154. Directions. (A) Charge E C; test its charge with your knuckle. Be sure that you get a good spark.
(B) Charge E C again, and hold it by its insulating handle, E R, long enough to count 10 before discharging it with your knuckle. Be sure that it holds its charge during this time.
(C) While E C is upon E S ([Fig. 34]), lay the bent pin upon E C, so that its point will project into the air. The point should stick out about ¼ in. from the edge of E C.
(D) Touch E C; raise it by E R; count 10 as before; then test with your knuckle to see if E C is still charged.
155. Electric Density; Electric Wind. A charge resides upon the outside of a conductor ([Exp. 73]), and it continually tries to escape. It seems to pile up at points and corners, and we say that it is denser at such places than at well-rounded parts of a charged conductor. All points and sharp places should be removed from a conductor, if it is desired to keep a charge for any length of time.
Electrification may escape from a point so rapidly that currents are produced in the surrounding air. As the particles of air become charged, they repel each other. The movement of the air particles may be so great that a lighted candle will be affected when placed near the point. This current of air is called electric wind.
Electrification easily passes from points, and the electrophorus may be easily and silently discharged by holding a pointed pin near it ([Exp. 71], C). Thorns, leaves with sharp edges, etc., have a great effect upon atmospheric electricity. They allow a silent escape of electrification from the earth to neutralize that in the clouds which is opposite in nature. (See [Atmospheric Electricity].)