We here make one alphabetical arrangement serve the double purpose of an Index referring to the pages where the respective matters are treated of, and of a Glossary affording explanation, or further remark, as may be, where required. This latter is by no means to be considered a complete or general Glossary of Architectural Terms, but merely as an accompaniment to the present Treatise, and a specimen, perhaps, of what is still a desideratum, namely, a _real Lexicon_—that is, one which explains _things_ as well as terms—of Ancient and Modern Architecture, similar to what has been provided with regard to the Mediæval Styles of the Art. ABACUS.—The _plate_ or shallow block forming the uppermost member of a capital is so called for the sake of distinction, for when a similar one is placed beneath the base of a column, it is called a _plinth_. The Doric abacus is spoken of at page 14, and is here shown in a plan of the capital and architrave; _a a a a_ being the angles of the soffit or underside of the abacus which overhang the echinus _e e e e_; and _s s_ the soffit of the architrave. From this, the relation between the abacus and architrave, and how much the former exceeds or projects out beyond the latter, will be better understood than by the engraving at page 14, where the capital is shown only in _elevation_. [Illustration] The next figure is still more indispensable for understanding the conformation of the Ionic capital. (See page 32.) Here the abacus shows itself only in front at _f f_, over the two voluted faces, the rest being concealed by the baluster sides _b b_ of the capital, which extend beyond the abacus, and convert the general plan into more than a square. Although the channels and other details of the baluster sides are omitted, and only their general shape shown, the engraving explains how those sides are _reduced_ (p. 33) by being hollowed out or curved concavely on the plan. [Illustration] In the next, or Corinthian Order, a similar curvature is given to the abacus itself on all its four sides; the capital of this Third Order having that in common with the First one, that it is quite regular. One great point of difference between the Doric and Corinthian abacus is, that in the former the angles are unsupported, and overhang the circular body of the capital, while in the Corinthian they are extended outwards diagonally, as _a a a a_ in the figure, and supported by the _caulicoli_ or small volutes, which they in turn serve to cover. The letters _f f f f_ indicate the rosettes or flowers on the four faces of the abacus. [Illustration]