BALLS, in Electricity, are two pieces of cork, or pith of elder, nicely turned in a lathe to the size of a small pea, and suspended by fine linen threads; intended as electrometers, and of excellent use to discover small degrees of electricity, to observe the changes of it from positive to negative, and vice versa; and to estimate the force of a shock before the discharge, so that the operator should always be able to tell very nearly before the discharge, by knowing how high he has charged his jars, what the explosion will be.