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 ;

to constitute a guide which, with careful application, will not lead astray materially in ;

computing the expense. The estimate is given in the report in detail, and amount in the aggregate, as follows :

Estimate for a high bridge, maintaining a uniform inclination of aqueduct $935,745 The plan of carrying the water across Harlem River by an inverted syphon, is next considered. It is proposed to erect a semi-circular arch, of 80 feet span, resting on abutment piers. The total height of the arch from the level of flood tide, to the under side of it, will be 50 feet. This arch is placed on the New York side of the river, and will form a sufficient channel way for navigation. From the north abutment of the arch, to the Westchester side of the river, will be constructed an embankment of stone, by casting them into the river until a sufficient bed shall be formed to support the foundation wall of the aqueduct. From the south abutment pier of the main arch, on the New York side of the river, an arcade, of three arches, will be built, one of 35, one of 30, and one of 25 feet span and, connected with this, a foun- ;