TO Experiments on Audition, 



line. The spring of the rods will be sufficient to fix the plates^ 



to the ears, but for greater security ribands may be attached 

 to each rod near its insertion iii the plate, and be tied behind 

 the head. 



A more simple instrument may be constructed to be applied 

 to one ear only, by inserting a straight rod perpendicularly into 

 a similar plate to those described above. 



The Microphone is calculated only for hearing sounds when 

 it. is in immediate contact with sonorous bodies ; when^ they 

 are diffused by their transmission through the air, this instru- 

 ment will not afford the slightest assistance. 



It is not my intention in this place to detail all the various 

 experiments which may be made with this instrument, a few 

 will suffice to enable the experimenter to vary them at his 

 pleasure. 



• 1. If a bell be rung in a vessel of water, and the point of the* 

 microphone be placed in the water at different distances from 

 the bell, the differences of intensity will be very sensible. 2. If 

 the point of the microphone be applied to the sides of a vessel 

 containing a boiling liquid, or if it be placed in the liquid itself, 

 the various sounds which are rendered may be heard very dis- 

 tinctly. 3. The instrument affords a means of ascertaining, 

 with considerable accuracy, the points of a sonorous body 

 at which the intensity of vibration is the greatest or least ; 

 thus, placing its point on different parts of the sounding board 

 of a violin or guitar, whilst one of its strings is in vibration, the 

 points of greatest and least vibration are easily distinguished. 

 4. If the stem of a sounding tuning-fork be brought in contact 

 with any part of the microphone^ and at the same time a musi- 

 cal sound be produced by the voice, the most uninitiated ear 



