ris

2.

Broke. that will serve for most chimneys. High funnels with going up a ladder till their heads are near the ceiling. Smokr.

small and low openings may indeed be supplied through It is then among this warm air that the wanted quan.
a less space; because, for reasons that will appear here- tity of outward air is best admitted, with which being
after, the force of levity, if one may so speak, being mixed, its coldness is abated, and its inconvenience di-
greater in such funnels, the cool air enters the room minished so as to become scarce observable. This may
with greater velocity, and consequently more enters in be easily done by drawing down about an inch the upper
the same time. This, however, has its limits; for ex- sash of a window; or, if not moveable, by cutting such
perience shows, that no increased velocity so occasioned a crevice through its frame ; in both which cases it will
has made the admission of air through the key hole be well to place a thin shelf of the length to conceal
equal in quantity to that through an open door, though the opening, and sloping upwards, to direct the entering
through the door the current moves slowly, and through air horizontally along and under the ceiling. In some
the key-hole with great rapidity.

houses the air may be admitted by such a crevice made It remains then to be considered, how and where in the wainscot, cornice, or plastering, near the ceiling this necessary quantity of air from without is to be ad- and over the opening of the chimney. This, if practic nnitted so as to be least inconvenient: for if at the door, cable, is to be chosen, because the entering cold air left so much open, the air thence proceeds directly to will there meet with the warmest rising air from before the chimney, and in its way comes cold to your back the fire, and be soonest tempered by the mixture. The and heels as you sit before your fire. If you keep the same kind of shelf should also be placed here. Another door shut, and raise a little the sash of your window, way, and not a very difficult one, is to take ont an upyou feel the same inconvenience. Various have been per pane of glass in one of your sashes, set it in a tin the contrivances to avoid this; such as bringing in fresh frame, giving it two springing angular sides, and then air through pipes in the jams of the chimney, which replacing it, with hinges below on which it may be pointing upwards should blow the smoke up the funnel; turned to open more or less above. It will then have opening passages into the funnel above, to let in air for the appearance of an internal sky-light. By drawing the same purpose. But these produce an effect con- this pane in, more or less, you may admit what air you trary to that intended : for as it is the constant current find necessary. Its position will naturally throw that of air passing from the room through the opening of the air up and along the ceiling. This is what is called in chimney into the funnel which prevents the smoke from France a Was ist das? As this is a German question,' coming out into the room, if you supply the funnel by the invention is probably of that nation, and takes its other means or in other ways with the air which it name from the frequent asking of that question when it wants, and especially if that air be cold, you diminish first appeared. In England some have of late years out the force of that current, and the smoke in its efforts to a round hole about five inches diameter in a pane of the enter the room finds less resistance.

sash, and placed against it a circular plate of tin hung on
The wanted air must then indispensably be admitted an axis, and cut into vanes; which, being separately
into the room, to supply what goes off through the bent a little obliquely, are acted upon by the entering
opening of the chimney. M. Gauger, a very ingenious air, so as to force the plate continually round like the
and intelligent French writer on the subject, proposes vanes of a windmill. This admits the outward air,
with judgment to admit it above the opening of the and by the continual wbirling of the vanes, does in
chimney; and to prevent inconvenience from its cold- some degree disperse it. The noise only is a little in-
Dess, he directs that it may be so made, that it shall convenient.
pass in its entrance tlırough winding cavities made be- 2. A second cause of the smoking of chimneys is,
bind the iron back and sides of the fire-place, and un- their openings in the room being too large; that is, too
der the iron hearih-plate; in which cavities it will be wide, too high, or both. Architects in general have no
warmell, and even heated, so as to contribute much, in- other ideas of proportion in the opening of a chimney
stead of cooling, to the warming of the room. This than what relate to symmetry and beauty respecting the
invention is excellent in itsell, and may be used with dimensions of the room; while its true proportion re-
ail vantage in building new houses ; because the chim- specting its function and utility depends on quite other
neys may then be so disposed as to admit conveniently principles; and they might as properly proportion the
the cold air to enter such passages: but in houses built step in a staircase to the beight of the story, instead of
witheut such views, the chimneys are ofien so situated the natural elevation of men's legs in mounting. The
as not to afford that convenience without great and ex- proportion then to be regarded, is what relates to the
pensive alterations. Easy and cheap methods, though height of the funnel. For as the funne!s in the diflerent
not quite so perfect in themselves, are of more general stories of a bouse are necessarily of different heights or
utility; and such are the following.

