The Cornish Mine experiment – Weighing the World part 2

In late 2019 I was part of a small group of enthusiastic scientists and historians who came together to discuss their love of Cornwall, the history of astronomy, old scientific instrumentation and the life and work of George Biddell Airy (1801–1892). As a group we were struck by one central aspect to our interests: his Cornish Dolcoath Mine Experiments of 1826 and 1828 to measure the density of the Earth. The discussion led us to devise a plan to get together in a Cornish mine to re-enact the experiment as close to the original as possible. It was an ambitious project and when we set off on this journey we could not foresee all the setbacks and delays that would hamper our efforts to reconstruct the experiment. There have been a number of times when it seemed an impossible task, but we kept moving forward, albeit in very slow increments at times and often with similar parallels that were faced by the original experiments. But before we reach the conclusion on our progress it is important to say a little about the experiment and the reasons why we are still determined to make this happen.

The Experiment
The use of pendulums to measure the difference in gravity around the Earth was nothing new when George Biddell Airy and William Whewell set off to Cornwall in 1826. It had been known that the Earth’s gravity was variable since 1671 when the French scientist Jean Richer made measurements with a pendulum clock and discovered that gravity was not uniform and that it was running over 2 seconds slower in French Guiana than in Paris. In 1737 the French mathematician Pierre Bouguer swung pendulums at different elevations and from the rate of swing was able to make the first estimate of the density of the Earth. There was a lot of concern over the accuracy of these early experiments due to the difficulty in measuring the period of the pendulum. These concerns continued unabated until the invention in 1817 of a reversible pendulum by British Captain Henry Kater. The invention would offer the opportunity to measure the local acceleration of gravity with much more accuracy than ever before.

The experiment required the free-swinging pendulum to be hung in front of a tall grandfather-style precision clock and the timing of the swing would be measured against the clock-driven pendulum behind. To get a measurement for the gravity of the Earth you would need to run the experiment in two locations with different altitudes. Using mountains would be one option, but the mines of Cornwall offered another.

Dolcoath 1826
Dolcoath Mine in the early 1800s was the deepest mine in England. Known locally as The Queen of Cornish Mines it was located in the far west of England near Redruth. It was a very profitable working mine mainly extracting copper, but also tin, silver, arsenic and other minerals. By 1826 it was over 2000ft in depth, with its deepest recesses accessed by long series of ladders. Any equipment, mine spoil and occasionally men would travel up and down the large shafts in buckets called kibbles. The laborious activities would not be limited to the underground, on the surface were noisy pressing stamps and arsenic works which ran beside the engine house. These were working environments before the times of health and safety where accidents were frequent and life was hard for the men, women and children who made their living through mining.

The main way to get goods and occasionally people in and out of the mine – Riding the Kibble
Credit: Mines and Miners. Louis Simonin, 1868
It was in this environment that the two scientists Airy and Whewell arrived first in the summer of 1826 and brought with them precious and expensive precision instrumentation to conduct a scientific experiment. What could possibly go wrong? Well, as it turned out, quite a lot! On arrival, two stations were set up, one underground and one on the surface (perpendicular above to the underground station). Two pendulums (named Foster and Hall after their previous owners) in the design of an invariable Kater one-second pendulum were suspended on knife edges and hung in position in front of a clock pendulum. Alongside the pendulums, they arrived with seven precious and valuable chronometers, tripods, telescope sights and tents.

The surface station was set up in a tent on top of a hill which rises to the south of Dolcoath mine while the subsurface location was 1200ft underground. The cavern in which it was located was split into two with a wooden screen. The experiment was placed behind one side of the screen and separated from the person who would watch the motion from the other side through a sighting telescope looking through a small hole in the screen.

Each pendulum swung for 6-8 hours a day while being watched by either Airy or Whewell, and then the timings were compared between the two stations. The chronometers were transported between both sites at the start and end of the experiment to compare with the clocks. There were some initial concerns. The stands were not up to the job as they were not stable enough. The fragility of the chronometers and lack of agreement between the timings of these was a major concern (two soon had broken glass, damaged from being carried up and down the ladders). It was decided to make the observation runs shorter – just 5 hours of observation a day – so they could compare the chronometers to the ‘clock’ more regularly with an ambition to lead to better accuracy.

After the first cycle of measurements was made there was an attempt to raise the Foster pendulum to the surface. At this point, there was an accident and the straw packing within the kibble caught fire and the bottom of the bucket burnt through. The pendulum plunged downwards and was lost to the abyss. Airy believed it was sabotage and certainly the miners could have been to blame. They were a suspicious lot, living in a remote part of the UK and working in a job where death was commonplace. The arrival of two scientists from London with their strange requests couldn’t have gone down well. At best they were seen as an inconvenience at worst they were regarded as the source of bad luck. Sedgewick encapsulates this in his accounts of the experiment “One morning I listened to two men who had watched our descent the day before: “I think they’re no good. There must be something wicked about them – the little one (that was Airy) especially. I saw him stand with his back to the Church, and make strange faces.” (Sedgewick, 1890)

Airy immortalised the moment of disaster in a poem
The ladders of mighty Dolcoath I descended
Through caverns that yawned like an entrance to hell:

All was silent, save when through the levels came blended
The roar of the blast and the kibbul’s deep knell.
To the right, a vile path round the South Shaft was bending:
Behind, a chain-ladder from hooks was depending:
Our station’s white door in the front was ascending:
When I marked the sad spot where the pendulum fell.
Dark and drear was the spot in Dolcoath’s deepest level
Where the pendulum’s fragments were scattered around,
As when, at the close of some drunken men’s revel,
Broken bottles and plates encumber the ground
Yet though scatter’d they lay, not entirely neglected:
For the men who had packed them, with spirits dejected,
And Mid Cattell and deads the small pieces selected,
And sent up to grass all the bits that they found.
Taken from George Biddell Airy, ‘Dolcoath’, in P. D. Hingley and T. C. Daniel (eds.), A far off vision: a Cornishman at Greenwich Observatory. ‘Auto-Biographical Notes’ by Edwin Dunkin, F.R.S., F.R.A.S., (1821-1898), with notes on the lives & work of his father, brother and son, (Royal Institution of Cornwall: Truro, 1999), p. 182.

