THE MAXIMUM POSSIBLE POPULATION OF THE WORLD.—Sir George H. Knibbs concludes in Scientia (Nov. 1925) his examination of the world-problems of population, with special reference to the conditions governing the maximum possible population. He gives various estimates (based upon certain con siderations) of the possible population ranging from 2942 millions—if the world's existing population increased in ratio of O. R. Baker's estimate of possible increase in the U.S. agricultural area—to 9792 millions —if all existing arable land in the world could support three persons per acre—and a final maximum of 13,440 millions if an average of a person per 2½ acres applied to the whole land surface of the world. But, as he points out, any one estimate is unsatisfactory, because the possible number must depend upon the world's social and economic organisation, upon ethical considerations governing these, and upon the extension of man's knowledge of Nature, and he briefly examines some of the main issues. Assuming that the present standard of living is retained, together with the present national prejudices and egoisms, Sir George considers it doubtful whether the population will ever reach the 5000 million limit. If man better co-ordinates his efforts so as to involve less expense in nonproductive effort, then possibly the advance of science may enable the 7000 million limit to be reached. The friendly study of universal economic conditions and of the adjustment of all territorial and economic relations, together with the advances made through systematised knowledge, would perhaps make possible a population of 9000 millions, though this would leave only a small area available to each individual.