III. THE INERTIA OF ENERGY
The patent clerk was not entirely pleased with his September 1905 derivation of the mass-energy equivalence.9 Coming at it from his hallmark Gedanken-experiment approach introduced all sorts of limitations, but in the early days before the theory had matured that seemed the best way to go. Still, each thought experiment set up an artificial landscape of assumptions that robbed the conclusions, however brilliantly obtained, of the sought-after generality.