Dolcoath 1828
After the ill-fated first attempt, Airy and Whewell would return in the summer of 1828. This time they arrived with reinforcements; the intention was to keep the experiment running twenty-four/seven. Accompanying them were the eminent astronomer Richard Sheepshanks and geologist Adam Sedgewick. They also had a number of additional helpers including Airy’s younger brother.
In another change to the original experiment instead of bunking down in the local count house (now Miss Mollies Tea Rooms) they were to stay within the houses of local mine owners and aristocrats, the experiment had become in all ways something much grander. They arrived on site on the 8 July with two pendulums named Sabine and Brisbane after their previous owners and used the same setup as before except they had calculated that a one-second difference between chronometers was less significant over a longer period. So instead of 5-6 hour shifts, they would watch the pendulums continually with no breaks. There would be 3 people at the surface and 3 people below, they would work in shifts with shift work starting at 6am, 2pm and 10pm. Sheepshanks was in charge of the upper station while Airy was in charge of the lower station and he made sure he climbed the ladders to watch over every changeover: a gruelling schedule for himself while the experiment was in progress.
But by the 10 August the observations started to show an issue, something which Sheepshanks would work upon, eventually showing that it was an issue with the knife edge and agate plate. The steel knife edges of Sabine were not accurate enough. When the two pendulums were hung back to back the error was obvious. Airy fixed and made adjustments accordingly. Once this was resolved the experiment started again in earnest and the main experiment ran between the 16–19 August, when it was abandoned due to rising water in a lower part of the mine which infringed on their area. Airy left the experiment running for as long as he could until even he had to admit defeat once more and return everything to the surface.

In total 127 hours of observations were made. From this, they were able to draw the conclusion that the lower station accelerated by 2 seconds a day. These early results must have been exciting to the team, unfortunately, the experiment was cut short again this time the mine had slippage and they had to come out of the lower levels, and the experiment closed.

The Rosevale Reconstruction
The first hurdle we had was finding a location in Cornwall where we could conduct the experiment. Dolcoath has been decommissioned and flooded with water, as have many of the deep mines within Cornwall. We were in luck when we identified Rosevale mine in Zennor; this was a working mine run by enthusiasts and ex miners and offered us the opportunity of access, albeit not to the depths that Airy would encounter at Dolcoath. A predominantly Victorian mine, access to levels is by ladders and there are wonderful features such as the original tools and candle wax running down the walls. Like all mines, it is the environment, which is prone to change, and 2020 saw our first hurdle as the mine had been shut due to covid restrictions. The pumps had stopped working and the lower levels flooded, making access an impossibility, so we turned our attention instead to the manufacture of the pendulum.

One of the mine’s core team is a clock repairer, maker, and member of the Royal Horological Society. This was key as Kater pendulums were once quite common but are now incredibly rare instruments. We could not take an original into the damp, dirty and dangerous environment of a mine and quickly identified that we would need to build one of our own, which could at worst take damage from transport in and out to its subsurface location.
The making of the pendulum would require detailed information about materials, fixings, sizes and processes. We soon discovered that pendulums had been made from a number of different materials, brass, copper, wood and in some cases steel. Our investigations into exact measurements of the pendulums were equally elusive. This led us to the conclusion that we needed to see an original for ourselves. We found that one of these pendulums was housed at the Science Museum in London and after many delays due to covid restrictions one of our team Dr Daniel Belteki had the opportunity to photograph one in the late summer of 2021. This information has allowed Wayne Ridgeway the clockmaker to make a replica pendulum. A last-minute change at the end of December due to one of our team contracting covid saw us delaying the experiment until Spring 2022.

The Experiment
On 9 April 2022 we finally got the opportunity to run the experiment. Wayne Ridgeway had completed his manufacture of a Katar Pendulum replica and he had acquired a regulator to be positioned behind. We had chosen a location in the mine which was not too wet or had too much of a draft. The temperature was cool around 11 degrees and we could see your breath in the air. Dr Edward Gillin, Dr Daniel Belteki and I waited patiently as Wayne positioned and started the regulator, before leaving it to settle. He then hung the free-swinging Katar pendulum a short distance in front.

The regulator pendulum had a white dot upon it and the Katar pendulum had a black piece of wood which extended below the bob. It would be these two key elements that we would be watching during the course of the experiment. Positioning ourselves a short distance away we placed a small antique brass sighting scope on a table. Looking through this scope we would be watching for the moment that the white dot was ‘eclipsed’ by the black rod. In effect, it would disappear. This would be the timing that the two pendulums would be swinging together and the original experiments were called coincidences. We could anticipate when these would be forthcoming, as the pendulums visually started to look as though they were swinging in harmony, rather than in opposite directions. A coincidence deep in a mine would occur faster than one at the surface and it is this difference which would allow Airy and Whewell to undertake their calculations.

The first coincidence was witnessed by me. I found myself at the sighting scope just minutes before it was due to occur. It had been a challenge to focus on the pendulum through the small sighting scope, and I had felt a moment of panic when I thought that would be visually usable to undertake the measurement. A realisation that I had to use my peripheral vision, much in the way an astronomer would when teasing out detail on a planetary disc. I allowed my eyesight to settle and soon saw the inverted small image of the white dot and black rod through the sighting scope. As the first person to witness the event, it was very hard to know what to expect what I can claim to have seen is the eclipsing of the white dot, not once but twice, the first time for less than a second and then the second time for a longer period of 16 seconds. My experience was similar but unique to those that followed. Daniel Belteki made the observation of the second coincidence and he didn’t see a complete covering of the white dot, but he did see a maximum covering not once but twice, shortly spaced apart in time, Edward Gillin saw something similar when he had a go at the third coincidence.

