270 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



and may be placed at any distance therefrom, and fastened 

 by a screw attached to the ball through which the rod 

 passes. Price, $3.50. 



Fig. 302. Dancing Pith Balls. (Fig. 302.) 



The dancing pith ball experiment 

 is exhibited as follows. Fasten to 

 the conductor of the electrical ma- 

 chine, a pointed wire. Mold a dry 

 and warm tumbler over the point and 

 turn the machine. After a few turns 

 the tumbler will be charged within- 

 side with positive electricity. Place 

 upon the metallic plate (the larger 

 plate used for the dancing images 

 will answer) about a dozen pith balls, 

 and cover them over with the charged 

 tumbler ; they will now jump up and 

 down, each one conveying some of 

 the fluid away from the glass, and 

 not towards it. They will continue to 

 dance for a long time, and when their 

 motion has ceased altogether, it may 

 be renewed by a touch of the hand to the outside of the 

 tumbler, when a fresh portion of electricity will be set 

 free on the interior, and the attraction and repulsion of the 

 balls will again take place, and thus for many times success- 

 ively the action will be renewed until the glass returns to 

 its natural state. 



The experiment may be varied thus. Hang to the con- 

 ductor a chain, which touches this tumbler ; upon turning 

 the machine, although glass intervenes between the exciting 

 power and the balls acted upon, yet the balls will fly rapidly 

 up and down within the glass tumbler. In this instance, 

 the outer part of the glass is by contact electrified posi- 

 tively ; the inner part, therefore, will be. by induction, 

 (afterwards to be explained), electrified negatively ; and 

 the balls are flying up and down to supply the deficiency 

 of the glass, each ball coming to deposit its load, and flying 

 down again for another. 



Price, pith balls per dozen, $0.25. 