lengths, that from the lowest floor being the highest or
In all rooms where there is a fire, the body of air longest, and those of the other floors shorter and shorter,
warmed and rarefied before the chimney is continually till we come to those in the garrets, which are of course
changing place, and making room for other air that is the shortest; and the force of drast being, as already
to be warned in its turn. Part of it enters and goes said, in proportion to the height of funnel filed with ra.
up the chimney, and the rest rises and takes place near refied air, and a current of air from the room into the
the ceiling. If the room be lofty, that warm air re- chimney, sufficient to fill the opening, being necessary
mains above our heads as long as it continues warn, to oppose and prevent the smoke from coming out into
and we are little benefited by it, because it does not the room ; it follows, that the openings of the longest
descend till it is cooler. Few can imagine the dillerence funnels may be larger, and that those of the shorter fun-
of climate between the upper and lower parts of such a nels should be smaller. For if there be a large opening
room, who have not tried it by the thermometer, or by. to a chimney that does not draw strongly, the funnel
Vol. XIX. Part II.

+

3G

may

a

room.

а

a

a

Smoke. way bappen to be furnished with the air which it de

Or you may in some cases, to advantage, build addi. Smokes mands by a partial current entering on one side of the tional stories over the low building, which will support opening, and leaving the other side free of any opposing a high funnel. current, may permit the smoke to issue there into the

If the low building be used as a kitchen, and a conMuch too of the force of drast in a funnel de- traction of the opening therefore inconvenient, a large pends on the degree of rarefaction in the air it contains, one being necessary, at least when there are great dinand that depends on the nearness to the fire of its pas- mers, for the free management of so many cooking utensage in entering the funnel. If it can enter far from sils; in such case the best expedient perhaps would be the fire on each side, or far above the fire, in a wide or to build two more funnels joining to the first, and har. high opening, it receives little heat in passing by the ing three moderate openings, one to each funnel, instead fire, and the contents of the funnel are by those means of one large one. When there is occasion to use but less different in levity from the surrounding atmosphere, one, the other two may be kept shut by sliding plates, and its force in drawing consequently weaker. Hence hereafter to be described ; and two or all of them may if too large an opening be given to chimneys in upper be used together when wanted. This will indeed be an rooms, those rooms will be smoky : On the other hand, expence, but not an useless one, since your cooks will if too small openings be given to chimneys in the work with more comfort, see better than in a smoky lower rooms, the entering air operating too directly and kitchen what they are about, your victuals will be violently on the fire, and afterwards strengthening the cleaner dressed and not taste of smoke, as is often the draft as it ascends the funnel, will consume the fuel too case; and to render the effect more certain, a stack of rapidly.

