It is worthy our notice, that although the Italian aqueducts have, to our cer tain knowledge, been duly supported for upwards of eight centuries, by a race of people far beneath us in the more noble sciences, in wealth, in population, and in many other circumstances in which we pride ourselves ; yet that Bri tain cannot boast of one aqueduct, made exclusively with the important view to improve her agriculture ; though it would be as easy to spew a thousand situa tions where such canals would double the value of the lands adjoining, as it would be to prove that such value would be doubled.
It is, indeed, only in a few counties, that irrigation is carried on to any ex tent ; though we may in various places see partial adoptions of this most benefi cial practice : yet we daily observe situa tions naturally offering this advantage, without the smallest attempt being made to retain streams which, from elevated situations, glide with some velocity tbrough deep vallies, whose very borders, perhaps, are verdant, but whose more retired parts would be doubled or trebled in value, by the influence of that element, which is allowed to pass by unheeded, to be lost in some marsh, or eventually in the ocean ! It is true, that, in some parts, irrigation is not understood ; and, that it is not always practicable to ob tain proper assistance ; whence many, who would willingly water their mea dows, are prevented from taking advan tage of streams capable of effecting the intention. For the benefit of such per sons, in particular, as well as of our rea ders in general, we shall endeavour to simplify, even this simple process, in such a manner as may prove perfectly intelli gible; and, by showing with what ease irrigation may be carried on, induce a portion of our landholders to attempt, even without professional aid, or the tui tion of experienced persons, that reten tion and gradual distribution of waters, whose sources are sufficiently elevated, which may favour such a slight and temporary inundation, as may give vigour and freshness both to the soil and to its produce.
We shall divide this subject into two distinct heads, viz. simple and compound irrigation ; observing that the former may be practical in various modes separately, as will be shown, and that they may be blended so as to come under the second term. We shall also, by way of prepara tion, give the reader an insight into some modes of cutting off; or of supplying wa ter, from sources of different heights, and under different circumstances : by this means, with a moderate portion of judgment, the novice in this art may speedily acquire sufficient of the princi ples to answer his own purposes, at least, if not to form a correct opinion of most of the cases which may come under his ob servation.
The greatest difficulty we generally ex: perience is, from the water lying below the level of the lands over which it is to be conducted. In many instances, the springs whence streams are fed, lie very deep ; and, though copious, for want of a sufficient inclination of their beds, move very slowly. In other parts, jealousy of improvement, personal enmity, the owner being a minor, or insane, and the pro perty in the hands of trustees, or the es tate being in Chancery, mortgaged, &c.
perhaps debars the possibility of taking advantage of some peculiarly favourable fall, front which the water might be conducted with perfect facility and ef fect, over inclined planes, which, by their sterility, seem to reproach the owner with neglect ! In treating this subject, we must sup pose the speculator to be a free agent, not shackled by such an unhappy neigh bourhood; and content ourselves with cautioning him not to injure the property of others, such as mills, bleachinggrounds below the lands, &c. &c., by drawing off that water on which their very existence depends : a want of attention to this par ticular, has ruined many a deserving and enterprising individual, and converted a blessing into a serious mischief! Where the stream is rapid, the bed has usually a very marked declivity, such as admits of throwing the water over the lands, and of withdrawing them when they have flowed, in every part, to a suf ficient height. The first step towards this, is to hold it up by means of a dam or weir, laid across the stream, (if its breadth admit, and that it be not naviga ble), so that, in the first place, the level may be raised as circumstances may ad mit. In this, it will be necessary to guard against injury to the property of other persons above the dam ; for the raising a head of water, by means of a dam, might subject lands, which before were perfectly dry, to be inundated ; and, even though such should actually prove beneficial thereto, the owners might re cover in a court of law, under various pleas of damage.
The water should, if practicable, be raised to one foot, at least, above the level of the highest land to be irrigated; because that depth may be then kept as a surplus, in case' of long-continued drought; being let in upon the first drain by a very small penstock, made only to the depth of the first level. The water, when abundant, may flow both into the upper level, and over the weir, so as to make a fall. When the water is not wanted over the laud, the penstock may be shut up altogether. It is to be re marked, that authors of eminence in this branch differ in opinion, though some suppose water to be more richly impreg nated with vegetable sustenance, in pro portion as it is taken nearer to the spring; provided the water be clear. The lands over which it is made to flow, will be benefited in exact proportion as they may be near to the first level, which will al ways receive the most obvious benefit. In foul streams, the result is usually found to be in an inverse ratio ; the water being richer, in proportion as it is more remote from its source, but the first level will still receive the greatest portion of the benefit. 'Where rivers are very mud dy, and of any magnitude, it is common to allow their flowing, to the depth of many feet, over low lands ; so that, when kept stationary for a few hours, the fecula and sediment may be deposited ; as is often the case, to the depth of many inches during a single tide ; and give a new stratum of the finest soil. See