Of this property advantage has been taken to draw off liquors from one vessel to another by means of a very simple in strument called a syphon. This is a pipe of tin, copper, &c. according to its pur pose, bent at any angle, but general ly about seventy to eighty degrees, in such manner that one limb may reach down through the bung-hole of the cask to be emptied, to its very bottom ; the other leg should be the longest, so that when filled it may contain a heavier body of fluid than that limb within the vessel. See fig. 5. in which the syphon, A B C, is inserted into a vessel to be emptied. In large syphons it is necessary to insert a cock at the lower end, to prevent the escape of the fluid when first filled. In small syphons it is common to put a small parallel tube, which being applied to the mouth, the end C, being immersed in the liquor to be drawn off, the opera tor inhales forcibly, and by thus drawing the air out of the syphon, causes the li quor to rise in its place. The absence of air, which first caused the fluid to as cend into the tube, occasions it to remain until the finger is removed from the end A ; when the pressure of the air within the vessel causes the liquor to press through the syphon, which continues to the last to draw off the contents of the vessel, they pressing forward through the long end, A. It is proper to remark, that large syphons sometimes require to be previ ously filled, and then to be set in the ves sels to be drawn off; but, in Feneral, the casks, &c. can be tilted sufficiently to an swer this purpose, and to bring the short er limb nearer to a horizontal position than the longer limb, whereby the lat ter my possess a greater perpendicular altitude, and consequently a greater ten dency to gravitation. For we trust, that, in Fig. 1, it has been demonstrated, that the pressure of a fluid is in proportion to its perpendicular height We must caution the reader, that as a column of water of thirty-three feet in perpendicu lar height is equal to the weight of the atmosphere pressing on the surface of such a column, it follows, that no syphon exceeding that length will act, because the power would be less than the weight to be raised.
A comical display of the properties of the syphon is seen in what is called "The cup of Tantalus ;" the designation of which is derivedfrom fabulous history, wherein we are told, that Tantalus, king of Phrygia, was condemned by Jupiter to suffer perpetual hunger and thirst, amidst a profusion of delicacies, which always receded when applied to his lips. To imitate this disappointment, a syphon, having its two limbs parallel and contigu ous, is fixed into the middle of a cup dou ble its height; one limb receiving the li quid at the bottom of the interior, and the other discharging it through the centre of the bottom, as seen in fig. 6. Thus, when the outlet is stopped by means of a finger applied thereto, the cup may be of fered quite full to the person on whom the joke is to be practised, observing that the syphon will not act until the liquor in the cup exceeds 'the level of its bend, when the whole will be drawn through the tube. This whimsical contrivance is rendered yet more diverting, by having the syphon so contrived, that its action may commence only when the cup is in clined a little, as is usual when a person is about to drink ; and if only a small flower, &c. be at the bottom of the vessel, appear
ing merely as an ornament, but allowing the liquor to pass under its petals, &c. in to a tube made through one of two hand les, and brought under the bottom. • Many springs are derived from natural syphons, existing in the sides of moun tains, &c. at various depths, and to vari. ous extents. Some springs, situated on the tops of hills, near to large ones, sup ply water all the year, others only peri odically, when they usually flow in pro. fusion. In either case, the ignorant mul titude rarely attribute the supply to the proper cause. We shall demonstrate from whence it originates.
When various caverns, in which water is either pent up or received, lay in a re gular descent, one below the other, the water will naturally pass from one to the other, and cause a regular flow, more or less abundant, according as the source may be more or less abundantly supplied If the soil through which it passes be close and retentive, the water will then be oc casionally raised, as well as lowered, in proportion to the weight of the incum bent fluid, and will rise, if so guided by the channel through which it passes, even to the height of the source, as may be proved by what has already been shewn in fig. 2. Thus, after various changes of altitude, the fluid may escape at any height not above that source ; or it may be carried away to any depth. The place where it issues forth is called a spring. Fig. 7. exhibits such a current, which we will suppose to have a perpetual supply.
But the intermitting spring may also have a regular supply. This is occasioned by the existence of caverns connected by syphons, as we may see by reference to fig. 8, where A is the source, b b the chan nel : B is a cavern, which by means of the arch, or rising channel, c c, becomes a syphon leading into D. It is obvious that, in the first instance, the water must, after fillingB, rise in the channel, b b, so as to be above the greatest height of c c, to cause its passing off into E, and thence ad libit um. Now the channel, c c, being of great er diameter than the channel, b b, when the former commences its operation, it will discharge more thin the latter can supply, so as to keep up the discharge from c c; therefore, after B has been ex hausted so far as to allow airto pass from it into c c, a certain quantity in that chan nel, which has not gained the summit, will recede into B, and the water must again rise to the height in b b, which shall cause it to flow over the summit of c c, before the spring can again appear to be supplied. Yet the flow from the source was never diminished.
the existence, or otherwise, of a va cuum, or void space, was long agitated, and that too with no small degree of acri mony, among the philosophers of old; and we may say of a date by no means an cient. Common sense should have told us, what experience so amply proves, that where one body or element retires, an other must supply its place, else the whole creation would inevitably be torn asunder. It is, indeed, well known, that the elasticity of the air, which could be rarified ad infinitum, if we had the means of effecting the process, enables it to oc cupy large spaces bn emergency, or to contract within the narrowest bounds. See PNEtracmcs. Under ordinary cir cumstances, however, we consider the air as being of a particular standard.