Celestial Objects For Common Telescopes (volume 1) by Thomas William WebbCelestial Objects For Common Telescopes (volume 1) by Thomas William Webb

Celestial Objects For Common Telescopes (volume 1)

byThomas William Webb

Paperback | January 10, 2012

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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. 1917. Not illustrated. Excerpt: ... is cooler, but seldom sufficiently thick. The Germans have employed deep yellow. Herschel I. adopted, with great success, a trough containing a filtered mixture of ink and water. Cooper, at Markree Castle, Ireland, used a * drum' of alum water and dark spectacles, and could thus endure the whole aperture, 13-- inches, of his 25-foot achromatic.1 With large apertures, a plane surface of unsilvered glass placed diagonally, as originally suggested by Herschel II., so as to reflect only a small fraction of the light and heat, is found of eminent service. Merz, of Munich, has so reduced the light by polarisation at four such surfaces, that a dark glass, the tint of which is of course better dispensed with, becomes unnecessary; and the same end is attained in a very ingenious double-prism eye-piece devised by Prof. Pickering: neither apparatus, however, is free from accidental colour.2 An eye-piece constructed by Andrews with two lenses of complementary tints, burnished in loosely to avoid fracture from expansion, has succeeded with a small aperture. In screen-glasses combinations of colour are good. Bed succeeds perfectly with green, or with green and blue. Herschel II. used green and cobalt blue.3 A Barlow lens, carefully silvered, is said to act admirably, though a light screen might still be necessary. If there is to be only one solar cap, deep bluish-grey, or neutral tint, will be quite satisfactory; if several, it would be worth 1 Not, however, an example to be imitated. Dawes thought that with a focus of 30 inches, 2 inches of aperture were enough for perfect security. A 4J-inch silvered mirror is not safe for screen-glasses. 2 An unsilvered glass mirror has been found an excellent instrument for solar observation.--(P.) * The value of complementary, or at any ...
Title:Celestial Objects For Common Telescopes (volume 1)Format:PaperbackDimensions:86 pages, 9.69 × 7.44 × 0.18 inPublished:January 10, 2012Publisher:General Books LLCLanguage:English

The following ISBNs are associated with this title:

ISBN - 10:0217694578

ISBN - 13:9780217694575

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