The length of each stone should be from one and a half to three times the height. Rustication may be used in the formation of the arch, which frequently has at its springing line a slightly projecting course, in which the vertical joints are not emphasised. [Illustration: No. 179. Rusticated Arcade.] Rustication is also used in columns, either square on plan or conforming to the plan of the column. Its most legitimate employment is in basements and to emphasise the angles of buildings. _Basement_ A basement is really a continuous pedestal on which an order rests. It necessarily varies in height according to conditions, thus if its purpose is merely to raise the ground floor it may be no more than three to six feet high, but if it is required to form a storey, it should not exceed the height of the order employed or be less than one half. The joints of the work in basements are generally accentuated by some form of rustication, and the heights of the horizontal courses should not be less than half a diameter of the column of the order above. When a high basement is used it is sometimes crowned with a cornice, or more frequently with a slightly projecting facia technically known as a plat-band. In either case, the height should be equal to that of the courses exclusive of moulded edges or chamfers. Also a plinth is placed at the base of the same height as the plat-band or a little more. When a cornice is used the plinth should be moulded and may then exceed the height of the courses. _Attic_ An attic storey is sometimes used instead of a second order, and this may vary from one-third to one-tenth the height of the order beneath it. The attic may be quite plain, but it often has breakings or projections on its face corresponding to the vertical features of the supporting order. It usually forms a storey in a building, and then is of necessity pierced with windows. In architectural design the character and requirements of the building must, of course, be the first consideration, but the basement may constitute the ground floor, the height occupied by the order may contain two stories and the attic may be an upper floor. When an order is not employed the divisions and proportions already stated may still be applied, the heights and widths should govern each other as would be the case if the façade were divided into bays by columns or pilasters. In the absence of the order a cornice is substituted for the entablature, and this, according to different authorities, may be from one-twelfth to one-sixteenth the total height from the ground, but one-fourteenth or one-fifteenth will be found a safe mean. _The Pediment_ The pediment in its original and orthodox employment was a gable conforming to the pitch of the roof. It is framed with mouldings, and the enclosed space is technically known as the tympanum. [Illustration: No. 180. Cornice where order is not employed.]