The History of Early Dead Reckoning and Celestial Navigation:
Empirical Reality Versus Theory
Douglas T. Peck
The European Renaissance, centered in the Mediterranean, saw the first meaningful but
tenuous advance in the art (or science) of ocean navigation. Ocean navigation advanced
from theory to widespread practical use in the thirteenth, fourteenth, and fifteenth-century
when the magnetic compass progressed from a magnetized needle floating on a straw to
the 32 point compass in use during the Columbian period.
The basic form of navigation during this period was the simple and easily mastered deadreckoning, using the magnetic compass for direction, and an estimate of the distance sailed
plotted on a portolan chart to fix position. By the late fifteenth-century, dead-reckoning
navigation had been refined to the point that Columbus and other competent navigators
were making long ocean passages to the New World and return with skill and accuracy.
During this same period, celestial navigation, which in an earlier crude form pre-dated
dead- reckoning, was also being developed for marine navigation. Fixing one s position on
the face of the earth by reference to the heavenly bodies had been practiced by
mathematicians and cosmographers since ancient times. However, it was during the late
fifteenth and early sixteenth- century that an attempt was made to move celestial
observations out of the hands of the land- bound and learned mathematicians and
cosmographers and make it available for practical marine navigation.
Integration of this new, complicated, and developing marine celestial navigation into the
established and trusted dead-reckoning navigation produced arguments pro-and-con
between the learned cosmographers and the experienced, practical, and conservative
seamen and pilots concerning the true role and application of celestial observations to
ocean navigation of the period. These arguments and indeed the conduct of just the basic
dead-reckoning navigation, as well as the conduct and application of celestial
observations, were little understood by the historians and writers of the period. For this
reason the true picture of late fifteenth and early sixteenth-century navigation is filled with
misconceptions, distortions, and in some cases, patently unfounded fiction.
Much of what we know of early navigation comes from the extant sixteenth-century
writings of Columbus, Martin Cortes, Pedro de Medina, Amerigo Vespucci, Peter Martyr,
Richard Eden, William Bourne, and Richard Hakluyt. The most prominent twentieth
century writers on the subject are, D. W. Waters, Eva G. R. Taylor, and Samuel Elliot
Morison, who draw heavily from these early writers and allied early documents. It should
be noted that most of the sixteenth- century writers on navigation were land-bound
theoretical mathematicians, cosmographers, or independent writers with little or no
empirical experience in navigation at sea. And in like manner, most of the current widely
published writers who interpret these early documents and write on the history of early
navigation are also from the ranks of theoretical rather than experienced professional
navigators. This over-emphasis on theory versus practical application has produced an
undue acceptance of numerous misconceptions related to early navigation. This study
examines the writings of both the early sixteenth-century and later twentieth century
historians to identify these misconceptions and errors that have been introduced into the
written history of early navigation.
1
Each individual misconception is listed as a bold sub-heading followed by a dialectical
analysis and technical explanation of the source and reason for the particular
misconception..
The first misconception is that late fifteenth and early sixteenth-century deadreckoning navigation using the 32 point magnetic compass, was inherently inaccurate
and unsuited for the long ocean passages of the Columbian era, so celestial
navigation was required to supply that needed accuracy.
This misconception in current historiography was first voiced by the learned
cosmographers who were advisors to the kings of Portugal and Spain, the first of the
maritime nations to venture across the Ocean Sea. And this alleged essential use of
celestial navigation to augment what was considered inaccurate dead-reckoning navigation
has been strengthened by prominent and respected twentieth century writers. An example
of this is in the prolific writing of Eva G. R. Taylor, Emeritus Professor of Geography,
London University, and Honorary Member of the Royal Institute of Navigation, who
stated in her comments on William Bourne s A Regiment for the Sea:
During the reign of Henry VIII there was scarcely an Englishman to be found who was
skilled in the New [Celestial] Navigation , new because it made use of mathematics and
astronomy. Spanish pilots were employing it for their regular sailings to the New World,
and Portuguese pilots for reaching Brazil, India and the Far East (emphasis added). The
portion of this statement concerning the early Spanish and Portuguese pilot s use of the
New Celestial Navigation for navigation to the New World and the Far East is
categorically and historically untrue!
The Spanish and Portuguese pilots during this period were still accurately navigating to
their destination (and return) by dead-reckoning. The so-called New Navigation was not
navigation at all, but consisted of occasional celestial observations usually performed on
land, not by the pilots who were navigating the vessel by dead reckoning, but by learned
cosmographers who were sent along on the voyage to determine the latitude of the
destination. The latitude of the destination and prominent capes en-route were needed so
these geographical landmarks could be located on the master chart maintained by the
crown.
This master chart was not for navigation, but primarily for use by geographers and
cartographers to establish sovereignty rights to new discoveries. The Portolan charts used
by the pilots contained no latitude lines or notations. The pilots did not navigate or steer to
a latitude in degrees on a chart, but followed their dead reckoning sailing directions or
rutter which gave them the magnetic heading and distance from their departure point to
the destination.
2
A recent article by W. G. L. Randles in The Journal of Navigation, Vol. 51, Cambridge
University Press (1998), contains a comprehensive account of the performance and use of
celestial observations related to early Portuguese voyages to Africa and India. Randles
article is on the broad subject of nautical astronomy and shows that the primary purpose of
these early celestial observations, performed for the most part on land, was not for
navigation, but to correct the charts used by the navigators to show the correct relative
linear distances to and between their several destinations. Yet Randles article also contains
a misleading statement by an Italian passenger on a 1505 voyage who stated: The
Portuguese navigate by the altitude of the sun or by that of the Pole Star with the aid of an
astrolabe. The Portuguese on occasion did fix the latitude position of their destination or
a cape by limited celestial observations, but they navigated to that cape or destination by
their trusted dead reckoning.
Enhanced drawing of the Carta Pisana portolan navigational chart showing the milage scale (in circles) and
the method of portraying magnetic compass courses to the principal central and eastern Mediterranean
ports.
3
This Italian passenger, like so many modern historians, confused an occasional celestial
observation to obtain (or confirm) a geographical position as their basic navigation at sea.
An uninformed Italian passenger can hardly be considered an expert witness to describe
the navigation method in use by the Portuguese pilots.
