## A Treatise on Geometrical Optics |

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### Common terms and phrases

aberration achromatic angle of divergence angle of incidence angular angular aperture aperture apparent distance axis caustic centre characteristic function colours concave convergent coordinates cos2 cosec curvature cusp denote direction direction-cosines dispersion emergent ray equal equation eye-glass eye-piece eye-ring field of view focal length focal plane foci formula geometrical focus given Hence image formed incident ray index of refraction lenses linear magnification magnifying power normal adjustment object-glass obtain optical order of approximation origin of light orthotomic curve orthotomic surface parallel rays pencil of rays perpendicular plane mirror plane of incidence planes of reference point of incidence point Q positive principal foci principal plane prism radii ratio ray passes reduced path reflected ray refracting surfaces refractive index retina second focus Shew sin2 small object small pencil sphere spherical surface telescope theorem thin lens unit plane unit points vertex zero

### Popular passages

Page 15 - When a ray of light passes from one medium to another, it is refracted so that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities in the two media.

Page 125 - ... the ratio of the angle which the image subtends at the eye to the angle which the object subtends when viewed directly in its actual position.

Page 2 - This law is: the incident and reflected rays make equal angles with the normal to the reflecting surface at the point of incidence, and are coplanar with the normal.

Page 160 - In a very dark chamber, at a round hole about onethird part of an inch broad made in the shutter of a window, I placed a glass prism, whereby the beam of the sun's light which came in at the...

Page 17 - ... may easily be negative (it cannot be less than — 2). The case of incidence at an angle greater than the critical angle cannot be treated by the usual method for a thin plate, using the set of waves formed by successive reflection at the front and back surfaces, as travelling waves are not propagated in the plate, and we cannot define the reflection coefficient of a surface in such a case*. We consider a medium for...

Page 12 - If the angle of a hollow cone, polished internally be any sub-multiple of two right angles, a cylindrical pencil of rays incident parallel to the axis will, after a certain number of reflexions, be a cylindrical pencil parallel to the axis, and of the same diameter as the incident pencil.

Page 161 - ... that is by a quarter of an inch, subtended an angle at the prism of about half a degree, which is the sun's apparent diameter. But the length of the image was about ten inches and a quarter, and the length of the rectilinear sides about eight inches, and the refracting angle of the prism whereby so great a length was made was 64°. With a less angle the length of the image was less, the breadth remaining the same.

Page 25 - The deviation or change of direction of light passing through a prism is a minimum when the angle of incidence is equal to the angle of emergence.

Page 160 - ... observed the figure and dimensions of the solar image formed on the paper by that light. This image was oblong and not oval, but terminated with two rectilinear and parallel sides, and two semicircular ends. On its sides it was bounded pretty distinctly, but on its ends very confusedly and indistinctly, the light there decaying and vanishing by degrees. The breadth of this image answered to the sun's diameter, and was about two inches and the eighth part of an inch, including the penumbra.

Page 160 - In a very dark Chamber at a round hole about one third part of an Inch broad made in the Shut of a Window I placed a Glass Prism, whereby the beam of the Sun's Light which came in at that hole might be refracted upwards toward the opposite Wall of the Chamber, and there form a coloured Image of the Sun.