Societies and Academies

Abstract

LONDON. Physical Society, June 14.-Prof. A. Schuster, F.R.S., president, in the chair.-T. H. Blakesley: Demonstration of the use of specific gravity balls for determining very small differences of density. Experiments were quoted which indicate a sensibility such that the error which might be expected in a properly conducted experiment would be of the order 5 in the sixth decimal place. Specific gravity balls have been employed for the purpose of discriminating between the qualities of potable waters in respect of density and of testing the efficacy of softening processes. A thermometer of open scale is employed to give the temperature at which a specific gravity ball is in equilibrium with a liquid being slowly warmed or cooled through that point of temperature. If such a determination is made in distilled water at ordinary atmospheric temperatures it fixes the specific gravity of the ball at the temperature of equilibrium within four or five units in the sixth place of decimals. If a second observation with the same ball is made in a slightly heavier liquid, the temperature of equilibrium will be considerably higher, perhaps 2° or more, than in distilled water. By applying the coefficient of cubical expansion the density of the ball at the higher temperature can be obtained, and this is the density of the second specimen of water at the second temperature. Reference to a table of densities of distilled water will furnish its density at the higher temperature, and the difference between the two numbers will give what the author calls the density excess of the second liquid over distilled water at the higher of the two temperatures. This density excess is best quoted in parts in one million.-Dr. H. F. Haworth: Maximum sensibility of a Duddell vibration galvanometer. The maximum sensibility of a moving coil vibration galvanometer as a voltage detector is obtained when the flux through it is so adjusted that the back E.M.F. of the coil is equal to its CR drop; then the back E.M.F. is equal to half the applied voltage, and the current is equal to V/aR, and is in phase with the applied voltage. Increases of current sensibility of about 30 per cent, at 200 ˜ and 40 per cent, at 1000 ˜ were obtained on running the instrument in a vacuum, thus showing that a large part of the mechanical work produced was used in overcoming the molecular friction of the system.-F. Stroude: An accurate examination of the Steinmetz index for transformer iron, stalloy, and cast-iron. Experiments to provide an experimental basis, suitable for mathematical analysis, with the view of discovering some relation connecting hysteresis loss and flux density which will accord with results obtained practically to a greater extent than the empirical law due to Steinmetz. Experiments were made with transformer iron stalloy (3 per cent, silicon iron) and cast-iron, two rings of each material being tested. A set of comparative tests on one of the transformer iron rings was made by the ballistic method, and these tests show that, in general, for a given value of B the hysteresis loss and the value of H for the ballistic tests are higher than the corresponding values for the slow cyclic tests.