SMOKE, a dense elastic vapour, arising from burning bodies. As this vapour is extremely disagreeable to the senses, and often prejudicial to the health, mankind have fallen upon several contrivances to enjoy the benefit of fire, without being annoyed by smoke. The most universal of these contrivances is a tube leading from the chamber in which the fire is kindled to the top of the building, through which the smoke ascends, and is dispersed into the atmosphere. These tubes are called chimneys; which, when constructed in a proper manner, carry off the smoke entirely; but, when improperly constructed, they carry off the smoke imperfectly, to the great annoyance of the inhabitants. As our masons at present seem to have a very imperfect knowledge of the manner in which chimneys ought to be built, we can hardly perform a more acceptable service to the public than to point out the manner in which they ought to be constructed, so as to carry off the smoke entirely; as well as to explain the causes from which the effects so often complained of generally proceed, and the method of removing them.
Although we would naturally imagine, that the causes which occasion smoke in rooms are exceedingly various, yet, upon examination, it will be found, that they may all be reduced to one of these three general heads, each of which will admit of several varieties.
I. To a fault in the form of the tube or chimney itself.
II. To some fault in the other parts of the building, and a wrong position of the chimney with respect to these. Or,
III. To an improper situation of the house with respect to external objects. And as it is of the utmost consequence, in attempting a cure, accurately to distinguish from which of these defects the smoke proceeds, it will be necessary to point out with care the several phenomena which are peculiar to each.
I. Of smoke occasioned by a fault in the form of the chimney itself. But, before we proceed, it will be necessary to premise something with regard to the general cause of the ascent of smoke in chimneys.
The earth is every where surrounded with a great body of air called the atmosphere. This air is an elastic fluid subjected to many particular laws, as hath been elsewhere fully explained. In particular, it hath, like other fluids, a constant tendency to preserve an equilibrium in all its parts; so that if at any time the weight of it at one place is diminished, the heavier air air rushes from all sides towards that point, till the
equilibrium be again restored. It is likewise known, that heat is one of the most powerful means of disturbing this general equilibrium of the air, by expanding it to a great degree, and making the same quantity occupy a much greater space than it did before, and consequently become lighter. Hence it necessarily follows, that wherever a fire is kindled, the air immediately contiguous to it will be heated, and of consequence rarefied and made light; which must ascend into the higher regions of the atmosphere, till it becomes of the same gravity with the air contiguous to it; while the denser cold air below rushes toward the point from which it departed, is there heated and rarefied in its turn, and ascends in the same manner, carrying the smoke or vapour arising from the burning body along with it. In this manner that constant suction of air towards every fire is produced, and from this cause proceeds the constant tendency of smoke to ascend upwards from the surface of the earth. But as the body of our atmosphere is often agitated with wind, &c. and as it is an elastic fluid, it endeavours to spread itself every way; from which causes the warm air would quickly be diffused among the cold air before it could arise to any considerable height; so that the smoke would always remain low, and be tossed about near the surface of the earth: all of which inconveniences are avoided by confining this heated air in a tube, which prevents it from mixing with the external air, till it arrive at the height to which we desire it should ascend.
To render this still more clear, see Plate CCLXXI. where AB (fig. 1.) represents the tube of a chimney, having a fire at the bottom at A. It is obvious, that, in this situation, the air which was heated by the fire at A will ascend directly upwards, without mixing with the external air, till it arrives at B, beyond which it will be at liberty to disperse in the atmosphere; and the more weighty air which presses in to supply its place can have no access to it but at the opening between A and E, where it also is heated by the fire, and in its turn ascends to the top of the chimney, thereby occasioning a constant stream of air to ascend up the vent, which carries the smoke along with it. This is the manner in which fuliginous vapours are made to ascend in chimneys; and by attending to it, we may draw the following corollaries with regard to the construction of this useful part of our habitations.
1st, The higher the chimney, that is, the greater the distance between the fire-place and the top of the chimney, the greater will be the difference between the weight of the column of heated air in the tube, and another column of the atmosphere of the same diameter without the chimney; and consequently the air will enter with the greater force at the opening AE, and carry up the smoke more readily along with it: for as the warm air within the tube continues rarefied to a high degree till it issues from the top of the chimney, and is, in every part of its length, lighter than the same bulk of external air marked by the dotted line CD, it follows, that the longer these two columns of unequal gravity are, the greater must be the difference of their weight. Hence it is that high chimneys (ceteris paribus) have a greater suction of air, and are less liable to vent ill, than low ones. A smoky chimney may therefore sometimes be cured by raising it higher.
Smoke. higher. It is likewise obvious, that if any opening is
Plate CCLXXI. made into the chimney, as at F, the air will enter
with less force at E, and carry up the smoke with less
velocity, and by that means be in danger of producing
smoke in the room; for this opening, as it admits the
fresh air into the tube, has nearly the same effect as
shortening the tube so much would have.
