The document outlines the early discoveries that led to the development of the periodic table, including Dobereiner's discovery of triads of elements with similar properties, Newlands' law of octaves noting patterns every eighth element, and Mendeleev and Meyer independently publishing the first periodic tables and Mendeleev's improvements by leaving gaps for undiscovered elements. It concludes with Moseley arranging the elements by atomic number instead of atomic mass, establishing the concept of atomic number and the periodic law that the properties of elements are periodic based on their atomic number.