The original passenger cars, however frail and light they may have been, were at least, when shackled together in a train, continuous in their bearings on each other,--that is, their sills and floor timbers were all on a level and in line, so that, if the cars were suddenly pressed together, they met in such a way as to resist the pressure to the extent of their resisting power, and the floor of one did not quietly slide under or over that of another. The bodies of these cars were about thirty-two inches from the rails. This was presently found to be too low. In raising the bodies of the cars, however, the mechanics of those days encountered a practical difficulty. The couplings of the cars built on the new model were higher than those of the old. They at once met, and, as they thought, no less ingeniously then successfully overcame this difficulty, by placing the couplings and draw-heads of their new cars below the line of the sills. This necessitated putting the platform which sustained the coupling also beneath the sills, and in doing that they disregarded, without the most remote consciousness of the fact, a fundamental law of mechanics. With a possible pressure, both sudden and heavy to be resisted, the line of resistance was no longer the line of greatest strength. During thirty years this stupid blunder remained uncorrected. It was as if the builders during that period had from force of habit insisted upon always using as supports pillars which were curved or bent instead of upright. At the close of those thirty years also the railroad mechanics had become so thoroughly educated into their false methods that it took yet other years and a series of frightful disasters, the significance of which they seemed utterly unable to take in, before they could be induced to abandon those methods.