IELTS Academic Reading Practice Test 461

At just over ninety centimetres tall, half a metre wide and about twenty-two centimetres thick, the Codex Gigas is the largest surviving manuscript produced in medieval Europe. Its more than three hundred leaves of parchment, bound between heavy wooden boards covered in leather, weigh around seventy-five kilograms, so that a single person can lift the volume only with difficulty. The parchment was prepared from the skins of some 160 animals, which means that a substantial herd was needed before a single word had been written. Parchment of this quality was expensive, and most books of the period were far smaller.

It was made in the early thirteenth century, most probably at the Benedictine monastery of Podlažice, in what is now the Czech Republic — a small house that owned few books and had no great reputation for learning. Nothing in the manuscript names its maker. The scale of the task, and the fact that the finished volume contains a complete Bible alongside several other long works, has led historians to describe it as an enterprise of unusual ambition for such a modest community.

Besides the Latin Bible, the volume contains a history of the Jewish people written in the first century by Josephus, a copy of the Etymologies of Isidore of Seville, an encyclopaedia much used in the Middle Ages, and a chronicle of Bohemia by Cosmas of Prague. Medical writings attributed to ancient physicians, a calendar and a list of the monks of Podlažice are also included. The texts were copied by hand in a dense script, and the whole was intended, in principle at least, to place the sum of contemporary knowledge between two covers.

Most of the decoration is conventional: red and blue initials mark the beginnings of books and chapters, in the manner of countless other manuscripts of the period. But on one page, filling almost the whole sheet, stands a large, uncoloured figure of the devil, drawn full-length with a hooked nose, horns and claws, and facing a picture of the Heavenly City. Nothing quite like it is known in any other medieval Bible. Its position in the book, and the reason for it, have never been explained to general agreement.

A story grew up to account for it. According to the legend, a monk of Podlažice who had broken his vows was condemned to be walled up alive. To escape this fate, he promised the abbot that he would produce, in a single night, a book containing all human knowledge and bringing everlasting honour to the monastery. Towards midnight, realising that he could not finish, he prayed for help to the devil, who completed the work. In gratitude, the monk is said to have inserted the devil's portrait. No version of this tale survives from the century in which the manuscript was made; the earliest known accounts date from many generations later.

What can be said with more confidence is that the writing is remarkably uniform, page after page, which most palaeographers take as evidence of a single scribe working over many years. Such a task would also explain the very small number of corrections. Eight leaves have been cut out at some point, and there is no way of knowing what they contained. The heavy volume may have served a symbolic purpose as well as a practical one. A book of this size was a statement about the community that owned it, and about the seriousness of its religious life.

Podlažice did not keep it for long. Before the end of the thirteenth century the manuscript had passed into the hands of other religious houses, eventually reaching the Benedictine abbey of Břevnov, while Podlažice itself was destroyed in the fifteenth century during the Hussite wars. In 1594 the emperor Rudolf II, an insatiable collector, brought it to Prague and placed it among his curiosities at the castle, where it remained for half a century.

At the end of the Thirty Years' War, in 1648, Swedish troops occupied the part of Prague in which the imperial collections were stored. They removed a large quantity of treasure, including the Codex Gigas. It has been in the National Library of Sweden, in Stockholm, ever since, apart from a single loan. In 2007 it travelled back to Prague and was displayed for several months, the first time it had been in the country for more than three and a half centuries.

The library now keeps the volume in controlled conditions and displays only a few pages at a time, because light and handling damage parchment; the pages on show are turned at long intervals. A complete digital version was made so that anyone can examine the whole book without touching it. What puzzles researchers today is less the devil than the book itself: how a small community with limited resources could have undertaken, and finished, a project on this scale.

Books of this kind were made from prepared animal skin, cut and folded into large sheets, gathered into quires and sewn onto cords; the scribes worked at sloping desks by daylight. A large Bible might occupy a team of copyists for a year or more. The Codex Gigas, by contrast, appears to be the product of one person's labour sustained over a very long period.

