IELTS Academic Reading Practice Test 174

For the settlers who moved onto the grasslands of the American West in the mid-nineteenth century, the absence of trees was a serious practical problem. Houses could be built of turf, but fences could not. Wood had to be hauled long distances at great expense, and hedges of thorny Osage orange took years to become stock-proof. The railways brought some timber, but the cost of transporting it across the plains remained high. Yet without fences, crops could be trampled by cattle, and the open range on which ranchers depended required that animals roam freely. A cheap, durable barrier was needed, and it was found in a product that would reshape the landscape: barbed wire.

The idea of adding sharp points to wire was not new. In 1867 Lucien B. Smith of Kent, Ohio, received a United States patent for a wire with metal barbs, and in the following year Michael Kelly of New York patented a 'thorny fence'. Other inventors proposed similar devices, but none solved the manufacturing problem. Smith's design, for example, fitted spiked spools onto a wire, and the result was awkward to make in quantity. The barbs either slipped along the wire, came loose or were too expensive to produce. What was required was a design that a machine could produce cheaply and that would hold firmly in place.

The decisive contribution came from Joseph Glidden, a farmer in DeKalb County, Illinois. In 1873, at the county fair, he saw a wooden rail studded with points, displayed by another inventor, and began experimenting in his kitchen. Glidden's design used a short piece of wire coiled around a straight strand; the ends of the coil were cut at an angle to leave two sharp points, and the barb was held in position by twisting a second strand around the first. This was simple and, crucially, could be made by machine. The barbs were spaced at regular intervals, and one machine could produce long lengths of wire quickly. Glidden filed for a patent in 1873 and it was granted in November 1874, though legal disputes with rival inventors continued for years.

With a local hardware merchant, Isaac Ellwood, Glidden established a company to manufacture the wire, and Glidden later sold his share to the Washburn and Moen company of Massachusetts, which had the capacity for large-scale production. Glidden became wealthy. Production expanded rapidly, and factories in several states were soon making the product. The price fell sharply as output grew, and by the early 1880s barbed wire was selling for only a fraction of its original cost. It was supplied in coils and stretched between wooden posts, with staples holding it in place; a farmer could enclose a field in a few days.

The consequences were enormous. On the Great Plains, farmers could at last protect crops from wandering cattle, while ranchers could fence their herds and improve breeds. The open range, across which cattle had been driven north to railway towns, was divided into claims. Long drives became impractical and largely ended by the late 1880s, and the cattle industry shifted towards enclosed ranching. For the first time, a family with modest means could mark the boundaries of a farm without hiring labour or buying expensive timber. Land that had seemed empty was parcelled into rectangular fields, a pattern still visible from the air across much of the western United States.

Not everyone welcomed the wire. Ranchers who relied on free grazing resented farmers who fenced land they did not own, and in Texas and neighbouring states a violent campaign of fence cutting broke out in 1883 and 1884. Some cattlemen regarded the wire as a threat to their way of life, while settlers saw it as the foundation of a stable community. Night riders cut miles of wire and sometimes burned pastures. State legislatures responded with severe penalties: Texas made fence cutting a felony in 1884, and the violence subsided, though disputes over boundaries continued.

The social effects extended beyond farming. For the Plains Indians, whose economies and hunting depended on the movement of bison, fencing fragmented the land and made traditional life harder. Bison herds declined for several reasons, including hunting, but the wire contributed by restricting their range. Barbed wire also became a symbol of ownership and exclusion. In Australia and parts of South America it was adopted just as enthusiastically, with similar effects on grazing and settlement, and in some colonial settings wire was used to divide land and restrict movement.

The military potential of the material soon became apparent. During the Second Boer War in South Africa, British forces used barbed wire to protect camps and block movement, and both sides employed it in the Russo-Japanese War. By the First World War, armies were using millions of yards of it, strung in dense belts in front of trenches. The wire was difficult to cut, especially under fire, and it channelled attackers into narrow gaps where machine guns could reach them. The wire was cheap, light and easily transported, which is why it spread so quickly from farms to battlefields. It has been used in conflicts and detention camps ever since.

