Geometrical optics / by Archibald Stanley Percival.

  • Percival, A. S. (Archibald Stanley), 1862-
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Geometrical optics / by Archibald Stanley Percival. Source: Wellcome Collection.

    71/148 (page 59)
    H'a parallel to the principal axis until it meets ACa in a. ' The point a is the image of the point A. It would appear, then, that the incident diverging cone HAH!’ becomes, after refraction, the converging cone HaH’, This is not strictly true, for the line AH does not represent any ray that is actually incident on the refracting surface ; but we are justified in asserting that a small centric pencil from A will come to its conjugate focus at the point of intersection of HF” and AC produced. Again, we know that all rays that pass through F’, such as AF’H’, must, after refraction, proceed in a direction (H'a) parallel to the axis, (B) Point on the Principal Axis—(Spaced and dotted lines.) | Through B draw any line BDH cutting the first focal plane in D and the principal plane at H”; join DC and draw Hd parallel to DC, cutting the principal axis in 0. Then the point 0 is the image of the point B. The reason of this construction is obvious from the pro- perty of the focal planes described on p. 26. Light from any point on this plane will, after refraction, travel in rays parallel to that axis on which the point lies. Now, DC is, of course, the axis on which D lies, and consequently the incident light ray DH” must, after refraction, take the direction Hd parallel to DC. Size of the Image.—In just the same way as we found the height of the image formed by reflection at a mirror, we can find in this case. (1) Noting that ba is equal to OH’, we find, by similar triangles, that— es ae OH ron gi ite AS ek oN au (2) And as BA is equal to OH, fet ba _ ba ot oh is Be Oh DOR eg