TABLE OF ANIMAL POWER APPLIED TO LIFTING WATER BY NORIAS.

Giving the Foot-pounds Corresponding to Each Amount of Work.

For higher lifts regular pumps should be employed, and the following table of the duties that may be obtained thereby can be readily varied.

TABLE OF HIGHER LIFTS OF PUMPING WORK DONE BY ANIMAL POWER, THE ANIMAL WALKING AT THE RATE OF THREE MILES PER HOUR, AND POWER DEVELOPED THROUGH HORSE GEAR ON TO PUMPS OF 9" STROKE AT 30 REVOLUTIONS PER MINUTE, ALLOWING II PER CENT. FOR LOSSES IN PUMPS.

CHAPTER VIII.

THE POWER OF WIND.

Of all common things, air is the most common.

It is free to all without let or price, and its movement, which we call the wind, affords a power, costing nothing for itself, and but a very moderate amount for the necessary mechanism to make use of it.

Constituent Features of Air.—

Air is of unlimited compressibility and elasticity.

Its elastic force is in direct proportion to the space it occupies.

A cubic foot at atmospheric pressure weighs 564.8 grains. A ton of air, 2,240 lbs., thus equals 27,810 cubic feet. The atmosphere extends above us some 50 miles, therefore each square inch of earth surface is sustaining a column of air of about that height, which in normal condition is equivalent to a load of 14.7 lbs. This is bearing on each square inch and is known as atmospheric pressure. It is subject to variations ascertainable by the use of a barom

eter.

Being a fluid, this pressure is exerted by it on all points of access.

Wind. When in motion the moving mass of air is called wind, and exerts a pressure due to its speed, upon surfaces exposed to it. This pressure is made use of in the sails of vessels for propulsion, and in the angular sails of windmills for obtaining a rotary motion.

A plane surface exposed angularly to the wind pressure. receives a motion due to the angle of impact. Being secured to a revolving shaft, it can only move in the rotary direction.

This faculty has been utilized in the familiar windmill, which is an excellent motor, and suited to a great variety of work requiring moderate power and not too great regularity.

The chief drawback of windmills is their unreliability for steady daily work, but this may be successfully dealt with by means detailed further on. Anyone who witnessed at the Chicago Exposition the multiplicity of duties to which the large number of windmills there exhibited were applied could not fail to be impressed with the future possibilities this simple system of power possesses.

Wind Powers.-To find the force of the wind, P = lbs. pressing on each square foot of surface. V = velocity of

wind in feet per second.

P=0.002288 × V2.

If the velocity in miles per hour is known, then, calling it "v,"

P = .00492 v2.

For the calculation of the safety of tall structures exposed to wind pressures it is usual to take 56 lbs. per square foot of exposed surface above 100 feet from the ground, and below that 40 or 45 lbs. Where the surface is at an angle to the direction of the wind the force exerted upon it may be found as follows:

P = .0023 V2 × the sine of the angle.

The best course to adopt before deciding for or against a windmill is to arrange with a resident to take daily notes of the force and direction of the wind in the locality where it is proposed to erect the apparatus.

Many such data may be gathered from the daily weather reports published by the Meteorological departments of

America and Great Britain, and also by the agents of Lloyds.

The following comparative table will afford ready information on this subject.

5,280 feet. Higher extreme pressures in cyclones have been

Locality. Naturally, as high and moderately exposed a position as is conveniently possible should be selected. The top of any well-built building or of a good barn will do. Where buildings are not available, a wooden, or better still a steel, frame tower may be used. Costs of these are given in the succeeding tables.

Very exposed headlands, where the full force of storms would be felt, should be avoided. The great point is to secure a position where the average prevailing winds will be caught freely.