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An illustration of a boy trying on a hat and looking at his reflection in the mirror.

Boy Trying on Hat and Looking at His Reflection

An illustration of a boy trying on a hat and looking at his reflection in the mirror.

A cut of a gemstone. A brilliant cut stone has fifty-eight facets.

Brilliant Cut

A cut of a gemstone. A brilliant cut stone has fifty-eight facets.

Illustration of an ellipse, whose major axis is vertical, inscribed in a circle whose diameter is equal to the length of the major axis of the ellipse. The ellipse is externally tangent to the circle.

Ellipse Inscribed In A Circle

Illustration of an ellipse, whose major axis is vertical, inscribed in a circle whose diameter is equal…

Illustration of 16 concentric congruent ellipses that are rotated about the center at equal intervals of 22.5°. The ellipses are externally tangent to the circle in which they are inscribed.

16 Rotated Concentric Ellipses

Illustration of 16 concentric congruent ellipses that are rotated about the center at equal intervals…

Illustration of 2 concentric ellipses, whose major axes are vertical, inscribed in a circle whose diameter is equal to the length of the major axes of the ellipses. The ellipses, which decrease in width in equal increments, are externally tangent to the circle. The illustration could be used as a 3-dimensional drawing of a sphere.

2 Ellipses Inscribed In A Circle

Illustration of 2 concentric ellipses, whose major axes are vertical, inscribed in a circle whose diameter…

Illustration of 2 concentric congruent ellipses that are rotated about the center at 90°. The ellipses are externally tangent to the circle in which they are inscribed.

2 Rotated Concentric Ellipses

Illustration of 2 concentric congruent ellipses that are rotated about the center at 90°. The ellipses…

Illustration of 4 concentric congruent ellipses that are rotated about the center at equal intervals of 45°. The ellipses are externally tangent to the circle in which they are inscribed.

4 Rotated Concentric Ellipses

Illustration of 4 concentric congruent ellipses that are rotated about the center at equal intervals…

Illustration of 8 concentric congruent ellipses that are rotated about the center at equal intervals of 22.5°. The ellipses are externally tangent to the circle in which they are inscribed.

8 Rotated Concentric Ellipses

Illustration of 8 concentric congruent ellipses that are rotated about the center at equal intervals…

Illustration of concentric ellipses, whose major axes are vertical, inscribed in a circle whose diameter is equal to the length of the major axes of the ellipses. The ellipses, which decrease in width in equal increments until the smallest one is a line, are externally tangent to the circle. The illustration could be described as a circle rotated about the poles of the vertical axis. It could also be used as a 3-dimensional drawing of a sphere.

Ellipses Inscribed In A Circle

Illustration of concentric ellipses, whose major axes are vertical, inscribed in a circle whose diameter…

Illustration of concentric ellipses, whose major axes are vertical, inscribed in a circle whose diameter is equal to the length of the major axes of the ellipses. The ellipses, which decrease in width in equal increments until the smallest one is a line, are externally tangent to the circle. The illustration could be described as a circle rotated about the poles of the vertical axis. It could also be used as a 3-dimensional drawing of a sphere.

Ellipses Inscribed In A Circle

Illustration of concentric ellipses, whose major axes are vertical, inscribed in a circle whose diameter…

A girl looking at her reflection in the water.

Girl

A girl looking at her reflection in the water.

Isosceles Triangle with a dotted vertical line that is a line of symmetry.

Vertical Line of Symmetry, Isosceles Triangle With

Isosceles Triangle with a dotted vertical line that is a line of symmetry.

Letter A with a dotted vertical line that is a line of symmetry.

Vertical Line of Symmetry, Letter A With

Letter A with a dotted vertical line that is a line of symmetry.

Letter B with a dotted horizontal line that is a line of symmetry.

Horizontal Line of Symmetry, Letter B With

Letter B with a dotted horizontal line that is a line of symmetry.

"The focus of a concave mirror is the point where the rays are brought together by reflection." -Comstock 1850

Focus of a Concave Mirror

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

"To explain this, let us suppose that the arrow a, is diminished by reflection from the convex surface, so that its image appearing a d, with the eye at c, shall seem as much smaller in proportion to the object, as d is less than a. Now keeping the eye at the same distance from the mirror, withdraw the object, so that it shall be equally distant with the eye, and the image will gradually diminish, as the arrow is removed." -Comstock 1850

Convex Mirror

"To explain this, let us suppose that the arrow a, is diminished by reflection from the convex surface,…

"Suppose the arrow a to be the object reflected b the mirror d c; the incident rays a, flowing from the end of the arror being thrown back by reflection, will meet the eye in the same state of dicergence that they would do, if they proceded to the same distance behind the mirrr, that the eye is before it, as at o." -Comstock 1850

Plane Mirror

"Suppose the arrow a to be the object reflected b the mirror d c; the incident rays a, flowing from…

This statue of Narcissus a Greek Mythological hero who was renown for his beauty. In this statue, he is represented leaning on his hunting-spear, and contemplating his reflection in the stream.

