Free Download Telescope
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This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1861. Not illustrated. Excerpt: ... OF THE METHODS PRACTISED IN THE ACTUAL CONSTRUCTION OF LENSES AND SPECULA. (84.) Having thus described the principal combinations of refracting and reflecting surfaces, which have been devised for the construction of telescopes, it remains to say something of the practical means which have been adopted for the actual manufacture of the specula and lenses. They require a delicate and difficult art, especially as regards the former, where parabolic, elliptic, or hyperbolic figures have to be communicated to the polished surfaces in the very act of polishing them. In the case of lenses, as we have seen, all the requisites of a perfect telescope can be attained by the use of truly spherical surfaces, and these it is comparatively easy to form, by reason of the natural tendency of two surfaces which grind each other by equable rubbing over every part, to work each other into a spherical concavity and convexity exactly fitting. Practically speaking, when it is intended to work a glass surface to a sphere of an exactly assigned radius, the nearly approximate spherical form of the right curvature is first communicated to it by grinding in a metal basin, of the proper concavity, which may be done to some considerable nicety by turning the tool in a lathe, to fit a guage. The lens is then connected, or otherwise firmly attached, to the lower end of a vertical rod of wood or metal AB (fig. 23), the upper end of which terminates in a steel ball F, working in a cup c, to which it has been accurately fitted by smooth grinding, so that every point of the surface A of the lens, when made to oscillate or revolve conically by a motion given to the rod by a hand grasping it at B (where it is enveloped in woollen cloth or felt, to prevent the communication of warmth), will move in ... Telescope - Wikipedia A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light). Orion Telescopes & Binoculars - Official Site The friendly experts at Orion will help you choose the right telescope binoculars or accessories. Same-day shipping. 100% satisfaction guarantee! Telescopes in Houston Texas with Reviews - YP.com Find 3 listings related to Telescopes in Houston on YP.com. See reviews photos directions phone numbers and more for the best Telescopes in Houston TX. Telescope: Reflecting & Refracting Telescopes - Best Buy Shop for telescopes online at BestBuy.com. Choose from a wide selection of reflecting and refracting telescopes from Best Buy. Telescopes - Celestron Celestron Telescopes- manufactures telescopes telescope accessories optics computerized telescopes binoculars spotting scopes and microscopes for serious and ... Best Telescopes for the Money - 2017 Reviews and Guide Here are the best telescopes for the money. Our top picks include recommendations for city dwellers and hobbyists as well as budget picks. : Telescopes - Binoculars & Scopes: Electronics ... Online shopping for Electronics from a great selection of Refractors Reflectors Catadioptric Telescopes & more at everyday low prices. Binoculars Telescopes Microscopes Spotting Scopes Marine ... Binoculars Telescopes Microscopes Spotting Scopes Marine & Nautical Sales - Service - Repair Land Sea Sky Texas Nautical Repair telescope eBay Find great deals on eBay for telescope and celestron telescope. Shop with confidence.
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