#OTD in 1905. Albert Einstein completes his doctoral thesis at the University of Zurich.
Titled "Eine neue Bestimmung der MolekĆ¼ldimensionen", he calculated the size of sugar molecules in solution and from this a value for the Avogadro constant. It is related to his work on Brownian motion, published in the same year, and supported the atomic hypothesis, which was still controversial among leading physicists at the time.
Books by Albert Einstein at PG:
https://www.gutenberg.org/ebooks/author/1630