Statue of Narcissus

This statue of Narcissus a Greek Mythological hero who was renown for his beauty. In this statue, he…

Oval with dotted vertical and horizontal lines that are lines of symmetry.

Lines of Symmetry, Oval With

Oval with dotted vertical and horizontal lines that are lines of symmetry.

"In order strictly to equalize a fixed light over the whole horizon, which could not possibly be done with separate reflectors, Marcet proposed this ingenious instrument, which is generated by the revolution of the parabolic profile pp' round its parameter as a vertical axis, instead of round a horizontal axis, as in all former reflectors." —The Encyclopedia Britannica, 1910

Parabolic Profile

"In order strictly to equalize a fixed light over the whole horizon, which could not possibly be done…

"In 1763, or at latest before 1777, parabolic reflectors were first used for lighthouse illumination by Mr. Hutchinson, dockmaster of Liverpool. In his work on Practica Scamanship, published in 1777, he states that the Mersey lights were fitted with reflectors formed of small fucets of silvered glass, and made, as he says "as nearly as they can be to the parabolic curve." This is unquestionably the earliest published notice of the use of parabolic reflectors for lighthouse illumination." —The Encyclopedia Britannica, 1910

Parabolic Reflector

"In 1763, or at latest before 1777, parabolic reflectors were first used for lighthouse illumination…

"In 1763, or at latest before 1777, parabolic reflectors were first used for lighthouse illumination by Mr. Hutchinson, dockmaster of Liverpool. In his work on Practica Scamanship, published in 1777, he states that the Mersey lights were fitted with reflectors formed of small fucets of silvered glass, and made, as he says "as nearly as they can be to the parabolic curve." This is unquestionably the earliest published notice of the use of parabolic reflectors for lighthouse illumination." —The Encyclopedia Britannica, 1910

Parabolic Reflector

"In 1763, or at latest before 1777, parabolic reflectors were first used for lighthouse illumination…

"It will be seen that the parabolic mirror a is at best but a very imperfect instrument, for even if the radiant were strictly a mathematical point, the cone of rays (shown undotted) escaping past the lips of the mirror must be lost." —The Encyclopedia Britannica, 1910

Paraboloid

"It will be seen that the parabolic mirror a is at best but a very imperfect instrument, for even if…

A young person adopts an attitude of thoughtful consideration when listening to Christ preaching. Detail from a larger engraving entitled "Consider the Lilies of the Field."

Young Person Thinking

A young person adopts an attitude of thoughtful consideration when listening to Christ preaching. Detail…

"...a tube with a slit at the further end through which the light enters, and at the other end a collimating lens which brings the rays into a parallel beam (the slit is formed between two parallel edges the distance between which can be varied at will)..." —Whitney, 1889

Prism Spectroscope from the Late 19th Century

"...a tube with a slit at the further end through which the light enters, and at the other end a collimating…

"Cathetal prisms readily yield the phenomena of total reflection as shown, and are often used when light is to be turned through a right angle." -Avery 1895

Cathetal Prism

"Cathetal prisms readily yield the phenomena of total reflection as shown, and are often used when light…

"From the surface of a plane mirror, parallel rays are reflected parallel; but the convex mirror causes parallel rays falling on its surface to diverge, by reflection." -Comstock 1850

Divergent Rays

"From the surface of a plane mirror, parallel rays are reflected parallel; but the convex mirror causes…

"The angle, ABD, included between the direction of the moving body before it strikes the reflecting surface, and a perpendicular to that surface drawn from the point of contact, is called the angle of incidence. The angle between the perpendicular and the direction of the moving body after striking is called the angle of reflection." -Avery 1895

Law of Reflected Motion

"The angle, ABD, included between the direction of the moving body before it strikes the reflecting…

"Let S be the position of the spectator; O and B the position of distant objects. The rays O R and B R which proceed from them, strike the surface of the water very obliquely, and the light which is reflected in the direction R S is sufficient to make a sensible impression upon the eye. But in regard to objects such as A placed near the spectator, they are not seen reflected, because the rays A R' which proceed from them strike the water with but little obliquity; and consequently, the part of their light which is reflected in the direction R' S, towards the spectator, is not sufficient to produce a sensible impression upon the eye." —Wells, 1857

Reflection

"Let S be the position of the spectator; O and B the position of distant objects. The rays O R and B…

"Here, of the rays S A, S B, and S C, only the ray S C meets the eye of the spectator D. The spot C, therefore, will appear luminous to the spectator D, but no other spot of the water A B C." —Wells, 1857

Reflection

"Here, of the rays S A, S B, and S C, only the ray S C meets the eye of the spectator D. The spot C,…

"Reflection of sound." -Comstock 1850

Reflection

"Reflection of sound." -Comstock 1850

"Angle of incidence equals angle of reflection." —Croft 1917

Reflection of Light

"Angle of incidence equals angle of reflection." —Croft 1917

"Reflection of light from a broken surface." —Croft 1917

Reflection of Light from a Broken Surface

"Reflection of light from a broken surface." —Croft 1917

"Mirror A/B is only half of person C's height. C is able to view his entire body through such a small mirror due to the angle of incidence from D to B to F." —Quackenbos 1859

