MECHANICS. 
Of Horizontal Wind mills. 
Various opinions have been entertained refpefiling the 
relative advantages of. horizontal and vertical wind¬ 
mills. Mr. Smeaton, with great juftice, gives a decided 
preference to the latter; but, when he afferts that hori¬ 
zontal wind-mills have only % or of the power of ver¬ 
tical ones, he certainly forms too low an eftimate of their 
power. Mr. Beatfon, on the contrary, who has received 
a patent for the conftrufifion of a new horizontal wind¬ 
mill, feenis to be prejudiced in their favour, and greatly 
exaggerates their comparative value. From an impartial 
invelligation, it will probably appear, that the truth ties 
between thefe two oppolite opinions; but, before entering 
on this difcuflion, we mult firft conftder the nature and 
form of horizontal wind-mills. 
In fig. 27. CK is the wind-fhaft, which moves upon 
pivots. Four crofs bars, CA, CD, IB, F G, are fixed 
to this arbor, which carry the frames A P I B, D E F G. 
The fails A I, EG, are ffretched upon thefe frames, and 
are carried round the axis CK, by the perpendicular im- 
pulfe of the wind. Upon the axis C K a toothed wheel 
is fixed, which gives motion to the particular machinery 
that is employed. In the figure, only two fails are repre- 
fented ; but there are always other two placed at right 
angles to thefe. Now, let the fails be expofed to the 
wind, and it is evident that no motion will enfue; for 
the force of the wind upon the fail A I, is counteracted 
by an equal and oppoiite force upon the fail EG. In 
order then, that the wind may communicate motion to 
the machine, the force upon the returning fail EG mult 
either be removed by fcreening it from the wind, or di- 
minifhed by making it prefent a lefs furface when return¬ 
ing a gain ft the wind. The firlt of thefe methods is adopted 
in Tartary, and in fome provinces of Spain ; but is ob¬ 
jected to by Mr. Beatfon, from the inconve-aience and 
expenfe of the machinery and attendance requifite for 
turning the fcreens into their proper pofitions. Notwith¬ 
standing this objection, however, we are difpofed to think 
that this is the heft method of diminifhing the aCtion of 
the wind upon the returning fails; for the moveable fcreen 
may ealily be made to follow the direction of the wind, 
and afl'urne its proper pofition, by means of a large 
wooden weathercock, without the aid either of men or 
machinery. It is true, indeed, that the refinance of the 
air in the returning fails is not completely removed ; but 
it is at leaft as much diininilbed a's it can be by any me¬ 
thod hitherto propofed. Befides, when this plan is re- 
forted to, there is no oecaflon for any moveable flaps and 
hinges, which mult add greatly to the expenfe of every 
other method. 
The mode of bringing the fails back againft the wind, 
•which Mr. Beatfon invented, is, perhaps, the fimpleft and 
belt of the kind. He makes each fail A I to conlilt of fix 
or eight flaps or vanes, AP h i, b 102, &c. moving upon 
hinges reprefented by the dark lines, A P, bs, cz, Sc c. fo 
that the lower fide, b 1, of the firlt flap, overlaps the hinge 
or higher fide of the fecond flap, and fo on. When the 
wind, therefore, afts upon the fail A I, each flap will prefs 
upon the hinge of the one immediately below it, and the 
whole furface of the fail will be expofed to its afition. But, 
when the fail A I returns againft the wind, the flaps will 
revolve round upon their hinges, and prefent only their 
edges to the wind, as is reprefented at EG ; fo that the 
refiftance occafioned by the return of the fail mult be 
greatly diminifhed, and the motion will be continued by 
the great fuperiority or force exerted upon the fails in the 
pofition A 1 . It^ computing the force of the wind upon 
the fail A I, and the refiftance oppofed to it by the edges 
of tlie flaps in EG, Mr. Beatlon finds, that, when the 
preflu re upon the former is 187a pounds, the refiftance 
oppofed by the latter is only about 36 pounds, or ^ part 
of the whole force ; but he neglects the afition of the 
w ind upon the arms C A, &c. and the frames which carry 
the fails, becaufe they expofe the fame furface in the po- 
687 
fition A I as in the pofition EG. This omiffion, how¬ 
ever, has a tendency to miflead 11s in the prefent cafe, as 
we ihall now fee ; for we ought to compare the whole 
force exerted upon the arms,, as well as the fail, with the 
whole refiftance which thefe arms and the edges of the 
flaps oppofe to the motion of the windmill. By infpefil¬ 
ing the figure, it will appear, that, if the force upon the 
edges of the flaps, which Mr. Beatfon fuppofed to be n 
in number, amounts to 36 pounds, the force {pent upon 
the bars CD, DG, GF, F E, &c. cannot be lefs than 
60 pounds. Now', fince thefe bars are afited upon with 
an equal force, when the fails have the pofition A I, 
1872 + 60=1932 will be the force exerted upon the fail 
A I, and its appendages, while the oppolite force upon 
the bars and edges of the flaps when returning againft the 
wind w ill be 36-}—60=296 pounds, which is nearly -^5 of 
1932, inftead of as computed by Mr. Beatfon. Hence 
vve may fee the probable advantages of a fcreen over 
moveable flaps, as it will preferve not only the fails, but 
the arms and the frame which lupport it, from the action 
of the wheel. 
