Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
The periodic table of elements as we know it today was the inspired work of Dmitri Ivanovich Mendeleyev (1834-1907). His generalization of sequences of atomic weights and properties of elements, data already known to other scientists and arranged systematically by them, was more than a convenient scheme positioning the elements as they were then known; it represented to him a "law of nature," containing gaps for elements yet undiscovered, and predicting their existence. Some of these elements were soon found, and had indeed the properties predicted by Mendeleyev: gallium and scandium.