IELTS Academic Reading Practice Test 23

Until the middle of the nineteenth century, no message could travel faster than the person or vehicle carrying it. A letter moved at the speed of a horse, a ship or, from the 1830s, a train. The first serious attempt to break this link came in France in the 1790s, when the inventor Claude Chappe built a chain of towers topped by movable wooden arms, whose positions could be read through telescopes by operators in the next tower. Chappe's optical telegraph could relay a short message across hundreds of kilometres in a matter of hours, but it was expensive to staff, and it was useless at night or in fog.

Scientists had speculated since the eighteenth century that electricity might carry signals, but practical systems depended on two later discoveries. The first was the battery, invented by Alessandro Volta in 1800, which provided a steady electric current. The second was electromagnetism. In 1820 the Danish physicist Hans Christian Ørsted showed that a current flowing through a wire could deflect a nearby compass needle, and within a few years other researchers had built electromagnets, coils of wire wrapped around iron that became magnetic only while a current flowed. These effects meant that a current switched on and off at one end of a wire could produce a visible movement at the other.

In Britain, William Cooke and Charles Wheatstone patented a telegraph in 1837 that used electric currents to swing magnetic needles, which pointed to letters arranged on a board. Railway companies were their first customers, since trains needed a way of signalling ahead, and in 1838 a line was installed along the Great Western Railway from Paddington station in London to West Drayton, 21 kilometres away. The public soon grasped what the invention could do. In 1845 a man suspected of murder boarded a train to London at Slough, to which the line had been extended; a description was telegraphed ahead to Paddington, and police were waiting to follow and arrest him when he arrived.

In the United States, the most famous name in telegraphy belonged to a man trained not as a scientist but as a painter. Samuel Morse, a successful portrait artist, became interested in electrical communication in the early 1830s and, with the help of his assistant Alfred Vail, developed both an apparatus and a code of short and long signals to represent letters and numbers. Persuading investors was difficult, but in 1843 Congress granted him $30,000 to build an experimental line between Washington and Baltimore. On 24 May 1844 Morse sent a short biblical phrase from the Capitol building in Washington, and Vail received it in Baltimore, some 60 kilometres away.

Morse's system was remarkable for its simplicity. The sender pressed a spring-loaded switch called a key, which closed an electrical circuit and allowed current from a battery to flow along a single wire. Outside towns, the wire was strung along lines of wooden poles and attached to them by glass insulators, which prevented the current from leaking away into the poles in wet weather. At the receiving station, the current passed through the coil of an electromagnet, which pulled down an iron lever known as an armature.

A steel point on this lever pressed into a strip of paper tape moved along by clockwork, leaving short or long marks according to how long the key was held down. Only one wire was needed because the circuit was completed through the earth itself, a technique demonstrated in 1838 by the German physicist Carl August von Steinheil, which halved the amount of wire required.

Operators soon discovered that they could understand messages simply by listening to the clicking of the receiving apparatus, and in time many offices replaced recording machines with simple devices called sounders. A greater difficulty was distance, since current weakened as it travelled along a long wire. The solution was the relay, in which the faint incoming current operated a switch that connected a fresh local battery, passing a strong signal on to the next section of line. Using relays, networks expanded rapidly. In October 1861 a telegraph line reached across the United States to California, and the Pony Express, a mail service using relays of horse riders, closed within days.

The commercial value of speed was demonstrated by Paul Julius Reuter. In 1850 a gap existed between the telegraph networks of Germany and Belgium, from Aachen to Brussels. Reuter bridged it with carrier pigeons, which carried stock market prices across the gap faster than the railway could. When the telegraph lines were joined, his pigeons became unnecessary, and he moved to London, where in 1851 he opened an office transmitting financial information between the London and Paris stock exchanges. The business he founded grew into one of the world's leading news agencies.

Crossing the sea required a new material. Cables laid underwater needed insulation that would not decay, and engineers found it in gutta-percha, a natural latex from trees of South-East Asia that hardened into a waterproof covering. A cable beneath the English Channel began working in 1851, and in 1858 a cable was completed across the Atlantic between Ireland and Newfoundland. Its performance was poor: a 98-word greeting from Queen Victoria to the American president took around sixteen hours to transmit, and the cable failed after about three weeks, partly because excessive voltage had been applied to it. A durable connection was not achieved until 1866, when the giant steamship Great Eastern laid a new cable. By the end of the century, telegraph cables linked every inhabited continent.

