This book has been professionally retyped and reformatted to fit modern day standards by officials of the Portuguese Institute of Higher Studies in Geopolitics and Auxiliary Sciences. * Organised crowds have always played an important part in the life of peoples, but this part has never been of such moment as at present. The substitution of the unconscious action of crowds for the conscious activity of individuals is one of the principal characteristics of the present age.I have endeavoured to examine the difficult problem presented by crowds in a purely scientific manner-that is, by making an effort to proceed with method, and without being influenced by opinions, theories, and doctrines. This, I believe, is the only mode of arriving at the discovery of some few particles of truth, especially when dealing, as is the case here, with a question that is the subject of impassioned controversy. A man of science bent on verifying a phenomenon is not called upon to concern himself with the