Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 13, MAT-MIC

M E C H
pra&iea one-fifth part of the work of a horfe. Upon thefe fa£b
Mechanics. we have conitruiled the following table, the four firft
A N I C S.
121
columns of which are taken from Mr Fenwick’s Effay*
on Pra&ical Mechanics.
Practical
Mechanic®.
TABLE Jhevoing the relativeJlrength of Overjhot Wheels, Steam Engines, Horfes, Men, and Wind-mills of
v different kinds.
Number of
ale gallons
delivered on
an overfliot
wheel, to
feet in dia¬
meter, every
minute.
230
390
528
660
79O
97O
II70
1445
!584
1740
1900
2100
2300
2500
2686
2870
3°55
3240
3420
3750
4000
4460
4850
5250
Diameter of
the cylinder
in the com¬
mon ftcam-
engine, in
inches.
8.
9-5
10.5
ir-5
12.5
I4‘
I5-4
16.8
17-3
18.5
I9-4
20.2
21.
22.
23.1
23-9
24.7
25-5
26.25
27‘
28.5
29.8
31*1
32.4
33-6
Diameter of
the cylinder
of the im¬
proved
fteam-engine,
in inches.
6.12
7.8
8.2
8.8
9-35
10- 55
11- 75
12.8
13.6
14.2
14.8
15.2
16.2
I7*
17.8
18.3
19.
19.6
20.1
20.7
22.2
23-
23-9
24.7
25-5
Number of
horfes work¬
ing 12 hours
per day, and
moving at
the rate of
two miles
per hour.
Z
2
3
4
5
6
7
8
9
10
11
12
J3
J4
J5
16
!7
18
!9
20
22
24
26
28
3°
Number of
men work¬
ing 12 hours
a-day.
5
10
15
20
25
30
35
40
45
5°
55
60
65
70
75
80
85
90
95
100
no
120
130
140
150
Radius of
Dutch fails
in their com¬
mon polition
in feet.
21.24
30.04
36.80
42.48
47-50
52.03
56.90
60.09
63-73
67.17
70.46
73-59
76-59
79-49
82.27
84.97
87.07
90.13
92.60
95.00
99.64
104.06
108.32
112.20
ij6-35
Radius of
Dutch fails
in their beft
pofition,
in feet.
Radius of
Mr Smea-
ton’s en¬
larged fails,
in feet.
17.89
25-30
30.98
35-78
40.00
43-8 2
47-33
50.60
53-66
56.57
59-33
61.97
64-5
66.94
69.28
7r-55
73-32
75-9°
77.98
80.00
83.90
87.63
91.22
94.66
97.98
15-65
22.13
27.11
3*-3°
35-oo
38-34
4I-4I
44.27
46.96
49-50
5I-9I
54.22
56.43
58.57
60.62
62.61
64.16
67.41
68.23
70.00
73-42
76.68
79.81
82.82
85-73
Height to
which thefe
different
powers will
raife 1000
pounds avoir¬
dupois in a
minute.
13
26
39
52
65
78
9°
104
217
130
M3
156
169
182
J9S
208
221
234
247
260
286
312
338
364
39°
426. Dutch fails are always conftrufted fo that the
angle of weather may diminifh from the centre to the
extremity of the fail. They are concave to the
wind, and are in their common poftion when their ex¬
tremities are parallel to the plane in which they move,
or perpendicular to the direftion of the wind. Dutch
fails are in their hefl poftion when their extremities
make an angle of feven degrees with the plane of their
motion. Mr Smeaton’s enlarged fails are Dutch fails
in their beft polition, but enlarged at their extremi¬
ties.
427. It appears from M. Coulomb’s experiments on
Dutch wind-mills, with rectangular fails, that when the
diftance between the extremities of two oppofite fails is
66 feet French, and the breadth of each fail fix feet,
a wind moving at the rate of 20 feet per fecond will
produce an effect equivalent to icoo pounds raifed
through the fpace of 218 feet in a minute.
According to Watt and Boulton, one of their
‘fleam-engines, with a cylinder 31 inches in diameter,
and which makes 17 double ftrokes per minute, is equi¬
valent to 40 horfes working day and night; that is, to
101 horfes working nine hours and a half, the time of
conftsmt exertion in the preceding table. When the
Vol. XIII. Part I.
cylinder is 19 inches in diameter, and the engine make*
25 ftrokes of four feet each per minute, its power
is equivalent to twelve horfes working conftantly, or
thirty horfes working nine hours and a half;—and
when the cylinder is 24 inches in diameter, and the
engine makes 22 ftrokes, of five feet each, in a mi¬
nute, ’ I s power is equal to that of 20 horfes working
conftantly, or 50 horfes working nine hours and a
half.
Chap VII. On the ConfruBion of Wind-mills.
428. A WIND-MILL is reprefented in fig. 1. w-here MN Plate
is the circular building that contains the machinery, E CCCXX.V.
the extremity of the windlhaft, or principal axis, which I"
is generally inclined from 8 to 15 degrees to the hori¬
zon } and EA, EB, EC, ED four reditangular frames
upon which fails of cloth of the fame form are ftretch-
ed. At the lower extremity G of the fails their fur-
face is inclined to the axis 7 2° 5 and at their fartheft
extremities A, D, &c. 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 di-
reflion of the windlhaft E, the impulfe of the wind
& ,