Coussinet

The intrados of a simple vault is generally formed of the portion of the surface of a cylinder, cylindroid, or sphere, never greater than that of half the solid; and the springing lines of the coussinet, which terminate the walls from which the vault rises, are generally straight lines, parallel to the axis of the cylinder or cylindroid.

It is to be observed that in most of , if not in all , their bridges , the ancients did not increase the dimensions of their voussoirs from the crown towards the springing or coussinet, but made them of an equal thickness throughout; in this they were followed by Palladio, and all the Italian architects.

Investigation by analysis of the pressures and resistances of an arch, 1st . Hypothesis of a plat-band; stability at the springing charge necessary on the coussinet; stability of the plat-band on its piers; thickness of the piers.

The term balteus is also used by Vitruvius to denote the strap which seems to bind up the coussinet or cushion of the Ionic capital.

Many details merely painted on in the Doric order, like the leaves on the molding, the coussinet, etc., are presented plastically in the Ionic.

It has not only a carved coussinet, little ledge and plinth, but receives both to the right and left a spiral winding, and at the sides a decorative kind of cushion, wfrom which is derivedi ts title of the pulvinated capital.