LII. A new treatment of anharmonicity in lattice thermodynamics: II

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Abstract
The thermodynamical formulae of the previous paper are worked out with the help of an adaptation of Debye's continuum approximation ; in particular, the specific heat at constant volume is put into a form suitable for numerical calculation. This formula contains, however, a factor which expresses the (possibly strong) volume dependence of the relation between the new frequency spectrum and that of the customary lattice dynamics : the factor appears in addition to the Debye characteristic temperature θ and must be estimated in any particular application—for example, in the following consideration of solid helium it will be approximated from a linear chain model. The meaning of a Debye characteristic temperature in the anharnionic theory is discussed, and the place of an empirical Debye temperature, determined by fitting specific heat measurements to a theoretical specific heat formula, is also considered. A discussion of this fitted Debye temperature (due to Domb and Salter) is adapted to the anharmonic theory in order to give later a correct application to solid helium.

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