190 



requiring such modulation, are transmitted by the vibrations of the 

 integrant parts of these bones, unaccompanied by muscular action. 



This reasoning, Mr. Carlisle says, is suggested by the columellse 

 in the aves and amphibia ; for, since many birds accurately imitate 

 a variety of sounds, it may be inferred that they hear as acutely and 

 as distinctly as mankind. 



The muscles of the ossicula auditus appear to be of the involun- 

 tary kind ; their peculiar stimulus is sound, and the chorda tympani 

 is a gaugliated nerve. If the above supposition is true, the muscles 

 may be considered as all acting together ; especially as it is well 

 known that some persons who hear imperfectly are more sensible to 

 sounds when in a noisy place ; as if the muscles were then excited 

 to action. 



It cannot, Mr. Carlisle thinks, be allowed, that the pressure of the 

 watery fluid in the labyrinth is necessary to produce the sensation of 

 hearing, since birds hear without any such mechanism : such pres- 

 sure, however, would give increased tension to the fenestra cochleae; 

 and, as the membrane of that fenestra is exposed to the air con- 

 tained within the cavity of the tympanum, it appears adapted to re- 

 ceive such sounds as pass through the membrana tympani, without 

 exciting consonant motions in the ossicula auditus. 

 ' In order to investigate the truth of the above opinions, Mr. Car- 

 lisle had water, at the temperature of his body, dropped from a small 

 vial into the meatus externus, the tragus being previously pulled to- 

 wards the cheek. The first drop produced a sensation like the report 

 of distant cannon ; and the same effect succeeded each drop until 

 the cavity was filled. 



In this experiment the vibrations of the membrana tympani must, 

 he says, have been impaired, if not destroyed ; yet the motions of the 

 membrane produced by each drop of water affected the air contained 

 in the tympanum, sufficiently to produce a sensible impression. 



That something like this occurs in many kinds of sounds, is, Mr. 

 Carlisle thinks, more than probable ; and as the cochlea consists of 

 two hollow half cones, winding spirally, and uniting at their apices, 

 it follows that the sounds affecting either of the cones must pass from 

 the wide to the narrow end ; and the tension of the parts, in either 

 case, will necessarily aid the impression. 



On an artificial Substance which possesses the principal characteristic 

 Properties of Tannin. By Charles Hatchett, Esq. F.R.S. Read 

 April 25, 1 805 . [JPhil. Trans. 1 805, p. 2 1 1 .] 



Mr. Hatchett, after mentioning the experiments made by several 

 eminent chemists on the substance generally called Tannin (but 

 which he thinks would be better expressed by the word Tan), ob- 

 serves, that the results of those experiments have established, that 

 tan is a peculiar substance, naturally formed, and existing in many 

 vegetable bodies, such as oak bark, &c. ; but that no one has ever 



