It is manifest that when liquid air is removed from the extremely low temperature necessary for its liquefaction, and introduced into ordinary atmospheric temperatures, it will exert a most tremendous expansive force which can be utilized for driving machinery and thereby producing heat or electricity, or for any other purpose for which force is required. But, by the law of Conservation of Energy, the liquefied air by expansion can yield no more energy than was required to extract the heat from the air and compress it into the liquid state. One enthusiastic individual who had worked in a plant for liquefying air announced throughout the United States of America, and perhaps throughout the civilized world, that he had a device by which the expansive force of three pounds of liquid air could be made to liquefy ten pounds, and that seven of the ten could be utilized for driving machinery, or for any other purpose for which force is required, the remaining three being utilized in the production of another ten pounds of liquid air, and so on ad infinitum. He boldly announced that thereby he had discovered an inexhaustible supply of energy at a nominal cost, whereby we could all be warmed and have our machinery of all kinds driven without the expense of gas, coal, fuel of any kind, wind, waves, tides or streams. This enthusiastic individual produced considerable excitement for a time, and then the public ceased to hear about either him or his device. He dropped out of sight and his name sank into oblivion. His claims were absurd, and the absurdity is readily apparent to anyone versed in thermodynamics or familiar with the principles of Conservation of Energy. There was little excuse for his ever having made such pretentions or for his pretentions ever to have been seriously listened to by any one; for the principle of Conservation of Energy had years before been fully established and heralded throughout the world. CHAPTER VIII Radium and Radio-Active Substances Considered as a Conceived Source of Perpetual Motion A few years ago when the remarkable properties of radium were discovered it was thought by many that here at last was the long sought solution of the problem of Perpetual Motion. Radium seemed to have the power of maintaining its own temperature _permanently_ above that of surrounding bodies. Many versed in the science of thermodynamics (heat power) shook their heads in doubt. If, indeed, it were really true that the substance, radium, or any other substance had the quality of remaining permanently warmer than surrounding bodies without having heat supplied to it, then, indeed, there was an inexhaustible supply of heat, and consequently power.