LONDON. Royal Society, Feb. 3. W. A. Bone, R. P. Fraser, and D. A. Winter: The initial stages of gaseous explosions. Part 1-Flame speeds during the initial ‘uniform movement.’ A gaseous explosive mixture is ignited at the open end of a horizontal tube 2.5 cm. in diameter. So long as the initial flame speed does not exceed about 4000 cm. per sec., there is a definite initial ‘uniform movement,’ the speed of which, under standard conditions of experiment, was nearly always fairly constant. But with initial flame speeds exceeding such limits, in ethylene-oxygen and acetylene-oxygen mixtures, the flame speed was continuously accelerated ab initio until detonation is set up, just as though the explosive mixture had been fired near the closed end of the tube. In hydrogenoxygen mixtures, whilst the uniformity of the initial movement was still maintained, its speed tended to vary. In certain circumstances, a slow ‘uniform movement’ of flame can be developed in an explosive mixture after an initial period of continuous acceleration. Thus the speed at which a slow uniform flame movement can travel through an explosive mixture cannot be regarded as a physical constant of it, in the same sense as its rate of explosion (that is, detonation).