In 1913, henry moseley systematically studied the x-ray spectra of various elements. he made use of bragg's discovery of x-ray diffraction to calculate the wavelengths of the spikes seen in the spectrum of x-rays emitted when high-energy electrons impact a target. he then found an empircal law relating the frequency f of the most intense x-ray spike--known as the k_{\alpha} line--to the atomic number z of the element. that empirical law, known as moseley's law, is

f=(2.48\times10^{15}\; {\rm hz})(z-1)^2.