The Stone Ray was a heavily featured item in "The Mysterious Unfinished Invention".
The Mysterious Unfinished Invention
The Stone Ray is a raygun that was invented by the Cabbage Professor. It is the first known raygun that he had made, and after the stone ray, he expanded to various other types of rayguns.
The ray had the ability to transform people to stones, and the Professor used it to protect the island he had retreated to (in order to invent fumeless cabbages) from the Beagle Boys, as well as the ducks.
Following the events of "The Mysterious Unfinished Invention", the Cabbage Professor had to leave his island, as it had ran out of cabbages. He later destroyed the stone ray.
The rayguns that he invented after the stone ray seemed to use one AA battery as their power supply.