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.

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    CHAPTER III REFLECTION AT A SPHERICAL SURFACE REFLECTION at irregularly curved surfaces can only be treated by the method mentioned on p. 11. At the point of incidence a tangent plane is drawn, and for that particular incident ray the reflection is considered as taking place at that tangent plane. Fortunately, however, there are much surfaces, with which alone we are now concerned ; these we proceed to describe in their simplest form. Concave Spherical Mirrors; Axial or Centric Pencils.—Let AK represent a concave mirror, its surface being part of a sphere of which the centre is at C (Fig. 9). Any line drawn through C to the mirror is called an axis of the mirror, and when the parts of the mirror on either side of the axis are symmetrical it is called the Principal Axis. In the figure CA is the principal axis, and A the vertex of the mirror. Let P be a luminous point on the axis distant PA or p from the mirror, and consider the incident ray PK when the point K is near the vertex A. Join CK and make the angle CKQ numerically equal to the angle of incidence CKP. If now the figure be supposed to revolve round the principal axis axial cone of incident light, while the point K will trace out a narrow circular zone on the mirror, and the reflected rays from this zone must all intersect the axis at the point Q. Consequently Q must be the image of P as formed by reflection at this narrow zone. Let CA, the radius of the mirror, be denoted by 7, and let QA be denoted by g.