Four distinct sources of sound were noticed in the course of the experiments.

1. The variation of the longitudinal tension of the wire, owing to variation in the heating, still appears to be the most likely explanation of the action of the wire telephone, when a very fine wire of ordinary metal is used. Experiments were tried with induction coils of various sizes, the violin and microphone being put into the primary circuit and the fine wire telephone into the secondary. It was found that the sound diminished as the spark-giving power of the coil increased. With Professor Tait's large induction coil no sound at all could be obtained, when the secondary was closed through the most sensitive wire I possess.