Chap. IV.
ROMAN.
127
Construction and Arrangement of the Furnaces and Conduits for Heat .— Vitruvius givesvery circumstantial detail on this subject. “ We must begin,” says he, “ by making aninclined area, laid with large bricks 1J feet square. This area should be so disposed,that a ball thrown in at the door of the furnace should not be able to stop in any part, butshould return to the door; in this manner the flame or heat should extend through all theturns and voids of the conduits formed under the pavement.
Fig. 133.
HYPOCAUSTUM.
Fig. 134.
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Fig. 135.
To form the double floor which covers these voids, and which Vitruvius calls Suspenstira ,there were constructed at equal distances little brick pillars, 8 inches square, at 2 feetdistant from centre to centre. These pillars should be about 2 feet high, in the part wherethe inclination was thelowest. When welllevelled, bricks 2 feetsquare were so placed,that each pillar re-ceived the angles offour bricks, and thereremained round each -pillar 16 inches ofvoid: above this brickfloor, carried by thepillars, was spread alayer of broken tilemixed with chalk, co-vered with a fine ce-ment, or a pavementof mosaic; that thebricks which restedon the pillars mightnot break before thewhole had acquiredsufficient consistencyto sustain itself inde-pendently of the brick,the space between onepillar and the other was arched.
Among the ruins of Pompeii are the remains of a private bath with stoves ; the doublefloor in suspensura formed nearly in the same manner, with this difference, that instead oflittle pillars in brick, they are pipes of terra cotta, made on purpose; these pipes are ter-minated by two square tiles, with a hole in the middle; they are 19 inches high, and about4^ inches in thickness about the middle : the square at bottom is 8 inches, and that at top6 inches ; no doubt this form was given for the purpose of a greater base ; the pipes wereplaced upright on an inclined bed,as prescribed by Vitruvius ; this is laid in large bricks, 8inches square, each pipe so placed that it covers the joint where the angles of the tilesunite, so that they are 18 inches apart from centre to centre. Above the pipes is a plat-form made by a double row of bricks, also 18 inches square, each placed on four pipes;on this double platform is a bed of mortar, made of pozzolana, covered with a mosaic pave-
Fig.136.
Fig. 137.
ment.
The place which served as a stove was small ; its plan is a rectangle, 10 feet long, by 5 wide,terminated by a niche forming a seat at bottom; the entrance is by a very small door,which is at the other extremity in an angle : as the walls are half demolished, and they havescarcely more than 2 or 3 feet of elevation, it is not possible to ascertain whether it was