Lectures on light, delivered in the United States in 1872-'73; with an appendix (1873)
Tyndall, John, 1820-1893 · New York, Appleton · leaf 96
f the beam into the two halves being,therefore, particularly striking. Before you is now projected an image of our carbon-points. Introducing the spar, the beam which buildsthe image is permitted to pass through it; instantlyyou have the single image divided into two. Pro-jecting an image of the… … The two beams into which the spar divides thesingle incident-beam do not behave alike. One of themobeys the ordinary law of refraction discovered bySnell, and this is called the ordinary ray. The otherdoes not obey the ordinary law. Its index of refraction,for example, is not constant, nor do the…
Optics
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