In the moral world there have always been mono-railists, men of one fixed idea, from which they could not, or would not, budge--apostles of an ambition, a creed, a theory, a political conviction. The world has had its Alexander the Great, its Napoleon, Buddha, St. Paul, Mahomet, Martin Luther, Ignatius Loyola, Wycliffe, its Palissy, George Stephenson, Mungo Park, John Bright, and Cobden. It has been left to the inventive mechanical genius of the nineteenth century to develop the mono-rail system. Doubtless those inscrutable people, the Chinese, knew of it, and applied it in some way long ago; and perhaps the yet more mysterious dwellers in ancient Egypt--whence all wisdom seems to have descended--utilised it after some unknown fashion. Blondin, in his marvellous feat of trundling a wheel-barrow containing a man along the high-level rope, used a hempen mono-rail; and the wire cables stretching across the Thames at the reconstructed bridges at Kew and Vauxhall, acting as travelling ways to convey the excavated soil from the coffer-dams in large iron “skips” or buckets, were another species of mono-rail; while at home in brickfields, and in mines, and on plantations in distant lands, miniature railways have been used for years to carry clay, ore, and produce, over plain and hill and dale. In India a peculiar kind of tramway truck has been in use for some time, with two or three flanged wheels which run on a single rail, and a large balance-wheel on one side of the truck to prevent it toppling over. Produce of all kinds can easily be drawn upon it by a couple of coolies, and its efficiency on country roads has been highly spoken of. Germany presents us with a recent and curious example of the application of the principle to locomotion. In the Wupper Valley near Dusseldorf and Cologne there are two towns, Barmen and Elberfeld, about eight miles apart, mutually engaged in chemical and textile industries, and this separation of the sister-towns was an obvious disadvantage to both. But now they are joined by a wonderful railway, constructed on an elevated line running six miles of its course above the River Wupper, a tributary of the Rhine, some sixty to a hundred feet wide. The carriages are suspended, and work upon a single rail, a development of the travelling cable-way system. This rail is rigidly fastened to an iron framework of girders, and supports the cars hanging therefrom by means of two steel “bogies” with two wheels. Thus they can pass round sharp curves without slackening speed and with the greatest safety, its motive power, electricity, being applied by two motors on each carriage which drive both wheels with equal force at a speed fixed at thirty-one miles an hour, and attainable fifteen seconds after starting.