243

from the axis to the circumference of the tympanum,which are equidistant. The horizontal face of the wheelor tympanum is close boarded, with apertures thereinhalf a foot in size to admit the water. On the axis alsochannels are cut for each hay. This machine, whenmoored like a ship, is turned round by men walking ina wheel attached to it, and, by receiving the water in theapertures which are in front of the wheel, brings it upthrough the channels on the axle into a trough, whenceit is conducted in abundance to water gardens, and dilutesalt in pits. If it he necessary to raise the water to ahigher level, it must he differently adjusted. Thewheel, in that case, applied to the axis must he of suchdiameter that it shall correspond with the requisiteheight. Round the circumference of the wheel buckets,made tight with pitch and wax, are fixed; thus whenthe wheel is made to revolve by means of the personstreading in it, the buckets being carried to the top fullof water, as they return downwards, discharge the waterthey bring up into a conduit. But if water is to besupplied to still higher places, a double chain of iron ismade to revolve on the axis of the wheel, long enoughto reach to the lower level; this is furnished withbrazen buckets, each holding about a gallon. Then byturning the wheel, the chain also turns on the axis, andbrings the buckets to the top thereof, on passing whichthey are inverted, and pour into the conduits the waterthey have raised.

CHAPTER X.

OP ANOTHER SORT OP TYMPANUM, AND OP WATER-MILLS.

Wheels on rivers are constructed upon the same princi-ples as those just described. Round their circumferenceare fixed paddles, which, when acted upon by the force