Chapter XVII: Part 17

IRON MOUNTAIN, a city and the county-seat of Dickinson county, Michigan, U.S.A., about 50 m. W. by N. of Escanaba, in the S.W. part of the Upper Peninsula. Pop. (1900) 9242, of whom 4376 were foreign-born; (1904) 8585; (1910) 9216. It is served by the Chicago & North Western and the Chicago, Milwaukee & Saint Paul railways. The city is situated about 1160 ft. above sea-level in an iron-mining district, and the mining of iron ore (especially at the Great Chapin Iron Mine) is its principal industry. Iron Mountain was settled in 1879, and was chartered in 1889.

IRONSIDES, a nickname given to one of great bravery, strength or endurance, particularly as exhibited in a soldier. In English history Ironside or Ironsides first appears as the name of Edmund II., king of the English. In the Great Rebellion it was first given by Prince Rupert to Cromwell, after the battle of Marston Moor in 1644 (see S. R. Gardiner's _History of the Great Civil War_, 1893, vol. ii. p. 1, and _Mercurius civicus_, September 19-26, 1644, quoted there). From Cromwell it was transferred to the troopers of his cavalry, those "God-fearing men," raised and trained by him in an iron discipline, who were the main instrument of the parliamentary victories in the field. This (see S. R. Gardiner, _op. cit._ iv. 179) was first given at the raising of the siege of Pontefract 1648, but did not become general till later.

IRONTON, a city and the county-seat of Lawrence county, Ohio, U.S.A., on the Ohio river, about 142 m. E.S.E. of Cincinnati. Pop. (1890) 10,939; (1900) 11,868, of whom 924 were negroes and 714 foreign-born; (1910 census) 13,147. It is served by the Chesapeake and Ohio, the Cincinnati, Hamilton and Dayton, the Norfolk and Western, and the Detroit, Toledo and Ironton railways, and by river steamboats. The city is built on a plain at the base of hills rising from the river bottom and abounding in iron ore and bituminous coal; fire and pottery clay also occur in the vicinity. Besides mining, Ironton has important lumber interests, considerable river traffic, and numerous manufactures, among which are iron, wire, nails, machinery, stoves, fire-brick, pressed brick, terra-cotta, cement, carriages and wagons, and furniture. The total value of its factory product in 1905 was $4,755,304; in 1900, $5,410,528. The municipality owns and operates its water-works. Ironton was first settled in 1848, and in 1851 was incorporated.

IRONWOOD, a city of Gogebic county, Michigan, U.S.A., on the Montreal river, in the N.W. part of the upper peninsula. Pop. (1890) 7745; (1900) 9705, of whom 4615 were foreign-born; (1910 census) 12,821. It is served by the Chicago and Northwestern and the Wisconsin Central railways. The city is situated about 1500 ft. above sea-level in the Gogebic iron-district, and is principally a mining town; some of the largest iron mines in the United States are within the city limits. Ironwood was settled in 1884, and was chartered as a city in 1889.

IRON-WOOD, the name applied to several kinds of timber, the produce of trees from different parts of the tropics, and belonging to very different natural families. Usually the wood is extremely hard, dense and dark-coloured, and sinks in water. Several species of _Sideroxylon_ (_Sapotaceae_) yield iron-wood, _Sideroxylon cinereum_ or _Bojerianum_ being the _bois de fer blanc_ of Africa and Mauritius, and the name is also given to species of _Metrosideros_ (_Myrtaceae_) and _Diospyros_ (_Ebenaceae_).

West Indian iron-wood is the produce of _Colubrina reclinata_ (and _C. ferruginosa_ (_Rhamnaceae_), and of _Aegiphila martinicensis Verbenacae_). _Ixora_ (_Siderodendron_) _triflorum_ (_Rubiaceae_) is the _bois de fer_ of Martinique, and Zanthoxylum _Pterota_ (_Rutaceae_) is the iron-wood of Jamaica, while _Robinia Ponacoco_ (_Leguminosae_) is described as the iron-wood of Guiana. The iron-wood of India and Ceylon is the produce of _Mesua ferrea_ (_Guttiferae_). The iron-wood tree of Pegu and Arracan is _Xylia dolabriformis_ (_Leguminosae_), described as the most important timber-tree of Burma after teak, and known as _pyingado_. The endemic _bois de fer_ of Mauritius, once frequent in the primeval woods, but now becoming very scarce, is _Stadtmannia Sideroxylon_ (_Sapindaceae_), while _Cossignya pinnata_ is known as the _bois de fer de Judas_. In Australia species of _Acacia_, _Casuarina_, _Eucalyptus_, _Melaleuca_, _Myrtus_, and other genera are known more or less widely as iron-wood. Tasmanian iron-wood is the produce of _Notelaea ligustrina_ (_Oleaceae_), and is chiefly used for making ships' blocks. The iron-wood or lever-wood of North America is the timber of the American hop hornbeam, _Ostrya virginica_ (_Cupuliferae_). In Brazil _Apuleia ferrea_ and _Caesalpinia ferrea_ yield a kind of iron-wood, called, however, the _Pao ferro_ or false iron-wood.

