

Spreading of electricity on glass 235 



bottom but a very short time, and then kept mid way for \ minute, and then 

 drawn up, the balls at first separated positively but closed very soon, and after 

 a long time separated negatively. 



If a sliding plate containing about \ part of the electricity in the plate L 

 was put on the positive side as an additional plate, and the apparatus was let 

 down and drawn up immediately, the balls separated about i diameter nega- 

 tively, but if it rested at the bottom \ a minute and was then drawn up im- 

 mediately they separated about i inch negatively. 



486] In order to see how fast the electricity spread on the surface of the 

 glass, the heavy paper cylinders* were placed in the usual place, and the light 

 ones on the wire Bb, the wires Gg and Ff were detached from Cc and rested at 

 bottom, and a coated plate on the positive side. The wire Cc was suffered to 

 rest on A a and Bb while the jars were charging, and the wire V drawn up so 

 as not to rest on the coated platef. 



When the heavy cylinders, and a fortiori the light ones, separated, the wire V 

 was let down on the plate and the wire Cc immediately drawn up, and the 

 time elapsed till the closing of the light cylinders counted, which was as follows: 



L reversed 50" 

 Trial plate H 7 

 D reversed 5 



487] Another way was taken to try the same thing, namely, the wire Ff 

 was taken off and Gg placed so as to lye below the wire Dd and to be drawn up 

 against it by a string. The coated plate to be tried was placed on the negative 

 side, the wire 8 touching its bottom coating. The jars were then charged, the 

 wire Cc resting all the while on Aa and Bb, and Gg drawn against Dd, and /3 

 drawn up so as not to rest on the plate. When the jars were sufficiently charged 

 |8 was let down on the plate, and the wire Gg dropt immediately after, so as to 

 take away the communication between Dd and the ground, so that the pith balls 

 which were hung to D shewed whether much electricity passed round to under 

 side of plate or spread on the surface. 



When the pith balls communicated with the ground they separated about 

 $ of an inch negatively by the repulsion of the wires on them. 



Coated 

 plates 



D of Nairne | 



not in cement/ 

 E of Nairne 



in cement 

 F do. 

 G do. 

 I do. 



Balls closed 

 in seconds 



3" or 4" 



25" 



25 

 20 



35 



Separated 

 again in 



30" in 3' separated about 

 2'. 30" in 4' separated about 



i'. 40" in 4' separated about 



* [Art. 248.] 



f [See Fig. 20, Art. 295.] 



