A very interesting instrument was devised by Sir William Strutt (now Lord Rayleigh) which has been called a “radium clock.” It consists of a glass vessel containing a tube of radium salts in the center, from which two gold leaves are hung. The inner surface of the containing vessel is coated with tinfoil, and this foil is grounded. The radium salts cause the leaves to become electrically charged. They then diverge, and, coming in contact with the grounded tinfoil coating, they are discharged, only to fall back again and repeat the process. This clock will operate as long as the supply of radioactive material will act, which in the case of pure radium would be nearly 2000 years. G. Lentner has recently succeeded in utilizing atmospheric potential by the aid of radioactive substances, which, in some way not yet clearly understood, exert an influence upon the transformer. The method is as follows: A post about 12 m. in height, forming a sort of antenna, is erected; the post ends in a collector consisting of an aluminum sphere provided with points covered with radioactive substances. This collector communicates by a conducting wire with a special transformer. Under these conditions the earth and atmospheric currents attract each other through reciprocal induction. Dr. S. A. Sochocky, the well known radium expert, has made radium oil paints, and made paintings with them. “Pictures painted with radium look like any other pictures in the daytime, but at night they illuminate themselves and create an interesting and weirdly artistic effect. This paint would be particularly adaptable for pictures of moonlight or winter scenes, and I have no doubt that some day a fine artist will make a name for himself and greatly interest us by painting pictures which will be unique, and particularly beautiful at night in a dark or semi-darkened room.” Dr. Sochocky also predicts that “the time will doubtless come when you will have in your own home (or someone you know will have) a room lighted entirely by radium. It would be possible today to illuminate a room, so that at night, without the aid of electricity or other artificial illumination, you could read fine newspaper print without difficulty. The light in such a room, thrown off by radium paint on walls and ceiling, would in color and tone be like soft moonlight, blue with a tint of yellow. Today, a room ten by nine feet could be illuminated in this way at a cost of $400, and the illumination would last ten years. “However, such illumination will soon be much cheaper, because of new discoveries as to the best materials to combine with radium to produce light.” CHAPTER III RADIUM AND THE AGE OF THE EARTH