Each coincidence was timed between 44 and 46 minutes apart and we felt this had more to do with the expertise of the instrument maker than the observers. With more time and coincidences I am sure we would have made improvements in the accuracy of the observations. It had taken a long time that morning to set up the equipment and get the regulator running smoothly. After nearly 5 hours of observations, we had to allow the mine to pack up and dismantle the experiment. Our limitations were very apparent, we had a lack of time to repeat the experiments to a similar length as Airy and Whewell (they conducted 127 hours in total), and we also lacked depth in which to conduct the experiment. Even so, this has whetted our appetite to try again and improve on our first attempt. We felt we were very successful in exploring the challenges involved in undertaking such an experiment in a less than ideal location and we are all looking forward to a time when we can reconvene and try it all over again.
See also:
George Biddell Airy, ‘Account of experiments made at Dolcoath Mine, in Cornwall, in 1826, & 1828 for the purpose of determining the density of the earth’, in P. D. Hingley and T. C. Daniel (eds.), A far-off vision: a Cornishman at Greenwich Observatory. ‘Auto-Biographical Notes’ by Edwin Dunkin, F.R.S., F.R.A.S., (1821-1898), with notes on the lives & work of his father, brother and son, (Royal Institution of Cornwall: Truro, 1999).
Sedgwick (1890) quoted in, John Willis Clark and Thomas McKenny Hughes, The Life and Letters of the Reverend Adam Sedgwick, LL.D., D.C.L., F.R.S., Fellow of Trinity College, Cambridge, Prebendary of Norwich, Woodwardian Professor of Geology, 1818-1873, Vol. I of II, (Cambridge University Press: Cambridge, 1890), p. 332.

Craddock Moor Circle and the Summer Solstice

Sun setting over a distant Brown Willy

On summer solstice eve I was able to photograph the alignment between the circle and the setting sun over Brown Willy and the setting sun lines up well with the prominent hill. Even taking into account that in prehistory the sun wouldn’t set in exactly the same position today (it would be 2 solar discs to the right in the photo above) there is a clear correlation between the two.

Craddock Moor circle isn’t the only prehistoric site where you can watch the summer solstice sunset over Brown Willy and there is an extended line of monuments across the moor where this can be seen. These include the standing stone above the Hurlers and at Goodaver circle.

Craddock Moor circle has another alignment this time with the rising summer solstice sun and Stowe’s Hill. The winter solstice sunrise and sunset have a loose arrangement with the barrows on Caradon Hill and a rolling sunset down Tregarrick Tor. This makes it a very remarkable solstice-aligned circle.

On solstice eve I was treated to sun dogs forming either side of the sun which was a magical sight which kept me watching the skies before the sunset.

The Cornish mine experiment to Weigh the World part 1

Descending ladders into the mine to seek a suitable sub-surface location to run the experiment to measure the density of the Earth. Photograph credit: © Carolyn Kennett, 2021

How did we weigh the Earth (and why did this go beyond simple curiosity)? This may be a question people asked themselves during childhood, and have not considered since. Yet it is a question a small group of scientists, including myself, have returned to as we research experiments conducted in the 1820s in a Cornish mine to measure the acceleration due to gravity of the Earth.

In 2022 our intention to re-create the mine experiments by building a replica Kater invariable pendulum and taking it down a Victorian mine in west Cornwall to make measurements of gravity. We will set the pendulum in two locations, one overground and one underground, and time the swing of the pendulum in both locations. The difference in the rate allows us to calculate the amount of gravitational pull on the pendulum, as the underground pendulum will swing at a slower rate. The original experiment was conducted by George Biddell Airy and William Whewell in the deepest mine in England, Dolcoath. This has unfortunately closed and the lower recesses are flooded, so we are using a mine named Rosevale, which gives us a difference of 250 metres between the overground and underground stations. Although Rosevale is not as deep as Dolcoath (700 metres at the time of the original experiment), it gives the opportunity to explore how the experiment was conducted in what can only be described as less than ideal conditions. Mines are dirty places which can be excessively damp and hot. During the original experiment the scientists would have had to contend with vibrations and noise from the working environment, making their achievements all the more significant.

Why is this all important now you may ask? Yes, simple curiosity does play into this but we find ourselves in a time when the power of gravity is something we have learnt to manipulate and overcome. There are frequent launches into space and discussions of journeys to far-flung destinations such as Mars. Without the arduous and at times dangerous early experimentations into measuring the gravity of the Earth untaken by Airy, Whewell and others we could still be stuck without the knowledge to reach beyond our own planet. Therefore we think it is the perfect time to highlight the work they undertook and their achievements in what was an important building block for us to travel into space.

Blog post first appeared here –

Goodaver: Then and Now

Please be aware Goodaver circle is on private land and permission must be sought before visiting it.

Within the digitalised Stanley Opie collection of photographs in Penzance’s Morrab Library, there are three images entitled “Unidentified stone circle. Possibly on Bodmin Moor”. The photos give an impression of a typical Bodmin Moor circle in the style of the Stripple Stones, situated on open moorland with extensive views. But on closer inspection, it cannot be the Stripple stones as the stones and landscape do not match details in the images.

Stanley Opie was an archaeologist who liked to take photographs of historic sites and archaeological digs in Cornwall. Born in Barncoose, Redruth in 1884 he used an Ensign Cameo No. 2 camera with Imperial Eclipse plates to take his photos between 1930–50. The collection is housed in the Morrab Library in Penzance and has been digitalised and is now accessible online and through authorised visits. During his career, he imaged many sites around Cornwall and some further afield and it must have been a huge job to try and identify some of the places in the images.

