Note 3 — PART I The Special Theory of Relativity

A direct comparison of this relation with experiment is not possible at the present time (1920; see3 Note, p. 48), owing to the fact that the changes in energy to which we can subject a system are not large enough to make themselves perceptible as a change in the inertial mass of the system. is too small in comparison with the mass m, which was present before the alteration of the energy. It is owing to this circumstance that classical mechanics was able to establish successfully the conservation of mass as a law of independent validity.