NATURAL HISTORY. 



179 



of us. The reason why you stand up straight 

 is because the air is pressing all around you ; 

 1 if it were on one side of you only, it would 

 press you down on the other side. Here is a 

 picture of the fly's foot, as it appears through 

 the microscope. You will see it has three 

 suckers with the edges all like saws ; these are 

 to make it stick the closer. This picture, boys, 

 is sixty-four hundred times as large as the fly's 

 foot is." 



Fly's foot magnified. 



" But, Uncle Philip, there is one thing yet 

 hard to understand." 