Examination of the three images shows them to be of Goodaver stone circle on Bodmin Moor. This may surprise people as a visit to the circle today is an entirely different prospect. The circle is surrounded by trees that have been grown as part of the local plantation. It gives an enticing view of how the circle may have been positioned and the possible sightlines. It allows us to postulates about astronomical alignments which may have been of importance to the original builders.

In recent times the whole site has become encircled by trees, other than a view to the west where the hillside drops to the farm and river bed below.

There was an opportunity to visit the site and image the circle before an attempt was made to match the orientation of the Opie photos and the landscape features within. It would be interesting to identify the possible sightlines from the circles if the trees were not in place, sightlines that the original builders may have had when choosing where to position their circle.

The Rabbit stone helped orientate the circle in the photos (to the left of the image

It helped that there are a number of unusually shaped stones. One in particularly got named the rabbit stone after having a similar profile of the Lindt rabbit, it can be seen on the left of this image. (I should say at this stage that the circle was heavily restored in 1906 and some of the stones are thought to have been replaced incorrectly, even upside down).

Opie Photograph no 1

This image took a bit of matching. The two central blocky looking stones and the rabbit-shaped stone on the right of the image helped orientate it. In my image below the rabbit, the stone is also to the right and slightly obscured by the rocks in front of it.

The rise in the ground beyond the circle is Brown Gelly, this is towards the southwest. This Tor is obscured by the trees in the left of the more recent image. The area has a number of interesting ancient sites on it including a number of Cairns on the top, which can be seen on the ridgeline of the image. There can be no solar or lunar alignment with these local cairns as they are too far to the south when standing within the circle.

Stanley Opie, “Unidentified stone circle. Possibly on Bodmin Moor,” Morrab Library Photographic Archive, accessed January 4, 2022,

Image 1 match

Opie Photograph number 2

This second image gives a more expansive view looking out from the circle to a number of ridgeways and hills beyond.

Looking at the stones in the image, the tall pointy stone and gap, next to the man at the front of the circle helped orientate the image, as did the rabbit-shaped stone behind him. The image looks from the south of the circle facing north.

The hill towards the centre-left of the image is Leskernick, it is possible that Bronn Wennili (Brown Willy) is visible to the left of the image. This is exciting as it means that standing in the circle you could have seen the summer solstice sunset over the distant hill. This is an extension of the line which starts at the newly discovered menhir on the ridge above the Hurlers circle, extends through Craddock Moor circle and the avenue at Craddock Moor, onwards to Goodaver circle. Making it possible to see the same summer solstice sunset at a number of important prehistoric locations across the moor.

Continuing to the centre-right of the image is the local plantation ridge. Fox Tor which is relatively local to the circle would have been to the right of the image.

The pointed stone which the man is stood beside in the Opie image is front left in the recent one. My image is orientated slightly differently from the old image. It would have been pointing directly down the field to the right of the modern image. Looking down the neighbouring field in recent times there is no possibility of seeing what hills lay beyond.

Stanley Opie, “Unidentified stone circle. Possibly on Bodmin Moor,” Morrab Library Photographic Archive, accessed January 4, 2022,

Image 2 Match 

Opie Photograph no 3

The Opie photo shows stones in profile against the sky above with no plantation beyond, the rabbit-shaped stone is in the front row of the circle on the central left. Matching it to my photos of the circle, it has been taken from the northwestern side of the circle down the ridge a little way. Kilmar Tor would have been visible if the photo had been taken with slightly increased elevation. This Tor is directly east from the circle and in the position of the rising sun at the equinox (midpoint between the solstices).  The modern photo has been taken from higher up the hill and the craggy tops of Kilmar Tor can still be seen through the gaps made by the less dense boundary of trees.

Stanley Opie, “Unidentified stone circle. Possibly on Bodmin Moor,” Morrab Library Photographic Archive, accessed January 4, 2022,

Image 3 Match

A plan of the matched direction of the photographs taken by Opie numbered 1-3

From matching the photographs old to modern I was able to make a plan of the directions that the Opie images were taken in: The plan below it is as follows:

R = Rabbit stone

L = taller long stone

Credit: Annotated Google maps image

Finally, I should add that within the Opie photographs none were taken in the direction of Hawks Tor in the west. This has been identified by Cheryl Straffon and John Barnett as an equinox setting position when standing in the circle. When visiting the circle in more recent times the Tor can still be seen in the gap made by the plantation to the west and is the one remaining solar alignment that could be viewed in action. Maybe one day the larger plantation trees will be replaced with smaller saplings and make the other viewpoints possible.

Access to the Stanley Opie collection and all the other wonderful historic digitalised images that the library has can be made here:

Sun and Moon at Boscawen-ûn

By Carolyn Kennett

First published in Meyn Mamvro 95 (Spring/Summer 2018) and still can be read in the collected works Watching the Sun Booklet by Meyn Mamvro and Mayes Creative (2021)

Boscawen-ûn summer solstice sunset (Credit Carolyn Kennett)

