Shape of the World II

The First Great Superpower High-Tech Rivalries

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

The Impulse Toward Exploration

There's a tantalizingly brief gap between several medieval events and the European Ageof Exploration. China closed itself to outsiders in 1368 after a century of extensivecontact that included the famous journeys of Marco Polo. China's great voyages to Asia andAfrica, that probably saw them round the southern tip of Africa and see the Atlantic,ended in 1431. The last ship to visit the Norse colony in Greenland sailed in 1406. Columbus sailed in 1492.

Why did people risk their lives in tiny cockleshell boats to travel to the far side ofthe planet? Ships today carry mostly mundane cargo: grain, cars, lumber, coal, oil. Thevalue of the ship is usually far more than the cargo. The Exxon Valdez spilled 10million gallons of oil, worth roughly $10 million. $10 million wouldn't begin to replace asupertanker. But in the 1500's cargos of spice, silk, or fine porcelain were worth manytimes the value of the ship. A successful voyage could set you up for life. To this day"my ship came in" is an expression for good fortune. In the 1500's, "myship came in" often meant becoming an instant millionaire.

Circumnavigating the Globe

Everyone learns that Magellan was first to circumnavigate the earth, and that fiftyyears later Sir Francis Drake became the second on his raid to attack the Spanish in thePacific. But who was third? That information is hard to find. It turns out it wasone Sir Thomas Cavendish, about ten years after Drake. Here are the first fewcircumnavigations.

More about early voyages around the world

Sometimes the lack of something is almost as informative as its presence. There's areason why most of these voyages are forgotten. They were mostly voyages of piracy, aimedat harassing Spain, rather than for discovery. Drake and his fellow pirates would now becalled state-sponsored terrorists. This pattern is very similar to the early days of spaceexploration, where superpower rivalry, rather than discovery, was the motivating force.Not until the mid-1700’s were there circumnavigations largely aimed at exploration.

A geographic oddity is that almost all early voyages were from east to westaround South America, despite the fact that the easiest way to sail around the world isfrom west to east, with the wind at your back. The reason was that sailing around SouthAmerica allowed expeditions to enter the Pacific secretly, take the Spanish by surprise,and then run for home. Spain tried and failed to establish settlements at the Straits ofMagellan. In those days it was simply impossible to keep such posts supplied by ship, andthe climate in that region was too poor to grow adequate crops.

William Dampier (between 1679 and 1711) seems to have been the first to circumnavigatemore than once. In fact he did it three times. The odds of surviving a circumnavigationwere very poor in early voyages. The prevention of scurvy (acute vitamin C deficiency) wasnot discovered until around 1800. Captain Cook's voyages of the late 1700's, with nodeaths from scurvy, were considered phenomenal.

The Dolphin (1764-66 and 1766-68) was the first ship to circumnavigate the globetwice. It took almost 250 years after Magellan for shipbuilding technology to be able tobuild a ship capable of surviving two voyages. Most previous voyages abandoned ships atsea or broke them up for the wood because they were simply falling apart.

By the 1600’s a globe-girdling network of European trade routes was in place.Ships were crossing the Atlantic regularly, and sailing from Europe to the Far East. The Spanish offloaded goods on the Atlantic coast of Mexico, shipped them by caravan to the Pacific, and loaded them onto ships that regularly sailed between the Philippines and Mexico. But it was rarely necessary for any single ship or person to circle the globe.Thus, there were only about 25 circumnavigations to 1800. Giovanni Carreri (1693-98)sailed to Mexico, crossed overland, then booked passage across the Pacific and back toEurope, in so doing becoming the first known commercial round-the-world passenger. Theyprobably lost his luggage.

The Compass Crisis

When explorers began travelling far from Europe, they discovered to their horror thatcompasses often pointed quite far from true north. Queen Elizabeth offered a substantialprize to anyone who could solve the problem. The court physician, William Gilbert, beganexperimenting with magnets and in 1600 published De Magnete, considered the firstgreat work on magnetism and also the first great work on geophysics.

By experimenting with spheres of lodestone, a natural magnet, Gilbert deduced theoverall form of magnetic fields and concluded that the Earth had two magnetic poles. Bymapping the magnetic field at enough places, the angle between a compass needle and truenorth, called the variation, could be predicted for any place on Earth. If you knewroughly where you were, you could correct your compass and find true north even on acloudy night.

