Common Science 



FIG. 5. The water is held in the tube by air pressure. 



tube, would have to leave a vacuum, which the air out- 

 side does not allow. But when you take your finger off 

 the top of the straw or tube, the air from above takes 

 the place of the water as rapidly as it flows out; so 

 there is no tendency to form a vacuum, and the water 

 leaves the tube. Now do you see why you make two 

 holes in the top of a can of evaporated milk when you 

 wish to pour the milk out evenly ? 



Experiment 4. Push a rubber suction cap firmly against 

 the inside of the bell jar of an air pump. Try to pull the 

 suction cap off. If it comes off, press it on again; place 

 the bell jar on the plate of the air pump, and pump the air 

 out of the jar. What must have been holding the suction 

 cap against the inside of the jar? Does air press up and 

 sidewise as well as down ? Test this further in the following 

 experiment: 