2d, As the smoke is forced up the chimney merely
by the rarefaction of the air in consequence of heat,
it is evident, that the more the air is heated, with the
greater force (ceteris paribus) will it ascend, because
the difference between the weight of the external and
internal air will be greater; and as the air will be the
more heated the nearer it is made to pass by the fire in
its entry into the chimney, it is evident, that the
smaller the opening at AE is, or, in other words, the
lower the mantle of the chimney is, the air will be
forced to pass the nearer the fire, and therefore be
more rarefied, and ascend with the greater velocity;
so that lowering the mantle of the chimney will often
cure smoke.
But it is frequently inconvenient to have the mantle
of the chimney too low. However, the same effect
may often be produced by another contrivance. For
as the fire-place is usually made wider than the length
of the grate, a great deal of cool air passes at the two
sides of the grate, without being much heated. This
greatly diminishes the suction of the chimney; but it
may easily be prevented by building up the vacancies
at each side of the grate, so as to allow no air to enter
from below, except what comes immediately through
or before the fire. For this purpose, grates consisting
of a neat hewed stone at each end, with a breast and
bottom of iron fitted to them, as represented at fig. 2.
are extremely convenient. But the aperture of the
chimney is often not suddenly contracted above the
mantle, but goes up tapering slowly, as in the same
fig. 2. This structure allows a quantity of cool air to
enter at the two corners of the mantle, and steal up
the tube without coming near the fire. The most easy
and effectual method of remedying this defect, is to place
a sheet of milled iron within the mantle on each side,
as low down as possible, making them slant a little up-
wards towards the middle of the chimney; as at A,
fig. 2. the mantle being represented by the dotted
line. By this contrivance, the air, which enters at
the side of the mantle, before it can ascend into the
chimney, is forced to pass very near the fire, and of
course is much rarefied. The good effects of this
would be still more strongly felt if one of these plates
were placed a little lower than the other, and made
so long that the ends should cross each other, as at
AB, fig. 2. by which means every particle of air that
went up the chimney behaved to pass immediately
above the fire. It is almost unnecessary to observe,
that these plates ought to be so contrived as to be tak-
en out at pleasure to allow the chimney to be cleaned.
A chimney may not only be defective by having the
mantle too high, or by being too wide from side to
side, but also by being too deep between the fore-side
and the back, as is often the case in very old houses.
In this case, the distance between the fire and the mantle
is so great, that much air passes up without being suf-
ficiently rarefied, as is represented at fig. 3. This may
be sometimes cured by bringing the grate a little for-
ward, which, by making the fire act more powerfully
upon the mantle, rarefies the air more in its passage.
But this can seldom produce the desired effect, and it
often does harm: for when the grate is brought for-
ward, there is a great vacancy left between it and the
back of the chimney, so that the air passes under the
grate, and ascends behind it very little rarefied; so
that if the feet of the grate are not very low, there
will be as much lost in this way as will be gained in the
other; and as there is not enough of heated air in the
chimneys of this kind to make the vapour ascend with
rapidity, they are often choked with thick fuliginous
vapours hanging in them, almost in equilibrio with the
rest of the atmosphere, so that the least puff of wind
beats them down the chimney, and pushes the smoke
into the room; whereas, when it is far back, it is
driven down upon the hearth, and rises upwards again
when the gust is over, and a great deal of it is catch-
ed within the mantle as it rises, which in the other
case would have been dispersed through the room.
When this is the case, the most effectual method of
cure is, to bring the grate forward till the fore-part
of it is immediately under the inner edge of the mantle;
then build up the vacancy at the back of it the whole
width of the fire-place from side to side, raising it per-
pendiculary till it is as high as the back of the grate,
and then bending it forward towards the mantle, as is
represented at fig. 4. When it is as high as the work-
man can reach, let it be suddenly turned backward again,
sloping a little upward, as in the figure; then fit a
sheet of milled iron to the inside of the mantle, making
it slant a little upward toward the back-part, at a small
distance above the new-erected masonry, and extending
within a few inches of the back-wall, as at A, fig. 4.
By this construction, all the air that enters into the
chimney is made to pass immediately above the fire,
between it and the heated iron, upon which the flame
acts with the greater force, as the back of the fire-
place is bent a little forward above the grate, and the
heat is likewise reflected into the room with the greater
force: at the same time, if the smoke is at any time
beat down the chimney by a sudden gust of wind, it
will be caught by the sheet of iron, and prevented
from coming into the room. If the fire place be very
wide between the one side and the other, the new ma-
sonry may be carried quite up to the sheet of iron on
each of the sides.
