168 PRESSURE OF AIR. 



If it were not that the air always comes between 

 the surfaces of all things, the bricklayer would 

 need no mortar, the joiner no nail and no glue ; 

 the tailor, too, would have no use for thread, and 

 the seams of shoes would never give way. A 

 world of that kind would be a very stable and 

 lasting world, and the words " wear and tear," 

 might be left out of the vocabulary. But there 

 would be too much of stability ; and there would 

 be little motion, or change, and no life. 



Thus the extreme pureness of the atmosphere, 

 and the property that it has, of insinuating itself 

 into the very smallest openings, and pressing 

 equally in all directions, makes it the grand path- 

 way on land ; for whatever is moved on land is 

 literally moved in the air ; and not only that, but, 

 as the air is pressed together by its own weight, 

 and thus heaviest nearest the earth, so that even 

 the heaviest substances are pressed a little more 

 upward than they are pressed downward by the 

 air, and their real weights are diminished by the 

 weight of a quantity of air equal to their bulk. At 

 the same time, they are held in their upright po- 

 sition by the pressure of the air all around them ; 

 and that pressure is so considerable as to amount to 

 about thirteen tons on the body of a man. That 

 weight is, however, so nicely balanced, so per- 

 fectly the same at all points of the same elevation 

 from the ground, and the air is so perfectly springy 

 or elastic, forms so delightfully soft a cushion 

 around all nature, that its resistance to ordinary 

 motions is not felt, and it does not ruffle the pow- 

 dery plumage on the wing of the most delicate 

 moth. Walking, we do not feel it at all ; and 

 even when we run with all our speed, it is nothing 