One reason given for the alleged inaccuracy of early dead-reckoning is tied to the
unsupported notion that early magnetic compass s were inherently inaccurate. The flawed
and even naive reasoning in this instance is that the very configuration of the card (or face)
with only 32 points indexed instead of 360 degrees would introduce a mathematical builtin error of 5.6 degrees (one-half of the 11.25 degree space between index points). It is
unreasonable for a theoretical mathematician to assume that an experienced early pilot
could not adapt to the limitations of the 32 point compass with methods of extrapolation to
steer to any desired heading with accuracy. Even the modern compass in use by the
military services and the airlines does not contain 360 index points and the spacing
between index points is normally between 2 and 4 degrees apart. Applying this same
theoretical (but unrealistic) reasoning would condemn the modern compass now in use to
a built-in error of 1 to 2 degrees.
The commonly-held belief that dead-reckoning navigation was inaccurate and unsuited for
the long ocean passages during the Columbian period flies in the face of documented
historical fact. There is ample evidence to show that Mediterranean navigators developed
dead-reckoning to a fine art and accurate science well over two centuries before the
Columbian era. The thirty- two point compass was refined into a usable and accurate
marine instrument in Amalfi and subsequently adopted and used by the navigators of Pisa,
Genoa, and Venice.
The oldest extant maritime dead-reckoning chart (frequently referred to as a portolan
chart) is the Carta Pisana dated to about 1275 (see Figure 1). This chart derives its name
from the fact that it was discovered in the archives of Pisa, which along with Amalfi was
one of the principal ports of Italy before the rise of Genoa and Venice. The Carta Pisana
chart shows sixteen primary winds (magnetic compass courses) which cover the shorelines
of central and eastern Mediterranean. The chart also carries an identical East-West and
North-South scale for ease of pricking off distance with dividers, and thus provides the
essential elements for accurate dead-reckoning navigation (i.e. magnetic compass course
and distance from departure point to destination). This general pattern of a Mediterranean
pilot s portolan chart was adopted by Spain (quite possibly introduced by Columbus) and
continued in use for dead reckoning navigation well into the seventeenth-century. But
these portolan charts used by the pilot s for navigation were kept aboard the vessels or in
the hands of the pilots rather than being filed away in the archives in Seville so none have
survived.
The maps from Ptolemy s Geography from earlier times, well before development of
portolan charts, showed latitude and longitude data on the borders for use in scaling
distances based on the length of a degree. But the Carta Pisana chart and later portolan
charts, prepared by pilots for use in dead reckoning navigation, depended only on the
arbitrary scale of distance and compass courses on the chart, independent of and without
reference to latitude and longitude. The Spanish schematic world maps produced for the
crown (Padron Real) were not for navigation, lacked definitive and accurate shoreline
4
details, and were primarily for the use of geographers and cartographers to establish
sovereignty rights to new discoveries.
In his four voyages to the New World, Columbus followed Mediterranean practice and
navigated solely by dead-reckoning, and he wisely chose to ignore his few defective and
wildly inaccurate celestial observations. Using only dead reckoning, Columbus was able
to sail with accuracy to the islands and capes of his previous voyages and then with the
same unerring accuracy returned to his home port in Spain.
The historian Andres Bernaldez, a friend and confidant of Columbus, confirmed this
accuracy of dead-reckoning navigation of the period when he reported that: A good pilot
or master is not considered such if, in traveling over a great distance from land to land, out
in the open sea with no indication of any land, he is off by ten leagues even when the trip
is a thousand leagues long. The successful conduct of Columbus s four voyages provides
general prima- facie evidence of his competence in performing accurate dead-reckoning
navigation. But the detailed log of Columbus s first voyage (from Bartolome de Las Casas
summary) containing the recorded compass headings (not courses) and estimated distance
sailed (through the water, not over-the-bottom) for 136 different legs, in sailing two ocean
passages from a known departure point to a known destination, provides adequate
navigational data to arrive at a finite mathematical degree of accuracy for his deadreckoning navigation. In a 1991 scientifically controlled empirical reconstruction of the
voyage from the data in the log, it was categorically and mathematically determined that
Columbus s dead-reckoning for the two long passages (west-bound and return), had an
accuracy factor of 99.7 percent. A complete report of this scientific empirical
reconstruction of Columbus s voyage conducted by an experienced professional ocean
navigator is contained in, Peck, Douglas T., Cristoforo Colombo - God s Navigator,
Columbian Publishers, Columbus, WI, (1993), pp. 51-115. The navigational data from this
research was verified for accuracy and validity in an independent audit by Admiral
William Lemos, USN (ret), an experienced ocean navigator and authority on 15th and 16th
century seafaring and navigation and member of the President s Columbus Quincentennial
Commission. An abridged summary of the reconstruction was contained in, Re-thinking
the Columbus Landfall Problem, Terrae Incognitae, Vol. 28, (1996), pp. 12-35.
Another misconception is the erroneous belief that the early pilots were unaware of
and did not correct for the unknown magnetic variation on long voyages, therefore
the courses given in their rutters, and navigation logs were unreliable and
inaccurate.
The unknown magnetic variation had no effect whatsoever on the dead-reckoning
navigation performed by the early pilots! The reason for this is that they sailed a magnetic
heading to their destination (and return) rather than a true course as performed by the
modern navigator who has an accurate chart showing local magnetic variation and the true
geographical latitude and longitude of his destination. There is a mistaken belief that early
pilots needed the same information and data available to the modern navigator in order to
perform accurate dead- reckoning navigation.
The early pilot who discovered new lands reported the magnetic heading and distance to
reach that destination, and it is this magnetic heading (frequently mis-labeled a course)
5
that appeared in their sailing directions and rutters. It was also these uncorrected magnetic
headings from their rutters which they sailed and plotted on their charts that enabled them
to sail to that destination and return with accuracy. Columbus is mistakenly credited with
being the first to note the magnetic variation in the North Atlantic on his 1492 voyage.
Columbus only noted the 3 _ degree procession of Polaris and considered it of little import
since he followed the observation with the comment: .... it seems that the star [Polaris or
North Star] moves like the other stars, and the compasses always seek the truth [in this
case the truth is magnetic north] (emphasis added). Columbus at this time was in an area
with very little magnetic variation, but his comment has been mistakenly interpreted (or
misinterpreted) as indicating a large westerly variation.
The early Spanish pilots fully understood that only the magnetic headings from their
rutters were needed for accurate dead-reckoning which is why they so vehemently resisted
the efforts of the court cosmographers to include the inclined (oblique) latitude scale on
the western edge of the charts. This inclined latitude scale was introduced early in the
sixteenth-century because of the extreme westerly variation in the northern area of
Newfoundland reported by John Cabot and others who sailed in far northern waters.
