lid LETTEBS ON NATUKAL MAGIC. 



or reflected, from any other body. If, in place 

 of polishing the depressed parts and roughening 

 its raised parts, we make the raised parts polished 

 and roughen the depressed parts, the inscription 

 will now be less luminous than the depressed 

 parts, and we shall still be able to read it, from 

 its being as it were written in black letters on a 

 white ground. The first time I made this ex- 

 periment, without being aware of what would be 

 the result, I used a French shilling of Louis XV., 

 and I was not a little surprised to observe upon 

 its surface, in black letters, the inscription BENE- 



DICTITM SIT NOMEN DEI. 



The most surprising form of this experiment is 

 when we use a coin from which the inscription 

 has been either wholly obliterated, or obliterated 

 in such a degree as to be illegible. When such 

 a coin is laid upon the red-hot iron, the letters 

 and figures become oxidated, and the film of 

 oxide radiating more powerfully than the rest of 

 the coin, the illegible inscription may be now 

 distinctly read, to the great surprise of the 

 observer, who had examined the blank surface 

 of the coin previous to its being placed upon the 

 hot iron. The different appearances of the same 

 coin, according as the raised parts are polished 

 or roughened, are shown in Fig. 23 and 24. 



In order to explain the cause of these remark- 

 able effects, we must notice a method which has 

 been long known, though never explained, of 

 deciphering the inscriptions on worn-out coins. 

 This is done by merely placing the coin upon a 

 hot iron ; an oxidation takes place over the whole 

 surface of the coin, the film of oxide changing 

 its tint with the intensity or continuance of the 



