With a view of deciding the question, as to the best manner of bringing the Croton water across the Harlem River, the chief engineer was instructed to furnish the Commissioners with an estimate of the cost of crossing said river by an aqueduct bridge, on an inclined plane and also by an inverted syphon, with iron pipes, on a low bridge. ; The following is a synopsis of so much of the report alluded to, as relates to the plan of construction, and some other matters connected with the subject. It appears the width of the river, on the high water level, was found to be 620 feet ;

and the distance across the valley of Harlem River, from the grade of aqueduct in the county of Westchester, to the grade of the same in the county of New York, is 1450 feet. The depth of the river, to the rock bottom, was found to be 32 feet below high water line, near the south shore and only 20 feet on the north shore. ;

The aqueduct bridge Avill have an elevation of 163 feet above the rock at the bottom of the river, or an average of about 138 above tide. The span of the arches over the river must be 80 feet, and will regularly diminish to 50 feet span, for those to be built on the land. All the piers are to be constructed hollow, except those of 50 feet span, which are to be built up solid. The piers to be built of large stone, of uniform thickness in each course, and the joints not to exceed two and a half eighths of an inch. The work generally to be performed in the most approved manner practicable. In making an estimate of the cost of this structure, the chief engineer observes, that he had been governed by the value of work of much similitude, estimated by several of the most competent men in this department of masonry; that there is no work under contract precisely similar, or of the same magnitude, or which, from its elevation and inconvenience of access, will be so expensive in laying up, or requires so great a portion of large stone, or the same exactness of execution at the same time, there is sufficient resemblance ;