SECT, xxvin.] ELECTRICS. 311 



from the redundancy and defect of their electricities, though 

 all the electrical phenomena can be explained on either hy- 

 pothesis. Bodies having a redundancy of the electric fluid 

 are said to be positively electric, and those in defect nega- 

 tively. As each kind of electricity has its peculiar proper- 

 ties, the science may be divided into four branches, of which 

 the following notice is intended to convey some idea. 



Substances in a neutral state neither attract nor repel. 

 There is a numerous class, called electrics, in which the elec- 

 tric equilibrium is destroyed by friction ; then the positive 

 and negative electricities are called into action or separated ; 

 the positive is impelled in one direction, and the negative in 

 another ; or, more correctly, the electricity is impelled in one 

 direction at the expense of the other where there is a defi- 

 ciency of it. Electricities of the same kind repel, whereas 

 those of different kinds attract each other. The attractive 

 power is exactly equal to the repulsive power at equal dis- 

 tances, and, when not opposed, they coalesce with great ra- 

 pidity and violence, producing the electric flash, explosion, 

 and shock ; then equilibrium is restored, and the electricity 

 remains latent till again called forth by a new exciting cause. 

 One kind of electricity cannot be evolved without the evolu- 

 tion of an equal quantity of the opposite kind. Thus, when 

 a glass rod is rubbed with a piece of silk, as much positive 

 electricity is elicited in the glass as there is negative in the 

 silk ; or, in other words, there is a redundancy in the glass, 

 and a proportional deficiency in the silk. The kind of elec- 

 tricity depends more upon the mechanical condition than on 

 the nature of the surface ; for, when two plates of glass, one 

 polished and the other rough, are rubbed against each other, 

 the polished surface acquires positive, and the rough nega- 

 tive electricity ; that is, the one gains and the other loses. 

 The manner in which friction is performed also alters the 

 kind of electricity. Equal lengths of black and white riband, 

 applied longitudinally to one another, and drawn between 

 the finger and thumb, so as to rub their surfaces together, 



