horizontal, 5^= o, for tha 

values, a: = oiiQd« = i. Jrom this last limit tlioreibro, there obtains, from Eq. (11), 

oz=~!iWl'~imt' + ft, 

Substitullug tills value of ji in Eq. (11) and reducing, there ohtaina 

= - ^W {Ix-}-") - i w (Pcc-s:?); (12) 
Integrating Eq, (12), and noting that Cot x= t, y~ 0, there obtains, 

.J/-iW(— |-+^ + -^) + j!«(-if- + ^ + -^). (13) 

for the equation of the curve ADD. 
Substituting a;=(i, ill Eq. (13), the oorregponding value for yi=/ becomes 

From this value of /it will be seen that it is the same as if one-half of the pressure 
uniformly distributed bad been cnnoentrated at tlie middle point; and, by making 
tu = and W =: o, respectively, in. it, that tbe corresponding values of/ohtained 
win ho in tbe relations of 4 and 5 respectively to 1, as compared with/ in tbe pre- 
ceding cases. 
Substituting in Eq. (10) for ^ its value, 

there obtains, for the boDding moment. 

From an c:i:amlnaUon of this equation it wilL be seen that 

for s = 0, and that aa x increases its absolute value decreases, up to a valuo a^ of « 

for which 

and which equation, solved with respect to ;>:', will ^ve oue po^tive root, comprised 
between the limits of ^?, and rz-vl tbo ilrst corresponding lo u; = 0, and the second 
1017= 0. With regard to the root *' of the preeuding expression, ag it corresponds 


lo the value -~- = o, it shows that there will be a point of iiiflectio!i in the curva 

corresponding to tlie abacissa a'j and, bejond this point, that Eq. (a) changes its 
sign, and continues Inoreasiag ia value; and, as the greatest negative value corre- 
aponda to ar = o, and greatest positive value to ar =: i, i' will bo seen, tlmt since these 
values, wliiob are respectively, 

- i W;-i to P, and i W i + J w i" 
are tlie one minua, the other pins, the greatest strains on the anit of area of the 
cross-secliona will therefore be at B and D ; the lower half of tlie eroBs-aection being 
compressed at B, yhilst that at D is in a state of tendon. 

The attains from the shearing force, at any croas-section, mill ariss from the two forces 
W, and w {I -ar) ; and aa the introduction of the moment ji of the couple does not 
affect these values, it will have no effect on these strains which wili be due alone to 

S. Beams eupporied at lliree poinls in ike same right line, and acted apint iy pres- 
sures dislributed wi ani/ majmer perpejtdiciilar to (fie mean^bre. 

When a rigid beam rests upon three or more supports, in the same right line, the 
crdinaryrulesofstaticsdonotfUrniBh the means of determining the amount of prea- 
Eures, and consequent reaction, at each point of support, arising from pressures acUng 
upon the beam; the problem in sudi a, case being indeterminate. 

Taking for example, Case 2 of a beam resting on two supports, and having a 
weight uniformly distributed along its length, it has been shown that each support 
bears one half the distributed load ; and that the deflection of the mean Sbro at the 
middle point, represented by/, ia the Barae as the beam would take were f tha of the 
load acting alone at the middle point Now, when tha beam is in this condition, it 
is dear that the pressure upon a support, in contact with it at its middle point, 
would be zero; and if the support is raised so as to bring the middle of the beam into 
some position intermediate between C and D, the pressure on it would be a certain 
portion of the entire pressure, whilst each extreme support would be relieved of a 
certain corresponding portion of this pressure ; and so on, ijnii!, the point of con- 
tact being brought in theaame right line with the extreme supports, Uie intermediate 
support would evidently counteract the total pressure at C to which tlie deflection is 
duo; which being -Sths of the entire load, the reaction of tho middle support would 
be equal to this. The two extreme supports, ia like manner, would furnish a reac- 
tion equal to the remaining f ths, or i^tlia of the total load for each. 

Case 1. (fig S). Beam resting on three poinls of support In the saine rig^l line 
dividing the length into tmo ■waequal segments. 

Let eich segment, A B, 
^^- ^ B C be supposed lo ba 

strained by a load uni- 
formly distributed along 
its length, but of unequd 
n the unt of 
length in the two. 

,dhy Google 

it by 

2 V and 2 1, the respective lengtha of A B and B C ; 

w, and !«', tlie pressures on llie unit of length of 3 V and 2 \ respectively; 

Q' and Q, the foroea of reaction at A and C ; 

P, the force of rouction at B ; 

a, ij, tlie coOrdiDatss of any point in either aagmcnt referred to llie rectangular 
coordinate axee having B for origin ; 

lA tlie angle wliicli the tangent to tlio carve at B makes with llie axis of Xi 

In this caae-tlie forces of reactions, Q', Q Kud P, are among the quantities to be 
determined from tlie conuilioos of the question. 

Aa the total load, or pressnre 3 u/ (' and Ivil, on each segment respectively, rany 
1)9 regarded as acting at the middle point of the segment^ and as their sum is equal 
to the sum of the forces of reaction ; from the principles of statics, there ohtaius the 

Q' + Q + p = 2»T -f 2^;, (a) 
Q'.x 2i'H-2iuixi=:Q X 2i + 2!c'r X ('; (b) 
in which Eq. (a) expreeaes the relations of the sums of the forces ; and Eq. (b) that 
belweon their moments with respect to the point B. 

Referring to Eq. (G), ftue 2, § r, there ohtiuns, to express the relation between 
the moment of flexibility for any cross-section of the segment B C, at the distance 

.-g- = i"(!il-«)'-«(3!-»)i<l) 
integrating between tlie limits of a:, and x = o, and observing tlint for the latter 
limit, -— = tan. a ; and that the constant introduced by tlie integration becomes 
t tan w ; there obtains 

integrating Eq. (3), there obtains 

.!, = i,i.(2^.^-jr«' + -J)- Q(i.:'--^)+ aan. ,.«, (3) 

Tor the equation of the curve of the mean fibre of the segment B C. 

By simply changing w, !, Q to correspond to the notation for the segment A B, and 
4- £ tan. to into — c tan. u, in Bqs. (1), (3) and (3), the same relations will bo ob- 
tained for the segment A B. 

