It may be said at once that, in the strictest interpretation of the title, this paper does not belong in this symposium, for it is one of the fundamental theorems of gravitational attraction that the same external gravity‐field may be produced by any number of different distributions of internal mass. However, the external gravity‐field may be incompatible with a proposed internal distribution; furthermore, by applying our other knowledge In a common‐sense way we may from a knowledge of the external field perhaps come close to the actual internal distribution of de