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.

    133/318 (page 123)
    . * THE EYE, AND OPTICAL INSTRUMENTS. 123 it may diverge from a virtual image at the distance of distinct vision, the object will then appear clear and magnified. Such a lens thus employed is called a simple microscope. Let RS [Fig. 75] be the lens almost in contact with the eye, LL' the object placed between the lens and its principal focus, and PP' the virtual image; then denoting the principal focal distance of the lens by/, 01 (which is nearly equal to the distance of distinct vision) by q, and O'U the distance of the object by p, we shall have the relation l_l_l p g~f and hence q_q+f p~ f Now the object is evidently magnified in its linear dimensions, in the ratio of PP' to LL'. Denoting this ratio, which is called the linear magnifying power of the lens, by x, we have __ PP' _ O'l _ g + / x ~~ lL7 — 07U ~~ ~f ; or, since / is always very small compared with q, f From this it appears that the object is magnified nearly in the ratio of the distance of distinct vision, to the focal distance of the lens, and hence, the for- mer distance being supposed constant, as it is for