LONDON. Royal Society, January 11. - Sir Archibald) Geikie, K.C.B., president, in the chair.—Lord Rayleigh: The propagation of waves through a stratified medium, with special reference to the question of reflection.—Prof. F. T. Tfouton: The mechanism of the semi-permeable membrane and a new method of determining osmotic pressure. The amount of water taken up by a liquid, such as ether, from an aqueous solution, the solute of which is insoluble in the liquid, diminishes as the strength of the solution increases, the maximum amount taken up being from pure water. Reasons are given in the paper for expecting that the amount of water taken up from a given solution would increase under pressure, and further, that at the osmotic pressure of the solution the amount taken up would be the same as that from pure water at the atmospheric pressure. An account is also given of an experimental investigation which has verified these conclusions in the case of a 60 per cent, solution of cane sugar when osmotic pressure is about 80 atmospheres.—Dr. Alois F. Kovarik: Mobility of the positive and negative ions in gases at high pressures. Rutherford and Child have shown that the current i per sq. cm., between two parallel plates when an intense ionisation is confined to the surface of one plate, is given by i = gV2K/2)27rd3, where V is potential difference, d distance between plates, and? mobility of ion. When theoretical conditions are fulfilled, the current through the gas in the two directions affords a direct measure of mobility of positive and negative ions. The surface ionisation was obtained by covering one of the plates with an active preparation of ionium, separated by Prof. Boltwood from the uranium residues lent by the Royal Society to Prof. Rutherford. Using high pressures, ionisation is mainly confined within a very short distance of the plate. The theory was tested experimentally, and it was found that over a considerable range i varied as V2 and inversely as d3. The results for the mobilities of the ions in these gases are as follows:-in dry air and dry hydrogen mobility varies inversely as pressure up to 75 atmospheres, the highest u ed; in moist carbon dioxide the product of mobility and pressure is constant up to 40 atmospheres, but for higher pressures the product decreases as the gas approaches the liquid state. The mean values for the products of mobility and pressure in atmospheres, for the range of pressures for which the product was constant, are for negative and positive ions, respectively, in dry air 1-89 and 1-346, in dry hydrogen 8-19 and 6-20, and in moist carbon dioxide 0-67 and 0-705 cm. per sec, for a potential gradient of one volt per cm.—G. A. Shake-spear: A new method of determining the radiation constant. The rate of loss of heat of a silvered surface at a temperature of ioo° C. in surroundings at 150 C. is observed (a) when the surface is polished, (6) when it is lamp-blacked. The difference is due to difference in radiation losses. The ratio of the rates of radiation is obtained by exposing the two hot surfaces in turn to a radiomicro-meter. The rate of radiation from the lamp-black is assumed to be proportional to the difference between the fourth powers of the absolute temperatures 373 and 288. The lamp-black at ioo° C is compared with a full radiator at the same temperature by means of the radiomicrometer. Certain corrections are necessary, and these are dealt with in the paper. As a check on the comparison given by the radiomicrometer, an instrument which constitutes a closer approximation to a full receiver was devised and used. It was found, incidentally, that the apparent radiation from lamp-black depends upon the surface upon which the lamp-black is deposited. The value obtained for? is 5-67 X 10-5 ergs per sq. cm. per sec. per deg4.—Dr. R. A. Houston: The mechanics of the water molecule. Suppose that a hydrogen atom loses one electron to a second hydrogen atom, and that the second hydrogen atom loses two electrons to an oxygen atom. Then the oxygen atom has two negative charges, each hydrogen atom one positive charge, there will be one line of force between the first and second hydrogen atoms and two lines of force between the second hydrogen atom and oxygen atom. Let the three lines of force act as equally strong spiral springs, and let a wave of light pass through a medium composed of such molecules. It is shown in the paper, by means of the ordinary theory of dispersion, that the absorption spectrum of such a medium consists of two bands, the ratio of the wave-lengths of which is 2-32. Also from the intensity and width of each band it is possible to calculate e/m, the ratio of unit charge to the mass of the hydrogen atom. Water is transparent in the ultra-violet and visible spectrum, and has two great bands in the infra-red at 3-07? and 6-15?, which are not present in oxygen or hydrogen. It is shown in the paper that the values of e/m calculated from these bands are respectively 7110 and 1550 electromagnetic units. Hence the structure assumed for the molecule cannot be far off the truth.