Experimental science. Elementary, practical and experimental physics (1890)
Hopkins, George M. (George Milton), 1842-1902 · New York, Munn & co. · leaf 246
If the sourcesof light when equally distant from the screen form shadowsof the same depth, their illuminating power is the same. When, however, the intensities of the two lights differ,the shadows will differ, and it will be necessary to removethe stronger light to a greater distance to secure… … Photometer. to secure shadows of the same intensit)r. Nine candleswould require removal to a distance of three feet, and so on.All the candles of the group must be in the same line in thedirection of the rod. The eye is able to detect a differenceof one-sixtieth in the values of the shadows,…
Physics · Lantern projection · Electric apparatus and appliances
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