. Bollettino - Stati Uniti Museo Nazionale. La scienza. Figura 8.-Baltimore e Ohio Railroad del Fiume Potomac crossing presso harpers Ferry, circa i860. Bollman ferro del "Winchester span" del 1851 si è visto all'estremità destra di Latrobe la struttura in legno del 1836, che costituisce il corpo del ponte. {Foto cortesia di harpers Ferry National Historical Park.) l'età di design intuitivo era stato morto per un decennio o più. Il B. & O. era in ogni modo un vero pioniere enterprise. È stata la prima ferrovia pratica in America; il primo ad utilizzare un American locomotive; prima di attraversare 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
