I am trying to find the first historical paper that uses light clocks for special relativity arguments (the famous photon bouncing off mirrors). It seems to me that actually Einstein wasn't the first one talking about this.
Any reference would be greatly appreciated! Thank you!
Mathematically, it already appeared in Michelson and Morley's famous paper from 1887, because the path of the transverse interferometer arm resembles the light clock perfectly. They obtained the formula on page 336:
$$ 2D \sqrt{1+\frac{v^2}{V^2}} $$
Michelson, Albert A.; Morley, Edward W. (1887), "On the Relative Motion of the Earth and the Luminiferous Ether", American Journal of Science, 34: 333–345 https://en.wikisource.org/wiki/On_the_Relative_Motion_of_the_Earth_and_the_Luminiferous_Ether
In the context of relativity, it seems that Lewis and Tolman in 1909 were the first to use it. They obtained the formula on p. 715:
$$ \frac{mn}{op}=\frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}} $$
Lewis, Gilbert N.; Tolman, Richard C. (1909), "The Principle of Relativity, and Non-Newtonian Mechanics", Proceedings of the American Academy of Arts and Sciences, 44: 709–726 https://en.wikisource.org/wiki/The_Principle_of_Relativity,_and_Non-Newtonian_Mechanics
