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HISTORY OF ENGINEERING.

Book I.

caused it to decay. Over this was a layer of rubbish, the stones of which were as largeas would lie in a man’s hand : on this layer the pavement was afterwards laid. New-rubbish required that every three portions should be mixed with one of lime; and old, fiveparts to two of lime. Wooden beaters were employed, which by repeated blow's reduced itto the thickness of nine inches. An upper layer, composed of three parts of potsherds andone of lime, was spread over this to a depth of six inches, on which was laid the slabs ofmarble, stone, or tessera?, care being taken that the whole should lie in a proper inclination :it was then rubbed off, and the joints or edges of the ovals, triangles, squares, hexagons, orother figures, made perfectly smooth. After rubbing and polishing, marble dust wasstrew'ed over; then lime and sand run into the joints.

Pavements in the open air had over the first flooring another layer of boards crossingthem, properly secured by nails, so that the joists were doubly covered. The pavementfirst laid was composed of two parts of fresh rubbish, one of potsherds and two of lime.After the first layer, a composition was spread over it, pounded into a mass, not less than

PAVEMENT.

twelve inches thick. The upper layer being spread, the pavement, consisting of tessera?,each about two inches thick, was laid on, with an inclination of two inches to ten feet,to prevent the frost from injuring it at the joints: before the winter it was saturated withdregs of oil. When great care was required, the pavement was covered with tiles twofeet square, properly jointed, having small channels an inch in depth cut in the edgeon each side. These, filled with lime, tempered with oil, had the edges rubbed in andpressed together. The lime in the grooves or channels growing hard, neither w'ater norany thing else would pass through. After this precaution, the upper layer was spread andbeaten with sticks ; over which, either large tessera? or angular tiles were laid with theproper inclination.

Tempering lime for stucco received considerable attention, that the lime should beof the best quality, and prepared long before required for use. When lime was notthoroughly slaked, and fresh from the kiln, it was found to blister, and destroy the evennessof the stucco. After it was properly slaked, and laid in a heap, it was chopped with ahatchet, when, if any lumps appeared, it was considered not sufficiently slaked; whenthe iron of the instrument used came out dry and clean, the lime was considered poor andweak ; but if it had any glutinous substance adhering to it, it indicated richness, andthat it was thoroughly slaked, and properly tempered. This was used to form the com-partments and last coat of the walls.

Stucco work , for arched ceilings, was executed by setting up parallel ribs about two feetapart, made of cypress, it not being so liable to rot as other woods. These ribs were cut tofit the curve, and secured in their place by iron nails: being fixed, Greek reeds, previouslybruised, were tied to them in the required form, with cords made of the Spanish broom.On the upper side of the arch a composition of lime and sand was laid, to prevent any water,that might fall from the floor above, penetrating through it.

When Greek reeds could not be obtained, common reeds were used, tied together inbundles ot appropriate lengths, but of equal thickness, observing that between each twoligatures there should not be a greater distance than two feet. These were bound withcord to the ribs, and made fast with wooden pins. The remainder of the work wasperformed as before described. The arches being prepared and interwoven with the reedsa coat was laid on the under side. The sand was afterwards placed on it, and then po-lished with chalk or marble. When the vault was polished, the cornices were run overthe springing, which were made as light as possible. A small quantity of plaster only wasused, and the stuff was of a uniform quality, such as marble dust ; plaster was apt to settoo quickly.