and the Storage of Water. 
31 
to become fast with corrosion, caused by the salt water. Larger 
sluices are built of brick. When the openings do not exceed 
from 2 to 4 feet in diameter, a single door hung from the top 
with crooks and bands, and inclined at a slight angle from the 
vertical, technically called a " tankard-lid door," is used. For 
larger openings the doors are hung vertically, and swing on pins 
working in a socket at the bottom, and with a collar and strap 
at the top. They vary in size from a single door for a four-feet 
culv^ert to the large double doors used on tidal streams in the 
Fens, with openings of 20 feet, and from 20 to 30 feet in height. 
A further description of these large sluices, however interesting, 
would be foreign to the purpose of this paper. 
Drainage of Lo^y-LY^NG Land. 
Raising Water from Low Levels. — When the land to be 
drained lies below the ordinary flood-level of the outfall stream, 
mechanical means must be adopted to ensure efficient drainage. 
Originally this was accomplished by wind-engines and scoop- 
wheels. Windmills have been extensively used in Holland for 
drainage purposes, where the practice was to employ one mill 
with sweeps from 80 to 90 feet in diameter for every 1250 acres 
drained. These mills work about sixty days in the year on an 
average.* But these engines, not being made on improved 
scientific principles, do not yield the same amount of work as 
those of modern construction. The Dutch engineers introduced 
them into the Fens of Lincoln and Cambridge, and many 
instances may yet be found in these counties of wind-engines 
draining large tracts of land. The high state of cultivation 
practised in the Fens has rendered efficient drainage of so much 
importance that the uncertainty of the wind has caused it to 
be almost entirely superseded by steam, and the scoop-wheel 
also is gradually giving place to the centrifugal pump. It is 
doubtful whether in thus entirely abandoning the power of the 
wind a wise course has been pursued, and whether the better 
and more economical plan would not have been to have supple- 
mented the wind with steam, using the latter only when the wind 
failed. There are many bogs and tracts of pasture land which 
would not bear the expense of steam-power, but which could be 
sufficiently drained by small wind-engines and scoop-wheels. 
The scoop-wheel is the simplest form of pump, and well 
adapted for the drainage of small areas, as it can be worked 
either by wind, horse-power, an ordinary locomotive, or a fixed 
engine. It consists of a wheel, not unlike the paddle-wheel of a 
* Bumell's ' Hydraulic Engineering.' Weale's Series, 1S58. 
