M E C H 
tain duty, and to fend their corn to be ground at his 
mill, their bread to be baked in his oven, and their grapes 
to be prefled at his wine-prefs. The origin of thefe fervi- 
tudes may, however, be accounted for on juller grounds. 
The building of mills was at all times expenfive, and un¬ 
dertaken only by the rich, who, to indemnify themfelves 
for the money expended in order to benefit the public, fti- 
pulated that the people in the neighbourhood fliouid grind 
their corn at no other mills than thole erected by them. 
A wind-mill, fuch as thofe in common ufe in this coun¬ 
try, is reprefented at fig. 23. Plate X. where MN is the 
circular building that contains the machinery, E the ex¬ 
tremity of the wind-fhaft, or principal axis, which is ge¬ 
nerally inclined from 8 to 15 debtees to the horizon ; and 
E A, E B, E C, ED, four refoangular frames upon which 
fails of cloth of the fame form are ftretched. At the lower 
extremity C of the fails, their furface is inclined to the 
axis 72 0 ; and at their fartheft extremities A, D, See. the 
inclination of the fail is about 83°. Now, when the fails 
are adjufted to the wind, which happens when the wind 
blows in the direction of the wind-fhaft E, the impulfeof 
the wind upon the oblique fails may be refolved into two 
forces, one of which acts at right angles to the wind- 
fhaft, and is therefore employed folely in giving a motion 
of rotation to the fails and the axis upon which they are 
fixed. When the mill is ufed for grinding corn, a crown¬ 
wheel, fixed to the principal axis E, gives motion to a lan¬ 
tern or trundle, whofe axis carries the moveable millltone. 
That the wind may adt with the greateft efficacy upon 
the fails, the wind-fhaft muff have the fame direction as 
the wind. But, as this direction is perpetually changing, 
fome apparatus is neceffary for bringing the wind-fhaft 
and fails into their proper pofition. This is fometimes 
effedled by fupporting the machinery on a ftrong vertical 
axis, whofe pivot moves in a brafs focket firmly fixed 
into the ground, fo that the whole machine, by means of 
a lever, may be made to revolve upon this axis, and be 
properly adjufted to the diredtion of the wind. Molt 
■wind-mills, however, are furnifhed with a moveable roof, 
which revolves upon fridtion-rollers inferted in the fixed 
kerb of the mill; and the adjuftment is effedted by the 
afliftance of a fimple lever. This laft kind of wind-mill 
is always built of ftone, in the form of a round turret, 
having a large wooden ring on the top of it, above which 
the roof, which mult .likewif'e be of wood, moves upon 
rollers, as has been already mentioned. To effedt this 
motion the more eafily, the wooden ring which lies on 
the top of the building is furnifhed with a groove, at the 
bottom of which are placed a number of brafs truckles 
at certain diftances, and within the groove is placed an¬ 
other ring, by which the whole roof is fupported. The 
beams ab and ac are connedted with the moveable ring, 
and a rope is fattened to the beam ab in b, which at the 
other extremity is fitted to a wihdlafs or axis in peritrochio ; 
and this rope being drawn through the iron hook G, and 
the windlafs turned round, the fails and roof will be turn¬ 
ed round aUo, in order to catch the wind in any direc¬ 
tion. Both thefe methods of conltrudtion have their ad¬ 
vantages and difadvantages. The former is the leaff ex¬ 
penfive, as the whole may be made of wood, and of any 
form that is thought proper ; while the other requires a 
coftly building of ftone ; and, the roof being round, the 
building mud alfo be fo ; while the other can be made of 
any form, but has the inconvenience of being liable to be 
carried off all together by a very high wind, of which an 
inftance occurred not long ago in Eflex. 
Fig. 2.4 (hows the internal mechanifm of a wind-mill, 
A H O is the upper room ; H eZ the lower one ; A B the 
axle-tree palling through the mill; ST V W the fails co¬ 
vered with canvas fet obliquely to the wind, and turning 
round in the order of the letters. C D is the cog-wheel, 
having about 48 cogs, a a a, See. which carry round the 
lantern E F, having eight or nine trundles b, b, See. along 
with the axis GN. IK is the upper mill-fione, LM the 
lower one ; Q R is the bridge fupporting the axis or fpin- 
Vol. XIV. No. 1005. 
