On the Elementary Electrical Charge and the Avogadro Constant

+»)»' e"=x ]ig(ap) i~F in which g is the coefficient of viscosity of air, o the density of the oil, p that of the air, vI the speed of descent of the drop under gravity and v2 its speed of ascent under the influence of an electric field of strength F.The essential feature of the method consisted in repeatedly changing the charge on a given drop by the capture. of ions from the air and in thus obtaining a series of charges with each drop.These charges showed a very exact multiple relationship under all circumstancesa fact which demonstrated very directly t' he atomic structure of the electric charge.IX Stokes's law were correct the greatest common divisor of this series of charges should have been the absolute value of the elementary electrical charge.But the fact that this greatest common divisor failed to come out a constant when drops of different sizes were used showed that Stokes's ' R. A. Millikan, PHvs.REv. , 3a, pp.349-397, x9I I.I IO R. A. MILLIKAN.t SEcowi SERIES.law breaks down when the diameter of a drop begins to approach the order of magnitude of the mean free path of a gas molecule.Conse- quently the following corrected form of Stokes's law for the speed of a drop falling under gravity was suggested.2 ga'(op) l I +2-9 G in which a is the radius of the drop, l the mean free path of a gas molecule and A an undetermined constant.It is to be particularly emphasized ' Lachlan Gilchrist, PHvs.REv. , 2d Ser., Vol.r, p. z24.' This investigation will shortly be published in full (PHvs.Rzv., ?