The following table illustrates the results obtained when the two plates were 3 mms. apart, and were both coated with thin aluminium foil. Potential Current in arbitrary units of lower plate Without magnetic With magnetic field field 0 — +·36 +2 volts 2·0 +·46} } ·39 −2 „ 2·5 +·33} +4 „ 2·8 +·47} } ·41 −4 „ 3·5 +·35} +8 „ 3·1 +·56} } ·43 −8 „ 4·0 +·31} +84 „ 3·5 +·77} } ·50 −84 „ 5·2 +·24} Let _n_ be the number of α particles, carrying a charge _e_, which are absorbed in the upper plate. Let ι₀ be the current due to the slight ionization of the residual gas. If only a small potential is applied to the lower plate, this current should be equal in magnitude but opposite in sign when the potential is reversed. Let ι₁ be the charge per sec. communicated to the upper electrode when the lower plate is charged positively and ι₂ the value when charged negatively. Then ι₁ = ι₀ + _ne_, ι₂ = ι₀ + _ne_; adding we get ι₁ + ι₂ _ne_ = ------ . 2 Now in the third column of the above table it is seen that (ι₁ + ι₂)/2 has the values ·39, ·41, ·43 for 2, 4, and 8 volts respectively. The numbers are thus in fairly good agreement. Similar results were obtained when a brass plate was substituted for the upper electrode shown in the figure. Taking into consideration that the magnitude of _ne_ is independent of the strength of the magnetic field above a certain small value, and the good agreement of the numbers obtained with variation of voltage, I think that there can be no doubt that the positive charge communicated to the upper electrode was carried by the α particles. This positive charge was not small, for using a weight of ·48 mgrs. radium bromide spread in a thin foil over an area of about 20 sq. cms., the charge communicated by the particles corresponded to a current 8·8 × 10⁻¹³ amperes, and, with the Dolezalek electrometer employed, it was necessary to add a capacity of ·0024 microfarads to the electrometer system.