We measure expenditures properly by the results. An improvement to a locomotive costing as much as $10,000 to buy and even as much as that to maintain each year is a good investment, is it not, if it saves $50,000 a year? The superheater, the arch, the booster, and the feed-water heater together vastly increase the power of the steam locomotive. To gain their equivalent in the locomotive itself, the average Mikado-type freight-puller of eight big drivers and with extra length boiler-tubes--nineteen or twenty feet--would have to have not less than fourteen driving-wheels and boiler-tubes of the almost incredible and impracticable length of thirty-six feet. Is that graphic enough for the layman to understand? Can you understand this about the booster alone? Take a reasonable stretch of level railroad division, say 125 to 175 miles. It is good low-grade line and an engine of even moderate capacity ought to handle a 3000-ton freight-train over it easily, if it were not for that nasty little hill half-way down the line. A chain is no better than its weakest link. A railroad division is no easier than its stiffest hill. This particular one means that the maximum train-load on that division may never exceed 2700 tons.
Now we put the booster on--that little miniature locomotive for the trailing-wheels that we saw a few minutes ago, built like an automobile engine and having the same gritty driving power. When the engineer comes to that nasty hill, in goes the booster and up goes the 3000-ton train over the hill, just as easily apparently as if it were coasting on a down-grade.
The most famous passenger-train to-day in America, if not indeed in the whole world, is the Twentieth Century Limited, running between New York and Chicago, 969 miles in a flat twenty hours. It began twenty years ago as a single train of moderate length--about seven or eight Pullman cars and a diner. To-day it almost always consists of at least two sections, each of ten to twelve heavy steel diners and Pullman sleepers. In figures, the weight increase is close to 216 per cent. The train easily might make the run through to Chicago in eighteen hours as it did at the outset if safety and other conditions permitted. The energy of the locomotive is not the limiting factor.