It follows from thefe experiments, 1. That the difcharge by different additional tubes, with the fame altitude of the refervoir, are nearly in proportion to the area of the apertures, or to the fquares of the

diameters.

2. That the difcharge of water by additional tubes of the fame diameter, with different altitudes of water in the refervoir, are nearly proportional to the fquare root of the altitude of the refervoir.

3. That in general the difcharge of water in the fame time, through different additional tubes, with different altitudes of water in the fame refervoir, are to each other nearly as the product of the Square of the diameters of the tubes by the fquare root of the altitude of the refervoirs.

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So that the efflux of water by additional tubes, follow (amongst themselves) the fame laws as through the thin orifice.

The following table was formed from the foregoing experiments.

OF JETS D'EAU.

We are now going to confider the nature of fountains. There are few things that give more pleasure to the eye than a diverfity in the play of water from a fountain: but thefe machines give additional pleasure in fultry climates, where they contribute to cool the air, as well as to enliven the profpect. With us they are chiefly made for the purposes of embellifhment, for here the air is feldom difageeable from too much warmth; and if there were fountains of fire, they would often make the moft grateful ornament.

Whatever be the direction of the jet, the difcharge of water is always the fame; provided that the ajutage, and the altitude of the refervoir above the ajutage, be the fame. This is a neceflary confequence of the equal preffure of fluids in all di

rections.

Water, fpouting from a fmall ajutage, has fufficient velocity to carry it to the fame height as the water in the refervoir; but it never attains entirely this height, being prevented by various concurring caufes. Firft, The friction in the tubes between the refervoir and the ajutage. Secondly, The friction against the circumference of the aperture. Thirdly, The refiftance of the air to the weight of the water at the top of the fpout; for this, having loft it's motion, refts on the part below, and by it's weight obftructs the motion of the column. The refiftance from this cause is so great, that the jet is frequently deftroyed, the rifing water being by fits and ftarts preffed down to the very orifice from which it fpouts: but this inconvenience is remedied, if you give the jet a little inclination; for then the particles which have loft their motion upwards do not

fall

fall back as before, but fall off from the rest, and thus do not incumber the rifing fluid; hence fuch jets as are a little inclined will rife higher than

thofe that are vertical.

When the ajutage is inclined to the horizon, the projectile force and the gravity of the water caufe the ftream to defcribe a parabola, whofe amplitude is greater in proportion to the height of the refervoir.

When the ajutage is in an horizontal direction, the jet defcribes a femi-parabola.

Jets of water rife higher in proportion as the aperture of the ajutage is large, becaufe, 1. of two jets proceeding from the fame refervoir with equal velocities, the largest undergoes lefs friction: 2. it has more mafs, and confequently more force to overcome obftacles. But though a large jet will rife higher than a fmall one, it does not discharge more water; for the discharge is as the product of the aperture by the velocity at the moment of efflux; and this velocity is the fame in each, friction not being confidered.

In order to make large jets rife higher than small ones, the conduit-pipe must be large enough to furnish a fufficient quantity of water; for experience has fhewn, that if these are narrow, fmall jets will rife higher than thofe that are larger. The diameter of the conduit-pipe fhould therefore bear a certain proportion to that of the ajutage, in order to make a jet rife to the greateft poffible height. If you compare two dif ferent jets, and are defirous that each fhould attain it's greatest altitude, the fquares of the diameters of the conduit-pipes, must be to each other in the componnd ratio of the fquares of the diameters of the ajutages, and the fquare root of the altitude of the refervoir. Thus, if you know by experience the diameter that ought to be given to a conduit

pipe,

pipe, to furnish water for the discharge of a given ajutage, with a refervoir of a given altitude, you may determine the diameter of another tube, to feed a given ajutage with a reservoir of a given altitude.

Experience has fhewn, that, for an ajutage fix lines diameter, with a refervoir of fifty-two feet, the conduit-pipe should be about thirty-nine lines; for an ajutage fix lines diameter, and a refervoir fixteen feet, the conduit-pipe twenty-eight and an half lines. There is no inconvenience in giving a conduit-pipe a greater diameter than is required by the above rule, but there would be a confiderable one in giving it a fmaller diameter.

From the comparison of feveral experiments made on jets d'cau, it appears that the difference between the altitudes of vertical jets, and the altitudes of the refervoirs, is to each other as the fquares of the jet's altitude. If you know, therefore, by experiment how far any jet falls fhort of the altitude of it's refervoir, you may find by the rule of three, how much any other jet falls fhort of it's refervoir. If you wish to know the altitude of the refervoir, you have only to add to the altitude of the jet the quantity found by the proportion. It is to be obferved, that conduit-pipes fhould never be fixed at right-angles to each other.

The following table will facilitate the appli cation of the foregoing principles. In the two firft columns are the altitudes of the jets, and the correfponding altitudes of the refervoir. The third column contains (in Paris pints, thirty-fix of which make a cubic foot) the discharge during one minute, through an ajutage fix lines diameter, relatively to the altitudes of the fecond column. Knowing the discharge with an ajutage of fix lines by the rule of three, you will difcover the discharge VOL. III.

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by.