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Alexandria, Pharos Island Lighthouse

Pharos Island Lighthouse

Alexandria, Pharos Island Lighthouse

"Beacons in exposed situations are constructed sometimes of stone, and cement-concrete or cement-rubble, but generally of castiron columns let into heavy base plates which are fixed to the rock by strong lewis bats. The small class iron beacons are generally of malleable iron and the larger of cast-iron butt steel or bronze might with advantage be used in very exposed places." —The Encyclopedia Britannica, 1910

Beacon

"Beacons in exposed situations are constructed sometimes of stone, and cement-concrete or cement-rubble,…

"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…

"Coal-gas was first used as a lighthouse illuminant at Salvore, near Trieste, in 1817. For many years it has been used in the harbour lights of Great Britain when in the neighborhood of gas-works. Mr. J. R. Wigham has designed a compound or crecus burner consisting of a group of twenty-eight vertical tubes, each carrying an ordinary double fish-tail burner, and the ignited gases issuing from all these jets unite into one large flame." —The Encyclopedia Britannica, 1910

Coal-gas

"Coal-gas was first used as a lighthouse illuminant at Salvore, near Trieste, in 1817. For many years…

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing principle all the light can be distributed with strict equality over 112 degrees, which is the arc prescribed for steamers by the Board of Trade. Several of the Transatlantic and other steamers have adopted this kind of apparatus, which is hung on gimbals and placed in iron towers, having an entry from below the deck, which can be made use of in bad weather." —The Encyclopedia Britannica, 1910

Condensing Apparatus

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing…

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing principle all the light can be distributed with strict equality over 112 degrees, which is the arc prescribed for steamers by the Board of Trade. Several of the Transatlantic and other steamers have adopted this kind of apparatus, which is hung on gimbals and placed in iron towers, having an entry from below the deck, which can be made use of in bad weather." —The Encyclopedia Britannica, 1910

Condensing Apparatus

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing principle…

"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 radius…

"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 radius…

"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 radius…

"Dioptric Floating Light. Elevation." —The Encyclopedia Britannica, 1910

Dioptric Light

"Dioptric Floating Light. Elevation." —The Encyclopedia Britannica, 1910

"Dioptric Floating Light. Horizontal Section." —The Encyclopedia Britannica, 1910

Dioptric Light

"Dioptric Floating Light. Horizontal Section." —The Encyclopedia Britannica, 1910

"aa is the mast, b tackle hook, c, c brass flanges for fixing parts of lantern together, e and g weather guards, h plate glass front of lantern, i shutter by which lamps are trimmed, k lamps, l silver reflector. Revolving catoptric apparatus was applied to floating lights in England, and M. Letourneau, in 1851, proposed to employ a number of sets of dioptric apparatus in one lantern." —The Encyclopedia Britannica, 1910

Floating Lights

"aa is the mast, b tackle hook, c, c brass flanges for fixing parts of lantern together, e and g weather…

An illustration of Fort Jefferson which is located today in what is Dry Tortugas National Park. Dry Tortugas National Park preserves Fort Jefferson and the Dry Tortugas section of the Florida Keys. The park covers 101 mi² (262 km²), mostly water, about 68 statute miles (109 km) west of Key West in the Gulf of Mexico.

Fort Jefferson

An illustration of Fort Jefferson which is located today in what is Dry Tortugas National Park. Dry…

"Holophotal Catadioptric Apparatus Revolving round a Central Flame." —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.—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." —The Encyclopedia Britannica, 1910

Holophotal Catadioptric

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

Incandescent bulbs are made in a wide range of sizes and voltages, from 1.5 volts to about 300 volts. They require no external regulating equipment and have a low manufacturing cost, and work well on either alternating current or direct current.

Incandescent Lamp

Incandescent bulbs are made in a wide range of sizes and voltages, from 1.5 volts to about 300 volts.…

A woman who resided in a lighthouse in Newport. She was an expert rower, and saved the lives of many sailors after wrecking their vessels on the rocks.

Ida Lewis

A woman who resided in a lighthouse in Newport. She was an expert rower, and saved the lives of many…

Lighthouse in the water.

Lighthouse

Lighthouse in the water.

"Lighthouse, Jupiter inlet, east coast of Florida."— Frank Leslie, 1896

lighthouse

"Lighthouse, Jupiter inlet, east coast of Florida."— Frank Leslie, 1896

An elevated structure or tower placed near a seaport or some headland for the purpose of protecting vessels at night by warning navigators of danger, and also serving as a general landmark.

Lighthouse

An elevated structure or tower placed near a seaport or some headland for the purpose of protecting…

"An iron pile light erected at Haneda, in the Bay of Yedo, Japan." —The Encyclopedia Britannica, 1910

Lighthouse

"An iron pile light erected at Haneda, in the Bay of Yedo, Japan." —The Encyclopedia Britannica,…

"A tower or other elevated structure bearing a light at the top and erected at the entrance of a harbor or on some rock or headland to serve as a guide or warning of danger to navigators at night." -Foster, 1921

Lighthouse

"A tower or other elevated structure bearing a light at the top and erected at the entrance of a harbor…

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures consisting of triangles, squares, and parallelograms are used to construct the given shape. This tangram depicts a lighthouse.

