the radius and
the density of the drop, and
the density of the medium. This last quantity was neglected in (6), [p. 55], because, with the rough measurements there possible, it was useless to take it into account, but with our oil drops in dry air all the other factors could be found with great precision.
When we assume the foregoing equation of Stokes and combine it with equation (5) on [p. 55], an equation whose exact validity was proved experimentally in the last chapter, we obtain, after substitution of the purely geometrical relation
, the following expression for the charge
carried by a drop loaded with