11 66

THEORY AND PRACTICE OF ENGINEERING.

Book II.

on the velocity with which the tube C D mounts and descends, and it should be sufficientto allow of the water preserving an upward motion in sliding on the sides of the tube,although the tube continues to descend.

Machine of Vialon -On a movable axis AB two helicoidal tubes are placed, whose

central lines are helices of the same number of turns drawn on the same cylinder, butplaced in an opposite direction; each extremity E, F, of the tubes is furnished with valveswhich open from without inwards; by means of a lever CD fixed to the axle AH, analternate circular motion is given to the tubes; at each impulse of the water on one of thevalves it opens and allows the water to rise, at the same time the other valve closes, andretains the water already elevated; the two helicoidal tubes unite in one, II KL, by whichthe water, when elevated, flows out. This machine and the hydraulic cane are constructedon the same principle; the tubes in both are terminated by a valve; they dififer in themanner of transmitting the motion to the tubes, the hydraulic cane having an alternaterectilineal motion, and the machine of Vialon, which is composed of two hydraulic canes,has an alternate circular motion.

Tig. 176S.

CENTRIFUGAL FORCE MACHINE.

Fig. 1767.

MACHINE OP VIALON,

Centrifugal Force Machine. — A B is a vertical axis movable on two gudgeons, and turnedby means of a winch A 1) E ; hollow tubes are ranged round this axis like truncated cones,the small base of which, Im , plunges into water; they are fixed on the circumferences ofcircles Im, L M, and are curved at the upper part, so that the water which escapes at theextremity of the tubes falls into a circular basin parallel to the circle L M : when the axisA B is turned, the water, to escape from the small circle Im, rises to the extremities of thetubes, through which it falls into the vessel GII. Girard made a report to the Academy,9th December, 1816, on a centrifugal pump, constructed on the same principle, byJorge: his pump, as first described in the collection of the Academy machines, 1732,was composed of a vertical tube, and transversal branches fixed thereon, movable roundthe same gudgeons. Jorge’s modification consisted in fixing the suction pipe, and onlyputting the transversal branches of the apparatus in motion above it: the inertia whichthe moving power had to overcome was thus reduced to that of the portion of the machinewhich it is indispensible to put in motion, and besides has the very great advantage ofallowing the suction pipe to be inclined at pleasure, or of giving it any form, and thusenabling it to be used in localities which would not permit of vertical suction tubes.

Archimedean Screw. — The newel and the barrel of the Archimedean screw are boundedby right cylindrical surfaces with circular bases, having a common axis: the threads of thescrew are comprised l>etween the newel and the barrel, and their threads are generated bymovable right lines always perpendicular to the axis of the screw; these right lines rest inhelices of the same number of turns as are drawn on the internal cylinder of the barrel,and which intersect the edges of the cylinder at an angle of 45° ; the distance between thetwo points of the circle at which the helices begin determines the thickness of the threads:here are generally three or four rows of similar fillets on the same newel, at the upper