Resistivity

Garden History research has benefitted greatly from the advances in remote sensing, more normally used in Archaeology. This can reveal the position of buried hard landscaping features such as paths and brick or stone features which in turn can be used to check the validity of historic maps and plans.

View of Wimpole Hall, Johannes Kip, 1707, National Trust

The resistivity system consists of a fixed frame connected via a battery to a remote probe.  The frame is placed in the ground every metre in a grid pattern to measure the electrical resistance between two points.  The strength of the electrical signal depends on the moisture content and the concentration of dissolved salts in the interstitial water.  For example, increased amounts of humus in the soil will retain more water and reduce the electrical resistance.  Conversely, building material retains less moisture giving a stronger signal due to higher resistance.

Wimpole Hall Resistivity Survey, Archaeology Rheesearch Group

A good example of how useful and effective this technique can be is demonstrated at Wimpole Hall in Cambridgeshire. There exists a typical bird’s eye plan, known from Kip’s engraving of 1707, but as always there was much debate as to how much of the plan was aspirational and how much was actually executed. One of the most striking features in the engraving is the fountain to the north of the Hall (circled, above). With the aid of a Resistivity survey (left) the fountain was located and excavated, and this gave a particularly useful sense of the scale of the plan and the grandeur of the Earl of Radnor’s garden design. The fountain was re-buried, but the ground staff now mow a circular patch of the park to show its location. In this instance there was an excavation but often, for example in locating paths which in turn outline flower beds, the survey alone is enough to demonstrate the accuracy or otherwise of the historic record.