In 1829, Dobereiner classified elements with similar chemical properties into groups of three called Triads. He noted that the atomic weight of the middle element in a triad is the arithmetic mean of the other two. This is called Dobereiner’s Law of Triads.
Newlands proposed a Law of Octaves which states, ‘When elements are arranged in the increasing order of their atomic masses, the properties of the eighth element are similar to the first’. Therefore, his classification was known as Newlands’ Octaves.