The Spanish pilots argued (quite correctly) that the corrected latitudes disagreed with their
basic and proven magnetic headings that they knew would direct them across the Ocean
Sea to their destination and return with accuracy. This is an important point to
understanding early dead reckoning practice and methodology and is little understood by
many historians writing on the subject. For further reading on the subject, see: Winter,
Heinrich, The Pseudo-Labrador and the Oblique Meridian, Imago Mundi, Vol.
MCMXXXVII, (1937), pp. 61-73, and Jean Rotz s treatise on magnetic variation in his
Boke of Idrography, (1542), reproduced and edited by Helen Wallis, Oxford, (1981). The
argument between the Spanish pilots and the cosmographers over charts with the inclined
western latitude scale is fully discussed in, Lamb, Ursula, Science by Litigation : A
Cosmographic Feud, Terrae Incognitae, Vol. 1, #1, (1969), p. 54.
A frequently voiced misconception is that speed was computed mathematically by
recording the time a chip of wood took to pass from the bow to the stern of a vessel of
known length.
This completely unrealistic and unworkable procedure has been put forward by theoretical
mathematicians, with little seafaring and navigation experience, from early times to the
present. The reason for this is because the early theoretical mathematicians who wrote on
the subject did not believe that an experienced seaman could accurately estimate his speed
by just observing the action of the wake and feel of the ship. The experienced pilot would
have learned from years of experience how to judge their speed when sailing from points
of a known distance in a known time, and then could easily pass this expertise on to the
apprentice seamen who served under them for many years learning the trade. In the late
thirteenth-century the author of the Documenti d Amore pointed out: For every master and
pilot prided himself on knowing exactly how much way [speed] his ship was making. He
knew the ship, he considered the wind, he watched the sails, he watched the water. In fact,
it was a matter which just could not be explained to the landsman. (emphasis added).
Just consider the involved and impractical mathematical exercise the unlettered pilot must
go through to use this method of estimating speed. As an example, the pilot would be
6
compelled to calculate that if the wood chip, by his estimate (without a stop-watch), took
10 seconds to go 60 feet (the length of the vessel), then in one second the boat would go
six feet, and in one hour (3600 seconds) go 6 X 3600 = 21,600 feet, and since there is
6076 feet in a nautical mile then 21,600 divided by 6076 equals 3.5 knots or nautical miles
per hour. This complicated and impractical mathematical procedure was far beyond the
ability of the unlettered pilots, yet modern writers faithfully and erroneously report that
this unworkable method, or variations of it, was used by the early pilots to estimate their
speed.
Since Columbus s log of his 1492 discovery voyage contains different estimates of
distances reported by Columbus for his navigation and for that furnished to the
Spanish crew, and neither of the figures agree with the distance actually covered;
there is a mistaken belief that either Columbus erred in his reported distances or he
was keeping a secret log so only he could find his way back to the Indies.
This misconception can be explained by quoting from the referenced report of the 1991
research and reconstruction of Columbus s 1492 voyage: From about day 9 to day 27,
Columbus was carried along in distance by the North Equatorial Current and gained
between 7- 12 miles each day because of the westerly flowing current. Columbus was not
aware that he was gaining this induced 7-12 miles each day which explains why his actual
distance covered was greater than his estimate in the log. This simple and elementary
navigational fact, so easily understood by any trained and experienced navigator, is
misunderstood by most historians who come up with all manner of invalid and convoluted
explanations for that difference in the log. The unsupported explanations for this
difference range from Columbus gross inability to estimate his speed and distance, to
preposterous theories about how he was trying to conceal the truth from the Spanish pilots.
Much of the misinterpretation of the data in Columbus s log stems from the fact that
Columbian historians are unaware (or refuse to accept) that he was using his
Mediterranean (Genoese) mile of 2.67 nautical miles to the league for navigation rather
than the widely different Portuguese or Spanish data for the length of a mile.
The
2.67 nautical miles to the league control factor is based on the Genoese navigator
Columbus using the Mediterranean 5000 palm mile of 4060 feet to the nautical mile for
his navigation. James E. Kelley Jr., fully substantiated this mile factor as that used by
Columbus for his navigation in a paper contained in the, Proceedings of the First San
Salvador Conference, in 1986. Kelley s factor of 2.67 nautical mile to the league was
proven accurate when it was used in the 1991 empirical reconstruction of Columbus
voyage from the known departure point of Samana Cay, Hispaniola, to the known
destination of Santa Maria in the Azores. The 2.67 nautical mile factor was then used in
the empirical reconstruction of Columbus s voyage from the known departure point of
Hierra to the unknown landfall on Guanahani. A full report of this research which
established San Salvador as Guanahani, the landfall of Columbus is contained in, Peck,
Douglas T., Cristoforo Colombo - God s Navigator, Columbian Publishers, Columbus,
WI, (1993), pp. 51-115, and an abridged summary in, Terrae Incognitae, Vol. 28, (1996),
pp. 12-35. This well supported research has established that Columbus s detailed log is
accurate and easily understood by an experienced navigator with expertise in early dead
reckoning methodology.
7
The apocryphal myth of Prince Henry the Navigator s school of navigation at Sagre
and the myth of the superiority of early Portuguese navigators.
The general consensus pictures the Infante Prince Henry the Navigator assembling learned
Moorish, Genoese, and Spanish scholars at Sagres in the fifteenth-century to instruct the
Portuguese pilots in advanced ocean navigation. As a result, many less than erudite
historians mistakenly considered Portuguese pilots as leaders in early ocean navigation.
There is no valid evidence that this school for navigators ever existed. A crude circle of
stones on the barren windswept Sagres peninsula is pointed to as a compass rose related to
Prince Henry s school. This archaeological site has not been dated with authority to Prince
Henry s time, and circles of stones related to ancient religious rites are common
throughout southwestern Europe. Prince Henry was not interested in ocean navigation nor
were his organized voyages down the coast of Africa seeking a way to the Indies. The
astronomers Henry assembled did not instruct the Portuguese pilot s in celestial
navigation, but instead went along on the voyages only to establish the latitude of each
new discovery. This latitude was needed, not for navigation, but for insertion on the
master chart in Lisbon to establish Henry s ownership of the new trading port or colony. It
is a complete misreading of history to take a few random facts and conclude that Prince
Henry had organized a school to train Portuguese pilots in advanced navigation.
The school that actually instructed the Portuguese pilots in navigation was formed in
Lisbon in the previous century (1317) by the Portuguese monarch King Denis. Having no
skilled Portuguese navigators, King Denis commissioned the Genoese Manuele Pessagno
as Grand Admiral of the Navy for life to insure that the Portuguese navy would always
have twenty-two skilled Genoese sea captains to instruct the Portuguese pilots and to lead
the fleet when required.
