Part 3
Now some writers have given the above explanation of the action of the siphon, saying that the longer leg, holding more, attracts the shorter. But that such an explanation is incorrect, and that he who believes so would be greatly mistaken if he were to attempt to raise water from a lower level, we may prove as follows. Let there be a siphon with its inner leg longer and narrow, and the outer much less in length but broader so as to contain more water than the longer leg. Then, having first filled the siphon with water, plunge the longer leg into a vessel of water or a well. Now, if we allow the water to flow, the outer leg, containing more than the inner, should draw the water out of the longer leg, which will at the same time draw up the water in the well; and the discharge having begun will exhaust all the water or continue for ever, since the liquid without is more than that within. But this is not found to be the case; and therefore the alleged cause is not the true one. Let us then examine into the natural cause. The surface of every liquid body, when at rest, is spherical and concentric with that of the earth; and, if the liquid be not at rest, it moves until it attains such a surface. If then we take two vessels and pour water into each, and, after filling the siphon and closing its extremities with the fingers, insert one leg into one vessel plunging it beneath the water, and the other into the other, all the water will be continuous, for each of the liquids in the vessels communicates with that in the siphon. If, then, the surfaces of the liquids in the vessels were at the same level before, they will both remain at rest when the siphon is plunged in. But if they were not, as soon as the water is continuous it must inevitably flow into the lower vessel through the channel of communication, until either all the water in both vessels stands at the same height, or one of the vessels is emptied. Suppose that the liquids stand at the same height; they will of course be at rest, so that the liquid in the siphon will also be at rest. If, then, the siphon be conceived to be intersected by a plane in the surface of the liquids in the vessels, even now the liquid in the siphon will be at rest, and, if raised without being inclined to either side, it will again be at rest, and that, whether the siphon is of equal breadth throughout or one leg is much larger than the other. For the reason why the liquid remained at rest did not lie in this, but in the fact that the apertures of the siphon were at the same level. The question now arises why, when the siphon is raised, the water is not borne down by its own weight, having beneath it air which is lighter than itself. The answer is that a continuous void cannot exist; so that, if the water is to descend, we must first fill the upper part of the siphon, into which no air can possibly force its way. But if we pierce a hole in the upper part of the siphon, the water will immediately be rent in sunder the air having found a passage. Before the hole is bored, the liquid in the siphon, resting on the air beneath, tends to drive it away, but the air having no means of escape does not allow the water to pass out: when however the air has obtained a passage through the hole, being unable to sustain the pressure of the water, it escapes. It is from the same cause that, by means of a siphon, we can suck wine upwards, though this is contrary to the nature of a liquid; for, when we have received into the body the air which was in the siphon, we become fuller than before, and a pressure is exerted on the air contiguous to us, and this in turn presses on the atmosphere at large, until a void has been produced at the surface of the wine, and then the wine undergoing pressure itself will pass into the exhausted space of the siphon; for there is no other place into which it can escape from the pressure. It is from this cause that its unnatural upward movement arises.
[Illustration: Two overlaping circles, A, B, C are on the left circle. F, B, D are on the right, a is a center point, F is on a line from a to A. There is a line from a to B, the intersection point of the two circles.]
That the water in the siphon will rest when its surface is spherical and concentric with that of the earth may be shewn otherwise. It is required to prove that a liquid is stationary when its surface is spherical and concentric with that of the earth. If possible let it not be stationary; it will of course become so after being moved; let it then have become stationary. Its surface will now be spherical and concentric with that of the earth, and it will cut the former surface; for, when the same liquid has taken two positions, there must be a line of intersection common to both. Let both surfaces be cut by a plane passing through the centre of the earth; the intersections will be the circumferences of circles concentric with the earth. Let these circumferences be A B C and F B D, (fig. 1 a.) Join B G; B G is equal to each of the lines G F, G A, which is absurd. The liquid will therefore be in equilibrium.
2. _Concentric or inclosed Siphon._
[Illustration: Diagram of apparatus as described in text]
There is another kind of siphon called _the concentric_ or _inclosed diabetes_, the principle of which is the same as that of the bent siphon. As before, let there be a vessel, A B (fig. 2), containing water. Through its bottom insert a tube, C D, soldered into the bottom and projecting below. Let the aperture C of the siphon approach to the mouth of the vessel A B, and let another tube, E F, inclose the tube C D, the distance between the tubes being every where equal, and the mouth of the outer tube being closed by a plate, E G, a little above the mouth C. The lower opening of the tube E F must be so far removed from the bottom of the vessel as to leave a passage for the water. These arrangements being completed, if we exhaust, by suction through the mouth D, the air in the tube C D, we shall draw into it the water in the vessel A B, so that it will flow out through the projection of the siphon until the water is exhausted. For the air contained between the liquid and the tube E F, being but little, can pass into the tube C D, and the water can then be drawn after it. And the water will not cease flowing because of the projection of the siphon below:—if, indeed, the tube E F were removed, the discharge would cease on the surface of the water arriving at C, in spite of the projection below; but when E F is entirely immersed no air can enter the siphon in place of that drawn off, since the air which enters the vessel takes the place of the water as it passes out:—the discharge then, will not cease, for the whole of the outer aperture of the tube, where the water issues forth, is always lower than the surface of the water in the vessel, and, as one level can never be attained, all the water is drained off, attraction being exerted by the deeper column. If we do not choose to draw out the air in the tube C D by suction, water may be poured into the vessel A B until, when it has risen above C, a discharge begins through C D. In this case, again, all the water in the vessel will be drawn out. This instrument is called, as we said before, _the inclosed siphon_, or _the inclosed diabetes_.
