ties are the first safeguard against such accidents. Metal plates under the rails are useful also; but one of the most efficient means of preventing displacement of the rails is the interlocking bolt shown above. These bolts cross in the timber, and slots cut in the two bolts engage with each other in such a way that when the nuts are screwed down on the rail-flange it is impossible to pull the bolts out. They can only be moved by tearing through the wood contained in the angle between them. This bolt is much used on bridges and trestles, where it is of vital importance that the rails should be held in place and no part of the floor broken. [Illustration: New South Norwalk Drawbridge. Rails held by safety bolts.] In 1853 an express train went through an open draw at South Norwalk, Conn., and forty-six lives were lost. This, one of the most serious railroad accidents that ever happened, is still remembered as an historical calamity. The bridge which stands on the same site is shown opposite. In May, 1888, a west-bound express train, consisting of an engine and seven cars, was derailed just as it was entering the draw-span. The train ran three hundred feet on the sleepers before it was stopped. Then it was found that all of the driving-wheels of the engine had regained the rails, but all the other wheels were off, except those of two sleeping-cars in the rear. This was a remarkable escape from a bad accident, and much of the credit of it has been given to the interlocking bolts with which the rails were fastened. They are supposed to have prevented the rails being crowded aside, and thus to have made possible the rerailing of the engine. Besides, they helped the oak guard-timbers to hold the ties in place. The destruction of a bridge in an accident frequently begins by the ties bunching in front of the wheels and allowing the wheels to drop through and strike the floor-beams below. For this reason guard-timbers, notched down over the ties, should always be used. [Illustration: Engines Wrecked during the Great Wabash Strike.]