Einstein devised a mathematical method of calculating the size of atoms and molecules in early 1905. From an analysis of sugar molecules dissolved in water, he calculated both the diameter of the sugar molecule and Avogadro’s number. Avogadro’s number is the number of molecules per unit volume under standard conditions. Even after Einstein did this, the very existence of atoms and molecules still had to be demonstrated. Einstein set out to prove molecules’ existence by using what was called “Brownian-motion.” He assumed that if there truly were molecules in a liquid, then they could push a body in the water in a zig-zag motion. French scientist Jean Perrin rose to Einstein’s challenge with a series of experiments in 1908. Equipped with nothing but a microscope and a stopwatch, he proved that Einstein’s predictions were right. This was the first unequivocal evidence of the reality of molecules.
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Brownian-motion...If they are all in motion, molecules should be able to push a body in a zig-zag pattern while continuing their motion.
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Nothing But A Stopwatch And A Microscope...Jean Perrin rose to Einstein’s challenge with a series of experiments that included nothing but a stopwatch and a microscope. With just these, he was able to prove Einstein theory.
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