Magnetism and Electricity 197 



But if you took the smallest atom in the world and 

 divided it into 1700 pieces, each one of these would be 

 about the size of a piece of electricity. 



Electricity is made up of the tiniest things known to 

 man things so small that nobody really can think of 

 their smallness. These little pieces of electricity are 

 called electrons, and for all their smallness, scientists 

 have been able to find out a good deal about them. 

 They have managed to get one electron all by itself on a 

 droplet of oil and they have seen how it made the oil 

 behave. Of course they could not see the electron, 

 but they could tell from various experiments that they 

 had just one. Scientists know how many trillions of 

 electrons flow through an incandescent electric lamp 

 in a second and how many quadrillions of them it would 

 take to weigh as much as a feather. They know what 

 the electrons do when they move, how fast they can 

 move, and what substances let electrons move through 

 them easily and what substances hold them back ; and 

 they know perfectly well how to set them in motion. 

 How the scientists came to know all these things you will 

 learn in the study of physics; it is a long story. But 

 you can find out some things about electrons yourself. 

 The first experiment is a simple one such as the Greeks 

 used to do with amber. 



Experiment 63. Rub a hard rubber comb on a piece of 

 woolen cloth. The sleeve of a woolen coat or sweater will 

 do. Rub the comb quickly in the same direction several 

 times. Now hold it over some small bits of paper or saw- 

 dust. What does it do to them? Hold it over some one's 

 hair. The rest of this experiment will work well only on 



