19 * 
renewed, we can then expend 24 such In the 
24 hours, or go on without intermission. The 
product or effect will then be in proportion 
to time, which is the common measure ; but 
the quantity of mechanic power arising from 
the flow of the two rivers, compared by tak- 
ing an equal portion of time, is double in the 
one to the other ; though each has a mill 
that, when going, will grind an equal quan- 
tity of corn in an hour.” 
The following is a description of a corn- 
mill of the most common sort. See Plate, 
Mills. 
AB (fig. 1) is the water- wheel, which is ge- 
nerally from 18 to 24 feet in diameter, 
reckoned from the outermost edge of any 
float-board at A, to that of the opposite one 
at B. The water striking on the floats of this 
wheel drives it round, and gives motion to 
the mill. 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 within the mill- 
house, is a wheel F, about eight or nine feet in 
diameter, having cogs all round, which work 
in the upright staves, or rounds, of a trundle 
G. This trundle is fixed upon a strong iron 
axis, called the spindle, the lower end of 
which turns in a brass foot fixed at H, in a 
horizontal beam H, called the bridge-tree ; 
and the upper end of the spindle turns in a 
wooden bush fixed into the nether mill-stone, 
which lies upon 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, abed (fig. 2), 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 does the 
rynd. 
TJre rynd is let into grooves in the under 
surface of the running mill-stone K, and so 
turns it round in the same time that the trun- 
dle G is turned round by the cog-wheel F. 
This mill-stone has a large hole quite through 
its middle, called the eye of the stone, through 
which the 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 spindle, rests upon the wall, whilst the 
other is let into a beam, called the brayer, 
LM. 
The brayer rests in a mortice at L ; and 
the other end M hangs by a strong iron rod 
x4, which goes through the fioor I, and has a 
screw-nut on its top at O ; by the turning of 
which nut, the end M of the brayer is raised 
or depressed at pleasure; and consequently 
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 
ether, the finer the corn is ground ; and the 
more remote from one another, the coarser. 
The upper mill-stone is inclosed in a round 
box, which does not touch it any where, and 
is about an inch distant from its edge all 
round. On the top of this box stands a 
frame for holding the hopper P, to which is 
hung the shoe Q, by two lines fastened to the 
hinder part of it, fixed upon hooks in the hop- 
per, and by one end of the string 11 fastened 
MILL. 
to the fore part of it ; the other end being 
twisted round the pin S. As the pin is turned 
one way, the string draws up the shoe closer 
to the hopper, and so lessens the aperture be- 
tween them ; and as the pin is turned the 
other way, it lets down the shoe, and en- 
larges the aperture. 
If the shoe is drawn up quite to the hop- 
per, no corn can fall from the hopper into the 
mill : if it is let down a little, some will fall ; 
and the quantity will be more or less, accord- 
ing as the shoe is more or less let down ; for 
the hopper is open at bottom, and there is a 
hole in the bottom of the shoe, not directly 
under the bottom of the hopper, but nearer to 
the lowest end of the shoe, over the middle 
eye of the mill-stone. 
There is a square hole in the top of the 
spindle, in which is put the feeder F (fig. 2) ; 
tins feeder, as the spindle turns round, jogs 
the shoe three times in each revolution, and 
so causes the corn to run constantly down 
from the hopper through the shoe into the 
eye of the mill-stone, where it falls upon the 
top of the rynd, and is, by the motion of the 
rynd, and the leather under it, thrown below 
the upper stone, and ground between it and 
the lower one. The violent motion of the 
stone creates a centrifugal force in the corn 
going round with it, by which means it gets 
farther and farther from the centre, as in a 
spiral, in every revolution, until it is quite 
throw'n out ; and being then ground, it falls 
through a spout, called the mill-eye, into a 
trough placed to receive it. 
When the mill is fed too fast the corn bears 
up the stone, and is ground too coarse ; and, 
besides, it clogs the mill, so as to make it go 
too slow. When the mill is too slowly fed, it 
goes too fast ; and the stones, by their attri- 
tion, are apt to strike fire. Both these in- 
conveniences are avoided by turning the pin 
S backward or forward, which draws up or 
lets down the shoe ; and thus regulates the 
feeding, as the miller sees convenient. 
