IELTS Academic Reading Practice Test 26

At some point after the age of about forty, almost everyone finds that small print has become harder to read. The cause, now known as presbyopia, is a gradual loss of flexibility in the lens of the eye, which makes it increasingly difficult to focus on nearby objects. For most of history there was no remedy. In medieval Europe this was more than an inconvenience: a scribe, a scholar or a skilled craftsman whose close vision failed might lose the ability to work at precisely the age when experience made him most valuable. The Roman writer Seneca had observed that letters looked larger when seen through a glass globe filled with water, but no one turned the observation into a practical aid.

The scientific groundwork was laid in the Islamic world. Around the year 1020 the scholar Ibn al-Haytham, working in Cairo, completed his Book of Optics, a systematic study of light, vision and the behaviour of lenses and mirrors. When the work was translated into Latin, it influenced a generation of European thinkers. In 1267 the English philosopher Roger Bacon wrote that a segment of a glass sphere, placed with its flat side on a page, would make letters appear larger and could therefore help older people to read. Such reading stones, made of glass or polished rock crystal, were used by some monks and scholars, but they had to be moved constantly across the page.

The decisive step, mounting a lens in a frame in front of each eye, was taken in northern Italy in the late thirteenth century. The best evidence comes from a sermon preached in Florence in 1306 by a Dominican friar, Giordano da Pisa, who told his listeners that the art of making eyeglasses had been discovered less than twenty years earlier, and that he had met and spoken with the man who first made them.

Unfortunately he did not record that man's name. Another Dominican, Alessandro della Spina of Pisa, who died in 1313, is said to have made spectacles himself and to have shared the method freely. A later claim that a Florentine named Salvino degli Armati was the inventor has been shown to rest on a forged inscription.

Italy's glass industry made the invention possible. Venice, and especially the nearby island of Murano, produced glass of unusual clarity, and regulations issued by the city's guild of crystal workers around 1300 already refer to discs of glass for the eyes. These rules prohibited craftsmen from passing off ordinary glass lenses as more valuable rock crystal, which suggests that a market for lenses already existed. The earliest spectacles consisted of two convex lenses set in frames of bone, wood, leather or metal, joined by a rivet and balanced on the nose. The oldest known painting of a person wearing them is a fresco completed in 1352 by Tommaso da Modena in Treviso, which shows a cardinal reading at his desk.

Demand grew dramatically after the invention of printing in the fifteenth century, which put books into the hands of far more readers. Florence became a major centre of production, and its spectacle makers began to offer lenses of different strengths, graded according to the age of the buyer. By the middle of the fifteenth century concave lenses had also appeared, providing help for short-sighted people, who see distant objects poorly. For the first time, spectacles could correct the two most common defects of vision rather than only the one associated with old age.

Keeping spectacles in place was a persistent problem. For centuries, wearers balanced them on the nose, held them up by hand or tied them on with ribbons or cords passed behind the head. Rigid side pieces resting on the ears, now so familiar that they seem obvious, were introduced only around 1730, when the London optician Edward Scarlett began to advertise them. Even then, many fashionable people preferred lenses on a handle, which could be raised to the eyes when needed and which did not suggest that the user's sight was poor.

Further refinements followed. In the 1780s the American statesman and scientist Benjamin Franklin described the bifocals he had devised, in which each frame held two half-lenses, one for distant vision and one for reading, so that he no longer had to change from one pair to another. In 1825 the British astronomer George Airy designed cylindrical lenses to correct his own astigmatism, a condition in which the eye focuses unevenly. Testing also became more systematic: in 1862 the Dutch ophthalmologist Herman Snellen published an eye chart with rows of letters of decreasing size, a design still used in clinics around the world.

Spectacles have since been joined by other ways of correcting vision. The German physician Adolf Fick made one of the first contact lenses in 1888, from glass, and modern soft lenses and laser surgery now offer alternatives for millions of people. Yet the need for correction is growing rather than shrinking. Short-sightedness has become far more common in recent decades, particularly in East Asia, and one widely cited study has projected that around half of the world's population may be short-sighted by 2050. Seven centuries after their invention, spectacles remain among the most widely used medical devices in existence.