three funnels may be safely built biglier above the roof Remedy. As diferent circumstances frequently mix than a single funnel. themselves in these matters, it is difficult to give precise The case of too short a funnel is more general than dimensions for the openings of all chimneys. Our fa- would be imagined, and often found where one would thers made them generally much too large : we have not expect it. For it is not uncommon, in ill-contrived lessened them ; but they are often still of greater di- buildings, instead of having a funnel for each room or mensions than they should be, the human eye not being fire-place, to bend and turn the funnel of an upper room easily reconciled to sudden and great changes. If you so as to make it enter the side of anotber funnel that suspect that your chimney smokes from the too great di- comes from below. By these means the upper room mension of its opening, contract it by placing moveable funnel is made short of course, since its length can only boards so as to lower and narrow it gradually till you be reckoned from the place where it enters the lower find the smoke no longer issues into the room. The pro- room lunnel; and that funnel is also shortened by all portion su found will be that which is proper for that the distance between the entrance of the second funnel chimney, and you may employ the bricklayer or mason and the top of the stack : for all that part being readily to reduce it accordingly. However, as in building new supplied with air through the second funnel, adds no houses something must be sometimes hazarded, Dr strength to the draft, especially as that air is cold when Franklin proposes to make the cpenings in tlie lower there is no fire in the second chimney. The only easy rooms about 30 inches square and 18 deep, and those in remedy here is, to keep the opening of that funnel shut the upper only 18 inches square and not quite so deep; in which there is no fire. the intermediate ones diminishing in proportion as the 4. Another very common cause of the smoking of height of the funnel is diminished. In the larger open- chimneys is, their overpowering one another. For inings, billets of two feet long, or balf the common length stance, if there be two chimneys in one large room, and of cordwood, may be burnt conveniently; and for the

you make fires in both of them, the doors and windows smaller, such wood may be sawed into thirds. Where close shut, you will find that the greater and stronger coals are the fuel, the grates will be proportioned to the fire shall overpower the weaker, from the funnel of openings. The same depth is nearly necessary to all, which it will draw air down to supply its own demand ; the funnels being all made of a size proper to admit a which air descending in the weaker funnel, will drive chimney-sweeper. If in large and elegant rooms cus- down its smoke, and force it into the room. If, instead tom or fancy should require the appearance of a larger. of being in one room, the two chimneys are in two difchimney, it may be formed of expensive marginal de- ferent rooms, communicating by a door, the case is the corations, in marble, &c. But in time perhaps, that same whenever that door is open. In a very tight which is fittest in the nature of things may come to be house, a kitchen chimney on the lowest floor, when it thought handsomest.

had a great fire in it, has been known to overpower 3. Another cause of smoky chimneys is too short a any other chimney in the house, and draw air and funnel. This happens necessarily in some cases, as smoke into its room as often as the door communicating where a chimney is required in a low building; for, if with the staircase was opened. the funnel be raised high above the roof, in order to Remedy. Take care that every room have the means strengthen its draft, it is then in danger of being blown of supplying itself from without with the air which its down, and crushing the roof in its fall.

chimney may require, so that no one of them may be · Remedies. Contract the opening of the chimney, so obliged to borrow from another, nor under the necessity as to oblige all the entering air to pass through or very of lending. A variety of these means have been alnear the fire ; whereby it will be more heated and rare- ready described. fied, the funnel itself be more warmed, and its contents 5. Another cause of smoking is, when the tops of have more of what may be called the force of lovity, so chimneys are commanded by higher buildings, or by a hill, as to rise strongly and maintain a good draft at the so that the wind blowing over such eminences falls like opening

water over a dam, sometimes almost perpendicularly on

the

a

a

Fig. 3.

Smoke. the tops of the chimneys that lie in its way, and bcats Remedy. There is but one remedy, which is to raise Smoke. down the smoke contained in them.

such a funnel higher than the roof, supporting it if ne-
To illustrate this, let A (fig. 3.) represent a small cessary by iron bars. For a turncap in this case has
building at the side of a great rock B, and the wind no eflect,' the dammed-up air pressing down through it
coming in the direction CD; when the current of air in whatever position the wind may have placed its open-
comes to the point D, being hurried forward with great ing.
velocity, it goes a little forward, but soon descends Dr Franklin mentions a city in which many houses
downward, and gradually is reflected more and more in- are rendered smoky by this operation. For their kitch-
ward, as represented by the dotted lines EE, &c. so, ens being built behind, and connected by a passage with
that, descending downwards upon the top of the chim- the houses, and the tops of the kitchen chimneys lower
ney A, the smoke is beat back again into the apart- than the tops of the houses, the whole side of a street
ments.

