## A Series of Figures Illustrative of Geometrical Optics |

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angles of incidence appear arrow ABC axis carried backwards catacaustic caustic line caustic surface caustic which belongs concave lens concave mirror conical surfaces convex lens corresponding cusp direction drop effect equation explain extended eye G eye Q figure represents figure shews figure to revolve focus form a caustic give rise incident ray infinity lenses luminous point magnified manifestly margin rays medium mutual intersection nearer NOTES ON PLATE object acb objective images observer parallel rays passes pencil of rays perpendicular plane point at infinity position principal rainbow prism prismatic colours proceed produced backwards ray of light rays fall rays proceeding rays which emerge rays which fall reach the eye red image red rays reflected ray reflecting circle reflexion and refraction retina seen separated side sphere spherical surface successive rays sun's suppose Telescope totally reflected touches the caustic undergo vertices violet rays visual angle

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Page i - Preparing. An EXPOSITION of the XXXIX ARTICLES, derived from the Writings of the Older Divines. By the Rev. WB HOPKINS, MA, Fellow and Tutor of St. Catharine's Hall, and formerly Fellow of Caius College, Cambridge.

Page 8 - Let ABCD be the given square. With DA as radius and D as center, draw the 90° arc AE. Proceed as for the involute of a triangle until a figure of the required size is completed. (d) To Draw an Involute of a Circle. — A circle may be regarded as a polygon with an infinite number of sides and the involute constructed, as shown, by dividing the circumference into a number of equal parts, drawing a tangent at each division point, setting off along each tangent the length of the corresponding circular...

Page 43 - Now if x and y be the coordinates of a point on the caustic, they will remain constant when a and /8 vary by an indefinitely small quantity.

Page 19 - Now it is known that every ray, when it undergoes refraction, is separated into a multitude of rays, of which the red rays are the least refrangible and the violet the most.

Page 3 - By a luminous point we understand a minute portion of a luminous surface in no direction perceptibly extended. And so by a luminous line we understand such a surface perceptibly extended only in one direction.

Page 47 - Let the origin and axes be taken as in the text, and let r be the radius of the circle, a the distance of...