John J, I hope you don't mind if a sceptic makes a suggestion. I think that your brain may do the job better if you have a clear idea of what you are dowsing for. Water and minerals are quite easy to form a mental model for, and to recognise previous experience of - you might find different results if you hold in your mind different interpretations of what leylines are - in the ground or overground, for example. Make sure you aren't picking up water, power lines (National GRid, I mean) and underground structures such as gas pipes.

And get someone else to verify your results without telling them or indicating in any way what your results were. There was an item way back on Tomorrow's World, not on April 1st, in which someone demonstrated setting up a leyline. I followed the instructions and had positive results, but they were not repeatable. Even by me.

Whatever happens, you will have a good time seeing the past. If you spot any ancient yew trees, do let me know!

Penny