These stories of useful inventions are chapters in the history of civilization and this little book is a book of history. Now we are told by Herodotus, one of the oldest and greatest of historians, that when the writer of history records an event he should state the time and the place of its happening. In some kinds of history—in the history of the world's wars, for example, or in the history of its politics—this is strictly true. When we are reading of the battle of Bunker Hill we should be told precisely when and where the battle was fought, and in an account of the Declaration of Independence the time and place of the declaration should be given. But in the history of inventions we cannot always be precise as to dates and places. Of course it cannot be told when the first plow or the first loom or the first clock was made. Inventions like these had their origin far back in the earliest ages when there was no such person as a historian. And when we come to the history of inventions in more recent times the historian is still sometimes unable to discover the precise time and place of an invention.

It is in the nature of things that the origin of an invention should be surrounded by uncertainty and doubt. An invention, as we shall see presently, is nearly always a response to a certain want. The world wants something and it promises a rich reward to one who will furnish the desired thing. The inventor, recognizing the want, sets to work to make the thing, but he conducts his experiments in secret, for the reason that he does not want another to steal his ideas and get ahead of him. We can see that this is true in respect to the flying machine. The first experiments with the flying machine were conducted in secret in out of the way places and pains were taken that the public should know as little as possible about the new machine and about the results of the experiments. The history of the flying machine will of course have to be written, but because of the secrecy and mystery which surrounded the beginnings of the invention it will be extremely difficult for the future historian to tell precisely when the first flying machine was invented or to name the inventor. If it is so difficult to get the facts as to the origin of an invention in our own time, how much more difficult it is to clear away the mystery and doubt which surround the beginnings of an invention in an age long past!

In a history of inventions, then, the historian cannot be precise in respect to dates and places. Fortunately this is not a cause for deep regret. It is not a great loss to truth that we cannot know precisely when the first book was printed, nor does it make much difference whether that book was printed in Holland or in Germany. In giving an account of an invention we may be content to treat the matter of time and place broadly, for the story is apt to carry us through a stretch of years that defies computation, a stretch that is immensely longer than the life of any nation. For our purpose these millenniums, these long stretches of time, may be thought of as being divided into three great periods, namely: the primitive, the ancient, and the modern period. Even a division so broad as this is not satisfactory, for in the progress of their inventions all countries have not kept equal step with the march of time. In some things ancient Greece was modern, while in most things modern Alaska is primitive and modern China is ancient. Nevertheless it will be convenient at times in this book to speak of the primitive, the ancient and the modern periods, and it will be useful to regard the primitive period as beginning with the coming of man on earth and extending to the year 5000 B.C.; the ancient period may be thought of as beginning with the year 5000 B.C. and ending with the year 476 A.D., leaving for the modern period the years that have passed since 476 A.D.

In tracing the growth of an invention the periods indicated above can serve as a time-guide only for those parts of the world where the course of civilization has taken its way, for invention and civilization have traveled the same road. The region of the world's most advanced civilization includes the lands bordering on the Mediterranean Sea, Central and Northern Europe, the British Isles, North America, South America and Australia. It is within this region that we shall follow the development of whatever invention is under consideration. When speaking of the first forms of an invention, however, it will sometimes be necessary, when an illustration is desired, to draw upon the experience of people who are outside of the wall of civilization. The reason for going outside is plain. The first and simplest forms of the useful inventions have utterly perished in civilized countries, but they still exist among savage and barbarous peoples and it is among such peoples that the first forms must be studied. Thus in the story of the clock, we must go to a far-off peninsula of Southern Asia (p. 190) for an illustration of the beginning of our modern timepiece. Such a departure from the beaten track of civilization does not spoil the story, for as a rule, the rude forms of inventions found among the lowest races of to-day are precisely the same forms that were in use among the Egyptians and Greeks when they were in their lowest state.

When studying the history of an invention there are two facts or principles which should ever be borne in mind. The first principle is this: Necessity is the mother of invention. This principle was touched upon when it was said that an invention appears as a response to a want. When the world wants an invention it usually gets it and makes the most of it, but it will have nothing to do with an invention it does not want. The steam-engine was invented two thousand years ago (p. 55) but the world then had no work for steam to do, so the invention attracted little attention and came to naught. About two hundred years ago, however, man did want the services of steam and inventors were not long in supplying the engine that was needed. About a hundred years ago the broad prairie lands of the United States began to be tilled but it was soon found that the vast areas could not be plowed and that the immense crops could not be harvested by the old methods. So improvements upon the plow and the reaper began to be made and in time the steam gang-plow and the complete harvester were invented. When the locomotive first came into use a simple handbrake was used to stop the slow-going trains, but as the size and the speed of trains increased the handbrake became more and more unsatisfactory. Sometimes a train would run as much as a half mile beyond a station before it could be stopped and then when "backed" it would again pass beyond the station. The problem of stopping the train promptly became fully as important as starting it. The problem was solved by the invention of the air-brake. And thus it has been with all the inventions which surround us: necessity has been the mother of them all.

The other principle is that a mechanical invention is a growth, or, to state the truth in another way, an invention nearly always is simply an improvement upon a previous invention. The loom, for example, was not invented by a particular person at a particular time; it did not spring into existence in a day with all its parts perfected; it grew, century by century, piece by piece. In the stories which will follow the steps in the growth of an invention are shown in the illustrations. These pictures are not for amusement but for study. As you read, examine them carefully and they will teach you quite as much about the growth of the invention as you can be taught by words.