SHANE STEINKAMP'S BACKPACKING BASE CAMP
ADDITIONAL FIRE RESOURCES
LAWS OF NAVIGATION1. In order to properly navigate, you must know three things: Where you are, where you are going, and the route you should take. Given any two of the three, the third can be calculated.
A BRIEF HISTORY OF NAVIGATION
I have never before used a GPS unit. In order to fairly evaluate the Magellan SporTrak Topo GPS unit for Backpackgeartest.org, I felt it necessary to review my knowledge of Navigation and to educate myself in several areas. This education proved to be a journey in and of itself, taking me through familiar territory and then out into the unknown. I know quite a bit about how to navigate by both land and sea, but I decided to review the entire History of Navigation as well. This did not prove a brief task, and that walk through time lead to this short essay. I think that an appreciation of the subject is helpful in appreciating the experience of navigation, even if it may be of little use to actual application. You might, however, be able to amaze your friends with bits of useless trivia after reading this.
Well, then--our course is chosen--spread the sail-- Heave oft the lead, and mark the soundings well-- Look to the helm, good master--many a shoal Marks this stern coast, and rocks, where sits the Siren Who, like ambition, lures men to their ruin. - Sir Walter Scott from Kenilworth (ch. XVII, verses at head of chapter)
Navigation is one of the primary foundations of civilization, like agriculture, language, writing, philosophy, and science. Indeed, navigation is inclusively a skill, a knowledge, and a science that draws on many areas of human learning. To study the History of Navigation is to study the History of Humanity.
Navigation is about wayfinding, you can't treat it as separate because many other things run parallel with it. If you look at studies in wayfinding, everything from exhibit design to building the cathedrals, it's about creating a complete system. It's about looking at the whole. - Clement Mok
Human origins are contentious. Most researchers agree that there have been several major migrations out of Africa. Some hold that human populations in many regions evolved in parallel after Homo erectus left Africa around two million years ago. Others think that a wave of modern humans from Africa replaced all previous Eurasian populations perhaps as recently as 50,000 years ago. How did they find their way? Perhaps migration doesn't require navigation. Perhaps all migration requires is a curiosity of what lies over the next hill. I still seem to have that instinctive curiosity, and if you've managed to read this far, you probably do too. Returning home again after giving in to such curiosity, however, requires some method of successfully finding your way back - assuming that you want to find your way back - and in that simple fact we have the necessary mother of the invention of Navigation.
Yet the best pilots have need of mariners, besides sails, anchor and other tackle. - Ben Jonson - Discoveries--Illiteratus Princeps
Egyptian sea voyages are recorded in hieroglyphics dating back to 3200 BC. The first Egyptian boats were built from reeds lashed together to create a concave-shaped vessel. Around 2700 BC, the Egyptians began constructing wooden sailing ships made from Lebanese cedar. The crews of these early vessels must have used some form of navigation to successfully find their way, even if that was just following the shoreline.
The Epic of Gilgamesh is, perhaps, the oldest written story on Earth. It comes to us from Ancient Sumeria, and was originally written on 12 clay tablets in cunieform script. It is about the adventures of the historical King of Uruk (somewhere between 2750 and 2500 BCE). In the very first tablet we are told, "he went on a distant journey, pushing himself to exhaustion, but then was brought to peace." We are not told how Gilgamesh successfully found their way to distant lands and back, but it is obvious that he did so - being brought back to peace - and therefore knew and understood some method of navigation both by land and by sea.
The Egyptian nobleman Harkuf, who lived around 2300 BC during the 6th Egyptian dynasty, is thought to be the first documented explorer. He led expeditions up the Nile to the land of Yam (southern Nubia). Queen Hatshepsut reigned in Egypt between 1501 and 1479 BC. In 1492 BC she ordered an expedition to the ancient land of Punt (probably in the modern-day East African country of Somalia). After crossing 150 miles of desert from the Nile to the Red Sea, a fleet of ships sailed and rowed 1500 miles toward the Arabian Sea. They returned to Thebes using an early form of Celestial Navigation (navigating by the stars). Since paper was known in Egypt at the time, we can probably assume that maps and travel logs had their origins during this time. Keeping a travel diary on clay tablets doesn't seem feasible.
