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TABLE OF SPECIFIC GRAVITIES.-Continued.

Orpiment from 3.048 to 3.500 Do. carbonate of,

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Oyster-shell
Pearl, oriental, from 2.510 Stone, Bristol, from 2.510

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from 3.658 to 3.675

0.561

Pearlstone

to 2.750 2.340

to 2.640

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Peruvian bark

0.784

hard

2.460

Cork

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It may be proper to add, that Mr. S. L. Kent, to whom we are indebted for much valuable information on this subject, has nearly completed the most extensive and accurate series of observations on the specific gravity of mineral bodies that has ever been attempted.

Having in the preceding portion of our article examined the nature of hydrostatic pressure, we may now proceed to treat of fluids in motion, and the structure of hydraulic machines.

One of the most simple instruments for raising water is the syphon; a bent tube which owes its operation to the pressure of the atmosphere. The ordinary syphon is represented at fig. 1, plate II., HYDROSTATICS and HYDRAULICS; and consists of a crooked tube ABC, of such a length, and with such an angle, or so bent at the vertex, as that, when the orifice A is placed on a horizontal plane, the height of A B may not exceed thirty-two or thirty-three feet. For common uses a foot or half a foot high suffices. If now the less arm A B be immersed in water, or any other liquid, and the air be sucked out of it by the aperture C till the liquor

follow, it will continue to flow out of the vessel, through the tube B C, as long as the aperture A is under the surface of the liquor. Or if the syphon be at first filled with the fluid, and the aperture C stopped with the finger until the aperture A is immersed, the event will be precisely the same. During the process of sucking, the air in the tube is rarefied, and the equilibrium destroyed; consequently the water must be raised into the less leg AB, by the preponderating pressure of the atmosphere. The syphon being thus filled, the atmosphere presses equally on each extremity, so as to sustain any equal quantity of water in each leg; but the air not being able to sustain all the water in the longer leg, and being more than able to sustain that in the shorter leg, with the excess of force, therefore, it will raise new water into the shorter leg; and this new water cannot make its way

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Sapphire, oriental, from

4.283 Uranite 2-143 Vesuvian Vinegar

2.360 2.190

from 3.300 to 3.575

from 1.013 to 1.080

1.000

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sea

1.028

Medlar

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Aleppo

1-274 Water, of Dead Sea
1-235 Wax, bees'

1.240

0.964

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Oak-heart, 60 yrs.

Schorl

from 2.922 to 3:452

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Pumice-stone from 0.752 to 0.914 Topaz

fused
from 2.080 to 3.000
0.941

from 4.010 to 4'061

Quartz from 2-624 to 3.750 Tourmaline from 3.086 to 3-362
Realgar from 3.225 to 3-338 Turquoise, from 2.500 to 3.000
Rock-crystal from 2.581 to 2.888 Ultramarine

Elder-tree
Elm-tree
Filbert-tree

Fir, male
Do. female
Hazel

Jasmin, Spanish
Juniper-tree
Lemon-tree

Lignum vitæ
Linden-tree
Mastick-tree
Mahogany
Maple-tree

Mulberry, Spanish 0-897

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1.990

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1.209.

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0.695

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0-671

0.600

0.550

0.498

0-600

0.770

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0.556

0.703.

1.333

0-604

0.849

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1.063

0-750

0.944

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but by protruding the first before it: by this means the water is continually driven out at the longer leg, as fast as it is raised by the shorter.

The syphon will raise a stream of water to a considerable altitude in every situation where a little descent can be procured, but, while the operation continues, no water can directly be taken out of the stream above the lowest part of the tube. When, however, the two open ends of a syphon are closed, a quantity of water may be let out of the highest part, and its place supplied by introducing a like quantity of no use: all the avenues for the purpose being then closed, and the stream suffered to flow through the tube, the useless water will be displaced, and a fresh quantity may be soon after drawn off. This mode of exchanging fluids may be useful in furnishing a supply for domestic purposes; but there are some cases in which the water drawn off by this arrangement would not be thought sufficiently pure. To effect the same end the following apparatus has been suggested. In the upper part of the syphon E E, fig. 2, plate II., are inserted two small pipes, and their apertures in the inside of the tube should be divided by a projecting piece a quarter of an inch thick; wherever the pipes are inserted, the piece must be placed in such a position that the current will strike against one of its flat sides. The pipe which opens on that side of the obstacle, or dam, struck by the stream, may be called the water-pipe, and that on the other side the air-pipe. Insert their other ends into a circular vessel, the air-pipe opposite to c must rise to near the top of this vessel, but the waterpipe o need not rise above the place of its insertion; a cock perfectly air-tight must be fixed in each pipe between the vessel and syphon; the vessel must also have a tube in its lower part for letting out water. This tube must have a cock fixed in it, or a valve, covered with leather, to close its lower end. To hasten the delivery of the water in this vessel, the external air may be admitted in such a manner as is most convenient.