But since, for a; =: o and » = 2 i, ^ becomes zero, there obtains by tbe substitution 
of B = 2 i for the segment B C, and e = 2 f for the' segment A B, the relations, 
= 2^;*- JQi>+aan...t (c) 

o ^ a )«w'i - 4 Q' p - aan. ,. z: (d) 

From Eqs. (a), (b), (c) and (d), by the ordinary process of elimination, the quantities 
P, Q, Q' and tan. lo can be readily found. 
Supposing w = w' and I =: i' ; then there obtains Q = Q', and tan. u = o, siuea 




Gm two gegmenls tecoine sjmmetrioal, and tlie tangent to the curve at B parallel to 
the asXs of X. Making tliese substjtutions io Eqa. (r) and (c), there obtains 
2Q+P = 4«-;, {a') 

By elimination bstwuen tlipse two Eqa., lliere obtaina 

Q = S l« I = ^V (4 1" 0. and P = J (4 w ?), 
which are the same values as alraaclj' given in the (ftcond paragraph of this section. 
t. (Fig. T) Beams resting upon any aumber cf micrmediate poiuls of siipjici-t 
ielmaeii iheir two ends, having their sBgrncnh imifui-mly loaded. 
The same processei!, Iblloweti in the preceding sections, find their appUcatious in 
the cases that laU under this 
V BecUon; the only difficulty 

in tlieir applicatian arl^ng 
fi'Omthetediousness of com- 
plication in arriving at the 
results sought. To avoid 
B t this, the expedient has been 

M 3 e: "■ adopted, instead of finding 

the valooB of the forces of 
reafftiou at the points of supporli directly, as in § S, to use the bending momenta 
taken with respect to tho oross-sectiona at the points of anpport, as auiiliary unknown 
terms, and from these to determine tlie Ebrces of reacljon, and also the heading 
moments and sliearing forces for any intermediate points between the supports. 

Let A B and C be any thteo of the consecutive points of support of fi benm, all of 
which are in the same right line. Kcpresent by 
I and I' , the segments A B, B C ; 

so, w', the pressures on the unit of length of I and I' respectively ; 
X', X', X"', the bending moments for the cross-sections at A B C ; 
X, y, the coordinates" of any point of the segment I referred to rectangular coordin- 
ates having A for origin. 
Talimg a eroas-seetJon at any point, at the distance e from the origin A, the weight 
uniformly distributed over the length (2— i) is w (l—x), and its momont will be 
— ^lH{i — »)', esUmating the direction of the rotation from A X towards AY as 
positive. Mien, in the expression of tho bending momont for this point, there wiE 
enter this momont, and also the moments of all the other forces, arising from tho 
reactions of the points of support, and tho pressures distributed uniformly over tho 
i^flerent segments, from A towards X ; the 'moments of which last forces will be 
expressed in terms containing the first degree of a only and constants; so that, 
definitively, the bending moment for this cross-section mill be of tho form A+Bi — 
iiBx'; in which A andB are constantg, to be subsequently found. 

Taking then tho general Eq. between the moment of flexibility and the bending 
momont, there obtains, 

- A +Bt 

,dhy Google 

Integrating between tlio limits ofs niiii ar = i, nod representing by K' what -j-bo- 
comes for a — ; and by K" for a: = i, in detertaining the value of tbe congtants of 
iategration, there obtains 

!(K"-K') = Ai + ^Bi'-Ju^C. (3) 
lategraling Eq. (2) again, between the limitaa: = o, and x = l, there obtains 

- tK' = iAi + iBf-i4-«'i', (4) 
Eliminating K' between Eqs. (3) and (4), there obtains 

iK:" = -iA; + iBr-i«ji'. (s) 

By placing the origin of coSrdiflates at B, tlie bending moment, for any cross-seo- 
tioD iQ the segment B C, will, in lilce manner, take the form A' + B' te— ivi' x', by 
uang the same processes as in the segment A B; and JVora these it will be seen, that 
Uiere will be the relation, analogous to Eq. (4), shown by the expression, 

— (K" =^A'i' + 4B'P — A'*''"- (G) 
EiiminaiJng K" between Eqs. (B) and (6), there obtains 

Now tlie quantities A, B, A', B',ean be expressed in terms of X', X", X'"; for 
the facction A4- Bar — Jwar' should have tlie sBmo values as X' and X", for 
!C = and a; ■= i; making these substil;utiona for x in this fanotion, there obtains 
A = X'forj;-o; and A + B7-iwf = X", for a = I. 

A = X', and B = i w i + - ^ ~^ -. (a) 
la like manner, 

A' = X",aniB'T=iv?'l'+-^~^. (b) 
Bnbatituting thcso values of A, B, A', B' in Eq. (7), there obtains 

i X' i -h i- X" {; + r) + i X"' r + a wi' + -/^ w' i" =o ; 


x'H-as"(; + i') + x'"i'+i{wf + «/;'») = o; (c) 

which expresses the relation between, the bending moments for any three eonseou- 
IJve pomts of support. 

This striking theorem furnishes the means of obtaining the relations between the 
bending moments for any number of cross-sections on oonsecutive points of support. 
Supposing n+l to be the number of conseoulivo supports, represented by A,,, A,, 

A] A„.i, A,_i, A„ ; and tbe corresponding bending moments by Sj, X,, X5, 

X,_„ X,. It will be apparent, in the tot place, that fiom the conditions of the 

problem, the bonding moments Xo and X, of the two extreraiUes must be zero; 
and that, llierefore, the quantities alone to be determined will be from X, to X,_i, 
or n - 1 unknown terms. To find these it will only be necessary to al>ply Eq. (c) 



Buoceaeively to each conBecuUve pair of segmcnla to obtain the number of equations 
from nhicb, hy succossive elimination, Xi, Xg, etc., can ha found. 

Having, in this manner, determined the bending moments X,, for the ccrrospond- 
ing pointa of euppon ; that for any point, between two supports, of an intermediate 
segment, can be found ; and the equation between it and the moment of flextbility 
be deduced ; by determining, from ICq. (a), the values of A and B corresponding to 
thifl segment, and substituting them in Eq, (1). Tlie final equation, determined by 
lotegrating the equation twice, will give the relations between x and y of the carve 
of the mean fibra in this segmenL 

ApplicaMoia of Fimmda (c). — This formula can be applied, first, to find the bend- 
ing momenta at the pointa of Bupport ; and second, from then' values to deduce the 
pressures or reactions at those points. 

Case 1 . Beam rssting on (Ai'ee poMt of su^ori al equal distaices apart — This ease, 
which has already been considered, is repeated here to compare more directly titi« 
method with the one treated in g S> In this case, the quantities represented by 
I, V, V), id'. Form (e), become respectively 2 I and !u; and 5', X'" are each aero. 
Mailing these changes, there obtains, 

aX"{2; + 2() + i(w8J= + io8i') = o, orSX"i + 4!«i' = o 
hence X' = - -iwP, 

But from Eq. (1), § s, making x = o, the value of tl:e bending moment for the in- 
termediate point of support 13 Q 2 i— 2 loP, by clianging the signs of both members 
of the equation to conform to the foregoing value of X'. Equating these two values 
of the bending moment, there obtains 

Q,2 ;-2 «j r = - i w l\ hence Q = J u^ ? =: A' (i vil); 
which Is the same valuo as before found. 

