SMY 
aiodioiis machine in a kitchen ; so called 
from its being moved by means of tlie 
smoke, or rarefied air, moving np the chim- 
ney, and striking against the tail of the ho- 
rizontal wheel, which, being inclined to the 
horizon, is thereby moved about the axis of 
the wheel, together with the pinion which 
carries the wiiecl, and this carries the cliain 
which turns the spit. The wheel should be 
placed in the narrow part of the chimney, 
where the motion of the smoke is swiftest, 
and the greatest part of it must be made 
strike upon the sails. 
The manner of operation of this useful 
machine is easily understood. The air which 
contributes to the burning of the fuel, and 
passes through the midst ol it, is greatly 
heated, and expanding prodigiously in bulk, 
becomes lighter than the neighbotiriug air, 
and is therefore pushed by it up the chim- 
ney. In like manner, all the air which 
comes near the fire is heated, expanded, be- 
comes lighter, and is driven up the chim- 
ney. This is called the draught or suction ; 
but would, with greater propriety, be term- 
ed the drift of the chimney. As the chim- 
ney gradually contracts in its dimensions, 
and as the same quantity of heated air 
passes through every section of it, it is plain 
that the rapidity of its ascent must be 
greatest in the narrowest place. There 
the fly should be placed, because it will 
there be exposed to the strongest current. 
This air, striking the fly vines obliquely, 
pushes them aside, and thus turns them 
round with a considerable force. If the 
joint of meat is exactly balanced on the 
spit, it is plain, that the only resistance to 
the motion of the fly is what arises from the 
friction of the pivots of the upright spindle, 
the friction of the pinion and wheel, the 
friction of the pivots of the horizontal axis, 
the friction of the small end of the spit, and 
the friction of the chain in the two pulleys. 
The whole of this is but a mere trifle. But 
there is frequently a considerable inequality 
in the weight of the meat on difierent sides 
of the spit: there must therefore be a suf- 
ficient overplus of force in the impulse of 
the ascending air on the vanes of the fly, to 
overcome this want of equilibrium occa- 
sioned by the unskilfulness or negligence of 
the cook. 
SMUT, a disease in corn, which destroys 
entirely the germ and substance of the 
grain. 
SMYRNIUM, in botany, Alexanders, a 
genus of the Pentandria Digynia class and 
order. Natural order of Umbellatse, or 
SNO 
Umbelliferaj, Essential character : petals 
acuminate, keeled; fruit oblong, striated. 
There are seven species. 
SNAFFLE, in the manege, is a very 
slender bit-mouth, without any branches, 
much used in England ; the true bridles be- 
ing reserved for the service of war. 
SNAIL. See Limax. 
SNAKE. See Anguis. The common 
snake is a harmless and iiioifensive animal, 
and might even be kept tame in houses to 
destroy vermin. 
SNAKING, in naval affairs, is the wind- 
ing small ropes spirally round a large one, 
the former lying in the intervals between 
the strands of the latter, and is frequently 
termed w'orming. 
SNOW, a well-known substance, formed 
by the freezing of the vapours in the atmos- 
phere. It differs from hail and hoar-frost, 
in being cis it were crystallized, which they 
are not. This appears on examining a 
flake of snow' by a magnifying glass ; vvheii 
the whole of it will appear to be composed 
of fine shining spicula, diverging like rays 
from a centre. As the flakes fall down 
through the atmosphere, they are conti- 
nually joined by more of these radiated 
spicula, and thus increase in bulk like the 
drops of rain or hail-stones. Dr. Grew, in 
a discourse of the nature of snow, observes, 
that many parts thereof are of a regular 
figure, for the most part stars of six points, 
and are as perfect and transparent ice as 
any we see on a pond, &c. Upon each of 
these points are other collateral points, set 
at the same angles as the main points them- 
selves : among which there are divers other 
irregular, which are chiefly broken points, 
and fragments of the regular ones. Others 
also, by various winds, seemed to have 
been thawed, and frozen again into irre- 
gular clusters; so that it seems as if the 
whole body of snow were an infinite mass 
of icicles irregularly figured : that is, a 
cloud of vapours being gathered into drops, 
the said drops forthwith descend ; upon 
which descent, meeting with a freezing air as 
they pass through a colder region, each drop 
is immediately frozen into an icicle, shootifig 
itself forth into several points ; but these 
still continuing their descent, and meetiug 
with some intermitting gales of warmer 
air, or in their continual waftage to and fro 
touching upon each other, some of them 
are a little thaw'ed, blunted, and agaiu 
frozen into clusters, or entangled so as to 
fall down in what we call flakes. The 
lightness of snow, although, it is firm iee, 
N 2 