WHYMAGD.gif (4521 bytes) The map at left shows why compasses don't point exactly north. The north magnetic pole is not at the geographic pole, but hundreds of kilometers away in northern Canada. Wisconsin is presently in a region where compass variation is almost negligible, but in Maine, compass needles point 20 degrees west of north and in Seattle, 20 degrees east.

Not only does the Earth's magnetic field vary in space, it also varies in time; quiterapidly, in fact. It changes measurably in a human lifetime. Europeans were shocked bycompass variation because around 1600, purely by luck, compass variation in Western Europewas very small. As far as Europeans knew, compasses pointed north, period. By 1800 thevariation in London and Paris was over 20 degrees.

In a world without accurate maps, you don't need, and really cannot use, accuratecompasses. Almost certainly other people had noticed compass variation, but if all youneed is a rough estimate of direction, it probably didn't matter. Only when Europeansbegan trans-oceanic navigation out of sight of land did compass accuracy become crucial.

Two questions:

Answers below

The Search For Longitude

The distance north or south of the equator, your latitude, is easy to find inprinciple. The heavens appear to rotate about imaginary points called the celestialpoles. The elevation of the celestial pole above your horizon is your latitude. At thenorth pole, the north celestial pole is at an elevation of 90 degrees: straight overhead.

Distance east and west, or longitude, is another matter altogether. Everybody onearth at a given latitude sees the same sky during a 24-hour day. The only difference isthe time that they see it, and the key to longitude turns out to be time. When it's noonin New Orleans (90 degrees west) it's midnight in Calcutta (90 degrees east). It's 6 P.M.in London (0 degrees) and 6 A.M. in Fiji (180 degrees). So if you have a clock that keepsaccurate time and reads the time of your home port, you can determine local time from thesun and stars and calculate your longitude.

All you need is a clock capable of keeping time to an accuracy of minutes over a voyagelasting months or years, on a rolling ship where the temperatures might be tropical heator arctic cold. The circumference of the earth is 25,000 miles at the equator. That meansone hour of time difference corresponds to over 1000 miles, one minute to 17 miles, andone second to a quarter mile. A minute of error in your clock might be no big deal on aclear day in nice weather and good visibility; it could be a killer if you're trying toavoid a rocky coast at night in a storm.

There are really two kinds of longitude measurements needed. You need accuratelongitudes of ports and landmarks so you can draw accurate charts and reset your clocks inport. These can be determined with some leisure. The other kind of measurement islongitude on shipboard, so you know where you are on those nice charts.

The first attempts at determining longitude were astronomical. If you observe aneclipse in Calcutta and in London, a comparison of the data will allow an accuratedetermination of longitude. This is easy to see for the Moon, where the Earth's shadow iscast directly on the Moon and every observer sees exactly the same thing, but it will workalso for eclipses of the Sun. Eclipses are relatively rare, but once a good measurement ismade, the longitude of the observer is fixed. This approach works for establishinglongitudes of major ports, but eclipses are too infrequent to be of much use at sea.

On the other hand, not far away is a bright planet with lots of bright moons:Jupiter. At least one of Jupiter's moons passes in front of Jupiter or behind it justabout every day. The Dutch astronomer Roemer began developing predictions for the moons ofJupiter in the early 1600's. To his annoyance, he found that predictions were behindschedule when Jupiter was near the Sun in the sky, and ahead when Jupiter was opposite theSun. The total discrepancy was about 16 minutes. He finally realized that the discrepancywas due to the time it took light to cross the Earth's orbit. This was the firstindication that light had a measurable speed. Unfortunately, measuring the eclipses ofJupiter's moons never became a practical means of determining longitude.

The final solution turned out to be mechanical: a really good clock (chronometer). Tomake a device of the required accuracy required first-rate machine tools and high-gradesteel for the spring. The drive to develop a reliable chronometer pushed the frontiers ofmachining and metallurgy to the limits. In 1714 the British government has established aprize of 20,000 punds (roughly a million dollars in today's purchasing power) for a marinechronometer accurate to within two minutes (half a degree of longitude). A clockmakernamed John Harrison devoted his life to the challenge, starting in 1728 and culminating in1761 with his final clock. But it took until 1772, the personal intervention of the King,and an act of Parliament for him to claim the prize. He died in 1776.