IRON-WORK, as an ornament in medieval architecture, is chiefly confined to the hinges, &c., of doors and of church chests, &c. Specimens of Norman iron-work are very rare. Early English specimens are numerous and very elaborate. In some instances not only do the hinges become a mass of scroll work, but the surface of the doors is covered by similar ornaments. In both these periods the design evidently partakes of the feeling exhibited in the stone or wood carving. In the Decorated period the scroll work is more graceful, and, like the foliage of the time, more natural. As styles progressed, there was a greater desire that the framing of the doors should be richer, and the ledges were chamfered or raised, then panelled, and at last the doors became a mass of scroll panelling. This, of course, interfered with the design of the hinges, the ornamentation of which gradually became unusual. In almost all styles the smaller and less important doors had merely plain strap-hinges, terminating in a few bent scrolls, and latterly in _fleurs-de-lis_. Escutcheon and ring handles, and the other furniture, partook more or less of the character of the time. On the continent of Europe the knockers are very elaborate. At all periods doors have been ornamented with nails having projecting heads, sometimes square, sometimes polygonal, and sometimes ornamented with roses, &c. The iron work of windows is generally plain, and the ornament confined to simple _fleur-de-lis_ heads to the stanchions. For the iron-work of screens enclosing tombs and chapels see GRILLE; and generally see METAL-WORK.

IRONY (Gr. [Greek: eironeia], from [Greek: eiron], one who says less than he means, [Greek: eirein], to speak), a form of speech in which the real meaning is concealed or contradicted by the words used; it is particularly employed for the purpose of ridicule, mockery or contempt, frequently taking the form of sarcastic phrase. The word is frequently used figuratively, especially in such phrases as "the irony of fate," of an issue or result that seems to contradict the previous state or condition. The Greek word was particularly used of an under-statement in the nature of dissimulation. It is especially exemplified in the assumed ignorance which Socrates adopted as a method of dialectic, the "Socratic irony" (see SOCRATES). In tragedy, what is called "tragic irony" is a device for heightening the intensity of a dramatic situation. Its use is particularly characteristic of the drama of ancient Greece, owing to the familiarity of the spectators with the legends on which so many of the plays were based. In this form of irony the words and actions of the characters belie the real situation, which the spectators fully realize. It may take several forms; the character speaking may be conscious of the irony of his words while the rest of the actors may not, or he may be unconscious and the actors share the knowledge with the spectators, or the spectators may alone realize irony. The _Oedipus Tyrannus_ of Sophocles is the classic example of tragic irony at its fullest and finest.

IROQUOIS, or SIX NATIONS, a celebrated confederation of North American Indians. The name is that given them by the French. It is suggested that it was formed of two ceremonial words constantly used by the tribesmen, meaning "real adders," with the French addition of _ois_. The league was originally composed of five tribes or nations, viz. Mohawks, Oneidas, Onondagas, Senecas and Cayugas. The confederation probably took place towards the close of the 16th century and in 1722 the Tuscaroras were admitted, the league being then called that of "the Six Nations." At that time their total number was estimated at 11,650, including 2150 warriors. They were unquestionably the most powerful confederation of Indians on the continent. Their home was the central and western parts of New York state. In the American War of Independence they fought on the English side, and in the repeated battles their power was nearly destroyed. They are now to the number of 17,000 or more scattered about on various reservations in New York state, Oklahoma, Wisconsin and Canada. The _Iroquoian stock_, the larger group of kindred tribes, of which the five nations were the most powerful, had their early home in the St Lawrence region. Besides the five nations, the Neutral nation, Huron, Erie, Conestoga, Nottoway, Meherrin, Tuscarora and Cherokee were the most important tribes of the stock. The hostility of the Algonquian tribes seems to have been the cause of the southward migration of the Iroquoian peoples. In 1535 Jacques Cartier found an Iroquoian tribe in possession of the land upon which now stand Montreal and Quebec; but seventy years later it was in the hands of Algonquians.

See L. H. Morgan, _League of the Hodeno Swanee or Iroquois_
(Rochester, N.Y., 1854); _Handbook of American Indians_ (Washington,
1907). Also INDIANS, NORTH AMERICAN.

