_The Arch_ [Illustration: No. 6. A. Structural Arch. B. Arch appearance, result of cutting away.] The principle of the Arch depends upon the separate pieces of material being formed to a wedge shape, the joints corresponding to radial lines drawn through the centre from which the Arch curve is struck. The weak part of the Lintel is the centre of the span which may have a tendency to give way under pressure, but the wedged construction of the Arch renders the centre strong enough to bear the imposed weight. In contrast with the Lintel, material of small size could be employed, not only stone, but brick being used in Arch construction. [Illustration: No. 7. Section of Gothic Vault showing courses of stone and centering.] The Lintel, in relatively small spans, is sometimes composed of separate small stones, shaped to fit each other in the form of Joggled joints. [Illustration: No. 8. A. Lintel in one piece. B. C. D. Various forms of Joggled joints.] [Illustration: No. 9. Gothic Vaulting showing intersecting ribs forming framework of structure.] The outward and manifest appearance suggests to the lay observer a striking divergence in the style known as Gothic from the Roman manner of building; but the main difference is in proportion and treatment of detail, the underlying principle being much the same. The use of the Arch and vaulting was common to both, but in the Gothic development greater strength was obtained, with even greater economy of material. The archivolts and intersecting ribs of vaults, with their supports, literally formed the bones of the building, constituting a framework to which the bays of walls and roofing were only a matter of filling in. In the words of Mr. C. H. Moore, in his work on “Development and Character of Gothic Architecture”--“the Gothic style developed into a system where stability depends not upon any inert massiveness except in the outermost abutments, but upon a logical adjustment of active parts whose opposing forces produce a perfect equilibrium. It is thus a system of balanced thrusts, as opposed to the former system of inert stability.” _Egyptian_ The Egyptian buildings, in common with those of Palestine, were frequently of mud, strengthened by wattle or reeds interwoven, evidence of which is apparent in later incised decoration. Buildings were also of sun-baked bricks, those of an important character being faced with stone; the exteriors of these latter were simple and severe, the walls being slightly tapered and surmounted by a simple cove cornice, with gateways and entrances of massive form.