Elements of natural philosophy (Volume 2-3) . white and pink. Pale blue-green, pale pink. The same as 6th, very faint. The other or-ders being too faint to be distinguishable. Waves whichinterfere toproduce thecolors by reflexion; Illustration andexplanation; These colors arise from the in-terference of waves reflected fromthe first, with those reflected fromthe second surface of the airplate. Suppose a small beam incidentperpendicularly or nearly so, onthe first surface MN of the plate,where the thickness is t. A partA 0 will be reflected back, therest A j5, being transmitted, will traverse t
Elements of natural philosophy (Volume 2-3) . white and pink. Pale blue-green, pale pink. The same as 6th, very faint. The other or-ders being too faint to be distinguishable. Waves whichinterfere toproduce thecolors by reflexion; Illustration andexplanation; These colors arise from the in-terference of waves reflected fromthe first, with those reflected fromthe second surface of the airplate. Suppose a small beam incidentperpendicularly or nearly so, onthe first surface MN of the plate,where the thickness is t. A partA 0 will be reflected back, therest A j5, being transmitted, will traverse the thickness t. At the second surface, againa part B C, is reflected, and the reflected portion return-ing through the thickness £, will emerge at the first sur-face in the direction C 0, and be superposed on that firstreflected at this surface, and these will either conspireand reinforce each other or will interfere and partiallyor wholly neutralize each other, according to any of theconditions explained in § 7, depending upon the differ-. ELEMENTS OF OPTICS. 287 even ence of route 2 t. Whenever 2 t is equal to any even if zt be anmultiple of | X, for any color, this color will be increased, multiple ofand when equal to any odd multiple of | X, it will besuppressed. Now, 2 £, will vary from a value sensiblynothing to one equal to many times X, for even the long-est waves, in passing outward from the point in whichthe spherical surfaces are tangent to each other, and if an oddhence the colored fringes and the intermediate dark multiplerings. But the portion reflected at the second surface will, Transmittedin part, be again reflected at the first, and will traverse ^en reflectedthe thickness £, a third time, and emerge below super- rinsa are dark;posed upon the portion first transmitted at the secondsurface. The difference of route of these portions willalso be 2 t, so that the effects should be the same oneither side of the lenses. Experiment shows, however,that this is not
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