LONDON. Royal Society, April 25.—Sir J. J. Thomson, president, in the chair.—Sir Charles Parsons: Bakerian lecture: Experiments on the production of diamond. The paper alludes to some of the results of experiments described in papers by the author to the Royal Society in 1888 and 1907, particularly to those on the decomposition by heat of carbon compounds under high pressure, and on the effect of applying pressure to iron during rapid cooling. A description is given of experiments designed to melt carbon under pressures up to 15,000 atmospheres by resistance heating and by the sudden compression of acetylene oxygen flame, also by the firing of high-velocity steel bullets through incandescent carbon into a. cavity in a block of steel. Allusion is made to experiments on chemical reactions under high pressure and their results. The pressures occurring in rapidly cooled ingots of iron, and experiments bearing upon this question, are discussed. Experiments at atmospheric pressure and also in vacuo are described. The main conclusions arrived at are:—That graphite cannot be converted into diamond by heat and pressure alone within the limits reached in the experiments; that there is no distinct evidence that any of the chemical reactions under pressure have yielded diamond; that the only undoubted source of diamond is from iron previously heated to high temperature and then cooled; and that diamond is produced, not by bulk pressure, as previously supposed, but by the action of the gases occluded in the metal and condensed into the centre on quick cooling.