130 A YEAR IN SCIENCE 



inside and the outside. We are so constructed as to be 

 most healthy when under this pressure. Without it we 

 feel uncomfortable. If this pressure is suddenly 

 changed outside of our bodies, we are at once conscious 

 of it. On tops of high mountains breathing becomes 

 more difficult, headaches and other results follow. 



Aeronauts have never ascended much higher than 

 seven miles. At that height the pressure, outside of 

 the body is reduced to about one-fifth of what it is 

 at sea level. As a result of the high internal pressure 

 the blood is forced to the surface, the walls of the 

 blood vessels frequently rupture, and other physical 

 difficulties result. 



Fish living at the bottom of the sea are subjected to 

 enormous pressure. Nevertheless they are* adapted to 

 those great depths. Were the pressure to which they 

 are accustomed diminished to any great extent, they 

 Avould suffer great pain, and possibly death. Alexander 

 Agassiz says: "In fish brought up from the deep 

 water, the swimming bladder often protrudes from the 

 mouth, the eyes are forced out of their sockets, the 

 scales fall off, and they present a most disreputable 

 appearance." 



Just as they are adapted to the pressure at the 

 bottom of a sea of water, so we are best adapted to 

 the pressure near the bottom of a sea of air. 



Air presses in all directions. Place a piece of paste- 

 board, or blotting paper, over the mouth of a tumbler 

 filled with water. Shake the tumbler until the paper 



