Sect. XIV. 5, OF IDEAS. 89 



Hence it appears, that the immediate organ of hearing is 

 not affected by the particles of the air themfelves, but is ftimn- 

 lated into animal motion by the vibrations of them. And it is 

 probable from the loofe bones, which are found in the heads of 

 fome fifties, that the vibrations of water are fenfible to the in- 

 habitants of that element by a fimilar organ. 



The motions of the atmofphere, which we become acquainted 

 with by the fenfe of touch, are combined with its folidity, 

 weight, or vis inertiae ; whereas thofe, that are perceived by 

 this organ, depend alone on its elafticity. But though the vi- 

 bration of the air is the immediate object of the fenfe of hear- 

 ing, yet the ideas, we receive by this fenfe, like thofe received 

 from light, are only as a language, which by acquired affocia- 

 tions acquaints us with thofe motions of tangible bodies, which 

 depend on their elafticity ; and which we had before learned 

 by our fenfe of touch. 



V. Of Smell and of Tafe. 



The objects of fmell are diflblved in the fluid atmofphere, 

 and thofe of tafte in the faliva, or other aqueous fluid, for the 

 better diffufing them on their refpective organs, which feem to 

 be ftimulated into animal motion perhaps by the chemical af- 

 finities of thefe particles, which conflitute the fapidity and odo- 

 rofity of bodies, with the nerves of fenfe, which perceive them. 



Mr. Volta has lately obferved a curious circurnftance relative 

 to our fenfe of tafte. If a bit of clean lead and a bit of clean 

 filver be feparately applied to the tongue and palate no tafte is 

 perceived ; but by applying them in contact in refpett to the 

 parts out of the mouth, and nearly fo in refpect to the parts, 

 which are immediately applied to the tongue and palate, a fa- 

 line or acidulous tafte is perceived, as of a fluid like a ftrearn of 

 electricity palling from one of them to the other. This new 

 application of the fenfe of tafte deferves further inveftigation, 

 as it may acquaint us with new properties of matter. 



From the experiments above mentioned of Galvani, Volta, 

 Fowler, and others, it appears, that a plate of zinc and a plate of 

 filver have greater effect than lead and filver. If one edge of a 

 plate of filver about the fize of half a crown-piece be placed up- 

 on the tongue, and one edge of a plate of zinc about the fame 

 fize beneath the tongue, and if their oppofite edges are the-n 

 brought into contact before the point of the tongue, a tafte is 

 perceived at the moment of their coming into contact -, fecond- 

 ly, if one of the above plates be put between the tipper lip and 

 the gum of the fore-teeth, and the other be placed under the 



Vol. I. N tongu*. 



