Abstract
LONDON. Physical Society, May 14.—Sir W. H. Bragg, president, in the chair.—Dr. F. Lloyd Hopwood: Experiments on the thermionic properties of hot filaments. The experiments shown were some of those.described by Dr. Hopwood in the Philosophical Magazine for March, 1915, p. 362, in which the glowing filament of a carbon lamp and glowing filaments of nichrome and platinum in air are made to move under the influence of positively and negatively charged rods brought into or withdrawn from their vicinity, the character of the effects observed being such as to give a qualitative indication of the thermionic emission from the filaments. In addition, he showed a type of tilted electroscope in which the gold-leaf was replaced by a narrow loop of Wollaston wire. When a current is passed through the wire so as to make it glow, it forms an electroscope of different sensitivity for +ve and –ve charges.—G. D. West: A modified theory of the Crookes radiometer. The paper gives a short account of, a theory of the Crookes radiometer worked out by Sutherland in 1896, but, unfortunately, much neglected. The theory as it stands will not explain many radiometric phenomena, but it is shown that when modifications depending on the modern knowledge of thermal surface conditions are made, such explanations become possible. Radiometer action, especially at the higher gas pressures, would appear to depend essentially on the formation of gas currents near the radiometer vane. These currents are distinct from convection currents, but are closely associated with the phenomena of thermal transpiration.—A. Campbell: The magnetic properties of silicon iron (stalloy) in alternating magnetic fields of low value. Measurements are described of the hysteresis losses in silicon iron sheet and wires, in very low alternating magnetic fields at low and telephonic frequencies, using an alternating-current method described in a former paper. The equations giving the hysteresis losses as a function of Bmax. are deduced in the case of the sheet material at low frequencies for ranges of Hmax. from 0.0002 to 0.02. Comparisons are made between sheet material and wires of different diameters, and curves are given showing the great improvement in the permeability of wires when thev are annealed. The behaviour of the material is studied, both by ballistic tests and at telephonic frequencies, as regards the alternating field when direct-current fields of various values are applied at the same time.—T. Smith: Tracing rays through an optical system. Equations for tracing rays in an axial plane through an optical system have the normal refraction terms separated from those representing aberrations. By expressing the latter as a fraction with the first-order aberration as the numerator and a correcting factor, which mav take various forms, as the denominator, rays may be traced exactly through the system, using a short table of cosines in terms of sines in place of the extensive tables, giving sines in terms of angles generally employed. A considerable saving of time is effected in the calculations, and the estimation, without calculation, of the aberrations of other rays is facilitated.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies. Nature 105, 473–475 (1920). https://doi.org/10.1038/105473a0
Issue Date:
DOI: https://doi.org/10.1038/105473a0