Some 66 million years ago, an asteroid roughly ten kilometres wide struck the Earth near what is now the Yucatán Peninsula in Mexico. The impact, which left a crater known as Chicxulub, triggered a global catastrophe that wiped out the non-avian dinosaurs and around three-quarters of all species. Objects of that size are extremely rare, but smaller ones arrive far more often and can still do great harm. In 1908 an explosion over the Tunguska region of Siberia flattened trees across more than 2,000 square kilometres. In 2013 an object less than 20 metres across burst in the sky near the Russian city of Chelyabinsk; its shock wave shattered windows, and more than a thousand people were injured, mostly by broken glass.

The first task of planetary defence is simply to find the threats. Since the 1990s, telescopic surveys funded mainly by NASA have catalogued the great majority of near-Earth asteroids larger than one kilometre, none of which poses any danger over the next century. Smaller objects are harder to find. In 2005 the US Congress directed NASA to locate 90 per cent of near-Earth objects at least 140 metres across, but less than half of these are thought to have been discovered so far. Many asteroids are very dark, reflecting little sunlight, which makes them difficult to see in visible light. NASA's planned NEO Surveyor telescope will therefore search in infrared, detecting the heat that asteroids give off after being warmed by the Sun.

Once an asteroid is found, astronomers calculate its orbit, but early estimates are uncertain because they rest on only a few nights of observations. As a result, the calculated chance of a collision often rises before falling to zero. Shortly after its discovery in 2004, the asteroid Apophis was briefly given a small but alarming probability of striking the Earth in 2029; further measurements ruled this out, and in April 2029 it will instead pass closer to the planet than some communications satellites. A similar sequence followed the discovery of 2024 YR4 in December 2024. Its estimated chance of hitting the Earth in 2032 climbed to about 3 per cent in February 2025, before further observations reduced the risk to almost nothing.

If a dangerous object were found, it would not need to be destroyed. It would be enough to change its speed very slightly, so that it arrived at the point where its orbit crosses the Earth's a few minutes early or late, by which time the planet would have moved on. A change of a few centimetres per second, applied many years before the expected impact, can shift an asteroid's position by thousands of kilometres by the time it arrives. The longer the warning, the smaller the push required, which is why experts regard early detection as the most important part of any defence.

The simplest way to deliver such a push is to crash a spacecraft into the asteroid. To test this method, NASA launched the Double Asteroid Redirection Test, or DART, in November 2021. Its target was Dimorphos, a body about 150 metres across that orbits a larger asteroid, Didymos; neither of them poses any threat to the Earth. Choosing a moonlet made the result easier to measure: rather than tracking a tiny change in an orbit around the Sun, astronomers could simply time how long Dimorphos took to circle its companion. Like many small asteroids, Dimorphos turned out to be a rubble pile, a loose collection of boulders and gravel held together by weak gravity.

On 26 September 2022, travelling at more than 20,000 kilometres per hour, DART struck Dimorphos head-on. NASA had said that it would regard the mission as successful if the moonlet's orbital period of almost twelve hours were reduced by at least 73 seconds. In fact, observations from telescopes on the Earth showed that it had been shortened by about 33 minutes. Much of this effect came not from the spacecraft itself but from the enormous plume of debris blasted off the surface, which pushed the asteroid like the exhaust of a rocket. A small Italian satellite released by DART photographed the impact, and the European Space Agency's Hera mission, launched in 2024, is due to survey the results in detail.

Other methods have been proposed for situations that a simple collision could not handle. A gravity tractor would be a heavy spacecraft that flies alongside an asteroid for years, using the slight gravitational attraction between them to tug the asteroid gradually onto a new course without touching it. The method is precise but very slow, and would require decades of warning. At the other extreme, a nuclear device exploded close to an asteroid's surface could vaporise a thin layer of rock, and the expanding vapour would push the object aside. This might be the only practical option for a large asteroid discovered late, but it raises legal and political difficulties, since international treaties restrict nuclear explosions in space.

