was attributed to the charcoal, it was admitted that this effect required a very frequent washing, drying, and renewal of it. Souchon's process, which is most extensively used, consists in passing the water through layers of woollen tissue, formed of clippings of wool laid on the frames which form the bottom of the filter. The water filters through five of these layers, of which the two lowest are the thickest, and are changed at intervals of about five days. The upper layers are changed twice or thrice a day. The water thus filtered is stated to have been inferior to the other, but the quantity passed through was greater, being as 162 to 110.

SECTION II.

Upper and Lower Districts.-River-watered and Sea-coast Districts.— Reclamation of Land.—Modes of Draining, Pumping, &c.—Water-wheel as applied for Draining and supplying Upland Districts.

53. The principal division of districts and lands, as subjects for watering and draining, is derived from their relative levels. The sources at command and methods of proceeding for high and low tracts are perfectly dissimilar, and hence the natural and necessary distinction which is adopted as the head of this section. And as the plains and valleys are far more extensive in themselves than the hill tops and uplands, and equally superior in importance as recipients of the drainer's care, it is proper to turn our attention to them in the first instance.

54. In this first class, the Lower Districts, we propose to include the following varieties of surface, viz. :— 1st, the low lands forming the margins of seas and rivers; and, 2nd, generally, the valleys in which natural watercourses have been formed, such as rivers, streams, &c.; 3rd, valleys in which lakes, or similar expanses of

water, do or might exist, and which, with that adaptation, have a continuously curved or basin-like contour; 4th, and plains which, although they may have a superior elevation to adjacent districts on one side, are correspondingly low in relation to the hills on the other. The sections sketched in the foreground of the Figs. Nos. 9 to 12 will illustrate the relationship of levels referred to in each of these four varieties.

55. The watering and drainage of districts belonging to the first of these varieties (Fig. 9) are frequently reduced to the sufficiently heavy task of getting rid of a large

surplus of water which collects from the adjacent estuaries of large streams, or is detained in the form of evaporation from the surface of the sea, and condensed by low temperature. If the level of the district is above that of the sea and river-mouths, surface drainage, of properly determined depth and extent, with ample main conducting channels, will suffice to keep the land in a tolerably dry condition. An opportunity very seldom exists in such districts for tapping, or getting rid of the excess by opening a communication with a lower and permeable stratum. Rock in some cases, and bog in others, usually form the inferior deposits. If the former, surface draining is certain of success, although the construction will probably be expensive; but if the substratum be bog, and its bed below the river or sea level, boring to lower strata is presented as the only chance of success.

56. If, however, the level of the district be below that of the contiguous waters, it will be manifestly impossible to dry the land without embanking. And it will be necessary either that this work be sufficiently substantial to prevent the ingress of the water, or that the surface of the land be simultaneously raised artificially until it has a superior level, or that mechanical means be constantly employed to pump out the surplus water. Our own island has been preserved in its borders, nay extended, by works of this class, which we shall now have to notice.

57. In pursuing this branch of our subject, we have the great gratification, through the kindness of Mr. Weale, of referring to one of the earliest and most interesting records of engineering art in this countrythe celebrated account of the Fens, by Sir William Dugdale, the earliest edition of which was published in

the year 1652, and the second edition, in folio, which we have consulted, in the year 1772, under the care of Charles Nelson Cole, Register to the Corporation of Bedford Level. Dugdale had been in the employment of the Corporation since the year 1643, and "published this History of Imbanking and Draining, at the request of Lord Gorges, who at that time had the principal direction of their works, and was, after their incorporation, for many years their Surveyor-General." The first sixteen pages of Sir William's book are occupied in brief notices of foreign works of this kind, beginning with Egypt, and thence passing to Babylon, Greece, and Rome, quoting his authorities from Herodotus, Strabo, Pliny, and others, and ending with Holland and the Netherlands. We cannot forego one short extract in reference to the troublesome Tiber, whose later tricks, we all remember, plunged so many of the poor Romans in ruin. Our quotation shows that, even in the time of Tiberius, public improvements were scandalously thwarted, as they are in our own day, by the petty jealousies of cities and corporations. "To restrain the exorbitant overflowing of this stream (the river Tiber), which was not a little choaked with dung and several old buildings that had fallen into it, I find that Augustus Cæsar bestowed some cost in the clearing and scouring of it; and that after this, through abundance of rain, the low grounds about the city, suffering much by great inundations thereof, the remedy in preventing the like for the future was, by the emperor Tiberius, committed to the care of Ateius Capito and L. Aruntius. Whereupon it was by them discussed in the senate, whether, for the moderating the floods of this river, the streams and lakes, whereby it increased, should be turned another way; but to that proposal there were