From 1000 BC to 800 AD the Polynesians nearly perfected naked eye Celestial Navigation, and used their astonishing navigational skills to find their way among the distant islands of the Pacific Ocean without the benefit of the instruments used by later sailors. They used their knowledge of the natural world to guide them on their voyages. The Polynesians had names for over 200 stars and knew exactly the time they rose and set, and how the celestial sky shifted through the seasons. They could figure out their latitude position by a system of "on-top" or zenith stars. For example, the star Sirius was directly "on top" of Tahiti so if a navigator saw that Sirius was directly above him, he knew he was in the same latitude as Tahiti. However, like everyone else in the world, they could not calculate longitude.
When the sky was overcast, the Polynesians had another navigational skill. Wave Navigation is the subtle skill of recognizing and reading various kinds of waves. They named each of these types, and navigators could distinguish between those caused by wind and those which bounced off of land. A navigator must be very skilled to detect these differences. Some used their sight, others used the touch of a hand or paddle, or the sensation of how the canoe was rocked by these distinct waves. They could literally feel distant lands in the water. The marvel of Polynesian Navigation doesn't end there, however. Another navigational technique was to follow the migratory path of sea birds. Sea birds go out to sea to feed in the morning and return to the islands at night. By observing the natural world around them and applying this knowledge to innovative methods of seafaring, the Polynesians were centuries ahead of other explorers in terms of finding their way.
While the Polynesians were approaching navigation from a naturalistic method, Western civilization was doing the same to a lesser degree. Around the time of Christ, the Greeks named eight different winds, while the Chinese devised a system of identifying 24 seasonal winds and measured them with vanes and kites. On early maps, you can find illustrations of human faces puffing their cheeks and blowing in different directions. These faces are not merely decoration, but symbolize the important use of winds as direction-markers.
The winds and waves are always on the side of the ablest navigators. - Edward Gibbon - Decline and Fall of the Roman Empire (ch. LXVIII)
The development of complex instruments also began in this time period. The Astrolabe came into being. The history of the astrolabe begins more than two thousand years ago. The principles of the astrolabe were known before 150 B.C., and true astrolabes were made before A.D. 400. The astrolabe was highly developed in the Islamic world by A.D. 800 and was introduced to Europe from Islamic Spain (Andalusia) in the early 12th century. The astrolabe continued to be the most popular astronomical instrument until about A.D. 1650, when it was replaced by more specialized and accurate instruments. Astrolabes are still appreciated for their unique capabilities and their value for astronomy education. While the astrolabe arose from the Science of Astronomy and isn't directly a navigational tool, it does provide much relevant data for solving navigational problems. Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions.
While the Astronomers were mapping the heavens, Cartography came into popular existence. The development of the Science of Geography was a boon to navigation, although it could be said that Geography was a natural child of navigation. Two of the most important geographers of the ancient world were Strabo and Ptolemy. Strabo (c. 64 BC – AD 20) was a Roman geographer who put together a massive collection of geographical research based on earlier writings and his own extensive travels. The concept of longitudes and latitudes goes back at least to Ptolemy. Ptolemy worked at the library in Alexandria, Egypt between AD 127 and 150. All 27 sheets of his world atlas from 150 AD have such lines drawn, together with a separate list of coordinates for all its named locations. The equator was on his atlas marked as the zeroth parallel (latitude) and the Canary Islands defined the zero meridian (longitude). This latter choice was quite arbitrary, and indicative of the coming difficulties in determining the longitude at sea. Before settling at Greenwich, 'prime meridians' were at times placed at the Azores, Cape Verde Islands, Rome, Copenhagen, Jerusalem, St. Petersburg, Pisa, Paris, Philadelphia and many other places as well.
