. The principles of physics. y betweenthem, what is the focal length ? 8. Find the focal length of a lens which throws the image of an object5 ft. distant on a screen 3 ft. distant. 9. A double concave lens having a focal length of 3 in. is held at adistance of 2 in. from a small object; find the position of the image. 368 ETHEE DYNAMICS. 10. If an object be at twice the focal distance of a convex lens, howwill the length of the image compare with the length of the object ? 11. To an eye whose distance of distinct vision is 25 cm, how manydiameters will a lens of 1 cm focus magnify ? 12. Show
. The principles of physics. y betweenthem, what is the focal length ? 8. Find the focal length of a lens which throws the image of an object5 ft. distant on a screen 3 ft. distant. 9. A double concave lens having a focal length of 3 in. is held at adistance of 2 in. from a small object; find the position of the image. 368 ETHEE DYNAMICS. 10. If an object be at twice the focal distance of a convex lens, howwill the length of the image compare with the length of the object ? 11. To an eye whose distance of distinct vision is 25 cm, how manydiameters will a lens of 1 cm focus magnify ? 12. Show that a concave air lens in water has the same effect on inci-dent light as a convex water lens in air. Section VIII. PRISMATIC ANALYSIS OF LIGHT. SPBCTEUMS. 329. Analysis of light which produces the sensation of white. Experiment 1. —Place a disk withan adjustable slit in the aperture ofa porte-lumifere, so as to exclude from a darkened room all light-wavesexcept those which pass through the slit. Near the slit interpose a. Fig. 278. double-convex lens of (say) 10-inch focus. A narrow sheet of light willtraverse the room and produce an linage, AB (Fig. 278), of the slit on awhite screen placed in its path. Now place a glass prism C in the pathof the narrow sheet of light and near to the lens, with its edge vertical. ANALYSIS 0¥ LIGHT. 369 (1) The light now is not only turned from its former path, but that whichbefore was a narrow sheet, is, after emerging from the prism, spread outfan-like into a wedge-shaped body, with its thickest part resting on thescreen. (2) The image, before only a narrow, vertical band, A B, is nowdrawn out into a long horizontal ribbon DE. (3) The image, beforewhite, now presents all the colors of the rainbow, from red at one endto violet at the other; it passes gradually through all the gradations oforange, yellow, green, blue, and violet. (The difference in deviationbetween the red and the violet is purposely much exaggerated in thefigure.) From th
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
