This brought us back to physical facts, and I asked M. Curie if the radium before us was at that moment giving out heat and light, for I could perceive neither.
"Of course it is," he replied. "I will take you into a dark room presently and let you see the light for yourself. As for the heat, a thermometer would show that this tube of radium is 2·7 degrees F. warmer than the surrounding air."
"Is it always that much warmer?"
"Always—so far as we know. I may put it more simply by saying that a given quantity of radium will melt its own weight of ice every hour."
"For ever?"
He smiled. "So far as we know—for ever. Or, again, that a given quantity of radium throws out as much heat in eighty hours as an equal weight of coal would throw out if burned to complete combustion in one hour."
"Suppose you had a considerable quantity of radium," I suggested, "say twenty pounds, or a hundred pounds?"
"The law would be the same, whatever the quantity. If we had fifty kilos (110 pounds) of radium"—he gave a little wondering cluck at the thought—"I say if we had fifty kilos of radium it would give out as much heat continuously as a stove would give out that burned ten kilos (twenty-two pounds) of coal every twenty-four hours, and was filled up fresh every day."
"And the radium would never cease to give out this heat and would never be consumed?"