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Ass’s milk has a very strong resemblance 
to human milk. It lias nearly the same colour, 
smell, and consistence. Y\ lien left at rest 
for a sufficient time, a cream forms upon its 
surface, but by no means in such abundance 
as in woman’s milk. This cream, by very long 
agitation, yields a butter, which is always soft, 
wnite, and tasteless; and, what is singular, 
very readily mixes again with the buttermilk; 
but it may lie again separated by agitation, 
while the vessel which contains it" is plunged 
in cold water. Creamed ass’s milk is thin, 
and lias an agreeable sweetish taste. Alcohol 
and acids separate from it a little curd, which 
'lias but a small degree'of consistence. The 
serum yields sugar of milk and muriat of lime. 
Ass’s milk therefore differs from cow’s milk 
in three particulars : 
Its cream is less abundant and more insipid. 
It contains less curd. It contains more su- 
gar of milk : the proportion is 35 to 80. 
Goat’s milk, it we except its consistence, 
which is greater, does not differ much from 
cow’s milk. Like that milk it throw s up abun- 
dance of cream, from which butter is easily 
obtained. The creamed milk coagulates just 
as cow’s milk, and yields a greater quantity of 
curd, its wiiey contains sugar of milk, mu- 
riat of lime, and muriat of soda. 
Ewe’s milk resembles almost precisely that 
of the cow r . Its cream is rather more abund- 
ant, and yields a buttei •which never acquires 
the consistence of butter from cow’s milk. 
Its curd has a fat and viscid appearance, and 
is not without difficulty made to assume the 
consistence of the curd of cow’s milk. It 
makes excellent cheese. 
Mare’s mi lk is thinner than that of the cow, 
but scarcely so tain as human milk. Its cream 
cannot be converted into butter by agitation. 
The creamed milk coagulates precisely as 
cow’s milk, but the card is not so- abundant. 
The serum contains sugar of milk, sulpliat of 
lime, and muriat of lime.. 
MILKY -WAY, in astronomy, a broad 
tr ick or path, encompassing the whole hea- 
vens, distinguishable by its white appearance : 
whence it obtains its name. See Astro- 
nomy. 
MILL, a machine or engine for grinding 
com, &e. of which there are several kinds, 
according to the various methods of applying 
the moving power; as water-mills, wind- 
mills, mills worked by horses, &c. 
In water-mills the momentum of the water 
is the moving power ; and the attrition of 
the two stones in grinding is the. force to be 
overcome. Of these there are two kinds, viz. 
those where the force of the water is applied 
above the wheel, and those where it is ap- 
plied below the wheel ; the former being called 
overshot, and the latter undershot mills : and 
to these we may add a breast-mill, where the 
water strikes against the middle of the w'heeh 
Few people are ignorant that corn is ground 
by tw'o mill-stones, placed one above the 
other, without touching. The lower, or ne- 
ther, mill-stone, is immoveable ; but the up- 
per one turns upon a spindle. The opposite 
surfaces of the two stones, w hich act to grind 
the corn, are not plane or Hat ; but the up- 
per one is hollow, and the under one swells 
upwards ; each of them being of a conic 
figure, whose axis indeed is very short in pro- 
portion to the diameter of its base : for the 
upper one, being six feet in diameter, is hol- 
lowed but about one inch at its centre i and 
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the lower one rises but about three-fourths of 
an inch, d irese two mill-stones conn 1 nearer 
and nearer towards their circumference, 
whereby the corn that fails from the hopper 
has room to insinuate between them as far as 
two-thirds of the radius, which is the place 
where it begins to be ground, and where it 
makes the greatest resistance that it is capable 
of; the space between the stones being in that 
place but about two-thirds or three-fourths 
of the thickness of a grain of corn. But as 
the millers have the means of raising or sink- 
ing the upper stone a little, they can propor- 
tion its distance from the lower one, accord- 
ing as they would have the flour finer or 
coarser. 
The circular motion of the upper mill- 
stone brings the corn out of the hopper by 
jerks, and causes it to recede from the centre 
towards the circumference; where being 
quite reduced to flour, it is thrown out of the 
mill, by the centrifugal force of the stone, 
through a hole provided on purpose. 
As the watt r acts upon an overshot-mill 
both by impulse and weight, so does it like- 
wise upon a breast-mill, or that where the 
water comes upon the breast or middle part 
ot the wheel : and here, though the weight of 
the water is not so great as in the overshot 
mill, being contained in the buckets of the 
lower quarter only; yet the impulse of the 
water is much greater, the height of the wa- 
ter being increased nearly the semidiameter 
of the great wheel, all other things being- 
equal. If the height of the water remains the 
same, the aperture of the penstock, or flood- 
gate, must be enlarged to nearly twice the 
area, that the force may be the same ; so 
that to produce the same effect, twice as 
much water is necessary for a breast-mill as 
for an overshot one, every thing else being 
the same. 
