Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

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AQUEDUCT.
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queduct. of L.160,000. In grandeur of design, solidity of construc-
—' tion, and, above all, in extensive utility, it mav challenge
competition with any similar work in the world.
Within the last century, the invention and improvement
of the manufacture of cast iron has completely changed the
mode of conducting water into cities, by the introduction of
cast-iron pipes instead of the stone conduits of former times.
These pipes can now be formed of almost any dimensions,
and united together into a continued series, so closely as to
prevent the escape of the water, even under a violent pres¬
sure arising from the altitude of the fountainhead. They
enable us, therefore, to take advantage of and give effect to
that grand principle in hydrostatics, that the fluid element
tends continually to a level, even though it be confined in
the smallest or most complicated system of pipes; so that
however low it be carried in any valley, or to whatever dis¬
tance, still it will rise on the opposite side to the original
altitude of the fountainhead—a principle which is most
important indeed in such works, seeing that by it we
are not restricted, as the Romans were, almost to a perfect
level in the line of the conduit. We have seen that, for the
purpose of attaining this level or very gentle declivity all
along the conduit, they were under the necessity of raising
it by arcades continued in one unbroken series, frequently
30 or 40 miles in extent; and, in addition to this, often pro¬
longing the length of the track by a circuitous route, turning
and winding for miles out of its course, for the very purpose
of increasing its length.
But the use of pipes enables us to dispense with these
long arcades all raised nearly to the same level with the
fountainhead; because the conduit may be varied in its level
to any extent, and still will rise at last to its original altitude.
The pipes, therefore, are merely laid all along the surface
of the ground, with a cover of 2 or 3 feet of soil to place
them beyond the reach of frost. To prevent, however, the
frequent or abrupt alternations of rise and fall, any sudden
inequalities in the ground are equalized by cuttings and em¬
bankments, but not to anything like the extent "that would
be required to raise the whole to a level. This, therefore,
forms a capital improvement in the method of conducting
water, and the greatest indeed which has ever been made in
this important branch of practical mechanics. That it was not
introduced by the Romans, is not to be ascribed, as many
have done, to their ignorance of the hydrostatic principle,
that the fluid would rise to a level in the opposite branches
of the same train of pipes. Professor Leslie has shown that
they were well acquainted with this principle, and has more¬
over obtained from Italy a portion of a leaden pipe, supposed
to have been used in the baths of Caracalla, which sets this
matter at rest. But, from the low state of the arts at that
period, they were unable to give effect to the principle.
They had not the means of fabricating pipes of such a mag¬
nitude as would have been required for the enormous quan¬
tities of water consumed in Rome, and at the same time of
strength sufficient to withstand the pressure from the foun¬
tainhead. Lead was the only material that could be used by
them for the purpose ; and besides the enormous thickness
that so weak a material would have required, and the imprac¬
ticability of their forming them, and uniting them together
endwise, they were too well acquainted with the tendency of
lead to render the water unwholesome by its poisonous im¬
pregnation. The use of cast iron was quite unknown. There
remained, therefore, no resource but in the aqueducts, which,
though attended no doubt with vast expense, and requiring
great enterprise, as well as both skill and patience, were yet
attainable by these means, and formed when completed a
simple and very perfect mode of effecting the object. Hence
arose all those works above described which have since ex¬
cited such astonishment. Now, however, when the manu-
acture of cast iron has been brought to such perfection,
VOL. in.
337
Dhlrfrm ds COntrived fo[ uniting perfectly together all the Aqueduct,
been universafl^adoptedf ^ ^ ^ haS
is sunnlied with aqi;eduCt’ ^ which the city of New York Croton
fippnt w L c tuA ?r, may be regarded as the most magni- Aqueduct,
ficent work of he kind executed in modern times. It was
8°^Omi 1837’and completed in 1842, at an expense of
8,575,000 dollars, the distribution pipes costing 1,800,000
dollars additional. Its length from the Croton lake to the
receiving reservoir is 38^ miles. The Croton lake, which
IS formed by the Croton Creek, a small stream of wholesome
water falling into the Hudson, covers 400 acres, and con¬
tains a body of water of about 500,000,000 gallons. To
the valley of the Harlem river, a distance of 33 miles, the
aqueduct is built of stone, brick, and cement, arched over
and under, 6 feet 3 inches wide at the bottom, 7 feet §
inches at the top, and 8 feet 5 inches high; and capable of
discharging 60,000,000 gallons per day. It is carried over
the Harlem valley in iron pipes laid upon a magnificent
bridge 1460 feet long, constructed of arches 114 feet above
high-water mark at Yorkville. These pipes pass into the
receiving reservoir, which is 1826 feet long and 836 feet
wide, covering an area of 37 acres, and capable of containing
150,000,000 gallons. Hence, to the distributing reservoir, a
distance of 2^ miles, the water is conveyed by a double line
of iron pipes 3 feet in diameter. This second reservoir is
420 feet square and 44 feet above the streets, with a capa¬
city of 20,000,000 gallons,—whence the water is conveyed
through the city by about 170 miles of pipe principally from
6 to 12 inches in diameter.
The works undertaken by the Edinburgh Water Com-Edinbur-.h
pany in 1819 were probably the most complete and perfect water-
of the time. They were designed by Mr Jardine, the thenworks-
engineer of the company, and carried out under his super¬
intendence in a style quite worthy of the city, and offering,
both in the general design and in all the details, a model of
propriety and skill in this species of hydraulic architecture.
The Crawley springs were conducted by an aqueduct into
a covered cistern at a point about 7 miles distant from Edin¬
burgh, and a supply from the stream called the Glencorse
Burn, conveyed by an open-work tunnel from about a mile
and a half westward. This tunnel is in some places upwards
of 30 feet deep, and the valley through which it passes, con¬
sisting entirely of gravel, acts as a filter through which the
water descends and percolates, all solid matter being inter¬
cepted in its passage to the tunnel from whence it is de¬
livered into the cistern, and conveyed to Edinburgh by a
chain of pipes varying from 20 to 15 inches of interior
diameter, without being exposed to the light of day. From
the numerous undulations of the surface, the fall of the
pipe is not uniform. Abrupt inequalities, however, were re¬
moved by cutting and embanking. Towards the northern
termination of the line the pipe is carried through a tunnel
of 2160 feet in length and about 70 or 80 feet under the
surface of Heriot’s Green. In crossing the Grassmarket it
forks off by one branch to a reservoir in the Castlehill, and
by another about 120 feet under the reservoir, through a
tunnel 740 feet in length, cut through the rock of which
the ridge leading to the Castle is composed. Branches were
laid through all the principal streets.
I he pipes are in lengths of 9^ feet each, and were tested
before being laid by a pressure equal to a vertical column
of 800 feet of water. The joints are what are termed spigot
and faucet. Cocks for the discharge of air accumulating
in the pipes are placed at the summits of all the considerable
elevations; and in the hollows are placed sluice cocks for the
purpose of running off sand or other solid matter which may
collect in the pipe. It is capable of delivering 253,56 cubic
feet of water per minute into the reservoir at the Castlehill.
The formation of the Compensation Reservoir, was un-
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