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portions are first joined together by a duced by Proust to express the chemical slender neck, which gradually fills up and · union of water with any substance, and esdisappears, the food passing from one part pecially with certain metallic oxides. The into the other; and thus we may form bydrate of copper is a blue-green oxide of polypes, not only from different portions this metal, which differs from the brown of the same animal, but from those of dif- oxide, only in containing a large quantity ferent animals. We may fix the head of of watet, which a low red heat will expel. one to the body of another, and the com HYDRAULICS teach us to ascertain the pound animal will grow, eat and multiply, velocity and impetus of Auids when in moas if it had never been divided. · By push- tion, and serve as the basis for computing ing the body of one into the mouth of ano the powers of various machinery acted upther, so far that their heads may be brought on by running water. into contact, and kept in that situation for The first principle we shall inculcate in some time, they will at last unite into one this service is, that water being an inelastic animal, only having double the usual num- fuid, (though many have thrown away much ber of arms. The hydra fusca may be time in the attempt to prove the contrary,) turned inside out like a glove, at the same can only be set in motion by two causes : time that it continues to eat and live as viz. the increased pressure of the air, as in before. The lining of the stomach now the air-vessels of fire-engines, and by gra: forms the outer skin, and the former epi- vitation; that is, where it is liberated from dermis constitutes the lining of the sto- confinement, and allowed to descend to an mach. See Adams on the Microscope. inferior level. In the former case, water

HYDRACHNA, a genus of insects of may be made to rise by machinery suited the order Coleoptera. Head, thorax, and to the purpose ; in the latter, it will inviola. abdomen united; two feelers, jointed; biy seek a lower situation. from two to six eyes; eight legs, ciliate and The velocity of water, proceeding throngh formed for swimming. The insects of this a hole in the side of a vessel, is ever proporgenus are inhabitants of the water, and tioned to the distance of the aperture from swim with considerable swiftness: they prey the level of the fluid, the square root of the on the larva of Tipulæ, and Monoculi: intermediate space being the guide. It must, the eggs are red and at first spherical, but however, be recollected, that in consequence afterwards become semi-lunar ; larva six- of the decrease of that space, as the water footed and furnished with a singular pro- is let out, the pressure becomes gradually boscis. There are about fifty speeies. H. less; therefore the medium, or mean disgeographica, so called from the fancied tance, between the surface and the vent map-like distribution of its variegations. It whence the water issues, will be found, in is one of the largest of the genus, and is general, a correct standard. Hence we see, occasionally seen in the clear ponds, and that, in order to force double the quantity other stagnant waters. This is reckoned of water through the lowest of two aper. one of the most beautiful of the British tures, the distance must be quadrupled. insects.

For if a hole made at C in the pipe A B, HYDRANGEA, in botany, a genus of fig. 1, will supply one gallon of water in a the Decandria Digynia class and order. minute; to draw double that quantity in the Natural order of Succulentæ. Saxifragæ, same time, the lower hole, D, must measure Jussieu. Essential character: capsule two. from the surface, B, four times as much as celled, two beaked, containing many seeds; from C to the surface. corolla five petalled; calyx, five-cleft, su This establishes the above position, and perior. There are three species.

proves besides, that the force is equal to the HYDRARGYRUM, an old name given velocity, as indeed we know to result in to mercury.

every branch of mechanism. To shew this; HYDRASTIS, in botany, a genus of the let the pipe, A B, be perforated in several Polyandria Polygynia class and order. Na- parts, as at CDE; the first, i. e. C, be. tural order of Ranunculaceæ, Jussieu. Es. ing one foot; that at D being four feet; and sential character: calyx none; petals three; that at E being seven feet below the surnectary none; berry composed of one seed- face, B; between E and A we will suppose ed acini, or granulations. There is but only one foot interval, so that D may be in one species, viz. H. canadensis, Canadian the centre of the height, A B. Draw the yellow rost.

