George Breeds electrical guitar is not an electric guitar in the modern sense. It did not electrically amplify the strings to make them louder. Instead it used electricity to sound the strings of an acoustic instrument. You did not need to strum or pluck this guitar: by pressing the string onto a fret a circuit was made which caused the string to vibrate automatically and continuously. you could there play it with a single hand. It was a bit like a steel string acoustic driven by a Ebow or Fernades Sustainer.

The guitar employs the Laplace Force (which arises when a wire carrying an electrical current is placed in a magnetic field) to vibrate the strings. The  strength of this force depends on the size of the current, the strength of the magnetic field and the length of the wire within that field. Breeds design means that the player is in electrical contact with the string current, so for saftey reasons this current has to be limited. This means that a relatively strong magnet was required: Breed used an electromagnet because the permanent magents of the day were rather weak.

A rotating slip ring modulates the current to the strings. The electrical track on the slip ring is broken in random intervals. This switches the string currents on and off randomly, which has the effect of causing the string to vibrate and sounding the instrument.

The guitar did not suceed, possibly because it was ergonomically poor: the huge electromagnet was very heavy and caused the guitar to fall forwards in the playing position. The sound was also less than spectacular. The organologist Matthew Hill has reconstructed a George Breed guitar from the patent designs, and you can hear a sound sample of his instrument at his website (archived 2009).

Source: George Beauchamp and the rise of the electric guitar up to 1939. PhD Thesis of Matthew Hill. 2014. University of Edinburgh