Abstract
LONDON. Physical Society, Oct. 25.—E. G. Richardson and E. Tyler: The transverse velocity gradient near the mouths of pipes in which an alternating or continuous flow of air is established. A comparison is made of the alternating and direct flow of air near the mouths of tubes of various sections, by traversal of a hot-wire anemometer across the tube. In the alternating flow, a peak of high average velocity is found near the walls of the pipe, but in one-way flow this annular peak is absent, the velocity falling continuously from the centre of the tube to within a short distance of the walls. The existence of a layer of laminar flow close to the walls, when the main body of air is in turbulent niotion, is demonstrated.—B. K. Johnson: Resolving-power tests on microscope objectives used with ultraviolet radiation. An object of known regular structure and of variable interval is produced by projecting in the object-plane of the lens under test a reduced image of grating, the apparent line separation of which is varied by rotation of the latter; thus the line interval can be determined when resolution just ceases. The results show that the fused quartz monochromatic object-glass of numerical aperture 0.35, computed for and used with radiation of wave-length 0.275 µ, gives nearly twice the resolving power of a lens of similar aperture computed for and used with light of wavelength 0.51 µ; while the fused quartz monochromatic lens of numerical aperture 1.2 has a resolving power 70 per cent higher than that of a well-corrected object-glass of the same numerical aperture when used with light of wave-length 0.51 µ.
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Societies and Academies. Nature 124, 861–863 (1929). https://doi.org/10.1038/124861a0
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DOI: https://doi.org/10.1038/124861a0