when the wind blows against its back forms such a dam
It is evident that houses situated near high hills or as above described; and the wind so obstructed forces
thick woods will be in some measure exposed to the down those kitchen-chimneys (especially when they have
same inconvenience; but it is likewise plain, that if a but weak fires in them) to pass through the passage and
house be situated upon the slope of a hill (as at F, house into the street. Kitchen-chimneys so formed and
fig. 3.), it will not be in any danger of smoke when the situated have another inconvenience. In summer, if you
wind blows towards that side of the bill upon wbich it open your upper room windows for air, a light breeze
is situated; for the current of air coming over the house. blowing over your kitchen chimney towards the house,
top in the direction GH, is immediately changed by the though not strong enough to force down its smoke as
slope of the hill to the direction HC, which powerfully aforesaid, is sufficient to wast it into your windows, and
draws the smoke upward from the top of the chimney. fill the rooms with it; which, besides the disagreeable-
But it is also evident, that a house in this situation will ness, damages your furniture.
be liable to smoke when the wind blows from the hill; 7. Chimneys, otherwise drawing well, are sometimes
for the current of air coming downwards in the direction made to smoke by the improper and inconvenient situa-
CH, will beat downward on the chimney F, and pre- tion of a door. When the door and chimney are on the
vent the smoke from ascending with freedom. The ef- same side of the room, if the door being in the corner
fect will be much beightened if the doors and windows is made to open against the wall, which is common, as
are chiefly in the lowerniost side of the house.

being there, when open, more out of the way, it fol.
Remedy. That commonly applied in this case is a lows, that when the door is only opened in part, a cun
turncap made of tin or plate iron, covering the chimney rent of air rusliing in passes along the wall into and
above and on three sides, opeu on one side, turning on across the opening of the chimney, and flirts some of the
a spindle; and which being guided or governed by a smoke out into the room. This bappeus more certainly
vane always presents its back to the current. This when the door is shutting, for then the force of the cur-
may be generally effectual, though not certain, as there rent is augmented, and becomes very inconvenient to
may be cases in which it will not succeed. Raising your those who, warming themselves by the fire, happen to
funnels if practicable, so as their tops may be higher, sit in its way.

.
or at least equal, with the commanding eminence, The remedies are obvious and easy. Either put an
more to be depended on. But the turning cap, being intervening screen from the wall round great part of
easier and cheaper should first be tried. “If obliged to the fireplace; or, which is perhaps preferable, shift the
build in such a situation, I would choose (says Dr hinges of your door, so as it may open the other way,
Franklin) to place my doors on the side next the hill, and when open throw the air along the other wall.
and the backs of my chimneys on the farthest side ; for 8. A room that bas no fire in its chimney is some-
then the column of air falling over the eminence, and of times filled with smoke which is received at the top of its
course pressing on that below, and forcing it to enter funnel, and descends into the room. Funnels without
the doors or was-ist-dases on that side, would tend to fires have an effect according to their degree of cold-
balance the pressure down the chimneys, and leave ness or warmth on the air that bappens to be contained
the funnels more free in the exercise of their func- in them. The surrounding atmosphere is frequently
tions."

changing its temperature; but stacks of funnels covered
6. There is another case which is the reverse of that from winds and sun by the house that contains them,
last mentioned. It is where the commanding eminence retain a more equal temperature. If, after a warm sea-
is farther from the wind than the chimney commanded. son, the outward air suddenly grows cold, the empty
To explain this a figure may be necessary. Suppose then warm funnels begin to draw strongly upward ; that is,
a building whose side AB happens to be exposed to the they rarefy the air contained in them, wbich of course
wind, and forms a kind of dam against its progress. rises, cooler air enters below to supply its place, is ra-
Suppose the wind blowing in the direction FE. The refied in its turn, and rises, and its operation continues
air obstructed by this dam or building AB will like till the funnel grows cooler, or the outward air warmer,
water press and search for passages through it; but find- or both, when the motion ceases. On the other hand,
ing none, it is beat back with violence, and spreads it. if after a cold season the outward air suddenly grows
self on every side, as is represented by the curved lines warm and of course lighter, the air contained in the
e, e, e, e, e, e. It will tberefore force itself down the cool funnels being heavier d: scends into the room ; and
small chimney C, in order to get through by some door the warmer air wliich enters their tops being cooled in
or window open on the other side of the building. And its turn, and made heavier, continues to descend; and
if there be a fire in such chimney, its smoke is of course this operation goes on till the funnels are warmed by the
beat down, and fills the room.

