MILL, 
however, strictly speaking, applies solely 
to such as receive their impulse somewhere 
above their centres; generally indeed at 
their summits. The breast-wheel, when 
well constructed, may carry an effect equal 
to half, or even to three-fiftlis’'of the power ; 
while the overshot wheel oldinarily works 
with a result equal to four-fifths of the mo- 
mentum : but Mr. Smeaton thinks the ge- 
nerality (owing to a want of exact levels, 
and of a due fitting and squaring of the 
parts, together with an inattention to the 
removal of friction,) do not perform work 
beyond half the power. Many attempt too 
great velocity, which, as already shewn, 
produces considerable diminution of power. 
Mens. Parent, whose principles were con- 
sidered by Dcsagiiliers and Maclaurin to be 
perfectly correct, con.sidered that the wheel 
should move with about |ths tlie velocity of 
the water: that ratio combining the essen- 
tial points of receiving the full force of the 
stream, and enabling the engineer to regu- 
late the interior or dependant parts in 
such a manner as might answer their in- 
tended purposes, and give perfect effect to 
the whole. As to the velocity of the strehm, 
that cannot always be made to equal our 
wishes, on account of the scanty supplies in 
the many instances where greater falls, or 
more impetuous force, would prove highly 
valuable. It is, however, generally' in our 
power to diminish the velocity by means of 
sluices, overflows, &c. so as to carry off any 
redundancy, and to limit the power within 
the bounds of safety and utility. But we 
trust it has already been partially shewn, 
that by confining a stream within more 
narrow bounds than its natural banks may 
afford, the velocity may be considerably in- 
creased ; and we presume it must have been 
already understood, that by giving addi- 
tional height to the fall, or head, whence the 
water flows upon the wheel, velocity, or at 
least power, may be greatly augmented. 
While on this part of our subject, it may 
be proper to state, that it is in almost every 
instance strongly advisable to form a large 
reservoir, and to uphold a sufficient quanti- 
ty of water, by means of a dam, &c. to af- 
ford a supply in case of long-continued 
drought. Such an excess can rarely prove 
inconvenient ; the only cases in which it 
might perhaps not be eligible are, where the 
supply may be considered as infallible, or 
tire expense prove too great a drawback on 
tire profits of the concern. 
We shall novv give a description of a 
double corn mill, of the most common sort. 
Sue Plate Mill- Work. 
. A B is a water wheel, which is over-shot 
11 feet 6 inches in diameter, with 36 buckets 
to receive the water, whose weight puts it 
in motion. The wheel is fixed upon a very 
strong axis or shaft, C, one end of which 
rests on D, and the other on E, within the 
mill-house. On this shaft or axis, and with- 
in the mill-hou.se, is a wheel, F, about 8 or 9 
feet in diameter, having cogs, 7:2 in number, 
all round, which work in the 23 upright 
staves or rounds of a trundle, G, fixed on a 
strong upright shaft, T, which has a cog- 
wheel, W, with 56 teeth fixed on its upper 
end to give a rotary motion to the two 
small trundles, gg, on each side, and which 
are exactly similar to each other. Each 
trundle is fixed upon a strong iron axis call- 
ed the spindle, the lower end of which turns 
in a brass foot fixed at H, in a horizontal 
bekm, H, called the bridgetree ; the upper 
end of the spindle turns in a wooden bush, 
fixed into the nether nrillstone. which lies 
■ upon the beams in the floor, I. The top of 
the spindle above the bush is square, and 
goes into a square hole in a strong iron 
cross, iih, called the rynd, under which, 
and close to the bush, is a round piece, of 
thick leather upon the spindle, which it 
turns round at the same time as it docs the 
rynd. The rynd is let into grooves in the 
under surface of the running mill-stone, K, 
and so turns it round in the same time as 
the trundle, g, is turned round by the cog- 
wheel, W ; this mill-stone has a large hole 
quite tlirougli its middle, called the eye of the 
stone, through which tire middle part of the 
rynd and upper end of the spindle may be 
seen, whilst the four ends of the rynd lie 
below the stone in their grooves. One end 
of the bridge-tree, which supports the spin- 
dle, rests upon the wall, whilst the other is 
let into a beam called the brayer, LM. 
The brayer rests in the wall at L; the 
other end, M, hangs by a strong iron rod 
which goes through the floor, I, and has a 
screw-nut at its top ; by the turning of 
which nut the end, M, of the brayer is rais- 
ed or depressed at pleasure, and conse- 
quently the bridge-tree and the upper mill- 
stone. By this means the upper mill-stone 
may be set as close to the under one, or 
raised as high from it as the miller pleases. 
The nearer the mill stones are to each other 
the finer the corn is giouiid, and the more 
remote from one another the coarser. Tlie 
upper mill-stone is inclosed in a round box, 
which doe^ not touch it any where, and is 
about an inch distance from its edge all 
round. On the top of this box stands a frame 
for holding tlte hopper, P, to which is hung 
