Professor Moser proved that bodies exert a very decided influence upon each other, by placing coins, cut stones, pieces of horn, and other substances, for a short time on a warm metallic plate: when the substance was removed, no impression appeared on the plate till it was breathed upon or exposed to the vapour of mercury, and then these vapours adhered only to the parts where the substance had been placed, making distinct images, which in some cases were permanent after the vapour was removed. Similar impressions were obtained on glass and other substances even when the bodies were not in contact, and the results were the same whether the experiments were performed in light or in darkness. Mr. Grove found, when plates of zinc and copper were closely approximated, but not in contact, and suddenly separated, that one was positively and the other negatively electric; whence he inferred that the intervening medium was either polarised, or that a radiation analogous, if not identical, with that which produces Moser’s images takes place from plate to plate. Mr. Hunt has shown that many of these phenomena depend on difference of temperature, and that, in order to obtain good impressions, dissimilar metals must be used. For example, gold, silver, bronze, and copper coins were placed on a plate of copper too hot to be touched, and allowed to remain till the plate cooled: all the coins had made an impression, the distinctness and intensity of which were in the order of the metals named. When the plate was exposed to the vapour of mercury the result was the same, but, when the vapour was wiped off, the gold and silver coins only had left permanent images on the copper. These impressions are often minutely perfect, whether the coins are in actual contact with the plate or one-eighth of an inch above it. The mass of the metal has a material influence on the result; a large copper coin makes a better impression on a copper plate than a small silver coin. When coins of different metals are placed on the same plate they interfere with each other. When, instead of being heated, the copper plate was cooled by a freezing mixture, and bad conductors of heat laid upon it, as wood, paper, glass, &c., the result was similar.