IELTS Academic Reading Practice Test 30

For most of history, people told the time by the sun. Sundials, which indicate the hour by the shadow cast by a pointer, were used in ancient Egypt, Greece and Rome, but they were useless at night and on cloudy days. Water clocks, in which time was measured by the steady flow of water into or out of a vessel, overcame this limitation and were sometimes elaborate devices, yet they could freeze in winter and needed constant attention. Candles and sandglasses offered other ways of measuring intervals, but none of these methods could keep track of time continuously and automatically over days and weeks.

One remarkable forerunner of the mechanical clock was built in China at the end of the eleventh century. The astronomical clock tower designed by the scholar and official Su Song at Kaifeng, then the imperial capital, was a multi-storey structure driven by a large water wheel. Its rotation was controlled by a mechanism that allowed the wheel to advance only one step at a time as each of its buckets filled, an arrangement based on earlier Chinese designs that historians regard as an early form of escapement. The tower displayed the movements of the heavens and announced the hours with bells, drums and mechanical figures. However, it was dismantled after invading forces captured the city in 1127, and later attempts to rebuild it failed.

The first true mechanical clocks appeared in Europe in the late thirteenth century, although their inventor is unknown. They were driven not by water but by a heavy weight attached to a rope, which was wound around a horizontal drum. As the weight descended, it turned the drum, and the drum turned a series of gears. Left to itself, a falling weight would simply accelerate and unwind the rope within seconds. The crucial invention was a device called the escapement, which interrupted the motion at regular intervals, allowing the gears to move forward only in small, equal steps. Because the weight gradually reached the bottom of the tower, someone had to haul it back up at regular intervals, often every day.

The earliest European escapement, known as the verge and foliot, worked as follows. The last wheel in the gear train, called the crown wheel because its saw-shaped teeth stood up like the points of a crown, was mounted beside a vertical rod, the verge. Two small metal plates, the pallets, projected from the verge at different angles, so that they engaged the teeth on opposite sides of the crown wheel in turn.

At the top of the verge was fixed a horizontal bar, the foliot, which swung back and forth as the pallets were pushed alternately by the teeth. Small regulating weights hung on the foliot could be moved inwards or outwards: moving them towards the centre made the foliot swing faster, so that the clock ran faster, while moving them outwards slowed it down.

Early clocks of this kind were large iron machines installed in the towers of cathedrals, monasteries and town halls. Many had no dial at all; instead, they struck a bell to mark the hours, and the English word 'clock' is related to the medieval Latin word for a bell. One of the oldest surviving examples, at Salisbury Cathedral in England, probably dates from the 1380s. Such clocks were far from accurate by modern standards and might gain or lose a quarter of an hour or more in a single day, so they had to be corrected regularly against a sundial.

Even so, public clocks changed the way people organised their lives. Previously, daylight and darkness had each been divided into twelve hours whose length varied with the seasons, so that a summer daylight hour was much longer than a winter one. A mechanical clock, by contrast, naturally measured hours of equal length, and over the fourteenth and fifteenth centuries these equal hours gradually replaced the older system in European towns. Merchants, employers and town councils began to regulate trade and working hours by the sound of the clock bell, and some historians have argued that the clock was as important as the steam engine in shaping industrial society.

In the fifteenth century, clockmakers began to use a coiled spring instead of a weight to store energy, which made it possible to build clocks small enough to be carried. A spring, however, pushes strongly when fully wound and weakly as it unwinds, so makers devised a cone-shaped pulley called the fusee, around which a chain or cord was wound, to even out the force. Spring-driven clocks and, later, pocket watches became prized possessions of the wealthy, although their timekeeping remained poor. The fusee itself proved remarkably durable, remaining in use in fine watches and marine timekeepers for several centuries.

The great advance in accuracy came in 1656, when the Dutch scientist Christiaan Huygens built the first pendulum clock. Galileo had earlier observed that a pendulum of a given length takes almost the same time to complete each swing, whatever the size of the swing, and Huygens used this property to regulate a clock. His early pendulum clocks erred by less than a minute a day, an extraordinary improvement, and minute hands soon became common on clock faces. Later in the century, a new escapement allowed clocks to use long pendulums swinging through small arcs, leading to the tall longcase clock that became a fixture of prosperous homes. In 1675 Huygens also introduced a spiral balance spring, which did for watches what the pendulum had done for clocks.

