Engineers are of two kinds: the creative and the constructive. The power to conceive great works demands imagination and faith. The creative engineer, like the poet, is born, not made. If to the power to conceive, is added the ability to execute, then have we one of those rare geniuses who not only give a decided impulse to civilization, but add new glory to humanity. Such men were Michael Angelo, Leonardo da Vinci, Watt, Wedgwood, Brunel, Stephenson and Bessemer; and such a man was John A. Roebling. It was his striking peculiarity, that while his conceptions were bold and original, his execution was always exact, and within the limits of cost which he assigned to the work of his brain. He had made bridges a study, and had declared in favor of the suspension principle for heavy traffic, when the greatest living authorities had condemned it as costly and unsafe. When he undertook to build a suspension bridge for railway use, he did so in the face of the deliberate judgment of the profession, that success would be impossible. Stephenson had condemned the suspension principle and approved the tubular girder for railway traffic. But it was the Nemesis of his fate, that when he came out to approve the location of the great tubular bridge at Montreal, he should pass over the Niagara River in a railway train, on a suspension bridge, which he had declared to be an impracticable undertaking. When Roebling suggested the Bridge over the East River, his ideas were limited to the demands of the time, and controlled by the necessity for a profitable investment. He had no expectation that the two cities would embark in the enterprise. Indeed, in one of his letters so late as April 14, 1860, he says, "As to the corporations of New York and Brooklyn undertaking the job, no such hope may be entertained in our time." In eight years thereafter, these cities had undertaken the task upon a scale of expense far exceeding his original ideas of a structure, to be built exclusively by private capital for the sake of profit.