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ceeding 50 feet, when, in such cases, it is applied to motive machines that will rarely be employed for agricultural purposes, such as Barker's mill, &c.

1722. When it is proposed to employ a stream of water for the purpose of power, the first step is to determine the quantity delivered by the stream in a given time; this, if the stream is not large, is easily accomplished by an actual measurement of the discharge, and is done by damming up the stream to a small height, say 1 or 2 feet, giving time to collect, so as to send the full discharge through a shoot, from which it is received into a vessel of any known capacity, the precise time that is required to fill it being carefully noted. This will give a correct measure of the water that could be delivered constantly for any purpose; if in too small a quantity to be serviceable at all times, the result may found a calculation of the time required to fill a dam of such dimensions as might serve to drive a thrashing-machine for any required number of hours. If the discharge of the stream is more than could be received into any moderately-sized vessel, a near approximation may be made to the amount of discharge by the following method: Select a part of its course, where the bottom and sides are tolerably even, for a distance of 50 or 100 feet; ascertain the velocity with which it runs through this space, or any measured portion of it, by floating light substances on its surface, noting the time required for the substance to pass over the length of the space. A section of the stream is then to be taken, to determine the number of superficial feet or inches of sectional area that is flowing along the channel, and this, multiplied into five-sixths of the velocity of the stream, will give a tolerable approximation to the true quantity of dischargefive-sixths of the surface velocity, at the middle of the stream, being very nearly the mean velocity of the entire section. Suppose the substance floated upon the surface of the stream passed over a distance of 100 feet in 20 seconds, and that the stream is 3 feet broad, with an average depth of 4 inches-here the area of the section is exactly 1 foot, and the velocity being 100 feet in 20 seconds, gives 300 feet per minute, less one-sixth: 250 feet, and this multiplied by the sectional area

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in feet, or 1 foot, is 250 cubic feet per minute for the discharge. It is to be kept in mind that this is only an approximation, but it is simple, and from repeated experiments I have found it to come near the truth. For those who wish to enter more elaborately into the subject, I may here state a formula derived from those of Sir John Leslie, for finding the mean velocity, and, having also the transverse section, to find the discharge of a stream or river.

Multiply the constant 16 into the hydraulic depth, and into the slope of the surface of the water per mile, the square root of the product will give the mean velocity of the stream in feet, per second; and the root, multiplied by the section of the stream in square feet, is the discharge per second. The hydraulic depth is the transverse section of the stream in square feet, divided by the periphery of the stream, less the surface breadth.

Example. If the surface breadth be 3 feet, the

bottom breadth 24 feet, and the slope of the sides each 9 inches, a transverse section of these dimensions will contain 2 square feet nearly, which, divided by the periphery, which is

3+75+75+25=7, the periphery, then the area of the section=2 feet;

and 2÷(7—3)='5 foot, or =6 inches, the hydraulic depth.

And suppose the slope at the place of section to be 1 inch on 100 feet, or 6.5 feet per mile, apply the formula

1.6 × 5 × 6·5=2.3 feet, the velocity per second nearly, and the delivery will be 2.3 x 246 cubic feet per second, which, multiplied by 60, gives 276 cubic feet per minute.

1723. The next step is to ascertain, by levelling, from the most convenient point at which the stream can be taken off, to the site where the water-wheel can be set down, and to that point in the continuation of the stream where the water can be discharged from the wheel, or what is called the outfall of the tail-race. If the water has to be conveyed to any considerable distance from the point where it is diverted from the stream to the wheel, a lade must be formed for it, which should have a fall of not less than 14 inches in 100 feet, and this is to be deducted from the entire fall. Suppose, after this deduction, the clear fall be 12 feet, and that the water is to be received on a bucket-wheel whose power shall be equal to 4 horses.

The rule for finding the quantity of water required per minute to produce 4 horses' power is to multiply the constant 44,000 by the horse-power, and divide the product by the product obtained by multiplying the constant,-the weight of water per cubic foot by the height of the fall.

