APPENDIX. 497 



ing. That extensive draining in the counties of Northampton, Huntingdon, 

 Cambridge, Lincoln, Norfolk, and Suffolk, which is known by the name of the 

 Bedford Level, was confided to the management of a chartered corporation, 

 with considerable powers, as early as the middle of the seventeenth century, 

 and by this means an immense extent of land has been rendered highly pro- 

 ductive, which before was nothing but one continued marsh or fen. 



In the valleys of the Jura, in the canton of Neufchatel in Switzerland, which 

 are noted for their industry and prosperity, and where the manufacture of 

 watches is so extensive as to supply a great part of Europe with this useful 

 article, extensive lakes and marshes have been completely laid dry, by making 

 a tunnel through the solid rock, and forming an outlet for the waters. All these 

 operations require the science and experience of civil engineers, and cannot be 

 undertaken without great means. The greater part of the lowlands in the 

 Netherlands, especially in the province of Holland, have been reclaimed from 

 the sea, or the rivers which flowed over them, by embanking and draining, and 

 are only kept from floods by a constant attention to the works originally erected. 



Where the land is below the level of the sea at high water, and without the 

 smallest eminence, it requires a constant removal of the water which perco- 

 lates through the banks or accumulates by rains; and this can only be effected 

 by sluices and mills, as is the case in the fens in England. The water is col- 

 lected in numerous ditches and canals, and led to the points where it can most 

 conveniently be discharged over the banks. The mills commonly erected for 

 this purpose are small windmills, which turn a kind of perpetual screw made 

 of wood several feet in diameter, on a solid axle. This screw fits a semicir- 

 cular trough which lies inclined at an angle of about 30 with the horizon. 

 The lower part dips into the water below, and by its revolution discharges the 

 water into a reservoir above. All the friction of pumps and the consequent 

 wearing out of the machinery is thus avoided. If the mills are properly con- 

 structed, they require little attendance, and work night and day whenever the 

 wind blows. 



In hilly countries it sometimes happens that the waters, which run down the 

 slopes 01 the hills collect in the bottoms where there is r.) outlet, and where 

 the soil is impervious. In that case it may sometimes be laid dry by cutting a 

 sufficient channel all round, to intercept the waters as they How down and to 

 carry them over or through the lowest part of the surrounding barrier. If there 

 are no very abundant springs in the bottom, a few ditches and ponds will suf- 

 fice to dry the soil by evaporation from their surface. We shall see that this 

 principle may be applied with great advantage in many cases where the water 

 could not be drained out of considerable hollows if it were allowed to run into 

 them. 



When there are different levels at which the water is pent up, the draining 

 should always be begun at the highest; because it may happen that when this 

 is laiil dry, the lower may not have a great excess of water. At all events, if 

 the water is to be raised by mechanical power, there is a saving in raising it 

 from the highest level, instead of letting it run down to a lower from which it 

 has to be raised so much higher. 



In draining av?reat extent of land it is often necessary to widen and deepen 

 rivers and alter their course; and not unfrequently the water cannot be let off 

 without being carried by means of tunnels under the bed of some river, the 

 level of which is above that of the land. In more confined operations cast-iron 

 pipes are often a cheap and easy means of effecting this. They may be bent 

 in a curve so as not to impede the course of the river or the navigation of a 

 canal. 



The draining of land which is rendered wet by springs arising from under 

 the soil is a branch of more general application. The principles on which the 

 operations are carried on apply as well to a small field as to the greatest extent 

 of land. The object is to find the readiest channels by which the superfluous 

 water may be carried off; and for this purpose an accurate knowledge of the 

 strata through which the springs rise is indispensable. It would be useless 

 labour merely to Jet the water run into drains after it has sprung through the 

 soil and appears at the surface, as ignorant men frequently attempt to do, and 

 thus carry it off after it has already soaked the soil. But the origin of the 



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