3d, As every fire requires a constant succession of
fresh air, the tube for conveying this rarefied air to the
higher regions of the atmosphere must be of a suffi-
cient size to contain the whole of it, and allow it a
ready passage; otherwise a part of it will be forced to
seek some other passage; by which means the apart-
ment in which the fire is placed will be constantly fill-
ed with smoke. Every chimney, therefore, ought to
have a degree of wideness sufficient to carry off the
whole of the smoke arising from the fire usually burnt
in it, otherwise the apartment will be almost conti-
nually filled with smoke. This is a fault more com-
mon at present than any of those already mentioned,
especially in large towns, where the number of chim-
neys in one wall is often so great that it is difficult to
get a sufficient space for each. The most obvious cure,
where the situation admits of it, is to widen the chim-
ney, by opening a hole a little above the grate thro'
Smoke. the back-wall of the chimney, flanting a little upward,
Plate and building on the outside of the wall a small chim-
CCLXXI. ney open from that hole to the top of the building, as
in fig. 5. where AB represents the new tube going
through the wall at the opening at A, which will re-
ceive the superfluous smoke, and carry it off. This
additional chimney must always be carried as high as
the other. But as there are many situations in which
this method of cure would be impracticable, we must
try every method for accelerating the ascent of the
smoke, (for the more quickly it ascends, the more nar-
row may the tube be); and with that view the chim-
ney may be heightened at top, and contracted at bot-
tom, in any or all the various ways we have men-
tioned. But if none of these methods prove effectual,
let the chimney be built quite close at the under part,
leaving only as much room as is sufficient to contain
the grate, having a cover of metal fitted to that open-
ing, which can be taken off or put on at pleasure; by
which the whole air that enters into the chimney is
made to pass through the fire like a furnace, and car-
ries the smoke up it with great velocity. These are
well known in large towns by the name smoke-chimneys;
but as they occasion a prodigious waste of fuel without
warming the room, and, unless attended with very
great care, are in danger of setting the building on fire,
they ought to be as much avoided as possible. But if
neither this nor any of the other methods prove effec-
tual, the wall must either be taken down and rebuilt
in a proper manner, or the chimney abandoned as in-
curable. As this is a defect more difficult to be re-
medied than any other, we would strongly recommend it
to every builder to build his chimneys of a sufficient
width throughout: there is no danger of error on
this extreme, as it is easy to remedy any defect that
might arise from it.
4th, As the air which ascends through the chimney
continues nearly of an equal degree of heat to the top,
the tube should be of an equal degree of width at the
top as at the bottom, as well as through the whole of
its length. It ought not therefore to be made taper-
ing gradually from the fire-place to the top, but to be
suddenly contracted above the grate, as in fig. 6. from
which it ought to be continued of an equal wideness
throughout its whole length; but if it is narrower at
any one place than another, it ought to be at the
under part, immediately above the fire, for a very
short space; because, as this is within reach of the
hand, the foot can be cleaned from it as often as is
necessary; so that when the other parts of the chim-
ney are clogged with soot, they will not be narrower
than this place is at that time.
5th, It seldom happens that a chimney can be car-
ried quite straight upwards: and it is an advantage
that it is so, as they ought always to be bent a little.
For if a chimney be straight, and of a proper width
to transmit the whole of the smoke and no more, it
will not be sufficient for that purpose, when there is a
heavy fall of rain, or snow, or hail, with little wind;
for the great drops will fall perpendicularly from the
top to the bottom of the chimney: and as they oc-
cupy a considerable space, the smoke will not have
room to ascend, but must be forced down with the
shower, and dispersed in the apartment; whereas, if
the chimney is bent, the rain falls upon some of the
sides, and glides gently down, without disturbing the
ascent of the smoke. The same inconvenience will be
felt in a straight chimney, where it is so placed as
to be exposed to winds, which sometimes enter the
top, and blow down with a sudden puff: for if it be
straight, the air meets with no interruption till it de-
scends into the chamber, and there disperses the smoke;
but if it be crooked, the descent of the wind will be
obstructed, its force broken, and the bad effects of it
in a great measure prevented. Upon the whole, bent
chimneys are always preferable to straight ones. How-
ever, a perpendicular chimney may be easily cured by
some of the contrivances after mentioned.
These are the most general defects arising from the
structure of the chimney itself, which are all reducible
to the following causes: 1. Too little height; 2. Too
great wideness of the bottom of the chimney; 3. Too
little width; 4. Unequal wideness between the top
and bottom; and, 5. Straightness of the tube. We
have pointed out the best methods of curing each
of these defects; and, to finish our remarks on this gen-
eral head, and give the reader a more perfect idea of
the best form of construction for a chimney, we have
drawn two different sections of one constructed on the
justest principles, in figures 6. and 7. the several parts
of which appear so plain from the figures, and the
reasons for this construction have been already so clearly
assigned, that a very short explanation will be sufficient.