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The rule for finding the horse-power of any ascertained discharge of water will be found in (117.)

1724. If the stream does not produce this quantity, a dam must be formed by embanking or otherwise, to contain such quantity as will supply the wheel for three or six hours, or such period as may be thought necessary. The quantity required for the wheel here supposed, for three hours, would be 42,120 cubic feet; but suppose the stream to supply one-fourth part of this, the remainder, or 31,590 feet must be provided for in a dam, which, to contain this, at a depth not exceeding 4 feet, would be 88 feet square. But the constant supply of water is often much smaller than here supposed, and in such cases the dam must be proportionally larger.

1725. The dam may be formed either upon the course of the stream, by a stoneweir thrown across it, and proper sluices formed at one side to lead off the water when required; or, what is much better, the stream may be diverted from its course by a low weir into an intermediate dam, which may be formed by digging and embankments of earth, furnished with sluice and waste-weir, and from this the lade to the wheel should be formed. The small weir on the stream, while it served to divert the water, when required, through a sluice to the dam, would, in time of floods, pass the water over the weir, the regulating sluice being shut to prevent the flooding of the dam. This last method of forming the dam is generally the most economical and convenient, besides avoiding the risk which attends a heavy weir upon a stream that may be subject to floods. When water is collected from drains or springs, it is received into a dam

formed in any convenient situation, and which must also be furnished with a wasteweir, to pass off flood waters, besides the ordinary sluice.

1726. The position of the sluice in the dam should be so studied as to prevent the wrack floating on the surface of the water finding its way into the sluice, and thence to the water-wheel. To avoid this inconvenience, the sluice should not be placed at the lowest point of the dam, where it most commonly is, but at one side, at which the water will pass into the lade, while the rubbish will float past to the lowest point.

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1727. The water-wheel should be on the bucket principle, and, for a fall such as we have supposed, should not be less than 14 feet diameter; the water, therefore, would be received on the breast of the wheel. Its circumference, with a diameter of 14 feet, will be 3.1416 × 14-44 feet; its velocity, at 5 feet per second, is 44 × 5 - 220 feet a minute; and 234 cubic feet, per minute (1723,) of water spread over this, gives a sectional area for the water laid upon the wheel of 234 =1.06 feet; but as the bucket should not be more than half filled, this area is to be doubled 2.12 feet; and as the breadth of the wheel may be restricted to 3 feet, then 704 foot, the depth of the shrouding, equal to 8 inches nearly; and if the wheel is to have wooden soleing, 1 inch should be added to this depth already found, making 9 inches.

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1728. The arc in which the wheel is to be placed must have a width sufficient to receive the wheel with the toothed segments attached to the side of the shrouding. For a bucket-wheel it is not necessary that it be built in the arc of a circle, but simply a square chamber-one side of it being formed by the wall of the barn, the other by a wall of solid masonry, at least 2 feet thick: one end also is built up solid, while the opposite end, towards the tail-race, is either left entirely open, or, if

the water is to be carried away by a tunnel, the water-way is arched over and the space above levelled in with earth. It is requisite that the walls of the wheelarc here described, should be built of square-dressed stone, having a breadth of bed not less than 12 inches, laid flush in mortar, and pointed with Roman cement.

1729. Fig. 140 is a sectional elevation of the wheel; a' a' is the barn-wall, b' b' Fig. 140.

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THE SECTION AND ELEVATION OF A BUCKET WATER-WHEEL.

