The elements are written in increasing order of atomic mass
The mass of middle element was roughly the average of atomic masses of other two elements
Elements in the Triads show similar properties.
Döbereiner showed that when the three elements in a triad were arranged in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. Moroever, elements in the traids show similar properties.