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differentiation is an effect of effort for conservation of energy. This thought, which is used in psychology as "the law of mini- mum effort," and in various ways in the natural sciences, should be made useful in sociology, Thus Simmel shows great skill in tracing the development of the ecclesiastical hierarchy, and of military ranks from the principle of the conservation of energy.

In a word Simmers method of sociological investigation is distinguished by profound psychological analysis and by histori- cal illumination of problems, though relatively less by the latter than by the former. This is methodologically justified, since historical phenonema can have no value for sociology until they have been brought into the clear light of social and individual psychology. 1

DR. O. THON.

BERLIN, GERMANY.

1 Translated by ALBION W. SMALL.

(To be continued.)