Today barbed wire remains a familiar sight along roads, railways and farms. Modern versions are galvanised to resist rust and may have barbs at intervals of a few inches. Its history shows how a modest technical change, driven by the needs of a particular place, can alter patterns of land use, property and conflict across the world. It is also a reminder that technologies are rarely neutral.

Lidar — an acronym for light detection and ranging — is a method of measuring distance with pulses of laser light. A transmitter fires a short burst of light, usually invisible to the eye, towards a target; some of it is scattered back and collected by a telescope or detector. Because light travels at a known speed, the time between the outgoing pulse and the returning echo gives the distance. By firing many thousands of pulses a second and sweeping them across a scene, a lidar instrument builds a three-dimensional map made of millions of measured points, known as a point cloud. Unlike a camera, which records the colour of surfaces, a lidar instrument records their position in space. The technique emerged in the early 1960s, soon after the first working laser was demonstrated.

The basic principle is the same as the echo sounding used by ships, but with light instead of sound. A pulse travels to an object and back, so the distance is half the speed of light multiplied by the time of flight. In practice, the electronics must time the round trip to within a fraction of a nanosecond, since light covers about 30 centimetres in one nanosecond. Most topographic lidar uses near-infrared wavelengths, around 1,000 nanometres, because these wavelengths are strongly reflected by vegetation and rock. The instrument also records the intensity of each return, which can help distinguish surfaces.

Lidar can be carried by aircraft, helicopters, drones, satellites or mounted on a tripod. An airborne system combines the laser with a scanner that sweeps the beam from side to side, and with satellite navigation and motion sensors that record exactly where the aircraft was and how it was tilted at each instant. A single flight can survey hundreds of square kilometres, producing a point cloud in which every point has a precise position on the Earth's surface. The result is a dense set of measurements rather than a photograph, and each point carries its own coordinates. Ground-based instruments, by contrast, are used for detailed surveys of buildings, bridges and rock faces. They are also used to check the accuracy of maps made from the air.

One of the most striking uses is in archaeology. Dense forest can hide the outlines of roads, walls and platforms, but a lidar pulse may pass between leaves and branches and reach the ground. The returns from the canopy and from the ground arrive at different times, and software can filter out the vegetation to reveal a 'bare earth' model. Surveys in Cambodia around Angkor, and later in the Maya lowlands of Central America, revealed extensive networks of ditches, causeways and buildings that had been invisible to people on the ground. The results transformed understanding of how large and how densely populated these societies were.

Lidar is equally valuable in forestry and environmental science. A pulse that hits a tree is reflected from leaves and branches as well as from the soil, so the difference in height between the canopy and the ground can be measured directly. From this, researchers estimate the height, density and biomass of forests, and hence how much carbon they store. Satellites now carry lidar instruments for this purpose: one, aboard the International Space Station, has been measuring tropical and temperate forests since 2018, while another, designed to monitor ice sheets and sea ice, uses an extremely sensitive photon-counting detector. Such measurements are difficult to make by any other means.

The technique has limitations. Lidar instruments are expensive, and airborne surveys require careful planning and processing. Clouds, fog and heavy rain scatter or block the beam, so mapping is often done in clear weather. Infrared light is absorbed by water, which means that standard topographic lidar cannot map the seabed; bathymetric systems therefore use green laser light, which penetrates water better. Laser safety rules also restrict the power that can be used, particularly where people may be present. The point clouds produced by a survey can be enormous, and turning them into useful maps requires substantial computing. Survey companies must therefore plan flights carefully and allow time for processing, which adds to the cost.

Research is addressing these problems in several ways. So-called single-photon lidar can detect individual particles of light, allowing lower-power pulses and longer ranges. Solid-state scanners, with no moving parts, are smaller and more robust than mechanical devices, and are being developed for cars, where lidar helps a vehicle build a picture of its surroundings. Engineers are also working on cheaper sensors and on software that can classify points automatically — labelling a return as road, building or tree. If these advances continue, lidar may become as common as the camera.