This Genoese colony in Lisbon consisted not only of seamen and navigators, but skilled
cartographers that produced the world maps for the Portuguese crown that were derived
from exploration voyages. This little-known, but significant historical fact, is covered in
detail in the writings of Paolo Emilio Taviani and summarized in his, Christopher
Columbus - The Grand Design, translated by L. F. Farina, Orbis Publishing Limited,
London (1985). These cartographers (and Bartolome Colon may have been one) would
have benefitted in their trade from the latitudes that Prince Henry furnished for his African
and later offshore island colonies. The existence of latitude observations made on the
shore by cosmographers is no indication of the superiority of Portuguese pilots in celestial
navigation at sea. The Portuguese under the auspices of Prince Henry claimed to have
discovered Madeira and Porto Santo in 1419-20 and the Azores in 1427 and this fact has
influenced the unfounded view of the superiority of early Portuguese navigators.
Yet these offshore islands in the Atlantic were known and charted by Genoese navigators
over a century earlier than the Portuguese claims. The Canary Islands were discovered (or
re-discovered) by the Genoese navigator Lanzarotto Malocello in 1336. Following this
discovery, the Italian charts of the fourteenth-century show the Canaries, Madeira, Porto
Santo, and the Azores with the Genoese coat of arms prominently displayed.
The belief that the Portuguese were the leaders in ocean navigation and that Columbus
learned his navigation while in Portugal has been promoted primarily by prominent
Portuguese historians (Bensaude, Coutinho, Fontoura da Costa, and Cortesao).
The
prominent historians Eva G. R. Taylor in England and Miles H. Davidson in the USA
8
have agreed with this unsupported view in their published works, thus giving this
historical error a seeming legitimacy that it does not deserve. With the preponderance of
valid historical evidence showing that the Portuguese learned their navigation from the
Genoese, it is difficult to understand why the belief still exists that the experienced
Genoese navigator Columbus learned his navigation from the Portuguese pilots.
Another well established and widely published misconception is that the term
latitude sailing is synonymous with celestial navigation since it is erroneously
believed that latitude was maintained by constant reference to celestial observations.
With the advent of the magnetic compass, latitude sailing was performed in the North
Atlantic by sailing due west on a compass heading from a known departure point with a
known latitude. Columbus practiced latitude sailing on his first voyage by sailing a
compass heading due west from Gomera and Hierra when he believed his destination was
at that latitude. At his destination in the Bahamas he gave his position as due west of
Hierra and not in degrees of latitude from a celestial observation. John Cabot practiced
latitude sailing when he departed on a compass heading due west from Cabo Dursal
(Dursey Head) since he believed his sought-for destination lay at that latitude. He reported
his latitude in Newfoundland as due west of Cabo Dursal and not in degrees of latitude
from a celestial observation.
There is no indication that Cabot had either a quadrant or astrolabe or knew how to use
them, yet Samuel Eliot Morison in his, The European Discovery of America: The
Northern Voyages, (1971), adopted unfounded literary license and reported that: At a
quiet anchorage or ashore, he [Cabot] took a meridional altitude of the sun, and dawn and
evening sights on Polaris, working them out as the approximate latitude of Dursey Head,
Ireland, 51 degrees, 33 minutes N. Morison s description of this apocryphal celestial
observation reveals his confusion and inexperience with instruments used for sixteenthcentury celestial observations. It is the modern sextant that requires the use of a visible
horizon for star sights, thus necessitating an observation at dawn or early evening. Neither
the astrolabe or the quadrant require a visible horizon since they depend on gravity to
obtain their sidereal angle. And the weak Polaris is best sighted in the dark of night and is
barely visible or disappears at dawn or early evening. This unfounded fiction should be
ignored, however, Morison is generally regarded as an experienced seafarer and navigator
because he was given a captain s commission (later Admiral) in the USN Reserve for
writing the Naval history of WW II and earlier had somewhat followed Columbus s route
in a chartered yacht. Morison was a respected professor of history at Harvard and wellread in general library navigational knowledge, for which he should be commended.
However, his limited knowledge in practical celestial observations is revealed by this
error-filled comment on Cabot s alleged observation together with his improbable
assertion that Columbus, when anchored off Cuba, mistook the weak and unlikely star
Alfirk for the North Star.
Cartier and Frobisher also practiced latitude sailing, but there is no indication they
maintained their latitude at sea by celestial observations rather than maintaining a westerly
compass heading. Frobisher had tables of declination and instruments aboard furnished by
the investors of the enterprise and he was coached in their use by John Dee, but it is
doubtful they were ever used as Frobisher, speaking for himself and the other pilots,
9
confessed themselves not able to be scholars.
Thus, the latitude sailing performed by the early pilots was actually dead reckoning on a
magnetic course, and not a form of celestial navigation, as asserted (or inferred) by many
current writers on navigation.
The commonly held belief that the Norsemen performed latitude sailing and offshore
navigation by reference to the North Star, has no basis in extant historical evidence.
Long before the advent of the magnetic compass, a crude and inaccurate form of offshore
navigation was performed by the Norsemen (often mistakenly called Vikings), but their
navigation did not include latitude sailing by reference to the North Star. Morison is
responsible for much of the consensus that the Norsemen used the North Star for
navigation. In what can only be labeled as naive and unfounded fictional nonsense,
Morison asserts: The Norsemen managed navigation by what through the ages has been
called latitude sailing. Once having found the Faroes [Faeroes], Iceland, and Cape
Farewell of Greenland, the Norse navigators took the latitude of each place by crudely
measuring the angular height of the North Star - and you can do it with a notched stick.
The Norsemen had no concept of latitude and in their offshore navigation used only the
known seasonal winds, the temperature and characteristics of the sea, the appearance of
sea life with known habitats, the flight of migratory birds, the lead line when on the
continental shelf, and possibly the sun. A description of Norse navigation is contained in
the Icelandic sagas which are detailed accounts (over 2500 pages) of voyages made in the
eighth, ninth, and tenth centuries to points in Norway, Ireland, Iceland, Greenland and
Newfoundland. For a full discussion of offshore navigation of the Norsemen, see, Marcus,
G. J., Ocean Navigation of the Middle Ages: Northern Waters, University of Oxford Press,
Oxford (1954), and, Grenlands Historiske Mindesmaerker, Copenhagen, 1838-1848,
reprinted by Rosenkilde & Bagger, Copenhagen (1985), and, Thirslund, Soren, Sailing
Directions of the North Atlantic Viking Age (from about the year 860 to 1400), The
Journal of Navigation, Cambridge University Press, Vol. 30, #1, (1997).
