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RON-FOUNDERY, the art of casting iron, and forming moulds, into which it is poured when in a fluid state.

The moulds are commonly made in sand, held in wooden frames, (fig. 3 and 4, Plate Iron-foundery.) Two of these frames, A B, (fig. 4.) are called a pair of flasks, and fit together by pins, a a, in one flask, entering eyes, b b, in the other. A wooden pattern of whatever is to be cast must first be made, exactly of the same dimensions as the article required. For an example, we have chosen to describe the manner of casting a roller, such as is used for the wheels of small waggons, the rolls of windmill heads, &c. The pattern is shown in fig. 5, 6, and 7: fig. 5 is a plan, fig. 6 a section, and in fig. 7 it is shown edgeways. This pattern is exactly similar to the wheel which is to be cast, except that, in place of the hole through the centre of the wheel, a pin, m, is struck on, projecting from each side in the same place that the holes will be: the use of these pins will be shown hereafter. The lower flask, A, (fig. 4.) is placed on a board laid on the ground; it is then filled with sand, and rammed down, first with the rammer, (fig. 9.) and afterwards with fig. 10, which is broader, and smooths the work. The workman then with the trowel, (fig. 8.) digs out a hole in the sand, and presses the pattern into it, the flat surface horizontal, and fills the sand in round the pattern, until it is exactly half buried; he then takes out the pattern, and if there are any holes in the under part, where the sand is not filled round

close to the pattern, he puts in a small quantity of sand, and presses the pattern down again, until a perfect impression of it is left in the sand, as in fig. 1. He now returns the pattern, and sprinkles some dry sand which has been burnt in the furnace, over the pattern and flask, and then places the upper flask, B, (fig. 4.) upon it: two small sticks are placed upon the pattern, and the sand filled in round them; the sand is rammed down by the rammers (fig. 9 and 10,) and the two sticks drawn out, leaving holes, 11, (fig. 2.) through the sand in the upper flask.The workman now takes off the upper flask, B, by its two handles, leaving the pattern in the lower flask; the burnt sand causes the two flasks to separate exactly at the joining of the flasks: the upper flask is now completely finished, the holes, 1 l, made by drawing out the sticks, being left to pour in the metal, and the pattern leaving a perfect print of its upper half in the flask. The next operation is lifting the pattern out of the lower flask, before which the workman wets the sand around the pattern, that it may adhere together, and not be broken by lifting the pattern. The two pins projecting from the wheel where the hole is to be, leave their impressions in the sand, forming two holes, ef, (fig. 2.) one in each flask. These holes receive the ends of a core, which is exactly the shape and size of the hole required in the wheel: the core is formed of a mixture of plaster of Paris and brick dust, and is made just the length and size of the pins in the pattern, that it

may be truly in the centre of the wheel. Fig. 2. is a section of the two flasks when put together; but the core is not put in : il are the holes for the metal, and ghik the hollow cavity to receive it.

The iron is melted in a furnace, and brought from it in a ladle (fig. 11.) which has three handles, and is carried by two men, the forked handle, M, giving a purchase to the man holding it, to turn over the ladle to deliver its contents. If the work is very small, the metal is conveyed

to the flasks in common ladles.

The more intricate cases of iron-foundery, as the casting of cylinders for steam engines, crooked pipes with various passages, &c. are cast in moulds formed of loam or clay, and are done nearly in the same manner as the moulding of plaster casts from busts, &c.; but our limits will not allow us to describe these curious branches of the founder's art.

IRONY, in rhetoric, is when a person speaks contrary to his thoughts, in order to add force to his discourse.

IRRATIONAL, an appellation given to surd numbers and quantities. See SURD. IRREDUCIBLE case, in algebra, is used for that case of cubic equations, where the root, according to Cardan's rule, appears under an impossible or imaginary form, and yet is real. Thus, in the equation, x3 90 x- - 1000, the root, according to Cardan's rule, will be x=3/ 50 + ✔ 24500+

350——24500, which is an impossible expression, and yet one root is equal to 10; and the other two roots of the equation are also real. Algebraists, for two centuries, have in vain endeavoured to resolve this case, and bring it under a real form; and the question is not less famous among them, than the squaring of the circle is among geometers. See EQUATION.

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It is to be observed, that as, in some other cases of cubic equations, the value of the root, though rational, is found under an irrational or surd form; because the root in this case is compounded of two equal surds with contrary signs, which destroy each other; as if x 5+√5 +55; then x = 10; in like manner, in the irreducible case, when the root it rational, there are two equal imaginary quantities, with contrary signs, joined to real quantities; so that the imaginary quantities destroy each other. Thus, the expression:

50+✔ 24500= 5+✔―5; and 13/50-24500—5—✔✅✔✅ —5. But

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−5+5−√− 5 = 10 = x, the root of the proposed equation..

