"The photographer's camera corresponds to the camera-obscura. A darkened box, adjustable in length, takes the place of the darkened room, and an achromatic convex lens is substituted for the aperture in the shutter." — Avery, 1895

Bellows camera

"The photographer's camera corresponds to the camera-obscura. A darkened box, adjustable in length,…

"Catadioptric Holophote.—Part of the anterior hemisphere of rays is intercepted and at once parallelized by the lens L, whose principal focus (i.e., for parallel rays) is in the center of the flame, while the remainder is intercepted and made parallel by the paraboloid a, and thus the double agents in Fresnel's design are dispensed with. The rays of the posterior hemisphere are reflected by the spherical mirror b back again through the foxus, whence passing onwards one portion of them falls on the lens and the rest on the paraboloid, so as finally to emerge in union with and parallel to the front rays." —The Encyclopedia Britannica, 1910

Catadioptric Holophote

"Catadioptric Holophote.—Part of the anterior hemisphere of rays is intercepted and at once parallelized…

"Catadioptric Holophote.—Part of the anterior hemisphere of rays is intercepted and at once parallelized by the lens L, whose principal focus (i.e., for parallel rays) is in the center of the flame, while the remainder is intercepted and made parallel by the paraboloid a, and thus the double agents in Fresnel's design are dispensed with. The rays of the posterior hemisphere are reflected by the spherical mirror b back again through the foxus, whence passing onwards one portion of them falls on the lens and the rest on the paraboloid, so as finally to emerge in union with and parallel to the front rays." —The Encyclopedia Britannica, 1910

Catadioptric Holophote

"Catadioptric Holophote.—Part of the anterior hemisphere of rays is intercepted and at once parallelized…

"A modification of the simple kaleidoscope was introduced by Sir David Brewster, whereby the images of large and distant objects can be introduced into the picture. This is effected by removing the object box and replacing it by a tube carrying at its outer end a double convex lens, represented by LL. By a screw adjustment the lens can be so placed as to focus the distant object exactly in the plane of the sector AOB, and so bring its image into the very best position for producing symmetrical patterns. When this instrument is directed towards a tree in full bloom, a very beautiful effect is produced, which can be varied by gradually moving the instrument. This form was called by Brewster the telescopic kaleidoscope." —The Encyclopedia Britannica, 1910

Convex Lens

"A modification of the simple kaleidoscope was introduced by Sir David Brewster, whereby the images…

A portion of the corona ciliaris magnified. The ciliary processes and the ciliary folds.

Magnified Corona Ciliaris

A portion of the corona ciliaris magnified. The ciliary processes and the ciliary folds.

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the radius of curvature of the inner face of an annular lens. The outer face is the same as that of an ordinary annular lens, which the other face, though straight in the vertical, is ground to the required curve in the horizontal plane. The rays f'fc falling upon the lens x converge to the vertical focal plane ff and afterwards diverge through the smaller horizontal angle x'f'x', and so for any other case." —The Encyclopedia Britannica, 1910

Differential Lens

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the…

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the radius of curvature of the inner face of an annular lens. The outer face is the same as that of an ordinary annular lens, which the other face, though straight in the vertical, is ground to the required curve in the horizontal plane. The rays f'fc falling upon the lens x converge to the vertical focal plane ff and afterwards diverge through the smaller horizontal angle x'f'x', and so for any other case." —The Encyclopedia Britannica, 1910

Differential Lens

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the…

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the radius of curvature of the inner face of an annular lens. The outer face is the same as that of an ordinary annular lens, which the other face, though straight in the vertical, is ground to the required curve in the horizontal plane. The rays f'fc falling upon the lens x converge to the vertical focal plane ff and afterwards diverge through the smaller horizontal angle x'f'x', and so for any other case." —The Encyclopedia Britannica, 1910