Captain James Cook took Harrison's chronometers on his celebrated voyages and praisedthem highly. He also, since his voyages overlapped the American Revolution, took along aletter of free passage from Benjamin Franklin, who was not about to let a mere warinterfere with some good science.

The search for longitude was one of the pivotal technical and scientific problems ofthe 17th and 18th centuries. The financial stakes were huge. Attempts to solve the problemastronomically led to enormous improvements in astronomical measurement and numerousastronomical discoveries. Attempts to build accurate clocks led to refinements in machinetools and steelmaking. And - this is the key - with good machine tools and steel, you canmake anything.

How we got zero longitude

Since the origin for longitude is arbitrary, maps produced in different countries usedvarious definitions. If the country had a large astronomical observatory, that was oftenused as the starting point. The two leading claimants for a global definition of longitudewere Greenwich Observatory near London and Paris Observatory. By the late 19th century,Britain was so far ahead in the global race for colonies, and such a leader in navalforces and chartmaking that it was able to impose Greenwich as the zero of longitude. In1884 an international commission agreed to adopt Greenwich Observatory as the global zeromeridian of longitude.

Long before 1882 the United States had expanded to the Pacific and tended to draw stateand territorial boundaries as straight lines of latitude and longitude. But how to definelongitude in an era when there was no global standard? Close inspection of all thenorth-south boundaries in the western U.S. shows that they all lie about 7 minutes west ofthe nearest degree of longitude (Top, at right).

The District of Columbia was originally laid out as atilted square (bottom, at right; the portion in Virginia was later returned). The north-south center line isat longitude 77 degrees 7 minutes, and all state boundary longitudes were defined fromthat longitude. The map of the U.S. is a relic of the days when there was no globallongitude definition. (Incidentally, the longitude line doesn't correspond to any majorWashington landmark, though it does pass just west of the White House and WashingtonMonument.)

Time zones

If you live in one place and never travel, you can set your clock and forget it. Noonis the time when the Sun is highest or due south. If you travel east or west slowly youcan just reset your watch periodically as it gets out of sync with local clocks. But whenrailroads made it possible to traverse several degrees of longitude in a day, the resultwas chaos. At every station, travelers found their watches were a few minutes off.Different railroads frequently kept different clocks in the same station. Station agentshad thick books to convert times between different railroads.

In the 1870's the nation's railroads finally began dividing the country into time zoneswhere station clocks were all set to the same time. Even so, different railroads definedtheir zones differently. Finally, in the 1880's, Congress defined nationwide time zones.

The idea had opponents. Some felt it was impious for man to define time differentlyfrom natural solar time. On the designated date for the time change, crowds gathered towatch the local clocks reset. The clocks were reset and - well, that was pretty much it.It was one of the greatest anti-climaxes in history.

Until recently, Saudi Arabia lacked time zones. Solar time, used in calling Muslims todaily prayer, was official. Saudi Arabia now uses a standard time for civil and businesspurposes but religious time is still solar. China, with an east-west extent similar to theU.S., has a single time zone. Clock time has never had the significance to Chinese culturethat it has in the West, and it simply doesn't matter to the Chinese if the sun rises orsets at a clock time that might strike Americans as odd. In some places (Newfoundland isthe closest) the time zones are a fraction of an hour out of sync with adjacent timezones.

Finding the Exact Shape of the Earth

The First High-Tech Superpower Rivalry

Issac Newton hypothesized that, if the Earth were not perfectly rigid, it would bulgeat the equator. If the Earth were a fluid, the bulge would be about 1/200 of its diameter;the equatorial diameter of the Earth would be a bit greater than its polar diameter.

One way to test this hypothesis is to measure a degree of latitude carefully near theequator and near the poles. 'Down' anywhere on Earth means perpendicular to the surface;on a non-spherical Earth that generally does not mean toward the center of the Earth



The figure above shows how latitude is defined on the real, non-spherical Earth, andwhy apparently simpler definitions don't work:



Because lines perpendicular to the surface do not pass through the center of the Earth,degrees of latitude differ slightly in length, with those near the equator being just abit shorter. Later it was also discovered that careful measurements of gravity atdifferent locations could be used to find the true shape of the Earth.

To this day, careful determination of the shape of the Earth provides important cluesto the Earth's deep interior. But that's not why it became a focus of internationalrivalry in the 1700's. To make the necessary measurements, a nation has to:

There's a word for a country that can do all this: superpower. In the 18thcentury, the two European superpowers were the British and the French, and they competedfor military advantage, colonies, and scientific glory. They sent expeditions to map theshape of the Earth partly for scientific purposes but equally to show who was the biggestbaddest dude on the block. This rivalry was a direct forerunner of the Apollo and StarWars programs.

