concrete, and are 7 ft. in height and width, the usual
thickness of the concrete being 15 in. The inclination is 20 in. per
mile. The floor is flat from side to side, and the side-walls are 5
ft. high to the springing of the arch, which has a rise of 2 ft. The
water from the lake is received in a circular well 65 ft. deep and 40
ft. in diameter, at the bottom of which there is a ring of wire-gauze
strainers. Wherever the concrete aqueduct is intersected by valleys,
cast-iron pipes are laid; in the first instance only two of the five
rows 40 in. in diameter were laid, the city not requiring its supply
to be augmented by more than 20,000,000 gallons a day, but in 1907 it
was decided to lay a third line. All the elaborate arrangements
described above for stopping the water in case of a burst have been
employed, and have perfectly fulfilled their duties in the few cases
in which they have been called into action. The water is received in a
service reservoir at Prestwich, near Manchester, from which it is
supplied to the city. The supply from this source was begun in 1894.
The total cost of the complete scheme may be taken at about
L5,000,000, of which rather under L3,000,000 had been spent up to the
date of the opening, at which time only one line of pipes had been
laid.

Vyrnwy.

The _Vyrnwy Aqueduct_ was sanctioned by parliament in 1880 for the
supply of Liverpool from North Wales, the quantity of water obtainable
being at least 40,000,000 gallons a day. A tower built in the
artificial lake from which the supply is derived, contains the inlet
and arrangements for straining the water. The aqueduct is 68 m. in
length, and for nearly the whole distance will consist of three lines
of cast-iron pipes, two of which, varying in diameter from 42 in. to
39 in., are now in use. As the total fall between Vyrnwy and the
termination at Prescot reservoirs is about 550 ft., arrangements had
to be made to ensure that no part of the aqueduct be subjected to a
greater pressure than is required for the actual discharge. Balancing
reservoirs have therefore been constructed at five points on the line,
advantage being taken of high ground where available, so that the
total pressure is broken up into sections. At one of these points,
where the ground level is 110 ft. below the hydraulic gradient, a
circular tower is built, making a most imposing architectural feature