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 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, $$\delta$$, 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,—

$$m$$ being the mass of the moving particles, $$e$$ its charge, $$v$$ its velocity, and $$\mathrm{F}$$ the strength of the field.

The experiments of M. Becquerel enable him to assign a value approaching to $$\delta$$.

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 $$\rho$$, so that—$$\mathrm{H}$$ being the strength of the field—we have the relation—

If, for the same ray, the deflection, $$\delta$$, and the radius of curvature, $$\rho$$, be measured in a magnetic field, values could be found from these two experiments for the ratio $$\frac{e}{m}$$ and for the velocity, $$v$$.