THE TOPOPHONE. iSl 



A continuous sound is a series of these particles or globules spreading and 

 expanding as the water-rings in a pond." This much will be at once 

 perceived. 



Now, suppose a person up to his shoulders in a pond of water, and 

 someone throws a stone into it. If that person extend his arms and hands 

 at right angles facing the sound, each hand would touch the edge of a ripple 

 as it came towards him across the pond. He would then be facing the 

 source of the ripples or waves, and look along a radius of the circle formed 

 by the waves. But if he please, he can move his body so that both hands 

 shall touch the same wave at the same time, or he might turn away from 

 the source, and only one hand would touch the wave. But when both hands 

 are actually washed by the same circular ripple he must be facing the source 

 of it. Any position in which his fingers did not touch the ripple almost at 

 the same instant, would not be facing the source of the wave ripples. So 

 by turning and extending his hands, he could with his eyes shut find out 

 whether he was or was not facing the original source of the waves. 



This applied to sound waves in the air is the whole theory of the 

 Topophone, which, however, depends for its usefulness upon the same note 

 being sounded by all horns and whistles. One note must be better than all 

 the others, and that nofe, probably C (treble), caused by about two hundred 

 and sixty vibrations per second, has been found most applicable. If all 

 whistles and horns can by law be compelled to adjust themselves to this 

 note, then the Topophone will be a real and lasting benefit. 



Let us now look at the apparatus itself. 



It being conceded that the resonators are in the same key as the Fog- 

 horn, and this is necessary, they are placed upon the deck of the vessel. 

 An ear-tube of indiarubber is carried from each of these " resonators " 

 into the cabin. These tubes unite and again separate, ending in small pieces 

 ready to be fitted to the ears. The apparatus is fixed on deck, and the 

 arrangement which supports it passes into the cabin, and can be turned 

 about in any direction. Of course in this case a dial point is necessary to 

 indicate the direction in which the instrument is turned. If the machine be 

 worn on the shoulders of the officer of the watch he can move as he pleases, 

 and wants no indicator. 



The Topophone when used is so constructed, that when a horn is heard, 

 and when the listener is facing the sound, he can Jiear nothing ! When not 

 facing the origin of the sound he can hear the horn very well, but the 

 moment the resonators receive the sound together as they face the source, a 

 very low murmur is heard, or perhaps no sound at all. Why ? 



A certain pitch of tone is composed of vibrations or waves of equal 

 length. In all waves there is a hollow and a crest. One neutralizes the 

 other. The hollow of a sound wave meeting the crest of another wave 

 "interferes" to produce silence, stillness, a dead level. So in "light"; two 

 rays will produce darkness. We will endeavour to explain this. 



If we have two equal strings, each performing an equal number of 