Case 9. Beam, resiiag on fow points of sv,ppoTl,the two extreme segments being eqwU 
and the midiSe one tineqval to either of Ste others. 

let A, B, C, D (Fig. XJ) be the four points 
Erf.U of support; the segment A B = C D. Re- 

present the segments A B, C D by ?, and B C 
. I . •, by ni; by w„ Wt. w, Iho pressures on the 

I L . _!__ — Jp uaiia of length on the segments A B, B C, C D 

Firal, to find the bending moments, S„ X,, for the cross-sections at B, C ther« 
obtains from Form, (c), for the segments A B, B C, 

2 X^ {I + nl)+X,nl + i(«,,l' + la^n'l')^ 0, (k) 
as Xo, = ; and for segments B C, C D, 

X,l + iX,{l + nli-i-i{m,n''C + io,P) = o,(j) 
as X, = o. 
Eliminating between Eqs. (s), (j), thcro obtains, 

l(J + »)(2 + 3») 

»)•■]. (•) 



Taking now the general exprcaaion for the bendir.g inometit, X, at any point of 
the segment C D, v^hich is of the form, 

aad determining the valuea of a and 0, as in Eqa. (a), (b) ; and maliing X = o, fol 
a: = <'; and X =^ Xj, for a; = Z ; tha values of x being estimated from D, there 

« = o,aaA0l--ivi,P = X,; 
which suhstituted in the preceding expression, there obtains 

X = (^'- + i^,i)x- iw. x\ (0) 
In liliB mannor, for tho segment C B, estimating the x's from C, tlic gfioeral value 
of X taiies the form 

■ X. = a' + /l'x,-iv:,x\; 
.ing a' and 3' from tlie conditions tliat for a ~ o, X ^ Xj , and for i, — a i 
; there obtains, after eliminating a', ff', 
/X, — X, 

f( ^'7^^' +iv,,^l)x,-i^,x\. (p) 

For the segment A B, estimating tho ic'a from A, by a simple change of the notation, 
placing X, for Xs, and wi for Wj, in the valae for X for tho segment C D, there 

X = (^—^--^iVHl)x,-iw,x\. (q) 

Now tho object of the proposition may be, either to find tho reaction at the 
points of support as in Case 1 ; or to find tlio strain on the unit of area at any 
cross-section. In tlio first case, tho modeof proceeding will be the same as in Cass 1. 
Tbe bending moment, arising from tbe force of reaction regarded as unl;nown, and 
from the total force distributed over the first segment which is Itnown, must be 
placed equal to the bending moment aa given in the ISq. (m), and from the resulting 
equation tlie force of reaction can be found. In like manner, tlie difference between 
tlie moments of the Ibrces of reaction at A and B, and of the total forces on the 
two segments, A B, B C, must be placed equal to the bending moment ^ven in 
Bq. (n), to find the force of reaction at B, The sarne proceasea must be followed for 
the two segmonta D C, C B. 

In the second case, to find Llio strain on tho unit of area fur any oross-secljon, in 
either segment, the Eqs. (o), (p), (q) must be used, os in Coses 3, 8, | r. 

Case 3. To determine the reactions at Oie poinit of stipport in a beam mtifonnli/ 
loaded on each unit, of length and Tesiing on five points of support at equal diatancet 

Let A, B, C, D, E, (Fig T.) be the five points of suppori. Represent by 
!, the equal distancea AB, B C, etc; 

HI, the weight on the unit of length; Btf.V 
P, the force of reaction at tiie middle point C ; 

P', P, tha equal foreea of reaction at tlie P p P 

point B, D; p" I j' I p" 

P", P", the same at the extreme pointa -^ i 1 i i 

A, E; f{ B C 5"^ E 

X', X", the beniimg momenta at B and C. 

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nudfor tho two BC, CD, 

X-,+ 2X" + Jwf = o; 
and by elimiuaiioa, 

X' = - ^\ w f, and X" = - ^^w f. 
Sow, for tlie SHgraeat A B, Oio forcca acting upon 11^ toprodueo deflGction, are the 
force of rpEction at A which is P", and the weight w I uniformly distributed over the 
BEgmont ; from thia tliere obtains, aa in the preceding cases, 

For tho segment B C, the forces producing deflection are the two forces of renc- 
tion P", P", acting with the reapootivo Brmg of levor 2 I and I; and tho two equal 
T/eighla w I, tlio one acting with tlio arm of lever ^ I, and tlie otlier with the arm 
of lever J i, hence 

heuee, aubstitnting for P'', and reducing, 

Having determined P" and P', tliero obtains, since the siira of tlie forces of renctiou 
is equal to the entire load, 

P + 2F' + 3P' = 4i«;. .-. P = if(4Mi). 

U. Application of ihs theorems in tlis preceding sections to teliriialing Oie effer.[ of 
the exlemal Jbrces inproducing strains on the parts eomposinff a frame. 

Every part of a frame may be subjected either to a direct strain of compreasiou, 
or estenaion, from an eztemal force acting in the direction of tiie librea ; to a strain 
on the fibres by a force actiag perpendioular to them ; or to one arising from a 
force acting obliquely to the fibroa so as to produce simple deflection, and either 
direct extension, or compression. 

The forces themselves may be classified under two heada. 1st Those which are 
d'j'eotly applied to certain points. 3d. Those which are Iranamitted, from the points 
of application of the first, through the intermedium of parts of the frame to oUier 
points, and which, from the relationship of the parts of tho frame to eachother, can 
be found, by the laws oE statics, vrhen the first are given, or can be determined, as 
in the cases Just examined of reactions. 

