The Johnstown Ribbed-Arch Bridge.

While the incidents of the Johnstown disaster are becoming ancient history to all, except those immediately interested in that section and in the survivors or the victims of the flood, engineers will doubtless be glad to know just what kind of a bridge it was that withstood the fury of a flood that in its upper path swept away masonry structures that had stood the test of years and were models of good work. By the courtesy of an officer of the Pennsylvania Railroad Co., we here give a reduced copy of official drawing No. 3,002, which shows the bridge as built in 1887-88.

A press of other matter has delayed the appearance of this plan, but as it is of engineering interest as a plan a side from its notoriety, no special apology is necessary. The drawing leaves little room for a detailed description, other than to say that the material used in construction was the ordinary mountain sandstone, laid in cement mortar. Its preservation was due to honest work and materials rather than to any peculiarity of design, though its width of 50 ft. with spans of only 58 ft. made it an unusually "stiff" structure. It is only fair and proper to say, in this connection, that the contractors for the bridge were Messrs. Sparks & Evans, of Philadelphia, and the cement used by them in their mortar was the ordinary "Union" brand of cement as made by Lesley & Trinkle of Philadelphia; and both of these firms have just cause to take pride in the work and materials that have successfully stood a test as severe probably as ever stone and mortar were before exposed to.