THE AUTOPHONE. 183 



one followed the other a little, so that the hollow of one coincided with the 

 crest of the other, and vice versa, the waves would obliterate each other, and 

 a dead level would result. One tube of the Topophone is half a wave length 

 longer than the other, and when the resonators are in a line and receive the 

 wave at the same time, one ear hears the elevation of the sound wave, and 

 the other the depression, the sound is neutralized, and comparative, if not 

 actual, silence results. The sailor knows in what direction the land lies, and 

 can calculate his distance, or anchor if he please. 



If amongst our readers there be any who wish to make for themselves 

 an acoustic signalling apparatus there is physically nothing to prevent them 

 from constructing such an instrument as that shown in the annexed woodcut 

 (fig. 185). It is founded upon the speaking-trumpet principle, which is 

 supposed to have been originated by Samuel Markland, in 1670. 



Kircher, in his "Ars magna et umbra" and in his "Phonurgia" mentions 

 a kind of speaking-trumpet, or porte voix, of gigantic dimensions, and called 

 the " Horn of Alexander." According to Kircher, the instrument was used 

 by Alexander the Great to summon his soldiers from a distance of ten 

 miles. The diameter of the circumference was about eight feet, and Kircher 

 conjectured that the instrument was mounted upon three supports. 



During the last century, a German professor, named Huth, made a 

 model of the horn, and found it answered every purpose of a speaking- 

 trumpet with most powerful results, but we beg leave to doubt whether 

 the instrument really carried the voice to any very great distance. 



The Acoustic Cornet, which is the counterpart of the speaking-trumpet, 

 has been made in many different forms during the last two centuries, but 

 none of them to the present time consist of anything more intricate than a 

 simple tube with a mouthpiece and bell-shaped orifice. 



Professor Edison, however, in his researches regarding the conveyance 

 of sounds, has made numerous and interesting experiments. On one 

 occasion, with his Megaphone he carried on a conversation at a distance of 

 nearly two miles, without any other assistance from instruments except a few 

 little cornets of cardboard. These constitute the Megaphone, which may be 

 regarded as a curiosity, considering the effects produced by such simple 

 means. The illustration (fig. 185) represents the instrument which is (or 

 was lately) fixed upon the balcony of Mr. Edison's house. At a mile- 

 and-a-half distant from the house, at a spot indicated by the two birds in 

 the picture, another instrument was fixed, and conversation was carried on 

 with ease. 



Perhaps the present opportunity will be the most convenient to speak 

 of the AUTOPHONE, although it is more a musical than an acoustic instru- 

 ment. Until lately Barbary organs and piano organs have been the only 

 means by which poor people have been able to hear aivy music, and that not 

 of a very elevated class. Besides, there is a good deal of expense connected 

 with the possession of an organ. But the Americans, with a view to 

 popularize music, have invented the AUTOPHONE, which is simply a 



