from timber;
but as it must be extremely difficult for the District Surveyors to
watch such minute proceedings, it becomes every one who is anxious for
safety to see that the District Surveyors have due notice of any
operation of this kind.

Another cause of fire which may come under this head is the use of
pipes for conveying away the products of combustion. Every one is
acquainted with the danger of stove pipes, but all are not perhaps
aware that pipes for conveying away the heat and effluvia from
gas-burners are also very dangerous when placed near timber. It is not
an uncommon practice to convey such pipes between the ceiling and the
flooring of the floor above. This is highly dangerous. Gas-burners are
also dangerous when placed near a ceiling. A remarkable instance of
this took place lately, where a gas-burner set fire to a ceiling
28-1/2 inches from it.

Another evil of furnaces is, that the original fireplace is sometimes
not large enough to contain the apparatus, and the party wall is cut
into. Perhaps it may be necessary to notice at this point the use of
gas, as it is becoming so very general. Gas, if carefully laid on, and
properly used, is safer than any other light, so far as actually
setting fire to anything goes, but the greater heat given out so dries
up any combustibles within its reach, that it prepares them for
burning, and when a fire does take place, the destruction is much more
rapid than in a building lighted by other means. Gas-stoves, also,
from the great heat given out, sometimes cause serious accidents; in
one instance, a gas-stove set fire to a beam through a two-and-half
inch York landing, well bedded in mortar, although the lights were
five or six inches above the stone. This is mentioned to show that
gas-stoves require quite as much care as common fires.

_Spontaneous ignition_ is believed to be a very fruitful cause of
fires; but, unless the fire is discovered almost at the commencement,
it is difficult to ascertain positively that this has been the cause.
Spontaneous ignition is generally accelerated by natural or artificial
heat. For instance, where substances liable to spontaneous ignition
are exposed to the heat of the sun, to furnace flues, heated pipes, or
are placed over apartments lighted by gas, the process of ignition
proceeds much more rapidly than when in a cooler atmosphere. Sawdust
in contact with vegetable oil is very likely to take fire. Cotton,
cotton waste, hemp, an