when they are arrested they can be shot forth again, just as they were from the radium itself. This explains the fact that ordinary substances, such as glass, which have been kept near radium, themselves become radioactive after a time. And this is what makes me think that there is an analogy between radium and genius. Both get their energy from within and both can impart some degree of their powers to their neighbors.
This property of evolving power within itself is one of the most extraordinary facts about radium. At first it was thought to get its power from sunlight, or from some sort of unknown waves in the ether. Then Sir William Crookes thought that the molecules in the air might constantly be striking the radium and so be imparting energy to it. But now we know that the energy of radium is derived from the motion of its electrons. And this is a new source of energy, greater than any which has hitherto been known.
We do not yet know whether there is any radium in the sun. We cannot detect in the spectrum of sunlight any of the lines that are characteristic of the spectrum of radium. But this may be due to the absorption of the characteristic light of radium as it passes through the atmosphere. I think it is highly probable that there is radium in the sun. For one thing, we know that there is helium in the sun. It was discovered there before it was discovered on the earth, and that is why it got its name. And if the helium on the earth is produced from radium, very likely the sun's helium has the same source. Furthermore, the physicists tell us that the sun is only about twenty millions of years old, whereas the geologists say that the crust of the earth is far older than that. This discrepancy was made a great deal of—far too much, indeed—by the late Marquis of Salisbury, when he attacked evolution in his presidential address to the British Association at Oxford in 1895. But if there is radium in the sun, it has another source of energy besides the shrinking on which Helmholtz made his calculation; so that it may be old enough to satisfy the geologists in their large drafts on the bank of Time. And we know that the sun gives out electrons, just as radium does. It is probably these electrons that hit a comet and develop its tail by causing its lighter parts to stream behind it; for a comet does not develop a tail until it approaches the sun, and the tail is always turned away from the sun. The electrons given out by the sun sometimes strike our atmosphere and make a rare gas, called krypton, that exists in the topmost layers of the atmosphere, to become luminous; and that, we believe, is the cause of the phenomenon known as the Aurora Borealis.
Now one word as to the practical uses to which radium has already been put. It gives us the easiest way of distinguishing diamonds from paste; for diamonds glow in the dark when a little radium is brought near them, and paste does not. Radium has already cured numerous cases of lupus, which is tuberculosis of the skin, and also many case of rodent ulcer, the most superficial form of cancer. The therapeutic properties of radium have only just begun to be investigated, and it is still doubtful whether it can do any more than the Roentgen rays, which also cure lupus and rodent ulcer; but there seems to be some evidence that radium is more potent than any other remedy in certain cases. If this be so, it will become a question whether private ownership in radium should be permitted, for there is only very little of it in the whole world, and if it can cure cases where nothing else will, then the whole planetary store of it must be given up to the doctors. Fortunately it does not wear out in a hurry, and Sir William Ramsay has plenty of time to see whether he can build up radium out of helium, reversing the normal process. Meanwhile radium has been used in Russia in cases of nearly, but not absolutely, complete blindness, and has enabled patients to see for a little time; long enough to learn the shapes of a few letters and to get a glimpse of their friends.
If there is radium in the sun, it will not lose its light and power nearly so soon as we had expected. Instead of three million years—after which the sun was expected to expire, leaving the earth lifeless and desolate—humanity may have fifty millions of years yet to run to and fro upon the earth.