Differential Lens

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the…

"Throw a sunbeam through a very small opening in the shutter of a darkened room. Receive the beam upon a convex lens of short focal length, placing a pieve of red glass between the aperture and the lens. Place and opaque screen with a sharp edge beyond the focal distance of the lens, as at a, so as to cut off the lower part of the cone of homogeneous light, and project the upper part thereof upon a screen at b." -Avery 1895

Diffraction

"Throw a sunbeam through a very small opening in the shutter of a darkened room. Receive the beam upon…

"Section through the lateral eye of Euscorpius italicus. lens, Cuticular lens. nerv.c, Retinal cells (nerve-end cells). rhabd, Rhabdomes. nerv.f, Nerve fibes of the optic nerve. int, Intermediate cells (lying between the bases of the retinal cells)." — The Encyclopedia Britannica, 1910

Euscorpius Italicus

"Section through the lateral eye of Euscorpius italicus. lens, Cuticular lens. nerv.c, Retinal cells…

"Diagram of the eye. C., Cornea; a.h., aqueous humour; c.b., ciliary body; l., lens; I., iris; Sc., sclerotic; Ch., choroid; R., retina; v.h., vitreous humour; y.sp., yellow spot; n., optic nerve." -Thomson, 1916

Eye

"Diagram of the eye. C., Cornea; a.h., aqueous humour; c.b., ciliary body; l., lens; I., iris; Sc.,…

The illustration of putting lenses in front of the eye. The focal point of the image is reflected into the eye. The focal point in the lens will end past the eye, creating a blurry image.

Optical Position and Size of Image Through Lens in Front of Eye

The illustration of putting lenses in front of the eye. The focal point of the image is reflected into…

"Section through the left eye, closed. 1, lifting muscle; 2, upper straight muscle; 3, optic nerve; 4, fatty cushion; 5, lower straight muscle; 6, vitreous humor; 7, lower cross muscle; 8, lower eyelid; 9, upper eyelid; 10, crystalline lens." -Foster, 1921

Eye Section

"Section through the left eye, closed. 1, lifting muscle; 2, upper straight muscle; 3, optic nerve;…

Plan of the eye seen in section. Labels: A, The Sclerotic Coat; B, The Choroid Coat; C, The Retina; D, The Optic Nerve; E, The Cornea; F, The Aqueous Humor; G, The Iris; H, The Ciliary Processes; I. The Crystalline Lens; K, The Vitreous Humor.

Diagram of the Eye

Plan of the eye seen in section. Labels: A, The Sclerotic Coat; B, The Choroid Coat; C, The Retina;…

The right eye in horizontal section.

Horizontal Section of Eye

The right eye in horizontal section.

"Section of the human eye." — Blaisedell, 1904

Human eye

"Section of the human eye." — Blaisedell, 1904

"Diagrammatic horizontal section of the eye of man. c, cornea; ch. choroid (dotted); C. P, ciliary processes; e. c, epithelium of cornea; e. cj, conjunctiva; f. c, yellow spot; I, iris; L, lens; ON, optic nerve; OS, ora serrata; o-x, optic axis; p. c. R, anterior non-visual portion of retina; P. E, pigmented epithelium (black); R, retina; sp. l, suspensory ligament; Scl, sclerotic; V. H, vitreous body." -Parker, 1900

Human Eye

"Diagrammatic horizontal section of the eye of man. c, cornea; ch. choroid (dotted); C. P, ciliary processes;…

Lens of the eye. The rays of light are brought nearer together by the lenses of the eye, just as they are by the lenses of the telescope.

Lens of the eye

Lens of the eye. The rays of light are brought nearer together by the lenses of the eye, just as they…

"Diagram showing the Change in the Lens during Accomadation. On the right the lens is arranged for distant vision, the cilliary muscle is relaxed, and the ligament <em>D</em> is tense, so flattening by its compression the front of the lens <em>C</em>, on the left the muscle <em>A</em> is acting, and this relaxes the ligament and allows the lens <em>B</em> to become more convex, and so fitted for the vision of near objects." &mdash; Blaisedell, 1904

Lens of the eye

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

The eye. Labels: a, sclerotica; e, cornea; b, choroid; d, optic nerve; f, aqueous humor; g g , iris; h, lens; i, vitreous humor; c, retina.

