This number of the Journal goes to press just before the third international Convention sponsored by the Institute with the Ausschuss für Funkortung and the French Institute of Navigation. As members will know, the theme of the present series of meetings is the prevention of collisions, at sea and in the air, by systems or methods based ashore or on the ground. An account of the meeting and summaries of the papers presented will be published in the next number of the Journal, and a selection of the papers themselves will be published in future numbers. Wing Commander Anderson's paper, in which he introduces the concept of a collision index by means of which travel risks may be related to the risks of other human activities, forms a suitable introduction to the series.