By this time, between the Egyptians and Greeks, navigation had become sophisticated. Celestial Navigation was well known. Rough estimates of Polaris' height over the horizon, together with 'Dead Reckoning' (from 'Deduced Reckoning', estimating distances from course, currents, winds and speeds), and early cartography were in common use. Unfortunately, these methods did not always suffice to find the intended destinations, and innumerable marine disasters have been caused by navigational errors. To quote Robert Herrick, "What though the sea be calm? trust to the shore, Ships have been drown'd, where late they danc'd before."
Fu-Hsien was a Chinese Buddhist monk who, in 399 AD, began a journey in search of Buddhist manuscripts and religious teachings. He traveled across China, passing the Takla Makan desert, and entered India. On his return, he sailed through the Bay of Bengal to Ceylon, and then to Java before his final passage through the South China Sea. Once home he wrote a detailed description of the places and people he had seen in a book called the Fo-Kwe-Ki (Memoirs of Buddha Dominions).
As late as the Viking age (800-1100 AD), despite many several millennia of nearly global travel, the navigation of the open sea was still in its infancy. The Viking contribution to the Science of Navigation seems to be the observation and understanding of the migratory patterns of whales. The Vikings relied on the same naturalistic tools that the Polynesians had developed separately. Observations of the sun and North Star (Polaris), currents, winds, and migratory whales and birds were clues for direction. For locating their nearness to land they used the depth, smell, and taste of water, cumulus clouds, reflections on the sky, and land birds like the raven. They would release a raven from the ship to see if it could find land, then follow it. The Vikings put marks on their masts to view against a star. Later if the same star lined up with the mark, they would know they were along the same latitude.
In about 1040, a Chinese alchemist discovered a curious thing. The magnetic properties of lodestone (iron oxide) were soon demonstrated to the Emperor, and first magnetized needle was used by the Chinese around 1100 AD. The first compasses were simple chunks of loadstone (magnetite, a common iron ore) which tend to orient themselves in a fixed direction, when suspended freely (by a string, or floated in a container of water). Navigators would take an iron needle, rub its point on the lodestone and then place it in a bowl of water. The needle would point north. Later on, the needle was pivoted on a brass spike or mounted on a compass card which marked direction. The first person recorded to have used the compass as a navigational aid was Zheng He (1371-1435), from the Yunnan province in China, who made seven ocean voyages between 1405 and 1433. Arabic traders brought this device back to numerous Islamic countries, where knowing the direction of Mecca was an important part of prayer. From the Islamic world, the compass traveled to western Europe. The first European use of magnetic compasses for navigation occurred in the Mediteranean during the 12th century. Magnetic compasses remain to this date indispensable on all ships, and to many other people as well, if for nothing else than as a navigational back-up device.
Marco Polo was the most famous traveler of medieval Europe. For 24 years, beginning in 1271, the Italian merchant traveled east with his uncles to China, Mongolia, Afghanistan, Armenia, India, Burma and Sumatra. He became friends with the powerful Chinese emperor Kublai Khan, and brought back to his home in Venice many exotic animals, plants, jewels, and stories of the various people and places he had visited. Europeans learned that there was another civilization in Asia that was more advanced than their own. The book The Travels of Marco Polo or The Description of the World became a best-seller and the geography of Marco Polo began appearing on maps, inspiring future generations of explorers and navigators. The Age of Discovery had begun.
The Moroccan traveler Ibn Battuta outdid Marco Polo. Fom 1235 to 1355 he spent 30 years on the road and sea, reaching the equivalent of 44 modern countries and covering over 73,000 miles. Ibn Battuta was born in Tangiers, Morocco and was trained as an Islamic scholar and judge (qaid). In 1325 when he was twenty-one years old, he left his home to make his first hajj, the religious journey to the sacred city of Mecca. His book The Travels was read all over the Arabic-speaking world.
