I read up on how to make one of those in the high School library when I was in high school... Graduated in 1968. It was an old book then.
How to make:
Take two wires, different metals, (Too many years but I think Copper and iron should do) cut a bunch of six inch lengths.
Make them into a daisy so that all the / wires are copper and all the \ are iron
/\/\/\/\/\/\/\/\/
Form into a circle
heat the center
Measure voltage at the ends.
The number of junctions determins voltage, I recommend a blocking diode (Electrical check valve) The important thing is one pair of wire ends (Copper/Iron) gets hot, the other (Outer ring) does not.
