Dumont's theory of the growth of population has no more scientific value than Malthus's theory. In conclusion, we may say that we are unable to formulate any laws of population which are worthy of the name of laws as yet, and it seems probable that, while we may understand clearly enough the factors which enter into the growth of population, we shall never be able to reduce these factors to a single formula or law. Social phenomena are too complex, we may here note, to reduce to simple formulas or laws as physical phenomena are reduced. Indeed, it is doubtful whether laws exist among social phenomena in the same sense in which they exist among physical phenomena, that is, as fixed relations among variable forces. Human society has in it another element than mechanical causation or physical necessity, namely, the psychic factor, and this so increases the complexity of social phenomena that it is doubtful if we can formulate any such hard and fixed laws of social phenomena as of physical phenomena. This is not saying, however, that social phenomena cannot be understood and that there are not principles which are at work with relative uniformity among them. It is only saying that the social sciences, even in their most biological or physical aspects, cannot be reduced to the same exactness as the physical sciences, though the knowledge which they offer may be in practice just as trustworthy. SELECT REFERENCES _For brief reading:_ MAYO-SMITH, _Statistics and Sociology_, Chaps. IV-VIII. BAILEY, _Modern Social Conditions_, Chaps. III-VI. _For more extended reading:_ BONAR, _Malthus and his Work._ BOWLEY, _Elements of Statistics._ MALTHUS, _Essay on the Principle of Population._ NEWSHOLME, _Vital Statistics._ CHAPTER IX THE IMMIGRATION PROBLEM In new countries population may increase by immigration as well as by the surplus of births over deaths. Immigration is, therefore, a secondary means of increasing the population of a country, and in new countries is often of great importance.