For some time he finds a ready sale at that price; but, as the day advances, the sale slackens, and at last no purchasers are to be found who will give that price. How is he to dispose of the portion of his meat still unsold, for it will spoil if left on his hand till next market - day? It is obvious, that he can now sell it only by reducing the price, so as to enable some to buy who otherwise could not afford to do so. Accordingly, rather than lose his meat, he sells it at whatever price it will fetch-it may be at eightpence, or sevenpence, or even at a sum which not only leaves him no profit, but causes him a loss. In this case, the butcher first fixes his price according to the cost of production, but is afterwards obliged to reduce it, because the quantity for sale is greater than the quantity wanted at the price, or, in other words, because the supply is greater than the demand.

On the other hand, let us suppose that the butcher, after selling for some time at ninepence, finds his meat going off so fast as to show that there is much more meat wanted than he has for sale; does he continue to charge only ninepence? No. Perceiving that there is not enough of meat for all who want it, and that some will give a little more for it rather than go without it, he raises his price, and probably gets tenpence or a shilling for what in the earlier part of the day he got only ninepence. In this latter case, the price rises, because the quantity wanted is greater than the quantity for sale, or, in other words, because the demand is greater than the supply.

Now, what is true of the price of butcher-meat, is equally true of the price of every other commodity. The seller fixes his price according to the cost of production, and when the demand is equal to the supply he gets that price; but whenever the demand and the supply are unequal, he has to vary his price-lowering it when the supply exceeds the demand, and raising it when the demand exceeds the supply.

But on what do supply and demand depend? what causes them to fluctuate?

There are two things on which the supply of commodities

chiefly depends. One is the state or vicissitudes of the weather; for a bad harvest cannot but cause a greatly diminished supply of food- a failure in the cotton crop cannot but lessen the supply of one of the chief materials of clothing. The other is, the skill and industry of the producers; for while a good farmer will be able, by foresight and activity, to raise and reap a considerable crop in spite of the badness of the season, an unskilled and careless farmer may, in the same circumstances, lose his whole crop. But supply is also, to some extent, dependent on the state of demand. Manufacturers find it to be their interest to produce commodities only in such quantities as they can sell at a profit; and hence they enlarge or lessen the supply according as the demand increases or decreases.

The supply of commodities, then, depends on the state of the weather, the industrial ability of the producers, and the state of demand. The demand for commodities, on the other hand, depends chiefly on what may be called their desirableness, that is, their usefulness or attractiveness in the eye of purchasers. Thus, there is a greater demand for iron than for lead, for paper than for parchment, for steelpens than for quills. In like manner, necessaries being more desirable than luxuries, the demand for the former is less fluctuating than the demand for the latter. Other things, however, besides desirableness affect demand. For instance, fluctuations in the supply of some commodities will affect the demand for others. A bad corn-harvest must give rise to an increased demand for potatoes, rice, and other articles, which can be substituted for bread; while, on the other hand, an abundant corn-harvest, by placing bread within the reach of most buyers, must diminish the demand for potatoes and other inferior kinds of food. The price of a commodity, too, while itself dependent on the demand, reacts upon the demand, and modifies it. Of two things which are equally desirable, there is always a greater demand for the cheaper. It is the high price of gold watches which causes them to be less in demand than silver watches; it is the lower price of fustian jackets that causes workingmen to purchase them in preference to coats of broadcloth.

Accordingly, manufacturers always find that by cheapening the price of their goods they increase the demand for them, and that by raising the price they lessen the demand. A large increase in the price of shoes would cause many who now wear them to go barefooted; while a large reduction of price would cause many to be well-shod who are now shoeless.

