312 
CHAPTER IX. 
OF ENGINES FOR RAISING WATER; AND FIRST OF 
THE TYMPANUM. 
I sHALL now explain the machines for raising water, and 
their various sorts. And first the tympanum, which, 
though it raise not the water to a great height, yet lifts 
a large quantity in a small period of time. An axis is 
prepared in the lathe, or at least made circular by hand, 
hooped with iron at the ends; round the middle whereof 
the tympanum, formed of planks fitted together, is ad¬ 
justed. This axis rests on posts also cased with iron 
where the axis touches them. In the hollow part of the 
tympanum are distributed eight diagonal pieces, going 
from the axis to the circumference of the tympanum, 
which are equidistant. The horizontal face of the wheel 
or tympanum is close boarded, with apertures therein 
half a foot in size to admit the water. On the axis also 
channels are cut for each bay. This machine, when 
moored like a ship, is turned round by men walking in 
a wheel attached to it, and, by receiving the water in the 
apertures which are in front of the wheel, brings it up 
through the channels on the axle into a trough, whence 
it is conducted in abundance to water gardens, and di¬ 
lute salt in pits. If it be necessary to raise the water to 
a higher level, it must be differently adjusted. The wheel, 
in that case, applied to the axis must be of such diameter 
that it shall correspond with the requisite height. Round 
the circumference of the wheel buckets, made tight with 
pitch and wax, are fixed; thus when the wheel is made to