VII. Design for a Bridge across the East River, New York, 

 AT Blackwell's Island. 



It is proper to say that the design for a bridge crossing the East 

 River at Blackwell's Island, New York, descril)ed in the following 

 paper, was intended only as a solution of a special problem in Engin- 

 eering, applicable to long spans in certain localities ; and that it does 

 not assume to be more than a suggestion in connection with the 

 actual execution of a bridge across the East River. It is intended 

 to show that if objections to such a i)roject shall arise on account of 

 the popular apprehension of the defects of the ordinary suspension 

 bridge, there is still a practical form of structure which may be em- 

 ployed with equal and perhaps greater advantage for bridges of 

 long span. 



The suspension system, although apparently the only one available 

 beyond the limits of the straight girder and arch, presents inherent 

 defects, which to say the least are a constant source of popular appre- 

 hension. It is, however, the only system possible for very great 

 spans, and the object of the form of bridge Avhich I wish to present, 

 as particularly applicable to the case presented at Blackwell's Island, 

 is to supply a link between the straight girder, or tube, and the sus- 

 pension system. There is an interval in the lengths of spans beyond 

 the practicable limits of the single girder, which I think this form of 

 construction will fill with advantage in stability, strength, and stiff- 

 ness over the suspension bridge, and advantage in economy over the 

 simple girder. 



The bridge at Blackwell's Island, when completed, must become a 

 great thoroughfare between two populous districts, and should not 

 only possess the elements of strength and stability, but of stiffness, or 

 immobility, under passing loads, under the action of high winds, and 

 under the influences of changes of temperature. 



Blackw^ell's Island divides the East River at New York into two 

 channels, each about 600 feet in width. At the location deemed most 

 favorable for a high bridge, opposite VGth street, the east channel is 

 600 feet in width from high-water mark to high-water mark, the west 

 channel being at the same point about 670 feet. This being a point 

 at which the section of the water-way in depth is greater than it is 

 either above or below, it will be practicable, if deemed desirable, to 

 make both spans of the bridge 600 feet, one of the piers of the west 