Fig. 6. represents a front-view of the fire-place; sup-
posing the fore-part of the wall taken down, and the
chimney laid bare from top to bottom; AB and DC,
representing the two sides of the fire-place; and BC,
the mantle, being cut through, to show the manner in
which the aperture is suddenly contracted, immediately
above the fire within the mantle. The tube from
the point E to the top ought to be of an equal wide-
ness, and bent in any direction that may be con-
venient. The two planes FF, represent the two sides
of the fire-place, which ought to be as much sloped in-
ward towards the back as the form of the grate will
admit of; for the more they are inclined, the more
powerfully will they reflect the heat into the apart-
ment. Fig. 7. represents a perpendicular section of
the wall, through the middle of the chimney, to dis-
cover its shape, if viewed from a side. And here it is
to be observed, that it ought ever to be a rule to bring
the building at the under part of the chimney im-
mediately behind the grate, as far forward as possible,
because this throws more heat into the chamber than
if it were placed farther back: but as the fore-part of
the grate ought never to project beyond the inner edge
of the mantle, care should be taken to have the under
part of the mantle wrought as thin as the nature of the
materials will admit of, making it thicker towards the
upper part, so as to slope inwards above the fire, as
represented at B, fig. 7. To throw the heat outward,
let the upper part of the back of the fire-place be a
little inclined outward, as at C; but after it is carried
up in this manner a little higher than the mantle, let
it be suddenly turned back as in the figure, the pro-
jection above the mantle inclining backward in the
same direction, being carried up to the top at an equal
wideness the whole way.
Although it is necessary to have all chimneys pretty
wide, yet this on many occasions is attended with in-
conv.
Smoke. conveniences: for as they transmit a great quantity of
heated air, too large a portion of that warm air which
ought to heat the chamber is carried off; and as it is
only when the fire is first kindled that the great quantity of gross vapour is exhaled, which fills the chimney, and maketh a large tube necessary, if it were so contrived as to contract or dilate at pleasure, we might have our chimney of a sufficient width to convey away the greatest quantity of smoke that could ever have occasion to pass through it, at the same time that we might never allow more air to pass off at other times than was necessary to carry away the whole of the smoke, by which means a much smaller quantity of fuel would keep our apartment equally warm. This, we apprehend, might be accomplished by the following simple apparatus. Let a sheet of milled iron be fixed at the upper part of the mantle, on the inside, at B, in such a manner as that, by means of a small wire d, passing through a small hole left for that purpose in the fore-part of the chimney, it might be let down at pleasure towards C, or drawn up towards B, so as to apply quite close to the upper edge of the chimney between B and C. This would leave the tube of its full wideness when necessary, or close it to any degree at pleasure, with the greatest ease (A.) It is unnecessary to add, that the plate at A, fig. 4, might be employed in the same manner, when it should be found convenient. So much for what relates to the construction of the chimney itself. We now proceed to consider the second general cause of smoke, viz.
II. Of smoky houses proceeding from faults of other parts of the building, altogether independent of the structure of the chimney itself.
1st, The first we shall mention is too great closeness of the room. Smoke, as shown above, is impelled up the chimney by the pressure of the air entering at the fire-place and ascending upwards; but if fresh air is not admitted into the apartment in sufficient quantities to supply the consumption by the fire, the room will be quickly exhausted, and the air in it become as light as the external air at the top of the chimney, so that the smoke will as readily be dispersed into the chamber as through the chimney. But if any door or window is opened so as to admit plenty of free air, the smoke will be quickly dispelled, and the proper circulation established: the same effect will be produced by making a small hole in some of the sides of the room; but unless this be done with some judgment, it may frequently add to the disease, as it may concur with some of the other causes of smoky houses, to be afterwards mentioned. A better method of remedying this evil would be to have a small hole made in the wall at the back of the chimney, and immediately underneath it: or a small perforation, made in the wall in any other convenient manner; the one
end of which should communicate with the external air, and the other communicate with the chamber in any place near the grate, and as low down as possible, through which a constant supply of air would be administered to the fire without the smallest inconvenience or trouble. If this were practised, doors and windows might with safety be made much closer than at present, and our apartments rendered equally warm and comfortable with a much smaller quantity of fuel than we use at present. For as the fire, in the present mode of constructing chambers, is kept alive by a constant succession of cold air from the doors, windows, and other crannies of the room, rushing towards the chimney in all directions, the air of the room, which, if not cooled by this means, would be quickly heated to a great degree, is constantly kept cold, in spite of the strong heat of a blazing fire; which, at the same time that it scorches the parts of our body which are most exposed to it, does not warm the parts which are turned from it; and we experience at the same time a burning heat and piercing cold, which is often productive of the most disagreeable effects. But if the fire were supplied with air in the manner above-mentioned, there would be less air drawn in through the crannies of the room, so that the air within would be soon warmed, and continue long so, even with a small degree of heat. However improper this might be for people in perfect health, it might surely be of great use for those who are in a weakly habit of body; especially if care were taken to carry off the foul air, by having a small tube leading from the upper part of the room to the top of the house, through which the air, which had been rendered noxious by the smoke of candles or perspiration, would be conveyed away, and a succession of fresh air admitted from the tube near the fire-place, to supply that want. That the reader may more readily comprehend what is here meant, we have represented in fig. 6. a view of two small tubes for this purpose, supposed to be laid open by taking away the boxing or inner coating of the wall which ought to cover them. These are of wood, and must not be above one inch in diameter. One end, g g, goes quite through the outer wall of the house, and communicates with the open air, having a small grate upon it to prevent vermin from entering. The other end, b b, passes behind the two slabs, at the side of the fire-place, and open in the inside of the fire-place at i i, at which place they have each of them a small bit of brass fixed to them, being closed with two sliding doors exactly like those that are used to cover the end of telescopes, by means of which more or less air may be admitted at pleasure.