As to tiie undershot-mill, it is evident that 
there can be only the impulse from the wa- 
ter ; and therefore the height of the water re- 
maining the same, there must be a larger 
aperture of the penstock for the discharge of 
a greater quantity of water in the same time, 
in order to produce the same effect, as in the 
overshot, or breast-mill : w hence a greater 
expence of water will be made here than in 
any other mill, and can only be supplied for 
a constancy by a river ; and where this can 
be had, the undershot is the easiest, cheapest, 
and most simple structure a mill is capable 
of. 
Mr. Smeaton has considered the best me- 
thods of constructing all these mills from 
machines and models made on purpose ; but, 
conscious of the inferiority of models to ac- 
tual practice, did not venture to give his opi- 
nion without having seen them actually tried, 
and the truth of his doctrines established by 
practice. 
Having described the machines and models 
used for making his experiments, he observes, 
that, with regard to power, it is most pro- 
perly measured by the raising of a weight; 
or, in other words, if the weight raised is 
multiplied by the height to which it can be 
raised in a given time, the product is the 
measure of the power raising it ; and, of 
consequence, all those powers are equal 
whose products made by such multiplication 
are equal : for if a power can raise twice the 
weight to the same height, or the same weight 
to twice the height, in the same time that an- 
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other can, the former power will be double 
the latter ; hut if a power can only raise half 
the weight to double the height, or double the 
weight to half the height, in the same lime 
that another can, the two powers are equal. 
This, how ever, must be under -food on!) of a 
slow and equable motion, without accelera- 
tion or retardation ; for, if the velocity is 
either very quickly accelerated or retarded, 
the vis inertia', in our author's opinion, will 
produce an irregularity. 
io compute the effects of water-wheels 
exactly, it is necessary to know, in the first 
place, what is the real velocity of the water 
which impinges on the wheel ; 2. The quan- 
tity of water expended in a given time ; and, 
3. How much of the power is lost by the Fic- 
tion of the machinery. 
1 . With regard to the velocity of the water, 
Mr. Smeaton determined by experiment? 
w ith machinery, that with a head of w ater 15 
inches in height, the velocity of the wheel is 
8.96 feet in a minute. The area of the head 
being 105.8 inches; this multiplied by the 
weight of a cubic inch of water, equal to .579 
of an ounce avoirdupoise, gives 61.26 ounces 
for the w eight of as much water as is contain- 
ed in the head upon one inch in depth ; and 
by further calculations derived from the ma- 
chinery made use of, lie computes that 264.7 
pounds of water descend in a minute through 
the space of 15 inches. The power of the 
water, therefore, to produce mechanical ef- 
fects in this case, will be 264.7 x 1 5, or 3970. 
From the result of tiie experiment, however, 
it appeared that a vast quantity of the power 
was lost ; tiie effect being only to raise 9.375 
pounds to the height of 135 inches: so that 
the power was to the effect as 3970 to 9.375 
X 135 = 1266, or as 10 to 3.18. 
This, according to our author, must be con- 
sidered as the greatest single effect of w ater 
upon an undershot-w heel, where the water de- 
scends from a height of 15 inches ; but as the 
torce of the current is not by any means ex- 
hausted, we must consider the true proportion 
betw ixt the power and effect to be that betwixt 
the quantity of water already mentioned, and 
the sum of all the effects producible from it. 
Tlfls remainder of power, it is plain, must be 
equal to that of the velocity of the wheel it- 
self multiplied into the weight of the water. 
In the present experiment, the circumference 
of the w heel moved with the velocity of 3.123 
feet in a second, which answers to" a head of 
1 .82 inches ; and this height being multiplied 
by 264.7, the quantity of water expended in 
a minute, gives 481 lor the power of the wa- 
ter after it has passed the wheel ; and hence 
the true proportion betwixt the powder and 
the effect will be as 3849 to 1266 ; or as 11 
to 4. 
As the wheel revolved 86 times in a mi- 
nute, the velocity of the water must be equal 
to 86 circumferences of the wheel ; which, 
according to the dimensions of the apparatus 
used by Mr. Smeaton, was as 86 to 30, or as 
20 to 7. The greatest load with which the 
wheel would move was 9 lb. 6 oz. ; and by 
12 lb. it was entirely stopped. Whence our 
author concludes, that the impulse of the wa- 
ter is more than double of what it ought to- 
be according to theory ; but this he accounts 
for ’by observing, that in his experiment the- 
wheel was placed not in an open river, where 
the natural current, after it has communicated, 