The Eye

The eye. Labels: a, sclerotica; e, cornea; b, choroid; d, optic nerve; f, aqueous humor; g g , iris;…

Horizontal section of the eyeball, showing the suspensory ligament of the lens, the aqueous and vitreous chambers, entrance of the optic nerve, and the fovea centralis.

Eyeball

Horizontal section of the eyeball, showing the suspensory ligament of the lens, the aqueous and vitreous…

The left eyeball in horizontal section from before back. Labels: 1, sclerotic; 2, junction of sclerotic and cornea; 3, cornea; 4, 5, conjunctiva; 7, ciliary muscle; 10, choroid; 11, 13, ciliary processes; 14, iris; 15, retina; 16, optic nerve; 17, artery entering retina in optic nerve; 18, fovea centralis; 19, 20, region where sensory part of retina ends; 22, suspensory ligament; 24, the anterior part of the hyaloid membrane; 26, the lends; 29, vitreous humor; 30, aqueous humor.

The Eyeball in Horizontal Section

The left eyeball in horizontal section from before back. Labels: 1, sclerotic; 2, junction of sclerotic…

The left eyeball in horizontal section from before back. Labels: 1, sclerotic; 2, junction of sclerotic and cornea; 3, cornea; 4,5, conjunctiva; 6, posterior elastic layer of cornea; 7, ciliary muscle; 10, choroid; 11,13, ciliary processes; 14, iris; 15, retina; 16, optic nerve; 17, artery entering retina in optic nerve; 18, fovea centralis; 19, region where sensory part of retina ends; 22, suspensory ligament; 23 is placed in the canal of Petit, and the line from 25 points to it; 24, the anterior part of the hyaloid membrane; 26, 27, 28, are placed on the lends; 28 points to the line of attachment around it of the suspensory ligament; 29, vitreous humor; 30, anterior chamber of aqueous humor; 31, posterior chamber of aqueous humor.

Section of Left Eyeball

The left eyeball in horizontal section from before back. Labels: 1, sclerotic; 2, junction of sclerotic…

A magnifying glass.

Magnifying glass

A magnifying glass.

"Holophotal Catadioptric Apparatus Revolving round a Central Flame." &mdash;The Encyclopedia Britannica, 1910

Holophotal Catadioptric

"Holophotal Catadioptric Apparatus Revolving round a Central Flame." —The Encyclopedia Britannica,…

"Holophotal Catadioptric Apparatus Revolving round a Central Flame.&mdash;If in place of Fresnel's compound arrangement of trapezoidal lenses and plane mirrors there are substituted mirrors R, R generated by the revolution of a parabolic profile round a horizontal axis, all the light will be at once sent out in parallel beams by them and the lenses L, and the apparatus is therefore geometrically perfect, but metallic instead of glass agents are still employed." &mdash;The Encyclopedia Britannica, 1910

Holophotal Catadioptric

"Holophotal Catadioptric Apparatus Revolving round a Central Flame.—If in place of Fresnel's compound…

This diagram shows a side view of the right eye of man. a.c., central artery; a.h., aqueous humor; b., blind spot, the entrance of the optic nerve; c, conjunctiva; ch., choroid layer of the eye-ball; c.l., crystalline lens; c.m.c., circular fibers of the ciliary muscles; c.m.r., radial fibers of the ciliary muscles; co., cornea, the transparent portion of the sclerotic; c.p., ciliary process; c.s., canal of Schlemm, a lymphatic vessel; fo., fovea centralis, the point of clearest vision; o.n., optic nerve; o.s., ora serrata, the anterior wavy margin of the visual portion of the retina; r, the retinal layer; sc., sclerotic layer; sh., sheath of theoptic nerve; v.h., vitreous humor.