During the last few years, in many ways, Boscawen-ûn became a second home to me. While waiting for sunrises and sunsets I observed the change in the seasons at the circle, all accompanied by the changing looks, sounds and smells.  But one thing remained the same and that was the tranquillity of the site.  I kept some strange hours, as I was mainly there for sunrises or sunsets and quite often at night.  More often than not I was alone in the circle, sometimes for hours on end.  One of these visits, in particular, comes to the forefront of my mind.  Having risen when it was still dark, I drove to the circle with the beginnings of dawn, hoping the low developing horizontal cloud would clear.  I arrived in time for the sunrise of the 25th June 2016.  The week had been wet and the solstice had passed behind a thick blanket of cloud. I stood atop Creeg Tol willing the low bank of clouds to blow out of the way, even though I knew I was nearly a week late to see the summer solstice sunrise.  The vantage point of Creeg Tol meant that I would see the Sun peer above the horizon, something that I could not replicate in person in the circle below due to the large hedge obscuring this direction. The dawn had a stillness about it which makes it one of my favourite times of the day.  The clouds were starting to disperse and right on schedule, the Sun started to peer above the horizon, accompanied by the mixed dawn chorus of birds, roosters and cattle.  I photographed the sunrise from my vantage point at Creeg Tol and set off down the hill towards the circle.  About halfway down into the hill I started to lose the sunrise, the Sun was setting behind the hill it had just risen from.  By the time I reached the circle the Sun was once again well below the horizon.  I realised that without the hedgerow I could witness the Sun rising twice, in effect a double sunrise.  Once from atop Creeg Tol and then again from inside the circle.  I hoped this would work in reverse: with the Sun setting visually from the circle and once again from Creeg Tol.  It was an idea I would test out repeatedly over the summer months with great success.  I think this double sunset and sunrise during the summer months is one of the most visually beautiful aspects of the circle.  A local settlement Goldherring, which has some Bronze Age round huts is north of the site and people could have accessed the circle from the direction of Creeg Tol.  Double sunsets and double sunrises are something that we can all witness from the site and this is only the beginning of what makes Boscawen-ûn astronomically special.

It is important to consider Boscawen-ûn in the landscape as holistically as possible.  During this project, I wanted to consider the way the circle sat at the base of the northern hill, in what would have been a marshy area and quite possibly difficult to get access to, particularly at wet times.  Why had it been positioned here?  What would have been seen in the sky?  It was equally important to view the site as a part of a changing landscape, where man has shaped and changed the site itself over a large period of time as well as the surrounding landscape.  I am a great believer in looking what archaeoastronomy ideas have been historically suggested about a site.  These historic ideas brought another list of questions such as: Is there any truth in a Lunar link at Boscawen-ûn? Does the carving on the back of the central stone light up at summer solstice?  These were just the start of a list of burning questions that would keep me returning to the site, making measurements, and calculating positions of celestial objects over the coming year.  Hopefully enabling me to answer if the site was built with astronomy in mind.

I started by considering if there were any alignments between the circle and features on the horizon.  This meant that I needed to map out all the natural and man-made features which would have been found from the period of the stone circle.  This was in itself quite a task.  The internet was a wealth of information, but local knowledge from people such as Cheryl was a great help to me.  Many local sites such as barrows and menhirs had disappeared and I needed to try to reconstruct where they were as accurate as possible in relation to the circle.  My final list identified 48 local features or as I would name them, targets.  These targets would then be considered against a number of pre-selected celestial events.  If all 48 targets were considered against the chosen celestial events, statistically a match would be highly likely.  For instance, if we were to consider the targets located around the site in a circle of 360 degrees. If each target considered covered 1 degree with an error of +/- 0.5 degrees a total of 96 degrees or just over a quarter of our circle would be covered in targets. (The error from this project was set as 1.04 degrees this came from a small amount of measurement error as well as error for refraction, extinction, and parallax).  Statistically, this would mean that it would be far more likely for a target to make a match with a considered event.  Therefore to make the project more robust I needed to reduce the number of targets.  I decided first of all to consider targets that were visible from the site and only targets that sat proud against the horizon.  The reduction in targets could have been undertaken in a number of ways but I felt that this made the most robust format for retesting any results.  This left me with just 7 remaining targets out of the original 48 to match with my events.  These were as follows:

The Lamorna Gap – yes it is just visible from the site through the hedgerows.  A smaller sea gap further south to the Lamorna gap, Creeg Tol.  A barrow just west of Creeg Tol, Chapel Carn Brea, Boscawen-ûn Field Menhir and finally Bunkers Hill Menhir (East).  Once the targets were identified I made on-site measurements of their azimuth and altitude and this was converted into an astronomical declination.  Alongside the on-site measurements, I ran a computer program called HORIZON.  This also gave me declinations for my 7 targets and it acted as a test of accuracy for the on-site measurement, as well as allowing for reconstruction of the horizon behind the hidden, hedgerow covered NE direction.

Boscawen-ûn Field Menhir, with possible fallen menhir in hedge behind (Credit Cheryl Straffon)

Next, I considered which astronomical events I would examine alongside the targets. I decided to look initially at five events in total.  These five events would give 14 positions along the horizon: 7 rising positions and 7 setting positions.  These were the extremes of the solar calendar or the solstices, as well as the solar equinox positions.  I also considered the lunar standstill positions both for lunar major and lunar minor.  I then calculated the declinations of these 14 events for a date of 2500BCE.  The horizon position of a solstice Sun and the lunar positions in 2500BCE has moved slightly compared to its current position, whereas the equinox would be in virtually the same place.  So a rising solstice Sun would have a declination of 23.9 degrees in 2500BCE whereas it would have a declination of 23.4 degrees currently which is on a flat horizon at the latitude of Boscawen-ûn equates to an azimuth difference of 1.02 degrees.

When all this was considered I could look for matches between my 14 events and 7 targets.  I could see immediately that 4 of my 7 targets declinations matched with one of the fourteen identified events, within the limits of the error I had set.  The first and probably most primary of these is that an observer in the circle at 2500BCE would see the winter solstice sunrise rising from the Lamorna Gap.  The Lamorna Gap at present is obscured by hedgerows, but without this vegetation would have been a subtle sea view at best.  The Lamorna gap declination was measured as -23.6 +/-1.04 degrees, matching a winter solstice sunrise of 23.9 degrees.  Also, you must consider that the sea view extends for more than 1 degree along the horizon and that this event could be observable over the coming millennia.