horizontal line, A F, and from D describe HYDRATE, in chemistry, lately intro- the semi-circle, B GA, having D G equal

to DA, or DB, for its radius. Now the retain its surface perfectly level; were it water will, as it flows from D, describe a otherwise, vessels would often run aground parabola, and will fall upon the line, A F, at where, at present, they find depth sufficient such a distance from A, as will be equal to to float them; and the whole body of a ridouble the radius, D G. In like manner the ver would present a thousand opposing and water flowing from the aperture, C, will unequal resistances; whereas we find the reach that point, viz. K, on the horizontal resistance to be uniform. To prove this, A F, which may measure double the sine, let a piece of wood be put into a pail of waCH, on the same semicircle : and the sine ter, the fluid will in every part remain of the arc taken opposite to E, i.e. E L, is equally dense, and the surface will be perequal to the sine, CH, the water rushing fectly level. For a further elucidation of from E will intersect, or meet, the water this property, we refer to HYDROSTATICI, falling from C, at the point K. It is to be wherein it will be found very conspicuobserved, that the parabolic curve of the ous. water proceeding from C to K, has a greater The ingenions Mr. Bramah has lately ap. tendency to gravitation than that issuing plied the inelasticity of water to a variety from E, which tnshes with far more force, of purposes, especially in the application of and consequently has a greater tendency to a power to remote effects. Thus, if water an horizontal direction. For the aperture be filled into the pipe, ABCD, fig. 3, at C is only acted upon by a column of one and that a piston be applied to A B, made foot deep, i. e. from B to C, but the column perfectly tight, so that no water can possi

. of water from B to E measures seven feet. bly escape, when that piston is pressed We have already stated, that the velocity down by means of a force capable of overis equal to the square root of the column's coming the friction of its sides, and the height above the aperture.

friction of the water within the tube, it will It is the peculiar property of fuids to cause the water to rise in the pipe, CD, preserve their level, notwithstanding any whatever may be the length of the conjuncvarieties of course, or inequality of eleva- tive part, A C. Therefore, if a piston is intion. Thus, supposing the pipe, ABCD, serted into the pipe, CD, it will be acted fig. 2, to be bent into the form required for upon in perfect conformity with the motion passing over declivities, as shown: the wa. of the piston in AB; the power to more ter will rise to the height, AD; but where which may be trifling, when the diameter the channel exceeds the level of that line, of the pipe is small, and the purpose not there will be a break in the course of the relating to forcible operations. Thus, for fluid, such as appears at B: yet the course the mere intention of ringing a bell at D, may descend to any depth as at C, provided a hundred yards distant from the pull, A, a the pipe be brought back to the original bore of less than a quarter of an inch in height. If either end be in the smallest diameter would answer every purpose, and degree lower than the other, the water will would yield to the pressure of the finger, sink to the level of the lower retaining with very little exertion. On the other brim. And if the supply be continual, the hand, when machinery is to be set in motion, water issuing from the lowest end will the size of the piston, and the force wheremount nearly to the level of the source. by it is to be moved, must be proportioned This is the principle on which fountains are to the resistance generated by friction, and in general found. To effect this, however, by the opposition to the action of the mathe pipe should be small, so as to contract chine. It is necessary to observe, that the issue of the Auid, and to give it greater where the two pistons are of equal diamevelocity, by causing it to expose a smaller ter, their actions will be equal; but that if surface for the air to press upon. This con the pipe, A B, be larger than CD, it will traction should not be carried to excess; produce an increased action in the latter, else the water would want force to pass which, in such case, must have a propor. through the atmosphere, and, being sub tionate increase of altitude, and, rice rersa, dued, would break into drops, and fall when the action of A B is to be greater without gaining any height. The conduit. than that of CD. Our readers will be senpipe is usually made about five diameters sible that a tube of less diameter can be of the fountain-pipe ; under such propor- made to contain the same quantity as that tions the water will ordinarily flow so freely of greater capacity, only by adding to its as to give a good jet.

