How did Newland know the true atomic weight of Beryllium(9¬13.5),before Mendeleev corrected it?

Question

Mendeleev gave his periodic table in 1860.He corrected the atomic mass of Be from 13.5 to 9.But Newland in his arangement of elements according to Law of Octaves placed Be between Li(7) and Br,though at that time Be's at.mass was taken to be 13.5.Therefore it should have been between C(12) and N.

Answer 1

His law of octaves. He came up with the theory that properties vary periodically at every eighth element.

Answer 2

Atomic Weight Beryllium