Excerpt from The Evolution of Vertical Lift Bridges Though the accuracy of these early traditions will probably remain shrouded in mystery, it is well known that movable bridges of the bascule type were very common during the Middle Ages, especially at the approaches to castles and walled cities, and quite elaborate drawings of such bridges are still extant, exhibiting a degree of inventive skill that has not been surpassed even in our own time. Indeed, most of the patented inventions of the last twenty years are merely revivals of earlier ones which were studied out or built during previous centuries. And many features of modern bridges, originality for which is claimed by recent proprietors, are found to have been in use long before the advent of the present generation. There is, therefore, no branch of engineering in which a knowledge of history is more essential. Movable bridges of the direct lift form are, however, of more recent origin, one of the first appearing previous to 1840, in the wooden trestle of twenty-three spans, over the Danube River at Vienna, the floor over one 30 foot opening being arranged to lift 6% feet. There was also, in 1846, on the Amsterdam and Rotter dam Railway, over the Poldervaart - a canal on the Folders - a bridge with two side openings of 21 feet and a center one of 13 feet, the last capable of being lifted about 5 feet vertically, by means of a crab and screw worked by hand power. It was a small structure, only 55 feet long and 10% feet wide, with floor less than 10 feet above water. Piers were on a slight skew and were founded on piles. The next vertical lift bridges appeared in England, two being placed over the Grand Surrey Canal at London under the direction of Robert J. Hood, to carry the Thames Junction branch of the London, Brighton and South Coast Railway. These bridges crossed the canal and tow path and the larger one had a Span of 35 feet between tower faces, though the channel opening was only 21 feet. It was 83 feet wide with a rail-track on one side. The moving platform, weighing 12% tons, was suspended by wire ropes over sheaves on top of four disconnected cast iron towers, and the 12% tons of counterweight descended into underground cast iron cylinders. It could be lifted by two men on a hand winch, the greatest rise being only 5 feet. The other bridge over the same canal was 12% feet wide and 31% feet long, the upper end of towers being connected by braces with curved bottom cords. Chains were used for the suspenders instead of ropes, and the rear tower faces were curved, giving them a graceful appearance. The total cost of the latter was These two bridges over the Grand Surrey Canal, were probably the first properly constructed ones of the vertical lift type, and for more than sixty years have served as pro totypes for many later and larger ones. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.