Illustrated scientific and descriptive catalogue of achromatic microscopes, manufactured by J. & W. Grunow & Co., New Haven, Conn.

  • J. & W. Grunow & Co.
Date:
1857
Catalogue details

Licence: Public Domain Mark

Credit: Illustrated scientific and descriptive catalogue of achromatic microscopes, manufactured by J. & W. Grunow & Co., New Haven, Conn. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

    97/124 (page 83)
    PARTIAL POLARIZATION. such a position that its vibrations are oblique to the polarizing planes or axes of the medium, they will be resolved into vibra- tions in J)ot]i those axes or polarizing planes, and two new polarized rays will result, each of which might be again sub- divided in the same manner by another polarizing prism placed in a position oblique to the new axes. 108. Familiar illustrations. A ray of common light is sometimes compared to a cylindrical rod, whereas the polarized rays are like two flat parallel rulers, one of which is laid hori- zontally on its broad suface, and the other horizontally on its edge. The alternate transmission and obstruction of one of the flattened beams, by the tourmaline, is similar to the facility with which a card, or flat ruler, may be passed between the wires of a cage if presented edgewise, and the impossibility of its passing in a transverse position. We may also suppose a refracting substance, with a reflect- ing surface, made up of parallel fibres. Such a surface would allow the passage of all the rays in common light which vibrate in a plane parallel to the direction of its fibres and M^ould reflect the rest; while polarized light, if vibrating in a plane parallel to the fibres, would be wholly transmitted, but if vibra- ting in a plane at right angles to the fibres, it would be wholly reflected. 109. Partial Polarization. Having already explained in the previous section how light is polarized, 1st, by reflection ; 2nd, by refraction ; 3rd, by transmission through bundles of thin plates ; and 4th, by double refraction ; it now remains to state that a great variety of substances, and in different condi- tions, ^vodnce partial polarization of light reflected from their surfaces or transmitted through them. It is well known that no substance either transmits, or reflects, all the light that falls upon it; even the most transparent sub- stances reflect a small portion of light, the proportion reflected and transmitted varying with every angle of incidence. While plate glass polarizes very nearly all the light that falls upon it at an angle of 57°, the intensity of the reflected ray is equal to only one-half the intensity of the incident ray, the other half of the light is transmitted through the glass, and is, at the