Lighthouse

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures consisting of triangles, squares, and parallelograms are used to construct the given shape. This tangram depicts a lighthouse.

Lighthouse

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

An illustration of a lighthouse in the distance on a rocky shoreline.

Lighthouse

An illustration of a lighthouse in the distance on a rocky shoreline.

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures consisting of triangles, squares, and parallelograms are used to construct the given shape. This tangram depicts a lighthouse.

Lighthouse

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures consisting of triangles, squares, and parallelograms are used to construct the given shape. This tangram depicts a lighthouse.

Lighthouse

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

The Sackett's Harbor lighthouse was erected on Horse Island during the War of 1812.

Lighthouse on Horse Island

The Sackett's Harbor lighthouse was erected on Horse Island during the War of 1812.

This sign is used to indicate that a lighthouse is located nearby.

Lighthouse, Black and White

This sign is used to indicate that a lighthouse is located nearby.

This sign is used to indicate that a lighthouse is located nearby.

Lighthouse, Color

This sign is used to indicate that a lighthouse is located nearby.

"Eddystone is a group of gneiss rocks, daily submerged by the tide, in the English Channel, 9 miles off the Cornish coast, and 14 S.S.W. of Plymouth Breakwater. The frequent shipwrecks on these rocks led to the erection of a lighthouse on them in 1669-1700, but the great storm of Nov. 20, 1703 completely washed it away. Another lighthouse was built in 1706-1709. This was burned in 1755. The next, noted for its strength and the engineering skill displayed in it, was constructed in 1757-1759. The granite was dovetailed into the solid rock, and each block into its neighbors. As the rock in which this tower was built became undermined and greatly weakened by the action of the waves, the foundation of another was laid on a different part of the reef in 1879. Its light is visible in clear weather at a distance of 17 and one half miles."—(Charles Leonard-Stuart, 1911)

Eddystone Lighthouse

"Eddystone is a group of gneiss rocks, daily submerged by the tide, in the English Channel, 9 miles…

This sign is used to indicate that a lighthouse is located nearby.

Lighthouse, Outline

This sign is used to indicate that a lighthouse is located nearby.

This sign is used to indicate that a lighthouse is located nearby.

Lighthouse, Silhouette

This sign is used to indicate that a lighthouse is located nearby.

"The United States gunboat <em>Mohawk</em> chasing the Confederate steamer <em>Spray</em> into the St. Mark's River." &mdash;Leslie, 1896

Mohawk

"The United States gunboat Mohawk chasing the Confederate steamer Spray into the St.…

"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." &mdash;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." &mdash;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." &mdash;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." &mdash;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…

"Plane mirrors M revolve on an endless chain placed outside of the apparatus and alter the direction of the flashes after they pass into the dark arc on the landward side so as to cause the lenses L, L to repeat their flashes over the seaward are which requires strengthening. The condensing spherical mirror and mirror of unequal areas will also be found applicable in cases where the flashes do not require to sweep over the whole horizon." —The Encyclopedia Britannica, 1910

Repeating Light

"Plane mirrors M revolve on an endless chain placed outside of the apparatus and alter the direction…

"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 illustration of Seahorse Key lighthouse which is located in Cedar Keys, a cluster of islands close to the mainland of Florida.

Seahorse Key

An illustration of Seahorse Key lighthouse which is located in Cedar Keys, a cluster of islands close…

A hunter, shepherd, and farmers working on the shore.

Shore Scene

A hunter, shepherd, and farmers working on the shore.

"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." —The Encyclopedia Britannica, 1910

Stevensons Revolving Light

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

"Condensing Straight Prisms.&mdash;These, either by reflexion or refraction or both, cause a ray fr proceeding in any compass bearing from a fixed light apparatus AA to emerge in the direction, e.g., parallel to the corresponding ray fb, which proceeds in the same compass bearing from another part of the apparatus and so of any other ray fc which is bent parallel to the ray fa." &mdash;The Encyclopedia Britannica, 1910

Straight Prisms

"Condensing Straight Prisms.—These, either by reflexion or refraction or both, cause a ray fr…

"Professor Swan's Designs.—Among several ingenious arrangements and new forms of agents proposed by Professor Swan is the mode of sending rays from prisms through interstices left between other prisms placed in front, and also a form of agent which he termed the triesoptric prism, in which the rays would undergo two refractions and three reflexions. a are the front and b the triesoptric prisms. The two upper and lower prisms a are constructed of flint glass of high refractive power. It will be observed from the drawing that this ingenious arrangement is nevertheless open to objection, for cones of light of 30 degrees in front and of 65 degrees at the back are lost through the interstices." —The Encyclopedia Britannica, 1910

Swans Designs

"Professor Swan's Designs.—Among several ingenious arrangements and new forms of agents proposed by…

An illustration of a three triangles created with boats and a lighthouse. This is an example illustration used to fine the height of an object situated about the plane of observation, and its height above the plane.

Triangle with Lighthouse

An illustration of a three triangles created with boats and a lighthouse. This is an example illustration…