Dr. Wallis seems to have intended to show, that there is no case of cubic equations irreducible, or impracticable, as he calls it, notwithstanding the common opinion to the contrary.

Thus in the equation r3 63 = 162, where the value of the root, according to Cardan's rule, is r = 3/81 + √ — 2700 that the cubic root of 81 +✔ - 2700, + 3/81 − √ - 2700, the doctor says, may be extracted by another impossible binomial, viz. by + √ —; and in the same manner, that the cubic root of 81

2

=

2700 may be extracted, and is equal to 93; from whence he infers, that is−3+§§ √−3 = 9, is one of the roots of the equation proposed. And this is true: but those who will consult his algebra, p. 190, 191, will find that the rule he gives is nothing but a trial, both in determining that part of the root which is without a radical sign, and that part which is within: and if the original equation had been such as to have its roots irrational, his trial would never have succeeded. Besides, it is certain, that the extracting the cube root of 81 +✔-2700 is of the same degree of difficulty, as the extracting the root of the original equation r3 - 63 r = 162; and that both require the tri-section of an angle for a perfect solution.

IRREGULAR, in grammar, such inflections of words as vary from the original rules: thus we say, irregular nouns, irregular verbs, &c.

IRRIGATION is the art of conducting water at pleasure over levels or inclined planes, in such manner that the whole may receive the benefit of partial immersion; whereby the surface may be duly supplied with moisture, and the vegetable productions intended to be encouraged should be enabled to put forth abundantly, and to yield a good crop. Irrigation is with us rather a novel practice, but was well understood by the ancients, and has been in use among the Chinese up to the earliest dates of their records. In Hindostan, the whole of the rubbee, or small-grain crop, is artificially watered; the grain being deposited in October, while the ground remains moist, after the heavy rains which had fallen for months previously to the operation for tillage; so that the seed speedily germinates. But the perfect drought attendant on the five successive months would infallibly destroy the promising verdure, were it not that the peasants divide their lands into small

squares, about four or five feet each way, between each pair of which a small channel, made by banking the soil, pro tempore, in a very simple manner, conducts the little stream supplied from numerous wells made expressly for the occasion. When the ear, or blossom, has shot forth, watering is discontinued. The Chinese proceed on the grand scale; they not only divide their fields by numerous channels, but even warp whole tracts of low land; whereby they insure immense returns. The Africans, in some parts, follow the Hindostanee plan; but raise their water chiefly from the rivers, or obtain their supplies of that invaluable element from natural reservoirs, formed by the hollows among hills. In every part of Asia, but especially in the Mysore country, formerly under the dominion of the late sultan Tippoo, the retention of water for the purposes of irrigation, is a matter of such importance as to be entirely under the auspices and controul of the government. Tippoo caused banks, or, as they are called in India, bunds, to be made between the bases of the hills, so as to intercept the copious streams, which, during the rainy seasons, flow from the hilly country. An example worthy of imitation! Thus immense bodies of water might be collected in many parts of the United Kingdoms, whence mills and various machinery might be worked, without causing any waste of valuable land; the soil, in situations appropriate to such purposes, being for the most part poor, and unfit for tillage.

The Milanese territory exhibits the greatest expanse of irrigation known in Europe. In that country are to be seen noble canals, running in every direction, totally exempted from local prejudice, private pique, or self interest. All are under the authority and protection of government, which lets out the water to the various occupiers of meadows, at a fixed rate, according to the quantity supplied. Sometimes these canals are farmed out, by putting up the several sluices to auction; in other instances the canals go with the lands.

Whatever may be the manner in which their water is dispersed, its due preservation is an object of general solicitude, on account of the benefits which individuals derive from its use; while the government, both from that motive, and the support of the revenue produced by farming of the canals, do not allow the smallest despoliation to pass unpunished. are assured by the best authorities, that

We

the whole of the pasture lands in the Milanese exhibit uncommon fertility; and that the canals are so very extensive, and the branches from them so numerous, that few need complain of a want of water for irrigation. These works are known to be of no modern date: some have existed for centuries, chiefly appertaining to monasteries, their waters being let out by measure, to fertilize their adjacent lands. The great canal, known by the designation of Vecchiabbia, was in a flourishing state early in the eleventh century, beyond which we do not know what might have been its age. In 1220, the great canal of Adda, which waters the plains of Lodi, was finished; in 1305, the canal of Treveglio, which communicated with four others of very ancient workmanship, was completed; and in 1460, the canal of Martesano, extending thirtytwo English miles: in this aqueduct, besides the main branch, of thirty-five feet in width, there were made nineteen scaricatori, or lesser canals, which served, when the waters rose very high, to draw off the surplus, so as to prevent injury to the main line, and to prevent inundation along its course: when the latter returned to a more tranquil state, the scaricatori, which were not so deep as the main line, served to supply it with what remained of their contents.