IRRAWADDY, or IRAWADI, the principal river in the province of Burma, traversing the centre of the country, and practically running throughout its entire course in British territory. It is formed by the confluence of the Mali and N'mai rivers (usually called Mali-kha and N'mai-kha, the _kha_ being the Kachin word for river) in 25 deg. 45' N. The N'mai is the eastern branch. The definite position of its source is still uncertain, and it seems to be made up of a number of considerable streams, all rising within a short distance of each other in about 28 deg. 30' N. It is shown on some maps as the Lu river of Tibet; but it is now quite certain that the Tibetan Lu river is the Salween, and that the N'mai has its source or sources near the southern boundary of Tibet, to the north-east or east of the source of the Mali. At the confluence the N'mai is larger than the Mali. The general width of its channel seems to be 350 or 400 yds. during this part of its course. In the rains this channel is filled up, but in the cold weather the average breadth is from 150 to 200 yds. The N'mai is practically unnavigable. The Mali is the western branch. Like the main river, it is called Nam Kiu by the Shans. It rises in the hills to the north of the Hkamti country, probably in about 28 deg. 30' N. Between Hkamti and the country comparatively close to the confluence little or nothing is known of it, but it seems to run in a narrow channel through continuous hills. The highest point on the Mali reached from the south by Major Hobday in 1891 was Ting Sa, a village a little off the river, in 26 deg. 15' N. About 1 m. above the confluence it is 150 yds. wide in January and 17 ft. deep, with a current of 3(3/4) m. an hour. Steam launches can only ascend from Myitkyina to the confluence in the height of the rains. Native boats ascend to Laikaw or Sawan 26 deg. 2' N., all the year around, but can get no farther at any season. From the confluence the river flows in a southerly direction as far as Bhamo, then turns west as far as the confluence of the Kaukkwe stream, a little above Katha, where it again turns in a southerly direction, and maintains this in its general course through Upper and Lower Burma, though it is somewhat tortuous immediately below Mandalay. Just below the confluence of the Mali and N'mai rivers the Irrawaddy is from 420 to 450 yds. wide and about 30 ft. deep in January at its deepest point. Here it flows between hills, and after passing the Manse and Mawkan rapids, reaches plain country and expands to nearly 500 yds. at Sakap. At Myitkyina it is split into two channels by Naungtalaw island, the western channel being 600 yds. wide and the eastern 200. The latter is quite dry in the hot season. At Kat-kyo, 5 or 6 m. below Myitkyina, the width is 1000 yds., and below this it varies from 600 yds. to 3/4 m. at different points. Three miles below Sinbo the third defile is entered by a channel not more than 50 yds. wide, and below this, throughout the defile, it is never wider than 250 yds., and averages about 100. At the "Gates of the Irrawaddy" at Poshaw two prism-shaped rocks narrow the river to 50 yds., and the water banks up in the middle with a whirlpool on each side of the raised pathway. All navigation ceases here in the floods. The defile ends at Hpatin, and below this the river widens out to a wet-season channel of 2 m., and a breadth in the dry season of about 1 m. At Sinkan, below Bhamo, the second defile begins. It is not so narrow nor is the current so strong as in the third defile. The narrowest place is more than 100 yds. wide. The hills are higher, but the defile is much shorter. At Shwegu the river leaves the hills and becomes a broad stream, flowing through a wide plain. The first defile is tame compared with the others. The river merely flows between low hills or high wooded banks. The banks are covered at this point with dense vegetation, and slope down to the water's edge. Here and there are places which are almost perpendicular, but are covered with forest growth. The course of the Irrawaddy after receiving the waters of the Myit-nge at Sagaing, as far as 17 deg. N. lat., is exceedingly tortuous; the line of Lower Burma is crossed in 19 deg. 29' 3" N. lat., 95 deg. 15' E. long., the breadth of the river here being 3/4 m.; about 11 m. lower down it is nearly 3 m. broad. At Akauk-taung, where a spur of the Arakan hills end in a precipice 300 ft. high, the river enters the delta, the hills giving place to low alluvial plains, now protected on the west by embankments. From 17 deg. N. lat. the Irrawaddy divides and subdivides, converting the lower portion of its valley into a network of intercommunicating tidal creeks. It reaches the sea in 15 deg. 50' N. lat. and 95 deg. 8' E. long., by nine principal mouths. The only ones used by sea-going ships are the Bassein and Rangoon mouths. The area of the catchment basin of the Irrawaddy is 158,000 sq. m.; its total length from its known source to the sea is about 1300 m. As far down as Akauk-taung in Henzada district its bed is rocky, but below this sandy and muddy. It is full of islands and sandbanks; its waters are extremely muddy, and the mud is carried far out to sea. The river commences to rise in March; about June it rises rapidly, and attains its maximum height about September. The total flood discharge is between four and five hundred million metre tons of 37 cub. ft. From Mandalay up to Bhamo the river is navigable a distance of nearly 1000 m. for large steamers all the year round; but small launches and steamers with weak engines are often unable to get up the second defile in the months of July, August and September, owing to the strong current. The Irrawaddy Flotilla Company's steamers go up and down twice a week all through the rains, and the mails are carried to Bhamo on intermediate days by a ferry-boat from the railway terminus at Katha. During the dry season the larger boats are always liable to run on sandbanks, more especially in November and December, when new channels are forming after the river has been in flood. From Bhamo up to Sinbo no steamers can ply during the rains, that is to say, usually from June to November. From November to June small steamers can pass through the third defile from Bhamo to Sinbo. Between Sinbo and Myitkyina small launches can run all the year round. Above Myitkyina small steamers can reach the confluence at the height of the flood with some difficulty, but when the water is lower they cannot pass the Mawkan rapid, just above Mawme, and the navigation of the river above Myitkyina is always difficult. The journey from Bhamo to Sinbo can be made during the rains in native boats, but it is always difficult and sometimes dangerous. It is never done in less than five days and often takes twelve or more. As a natural source of irrigation the value of the Irrawaddy is enormous, but the river supplies no artificial systems of irrigation. It is nowhere bridged, though crossed by two steam ferries to connect the railway system on either bank. (J. G. Sc.)

