196 



I have constructed the instrument which I propose to call the 

 Stereomonoscope, as it exhibits in perfect relief a picture which 

 appears single on the ground glass of the new instrument, and as 

 single as the image of the camera obscura has always been supposed 

 to be. 



The instrument, in its present rough state, is undoubtedly very im- 

 perfect and susceptible of many improvements which time and ex- 

 perience will suggest. I present it as the result of a first attempt, 

 hoping that it will be found curious as illustrating a new and inter- 

 esting scientific fact and producing an effect quite unexpected in 

 optics. 



April 22, 1858. 

 Major-General SAB1NE, Treasurer and V.P., in the Chair. 



Professor Julius Pliicker, Foreign Member, was admitted into the 

 Society. 



The following communications were read : 



I. " On the Differential Stethophone, and some new Phenomena 

 observed by it." By S. SCOTT ALISON, M.D., Assistant 

 Physician to the Hospital for Consumption. Com- 

 municated by Prof. TYNDALL, F.R.S. Received March 

 22, 1858. 



Engaged for some years in investigations into the phenomena of 

 audition, I have become cognizant of some facts which I believe have 

 hitherto remained unnoticed, and which are certainly not generally 

 known to physicists and physiologists. 



The first of which I shall treat is the restriction of hearing 

 external sounds of the same character to one ear, when the intensity 

 is moderately, yet decidedly greater in one ear than in the other, the 

 hearing being limited to that ear into which the sound is poured in 

 greater intensity. The sound is heard alternately in one ear and in 

 the other, as it is conveyed in increasing degrees of intensity, and 

 hearing is suspended alternately in one ear and in the other, as the 

 sound is conveyed in lessening degrees of intensity. 



Sound, as is well known, if applied to both ears in equal intensity, 