Human Eye

This diagram shows a side view of the right eye of man. a.c., central artery; a.h., aqueous humor; b.,…

"Diagrams showing some of the stages in the increasing complexity of the simple eye in Invertebrates. A, simple pigment spot in epithelium having nerve-endings associated with pigment cells (as in some medusae); B, pigment cells in a pit-like depression (as in Patella); C, with pin-hole opening and vitreous humor in cavity (as in Trochus); D, completely closed pit, with lens and cornea (as in Triton and many other Mollusks); E, pigment area elevated instead of depressed, lens of thickened cuticula (as in the Medusa, Lizzia); F, retinal cells more highly magnified. ep., epidermis; f, nerve fibre; l, lens; op, optic nerve; p, pigment cells; r, retina; v.h., vitreous humor." -Galloway, 1915

Invertebrate Simple Eye

"Diagrams showing some of the stages in the increasing complexity of the simple eye in Invertebrates.…

This lamp body is used for a lighting fixture; an electrical device used to create artificial light. A luminaries is a lighting fixture complete with the light source or lamp.

Lamp Body

This lamp body is used for a lighting fixture; an electrical device used to create artificial light.…

A converging leaf, curved inward.

Converginerved Leaf

A converging leaf, curved inward.

"A lens is a transparent body the two refracting surfaces of which are curved, or one of which is curved and the other plane.(1) Double convex(2) Plano convex(3) Meniscus(4)Double concave(5) Plano concave(6) Concavo concave." -Avery 1895

Lens

"A lens is a transparent body the two refracting surfaces of which are curved, or one of which is curved…

The common name of lens is lentils. Lens esculenta is the edible variety. The flowers are small and pale blue. The plant grows between six and eighteen inches tall. The seeds are used as food.

Upper Portion of Plant of Lens Esculenta

The common name of lens is lentils. Lens esculenta is the edible variety. The flowers are small and…

Meridional section through the lens of a rabbit. Labels: 1, Lens capsule; 2, epithelium of lens; 3, transition of the epithelium into the fibers; 4, lens fibers.

Lens of a Rabbit

Meridional section through the lens of a rabbit. Labels: 1, Lens capsule; 2, epithelium of lens; 3,…

Flexible crystalline lens of the eye.

Lens of the Eye

Flexible crystalline lens of the eye.

"...let LN represent a glass biconvex lens, with centres of curvature at C and C', and AB, the incident ray." -Avery 1895

Refraction of Light through Bi Convex Lens

"...let LN represent a glass biconvex lens, with centres of curvature at C and C', and AB, the incident…

"The shape of the double convex lens, d, c, is that of two plano-convex lenses, placed with their plane surfaces in contact, and consequently the focal distance of this lens is nearly the centre of the sphere of which one of its surfaces is a part." -Comstock 1850

Double Convex Lens

"The shape of the double convex lens, d, c, is that of two plano-convex lenses, placed with their plane…

"Double convex lenses are used in the eyeglasses for old people, becoming more spherical according to the age of the person or the magnifing power required." -Comstock 1850

Double Convex Lens Magnifing an Arrow

"Double convex lenses are used in the eyeglasses for old people, becoming more spherical according to…

"The double convex lens may be described as the part common to two spheres that intersect each other. The centers of the limiting spherical surfaces, as c and C, are the centers of curvature. The straight line, XY, passing through the centers of curvature is the principal axis of the lens." -Avery 1895

Double Convex Lens

"The double convex lens may be described as the part common to two spheres that intersect each other.…

"Thus the pencils of converging rays, are rendered still more convergent by their passage through the lens, and are therefore brought to a focus nearer the lens, in proportion to their previous convergency." -Comstock 1850

Converging Rays and a Double Convex Lens

"Thus the pencils of converging rays, are rendered still more convergent by their passage through the…

"If diverging rays fall on the surface of the same lens, they will, by refraction, be rendered less divergent, parallel, or convergent, according to the degrees of their divergency, and the convexity of the surface of the lens." -Comstock 1850

