must be attended with many unforeseen difficulties and casualties ; and should the least variation from plumb occur, or the least settlement on the foundation take place, it would carry with it very injurious results to the work ; while with the low bridge and iron pipes, the same occurrence would be attended with but trifling injury, and could very soon be repaired. 4th. The water in the large aqueduct of masonry would, with much more uncer- tainty, be protected from frost on the high bridge, from the greatly elevated exposure and difficulty in surrounding it with a sufficient quantity of earth, than when constructed on the land ; while the iron pipes, from their comparative size, may be bedded in earth of sufficient depth and compactness, to avoid all possibility of being affected by the frost. 5th. The effects of leakage have been found very injurious to the aqueduct bridges on our canals, and it is therefore a part of our contract to line the aqueduct, when the crossing of streams on bridges is necessary, with plates of cast iron, in order to avoid the possibility of repairs, which might require the shutting out of the water while effecting them, and thus be attended with serious consequences to the city. This evil will be entirely avoided by the use of iron pipes ; but should anything occur to injure one of the pipes, the other would still be kept in operation, and conduct a sufficient supply of water through the aqueduct to the reservoir for all ordinary purposes. 6th. The time necessary to complete the high bridge, would be considerably more than what would be required for constructing the low one, and a saving of time in bring- ing to the city a sufficient supply of the Croton water, is a consideration worthy of at- tention. 7th. If the river should ever be made navigable, by the removal of the mills at Kings- bridge, and of the obstruction of the dam at Macomb's Bridge, the facility afforded by the low bridge, of an archway of 80 feet in width, and 50 feet in height above full tide, will admit the passage of vessels of sufficient burthen and capacity, for every useful and ne- cessary purpose, and the high bridge could do no more. Although the Commissioners have thus decided, based upon the foregoing reasons, and in accordance with what they deemed their duty, they nevertheless admit, so far as architectural display is involved, that the high bridge has the preference ; and if your honorable body should be of opinion, notwithstanding the great additional expense, that the aqueduct should cross the Harlem River on a high bridge, and will fortify that opinion by an ordinance, passed by both Boards, and approved by the Mayor, the aqueduct shall be constructed in accordance with the provisions of such ordinance. The necessary surveys and levels, to ascertain the most suitable course for the aque- duct on the island of New York, have only recently been effected ; some demonstration, however, towards completing a plan, had been made, under the direction of Major Douglas ; but it was found necessary to go over the whole ground again, in order to arrive at a result satisfactory to the present chief engineer ; and an earlier attention to the subject was prevented by the pressing necessity of preparing the first and second divisions of the aqueduct for contract, and also the great care required in a work of such magnitude and CROTON AaUEDUCT. 153 importance, that the first portions of the project should be well and permanently executed, as a guide and example for the future. The result of these examinations carries the aqueduct from the Harlem River to the receiving reservoir as follows : it commences on the New York side of the river, at the effluent pipe chamber, on land belonging, or lately belonging, to the estate of Stephen Jumel, where a tunnel of 200 feet is contemplated. It then takes a southerly course, crossing the land of Mr. Watkins ; then runs westerly on the land of Carman and Con- nor, and enters the 10th avenue at 151st street, where a tunnel, averaging 45 feet below the surface, must be made from 140th to 135th street inclusive. The line then continues in the 10th avenue to 107th street, and makes a curve easterly to 104th street, and from thence runs parallel with, and 125 feet from, the northerly line of the 9th avenue to 90th street, where another curve occurs, carrying the line to 85th street, where it enters the receiving reservoir. From this reservoir it is proposed to conduct the water, through the 5th avenue, to the distributing reservoir on Murray Hill, by iron pipes. In following the line of aqueduct