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    THE MOON'S APPARENT DIAMETER.—A recent number of ciel et Terre (April 2) contains an article on the moon's angular diameter, by M. P. Stroobant, of which a translation, with copious notes, appears in the Observatory for May. The methods employed in the determination of the apparent diameter of ourfatellite are (1) micrometer measures, (2) meridian passages, (3) heliometer measures, (4) photography, (5) occultation of stars by the moon, (6) eclipses. A comparison of the principal results obtained during the present century by these various methods indicates that occultations give the most accordant values, and M. Stroobant remarks that the method of occultation is the only one in which the apparent diameter of the moon is not augmented by physical or physiological causes. Accurate observations of occultations indicate that the lunar diameter has a value lying between 31′ 5″ and 31′ 6″, but M. Stroobant urges that this approximation is not sufficient. He concludes by saying:—“The application of photography to the determination of the exact instant of disappearance or of reappearance of a star would permit, without doubt, the attainment of great precision, especially when these phenomena occur at the dark limb of the moon, or during eclipses, when a number of small stars can be observed.... About every nineteen years the moon passes over the Pleiades in conditions more or less advantageous for observation; this phenomenon will occur next year. Might not the occasion be profitably used in securing a number of photographs at various observations? If these are sufficiently separated from one another, it would be possible to deduce a new value for the parallax of the moon.”

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