4o SCIENTIFIC RECREATIONS. 



the egg is gradually thrust in by the atmospheric pressure outside. Fig. 43 

 exhibits it slowly lengthening and stretching out as it passes through the 

 aperture ; then it is suddenly thrust completely into the bottle with a little 

 explosive sound, like that produced by striking a paper bag expanded with 

 air. This is atmospheric pressure demonstrated in the clearest manner, and 

 at little cost. 



If it is desired to pursue a little further the experiments relating to 

 atmospheric pressure, it will be easy enough to add to the before-mentioned 

 appliances a closed glass-tube and some mercury, and one will then have 



ig. 42. Coin adhering by pressure of air. 



the necessary elements for performing Torricelli's and Pascal's experiments, 

 .and explaining the theory of the barometer (page 52). 



An amusing toy, well-known to schoolboys, called the "sucker," may 

 also be made the object of many dissertations on the vacuum and the 

 pressure of air. It is composed of a round piece of soft leather, to the centre 

 of which is attached a small cord. This leather is placed on the ground and 

 pressed under foot, and when the cord is pulled it forms a cupping-glass, and 

 is only separated with difficulty from the pavement. 



Atmospheric air, in common with other gases, has a tendency to fill any 

 space into which it may enter. The mutual attraction of particles of air is 

 nil; on the contrary, they appear to have a tendency to fly away from each 

 -other; this property is called "repulsion." Air also possesses an expansive 



