obvious.  The differences in sentiment, politically, nationally, and morally, which arose aforetime when people under the same government lived 3,000 miles apart have disappeared to be replaced by a powerful unanimity that renders possible great social movements, utterly impossible in the railway age, when seven days were consumed in journeying from east to west.  The old idea that balloons would be used in this century for travelling has proved a delusion, almost their only use now being a meteorological one.

Our rocket cars were only perfected in the usual slow course of invention, and could neither have been constructed nor propelled a hundred years ago, for neither was the metal of which they are constructed produced, nor had the method of propulsion or even the propulsive power been developed.  Inventors had to wait till science had given us in abundance a metal less than a quarter the weight of iron, but as strong and durable, and this was not until some fifty years ago when a process was discovered for producing cheaply the beautiful metal calcium.  But calcium would have been little use alone.  Aluminium, which is now so plentiful, had to be alloyed with it, and aluminium was not used to any great extent till the beginning of this century, when an electric process of reducing it quickly from its ore—­common clay—­was discovered.  The metal known as calcium bronze, which is now so common, is an alloy of calcium, 0.75; aluminium, 0.20; and 0.05 of other metals and metalloids in varying proportions according to different patents.  This alloy has all the useful properties of the finest steel with about one-fourth its weight, and is besides perfectly non-oxydisable and never tarnishes.  Without the production of a metal with all these combined qualities, we might still in our journeys, be dawdling along at sixty miles an hour in a cumbrous railroad car behind a snorting, screaming locomotive.

Our swiftly darting cars were not at first constructed on such perfect principles as now.  Invention seems to follow certain laws, and has to take its time.  A new discovery in physics has to be supplemented by one in chemistry, and one in chemistry by another in physics, and so on through a whole century, perhaps, before any great invention is perfected.  Thus it happens that, though the principle of the rocket has been known for an age, it is only comparatively recently that it has been applied to the propulsion of cars.  An invention, too, always presents itself to an inventor at first in the most complicated form, and frequently many years are passed in attempts at simplification.  What a wide interval is there between the steam locomotive with all its complex mechanism, and the magnificently simple rocket car!  A century of ceaseless invention is comprehended between the two!  Before the simplicity of our cars was arrived at, inventors had to give up boilers, fire-boxes, valves, steam-pipes, cylinders, pistons, wheels, cranks,