town mansion.

IMPOST.--A moulding or other line marking the top of the
jambs of an arched opening, and the starting point, or
apparent starting point, of the arch.

INLAY.--A mode of decoration in which coloured materials
are laid into sinkings of ornamental shape, cut into the
surface to be decorated.

INTERSECTION (OR CROSSING).--The point in a church where the
transepts cross the nave.

INTERSECTING VAULTS.--Vaults of which the surfaces cut one
another.

INTERPENETRATION.--A German mode of treating mouldings, as
though two or more sets of them existed in the same stone
and they could pass through (interpenetrate) each other.

JAMB.--The side of a door or window or arch, or other
opening.

[Illustration: FIG. _V_.--PLAN OF A JAMB AND CENTRAL
PIER OF A GOTHIC DOORWAY.]

KEEP.--The tower which formed the stronghold of a mediaeval
castle.

KING POST.--The middle post in the framing of a timber roof.

LANCET ARCH.--The sharply-pointed window-head and arch,
characteristic of English Gothic in the thirteenth century.

LANTERN.--A conspicuous feature rising above a roof or
crowning a dome, and intended usually to light a Hall, but
often introduced simply as an architectural finish to the
whole building.

LIERNE (rib).--A rib intermediate between the main ribs in
Gothic vaulting.

LIGHT.--One of the divisions of a window of which the entire
width is divided by one or more mullions.

LINTEL.--The stone or beam covering a doorway or other
opening not spanned by an arch. Sometimes applied to the
architrave of an order.

LOGGIA (Italian).--An open arcade with a gallery behind.

LOOP.--Short for loophole. A very narrow slit in the wall of
a fortress, serving as a window, or to shoot through.

LUCARNE.--A spire-light. A small window like a slender
dormer window.

MOAT (or Fosse).--The ditch round a fortress or
semi-fortified house.

MOSAIC.--An ornament for pavements, walls, and the surfaces
of vaults, formed by cementing together small pieces of
coloured material (stone, marble, tile, &c.) so as to
produce a pattern or picture.

MOULDING.--A term applied to all varieties of contour or
outline given to the angles, projections, or recesses of the
various parts of a building. The object being either