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"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…

"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…