Abstract
LONDON. Physical Society, March 27.—Dr. R. T. Glazebrook,. F.R.S., president, in the chair.—On refraction at a cylindrical surface, by Mr. A. Whitwell. The object of the paper is to describe and illustrate the position and form of the focal areas produced by the refraction, at a cylindrical surface, of light diverging from or converging to a point. In general, if a plane can be drawn through the point to cut the surface symmetrically, then all the light passes really or virtually through an area in this plane. In the case of the cylinder there are two such planes. One contains the radiant point and the axis of the cylinder, the other contains the point, and is normal to the axis. The equation of the locus of intersections of symmetrical rays which intersect in the first plane, for small apertures, is obtained in terms of the distance of the radiant point from the axis of the cylinder α, the radius r, and the index of refraction µ. The loci of the intersections of symmetrical rays which intersect in the second plane, when the aperture is small, are shown to be circles described about the radiant point as centre and having radii equal to (µ - I) (α -r).— The evaluation of the absolute scale of temperature, by Dr. R. A. Lehfeldt. Formulae are given for the constant-pressure and constant-volume thermometers. An attempt is made to work out the latter with the aid of existing data. It is found that To = 273.18 from hydrogen and 273.2 from nitrogen. The deviation of the constant-volume scale from the absolute scale is indicated by curves. At 100° absolute the constant volume (hydrogen) thermometer reads 0.1 or 0.2 too low.—Prof. Callendar, in a communication sent subsequent to the meeting, said that in his paper on the thermodynamical correction of the gas thermometer (Phil. Mag., January) he had incidentally mentioned that the correction for the constant-volume gas thermometer could not be directly deduced from the Joule-Thomson cooling-effect alone, without additional data, unless a formula were assumed for the variation of the cooling-effect with temperature; but that the value of the absolute zero could be deduced from the pressure coefficient if the Joule cooling-effect in free expansion were known. The experimental measurement of the latter was, however, impracticable.—Mr. Blakesley exhibited and described a lens possessing the, following properties:—The two conjugate foci always move with the same relative rate along the axis. The size of the object always bears to the size of the image the same ratio, so that using the same object the image is always of the same size. The instrument is of one piece of glass, and constitutes a telescope the magnifying power of which is the ratio which the object bears to the image in size, linear. The relation of the rate of motion of the object to that of the image is the square of the magnifying power.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 67, 550–552 (1903). https://doi.org/10.1038/067550b0
Issue Date:
DOI: https://doi.org/10.1038/067550b0