118 Mr. R. Moon on the Structure of the Human Ear, and on 



such oscillation of the temperature up and down in the course 

 of the day and night contributed to the daily descent ; and it is 

 the effect of these oscillations, however numerous and however 

 separately small, which that descent totalizes. I accordingly 

 remarked that it was on days when the thermometer in the sun 

 varied its height rapidly and much (as on bright days with cold 

 winds, or when clouds were driven over the sun) that the de- 

 scent was greatest. So remarkably indeed was this the case, 

 that every cloud which shut off the sun for a time from the lead, 

 and every cold gust of wind which blew upon it in the sunshine, 

 seemed to bring it a step down. On the contrary, when the sky 

 was open and clear, and the heat advanced and receded uniformly, 

 the descent was less, although the difference of the extreme tem- 

 peratures of the day might be greater. It was least of all on 

 days when there was continuous rain. During the night it 

 was often imperceptible — especially in the earlier months of the 

 year, when it was dark from the time of the evening observation 

 to that of the morning. In April and May this interval included 

 a period of sunlight in the early morning, to which the descent 

 registered as having taken place in the night was no doubt due, 



XIII. On the Structure of the Human Ear, and on the Mode in 

 which it administers to the Perception of Sound. By R. Moon, 

 M. A., Honorary Fellow of Queen's College, Cambridge*. 



I STATED in a former paper f that the human ear is so con- 

 structed as to suppress vibrations arising from waves of 

 condensation which become incident upon it, at the same time 

 that it transmits to the sensorium vibrations arising from waves 

 of rarefaction. I now propose to exhibit the grounds upon 

 which I rest this assertion. 



The view of the constitution and functions of the organ of 

 hearing which I have just expressed, incredible as it may at first 

 sight appear, will be found, if I mistake not, to dissipate the 

 mystery which has hitherto characterized that most complicated 

 anatomical problem. The circumstances by which this view of 

 the subject was first suggested to me require some words of ex- 

 planation. 



I have elsewhere shown J that if the problem of the propaga- 

 tion of sound through air be pursued by a strict analysis, we 

 shall be led to a conclusion with regard to the velocity of pro- 



* Communicated by the Author. 



t " On the Theory of Sound." See Phil. Mag. for March last. 

 X See the paper last referred to, and an earlier one, "On the Theory of 

 Pressure in Fluids," in the Phil. Mag. for August 1868. 