is the sole of the arc or chamber, formed of solid ashler, having an increased slope immediately under the wheel, to clear it speedily of water. The shaft, the arms, and shrouding, are all of cast-iron, the buckets and sole being of wood; and, to prevent risk of fracture, the arms are cast separate from the shrouding. The width of the wheel being 3 feet, the toothed segments 4 inches broad, and they being 1 inch clear of the shrouding, gives a breadth over all of 3 feet 5 inches, and, when in the arc, there should be at least 1 inch of clear space on each side, free of

the wall. The shaft is not required to be longer than just to pass through the bearings; for, in wheels of this kind, it is improper to take any motion directly from the shaft. The eye-flanges b, 2 feet diameter, are separate castings, to which the arms c are bolted; the flanges being first keyed firmly upon the shaft. The shrouding d d is cast in segments, and bolted to the arms and to each other at their joinings. On the inside of the shroudplates are formed the grooves for securing the ends of the buckets and of the soleboarding, in the form as shown in the

section from e to e. The form of the buckets should be such as to afford the greatest possible space for water at the greatest possible distance from the centre of the wheel, with sufficient space for the entrance of the water and displacement of the air. In discharging the water from the wheel also, the buckets should retain the water to the lowest possible point. These conditions are attained by making the pitch ff of the buckets, or their distance from lip to lip, 14 times the depth of the shrouding; the depth of the front of the bucket fg inside, equal to the pitch; and the breadth of the bottom g h as great as can be attained consistently with free access of the water to the bucket immediately preceding; this breadth, inside, should not exceed two-fifths of the depth of the shrouding. The figure represents one-half of the shrouding-plates removed, in order the better to exhibit the position of the buckets.

this pinion is in a line horizontal to the axis of the water-wheel: here the whole weight of the water acts in impelling the pinion, while no strain is brought on the shaft beyond the natural weight of the wheel. In every position above this, unnecessary strains are brought upon the shaft and other parts of the wheel, and these increase with the distance from the first point k, till, if placed at the opposite point horizontal to the axis, the load upon the shaft would be double the weight of all the water upon the wheel, over and above the weight of the wheel itself.

1732. Laying the water upon the wheel is another point of some consequence; but whether it be delivered over the crown of the wheel, or at any point below that, the water should be allowed to fall through such a space as will give it a velocity equal to that of the periphery of the wheel when in full work. Thus, if the wheel move at the rate of 5 feet per 1730. The shrouding-plates are bolted second, the water must fall upou it upon the buckets and soling by bolts pass-through a space of not less than 4 foot; ing from side to side; and, in order to prevent resilience in the wheel, the arms are supported with diagonal braces. The toothed segments which operate on the pinion k, are bolted to the side of the shrouding through palms cast upon them for that purpose, and the true position of these segments requires that their pitchlines should coincide with the circle of gyration of the wheel: when so placed, the resistance to the wheel's action is made to bear upon its parts, without any undue tendency to cross strains. For that reason, it is improper to place the pitch-line beyond the circle of gyration, which is frequently done, even upon the periphery of the water-wheel. The determination of the true place of the circle of gyration is too abstruse to be introduced here, nor is it necessary to be so minute in the small wheels, to which our attention is chiefly directed; suffice it to say, that the pitchline of the segment wheel should fall between one-half and two-fifths of the breadth of the shrouding, from the extreme edge of the wheel.

1731. Another important point is that where the power is taken off from the wheel, that is, the placing of the pinion k. The most advantageous part for placing

for, by the laws of falling bodies, the velocities acquired are as the times and whole spaces fallen through, to the squares of the time. Thus the velocity acquired in 1" being 32 feet, a velocity of 5 feet will be acquired by falling .156"; for 32: 1":: 5: .156", and 1"2: 16:: .156′′: .4 foot, the fall to produce a velocity of 5 feet. But this being the minimum, the fall from the trough to the wheel may be made double this result, or about 10 inches. The trough which delivers the water upon the wheel should be at least 6 inches less in breadth than the wheel, to give space for the air escaping from the buckets, and to prevent the water dashing over at the sides; l, fig. 140, is the trough and m the spout that conveys the water to the wheel. It is convenient to have a regulating sluice n, that serves to give more or less water to the wheel; and this is worked by a small shaft passing to the inside of the barn. The shaft carries a pinion q, working the rack of the sluice-stem r, a small friction-rollers being placed in proper bearings on the crosshead t of the sluiceframe; and this apparatus is worked inside the barn by means of a lever handle upon the shaft of the pinion q. As a wastesluice, the most convenient and simple, in a mill of this kind, is the trap-sluice o,

