The Wandering Cardinal Points & Digital Heritage March 21st

Photo  by Jordan Ladikos on Unsplash of a weather vane showing the cardinal points
Photo by Jordan Ladikos on Unsplash

This post was originally part of the Equinox Post but it was too long and I have moved the section on the cardinal points of the compass to here.

So, Spring has sprung. At the Equinox the sun now rises due East, and sets due West. The rising and setting points vary throughout the year, further North each day as we move to Summer Solstice, and further South as Winter Solstice approaches. Dawn and Dusk vary accordingly. The only fixed point in the Sun’s journey (as seen from Earth) is Noon. Every day, the Sun is at it highest point at Noon. And this is the definition of South, something that can be seen and measured. The Sun never strays into the North so the North is cold, remote, more mysterious, unknowable almost, except that it is defined by the opposite direction to South.

To my mind, it makes South/Noon very special. At Stonehenge, there are two exits. The biggest is aligned to the Midsummer Sunrise and Midwinter Sunset direction, but there is a smaller second entrance and this aligned due South. There is also a uniquely small standing stone in the main circle of Sarsens, and there was some sort of corridor heading South through the mysterious wooden phase which precedent the stone Stonehenge. So, we can be sure Noon\South was important at Stonehenge.

Sketch of Stonehenge showing the smallest Sarsen stone to the North of the Southern Entrance

Noon, derived from ‘nona hora’ in Latin and is ‘one of the seven fixed prayer times in traditional Christian denominations.’ (Wikipedia)

Strangely, North, somehow, has come to be the principal direction, the one that is shown on all decent maps, and the one that people of my generation and hemisphere think of as being ‘up’. The Google generation sees things differently. You have to fight with Google Maps to get it to put North at the top of the map, and all over Britain, tourist maps on walls or plinths, increasingly show up as being the way you are looking and nothing to do with North. My children mock me when I say ‘You come out of the Tube station and you turn up the High street Northwards.’ Their view of maps is completely relational – you turn left out of the tube station, you walk past the M&S. you cross the road and walk along the park. They do not see any reason to know where the cardinal points are. Although I see this as being part of the Decline of the West, and ‘things were better in my day’, it is simply returning to the way maps were produced in the past.

Representation of a Roman Map with the top being roughly East.
Representation of a Roman Map with the top being roughly East.

The four points of the Compass are called the cardinal points: “chief, pivotal,” early 14c., from Latin cardinalis “principal, chief, essential,” (online etymological dictionary).

Of course, there is another version of the cardinal points: the magnetic cardinal points. The magnetic cardinal points wanders over time and does not coincide with geographic north. In recent times they are close enough, but in the past there have been huge variations and occasionally the earth has had geomagnetic reversals when the north pole has pointed in different directions, including southwards. The last one was 780,000 years ago, and they take place on average very roughly every 500,000 years. The magnetic pole is caused by the molten iron in the earth’s core and mantle, which creates a dipole. Fluctuations in the dynamo flow of the molten iron cause occasional reverses. The science is very complicated and, even now, not entirely understood. Is it a random consequence of flow dynamics? Or do external events, like sinking continents, or meteor strikes cause the reversal? Of course, since the first use of compasses for navigation in the 11th/12th Centuries,  the magnetic pole hasn’t wandered enough to be of concern to navigation. It has wondered a few hundred miles of over the last 500 years but is speeding up, from 9km a year to 52km (since 1970).

Cavit – Own work Observed pole positions taken from Newitt et al., “Location of the North Magnetic Pole in April 2007“, Earth Planets Space, 61, 703–710, 2009 Modelled pole positions taken from the National Geophysical Data Center, “Wandering of the Geomagnetic Poles” Map created with GMT Wiipedia CC BY 4.0

My first proper job after university was as a technician then research assistant at Oxford University studying these phenomena. I say ‘proper’ because when I left University, I became an itinerant archaeologist, digging in Switzerland, Northampton, East Anglia and Nottingham before I got the job at the Research Laboratory for Archaeology and the History of Art, Keble College, Oxford.

I worked for Dr. Mike Barbetti who was an expert on the wanderings of the Magnetic Pole. His interest was firstly in the pure science of the subject, but he was keen to explore the applied uses of the science to Archaeology as well. So, after being appointed as a Research Fellow at Oxford, he set up an epic journey from his native Australia to Oxford that went via some of the iconic sites of Palaeolithic Archaeology, such as Olduvai Gorge, Tanzania, site of excavations by Mary and Louis Leakey.

In order to plot the movements of the magnetic north, scientists needed dated samples, and early human sites provided dated sites over a long timespan. Also, archaeomagnetism, as the discipline became known, offered the possibility of dating sites. Another application was to determine whether deposits were fired or not. One of the sites Mike sampled was a candidate for the first evidence of fire in human existence. But was the scorched earth actually scorched rather than just discoloured?

As I said, Mike’s interest was discovering how the magnetic field of the earth changed over time, and, more importantly, what was the mechanism. He shipped back to Oxford samples of soil cast in Plaster of Paris. My job was to cut the samples up and to measure the strength and direction of the magnetic field in the samples. I cut them up with an electric saw in a shed in the backyard of the Laboratory, and then we used a mini-computer to measure the direction and intensity of the magnetic field in the samples.

Soil contains particles of iron, and they align randomly, so a sample of soil has a low magnetic intensity and a random direction of magnetic field. But once heated up, the iron particles align to the current direction of the magnetic pole and its intensity is proportional to the intensity of the Earth’s magnetic field. These measurements provide a method of plotting the changes of the magnetic field over time. And from these data, models could be constructed explaining how the iron in the earth’s core worked as a giant magnet.

We could, therefore, tell if a sample of soil had been heated by fire. Once we had built a reference curve for the movements of the direction of the magnetic pole and the changing intensity of the magnetic pole we might be able to develop another dating method to rival radio carbon, thermoluminescence, and tree ring dating, all of which were being developed at the Research Laboratory in Oxford.

Having got the results, I then typed them up onto machine-readable cards, took them to the Oxford University Computer Centre with a copy on cards of the programme written in Fortran, and gave them to the Computing Staff. They were run through the Centre’s mainframe computer which was probably an IBM or ICL computer, and 24 hours later I received a print-out to proofread. When I located mistakes, I ran an editing run of punched cards, essentially instructing the computer: ‘on card two replace 2.5 with 2.6, and run the programme again’. I would pick up the results 24 hour hours later. It seems extraordinarily primitive now, but then it was an enormous saving of time.

And that, patient reader, was my early contribution to Digital Heritage and pure science. We published at least three articles in the prestigious Science Journal Nature. And it is slightly annoying that my citations in the groves of academia are still dominated by articles I co-wrote in the late 1970s!

The work was important in the development of the study of the earth’s magnetic field. However, the use of archaeomagnetism in archaeology has never risen above strictly limited. Occasionally, in specific circumstances, it can be useful, but those circumstances tend to be times when no other methods came up with the goods and most often in attempting to date kilns.

These are the papers:

Barbetti. M and K. Flude, ‘Palaeomagnetic Field Strengths from Sediments baked by Lava flows of the Chaine des Puys, France.’ Nature, Vol. 278 No 5700. 1979

Barbetti. M and K. Flude, ‘Geomagnetic Variation during the Late Pleistocene Period and changes in the radiocarbon time scale.’ Nature, Vol. 279 No 5710. 1979

Barbetti M., Y. Taborin, B. Schmider and K. Flude ‘Archaeomagnetic Results from Late Pleistocene Hearths at Etoilles and Marsangy, France’. Archaeometry 22. 1980

First written March 2023, revised 21st March 2024

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