On this page, observations of various kinds will appear that are related to big history teaching as well as to big history
HOW DID EUROPEAN MARINERS CHART UNKNOWN COASTLINES ALL AROUND THE WORLD?
2017 (with later additions)
The European nautical expansion into the wider world starting in the 1450s CE led to an unprecedented
effort of mapping it, first of all its coastlines. Yet while a great deal is known about the early global map makers and their
products, such as Martin Waldseemüller, Abraham Ortelius, Gerardus Mercator, and many others, very little seems to be known about
how the data were obtained on which these maps were based.
How did those adventurous sailors take such measurements, most notably:
how did they chart the unknown coastlines that they encountered? Who were these mariners, and what did their data looked like? And
how did these data arrive at the map makers workshops?
Yet it seems to me that the question of how these data were obtained and what they
looked like is essential for understanding mapmaking during this period in time.
So how did these salty dogs do all of that?
For lack of scholarly studies we can only speculate. Yet some of my speculations seem to be in line with evidence that can be found
in contemporary images, which strengthens the impression that this may be a reasonable track to explore.
Determining reasonably accurate latitudes was not the biggest problem. Taking
celestial observations with quadrants on shore yielded a precision of a degree or less already at the time of Columbus, while
mariner’s astrolabes could yield a precision of about one degree at sea. But measuring longitudes accurately did remain a big problem,
especially onboard a sailing ship.
In combination with sailed distances and mapped coastlines this yielded the information
on which the first reasonably accurate maps of the Americas were based. Yet it seems to be unknown how exactly those coastlines were
mapped and what the resulting data looked like.
On board, however, none of these methods worked very well, because it was hard to keep
an eye on Jupiter and its satellites through a telescope on the deck of a moving ship, if visible at all (Jupiter does not always
appear in the sky at night), while suitable lunar eclipses happen only very sporadically.
As a result, measuring longitude on
the high seas remained a problem until reliable chronometers were invented in the middle of the eighteenth century, even though a
century earlier the method of measuring lunar distances
had already solved this problem to some extent. Yet also the moon is
not always visible in the sky. In consequence, much like the tracking of Jupiter's moons, the method of measuring lunar distances
was similarly limited.
While it remained unclear for a long time where exactly the unknown coastlines were situated
on the globe, for obvious reasons it was important to map them. Ashore, it is relatively easy to do so using the method of triangulation
proposed in 1533 CE by Dutch scholar Gemma Frisius
(1508-1555 CE), while teaching at Louvain University, now in Belgium.
the Spanish and Portuguese may have started doing so on land whenever feasible and judged necessary. That may have yielded excellent
coastlines, yet no data of such efforts seem to be available. This description
shows how the British sea captain and explorer James
Cook did it, much later, in the 1760s.
More likely than not, in the sixteenth and seventeenth centuries the opportunities for doing
so on land by the seafaring predecessors of captain Cook were often not sufficiently available, simply because there were often no
good places to go ashore or no pressing reasons or sufficient time to do so. So how did these mariners map such coastlines?
those days, the practical way of charting coastlines consisted of using triangulation from the deck of a ship while sailing along
the coast, by measuring a great number of horizontal angles between clearly recognizable points such as mountain tops, islands, inlets,
etc. This method is known as the running traverse, of which remarkable little information appears to be available on the Internet.
one knows the baseline, such as the distance covered by one's ship sailing along the coast, and also its positions during the
measurements, this can yield a reliable coastline chart. Coastlines charted in the sixteenth century with the aid of the running traverse
can sometimes be recognized on old maps
, since they show inlets as semi-circles (because these were not yet well known),
while markers used on the coastlines may also show up.
On land, triangulation works well, because it is possible to position
one’s instruments in stable ways on fixed points for longer periods of time. As a result, a high degree of accuracy can be obtained
with the aid of instruments that could measure precise angles. But how could such angles reliably be measured on a moving and shaking
ship, while the sailed distances could also be determined much less accurately?
Yet the ship’s movements make such observations a little difficult to do in
practice, because they may contain relatively large errors as a result of the ship's movements, and also because compass angles
cannot be read very precisely. The variation and deviation of the compass readings introduced further complications.
compasses may well have been used during early attempts at charting unknown coastlines, including by Columbus and those who followed
him, to obtain basic coordinates.
Quadrants and mariner’s astrolabes can also be used for this purpose to some extent, and may
have been used to do so as well. But they are far less handy, while also in such cases the precision must have left a lot to be desired
because of the ship’s movements as well as because of the problems of reading the instrument scales accurately.
So how may these
unknown seafaring explorers have performed their triangulation measurements, if that is what they did?
In 2014 CE, as part of
my experiments with replicas of ancient navigational instruments, I built a so-called cross-staff
. Such an instrument consists
of a wooden stick with markers on it, over which a perpendicularly mounted stick, called a vane, can slide.
Observing both ends
of the vane and lining it up with the objects to be measured by sliding the vane into the required position allows one to measure
the angle between those two objects, such as the altitude of the sun or of certain stars above the horizon.
Although the design was
(at least) centuries older, from about 1515 CE the cross-staff was introduced on board Portuguese ships, and soon also on Spanish
vessels, for navigational purposes, where it began to replace quadrants and mariner’s astrolabes (The Cross-Staff: History and Development
of a Navigational Instrument
by W.F.J. Mörzer Bruyns
, 1994, Walburg Pers, p.14). The cross-staff was a relatively
cheap instrument, while it yielded more accurate readings than its predecessors, which helps to explain its rapid introduction.
the 1730s CE onward, the cross-staff was, in its turn, replaced by octants, followed by sextants, because those instruments yielded
even more precise angle measurements. Sextants remained in general use among seafarers until the 1980s CE when satellite navigation
replaced them. But they are still in use as a back-up option in case the electronic technology fails.