The problems, therefore, which present themselves for solution in this section, are 
to find the directions and intensities of the foi'ces acting on each piece ; and to de- 
termine from thero the form and dimenEiona of the croaa-scction of each, so that the 
strain on llie unit oE surface shall at no point h^ '-reater than the limit allowed for 

Ca-'ji: 1, (Kg. W.). Biam rsiiing al the louxr end upon ahorisonlal auppoil, and al 


Ihe upper oja&tt a verlUal surface, 

L(!t A B be the axis of tlia 
beam; tlie middle point where 
the weight W ia applied. Eepre- 
aent by I, the length A B ; by «, 
the angle between A B and tho 
vertical line through ; H, the 
horizontal f f t t tiie 

tnd ilrained hj a vidyhi applied at ii 





....._ /p H 

. / 




y : H-' 


„ e_ 


clion of W, froi 

c coaditioiia of eciuilL- 

ilistituting these 

<! forco of vcrtienl reaction 

which is equ 1 nd 
correspond ng h x> 
Ht the po t A a 
shoulder nl h p 
lower end from niovii 

As the couple H, — H tends to 
turn A B in a direction oontrary to the i 
brium their moments must bs equal, hence 

llx CD = W X AD, 
But CII = BE=icos. o; and AD-4AE = i;. 
values in tho preceding expression, tliere obtains, 

Il.lcos.a^-Wilsin.a, .: H- 
Tho beam therefore is subjected at its lower end t 
W, and one of horbvontal reaction H. 

Now representing the force W, by tho line A b ; and tlio ono H bj tlie line A p ; 
and conatcuctiag tho parallelograms of forces, on these two lines respectively as 
rcsaltanCs, having the components perpendicukr and parallel to A B ; Ad and 
A m will be the perpendicular eomponenla of A b and A p, and A c, A n the parallel 
components, finding the values of those components from the diagram, there 

Ad="WEin. ^, Ac = Wcos. a; Am = fWtan. a cos. o, An =i W tan. i sin. a. 

The two perpendicular components, it will bo seen, act in a contrary direellon, and 
therefore the strain on the fibres, arising from simple doBootlon, will be due to their 
difference ; whilst the components along A B acting in the same direoKon will pro- 
duce a direct strain of compression on the fibres due to their sun-,. 

The greatest value for the bending moment will evidently be for the cross-section, 
of the beam at where the wcighl, W acts. Therefore to espress its value for this 
point, there obtains 

(Wsin. n — JWtan. aeoa 

Supposing tJiQ oroas-seaOon of the beam Ic 
in tbe direction in which W acts by d, and I 
the limit of the strain on the unit of aroii at 

I be a rectnnglo, and representing the sido 
.ho breadth by 6, there obtains, § q for 

the oxtTcme fibre, daa to tlie deaection, 

H,' ■■ 

_ iWsi 

^ I W si 


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■For tlJS strain on the anit of Burfane' from tlie direct eompTepsion arising from llie 
sum of tlie parallel componenla, there obtains 

.e limit R'" of llio st 

E"' < R' + R". 
In the preceding example, as in the following in this section, tlie relniive diraen- 
Bions of tbe lengths of tho beams and tlieir croBS-seotion are Kuppoaod to be auch 
that/ or the greatest ordinate of the curve of the msBQ fibre, arising from tlie de- 
flection, maj hs regarded as so small that tbe direcdon of the components of the 
external forces parallel to this flbra shall deviate so alightlj from a right liae that it 
majbo regarded as auch. In anj other ease the moment of the algebraic sum of 
these components would have to be added to tho moment of the olgobraic sum of 
the perpendicular componenla to obtain Oie bending moment. In practice it is 
seldom that this is necessary, as the amount of deflection alloivsd is always very 

Ca$e 2. (Fig. X.) Beam hauing one end solidly jixed and mpporled ai smae tnler- 
mediale point lehcetn the Ivio ends, sither by /mother indimd Icmn helow, orbyahar 
above if, to sudain the adum of a weight at the oSisr end. 

Let A B be the projecting portion of the 
beam, C the intermediate point to which a 
beam F C, or a bar E C is Attached. 

Represent by "W, tiie weight acting at B per- 
pendicular to A B ; A C — i and B C = i' the 
Icngllia cf tho two segments; a, the aiigla 

The beam being held in its position and pre- 
vented from turningaround C b7 the downward 
vertical reaction at tlie point A. Represent- 
ing this force of reaction by W', tliere obtains, 
from the theorem of parallel forces. 

i'i = we, 

and for tho resultant of W and W which ai 
through the point C, 

Ce = "W^— tan. «; Cd = W--^— 
Taking tho segment A C, It will be seen that its fibres will bo alralned by the 




force W — , i 

acting at A 

to produci 

3 simple 

defieotioa ; 


by the force W ~~ 

tan. a, DctiQg 

in the direetioii C e, 

to produ 

pe direct t 



The limits of thB 

Etrains on the 

unit of ai 

-ea of Hio 


tion an a 


in which d and * 

represent the 

sides, 33 ia 

tlie preceding case. 

, will be, 

d for W" < R' + R", 

iirect compression, tliere obtains for this liml^ 

e of three beams ariiiiig fiw, 

in which i" and (f are the sides of the rectangular cr 

Like eipreBaona would bo found for the bar, tha directions of the direct strains 
being reversed. Those on the segment A C being compressions, and those on the 

Case 8. (Fig. T.) Slmina on the parts ef afran 
presiure at one of the angular pointu, or from pressures iiniformly distributed tn> 
lengths of imo of the parts. 

In this comhitiation the beams are 
united at the angular points by some of 
tlio usual joints for such purposes. 

Suppose, in the first place, the beam 
B C to be horizontal, and to rest on two 
filed supports at B, C, and the pressure 
ntA to arise from a weight W. 

Setting off from A the length A b along 
a vertical line, to represent the weight W , conslruclnig on (his line, as a roauICant, 
the parallelogram of forces, having the components A d, A c, in the directions 
of the two beama A B, B C ; Snd denoting the angles between A b and its two 
components by p and j, there obtains 

Ad = 


iiu. (p + g)' sin. ip + g)' 

If, from d and c, two lines d m, e n be drawn perpendicular to A h, they will ba 
equal, and will represent the horizontal pressure, or reaction of the beams at ths 
point A, which ia expressed by 

.in.(p + a) ■ 

Now as the pressiires, represented by the components A d, A c, are IranBmilted 
through the beams to the poinla B and C teupectively, they can each be resolved into 



two components, one vertical which will be counteracted by the points of support 
B. C ; nnd one horizontal, counteracted by the resialance offered by tlio beara B C. 
■ The vertical component at B ia evidently equal to A m, and tlie oue at C to 
A n ; Iho horizontal oomponeola nt B and C are each equal to d m = c n. From 
the diagram there oblaina 

Aii = -W" 

s'li.j' c 

ain.(;. + 3) ' 

for the vertical componeota, or preeaures on llio pointa of snppoit. 
Wlieii the angles, p and j are equal, there obtains 

Ad = A<. = i- 

a = cn = iWte 

= iW. 

