On this day, 138 years ago, November 23, 1887 (October 9, 1887 in the lunar calendar), Mosley, the discoverer of atomic number, was born in England. Henry Gwyn Jeffreys Moseley (November 23, 1887-August 10, 1915) was the discoverer of atomic number. Mosley was born in England. He used experiments to prove that the main characteristics of an element are determined by its atomic number, not by its atomic weight, and established the relationship between atomic number and nuclear charge. When Mosley studied the X-ray spectra of elements, he found that when different elements were used as targets for generating X-rays, the wavelengths of the characteristic X-rays produced were different. After he arranged the various elements according to the wavelength of the characteristic X-rays produced, he found that the order was consistent with the order in the periodic table of elements. He called this order atomic number and believed that the nature of the element was a periodic function of its atomic number. The discovery of atomic number is called Mosley's Law. Comment: Moseley was killed in World War I and only lived to the age of 27