IRREDENTISTS, an Italian patriotic and political party, which was of importance in the last quarter of the 19th century. The name was formed from the words _Italia Irredenta_--Unredeemed Italy--and the party had for its avowed object the emancipation of all Italian lands still subject to foreign rule. The Irredentists took language as the test of the alleged Italian nationality of the countries they proposed to emancipate, which were South Tirol (Trentino), Gorz, Istria, Trieste, Tessino, Nice, Corsica and Malta. The test was applied in the most arbitrary manner, and in some cases was not applicable at all. Italian is not universally spoken in South Tirol, Gorz or Istria. Malta has a dialect of its own though Italian is used for literary and judicial purposes, while Dalmatia is thoroughly non-Italian though it was once under the political dominion of the ancient Republic of Venice. The party was of little note before 1878. In that year it sprang into prominence because the Italians were disappointed by the result of the conference at Berlin summoned to make a European settlement after the Russo-Turkish War of 1877. The Italians had hoped to share in the plunder of Turkey, but they gained nothing, while Austria was endowed with the protectorate of Bosnia, and the Herzegovina, the vitally important hinterland of her possessions on the Adriatic. Under the sting of this disappointment the cry of Italia Irredenta became for a time loud and apparently popular. It was in fact directed almost wholly against Austria, and was also used as a stalking-horse by discontented parties in Italian domestic politics--the Radicals, Republicans and Socialists. In addition to the overworked argument from language, the Irredentists made much of an unfounded claim that the Trentino had been conquered by Giuseppe Garibaldi during the war of 1866, and they insisted that the district was an "enclave" in Italian territory which would give Austria a dangerous advantage in a war of aggression. It would be equally easy and no less accurate to call the Trentino an exposed and weak spot of the frontier of Austria. On the 21st of July 1878 a noisy public meeting was held at Rome with Menotti Garibaldi, the son of the famous Giuseppe, in the chair, and a clamour was raised for the formation of volunteer battalions to conquer the Trentino. Signor Cairoli, then prime minister of Italy, treated the agitation with tolerance. It was, however, mainly superficial, for the mass of the Italians had no wish to launch on a dangerous policy of adventure against Austria, and still less to attack France for the sake of Nice and Corsica, or Great Britain for Malta. The only practical consequences of the Irredentist agitation outside of Italy were such things as the assassination plot organized against the emperor Francis Joseph in Trieste in 1882 by Oberdank, which was detected and punished. When the Irredentist movement became troublesome to Italy through the activity of Republicans and Socialists, it was subject to effective police control by Signor Depretis. It sank into insignificance when the French occupation of Tunis in 1881 offended the Italians deeply, and their government entered into those relations with Austria and Germany which took shape by the formation of the Triple Alliance. In its final stages it provided a way in which Italians who sympathized with French republicanism, and who disliked the monarchical governments of Central Europe, could agitate against their own government. It also manifested itself in periodical war scares based on affected fears of Austrian aggression in northern Italy. Within the dominions of Austria Irredentism has been one form of the complicated language question which has disturbed every portion of the Austro-Hungarian empire.

See Colonel von Haymerle, _Italicae res_ (Vienna, 1879) for the early
history of the Irredentists.

IRRIGATION (Lat. _in_, and _rigare_, to water or wet), the artificial application of water to land in order to promote vegetation; it is therefore the converse of "drainage" (q.v.), which is the artificial withdrawal of water from lands that are over-saturated. In both cases the object is to promote vegetation.

I. _General._--Where there is abundance of rainfall, and when it falls at the required season, there is in general no need for irrigation. But it often happens that, although there is sufficient rainfall to raise an inferior crop, there is not enough to raise a more valuable one.

Irrigation is an art that has been practised from very early times. Year after year fresh discoveries are made that carry back our knowledge of the early history of Egypt. It is certain that, until the cultivator availed himself of the natural overflow of the Nile to saturate the soil, Egypt must have been a desert, and it is a very small step from that to baling up the water from the river and pouring it over lands which the natural flood has not touched. The sculptures and paintings of ancient Egypt bear no trace of anything approaching scientific irrigation, but they often show the peasant baling up the water at least as early as 2000 B.C. By means of this simple plan of raising water and pouring it over the fields thousands of acres are watered every year in India, and the system has many advantages in the eyes of the peasant. Though there is great waste of labour, he can apply his labour when he likes; no permission is required from a government official; no one has to be bribed. The simplest and earliest form of water-raising machinery is the pole with a bucket suspended from one end of a crossbeam and a counterpoise at the other. In India this is known as the _denkli_ or _paecottah_; in Egypt it is called the _shaduf_. All along the Nile banks from morning to night may be seen brown-skinned peasants working these _shadufs_, tier above tier, so as to raise the water 15 or 16 ft. on to their lands. With a _shaduf_ it is only possible to keep about 4 acres watered, so that a great number of hands are required to irrigate a large surface. Another method largely used is the shallow basket or bucket suspended to strings between two men, who thus bail up the water. A step higher than these is the rude water-wheel, with earthen pots on an endless chain running round it, worked by one or two bullocks. This is used everywhere in Egypt, where it is known as the _sakya_. In Northern India it is termed the _harat_, or Persian wheel. With one such water-wheel a pair of oxen can raise water any height up to 18 ft., and keep from 5 to 12 acres irrigated throughout an Egyptian summer. A very familiar means in India of raising water from wells in places where the spring level is as much sometimes as 100 ft. below the surface of the field is the _churras_, or large leather bag, suspended to a rope passing over a pulley, and raised by a pair of bullocks which go up and down a slope as long as the depth of the well. All these primitive contrivances are still in full use throughout India.

It is not improbable that Assyria and Babylon, with their splendid rivers, the Euphrates and Tigris, may have taken the idea from the Nile, and that Carthage and Phoenicia as well as Greece and Italy may have followed the same example. In spite of a certain amount of investigation, the early history of irrigation in Persia and China remains imperfectly known. In Spain irrigation may be traced directly to the Moorish occupation, and almost everywhere throughout Asia and Africa where the Moslem penetrated is to be found some knowledge of irrigation.

Spain.

India.

