OF SOUND. 231 



from all the trumpets. This effect was produced 

 by one of the standards of the frame being hollow, 

 opening opposite the mouth of the trumpets, and 

 communicating with a large case placed in an 

 adjoining room, and containing the confederate. 



Upon this principle also is constructed the 

 oracular bust, which is made in this manner. Place 

 a bust on a pedestal in the corner of a room, and 

 let there be two tin tubes, one going from the 

 mouth and the other from the ear of the bust, 

 through the pedestal and floor, to an under apart- 

 ment j there may likewise be wires that go from 

 the under jaw and the eyes of the bust, by which 

 they may be easily moved. A person being placed 

 in the under room, and at a signal given, applying 

 his ear to one of the tubes, will hear any question 

 that is asked by another person above who speaks 

 into the ear of the bust, and immediately reply j 

 the sound will move through the tube, and seem 

 to come from the mouth of the bust. 



Contrivances such as these have been thought to 

 be magical, by ignorant persons who were not in the 

 secret. 



The speaking trumpet is an instrument for con- 

 veying sounds to considerable distances. The 

 form has sometimes been directed to be hyperbolic 

 or parabolic, but it is found that a conical form 

 succeeds better than any other. 



The hearing trumpet is in form like the speaking 

 trumpet, the vertex of the cone being placed to 

 the ear. 



c> 4> 



