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.

    17/318 page 7
    image. In this case the solar image would be made up of an infinite number of superimposed triangular images. The images formed by the beams emana- ting from the sun's circumference would be arranged circularly, and hence the • contour of the whole would be circular. In the same manner may be explained the forma- tion of the images of the sun, which are sometimes observed under the dense shade of trees, circular or elliptical, according to the inclination of the rays; and also the formation of the inverted images of external objects, seen on the wall of a dark chamber when the light is admitted by a small aperture. The reason of the inversion of the images is appa- rent from figure 3. As a beam or pencil of light enters the aperture from every point of the sun or other object, it is evident, that what we have called the image, is the intersection, by the screen, of an infinite number of beams or pencils, more or less inclined to each other. Such a collection of beams or pencils may be called a compound beam or pencil. The term image is here used in a popular sense : a true optical image is a collection of foci. Figs. 3 and 4 will illustrate the preceding remarks. 20. When a pencil of light LI [Fig. 5], moving in a homogeneous medium, arrives at the surface AB of a new medium, it undergoes important changes. It is separated into parts.
    digitised image 1
    digitised image 2
    digitised image 3