=Mechanical Development.=--There is not space to follow in detail the mechanical development of railroads. The rail, for instance, was at first a mere plank placed in the cart track to prevent rutting; this evolved into a rail of timber about 4 x 6 inches held in proper position by cross-ties not to be considered as sleepers or supports especially. On top of the rail was later placed a strap iron. Since this strap iron under the wheel loads curled up, thicker plates began to be used. Then cast-iron rails some 4 or 5 feet long from tie to tie, cast deeper at the middle for greater strength. Then the rolling mills were becoming sufficiently improved to roll out wrought-iron rails, at first rectangular plates, then T-rails held up by chairs and finally through a dozen or more forms to Bessemer, then open-hearth steel rail shapes as at present used. The fastenings and fish plates have gone through a stage of evolution. The track soon assumed a standard form and has retained it with little variation notwithstanding attempts to use steel and concrete ties. The freight cars, at first boxes with wheels on them, have gradually developed into monsters of steel with draw bars, automatic brakes and couplings. Passenger cars at first very variable were developed from stage coaches and Conestoga wagons hitched together. In Europe they remained short, like stage coaches with side doors. In the United States they lengthened out with seats through the interior and doors and platforms at the ends. Platforms were eventually housed in with vestibules. Both types have their advantages and disadvantages. Sleeping cars seem to be a development of the canal and steamboat sleeping quarters. Here a single company early obtaining a working, if not a legal, monopoly of the business of making and operating sleepers. As a result no improvements of note have appeared in them for years. For financial efficiency the monopoly seems to be a good thing; for mechanical progress it is not. Locomotives have shown a continual progress. One reason perhaps is their short lives; new ones must always be coming along and there is ample opportunity for experimentation. From the _Tom Thumb_ to the powerful Mountain Type is a long climb, but as each step was taken the individual changes were not very noticeable. Like the hour-hand of a watch only by observing its position at times quite separated can it be noticed to have traveled.