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Societies and Academies

Nature volume 96, pages 640642 (03 February 1916) | Download Citation




Royal Society, January 27.-Sir J.- J. Thomson, president, in' the chair.-Prof. J. Joly: A collision predictor. The collision predictor is a mathematical instrument of simple construction. It enables the mariner when navigating in fog or thick weather to foretell risk of collision with another ship, and also the moment at which the risk is greatest. The ships concerned are supposed to be aware of each other's course and speed, and (at intervals) of their distance apart. The determination of distance is made according to principles described in a previous communication to the Royal Society. The operation of taking a reading on the collision predictor takes less than half a minute. The construction of the instrument and the principles involved cannot be conveyed without diagrams.-Dr. C. Chree: Discussion of Kew magnetic data, especially the diurnal irregularities of horizontal force and vertical force, from ordinary days of the eleven years 1890 to 1900. The paper is mainly devoted to a discussion of the results of measurements of the horizontal force and vertical force curves from the magnetographs at Kew Observatory for the eleven years 1890 to iqoo. Subsequent to 1900, artificial electric currents diminished the value of the curves. One of the main objects is the study of the diurnal variation as given by "ordinary" days, i.e. all days with the exception of the highly disturbed. The changes of the regular diurnal o variation throughout the year are dealt with in detail, and the inequalities are expressed in Fourier series. An investigation is also made of the annual inequality. For this purpose use is made of results for years subsequent to 1900, as well as of those between 1890 and 1900. The relation of the diurnal inequality to sun-spot frequency is considered in the light of Wolf's formula, the constants in the formula being determined by least squares. Considerable attention is also paid to the absolute odaily range or difference between the extreme values for the day. The frequency of occurrence of ranges of different size is 'considered in detail.-G. W. Walker: A portable variometer for magnetic surveying. The paper contains an account of a portable magnetic variometer for measuring horizontal force in a magnetic survey. The results obtained with it and with a Kew unifilar at forty-eight stations in the course of the magnetic survey of the British. Isles in 1915 are discussed. The operation of measuring force is reduced to a single reading of the instrument, with a reading of the temperature, at a definite instant of time, in place of the elaborate system of readings taking over an hour when a unifilar is used. It is oestimated that the normal error is not likely to exceed 57.-Prof. J. C. McLennan: The single-line spectrum of magnesium and other metals, and their ionising potentials. It has been shown that magnesium vapour traversed by electrons can be stimulated to the emission of a single-line spectrum consisting of the wave-, length A=2852-22 A.U. It has been shown that the absorption spectrum of non-luminous magnesium vapour contains an absorption band at A = 2852-22 A.U., and one at A = 2o73-36 A.U. As the lines A = 2852-22A.U., and A = 2073>36 A.U., are respectively the first members of the series v - 2,p2-1-5, S, and v=i-5, S - in, P, respectively, the absorption spectrum of magnesium vapour has been shown to be analogous to the absorption spectra of the vapour of mercury, zinc, and cadmium. The ionising potentials have been deduced for atoms of magnesium, in addition to those for the atoms of mercury, zinc, and cadmium. Considerations have also been presented which show that if Bohr's theory affords an explanation of the origin of single-line spectra, then Frank and Hertz and also Newman must have placed a wrong interpretation on the results of their direct investigation of the ionising potentials for mercury atoms.-F. Tinker: The microscopic structure of semi-permeable membranes, and the part played by. surface forces in osmosis. Micro-photographs of the common precipitation membranes, taken by a new method, show that such membranes are composed of small precipitate particles packed closely together, and ranging from o-i / to rq /t in diameter.. Each of these precipitate particles is, however, not simple in structure, but is itself an aggregate formed by the flocculation of smaller ultra-microscopic particles. Of the membranes examined, copper ferrocyanide and Prussian-blue have the smallest par-' tides. Precipitation membranes show most of the physical properties of gels as ordinarily prepared by bulk precipitation, but they have not the same mechanical structure as the latter, the membrane having a much finer texture than the gel proper. The pores in a copper ferrocyanide membrane range from 8 pn to 60 /*/* in diameter. Their size is such that they can block colloidal molecules mechanically, but not the ordinary crystalloidal molecules even when highly hydrated. The order of a series of membranes with respect to pore size is the same as that of their efficiency as semi-permeable membranes. Copper ferrocyanide and Prussian-blue are the most efficient membranes, and they have also the smallest pores. There is a very close connection between the osmotic properties of a membrane and the extent to which the membrane capillaries are under the control of surface forces. Osmotic effects are probably the result of adsorption phenomena occurring at the surface of the membrane and in the capillaries, the membrane being relatively impermeable t6 solutes negatively adsorbed, but permeable to solutes positively adsorbed.-E. Newbery and J. N. Pring: The reduction of metallic oxides with hydrogen at high pressures. Metallic okides have been heated to temperatures of 2500° C. in dry hydrogen at pressures up to 150 atmospheres, water vapour being removed by metallic sodium. The following oxides were reduced to metals:—

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