AN elegant series of researches in photophony have lately been published by M. E. Mercadier of Paris, who has very carefully examined the phenomenon discovered by Graham Bell and Sumner Tainter, that an intermittent beam of light may generate a musical tone when it falls upon a thin disk. By way of distinguishing this phenomenon and its applications from the phenomenon of sensibility to light exhibited by annealed selenium, which constitutes the essential principle of the articulating photophone, M. Mercadier adopts the name of radiophony for the subject of his research: a name which appears moreover to have the advantage of not assuming à priori what kind of radiations, luminous, calorific, or actinic, are concerned in the production of the phenomenon. It is agreed by all who have experimented in this direction that the pitch of the note emitted by the disk corresponds precisely with the frequency of the intermittent flashes of light: but it has been disputed whether the effect is due to light or to heat. Prof. Bell found that the beam filtered through alum water to absorb the calorific ultra-red rays produced tones; and that even when a disk of thin ebonite rubber was interposed, the beam robbed of both heat-rays and light-rays could still generate tones. On the other hand, from the list of substances given by the original discoverers, it was evident that since dark and opaque substances with dull surfaces, and those which, like zinc and antimony, have high coefficients of thermal expansion, produce, cæteris paribus, the best results, the effects must probably arise from heating effects due to absorption of radiations of some kind and their degradation into heat of low temperature.