2d, A second cause of smoke is the wrong position of doors and windows with respect to the fire places.
As the smoke is impelled up the chimney by the pressure
40 Y 2
(A) If any one should think, that the wire d would be a disagreeable object in the middle of a chimney-piece, it might easily be hid by a picture of any kind. The wire might be fixed to a small brass handle, moving freely upward and downward like that for a bell; only this should have a long slit in the middle of it, with notches on each side, to receive a pin placed in the middle of the slit, by means of which the wire might be lengthened or shortened at pleasure. The whole of this apparatus is represented at fig. 16. where (a) represents the wire fastened to the brass plate; (b) a piece of brass, raised a little, to serve as a handle. The slit in the middle is represented by the dark line, having notches, c c c, at convenient distances. The pin d is fixed into the wall, but left at liberty to turn about with ease; and its head stands up a little, so as to be easily turned with the finger and thumb. The body of this nail is made so thin in one direction, that when it is turned half round, it easily passes thro' the slit in the plate; but in the other direction its diameter is greater, so that when the plate is brought so as to have one of the notches opposite to the nail, and it is then turned half round, it catches the plate so that it cannot be moved till the nail is again turned about.
Smoke. pressure of the air, if that air is driven away from the
Plate fire-place by any cause more powerful than the suction
CCLXXI. occasioned by the fire, the smoke must also be drawn
away with it, and follow the same directions with that
current of air; so that whatever tends to draw a cur-
rent of air from the under-part of the chimney, will
also tend to produce smoke in the house; from whence
it is easy to conceive how doors or windows may oc-
casion smoke when the wind is in certain directions.
Thus, suppose a chamber, A, B, C, D, fig. 8. having
a door or window at E, another at F, and a fire-place
at G; when the wind is in the direction D A or C B,
the general current of air will occasion a sort of suction
at the opening E, so that the air will be drawn from
the chimney G towards E: and if the current be
strong, and the opening at E large, it will become
more powerful than the suction of the chimney, and
produce smoke in the apartment. If the window at F
should be opened in this case, it would not mend the
matter; for any wind which should enter at F, would
be carried straight out at the opening E, and the cur-
rent of air would be drawn from the chimney as strong
as ever. If the window at E were shut, and that at F
left open, and the wind still continued in the same di-
rection as before, the current of air rushing past the
window would have a tendency to draw the air of the
room along with it, and occasion smoke, but not so
powerfully as if the window at E were open; but if
the wind were in the direction D B, it would be very
bad: but if it blew in the direction C A, the case
would be very much altered; for then a quantity of air
being forced in at the opening F, and finding no ready
passage, it would be pent up in the chamber, and force
itself up the chimney with violence. We omit men-
tioning what would be the effect if the wind were in
other directions, as it is imagined these will be suffi-
ciently obvious to every attentive observer. It is only
necessary here to observe, that as doors or windows
are seldom so exactly made, but they produce some ef-
fect, as they always admit some air even when shut,
and often occasion smoke when the wind blows from a
particular quarter; and as workmen and others gene-
rally apprehend, when houses are troubled with smoke
in this manner, that it is occasioned by some external
cause, and apply their attention to cure it by altering
the top of the chimney, which never can produce the
smallest service in this case; we would recommend a
more particular attention to be paid to the situation of
doors and windows than is generally bestowed; espe-
cially in such situations where they are exposed to any
violent current of air in a particular direction, as in
narrow lanes, or defiles of any sort, where the wind,
when in particular directions, is hurried along with a
prodigious rapidity. And, that the effects of different
positions may be still more obvious, we shall produce
several other examples.
