452 Mr. Downing on the Drainage of Haarlem Lake. 



inc waters. These districts have been placed under regular administrations, 

 whose rights and privileges have been guaranteed by the head of the State, and 

 have always been respected through every change and revolution, and notwith- 

 standing all the other divisions and subdivisions of the country, whether fiscal or 

 judicial. Their principal duty always has been to make and maintain the means 

 of defence against an invasion of the surrounding waters, whether from the sea, 

 the rivers, or conterminous administrations. All these waters, of whatever kind, 

 which threaten the boundary dyke, are denominated the external waters. But 

 within this bounding dyke are also found extensive areas of water, arising 

 either from rain or snow, or infiltration from surrounding waters, or from natural 

 springs ; which last are, however, but rare. These interior waters, although 

 in part carried off by evaporation, would, nevertheless, rise too high within the 

 dyke (and become as injurious as the external waters) if they could not flow 

 off whenever circumstances may lower the surface of the latter. Every boundary 

 dyke has, therefore, one or more self-acting sluices, which permit the discharge 

 outwards, but close whenever the external waters are higher than the internal. 

 Other communications are also opened through the boundary dyke, for the 

 purposes of navigation and irrigation. 



The Administration for Hydraulic Works of the Eynland, as containing the 

 Lake of Haarlem, of which we are treating, will best illustrate the nature of 

 this territorial division. Its artificial boundary is shown by a dotted line upon 

 the Map, Fig. 1, Plate X. It discharges its waters at three points: — 1. On 

 the north, at Sparndam and Halfwege (that is halfway between Haarlem and 

 Amsterdam), into the River Y, and so into the Zuyder Zee. 2. On the south 

 into the German Ocean, at Katwyck sluices. 3. Into the Eiver Yssel at Gouda ; 

 in all, eleven sluices, having a total breadth of about 280 feet. 



Within the bounds of every Hydraulic Administration are found three great 

 divisions of the surface, technically named the natural lands, the basin., and 

 the polders. The Natceal Lands are those which, as being above the 

 surface of the internal waters, permit the rain to flow naturally oS" their sur- 

 face. The Basin consists of the surface of all the internal waters what- 

 ever, marshes, lakes, canals, and drains, — all having one surface level, and in 

 free communication ; the level of the surface of the basin is in general a little 

 lower than that which the waters would have in summer, if the boundary dyke 



