Page:Popular Science Monthly Volume 11.djvu/46

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36
THE POPULAR SCIENCE MONTHLY.

and Sixth Avenues, Fortieth and Forty-second Streets. Its walls are 45 feet high, and they inclose a little more than 4 acres. The water is brought down in five lines of iron pipe, two of which are 30 inches in diameter, two three feet, and one four feet. The distributing-pipes, ramifying throughout the city, are about 340 miles long. The "mains" are laid near the sidewalks on either side of the streets, and at every crossing are provided with branches for supplying the adjacent buildings. These branches are provided with stopcocks for turning off the water when necessary. The higher parts of the city lying north of Manhattan Valley are supplied from a tower and reservoir recently built on high ground near One Hundred and Seventy-third Street and Tenth Avenue, to which the water is raised by powerful pumps. The reader will have been struck with the similarity between this aqueduct and those of ancient Rome; it remains to be shown that there is one other point of resemblance, in the air-shafts that are built at intervals of a mile. They rise 14 feet above the ground, and, like the old Roman ones, are in the form of towers. Every third one is provided with a door and way of access into the conduit. But the conduit is without the filtering-places and the angles. The conduit does, indeed, make several curves of 500 feet radius, but these are for changing the course of the aqueduct to avoid obstacles, instead of for breaking the force of the water, which in fact is unnecessary, the inclination being, as already shown, insignificant. The level of Croton Lake is about 115 feet above that of Manhattan Valley, and when the old reservoir in Central Park was yet building, the citizens of New York were afforded the magnificent spectacle of a vertical column of water shooting up over 100 feet from the bottom of the valley.

In connection with our subject, though not strictly belonging to it, may be mentioned the fact that canals are in many places carried across valleys and rivers upon bridges. Examples have long existed on the Languedoc Canal in France. The first in England was the Barton Bridge, which carries a canal across the river Irwell 39 feet above the surface. It was constructed by Brindley, for the Duke of Bridgewater. Says a contemporary English writer: "It was commenced in September, 1760; and in July of the following year the spectacle was first presented, in this country, of vessels floating and sailing across the course of the river, while others in the river itself were passing under them." The Lancaster Canal has one of five arches of 72 feet span each, and 65 feet high, across the river Lune. Later and more celebrated examples, though, are those of Pont-y-Cysylte and Chirk in Wales. The former, constructed by Mr. Telford, "is justly celebrated for its magnitude, simplicity of desgin, and skillful disposition of parts, combining lightness with strength in a degree seldom attempted. It consists of cast-iron arches resting on pillars of stone; the length is 1,000 feet, the number of arches 19, and the height 126 feet." In this country these bridges are numerous, there being