HAND-BOOK OF WASHINGTON. 120 cement or water lime, which in time becomes as hard as the brick itself. The whole length of the work from the Great Falls of the Potomac, to the Distributing Reser voir above Georgetown, is 12£ miles. The capacity of the work is to supply 07,596,400 gallons of water every 24 hours. New York has a supply of about 30,000,000 gallons The greater part of the work is under ground, many hills have been tunneled; many ravines crossed by embankments with culverts for tho passage of tho streams beneath the Aqueduct; but it is only at a few bridges that the Aqueduct itself can be seen, as all else is carefully covered with earth to protect it from frost or from decay, and the Aqueduct looks like an abandoned rail way route from which the rails have been re moved. The first structure to be seen in connection with the Aqueduct, is the bridge by which the water pipes arc carried over Rock creek, which separates the cities of Washington and George town. This is an arch of 200 feet clear span, com posed of two immense cast iron pipes, four feel