Abstract
LONDON. Royal Society, November 11.—Sir J. J. Thomson, president, in the chair.—Lord Rayleigh: The reflection of light from a regularly stratified medium. The remarkable coloured reflection from some crystals of chlorate of potash described by. Stokes, the colours of opals and of old decomposed glass, etc., lend interest to the calculation of reflection from a regularly stratified medium, in which the alternate strata, each of constant thickness, differ in refrangibility. The higher the number of stratifications, supposed perfectly regular, the nearer is the approach to homogeneity in the light of the favoured wave-lengths. A general idea of what is to be expected may be arrived at by considering the case where a single reflection is very feeble, but when the component reflections are more vigorous, or when the number of alternations is very great, a more detailed examination is required. An important distinction reveals itself according to the relative values of the refractivity and thicknesses. In one case a sufficient multiplication of the number of strata leads to complete reflection; in the other it does not.—Sir William Abney: Two cases of congenital night-blindness. The two cases were examined spectroscopically. An interesting fact appeared that in their extinction of the different rays of the spectrum all light disappeared throughout the spectrum at the same moment that the colour vanished, and that the colour vanished to the normal eye at the same point that it did to the colour-blind. This pointed to the fact that the colourless part of the rays failed to give any sensation of light. As normal eyes see in a faint light with these colourless rays, it is to be presumed that the night-lind owe their blindness in faint lights to the absence of certain retinal processes which the normal eyes possess.—Hon. R. J. Strutt: Duration of luminosity of electric discharge in gases and vapours further studies, (1) The behaviour of jets of luminous gas flowing away from the region of discharge at a low gaseous pressure has been investigated, using the principal permanent gases, also mercury vapour. In a transverse electrostatic field the luminosity is deflected, part of it in most cases going to the positive plate, and part to the negative. But in hydrogen, when the pressure is not very low, nearly the whole of the luminosity is deflected to the positive plate, a small part remaining undeflected. As the pressure is reduced, an increasing part of the luminosity goes to the negative-plate. Similar results, are observed in mercury vapour. (2) Further observations are recorded on these jets at higher pressures, arranging a spark discharge so that the gas can flow out from it through an orifice into a sustained vacuum. With hydrogen (condensed discharge) the exuded iet of luminositv, about q mm. long, shows the Balmer series,. The discharge spectrum shows widened lines. These become narrow as the luminous gas emerges. (3) Nitrogen in the same arrangement, with an un-condensed discharge, shows a jet with periodic swellings similar to those observed by.Mach and Salcher and Emden when a jet of compressed air, examined by the shadow, method, escapes into the open. The wave-length agrees with that to be anticipated from their experiments. (4) This nitrogen jet luminosity is not to be confused in any way with active nitrogen. The time for which it endures is of quite a different order of magnitude, and the spectrum is essentially different.—G. W. Walker: Surface reflection of earthquake waves.—Dr. H. S. Allen: Characteristic frequency and atomic number, (1) Simple relations are. found to hold between the values of the product Ny for different elements (N being Moseley's atomic number and v the characteristic frequency). (2) For twenty-five metals it is found that the product can be expressed in the form Nv = nvA (n a whole number and v a constant of value 21.3×10.12 sec.—1 approximately). (3) The same rule is obeVed in the case of certain non-metallic elements. (4) Similar results are found when the characteristic frequency is calculated from the elastic constants by Debye's formula. The value of n thus obtained is not in all cases the same as that deduced from the specific heats. (5) Application of the theory of probability, shows, that there is but a small chance of the product Nv approaching so nearly to integral multiples of a, constant frequency by a mere accident. (6) It is found that the atomic num-bers of Moseley give better agreement with the proposed relation than do the atomic ordinals of Rydberg. (7) The empirical results are discussed from -the viewpoint of the quantum theory, and it is suggested that the integer n may be related to the number of electrons concerned in determining the crystalline space-lattice of the element in the solid state. (8) A relation similar in character is found to hold for certain electronic frequencies. In such cases VA must be replaced by VE = 3-289x to 15 sec.-1 (Rydberg*s constant). (9) This relation is considered with reference to the maximum of the photoelectric effect, the limiting frequency of this effect, ionisation potentials, and thermionic potentials.—Dr. C. Chree: Historical note on a relation between trie gravitational attraction exercised and the elastic depression caused by load on the plane surface of an isotropic elastic solid.
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Societies and Academies . Nature 100, 199–200 (1917). https://doi.org/10.1038/100199a0
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DOI: https://doi.org/10.1038/100199a0