1. P. Lenard, Ueber die lichtelektrische Wirkung. Ann. Physik 8, 149 (1902) [This is in German, Interested readers can refer to ‘B. R. Wheaton, “Philipp Lenard and the Photoelectric Effect, 1889–1911”, Historical Studies in Physical Sciences, Vol – 9 (1978)’ for a more comprehensive account on the discovery of photoelectric effect]
2. J.D. Norton, Chasing a Beam of Light: Einstein’s Most Famous Thought Experiment, https://www.pitt.edu/~jdnorton/Goodies/Chasing_the_light/
3. A.A. Mills, R. Clift, Reflections of the ‘Burning mirrors of Archimedes’. With a consideration of the geometry and intensity of sunlight reflected from plane mirrors. Eur. J. Phys. 13, 268 (1992)
4. N. Bohr, On the constitution of atoms and molecules. Philos. Magaz. Ser. 6 26(151), 1–25 (1913)
5. A. Einstein, On the quantum theory of radiation. Phys. Z. 18, 121 (1917)