Angle of Incidence and Reflection

"Mirror A/B is only half of person C's height. C is able to view his entire body through such a small…

"Irregular reflection or diffusion results from the incidence of radiant energy upon an irregular surface, as is illustrated. Bodies are made visible to the eye mainly by the light that they thus diffuse." -Avery 1895

Irregular Reflection or Diffusion

"Irregular reflection or diffusion results from the incidence of radiant energy upon an irregular surface,…

"Thus, if a sunbeam, passing through a small aperure in the window shutter a, be permitted to fall upon the plane mirror, or looking glass, c, d, at right-angles, it will be reflected back at right-angles with the mirror, and therefore will pass back again in exactl the same direction in which it approached." -Comstock 1850

Reflection of Light

"Thus, if a sunbeam, passing through a small aperure in the window shutter a, be permitted to fall upon…

"The ray a, c, is the ray of incidence, and that from c, to d, is the ray or reflection. The angles which a, c, make with the perpendicular line, and with the plane of the mirror, is exactly equal to those made by c, d, with the same perpendicular, and the same plane surface." -Comstock 1850

Reflection of Light

"The ray a, c, is the ray of incidence, and that from c, to d, is the ray or reflection. The angles…

"Regular reflection results from the incidence of radiant energy upon a polished surface. When a beam of light falls upon a mirror, the greater part of it is reflected in a definite direction as is illustrated, and forms an image of the object from which it came. A perfect mirror would be invisible." -Avery 1895

Regular Reflection

"Regular reflection results from the incidence of radiant energy upon a polished surface. When a beam…

"Reflection of light from a smooth surface." —Croft 1917

Reflection of Light from a Smooth Surface

"Reflection of light from a smooth surface." —Croft 1917

A polished surface of metal, or any other suitable material, applied for the purpose of reflecting rays of light, heat, or sound in any required direction.

Parabolic, Reflector

A polished surface of metal, or any other suitable material, applied for the purpose of reflecting rays…

"In order to produce, on the catoptric system, a fixed light showing all round the circle, a number of reflectors are fixed round the outside of a stationary chandelier n. As the ordinary paraboloid has about 14 degrees of divergence, twenty-five reflectors were needed to light up continuously (though not equally) the whole horizon." —The Encyclopedia Britannica, 1910

Revolving Light

"In order to produce, on the catoptric system, a fixed light showing all round the circle, a number…

"If again the light was to revolve, then a revolving chandelier was employed having a certain number of flat faces, on each of which was fixed a number separate lamps and reflectors with their axes parallel to each other. When the chandelier revolved, and one of the flat sides was turned towards the sailor, he would, when at some distance from the shore, receive a flash at once form each of the mirrors which were on that face, but when the face was turned away from him a dark period would intervene until the next face came round again." —The Encyclopedia Britannica, 1910

Revolving Light

"If again the light was to revolve, then a revolving chandelier was employed having a certain number…

"...an instrument which gives a spectrum when the source of the light is in a straight line with the eye—that is, which gives dispersion without deviation—is called a direct vision spectroscope..." —Whitney, 1889

Direct Vision Spectroscope

"...an instrument which gives a spectrum when the source of the light is in a straight line with the…

Square with dotted vertical, horizontal, and diagonal lines that are lines of symmetry.

Lines of Symmetry, Square With

Square with dotted vertical, horizontal, and diagonal lines that are lines of symmetry.

Tree with dotted vertical line that shows symmetry.

Line of Symmetry, Tree With

Tree with dotted vertical line that shows symmetry.

Tree that has no symmetry.

Symmetry, Tree With No

Tree that has no symmetry.

Square with dotted lines that are lines of symmetry.

Lines of Symmetry, Triangle With

Square with dotted lines that are lines of symmetry.

"Start a trough from A. At the moment of its reflection as a crest a B, start a crest at A as shown. The two crests will meet near the middle of the rope. The crest at the point and moment of meeting results from two forces acting in the same direction; their resultatnt is greater than either of the components." -Avery 1895

Constructive Interference

"Start a trough from A. At the moment of its reflection as a crest a B, start a crest at A as shown.…

"It is apparent that the auditor, in this case, must be placed in the centre from which the sound proceeds, to receive the greatest effect. But if the shape of the room be elliptical, the sound may be made in one part, and the echo will be heard in another part, because the ellipse has two points, called foci, at one of which, the sound being produced, it will be concentrated at the other." -Comstock 1850

Whispering Gallery

"It is apparent that the auditor, in this case, must be placed in the centre from which the sound proceeds,…

An illustration of a woman looking at her reflection in a mirror.

Woman Looking in Mirror

An illustration of a woman looking at her reflection in a mirror.

An illustration of a woman looking at her reflection in a mirror.

Woman Looking in Mirror

An illustration of a woman looking at her reflection in a mirror.

An illustration of a woman looking into a mirror.

Woman Looking in Mirror

An illustration of a woman looking into a mirror.

An illustration of a woman looking at her reflection in a mirror.

Woman Looking in Mirror

An illustration of a woman looking at her reflection in a mirror.