페이지 이미지
[merged small][ocr errors]
[merged small][ocr errors][merged small][merged small][merged small][merged small]

, , iron, and forming moulds, into which quantity of sand, and presses the pattern it is poured when in a fluid state. down again, until a perfect impression of

The moulds are commonly made in it is left in the sand, as in fig. 1. He now sand, held in wooden frames, (fig. 3 and returns the pattern, and sprinkles some 4, Plate fron-foundery.) Two of these dry sand which has been burnt in the frames

, A B, (fig. 4.) are called a pair of furnace, over the pattern and fàsk, and fasks, and fit together by pins, a a, in one

then places the upper flask, B, (fig. 4.) fask, entering eyes, bb, in the other. A upon it: two small sticks are placed upon wooden pattern of whatever is to be cast the pattern, and the sand filled in round must first be made, exactly of the same them; the sand is rammed down by the dimensions as the article required. For rammers (fig. 9 and 10,) and the two an example, we have chosen to describe sticks drawn out, leaving holes, ll, (fig. the manner of casting a roller, such as is 2.) through the sand in the upper flask.used for the wheels of small waggons,

The workman now takes off the upper the rolls of windmill heads, &c. The pat- flask, B, by its two handles, leaving the tern is shown in fig. 5, 6, and 7: fig. 5 is a pattern in the lower flask; the burnt sand plan, fig. 6 a section, and in fig. 7 it is causes the two fiasks to separate exactly shown edgeways. This pattern is exact- at the joining of the flasks: the upper ly similar to the wheel which is to be cast, Aask is now completely finished, the except that, in place of the hole through holes, ll, made by drawing out the sticks, the centre of the wheel, a pin, m, is struck being left to pour in the metal, and the on, projecting from each side in the same pattern leaving a perfect print of its upper place that the holes will be: the use of half in the flask. The next operation is these pins will be shown hereafter. The lifting the pattern out of the lower flask, lower flask, A, (fig. 4.) is placed on a

before which the workman wets the sand board laid on the ground; it is then filled around the pattern, that it may adhere to. with sand, and rammed down, first with gether, and not be broken by lifting the the rammer, (fig. 9.) and afterwards with pattern. The two pins projecting from fig

. 10, which is broader, and smooths the the wheel where the hole is to be, leave work. The workman then with the trow- their impressions in the sand, forming el, (fig. 8.) digs out a hole in the sand, two holes, e f, (fig. 2.) one in each fask. and presses the pattern into it, the flat These holes receive the ends of a core, surface horizontal, and fills the sand in which is exactly the shape and size of the round the pattern, until it is exactly half hole required in the wheel : the core is buried; he then takes out the pattern, formed of a mixture of plaster of Paris and if there are any holes in the under and brick dust, and is made just the length part, where the sand is not filled round and size of the pins in the pattern, that it

[ocr errors][ocr errors]

may be truly in the centre of the wheel. 5*v-5+5-V-5= 10 = č,
Fig. 2. is a section of the two flasks when the root of the proposed equation. .
put together; but the core is not put in: Dr. Wallis seems to have intended to
il are the holes for the metal, and ghik show, that there is no case of cubic equa.
the hollow cavity to receive it.

tions irreducible, or impracticable, as he The iron is melted in a furnace, and calls it, notwithstanding the common opibrought from it in a ladle (fig. 11.) which nion to the contrary, has three handles, and is carried by two Thus in the equation r3 — 63% = 162, men, the forked handle, M, giving a pur where the value of the root, according to chase to the man holding it, to turn over Cardan's rule, is a 3/81 +7 – 2700 the ladle to deliver its contents. If the work is very small, the metal is conveyed that the cubic root of 81 + ✓ - 2700,

+ 381 – V – 2700, the doctor says, to the flasks in common ladles. The more intricate cases of iron-found. binomial, viz. by + 1 v

may be extracted by another impossible

-; and in the ery, as the casting of cylinders for steam engines, crooked pipes with various pas

same manner, that the cubic root of 81 sages, &c. are cast 'in moulds formed of V - 2700 may be extracted, and is equal loam or clay, and are done nearly in the

to - -3; from whence he infers, same manner as the moulding of plaster that i + is 5 V-3+* - *V-3 = casts from busts, &c.; but our limits will 9, is one of the roots of the equation pronot allow us to describe these curious posed. And this is true: but those who branches of the founder's art.

will consult his algebra, p. 190, 191, will IRONY, in rhetoric, is when a person find that the rule he gives is nothing but speaks contrary to his thoughts, in order

a trial, both in determining that part of to add force to his discourse.

the root which is without a radical sign, IRRATIONAL, an appellation given to and that part which is within : and if the surd numbers and quantities. See SURD. original equation had been such as to have

IRREDUCIBLE case, in algebra, is its roots irrational, his trial would never used for that case of cubic equations, have succeeded. Besides, it is certain, where the root, according to Cardan's that the extracting the cube root of 81 rule, appears under an impossible or tv - 2700 is of the same degree of imaginary form, and yet is real. Thus, difficulty, as the extracting the root of the in the equation, x3 - 100 = 0, original equation r3 63 r = 162; and the root, according to Cardan's rule, that both require the tri-section of an anwill be x 350 + ✓ 24500 + gle for a perfect solution.

