Đề thi thật IELTS Academic Reading — tháng 2/2026 Test 223

In the ancient world, the waxy grey substance we now refer to as ambergris was highly prized for its medicinal properties, and was widely used as a spice, which was believed to be an aphrodisiac when added to food or wine. Ambergris itself is pleasantly aromatic, especially when warmed, and it was also highly valued as a fixing agent in the making of perfume, since it enabled a scent to retain its fragrance for much longer than might otherwise have been possible. Most ambergris was found in the form of lumps floating on the surface of the sea, or washed up on the shores of tropical and temperate oceans. At one time, ambergris was worth its weight in gold, but there was much confusion about its origins.

Ambergris was known to the Arabs as ‘ambar’ and was originally called amber in the West in the Middle Ages. This eventually led to further confusion in the popular mind between ambergris and true amber, the mineral known to mineralogists as succinite, which is actually fossilised tree resin, and generally yellow in colour. Both substances were rare and costly, and both were associated with the sea, largely because for Europeans the most common source of amber was the shores of the Baltic. In Chapter 92 of Moby Dick, the American writer Herman Melville pours scorn on those who believed the two substances to be the same: ‘Though the word ambergris is but the French compound for grey amber, yet the two substances are quite distinct. For amber, though at times found on the sea-coast, is also dug up in some far-inland soils, whereas ambergris is never found except upon the sea. Besides, amber is a hard, transparent, brittle, odourless substance, used for mouth-pieces to pipes, for beads and ornaments; but ambergris is soft, waxy, and so highly fragrant that it is largely used in perfumery.’

Moby Dick was published in 1851, by which time the mystery of the origins of ambergris had been resolved by the scientific community. In 1783, the botanist Joseph Banks, who had accompanied Captain James Cook on his voyages of discovery in the Pacific, presented a paper to the Royal Society of London by the German physician Dr Franz Xavier Schwediawer in which it was conclusively proved that ambergris came from sperm whales. In this, he was confirming an observation made in the 13th century by the great Venetian traveller Marco Polo who, while on the island of Socotra in the Indian Ocean, had witnessed a sperm whale vomiting up ambergris. But whereas Marco Polo imagined that the whale had swallowed the lump in the depths of the sea, Schwediawer showed that the origin of the material was inside the whale itself.

The sperm whale is the largest of the odontocetes, or toothed whales. Males can grow up to 20 metres in length. Melville described the sperm whale as ‘the king of whales’, and his novel Moby Dick is based on the pursuit of one such creature. Sperm whales are renowned for their ability to dive to great depths, possibly as far as 3,000 metres below the surface, and for remaining underwater for periods of two hours or more in pursuit of their favourite prey, the giant squid.

It is from the problems the whales have in digesting the beaks of such creatures that ambergris has its origins. The beak is sharp and irritates the whale’s lower intestine, which responds by producing a black, foul-smelling liquid. It is not clear to scientists whether this secretion should be considered a normal response by the whale’s digestive system or a pathological one, but from time to time large quantities of the liquid are vomited up by the whale. Once outside the whale’s body and exposed to air, the substance hardens, acquiring the waxy, greyish and pleasantly aromatic characteristics of ambergris. Often the beaks of squid are still found embedded in lumps of ambergris, some of which can weigh several hundred kilograms. Melville took some delight in contrasting the origins of ambergris with the high value placed upon it by refined society: ‘Who would think, then, that such fine ladies and gentlemen should regale themselves with an essence found in the inglorious bowels of a sick whale!’

Sperm whales were ruthlessly pursued by commercial whalers in the 19th and 20th centuries. In 1963-64 alone, almost 30,000 individuals were killed, and only the imposition of a ban on the hunting of sperm whales in 1984 saved the species from extinction. Ambergris was by far the most valuable product to be extracted during the processing of the whales’ carcasses, and over 90 per cent of the annual worldwide total was acquired in this way, as a by-product of commercial whaling. However, even before the ban on hunting sperm whales was imposed, the 1972 Marine Mammal Protection Act had prohibited trade in ambergris. Just as petroleum and plastic products were replacing other natural products of whaling, so ambergris was supplanted in the making of perfume by other materials, some natural and some synthetic in origin. Nevertheless, it is possible that, as sperm-whale populations recover to their former numbers in the wild, so the sight of lumps of ambergris washed ashore along the tide-line will once again become a familiar one to beach-combers the world over.

Dreams have captivated thinkers since ancient times, but their mystery is now closer than ever to resolution, thanks to new technology that allows scientists to watch the sleeping brain at work.

