Well's natural philosophy : for the use of schools, academies and privte students, introducing the latest results of scientific discovery and research ; arranged with special reference to the practical application of physical science to the arts and the experiences of everyday life ; with three hundred and seventy-five engravings (1873)
Wells, David A · New York : Ivison, Blakeman, Taylor and Co. · leaf 365
Fig. 291, OPTICAL INSTRUMENTS, 717. The portable camera obscura, such as is ordinarilyused for photographic purposes, consists of a pair of achro-matic double convex lenses, set in a brass mounting (see Fig,291), into a box consisting of two parts, one of which ,^i| slides within the otlier. The… … -^ objects to which the lens is directed, and hy slidixig themovable part of the box in or out, the ground glass can be brought to the ^IG- 292. precise focus. The interior of the boxis blackened all over to extinguishany stray light. The appearance of the camera asdescribed is represented by Fig.…
Physics · Science · Technology
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