358 ELECTRICITY. 



The Course of the Electric Fluid in the Discharge, 

 rendered visible by the Star and Pencil. 



When a jar is charged, take a discharging-rod 

 having its ends pointed, i. e. the discharging-rod 

 represented in Fig. 14., without its knobs, and keep 

 it in such a situation, that one of its points may be 

 at about one inch distance from the knob A, and 

 the other point at an equal distance from the out- 

 side coating of the jar: by these means the jar will 

 be discharged silently; and if its inside be electri- 

 fied positively, you will see that the point of the 

 discharging-rod is illuminated with a star, and the 

 point B with a pencil; because, in this case, the 

 electric fluid, going from the inside to the outside 

 of the jar, enters the point C, and issues from the 

 point B. But if the jar is electrified negatively on 

 the inside, and consequently positive on the out- 

 side, then the pencil of rays will appear upon the 

 point C, and the star upon the point B: for in this 

 case, the electric fluid passes from the outside to the 

 inside of the jar. This experiment, as well as any 

 other in which the electric light is to be observed, 

 must be made in the dark. 



The Ley den Vacuum. 



Fig. 15. is a small phial, coated on the outside 

 about three inches up the side with tin-foil; at the 

 top of the neck of this phial a brass top is cemented, 

 having a hole with a valve; and from the cap a 

 wire proceeds a few inches within the phial, ter- 

 minating in a blunt point. When this phial is 

 exhausted of air, a brass ball is screwed upon the 

 cap, which is cemented into its neck, so as to defend 