Winter Solstice sunrise

This first alignment extends through the circle to my second alignment.  This is to a barrow which is no longer visible, it was located to the west of Creeg Tol. It would be in the position of the summer solstice sunset when observed from the circle.  It had a measured declination of 24.3 +/- 1.04 degrees coinciding with the declination of 24.9 degrees.  Equally an observer at the barrow would have been in a position to observe the winter solstice sunrise out of the Lamorna Gap.  Its position just above the circle would give an observer a more advantageous height and a more pronounced view of the winter solstice sunrise from the Lamorna Gap.  It is interesting to note that the winter solstice sunset at this time would just fall into the large sea gap at the Tregeseal stone circles.  Although at Tregeseal the sea gap is far more pronounced, there is possible that there is a connection between the two sites on this date.  

The other two matched alignments came between the circle and lunar major standstill positions.  I found that the position of Creeg Tol matched the lunar major sunset northernmost position, it had a measured declination of 28.3+/-1.04 degrees coinciding with an event declination of 28.9 degrees.  The nearby Boscawen-ûn Field menhir was the final alignment and it was in the lunar major sunrise position.  This had a measured declination of 28.9+/1.04-degrees which coincided with the event declination of 28.15 degrees in 2500BCE. The position of the Field menhir was slightly to the west of calculated declination for the lunar alignment, but it is conceivable that another stone now recumbent in the hedge made a pair and this pair once framed the rising Moon at the extreme of the lunar major cycle.  Although we should note here that it may not have necessarily been a full Moon at that time, as the Moon at its standstill declination can be at a number of positions within in its phase cycle.

Lunar standstill links are not well documented in Cornwall.  They are considered a feature of recumbent stone circles in East Scotland but have also been found in western Ireland and more recently in western Scotland.  The discovery of two lunar standstill points at Boscawen-ûn is both interesting and intriguing; raising more questions than it answers.  Boscawen-ûn does have myths surrounding it which are linked to the lunar cycle, so this could be a feature of this site.  Future work in west Penwith will consider evidence for lunar links. For instance, the Merry Maidens which I had discounted through my reduction of data, as it did not stand proud against the horizon is in the Lunar Major Standstill Southern rising position from Boscawen-ûn with a declination of 29.9 degrees.  This concludes the main horizon findings but as I said I also looked at other features within the circle.

Boscawen-ûn hedge menhir (Credit Carolyn Kennett)

The positioning of the quartz stone to the SW of the circle could signify the start or end of the winter season, but due to its localised vicinity to an observer, it could never pinpoint an actual date, without another position to line it up.  The stone on the opposite side could have well been used to align the position but this does not line up with anything calendrically significant.  The quartz stone does though align with the cist (located in the NE of the circle) and the out of sight Boscawen-ûn Hedge menhir.  The summer solstice sunrise would have occurred along this alignment around 2500BCE.  This alignment was first suggested by Norman Lockyer in his consideration of the circle.  There is another stone between the Hedge menhir and the stone circle, this would possibly bring inter-visibility between the circle and the Boscawen-ûn Hedge menhir.  Even so, there are numerous examples of standing stones being just over brows of ridges that form alignments so this could be a viable consideration when looking at this alignment.

The edge of the foot at the bottom of the central stone is illuminated (Credit Carolyn Kennett)

Rock art carving (or either foot or axes) have been identified on the central stone.  I was able to calculate the amount of time the art would be illuminated for in the year 2500BCE. The art on the back of the central stone is only fully illuminated in and around summer solstice sunrise.  Without any vegetation, a full illumination would occur for 30 days on either side of the solstice.  The maximum time in minutes that the art would be illuminated would occur on the summer solstice.  This amount of time would reduce each day until a full illumination could not happen 31 days later.  It must be noted that this measurement takes into account a completely flat landscape.  Any vegetation would significantly reduce the length of time and amount of days the art would be fully illuminated.  Partial illumination of the art also occurs and this time it happens both in the morning and the evening in and around the summer solstice, this partial illumination would occur over a much longer period.

There are many more suggestions that could be made particularly linking stellar events to the site. Without more accurate dating these suggestions must be taken under advisement.  For instance, the Pleiades would set over Chapel Carn Brea in 1500BCE but at an earlier date of 1800BCE, it would have set to the south of the framed hill.  I did consider if the central stone could have pointed at a star.  The only bright star that it could have pointed at was Arcturus and this would have been at a remarkably early date of 3820BCE.  This must be taken under advisement, as the stone could have moved over time.  Overall the suggestions of stellar alignments without accurate dating are always difficult to suggest. It does seem that a number of astronomical features were considered by the builders of Boscawen-ûn.  They certainly had an eye for the solar calendar within the design but perhaps more unusually a knowledge of the lunar cycle.  This project, for me, has raised more questions than it answered and I will be continuing it by looking for further examples of lunar alignments within Cornwall and trying to draw more conclusions about the astronomical features at some of the other Cornish circle sites.

More of this story can be read about in my book Celestial Stone Circles of West Cornwall. Which can be accessed here

Winter Solstice Walk 2021

Winter Solstice is the day we mark the longest hours of darkness and the movement towards the lengthening of daylight hours once more. For many it is a powerful time in their calendar, a day to mark the start of a new year, to reflect on what they can leave behind and look forward to the time ahead. There are a number of ancient sites within Cornwall that have links to the Solstice and many of these suggest a relationship that our ancestors had with this moment within their in their lives. Connectivity that we feel resonating through the ages and is particularly heightened at times such as this one.

