Brownian motion
Annalen der Physik receives Einstein’s Brownian-motion manuscript
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A receipt stamp in Leipzig
On 11 May 1905, Annalen der Physik recorded receiving a manuscript from Albert Einstein, then a technical expert at the Swiss patent office in Bern, titled "Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen."
That receipt is the documented event. The publication record establishes 11 May as the journal's receipt date, not necessarily the day Einstein put the manuscript in the mail, and it is not the publication date.
The paper appeared later that year on pages 549–560 of Annalen der Physik, volume 17.
What the manuscript predicted
Einstein argued that microscopic particles suspended in a liquid would undergo observable, irregular motion as a consequence of molecular-kinetic theory. He supplied a quantitative relation between elapsed time and mean displacement.
In a worked example, a particle 0.001 millimetre in diameter was predicted to have a mean displacement of about 6 micrometres in one minute. He proposed using measurements of that motion to determine Avogadro's number.
The work grew out of his just-completed doctoral dissertation on molecular dimensions, whose treatment of diffusion supplied a formula the new paper needed.
Einstein hedged where later accounts do not
The paper was theoretical. Einstein did not conduct the confirming particle-tracking experiments that later accounts attach to him, and he wrote only that the predicted motion might be identical with the phenomenon called Brownian motion — not that he had explained an already-identified effect.
The objects in Robert Brown's famous observations were minute particles released from Clarkia pulchella pollen, not whole pollen grains. Brown acknowledged earlier observers, and his account of observations made in 1827 was published in 1828.
Einstein's paper ended by hoping that an experimenter would soon solve the problem he had posed.
Sources
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What the sources leave uncertain
- The publication record establishes May 11 as the journal’s receipt date, not necessarily the day Einstein placed the manuscript in the mail.
- Einstein initially wrote only that the predicted motion might be identical to the phenomenon called Brownian motion; he did not present himself as having experimentally identified it.