Farms and Villages. 
61 
the main-shaft of the sail-wheel, and the position of this disc^ 
and therefore of the sail, is regulated bv a bell-crank lever and 
balance-weigh*^, which can be controlled by means of a wire bv 
the attendant on the ground, or bv a float in a water-tank, or bv 
a loaded hvdraulic-cy Under in communication with the risings 
main of a pump when the mill is used for lifting water. The 
weight on the regulating lever is set to yield at anv desirec) 
pressure or speed of wind. The sail-wheel is mounted on a. 
fixed turret, of suitable height, usually formed of open wood- 
work, and is turned to the wind by a powerful vane, which 
also serves to balance the weight of the wheel. 
A wind speed of 18 miles per hour is taken as the standard 
for estimating horse-power, and under such conditions a sail- 
disc 8 feet in diameter will give one-man power, or say 20OO 
foot lbs., per minute. ^^ indmills have been constructed of 60 
feet in diameter, estimated to yield 40 horse-power. 
The following table gives the size of mills required to raise 
various quantities of water to a height of 25 feet : — 
Diimeter of 
E^volntions 
Water raised 
25 fett per 
MiBUte. 
Saa-WheeL 
per ilincte. 
fe«t. 
gallons. 
10 
50 
10 
12 
48 
15} 
14 
44 
25* 
16 
40 
67" 
18 
37 
89 
20 
»4 
99 
22 
32 
107 
25 
30 
217 
28 
28 
368 
30 • 
26 
524 
For greater lifts the size of the windmills must be increaseci 
in proportion. Thus, for example, a 12-feet mill will raise 
151 gallons 25 feet high : but if it is required to be lifted four 
times the height, or 100 feet, it would need a mill of four times 
the power, or one capable of raising 62 gallons 25 feet, which, 
according to the table, will have a ItJ-feet sail-wheel. 
The prices of the mills range from 16/. for the 8-foot wheel, 
to 120/. for the 30-foot, but this does not include the derrick or 
turret, the cost of which depends upon its height, and therefore 
on the locality. The cost of fixing cannot, for the same reason, 
be defined.* 
* Further information respecting windmills vrill be found in Mr. Ccleman's 
report on the agricultural implements in the Philadelphia Exhibition, ici 
volume riiL of the ' Journal,' 1S77. page 67, and in 3Ir. Wheeler's paper on the- 
storage of water, in volume xiv., 1S78, page 47. 
