Robinson, H. P. (Henry Peach), 1830-1901, author, Abney, William de Wiveleslie, Sir, 1843-1920, author, Piper & Carter, publisher · London : Piper & Carter · leaf 75
l away from tlie sun. 3t will be found that the gradations are equal, and the greatest darkening exactly opposite the hole, liaise the card next to the height of one inch, and the gradations will be found to be more extended and softer. The reason of this can be well understood by a glance at the… … Fig. 22. three instances see what relative illumination they will receive. a is opposite the hole, and receives the light from a circle of sky of which d e is diameter, and b from an ellipse of which h 1c is one diameter, and e from an ellipse of which f g is one diameter. In the first case, where…
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Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
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