The most direct measurement of the thermodynamic Gr¿neisen parameter &ggr; of a material is by observation of temperature changes accompanying sudden (adiabatic) compressions or decompressions. Measurements over a wide pressure range permit the dependence of &ggr; upon density &rgr; to be inferred, but if measurements are made below the Debye temperature of the material, interpretation of the results may be confused by the temperature dependence of &ggr;. If the temperature dependence is measured for the same samples, the density dependence may be adjusted to refer to a specimen held at a constant fraction of its Debye temperature ϑ, instead of constant temperature, by the equation <-(∂ln&ggr;/∂ln&rgr;)T/ϑ> = <-(∂ln&ggr;/∂ln&rgr;)T> ¿<1+αT(dlnϑ/dln&rgr;)> -(∂ln&ggr;/∂lnT)P(dlnϑ/dln&rgr;) where (∂ln&ggr;/∂ln&rgr;)T/ϑ is the more fundamental quantity and for crystals with high Debye temperatures, will commonly be smaller in magnitude than (∂ln&ggr;/∂ln&rgr;)T (both being negative) because (∂ln&ggr;/∂lnT)P is positive at Tϑ which is probably not very dependent on T and for which (∂ln&ggr;/∂ln&rgr;)T/ϑ at T<ϑ appears to be a good approximation, but (∂ln&ggr;/∂ln&rgr;)T for T<ϑ is not. However, the difference appears to be small for Cu, NaCl, CaF2 and α-SiO2.