Narrow-gauge railways, of gauges varying from 1 foot 10½ inches on the Festiniog Railway, to 3 feet, 3 feet 3 inches (metre), and 3 feet 6 inches, have been made in several places both at home and abroad. Generally speaking, they have been constructed as subsidiary or auxiliary lines in thinly populated districts, with a view to afford some railway accommodation where it was considered that lines of the standard gauge would not pay. In some instances abroad long lines of narrow gauge--3 feet and 3 feet 6 inches--have been constructed as main trunk lines in newly opened out districts. Some of these have since been altered to a wider gauge as the traffic developed, and experience proved that the narrow width of the vehicles was unsuitable for quick transit, or convenience in the accommodation of passengers and goods. The object in making a line to a narrow gauge is doubtless to save cost in the original construction; but when a scheme for an altered gauge is put forward, it will be well to consider what amount of advantage or saving would be effected by deviating from the standard gauge. If there be almost a certainty that such proposed line will always remain isolated from all other existing railways of the standard gauge, then perhaps the selection of gauge may be one of minor importance, and there remains but the question whether the description of traffic, and the weights to be carried, can be worked to any greater advantage, or more economically, by deviating from the standard gauge. If, however, there be a fair probability that such proposed line may at some future time become part of an already established railway system, it would appear to be more prudent to make the line to the standard gauge, and effect economies by introducing steeper gradients, 41 sharper curves, and lighter permanent way, and keep down working expenses by using lighter locomotives, worked at slower speeds. High speeds are not expected on narrow gauge railways, and no complaints are made about passenger trains whose highest running speed does not exceed 20 miles per hour. By conceding the same indulgence to light railways made to the standard gauge, great economies might be introduced both in their construction and working. The similarity of gauge would admit the transit of the carriages and waggons of other standard gauge lines, and so avoid all cost and delay in transshipment. The heavy engines could be kept for the main-line working, and light engines for slow speeds would serve for the light standard-gauge lines. As traffic developed, and the train service required heavier and faster trains, the light rails could be removed, and replaced by those of heavier section to correspond to the main line. The similarity of gauge would permit uninterrupted transit of all vehicles to a common centre for repairs, whereas the narrow gauge carriages and waggons, being limited to running only on their own district, must have separate workshops for their repair.