Suppose a chamber, fig. 9. having a door at A, and
two windows B C, with a fire-place D. If the wind
came in the direction D A, and if the door trans-
mitted as much or more air than was admitted at both
the windows, a current of air would run from all parts
of the chamber towards A, and therefore would have
a tendency to occasion smoke: but if as much or more
air came in at the windows than could get out at the
door, there could be no such current; but, on the
contrary, it would be forced up the chimney, and carry
the smoke along with it: wherefore, in this situation,
a room might sometimes be cured of smoke, by making
the door as close as possible; nothing could be more
hurtful in this case than boring a hole in the door.
But if the house was in such a situation as to be more
frequently exposed to a wind which came in the direc-
tion of A D, it would run little risk of being troubled
with smoke.
Suppose a room, fig. 10. having a door at A, and
two windows B and C, with a fire-place D. If the
wind came in the direction C B or B C, and both the
windows were open, it is evident that the smoke would
be drawn from the chimney by the strong current of
air passing through the room; or if the window upon
which the wind came were closed, and the opposite one
open, nearly the same effect would be produced: but
if the window upon which the wind blew were open,
and the opposite one and the door shut, the room would
be immediately cleared of smoke entirely. In this
situation, it is evident, that if the windows were badly
made, so as to admit much air, it would tend to oc-
casion smoke, especially if the door were in the same
situation; it is therefore of consequence to attend to
this circumstance in a situation similar to this.
Having premised so much with regard to single
rooms, we shall now proceed to consider a more com-
pound structure. Thus, let fig. 11. represent a build-
ing consisting of two chambers, K L, joined by a pas-
sage. The chamber K having a door B communicating
with the passage, a window F, and fire-place
G; and that at L having a door C, another door or
window D, the window E, and fire-place H, the en-
try to the whole being by the door A. Let us now
consider what would be the effect of the wind coming
from different directions upon this building. And first,
suppose the wind blew in the direction A M: If all the
doors and windows were close shut, and very little air
were admitted, there would be little risk of smoke;
but as there would surely be some admitted through
these different openings, there would be some chance
that the chamber L would be troubled with smoke,
because some of the air which forced its passage thro'
the chinks of the door A would pass through the doors
C and D, which might produce smoke in a small de-
gree. There would be little chance that the chamber
K would smoke in this case; because although there
is a general suction through the passage from B to D,
yet as it is in some measure interrupted by the close
door at C, it will be but small; and as the wind is
interrupted in its course by the wall of the passage,
some of it will be forced through the chinks of the
window F, which would more than counterbalance the
effects of the other suction. But if the door D were
open, both the chimneys would smoke; especially if
the doors B and C were open also, as the current would
be then very strong towards that point. But in all
cases the smoke of this house would be prevented by
keeping the door at D shut, and that at A open; but
if the house was in such a situation as to be more ex-
posed to that wind than any other, it would be better
to close up the door D altogether. If the wind more
commonly came from M towards A, it is more than
probable that a house situated like this would be quite
free of smoke, as the general current of air would be
to-
Smoke. towards the chimneys; but the chamber K would run
Plate greater risk than L, as the fusion might sometimes be
CCLXXI. drawn towards the window F; but if the door A were
in the opposite side of the passage, that inconvenience
would be avoided also. If the more general current
of air were from K towards L, this house behaved to
be troubled with smoke, unless the windows were very
close; but there would not be the smallest chance for
that when it came from L towards K.
We might now proceed to give more examples of
this sort: but as it would be impossible to enumerate
all the variety of cases that might occur, it is imagined
that these will be sufficient to give the reader an idea
of the manner in which any building ought to be exam-
ined in this respect; and he must be left to his own
discretion to apply the principles above explained to
all the variety of cases that may occur. In large com-
plicated buildings, it no doubt requires a greater ex-
tent of thought to combine all the various circumstances
together, and draw a general conclusion, than in smaller
and more simple ones; but if the following general
rules are attended to, the complaints arising from this
cause would be but few. 1st, Avoid as much as may
be long passages leading to very distant parts of a
building, as there is often a strong current of air in
these which helps to disturb the free circulation of air
up the chimneys. 2d, Place the chimneys in general
in that side of the apartment towards which the wind
which in general prevails most in the situation where
the house is placed blows. And, 3d, make as many,
if not more, doors and windows (especially such as
have occasion to be most frequently open) on that side
of the building from whence the most prevalent wind
does come.
