At the time of the Tariffville catastrophe, it was gravely stated at the coroner's inquest, and by railroad officers who claimed to know about such things, that the disaster was caused by the tremendous weight of two locomotives which were coupled together, and it was stated that one engine would have passed in safety; and directly afterwards the superintendent of a prominent railroad in New England issued an order forbidding two engines connected to pass over any iron bridges. It is all very well for a company to issue such an order, so far as it may give the public to understand that it is determined to use every precaution against disaster; but such an order may have the effect of creating a distrust which really ought not to exist. If a railway bridge is not entirely safe for two engines, it is certainly entirely unsafe for one engine and the train following; the only saving in weight by taking off one engine being the difference between the weight of that engine and the weight of the cars that would occupy the same room. For example, a bridge of 200 feet span will weigh 1,500 pounds per lineal foot. An engine and its tender will weigh 60 tons in a length of 50 feet, and a loaded freight-train may easily weigh 2/3 of a ton per lineal foot. The total weight of the span, with two engines, and the rest of the bridge covered with loaded freight-cars, would thus be 320 tons. If we take off one engine, and fill its place with cars, we take off 60 tons, and put in its place 33 tons; i.e., we remove 27 tons, or just about 1/12 of the working-load. Taking off a large part of the working-load, however, is taking off a very small part of the breaking-load; with a factor of safety of six, for example, taking off 1/12 of the working-load is taking off less than 1/70 of the breaking-load. An order, therefore, like that above, can only be of use when the working-load and the breaking-load are so nearly alike that the actual load is a dangerous one: that is when the bridge is unfit for any traffic whatever; so that, if such an order was really needed, it would, in itself, be, in the eyes of an engineer, a condemnation of the bridge.