Abstract
LONDON. Physical Society, March 26.—Dr. A. Russell, vice-president, in the chair.—Prof. A. W. Porter and F. Simeon: The change of thermal conductivity with fusion. The change in question was determined for mercury and for sodium by finding the temperatures at different points of a cylinder of ttie metal contained in a glass tube. The ends of the cylinder were maintained at such temperatures that the metal was liquid half-way down its length, the remaining part being solid. The temperatures were taken by means of thermo-electric junctions inserted in narrow tubular depressions which had been formed in the glass tube by forcing a knitting needle down into the locally heated glass. The ratio of the thermal conductivity for solid and liquid was estimated from the slope of tangents drawn to the temperature-curve on each side of the melting point. The values of these ratios are of the same order as the ratio of the corresponding values of the electrical conductivities. The mean value for mercury is 3.91, and for sodium 1-31.—Dr. J. A. Fleming: An instrument for the optical delineation and projection of physical curves such as hysteresis, resonance, and characteristic curves. This instrument is designed for projecting on to a screen or photographing on a plate such curves as magnetic hysteresis, resonance, or characteristic curves which can be performed slowly, or are non-periodic or non-repetitive.—Dr. P. Phillips and J. Rose Innes: The stability of some liquid films. The authors give a simple method of calculating the equilibrium form of a thin film which is a surface of revolution. They then consider the stability for certain kinds of displacement of three classes of such films, viz., the sphere, the cylinder and the catenoid. The mathematics used is quite elementary throughout and the treatment is rigorous.—Prof. A. W. Porter and E. Talbot Paris: A demonstration of the green-flash of the setting of an artificial sun. A large disc of card mounted so that it can be slowly rotated has a hole, 1 in. in diameter, cut in it about 2 in. from the periphery. This is covered with red gelatine films, and is illuminated from behind so as to form an artificial sun. The front of the disc is covered with white Bristol board and is moderately' illuminated by a lamp in front. This sun is viewed through a rectangular aperture (4 in. wide) in a blackened board, the lower edge of the aperture serving as the horion. When the disc is rotated the artificial sun sets and green afterimages are obtained of characters varying according to the amount that the eye has been exposed to the bright sun. If the sun is not viewed until immediately before the complete setting the after-image represents simply the disappearing segment to which it is due. The authors claim that this phenomenon is what is often described as the green-flash at sunset, though they are ready to admit that other (but probably rarer) phenomena also go under the same name.
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Societies and Academies . Nature 95, 194–196 (1915). https://doi.org/10.1038/095194a0
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DOI: https://doi.org/10.1038/095194a0