Trained as a medical doctor at the [University of Uppsala]?, in 1807 he became a professor at the [University of Stockholm]?. Not long after arriving there he wrote a chemisty textbook for his medical students, from which point a long and fruitful career in chemistry began. While conducting experiments in support of the textbook he discovered the [Law of Constant Proportions]?, which showed that inorganic substances are composed of different elements in constant proportions by weight. From this, by 1828 he compiled a table of the relative atomic weights (with oxygen set to 100) of all elements then known. Taken together, this work was a strong confirmation of the atomic hypothesis; that inorganic chemical compounds were composed of atoms combining in whole number amounts. In discovering that the atomic weights were also not integer multiples of hydrogen's, Berzelius also disproved [Prout's Hypothesis]? that elements were built up from atoms of hydrogen.
In order to aid his experiments, he developed a system of chemical notation in which the elements were given simple written labels -- such as O for oxygen, or Fe for Iron -- and proportions were noted with numbers. This is the same basic system as is used today, the only difference being that where we would use a subscript number (i.e., H20), Berzelius would use a superscript.
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