Physiological Optics: Being an Essay Contributed to the American Encyclopedia of Ophthalmology (Classic Reprint) - Hardcover
Synopsis
Excerpt from Physiological Optics: Being an Essay Contributed to the American Encyclopedia of Ophthalmology
These four fundamental experimental facts as to the direction of rays Of light are comprehended in a general way in a Single law Often referred to as the principle of least path or Fermat's principle of least time. If a ray of light passes from a point A to a point B and suffers any number Of reflections and refractions, then the sum of the products of the index of refraction (n) Of each medium multiplied by the distance traversed (l) in it differs from a like sum for all other paths which are infinitely close to it by terms Of the second or higher order; i. E., the variation in the total paths, optically considered, approaches zero. This principle finds frequent and important appli cation in geometrical optics. The four fundamental laws above enumerated relate only to geometrical determinations of the prope gation of light and constitute, therefore, a sufficient basis for geo metrical Optics. We shall assume their validity and proceed to use them in the deductions Of ocular constants and data.
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