People had long been experimenting with paint made from phosphorous in order to give off a glow in the darkness which would be sufficient for time reading, but phosphorus has its limitations; it must first be exposed to light before it is taken into the darkness, and if a watch-dial treated with phosphorus is buried in the pocket it cannot absorb enough light in the daytime to be luminous at night. With radium, however, the problem was solved. It was found that this amazing substance would affect certain other substances, causing them to shine for years in the darkness by means of their own light. Thus it became possible to develop a luminous coating which the Ingersolls applied to the hands and figures of their "Radiolite" watch and, presto! the problem of telling time in complete darkness was mastered to the advantage of every buyer. The inexpensive watch revealing the hour with equal visibility in inky darkness as in bright daylight had become a reality. In passing, it is interesting to note that the experiments with the watch-face led to many other developments, such as luminous compasses, gun-sights, airplane guides, and the like. Then came the World War, and the wrist-watch which had been often ridiculed as effeminate (although it is hard to explain why, since it was first adopted as an obvious convenience in the Army and on the hunting-field—two of the most masculine spheres of activity it would be possible to imagine) was seen at once to be the most easy means of knowing the time in actual warfare. Millions of watches, consequently, were strapped to wrists of soldiers and sailors, and the obvious advantages of the luminous dial placed it in enormous demand. Thus it came about that the scene described in the opening pages was typical of countless instances upon various fronts. Although a matter of surprisingly few years, considered chronologically, there is a long distance, measured by the scale of progress, between the moment when a young man, glancing casually at the clock on his bedroom wall read wonderful possibilities in its face, and the time when the firm he founded was able to take note of such achievements as these: [Illustration: TELLING TIME BY DARKNESS _Many a soldier waited in the darkness for the perilous moment to go "over the top," with his eyes fixed upon the luminous hands and figures of his Ingersoll Radiolite._]