DR. B. E. STRADLING, chief adviser for research and experiment, A.R.P. Department, Home Office, delivered the first of three lectures arranged by the Institution of Civil Engineers on air raid precautions. After referring to the creation some months ago of the special Research Branch of the A.R.P. Department of the Home Office, and to the recent appointment of a Civil Defence Research Committee under the chairmanship of Dr. E. V. Appleton, which would ensure that the full resources of the scientific world would be enlisted in the services of that section of Government activity, Dr. Stradling dealt with the question of protection from the effects of the high-explosive bomb. On detonation, a very high pressure is produced which causes the metal case to expand to possibly one and a half times its original size and then burst into fragments. In addition to the formation of splinters, the expanding gases have two effects: actual movement of gas giving the effect of a very ‘high wind’, and a wave sent out through the air which is similar to a sound wave. The first effect causes major destruction on a surprisingly local scale; about 30 feet from a large bomb, the effect has practically disappeared. Outside that zone the acoustic type of wave can spread a very long distance. Its effects on a structure can be disastrous, but more especially on those portions which have a high-natural frequency, such as windows and the like. Experiments show that the effect is dependent upon the structure itself, as well as upon the form of the wave. Due to the adoption of basements as shelters, the question of earth movements around an exploding bomb is also of importance. There is a zone around the bomb in which few normal structures can be expected to stand, but it is very limited in extent. The wave which is effective at longer distances is somewhat similar to a very slight earthquake and has little effect upon a normal building. Further lectures in the series will be given by Colonel F. J. Wyatt, on camouflage, on June 12; by D. Anderson, on the design of bomb-proof shelters, on June 20; and by Brigadier C. A. Bird, on the work of the military engineer in war, on June 27.