AN account of the preparation and testing of an international radium standard was given in the issue of this journal for April 4, 1912 (vol. lxxxix., p. 115). It will be remembered that a radium standard containing 21.99 milligrams of pure radium chloride was prepared by Mme. Curie for the International Committee. At a meeting in Paris the standard of Mme. Curie was compared with another independent standard prepared in Vienna by Professor Hönigschmidt, and the two were found to agree well within the limits of ac-curacy of measurements by the γ ray method. The preparation of Mme. Curie was accepted by the Committee as the International Standard, and was deposited in the Bureau du Poids et Mesures at Sevres, near Paris. At the same time it was arranged that the Vienna preparation should be retained in Vienna as a secondary standard. Arrangements were made to allow Governments to obtain duplicates of the international standard. For this purpose the Austrian Government gener-ously offered to provide the radium required at a considerable reduction in price. It was arranged that duplicate standards should be prepared and tested in Vienna in terms of their secondary standard, and then sent on to Paris to be tested again in terms of the international standard. In all six duplicate standards have now been prepared for different Governments, and the independent standardisations of the radium content in Vienna and Paris has been found to be in remarkably good agreement. The com-parisons of the quantities of radium is made by means of the penetrating γ rays, and it is a striking testimony to the accuracy of this method that the independent measurements have agreed so closely, although widely differing experimental arrangements have been employed in the two places.