A familiar introduction to the study of polarized light; with a description of, and instructions for using the table and hydro-oxygen polariscope and microscope / [Charles Woodward].

  • Woodward, Charles
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: A familiar introduction to the study of polarized light; with a description of, and instructions for using the table and hydro-oxygen polariscope and microscope / [Charles Woodward]. Source: Wellcome Collection.

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    the perpendicular, the light reflected by the first will be again reflected by the second glass when the planes of the two glasses are parallel to each other; but if, without altering its angle to the horizon, we turn the second glass a quarter of a circle, the light will be transmitted and not reflected: if we turn it. another quarter, the light will be reflected and not transmitted; and so on alternately for every quarter of a revolution that the second glass is made to perform round the ray reflected by the first glass. (40.) A ray of light, then, when reflected at an angle of incidence of 56° 45’ from the perpendicular, has undergone some modification: it has acquired the properties of sides; it has two sides on which it can and two on which it cannot be again reflected, and as these opposite properties of the different sides were supposed to bear some analogy to the opposite properties of the different poles of a magnet, a ray of light so modified was said to be polarized. It is, however, universally admitted that the term is unfortunate, as it affords no indication of the phenomena it professes to describe. (41.) In order to develop by degrees a subject confessedly abstruse, we have hitherto noticed only one plane of vibration of the ethereal particles; but Fresnel assumes that the vibra- tions are performed in two planes at right angles to the direction of the progress of the wave, which is analogous to the motions of the waves of the sea, as experienced by those who have crossed the channel in a steam-boat during a brisk gale, when the rectangular vibrations occasioned by the alter- nate pitchings and rockings of the vessel have caused the mast-head to describe a circle or an oval, as the case might be, and afforded those who could enjoy the scene a fine opportunity of studying the resolution of forces. (42.) Let A B, Fig. 7, represent the perpendicular and C D the horizontal vibrations of the ethereal particles, by which a ray of common light is supposed to be propagated; and let K F and G H represent the two plates of glass used as reflectors.