Their lii 

on A B, A C will be compressions; and tliat on B C cjxteQsion. 
the unit of area will be determined as in the preceding cases for direct 
r extenaon; whicli values, liowever, would be true oulj under the 
snppoalion that the relntiona between the longtha A B, A C and ilie areas of their 
croas-Hections were such that there would be no strain from deflectioQ. 

It is woll in thia and like cases, for convenience, to note, that the two triangles A d b, 
A e b into which the pavallelc^raai is divided by A b, ate Eitnilar to the triangle B A C ; 
that the perpendiculars d m, d n divide A b into segments which are reepeclirely 
proportional to the two aegmenta into which B C ia divided by A b prolonged; and 
tliat in the resolution of either component of A b, aa A d for example, at any 
point, as B, on its line of direction, into componenta perpendicular and parallel to 
A b, the two components will be respectively d tn, and A rn, which ia tlie segment 
of A b between A and d m. 

Id the case of an equal pressure, w, on eacli unit of length of A B, A C, repre^ 
aented by /, / respectively, each beam may be regarded as in Case 1 ; the straina 
arising from the vertical preasureswi and ID i' acting at the middle pointa of tliebeonia. 
Ciwe 4. (Fig. Z). Hoqf tntss framed miOi siruU and kvag-post. 

The strains On the 
Titf. Z different pnrta in tiiis 

usually due to a 
weight uniformly dis- 
tributed along the 
rartera, in which may 
be included the weight 
oC eacli rafter. 

The struts E D, F 
D are intended to di- 
ininlsh the amount of deflection of the raders, keeping the middle point of each 
io the same right line as the two ends. Each rafter therefore Will be in the condition 
of a beam resting on three supports in a light line, in which ftha of the component 
of wlperpeniUouIar to the rafter will act at the middle point, and j^tha at each end. 
Eepresenling by I the length A C, B C of the rafters; by mtho weight on the unit 



of loQgth] and by a, the angle CAB between eacli rafter aud the tio-bcam A B; 
then the normal presaure at tbe middle point of eadl rafter will be^ lal cos. n, ani 
that at each, end pg wlaos. «. The components parallel to or along tiie rafters Mill 
produce direct compression. 

Fressure onthe Struts. — This pressure will arise rronif laicoa. o. RepreBentIng by 
$ the angle between the strut and rafter, and by P the pressure in llie direction of 
lUe strut, the component of P perpendicular to the ralter ninst be equal to the nor- 
mal pressure on tlie rafter, or, 

Ps;n.;? = iw;cos. „. .-. p = |.„/-^l^-. 

Tendon vn King-pott.— This tension arises from the downward pull of the pressara 
' P on each strut, which is transmitted to the lower end of the king.poat, and from 
thfi weight of the tie-beam. 

Aa each strut makes an angle (5— o) with the tie-beam, the component of P along 
the king-post will be P sin, ((?— o), and as the king-post prevents deflection of the 
tie-beam at the middle point, the additional pull on the part of the king-post ahovethft 
lower end of the struts will he J W ; in whicli W represents the weight of tho tie- 
beam. Therefore callmg the totsi put! T', there obtains, 
Verticai reaction of the points of support on the foul of each rafter from the vidgld 
of the roof-conering and tie-beam. 

Hepresenting by W the vertical reaction at A, B, 2 W will evidently be equal to 
thesumcf 3 wi tho weight of the roof-covering, and of f W which is the pull on 
the king-post from the weight of the Ue-beam transmitted to the junction C of the 
rafters; there obtiilns to express the equality 

Jinsion on the tie-beam. — The forces applied to the foot of each rafter at A, B, are 
tlje vertical reactions W, the weight ft, lo ^ and tlie tension on the tio-beatn. 

HeprcBOtiting this tension by T, it is evident that the difference between thecom- 
ponenlB of W and T normal to the rafter must be eqnal to the normal componentof 
ft «p / ; from this there obtains 

When the weight of tho tie-beam may be disregarded in producing dellection it will 
be subjected to tho strain arising from T alone. 

From the preceding expressions, the values of T and T' can be obtained by sub- 
stituting for tlio values of P and W respectively. 

The Efraina on each segment of the rafier A C, for any cross-section, will arise 
from the forces acting normally to theaegmenls nt A and C which produce deflection, 
and from the forces acting along the rafter producing compression at the cross-sectjoo. 
Tliese can be readily found in & similar manner to Owe 1. 

Having found the amount of strain for each piece of the frame, the limit of the 
strain on the unit of area of the cross-section can be determined in the usnal way. 

Case 6. (Fig. A') Itoof irtiss in viMch the rafters are diuided into iliree equal teg- 


tnenls, anS si^poriei at tin points of dMdon li/ struts, the loner ends of tehick art 
BMppiwfeii 6y a king or q-aeen-posl. 

let AF, FE, EC 

Tl^,A be the Ibiee equal 

segmentG; FC, E D 

F, E, a 

at tlici 

tho .poiiila 
d supported 

by tlio 



i^iieen and 
IsEC, CD. 
more uaaal 

manner of determining the amount of strain on eaoli part of tlie truss is to con- 
Bider it aa composed of several secondary triangular frames or trusaca in wliicil the 
piece common to any tn-o of the secondaTj trusses, as a strut or tie-beam, for oi- 
arapl^ is subjected to tlie strains arising from the comprcssiona or extenaiona brouglit 
■upon it from the forces actiug on the parts ivitli wliicii it is connected. 

Taldiig Ihe half A C D of the primary A C S, it may be regarde 
the secondary truasea A F C, A E D, E C D ; in ivliich tho strut F C, 
A G of the tie-beam form parts of tlie two first, etc. 

Aa eaoli of the equal aegmonla of the rafter bears ono-tlurd of tbi 
uniformly distributed over it^ and is supported at its two ends, the support of eaoli 
end will sustain one-half of this third or ^. ^ w i = J lu /. In lliis way tho supports 
A, C, hear directly i loZ; and the two F, Ebearjwi. 

Now eacli of these triangular frames may ba regarded, as in Case 3, as acted upon 
by a vertical force at its verteiir, tlie effect of which ia to produce a direct compression 
on the two sidea, and extenaon on the base. To find the amount of these for 
AEG. construct the parallelogram of forces having ^ » Z for the resultant^ and the 
componenta in tiio directions F A, F C. ilepreaentiiig by a the angle F A C, these 
3 triangle A F G ia isosceles, will bo equal, and each equal to 

composed of 
tlio segment 

)r ivjl. 


