Keith Wilson - Electrical engineer
For generations, people have been tantalised by the thought of recovering King John’s treasure, which was supposedly lost when his baggage train was caught by the incoming tide as it tried to cross the Wash, a shallow but treacherous area of sand and quicksand in Norfolk. The treasure, which was lost on 11th October 1216, is widely thought to include the English crown jewels of the time so its finder would be amply rewarded.
In the early part of the 20th century, there were suggestions that electrical measurements – specifically earth resistance measurements – might be a useful guide to the location of the treasure, since buried objects or other discontinuities in the soil structure produce detectable changes in earth resistance. Because of problems over land ownership, the difficult terrain and the intervention of two world wars, little was done to put these suggestions into practice until the 1950s.
At that point, Evershed & Vignoles, one of the major constituent companies of today’s Megger Group and then, as now, a leading supplier of earth resistance testing instruments, agreed to cover the costs of a preliminary survey. In 1972, Dr George Tagg, manager of the Evershed and Vignoles Research Department presented a paper discussing the results to the Royal Society of Arts.
Tagg explains that from the outset, those working on the project knew that earth resistance testing could never locate the actual treasure which, his investigations had suggested, would be made up of comparatively small items – small enough to be transported by horses – that would be buried more than 15 m deep. An indirect approach was therefore adopted.
This was based on careful analysis of historical documents describing how the treasure was lost and, it has to be said, a degree of speculation. The conclusion reached was that the sand in the Wash was so treacherous that the baggage train could never even have attempted to cross it had there not been a pathway formed, the paper says, “by the introduction of some comparatively hard material, such as clay.”
Earth resistance measurements were unlikely to find the treasure, but there was a good chance that they could locate a much larger feature, like the route of the pathway, thereby providing an important clue to the treasure’s most probable location.
To validate this idea, and to gain an insight into the type of resistivity change that could be expected, Tagg and his associates first built a model comprising a shallow bath containing water to represent the sand and an aluminium sheet to represent the underlying soil.
A bump was introduced into the aluminium sheet to represent the pathway. Tagg reports that careful tests with this model established exactly the type of resistivity variation that could be expected when work started in the field.
The resistivity survey itself was fraught with difficulties. For example, the trolley-mounted instruments had to be towed over stubble left after the harvesting of crops and even over ploughed fields. At first a van was used as the towing vehicle but, after the van’s clutch had burned out on several occasions, a tractor was procured. Even then, there were many areas where the equipment could only be moved around by sheer physical effort.
In spite of these and many other difficulties, thousands of readings were acquired and taken back to Evershed & Vignoles in London for analysis. Ultimately it was possible to construct a map showing equal resistivity lines for the area surveyed. This is reproduced in the picture. Tagg comments, “There is a trough running across this map, as indicated by the line from A to B, and the resistivity contours on either side of this trough are very close together, showing a rapid change in value. This is an indication of … the pathway.”
Taking all of their results together, Tagg and his team saw a line of low resistivity three miles long. They concluded that this was the pathway, and this conclusion was backed up by independent evidence from aerial photographs. To provide further corroboration, a drilling rig was borrowed from Nottingham University and a number of holes were drilled alongside the supposed route of the pathway.
When the core samples from these holes were analysed, they confirmed that the area had at some stage been covered by the sea. The samples were also found to contain larger amounts of gold, silver and iron than would have been expected.
It would be wonderful to report that, building on these encouraging results, Tagg and his colleagues found King John’s treasure but, of course, they didn’t. In fact, even now, after another 60 years during which earth resistance surveys have become an everyday archaeological tool, the treasure is still lost. Nevertheless, Tagg and his team, with their Evershed & Vignoles instruments, were true pioneers of this invaluable technology.
And, of course, if you fancy your luck making an up-to-date survey with one of earth resistance testers in Megger’s latest DET4 series, the treasure could be yours. But please bear in mind that you might find even with these easy-to-use instruments making the thousands of readings necessary is a rather daunting task!