RORIC FIGURES, images produced by on glass or other polished sur faces which have been covered by some object. Dr. J. W. Draper, in 1840, called attention to the subject in the Philosophical Magazine. Moser of Konigsberg, in 1892, made a communication to the French academy through lI. Regnault, in which he stated that, when two bodies are very near each other, they receive impressions of each other's images, or, if a smooth surface has been touched by another body, it acquires the prop erty of precipitating vapors, which, by their action, cause an impression which gives to the surface a different appearance. These roHe figures are often called by the Germans hauckfiguren, or breath figures. Mr. Grove has called them molecular impressions, Mr. Hunt has produced similar effects by heat. He placed gold, silver, and bronze coins and medals on a polished heated copper-plate. After cooling lie removed the coins, etc., and exposed the plate to the vapor of mercury. The parts which had been covered by gold and silver coins gave the most distinct impressions, the gold more than the silver. Bregnet, a French watchmaker, found markings on the exterior of the inner it case of a watch reproduced inversely on the inner surface of the outer case. Phenomena of this kind hare been observed by thousands, but the explanations vary, as probably do the causes; there sometimes being a transfer of matter from one body to the other, and sometimes a molecular change in the surface in consequence of its having been for some time exposed to different external circumstances. There is always a molecular
change taking place on the surfaces of all bodies; the very constitution of matter neces sitates it. The molecules of all matter are in a constant state of vibration: often there is a loss of substance in consequence of such vibration; hut when there is no loss there is necessarily some change in the surface, and this change will vary with •the aiaterial by which the surface is covered. A gold coin will exert a different impression from a silver one. or from a steel, iron, or bronze and a woolen or silk fabric will pro duce a still different effect. The surfaces of all these objects are constantly throwing off, it may be infinitesimal, particles of matter, end the mutual action between two surfaces must vary with the relative properties of those surfaces. The surface of a piece of pol ished steel or silver will change more rapidly in a heated than in a cool room, other cir cumstances being the same; and also faster in a light than in a dark room. The kinematic energy of the surface, and therefore its change, will vary with circum stances.
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