In 1827, Brown was observing pollen grains suspended in water under a microscope. He noticed that the pollen grains were not stationary but moved in a haphazard, erratic manner. He initially thought this movement was due to the pollen grains themselves being alive, but further experiments showed that the same movement could be observed with inanimate particles.
This random movement of particles, now known as Brownian motion, was later explained by Albert Einstein in 1905. Einstein's explanation provided strong evidence for the existence of atoms and molecules, which were still a matter of debate at the time.
Therefore, while Brown is credited with the discovery of the random movement, Einstein provided the explanation for it.
