Lord Rayleigh’s series of researches for the purpose of determining the quantity of radium present in a number of representative rocks, both igneous and sedimentary, seems to prove that the average amount of radium in the earth’s crust is about 20 times larger than the amount calculated by Rutherford to be necessary to retain its temperature unaltered. Joly’s investigations revealed values in general agreement with these, but in many cases he obtained a value several times greater than the amount found by Lord Rayleigh. Further investigations showed that thorium is as widely distributed as radium in the earth’s crust, which is true also of uranium. “Incredible as it may appear,” remarks Rutherford, “the radioactive bodies must have been steadily radiating energy since the time of their formation in the earth’s crust. While the activity of uranium itself must decrease with the lapse of time, the variation is so slow that an interval measured by millions of years would be required to show any detectible change.” In his 1921 address to the British Association for the Advancement of Science, Lord Rayleigh said: “It appears certain that the radioactive materials present in the earth are generating at least as much heat as is now leaking out from the earth into space. If they are generating more than this (and there is evidence to suggest that they are), the temperature must, according to all received views, be rising.” CHAPTER IV AN EPOCH-MAKING DISCOVERY When radium was discovered by Mme. Curie in 1898, the effect upon the scientific world was startling, not to say “catastrophic”--as one author wrote at the time--since its activities ran counter to every known principle of physical science. “Some of the most solid foundations of science were destroyed, some of its noblest edifices wrecked, and scientists had to nerve themselves to face and investigate a new form of energy.” So soon as radium compounds (salts) became available, however, the amount of energy given out in radioactive processes--the emission of powerful radiations which can be transformed into light and heat--was measured; and it was found that radium, weight for weight, gives out as much heat as any known fuel every three days, and in the course of fifteen years releases a quantity of energy nearly 2,000 times as much as is obtained from the best fuel, with no signs of exhaustion (Soddy). In the combustion of coal, the heat evolved is sufficient to raise a weight of water some 80 to 100 times the weight of the fuel from the freezing-point to the boiling-point. The spontaneous heat from radium is sufficient to heat a quantity of water equal to the weight of radium from the freezing-point to the boiling-point every three-quarters of an hour. In other words, a pound of radium contains and evolves in its changes the same amount of energy as 100 tons or more of coal evolve in their combustion.