12 



Common Science 



FIG. 4. When the point is knocked off the electric lamp, the water is forced 

 into the vacuum. 



Experiment 2. Hold a burned-out electric lamp in a 

 basin of water, break its point off, and see what happens. 



All the common electric lamps (less than 70 watts) 

 are made with vacuums inside. The reason for this is 

 that the fine wire would burn up if there were any air 

 in the lamps. When you knock the point off the globe, 

 it leaves a space into which the water can be pushed. 

 Since the air is pressing hard on the surface of the 

 water except in the one place where the vacuum in the 

 lamp globe is, the water is forced violently into this 

 empty space. 



It really is a good deal like the way mud comes up 

 between your toes when you are barefoot. Your foot 

 is pressing on the mud all around except in the spaces 

 between your toes, and so the mud is forced up into 