We fliall conclude this head with a comparifon of the 
power of horizontal and vertical wind-mills. It was al¬ 
ready ftated, that Mr. Smeaton rather under-rated the 
former, while he maintained that they have only ^ or ^3 
the pow'erof the latter. He obferves, that, when the vanes 
of a horizontal or a vertical mill are of the fame dimen- 
fions, the power of the latter is four times that of the 
former, becaufe, in the firft cafe, only one fail is afited 
upon at once, while, in the fecond cafe, all the four re¬ 
ceive the impulfe of the wind. This, however, is not 
ftrifitly true, fince the vertical fails are all oblique to the 
direflion of the wind. Let us fuppofe that the area of 
each {ail is 100 fquare feet; then the power of the hori¬ 
zontal fail will be 100, and the power of a vertical fail 
may be called looXfme 70 2 (70 0 being the common angle 
ot inclination) = 88 nearly ; but, fince there are four ver¬ 
tical fails, the power of them all will be 4X88 = 352 ; fo 
that the power of the horizontal fail is to that of the four 
vertical ones, as 1 to 3*52, and not as 1 to 4, according 
to Mr. Smeaton. But Mr. Smeaton alfo obferves, that, if 
we conftder the farther difadvantage which arifes from 
the difficulty of getting the fails back againft the wind, 
vve need not wonder if horizontal wind-mills have only 
about § or ^ the power of the common fort. We have 
already feen, that the refiftance occafioned by the returra- 
of the fails amounts to of the whole force which they 
receive; by fubtrafiling — therefore, from -E-, we fliall 
20 3*52 
find that the power of horizontal wind-mills is only 
i ’o 3 
--, or little more than h that of vertical ones. Tins 
4'+° 
calculation proceeds upon a fuppofition, that the whole 
force exerted upon vertical fails is employed in turning 
them round the axis of motion ; whereas a confiderable 
part of this force is loft in preffing the pivot of the axis 
or windfhaft againft its gudgeon. Mr. Smeaton has over¬ 
looked this circumftance, otherwile he could never have 
maintained that the power of four vertical fails was qua¬ 
druple the power of one horizontal fail, the dimenfions 
of each being the fame. Taking this circumftance into 
the account, we cannot be far wrong in faying, that in 
theofy at leaft, if not in practice, the power of a hori¬ 
zontal wind-mill is about § or % of the power of a verti¬ 
cal one, when the quantity of furface and the form of the 
fails is the fame, and when every part of the horizontal 
fails has the fame diftance from the axis of motion as the 
correfponding parts of the vertical fails. But, if the ho¬ 
rizontal fails have the pofition A I, EG, inftead of the 
pofition CA dm, C Do?i, their power will be greatly in- 
creafed, though the quantity of furface is the lame, be¬ 
caufe the part CP3WZ being transferred to B I jr/, has 
much more power to turn the fails. 
MACHINES 