The sailing directions in the Icelandic sagas contain only the name of the point of
departure, the name of the destination (given as an easily recognized high promontory),
the direction (given as one of sixteen cardinal points from north), and the distance
(expressed in sailing days ). The sailing directions also give a detailed description of en
route sea characteristics but there is no mention of the North Star to fix a position for
reasons that are well known to navigators of far northern latitudes. In the sailing season
between May and October there is too much light for the weak Polaris to be seen by the
naked eye. However, the Norse were familiar with Polaris which they called
Leitharstjaerna, but since it was only visible in their dark stormy winter nights, it
probably was of interest only to astrologers and priests and of no use to the ocean
navigator. There is evidence that the Icelandic seafarers possessed a navigational
instrument called a Solskuggefjol or Sun shadow board, a circular board with an upright
post in the center and floating in a bowl of water.
When sailing on an east or west heading, a measurement of the shadow of the Sun at noon
on successive days would indicate if the vessel had strayed north or south of the desired
course. But the discussion of offshore navigation in the Icelandic sagas indicates that the
10
well known seasonal winds were the primary directional factor used for navigation
(common also to early Mediterranean navigation) and there is no mention of use of the
Sun shadow board or any other sidereal measuring device. Thus the commonly held belief
that the early Norsemen used the North Star for offshore navigation (or latitude sailing)
has no merit.
Another common misconception is that the office of Pilot Major ( Piloto Mayor),
which was established soon after Columbus first voyage, gave instruction to Spanish
pilots who were then able to perform the New celestial navigation.
The Casa de Contratacion established the office of Pilot Major ( Piloto Mayor ) soon after
Columbus s discovery when it was realized that navigation to and from the New World
was a vital factor in success of the venture. Columbus was first offered the position of
Pilot Major but declined and continued his exploration. Peralonzo Nino was then
appointed as the first Pilot Major probably around 1496. The twenty-four year old
Peralonzo, who learned his limited dead- reckoning skills from Columbus on the first
voyage, was hardly qualified for the job so this was manifestly a political appointment
because his family owned the Santa Maria and was one of the principal supporters of the
enterprise. Amerigo Vespucci followed Nino as Pilot Major in 1508, and in the next few
decades, the office of Pilot Major passed from Vespucci to Juan de Solis, to Sebastian
Cabot, followed by Alonso de Chaves in 1552 which is the period covered by this study.
Historians are quick to assume that because instruction in navigation was ordered by the
crown that it was indeed carried out, and thus (without foundation) report this instruction
of the pilots as historical fact. The historical fact is the office of Pilot Major was slow in
growing into an effective instrument of government because the political appointees to the
office lacked the ability to give instruction in either dead-reckoning or celestial navigation.
This study will later show that two of the most prominent Pilot Major s, Amerigo
Vespucci and Sebastian Cabot, who held the office for the longest period of time, were
incompetent dilettantes who were incapable of giving instruction in either celestial
navigation or dead-reckoning. The pilots did receive instruction but it was at sea in the
time honored apprentice program (60% of Columbus s crew were apprentice seamen)
where they learned only dead-reckoning.
The over-blown and inaccurate picture of the effectiveness of the office of the Pilot Major
in producing Spanish pilots who were proficient in celestial navigation originated for the
most part with English writers rather than Spanish sources. D. W. Waters, in his, The Art
of Navigation (1958), reports this admiration of the English for Spanish navigation
expertise was understandable in that, in 1558 probably not one English seaman was
capable of navigating to the West Indies without the aid of Portuguese, French, or Spanish
pilots. It was in this environment that Stephen Borough, Chief Pilot of the Muscovy
Company and an agent for the Trinity Houses visited the office of the Pilot Major in
Seville in 1558. Speaking only to the officials in Seville who were responsible to the
crown for conduct of the office, he came away with a glowing report of how the Spanish
office of Pilot Major had produced manuals and instruments for celestial navigation and
instructed the Spanish pilots in their use. Borough brought back a copy of Martn Cortes s
Arte de Navegar where it was translated into English by Richard Eden. Eden was a
scholarly linguist and writer and not a trained and experienced navigator, although he
quickly attained a reputation as such because of his published translation of Cortes and
11
other plagiarized works on navigation. Eden restated the glowing reports of Borough
concerning the (alleged) celestial navigation expertise of Spanish pilots and asserted his
translation of Cortes was a manual of navigation designed from the start and written
throughout for the instruction and use of practical seamen. Neither of these claims were
true.
The contents of Cortes s manual is primarily devoted to construction of the new
navigational instruments (with little said about their use), but also contains some limited
tables of declinations. Cortes s tables were based on the Almagest of Claudius Ptolemy
(circa 150 AD) and while correcting some, inherited many of Ptolemy s errors. A simple
way to study the errors of Ptolemy s data is to compare his map with a modern map of the
Mediterranean and the significant errors become apparent.
William Bourne in 1574 wrote a manual of navigation, The Regiment for the Sea, based
largely on Eden s translation of Cortes, which was billed as a manual for the common
seaman. In commenting on Cortes s Arte de Navegar, Bourne stated that even the older
[experienced] men could not handle an astronomer s Ephemerides or work out the sun s
declination from his place in the Zodiac as Cortes apparently expected pilots to do. Bourne
asserted his book was written for the common sailor rather than for the educated scholar
and it was some improvement in that respect, but the fact is he was writing far above the
comprehension of the ordinary English sailor or pilot (i.e. Frobisher s comment).
Most modern historians base their description of the Spanish Office of Pilot Major on the
sixteenth-century writings of the secondary and poorly informed English works of Richard
Hakluyt and Richard Eden. Currently, the little-known published works of Ursula Lamb
related to the subject are the most unbiased and accurate accounts of the Office of Pilot
Major since they are based on contemporary Spanish sources. See, Lamb, Ursula, The
Cosmogaphies of Pedro de Medina, Estudios de Erudicion que le Ofrecen o Hispanistas,
Madrid, (1966); Science by Litigation, Terrae Incognitae, Vol. 1, #1, (1969), pp. 40-57;
The Spanish Cosmographic Juntas of the Sixteenth-Century, Terrae Incognitae, (1973),
pp. 51-63; A Navigator s Universe: The Libro de Cosmographia of !538, The University
of Chicago Press, Chicago, (1972).