passing of warm air through them, or the air itself grown
3 G 2

a

may

Smoke. cooler. When the temperature of the air and of the ces the effect, because when yon most want your fire smoke..

funnels is nearly equal, the difference of warmth in the you are sometimes obliged to extinguish it. To under-
air between day and night is sufficient to produce these stand this, it may be considered that the rising light air,
currents: the air will begin to ascend the funnels as the to obtain a free issue from the funnel, must push out of
cool of the evening comes on, and this current will con- its way or oblige the air that is over it to rise. In a
tinue till perhaps nine or ten o'clock the next morning, time of calm or of little wind this is done visibly; for
when it begins to hesitate ; and as the heat of the day we see the smoke that is brought up by that air rise in a
approaches, it sets downwards, and continues so till to- column above the chimney : but when a violent current
wards evening, when it again besitates for some time, -of air, that is, a strong wind, passes over the top of a
and then goes upwards constantly during the night, as chimney, its particles have received so much force, wbich
before mentioned. Now when smoke issuing from the keeps them in a horizontal direction and follow each
tops of neighbouring fannels passes over the tops of fun- other so rapidly, that the rising light air has not strength
nels which are at the time drawing downwards, as they sufficient to oblige them to quit that direction and move
often are in the middle part of the day, such smoke is upwards to permit its issue.
of necessity drawn into these funnels, and descends with Remedies. lo Venice, the custom is to open or viden
the air into the chamber.

the top of the five, rounding it in the true form of a funThe remedy is to have a sliding plate that will shut nel. In other places the contrary is practised; the tops perfectly the offending funnel. Dr Franklin has thus of the Aues being narrowed inwards, so as to form a slit described it: “The opening of the chimney is contract- for the issue of the smoke, long as the breadth of the funed by brick-work faced with marble slabs to about two nel, and only four inches wide. This seems to have been seet between the jams, and the breast brought down to contrived on a supposition that the entry of the wind within about three feet of the bearth. An iron frame is would thereby be obstructed; and perhaps it might bave placed just under the breast, and extending quite to the been imagined, that the whole force of the rising warm back of the chimney, so that a plate of the same metal air being condensed, as it were, in the narrow opening,

slide horizontally backwards and forwards in the would thereby be strengthened, so as to overcome the rogrooves on each side of the frame. This plate is just so sistance of wind. This, however, did not always succeed; large as to fill the whole space, and sbut the chimney for when the wind was at north-east and blew fresh, the entirely when thrust quite in, which is convenient when smoke was forced down by fits into the room where Dr there is no lire. Draw it out, so as to leave between Frauklin commonly sat, so as to oblige him to shift the its further edge and the back a space of about two inches; fire into another. The position of the slit of this funthis space is sufficient for the smoke to pass; and so large nel was indeed north-east and south-west. Perhaps if a part of the funnel being stopt by the rest of the plate, it had lain across the wind, the effect might have been the passage of warm air out of the room, np the chim- different. But on this we can give no certainty. I: ney, is obstructed and retarded; and by those means seems a matter proper to be referred to experiment. much cold air is prevented from coming in through cre- Possibly a turncap might have been serviceable, but it vices, to supply its place. This effect is made manifest ,

was not tried. 1. When the fire burns briskly in cold With all the science, however, that a man shall supweather, the howling or whistling noise made by the pose himself possessed of in this article, he may sometimes wind, as it enters the room through the crevices, when meet with cases that shall puzzle him. “ I once lodged the chimney is open as usual, ceases as soon as the plate (says Dr Franklin) in a house at London, which in a is slid in to its proper

