(1) The second edition of Dr. Norman Camp-bell's “Modern Electrical Theory,” reviewed first in NATURE, May 28, 1908, is practically a new book. The work of Barkla and Bragg, and the theories of Einstein and Planck have rendered necessary a fresh treatment of part ii., dealing with radiation. The principle of relativity and Stark's work on valency alter completely part iii., which deals with electricity and matter, a field in which second thoughts have proved notoriously less ambitious than the first, whilst the first part, which deals with the electron theory proper, has also been entirely re-written. (1) Modern Electrical Theory. By Dr. N. R. Campbell. Second edition. Pp. xii + 400. (Cambridge: University Press, 1913.) Price 9s. net. (2) Les Ides Modernes sur la Constitution de la Matire. Confrences Faites en 1912. By E. Bauer A. Blanc E. Bloch Mme. P. Curie A. Debierne, and others. Pp. 370. (Paris: Gauthier-Villars, 1913.) Price 12 francs. (3) Researches in Physical Optics, with especial reference to the Radiation of Electrons. Part i. By Prof. R. W. Wood. Pp. vii + 134 + x plates. (New York: Columbia University Press, 1913.)