During the Ming dynasty, Zheng Ho led more than 60 Chinese ships, called junks, on four expeditions between 1405 and 1433 AD which sailed to the Philippines, Timor, India and around the west coast of Australia. His fleets traveled the Indian Ocean to the Cape of Good Hope, and up the east coast of Africa, stopping in Zanzibar, Kenya and Somalia and continued on to the Red Sea and the Bay of Bengal. The Chinese junks were far in advance of anything the Europeans had afloat, and Chinese navigators were skilled at using the compass and charts by this time.
Prince Henry the Navigator (1394-1460) of Portugal earned his nickname from the school for navigation he established at Sagres in Portugal. Shipbuilders experimented with different designs. Techniques learned from Jewish and Arabic navigators and astronomers were taught. In 1415, The Portuguese captured the Moroccan port of Ceuta and used it to launch expeditions towards the west coast of Africa. In 1445 Dinis Dias had rounded Cape Verde, and after that the Portuguese extended their voyages further down the coast and began capturing, enslaving and trading West Africans.
The mariner's astrolabe came into common use around 1480 AD, despite the fact that the Astrolabe had been around for centuries. The upper rim showed a marked scale of degrees. The quadrant also became a navigator's tool around this time. Sailors used it to measure the altitude of the sun to locate their latitude. The quadrant is a quarter circle or 90° arc with holes on one side. The navigator would line up Polaris, the Pole Star through the holes, then hang a plumb line straight down to determine the angle of Polaris to determine latitude. The latitude at the North Pole was 90° and the Equator was 0°.
In 1487 Bartolomeu Dias became the first European to round the Cape of Good Hope at the southern tip of Africa. Vasco da Gama continued the Portuguese's search for new trading ports when he rounded the Cape of Good Hope in 1497 and arrived in India in 1498. This established a new European trade route to the Indian Ocean.
Christopher Columbus The 15th century also saw the beginning of European exploration to the "New World". Christopher Columbus was inspired by Marco Polo's tales of Cathay (China) and Cipangu (Japan) and thought he could reach them and the East Indies by sailing through the Atlantic. Unfortunately, it was his lack of knowledge about longitude that caused his poor calculations. Columbus based his math on estimations of earlier geographers, and threw in some of his own approximations. The result was that he thought 2,278 miles separated Asia from the west of Europe; only a quarter of the actual distance.
We have ploughed the vast ocean in a fragile bark. [Lat., Nos fragili vastum ligno sulcavimus aequor.] - Ovid (Publius Ovidius Naso) - Epistoloe Ex Ponto (I, 14, 35)
By 1500, Portugal had a sea route to the Spice Islands, around the Cape of Good Hope. Like Columbus, Ferdinand Magellan thought he could find a westward route to these islands. He was a brave man, not just in his exploration of the world, but also his commentary on Science. He wrote, "The Church says that the earth is flat, but I know that it is round, for I have seen the shadow on the moon, and I have more faith in a shadow than in the Church." In 1519, Magellan set sail from Spain with five boats. He sailed through the strait at the tip of South America that now bears his name and into the Pacific Ocean. Although Magellan died during this journey, one ship managed to survive this voyage and return to Spain in 1522. This first sea voyage around the world took three difficult years. No one attempted to duplicate Magellan's efforts for over fifty years, until the Englishman Francis Drake completed a second voyage around the world in 1577. These journeys helped provide more accurate information about the size of the Earth and produce better globes and other navigational instruments.
Skill'd in the globe and sphere, he gravely stands, And, with his compass, measures seas and lands. - John Dryden - Sixth Satire of Juvenal (l. 760)
Between 1550 and 1600 the cross-staff came into common use by European navigators to help determine a vessel's latitude by making solar observations. A navigator would place one end of the cross-staff against his eye, and slide the horizontal stick along the staff until one end lined up with the horizon and the other end with the sun. A scale was written along the staff which provided the angle between the two. A similar tool was already in use by Arab navigators called a kamal. The kamal was a square table which had a string with knots threaded through it. Each knot represented a different port. The navigator would select the port he was trying to reach, and hold the knot in his teeth to tighten the string, while he he held the table to his eye. Latitude was found when the horizon was at the lower edge of the table and the Pole Star at the upper edge.
