chimney-pot, which is a hollow truncated cone of earthenware placed
upon the top of the flue. The intention of this contrivance is, that the
wind and eddies which strike against the oblique surface of these covers
may be reflected upwards instead of blowing down the chimney. The bad
construction of _fire-places_ is another cause of smoking chimneys; and
this case will lead us to the consideration of the methods of increasing
the heat and diminishing the consumption of fuel; for it will be found
that the improvements necessary to produce the last-mentioned end will
also have a general tendency to cure smoky chimnies. On this subject the
meritorious labours of Count Rumford are conspicuous, and we shall
proceed to give an abridged account of his method. In investigating the
best form of a fire-place, it will be necessary to consider, first, what
are the objects which ought principally to be had in view in the
construction of a fire-place; and, secondly, to consider how these
objects can best be attained. Now the design of a chimney-fire being
simply to warm a room, it is essential to contrive so that this end
shall be actually attained, and with the least possible expence of fuel,
and also that the air of the room be preserved perfectly pure and fit
for respiration, and free from smoke and all disagreeable smells. To
cause as many as possible of the rays, as they are sent off from the
fire in straight lines, to come directly into the room, it will be
necessary, in the first place, to bring the fire as far forward, and to
leave the opening of the fire-place as wide and high as can be done
without inconvenience; and secondly, to make the sides and back of the
fire-place of such form, and of such materials, as to cause the direct
rays from the fire which strike against them, to be sent into the room
by reflection in the greatest abundance. Now, it will be found, upon
examination, that the best form for the vertical sides of a fire-place,
or the _covings_, as they are called, is that of an upright plane,
making an angle with the plane of the back of the fire-place of about
135 degrees. According to the old construction of chimnies, this angle
is 90 degrees, or forms a right angle; but, as in this case the two
covings are parallel to each other, it is evident that they are very ill
contrived for throwing into the room, by reflection, the rays from the
fire which fall on them. The next improvement will be to reduce the
throat of