THE preceding volume dealt with the general principles of application and transformation of the powers of Nature through which the world's work is carried on. In the present volume we are chiefly concerned with man's application of the same principles in his efforts to set at defiance, so far as may be, the limitations of time and space.

Something has already been said as to the contrast between the material civilization of to-day and that of the generations prior to the nineteenth century. The transformation in methods of agriculture and manufacture has been referred to somewhat in detail. Now we have to do with contrasts that are perhaps even more vivid, since they concern conditions that come within the daily observation of everyone. Steamships, locomotives, electric cars, and automobiles, are such commonplaces of every-day life that it is difficult to conceive a world in which they have no part. Yet everyone is aware that all these mechanisms are inventions of the nineteenth century. Meantime the aeroplane, which bids fair to rival those other means of transportation in the near future, is a creation of the twentieth century.

In order to visualize the contrast between the practical civilization of to-day and that of our grandparents, it suffices to recall that the first steam locomotive that carried passengers over a railway was put in operation in the year 1829; and that the first ship propelled by steam power alone did not cross the ocean until 1838. Not until well towards the middle of the nineteenth century, then, were the conditions of transportation altered materially from what they had been since the very dawn of civilization,—conditions under which one hundred miles constituted about the maximum extent of a hard day's land journey.

The elaboration of railway and steamship lines through which nearly all portions of the habitable globe have been made accessible, has constituted one of the most remarkable examples of economic development that man has ever achieved. It requires but the slightest use of the imagination to realize with some measure of vividness the extent to which the entire structure of present-day civilization is based upon this elaboration of means of transportation. To point but a single illustration, the entire central and western portion of the United States must have remained a wilderness for decades or centuries had not the steam locomotive made communication easy between these regions and the seaboard.

Contrariwise no such development of city life as that which we see throughout Christendom would have been possible but for the increased facilities, due primarily to locomotives and steamships, for bringing all essential food-stuffs from distant regions.

What this all means when applied on a larger scale may be suggested by the reflection that the entire character of the occupation of the average resident of England has been changed within a century. A century ago England was a self-supporting nation, in the sense that it produced its own food-stuffs. To-day the population of England as a whole is dependent upon food shipped to it from across the oceans. Obviously such a transformation could never have been effected had not the application of steam revolutionized the entire character of transportation.

Far-reaching as are the economic aspects of the problem of transportation, this extraordinary revolution, the effects of which are visible on every side, has been brought about by the application of only a few types of mechanisms. The steam engine, the dynamo, and the gas engine are substantially responsible for the entire development in question. In the succeeding pages, which deal with the development of steamships, locomotives, automobiles, and flying machines, we have to do with the application of principles with which our previous studies have made us familiar; and in particular with the mechanisms that have engaged our attention in the preceding volume. Yet the application of these principles and the utilization of these mechanisms gave full opportunity for the exercise of inventive ingenuity, and the story of the development of steamships, locomotives, electric vehicles, automobiles, gyro cars, and flying machines, will be found to have elements of interest commensurate with the importance of these mechanisms themselves. Before we take up these stories in detail, however, we shall briefly review the story of geographical discovery and exploration in its scientific aspects.