A big problem with the cross-staff was that it required squinting into the sun for long periods of time. The back-staff, invented around 1595, was an improved version of the cross-staff. The navigator could now stand with his back towards the sun and hold the back-staff vertically. He observed the horizon through a sight on the staff, and slid a cross-piece until the edge of its shadow met the sight.
In the 16th century, European explorers began seeking a sea route to China around North America - to the north! In 1576, Queen Elizabeth I of England sent Martin Frobisher on an expedition to find the Northwest Passage to China. He only made it to Baffin Island. Henry Hudson picked up the search in 1609 and set sail in a voyage paid for by the Dutch East India company. His ship encountered so much ice that his crew threatened to mutiny unless he turned back, so he sailed south and reached the island that became known as Manhattan. He sailed up the Hudson River (named after him) far enough to know that it was not the strait leading to China. On a second voyage in 1610, he discovered the Hudson Strait and Hudson Bay, but this time his crew did mutiny and Hudson, his son, and a few loyal men were cast adrift in a small boat did not survive. Despite a $50,000 reward offered by the British government in 1814 to whomever found the Northwest Passage, no one succeeded until 1906 when Norwegian sailor Roald Amundsen charted the route.
Despite all the advances in navigation through the centuries, there was still no reliable method for determining longitude. Latitude could be figured out by determining the angle of position from the Polaris, but Longitude was still a problem. During the 17th century, the quest for finding an accurate method of longitude became nearly frantic.
New scientific instruments were being developed. The telescope had been invented in 1608, and improved by Galileo. His astronomical discovery, the moons of Jupiter, became used as a means of determining longitude. Navigators knew that being able to keep track of time was important for finding longitude, but an accurate time piece had still not been developed. Other measurement methods were attempted, such as lunar-distance or magnetic variation, but none of these proved practical.
In 1675, Charles II of England sponsored an official quest for a longitude solution by establishing a Royal Observatory at Greenwich. The French Academie des Sciences narrowed the possibilities to the pendulum clock and the moons of Jupiter. Cassini provided the Academie with precise tables of the moons of Jupiter and used his observations to mark positions of latitude and longitude in France and Denmark. The Dutch scientist Christiaan Huygens came to the Academie in 1666, and shortly after tested his pendulum clock in a trial at sea. However, no matter how protected his clock was, rough waves and ship motion prevented it from maintaining accurate time.
At the British Royal Academy, Robert Hooke experimented with a spring-driven marine pendulum clock and made improvements, but his clocks were still inconsistent. Ironically, Hooke doubted that there would be much profit in finding longitude at sea and wrote "no king or state would pay a farthing for it". The Longitude Act of 1714 proved him wrong. The famous British astronomer Edmond Halley also began to seriously study the longitude problem in 1694. Although he believed strongly in a lunar-distance method of calculating longitude, he became a great supporter of time piece devices.
The lack of an accurate, reliable, and practical method of determining longitude had serious consequences. Maritime disasters were numerous, and a major tragedy occurred in 1707 when two thousand men perished in a shipwreck off Scilly Island. This incident spurred the British government to establish The Longitude Act of 1714.
The British government consulted leading scientists: Sir Isaac Newton, Edmund Halley, and Robert Hooke. Newton didn't think any of the current methods for calculating longitude could work. Telescopes would be too long and a ship's motion too rough to accurately use Jupiter's satellites. Research of the moon was not advanced enough for the lunar-distance method. An accurate timekeeper would be the ideal answer, but ship motion, changing temperature, and other environmental factors overwhelmed the development of a reliable, seaworthy clock.
As an aside, Isaac Newton becomes very important in this story later on. He explained the workings of the universe through mathematics. He formulated laws of motion, gravitation, and planetary orbits.
Britain was desperate for a solution, and Parliament established an official Board of Longitude and offered a prize of 20,000 pounds (several millions of dollars today) to whomever could come up with a method for determining longitude within a distance of 30 nautical miles during a voyage from England to the West Indies. A marine timekeeper would have to be accurate to within two minutes for the outward journey. Given the state of clock-making at the time, this seemed nearly impossible.
