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 system is in its state of maximum probability. The holding of a perfect bridge hand is considered a news item because the number of highly shuffled, random, chaotic arrangements are hundreds of millions of times greater than the perfectly ordered hand. Yet the probabilities in this case are based upon a deck of only fifty-two cards. Because of the unimaginable number of molecules involved, Dodge has said: "Any arrangement in which the hot molecules would predominate to permit an observable difference in temperature between any macroscopic portions of the gas is so improbable as to be nonexistent." (Dodge, B. F. Chemical Engineering Thermodynamics.) If only molecules could be dealt with as individuals, thought Maxwell, the laws of probability would no longer apply and the Second Law of Thermodynamics would lose its rigor.

Maxwell conceived of a tiny being, since come to be affectionately known as "Maxwell's demon", who could handle the individual molecules of a gas. He made this demon the guardian of an opening between two boxes containing a gas at uniform conditions of temperature and pressure. The demon was to control the opening by a shutter, and by judicious opening and closing of the shutter- he would be able to effect a concentration of hot—high translational energy—molecules in one box and a concentration of cold—low translational energy—molecules in the other, thereby bringing about an appreciable temperature difference between the two, and hence decreasing the entropy of the system.

For some reason or other, the remarkable nature of George Joseph Ranque's invention seems to have been overlooked in this country for a good many years. It simply lapsed into the Limbo of forgotten things. But in 1946, Dr. R. M. Milton of The Johns Hopkins University visited Germany to investigate low temperature work in connection with superconductivity research. There, in the laboratory of Dr. Rudolf Hilsch, at the Physikalischen Institut, Erlangen, Germany, he found the device in the form illustrated in this article—Ranque in his patent lists a total of fifteen forms the device may take!—where it replaced the usual ammonia pre-cooling apparatus in a liquid air machine. (It is interesting to note that Dr. John R. Roebuck of The University of Wisconsin, writing in the Journal of Applied Physics, 16, 285 (1945) had independently presented a fully developed theory for a rotor device to serve the same purpose.) The very considerable experimentation carried out by Dr. Hilsch upon this device, and the publicity attendant to Dr. Milton's announcements has led to the general adoption of the name

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