IELTS Academic Reading Practice Test 34

A The notion of relying on a counterweighted box to convey people and goods between storeys is, in fact, considerably older than the modern metropolis. According to surviving evidence, Roman engineers assembled rope-and-pulley platforms that were used to hoist gladiators and wild beasts from beneath the Colosseum up to the arena floor, and some seventeenth-century European palaces contained what was termed a "flying chair," worked by servants tugging on ropes in an adjoining chamber. Such early contrivances, however, remained curiosities reserved largely for ceremonial occasions. They could not be built tall, and a snapped rope almost invariably meant a fatal plunge. So long as that hazard persisted, multi-storey buildings would have to remain limited to whatever stair-climbing the public was willing to tolerate, which in practice tended to mean roughly six or seven storeys at most.

B The decisive shift, it appears, came not from a swifter hoist but from a more reliable braking arrangement. In 1853, at the Crystal Palace exhibition in New York, the Vermont-born mechanic Elisha Otis publicly demonstrated what he termed a "safety hoist." Otis is said to have stood on a raised platform suspended by a rope above an astonished crowd while an assistant severed the rope with a sword. Rather than plunging downward, the platform dropped only a few centimetres before a set of spring-loaded pawls sprang outward and caught in iron teeth fixed to the guide rails. The demonstration was repeated several times daily for the duration of the fair, and although Otis is recorded to have sold only three of his machines that year, the principle of an automatic safety brake transformed the public perception of the elevator from a death trap into a viable form of vertical transport.

C The first passenger elevator deploying Otis's safety system was installed in 1857 at the E. V. Haughwout & Co. store on Broadway in New York, a five-storey emporium specialising in china and glassware. The cab itself was steam-powered, ascending at roughly twelve metres per minute, and operated for three years before the building's proprietor concluded that the extra fares it generated did not justify its coal bill. The machine had nevertheless seemingly settled a point of principle. By 1870, Otis Brothers and Company had installed more than two thousand passenger and freight elevators across the United States, and rival firms such as Hagan Elevator and Crane Elevator had emerged in Pittsburgh and Chicago respectively.

D Steam, however, was a clumsy energy source for a comparatively small lifting machine. Boilers had to be tended, water replenished, and pipes routed through inhabited premises. Hydraulic elevators, in which water under pressure is widely thought to have droved a piston that pushed the cab upward, gradually displaced steam for taller and more elegant installations from roughly the 1870s onward. Hydraulics offered two crucial advantages: smooth, quiet running, and a piston shaft that could in principle be made as long as the building itself was tall. Their disadvantage, however, was that the piston had to be sunk into a borehole at least as deep as the elevator's rise, a constraint that limited their adoption above ten or twelve storeys.

E The breakthrough that allowed buildings to climb truly skyward was electricity. The first electric passenger elevator was probably installed in 1880 by the German firm Siemens at an industrial exhibition in Mannheim, and within a decade electric machines had become standard in new construction. Electric elevators typically rely on a powerful motor mounted at the top of the shaft to drive a sheave, which moves the cab up and down by means of cables and a counterweight. Because the counterweight balances the cab's static load, the motor needs only to lift the difference, which tends to make the system remarkably efficient. Modern gearless traction elevators in supertall buildings are said to travel at over ten metres per second using motors of comparatively modest power.

F With the technical obstacles removed, architectural ambition appears to have expanded accordingly. Chicago and New York competed through the 1890s to erect the world's tallest commercial buildings, and the speed of elevators became, in itself, a marketing point. The Empire State Building, completed in 1931, offered seventy-three Otis elevators that travelled at up to seven metres per second; visitors regarded the ride almost as much a part of the attraction as the view from the observation deck. By the turn of the twenty-first century, the Burj Khalifa in Dubai was operating double-decker cabs travelling more than half a kilometre between floors, and elevator manufacturers were experimenting with cable-free, magnetically levitated systems capable of moving sideways as well as up and down. From a fairground stunt with a sword, the elevator had quietly, and almost imperceptibly, become the technology that made the modern skyline possible.

A The world's oceans absorb roughly a quarter of the carbon dioxide that humans release into the atmosphere each year, a service that has largely substantially slowed the warming of the climate. The benefit, however, comes at a chemical cost. When carbon dioxide dissolves in seawater it reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions; the resulting accumulation of hydrogen ions lowers the pH of the water. Average surface-ocean pH has fallen from around 8.2 in pre-industrial times to about 8.05 today, a decrease of roughly 0.15 units. Because the pH scale is logarithmic, this corresponds to a rise of approximately thirty percent in hydrogen-ion concentration. The phenomenon, baptised "ocean acidification" by a 2005 report from the Royal Society of London, is sometimes described as the other CO2 problem.

