Geometrical optics / by Val H. Mackinney and Harry L. Taylor.

  • Mackinney, Val H., 1791-1868.
Date:
1908
Catalogue details

Licence: In copyright

Credit: Geometrical optics / by Val H. Mackinney and Harry L. Taylor. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    AT • • CD , . BE Now sm . - and sm . - CD And = BD _ CD sm /• BE BE BD But CD and BE represent the velocities and V.^ Vo sin I n.j^ Yt sin r n ^, The above holds good for all angles of incidence. We know also, from our second law of refraction, that for tAvo given media, and a particular colour of light, is a constant. ^ sm /' Diffraction. Although we may consider light as a grand wave motion and represent it diagramatically by concentric circles, experiment sliows that the motion set up in the ether is a very complex one indeed. In Fig. 1) let 0 be a luminous source, 7f ^ then if A B is the first main ov grand ! \ wave, it will be formed by the mutual interference of the little secondare/ waves, which all assist to that end. If C D is an aperture, then only a portion of the main wave can pass on, and at each edge of the aperture Pig^ g some of the secondary waves will become detached from the main beam and proceed in the direction shown, very diagramatically, by the arrows. Some of these will meet in opposition and destroy one another, others will meet in such a manner as to assist one another, the final result being that to an eye placed on either side of the transmitted portion of the main wave, alternate dark and light bands of light will api)ear. If the source 0 is white, or other compound light, then alternate dark and spectral coloured bands will be seen. This is one method of producing diffraction spectra, and the further we move the eye from the main beam the fainter will become the luminous dilfaction bands or spectra. Interference. Just as secondary waves assist or annul one another, so do main waves assist or annul one another. But here at least two sources, or two apparent sources, of illumination are necessary. Phenomena due to the interference of the main waves of light are called interference phenomena.