MILL. 
VELOCITY OF THE WIND. 
Perpendicular 
Force on one 
Square Foot in 
Avd. Pounds. 
Miles in one 
Hour. 
^2 Feet in one 
Second. 
1 
1.47 
.005 
2 
2.93 
.020 
3 
4.40 
.044 
4 
5.87 
.079 
5 
7.33 
.123 
10 
14.67 
.492 
15 
22.00 
1.107 
go 
29.34 
1.968 1 
25 
36.67 
3.075 1 
30 
44.01 
4.429 1 
So 
51.34 
6.027 ! 
40 
58.68 
7.873 
45 
66.01 
9.963 
50 
, 73.35 
12.300 
60 
88.02 
17.715 
80 
117.36 
31.490 
100 
! 
146.70 
49.200 
Whatever varieties may arise as to tlie 
internal structure of wind-mills, there are 
certain rules with regard to the position, 
shape, and magnitude of sails, which will 
bring them into the best state to receive 
the action of the w'ind, and to produce a 
full effect. M. Parent set his sails, or 
vanes, at an angle of 55° from the axis on 
which they project ; and that would have 
certainly proved the best if no other object 
than the acquisition of a certain degree of 
velocity had been desirable ; but we find 
that from 72° to 75° gives a greater pow’er; 
consequently, in their general application, 
vanes standing at that angle, or within one 
or two degrees, more or less, are best cal- 
culated to produce a sufficient impetus for 
light breezes. 
Mr. Sraeaton made several experiments, 
which gave results proving the hypothesis 
Just stated. He had vanes set at the fol- 
lowing angles, and founjd it better to give 
an excess of retirement from, than an ex- 
cess of exposure to, the wind. 
No. 
Angle with 
Angle with the Plane 
the axis. 
of Motion. 
1 ... 
72° ... 
0 
19 ° 
3 ... 
4 ... 
16° 
5 ... 
771 .. 
12'° 
6 ... 
He also tried the effects of a greater ex- 
panse of surface upon the same radius ; the 
result was, that a broader sail, in all cases, 
required a larger angle ; and that frustrated 
pyramidal sails, having their bases outwards, 
were more powerful than parallelograms ; the 
extreme or outer bar being one third the 
depth of the whip, or vane staff. Attempts 
were made to fill the whole space with 
sails ; but it was evident that, for want of 
sufficient passage for the wind, the inten- 
tion was not fulfilled : when more than |ths 
of the area was spread with sail, there was 
an immense pressure, which caused much 
friction and imminent danger, while the 
velocity was rather diminished than aug- 
mented. Length of sail is a great object, 
so far as relates to the acquisition of power, 
but where an excess prevails, many injuries 
are sustained ; notwithstanding the boom 
and guys, used in many places for the sup- 
port of long arms. 
As water-mills are, in general, stopped by 
shutting out the water, and thus debarring 
further influence of the power at pleasure ; 
so wind mills are commonly stopped by a 
pinch, or pressure, on the axis bearing the 
vanes. Some are likewise acted upon by a 
weight which tends to retard the motion, 
and so slackens the rotation as to enable 
the pinch to have more effect. We have 
seen instances where the great axle could 
be cast off in an instant ; so that, although 
the vanes might continue to go round, the 
interior movements were stopped. Tliis is 
an excellent contrivance, and may often 
save a mill from being burnt, when by acci- 
dent, or neglect, the stones have come in 
contact and produced collisive sparks. But 
in such case, it is obvious that a sufficient 
counter-check should be created to retard 
the motion of the vanes ; else they wmuld, 
from want of due opposition, move round 
with great rapidity, and produce other dan- 
gers no less imminent. This prevention is 
easily effected by causing the lever, which 
raises the main axle, to act against a stiff- 
set wlieel, capable of checking its progress. 
Some mills have a weathercock placed in 
the line with the axis, projecting several 
feet, and having sufficient surface to cause 
the cap to move round, so as always to keep 
the butt of the axle direct to the wind. 
This is an admirable expedient, inasmuch as 
it effectually answers the intention, and 
supersedes the necessity for the miller’s 
constant attention to the wind ; which, 
when variable, occasions considerable in- 
terruption to other avocations, and may, 
eventually, be attended both with loss of 
time and some damage. 
Mr. John Bywater, of Nottingham, ob- 
tained a patent for clothing, or unclothing, 
the sails of wind-mills while in motion : hi* 
