THE NATURE OF ELECTRICITY, 41 



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positive is now used instead of vitreous, and negative 

 instead of resinous. Used in this way, these terms 

 have no reference to a difference either in quantity or 

 intensity ; they express only a supposed difference in 

 kind, not in degree. 



-This doctrine of the dual nature of electricity was 

 first proposed by Dufaye, and has since been strongly 

 maintained by many eminent scientists. Deschanel, 

 speaking of the phenomena under consideration, says : 

 " These phenomena clearly show that the electricity de- 

 veloped on the resin is not of the same kind as the elec- 

 tricity developed on the glass." 



Now the only thing "clearly shown " is the difference 

 in the substances, not in the electricity. For we have 

 precisely the same electric phenomena of attraction 

 and repulsion with the glass as with the sealing-wax ; 

 but a third substance, the electrified pith ball, is at- 

 tracted by one and repelled by the other ; a result 

 which it would seem more reasonable to attribute to 

 the difference known to exist between the substances, 

 than to a difference supposed to exist in the electricity. 

 For it has already been shown that different causes, as 

 conductivity or resistance, influence the intensity of 

 electrification on different substances. Other causes 

 also, as a difference of temperature or mass, of hard- 

 ness or softness, density or porosity, doubtless contribute 

 to the same result. 



But considering the quality of resistance alone, the 

 potential of any non-conductor, as glass, is liable to 

 vary greatly on different parts of its surface, when 

 electrified by friction ; and to differ from the potential 

 of sealing-wax, similarly produced on different parts 

 of its surface. 



