A text-book on chemistry. For the use of schools and colleges (1866)
Draper, Henry, 1837-1882 · New York, Harper & brothers · leaf 103
y make them illuminate the surfaces equal-ly, and then, measuring their distances from e, their il-luminating powers are as the squares of those distances.In both this and the preceding method a difficultyarises when the lights to be compared are of differenttints. To some extent this may be… … PHOTOMETERS. 91 Fig. 6G. exact, differences in the colors of the lights even serv-ing to give greater accuracy. It depends on the follow-ing principle. If a light is made to throw the shadowof an opaque object upon a white screen, there is a cer-tain distance at which, if a second light be brought,…
Chemistry · Physics
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