314 
CHAPTER X. 
OF ANOTHER SORT OF TYMPANUM, AND OF WATER¬ 
MILLS. 
WHEELS on rivers are constructed upon the same princi¬ 
ples as those just described. Round their circumference 
are fixed paddles, which, when acted upon by the force 
of the current, drive the wheel round, receive the water 
in the buckets, and carry it to the top with the aid of 
treading; thus by the mere impulse of the stream supply¬ 
ing what is required. Water mills are turned on the same 
principle, and are in all respects similar, except that at 
one end of the axis they are provided with a drum-wheel, 
toothed and framed fast to the said axis; this being 
placed vertically on the edge turns round with the wheel. 
Corresponding with the drum-wheel a larger horizontal 
toothed wheel is placed, working on an axis whose up- 
per head is in the form of a dovetail, and is inserted 
into the mill-stone. Thus the teeth of the drum-wheel 
which is made fast to the axis acting on the teeth of the 
horizontal wheel, produce the revolution of the mill-stones. 
and in the engine a suspended hopper supplying them 
with grain, in the same revolution the flour is produced.