Diverging Rays from a Double Convex Lens

"If diverging rays fall on the surface of the same lens, they will, by refraction, be rendered less…

"Diagram showing how the lens changes its form for near and far sight." &mdash; Tracy, 1888

Eye lens

"Diagram showing how the lens changes its form for near and far sight." — Tracy, 1888

"If the whole circle be considered the circumfrence of a sphere, of which the plano-convex lens b, a, is a section, then the focus of parallel rays, or the principal focus, will be at the opposite side of the sphere, or at c." -Comstock 1850

Plano Convex Lens

"If the whole circle be considered the circumfrence of a sphere, of which the plano-convex lens b, a,…

"View of an arrow through a plano convex lens will have the arrow appear smaller than it actually is." -Comstock 1850

View of an Arrow Through a Plano Convex Lens

"View of an arrow through a plano convex lens will have the arrow appear smaller than it actually is."…

Section through the equator of the lens. Showing gradual transition of the epithelium into lens fibers.

Section Through Lens

Section through the equator of the lens. Showing gradual transition of the epithelium into lens fibers.

"a, prism; b, plane glass; c, spherical lens; d, double-convex; e, plano-convex, f, double-concave; g, plano-concave; h, meniscus; i, concavo-convex lenses." -Comstock 1850

Lenses of Various Forms

"a, prism; b, plane glass; c, spherical lens; d, double-convex; e, plano-convex, f, double-concave;…

"Section through one of the central eyes of a young Limulus. L, Cuticular or corneous lens. hy, Epidermic cell-layer. corn, Its corneagen portion immediately underlying the lens. ret, Retinula cells. nf, Nerve fibers. con. tiss, Connective tissue (mesoblastic skeletal tissue)." &mdash; The Encyclopedia Britannica, 1910

Limulus

"Section through one of the central eyes of a young Limulus. L, Cuticular or corneous lens. hy, Epidermic…

"The lens is spherically corrected for OO', but the sinecondition is not fulfilled. Hens the different magnifications of a point O1 beyond the axis." &mdash;Encyclopaedia Britannica, 1910

Magnification of Image Beyond Axis with Lens

"The lens is spherically corrected for OO', but the sinecondition is not fulfilled. Hens the different…

"A microscope consists of a lens or a combination of lenses used to observe small objects, often so minute as to be invisible to the unaided eye." &mdash; Avery, 1895

Microscope

"A microscope consists of a lens or a combination of lenses used to observe small objects, often so…

"This consists of two lenses, one of which is called the condesner, because it is employed to concentrate the rays of the sun...The other is a double convex lens, of considerable magnifing power, by which the image is magnified." -Comstock 1850

Solar Microscope

"This consists of two lenses, one of which is called the condesner, because it is employed to concentrate…

"Ocellus of a medusa (Lizzia Koellikeri). oc, pigmented ectodermal cells; l, lens." &mdash; Encyclopedia Britannica, 1893

Ocellus

"Ocellus of a medusa (Lizzia Koellikeri). oc, pigmented ectodermal cells; l, lens." — Encyclopedia…

"If y be the object the image appears to a normal eye situated behind the system L with passive accommodation at a very great distance under the angle w'. Since H' P&#61; F O, &#61; y, from the focal length of the simple microscope is the image side focal length." &mdash;Encyclopaedia Britannica, 1910

Optical Position and Size of Image Through Magnifying Glasses

"If y be the object the image appears to a normal eye situated behind the system L with passive accommodation…

"The intersection of the principal rays in this case lies in the middle of the entrance pupil or of the exit pupil. By head and eye motion the various parts of the whole field can be viewed one after another." &mdash;Encyclopaedia Britannica, 1910

Optical Position of Diaphragms using Lens

"The intersection of the principal rays in this case lies in the middle of the entrance pupil or of…

