The original design was to continue the inclination which the second plane has, up to the Fountain Reservoir ; but it was considered desirable to draw from this Reservoir at a lower level, and the head of the Aqueduct was depressed for that purpose, and a less inclination adopted for the length of

the first plane. The roofing arch was left on the same inclination as was originally designed, except for the distance

of 2244. feet from the gate chamber, where it was built on a level.

The curves which are used to change the direction of the line of the Aqueduct are generally formed with a radius of

500 feet some have a radius of 1000 feet, and in a few in- ;

stances larger ones are adopted, but the majority of them are of 500 feet radius. The velocity of the water in the Aqueduct has been ascertained to be about one mile and a half an hour when it is 2 feet deep this was determined by floating billets of wood ;

from the Croton Dam to Harlem River and noting the time of their passage. Such an experiment would express the surface velocity and would give a greater velocity than it

would be proper to attribute to the whole body of water in the Aqueduct ; but the depth of water in the Aqueduct will be probably 4 feet as soon as it is brought into general use, and then there will be a corresponding increase in the velocity of the body of water. This velocity of a mile and a half an hour may be taken in general terms as the velocity of the water in the Aqueduct,