which is simply a board hinged in the sole of the trough, and opening from the wheel; it is made to shut close down to the level of the sole, and, when so shut, the water passes freely over it to the wheel. The lifting of this sluice is effected by means of the connecting-rod u and crank-lever, the latter being fixed upon another small shaft, which passes through the wall to the interior of the barn, where it is worked in the same manner as the former. When it is found necessary to stop the wheel, the trap is lifted, and the whole supply of water falls through the shoot o p, leading it to the bottom of the wheel-arc b'b', by which it runs off, until the sluice at the dam can be shut, which stops further supply. The wheel here described, if it moves at the rate of 5 feet per second, will make 63 revolutions per minute. The pinion-shaft of k will carry a spur-wheel by which all the other parts of the machine can be put in motion. The rate of the spur-wheel depends on the relation of the water-wheel and its pinion. In the present case they are in the proportion of 8 to 1, and, as the water-wheel makes 6 revolutions per minute, this, multiplied by 8, will give 54 to the spurwheel.

1733. There is a diminutive form of thrashing-machine that merits notice, a one-horse machine. In some of our pastoral districts, where the proportion of arable land is so small as not to warrant the expense of a large thrashing-machine, these have been very successfully adopted. They are constructed with a small horsewheel, generally over-head; and the motion is carried into the barn in the usual form, where a spur-wheel drives the drum-pinion at a velocity of 250 turns per minute. The drum strikes downward, and has a pair of feeding-rollers. There is neither shaker or fan attached to the machine, and four people are required to carry on the process, the dressing being an after operation. With this little machine 12 bushels of oats can be thrashed in an hour; and the whole cost of it is about £20.

1734. There remains to be noticed one more member of this family of machines, -the English portable thrashing-machine. It is now most extensively employed in

the southern parts of the kingdom, and apparently to good purpose. But while this may be granted to the machine, I demur to the practice which involves outof-door thrashing, and a system of half performed work. But it is to the machine, and to one member of it alone, that I wish to direct attention, namely, the drum. It appears to me, in regard to this member, that the English and the Scotch machines operate on different principles. In the latter, as is well known, the thrashing is performed by a process of beating, and the instrument acts over but a short space, upon the grain undergoing the process-that is, while it is under the drumcover, or about one-fourth the circumference of the drum-case; and even during a part of this progress, the cover is so distant from the beaters-about 3 inchesthat little effect is produced upon the straw beyond a few inches from the feeding-rollers. There can be no doubt that, owing to this peculiar construction, when a stray ear of corn, or a sheaf-band, happens to enter root foremost, they are very likely to pass unthrashed, for the rollers have no hold of them; and they are so lightly pressed upon the beaters that we cannot be surprised at their passing in an imperfectly thrashed state. It has come under observation, also, that, taking our machines as usually worked, and applying them to the thrashing of corn cut by the scythe, the work, from the same cause, is often imperfectly performed, mainly in consequence of many of the ears entering by the reverse end. Of late years, many attempts have been made to improve our thrashing-machines, by improving the shaking apparatus, apparently forgetting that the shaker should have nothing to do beyond separating loose grains from the straw. The duty of the shaker is not to thrash; and when foul thrashing appears, it is the drum, not the shakers, that are in fault.

1735. Let us turn to the English machine, which has nothing, it is true, beyond a drum and feeding-rollers, and they even the rollers-can be left out. The drum, or, as it might be called, the rubber, though armed with what may be termed beaters, does not, in fact, thrash by beating, but by rubbing the grain. against a wire grating; and in this lies its

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