VArUE. 808 VALVE. half of the nineteenth century, when the concept 'marginal utility' was discovered. By a well- known psychological principle, the pleasure de- rived from the satisfaction of any given want de- clines with each successive unit of satisfaction experienced. If an individual possesses a stock of goods for consinnption. some luiits of this stock may be so used as to yield a high degree of satis- faction : other units will yield less, and the 'final' or "marginal' unit may yield but little satisfaction, however great the satisfaction from the first unit may have been. The absolute im- portance to the individual of any unit in his possession will be measured by the utility of the marginal unit, since the loss of any other unit would at once be made good by the sub- stitution of the marginal unit. In his private economy, an individual values his goods accord- ing to their marginal utilities. In exchange, both buyer and seller compare the marginal util- ity of tiie commodity to be bought and sold with the marginal utility of mone,y. If the seller finds that the marginal utility of the money of- fered him exceeds the marginal utility of the commodity for sale, he is naturally willing to sell: if the buyer finds that the marginal utility of the commodity exceeds that of the money de- manded, he purchases. ISraturally, many sellers would be willing to take a price less than that which they are ofl'ercd ; many buyers would pay more than they do rather than go without the commodity they desire. A certain munber of buyers, however, possess limited means, and would not purchase if the price rose above a cer- tain figure. A number of sellers would hold their property rather than take a lower price. It is these buyers who are least eager to buy and sellers least eager to sell who hold the power of determining ratios of exchange, all other pur- chases and sales, in an open market, conform- ing to the values set by these. The marginal utility theory does not deny that in the long run the values of commodities tend to correspond with their respective costs of pro- duction : but it gives a new interpretation to the fact. 'Costs' consist themselves in values — value of labor, capital, use of land, etc.. used up in the manufacture of a conmiodity. These things are not valued for their own sake, but for the sake of the products for final consumption into which they enter. Naturally, these commodities are valued marginally. If pig iron in one use creates a value equal to 40, in another use a value rep- resented by 10, the latter use will determine the value of pig iron. But under free competition there would be a tendency to increase the pro- duction of commodities in which pig iron created a value of 40, withdrawing iron, if necessary, from the less productive use. The result would be that the value of iron in the more profitable use would decline, and with it the value of the commodity into which it entered. In this way it appears as if value were determined by costs. On the other hand, the increase in value of iron in the least profitable use, resulting from the withdrawal of iron from that use, shows quite clearly that in a broad view it is the commodity for final consumption that determines the value of the elements in cost, not cost that determines values. This theory was originated by Gossen in the fifties, but gained no attention at the time. Two decades later it was rediscovered by .Jevons, Men- ger, Walras, and J. B. Clark, working independ- ently. Through the consistency with which it ex- plains the diverse phenomena of value, it has re- ceived wide acceptance, although it has been un- able to displace the classical theory conipletel,v. Marshall has endeavored to reconcile the two theories, holding that cost of production and marginal utility, taken together, explain value, b>it that neither theory alone explains it satis- factorily. In this view he is followed by proba- bly the maJorit,v of American and English econo- mists. 8ee Political Eco>'Omt. BiBLlOGR.PHT. All standard works on econom- ics present a general theorv of value. For the classical theoiy, the best expositions arc Mill, Principles of PoJitical Economy (London, numer- ous editions), and Cairnes, I'olitictd Economy (Xew York, 1874). For the labor theory, see !Marx, Capital (London, 1887). For the margi- nal utility theory, consult Gossen, Gesetze des vicnschlichen Verkehrs (Brunswick, 1854) ; Jevons, Theory of Political Economy (London, 1871); Clark, Philosophy of ^yealth (Boston, 1804); Wieser, Xntiiral Value (London, 1893); Smart, Introduction to the Theory of Value (ib., 1891); Marshall, Principles of Econom- ics (3d ed., ib., 189.5). VALUE. In music, the time-value of a note or rest, in a general sense, is the length of its duration as compared with the whole note, which is the unit of time-measure. In a special sense, the value of a note or rest is the length of its duration as compared with the particular note adopted as the unit of measure for a particular composition. Thus, in J time the unit of meas- ure is the quarter note, in ~ time the eighth note, etc. VALVA'TA. A small pulmonate mollusk of American fresh waters, remarkable for the squareness of its whorls. See Colored Plate of Snails. VALVE. A device or appliance for control- ling the flow of liquids, gas, or loose material through a pipe, chuje, or other form of passage- way. With the general use of steam, water, gas, and other fluids, a great variety of valves have been invented and are in daily use. These valves bear various trade names based on their purpose, the shape or motion of the valve, and the method of operation. Thus we have safety valves, globe valves, slide valves, screw valves, etc. Valves generally, whatever their specific names may be, can be included in a general classification with reference to the manner in which their motion is obtained, or in a general classification with re- gard to the motion relative to the valve seat. En the first classification are: (1) Valves opened and closed by hand; (2) valves operated b.v in- dependent mechanism; (3) valves operated by mechanism connected with the machine whose operation the,v control: and (4) valves opened and closed by the motion of the fluid whose flow they control. Classified with regard to their motion relative to the valve seat there are: (1) valves which rotate in the opening, (2) valves which rise and fall perpendicularly from and to their seat's, and (3) valves which open and close by sliding on and parallel to their seats. It is obvious that the characteristics of the first and second classifications may be combined in one
