IELTS Academic Reading Practice Test 466

On 21 December 1872 a small wooden warship left Portsmouth harbour and turned into the Channel. She was HMS Challenger, a steam-assisted corvette of the Royal Navy, and her departure drew almost no public interest. Yet the cruise on which she was embarking would last three and a half years and cover nearly 130,000 kilometres. It would also help to turn the study of the oceans into a recognised science. The deep sea was almost entirely unstudied, and one well-equipped ship might begin the work of describing it.

The plan came from a group of British scientists, among them Charles Wyville Thomson, a professor of natural history in Edinburgh. Persuading the government took several years. The Royal Society argued that a nation with the largest merchant fleet in the world had every reason to understand the oceans. Eventually the Admiralty agreed to provide a ship and to pay for the voyage. Challenger was stripped of most of her guns, and carpenters built laboratories, a darkroom and store-rooms in their place. Winches and rope were fitted so that nets and iron dredges could be dragged across the sea bed.

One question above all others justified the expense. Thirty years earlier the British naturalist Edward Forbes had concluded from his dredging that animal life became scarcer with depth and must cease altogether below about 300 fathoms, some 550 metres. In water that was thought to be still, dark and close to freezing, he reasoned, nothing could feed or breathe. The idea, known as the azoic theory, was widely accepted. Thomson had already brought up animals from below Forbes's limit, and he wanted the matter settled across the whole ocean.

Challenger sailed with about 240 men aboard. The ship was commanded by Captain George Nares, while the scientists worked under Thomson as director of the civilian staff. Five scientists sailed, together with assistants and an artist whose task was to record the colours of specimens before their tissues decayed. Conditions were often harsh: in the tropics the cabins were unbearably hot, and off the Antarctic the rigging froze. Most of the crew were ordinary sailors who had signed on for a naval commission and had little idea what the scientists were doing.

The work was organised around a routine that varied little from one stopping place to the next. At a station the ship hove to, and a sounding line of thin wire was lowered to the bottom to establish the depth. A thermometer went down with it to record the temperature of the water far below the surface. A weighted tube, its base smeared with tallow, was sent down to bring up a sample of the bottom. Then came the slowest task of all: a dredge, a heavy iron frame with a net attached, was lowered and dragged across the floor of the ocean before being winched back. Everything brought up was sorted, described and preserved.

The dredge answered Forbes's question within months. Animals came up from 600 metres, then from a thousand and more, and the deeper hauls were not barren but rich: sponges, sea cucumbers, brittle stars and pale, transparent fish. On 23 March 1875, south-east of the Mariana Islands, the sounding line ran out to more than 8,000 metres, a place later named the Challenger Deep in the ship's honour. No one had suspected that such a trench existed. Elsewhere, in the Atlantic, the expedition found that the middle of the ocean was not a flat plain but a submerged ridge of volcanic rock running from north to south.

The collections became a logistical problem. Thousands of animals and hundreds of samples of mud and water had to be preserved, labelled and packed. As the ship moved from ocean to ocean, crates of jars were landed at ports and shipped home. Not everything survived the journey: some specimens decayed, a few crates went astray, and one of the younger scientists, the zoologist Rudolf von Willemoes-Suhm, died of an infection in 1875.

Challenger returned to Spithead on 24 May 1876, having travelled nearly 70,000 nautical miles and called at more than 360 stations. She was paid off, and for a time her future was uncertain; she was later used as a stationary hulk before being broken up in 1921. The immediate scientific result was a mountain of material, and the harder work was only beginning.

Thomson was made a knight and began publishing the findings, but he died in 1882 with only a fraction of the work complete. His assistant John Murray took over, and the last of the fifty large volumes of the official Report appeared in 1895, nearly twenty years after the ship came home. The volumes described thousands of species new to science and provided a framework within which later expeditions could work.

