110 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK n. 



II. THE SPEAKING-TRUMPET. 



The human voice is also transmitted to great distaucos by em- 

 ploying an instrument much used at sea, called a speaking-trumpet. 

 This is a tube of a conical form having at its narrowest end a wide 

 cup-like mouthpiece; on putting it to the mouth the mouthpiece 



FK;. (i(i. Speaking-trumpet. 



covers it entirely, so that the movement of the lips can be made ' 

 inside with ease. The opposite extremity, which is bell-shaped, is 

 turned in the direction whither the sound is to be sent. Kircher in 

 his great work, Ars Magna Lucis ct Umbrce, and in his Pkonuryia, 



Fit;. 07. The horn of Alexander the Great (Kircher). 



mentions a kind of gigantic speaking-trumpet, described as the horn 

 of Alexander the Great, which was used in the armies of the Conqueror 

 to recall soldiers even at a distance of a hundred stadia. It is cer- 

 tain, however, that the speaking-trumpet is of modern invention and 



