the work done inside, and nothing has since appeared to indicate any defect in the work. The reservoirs, during the time the water was shut off from the aqueduct, proved amply sufficient for the supply of the city, and indeed much beyond a supply, as a large quantity of water had to be wasted from the receiving reservoir before the lower end of the aqueduct could be examined. By a proper watchfulness, any material defect in the aqueduct may be timely dis- covered, by appearances on the outside, or examinations by means of a boat floating through the inside. The latter should be done generally once in each month, and more frequently on parts most liable to prove defective. In addition to this, it should be es- tablished as a rule, that the water is to be shut off twice in a year, for a thorough inside examination, when all repairs that may appear necessary should be made. With suitable preparations, the examination and work required could ordinarily be accomplished in about ten days, during this time, the reservoirs would amply supply the city with water. With proper regulations, they would give a sufficient supply to 500,000 people for double the time proposed. The most suitable time for such examinations would be early in the months of April and November, when the temperature of the water in the reservoirs would not be materially affected. The water has usually flowed at the depth of two and a quarter feet in the aqueduct, but has been as- high as three and a half feet, and between the Croton Dam and Sing Sing waste wier (nearly 8 miles) was for several weeks from five to six feet deep. The water in the receiving reservoir has been gradually raised to its present height of eighteen feet in the northern division, and twenty-six feet in the southern division. When full, the northern division will have twenty feet, and the southern thirty feet. It will be proper, for the winter, to keep the water at its present level in the northern, and to raise it gradually to twenty-seven feet in the southern division. I recently made a careful examination, in company with Mr. Hastie, the resident engineer, of the vaults of this reservoir. We found some leakage through the walls, but not sufficient to give any ap- prehension for the security of the work. The same day we examined the vaults of the 2QO MEMOIR OF THE distributing reservoir. At four places we found the earth between the walls to be quite soft, indicating that some water had percolated from the bottom of the reservoir, passed under the inner wall, and made its appearance in the vault between the exterior and inte- rior walls. The quantity of water was extremely small, in some cases not sufficient to make a perceptible stream in the channel designed to carry any leakage that might occur to the sewers on the outside, but the earth was fully saturated, and in other cases a very small trickling stream passed off in the channel. The extent of this leakage is small, the main part of the bottom appearing well. The leakage through the interior walls is very small ; they are as impervious as could have been anticipated, in view of the great pres- sure to which they are exposed. Their greatest leakage is at the junction of the division walls with the influent and effluent cock vaults. In each direction from them, the leak- age decreases, and in about half of the western division the walls (and channel to carry off leakage water) are entirely dry. There is conclusive evidence that the leakage through the walls has to some extent subsided, although the pressure, by gradually raising the water, has been increasing. The water now stands in the reservoir at about thirty-three feet above the sills of the gate frames, or thirty-five feet above the bottom, and within three feet of the designed top water level. Some small leakages have occurred in the joints of the iron pipes, that have been laid down in connexion with the aqueduct work ; the most troublesome has occurred in the temporary pipe at Harlem River, and is mainly to be attributed to the manner in which it was necessary to lay down this pipe, not allowing all the freedom of action that is necessary to provide for the expansion and contraction occurring in the different tem- peratures to which they are exposed. The aqueduct and its appurtenances have been subjected to the trial of near seven months, and I have endeavored to detail fully the effect the water has produced, and the prospect of its capacity to fulfil, with regularity and permanence, the object of its con- struction. It has been the subject of