The conventionality of simultaneity at distant points is defended partly by reference to Einstein's 1905 paper founding special relativity. His famous light-signaling definition takes the transit time of light in one direction to be equal to that in the other. Conventionalists such as Reichenbach and Grunbaum argue that he could have made them unequal without denying any physical fact. However, Einstein's more detailed treatment in the 1910 Archives des sciences runs counter to this thesis. There he required that the two (...) signal-paths be physically equivalent and thus that whatever the signals travel through have no perturbing affect on their motions. (shrink)