The destruction of the Wheeling bridge by a high wind on the 17th of May last year, the greatest disaster of the kind on record, has naturally given rise to doubts as to the safety of suspension bridges generally. One of the scientific journals remarked at the time, that the failure of this bridge would appear to be conclusive evidence against the practicability of large spans. Although I would much prefer to leave this subject alone, I cannot conscientiously do so. It is my duty to establish the safety of the Niagara Bridge, which has already, and in the brief space of one month, become one of the greatest thoroughfares on this continent. I cannot do so without drawing a comparison with other works, and without pointing out the defects which caused the destruction of the Wheeling bridge, and on the other hand explaining the means of safety which have been employed in the Niagara Bridge.

The Wheeling bridge formed a span of 1010 feet from centre to centre of towers; the floor was 960 feet long, and 26 feet wide outside of railings, its weight, including cables, was about 440 tons. The number of cables was 12, containing in all 6600 wires of No. 10. With the exception of two small stays under the floor at each tower, which appeared to be put up after the completion of the work, and were in a loose and ineffective condition at the time I examined it, there was no provision in the whole structure, aside from the inherent stiffness of the floor, which could have had an effect in checking vibrations. Owing to the provisions made for resting the cables on the towers by means of large rollers, and to the wire being arranged in a number of small cables in place of one large one, is to be attributed the fact of the ready communication of vibratory motion from the suspension cables to the land cables. The motion caused by the transit of a single team was readily communicated to the land cables. In consequence of this sensitiveness the great force to which the suspension cables were subjected on the 17th of May, was fully transferred to their connection with the anchor chains: the result was their failure on the Wheeling side. A competent eyewitness stated, that the waves of the floor, caused by the wind, rose to a height of over 20 feet. This may have been an exaggeration, but no ordinary strength of cables can resist the momentum produced by such a weight falling even 15 feet. The destruction of that bridge was clearly owing to a want of stability, and not to a want of strength. This want of stiffness could have been supplied by over-floor stays, truss railings, under-floor stays, or cable stays. If by these means no high degree of sufficient could have been obtained, they would at any rate have proved quite sufficient to check oscillations, and to keep them within safe limits. In the Niagara Bridge most ample provisions for stability have been made. The superstructure, forming a hollow box or beam, of 24 feet wide by 20 feet deep, with solid girders of five feet depth, and effective trusses, possesses enough of stiffness to resist the action of any gale. To be prepared, however, for the greatest emergency, there are 56 wire rope stays or guys attached to the lower floor, which are firmly anchored either to the solid rock of the cliffs, or to large masses of detached rock. Each of these ropes has an ultimate strength of 30 tons, they would therefore resist with an aggregate force of 1680 tons. But, owing to their inclinations, they would probably not oppose a greater resistance than 1000 tons, if that pressure was vertically applied against the lower floor. The ordinary tension of these stays does not exceed from two to three tons.

Now the weight of the bridge without the cables and stays is.	600 tons.
To this add the anchorage at each end of the lower floor, which is estimated at . . . . . . . . .	300 "
Resistance of cables in centre . . . . . . .	100 "
Resistance of stays is . . . . . . . . .	1000 "
Total . . . . . . . . . . . . .	2000 tons.

Let us suppose a hurricane expending its power upon the whole extent of both floors, and at the rate of 50 lbs. per superficial foot uplifting force.

to which a resistance is opposed of 2000 tons. No tornado, however, will act with equal force upon both floors at the same time, nor uniformly throughout their whole extent. Before the two floors were connected I noticed, that while the lower one was sensibly affected by a gale the upper one showed no motion at all, its force appeared to be expended below. Owing to the bend of the river the Canada shore is well protected, while the opposite side is exposed from all quarters. Not the slightest motion from high winds was ever noticed since the two floors were connected. The work has been frequently tested by the strongest gales that blow in this vicinity. I am also convinced that it will be proof against a hurricane.

The tornado which recently made such havoc at the town of Niagara, and was also severely felt at Lockport and Rochester, did not expend its full force upon the bridge. Its vortex was either too much elevated, or too far north east. Only a severe momentary shock, accompanied by great darkness was experienced, and lasted but a few seconds. This shock did not produce the slightest perceptible motion. Tornadoes are believed to be whirlwinds on a large scale, produced by the struggle of two u7inds moving in opposite directions in the upper regions of the air. Impelled in the directions of the strongest wind, the two contending forces move on within the sphere of a double cone, the most violent action being at the union of the two bases. This view being correct, the Niagara Bridge can never experience the full force of a hurricane. The towers may come within the sphere of its action, but not the bridge itself; certainly not enough to experience a great uplifting force.