914 



THEOUT OF EAR TRUMPETS. 



form, and an explanation will be expected. By a drum I 

 mean a circular box, or funnel, furnished with nn car pipe, 

 and having its mouth or widest aperture covered with a thin 

 elastic membrane, which must be stretched with an uniform 

 force in every direction, like the vellum of a military drum. 

 The pulses which fall from the atmosphere upon this mem- 

 brane will be immediately transmitted by it to the air con- 

 fined in the box, and their escape from this cavity must evi- 

 flently he through the" ear tube, because the covering of the 

 mouth will not permit them to return into the atmosphere by 

 that aperture. 

 An experi- The instrument here recommended is not a mere project of 



with such an ^^^^'T? ^^^ ^ \mve made some experiments, which induce me 

 instrument. to hope for beneficial consequences from a contrivance of the 

 kiiSdV'' I tooka metal funnel of 2 inches radius, And a circu^ 

 lal- wood box of the same diameter, which was a' segment 6f 

 '^ A sphere of 8 inches radius. The mouth of each vessel was 

 covered with apiece of hog's bladder, moistened in water, 

 and securely fixed by a thread to the outside of the instru- 

 tieiiC The bladder contracted in drying, by whicih it ac- 

 quired a considerable degree of tension; and I do not hesitate 

 to say, that both these drums, when properly applied to my 

 ^a'r, augmented the beats of a watch and other weak sou rid «, 

 The further in a manner which was very perceptible. Should tHe experi- 

 thre'^jeT °^"l^"^ however, appear worthy of further attention, it must 

 jnent left to be left in future to those who expect advantage from it', Be- 

 ^epartially cause such inquiries are attended with the greatest difficul- 

 ties, when undertaken by persons who possess the sense of 

 hearing in perfection. If your correspondent A. B. should 

 conclude to pursue the subject, he will recollect, that a fine 

 membrane is prepared from the intestines of cattle, which is 

 called gold beater's skin, at least in the north of England ; 

 and it is unnecessary to inform him, that this substance is 

 preferable; in every point of view to the bladder which 1 used 



in my experiment. 



JOHN GOUGH. 



P, S. I have long expected, that some of your corrcspon- 

 dentb would call an opinion in question, which \ advanced 



nearly 



