200 



WELLS'S NATURAL THILOSOPHY. 



Fig. 192. The course of the rays of 



souud proceeding from the 

 mouth through this instru- 

 ment, may be shown by 

 Fig. 192. The trumpet be- 

 ing direetfid to any point, a 

 coliection of p.irallel rays of 

 sound moves toward such 

 point, and they rea/^h the 

 ear in much greater number than would the divergmg rays which would pro- 

 ceed from a speaker without such an instrument. 



\vh.it is an 434. An Ear-Trumpet is, in form and appli- 

 Ear-Trumpet? cution, tliG TeversG of a speaking-trumpet, but 

 in principle the same. The rajs of sound proceeding from 

 a speaker, more or less distant, enter the hearing-trumpet 

 and are reflected in such a manner as to concentrate the 

 sound upon the opening of the ear. 



Fig. 193 represents the form of the ear-trumpet gen- 

 erally used by deaf persons. The aperture A is placed 

 within the ear, and the sound which enters at B is, by a 

 series of reflections from the interior of the instrument, 

 concentrated at A. 



In the same manner persons hold the hand concave 

 behind the ear, in order to hear more distinctly. The 

 concave hand acts, in some respects, as an ear-trumpet, and reflects the sound 

 into the ear. 



Most of the stories in respect to the so-called " haunted houses" can be all 

 satisfactorily explained by reference to the principles which govern the re- 

 flection of sounds. Owing to a peculiar arrangement of reflecting walls and 

 partitions, sounds produced by ordinary causes are ofl:en heard in certain 

 localities at remote distances, in apparently the most unaccountable manner. 

 Ignorant persons become alarmed, and their imagmation connects the phe- 

 nomenon with some supernatural cause. 



435. A right understanding of the principles which govern the reflection 

 of sound is often of the utmost importance in the construction of buildings 

 intended for public speaking, as halls, churches, etc. 



Experience shows that the human voice is capable of fllling a larger -space 

 than was ever probably inclosed within the walls of a single room. 



The circumstances which seem necessary in order that the 

 human voice should be heard to the greatest possible distance, 

 and with the greatest distinctness, seem to be, a perfectly 

 tranquil and uniformly dense atmosphere, the absence of all 

 extraneous sounds, the absence of echoes and reverberations^ 

 and the proper arrangement of the reflecting surfaces. 



"What circum- 

 stances are nec- 

 essary to in- 

 sure the utmost 

 distinctness in 

 hearins' ? 