A N I C S. 685 
die G N, which reds upon the beams X Y, wedged up 
at c, d, and X. Z Y is the lifting-tree, which ftands up¬ 
right; ab and ef a re levers, having Z and e as centres of 
motion ; f g h i is a cord, with a ftone i wound about the 
pins gh, and which thus ferves as a balance or counter- 
poife. The fpindle / N is fixed to the upper mill-fione 
I K by means of a piece of iron called the rynd, and fixed 
in the lower fide of the ftone, the whole weight of which 
refts upon a hard ftone fixed in the bridge Q R at N. The 
trundle EF and axis G may be taken away ; for it refts 
its lower part by t in a fquare focket, and the top runs in 
the edge of the beam w. By bearing down the end f of the 
lever fe we raife b„ which raifes all'o Z Y, and this raifes 
Y X, which lifts up the bridge QR, with the axis N G, 
and the upper ftone IK ; fo that by this contrivance the 
ftones may, as in the water-mill, be fet at any difiance. 
The lower ftone is fixed upon ftrong beams, and is broader 
than the upper one; the flour being conveyed through 
the tunnel no into a cheft. P is the hopper into which 
the corn is put, and which runs along the fpout r into the 
hole t, and fo falls between the ftones, where it is ground. 
The fquare axis G t fliakes the fpout r as it turns round, 
and makes the corn run out; at r is a firing going round 
the pin s, which ferves to bring the fpout nearer or let it 
go farther from the axis, and thus makes the corn to run 
fader or flower according to the velocity of the wind. If 
the wind be very ftrong, only part of the fails S,T, V, W, 
is covered, or perhaps only one half of the two oppofite 
fails. Another cog-wheel B is placed towards the end B 
of the axle-tree, with a trundle and mill-ftones like thofe 
already deferibed; fo that, when the wind is ftrong, the 
mill may do twice the bufinefs it ordinarily does. When 
only one pair is to grind, the trundle E F and axis G t 
are taken out from the other; xyl is a girt of pliable 
wood, fixed at the end x ; and the other end l is tied to 
the lever k m , moveable about k ; and the end in being put 
down, draws the girt xyl clofe to the cog-wheel ; and 
thus the motion of the mill may be flopped at pleafure ; 
fq is a ladder for afeending to the higher part of the 
mill; and the corn is drawn up by means of a rope rolled 
about the axis A B. 
Of the Form and Pojilion of Wind-mill Sails. 
It appears from the inveftigations of Parent, that a 
maximum effedl will be produced when the fails are in¬ 
clined 54§ degrees to the axis of rotation, or when the an¬ 
gle of weather is 355 degrees. (The weather of the fails 
is the angle which the furface forms with the plane in which 
they move, and is equal to the complement of the angle 
which that furface forms with the axis.) In obtaining 
this conclufion, however, M. Parent has affumed data 
which are inadmiflible, and has neglected feveral circum- 
ftances which moll materially affeft the refult of his in¬ 
veftigations. The angle of inclination affigned by Parent 
is certainly the mod efficacious for giving motion to the 
fails from a Hate of reft, and for preventing them from flop¬ 
ping when in motion ; but he has not confidered that the 
aclicn of the wind upon a fail at reft is different from its 
adlion upon a fail in motion ; for, fince the extremities of 
the fails move with greater rapidity than the parts nearer 
the centre, the angle of weather (hould be greater towards 
the centre than at the extremity, and (hould vary with the 
velocity of each part of the fail. The reafon of this is very 
obvious. It has been demonftrated by Bolfut, and efta- 
blifhed by experience, that, when any fluid ails upon a 
plain furface, the force of impullion is always exerted mod 
advantageonfly when the impelled furface is in a (late of 
reft, and that this force diminifhes'as the velocity of the 
furface increafes. Now, let us fuppofe with Parent that 
the moft advantageous angle of weather for the fails of 
wind-mills is 3sf degrees for that part of the foil which 
is neareft the centre of rotation, and that the foil has every¬ 
where this angle of weather; then, fince the extremity of 
the fail moves with the greateft velocity, it will, in a man¬ 
ner, withdraw itfelf from the action of the wind, or, to 
% M fpeak. 
