Moseley's Work and Modern Periodic Law

In 1913 Henry Moseley bombarded a series of elements with high-energy electrons and studied the characteristic X-rays each element emitted in response. He found a clean linear relationship between the square root of the X-ray frequency and the element's atomic number:

where $\nu$ is the frequency of the X-rays emitted by the element of atomic number $Z$, and $a$ and $b$ are constants with the same value for every element. A plot of $\sqrt{\nu}$ against $Z$ is a straight line, and this relationship could even be used in reverse -- to determine the atomic number of a newly discovered element from the frequency of the X-rays it emits. …