B The chemistry has been well understood since the work of the Swedish oceanographer Stig Fonselius in the 1950s, but its biological consequences only began to receive systematic attention in the early 2000s. The principal worry is that lower pH and reduced concentrations of carbonate ions make it harder for marine organisms to build and maintain shells and skeletons composed of calcium carbonate. Corals, molluscs, foraminifera, sea urchins, and some plankton species all depend on this mineral, and laboratory experiments have shown that many of them grow more slowly, or even dissolve, when seawater chemistry is shifted toward the levels expected by the end of this century.

C Some of the strongest evidence comes from natural underwater carbon dioxide vents. Off the coast of Ischia in the Mediterranean, volcanic seeps continuously discharge CO2 into shallow water, producing a long-term, naturally acidified environment along an otherwise typical Mediterranean shoreline. Marine ecologist Jason Hall-Spencer and colleagues surveyed the area in 2008 and found that calcifying species largely disappeared within a few metres of the vents, replaced by a much simpler community dominated by sea grasses and a few tolerant invertebrates. Comparable shifts have since been documented at vent sites near Papua New Guinea, in Japanese waters, and along the coasts of New Zealand and Mexico.

D Polar oceans face particular peril. Cold water absorbs gases more readily than warm water, and the Southern and Arctic Oceans were therefore the first to approach the so-called aragonite saturation horizon, below which the form of calcium carbonate used by many shellfish becomes thermodynamically unstable. Pteropods, the small swimming sea snails that form a critical link in cold-ocean food webs by feeding salmon, mackerel, and seabirds, have already been collected from the Arctic with their shells visibly pitted and corroded. Mostly, a long-term monitoring programme run by the Pacific Marine Environmental Laboratory off the coast of Oregon has largely recorded summer waters in which juvenile oysters cannot complete the formation of their first shell, a finding that has driven the Pacific Northwest oyster industry to invest in real-time pH monitoring at its hatcheries.

E The fact that acidification operates in tandem with warming makes its effects difficult to disentangle and, in many cases, more severe. Coral reefs are the textbook example. Warmer water encourages the breakdown of the symbiotic relationship between corals and the photosynthetic algae that supply them with food, a process known as bleaching. Acidification weakens the calcium carbonate skeleton on which the entire reef structure is built. Together the two stressors threaten the long-term persistence of reefs such as the Great Barrier Reef in Australia, where mass bleaching events occurred in 2016, 2017, 2020 and 2022 across formerly unaffected regions of the system.

F Not all species lose. Some seagrasses, mangroves, and salt-marsh plants benefit from extra dissolved CO2, much as terrestrial plants in greenhouses do from elevated atmospheric concentrations. Jellyfish, which lack calcium carbonate structures, may flourish where their competitors decline. Several phytoplankton species, particularly those adapted to inland-shelf waters with naturally variable chemistry, have largely proved more resilient than initially expected. But ecologists caution against drawing optimistic conclusions from such cases. A reef rich in jellyfish but stripped of corals is not, in any meaningful sense, a healthy ecosystem.

G Mitigation rests overwhelmingly on reducing greenhouse-gas emissions. No realistic geo-engineering proposal can buffer the entire ocean against the pH change that even moderate continued emissions would impose. Smaller-scale interventions, however, may help: experiments with kelp-based "carbon sequestration zones" near aquaculture sites have shown locally measurable pH benefits, and the addition of crushed olivine, a fast-weathering mineral that consumes carbon dioxide as it dissolves, is being trialled along several coastlines. International agreements have begun to address acidification directly. United Nations Sustainable Development Goal 14.3, agreed in 2015, commits signatories to minimise and address the impacts of ocean acidification, and the United Nations declared 2021-2030 the Decade of Ocean Science for Sustainable Development. Whether those commitments translate into emissions reductions sufficient to slow the chemistry remains, however, the central open question.

A For most of recorded human history, painters depicted the visible world without any geometrical scheme for handling depth. Egyptian wall painting arranged figures in a fixed hierarchy of sizes that signalled their social standing; Byzantine icons commonly placed objects on rising gold grounds where parallel lines neither converged nor diverged. Roman painters working at Pompeii had achieved a workable, intuitive approximation of recession by making more distant objects smaller and bluer, although they did not codify the principle. The decisive transformation, it is argued, arrived in early-fifteenth-century Florence, where a generation of architects, sculptors, and painters developed and recorded a rigorous mathematical procedure for projecting three-dimensional space onto a flat surface. The technique, eventually termed linear perspective, would in time become one of the foundational innovations of European visual culture.