The misconception by historians that the Spanish office of Pilot Major was effective in
instructing the early pilots in the new celestial navigation results largely from a mistaken
belief that conversion of a celestial sight to a fix on their chart required only a simple
procedure with reference to the tables of declination contained in their almanacs or
regiomontanous. Instead, the procedure required complicated computations in higher
mathematics and the regiomontanus did not contain instructions on how to use the tables.
Even today it requires five steps from four pre- computed tables in HO 249 and a current
(annually updated) nautical almanac, and still the procedure is prone to error unless
performed by a trained and experienced navigator using a calibrated and accurate sextant.
Unfortunately this inaccurate picture of Spanish accomplishments in early celestial
navigation, voiced by Borough, Eden, and Hakluyt, has been repeated without question by
modern historians so this misreading of history has been firmly set in current academic
and lay literature on the subject.
12
The continuing controversy over the true landfall of Columbus in the Bahamas and
the true landfall of Ponce de Leon on the shores of Florida.
Both Columbus and Ponce de Leon left detailed logs of their voyages giving accurate
navigational data that can be followed by a knowledgeable navigator to accurately trace
their track from the departure point to the destination. Yet historians in their study of these
logs have been unable to agree on their landfall sites and their conclusions vary hundreds
of miles from the actual landfall site clearly indicated in the logs. The basic reason for this
wide disagreement on the landfall sites is a misunderstanding and a misinterpretation of
the navigational data in the logs because the most widely published academic historians in
the discipline lack meaningful expertise in fifteenth and sixteenth-century navigation and
seafaring methodology. .
The location of the landfall of Columbus in the Bahamas has generated the most
controversy, in some cases more emotional than rational, spurred on by the recent
Columbus Quincentennial Celebration. This controversy started in the eighteenth-century
when Juan Bautista Munoz in writing the official history of Spain s overseas empire
named Watlings/San Salvador in the central Bahamas as the Indian island of Guanahani,
where Columbus first landed in the New World. Munoz was followed by a spate of
historians who named nine different islands ranging for hundreds of miles through the
Bahamas and Turks islands. These different views with the date and the island proposed
are as follows: -- Munoz (1779) Watlings/San Salvador; Navarrete (1825) Grand Turk;
Irving (1828) Cat Island; Gibbs (1846) Grand Turk; Becher (1856) Watlings/San
Salvador; Varnhagen (1864) Mayaguana; Fox (1880) Samana Cay; Murdock (1884) San
Salvador; McElroy (1941) San Salvador; Morison (1942) San Salvador; Gould (1943)
Conception Island; Verhoog (1947) South Caicos; Weems (1950) South Caicos; Link
(1958) South Caicos; Fuson (1961) South Caicos; Power (1983) Grand Turk; Molander
(1981) Egg Island; Fuson (1986) Grand Turk; Judge (1986) Samana Cay; Fuson (1987)
Samana Cay; Peck (1992) San Salvador; Mitchell (1992) Conception Island; Keegan
(1992) San Salvador; and Pickering (1994) Plana Cays.
All of these widely different views are based on interpretation of the navigational data in
the same source document, - Bartolome de Las Casas s summary of Columbus s log.
The reason for the widely different conclusions is not due to inaccurate data in
Columbus‘s log, but due to a misreading and misinterpretation of that data. And one of the
primary reasons that fuels the misinterpretation is the mind-set among historians that early
dead reckoning navigation was inherently inaccurate, therefore the logs of the navigators
were inaccurate.
13
Chart of Columbus s 1492 voyage: The perceived track, as plotted and recorded in the log, is shown as a
dotted line with an X at day s end.. The actual track over the bottom, as corrected for fifteenth-century
magnetic variation, Columbus s Genoese mile and nautical mile differential, and effect of the ocean
currents, is shown as a solid line with a dot at day s end. This chart graphically illustrates why historians
wrongly conclude that Columbus s log is inaccurate, since the uncorrected (or improperly corrected) track
plotted directly from the data in the log (dotted line) ends a considerable distance northeast of any possible
island landfall. When corrected for influencing factors, - unknown to Columbus, - the data in the log is then
revealed as accurate, and leads to San Salvador as the landfall island in his 1492 discovery voyage.
From Peck, Cristoforo Colombo - God s Navigator.
It is beyond the scope of this study to give a dialectic analysis of each proposed landfall
site and provide an argument to eliminate those with no merit and then an argument to
support the San Salvador site. But such a study does exist in available publications:
Cristoforo Colombo – God’s Navigator , (1993), and in Rethinking the Columbus
Landfall Problem, T e r r a e Incognitae, Vol. 28, (1996). The empirical reconstructed
track of Columbus which substantiates San Salvador as the landfall island, contained in
these publications, is graphically portrayed in Figure 2. The landfall and landing site of
Juan Ponce de Leon on the shore of Florida has produced a controversy similar to that of
the Columbus landfall and for the same reasons. Anton de Alaminos was Ponce de Leon s
pilot (navigator) and his navigational data for the voyage is contained in Antonio de
Herrera s account of the voyage. Herrera s account, which is the only source giving
substantial details of the voyage, is in his, Historia General de los Castellanos en las
Islasi Tierra Firma del Mar Oceano, published around 1601. There are several English
translations of Herrera s account available, but the latest and best of these is that by James
E. Kelley Jr. Kelley s work is from the original 1601 script rather than a later modern
Spanish publication, has the Spanish script in the text adjacent to the English translation,
and contains copious footnotes explaining troublesome parts of the script. See, Kelley,
James E. Jr., Juan Ponce de Leon s Discovery of Florida: Herrera s Narrative Revisited,
Revista de Historia de America, Instituto Panamericano de Geografia e Historia, Vol. III,
14
(1991).
Some scholars doubt the validity of the navigational data in Herrera s account, questioning
whether it was obtained directly from the original log. Herrera summarized and abridged
Ponce de Leon s log in the same manner that Bartolome de Las Casas summarized and
abridged Columbus s log. It is quite apparent from the content that both were done from
the original holograph document or a scribe s copy. Unfortunately, Herrera added
numerous comments that were based on knowledge obtained much later than 1513, and
were not part of the original log. However, these additions by Herrera are easily identified,
and when they are removed (or disregarded), the original log entries of compass headings,
times, distances, descriptions of landfalls, latitudes, identification of known islands with
Indian names, sea and weather conditions, — all of which are elements of a navigator s
log — come through with clarity.
