266 POPULAR LECTURES AND ADDRESSES. 



diving bell have exactly the same sensation as 

 they would experience if from some unknown 

 cause the barometer quickly, in the course of half 

 a minute, were to rise five or six inches far 

 above the greatest height it ever stands at in the 

 open air. Well now, we have a sense of barometric 

 pressure, but we have not a continued indication 

 that allows us to perceive the difference between 

 the high and low barometer. People living at 

 great altitudes up several thousand feet above 

 the level of the sea, where the barometer stands 

 several inches lower than at sea level feel very 

 much as they would do at the surface of the sea, 

 so far as any sensation of pressure is concerned. 

 Keen mountain air feels different from air in 

 lower places partly because it is colder and drier, 

 but also because it is less dense, and you must 

 breathe more of it to get the same quantity of 

 oxygen into your lungs, to perform those functions 

 which the students of the Institute who study 

 animal physiology and I understand there are 

 a large number will perfectly understand. The 

 effect of the air in the lungs the function it 



