Paul Bowersox at Nuclear Newswire.
"The idea of atoms as a shortcut for thinking about how matter worked seemed quite useful even more than a century ago-but then again, so did ideas like a stationary earth at the center of the universe. When Einstein was a young man, atoms had never been observed. Was the idea of atoms actually 'real?' Or was something else, perhaps something unexpected, going on?"[link fixed -ed.]
See Albert Einstin, "The Rise and Fall of Classical Physics", from The Evolution of Physics (with Leopold Infeld), in Gateway to the Great Books (10 Vol., 1963) volume 8; Relativity: The Special and the General Theory, in Great Books of the Western World (second edition, 60 Vol., 1990) volume 56.