Thousands of years ago, dreams were seen as messages from the gods, and in many cultures, they are still considered prophetic, foretelling things to come. In ancient Greece, sick people slept at the temples of Asclepius, the god of medicine, in order to receive healing dreams. Modern dream science really begins at the end of the 19th century with Sigmund Freud, who theorized that dreams were the expression of unconscious desires often from childhood. He believed that exploring these hidden emotions through analysis could help cure mental illness. After Freud, the most important event in dream science was the discovery in the early 1950s of a phase of sleep characterized by intense brain activity and rapid eye movement (REM).

Adult humans spend about a quarter of their sleep time in REM, much of it dreaming. People awakened in the midst of REM sleep reported vivid dreams, which led researchers to conclude that most dreaming took place during REM. Using a machine called the electroencephalograph (EEG), researchers were able to see that brain activity during REM resembled that of the brain when the body is awake. The mystery of REM sleep is that even though it may not be essential, it is universal – at least in mammals and even birds. Some researchers think REM may have evolved for physiological reasons. “One thing that’s unique about mammals and birds is that they regulate body temperature,” says neuroscientist Jerry Siegel, director of UCLA’s Center for Sleep Research. “There’s no good evidence that any cold-blooded animal has REM sleep.” REM sleep heats up the brain and non-REM cools it off, Siegel says, and that could mean that the changing sleep cycles allow the brain to repair itself. “It seems likely that REM sleep is filling a basic physiological function and that dreams are a kind of a side effect, or by-product of this.”

There is great disagreement about the psychological function of dreams and researchers have come up with some differing theories. On one side are scientists like Harvard’s Allan Hobson, who believes that dreams are essentially random. In the 1970s, Hobson and his colleague Robert McCarley proposed what they called the “activation-synthesis hypothesis,” which describes how dreams are formed by nerve signals sent out during REM sleep from a small area at the base of the brain called the pons. These signals, the researchers said, activate the images that we call dreams. That raised questions about dream research. If dreams are insignificant night-time images created by the brain, what is the point of studying them?

But more recently, new theories have made some scientists take dreams more seriously. In 1997, Mark Solms of the University of Cape Town in South Africa found that there was more than one mechanism in the brain for activating dreams. Since then, Solms has argued that medical diagnostic equipment like functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) that helps researchers watch dreaming brains might actually lend new support to Freud’s ideas because the parts of the brain that are most active during dreaming control emotion. Further research has supported Solms’s findings. Scientists using PET and fMRI technology to watch the dreaming brain have found that one of the most active areas during REM is the limbic system, which controls our emotions.

Much less active during REM sleep is the prefrontal cortex, which is associated with logical thinking. That could explain why dreams in REM sleep often lack a coherent story line. Some researchers have also found that people dream in non-REM sleep as well, although those dreams generally are less vivid. Another active part of the brain in REM sleep is the anterior cingulate cortex, which detects differences or inconsistencies. Eric Nofzinger, director of the Sleep Neuroimaging Program at the University of Pittsburgh Medical Center, thinks that could be why people often solve tricky problems in their dreams.

Deirdre Barrett, assistant professor at Harvard Medical School, would agree. In her book “The Committee of Sleep,” she describes how painters like Jasper Johns and Salvador Dali found inspiration in their dreams. In her own research on problem solving through dreams, Barrett has found that even ordinary people can solve simple problems in their lives (like how to fit old furniture into a new apartment) if they focus on the dilemma before they fall asleep. There is also evidence that dreaming helps certain kinds of learning. Some researchers have found that dreaming about physical tasks, like a gymnast’s floor routine, enhances performance.

Whatever the function of dreams at night, they clearly can play a role in therapy during the day. The University of Maryland’s Clara Hill, who has studied the use of dreams in therapy, says that dreams are a “back door” into a patient’s thinking. “Dreams reveal stuff about you that you didn’t know was there,” she says. The therapists she trains to work with patients’ dreams use dream imagery to uncover hidden emotions and feelings. Rosalind Cartwright from the university medical center in Chicago has been studying depression in divorced men and women, and she is finding that “good dreamers,” people who have vivid dreams with strong story lines, are less likely to remain depressed. She thinks that dreaming helps diffuse powerful emotions. “Dreaming is a mental-health activity,” she says.

