The trouble with the theory is that it seems impossible to regulate the temperature from the other end. A star whose central temperature is below 32,000,000 degrees must be contracting without generating heat. The contraction will not stop dead the moment the critical temperature is attained; its momentum will carry it on until the central temperature substantially exceeds 32,000,000 degrees. As soon as the temperature seriously exceeds 32,000,000 degrees at the centre, that of a substantial piece of the star will be 32,000,000 degrees or higher. The annihilation of all this matter must produce a profusion of heat which would raise the temperature of the star still further, resulting in more and more annihilation of matter, until finally the whole star disappeared in a flash of radiation. Indeed Russell’s theory supposes that matter at 32,000,000 degrees is in a similar condition to gunpowder at its flash point. Mathematical analysis then shews that a star whose centre is at a temperature of 32,000,000 degrees would be in the state of a keg of gunpowder with a spark at its centre, and—well, “ohne hast, ohne rast” hardly describes the subsequent course of events. Eddington has suggested that the stability of the stars might be saved by imagining a time-lag between the instant at which matter attained the critical temperature necessary for annihilation and the instant at which this annihilation occurred. It has not yet been proved that the proposed remedy could be made effective, but even if it could, other difficulties remain. As the normal star inhabits the main-sequence, Russell supposed it to be a property of normal matter to annihilate itself at a temperature of about 32,000,000 degrees, the supposedly uniform central temperature of all main-sequence stars. It then became necessary to introduce further special assumptions to explain the luminosity of white dwarfs and of stars on the red giant spur line, whose centres are at temperatures very different from 32,000,000 degrees. He accordingly supposed that such stars contained other types of matter which dissolved into radiation at temperatures which were respectively higher and lower than 32,000,000 degrees. Even if the stability difficulty could be overcome, this latter series of assumptions seems to me to be so artificial as to compel the abandonment of this interesting theory.