The Dikes of Holland 



22 



charge the surplus water into the sea at 

 times of low tide, while at times of high 

 tide they are closed by means of locks. 

 Even after the lake had been drained 

 the same system was preserved, only 

 less windmills being required to keep 

 the lake bottom dry. In general, anj'^ 

 section of land artificially drained, and 

 known in the Dutch language as a 

 ' ' polder, ' ' has a ' ' bosom ' ' surrounding 

 it, into which is delivered b}' the wind- 

 mills all the water that collects in the 

 polder. The polder, for this reason, is 

 intersected bj^ a network of ditches, care- 

 fully spaced and graded in such a man- 

 ner as to drain the surplus moisture from 

 the soil and conduct it to the windmills. 

 The amount of ditching required to ac- 



complish this as a rule covers an area 

 equivalent to one-twelfth of the total 

 area to be drained. Thus the Holland- 

 ers not only keep their polders dry, but 

 provide at the same time ample means 

 for navigation, the main canals and 

 ditches being from 25 to 40 feet in 

 width. 



Before the invention of the steam- 

 engine, windmills were exclusively em- 

 ployed in the work of draining the 

 polders, but as the power of a windmill 

 is rather limited, the lift was as a rule 

 inconsiderable. In later years, when 

 deeper lakes were drained, either steam- 

 engines or series of windmills placed at 

 successive levels had to be resorted to. 

 Thus at the time of the reclamation of 



Successive Enlargements of Haarlem Lake 