III. The third general cause of smoke in houses is
the wrong position of the house with regard to external
objects, which, by interrupting the course of the
air, makes it assume various directions, and wheel about
in eddies, so as to prevent it from ascending with ease
from the chimney-top, or beats it down into the room
with violence. This is more seldom the cause of smoky
houses than either of the two before-mentioned; al-
though it seems to be almost the only one attended to
by the persons who pretend to cure smoky houses at
present, as most of their remedies are adapted to re-
move the disorders arising from this cause alone. We
shall briefly point out the several cases in which this
can occur, that every one may be enabled to judge for
himself when these cures are proper or not.
The air (as has been said) is a fluid, and wind a
current of that fluid; which, when driven along the
surface of the earth, flows with a smooth and equal
stream, unless when opposed by some object which in-
terrupts its course; but when it meets with any object
which directly opposes its course, it is in some measure
pushed back again, and made to spread on every side,
till it meets with some open side, towards which it
flows with great impetuosity. It is likewise a fluid of
considerable gravity, and therefore presses upon the
surface of the earth with great force; so that, when a
current of it flows along the surface of our globe, it
has a tendency to move forward and press downward
at the same time: from whence it happens, that when
a current of air is forced over the top of any high ob-
ject, the side of which descends perpendicularly down-
ward, the velocity of the current at first overcomes the
gravity, and it flies a short way over in that direction;
but the power of gravity acting upon the under sur-
face, draws it downward, and in a short time over-
comes the impetus that it had to rush forward, and
occasions a sort of eddy nearly similar to what we see
among water behind a stone which interrupts the vio-
lence of its currents.
To illustrate this more plainly, let AB, fig. 12. re-
present a part of a high building, near to which is a
smaller one CD; and let the dotted line EF represent
a current of air flowing with considerable force in the
direction FE. It is plain that it will flow straight
forward over the top of the small building; but when
it meets with the large object, it will be interrupted in
its course, and spread itself on every side, as represented
by the dotted lines GG, &c. at last it will flow towards
that place through which it can escape with the great-
est ease. If the opposing object be large, and has no
opening through which it can issue near the ground,
then it will ascend to the top of it, and flow off in that
direction, carrying the smoke which ascends from the
small chimney C along with it: but if there is any
opening below, either a street or lane, or any other
passage that will admit the wind to pass, then will the
natural gravity of the air draw the general current
downward to flow off through the lower passage; in
which case, the smoke which ought to ascend through
the chimney C, meeting with a current of air oppo-
sing its passage, will not be at liberty to issue forth,
but be forced back again into the room from whence
it proceeded, unless some contrivance is fallen upon to
prevent it.
Again, let A, fig. 13. represent a small building at
the side of a great rock B, and the wind coming in
the direction CD; when the current of air comes to
the point D, being hurried forward with great velo-
city, it goes a little forward, but soon descends down-
ward, and gradually is reflected more and more in-
ward, as represented by the dotted lines EE, &c.
so that, descending downwards upon the top of the
chimney A, the smoke is beat back again into the
apartments. Thus it is that low houses, when con-
tiguous to high objects, are in danger of being disturb-
ed with smoke. If the contiguous object be not very
high, the disorder may be cured by heightening the
chimney of the low house; but if it is very high, it
will be necessary to cover the top of the chimney in
such a manner as to prevent the wind from entering it,
at the same time that a passage is left at some of the
sides through which the smoke may issue with freedom.
Many are the contrivances which have been invented
for this purpose, which are to be met with every-where;
and as there is no difficulty in accomplishing the de-
sired end by an infinite variety of methods, every one
who needs such a thing may please his own fancy in
the choice. We have thought it unnecessary to add
any more but one kind of these, fig. 14. which will
answer the end effectually.
It is evident that houses situated near high hills, or
thick woods, will be in some measure exposed to the
same inconvenience; but it is likewise plain, that if a
house be situated upon the slope of a hill, as at E,
fig. 13. it will not be in any danger of smoke when the
wind blows towards that side of the hill upon which it
is.
Smoke. is situated; for the current of air coming over the
Plate house-top in the direction GH, is immediately changed
CCLXXI. by the slope of the hill to the direction HC, which
powerfully draws the smoke upward from the top of
the chimney. But it is also evident, that a house in
this situation will be liable to smoke when the wind
blows from the hill; for the current of air coming
downward in the direction CH, will beat downward
on the chimney F, and prevent the smoke from ascend-
ing with freedom. But the effect will be much height-
ened if the doors and windows are chiefly in the lower-
most side of the house.
