It is shown that the data on the energy and temperature dependence of the secondary yield of magnesiumoxide single crystals, recently published by Johnson and McKay, can be understood on the basis of a simple model. In fact, quantitative agreement is obtained for the temperature coefficient of the yield. The importance of measurements far away from either side of the maximum of the yield curve is stressed.

• Received 18 January 1954

DOI:https://doi.org/10.1103/PhysRev.94.1179