Reservoirs are familiar everywhere for the water-supply of towns, but as the volume necessary, even for a large town, does not go far in irrigating land, many sites which would do admirably for the former would not contain water sufficient to be worth applying to the latter purpose. In the Mediterranean provinces of Spain there are some very remarkable irrigation dams. The great masonry dam of Alicante on the river Monegre, which dates from 1579, is situated in a narrow gorge, so that while 140 ft. high, it is only 190 ft. long at the crest. The reservoir is said to contain 130 million cub. ft. of water, and to serve for the irrigation of 9000 acres, but unless it refills several times a year, it is hardly possible that so much land can be watered in any one season. The Elche reservoir, in the same province, has a similar dam 55 ft. high. In neither case is there a waste-weir, the surplus water being allowed to pour over the crest of the dam. South of Elche is the province of Murcia, watered by the river Segura, on which there is a dam 25 ft. high, said to be 800 years old, and to serve for the irrigation of 25,000 acres. The Lorca dam in the same neighbourhood irrigates 27,000 acres. In the jungles of Ceylon are to be found remains of gigantic irrigation dams, and on the neighbouring mainland of Southern India, throughout the provinces of Madras and Mysore, the country is covered with irrigation reservoirs, or, as they are locally termed, tanks. These vary from village ponds to lakes 14 or 15 m. long. Most of them are of old native construction, but they have been greatly improved and enlarged within the last half century. The casual traveller in southern India constantly remarks the ruins of old dams, and the impression is conveyed that at one time, before British rule prevailed, the irrigation of the country was much more perfect than it is now. That idea, however, is mistaken. An irrigation reservoir, like a human being, has a certain life. Quicker or slower, the water that fills it will wash in sand and mud, and year by year this process will go on till ultimately the whole reservoir is filled up. The embankment is raised, and raised again, but at last it is better to abandon it and make a new tank elsewhere, for it would never pay to dig out the silt by manual labour. It may safely be said that at no time in history were there more tanks in operation than at present. The ruins which are seen are the ruins of long centuries of tanks that once flourished and became silted up. But they did not all flourish at once.

In the countries now being considered, the test of an irrigation work is how it serves in a season of drought and famine. It is evident that if there is a long cessation of rain, there can be none to fill the reservoirs. In September 1877 there were very few in all southern India that were not dry. But even so, they helped to shorten the famine period; they stored up the rain after it had ceased to fall, and they caught up and husbanded the first drops when it began again.

Irrigation canals.

Irrigation effected by river-fed canals naturally depends on the regimen of the rivers. Some rivers vary much in their discharge at different seasons. In some cases this variation is comparatively little. Sometimes the flood season recurs regularly at the same time of the year; sometimes it is uncertain. In some rivers the water is generally pure; in others it is highly charged with fertilizing alluvium, or, it may be, with barren silt. In countries nearly rainless, such as Egypt or Sind, there can be no cultivation without irrigation. Elsewhere the rainfall may be sufficient for ordinary crops, but not for the more valuable kinds. In ordinary years in southern India the maize and the millet, which form so large a portion of the peasants' food, can be raised without irrigation, but it is required for the more valuable rice or sugar-cane. Elsewhere in India the rainfall is usually sufficient for all the cultivation of the district, but about every eleven years comes a season of drought, during which canal water is so precious as to make it worth while to construct costly canals merely to serve as a protection against famine. When a river partakes of the nature of a torrent, dwindling to a paltry stream at one season and swelling into an enormous flood at another, it is impossible to construct a system of irrigation canals without very costly engineering works, sluices, dams, waste-weirs, &c., so as to give the engineer entire control of the water. Such may be seen on the canals of Cuttack, derived from the Mahanadi, a river of which the discharge does not exceed 400 cub. ft. per second in the dry season, and rises to 1,600,000 cub. ft. per second in the rainy season.

Very differently situated are the great canals of Lombardy, drawn from the Ticino and Adda rivers, flowing from the Maggiore and Como lakes. The severest drought never exhausts these reservoirs, and the heaviest rain can never convert these rivers into the resistless floods which they would be but for the moderating influence of the great lakes. The Ticino and Adda do not rise in floods more than 6 or 7 ft. above their ordinary level or fall in droughts more than 4 or 5 ft. below it, and their water is at all seasons very free from silt or mud. Irrigation cannot be practised in more favourable circumstances than these. The great lakes of Central Africa, Victoria and Albert Nyanza, and the vast swamp tract of the Sudan, do for the Nile on a gigantic scale what Lakes Maggiore and Como do for the rivers Ticino and Adda. But for these great reservoirs the Nile would decrease in summer to quite an insignificant stream. India possesses no great lakes from which to draw rivers and canals, but through the plains of northern India flow rivers which are fed from the glaciers of the Himalaya; and the Ganges, the Indus, and their tributaries are thus prevented from diminishing very much in volume. The greater the heat, the more rapidly melts the ice, and the larger the quantity of water available for irrigation. The canal system of northern India is the most perfect the world has yet seen, and contains works of hydraulic engineering which can be equalled in no other country. In the deltas of southern India irrigation is only practised during the monsoon season. The Godaveri, Kistna and Kaveri all take their rise on the Western Ghats, a region where the rainfall is never known to fail in the monsoon season. Across the apex of the deltas are built great weirs (that of the Godaveri being 2(1/2) m. long), at the ends and centre of which is a system of sluices feeding a network of canals. For this monsoon irrigation there is always abundance of water, and so long as the canals and sluices are kept in repair, there is little trouble in distributing it over the fields. Similar in character was the ancient irrigation of Egypt practised merely during the Nile flood--a system which still prevails in part of Upper Egypt. A detailed description of it will be found below.

Distribution of the water.

