THEQRY PF EAR THUMPETS, gjj 



greater effect into the auditory ducts; our attention therer- 

 fore, must be turned in future to the most probable means of 

 increasing the condensing power oi the instrument, if we wish 

 to mitigate the inconvenience of nervous deafness. 



A vessel of a parabolical figure, and well polish(>d, promise^ Parabolictruift. 

 to be of service to the infirmity of partial deafness, on asu- Jered*^"^*' 

 perficial consideration of the subject, because such an in- 

 strument would concentrate in its focus all the pulses whiclji 

 happened to enter its mouth at the same instant, in a direc- 

 tion parallel to its axis. A trumpet of this description is 

 liable to two serious objections, for the construction of it is 

 very difficult, if not impossible; and if such a thing could 

 be made, it would be attended with inconveniences, arising 

 from its shape and ilimensions, that would render the appli- 

 cation of it very troublesome. This may be easily proved by 

 Q. few simple calculations derived from the properties of the 

 parabola; in reality it may be feared, that the partially deaf 

 have little to expect from any kind of ear trumpets, but those The itnprore- 



of a conical fisuie; and apparently strong reasons lead me ments of coni- 



" ' * ^ . ^ cal trumpets 



to suspect the best of them to be very imperfect augmenters difficult, 



of sound. Perhaps! may take a future opportunity to con- 

 sider their defects mathematically; Out it will be sufticient 

 for the present purpose to observe, that very few of the 

 pulses received at the mouth of a conical tube are trans- 

 mitted "^o the ear through the opposite extrcxiiity. This 

 might be demonstrated on the well known laws of incidence 

 and reflection, and the truth of it is experimental!, proved 

 by the office of the funnel in the invisible lady, which does ** 



not transmit the whisper committed to ic so much as it re- 



■ . ■ -'♦ 



fleets it. 



It may be here naturally asked, if the partially deaf are to Anmstrument 



lay aside all future hopes of additional relief from the im- ^^'^ ^^® P""^^' 

 . ^ . . > T -11 ' . ' pie of a drum 



provement ot acoustic instruments? 1 will not venture to give recommended. 



a decisive answer to this question ; perhaps future experi- 

 ments may discover a more convenient and efficacious form of 

 the ear trumpet ttiaij any in use at present; but I would re- 

 commend your correspondent A. B. or some one of his fellow 

 sufferers, to exchange his trumpet f)r a drum, by way of 

 trial. Perhaps tliij> hint will appear obscure in its present 



form, 



