\assaethies cao ema eareee See 
128 WINDMILL. 
ance, and there would be no motion. In order 
to make the arms revolve, the sails must, there- 
fore, be placed in some direction intermediate 
between those of the wind and the plane in which 
the arms revolve. In determining the angle at 
which the planes of the sails should be inclined 
to the axis of motion, or the direction of the 
wind, it is necessary to consider the sail in mo- 
tion; and the neglect of this element in the cal- 
culation has led to very great errors in theoreti- 
cal calculations, The sail being in motion, the 
velocities of the sail and the wind must both be 
taken into account; for, if the sail moved before 
the wind with a speed equal to that of the wind 
itself, no effect would be produced. The effect 
will depend on the difference of the velocities, 
that being the velocity with which the wind 
| strikes the sail. Now, as the obliquity of the 
sail to the wind should depend on the force with 
which the wind acts upon it, and as those parts 
of the sail which are nearer to the centre of mo- 
tion move more slowly than those which are more 
remote, it follows that the position of the sail 
_ should vary at different distances from the centre 
of rotation. From the experiments of Mr. Smea- 
_ ton on this subject (Philosophical Transactions, 
| 1759), it appears that the following positions are 
| the best. Suppose the radius to be divided into 
six equal parts, and call the first part, beginning 
from the centre, one, the second two, and so on, 
the extreme part being six :— 
Angle Angle with the 
with Plane of Motion, or 
No. the Axis, Angle of Weather. 
1 2° 18° 
VASE Savill 19 
3 72 18 
4, 74 16 
4) : leg ve . 6 124 
Gules 3 Sone . ¢ . 7 
As it is necessary that a windmill should face 
the wind from whatever point it blows, the whole 
machine, or a part of it, must be capable of turn- 
ing horizontally. Sometimes the whole mill is 
made to turn upon a strong vertical post, and is 
therefore called a post mill; but, more commonly, 
the roof or head only revolves, carrying with it 
the windwheel and its shaft, the weight being 
supported on friction rollers. In order that the 
wind itself may regulate the position of the mill, 
a large vane, or weathercock, is placed on the 
side which is opposite the sails, thus turning 
them always tothe wind. But in large mills the 
motion is regulated by a small supplementary | 
| windwheel, or pair of sails, occupying the place 
| of the vane, and situated at right angles with 
the principal windwheel. When the windmill is 
| in its proper position, with its shaft parallel to 
| the wind, the supplementary sails do not turn, 
But when the wind changes, they are imme- 
diately brought into action, and, by turning a 
series of wheelwork, they gradually bring round 
the head to its proper position. 
| On account of the inconstant nature of the 
_ motion of the wind, it is necessary to have some 
WINE. 
provision for accommodating the resistance of 
the sails to the degree of violence with which 
the wind blows. This is commonly done by cloth- 
ing and unclothing the sails; that is, by covering, 
with canvass or thin boards, a greater or smaller 
portion of the frame of the sails, according to the 
force of the wind at different times. A method 
has been devised for producing the same effect, 
by altering the obliquity of the sails; and wind- 
mills have been so made as to regulate their own 
adjustment by the force of the wind. If we sup- 
pose a windmill, or windwheel, to consist of four 
arms, and that the sails were connected to these 
arms at one edge by means of springs, the yield- 
ing of these springs would allow the sails to turn 
back when the wind should blow with violence; 
and their elasticity would bring them up to the 
wind whenever its force abated. This effect has 
been produced by a weight acting on the sails 
through a series of levers. A loose iron rod, pass- 
ing through the centre of the axle of the wind- 
wheel, receives the action of the weight at one 
end, and communicates it to the sails at the 
other. See the articles Minn and Turasurne- 
Macuine. 
WINDPIPE. The trachea or grand air-pas- 
sage to the lungs of animals. It comprises the 
most admirable adaptations to the joint proper- 
ties of flexibility and permanent tubularity ; and 
is beautifully suited, in form and capacity, to the 
precise wants and habits of each species; and it 
is lined with a very vascular mucous membrane | 
to supply all its interior surface with a secretion 
for defending it against the irritating effects of 
diversified temperature in the air. The wind- 
pipe of the ox comprises 8 or 10 more cartilagi- 
nous rings than that of the horse, or altogether 
about 60; but it is smaller in diameter, looser in 
construction, and weaker in the interposed liga- 
mentous substance,—and it also exhibits other 
differences, involved in its perfect adaptation to 
the ox’s habits. 
WINDROW. The green part or border of a 
field dug up in order to furnish material for 
ameliorating the rest of the land,—and is called 
a windrow because it is laid in rows and exposed 
tothe wind. A windrow is also a particular kind 
of heap or collecting of hay in the process of hay- 
making; and is likewise a row of peats in the 
process of cutting turbary for fuel,—and a row 
of turf in the process of georgical improvement 
by paring and burning. I 
WINE. Any fermented vegetable juice which 
contains sugarand an acid. All the truest wines 
consist of the fermented juice of the grape; but | 
inferior wines may consist of the fermented juice 
of various other fruits, or even of the fermented 
juice of some leaves and stems. The chemical 
process by which the juice passes into wine is 
described in the article Fnrmenration; and the 
kinds of grape used for making the best wines 
are described in the article GrapE-VINE. : 
The History of Wines.—The discovery or in- 
