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nearly cubical, with several outlets, having each a stop-cock, and to which hose, or the ends of pipes, may be screwed, to carry the water in different directions, or in cases of fire. Such a machine for raising water will become of great importance in mines and collieries, for coffer-dams, well-sinking, theatres, factories, breweries, and all large buildings requiring a high service of water; and its application to garden and fire-engines will render them far more effective than any of the present plans.-Mining Journal.

WATER-JET PROPELLERS.

A CURIOUS mode of propelling steam-ships has been invented by Mr. Ruthven, of Edinburgh, who proposes to give a better direction to the propelling power by forcing jets of water through nozzles placed below the water line. One novel feature of the invention is, that it contemplates employing the head-wave, which is now one great obstacle to the progress of vessels through water, as a means of propulsion. To effect this, the water heaped up at the bow is to be admitted into two large orifices, which are to conduct it to a hollow axle; thence it is to be driven by the "centrifugal force" of revolving wheels to the peripheries, and forced through the jet-pipes into the water, the reaction of which it is expected will be a more effective and useful propeller than either paddle-wheels or screw. The plan is as yet only in model; and without wishing to prejudice the jet principle of propulsion, we must observe, that the notion of diminishing the resistance of the head-wave, by admitting the water to pass through orifices, is but little in advance of the Portuguese scheme for raising a car in the air by fixing a magnet at the top. We must add to that, the scheme is not a new one it has been often tried, and always without success.— The Artizan, No. 9.

WATER-WHEELS.

MR. MALLETT, of Dublin, has read to the Institution of Civil Engineers, a long mathematical inquiry on this subject, and developed the following conclusions:

1st. When the depth of water in the reservoir is invariable, the diameter of the water-wheel should never be greater than the entire height of the fall, less so much of it as may be requisite to give the water a proper velocity on entering the buckets.

2nd. When the depth of water in the reservoir varies considerably and unavoidably in depth, an advantage may be obtained by applying a larger wheel, dependent upon the extent of fluctuation and ratio in time, that the water is at its highest and lowest levels during a given prolonged period: if this be a ratio of equality in time, there will be no advantage; and hence, in practice, the cases will be rare when any advantage will obtain by the use of an over-shot wheel greater in diameter than the height of fall-minus, the head due to the required velocity of the water reaching the wheel.

3rd. If the level of the water in the reservoir never fall below the mean depth of the reservoir, when at the highest and lowest,

and the average depth be between an eighth and a tenth of the height of the fall, then the average labouring force of the large wheel will be greater than that of the small one; and it will of course retain its increased advantage at periods of increased depth of the reservoir.

THE WATER-POWER OF GREAT BRITAIN.

vapour,

IN estimating, numerically, in any known measures, the average quantity of water which rises from the earth in descends upon it in rain, or exists in the atmosphere, there are imperfections in the data, and other difficulties, which reduce the conclusions to mere approximations; and even as such they are far from satisfactory, though, so far as observation and experience have gone, there is some agreement between them and the theories.

According to the calculations, the average quantity of water suspended in the atmosphere, if it were all precipitated to the surface of the land and sea, would amount to four inches in depth, or 11,794 cubic miles of water. This is greatest at the equator, being about 8 inches, while at the poles it is only about 1; in the average latitude of Britain it is about 2 inches. The quantity of rain which falls would follow the same law, if it were not that different surfaces do not equally supply the same evaporating power. The average annual depth of rain for Britain, according to the experiments of Dr. Dalton and others, may be taken at 30 inches. This supplies all the springs, and all the water which works on the surface of the earth, including streams and rivers, and their floods; and the quantity discharged annually into the sea is estimated at about 13 inches depth in the year; but here it will be no great error if, for the sake of simplifying the calculation, it is taken at 12 inches, or four-tenths of the average fall of rain.* The surface of the British islands, in round numbers, as already hinted, is 77,000,000 acres, and, at the average given, it would be easy to calculate the quantity of water which falls upon it during any given time. If, however, the power of this water is sought, a smaller, but indefinite breadth of land must be taken, because there are some places which discharge no water, and others where it cannot be rendered available as a power. Say that the total breadth, in all the lands in Britain, from which it is available, is 50,000,000, and that for England and Wales 20,000,000; and, making allowance for waste, one foot in depth of water over each of these is a power, whether it can be turned to account or no.

