Don't try this at home!
These plans were discovered by cigar box guitar builder and researcher, John "Reddog" McNair. I'm not sure whether to thank him for the discovery or scold him for digging up such a dangerous project!
In the directions of this 1919 article, readers are advised to hook up batteries and a rheostat to a single string which heats it, lowering the tension. The guitar is played by heating and cooling the string while strumming it at the same time.