During the time that these business principles were being formulated, the line of watches was also in process of development with the goal of universality in view. Thus, it was presently realized that while the dollar watch was essentially a man's timepiece, watches were also needed by women and by children. Accordingly, smaller models were developed to meet these needs. At a later date, the Ingersoll business principles were extended into the field of jeweled watches, when the factories of the Trenton Watch Company and the New England Watch Company were acquired. At the date of the present writing, there are more than a dozen models, each of which is adapted to a different need and use, but the manufacture of no model is undertaken unless there is a market for at least a thousand watches a day. And the latest development as this is written is the time-in-the-dark watch. Do you recall a soldier in the "foreword" waiting in the darkness for the perilous moment to go "over the top" with his eyes fixed upon the luminous hands and figures of the watch strapped to his wrist? This watch may now be named; it was the "Radiolite." How it came into existence in time to go into the Great War is a story in itself. This story is the latest step in that steady progress of democratization by which accurate timetelling, once a privilege of the few, became the possession of the many. A good many people wish to tell time in the darkness as well as in the light, and if these people could afford to, they bought expensive repeaters. Such watches, however, cost hundreds of dollars, so that while telling time in the light had come within the reach of everyone, telling time in the darkness was still possible for very few. Therefore, the watch could not yet be held to be of equal service to all humanity in every one of the twenty-four hours. This equal service at any moment was finally made possible in a somewhat extraordinary manner. In the year 1896, Monsieur and Madame Curie startled the world with the discovery of radium. They found that certain substances emitted rays that would pass through solid matter as light passes through glass or as the wind blows through a screen. They were finally able to secure tiny quantities of a whitish powder, salt of radium, which gave forth an energy that acted upon everything brought near to it and this energy they calculated, would be protected uninterruptedly for three thousand years. Up to the present time, radium and radioactivity are subjects of constant study and research, but radium exists in such small quantities and is so enormously costly that comparatively few have had a chance to experiment with it. It seems a little strange to think of using the most precious substance in the world—many times more costly than diamonds—in order to bring time-telling-in-the-dark within the reach of every person, but this is exactly what has been done.