272 EXPLANATIONS OF VARIOUS PHENOMENA. J>ECT. xxv. 



exposed to the vapours of mercury, which became uniformly 

 deposited on the iodized plate, but on the silver one there 

 was a sharp image of the string, so that this image was 

 formed in the dark, and even without contact. Coins or 

 other objects leave their impressions in the same manner 

 with perfect sharpness and accuracy, when brought out by 

 vapour without contact, in darkness, and on simple metals. 

 Heat, electricity, and the evaporation of unctuous matter, 

 may account for some of these phenomena, but others clearly 

 point at some unknown influence exerted between the sur- 

 faces of solid bodies, and affecting their molecular structure 

 so as to determine the precipitation of vapours, an influence 

 which in all probability will ultimately be found to be either 

 the parathermic rays of Sir John Herschel, or intimately 

 connected with them. 



