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Knight's Mechanical Encyclopedia (ed. Knight) 3 1 Browse Search
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Knight's Mechanical Encyclopedia (ed. Knight), M. (search)
lowest points of the wheel respectively are the required altitude and zenith distance of the sun. Among celebrated instruments may be mentioned the mural circle made by Graham, for Halley, at Greenwich, and those made by Ramsden in 1788, for Piazzi, at Palermo, and one for Dublin. See graduating-instruments. The mural circle is so called because it is supported by means of a long axis passing into a wall. The mural circle of the National Observatory in Washington was made by Mr. William Simms of London. It is 5 feet in diameter, made of brass, and cast in a single piece. It is divided into spaces of 5′ each, upon a band of gold-inlaid on the rim and perpendicular to the plane of the circle. Placed at equal distances round the circle are six micrometer microscopes, with an acute cross of wires at their foci for reading angles less than 5′. Five revolutions of the micrometer are designed to measure 5′ upon the circle. The micrometer heads being divided into 60 equal parts<
Knight's Mechanical Encyclopedia (ed. Knight), T. (search)
rkable, the tendency of late having been to reduce this as far as possible in proportion to the aperture of the lens. A telescope is now in course of construction in Dublin for the Austro-Hungarian government. Its object-glass will have an aperture of 27 inches, and its total length will be about 32 feet. The ratio of focal lengths, mode of construction, powers, proportions, adjustments, and mounting are fully explained in many treatises on the subject. See Pearson, Loomis, Heather, Simms, etc., etc. See under the following heads:— Astronomical telescope.Newtonian telescope. Binocular telescope.Object-glass. Cassegrainian telescope.Opera-glass. Comet-seeker.Perspective-glass. Equatorial telescope.Reflecting-telescope. Eye-glass.Refracting-telescope. Field-glass.Submarine telescope. Finder.Teinoscope. Galilean telescope.Telemeter. Gregorian telescope.Terrestrial telescope. Herschelian telescope.Transit-instrument. One of the most important applications of t