The starkly modern Beinecke Library at Yale University is home to some of the most valuable books in the world: first folios of Shakespeare, Gutenberg Bibles and manuscripts from the early Middle Ages. Yet the library’s most controversial possession is an unprepossessing vellum manuscript about the size of a hardback book, containing 240-odd pages of drawings and text of unknown age and authorship. Catalogued as MS 408, the manuscript would attract little attention were it not for the fact that the drawings hint at esoteric knowledge, while the text seems to be some sort of code — one that no-one has been able to break. It is known to scholars as the Voynich manuscript, after the American book-dealer Wilfrid Voynich, who bought the manuscript from a Jesuit college in Italy in 1912. Over the years, the manuscript has attracted the attention of everyone from amateur dabblers to top code-breakers, all determined to succeed where countless others have failed. Academic research papers, books and websites are devoted to making sense of the contents of the manuscript, which are freely available to all. “Most other mysteries involve second-hand reports,” says Dr Gordon Rugg of Keele University, a leading Voynich expert. “But this is one that you can see for yourself.” It is certainly strange: page after page of drawings of weird plants, astrological symbolism and human figures, accompanied by a script that looks like some form of shorthand. What does it say — and what are the drawings about? Voynich himself believed that the manuscript was the work of the 13th-century English monk Roger Bacon, famed for his knowledge of alchemy, philosophy and science. In 1921 Voynich’s view that Bacon was the writer appeared to win support from the work of William Newbold, Professor of Philosophy at the University of Pennsylvania, who claimed to have found the key to the cipher system used by Bacon. According to Newbold, the manuscript proved that Bacon had access to a microscope centuries before they were supposedly first invented. The claim that this medieval monk had observed living cells created a sensation. It soon became clear, however, that Newbold had fallen victim to wishful thinking. Other scholars showed that his “decoding” methods produced a host of possible interpretations. The Voynich manuscript has continued to defy the efforts of world-class experts. In 1944, a team was assembled to tackle the mystery, led by William Friedman, the renowned American code-breaker. They began with the most basic code-breaking task: analysing the relative frequencies of the characters making up the text, looking for signs of an underlying structure. Yet Friedman’s team soon found themselves in deep water. The precise size of the “alphabet” of the Voynich manuscript was unclear: it is possible to make out more than 70 distinct symbols among the 170,000-character text. Furthermore, Friedman discovered that some words and phrases appeared more often than expected in a standard language, casting doubt on claims that the manuscript concealed a real language, as encryption typically reduces word frequencies. Friedman concluded that the most plausible resolution of this paradox was that “Voynichese” is some sort of specially created artificial language, whose words are devised from concepts rather than linguistics. So could the Voynich manuscript be the earliest-known example of an artificial language? “Friedman’s hypothesis commands respect because of the lifetime of cryptanalytic expertise he brought to bear,” says Rob Churchill, co-author of The Voynich Manuscript. That still leaves a host of questions unanswered, however, such as the identity of the author and the meaning of the bizarre drawings. “It does little to advance our understanding of the manuscript as a whole,” says Churchill. Even though Friedman was working more than 60 years ago, he suspected that major insights would come from using the device that had already transformed code-breaking: the computer. In this he was right — it is now the key tool for uncovering clues about the manuscript’s language. The insights so far have been perplexing. For example, in 2001 another leading Voynich scholar, Dr Gabriel Landini of Birmingham University in the UK, published the results of his study of the manuscript using a pattern-detecting method called spectral analysis. This revealed evidence that the manuscript contains genuine words, rather than random nonsense, consistent with the existence of some underlying natural language. Yet the following year, Voynich expert René Zandbergen of the European Space Agency in Darmstadt, Germany, showed that the entropy of the text (a measure of the rate of transfer of information) was consistent with Friedman’s suspicions that an artificial language had been used. Many are convinced that the Voynich manuscript is not a hoax. For how could a medieval hoaxer create so many tell-tale signs of a message from random nonsense? Yet even this has been challenged in new research by Rugg. Using a system first published by the Italian mathematician Girolamo Cardano in 1150, in which a specially constructed grille is used to pick out symbols from a table, Rugg found he could rapidly generate text with many of the basic traits of the Voynich manuscript. Publishing his results in 2004, Rugg stresses that he had not set out to prove the manuscript a hoax. “I simply demonstrated that it is feasible to hoax something this complex in a few months,” he says. Inevitably, others beg to differ. Some scholars, such as Zandbergen, still suspect the text has genuine meaning, though believe it may never be decipherable. Others, such as Churchill, have suggested that the sheer weirdness of the illustrations and text hints at an author who had lost touch with reality. What is clear is that the book-sized manuscript, kept under lock and key at Yale University, has lost none of its fascination. “Many derive great intellectual pleasure from solving puzzles,” says Rugg. “The Voynich manuscript is as challenging a puzzle as anyone could ask for.”