Where irrigation is carried on throughout the whole year, even when the supply of the river is at its lowest, the distribution of the water becomes a very delicate operation. It is generally considered sufficient in such cases if during any one crop one-third of the area that can be commanded is actually supplied with water. This encourages a rotation of crops and enables the precious liquid to be carried over a larger area than could be done otherwise. It becomes then the duty of the engineer in charge to use every effort to get its full value out of every cubic foot of water. Some crops of course require water much oftener than others, and much depends on the temperature at the time of irrigation. During the winter months in northern India magnificent wheat crops can be produced that have been watered only twice or thrice. But to keep sugar-cane, or indigo, or cotton alive in summer before the monsoon sets in in India or the Nile rises in Egypt the field should be watered every ten days or fortnight, while rice requires a constant supply of water passing over it.

Experience in these sub-tropical countries shows the absolute necessity of having, for successful irrigation, also a system of thorough drainage. It was some time before this was discovered in India, and the result has been the deterioration of much good land.

In Egypt, prior to the British occupation in 1883, no attempt had been made to take the water off the land. The first impression of a great alluvial plain is that it is absolutely flat, with no drainage at all. Closer examination, however, shows that if the prevailing slopes are not more than a few inches in the mile, yet they do exist, and scientific irrigation requires that the canals should be taken along the crests and drains along the hollows. In the diagram (fig. 1) is shown to the right of the river a system of canals branching out and afterwards rejoining one another so as to allow of no means for the water that passes off the field to escape into the sea. Hence it must either evaporate or sink into the soil. Now nearly all rivers contain some small percentage of salt, which forms a distinct ingredient in alluvial plains. The result of this drainless irrigation is an efflorescence of salt on the surface of the field. The spring level rises, so that water can be reached by digging only a few feet, and the land, soured and water-logged, relapses into barrenness. Of this description was the irrigation of Lower Egypt previous to 1883. To the left of the diagram is shown (by firm lines) a system of canals laid out scientifically, and of drains (by dotted lines) flowing between them. It is the effort of the British engineers in Egypt to remodel the surface of the fields to this type.

Further information may be found in Sir C. C. Scott-Moncrieff,
_Irrigation in Southern Europe_ (London, 1868); Moncrieff, "Lectures
on Irrigation in Egypt," _Professional Papers of the Corps of Royal
Engineers_, vol. xix. (London, 1893); W. Willcocks, _Egyptian
Irrigation_ (2nd ed., London, 1899).

II. _Water Meadows._--Nowhere in England can it be said that irrigation is necessary to ordinary agriculture, but it is occasionally employed in stimulating the growth of grass and meadow herbage in what are known as water-meadows. These are in some instances of very early origin. On the Avon in Wiltshire and the Churn in Gloucestershire they may be traced back to Roman times. This irrigation is not practised in the drought of summer, but in the coldest and wettest months of the year, the water employed being warmer than the natural moisture of the soil and proving a valuable protection against frost.

Before the systematic conversion of a tract into water-meadows can be safely determined on, care must be taken to have good drainage, natural or artificial, a sufficient supply of water, and water of good quality. It might indeed have been thought that thorough drainage would be unnecessary, but it must be noted that porous subsoils or efficient drains do not act merely by carrying away stagnant water which would otherwise cool the earth, incrust the surface, and retard plant growth. They cause the soil to perform the office of a filter. Thus the earth and the roots of grasses absorb the useful matters not only from the water that passes over it, but from that which passes through it. These fertilizing materials are found stored up in the soil ready for the use of the roots of the plants. Stagnation of water is inimical to the action of the roots, and does away with the advantageous processes of flowing and percolating currents. Some of the best water-meadows in England have but a thin soil resting on gravel and flints, this constituting a most effectual system of natural drainage. The fall of the water supply must suffice for a fairly rapid current, say 10 in. or 1 ft. in from 100 to 200 yds. If possible the water should be taken so far above the meadows as to have sufficient fall without damming up the river. If a dam be absolutely necessary, care must be taken so to build it as to secure the fields on both sides from possible inundation; and it should be constructed substantially, for the cost of repairing accidents to a weak dam is very serious.

Quantity of water.

Even were the objects of irrigation always identical, the conditions under which it is carried on are so variable as to preclude calculations of quantity. Mere making up of necessary water in droughty seasons is one thing, protection against frost is another, while the addition of soil material is a third. Amongst causes of variation in the quantity of water needed will be its quality and temperature and rate of flow, the climate, the season, the soil, the subsoil, the artificial drainage, the slope, the aspect and the crop. In actual practice the amount of water varies from 300 gallons per acre in the hour to no less than 28,000 gallons. Where water is used, as in dry and hot countries, simply as water, less is generally needed than in cold, damp and northerly climates, where the higher temperature and the action of the water as manure are of more consequence. But it is necessary to be thoroughly assured of a good supply of water before laying out a water-meadow. Except in a few places where unusual dryness of soil and climate indicate the employment of water, even in small quantity, merely to avoid the consequences of drought, irrigation works are not to be commenced upon a large area, if only a part can ever be efficiently watered. The engineer must not decide upon the plan till he has gauged at different seasons the stream which has to supply the water, and has ascertained the rain-collecting area available, and the rainfall of the district, as well as the proportion of storable to percolating and evaporating water. Reservoirs for storage, or for equalizing the flow, are rarely resorted to in England; but they are of absolute necessity in those countries in which it is just when there is least water that it is most wanted. It is by no means an injudicious plan before laying out a system of water-meadows, which is intended to be at all extensive, to prepare a small trial plot, to aid in determining a number of questions relating to the nature and quantity of the water, the porosity of the soil, &c.