■raponenls e: 

n FA, FC, which are transmitted to 

the points A and G. Here the first ia sustained by the vertical reaction of the point 
of support, and that of tlie segment o£ tho tie-beam A G. To find these reactions, 

resolve i- — at A into two components, onsTcrtioal, the otlier horizontal. The first 

■will bo J w i ; the second J w) I cot. n. By a lliro process, the vertical and horlzonid 

components of ^ -; — at C wiU bo J w i which is sustained by the queen-post E C 

and transmitted through It to the point E, thus producing dhwit extension on the 
queen-post Jw ^cot. a; and thehorizoctal component will bo equal and oppoaite to tlie 
ono at A, and will produce direct extension on the segment A G of the tie-beam, 

For the second truss A E D, there will be a direct force iwl, and the IransDiitted 
force ^10?, or ^111! + iw? = Jwi acting at E. This resolved In the directions 

EA, ED, will 

- for the component along E A, and J — 


- for that 

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along E D. These two oomponeuls are tfausmilted, through tha rafler and strut re- 
spectively, to llic points A, D, and are there oouuteraoled by the reactions of the support 
A, and the tie-beam on the one hand, and Ijj- tlioae of the fcing-poat C D and tha 
tie-beanj on the other. The estension on the tie-beam will be J m i tan. a ; the ver- 
tical presaaro at A, ^wl; and tho pull on the king-post Iw^. 

For the half A C D of the primary trusa, tliere is a direct force ^wl, and the 
transmitted force J ju ;, or ^ m i + i ic i = i w Z, acting at C, This resolved at C in the 

direclioQ C A and perpendicular to the direction J m /, givea for the first J - — ■ and 

i ID ?eot. n. This last component is equal and contrary lo t!ie like component of 
J w I, for the other half B C D of the primary Ithss. 

From this method of considering tlie connection of the secondaiy trusses with 
each othor, and with llie primary trusa, and the pressures to which they are subjected, 
it will he seen that tha segment A F of the Eooondary tnisa, A F G, will be strained 
by the preeaure at F, and by those on the segments F E, E C of tiie rafter ; and 
the segment A G of the tie-beam bythose on G D, by which it is connected with 
A E D and A C D, In hko manner the strains on the parts, E F, C D, which con- 
nect the secondary truss A E D with the primary, will arise from the pressures at 
E and C. Adding together these different forces, there obtains 


= 8- 

LB compression of the segment A F. 

-, for tha 

— , for the Gompreasion on the segmeut F E. 

I EC. 

In like manner the tension on the segment A C of tiie tie-beam will in 
ta ^vil cot. a; and that on the segment C D, JaiZcot. a, as this segc 
part both of the secondary truss A E D and of the primary, 
ts of iuroiiglii and ctist-iron. 

Case 6. (Fig. B'). Jtoof Ir 
In these combina- 
tions the rafters of 


; the s 

3 of 

cast-iron, and tha 
tie-beams ar.d rods 
of wrought-iron, of 
round or rectangul a r 

In ordinarjspanatherafterB are supported by asingle strut, as at E' D', which pro- 
venta the deBeotion at tha middle point, by the reaction of the two tie-rods A D', C D', 
to which the lower end of the strut is Eislened. "When the length of the rafter is 
so groat that one strut would not give sufficient stiSuesa, two intermediate struts tra 
inserted, dividing the raiter into lour equal segments; the intermediate, like the loaiS 
strut, being hcl i In place by tie-rods. 



In tbe Brat combination, there will be one Becondsry truss only, as shown In th« 
left half of the Fig. IntheBeeond, there will bo Ihree aeoondarytruases; buteach 
of tho two smaller ones, being connected only with the larger secondary anil tha 
primary, will be affected only by tlio pressurea on these two. 

Taking the case of a single strut, represent by w, aa in the preceding eases, tho 
woigiit on the unit of length of the rafter; I, ita length; o, tlio angle CAB; H, 
tlie horb«ntal reaction of the rafters at the point C ; R, the pressure on the strut 
E\D' ; T, the tension on the tie-rod AD'; S, the tension on C D'. 

leaving out of conaideratioQ the weights of the strut and tie-rods, as small in 
comparison with lu I, the weight of the raHors and rootcoTerlng, w I may be taken aa 
acting through tbe middle point E' of A C, and its moment therefore will he equal 
to the moment of the couple H, — H, at C and A. From this there obtains 

»;.^AD" = H. CD", 
or, placing for i AD" and C D", their Taiuos i-Icoa, a, Isia.a, 

iiflf eo3.o = HZsin.a. .-. 11 = i w I cot. „. 

Con^dering tha rafter as a single beam, calling R tho normal pressure at the point 
E', and R' those at the pointa A, C, thcro obtains, Gase 4, 

R = f UF ; coa. a. E' = ^ IB i COS. n. 

To find the tension T on the tie-rod A D'; the difference between the normal com- 
ponent of the tension and that of the reaction lo J of the weight of tlio roof at the 
point A is equal to the normal component R', therefore 

!.;cos.«--Tain.« = ^'^«,Jcos.<,. .-. T ==|«.icot. .^ 

To find tlie tension S on C D' ; the difference of tlie component of tbia tension and 
of the component of H perpendicular to the rafter is also equal to R', therefore, 
i«,rcos.«-Ssin.a = ^Micoa,«, .-. S = J-^wlcot. ... 

Astheportionoftlio tie-beam between tlio pointa D' D belongs only to tho primary 
truss A C B, the strain upon it will be duo to the horijontal reaction H of tlie two 
halvea of the truss at C, and will therefore be equal to iw t cot. u. 

From these values of the forces of compression and extension on the diQerent parts 
of the tnisa, the strains on the unit of area on each part cjn be found as in tho pre- 
ceding case. 

Case 1 (Fig, B'), Aa the rafter is here supported at three intermediate points of 
support, dividing it into four equal segmenta, each of which austalna f w i uniformly 
distributed, tlia nortoal pressure, and consequent reactions, at the points of aupport 
wil! be the same as found, Case 3, § t. 