IRREGULAR, in grammar, such in. 24500, which is an impos- Alections of words as vary from the origisible expression, and yet one root is equal nal rules: thus we say, irregular nouns, to 10; and the other two roots of the irregular verbs, &c. equation are also real. Algebraists, for IRRIGATION is the art of conducting two centuries, have in vain endeavoured

water at pleasure over levels or inclined to resolve this case, and bring it under a planes, in such manner that the whole real form; and the question is not less fa

may receive the benefit of partial immer. mous among them, than the squaring of sion; whereby the surface may be duly the circle is among geometers. See supplied with moisture, and the vegetable EQUATION.

productions intended to be encouraged It is to be observed, that as, in some should be enabled to put forth abunother cases of cubic equations, the value dantly, and to yield a good crop. Irrigaof the root, though rational, is found under tion is with us rather a novel practice, an irrational or surd form; because the but was well understood by the ancients, root in this case is compounded of two and has been in use among the Chinese equal surds with contrary signs, which up to the earliest dates of their records. destroy each other; as if x = = 5 + ✓ 5 In Hindostan, the whole of the rubbee, or +5-5;

then x =

10; in like man. small-grain crop, is artificially watered ; ner, in the irreducible case, when the root the grain being deposited in October, it rational, there are two equal imaginary while the ground remains moist, after the quantities, with contrary signs, joined heavy rains which had fallen for months to real quantities; so that the imaginary previously to the operation for tillage ; so quantities destroy each other. Thus, the

that the seed speedily germinates. But expression :

the perfect drought attendant on the five 350+ ✓ 24500 =5+ V-5; and successive months would infallibly destroy

the promising verdure, were it not that 350

✓-24500 = 5-V-5. But the peasants divide their lands into small

90 x

[ocr errors]
[ocr errors]
[ocr errors][ocr errors][ocr errors][merged small][merged small][merged small]

squares, about four or five feet each way, the whole of the pasture lands in the between each pair of which a small chan. Milanese exhibit uncommon fertility; and nel, made by banking the soil, pro tempore, that the canals are so very extensive, and in a very simple manner, conducts the the branches from them so numerous, little stream supplied from numerous that few need complain of a want of water wells made expressly for the occasion. for irrigation. These works are known When the ear, or blossom, has shot forth, to be of no modern date: some have exwatering is discontinued. The Chinese isted for centuries, chiefly appertaining proceed on the grand scale; they not only to monasteries, their waters being let out divide their fields by numerous channels, by measure, to fertilize their adjacent but even warp whole tracts of low land; lands. The great canal, known by the whereby they insure immense returns. designation of Vecchiabbia, was in a The Africans, in some parts, follow the fourishing state early in the eleventh Hindostanee plan; but raise their water century, beyond which we do not know chiefly from the rivers, or obtain their what might have been its age. In 1220, supplies of that invaluable element from the great canal of Adda, which waters the natural reservoirs, formed by the hollows plains of Lodi, was finished; in 1305, the among hills

. In every part of Asia, but canal of Treveglio, which communicated especially in the Mysore country, former- with four others of very ancient workly under the dominion of the late sultan manship, was completed ; and in 1460, Tippoo, the retention of water for the the canal of Martesano, extending thirtypurposes of irrigation, is a matter of such two English miles: in this aqueduct, beimportance as to be entirely under the sides the main branch, of thirty-five feet auspices and controul of the government. in width, there were made nineteen scaTippoo caused banks, or, as they are call- ricatori, or lesser canals, which served, ed in India, bunds, to be made between when the waters rose very high, to draw the bases of the hills, so as to intercept off the surplus, so as to prevent injury to the copious streams, which, during the the main line, and to prevent inundation rainy seasons, flow from the hilly coun- along its course: when the latter returntry. An example worthy of imitation!ed to a more tranquil state, the scaricaThus immense bodies of water might be tori, which were not so deep as the main collected in many parts of the United line, served to supply it with what reKingdoms, whence mills and various ma- mained of their contents. chinery might be worked, without caus- It is worthy our notice, that although ing any waste of valuable land; the soil, the Italian aqueducts have, to our certain in situations appropriate to such pur, knowledge, been duly supported for upposes, being for the most part poor, and wards of eight centuries, by a race of unfit for tillage.

people far beneath us in the more noble The Milanese territory exhibits the sciences, in wealth, in population, and in greatest expanse of irrigation known in many other circumstances in which we Europe. In that country are to be seen pride ourselves, yet that Britain cannot noble canals, running in every direction, boast of one aqueduct, made exclusively totally exempted from local prejudice, with the important view to improve her private pique, or self interest. All are agriculture; though it would be as easy under the authority and protection of to show a thousand situations, where government, which lets out the water to such canals would double the value the various occupiers of meadows, at a of the lands adjoining, as it would be fixed rate, according to the quantity sup- to prove that such value would be douplied. Sometimes these canals are farm- bled. ed out, by putting up the several sluices It is, indeed, only in a few countries, to auction; in other instances the canals that irrigation is carried on to any exgo with the lands.

