the line ; it consists of 800 feet of tunnel cut through rock, and about three-fourths of a mile of grading for two lines of iron pipes of 36 inches diameter. This last section is about one half completed, and will easily be completed the next fall. We then arrive at section 92, which is nearly completed, with the exception of the tunnel, which is 420 feet long, through rock, 120 feet of which is excavated. The next section, No. 93, is com- pleted, and the account settled. Section No. 94 crosses the Clendening Valley, and em- braces a very heavy stone foundation wall and three arches, or aqueduct bridges, for con- templated streets. This section is about three eighths of a mile long, is about two-thirds finished, and the contract for completion expires next fall. Section 95 is also about two- thirds completed. No. 96 embraces the receiving reservoir, which covers a surface of thirty-two acres, at Eighty-sixth-street, and is about one-half completed ; the contract ex- pires next fall. Sections 97 and 98, together two miles in length, are to be constructed by laying down two lines of iron pipes of thirty-six inches interior diameter, which are to form the connexion between the two reservoirs ; about one-fourth of this work is done. We then come to section 99, which is composed of the distributing reservoir, which work is about one-half completed. In reference to this work it is greatly to be regretted that Forty-second-street should have been reduced to so low a grade, which has increased very greatly the cost of the walls, without adding in any respect to the utility or beauty of the work. This location being higher than any of the adjoining lands, it is not obvious why your predecessors required it to be cut down at so great an expense to the city, and dis- advantage to the reservoir, as it required the walls on Forty-second-street to be sunk nearly twelve feet lower, and on the sides, fronting the Fifth avenue and Fortieth-street, an average of eight feet lower than would otherwise have been required. The remaining work, south of the distributing reservoir, consists in laying down the large mains to supply the lower parts of the city with water, and the small pipes to distri- bute it through the streets, the progress of which is known to your honorable bodies. 46 182 MEMOIR OF THE During the last fall, the water was introduced, several times, from the Croton Lake into the aqueduct. For greater security it is made to pass through two chambers, each having nine small gates, of 16 inches by 40 inches, by which any unusual velocity, growing out of the variations in the head of the water in the lake, may be controlled or equalised. In the instances we have referred to, the water passed through the first eight miles of the aqueduct, to a waste weir at Sing Sing, where it was discharged in six hours. This strengthens the opinion, that it will certainly pass through the whole line, as fast as at the rate of one mile per hour, which is the rate calculated on. The frequent use of the thermometer has shown that the temperature of the aque- duct was fifty degrees, in our coldest days previous to the 1st of January. This proves that neither the water nor the masonry of the arch will be exposed to frost. The varia- tion of temperature between summer and winter is found to be only five degrees. We have only excavated the rock and earth between the two reservoirs of a width sufficient for two, instead of three lines of large pipes, which will furnish a sufficient sup- ply for at least half a century. The saving in this particular amounts to 10,000 dollars. We were not able to make any arrangement with the contractors for the receiving reservoir at Yorkville, by which we could abandon, for the present, the construction of the northern division of this work, as proposed by us, with any advantage to the public ; so much work having been already executed, and so much of the earth being required for the embankments of the streets surrounding the reservoir and the southern division, that we were obliged to let this reservoir proceed, as contemplated by our predecessors ; except, that we do not excavate the rock, as was previously intended, by which there is a saving, as estimated, of 75,000 dollars. We have added to the expense of the distributing reservoir about $9,000, in conse- quence of having adopted a different finish from that contemplated by our predecessors. With the exceptions above stated, and the abandonment of the three arched bridges at Clendening Valley, the work has in all other respects been progressing agreeably