The heavier the running mill-stone is, and 
the greater the quantity of water that falls 
upon the w'heel, the faster will the mill bear 
to be fed, and consequently it will grind the 
more: and, on the contrary, the lighter the 
stone, and the less the quantity of water, so 
much the slower must the feeding be. But 
when the stone is considerably worn, and be- 
come light, the mill must be fed slowly at 
any rate ; otherwise the stone will be too 
much borne up by the corn under it, which 
will make the meal coarse. 
The quantity of power sufficient to turn a 
heavy mill-stone, is but very little more than 
what is necessary to turn a light one ; for as 
it is supported upon the spindle by the bridge- 
tree, and the end of the spindle that turns in 
the brass foot therein being but small, the 
difference arising from the weight is but very 
inconsiderable in its action against the power 
or force of the water ; and, besides, a heavy 
stone has the same advantage as a heavy fly, 
namely, that it regulates the motion much 
better than a light one. 
The centrifugal force carrying the corn to- 
wards the circumference, it is natural it should 
be crushed, when it comes to a p’ace where 
the interval between the two mill-stones is 
less than its thickness ; yet the upper mill- 
stone being supported on a point which it can 
never quit, it does not so clearly appear why 
it should produce a greater effect when if i* i 
heavy than when it is light ; since, if ii were 
equally distant from the nether mill-stone, it 
could only be capable of a limited impres- 
sion. But as experience proves that this i» 
really the case, it is necessary to discover the 
cause. The spindle of the mill-stone being 
supported by a horizontal piece of timber, 
about nine or ten feet long, resting only on 
both its ends, by the elasticity of this piece,, 
the upper mill-stone is allowed a vertical mo- 
tion, playing up and down ; by which move- 
ment, the heavier the stones are, the more 
forcibly is the corn wedged in between them.. 
In order to cut and grind the corn, both 
the upper and under mill-stones have chan- 
nels or furrow’s cut into them, proceeding ob- 
liquely from the centre to the circumference. 
And these furrows are cut perpendicularly on 
one side, and obliquely on the other, which 
gives each furrow a sharp edge ; and in the 
two stones they come against one another,, 
like the edges of a pair of scissars ; and so' 
cut the corn, to make it grind the easier,, 
when it falls upon the places between the 
furrows. These are cut the same way in both- 
stones, when they lie upon their backs, which 
makes them run crossways to each other 
wlren the upper stone is inverted, by turning 
its furrowed surface towards that of the lower ; 
for if the furrows of both stones lay the same' 
way, a great deal of the corn would be driven, 
onward in the lower furrows, and so come- 
out from between the stones, without being, 
either cut or bruised. 
The grinding surface of the under stone is* 
a little convex from the edge to the centre,, 
and that of the upper stone a little concave 
so that they are farthest from one another in* 
the middle, and approach gradually nearer 
towards the edges. By this means the coni, 
at its first entrance between the stones, is- 
only bruised ; but as it goes farther on to- 
wards the circumference or edge, it is cut 
smaller and smaller ; and, at last, finely;, 
ground, just before it comes out from be twee a; 
them. 
When the furrows become blunt and shal- 
low by wearing, the running-stone must be 
taken up, and both stones new drest with a. 
chisel and hammer ; and every time the- 
stone is taken up there must be some tallows 
put round the spindle upon the bush, which; 
will soon be melted by the heat the spindle-: 
acquires from its turning and rubbing against, 
the bush, and so will get in betwixt them ? 
otherwise the bush would take fire m a very I 
little time. w 
The bush must embrace the spindle quite* 
dose, to prevent any shake in the motion,, 
which would make some parts of the stones 
grate and fire against each other ; whilst the- 
other parts of them would be too far asunder,, 
and by that means spoil the meal. 
Whenever the spindle wears the bush, sol 
as to begin to shake in it, the stone must be 
taken up, and a chisel driven into several 
parts of the bush ; and when it is taken out r 
wooden wedges must be forced into the holes 
by which means the bush will be made to em- 
brace the spindle again, dose all round. In. 
doing this, great care must be taken to drive 
equal wedges into the bush on opposite sides 
of the spindle ; otherwise it will be thrown, 
out of the perpendicular, and so hinder the. I 
upper stone from being set parallel to the 4 
under one, which is absolutely necessary for 
