SCIENCE has made the world of to-day. It has created the tools of our modern life. But the science on which we depend for all our comforts and conveniences is no cold and remote force, acting on us impersonally from without. Science is human knowledge, gained slowly and painstakingly by men like ourselves and applied by them to the service of mankind.

This book introduces us to those pioneers in science who have created our modern world. In its stories we meet them at the high moments of their achievement. All down the ages there have been moments which made history. An invention which was hardly noted at the time, save by the few far-seeing men who projected it, stands to us for the beginning of a new epoch in the life of man.

Printing, self-running machinery, and talking across space, either with or without wires, are examples of those discoveries which have changed the world. Back of every such discovery there was a man or a group of men, bold, adventurous, clever, interesting. In these pages we meet those men, some familiar, and some unfamiliar, but all men to whom we owe a tremendous debt. And we meet them in the thrilling moment of their triumph.

We are all interested in ourselves, in our own world. Each group of stories, tracing some line of human thought, is brought to a focus in our present life. There is a happy arrangement of material by which we come in each group to our own interests.

Early man invented the wheel; modern man has invented machinery to turn the wheels of the world and has discovered how to use fuel, water power, and electricity to keep that machinery going. Man has always wanted to fly. The gasoline engine made it possible.

Time and space were baffling problems to the man of long ago. He was forced to live in a tiny, enclosed world of his own present existence. Writing, printing, photography, and the phonograph have given him one kind of control; clocks, telescopes, the telegraph, the telephone, radio, the steam engine, the automobile, and the airplane have won him other victories over time and space.

Boys and girls find themselves in this new, wonderful world. They are eager to continue its conquest. They are thrilled by its possibilities. It will help them in their understanding of the world to see how our modern civilization has been built up. To read of these pioneers and appreciate our debt to them is like rendering thanks at table for the meal that is spread before us. It will make young people more proud of their human inheritance when they see how the battles of science have been fought all down the ages by men and women like ourselves. As these great moments in science flash on the screen of their consciousness, they will catch a glimpse not only of the past and of the present but of those great moments in which they may have a part when the next great discoveries will be made, the next great conquests won.

The man, the place and period in which he lived, and the moment in which he won an immortal victory—this is the subject matter for the stories of this book.

Cambridge, Massachusetts.