ARCHITECTURE, 



237 



roof is the least advantageous for shedding rain, and 

 is seldom used in northern countries. The pent roof, 

 consisting of two oblique sides meeting at top, is the 

 most common form. These roofs are made steepest 

 in cold climates, where they are liable to be loaded 

 with snow. Where the four sides of the roof are all 

 oblique, it is denominated a hipped roof, and where 

 there are two portions to the roof, of different obli- 

 quity, it is a curb, or mansard roof. In modern times, 

 roofs are made almost exclusively of wood, though 

 frequently covered with incombustible materials. The 

 internal structure or carpentry of roofs is a subject 

 of considerable mechanical contrivance. The roof is 

 supported by rafters, which abut on the walls on each 

 side, like the extremities of an arch. If no other 

 timbers existed, except the rafters, they would exert 

 a strong lateral pressure on the walls, tending to se- 

 parate and overthrow them.* To counteract this 

 lateral force, a tie-beam, as it is called, extends across, 

 receiving the ends of the rafters, and protecting the 

 wall from the horizontal thrust. To prevent the tie- 

 beam from sagging, or bending downward with its 

 own weight, a king-post is erected from this beam, 

 to the upper angle of the rafters, serving to connect 

 the whole, and to suspend the weight of the beam. 

 This is called trussing. Queen-posts are sometimes 

 added, parallel to the king-post, in large roofs ; also 

 various other connecting timbers. In Gothic buildings, 

 where the vaults do not admit of the use of a tie-beam, 

 the rafters are prevented from spreading, as in an 

 arch, by the strength of the buttresses. In compar- 

 ing the lateral pressure of a high roof with that of a 

 low one, the length of the tie-beam being the same, 

 it will be seen that a high roof, from its containing 

 most materials, may produce the greatest pressure, as 

 far as weight is concerned. On the other hand, if the 

 weight of both be equal, then the low roof will exert 

 the greater pressure ; and this will increase in pro- 

 portion to the distance of the point at which perpen- 

 diculars, drawn from the end of each rafter, would 

 meet. In roofs, as well as in wooden domes and 

 bridges, the materials are subjected to an internal 

 strain, to resist which, the cohesive strength of the 

 material is relied on. On this account, beams should, 

 when possible, be of one piece. Where this cannot 

 be effected, two or more beams are connected together 

 by splicing. Spliced beams are never so strong as 

 whole ones, yet they may be made to approach the 

 same strength, by affixing lateral pieces, or by mak- 

 ing the ends overlay each other, and connecting them 

 with bolts and straps of iron. The tendency to se- 

 parate is also resisted, by letting the two pieces into 

 each other, by the process called scarfing. Mortises, 

 intended to truss or suspend one piece by another, 

 should be formed upon similar principles. Roofs in 

 many instances, after being boarded, receive a se- 

 condary covering of shingles. When intended to be 

 incombustible, they are covered with slates or earthen 

 tiles, or with sheets of lead, copper, or tinned iron. 

 Slates are preferable to tiles, being lighter, and ab- 

 sorbing less moisture. Metallic sheets are chiefly 

 used tor flat roofs, wooden domes, and curved and 

 angular surfaces, which require a flexible material to 

 cover them, or have not a sufficient pitch to shed the 

 rain from slates or shingles. Various artificial com- 

 positions are occasionally used to cover roofs, the most 



The largest roof that has hitherto been built us suppos- 

 ed to have been that of the riding-house at Moscow. Its 

 span was 235 feet, and the slope of the roof about 19 degrees. 

 The principal support of this immense truss consisted in an 

 arch of timber in three thicknesses, indented together, and 

 strapped and bolted with iron. The principal rafters and 

 tie-beams were supported by several vertical pieces, notched 

 to tliis arch, and the whole stiffened by diagonal braces. 

 Tredgold's Carpentry 



common of which are mixtures of tar with lime, and 

 sometimes with sand and gravel. Styles of build- 

 ing. The architecture of different countries has been 

 characterized by peculiarities in external form, and in 

 modes of construction. These peculiarities, among an- 

 cient nations, were so distinct, that their structures may 

 be identified even in the state of ruins ; and the origin 

 and era of each may be conjectured with tolerable 

 accuracy. Before we proceed to describe architec- 

 tural objects, it is necessary to explain certain terms, 

 which are used to denote their different constituent 

 portions. The architectural orders will be spoken ot 

 under the head of the Grecian and Roman styles, but 

 their component parts ought previously to be under- 

 stood. The front or facade of a building, made 

 after the ancient models, or any portion of it, 

 may present three parts, occupying different heights. 

 The pedestal is the lower part, usually supporting a co- 

 lumn. The single pedestal is wanting in most antique 

 structures, and its place supplied by a stylobate. This 

 stylobate is either a platform with steps, or a continu- 

 ous pedestal, supporting a row of columns. .The 

 lower part of a finished pedestal is called the plinth ;* 

 the middle part is the die, and the upper part the 

 cornice of the pedestal, or surbase. The column is 

 the middle part, situated upon the pedestal or stylo- 

 bate. It is commonly detached from the wall, but is 

 sometimes buried in it for half its diameter, and is 

 then said to be engaged. Pilasters are square or flat 

 columns, attached to walls. The lower part of a 

 column, when distinct, is called the base; the mid- 

 dle, or longest part, is the shaft ; and the upper, or 

 ornamented part, is the capital. The height of 

 columns is measured in diameters of the column it- 

 self, taken always at the base. The entablature is 

 the horizontal, continuous portion, which rests upon 

 the top of a row of columns. The lower part of the 

 entablature is called the architrave, or epistylium. 

 The middle part is the frieze, which, from its usually 

 containing sculpture, was called zophorus by the an- 

 cients. 1 he upper, or projecting part, is the cornice. 

 A pediment is the triangular face, produced by the 

 extremity of a roof. The middle, or flat portion, 

 enclosed by the cornice of the pediment, is called the 

 tympanum. Pedestals for statues, erected on the 

 summit and extremities of a pediment, are called 

 acrottiria. A\\ attic is an upper part of a building, 

 terminated at top by a horizontal line, instead of a 

 pediment. The different mouldings in architecture 

 are described from their sections, or from the profile 

 which they present, when cut across. Of these, the 

 torus is a convex moulding, the section of which is a 

 semi-circle, or nearly so. The astragal is like the 

 torus, but smaller. The ovolo is convex, but its out- 

 line is only the quarter of a circle. The echinus re- 

 sembles the ovolo, but its outline is spiral, not circu- 

 lar. The scotia is a deep, concave moulding. The 

 cavetto is also concave, and occupying but a quarter 

 of a circle. The cymatium is an undulated moulding, 

 of which the upper part is concave, and the lower 

 convex. The ogee or talon is an inverted cymatium. 

 The fillet is a small, square, or flat moulding.f In 

 architectural measurement, a diameter means the 

 width of a column at the base. A module is half a 

 diameter. A minute is a sixtieth part of a diameter. 

 In representing edifices by drawings, architects make 

 use of the plan, elevation, section, and perspective. 

 The plan is a map, or design, of a horizontal surface, 

 showing the ichnographic projection, or ground-work, 



* The name plinth, in its general sense, is applied to 

 any square, projecting basis, such as those at the bottom of 

 walls, and under the base of columns. 



t By a singular mixture of derivations, the Greek, Latin, 

 Italian, French, and English languages are laid under 

 contribution for the technical terms of architecture. 