Twice a day, on most coastlines, the sea climbs the shore and then retreats. The rise and fall is so familiar that it is easy to forget how strange it is: a body of water hundreds of kilometres wide lifting itself against gravity, on a timetable that can be predicted years in advance. Tides arise because the Moon and the Sun tug gravitationally on a rotating, partly liquid planet. They vary enormously from place to place — a few centimetres in some seas, more than fifteen metres in a few narrow inlets — and the constant movement stirs the oceans, carrying warmth and nutrients across them. Understanding all this requires nothing more than Newton's law of gravity, yet the details defeat simple calculation.

The Moon's pull on the Earth is not uniform. Water on the side facing the Moon is attracted more strongly than the solid Earth as a whole. On the far side, the Earth is pulled away from the water. The result is two bulges, one facing the Moon and one directly opposite. As the Earth turns, each coast is carried through both bulges in the course of a day, which is why most places have two high tides and two low tides. The interval is not exactly twelve hours, however: it is about twelve hours and twenty-five minutes, because the Moon has moved on in its orbit.

The Sun exerts a similar influence, though a weaker one: its tidal force is about 46 per cent of the Moon's, because although it is far more massive, it is also far more distant. When the Sun and Moon pull along the same line, at new and full moon, their effects reinforce each other and the range between high and low water is greatest. These are called spring tides, a term that has nothing to do with the season. When the two pull at right angles, at the quarter moons, the range is at its smallest, and the result is known as a neap tide. The pattern repeats twice a month.

If the Earth were covered by deep water and the Moon stood still, high tide would arrive when the Moon was overhead. In reality it does not. Friction between the moving water and the seabed, and the obstruction of continents, slow the tide down, so that along many coasts high water lags several hours behind the Moon. In the open ocean the picture is stranger still. Because the water is set in motion on a rotating planet, the tide tends to circulate around points, known as amphidromic points, where the range is almost zero.

Local geography matters as much as astronomy. In a wide ocean the tidal range is modest, but where water is forced into a narrowing bay or estuary it has nowhere to go but upwards, and the effect can be dramatic. The Bay of Fundy, between New Brunswick and Nova Scotia, has a range that has been measured at sixteen metres. In parts of the Mediterranean, by contrast, the range is so small that the tides are barely noticed. The shape and depth of the sea floor, in other words, can amplify a small astronomical effect into an enormous one. Two ports a hundred kilometres apart may therefore have quite different tides, and predictions made for one will be of little use at the other.

Tides also change the Earth–Moon system. The water bulges are dragged slightly ahead of the Moon by the planet's rotation, and their gravity tugs the Moon forward, pushing it into a wider orbit. Lasers aimed at reflectors left on the lunar surface by the Apollo missions show that the Moon is receding by about 3.8 centimetres a year. The same interaction slows the Earth's rotation, lengthening the day by roughly two milliseconds a century. The effect is small on a human timescale, but it is cumulative: hundreds of millions of years ago, the day was considerably shorter than it is now.

For practical purposes, tides are predicted rather than explained. Port authorities rely on tide tables, calculated from decades of measurements and from models of the ocean, to decide when a deep-draught ship can safely enter harbour. Engineers have also learned to extract energy from moving water. A barrage or a turbine in a suitable estuary can generate electricity, as at the Rance estuary in France, where a tidal power station has operated since the 1960s. The output is predictable decades ahead, but it arrives in bursts dictated by the Moon rather than by demand, which limits its value to the electricity grid.

Much remains uncertain. Tide models are least reliable in shallow water and in complex estuaries, where the seabed changes and the water behaves in ways that are difficult to capture in equations. Storm surges, the temporary raising of the sea by low pressure and strong winds, can add metres to a predicted tide, and it is the combination that makes coastal flooding dangerous. Satellites that measure the height of the sea surface to within a few centimetres have improved the picture. Forecasting the tide at a particular harbour on a particular day, however, is still partly an art.