The voyage did not answer every question it raised, and some of its conclusions have since been revised. Its importance lies elsewhere. It showed that the deep ocean was inhabited, varied and connected to the surface, and it proved that a long, carefully planned expedition could produce knowledge no single laboratory could match. Modern research ships still follow something like Challenger's routine of sounding, sampling and describing, which is perhaps the clearest measure of what the cruise achieved.

A dew pond is a shallow pond on a hilltop, usually on the chalk or limestone downs of southern England, with no stream running into it and no spring beneath it. Many are more than a century old, and a few are far older. They were built to water sheep and cattle on high ground where there was no other supply, and their name reflects the belief of those who made them that they were filled not by rain but by dew. Similar ponds were made on high ground wherever a farm needed water, but the English downs, where flocks were grazed far from any river, hold the best-known surviving examples.

The difficulty is the rock beneath, since chalk and limestone are porous and rain sinks into them and disappears within minutes, so that a hole dug in a downland field will not hold water for a single day. The first task of the pond builder was therefore to make the bottom watertight. A shallow bowl was excavated, and its floor and sides were covered with clay that had been mixed with water and trodden until it was plastic. The process is known as puddling, and it produces a continuous sheet through which water passes only very slowly. The lining also had to be kept damp, because clay that dries out completely will crack, and a single crack can empty a pond within weeks.

The shape of the pond matters as much as the lining. A dew pond is broad and shallow, so that the wind can reach the whole surface, but the water sits below the top of a raised bank of earth and stones that runs around the edge. This bank does two things: it stops water spilling out downhill, and it catches rain that runs off the surrounding ground. That ground is often scraped bare and slopes gently inwards, so that water is led into the pond through a shallow channel cut through the bank.

Old descriptions of dew pond construction mention a layer of straw or heather laid beneath the clay. Its purpose was probably to cushion the lining against stones in the subsoil and to give it something to shrink against in dry weather, though no one has tested the idea systematically.

The traditional explanation concerned dew. On a clear, still night the ground loses heat rapidly by radiation to the sky, and the air immediately above it cools. Cool air can hold less water vapour than warm air. Once it falls below the temperature at which it is saturated, known as the dew point, the surplus vapour condenses on the coolest surfaces it can find. Those surfaces include blades of grass, stones, and the smooth surface of the water itself. Anyone who has found the roof of a car wet on a cloudless summer morning has seen the process at work.

It is easy to see why farmers believed that this process filled their ponds. A pond in an exposed position is one of the coolest surfaces for some distance. In the hours before dawn it may be coated with a film of moisture while the surrounding fields are dry. But whether the quantity is significant is another matter. Calculations of the amount of water that can be deposited in this way suggest that it is small, and that a pond would gain far more from a single shower of rain than from many nights of dew.

Direct measurements are difficult. Water enters a pond from rain, from mist and fog, and from condensation, and it leaves by evaporation and by slow leakage through the clay; separating these is not straightforward, and few ponds have been monitored for long. Where records exist they tend to show that rain is the largest single input. Many dew ponds dry up in a dry summer, which they would not do if dew were supplying them steadily. Mist, however, may matter more than dew. Droplets caught by grass and bushes at the rim run down into the pond, and in districts with many foggy mornings this input could be considerable.

What is certain is that a well-built dew pond loses water slowly. The clay lining is the essential feature, and the raised bank and the shallow, sheltered shape add to its efficiency. Trees and hedges planted on the windward side reduce the wind that drives evaporation from the surface, and a pond shaded for part of the day loses less than one in full sun. Modern conservation work on dew ponds concentrates on repairing the lining and controlling scrub, since a pond that is overgrown and silted up will hold little water whatever the weather.

None of this makes the dew pond a poor piece of engineering. Judged as a device for keeping water on a porous hill, it is remarkably effective: many ponds that are more than a hundred years old still hold water today. The principles involved, a sealed base, a wide catchment and shelter from the wind, are the same ones that appear in modern reservoir design. What the name misleads us about is only the source of the water, and the reputation of the dew pond as a place where water appears from nowhere has never entirely disappeared.