Somewhere around this point in the timeline, after eons of superstitious imaginations about electricity, Ben Franklin figured out that static electricity and lightening were the same. His correct understanding of the nature of electricity paved the way for the future - and that was a future full of innovations for Navigation.
John Hadley invented a new quadrant in 1731. Hadley's quadrant, also called an octant, had an arc which measured one-eight of a circle and two mirrors which allowed the Sun (or another star) and the sea horizon to be seen simultaneously. This allowed for much more accurate measurements at sea and easier observations of the lunar-distance method, but this still had disadvantages.
Several other, less promising methods were proposed. Placing light-ships at known strategic locations, for instance, to send up at various intervals a rocket that exploded brightly and would be visible at night for up to 100 miles, providing travelers within that range a time signal. Alternatively, mapping the vertical inclination of the earth's magnetic field was suggested. Lines of equal inclination would generally intersect the lines of constant latitude (or the angle could be mapped), thus together with the latitude providing complete positional information. However, not only does the earth's magnetic field change slowly with time, it can also fluctuate with solar activities.
John Harrison (1693-1776) thought he could create an accurate timepiece, and spent nearly 50 years proving himself right. His accurate timepiece is called a chronometer, from the Greek words for time (chrono) and measure (metron). The chronometer - a small, accurate clock - was designed to be insensitive to motions and changes in temperature, humidity and gravity. This became the winner in the longitude competition. Harrison produced a series of increasingly accurate chronometers, culminating in 1760 with the pocket-sized "H-4". On its first sea trial - UK to Jamaica, arriving in January 1762 - it lost only 5 seconds. This corresponds to an error of only 2 km after 81 days at sea. An error of about one minute or 24 km could have been expected; and even that would have been a vast improvement over other methods. By 1780, chronometers were starting to come into wide use throughout the British and other navies.
The quadrant was further refined by John Bird who invented the sextant in 1757. The Age of Enlightenment continued to provide for the technology of navigation. Navigation benefited greatly from many associated fields that at first glance seem to have nothing at all to do with navigation.
Soon shall thy arm, unconquered steam, afar Drag the slow barge, or drive the rapid car; Or on wide waving wings expanded bear The flying chariot through the fields of air. - Erasmus Darwin from The Botanic Garden (pt. I, 1, 289)
The electric motor was invented by Michael Farady. Faraday set out to show that electrical energy could be converted into mechanical energy. Faraday did this by holding a piece of wire above a bowl of mercury. A magnet was put upright in the bowl. The wire was connected to the battery. The bowl began to rotate. The first motor able to produce work was build by Joseph Henry in 1830. By the year 1840, motors were powering machinery.
C.A. Bohnenberger is generally credited with the first recorded construction of a gyroscope in 1810. Jean Bernard Léon Foucault (of Pendulum fame) first conceived of the gyro as an inertial reference in 1851. Foucalt is responsible for giving the name gyroscope to a wheel or rotor mounted in gimbal rings; a set of rings that permit the rotor to turn freely in any direction. Foucault named his gyroscope in 1852. In 1890, one other event was to allow the practical application of the gyrocompass; the development of the first electrically driven gyroscope by G. M. Hopkins. The gyroscope went quickly from a child's toy to a tool of science for three reasons. These were the increasing use of steel in ships which then brought about the second need; to overcome the unreliability of the magnetic compass within a steel ship, and finally, the great powers were preparing to conduct underwater warfare - in steel hull ships. In this age of the Edison's, Bell's and Wright brothers, two further inventors, one on either side of the Atlantic, sought solutions to these problems.
James Clerk Maxwell was born in Scotland in 1831. He is generally considered the greatest theoretical physicist of the 1800s, if not the century's most important scientist - but few people have even heard his name outside college physics courses. He combined a rigorous mathematical ability with great insight into the nature of science. This ability enabled him to make brilliant advances in the two most important areas of physics at that time (electromagnetism and a kinetic theory of gases), in astronomy, and in biology as well. It has been noted that Maxwell was probably the first geek.