Representing by 

P, the normal pressure at the middle point of the rafter; 

P', P', those at the other two intermediate points ; 

P", P", those at the ends ; 

T, T', the tensions on the segments B H, D H of the horizontal tie-rod of the larger 
secondary truss ; 

^ S', those on the corresponding segments of the inclined tie-rod ; 

■£", 3", those on the two tie-Mds of the smaller secondary trusses; 


H, the liorizontal reaction of llie lialves of the primary tnisa, and which ia et^m, 

to the tension on the segmeiit D D' of lliB tie-rod which connects them ; 
,cl, the Terticul reaction at B ; 
n, the angle CBD"; 
R. the pressure on tlie main strut D f. 
Then there obwius for the tension H of the segment D D' of tlio tie-beam 
H - } uj Z cot. n 
For tlio tension T of the segment B H of tlie tie-beaiu 

Mjicos. B- Tain. a = F'. .-. T= -^"^ '' '^ ■ J — .. 
For the corresponding tension S on tlie sesmeat C I of tiie inclined tie-roii, 

n.ta..-s.m.. = P". ...s = i^T_Z; 

Jfcr the tensions T' T", ns they ivitli T and P' are in equilibrio at the point H, the 
nlgebraio sums of ihelrcomponenta perpendicular and parallelto H G. will respectively 
be cqnal to zero ; therefore 

T' COS. o + T" COS. - Tcoa. a = o .: T + T" - T = o 
T' sin. a — T" sin, o - T sin. i + V — o. .: (T— T"— T)siii. u + P' = o 
In liko manner, for the tensinns S', S", S and the pressure P'^ there obtains, 

Tlie strain upon tlie main strut in due to the normal pressure P and tiie components 
of T" nnd S" in the direction of 1^ ; there obtains therefore, 

R = P 4- (T" + S") Bin. a. 
Tills value of R is balanced by the components of T', S' iu the couli-urj direction. 

Case 8. (Fig. C) Siiigle lattice siider, — This girder, whieli consists of an upper and 
lower beam A' D', A D, connected by diagonal braces A A' A' B, B B', etc., which 
make eqnal angles with A D, A' D', may be regarded as an articulated system in 
which the points of articulation are A, A', B, B', etc. ; and the strains upou each 
piece may befound as In Cass 5, 

The girder may be strained' either by a single force acting at any point of it pah 
pendicular to A' D' or A D ; or by equal forces acljn^ at the points of EUliculatJon 
B, C, D. etc., which would result from a uniform pressure along rtio lower beam. 

,dhy Google 


Supposing tlio gifdor io rest on kotizontal points of support ul 
3 W lie a weight suspended at ila middle poinl, and o tlie angle between the braces 
ac4 a vertical line; then each point of support will jield a reaction W, and will 
cause a strain in ttio direction of the axes of eacb of the two pieces A A', A B cou' 
aected at A, To Sud the direction and amount of each of these rorcea, let a length 
equal to W be set off from A on llie vertical through it, as the resultanl; pressure, 
and tlie parallelogram of forces be constructed on il, having its componenla in the 

direclion A A', B A; that in tlie du^clJon A A' will be , tlie other W tan. a; 

Bhowiog tliBt A A' is subjected to compression and B A to ostension, 

Tlje force ■ — - — is transmitted to the point A', wiiere it is received and counter- 
balanced by tlie resistances offered bj the pieces A' B' and A' B. Prolonging A Ai 

bejond A, setting off from A' on this prolongation as a resultant, and oon- 

Btrncting the parallelogram of forces in the direction B A' and A' B' ; the compo- 
nent in tl:e direction B A' will be -— ; that in A' B', 2 W tan a. The first will 
cause extension, the second comproaaion. 

TheforcB is transmitted to the point B, where, resolved in tlio direcllona 

B B', B A, the two componenla will be as before — — , and 2 W tan. u ; and the 
same will obtain by a like process at th<- other points of articulation. 
From, this it is seen that each brace hears a strain due to ; the one 

A A' and lliosa parallel to it being compressed, the others subjected to tension. 
That, at tlie points, A', B', C, etc, there is a compression of the segment to the right 
equal to 2 W tan. a, from the action of each brace separately, but as these pressures 
colieotively accumulate from A', by 2 W tan. a at B', P', D', etc. ; the pressures oil 
the successive segments will be 

2 W tan. a for A' B' ; 4 W tan. i for B' C ; G W tan. o for 0' D', etc 

On tlie lower beam, in like manner, the tension on the segment A B is W Ian. n ; 
that on B C, S "W tan a ; on D, 5 W tan n, etc. The compressions and tensions 
thus increaang towards the middle of the upper and lower beams. 

It may be remarked that the directions of the eomprcaalon are from A' towards 
A, etc., for the compressed braces ; and tlioso of the tensions from A' towards B, eto. 

"Ware the fore© 2 W to act at any other point, it would be slmplynecessary to find, 
from the theorem of parallel Ibroes, the components at the points cf support, and find 
from these, regarded as the reactions of these points, the strains as just ex- 

In the case where the weight is uniformly distributed, let Siohe tho vertical weight 
nt each lower point B, C, etc., and n the number of tbese lower paints. The entire 
diatributcd weight will be 2nvi, from which there will bs a reaction nioat eact 

,dt>y Google 


It is to bo noted, ia the first place, that following out the same inethoda for tho 
feaoKon nio as in the preceding example lor lliat W, llie same law of compreseiona 
and len^ona wouM obtain ; but as at eacli point B, C, D, etc., there is a direct ver 
tical force 2 w, acting in oppoaition to the transmitted force liirough tha braces, the 
components of 2 m in the direction of the braces and lower beam nmat be subtracted 
fi'om those of the transmitted forces along these pieces. 

Thus for tho point A, the components of h mj are. , aud « ic tan. u; at the point 

nw !iio 2 «■ (« — 2)w 
A'liiey are -——and 2!iUJtan.n;Bt the point B theyarO' ■ -= — 

and 2 nio tan. o— 2 nit tan. a = (2ji-2) ct itin. b ; at the point B' tliey nro and 


To obtain the compression or extension on any brace it will only be necessary to 
subtract from that on tlie one preceding. 

To obtain tha compression on any segment of the upper beam, there must be 
added to the compression transmitted to it by the brace with which it is connected, 
the respective compressions on each of tha segments preceding It. The same law 
obtains for the segments of the lower beam. 

Thus for the compressed braces A A', B B', C C i etc., tho forces of compresaiou 
are respectively 

For the upper sesnientE A' B', B' C, C D', etc., the forces of compression are 

" respectively, 

2nMJ tan. o, 4 (rt— 1) lu tan. a, e(«— 3) w tan, o, 8 (a— 3) w tan. a, etc 

Por the lower segraents A B, B C, C D, etc., the forces of tension are respectivolj, 

««,tan.=, [n + 2 (n~l)] wtan. c, [n+i (n--2)] w tan », [»+6 (ji-S) ] i« tan. 

From the preceding exprossions it will be seen that tho stra ns on the atnits 
decrease from tho points of support towards the middle of the trus^ , and the com- 
pressions on the upper segments and the tensions on Iholo^or mcieiao from Ihesa 
points to Uifl middle. 

