Light; a course of experimental optics, chiefly with the lantern . lm from the least breath of air is pictured plainly (PlateIII. C). Simple as it is, there is no more beautiful experimentthan this, and the film with a good solution will last foran hour. Any surface (not too convex) of iridescent glass (whichhas a film on the surface whose refractive power has beenaltered by a chemical process) may be focused in the sameway as the soap-film. ^ The film almost always lasts much longer than if the Stem is upper-most, owing to the thinnest portion being dependent from the smoothand unbroken circu
Light; a course of experimental optics, chiefly with the lantern . lm from the least breath of air is pictured plainly (PlateIII. C). Simple as it is, there is no more beautiful experimentthan this, and the film with a good solution will last foran hour. Any surface (not too convex) of iridescent glass (whichhas a film on the surface whose refractive power has beenaltered by a chemical process) may be focused in the sameway as the soap-film. ^ The film almost always lasts much longer than if the Stem is upper-most, owing to the thinnest portion being dependent from the smoothand unbroken circular wire. FILMS OF AIR. i6s Another beautiful experiment is with a film of a piece of glass on the back, rub a pieceof soap over the surface, and clean off with a chamoisleather. Pinch this in the clip, adjust it like the soap-film at 45° and focus; but keep it cool by interposingone of the glass cells filled with alum solution, or theexperiment will fail, as it depends on condensation of thebreath by the cold surface. Then blow on the centre. Fig. 97.—Flat Soap Film. through an india-rubber tube of -j-inch bore. As the breathcondenses roughly circular coloured rings will form, andgradually change as the moisture evaporates. Next we may take a film of air. Buy two squares , say 3 inches square, and grind off the sharpedges to prevent scratching. Carefully clean them, andthen carefully slide or grind them with moderate pressuresmoothly together. We very soon see beautiful fringes ofgorgeous colour. When satisfactory, pinch one lower corner 166 LIGHT. [chap. of the double plate in the clip, and the three others withloose wooden spring letter-clips. Focus as before : all willbe reproduced on the screen, and as we further pinch any-where, even with the finger and thumb, changes and move-ments of the colours will demonstrate that the particulsircolour wholly depends on the thickness of the film. Fig. 98.—Newtons Rings. 99. Thickness of the Film.
Size: 1609px × 1553px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidcu3192403121, bookyear1882
