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Nature volume 110, pages 721724 (25 November 1922) | Download Citation

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LONDON. Royal Society, November 16.—Sir Charles Sherrington, president, in the chair.—A. S. Eddington: The propagation of gravitational waves. The potentials given in Einstein's theory represent not only the absolute gravitational disturbance of the field, but also the metric of the co-ordinate system which is to a great extent arbitrary; consequently the speed of propagation of the potentials is not necessarily the speed of the absolute disturbance. Einstein showed that, when the co-ordinate frame is chosen subject to a certain restriction, the potentials are propagated with the speed of light. Considering the propagation of plane waves on unrestricted coordinates, it is found that “transverse-transverse” waves continue to have the speed of light, whereas the other two types of waves have no fixed speed when Einstein's restriction is removed. The latter types do not correspond to any absolute disturbance of the field. Of the three conceivable types of transverse-transverse waves, one is inconsistent with the equations of entirely empty space, Gμv = 0; but this type nevertheless commonly occurs in Nature, namely, as a propagation of gravitational disturbance by light-waves. Divergent waves are also considered. Although the equations correspond to those of sound-propagation, no uniform spherical waves of gravitation can occur; they must always be complicated by doublet-sources for some of the components. The waves emanating from a spinning rod are worked out in detail, and it is found that (in agreement with Einstein) the rod must slowly lose energy by these waves; for a typical example the period of decay of the rotation is found to be of the order 1035 years. —J. H. Jeans: The theory of the scattering of α-and β-rays. A theory of scattering is developed in which both the feeble encounters of the theory of multiple scattering and also the violent encounters of the theory of single scattering are taken into account. The presence of single scattering produces very nearly the same effect as can be produced by a suitable adjustment of the constants in the law of multiple scattering, and this renders the separate experimental study of single scattering very difficult. —A. P. Chattock and L. F. Bates: On the Richardson gyro-magnetic effect. Richardson has shown that the angular momentum arising in a ferro-magnetic substance from unit change in its magnetic moment should have the value of 1.13×10-7 if gyrating electrons are responsible for its magnetism. Measurements of this quantity by the ballistic method for three specimens of iron and one of nickel are given. The results, divided by 1.13×10-7, agree to within 1½ per cent, with one another, and their mean is 0.6 per cent, greater than 0.500. Close proportionality also exists between the change of magnetic moment and the angular momentum resulting. The specimen used consisted of an upright wire suspended by a quartz fibre. By the introduction of a hinged joint between wire and fibre the adjustment of the magnetic axis of the wire to the vertical is much facilitated, and measurements were made on reversal of magnetism instead of on merely reducing it to zero. The more perfect symmetry resulting from this procedure may be the cause of the more consistent results obtained. The effect on the results of the eddy currents in the specimen was not more than a small fraction of 1 per cent, for the specimens used. At high dampings the ordinary damping correction gives values that are too large.—P. M. S. Blackett: On the analysis of a-ray photographs. A large number of photographs were taken of the ends of the tracks of a-rays from polonium in both air and argon, using C. T. R. Wilson's expansion method. There are sudden bends made by the tracks due to collision with the atomic nuclei, and the actual form of these bends is obtained from measurements of the double images given by the special camera designed for the work by Shimizu. The frequency of occurrence of bends of given type are consistent with the existence of an inverse-square law of force between the α-particles and the nuclei, when their distance apart lies between 6×10-12 and 10-9 cm. for argon, and 3 × 10-12 and 5×10-10 cm. for air. The velocity of the a-particles along the latter part of their tracks was also calculated from the frequency of the bends and found to be much lower than had been expected. Velocities so low as 10 cm. per second were obtained, and the relation connecting the velocity v and the range r was found to be roughly of the form v∞2, instead of the form v∞2⅓ found by Marsden and Taylor for the early part of tracks by other methods. No anomalous effects were discovered as regards frequency or type of collision.— J. H. Jones: The kinetic energy of electrons emitted from a hot tungsten filament. When allowance is made for experimental and secondary effects the distribution of energy agrees with that given by Maxwell's law. Of experimental errors the most serious are probably due to difficulties of measuring the small currents involved and the temperatures. These lead to uncertainties which in individual experiments may amount to so much as 10 per cent. The secondary effects probably arise from contamination of the heated surfaces. This tends to increase the apparent energy of electrons emitted and the increase may amount to so much as 20 per cent. The abnormal electron energies found by Ting, which were as much as 100 per cent, in excess of the Maxwell distribution value, do not appear under satisfactory experimental conditions.—W. Wilson: The quantum theory and electromagnetic phenomena. From the point of view of the quantum theory such systems as atoms possess stationary states which are subject to conditions expressed by the equations—

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https://doi.org/10.1038/110721b0

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