Mantis shrimps are not true shrimps but a separate and ancient group of crustaceans, known to biologists as stomatopods. Around 450 species have been described, most of them living in warm, shallow seas, where they hide in burrows or crevices in coral reefs and ambush passing prey. Many are brightly coloured, and they range in length from a couple of centimetres to more than thirty. Divers and aquarium owners know them for two remarkable abilities: the violence of their strike, and the extraordinary complexity of their eyes, which have made them a subject of intense research by biologists and, more recently, by engineers.

Mantis shrimps are usually divided into spearers, which impale soft-bodied fish with spiny appendages, and smashers, which batter hard-shelled prey with a pair of club-like limbs. In 2004 the biologist Sheila Patek and her colleagues used high-speed cameras to show that a smasher's club accelerates faster than almost any other movement known in the animal kingdom. The energy is stored in a spring-like structure and released by a latch, rather than being supplied by muscles alone. The strike is so rapid that it creates bubbles in the surrounding water, which collapse with a further burst of energy. Together, these blows allow the animals to smash the shells of snails and crabs.

The eyes are equally unusual. Each sits on a mobile stalk and can move independently of the other, scanning the surroundings in different directions at once. Like the eyes of insects, they are compound eyes, made up of thousands of small units. Each eye, however, is divided into an upper and a lower half by a central band of six rows of enlarged units, known as the midband. Because the two halves and the midband can all view the same object from slightly different angles, a mantis shrimp can judge distance using a single eye, an ability that most animals possess only by comparing the images from two eyes.

It is the midband that gives mantis shrimps their reputation for colour vision. Human colour vision depends on just three types of cone cell in the retina, sensitive to red, green and blue light, and the brain works out colours by comparing the signals from them. Honeybees also have three types of colour receptor, but theirs are shifted towards shorter wavelengths, so that bees can see ultraviolet light but not red. Mantis shrimps have twelve types of photoreceptor devoted to colour, more than any other animal known when they were discovered, although some butterflies come close: in 2016 researchers reported fifteen classes of photoreceptor in the common bluebottle butterfly.

It was natural to assume that twelve receptors would allow mantis shrimps to see colours with exceptional precision. In 2014, however, Hanne Thoen, Justin Marshall and colleagues at the University of Queensland tested this assumption by training the animals to choose particular colours in return for food. The shrimps turned out to be surprisingly poor at telling apart similar colours, failing when two colours differed by around 12 nanometres in wavelength, whereas humans can detect differences of just a few nanometres. The researchers suggested that mantis shrimps do not compare signals between receptors as we do, but recognise colours directly according to which receptor responds, a system that requires little processing and may allow a fast-moving predator to identify colours almost instantly.

Mantis shrimps also see a wide range of ultraviolet light. In 2014 Michael Bok, Thomas Cronin and their colleagues reported that one species has six different types of ultraviolet receptor, each tuned to a slightly different band of wavelengths. Remarkably, this tuning is achieved partly by filters inside the eye made from compounds that act as a natural sunscreen in many marine organisms. By absorbing some wavelengths and transmitting others, the filters allow receptors that would otherwise respond alike to divide the ultraviolet spectrum between them. Similar compounds protect corals and other reef animals from the intense sunlight of shallow tropical waters.

The most surprising discovery concerns polarised light, in which light waves vibrate in a particular pattern. Many animals, including bees and octopuses, can detect linearly polarised light, but in 2008 a team including Tsyr-Huei Chiou, Thomas Cronin and Justin Marshall showed that mantis shrimps can also detect circularly polarised light, the first animals known to do so. Specialised cells in the eye act as quarter-wave retarders, converting circular polarisation into a linear form that receptors can detect. Later work suggested that these biological structures perform consistently across a broader range of colours than comparable artificial devices. Since some mantis shrimps have body parts that reflect circularly polarised light, the ability may provide a private channel of communication.

Such findings have attracted the interest of engineers. Researchers have built experimental cameras inspired by the mantis shrimp eye that record polarisation as well as colour, with possible uses ranging from underwater navigation to the detection of diseased tissue in medicine. For biologists, the main lesson is a different one. More receptors do not simply mean better vision in the human sense. The mantis shrimp's eyes appear to be adapted to the particular demands of its life as a fast, aggressive predator in a bright, colourful environment, rather than to seeing the world as we do, only more richly.

