1859.] Dr. Alison on certain Auditory Phenomena, 63 



WEEKLY EVENING MEETING, 



Friday, February 18, 1859. 

 Charles Wheatstone, Esq. F.R.S. Vice-President, in the Cliair. 



SOMERVILLE ScOTT AlISON, M.D. 



On certain Auditory Phenomena. 



[Through the indisposition of Dr. Alison, the subject of the 

 discourse, of which the following is an abstract, was kindly laid before 

 the Members by Dr. Tyndall.] 



Certain auditory phenomena, hearing upon the correlation of the 

 ears, and possessing some interest, have been recently made out by the 

 employment of a double stethoscope, which has been called the differ- 

 ential stethophone, contrived by Dr. Scott Alison.* This instrument, 

 {see p. 64) like the first double stethoscope, viz., that of Dr. Leared, is 

 applied to both ears, and has the self-adjustment of that of Dr. Camman of 

 New York. It consists of two tubes for the two ears respectively, each 

 independent of the other except for purposes of adjustment, manual 

 management, and convenience of application. Each tube consists 

 again of two parts, a tube part and a cup or sound-collecting aperture. 

 The cup, made of mahogany or other freely vibrating wood, is about 

 one inch in diameter at its mouth, and about one-eighth of an inch in 

 diameter at its proximal extremity. The tube near the cup is made of 

 flexible wire, and is covered with silk ; the part nearer the ear is made 

 of metal, and at the aural extremity is furnished with an ear-knob of 

 ivory for insertion into the cavity of the external ear. The bore of 

 the knob and of the metal part of the tube is about one-eighth of an 

 inch in diameter. 



An instrument possessing the same acoustic value may be made at 

 much less expense than that above described. A piece of india 

 rubber tube, about 18 inches long, having a bore of one-fifth of an 

 inch in diameter, may have fitted upon one extremity an ear-knob, and 



* It is to be observed, that for the differential stethophone to have its properties 

 made available, it is necessary that both ears of the observer should be alike in 

 acuteness. 



