398 Analysis of Scientific Books, 



vi. On Sounds inaudible by certain Ears. Bi/ William 

 Hyde Wollaston, M.D., P.R.S. 



This paper contains some interesting elucidations of the phy- 

 siology of the sense of hearing. Dr. Wollaston observes that 

 deaf persons are in general more susceptible of sharp than low 

 sounds ; and that in the healthy state of the ear this partial in- 

 sensibility may be brought on by throwing the membrane of the 

 tympanum into a state of tension from external pressure, by 

 attempting forcibly to draw breath when the nose and mouth 

 are closed. In this way the ear may be rendered insensible to 

 sounds below F marked by the base cliff; and in illustration. 

 Dr. Wollaston observes, that, in such state of the ear, listen- 

 ing to the sound of a carriage, the deep rumbling noise of 

 the body is not heard, but the rattle of a chain, or loose screw, 

 remains at least as audible as before. *' Although," continues 

 the author, ^' I cannot propose such an experiment as a means 

 of improving the effect of good music, yet, as a source of 

 amusement, even from a defective performance, I have occa- 

 sionally tried it at a concert with singular effect, since none of 

 the sharper sounds are lost, but, by the suppression of a great 

 mass of louder sounds, the shriller ones are so much the more 

 distinctly perceived, even to the rattling of the keys of a bad 

 instrument, or scraping of catgut unskilfully touched." 



In the healthy state of the ear there seems no limit to the 

 discernment of low sounds; but if we turn our attention to the 

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

 series of pipes exceeding each other in sharpness, examine their 

 effects successively upon the ears of several persons, we find a 

 striking difference in their powers of perceiving very sharp 

 sounds. It is thus that certain persons are perfectly insensible 

 to the chirping of the cricket and grasshopper, to the squeak 

 of the bat, and even to the chirping of the sparrow. 



Since there is nothing in the constitution of the atmosphere 

 to prevent vibrations much more frequent than any of which we 

 ajre conscious, we may imagine that animals, like the grylli. 



