Heat and Static Electricity. 263 



§ 34. Experiment. — If a series of dielectric non-conductors, 

 such as a series of plates of varnished glass, be placed on an 

 electroscope which is then charged with — electricity, a dull 

 red-hot ball or platinum wire a few inches above the electroscope 

 causes the leaves to collapse, but does not discharge the system. 

 On removing the plates in succession (after the removal of the 

 heated discharger), the leaves diverge more and more, till the 

 withdrawal of the last leaves them nearly fully charged. The 

 bottom of each plate is found to be charged with -f electricity. 

 A similar effect is produced, changing the changeables, by a 

 white-hot ball or wire above the upper of a series of varnished 

 glass plates on the top of a positively charged electroscope. 



§ 35. The experiments with electroscopes may be repeated 

 almost one for one with the condensed electricity of a Leyden jar. 

 Owing, I presume, to the closeness of the two condensed elec- 

 tricities to one another on the metallic coatings, and to that pe- 

 netration of the two kinds into the glass which furnishes the 

 potential residual charge, the discharge of a jar is never so rapid 

 or complete under the same circumstances as that of an elec- 

 troscope. 



§ 36. Experiment. — A Leyden jar of about 1 \ square foot 

 outer foil surface is fully charged with -f- electricity. A white- 

 hot earth-connected iron ball, at a distance of 3 inches above the 

 electroscope, discharges the jar, but by no means completely, in 

 thirty seconds (when the ball had become dull red). A jar 

 charged with — electricity is discharged under like conditions 

 almost completely in thirty seconds. The remaining charge is 

 not greater than the first residual charge under ordinary circum- 

 stances (the glass being about \ inch thick). 



§ 37. A dull red-hot ball earth-connected at a distance of 2 

 inches from a + -electrified jar discharges scarcely any of the 

 charge in a minute, while a — charge in the same time is con- 

 siderably diminished. 



§ 38. Experiments. — A platinum spiral of wire 4 inches long 

 and '01 inch thick is fixed 4 inches above a charged jar. The 

 latter loses little of its charge in one minute. When the cur- 

 rent passes through the wire from eight platin-zinc cells the 

 wire becomes white-hot, and the charge, whether -f or — , is 

 lost in one minute. For the success of this experiment, especi- 

 ally when -f electricity is dealt with, the wire must be almost 

 at the point of fusion. 



§ 39. Experiment. — A 9-inch single-loop wire, one inch 

 from the jar, heated to incipient redness, discharges about half 

 of the electricity of a -[--charged jar and almost the whole of a 

 — charged one. 



§ 40. Two electroscopes, charged respectively with + and — 