It may be noted that in this ease, as in Case B, the successive resolutions of the 
external forces might have been made by commencing at the middle seeondary truss, 
composed of the two middle braces and the segment of either the lower or upper 
beam connecting their two divei^nt sides at the base, and in this way thesame 
reatdts have been arrived at by the successive accumulations of presstire at the points . 
of articuladon, from the auecessivB additions of tho secondary triangular trusses 
which compose the entire truss. In Case 5 also, as in tbia case, the resolutions of 
the external forces might have commenced with the primary trusB, descending from 
this to each secondary truss in its order. Tlie mode of building up the main trus^ 
piece by piece, and showing the effect of these successive additions upon the atraina, 
U more palpable U> many than the contrary process. 


Tlie forgoing expressions can each be deduced from a general tf 
let i represent the numliera 1, 3, 3, Sco., or the order of each term ; 


TviU be the general term Tram which the coaipression on each se, 
horizontal beam can be deduced ; and 

gment of the 


i„ + 2(i-l)(«-i+ l)[»tana 

that from which the leusioas on the segraenls of the bottom bee 

Lm can be fonn 


The maximum of the flrst expression is given by tlio relal 

■ion i ^ 't±: 

-; ai.d 

that of tiiB second bj i = ^-±-?. Tlieae values cannot obtai 

a rigorously a 

it tlio 

same time, since i can only be an cntiro number ; but one nf 1 
ously trae and the other very nearly ao when the value oi' n m 
two maximum yaluoH will be 

.hern mnyhe 



In other words, if N represents the number of' times that the Regmeut A B is con- 
tained in the horizontal distance between the end aupporta ; then the greatest hori- 
zontal compression or tension will bo sensibly expressed by J- lu tan a N'. 

To pass now &om the abstract case above to the ordinary lattice truss, like those 
used in our country, the following approximate methods may be employed. In the 
firat place, the segments of the horiKontal chorda which are supposed to be a system 
artioulated at their extremities may be replaced by two entire beams, the mean 
flbrefi ot which will be A B C D . , . and A' B' C D' , . . ; for as the transversal 
dimensions of each of them is very small compared to their length, they will bo 
very flexible, which will permit of their being assimilated to a system articulated as 
above mentioned. In tlie second place, the angle brace A A' may be subdivided 
into several others inclined like it in the same direction and at equal distances apart 
so as to occupy the space between A A' and B B' ; the same transformation may be 
supposed made with respect to the other set of braces. It will readily be inferred 
that if A B is but a smalt porljon of the entire distances between the supporte, the 
second transformation wiil have but a slight effect on the compressions and tensioca 
of tlie horizontal beams ; and as regards tlie braces, compressed between any two 
coaseoutive parallel ones of the first system, they will as a whole produce about 
the same effecla as the two they repiace ; and the sum of the areas of their cross 
sections should therefore be the same as that of the two lliey replace. 

It should be well understood that in tliis change the braces of t!io new system 
are supposed to bo connected only at their ends. But in fact they are uiually con- 
nected where they ci'osa each other, whiah is in favor of the safety of tlie system, 
but us it is not easy to render a satisfactory account of the effect of this oonneetiOQ 
It may be left out of consideration. 

V Curved Beams. By a curved beam will be nnderstood a beam which is made 
to assume any curvilinear form in the direction of its length, most generally, in 


oaaes of practice, sillier that of a circular or a parabolic arc, and mliicii ia uned lo 
reast and transmit to fixed poicts of support the strains caused by tha exterioi 
forces to wliicli it may be subjected. 

In conformity to what most generally obtains in practioe, and for ttio greater 
sirapliflcatiou of tbo analytical reaulta, Buch a lieam will be supposed, lat, to be of 
uniform oroas seetlou; ad, to bo generated by the cross section beujg moved along 
tlie mean fibre of the beam, which ia assumed to be a plane curve, so that it shall 
always bo ia a plane perpendicular to that of the mean fibre and normal to it, and 
have its centre of gravity on the moan fibre ; 3d, ihat the dimeaaioaa of the cross 
section, ia the direction of the radius of curvature of tlie mean fibre, shall bo but a 
very small fracljou of this radius. These condiLiona being satisfied, any very small 
fractional portion of the beam, comprised between two consecutive posiUons of the 
generating cross section, may be regarded as a right prism, composed of elementary 
fibres, each of which has an clcmeut of the cross section for its base, and the dis- 
tance between the two consecutive planes for its longlb. 

A curved beam, as above defined, when subjected to the action of external forces, 
wiiicb, for greater simpUci^i', will be asanmed aa acting in ttie plane of the mean 
fibre, may give rise to three distinct problems connected with these external forces. 

In Hio first place, all the external forces are not in all easea given ; as a part of 
them may be occasioned by the reactions caused by the fixed points, or other means 
by which the extremities of the beam are kept in position, and tliis reaction, being 
an untcnowu force, has to be found, as a preliminary step to tho Eolution of two other 
problems : The one to Snd the tensions or pressures on the fibres caused by the 
external forces; the otlier to find the change of form in the beam caused by tho 

Prob. 1. To Jind Oie forces ofreadian creased hy the exlemal forces at Hie points of ■ 
support of the caned leam. 

With the conditions already laid down, to further simplify the problem, and bring 
it within what csually obtains in practice r let us suppose tho curved beam to bo 
symmetrical with respect to a vertical line drawn through tho top point of tho moan 
fibre; that it rests at its lowest points on two supports which are on the same hori- 
zontal line ; and that it is acted upon either by a single vertical force, at some point 
between the top and bottom ; 
it is subjected to a strain arising from I 
a weight uniformly distributed along a 
horizontal line, and transmitted to the 
beam, or by one which is uniformly 
distributed directly along the bean 

Case 1. Lst A B, Fig. D', be the * 
curve of the mean fibre, regarded as 
symmetrical with respect to tho verti- 
cal D, resting on the points of sup- 
port A, B, on tlie same horiaontal line A B; and let W be the vertical force acting 
on it at the poiut E, 

Repreacnt by W and W" tho two vertical components of the foroea of reaction 




A (t H 



430 AppEsnct 

at Ihp poLiits A and E ; by Q' and Q tbo horizontftl coraponeata of tlie same forces ; 
Dy 3 a the chord A B of the arc; by d the arm of lever of W with respect to the 
point A, regarded as the centre of Biotoenta. 

From the conditions of statical equilibrium, there obtains 


W + W" + W = 0. 
W."2 a — W. d = 0; 
Here we have but throe equations and four unknown quantitiea. A fourth equation 
may be obtaiued, and tlie problem thus made determinate, by Introduoing the con- 
dition that the points of support shall remain fixed. 

To espresa th