Dr. Harris, and the rest of die Dictionary-Writers, make the Abacus to be the Capital it self ; which is altogether as just, as to make the Crown of the Head the whole Head. See CAPITAL, and CROWNING.
Vitruvius, and others after him, who give the History of the Orders, tell us, the Abacus was originally intended to represent a square Tile laid over an Urn, or rather over a Basket. An Athenian old Woman happening to place a Basket thus cover'd over the Root of an Acanthus ; that Plant shooting up the following Spring, encompass'd the Basket all around, till meeting with the Tile, it curl'd back in a kind of Scrolls. An ingenious Sculptor passing by, took the Hint, and immediately executed a Capital on this Plan 5 representing the Brick by the Abacus, the Leaves by the Volutes, and the Balket by the Vase, or Body of the Capital. Such was the Rise of the first regular Order. See ORDER, ACANTHUS, VOLUTE, CORINTHIAN, &c.
There is some difference in the Form of the Abacus in different Orders. In the Tuscan, "Doric, and antient Ionic, it is a flat, square Member, well enough representing its original Tile ; whence the French call it Tailloir, Trencher. See TUSCAN, DORIC, and IONIC.
In the richer Orders it has lost its native Form ; its four Sides, or Faces, being arch'd, or cut inwards ; with some Ornament, as a Rose, or other Flower, or Fishes Tail in the middle of each Arch. See CORINTHIAN, and COMPOSITE ; see also FLOWER, &c.
But some Architects take other Liberties in the Abacus, both in respect of its Name, Place, and Office. Thus, in the Tuscan Order, where it is the largest and most massive, as taking up one third of the height of the whole Capital, it is sometimes call'd the Die of the Capital.---- In the Doric 'tis not always the uppermost Member of the Capital ; a Cymatium being frequently placed over it.—--- In the Ionic, some make it a persect Ogee, and crown it with a Fillet. See DIE, CYMATIUM, OGEE, &c.
Add, that the Abacus is not constantly restrain'd to the Capital of the Column ; Scamozzi using the Name for a concave Moulding in the Capital of the Tuscan Pedestal. See PEDESTAL.