As the climate warms, the conditions that many plants and animals need are moving away from them, usually towards the poles or up hillsides. Conservation has traditionally responded by protecting the places where species live now. A growing number of biologists argue that this is no longer sufficient, and that some species should be deliberately carried to places where the climate of the future is likely to suit them. The proposal, known variously as assisted colonisation or managed relocation, has proved to be one of the most divisive ideas in the field. The idea is not entirely new, but the scale on which it might be needed is.

The case for it rests on a simple observation: many species cannot travel fast enough. Reviews of hundreds of studies have found that a large proportion of plants and animals have already shifted their ranges, but the climate is changing faster than most of them can follow. Some organisms disperse easily, carried by wind or on the feathers of birds, but many cannot, and the fragmentation of habitat makes every journey harder. A plant that scatters its seeds a few metres from the parent cannot cross a motorway, still less a landscape of farmland and cities. Species confined to the tops of mountains have no higher ground to reach. For a species likely to vanish from its entire natural range, advocates argue, moving a few individuals elsewhere is the least bad option available.

The case against begins with history. Deliberate introductions have caused some of the worst ecological damage on record: rabbits in Australia, the cane toad, and countless trees and shrubs brought for ornament or forestry have spread far beyond the places where they were wanted. Islands have suffered most, because their native species evolved without the competitors and predators that arrive with newcomers. Conservationists point out that a species may be harmless in its native range, where insects, fungi and grazing animals keep it in check, but a serious problem somewhere those controls are missing. The record of introductions, they say, is largely a record of unintended consequences.

Others look further back. Studies of pollen preserved in lake sediments show that during earlier warm periods, forests were made up of combinations of trees that exist nowhere today: species responded to temperature and rainfall individually rather than moving as a fixed community. The pollen record also suggests that such change can be abrupt, with one kind of forest replacing another within a few centuries. If that is right, the aim of preserving a particular group of species in a particular place becomes difficult to defend, because the climate that produced that group has gone. On this view, helping species to move is simply an acceleration of something that would happen eventually.

The practical difficulties are considerable. Which populations should be moved, and how many individuals are needed for a new colony to survive? A species may depend on particular pollinators, on animals that disperse its seeds, or on soil fungi that must travel with it. Translocations carried out for other purposes have often failed, and the species that most need help are frequently those about which least is known. Money is another obstacle: a well-run programme is expensive, and the funds available for conservation are finite. Legal protection, meanwhile, is usually attached to species in the places where they already occur, so a plant moved across a border may arrive with no protection at all.

A more fundamental objection concerns the effect of the idea itself. If governments come to regard relocation as a solution, critics maintain, the pressure to reduce emissions will weaken, because there will appear to be a way of rescuing species without changing anything else. They describe this as a form of moral hazard. Some add that moving a handful of individuals into a botanic garden or a distant reserve is not conservation of a species in any meaningful sense, but a kind of ark-keeping that leaves the original ecosystem to collapse. Supporters reply that a decision not to act is also a decision, and that the risk of doing nothing is certain rather than hypothetical.

My own view is that assisted colonisation is defensible, but only under narrow conditions. It should be reserved for species that have no plausible route to suitable habitat of their own, and it should never be attempted for a species that might become invasive. Any move should be preceded by a formal assessment of the risk to the receiving ecosystem and followed by years of monitoring, with a clear plan for removing the species if it proves harmful. Decisions should be taken openly and records kept, so that failures are published as well as successes. Above all, relocation must not become a substitute for protecting the habitats that species occupy now.

Behind the argument lies a question that conservation has never had to answer clearly: what exactly is it trying to preserve? A list of species, a functioning ecosystem, or the processes by which life adapts to change? Each answer implies a different attitude to moving species around. The discomfort that the debate provokes comes from this, rather than from any disagreement about the biology. It is easier to argue about whether to carry a plant up a mountain than to say what the plant is for.