This year a small group of us decided to join the ancient pathway the Tinners Way to the north of Zennor and walk to the Tregeseal stone circle. A walk which we would start in the half-light before sunrise and end after we had watched the sunset at the stone circle. Anyone who knows me will hear me talk about my love of the wider Tregeseal landscape and how I believe it lends itself to a winter solstice gathering; where people can watch the sunset over the distant Isles of Scilly. The whole of Penwith is rich with prehistory, and a large number of the sites are along the Tinners Way and the direction of travel we would be moving in would take us towards the southwest and the setting sun. An imaginary line could be drawn through the monuments we were to visit and a number of them, if you had stopped there, would have the setting winter sun at another monument further along our journey, making a long winter solstice line of running down the spine of Penwith hills and part of this journey for me is to see how far people could process through the landscape, on the shortest day of the year, with a final destination in mind.

I am very interested in the ideas around processional journeys and movement through the landscape, particularly ones which would connect people to the ideas of cosmologies and be started in the time of dawn and end after sundown. I hoped the small group who joined me that day were also in the same mind. This was also a time for us to take a moment out of the daily grind and reflect on what we wanted to leave behind and how we would move forward, with mindfulness, into the next year of our lives. Walking has become a really important part of my life and during the last two years of upheaval and turmoil, I have come to appreciate the quiet and reflective time I can enjoy when out in the landscape, but it is always wonderful to be joined on an adventure especially a journey of such length, which would require both fortitude and endurance.

We met in Zennor just before dawn and the sky was in the main overcast, the clouds pink with the nearing sunrise. The Moon, which had been full two days prior, was still in the sky in the northwest, bringing an added element of light. Starting our journey we travelled up Rosevale valley, stopping to gather our thoughts for the day in the old and ruined miners cottage by the riverbed. It was commented on how we were a group of seven, six humans and a white wolf and in that moment of time it all felt a little otherworldly, like the start of a plagiarised fantasy tale., we all laughed at the sentiment and with the sunrise, we started on our way. Mulfra Quoit was a couple of miles away and we had to initially join the Tinners way, reaching it at the roadside near where the once impressive Tol Creeg passage grave had been destroyed and then removed in the 1960s. looking behind us we could see Zennor Quoit standing proud on the ridgeway and we got out first view of the southern coastline looking down the valley to the bay and St Michaels Mount.

The first hill of the day was in front, with Mulfa standing prominent on the top. We had settled into a nice pace at this point and think we were all excited about reaching our first ancient site of the day, one of many more to come. We had dropped into a rhythm of walking in pairs with the white wolf running back and forth between us covering triple the distance we were.

My 100 year old Box Brownie makes an appearance

Mulfra was an opportunity to take a morning break. We huddled inside the quoit listening to the wind rip around outside. We marked the occasion with songs, poems and blessings while thinking about the journey ahead. We had a decision to make, would we continue along the Tinners or drop through Bodrifty courtyard house village and head towards Ding Dong mine, which would enable us to walk the processional route past Nine Maidens, we chose the latter. Walking down the hill to Bodrifty courtyard house village proved interesting, the white wolf, who often chose to be in front, stopped short and started to howl, spooked by something we could not see, but it nevertheless brought us all up short with notions of ancestors, meaning and what the animal could sense that we couldn’t. I must admit I really like Bodrifty, I often spend time here in the summer and as ancient sites go, I always find it peaceful, and have never had a sense of anything foreboding at the site, neither had anyone else when we discussed it, but its amazing how common ancient sites invoke feelings that we cannot explain, that connectivity with the past runs deep through us all and visiting some sites can have profound effects on peoples emotions and sense of being. With some convincing, the animal seemed to move beyond what had been bothering it and started to visit the ruined huts alongside us all. As we explored the sun started to send shafts of light onto the southern coastline and even at the distance we were from it, we could see part of the ocean shining golden. A promise of what was to come and a brightening of the skies ahead.

On reaching the path to Ding Dong we swung our journey to face to the north and started to walk the pathway to Nine Maidens on the top of Boskednan moor. Taking a moment to stop at the barrow we faced the impressive rocky outcrop of Carn Galva and took a moment to reflect on the people past doing the same of what we were about to today. This ridgeway is lined with barrows on both sides and by moving along it towards Carn Galver you really are walking in the footsteps of the many who have come before. I thought about the people who had built the monuments, those that had excavated them in the Victorian people (bless William Copeland Borlase and his dodgy excavation techniques :)) and the people who still come here today. The circle itself was a natural place to stop and talk about the Moon. If you are able to return here in 2025, the standstill year, you will see the moon set over Carn Galva. I would recommend heading to see the bright winter full Moon which will set over the rocky outcrop. This is a possible reason for them positioning the stone circle as they did. From here we could see the hills which we would be approaching later in our walk, those of Chûn and Kenidjack. We could also see the marker Boswen’s Menhir, which has been positioned in the winter solstice sunset position from the circle.

Box brownie image

This seemed like a good spot for a break for lunch, the ridgeway is exposed we headed for the ring cairn and its large triangular stone., where we chatted and watched the sun emerge from behind the clouds for the first time that day.

Rested up we headed down the hill to Mên Scryfa, an inscribed stone which was recommissioned in the early medieval period, originally, most likely, being a much earlier menhir. the inscription reads Royal Raven and could mark the resting place of Bran, Welsh King who had been hiding out at Caer Bran before being attacked and chased to his death at this spot. I like to think there is treasure underneath but maybe treasure from the Bronze Age, a Trevisker Style Urn with cremated remains in, rather than a king from the dark ages. The Mên-an-Tol was one of the first times we met people, others out marking the solstice day, a number of us took the opportunity to wiggle through the holed stone, the lack of water at its base made it a more present prospect than usual.

