I R O 



.-3 1 1 



I R R 



Iron 

 I rri (ration 



PLATE 



CCCXI,. 

 Fig. 81. 



Irrigation 

 partly na- 

 tural and 

 partly arti 

 licial. 



Advan- 

 tages, how 

 illustrated. 



rxpels the oxide more than is effected by the rollers. 

 In joiiii' \v,.rl;s. the lull-, fir-t drawn from the puddling 

 , furnace, are first subjected to the stamping hammer, as 

 in the old method,thc stampings beingafterwards heated 

 in n reverberntorv furnace- in piles or pyes, and passed 

 through the rollers a* in the first rolling above described. 



The second pair of rollers are different merely in the 

 form of the paten. The angular gates are for rolling 

 square bars. Tlfe bar is turned .1 quarter round every 

 time it. passes through a gate, in order to reverse the 

 position of the angles. An I it passes through the hit 

 gate a second time, reversed, to take away the rhom- 

 boid:d form of the bar which the first time through 

 gives to it. The first rollers, which the balls are pass- 

 ed through, are generally confined to that part only, 

 having no other gates than what are required to form 

 the bars, which arc afterwards broken up to form the 

 bundles for the second rolling. , 



When the iron is intended to be rolled into sheets, 

 it is first formed into li it bars, and these are cut by 

 large shears into lengths suitable to the breadths of the 

 intended sheets. These pieces are transversely passed 

 through plain rollers, differing from those described in 

 nothing but the gates or grooves for the bars. Fig. 21. 

 is an end-view of the rollers, shewing the iron shelf on 

 which the heated masses are laid before they pass 

 through, and a similar one on the other side to receive 

 the same, a a, are nuts working on screws to regulate 

 the distance of the rollers from each other. 



For the particular combination of iron with carbon, 

 called steel, see STEEL. For its chemical properties and 

 respective combinations, see CHEMISTRY, (c. s.) 



IROQUOIS. See CANADA, Vol. V. p. 312. 



IRREGULAR DOUZEAVES, in music, are all such 

 tempered systems of twelve notes in the octave, as have 

 more than two magnitudes of fifths in their scale, whose 

 single resulting, bearing, or wolf fifth, does not fall be- 

 tween $G and bE, which is the proper place of the 

 wolf in REOULAR Dm/zcaves, which see. (g) 



IRREGULAR Intervals are such, whose expression 

 in FAREY'S Notation (see that Article) has one or more 

 of its terms 2, f, or m, larger or smaller than the regu- 

 lar and progressive increase of them, which obtains 

 throughout an arranged table of regular intervals, ex- 

 pressed in this notation. (5) 



IRRIGATION. The improving of land by means 

 of water, is an object of importance throughout the 

 greater part of the globe. In various countries it is ef- 

 fected by nature on the great scale, occasionally or par- 

 tially modified by human skill and labour. In others, 

 nature applies this powerful mean of improvement in 

 efforts more detached and confined. In some parts, ir- 

 rigation, as a mode of improvement, is effected princi- 

 pally by the agency of man ; and in all cases, this 

 agency, skilfully applied, is more or less useful. 



A just view of the fatal effects produced by destruc- 

 tive floods, compared with those which are the result of 

 judicious irrigation, and of that sterility which is occa- 

 sioned by excess or by want of water, compared with 

 the fertile produce of lands properly irrigated, would 

 set in a proper light the advantages resulting from this 

 natural mode of improvement, by which water is turn- 

 ed to use, instead of being left to run to waste and ruin. 



According to circumstances, it may be employed for 

 meliorating soils of different characters, and for in- 

 creasing the produce in many variegated forms in 

 most of the populous districts of the globe. The tro- 

 pical rivers convey to the plains over which they flow, 

 those annual and immense supplies of enriching depo- 



sit, which nourish the corn that sustains a coiv-i,'.. 

 proportion of the population*, or they teiul tui'orni and 

 to enrich those vast savannahs, which occur in th. 

 tensive portion of the earth. In the warm but more 

 temperate climates, there are considerable tracts of soil, 

 which, if not irrigated, are almost wholly barren ; and 

 water is also employed there, for the purpose of enrich, 

 ing soils already fertile. It is a chenp and poverful 

 manure f<T various crops of great value to man ; and 

 the use of it is extended, according to the views and 

 circumstances of the husbandman, into the vineyard, 

 the corn field, the garden, the orchard, or the meadoW. 



Instructed by nature, and improved by experience 

 in the use of this element for meliorating this soil, man- 

 kind has already felt that it is of great value and im- 

 portance from the equator nearly to the 60th degree of 

 north latitude, and from the same extending on a more 

 limited scale partly into the southern temperate zone ! 

 The periodical rains within the tropics could not be 

 sufficient in that burning climate, for nourishing the 

 crops necessary to support the people, if nature itself 

 had not employed them, and if art and labour were not 

 also employed in fertilizing vast tracts of soil. Even in 

 the milder climates of Italy and France, immense ad- 

 vantages are derived from the judicious application of 

 this mode of improvement ; and, though it may appear 

 paradoxical, it is perhaps more productive still in the 

 climate of England, notwithstanding its high northern 

 latitude, and the moisture of its climate. 



The truth is, that irrigation, when conducted on the 

 right plan, is generally either preceded or accompanied 

 by draining, embanking, or both ; and that it has there- 

 fore a tendency at one time to improve the soil and 

 the climate also, while the element of water, instead 

 of being destructive, is directed to purposes the most 

 useful to mankind. 



It is chiefly in this view, that a proper general idea 

 maybe formed of irrigation. The advantages of this 

 mode of improvement are greatest in populous districts, 

 where the produce of land is of superior value, and the 

 labour necessarily bestowed on it may be- had at an in- 

 ferior price; but in all situations water is valuable, 

 when it can be safely directed to enrich the soil, and to 

 improve and augment the produce. Every one admires 

 that beautiful arrangement of nature, under which pu- 

 trescent substances, instead of being useless or noxi- 

 ous, become valuable, by affording new supplies of nu- 

 triment for living vegetables, and of course for animals ; 

 but water either is, or may become one of the most va- 

 luable means known for improving the soil in every 

 climate, excepting that where the cold is long continu- 

 ed and severe. 



Though much has been done in many parts of the 

 globe, in order to attain the proper advantages to be 

 derived from irrigation, it is probable'that few of these 

 in proportion have yet been secured. The rains which 

 inundate the Nile, the Ganges, and other great rivers, 

 do not convey the full benefits to the rich plains which 

 they fertilize, unless by embankments the management 

 and distribution of the water be secured, and the cul- 

 ture of the soil duly attended to. The deadly swamp, 

 which is occasioned by water permitted to go to w;i-te 

 by stagnation, may be converted in many instances, 

 by industry and skill, into fertile soil. Even the most 

 barren mossy flats have often been converted into mea- 

 dows by natural irrigation. But in how many instan- 

 ces is this neglected, where it might by art and labour 

 be done ? England furnishes the most alluring speci- 

 mens of what is possible artificially, by means of wa- 



Irrigation. 



In very dif- 

 ferent lati- 

 tudes und 



climates. 



Ought to b 

 connected 

 with drain- 

 ing and em- 

 bunking. 



lii wliat cir- 

 cumstances 

 I'in.-t pro- 

 iUable. 



Much re- 

 mains to be 

 done in this 

 art. 