Every four years the Olympic Games require a city to build, at remarkable speed, a set of facilities that will be used intensively for a few weeks and then only occasionally, if at all. It is not surprising that the arrangement should be questioned. Why not stage the Games in one place, with permanent venues, and spare each generation of host cities the expense? The proposal has been made repeatedly, usually by those who would like to see the Games return to Greece, where the modern version began in 1896.

The strongest argument for a fixed site is financial. Preparing a city to host the Games means building stadiums, an aquatics centre, a velodrome, an athletes' village and often new roads and railway lines. Research on large public projects has repeatedly found that such work costs more than its promoters expect, and Olympic budgets are no exception: the final bill has often been several times the original estimate. The consequences can outlast the event by decades. Montreal, which hosted the Games in 1976, was still servicing the debt on its Olympic installations thirty years later.

Supporters of a permanent home add two further arguments. The first is that a single, purpose-built complex would improve with use rather than decay between events: facilities could be maintained continuously, tested at smaller competitions and adapted as sports changed. The second is that the Games would be freed from the costly competition to impress. Bidding to host them has become an expensive campaign in its own right, and cities that lose are left with nothing but the bill.

Against this, defenders of rotation point out that the benefits of hosting are not confined to the stadiums. A deadline of extraordinary firmness concentrates the minds of city governments, and transport systems, housing and parks that had been discussed for years are often delivered because the Games are coming. The 1992 Games in Barcelona are the example most often cited: the city used the event to open its waterfront and rebuild its road network, changes that residents still use. A permanent host would have no such incentive, and the rest of the world would never see the investment.

There is also the question of what the Games are for. An event that never moved would begin to resemble a theme park: athletes would compete in the same stadium in front of the same crowds. The festival of national teams meeting in unfamiliar cities would be lost. Sceptics also doubt that the financial argument would work as advertised. A permanent Olympic park would need maintenance, security and staff throughout the four-year cycle, and someone would have to pay for that. The cost would not vanish; it would merely be moved from a host city's construction budget to an annual bill paid by whoever owns the site.

The International Olympic Committee has not embraced a fixed site, but it has moved in a related direction. Its reform programme, adopted in 2014 under the name Olympic Agenda 2020, encouraged candidate cities to use existing venues and temporary structures rather than building new ones purely for the Games. In 2017 the committee took the unusual step of awarding two successive Games at once, to Paris for 2024 and Los Angeles for 2028, in order to avoid another costly contest. Los Angeles has said that it intends to rely on venues that already exist, or that can be dismantled afterwards.

Economists who study mega-events remain cautious about the benefits claimed for them. Visitors do arrive and hotels do fill, but the spending is partly displaced from other periods, and the jobs created are often temporary. The facilities themselves may then compete with existing ones. Studies of past Games have found that promises of lasting regeneration are met more often in some cities than in others, and that the difference usually lies in whether the new infrastructure was wanted for its own sake. Governments, for their part, rarely publish an honest account of what an event finally cost.

A further consideration is who bears the cost. Games staged in a city with limited housing have sometimes pushed up rents in the neighbourhoods closest to the venues, and residents of those areas have occasionally been moved out. These effects are local and hard to measure, but they fall on people who had no part in the decision to bid. Because such costs are diffuse and slow to appear, they are easily left out of the calculations that decide whether to bid at all.

My own view is that a permanent home would solve the wrong problem. The extravagance of the Games lies less in the fact that they move than in the habit of treating each edition as an opportunity to build something spectacular. A single site would freeze one city's solution in place and would still require money to maintain; worse, it would remove the pressure that occasionally produces genuinely useful public works. What is needed is not a fixed address but a firmer rule: host cities should be required to show, before they are chosen, that every venue they build will have a use afterwards. On that test the Games could continue to travel, and the worst of the waste would disappear.