Both ends of the bridge rest upon the cliffs, and are anchored to the rock. As far as supported by the cables, it is estimated that its weight is less than 1000 tons, which includes the weight of cables between towers and the pressure of the river stays below. For convenience sake I will assume this weight at 1000 tons of 2000 lbs. each. By multiplying with the factor 1.81-see Appendix B., we find the tension of the cables, which results from this weight, 1810 tons. Their ultimate strength was stated at 12,000 tons, therefore their permanent tension is to their ultimate capacity, as 1810 is to 12,000, or as 1: 6.63.

The sixty-four over-floor stays have an ultimate strength of 30 tons each, or 1920 tons in all. Their average supporting: capacity is to their strength as one to two and a half, or equal to 768 tons. With no loads on the bridge, their tension is about 5 tons each, consequently they relieve the cables 768/5 = 153 tons. But their principal service is to preserve the equilibrium of the structure under heavy loads, and to assist the trusses and girders. Being under that tension, and kept in a straight line, they yield but little under passing loads. Their action is within the tangent of the cables near the towers, where stiffness is most wanted. Being not carried back to the anchorage, they are of no assistance to the land cables.

Trains of more than 200 tons weight will only cross the bridge experimentally, or at any rate but very seldom. Add to this a number of teams and persons on both floors, weighing in all about 50 tons, and we have a total weight of 250 tons, to which the bridge will be occasionally subjected. Ordinary passing loads are within this figure. The tension produced by this weight is 250 X 1.81 = 452 tons. Add permanent tension of 1810 tons and we get 2262 tons, to which a strength is opposed of 12,000 tons, or over five times, without counting upon the stays at all. Now the facts show that the motion of trains and their speed has no perceptible effect upon the cables, and will be, at any rate, greatly overbalanced by the assistance of the stays, consequently we may rely upon the unimpaired capacity of the cables for support, and consider transient loads as at rest. There is a possibility of much heavier loads taxing the bridge occasionally, but this may not happen once in a year. A large crowd of persons and teams on the lower floor, while a heavy train is passing above, may add considerably to the above tension, but there is an abundance of strength to meet it. What is considered of most importance to the durability of the cables is the fact that the strength is nearly six times as great as their ordinary working tension, and equally important is the fact that their strength will never be impaired by vibration. In calculating the strength of suspension bridges it has been customary to allow from three to five times of ultimate strength for the support of a maximum tension. This is a good rule provided the maximum load bears a large proportion to the weight of the structure. But if this proportion is small, as must be the case in railway suspension bridges, it is a bad rule, as it allows too little strength for the permanent and ordinary tension.

There are 624 suspenders, each capable of sustaining 30 tons, which makes their united strength equal to 18,720 tons. The ordinary weight they have to support is only 1,000 tons. A locomotive of 34 tons weight, including tender, spreads its weight, by means of the girders and trusses, over a length of no less than 200 feet. Of course the greatest pressure is under the engine, and is there supported by no less than 20 suspenders. If by any accident a sudden blow or jar should be produced, the strength of suspenders will be abundant to meet it. Although the tension of the different suspenders is not by any means as uniform as that of the wires in the cables, it being impracticable to secure a perfectly uniform bearing; their strength is so abundant that they will easily resist a hurricane, should they ever become exposed to such a trial.