ARCHITECTURE. 



235 



unsafe to build, unless we can reach the solid bottom 

 below. In salt marshes and flats, this is done by 

 depositing timbers, or driving wooden piles into the 

 earth, and raising walls upon them. The preserva- 

 tive quality of the salt will keep these timbers unim- 

 paired for a great length of time, and makes the 

 foundation equally secure with one of brick or stone. 

 The simplest member in any building, though by 

 no means an essential one to all, is the column or 

 pillar. - This is a perpendicular part, often of 

 equal breadth and thickness, not intended for the 

 purpose of enclosure, but simply for the support of 

 some part of the superstructure. The principal force 

 which a column has to resist, is that of perpendicular 

 pressure. In its shape, the shaft of a column should 

 -not be exactly cylindrical, but, since the lower part 

 must support the weight of the superior part, in ad- 

 dition to the weight which presses equally on the 

 whole column, the thickness should gradually de- 

 crease from bottom to top. The outline of columns 

 should be a little curved, so as to represent a portion 

 of a very long spheroid, or paraboloid, rather than of 

 a cone. This figure is the joint result of two calcu- 

 lations, independent of beauty of appearance. One 

 of these is. that the form best adapted for stability of 

 base is that of a cone ; the other is, that the figure, 

 which would be of equal strength throughout for 

 supporting a superincumbent weight, would be ge- 

 nerated by the revolution of two parabolas round the 

 axis of the column, the vertices of the curves being 

 at its extremities.* The swell of the shafts of 

 columns was called the entasis by the ancients. It 

 lias been lately found,f that the columns of the Par- 

 thenon, at Athens, which have been commonly sup- 

 posed straight, deviate about an inch from a straight 

 line, and that their greatest swell is at about one- 

 third of their height. Columns in the antique orders 

 are usually made to diminish one-sixth or one-seventh 

 of their diameter, and sometimes even one-fourth. 

 The Gothic pillar is commonly of equal thickness 

 throughout. The- wall, another elementary part of a 

 building, may be considered as the lateral continua- 

 tion of a column, answering the purpose both of en- 

 closure and support. A wall must diminish as it 

 rises, for the same reasons, and in the same propor- 

 tion, as the column. It must diminish still more 

 rapidly if it extends through several stories, support- 

 ing weights at different heights. A wall, to possess 

 the greatest strength, must also consist of pieces, the 

 upper and lower surfaces of which are horizontal and 

 regular, not rounded nor oblique. The Avails of most 

 of the ancient structures, which have stood to the 

 present time, are constructed in this manner, and 

 frequently have their stones bound together with bolts 

 and cramps of iron. The same method is adopted in 

 such modern structures as are intended to possess 

 great strength and durability, and, in some cases, the 

 stones are even dovetailed together, as in the light- 

 houses at Eddystone and Bell Rock. But many of 

 our modern stone walls, for the sake of cheapness, 

 have only one face of the stones squared, the inner 

 half of the wall being completed with brick ; so that 

 they can, in reality, be considered only as brick walls 

 faced witli stone. Such walls are said to be liable to 

 become convex outwardly, from the difference in the 

 shrinking of the cement. Rulble walls are made of 

 rough, irregular stones, laid in mortar. The stones 

 should be broken, if possible, so as to produce hori- 

 zontal surfaces. The coffer walls of the ancient 

 Romans were made by enclosing successive portions 

 of the intended wall in a box, and filling it with 



See Tredgold's Principles of Carpentry, p. 50- 

 By Messrs Allasou ami Cockercll. See J5ruml"s Jour- 

 nal, vo) x. p. -204. 



stones, sand, and mortar, promiscuously. This kiiid 

 of structure must have been extremely insecure. 

 The Pantheon, and various other Roman buildings, 

 are surrounded with a double brick wall, having its 

 vacancy filled up with loose bricks and cement. The 

 whole has gradually consolidated into a mass of great 

 firmness. The reticulated walls of the Romans, hav 

 ing bricks with oblique surfaces, would, at the pre- 

 sent day, be thought highly unphilosophical . Indeed, 

 they could not long have stood, had it not been for 

 the great strength of their cement. Modern brick 

 walls are laid with great precision, and depend for 

 firmness more upon their position than upon the 

 strength of their cement. The bricks being laid in 

 horizontal courses, and continually overlaying each 

 other, or breaking joints, the whole mass is strongly 

 interwoven, and bound together. Wooden walls, 

 composed of timbers covered with boards, are a com- 

 mon, but more perishable kind. They require to be 

 constantly covered with a coating of a foreign sub- 

 stance, as paint or plaster, to preserve them from 

 spontaneous decomposition. In some parts of France, 

 and elsewhere, a kind of wall is made of earth, ren- 

 dered compact by ramming it in moulds or cases. 

 This method is called building in pise, and is much 

 more durable than the nature of the material would 

 lead us to suppose. Walls of all kinds are greatly 

 strengthened by angles and curves, also by projections, 

 sucli as pilasters, chimneys, and buttresses. These 

 projections serve to increase the breadth of the foun- 

 dation, and are always to be made use of in large 

 buildings, and in walls of considerable length. The 

 lintel, or beam, extends in a right line over a vacant 

 space, from one column or wall to another. The 

 strength of the lintel will be greater in proportion as 

 its transverse, vertical diameter exceeds the horizon- 

 tal, the strength being always as the square of the 

 depth. The/oor is the lateral continuation or con- 

 nexion of beams by means of a covering of boards. 

 The arc/i is a transverse member of a building, an- 

 swering the same purpose as the lintel, but vastly ex- 

 ceeding it in strength. The arch, unlike the lintel, 

 may consist of any number of constituent pieces, 

 without impairing its strength. It is, however, neces- 

 sary, that all the pieces should possess a uniform 

 shape, the shape of a portion of a wedge, and that 

 the joints, formed by the contact of their surfaces, 

 should point towards a common centre. In this case, 

 no one portion of the arch can be displaced or forced 

 inward ; and the arch cannot be broken by any force 

 which is not sufficient to crush the materials of which 

 it is made. In arches made of common bricks, the 

 sides of which are parallel, any one of the bricks 

 might be forced inward, were it not for the adhesion 

 of the cement. Any two of the bricks, however, con- 

 stitute a wedge, by the disposition of their mortar, 

 and cannot collectively be forced inward. An arch 

 of the proper form, when complete, is rendered 

 stronger, instead of weaker, by the pressure of a con- 

 siderable weight, provided this pressure be uniform. 

 While building, however, it requires to be supported 

 by a centring of the shape of its internal surface, un- 

 til it is complete. The upper stone of an arch is 

 called the key-stone, but is not more essential than any 

 other. In regard to the shape of the arch, its most 

 simple form is that of the semi-circle. It is, however, 

 very frequently a smaller arc of a circle, and, still 

 more frequently, a portion of an ellipse. The sim- 

 plest theory of a arch supporting itself only, is that 

 of Dr Hook. The arch, when it has only its own 

 weight to bear, may be considered as the inversion 

 ot a chain, suspended at each end. The chain hangs 

 in such a form, that the weight of each link or portion 

 is held in equilibrium by the result of two forces act 

 ing at its extremities ; and these forces, or tensions, 



