What is the reason for these extraordinary properties? Is it not "perpetual motion"? All the great scientists of the world have been trying in vain to answer these questions. Several theories have been advanced, of which I shall speak later, but none seems a satisfactory explanation. When we know more of radium perhaps we shall be better prepared to say what it really is, and we may have to unlearn many of the great principles of physics and chemistry which were seemingly settled for all time. Radium would seem, indeed, to defy the very law of the conservation of energy. The practical mind at once sees radium in use as a new source of heat and light for mankind, a furnace that would never have to be fed or cleaned, a lamp that would glow perpetually--and the time may really come, the inventor having taken hold of the wonder that the scientist has produced, when many practical applications of the new element may be devised. At present, however, the scarcity and cost and danger of radium will keep it in the hands of the experimenter. Another astonishing property of radium is its power of communicating some of its strange qualities to certain substances brought within its influence. Mr. Hammer kept his radium tubes for a time in a pasteboard box. This being broken, he removed the tubes and threw the pasteboard aside. Several days later, having occasion to turn off the lights in the laboratory, he found that the discarded box was glowing there in the dark. It had taken up some of the rays from the radium. Nearly everything that comes in contact with radium thus becomes "radio-active"--even the experimenter's clothes and hands, so that delicate instruments are disturbed by the invisible shine of the experimenter. Photographs can be taken with radium; it also makes the air around it a better conductor of electricity. And still more marvellous, besides being an agency for the destruction of life, as I shall show later, it can actually be used in other ways to prolong life, and the future may show many wonderful uses for it in the treatment of disease. Already, in Paris, several cases of lupus have been cured with it, and there is evidence that it will help to restore sight in certain cases of blindness. I held a tube of radium to my closed eye and was conscious of the sensation of light; the same sensation was present when the tube was held to my temple, thus showing that the radium has an effect on the optic nerve. A little blind girl in New York, who had never had the sensation of light, began to see a little after one treatment with radium, and experiments are still going on, but cautiously, for fear that injuries may result.