The average daily evaporation from Bear Lake in Utah and Idaho has been found to be 0.23 inch of depth, which is four per cent more than the simultaneous Weather Bureau pan‐reading. A thermally insulated pan lost 0.24 inch per day.This result was obtained by the aid of the energy‐equations which are based on such well‐established physical principles that their validity cannot be questioned. These equations contain no arbitrary constants and are therefore free from the highly questionable evaluation that is always necessary when such constants occur.