416 IRRIGATION ly, in the proper quantities, and at the right times, require good judgment, close attention, and much experience. The irrigating season in England is the colder portion of the year, commencing in October or November, and ter- minating in March or April. The letting the water on or off during frosty weather is to bo avoided, as a crust of ice may root out the grass as it thaws. As nearly as may be, with reference to this danger, the water is allowed to flow through the channels for two or three weeks at a time, and is then drawn completely off, so that the ground may become as thor- oughly dry as possible. In this condition it is left for five or six days, when if there is no fear of freezing the operation is repeated ; and so on through the winter". "When the grass begins to vegetate, the periods of irrigation should be shortened, and cease entirely when it is sufficiently forward to make good pasture. The effect of this practice is often very stri- king ; the grass is brought forward very early in the spring. After feeding off one crop or mowing the grass, the land is sometimes again irrigated for a short time to great advantage. A second crop is ready to be cut by the time the first has ripened on the dry meadows. Three or four crops of grass are thus obtained in each season. But the perfection of irriga- tion is when it is combined with thorough un- der-draining. The water flowing in brings with it in solution and suspension various min- eral and organic substances suitable for the food of plants. By evaporation and by vari- ous chemical reactions the soluble ingredients may be set free, when they become entangled with the other foreign matters in the grass and in the soil beneath, both of which act as filters. Thus the finely comminuted sediments and the soluble salts are equally distributed among the rootlets, and these are refreshed by the new supplies furnished by each repetition of the process. By the drains the excess of moisture is soon removed, stagnation, so injurious to vegetation, is prevented, and the elements that feed the plants below the surface are kept in a similar condition of healthy renewal with those of the air circulating among the branches and adding to the vegetable growth by assimilation going on through the leaves. The benefits de- rived from the process vary of course with the quality of the ingredients brought in by the water, according as these are more or less suit- ed to the requirements of the soil and of the crop. The hard water, charged with carbon- _ ate of lime, which it has gathered in flowing ' through a limestone region, brings a valuable fertilizing ingredient to silicious soils deficient in lime ; and the clayey sediment washed out of alluvial bottoms is spread with the most beneficial effect over loose sandy soils. Some- times organic liquid manures, such as the drain- age of farmyards and 1 cachings of compost heaps, are supplied to the soil by being min- gled with the water used in irrigating ; but the principal object of irrigation is to supply mois- IRVINE ture, as it is always easy to add manure in a solid form. Much attention is now given to the subject of irrigation in that portion of the United States lying between the Mississippi river and the Rocky mountains ; so that a vast region, some of which was long known as the Great American desert, bids fair in time to be for the most part brought under fair cultiva- tion. The Mormons in Utah by means of irri- gation render their barren country fertile. The general plan with them, and also in California, is to lead the water in canals from the rivers or the mountains, and allow it to flow over the fields, either through small channels made in the soil, or over the even surface. IRVINE, a parliamentary borough and sea- port of Ayrshire, Scotland, on both banks of the river of the same name, 1 m. above its entrance into the Firth of Clyde, 20 m. S. W. of Glasgow ; pop. in 1871, 6,866. It has a fe- male academy, ship yards, and some manufac- tories of book muslins, jaconets, and checks. The harbor, having become shallow from sand bars, now admits only vessels of about 100 tons. IRVINE, William, an American soldier, born near Enniskillen, Ireland, about 1742, died in Philadelphia, July 30, 1804. He graduated at Dublin university, studied medicine and sur- gery, and was appointed surgeon on board a ship of war, serving during a part of the war of 1756-'63 between Great Britain and France. On the declaration of peace he emigrated to America, and in 1764 settled in Carlisle, Pa. At the opening of the revolution he took part with the colonies. He was a member of the provincial convention assembled July 15, 1774, until he was appointed by congress, Jan. 10, 1776, colonel of the 6th battalion of the Penn- sylvania line, and was ordered to join the army in Canada. He was made prisoner at the bat- tle of Three Rivers in June of the same year, and was released on parole, Aug. 3, but was not exchanged until April, 1778. In July, 1778, he was a member of the court martial which tried Gen. Charles Lee. On Jlay 12, 1779, he was promoted to the rank of briga- dier general, and was assigned to the command of the 2d brigade of the Pennsylvania line. In the unsuccessful attack of Gen. Wayne at Bull's Ferry, July 21 and 22, 1780, he com- manded his brigade. In the autumn of 1781 he was ordered to Fort Pitt, to take command of the troops on the western frontier, where he remained till Oct. 1, 1783. In 1785 he was appointed agent for the state under an "act for directing the mode of distributing the do- nation lands promised to the troops of the commonwealth." He became a member of con- gress in 1787, and was selected, with Mtssrs. Gilman and Kain, one of the commission- ers for settling the accounts of the United States with the several states. He was a mem- ber of the convention for revising the consti- tution of Pennsylvania, and again from 1793 to 1795 a member of congress. In 1794 he was assigned to the command of the Pennsylva-
