In 1827, Robert Brown observed through the microscope that some pollen grains suspended in water were moving constantly and randomly in no specific direction. The Brownian Motion was observed not only in pollen grains but also in other small particles such as dust and smoke particles. When smoke particles in the air were view through a microscope under the bright light, they were seen as bright points moving about constantly and randomly with no specific directions in the air. It was aboout eighty years later, 1905 that Albert Einstein came up with a theory to explain Brownian Motion. Another scientist Jean Baptiste Perrin, carried out experiments to show that Einstein's theory could better explain the movement of particles. Einstein explained that the pollen grains in the water moved constantly and randomly because they were bombarded all around by water particles which themselves were moving constantly and randomly. Remember that although the pollen grains are microscopic, the water particles are even smaller and cannot be observed with a normal microscope. Similarly, tiny air particles which are moving constantly and randomly bombard or hit the larger smoke or dust particles in the air in all directions, causing the jittery motions of the smoke and dust particles.
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