A treatise that is closely related, in point of subject-matter, on the one hand to the works of Emminghaus and Moreau, and on the other to the books of Preyer (_Die Seele des Kindes_) and Pérez (_Les trois premières années de l’enfant_ and _L’enfant de trois à sept ans_) on the development of children, has just been published by a Leipsic teacher under the title of _Die Periodicität in der Entwickelung der Kindesnatur_, _Neue Gesichtspunkte für Kinderforschung und Jugenderziehung_, by GUSTAV SIEGERT, Leipsic, 1891, R. Voigtländer. The author endeavors, in a very interesting manner we must admit, to show that, in the development of the child, lasting states in regular alternate succession occur of mental and physical buoyancy on the one hand and depression on the other, of moral exaltation, likewise, and moral subsidence. The fundamental cause of this periodical alternation, of the general existence of which numerous proofs are adduced, is supposed to lie in the alternate strengthening and relaxation of the individual’s forces of action, brought on by the expenditure and reproduction of energy; additional determinative causes, accelerative as well as retardatory, are found in intercourse with the world and with other human beings. We may call the former the individual and the latter the social cause of the phenomena of periodicity. In the application of his results to juvenile education the author arrives at some far-reaching propositions of reform, the consideration of which, however, we shall have to leave to the pedagogical press.