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LONDON. Physical Society, April 23.—Prof. W. G. Adams, Vice-President, in the chair.—The following papers were read:—On delicate calorimetrical thermometers, and on expansion of thermometer-bulbs under pressure, by Prof. Pickering. The reading of a delicate mercurial thermometer, when placed in a bath at constant temperature, is found, to depend on whether the thermometer was at a higher or lower temperature than the bath, before immersion. Capillarity was suggested as an explanation, but experiment showed that the effect was not always greatest at the narrow parts of the tube, and hence this idea was discarded. By using the same tube with different bulbs attached, the differences varied, and eventually the effect was found to be caused by exposing the inside of the tube to air and moisture; for when bulbs were attached to new tubes, without being so exposed, the differences between the rising and falling readings disappear. Hence, for very delicate thermometers great care should be taken not to expose the bore of the tube, and calibration of a tube before attaching the bulb must not be attempted. Even in the best tubes, after every possible precaution has been taken, the author finds some parts about which the mercury appears to stick, and in delicate observations these parts of the tube are to be avoided. He also finds it necessary to gently tap the top of the tube to relieve any friction, and has devised a clockwork arrangement for performing the operation uniformly. In the second part of the paper the author describes the want of concordance between the thermometers which have been compared with the same standard, and finds it due to the expansion of the bulbs not being in all cases proportional to the difference of pressure between the inside and outside. Thermometers with large thin bulbs show greatest discrepancies, and the remedy is found to be in making the bulbs more rigid. This is done by having a double bulb, making them from a cylindrical tube instead of by blowing, and increasing the thickness of the walls of the bulb. A knife-edge arrangement in the upper part of a thermometer is described, by which the same part of the graduated tube can be used, whatever the temperature (about which small changes are to be observed) may be. The proper amount of the mercury column can be cut off with the greatest nicety by its use. Mr. Whipple remarked that phenomena similar to those described in the paper were constantly coming under his notice, and mentioned the pressure-corrections they were applying to thermometers used in vacuo, during some pendulum experiments at present being carried out. He also described the Kew method of determining the pressure-correction in deep-sea thermometers, which are protected by an outer glass jacket filled with alcohol. Mr. Lant Carpenter described the first comparison experiments made at sea with protected and unprotected bulb thermometers. In answer to questions, Prof. Pickering said the range of pressure used was from 0 to 3 atmospheres, and in his most delicate thermometer, where 200 millimetres correspond to 1° C., the difference between readings taken in horizontal and vertical positions amounts to 30 millimetres.—Note on magnetisation; on sequences of reversals, by Mr. R. H. M. Bosanquet. Some experiments have recently been made on an iron bar whose magnetic properties under reversals with ascending values of current were first determined some years ago. The magnetic resistances have again been determined, first with ascending values of current, and afterwards with descending values. In all cases the induction was measured by reversing the current. The results generally show a greater magnetic resistance for descending values of current, except for small inductions where the resistance was less, when the experiments were performed in the above order. The paper concludes with a molecular hypothesis to explain the above results.—On a thermo-dynamical relation, by Prof. Ramsay and Dr. S. Young. The paper is an extension of one presented to the Society on February 26, and of which an abstract was read by the Secretary. The numerical results are given, from which the authors deduce the relation p = b t - a, for constant volume, and additional reasons are given for believing acetic acid (whose vapour-density at ordinary temperatures is abnormal) to be a mixture of C2H4O2 and C2H8O4 the former preponderating as the temperature rises. The authors ask the Society for a name to designate lines connecting pressure and temperature at constant volume, and for which they suggested “isochor” in their previous paper.