This time it is a high-voltage generator that is powered by falling droplets of water.
Two streams of separate drips pass through two metal sleeves, and then fall into two metal buckets.
The sleeves and buckets are cross-connected, and sparks are produced between the two halves of the circuit.
Given the set-up, I wold never have predicted any electrical activity at all- which is one of the many differences between me and Lord Kelvin.
I am still enjoying trying to work out why it makes sparks, and so will hold off googling until the frustration becomes unbearable.