146 Proceedings of Philosophical Societies. [Aug. 



insensibility to certain sounds in persons not otherwise deaf, 

 which he was led to observe by trying different modes of dimi- 

 nishing the sense of hearing in himself. He found, for example, 

 that when the membrana tympani was thrown into a state of 

 tension by external pressure by closing the nose and mouth, and 

 expanding the chest, the ear was rendered insensible to grave 

 tones, while its sensibility to sharper sounds was not affected. 

 In this case all sounds below F in the bass cliff were inaudible. 



In the healthy state of the ear, the power of discerning low 

 sounds is great, and of uncertain limits ; but if we attend to the 

 opposite extremity of the scale of audible sounds, and with a 

 series of small pipes exceeding each other in sharpness observe 

 their effects successively upon the ears of different persons, we 

 shall find considerable difference in their powers of hearing them, 

 ■and see i-eason to infer that the sense of hearing in man is more 

 limited than has been supposed. The author's attention was 

 particularly called to this circumstance by observing a person 

 insensible to the sound of a small organ pipe, which, with 

 respect to acuteness, was far within the limits of his own hear- 

 ing. By subsequent examination, it was found that this person's 

 hearing terminated at a note four octaves above the middle E of 

 the piano-forte. Other instances were then referred to of the 

 insensibility of certain persons to various acute sounds ; such as 

 the chirping of the grasshopper, cricket, and sparrow, and espe- 

 cially the squeak of the bat, the existence of which is unknown 

 to many individuals from its being inaudible to them. The pitch 

 of this sound was stated to be about five octaves above the mid- 

 dle E before mentioned. The author fixed the limits of his own 

 hearing at six octaves above the same note, and stated that from 

 numerous trials he was induced to think that the interval of a 

 sino-le note between two sounds was sufiicient to render the 

 higher note mandible. 



The range of human hearing includes upwards of nine 

 octaves, the whole of which are distinctly audible to most ears, 

 although the vibrations of the acuter sounds are 600 or 700 times 

 Tuore frequent than those of the lower; and the author concluded 

 by observing that it is very probable that other animals are so 

 organized as to be able to distinguish sounds still more acute, and 

 of course inaudible by human ears, and thus to possess what 

 may be considered as a new sense. 



At this meeting a paper was read by the Kev. F. H. WoUas- 

 ton, on the Measurement of Snowdon by the Thermometrical 

 Barometer. After some preliminary observations, the author 

 stated, that, as obtained by the thermometrical barometer when 

 the proper corrections were made, the height of this mountain 

 above the N.E. end of Caernarvon Quay was3546'25 feet. Gen. 

 Roy found it trigonometrically to be 3555'4 feet, and by the 

 barometer, 3548"9. An opportunity was also taken of comparing 

 the height of another luouatain as taken bv the thermometrical 