tent, though we may in various places Whatever may be the manner in which see partial adoptions of this most benefitheir water is dispersed, its due preserva- cial practice, yet we daily observe situation is an object of general solicitude, on tions naturally offering this advantage, account of the benefits which individuals without the smallest attempt being made derive from its use ; while the govern- to retain streams, which, from elevated ment, both from that motive, and the sup- situations, glide with some velocity port of the revenue produced by farming through deep vallies, whose very borders, of the canals, do not allow the smallest perhaps, are verdant, but whose more despoliation to pass unpunished. We retired parts would be doubled or trebled are assured by the best authorities, that in value, by the influence of that element,

[ocr errors][merged small][ocr errors][ocr errors][ocr errors][merged small][merged small][ocr errors]
[ocr errors]

ter: ctober


[ocr errors][ocr errors][ocr errors][ocr errors]

which is allowed to pass by unheeded, pose the speculator to be a free agent, to be lost in some marsh, or eventually not shackled by such an unhappy neighin the ocean! It is true, that in some bourhood; and content ourselves with parts, irrigation is not understood; and cautioning him not to injure the property that it is not always practicable to obtain of others, such as mills, bleaching grounds proper assistance; whence many, who below the lands, &c. &c., by drawing off would willingly water their meadows, that water on which their very existence are prevented from taking advantage of depends : a want of attention to this parstreams capable of effecting the inten- ticular has ruined many a deserving and tion. For the benefit of such persons, enterprising individual, and converted a in particular, as well as our readers in blessing into a serious mischief! general, we shall endeavour to simplify Where the stream is rapid, the bed has even this simple process, in such a man. usually a very marked declivity, such as ner as may prove perfectly intelligible; admits of throwing the water over the and, by showing with what ease irriga- lands, and of withdrawing them when tion may be carried on, induce a portion they have flowed, in every part, to a sufof our landholders to attempt, even with- ficient height. The first step towards out professional aid, or the tuition of ex- this is, to hold it up by means of a dam perienced persons, that retention and or weir, laid across the stream, (if its gradual distribution of waters, whose breadth admit, and that it be not navigasources are sufficiently elevated, which ble), so that, in the first place, the level may favour such a slight and temporary may be raised as circumstances may adinundation, as may give vigour and fresh.

mit. In this it will be necessary to ness both to the soil and to its produce. guard against injury to the property of

We shall divide this subject into two other persons above the dam ; for the distinct heads, viz. simple and compound raising a head of water, by means of a irrigation; observing that the former may dam, might subject lands, which before be practical in various modes separately, were perfectly dry, to be inundated; and, as will be shown, and that they may be even though such should actually prove blended so as to come under the second beneficial thereto, the owners might reterm. We shall also, by way of prepara- cover in a court of law, under various tion, give the reader an insight into some pleas of damage. modes of cutting off, or of supplying wa- The water should, if practicable, be ter, from sources of different heights, and raised to one foot, at least, above the under different circumstances: by this level of the highest land to be irrigated; means, with a moderate portion of judg- because that depth may be then kept as ment, the novice in this art may speedily a surplus, in case of long-continued acquire sufficient of the principles to an- drought; being let in upon the first drain swer his own purposes at least, if not to by a very small penstock, made only to form a correct opinion of most of the cases the depth of the first level. The water, which may come under his observation. when abundant, may flow both into the

The greatest difficulty we generally upper level, and over the weir, so as to experience is, from the water lying be- make a fall. When the water is not low the level of the lands over which it wanted over the land, the penstock may is to be conducted. In many instances, be shut up altogether. It it to be rethe springs whence streams are fed lié marked, that authors of eminence in this very deep; and, though copious, for want branch differ in opinion, though some of a sufficient inclination of their beds, suppose water to be more richly impregmove very slowly. In other parts, jea. nated with vegetable sustenance, in prolousy of improvement, personal enmity, portion as it is taken nearer to the spring, the owner being a minor, or insane, and provided the water be clear. The lands the property in the hands of trustees, or over which it is made to flow will be the estate being in Chancery, mortgaged, benefited in exact proportion as they may &c. perhaps debars the possibility of tak be near to the first level, which will aling advantage of some peculiarly favour ways receive the most obvious benefit. able fall, from which the water might be In foul streams, the result is usually found conducted with perfect facility and ef- to be in an inverse ratio : the water fect, over inclined planes, which, by being richer, in proportion as it is more their sterility, seem to reproach the own. remote from its source, but the first level er with neglect.

will still receive the greatest portion of In treating this subject, we must sup- the benefit. Where rivers are very mud.

« 이전계속 »