It is evident from what has been proved above that as long as the siphon is stationary the stream through it will be of irregular velocity, for the result is the same as in a discharge through a hole pierced in the bottom of a vessel, where the stream is irregular from the pressure of a greater weight on the discharge at its commencement, and, of a less, as the contents of the vessel are reduced. In like manner, in proportion as the excess of the outer leg of the siphon is greater, the velocity of the stream is greater; for a greater pressure is exerted on the discharge than when the projection of the outer leg below the surface of the water in the vessel is less. Therefore we have said that the discharge through the siphon is always of variable velocity. But we must contrive a siphon in which the velocity of the discharge shall be uniform.
3. _Uniform discharge Siphon._
[Illustration: Diagram of apparatus as described in text]
Let there be a vessel, A B, (fig. 3.) containing water, on which a small basin, C D, floats, having its mouth covered with the lid C D. Through this lid and the bottom of the basin insert one leg of the siphon soldering it into the holes with tin. Let the other leg be outside the vessel A B, having its mouth lower than the surface of the water in A B. If we draw the air in the siphon through the outer extremity, the water will at once follow because of the impossibility of a continuous vacuum in the siphon; and the siphon, having begun to flow, flows on until it has exhausted all the water in the vessel: but the discharge will be uniform, since the projection of the outer leg below the surface of the water does not vary; for, as the vessel becomes empty, the basin sinks with the siphon. The greater the excess of the outer leg the greater will be the velocity of the discharge, yet still uniform. In the figure, E F G is the siphon described, and the surface of the water is in the line H K.
4. _Siphon which is capable of discharging a greater or less quantity of Liquid with uniformity._
[Illustration: Diagram of apparatus as described in text]
By the following arrangement we can produce a discharge at once uniform and variable; that is, a discharge in which, for a certain time at pleasure, the stream continues uniform from the beginning, and again, for any other period, is slower or quicker than before, but still uniform with itself. As before, let A B (fig. 4.) be a vessel of water, and C D a basin. Into the lid and bottom of the basin solder a tube L M wider than the inner leg of the siphon. On the lid place a wooden frame, C N X D, consisting of two upright pieces and a third lying across them on the top. In the inner sides of the upright pieces let grooves be cut down their whole length, along which another piece O P is to move freely. Let R S be a screw, working perpendicularly in the direction of the lid C D, and passing through a hole in O P: in O P let a pin be so fixed as to enter the spiral thread of the screw. The screw must project above N X, and a handle be fastened to its top by which to turn it, and by this means O P can be raised or lowered. Let the inner leg of the siphon be fixed in O P, and pass through the tube L M, so that its mouth may dip into the water in the vessel. Now if, as before, we draw off the liquid through the outer mouth, the siphon will flow with a uniform stream until the whole be exhausted. And when it is wished that a quicker stream should be produced through the siphon, but uniform with itself, let the screw be turned so as to lower the board O P; for then the excess of the outer leg is increased, and thus the stream is still of uniform velocity, but quicker than before. If a still greater velocity is desired, turn the screw again, so as to lower O P still further; and if a less velocity is sought, let O P be raised. Thus a discharge is produced through a siphon in one sense uniform, in another variable.
5. _A vessel for withdrawing Air from a Siphon._
[Illustration: Diagram of apparatus as described in text]
To avoid the necessity of drawing off the water through the mouth, which is only possible in very small siphons, the following contrivance may be used. Take a double tube (fig. 5) one part of which fits into the other, and attach the smaller part to the outer leg of the siphon, so that the discharge may pass through it. Let T N be the smaller tube, and Q U the greater, which must be previously fitted tightly into a vessel, W Y, containing somewhat more water than the siphon will hold, and having an outlet, Z, at the bottom. When it is wished to draw off the water in A B, close the outlet of W Y with the finger, then apply the larger tube Q U to the smaller, and leave the outlet Z free. As the vessel W Y becomes empty the air in the siphon will pass into the exhausted space, and the liquid in A B will follow so as to fill the siphon: then remove the vessel W Y, and let the siphon run.
To act properly the siphon must be perpendicular; and this may be secured by fixing two straight bars to the lip of the vessel A B, and placing the inner leg of the siphon between them so as to touch each of the bars: then fasten a small bar crosswise on each side of the leg of the siphon, so as to touch the former bars within. Thus, if the smaller bars touch the larger, the siphon will neither lean sideways nor forwards, but will hang perpendicularly.