The communication between the vessel and syphon being intercepted by turning the cocks in the pipes co, and the branches closed at their lower ends, the tube may be filled with water through an aperture in the top. After this aperture is closed, and a stream of water let into the cistern o for supplying the syphon, the ends of the branches may be opened, and a continued stream will flow through the tube.

When it is required to fill the vessel c o with water, exclude the external air, and open the pipes between it and the syphon. The vessel will soon be filled, and the water may be let out by opening the tube for that purpose; after which the small pipes are again closed by turning

the cocks.

In estimating the discharge by a syphon, the head of water must be reckoned equal to the difference between the levels of the surface of the water, and of the lower orifice. The reason of this will be obvious, when it is recollected that the length of the shorter leg is only measured to the surface of the water, however far it may reach below; and that, as the action of the

instrument is dependent on the discharging leg being the longer of two, the greater the difference in favor of this leg, the greater will be the force employed in promoting the discharge.

The improved syphon of M. Buten is shown at fig. 3, where A B is the long branch, with a bulb at A, and DC the short branch. This syphon requires neither to be blown into, nor any suction. It is sufficient to fill the long branch A B, and the ball A with the liquid, and to plunge the short branch C D into the liquid to be decanted. The bulb A, in emptying itself, draws off the liquid in contact with the short branch, and, though the bulb itself is partly empty, the flow is unremitting.

Another improved syphon by M. Hempel, is shown at fig. 4. It has the same advantages as that of M. Buten, and is more easily constructed on a large scale. A part of the liquid to be decanted is poured into the funnel A, at the top of the tube A B, which is fitted into the short branch of the syphon. As soon as the flow commences, through the long branch DC, the tube A B is withdrawn, and the flow of water continues.

The syphon is also occasionally disguised to form a philosophical toy, called Tantalus's cup, from the well known fable. This cup has a hollow stem, as at y, fig. 5, into which a small glass syphon z is cemented in such a manner that the upper bend of the syphon may be a little below the top of the cup, and the shortest leg a may very nearly touch it. On pouring water into the cup it will rise to its proper level in the tube a, but still the cup will hold water, but, on attempting to fill it, the water will still rise up the tube a until it reaches the bend, which it will flow over and thus fill the whole of the longer leg zb, and the instant this is effected the water will flow continuously from b until the cup is quite emptied. The upper part of the syphon z a may be concealed by placing a hollow image of a man over it, with the chin on a level with the bend of the syphon, when the cup will hold water until filled to the chin of the figure, but the water will begin to flow away as soon as it reaches that point.

The strange appearance of intermitting springs, or springs which run for a time and then stop altogether, and after a time run again, and then stop, is entirely occasioned by the channels in which the water flows being formed like syphons. Thus if A B C fig. 6, plate II., represents a hill or mountain, in which there is a hollow E F G, and a channel bent like a syphon F H B leading out of it. The water collected from the rills d will fill the hollow, and, as soon as it rises to the line O P, of the same height with H, it will rise to H in the channel, and then flow out through B, till the whole runs off to the level of F.

It will then cease to flow until the hollow is again filled to the level O P, when it will flow again, and so on. Some springs called variable or reciprocating, do not cease to flow, but only discharge a much smaller quantity of water for a certain time, and then give out a greater quantity. This is owing to the hollow being supplied from another hollow, which is situated higher up, and has a common runner going to join the stream below the bend H; for this

runner keeps the stream always supplied to a certain degree, and when the lower hollow, which feeds the syphon runner F H, is filled up to OH, both the common runner and the syphon runner feed the stream together, until the lower hollow is drained.

