Orest Danilovich Khvolson (4.12.1852—11.05.1934) was a Soviet physicist, an honorary academician (1920) and a corresponding member of the St Petersburg Academy of Sciences (1895). He was born in St Petersburg. He graduated from St Petersburg University (1873) and taught there from 1876 (as professor from 1891) and at the same time at other educational institutions in St Petersburg.
His work concerned electrophysics, magnetism, photometry, actinometry and the study of the regime of solar radiation. He designed an actinometer and a pyrheliometer, the best of their time. He entered the history of Russian physics as a brilliant lecturer and popularizer of physics, the teacher of several generations of St Petersburg and Leningrad physicists, and the author of the well-known five-volume “Course of Physics”, which he kept improving for almost forty years, from the first edition of the first volume in 1897, constantly taking into account the new achievements of science. He wrote over 30 popular-science books, in particular “Popular Lectures on Electricity and Magnetism” (1884), “Röntgen Rays” (1896) and “The Physics of Our Day” (4th edition, 1932), which acquainted readers with the newest achievements of physics. Khvolson's philosophical views were at times mistaken.