The first gives 2,178,000,000,000 cubic feet of water, and the second 871,200,000,000 cubic feet.

To reduce these, or either of them, into horse-power, there is this datum, according to the ordinary estimates: about 37, say 38 cubic feet of water, falling every minute on an overshot wheel of 10 feet

*Prize Essays of the Highland Society, vol. vi.-On the Construction of Resorvoirs of Water for Agricultural Purposes. By Messrs. James Adam and Findlater.

The depth of twelve inches is quoted, without acknowledging that it is correct: it is believed to be much more.

diameter, is reckoned the power of one horse. Divide each of these numbers by 525,960, the minutes in a year, and the first is the cubic feet for all Britain in each minute, and the second the same for England and Wales. Divide, again, by 38, and the results are the horsepower; that for the whole islands being a constant power of 108,973, and that for England, 43,590. This, however, supposes the waterpower to be only on a ten-feet wheel, and that wheel to be in motion every minute of the year.

But in no one instance will such be the case. Twelve hours in the day will be the utmost length of working, and one-sixth of the year will suffice for ordinary farm work, and this gives twelve times the above number, or 523,080 horse-power. But this is supposing only a single ten-feet fall, and every additional ten feet doubles the power. Say that the average of falls, one with another, in England and Wales, is fifty feet, and the total horse-power working, as above stated, will be upwards of 2,000,000. This is for the surface water alone; and if the floods were conserved in tanks and reservoirs, judiciously placed, and of proper size, this power would be increased, and a great saving of alluvial matter effected; but there are no satisfactory data for calculating the amount.*

Then for the water which will be obtained by general drainage over and above the quantity which escapes from the lands, there are absolutely no data whatever, for that must depend on the breadth of land which is drained, and the quantity of water afforded by the subsoil springs. It has been calculated that, where the land before draining is very moist, the drainage water will irrigate, in a proper manner, one-fifth as much water meadow as the land drained. But this is too much for the average of England, and we must not allow more than one-eighth, and perhaps one-tenth would be nearer the truth.

The usual estimate is, that 10,000,000 of the 12,000,000 acres of arable land in England and Wales require drainage; and, in order to carry the system of irrigation as far up the hills as possible, 10,000,000 more out of the residue, and which require draining, would be added to that amount. All this could not be done in a year, or probably in a century; but it is a result which could be aimed at, and therefore it may be kept in view. Water sufficient to irrigate about twenty acres would on a wheel twenty feet in diameter, give one-horse power; and if we divide by this, the 2,000,000 acres, irrigated by the drainwater of 20,000,000 acres, it would give us a power of 100,000 horsepower, upon a single fall of twenty feet. But when tanks and reservoirs are used, the last, if there be more than one, should be made to answer as mill-ponds. During heavy rain this would retain the flood

* The alluvial soil deposited by the waters of the Nile, according to Mr. Rennell, is 14,784,000 solid feet per hour, and by the Ganges, 2,509,056,000 solid feet per hour.

The Mississippi deposits 8,000,000 solid feet per hour; and the Koangho, according to Barrow, carries into the sea 2,000,000 solid feet of sediment every hour.

+ See page 34 of the Fourth Report of the Commissioners on the Nature and Extent of the Bogs in Ireland.

water and the substances with which it is charged, and thus conserving both the fertilizing and the mechanical power in those places where they might be most advantageously applied.

What have been stated are only approximations; but the principles are sound, and it may be of advantage to those who wish to study the subject, and profit by studying it, to have the outline of all its advantages before them. The next inquiry will be into the nature of the substances by which water should be impregnated for irrigation, and also the increase of manures for cultivated land that might be obtained by preserving the sewerage and refuse of towns.-From an exceedingly valuable and interesting pamphlet, by Mr. J. Bailey Denton, just published, entitled, "The Question, What can be done for British Agriculture? Answered ;" quoted in the Mechanics' Magazine, No. 1024.

POWER TRANSMITTED BY BELTS.