These are some of the most general circumstances
which prevent the free ascent of smoke, arising from
external objects: but there are many other lesser
causes which may at times occasion smoke, all of which
it would be tedious here to enumerate; such as, blasts
of air, reflected from the sides of mountains, and com-
ing down valleys with great impetuosity, occasioning,
in particular situations, eddies or whirlwinds of different
sorts. In short, whatever in any measure disturbs the
free motion of the air, is in danger of producing sud-
den gusts, which may occasion smoke. Therefore,
whoever builds in a situation which is not altogether
free, may lay his account with having some sudden gusts
of smoke, unless he forms the top of his chimney so as
to obviate it. And there are some situations so much
exposed to sudden gusts of wind, sometimes whirling
round, sometimes beat suddenly downward, or as sud-
denly carried up again, that it is difficult to guard
against every danger. In these situations we would
recommend something of the form of what is repre-
sented at fig. 15. which would be proof against every
wind whatever.
Having thus traced the causes of smoky houses, and
reduced them to distinct classes for the sake of distinc-
tions; it is necessary, before we quit this subject, to
observe, that in many cases, two or more of these may
be combined to augment the malady, and therefore it
is necessary to have all these circumstances in view in
every particular case. It now only remains that we
point out the several phenomena which may lead us to
distinguish from which of these general causes the dis-
order complained of may proceed. And,
1st, If it is owing to a fault in the construction of
the chimney itself, it will smoke almost continually,
especially in calm weather.
2d, If it does not smoke in calm weather, or only
when the wind comes from some particular quarter,
and can then be cured by opening some door or win-
dow, the fault may be looked for in the distribution of
the doors or windows of the house. The only case in
which there is a difficulty to distinguish whether it is
owing to the fault of the chimney or the house, is
when it proceeds from too much closeness of the apart-
ment. But this may be easily known by trying it in
a calm: for if it proceeds from this cause, there will
be no smoke in a perfect calm, if the doors are left
open; whereas, if the defect proceeds from a fault in
the chimney itself, it will still continue to smoke when
calm, even when the doors are open.
3d, When the smoke is occasioned by external causes,
these can be generally seen; but it may be likewise
known by this, that it descends in sudden puffs with
great violence at times, even when the doors and win-
dows are not altered. By attending to these few rules
with care, there will be little danger of mistaking the
cause from whence this disorder proceeds.
We shall conclude these observations with a few re-
marks on some particular cases, which can hardly be
reduced to any of the foregoing heads. And,
1st, It sometimes happens that the smoke is pre-
vented from ascending with freedom, by having a small
part of the top of the chimney broke down, so as that
some parts of it remain higher than others, which in
some measure reduces it to the state of a chimney at
the side of a higher one. To prevent this, it is al-
ways proper to have the top of the chimney finished
with stones neatly cut, and firmly built. It is not to
be doubted but that those things which are placed up-
on particular chimneys with a view to cure them of
smoke, do often, from the same cause, hurt the neigh-
bouring chimneys built in the same wall.
2d, A chamber is sometimes filled with smoke,
when a fire is kindled in a neighbouring chimney, and
none in it, although there is no appearance of smoke
when it has a fire burning in its own grate. This may
sometimes proceed from a small hole breaking through
the thin partition that divides the two chimneys from
one another; and as smoke is a weighty body, which
is only buoyed up by the warm air which passes thro'
the fire, when it penetrates into the cold chimney it
naturally subsides, and comes down to the chamber
with which the chimney communicates, when there is
no fire to carry it off. But this disease is generally
produced by the smoke entering at the top of the
chimney, and descending downwards: if this last is
the case, it may be cured, on many occasions, by set-
ting a pretty high stone at the top of the chimney, as
a division between each two: but the surest method, in
all cases, is to have a smoke-board exactly fitted into
the chimney above the grate, which on all occasions
effectually prevents it.
3d, It frequently happens, that a chimney does not
carry off the smoke well at first when the fire is kind-
led, although there is not the smallest tendency to it
at other times. This proceeds from the narrowness of
the chimney; for when the fire is kindled, the whole
tube is filled with cold air, as weighty as that in the
apartment; and being expanded by the fire at the bot-
tom, it endeavours to ascend upward; but being pent
in by the narrowness of the tube, and pressed by the
column of cold air above it, it is some time before it
can wholly overcome that resistance, and some of it is
forced into the chamber, till by degrees the whole
chimney is heated, and then it vents quite well. If
the smoke produced by this means is not very trouble-
some, it may be borne with; but if it be extremely
disagreeable, it may be cured by having a large sheet
of milled iron, large enough to reach between the two
sides of the fire-place, and as deep as to reach from
the mantle to the grate, or lower, which might by any
contrivance be hung up before the fire at that time to
act in some measure as a smoke-chimney. This would
quickly make the fire burn, and carry off the smoke
entirely. After that is effected, it might then be re-
moved till another occasion.
Smoks-Farthings. The pentecostals, or customary
oblations offered by the dispersed inhabitants within a
diocese when they made their procession to the mother-
Smoke cathedral church, came by degrees into a standing annual-rent, called smoke-farthings.