1596.

THEORY AND PRACTICE OF ENGINEERING.

Book II.

A building, though entirely devoid of ornament, may be rendered beautiful by thejustness of its proportion, and the richest edifice wanting in this never can excite admira-tion : facades having but height and breadth, these two dimensions must be equal to eachother, if we adopt the symmetrical proportions prescribed by Vitruvius , for he observes“ the square includes the human figure either lying down or standing in an erect posture,the arms being stretched out.” Temples, triumphal arches, and other buildings left us bythe Greeks and Romans were decidedly designed upon this principle, as were most of thetirades of the religious structures erected since the fall of the Roman empire.

In the “ Songe de Poliphele,” originally published in Italian by Aldus in the year 1499,are some observations on setting out a fa9ade, which convey some idea of the principlesadopted for the formation of a perfect and harmonious design on the revival of Romanarchitecture.

“ Draw a square figure, divided by three perpendicular and three horizontal lines, atequal distances from each other, forming sixteen squares; on the top of the square add ahalf square, which, similarly divided, makes altogether twenty-four squares : in the lowersquare draw two diagonals, crossing eight squares in the same manner; then form a lozengeabove the great square, tracing within it four lines on the four principal points that separatethe four sides of the void.”

After understanding this figure, I thought within myself what can modern architects do,who esteem themselves so learned without letters or principles? They neither know rulesnor dimensions, and therefore corrupt and deform all sorts of buildings, both public andprivate, despising nature, who teaches them to do well if they would imitate her:good workmen, besides their science, may enrich their work either by adding to or diminishingtherefrom, the better to please the eye, but the mass should remain entire, with which allshould be made to harmonise. By the mass is understood the body of the edifice, which,without any ornament, shows the knowledge and spirit of the master, for it is easy toembellish after any invention; the distribution and arrangement of the parts is also a matterof consideration ; hence we may conclude that any workmen or their apprentices knowhow to ornament a work, but to invent lies only in the heads of the wise.

Taking from the square and a half, the lozenge and the diagonal lines leaves the threeperpendicular and the three horizontal, except that in the middle, which terminates in thecentre of the perpendicular, cutting it into four parts or portions ; by this rule will be foundtwo perfect squares, one above and one below, each containing four small squares, whichform the opening or doorway ; now if you take the diagonal of the lower square, it will showyou what thickness must be given to the centre of the portico; if you carry it straight, theline will serve to denote the architrave : and the point of the centre of the upper squarewill show you the centre of the arch or curve to be given to the door ; turning a semicircleit will rest on the transverse line, which cuts the square and a half into two equal parts ; butif done by any other means 1 do not esteem it perfect. This method was invented by an-cient and expert masons, and observed in their arches and vaults, to give them both graceand solidity ; the pedestal on which the columns rest commences at the level of the pave-ment by a plinth, and the whole is a foot high, furnished with mouldings; one portionis divided into architrave, frieze, and cornice, the latter being something more than theothers; that is to say, if the architrave and frieze contained five parts, the cornice shouldbe six. The whole twenty-four, squares form a square and a half; then divide the upperhalf into six parts by five horizontal and five perpendicular lines, and draw a line from thecentre of the fifth transverse to the corner of the great perfect square, where the architravecommences; then draw it perpendicular on the key of the archivolt, and it will show youthe height to be given to the frontispiece above, the extremities of which should unite andrelate to the projection of the cymatium and its mouldings.

General Principles _It would appear that all the principal Roman triumphal arches with

single openings were a square, either comprising or excluding their attics : that the centrefrom whence the archivolt was struck was the centre of the square, or if the facade wasmore than a square, as the arch of Trajan at Ancona , then where the two diagonals crossedthe centre was fixed. The width of the opening is generally half the entire extent, some-times three parts out of seven.

These triumphal arches were generally surmounted by a group of figures, or the car andhorses of the conqueror, accompanied by his companions in arms and the trophies obtainedfrom the enemy; these, as shown on several medals, appear to be equal in height to £ ofthe entire edifice upon which they are placed, the attic and entablature representing andthe columns and pedestals the other §; and as the former are nearly equal in their height, itfollows that the horse and his rider, or the car and its triumphant hero, were double theheight of the pedestal on which they were placed, for so we may consider the atticwhich contained the inscription, the body of the arch being a perfect square, and in correctproportion, without the attic. The depths of these arches varied ; that of Constantine atRome is nearly the same as the width of the great centre opening; many of theothers are less than that proportion; but it seems that the cube was the measure that