A PAPER, by Mr. Sang, has been read before the Royal Scottish Society of Arts, descriptive of a method of ascertaining the amount of force transmitted by a Belt, and consequently the amount of power consumed by any machine driven by a belt. His method of finding out this will be understood from the following explanation :—When we see a belt passed over two pulleys, and look without any narrow examination at the motion, we regard the action as a very simple one; there is more in it, however, than appears at first sight. For the sake of clearness, let us call the driving-pulley the drum, and the other the pulley. The belt passed over them, whether plain or crossed, has two free parts, one of which draws, and the other of which follows. If it were possible that no force were needed to turn the pulley, these two free parts would be in the same state of tension; but whenever any resistance is made to the motion of the pulley, the drawing part is distended more, and the following part less than usual; and experiments show, that, within all practical limits, this change is exactly proportional to the pressure necessary for overcoming the resistance. As the movement proceeds, the distended part of the belt is lapped over the drum, and, so to speak, the contracted part is lapped over the pulley, so that the circumference of the drum moves more swiftly than that of the pulley thus, if the distension be 1 to 100 for 100 inches of the drum there would only be 99 inches of the pulley passed over. The difference between the velocity of the drum and that of the pulley thus indicates the pressure needed to carry the drum round. Now this pressure, combined with the distance through which it acts, gives the force used; and hence, the simple difference between the distances passed over by the circumference of the drum and by that of the pulley is exactly proportional to the force; and we have only to contrive some method of registering this difference, in order to have a record of the total force transmitted by the belt. There may easily be contrived a variety of arrangements for showing the difference between the motions of the drum and pulley. Thus a pair of indicators may be fitted, one to each shaft, so as to tell the total number of turns made by each; from this number, by help of the measured diameter, the

distance passed over by each circumference can be found, and thus the element for knowing the force transmitted can be had. Or otherwise -and this, perhaps, is the most convenient arrangement—a light pulley, having its circumference one foot, may be brought to bear against the belt on the drum, and another against the belt on the pulley; if these light pulleys have counting ears attached, a simple reading off and subtraction will give the difference of distance.

These remarks will, probably, sufficiently elucidate the principle of the plan. The actual amount of force corresponding to a certain indication must of course be ascertained by an independent method for the first belt; but that once ascertained, the amount of force due to any other indication, or any other belt of the same material, may be approximately computed, regard being had to the weight of a foot of belt. We look upon this expedient as one distinguished by great penetration, and by an ingenuity of the most refined description.Artizan.

ROE'S ANTI-FRICTION PUMP.

A PUMP lately prepared by Mr. Roe for her Majesty's dockyard, upon the principle denominated by him as his Anti-friction Pump, promises to be of great power and utility, and is very simple, which in all things of this class is a great merit. The principal difference between it and the old pump consists in a reversal of the old method, inasmuch as in the old pump a leathern bucket is made to work in the pump-barrel or cylinder, while in this new and improved pump a cylindrical metallic piston is made to work in a metallic ring; and it will be instantly perceived that the difficulty of tight working may be abated with a corresponding decrease of friction. In the old pump the bucket plunger, by hard pressure against the sides of the pumpbarrel, caused considerable labour to overcome, while in this the labour is so far diminished as to encourage the presumption that two men, with a double-action pump of 61⁄2 barrels, will raise 120 gallons of water per minute. In ordinary calculation, however, it would be safe to say that the friction is diminished full 25 per cent. We can conceive nothing more admirable than this pump as a portable machine, to be fixed in a wooden case upon wheels, and transported to the scene of work in foundations, sewers, &c. The cost is not greater

than that of the ordinary pump.

SHALDERS'S FIRE-ENGINE.

THE entire weight of this brass engine is only 26lbs. exclusive of the reservoir steadying stand, and it can be used wherever a lad four feet high can find elbow-room; a man working the lever with one hand and guiding the jet-pipe with the other, delivers at a moderate speed eight gallons of water per minute to an elevation, in calm air, of 45 feet, or to a distance of 60 feet. It is not subject to choke or to get out of order, whether it is much used, or remains for months idle. Access is had to the hydraulic working parts merely by turning one large screw.

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