The interior dome is also constructed of 18 inch brick work, whichhad a course the whole thickness for every. five feet, and the intermediate parts had two bricks in length in the thickness. This dome was turned upon a centre, which support ed itself without any standards from be low. From the inclined position of its supporting walls it had little or no trans verse pressure, yct, for the greater SCCLI. rity, it was hooped with iron at the bot tom. This is accurately represented in Gywn's Section.
,Though modern architecture is, for the flu. acute r part, indebted to the construc tions and decorations of Grecian and Bo man edifictiS, yet we still retain consider able tracrs of the Gothic style in many of our battings.
Ttre spire is of Gothic invention ; it is imitated in our churches and some other buildings, by erecting one, or two, or A se ries of Grecian temples over each other, every superior one being less in its hori zontal dimensions than that immediately below.
Frustrums of pyramids mild cones are also the ornaments of oitr steeples; but ttliether the component parts be one, two, or a series oftemples,continually di minished, or temples supporting trunca ted pyramids, the general contour of the agg-regate is still pyramidal.
The plans of Grecian buildings were simple geometrical forms; but these of our structures are symmetiical and com plex figures, more in imitation of those of the Romms.
The materials used in our modern buil dings are stone, brick and timber. In rustic buildings, the stones are either laid dry or with mortar. In finished edifices, the stones of the facings are sytared and laid in mortar, and the backs and cores are most generally made up with brick or rubble. Walls constructed entirely of squared stones are ra. re : for, allotting the materials may be easily procured in great abundance, a vast expense will be incurred by enormous additional work. manship. This construction of walling is therefore seldom or never used but in aquatic buildings, where the greatest strength is frequently necessary.
The French have not only shown much ingenuity in the binding and cementing of walls, but also in the cutting of stones with geometrical exactness, so aS tO fit vaulted surfaces, of variously formed fi gures.
Iron mused for cramping stones, some times in binding the face and back of a wall together, when there is little heart. In domes it is frequently used in circular chains, in order to remove lateral pres sure, and make the weight of the super structure act perpendicularly upon the • supports. It is also used in fastening wood together, and wood to stone work.
Timber is used also as ligatures to walls ; in this situation it is called bond timber, which also serves for securing the internal finishings. limber is fre quently usedin foundations, in floors, in roofing, in internal finishing, Ste. Tim ber, besides being used in bond, flooring, ancl roofing, in conjunction with stone or brickwork, is sometimes uted as the only material, excepting the chromies, nails, and other iron fastenings.
Moulding& In architectural decora tions, the materials are formed imo a va riety of shapes; which have inany two places sections of equal and similat fi gures, at right angles to their surface, to these two places ; thin forms of this pro perty are called mouldings.
-When the section is semicircular, or semielliptical, it is called a torus or astra gal : when large, it is called a torus ; and when stnall, an astragal.
When the section is a concave curve, and when the concavity recedes beyond either of the extremities of the curve, the moulding's called a scotia or trochilus.
NVhen the section is concave, one ex tremity being above the other and the upper extremity projecting out beyond the lower, and when the lower extremity recedes frown a vertical line equal to the greatest recess of the concavity, or more, the moulding is called a cavetto.
When the section is a convex curve with one extremity below the other, and the upper extremity projecting farther than the lower, without any part of the convexity being lower than the loWer ex tremity of the section, thc moulding is called an ovolo or echinus.
When the section is a curve of contra ry flexure, like a flat S, the moulding is called an ogee ; and when the concave part of the ogee projects, and the convex part recedes, the ogee in this position is called a sima recta: but when the parts lie the contrary way, it is called a sima inversa.
When thc section is straight, and is either perpendicular to the horizon, or nearly so, then the flat member is called a fillet, plat.band, or facia, according to its breadth and comparison with other contiguous mouldings.
When it is very narrow, and either crowns an upper moulding, or divides one member from another, it is called a fillet, or listello ; when it is broader, it is called a plat-band or plinth ; and when very broad, it is called a facia or face.
Compound Mouldinge. When one, two, or a collection of mouldings, with or with out fillets, crown a broad flat member, this collection is called a cymatium. Other names are particularly applied to the orders, and are explained under that head.