north, to grade on the south side of the valley, are as follows : First, or diagonal line, - 3,300 feet. Second, running 125 feet east of 10th Avenue, - - 3,700 feet. Third line, running through the 10th Avenue, 3,700 feet. The maximum elevation of the bridge above the natural surface of the ground to grade line, is about 103 feet, and to the top of the parapet wall 116 feet. To erect a bridge on the first or diagonal line, as per estimate, will cost $983,000 00 The same for the second line, - 1,286,880 00 The same for the third line, 1,286,020 00 $3,555,900 00 It thus appears that making an average of the cost of crossing the valley on an arched bridge, by the three lines designated, and continuing the aqueduct on its regular inclina- tion, will amount to $1,188,633. An estimate is then presented, for crossing the valley with pipes, or inverted syphons, of three feet diameter. The estimate proceeds upon the principle, that only two pipes will be required at present, which will supply about nineteen millions of gallons per day, and allow thirty gallons to each person, of a population of 600,000 inhabitants ; and in order to show the economy of the plan of crossing the valley by pipes, instead of an aqueduct bridge, a sum or capital is added to the estimate, the interest of which will pay for any additional number of pipes that may, in future be required, from time to time, as the population increases, sufficient to carry the whole produce of the Croton river to the reservoirs. The estimate for crossing with four pipes of 3 feet diameter, all laid, amounts to $453,670 For two pipes of the same dimensions - 303,926 For five pipes, all laid down 550,988 For only two pipes of the five laid down - 346,372 It thus appears, if it should be deemed necessary to lay down four pipes in the firs-t instance, at a cost of $453,670, which would furnish 38 million of gallons every twenty- four hours, there would still be a saving in the expense, by carrying the water over the valley by pipes, of $734,963, adopting the average cost of carrying it by an aqueduct bridge; and comparing the cost of building the bridge on the diagonal line, which is the cheapest, with the estimate for laying two pipes that will carry 19 millions of gallons daily, there is still a saving by the latter plan of $679,074. CROTONAdUEDUCT. 155 The Commissioners were in hopes, as they had abandoned the idea of crossing the Harlem river with an aqueduct bridge, that they would have been enabled to recommend the building of a similar structure for carrying the water over the Manhattan Valley ; a work that must have been an ornament to the city and a credit to the Corporation, as well as to the individuals having charge of its execution ; but the vast difference in the cost, has put it entirely out of the question, and they have accordingly adopted the plan of carrying the water over the valley, by pipes, or inverted syphons. In adopting the foregoing plans, for conducting the water over the Harlem river, and in crossing the valley at Manhattanville, on the island of New York, both the Commission- ers and engineers have been governed by a wish to reduce the cost of the work to the lowest possible sum, consistent with its durability and permanence. The plan, however, may be modified, both in those particulars as well as others, if deemed expedient by your honorable body, and a high bridge may be substituted, instead of the syphon at the Har- lem river and Manhattanville, by incurring an additional expenditure of one million, one hundred and eighty -eight thousand, seven hundred and ninety-two dollars; and by delivering the water in the city, at a much less elevation than what has been contemplated, a lower grade may be adopted for the aqueduct, that would prevent its rising above the present surface on this island. The Commissioners, however, do by no means recommend this deviation from the plan proposed ; but as some of their fellow citizens have expressed a solicitude that the water might be carried on an aqueduct bridge with architectural display, the Commissioners are disposed to be guided by the opinion, legally expressed, of your honorable body on the subject. That the permanent grade of the several streets and avenues, adjacent to the line of the aqueduct, ought, as far as practicable, to be made to conform to such line, the Commis- sioners think must be admitted ; and they trust, therefore, that the whole subject may be specially referred to a Joint Committee of both Boards and the Street Commissioner,