He picked up a long glass test tube and holding it between his fingers said: "Now if this tube were exhausted of air to a vacuum, and we had an ingenious little device at each end which would allow just the right amount--no more, no less--of carbon dioxide gas to enter it, and also we had electrodes at either end, and connected them to an alternating current, we would have a rough model of the light that duplicates daylight. "In actual practice the vacuum tubes are long, and turn upon themselves in many lengths. You have seen these lights in many places, for photographers, lithographers, dye works, textile mills, and all other places where the true light of day is necessary for the judgment of colours are adopting them for their night work." "But the light is a ghastly pale blue," interrupted the boy. "It doesn't look like daylight to me." "No, you are thinking of the mercury light, which also is strung around in tubes. That has a blue-greenish tinge to it, and gives people's faces a disagreeable greenish tinge, but this carbon dioxide electric light is white with a salmon pink tinge. Of course it isn't perfect, but the men who developed it from the work of others who started on this idea years ago, are constantly at work trying to improve it." THE PULMOTOR "My father read in the paper to-day about a new machine called the pulmotor, which he said was one of the greatest inventions ever brought out," said our boy friend one day in the winter of 1911-12. "Yes, it is a great invention," replied the scientist, "and like so many other big things it is so simple we wonder how it is no one was bright enough to think of it before. I suppose most of us are too busy trying to make money." "My father said it would be a fine thing for humanity and that it would save hundreds of lives every year." "That is true, and the pulmotor is just about the newest invention of our time, along those lines. When I first heard of it, I wrote to a friend of mine in Chicago, where it was brought out, and asked him about it." "How does it work?" asked the boy, and ever willing to explain the marvels of science to his young friend, the scientist took a pencil and a piece of paper to illustrate as he talked. As every boy knows, oxygen is the property in the air we breathe that gives us life. Also, every boy knows that physicians and surgeons use pure oxygen stored in iron tanks to restore respiration to the lungs of their patients when breathing has almost stopped. Until the invention of the pulmotor, how ever, this oxygen was simply introduced into the patient's lungs by placing the tube in his mouth and turning on the valve.