Maxwell is best known for his work on the connection between light, electricity, magnetism, and electromagnetic waves (traveling waves of energy). "Maxwell's Equations" are the group of four equations that revolutionized the way we understood electricity, magnetism, and light. This simple group of equations, together with the definitions of the quantities used in them and auxiliary relations defining material properties, fully describe classical electromagnetism. He discovered that light consists of electromagnetic waves. He not only explained how electricity and magnetism are really electromagnetism, but also paved the way for the discovery and application of the whole spectrum of electromagnetic radiation that has characterized modern physics. Physicists now know that this spectrum also includes radio, infrared, ultraviolet, and X-ray waves, to name a few.
Dr. H. Anschutz of Germany and Elmer Sperry both built on the properties of the gyroscope; stability and precession. A gyroscope will always point to a fixed point in space if left undisturbed. If force is exerted upon it, it will react at right angles to the force applied. This characteristic of a gyro combined with other elements of precession, pendulocity and damping will allow the gyro to settle toward true north. In 1908 Dr. Anschutz patented the first north seeking gyrocompass with the United Kingdom's Patent Office (Patent Number 10382/08). That same year, Elmer Sperry invented and introduced the first ballistic gyrocompass, which included vertical damping (his device was subsequently patented with the British in 1911 - Patent Number 15669/11). Both of these first devices were of the single pendulum type. Gyro-compasses work by a unique principle - a suitably suspended rapidly rotating disc will keep its axis aligned with that of the earth. These compasses will always point to true north, and are insensitive to variations in the magnetic field (which can be due to geological anomalies or solar activity).
In 1911 the first Sperry gyro (Unit Number 100) was installed aboard the Old Dominion Line PRINCESS ANNE for a trial run from New York to Hampton Roads, Virginia. Upon completing this trial the unit was brought back to New York and installed aboard the U.S.S. DELAWARE. Although far more complicated than magnetic compasses, they are now used in most larger ships and aircraft, often in connection with 'inertial guidance' devices that compute changes in positions from sensed accelerations.
The gears of science were grinding more quickly than they ever had before, however, and even the amazing gyrocompass would soon be eclipsed - by radio.
In 1895, the lightning-recording antenna was invented by Aleksandr S. Popov. In 1895, the first experimental transmission of wireless signals was carried out by Guglielmo Marconi near Bologna, Italy. On June 2, 1896, a patent for a system of wireless communication was filed in England by Guglielmo Marconi, and Marconi later transmitted and received Morse code signals over a 3 km distance. A 42 km link was established between two cruisers equipped with Ducretet-Popov devices in France in 1899. In 1899, a wireless transmission was made across the English Channel from Dover to Wimereux by Marconi. The age of radio had arrived. Navigation quickly adopted this new and important science to its own ends.This cannot be understated. Maxwell's equations show that a rapidly varying electric field ought to generate electromagnetic waves. In 1888 the German physicist Heinrich Hertz did the experiment and found that he had generated a new kind of radiation; radio waves. Seven years later, British scientists in Cambridge transmitted radio signals over a distance of a kilometer. By 1901, Guglielmo Marconi of Italy was using radio waves to communicate across the Atlantic ocean. The linking-up of the modern world economically, culturally, and politically by broadcast towers, microwave relays, and communication satellites traces directly back to Maxwell's equations.
The first radio-based navigation technique amounted to determining the direction to a known transmitter by rotating a direction-sensitive antenna. Much higher precision was offered by a series of systems known as OMEGA, DECCA, GEE and LORAN (long range navigation). These were developed around the time of World War II. By timing the difference in arrivals of radio signals from a 'master' and a 'slave' transmitter (which re-transmitted the master signal the moment it received it), a ship could locate itself along a specific curve (in the 2-D plane case, a hyperbola). By also receiving signals from another transmitter pair, the ship could determine its location from the intersections of the two curves. This system gave a typical accuracy of around 1 km and a useful range of about 1000 km at daytime, and about double that at night. Both allied and enemy ships and airplanes used ground-based radio-navigation systems as the technology advanced.
