AQUEDUCTS. 35 



to insure its being pure, and is then pumped up into service-reser- 

 voirs, whence it is distributed in the usual manner. The Chicago tun- 

 nel is three miles long, that of Milwaukee is shorter. 



The Washington Aqueduct leads from a reservoir which impounds 

 the river-water at the Potomac Falls, is 16 miles long, and supplies 

 the cities of Washington and Georgetown. Its capacity is 70,000,000 

 gallons per day. The water is conveyed in a brick-and-rubble masonry 

 conduit, of circular form, to the service-reservoir five miles from the 

 city, and the rest of the way in three large cast-iron pipes capable of 

 delivering 30,000,000 gallons per day. This aqueduct was constructed 

 at the expense of the United States Government, and cost 13,000.000. 

 It has several fine bridges, of which the most notable is the one across 

 Cabin John Creek. This is a single granite arch, 100 feet high and 

 220 long. Another remarkable example of the wide, single arch oc- 

 curs on the Lisbon Aqueduct, finished in 1738. It is 115 feet wide 

 and 250 high. 



By far the finest aqueduct in America is the Croton. This was 

 begun in 1837, and finished in 1842, at a cost of |8,575,000, with- 

 out the means of distribution, which cost $1,800,000 more. The 

 length of conduit from the impounding to the receiving-reservoirs in 

 Central Park is 38^ miles, for 33 of which the conduit is built of 

 stone, brick, and cement, arched above and below, 8 feet 5 inches 

 high, Q)\ feet wide at the bottom, and 7f at the top. The water 

 crosses Harlem River in two cast-iron pipes 3 feet in diameter, and 

 one wrought-iron pipe 7 feet 6 inches in diameter, laid upon High 

 Bridge, a magnificent granite arcade 1,460 feet long and 114 high. 

 It comprises 15 arches, 7 of which have 50 feet span, and 8, those over 

 the river, 80 feet. The fall is 1.10 foot per mile, the velocity of the 

 water 1^ mile an hour, and the possible discharge 115,000,000 gal- 

 lons per day. 



For the first six years after the completion of the aqueduct, the 

 quantity of water used was only 18,000,000 gallons per day, but it has 

 now increased to over 88,000,000. The supply is drawn from Croton 

 River, a small stream that flows into the Hudson, a short distance 

 above Sing Sing. The river was arrested by a dam 40 feet high, and 

 made to form what is now called Croton Lake. The mouth of the 

 aqueduct is 12 feet below the surface of the lake, whereby it is pro- 

 tected from freezing up in winter, and the water is obtained pure 

 and cool in summer. The lake has an area of 400 acres, and usually 

 affords a daily supply of 50,000,000 gallons ; but this fell oflf, during a 

 severe drought seven or eight years ago, to only 27,000,000, and since 

 then another source has been added by damming up the western branch 

 of Croton River. The receiving-reservoirs, two in number, are located 

 in Central Park : the " old " covers 35 acres, and holds 150,000,000 

 gallons; the "new" covers 100 acres, and holds 1,030,000,000. The 

 distributing-reservoir is situated 2\ miles farther down, between Fifth 



