Mr. Boltwood, of New Haven, has devoted considerable attention to the study of radioactivity in mineral springs and finds that many of the waters of America contain radium emanation.
It does not appear that any extensive or systematic investigation of the emanations of active volcanos and volcanic gases has been hitherto made. The only one I can discover is the observation of Rausch von Trauenberg on the crater Vesuvius. The gases from that orifice produced marked ionization and a prompt discharge of the leaves of the electroscope. The subject, however, needs thorough investigation at many other volcanic vents.
The general result of the investigation, so far as it has gone, has been to make clear the fact that the amount of radioactivity in the earth much exceeds the amount which is necessary, so far as the heat generated by it is concerned, to compensate the loss of heat by conduction and radiation. In fact, it appears that the thermal condition at present is one of continual increase of internal temperature of a large portion of the earth, or is so in part; or else, is one of equilibrium between loss and gain. Undoubtedly the amount of radioaction varies somewhat widely in different portions of the earth's interior, in some portions permitting a loss of heat, in others permitting a gain. And when there is a gain, it may proceed in the portions near the surface so far as to liquefy the rocks, and thus furnish all the conditions necessary to volcanic eruptions.
One of the problems at present unsolved is whence comes this radioactive material, and what maintains its activity? For the most part, it gives us the characteristics of radium and in smaller degree those of thorium and uranium. The action of actinium has not yet been sufficiently pronounced to be recognized. Polonium is believed to be one of the transitional forms of radium. No other radioactive substances are yet known. The most important one thus far identified is radium. But the life and activity of radium is, from a geological standpoint, very brief. According to Professor Rutherford, and he is sustained by nearly all other physigists, radium is half consumed in a period of 1,300 years. In 13,000 years only the thousandth part of what now exists will be left, and in 26,000 years, only the millionth part will remain. Quite independently of geological reasons, the belief has been that radium is generated as the product of decay of some other element, and that the amount of it in nature is sensibly constant. It is generated as rapidly as it decays. The parent element from which it may be derived is not yet decided, but there are some who suspect it to be uranium, which has immensely long life. It requires nearly 120,000,000 years to be half consumed by its own decay.
But we are not interested in pursuing and trying to test these unsolved problems. It is enough for us that radioaction exists in suffi-
