decrease of 957,500 gallons in the volume of the pond ; showing that, during the time observed, the supplies of the pond, from whatever quarter they come, were in quantity about 7,000 gallons per day less than the evaporation.

By damming the valley, about three-fourths of a mile below the small pond, so as to back up the water to three feet above the ordinary level of the upper pond, a reservoir of 360 acres will be formed and by deepening the outlet of the upper pond, so as to ;

command a draught of five feet in all, we shall obtain a volume of 705,672,000 gallons, or 3,920,400 gallons daily, for 180 days of drought. Deducting from this the daily loss by evaporation = 1,633,500 gallons, which is the lowest admissible calculation for the six warm months, we obtain a disposable surplus of 2,286,900 gallons per day. This is believed to be the maximum which should be calculated upon from the storage of the Rye ponds ; and the writer is not aware of any source from which it might be advisedly augmented. A small additional supply is doubtless obtainable from Byram river, if it were not necessary, in availing of it, to resort to the territory as well as the waters of another State.

The running supply of the Bronx was ascertained on the 4th and 5th of September. It was necessary to repeat the guaging several times in order to separate the accidental flow of the mills from the regular discharge of the river. The latter, however, was at