•332 COLLECTIONS ILLUSTRATIVE OF lip into the wall which divided the apartment from that in which the other pavement was fonnd ; the large archway of commnnication with the pr?efurniura also remains entire. The three archways are formed of bricks of the kind called by Phny^ "Didoron," measuring 1 foot 6 inches by 1 foot, and being 2 inches thick. The larger arch w^as formed of the kind called " Tetradoron." The pilce under the suspensura? of both apartments were variously formed ; some in the usual way, with the " laterculai bessales ;" others of concrete, with tiles for caps and bases ; others were formed by flue tiles set on end ; and others again were the bottoms of small stone columns cut to the length required, and taken, appa- rently, from some other building : the bottom of the Hypo- caust was irregularly made, partly with concrete, and partly Avith tiles. The " Tegula) bipedales," resting on the pilse to receive the concrete, were laid with the flanges downwards, whilst those in the Hypocaust in Thames Street, London, had the flanged edges upwards. In the Hypocaust opened in 1683, and also in those at Woodchester, they are used in rows, with the flanged edges against the walls, so as to form channels for the passage of hot air. Where the pavement is not on a suspensura, the substratum seems to be formed thus : — rammed ground at bottom, on that about six inches of gravel, lime, sand, broken tiles, and rubbish, above wdiich is a stratum of about four inches of pounded brick, mixed with lime and sand ; the materials of the concrete most usually met with, and agreeing with the direction of Vitru- vius for forming the "ruderatio," viz., at the bottom the " statumen," next above that the " rudus," and above that the " nucleus " on which the tessellae rest. Few objects of domestic use w^ere met with ; the annexed wood-cut (size of orig.) represents a small article in bronze, probably the handle of an instrument, which was found near the fii'st opened pavement. Here were also a few other small objects in bronze, many flue tiles, not in situ, bases and shafts of small columns, much broken earthenware, a few fragments of Sann'an, and the piece of tile bearing the potter's initials TC'Manu (see wood-cut, -^ orig. size). In more than twenty ^ " Genera eornm tria ; didoron,* quo utimur, longuni sesqui-pede, latum pede; alterum tetradoron ; tertium pentadoron ; eadoni est latitude. " — Plin. N.li. lib. xxxv., cap. xiv.
- Didoron, i.e., poUicum decora et octo : tetni- pnntiidoron, ponicuraquadragiiitaqiiinque,iiempe
doroii, poUicuin trigintasex, neuipe triuiii pedum : trium pedum et novem poUicum. Vitruvius, lib.ii., c:y. iii.
