EXPERIMENTS WITH THE TOPLER MACHINE. 133 



alone; and, so far as the electricity is obtained from 

 this source, the glass acts only as an insulator to pre- 

 vent the escape of the electricity generated by the 

 friction, from which the initial charge is derived. 



It is not even necessary that the metals should be 

 different. The machines here described are constructed 

 with brass carriers, and brushes of brass wire; and, 

 though the carriers are nickel-plated, so that the friction 

 is that of brass brushes on a nickel surface, yet carriers 

 left.unplated give equally as good results. 



THE SPARK; ITS DIRECTION, SUBDIVISION, AND 

 COLOR. The spark from a Topler machine presents 

 phenomena which demand careful investigation. 



As already shown, the apparent time of the discharge 

 is an optical illusion, time being practically annihilated; 

 so that it is impossible, from observation, to tell in what 

 direction the discharge takes place. A brilliant streak 

 of white light, extending from one electrode to the other, 

 suddenly appears and disappears, leaving us in igno- 

 rance as to the direction in which it moves. But the 

 following experiment affords better opportunity for 

 observation. 



As already shown, the electric connection between the 

 inside coatings of the Leyden jars may be interrupted 

 by separating the sliding electrodes, and that between 

 their outside coatings by opening the switch. Put the 

 machine in operation in a darkened room at night, with 

 the switch open, arid the sliding electrodes separated 

 three or four inches. From the electrode P, Fig. 42, 

 a brush of violet -colored light, diverging from a small, 

 circular space, extends about f of an inch towards the 

 opposite electrode, accompanied by a hissing sound. 

 The opposite electrode, R, remains comparatively qui- 