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In some places the most absurd tales are told and believed by ignorant people respecting such springs; their flowing and ceasing are ascribed to witchcraft; and designing men have sometimes taken advantage of the credulity of others, and gained credit for themselves, by fortelling the return of the spring after it had ceased, or pretending to stop it when it was running. Some notions connected with superstitions of this kind are adverted to in the account given of an intermitting, or rather a variable spring, at Laywell, near Torbay, in Devonshire, by Dr. Atwell, the first person who distinctly explained these appearances by a reference to the nature of the syphon. It is a long mile,' says he, distant from the sea, upon the north side of a ridge of hills lying between it and the sea, and making a turn or angle near this spring. It is situated in the side of those hills, near the bottom, and seems to have its course from the south-west towards the north-east. There is a constantly running stream which discharges itself near one corner into a basin, about eight feet in length, and four feet and a half in breadth, the outlet of which is at the farthest end from the entrance of the stream, about three feet wide and of a sufficient height. This I mention that a better judgment may be made of the perpendicular rise of the water in the basin at the time of the flux or increase of the stream. Upon the outside of the basin are three other springs which always run, but with streams subject to a like regular increase and decrease with the former: they seem indeed only branches of the former, or rather channels discharging some parts of the constantly running water, which could not empty itself all into the basin; and, therefore, when by means of the season or weather the springs are large and high, upon the flux or increase of this fountain, several other little springs are said to break forth, both at the bottom of the basin and without it, which disappear again upon the ebb or decrease of the fountain. All the constant running streams put together at the time I saw them, were, I believe, more than sufficient to drive an overshot mill, and the stream running into the basin might be one-half of the whole. I had made a journey, purposely to see it, in company with a friend; when we came to the fountain we were informed by a man working just by the basin, that the spring had flowed and ebbed about twenty times that morning, but had ceased doing so about half an hour before we came. I observed the stream running into the basin for more than an hour by my watch, without perceiving the least variation in it, or the least alteration in the height of the surface of the water in the basin; which we could observe with great nicety by means of a broad stone laid in a shelving position in the water. Thus disappointed, we were obliged to go and take some little refreshment at our inn; after which, we intended to come back and spend the rest of our time by the fountain,

before we returned home. They told us in the house that many had been disappointed in this manner, and the common people superstitiously imputed it to I know not what influence which the presence of some people had over the fountain; for which reason they advised, that, in case it did not flow and ebb when we were both present, one of us should absent himself, to try whether it would do so in the presence of the other. Upon our return to it, the man, who was still at work, told us that it had begun to flow and ebb about half an hour after we went away, and had done so ten or twelve times in less than a minute. We saw the stream coming into the basin, and likewise the others on the outside of the basin began to increase, and to flow with great violence, upon which the surface of the water in the basin rose an inch and a quarter perpendicularly, in nearly the space of two minutes; immediately after which the stream began to abate again to its ordinary course, and in nearly two minutes time the surface was sunk down to its usual height, where it remained two minutes more; then it began to flow again as before, and, in the space of twenty-six minutes, flowed and ebbed five times; so that an increase, decrease, and pause, taken together, were made in about five minutes, or a little more. I could observe by the mark upon the stones, that the surface of the water in the basin had risen, before we came, at least three quarters of an inch perpendicularly higher than we saw it; and I thought that I could perceive some very little abatement each turn, both in the height, and in the time of its sinking; but the time of the pause, or standing on the surface at its usual height, or equable running of the stream, was lengthened, yet so as to leave some abatement in the time of the rising, sinking, and pause al together.'

It should seem, that, in the hill from which this stream comes, there are three hollows, or reservoirs, of different sizes, and connected by syphons of different widths. The times of the increase and decrease lengthening, arises from the water sinking in one of the reservoirs, which makes it flow more slowly than when it is full.

Having already briefly adverted to the principle upon which the syphon acts, it will now be necessary for us to show in what manner this instrument may be employed as a prime mover. The apparatus to which we allude was contrived by Mr. C. A. Busby, the son of Dr. Busby, and termed the hydraulic orrery. The original apparatus, as described by Mr. Busby, in the fortieth volume of the Transactions of the Society of Arts, is exceedingly complicated; but the following arrangement, as constructed by Mr. Partington, and employed by him in his publie lectures, will be found to possess much greater simplicity, and its construction will be easily understood. A, fig. 7, plate II., represents a tin water-tight vessel, placed in a circular trough C. The upper vessel of water is furnished with an upright stem of wire, supporting a ball S, which is intended to represent the sun. The smaller balls, E and m, revolve round the larger sphere in the same time that the earth and moon revolve round the sun, and as such, serve to convey a

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