. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 120 COLORS OF THICK PLATES. When llie system of lenses det-cribed above is held between the eye and the li;^lit, another .•system of ruigs makes its appearance, which is formed by the transmitted light. In this case the tints are much feebler, being diluted by the intermixture (;f a great deal of whit3 liglit, which, as we shall see hereafter, lias nothing to do with their formation. Of these it is remarkable that the diame- ters of the bri
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 120 COLORS OF THICK PLATES. When llie system of lenses det-cribed above is held between the eye and the li;^lit, another .•system of ruigs makes its appearance, which is formed by the transmitted light. In this case the tints are much feebler, being diluted by the intermixture (;f a great deal of whit3 liglit, which, as we shall see hereafter, lias nothing to do with their formation. Of these it is remarkable that the diame- ters of the briglit rings correspond with those of tlie dark rings seen by reflec- tion. Tims the thicknesses at which the bright rings by transmitted light appear form a scries corresponding witli the progression of even numbers, 0, 2, 4, G, &c.; and the thicknesses at which the intervening dark rings are seen cor- respond to the progression 1, 3, 5, 7, &c. Also the tints reflected and trans- mittt'd at any given point are complementary to each other, or are such as, united, produce white. The measurements above given are those which correspond to rings formed by light perpendicularly incident upon the thin lamina. But wlien the rings arc observed obliquely, their diameters are rapidly enlarged with increase of obliquity. Sir Isaac Newton ascertained the law of this increase to be this : that the squares of the diameters arc inversely as the cosines of incidence. When the incidence exceeded GO^, it appeared to him that this law uo longer held good; and this conclusion, which, up to a recent period, had not been invalidated, has formed a serious diiliculty in the way of any tlieory of light. Ilecent experiments, however, made by Messi's. Provostayc and Desains, with monocliromatic light, and with special arrangements to eliminate the sources of error in m(;asurement which must liavi; vitiated Newton's results at high inci- dences, have fully established the; universality of the law.
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