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same subject bas again and quite recently, occupied the attention of the English admiralty. The Chester and Holyhead Railway Company is about construct-ing a railroad bridge over the same strait, and is allowed to reduce the lengthof the two middle spans to 450 feet.

It would appear that spans of 400 feet are ample for all purposes of navigartion. But there is no necessity of adopting this limit on the Ohio river. Theconstruction of suspension bridges is now so well understood, that no competentbuilder will hesitate to resort to spans of 1500 feet and more, where localitiesmay require it, and where the object will justify the expense. It may be obser-ved here, that as a general rule, the expense of a superstructure will be in pro-portion to its span. Large spans will therefore not be adopted without necessity.There are locations, however, where a large span alone is practicable, as whereexpense can be saved by their adoption, in consequence of the reduction ofmasonry. The largest suspension bridge in the world, with spans of 1000 feet,is now being erected over the river Danube , at Pesih and Ofen, in Hungary , at anelevation sufficient to leave the navigation unobstructed. But it is on the greatrivers of the new world , where this system of bridge-building will, in course oftime, be fully applied and perfected.

The next consideration which is entitled to our attention, is the elevation atwhich the roadway or floor of a suspension bridge should be suspended abovethe river, so as to be not only above the reach of the highest flood, but to leavealso the navigation unimpeded. The supposed want of height for the freepassage of steamers has indeed been the most fertile source of opposition to theconstruction of bridges over the Ohio river. I propose to enter into the discus-sion of this question more at large, and I flatter myself, that the subsequentremarks will be sufficient to remove the fears of those who honestly believe allbridges to be fatal to the navigation. I should not countenance a scheme whichwas calculated to bring about results so disastrous. The remark has been madeby the commander of a steamer, that he should consider any bridge anobstruction, even if erected at an elevation of two hundred feet. Such objectionsare, of course, beyond the reach of argument, and not deserving of any notice.

The floor of the contemplated bridge is proposed to be suspended at an eleva-tion of 90 feet above low water, near the wharf, and at an elevation of 121 feetnear the pier. From this we have to deduct 4 feet of framing below the floor,leaving 117 feet clear next the centre pier, and 86 feet next the wharf.

THE HEIGHT OF CHIMNEYS OF STEAMBOATS.

South America measures 63 feet above water, with 12 feet joint.

Eldorado “ 59 “ “ 10 “

Wisconsin “ 54 “ “ when light.

Clipper, No. 2, “ 64 “ “ “ “

The last named boat is the largest Packet now running on the Ohio riverbetween Pittsburgh and Cincinnati .

The largest Packet on the Cincinnati and Louisville line, Pike, No. 7, hasthe following measurements, taken by myself:

Hull, when light, measures ------ 4 feet.

Boiler deck measures - - - - - - - 15“

Cabin deck “.8“

Chimney above deck measures - - - - 42 “

Top of chimneys above water, - - - - - - 69 feet.