16*6 SENSATION OF AIR. 



can cpntrive, and no thermometer can measure 

 heat with nearly the precision of an air one. The 

 air is, indeed, not only fine beyond all sensation, 

 but it is the immediate object of all the senses. It is 

 the air which the eye sees, the ear hears, the nose 

 scents, and the finger touches. We know nothing 

 of what sight might be in a vacuum, or space 

 where there were no air, because the eye would be 

 destroyed if it were in such a place, even though 

 the apparatus were so contrived as that the opera- 

 tion of breathing could still be carried on. Once 

 remove the pressure of the atmosphere, and the 

 fluids of the eye would burst the vessels and coats, 

 and there would be an end of its curious structure, 

 as well as its power of seeing. 



Smell and taste are not the air, but still the 

 fragrance and the sapidity are " melted or dis- 

 solved in air," before we can perceive them; and 

 in those internal parts of the body, which we may 

 suppose that the atmospheric air does not reach, 

 we have no perception of any thing like either 

 smell or taste. Then as to hearing, it is the air 

 that we hear. Air is the instrument, and the only 

 instrument of sound ; and if it were taken away, 

 all nature would be as dumb as a little bell is 

 when it is tolled or struck within an exhausted 

 receiver. Indeed, it not only requires air, but it 

 requires some body or substance of air to produce 

 a sound that can be heard ; for we are not able, 

 by even the best air-pump, to exhaust even the 

 smallest vessel completely of air, as there must 

 always be as much remaining as has spring enough 

 to raise the valve of the pump. 



Then as to touching, if we touched things them- 



