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"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…

"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…

"Suppose a cannon be loaded with a ball, and placed on top of a tower, at such a height from the ground, that it would take just three seconds for the ball to descend from it to the ground, if let fall perpendicularly. Now, suppose the cannon to be fired in an exact horizontal direction, and at the same instant, the ball to be dropped towards the ground. They will both reach the ground at the same instant..." -Comstock 1850

Projectile Motion of a Cannonball

"Suppose a cannon be loaded with a ball, and placed on top of a tower, at such a height from the ground,…

"Light projected by a parabolic reflector." —Croft 1917

Parabolic Reflector

"Light projected by a parabolic reflector." —Croft 1917

"...represents two parabolic reflectors, mn and op. It is a peculiarity of such reflectors that rays starting from the focus, as F will be reflected as parallel rays, and that parallel rays falling upon sucha reflector will converge at the focus, as F'. Hence, two such reflectors may be placed in such a sposition that sound waves starting from one focus shall, after two reflections, be converged at the other focus...Two reflectors so placed are said to be conjugate to each other." -Avery 1895

Parabolic Reflectors

"...represents two parabolic reflectors, mn and op. It is a peculiarity of such reflectors that 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…