A few ground-based radio-navigation systems are still in use today. One drawback of using radio waves generated on the ground is that you must choose between a system that is very accurate but doesn't cover a wide area, or one that covers a wide area but is not very accurate. High-frequency radio waves (like UHF TV) can provide accurate position location but can only be picked up in a small, localized area. Lower frequency radio waves (like AM radio) can cover a larger area, but are not a good yardstick to tell you exactly where you are.
To detail all the innovations in radio, radar, astrophysics, cartography, the space program, and all the other sciences beneficial to navigation would take many volumes. Indeed, whole books are dedicated to the subject. At this point it is necessary to skip ahead a bit and examine the latest technology available for navigation - the Global Positioning System. Scientists decided that the only way to provide accurate coverage for the entire world was to place high-frequency radio transmitters in space. A transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area and still overcome much of the "noise" encountered on the way to the ground.
The Global Positioning System (GPS) is the only system today able to show you your exact position on the Earth anytime, in any weather, anywhere - in theory, and very often in practice. (It should be noted that the Soviets have a parallel system (GLONASS), but here we will talk about the American system.) 24 GPS satellites orbit the Earth at an altitude of 11,000 nautical miles. They are continuously monitored by worldwide ground stations. The satellites transmit signals that can be detected by anyone with a GPS receiver. Using the receiver, you can determine your location - and several other things useful for navigation as well, like the exact time. The GPS system has 3 parts: the space segment, the user segment, and the control segment. The space segment consists of 24 satellites, each in its own orbit. The user segment consists of receivers, which you can hold in your hand or mount in your car, boat, or airplane. The control segment consists of five ground stations that make sure the satellites are working properly. The GPS satellites each take 12 hours to orbit the Earth, and each is equipped with an atomic clock ( that keeps accurate time to within three nanoseconds - that's 0.000000003, or three billionths, of a second) to let it broadcast signals coupled with a precise time component. The cesium or rubidium clocks in the GPS satellites operate at 10.22999999545 MHz rather than the nominal 10.23 MHz to compensate for both the special relativity effect of a moving source and the general relativity effect of operating from a point of higher gravitational potential. The master clock at the GPS control center near Colorado Springs is set to run 16 ns a day fast to compensate for its location 1830 m above sea level.
The ground unit receives the satellite signal, which travels at the speed of light as proved by Maxwell. Still, the signal takes a measurable amount of time to reach the receiver. The difference between the time the signal is sent and the time it is received, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite. To measure precise latitude, longitude, and altitude, the receiver measures the time it took for the signals from four (or more) separate satellites to get to the receiver. They are positioned so that any receiver can resolve signals from six of them nearly 100 percent of the time at any point on Earth. That many signals are needed to get the best position. Satellites are equipped with very precise clocks
The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block I. From 1989 to 1993, 23 production satellites, called Block II, were launched. The launch of the 24th satellite in 1994 completed the system - which had a 12 billion dollar price tag.
The fact that both systems (American and Soviet) now are available to the
general public, without any charge, is almost as impressive as their
technical capabilities. With low cost handheld receivers, anyone can now
determine his/her position to within just a few meters at any time, in any
weather, at any point on earth. With the best and more expensive receiving
equipment available, that accuracy can be improved to an amazing 1 mm both
horizontally and vertically. Of course, a hiker or backpacker doesn't
need that kind of accuracy, so trading a little accuracy for portability is
desirable.
The hand-held units distributed to U.S. armed forces personnel during the
Persian Gulf war weighed 28 ounces. The lightest available units today
weigh less than four ounces - including batteries. GPS watches
are now available. The technology will only get better.
And as great seamen, using all their wealth And skills in Neptune's deep invisible paths, In tall ships richly built and ribbed with brass, To put a girdle round about the world. - George Chapman - Bussy d'Ambois (act I, sc. I, l. 20)
