Part 22 (1/2)

A boat sailing across the wind is acted on in a si

170) The wind strikes the sail obliquely, and would thrust it to leeere it not for the opposition of the water The force A is resolved into forces B and C, of which C propels the boat on the line of its axis The boat can be ht round until a point is reached at which the force B on the boat, masts, etc, overco up wind depends on her ”lines” and the amount of surface she offers to the wind

THE BALLOON

is a pear-shaped bag--usually hter than air The tendency of a heavier as upwards, and with it the bag and the wicker-work car attached to a network encasing the bag The tapering neck at the lower end is open, to peras as the at elevation At the top of the bag is a wooden valve opening inwards, which can be dran by a rope passing up to it through the neck whenever the aeronaut wishes to let gas escape for a descent He is able to cause a very rapid escape by pulling another cord depending froency this is torn away bodily, leaving a large hole The ballast (usually sand) carried enables him to maintain a state of equilibriuas and the doard pull of gravity To sink he lets out gas, to rise he throws out ballast; and this process can be repeated until the ballast is exhausted The greatest height ever attained by aeronauts is the 7-1/4 miles, or 37,000 feet, of Messrs

Glaisher and coxwell on September 5, 1862 The ascent nearly cost them their lives, for at an elevation of about 30,000 feet they were partly paralyzed by the rarefaction of the air, and had not Mr coxwell been able to pull the valve rope with his teeth and cause a descent, both would have died from want of air

[Illustration: FIG 171]

The _flying- to produce, will probably be quite independent of balloons, and will depend for its ascensive powers on the action of air on oblique surfaces Sir Hiram Maxim's experi 171 On a deck was ht This drove large propellers, S S

Large aeroplanes, of canvas stretched over light fraher than the rear TheUnfortunately an accident happened at the first trial and destroyed the ht it would be necessary to have a vertical rudder for altering the horizontal direction, and a horizontal ”tail” for steering up or down The principle of an aeroplane is that of the kite, with this difference, that, instead ofbody is propelled against more or less stationary air The resolution of forces is shown by the arrows as before

Up to the present ti-machine has appeared But experi the conditions which must be fulfilled to enable man to claim the ”dominion of the air”

[34] The ”Romance of Modern Mechanism,” p 243

Chapter XVIII

HYDRAULIC MACHINERY

The siphon--The bucket pump--The force-pump--The most marvellous pump--The blood channels--The course of the blood--The hydraulic press--Household water-supply fittings--The ball-cock--The water-meter--Water-supply systeines--The cream separator--The ”hydro”

In the last chapterthat the pressure of the atmosphere is 15 lbs to the square inch Suppose that to a very long tube having a sectional area of one square inch we fit an air-tight piston (Fig 172), and place the lower end of the tube in a vessel of water On raising the piston a vacuum would be created in the tube, did not the pressure of the atmosphere force water up into the tube behind the piston The water would continue to rise until it reached a point 34 feet perpendicularly above the level of the water in the vessel The coluh 15 lbs, and exactly counterbalance the at of the piston would not raise the water any farther At sea-level, therefore, the _lifting_ power of a pump by suction is limited to 34 feet On the top of a lofty ht of the column would be diminished--in fact, be proportional to the pressure

[Illustration: FIG 172]

[Illustration: FIG 173]

THE SIPHON

is an interesting application of the principle of suction By its oeight water34 feet This is explained by Fig 173 The siphon pipe, A B C D, is in the first instance filled by suction The weight of the water between A and B counter-balances that between B and C But the colus, as it were, to the heels of B C, and draws it down Or, to put it otherwise, the colu heavier than the column B A, draws it over the top between the columns, provided that B A does not exceed 34 feet, is impossible, as the pressure of the atmosphere on the mouth of B A is sufficient to prevent the formation of a vacuum

THE BUCKET PUMP

We may now pass to the coardens, etc (Fig 174) The piston has a large hole through it, over the top of which a valve is hinged At the botto upwards, seated on the top of the supply pipe In sketch (_a_) the first upstroke is in progress A vacuuer, and water rises up the barrel to fill it

The next diagraer valve now opens and alloater to rise above the piston, while the lower closes under the pressure of the water above and the pull of that below

During the second upstroke (_c_) the water above the piston is raised until it overflows through the spout, while a fresh supply is being sucked in below