An elementary treatise on optics / by I.W. Jackson.

  • Jackson, I. W. (Isaac Wilber), 1804-1877.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: An elementary treatise on optics / by I.W. Jackson. 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.

    214/318 (page 204)
    143. Rings formed by transmitted light. In this system of rings, when the light is homo- geneous, the central spot is of the same color as the light employed; and any bright transmitted ring is at the same distance from the centre as the corre- sponding dark one of the reflected system. When the light is white, the central spot is also white; and the color transmitted at any particular thickness of the plates, is complementary to that which is reflected at the same thickness. In all other respects, the rings observe the same laws as those formed by reflected light. 144. Explanation of the preceding phenomena. The principle of interferences furnishes a simple and satisfactory explanation of the phenomena just described. We shall first consider the case in which the light, supposed to be homogeneous, falls upon the surface of the plate of air at right angles, or nearly so. Let LI [Fig. Ill] be one of the rays of such a pencil, incident upon the first surface of the plate at I, and* upon the second at I'; then there will be a partial reflection at both these points, and the point I may be regarded as the origin of two new systems of undulations, the one proceeding directly from I to L any point in its direction, the other from I to I' and thence to L ; the lengths of the paths by which they reach the point L differing by twice the thickness II', or, denoting II' by e, by2e.