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... oblong and not oval, but terminated with two rectilinear and parallel sides, and two semicircular ends. On its sides it was bounded pretty distinctly, but on its ends very confusedly and indistinctly, the light there decaying and vanishing by degrees....

The Elements of Optics: Designed for the Use of Students in the University - Page 195
by James Wood - 1801 - 251 pages
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The Progress of Scientific Chemistry in Our Own Times: With Biographical Notices

Sir William Augustus Tilden - 1913 - 390 pages

...the light there decaying and vanishing by degrees. The breadth of this image answered to the sun's diameter, and was about two inches and the eighth...the penumbra. For the image was eighteen feet and a half distant from the prism; and at this distance that breadth, if diminished by the diameter of...

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