It is worthy our notice, that although the Italian aqueducts have, to our certain knowledge, been duly supported for upwards of eight centuries, by a race of people far beneath us in the more noble sciences, in wealth, in population, and in many other circumstances in which we pride ourselves, yet that Britain cannot boast of one aqueduct, made exclusively with the important view to improve her agriculture; though it would be as easy to show a thousand situations, where such canals would double the value of the lands adjoining, as it would be to prove that such value would be doubled.

It is, indeed, only in a few countries, that irrigation is carried on to any extent, though we may in various places see partial adoptions of this most beneficial practice, yet we daily observe situations naturally offering this advantage, without the smallest attempt being made to retain streams, which, from elevated situations, glide with some velocity through deep vallies, whose very borders, perhaps, are verdant, but whose more retired parts would be doubled or trebled in value, by the influence of that element,

which is allowed to pass by unheeded, to be lost in some marsh, or eventually in the ocean! It is true, that in some parts, irrigation is not understood; and that it is not always practicable to obtain proper assistance; whence many, who would willingly water their meadows, are prevented from taking advantage of streams capable of effecting the intention. For the benefit of such persons, in particular, as well as our readers in general, we shall endeavour to simplify even this simple process, in such a manner as may prove perfectly intelligible; and, by showing with what ease irrigation may be carried on, induce a portion of our landholders to attempt, even without professional aid, or the tuition of experienced persons, that retention and gradual distribution of waters, whose sources are sufficiently elevated, which may favour such a slight and temporary inundation, as may give vigour and freshness both to the soil and to its produce.

We shall divide this subject into two distinct heads, viz. simple and compound irrigation; observing that the former may be practical in various modes separately, as will be shown, and that they may be blended so as to come under the second term. We shall also, by way of preparation, give the reader an insight into some modes of cutting off, or of supplying water, from sources of different heights, and under different circumstances: by this means, with a moderate portion of judgment, the novice in this art may speedily acquire sufficient of the principles to answer his own purposes at least, if not to form a correct opinion of most of the cases which may come under his observation.

The greatest difficulty we generally experience is, from the water lying below the level of the lands over which it is to be conducted. In many instances, the springs whence streams are fed lie very deep; and, though copious, for want of a sufficient inclination of their beds, move very slowly. In other parts, jealousy of improvement, personal enmity, the owner being a minor, or insane, and the property in the hands of trustees, or the estate being in Chancery, mortgaged, &c. perhaps débars the possibility of taking advantage of some peculiarly favourable fall, from which the water might be conducted with perfect facility and effect, over inclined planes, which, by their sterility, seem to reproach the owner with neglect.

In treating this subject, we must sup

pose the speculator to be a free agent, not shackled by such an unhappy neighbourhood; and content ourselves with cautioning him not to injure the property of others, such as mills, bleaching grounds below the lands, &c. &c., by drawing off that water on which their very existence depends: a want of attention to this particular has ruined many a deserving and enterprising individual, and converted a blessing into a serious mischief!

Where the stream is rapid, the bed has usually a very marked declivity, such as admits of throwing the water over the lands, and of withdrawing them when they have flowed, in every part, to a sufficient height. The first step towards this is, to hold it up by means of a dam or weir, laid across the stream, (if its breadth admit, and that it be not navigable), so that, in the first place, the level may be raised as circumstances may admit. In this it will be necessary to guard against injury to the property of other persons above the dam; for the raising a head of water, by means of a dam, might subject lands, which before were perfectly dry, to be inundated; and, even though such should actually prove beneficial thereto, the owners might recover in a court of law, under various pleas of damage.

The water should, if practicable, be raised to one foot, at least, above the level of the highest land to be irrigated; because that depth may be then kept as a surplus, in case of long-continued drought; being let in upon the first drain by a very small penstock, made only to the depth of the first level. The water, when abundant, may flow both into the upper level, and over the weir, so as to make a fall. When the water is not wanted over the land, the penstock may be shut up altogether. It it to be remarked, that authors of eminence in this branch differ in opinion, though some suppose water to be more richly impregnated with vegetable sustenance, in proportion as it is taken nearer to the spring, provided the water be clear. The lands over which it is made to flow will be benefited in exact proportion as they may be near to the first level, which will always receive the most obvious benefit. In foul streams, the result is usually found to be in an inverse ratio: the water being richer, in proportion as it is more remote from its source, but the first level will still receive the greatest portion of the benefit. Where rivers are very mud

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