6. _A Vessel for retaining or discharging a Liquid at pleasure._
[Illustration: Diagram of apparatus as described in text]
Let us now proceed to construct the necessary instruments, beginning with the less important, as from the elements. The following is a contrivance of use in pouring out wine. A hollow globe of bronze is provided, such as A B (fig. 6) pierced in the lower part with numerous small holes like a sieve. At the top let there be a tube, C D, the upper extremity of which is open, communicating with and soldered into the globe. When it is desired to pour out wine, with one hand grasp the tube C D near the mouth C, and plunge the globe into the wine until it is wholly immersed. The wine enters through the holes, and the air within, being driven out, passes through the tube C D: and if, pressing the thumb on the aperture C, you lift the globe out of the wine, the wine contained in the globe will not flow out, as no air can enter to supply the vacuum, for the only entrance is through the mouth C, which is closed by the thumb. When, then, we desire to let the wine flow, we remove the finger, and the air, rushing in, fills the vacuum produced. If we again press the finger on the air-hole C, there will be no discharge until we once more remove the finger from the vent. We may, in like manner, dip the globe into hot or cold water, and then retain or let out the contents at pleasure, until all the water within is exhausted. If the extremity C of the tube C D is bent, the action will be the same, and it is then easier to stop the orifice with the finger.
7. _A Vessel for discharging Liquids of different temperatures at pleasure._
[Illustration: Diagram of apparatus as described in text]
By the same means it is possible to discharge from the same globe both hot and cold water in any quantity. The globe A B (fig. 7) is constructed as before, but furnished with a perpendicular partition, C D, dividing it equally. At the top a tube, H F, soldered into the globe, communicates with the interior; this tube is also furnished with a partition, C G, a continuation of the partition C D, and its openings, H, K, must curve over in the directions C and F. On each side of the partition C D, at the bottom of the globe towards D, let holes be made like those in a cook’s ladle. When it is desired to draw hot water, take the apertures H and K by the two fingers and plunge the globe into hot water, and then unclose one of the vents, H, that the air in the hemisphere B C D may be driven out through H: the hot water, entering through the holes, will fill the hemisphere B C D: again stopping the vent H take the globe out of the water, and its contents will be retained, as the air has no entrance. Then, in like manner, plunge the globe into cold water, unclosing the vent K, and, when the hemisphere A C D is filled, close K and draw the globe out. The globe is now full of hot and cold water, and when it is desired to discharge either of these, unclose the proper vent: in like manner close it again when the discharge is sufficient; and this may be repeated till the contents are exhausted. In the same way it is possible to draw up into and discharge from the same vessel wine, and cold or hot water, and anything else whatever, at any time, and in any quantity, by making the necessary partitions and orifices through which the air may enter into each chamber and leave it again. Instead of the curved outlets, holes may be made in the upper part of the sides of the tube in various directions; and these holes are of course to be closed when it is required to shut out the air. That the holes pierced in the bottom of the vessel may not be seen, both sets may be included in one channel, so that both streams may appear to flow from the same source.
8. _A Vessel for discharging Liquids in varying proportions._
[Illustration: Diagram of apparatus as described in text]
A jar can be made receiving and discharging a greater quantity of liquid at one time than at another, and in such a way that, when wine and water are poured into it, it shall discharge at one time pure water, at another time unmixed wine, and, again, a mixture of the two. Its construction is as follows. Let A B (fig. 8) be a pitcher having a partition in the middle, C D. In the partition, near the circumference of the vessel, let small holes be pierced in a curve, as at E. In the opposite side of the partition let there be a circular aperture, F, through which the tube F G H is to be inserted, being soldered into the partition, and reaching nearly to the bottom of the vessel at G. Let the other mouth of the tube H issue at the side of the pitcher, under the handle, and be soldered into the handle which must be hollow, and have a hole on its outer surface at K, which may be closed with the finger when necessary. If, then, closing the vent, as before, we pour any liquid into the jar, the liquid poured into the upper chamber will remain there, not being able to continue its way through the narrow holes into the lower chamber, as there is no other outlet for the air than through the vent K. When, however, we unclose the vent, the liquid will descend into the chamber beneath, and then the jar will hold more. If, then, we first pour in wine so as to fill the chamber B C D, and then, closing the vent, pour water upon it, the two cannot mix, and if we invert the jar it will emit pure water. But, when we unclose the vent, the water continuing to flow, the wine will flow out also, since air can enter through K to fill up the void left; and afterwards the wine will flow out unmixed. We may also pour in the water first, and then, stopping the vent, pour wine upon it, so as to pour out wine for some, wine and water for others, and mere water for those whom we wish to jest with.
9. _A Water Jet produced by mechanically compressed Air._
[Illustration: Diagram of apparatus as described in text]