The theory of optics / by Paul Drude ; translated from the German by C. Riborg Mann and Robert A. Millikan.

Date:
1902
Catalogue details

Licence: In copyright

Credit: The theory of optics / by Paul Drude ; translated from the German by C. Riborg Mann and Robert A. Millikan. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    offers of interference. The difficulties were not removed until a too close analogy between sound and light was given up. This point, too, will be considered in a later chapter. Here the explanation of refraction as furnished by the wave theory will be briefly presented. If a plane wave is incident obliquely upon the surface of a refracting body, the normal to the wave front is bent toward the perpendicular to the surface if the velocity of light in the body is less than in the surrounding medium, which will in general be assumed to be air. Upon the incident wave front consider one point A which lies upon the surface, and another WAVE LENGTHS. Kind of Light. A in mm. Limit of the photographic rays in vacuum Limit of the photographic rays in air. Limit of visible light in the blue Blue hydrogen line Yellow sodium line Red hydrogen line Limit of visible light in the red Longest heat-waves as yet detected Shortest electric waves o.oooioo 0.000185 0.000330 0.000486 0.000589 0.000656 0.000812 0.06 6 point B which is still outside in the air. If now the wave from A travels more slowly than that from B, it is evident that the wave front, which is the locus of the points at which the light has arrived in a given time, must be bent upon entrance into the refracting medium in such a way that the normal to the wave front (the ray) is turned toward the perpendicular. Hence the wave theory requires the result given by experi- ment that the velocity of light is smaller in water than in air. The more exact determination of the position of the refracted wave front will be given in connection with the discussion of Huygens’ principle, and again more rigorously in Chapter I of Section 2. Here but one important result will be mentioned, namely: When light passes from a medium A to a medium B