Thanks guys, very very useful posts

I hadn't seen LS's latest upload. It brings in much of the thinking, experimental oddities and interests that probably many of us share. Except, being Lasersaber, he's done it in a way that screams 'I have to replicate this right now' lol
It seems to show potential differences quite clearly, where a circuit connected to a strongly opposite polarity that's unconnected to anything else, can influence its operation. Reminds of the trick to starting some wireless electricity circuits by using a piezo BBQ lighter.
How on earth the video has 12 dislikes is beyond me.
Own experiments have shown odd effects and I was/am very interested in Grumage's back garden experiments of a similar nature. Graham has apparently run out of time or such to continue, but I do hope he does so.
One of my own observations was when solar charging a car battery. i could connect an LED to just the positive terminal and via a blocking oscillator to a ground post. It fired up.
[youtube]qzrLxCxJyZw[/youtube]
The vid above also shows the odd effects of solar charging the previously rubbish, alum converted battery, with a set of solar bits that totaled 40V but only a hundred or so mA.
Related to all this are the experiments a couple of years back with the Stubblefield telephone type of circuits.
In one fun quick test, that was the transmission of music, from the PC in the house, out to the backyard over 1 wire. it works with the earphone output from PC speakers, but would be much enhanced by using an amplifier.
What you do, is plug in a jack plug, but only run the signal wire, not the ground part outside.
Attach a 1/4W regular 8ohm speaker to the wire and put a 1ft metal rod in the ground that connects to the other side of the speaker.
Audio will be heard

I think the direction will be similar to Lasersaber's circuit for the moment (thanks very much A.King for the other circuit types to try) and i'll see about using just the ground itself to fire one up.
Perhaps related, is that when using my galvanism powered Garden lights from a few years back now, the earth around the electrodes would dry in the area they were put. Move a light even an inch away and it would again fire up for a few days. Water the ground, same thing, it would fire back up. The drying of the ground has always been of interest.