Berzelius (1779-1848) accurately determined more than 2000 relative atomic and molecular masses. He was the first to prepare silicon in its amorphous form and to isolate zirconium. He proposed oxygen as a reference standard for atomic masses and devised the system of chemical symbols and formulae now in use. His discoveries include the elements cerium (1804), selenium (1817), and thorium (1828).
University College, Cork, website http://www.ucc.ie/ucc/depts/chem/dolchem/html/biog/biog001.html