Light is often limited or misapplied on account of faulty position or
size of windows. The use of pilastered walls permits the introduction
of larger windows, which are in most instances virtually double
windows, the two pairs of sashes being set in one frame separated by a
mullion. A more recent arrangement, widely adopted in English
practice, is to place a swinging sash at the top of the window, which
can be opened, when necessary, to assist in the ventilation, while the
main sashes of the window are permanently fixed.
Rough plate glass is used in such windows, because it gives a softer
and more diffused light, which is preferred to that from ordinary
clear glass. White glass may be rendered translucent by a coat of
white zinc and turpentine.
The top of a window should be as near the ceiling as practicable,
because light entering the upper portion of a room illuminates it more
evenly, and with less sharply marked shadows, than where the windows
are lower down.
The walls below the windows should be sloped, in order that there may
be no opportunity to use them as a resting place for material which
should be placed elsewhere.