Quality of water.

The quality of the water employed for any of the purposes of irrigation is of much importance. Its dissolved and its suspended matters must both be taken into account. Clear water is usually preferable for grass land, thick for arable land. If it is to be used for warping, or in any way for adding to the solid material of the irrigated land, then the nature and amount of the suspended material are necessarily of more importance than the character of the dissolved substances, provided the latter are not positively injurious. For use on ordinary water-meadows, however, not only is very clear water often found to be perfectly efficient, but water having no more than a few grains of dissolved matter per gallon answers the purposes in view satisfactorily. Water from moors and peat-bogs or from gravel or ferruginous sandstone is generally of small utility so far as plant food is concerned. River water, especially that which has received town sewage, or the drainage of highly manured land, would naturally be considered most suitable for irrigation, but excellent results are obtained also with waters which are uncontaminated with manurial matters, and which contain but 8 or 10 grains per gallon of the usual dissolved constituents of spring water. Experienced English irrigators generally commend as suitable for water-meadows those streams in which fish and waterweeds abound. But the particular plants present in or near the water-supply afford further indications of quality. Water-cress, sweet flag, flowering rush, several potamogetons, water milfoil, water ranunculus, and the reedy sweet watergrass (_Glyceria aquatica_) rank amongst the criteria of excellence. Less favourable signs are furnished by such plants as _Arundo Donax_ (in Germany), _Cicuta virosa_ and _Typha latifolia_, which are found in stagnant and torpid waters. Water when it has been used for irrigation generally becomes of less value for the same purpose. This occurs with clear water as well as with turbid, and obviously arises mainly from the loss of plant food which occurs when water filters through or trickles over poor soil. By passing over or through rich soil the water may, however, actually be enriched, just as clear water passed through a charcoal filter which has been long used becomes impure. It has been contended that irrigation water suffers no change in composition by use, since by evaporation of a part of the pure water the dissolved matters in the remainder would be so increased as to make up for any matters removed. But it is forgotten that both the plant and the soil enjoy special powers of selective absorption, which remove and fix the better constituents of the water and leave the less valuable.

Seeds for water-meadows.

Of the few leguminous plants which are in any degree suitable for water-meadows, _Lotus corniculatus major_, _Trifolium hybridum_, and _T. pratense_ are those which generally flourish best; _T. repens_ is less successful. Amongst grasses the highest place must be assigned to ryegrass, especially to the Italian variety, commonly called _Lolium italicum_. The mixture of seeds for sowing a water-meadow demands much consideration, and must be modified according to local circumstances of soil, aspect, climate and drainage. From the peculiar use which is made of the produce of an irrigated meadow, and from the conditions to which it is subjected, it is necessary to include in our mixture of seeds some that produce an early crop, some that give an abundant growth, and some that impart sweetness and good flavour, while all the kinds sown must be capable of flourishing on irrigated soil.

The following mixtures of seeds (stated in pounds per acre) have been recommended for sowing on water-meadows, Messrs Sutton of Reading, after considerable experience, regarding No. I. as the more suitable:

I. II.| I. II.
|
_Lolium perenne_ 8 12 | _Festuca pratensis_ 0 2
_Lolium italicum_ 0 8 | _Festuca loliacea_ 3 2
_Poa trivialis_ 6 3 | _Anthoxanthum odoratum_ 0 1
_Glyceria fluitans_ 6 2 | _Phleum pratense_ 4 2
_Glyceria aquatica_ 4 1 | _Phalaris arundinacea_ 3 2
_Agrostis alba_ 0 1 | _Lotus corniculatus major_ 3 2
_Agrostis stolonifera_ 6 2 | _Trifolium hybridum_ 0 1
_Alopecurus pratensis_ 0 2 | _Trifolium pratense_ 0 1
_Festuca elatior_ 3 2 |

Changes in irrigated herbage.

In irrigated meadows, though in a less degree than on sewaged land, the reduction of the amount or even the actual suppression of certain species of plants is occasionally well marked. Sometimes this action is exerted upon the finer grasses, but happily also upon some of the less profitable constituents of the miscellaneous herbage. Thus _Ranunculus bulbosus_ has been observed to become quite rare after a few years' watering of a meadow in which it had been most abundant, _R. acris_ rather increasing by the same treatment; _Plantago media_ was extinguished and _P. lanceolata_ reduced 70%. Amongst the grasses which may be spared, _Aira caespitosa_, _Briza media_ and _Cynosurus cristatus_ are generally much reduced by irrigation. Useful grasses which are increased are _Lolium perenne_ and _Alopecurus pratensis_, and among those of less value _Avena favescens_, _Dactylis glomerata_ and _Poa pratensis_.

Methods.

Four ways of irrigating land with water are practised in England: (1) bedwork irrigation, which is the most efficient although it is also the most costly method by which currents of water can be applied to level land; (2) catchwork irrigation, in which the same water is caught and used repeatedly; (3) subterraneous or rather upward irrigation, in which the water in the drains is sent upwards through the soil towards the surface; and (4) warping, in which the water is allowed to stand over a level field until it has deposited the mud suspended in it.

There are two things to be attended to most carefully in the construction of a water-meadow on the first or second of these plans. First, no portion of them whatever should be on a dead level, but every part should belong to one or other of a series of true inclined planes. The second point of primary importance is the size and slope of the main conductor, which brings the water from the river to the meadow. The size of this depends upon the quantity of water required, but whatever its size its bottom at its origin should be as low as the bed of the river, in order that it may carry down as much as possible of the river mud. Its course should be as straight and as near a true inclined plane as possible. The stuff taken out of the conductor should be employed in making up its banks or correcting inequalities in the meadow.

