RESULTS OF ATMOSPHERIC PRESSURE. 187 



feathered tribes, that the air should be suffi- 

 ciently dense to offer resistance to the play of 

 their pinions ; so also, though in a less degree, 

 to insects. Some birds, taken up on one occasion 

 by an aeronaut in a balloon to a great height, and 

 set at liberty, refused to leave the machine, and 

 clung to its sides in great terror, being appa- 

 rently sensible that the air was too thin to 

 trust the weight of their bodies to. To fishes, 

 the atmospheric pressure is also of vital con- 

 sequence. If this pressure were removed the 

 result would be, that the air now dissolved by 

 water, would immediately rise from it, and 

 the inhabitants of our lakes, rivers, and seas, 

 would die in consequence. To plants, it is also 

 of great moment ; it restrains that excessive 

 loss of fluids which would follow if it was in 

 * any degree removed ; for just as a diminished 

 pressure lowers the boiling point,* so it increases 

 the facility with which the evaporation of fluids 

 takes place. In various ways atmospheric 

 pressure exerts a beneficial influence upon their 

 growth and functions, and upon the motion of the 

 vegetable juices. 



If we place a piece of solid ice under the 

 exhausted receiver of an air-pump, and take 

 care that the experiment is conducted in a room 



* Water in the imperfect vacuum of an air-pump, will boil 

 at the low temperature of 67 ! 