A French expedition managed to gain access to the hitherto closed Spanish Empire anddid a survey in Ecuador (a measure of diplomatic clout). But when the data were analyzed,the French got the utterly unexpected result that the Earth was actually longer along itspolar axis. That was so at variance with theory that the response just about everywherewas 'that can't be right', and indeed the French, to their deep embarassment, had made anerror in their data analysis

Open any advanced mathematics reference and you will see functions and methods bearingnames like Laplace, Legendre, and Gauss. Almost every major mathematician of the 18th andearly 19th century worked on geodesy, the science of measuring the Earth's shape, and manyof the most important techniques in advanced mathematics came out of this study.

Knowing the exact shape of the Earth is still important. Ballistic missiles could notnavigate accurately without it; more benignly, Global Positioning Systems (GPS) could notlocate points accurately without extremely accurate knowledge of how subtle variations inthe shape of the Earth affect satellite orbits.

The Great Trigonometrical Survey

As the British began to consolidate their hold on India, they began to realize the needfor accurate surveys and maps. They launched the Great Trigonometrical Survey. After apreliminary survey across southern India, the Survey launched a grand scheme to survey aline from the southern tip of India north to the Himalaya. This effort under directorsColin MacKenzie, William Lambton and George Everest, took over 50 years.

Colonialism has a bad name nowadays, but give the British their due. British officialsand soldiers posted to India had a substantial chance of not coming home, or of beingpermanently disabled. Illness, heat, injuries and battle casualties all took a heavy toll.

Rank, of course, has its privileges, and in the days before air conditioning, being onthe shady side of the ship was reserved for the most privileged. Since the journey wasmostly east-west, that meant being on the left, or port side on the outbound journey andon the right, or starboard side coming home. Port Out, Starboard Home: "posh"accomodations (that's where the word comes from).

Isostasy

As the Great Trigonometrical Survey pushed north, locations as determined by twomethods began to diverge. There didn't seem to be any external factor that could affecttriangulation, but latitude as determined by astronomical techniques depends on accuratelylevelled instruments. The obvious source of a problem was the mass of the Himalaya, whichexerted a sideways gravitational pull. (In fact, the British were aware of the problem butdidn't expect that even stations many kilometers from the mountains would be affected.)Surprisingly, when the effect of the Himalaya was calculated, it turned out to be threetimes as large as the observed effect. Something deep in the Earth must be offsetting theeffect of the Himalaya. The crust of the Earth is lighter than its interior and floats.Under mountain ranges, the crust is thicker, and the crust floats higher. This balancingprocess is termed isostasy.

Mount Everest

One offshoot of the British mapping effort in India was the discovery of Mount Everest.With Nepal and Tibet forbidden to foreigners, the British could only survey the Himalayafrom afar. They picked six survey points and measured the directions and altitudes ofevery peak visible. Then they plotted all the lines of sight on a single map. Where manylines crossed was the true location of a peak.

One day the Indian assistant came into the Survey office and announced he had found thehighest mountain in the world. It was an apparently unremarkable peak but seemed low onlybecause it was far away. The peak was named Mount Everest after the director of the IndianSurvey.

The irony is that the British Survey, unlike many colonial officials, had insisted onretaining local place names. With Nepal and Tibet off-limits, the local name of the peakwas unknown. The peak is called Sagarmatha in Nepali and Qomolongma in Tibetan.

Answers

A ship's compass, mounted on a structure called a binnacle, has two large iron balls oneither side, mounted on an arm. The balls can be moved in and out to compensate for themagnetic fields of everything else on the ship. An object of known direction is sighted,and the balls adjusted until the compass reads the correct direction.

To magnetize lodestone, you need a powerful source of natural magnetic fields, say areally powerful electric current. Lightning. Even ordinary rocks can be magnetizednoticeably by lightning strikes because they have small amounts of magnetite in them.While doing field work in Ontario I once sat on a rocky knob and found all my compassazimuths were 10 degrees in error. I moved a few feet away and got correct readings.Mountain peaks that are struck repeatedly can throw compass needles 180 degrees off.

Essential Points

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Created 13 January 1998, Last Update 20 January 2020