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strain which would produce this result is in the ratio of thebreadth multiplied into the square of the depth, and inverselyas the length ; and the square of the secant of the angle ofdeflexion, immediately before giving way altogether, mustalso form an element of the calculation. When this is ascer-tained, one-tliird of this breaking weight must be taken forthe maximum load with which it must be weighted.

The inherent qualities of timber and other materials whichenable them to resist the force of compression acting in thedirection of their length, is directly as the fourth power oftheir sides in cubic blocks, and as the square of their heightinversely. The cohesion of wood, &c., by which it is able toresist the force of tension, or a drawing force, exerted in thedirection of its length, varies in the proportion of its crosssection. The power of resisting a tensile strain, in differentkinds of wood, varies in the ratio of their different specificgravities.

All materials withstand the twisting force of tension when| >n the form of cylinders, in the ratio of the angle of tension,and the fourth power of the diameter directly, and in the in-verse proportion of their length.

The resistance of different woods to pressure, as derivedj from actual experiment made with blocks of an inch cube, isI found to be—for elm, 1,284 lbs.; white deal, 1,928 lbs.; oak,(English ) 3,860 lbs. ; and pine, (American) 1,606 lbs.

; > The resistance to tension for bars of an inch square of! ! transverse section, is ascertained to be—for ash, aboutI 11,970 lbs.; beech, 17,371 lbs. ; elm, 12,231 lbs.; fir (pitchI pine), about 12,917 lbs.; fir (red), 10,829 lbs. ; fir (Memel),j j 10,662 lbs. ; fir (Russian), about 9,992 lbs. ; fir (American),

| 870 lbs.; fir (yellow deal), 8,316 lbs. ; fir (white deal),

; 4,204 lbs. ; fir (Scotch), 6,569 lbs.; larch, 10,875 lbs. ; oakj (English), 18,943 lbs. ; oak (French ), about 14,405 lbs.; oak(Baltic), 11,189 lbs.; oak (American), 10,154 lbs. ; oak(Dantzic), 7,558 lbs.; and for willow, about 12,538 lbs.

Oak and fir are principally used in bridge-building, on*ccount of their great durability and hardness, which is ai Point of very great importance ; for the principal objectioni to wooden bridges in general is, that they are extremely: liable to decay ; still, their great cheapness, in comparison; with bridges constructed of other materials, makes themj | very suitable in many instances.

; WOODEN COLUMN, a column consisting of a trunk,

! i base, and capital, each constructed of wood. The column isI : glued up in staves, the base in regular sectors, and the| I capital in blocks used externally. The whole ought to| ■ be painted and sanded, in order to produce the effect of| j * stone column ; but if used internally, the painting ought: to correspond with that of the apartment in which it isplaced.

j WORKING DRAWINGS, consist of plans, elevations,and sections of the whole, and all the parts, of an edifice, to, 48 large a scale as may be found convenient ; generally in; ’ outline, excepting the sectional parts, which are frequently; abadowed, or scratched, in order to make them more obviousj to the workman, for whose use the drawings are made.

! The general plans, elevations, and sections, as they cannot: be made to the full size of the object to be executed, shouldall be figured with numbers of measurement, to show thedimensions of all the parts of the edifice, without obliging; the workman to refer to the scale, which is not only verytroublesome, but liable to lead to many mistakes detrimentalt° the work.

The plans, elevations, and sections, of the parts of ane difice, ought to be made to the full size ; in which case the' %uring of the dimensions becomes unnecessary.

Working drawings may be divided into three classes;

distinguished severally as Block Plans, General Drawings, 'and Detailed Drawings. j

Block Plans show no more than the outline of the proposed jworks or buildings, and their position with reference to ;surrounding objects; in fact, they point out the site of the j ,buildings, and determine the space to be occupied by them. ! IThey are drawn to a small scale, so as to embrace the entire !site of the works, and so much of the neighbourhood as may \be necessary. They contain every information respectingthe present state of the building-ground and its vicinity, and >the manner in which it will be affected by the new work ; !thus, in most instances, it is necessary to show the proposed jmethod of drainage, lighting, water-supply, &c.; and as this iwill necessarily depend upon the existing state of things, wemust mark out the old drains, gas, and water-mains, and the jmethod of connecting them with the new works. 1 It is wellalso, on such drawings, to give some idea of the comparative |levels of the district. I

The General Drawings show the whole extent of the new \works, and the arrangement and distribution of the several :parts. They consist of plans of the various stories, including \those of the foundations, and roofs, and indeed of any part j !of the building where some peculiar treatment renders I ;explanation necessary ; elevations of every side of the build- jing, or of so many sides as present a different appearance; ;and sections showing the internal structure and arrangementof the works. On each of these drawings, the dimensionsof the whole, and of the various parts, should be carefully jfigured ; the directions in which the measurement are taken,being figured in dotted lines, and the points from and to j

which they are measured, being clearly defined by an arrow- j

head, or some such contrivance. So much of the details areshown on these drawings as the scale will allow. Perspec-tive drawings or sketches may be added, to give a moregeneral idea of the undertaking.

The Detailed Drawings show such parts of the work ascannot be shown on the general drawings with sufficientclearness and accuracy; and are drawn either of full size, orto such a scale as shall make them clearly intelligible to theworkman. Such drawings are required both for the decora-tive and constructive parts of the building; thus are includedthe capitals and bases of columns, entablatures, cornices,tracery, or any other enrichment; as also the sections ofmouldings, string - courses, &c. ; and besides these, themethod of framing floors, roofs, &c., the patterns of cast-ironor trussed girders, story-posts, and such like, of everything,in short, of which a particular description is necessary. Itsaves much trouble, if the detailed drawings are made out onseparate sheets for the different trades. These drawings,like the others, should have their dimensions clearly figuredupon them, and every drawing should be provided witha scale, from which any further dimensions may be taken bythe compasses. ,

It is usual in drawings, to tint only such parts as are insection ; but it will frequently be found desirable to colouralso the parts which stand back, and are in elevation; andsometimes also to project the shadows, or shade up suchparts, so as to give a general idea of their distance from,and relation to each other, as also of their forms, as whetherflat, concave, or convex, &c.

WREATHED COLUMNS, such columns as are twistedin the form of a screw. They are very appropriately calledcontorted columns, as being the offspring of a false taste ;for as the primitive use of columns is for supporting a super-incumbent weight, whatever diminishes the idea of the sta-bility they ought to afford, is a real blemish ; and the veryappearance of a twisted column is indicative of weakness.