Because an impact could affect any country, planetary defence is increasingly organised internationally. The International Asteroid Warning Network, endorsed by the United Nations, issues a notice when an object larger than ten metres has more than a one per cent chance of hitting the Earth, as happened with 2024 YR4. A related group of space agencies would plan any deflection mission. Experts emphasise, however, that the structure of each asteroid matters: a loose rubble pile and a solid lump of metal would respond very differently to the same push, so missions to study asteroids at close range remain essential.

Ask a group of teachers whether pupils learn best when lessons match their individual learning style, and most will say yes. A widely cited survey published in 2012 found that more than nine in ten teachers in Britain and the Netherlands agreed with this idea, and similar results have been reported in many other countries. The belief is intuitively appealing. People obviously differ, and it seems only fair that teaching should take those differences into account. Yet after several decades of research, there is remarkably little evidence that identifying a pupil's learning style and teaching accordingly improves learning. In my view, the persistence of the idea says more about its attractiveness than about its truth.

The concept takes many forms. A review published in 2004 for the Learning and Skills Research Centre in England, led by the education researcher Frank Coffield, identified 71 different models of learning styles. Some classify people according to whether they prefer to reflect or to act, others according to whether they think in wholes or in sequences. The best-known version in schools, however, concerns the senses. The VARK questionnaire, developed in New Zealand by Neil Fleming in the late 1980s, sorts learners into visual, aural, read/write and kinaesthetic types, and many teachers have been trained to adapt their lessons for visual or kinaesthetic learners accordingly.

It is important to be clear about what the theory actually claims. Few researchers doubt that people have preferences: many of us would rather look at a diagram than read a paragraph. The strong claim is something different, namely that a visual learner will learn more from visual teaching, while an aural learner will learn more from spoken explanation.

In 2008 the psychologists Harold Pashler, Mark McDaniel, Doug Rohrer and Robert Bjork called this the meshing hypothesis and set out what would be needed to test it. Learners would have to be classified by style and then randomly assigned to different kinds of teaching. The theory would be supported only if each group did best with the method matched to its style.

When Pashler and his colleagues searched the literature, they found that very few studies had used a design capable of testing the hypothesis properly, and that several of those that had done so produced results contradicting it. Later research has reached the same conclusion. In one study of university anatomy students, for example, those whose study habits matched their measured learning style did not achieve better grades than those whose habits did not. What did predict success were particular study strategies, which helped students regardless of their supposed style. Learning styles, in short, appear to describe what people like rather than what helps them learn.

There are good reasons why the matching idea might fail. For most subjects, the best way to present information depends on the content rather than the learner. Geography is best taught with maps, pronunciation with sound and dance with movement, whatever a student's preferences. Moreover, research on what psychologists call dual coding suggests that combining words with relevant pictures tends to help almost everyone, not only those who describe themselves as visual. A lesson about a historical battle, for instance, may be clearer with a map, a timeline and a spoken account together than with any one of them alone. Restricting a supposedly aural learner to spoken explanations could therefore deprive that student of a valuable form of support.

Defenders of learning styles sometimes argue that, even if the evidence is weak, the approach does no harm. I disagree. Teachers have limited time, and every hour spent preparing several versions of a lesson for different learning styles is an hour not spent on methods with strong research support, such as spacing practice over time or regularly testing pupils on what they have learned. There is also a risk that pupils come to see themselves in narrow terms. A child told that she is a kinaesthetic learner may conclude that reading is simply not for her, and avoid the very activities she most needs to practise.

Why, then, has the idea survived? Part of the answer is commercial: questionnaires, training courses and teaching materials based on learning styles have been sold widely. Part is psychological, since people readily recognise themselves in flattering descriptions of their personalities. And part is that the theory contains a grain of truth. Learners really do differ, but the differences that matter most are in prior knowledge, motivation and skill, which teachers can observe directly, not in fixed sensory types. In 2017 a group of neuroscientists and educators wrote publicly to warn that learning styles were a neuromyth with no sound scientific basis.

None of this means that teachers should stop paying attention to individual pupils. Varying the way material is presented keeps lessons engaging, and using several forms of representation helps everyone. What the evidence does not support is the practice of diagnosing a fixed style and tailoring teaching to it. Teachers who wish to respond to individual differences would do better to find out what each pupil already knows and build on it. Teacher training courses that still present learning styles as established science should, in my view, replace them with the findings of cognitive psychology, which offer teachers far more reliable guidance.