82 ELEMENTS OF STATIC ELECTRICITY. 



In this way a book of one hundred or more pages may 

 be perforated. 



If the book is first placed in contact with the knob 

 of the jar, part of the charge will escape from the edges 

 and corners of the leaves, and the experiment is liable 

 to fail. 



The burr projecting from each surface, after the dis- 

 charge through a book or card, has been relied on as a 

 proof of the dual nature of electricity, and ascribed to 

 the rush of positive and negative in opposite directions. 

 It is also attributed to the expansive force of heat, or of 

 gas, generated by the discharge. 



The first theory cannot be accepted, unless we have 

 stronger proof of the dual nature of electricity than is 

 afforded by this experiment. And the second also fails ; 

 since in the case of a discharge through a book, the 

 leaves may be held so loosely as to allow a free outlet 

 for expansion from heat or gas, and yet the burr turns 

 in opposite directions from a point near the center of 

 the book, and becomes more prominent when the leaves 

 are thus held than when they are compressed ; whereas, 

 if the burr were due to the expansive force of confined 

 heat or gas, the reverse would be true. 



Since these theories are unsatisfactory, let us en- 

 deavor to explain this phenomenon in accordance with 

 the principles which we have been considering. 



Let a jar be charged on its inner coating, and 

 discharged through a book, as represented in Fig. 23. 

 Suppose the charge to be positive, electric movement 

 being from higher to lower potential, it would be from 

 the knob of the jar to the nearest knob of the dis- 

 charger. The entire charge of the inner coating, 

 passing out through the knob, would induce a high 



