ment, fitted with louvres of plate
glass with polished edges. Between the rebate and the casement it is a
good plan to leave a space of an inch and a half for a movable
stretcher-frame holding several layers of "cheese-cloth" to filter the
air. The construction of such an air filter is shown at Fig. 7. The
glass louvres keep out the wet, and throw off coarse particles of
falling soot; and the provision of a movable stretcher permits the
cloths to be frequently changed for clean ones--a very important point,
though little heeded, if not, perhaps, wholly ignored.

[Illustration: FIG. 8.

Plans and Section of a Furnace Chamber, &c., for a Bath on the ordinary
Hot-air Principle.]

The position of air intake is a matter of great importance, especially
in large towns. It evidently is bad to draw a supply of air from the
bottom of an area. Even the position shown in Fig. 8 is not good: the
shaft should be carried higher. The best places for the intakes are
where there is always a current of pure air blowing, and away from smoky
chimneys. Theoretically, it would seem that the higher the level of
intake the better; but in cities, by going high we get among the
belching chimney-tops, even if we escape the stagnation below. Moreover,
a high inlet with a strong wind tending to exhaust the air in the shaft
might find the architect with the cold air sweeping through his bath,
and all the heated air rushing up the supply-shaft. A large
"lobster-back" automatically turning _towards_ the wind, would in many
cases prevent such a disastrous result. Even in low-level intakes, as I
have said, trouble will sometimes arise from the same cause. This may be
remedied by providing more than one inlet, so that only the one facing
the current of air will be employed, the other being closed, which could
be effected by fixing the glass louvres, spoken of above, on pivots, and
connecting them with a rod and adjustable rack. It would be a very
simple matter to make the wind itself automatically open and shut the
louvres.

The theory of the heating and ventilation of the hot rooms requires most
careful study, and the particular scheme to be adopted in any new bath
must be well considered with respect to the restrictions of the site. At
Fig. 8, I have endeavoured to show how to make the best of what is
perhaps a bad job: the site only admits of ventilation at a back area,
it is impossible to construct flues anywhere else, and the fresh air
must be d