STE

465

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J" 1 which existed in the atria of the early churches. The.’"'P, or benatura, in our old churches, is of small size,tally situated in an arched recess, and of similar form to thej °ina, which, however, has its place by the side of an altar,Was used for a different purpose. Many examples still existVarious forms, and of different degrees of ornamentation.

I straight-jointed floor, a floor in

which the

continued from one end of the apartments to the

' er : and where the heading-joints are not in the same

C are

S?lit line, as in folded floors.t | S TRAINING-PIECE, or Strutting-Piece, a piece of. er acting in opposition to two equal and opposite forcesr '* 3 extremities, for the purpose of preventing their nearerli& ° a °h towards each other. Principal rafters, camber-s i hip-and-valley rafters, collar-beams, or straining-a, *is, auxiliary rafters, or principal braces, struts, studs, anddi'7-posts, are all of this description. Straining-pieces areiiii ^uished a8 beams or sills by the term beam or sill.^ediately following the word straining; as straining-beams,ning-braaes , or straining-sills.

* ~ t Raining-Sill, or Strutting-Sill, a beam that is bothfaitiing.piece and a sill.

Mat (from the Dutch, stroppe,) in carpentry, an iron

i) r e placed across the junction of two or more timber's, eitherW* C le d ou t or straight, as may be found requisite, and eachti lr nc L bolted, or keyed, with one or more bolts, or keys,to* ’(S' 1 e ach of the timbers, for the purpose of securing themi 5 j ler ' When one piece of timber stands upon another,in* , to form two right angles on the same side of the stand-5( v' e . ee ’ t l le s tra P is most frequently made to go round the(, atiri'P' ece , anc l to embrace the two opposite sides of thetfy 0 < } ln :g-piece, which may be bolted, or keyed, with one oriq e b °lts passing through the tails of the strap. When it isVe nient to make a strap embrace both opposite sides ofJjnbers, it j a necessary that a branched strap should beto"

^ed

the

upon each side, and every timber must be bolted°Pposite branches.

of ,1 ° en two pieces of timber press upon each other, and oneteaj 111 extends on both sides of the joint, a strap is unne-: but where, neither extends beyond the joint, it is'?ai Sar T t° have one. All ties having shoulders abuttinghw s t transverse pieces at the ends, whether the anglel*e ^7 the transverse pieces be right or oblique, shoulda PP e d to those pieces.

•to^ATA, the layers of earth, sand, gravel, clay, chalk,an d other substances, which form the crust of the

l °0e

h:

^ 11 ,

A knowledge of geological strata is very necessaryjj-jJ^tensive building-operations.

OF MATERIALS, the force which anyHi n la ”8 capable of resisting before it breaks, whether fromk ’ com pressing, squeezing, or from being twisted, orAs e , nt H n g by a force applied laterally.v?t(;r' i 6 ' aws resistance are the same, whatever be thea employed, under the specific name of Strength oftpr,* - ’ reader will find ample satisfaction, at least as faruseful knowledge in its application to practical

ate ctur e .

a of Timber, the resistance that a bar, or beam,

6 exerting against a superior power, before it’ whether the force be applied in its longitudinal orw 'se direction, or by twisting. The theory of thisMlo*,.’ Mlustrated by various examples, will be found in theh 'Vm" Propositions : —

‘'I'liof, Osition I.— The force which elastic strings, or fibrousj exert, when drawn or compressed in a direction of\'K« gth : is proportional to the increased or contracted0 which they are lengthened or shortened.

,T 6 c

As the extension or contraction of bodies, when drawnout or compressed by superior forces, depends entirely onthe law of corpuscular attraction ; and as this law has notyet been developed, it does not, therefore, come within thelimits of demonstration : but from numerous experiments ondifferent elastic bodies, it has been sufficiently proved, thatwhen these bodies have been stretched by forces at each end,the additional lengthening was always as the force applied,except when near the point of breaking, where the force wassomething less than in that proportion; and when compressedby forces, this law has been found to hold equally, exceptwhere the compressing forces were enormous ; in which case,the contracted spaces were less than the proportion of theforce ; the truth may, therefore, be looked upon as sufficientlyestablished.

Remark. —Dr. Robert Hook was the first who attended tothis subject, and assumed this law as a property of bodies.

Proposition II.— If a beam be supported at the two ends,and a force, or weight, applied to the middle of it, the deflec-tion of the beam, or space through which it bends, will be asthe force applied, nearly.

This Proposition may be determined from the law of elas-ticity and attraction, supposing them once established; but,perhaps it will be more easily determined by experiment; andthe analogy is the same with regard to the deflection in this,as it is in the preceding Proposition , with respect to theincrease or decrease of length ; and it is found also in this,as in the extended state of the other, that when the beam isnearly upon the point of breaking, a less proportion of weightis required, than the space through which the beam descends.Therefore this Proposition may also be looked upon as suffi-ciently established.

Proposition III.— If a solid be supported by four forces,of which two and two are parallel: then, in each pair ofparallel forces, one force is equal to the other, and its direc-tion contrary.

Plate I. Figure 3.—Let abcd represent the section ofa solid, supported in the plane of its section, in the paralleldirections ag,cp, and a f, c s, by four forces, h, p, i, l, threeof which may be weights going over the pulleys G, f, s.Join AC; then let the weight P be represented by the part C M,and complete the parallelogram c m n o; make a r equalto o c ; produce G a to k ; and complete the parallelogramA k r q. The point C is now sustained by the three forces,C o, c n, c m, and the point A by the three forces a q, a r, a k;and the forces A r and o C being equal, and opposite in thesame straight line, they mutually balance each other. * Nowthe triangles a k r and onc are similar, and A r is equalto O C ; therefore a k and o n are equal ; that is, a k isequal to c m, as A Q is to c n ; but a k and c m are the forcesat h, as p and A Q and c N are the forces at i and L ; there-fore the forces at h and p are equal to each other, as are alsothe forces at i and L. Now, as the string c P is in a state oftension, and as any two of the three angles pcs, s c a, a c p,are greater than two right angles, the lines c s and c a are ina state of tension ; and because A c is in a state of tension,a G and a f are so likewise ; because any two of the threeangles gaf, f a c, C a g, are greater than two right angles ;therefore the forces in each pair of parallel lines, A g, c p, a f,and c s, act equal and contrary to each other.

Corollary. —If the body be a prism, and a b c d a sectionparallel to one of its faces ; and if the directions of the forcesbe in the lines a b, b c, c d, d a, then the force at p, or thecontrary force at h, is to the force l, or its contrary force i,as the breadth of the prism to the length; for as the trianglesONC and A d C are similar, ON :NC ::ad :dc.

Definition. — Power is the weight, or force, employed to