In "de relativiteitstheorie"; J.D.v.d.Waals, 1923, de Erven... pg 91. V.d Waals reports that Sommerfeld possibly has another gamma then 1/sqrt(1-v^2/c^2) using a method that the spectral lines emitted by hydrogen could be related to the mass of the moving electron.
Am very interested in the mass-velocity relation...
Does anabody know what v.d.Waals could have meant here?