the whole length of pipe perfectly
air-tight, and attaching it in such a way as to be readily removed for
inspection; and, secondly, by placing the outward vent in such a
position that the gentle current must mount upwards, and any dust must
fall back again into a wide funnel-shaped orifice, and by covering the
latter with fine wire gauze. An apparatus of this kind acts as a
remover of dust from the room instead of adding any to it. One
necessity, however, is the provision of motive power, very small
though it be, to work the fan or otherwise promote a draught.

Electric heating is, however, the method which will probably take
precedence over others in all those cases where systems are tried on
their actual merits apart from sentiment or usage. The wonderful
facility afforded by the electric heating wire for the distribution of
a moderate degree of warmth, in exactly the proportions in which it
may be needed, gives the electric method an enormous advantage over
its rivals. The fundamental principle upon which heating by
electricity is generally arranged depends upon the fact that a thin
wire offers more electrical resistance to the passage of a current
than a thick one, and therefore becomes heated. In the case of the
incandescent lamp, in which the carbon filament requires to be raised
to a white heat and must be free to emit its light without
interference from opaque matter, it is necessary to protect the
resisting and glowing material by nearly exhausting the air from the
hermetically sealed globe or bulb in which it is enclosed.

But in electrical house-warming, for which a white heat is not
required and in which the necessary protection from the air can be
secured by embedding the conveying medium in opaque solid material,
the problem becomes much simpler, because strong metallic wires can be
used, and they may be enclosed in any kind of cement which does not
corrode them and which distributes the heat while refusing to conduct
the electric current. A network of wire, crossing and recrossing but
always carrying the same current, may be embedded in plaster and a
gentle heat may be imparted to the whole mass through the resistance
of the wires to the electricity and their contact with the
non-conducting material.

Concurrently with this method of heating there is gradually being
introduced a practice of using metallic lathing for the plastering of
dwelling-rooms in place of the old wooden battens generally employe