There are many thrilling incidents - all the more attractive because of their truth - in the study, the trials, the disappointments, the obstacles overcome, and the final triumph of the successful inventor. Every great invention, afterward marvelled at, was first derided. Each great inventor, after solving problems in mechanics or chemistry, had to face the jeers of the incredulous. The trials and dangers of the builders of the submarine; the triumphant thrill of the inventor who hears for the first time the vibration of the long-distance message through the air; the daring and tension of the engineer who drives a locomotive at one hundred miles an hour - these are the true stories of great inventors.