A bit like our old friend Zebedee?
One end of the wire is bent into a 1/4" circle to balance the penny on... the other end is stuck into a little glob of modelling clay (which is stuck on the bottom of the bowl)... an when viewed from a particular angle... the wire is not visible an the penny now apears to be floating in air.!!!
Then cool water (keeping the clay firm) is added to the bowl just until it rises above the penny... which is easy to do since the penny has a thin coat of Vaseline on it.!!!