It is right, however, to add, that these various causes of fluctuation in supply and demand are themselves controlled by other causes which tend to keep the supply of commodities and the demand for them tolerably equal upon the whole. Suppose a publisher to bring out a new book which he expects to sell well, but which, in point of fact, does not sell. He is, of course, a loser by the venture-he loses all he has expended on paper, printing, and binding-and the reason of his loss is, that he has produced a book which was not wanted. What effect will this loss have upon him? Why, it will cause him to take greater pains in future to find out what is really wanted by the public, and to produce only such a book as is wanted. Or let us suppose him to produce a book which is very much wanted. It commands a ready and extensive sale, and yields him a large profit. Encouraged by this large profit, he brings out edition after edition, until at last the supply exceeds the demand, and he is left with a stock of unsaleable copies which are a dead loss to him. Here, again, he is punished by loss for having produced more than was wanted; and the effect will be to make him yet more careful to keep the supply of his commodities rather below than beyond the demand.

Such is the way in which over-production is controlled and corrected. In cases of under-production-that is, where the goods supplied fall short of the demand for them-the inequality is removed by the operation of what is called competition. As an article is sure to rise in price and to yield a large profit whenever the supply is short of the demand, other persons, besides the original producer, are naturally tempted by the hope of profit to produce and bring to market that article; and the effect of such competition is, of course, to increase the supply and remedy the previous under-production.

In these ways it is that supply and demand are kept, upon the whole, equal or nearly equal. It is a part of every producer's business to know how the supply and demand stand-or, as it is called, "the state of the market"—and to regulate production accordingly. Producers who do not attend to this are soon driven out of business by their losses. Compiled from TEMPLAR and DAWES.

PRESSURE OF WATERY FLUIDS.

ALL the particles of fluids are so connected together, that they press equally in every direction, and are equally pressed upon; each particle presses equally on all the particles that surround it, and is equally pressed upon by these; it equally presses upon the solid bodies which it touches, and is equally pressed upon by those bodies. From this, and from its gravity, it follows, that when a fluid is left to itself, its surface will rise or fall so as to settle at the same level. Hence, if we pour water or any other liquid into

a tube or pipe bent double like a U, it will stand at the very same height in both limbs. Nor does it make any difference if one limb is wider than the other. Generally, and in every case, if there be two tubes or limbs of a tube connected together, however different their width, a fluid poured into them will stand at the same level, and thus a portion of fluid,

however small, will resist the pressure of a portion, however large, and balance it.

From these considerations two most important conclusions follow. The one is, that water, by being confined in pipes or close channels of any kind, will rise to the height from which it came—that is, as high as its source—and upon this principle depend all the useful contrivances for conveying water by pipes, in a way far more easy, cheap, and effectual than those vast buildings called aqueducts, by which the ancients carried their supplies of water in artificial

rivers over arches for many miles. The other is far more extraordinary; it is, that the pressure of the water upon any object is not at all in proportion to the bulk of the water, but only to the size of the surface on or against which it presses, and its own height above that surface; in other words, that any quantity of water, however small, may be made to support any quantity, however great. This principle is called the Hydrostatical paradox; paradox signifying something which, though true, appears, when first considered, to be untrue. We are at first startled by the apparent impossibility of the statement. But when we come to examine it more closely, we find it to be accurately true; for the small tube in the case just mentioned may be made ever so narrow, and to hold ever so little water, while the wide tube communicating with it may be made ever so large, and to hold ever so much water: yet the level at which the water stands in both tubes will be the same.

Everything thus depending upon the height and the surface, and nothing upon the bulk of the fluid, we may easily perceive what mischief may be sometimes done by a very small quantity of water. Thus, if you fix a small strong pipe in the bunghole of a cask of water, and pour water through the pipe till it rises in the pipe to a sufficient height, the barrel will burst, although but a very small quantity of water may have been poured into the pipe.

The same effect may be produced naturally, by the rain falling into and filling some long narrow chink or fissure that communicates with an enclosed body of water. Suppose, in the bowels of some mountain there should be an empty space of ten yards square and only an inch deep, in which a layer of water had lodged so as to fill it entirely; and suppose that in the course of time, a small crack of no more than an inch in diameter should be worn from above 200 feet down to the layer of water; if the rain were to fill this crack, the mountain would be shaken, perhaps rent in pieces with the greatest violence, being acted on by a force equal to the pressure of above 5000 tons of water, though not above a ton and a half altogether had been actually

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