414 



MY LIFE 



[Chap. 



(2) To a person who has not studied the question air has no weight. 

 If air has weight, why do we not get tired of bearing that weight ? To 

 prove to that person that air has weight, ask — How do you take head- 

 aches ? We take headaches because the air gets light and some of the 

 usual weight is taken off the head, and we get giddy. 



These two young men write with an air of authority, as if 

 they were teachers rather than learners, yet it is hard to say 

 which of the two is the more profoundly ignorant. The 

 other four, while equally ignorant, are more modest in their 

 style. 



(3) We are able to move under the pressure of the atmosphere by im- 

 purities and other bodies displacing the air. If there were no impurities 

 in the air we could not move about. For example, water-vapour gets into 

 the air, and displaces it making the air Hghter. 



(4) We are able to bear a certain amount of the weight of the 

 atmosphere and a very little more would kill us. 



(5) We are able to move about on the earth's surface because^ 

 although the atmosphere is pressing us down we have the sun attract- 

 ing us. 



(6) The reason that we are able to move about under the weight of 

 the atmosphere is that the atmosphere is two hundred miles away from 

 the surface of the earth. 



Passing on to 1891, such a common instrument as the 

 barometer, which can be so easily explained by simple ex- 

 periments, is thus hopelessly blundered : — 



(1) Air occupies the space above the mercury. If a hole were bored 

 through the glass above the mercury the air would escape and probably 

 the tube would burst. 



(2) The air would escape and the mercury would remain dormant. 



(3) The principle on which the action of the mercurial barometer 

 depends is, that it must be enclosed in a strong case and must not be 

 touched in any way. 



(4) A water barometer is longer than a mercurial barometer because 

 it has to go down to the bottom of the sea to see how deep it is. A 

 mercurial barometer has to see how high a thing is, and no hill is higher 

 than the depth of the ocean except a few high mountains which nobody 

 can get to the top of. Oxygen occupies the space above the mercury, 

 and if a hole were bored the oxygen would flow out and the mercury rise 

 to the top and flow out also. 



In 1893, in order to correct some popular errors, the 