length; and that both their areas being The inelastic nature of water causes it to filled and emptied alternately by the same

action, and in the same time, that which limb may reach down through the bungbas the greatest altitude must have the hole of the cask to be emptied, to its very greatest scope of action, and move with an bottom; the other leg should be the longest, increased velocity in exact ratio with the so that when filled it may contain a heavier difference of the diameters. When the ve. body of Auid than that limb within the veslocity of the machinery attached to the sel. See fig. 5, in which the syphon, movement-tube is to be diminished, with. A B C, is inserted into a vessel to be emp. out losing the height to which the secondarytied. In large syphons it is necessary to power is thus raised by the additional length insert a cock at the lower end to prevent of the tube, the segment on which it is the escape of the fluid when first filled. In made to act must be that of a larger cir- small syphons it is common to put a small cle, as shewn in fig. 4, where the tube, A B, parallel tube, which being applied to the is of double the diameter of that at CD, mouth, the end, C, being immersed in the which would raise the lever, E, to the height liquor to be drawn off, the operator inhales F. Now, if this lever were the handle of forcibly, and by thus drawing the air out of a pump, requiring a considerable exercise the syphon, causes the liquor to rise in its of power, it is evident the fulcrum, G, must place. The absence of air, which first be placed very near to the pump-tube, H; caused the fluid to ascend into the tube, whereby the radius of the circle, GF, is occasions it to remain until the finger is greatly increased, and the plonge of the removed from the end, A; when the pres. pomp-piston, H, mucli diminished. If, on sure of the air within the vessel causes the the contrary, the fulcrum had been at 0, liquor to press through the syphon, which i. e. dividing the distance between D and continues to the last to draw off the conX into three parts, of which two are given tents of the vessel, they pressing forward to the lever, N, the plonge would be far through the long end, A. It is proper to deeper, but the power would be greatly remark, that large syphons sometimes rereduced; the segment, D F, occupying a quire to be previously filled, and then to be greater angle with the fulcrum O, than it set in the vessels to be drawn off; but, in does with the fulcrum G. This is amply general, the casks, &c. can be tilted sufficiexplained under the head of MECHA. ently to answer this purpose, and to bring

the shorter limb nearer to a horizontal posiWhere water is enclosed within a vesse!, tion than the longer limb, whereby the lat. or in a tube, in such manner that air cannot ter may possess a greater perpendicular penetrate, it will not filow out in the same altitude, and consequently a greater tenmanuer as if air were admitted to supply dency to gravitation. For, we trust, that, the place of any quantity that might be in fig. 1, it has been demonstrated, that the required to be drawn off. Of this every pressure of a fluid is in proportion to its person must be sensible who has ever at perpendicular height. We must caution tempted to draw wine, beer, &c. from a 'the reader, that as a column of water of full cask, without opening a vent at the top, thirty-three feet in perpendicular height is near the bung, to admit air, as the fluid equal to the weight of the atmosphere press. might evacuate the upper part of the vessel. ing on the surface of such a column, it folFrom this we prove, that although all Nuids lows that no syphon exceeding that length have a direct disposition to gravitation, they will act, because the power would be less are perfectly inelastic, if they were other. than the weight to be raised. wise, we should find that, by expansion, they A comical display of the properties of would be capable of filling a greater or the syphon is seen in what is called “ The lesser space at times; and that as the wine, Cup of Tantalus;" the designation of which &c. were drawii off' below, the portion re is derived from fabulons history, wherein we maining in the vessel would expand, and are told, that 'Tantalns, king of Phrygia, though less druse, would fill the whole was condemned by Jupiter to suffer perpeinterior.

