LONDON. Royal Society, Jan. 22.— P. M. S. Blackett and F. C. Champion: The scattering of slow α-particles in helium. Mott has calculated the scattering of α-particles by helium atoms on the assumption that the particles interact according to the inverse square law, that they have no nuclear spin, and that they obey the Einstein-Bose statistics. It is found that the scattering should vary periodically with changing angle and velocity; in fact, an interference pattern should be obtained the scale of which depends on the velocity. This theory has been tested by photographing the collisions between slow α-particles and helium atoms in a Wilson chamber. The results are in com-plete agreement with Mott's theory.— W. A. Bone, R. P. Fraser, and F. Lake: Explosions of mixtures of acetylene and electrolytic gas. The disturbing influ-ence of successive additions of acetylene upon the uniformity of the initial flame movement in an ex-plosion of electrolytic gas attains a maximum when 20 per cent of acetylene is present in the medium, thereafter declining, and eventually disappearing when 30 per cent of acetylene is present. There is a Primary selective partial combustion of acetylene, 2H2 + O2 = 2CO + H2, in the flame front, followed, behind the flame front, by either (i), when sufficient oxygen is present, a highly luminous combustion of the nascent carbon monoxide, or (ii) otherwise, by a thermal decomposition of any unburnt acetylene. The explosion of a C2H2 + O2 + 2H2 mixture is differ-ently affected by an equal dilution with argon or nitrogen.— W. A. Bone and R. P. Fraser: Flame speeds in the inflammation and detonation of CO-O2 mixtures. In the initial phase of ' inflammation ', and in the final stage of ‘detonation’, the maximum flame speed for moist mixtures at atmospheric press-ure is obtained with a circa 3CO + O2, instead of a theoretical 2CO + O2, mixture. Dilution of the medium with either argon, helium, or nitrogen does not materi-ally alter the proportions of carbonic oxide and oxygen in the maximum-speed mixture. Hence the point of maximum flame speed is principally deter-mined by the concentration of carbon monoxide, and the combustion of moist carbonic oxide is conditioned by a prior ‘excitation’ of its molecules, which are then rendered combustible.— C. V. Jackson: Inter-ferometric measurements in the arc spectrum of iron. Ten lines in the spectrum of the iron arc in air, between λ4000 and λ4400, have been measured by interferometric comparison with the red line of cad-mium or with the secondary standards of neon. Sixty-eight lines in the spectrum of the iron arc in air between λ2300 and λ3100 have also been measured interferometrieally. The results are in good accord with the wave-lengths recommended by the International Astronomical Union in 1928.