196 ALL SUBSTANCES ELECTRIC. 



out of the material body, of some principle which is 

 ever active in maintaining its equihbrium, which, conse- 

 quently, must act in two directions, and always exhibit 

 that duality which is a striking characteristic of this 

 subtile agent. It is a curious, and it should be an 

 instructive fact, that each of the three theories of elec- 

 tricity is capable of proof, and has, indeed, been most 

 ably supported by the rigorous analysis of mathematics. 

 When we remember that some of the most enlightened 

 investigators of this and the past age have severally 

 maintained, in the most able manner, these dissimilar 

 views, we should hesitate before we pronounce an opinion 

 upon the cause or causes of the very complicated pheno- 

 mena of electrical force. 



Although we discover, in all the processes of nature, 

 the manifestations of this principle or force in its cha- 

 racteristic conditions, it will be necessary, before we 

 regard the great phenomena, to examine the known 

 sources from which we can most readily evoke the 

 mighty power of electricity. If we rub a piece of glass 

 or resin, we readily render this agent active ; these sub- 

 stances appear, by this excitement, to become surrounded 

 by an attractive or a repellent atmosphere. Let us rub 

 a strip of writing paper with Indian rubber, or a strip 

 of Gutta Percha with the fingers, in the dark, and we 

 have the manifestation of several curious phenomena. 

 We have a peculiar attracting power ; we have a lumi- 

 nous discharge in the shape of a spark ; and we have 

 very sensible evidence of muscular disturbance produced 

 by applying the knuckle to the surface of the material. 

 In each case we have the development of the same 

 power. 



Every substance in nature is an electric, and, if so 

 disposed that its electricity may not fly off as it is deve- 

 loped, we may, by friction, manifest its presence, and, 

 indeed, measure its quantity or its force. All bodies 

 are not, however, equally good electrics; shell-lac, 



