I love the “Cartesian Diver” experiment (see here for how to make it). My one issue is that the presenter needs to hold the bottle to cause the effect. If the “submarine” is well balanced only a moderate amount of squeezing is needed but still there’s some tell tale signs of muscles contracting – it just doesn’t look natural!
On the hunt for a way to present the effect remotely I had the idea of using a blood pressure cuff to squeeze the bottle. I removed the pressure gauge and just directly linked the ‘squeeze bulb’ to the cuff. It now means you can stand a distance away and move the submarine. It’s also brilliant for young children or those with a physical disability who don’t have the hand strength to squeeze the bottle tight enough themselves. I can also see this being turned into an exhibition at a science centre.