One result is borrowed, not rediscovered
The light-energy transformation is an input from relativity; the body’s mass change is not an input.
Read · Mass and energy: two accounts, one subtraction · Results
The unsectioned argument · explanatory reading
Follow the light-energy input, the two balances, the unchanged-offset premise, and the low-speed coefficient without assigning an absolute rest energy in advance.
Newly authored explanatory preview in modern notation; editorial and physics review are pending. This is not a German source transcription, this edition’s English translation, or a complete critical edition. The source faces and pinned facsimile remain in preparation. The paper has no numbered sections: s0 is an editorial route identifier, and the headings below organize this explanation, not a verified printed inventory.
Choose the emission that removes recoil
Symmetric emission keeps the body’s speed unchanged, isolating an energy change.
Two accounts of the same loss
The rest account loses L and the moving account loses γL; each balances internally.
Subtract what you cannot measure
Subtracting the energy losses gives L(γ − 1), without choosing the body’s internal energy.
The premise that the subtraction needs
The kinetic interpretation assumes that the additive energy offset is unchanged during emission.
Read the slow-speed coefficient
The low-speed coefficient identifies inertia; a finite-speed ratio is only a proxy.
A decrease, a signed change, and a conversion
The positive mass lost is L/c²; the signed body-mass change is −L/c².
The light has left the body, not vanished
The body’s loss is the radiation’s gain; distinguish a calculation, a broader inference, and an experimental test.