The vacuum stresses between a metal half-space and a metal sphere were recently measured at room temperature, in the $0.6–6\mu \mathrm{m}$ range, with an estimated accuracy of $5\%$. In the interpretation it was assumed that the accuracy was not good enough for observing any thermal effects. We claim that thermal effects are important in this separation range and back up this claim with numerical calculations of the Casimir force at zero temperature and at 300 K, based on tabulated optical data of gold, copper, and aluminum. The effects of dissipation and temperature are investigated and we demonstrate the importance of considering these two corrections together.

• Received 29 September 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.4757