Herman Haga (24.01.1852-11.09.1936) - Dutch physicist. Born in Oldeboorn. Graduated from Leiden University (1876). In 1886 — 1922 he was a professor at the University of Groningen and (from 1903) director of the Physical Institute. His research concerned X-rays and X-ray structure analysis. In 1899 he was the first to prove the wave nature of X-rays, in an attempt to observe their interference, and estimated the wavelength of X-radiation (10-8 cm). He improved a number of measuring and demonstration instruments.