. Biographies of distinguished scientific men. Scientists; genealogy. 146 MALUS. 1802). Any substance «, of less refractive power than glass in opti- cal contact -with the base of a glass prism m, can be seen by an eye. at e at any incidence ivlthin the limit just mentioned, or while the rny i entering the other side of the prism and impinging on its base, is in- capable of being refracted out at the base, and therefore reflected from within; but as soon as this limit is exceeded, or the ray is refracted out at the base, then n ceases to be visible at e. The exact incidence or " critical
. Biographies of distinguished scientific men. Scientists; genealogy. 146 MALUS. 1802). Any substance «, of less refractive power than glass in opti- cal contact -with the base of a glass prism m, can be seen by an eye. at e at any incidence ivlthin the limit just mentioned, or while the rny i entering the other side of the prism and impinging on its base, is in- capable of being refracted out at the base, and therefore reflected from within; but as soon as this limit is exceeded, or the ray is refracted out at the base, then n ceases to be visible at e. The exact incidence or " critical angle " at which this takes place, is measured by an appropriate apparatus, and the refractive index for n deduced, that of the prism being known, a series of substances being applied in suc- cession, whether transparent or opaque. Dr. Woilaston in this way determined their refractive indices. As the different primary rays have indices a little differing, and which are greatest for red light. Dr. Young remarked that the limit thus found applies in strictness to the extreme red ray. In this way Dr. Woilaston found the refractive indices as follows:â White wax, boiling _ _ _ Ditto cold - - - - In the same way Malus found Wax at 14° Reaum. (=63° Fahr.) - - Ditto melting _ _ _ 1,4503 Ditto boiling _ _ - (These numbers are all lower than the former, probably from a dif- ferent sort of wax being used.) Dr. Woilaston, in applying the simple calculation above indicated to the observed angles, did not question tlie very natural assumption, that the same formulas would apply to the observed angles equally, â whether the substance was opaque or transparent, solid or fluid. Laplace, in a theoretical investigation founded on certain consider- ations derived from the molecular theory, framed his formulas on the assumption that the conditions were difl'erent for opaque and for transparent bodies, and even for the same substances in the two states resp
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