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Updated: June 8, 2025
In a short time a brilliant revolving light flashed across the waters. It can be seen nineteen miles off, the tower being two hundred and four feet above high-water. In the tower is a bell, which is rung during fogs, to warn ships from approaching too near. The light is a dioptric or lens-light of the first order.
Hence by dioptric means the consumption of oil necessary for the fourteen reflectors will produce almost as powerful a light as that which would require the oil of twenty-four reflectors in the catoptric system, and consequently there is an excess of oil equal to that consumed by ten reflectors, or four hundred gallons in the year against the Scotch system.
In a lighthouse on the dioptric system, the lantern is constructed with eight sides, which form an octagonal prism around the lamp in the centre. The centre of each side is occupied by a plano-convex lens, something similar to a burning-glass, having a diameter of about fifteen inches. This central lens is not sufficient to cover the entire side.
The ones that are lost bear the following suggestive titles: On the Construction of Slings; On the Construction of Missiles; On the Automaton; On the Method of Lifting Heavy Bodies; On the Dioptric or Spying-tube. The work that remains is called Pneumatics, and so interesting a work it is as to make us doubly regret the loss of its companion volumes.
"What ails Yásha?" asked Platonída Ivánovna, as she handed Paramón Paramónitch a three-ruble bank-note on the threshold. The district doctor, who, like all contemporary doctors, especially those of them who wear a uniform, was fond of showing off his learned terminology, informed her that her nephew had all the dioptric symptoms of nervous cardialgia, and that febris was present also.
I refer to the use of dioptric media which correct the diminished refracting power of the humors of the eye, in other words, spectacles. I don't use them. All I ask is a large, fair type, a strong daylight or gas-light, and one yard of focal distance, and my eyes are as good as ever. But if YOUR eyes fail, I can tell you something encouraging.
They investigated the subject with their usual scientific skill, and the result was the invention and adoption of the system of lenses instead of reflectors, known as the Dioptric system. A transparent lens reduces to parallelism all the luminous rays which traverse it, whatever be their original amount of divergence, provided these rays proceed from a point or focus suitably situated.
The present lighthouse is 30 feet higher than Smeaton's, and is fitted with the modern system of dioptric refractors, giving a light of 519,000 candle-power, which is greater than any other on the east coast of England. The need for a second structure has been obviated by placing the low lights half-way down the existing tower.
It is of the dioptric kind, and is bright, steady, and uniform, ranging over an horizon of eight miles, and visible at the distance of ten miles from a coaster’s deck. During foggy weather a bell is tolled by machinery. Tide-time for vessels of twelve feet draft is also denoted by signals.
But Sir Isaac has shown that dioptric telescopes cannot be brought to a greater perfection, because of that refraction, and of that very refrangibility, which at the same time that they bring objects nearer to us, scatter too much the elementary rays.
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