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Glasses

Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the eyes, normally for vision correction, eye protection, or for protection from UV rays.

Modern glasses are typically supported by pads on the bridge of the nose and by temples placed over the ears. Historical types include the pince-nez, monocle, and lorgnette.

<a href="http://www.himfr.com/buy-magnetic_loop/">magnetic loop</a>Eyeglass frames are commonly made from metal or plastic. Lenses were originally made from glass, but many are now made from various types of metal plastic, including CR-39 and polycarbonate. These materials reduce the danger of breakage and weigh less than glass lenses. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light.[1] Some plastics have a greater index of refraction than most types of glass; this is useful in the making of corrective lenses shaped to correct various vision abnormalities such as myopia, allowing thinner lenses for a given prescription. Newer plastic lenses, called izon, can also correct for the higher order aberrations that naturally occur in the surface of our eye. These lenses create sharper vision and help with the halos, starbursts, and comet-tails often associated with night time driving glare. Wavefront guided LASIK surgery also corrects for the higher order aberrations.

Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to reduce glare, improve night vision and make the wearer's eyes more visible.

CR-39 lenses are the most common plastic lenses due to their low weight, high scratch resistance, and low transparency for ultra violet and infrared radiation. Polycarbonate and Trivex lenses are the lightest and most shatter-resistant, making them the best for impact protection,[1] yet offer poor optics due to high dispersion, and having a low Abbe number of 31.

Not all glasses are designed solely for vision correction but are worn for protection, viewing visual information (such as stereoscopy) or simply just for aesthetic or fashion values. Safety glasses are a kind of eye protection against flying debris or against visible and near visible light or radiation. Sunglasses allow better vision in bright daylight, and may protect against damage from high levels of ultraviolet light.

The earliest historical reference to magnification dates back to ancient Egyptian hieroglyphs in the 8th century BC, which depict "simple glass meniscal lenses". The earliest written record of magnification dates back to the 1st century AD, when Seneca the Younger, a tutor of Emperor Nero, wrote: "Letters, however small and indistinct, are seen enlarged and more clearly through a globe of glass filled with water".[3] Emperor Nero is also said to have watched the gladiatorial games using an emerald as a corrective lens.

Corrective lenses were said to be used by Abbas Ibn Firnas in the 9th century, who had devised a way to produce very clear glass. These glasses could be shaped and polished into round rocks used for viewing and were known as reading stones. The earliest evidence of "a magnifying device, a convex lens forming a magnified image," dates back the Book of Optics published by Alhazen in 1021. Its translation into Latin in the 12th century was instrumental to the invention of eyeglasses in 13th century Italy.

Sunglasses, in the form of flat panes of smoky quartz, protected the eyes from glare and were used in China in the 12th century or possibly earlier. However, they did not offer any corrective powers.

Around 1284 in Italy, Salvino D'Armate is credited with inventing the first wearable eye glasses.The earliest pictorial evidence for the use of eyeglasses, however, is Tomaso da Modena's 1352 portrait of the cardinal Hugh de Provence reading in a scriptorium. Another early example would be a depiction of eyeglasses found north of the Alpes in an altarpiece of the church of Bad Wildungen, Germany, in 1403.

Many theories abound for who should be credited for the invention of traditional eyeglasses. In 1676, Francesco Redi, a professor of medicine at the University of Pisa, wrote that he possessed a 1289 manuscript whose author complains that he would be unable to read or write were it not for the recent invention of glasses. He also produced a record of a sermon given in 1305, in which the speaker, a Dominican monk named Fra Giordano da Rivalto, remarked that glasses had been invented less than twenty years previously, and that he had met the inventor. Based on this evidence, Redi credited another Dominican monk, Fra Alessandro da Spina of Pisa, with the re-invention of glasses after their original inventor kept them a secret, a claim contained in da Spina's obituary record.

Other stories, possibly legendary, credit Roger Bacon with the invention. Bacon is known to have made one of the first recorded references to the magnifying properties of lenses in 1262,[9] though this was predated by Alhazen's Book of Optics in 1021.[3] Bacon's treatise De iride ("On the Rainbow"), which was written while he was a student of Robert Grosseteste, no later than 1235, mentions using optics to "read the smallest letters at incredible distances". While the exact date and inventor may be forever disputed, it is almost certainly clear that spectacles were invented between 1280 and 1300 in Italy.

These early spectacles had convex lenses that could correct both hyperopia (farsightedness), and the presbyopia that commonly develops as a symptom of aging. Nicholas of Cusa is believed to have discovered the benefits of concave lens in the treatment of myopia (nearsightedness). However, it was not until 1604 that Johannes Kepler published in his treatise on optics and astronomy, the first correct explanation as to why convex and concave lenses could correct presbyopia and myopia.

The American scientist Benjamin Franklin, who suffered from both myopia and presbyopia, invented bifocals in 1784 to avoid having to regularly switch between two pairs of glasses.[10] The first lenses for correcting astigmatism were constructed by the British astronomer George Airy in 1825.[10]

Over time, the construction of spectacle frames also evolved. Early eyepieces were designed to be either held in place by hand or by exerting pressure on the nose (pince-nez). Girolamo Savonarola suggested that eyepieces could be held in place by a ribbon passed over the wearer's head, this in turn secured by the weight of a hat. The modern style of glasses, held by temples passing over the ears, was developed in 1727 by the British optician Edward Scarlett. These designs were not immediately successful, however, and various styles with attached handles such as "scissors-glasses" and lorgnettes remained fashionable throughout the 18th and into the early 19th century.

In the early 20th century, Moritz von Rohr at Zeiss (with the assistance of H. Boegehold and A. Sonnefeld[11]), developed the Zeiss Punktal spherical point-focus lenses that dominated the eyeglass lens field for many years.

Despite the increasing popularity of contact lenses and laser corrective eye surgery, glasses remain very common as their technology has improved. For instance, it is now possible to purchase frames made of special memory metal alloys that return to their correct shape after being bent. Other frames have spring-loaded hinges. Either of these designs offers dramatically better ability to withstand the stresses of daily wear and the occasional accident. Modern frames are also often made from strong, light-weight materials such as titanium alloys, which were not available in earlier times.

On May 1, 1992 the United States Federal Trade Commission declared (section 456.2) that optometrists be required to provide the patient with a complete prescription immediately following an eye exam, effectively giving the patient the choice of where to purchase their glasses.[12] The result was greater competition between the glasses manufacturers and thus lower prices for consumers. This trend has been accelerated by the proliferation of Internet technology, giving consumers the chance to bypass traditional distribution channels and buy glasses directly from the manufacturers.

About the Author

Himfr is a scholar, focusing his research on Chinese cultures. If you are interested in purchasing China goods, please visit www.himfr.com

Are Fire signs more likely to be pyromaniacs?

I have no fire signs at all, but I was your average little pyro. I loved the fact that I could start a fire with just a magnifing glass and did so on many osscasions. I stopped after I set my cousins swimsuite on fire at a family reunion - no! I'm not going to elaborate.....let's just say he was lucky his sister was there to happily push him in the pool. Aw, good times...good times... =)

Hahahaha! Never thought about that. I am a Sadge and I do like fire but I was never much of a pyro. My sister on the other hand is a Leo and OMG was she the biggest pyro! She loves loves loves fire. So does my dad and he's Aquarius.

Don't really know if being a fire sign has anything to do with it because I do know other pyros but I don't know their b'days so I can't be sure---but maybe they have fire in other parts of their chart---Hmmm, interesting thought.

Libra's come up with some great questions---hi Bumby and Rach )))

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