tual hunger and thirst, amidst a profusion Of this property advantage has been ta of delicacies, which always receded when ken to draw off liquors from one vessel to applied to his lip. To imitate this disapanother, by means of a very simple instru- pointment, a syphon, having its two limbs ment, called a syphon. This is a pipe of parallel and contiguous, is fixed into the tin, copper, &c. according io its purpose, middle of a cup double its height; one bent at any angle, but generally about 70 limb receiving the liquid at the bottom of to 80 degrees, in such manner that one the interior, and the other discharging it


through the centre of the bottom, as seen in instance, the water must; after filling B, fig. 6. Thus, when the outlet is stopped by rise in the channel, bb, as to be above the means of a finger applied thereto, the cup greatest height of c e, to cause its passing may be offered, quite full, to the person on off into E, and thence ad libitum. Now the whom the joke is to be practiced, observ. channel, c c, being of greater diameter than ing that the syphon will not act until the the channel, bb, when the former comliquor in the cup exceeds the level of its mences its operation, it will discharge more bend, when the whole will be drawn through than the latter can supply, so as to keep up the tube. Tluis whimsical contrivance is the discharge from cư; therefore, after B rendered yet more diverting by having the has been exhausted so far as to allow air to syphon so contrived, that its action may pass from it into c e, a certain qnantity in commence only when the cup is inclined a that channel, which has not gained the sum. little, as is usual when a person is about to mit, will recede into B, and the water drink; and if only a small flower, &c. be must again rise to the height in bb, which at the bottom of thevessel, appearing merely shall cause it to flow over the summit of as an ornament, but allowing the liquor to cc, before the spring can again appear to pass under its petals, &c. into a tube made be supplied. Yet the flow from the source through one of two bandles, and brought was never diminished. under the bottom.

The existence, or otherwise, of a vacuum, Many springs are derived from natural

or void space, was long agitated, and that too syphons, existing in the sides of mountains, with no small degree of acrimony, among &c. at various depths, and to various ex the philosophers of old; and we may say of a tents. Some springs, situated on the tops date by no means ancient. Common sense of hills, near to larger ones, supply water should have told us, what experience so all the year, others only periodically; when amply proves, that where one body or ele. they usually flow in profusion. In either ment retires, another must supply its place, case the ignorant multitude rarely attribute else the whole creation would inevitably be the supply to tie proper cause. We shall de torn asunder. It is, indeed, well known, monstrate from whence it originates. that the elasticity of the air, which could be

When various caverns, in which water is rarified ad infinitum, if we had the means of either pent up or received, lay in a regular effecting the process, enables it to occupy descent, one below the other, the water large spaces on emergency, or to contract will naturally pass from one to the other, within the narrowest bounds. See Prer. and cause a regular flow, more or less abun- MATICS. Under ordinary circumstances, dant, according as the source may be more however, we consider the air as being of a or less abundantly supplied. If the soil particular standard, namely, that a column through which it passes be close and reten- ascending to the summit of our atmosphere, tive, the water will then be occasionally corresponds in weight with a column of raised, as well as lowered, in proportion to water of thirty-three feet in height, allow. the weight of the incumbent fluid, and ing the bases, i. e. of the air, and of the will rise, if so guided by the channel water to be equal. · Thus we find that through which it passes, even to the where the air is withdrawn, by means of height of the source, as may be proved suckers, pistons, valves, &c. from within a by what has already been shewn in fig. 2. pipe, of which the lowest part is immersed Thus, after various changes of altitude, the in the water contained in a well, &c. the Puid may escape at any height not above fluid will rise to the height of thirty-three that source; or it may be carried away to feet within the pipe, supplying the place of any depth. The place where it issues forth the air thus withdrawn. This is effected by is called a spring. Fig. 7, exhibits such a the pressure of the atmosphere on the sur current, which we will suppose to have a face of the water; whereby it is forced perpetual supply.

into the space formerly occupied by the But the intermitting spring may also have air. Generally speaking, it is not a sudden a regular supply. This is occasioned by the operation ; for unless the well be very shalexistence of caverns connected hy syphons, low, it will require many strokes of a pump as we may see by reference to fig. 8, where to withdraw so much air as may so far rarifý A is the source, bb the channel ; B is a the residue, within the pipe, as to allow the cavern, which by means of the arch, or ris- water to rise thirty-three feet above its leing channel, cc, becomes a syphon leading vel. This is the greatest height to which ing into D. It is obvious that, in the first water can be induced by a sucking pump.

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