"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?" "Never is a hard word, but one of our professors has calculated that a given quantity of radium, after throwing out heat as I have stated for a thousand million years, would have lost only one-millionth part of its bulk. Others think the loss might be greater, say an ounce to a ton in ten thousand years, but in any case it is so infinitesimally small that we have no means of measuring it, and for practical purposes it does not exist." [Illustration: M. AND MME. CURIE FINISHING THE PREPARATION OF SOME RADIUM.] After this M. Curie took me into a darkened room, where I _saw_ quite plainly the light from the radium tube, a clear glow sufficient to read by if the tube were held near a printed page. And, of course, this was a very small quantity of radium, about six centigrammes (nine-tenths of a grain troy). "We estimate," said he, "that a decigramme of radium will illuminate a square décimètre (fifteen square inches) of surface sufficient for reading." "And a kilogramme (2·2 pounds) of radium?" "A kilogramme of radium would illuminate a room thirty feet square with a mild radiance; and the light would be much brighter if screens of sulphide of zinc were placed near the radium, for these are thrown by the metal into a brilliant phosphorescence." "Then radium may be the light of the future?" M. Curie shook his head. "I am afraid that we should pay rather dearly for such a light. There is first the money cost to be considered, and then the likelihood that the people illuminated by radium would be also stricken with paralysis, blindness, and various nervous disorders. Possibly protective screens might be devised against these dangers, but it is too soon to think of that. For a long time to come the radium light will be only a laboratory wonder." After we had been in the darkness for some time M. Curie wrapped the radium tube in thick paper and put it in my hand. "Now," said he, "shut your eyes and press this against your right eyelid." I did as he bade me, and straightway had the sensation of a strange diffused light outside my eye. M. Curie assured me, however, that the light was not outside but _inside_ the eye, the radium rays having the property of making the liquids of the eyeball self-luminous, a sort of internal phosphorescence being produced. He warned me that it would be dangerous to leave the radium against the eyelid very long, as a serious disturbance to the eyesight, or even blindness, might result.