distance. 2. Opening the door little room bad a single chimney and funnel. The openof the room about half an inclı, and holding your hand ing was very small, yet it did not keep in the smoke, against the opening, near the top of the door, you feel and all attempts to have a fire in this room were fruitthe cold air coming in against your hand, but weakly, less. I could not imagine the reason, till at length obif the plate be in. Let another person suddenly draw it serving that the chamber over it, which had no fireplace out, so as to let the air of the room go up the chimney, in it, was always filled with smoke when a fire was kindwith its usual freedom where chimneys are open, and led below, and that the smoke came through the cracks you immediately feel the cold air rushing in strongly. and crevices of the wainscoat; I had the wainscot taken 3. If something be set against the door, just sufficient, down, and discovered that the funnel which went up when the plate is in, to keep the door nearly shut, by behind it had a crack many feet in length, and wide resisting the pressure of the air that would force it

open : enough to admit my arm; a breach very dangerous with then, when the plate is drawn out, the door will be for- regard to fire, and occasioned probably by an apparent ced open by the increased pressure of the outward cold irregular settling of one side of the house. The air enair endeavouring to get in to supply the place of the tering this breach freely, destroyed the drawing force warm air that now passes out of the room to go up the of the funnel. The remedy would have been, filling chimnes. In our common open chimneys, half the fuel up the breach, or rather rebuilding the funnel : but the is wasted, and its effect lost; the air it has warmed be- landlord rather chose to stop up the chimney. ing immediately drawn off.”

“ Another puzzling case I met with at a friend's 9. Chimneys which generally draw well, do neverthe- country house near London. His best room bad a less sometimes give smoke into the rooms, it being driven chimney in which, he told me, he never could bave a down by strong winds passing over the tops of their funnels, fire, for all the smoke came out into the room. I flate though not descending from any commanding eminence. tered myself I could easily find the cause and prescribe This case is most frequent where the funnel is short and the cure. I opened the door, and perceived it was not the opening turned from the wind.

It is the more want of air. I made a temporary contraction of the grievous, when it happens to be a cold wind that produ- opening of the chimney, and found that it was not its

three ways:

Jack.

Smoke, being too large that caused the smoke to issue. I went, The nanner of operation of this useful machine is. Smuke-,
Suske. out and looked up at the top of the chimney: Its fun- easily understood. The air which contributes to the Jack.

nel was joined in the same stalk with others; some of burning of the fuel, and passes through the midst of it,
them shorter, that drew very well, and I saw nothing to is greatly heated, and expanding prodigiously in bulk,
prevent its doing the same. In fine, after every other becomes lighter than the neighbouring air, and is there-
examination I could think of, I was obliged to own the fore pushed by it up the chimney. In like manner, all
iasufficiency of my skill. But my friend, who made no the air which comes near the fire is heated, expanded,
pretension to such kind of knowledge, afterwards disco- becomes lighter, and is driven up the chimney. This
vered the cause himself. He got to the top of the fun- is called the draught or suction, but would with greater
vel by a ladder, and looking down found it filled with propriety be termed the drifi of the chimney. As the
twigs and straw cemented by earth and lined with fea- chimney gradually contracts in its dimensions, and as.
thers. It seems the house after being built, had stood the same quantity of heated air passes througlı every.
empty some years before he occupied it; and he con- section of it, it is plain that the rapidity of its ascent
cluded that some large birds had taken the advantage of must be greatest in the narrowest place. There the fly
its retired situation to make their nest there. The rub. G should be placed, because it will there be exposed to
bish, considerable in quantity, being removed, and the the strongest current. The air, striking the fly vanes
funnel cleared, the chimney drew well, and gave satis- obliquely pushes them aside, and thus turns them round,
faction."

with a considerable force. If the joint of meat is ex-
Chimneys whose funnels go up in the north wall of a actly balanced on the spit, it is plain that the only re-
house, and are exposed to the north winds, are not so apt sistance to the motion of the fly is what arises from the
to draw well as those in a south wall; because when friction of the pivots of the upright spindle, the friction,
reodered cold by those winds, they draw downwards. of the pinion and wheel, the friction of the pivots of

Chimneys inclosed in the body of a house are better the horizontal axis, the friction of the small end of the than those whose funnels are exposed in cold walls. spit, and the friction of the chain in the top pulleys.

