THEORY OF EAU TRUMPETS. 3]! 



After taking this view of the subject, I was inclined to M^. Nichol- 



^ r t • 4 son's idea, vol, 



Adopt your opinion in vol. XIIi, page 52, that an instrument xiii, page 52, 



Cppsisting of a broad thin surface, furnished with a tail or exwnined, 

 Stem, promises to relieve partial deafness as effectually and 

 more conveniently than a trumpet. A number of experi- 

 ments, however, made for the purpose, have convinced me, 

 that the vibration excited in thin plates of metal, wood and 

 pasteboard, by sonoriferous pulses of air, cannot be condensed 

 in a stem attached to these substances, so as to be conveyed 

 with effect to the seat of hearing. My first trial was con- Not continued 

 ducted in the foUowing manner : a hole was made through a ^g^^^^^^* • 

 partition of lath and plaster, which was just large enough to 

 receive a rod of deal 2 feet long, and f an inch in diameter. 

 Some circular plates of metal were provided at the same 

 time, as well as thin boards and pieces of pasteboard of the 

 same figure, which were fixed at pleasure on the ends of the i 



rod, by means of holes in their centres. This contrivance 

 gives the observer an opportunity of placing himself in one 

 room and the sonorous body in another; and this precaution 

 prevents all the pulses from reaching his ear, except those 

 that are conveyed by the rod, provided the force of the sound 

 be too weak to make its way through the partition itself. 

 The eff<»cts produced by this apparatus were the following: 

 when one of the circular plates properly mounted on the end, 

 was slightly scratched with a pin, or even with a piece of 

 twisted paper, the sound passed very distinctly along the deal 

 into the room where the observer was situated, and was 

 thrown off into the air from a circle of wood or metal fixed 

 on the rod in that apartment. The same circumstance took^ 

 place when a watch was brought into contact wifh one of the 

 circles, and the observer stood near the other; but absolute 

 contact was found to be necessary, for the sound ceased as 

 oft as the watch was removed the shortest distance from the 

 circle. 



The discovery of this fact damped the expectation which I Other experi- 

 had hitherto entertained of affording relief to partial deafness "»^"'s to the 

 by solid conductors of sound, but not to dismiss the inquiry 

 apparently- in a negligent manner, I procured two or three 

 plates of different elastic substances, furnished with slender 



tails 



