96 THE REALITIES OF MODERN SCIENCE 



some of the electrons of the pith ball. The side of the 

 ball near the rod has more and the opposite side less 

 than its normal number of electrons. The nearer side 

 is negative and the more distant positive. The at- 

 traction of the rod for the nearer side is greater than its 

 repulsion of the more distant side, with the result that 

 the pith ball is urged toward the rod. 



Returning to our consideration of the atom we may 

 now summarize as follows : (1) the normal state of 

 an atom is uncharged ; (2) the atom consists of a num- 

 ber of electrons, and a nucleus which has a positive 

 charge just equal to the negative electricity of the 

 electrons; (3) the operation of charging a body with 

 electricity consists in causing either an excess or a de- 

 ficiency in the number of electrons in the body. 



The nucleus attracts the electrons and they are in 

 general very firmly held in the atomic radius. But 

 why doesn't the attraction which exists between the 

 positive nucleus and the negative electrons draw them 

 together? To this question the scientist has as yet 

 been unable to obtain an entirely satisfactory answer. 

 For this and other questions we must await either fur- 

 ther theories or more experimental evidence. The 

 statements, however, which we have so far made as to 

 the nature of the atom are supported by experimental 

 evidence and are commonly accepted. 



The nucleus we recognize as positive electricity, but 

 we mean thereby merely that it has an excess of pos- 

 itive electricity over any negative which it may also 

 include. In fact there is evidence that the nucleus 

 itself contains some electrons. In the case of radio- 

 active substances we find that electrons are shot off and 



