 ### Diagram Illustrating Astigmatism

An illustration depicting an astigmatism. An optical system with astigmatism is one where rays that… ### Construction of a Conic

Diagram showing how to construct a conic when given the focus and the auxiliary circle. If the focus… ### Focus In Auxiliary Circle of Conic

Diagram showing how to construct a conic when given the focus and the auxiliary circle. The focus is… ### Focus In Auxiliary Circle of Conic

Diagram showing how to construct a conic when given the focus and the auxiliary circle. As the focus… ### Corresponding Points in an Ellipse and Circle

Illustration of half of an ellipse. "The ordinates of two corresponding points in an ellipse and its… ### Conjugate Diameters of an Ellipse

Illustration showing that if one diameter is conjugate to a second, the second is conjugate to the first. ### Construction of an Ellipse

Illustration of half of an ellipse and its auxiliary circle used to construct an ellipse by points,… ### Construction of an Ellipse

Diagram showing how to construct an ellipse when given the two foci and the length of the major axis… ### Definition of Ellipse

Diagram of an ellipse that can used to illustrate the definition. "The constant ration between the distances… ### Demonstration of Ellipse Definition

Illustration showing the definition of an ellipse. "An ellipse is a curve which is the locus of a point… ### Focal Radii of an Ellipse

Illustration of half of an ellipse. "If d denotes the abscissa of a point of an ellipse, r and r' its… ### Foci Distances on an Ellipse

Diagram that illustrates "The algebraic sum of the distances of any point from the foci of a conic is… ### Graph of Ellipse with Foci and Center Labeled

A graph of tan ellipse with Foci and Center. ### Ellipse With Parts Labeled

Illustration of an ellipse with foci F' and F, major axis A' to A, minor axis B' to B, and center O. ### Line Bisecting Angle Between Focal Radii on Ellipse

Illustration of half of an ellipse. "If through a point P of an ellipse a line is drawn bisecting the… ### Ordinate and Major Axis of Ellipse

Illustration of half of an ellipse. The square of the ordinate of a point in an ellipse is to the product… ### Parallel Tangents to an Ellipse

Illustration showing that tangents drawn at the ends of any diameter are parallel to each other. ### Ellipse With Parts Labeled

Illustration of ellipse with parts labeled. ### Parts of Ellipse

Diagram of an ellipse that can used to illustrate the different parts. Segment MN is the major axis,… ### Point Distances to Foci on Ellipse

Illustration of half of an ellipse. "The sum of the distances of any point from the foci of an ellipse… ### Tangent From External Point to an Ellipse

Illustration of how to draw a tangent to an ellipse from an external point. ### Tangent to an Ellipse

Diagram an ellipse with a tangent line that illustrates "A line through a point on the ellipse and bisecting… ### Tangents to an Ellipse

Illustration showing the tangents drawn at two corresponding points of an ellipse and its auxiliary… ### Lens of the eye

"Diagram showing the Change in the Lens during Accomadation. On the right the lens is arranged for distant… ### Focus

"A fire-place; a hearth; a brazier. The fire-place possessed a sacred character, and was dedicated among… ### Formation of Circles of Diffusion

An illustration depicting the formation of circles of diffusion. "From point A luminous rays enter the… ### Reflection of Radiant Heat

"Heat is radiated at C, which is placed at mirror A's focus. Mirror A catches some of the heat and reflects… ### Auxiliary Circle and Hyperbola

Illustration of a hyperbola and its auxiliary circle. "Any ordinate of a hyperbola is to the tangent… ### Cone Intersected by a Plane to Form a Hyperbola

Diagram depicting a cone with both nappes intersected by plane J to form a hyperbola. ### Conjugate Axis of a Hyperbola

Illustration showing how the a hyperbola is symmetrical with respect to its conjugate axis. ### Construction of Hyperbola

Illustration showing how a hyperbola con be constructed by points, having been given the foci and the… ### Construction of a Hyperbola

Diagram showing how to construct a hyperbola when given the two foci and the length of the major axis… ### Demonstration of Hyperbola Definition

Illustration showing the definition of an hyperbola. "An hyperbola may be described by the continuous… ### Foci Distance of Hyperbola

Illustration of a hyperbola with distances to foci drawn. "The difference of the distances of any point… ### Line Bisecting Angle Between Focal Radii in Hyperbola

Illustration of a hyperbola with a line bisecting the focal radii. "If through a point P of an hyperbola… ### Point on a Hyperbola

Illustration of a point on a hyperbola. "If d denotes the abscissa (x-coordinate) of a point of an hyperbola,… ### Tangent to Hyperbola

Illustration showing how to draw a tangent to an hyperbola from a given point P on the convex side of… ### Tangent to a Hyperbola

Diagram part of a hyperbola with a tangent line that illustrates "A line through a point on the hyperbola… ### Concave Mirror

"A concave mirror reflects from a curved surface hollowing in like he inside of an orange." —Quackenbos… ### Focus of a Concave Mirror

"The focus of a concave mirror is the point where the rays are brought together by reflection." -Comstock… ### Reflection from Concave Mirrors

"Parallel rays of light strike the concave mirror. The rays converge at the focus, F, which is halfway… ### Divergent Rays in a Concave Mirror

"...be made obvious...where the diverging rays 1, 2, 3, 4 form a focus at the point o, whereas, had… ### Rays Diverging from Beyond the Center of Curvature on a Concave Mirror

"When the rays diverge from a point beyond the center of curvature, as B, the focus falls on the same… ### Rays Diverging from Beyond the Center of Curvature on a Concave Mirror

"When the rays diverge form a point at a distance from the mirror less than that of the principal focus,… ### Concave Mirror with Image and Focus

"The focus of each point chose may be determined by tracing two rays from the point, and locating their… ### Image Beyond the Curvature of a Concave Mirror

"When the object is at a distance from the mirror somewhat greater than the center of curvature, as… ### Object Beyond the Focus in a Concave Mirror

"...if the object is placed more remote from the mirror than the principal focus, and between the focus… ### Object Within the Focus in a Concave Mirror

"...let us suppose the object a, to be placed before the mirror, and nearer to it than the principal… ### Deception by Mirrors

"Suppose the tumbler, a, to be filled with water, and placed beyond the principal focus of the concave… ### Convex Mirror

"A convex mirror reflects from a curved surface rounding out like the outside of an orange." —Quackenbos… ### Reflection by Convex Mirrors

"Parallel rays strike the convex mirror, reflect, and diverge as if they had originated from a virtual… ### Conjugate Mirrors

Two concave mirrors facing each other to concentrate light. ### Parabola Foci Properties

The segments between the point of intersection of two tangents to a conic and their points of contact… ### Cone Intersected by a Plane to Form a Parabola

Diagram of a cone intersected by plane J to form a parabola. Also pictured is a circle formed by the… ### Conic Section Showing Parabola

Illustration showing the definition of a parabola as a conic section. "The section of a right circular… ### Conic Section Showing Parabola

Illustration showing the definition of a parabola as a conic section. "The section of a right circular… ### Construction of a Parabola

Diagram showing how to construct a parabola when given the directrix (d), the focus (F) and the eccentricity… ### Parabola With Coordinates and Latus Rectum

Illustration of a parabola showing that any point of a parabola is the mean proportional between the… ### Parabola With Focus and Directrix

Illustration of a parabola - a curve which is the locus of a point that moves in a plane so that its…