Elementary treatise on physics, experimental and applied : for the use of colleges and schools (1906)
Ganot, A. (Adolphe), 1804-1887, Atkinson, Edmund, 1831-1901, Reinold, A. W. (Arnold William), 1843-1921 · New York : Wood · leaf 645
mirrors were used in sending the light of beaconsand lighthouses to great distances, but they have been supplanted by the useof lenses of the above construction. In most cases oil is used in a lamp ofspecial construction. The light is placed at the principal focus of the lens,so that the emergent… … Fig. 615 Fig. 614 62 8 On Light [619- illuminated, the lens is continually moved round the lamp by clockworkmotion, the rate of which varies with different lighthouses. Hence, atthe same place the light alternately appears and disappears after equalintervals of time. These alternations serve to…
Physics
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