Anyone who has watched a shark hunting might assume that it relies mainly on smell or sight. Sharks do possess an acute sense of smell and good vision in dim light, as well as a lateral line system that detects movements in the surrounding water. Yet in the final moments of an attack, when the prey is only centimetres away, many species depend on a sense that humans do not share at all: the ability to detect the weak electric fields produced by other living things. All animals generate such fields, because their nerves and muscles work by moving charged particles, and in seawater, which conducts electricity well, these fields extend a short distance beyond the body. Sharks belong to a group of cartilaginous fishes, the elasmobranchs, which also includes skates and rays, and the electrical sense is found throughout the group.

The organs responsible were described long before anyone understood their purpose. In 1678 the Italian physician Stefano Lorenzini noted that the heads of sharks and rays were dotted with small pores, each leading to a canal filled with a clear jelly. For almost three centuries these structures, now called the ampullae of Lorenzini, puzzled zoologists, who variously suggested that they produced mucus or detected pressure or temperature. Only in the twentieth century did experiments reveal that they were extraordinarily sensitive to electric fields.

Each ampulla consists of a pore in the skin, a canal running beneath it and a small chamber at its base lined with sensory cells. Because the jelly conducts electricity, the voltage at the pore is carried down to the sensory cells, which compare it with the voltage inside the animal's body. In 2016 a team of American researchers reported that this jelly has the highest proton conductivity yet measured in any biological material, although exactly how this property contributes to the sense remains unclear. The ampullae are concentrated around the snout and mouth, where they are best placed to guide the final strike.

The decisive evidence came from experiments published in 1971 by the Dutch biophysicist Adrianus Kalmijn. He placed a flatfish in an enclosure made of agar, a jelly-like material that allows electric fields to pass through but blocks the chemical scent of the fish, and buried it in the sand of a tank containing small sharks. The sharks located and attacked the hidden fish accurately. When the agar was covered with a thin plastic film, which blocks electric fields, they failed to find it. Most strikingly, when Kalmijn buried a pair of electrodes producing a field similar to that of the fish, the sharks dug at the electrodes in preference to pieces of fish placed nearby.

Later measurements suggested that some sharks and rays can respond to fields as weak as a few billionths of a volt per centimetre, making their electrical sense one of the most sensitive known in the animal kingdom. Such sensitivity allows a shark to detect a fish buried in sand or hidden in darkness at close range. Rays, which often feed on animals buried in sediment, use the same ability to locate hidden clams, worms and crabs. The odd shape of the hammerhead's head may be partly explained by this sense. Its wide, flattened head spreads the ampullae over a greater area, and a 2002 study comparing young hammerheads with sandbar sharks found that, although the two species were similarly sensitive, the hammerhead could sweep a broader strip of the sea floor as it searched.

Electroreception may also help sharks to avoid becoming prey. In a 2013 study, researchers in Australia exposed embryos of the brownbanded bamboo shark, still developing inside their egg cases, to weak electric fields resembling those of a predator. The embryos responded by stopping the gill movements they normally use to circulate water through the case and by wrapping their tails around their bodies, behaviour that probably reduces the signals they give off. The response weakened when the stimulus was repeated, suggesting that the embryos learned to ignore a signal that posed no real threat.

Many shark species migrate over great distances and return to the same feeding or breeding grounds year after year, and there is growing evidence that the Earth's magnetic field helps to guide them. One proposed mechanism involves the ampullae themselves: a shark swimming through the magnetic field generates tiny electric currents in its own body, which its electrical sense might detect. In 2021 researchers in Florida exposed juvenile bonnethead sharks to magnetic conditions matching locations hundreds of kilometres from where they had been caught, and the sharks oriented themselves as if trying to return home. How sharks actually perceive magnetism, however, has not been established, and it is possible that they rely on a different, as yet undiscovered, sensory organ.

Understanding this sense has practical uses. Several companies sell devices that produce strong electric fields intended to overwhelm the ampullae and drive sharks away from swimmers and surfers, and independent tests have found that some models reduce, though do not eliminate, the likelihood of an approach. Conservationists, meanwhile, are investigating whether the electromagnetic fields produced by undersea power cables, including those linking offshore wind farms to the shore, could confuse sharks and rays. Ironically, the sense that makes sharks such effective hunters may leave them vulnerable in an ocean increasingly filled with human electrical noise.

