132 ELEMENTS OF STATIC ELECTRICITY. 



merit similar to that which takes place in the hot and 

 cold currents round a heated stove. 



But the initial charge is undoubtedly from the ma- 

 terial of the machine itself, and results from the friction 

 of the brushes on the carriers ; after which follows the 

 increase by induction and the action on the air. 



ELECTRICITY GENERATED BY THE FRICTION OF 

 METALS. The old division of all substances into elec- 

 trics and non-electrics was the exponent of the idea 

 then prevalent, that only certain substances, as glass, 

 sealing-wax, and other non-conductors, comprised in a 

 very brief list, were capable of electric excitation. 

 While this view is no longer maintained, yet, since in 

 nearly all experiments illustrating the elements of static 

 electricity, glass, sealing-wax, ebonite, silk, wool, fur, 

 and other non-conductors, are almost exclusively em- 

 ployed as generators, we are apt to lose sight of the 

 fact that metals and other conductors are capable of 

 generating electricity by their mutual friction. And 

 yet this is one of the most important principles of static 

 electricity. It is that which liberates our ideas of elec- 

 tricity from the narrow bounds to which they were 

 once confined, proving that it is not a special property 

 of certain substances, but a universal property of mat- 

 ter, one form of that energy which pervades and con- 

 trols the universe. 



This point has been already illustrated, but the 

 Topler machine affords special facilities for illustrating 

 it more fully. In it the initial charge is produced by 

 the friction of metal brushes on metal carriers. True, 

 both carriers and brushes are attached to glass, and the 

 glass subsequently acts by induction as a generator; 

 but the friction is confined to the carriers and brushes 