Bedwork.

In bedwork irrigation, which is eminently applicable to level ground,
the ground is thrown into beds or ridges. Here the conductor should be
led along the highest end or side of the meadow in an inclined plane;
should it terminate in the meadow, its end should be made to taper
when there are no feeders, or to terminate in a feeder. The main drain
to carry off the water from the meadow should next be formed. It
should be cut in the lowest part of the ground at the lower end or
side of the meadow. Its dimensions should be capable of carrying off
the whole water used so quickly as to prevent the least stagnation,
and discharge it into the river. The next process is the forming of
the ground intended for a water-meadow into beds or ridges. That
portion of the ground which is to be watered by one conductor should
be made into beds to suit the circumstances of that conductor; that
is, instead of the beds over the meadow being all reduced to one
common level, they should be formed to suit the different swells in
the ground, and, should any of these swells be considerable, it will
be necessary to give each side of them its respective conductor. The
beds should run at or nearly at right angles to the line of the
conductor. The breadth of the beds is regulated by the nature of the
soil and the supply of water. Tenacious soils and subsoils, with a
small supply of water, require beds as narrow as 30 ft. Porous soils
and a large supply of water may have beds of 40 ft. The length of the
beds is regulated by the supply of water and the fall from the
conductor to the main drain. If the beds fall only in one direction
longitudinally, their crowns should be made in the middle; but, should
they fall laterally as well as longitudinally, as is usually the case,
then the crowns should be made towards the upper sides, more or less
according to the lateral slope of the ground. The crowns should rise 1
ft. above the adjoining furrows. The beds thus formed should slope in
an inclined plane from the conductor to the main drain, that the water
may flow equably over them.

The beds are watered by "feeders," that is, channels gradually
tapering to the lower extremities, and their crowns cut down, wherever
these are placed. The depth of the feeders depends on their width, and
the width on their length. A bed 200 yds. in length requires a feeder
of 20 in. in width at its junction with the conductor, and it should
taper gradually to the extremity, which should be 1 ft. in width. The
taper retards the motion of the water, which constantly decreases by
overflow as it proceeds, whilst it continues to fill the feeder to the
brim. The water overflowing from the feeders down the sides of the
beds is received into small drains formed in the furrows between the
beds. These small drains discharge themselves into the main drain, and
are in every respect the reverse of the feeders. The depth of the
small drain at the junction is made about as great as that of the main
drain, and it gradually lessens towards the taper to 6 in. in
tenacious and to less in porous soils. The depth of the feeders is the
same in relation to the conductor. For the more equal distribution of
the water over the surface of the beds from the conductor and feeders,
small masses, such as stones or solid portions of earth or turf
fastened with pins, are placed in them, in order to retard the
momentum which the water may have acquired. These "stops," as they are
termed, are generally placed at regular intervals, or rather they
should be left where any inequality of the current is observed. Heaps
of stones answer very well for stops in the conductor, particularly
immediately below the points of junction with the feeders. The small
or main drains require no stops. The descent of the water in the
feeders will no doubt necessarily increase in rapidity, but the
inclination of the beds and the tapering of the feeders should be so
adjusted as to counteract the increasing rapidity. The distribution of
the water over the whole meadow is regulated by the sluices, which
should be placed at the origin of every conductor. By means of these
sluices any portion of the meadow that is desired can be watered,
whilst the rest remains dry; and alternate watering must be adopted
when there is a scarcity of water. All the sluices should be
substantially built at first with stones and mortar, to prevent the
leakage of water; for, should water from a leak be permitted to find
its way into the meadow, that portion of it will stagnate and produce
coarse grasses. In a well-formed water-meadow it is as necessary to
keep it perfectly dry at one time as it is to place it under water at
another. A small sluice placed in the side of the conductor opposite
to the meadow, and at the upper end of it, will drain away the leakage
that may have escaped from the head sluice.

To obtain a complete water-meadow, the ground will often require to be
broken up and remodelled. This will no doubt be attended with cost;
but it should be considered that the first cost is the least, and
remodelling the only way of having a complete water-meadow which will
continue for years to give satisfaction. To effect a remodelling when
the ground is in stubble, let it be ploughed up, harrowed, and cleaned
as in a summer fallow, the levelling-box employed when required, the
stuff from the conductors and main drains spread abroad, and the beds
ploughed into shape--all operations that can be performed at little
expense. The meadow should be ready by August for sowing with one of
the mixtures of grass-seeds already given. But though this plan is
ultimately better, it is attended with the one great disadvantage that
the soft ground cannot be irrigated for two or three years after it is
sown with grass-seeds. This can only be avoided where the ground is
covered with old turf which will bear to be lifted. On ground in that
state a water-meadow may be most perfectly formed. Let the turf be
taken off with the spade, and laid carefully aside for relaying. Let
the stript ground then be neatly formed with the spade and barrow,
into beds varying in breadth and shape according to the nature of the
soil and the dip of the ground--the feeders from the conductor and the
small drains to the main drain being formed at the same time. Then let
the turf be laid down again and beaten firm, when the meadow will be
complete at once, and ready for irrigation. This is the most beautiful
and most expeditious method of making a complete water-meadow where
the ground is not naturally sufficiently level to begin with.