"Another form is called the polyangular kaleidoscope. The only essential difference in it is that the mirrors are so arranged that the angle between them can be varied at pleasure. This, being very useful for illustrating the theory of the instrument, is the form usually found in collections of philosophical apparatus." &mdash;The Encyclopedia Britannica, 1910

Polyangular Kaleidoscope

"Another form is called the polyangular kaleidoscope. The only essential difference in it is that the…

"Fill with carbon dioxide a large rubber toy balloon or other double-convex lens having easily flexible walls. Suspend a watch, and place yourself so that you can just hear its ticking. Have the gas-filled lens moved back and forth in the line between watch and and ear until the ticking is much more plainly heard. Use a glass funnel as an ear-trumpet." -Avery 1895

Sound Refraction

"Fill with carbon dioxide a large rubber toy balloon or other double-convex lens having easily flexible…

"Showing how an object is refracted through a biconvex lens." -Avery 1895

Object Refracted through Biconvex Lens

"Showing how an object is refracted through a biconvex lens." -Avery 1895

"In 1835 Mr. Stevenson, in a report to the Northern Lighthouse Board, proposed to add fixed reflecting prisms p below the lenses of Fresnel's revolving light, and he communicated this proposal to M. L. Fresnel, who approved of his suggestion, and assisted in carrying out the design in 1843. This combination added, however, but little to the power of the flash, and produced both a periodically flashing and constantly fixed light; but it must be remembered that the prism for fixed lights was the only kind of reflecting prism then known." &mdash;The Encyclopedia Britannica, 1910

Stevensons Revolving Light

"In 1835 Mr. Stevenson, in a report to the Northern Lighthouse Board, proposed to add fixed reflecting…

"The following description of a section of Lord Rosse's telescope, though not so perfect as could be desired, is the best we could obtain. it exhibits a view of the inside of the eastern wall, with the tube, and machinery by which it is moved. A is the mason-work on the ground; B the universal joint, which allows the tube to turn in all directions; C the speculum in the tube; E the eye-piece through which the observer looks; F a pulley by which the tube is moved; H a chain attached to the pulley, and to the side of the tube; I, a chain running to K, the counterpoise; L, a lever connecting the chain M with the tube; Z another chain which passes from the upper part of the tube over a pulley at W, (not seen) and crosses to the opposite wall; X a railroad on which the speculum is drawn either to or from the tube. The dotted line H, shows the course of the weight R, as the tube rises or falls. The tube is moved from wall to wall by a ratchet wheel at R, which is turned by the lever O, on the circle N, the ends of which are fixed in the two walls." &mdash;Comstock, 1850

Telescope

"The following description of a section of Lord Rosse's telescope, though not so perfect as could be…

"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having a long, and the other a short, focal distance." -Comstock 1850

Refracting Telescope

"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having…

"Suppose the object o to be at such a distance, that the rays of light from it pass in parallel lines, p, p, to the great reflector, r, r. this reflector being concave, the rays are converged by reflection, and cross each other at a, b which the image is inverted. The rays then pass to the small mirror, b, which being also concave, they are thrown back in nearly parallel lines, and having passed the aperture in the centre of the great mirror, fall on the plano-convex lens e." -Comstock 1850

Refracting Telescope

"Suppose the object o to be at such a distance, that the rays of light from it pass in parallel lines,…

"Diagrams illustrating two stages in the development of the vertebrate eye. A, showing the relation of the ectoderm, the brain vesicle, and the optic vesicle. The right side of the figure shows a later stage than the left. B, later stage, showing the lens, eye-ball and retina in position. b.v., brain vesicle formed by the invagination oof the ectoderm (ect.); l, lens; mes., mesodermal tissue; o.n., optic nerve; o.s., optic stalk; o.v., optic vesicle, a portion of the brain vesicle; r, retinal layer; v.h., interior of eye-ball which comes to contain the vitreous humor." &mdash; Galloway

Vertebrate Eye

"Diagrams illustrating two stages in the development of the vertebrate eye. A, showing the relation…