This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1876 Excerpt: ...few trials of both methods, I decided to have the photographs of the eclipse taken in the principal focus of the object-glass. "A second question, relating to the method of exposing the photographic plate, was also to be considered. At first, some experiments were tried with slides having openings with rounded ends or ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1876 Excerpt: ...few trials of both methods, I decided to have the photographs of the eclipse taken in the principal focus of the object-glass. "A second question, relating to the method of exposing the photographic plate, was also to be considered. At first, some experiments were tried with slides having openings with rounded ends or sides, under the impression that the exposure could thus be made more uniform. But experience and a more attentive consideration of the subject soon showed that the opening should have straight edges; for if we suppose two lines drawn through the centre of the image, one in the direction of the motion of the slide, and the other at right angles with the first, the parts of the picture lying along one of these lines will be exposed differently from those lying along the other by a slide having an opening with curved edges. Of course, when the slide is placed before the object-glass, this matter becomes unimportant; but such an arrangement would be inconvenient in telescopes of the ordinary pattern. "The photographs of the various phases of the eclipse of 1869, taken at Shelbyville, justified my expectations of the advantage to be derived from discarding the eye-piece generally used in such work. It occurred to me immediately after the eclipse that for photographs of the disk of the sun, since its apparent motion during the required time of exposure is insignificant, the telescope used might be advantageously reduced to a single fixed lens of long focus and small aperture, which would produce no sensible chromatic aberration. In this way the picture could be made as large as was found convenient for measurement, while distortion and curvature were avoided. "In order to test this idea, I applied at once to Messrs. A. Clark & So...
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Add this copy of Annals of the Astronomical Observatory of Harvard to cart. $17.82, very good condition, Sold by Prominent Trading Company rated 4.0 out of 5 stars, ships from Hereford, HEREFORDSHIRE, UNITED KINGDOM, published 2012 by RareBooksClub. com.