THE measurements of the thermal expansion of diamond made by Dembowska, which according to $Gr\"{u}neisen$1 appeared to support his well-known formula connecting the specific heat and thermal expansion coefficient of simple solids, covered only a rather small range of temperature. A satisfactory-test of the $Gr\"{u}neisen$ relationship appeared to require data over a wider range of temperature. I have accordingly measured the change in the lattice spacing of diamond with temperature over the range $25^o-650^o C$.