VOL. XIV.] PHILOSOPHICAL TRANSACTIONS. 7 



much when the air passes over an uneven surface. But the smooth surface of 

 the water conveys a sound more entire, and to a greater distance than the plane 

 surface of a piece of ground, a wall, or any other solid body whatever. 



The organ, which is the ear, is helped much by placing it near a wall, 

 especially at one end of an arch, when the sound is produced at the other, or 

 near the surface of water, or of the earth, along which the sounds are most 

 easily and naturally conveyed. Indeed it is incredible, how far a sound made 

 on the earth may be heard in a still night, if a man lay his ear close to the 

 ground in a large plain. Here otacoustics help the ear; which may be so con- 

 trived, that the sound might enter the ear without any refraction. 



As to refracted vision, it arises from the different density, figure and magni- 

 tude of the medium ; which is somewhat altered also by the divers incidence of 

 the visjve rays : and so it is in refracted hearing, all these causes concur to its 

 production, and some others to be hereafter considered. Now as any object, a 

 man for instance, seen through a thickened air, by refraction appears larger 

 than he really is : so likewise a sound, heard through the same thickened part 

 of the atmosphere, will be considerably varied from what it would seem to be, 

 if heard through a thinner medium. And this I call a refracted sound. Im- 

 provements of refracted vision have been made by artificial instruments, bv 

 grinding or blowing glasses into a certain figure, and placing them at due 

 distances; whereby the object may be enabled to emit its rays more vigorously, 

 and the visive faculty empowered the better to receive them. And thus also in- 

 struments may be contrived for assisting both the sonorous body, to send forth 

 its sound more strongly, and the acoustic faculty to receive and discern it more 

 easily and clearly. Thus, a fine glass bubble, filled with clear water, and 

 placed before a burning candle or lamp, enables it to dart forth its rays to a 

 prodigious length and brightness : so an instrument may be invented, which 

 applied to the mouth, shall send forth the voice distinctly to as prodigious a 

 distance and loudness. 



As instruments have been invented to help the eye, so likewise are there 

 some, and more such there may be, for the ear. For, as spectacles and other 

 glasses are made to help the purblind and weak eyes to see at any competent 

 distance : so there are otacoustics to help weak ears to hear at a reasonable dis- 

 tance also. Which would be as great a help to the infirmity of old age as the 

 other invention of spectacles is, and perhaps greater; forasmuch as the hearing 

 what is spoken is of more daily use and concern to such men, than to be able 

 to read books, or to view pictures. Also, as perspective-glasses and telescopes 

 help the eye to see objects at a very great distance, which otherwise would not 

 be discernible ; in like manner may a sort of otacoustics be so contrived, as 



