The results achieved by the special theory of relativity may be tabulated as follows:—
(1) It gives a consistent explanation of Fizeau's and Michelson and Morley's experiment.
(2) It leads mathematically at once to the value suggested by Fresnel and experimentally verified by Fizeau for the velocity of a beam of light through a moving refracting medium without making any hypothesis about the physical nature of the liquid.
(3) It gives the contraction in the direction of motion for electrons moving with high speed, without requiring any artificial hypothesis such as that of Lorentz and Fitzgerald to explain it.
(4) It satisfactorily explains aberration, i.e. the influence of the relative motion of the earth to the fixed stars upon the direction of motion of the light which reaches us.
(5) It accounts for the influence of the radial component of the motion of the stars, as shown by a slight displacement of the spectral lines of the light which reaches us from the stars when compared with the position of the same lines as produced by an earth source.
(6) It accounts for the "fine structure" of the spectral lines emitted by the atom.[20]
(7) It gives the expression for the increase of inertia, owing to the addition of (apparent) electromagnetic inertia of a charged body in motion.
[20]See Sommerfeld, "Atomic Structure and Spectral Lines," p. 474.
The last result, however, introduces an anomaly inasmuch as the inertial mass of a quickly-moving body increases, but not the gravitational mass, i.e. there is an increase of inertia without a corresponding increase of weight asserting itself. One of the most firmly established facts in all physics is hereby transgressed. This result of the theory suggested a new basis for a more general theory of relativity, viz. that proposed by Einstein in 1915. As the special theory of relativity deals only with uniform, rectilinear motions, its structure is not affected by any alteration of the ideas underlying gravitation.