Page:Popular Science Monthly Volume 71.djvu/535

Rh distributed over the earth. As this kind of work will probably have considerable geological importance, a few of Strutt's results will be given. A solution of a definite amount of the rock was stored until the equilibrium amount of radium emanation had accumulated. Now, as we have seen that uranium and radium occur in a constant proportion, it is possible to use a mineral of known uranium content and to compare the amount of radium emanation emitted by this and that emitted by the given rock. Following are some of Strutt's results, using $$3.8\ (10)^{-7}$$ grms. of radium as accompanying 1 gram of uranium in uranium minerals.

These two tables give but a few of the analyses of Strutt. They show the very wide distribution of radium both in the igneous and in the sedimentary rocks. The average radium content of the rocks examined by Strutt is high, whereas that of sea salt is quite small. Strutt finds that the radium content necessary to maintain the earth at a constant temperature is about $$1.75\ (10)^{-13}$$ grms. of radium per cubic centimeter of the earth. This is very much less than the lowest radium content of any of the rocks. For this reason he believes that