For all its sophistication, lidar is only one tool among many, and it is most powerful when combined with other data. Satellite images show colour and texture; radar can see through cloud; ground surveys provide detail and verification. Lidar supplies something none of these can easily provide: accurate, three-dimensional measurements of a surface at high resolution. That is why it has moved from a specialist instrument to a standard part of mapping, planning and environmental monitoring. Its data are now used by planners, engineers, farmers and scientists, often without their realising where the measurements came from.

A child born today may play with a teddy bear that listens, a doll that answers questions, or a building set that connects to a tablet and instructs its builder. These are smart toys: products that contain microphones, cameras, motion sensors or wireless connections and that rely on software, often running on remote servers, to respond to a child. Sales have grown rapidly, and manufacturers promise education, companionship and creativity. The question is not whether connected toys can be good for children — they can — but whether the way they are designed and sold currently makes that likely.

Technically, the key change is that the toy is no longer a self-contained object. A microphone captures a child's speech, software converts it into text, and a remote service interprets the request and sends back a reply. Because the heavy computing happens elsewhere, the toy itself can be cheap and small, and its responses can improve as the service is updated. This is genuine artificial intelligence of a limited kind, and it is what separates a smart toy from a toy that merely makes noises.

The benefits are real, particularly for children who find conventional play difficult. A toy that gives clear spoken instructions can make play more accessible for a child with a visual impairment; one that responds patiently to repeated questions can help a child with autism practise conversation; and a device that translates words can encourage a child learning a second language. Well-designed adaptive games can keep a struggling learner engaged without the embarrassment of failing in front of classmates. For parents working away from home, a connected toy can also allow a grandparent to read a story aloud from another city. These are not trivial advantages.

Yet a toy that listens is also a device that records. Many connected toys collect voice recordings, photographs, location data and details of a child's responses, and some send this material to company servers. The information may be used to improve the product, but it may also be used for marketing, shared with partners or stored indefinitely. Children are not in a position to understand what they are giving away, and a five-year-old cannot give meaningful consent. Parents can read privacy policies, but few have the time or expertise to interpret them.

Security is a further problem. In 2015 a breach at the toymaker VTech exposed records relating to millions of parents and children. Two years later, researchers found that voice messages recorded by a popular connected teddy bear could be accessed online. In 2017 Germany's network regulator ruled that a doll called Cayla, which could record and transmit conversations, was a concealed transmitting device and ordered it withdrawn from sale. These cases are not isolated accidents; they reflect a market in which speed to market matters more than security.

Connected toys also change the nature of play. A toy that supplies a stream of prompts and rewards may hold a child's attention, but it can leave little room for the child to invent a game or negotiate rules with friends. Play is valuable precisely because it is unstructured: children try out roles, test boundaries and solve problems without an adult or an algorithm directing them. A playroom dominated by devices that respond to every action may narrow rather than expand what a child imagines.

Regulation has begun to catch up, though unevenly. In the United States, a federal law obliges companies to secure a parent's verifiable agreement before gathering personal details from any child under the age of thirteen. Europe's data protection rules impose stricter conditions on children's data, and the UK has introduced a design code requiring services likely to be used by children to default to high privacy settings. These laws help, but enforcement is difficult when products are made abroad and sold online.

There is also the question of cost and obsolescence. A smart toy is more expensive than a wooden one, and it depends on a smartphone, a reliable internet connection and a company that continues to support it. When a manufacturer stops updating its software or shuts down its servers, the toy may stop working altogether, becoming electronic waste. Families who cannot afford the latest device are excluded, and schools that buy connected equipment may find it unsupported within a few years. The digital divide does not disappear at the nursery door.

What, then, should be done? I do not think a ban is either practical or desirable. The benefits for some children are too great, and the technology is not going away. But the burden of protection should not fall on parents alone. Manufacturers should be required to collect only the data a toy actually needs, to secure it properly, to explain in plain language what is recorded and to stop collecting when a child stops playing.

Parents, for their part, can ask simple questions: does this toy need a microphone, and who can hear what it records? But individual vigilance is a weak substitute for good design. The most important lesson of the past decade is that a toy is now part of a system of servers, apps, policies and supply chains, and that system is not designed with children's interests first. Connected toys can enrich childhood, but only if the industry is obliged to treat the child as a person rather than a source of data. Until then, selective enthusiasm is the wisest approach.