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 could come from a store of energy lost out of a gramme of radium in ten thousand hours. It seemed to him, therefore, absolutely certain that if emission of heat at the rate of 90 calories per gramme per hour, found by Curie at ordinary temperatures, or even at the rate of 38, found by Sir James Dewar and Monsieur Curie from a specimen of radium at the temperature of liquid oxygen, could go on for month after month, energy must somehow be supplied from without, to give the energy of the heat getting into the material of the calorimetric apparatus. It was suggested that somehow ethereal waves might supply energy to the radium while it was giving out heat to the ponderable matter around it. Think of a piece of black cloth hermetically sealed in a glass case and sunk in a glass vessel of water exposed to the sun, and think of another equal and similar glass case containing white cloth submerged in an equal and similar glass vessel of water, similarly exposed to the sun. The water in the former glass vessel would be kept very sensibly warmer than the water in the latter. This was analogous to Curie's first experiment, in which he found the temperature of a thermometer with a little tube containing radium kept beside its bulb in a little bag of soft material to be permanently about 2° C. higher than that of another equal and similar thermometer, similarly packed with a little glass tube not containing radium beside its bulb. By changing the water in the two glass vessels a calorimetric