Abstract
LONDON. Royal Society, May 11.—Sir Archibald Geikie, K.C.B. president, in the chair.—C. T. R. Wilson: A method of making visible the paths of ionising particles through a gas. The paths are made visible by condensing water upon the ions immediately after their liberation, an expansion apparatus being used which works without appreciable stirring up of the air. The trails of ions formed by the a particles from radium have in this way been made visible and photographed, very dense and sharply defined rays of cloud being formed on expansion. Air exposed to B rays gives clouds consisting mainly of faint straight threads radiating. Irom tne source; these have not yet been photographed. In air exposed to γ rays, the cloud is again in the form of straight threads traversing, the cloud chamber-the tracks of particles from the walls. The cloud formed in air exposed to Rontgen rays is entirely concentrated in minute streaks and patches. A photograph shows these to consist mainly of fine threads not exceeding a few mm. in length, and generally far from straight, probably the tracks of kathode rays produced in the air by the X-rays. The whole of the ionisation would appear, as Bragg has already suggested, to be effected by the kathode rays derived from the X-rays.—W. H. Dines: The vertical temperature distribution in the atmosphere over England, and some remarks on the general and local circulation. This paper gives an account of the results of some 200 observations made in the British Isles in the years 1908, 1909, and 1910 on the temperature of the upper air. It discusses the annual variation of the temperature up to 14 kilometres, and shows that the annual range remains fairly steady, with a total amplitude of about 12° C. up to 11 km., above which the range suddenly drops to 3°, and the times of the maxima and minima go back two months. The question of the daily variation at great heights is then discussed. The relation between the temperature at various heights and the height of the baro meter at the surface is dealt with, and it is shown how over a low-pressure area with the barometer below 740 mm. the temperature of the first 8 km. is very low, reaching at 7 km. a value of nearly 10° C. below its average value, and that above 10 km. it is considerably above the average. In the anti-cyclonic parts the conditions are reversed, and it is warm below and cold above. The height at which the isothermal region is met with in summer and winter and in times of high and low barometer is then referred to. A statement with regard to the existence of similar con ditions that have been found to- exist on the Continent is also given. In the second part of the paper various theoretical considerations are taken into account. It is shown that if an extensive and strong wind exists in any part of the atmosphere, warm air will be found somewhat below it on its right hand, and cold air above it on the right, with converse conditions on the left, and it is pointed out that this agrees with the distribution of temperature that is found to exist at the various levels of cyclones and anticyclones.—Prof. W. N. Hartley: Some mineral con stituents of a dusty atmosphere.—Dr. H. Stanley Allen: The path of an electron in combined radial magnetic and electric fields. The path of an electron in a radial electric field superposed on a radial magnetic field is found to lie on a circular cone the vertex of which coincides with the magnetic pole. If the surface of the cone is developed into a plane, the trace of the path is a conic section with trie vertex as focus. The solution in the particular case in which there is no electric field has been given by Poincare; the path is then a geodesic line on the surface of the cone, and, of course, becomes a straight line when the cone is developed. In cases which can be realised experimentally, the developed path is hyperbolic, and does not in general differ greatly from a straight line. An account is given of some experiments carried out to illus trate the theory. The first observations were made with a focus tube in which the antikathode was the pole of an electromagnet. The phenomena observed are easily ex plained in terms of the theory. Other vacuum tubes were prepared in which a fine pencil of kathode rays could be produced by means of a Wehnelt kathode. In a radial magnetic field the stream of electrons assumed a spiral form, and a number of photographs were obtained snow ing the spiral paths on a cone of revolution.—Dr. R. A. Houstoun: The absolute measurement of light-a pro posal for an ultimate light standard. A thermopile cannot be used for the measurement of candle-power, because it gives the same value to the energy of every wave-length, invisible as well as visible. The author has, however, found by spectrophotometric investigation in the ultra violet, visible, and infra-red parts of the spectrum that if a filter consisting of aqueous solutions of copper sulphate and potassium bichromate in a particular strength in glass cells be placed before the thermopile, then this filter stops the ultra-violet and infra-red entirely, and lets through a fraction of each wave-length in the visible spectrum proportional to its visibility. In other words, it weights each radiation according to its visibility. The voltage on a tantalum lamp was varied over a wide range, and its candle-power as read by thermopile and filters agreed well with the readings of a photometer. Owing to the high sensitiveness of the galvanometer required, the method is not suitable for commercial application, except perhaps for integration photometry, when a number of thermopiles might be connected in series with the one galvanometer. The importance of the method lies in the fact that it pro vides a satisfactory basis for heterochromatic photometry independent of the Purkinje phenomenon at all intensities. The author therefore proposes to use it for defining the unit of light intensity. He would define the latter as that source, the total intensity of radiation from which at a distance of 1 metre after passing through his filters would be ergs/sq. cm., sec. For the standard candle x should be about 0.8.—Prof. A. C. Dixon: Harmonic expansions.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 86, 404–406 (1911). https://doi.org/10.1038/086404a0
Issue Date:
DOI: https://doi.org/10.1038/086404a0