of a joint special committee of both Boards. To this Committee were to be referred all matters relating to the aqueduct, except the sale and disposal of stock and other duties ordinarily belonging to the Finance Committee. The new Commissioners retained the corps of engineers as they found it, with the very capable chief at its head, and the work made rapid progress during the year. The first report in January, 1841, and embracing the period from 20th March, to December 31st, gives this summary of what was done. Present state of the Work. It will be recollected that the whole work is divided into four great divisions, and which collectively, are divided into one hundred and one sections, generally one half of a mile in length. The First Division, which embraces the Croton Dam, Croton River, and first 10 177-1000 miles adjoining the same, may be said to be completed. The dam requires an expenditure of about one thousand dollars to complete the contract. The bridge across the Croton River, which was made in lieu of the one overflown by the water of the river, and the portion of the turnpike also required to be made, are both done, as well as the private road adjacent to the river, and it is expected the Commissioners appointed by the State to judge of this matter, will receive the bridge and roads, as a full substitute for those which our works rendered useless. There is an iron railing and gatekeeper's house, with some other small contingencies, which are estimated at four thousand dollars, to complete all the work at and near the dam. The dam across the Croton River was commenced in January, 1838, and is now all but completed. It is believed to be durable in its character, and possessed of sufficient strength to resist the Croton, which is, however, a stream occasionally rendered by freshets, very powerful and turbulent. The dam is formed of hydraulic stone masonry, connected with an earthen embank- ment. The embankment is about 250 feet long, 65 feet high at its extreme height, 250 feet wide at base, and 55 wide at top. This embankment is supported and protected on its lower side by a heavy protection wall 20 feet wide at base. The portion of the dam over which the water flows, together with the abutment and bulkhead adjacent, is of hydraulic stone masonry ; their united length is 105 feet. The width of the sheet of water flowing over the dam is 90 feet, and it is sup- posed in times of a freshet will be from four to six feet deep ; it has already in the last autumn been equal to three feet. The area of the Croton Lake is about 400 acres, the available capacity of the lake taken at seven feet deep, (the depth to which the water can 180 MEMOIR OF THE be drawn down,) and of an average area of more than 300 acres, may be stated at 600 millions of gallons. The total capacity of delivery of the aqueduct is about 50 millions of gallons for 24 hours, but in case the lake is being reduced seven feet, by a discharge through the aqueduct, not more than 35 millions can be calculated on as the average delivery during that time. The flow of the Croton in ordinary low water exceeds 50 millions for 24 hours, and the minimum flow after long continued drought has been ascertained to exceed 25 millions, consequently, assuming the Croton at its lowest rate of flow, there would elapse 60 days before the lake would be reduced seven feet, and 60 days before the delivery of the aqueduct would fall below 35 millions of gallons in 24 hours. In addition to this abundant supply, the water of the river at various parts for the dis- tance of 15 or 20 miles could be dammed up, at a small expense, and large ponds made to discharge into the Croton, which would always furnish a supply far beyond the capa- city of the aqueduct to discharge ; and the singular fact also exists, that a stream called the Ten Mile River, of very considerable supply of water, which now discharges into Long Island Sound, might be diverted or made to pass into the Croton. This fact is mentioned for its singularity, rather than from its being of any importance to the work. The lake, formed by the dam, flows already over some lands not embraced by the deeds or rights obtained by our predecessors ; and when it is considered that it is liable to rise three feet higher than it has yet been, it will be perceived that the extent of our water line must be considerably increased ; but as the surface