The interpretation of this navigational data has suffered the same fate as the Columbus log
and produced controversy because the most prominent Florida historians lack meaningful
expertise in sixteenth-century navigation and seafaring. In this instance, one of the most
glaring errors that adversely influenced accurate determination of the track, was the
unfounded belief that Alaminos was capable of and used celestial navigation rather than
the prevalent and proven dead-reckoning. To a lesser degree than the Columbus problem,
but in the same manner, historians have named several sites for Ponce de Leon s landfall
that range for hundreds of miles along the coast of Florida and into southern Georgia.
These different views for the landfall are listed with the source, date, and location as
follows: -- Scisco (1913) Ponce de Leon Inlet; T. Frederick Davis (1935) St. Augustine;
Lawson (1946,1956) St. Augustine; Tio (1972) Ponce de Leon Inlet; Morison (1974)
Ponce de Leon Inlet; Sanz (1984) St Augustine; Weddle (1985) Ponce de Leon Inlet;
Kelley (1991) South of Cape Canaveral; Peck (1992, 1993) Melbourne Beach; Devereux
(1993) Ponce de Leon Inlet; Milanich (1996) offshore island, S. Georgia; and Fuson
(2000) Palm Coast.
The scope of this study is limited to a discussion of why these widely different landfall
sites exist. However, a comprehensive study that supports the Melbourne Beach site and
refutes the others is contained in several published books and papers on the subject. See,
Kelley, James E. Jr., Juan Ponce de Leon s Discovery of Florida: Herrera s Narrative
Revisited, Revista de Historia de America, Vol. III, (1991), p. 56; Peck, Douglas T.,
Reconstruction and Analysis of the 1513 Discovery Voyage of Juan Ponce de Leon,
The Florida Historical Quarterly, Vol. LXXI, #2, (1992), pp. 144-147; Gannon, Michael
V., The New History of Florida, University Press of Florida, Gainesville (1996), pp. 1720; Peck, Anatomy of an Historical Fantasy : The Ponce de Leon-Fountain of Youth
Legend, Revista de Historia de America, Numero 123, (1998), pp. 70-71; The National
Geographic Society s Annotated Map, The Explorers, (1998); Peck, The Depiction of
Florida on the early Conte Ottomano Freducci Map, The Portolan, Vol. 50, #1, pp. 24-27;
and, Peck, The Epic 1513 Exploration Voyage of Juan Ponce de Leon, Early Seafaring
Exploration Series, Vol. 2, #5, New World Explorers, Inc., Bradenton, FL (2002).
15
Annotated chart showing Ponce de Leon s track though the Bahamas from Puerto
Rico to the landing on Florida. From, Peck, Ponce de Leon and the Discovery of
Florida.
(1) March 3 - Departed San German off Puerto Rico on heading of northwest by north. (2) March 8 Anchored at El Viejo on Banks of Babueca after 3 _ days sail. (3) March 9 - Anchored at Caycos after an
easy day s sail. (4) March 10 - Anchored at Yaguna again after an easy day s sail.
(5) March 11-12 - Hove-to off Amaguayo after an overnight sail. (6) March 13 - Passed Manegua during
overnight sail. (7) March 14-25 - Anchored at Guanahani, provisioned and re-rigged the vessels. (8)
March 27 - Passed unidentified island (Eleuthera) on a heading of northwest. (9) March 29-30 - Hove-to
during storm, changed heading to west-northwest. (10) April 2 - Anchorage and landing on La Florida, at
28 degrees latitude, south of Cape
Canaveral near Melbourne Beach.
The reconstructed track of Ponce de Len s voyage contained and substantiated in these
several publications is shown in Figure 3. Note that the track of Ponce de Leon not only
confirms his landfall at Melbourne Beach, but identifies San Salvador as the Indian island
of Guanahani, the landfall of Columbus in the New World.
Another popular misconception is that Amerigo Vespucci was a learned
cosmographer and navigator and that was the reason for his appointment as Spain’s
Pilot Major.
16
Amerigo Vespucci was not a cosmographer, seaman, or navigator. He was a well educated
aristocrat from a leading Florentine family and spent his early years among the great and
near great of that city. He moved to Seville when almost forty as head of a banking and
ship chandlery business for the powerful commercial house of Lorenzo di Pier Francisco
de Medici.
Vespucci s first venture at sea was with Alonso de Hojeda s (Ojeda) 1499 exploration
voyage (he may have helped finance it) to the Caribbean as a gentleman volunteer (i.e.
paid passenger). In his published account of this voyage he pictured himself as captain and
navigator without mentioning Hojeda. Following this were two voyages to the coast of
Brazil with the respected Portuguese captain, Goncalo Coelho in 1501 and 1503 in which
he also pictured himself as the principal navigator and savior of the fleet. Details of these
voyages as well as a patently fictitious voyage of 1497 (for which there is no
documentation other than Vespucci s account) are primarily contained in two published
accounts, his Lettera in 1504, and his Mundus Novus circa 1505.
Vespucci s published account of his voyages (including the fictitious 1497 voyage)
contained detailed accounts of his alleged practice of celestial navigation and received
wide distribution throughout Europe, which readily earned him a reputation as one of the
leading navigators of the period. It was solely for this reason, and the fact that he was a
high-born favorite of the court, that he was given the political appointment as Pilot Major
in 1508. Queen Joanna instructed Vespucci shortly after his appointment as Pilot Major to
instruct the Spanish pilots in the new celestial navigation (no doubt on the advice of the
cosmographers in the court), but there is no record of this instruction ever taking place or
attempted. As documented in this study, Amerigo Vespucci and Sebastian Cabot, who
together held the office of Pilot Major for the longest period of time, were incompetent
dilettantes who were incapable of giving instruction in either dead-reckoning or celestial
navigation An examination of Vespucci s reported instances of performing celestial
navigation shows that he does not deserve his reputation as an expert navigator. In his
comprehensive research into the history of the early explorers, Morison devotes twentyfour pages in text and notes to refute the claim that Vespucci was a competent navigator.
Vespucci received an undeserved major boost in his reputation as an experienced
navigator with publication of Waldseemuller s 1507 book on cosmography in which he
lauded Vespucci s four voyages (including his fictitious 1497 voyage) and on one of his
maps accompanying the book, showed Vespucci in an inset suggesting that he discovered
the major shorelines from Brazil north to the eastern seaboard of the USA. Waldseemuller
later recanted his support of Vespucci as a discoverer, Peter Martyr who usually accepted
these tale tales by court favorites completely ignored him, and Bartolome de Las Casas
wrote a scathing repudiation of him as a seafarer, navigator, and discoverer of the shores
of North or South America. However, in spite of this repudiation of him by his peers,
Vespucci in the centuries that followed picked up advocates from some well known and
respected historians (i.e., Harrisse, Fiske, Varnhagen, Vignaud) none of whom possessed
expertise in seafaring and navigation. These historians supported their case for Vespucci
with irrational arguments, completely at odds with mathematical, navigational,
geophysical, and geographical reality, and yet current Vespucci advocates still cite these
sources to support their view.
