The periodic table of Mendeleef, and the physical periodicity
typified by Lothar Meyer's atomic volume curve, were of immense
value to the development of chemistry from the mid-nineteenth to
early in the present century, despite the fact that the quantity chosen
ATOMIC NUMBER
In 1913 the English physicist Moseley examined the spectrum
produced when X-rays were directed at a metal target. He found that
the frequencies v of the observed lines obeyed the relationship
v = a(Z ~ b)2
where a and b are constants. Z was a number, different for each metal,
found to depend upon the position of the metal in the periodic table.