curvature of the path of the same rays is observed in a magnetic field of strength H perpendicular to the rays,
Combining these two equations we get
A difficulty arose in identifying the part of the complex pencil of rays for which the electric and magnetic deviations were determined. Becquerel estimated that the value of HR for the rays deflected by the electric field was about 1600 C.G.S. units. Thus
Thus these rays had a velocity more than half the velocity of light, and an apparent mass about the same as the cathode ray particles, i.e. about ¹⁄₁₀₀₀ of the mass of the hydrogen atom. The β ray is therefore analogous in all respects to the cathode ray, except that it differs in velocity. In a vacuum tube the cathode rays generally have a velocity of about 2 × 109 cms. per sec. In special tubes with strong fields the velocity may be increased to about 1010 cms. per sec. These β particles, then, behave like isolated units of negative electricity, identical with the electrons set free by an electric discharge in a vacuum tube. The electrons projected from radium have velocities varying from about 0·2V to at least 0·96V, where V is the velocity