Fun at the holed stone

Once more we had a decision. we could head towards Chûn from here, but as we had time we decided to zigzag and include Bosiliack and Lanyon on our journey and I am so pleased we made that choice. A number of the group had never been to Bosiliack Scillonian style passage grave before and the adjoining Bronze Age village. This is such an impressive monument, perhaps even more so since it wasn’t known about until the 1980s when a gorse fire uncovered it from the undergrowth. The excavation revealed so much about the tomb, and it contained cremated remains from the Bronze Age, along with a much later dated skeleton. The tomb felt important to me to visit on this day, as it is orientated towards the sunrise at this time, and I have photographed it myself in a previous year. I doubt anyone would have been able to watch from inside, but it shows how as a community that wanted to mark this day and maybe bring light to their own ancestors who were buried within the tomb.

It had been a long time since I had approached Lanyon Quoit from this direction and although viewed from nearly everywhere else it sits within the landscape, this is one direction where it stands proud on the horizon, impressively towering up above everything around it. This quoit is interesting in that it was rebuilt after falling over and is not necessarily how the original designers, back in the neolithic imagined it.

From here we started to see the sun break through the clouds with more regularity, it was arching low in the sky and we realised that although we had a fair way to travel, the sun was well past the mid part of the day, time for us all to move on again.

The next stretch was longer again and we approached Chûn Castle from the farm in the dip. The wind was howling and we didn’t hang around too long in the Iron Age hill fort before we headed down the hillside to the neolithic quoit of Chûn. Unlike Lanyon this quoit is in fantastic condition, which says a lot about our ancestors. The people who came millennia later in the Iron Age and built the hill fort must have held some beliefs about the monument, as they left it intact on the hillside and did not rob the stone from their grand hilltop fortress. The quoit’s capstone is heavily decorated with cup marks and there is still room to wiggle inside, which is fun. Standing here for sunset you would see the sun dip behind Carn Kenidjack and a number of people were already making their way up the hillside, in the opposite direction to us watch the sunset from this location as we headed down the hillside to Tregeseal.

I had wondered if our small group were rocked out!! But they were still keen to see as much as we could and we stopped at Portherras cist and after much chatter all day we decided we would walk the next section to the inscribed stone in quiet, giving us a time to reflect on the journey we had made already and the time ahead at the stone circle. As we walked in the direction the sun was already dropping fast and low in the sky. This was a moment I think we will all cherish from the walk, as a group we can often lose the quiet purpose behind our decision to make the journey.

The inscribed stone was very apt, most likely a Christianised menhir this stones inscription reads TAETVERA. This is Latinised 7th century Cornish: Taithuere, or “exalter of the journey”. I have read that St Just himself could be buried here, once more I like to think that if anyone was then it is most likely an urn of Bronze Age cremated remains underneath the cairn at its base.

As we reached the holed stones it was incredible to see the low golden sunlight come along the row of stones, making shadows along the line of them. I love these holed stones and feel they have a really important role to play on the wider Tregeseal landscape, I reflected how long it must have taken for people to have made the holes and how they could have been used to mark the days, through the shadows and beams of light shining through the holes, possibly at this time of year. As we sat watching the sun from this location I checked my watch and the sun passed the actual moment of solstice. The time when the sun is directly above the Tropic of Capricorn. The sunset was also fast approaching and we needed to move to the circle below to watch it.

Tregeseal is such a special landscape to watch the winter solstice sunset from. A lot has changed since the circle was built. Originally another circle stood next to this one, and the huge hedge to the south was not put in place until the mid 20th century. Nevertheless, you can get a small sense of what it was like for people who made the journey to this site to watch the sunset on the solstice. There is a small glimpse of the sea, and on this sea gap on a clear day you can see the distant Isles of Scilly and it is on these islands that the sun will set. Suggesting connectivity which we can see reflected in shared monuments and material goods between the islands and mainland. At this moment more people came to add to our group and we celebrated the closing of one chapter and moved into the next with the setting of the sun on the shortest day of the year.

With weary legs and tired feet we had one more hill to climb back to our transport, we made this in the gloom of dusk; the night was fast approaching and by the time we reached the end, reflected sunlight could be seen on Venus and Jupiter. A reminder that sunlight was ever-present even in the darkest of times

I want to thank everyone who joined me on this walk and I am so pleased the weather was much improved to last years, Lanomrna Gap to Tregeseal.

We will be back next year with another walk, so if you are mad enough to want to join a hardy but fun bunch of people on a full day winter solstice walk let me know.

At Tregeseal stone circle

Places visited

Mulfra Quoit, Bodrifty courtyard house village, Nine Maidens stone circle, Nine Maidens barrows, Ring Cairn, Mên Scryfa, Mên-an-tol, Bosiliack passage grave, Bosiliack bronze age village, Lanyon Quoit, Chûn Castle, Chûn Quoit, Portharras barrow cist, Inscribed Menhir, Kenidjack Stone row, Tregeseal barrows, Tregeseal stone circle 

Some Bodmin viewing frames and propped stones

Wandering around Bodmin Moor there are a number of well known viewing frames and propped stones. Positioned on the hilltops and slopes of the better known tors a large number were identified by Roger Farnworth. Articles about aome of these appear in Meyn Mamvro issues 63 and 85. (

Some of them appear to have an astronomical alignment such as the Leskernick Propped stone which has a summer solstice alignment. Many of these frame other hilltops and significant rocky outcrops. Here are two which have not been mentioned by Rogers in the articles.

Garrow Tor prop. Found of the western slopes of Garrow this propped stone frames Alex Tor. Initial assessment shows this to be orientated to the west and Alex Tor would be in the position of the midpoint (equinox) sunset. Prop found by Jamie Ashley.

A second prop on the southern slopes of Brown Willy. This one frames Hawks Tor to the south. There does not seem to be any obvious astronomical connection and the frame points in a just of South direction. Thanks to William Arnold for pointing this one out.

There are lots of props and framing stations to be found in both Penwith and on Bodmin Moor. Other blog posts on this site about these include; Little Galva framing station and Carn Kenidjack propped stone.