Abstract
LONDON. Royal Society, May 11.—Sir Charles Sherrington, president, in the chair.—Lord Rayleigh: (i) A photographic spectrum of the aurora of May 13–15, 1921, and laboratory studies in connection with it, A photographed spectrum of the aurora on the night of May 14, 1921, shows the negative bands of nitrogen in detail, and the green aurora line which, however, is subordinate. With atomic ray excitation of nitrogen in the laboratory, and better, in the narrow positive column (capillary tube) at low pressure, the development of the negative bands can be imitated, but other nitrogen spectra (line spectrum and second positive band spectrum) persistently appear in addition. The cathode ray spectrum is free from the latter, but the negative bands produced are not developed like those in the aurora, the intensity being much more concentrated in the first band of each group. Hard and soft cathode rays behave alike in this respect. Assuming that helium is the main constituent of the atmosphere above 130 kilorn., as the theory of diffusion indicates, then it is difficult, on the hypothesis of positive ray excitation, to explain its absence from the spectrum of this particular aurora, which at Christiania reached to 470 kilom. Experiments on artificial mixtures indicate that it should be visible. With cathode ray excitation, this difficulty would be lessened, but the different development of the nitrogen bands remains.—(2) A study of the presence or absence of nitrogen bands in the auroral spectrum. Spectra of the “Northern Lights” taken in Shetland are compared with spectra of the ordinary night sky at Terling near London. Most of the Shetland spectra show nitrogen bands. None of the ordinary Terling spectra show these bands, though, owing to the long exposure given, the Terling plates show the green aurora line as strongly, or more strongly, than the Shetland spectra. On the occasion of the great magnetic storm and world-wide auroral display of May 13–14, the nitrogen bands were strongly developed at Terling. —C. Chree: The 27-day period (interval) in terrestrial magnetism. There is a tendency in terrestrial magnetism for disturbance to follow disturbance, and calm to follow calm, after an interval which does not depart much from 27 days. The absolute daily range of declination at Kew Observatory from 1858 to 1900 and the international “character” figures from 1906 to 1920 both show the phenomenon. Generally, it is more clearly exhibited in years when sun spots are few in number or are situated in low solar latitudes. The season of the year seems to have little, if any, influence.—M. Barker: On the use of very small Pitot tubes for measuring wind velocity. The finite pressure in a one-sided Pitot tube for infinitely small openings is comparable with that at the nose of a sphere, of diameter equal to the breadth of the opening, placed in a stream moving with a velocity equal to that at the centre of the pitot opening. This indicates a breakdown in the p = 12 law for Pitot tubes, when the dimensions of the pitot are very small or the velocity very low, p being the density and the velocity of the fluid and p the pressure difference. The value of ruv below which the fut law ceases to hold, r being the radius of the circular Pitot tube and v the kinematical viscosity of the fluid, has been determined. For values of rv3o, ppv2 is greater than below this value there is a viscosity effect in the form of an additional pressure comparable, as before, with that at the nose of a certain sphere.—E. T. Paris: On doubly resonated hot-wire microphones. The properties of double resonatorsjior use with hot-wire microphones in order to increase sensitivity and also, if desired, to widen the range of response were investigated. Two types of resonator were dealt with: (a) The “Boys double resonator,” consisting of a “stopped pipe” in series with a Helmholtz resonator; and (b) the “Helmholtz double resonator,” consisting of two Hehnholtz resonators in series.—J. C. McLennan and D. S. Ainslie: On the structure of the line X = 6708 A of the isotopes of lithium. A vacuum arc in the vapour of the metal together with Lummer plates and a 3O-plate 6chelon grating crossed with a Lummer plate to effect the resolution were used. With strong arcs, X = 6708A consists of two doublets, with a separation of the doublet components of 0-128 A and 0-165 A respectively. The mean dis placement of the two doublets is 0-32 A, which is 3-4 times that demanded on Bohr's theory for isotopes of lithium having atomic weights 6. and 7. Merton and also Aronberg in studying X = 4058 A, in the spectrum of ordinary lead, and in that of lead having a radio-active origin, found that the observed difference in wave-length was between 80 and 90 times as great as the difference to be expected from Bohr's theory. With both lead and lithium, in what would appear to be isotopic spectral displacements, the value found by observation is about the atomic number times the value obtained by calculation on the basis of Bohr's theory.
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Societies and Academies. Nature 109, 698–700 (1922). https://doi.org/10.1038/109698b0
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DOI: https://doi.org/10.1038/109698b0