Page:Popular Science Monthly Volume 23.djvu/362

348 delayed through want of means, and unnecessary obstacles interposed by mistaken public officials. Moreover, measured by its capacity, and the limitations imposed on its construction by its relation to the interests of traffic and navigation, it is the cheapest structure ever erected by the genius of man. This will be made evident by a single comparison with the Britannia Tubular Bridge, erected by Stephenson over the Menai Strait. He adopted the tubular principle because he believed that the suspension principle could not be made practical for railway-traffic, although he had to deal with spans not greater than 470 feet. He built a structure that contained 10,540 tons of iron, and cost £601,000, or about $3,000,000. Fortunately, he has left a calculation on record as to the possible extension of the tubular girder, showing that it would reach the limits in which it could bear only its own weight (62,000 tons) at 1,570 feet. Now, for a span of 1,600 feet, the Brooklyn Bridge contains but 6,740 tons of material, and will sustain seven times its own weight. Its cost is $9,000,000, whereas a tubular bridge for the same span would contain ten times the weight of the metal, and, though costing twice as much money, would be without the ability to do any useful work.

Roebling, therefore, solved the problem which had defied Stephenson, and upon his design has been built a successful structure at half the cost of a tubular bridge that would have fallen when loaded in actual use. It is impossible to furnish any more striking proof of the genius which originated and of the economy which constructed this triumph of American engineering.

We have thus a monument to the public spirit of the two cities, created by an expenditure as honest and as economical as those which gave us the Erie Canal, the Croton Aqueduct, and the Central Park. If it had been otherwise, it would have been a monument to the eternal infamy of the trustees and of the engineers under whose supervision it has been erected; and this brings me to the final consideration which I feel constrained to offer on this point.

During all these years of trial and false report a great soul lay in the shadow of death, praying only to stay long enough for the completion of the work to which he had devoted his life. I say a great soul, for in the spring-time of youth, with friends and fortune at his command, he gave himself to his country, and for her sake braved death on many a well-fought battle-field. 'When restored to civil life, his health was sacrificed to the duties which had devolved upon him as the inheritor of his father's fame and the executor of his father's plans. Living only for honor, and freed from the temptations of narrow means, how is it conceivable that such a man—whose approval was necessary to every expenditure—should, by conniving with jobbers, throw away more than the life which was dear to him that he might fulfill his destiny and leave to his children the heritage of a good name and the glory of a grand achievement? Well might this