A PAPER on stellar structure appears in the Observatory of May, in which Dr. T. G. Cowling gives a brief summary of the work of various physicists on the theory of stellar structure during the past ten years. A large portion of the paper is devoted to recent developments in the physical theory of the generation of stellar energy. The work of Gamow, Weiszacker and Bethe has shown that the most probable mode of generation of energy is by the transmutation of hydrogen into helium, atoms of carbon and nitrogen acting as catalysts in the reaction. Assuming that the temperature at the centre of a star is about 20,000,000° K., increasing temperature implies increasing rate of generation of energy- approximately as the seventeenth power of the temperature-and the popular idea was that instability of the star would ensue. This view is erroneous because the generation of energy does not affect the internal temperature for a period of the order of a million years, and in this time the star can adjust itself so as to dispose of the extra energy.