Abstract
THE second Poynting Memorial Lecture in the University of Birmingham was delivered by Dr. H. B. G. Casimir, of Leyden, on March 7, on “The approach to the absolute zero of temperature and some properties of matter at the lowest tempsratures at present attainable”. Dr. Casimir remarked that the subject, being one in which the combination of the theoretical and experimental had been so fruitful, was an appropriate one with which to commemorate a man who had in himself so remarkably embodied this combination. The definition of temperature in terms of an ideal gas enables us to say that the ice-point is 273-15° K., but in practice the gas scale cannot be used directly below 1° K., for at such temperatures gases cease to exist. It is possible, however, by other methods, for example, the resistance of phosphor bronze, to extrapolate to 0.2° K., and very small temperature changes can be measured by using the magnetic properties of substances, so that measurements down to a few hundredths of a degree absolute or even less can be made with a good deal of confidence. Methods of experimenting were explained and the remarkable properties of helium II were described.
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Approach to the Absolute Zero. Nature 143, 465 (1939). https://doi.org/10.1038/143465b0
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DOI: https://doi.org/10.1038/143465b0