Abstract
LONDON. Optical Society, November 11.—J. W. T. Walsh and W. Barnett: The effect of slightly selective absorption in the paint used for photometric integrators. A sensibly non-selective internal coating for photometric integrators is very difficult to produce and still more difficult to maintain. When lamps of different colour temperatures are compared in an integrator with an internal coating which shows selective absorption in, say, the blue, the values of candle-power obtained for the lamps of lower colour temperature will be too high, and vice versa. A simple method is given for calculating the magnitude of the effect for sources having a spectrum approximating to that of a black body. In work on normal type electric lamps, to an accuracy of i to 2 per cent., a quite noticeable coloration of the light may be produced by the sphere (either on account of paint or window selectivity or both) without the necessity for making any correction to the measured values of candle-power.—Conrad Beck: An accurate method of ascertaining the position of the focal point of an optical system. The method consists essentially in placing a diaphragm with two slit apertures behind the object-glass to be tested, the directions of the slits being at right angles to one another, and finding the position where the images form a symmetrical cross. Results of measurements by this method of the zonal aberrations of apochromatic microscope object-glasses are given.
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Societies and Academies. Nature 118, 898–899 (1926). https://doi.org/10.1038/118898b0
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DOI: https://doi.org/10.1038/118898b0