_The aqueduct for Glasgow_ is thirteen miles in tunnels, 3¾ miles of iron-piping across valleys, and nine miles of opening cutting and bridges. There are eighty distinct tunnels, and twenty-five important iron and masonry aqueducts. On the line is the Drymen bridge on masonry piers, eighteen feet apart, with two pipes surrounded by wood lagging, a forty-eight-inch syphon at Aberfoyle Road, and a lofty bridge at Ballewan, seventy feet in height. _The Aberdeen water-works_ has a thirty-six-inch syphon, 1,200 feet in length, across Cullen Burn, supported by granite piers. The Croton aqueduct is a masonry channel lined with brick. The bottom is an inverted arch with cord 6.75 feet, and versed sine 0.75 feet; side walls are 4 feet high, and battered so that at the top they are 7′ 4″ apart, and surmounted with a semi-circular arch. The interior is 8.64 feet high, and area 53.34 square feet. The grade is 0.021 feet per 100 feet, total length 38 miles. It crosses the Manhattan Valley 2 miles in extent, with two 36-inch, one 48, and one 60-inch cast-iron pipes, and over the Harlem River by granite bridge, known as High bridge, 100 feet above high water, composed of seven 50-feet and eight 80-feet spans. The conduit over the bridge consists of two 36-inch cast-iron pipes, and a wrought pipe 7 feet 6½ inches in diameter, resting upon saddles, supported by cast-iron standards placed 12 feet apart between the 36-inch pipes. _The aqueduct over Cabin John Creek_, of Washington, D. C., water supply, consists of a single arch of masonry 220 feet span, is the largest masonry arch in the world. The rise is 57 feet 7 inches, thickness of crown 4 feet 2 inches, and at spring 6 feet 2 inches. Water is conveyed in an iron pipe 9 feet in diameter, built in solid masonry. The bridge over Georgetown Creek, on line of Washington Conduit, is 200 feet span with two cords of iron pipe 4 feet in diameter, 1½ inches thickness, used as water conductors. The pipes were first lined with staves of resinous pine 3 inches thick to prevent freezing, but have been taken out. No allowance is made for expansion or contraction. A similar plan is in use at Philadelphia, over the valley of Wissahikon, consisting of two 20 inch cast-iron flange pipes serving as top members of a series of inverted bow-string trusses. There are four spans, each 169 feet 9 inches. Center span 100 feet above ordinary level of the water. The Boston aqueduct crosses the Charles River by syphon pipes--two, 30 inches, and the other 36 inches in diameter. Starting from a pipe chamber on the western side of the valley, the pipe descends 52.11 feet below the level of conduit, and rests on a masonry bridge of three arches. One of the syphons for supplying Madrid, Spain, crosses a valley 4,560 feet in length, consisting of four lines of cast-iron pipes three feet in diameter.