Abstract
LONDON. Physical Society, June 28.-Mr. A. Campbell, vice-president, in the chair.-Prof. E. Wilson, B. C. Clayton, and A. E. Power: Hysteresis loss as affected by pre vious magnetic history. Hysteresis loss in iron at atmospheric and liquid air temperatures under three different conditions: (i) after the iron has been care-fullv demagnetised; (2) after it has been subjected to a large force (previous history) of about 26 C.G.S. units; and (3) whilst it is under the influence of an external constant magnetising force after demagnetisa tion.-Prof. W. M. Thornton: Dielectric hysteresis at low frequencies. An attempt to determine from di electric hysteresis loops the nature of the change of polarisation which gives rise to the absorption of energy.-Prof. G. W. O. Howe and J. D. Peattie: The efficiency of generation of high-frequency oscillations by means of an induction coil and ordinary spark-gap. The apparatus used was similar to that employed in small radio-telegraph stations. A 10 in. induction coil, operated from cells through a mercury inter rupter, supplied power to an oscillatory circuit con taining a spark-gap between spherical electrodes. Coupled to this circuit was another oscillatory circuit representing the aerial, and containing a variable resistance which constituted the high-frequency load. The input, output, and efficiency were determined for various degrees of coupling, various aerial decre ments, different lengths of spark-gap and with various primary voltages, the object being to determine the effect of these various factors on the working of a small radio-telegraph station.-Dr. A. Griffiths and Miss C. H. Knowles: The resistance to the flow of water along a capillary soda-glass tube at low rates of shear.-S. W. J. Smith and J. Guild: The self-demagnetisation of steel. The constituents, iron and iron carbide, are easily traceable in annealed steel, owing to the differences between their magnetic pro perties. The ferro-magnetic transition point of the carbide is about 500° C. lower than that of the iron. The carbide is also magnetically harder at ordinary temperatures and possesses greater coercive force,.although, like iron, it is magnetically very - soft at temperatures near the transition point. In conse quence of these facts, the effect of heat upon the residual magnetism of an annealed steel rod is peculiar and at first sight mysterious. As the temperature rises the residual magnetism falls continuously until it becomes zero in the neighbourhood of 200° C. It then changes sign and reaches a maximum negative value at about 220° C. Beyond this, the negative magnetisation decreases slowly, and finally becomes imperceptible between 700° C. and 800° C. If the rod is cooled from 800° C. it remains without per ceptible polarity as the temperature falls; but if the heating is interrupted before the whole of the residual magnetism is destroyed the behaviour on cooling is quite different.
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Societies and Academies . Nature 89, 546–548 (1912). https://doi.org/10.1038/089546b0
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DOI: https://doi.org/10.1038/089546b0