234 DISCOVERIES OF PROFESSOR MOSER. SECT. XXV. 



surface has been touched in any particular parts by any 

 body, it acquires the property of precipitating all va- 

 pors, and these adhere to it or combine chemically with 

 it on those spots differently to what they do on the un- 

 touched 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 al- 

 ways reappear if the plate or surface be breathed upon, 

 and the same effect may be produced even on the sur- 

 face of mercury ; nor is absolute contact necessary. If 

 a screen cut in a pattern be held over a polished me- 

 tallic surface at a small distance, and the whole breathed 

 on : after the vapor has evaporated so that no trace is 

 left on the surface, the pattern comes out when it is 

 breathed on again. 



Professor Moser proved that bodies exert a very de- 

 cided 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 impression appeared on the plate till it 

 was breathed upon or exposed to the vapor of mercury, 

 and then these vapors adhered only to the parts where 

 the substance had been placed, making distinct images, 

 which in some cases were permanent after the vapor 

 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. 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 was in the order of the metals 

 named. When the plate was exposed to the vapor of 

 mercury the result was the same, but when the vapor 

 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 of an inch above it. 



