THE ELECTRON 89 



fairly well everything else, or at least there is promise 

 that ultimately everything else will be so explained. 

 But as to the electron itself no explanation can be 

 given. If any explanation is ever obtained it will be 

 in terms of something else which in its turn will be un- 

 explainable and have to be accepted as the fundamental 

 element or beginning from which all other explanations 

 start. The electron is the fundamental entity with 

 which modern science starts. 



But what is the nucleus? That we do not as yet 

 know. To learn what we do know of it we must con- 

 sider further the behavior of electrons. These are, so 

 far as we know, all alike without regard to the atoms 

 from which they are derived. An electron from a 

 hydrogen atom is just the same as one from an atom 

 of copper or one from an atom of radium. They are 

 very small 1 as compared to an atom although they 

 are for their size much heavier. When it comes to 

 moving an electron, as for example starting one, it is 

 found that it has about T^ of the inertia of the hy- 

 drogen atom. If you realize that it takes about 

 1.70X10 25 hydrogen atoms to weigh an ounce you will 

 see how small is the mass of an electron. 



Now, electrons have a peculiar property of repelling 

 each other. Two electrons always exert a force push- 

 ing each other apart even though they may not be in 

 contact. How can an electron which is not touching 

 another, push on it, urging the second electron away 

 from itself? Again the answer is that we do not know. 

 They must act on each other through a "medium," a 

 "something between." Such a medium the physicist 

 1 What we mean by "size" is discussed a little later. 



