Note Note 5 — § 1 THE "SPECIAL" THEORY OF RELATIVITY AS A STEPPING STONE TO THE "GENERAL" THEORY OF RELATIVITY
Henry L. (Henry Leopold) Brose translation
(p. 15). Einstein has shown in a simple example how, on the basis of the formulæ of the special theory of relativity, a point-mass loses inertial mass when it radiates out energy.