Law of Octaves
 

English chemist John Newlands (1837-1898), having arranged the 62 known elements in order of increasing atomic weights, noted that after interval of eight elements similar physical/chemical properties reappeared.  Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. In 1863 he wrote a paper proposing the Law of Octaves: Elements exhibit similar behavior to the eighth element following it in the table.

Source of this page:  http://mooni.fccj.org/~ethall/period/period.htm