Royal Society, January 21.-R. E. Gibbs: Structure of a quartz. Investigations on quartz have shown that symmetry and X-ray data enable only partial definition of structure. Intensity measurements and general physical properties of the material must also be studied. Oxygen atoms occupy positions c/g above and below the silicon atoms. Only a small structural change accompanies the transition from ft to a quartz, but still the tetrahedral character of ft quartz is lost. The structure proposed assumes the crystal to be non-molecular and the oxygen to occupy basal planes as noted above. The silicon atoms seem to move about 0-3 A.U. from their /3-positions.-N. K. Adam and G. Jessop: The structure of thin films, Pt. vii. Critical evaporation phenomena at low pressures. By means of a new apparatus, measurements of the surface pressure of monomolecular films have been made at room temperature, down to o-oi dyne per cm. At areas greater than about 5000 sq. A.U. per molecule, the pressures exerted by films of insoluble fatty substances tend to a value within 25 per cent, of that given by the equation Fa = RT, R having the same value as in a perfect gas. The divergences from the theoretical values are probably within experimental error. Between 100 and 5000 sq. A.U. the pressure-area isothermals closely resemble those for liquid and vapour in three dimensions. Expanded films are analogous to liquids, not vapours, and there is considerable cohesion between the molecules in them.- H. J. Gough, D. Hanson and S. J. Wright: The behaviour of single crystals of aluminium under static and repeated stresses.-C. H. M. Jenkins: The determination of the vapour tensions of mercury, cadmium, and zinc by a modified manometric method. The apparatus consists of a specially designed manometer, using the material under determination as the observed liquid in this gauge; it can be inserted in a 3-inch diameter electric tube furnace. The pressure on the apparatus is regulated by means of nitrogen, the pressure of which is measured on an independent barometer. The vapour pressure of the liquid is measured over a free surface in the closed end of the manometer by alterations in the pressure of the nitrogen to bring both liquid surfaces in this gauge level. The apparatus is similar to the letter V in shape. One extremity is closed; the other opens into a long straight column bent at right angles to it. Into this column specially shaped pieces are inserted, transforming it into a reflux condenser, which counteracts the diffusion of the nitrogen into the vapour. Values have been obtained for the vapour tensions of mercury, cadmium, and zinc over the range of pressure from 15 to 1500 mm. The boiling-points (760 mm.) have been found to be 357°, 767° and 906° C. respectively.-W. Barlow: The configuration of the carbon atom and the geometrical relations of this configuration to those of other atoms, as evidenced in the chemical and crystallographic structures of organic chemistry. Pt. i.-Ursula Andrewes, Ann C. Davies and F. Horton: The soft X-ray absorption limits of certain elements. Investigations have been made of the voltages corresponding to critical values of electron energy associated with some of the longer wave-length absorption stages of seven successive elements, chromium, manganese, iron, cobalt, nickel, copper and zinc. The generally accepted value of an absorption limit, obtained by spectroscopic methods, corresponds not to ionisation of the atom by the detachment from it of an electron in the sub- group concerned, but to the transportation of the electron from the sub-group to the periphery of the atom, i.e. to the levels of the most loosely bound electrons. The values obtained in this investigation are associated with absorption of energy by electrons in the M sub-groups, the several values obtained for each element being attributed to selective absorption stages, and not to actual ionisation of the atom.- W. L. Bragg and G. B. Brown: The crystalline structure of chrysoberyl. Chrysoberyl, BeAl2O4, is analogous in chemical composition to the spinel group of minerals R"R2""O4. It is entirely different in its crystalline form, being orthorhombic, whereas the spinels are cubic. It may be supposed that the oxygen ions occupy the greater part of the volume in the crystal, and the metal ions are placed in the interstices between a close-packed assemblage of oxygen ions. A comparison of BeO, A13O3, BeAl2O4, shows that in each case the oxygen atoms r,re very nearly in a close-packed hexagonal arrangement and that the distances between atomic centres are almost identical from the three crystals, being about 2-7 A.U. Each aluminium atom in A12O3 and BeAl2O4 occupies a position between six oxygen atoms. The hexagonal close-packed lattice can be referred to orthorhombic axes with ratios \/2./3: i 'oo\/3/3--H. G. Telling: On a set of quartic surfaces in space of four dimensions, and a certain involutory transformation. Each of the surfaces in four dimensions may be generated by taking three arbitrary skew lines and two arbitrary points, drawing a plane through each of the points to meet the three lines, and then finding the locus of the intersection of the plane through the first point with the plane through the second point. The geometry of the surface then suggests the consideration of, in all, fifteen lines, of which that joining the two given points is one; and then passing through an arbitrary given point of the space, there are fifteen such surfaces, one associated with each of the lines. The paper is concerned with determining the intersection of any two of these fifteen surfaces.