While I was calibrating
my cross-staff replica in the spring of 2015 CE by measuring horizontal angles across the Amsterdam horizon as seen from my window
and comparing those values with the same angles taken with a Davis Mark 15 sextant
, I realized that, in contrast to my quadrant and
astrolabe replicas, the cross-staff was well suited for measuring horizontal angles, even on a moving ship.
So was the cross-staff
perhaps used for charting coastlines, I wondered, and was that perhaps another reason for its relatively rapid introduction among
the European mariners, simply because it yielded a quick, efficient, and relatively precise way of doing so?
How would I find
out? My searches on the Internet did not yield any analyses or references that could throw any light on this question. I then consulted
one of the world’s foremost experts on the cross-staff, the Dutch scholar Dr. W.F.J. Mörzer Bruyns, former curator of the Maritime
Museum Amsterdam, and author of the aforementioned excellent book Cross-Staff: History and Development of A Navigational Instrument
Dr. Mörzer Bruyns did not know either how such measurements had been obtained or whether the cross-staff had been used for such purposes.
His book did not yield any further data other than that the earliest reported use of the cross-staff had been for measuring angles
between stars, and between stars and the moon, so for measuring non-vertical angles, for which quadrants and astrolabes were less
I then started looking at contemporary pictures. Already in 2003 I had taken a picture of a gable stone on a house
on the Prins Hendrikkade in Amsterdam, probably dating from eighteenth century, which prominently shows a cross-staff
as a tool of navigation.
Furthermore, in 2014 CE, while being shown around in the Supreme Court in the Hague, to my great surprise
I saw a ceiling painting that even more prominently displays the cross-staff
. This piece of art called ‘Allegory of Seafaring,’ as
I later found out, probably dates from around 1680 CE and was made by Philip Tideman
from Hamburg (1657–1705 CE). Also Mörzer Bruyns’s
book Cross-staff contains such pictures
, most notably on the front cover.
All of that confirms the importance of the cross-staff
for contemporary seafaring. But it does not offer any conclusive evidence for its possible use while charting coastlines.
the spring of 2015 CE I was working on a presentation about the first wave of globalization, for which I had been using a picture
of the illustrious map makers Gerardus Mercator and Jodocus Hondius seated at a table in their office. I decided to give that picture
a closer look.
And what could be seen in this picture, to my great surprise? On top of the cabinet two cross-staffs are prominently
, each of them sitting next to a globe: a celestial globe on the left and a world globe on the right. Next to each of these
instruments a roll of paper can be seen, which appears to suggest that on those rolls the data had been recorded that were important
for mapping the heavens and the earth by using those instruments.
Of course this does not yet provide conclusive evidence. But
it does provide another hint that the hypothesis advanced here could be realistic. Much more research is needed to provide more clarity,
most notably in archives by perusing ancient mariner’s journals and logbooks.
Right now, this idea is no more than a hypothesis
about how such geographical observations may have been made, at least partially, always supplemented by compass readings from
time to time, one would assume.
Whatever the case may turn out to be, these coastal observations must have been made in one way
or the other. The question remains how this was done. One would expect that some traces of such measurements must still exist in the
If these ideas turn out to be correct, making replicas of those instruments and attempting to perform ancient measurements
may have helped to throw some fresh light onto what the mariners and map makers of old achieved while making their careful measurements
and engaging in equally careful scholarly interpretations.
Postscript: chart dividers
the Datema store I was told that both the US and British navies as well as Asian maritime businesses still use the curved chart dividers,
while the British merchant fleet and mariners from the entire European continent use the straight ones.
Like everything else
in the universe, both types of dividers have their pros and cons. The curved chart dividers can be handled more comfortably with one
hand, which is why they are designed like that, while the straight chart dividers can cover more distance. It is unknown to me how
this division among seafarers originated and has persisted, if this is indeed a correct view. In addition I was told that navigational
instructors in the Netherlands still tend to be very firm in their opinions about what the preferred dividers are.
The fact that
on the Mercator-Hondius picture both types of dividers are shown indicates that also at that time these two instruments already existed.
Perhaps the idea of the depiction was to convey that whatever chart dividers were preferred for whatever reasons, the resulting maps
were reliable. In other words, this may have represented an attempt to capture the entire market. It would be interesting to look
at other contemporary pictures and see what types of dividers were depicted.
There may well be many further details on that picture
that had specific meanings to those who drew it, that have now been lost. This may include the idea that this picture appears
to suggest, namely that these charts made by these illustrious map makers were produced with the greatest possible precision available
at the time, and that by buying them, the customers were assured to have acquired the latest and best available knowledge.
was actually not the case. Many of the latest and best coastal maps were carefully kept under wraps by the United East India Company
(VOC), who used them for navigation. These sea charts were not printed, but were instead drawn on parchment, which was considered
the most durable material for long oceanic voyages. As a result, many of these maps have been lost. Yet a few of them have survived
and can be seen at the National Maritime Museum Amsterdam
I do not know whether these intriguing little details have already
been noticed by scholars. I have not yet found any references to them, and only noticed them after starting to experiment
with chart dividers myself after having been informed about them by experienced sailors. Nothing surpasses trying out things
oneself, or so it seems to me, or learning from the practical experiences of competent others.