. Bulletin - United States National Museum. La science. Figure 8.-Le Baltimore and Ohio Railroad Potomac River Crossing à Harpers Ferry, sur i860. Bollman, iron "span" de Winchester 1851 est considéré à l'extrémité droite de la structure de bois de Latrobe, 1836 qui forme le corps du pont. {Photo gracieuseté de Harpers Ferry National Historical Park.) l'âge de conception intuitive était mort depuis une décennie ou plus. La B. &AMP ; O. a été dans tous les sens un véritable pionnier de l'entreprise. Il a été le premier chemin de fer en Amérique latine ; le premier à utiliser une locomotive américaine ; le premier à traverser la

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. Bulletin - United States National Museum. Science. Figure 8.—The Baltimore and Ohio Railroad's Potomac River crossing at Harpers Ferry, about i860. Bollman's iron "Winchester span" of 1851 is seen at the right end of Latrobe's timber structure of 1836, which forms the body of the bridge. {Photo courtesy of Harpers Ferry National Historical Park.) the age of intuitive design had been dead for a decade or longer. The B. & O. was in every way a truly pioneer enterprise. It was the first practical railroad in America; the first to use an American locomotive; the first to cross the Allcghenies. The spirit of in- novation had been encouraged by the railroad's directors from the outset. It could hardly have been otherwise in light of the project's elemental daring. I he first few major bridges beyond the line's starling point on Pratt Street, in Baltimore, were of rather elaborate masonry, but this may be explained by the projectors' consciousness of the railroad's significance and their desire for permanence. How- ever, the aforementioned economic factors shortly made obvious the necessity of departure from this system, and wood was thereafter employed for most long spans on the line as far as Harpers Ferry and beyond. Only the most minor culverts and short spans, and those only in locations near suitable quar- ries, were built of stone. In addition to the economic considerations which prompted the company to revert to timber for the major bridges, there were several situations in which masonry construction was unsuitable for practical reasons. If stone arches were used in locations where the grade of the line was a relatively short distance above the surface of the stream to be crossed, a number of short arches would have been necessary to avoid a very flat single arch. In arch construction, 84 BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY. Please note that these images are extracted from scanned page images that may have been di

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