Chimneys in stacks are apt to draw better than se- The whole of this is but a mere trifle. But there is freparate funnels, because the funnels that have constant quently a considerable inequality in the weight of the fires in them warm the others in some degree that have meat on different sides of the spit: there must therefore none.

be a sufficient overplus of force in the impulse of the SHOKE-Jark. This ingenious mac'ıine is of German ascending air on the vanes of the fly, to overcome this, origin, and Messinger, in his Collection of Mechanical want of equilibrium occasioned by the unskilfulness or Performances, says it is very ancient, being represent- negligence of the cook. There is, however, commoned in a painting at Nurenbergh, which is known to be ly enough of power when the machine is properly conolder than the year 1350.

structed. The utility of this machine will, we hope, Its construction is abundantly simple. An upright procure us the indulgence of some of our readers, while ccecxcvn. iron spindle GA (fig. 5.), placed in the narrow part of we point out the circumstances on which its performance. fig. s.

the kitchen chimney, turns round on two points H and depends, and the maxims which should be followed in.
1. The upper one H passes through an iron bar, which its construction.
is built in across the chimney; and the lower pivot I is The upward current of air is the moving power, and
of tempered steel, and is conical or pointed, resting in a should be increased as much as possible, and applied in,
conical bell metal socket fixed on another cross bar. the most advantageous manner. Every thing will in-
On the upper end of the spindle is a circular fly G, con- crease the current which improves the draught of the
sisting of 4, 6, 8, or more thin iron plates, set obliquely chimney and secures it from smoking. A smoky chim-
on the spindle like the sails of a windmill, as we shall ney must always have a weak current. For this parti-
doscribe more particularly by and by. Near the lower cular, therefore, we refer to what has been delivered in,
end of the spindle is a pinion A, which works in the the article PNEUMATICS, N° 359; and the article
teeth of a contrate or face wheel B, turning on a bo- SMOKE.
rizontal axis BC. One pivot of this axis turns in a With respect to the manner of applying this force, it
cock fixed on the cross bar, which supports the lower is evident that the best construction of a windmill sails,
eod of the upright spindle HI, and the other pivot turns will be nearly the best construction for the fly. Ac-
in a cock fixed on the side wall of the chimney ; so cording to the usual theory of the impulse of Auids,
tbat this axle is parallel to the front of the chimney. the greatest effective impulse (that is, in the direction of
On the remote end of this horizontal axle there is a the fly's motion will be produced if the plane of the
small pulley C, having a deep angular groove. Over vane be inclined to the axis in an angle of 54 degrees.
this pulley there passes a chain CDE, in the lower bight 46 minutes. But, since we have pronounced this the..
of which hangs the large pulley E of the spit. This ory to be so very defective, we bad better take a deter-
end of the spit turns loosely between the branches of the mination founded on the experiments on the impulse of
fork of the rack or raxe F, but without resting on it. fluids made by the academy of Paris. These authorise
This is on the top of a moveable stand, which can be us to say, that 495 or 50 degrees will be the best angle
shifted nearer to or farther from the fire. The other to give the vane: but this most be understood only of
end turns in one of the notches of another rack. The that part of it which is close adjoining to the axis. The
number of teeth in the pinion A and whcel B, and the vane itself must be twisted, or weathered as the mill-
diameters of the pulleys C and E, are so proportioned wrights term it, and must be much more oblique at its ,
that the fly G makes from 12 to 20 turns for one turn outer extremity. The exact position cannot be deter-
of the spit.

mined with any precisio: ; because this depends on the

proportion

Plate

a