As fortune favors the brave, so accident aids the ingenious. After Professor Galvani had touched the muscles and nerves of many frogs with the spark drawn from the electrical machine, another accident occurred which led directly to the discovery of the galvanic battery. Having skinned a frog, he chanced to hang it by a _copper_ hook upon an _iron_ nail; and thus, without knowing it, he brought together the elements of a battery,--two metals and a wet frog. His object in hanging up this frog was to see if the electricity of the atmosphere would produce any effects, however slight, similar to those produced when the spark of the machine was applied to the creature. It did not. After watching his frog awhile, the Professor was proceeding to take it down, and while in the act of doing so the legs were convulsed! Struck with this occurrence, he replaced the frog, took it down again, put it back, took it down, until he discovered that, as often as the damp frog (still hanging upon its copper hook) touched the iron nail, the contraction of the muscles took place, as if the frog had been touched by a conductor connected with an electrical machine. This experiment was repeated hundreds of times, and varied in as many ways as mortal ingenuity could devise. Galvani at length settled down upon the method following: he wrapped the nerves taken from the loins of a frog in a leaf of tin, and placed the legs of the frog upon a plate of copper; then, as often as the leaf of tin was brought in contact with the plate of copper, the legs of the frog were convulsed.