The famous Tesla electric car company takes its brand name from the wacky but hugely inventive Nikola Tesla. Beginning in Victorian times, Tesla discovered and invented a tonne of stuff like the AC electricity system we use today, radio, radio control and – what we are interested in here – the ability of rotating smooth discs to produce a jet of liquid.
Normally a paddle steamer is propelled by one or two huge wheels with their lower rim in the water. The wheels have blades on them which push the water backwards. But amazingly, you don’t have to put blades on the wheels to make them ‘grip’ the water. You can use a plain smooth disc and rely on the ‘grip’ of viscosity.
Image credit: E&T
As a wheel spins in water, it will pull along a thin layer of water next to the wheel, and that layer...