Standardised tests, in which every candidate answers the same questions under the same conditions and is scored in the same way, are among the most criticised institutions in modern education. Teachers complain that they narrow the curriculum, parents that they cause anxiety, and researchers that they capture only a fraction of what matters. Much of this criticism is justified. Yet I want to argue that the problem lies less in the tests themselves than in the uses to which they are put, and that abandoning them altogether would make education less fair, not more.

The idea that ability should be judged by a common examination is far older than modern schooling. Imperial China selected officials through written civil service examinations for some thirteen centuries, until the system was abolished in 1905, and in principle a candidate from a modest family could rise to high office through success in them. In the United States, the educational reformer Horace Mann championed written examinations for Boston's schools in the 1840s, partly because he believed they would provide more objective evidence of what pupils had learned than oral questioning by individual examiners. Formal intelligence testing followed in the early twentieth century, and the SAT, which became the best-known American admissions test, was first administered in 1926. The appeal, then as now, was impartiality: everyone faced the same test.

This argument deserves more weight than critics usually give it. The alternatives to standardised testing, such as teacher assessments, interviews, personal statements and portfolios of work, all depend to some degree on human judgement, and human judgement is vulnerable to bias. Teachers' assessments can be influenced, often unconsciously, by a pupil's behaviour, appearance or background. Personal statements and portfolios tend to reward students whose families can afford coaching and enriching experiences. Interviews, similarly, may favour candidates who share the interviewer's background or manner. A well-constructed test, whatever its limitations, is at least blind to who is taking it.

Recent events in American higher education illustrate the point. During the COVID-19 pandemic, many selective universities stopped requiring applicants to submit scores from admissions tests such as the SAT. Several have since reversed that decision. The Massachusetts Institute of Technology reinstated its requirement in 2022, and Dartmouth College followed in 2024 after its own researchers concluded that scores helped to identify talented applicants from low-income and under-resourced schools, some of whom had withheld scores that would in fact have strengthened their applications. Whether other institutions will draw the same conclusion remains to be seen, but these cases show that tests can work in favour of disadvantaged students as well as against them.

The real difficulty arises when test results are used not merely to inform decisions about individual students but to reward or punish schools and teachers. The social scientist Donald Campbell observed in the 1970s that the more heavily a numerical indicator is relied upon in making social decisions, the more it becomes subject to pressures that distort both the indicator and the processes it is supposed to monitor. The British economist Charles Goodhart made a similar point about targets in economic policy, and the idea is now widely known as Goodhart's law. Educational testing provides a vivid illustration. In the United States, the No Child Left Behind Act of 2002 required annual testing in reading and mathematics and imposed sanctions on schools that failed to show sufficient progress. Many schools responded by devoting more time to tested subjects at the expense of others, such as science, history and the arts, and by drilling pupils in the formats of particular tests.

In extreme cases, pressure produced outright fraud. In Atlanta, a state investigation found that teachers and administrators at dozens of schools had altered pupils' answers on state tests in 2009, and in 2015 eleven educators were convicted of racketeering and other charges. Less dramatically, the education researcher Daniel Koretz has documented what he calls score inflation: rises in results on high-stakes tests that are not matched by similar gains on other, low-stakes assessments of the same subjects. When this happens, the scores no longer mean what they appear to mean, and the improvements celebrated by politicians may be largely illusory.

The lesson, in my view, is not to abolish standardised tests but to lower their stakes for schools and teachers. One model is the National Assessment of Educational Progress, often called the Nation's Report Card, which tests a representative sample of American students rather than every child and attaches no consequences to individual schools. Because nobody gains by gaming it, it has become one of the most trusted sources of information about long-term trends in American education. Sampling of this kind can tell governments how a system is performing without distorting what happens in every classroom.

Tests are tools, and like other tools they can be used well or badly. Used to give teachers diagnostic information, to monitor national standards or to offer students an impartial opportunity to demonstrate their ability, they serve valuable purposes. Used as the sole basis for judging schools and the people who work in them, they become targets, and targets invite manipulation. The challenge for policy-makers is to keep the benefits of common measurement while removing the incentives that corrupt it.