IN commemoration of the birth of J. D. v. d. Waals on November 23, 1837, an international conference on interaction between molecules will be organized by the "van der Waals Fonds" and the "Neder-landsche Natuurkundige Vereeniging". The ordinary sessions will be held in the van der Waals Laboratorium at Amsterdam on November 25 and 26, and an official celebration will take place on November 27. The object of the conference is to give a survey of some of the recent work connected with the idea of van der Waals forces. The programme will be published later. Sufficient time will be left for general discussion. A special number of Physica will appear during the conference ; it is hoped to be able to publish in this issue a number of papers on a variety of questions having some relation to the work of van der Waals. Physicists willing to contribute to it should send in their manuscripts before October 15, and though it will be impossible to read all these papers during the conference, it is hoped that they will play an important part in the discussions. The organizing committee, comprising Prof. J. D. v. d. Waals, Dr. A. Michels, Prof. Dr. J. A. Prins and Dr. H. B. G. Casimir, van der Waals Laboratorium, Nieuwe Achtergracht 129, Amsterdam (C), will be glad to give further information.