AbstractThe polarizabilities of the alkali and halogen ions are calculated by means of a new method.It is proved that the polarizabilities of the mononuclear ions are constant and not (as Fajans and Joos had to assume) dependent on the surroundings.The values obtained for the alkali ions are in good agreement with those calculated by other writers; the values for the halogen ions are lower than those given by Fajans and Joos, but it is shown that the method they adopted in calculating them was incorrect.