17
Sebastian Cabot is pictured in most historical publications as a highly qualified
seafarer and navigator who was justly called the Father of English Navigation and
served with distinction as Spain s Pilot Major. None of these claims are true.
This view was popular among the courtiers and aristocracy of Europe during his lifetime
and is the view that still persists in popular literature today. However, a severe scrutiny of
extant source documents of the period reveals a far different picture. Sebastian Cabot was
a charismatic dilettante in the mold of Vespucci, who rode to fame on the coattails of his
father John Cabot. John Cabot was an Italian pilot (Giovanni Coboto), trained in Venice
and Genoa for long dead- reckoning ocean passages who was called by Henry VII to lead
the epic 1497 voyage to the New World because English pilots were experienced only in
coastal pilotage and short cape to cape navigation using the lead line to fix position.
John Cabot was hailed as a national hero for his 1497 voyage but he was lost without trace
on his follow-up 1498 voyage. Sebastian was only fourteen or fifteen years old at the time
of the first voyage (and there is some doubt that he was aboard) and he did not accompany
his father on the ill-fated 1498 voyage. Yet in the following years, Sebastian easily
inherited the fame of his father and was acclaimed throughout the courts of Europe as an
outstanding navigator.
Sebastian was inept and incompetent in both dead-reckoning and celestial navigation and
his reputation came solely from his own spurious braggadocio, helped along and given
authority by the writings of Peter Martyr and Richard Hakluyt. Martyr and Hakluyt had no
first-hand knowledge of Sebastian s alleged voyages and apparently took Sebastian s
accounts as historically true. They not only lauded him for his navigation expertise, but
without foundation credited him with the discovery and exploration of the entire eastern
seaboard of North America from Canada to Florida.
There are no extant examples of Sebastian s practice of celestial navigation at sea from
either his father s voyage or his one voyage to the River Plate (La Plata), because none are
reported. To verify his expertise as a celestial navigator we are confined solely to an
examination of his bold assertions that he was an expert in celestial navigation far ahead
of his fellow navigators. But strangely, this unfounded braggadocio of a popular and
flamboyant court favorite worked on the Spanish court for Sebastian as it had done for
Vespucci, and the Crown appointed him Pilot Major in 1518.
When confronted by Pedro de Medina and Alonso de Chavs (two of Spain s most
knowledgeable cosmographers) in a celebrated court case in 1544, Sebastian used his
argument by assertion to prove his scientific knowledge of celestial navigation by simply
stating when he had sailed to La Plata (as Captain-General of a fleet well supplied with
experienced masters and pilots) he had lost his instruments on the voyage and had made
new ones. In this same court action, Alonso de Chavs, the Cosmographer Major testified
that while Sebastian Cabot was Pilot Major, the Padron Real was not kept up to date and
the pilots had not been instructed in celestial navigation because Sebastian Cabot knew
nothing of regiments [declination computation] (emphasis added). Pedro de Medina was a
respected Spanish cosmographer and author of the widely distributed, Arte de Navegar,
and Alonso de Chaves was a learned cosmographer in Seville who later became Pilot
Major. The account of this court case is in Ursula Lamb s Science by Litigation : A
18
Cosmographic Feud, Terrae Incognitae, Vol. 1, #1, (1969)), pp. 40-57.
Suffering from a lack of knowledge to prove his expertise in celestial navigation,
Sebastian relied not only on bold assertion, but also Divine revelation. Richard Eden, a
long time friend of Sebastian, when speaking of a method of determining longitude in
William Bourne s A Regiment of the Sea, stated with misplaced conviction: Sebastian
Cabot on his death bed tolde me that he had knowledge thereon by Divine revelation, yet
so, that he myght not teach any man.
It is not clear where the pseudo title Father of English Navigation for Sebastian originated
but it was probably coined by Richard Eden, a long time friend and confidant. The title is
hardly appropriate for Sebastian and more properly should belong to William Borough
whose heroic attempts to institute a central office for navigation in London ultimately
resulted in England taking the lead in developing the refined instruments and accurate and
usable almanacs that much later made celestial observations practical as an adjunct to
dead-reckoning navigation at sea.
Conclusions
This study has noted the wide difference between untested theory and practical experience
that applies to both dead-reckoning and celestial navigation. Dead-reckoning remained the
basic and inherently accurate form of navigation in use for ocean passages well into the
nineteenth century. And navigation was not influenced to a significant degree by celestial
observations until the nineteenth and twentieth century, after introduction of John Davis s
reflecting backstaff, the forerunner of the modern sextant, together with improved,
accurate, and understandable pre- computed tables in the nautical almanacs and manuals.
A more significant improvement to the science of navigation in this early period was
provided by the vast improvement in Mercator projection charts which showed islands,
capes, inlets, and harbors in their true geographical latitude and longitude position,
together with accurate isogonic lines, which allowed correcting the magnetic heading
sailed in dead-reckoning, to a true geographical course. This significant improvement in
the charts in the late sixteenth and seventeenth-century was obtained for the most part by
celestial observations on land and geodetic triangulation surveys on land rather than the
uncertain celestial observations from navigators at sea. Contrary to widely accepted
beliefs concerning early navigation, pilots of the fifteenth, sixteenth, seventeenth and into
the eighteenth centuries, did not have usable almanacs or instruments, were unskilled in
celestial observations, and were navigating to their destinations by their proven and
accurate dead reckoning.
The sextants, tables of declination, and annually up-dated nautical almanacs for the former
so- called celestial navigation are now obsolete being replaced by a stationary satellite and
one small instrument called a GPS. Note that the GPS is not referred to as a form of
navigation. The initials GPS stands for Global Positioning System, and that is all the
satellite reading does, - it provides only a fix or position in latitude and longitude at the
moment it is read. However, within the GPS instrument there is a computer that records a
series of positions, and then by simple arithmetical dead reckoning, computes the speed,
19
course made good (as steered by use of a magnetic compass), and distance to the
destination as programmed. So in spite of our vast improvement in technology, dead
reckoning with use of a magnetic compass, is still the basic form of navigation, the main
difference being the computation (or reckoning) is now performed by a computer within
the modern GPS instrument instead of manually as before.
20