An investigation has been made of the charging of fused quartz and borosilicate glass spheres rolling on a clean nickel surface. The results indicate that the process of acquiring charge depends only upon the nature and surface condition of the materials in contact and is independent of the pressure of an atmosphere of dry N2. The total charge, however, is limited by gaseous discharge to the metal and therefore does depend upon the pressure. Such gaseous discharge has been verified by the observation of individual discharge pulses. The rate of acquiring charge and maximum charge in vacuum has been found to depend upon rolling speed, both reaching a maximum at an intermediate speed, and to decrease with increasing surface conductivity. Since both fused quartz and borosilicate glass charge negatively in contact with clean nickel, it is inferred that both have higher effective work functions than nickel. The surface conductivity of borosilicate glass has been found to be three of four orders of magnitude higher than that of quartz. Therefore, since the charging of the two materials is of the same order of magnitude, the effective work function of the glass appears to be considerably higher than that of fused quartz.