The same phenomenon occurred with another glass. Further, at the moment of the passing of the spark, M. Curie, who was holding the glass, felt the electric shock of discharge in his fingers. Certain kinds of glass have good insulating properties. If the radium is enclosed in a sealed glass vessel, well insulated, it is to be expected that, at a given moment, the vessel will be spontaneously perforated. _Radium is the first example of a body which is spontaneously charged with electricity._ _Action of the Electric Field upon the Deflected β-Rays of Radium._ The β-rays of radium, being analogous to the cathode rays, should be deflected by an electric field in a manner similar to the latter; _i.e._, as would a particle of matter negatively charged and hurled into space with a great velocity. The existence of such a deflection has been demonstrated both by M. Dorn and M. Becquerel. Let us consider the case of a ray which traverses the space situated between the two plates of a condenser. Suppose the direction of the ray parallel to the plates: when an electric field is established between the latter, the ray is subjected to the action of this uniform field along its whole path in the condenser l. By reason of this action the ray is deflected towards the positive plate and describes the arc of a parabola; on leaving the field, it continues its path in a straight line, following the tangent to the arc of the parabola at the point of exit. The ray can be received on a photographic plate perpendicular to its original direction. Observations are taken of the impression produced on the plate when the field is zero, and when it has a known value, and from that is deduced the value of the deflection, δ, which is the distance of the points in which the new direction of the ray and its original direction meet a common plane perpendicular to the original direction. If h is the distance of this plane from the condenser, _i.e._, at the edge of the field, we have, by a simple calculation,— _e_F_l_ (_l_/2 + _h_) δ = —————————————————————; _mv_^2 _m_ being the mass of the moving particles, _e_ its charge, _v_ its velocity, and F the strength of the field. The experiments of M. Becquerel enable him to assign a value approaching to δ. _Relation of the Charge to the Mass for a Particle Negatively Charged Emitted by Radium._ When a material particle having a mass _m_ and a negative charge _e_, is projected with a velocity _v_ into a uniform magnetic field perpendicular to its initial velocity, this particle describes, in a plane normal to the field and passing through its initial velocity, an arc of a circle of radius ρ, so that—H being the strength of the field—we have the relation— _m_ Hρ = ——— _v_. _e_