268 DISCOVEKIES OF PROFESSOR MOSER, [SKCT.XXV. 



Moser that the subject of solar radiation would be imperfect 

 were they omitted. The discovery of Daguerre shows that 

 the action of light on the iodide of silver renders it capable 

 of condensing the vapour of mercury which adheres to the 

 parts affected by it. Professor Moser of Konigsberg has 

 proved that the same effect is produced by the simple contact 

 of bodies, and even by their very near juxtaposition, and 

 that in total darkness as well as in light. This discovery he 

 announced in the following words : " If a surface has been 

 touched in any particular parts by any body, it acquires the 

 property of precipitating all vapours, and these adhere to it 

 or combine chemically with it on these spots differently to 

 what they do on the untouched parts." If we write on a 

 plate of glass or any smooth surface whatever with blotting 

 paper, a brush, or anything else, and then clean it, the 

 characters always reappear if the plate or surface be breathed 

 upon, and the same effect may be produced even on the 

 surface of mercury ; nor is absolute contact necessary. If a 

 screen cut in a pattern be held over a polished metallic 

 surface at a small distance, and the whole breathed on, after 

 the vapour has evaporated so that no trace is left on the sur- 

 face, the pattern comes out when it is breathed on again. 



Professor Moser proved that bodies exert a very decided 

 influence upon each other, by placing coins, cut stones, 

 pieces of horn, and other substances, a short time on a warm 

 metallic plate ; when the substance was removed, no impres- 

 sion appeared on the plate till it was breathed upon or ex- 

 posed 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 impres- 

 sions 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. Hunt has shown that many of these phenomena de- 



