4 JUNE 1927, Page 17

Professor McDougall has written a deeply interesting and fair-minded study

of the causes of war and the possibilities of their prevention in his Janus, the Conquest of War (To-day and To-morrow Series. Kegan Paul. 2s. Od.). Every word of this book is sound, but. the conclusion the author arrives at may be impossible of attainment—i.e., an International Air Force, although could such a force be established it would undoubtedly contribute to peace. The nations must surrender some part. of their rights in the cause of freedom, even as the individual in order to have liberty to go about hiS occasions must surrender his weapons and trust to the policeman.