158 LETTERS ON NATURAL MAGIC. 



and shutting of the doors themselves afforded a 

 sufficient imitation of ordinary thunder. In the 

 palace of the Persian king, however, a more 

 artificial imitation is likely to have been employed, 

 and it is not improbable that the method used in 

 our modern theatres was known to the ancients. 

 A thin sheet of iron, three or four feet long, such 

 as that used for German stoves, is held by one 

 corner between the finger and the thumb, and 

 allowed to hang freely by its own weight. The 

 hand is then moved or shaken horizontally, so as 

 to agitate the corner in a direction at right angles 

 to the surface of the sheet. By this simple pro- 

 cess a great variety of sounds may be produced, 

 varying from the deep growl of distant thunder 

 to those loud and explosive bursts which rattle in 

 quick succession from clouds immediately over 

 our heads. The operator soon acquires great 

 power over this instrument, so as to be able to 

 produce from it any intensity and character of 

 sound that may be required. The same effect 

 may be produced by sheets of tin-plate, and by 

 thin plates of mica ; but, on account of their 

 small size, the sound is shorter and more acute, 

 In modern exhibitions an admirable imitation of 

 lightning is produced by throwing the powder of 

 rosin, or the dust of lycopodium, through a flame ; 

 and the rattling showers of rain which accompany 

 these meteors are well imitated by a well-regu- 

 lated shower of peas. 



The principal pieces of acoustic mechanism 

 used by the ancients were speaking or singing 

 heads, which were constructed for the purpose of 

 representing the gods, or of uttering oracular 

 responses. Among these, the speaking head of 



