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 build- 

 ings. 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 sujiplied 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 powerfid 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 condidt 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 afibrded 

 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 Bar- 

 ton Bridsce, which carries a canal across the river Irwell 39 feet above 

 the surface. It was constructed by Brindley, for the Duke of Bridge- 

 water. 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 i-iver, 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 cele- 

 brated for its magnitude, simplicity of desgin, and skillful disposition 

 of parts, combining lightness with strength in a degree seldom at- 

 tempted. 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 