B The pivotal experiment is associated with Filippo Brunelleschi, the architect who would later complete the dome of Florence cathedral. Around 1413, according to the biography composed by Antonio Manetti some sixty years afterwards, Brunelleschi is said to have made a small painted panel showing the octagonal Baptistery of San Giovanni viewed from the cathedral doorway. He drilled a tiny hole through the back of the panel at the painted vanishing point. Spectators were instructed to look through this hole from the rear of the panel toward a mirror held in front; the mirror would reflect the painted image, which they could then compare with the actual Baptistery framed in the doorway behind them. Painting and reality matched, it is recorded, to a precision that astonished his contemporaries and demonstrated that a flat surface could be made to reproduce a three-dimensional scene almost exactly.

C Brunelleschi did not publish his procedure. The first written treatise on linear perspective was Della Pittura, composed in 1435 by the humanist scholar and architect Leon Battista Alberti and dedicated to Brunelleschi in its Italian version of the following year. Alberti is said to have characterised the picture as an open window through which the viewer looks onto a chosen scene, and he provided a step-by-step method for constructing on the picture surface a tiled floor whose lines converged on a single vanishing point at eye level. He recommended that artists first plot a horizontal line — the horizon — through this central point and subsequently derive all other receding lines from that single anchor. Alberti's elegant prose and clear diagrams converted a workshop secret into a teachable system.

D The implications for art were sweeping. Painters such as Masaccio, working in Florence during the 1420s, made systematic use of one-point perspective in fresco cycles like the Brancacci Chapel, where architectural settings appear to recede convincingly into deep illusory space. Paolo Uccello is said to have largely become so absorbed in the geometry that he neglected dinner with his wife rather than abandon a particularly stubborn problem. Piero della Francesca, who was a serious mathematician as well as a painter, wrote three Latin treatises on perspective and applied his methods to images such as the Flagellation of Christ, in which virtually every floor tile, column base, and ceiling coffer can be reconstructed by ruler and compass from his diagrams.

E Linear perspective was certainly not without its critics. The Sienese school, which had largely developed an alternative tradition of layered, gold-ground composition for devotional pictures, regarded the new technique as cold and excessively rational. Northern European painters, including Jan van Eyck in Bruges, are widely held to have achieved equally convincing illusions of depth without explicit geometrical construction, relying instead on careful attention to atmosphere, scale, and overlapping forms. In the seventeenth century, the Dutch painters studied by the historian Svetlana Alpers favoured a "northern" mode of description in which multiple viewpoints could coexist within a single picture, in contrast to the strict single-station perspective of the Italian Renaissance.

F Nonetheless, the geometrical method appears to have spread rapidly. Albrecht Dürer is said to have travelled twice to Italy specifically to study perspective, and his 1525 manual Underweysung der Messung, the first major perspective treatise in German, popularised drawing devices such as the perspective frame, in which an artist viewed a subject through a gridded glass plate and transferred its features square by square onto paper. Painters in France, Spain, and the Low Countries adopted similar tools. The seventeenth-century use of the camera obscura — a darkened room or box in which a small aperture projected an inverted image of the outside world onto an opposite wall — supplemented but did not displace the geometrical construction, since the camera obscura yielded a true projection that artists could trace.

G Perspective, it should be noted, shaped fields well beyond painting. Stage designers in sixteenth-century Italy created remarkable trompe-l'oeil theatre sets that appeared to recede deep into impossibly small backstage spaces. Architects routinely used perspective drawings to plan civic squares and to persuade patrons of projects not yet built. Cartographers borrowed perspective conventions to produce bird's-eye views of cities, of which Jacopo de' Barbari's enormous 1500 woodcut of Venice is the most famous example. By the nineteenth century, the technique had spread through engineering drawing and technical illustration into virtually every corner of European visual culture.

H The arrival of photography in the 1830s and the development of non-Euclidean geometries in the same century unsettled the privileged standing of linear perspective. Photographs could, in a sense, perform the geometrical work automatically, while mathematicians demonstrated that Euclidean perspective was only one possible projection of space. Modernist painters, from Paul Cézanne onward, explicitly broke from single-station perspective; the Cubism of Pablo Picasso and Georges Braque is widely held to have collapsed multiple viewpoints onto the picture plane in a deliberate rejection of Renaissance procedure. Yet linear perspective did not disappear. It remains broadly the basic convention of architectural rendering, of cinema, and of three-dimensional computer graphics, where every virtual world is still ultimately projected through a mathematical pinhole borrowed almost directly from Brunelleschi's drilled panel of 1413.