1859.] on certain Auditor?/ Phenomena, 67 



on from one ear to the other. This corresponds with ordinary audi- 

 tion : for if we draw a circle around the head in the plane of the 

 horizon, which may be callec^an acoustic circle, we shall find that on 

 carrying a sounding- body round it, binaural sensation is procured only 

 so long as the body is within about 10° on either side of a line drawn for- 

 wards and backwards at right angles with the transverse line of the head. 

 In the case then of such a circle we have distinct binaural sensation 

 limited to a region of about 20° in front and 20° behind. The inter- 

 mediate arcs are the regions of uno-aural sensation ; it thus appears 

 that in ordinary audition a moderate superiority in respect of intensity 

 of sound gives a monopoly of hearing to one ear. 



The intensity of sourxi in the ear which has served to give it a 

 monopoly of hearing to the disadvantage of the other ear, has in the 

 foregoing observations been chiefly obtained by greater proximity of 

 one cup of the stethophone to the sounding body over the other ; but 

 this may be procured by other means. A superior mode of con- 

 duction in respect of one ear over the other, or of one cup of the 

 stethophone over the other, when the ears and the cups are similarly 

 placed in respect of the sounding body, will give a like intensity. A 

 solid rod in the case of one ear, while the atmosphere is the only 

 medium of communication in the case of the other, in respect of a 

 sound of a solid body, will suffice to give the monopolizing intensity. 

 In the same way it has been recently ascertained by Dr. Scott Alison, 

 that water placed at the distal extremity of a hearing tube will give 

 an advantage of intensification or of more perfect conduction, sufficient 



to restrict hearing to that ear favoured with its aid, and to render sen- 

 sationless the ear connected with the sounding body by means of a 

 hearing tube having no water at its extremity to intensify or economize 

 sound by superior conduction. A ring of water between the edge of 



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