Photographic optics and colour photography : including the camera, kinematograph, optical lantern, and the theory and practice of image formation (1909)
Johnson, G. Lindsay (George Lindsay), 1853-1943 · New York : D. Van Nostrand Co. · leaf 323
back along its original path. If, therefore, a darkened chamber has only a single small window, and its interior be lit up by a light on the outside, it will be impossible to see anything inside the chamber unless the observer can place his eye somewhere inside the emergent cone of rays. This is… … Pig. 186. and perceive the returning beam through the aperture, or to use a very small mirror, and keep one’s eye close to its edge so as to catch a portion of the reflected light. It was this principle which Helmholtz adopted in his ophthalmoscope. Dr. Thorner elaborated this instrument so as to…
Photographic optics · Color photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
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