Little more than fifteen years ago, the phrase sharing economy promised a quiet revolution. Digital platforms would allow ordinary people to rent out spare rooms, lend tools, share car journeys and make use of possessions that otherwise sat idle. In their 2010 book What's Mine Is Yours, Rachel Botsman and Roo Rogers described this as collaborative consumption, a shift from owning things to accessing them that would save money, build trust between strangers and reduce waste. Some of that promise has been fulfilled. But the term itself has become misleading, and in my view the debate about these businesses would be clearer if we described them more accurately.

The genuine advantage of the platforms lies in using assets that would otherwise be wasted. The average private car, for instance, is parked for around 95 per cent of its life, and many homes contain rooms that stand empty for much of the year. By matching people who have such resources with people who need them, platforms can reduce costs for consumers and provide extra income for owners. Travellers gain cheaper and more varied accommodation, and in cities with poor public transport, ride-hailing apps can make journeys easier for people without cars. These benefits are real and should not be dismissed.

Yet very little of what happens on the largest platforms is sharing in any ordinary sense. Couchsurfing, founded in 2004, allowed travellers to stay with local hosts free of charge, and it captured the original spirit of the idea; even so, it became a profit-making company in 2011. Airbnb, founded in San Francisco in 2008, and Uber, founded the following year, grew into some of the most valuable companies in the world by organising paid transactions. Many listings on short-term rental sites in popular cities are entire homes let throughout the year, and some hosts manage dozens of properties. These are businesses, and the label sharing economy has allowed them to present themselves as something gentler.

This matters because the costs of these businesses fall on people who never use them. When homes are converted into permanent tourist accommodation, the supply of housing for residents shrinks. A study of the United States by Kyle Barron, Edward Kung and Davide Proserpio found that each additional listing had only a small effect on rents, but that the effect added up in places where listings were concentrated. Research in Barcelona found much larger increases in the neighbourhoods most popular with tourists than in the city as a whole. The effect of short-term rentals on housing, in other words, depends heavily on where they are.

Ride-hailing raises similar questions. Studies in San Francisco have concluded that app-based vehicles were responsible for a substantial share of the increase in traffic congestion there in the 2010s, since many trips replaced journeys that would otherwise have been made by public transport, on foot or not at all. There are also questions about the people who do the work. Platforms have generally treated drivers as independent contractors rather than employees, which means they are not entitled to a minimum wage or holiday pay. Drivers can choose their own hours, which many value, but their earnings are often uncertain, and they usually bear the costs of running their vehicles themselves.

Courts and governments have begun to challenge this arrangement. In 2021 the UK Supreme Court ruled that Uber drivers were workers entitled to the minimum wage and paid holidays, not self-employed contractors. In California, by contrast, voters approved a measure in 2020 that allowed app-based drivers to continue to be treated as contractors, in exchange for certain limited benefits. Cities have also acted on housing. Amsterdam has limited the number of nights for which an entire home can be let to tourists each year, New York introduced strict registration rules in 2023, and Barcelona has announced that it will withdraw all of its roughly 10,000 tourist-apartment licences by 2028.

Critics of such measures argue that they protect established hotels and taxi companies from competition and deprive homeowners of income. There is some truth in this: regulation can certainly be designed to favour existing businesses. But the alternative, allowing platforms to operate under lighter rules than their competitors simply because they are new, is not a neutral choice either. It gives an advantage to companies that have done nothing more than find a way around rules that others must follow. Nor is regulation necessarily hostile to innovation, since clear rules can give responsible operators the confidence to invest.

The sensible approach, I believe, is to judge these businesses by what they do rather than by what they call themselves. A company that rents out apartments to tourists should face the same expectations as other providers of accommodation, and a company that directs the work of drivers should accept responsibilities towards them. Where genuine sharing does occur, such as a resident occasionally letting a spare room or neighbours lending tools, lighter rules may well be justified. Technology has made it easier to use idle resources, and that is a real gain. It should not become a reason for exempting large commercial enterprises from obligations that apply to everyone else.