Cartesian Diver

Also known as a Cartesian devil, it was first mentioned by Raffaello Magiotti in 1648.

Picture from: A. Privat Deschanel Elementary Treatise on Natural Philosophy Part I. Mechanics, Hydrostatics, and Pneumatics (New York: D. Appleton and Company, 1884)

Versions of these vary greatly, ranging from a ketchup packet

to hand blown glass.

You can even use a lego mini fig, as shown here.

Pop Pop Boats

  Pop pop boats are an old toy, the first ones came out around the late 1800's. Essentially a simple toy steam boat with no moving parts, engines are either coil (which are silent), or diaphragm. It is the diaphragm engine which makes the noise from whence this toy got its name.

DIY coil engine pop pop boat

Video - diy coil engine and made in India pop pop boats.

Baking powder submarine

  I recall getting this from a Captain Crunch cereal box in the 70's. Long gone, I found a picture of it online. Basically you add a little baking powder (NOT baking soda, that won't work!) to it and it sinks and rises repeatedly.

A youtube video of one.