- L. F. Richardson: Atmospheric diffusion shown on a distance-neighbour graph. The atmospheric diffus-ivity in Fick's equation has been found by various investigators to increase from 0-2 cm.2 sec.'1 to zo11 cm.2 sec."1 as the size of the cluster of diffusing particles increases from io˜2 to io8 cm. The effect is due to eddies of many sizes acting together. There is apparently no way of modifying Fick's equation in order to describe this phenomenon. But a new mathematical method is here developed, in which, instead of thinking about concentration as a function of position, we think about q, the mean number of neighbours per length, as a function of /, their distance apart. This gives a rough average value 0-6 /*'* cm.2 sec.'1 for the atmosphere, when I lies between i metre and io km.-T. Alty: Some phenomena occurring at the surface of bubbles in water. The surface tensions of water in contact with various gases are compared by the drop-weight method. The weight of a bubble is independent of the gas used if the rate of flow is slow enough. To examine a new water surface, the rate of flow is increased until several bubbles emerge per second. When flowing from the same capillary, the gases form bubbles the volumes of which can be arranged in decreasing order as follows: argon, nitrogen, oxygen, ozone, hydrogen, nitric oxide, carbon dioxide. These differences are related to the adsorbability of the gases.-A. L. M. Sowerby and S. Barratt: The line absorption spectra of the alkali metals. The alkali metals are all able to absorb the lines of the combination series is-md, contrary to the Selection Principle. The caesium series of this type has been observed for the first time. The absorption of this series by potassium is uninfluenced by the presence of argon at two atmospheres pressure. It is estimated that 12,000 times as many atoms can absorb the first member of the principal series of potassium and rubidium as can absorb the line is-^d, the ratio being the same for the two metals. The "atomic extinction coefficients "of the different alkali metals are approximately the same for corresponding lines.-A. M. Tyndall and G. C. Grindley: The mobility of ions in air. Pts. i. and ii. The improved method of measuring mobility depends on producing ions by flashes of a-rays subjected to a special alternating / field. The effect of. water vapour is to cause fall of mobility of fully formed negative ions down to a value i -6 in saturated air. Positive ions of two types were found-initial and final. The mobility of the initial type is indistinguishable from that of the negative and is similarly affected by water vapour. Water vapour has a retarding influence on rate of transformation into final ions. In ordinary dry air much transformation occurs within 0-007 sec' °f birth, but in wet air the ions nearly all remain in the initial stage at double this age.-W. Jevons: A band spectrum of tin monochloride exhibiting isotope effects. The spectrum of the uncondensed discharge through SnCl4 vapour comprises a continuous spectrum between X 4900 and X 3950, and a hitherto unrecorded band spectrum consisting of two distinct sets of bands occupying the regions X 3910 - X 3486 and X 3405 -X 2830 respectively. Each set is attributed to a chloride of tin. The bands in the more refrangible set constitute two systems a and /3 of the normal Deslandres type. If they be ascribed to SnCl35, a few additional bands in the same region are attributable to SnCl37. There is also some indication of the tin isotope effect. The less refrangible set consists of several groups, each containing a few close bands degraded towards the red. Too little is known of these bands to say whether they are emitted by SnCl or by a polyatomic chloride.-J. H. Andrew, M. S. Fisher and J. M. Robertson: Some physical properties of steel and their determination. Methods of measuring electrical resistance, electrode potential, and continuous change of resistance during tempering, are described. The change from martensite to granular pearlite is gradual and only proceeds to a certain stage at each temperature. Martensite is not formed during tempering at constant temperature, but results from the decomposition of austenite during cooling from the tempering temperature. The rate of tempering of martensite is not affected by the addition of moderate amounts of special elements. Austenite tempers more slowly, and its rate of tempering is considerably reduced by addition of special elements.-N. K. Adam and G. Jessop: Note on the spreading of solids on water surfaces. Gary and Rideal's observations on the spreading of myristic acid on water have been continued down to very low compressions. A small pressure, that of the "gaseous "state of the film, is set up immediately the crystal touches the surface, and the "two-dimensional vapour pressure"very soon afterwards.