In the month of February 1829, I discovered accidentally that a bar of iron, when heated and placed with one end on a solid block of lead, in cooling vibrated considerably, and produced sounds similar to those of an Æolian harp.

1. I have lately made further experiments with bars of copper, zinc, brass, and bell-metal, which, when heated and placed on blocks of lead, tin, or pewter, produce the same effect as the iron.

2. The bars I generally used in making the experiments, were 4 inches long, 1½ inch wide, and 1½ inch thick, with a rod 7 inches long attached to one end, to serve as a handle. A ridge is formed along the centre of one side of the broad part, by its being bevelled off towards each edge; the other side is flat. The longitudinal ridge is the part that rests on the block.