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In Ist die Tragheit eines Korpers von seinem Energieghalt abhangig?, published in Ann. Phys. 17 (English translation in Lorentz, et al. (1923)). Einstein showed that if a body gives off energy E in the form of radiation, then its mass diminishes by E /c2, though his derivation has caused its fair share of controversy (see Fadner (1988)).

According to Pais (1982), p. 150, Planck's was the first paper on the new relativity theory published by somebody other than Einstein. Planck was one of only a handful of physicists who realized immediately that the consequences of Einstein's ideas, whether they turned out to be correct or not, needed to be investigated (see Goldberg (1976)).

Planck's work showed that, as in other aspects of the relativity theory, Einstein's and Lorentz's predictions for the mass-velocity relation were equivalent mathematically, but Lorentz had founded his model on dynamical principles, whereas Einstein's theory was entirely kinematic.

In his first paper on special relativity, Einstein calculated the kinetic energy ofthe electron to be K = m 0c2(y — 1), which becomes unphysical when v > c, and thus deduced that 'velocities greater than that of light... have no possibility of existence'. When combined with the mass-energy relation from the second relativity paper we get

for the total energy of a body. When v ^ c, the energy due to the motion (i.e. the kinetic energy) in a given frame is thus consistent with the Newtonian value.

Astronomers were well aware that a velocity-dependent mass would have an effect on the precessional motion of planets. George Darwin, referring to a meeting held in Gottingen in 1902, recounted that 'the greater part of one day's discussion was devoted to the astronomical results which would follow

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