Chap. XVII.

THEORY OF THE MOTION OF FLUIDS.

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river, the difference of level being l metre: the long branch of the siphon was 30 metres,and the diameter 8 centimetres ; the two extremities of the siphon were closed with woodenplugs : the siphon was filled with water through the funnel I; the air escaped by the cockI\I ; when full of water this cock was closed, a cover LO was screwed on the funnel, andthe cock K was kept open; the velocity of the water in the siphon not being verygreat, the air brought up by this water accumulated at the highest point of the siphon, andlodged in the funnel I : to let it out, the cock K was closed, the cover L O taken off, thefunnel filled with water, after which the cock K was again opened, and the cover screwed onthe funnel; the part L O of the cover is a glass tube, which contains a needle supportedby a float to show when the funnel I must be filled with water.

f'erra's Machine. — This machine is a species of chain-pump or endless rope turning onpulleys, and drawing a certain quantity of water with it; the pulleys, PP and P'P', aretraversed by parallel axes A, B, and united by endless ropes two and two: the pulleysP, P', plunge into the water, which is to he elevated, and by turning the handle E F, the cordwhich passes over the pulleys D, H, and C turns the axle A B, and the pulleys P, P'; theendless rope that unites the pulleys acquires, by simple friction, a continuous motion, whichcommunicates itself to the water in the lower reservoir Z INI, and forces it into the upperreservoir N O. The play of this machine chiefly depends on the tension of the endlessropes by which the required friction is obtained: if this be too great, the pulleys P, P',cannot turn ; if too slight, the pulleys slip on the ropes, and do not communicate any motionto them. The adherence of the water to the cords favoursthe transmission of their motion to the molecules of water.

Fig 176-5. vkjira’s machinb. Fig. 1766. hydraulic cane.

Hydraulic Cane. — This consists of a hollow tube ABCD furnished with a valve D inthe lower part; the extremity of the tube dips into water, and an alternate rectilinearmotion is given to it; the water is elevated, and issues through the upper extremity A ; torender the motion of the column continuous, an air reservoir, R, is added, which separatesthe two parts of the tube A B, C D. The cane or tube is fixed by cords to the woodenspring-blocks E F, GII, fixed to the wall of a well by a cross-piece ZM: as a substitutefor these spring-blocks, a pole may be placed from an edifice at some distance from thereservoir containing the water to be raised. The play of this machine depends principally