5 to 9 0 seconds the measured surface potential was constant having a value of approximately u2212 350 volts on the plot in fig7 for the time from 9 0 to 16 5 seconds the probe 615 was moved by hand from the second end 630 back to the first end 629 of the sheet 601 in fig6 during the period of time from 9 0 to 16 5 seconds the measured surface potential v esvm 614 again alternated 3 times from a voltage having a negative polarity and a magnitude exceeding 200 volts to a voltage having a positive polarity and a magnitude exceeding 400 volts during the period of time from 9 0 to 16 5 seconds the shape of the surface potential is a mirror image of the shape of the surface potential measured during the period of time from 2 0 to 8 5 seconds because the probe 615 was moved over the exposed top surface 603 of sheet 601 having the same positive electrostatic charges arranged in rows 604 and the same negative electrostatic charges arranged in row 606 on the plot in fig7 for the time from 16 5 to 20 0 seconds the probe 615 in fig6 was stationary positioned over the first end 630 of sheet 601 during the period of time from 16 5 to 20 0 seconds the measured surface potential was constant having a value of approximately 120 volts the surface potential measured during the time period from 16 5 to 20 0 seconds is different from the.