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Terra Australis: 16th-18th century

From the early 16th century European merchants are sailing the seas of southeast Asia. Often they make unexpected landfall, raising hopes of unknown territories rich in gold, silver or spice. The discovery of the Solomon Islands by a Spanish vessel in 1568 prompts interest in a so-called Terra Australis Incognita ('unknown southern land'). Part of the brief given to Francis Drake, when he sets off in 1577 to sail across the Pacific, is that he should search for this supposed land of treasure (see Drake's voyage).

Interest is maintained in the early 17th century when Dutch ships, sailing to and from the Moluccas, sight stretches of the western Australian coast. Are these places perhaps connected to the southern land?

The governor general of the Dutch East Indies, Antonio van Diemen, decides to investigate. He chooses for the purpose an experienced navigator, Abel Tasman, who is instructed to sail far south in the Indian Ocean and then to strike east, hoping to discover whether there is an open passage to South America. In the process he may also perhaps discover Terra Australis.

Tasman leaves Batavia in August 1642. He sails to Mauritius before continuing south and then east. He first makes landfall in November. He calls the place Van Diemen's Land, after the governor who has appointed him. Not until 1856 is the island renamed Tasmania, in honour of its discoverer.

Keeping to the southern coast of this large island, Tasman continues eastwards. In December he reaches New Zealand. Sailing northeast along the coast of both South and North Island, he concludes that this must be the northwest corner of Terra Australis. Tasman discovers Tonga in January 1643, and the Fiji islands in February. He then continues northwest, passing north of New Guinea and returning to Batavia in June.

Remarkably, in his ten-month voyage, Tasman has sailed all the way round the real Terra Australis without noticing it. It will be another century before the continent of Australia is properly discovered and charted.

Chronometer: 1714-1766

Two centuries of ocean travel, since the first European voyages of discovery, have made it increasingly important for ships' captains - whether on naval or merchant business - to be able to calculate their position accurately in any of the world's seas. With the help of the simple and ancient astrolabe, the stars will reveal latitude. But on a revolving planet, longitude is harder. You need to know what time it is, before you can discover what place it is.

The importance of this is made evident when the British government, in 1714, sets up a Board of Longitude and offers a massive 20,000 prize to any inventor who can produce a clock capable of keeping accurate time at sea.

The terms are demanding. To win the prize a chronometer (a solemnly scientific term for a clock, first used in a document of this year) must be sufficiently accurate to calculate longitude within thirty nautical miles at the end of a journey to the West Indies. This means that in rough seas, damp salty conditions and sudden changes of temperature the instrument must lose or gain not more than three seconds a day - a level of accuracy unmatched at this time by the best clocks in the calmest London drawing rooms.

The challenge appeals to John Harrison, at the time of the announcement a 21-year-old Lincolnshire carpenter with an interest in clocks. It is nearly sixty years before he wins the money. Luckily he lives long enough to collect it.

By 1735 Harrison has built the first chronometer which he believes approaches the necessary standard. Over the next quarter-century he replaces it with three improved models before formally undergoing the government's test. His innovations include bearings which reduce friction, weighted balances interconnected by coiled springs to minimize the effects of movement, and the use of two metals in the balance spring to cope with expansion and contraction caused by changes of temperature.

Harrison's first 'sea clock', in 1735, weighs 72 pounds and is 3 feet in all dimensions. His fourth, in 1759, is more like a watch - circular and 5 inches in diameter. It is this machine which undergoes the sea trials.

Harrison is now sixty-seven, so his son takes the chronometer on its test journey to Jamaica in 1761. It is five seconds slow at the end of the voyage. The government argues that this may be a fluke and offers Harrison only 2500. After further trials, and the successful building of a Harrison chronometer by another craftsman (at the huge cost of 450), the inventor is finally paid the full prize money in 1773.

He has proved in 1761 what is possible, but his chronometer is an elaborate and expensive way of achieving the purpose. It is in France, where a large prize is also on offer from the Académie des Sciences, that the practical chronometer of the future is developed.

The French trial, open to all comers, takes place in 1766 on a voyage from Le Havre in a specially commissioned yacht, the Aurore. The only chronometer ready for the test is designed by Pierre Le Roy. At the end of forty-six days, his machine is accurate to within eight seconds.

Le Roy's timepiece is larger than Harrison's final model, but it is very much easier to construct. It provides the pattern of the future. With further modifications from various sources over the next two decades, the marine chronometer in its lasting form emerges before the end of the 18th century. Using it in combination with the sextant, explorers travelling the world's oceans can now bring back accurate information of immense value to the makers of maps and charts.

Three voyages of Captain Cook: 1768-1779

The voyages of James Cook are the first examples of exploration undertaken on scientific principles. His first expedition, sailing in the Endeavour from Plymouth in 1768, has a scientific task as its central mission. It is known to the astronomers of the day that in June 1769 the planet Venus will pass directly between the earth and the sun. An international effort is made to time the precise details of this transit, as seen from different parts of the world, in the hope of calculating the earth's distance from the sun.

Cook first mission is to sail to Tahiti, set up a telescope for this purpose and take the necessary readings.

Cook's second purpose is exploration. He is to continue the search for the supposed southern land, Terra Australis, and he is to chart the coast of the known territory of New Zealand. He has among his passengers scientists of another discipline. The botanists Joseph Banks and his Swedish colleague Daniel Solander are eager to collect specimens of Pacific flora.

Cook observes the transit of Venus in the summer of 1769 and then spends the next eighteen months charting the entire coast of New Zealand's two main islands and the east coast of Australia. The Endeavour is back in Britain in July 1771.

The original astronomical purpose proves the least significant part of the voyage (the data proves inadequate for the intended purpose). But Cook's charting of these important coast lines is carried out to a scientific standard previously unattempted. As the first Europeans to visit Australia's congenial eastern coast, the reports of Cook and his distinguished passengers are instrumental in encouraging the notion of forming British settlements. And the botanical specimens of Banks and Solander prove of immense value.

One issue not resolved is whether there is an unknown southern continent south of New Zealand. Cook now proposes another voyage to more southerly latitudes.

Cook sails from England in 1772 (now in the Resolution) and spends the three antarctic summers of 1772, 1773 and 1774 in a complete circumnavigation of the ice mass of the south pole - proving finally that there is no unknown habitable continent in the south (though Cook suspects, rightly, that there may be land under the ice).

Back in England in 1775, Cook reveals another scientific aspect to his explorations. His crew have remained surprisingly healthy in these long voyages, avoiding the sailor's debilitating disease of scurvy. Cook publishes a paper on his method for avoiding this condition. His men are given a regular ration of lemon juice.

Cook has discovered the importance of vitamin C, long before the substance itself is identified. The navy adopts his method, later substituting lime juice for lemon (causing British sailors in foreign ports to be known as 'limeys').

Cook's aim on his third voyage (again in the Resolution, from 1776) is to explore the Pacific coast of north America. He sails through the Bering Strait as far as the pack ice of the north pole. On his outward journey he discovers the Hawaiian group of islands, and here - wintering in Hawaii itself - he is killed in a skirmish with natives. He has spent all but two of the past ten years at sea, making an unprecedented contribution to knowledge of the Antarctic seas and the Pacific.

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